阅读说明：本技术 用于可变压缩比发动机的系统和方法 (System and method for variable compression ratio engine ) 是由 法比安·加多 克里斯多夫·格鲁格拉 于 2019-06-25 设计创作，主要内容包括：本公开提供了“用于可变压缩比发动机的系统和方法”。提供了用于经由制动器维持发动机的压缩比以及同时禁用施加到相关联的可变压缩比机构的致动器的电流的方法和系统。在压缩比转变之前和期间改变经由所述制动器施加在压缩比控制轴上的制动力以使所述控制轴按所需速度移动。将制动扭矩施加与来自VCR致动器的马达扭矩和施加在所述控制轴上的发动机扭矩进行协调以实现平滑的CR转变。(The present disclosure provides a system and method for a variable compression ratio engine. Methods and systems are provided for maintaining a compression ratio of an engine via a brake while disabling current applied to an actuator of an associated variable compression ratio mechanism. The braking force applied to the compression ratio control shaft via the brake is changed before and during the compression ratio transition to move the control shaft at a desired speed. Brake torque application is coordinated with motor torque from VCR actuators and engine torque applied on the control shaft to achieve a smooth CR transition.)

1. A method for an engine, the method for an engine comprising:

maintaining a position of a control shaft for changing a compression ratio of the engine via a braking force from a brake; and

adjusting the braking force based on operating conditions before and during actuation of the control shaft.

2. The method of claim 1, wherein actuation of the control shaft comprises changing the compression ratio via a Variable Compression Ratio (VCR) actuator coupled to the control shaft, and wherein the position of the control shaft is not maintained via torque from the VCR actuator.

3. The method of claim 1, further comprising actuating the control shaft in response to an upcoming transmission shift, a transmission shift schedule being adjusted based on the braking force.

4. The method of claim 1, wherein the adjusting comprises reducing the braking force prior to actuation of the control shaft, and changing the braking force while actuating the control shaft, the changing based on a first compression ratio prior to the actuation of the control shaft relative to a second compression ratio after the actuation of the control shaft.

5. The method of claim 4, wherein when the first compression ratio is higher than an upper threshold or lower than a lower threshold and the second compression ratio is between the upper threshold and the lower threshold, the changing includes reducing the braking force when the compression ratio is moved from the first compression ratio to the second compression ratio.

6. The method of claim 4, wherein when the first compression ratio is higher than the second compression ratio, the varying comprises increasing the braking force as one or more of engine torque on the control shaft and motor torque from the VCR actuator increases, the braking force increasing to transition from the first compression ratio to the second compression ratio at a target speed, the target speed selected according to hardware limitations of the control shaft.

7. The method of claim 1, wherein the brake is coupled to a spring-loaded valve, and wherein adjusting the braking force comprises:

reducing the braking force by increasing a pressure exerted on a spring of the spring-loaded valve opposite a spring-biased direction; and

increasing the braking force by reducing the pressure exerted on the spring.

8. The method of claim 1, wherein the actuation of the control shaft comprises transitioning the engine from a first compression ratio setting to a second compression ratio setting, and wherein the adjusting comprises:

during a first condition, reducing the braking force prior to the actuation of the control shaft and then increasing the braking force to maintain the engine in the second compression ratio setting while achieving a lower degree of control shaft movement; and

during a second condition, reducing the braking force prior to the actuation of the control shaft and then increasing the braking force to maintain the engine in the second compression ratio setting while achieving a higher degree of control shaft movement.

9. The method of claim 8, wherein during the first condition the second compression ratio setting corresponds to a lower rate of change of engine speed and load zone, and wherein during the second condition the second compression ratio setting corresponds to a higher rate of change of engine speed and load zone.

10. An engine system, the engine system comprising:

an engine;

a control shaft for changing a compression ratio of the engine;

a brake for applying a braking torque to the control shaft, the brake being actuated via a spring-loaded solenoid valve;

an electric compression ratio actuator for applying a motor torque to the control shaft;

a transmission including a plurality of gears; and

a controller storing executable instructions in a non-transitory memory that, when executed, cause the controller to:

maintaining a fixed position of the control shaft via braking force from the brake during a first condition outside a threshold compression ratio range; and

during a second condition within the threshold compression ratio range, continuously changing the position of the control shaft within a range of positions via the braking force.

11. The system of claim 10, wherein during the first condition the compression ratio of the engine is above an upper threshold or below a lower threshold, and wherein during the second condition the compression ratio of the engine is below the upper threshold and above the lower threshold.

12. The system of claim 10, wherein the continuously varying comprises: increasing the braking force until the control shaft moves in a first direction outside of the position range; and in response to the movement, reducing the braking force until the control shaft moves in a second opposite direction outside of the position range, the position range being based on the threshold compression ratio range.

13. The system of claim 12, further comprising: learning the braking force as a function of control shaft position and the engine compression ratio relative to the range of positions during the second condition; and adjusting the hydraulic pressure applied to the solenoid valve based on the knowledge.

14. The system of claim 10, wherein during the first condition, the electric compression ratio actuator coupled to the control shaft is disabled and no motor torque is applied to the controller via the actuator, and wherein during the second condition, the electric compression ratio actuator coupled to the control shaft is enabled and at least some motor torque is also applied to the control shaft via the actuator.

15. The system of claim 14, further comprising during both the first and second conditions requiring a change in engine compression ratio and a transmission shift in response to a change in engine operating conditions, increasing the braking force to lock the brake before initiating the transmission shift, and then decreasing the braking force on the control shaft from the brake after completing the transmission shift while increasing the motor torque on the control shaft from the electric compression ratio actuator to move the control shaft to a position corresponding to the change in engine compression ratio, wherein when the change in engine compression ratio comprises a decrease in compression ratio, the ratio of braking force on the control shaft from the brake to motor torque from the electric compression ratio actuator is adjusted based on engine torque applied to the control shaft via a piston due to cylinder combustion, such that the control shaft transitions at a target speed via the reduction in compression ratio.

Technical Field

The present description relates generally to methods and systems for variable compression ratio engines.

Background

The Compression Ratio (CR) of an internal combustion engine, which is the ratio of the cylinder volume when the piston is at Bottom Dead Center (BDC) relative to Top Dead Center (TDC), is defined by the cylinder geometry. Higher compression ratios are generally associated with higher thermal efficiency and engine fuel economy. Variable Compression Ratio (VCR) engines can mechanically vary the compression ratio of each cylinder between a High Compression Ratio (HCR) and a Low Compression Ratio (LCR) setting. For example, by mechanically shifting the position of the piston in the cylinder barrel so that it is closer or farther from the top of the cylinder barrel (such as via an eccentric coupled to the piston), the volume at TDC, and thus the compression ratio setting, may be changed. The HCR setting may be selected at light to medium load (i.e., during no knock conditions) to take advantage of higher thermal efficiency and resulting improved fuel economy, and maintained until spark retard from the onset of early knock outweighs the fuel economy benefit. The LCR setting may then be selected to trade off thermal efficiency and combustion phasing efficiency. A continuously variable system may adjust the compression ratio to a variable value between the LCR setting and the HCR setting to optimize combustion phasing efficiency and thermal efficiency at any operating conditions.

One example of a VCR engine is shown by Kamada et al in US 7,802,544, in which the piston and crankshaft are connected to each other via a plurality of connecting rods (two there). However, there may be operating conditions where the engine needs to operate at a fixed compression ratio, such as during engine start-up. Maintaining a position corresponding to a fixed compression ratio may require torque from the VCR actuator, which in turn requires the actuator to draw constant power. This may waste the fuel economy benefits of a VCR engine. During engine starting, the current required to maintain a fixed CR may add significant starting current load to the engine, causing the engine to stall. Additionally, VCR engine component durability may be reduced due to constant torsion.

In other examples, the VCR actuator may be configured with a brake mechanism that holds the VCR control shaft in a fixed position corresponding to a desired fixed CR setting. An example of such a braking mechanism coupled to a VCR control shaft is shown by meitschel et al in US 7,934,475. Wherein the drive device for controlling the VCR actuator has a coupling mechanism with an integrated braking function. Windings mounted to the housing are energized to activate a braking function.

However, the inventors have recognized that a possible problem with such braking mechanisms is that it may be difficult to balance the conflicting needs of quickly transitioning between CR settings with maintaining a fixed CR setting. In particular, maintaining a fixed CR setting may require activating a brake function and locking the control shaft in a position corresponding to the fixed CR setting. On the other hand, when the brake function is activated and the control shaft is locked, the engine may not be able to quickly shift from the high compression ratio to the low compression ratio. Since the rate at which the engine can switch compression ratios during transient conditions depends on the speed at which the VCR control shaft can be moved by the VCR actuator, the braking function can negatively impact the transient acceleration problem of the engine. Slow transitions may result in slow accelerations that are objectionable to the driver.

Disclosure of Invention

In one example, the above problem may be solved by a method for an engine, comprising: maintaining a position of a control shaft for changing a compression ratio of the engine via a braking force from a brake; and adjusting the braking force based on operating conditions before and during actuation of the control shaft. In this manner, the VCR engine can be maintained in a fixed CR setting with reduced power consumption while being able to quickly switch between CR settings during torque transients.

As one example, the VCR mechanism may include an eccentric for varying the piston position of the cylinder according to the commanded compression ratio. The engine controller may vary the piston position by sending a control signal to a VCR actuator coupled to a control shaft (CRCS) of the VCR mechanism to vary the piston position. The VCR mechanism may include a brake device, such as a band brake, for applying a braking force to the control shaft. The band brake can be opened or closed (to unlock or lock it, respectively) via a spring-loaded solenoid valve that is actuated hydraulically or electrically. The spring-loaded valve may be biased in a direction to close/lock the band brake when in the default position. When the band brake is locked, it applies a braking force to the control shaft, thereby reducing shaft motion and locking the CR setting of the engine. By adjusting the pressure exerted on the spring in the direction opposite to its bias, the band brake can be relaxed, which reduces the braking torque exerted on the control shaft. The applied braking torque may vary based on engine operating conditions (such as engine speed, load, and torque demand) as well as based on scheduled CR transitions and transmission shifts. For example, the braking torque applied to the control shaft via the band brake may be reduced before and during the CR transition and coordinated with the torque applied to the shaft by the VCR actuator to enable the CR transition to be completed at the desired rate. The higher brake torque may be coordinated with the VCR actuator deactivation power during engine speed-load conditions where a sudden large change in speed-load or required CR is not expected, where the engine needs to remain at a high CR setting (e.g., above an upper threshold) or a low CR setting (e.g., below a lower threshold). However, during conditions where the engine needs to remain at a centered CR setting (e.g., below an upper threshold and above a lower threshold), such as during gear shifts, even when the engine speed-load is not changing, a lower braking torque may be applied to keep the control shaft sufficiently slack because a sudden transition is expected. Additionally, during torque transients, such as when engine speed-load changes, lower braking torque may be applied to improve transient response.

Additionally, during the CR transition, the braking torque may be adjusted relative to the actual CR transition rate based on the desired CR transition rate. For example, during a transition from a higher CR setting to a lower CR setting, engine torque may be used to effect at least a portion of the transition. Then, if additional torque is required to complete the transition or accelerate the transition, the braking torque applied to the control shaft via the braking mechanism may be reduced. Alternatively, if additional braking torque is required to slow the transition, the braking torque applied to the control shaft via the braking mechanism may be increased.

In this way, the braking torque applied to the control shaft of the VCR engine via the braking mechanism can be used to maintain a fixed CR setting for the VCR engine with reduced power consumption, thereby improving the fuel economy of the engine. The technical effect of varying the brake pressure (or brake torque) applied to the VCR control shaft (via the brake mechanism) depending on operating conditions is that transient response time can be improved. In addition, position signals received via the VCR actuator can be used to calculate the speed of the control shaft, allowing finer control of the CR transition rate. A technical effect of adjusting the braking torque applied to the shaft based on the shaft speed and the CR setting is that a CR transition can be achieved at a desired transition rate. The braking torque from the braking mechanism can be coordinated with the motor torque applied to the shaft via the VCR actuator to achieve a smoother and faster CR transition. In addition, mechanical emergency stops of the control shaft may be reduced. By improving the CR transition while reducing power consumption, performance and fuel economy of a VCR engine may be improved.

It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

Drawings

FIG. 1 shows an example engine system in which the compression ratio is variable.

FIG. 2 illustrates an example embodiment of a Variable Compression Ratio (VCR) engine system including a VCR actuator and a control shaft brake mechanism.

3-4 illustrate high-level flow charts of methods for operating the VCR actuators and brake mechanisms of a VCR engine based on engine operating conditions.

FIG. 5 shows a high level flow chart of a method for coordinating the operation of the VCR actuators and braking mechanisms with engine torque actuation of the Compression Ratio Control Shaft (CRCS).

6A-6B illustrate an example embodiment of an actuator for operating a control shaft brake mechanism.

FIG. 7 illustrates an example compression ratio map that may be used to adjust the brake pressure applied by the brake mechanism on the CRCS.

FIG. 8 illustrates an example map of engine torque variation versus compression ratio applied to a CRCS.

FIG. 9 shows a table of example settings of the CRCS, VCR actuator and brake band under different engine operating conditions.

FIG. 10 shows a prophetic example of varying brake pressure from the brake mechanisms on the CRCS as engine operating conditions change.

Detailed Description

The following description relates to systems and methods for an engine system configured with a Variable Compression Ratio (VCR) mechanism, as described with reference to the engine system of fig. 1-2. The controller may be configured to execute a control program, such as the example programs of fig. 3-4, to lock the band brake coupled to the VCR control shaft to maintain a fixed CR setting, and to vary the brake pressure applied by the band brake to improve the CR transition. As detailed in fig. 5, the brake pressure may be adjusted during the CR transition based on the engine torque applied to the control shaft, which is known from the engine speed-load (fig. 8). The brake pressure applied via the band brake may be adjusted via a hydraulic or electric actuator, as elaborated on in fig. 6A-6B. The controller may lock the band brake when the CR setting of the engine is in a high zone or a low zone, and unlock the band brake and adjust the brake pressure when the CR setting is in a mid-zone, such as with reference to the CR map of fig. 7. Example settings for the band brake are tabulated in fig. 9. An example VCR operation with respect to locking and unlocking of the brake mechanism and adjustment of the brake pressure applied to the VCR control shaft is shown in fig. 10. In this way, the performance and fuel economy of a VCR engine can be improved.

FIG. 1 illustrates an example embodiment of a combustion chamber or cylinder of an internal combustion engine 10. Engine 10 may receive control parameters from a control system including controller 12 and input from a vehicle operator 130 via an input device 132. In this example, the input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. A cylinder (also referred to herein as a "combustion chamber") 30 of engine 10 may include combustion chamber walls 32 with a piston 38 located therein. Piston 38 may be coupled to crankshaft 40 such that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft 40 may be coupled to at least one drive wheel of a passenger vehicle via a transmission system. Further, a starter motor may be coupled to crankshaft 40 via a flywheel to enable a starting operation of engine 10.

The engine 10 may be configured as a Variable Compression Ratio (VCR) engine in which the Compression Ratio (CR) of each cylinder (that is, the ratio of the cylinder volume when the piston is at Bottom Dead Center (BDC) to the cylinder volume when the piston is at Top Dead Center (TDC)) may be mechanically modified. The CR of the engine may be changed via actuating the VCR actuator 192 of the VCR mechanism 180. In some example embodiments, the CR may vary between a first, lower CR (where the cylinder volume when the piston is at BDC is smaller than the cylinder volume when the piston is at TDC) and a second, higher CR (where the ratio is higher). In other example embodiments, there may be a predefined number of stepped compression ratios. Additionally, the CR may vary continuously between (to any CR in between) a first, lower CR and a second, higher CR.

The VCR mechanism 180 includes a VCR actuator 192 (which includes a speed reduction mechanism 194), a VCR actuator linkage 195, a control shaft 196, a position sensor 193, a control link 197, a lower link 198, and an upper link 199. In some examples, the VCR actuator may additionally have one or more intermediate links between the upper and lower links. The VCR actuator 192 is coupled to a control shaft 196 via an actuator linkage 195. A position sensor 193 may be coupled to the control shaft 196 and may be configured to provide feedback to the controller 12 regarding the position of the control shaft 196. In one example, the position sensor 193 indicates the degree of rotation of the control shaft 196. The control shaft 196 is coupled to a lower link 198 via a control link 197. Lower connecting rod 198 is coupled to crankshaft 40, and crankshaft 40 is further coupled to piston 38 via upper connecting rod 199. A brake mechanism, also referred to herein as a band brake 191, may be coupled to the control shaft 196 for locking movement of the control shaft. By locking the control shaft, a fixed compression ratio can be maintained. A detailed embodiment of the VCR actuation mechanism and brake mechanism is discussed with reference to fig. 2.

In the example shown in fig. 1-2, the VCR actuator 192 is an electric motor and is supplied with electrical power via the battery 58 to generate motor torque. In other examples, VCR actuator 192 may be hydraulically or pneumatically driven. In one example, the speed reduction mechanism 194 may be a harmonic drive and the VCR actuator may be an electric motor, such that the harmonic drive in conjunction with the actuator linkage 195 may convert a given amount of electric motor rotation into a smaller amount of control shaft 196 rotation but a high enough torque to withstand the combustion load. The reduction mechanism 194 may alternatively include a cycloidal reduction gear. In the illustrated example, the position sensor 193 is a rotary potentiometer for sensing the rotational angle of the control shaft 196. In the example shown in fig. 1, the actuator linkage 195 is an S-linkage and the control shaft 196 is rotatably supported in the engine body and possesses an eccentric region. The control link 197 may be attached to an eccentric region of the control shaft 196 such that when the control shaft 196 changes angular position, the eccentric region also changes angular position, causing the control link 197 to move up (toward the piston 38) or down (away from the piston 38) depending on the initial and final positions of the control shaft 196. In one example, the lower connecting rod may be attached to crankshaft 40 at a central or intermediate region (of lower connecting rod 198) where control connecting rod 197 and upper connecting rod 199 are attached on opposite sides of the central region, such that when lower connecting rod 198 pivots about its crankshaft 40 attachment point, movement of the control connecting rod upward (toward piston 38) causes the upper connecting rod to move downward (away from piston 38), or vice versa. As the upper connecting rod 199 moves up or down, the piston stroke characteristics, including the piston TDC position relative to the piston BDC position, will change, thereby changing the cylinder CR.

The control system 12 may measure the position of the control shaft 196 via a position sensor 193. The current supplied by the battery 58 to the VCR actuator 192 may be controlled by the controller 12 based on the desired position of the VCR actuator that provides the target CR setting. After commanding the CR setting, the controller may further control VCR actuator position via position feedback control based on input from a position sensor (such as position sensor 193). Wherein the control shaft 196 position corresponding to the commanded CR setting is maintained based on the measured position of the control shaft 196 as determined by the position sensor 193. When the control shaft is subjected to forces caused by combustion within the engine cylinders 30, the controller 12 may apply a current from the battery 58 to the VCR actuator 192 that is proportional to the control shaft torque and in one direction to maintain the control shaft position (and thus CR) at the commanded set point. This current is also referred to herein as the hold current, that is, the current that needs to be applied in order to hold the VCR actuator in a given position (corresponding to the commanded CR).

The VCR 180 mechanism may be coupled to a conventional crank linkage (cranktrain) or an unconventional crank linkage. Non-limiting examples of unconventional crank-link mechanisms to which the VCR mechanism 180 may be coupled include a variable-distance top crankshaft and a variable-length-of-motion crankshaft. In one example, crankshaft 40 may be configured as an eccentric shaft. In another example, an eccentric may be coupled to or in the region of the wrist pin, the eccentric changing the position of the piston within the combustion chamber. The movement of the eccentric can be controlled by means of an oil channel in the piston rod.

It will be appreciated that other VCR mechanisms that mechanically alter the compression ratio may be used. For example, the CR of an engine may be changed via a VCR mechanism that changes the cylinder head volume (i.e., the clearance volume in the cylinder head). In yet another example, the VCR-mechanism may include a hydraulic, air pressure or mechanical spring-reaction piston. In addition, the VCR mechanism may include a multi-link mechanism or a bent-bar mechanism. Other VCR mechanizations may be possible. It will be appreciated that, as used herein, a VCR engine may be configured to adjust the CR of the engine via mechanical adjustment that changes the piston position or cylinder head volume. Thus, the VCR mechanism does not include an effective CR adjustment via adjustment of valve or cam timing.

By adjusting the position of the piston within the cylinder, the actual (static) compression ratio of the engine (that is, the difference between the cylinder volume at TDC relative to the cylinder volume at BDC) can be varied. In one example, reducing the compression ratio includes reducing the displacement of the piston within the combustion chamber by increasing the distance between the top of the piston and the cylinder head. For example, the engine may be operated at a first lower compression ratio by the controller sending a signal to the VCR actuator 192 to actuate the VCR mechanism 180 to a first position where the piston has a smaller effective displacement within the combustion chamber. As one example, controller 12 may select a lower CR setting during engine start-up and in a high engine speed-load region. The controller 12 may command a corresponding current to the VCR actuator 192, which may be a harmonic drive motor. This causes the harmonic drive motor to experience a specified amount of rotation, which is translated to the control shaft 196 via the S-link mechanism. The eccentric region of the control shaft 196 then undergoes an angular displacement causing the control link 197 to move upwardly toward the piston 38. Via the pivoting action of the lower connecting rod 198, the upper connecting rod 199 and piston 38 move lower in the cylinder 30 at TDC, reducing the cylinder CR. As another example, the engine may be operated at the second higher compression ratio in response to a decrease in engine speed or load. The controller may send a signal to the VCR actuator 192 to actuate the VCR mechanism 180 to a second position where the piston has a greater effective displacement within the combustion chamber. As one example, the controller 12 may select a higher CR setting and command a corresponding current to the harmonic drive motor. This causes the harmonic drive motor to experience a specified amount of rotation, which is translated to the control shaft 196 via the S-link mechanism. The eccentric region of the control shaft 196 then undergoes an angular displacement causing the control link 197 to move downward away from the piston 38. Via the pivoting action of the lower connecting rod 198, the upper connecting rod 199 and piston 38 move higher in the cylinder 30 at TDC, thereby increasing the cylinder CR.

Changes in engine compression ratio may be advantageously used to improve fuel economy. For example, a higher compression ratio may be used to improve fuel economy at light to medium engine loads until spark retard from the onset of early knock outweighs the fuel economy benefit. The engine can then be switched to a lower compression ratio, thereby trading the efficiency benefits of the higher compression ratio with the efficiency benefits of optimized combustion phasing. Continuous VCR systems can continuously optimize the tradeoff between combustion phasing and efficiency benefits of higher compression ratios to provide an optimal compression ratio between the higher and lower compression ratio limits at a given operating condition. In one example, the engine controller may reference a look-up table to select a compression ratio to apply based on engine speed-load conditions. As set forth in detail below, the selection may include selecting a lower compression ratio at higher engine loads and selecting a higher compression ratio at lower engine loads.

Cylinder 30 may receive intake air via a series of intake passages 42 and 44. Intake passage 44 may communicate with other cylinders of engine 10 in addition to cylinder 30. In some embodiments, one or more of the intake passages may include a boosting device, such as a turbocharger or a supercharger. For example, FIG. 1 shows engine 10 configured with a turbocharger including a compressor 162 disposed between intake passages 42 and 44 and an exhaust turbine 164 disposed along exhaust passage 48. Compressor 162 may be at least partially powered by exhaust turbine 164 via shaft 163, with the boosting device configured as a turbocharger. However, in other examples, such as where engine 10 is provided with a supercharger, exhaust turbine 164 may optionally be omitted, where compressor 162 may be powered by mechanical input from the engine's motor. A throttle 62 including a throttle plate 64 may be provided along an intake passage of the engine for varying the flow rate and/or pressure of intake air provided to the engine cylinders. For example, throttle 62 may be disposed downstream of compressor 162 as shown in FIG. 1, or alternatively may be disposed upstream of compressor 162. Additionally, the engine system may include An Intake System (AIS) throttle 63 and a throttle plate 65 located upstream of the compressor in intake passage 42.

Exhaust passage 48 may receive exhaust from other cylinders of engine 10 in addition to cylinder 14. Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstream of emission control device 72. Sensor 126 may be selected from a variety of suitable sensors for providing an indication of exhaust gas air/fuel ratio, such as, for example, a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO (as shown), a HEGO (heated EGO), a NOx, HC, or CO sensor. Emission control device 72 may be a Three Way Catalyst (TWC), NOx trap, various other emission control devices, or a combination thereof.

Exhaust temperature may be estimated by one or more temperature sensors (not shown) located in exhaust passage 48. Alternatively, exhaust temperature may be inferred based on engine operating conditions such as speed, load, air-fuel ratio (AFR), spark retard, etc. Further, exhaust gas temperature may be calculated by one or more exhaust gas sensors 126. It will be appreciated that the exhaust temperature may alternatively be estimated by any combination of the temperature estimation methods listed herein.

Each cylinder of engine 10 may include one or more intake valves and one or more exhaust valves. For example, cylinder 30 is shown to include at least one intake poppet valve 52 and at least one exhaust poppet valve 54 located in an upper region of cylinder 30. In some embodiments, each cylinder of engine 10 (including cylinder 30) may include at least two intake poppet valves and at least two exhaust poppet valves located in an upper region of the cylinder.

Intake valve 52 may be controlled by controller 12 through cam actuation via cam actuation system 51. Similarly, exhaust valve 54 may be controlled by controller 12 via cam actuation system 53. Cam actuation systems 51 and 53 may each include one or more cams and may utilize one or more of Cam Profile Switching (CPS), Variable Cam Timing (VCT), Variable Valve Timing (VVT) and/or Variable Valve Lift (VVL) systems operable by controller 12 to vary valve operation. The position of intake valve 52 and exhaust valve 54 may be determined by valve position sensors 55 and 57, respectively. In alternative embodiments, the intake and/or exhaust valves may be controlled by electric valve actuation. For example, cylinder 30 may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including CPS and/or VCT systems. In other embodiments, the intake and exhaust valves may be controlled by a common valve actuator or actuation system or a variable valve timing actuator or actuation system.

Cylinder 30 may have a compression ratio, which is the ratio of the volume when piston 38 is at bottom dead center to the volume at top dead center. Conventionally, the compression ratio is in the range of 9:1 to 10: 1. However, in some examples where different fuels are used, the compression ratio may be increased. This may occur, for example, when higher octane fuels or fuels with higher latent enthalpy of vaporization are used. If direct injection is used, the compression ratio may also be increased due to its effect on engine knock via charge cooling. The compression ratio may also be mechanically changed based on driver demand via adjustment of the VCR mechanism by the VCR actuator 192 to change the effective position of the piston 38 within the combustion chamber 14.

In some embodiments, each cylinder of engine 10 may include a spark plug 92 for initiating combustion. Ignition system 88 can provide an ignition spark to combustion chamber 30 via spark plug 92 in response to spark advance signal SA from controller 12, under select operating modes. However, in some embodiments, spark plug 92 may be omitted, such as may be the case with some diesel engines where engine 10 may initiate combustion by auto-ignition or by fuel injection.

In some embodiments, each cylinder of engine 10 may be configured with one or more fuel injectors for providing fuel thereto. As a non-limiting example, cylinder 30 is shown including one fuel injector 66. Fuel injector 66 is shown coupled directly to cylinder 30 for injecting fuel directly into cylinder 30 in proportion to the pulse width of signal FPW received from controller 12 via electronic driver 68. In this manner, fuel injector 66 provides what is known as direct injection (hereinafter also referred to as "DI") of fuel into combustion chamber 30. Although FIG. 1 shows injector 66 as a side injector, the injector may also be located at the top of the piston, such as near the location of spark plug 92. Such a location may improve mixing and combustion when operating an engine with an alcohol-based fuel due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be located overhead and near the intake valve to improve mixing. Fuel may be delivered to fuel injector 66 from a high pressure fuel system including a fuel tank, fuel pumps, and a fuel rail. Alternatively, fuel may be delivered by a single stage fuel pump at a lower pressure, in which case the timing of the direct fuel injection is more limited during the compression stroke than if a high pressure fuel system were used. Further, although not shown, the fuel tank may have a pressure transducer that provides a signal to controller 12. It will be appreciated that, in an alternative embodiment, injector 66 may be a port injector that provides fuel into the intake port upstream of cylinder 30.

It will also be appreciated that while the illustrated embodiment shows the engine being operated by injecting fuel via a single direct injector; however, in alternate embodiments, the engine may be operated by using two or more injectors (e.g., one direct injector and one port injector per cylinder, or two direct injectors/two port injectors per cylinder, etc.) and varying the relative amount of injection from each injector into the cylinder.

During a single cycle of the cylinder, fuel may be delivered to the cylinder by the injector. Further, the distribution and/or relative amount of fuel delivered from the injector may vary with operating conditions. Further, multiple injections of delivered fuel per cycle may be performed for a single combustion event. Multiple injections may be performed during a compression stroke, an intake stroke, or any suitable combination thereof. Also, fuel may be injected during the cycle to adjust an injected air-fuel ratio (AFR) of combustion. For example, fuel may be injected to provide a stoichiometric AFR. An AFR sensor may be included to provide an estimate of in-cylinder AFR. In one example, the AFR sensor may be an exhaust gas sensor, such as EGO sensor 126. By measuring the amount of residual oxygen (for lean mixtures) or unburned hydrocarbons (for rich mixtures) in the exhaust, the sensor can determine the AFR. Thus, the AFR can be provided as Lambda (λ) value, i.e., as the ratio of the actual AFR to the stoichiometry for a given mixture. Thus, a lambda of 1.0 indicates a stoichiometric mixture, a stoichiometric-rich mixture may have a lambda value less than 1.0, and a stoichiometric-lean mixture may have a lambda value greater than 1.

As described above, FIG. 1 shows one cylinder of a multi-cylinder engine. Thus, each cylinder may similarly include its own set of intake/exhaust valves, fuel injectors, spark plugs, and the like.

Engine 10 may also include a knock sensor 90 coupled to each cylinder 30 for identifying abnormal cylinder combustion events. In an alternative embodiment, one or more knock sensors 90 may be coupled to selected locations of the engine block. The knock sensor may be an accelerometer on the cylinder block, or an ion sensor disposed in the spark plug of each cylinder. The output of the knock sensor may be combined with the output of a crankshaft position sensor (such as a hall effect sensor) to indicate an abnormal combustion event in the cylinder. In one example, abnormal combustion due to one or more of knock and pre-ignition may be identified and distinguished based on the output of knock sensor 90 in one or more defined windows (e.g., crank angle timing windows). For example, knock may be identified in response to the estimated knock sensor output being above a knock threshold in a knock window, while pre-ignition may be identified in response to the estimated knock sensor output being above a pre-ignition threshold in a pre-ignition window, the pre-ignition threshold being above the knock threshold, the pre-ignition window being earlier than the knock window. In addition, abnormal combustion can be solved accordingly. For example, knock may be addressed by reducing the compression ratio and/or retarding spark timing, while pre-ignition may be addressed by strengthening the engine and/or limiting engine load. In addition, lowering the compression ratio also reduces the variation in further pre-ignition.

In some examples, vehicle 5 may be a hybrid vehicle having multiple torque sources available for one or more wheels 59. In other examples, the vehicle 5 is a conventional vehicle having only an engine, or an electric vehicle having only an electric machine. In the illustrated example, the vehicle 5 includes an engine 10 and a motor 52. The electric machine 52 may be a motor or a motor/generator. When the one or more clutches 56 are engaged, the crankshaft 40 of the engine 10 and the electric machine 52 are connected to wheels 59 via the transmission 48. In the illustrated example, the first clutch 56 is disposed between the crankshaft 40 and the electric machine 52, while the second clutch 56 is disposed between the electric machine 52 and the transmission 48. Controller 12 may send a signal to an actuator of each clutch 56 to engage or disengage the clutch to connect or disconnect crankshaft 40 from motor 52 and components connected thereto, and/or to connect or disconnect motor 52 from transmission 48 and components connected thereto. The transmission 48 may be a gearbox, a planetary gear system, or another type of transmission. The powertrain may be configured in various ways, including a parallel, series, or series-parallel hybrid vehicle.

The electric machine 52 receives power from the traction battery 58 to provide torque to the wheels 59. The electric machine 52 may also operate as a generator to provide electrical power to charge the battery 58, for example, during braking operations.

The controller 12 is shown as a microcomputer including a microprocessor unit 102, an input/output port 104, an electronic storage medium for executable programs and calibration values (shown in this particular example as a read only memory chip 106), a random access memory 108, a keep alive memory 110 and a data bus. In addition to those signals previously discussed, controller 12 may receive various signals from sensors coupled to engine 10, including: a measurement of intake Mass Air Flow (MAF) from mass air flow sensor 120; engine Coolant Temperature (ECT) from temperature sensor 112 coupled to cooling sleeve 114; a surface ignition pickup signal (PIP) from Hall effect sensor 118 (or other type) coupled to crankshaft 40; a Throttle Position (TP) from a throttle position sensor; absolute manifold pressure signal (MAP) from sensor 122; cylinder AFR from EGO sensor 126; abnormal combustion from knock sensor 90 and a crankshaft acceleration sensor. The VCR mechanism position can be obtained from a sensor 193, and the sensor 193 can be a rotary potentiometer or rotary encoder for sensing rotation of the control shaft 196 or the actuator linkage 195. Engine speed signal, RPM, may be generated by controller 12 from signal PIP. Manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum or pressure in the intake manifold. The controller 12 receives signals from the various sensors of FIG. 1 and, based on the received signals and instructions stored on the controller's memory, employs the various actuators of FIG. 1 to adjust engine operation. Example actuators include throttle 62, fuel injector 66, VCR actuator 192, EGR valve 152 (which controls flow through EGR conduit 150), and wastegate 82. As one example, based on engine speed and load, the controller may adjust the compression ratio of the engine by sending a signal to the VCR actuator 192, which the VCR actuator 192 actuates the control shaft 196, which the control shaft 196 in turn adjusts the strut of the lower link 198 to mechanically move the piston closer or farther from the cylinder head, thereby changing the volume of the combustion chamber.

The non-transitory storage medium read-only memory 106 may be programmed with computer readable data representing instructions executable by the processor 102 for performing the methods described below as well as other variants that are anticipated but not specifically listed.

Turning now to fig. 2, an exemplary embodiment 200 of a VCR mechanism and its associated brake mechanism is shown. In one example, the VCR mechanism of embodiment 200 comprises VCR mechanism 180 of fig. 1. Previously described components are similarly numbered and are not re-described.

Engine 10 is illustrated herein as a 4-cylinder inline engine with a piston 98 of each cylinder coupled to crankshaft 40. The Compression Ratio (CR) of each cylinder (i.e., the ratio of the cylinder volume when the piston 98 is at Bottom Dead Center (BDC) to the cylinder volume when the piston is at Top Dead Center (TDC)) may be mechanically modified. The CR of the engine may be varied via the VCR actuator 192. In the example shown, the VCR actuator 192 is electrically actuated upon drawing power from the battery 58. Specifically, the VCR actuator 192 is an electric motor that uses power from the battery 58 to generate motor torque to adjust the position of the piston 98.

The VCR actuator 192 is coupled to the actuator linkage 195 via an output shaft 202. In the illustrated example, the actuator linkage 195 is an S-link. An actuator linkage 195 couples the VCR actuator to a Compression Ratio Control Shaft (CRCS) 196. CRCS196 is coupled via a control connecting rod 204 to an intermediate connecting rod 206, which intermediate connecting rod 206 is in turn connected to crankshaft 40. CRCS196 is rotatably supported on the body of engine 10, specifically to crankshaft 40 via an intermediate connecting rod 206 that rotates with the crankshaft. Thus, the connecting rod 204 moves laterally. The control connecting rod 204 may be attached to an eccentric region of the CRCS196 such that when the control shaft 196 changes angular position, the eccentric region also changes angular position. For example, a duty cycle is commanded to the VCR actuator that moves the actuator linkage 195 in response to a change in engine operating conditions that requires a corresponding change in CR. This in turn moves the CRCS196, which contains the eccentric. This in turn moves the connecting rod 204 up and down and then moves the connecting rod and piston up and down in the cylinder bore on the other side of the intermediate connecting rod 206 (which behaves like a seesaw). This changes the piston stroke characteristics, including the piston TDC position relative to the piston BDC position, thereby changing the cylinder CR.

A position sensor 193 is coupled to CRCS196 and is configured to provide feedback to controller 12 regarding the position of CRCS 196. For example, the degree of rotation and rotational speed of CRCS196 may be inferred based on the output of position sensor 193. Additionally, during conditions when the CRCS is locked, the CR setting of the engine may be inferred with greater accuracy and reliability. Additionally, when the CRCS is locked, the path of the piston 98 may be inferred with greater fidelity, which enables better engine knock control and reduced impact on exhaust emissions and fuel economy.

Power is drawn at the VCR actuator 192 to enable the CR transition. However, to reduce power consumption during conditions when a fixed CR setting is required (such as when the engine is at a high or low CR setting and significant changes in engine speed-load points are not expected), the VCR actuators 192 may be disabled (by disabling power to the actuators) and the position of the CRCS196 may be locked via a braking mechanism (shown herein by band brake 191). The band brake may be a brake disc coaxially coupled to the CRCS 196. The degree to which the band brake is tightened or locked over the control shaft 196 may be adjusted via a spring-loaded solenoid valve 210, the spring-loaded solenoid valve 210 having a spring 216 biased in a direction that keeps the valve 410 closed. Band brake 191 is coupled to valve 210 via connector 222. Specifically, the position of the stem 218 is adjustable along the length L2 of the valve 210 between a first fully closed position and a second fully open position. The first fully closed position is a default position due to the bias of the spring 216. The position of the stem 218 may be changed by adjusting the hydraulic pressure (e.g., oil pressure) applied within the chamber 220. As the hydraulic pressure in the chamber 220 increases, the pressure can overcome the spring pressure, moving the valve farther away from the first fully closed position toward the second fully open position. The pressure change at the chamber 220 may be achieved via hydraulic or electric actuation.

When the valve 210 is fully closed, the band of the band brake 191 is held tightly over the control shaft. Thus, the brake pressure applied by band brake 191 on CRCS196 increases and CRCS196 remains locked. When the valve 210 is fully open, the band of the band brake 191 remains loosely over the control shaft. Thus, the brake pressure applied by band brake 191 on CRCS196 is reduced and CRCS196 remains unlocked. At this location, the CRCS is able to move freely. Thus, when motor torque is applied to CRCS196 via VCR actuator 192, the CRCS can be quickly transitioned to the desired setting. The tightness of the band of band brake 191 is variable when valve 210 is partially open, such as when the position of handle 218 is between a fully open position and a fully closed position. Thus, the brake pressure applied by band brake 191 on CRCS196 changes, which affects the degree of movement of CRCS 196. In one example, the brake pressure may be varied based on engine operating conditions to hold the CRCS in place without the assistance of the VCR actuator 196 while still maintaining the CRCS sufficiently slack to allow the VCR actuator to move the CRCS with the desired compression ratio change.

Band brake 191 may be hydraulically or electrically actuated. In the example shown, band brake 191 is hydraulically actuated by varying the hydraulic pressure in chamber 420. Hydraulic actuator 210 of band brake 191 may be bolted to a side of engine 10 or an oil pan with a gasket 212 to keep the oil seal intact. Cylindrical feature 214 may be cast into CRCS196 with which band brake 191 interfaces. The cylindrical feature is coaxial with CRCS196 and is configured to have a diameter D1 and a length L1. The location at which cylindrical feature 214 is placed along CRCS196 is selected to increase the diameter of the brake disc of the braking band before causing interference with crank lobe 216.

In an alternative example, band brake 191 is electrically actuated. Wherein the pulse width of the duty cycle applied to the valve 210 varies the position of the stem 218 between the fully open position and the fully closed position. As with hydraulic actuation, when no electrical power is provided, the valve defaults to a closed position in which the band brake locks the CRCS.

In this manner, the components of fig. 1-2 implement an engine system comprising: an engine; a control shaft for changing a compression ratio of the engine; a brake for applying a braking torque to the control shaft, the brake being actuated via a spring-loaded solenoid valve; an electric actuator for applying a motor torque to the control shaft; a transmission including a plurality of gears; and a controller storing executable instructions in a non-transitory memory that, when executed, cause the controller to: maintaining the control shaft in a fixed position via the brake to maintain a first compression ratio setting of the engine; and adjusting a ratio of the braking torque from the brake on the control shaft to the motor torque from the electric actuator according to an engine torque exerted on the control shaft due to cylinder combustion in response to a request to transition the engine to a second compression ratio setting lower than the first setting. The controller may also include instructions that cause the controller to: after transitioning to the second compression ratio setting, increasing the braking torque while decreasing the motor torque to maintain the position of the control shaft; and then initiating a transmission shift. Herein, when the second compression ratio is set within a threshold compression ratio range corresponding to a higher rate of change of engine speed or load, increasing the braking torque may include increasing the braking torque to achieve a first degree of control shaft movement, and when the second compression ratio is set outside the threshold compression ratio range, increasing the braking torque may include increasing the braking torque to achieve a second degree of control shaft movement that is less than the first degree. The controller may effect the first degree of control shaft movement by increasing the braking torque until the position of the control shaft is outside an upper limit of a range of positions corresponding to the threshold range, and then decreasing the braking torque until the position of the control shaft is outside a lower limit of the range of positions.

Turning now to fig. 3-4, an example routine 300 for selecting and commanding a CR setting for a VCR engine based on engine operating conditions and coordinating VCR actuator operation with control axle brake operation is described. It will be appreciated that the method of fig. 4 is part of the method of fig. 3. The instructions for performing method 300, as well as other methods included herein, may be executed by a controller based on instructions stored in a memory of the controller in conjunction with signals received from sensors of an engine system, such as the sensors described above with reference to fig. 1. The controller may employ engine actuators of the engine system to adjust engine operation according to the methods described below.

At 302, method 300 includes estimating and/or measuring engine operating conditions. Engine operating conditions may include, for example: driver power demand (e.g., based on an output of a pedal position sensor coupled to an accelerator pedal); ambient temperature, pressure and humidity; engine speed, engine temperature; manifold pressure (MAP); manifold Air Flow (MAF); the temperature of the catalyst; the temperature of the intake air; a boost level; the fuel octane number of the fuel available in the fuel tank; and so on.

At 304, the method includes retrieving a current Compression Ratio (CR) setting of the engine, indicated herein as CRc. For example, the compression ratio setting may be retrieved based on input from a position sensor coupled to a control shaft of the VCR mechanism. As another example, the compression ratio setting may be retrieved from the memory of the controller based on the CR setting of the last command.

A VCR mechanism (e.g., VCR mechanism 180 of fig. 1) is configured to mechanically alter the Compression Ratio (CR) setting of the engine. For example, the CR setting may be varied between a first lower compression ratio setting and a second higher compression ratio setting, or as one or more discrete settings between a lower CR setting and a higher CR setting. For example, the VCR mechanism for each cylinder may be actuated in series to move the engine between low CR8.0, high CR14.0, and centered CR 11.0. Other arrangements may be possible. As discussed with reference to fig. 1-2, the VCR mechanism can adjust the CR setting of the engine by mechanically altering the piston position within each cylinder via a duty cycle commanded to a VCR actuator that moves a Compression Ratio Control Shaft (CRCS). In one example, a VCR mechanism such as that described in fig. 1 may achieve different CR settings by employing VCR actuator 192 to change the position (angle) of CRCS196 via actuator linkage 195. As one example, the VCR actuator is a harmonic drive motor, the control shaft is a shaft containing an eccentric region (e.g., an ellipse), and the actuator linkage is an S-linkage. Control links (such as control link 197) change position when the control shaft position (angle) is changed by the action of the VCR actuator and actuator linkage. When the eccentric region of the control shaft rotates, the control link attached thereto will move up (towards the piston top) or down (away from the piston top) depending on the angular orientation of the eccentric region. In one example, the CR of the cylinder may be reduced by changing the angular position of the control shaft such that the control link moves upward, causing the lower link to pivot, causing the upper link and the piston crown to move downward. This results in a larger combustion chamber volume when the piston crown is at TDC, and therefore a smaller CR. Alternatively, the CR of the cylinder may be increased by changing the angular position of the control shaft so that the control link moves downward, causing the lower link to pivot, causing the upper link and piston crown to rise higher during combustion. This results in a smaller combustion chamber volume when the piston is at TDC and therefore a larger CR. In this way, the VCR mechanism can continuously control the engine CR between a maximum CR and a minimum CR as determined by the shape and size of the eccentric of the control shaft. As described in detail below, when the CR setting is to be maintained at a fixed setting, movement of the CRCS may be disabled by locking the CRCS via a brake mechanism (herein a band brake).

At 306, it is determined whether engine starting is confirmed based on engine operating conditions. The engine start may be requested after a period of engine shutdown, such as because the driver requests torque to propel the vehicle or to operate the compressor in response to a request for cabin air conditioning. Alternatively, where the engine is configured with idle start/stop capability, the engine may be automatically restarted without driver input because the battery state of charge drops.

After the engine start is confirmed, it may be determined at 308 whether the engine is already in the low CR setting. It may be desirable to start the engine while in the low CR setting to improve startability. For example, the engine may have been shut down with the engine in the lowest possible CR setting for a given VCR configuration. In one example, where the lowest compression ratio possible is set to 8.0, it may be confirmed that the engine is already at CR 8.0. If the engine is already in the lowest CR setting, then at 309, the method includes closing a valve coupled to the brake band to lock the CRCS in place, which keeps the engine fixed in the current CR setting. The brake band can limit movement of the control shaft when the brake band valve is closed. Therefore, the CR of the engine is set to be fixed. Locking the brake band includes disabling power to the brake band actuator (or maintaining power disabled). As discussed with reference to fig. 2, the brake band state is changed by hydraulically or electrically actuating a spring-loaded valve. When power is disabled, the spring loading biases the valve, and thus the brake band, to the default closed position. After locking the brake band, the control shaft is held in a fixed position, allowing the controller to maintain power to the VCR actuator disabled. In this manner, the CRCS may be maintained in a fixed location without consuming power, thereby improving fuel economy and engine startability. Additionally, the VCR actuator is not challenged by the above-normal net change in torque due to the above-normal start and idle combustion variability inherent.

If the engine is not already in the low CR setting, then at 310, the method includes confirming that sufficient oil pressure is available to open the band brake and change the CR setting. Without oil pressure from the engine operation, it may not be possible to disable the band brake until sufficient oil pressure is developed. Thus, if the oil pressure is not sufficient, at 311, the method includes maintaining the band brake locked until sufficient oil pressure is generated via engine operation. If sufficient oil pressure is identified, the method moves to 312. It will be appreciated that in embodiments where the band brake is actuated via an electronic solenoid rather than a hydraulic (oil pressure actuated) solenoid, the method may move directly from 310 to 312 without confirmation of oil pressure. At 312, the method includes commanding the band brake to open to enable free movement of the CRCS. Additionally, the VCR actuator may be commanded to transition the engine to the low CR setting. Commanding the band brake to open includes actuating a hydraulic or electric actuator coupled to the band brake valve to provide a single "pull action" that moves the spring in the opposite direction of its bias. By opening the valve and letting the band brake loose, the control shaft is unlocked and then a change of position of the control shaft can be achieved by a torque applied to the shaft via the VCR actuator. This allows the engine to quickly transition to the low CR setting required to achieve a smooth engine start. After the engine reaches the low CR setting, the band brake may be closed to lock the CRCS and hold the engine in the low CR setting. Commanding the band brake to close includes disabling a hydraulic or electric actuator coupled to the band brake to allow the spring to return to the default locked position based on its bias.

At 314, it may be determined whether the engine has reached idle speed after the engine is started. For example, it may be determined whether the engine speed is at or above 400 rpm. If not, at 316, the engine may be maintained in the low CR setting with the CRCS locked. Otherwise, if engine speed has been reached, at 318, it may be determined whether idle speed has been requested. The idle ratio at higher CR settings is more efficient at lower CR settings unless accessory loads from the AC compressor, etc., cause the engine load to be high enough to knock or spark retard to reduce efficiency. At that time, it would be advantageous to unlock and move the CRCS to a slightly lower CR and relock. Accordingly, the method moves from 318 to 320 to determine the desired CR setting. This includes the CR setting required to idle the engine if engine idle speed is requested at 318, or to transition the engine if engine idle speed is not requested. The controller may then position the engine accordingly.

Specifically, at 320, the method includes determining a desired CR setting (CRd) based on current engine operating conditions. In one example, the desired CR setting may be a higher CR setting when engine idle speed is requested. In another example, CRd is determined based on engine speed-load and torque demand. For example, the controller may calculate the fuel efficiency at each possible compression ratio setting of the engine given the driver power demand and select the compression ratio that provides the highest fuel efficiency. The controller may compare the fuel efficiency at each compression ratio by comparing the Brake Specific Fuel Consumption (BSFC) of the engine at each CR setting (e.g., CR8.0, 11.0, and 14.0). The fuel efficiency of the engine at each compression ratio may be determined via a look-up table, map, algorithm, and/or equation, each stored according to operating conditions (e.g., engine speed, torque, temperature, humidity, inferred fuel octane, etc.), with the settings populated during initial engine calibration being based on the prototype engine. In general, as engine load or BMEP increases, the selected compression ratio may decrease due to a tradeoff between the efficiency benefit of higher CR (which dominates at lower loads) and the efficiency loss of knock-limited combustion phasing (which dominates at higher loads). Thus, a lower compression ratio is selected at higher engine loads, and a higher compression ratio is selected at lower engine loads.

At 322, it is determined whether the current CR setting matches the desired CR setting. For example, if the engine is already in the low CR setting during engine start-up and high speed to idle, it may be determined whether operating conditions require the engine to continue in the low CR setting. If the desired CR setting matches the current CR setting, then at 324, the method includes closing the band brake to lock the CRCS and disabling further movement.

If the current CR setting does not match the desired CR setting, at 326, the method includes determining a desired rate at which to transition from the current CR setting to the desired CR setting. For example, it may be determined whether the engine is transitioning as quickly as possible, or whether the engine is transitioning gradually. The method then moves to step 328 of fig. 4.

Next, at 328, it may be determined whether the desired CR setting (CRd) is lower than the current CR setting (CRc). If not, i.e., when CRd is higher than CRc, then at 330, the method includes commanding the VCR actuators to transition the engine to CRd. The controller may send a signal to the VCR actuator to move the CRCS to a position where the engine piston reaches the desired CR. Additionally, the method includes opening the band brake and adjusting (e.g., reducing) the brake pressure applied to the CRCS via the band brake to enable the CRCS to move at the desired CR transition rate. In this manner, by reducing the brake pressure applied via the brake mechanism, the CRCS may transition to a position corresponding to a desired CR setting at a desired rate.

If the desired CR setting (CRd) is lower than the current CR setting (CRc), then at 332 the method includes commanding the VCR actuators to transition the engine to CRd while using at least some of the engine actuator torque to move the CRCS. As elaborated in FIG. 5, by using at least some of the engine torque to actuate the transition to the lower CR setting, the power consumed by the VCR actuators is reduced, thereby improving fuel economy. Herein, engine torque is the torque exerted on the control shaft via the engine pistons as a result of cylinder combustion. It normally tends to move the control shaft in a direction toward the lower compression ratio setting. Thus, the engine torque may be used to reduce the motor torque required by the VCR actuator to effect the CR transition.

The controller may also adjust the brake pressure applied to the CRCS via the band brake to enable the CRCS to move to the desired CR setting at the desired transition rate. The controller may open the oil control solenoid to unlock the band brake, which unlocks the CRCS. The method then moves to step 334.

As an example, the controller may increase the braking force exerted by the band brake on the CRCS as one or more of the engine torque on the control shaft and the motor torque from the VCR actuator increases to transition from the first current compression ratio setting to the second desired compression ratio setting at a target shaft movement speed, the target speed being selected based on hardware limitations of the control shaft. The controller may increase the braking force by reducing the pressure exerted on a spring coupled to a spring-loaded valve of the band brake in a direction opposite to the spring-biased direction.

In another example, the controller may adjust the ratio of brake torque from the brake to motor torque from the VCR actuator on the control shaft based on engine torque applied to the control shaft due to cylinder combustion. This may include increasing the braking torque and decreasing the motor torque to slow the shaft rotation and CR transition when more (e.g., more than a threshold) engine torque is available to move the shaft. This may also include reducing the braking torque and increasing the motor torque to accelerate the shaft rotation and accelerate the CR transition when less (e.g., less than a threshold) engine torque is available to move the shaft.

At 334 from each of 330 and 332, the method includes determining whether the desired CR setting to which the engine has transitioned is in a zone δ defined by an upper threshold and a lower threshold. Specifically, it may be determined whether the CR setting of the engine after the transition is above the lower threshold and below the upper threshold. The controller may reference a map, such as the example map 700 of FIG. 7, to determine whether the engine is in zone δ.

Referring to fig. 7, the engine CR setting may be continuously varied between the lowest possible CR setting (shown at region 704, here CR 8.0) and the highest possible CR setting (shown at region 708, here CR14.0) by the VCR actuators based on engine speed and load (along the x-axis and y-axis). In the center region 706 defined by the dashed line 702, the engine may be set to a centered or intermediate CR setting (herein CR 11.0). When the engine is in either zone 704 or zone 708, a sudden CR transition is not expected. In these regions, the engine speed-load point changes at a small rate (e.g., does not substantially change). Thus, when in these zones, the band brake may remain fully locked without affecting fuel economy. For example, the band brake may be locked by reducing the pressure in the hydraulic actuator of the band brake, thereby increasing the braking pressure applied by the band brake on the CRCS. In one example, power to the band brake may be disabled. This increases fuel economy when operating under these conditions by not powering the VCR actuator and reducing reliance on its control. However, when the engine is in zone 706, a sudden CR transition to zone 704 or zone 708 is expected, as this is a boundary zone. Specifically, while in region 706, engine speed and load may change at a faster rate than either region 704 or region 708. Thus, in this region, the brake pressure applied to the CRCS via the band brake may be adjusted to enable movement of the CRCS. For example, as CR moves from zone 704 or zone 708 toward zone 706, pressure on the band brake may decrease (by increasing pressure on the hydraulic actuator of the band brake). The resulting smaller pressure differential in the hydraulic actuator allows the VCR actuator to move the CRCS with the desired compression ratio change. At the same time, the pressure on the band brake remains high enough to hold the CRCS in place without the assistance of the VCR actuator.

In some examples, it may be advantageous to pick an intermediate compression setting or select a CR setting with a large amount of hysteresis around and make the CRCS locked when in the intermediate load region 706. Each time the CRCS is unlocked and the CR is moved, a certain amount of power is consumed. Thus, in some examples, the controller may choose to unlock the CRCS only when there is sufficient benefit, such as when energy consumption is not greater than fuel savings at the new CR. The oil control valve may draw significantly less energy than the CR actuator motor. In other words, effectively digitizing into multiple (e.g., 3, 4, or 5) discrete states may be more efficient than consuming energy to constantly react to changes in the required CR setting (CRd).

It will also be appreciated that when in zone δ, if the speed/load point is not changed, the band brake can be locked by reducing the pressure in the hydraulic actuator.

Returning to FIG. 4, if at 334, it is determined that the engine is not in the delta zone (defined by Thr1 and Thr 2), such as when the engine is in zone 704 or 708 of FIG. 7, then at 336 the method includes closing the band brake by closing the oil control solenoid to lock the CRCS. This allows the engine to remain in a higher or lower CR setting.

If it is determined that the engine is in the delta zone, then at 338 the method includes maintaining the oil control solenoid open to reduce the pressure on the brake band. The brake pressure applied by the brake band on the CRCS is then reduced in order to effect CRCS movement (if needed in response to changes in the required CR) while maintaining the CRCS in place. Specifically, the band brake may be opened to the extent that it is sufficiently slack to enable the CRCS to move without causing the CRCS to move completely. This allows the CRCS to be easily moved when the CR is commanded to change, thereby improving transient response. In one example, relaxing the band brake to reduce the brake pressure on the CRCS includes adjusting a duty cycle commanded to an electric actuator coupled to the band brake to move a spring of the band brake a certain amount in a direction opposite of its bias. The commanded duty cycle varies with the desired degree of opening. In particular, the commanded duty cycle may be adjusted to maintain the control shaft sufficiently slack to allow a degree of movement that is higher than would be allowed when the control shaft is locked, but lower than would be allowed when the control shaft is fully unlocked. In this way, some preload of the band is arranged by reducing band brake friction when an imminent CR change is expected (such as in response to a sudden high torque request). As set forth in detail below (at 340-.

By reducing the band brake pressure to achieve a degree of shaft motion that is higher than would be allowed when the shaft is fully locked, but lower than that which would be allowed when the shaft is fully unlocked, the shaft is prepared so that it can be easily and quickly moved via motor torque from the VCR actuator in rapidly changing engine speed/load regions when a change in CR is required. Additionally, the controller may be informed of the braking force required to hold the shaft in the "slack" position as a function of engine speed/load conditions and further as a function of the current CR setting. In some examples, the controller may learn the braking force as a function of control shaft position and engine compression ratio relative to a range of positions. For example, the controller may increase the braking torque applied by the band brake until the position of the control shaft is outside the upper limit of the permissible position range, and then decrease the braking torque until the position of the control shaft is outside the lower limit of the position range. In this way, the controller can learn the braking force required to maintain the control shaft at a degree of movement between the upper and lower limits of the permitted position range. Herein, the position range may correspond to a threshold compression ratio range, such as the centered range δ of fig. 7. After learning the braking force as a function of the control shaft position and the (current) engine compression ratio setting relative to the range of positions, the controller may adjust the hydraulic pressure applied to the solenoid valve coupled to the band brake based on this knowledge.

In some examples, the pressure applied via the oil control valve and the band brake may also be controlled in a closed loop by allowing angular movement of the CRCS at a target rate (in radians/second). Control is achieved by a minimum power consumption balance between the belt brake force required to achieve the target angular acceleration and velocity and the VCR actuator motor current.

Next, at 340, it is determined whether a shift has been scheduled. The shift may be scheduled in response to a change in torque demand. If a shift is scheduled, then at 342 the method includes adjusting the state of the VCR actuator and the band brake based on the desired CR setting after the shift. The method may initiate a shift after locking the band brake and then initiate a VCR transition to a desired CR setting (CRd) after completing the transmission shift. For example, if a change in the CR setting is required after a shift, the band brake may be closed to lock the brake and the CRCS. Then, with the CRCS remaining locked, transmission shifts can be initiated and completed. After the transmission shift is completed, the band brake may be opened and the brake pressure applied by the band brake on the CRCS may be reduced to enable the CRCS to move (at full degree of motion). The VCR actuator can then be actuated to transition the engine and move the CRCS to a position corresponding to the desired CR setting. Then, after the CR transition is completed, the band brake may be closed again to lock the CRCS in the current CR setting. In this manner, initiation and completion of a transmission shift may be delayed until the band brake has been locked, and the CR transition may be delayed until the transmission shift has been completed.

Large torque disturbances may occur during a shift. Since the engine is held at the same (high) compression ratio during most transient operations, the CRCS may be held locked during the shift. Durability, efficiency, and power targets are better met by more reliably enabling piston position determination relative to the crankshaft via a locked CRCS during gear shifting.

It will be appreciated that CR may be reduced from high to low when the transmission is downshifted to obtain a higher power output of the engine. This transition may occur relatively quickly when the vehicle is already at a relatively high engine speed to actuate with engine torque, as elaborated in fig. 5.

If a shift is not scheduled, at 344, it may be determined whether an engine stop condition has been met. In one example, an engine-off condition may be confirmed if the torque demand is less than a threshold, if the vehicle speed is less than a threshold, if the battery is not fully charged, and there is no need for cabin cooling/heating. If the engine stop condition is not met, then at 346, engine operation is maintained. The controller may continue to adjust the CR setting of the engine based on changes in engine speed/load while the engine is operating. Additionally, based on the selected CR setting, the controller may adjust the brake band and VCR actuator states to enable the CRCS to lock when the CR setting is to be maintained and to enable the CRCS to move when the CR setting may change.

If the engine stop condition is met, at 348, it may be determined whether the engine is already in a low CR setting, such as a low setting required upon a subsequent engine restart. For example, it may be determined whether the engine is already at CR 8.0. If so, at 356, the method includes shutting down the engine. Stopping the engine includes disabling fuel and spark and allowing the engine to slow to rest. Additionally, the controller may disable power to the hydraulic actuator coupled to the band brake to close the band brake, which locks the CRCS and enables the engine to stop at the low CR setting. Thus, the engine may be pre-positioned for starting in the low CR setting when the engine is subsequently restarted.

Otherwise, if the engine is not in the low CR setting, at 350, it may be determined whether the band brake is currently locked. If not, at 354, the controller may keep the engine running and command the VCR actuators to the low CR setting. Herein, since the band brake is unlocked (i.e., it is open), the CRCS is able to move and move when power is applied to the VCR actuator to move the engine to the low CR setting. If the band brake is locked, then at 352, the method includes keeping the engine running and opening the band brake. Opening the band brake includes powering an actuator coupled to the band brake to apply a force to the spring in a direction opposite the default bias of the spring. This allows the CRCS to move. The controller may then command the VCR actuators to the low CR setting required for a subsequent engine start.

From each of 352 and 354, after transitioning the engine to the low CR setting, the method moves to 356 to stop the engine and disable power to hydraulic actuators coupled to the band brakes to close the band brakes. This locks the CRCS and enables the engine to be shut down in the low CR setting. Thus, the engine may be pre-positioned for starting in the low CR setting when the engine is subsequently restarted.

Turning now to fig. 5, an example method 500 for coordinating engine torque actuation with VCR actuator operation and band brake actuation to effect a CR transition is shown. The method of fig. 5 may be performed as part of the method of fig. 3, such as at 332. The method enables to improve the transient response time of the CR transition. At the same time, transient response time can be balanced with CRCS hardware durability to extend component life.

The torque required to overcome the combustion forces can be calculated from the engine torque applied directly to the VCR actuator via the crankshaft, rod, intermediate link (e.g., intermediate link 206 of fig. 2), connecting rod (such as rod 204 of fig. 2), and eccentricity of the connecting rod attached to the CRCS, the "s" link lever ratio, and a gear set in the VCR resolver motor. The duty cycle may then be scheduled to control the torque (force) required to overcome the friction of the band clutch and move the CRCS at the desired angular velocity by knowing the braking force applied to the band brake from the band brake solenoid valve (such as valve 210). Referring to the map 800 of fig. 8, the sign of the sum of the torques during the combustion cycle at various CRs (as defined by the different lines in fig. 8) may be determined. This determines the direction of movement of the CRCS when no other actuator or brake is acting on the CRCS. The sum allows for accurate calculation of band brake friction or pressure to be applied. Turning now to fig. 5, at 502, the method includes retrieving a current CR setting (CRc), such as via a sensor coupled to the CRCS or based on engine operating conditions, as previously described at 304. At 504, the method includes determining a desired CR setting based on engine operating conditions, as depicted at 320. At 506, the method includes determining whether CRc is higher than CRd. If not, at 508, the method includes opening the band brake and commanding the VCR actuator to transition the engine from CRc to CRd. Opening the band brake includes commanding electrical power to a hydraulic solenoid of the band brake to move a spring of the valve in a direction opposite the inherent bias of the spring. Commanding the VCR actuator to effect the transition includes commanding power to the VCR actuator to move the CRCS.

If CRc is higher than CRd, then at 510, it may be determined that the engine torque on the CRCS has been higher than a threshold throughout the combustion cycle (such as confirming the presence of any positive engine torque on the CRCS). In one example, a positive engine torque application on the CRCS may be inferred based on the speed and direction of shaft rotation. If not, the method returns to 508 to open the band brake and command the VCR actuator to transition the engine from CRc to CRd. Otherwise, if there is already positive engine torque on the CRCS during the combustion cycle, it may be determined at 512 whether the band brake has been locked. The band brake may be locked when no electric power is supplied to the hydraulic actuator of the band brake. The locked position may be a default position of the band brake, wherein the spring of the hydraulic actuator is biased in a direction.

If the band brake is locked, then at 514, the method includes releasing the band brake and reducing the brake pressure applied by the band brake on the CRCS. For example, the band brake may be released by applying power to a hydraulic actuator of the band brake to open the solenoid-operated valve. The band brake may be opened to an extent that allows the control shaft to move at a rotational degree lower than that allowed when fully unlocked. The inventors herein have recognized that due to the configuration of the VCR mechanism, after CR drops below the threshold CR, torque is exerted on the CRCS during combustion, which naturally moves the shaft from high CR to low CR. For example, when CR falls below CR 12.5, engine torque may be applied. The rotational speed of the CRCS can be increased using this inherent torque plus the force from the VCR actuator. This may improve the transient response time. Thus, by relaxing the band brake and enabling the CRCS to move, the engine torque can be utilized to quickly transition the engine from a higher CR to a lower CR in addition to the VCR actuator torque. Improving the time to reduce the compression ratio may improve vehicle response during events requiring vehicle acceleration.

If the band brake is not locked, then at 516, it may be determined whether the CRCS is moving at a speed that may cause damage to the component. For example, based on the position signal from the VCR actuator (or the signal coupled to the CRCS), the controller may calculate the speed of movement of the control shaft. If the estimated speed is above the threshold speed, then at 518, the brake pressure applied by the band brake on the CRCS may be adjusted to reduce the speed to within the target speed range. By reducing the speed of the CRCS, the shaft may be protected from speed-induced damage. If combustion forces are used to move quickly to the low CR position, angular velocity may not be as important until resting in the low CR position. Thus, by measuring the rate of change of angle (in radians/second) of the CRCS, the controller can predict that it is in the future of that rate of change when the shaft will come to rest, and apply the brake to slow that rate and "soft land". As an example, the controller may tighten the band brake to reduce the speed of movement of the CRCS during the transition of the engine from a higher CR to a lower CR. This includes the controller reducing power to the hydraulic actuator of the band brake to move the spring mechanism in its default biasing direction. This increases the braking torque that counteracts the engine torque applied to the CRCS. Additionally, the controller may power the VCR actuator to increase the power of the CRCS in a direction opposite the engine torque.

If the CRCS is not moving at a higher speed than desired, at 520, the method includes releasing the band brake to allow the CR to transition at the same (or higher) speed. This includes the controller providing power to the hydraulic actuator of the band brake to move the spring mechanism in a direction opposite its default bias. The controller may also optionally power the VCR actuator to increase the power to the CRCS in the same opposite direction as the engine torque.

In this manner, the band brake and VCR actuator can cooperate to improve transient engine response while also reducing the likelihood of the CRCS affecting a mechanical emergency stop. Thus, the component life of the VCR mechanism is extended.

It will be appreciated that the actuator coupled to the band brake may be a hydraulic actuator or an electric actuator. In either case, the actuator is coupled to a spring-loaded valve and must be powered to overcome the spring force to unlock the brake. When not powered, the spring is biased in a default position, which locks the brake. Thus, if there is an electrical failure or degradation of any component of the hydraulic or electric actuator, the brake defaults to the locked position, thereby ensuring that the CRCS is locked in place.

The controller may learn the brake engagement position and the fully locked position within the iterative actuation event to achieve a "smoother" landing. This achieves a faster time to the fully unlocked position. By locking the CRCS in the default position, the hydraulic or electric actuator allows the VCR actuator to operate at maximum power during the CR transition phase while remaining unpowered while operating at fixed CR, further improving fuel economy. The tip of the brake band actuator may be attached to the slack band during assembly such that the actuator is in a fully extended state. The strap may lock the control shaft in place when the actuator is tightened.

In this way, the controller can maintain the position of the control shaft for changing the compression ratio of the engine via the braking force from the brake; and adjusting the braking force based on operating conditions before and during actuation of the control shaft. Herein, actuation of the control shaft includes changing the compression ratio via a Variable Compression Ratio (VCR) actuator coupled to the control shaft, and wherein the position of the control shaft is not maintained via torque from the VCR actuator. The controller may also actuate the control shaft in response to an upcoming transmission shift schedule that is adjusted based on the braking force. Wherein the controller may reduce the braking force prior to actuation of the control shaft, and change the braking force upon actuation of the control shaft, the change being based on a first compression ratio prior to the actuation of the control shaft relative to a second compression ratio after the actuation of the control shaft. In one example, when the first compression ratio is higher than an upper threshold or lower than a lower threshold and the second compression ratio is between the upper threshold and the lower threshold, the changing includes decreasing the braking force when the compression ratio is moved from the first compression ratio to the second compression ratio. In another example, the varying includes increasing the braking force when one or more of engine torque on the control shaft and motor torque from the VCR actuator increases when the first compression ratio is higher than the second compression ratio, the braking force increasing to transition from the first compression ratio to the second compression ratio at a target speed, the target speed selected based on hardware limitations of the control shaft. The brake may be coupled to a spring-loaded valve, and adjusting the braking force may include decreasing the braking force by increasing a pressure exerted on a spring of the spring-loaded valve opposite a spring-biased direction; and increasing the braking force by reducing the pressure exerted on the spring. The pressure may be applied hydraulically by a hydraulic actuator or electrically via an electric actuator, as depicted in fig. 6A-6B. Actuation of the control shaft may include transitioning the engine from a first compression ratio setting to a second compression ratio setting. The adjusting may include: during a first condition, reducing the braking force and then increasing the braking force prior to the actuation of the control shaft to maintain the engine in the second compression ratio setting while achieving a lower degree of control shaft motion; and during a second condition, reducing the braking force and then increasing the braking force prior to the actuation of the control shaft to maintain the engine in the second compression ratio setting while achieving a higher degree of control shaft motion. For example, during the first condition, the second compression ratio setting may correspond to a lower rate of change region of engine speed and load, while during the second condition, the second compression ratio setting may correspond to a higher rate of change region of engine speed and load.

Fig. 6A-6B detail actuation of a band brake via a hydraulic actuator (method 600 of fig. 6A) and via an electric actuator (method 620 of fig. 6B).

Turning first to method 600 of fig. 6A, hydraulic actuation of the band brake during VCR operation is detailed. The hydraulic actuator of the band brake may be bolted to one side of the engine or to the oil pan with a gasket to keep the oil seal intact.

At 602, the method determines whether the CRCS is to be locked. As previously discussed, the CRCS may be locked when the engine is to be operated in a fixed CR setting, which may be the highest possible or lowest possible CR setting for the VCR mechanism. Additionally, the CRCS may be locked when the engine is in a speed-load region where engine speed and load do not change rapidly, such as when the engine is outside region δ of FIG. 7. If the CRCS is to be locked, then at 604, the method includes disabling power to the VCR actuator while opening the band brake solenoid valve. After the band brake solenoid is opened, CRCS lock is maintained via the spring-loaded mechanism of the solenoid. After the power is disconnected, the solenoid valve opens, locking the mechanism in place independent of hydraulic fluid (e.g., oil) temperature and hydraulic fluid level.

If the CRCS has locked (and thus no longer needs to be locked), then at 606, a determination is made as to whether the brake pressure applied by the brake band on the CRCS needs to be reduced. If so, at 608, the method includes commanding a single "pull" action via the actuator in a first direction (opposite the spring bias direction) to provide a short stroke against the spring loading. The short stroke allows a low profile in the opposite direction for smaller packages and uses less hydraulic volume.

Turning now to method 620 of fig. 6B, the electric actuation of the band brake during VCR operation is detailed. The electric actuator of the band brake may be coupled to the same location of the engine as the AC or DC motor, with integrated or external controls attached to the working gear without springs or spring-loaded general mechanisms (similar to those used for hydraulic actuation).

At 622, the method determines whether the CRCS is to be locked, as at 602. As previously discussed, the CRCS may be locked when the engine is to be operated in a fixed CR setting, which may be the highest possible or lowest possible CR setting for the VCR mechanism. Additionally, the CRCS may be locked when the engine is in a speed-load region where engine speed and load do not change rapidly, such as when the engine is outside region δ of FIG. 7. If the CRCS is to be locked, then at 624 the method includes disabling power to the VCR actuator while opening the band brake solenoid valve. After the band brake solenoid is opened, CRCS lock is maintained via the spring-loaded mechanism of the solenoid. After the power is turned off, the solenoid valve opens, locking the mechanism in place.

If the CRCS has locked (and thus no longer needs to be locked), then at 626, it is determined whether the brake pressure applied by the brake band on the CRCS needs to be reduced. If so, at 628, the method includes applying a voltage to move the spring-loaded mechanism in a first direction (opposite the spring-biased direction) to provide a short stroke against the spring loading.

The table 900 of FIG. 9 tabulates the positions of various mechanisms and actuators during various engine operating conditions.

It will be appreciated that fig. 9 shows that for engine idle conditions, the CRCS is typically locked because little to no movement is expected at idle (and a high CR setting is the most efficient setting). However, in some conditions, the CRCS may unlock, such as during small engine displacements at high temperatures under high accessory load conditions (e.g., where AC is on, and high output from the generator).

Turning now to FIG. 10, an example VCR adjustment for a vehicle having a VCR engine is shown. Map 1000 shows a change in engine speed, indicating a change in torque demand, as curve 1002. Based at least on engine speed and load, the desired CR setting for the engine, shown as curve 1004, may be changed. For example, the CR setting may be varied between low, medium, and high CR settings. In one non-limiting example, these may include CR8, 11, and 14, respectively. CR setting adjustment may be achieved via electrical actuation of the VCR actuator (curve 1010) and the state of the band brake coupled to the control shaft (CRCS) of the VCR mechanism (curve 1006). The degree and rate of rotation of the CRCS during the CR transition may be varied by varying the hydraulic pressure applied to the spring-loaded actuator of the band brake, which varies the degree of locking of the band brake, as shown by curve 1008. The adjustments may be coordinated with the transmission shift schedule (curve 1012) to achieve smoother transitions. The engine load is shown in curve 1014. The engine speed (curve 1002) and load (curve 1014) adjustments may be coordinated as the driver demand changes during vehicle propulsion.

Before t1, the engine is stopped. Herein, the engine may have been shut down in the low CR setting. At t1, in response to an increase in driver torque demand, the engine is restarted and engine speed begins to increase. Since the engine is stopped in the low CR setting required to restart the engine, the engine can be restarted without the need to provide power to the VCR actuators and keep the CRCS fixed via locking of the band brake. Since the closed or locked position of the band brake is the default position, there is no need to apply hydraulic pressure on the spring that actuates the solenoid valve of the band brake.

After the engine is started and cranked at t1, the engine moves to and remains at the idle speed. At t2, the low CR setting is maintained without actuating the VCR actuators since the engine remains in the idle condition. In an alternative example, the engine may be idling in a high CR setting, such as when the catalyst is completely warmed. Wherein the band brake can be momentarily unlocked and the VCR actuator can be actuated to move the engine from the low CR setting to the high CR setting and then the band brake can be relocked and engine idle speed maintained in the high CR setting with the CRCS locked, as shown by dashed line segments 1003, 1007, 1011 and 1009.

In this example, a sudden change in engine speed and load, and thus a change in CR, is expected, with the band brake being partially unlocked by applying pressure to the spring to move the spring in a direction opposite its bias. This reduces the brake pressure exerted by the band brake on the control shaft to a level where the shaft can move to some extent but not freely. At the same time, the current low CR setting may be maintained without applying motor torque through the VCR actuator. To reduce the effect of idle combustion changes on the VCR actuator, the CRCS is held in place by continuing to hold the brake band partially locked and the low CR setting is held fixed.

At t3, in response to a change in driver torque demand (such as a light touch requesting additional torque), there is a change in engine speed (which increases as the vehicle accelerates) and load, requiring the CR to transition to the high CR setting. To effect the transition, the brake pressure applied by the band brake on the CRCS is reduced by increasing the pressure on the spring, thereby moving the band brake to the fully unlocked position, before the VCR actuator is powered to effect the transition. Since the CRCS can move, the VCR actuators are powered for a period of time to apply motor torque to the CRCS to move the engine to the high CR setting. After the transition is completed, the CRCS is locked in the high CR setting by reducing the pressure applied to the spring, which locks the band brake (in its default position). In addition, power to the VCR actuator is disabled. Thereafter, between t4 and t5, the engine is held in the high CR setting via the band brake.

At t5, there is a change in engine operating conditions, requiring a transition to the intermediate CR setting. To effect the transition, the band brake is first unlocked, allowing the CRCS to move. The VCR actuator is momentarily powered to apply torque to the CRCS and move it to a position corresponding to the desired CR setting. When CR transitions between t5 and t6 to an intermediate CR setting (which is in zone δ where there may be a high rate of change in engine speed and load), where the CR transition may occur suddenly, the CRCS moves from the fully unlocked state to the partially locked state by reducing the pressure on the spring. The pressure may decrease as CR moves from the high CR setting toward the intermediate CR setting. After the desired CR setting is reached, the VCR actuator is disabled.

When in this CR setting, between t6 and t7, the band brake holding portion is locked and the CRCS is held loose enough so that the VCR actuator torque can again move the CRCS when needed without the VCR actuator torque being required to hold the CRCS in its current position. It will be appreciated that although the example shows the pressure on the spring to remain stable between t6 and t7, this may reflect an average pressure. The controller may continuously make changes to the pressure applied to the spring to vary the braking torque applied by the band brake on the CRCS. The resulting relaxation of the CRCS may result in a small degree of CRCS movement, which may cause the CR setting to deviate from the desired setting and cause the CRCS position to deviate from the desired position (corresponding to the selected CR setting). For example, spring pressure may be applied and braking torque reduced until motion of the CRCS in the first direction is noted. In response to the detected motion, the spring pressure may be reduced and the braking torque increased until motion of the CRCS in a second, opposite direction is noted. In response to the detected movement, the braking torque may be reduced again. In this way, the CRCS can be made to move continuously to a small degree so that the CR setting is kept on average at the desired setting without requiring motor torque from the VCR actuators. At the same time, the CRCS is slack enough that it can move upon application of motor torque thereto via the VCR actuator.

As an example, for all modes where the band brake remains relaxed, the controller may refer to a mapped value of the minimum CR change required to actuate (relax) the band. When the oil solenoid is consuming power, the controller may lock the band brake at a fixed discrete CR level (e.g., 1 CR point) because more energy is spent holding the solenoid open and the band slack than in response to a CR change of less than 1 CR point.

As another example, the controller may continuously vary the braking torque by increasing the braking force applied by the band brake until the control shaft moves in the first direction outside of the permitted range of positions of the CRCS (while at the intermediate CR setting). In response to the movement, the controller may immediately reduce the braking force until the control shaft moves outside of the position range in a second opposite direction. Herein, the position range may be based on the current CR setting or a permitted threshold compression ratio range, where the CRCS remains at a setting that achieves a certain degree of rotation.

At t7, there is another change in engine operating conditions, requiring a decrease in CR. Additionally, until t7, the transmission is in first gear. Changes in engine operating conditions may also require the transmission to shift to a second gear that is different from the first gear. In one example, the requested transmission shift is an upshift (as shown herein). In another example, the requested transmission shift may be a downshift. In either case, initiation of transmission gear shifting is delayed until the band brake is locked. Specifically, at t7, the pressure on the spring is reduced to return the band brake to the default closed (closed) position. Then, while the band brake remains locked, a transmission shift is initiated and is completed at t 8. At t8, the requested CR transition is initiated. Since the desired CR is now lower than the current CR, at least some of the engine combustion torque experienced by the CRCS due to cylinder combustion may be used to move the CRCS in the direction of the lower CR setting. This engine torque application is coordinated with the VCR torque and the band brake torque application so that the transition can occur at the required rate and not faster (as may occur without the band brake torque being applied). Specifically, the ratio of the braking torque applied to the CRCS via the band brake to the motor torque applied to the CRCS via the VCR actuator is adjusted according to the engine torque to enable a transition from the intermediate CR setting to the low CR setting at the target rate. Specifically, the VCR actuator is powered to apply a motor torque to the shaft. When the motor torque increases, and since the engine torque is also simultaneously applied to the shaft in the same direction as the motor torque (so as to move the shaft in the direction of the lower CR setting), the braking torque applied by the brake band to the shaft is increased by reducing the pressure on the spring. This allows the CR transition to occur gradually. Otherwise, in the absence of braking torque, the transition may occur faster, as indicated by dashed segment 1005, and this may lead to hardware durability issues.

After the transition to the lower CR setting is complete, the CRCS is locked by reducing the pressure on the spring to close and lock the band brake, and power to the VCR actuator is disabled. Thereafter, the engine is held in the lower CR setting via the locked band brake.

At t9, there is another change in engine operating conditions, requiring a transition to a high CR setting and another transmission shift, here a downshift. Since the band brake is already locked, the transmission shift is initiated immediately. Then, after the transmission shift is completed, a CR transition is initiated. To effect the transition, the brake pressure applied by the band brake on the CRCS is reduced by increasing the pressure on the spring, thereby moving the band brake to the fully unlocked position, before the VCR actuator is powered to effect the transition. Since the CRCS can move, the VCR actuators are powered for a period of time to apply motor torque to the CRCS to move the engine to the high CR setting. After the transition is completed, the CRCS is locked in the high CR setting by reducing the pressure applied to the spring, which locks the band brake (in its default position). In addition, power to the VCR actuator is disabled. Thereafter, the engine is held in the high CR setting via the band brake while the transmission is also oriented toward a higher gear. In this way, in response to a change in engine operating conditions requiring a change in engine compression ratio and a transmission shift, the controller may increase the braking force to lock the brake before initiating the transmission shift. Then, after the transmission shift is completed, the controller may reduce the braking force on the control shaft from the brake while increasing the motor torque on the control shaft from the electric compression ratio actuator to move the control shaft to a position corresponding to the change in the engine compression ratio.

At t10, the engine idle-stop condition is satisfied and engine shutdown is requested. Since the engine needs to be restarted at the low CR setting during a subsequent restart (as during an engine restart at t 1), the transition from the high CR setting to the low CR setting is effected before the engine is actually shut down. In other words, the shutdown is delayed until the CR transition is completed. Specifically, the brake pressure applied by the band brake on the CRCS is reduced by increasing the pressure on the spring, thereby moving the band brake to the fully unlocked position, before powering the VCR actuator to effect the transition. Since the CRCS can move, the VCR actuators are powered for a period of time to apply motor torque to the CRCS to move the engine to the low CR setting. After the transition is completed, the CRCS is locked in the low CR setting by reducing the pressure applied to the spring, which locks the band brake (in its default position). After the CR transition is completed, the engine is shut down by disabling fuel and spark to the engine cylinders at t11, which causes the engine to slow down to rest while the CR is maintained at the low CR setting by the locked band brake. Therefore, when the engine is restarted after t11, the engine may be restarted in the low CR setting, thereby improving engine startability.

In this manner, during a first condition outside of the threshold compression ratio range, the controller may maintain a fixed position of the control shaft via braking force from the brake, the control shaft changing the compression ratio of the engine. In contrast, during a second condition within the threshold compression ratio range, the controller may continuously change the position of the control shaft within the range of positions via the braking force. In one example, during a first condition, the compression ratio of the engine is above an upper threshold or below a lower threshold, and during a second condition, the compression ratio of the engine is below the upper threshold and above the lower threshold. The continuously varying may include: the method further includes increasing the braking force until the control shaft moves in a first direction outside of a position range, and in response to the movement, decreasing the braking force until the control shaft moves in a second, opposite direction outside of the position range, the position range being based on the threshold compression ratio range. Additionally, during a second condition, the controller may learn a braking force that varies with the position of the control shaft relative to the range of positions and the engine compression ratio; and adjusting a hydraulic pressure applied to a solenoid valve coupled to the brake based on the knowledge. In a further example, during the first condition, the electric compression ratio actuator coupled to the control shaft may be disabled and no motor torque may be applied to the control shaft via the actuator. In contrast, during the second condition, an electric compression ratio actuator coupled to the control shaft may be enabled and at least some motor torque may also be applied to the control shaft via the actuator. Additionally, during both the first and second conditions, in response to a change in engine operating conditions requiring a change in engine compression ratio and a transmission shift, the controller may reduce braking force on the control shaft from the brake while increasing motor torque on the control shaft from the electric compression ratio actuator to move the control shaft to a position corresponding to the change in engine compression ratio, and then increase braking force to maintain the fixed position of the control shaft prior to initiating the transmission shift. If the change in the engine compression ratio includes a decrease in the compression ratio, the controller may also adjust the ratio of the braking force from the brake on the control shaft to the motor torque from the electric compression ratio actuator based on the engine torque applied to the control shaft via the piston due to the combustion in the cylinder to cause the control shaft to transition at the target speed via the decrease in the compression ratio.

In this way, a fixed CR setting may be maintained while reducing power consumption at the VCR actuator. By varying the braking torque applied to the control shaft of a VCR engine via the band brake, the compression ratio control shaft can be held sufficiently slack to transition to the desired CR setting during transient torque demands. At the same time, the control shaft may be held tight enough to maintain the current CR setting. Transient response time is improved by relaxing the control shaft via the band brake when operating in the engine speed-load region where sudden changes in CR are expected. By tightening the control shaft via the band brake when sudden changes in CR are not expected, power can be disabled to the VCR actuator while a more accurate estimate of piston position is achieved. In addition, the position of the control shaft may be used to calculate the speed of movement of the control shaft, allowing for finer control of the CR transition rate. By coordinating the torque on the control shaft applied via the band brake and VCR actuator with the engine torque inherently applied on the control shaft during the shift to the lower compression ratio, a CR shift can be achieved at a speed that does not cause hardware problems while still providing the required transition response time. By also coordinating the adjustments with the transmission shift schedule, smoother transmission shifts may be achieved. By improving the CR transition while reducing power consumption, performance and fuel economy of a VCR engine may be improved.

One example method for an engine includes: maintaining a position of a control shaft for changing a compression ratio of the engine via a braking force from a brake; and adjusting the braking force based on operating conditions before and during actuation of the control shaft. In the previous example, additionally or alternatively, the actuation of the control shaft includes changing the compression ratio via a Variable Compression Ratio (VCR) actuator coupled to the control shaft, and wherein the position of the control shaft is not maintained via torque from the VCR actuator. In any or all of the preceding examples, additionally or alternatively, the method further comprises actuating the control shaft in response to an upcoming transmission shift, the transmission shift schedule being adjusted based on the braking force. In any or all of the preceding examples, additionally or alternatively, the adjusting includes reducing the braking force prior to actuation of the control shaft, and changing the braking force while the control shaft is actuated, the changing based on a first compression ratio prior to the actuation of the control shaft relative to a second compression ratio after the actuation of the control shaft. In any or all of the preceding examples, additionally or alternatively, when the first compression ratio is above an upper threshold or below a lower threshold and the second compression ratio is between the upper threshold and the lower threshold, the changing comprises decreasing the braking force when the compression ratio is moved from the first compression ratio to the second compression ratio. In any or all of the preceding examples, additionally or alternatively, when the first compression ratio is higher than the second compression ratio, the varying comprises increasing the braking force as one or more of an engine torque on the control shaft and a motor torque from the VCR actuator increases, the braking force increasing to transition from the first compression ratio to the second compression ratio at a target speed, the target speed selected according to a hardware limit of the control shaft. In any or all of the preceding examples, additionally or alternatively, the brake is coupled to a spring-loaded valve, and wherein adjusting the braking force comprises: reducing the braking force by increasing a pressure exerted on a spring of the spring-loaded valve opposite a spring-biased direction; and increasing the braking force by reducing the pressure exerted on the spring. In any or all of the preceding examples, additionally or alternatively, the actuation of the control shaft includes transitioning the engine from a first compression ratio setting to a second compression ratio setting, and wherein the adjusting includes: during a first condition, reducing the braking force prior to the actuation of the control shaft and then increasing the braking force to maintain the engine in the second compression ratio setting while achieving a lower degree of control shaft movement; and during a second condition, reducing the braking force prior to the actuation of the control shaft and then increasing the braking force to maintain the engine in the second compression ratio setting while achieving a higher degree of control shaft movement. In any or all of the preceding examples, additionally or alternatively, during the first condition the second compression ratio setting corresponds to a lower rate of change zone of engine speed and load, and wherein during the second condition the second compression ratio setting corresponds to a higher rate of change zone of engine speed and load.

Another example method for an engine includes: maintaining a fixed position of a control shaft that changes a compression ratio of the engine via a braking force from a brake during a first condition outside a threshold compression ratio range; and continuously changing the position of the control shaft within a range of positions via the braking force during a second condition within the threshold compression ratio range. In any or all of the preceding examples, additionally or alternatively, during the first condition the compression ratio of the engine is above an upper threshold or below a lower threshold, and wherein during the second condition the compression ratio of the engine is below the upper threshold and above the lower threshold. In any or all of the preceding examples, additionally or alternatively, the continuously varying comprises: increasing the braking force until the control shaft moves in a first direction outside of the position range; and in response to the movement, reducing the braking force until the control shaft moves in a second opposite direction outside of the position range, the position range being based on the threshold compression ratio range. In any or all of the preceding examples, additionally or alternatively, the method further comprises: learning the braking force as a function of control shaft position and the engine compression ratio relative to the range of positions during the second condition; and adjusting hydraulic pressure applied to a solenoid valve coupled to the brake based on the knowledge. In any or all of the preceding examples, additionally or alternatively, during the first condition, disabling an electric compression ratio actuator coupled to the control shaft and applying no motor torque to the controller via the actuator, and wherein during the second condition, enabling the electric compression ratio actuator coupled to the control shaft and also applying at least some motor torque to the control shaft via the actuator. In any or all of the preceding examples, additionally or alternatively, the method further comprises during both the first and second conditions, in response to a change in engine operating conditions requiring a change in engine compression ratio and a transmission shift, increasing the braking force to lock the brake before initiating the transmission shift, and then after completing the transmission shift, decreasing the braking force on the control shaft from the brake while increasing the motor torque on the control shaft from the electric compression ratio actuator to move the control shaft to a position corresponding to the change in engine compression ratio. In any or all of the preceding examples, additionally or alternatively, when the change in engine compression ratio comprises a decrease in compression ratio, a ratio of a braking force on the control shaft from the brake to a motor torque from the electric compression ratio actuator is adjusted based on an engine torque exerted on the control shaft via a piston due to cylinder combustion to transition the control shaft at a target speed via the decrease in compression ratio.

Another example engine system includes: an engine; a control shaft for changing a compression ratio of the engine; a brake for applying a braking torque to the control shaft, the brake being actuated via a spring-loaded solenoid valve; an electric actuator for applying a motor torque to the control shaft; a transmission including a plurality of gears; and a controller storing executable instructions in a non-transitory memory that, when executed, cause the controller to: maintaining the control shaft in a fixed position via the brake to maintain a first compression ratio setting of the engine; and adjusting a ratio of the braking torque from the brake on the control shaft to the motor torque from the electric actuator according to an engine torque exerted on the control shaft due to cylinder combustion in response to a request to transition the engine to a second compression ratio setting lower than the first setting. In any or all of the preceding examples, additionally or alternatively, the controller further comprises instructions that cause the controller to: after transitioning to the second compression ratio setting, increasing the braking torque while decreasing the motor torque to maintain the position of the control shaft; and then initiating a transmission shift. In any or all of the preceding examples, additionally or alternatively, increasing the braking torque includes increasing the braking torque to achieve a first degree of control shaft motion when the second compression ratio is set within a threshold compression ratio range corresponding to a higher rate of change of engine speed or load, and increasing the braking torque includes increasing the braking torque to achieve a second degree of control shaft motion less than the first degree when the second compression ratio is set outside the threshold compression ratio range. In any or all of the preceding examples, additionally or alternatively, implementing the first degree of control shaft motion includes increasing the braking torque until a position of the control shaft is outside an upper limit of a range of positions corresponding to the threshold range, and then decreasing the braking torque until the position of the control shaft is outside a lower limit of the range of positions.

In further expressions, a method includes delaying transmission shifting until a compression ratio control shaft has been locked via a braking force applied through a brake. In the previous example, additionally or alternatively, the method further comprises initiating a compression ratio setting transition via an electric VCR actuator after completing the transmission shift, the initiating the VCR transition comprising unlocking the brake after the transmission shift and before actuating the VCR actuator. In any or all of the preceding examples, additionally or alternatively, the method further comprises disabling power to an electric VCR actuator that actuates the shaft before and during the transmission shift. In any or all of the preceding examples, additionally or alternatively, the method further comprises locking the control shaft after actuating the control shaft via motor torque from a VCR actuator to effect the engine CR transition. In any or all of the preceding examples, additionally or alternatively, the method further comprises unlocking the control shaft by reducing the braking force before the engine CR is transitioned.

In another further expression, a method includes maintaining a first degree of rotation of a control shaft for varying an engine compression ratio via a ratio of brake torque from a brake to motor torque from a VCR actuator while maintaining the engine compression ratio fixed. In the previous example, additionally or alternatively, the method further comprises maintaining a second lower degree of rotation of the control shaft via braking torque from the brake and without motor torque from the VCR actuator while keeping the engine compression ratio fixed. In any or all of the preceding examples, additionally or alternatively, a fixed engine compression ratio applied when maintaining the first degree of rotation of the shaft is below an upper threshold or above a lower threshold, and a fixed engine compression ratio applied when maintaining the second degree of rotation of the shaft is above the upper threshold or below the lower threshold. In any or all of the preceding examples, additionally or alternatively, the fixed engine compression ratio applied when maintaining the first degree of rotation of the shaft corresponds to a higher rate of change of engine speed and load and the fixed engine compression ratio applied when maintaining the second degree of rotation of the shaft corresponds to a lower rate of change of engine speed and load.

Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and programs disclosed herein may be stored as executable instructions in a non-transitory memory and executed by a control system including a controller in conjunction with various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various acts, operations, or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated acts, operations, and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described acts, operations, and/or functions may graphically represent code to be programmed into the non-transitory memory of a computer readable storage medium in an engine control system, wherein the described acts are implemented by executing instructions in a system comprising the various engine hardware components and an electronic controller.

It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above techniques may be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to "an" element or "a first" element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.

According to the invention, a method for an engine comprises: maintaining a position of a control shaft for changing a compression ratio of the engine via a braking force from a brake; and

adjusting the braking force based on operating conditions before and during actuation of the control shaft.

According to an embodiment, the actuation of the control shaft comprises changing the compression ratio via a Variable Compression Ratio (VCR) actuator coupled to the control shaft, and wherein the position of the control shaft is not maintained via torque from the VCR actuator.

According to an embodiment, the invention is further characterized by actuating the control shaft in response to an upcoming transmission shift, the transmission shift schedule being adjusted based on the braking force.

According to an embodiment, said adjusting comprises reducing said braking force before actuation of said control shaft, and changing said braking force when actuating said control shaft, said changing being based on a first compression ratio before said actuation of said control shaft relative to a second compression ratio after said actuation of said control shaft.

According to an embodiment, when the first compression ratio is higher than an upper threshold or lower than a lower threshold and the second compression ratio is between the upper threshold and the lower threshold, the changing comprises decreasing the braking force when the compression ratio is moved from the first compression ratio to the second compression ratio.

According to an embodiment, said changing comprises increasing said braking force when one or more of engine torque on said control shaft and motor torque from said VCR actuator is increased when said first compression ratio is higher than said second compression ratio, said braking force being increased to transition from said first compression ratio to said second compression ratio at a target speed, said target speed being selected according to hardware limitations of said control shaft.

According to an embodiment, the brake is coupled to a spring loaded valve, and wherein adjusting the braking force comprises: reducing the braking force by increasing a pressure exerted on a spring of the spring-loaded valve opposite a spring-biased direction; and increasing the braking force by reducing the pressure exerted on the spring.

According to an embodiment, said actuation of said control shaft comprises transitioning said engine from a first compression ratio setting to a second compression ratio setting, and wherein said adjusting comprises: during a first condition, reducing the braking force prior to the actuation of the control shaft and then increasing the braking force to maintain the engine in the second compression ratio setting while achieving a lower degree of control shaft movement; and during a second condition, reducing the braking force prior to the actuation of the control shaft and then increasing the braking force to maintain the engine in the second compression ratio setting while achieving a higher degree of control shaft movement.

According to an embodiment, during said first condition said second compression ratio setting corresponds to a lower rate of change of engine speed and load zone, and wherein during said second condition said second compression ratio setting corresponds to a higher rate of change of engine speed and load zone.

According to the invention, a method for an engine comprises: maintaining a fixed position of a control shaft that changes a compression ratio of the engine via a braking force from a brake during a first condition outside a threshold compression ratio range; and continuously changing the position of the control shaft within a range of positions via the braking force during a second condition within the threshold compression ratio range.

According to an embodiment, during said first condition, said compression ratio of said engine is higher than an upper threshold or lower than a lower threshold, and wherein during said second condition, said compression ratio of said engine is lower than said upper threshold and higher than said lower threshold.

According to an embodiment, said continuously varying comprises: increasing the braking force until the control shaft moves in a first direction outside of the position range; and in response to the movement, reducing the braking force until the control shaft moves in a second opposite direction outside of the position range, the position range being based on the threshold compression ratio range.

According to an embodiment, the invention is further characterized in that during said second condition, the braking force is known as a function of the control shaft position and the engine compression ratio relative to said range of positions; and adjusting hydraulic pressure applied to a solenoid valve coupled to the brake based on the knowledge.

According to an embodiment, during the first condition, an electric compression ratio actuator coupled to the control shaft is disabled and no motor torque is applied to the control shaft via the actuator, and wherein during the second condition, the electric compression ratio actuator coupled to the control shaft is enabled and at least some motor torque is also applied to the control shaft via the actuator.

According to an embodiment, the invention is further characterized by, during both the first and second conditions, requiring a change in engine compression ratio and a transmission shift in response to a change in engine operating conditions, increasing the braking force to lock the brake before initiating the transmission shift, and then after completing the transmission shift, decreasing the braking force on the control shaft from the brake while increasing the motor torque on the control shaft from the electric compression ratio actuator to move the control shaft to a position corresponding to the change in engine compression ratio.

According to an embodiment, when said change in engine compression ratio comprises a decrease in compression ratio, the ratio of the braking force from said brake on said control shaft to the motor torque from said electric compression ratio actuator is adjusted based on the engine torque exerted on said control shaft via the piston due to the cylinder combustion to shift said control shaft at the target speed via said decrease in compression ratio.

According to the present invention, there is provided an engine system having: an engine; a control shaft for changing a compression ratio of the engine; a brake for applying a braking torque to the control shaft, the brake being actuated via a spring-loaded solenoid valve; an electric actuator for applying a motor torque to the control shaft; a transmission including a plurality of gears; and a controller storing executable instructions in a non-transitory memory that, when executed, cause the controller to: maintaining the control shaft in a fixed position via the brake to maintain a first compression ratio setting of the engine; and adjusting a ratio of the braking torque from the brake on the control shaft to the motor torque from the electric actuator according to an engine torque exerted on the control shaft due to cylinder combustion in response to a request to transition the engine to a second compression ratio setting lower than the first setting.

According to an embodiment, the controller further comprises instructions that cause the controller to: after transitioning to the second compression ratio setting, increasing the braking torque while decreasing the motor torque to maintain the position of the control shaft; and then initiating a transmission shift.

According to an embodiment, when the second compression ratio is set within a threshold compression ratio range corresponding to a higher rate of change of engine speed or load, increasing the braking torque comprises increasing the braking torque to achieve a first degree of control shaft movement, and when the second compression ratio is set outside the threshold compression ratio range, increasing the braking torque comprises increasing the braking torque to achieve a second degree of control shaft movement less than the first degree.

According to an embodiment, achieving the first degree of control shaft motion comprises increasing the braking torque until a position of the control shaft is outside an upper limit of a range of positions corresponding to the threshold range, followed by decreasing the braking torque until the position of the control shaft is outside a lower limit of the range of positions.