阅读说明：本技术 车辆制动系统和检测柱塞组件的活塞定位的方法 (Vehicle braking system and method of detecting piston positioning of plunger assembly ) 是由 W·张 P·哈特曼 W·孔 于 2018-12-31 设计创作，主要内容包括：一种在车辆的点火循环开始时确定用于车辆制动系统的柱塞组件内的活塞的归位位置的方法,该方法包括首先提供柱塞组件,该柱塞组件具有在其中限定了孔的壳体。柱塞组件包括活塞,该活塞能够滑动地设置在孔中,用于在活塞沿第一方向移动时对压力腔室内的流体进行加压。柱塞组件进一步包括用于使活塞在孔内移动的电操作式线性致动器。该方法进一步包括对柱塞组件的线性致动器提供电力。致动线性致动器以使活塞沿与第一方向相反的第二方向朝向端部止挡件缩回。然后检测活塞与端部止挡件的接合。(A method of determining a home position of a piston within a plunger assembly for a vehicle braking system at the beginning of an ignition cycle of a vehicle includes first providing a plunger assembly having a housing defining a bore therein. The plunger assembly includes a piston slidably disposed in the bore for pressurizing fluid within the pressure chamber when the piston moves in a first direction. The plunger assembly further includes an electrically operated linear actuator for moving the piston within the bore. The method further includes providing power to a linear actuator of the plunger assembly. The linear actuator is actuated to retract the piston in a second direction opposite the first direction toward the end stop. The engagement of the piston with the end stop is then detected.)

1. A method of determining a home position of a piston within a plunger assembly for a vehicle braking system at the beginning of an ignition cycle of a vehicle, the method comprising:

(a) providing a plunger assembly having a housing defining a bore therein, wherein the plunger assembly includes a piston slidably disposed in the bore for pressurizing fluid within a pressure chamber when the piston moves in a first direction, and wherein the plunger assembly further includes an electrically operated linear actuator for moving the piston within the bore;

(b) providing power to the linear actuator of the plunger assembly;

(c) actuating the linear actuator to retract the piston in a second direction opposite the first direction toward an end stop; and

(d) detecting engagement of the piston with the end stop.

2. The method of claim 1, wherein after step (d), actuating the linear actuator to advance the piston a predetermined distance forward in the first direction to place the piston in a home position.

3. The method of claim 1, wherein after step (d), actuating the linear actuator to stop movement of the piston.

4. The method of claim 1, wherein in step (d) the engagement of the piston with the end stop is detected by detecting an increase in current to the linear actuator to a predetermined current value.

5. The method of claim 1, wherein in step (d) the engagement of the piston with the end stop is detected by detecting a decrease in the speed of the piston to a predetermined speed value.

6. The method of claim 1, wherein the end stop of the plunger assembly comprises a spring element.

7. The method of claim 6, wherein in step (d) the piston contacts the end stop compressing the spring element.

8. The method of claim 6, wherein in step (d) the engagement of the piston with the end stop is detected by the speed of the piston decreasing to a predetermined speed value as the spring element is compressed as it engages the piston.

9. The method of claim 1, wherein the linear actuator comprises a motor.

10. The method of claim 9, wherein the linear actuator further comprises a ball screw mechanism operated by the motor.

11. The method of claim 1, wherein the braking system is provided with a fluid reservoir and the plunger assembly further comprises a port in fluid communication with the fluid reservoir and the pressure chamber when the piston is in a first position, and wherein the port is prevented from being in fluid communication with the pressure chamber when the piston is in a second position due to a spatial relationship between a seal within the housing of the plunger assembly and the port.

12. The method of claim 11, wherein, after step (d);

(e) measuring a difference between a retracted position of the piston and a linear zero position of the piston in which the port is positioned adjacent the seal at a relatively small distance such that the port is in fluid communication with the fluid reservoir and the pressure chamber.

13. The method of claim 12, wherein in step (e), the difference is measured by:

(f) advancing the piston in the first direction from the retracted position; and

(g) detecting an increase in pressure in the pressure chamber of the plunger assembly, thereby detecting movement of the seal relative to the compensation port that results in a loss of fluid communication between the reservoir and the pressure chamber.

14. The method of claim 13, wherein after step (g), the method further comprises:

(h) retracting the piston in a second direction opposite the first direction, thereby causing an increase in pressure in a second pressure chamber within the plunger assembly; and

(i) detecting a pressure drop in the second pressure chamber of the plunger assembly, thereby detecting movement of the seal relative to the compensation port.

15. A method of detecting a position of a piston relative to a compensation port and seal structure of a plunger assembly, the method comprising:

(a) providing a fluid reservoir;

(b) providing a plunger assembly having a housing defining a bore therein, wherein the plunger assembly includes a piston slidably disposed in the bore for pressurizing fluid within a pressure chamber when the piston is moved in a first direction by a linear actuator, and wherein the plunger assembly includes a port in fluid communication with the fluid reservoir and the pressure chamber when the piston is in a first position, and wherein the port is prevented from being in fluid communication with the pressure chamber when the piston is in a second position due to a spatial relationship between a seal within the housing of the plunger assembly and the port;

(c) positioning the piston in a retracted position; and

(d) measuring a difference between the retracted position of the piston and a linear zero position of the piston in which the port is positioned adjacent the seal at a relatively small distance such that the port is in fluid communication with the fluid reservoir and the pressure chamber.

16. The method of claim 15, wherein in step (d), the difference is measured by:

(e) advancing the piston in the first direction from the retracted position; and

(f) detecting an increase in pressure in the pressure chamber of the plunger assembly, thereby detecting movement of the seal relative to the compensation port that results in a loss of fluid communication between the reservoir and the pressure chamber.

17. The method of claim 16, wherein after step (f), the method further comprises:

(f) retracting the piston in a second direction opposite the first direction, thereby causing an increase in pressure in a second pressure chamber within the plunger assembly; and

(g) detecting a pressure drop in the second pressure chamber of the plunger assembly, thereby detecting movement of the seal relative to the compensation port.

Background

The present invention generally relates to vehicle braking systems. Vehicles are typically slowed and stopped with a hydraulic braking system. These systems vary in complexity, but the basic braking system typically includes a brake pedal, a tandem master cylinder, fluid conduits arranged in two similar but independent brake circuits, and wheel brakes in each circuit. The driver of the vehicle operates a brake pedal connected to the master cylinder. When the brake pedal is depressed, the master cylinder generates hydraulic pressure in both brake circuits by pressurizing brake fluid. The pressurized fluid travels through the fluid conduits in both circuits to actuate the brake cylinders at the wheels of the vehicle, thereby decelerating the vehicle.

Basic braking systems typically use a brake booster that provides a force to a master cylinder to assist a pedal force generated by a driver. The booster may be vacuum or hydraulically operated. A typical hydraulic booster senses movement of the brake pedal and generates pressurized fluid that is introduced into the master cylinder. Fluid assist pedal force from the booster acts on pistons of the master cylinder, which produce pressurized fluid in conduits in fluid communication with the wheel brakes. Therefore, the pressure generated by the master cylinder is increased. The hydraulic booster is typically positioned adjacent the master cylinder piston and uses a boost valve to control the pressurized fluid applied to the booster.

Braking the vehicle in a controlled manner under adverse conditions requires the driver to apply the brakes with precision. Under these conditions, the driver may be prone to apply excessive brake pressure, thereby causing one or more wheels to lock, resulting in excessive slip between the wheels and the road surface. Such a wheel lock condition may result in a greater stopping distance and may lose directional control.

Advances in braking technology have led to the introduction of anti-lock braking systems (ABS). The ABS system monitors wheel rotation behavior and selectively applies and releases brake pressure in the corresponding wheel brakes to maintain wheel speed within a selected slip range to achieve maximum braking force. While such systems are typically adapted to control the braking of each braked wheel of the vehicle, some systems have been developed to control the braking of only a portion of the plurality of braked wheels.

Electronically controlled ABS valves (including apply and dump valves) are located between the master cylinder and the wheel brakes. The ABS valve regulates pressure between the master cylinder and the wheel brakes. Typically, when enabled, these ABS valves operate in the following three pressure control modes: pressure application, pressure dump, and pressure hold. The apply valves allow pressurized brake fluid entering respective ones of the wheel brakes to increase in pressure during an apply mode, while the dump valves release brake fluid from their associated wheel brakes during a dump mode. During the hold mode, the wheel brake pressure is held constant by closing both the apply and dump valves.

In order to achieve maximum braking force while maintaining vehicle stability, it is desirable to achieve an optimum level of slip at the wheels of both the front and rear axles. During vehicle deceleration, different braking forces are required at the front and rear axles to achieve the desired slip level. Therefore, the brake pressure should be apportioned between the front and rear brakes to obtain maximum braking force at each axle. An ABS system with such capability, known as a Dynamic Rear Proportioning (DRP) system, uses ABS valves to control brake pressure on the front and rear wheels, respectively, to dynamically achieve optimal braking performance at the front and rear axles under current conditions.

Further developments in braking technology have led to the introduction of Traction Control (TC) systems. Typically, valves have been added to existing ABS systems to provide a braking system that controls wheel speed during acceleration. Excessive wheel speed during vehicle acceleration can result in wheel slip and loss of traction. The electronic control system senses this condition and automatically applies brake pressure to the wheel cylinders of the slipping wheels to reduce slip and increase available traction. To achieve optimal vehicle acceleration, pressurized brake fluid is made available to the wheel cylinders even if the driver does not actuate the master cylinder.

During vehicle motion, such as cornering, dynamic forces are generated, which may reduce the stability of the vehicle. Vehicle Stability Control (VSC) braking systems counteract these forces through selective brake actuation, thereby improving the stability of the vehicle. These forces and other vehicle parameters are detected by sensors that send signals to an electronic control unit. The electronic control unit automatically operates the pressure control device to adjust the amount of hydraulic pressure applied to a particular individual wheel brake. In order to obtain optimum vehicle stability, it is necessary to always obtain a brake pressure that is greater than the master cylinder pressure quickly.

The braking system may also be used for regenerative braking to recapture energy. The electromagnetic force of the electric motor/generator is used for regenerative braking to provide a portion of the braking torque to the vehicle to meet the braking demands of the vehicle. A control module in the braking system communicates with the powertrain control module to provide coordinated braking during regenerative braking and braking for wheel lock-up and slip conditions. For example, when an operator of the vehicle initiates braking during regenerative braking, the electromagnetic energy of the motor/generator will be used to apply a braking torque to the vehicle (i.e., electromagnetic resistance is used to provide torque to the powertrain). If it is determined that there is no longer a sufficient amount of storage to store energy recovered from regenerative braking, or if regenerative braking fails to meet the operator demand, hydraulic braking will be applied to complete all or a portion of the braking action requested by the operator. Preferably, the hydraulic brakes are operated in a regenerative braking compounding manner, so that compounding is effectively and not significantly performed in the case of insufficient electromagnetic braking (left off). It is desirable that the vehicle movement should have a smooth transition change to the hydraulic brake so that the transition is not noticed by the driver of the vehicle.

The braking system may also include autonomous braking capability, such as Adaptive Cruise Control (ACC). During an autonomous braking event, various sensors and systems monitor traffic conditions ahead of the vehicle and automatically activate the braking system to slow the vehicle as needed. Autonomous braking may be configured to respond quickly to avoid emergency situations. The brake system may be activated without the driver depressing the brake pedal or even if the driver fails to apply sufficient pressure to the brake pedal. Advanced autonomous braking systems are configured to operate the vehicle without any driver input and rely solely on various sensors and systems that monitor traffic conditions around the vehicle.

Disclosure of Invention

The present invention relates to a method of determining a home position of a piston within a plunger assembly for a vehicle braking system at the beginning of an ignition cycle of a vehicle, the method comprising first providing a plunger assembly having a housing defining a bore therein. The plunger assembly includes a piston slidably disposed in the bore for pressurizing fluid within the pressure chamber when the piston moves in a first direction. The plunger assembly further includes an electrically operated linear actuator for moving the piston within the bore. The method further includes providing power to the linear actuator of the plunger assembly. Actuating the linear actuator to retract the piston in a second direction opposite the first direction toward an end stop. The engagement of the piston with the end stop is then detected.

The present invention also relates to a method of detecting the position of a piston relative to a compensating port and seal arrangement of a plunger assembly. The method includes first providing a fluid reservoir and a plunger assembly having a housing defining an aperture therein. The plunger assembly includes a piston slidably disposed in the bore for pressurizing fluid within a pressure chamber when the piston is moved in a first direction by a linear actuator. The plunger assembly includes a port in fluid communication with the fluid reservoir and the pressure chamber when the piston is in a first position. When the piston is in the second position, the port is prevented from fluid communication with the pressure chamber due to a spatial relationship between a seal within the housing of the plunger assembly and the port. The method includes positioning the piston in a retracted position, and then measuring a difference between the retracted position of the piston and a linear zero position of the piston in which the port is positioned adjacent the seal a relatively small distance such that the port is in fluid communication with the fluid reservoir and the pressure chamber.

Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.

Drawings

FIG. 1 is a schematic view of a first embodiment of a braking system.

FIG. 2 is an enlarged schematic view of a plunger assembly of the braking system of FIG. 1.

Fig. 3 is an enlarged partial schematic view of the plunger assembly showing the pistons of the plunger assembly in a random orientation prior to the homing initialization process.

Fig. 4 is an enlarged partial schematic view of the plunger assembly showing the piston of the plunger assembly in a retracted position during a homing initialization process.

Fig. 5 is an enlarged partial schematic view of the plunger assembly of fig. 3 in a linear zero home position.

FIG. 6 is an enlarged partial schematic view of the plunger assembly showing the piston in a forward position just after the compensating port is shut off.

FIG. 7 is a graphical representation of control of the plunger assembly during a compensation port learning process.

FIG. 8 is an enlarged partial schematic view of the plunger assembly showing the piston in an advanced forward position after the compensation port is shut off.

Detailed Description

Referring now to the drawings, FIG. 1 schematically illustrates a first embodiment of a vehicle braking system, generally indicated at 10. The brake system 10 is a hydraulic brake system in which fluid pressure from a source is operated to apply a braking force to the brake system 10. The braking system 10 may be suitably employed on a land vehicle, such as a motor vehicle having four wheels. In addition, the brake system 10 may be provided with other braking functions, such as anti-lock braking (ABS) and other anti-skid control features, to effectively brake the vehicle, as will be discussed below. In the illustrated embodiment of the braking system 10, there are four wheel brakes 12a, 12b, 12c and 12 d. The wheel brakes 12a, 12b, 12c and 12d may have any suitable wheel braking configuration that is operated by the application of pressurized brake fluid. The wheel brakes 12a, 12b, 12c and 12d may, for example, include brake calipers mounted on the vehicle to engage friction elements (e.g., brake discs) that rotate with the vehicle wheels to effect braking of the associated vehicle wheels. The wheel brakes 12a, 12b, 12c, and 12d may be associated with any combination of front and rear wheels of a vehicle in which the braking system 10 is installed. A diagonally split braking system is shown such that the wheel brake 12a is associated with the rear left wheel, the wheel brake 12b is associated with the front right wheel, the wheel brake 12c is associated with the front left wheel and the wheel brake 12d is associated with the rear right wheel. Alternatively, for a vertically split system, the wheel brakes 12a and 12b may be associated with the front wheels and the wheel brakes 12c and 12d may be associated with the rear wheels.

The braking system 10 includes a brake pedal unit (generally indicated at 14), a pedal simulator 16, a plunger assembly (generally indicated at 18), and a reservoir 20. The reservoir 20 stores and holds hydraulic fluid for the brake system 10. The fluid within the reservoir 20 is preferably maintained at or about atmospheric pressure, but may be stored at other pressures if desired. The brake system 10 may include a fluid level sensor (not shown) for detecting the fluid level of the reservoir 20. It should be noted that in the schematic diagram of fig. 1, the conduit line leading to the reservoir 20 may not be specifically drawn, but may be represented by a conduit that marks the end of T1, T2, or T3 (indicating that these respective conduits are connected to one or more tanks or sections of the reservoir 20). Alternatively, the reservoir 20 may comprise a plurality of separate housings. As discussed in detail below, the plunger assembly 18 of the brake system 10 functions as a pressure source to provide a desired pressure level to the wheel brakes 12a, 12b, 12c and 12d during a typical or normal brake application. Fluid from the wheel brakes 12a, 12b, 12c, and 12d may be returned to the plunger assembly 18 and/or diverted to the reservoir 20.

The brake system 10 includes an Electronic Control Unit (ECU) 22. The ECU22 may include a microprocessor. The ECU22 receives various signals, processes the signals, and controls the operation of various electrical components of the brake system 10 in response to the received signals. The ECU22 may be connected to various sensors such as a pressure sensor, a travel sensor, a switch, a wheel speed sensor, and a steering angle sensor. The ECU22 may also be connected to an external module (not shown) for receiving information relating to the yaw rate, lateral acceleration, longitudinal acceleration of the vehicle, such as for controlling the braking system 10 during vehicle stability operations. Additionally, the ECU22 may be coupled to an instrument panel for collecting and providing information related to warning indicators, such as ABS warning lights, brake fluid level warning lights, and traction control/vehicle stability control indicator lights.

The braking system 10 further includes a first isolation valve 30 and a second isolation valve 32. The isolation valves 30 and 32 may be solenoid actuated three-way valves. The isolation valves 30 and 32 are generally operable to two positions, as schematically illustrated in FIG. 1. The first and second isolation valves 30, 32 each have a port in selective fluid communication with an output conduit 34 that typically communicates with an output end of the plunger assembly 18, as will be discussed below. As shown in FIG. 1, the first and second isolation valves 30 and 32 also include ports that are selectively in fluid communication with conduits 36 and 38, respectively, when the first and second isolation valves 30 and 32 are not energized. The first and second isolation valves 30 and 32 further include ports in fluid communication with conduits 40 and 42, respectively, which provide fluid to and from the wheel brakes 12a, 12b, 12c and 12 d.

In a preferred embodiment, first isolation valve 30 and/or second isolation valve 32 may be mechanically designed such that when in their de-energized positions, flow is permitted in the opposite direction (from conduit 34 to conduits 36 and 38, respectively), and the normally closed valve seats of valves 30 and 32 may be bypassed. Thus, while the three-way valves 30 and 32 are not schematically illustrated as indicating such fluid flow positions, it should be noted that the valve design may permit such fluid flow. This may facilitate the execution of diagnostic routines and air bleeding of the brake system 10.

The system 10 further includes a plurality of different solenoid actuated valves (slip control valve arrangements) to permit control of the following braking operations: such as ABS, traction control, vehicle stability control, and regenerative braking compounding. The first set of valves includes a first apply valve 50 and a first dump valve 52 in fluid communication with the conduit 40 for cooperatively supplying fluid received from the first isolation valve 30 to the wheel brakes 12a and cooperatively releasing pressurized fluid from the wheel brakes 12a to a reservoir conduit 53 in fluid communication with the reservoir 20. The second set of valves includes a second apply valve 54 and a second dump valve 56 in fluid communication with conduit 40 for cooperatively supplying fluid received from the first isolation valve 30 to the wheel brakes 12b and cooperatively releasing pressurized fluid from the wheel brakes 12b to the reservoir conduit 53. The third set of valves includes a third apply valve 58 and a third dump valve 60 in fluid communication with the conduit 42 for cooperatively supplying fluid received from the second isolation valve 32 to the wheel brakes 12c and cooperatively releasing pressurized fluid from the wheel brakes 12c to the reservoir conduit 53. The fourth set of valves includes a fourth apply valve 62 and a fourth dump valve 64 in fluid communication with conduit 42 for cooperatively supplying fluid received from second isolation valve 32 to wheel brakes 12d and cooperatively releasing pressurized fluid from wheel brakes 12d to reservoir conduit 53. It should be noted that during a normal braking event, fluid flows through the open apply valves 50, 54, 58, and 62 that are not energized. Additionally, dump valves 52, 56, 60, and 64 are preferably in their non-energized closed positions to prevent fluid flow to reservoir 20.

The brake pedal unit 14 is connected to a brake pedal 70, and is actuated by a driver of the vehicle when the driver depresses the brake pedal 70. A brake sensor or switch 72 may be connected to ECU22 to provide a signal indicating that brake pedal 70 is depressed. As will be discussed below, brake pedal unit 14 may be used as a backup source of pressurized fluid to substantially replace the normal supply of pressurized fluid from plunger assembly 18 under certain fault conditions of brake system 10. The brake pedal unit 14 may supply pressurized fluid in conduits 36 and 38 (normally closed at the first and second isolation valves 30 and 32 during normal brake application) to the wheel brakes 12a, 12b, 12c and 12d as needed.

The brake pedal unit 14 includes a housing having a multi-step bore 80 formed therein for slidably receiving the respective cylindrical pistons and other components therein. The housing may be formed as a single unit or comprise two or more separately formed parts coupled together. An input piston 82, a primary piston 84, and a secondary piston 86 are slidably disposed within bore 80. The input piston 82 is connected to the brake pedal 70 via a link arm 76. Under certain conditions, leftward movement of input piston 82, primary piston 84, and secondary piston 86 may cause an increase in pressure within input chamber 92, primary chamber 94, and secondary chamber 96, respectively. The various seals of the brake pedal unit 14 and the structure of the housing and pistons 82, 84, and 86 define chambers 92, 94, and 96. For example, an input chamber 92 is generally defined between the input piston 82 and the master piston 84. A primary chamber 94 is generally defined between primary piston 84 and secondary piston 86. A secondary chamber 96 is generally defined between the secondary piston 86 and the end wall of the housing formed by the bore 80.

The input chamber 92 is in fluid communication with the pedal simulator 16 via a conduit 100 for reasons that will be explained below. An input piston 82 is slidably disposed in the bore 80 of the housing of the brake pedal unit 14. The outer wall of the input piston 82 engages a lip seal 102 and a seal 104 mounted in a groove formed in the housing. A passageway 106 (or passageways) is formed through the wall of the piston 82. As shown in fig. 1, when the brake pedal unit 14 is in its rest position (the driver is not depressing the brake pedal 70), the passageway 106 is located between the lip seal 102 and the seal 104. In the rest position, the passageway 106 permits fluid communication between the input chamber 92 and the reservoir 20 via the conduit 108. As viewed in fig. 1, sufficient leftward movement of the input piston 82 causes the passageway 106 to move past the lip seal 102, thereby preventing fluid from flowing from the input chamber 92 into the conduit 108 and reservoir 20. Further leftward movement of the input piston 82 pressurizes the input chamber 92, thereby causing fluid to flow into the pedal simulator 16 via conduit 100. As fluid is diverted into the pedal simulator 16, the simulation chamber 110 within the pedal simulator 16 expands, causing the piston 112 to move within the pedal simulator 16. Movement of the piston 112 compresses a spring assembly, schematically represented as a spring 114. The compression of the spring 114 provides a feedback force to the driver of the vehicle that simulates the force the driver would experience on the brake pedal 70 in a conventional vacuum assisted hydraulic brake system, for example. The springs 114 of the pedal simulator 16 may include any number and type of spring members as desired. For example, the spring 114 may include a combination of low-rate and high-rate spring elements to provide non-linear force feedback. The spring 114 of the pedal simulator 16 may be housed within a non-pressurized chamber 122 that is in fluid communication with the reservoir 20 (T1).

The simulation chamber 110 of the pedal simulator 16 is in fluid communication with a conduit 100 that is in fluid communication with the input chamber 92. A normally closed solenoid actuated simulator valve 116 is positioned within conduit 100 for selectively preventing fluid flow from input chamber 92 to simulation chamber 110, such as during a fault condition in which brake pedal unit 14 is being used to provide a source of pressurized fluid to the wheel brakes. The simulator valve 116 permits fluid communication between the input chamber 92 of the brake pedal unit 14 and the simulation chamber 110 of the pedal simulator 16 when in its energized, open position. The braking system 10 may further include a check valve 118 in a parallel path arrangement with a restricted orifice 120 in the conduit 100. The check valve 118 and the restrictive orifice 120 may be integrally constructed or formed in the simulator valve 116, or may be formed separately from the simulator valve. The restricted orifice 120 provides damping during spike applications when the driver quickly and forcefully depresses the brake pedal 70. This damping provides force feedback so that depressing the brake pedal 70 feels more like a conventional vacuum booster, which may be a desirable characteristic of the brake system 10. Damping may also provide a more accurate relationship between brake pedal travel and vehicle deceleration by substantially avoiding too much brake pedal travel for vehicle deceleration to be transmitted by brake system 10. The check valve 118 provides an easy flow path and allows for a quick return of the brake pedal 70, which allows for a quick reduction of the associated brake pressure according to the driver's intent.

As discussed above, the input chamber 92 of the brake pedal unit 14 is selectively in fluid communication with the reservoir 20 via the conduit 108 and the passage 106 formed in the input piston 82. The braking system 10 may include an optional simulator test valve 130 located within the conduit 108. The simulator test valve 130 may be electronically controlled between an open position as shown in fig. 1 and a powered closed position. The simulator test valve 130 is not necessary during normal boosted brake application or for manual boost mode. The simulator test valve 130 may be energized to a closed position during various test modes to determine proper operation of other components of the brake system 10. For example, the simulator test valve 130 may be energized to a closed position to prevent bleeding to the reservoir 20 via the conduit 108 so that the pressure established in the brake pedal unit 14 may be used to monitor fluid flow to determine if leakage past seals of various components of the brake system 10 may occur.

The main chamber 94 of the brake pedal unit 14 is in fluid communication with the second isolation valve 32 via conduit 38. The master piston 84 is slidably disposed in the bore 80 of the housing of the brake pedal unit 14. The outer wall of the main piston 84 engages a lip seal 132 and a seal 134 mounted in a groove formed in the housing. One or more passageways 136 are formed through the wall of the primary piston 84. As shown in fig. 1, when the main piston 84 is in its rest position, the passage 136 is located between the lip seal 132 and the seal 134. It should be noted that in the idle position, the lip seal 132 is only slightly to the left of the passageway 136, thereby permitting fluid communication between the main chamber 94 and the reservoir 20.

The secondary chamber 96 of the brake pedal unit 14 is in fluid communication with the first isolation valve 30 via the conduit 36. The secondary piston 86 is slidably disposed in the bore 80 of the housing of the brake pedal unit 14. The outer wall of the secondary piston 86 engages a lip seal 140 and a seal 142 mounted in a groove formed in the housing. One or more passageways 144 are formed through the wall of the secondary piston 86. As shown in fig. 1, when the secondary piston 86 is in its rest position, the passage 144 is located between the lip seal 140 and the seal 142. It should be noted that in the idle position, the lip seal 140 is only slightly to the left of the passageway 144, thereby permitting fluid communication between the secondary chamber 96 and the reservoir 20 (T2).

If desired, the primary piston 84 and the secondary piston 86 may be mechanically coupled with limited movement therebetween. The mechanical coupling of primary piston 84 and secondary piston 86 prevents a large gap or distance between primary piston 84 and secondary piston 86 and prevents primary piston 84 and secondary piston 86 from having to advance a relatively large distance without any pressure increase in a non-faulted circuit. For example, if the brake system 10 is in the manual actuation mode and fluid pressure is lost in the output circuit (such as in conduit 36) relative to the secondary piston 86, the secondary piston 86 is forced or biased in the leftward direction due to the pressure within the primary chamber 94. If the primary and secondary pistons 84, 86 are not connected together, the secondary piston 86 will be free to travel to its left-most position, as viewed in FIG. 1, and the driver will have to depress the pedal 70 a distance to compensate for this travel loss. However, since the primary and secondary pistons 84 and 86 are connected together, such movement of the secondary piston 86 is prevented, and the loss of travel that occurs in this type of failure is relatively small. Any suitable mechanical connection between primary piston 84 and secondary piston 86 may be used. For example, as schematically shown in FIG. 1, the right end of the secondary piston 86 may include an outwardly extending flange that extends into a groove formed in the inner wall of the primary piston 84. The width of the groove is greater than the width of the flange, thereby providing a relatively small amount of travel between the first and second pistons 84 and 86 relative to each other.

The brake pedal unit 14 may include an input spring 150 disposed generally between the input piston 82 and the master piston 84. In addition, brake pedal unit 14 may include a primary spring (not shown) disposed between primary piston 84 and secondary piston 86. A secondary spring 152 may be included and disposed between the secondary piston 86 and the bottom wall of the bore 80. The input, primary and secondary springs may have any suitable configuration, such as a cage spring assembly, to bias the pistons in directions away from each other and also to properly position the pistons within the housing of the brake pedal unit 14.

The braking system 10 may further include a pressure sensor 156 in fluid communication with the conduit 36 to detect the pressure within the secondary pressure chamber 96 and for transmitting a signal indicative of the pressure to the ECU 22. Additionally, the braking system 10 may further include a pressure sensor 158 in fluid communication with the conduit 34 for transmitting a signal indicative of the pressure at the output of the plunger assembly 18.

As shown schematically in fig. 2, the plunger assembly 18 includes a housing having a multi-step bore 200 formed therein. The aperture 200 includes a first portion 202 and a second portion 204. A piston 206 is slidably disposed within the bore 200. The piston 206 includes an enlarged end portion 208 that is connected to a smaller diameter central portion 210. The piston 206 has a second end 211 connected to a ball screw mechanism, generally indicated at 212. A ball screw mechanism 212 is provided for translating or linearly moving the piston 206 within the bore 200 of the housing along an axis defined by the bore 200 in a forward direction (to the left as viewed in fig. 1 and 2) and a rearward direction (to the right as viewed in fig. 1 and 2). In the illustrated embodiment, the ball screw mechanism 212 includes a motor, indicated schematically and generally at 214, electrically connected to the ECU22 to actuate the motor 214 thereof to rotatably drive a screw shaft 216. The motor 214 generally includes a stator 215 and a rotor 217. In the exemplary embodiment shown in fig. 2, the rotor 217 and the screw shaft 216 are integrally formed together. The second end 211 of the piston 206 includes a threaded bore 220 and functions as a follower nut for the ball screw mechanism 212. The ball screw mechanism 212 includes a plurality of balls 222 that are retained within a helical raceway 223 formed in the screw shaft 216 and within the threaded bore 220 of the piston 206 to reduce friction.

Although the ball screw mechanism 212 is shown and described with respect to the plunger assembly 18, it should be understood that other suitable mechanical linear actuators may be used to cause the piston 206 to move. It should also be understood that although the piston 206 serves as a nut of the ball screw mechanism 212, the piston 206 may be configured to serve as a screw shaft of the ball screw mechanism 212. Of course, in this case, the screw shaft 216 is configured to function as a nut having an internal helical raceway formed therein. The piston 206 may include structure (not shown) that engages cooperating structure formed in the housing of the plunger assembly 18 to prevent the piston 206 from rotating as the screw shaft 216 rotates about the piston 206. For example, the piston 206 may include outwardly extending splines or tabs (not shown) that are disposed within longitudinally extending grooves (not shown) formed in the housing of the plunger assembly 18 such that the tabs slide within the grooves as the piston 206 travels within the bore 200.

As discussed below, the plunger assembly 18 is preferably configured to provide pressure to the conduit 34 as the piston 206 moves in the forward and rearward directions. Plunger assembly 18 includes a seal 230 mounted on enlarged end portion 208 of piston 206. The seal 230 slidably engages the cylindrical inner surface of the first portion 202 of the bore 200 as the piston 206 moves within the bore 200. The seal 234 and the seal 236 are mounted in a groove formed in the second portion 204 of the bore 200. The seals 234 and 236 slidably engage the cylindrical outer surface of the central portion 210 of the piston 206. The first pressure chamber 240 is generally defined by the first portion 202 of the bore 200, the enlarged end portion 208 of the piston 206, and the seal 230. An annular second pressure chamber 242 generally located behind the enlarged end portion 208 of the piston 206 is generally defined by the first and second portions 202 and 204 of the bore 200, the seals 230 and 234, and the central portion 210 of the piston 206. The seals 230, 234, and 236 may have any suitable sealing structure.

While the plunger assembly 18 may be configured in any suitable size and arrangement, in one embodiment, the effective hydraulic area of the first pressure chamber 240 is greater than the effective hydraulic area of the annular second pressure chamber 242. The first pressure chamber 240 generally has an effective hydraulic area corresponding to the diameter of the central portion 210 of the piston 206 (the inner diameter of the seal 234) because fluid is diverted through the conduits 254, 34, and 243 as the piston 206 advances in the forward direction. The second pressure chamber 242 generally has an effective hydraulic area corresponding to the diameter of the first portion 202 of the bore 200 minus the diameter of the central portion 210 of the piston 206. This configuration provides that during the rearward stroke of the rearward movement of the piston 206, the motor 214 requires less torque (or power) to maintain the same pressure as during its forward stroke. In addition to using less power, the motor 214 may also generate less heat during the rearward stroke of the piston 206. In the event that high brake pressure is desired, the plunger assembly 34 may be operated from a forward stroke to a rearward stroke. Thus, although a forward stroke is used in most braking applications, a rearward pressure stroke may be utilized. Additionally, in the event that the driver depresses the pedal 90 for a long duration, the brake system 10 may be operated by controlling the first and second spool valves 250, 252 (as will be discussed below) to a closed position to maintain brake pressure (rather than continuously energizing the spool assembly 34), and then shutting off the motor or spool assembly 34.

The plunger assembly 18 preferably includes a sensor (shown schematically at 218) for indirectly sensing the position of the piston 206 within the bore 200. The sensor 218 communicates with the ECU 22. In one embodiment, the sensor 218 detects the rotational position of the rotor 217, which may have a metallic or magnetic element embedded therein. Since the rotor 217 is integrally formed with the shaft 216, the rotational position of the shaft 216 corresponds to the linear position of the piston 206. Accordingly, the position of piston 206 may be determined by sensing the rotational position of rotor 217 via sensor 218.

The piston 206 of the plunger assembly 18 includes a passage 244 formed therein. Passageway 244 defines a first port 246 extending through the cylindrical outer wall of piston 206 and is in fluid communication with secondary chamber 242. The passageway 244 also defines a second port 248 extending through the cylindrical outer wall of the piston 206 and in fluid communication with a portion of the bore 200 located between the seals 234 and 236. The second port 248 is in fluid communication with a conduit 249, which is in fluid communication with the reservoir 20 (T3). When in the rest position (as shown in fig. 2), the pressure chambers 240 and 242 are in fluid communication with the reservoir 20 via conduit 249. This helps to ensure proper release of pressure at the output end of the plunger assembly 18 and within the pressure chambers 240 and 242 themselves. The relief of pressure prevents the wheel brakes 12a, 12b, 12c and 12d from being accidentally actuated due to any pressure remaining in the pressure chambers 240 and 242. After initial forward movement of the piston 206 from its rest position, the port 248 will move past the lip seal 234, thereby disconnecting the pressure chambers 240 and 242 from fluid communication with the reservoir 20, thereby permitting the pressure chambers 240 and 242 to build pressure as the piston 206 moves further.

Referring back to fig. 1, the braking system 10 further includes a first plunger valve 250 and a second plunger valve 252. The first plunger valve 250 is preferably a normally closed solenoid actuated valve. Thus, in the de-energized state, the first plunger valve 250 is in a closed position, as shown in FIG. 1. The second plunger valve 252 is preferably a normally open solenoid actuated valve. Thus, in the de-energized state, the second plunger valve 252 is in an open position, as shown in fig. 1. A check valve may be disposed within the second plunger valve 252 such that when the second plunger valve 252 is in its closed position, fluid may still flow through the second plunger valve 252 in a direction from the first output conduit 254 (from the first pressure chamber 240 of the plunger assembly 18) to the conduit 34, thereby opening into the isolation valves 30 and 32. It should be noted that during the rearward stroke of piston 206 of plunger assembly 18, pressure may be generated within second pressure chamber 242 for output into conduit 34.

Generally, the first and second plunger valves 250, 252 are controlled to permit fluid flow at the output of the plunger assembly 18 and to permit bleeding through the plunger assembly 18 to the reservoir 20 when desired (T3). For example, the first spool valve 250 may be energized to its open position during a normal braking event such that both the first spool valve 250 and the second spool valve 252 are open (which may reduce noise during operation). Preferably, the first spool valve 250 is energized almost always during the ignition cycle when the engine is running. Of course, the first plunger valve 250 may be purposefully moved to its closed position, such as during a pressure-producing rearward stroke of the plunger assembly 18. The first and second plunger valves 250, 252 are preferably in their open positions when the piston 206 of the plunger assembly 18 is operating in its forward stroke to maximize flow. When the driver releases the brake pedal 70, the first and second plunger valves 250, 252 preferably remain in their open positions. It should be noted that fluid may flow through the check valve within the closed second plunger valve 252, and through the check valve 258 from the reservoir 20, depending on the direction of travel of the piston 206 of the plunger assembly 18.

It may be desirable for the first plunger valve 250 to be configured with a relatively large orifice therethrough when in its open position. The relatively large bore of the first plunger assembly 250 helps to provide a simple flow path therethrough. The second plunger valve 252, in its open position, may be provided with a much smaller orifice than the first plunger valve 250. One reason for this is to help prevent the piston 206 of the plunger assembly 18 from being driven back quickly in the event of a failure due to fluid rushing into the first pressure chamber 240 of the plunger assembly 18 through the first output conduit 254, thereby preventing damage to the plunger assembly 18. Since the fluid is restricted as it flows through the relatively small orifice, dissipation occurs as some of the energy is converted into heat. Accordingly, the orifice should be of a sufficiently small size to help prevent the piston 206 of the plunger assembly 18 from being suddenly and catastrophically back-driven upon failure of the braking system 10, such as, for example, when the motor 214 is de-energized and the pressure within the conduit 34 is relatively high.

As shown in fig. 2, the plunger assembly 18 may include an optional spring member, such as a spring washer 277, to assist in such rapid rearward back-driving of the damping piston 206. Spring washer 277 may also assist in damping the movement of piston 206 at any such speed as it approaches its most retracted position within bore 200 as it approaches the rest position. As schematically shown in fig. 2, the spring washer 277 is located between the enlarged end portion 208 and a shoulder 279 formed in the bore 200 between the first portion 202 and the second portion 204. Spring washer 277 may have any suitable configuration that deflects or compresses upon contact with piston 206 as piston 206 moves rearward. For example, the spring washer 277 may be in the form of a metal conical spring washer. Alternatively, the spring washer 277 may be in the form of a wave spring. Although spring washer 277 is shown mounted within bore 200 of plunger assembly 18, spring washer 277 may alternatively be mounted on piston 206 such that spring washer 277 moves with piston 206. In this configuration, spring washer 277 engages shoulder 279 and compresses when piston 206 is moved sufficiently to the right.

The first and second spool valves 250 and 252 provide open parallel paths between the pressure chambers 240 and 242 of the spool assembly 18 during normal braking operation. While a single open path may be sufficient, an advantage of having both the first and second plunger valves 250, 252 is that the first plunger valve 250 may provide an easy flow path through its relatively large orifice, while the second plunger valve 252 may provide a restricted orifice path during certain fault conditions (when the first plunger valve 250 is de-energized to its closed position).

During a typical or normal braking operation, the driver of the vehicle depresses the brake pedal 70. In a preferred embodiment of the brake system 10, the brake pedal unit 14 includes one or more travel sensors 270 (for redundancy) to generate signals that are transmitted to the ECU22 that are indicative of the length of travel of the input piston 82 of the brake pedal unit 14.

During normal braking operation, the plunger assembly 18 is operated to provide pressure to the conduit 34 to actuate the wheel brakes 12a, 12b, 12c and 12 d. Under certain driving conditions, the ECU22 communicates with a powertrain control module (not shown) and other additional brake controllers of the vehicle to provide coordinated braking during advanced brake control schemes such as anti-lock braking (AB), Traction Control (TC), Vehicle Stability Control (VSC), and regenerative braking compounding. During a conventional brake application, the flow of pressurized fluid from the brake pedal unit 14 resulting from depression of the brake pedal 70 is diverted into the pedal simulator 16. The simulator valve 116 is actuated to divert fluid from the input chamber 92 through the simulator valve 116. It should be noted that the simulator valve 116 is shown in its energized state in FIG. 1. Thus, the simulator valve 116 is a normally closed solenoid valve. It is also noted that once the passage 106 in the input piston 82 moves past the seal 104, fluid flow from the input chamber 92 to the reservoir 20 is blocked.

Preferably, the simulator valve 116 remains open during the duration of the normal braking event. Additionally, during normal braking operation, isolation valves 30 and 32 are energized to the second position to prevent fluid flow from conduits 36 and 38, respectively, through isolation valves 30 and 32. Preferably, the isolation valves 30 and 32 are energized during the entire duration of the ignition cycle, such as when the engine is running, rather than being energized and de-energized to help minimize noise. It should be noted that primary piston 84 and secondary piston 86 are not in fluid communication with reservoir 20 due to their passageways 136 and 144, respectively, being positioned past lip seals 132 and 140, respectively. Preventing fluid flow through isolation valves 30 and 32 hydraulically locks primary chamber 94 and secondary chamber 96 of brake pedal unit 14, thereby preventing further movement of primary piston 84 and secondary piston 86.

It is generally desirable to maintain the isolation valves 30 and 32 energized during the normal braking mode to ensure that fluid is bled off through the plunger assembly 18 to the reservoir 20, such as during driver release of the brake pedal 70. As best shown in fig. 1, a passage 244 formed in the piston 206 of the plunger assembly 18 permits such venting.

During normal braking operation, the plunger assembly 18 may be actuated by the ECU22 to provide actuation of the wheel brakes 12a, 12b, 12c and 12d when the pedal simulator 16 is actuated by depression of the brake pedal 70. The plunger assembly 18 is operated to provide a desired pressure level to the wheel brakes 12a, 12b, 12c and 12d as compared to the pressure generated by the brake pedal unit 14 by the driver depressing the brake pedal 70. The electronic control unit 22 actuates the motor 214 to rotate the screw shaft 216 in the first rotational direction. Rotation of the screw shaft 216 in a first rotational direction causes the piston 206 to advance in a forward direction (to the left as viewed in fig. 1 and 2). Movement of the piston 206 causes the pressure in the first pressure chamber 240 to increase and fluid flows out of the first pressure chamber 240 and into the conduit 254. Fluid may flow into conduit 34 via open first and second plunger valves 250 and 252. It should be noted that as the piston 206 advances in the forward direction, fluid is allowed to flow into the second pressure chamber 242 via conduit 243. Pressurized fluid from conduit 34 is directed through isolation valves 30 and 32 into conduits 40 and 42. Pressurized fluid from conduits 40 and 42 may be directed to wheel brakes 12a, 12b, 12c, and 12d through open apply valves 50, 54, 58, and 62, while dump valves 52, 56, 60, and 64 remain closed. When the driver raises or releases the brake pedal 70, the ECU22 may operate the motor 214 to rotate the screw shaft 216 in the second rotational direction to retract the piston 206 to thereby exhaust fluid from the wheel brakes 12a, 12b, 12c, and 12 d. The speed and distance that the piston 206 is retracted is based on the driver's request to release the brake pedal 70, as sensed by the sensor 218. Of course, if the driver quickly releases the brake pedal 90, the plunger assembly 14 may be operated to avoid such a transient pressure drop. Under certain conditions, such as during a non-power assisted slip control event, pressurized fluid from the wheel brakes 12a, 12b, 12c, and 12d may assist in back-driving the ball screw mechanism 212, thereby returning the piston 206 toward its rest position. It should be noted that the first and second plunger valves 250, 252 preferably maintain their open positions during non-slip control events when the driver releases the brake pedal 90.

In some cases, the piston 206 of the plunger assembly 18 may complete its entire stroke length within the bore 200 of the housing and still expect additional boost pressure to be delivered to the wheel brakes 12a, 12b, 12c, and 12 d. Plunger assembly 18 is a dual action plunger assembly such that it is configured to also provide boost pressure to conduit 34 when piston 206 completes a stroke in the rearward (rightward) or reverse direction. This has advantages over conventional plunger assemblies: it is first necessary to bring its piston back to its rest or retracted position and then the piston can be advanced again to create pressure in the single pressure chamber. For example, if the piston 206 completes its full stroke and additional boost pressure is still desired, the second plunger valve 252 is energized to its check valve closed position. The first plunger valve 250 is de-energized to its closed position. The electronic control unit 22 actuates the motor 214 in a second rotational direction opposite the first rotational direction to rotate the screw shaft 216 in the second rotational direction. Rotation of the screw shaft 216 in the second rotational direction causes the piston 206 to retract or move in a rearward direction (to the right as viewed in fig. 1 and 2). Movement of the piston 206 causes the pressure in the second pressure chamber 242 to increase and fluid flows out of the second pressure chamber 242 and into the conduit 243 and the conduit 34. Pressurized fluid from conduit 34 is directed through isolation valves 30 and 32 into conduits 40 and 42. Pressurized fluid from conduits 40 and 42 may be directed to wheel brakes 12a, 12b, 12c, and 12d through open apply valves 50, 54, 58, and 62, while dump valves 52, 56, 60, and 64 remain closed. In a similar manner to during the forward stroke of piston 206, ECU22 may also selectively actuate apply valves 50, 54, 58, and 62 and dump valves 52, 56, 60, and 64 to provide the desired pressure levels to wheel brakes 12a, 12b, 12c, and 12d, respectively. When the driver lifts or releases the brake pedal 70 during the pressurized rearward stroke of the plunger assembly 18, the first and second plunger valves 250 and 252 are preferably operated to their open positions, but it is generally sufficient to have only one of the valves 250 and 252 open. It should be noted that when transitioning away from a slip control event, it is desirable to positively correlate the position of the piston 206 and the displaced volume within the plunger assembly 18 with a given pressure and fluid volume within the wheel brakes 12a, 12b, 12c, and 12 d. However, when the correlation is not exact, fluid may be drawn from reservoir 20 into chamber 240 of plunger assembly 18 via check valve 258.

During a braking event, ECU22 may selectively actuate apply valves 50, 54, 58, and 62 and dump valves 52, 56, 60, and 64 to provide a desired pressure level to the wheel brakes, respectively. The ECU22 may also control the braking system 10 during ABS, DRP, TC, VSC, regenerative braking, and autonomous braking events through the general operation of the plunger assembly 18 along with the apply and dump valves. Even if the vehicle operator does not depress the brake pedal 70, the ECU22 may operate the plunger assembly 18 to provide a source of pressurized fluid directed to the wheel brakes, such as during an autonomous vehicle braking event.

In the event of loss of power to portions of the brake system 10, the brake system 10 provides manual actuation or manual application such that the brake pedal unit 14 may supply relatively high pressure fluid to the conduits 36 and 38. During an electrical fault, the motor 214 of the plunger assembly 18 may cease to operate, thereby failing to generate pressurized hydraulic brake fluid from the plunger assembly 18. The isolation valves 30 and 32 shuttle (or remain) in positions where they permit fluid flow from the conduits 36 and 38 to the wheel brakes 12a, 12b, 12c, and 12 d. The simulator valve 116 is shuttled to its closed position to prevent fluid from flowing out of the input chamber 92 to the pedal simulator 16. During manual actuation application, input piston 82, primary piston 84, and secondary piston 86 advance to the left such that passageways 106, 136, 144 move past seals 102, 132, and 140, respectively, to prevent fluid flow from their respective fluid chambers 92, 94, and 96 to reservoir 20, thereby pressurizing chambers 92, 94, and 96. Fluid flows from chambers 94 and 96 into conduits 38 and 36, respectively, to actuate wheel brakes 12a, 12b, 12c, and 12 d.

For proper operation of the plunger assembly 18, it is clearly desirable that the ECU22 know the actual position of the piston 206 within the housing of the plunger assembly 18. It is important that the actual position of the piston 206 be determined not only initially after manufacture and assembly of the plunger assembly 18, but also during the operational life of the plunger assembly 18. The accuracy of the sensor 218 and the accuracy of the ball screw mechanism 212 may be designed and manufactured such that the position of the piston 206 can be correctly determined with sufficient tolerance during movement of the piston 206 within the plunger assembly 18. In other words, the ball screw mechanism 212 can be designed with such a high level of mass and precision that the sensor 218 will be able to reliably track the position of the piston 206 as the piston 206 is moved within the plunger assembly 18 by the motor 214 and the ball screw mechanism 212. The ECU22 may receive a continuous signal from the sensor 218 to ensure that the correct position of the piston 206 relative to the housing of the plunger assembly 18 is maintained. Thus, knowledge of the position of the piston 206 during operation of the plunger assembly 18 is generally not an issue with respect to proper operation of the plunger assembly 18.

However, it is important to know and determine the home or starting position of the piston 206 within the bore 200 so that all subsequent positions of the piston can be derived from and determined from the known home position. ECU22 may be configured to store data associated with the last known position of piston 206 prior to an electrical shutdown of brake system 10. This last known position may be used to re-determine the position of the piston 206 on the next power-up cycle of the brake system 10. However, during periods when the brake system 10 is not powered, the position of the piston 206 may be physically displaced or moved from a previously known position prior to the last electrical shut-off. For example, vibrations experienced by the plunger assembly 18 during a power-off event may displace the piston 206 from a previously known position. This displacement of the piston 206 will result in a false assumption of the physical position of the piston 206. To overcome these problems, it is desirable to provide an initialization process at each start-up of the electrical system so that the actual position of the piston 206 can be determined and detected to provide a starting or home position (initial linear zero position) of the piston 206. After determining the home position of the piston 206, each position of the piston 206 may then be tracked based on and from the starting position.

The parking initialization process preferably begins when the system is powered up so that power is supplied to the brake system 10. The system power-up may correspond to a firing cycle in which the vehicle is started. For example, for a vehicle having an internal combustion engine, the ignition cycle generally corresponds to the starting or ignition of the engine and ends when the engine is shut down. Typically, when the engine is shut down, most of the vehicle's electrical systems are also shut down and powered down. The braking system 10 may be one such system that is powered down. The ignition cycle can be used to describe the shutdown and power-off cycles of the brake system even for vehicles without an internal combustion engine, such as pure electric or hybrid vehicles.

A schematic representation of the plunger assembly 18 is shown in fig. 3 in a random orientation such that the piston 206 has moved from the rest position shown in fig. 2 to an unknown random forward position. For example, the position of the piston 206 in fig. 3 may have been caused by vibrations acting on the plunger assembly 18 when the engine is off and the braking system 10 is de-energized. In fig. 3, the piston 206 is shown such that a gap exists between the spring washer 277 and the enlarged end portion 208 of the piston 206. It should be understood that the schematic illustrations of the plunger assembly 18 herein are not drawn to scale, and certain features of the plunger assembly 18 are shown exaggerated for clarity and description. Exaggeration may also apply to the position of the various components of the plunger assembly 18, as the actual movement and position may be so small as to be unnoticeable in the drawings. For example, in FIG. 3, the piston 206 may have moved only a millimeter or a fraction of a millimeter to its random unknown position. Thus, fig. 3 shows an exaggerated movement of the position of the piston 206 from the rest position such as in fig. 2.

To begin the diagnostic homing initialization process, the brake system 10 is first powered up, such as during the beginning of a vehicle ignition cycle. Thus, power will be re-routed to the ECU22 and/or the plunger assembly 18, etc. components in the brake system 10. The ECU22 may operate the brake system 10 in any suitable configuration during the homing initialization. However, preferably, during this process, all valves of the brake system 10 are not energized. The ECU22 controls the motor 214 to actuate the ball screw mechanism 212 to rotate the screw shaft 216 in the second rotational direction, thereby retracting the piston 206 to the right (as viewed in fig. 3). It should be noted that piston 206 will now move in a direction toward spring washer 277. However, if desired, ECU22 may first actuate motor 214 to rotate in the first rotational direction, urging piston 206 leftward (as viewed in fig. 3) to ensure that there is some clearance between spring washer 277 and tip portion 208 of piston 206 before urging piston 206 rearward toward spring washer 277.

To determine the home position, travel of the piston 206 in the right direction continues and is monitored by the ECU22 via readings from the sensor 218 until certain conditions are met indicating that the piston 206 has moved to the desired position. Generally, the piston 206 moves to the right until the piston 206 is detected to engage an end stop. The end stop may be defined as a shoulder 279 or an optional spring washer 277. Preferably, piston 206 is moved rightward until enlarged end portion 208 of piston 206 engages spring washer 277. At this point, the spring washer 277 may compress slightly, as shown exaggerated in FIG. 4. Fig. 4 shows the piston 206 in its retracted position. To help prevent damage to the components of plunger assembly 18, spring washer 277 is used to cushion or bias piston 206 as it moves toward shoulder 279. Thus, the spring washer 277 helps prevent the enlarged end portion 208 of the piston 206 from directly contacting the shoulder 279. However, it should be understood that the use of spring washer 277 is optional and that plunger assembly 18 may be configured without spring washer 277 such that enlarged tip portion 208 directly engages against shoulder 279.

As will be explained in further detail below, certain conditions will be met, and the ECU22 can determine that the spring washer 277 has contacted and engaged the enlarged end portion 208, and thus will stop the motor 214 to prevent further compression of the spring washer 277. At this time, the ECU22 may regard the retracted position (shown in fig. 4) as the home position. As shown in fig. 4, this home position generally corresponds to the rightmost position within the bore 200 of the housing of the plunger assembly 18. Alternatively, the ECU22 may slightly advance the piston 206 in the leftward direction to decompress the spring washer 277 and determine the new piston position as the home position, such as shown in fig. 2. In yet another preferred process, which will be described in detail below, the ECU22 may have performed a compensated port determination process and moved the piston 206 forward by approximately the distance D1, as shown in fig. 4, and stopped the piston 206 in the "linear zero" position such that the second port 248 is only slightly to the right of the lip seal 234, as shown in fig. 5.

One of the conditions that may be monitored for detecting engagement of the piston 206 with an end stop, such as a spring washer 277, is the state of the motor 214. More specifically, the ECU22 may monitor the current applied to the motor 214 to sense when the motor 214 stalls or stops after engaging the spring washer 277. During the homing initialization process, the motor 214 is preferably controlled at a low torque and low speed so as not to cause significant compression of the spring washer 277. In contrast to the relatively smooth operation of the motor 214 when the piston 206 is moving freely, the ECU22 monitors the motor current during movement of the piston 206 to sense when there is a significant current rise when the enlarged portion 208 engages the spring washer 277. The method indirectly senses the torque output of the motor 214. For example, it may be preferred to stop the motor 214 when a torque threshold of about 0.3N is reached.

Another condition that may be monitored to detect when the piston 206 engages an end stop is the speed at which the piston 206 is retracted. The ECU22 may control the motor 212 in a constant state to move the piston 206 at a relatively constant speed via the ball screw mechanism 212. From this information, the speed at which the piston 206 should travel assuming it is not compressing the spring washer 277 may be calculated based on information from the sensor 218. Upon engaging and compressing spring washer 277, the speed of piston 206 will generally stop (or be slowed by the compression of spring washer 277). The detection of an immediate decrease in speed by sensor 218 indicates that piston 206 is beginning to compress spring washer 277. Preferably, during the homing initialization process, the ECU22 controls the motor 214 at a relatively low speed and low torque. For example, the piston 206 may move at a speed of about 10 mm/sec. At such low speeds, it may be determined that the optional spring washer 277 need not be present and, therefore, may be omitted without fear of damaging the plunger assembly 18.

The ECU22 may stop the movement of the piston 206 when any one of the current sensed condition or the predetermined speed value condition corresponding to the initial compression of the spring washer 277 is satisfied. This retracted position of the piston 206 may then be used as a home position, as described above.

In connection with the diagnostic homing initialization routine, it may be desirable to perform a method of determining the desired position of the compensating port of the piston 206, i.e., the positioning of the compensating port 248 relative to the position of the lip seal 234. This procedure can be performed at any time. For example, the procedure may be performed after each homing initialization and/or periodically throughout the life of the plunger assembly 18. However, it has been found that this procedure need only be performed once after manufacture and assembly of the brake system 10, such as immediately after the brake system 10 has been filled with brake fluid and deflated.

Referring now to fig. 5, the piston 206 is in its rest position, and thus generally does not generate pressure from the plunger assembly 18. Spring washer 277 is not subject to any significant compression. The piston 206 is shown in a preferred position with the port 248 adjacent to but only slightly to the right of the inner diameter engaging edge 235 of the lip seal 234. In fig. 5, the engagement edge 235 of the lip seal 234 is shown spaced a very small distance D2 from the port 248. In this position, the pressure chambers 240 and 242 are in fluid communication with the reservoir 20 via the passageway 244 and conduit 249. The fluid communication between the reservoir 20 and the pressure chambers 240 and 242 helps to ensure that no pressure builds up in the chambers 240 and 242, which may cause unnecessary caliper wear at the associated wheel brakes, for example. Thus, when the plunger assembly 18 is in its rest position, pressure at the wheel brakes 12a, 12b, 12c and 12d may be vented through the plunger assembly 18 to the reservoir 20.

As described above, with respect to operation of the plunger assembly 18, fluid communication from the port 248 to the reservoir 20 is shut off or closed in order to build pressure within the pressure chambers 240 and 242. This is accomplished by moving the piston 206 in a leftward direction (as viewed in fig. 5) until the port 248 is located a distance D3 to the left of the inner diameter tip 235 of the lip seal 234, as shown in fig. 6. Because the piston 206 of the plunger assembly 18 may be precisely controlled in the fore-aft direction at a given speed, the compensated port ideal position of the piston 206 may be determined by monitoring the boost pressure variation characteristics of the plunger assembly 18. The compensated port ideal position of the piston 206 is generally shown in fig. 5, where the port 248 is shown only slightly to the right of the engagement edge 235 of the lip seal 234. This position is also defined as the linear zero position. The piston 206 needs to travel less in the left direction to close the port 248 than the position of the port 248 in fig. 2, thereby providing a faster pressure build-up of the pressure chambers 240 and/or 242 of the plunger assembly 18. Due to design and manufacturing tolerances, different plunger assemblies may be constructed such that the positioning of the pistons 206 within the bores 200 are slightly different from each other. However, all plunger assemblies are preferably designed so that after assembly, the port 248 is secured to the right of the lip seal 234. However, to ensure this position, the port 248 may be farther to the right of the lip seal 234 than is ideally desired. Accordingly, it is desirable to determine the location of the ideal position of the compensation port of the piston 206 for each plunger assembly 18. Fig. 2 may represent plunger assembly 18 after initial manufacture and assembly and prior to any method of determining the location of a desired compensation port having been performed on plunger assembly 18. The method of determining the location of the compensation port desired position of the piston 206, i.e., the position of the compensation port 248 relative to the engagement edge 235 of the lip seal 234, may begin after manufacture and assembly of the plunger assembly 18. Because design and assembly tolerances may vary slightly from one unit to another, it may be desirable to precisely locate the compensating port 248 for each plunger assembly 18.

A method of determining the location of the desired position of the compensation port of the piston 206 (the location of the compensation port 248 relative to the engagement edge 235 of the lip seal 234) may be accomplished by monitoring the boost pressure variation characteristics of the plunger assembly 18. Different methods may be used. For example, a compensated port ideal position or linear zero may be obtained by first finding when a minimum pressure is established in the pressure chamber 240 as the piston 206 advances in the forward direction. The method will now be described. In a first step, the piston 206 of the ram assembly 18 is preferably retracted to a rest or home position, as shown in fig. 4. Preferably, all of the valves in the brake system 10 are in their de-energized positions. The ECU22 actuates the motor 214 in a second rotational direction to retract the piston 206 in a rightward direction to place the plunger assembly 18 in its rest or home position, as shown in fig. 4. In this position, the port 248 is to the right of the lip seal 234 such that the pressure chambers 240 and 242 are in fluid communication with the reservoir 20. The motor 214 is preferably moved at a relatively low speed, such as at about 250 rpm.

It should be noted that in the position shown in fig. 5, the spring washer 277 may be in a relaxed state such that the enlarged end portion 208 of the piston 206 either rests against the spring washer 277 or is slightly spaced from the spring washer. Alternatively, spring washer 277 may be slightly compressed by enlarged end portion 208 of piston 206. The ECU22 may monitor the state of the plunger assembly 18 by determining when the piston 206 has reached its idle position while the piston 206 is no longer moving (as sensed by the sensor 218) while the motor 214 is still operating. ECU22 may then stop motor 214. A small amount of time may be spent in this determination, which may cause spring washer 277 to compress slightly. In addition, slight compression may result due to the presence of a return spring (not shown) that biases the piston 206 in the right direction.

In a preferred embodiment of the method, the ECU22 operates some of the valves of the brake system 10 to their energized positions after the plunger assembly 18 has been placed in its rest or home position, as discussed above. For example, the ECU22 may energize the first three-way isolation valve 30 and the second three-way isolation valve 32 to permit fluid flow from the conduit 34 through the first isolation valve 30 and the second isolation valve 32. The first plunger valve 250 is also preferably energized to its open position. Further, all of the dump valves 52, 56, 60 and 64 are preferably energized to their open positions to permit fluid flow to the reservoir 20. When the plunger assembly 18 is in its rest position as shown in fig. 5, the ECU22 preferably records or writes the position of the piston 206 in the NVRAM so that a basic knowledge of the position of the piston 206 prior to testing is known. It should be noted that sensor 218 detects the rotational position of rotor 217, which corresponds to the linear position of piston 206, so that ECU22 can track and record the position of piston 206 during this process.

The ECU22 then actuates the motor 214 and the ball screw mechanism 212 in a first rotational direction to drive the piston 206 in a first direction or to the left as viewed in fig. 5. The motor 214 may be actuated to any speed, such as about 750 rpm. The initial movement of the piston 206 is represented diagrammatically in fig. 7 as a relatively small horizontal path 300. Fig. 7 is a graphical representation of control of the plunger assembly 18 during the compensation port learning process. It should be noted that the diagrammatic representation of fig. 7 is not drawn to scale and is used for descriptive purposes. After the piston 206 has moved sufficiently, the port 248 moves past the lip seal 234, causing the compensation port to be shut off (such as shown in fig. 6), thereby closing fluid communication between the reservoir 20 and the pressure chambers 240 and 242. At this point, continued movement of piston 206 causes a pressure increase within pressure chambers 240 and 242, which may be sensed by pressure sensor 156 (at the output of plunger assembly 18) in fluid communication with conduit 34. This pressure build-up is represented in fig. 7 as path 302 as piston 206 advances in a forward direction.

It should be noted that the inflection point 304 in the graph of fig. 7 represents the closing or shutoff of the port 248, which may be detected as a change in boost pressure characteristics sensed by the pressure sensor 156. Thus, the position of the port 248 relative to the lip seal 234 may be determined at this inflection point 304. The ECU22 may write this position information in NVRAM at shutdown. Fig. 8 illustrates the position of the piston 206 at point 305 at the end of the path 302 after the piston 206 has moved a distance D4 (e.g., 25mm) beyond the compensation port shut off (represented by 304). Due to the high accuracy and precision of the plunger assembly 18, the distance traveled by the piston 206 may be monitored by the sensor 218, thereby providing accurate positioning of the piston 206 within the bore 200. The position of the piston 206 at the inflection point 304 may be logged by the ECU 22. Based on this information, it may then be desirable to determine a new home position for the piston 206 such that the compensation port 248 is positioned adjacent to but only slightly to the right of the inner diameter engagement edge 235 of the lip seal 234, as shown in fig. 5. This position is referred to as the linear zero position. In this position, the pressure chambers 240 and 242 are in fluid communication with the reservoir 20 via conduit 249, but only a very small distance of travel of the piston 206 in the left direction is required to close such fluid communication. Although shown exaggerated in fig. 5, the distance between the port 248 and the inner diameter engaging portion of the lip seal 234 may be relatively small, such as about 0.5 mm.

In this first method of determining the location of the compensation port ideal position of the piston 206 as described above, the process essentially measures the difference between the retracted position of the piston 206 such as shown in FIG. 4 and the linear zero position of the piston 206 such as shown in FIG. 5. In the linear null position, the port 248 is positioned adjacent the engagement edge 235 of the lip seal 234 by a relatively small distance D2 such that the port 248 is in fluid communication with the fluid reservoir 20 and with the pressure chamber 240.

In a second method of determining the location of the compensation port ideal position of the piston 206, a significant pressure drop in the output of the plunger assembly 18 is detected when the piston 206 completes a stroke in the reward pressure mode. This second method may be used as a redundancy test performed immediately after the first method described above, or only the second method may be implemented. If done immediately thereafter, the piston 206 is in the position shown in FIG. 8 and is represented by point 305 in the graphical representation of FIG. 7. The ECU22 then preferably maintains the first and second three-way isolation valves in their energized states. The second plunger valve 252 is preferably energized to its closed position. The first plunger valve 250 is de-energized to its closed position. The dump valve is also preferably de-energized to its closed position. ECU22 then operates plunger assembly 18 to retract piston 206 on the rearward stroke to build pressure in secondary pressure chamber 242 and conduit 34. The motor 214 may be operated at any suitable speed in the second rotational direction, such as about 750 rpm. This rearward stroke pressure buildup is represented in the graph of FIG. 7 as path 306. Instead of continuing along path 306 until the compensation port is shut off, it is desirable to relieve the pressure to reduce any high torque load on motor 214 to prevent any damage to motor 214. Thus, at a predetermined distance represented by the inflection point 314 of the plot in fig. 7, the ECU22 preferably energizes the first plunger valve 250 to its open position and de-energizes the second plunger valve 252 to its open position. First isolation valve 30 and second isolation valve 323 are preferably left energized. ECU22 preferably waits a set period of time until the pressure within secondary pressure chamber 242 and conduit 34 stabilizes.

ECU22 then preferably rotates motor 214 at a relatively low speed (e.g., about 60rpm) in the second rotational direction while calculating the pressure drop as a function of the decreasing piston stroke. When the port 248 moves to the right of the inner diameter portion of the lip seal 234, a compensating port is detected. At this point, as represented by inflection point 310 in fig. 7, a significant increase in pressure drop as a function of decreasing piston travel may be sensed via pressure sensor 156 and sensor 218, indicating that port 248 of piston 206 has just passed lip seal 234, as fluid is now permitted to flow from secondary pressure chamber 242 into reservoir 20 via passageway 244 and conduit 249. Similar to the first method, the positioning of the piston 206 may be logged by the ECU22 to the NVRAM. The piston position for the compensation port shut off may be compared and/or updated relative to the position known in the first method. It should be noted that continued rearward movement of the piston 206 is represented by path 312 in fig. 7. The ECU22 continues to move the piston 206 rearwardly until a zero pressure level is reached or a predetermined timeout has been reached, such as for example about 5 seconds.

Once the off position has been determined by one or both of the above methods, the ECU22 may continuously park or position the piston 206 so that the port 248 is only slightly to the right of the engagement edge 235 of the lip seal 234, as shown in fig. 5, in the linear zero position. This compensated port ideal position of the piston 206 (with the port 248 being only slightly to the right of the engagement edge 235 of the lip seal 234) provides the small stroke in the left direction required by the piston 206 to close the port 248. Accordingly, a faster pressure build-up is provided in the pressure chambers 240 and/or 242 of the plunger assembly during operation of the plunger assembly 18. The linear zero position of the piston 206 within the bore 200 is then used as the starting position for each braking cycle. All subsequent positions of the piston 206 may be derived from and determined from this known linear zero position.

With respect to the various valves of the braking system 10, the terms "operate" or "operating" (or "actuating", "moving", "positioning") as used herein (including the claims) may not necessarily refer to energizing a solenoid of the valve, but rather to placing or permitting the valve in a desired position or valve state. For example, a solenoid actuated normally open valve may be operated to an open position by simply permitting the valve to remain in its unenergized, normally open state. Operating the normally open valve to the closed position may include energizing a solenoid to move internal structure of the valve to block or prevent fluid flow therethrough. Thus, the term "operating" should not be construed to mean moving the valve to a different position, nor should it be intended to always energize the valve's associated solenoid.

The principles and modes of operation thereof have been explained and illustrated in the preferred embodiments of the present invention. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.