阅读说明：本技术 用于改变四轮驱动车辆的挡位范围的系统和方法 (System and method for changing gear range of four-wheel drive vehicle ) 是由 陈伟添 戴征宇 江宏 于 2020-08-19 设计创作，主要内容包括：本公开提供了“用于改变四轮驱动车辆的挡位范围的系统和方法”。描述了用于将传动系挡位范围从较高挡位范围改变为较低挡位范围的方法和系统。所述传动系可包括两个电机和呈四轮驱动配置的四个离合器。所述方法和系统允许传动系在不使车辆停止的情况下从较高挡位范围改变为较低挡位范围。(The present disclosure provides a system and method for changing a range of gears for a four wheel drive vehicle. Methods and systems for changing a powertrain gear range from a higher gear range to a lower gear range are described. The drive train may include two electric machines and four clutches in a four-wheel drive configuration. The method and system allow the powertrain to change from a higher gear range to a lower gear range without stopping the vehicle.)

1. A method for operating a vehicle, comprising:

in response to a request to disengage a higher gear in the first axle and engage a lower gear in the first axle, reducing an output of a first motor coupled to the first axle and increasing an output of a second motor coupled to the second axle.

2. The method of claim 1, further comprising disengaging a first clutch coupled to a higher gear in response to the request to disengage the higher gear in the first axle.

3. The method of claim 2, further comprising closing a second clutch coupled to the lower gear in response to the request to disengage the higher gear in the first axle, the second clutch included in the first axle.

4. The method of claim 3, wherein the first axle is a front axle, and wherein the second axle is a rear axle.

5. The method of claim 3, wherein the first axle is a rear axle, and wherein the second axle is a front axle.

6. The method of claim 3, further comprising adjusting an output of the first electric machine after opening the first clutch to reduce slip across the second clutch.

7. The method of claim 6, wherein adjusting the output of the first electric machine comprises increasing a torque output of the electric machine when the first clutch and the second clutch are fully disengaged.

8. A vehicle system, comprising:

a first electric machine coupled to a front axle;

a second electric machine coupled to the rear axle;

a controller including executable instructions stored in non-transitory memory to decrease the output of the first electric machine and increase the output of the second electric machine in response to a request to switch a powertrain from a higher gear range to a lower gear range.

9. The system of claim 8, further comprising additional instructions for decreasing the output of the second electric machine and increasing the output of the first electric machine in response to the request to switch the powertrain from the higher gear range to the lower gear range.

10. The system of claim 9, wherein the output of the second motor is decreased after increasing the output of the second motor.

11. The system of claim 8, further comprising a first clutch in the front axle and a second clutch in the front axle.

12. The system of claim 11, further comprising additional instructions for opening the first clutch and closing the second clutch in response to the request to switch the driveline from the higher gear range to the lower gear range.

Technical Field

The present description relates generally to methods and systems for shifting a range of an axle of a four-wheel drive electric vehicle. The electric vehicle may include an electric machine that may provide power to a front axle and a rear axle.

Background

The vehicle may include two propulsion sources. One propulsion source may selectively supply power to the forward axle and the other propulsion source may selectively supply power to the rear axle. Each axle may include a gearbox, and the gearbox may include a high range gear and a low range gear. The high-range gear may be selectively engaged to operate the vehicle at a higher speed, and the low-range gear may be selectively engaged to operate the vehicle at a lower speed. Additionally, a lower range gear may be selected when it may be desirable to supply a greater amount of wheel torque. For example, the low range gear may be engaged when the vehicle is climbing a steep hill or when the vehicle is traveling through deep snow or mud.

The gearbox may be shifted from the high gear range to the low gear range via bringing the vehicle to a full stop and manually selecting the low gear range when the vehicle is at a full stop. However, a human driver may find it inconvenient to stop the vehicle to shift from the high axle range to the low axle range. Furthermore, human drivers may find stopping the vehicle and restarting the vehicle in a different axle range a time consuming activity they may not wish to engage in as this may require some additional effort. However, if the vehicle is not engaged in the lower gear range during some conditions, the vehicle may exhibit reduced traction and reduced climbing capability.

Disclosure of Invention

The inventors herein have recognized the above-mentioned problems and have developed a method for operating a vehicle, the method comprising: in response to a request to disengage a higher gear in the first axle and engage a lower gear in the first axle, the output of the first motor coupled to the first axle is reduced and the output of the second motor coupled to the second axle is increased.

By reducing the output of the first electric machine coupled to the first axle and increasing the output of the second electric machine coupled to the second axle, the drive train can be changed from a high gear range to a lower gear range without stopping the vehicle. Furthermore, the drive train may be switched from a high gear range to a lower gear range when the driver of the vehicle is applying an accelerator pedal. Reducing the output of the first electric machine allows the first clutch in the first axle to disengage without creating large driveline torque disturbances. Further, increasing the output of the second motor when the output of the first motor is decreasing may reduce the likelihood of a decrease in wheel torque or a "torque hole" that may be noticed by a vehicle occupant.

The present description may provide several advantages. In particular, the method allows the drive train to be switched from a higher gear range to a lower gear range without having to stop the vehicle. In addition, the method allows for maintaining vehicle speed during a shift from a higher gear range to a lower gear range. The method also controls clutch slip so that the likelihood of clutch degradation may be reduced.

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 meant 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 is a schematic illustration of a vehicle powertrain;

fig. 2 and 3 show two different drive train operating sequences; and

fig. 4 and 5 show an example of a method for operating a drive train of a four wheel drive vehicle.

Detailed Description

The following description relates to systems and methods for operating a driveline or driveline of a four-wheel drive vehicle. The four-wheel drive vehicle may be configured as an electric vehicle, or alternatively, the vehicle may be configured as a hybrid vehicle. An exemplary vehicle and drive train or drivetrain are shown in FIG. 1. Fig. 2 and 3 show exemplary drive train operating sequences according to the methods of fig. 4 and 5. A method for operating a four wheel drive vehicle and shifting the drive train from a higher gear range to a lower gear range is shown. The methods of fig. 4 and 5 allow the powertrain to shift from a higher gear range to a lower gear range while the vehicle is moving and when the driver of the vehicle requests positive torque via an accelerator pedal or other powertrain input.

FIG. 1 illustrates an exemplary vehicle propulsion system 100 for a vehicle 121. The front of the vehicle 121 is indicated at 110 and the rear of the vehicle 121 is indicated at 111. The vehicle propulsion system 100 includes at least two propulsion sources including a front motor 125 and a rear motor 126. The motors 125 and 126 may consume or generate power depending on their mode of operation. Throughout the description of fig. 1, the mechanical connections between the various components are shown as solid lines, while the electrical connections between the various components are shown as dashed lines.

Vehicle propulsion system 100 has a front axle 133 and a rear axle 122. In some examples, the rear axle may include two half shafts, such as a first half shaft 122a and a second half shaft 122 b. Likewise, the front axle 133 may include a first half-shaft 133a and a second half-shaft 133 b. The vehicle propulsion system 100 also has front wheels 130 and rear wheels 131. In this example, the front wheels 130 are selectively drivable via the motor 125. The rear wheels 131 may be driven via the motor 126.

The rear axle 122 is coupled to a motor 126. The rear drive unit 136 may transmit power from the motor 126 to the axle 122, causing the drive wheels 131 to rotate. Rear drive unit 136 may include a low range group 175 and a high range 177 coupled to motor 126 via output shaft 126a of rear motor 126. Low range 175 may be engaged via full closing of low range clutch 176. High range 177 is engageable via full closure of high range clutch 178. The high range clutch 177 and the low range clutch 178 CAN be opened and closed via commands received by the rear drive unit 136 through CAN 299. Alternatively, the high clutch 177 and the low clutch 178 may be opened and closed via a digital output or pulse width provided by the control system 14. The rear drive unit 136 may include a differential 128 such that torque may be provided to the axles 122a and 122 b. In some examples, an electronically controlled differential clutch (not shown) may be included in the rear drive unit 136.

The front axle 133 is coupled to the motor 125. The front drive unit 137 may transmit power from the motor 125 to the axle 133, causing the drive wheels 130 to rotate. The front drive unit 137 may include a low range group 170 and a high range 173 coupled to the electric machine 125 via an output shaft 125a of the front electric machine 125. Low range 170 is engagable via full closure of low range clutch 171. High range 173 is engageable via fully closing high range clutch 174. The high range clutch 174 and the low range clutch 171 may be opened and closed via commands received by the front drive unit 137 via the CAN 299. Alternatively, the high clutch 174 and the low clutch 171 may be opened and closed via a digital output or pulse width provided by the control system 14. The front drive unit 137 may include a differential 127 so that torque may be provided to the axles 133a and 133 b. In some examples, an electronically controlled differential clutch (not shown) may be included in the rear drive unit 137.

The electric machines 125 and 126 may receive electrical power from an on-board electrical energy storage device 132. Further, the electric machines 125 and 126 may provide a generator function to convert kinetic energy of the vehicle into electrical energy, wherein the electrical energy may be stored at the electrical energy storage device 132 for later use by the electric machine 125 and/or the electric machine 126. The first inverter system controller (ISC1)134 may convert the alternating current generated by the rear motor 126 to direct current for storage at the electrical energy storage device 132, and vice versa. The second inverter system controller (ISC2)147 may convert the alternating current generated by the front motor 125 to direct current for storage at the electrical energy storage device 132, and vice versa. The electrical energy storage device 132 may be a battery, capacitor, inductor, or other electrical energy storage device.

In some examples, electrical energy storage device 132 may be configured to store electrical energy that may be supplied to other electrical loads (other than motors) resident on the vehicle, including cabin heating and air conditioning systems, engine starting systems, headlamp systems, cabin audio and video systems, and the like.

The control system 14 may be in communication with one or more of the electric machine 125, the electric machine 126, the energy storage device 132, and the like. The control system 14 may receive sensory feedback information from one or more of the motor 125, the motor 126, the energy storage device 132, and the like. Further, the control system 14 may send control signals to one or more of the electric machine 125, the electric machine 126, the energy storage device 132, etc., in response to such sensed feedback. The control system 14 may receive an indication of an operator requested output of the vehicle propulsion system from the human operator 102 or an autonomous controller. For example, control system 14 may receive sensory feedback from a pedal position sensor 194 in communication with pedal 192. Pedal 192 may be schematically referred to as an accelerator pedal. Similarly, control system 14 may receive an indication of operator requested vehicle braking via human operator 102 or an autonomous controller. For example, the control system 14 may receive sensory feedback from a pedal position sensor 157 in communication with the brake pedal 156.

The energy storage device 132 may periodically receive electrical energy from a power source, such as a stationary electrical grid (not shown), that resides external to (e.g., not part of) the vehicle. As one non-limiting example, the vehicle propulsion system 100 may be configured as a plug-in Electric Vehicle (EV), whereby electrical energy may be supplied to the energy storage device 132 via a power grid (not shown).

The electrical energy storage device 132 includes an electrical energy storage device controller 139 and a power distribution module 138. The electrical energy storage device controller 139 may provide charge balancing between the energy storage elements (e.g., battery cells) and communication with other vehicle controllers (e.g., controller 12). The power distribution module 138 controls the flow of power into and out of the electrical energy storage device 132.

One or more Wheel Speed Sensors (WSS)195 may be coupled to one or more wheels of the vehicle propulsion system 100. The wheel speed sensor may detect a rotational speed of each wheel. Such examples of WSSs may include permanent magnet type sensors.

The vehicle propulsion system 100 may also include a Motor Electronics Coolant Pump (MECP) 146. The MECP 146 may be used to circulate a coolant to dissipate heat generated by at least the electric machine 120 and the electronics system of the vehicle propulsion system 100. As an example, the MECP may receive power from the on-board energy storage device 132.

Controller 12 may form part of control system 14. In some examples, the controller 12 may be a single controller of the vehicle. The control system 14 is shown receiving information from a plurality of sensors 16 (various examples of which are described herein) and sending control signals to a plurality of actuators 81 (various examples of which are described herein). As one example, the sensors 16 may include a tire pressure sensor (not shown), a wheel speed sensor 195, and the like. In some examples, sensors associated with the electric machine 125, the electric machine 126, the wheel speed sensor 195, etc. may communicate information to the controller 12 regarding various states of electric machine operation. The controller 12 includes non-transitory (e.g., read only) memory 165, random access memory 166, digital input/output 168, and microcontroller 167.

The vehicle propulsion system 100 may also include an on-board navigation system 17 (e.g., a global positioning system) on the dashboard 19, with which the operator of the vehicle may interact 17. The navigation system 17 may include one or more location sensors for assisting in estimating the location (e.g., geographic coordinates) of the vehicle. For example, the in-vehicle navigation system 17 may receive signals from GPS satellites (not shown) and identify the geographic location of the vehicle from the signals. In some examples, the geographic location coordinates may be communicated to the controller 12.

The instrument cluster 19 may also include a display system 18, the display system 18 configured to display information to a vehicle operator. By way of non-limiting example, the display system 18 may include a touch screen or Human Machine Interface (HMI), i.e., a display that enables a vehicle operator to view graphical information and enter commands. In some examples, display system 18 may be wirelessly connected to the internet (not shown) via controller (e.g., 12). Thus, in some examples, the vehicle operator may communicate with an internet website or software application (app) via display system 18.

The instrument cluster 19 may also include an operator interface 15 via which a vehicle operator may adjust the operating state of the vehicle. Specifically, operator interface 15 may be configured to initiate and/or terminate operation of the vehicle driveline (e.g., electric machine 125 and electric machine 126) based on operator inputs. Various examples of operator ignition interface 15 may include an interface that requires physical equipment, such as an active key, that may be inserted into operator interface 15 to start electric machines 125 and 126 and turn the vehicle on, or may be removed to turn off electric machines 125 and 126 to turn the vehicle off. Other examples may include a passive key communicatively coupled to operator interface 15. The passive key may be configured as an electronic key fob or smart key that does not have to be inserted into or removed from the interface 15 to operate the vehicle motors 125 and 126. In contrast, a passive key may need to be located inside the vehicle or in the vicinity of the vehicle (e.g., within a threshold distance of the vehicle). Other examples may additionally or alternatively use a start/stop button that is manually pressed by the driver to start or shut off motors 125 and 126 to turn the vehicle on or off. In other examples, the remote motor start may be initiated by a remote computing device (not shown) (e.g., a cell phone or smartphone-based system) where the user's cell phone sends data to the server and the server communicates with the vehicle controller 12 to start the engine.

The system of fig. 1 provides a vehicle system comprising: a first electric machine coupled to a front axle; a second electric machine coupled to the rear axle; a controller including executable instructions stored in non-transitory memory to decrease the output of the first electric machine and increase the output of the second electric machine in response to a request to switch a powertrain from a higher gear range to a lower gear range. The system further includes additional instructions for decreasing the output of the second electric machine and increasing the output of the first electric machine in response to a request to switch the powertrain from a higher gear range to a lower gear range. The system comprises: wherein the output of the second motor is decreased after the output of the second motor is increased. The system also includes a first clutch in the front axle and a second clutch in the front axle. The system further includes additional instructions for opening the first clutch and closing the second clutch in response to a request to switch the powertrain from a higher gear range to a lower gear range.

Referring now to fig. 2, a predictive vehicle operating sequence according to the method of fig. 4 and 5 is shown. The vehicle operation sequence illustrated in fig. 2 may be provided via the methods of fig. 4 and 5 in cooperation with the system illustrated in fig. 1. The graphs shown in fig. 2 occur at the same time and are aligned in time. The vertical lines at t0 to t5 represent times of interest during the sequence. The sequence of fig. 2 occurs when the driver applies the accelerator pedal such that the wheel torque request is non-zero and when the vehicle is moving on the road.

The first plot from the top of fig. 2 is a plot of motor torque versus time. The vertical axis represents the motor torque, and the motor torque increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Trace 204 represents the rear axle motor torque. Trace 202 represents front axle motor torque.

The second plot from the top of fig. 2 is a plot of total wheel torque (e.g., the sum of front wheel torque and rear wheel torque) versus time. The vertical axis represents the total wheel torque at the wheels, and the magnitude of the total wheel torque increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Line 206 represents the total wheel torque (e.g., the torque of all four wheels).

The third plot from the top of fig. 2 is a plot of front axle high range clutch operating state versus time. The vertical axis represents the front axle high range clutch operating state, and when trace 208 is at a higher level near the vertical axis arrow, the front axle high range clutch operating state is closed. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Trace 208 represents the front axle high clutch state.

The fourth plot from the top of fig. 2 is a plot of rear axle high range clutch operating state versus time. The vertical axis represents the rear axle high range clutch operating state, and when trace 210 is at a higher level near the vertical axis arrow, the rear axle high range clutch operating state is closed. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Trace 210 represents the rear axle high clutch state.

The fifth plot from the top of fig. 2 is a plot of front axle low range clutch operating state versus time. The vertical axis represents the front axle low range clutch operating state, and the front axle low range clutch operating state is closed when trace 212 is at a higher level near the vertical axis arrow. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Trace 212 represents the front axle low range clutch state.

The sixth plot from the top of fig. 2 is a plot of rear axle low range clutch operating state versus time. The vertical axis represents the rear axle low range clutch operating state, and when trace 214 is at a higher level near the vertical axis arrow, the rear axle low range clutch operating state is closed. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Trace 214 represents the rear axle low range clutch state.

At time t0, the front and rear motor torques are non-zero and are based on a non-zero or applied accelerator pedal position (not shown). The total wheel torque is at an intermediate level and the front and rear axle high range clutches are fully closed. The front axle low range clutch and the rear axle low range clutch are fully disengaged. Thus, the power train is in a high gear range suitable for driving the vehicle at higher speeds.

At time t1, a request (not shown) to change the powertrain from a higher gear range to a lower gear range occurs. The illustrated sequence begins by changing the gear ratio of the front axle and then changing the gear ratio of the rear axle. The output torque of the front motor starts to decrease, and the output of the rear motor starts to increase. This allows for maintaining vehicle speed and reduces the likelihood of creating a "torque hole" in the driveline torque output (e.g., a reduction in driveline torque, which may reduce vehicle speed and may be perceived by vehicle occupants). Therefore, vehicle handling is improved. The total wheel torque remains constant as the torque of the front and rear motors changes. The front axle high gear clutch and the rear axle high gear clutch are completely closed. Thus, the high gears of the front and rear axles are engaged to allow the electric machine to provide torque to the wheels via the front and rear axle high gears. The front axle low-gear clutch and the rear axle low-gear clutch are completely disconnected, so that the motor torque is not transmitted through the lower gears of the front axle and the rear axle.

At time t2, the output torque of the front electric machine reaches zero, and the front axle high range clutch is fully disengaged in response to the front electric machine torque being zero. The rear motor torque output has leveled off and the total wheel torque has remained constant. The front axle low clutch remains fully open and the rear axle high clutch remains fully closed to allow propulsion of the vehicle via the rear electric machine only. The rear axle low range clutch remains fully disengaged.

Between time t2 and time t3, the front axle motor torque increases until the speed of the front axle motor output shaft equals the speed of the front axle lower gear. The front axle lower gear speed is a function of vehicle speed. The front axle motor torque is reduced after the speed of the front axle motor output shaft equals the speed of the front axle lower gear. The front axle low clutch remains fully disengaged while the rear axle high clutch remains fully engaged. The rear axle low range clutch remains fully disengaged.

At time t3, the torque of the front axle motor is reduced to zero, and the front axle lower range clutch is fully engaged in response to the front axle motor torque being zero. This allows torque to be transferred from the front electric machine to the front wheels via the lower axle gear. The rear axle high clutch remains fully closed while the rear axle low clutch remains fully open.

Between time t3 and time t4, the front axle motor torque is increased and the rear axle motor torque is decreased in preparation for the rear axle gear shift. The front axle high clutch remains fully disengaged while the front axle low clutch remains fully engaged. The rear axle high clutch remains fully closed while the rear axle low clutch remains fully open. Thus, the front electric machine transfers torque to the front axle via the front axle low gear, while the rear electric machine transfers torque to the rear axle via the rear axle high gear.

At time t4, the output torque of the rear electric machine reaches zero, and the rear axle high range clutch is fully disengaged in response to the rear electric machine torque being zero. The front motor torque output has leveled off and the total wheel torque has remained constant. The rear axle low range clutch remains fully open while the front axle low range clutch remains fully closed to allow propulsion of the vehicle via the front electric machine only. The rear axle low range clutch remains fully disengaged and the front axle high range clutch remains fully disengaged.

Between time t4 and time t5, the rear axle motor torque increases until the speed of the rear axle motor output shaft equals the speed of the rear axle lower gear. The rear axle lower gear speed is a function of vehicle speed. And reducing the torque of the rear axle motor after the speed of the output shaft of the rear axle motor is equal to the speed of the lower gear of the rear axle. The rear axle low range clutch remains fully open while the front axle low range clutch remains fully closed. The rear axle high range clutch remains fully disengaged.

At time t5, the rear axle motor torque is reduced to zero and the rear axle lower range clutch is fully engaged in response to the rear axle motor torque being zero. This allows torque to be transferred from the rear electric machine to the rear wheels via the lower axle gear. The front axle low range clutch remains fully closed and the front axle high range clutch remains fully open.

In this way, the wheel torque of the vehicle may remain substantially constant (e.g., torque variation less than 5%) as the driveline changes from a high gear range to a low gear range. Furthermore, the rotational speed of the electric machine may be closed loop controlled so that driveline torque disturbances may be low.

Referring now to fig. 3, a second predictive vehicle operating sequence in accordance with the method of fig. 4 and 5 is shown. The vehicle operation sequence illustrated in fig. 2 may be provided via the methods of fig. 4 and 5 in cooperation with the system illustrated in fig. 1. The graphs shown in fig. 2 occur at the same time and are aligned in time. The vertical lines at t10 to t14 represent times of interest during the sequence. The sequence of fig. 3 occurs when the driver is not applying the accelerator pedal such that the wheel torque request is zero and when the vehicle is moving on the road.

The first plot from the top of fig. 3 is a plot of motor torque versus time. The vertical axis represents the motor torque, and the motor torque increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Trace 304 represents rear axle motor torque. Trace 302 represents front axle motor torque.

The second plot from the top of fig. 3 is a plot of total wheel torque (e.g., the sum of front wheel torque and rear wheel torque) versus time. The vertical axis represents the total wheel torque at the wheels, and the magnitude of the total wheel torque increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Line 306 represents the total wheel torque (e.g., the torque of all four wheels).

The third plot from the top of fig. 3 is a plot of front axle high range clutch operating state versus time. The vertical axis represents the front axle high range clutch operating state, and when trace 308 is at a higher level near the vertical axis arrow, the front axle high range clutch operating state is closed. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Trace 308 represents the front axle high clutch state.

The fourth plot from the top of fig. 3 is a plot of rear axle high range clutch operating state versus time. The vertical axis represents the rear axle high range clutch operating state, and when trace 310 is at a higher level near the vertical axis arrow, the rear axle high range clutch operating state is closed. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Trace 310 represents the rear axle high clutch state.

The fifth plot from the top of fig. 3 is a plot of front axle low range clutch operating state versus time. The vertical axis represents the front axle low range clutch operating state, and the front axle low range clutch operating state is closed when trace 312 is at a higher level near the vertical axis arrow. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Trace 312 represents the front axle low range clutch state.

The sixth plot from the top of fig. 3 is a plot of rear axle low range clutch operating state versus time. The vertical axis represents the rear axle low range clutch operating state, and when trace 314 is at a higher level near the vertical axis arrow, the rear axle low range clutch operating state is closed. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Trace 314 represents the rear axle low range clutch state.

At time t10, the front and rear motor torques are zero and are based on a zero accelerator pedal position (not shown). The total wheel torque is also zero and the rear axle high range clutch is fully closed. The front axle low range clutch and the rear axle low range clutch are fully disengaged. Thus, the power train is in a high gear range suitable for driving the vehicle at higher speeds.

At time t11, a request (not shown) to change the powertrain from a higher gear range to a lower gear range occurs. The illustrated sequence begins by changing the gear ratio of the front axle and then changing the gear ratio of the rear axle. The output torque of the front motor remains zero and the output of the rear motor remains zero. The total wheel torque remains zero. The front axle high range clutch is fully open and the rear axle high range clutch is fully closed. Thus, in the event of an increase in requested wheel torque, the high gear of the front axle is disengaged to initiate a front axle shift and the rear axle remains engaged so that the driveline can respond by increasing the output of the rear electric machine. The front axle low range clutch and the rear axle low range clutch are fully disengaged.

Between time t11 and time t12, the front axle motor torque increases until the speed of the front axle motor output shaft equals the speed of the front axle lower gear. The front axle lower gear speed is a function of vehicle speed. The front axle motor torque is reduced after the speed of the front axle motor output shaft equals the speed of the front axle lower gear. The front axle low clutch remains fully disengaged while the rear axle high clutch remains fully engaged. The rear axle low range clutch remains fully disengaged.

At time t12, the front axle motor torque is reduced to zero and the front axle lower gear clutch is fully engaged in response to the front axle motor torque being zero. The rear axle high clutch remains fully closed while the rear axle low clutch remains fully open.

At time t13, the rear axle high range clutch is fully disengaged in response to completing the shift of the front axle gear. In the event of an increase in driver demand torque, the rear axle low clutch remains fully open, while the front axle low clutch remains fully closed.

Between time t13 and time t14, the rear axle motor torque increases until the speed of the rear axle motor output shaft equals the speed of the rear axle lower gear. The rear axle lower gear speed is a function of vehicle speed. And reducing the torque of the rear axle motor after the speed of the output shaft of the rear axle motor is equal to the speed of the lower gear of the rear axle. The rear axle low range clutch remains fully open while the front axle low range clutch remains fully closed. The rear axle high range clutch remains fully disengaged.

At time t15, the rear axle lower range clutch is fully engaged in response to the rear axle motor torque being zero. The front axle low range clutch remains fully closed and the front axle high range clutch remains fully open.

In this way, the wheel torque of the vehicle may remain substantially constant (e.g., torque variation less than 5%) as the driveline changes from a high gear range to a low gear range. Furthermore, the rotational speed of the electric machine may be closed loop controlled so that driveline torque disturbances may be low.

Referring now to fig. 4 and 5, an exemplary method for operating a vehicle including a first electric machine coupled to a front axle or a first axle and a second electric machine coupled to a rear axle or a second axle is shown. The methods of fig. 4 and 5 may be incorporated into and cooperate with the system of fig. 1. Furthermore, at least portions of the methods of fig. 4 and 5 may be combined as executable instructions stored in a non-transitory memory, while other portions of the methods may be performed via a controller that transitions the operating states of the devices and actuators in the physical world.

At 402, method 400 determines vehicle operating conditions. Vehicle operating conditions may include, but are not limited to, vehicle speed, accelerator pedal position, operating state of axle clutches, current wheel torque, and brake pedal position. The method 400 proceeds to 404.

At 404, method 400 determines whether the vehicle speed is less than a threshold speed, the accelerator pedal is less than a threshold applied amount, and a request to shift the driveline from a high gear ratio of the oncoming axle to a lower gear ratio of the oncoming axle. In one example, the threshold speed may be a speed less than a predetermined speed (e.g., 60 km/h) and the threshold accelerator pedal application amount is a predetermined amount (e.g., less than 50% of full-scale accelerator pedal position). A change of the drive train from a high gear ratio of the axle to a low gear ratio of the axle may be requested via the vehicle operator and the human/machine interface. Alternatively, a shift of the driveline from a high gear ratio to a low gear ratio of the axle may be automatically requested in response to vehicle operating conditions. For example, when vehicle speed is less than a threshold speed or when wheel slip exceeds a threshold level, a shift of the driveline from a high gear ratio to a low gear ratio of the axle may be requested. If method 400 determines that there is a request to shift the driveline from a high gear ratio of the axle to a low gear ratio of the axle, the answer is yes and method 400 proceeds to 406. Otherwise, the answer is no, and method 400 proceeds to 450.

At 450, method 400 continues to operate the powertrain with the gear of the axle engaged in its current configuration. For example, if method 400 determines that the driveline is operating at a high gear ratio to engage the axle, the driveline continues to operate at the high gear ratio to engage the axle. Method 400 proceeds to exit.

At 406, method 400 determines whether it is necessary to shift the front axle from its higher gear ratio to its lower gear ratio before shifting the rear axle from its higher gear ratio to its lower gear ratio. The method 400 may determine to shift the front axle from its higher gear ratio to its lower gear ratio before shifting the rear axle from its higher gear ratio to its lower gear ratio based on road conditions, wheel slip, or other conditions. For example, if the method 400 determines that wheel slip of the rear wheels of the vehicle is present and wheel slip of the front wheels is not present, the method 400 may determine whether to shift the front axle from its higher gear ratio to its lower gear ratio before shifting the rear axle from its higher gear ratio to its lower gear ratio so that a high level of traction may be maintained at the front axle. If method 400 determines to shift the front axle from its higher gear ratio to its lower gear ratio before shifting the rear axle from its higher gear ratio to its lower gear ratio, the answer is yes and method 400 proceeds to 408. Otherwise, the answer is no, and method 400 proceeds to 430.

At 408, method 400 reduces the torque output of the front axle motor to zero and increases the torque output of the rear axle motor to maintain vehicle speed via maintaining wheel torque as it existed immediately prior to shifting the driveline from the higher gear ratio to the lower gear ratio. Such operation may be commanded when the accelerator pedal is applied and the wheel torque is non-zero. However, if the output of the front axle motor is zero immediately prior to the request to shift the powertrain from the higher gear ratio to the lower gear ratio, the method 400 may not change the torque output of the front axle motor. Further, the method 400 may not change the torque output of the rear axle motor if the output of the rear axle motor is zero immediately prior to the request to shift the powertrain from the higher gear ratio to the lower gear ratio. Method 400 proceeds to 410.

At 410, method 400 disengages the front axle high range clutch in response to the torque of the front axle motor being zero. However, if the wheel torque is zero immediately prior to the request to shift the powertrain from the higher gear range to the lower gear range, the method 400 may disengage the high gear ratio clutch in response to the request to shift the powertrain from the higher gear range to the lower gear range. Method 400 proceeds to 412.

At 412, method 400 adjusts the slip of the front axle lower clutch. In other words, the method 400 adjusts the speed differential across the front axle lower clutch to zero. In one example, method 400 operates the front axle motor in a speed control mode (e.g., adjusts motor torque such that the front axle motor speed follows a requested or desired speed). Method 400 may increase the rotational speed of the output shaft of the front axle motor such that the rotational speed of the output shaft of the front axle motor is equal to the rotational speed of the lower gear of the front axle. As soon as the rotational speed of the output shaft of the front axle motor is equal or almost equal to the rotational speed of the low gear of the front axle, the torque of the front axle motor is reduced.

In one example, the front axle motor may be operated in a closed loop speed control mode that utilizes a proportional/integral controller and relies on speed feedback of a lower gear to drive the speed error between the rotational speed of the front axle motor and the speed of the front axle lower gear to zero.

The method 400 also adjusts the torque output of the rear axle motor to meet the driver demand torque (e.g., via torque requested by the human driver by applying the accelerator pedal). If the driver demand torque increases, the method 400 increases the torque of the rear axle motor so that the driveline responds to the driver demand torque. If the driver demand torque is not increasing, the method 400 maintains the total wheel torque (e.g., the sum of the torques applied to all wheels) at the amount of total wheel torque immediately prior to the requested driveline shift from the higher gear range to the lower gear range. The method 400 proceeds to 414.

At 414, method 400 fully closes the low range clutch of the front axle to engage the lower range of the front axle. The method 400 may fully engage the low range clutch in response to the output torque of the front electric machine being zero after the output shaft of the front axle electric machine accelerates to the rotational speed of the front axle low range gear. Method 400 proceeds to 416.

At 416, method 400 decreases the torque output of the rear axle motor to zero and increases the torque output of the front axle motor to maintain vehicle speed via maintaining the total wheel torque as the wheel torque that existed immediately prior to the request to shift the driveline from the higher gear ratio to the lower gear ratio. The rear axle motor torque may be reduced to zero in response to fully closing the low range clutch of the front axle. However, if the output of the rear axle motor is zero immediately prior to the request to shift the powertrain from the higher gear ratio to the lower gear ratio, the method 400 may not change the torque output of the rear axle motor. Further, the method 400 may not change the torque output of the front axle motor if the output of the front axle motor is zero immediately prior to the request to shift the powertrain from the higher gear ratio to the lower gear ratio. The method 400 proceeds to 418.

At 418, method 400 disengages the rear axle high range clutch in response to the torque of the rear axle motor being zero. However, if the wheel torque is zero immediately prior to the request to shift the powertrain from the higher gear range to the lower gear range, the method 400 may disengage the rear axle high range clutch in response to the front axle low range clutch being fully closed. Method 400 proceeds to 420.

At 420, method 400 adjusts the slip of the rear axle lower clutch. In other words, method 400 adjusts the speed differential across the rear axle low range clutch to zero. In one example, the method 400 operates the rear axle motor in a speed control mode (e.g., adjusts the motor torque such that the motor speed follows a requested or desired speed). Method 400 may increase the rotational speed of the output shaft of the rear axle motor such that the rotational speed of the output shaft of the rear axle motor is equal to the rotational speed of the lower gear of the rear axle. Once the rotational speed of the output shaft of the rear axle motor is equal or nearly equal to the rotational speed of the rear axle low gear, the torque of the front axle motor is reduced.

In one example, the rear axle motor may be operated in a closed loop speed control mode that utilizes a proportional/integral controller and relies on speed feedback of the lower gear to drive the speed error between the rotational speed of the rear axle motor and the speed of the rear axle lower gear to zero.

The method 400 also adjusts the torque output of the front axle motor to meet the driver demand torque (e.g., torque requested via application of an accelerator pedal by a human driver). If the driver demand torque increases, the method 400 increases the torque of the front axle motor so that the driveline responds to the driver demand torque. If the driver demand torque is not increasing, the method 400 maintains the total wheel torque (e.g., the sum of the torques applied to all wheels) at the amount of total wheel torque immediately prior to the requested driveline shift from the higher gear range to the lower gear range. The method 400 proceeds to 422.

At 422, method 400 fully closes the low range clutch of the rear axle to engage the lower range of the rear axle. The method 400 may fully engage the rear axle low range clutch in response to the output torque of the rear electric machine being zero after the output shaft of the electric machine accelerates to the rotational speed of the rear axle low range. Method 400 proceeds to exit.

At 430, method 400 decreases the torque output of the rear axle motor to zero and increases the torque output of the front axle motor to maintain vehicle speed via maintaining wheel torque as that existed immediately prior to the request to shift the driveline from the higher gear ratio to the lower gear ratio. Such operation may be commanded when the accelerator pedal is applied and the wheel torque is non-zero. However, if the output of the rear axle motor is zero immediately prior to the request to shift the powertrain from the higher gear ratio to the lower gear ratio, the method 400 may not change the torque output of the rear axle motor. Further, the method 400 may not change the torque output of the front axle motor if the output of the front axle motor is zero immediately prior to the request to shift the powertrain from the higher gear ratio to the lower gear ratio. Method 400 proceeds to 432.

At 432, method 400 disengages the rear axle high range clutch in response to the torque of the rear axle motor being zero. However, if the wheel torque is zero immediately prior to the request to shift the powertrain from the higher gear range to the lower gear range, the method 400 may disengage the high gear ratio clutch of the rear axle in response to the request to shift the powertrain from the higher gear range to the lower gear range. Method 400 proceeds to 434.

At 434, method 400 adjusts the slip of the rear axle lower clutch. In other words, the method 400 adjusts the speed differential across the lower clutch to zero. In one example, the method 400 operates the rear axle motor in a speed control mode (e.g., adjusts the motor torque such that the motor speed follows a requested or desired speed). The method 400 may increase the rotational speed of the output shaft of the rear axle motor such that the rotational speed of the output shaft of the rear axle motor is equal to the rotational speed of the lower gear of the rear axle. Once the rotational speed of the output shaft of the rear axle motor is equal or nearly equal to the rotational speed of the low gear of the rear axle, the torque of the rear axle motor is reduced.

In one example, the rear axle motor may be operated in a closed loop speed control mode that utilizes a proportional/integral controller and relies on speed feedback of the lower gear to drive the speed error between the rotational speed of the rear axle motor and the speed of the rear axle lower gear to zero.

The method 400 also adjusts the torque output of the front axle motor to meet the driver demand torque (e.g., torque requested via application of an accelerator pedal by a human driver). If the driver demand torque increases, the method 400 increases the torque of the front axle motor so that the driveline responds to the driver demand torque. If the driver demand torque is not increasing, the method 400 maintains the total wheel torque (e.g., the sum of the torques applied to all wheels) at the amount of total wheel torque immediately prior to the requested driveline shift from the higher gear range to the lower gear range. The method 400 proceeds to 436.

At 436, the method 400 fully closes the low range clutch of the rear axle to engage the lower range of the rear axle. The method 400 may fully engage the low range clutch in response to the output torque of the rear electric machine being zero after the output shaft of the rear electric machine accelerates to the rotational speed of the rear axle low range. The method 400 proceeds to 438.

At 438, the method 400 decreases the torque output of the front axle motor to zero and increases the torque output of the rear axle motor to maintain vehicle speed via maintaining the total wheel torque to the wheel torque that existed immediately prior to the request to shift the driveline from the higher gear ratio to the lower gear ratio. In response to fully closing the low range clutch of the rear axle, the front axle motor torque may be reduced to zero. However, if the output of the rear axle motor is zero immediately prior to the request to shift the powertrain from the higher gear ratio to the lower gear ratio, the method 400 may not change the torque output of the front axle motor. Further, the method 400 may not change the torque output of the rear axle motor if the output of the rear axle motor is zero immediately prior to the request to shift the powertrain from the higher gear ratio to the lower gear ratio. Method 400 proceeds to 440.

At 440, method 400 disengages the front axle high range clutch in response to the torque of the front axle motor being zero. However, if the wheel torque is zero immediately prior to the request to shift the powertrain from the higher gear range to the lower gear range, the method 400 may disengage the front axle high range clutch in response to the rear axle low range clutch being fully closed. Method 400 proceeds to 442.

At 442, method 400 adjusts the slip of the front axle lower clutch. In other words, the method 400 adjusts the speed differential across the front axle lower clutch to zero. In one example, the method 400 operates the front axle motor in a speed control mode (e.g., adjusts the motor torque such that the motor speed follows a requested or desired speed). Method 400 may increase the rotational speed of the output shaft of the front axle motor such that the rotational speed of the output shaft of the front axle motor is equal to the rotational speed of the low gear of the front axle. As soon as the rotational speed of the output shaft of the front axle motor is equal or almost equal to the rotational speed of the low gear of the front axle, the torque of the rear axle motor is reduced.

In one example, the front axle motor may be operated in a closed loop speed control mode that utilizes a proportional/integral controller and relies on speed feedback of a lower gear to drive the speed error between the rotational speed of the front axle motor and the speed of the front axle lower gear to zero.

The method 400 also adjusts the torque output of the rear axle motor to meet the driver demand torque (e.g., torque requested via application of an accelerator pedal by a human driver). If the driver demand torque increases, the method 400 increases the torque of the rear axle motor so that the driveline responds to the driver demand torque. If the driver demand torque is not increasing, the method 400 maintains the total wheel torque (e.g., the sum of the torques applied to all wheels) at the amount of total wheel torque immediately prior to the requested driveline shift from the higher gear range to the lower gear range. The method 400 proceeds to 444.

At 444, method 400 fully closes the low range clutch of the front axle to engage the lower range of the front axle. The method 400 may fully engage the low range clutch of the front axle in response to the output torque of the front electric machine being zero after the output shaft of the front electric machine accelerates to the rotational speed of the low range of the front axle. Method 400 proceeds to exit.

Thus, the methods of fig. 4 and 5 may shift the higher gear of the front axle to the lower gear of the front axle before shifting the higher gear of the rear axle to the lower gear of the rear axle. Alternatively, the methods of fig. 4 and 5 may shift the higher gear of the rear axle to the lower gear of the rear axle before shifting the higher gear of the front axle to the lower gear of the front axle. Further, the methods of fig. 4 and 5 may be performed when driver demand is non-zero and when the vehicle is moving. Vehicle operators may find such powertrain shifts to be efficient and time-efficient.

The methods of fig. 4 and 5 provide a method for operating a vehicle, the method comprising: in response to a request to disengage a higher gear in the first axle and engage a lower gear in the first axle, the output of the first motor coupled to the first axle is reduced and the output of the second motor coupled to the second axle is increased. The method also includes disengaging a first clutch coupled to a higher gear in the first axle in response to a request to disengage the higher gear. The method also includes closing a second clutch coupled to a lower gear in response to a request to disengage a higher gear in the first axle, the second clutch included in the first axle. The method comprises the following steps: wherein the first axle is a front axle and wherein the second axle is a rear axle. The method comprises the following steps: wherein the first axle is a rear axle and wherein the second axle is a front axle. The method also includes adjusting an output of the first electric machine after opening the first clutch to reduce slip across the second clutch. The method comprises the following steps: wherein adjusting the output of the first electric machine comprises increasing the torque output of the electric machine when the first clutch and the second clutch are fully disengaged.

The methods of fig. 4 and 5 also provide a method for operating a vehicle, the method comprising: decreasing an output of a first electric machine coupled to the first axle and increasing an output of a second electric machine coupled to the second axle in response to a request to switch the powertrain from a higher gear range to a lower gear range; and decreasing the output of the second electric machine and increasing the output of the first electric machine in response to a request to switch the powertrain from a higher gear range to a lower gear range. The method comprises the following steps: wherein the higher gear range is switched to the lower gear range via disengaging the higher gear in the first axle and engaging the lower gear in the first axle. The method comprises the following steps: wherein the higher gear range is switched to the lower gear range via disengaging the higher gear in the second axle and engaging the lower gear in the second axle. The method comprises the following steps: wherein the first axle is a rear axle and the second axle is a rear axle. The method comprises the following steps: wherein the first axle is a rear axle and the second axle is a front axle.

The methods of fig. 4 and 5 may also include disengaging a first clutch coupled to a higher gear in response to a request to switch the powertrain from a higher gear range to a lower gear range. The method further includes adjusting an output of the first electric machine to reduce slip across the second clutch in response to a request to switch the powertrain from a higher gear range to a lower gear range. The method comprises the following steps: wherein adjusting the output of the first electric machine includes increasing a torque output of the first electric machine to accelerate the speed of the first electric machine to the gear speed.

In another representation, the methods of fig. 4 and 5 provide for decreasing the output of a first electric machine coupled to the first axle and increasing the output of a second electric machine coupled to the second axle in response to a request to disengage a higher gear in the first axle and engage a lower gear in the first axle; and operating the first electric machine in a speed control mode after disengaging the high range clutch of the first axle, the speed of the first electric machine being controlled to the speed of the lower gear of the first axle when operating the first electric machine in said speed control mode. The method also includes closing the low range clutch in response to the first electric machine reaching a speed of a lower gear of the first axle.

It should be noted that the exemplary control and estimation routines included herein may 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. Furthermore, part of the method may be a physical action taken in the real world to change the state of the device. 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, and/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 examples 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 the computer readable storage medium in the engine control system, wherein the described acts are performed by executing instructions in conjunction with the electronic controller in the system including the various engine hardware components. One or more of the method steps described herein may be omitted, if desired.

It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific examples are not to be considered in a limiting sense, because numerous variations are possible. For example, the above-described 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 operating a vehicle comprises: in response to a request to disengage a higher gear in the first axle and engage a lower gear in the first axle, the output of the first motor coupled to the first axle is reduced and the output of the second motor coupled to the second axle is increased.

In one aspect of the invention, the method includes disengaging a first clutch coupled to a higher gear in the first axle in response to a request to disengage the higher gear.

In one aspect of the invention, the method includes closing a second clutch coupled to a lower gear in response to a request to disengage a higher gear in a first axle, the second clutch included in the first axle.

In one aspect of the invention, the first axle is a front axle and wherein the second axle is a rear axle.

In one aspect of the invention, the first axle is a rear axle, and wherein the second axle is a front axle.

In one aspect of the invention, the method includes adjusting the output of the first electric machine after disengaging the first clutch to reduce slip across the second clutch.

In one aspect of the invention, adjusting the output of the first electric machine includes increasing the torque output of the electric machine when the first clutch and the second clutch are fully disengaged.

According to the invention, a method for operating a vehicle comprises: decreasing an output of a first electric machine coupled to the first axle and increasing an output of a second electric machine coupled to the second axle in response to a request to switch the powertrain from a higher gear range to a lower gear range; and decreasing the output of the second electric machine and increasing the output of the first electric machine in response to a request to switch the powertrain from a higher gear range to a lower gear range.

In one aspect of the invention, the higher gear range is shifted to the lower gear range via disengaging the higher gear in the first axle and engaging the lower gear in the first axle.

In one aspect of the invention, the higher gear range is shifted to the lower gear range via disengaging the higher gear in the second axle and engaging the lower gear in the second axle.

In one aspect of the invention, the first axle is a front axle and the second axle is a rear axle.

In one aspect of the invention, the first axle is a rear axle and the second axle is a front axle.

In one aspect of the invention, the method includes disengaging a first clutch coupled to a higher gear in response to a request to switch the powertrain from a higher gear range to a lower gear range.

In one aspect of the invention, the method includes adjusting the output of the first electric machine to reduce slip across the second clutch in response to a request to shift the powertrain from a higher gear range to a lower gear range.

In one aspect of the invention, adjusting the output of the first electric machine includes increasing a torque output of the first electric machine to accelerate the speed of the first electric machine to the gear speed.

According to the present invention, there is provided a vehicle system having: a first electric machine coupled to a front axle; a second electric machine coupled to the rear axle; a controller including executable instructions stored in non-transitory memory to decrease the output of the first electric machine and increase the output of the second electric machine in response to a request to switch the powertrain from a higher gear range to a lower gear range.

According to one embodiment, the invention is further characterized by additional instructions for decreasing the output of the second electric machine and increasing the output of the first electric machine in response to a request to switch the powertrain from a higher gear range to a lower gear range.

According to one embodiment, the output of the second motor is decreased after the output of the second motor is increased.

The invention also features, according to one embodiment, a first clutch in the front axle and a second clutch in the front axle.

According to one embodiment, the invention is further characterized by additional instructions for opening the first clutch and closing the second clutch in response to a request to switch the driveline from a higher gear range to a lower gear range.