System and method for controlling electric motor to act as virtual electronic locking differential

Abstract

A system includes a reference speed module and a motor control module. The reference speed module is configured to determine a reference speed range based on a speed of a left wheel of a pair of front wheels or rear wheels of a vehicle and a speed of a right wheel of the pair of front wheels or rear wheels. The right wheel is decoupled from the left wheel. The motor control module is configured to control at least one of a first electric motor and a second electric motor based on the reference speed range. The first electric motor is connected to the left wheel. The second electric motor is connected to the right wheel.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to systems and methods for controlling electric motors to act as virtual electronic locking differentials. BACKGROUND

[0002] The information provided in this section is for the purpose of generally presenting the context of the disclosure. Aspects described in this section to the extent that they are not otherwise explicitly disclosed in the description and claims are neither admitted to be prior art nor necessary to the disclosure.

[0003] A differential transmits torque from a power source, such as an engine or electric motor, to a pair of wheels on an axle. An open differential provides the same torque to each of the wheels. As a result, the wheels have different levels of traction and the wheels rotate at different speeds. In contrast, a locking differential locks the wheels together, as if the wheels were rotating on a common axle, such that the wheels rotate at the same speed, regardless of the level of traction of each wheel. An electronic locking differential includes an electronic solenoid that is operable to lock the wheels together or unlock the wheels from each other. SUMMARY

[0004] An example of a system according to the present disclosure includes a reference speed module and a motor control module. The reference speed module is configured to determine a reference speed range based on a speed of a left wheel of a pair of front or rear wheels of a vehicle and a speed of a right wheel of the pair of front or rear wheels. The right wheel is disconnected from the left wheel. The motor control module is configured to control at least one of a first electric motor and a second electric motor based on the reference speed range. The first electric motor is connected to the left wheel. The second electric motor is connected to the right wheel.

[0005] In one aspect, the reference speed module is configured to select one of the left wheel speed and the right wheel speed based on a magnitude of the left wheel speed and the right wheel speed, set a reference speed in the middle of the range to the selected speed, and determine the reference speed range based on the reference speed in the middle of the range and an allowable slip.

[0006] In one aspect, the reference speed range extends from a minimum reference speed to a maximum reference speed, the reference speed module is configured to determine the minimum reference speed by subtracting the allowable slip from the reference speed in the middle of the range, and the reference speed module is configured to determine the maximum reference speed by adding the allowable slip to the reference speed in the middle of the range.

[0007] In one aspect, the reference speed module is configured to set the reference speed in the middle of the range to equal a minimum of the left wheel speed and the right wheel speed when a driver of the vehicle requests the vehicle to accelerate, and set the reference speed in the middle of the range to equal a maximum of the left wheel speed and the right wheel speed when the driver requests the vehicle to decelerate.

[0008] In one aspect, the reference speed module is configured to determine whether the driver is requesting the vehicle to accelerate or decelerate based on at least one of the accelerator pedal position and the brake pedal position.

[0009] In one aspect, the reference speed module is configured to determine the allowable slip based on at least one of the driver input and whether the vehicle is turning.

[0010] In one aspect, the motor control module is configured to control one of the first electric motor and the second electric motor connected to one of the left wheel and the right wheel to adjust the speed of the one of the left wheel and the right wheel to a value within the reference speed range and control the other of the first electric motor and the second electric motor based on the wheel torque request when one of the left wheel speed and the right wheel speed is outside the reference speed range.

[0011] In one aspect, the motor control module is configured to maintain the wheel torque request at a constant value when one of the left wheel speed and the right wheel speed is outside the reference speed range.

[0012] In one aspect, the motor control module is configured to stop maintaining the wheel torque request at a constant value, adjust the wheel torque request to the driver torque request, and control both the first electric motor and the second electric motor based on the wheel torque request when (i) one of the left wheel speed and the right wheel speed is within the reference speed range, and (ii) the driver torque request is less than the estimated wheel torque.

[0013] In one aspect, the motor control module is configured to control both the first electric motor and the second electric motor based on the reference speed range.

[0014] Another example of a system according to the present disclosure includes a reference speed module and a motor control module. The reference speed module is configured to determine a reference speed range based on at least one of a speed of a left wheel of a pair of front wheels or rear wheels of a vehicle and a speed of a right wheel of the pair of front wheels or rear wheels. The right wheel is decoupled from the left wheel. The motor control module is configured to control one of the first electric motor and the second electric motor based on the reference speed range when one of the left wheel speed and the right wheel speed is outside the reference speed range. The one of the first electric motor and the second electric motor is connected to the one of the left wheel speed and the right wheel speed. The motor control module is configured to control the other of the first electric motor and the second electric motor based on a wheel torque request. The other of the first electric motor and the second electric motor is connected to the other of the left wheel speed and the right wheel speed.

[0015] In one aspect, the reference speed module is configured to set the mid-range reference speed to one of the left wheel speed and the right wheel speed, and to determine the reference speed range based on the mid-range reference speed and the allowable slip.

[0016] In one aspect, the reference speed range extends from a minimum reference speed to a maximum reference speed, the reference speed module is configured to determine the minimum reference speed by subtracting the allowable slip from the mid-range reference speed, and the reference speed module is configured to determine the maximum reference speed by adding the allowable slip to the mid-range reference speed.

[0017] In one aspect, the reference speed module is configured to set the mid-range reference speed to equal the minimum of the left wheel speed and the right wheel speed when a driver of the vehicle requests the vehicle to accelerate, and to set the mid-range reference speed to equal the maximum of the left wheel speed and the right wheel speed when the driver requests the vehicle to decelerate.

[0018] In one aspect, the motor control module is configured to control one of the first electric motor and the second electric motor connected to one of the left wheel and the right wheel to adjust the speed of the one of the left wheel and the right wheel to a value within the reference speed range, and to maintain the wheel shaft torque request at a constant value.

[0019] In one aspect, the motor control module is configured to stop maintaining the wheel shaft torque request at a constant value, adjust the wheel shaft torque request to the driver torque request, and control both the first electric motor and the second electric motor based on the wheel shaft torque request when (i) one of the left wheel speed and the right wheel speed is within the reference speed range, and (ii) the driver torque request is less than the estimated wheel shaft torque.

[0020] A vehicle according to the present disclosure includes a left wheel, a right wheel disconnected from the left wheel, a first electric motor connected to the left wheel, a second electric motor connected to the right wheel, a reference speed module, and an electric motor control module. The left wheel and the right wheel make up a pair of front wheels or a pair of rear wheels of the vehicle. The reference speed module is configured to determine a reference speed range based on at least one of a speed of the left wheel and a speed of the right wheel. The motor control module is configured to control one of the first electric motor and the second electric motor based on the reference speed range when one of the left wheel speed and the right wheel speed is outside the reference speed range. The one of the first electric motor and the second electric motor is connected to the one of the left wheel speed and the right wheel speed. The motor control module is configured to control the other of the first electric motor and the second electric motor based on a wheel shaft torque request. The other of the first electric motor and the second electric motor is connected to the other of the left wheel speed and the right wheel speed.

[0021] In one aspect, when one of the speeds of the left wheel and the right wheel is outside the reference speed range, the motor control module is configured to control one of the first and second electric motors connected to one of the left and right wheels to adjust the speed of one of the left and right wheels to a value within the reference speed range and to keep the wheel axle torque request constant.

[0022] In one aspect, the motor control module is configured to stop maintaining the axle torque request at a constant value, adjust the axle torque request to the driver torque request, and control both the first electric motor and the second electric motor based on the axle torque request when (i) one of the left wheel speed and the right wheel speed is within the reference speed range and the driver torque request is less than the estimated axle torque.

[0023] In one aspect, the first electric motor is configured to rotate the left wheel independently of the second electric motor that rotates the right wheel, and the first electric motor is configured to rotate the right wheel independently of the first electric motor that rotates the left wheel.

[0024] This invention includes the following solutions:

[0025] 1. A system comprising:

[0026] A reference speed module is configured to determine a reference speed range based on the speed of the left wheel of a pair of front or rear wheels of a vehicle and the speed of the right wheel of the pair of front or rear wheels, wherein the right wheel is disconnected from the left wheel.

[0027] A motor control module configured to control at least one of a first electric motor and a second electric motor based on the reference speed range, wherein: the first electric motor is connected to the left wheel; and the second electric motor is connected to the right wheel.

[0028] 2. The system according to Scheme 1, wherein the reference speed module is configured to: select one of the left wheel speed and the right wheel speed based on the magnitude of the left wheel speed and the right wheel speed; set a reference speed in the middle of the range as the selected speed; and

[0029] The reference speed range is determined based on a reference speed in the middle of the range and the allowable slip.

[0030] 3. The system according to Scheme 2, wherein:

[0031] The reference speed range extends from the minimum reference speed to the maximum reference speed;

[0032] The reference speed module is configured to determine the minimum reference speed by subtracting the permissible slip from a reference speed in the middle of the range; and

[0033] The reference speed module is configured to determine the maximum reference speed by adding the allowable slip to a reference speed in the middle of the range.

[0034] 4. The system according to Scheme 2, wherein the reference speed module is configured to: when the vehicle driver requests the vehicle to accelerate, set the reference speed in the middle of the range to be equal to the minimum value of the left wheel speed and the right wheel speed; and

[0035] When the driver requests the vehicle to slow down, the reference speed in the middle of the range is set to the maximum value of the left wheel speed and the right wheel speed.

[0036] 5. The system according to claim 4, wherein the reference speed module is configured to determine whether the driver requests the vehicle to accelerate or decelerate based on at least one of the accelerator pedal position and the brake pedal position.

[0037] 6. The system according to claim 2, wherein the reference speed module is configured to determine the permissible slip based on at least one of driver input and whether the vehicle is turning.

[0038] 7. The system according to Scheme 1, wherein when one of the left wheel speed and the right wheel speed is outside the reference speed range, the motor control module is configured to:

[0039] Controlling one of the first and second electric motors connected to one of the left and right wheels to adjust the speed of the one of the left and right wheels to a value within the reference speed range; and

[0040] Control one of the first and second electric motors based on the wheel axle torque request.

[0041] 8. The system according to claim 7, wherein the motor control module is configured to maintain the axle torque request at a constant value when one of the left wheel speed and the right wheel speed is outside the reference speed range.

[0042] 9. The system according to claim 8, wherein the motor control module is configured to stop maintaining the axle torque request at the constant value, adjust the axle torque request to the driver torque request, and control both the first electric motor and the second electric motor based on the axle torque request:

[0043] When one of the left wheel speed and right wheel speed is within the reference speed range; and

[0044] When the driver's torque request is less than the estimated wheel axle torque.

[0045] 10. The system according to Scheme 1, wherein the motor control module is configured to control both the first electric motor and the second electric motor based on the reference speed range.

[0046] 11. A system comprising:

[0047] A reference speed module configured to determine a reference speed range based on at least one of the speed of the left wheel of a pair of front or rear wheels of a vehicle and the speed of the right wheel of the pair of front or rear wheels, wherein the right wheel is disconnected from the left wheel; and

[0048] The motor control module is configured as follows:

[0049] When either the left wheel speed or the right wheel speed is outside the reference speed range, one of the first electric motor and the second electric motor is controlled based on the reference speed range, wherein the first electric motor and the second electric motor are connected to the wheel speed of either the left wheel speed or the right wheel speed; and

[0050] Control one of the first electric motor and the second electric motor based on the wheel axle torque request, wherein the other of the first electric motor and the second electric motor is connected to the other of the left wheel speed and the right wheel speed.

[0051] 12. The system according to claim 11, wherein the reference speed module is configured to: set a reference speed in the middle of the range as one of the left wheel speed and the right wheel speed; and determine the reference speed range and the allowable slip based on the reference speed in the middle of the range.

[0052] 13. The system according to claim 12, wherein:

[0053] The reference speed range extends from the minimum reference speed to the maximum reference speed;

[0054] The reference speed module is configured to determine the minimum reference speed by subtracting the permissible slip from a reference speed in the middle of the range; and

[0055] The reference speed module is configured to determine the maximum reference speed by adding the allowable slip to a reference speed in the middle of the range.

[0056] 14. The system according to claim 12, wherein the reference speed module is configured to: set the reference speed in the middle of the range equal to the minimum of the left wheel speed and the right wheel speed when the driver of the vehicle requests the vehicle to accelerate, and

[0057] When the driver requests the vehicle to slow down, the reference speed in the middle of the range is set to the maximum value of the left wheel speed and the right wheel speed.

[0058] 15. The vehicle according to claim 11, wherein the motor control module is configured to: control one of the first and second electric motors connected to one of the left and right wheels to adjust the speed of the one of the left and right wheels to a value within the reference speed range; and

[0059] The axle torque is required to be kept constant.

[0060] 16. The system according to claim 15, wherein the motor control module is configured to stop maintaining the axle torque request at the constant value, adjust the axle torque request to the driver torque request, and control both the first electric motor and the second electric motor based on the axle torque request:

[0061] When the speed of one of the left and right wheels is within the reference speed range; and

[0062] When the driver's torque request is less than the estimated wheel axle torque.

[0063] 17. A vehicle comprising:

[0064] Revolver;

[0065] The right wheel is disconnected from the left wheel, and the left wheel and the right wheel form a pair of front or rear wheels of the vehicle;

[0066] A first electric motor connected to the left wheel;

[0067] A second electric motor connected to the right wheel;

[0068] A reference speed module, configured to determine a reference speed range based on at least one of the speeds of the left wheel and the right wheel; and

[0069] Motor control module, the motor control module being configured to:

[0070] When either the left wheel speed or the right wheel speed is outside the reference speed range, one of the first electric motor and the second electric motor is controlled based on the reference speed range, wherein the first electric motor and the second electric motor are connected to the wheel speed of either the left wheel speed or the right wheel speed; and

[0071] Control one of the first electric motor and the second electric motor based on the wheel axle torque request, wherein the other of the first electric motor and the second electric motor is connected to the other of the left wheel speed and the right wheel speed.

[0072] 18. The vehicle according to claim 17, wherein when one of the left wheel speed and the right wheel speed is outside the reference speed range, the motor control module is configured to:

[0073] Controlling one of the first and second electric motors connected to one of the left and right wheels to adjust the speed of the one of the left and right wheels to a value within the reference speed range; and

[0074] Maintain the requested wheel axle torque at a constant value.

[0075] 19. The vehicle according to claim 18, wherein the motor control module is configured to stop maintaining the axle torque request at the constant value, adjust the axle torque request to a driver torque request, and control both the first electric motor and the second electric motor based on the axle torque request:

[0076] The speed of one of the left and right wheels is within the reference speed range; and

[0077] The driver's torque request is less than the estimated wheel axle torque.

[0078] 20. The vehicle according to Scheme 17, wherein:

[0079] The first electric motor is configured to rotate the left wheel independently of the second electric motor that rotates the right wheel; and

[0080] The first electric motor is configured to rotate the right wheel independently of the first electric motor that rotates the left wheel.

[0081] Further applications of this disclosure will become apparent from the detailed description, claims, and drawings. The detailed description and specific examples are intended for illustrative purposes only and are not intended to limit the scope of this disclosure. Attached Figure Description

[0082] This disclosure will be more fully understood from the following detailed description and accompanying drawings, in which:

[0083] Figure 1 This is a functional block diagram of an example vehicle based on this disclosure;

[0084] Figure 2 This is a functional block diagram of an example powertrain control module based on this disclosure;

[0085] Figure 3 This is a flowchart illustrating an example powertrain control method according to the present disclosure.

[0086] In the accompanying drawings, reference numerals may be used repeatedly to identify similar and / or identical elements. Detailed Implementation

[0087] The vehicle according to this disclosure includes a front axle or a rear axle, each axle having a pair of electric motors that independently drive a pair of wheels on the axle. The electric motor and wheel on one side of the axle are mechanically disconnected from the electric motor and wheel on the other side, and vice versa. Therefore, the vehicle does not include a differential for transmitting torque from the electric motors to the wheels. Thus, if the traction level at one wheel differs from the traction level at the other wheel, and the electric motors provide the same amount of torque to each wheel, the wheels can rotate at different speeds. Therefore, the speed of one of the wheels may abruptly change.

[0088] To avoid these problems, the control system according to this disclosure controls an electric motor to drive the wheels in a manner that acts as a virtual electronic locking differential. The control system achieves this by determining a reference speed range based on the wheel speed and controlling at least one of the electric motors based on that reference speed range. In one example, the reference speed range is small and centered on the speed of one of the wheels, and the control system controls an electric motor connected to the other wheel to maintain the speed of that other wheel within the reference speed range. In this way, the control system controls the electric motor to act as a virtual electronic locking differential by rotating the wheel at the same or nearly the same speed.

[0089] The virtual electronic locking differential according to this disclosure has several advantages over physical or mechanical locking differentials. For example, a mechanical locking differential allows zero slip between the speeds of the wheels connected to the locking differential. However, in some situations, such as when the vehicle is cornering, a small amount of slip may be required. In contrast, the virtual electronic locking differential can vary the amount of slip allowed.

[0090] Furthermore, mechanical locking differentials can experience delays in engagement because the speed of the wheel connected to the differential must be below a threshold for physical engagement. Additionally, mechanical locking differentials can experience delays in disengagement because the differential may bind according to the traction level of each wheel, potentially leading to high axle loads and bouncing on dry surfaces. In contrast, virtual electronic locking differentials can lock or unlock wheels by varying the permissible slip amount without any delay in engagement or disengagement. Moreover, mechanical locking differentials can be noisy, while virtual electronic locking differentials are virtually noiseless.

[0091] In the example below, the vehicle includes a pair of rear electric motors that independently drive a pair of rear wheels, and the control system controls the rear electric motors to act as virtual electronic locking differentials. Additionally, the vehicle includes a single front electric motor that drives a pair of front wheels via a physical electronic locking differential. However, instead of having only one front electric motor, the vehicle may include a pair of front electric motors that independently drive the front wheels, and the control system may control the front electric motor to act as a virtual electronic locking differential. Furthermore, the rear wheels may be driven by a single rear electric motor via a physical electronic differential, or the rear wheels may be driven independently by a pair of rear electric motors. In the latter case, the control system may control each pair of front and rear electric motors to act as virtual electronic locking differentials.

[0092] Now for reference Figure 1 The vehicle 10 includes a front electric motor 12, a left rear electric motor 14, a right rear electric motor 16, an electronic locking differential 18, a front half-shaft 20, a left rear half-shaft 22, a right rear half-shaft 24, a left front wheel 26, a right front wheel 28, a left rear wheel 30, and a right rear wheel 32. The front electric motor 12 outputs drive torque to rotate the left front wheel 26 and the right front wheel 28. The electronic locking differential 18 transmits drive torque from the front electric motor 12 to the left front wheel 26 and the right front wheel 28. Furthermore, the electronic locking differential 18 is operable to lock the left front wheel 26 and the right front wheel 28 together, causing them to rotate at the same or nearly the same speed. The electronic locking differential 18 includes a solenoid that is electronically controlled to lock or unlock the left front wheel 26 and the right front wheel 28.

[0093] The front half-shaft 20 connects the electronic locking differential 18 to the left front wheel 26 and the right front wheel 28. In various embodiments, the vehicle 10 includes a front reduction gear (not shown) that transmits torque from the front electric motor 12 to the electronic locking differential 18 at one or more gear ratios. The electronic locking differential 18 and the front half-shaft 20 together form the front axle 34 of the vehicle 10. The front electric motor 12, the reduction gear, and / or the left front wheel 26 and the right front wheel 28 can also be considered as part of the front axle 34.

[0094] The left rear electric motor 14 outputs drive torque to rotate the left rear wheel 30. The right rear electric motor 16 outputs drive torque to rotate the right rear wheel 32. The left rear half-shaft 22 connects the left rear electric motor 14 to the left rear wheel 30. The right rear half-shaft 24 connects the right rear electric motor 16 to the right rear wheel 32. In various embodiments, the vehicle 10 includes a rear reduction gear (not shown) that transmits torque from the left rear electric motor 14 and the right rear electric motor 16 to the left rear half-shaft 22 and the right rear half-shaft 24 at one or more gear ratios, respectively. The left rear half-shaft 22 and the right rear half-shaft 24 together form the rear wheel axle 36 of the vehicle 10. The left rear electric motor 14 and the right rear electric motor 16 and / or the rear reduction gear may also be considered as part of the rear wheel axle 36.

[0095] The left rear electric motor 14 rotates the left rear wheel 30 independently of the right rear electric motor 16, which rotates the right rear wheel 32. The right rear electric motor 16 rotates the right rear wheel 32 independently of the left rear electric motor 14, which rotates the left rear wheel 30. The left rear wheel 30 and the right rear wheel 32 are on the rear axle 36 and aligned with each other in the longitudinal (front-to-back) direction 38 of the vehicle 10. However, since the rear axle 36 does not connect the left rear wheel 30 and the right rear wheel 32 to each other, the left rear wheel 30 and the right rear wheel 32 are disconnected from each other.

[0096] Vehicle 10 also includes an accelerator pedal 40, a brake pedal 42, a steering wheel 44, a left front wheel speed sensor 46, a right front wheel speed sensor 48, a left rear wheel speed sensor 50, a right rear wheel speed sensor 52, an accelerator pedal position sensor 54, a brake pedal position sensor 56, a steering wheel position sensor 58, a vehicle motion sensor 60, and a powertrain control module 62. The driver of vehicle 10 depresses the accelerator pedal 40 to accelerate vehicle 10. The driver depresses the brake pedal 42 to decelerate or stop vehicle 10. The driver rotates the steering wheel 44 to turn vehicle 10. In various embodiments, vehicle 10 may be an autonomous vehicle, in which case the accelerator pedal 40, steering wheel 44, and brake pedal may be omitted, and / or an autonomous driver module (not shown) may control the acceleration, turning, and braking of vehicle 10.

[0097] The left front wheel speed sensor 46 measures the speed of the left front wheel 26 and generates a signal indicating the speed of the left front wheel. The right front wheel speed sensor 48 measures the speed of the right front wheel 28 and generates a signal indicating the speed of the right front wheel. The left rear wheel speed sensor 50 measures the speed of the left rear wheel 30 and generates a signal indicating the speed of the left rear wheel. The right rear wheel speed sensor 52 measures the speed of the right rear wheel 32 and generates a signal indicating the speed of the right rear wheel.

[0098] Accelerator pedal position sensor 54 measures the position of accelerator pedal 40 and generates a signal indicating the accelerator pedal position. Brake pedal position sensor 56 measures the position of brake pedal 42 and generates a signal indicating the brake pedal position. Steering wheel position sensor 58 measures the position of steering wheel 44 and generates a signal indicating the steering wheel position.

[0099] Vehicle motion sensor 60 measures the longitudinal (forward / backward) acceleration, lateral (left / right) acceleration, and yaw rate of vehicle 10. Vehicle motion sensor 60 may be an inertial measurement unit, which may include an accelerometer for measuring longitudinal and lateral vehicle acceleration and a gyroscope for measuring vehicle yaw rate. Vehicle motion sensor 60 generates signals indicating longitudinal vehicle acceleration, lateral vehicle acceleration, and vehicle yaw rate.

[0100] The powertrain control module 62 controls the front electric motor 12, the left rear electric motor 14, the right rear electric motor 16, and the electronic locking differential 18 based on inputs from sensors in the vehicle 10. In one example, the powertrain control module 62 controls the left rear electric motor 14 and the right rear electric motor 16 based on sensor inputs to independently drive the left rear wheel 30 and the right rear wheel 32, acting as a virtual electronic locking differential. The powertrain control module 62 can achieve this by determining a reference speed range based on the rear wheel speed and controlling the left rear electric motor 14 and / or the right rear electric motor 16 based on the reference speed range. In one example, the reference speed range is relatively small and centered on the speed of one of the rear wheels, and the powertrain control module 62 controls the rear electric motor 14 or 16 connected to the other rear wheel to maintain the speed of the other rear wheel within the reference speed range. In this way, the powertrain control module 62 controls the left rear electric motor 14 and the right rear electric motor 16 to act as a virtual electronic locking differential by rotating the left rear wheel 30 and the right rear wheel 32 at the same or nearly the same speed.

[0101] Now for reference Figure 2 An example implementation of the powertrain control module 62 includes a reference speed module 64, an estimated torque module 66, and a motor control module 68. The reference speed module 64 determines a reference speed range based on the left and right rear wheel speeds from the left rear wheel speed sensor 50 and the right rear wheel speed sensor 52. The reference speed range extends from a minimum reference speed to a maximum reference speed. The reference speed module 64 outputs the reference speed range.

[0102] In one example, the reference speed module 64 selects one of the rear wheel speeds, sets a reference speed equal to the middle of the range of the selected speed, and determines minimum and maximum reference speeds based on the middle reference speed and the permissible slip. The permissible slip is the difference between permissible rear wheel speeds. The reference speed module 64 may determine the permissible slip based on driver input and / or whether the vehicle 10 is turning.

[0103] In one example, the driver can touch a button or touchscreen (not shown) on vehicle 10 to enable or disable the virtual electronic differential (eLocker) function. When the virtual eLocker function is enabled, the reference speed module 64 can set the permissible slip to a small value, such as 1 revolution per minute (RPM). The reference speed module 64 can set the permissible slip to a large value when the virtual eLocker function is disabled.

[0104] In one example, when vehicle 10 is moving in a straight line, reference speed module 64 sets the allowable slip to a small value, and when vehicle 10 is turning, reference speed module 64 increases the allowable slip to prevent binding. The amount by which the allowable slip is increased can be based on the turning size and / or speed of vehicle 10. Reference speed module 64 can determine whether vehicle 10 is turning and the size of the turn based on the steering wheel position from steering wheel position sensor 58.

[0105] Before setting a reference speed in the middle of the range equal to the selected speed, the reference speed module 64 selects one of the rear wheel speeds based on the magnitude of the rear wheel speeds. In one example, when the driver requests the vehicle 10 to accelerate, the reference speed module 64 sets the reference speed in the middle of the range equal to the minimum value of the left and right rear wheel speeds. Conversely, when the driver requests the vehicle 10 to decelerate, the reference speed module 64 sets the reference speed in the middle of the range equal to the maximum value of the left and right rear wheel speeds. The reference speed module 64 can determine whether the driver requests acceleration or deceleration based on the accelerator pedal position and brake pedal position from the accelerator pedal position sensor 54 and brake pedal position sensor 56, respectively.

[0106] The torque estimation module 66 estimates the drive torque of the rear axle 36. The rear axle torque can be equal to the sum of the torques output by the left rear electric motor 14 and the right rear electric motor 16. The torque estimation module 66 can estimate the rear axle torque using, for example, a function or mapping, based on the speeds of the left rear electric motor 14 and the right rear electric motor 16 and the amount of power supplied to them. Additionally or alternatively, the torque estimation module 66 can estimate the rear axle torque based on one or more of the vehicle 10's speed, the vehicle 10's longitudinal acceleration, the vehicle 10's lateral acceleration, and the vehicle 10's yaw rate. The torque estimation module 66 can determine the vehicle speed based on one or more of the wheel speeds from the left front wheel speed sensor 46, the right front wheel speed sensor 48, the left rear wheel speed sensor 50, and the right rear wheel speed sensor 52. The torque estimation module 66 outputs the estimated axle torque (estimated torque of the rear axle 36).

[0107] Motor control module 68 controls the left rear electric motor 14 and the right rear electric motor 16. In one example, motor control module 68 controls the amount of torque output by the left rear electric motor 14 and the right rear electric motor 16 to minimize the difference between the axle torque request and the estimated wheel axle torque. Motor control module 68 can set the wheel axle torque request to be equal to the driver's torque request. Motor control module 68 can determine the driver's torque request based on the accelerator pedal position from accelerator pedal position sensor 54.

[0108] In one example, as long as the rear wheel speed is within the reference speed range, the motor control module 68 controls the left rear electric motor 14 and the right rear electric motor 16 based on the axle torque request. If the speed of one of the rear wheels 30 or 32 is outside the reference speed range, the motor control module 68 controls the rear electric motor 14 or 16 connected to it to adjust the speed of one rear wheel 30 or 32 to a value within the reference speed range. Additionally, the motor control module 68 maintains the axle torque request at a constant value and controls the other rear wheel 30 or 32 based on the axle torque request. The constant value can be the value of the rear axle torque request when the speed of one rear wheel 30 or 32 first falls outside the reference speed range.

[0109] The motor control module 68 continues to maintain the axle torque request at a constant value until the speed of one rear wheel 30 or 32 is within the reference speed range and the driver torque request is less than the estimated axle torque. At this point, the motor control module 68 can stop maintaining the axle torque request at a constant value, adjust the axle torque request to match the driver torque request, and control both the left rear electric motor 14 and the right rear electric motor 16 based on the axle torque request. The motor control module 68 can adjust the axle torque request to match the driver torque request at a predetermined rate.

[0110] Now for reference Figure 3The method for controlling the left rear electric motor 14 and the right rear electric motor 16 to independently drive the left rear wheel 30 and the right rear wheel 32 to perform the virtual eLocker function begins at 70. At 72, the reference speed module 64 determines whether the driver of vehicle 10 intends to accelerate vehicle 10. The reference speed module 64 may make this determination based on the accelerator pedal position from the accelerator pedal position sensor 54. If the driver intends to accelerate vehicle 10, the method continues at 74. Otherwise, the method continues at 76. At 74, the reference speed module 64 selects the minimum rear wheel speed as the reference speed in the middle of the range.

[0111] At 76, the reference speed module 64 determines whether the driver intends to decelerate the vehicle 10. The reference speed module 64 may make this determination based on the brake pedal position from the brake pedal position sensor 56. If the driver intends to decelerate the vehicle 10, the method continues at 78. Otherwise, the method continues at 80. At 78, the reference speed module 64 selects the maximum value of the rear wheel speed as the reference speed in the middle of the range.

[0112] At 80, the reference speed module 64 determines the minimum and maximum reference speeds based on a reference speed in the middle of the range and an allowable slip. The reference speed module 64 determines the minimum reference speed by subtracting the allowable slip from the reference speed in the middle of the range. The reference speed module 64 determines the maximum reference speed by adding the allowable slip to the reference speed in the middle of the range.

[0113] At 82, the motor control module 68 determines whether one of the rear wheel speeds is outside the reference speed range. If one of the rear wheel speeds is outside the reference speed range, the method continues at 84. Otherwise, the method continues at 86.

[0114] At 84, if the virtual eLocker function is not already enabled, the motor control module 68 enables the virtual eLocker function. At 88, the motor control module 68 freezes the wheel axle torque request at its value corresponding to the time point when the virtual eLocker function is enabled and / or when a rear wheel speed is initially outside the reference speed range. At 90, the motor control module 68 uses proportional-integral-derivative (PID) control to keep a rear wheel speed within or maintain within the reference speed range. The reference speed module 64 adjusts the reference speed range based on the speed of the other rear wheel when the virtual eLocker function is enabled. The reference speed module 64 achieves this by setting the reference speed in the middle of the range equal to the speed of the other rear wheel and determining the minimum and maximum reference speeds based on the reference speed in the middle of the range and the allowable slip.

[0115] At 92, the motor control module 68 determines whether a rear wheel speed is within the reference speed range. If a rear wheel speed is within the reference speed range, the method continues at 94. Otherwise, the method returns to 90.

[0116] At 94, the motor control module 68 determines whether the driver's torque request is less than the estimated axle torque. If the driver's torque request is less than the estimated axle torque, the method continues at 96. Otherwise, the method returns to 90. At 96, the motor control module 68 disables the virtual eLocker function. Then, the motor control module 68 stops freezing axle torque requests, adjusts the axle torque request to the driver's torque request, and controls both the left electric motor 14 and the right electric motor 16 based on the axle torque request.

[0117] At 86, motor control module 68 determines whether the virtual eLocker function is enabled. If the virtual eLocker function is enabled, the method continues at 90. Otherwise, the method continues at 98. The method ends at 98.

[0118] The preceding description is illustrative in nature and is in no way intended to limit this disclosure, its application, or use. The broad teachings of this disclosure can be implemented in many forms. Therefore, while this disclosure includes specific examples, its true scope should not be so limited, as other modifications will become apparent upon examination of the drawings, specification, and appended claims. It should be understood that one or more steps in the method may be performed in a different order (or simultaneously) without altering the principles of this disclosure. Furthermore, although each embodiment is described above as having certain features, any one or more of those features described with respect to any embodiment of this disclosure may be implemented in any other embodiment and / or combined with features of any other embodiment, even if such combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and the arrangement of one or more embodiments with respect to each other remains within the scope of this disclosure.

[0119] Spatial and functional relationships between components (e.g., between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including “connected,” “joined,” “linked,” “adjacent,” “right next to,” “on top of,” “above,” “below,” and “set on.” Unless explicitly described as “direct,” when describing a relationship between a first component and a second component in the foregoing disclosure, the relationship can be a direct relationship in which no other intermediate components exist between the first and second components, but it can also be an indirect relationship in which one or more intermediate components (spatially or functionally) exist between the first and second components. As used herein, the phrase “at least one of A, B, and C” should be interpreted as using the non-exclusive logic “OR” to represent logic (A or B or C) and should not be interpreted as representing “at least one of A, at least one of B, and at least one of C.”

[0120] In the accompanying drawings, the direction of the arrowhead typically indicates the flow of information (such as data or instructions) of interest in the illustration. For example, when components A and B exchange various types of information, but the information transmitted from component A to component B is relevant to the illustration, the arrow may point from component A to component B. This unidirectional arrow does not imply that no other information is transmitted from component B to component A. Furthermore, for information transmitted from component A to component B, component B may send a request for the information to component A or receive an acknowledgment.

[0121] In this application, including the following definitions, the term "module" or "controller" may be replaced by the term "circuit". The term "module" may refer to, be a part of, or include: application-specific integrated circuit (ASIC); digital, analog, or mixed-signal analog / digital discrete circuit; digital, analog, or mixed-signal analog / digital integrated circuit; combinational logic circuit; field-programmable gate array (FPGA); processor circuitry (shared, dedicated, or grouped) that executes code; memory circuitry (shared, dedicated, or grouped) that stores code executed by the processor circuitry; other suitable hardware components that provide the described functionality; or some or all of the foregoing, such as in a system-on-a-chip.

[0122] A module may include one or more interface circuits. In some examples, the interface circuits may include wired or wireless interfaces that connect to a local area network (LAN), the Internet, a wide area network (WAN), or a combination thereof. The functionality of any given module disclosed herein may be distributed across multiple modules connected via the interface circuits. For example, multiple modules may allow for load balancing. In another example, a server (also referred to as a remote or cloud) module may perform some functions on behalf of a client module.

[0123] As used above, the term "code" can include software, firmware, and / or microcode, and can refer to programs, routines, functions, classes, data structures, and / or objects. The term "shared processor circuitry" covers a single processor circuitry that executes some or all of the code from multiple modules. The term "group processor circuitry" covers a processor circuitry that, in conjunction with additional processor circuitry, executes some or all of the code from one or more modules. References to multiple processor circuitry cover multiple processor circuitry on a discrete die, multiple processor circuitry on a single die, multiple cores of a single processor circuitry, multiple threads of a single processor circuitry, or a combination thereof. The term "shared memory circuitry" covers a single memory circuitry that stores some or all of the code from multiple modules. The term "group processor circuitry" covers a memory circuitry that, in conjunction with additional memory, stores some or all of the code from one or more modules.

[0124] The term "memory circuit" is a subset of the term "computer-readable medium." As used herein, the term "computer-readable medium" does not cover transient electrical or electromagnetic signals propagated through a medium (such as a carrier wave); therefore, the term "computer-readable medium" can be considered tangible and non-transient. Non-limiting examples of non-transient tangible computer-readable media are non-volatile memory circuits (such as flash memory circuits, erasable programmable read-only memory circuits, or mask read-only memory circuits), volatile memory circuits (such as static random access memory circuits or dynamic random access memory circuits), magnetic storage media (such as analog or digital magnetic tape or hard disk drives), and optical storage media (such as CDs, DVDs, or Blu-ray discs).

[0125] The apparatus and methods described in this application can be implemented, in part or in whole, by a special-purpose computer created by configuring a general-purpose computer to perform one or more specific functions embodied in a computer program. The function blocks, flowchart components, and other elements described above serve as software specifications that can be translated into computer programs through the routine work of a skilled technician or programmer.

[0126] A computer program includes processor-executable instructions stored on at least one non-transitory, tangible, computer-readable medium. A computer program may also include or depend on stored data. A computer program may encompass a basic input / output system (BIOS) that interacts with the hardware of a special-purpose computer, device drivers that interact with specific devices of the special-purpose computer, one or more operating systems, user applications, background services, background applications, etc.

[0127] Computer programs may include: (i) descriptive text to be parsed, such as HTML (Hypertext Markup Language), XML (Extensible Markup Language), or JSON (JS Object Notation), (ii) assembly code, (iii) object code generated from source code by a compiler, (iv) source code executed by an interpreter, (v) source code compiled and executed by a just-in-time (JIT) compiler, and so on. As an example only, source code may be written using the syntax of languages ​​including: C, C++, C#, Objective-C, Swift, Haskell, Go, SQL, R, Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5 (Hypertext Markup Language version 5), Ada, ASP (Active Server Pages), PHP (PHP: Hypertext Preprocessor), Scala, Eiffel, Smalltalk, Erlang, Ruby, Flash®, Visual Basic®, Lua, MATLAB, SIMULINK, and Python®.

Claims

1. A system comprising: a reference speed module configured to determine a reference speed range based on a speed of a left wheel of a pair of front or rear wheels of a vehicle and a speed of a right wheel of the pair of front or rear wheels, wherein the right wheel is disconnected from the left wheel, and a motor control module configured to control at least one of a first electric motor and a second electric motor based on the reference speed range, wherein: the first electric motor is connected to the left wheel; the second electric motor is connected to the right wheel; wherein the reference speed module is configured to: select one of the left wheel speed and the right wheel speed based on a magnitude of the left wheel speed and the right wheel speed; set a reference speed in the middle of a range to the selected speed; and determine the reference speed range based on the reference speed in the middle of the range and an allowable slip.

2. The system of claim 1, wherein: the reference speed range extends from a minimum reference speed to a maximum reference speed; the reference speed module is configured to determine the minimum reference speed by subtracting the allowable slip from the reference speed in the middle of the range; and the reference speed module is configured to determine the maximum reference speed by adding the allowable slip to the reference speed in the middle of the range.

3. The system of claim 1, wherein, the reference speed module is configured to set the reference speed in the middle of the range to equal a minimum of the left wheel speed and the right wheel speed when a driver of the vehicle requests the vehicle to accelerate; and set the reference speed in the middle of the range to a maximum of the left wheel speed and the right wheel speed when the driver requests the vehicle to decelerate.

4. The system of claim 3, wherein, the reference speed module is configured to determine whether the driver requests the vehicle to accelerate or decelerate based on at least one of an accelerator pedal position and a brake pedal position.

5. The system of claim 1, wherein, the reference speed module is configured to determine the allowable slip based on at least one of a driver input and whether the vehicle is turning.

6. The system of claim 1, wherein, when one of the left wheel speed and the right wheel speed is outside the reference speed range, the motor control module is configured to: control the one of the first electric motor and the second electric motor connected to the one of the left wheel and the right wheel to adjust the speed of the one of the left wheel and the right wheel to a value within the reference speed range; and control the other of the first electric motor and the second electric motor based on a wheel shaft torque request. the motor control module is configured to maintain the wheel shaft torque request at a constant value when the one of the left wheel speed and the right wheel speed is outside the reference speed range.

7. The system of claim 6, wherein, the motor control module is configured to stop maintaining the wheel shaft torque request at the constant value, adjust the wheel shaft torque request to a driver torque request, and control both the first electric motor and the second electric motor based on the wheel shaft torque request:

8. The system of claim 7, wherein, when the one of the left wheel speed and the right wheel speed is within the reference speed range; and when the driver torque request is less than an estimated wheel shaft torque. the reference speed module is configured to determine the allowable slip based on a difference between a maximum wheel speed and a minimum wheel speed of the pair of front or rear wheels.

9. The system of claim 1, wherein, The motor control module is configured to control both the first electric motor and the second electric motor based on the reference speed range.

10. A system comprising: a reference speed module configured to determine a reference speed range based on at least one of a speed of a left wheel of a pair of front or rear wheels of a vehicle and a speed of a right wheel of the pair of front or rear wheels, wherein the right wheel is disengaged from the left wheel; and a motor control module configured to: control one of a first electric motor and a second electric motor based on the reference speed range when one of the left wheel speed and the right wheel speed is outside the reference speed range, wherein the one of the first electric motor and the second electric motor is connected to the one of the left wheel speed and the right wheel speed; and control the other of the first electric motor and the second electric motor based on an axle torque request, wherein the other of the first electric motor and the second electric motor is connected to the other of the left wheel speed and the right wheel speed; wherein the reference speed module is configured to set a mid-range reference speed to one of the left wheel speed and the right wheel speed and determine the reference speed range based on the mid-range reference speed and an allowable slip.

11. The system of claim 10, wherein: the reference speed range extends from a minimum reference speed to a maximum reference speed; the reference speed module is configured to determine the minimum reference speed by subtracting the allowable slip from the mid-range reference speed; and the reference speed module is configured to determine the maximum reference speed by adding the allowable slip to the mid-range reference speed.

12. The system of claim 10, wherein, the reference speed module is configured to set the mid-range reference speed equal to a minimum of the left wheel speed and the right wheel speed when a driver of the vehicle requests the vehicle to accelerate, and set the mid-range reference speed to a maximum of the left wheel speed and the right wheel speed when the driver requests the vehicle to decelerate.

13. The system of claim 10, wherein, the motor control module is configured to control the one of the first electric motor and the second electric motor connected to the one of the left wheel and the right wheel to adjust a speed of the one of the left wheel and the right wheel to a value within the reference speed range; and maintain the axle torque request at a constant value.

14. The system of claim 13, wherein, the motor control module is configured to stop maintaining the axle torque request at the constant value, adjust the axle torque request to a driver torque request, and control both the first electric motor and the second electric motor based on the axle torque request when: the one of the left wheel speed and the right wheel speed is within the reference speed range; and the driver torque request is less than an estimated axle torque.

15. A vehicle comprising: a left wheel; a right wheel disengaged from the left wheel, the left wheel and the right wheel forming a pair of front or rear wheels of the vehicle. a first electric motor connected to the left wheel; a second electric motor connected to the right wheel; a reference speed module configured to determine a reference speed range based on at least one of a speed of the left wheel and a speed of the right wheel; and a motor control module configured to: control one of the first electric motor and second electric motor based on the reference speed range when one of the left wheel speed and right wheel speed is outside the reference speed range, wherein the one of the first electric motor and second electric motor is connected to the one of the left wheel speed and right wheel speed; and control the other of the first electric motor and second electric motor based on an axle torque request, wherein the other of the first electric motor and second electric motor is connected to the other of the left wheel speed and right wheel speed; wherein the reference speed module is configured to: select one of the left wheel speed and right wheel speed based on a magnitude of the left wheel speed and right wheel speed; set a reference speed in the middle of a range to the selected speed; and 16. The vehicle of claim 15, wherein, determine the reference speed range based on the reference speed in the middle of the range and an allowable slip. when one of the left wheel speed and right wheel speed is outside the reference speed range, the motor control module is configured to: control the one of the first electric motor and second electric motor connected to the one of the left wheel and right wheel to adjust the speed of the one of the left wheel and right wheel to a value within the reference speed range; and maintain the axle torque request at a constant value.

17. The vehicle of claim 16, wherein, the motor control module is configured to stop maintaining the axle torque request at the constant value, adjust the axle torque request to a driver torque request, and control both the first electric motor and second electric motor based on the axle torque request: the one of the left wheel speed and right wheel speed is within the reference speed range; and the driver torque request is less than an estimated axle torque.

18. The vehicle of claim 15, wherein: the first electric motor is configured to rotate the left wheel independently of the second electric motor rotating the right wheel; and the second electric motor is configured to rotate the right wheel independently of the first electric motor rotating the left wheel.

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