Use of rear wheel steering data for controlling a vehicle drive torque distribution

Abstract

Aspects and embodiments of the invention relate to a control system (300), a system (209), a vehicle (1), a method (700), and computer readable instructions (308) for controlling a drive torque distribution between a set of drive wheels of a vehicle (1). The method (700) comprises receiving (702) a torque request for the set of drive wheels of the vehicle (1), the set of drive wheels including rear left and rear right drive wheels. The method (700) further comprises receiving (704) rear wheel steering data from a rear wheel steering controller (328) of the vehicle (1), the rear wheel steering controller (328) configured to control a steering angle of the rear left and rear right drive wheels. The method (700) further comprises determining (706) at least one drive torque distribution between the set of drive wheels, in dependence on the torque request and the rear wheel steering data. The method (700) further comprises outputting (708) one or more control signals to control torque applied to the set of drive wheels, in dependence on the torque request and the determined drive torque distribution.

Description

[0001] USE OF REAR WHEEL STEERING DATA FOR CONTROLLING A VEHICLE DRIVE TORQUE DISTRIBUTION

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to use of rear wheel steering data for controlling a vehicle drive torque distribution. Aspects of the invention relate to a control system, to a system, to a vehicle, to a method, and to computer readable instructions.

[0004] BACKGROUND

[0005] It is known to control a vehicle drive torque distribution of a vehicle, in a drive-by-wire system. A driver torque demand is processed and converted into a drive control signal for controlling a torque source of the vehicle.

[0006] It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

[0007] SUMMARY OF THE INVENTION

[0008] Aspects and embodiments of the invention provide a control system, a system, a vehicle, a method, and computer readable instructions as claimed in the appended claims.

[0009] According to an aspect of the invention there is provided a control system for controlling a drive torque distribution between a set of drive wheels of a vehicle (e.g., electric vehicle), the control system comprising one or more processors collectively configured to:

[0010] receive a torque request for the set of drive wheels of the vehicle;

[0011] receive rear wheel steering data from a rear wheel steering controller of the vehicle, the rear wheel steering controller configured to control a steering angle of rear left and rear right wheels of the vehicle;

[0012] determine at least one drive torque distribution between the set of drive wheels, in dependence on the torque request and the rear wheel steering data; and

[0013] output one or more control signals to control torque applied to the set of drive wheels, in dependence on the torque request and the determined drive torque distribution.

[0014] An advantage is enhanced control of vehicle dynamics, because the function for controlling the at least one drive torque distribution is made aware of the control output of the rear wheel steering controller. This allows the relative contributions of rear wheel steering and torque distribution to be optimised, for example for satisfying yaw or stability targets. This approach also allows faster and more accurate control compared to an embodiment in which no information is received from the rear wheel steering controller such that rear wheel steering and torque distribution operate independently of each other.

[0015] The control system comprises one or more controllers collectively comprising at least one electronic processor having an electrical input for receiving an input signal; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to:

[0016] receive the torque request;

[0017] receive the rear wheel steering data;

[0018] determine the at least one drive torque distribution; and

[0019] output the one or more control signals.

[0020] Optionally, the at least one drive torque distribution comprises a torque distribution between a left drive wheel and a right drive wheel, of the set of drive wheels of the vehicle. The torque distribution can be referred to as a lateral torque distribution. Optionally, the left and right drive wheels are the rear left and rear right wheels that the rear wheel steering controller is configured to control the steering angle of.An advantage is enhanced control of lateral vehicle dynamics, because the contribution of rear wheel steering is considered when determining the amount of torque vectoring (lateral torque distribution) required.

[0021] Optionally, the steering function is a rear wheel steering function.

[0022] Optionally, the rear wheel steering data is indicative of a steering angle of the rear left and rear right drive wheels.

[0023] Optionally, determining the (lateral) torque distribution comprises determining, in dependence on the rear wheel steering data, at least one of: a requested difference between left and right torque requests for the left and right drive wheels; or

[0024] a difference threshold, wherein the (lateral) torque distribution is configured to remain within the difference threshold.

[0025] Optionally, the control system is configured to increase the at least one of the requested difference or the difference threshold in dependence on the rear wheel steering data indicating a steering angle change of the rear left and rear right wheels in a vehicle yaw-rate reducing direction.

[0026] An advantage is enabling improved vehicle acceleration or deceleration during cornering and / or driving on low-friction surfaces, because a higher magnitude of torque vectoring may be permitted while maintaining a desired stability of the vehicle via rear wheel steering. A higher torque vectoring magnitude allows greater vehicle acceleration or deceleration because the commanded torque to a slipping wheel may not need to be reduced as much.

[0027] Alternatively, or additionally, the at least one drive torque distribution may comprise a longitudinal torque distribution between front and rear drive wheels of the set of drive wheels of the vehicle, the rear drive wheels comprising the rear left and rear right wheels.

[0028] An advantage is enhanced control of vehicle dynamics. For example, the longitudinal torque distribution can affect vehicle lateral dynamics in situations such as throttle liftoff during cornering which induces regenerative braking, in vehicles with different regenerative braking rates at the front and rear axles.

[0029] Optionally, determining the longitudinal torque distribution comprises determining, in dependence on the rear wheel steering data, at least one of:

[0030] a requested difference between front and rear torque requests for the front and rear drive wheels; or

[0031] a difference threshold, wherein the longitudinal torque distribution is configured to remain within said difference threshold.

[0032] Optionally, the requested difference or difference threshold is configured to bias the longitudinal torque distribution towards the rear drive wheels in dependence on the rear wheel steering data indicating a steering angle change of the rear left and rear right wheels in a vehicle yaw-rate reducing direction.

[0033] An advantage is enhanced control of vehicle dynamics. For example, a vehicle with greater regenerative braking capability at the rear axle than the front axle can be allowed a greater magnitude of regenerative braking at the rear axle if the rear wheel steering system is stabilising the vehicle by actively reducing the vehicle yaw rate. This can be useful in situations such as throttle lift-off regenerative braking during cornering.

[0034] Optionally, the rear wheel steering data comprises an indication of whether a rear wheel steering function is active, and wherein the at least one drive torque distribution is dependent on the indication. In dependence on the rear wheel steering function being inhibited, a lower magnitude torque distribution may be allowed compared to the rear wheel steering function being active.

[0035] An advantage is enhanced control of vehicle dynamics, allowing the torque distribution to take into account situations where rear wheel steering may be inactive, such as user-deactivation of the function, driving on snow chains, or due to a rear wheel steering fault.Optionally, the control system is configured to output torque distribution data to the rear wheel steering controller, wherein the torque distribution data comprises an indication of the at least one drive torque distribution.

[0036] An advantage is enhanced control of vehicle dynamics, because each controller is aware of each other’s control signals, allowing their relative contributions for satisfying a yaw target to be optimised. The controllers may hand over between rear wheel steering and torque distribution / vectoring in a predictive manner.

[0037] Optionally, the one or more control signals are transmitted to two or more drive units of the vehicle, and wherein the drive units are coupled to different subsets of the set of drive wheels of the vehicle. If the vehicle is an electric vehicle, the drive units may comprise electric drive units.

[0038] Optionally, the control system further comprises the rear wheel steering controller.

[0039] According to another aspect of the invention, there is provided a system comprising the control system and a powertrain coupled to the set of drive wheels, and wherein the one or more control signals are configured to control the powertrain.

[0040] According to a further aspect of the invention, there is provided a vehicle comprising the control system or the system.

[0041] According to a further aspect of the invention, there is provided a method for controlling a drive torque distribution between a set of drive wheels of a vehicle, the method comprising:

[0042] receiving a torque request for the set of drive wheels of the vehicle, the set of drive wheels including rear left and rear right drive wheels; receiving rear wheel steering data from a rear wheel steering controller of the vehicle, the rear wheel steering controller configured to control a steering angle of the rear left and rear right drive wheels;

[0043] determining at least one drive torque distribution between the set of drive wheels, in dependence on the torque request and the rear wheel steering data; and

[0044] outputting one or more control signals to control torque applied to the set of drive wheels, in dependence on the torque request and the determined drive torque distribution.

[0045] According to an aspect of the invention there is provided a method comprising and / or a control system comprising one or more processors collectively configured to:

[0046] receive a torque request;

[0047] receive steering data;

[0048] determine at least one drive torque distribution between drive wheels, in dependence on the torque request and the steering data; and output one or more control signals to control torque applied to the drive wheels, in dependence on the torque request and the determined drive torque distribution.

[0049] According to a further aspect of the invention there is provided computer readable instructions which, when executed by a computer, are arranged to perform any one or more of the methods described herein. According to a further aspect of the invention there is provided a non-transitory computer readable medium comprising computer readable instructions that, when executed by one or more electronic processors, causes the one or more electronic processors to carry out any one or more of the methods described herein.

[0050] Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination that falls within the scope of the appended claims. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination that falls within the scope of the appended claims, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner.BRIEF DESCRIPTION OF THE DRAWINGS

[0051] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 illustrates a perspective view illustrating an example of a vehicle;

[0052] FIG. 2A illustrates a schematic view illustrating an example of an electric drive system of a vehicle;

[0053] FIG. 2B illustrates a schematic view illustrating an example of front and rear steering systems of a vehicle;

[0054] FIG. 3 illustrates a schematic view illustrating an example of a control system comprising a drive torque distribution controller;

[0055] FIG. 4 illustrates a schematic view illustrating an example of a front wheel steering controller and a rear wheel steering controller;

[0056] FIG. 5 illustrates a schematic view illustrating an example of a non-transitory computer-readable storage medium;

[0057] FIG. 6 illustrates a schematic view illustrating an example of a vehicle systems controller hosting a drive torque distribution controller;

[0058] FIG. 7A illustrates a flowchart illustrating an example of a method;

[0059] FIG. 7B illustrates a graph illustrating example yaw rate gain and vehicle speed, with rear wheel steering on and off; and

[0060] FIG. 8 illustrates a flowchart illustrating an example of a method.

[0061] DETAILED DESCRIPTION

[0062] A vehicle 1 in accordance with an embodiment of the present invention is described herein with reference to the accompanying FIG. 1. In some, but not necessarily all examples, the vehicle 1 is a passenger vehicle, also referred to as a passenger car or as an automobile. In other examples, embodiments of the invention can be implemented for other applications, such as commercial vehicles.

[0063] FIG. 2A illustrates a schematic view of the vehicle 1 where the vehicle is a battery electric vehicle (BEV) or hybrid electric vehicle (HEV).

[0064] FIG. 2A illustrates components of an electric drive system 200. The vehicle 1 comprises a traction battery 202 or an equivalent electrical energy storage means. The traction battery 202 is electrically connected to a DC bus 204.

[0065] The DC bus 204 is an electrical bus for transferring DC power. DC means direct current and AC means alternating current. The DC bus 204 comprises positive and negative conductors, each connected to the traction battery 202 and to one or more loads. In FIG. 2A, the loads comprise a plurality of electric drive units (EDUs) 208A, 208B, 208C, together defining a powertrain 201 of a system 209.

[0066] A first EDU 208A is configured to drive a rear right wheel RR of the vehicle 1 and a second EDU 208B is configured to drive a rear left wheel RL of the vehicle 1 , or vice versa. A third EDU 208C is configured to drive the front left and front right wheels FL, FR of the vehicle 1. Therefore, all four wheels are drive wheels.

[0067] In another implementation, separate EDUs drive the front left and front right wheels FL, FR individually, and the rear wheels RL, RR may be driven by either one EDU or by separate individual EDUs. In a further implementation, only the rear wheels RL, RR are drive wheels, or only the front wheels FL, FR are drive wheels.

[0068] The vehicle 1 comprises an axle 214 connected to the rear left and right wheels RL, RR. In some examples, the axle 214 may be a virtual axle such that the left and right wheels are rotationally decoupled from one other, with no mechanical torque transfer therebetween. The virtual axle simply refers to the wheels being aligned longitudinally such that they are both rear wheels or both front wheels, for example.

[0069] The EDUs 208A, 208B, 208C share the same DC bus 204 and fraction battery 202, but could alternatively be connected to separate DC buses 204 and traction batteries 202.

[0070] Each EDU 208 comprises an inverter 206, an inverter controller 336, 338, or 340 configured to control the inverter 206, an electric machine 210 operable as a traction electric machine, and a transmission 212.The inverter 206 is a DC-AC power converter to convert between DC electrical energy on the DC bus 204 and AC energy for the electric machine 210. The inverter 206 is further configured to control the torque of the electric machine 210. The conversion and torque control are controlled by the inverter controller 336 or 338 or 340.

[0071] The inverter 206, when controlled by the inverter controller 336, 338, or 340, is configured to control the frequency and magnitude of electrical signals supplied to the electric machine 210. The inverter controller 336, 338, 340 regulates the torque of an electric motor primarily by controlling the frequency and magnitude of the electrical signals supplied to the electric machine 210.

[0072] For example, the inverter controller 336, 338, 340 may be configured to adjust the magnitude of the voltage supplied by the inverter 206 to the electric machine 210 to control the EDU's torque output. The inverter controller 336, 338, 340 may be configured to adjust the frequency of the electrical signals supplied to the electric machine 210, to control the electric machine’s speed, thus indirectly controlling torque output.

[0073] The inverter controller 336, 338, 340 may be configured to control a gate control section of the inverter 206 to adjust the magnitude and frequency by pulse-width modulation (PWM), which comprises adjusting the duty cycle of transistor gates in the gate control section such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) or IGBTs (Insulated Gate Bipolar Transistors). The inverter controller 336, 338, 340 transmits gate control signals to the transistor gates, to control the torque output of the electric machine 210. The gate control signals are transmitted over a local communication network / bus of the electric machine 210 or of the inverter 206, to the gate control section. The inverter controller 336, 338, 340 has a low-latency connection to the gate control section, and for example may comprise a microcontroller mounted to a same circuit board as the gate control section.

[0074] The electric machine 210 comprises a rotor-stator pair. The electric machine 210 can comprise a Permanent Magnet Synchronous Motor (PMSM), or alternatively an Induction Motor (IM) or Switched Reluctance Motor (SRM) or axial flux motor.

[0075] The transmission 212 is located in a torque path between the electric machine 210 and one or more wheels of the vehicle 1. The transmission 212 provides at least one gear ratio between an output of the electric machine 210 and the one or more wheels of the vehicle 1. In another example, the electric machine 210 comprises a direct drive motor so lacks a transmission 212.

[0076] FIG. 2B shows a steering wheel 220 and a front wheel steering system 216 configured to enable steering of the vehicle 1. The front wheel steering system 216 comprises a front wheel steering actuator 224 configured to cause steering of driven front wheels FL, FR of the vehicle 1 , and includes a front wheel steering controller 326 of a control system 300, comprising a front wheel steering function (front wheel steering module) configured to control the operation of the front wheel steering actuator 224.

[0077] The front wheel steering actuator 224 may be a steer-by-wire actuator if the front wheel steering system 216 is a steer-by-wire steering system, or an electronic power assist actuator if the front wheel steering system 216 is a mechanical steering system.

[0078] FIG. 2B also shows a rear wheel steering system 218 configured to enable steering of the vehicle 1. Together, the front and rear wheel steering systems 216, 218 define a four-wheel steering system of the vehicle 1. The rear wheel steering system 218 comprises a rear wheel steering actuator 228 configured to cause steering of rear driven wheels RL, RR of the vehicle 1. The rear wheel steering system 218 also includes a rear wheel steering controller 328 of the control system 300, comprising a rear wheel steering function (rear wheel steering module) configured to control the operation of the rear wheel steering actuator 228.

[0079] Alternatively, or additionally, one or more of the wheels FL, FR, RL, RR may be mechanically connected to a steering wheel 220 of the vehicle 1. In other words, the steering systems 216, 218 may comprise a drive-by-wire system and / or a power-assisted mechanical steering system.

[0080] The front wheels FL, FR of the vehicle 1 are steered by the front wheel steering actuator 224, which is connected to a rack 226 which is connected to steering knuckles by tie rods. Alternatively, separate actuators 224 may be provided for each wheel FL, FR.The rear wheels RL, RR of the vehicle 1 are steered by the rear wheel steering actuator 228, which is connected to a rack 230 which is connected to steering knuckles by tie rods. Alternatively, separate actuators 228 may be provided for each wheel RL, RR.

[0081] A steering input sensor 222 is configured to sense the orientation of the steering wheel 220 and provide signals to the control system 300 indicative of the orientation of the steering wheel 220 and therefore also indicative of the orientation of the front wheels FL, FR. The front wheel steering controller 326 is configured to output one or more front steering control signals to the front wheel steering actuator 224 to cause steering of the front wheels FL, FR in dependence on the signals received from the steering input sensor 222.

[0082] The rear wheel steering controller 328 is configured to output one or more rear steering control signals to the rear wheel steering actuator 228 to cause steering of the rear wheels RL, RR in dependence on a front steering angle. For example, the rear steering control signal may be dependent on the front steering control signal. The rear steering control signal may be proportional to the front steering control angle. The control signals may control the rear wheel steering angle proportionally to the front wheel steering angle. The rear wheel steering controller 328 may comprise a transfer function for converting front steering control signals to rear steering control signals. For example, the transfer function may apply a gain dependent on vehicle speed to the front steering control signal to calculate the rear steering control signal. Alternatively, the control system 300 determines rear steering control signals independently of the front steering control signals, based on the sensed inputs.

[0083] Wheel speed sensors 320A, 320B, 320C, 320D are configured to sense the wheel speeds of the wheels FL, FR, RL, RR respectively. They output sensed wheel speeds 320 to the control system 300. The control system 300 may determine a vehicle speed of the vehicle 1 , in dependence on the sensed wheel speeds. The one or more steering control signals are dependent on the vehicle speed and therefore dependent on the signals received from the wheel speed sensors 320A, 320B, 320C, 320D.

[0084] In examples, the rear wheel steering angle transitions from being antiphase (out-of-phase countersteer) with the front wheel steering angle to being in-phase (parallel) with the front wheel steering angle, in dependence on the vehicle speed increasing. This prioritises vehicle stability, based on the vehicle speed of the steering manoeuvre. In an implementation, at lower speeds the front and rear wheels are antiphase with each other which makes the vehicle 1 more agile, whereas for example, over approximately 50 kilometres per hour (kph) the wheels become in phase which makes the vehicle 1 more stable.

[0085] At low speed, the system 218 turns the rear wheels RL, RR in the opposite direction to the front steering angle; this serves to reduce the turning circle of the vehicle 1. At higher vehicle speeds, the wheels RL, RR steer in the same direction as the front steering angle, having the effect of reducing the effective wheelbase and making the vehicle 1 change direction quicker, improving feel and feedback to the driver. Advantages of rear wheel steering / all wheel steering are stated below.

[0086] Improved dynamics - By actively changing the rear toe angle on the move, the vehicle dynamics are improved related to the speed of the vehicle 1. The effect is similar to reducing the wheelbase of the vehicle 1 , improving the ability to change direction quickly. This gives the driver a better driving experience and improved feedback.

[0087] Improved manoeuvrability - At low speeds, for example during turning, the rear wheels RL, RR turn to the opposite angle to the front wheels FL, FR. This reduces the turning circle of the vehicle 1 , ensuring it can make easier progress around obstacles. In urban situations, this makes the vehicle 1 easier to manoeuvre, aiding parking.

[0088] Improved stability - At high speed, especially during lane-change scenarios, the system 218 adds stability to the vehicle 1 through changing the angles of the rear wheels RL, RR to compensate for the shifting mass brought on by the manoeuvre.With reference to FIG. 3, there is illustrated a control system 300 for a vehicle 1. The control system 300 comprises one or more controllers 301 including a drive torque distribution controller 332. The term ‘torque distribution’ (also ‘torque split’) refers to the requested or allowed difference between the torque requests sent to different EDUs 208A, 208B, 208C concurrently.

[0089] The drive torque distribution controller 332 of the control system 300 is configured to receive a torque request from a requestor 314 of the vehicle 1. The requestor 314 is configured to determine a vehicle torque request in dependence on inputs from one or more torque control modules such as an accelerator pedal module, or an autonomous driving module, etc. (not shown). The drive torque distribution controller 332 is also configured to receive rear wheel steering data from the rear wheel steering controller 328. The control system 300 may then output drive control signals to the inverter controllers 336, 338, 340 to control the inverters 206 of the EDUs 208A, 208B, 208C in dependence on the torque request and the rear wheel steering data.

[0090] The control system 300 as illustrated in FIG. 3 comprises one or more controllers 301 , although it will be appreciated that this is merely illustrative. Each controller 301 comprises processing means 304 and memory means 306. The processing means 304 may be one or more electronic processing device 304 which operably execute computer-readable instructions. The memory means 306 may be one or more memory device 306. The memory means 306 is electrically coupled to the processing means 304. The memory means 306 is configured to store instructions, and the processing means 304 is configured to access the memory means 306 and execute the instructions stored thereon.

[0091] The controller 301 comprises an input means 310 and an output means 312. The input means 310 may comprise an electrical input 310 of the controller 301. The output means 312 may comprise an electrical output 312 of the controller 301. The controller 301 may have an interface 302 comprising an electrical input / output I / O 310, 312, or an electrical input 310, or an electrical output 312, for receiving information and interacting with external components.

[0092] To implement the functionality of the drive torque distribution controller 332, the input 310 is arranged to receive a torque request from a requestor 314. The torque request is an electrical signal which is indicative of a requested torque of the vehicle 1. The output 312 is arranged to output drive control signals, indicative of torque requests for controlling the gate control section of each inverter 206, via any lower level torque modification functions between the controller 301 and the inverters 206.

[0093] With reference to FIG. 4, there is illustrated a front wheel steering controller 326 and a rear wheel steering controller 328 of the control system 300. The front and rear wheel steering controllers 326, 328 may each be implemented as different controllers 301 (e.g ., control functions / modules) than the torque controller. The front and rear wheel steering controllers 326, 328 may be executed by the same or different hardware (e.g., 302, 304, 306, 308, 310, 312) as that shown in FIG. 3.

[0094] The front wheel steering controller 326 is configured to receive a steering input signal from the steering input sensor 222 of the vehicle 1 , and obtain a vehicle speed signal via information from the wheel speed sensors 320. In some examples, the front wheel steering controller 326 also obtains torque distribution data from the drive torque distribution controller 332. The front wheel steering controller 326 is configured to determine one or more front steering control signals. The front wheel steering controller 326 may then output a front steering control signal to the front wheel steering actuator 224, to control the actuator 224 in dependence on the steering input signal, the vehicle speed signal, and the torque distribution data.

[0095] The rear wheel steering controller 328 comprises the rear wheel steering function configured to receive information indicative of a front steering angle, such as the front steering control signal, and is also configured to obtain torque distribution data from the drive torque distribution controller 332. The rear wheel steering controller 328 is configured to determine one or more rear steering control signals. The rear wheel steering function of the controller 328 may then output a rear steering control signal to the rear wheel steering actuator 228, to control the actuator 228 in dependence on the front wheel steering angle and the torque distribution data.

[0096] FIG. 5 illustrates a non-fransitory computer-readable storage medium 500 comprising the instructions (computer software).FIG. 6 illustrates an example implementation of the drive torque distribution controller 332 of the control system 300. The drive torque distribution controller 332 is hosted by a Vehicle Systems Controller (VSC) 331 . The VSC 331 is hosted outside the inverters 206. The VSC 331 is configured to communicate with the inverter controllers 336, 338, 340 hosted within the inverters 206. It would be appreciated that in other implementations, the methods described herein may be executed wholly inside or wholly outside an inverter, by one or more controllers 301.

[0097] The VSC 331 receives a torque request 329, a yaw target 330, wheel speeds 320, inertial signals 324 including vehicle yaw rate, and the rear wheel steering data from the rear wheel steering controller 328.

[0098] The torque request may be a vehicle torque request dependent on a driver torque demand (accelerator pedal module) and / or an autonomous driving torque demand (autonomous driving module).

[0099] The yaw target 330 may be dependent on a detected steering wheel angle and / or rate by the steering angle sensor 222. In an example, the yaw target 330 may indicate a target yaw rate of the vehicle 1 based on the current steering wheel angle. The yaw target 330 may be dependent on calibration data to provide a desirable relationship between steering angle and vehicle yaw rate.

[0100] The drive torque distribution controller 332 is configured to determine a lateral (leftright) torque distribution between the EDUs 208A, 208B for satisfying the vehicle torque request and yaw target 330. The drive torque distribution controller 332 is configured to determine a longitudinal (frontrear) torque distribution between the EDUs 208C and 208A+ 208B.

[0101] FIG. 7A illustrates a method 700 according to an embodiment of the invention. The method 700 is a method of controlling a drive torque split between a set of drive wheels of a vehicle 1 , such as the vehicle 1 illustrated in FIG. 1. In particular, the method 700 is a method of controlling a lateral wheel torque distribution between the rear drive wheels RL, RR, and / or a lateral wheel torque distribution between the front drive wheels FL, FR (if a separate EDU exists for each front wheel FL, FR), and / or a longitudinal wheel torque distribution between the front drive wheels FL, FR and the rear drive wheels RL, RR.

[0102] The method 700 may be performed by the control system 300 illustrated in FIG. 3. In particular, the memory 306 may comprise computer-readable instructions 308 which, when executed by the processor 304, perform the method 700. The method 700 may be performed by the drive torque distribution controller 332 of FIG. 6.

[0103] At block 702, the method 700 comprises receiving a torque request for the set of drive wheels of the vehicle, the set of drive wheels including the drive wheels FL, FR, RL, RR. The torque request may be a vehicle torque request as defined earlier. A vehicle torque request indicates requested overall vehicle torque. The vehicle torque request therefore requests a sum of torques of the EDUs 208A, 208B, 208C from the drive torque distribution controller 332.

[0104] At block 704, the method 700 comprises receiving rear wheel steering data from the rear wheel steering controller 328 of the vehicle 1 , the rear wheel steering controller 328 configured to control the steering angle of the rear left and rear right drive wheels RL, RR. The rear wheel steering data may be received from block 810 of the method 800 of FIG. 8, described later.

[0105] In an example, the rear wheel steering data comprises an indication of a rear wheel steering angle requested by the rear wheel steering controller 328. The indication may comprise a magnitude of an absolute angle or a relative angle compared to a front wheel steering angle, or any other appropriate indication.

[0106] Alternatively, or additionally, the rear wheel steering data comprises an indication (e.g . , state) of whether the rear wheel steering function of the rear wheel steering controller 328 is active or inhibited. When the function is inhibited, the rear wheel steering controller 328 may be inoperable to cause rear wheel steering despite the inputs (e.g., front steering angle and vehicle speed) having values that would otherwise cause nonzero rear wheel steering. Therefore, inhibiting the function is different from the rear wheels merely being centred. The rear wheels RL, RR may remain aligned withthe longitudinal axis of the vehicle 1 despite the front wheels FL, FR being steered. When the function is active, the rear wheel steering function is operable to output rear steering control signals, for example to control the rear wheel steering angle in dependence on the front wheel steering angle.

[0107] The rear wheel steering controller 328 may be configured to inhibit the rear wheel steering function in dependence on receiving a deactivation signal. The deactivation signal may be received from a human-machine interface, such as a touchscreen input device or mechanical input device. Therefore, a user can deactivate rear wheel steering for certain manoeuvring situations, or when snow chains are attached to their wheels, or the like. In some examples, the deactivation signal may be initiated automatically, for example in dependence on a sensor detecting that a condition is satisfied.

[0108] At block 706, the method 700 comprises determining at least one drive torque distribution between the set of drive wheels. This can comprise determining a lateral drive torque distribution between the left and right drive wheels for torque vectoring. Alternatively, or additionally, this can comprise determining a longitudinal drive torque distribution between the front wheels FL, FR and rear wheels RL, RR.

[0109] The drive torque distribution determined at block 706 is dependent on the torque request of block 702.

[0110] Determining at least one drive torque distribution may comprise determining the longitudinal torque distribution. Determining the longitudinal torque distribution can comprise determining, in dependence on the vehicle torque request, a front axle torque request 208C and a rear axle torque request 208A+208B. The sum of the front and rear axle torque requests adds up to the vehicle torque request. The longitudinal torque distribution refers to the difference between the front and rear axle torque requests.

[0111] Determining at least one drive torque distribution may comprise determining the lateral torque distribution for the EDUs 208A and 208B. Determining the lateral torque distribution can comprise determining, in dependence on the rear axle torque request, a left torque request for the wheel RL and a right torque request for the wheel RR. The sum of the left and right torque requests adds up to the rear torque request. The lateral torque distribution refers to the difference between the left and right torque requests. The same general approach may be used for EDUs of the front wheels FL, FR, in examples where the front wheels FL, FR are driven by separate EDUs.

[0112] Under constant throttle (e g., accelerator pedal depression), the longitudinal torque distribution may be based on a static load distribution of the vehicle 1. The longitudinal torque distribution may be changed in dependence on regenerative braking being requested (e g., negative received torque request), to bias the torque distribution towards the front wheels FL, FR during deceleration, if required for braking stability.

[0113] The lateral torque distribution may be determined in dependence on lateral acceleration from the inertial signals 324. The lateral torque distribution may be determined in dependence on suspension height signals from wheel height sensors (not shown). The lateral torque distribution may be determined in dependence on wheel speed signals 320. Determining the lateral torque distribution may comprise directing torque away from a slipping wheel. Determining the lateral torque distribution may comprise directing more torque to the more heavily-loaded side of the vehicle 1 (e g., based on lateral acceleration direction or suspension compression amount), to increase fraction.

[0114] The lateral torque distribution may be determined in dependence on the yaw target 330. The yaw rate from the inertial signals 324 may be compared with the yaw target 330. The lateral torque distribution may be changed in dependence on the yaw rate and the yaw target to reduce a difference between the yaw rate and the yaw target 330. This reduces understeer and oversteer.

[0115] The drive torque distribution is further dependent on the rear wheel steering data of block 704. This enables the drive torque distribution to allow or request a greater or smaller difference between its torque requests for the EDUs 208A, 208B, in dependence on the magnitude of the rear wheel steering angle and / or whether the rear wheel steering function is inhibited. Therefore, the relative contributions of the rear wheel steering controller 328 and the drive torque distribution controller 332 for satisfying the yaw target 330 can be optimised and arbitrated.

[0116] FIG. 7B is a graph illustrating an example of the on centre yaw gain of a vehicle 1 steered at 0.2g of lateral acceleration. The graph illustrates yaw rate gain (degrees per second per 100 degrees steering wheel angle) along the y-axis, and vehicle speed along the x-axis. The solid line 712represents the yaw rate gam when the rear wheel steering function is inhibited. The broken line 714 represents the yaw rate gam when the rear wheel steering function is active.

[0117] The yaw rate gain is increased through out-of-phase rear wheel steering at a below-threshold vehicle speed <V1 (e.g., <50kph). The yaw rate gain is greater when the rear wheel steering function is active compared to when it is inhibited.

[0118] The yaw rate gain is decreased at above-threshold vehicle speeds >V1 through in-phase rear wheel steering (e.g., >50 kph). The yaw rate gain is lower when the rear wheel steering function is active compared to when it is inhibited.

[0119] The transfer function of the rear wheel steering controller 328 may be configured to control the rear wheel steering angle to provide the relationship between yaw rate gain and vehicle speed that is described above in relation to FIG. 7B. As described above, the rear wheel steering angle or state also acts as an input 704 for torque arbitration (torque vectoring) between the left and right rear wheels RL, RR, so that the lateral torque distribution may be configured to provide the relationship between yaw rate gain and vehicle speed that is described above in relation to FIG. 7B.

[0120] At block 708, the method 700 comprises outputting one or more drive control signals to control torque applied to the set of drive wheels, in dependence on the torque request and each determined drive torque distribution.

[0121] For example, block 708 of the method 700 can comprise:

[0122] - outputting a first drive control signal (rear left torque request) to the inverter controller 336 of the rear left wheel RL, in dependence on the torque request and the longitudinal drive torque distribution and the lateral drive torque distribution;

[0123] - outputting a second drive control signal (rear right torque request) to the inverter controller 338 of the rear right wheel RR, in dependence on the torque request and the longitudinal drive torque distribution and the lateral drive torque distribution;

[0124] - outputting a third drive control signal (front torque request) to the inverter controller 340 of the front wheels FL, FR, in dependence on the torque request and the longitudinal drive torque distribution and the lateral drive torque distribution.

[0125] At block 710, the method 700 comprises outputting torque distribution data to the rear wheel steering controller 328, wherein the torque distribution data comprises an indication of the lateral drive torque distribution and / or longitudinal drive torque distribution. For example, the torque magnitudes of the individual drive control signals requests to the EDUs 208A, 208B, 208C may be output to the rear wheel steering controller 328, or the differences therebetween.

[0126] Therefore, each controller 328, 332 is aware of each other’s control signals, which further allows their relative contributions for satisfying the yaw target 330 to be optimised. The controllers 328, 332 may handover from one to the other in a predictive manner.

[0127] An example use case is described, with reference to a lateral torque distribution between the left and right rear wheels RL, RR.

[0128] In this example, but not necessarily all examples, the left and right drive wheels RL, RR are on surfaces with different friction coefficients, such as tarmac and ice. Furthermore, the torque request of block 702 is positive to request vehicle acceleration. The vehicle 1 may begin to yaw towards the lower-friction surface due to wheelspin of the wheel FR, RR on the lower-friction surface. The driver may apply countersteer via the steering wheel 220. Therefore, the front wheels FL, FR are steered. The rear wheel steering controller 328 steers the rear wheels RL, RR in dependence on the front wheel steering angle and the vehicle speed, to change the rear wheel steering angle in a vehicle yaw-rate reducing direction. For example, the rear wheels may be steered in a countersteer direction (out-of-phase) or in a parallel-steer (in-phase) direction, dependent on vehicle speed.

[0129] The rear wheel steering data is sent to the drive torque distribution controller 332 at block 704, indicating the steering angle change of the rear wheels in a vehicle yaw-rate reducing direction. A vehicle yaw-rate reducing direction comprises whichever steering direction would reduce the yaw rate of the vehicle 1 towards the yaw target 330. The direction may depend on vehicle speed. A transfer function of the rear wheel steering controller 328may either request countersteer or parallel steer depending on how fast the vehicle is travelling. Therefore, a yaw-rate reducing direction may either request more or less countersteer, or more or less parallel steer, to reduce the yaw rate of the vehicle towards the yaw target 330.

[0130] Therefore, if the steering angle changes in a yaw-rate reducing direction, this indicates that the rear wheel steering system 218 is assisting with reducing vehicle yaw 324 towards the yaw target 330. Therefore, the drive torque distribution controller 332 can request more torque vectoring (higher lateral torque distribution).

[0131] Therefore, as the rear wheel steering data indicates a steering angle change in a vehicle yaw-rate reducing direction, the requested difference between the left and right torque control signals for the rear EDUs 208A, 208B can increase in dependence thereon. A greater torque distribution may allow higher vehicle acceleration despite the different surface friction under the wheels RL, RR. If the steering angle change is in a vehicle yawrate increasing direction, the requested difference between the left and right torque control signals can decrease in dependence thereon.

[0132] By contrast, if the drive torque distribution controller 332 is unaware of the rear wheel steering controller’s control actions, an above-target yaw rate may result in a more conservative (reduced) lateral torque distribution, which may inhibit vehicle acceleration.

[0133] The above control logic can apply to situations other than split friction surfaces. For example, the logic can be useful when a torque request increases during vehicle cornering.

[0134] Alternatively, or additionally, the drive torque distribution controller 332 controls an allowed torque distribution rather than a requested torque distribution. The allowed torque distribution sets an allowable torque difference for difference monitors. The inverter controllers 336, 338, 340 each host a torque modification function (not shown) which may individually reduce a torque request for that EDU 208. The difference monitors are downstream of the torque modification function, to check that the torque distribution after the torque modification functions is less than a difference threshold, and modify the torque request if past the threshold. The drive torque distribution controller 332 may set a leftrig ht difference threshold, defining a threshold of a difference between the left and right torque requests for the left and right drive wheels. The difference threshold may be configured to require the torque distribution to remain within said difference threshold. In other words, the difference between the left and right torque requests is required to remain within said difference threshold. In this use case, the difference threshold may be increased in dependence on the rear wheel steering data indicating a steering angle change in a vehicle yaw-rate reducing direction, allowing for more torque vectoring.

[0135] In situations where the rear wheel steering data indicates that the rear wheel steering function is inhibited / inactive, the requested or allowed torque distribution may decrease in dependence on the yaw rate being above the yaw target 330. When rear wheel steering is active, the torque distribution may increase.

[0136] Another example use case is described, with reference to a longitudinal torque distribution between the front wheels FL, FR and the rear wheels RL, RR being dependent on the rear wheel steering data.

[0137] The torque request of block 702 may be negative, requesting regenerative charging by one or more of the EDUs 208. A vehicle architecture having greater regenerative braking capability on the rear axle 214 (e g., two rear EDUs 208A, 208B and just one front EDU 208C) could lead to more regenerative braking on the rear axle 214 than the front axle, to increase energy recovery from braking. If regenerative braking occurs while the vehicle 1 is steering and / or driving on a split-friction surface as described above, this may cause vehicle yaw in some situations. If the rear wheel steering function is inhibited or requesting a steering angle change in a vehicle yaw-rate increasing direction, the drive torque distribution controller 332 may bias the longitudinal torque distribution away from the rear wheels RL, RR towards the front wheels FL, FR during deceleration for braking stability. This may have the effect of reducing the vehicle’s regenerative braking capability if the vehicle 1 has more rear axle regenerative braking capability than front axis regenerative braking capability. By contrast, if the rear wheel steering function is active and requesting a steering angle change in a vehicle yaw-rate reducing direction, the drive torque distribution controller 332 may bias the longitudinal torque distribution relatively towards the rear wheels RL, RR and away from the front wheels FL, FR. This has the effect of increasing the regenerative braking capability of the vehicle 1.Therefore, as the rear wheel steering data indicates a steering angle change of the rear left and rear right drive wheels RL, RR, the drive torque distribution controller 332 controls a requested difference between the front and rear torque requests, in dependence on the steering angle change.

[0138] FIG. 8 illustrates a method 800 according to some examples of the disclosure. The method 800 is a method of controlling a steering system of a vehicle 1 , such as at least one of the steering systems 216, 218 of the vehicle 1 illustrated in FIG. 1. The method 800 may be performed by the front wheel steering controller 326 and / or rear wheel steering controller 328 of the control system 300 illustrated in FIG. 4. In particular, the memory 306 may comprise computer-readable instructions 308 which, when executed by the processor 304, perform the method 800.

[0139] At block 802, the method 800 may comprise receiving a steering input signal.

[0140] For example, the steering input signal received by the front wheel steering controller 326 may be from the steering input sensor 222 and may indicate the orientation of the steering wheel 220.

[0141] The steering input signal received by the rear wheel steering controller 328 may comprise the front steering control signal.

[0142] At block 804, the method 800 may comprise receiving torque distribution data from the drive torque distribution controller 332 of the vehicle 1. The torque distribution data may be from block 710 of the method 700 of FIG. 7A, as described above. The torque distribution data may comprise an indication of the lateral drive torque distribution and / or longitudinal drive torque distribution. For example, the torque magnitudes of the individual drive control signals requests to the EDUs 208A, 208B, 208C may be received by the rear wheel steering controller 328, or the differences therebetween.

[0143] The torque distribution may comprise the requested torque distribution, or the difference threshold indicative of the allowable torque distribution.

[0144] At block 806, the method 800 may comprise determining a steering angle in dependence on the steering input signal of block 802 and the torque distribution data of block 804. For example, the front wheel steering controller 326 may determine the front wheel steering angle in dependence on the orientation of the steering wheel 220 and the torque distribution data. The rear wheel steering controller 328 may determine the rear wheel steering angle in dependence on the torque distribution data.

[0145] At block 808, the method 800 may comprise outputting one or more steering control signals to control one or more actuators of the steering system 216 or 218, in dependence on the steering input signal and the torque distribution data.

[0146] For example, the rear steering control signal from the rear wheel steering controller 328 may depend on the lateral torque distribution and / or longitudinal torque distribution. Both could be received, because both are relevant to vehicle yaw. The lateral torque distribution provides torque vectoring which controls vehicle yaw relative to the yaw target 330, while the longitudinal torque distribution also controls vehicle yaw during acceleration or deceleration events when cornering.

[0147] The front steering control signal from the front wheel steering controller 328 may depend on the lateral torque distribution and / or longitudinal torque distribution.

[0148] At block 810, the method 800 may be configured to output steering data to the drive torque vectoring controller, indicative of at least one steering angle requested by the one or more control signals of block 808. For example, the rear wheel steering controller 328 may output steering data comprising the rear wheel steering data, to block 704 of the method 700 of FIG. 7A. This allows each controller to be aware of each other’s signals, allowing blending and transitions of their control outputs.

[0149] An example use case is described, with reference to controlling rear wheel steering by the rear wheel steering actuator 228 in dependence on the torque distribution data comprising an indication of a lateral torque distribution between the rear left and rear right drive wheels RL, RR.The indication may comprise the requested difference between the left and right torque requests for the EDUs 208A, 208B of the left and right rear wheels RL, RR. The rear steering control signal by the rear wheel steering controller 328 requests a steering angle which depends on the requested difference between the left and right torque requests.

[0150] In dependence on an increasing requested difference or difference threshold between the left and right torque requests, the rear wheel steering controller 328 changes the steering angle in a vehicle yaw-rate reducing direction. In dependence on a decreasing requested difference or difference threshold between the left and right torque requests, the rear wheel steering controller 328 changes the steering angle in a vehicle yaw-rate increasing direction. This may not always be the case. If for example the vehicle 1 demonstrates insufficient yaw rate gain through torque distribution, then both the lateral torque distribution and the rear steering angle may increase together to achieve the target yaw rate gain 330.

[0151] Therefore, when the drive torque distribution controller 332 bears more responsibility for satisfying the target yaw rate 330, there is less need for high rear wheel steering angles. This may be preferrable for driver sensation, because rear wheel steering can produce a different sensation than torque vectoring at high steering angles. An example is power-on while cornering.

[0152] A power-on cornering example is described in more detail below, in which the rear wheel steering system 218 is controlled to deliver a desired throttle on / off handling balance, whilst leaving the torque distribution as it is to fully exploit the available traction potential from all four tyres.

[0153] In this use case, the vehicle 1 is traversing a constant-radius corner near its lateral stability limits, then the driver lifts off the throttle (accelerator pedal) and so a vehicle-level regenerative braking torque is requested. A dynamic stability control system of the vehicle 1 is active.

[0154] Prior to the throttle lift-off event, the actual yaw rate of vehicle may be closely following the target yaw rate 330 (intended behaviour).

[0155] In the absence of rear wheel steer, during the throttle lift-off event where the vehicle level torque demand changes from positive to negative at a high rate, the resultant transient change in longitudinal load distribution away from the rear axle 214 may result in a reduction in longitudinal traction capacities at the rear axle 214, necessitating either a shift in longitudinal torque distribution away from the rear axle, or an overall limitation of the regenerative braking torque request in order to maintain acceptable vehicle lateral stability.

[0156] If rear wheel steer demand (rear lateral torque distribution) can be made in dependence on the total vehicle level torque demand or rate of change thereof, or axle level torque demand or rate of change thereof, the rear wheel steering controller 328 can command a rear wheel steer angle in a vehicle yaw-rate reducing direction, in anticipation of the yaw rate change that is expected to occur as a result of the change in torque demand. This permits the front / rear torque split and total vehicle torque demand to be calculated to optimise use of available traction across all four wheels, and minimise error between vehicle level torque demand vs. delivered.

[0157] Conversely, if in the absence of rear wheel steer outputs in dependence of torque demand, the vehicle demonstrates insufficient yaw rate gain or line tightening in response to throttle lift-off events, the rear wheel steer system may command a rear wheel steer angle in a vehicle yaw-rate increasing direction to achieve target yaw rate gain.

[0158] The above concept may also be replicated for throttle tip-in (acceleration in bend manoeuvres) to achieve the desired throttle on / off handling balance requirements of the vehicle.

[0159] Another example use case is described, for an alternative vehicle comprising an EDU for each front wheel FL, FR rather than one EDU 208C for driving both front wheels FL, FR.

[0160] Furthermore, the front wheel steering controller 326 is configured to control front wheel steering by the front wheel steering actuator 226 in dependence on the torque distribution data comprising an indication of a lateral torque distribution between the front left and front right drive wheels FL, FR.The front wheel steering controller 326 may comprise the functionality to request counter-torque at the front wheels FL, FR against a steering wheel input. The controller 326 may receive a signal indicative of a steering angle or steering torque from the steering input sensor 222. The controller 326 may be configured to determine whether the steering torque is greater than a target electrical power assisted steering torque target. If higher, the controller 326 may be configured to modify a power steering torque request, and output the modified power steering torque request to reduce human torque required to turn the steering wheel 220. If the torque distribution data from the drive torque distribution controller 332 informs the front wheel steering controller 326 of the front wheel torque vectoring amount (requested difference or difference threshold between left and right front torque requests), the front wheel steering controller 326 may be configured to predictively modify the power steering torque request in dependence on the torque distribution data. This enables optimal power steering assistance.

[0161] In another example use case, the front and / or rear wheel steering controller 326, 328 is configured to control the steering angle in dependence on the torque distribution data comprising an indication of the longitudinal torque distribution between the front wheels FL, FR and the rear wheels RL, RR.

[0162] It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

[0163] It is to be understood that the, or each, controller 301 can comprise a control unit or computational device having one or more electronic processors (e.g., a microprocessor, a microcontroller, an application specific integrated circuit (ASIC), etc.), and may comprise a single control unit or computational device, or alternatively different functions of the or each controller 301 may be embodied in, or hosted in, different control units or computational devices. As used herein, the term “controller,” “control unit,” or “computational device” will be understood to include a single controller, control unit, or computational device, and a plurality of controllers, control units, or computational devices collectively operating to provide the required control functionality. A set of instructions could be provided which, when executed, cause the controller 301 to implement the control techniques described herein (including some or all of the functionality required for the method(s) described herein). The set of instructions 308 could be embedded in said one or more electronic processors 304 of the controller 301 ; or alternatively, the set of instructions 308 could be provided as software to be executed in the controller 301. A first controller or control unit may be implemented in software run on one or more processors. One or more other controllers or control units may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller or control unit. Other arrangements are also useful.

[0164] The, or each, electronic processor 304 may comprise any suitable electronic processor (e.g., a microprocessor, a microcontroller, an ASIC, etc.) that is configured to execute electronic instructions 308. The, or each, electronic memory device 306 may comprise any suitable memory device and may store a variety of data, information, threshold value(s), lookup tables or other data structures, and / or instructions therein or thereon. In an embodiment, the memory device 306 has information and instructions for software, firmware, programs, algorithms, scripts, applications, etc. stored therein or thereon that may govern all or part of the methodology described herein. The processor, or each, electronic processor 304 may access the memory device 306 and execute and / or use that or those instructions and information to carry out or perform some or all of the functionality and methodology described herein.

[0165] The at least one memory device 306 may comprise a computer-readable storage medium (e.g. a non-transitory or non-transient storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors / computational devices. Examples of the form include, without limitation: a magnetic storage medium (e.g. floppy diskette); optical storage medium (e.g. CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g. EPROM ad EEPROM); flash memory; or electrical or other types of medium for storing such information / instructions.

[0166] It will be appreciated that embodiments of the present invention can be realised in any suitable form of hardware, software or a combination of hardware and software. For example, it is contemplated that the present invention is not limited to being implemented by way of programmableprocessing devices, and that at least some of, and in some embodiments all of, the functionality and or method steps of the present invention may equally be implemented by way of non-programmable hardware, such as by way of non-programmable ASIC, Boolean logic circuitry, etc.

[0167] It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application. For example, some or all of the method 500 may be implemented by a control system 300 without an inverter controller 301.

[0168] The blocks illustrated in FIG. 7A and 8 may represent steps in a method and / or sections of code in the computer program 308. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some steps to be omitted.

[0169] Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Claims

CLAIMS1. A control system for controlling a drive torque distribution between a set of drive wheels of a vehicle, the control system comprising one or more processors collectively configured to:receive a torque request for the set of drive wheels of the vehicle;receive rear wheel steering data from a rear wheel steering controller of the vehicle, the rear wheel steering controller configured to control a steering angle of rear left and rear right wheels of the vehicle;determine at least one drive torque distribution between the set of drive wheels, in dependence on the torque request and the rear wheel steering data; andoutput one or more control signals to control torque applied to the set of drive wheels, in dependence on the torque request and the determined drive torque distribution.

2. The control system of claim 1 , wherein the at least one drive torque distribution comprises a torque distribution between a left drive wheel and a right drive wheel of the set of drive wheels of the vehicle.

3. The control system of claim 2, wherein determining the torque distribution comprises determining, in dependence on the rear wheel steering data, at least one of:a requested difference between left and right torque requests for the left and right drive wheels; anda difference threshold, wherein the torque distribution is configured to remain within the difference threshold.

4. The control system of claim 3, configured to increase the at least one of the requested difference and the difference threshold in dependence on the rear wheel steering data indicating a steering angle change of the rear left and rear right wheels in a vehicle yaw-rate reducing direction.

5. The control system of any preceding claim, wherein the at least one drive torque distribution comprises a longitudinal torque distribution between front and rear drive wheels of the set of drive wheels of the vehicle.

6. The control system of claim 5, wherein determining the longitudinal torque distribution comprises determining, in dependence on the rear wheel steering data, at least one of:a requested difference between front and rear torque requests for the front and rear drive wheels; anda difference threshold, wherein the longitudinal torque distribution is configured to remain within said difference threshold.

7. The control system of claim 6, wherein the requested difference or the difference threshold is configured to bias the longitudinal torque distribution towards the rear drive wheels in dependence on the rear wheel steering data indicating a steering angle change of the rear left and rear right wheels in a vehicle yaw-rate reducing direction.

8. The control system of any preceding claim, wherein the rear wheel steering data comprises an indication of whether a rear wheel steering function is active, and wherein the at least one drive torque distribution is dependent on the indication.

9. The control system of any preceding claim, configured to output torque distribution data to the rear wheel steering controller, wherein the torque distribution data comprises an indication of the at least one drive torque distribution.

10. The control system of any preceding claim, wherein the one or more control signals are transmitted to two or more drive units of the vehicle, and wherein the drive units are coupled to different subsets of the set of drive wheels of the vehicle.

11. The control system of any preceding claim, further comprising the rear wheel steering controller.

12. A system comprising the control system of any one of claims 1 to 11 and a powertrain coupled to the set of drive wheels, and wherein the one or more control signals are configured to control the powertrain.

13. A vehicle comprising the control system of any one of claims 1 to 11 or the system of claim 12.

14. A method for controlling a drive torque distribution between a set of drive wheels of a vehicle, the method comprising:receiving a torque request for the set of drive wheels of the vehicle, the set of drive wheels including rear left and rear right drive wheels; receiving rear wheel steering data from a rear wheel steering controller of the vehicle, the rear wheel steering controller configured to control a steering angle of the rear left and rear right drive wheels;determining at least one drive torque distribution between the set of drive wheels, in dependence on the torque request and the rear wheel steering data; andoutputting one or more control signals to control torque applied to the set of drive wheels, in dependence on the torque request and the determined drive torque distribution.

15. Computer readable instructions which, when executed by a computer, are arranged to perform a method according to claim 14.

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