Controlling a drive torque split between left and right wheels of a vehicle

Abstract

Aspects and embodiments of the invention relate to a control system (300), to a vehicle (1), to a method (800), and to computer readable instructions (308), for controlling a drive torque split between left and right wheels of a vehicle (1). The method (800) comprises receiving (802, 804) left and right torque requests (516, 518) for first and second electric machines (208A, 208B) coupled to the left and right wheels. The method (800) comprises determining (806) a difference (ΔTq) between the left and right torque requests (516, 518), and whether the difference (ΔTq) satisfies a difference limit condition (702UL, 702LL). The method (800) comprises determining (808) a modified torque request (554) for increasing or decreasing the difference, in dependence on the difference (ΔTq) not satisfying the difference limit condition (702UL, 702LL). The method (800) comprises outputting (810) first and second torque control signals (557) for the first and second electric machines (208A, 208B). One of the first and second torque control signals (557) is dependent on the modified torque request (554), if the difference (ΔTq) does not satisfy the difference limit condition (702UL, 702LL).

Description

[0001] CONTROLLING A DRIVE TORQUE SPLIT BETWEEN LEFT AND RIGHT WHEELS OF A VEHICLE

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to controlling a drive torque split between left and right wheels of a vehicle. Aspects of the invention relate to a control system, to a vehicle, to a method, and to computer readable instructions.

[0004] BACKGROUND

[0005] It is known to provide torque vectoring between left and right wheels of a vehicle, by torque sources such as electric motors. A driver torque demand is processed and then converted into drive control signals for left and right wheels of the vehicle, based on one or more criteria.

[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 vehicle, a method, and computer readable instructions as claimed in the appended claims.

[0009] According to an aspect of the present invention there is provided a control system for controlling a drive torque split between left and right wheels of a vehicle, the control system comprising one or more processors collectively configured to:

[0010] receive a left torque request for a first electric machine coupled to the left wheel;

[0011] receive a right torque request for a second electric machine coupled to the right wheel;

[0012] determine a difference between the left and right torque requests;

[0013] determine whether the difference satisfies a difference limit condition;

[0014] determine a modified torque request for increasing or decreasing the difference, in dependence on the difference not satisfying the difference limit condition;

[0015] output a first torque control signal for the first electric machine; and

[0016] output a second torque control signal for the second electric machine, and

[0017] wherein one of the first and second torque control signals is dependent on the modified torque request, if the difference does not satisfy the difference limit condition.

[0018] An advantage is improved control of torque vectoring of the electric machines The difference limit condition is checked after the left and right torque requests have been determined, so the difference limit condition can be described as a torque imbalance monitor (torque vectoring monitor). The torque imbalance monitor can reside downstream of a torque distribution function in a signal processing chain. In some examples, the torque imbalance monitor allows vehicle acceleration to be maximised via torque vectoring, if the torque vectoring is within suitable constraints such as yaw constraints which govern oversteer and understeer.

[0019] 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: receive the torque requests; determine thedifference; determine whether the difference satisfies the difference limit condition; determine the modified torque request; and output the first and second control signals.

[0020] Optionally, the control system is configured to determine or receive upper and lower torque vectoring limits relative to a target vehicle yaw, and wherein the difference limit condition is dependent on the upper and lower torque vectoring limits. Optionally, the difference limit condition comprises a range, wherein the difference limit condition is satisfied in dependence on the difference being within the range.

[0021] An advantage is improved control of torque vectoring. By having different limits, it is possible to limit torque vectoring in an oversteering direction differently than an understeering direction. For example, if the vehicle is steering in a counterclockwise direction, then changing torque vectoring in a counterclockwise yaw direction can bias vehicle handling towards oversteer whereas changing torque vectoring in a clockwise yaw direction can bias vehicle handling towards understeer. Therefore, separate tuneable upper and lower limits (clockwise and counterclockwise limits) allows oversteer and understeer characteristics to be optimised independently of each other.

[0022] Optionally, an asymmetry of the upper and lower torque vectoring limits about the target vehicle yaw is dependent on at least one of: a magnitude of the target vehicle yaw; or vehicle speed. Optionally, the asymmetry is dependent on both the magnitude of the target vehicle yaw, and vehicle speed. Optionally, the asymmetry increases in dependence on increasing vehicle speed, and increases in dependence on increasing magnitude of the target vehicle yaw. Optionally, a range between the upper and lower torque vectoring limits decreases with increasing vehicle speed.

[0023] An advantage is improved control of torque vectoring. The limits may be wide and symmetric to provide more headroom for oversteer and understeer at low vehicle speeds, with the consequence of allowing greater acceleration via torque vectoring. At higher vehicle speeds, the limits may be narrowed, to provide less headroom. Furthermore, the asymmetry of the limits depending on the amount of vehicle yaw allows different levels of headroom for understeer than oversteer. For example, during cornering, the limits may allow more clockwise torque vectoring than counterclockwise torque vectoring, or vice versa depending on the cornering direction. The asymmetry may blend in as vehicle speed increases, whereas the limits may remain symmetric during low-speed cornering. Therefore, yaw stability is improved during high-speed cornering, whereas acceleration is prioritised during low-speed cornering.

[0024] Optionally, an asymmetry of the upper and lower torque vectoring limits about the target vehicle yaw is dependent on a difference between the target vehicle yaw and an initially requested vehicle yaw. Optionally, the lower torque vectoring limit is further from the target vehicle yaw than the upper torque vectoring limit in dependence on the target vehicle yaw being positively offset from the initially requested vehicle yaw, and wherein the upper torque vectoring limit is further from the target vehicle yaw than the lower torque vectoring limit in dependence on the target vehicle yaw being negatively offset from the initially requested vehicle yaw.

[0025] An advantage is improved control of torque vectoring in a system where the initially requested vehicle yaw may be modified during signal processing. The torque imbalance monitor can reside downstream of functions capable of changing the torque requests after the target vehicle yaw has been determined, such as individual-wheel torque intervention functions related to traction control and / or stability control. Therefore, the torque imbalance monitor may be configured to determine whethermodifications to left and right torque requests after the initially requested vehicle yaw was determined result in an amount of target vehicle yaw through torque vectoring that is within the limits.

[0026] Optionally, the upper torque vectoring limit is dependent on a difference between the target vehicle yaw and an initial upper yaw limit, and wherein the lower torque vectoring limit is dependent on a difference between the target vehicle yaw and an initial lower yaw limit.

[0027] An advantage is improved control of torque vectoring because the upper and lower torque vectoring limits can be modified relative to the initial yaw limits. For example, the initial yaw limits may be determined by an external controller such as an anti-lock braking system controller, or based on constraints set by such a controller. The upper and lower torque vectoring limits can therefore be modified relative to the initial yaw limits based on one or more criteria, such as those described above. For example, the difference between the target vehicle yaw and an initially requested vehicle yaw may cause the upper and lower torque vectoring limits to differ from the initial yaw limits, to provide different headroom for oversteer and understeer as described above.

[0028] Optionally, the imbalance limit condition is dependent on one or more of the following sensed parameters: vehicle speed; a drive mode of the vehicle; foundation braking of the vehicle; a steering angle of the vehicle; or lateral acceleration of the vehicle. Optionally, the initial upper and lower yaw limits are dependent on one of more of the sensed parameters.

[0029] An advantage is improved control of torque vectoring because several variables can potentially be considered when determining the imbalance limit condition. Therefore, the imbalance limit condition can become more stringent at high vehicle speeds, at high lateral accelerations, at high steering angles, during heavy braking, or a combination thereof. The imbalance limit condition can allow more or less oversteer depending on the selected drive mode (sporty vs comfort).

[0030] Optionally, the left and right torque requests are arbitrated left and right torque requests output by arbitration functions for each of the first and second electric machines, wherein:

[0031] the arbitration function for the first electric machine is configured to determine the left arbitrated torque request in dependence on a pre-arbitrated left torque request and a set of one or more first torque restrictions, and

[0032] the arbitration function for the second electric machine is configured to determine the right arbitrated torque request in dependence on a pre-arbitrated right torque request and a set of one or more second torque restrictions.

[0033] An advantage is improved control of torque vectoring because the torque imbalance monitor can check that the arbitration functions are outputting acceptable torque requests to satisfy imbalance limits. This post-arbitration monitor ensures that the left and right arbitrated torque requests keep vehicle yaw within desired limits. An example use case is where the vehicle is accelerating around a corner, but one wheel starts to slip, so a traction control function reduces a torque limit which causes the arbitration function for the slipping wheel to reduce the corresponding torque request. This could cause the difference / torque imbalance to not satisfy the imbalance limit condition.

[0034] Optionally, the set of one or more first torque restrictions comprises a first torque limit associated with a torque requirement of the first electric machine, the set of one or more second torque restrictions comprises a second torque limit associated with a torque requirement of the second electric machine, and at least one of the arbitrated left and right torque requests is modified by the corresponding first or second torque vectoring limit.This relates to the arbitration functions being capable of imposing different torque limits on the left and right wheels concurrently, therefore giving them the control authority to change the actual vehicle yaw relative to the target vehicle yaw. Advantageously, the torque imbalance monitor may reside downstream of said functions as described above, to ensure that the actual vehicle yaw is close enough to the target vehicle yaw.

[0035] Optionally, the determination of the modified torque request is allowed to reduce a magnitude of one of the left and right torque requests towards zero, and is prohibited from increasing the magnitude from zero, and wherein the modified torque request is determined for whichever one of the first and second torque control signals can be reduced towards zero and change the difference towards satisfaction of the difference limit condition.

[0036] An advantage is improved control of torque vectoring because a monitor that can only decrease the torque magnitude towards zero is incapable of requesting excessive torque. Something which can increase the magnitude of a torque request in response to non-satisfaction of the imbalance limit condition is possible, but if implemented may require further signal processing afterwards to monitor that the increased torque request satisfies various further conditions associated with high torque requests.

[0037] Optionally, at least one of the processors is hosted in an inverter for the first electric machine, or at least one of the processors is hosted in an inverter for the second electric machine, or a combination thereof.

[0038] An advantage of hosting at least part of the control in the inverters is improved control of torque vectoring, because fast, low-latency control loops can be created that do not require the exchange of signals through a slower vehicle communication network.

[0039] According to another aspect of the present invention there is provided a vehicle comprising the control system.

[0040] According to a further aspect of the present invention there is provided a method of controlling a drive torque split between left and right wheels of a vehicle, the method comprising:

[0041] receiving a left torque request for a first electric machine coupled to the left wheel;

[0042] receiving a right torque request for a second electric machine coupled to the right wheel;

[0043] determining a difference between the left and right torque requests;

[0044] determining whether the difference satisfies a difference limit condition;

[0045] determining a modified torque request for increasing or decreasing the difference, in dependence on the difference not satisfying the difference limit condition;

[0046] output a first torque control signal for the first electric machine; and

[0047] output a second torque control signal for the second electric machine, and

[0048] wherein one of the first and second torque control signals is dependent on the modified torque, if the difference does not satisfy the difference limit condition.

[0049] According to a further aspect of the present invention there is provided a 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, whenexecuted 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] According to a further aspect of the present invention there is provided a control system and / or a method for controlling a torque split between left and right wheels of a vehicle, the control system comprising one or more processors collectively configured to, or the method comprising:

[0051] receive a left request for controlling a torque applied by a first actuator to the left wheel;

[0052] receive a right request for controlling a torque applied by a second actuator to the right wheel;

[0053] determine a difference between the left and right requests;

[0054] determine whether the difference satisfies a difference limit condition;

[0055] determine a modified request for increasing or decreasing the difference, in dependence on the difference not satisfying the difference limit condition;

[0056] output a first control signal for the first actuator; and

[0057] output a second control signal for the second actuator, and

[0058] wherein one of the first and second control signals is dependent on the modified torque request, if the difference does not satisfy the difference limit condition.

[0059] Optionally, the first and second actuators are foundation brakes or electric machines.

[0060] 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.

[0061] BRIEF DESCRIPTION OF THE DRAWINGS

[0062] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0063] FIG. 1 illustrates a perspective view of an example vehicle;

[0064] FIG. 2 illustrates a schematic view of an example electric drive system of a vehicle;

[0065] FIG. 3A illustrates a schematic view of an example control system, and FIG. 3B illustrates a schematic view of an example non-transitory computer-readable medium;

[0066] FIG. 4 illustrates a schematic view of an example control system comprising multiple controllers;

[0067] FIG. 5 illustrates a schematic view of an example flowchart illustrating a method;

[0068] FIG. 6 illustrates an example torque-time graph depicting requested torque imbalances and initial torque limits;

[0069] FIG. 7 illustrates an example torque-time graph depicting post-arbitration torque limits; and

[0070] FIG. 8 illustrates a schematic view of an example flowchart illustrating a method.DETAILED DESCRIPTION

[0071] 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.

[0072] FIG. 2 illustrates a schematic view of the vehicle 1 where the vehicle is a battery electric vehicle (BEV) or hybrid electric vehicle (HEV).

[0073] FIG. 2 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.

[0074] 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. 2, the loads comprise a pair of electric drive units (EDUs) 208A, 208B, together defining a system 209. In other examples, only a single EDU 208 is provided.

[0075] A first EDU 208A drives a left wheel of the vehicle 1 and the second EDU 208B drives a right wheel of the vehicle 1, or vice versa. The vehicle 1 comprises an axle 214 connected to the left and right wheels. 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.

[0076] The EDUs 208A, 208B share the same DC bus 204 and traction battery 202, but could alternatively be connected to separate DC buses 204 and traction batteries 202.

[0077] Each EDU 208 comprises an inverter 206, an inverter controller 336, 338 configured to control the inverter 206, an electric machine 210 operable as a traction electric machine, and a transmission 212.

[0078] 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.

[0079] The inverter 206, when controlled by the inverter controller 336 or 338, is configured to control the frequency and magnitude of electrical signals supplied to the electric machine 210. The inverter controller 336 or 338 regulates the torque of an electric motor primarily by controlling the frequency and magnitude of the electrical signals supplied to the electric machine 210.

[0080] For example, the inverter controller 336, 338 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 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.The inverter controller 336, 338 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 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 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.

[0081] 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.

[0082] The transmission 212 is located 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.

[0083] In some embodiments, the inverter controller 336, 338, inverter 206, electric machine 210, and transmission 212 may be integrated into a single unit or housing to provide the EDU 208 for the vehicle 1. The EDU 208 comprises a housing arrangement. For example, the housing arrangement comprises one or more enclosures containing various components of the EDU 208. If there are multiple enclosures, the enclosures may be connected to each other, for example by mechanical fixings / sealant, to form a module.

[0084] With reference to FIG. 3A, there is illustrated a control system 300 for a vehicle 1. The control system 300 comprises one or more controllers 301.

[0085] The control system 300 is configured to receive one or more torque requests from a source 314 of the vehicle 1 and determine one or more arbitrated torque requests. The control system 300 may then output a control signal to control the inverter 206 in dependence on the one or more arbitrated torque requests. The source 314 may comprise an accelerator pedal module or an autonomous driving module, for example.

[0086] The control system 300 as illustrated in FIG. 3A 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.

[0087] For example, an inverter control module fitted to one axle, could control both the left- and right-hand side electric machines 210 of that axle, having a single control unit but two sets of electric machine drivers.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. The input 310 is arranged to receive a torque request signal from a source 314. The torque request is an electrical signal which is indicative of a pre-arbitrated requested torque of the vehicle 1 or of the EDU 208. The output 312 is arranged to output a torque control signal, indicative of a gate control signal for controlling the gate control section of the inverter 206.

[0088] The above description defines the signals in terms of torque, but they could also be expressed as a force, or as a non-dimensional quantity (e.g. a duty percentage) that gets converted back into a physical quantity via a prescribed convention (e.g. 1 % duty = 400Nm wheel torque). The control mechanism described here would work in the same way even if the interfaces were expressed in different units.

[0089] FIG. 3B illustrates a non-transitory computer-readable storage medium 400 comprising the instructions (computer software).

[0090] FIG. 4 illustrates an example implementation of the control system 300, comprising a Vehicle Systems Controller (VSC) 331, a Stability Control System controller (SCS) 326, and inverter controllers 336, 338. These may be referred to as first, second, and third controllers, respectively. The VSC 331 and SCS 326 are hosted outside the inverters 206. The inverter controllers 336, 338 are 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.

[0091] The VSC 331 arbitrates a vehicle torque request 328 and a yaw target 330. The VSC 331 may also receive one or more of: wheel speeds 320; or inertial signals 324 such as vehicle yaw rate, detected vehicle longitudinal acceleration, and / or detected vehicle lateral acceleration. The VSC 331 may also receive a detected steering wheel angle and / or rate. The vehicle torque request may depend on a driver torque demand and / or an autonomous driving torque demand. The yaw target may depend on one or more of the above variables.

[0092] The VSC 331 hosts a torque distribution function (torque distribution unit), which is configured to determine an initial torque distribution between the EDUs 208A, 208B for satisfying the vehicle torque request and yaw target.

[0093] The VSC 331 also hosts an intervention function 334 (intervention unit) downstream of the torque distribution function, configured to modify the initial torque distribution in dependence on wheel speed torque limits received from the SCS 326.

[0094] The intervention function 334 is configured to determine and send left and right torque requests 508 to the inverter controllers 336, 338.

[0095] FIG. 5 illustrates a method 500 according to an embodiment of the invention. The method 500 is a method of controlling a drive torque split between left and right wheels of a vehicle 1, such as the vehicle 1 illustrated in FIG. 1. In particular, the method 500 is a torque arbitration method. In particular, the memory 306 may comprise computer-readable instructions 308 which, when executed by the processor 304, perform the method 500. The method 500 is hosted in the inverter controller 336, 338 of the control system 300 illustrated in FIG. 3A and 4.Before describing the method 500 in full, some advantages are summarised below.

[0096] An advantage of hosting at least part of the method 500 in the inverter controller 336, 338 is that the torque arbitration is carried out with low latency. Therefore, control loops can be executed at a significantly faster frequency than a vehicle communication network which has higher latency. Examples of vehicle communication networks are a Controller Area Network (CAN) bus or Flexray(TM) bus. The transport delay expected over the vehicle communication network may be greater than 20 milliseconds.

[0097] In particular, the later-described blocks 511 and 522 significantly benefit from being hosted in the inverter controller 336, 338, because they comprise fast control loops and therefore benefit significantly from the low latency of the inverter controller 336, 338.

[0098] Furthermore, the method 500 sets a particular order of priority of the arbitration blocks. If a priority were not specified, this can lead to a conflict of requests which can lead to unintended acceleration or deceleration of the EDU 208. Therefore, the method 500 is robust against conflicting requests.

[0099] In vehicles with multiple EDUs 208A, 208B as shown in FIG. 2, the method 500 may be implemented concurrently by both EDUs 208A, 208B, with messages exchanged between their respective inverter controllers 336, 338 (501, 502, 517, 518, 519, 520).

[0100] Blocks 501, 502, 503, 504, 505, 506, 507, 508, 510, 511, 512, 513, 513A, 511A, 515, 553 relate to an arbitration function 515 (arbitrator).

[0101] The arbitration function 515 receives a torque request 508 and a plurality of torque restrictions 506, 507, 511A, 513A, 553. Each of these torque restrictions is a separate de-rate parameter such as a torque limit or demand. A limit as defined herein may be implemented as a 'hard limit’ or a 'soft limit’.

[0102] The arbitration function 515 comprises a minimum magnitude torque selector. The minimum magnitude torque selector of the arbitration function 515 is configured to determine and output a firstarbitrated torque request 516 in dependence on the plurality of torque restrictions 506, 507, 511, 513A, 553 and the received torque request 508.

[0103] Specifically, the minimum magnitude torque selector arbitrates the de-rate parameters 506, 507, 511, 513A, 553 to determine a most restrictive one of the plurality of de-rate parameters. The arbitration function 515 saturates the torque request 508 in dependence on the most restrictive one of the de-rate parameters 506, 507, 511, 513A, 553. Therefore, the first arbitrated torque request 516 comprises a saturated torque request 508. Where the de-rate parameters may comprise torque limits, the most restrictive one may be the one with the lowest positive or negative magnitude.

[0104] The torque request 508 received by the arbitration function 515 may be a pre-arbitrated torque request. The torque request 508 may be determined, either locally or remotely, in dependence on sensed accelerator pedal depression. If the vehicle 1 is autonomously driven, the pre-arbitrated torque request 508 may be determined by an autonomous driving controller in dependence on a vehicle speed target and in dependence on machine vision sensing. If the pre-arbitrated torque request 508 is determined externally, the signal 508 may arrive at the inverter controller 336, 338 over the vehicle communication network.Optionally, in a vehicle with multiple torque sources, the pre-arbitrated torque request 508 is an EDU torque request for the EDU 208A, split from an overall vehicle torque request by an external torque split controller (torque distribution function 332 of Vehicle Systems Controller 331 of FIG. 4). The torque distribution function 332 may split the overall vehicle torque request between the various torque sources of the vehicle, which include the EDUs 208A and 208B. The torque distribution function 332 may output an individual EDU torque request for each EDU 208A, 208B. The illustrated pre-arbitrated torque request 508 is for the EDU 208A but not the EDU 208B.

[0105] The de-rate parameters for saturating the torque request 508 are now described.

[0106] FIG. 5 illustrates an axle torque de-rate parameter 506 to limit a total torque produced at the axle 214 of the vehicle 1. The axle torque de-rate parameter 506 may comprise a torque limit of the total torque request for the axle 214, defined as the sum of pre-arbitrated torque requests for both EDUs 208A, 208B. This is useful for the architecture of FIG. 2 in which the EDUs 208A, 208B are configured to drive different wheels of the same axle 214 of the vehicle 1. Such an arrangement may be described as a 'Twin EDU’ architecture. Other architectures may not require an axle torque de-rate parameter 506.

[0107] To determine the axle torque de-rate parameter 506, FIG. 5 illustrates an axle torque de-rate function 504 (axle torque de-rate unit) configured to:

[0108] - receive a first signal 501 indicative of a torque request of the host EDU 208A that the method 500 is controlling;

[0109] - receive a second signal 502 indicative of a torque request of the other EDU 208B;

[0110] - receive a third signal 503 indicative of a de-rate limit; and

[0111] - determine the axle torque de-rate parameter 506 in dependence on the signals 501, 502, 503.

[0112] The pre-arbitrated torque request 508 may be the same as the torque request signal 501 for the host EDU 208A in which the method 500 is being executed.

[0113] In an implementation, determining the axle torque de-rate parameter 506 comprises determining whether the sum of the EDU torque requests 501, 502 exceeds the de-rate limit 503. The de-rate limit 503 sets an axle-level torque limit to limit the total torque produced at the axle 214 of the vehicle 1. The de-rate limit 503 may be calculated by the inverter controllers 336, 338 of both EDUs 208A, 208B.

[0114] The axle torque de-rate parameter 506 may comprise a self-inverter torque limit imposing a peak allowable torque for the inverter 206 of the host EDU 208A. The self-inverter torque limit 506 is in respective proportion to the other inverter torque request 502. The signals 502 and 506 may collectively adhere to the axle-level limit 503. For example, the self-inverter torque limit 506 may be substantially equal to the axle-level de-rate limit 503 minus the other inverter torque request 502.

[0115] The signals 501, 502 are received from the VSC 331, configured to output torque requests. The signal 503 may be received from a de-rate function within the inverter controller 336, 338 of the host EDU 208A.

[0116] The signals 501 , 502 of a given axle already contain a desired left / right torque vectoring request from the torque distribution function 332 of the supervisory controller (VSC 331). The signals 501, 520 are determined based on a range of parameters, such as estimated vertical load on each wheel, torque / force applied at each wheel, estimated ground surface friction coefficient,front and rear wheel steering system position, selected driver mode, etc.

[0117] The same logic can apply between the front and rear axle EDUs for vehicles fitted with at least one electric machine per axle. The supervisory controller 331 will define a desired torque distribution request between the front and rear axles.

[0118] The axle torque de-rate function 504 of the inverter controller 338 of the EDU 208A may also output a second signal 505 sending the axle torque de-rate parameter 506 to the inverter controller 336 of the other EDU 208B. This signal 505 may be utilised in the corresponding flowchart 500 for the other EDU 208B, as a signal 502.

[0119] FIG. 5 also illustrates an individual EDU de-rate parameter 507 to limit torque produced by the host EDU 208A separately from the other EDU 208B. The individual EDU de-rate parameter 507 is a torque limit of the requested torque of the EDU 208A, independent of the requested torque of the EDU 208B. Therefore, each EDU 208A, 208B may have a different individual EDU de-rate parameter 507. The individual EDU de-rate parameter can be regarded as a torque requirement specific to the EDU 208A or 208B associated with the inverter controller 336, 338 executing the method 500.

[0120] The arbitration function 515 receives the individual EDU de-rate parameter 507 from a de-rate function within the inverter controller 338 of the host EDU 208A. For example, the de-rate function can comprise a diagnostic function configured to monitor one or more sensors of the host EDU 208A to monitor a diagnostic condition, and output an individual EDU de-rate parameter 507 in dependence on the diagnostic condition being satisfied.

[0121] FIG. 5 also illustrates a traction control de-rate parameter 511A to limit torque produced by the EDU 208 in dependence on a traction control function 511. This may comprise a torque limit or demand which is dependent on a detected difference between a sensed wheel speed of the vehicle 1 , and a sensed vehicle speed of the vehicle 1. The traction control de-rate parameter 511A can be regarded as a torque requirement specific to the EDU 208A or 208B associated with the inverter controller 336, 338 executing the method 500.

[0122] Traction control is usually implemented by controlling friction brakes, so it is advantageous to incorporate it within the method 500 of FIG. 5 because the EDU 208 is very responsive in comparison to friction brakes.

[0123] FIG. 5 illustrates the inverter controller 336, 338 hosting at least part of the traction control function 511. This is advantageous compared to hosting the function 511 in an external controller, separated from the inverter controller 336, 338 across the vehicle communication network. The local hosting of the function 511 allows a fast control loop for traction control, to allow rapid responses to detected traction loss events.

[0124] The traction control function 511 is configured to receive a torque request 510 for the host EDU 208. This may be the same as the pre-arbitrated torque request 501 / 508 for the host EDU 208.

[0125] Although not shown, the traction control function 511 may receive a motor speed target (or speed limit) as well as sensed feedback indicative of the current speed of the EDU 208. The motor speed target (or speed limit) is determined externally or internally in dependence on a detected difference between a sensed wheel speed of the wheel driven by the EDU 208, and a reference “vehicle speed over ground”.The reference “vehicle speed over ground” is defined based on a vehicle model dependent on one or more inputs such as individual wheel speeds, inertial measurement unit data, steering system position, satellite-derived vehicle positioning data, or a combination thereof. The traction control function 511 is configured to reduce the sensed wheel speed towards the reference “vehicle speed over ground” to deliver the best grip available at the contact patch tyre / ground. Specifically, the traction control function 511 may be configured to determine a torque limit in dependence on the motor speed target (or speed limit) and current speed of the EDU 208.

[0126] Then, the traction control function 511 may output a de-rate parameter 511A such as a torque demand or limit, which is dependent on the torque request 510 and the torque limit determined above. The de-rate parameter 511A restricts the maximum allowable torque which the EDU 208 can output while the traction control function 511 is active. The de-rate parameter 511A could comprise a lower magnitude positive torque limit, so that if the pre-arbitrated torque request 508 is positive it will be saturated to a low magnitude or zero value. Therefore, the speed of a spinning wheel will decrease until traction is regained.

[0127] The traction control function 511 may also output a second signal 514 sending the traction control de-rate parameter 511A to a first monitor 548, 551 which is described later.

[0128] It is not essential for the arbitration function 515 to receive all the illustrated parameters 506, 507, 511A, 513A, 553. One or more of the parameters could be omitted. One or more functions 504, 511, 513, 551 for calculating the omitted parameters could therefore be omitted, or implemented outside the inverter controller 336, 338.

[0129] FIG. 5 also shows an energy availability de-rate parameter 513A to limit torque produced by the electric drive unit 208 in dependence on a capability of an electrical energy storage apparatus 202 of the vehicle 1. This may comprise a torque limit which is dependent on an electrical power limit of the DC bus 204 and / or traction battery 202.

[0130] FIG. 5 illustrates the inverter controller 336, 338 hosting an energy availability de-rate function 513 (energy available de-rate unit) configured to determine the energy availability de-rate parameter 513A.

[0131] To determine the energy availability de-rate parameter 513A, the energy availability de-rate function 513 is configured to receive one or more signals 512 indicative of one or more electrical power limits associated with the traction battery 202 (and / or DC bus 204), and determine the energy availability de-rate parameter 513A in dependence on the electrical power limit or limits 512. For example, the electrical power limit 512 may be converted to a torque limit 513A.

[0132] The energy availability de-rate function 513 may be configured to receive the electrical power limit 512 from another controller of the vehicle.

[0133] FIG. 5 further illustrates a first monitor 548 configured to monitor an output 547 of the arbitration function 515. The output 547 comprises the first arbitrated torque request 516.

[0134] The first monitor 548 may comprise a traction control plausibility monitor. The traction control plausibility monitor 548 may be configured to receive a first signal 547 comprising the first arbitrated torque request 516, and a second signal 514 comprisingthe traction control de-rate parameter 511A. The traction control plausibility monitor 548 may be configured to determine a traction control override parameter 549 in dependence on the signals 547, 514 indicating the first arbitrated torque request 516 and the traction control de-rate parameter 511 A.

[0135] For example, the determination by the traction control plausibility monitor 548 may comprise determining if the first signal 547 is less than or equal to the second signal 514. The traction control override parameter may be set to ONm if signal 547 is less than signal 514, for example.

[0136] The first monitor 548 outputs the traction control override parameter 549 to a second monitor 551, which is now described. Alternatively, the parameter 549 may be output directly to the arbitration function 515.

[0137] The second monitor 551 may comprise a vehicle stability control scheme. The second monitor 551 is configured to determine a stability intervention torque limit parameter 553 to limit torque produced by the EDU 208 in dependence on the vehicle stability control scheme. Stability in this context refers to the stability of motion of the vehicle 1 over ground, such as yaw stability.

[0138] The stability intervention torque limit parameter 553 forms one of the torque restrictions input to the arbitration function 515. The effect of the second monitor 551 is therefore to ensure that the arbitration function 515 considers torque limit parameters for vehicle yaw stability.

[0139] The second monitor 551 may comprise an arbitration function. The vehicle stability control scheme of the second monitor 551 may comprise an arbitration function comprising a minimum magnitude torque selector. The minimum magnitude torque selector may be for treating over-rotating wheel slip. Alternatively, or additionally, the vehicle stability control scheme of the second monitor 551 may comprise a maximum magnitude torque selector for treating under-rotating wheel slip.

[0140] The minimum magnitude torque selector of the second monitor 551 receives a signal 545 indicative of the pre-arbitrated torque request 508 for the EDU 208, and receives a plurality of torque restrictions 544, 546, 549. Unlike the arbitration function 515, the minimum magnitude torque selector of the second monitor 551 is only dependent on parameters configured to control vehicle stability (544, 546, 549), and ignores parameters which are not configured to control vehicle stability (506, 507, 513A).

[0141] The parameter 549 is a traction control override parameter is as described above. The parameter 546 is an override torque request parameter, configured to impose a torque limit in dependence on a controller determining that the vehicle 1 is braking above a threshold while vehicle-accelerating torque is being requested.

[0142] The parameter 544 is indicative of a set of one or more stability control torque limits.

[0143] The minimum magnitude torque selector of the second monitor 551 arbitrates the torque limit parameters 544, 546, 549 to determine a most restrictive one of the plurality of torque limit parameters. The minimum magnitude torque selector of the second monitor 551 saturates the signal 545 indicative of the pre-arbitrated torque request 508 in dependence on the most restrictive one of the torque limit parameters 544, 546, 549. Therefore, the stability intervention torque limit parameter 553 sent to the arbitration function 515 comprises a saturated torque request. Where the torque limit parameters 544, 546, 549 may comprise torque limits, the most restrictive one may be the one with the lowest positive or negative magnitude.Based on the above definitions, it would be appreciated that the output 516 of the arbitration function 515 comprises an arbitrated torque request which may be equal to or less than the pre-arbitrated torque request 508, in dependence on the values of the other inputs to the arbitration function relative to the pre-arbitrated torque request 508.

[0144] FIG. 5 next illustrates an imbalance limiting function 521 (imbalance limiter) after the arbitration function 515, which is configured to control torque imbalance between EDUs 208A, 208B.

[0145] The imbalance limiting function 521 is configured to further modify the first arbitrated torque request 516 to restrict yaw of the vehicle 1 specifically arising from the inverter-hosted arbitration functions 515 modifying the pre-arbitrated torque requests 508 by different amounts. Due to the arbitration function 515 implementing a traction control intervention function 511 , among other things, inverter arbitrator-induced vehicle yaw can arise during acceleration of the vehicle 1 on surfaces with unequal surface friction beneath the first and second wheels, among other situations such as acceleration changes during cornering. The imbalance limiting function 521 may be configured to limit a difference in magnitude between requested output torques of the EDUs 208A, 208B.

[0146] The imbalance limiting function 521 of each inverter controller 336, 338 is configured to receive a left torque request for the left EDU (e.g., 208A) coupled to a left wheel, and a right torque request for the right EDU (e.g., 208B) coupled to the right wheel.

[0147] The imbalance limiting function 521 is configured to receive the arbitrated torque request 516 of the host EDU 208A or 208B, and a signal 518 indicative of the arbitrated torque request 516 of the other, non-host EDU 208A or 208B. If the imbalance limiting function 521 is for the left EDU 208A, the signal 516 is a left torque request, and the signal 518 is a right torque request. If the imbalance limiting function 521 is for the right EDU 208B, the signal 516 is a right torque request, and the signal 518 is a left torque request.

[0148] The imbalance limiting function 521 is configured to determine a difference (FIG. 7, ATq) between the arbitrated left and right torque requests 516, 518. The difference ATq is referred to herein as an amount of “post-arbitration torque vectoring” or “requested torque imbalance”, because the difference ATq represents different amounts of requested torque vectoring between the left and right drive wheels of the vehicle 1. The requests 516, 518 could be the same sign or opposite signs.

[0149] The imbalance limiting function 521 is then configured to determine whether the post-arbitration torque vectoring ATq satisfies a difference limit condition. The difference limit condition may be obtained by the function 521 by receiving it from the VSC 331 and / or by determining it locally. As described later, the difference limit condition may comprise:

[0150] a post-arbitration upper torque vectoring limit 702UL in FIG. 7; and

[0151] a post-arbitration lower torque vectoring limit 702LL in FIG. 7.

[0152] The imbalance limiting function 521 is configured to determine a modified torque request 554 for increasing or decreasing the difference ATq, in dependence on the difference ATq not satisfying the difference limit condition. Specifically, the imbalance limiting function 521 for the left EDU 208A is configured to modify the left torque request 516 to increase or decrease the difference ATq towards satisfaction of the difference limit condition, in dependence on the difference ATq not satisfying the difference limit condition. The imbalance limiting function 521 for the right EDU 208B is configured to modify the right torque request 516 to increase or decrease the difference ATq towards satisfaction of the difference limit condition, in dependence on the difference ATq not satisfying the difference limit condition.In dependence on the difference ATq satisfying the difference limit condition, the imbalance limiting function 521 may be configured to maintain / pass through the unmodified value of the arbitrated torque request 516. Therefore, the signal 554 may be equal to the arbitrated torque request 516.

[0153] In some, but not necessarily all implementations, the difference limit condition comprises a range of allowable torque variation relative to an amount of pre-arbitrated torque vectoring. The difference limit condition may comprise post-arbitration upper and lower torque vectoring limits 702UL, 702LL (FIG. 7), characterising the range. The role of the imbalance limiting function 521 can therefore be summarised as a supervisory function to ensure that the amount of post-arbitration torque vectoring after inverter-hosted arbitration by block 515 is within range of the amount of pre-arbitrated, pre-inverter requested torque vectoring requested before block 515. In other words, the imbalance limiting function 521 is configured to ensure (if possible) that the difference ATq between the outputs 516 from the arbitration functions 515 for the EDUs 208A, 208B is within an allowable range of the difference between the inputs 515 to the arbitration functions 515 for the EDUs 208A, 208B. This prevents issues such as a traction control intervention for just one EDU 208A or 208B resulting in excessively more torque vectoring than what was planned by upstream controllers (e.g., 332 / 334).

[0154] FIGS. 6 and 7 are torque-time graphs representing an example implementation of how the difference limit condition may be determined. FIG. 6 illustrates the initial calculation of the difference limit condition, optionally performed at the VSC 331. FIG.

[0155] 7 illustrates the limits 702UL, 702LL of the resulting final difference limit condition obtained by each of the inverter controllers 336, 338, for application to incoming torque requests 516, 518.

[0156] In FIG. 6, the line 601 represents an initial requested torque imbalance, calculated as the difference between the two initial torque requests calculated by the torque distribution function 332 of the VSC 331. This can also be described as an initial requested torque vectoring amount. Its value may be zero or nonzero, and positive or negative (clockwise / counterclockwise vehicle yaw).

[0157] For example, the initial requested torque imbalance 601 may have been calculated in dependence on the vehicle torque request, and further in dependence on one or more of the following sensed parameters: a steering angle of the vehicle 1; a detected lateral acceleration of the vehicle 1; a detected longitudinal acceleration of the vehicle 1; a detected yaw angle / rate of the vehicle 1; vehicle speed; a drive mode of the vehicle 1; foundation braking of the vehicle 1 (e.g., friction brakes or equivalent braking systems). The initial requested torque imbalance 601 may become positive or negative during vehicle cornering, depending on the direction of requested torque vectoring.

[0158] The line 602UL represents an initial positive torque vectoring limit (initial upper yaw limit) relative to the initial requested torque imbalance 601 (initially requested vehicle yaw). The line 602LL represents an initial lower torque vectoring limit (initial lower yaw limit) relative to the initial requested torque imbalance 601 (initially requested vehicle yaw). The initial upper and lower torque vectoring limits 602UL, 602LL represent a range of allowable torque imbalance relative to the initial requested torque imbalance 601. They can be described as initial upper and lower limits calculated in dependence on the initial requested torque imbalance 601. The line 601 is within the range, with the lines 602UL, 602LL representing upper and lower offsets from the line 601.The initial upper and lower torque vectoring limits 602 U L, 602LL may be determined by an external controller, such as an anti-lock braking system controller, in some examples.

[0159] When the initial requested torque imbalance 601 is zero, due to straight-line steady-state driving, the initial upper and lower torque vectoring limits 602UL, 602LL may have positive and negative polarities, one of them limiting torque vectoring in a clockwise yaw direction, and the other limiting torque vectoring in a counterclockwise yaw direction.

[0160] The initial upper and lower torque vectoring limits 602UL, 602LL may each be a variable, or a fixed value, or a combination thereof. If variables, the limits 602UL, 602LL may be determined by the VSC 331 in dependence on one or more of: the direction and magnitude of the requested vehicle yaw 601; the vehicle torque request 328; the yaw target 330; a steering angle of the vehicle 1 ; wheel speeds 320; vehicle speed; selected vehicle drive mode; foundation braking; or an inertial signal 324 such as a detected lateral acceleration of the vehicle 1 , a detected longitudinal acceleration of the vehicle 1 , a detected yaw angle / rate of the vehicle 1, or a combination thereof.

[0161] FIG. 6 shows the initial upper and lower torque vectoring limits 602UL, 602LL calculated as offsets relative to the initial requested torque imbalance 601. The offset amounts may be determined in dependence on one or more of the above-listed variables.

[0162] Although the initial upper and lower torque vectoring limits 602UL, 602LL are summarised as relative quantities relative to a requested torque imbalance 601, this encompasses signals comprising either relative or absolute quantities (601+602UL; 601+602LL).

[0163] Furthermore, FIG. 6 shows that the initial upper and lower torque vectoring limits 602UL, 602LL may converge towards the initial requested torque imbalance 601 in dependence on the vehicle speed increasing. In other words, the offsets of the initial upper and lower torque vectoring limits 602UL, 602LL may be determined in dependence on vehicle speed such that the range therebetween decreases in dependence on increasing speed. This is shown from t=0-3 seconds of FIG. 6 when the vehicle is travelling slowly, and is because sudden vehicle yaw is easier to control at low vehicle speeds than at high vehicle speeds. Therefore, more vehicle yaw may be allowed at low vehicle speeds.

[0164] Furthermore, an asymmetry of the initial positive and negative torque vectoring limits 602P, 602N relative to the magnitude of the initial requested torque imbalance 601 may depend on vehicle speed such that an imbalance-dependent asymmetry of the limits builds with increasing vehicle speed. This speed dependency is shown in t=9 to 12 seconds of FIG. 6 when the vehicle 1 is travelling at a high speed and starts turning a corner as shown by the nonzero line 601. FIG. 6 shows that in dependence on the initial requested torque imbalance 601 being positive, the initial positive torque vectoring limit 602P may be further from the initial requested torque imbalance 601 than the initial negative torque vectoring limit 602N.

[0165] The left / right torque vectoring logic can be used for a variety of use cases, such as:

[0166] - to deliver yaw damping e.g. during an evasive lane change manoeuvre on the motorway, or

[0167] - to change the vehicle feel between different selected driving modes (e.g. from an understeering behaving car in comfort mode to an oversteering behaving car in dynamic mode).In some examples, the amount of asymmetry of the determined initial torque vectoring limits 602UL, 602LL may vary in dependence on input variables such as a selected vehicle drive mode (comprising sport-focussed and comfort-focussed modes), and / or vehicle speed, lateral acceleration, front and rear steering system positions etc.

[0168] The initial limits 602UL, 602LL of FIG. 6 may be different than the final limits 702UL, 702LL used by the inverter controller 336, 338. The final limits (FIG. 7, 702UL, 702LL) are determined in dependence on the initial limits 602UL, 602LL, and further in dependence on a modified requested torque imbalance denoted by the further line 603 in FIG. 6. The modified requested torque imbalance 603 can also be described as a setpoint or target vehicle yaw / torque vectoring amount, relative to which the upper and lower torque vectoring limits 702UL, 702LL are calculated. In some examples, the final torque vectoring limits 702UL, 702LL can be equal to the initial torque vectoring limits 602UL, 602LL converted in relative torque, and can also be unequal from those in some conditions described below.

[0169] In FIG. 6, the modified requested torque imbalance 603 is calculated by the torque distribution function 332 or intervention function 334 of the VSC 331. This can differ from the initial requested torque imbalance 601. For example, an individual torque request for one of the EDUs 208A or 208B may have been modified by a lash crossing rate limiter to control lash when a torque request changes sign between positive and negative torque, while the other EDU 208A or 208B does not pass through lash. As a result, the modified requested torque imbalance 603 is different than the initial imbalance 601. Another reason may be that the intervention function 334 has reduced one or both pre-arbitrated torque requests 508 from the torque distribution function 332 in an imbalance-increasing manner, to satisfy a wheel speed torque limit from the SCS 326. The modified requested torque imbalance 603 in FIG. 6 may correspond to the difference between the pre-arbitrated torque requests 508.

[0170] With reference to FIGS. 6 and 7, the VSC 331 and / or inverter controller 336, 338 is configured to determine the final difference limit condition in the form of a post-arbitration upper torque vectoring limit 702UL and a post-arbitration lower torque vectoring limit 702LL, both of which may be sent to each of the inverter controllers 336, 338, for the EDUs 208A, 208B.

[0171] Determining the post-arbitration torque vectoring limits 702UL, 702LL comprises determining the differences between the modified requested torque imbalance 603 and each initial torque vectoring limit 602UL, 602LL, wherein:

[0172] - the post-arbitration upper torque vectoring limit 702UL comprises the difference between the initial upper torque vectoring limit 602UL and the modified requested torque imbalance 603; and

[0173] - the post-arbitration lower torque vectoring limit 702LL comprises the difference between the initial lower torque vectoring limit 602LL and the modified requested torque imbalance 603.

[0174] In summary, the above involves a conversion from absolute imbalance torque vectoring limits 602UL and 602LL into relative torque vectoring limits 702UL and 702LL referenced to an imbalance 603. Such a conversion is not mandatory: the limits 602UL, 602LL could be sent directly to the inverter controller 336, 338 in some implementations.

[0175] The post-arbitration torque vectoring limits 702UL, 702LL differ from each other in the sense of being asymmetric relative to the modified requested torque imbalance 603, whenever the modified requested torque imbalance 603 is unequal to the initial requested torque imbalance 601. If the modified requested torque imbalance 603 represents a modification in a positive or negative direction from the initial imbalance 601, this uses up some of the ‘headroom’ provided by one the initial torque vectoring limits in that direction 602UL, 602LL. This logic ensures that the inverter controllers 336, 338 are given less ‘headroom’ to modify torque imbalance further in the same direction, during inverter-level arbitration.For example, if the modified imbalance 603 is positively offset relative to the initial imbalance 601 as shown in t=3.5-5.5 seconds of FIG. 6, the post-arbitration upper torque vectoring limit 702UL is closer to the modified imbalance 603 than the postarbitration lower torque vectoring limit 702LL as shown in t=3.5-5.5 seconds of FIG. 7. However, if the modified imbalance 603 is negatively offset relative to the initial imbalance 601 as shown in t=8-10 seconds of FIGS. 6 and 7, the post-arbitration lower torque vectoring limit 702LL is closer to the modified imbalance 603 the post-arbitration upper torque vectoring limit 702UL.

[0176] Based on the above definitions, an example use case is now described with reference to FIGS. 6 and 7.

[0177] The vehicle 1 may be accelerating from a standstill at t=0. From t=0 to 3 seconds, the vehicle 1 may be accelerating in a straight line. Therefore, the initial and modified requested torque imbalances 601, 603 may be zero. As the vehicle speed increases, the initial upper and lower torque vectoring limits 602UL, 602LL converge towards the initial requested torque imbalance 601 , representing a narrowing initial range. The modified requested torque imbalance 603 is also zero. The resulting post-arbitration upper and lower torque vectoring limits 702UL, 702LL in FIG. 7 are equally offset from the torque imbalance 603 as each other, and may also be equal to the initial limits 602UL, 602LL.

[0178] From t=3.5 to 9 seconds, the vehicle 1 turns a first corner. The initial requested torque imbalance 601 becomes nonzero and negative to request torque vectoring in a direction dependent on the cornering direction. Depending on the currently requested torque, this may require the torque output of one of the EDUs 208A, 208B to pass through zero. Therefore, from t=3.5 to 5.5 seconds, a lash crossing function applied to one of the EDUs 208A, 208B causes the modified requested torque imbalance 603 to be offset from the initial imbalance 601, in a positive direction. The resulting post-arbitration upper and lower torque vectoring limits 702UL, 702LL from t=3.5 to 5.5 seconds in FIG. 7 are asymmetric relative to the torque imbalance 603, with the upper limit 702UL being offset from the torque imbalance 603 by less than the lower limit 702LL based on the calculation methodology described earlier.

[0179] From t=3.5 to 9 seconds, during vehicle cornering, the initial limits 602UL, 602LL vary with the initial imbalance 601, because they are offsets. The initial upper torque vectoring limit 602UL may even become a negative torque magnitude, as seen from t=5 to 7 seconds.

[0180] From t=5.5 to 8 seconds, the modified imbalance 603 is again equal to the initial imbalance 601, so the post-arbitration torque vectoring limits 702UL, 702LL are again symmetric about the modified imbalance 603. The final limits 702UL, 702LL may be offset from the modified imbalance 603 by the same amount that the initial limits 602UL, 602LL are offset from the initial imbalance 601. The limits 702UL, 702LL have a low magnitude because the vehicle 1 is travelling at a higher speed.

[0181] From t=10 to 12 seconds, the vehicle 1 turns into a second corner in an opposite steering direction than the first corner. The initial requested torque imbalance 601 changes sign to become positive to request torque vectoring in this opposite direction. From t=8 to 10 seconds, another lash crossing occurs in one of the EDUs 208A, 208B. The modified requested torque imbalance 603 becomes offset from the initial imbalance 601 in a negative direction, due to the lash crossing function. The resulting post-arbitration upper and lower torque vectoring limits 702UL, 702LL in FIG. 7 are asymmetric about the modified imbalance 603, with the post-arbitration lower limit 702LL being closer to the modified imbalance 603 than the upper limit 702UL.From t=10-12 seconds, the vehicle 1 continues to navigate the second corner. The vehicle speed is high enough that the initial limits 602UL, 602LL become noticeably asymmetrical in dependence on the direction and magnitude of the initial imbalance 601, as described earlier. Therefore, the post-arbitration upper and lower limits 702UL, 702LL become asymmetric even though the modified imbalance 603 is equal to the initial imbalance 601. If the lines 601, 603 diverge during this time, the asymmetry may increase or decrease in accordance with the principles described in relation to t=3.5 to 5.5 seconds. This demonstrates that their asymmetry can be based on variables other than the difference between the initial and post-arbitration imbalances 601, 603.

[0182] When the post-arbitration upper and lower limits 702UL, 702LL are applied in the inverter controllers 336, 338, the difference ATq between the arbitrated torque requests 516, 518 of the EDUs 208A, 208B is determined, and then the inverter controller 336, 338 determines whether the difference ATq is within the limits 702UL, 702LL.

[0183] If the difference ATq is within the limits 702UL, 702LL, the difference limit condition is satisfied. If outside the limits 702UL, 702LL, the difference limit condition is unsatisfied. For example, in FIG. 7, the difference ATq is equal to the modified requested torque imbalance 603, in other words equal to the target vehicle yaw, until t=5.5-6.5 seconds when ATq spikes, for example due to one of the torque requests 516, 518 being decreased at inverter level by a respective arbitration function 515, but not the other. During this time, ATq exceeds the limit 702UL. In response, the imbalance limiting function 521 modifies the torque request until the limit 702UL is no longer exceeded.

[0184] Specifically, when the difference limit condition is unsatisfied, due to the difference ATq between the requests 516-518 being outside the limits 702UL, 702LL, the imbalance limiting function 521 is configured to determine a modified torque request 554, modified relative to the request 516 for the host EDU. If the difference limit condition is satisfied, the request / output 554 of the function 521 may be equal to the request 516.

[0185] The imbalance limiting function 521 may further comprise a timer / debounce timer such that the modification of the request 516 is performed in dependence on the difference ATq being outside the limits 702UL, 702LL for at least the duration of the timer, in other words how long the difference limit condition is non-satisfied.

[0186] Within the inverter hosted imbalance torque limit application logic, it is possible to calibrate both a debounce time and / or a blend function towards the imbalance torque vectoring limits 702UL, 702LL based on the size of the torque reduction applied on the other side wheel.

[0187] For illustration, taking the example of one wheel going airborne very transiently due to a bump on the road under a high load acceleration from the driver, this wheel will overspin whilst airborne leading to an aggressive traction control torque limit applied to it to maintain a slip level of that wheel vs the reference vehicle speed over ground, but the event could be very transient (finished in 100 milliseconds). Passing the same torque reduction at the same dynamic to the other side wheel could cause an unnecessary perceptible thump. One of the calibration approaches could be to configure the timer duration and / or the blend rate in dependence on the magnitude of the torque reduction on the other side wheel than that of the host EDU, to always have a minimum debounce time to avoid reacting to very transient events.When the imbalance limiting function 521 in each inverter determines that the difference limit condition is not satisfied, conditions may be in place to control whether the left or right (or both / neither) torque requests 516 are modified, and by what amount. These conditions are set out below.

[0188] Firstly, the imbalance limiting function 521 for the host EDU can modify the torque request 516 of the host EDU but not the torque request 518 for the other EDU.

[0189] Secondly, the imbalance limiting function 521 is configured to modify the torque request 516 towards satisfaction of the difference limit condition, in other words towards the limit 702UL or702LL that was passed, which could mean either increasing or decreasing the difference ATq in dependence on whether the difference ATq is above the upper limit 702UL or below the lower limit 702LL.

[0190] Thirdly, the inverter controller 336, 338 may be prohibited from increasing a magnitude of the torque request 516 from zero, and only reducing the magnitude towards zero. Therefore, if the imbalance limiting function 521 for one of the EDUs 208A, 208B determines that it is unable to bring the torque request 516 within the limits 702UL, 702LL by decreasing its magnitude, then the imbalance limiting function 521 may pass through the torque request 516 unmodified. The other imbalance limiting function 521 for the other EDU 208A or 208B may perform the same check. Therefore, the modification of the torque request 516 is performed by whichever one of the imbalance limiting functions 521 can reduce the torque request 516 towards zero and change the difference ATq towards satisfaction of the difference limit condition. If neither of the functions 521 can comply, then both arbitrated torque requests 516 may be passed through / unmodified despite their torque imbalance being outside the limits 702UL, 702LL.

[0191] The limits 702UL, 702LL may be obtained by the inverter controller 336, 338 receiving a signal 519 from an upstream controller 331 of the control system that determines the limits 702UL, 702LL. Alternatively, or additionally, the inverter controller 301 may obtain the limits 702UL, 702LL by determining them locally.

[0192] Regarding signalling, the imbalance limiting function 521 of FIG. 5 may receive a plurality of signals:

[0193] - signals 516, 518 indicative of the arbitrated torque requests 516 for the EDUs 208A and 208B;

[0194] - at least one signal 519 indicative of the upper and lower torque vectoring limits 702UL, 702LL; and

[0195] - optionally, signals 517, 520 indicative of the pre-arbitrated torque requests 508 for the EDUs 208A and 208B, if the limits 702UL, 702LL are calculated or recalculated locally at the imbalance limiting function 521.

[0196] The signals 516, 518, and 519 allow the difference ATq between the torque requests 516, 518 to be determined, and compared with the limits 702UL, 702LL, as described above.

[0197] A numerical example of the above-described methodology at the imbalance limiting function 521 is provided below:

[0198] Determine allowable imbalance:

[0199] Left pre-arbitrated torque request 508 for EDU 208A = +150Nm

[0200] Right pre-arbitrated torque request 508 for EDU 208B = +50Nm

[0201] Modified requested torque imbalance 603 = Left - Right = +100Nm

[0202] Positive deviation allowed = +50Nm (oversteer)Negative deviation allowed = -75Nm (understeer)

[0203] Post-arbitration upper torque vectoring limit 702UL = 100 + 50 = 150Nm

[0204] Post-arbitration lower torque limit vectoring 702LL = 100 - 75 = 25Nm

[0205] Detect post-arbitration imbalance:

[0206] Left Arbitrated Torque Request 516 / 518 = [[+150Nm]] +70Nm (e.g. due to traction control)

[0207] Right Arbitrated Torque Request 516 / 518 = +50Nm

[0208] Difference ATq = Requested Arbitrated Torque Imbalance = Left - Right = 70 - 50 = +20 Nm

[0209] 20Nm is outside the limits 25 - 150Nm

[0210] Intervention:

[0211] Right Modified Torque Request = [[+50Nm]] +45Nm

[0212] Imbalance is now 25Nm which is within the limits 25 - 150Nm.

[0213] The logic and routines described above provide a technical effect that torque is distributed in a similar manner to a mechanical limited slip differential, except electronically and considering a plurality of variables. Furthermore, torque imbalance limits are determined as variables to allow yaw rates to increase in certain situations but not others. Furthermore, torque imbalance control may not be solely performed at the VSC 311, and is split between the VSC 331 and the inverter controllers 336, 338 with the latter performing the steps that require fast control loops (without use of the vehicle communication network) to allow precise and optimal control.

[0214] Finally, it should be noted that the illustrated imbalance limiting function 521 has a higher priority than the arbitration function 515, meaning it is downstream of the function 515 and arbitrates the output 516 of the function 515 to ensure that imbalance limits are respected.

[0215] Although the post-arbitration upper and lower torque vectoring limits 702UL, 702LL are shown in FIG. 7 as relative quantities (offsets) relative to the modified requested torque imbalance 603, this encompasses signals comprising either relative or absolute quantities (603+702UL; 603+702LL).

[0216] FIG.5 further illustrates optional torque-shaping functions downstream of the imbalance limiting function 521 , outside the scope of this disclosure. Once the last torque-shaping function has been executed, a torque control signal block 536 is executed. The torque control signal block 536 is configured to output a control signal 557 (torque control signal) to the inverter 206 in dependence on the torque request output from the final torque shaping function. In use, at least one of the torque control signals is dependent on a modified torque request 554 that has been modified by the imbalance limiting function 521, when the imbalance limiting function 521 has determined that the difference limit condition is not satisfied.

[0217] The block 536 may comprise a torque-to-current block configured to determine the control signal 557 in the form of gate control signals (electrical currents) to control the gate control section of the inverter 206.

[0218] FIGS. 3 and 5 also set a particular order of the functions / limiters. Reasons are given earlier in the document about why some functions / limiters may advantageously come before or after others. If an advantage is not specified, then there is no reason for the order to be as described. Furthermore, even if an advantage to a particular order has been mentioned, this does not mean that this order / priority is essential for all implementations of the invention.FIG. 8 illustrates a flowchart setting out an example method 800 according to an embodiment of the invention. The method 800 is a method of for controlling a drive torque split between left and right wheels of a vehicle 1 , such as the vehicle 1 illustrated in FIG. 1. In particular, the method 800 is a torque arbitration method. In particular, the memory 306 may comprise computer-readable instructions 308 which, when executed by the processor 304, perform the method 800. The method 800 is hosted in each inverter controller 336, 338 of the control system 300 illustrated in FIG. 3A and 4.

[0219] At block 802, the method 800 comprises receiving a left torque request 516 / 518 for a first electric machine 208A coupled to the left wheel of the vehicle 1. As described above, the torque request 516 / 518 may be an arbitrated torque request from an arbitration function 515 for the left EDU 208.

[0220] At block 804, the method 800 comprises receiving a right torque request 516 / 518 for a second electric machine 208B coupled to the right wheel of the vehicle 1. As described above, the torque request 516 / 518 may be an arbitrated torque request from an arbitration function 515 for the left EDU 208.

[0221] At block 806, the method 800 comprises determining a difference ATq between the left and right torque requests 516, 518. For example, one may be subtracted from the other.

[0222] At block 807, the method 800 comprises determining whether the difference ATq satisfies the difference limit condition. For example, block 807 may determine whether the difference ATq between the requests 516, 518, in other words the arbitrated requested amount of torque vectoring, is within the post-arbitration upper and lower torque vectoring limits 702UL, 702LL. The post-arbitration upper and lower torque vectoring limits 702UL, 702LL may be received by the inverter controller 336, 338 from the VSC 331. Alternatively, or additionally, the limits 702UL, 702LL may be determined by the inverter controller 336, 338 locally.

[0223] In some implementations, the limits 702UL, 702LL do not exist and instead the limits 602UL, 602LL define the difference limit condition. In some implementations, the difference limit condition comprises only an upper limit, or only a lower limit. In some implementations, the limit or limits are fixed predetermined values, and are not calculated.

[0224] At block 808, the method 800 comprises determining a torque request 554, which is a modified torque request 554 for increasing or decreasing the difference ATq in dependence on the difference ATq not satisfying the difference limit condition. If the condition is satisfied, block 808 may determine an unmodified torque request 554. The modification is with respect to the torque request 516 for the EDU 208A or 208B associated with the inverter controller 336 or 338.

[0225] At block 810, the method 800 comprises the inverter controller 336 or 338 outputting a torque control signal for the first electric machine. One of the inverter controllers 336 sends a first torque control signal, and the other sends a second torque control signal. One of the first and second torque control signals is dependent on the modified torque request, if the difference ATq does not satisfy the difference limit condition.

[0226] In some implementations, the control system 300 further comprises an imbalance limiting monitor. The imbalance limiting monitor is configured to receive data indicative of a torque delivered to the left drive wheel of the vehicle 1 in response to the first torque control signal, and data indicative of torque delivered to the right drive wheel of the vehicle 1 in response to the second control signal. The imbalance limiting monitor is configured to determine a difference between the torque delivered tothe left drive wheel and the torque delivered to the right drive wheel, and determine whether the difference satisfies the difference limit condition. The difference limit condition may be the same difference limit condition used by the imbalance limiting function 521, against which the post-arbitration torque vectoring ATq is assessed.

[0227] The control system 300 is configured to output a command to place the first and / or second electric machines into a safe state if the difference between the torque delivered to the left drive wheel and the torque delivered to the right drive wheel does not satisfy the difference limit condition. Placing the first and / or second electric machines into a safe state may comprise preventing torque production by the first and / or second machines (e.g. by placing the respective inverters 206 into a six-switch open state), or for example, initiating a controlled shutdown. In some implementations, the first and / or second electric machines may be placed in the safe state if the difference between the torque delivered to the left and right drive wheels does not satisfy the difference limit condition for a predetermined period of time. Alternatively, or additionally, the first and / or second electric machines may be placed in the safe state if the difference between the torque delivered to the left and right drive wheels does not satisfy the difference limit condition by a threshold magnitude.

[0228] In some implementations, the imbalance limiting monitor may be hosted outside of the inverters 206, for example the imbalance limiting monitor may form part of the VSC 331. In alternative implementations, the imbalance limiting monitor may be alternatively or additionally hosted within the inverters 206, for example forming part of the inverter controllers 336, 338.

[0229] 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.

[0230] 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.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.

[0231] 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 programmable processing 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.

[0232] 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.

[0233] The blocks illustrated in FIG. 5 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.

[0234] 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 split between left and right wheels of a vehicle, the control system comprising one or more processors collectively configured to:receive a left torque request for a first electric machine coupled to the left wheel;receive a right torque request for a second electric machine coupled to the right wheel;determine a difference between the left and right torque requests;determine whether the difference satisfies a difference limit condition;determine a modified torque request for increasing or decreasing the difference, in dependence on the difference not satisfying the difference limit condition;output a first torque control signal for the first electric machine; andoutput a second torque control signal for the second electric machine, andwherein one of the first and second torque control signals is dependent on the modified torque request, if the difference does not satisfy the difference limit condition.

2. The control system of claim 1, configured to determine or receive upper and lower torque vectoring limits (702UL, 702LL) relative to a target vehicle yaw, and wherein the difference limit condition is dependent on the upper and lower torque vectoring limits.

3. The control system of claim 2, wherein an asymmetry of the upper and lower torque vectoring limits about the target vehicle yaw is dependent on at least one of: a magnitude of the target vehicle yaw; vehicle speed; or a difference between the target vehicle yaw and an initially requested vehicle yaw.

4. The control system of claim 3, wherein the lower torque vectoring limit is further from the target vehicle yaw than the upper torque vectoring limit in dependence on the target vehicle yaw being positively offset from the initially requested vehicle yaw, and wherein the upper torque vectoring limit is further from the target vehicle yaw than the lower torque vectoring limit in dependence on the target vehicle yaw being negatively offset from the initially requested vehicle yaw.

5. The control system of any one of claims 2, 3, or 4, wherein the upper torque vectoring limit is dependent on a difference between the target vehicle yaw and an initial upper yaw limit, and wherein the lower torque vectoring limit is dependent on a difference between the target vehicle yaw and an initial lower yaw limit.

6. The control system of any preceding claim, wherein the imbalance limit condition is dependent on one or more of the following sensed parameters:vehicle speed;a drive mode of the vehicle;foundation braking of the vehicle;a steering angle of the vehicle; orlateral acceleration of the vehicle.

7. The control system of claim 5 and claim 6, wherein the initial upper and lower yaw limits are dependent on one of more of the sensed parameters.

8. The control system of any preceding claim, wherein the difference limit condition comprises a range, wherein the difference limit condition is satisfied in dependence on the difference being within the range.

9. The control system of any preceding claim, wherein the left and right torque requests are arbitrated left and right torque requests output by arbitration functions for each of the first and second electric machines, wherein:the arbitration function for the first electric machine is configured to determine the left arbitrated torque request in dependence on a pre-arbitrated left torque request and a set of one or more first torque restrictions, andthe arbitration function for the second electric machine is configured to determine the right arbitrated torque request in dependence on a pre-arbitrated right torque request and a set of one or more second torque restrictions.

10. The control system of claim 9, wherein:the set of one or more first torque restrictions comprises a first torque limit associated with a torque requirement of the first electric machine,the set of one or more second torque restrictions comprises a second torque limit associated with a torque requirement of the second electric machine, andat least one of the arbitrated left and right torque requests is modified by the corresponding first or second torque vectoring limit.

11. The control system of any preceding claim, wherein the determination of the modified torque request is allowed to reduce a magnitude of one of the left and right torque requests towards zero, and is prohibited from increasing the magnitude from zero, and wherein the modified torque request is determined for whichever one of the first and second torque control signals is able to be reduced towards zero and change the difference towards satisfaction of the difference limit condition.

12. The control system of any preceding claim wherein the one or more processors are further collectively configured to:receive data indicative of a torque delivered to the left wheel of the vehicle in response to the first torque control signal;receive data indicative of a torque delivered to the right wheel of the vehicle in response to the second torque control signal;determine a difference between the torque delivered to the left wheel of the vehicle and the torque delivered to the right wheel of the vehicle;determine whether the difference satisfies the difference limit condition; andoutput a command to place the first and / or second electric machine into a safe state if the difference between the torque delivered to the left wheel of the vehicle and the torque delivered to the right wheel of the vehicle does not satisfy the difference limit condition.

13. The control system of any preceding claim, wherein at least one of the processors is hosted in an inverter for the first electric machine, or at least one of the processors is hosted in an inverter (206) for the second electric machine, or a combination thereof.

14. A vehicle comprising the control system of any one of the preceding claims.

15. A method of controlling a drive torque split between left and right wheels of a vehicle, the method comprising:receiving a left torque request for a first electric machine coupled to the left wheel;receiving a right torque request for a second electric machine coupled to the right wheel;determining a difference between the left and right torque requests;determining whether the difference satisfies a difference limit condition;determining a modified torque request for increasing or decreasing the difference, in dependence on the difference not satisfying the difference limit condition;output a first torque control signal for the first electric machine; andoutput a second torque control signal for the second electric machine, andwherein one of the first and second torque control signals is dependent on the modified torque request, if the difference does not satisfy the difference limit condition.Tl

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