Vehicle deceleration torque control in low friction conditions

Abstract

Aspects of the present invention relate to a control system for use in control of a foundation brake system and an electric powertrain of a vehicle during single-pedal driving, the control system comprising one or more processors collectively configured to: receive a first signal indicative of modulation of an accelerator pedal by a driver; in dependence on receiving the first signal, determine a deceleration torque demand; receive a second signal indicative of a stability control event being identified; in dependence on receiving the second signal: determine an electric powertrain deceleration torque limit; determine if the deceleration torque demand exceeds the electric powertrain deceleration torque limit; in dependence on determining that the deceleration torque demand exceeds the electric powertrain deceleration torque limit, generate a foundation brake torque request signal to cause the foundation brake system to provide deceleration torque to achieve the deceleration torque demand.

Description

[0001] VEHICLE DECELERATION TORQUE CONTROL IN LOW FRICTION CONDITIONS

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to deceleration torque control. More particularly the present disclosure relates to deceleration torque control in low friction conditions. Aspects of the invention relate to a control system, to a system, a vehicle, a method and to computer readable instructions.

[0004] BACKGROUND

[0005] It is known for some vehicles having an electric powertrain, for example hybrid vehicles, Plug-in Hybrid Electric Vehicles (PHEV), and Battery Electric Vehicles (BEV), to have an operation mode known as “single pedal driving”, or “one pedal driving”. In such an operation mode the electric powertrains are capable of providing deceleration torque, for example during regenerative braking. In such a mode of operation it is known to provide electric powertrain deceleration torque (or “negative torque”) when a driver modulates an accelerator pedal / input, such that the vehicle can be slowed or brought to a stop by the driver in a controlled manner using only the accelerator pedal / input (that is, without making an input to a foundation brake system on the vehicle). For example, in the context of a car, a driver lifting an accelerator pedal is used to instruct the electric powertrain to provide “negative” or deceleration torque, thereby reducing the car’s speed. Deceleration torque provided by the electric powertrain in response to a driver modulating the accelerator pedal / input is known as “overrun”.

[0006] When a vehicle provides single pedal driving, there is the potential that the user is expecting a certain overrun behaviour. However, when the vehicle is being driven in low friction conditions (for example when a vehicle is being driven over a wet surface, a loose surface, ice, snow, mud, etc.) there is the potential that the deceleration torque supplied by the electric powertrain results in an altered driving feel, or experience, compared with that which the user was expecting.

[0007] It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

[0008] SUMMARY OF THE INVENTION

[0009] Aspects and embodiments of the invention provide a control system for use in control of a foundation brake system and an electric powertrain of a vehicle during single-pedal driving, a system, a vehicle, a method for controlling a foundation brake system and an electric powertrain of a vehicle during single-pedal driving, and computer readable instructions as claimed in the appended claims.

[0010] According to an aspect of the present invention there is provided a control system for use in control of a foundation brake system and an electric powertrain of a vehicle during single-pedal driving. The control system is configured to (for example via one or more processors): receive or obtain a first signal indicative of modulation of an accelerator pedal (or other accelerator input) by a driver; in dependence on (for example responsive to) receiving or obtaining the first signal, determine / identify a deceleration torque demand; receive or obtain a second signal indicative of a stability control event being identified; in dependence on (for example responsive to) receiving or obtaining the second signal: determine / identify an electric powertrain deceleration torque limit; determine / identify if the deceleration torque demand exceeds the electric powertrain deceleration torque limit; in dependence on (for example responsive to) determining that the deceleration torque demand exceeds the electric powertrain deceleration torque limit, cause the foundation brake system to provide deceleration torque to achieve at least part of the deceleration torque demand (for example via generating a foundation brake torque request signal).

[0011] According to another aspect of the present invention, there is provided a control system for use in control of a foundation brake system and an electric powertrain of a vehicle during single-pedal driving. 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:

[0012] • receive a first signal indicative of modulation of an accelerator pedal (or other accelerator / throttle input) by a driver;

[0013] • in dependence on receiving the first signal, determine a deceleration torque demand;

[0014] • receive a second signal indicative of a stability control event being identified;

[0015] • in dependence on receiving the second signal:

[0016] • determine an electric powertrain deceleration torque limit;

[0017] • determine if the deceleration torque demand exceeds the electric powertrain deceleration torque limit;

[0018] • in dependence on determining that the deceleration torque demand exceeds the electric powertrain deceleration torque limit, generate a foundation brake torque request signal to cause the foundation brake system to provide deceleration torque to achieve the deceleration torque demand.

[0019] Optionally, the one or more processors are collectively configured to generate an electric powertrain deceleration torque request signal to cause the electric powertrain to provide deceleration torque, less than the electric powertrain deceleration torque limit, to achieve the deceleration torque demand in combination with the foundation brake system.

[0020] Advantageously, by transferring at least some of the requested deceleration torque away from the electric powertrain and onto the foundation brakes during overrun, the invention reduces the possibility of the wheels being counter rotated to the direction of travel of the vehicle by the electric powertrain in low friction conditions, for example when the road is icy. The deceleration behaviour of the vehicle during overrun in low friction conditions may thus feel closer to driver expectation for low friction conditions.

[0021] In an embodiment, the stability control event: corresponds to a wheel slip condition of one or more vehicle wheels; and / or is based on a user selected drive mode.

[0022] In another embodiment, the one or more controllers are collectively configured to receive the second signal prior to the first signal. Advantageously, the invention thus allows for both reactive and pre-emptive modification of overrun deceleration behaviour. In yet another embodiment, the one or more processors are collectively configured to: determine that a predefined period of time has elapsed since receiving the second signal; in dependence on determining that the predefined period of time has elapsed since receiving the second signal: generate the foundation brake torque request signal to cause the foundation brake system to stop providing deceleration torque; and generate a powertrain torque request signal to cause the electric powertrain to provide deceleration torque to achieve the deceleration torque demand.

[0023] Advantageously, this allows for dynamic adjustment of overrun deceleration behaviour according to changing road conditions.

[0024] In a further embodiment, the one or more processors are collectively configured to: receive a third signal indicative of a stability control intervention being performed by a stability control system of the vehicle; in dependence on receiving the third signal: generate the powertrain torque request signal to cause the electric powertrain to stop providing deceleration torque; and generate the foundation brake torque request signal to cause the foundation brake system to provide deceleration torque corresponding to a full amount of the deceleration torque demand.

[0025] Advantageously, this process further dynamically adjusts of the level of overrun deceleration torque intervention responsive to changes in the coefficient of friction between the vehicle’s wheels and the surface being driven on.

[0026] In yet another aspect of the invention, there is provided a system comprising the control system above; the electric powertrain; and the foundation brake system.

[0027] In a further aspect of the invention, there is provided a vehicle comprising the system or the control system above.

[0028] In a further aspect of the invention, there is provided a method for controlling a foundation brake system and an electric powertrain of a vehicle during single-pedal driving, the method comprising: receiving a first signal indicative of modulation of an accelerator pedal by a driver; in dependence on receiving the first signal, determining a deceleration torque demand; receiving a second signal indicative of a stability control event being identified; in dependence on receiving the second signal: determining an electric powertrain deceleration torque limit; determining if the deceleration torque demand exceeds the electric powertrain deceleration torque limit; in dependence on determining that the deceleration torque demand exceeds the electric powertrain deceleration torque limit, generating a foundation brake torque request signal to cause the foundation brake system to provide deceleration torque to achieve the deceleration torque demand.

[0029] Optionally the method comprises generating an electric powertrain deceleration torque request signal to cause the electric powertrain to provide deceleration torque, less than the electric powertrain deceleration torque limit, to achieve the deceleration torque demand in combination with the foundation brake system. Advantageously, by transferring at least some of the requested deceleration torque away from the electric powertrain and onto the foundation brakes during overrun, the invention reduces the possibility of the wheels being rotated counterto the direction of travel of the vehicle by the electric powertrain in low friction conditions. The deceleration behaviour of the vehicle during overrun in low friction conditions may thus feel closer to driver expectation for low friction conditions.

[0030] In an embodiment, the stability control event: corresponds to a wheel slip condition of one or more vehicle wheels; and / or is based on a user selected drive mode.

[0031] In another embodiment the method comprises receiving the second signal prior to receiving the first signal. Advantageously, the invention thus allows for both reactive and pre-emptive modification of overrun deceleration behaviour.

[0032] In yet another embodiment, the method comprises: determining that a predefined period of time has elapsed since receiving the second signal; in dependence on determining that the predefined period of time has elapsed since receiving the second signal: generating the foundation brake torque request signal to cause the foundation brake system to stop providing deceleration torque; and generating a powertrain torque request signal to cause the electric powertrain to provide deceleration torque to achieve the deceleration torque demand. Advantageously, this allows for dynamic adjustment of overrun deceleration behaviour according to changing road conditions.

[0033] In a still further embodiment, the method comprises: receiving a third signal indicative of a stability control intervention being performed by a stability control system of the vehicle; in dependence on receiving the third signal: generating the powertrain torque request signal to cause the electric powertrain to stop providing deceleration torque; and generating the foundation brake torque request signal to cause the foundation brake system to provide deceleration torque corresponding to a full amount of the deceleration torque demand. Advantageously, this further dynamically adjusts of the level of overrun deceleration torque intervention responsive to instantaneous reductions in the coefficient of friction between the vehicle’s wheels and the surface being driven on.

[0034] In a still further aspect of the invention, there is provided computer readable instructions which, when executed by a computer, are arranged to perform a method above.

[0035] 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 is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0037] Figure 1 shows a vehicle in accordance with an embodiment of the invention;

[0038] Figure 2 shows a schematic representation of the vehicle of Figure 1 in accordance with an embodiment of the invention; and

[0039] Figures 3A, 3B and 3C show flow charts for controlling the foundation brake system and the electric powertrain of the vehicle of Figure 1 in accordance with an embodiment of the invention

[0040] Figure 4 shows a graph showing an example transition between electric powertrain deceleration torque and foundation brake deceleration torque using the method of Figures 3A to 3C.

[0041] DETAILED DESCRIPTION

[0042] A vehicle 10 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figures 1 and 2.

[0043] With reference to Figure 2, the vehicle 10 of Figure 1 is illustrated schematically. The vehicle 10 includes a control system 100, a foundation brake system 110 and an electric powertrain 120.

[0044] The foundation brake system 1 10 comprises one or more brake assemblies 112, configured to controllably apply braking torque to one or more wheels 20. It will be appreciated that the type of brake assemblies 112 may be chosen according to the braking characteristics of the vehicle. The one or more brake assemblies 112 may include any system which decelerates the vehicle by converting kinetic energy of the vehicle into heat, as opposed to a regenerative brake, such as may be provided by an electric machine. In some embodiments, the brake assemblies 112 are friction brakes (for example comprising a calliper configured to press pads against a disc rotating with the wheel 20 as known in the art). In some embodiments, the brake assemblies 112 are eddy current brakes.

[0045] The foundation brake system 110 further comprises a brake controller 114. The brake controller 114 is configured to control actuation of the brake assemblies 112. The brake controller 114 is optionally part of an automatic brake system (ABS).

[0046] The vehicle 10 comprises an electric powertrain 120. The electric powertrain 120 comprises at least one electric machine 122. The electric machine 122 is an electric motor arranged to convert electrical energy into kinetic energy in the form of mechanical torque and is also arranged to convert kinetic energy in the form of torque applied by the wheels of the moving vehicle into electrical energy (for example during regenerative braking). The electric machine 122 may be an alternating current induction motor or a permanent magnet motor, or another type of suitable electric machine. The electric machine 122 is a traction motor to drive the vehicle 10. Another term for the electric machine 122 is an electric drive unit (EDU).

[0047] The electric machine 122 is configured to drive at least one of the wheels 20 (typically at least two wheels 20, and optionally four wheels 20 as illustrated), for example via a transmission output shaft 124 and one or more sets of gears 126 (for example one or more differentials or transaxles) as shown in Figure 2. In alternative embodiments, a plurality of electric machines 122 may be provided, with each electric machine driving a respective wheel 20 or axle.

[0048] The electric powertrain 120 optionally further comprises a powertrain controller 128 configured to control operation of the electric machine 122.

[0049] The vehicle 10 also comprises an electrical energy storage 130, for example a traction battery. The electrical energy storage 130 is configured to deliver electrical energy to the electric machine 122 when the electric machine is driving one or more wheels 20, and to receive and store electrical energy generated by the electric machine (for example during regenerative braking). The electric machine 122 is electrically connected to the electrical energy storage 130, optionally by an inverter (not shown). In some embodiments, the electrical energy storage 130 is communicatively coupled to the powertrain controller 128. The electrical energy storage 130 is optionally a high voltage battery. The traction battery 130 may have a voltage and capacity to support electric only driving for sustained distances. The traction battery 130 may have a capacity of several kilowatt- hours, to increase range. The capacity may be in the tens of kilowatt-hours, or even over a hundred kilowatt- hours.

[0050] The vehicle 10 optionally further comprises a vehicle stability control system 140. As illustrated, the vehicle stability control system 140 is communicatively coupled to the foundation brake controller 114 and the control system 100. It will be appreciated that in other embodiments the foundation brake controller 114, and / or the electric powertrain controller 128 may be part of the vehicle stability control system 140, or vice versa. The vehicle stability control system 140 is configured to monitor for wheel slip (for example over-rotation or underrotation of one or more vehicle wheels 20 as compared to expected wheel rotation speeds) and other conditions indicative of a vehicle stability event (for example via one or more wheel sensors and yaw acceleration sensors). The vehicle stability control system 140 can also be configured to monitor for user selection of vehicle drive modes, such as a winter driving mode - selection of certain vehicle drive modes configured for driving the vehicle on low friction surfaces, are taken to be vehicle stability control events.

[0051] The control system 100 as illustrated in Figure 2 comprises one controller 101 , although it will be appreciated that this is merely illustrative. The controller 101 comprises processing means 102 and memory means 103. The processing means 102 may be one or more electronic processing device 102 which operably executes computer-readable instructions. The memory means 103 may be one or more memory device 103. The memory means 103 is electrically coupled to the processing means 102. The memory means 103 is configured to store instructions, and the processing means 102 is configured to access the memory means 103 and execute the instructions stored thereon. Optionally the control system 100 is, or is part of, the powertrain controller 128 or the foundation brake controller 1 14.

[0052] The controller 101 comprises an input means 104 and an output means 105. The input means 104 may comprise an electrical input of the controller 101. The output means 105 may comprise an electrical output of the controller. The input 104 is arranged to receive signals from other components in the vehicle 10, for example from powertrain controller 128 and foundation brake controller 114. In some embodiments, the received signals are electrical signals indicative of, for example, modulation of an accelerator pedal, a stability control event having been detected, a stability control intervention having been performed / instigated, among other things, as described in more detail below. The output 105 is arranged to output control signals, for example electrical signals comprising foundation brake torque requests and electric powertrain deceleration torque requests as described in more detail below. The stability control event may correspond to dynamic events such as one or more wheels 20 being in a wheel slip condition, loss of traction etc. In some examples, the stability control event may be based at least in part on a user-selected drive mode. For example, the user has selected a winter drive mode, or another mode used when the vehicle is expected to be driven on low friction surfaces.

[0053] The control system 100 is configured to control operation of the foundation brake system 110 and the electric powertrain 120 during single pedal driving of the vehicle 10. As used herein, “single pedal driving” refers to a driver controlling deceleration of the vehicle 10 via operation of an accelerator input (for example an accelerator pedal) only, that is to say without operation of a brake input (for example a brake pedal). Active deceleration during single pedal driving is also called overrun. It is noted that although the driver has the ability to control deceleration of the vehicle via modulation of the accelerator pedal / input during single pedal driving, the driver is still able to separately modulate a brake pedal / input to further control deceleration of the vehicle. The present invention is primarily described in relation to driver modulation of an accelerator pedal, however, it will be appreciated that the present invention may also be applied to driver modulation of a different accelerator input, for example a hand-operated throttle as typically found on motorcycles.

[0054] In some prior art vehicles, in low friction environments (for example when driving on snow or ice), deceleration torque applied by an electric powertrain during regenerative braking may result in the wheels slipping, and in some cases rotating in a direction counter to the direction of travel of the vehicle. In such situations, the feel or behaviour of the vehicle may be different to that which the driver is expecting.

[0055] In contrast, as described in detail below, the present invention selectively causes at least some deceleration torque to be provided by foundation brakes instead of the electric powertrain in these situations. This reduces, and preferably eliminates, the wheel slippage and counter rotation. Advantageously, the feel and / or behaviour of the vehicle more closely match the driver’s expectations.

[0056] Figure 3A illustrates a method 300 according to an embodiment of the invention. The method 300 is a method of controlling a foundation brake system and an electric powertrain of a vehicle 10, such as the vehicle 10 illustrated in Figures 1 and 2. In particular, the method 300 is a method of controlling a foundation brake system 110 and an electric powertrain 120 of a vehicle 10 during single-pedal driving, in particular when the vehicle is being driven on low friction surfaces, such as ice or an icy road. The method 300 may be performed by the control system 100 illustrated in Figure 2. In particular, the memory 103 may comprise computer- readable instructions which, when executed by the processor 102, perform the method 300 according to an embodiment of the invention. The method 300 starts at step S-302, in which a first signal indicative of modulation of an accelerator pedal (or other accelerator input device) by a driver is received. In one example, the control system 100 receives the first signal from the powertrain controller 128 or another system within the vehicle 10. The first signal is generated in response to the driver modulating the accelerator pedal in such a way as to indicate that deceleration of the vehicle is required (for example by partially or completely lifting an accelerator pedal that is normally depressed against a spring bias to indicate a desire to accelerate the vehicle).

[0057] At step S-304, in dependence on receiving the first signal, a deceleration torque demand is determined. The deceleration torque demand is based on the driver’s modulation of the accelerator pedal, and represents the negative torque that would have to be applied to the wheels 20 in order to slow the vehicle 10 in a manner corresponding to the driver’s modulation of the accelerator pedal. In some embodiments, the deceleration torque demand is based on a predetermined deceleration profile. For example, the predetermined deceleration profile determines how modulation of the accelerator pedal by the driver (for example at a particular speed of the vehicle) maps to a particular deceleration (“overrun”) behaviour of the vehicle 10. Advantageously, the use of predefined profiles helps to ensure that the overrun behaviour of the vehicle 10 is consistent across different driver inputs via the accelerator pedal.

[0058] In some examples, different predetermined profiles can be selected, for example according to a user-selected drive mode. For example, the vehicle 10 may provide a first user-selectable drive mode having a predetermined profile corresponding to relatively high deceleration on lifting the accelerator pedal, so as to increase energy recovered and provided to the electrical energy storage 130 via regenerative braking, and a second user-selectable drive mode having a predetermined profile corresponding to lower deceleration when the driver lifts the accelerator pedal.

[0059] In one example, the control system 100 calculates a deceleration torque demand (for example in accordance with the predetermined profile) based on information contained in the first signal. In another example, the deceleration torque demand is calculated by another system within the vehicle 10 (for example the powertrain controller 128), said other system indicating the deceleration torque demand in the first signal. In this latter case, the control system 100 determines the deceleration torque demand by reading / identifying the deceleration torque demand in the first signal.

[0060] At step S-305, a second signal is received (for example by the control system 100). The second signal is indicative of a stability control event being identified. The stability control event may correspond to one or more wheels 20 being in a wheel slip condition (that is, one or more wheels 20 are rotating faster or slower than would be expected for a current speed of the vehicle 10), or to a yaw sensor or other sensor indicating that the vehicle 10 on a low friction surface and / or experiencing a loss of traction. In some examples, the vehicle stability control system 140 determines, or detects, that a stability control event has occurred and sends the second signal to the control system 100. If the stability control event is determined to be significant enough, the stability control system 140 may also instigate a stability control intervention (for example operating an automatic brake system and / or traction control system) as is known in the art. In some examples, the stability control event may be based at least in part on a user-selected drive mode. For example, the second signal may indicate that a user has selected a winter drive mode, and that therefore low friction surfaces should be expected.

[0061] In dependence on receiving the second signal, step S-306 is performed. As described in detail below with reference to Figure 3B step S-306 is equivalent to step S-324. At step S-306 an electric powertrain deceleration torque limit is determined. The electric powertrain deceleration torque limit is optionally a predetermined value or selected from one or more predetermined values. The electric powertrain deceleration torque limit may also depend on the type of stability control event: for stability control events where no stability control intervention is required, the electric powertrain deceleration torque limit is optionally non-zero; for stability control events where a stability control intervention is required, the electric powertrain deceleration torque limit is optionally zero.

[0062] At step S-307, it is determined (for example by the control system 100) whether the deceleration torque demand exceeds the electric powertrain deceleration torque limit. If the deceleration torque demand does not exceed the electric powertrain deceleration torque limit, the method proceeds to step S-309, in which a signal is generated (for example by the control system 100) and sent to the powertrain controller 128 so as to cause the powertrain 120 to provide the deceleration torque demand in full (for example through regenerative braking).

[0063] If the deceleration torque demand exceeds the electric powertrain deceleration torque limit, the method proceeds to step S-312. A foundation brake torque request signal is generated (for example by the control system 100) to cause the foundation brake system 110 to provide deceleration torque to achieve the deceleration torque demand. In the case of friction brake assemblies 1 12, deceleration torque is applied to the wheels via pressing brake pads against a brake disc to provide additional mechanical resistance to rotation of the wheels 20 when the vehicle is in motion, the pressure between the brake disc and the brake pads determining the amount of resistance and thus the amount of deceleration torque. Other types of brake assembly 1 12 can analogously apply deceleration torque to the wheels through providing varying amounts of resistance to rotation of the wheels 20 when the vehicle 10 is in motion.

[0064] The foundation brake torque request signal is sent to the foundation brake system 110, for example to foundation brake controller 114, causing the brake assemblies 112 to apply an amount of deceleration torque to the wheels 20 such that overall, the deceleration demand is met.

[0065] Advantageously, moving at least some of the deceleration torque away from the electric powertrain and onto the foundation brakes in this manner reduces the possibility of the wheels 20 being rotated counter to the direction of travel of the vehicle 10 by the electric powertrain in low friction conditions. The deceleration behaviour of the vehicle 10 during overrun in low friction conditions may thus feel closer to driver expectation for low friction conditions.

[0066] In some examples, the foundation brake system 110 may provide deceleration torque corresponding to the entirety of the deceleration torque demand. In some examples, the foundation brake system 110, responsive to the foundation brake torque request signal, provides deceleration torque corresponding to the entirety of the deceleration torque demand, when the control system 100 determines (e.g., based on a signal from the vehicle stability control system 140) that a stability control intervention (e.g., activating ABS) has been instigated.

[0067] Alternatively, an electric powertrain deceleration torque request signal is also generated at step S-314 (for example by the control system 100) to cause the electric powertrain 120 to provide deceleration torque to achieve the deceleration torque demand in combination with the foundation brake system 110 (e.g., if a stability control event has been detected but no stability control intervention has been instigated). For example the control system 100 may send the electric powertrain deceleration torque request signal to the powertrain controller 128, thereby causing the electric powertrain 120 to provide a non-zero deceleration torque (up to a maximum corresponding to the electric powertrain deceleration torque limit), and send the foundation brake torque request signal to the foundation brake controller 114, thereby causing the foundation brake system 110 to provide deceleration torque corresponding to the deceleration torque demand less the deceleration torque provided by the electric powertrain 120.

[0068] Although Figure 3A shows step S-305 following step S-304, the order of these steps in other examples is reversed. Put differently, in some examples, the second signal (i.e., the stability control event signal) is handled before the first signal. Accordingly, the invention is advantageously both reactive (action is taken if a stability control event is detected during single pedal driving overrun) and pre-emptive (detection of a stability control event prior to single pedal driving overrun still results in modified behaviour when the single pedal driving overrun later occurs). As noted above, in some embodiments, the stability control event corresponds to a driver selecting a particular drive mode (for example a winter mode), thus the pre-emptive behaviour exhibited by the vehicle can advantageously be triggered according to user-selected drive mode, in addition to other stability control events (for example wheel slip).

[0069] Figure 3B illustrates an example in which, the control system 100 is only configured to move at least some of the deceleration torque away from the electric powertrain and onto the foundation brakes for a limited time after receipt of the second, stability control event signal. Such an example can be implemented when the system is acting pre-emptively, and the vehicle has undergone a stability control event. By moving at least some of the deceleration torque to the foundation brakes for a limited time after a stability control event the vehicle therefore pre-empts the likely occurrence of a subsequent, further, stability control event.

[0070] At optional step S-320, it is determined whether a predefined period of time has elapsed since receiving the second signal. Where multiple second signals have been received (for example because multiple stability control events have been detected), it is determined whether the predefined period of time has elapsed since receiving the most recent second signal.

[0071] In response to determining that the predefined period of time has elapsed, at step S-322 the foundation brake torque request signal is generated (either an existing foundation brake torque request signal is modified / updated, or a new foundation brake torque request signal is generated), the foundation brake torque request signal now causing the foundation brake system 110 to stop providing deceleration torque (or forgo providing deceleration torque when the vehicle next enters an overrun condition, if the vehicle 10 is not already in an overrun condition).

[0072] Correspondingly, at step S-324 a powertrain torque request signal is generated (for example the existing electric powertrain torque request signal is modified / updated, or a new electric powertrain torque request signal is generated) to cause the electric powertrain 120 to provide deceleration torque to achieve the deceleration torque demand (similarly to the step S-309 described above). Accordingly, in this embodiment, the invention advantageously dynamically adjusts to changing road conditions - deceleration torque is moved away from the electric powertrain and onto the foundation brakes when a stability control event corresponding to the vehicle driving over a low friction surface is detected, but behaviour is returned to normal (for example to enable greater regenerative braking) when the vehicle has passed the low friction surface and is driving along a surface with a greater coefficient of friction and therefore less likely to undergo a further stability control event.

[0073] As described above, in the event of a stability control intervention being instigated / performed, all of the deceleration torque demand can be put onto the foundation brakes, thereby avoiding electric powertrain deceleration causing the wheels 20 to counter- rotate in extreme low friction situations.

[0074] As illustrated in the example of Figure 3C, existing deceleration torque arbitration can also be interrupted in the event of a stability control intervention being instigated / performed.

[0075] At step S-330, a third signal is received (for example received by the control system 100 from the vehicle stability control system 140), indicative of a stability control intervention being instigated or performed by the vehicle stability control system 140. In dependence on the third signal, at step S-332 a powertrain torque request signal is generated (for example the existing electric powertrain torque request signal is modified / updated, or a new electric powertrain torque request signal is generated) to cause the electric powertrain 120 to stop providing deceleration torque. Correspondingly at step S-334, the foundation brake torque request signal is generated (either an existing foundation brake torque request signal is modified / updated, or a new foundation brake torque request signal is generated), the foundation brake torque request signal now causing the foundation brake system 110 to provide deceleration torque to achieve all of the deceleration torque demand.

[0076] Advantageously, this embodiment thus allows for dynamic adjustment of the level of deceleration torque intervention responsive to changing conditions. After detecting a stability control event, the amount of deceleration torque requested from the foundation brakes is then increased if friction between the vehicle and the source being driven on decreases further and / or if vehicle stability is further reduced.

[0077] In some embodiments, there may be specific situations in which foundation brake torque requests are not sent in response to detecting a stability control event or stability control intervention. In one example, if the stability control event or stability control intervention corresponds to the vehicle experiencing oversteer or understeer, the electric powertrain deceleration torque request is sent in step S-314 causing the electric powertrain 120 to provide less than the full amount of the deceleration torque demand (or alternatively no electric powertrain deceleration torque request is sent and the electric powertrain 120 provides no deceleration torque). However, no foundation brake deceleration torque request signal is sent, and the foundation brake system 110 provides no deceleration torque responsive to driver modulation of the accelerator pedal.

[0078] An example of the behaviour of the vehicle 10 when the method 300 above is followed is illustrated in Figure 4.

[0079] Figure 4 shows a graph 400 showing deceleration torque T along the y-axis, and time along the x-axis. In the illustrated example, priorto time to, a second signal indicative of a stability control event having occurred (e.g., wheel slip has been detected) has been received by the control system 100 (see step S-305 above).

[0080] At time to, driver modulation of the accelerator pedal leads to a determination of a deceleration torque demand of To (see steps S-302 and S-304 above). Because the second signal has already been received, a friction brake torque request signal is generated by the control system 100 as per step S-312 above. In response, the friction brake system 110 provides deceleration torque corresponding to line 404. In the example shown, an electric powertrain deceleration torque request signal is also generated at step S-314, and the electric powertrain 120 provides deceleration torque corresponding to line 402. Together, the respective deceleration torques 402, 404 provided by the friction brake system 110 and the electric powertrain 120 sum to provide the deceleration torque demand Td.

[0081] At a later time ti, it is determined that a stability control intervention has occurred (see step S-330). For example, the vehicle stability control system has activated an automatic brake system or traction control system. At a time ti, a friction brake torque request signal is generated to cause the friction brake system 110 to provide deceleration torque corresponding to the deceleration torque demand Td in full (for example as described in relation to step S-334 above). A powertrain torque request signal is also generated to cause the electric powertrain 120 to stop providing deceleration torque (for example as described in relation to Step S- 332 above).

[0082] After time ti, for example until the vehicle stability intervention has ended, the foundation brake system 110 provides deceleration torque corresponding to driver accelerator input modulation in accordance with the predefined profile.

[0083] 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.

Claims

CLAIMS1 . A control system for use in control of a foundation brake system and an electric powertrain of a vehicle during single-pedal driving, the control system comprising one or more processors collectively configured to: receive a first signal indicative of modulation of an accelerator pedal by a driver; in dependence on receiving the first signal, determine a deceleration torque demand; receive a second signal indicative of a stability control event being identified; in dependence on receiving the second signal: determine an electric powertrain deceleration torque limit; determine if the deceleration torque demand exceeds the electric powertrain deceleration torque limit; in dependence on determining that the deceleration torque demand exceeds the electric powertrain deceleration torque limit, generate a foundation brake torque request signal to cause the foundation brake system to provide deceleration torque to achieve the deceleration torque demand.

2. The control system of claim 1 , wherein the one or more processors are collectively configured to generate an electric powertrain deceleration torque request signal to cause the electric powertrain to provide deceleration torque, less than the electric powertrain deceleration torque limit, to achieve the deceleration torque demand in combination with the foundation brake system.

3. The control system of claim 1 or claim 2, wherein the stability control event: corresponds to a wheel slip condition of one or more vehicle wheels; and / or is based on a user selected drive mode.

4. The control system of any preceding claim, wherein the one or more processors are collectively configured to receive the second signal is prior to the first signal.

5. The control system of any preceding claim, wherein the one or more processors are collectively configured to: determine that a predefined period of time has elapsed since receiving the second signal; in dependence on determining that the predefined period of time has elapsed since receiving the second signal: generate the foundation brake torque request signal to cause the foundation brake system to stop providing or reduce deceleration torque; and generate a powertrain torque request signal to cause the electric powertrain to provide deceleration torque to achieve the deceleration torque demand.

6. The control system of any preceding claim, wherein the one or more processors are collectively configured to: receive a third signal indicative of a stability control intervention being performed by a stability control system of the vehicle; in dependence on receiving the third signal: generate the powertrain torque request signal to cause the electric powertrain to stop providing deceleration torque; and generate the foundation brake torque request signal to cause the foundation brake system to provide deceleration torque corresponding to a full amount of the deceleration torque demand.

7. A system comprising: the control system of any of claims 1 to 6; the electric powertrain; and the foundation brake system.

8. A vehicle comprising the system of claim 7 or the control system of claims 1 to 6.

9. A method for controlling a foundation brake system and an electric powertrain of a vehicle during single-pedal driving, the method comprising: receiving a first signal indicative of modulation of an accelerator pedal by a driver; in dependence on receiving the first signal, determining a deceleration torque demand; receiving a second signal indicative of a stability control event being identified; in dependence on receiving the second signal: determining an electric powertrain deceleration torque limit; determining if the deceleration torque demand exceeds the electric powertrain deceleration torque limit; in dependence on determining that the deceleration torque demand exceeds the electric powertrain deceleration torque limit, generating a foundation brake torque request signal to cause the foundation brake system to provide deceleration torque to achieve the deceleration torque demand.

10. The method of claim 9, comprising generating an electric powertrain deceleration torque request signal to cause the electric powertrain to provide deceleration torque, less than the electric powertrain deceleration torque limit, to achieve the deceleration torque demand in combination with the foundation brake system.11 . The method of claim 9 or claim 10, wherein the stability control event: corresponds to a wheel slip condition of one or more vehicle wheels; and / or is based on a user selected drive mode.

12. The method of any of claims 9 to 11 , comprising receiving the second signal prior to receiving the first signal.

13. The method of any of claims 9 to 12, comprising: determining that a predefined period of time has elapsed since receiving the second signal; in dependence on determining that the predefined period of time has elapsed since receiving the second signal: generating the foundation brake torque request signal to cause the foundation brake system to stop providing or reduce deceleration torque; and generating a powertrain torque request signal to cause the electric powertrain to provide deceleration torque to achieve the deceleration torque demand.

14. The method of any of claims 9 to 13, comprising: receiving a third signal indicative of a stability control intervention being performed by a stability control system of the vehicle; in dependence on receiving the third signal: generating a powertrain torque request signal to cause the electric powertrain to stop providing deceleration torque; and generating the foundation brake torque request signal to cause the foundation brake system to provide deceleration torque corresponding to a full amount of the deceleration torque demand.

15. Computer readable instructions which, when executed by a computer, are arranged to perform a method according to any of claims 9 to 14.

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