Vehicle deceleration torque control

Abstract

Control method during one-pedal driving, by determining braking torque demand depending on accelerator pedal position, determining electric powertrain 122 deceleration torque available, and if the braking torque demand exceeds the available electric braking torque, the foundation brake 112 (e.g. friction brake discs or drums) are engaged. The friction brakes 112 may be used in combination with electric braking (e.g. regenerative braking). The available electric brake torque may depend on battery state of charge (SoC), temperature, condition of the battery and / or inverter, or speed of vehicle, or may be a predefined electric deceleration torque threshold. Available friction brake deceleration torque may be calculated based on temperature or condition of the friction brake components. Braking torque demand request may be calculated from a deceleration profile.

Description

TECHNICAL FIELD The present disclosure relates to deceleration torque control. Aspects of the invention relate to a control system, to a system, a vehicle, a method and to computer readable instructions. BACKGROUND 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”. When a vehicle provides single pedal driving, there is the potential that the user is expecting a certain characteristic overrun behaviour. However, there is also the potential that the deceleration torque capable of being provided by the electric powertrain may vary according to certain conditions. This may result in an altered driving feel, or experience, to that which the user was expecting, wherein the same user input can result is different deceleration behaviour at different times. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION 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. 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 / identity a deceleration torque demand; determine / identify an available electric powertrain deceleration torque; determine / identify if the deceleration torque demand exceeds the available electric powertrain deceleration torque; and in dependence on (for example responsive to) determining / identifying that the deceleration torque demand exceeds the available electric powertrain deceleration torque, cause the foundation brake system to provide deceleration torque to achieve at least part the deceleration torque demand (for example via generating a foundation brake torque request signal). 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 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 a first signal indicative of modulation of an accelerator pedal (or other accelerator / throttle input) by a driver; • in dependence on receiving the first signal, determine a deceleration torque demand; • determine an available electric powertrain deceleration torque; • determine if the deceleration torque demand exceeds the available electric powertrain deceleration torque; and • in dependence on determining that the deceleration torque demand exceeds the available electric powertrain deceleration torque, generate a foundation brake torque request signal to cause the foundation brake system to provide deceleration torque to achieve the deceleration torque demand. 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 to achieve the deceleration torque demand in combination with the foundation brake system. Advantageously, the invention thus passes some or all of deceleration torque requested by the driver through modulation of the accelerator, from the electric powertrain to the foundation brake system if the electric powertrain is unable to provide the full amount of the request deceleration torque. In contrast to known systems, this means that the vehicle exhibits consistent deceleration behaviour during single pedal driving, regardless as to whether regenerative braking via the power train is available for example. Therefore, the user of the vehicle will experience the deceleration behaviour they are expecting. In an embodiment, the one or more processors are collectively configured to determine the available electric powertrain deceleration torque based on one or more of: a state of charge of a battery of the electric powertrain; a temperature of the battery; a condition status of the battery; a condition status of an inverter of the electric powertrain; a predefined threshold electric powertrain torque; a vehicle speed. Advantageously, the invention can thus dynamically maintain consistent vehicle deceleration behaviour as the vehicle battery charges and undergoes changes in temperature, and further can be used to limit the total amount of deceleration torque regenerative braking that can be applied (e.g., to maintain good powertrain / battery condition). In another embodiment, the one or more processors are collectively configured to: determine an available foundation brake system deceleration torque; generate the foundation brake torque request signal in dependence on the available foundation brake system deceleration torque. Optionally, the one or more processors are collectively configured to determine the available foundation brake system deceleration torque based on one or more of: a temperature of one or more brake components of the foundation brake system; and a condition status of the foundation brake system. Advantageously, the invention can thus dynamically account for variations in foundation braking characteristics, for example when friction brake components are at a high temperature. In yet another embodiment, the deceleration torque demand is based on a predetermined deceleration profile. Advantageously, this further enhances the consistency of deceleration behaviour of the vehicle under modulation of the accelerator pedal by the driver. For example, the predetermined deceleration profile may be linked to a user selectable drive mode, giving the driver the ability to tailor how the vehicle’s deceleration characteristics when modulating the accelerator pedal / input. In another aspect of the invention, there is provided a system comprising the control system above; the electric powertrain; and the foundation brake system. In yet another aspect of the invention, there is provided a vehicle comprising the system or the control system above. 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; determining an available electric powertrain deceleration torque; determining if the deceleration torque demand exceeds the available electric powertrain deceleration torque; and in dependence on determining that the deceleration torque demand exceeds the available electric powertrain deceleration torque, generating a foundation brake torque request signal to cause the foundation brake system to achieve the deceleration torque demand. Optionally the method comprises generating an electric powertrain deceleration torque request signal to cause the electric powertrain to provide deceleration torque to achieve the deceleration torque demand in combination with the foundation brake system. Advantageously, the invention thus passes some or all of deceleration torque requested by the driver through modulation of the accelerator, from the electric powertrain to the foundation brake system if the electric powertrain is unable to provide the full amount of the request deceleration torque. In contrast to known systems, this means that the vehicle exhibits consistent deceleration behaviour during single pedal driving, regardless as to whether regenerative braking via the power train is available for example. In an embodiment, the method comprises determining the available electric deceleration torque based on one or more of: a state of charge of a battery of the electric powertrain; a temperature of the battery; a condition status of the battery; a condition status of an inverter of the electric powertrain; a predefined threshold electric powertrain torque. Advantageously, the invention can thus dynamically maintain consistent vehicle deceleration behaviour as the vehicle battery charges and undergoes changes in temperature, and further can be used to limit the total amount of deceleration torque regenerative braking that can be applied (e.g., to maintain good powertrain / battery condition). In another embodiment, the method comprises: determining an available foundation brake system deceleration torque; generating the foundation brake torque request signal in dependence on the available foundation brake system deceleration torque. Optionally, determining the available foundation brake system deceleration torque is based on one or more of: a temperature of one or more brake components of the foundation brake system; and a condition status of the foundation brake system. Advantageously, the invention can thus dynamically account for variations in foundation braking characteristics, for example when friction brake components are at a high temperature. In yet another embodiment, the deceleration torque demand is based on a predetermined deceleration profile. Advantageously, this further enhances the consistency of deceleration behaviour of the vehicle under modulation of the accelerator pedal by the driver. For example, the predetermined deceleration profile may be linked to a user selectable drive mode, giving the driver the ability to tailor how the vehicle’s deceleration characteristics when modulating the accelerator pedal / input. 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. 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 anyway 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 One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a vehicle in accordance with an embodiment of the invention; Figure 2 shows a representation of system architecture of the vehicle of Figure 1 in accordance with an embodiment of the invention; Figure 3 shows a flow chart for controlling the foundation brake system and the electric powertrain of the vehicle of Figure 1 in accordance with an embodiment of the invention; Figure 4 shows a graph showing an example transition between electric powertrain deceleration torque and foundation brake deceleration torque using the method of Figure 3; and Figure 5 shows a logical architecture diagram in accordance with an embodiment of the invention. DETAILED DESCRIPTION A vehicle 10 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figures 1 and 2. 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. The foundation brake system 110 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. 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). 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 forthe electric machine 122 is an electric drive unit (EDU). 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. The electric powertrain 120 optionally further comprises a powertrain controller 128 configured to control operation of the electric machine 122. The vehicle 10 also comprises an electrical energy storage / battery 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. 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 114. 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 101. 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, state of charge of the electrical energy storage 130, temperature of foundation brake components, 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 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). 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. As described below, there may be times when the electric powertrain 120 is unable to provide deceleration torque through regenerative braking, or where the ability of the electric powertrain 120 to provide deceleration torque is limited. For example, if the electric energy storage / battery 130 is fully charged, it cannot accept further charge, and thus the electric machine 122 cannot perform regenerative braking. Similarly, if the state of charge of the battery 130 is high, and / or if the battery 130 is at a particularly high or low temperature, the ability of the battery 130 to accept charge is limited, and thus the level of regenerative braking that can be performed by the electric machine 122 is reduced. In addition, it is desirable to reduce deceleration torque provided by regenerative braking using the electric powertrain 120 as the vehicle speed approaches zero (and ensuring that no deceleration torque is provided by the electric powertrain 120 when the vehicle speed reaches zero) to avoid unintended reversing of the vehicle direction of travel. In such situations, some prior art systems forgo the provision of deceleration torque in response to driver modulation of an accelerator input. The deceleration, or “overrun”, behaviour of such prior art vehicles therefore changes depending on, for example, battery condition. This can lead to prior art vehicles behaving in a manner that the driver is not expecting, when performing single pedal driving. In the most extreme example, where no regenerative braking is available (e.g., the battery is full) such prior art vehicles may provide no active deceleration torque responsive to a driver input lifting an accelerator pedal (i.e., indicating that the driver wishes to decelerate the vehicle), meaning that the driver may have to manually activate foundation brakes. In contrast, the present invention provides “overrun simulation” to address situations where electric powertrain deceleration torque is unavailable or has only limited availability. As described below, in such situations the control system 100 causes the foundation brake system 110 to decelerate the vehicle 10 (alone or in combination with the electric powertrain 120). The vehicle 10 can thus decelerate in substantially the same manner (it can exhibits substantially the same overrun behaviour) responsive to a driver modulation of the accelerator pedal, even if the electric powertrain 120 is unable to provide a full amount of the requested deceleration torque through regenerative braking (for example because the battery 130 is fully charged or the vehicle speed is approaching zero). Advantageously, such a system ensures that the driver does not experience any different responses when driving and would remain unaware that the vehicle has responded in a different manner. 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. Figure 3 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. 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). 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. 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. 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. In step S-306 an available electric powertrain deceleration torque is then determined. The available electric powertrain deceleration torque is the maximum deceleration torque that can be applied by the electric powertrain 120 to the wheels 20 (for example via regenerative braking) at a given point of time. In some embodiments, the control system 100 receives signals from the powertrain controller 128 and / or other systems or sensors on the vehicle 10 indicative of the available electric powertrain deceleration torque, and calculates, reads or otherwise identifies the available electric powertrain deceleration torque based on the signals. The available electric powertrain deceleration torque is determined based on one or more factors. If the electrical energy storage 130 is at a high state of charge (for example fully charged or close to fully charged) it may have limited or no ability to take additional charge from the electric machine 122, in turn meaning that the electric machine 122 has limited ability to provide deceleration torque through regenerative braking. Similarly, if the electrical energy storage 130 is at a very high or very low temperature, it may again have limited or no ability to accept charge generated by the electric machine 122. Further, if the vehicle speed is approaching zero (for example is below a threshold speed), available electric powertrain deceleration torque may be reduced (for example to zero) to avoid reversal of vehicle direction of travel. In such situations, the electric powertrain 120 may be unable to provide the full amount of the deceleration torque demand, or in some cases any deceleration torque. Further, as a precaution it may be determined that no deceleration torque can be provided by the electric powertrain 120 in the event that any fault is detected in the electrical energy storage 130 and / or inverter. Alternatively or in addition, a predetermined threshold electrical powertrain torque can be defined based on the properties of the powertrain 120 components and electrical energy storage 130, for example corresponding to a maximum permitted rate of regenerative charging. At step S-308, it is determined (for example by the control system 100) whether the deceleration torque demand exceeds the available electric powertrain deceleration torque. If the deceleration torque demand does not exceed the available electric powertrain deceleration torque, 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). If the deceleration torque demand exceeds the available electric powertrain deceleration torque, 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 112, 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 112 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. 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. In situations where no deceleration torque can be provided by the electric powertrain 120 (the available electric powertrain deceleration torque is zero), the foundation brake system 110 may provide deceleration torque corresponding to the entirety of the deceleration torque demand. In situations where the available electric powertrain deceleration torque is above zero, but less than the deceleration torque demand, optionally an electric powertrain deceleration torque request signal is 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. 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 (upto a maximum corresponding to the available electric powertrain deceleration torque), 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. Advantageously, the present invention ensures that the vehicle 10 responds to driver accelerator modulation in a consistent manner, even at times when the electric powertrain 120 has reduced ability to provide declaration torque though regenerative braking. The invention leverages the foundation brake system 110 to fill in gaps in electric powertrain deceleration torque, for example such that the deceleration of the vehicle 10 still conforms to the single pedal driving predetermined deceleration profile for a current drive mode. In some embodiments, priorto generating the foundation brake torque request signal at step S-312, optionally S-310 is performed, in which an available foundation brake system deceleration torque is determined (for example by control system 100). Optionally this involves determining a temperature of one or more components of the foundation brake system (for example the temperature of one or more brake pads or discs in a friction brake actuation assembly), and / or determining a condition status of the foundation brake system. In one example, the control system 100 determines an amount of deceleration torque that can be provided by the foundation brake system based on the determined temperature of the one or more components (e.g. brake disc and / or brake pads). As the performance of the components can vary with temperature in an example adaption of the response is made according to the temperature. The temperature is determined using known temperature sensors for the various components. For example: • when the temperature is at or below a first value the control system 100 determines a first maximum amount of deceleration torque that can be provided by the foundation brake system 110; • when the temperature is above the first value but below a second value, the control system 100 determines a second maximum amount of deceleration torque that can be provided by the foundation brake system 110, the second maximum amount lower than the first maximum amount; • when the temperature is above the second value but below a third value, the control system 100 determines a third maximum amount of deceleration torque that can be provided by the foundation brake system 110, the third maximum amount lower than the second maximum amount; and • when the temperature is above the third value, the control system 100 determines that no deceleration torque can be provided by the foundation brake system 110. In this way, the foundation brakes are “de-rated” for providing deceleration during overrun as brake temperature increases. Advantageously, a reduced amount of overrun simulation is provided using the foundation brake system 110 when the brake components are at a high temperature and may have lower braking efficiency. While described in relation to four temperature bands (below a first temperature, between a fist and second temperature, between a second and third temperature, and above a third temperature) it will be appreciated that fewer or more temperature bands could be utilised. The method 300 may be performed iteratively, for example continuously, overtime, allowing for deceleration torque to be transitioned between the electric powertrain 120 and the foundation brake system 110, as illustrated in the example of Figure 4. Figure 4 shows a graph 400 showing deceleration torque T along the y-axis, and time along the x-axis. At time to driver modulation of the accelerator pedal leads to a determination of a deceleration torque demand of Td. Initially, it is determined (see step S-308 above) that the electric powertrain 120 can provide all of the deceleration torque demand Td, and the deceleration torque provided by the electric powertrain 120 is ramped up (see line 402). The electric powertrain 120 provides all the deceleration torque demand Td (see step S-309 above). At a later time ti, it is determined (see step S-308 above) that the torque demand Td exceeds the available electric powertrain deceleration torque (for example because the electric energy storage 130 has become fully charged or close to fully charged through regenerative braking). At this point, the deceleration torque 402 provided by the powertrain 120 is ramped down, while deceleration torque 404 provided by the foundation braking system 110 is ramped up, such that the torque demand Td continues to be met overall (see steps S-312 and S-314 above). The invention thus allows for the dynamic transition between using the electric powertrain 120 and the foundation brake system 110 when providing deceleration control for single pedal driving. Figure 5 shows a logical architecture diagram of one implementation of the method described above in relation to Figure 3. The control system 100 receives various signals / data 501,502, 503, 504, 505, 506, 507 regarding the current state of the vehicle 10, for example via input means 104. In this example, the control system 100 receives: • an overrun mode signal 501, indicating a selected overrun predetermined profile discussed above; • a vehicle operating state signal 502, indicating information such as vehicle speed, gradient of the surface the vehicle is being driven on, vehicle stability limits, selected gear information; • an accelerator pedal position signal 503, indicating the extent to which the accelerator is depressed / actuated by the driver (this is as per step S-302 as described above); • a creep mode signal 504 indicative of a driver selected vehicle creep; • a traction battery signal 505 indicating the operating state of the battery 130, for example including state of charge and temperature; • a drive mode signal 506 indicating a user-selected drive mode which allows a user to select a driving mode in the known manner; and • a powertrain system capability signal 507 indicating the amount of power which can be delivered by the powertrain at a given moment in time. In this example, the overrun mode signal 501, the vehicle operating state signal 502, the accelerator pedal position signal 503, the creep mode signal 504, the traction battery signal 505, the drive mode signal 506 and the powertrain system capability signal 507 are used as the basis for calculating an overrun deceleration torque demand 512 (see also step S-304 above). As detailed above, the ability of the powertrain to deliver a deceleration torque demand can depend on the operating parameters of the vehicle. The above signals 501-507, enable the determination of the overrun deceleration torque demand 512. In one example, the overrun deceleration torque demand 512 is determined using a predetermined model for the vehicle. Separately, a foundation brake status 510 is determined. The foundation brake status 510 indicates whether / to what extent the foundation brake system 110 is available for providing deceleration torque for overrun simulation (for example, based on the temperature of brake components as discussed in detail above). The deceleration torque demand 512 is used to determine an advanced driver assistance system wheel torque demand 514. Together, the deceleration torque demand 512, the advanced driver assistance system wheel torque demand 514, the foundation brake status 510 and the powertrain system capability signal 507 are used to determine a deceleration torque split 516, i.e., how deceleration torque should be split between the electric powertrain 120 and the foundation brake system 110 to meet the deceleration torque demand. The determination of the split is as described with reference to Figures 3 and 4. At this stage the control system 100 generates the foundation brake torque request signal as per step S-312 and the electric powertrain deceleration torque request as per step S-314 as described in detail above. The foundation brake torque request signal and the electric powertrain deceleration torque request are then delivered 520 to the foundation brake system 110 and the electric powertrain 120 respectively in the known manner. The requests thereby cause the driver demanded deceleration torque to be applied 524 to the wheels. Optionally in this example, visual feedback relating to the overrun of the vehicle 10 is displayed 522 to the driver via an interface, such as a display screen present in the vehicle. 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

1. 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;determine an available electric powertrain deceleration torque;determine if the deceleration torque demand exceeds the available electric powertrain deceleration torque; andin dependence on determining that the deceleration torque demand exceeds the available electric powertrain deceleration torque, 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 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 one or more processors are collectively configured to determine the available electric powertrain deceleration torque based on one or more of:a state of charge of a battery of the electric powertrain;a temperature of the battery;a condition status of the battery;a condition status of an inverter of the electric powertrain;a predefined threshold electric powertrain torque; and a speed of the vehicle.

4. The control system of any preceding claim, wherein the one or more processors are collectively configured to:determine an available foundation brake system deceleration torque; andgenerate the foundation brake torque request signal in dependence on the available foundation brake system deceleration torque.

5. The control system of claim 4, wherein the one or more processors are collectively configured to determine the available foundation brake system deceleration torque based on one or more of:a temperature of one or more brake components of the foundation brake system; and a condition status of the foundation brake system.

6. The control system of any preceding claim, wherein the deceleration torque demand is based on a predetermined deceleration profile.

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

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

9. A method for controlling a foundation brake system and an electric powertrain of a vehicle duringsingle-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;determining an available electric powertrain deceleration torque;determining if the deceleration torque demand exceeds the available electric powertrain deceleration torque; andin dependence on determining that the deceleration torque demand exceeds the available electric powertrain deceleration torque, generating a foundation brake torque request signal to cause the foundation brake system 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 to achieve the deceleration torque demand in combination with the foundation brake system.

11. The method of claim 9 or claim 10 comprising determining the available electric deceleration torque based on one or more of:a state of charge of a battery of the electric powertrain;a temperature of the battery;a condition status of the battery;a condition status of an inverter of the electric powertrain;a predefined threshold electric powertrain torque; anda speed of the vehicle.

12. The method of any of claims 9 to 11, comprising:determining an available foundation brake system deceleration torque; andgenerating the foundation brake torque request signal in dependence on the available foundation brake system deceleration torque.

13. The method of claim 12, comprising determining the available foundation brake system deceleration torque based on one or more of:a temperature of one or more brake components of the foundation brake system; anda condition status of the foundation brake system.

14. The method of any of claims 9 to 13, wherein the deceleration torque demand is based on a predetermined deceleration profile.

515. Computer readable instructions which, when executed by a computer, are arranged to perform a method according to any of claims 9 to 14.1016

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