Vehicle brake cleaning during single pedal driving

Abstract

Method of controlling vehicle friction brakes 112 and electric powertrain 122 during single-pedal driving: depending on friction brake cleaning criteria being satisfied and accelerator pedal position,

Description

TECHNICAL FIELD The present disclosure relates to vehicle brake cleaning during single pedal driving. 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”. In some vehicles, the foundation brake system may be based, for example, on eddy current brakes and although the term “foundation” brakes may be used herein, the present invention primarily concerns friction brakes and the term foundation should be understood to mean friction brakes in the case of the present disclosure. It is known that for friction brakes, corrosion and dirt may accumulate on brake components (for example brake discs) between brake actuations. Such dirt is typically removed by the friction brakes in use. Because vehicles that provide single pedal driving use the electric powertrain to decelerate the vehicle at least some of the time, vehicle friction brakes are typically actuated less frequently. This in turn means that friction brake components may accumulate higher levels of dirt and / or corrosion. 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 or friction brake system and an electric powertrain of a vehicle during single-pedal driving, a system, a vehicle, a method for controlling a foundation or friction 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 friction 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 one or more criteria for friction brake cleaning being satisfied; and receive or obtain a second signal indicative of modulation of an accelerator pedal by a driver. In dependence on (for example responsive to) receiving or obtaining the second signal, the control system is configured to determine / identify a deceleration torque demand; and in dependence on (for example responsive to) receiving the first signal; cause the friction brake system to provide deceleration torque to achieve at least part of the deceleration torque demand (for example via generating a suitable signal). According to another aspect of the present invention there is provided a control system for use in control of a foundation or friction 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 one or more criteria for friction brake cleaning being satisfied; • receive a second signal indicative of modulation of an accelerator pedal by a driver; • in dependence on receiving the second signal, identify a deceleration torque demand; and • in dependence on receiving the first signal, generate a friction brake torque request signal to cause the friction brake system to provide deceleration torque to achieve the deceleration torque demand. Generation of the friction brake torque request signal so as to cause the friction brake system to provide deceleration torque to achieve the deceleration torque demand thereby cleans the friction brake system. For example, exerting pressure on a brake disc using brake pads acts to remove dirt and / or corrosion that may have accumulated on the brake disc. 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 or friction brake system. Advantageously, the present invention selectively cleans brakes during single pedal driving through selective actuation of the friction brakes instead of providing all deceleration via the electric powertrain. Whilst regenerative braking is in general preferred to improve vehicle performance, the lack of usage of the friction brakes can, over extended periods of time, reduce brake performance. Thus, by monitoring the brakes, and identifying when they need to be cleaned, the friction brakes can be selectively used which results in the cleaning of the brakes. This can enhance the longevity and performance of friction brake components, while still allowing for significant energy recovery during deceleration through the electric powertrain in general. Moreover, the present invention allows the deceleration behaviour of the vehicle responsive to driver input to remain consistent, even when brake cleaning is taking place. In an embodiment, the one or more criteria for friction brake cleaning comprises an amount of energy dissipated through one or more brakes of the friction brake system within a rolling time period being below a first predefined energy threshold. The rolling time period is a fixed amount of time preceding a current time, for example a particular number of minutes prior to the present time. In this way the start and end points of the rolling time period change as time advances, but the length of time between the start and end points remains the same. Optionally, the first predefined energy threshold is based on an estimated corrosion level according to a predefined model. Advantageously, this provides for dynamic, usage-based cleaning of the friction brakes, wherein the friction brakes are only cleaned via actuation when necessary and when the energy dissipated through the friction brakes during deceleration is sufficient to clean the brakes. In another embodiment, the one or more processors are collectively configured to, subsequent to receiving the first signal: receive a third signal indicative of the energy dissipated through the one or more brakes of the friction brake system within the rolling time period exceeds a second predefined energy threshold; in dependence on receipt of the third signal: generate a friction brake torque request signal to cause the friction brake system to stop providing deceleration torque; generate a powertrain torque request signal to cause the electric powertrain to provide deceleration torque corresponding to the deceleration torque demand. Advantageously, cleaning is dynamically ended according to the cleaning delivered to the friction brakes, ensuing that the vehicle is able to return to regenerative braking in an efficient manner, thereby minimising the impact on energy recovery. In yet another embodiment, the one or more processors are collectively configured to generate the friction brake torque request signal in dependence on the deceleration torque demand being greater than or equal to a threshold torque value. Advantageously, this ensures that friction brake cleaning is dynamically performed according to the level of abrasion that can be achieved between friction brake components. In a further embodiment, the one or more criteria for friction brake cleaning comprises a state of charge of a battery of the electric powertrain exceeding a threshold state of charge. Advantageously, this allows energy recovery through regenerative braking to take priority when the range of the vehicle is relatively low. In yet another aspect of the invention, there is provided a system comprising: the control system above; the friction brake system; and the electric powertrain. In further aspect of the invention, there is provided a vehicle comprising the system above orthe control system above. In a still further aspect of the invention, there is provided a method for controlling a friction brake system and an electric powertrain of a vehicle during single-pedal driving, the method comprising: receiving a first signal indicative of one or more criteria for friction brake cleaning being satisfied; receiving a second signal indicative of modulation of an accelerator pedal by a driver; in dependence on receiving the second signal, identifying a deceleration torque demand; in dependence on receiving the first signal; generating a friction brake torque request signal to cause the friction brake system to provide deceleration torque 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 or friction brake system. Advantageously, the present invention dynamically and selectively cleans brakes during single pedal driving through actuation of the friction brakes instead of providing all deceleration via the electric powertrain. This can enhance the longevity and performance of friction brake components, while still allowing for significant energy recovery during deceleration through the electric powertrain in general. Moreover, the present invention allows the deceleration behaviour of the vehicle responsive to driver input to remain consistent, even when brake cleaning is taking place. In an embodiment, the one or more criteria for friction brake cleaning comprises an amount of energy dissipated through one or more brakes of the friction brake system within a rolling time period (as discussed above) being below a first predefined energy threshold. Advantageously, this provides for dynamic, usagebased cleaning of the friction brakes, wherein the friction brakes are only cleaned via actuation when necessary. In another embodiment, the method comprises receiving a third signal indicative of the energy dissipated through the one or more brakes of the friction brake system within the rolling time period exceeds a second predefined energy threshold; in dependence on receipt of the third signal: generating a friction brake torque request signal to cause the friction brake system to stop providing deceleration torque; generating a powertrain torque request signal to cause the electric powertrain to provide deceleration torque corresponding to the deceleration torque demand. Advantageously, cleaning is dynamically ended according to the cleaning delivered to the friction brakes, ensuing that the vehicle is able to return to regenerative braking in an efficient manner. In yet another embodiment, the method comprises generating the friction brake torque request signal in dependence on the deceleration torque demand being greater than or equal to a threshold torque value. Advantageously, this ensures that friction brake cleaning is dynamically performed according to the level of abrasion that can be achieved between friction brake components. 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 schematic representation 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; and 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. 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 friction brake system 110a and an electric powertrain 120. The friction brake system 110a 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. In the illustrated embodiment, 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). The friction brake system 110a 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 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. 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, criteria for friction brake cleaning being satisfied, 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 friction brake system 110a 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. 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 friction brake system 110a 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. As illustrated, the method 300 starts at step S-301, in which a first signal is received (for example by the control system 100). The first signal (which can also be referred to as a cleaning criteria signal) is indicative of one or more criteria for friction brake cleaning being satisfied. The one or more criteria for cleaning being satisfied indicates that the friction brakes 112 require cleaning, in other words a certain level of corrosion and / or dirt has, or is expected to have, built up on one or more components of the friction brakes 112 (for example rust on a steel brake disc). The one or more criteria may be determined to be satisfied based on a signal from a sensor monitoring the condition of friction brake components, in which case the first signal may be generated by the foundation brake controller 114 based on information from the sensor, or generated by the sensor itself. The monitoring of the condition of the friction brake components occurs in a known manner. Alternatively, the first signal may be generated by the foundation brake controller 114 and indicate a most recent actuation of the friction brake assemblies, and the control system 100 is configured to determine whether the one or more criteria are satisfied based at least in part on tracking actuations of the friction brake assemblies 112. This latter provision is discussed in more detail below. Optionally, the criteria include a criterion that an amount of energy dissipated through one or more friction brake assemblies 112 of the friction brake system 110a within a rolling time period (that is a period of time of fixed length immediately preceding a current time) is below a first predefined energy threshold. For example, the control system 100 or brake controller 114 determines the amount of energy dissipated by the brakes in the previous 12 hours, (or previous 24 hours, 48 hours, 1 week, or other time period). The amount of energy may be determined for example by direct measurement, or prediction based on the number of times the friction brake assemblies 112 have been actuated and the pressure / force exerted by, or instructed to be exerted by, brake pads on brake discs or similar. In some examples a proxy to the amount of energy dissipated through one or more friction brake assemblies 112 may be used instead. This provision can be thought of as a counter, the value of the counter decreasing as the amount of energy dissipated through the brake assemblies 112 falls (due to increasing time since the brake assemblies 112 were last actuated), and increases as the amount of energy dissipated through the brake assemblies 112 increases (when the brake assemblies 112 are actuated again). The criterion is determined to be satisfied (e.g., by the control system 100 or the brake controller 114) when the value of the counter (the amount of energy dissipated through one or more friction brake assemblies 112 or a proxy therefor) falls below the first predefined energy threshold. Optionally the first predefined energy threshold is based on an estimated corrosion level according to a predefined model, for example an amount of corrosion deemed to require cleaning to improve friction brake performance. It will be appreciated that the first predefined energy threshold may be chosen according to the particular vehicle 10 in question, which may have different requirements regarding how much corrosion and / or dirt on the friction brake assemblies 112 is acceptable. As illustrated the method then proceeds to step S-302, in which a second signal indicative of modulation of an accelerator pedal (orotheraccelerator input device) by a driver is received. In one example, the control system 100 receives the second signal from the powertrain controller 128 or another system within the vehicle 10. The second signal (which may also be referred to as deceleration input 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 the accelerator pedal that is normally depressed against a spring bias to indicate a desire to accelerate the vehicle or by partially or completely releasing the accelerator grip on a motorcycle). It will be appreciated that in some embodiments, the second signal may be received before the first signal, that is step S-302 may be performed before step S-301 is performed. At step S-304, in dependence on receiving the second 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 second 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 second signal. In this latter case, the control system 100 determines the deceleration torque demand by reading / identifying the deceleration torque demand in the second signal. As illustrated in Figure 3, the method 300 assumes that the first signal has been received at step S-301 before the second signal has been received at step S-302. In situations where the second signal is received and the deceleration torque demand has been determined at steps S-302 and S-304 before any first signal has been received, the method then proceeds to step S-306, in which it is determined whether or not any first signal has been received (i.e., whether step S-301 has occurred). If yes, the method proceeds to step S-312 described below. If not, the method proceeds to step S-308 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 step S-301 has occurred (either before or after steps S-302 and S-304), a foundation brake torque request signal is generated at step S-312 (for example by the control system 100) to cause the friction brake system 110a to provide deceleration torque to achieve the deceleration torque demand. Deceleration torque is applied to the wheels 20 via pressing brake pads against a brake disc to provide additional mechanical resistance to rotation of the wheels 20 when the vehicle 10 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. The foundation brake torque request signal is sent to the friction brake system 110a, 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. The friction brake components may thereby be cleaned of corrosion and / ordirt-for example, actuation of a brake calliper to press brake pads againsta brake disc acts to abrade corrosion from a brake disc. The friction brake system 110a may provide deceleration torque corresponding to the entirety of the deceleration torque demand. Alternatively, optionally 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 friction brake system 110a. 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 nonzero deceleration torque (up to 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 friction brake system 110a to provide deceleration torque corresponding to the deceleration torque demand less the deceleration torque provided by the electric powertrain 120. Advantageously, the present invention dynamically and selectively offloads single pedal driving overrun deceleration torque demands to the friction brakes 112 when cleaning is required, while maintaining consistent deceleration behaviour. For example, the driver may be unaware that friction brake cleaning is taking place, as the vehicle 10 decelerates during overrun conditions in the same manner as if the electric powertrain 120 were providing all of the deceleration torque. By periodically cleaning the friction brakes 112 in this manner, corrosion build up on the brake components is reduced, and may improve the longevity and performance of the friction brake system 110a. In addition, the invention maintains the ability to use regenerative braking for most single pedal deceleration inputs (i.e., when the one or more criteria are not satisfied). Optionally, the friction brake torque request signal is only generated in step S-312 if it is determined (for example by the control system 100) that the deceleration torque demand is greater than or equal to a threshold torque value. The threshold torque value may be selected to correspond to a minimum pressure applied by brake pads to a brake disc required to provide sufficient abrasion to remove corrosion from the brake disc. The minimum pressure may be selected based on properties and / or materials of the brake pads, brake disc, and optionally other factors. Alternatively, the threshold torque value may be a predetermined value e.g., 10NM. Optionally, following step S-312, the method proceeds to steps S-322 to S-326. At step S-322, a third signal (which can also be referred to as a brake cleaned signal) is received, for example by control system 100. The third signal is indicative of the energy dissipated through the one or more brakes of the friction brake system within the rolling time period exceeding a second predefined energy threshold. The third signal thus gives an indication that the friction brake assemblies have been actuated a sufficient amount to have cleaned at least some of any corrosion present, for example on brake discs. In some embodiments, the value of the second predefined energy threshold is the same as the value of the first predefined energy threshold. Alternatively, the value of the second predefined energy threshold is higher than the value of the first predefined energy threshold, thereby introducing hysteresis (the brake assemblies are only considered to have been cleaned when the energy dissipated through the brake assemblies 112 has exceeded the first threshold plus an additional amount). At steps S-324, in dependence on receipt of the third signal, a friction brake torque request signal is generated (e.g., by the control system 100) to cause the friction brake system 110a to stop providing deceleration torque. In addition, at step S-326, a powertrain torque request signal is generated (e.g., by the control system 100) to cause the electric powertrain 120 to provide deceleration torque corresponding to the deceleration torque demand. Accordingly, once the brake assemblies 112 (e.g., brake discs) have been cleaned, the provision of deceleration torque is passed back to the electric powertrain 120 such that full regenerative braking can be resumed. The one or more criteria for friction brake cleaning mentioned may comprise further criteria to those mentioned above. For example, the one or more criteria may further comprise a criterion that a state of charge of the electrical energy storage 130 exceeds a threshold state of charge. Advantageously, this criterion can be used to prioritise regenerative braking over friction brake cleaning in the event of a low state of charge of the electrical energy storage 130. This in turn increases the range of the vehicle 10. An example of the behaviour of the vehicle 10 when the method 300 above is followed is illustrated in figure 4. Figure 4 shows a graph 400 showing deceleration torque T along the y-axis, and time along the x-axis. Prior to time to, a first signal indicative of one or more criteria for friction brake cleaning being satisfied is received by the control system 100 (see step S-301 above). At time to, driver modulation of the accelerator pedal leads to a determination of a deceleration torque demand of Td (see steps S-302 and S-304 above). Because the first signal has already been received, a friction brake torque request signal is generated by the control system 100 as per stepS-312 above. In response, the friction brake system 110a 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 110a and the electric powertrain 120 sum to provide the deceleration torque demand Td. At a later time ti, it is determined that the friction brake cleaning should end (for example, one or more of the criteria for friction brake cleaning as discussed above in relation to step S-301 are no longer satisfied). In some examples, this corresponds to the receipt of the third signal as described above in relation to step S-322. At a time ti, a friction brake torque request signal is generated to cause the friction brake system 110a to stop providing or reduce deceleration torque (for example as described in relation to Step S-324 above). A powertrain torque request signal is also generated to cause the electric powertrain 120 to provide deceleration torque corresponding to the deceleration torque demand Td in full (for example as described in relation to Step S-326 above). After time ti, the electric powertrain 120 provides deceleration torque (for example through regenerative braking) corresponding to driver accelerator input modulation in accordance with the predefined profile. 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 friction 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 one or more criteria for friction brake cleaning being satisfied;receive a second signal indicative of modulation of an accelerator pedal by a driver;in dependence on receiving the second signal, identify a deceleration torque demand; andin dependence on receiving the first signal, generate a friction brake torque request signal to cause the friction 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 friction brake system.

3. The control system of claim 1 or claim 2, wherein the one or more criteria for friction brake cleaning comprises an amount of energy dissipated through one or more brakes of the friction brake system within a rolling time period being below a first predefined energy threshold.

4. The control system of claim 3, wherein the first predefined energy threshold is based on an estimated corrosion level according to a predefined model.

5. The control system of claim 3 or claim 4 wherein the one or more processors are collectively configured to, subsequent to receiving the first signal:receive a third signal indicative of the energy dissipated through the one or more brakes of the friction brake system within the rolling time period exceeding a second predefined energy threshold;in dependence on receipt of the third signal:generate a friction brake torque request signal to cause the friction brake system to stop providing or reduce deceleration torque;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 generate the friction brake torque request signal in dependence on the deceleration torque demand being greater than or equal to a threshold torque value.

7. The control system of any preceding claim, wherein the one or more criteria forfriction brake cleaning comprises a state of charge of a battery of the electric powertrain exceeding a threshold state of charge.

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

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

10. A method for controlling a friction brake system and an electric powertrain of a vehicle during singlepedal driving, the method comprising:receiving a first signal indicative of one or more criteria for friction brake cleaning being satisfied;receiving a second signal indicative of modulation of an accelerator pedal by a driver;in dependence on receiving the second signal, identifying a deceleration torque demand; and in dependence on receiving the first signal, generating a friction brake torque request signal to cause the friction brake system to provide deceleration torque to achieve the deceleration torque demand.

11. The method of claim 10, 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 friction brake system.

12. The method of claim 10 or claim 11, wherein the one or more criteria for friction brake cleaning comprises an amount of energy dissipated through one or more brakes of the friction brake system within a rolling time period being below a first predefined energy threshold.

13. The control system of claim 12 comprising:receiving a third signal indicative of the energy dissipated through the one or more brakes of the friction brake system within the rolling time period exceeding a second predefined energy threshold;in dependence on receipt of the third signal:generating a friction brake torque request signal to cause the friction brake system to stop providing or reduce deceleration torque; andgenerating a powertrain torque request signal to cause the electric powertrain to provide deceleration torque to achieve the deceleration torque demand.

14. The control system of any of claims 10 to 13, comprising generating the friction brake torque request signal in dependence on the deceleration torque demand being greater than or equal to a threshold torque value.

15. Computer readable instructions which, when executed by a computer, are arranged to perform a method according to any of claims 10 to 14.14

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