A control system for controlling a braking system of a vehicle

Abstract

A control system and method for controlling a vehicle braking system to brake when the vehicle is in a neutral drive mode that the driver does not expect. The method includes S710 receiving input parameters, S720 determining a braking condition is satisfied, and, if it is, S725 outputting a braking torque request signal to the braking system. The input parameters include an active drive mode signal and a driver selected drive mode signal (e.g. from a gear lever used for selecting between different gears and / or forward D, reverse R, neutral N and park P modes). The input parameters may additionally include: a request to change from initial drive mode in a first travel direction to driver selected mode in a second travel direction, vehicle speed, and driving surface gradient. The braking condition requires that the driver selected mode is not a neutral drive mode but the active drive mode is a neutral drive mode – e.g. due to overriding control logic the system has defaulted to neutral rather than the driver requested mode, such as when driver tries to switch to reverse when travelling forwards above threshold speed. The braking torque request may be tapered / gradually changed (re figure 8).

Description

TECHNICAL FIELD The present disclosure relates to a control system for controlling a braking system of a vehicle. Aspects of the invention relate to a control system, to a system, a vehicle, a method for controlling a braking system, and to computer readable instructions. BACKGROUND It is known to provide a vehicle with a powertrain having multiple drive modes by which the torque transfer to the wheels can be modified by the driver using a drive mode selector device. In automatic transmission vehicles, the powertrain is generally operable in one or more drive modes including: a forward drive mode ‘D’, a reverse drive mode ‘R’, a neutral drive mode ‘N’ and a park drive mode P. These drive modes can be selected by the driver using a drive mode selector, typically in the form of a lever, switch and / or rotary selector. In manual transmission vehicles, the powertrain is generally operable in number of drive modes including: a reverse drive mode 'R', a neutral drive mode ‘N’, and multiple forward drive modes (1st, 2nd, 3rd...) which are typically selected by the driver using a drive mode selector in the form of a gear lever. With either type of transmission, it is possible for the driver to inadvertently select the neutral drive mode ‘N’ without realising. As will be understood, torque is not transferred to the wheels by the powertrain when the neutral drive mode ‘N’ is selected. This can result in unexpected vehicle behaviour. 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 controlling a braking system of a vehicle. Aspects of the invention relate to a control system, to a system, a vehicle, a method for controlling a braking system, and to computer readable instructions as claimed in the appended claims. According to a first aspect of the present invention there is provided a control system for controlling a braking system of a vehicle. The control system comprises one or more processors collectively configured to receive input parameters at least comprising a drive mode signal indicative of a driver selected drive mode of the vehicle, and an active drive mode signal indicative of an active drive mode of the vehicle. The one or more processors are collectively configured to determine a braking condition is satisfied, wherein the braking condition requires at least that the received input parameters are indicative of: the driver selected drive mode is not a neutral drive mode, and the active drive mode is a neutral drive mode. In response to determining that the braking condition is satisfied, the one or more processors are collectively configured to output a braking torque request signal to the braking system to request a braking torque from the braking system. In some circumstances, the vehicle may default to a neutral drive mode ‘N’ when the driver has selected a non-neutral drive mode (e.g., a forward drive mode ‘D’ or a reverse drive mode ‘R’). The default to the neutral drive mode may occur due to some overriding control system logic of the vehicle, powertrain or transmission system, for example, in cases where the driver has requested a change in drive mode (e.g., from a forward drive mode to a reverse drive mode, or vice versa) and the vehicle is travelling above a threshold speed such that the change in drive mode cannot be affected. In such cases the driver may be expecting the vehicle to proceed to the driver selected drive mode and provide powertrain torque from the motor, however the vehicle is instead in a neutral drive mode. In the neutral drive mode the accelerator pedal will not result in a torque response from the powertrain resulting in motion of the vehicle by the powertrain’s prime mover(s). In this drive mode the prime mover(s) of the vehicle are not providing torque to the vehicle axles and / or wheels. As a result, for example, where the user is expecting a change in direction (from a reverse drive mode to a forward drive mode) depressing the accelerator pedal will not provide the torque they are requesting and the vehicle may accelerate in the opposite direction under its own weight. The control system therefore requests braking torque from the braking system of the vehicle as the driver could be unaware that the vehicle is in fact in a neutral drive mode. The braking torque arrests movement of the vehicle or decreases the likelihood of the vehicle accelerating under its own weight. The braking torque is a torque applied by the brakes to arrest motion of a wheel. For example, where the brake is a brake calliper, the braking torque is generated by pressure applied by the calliper to a brake disc. In another example, where the brake is an eddy current brake, the braking torque is generated by the induction of eddy currents. The driver selected drive mode may be different to a neutral drive mode. Alternatively, or optionally, in response to identifying that the condition is satisfied the one or more processors may output a braking force request signal to request a braking force instead of a braking torque request signal. Alternatively, or optionally, in response to identifying that the condition is satisfied the one or more processors may output a braking pressure request signal to request a braking pressure instead of a braking torque request signal. Optionally, the drive mode of the vehicle comprises one or both of: a transmission operating mode, and a driving operating mode comprising one or more sub-system modes indicating an operation of one or more vehicle sub-systems. The transmission operating modes may include at least one selected from amongst a Park, Reverse, Neutral, Drive mode, and Sport mode. These transmission positions are selectable in both High Range (focuses more on on-road driving and the comfort of the passenger) and Low Range (focuses more on off-road capability) and a manually selectable gear mode. The sport mode is a forward drive mode and may be a performance-oriented transmission mode. The driving operating mode may correspond to one or more terrain response modes. Optionally, the one or more vehicle sub-systems include at least one selected from amongst a powertrain controller arranged to select a correspondence between accelerator control and powertrain torque in dependence at least in part on the driving operating mode, a suspension control system, a steering control system and a brake control system. Optionally in response to identifying that the braking condition is not satisfied, output a drive mode change instruction signal to request the active drive mode change to the driver selected drive mode Optionally, the control system is for controlling the braking system of a vehicle comprising a drive mode selector. The drive mode selector may be movable between at least a drive position, a neutral position, and a reverse position. In some examples, the neutral position may be an intermediate position between the drive position and reverse position. That is, a user must cross the intermediate, neutral position when moving between the drive mode and reverse mode or vice versa. 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 input parameters at least comprising: a drive mode signal indicative of a driver selected drive mode of the vehicle; and an active drive mode signal indicative of an active drive mode of the vehicle; determine a braking condition is satisfied, wherein the braking condition requires at least that the received input parameters are indicative of: the driver selected drive mode is not a neutral drive mode; and the active drive mode is a neutral drive mode; and in response to determining that the braking condition is satisfied, output a braking torque request signal to the braking system to request a braking torque from the braking system. Optionally, there is provided a control system for controlling a braking system of a vehicle. The control system comprising one or more processors collectively configured to receive input parameters at least comprising an active drive mode signal indicative of an active drive mode of the vehicle; determine a braking condition is satisfied, wherein the braking condition requires at least that the received input parameters are indicative of: the active drive mode is a neutral drive mode; and in response to determining that the braking condition is satisfied, output a braking torque request signal to the braking system to request a braking torque from the braking system. Optionally, the drive mode signal further comprises information indicative of a request to change from an initial drive mode to the driver selected drive mode, wherein the initial drive mode is indicative of a first direction of travel and the driver selected drive mode is indicative of a second direction of travel opposite to the first direction of travel. The drive mode signal indicates that the drive mode is being requested to change from an initial drive mode to the driver selected drive mode. The initial and driver selected drive modes are both drive modes where the vehicle is intended to be moving, e.g. a reverse drive mode and forward drive mode. The driver is wanting to transition from a first direction of travel to a second direction of travel opposite the first direction of travel. Where this request is made by the driver there can be situations which cause the drive mode change not to proceed and the neutral drive mode to be engaged. When this occurs, the braking torque requested arrests or slows vehicle movement which is useful where the driver is travelling in a first direction and believes they will be immediately (or relatively shortly after be) travelling in a second direction. Optionally, the input parameters further comprise a vehicle speed signal indicative of a vehicle speed, wherein the braking condition further at least requires that the vehicle speed is above a vehicle speed threshold, and wherein the one or more processors are collectively configured to, in response to identifying that the braking condition is satisfied, delay output of a drive mode change instruction signal to request the active drive mode change to the driver selected drive mode until the vehicle speed is at or below the speed threshold. The control system may delay output of a drive mode change from the active drive mode to the driver requested drive mode when the vehicle speed reaches or goes below the speed threshold. The result is that the drive mode that was initially requested by the driver can then be activated. Optionally, the speed threshold is 8 kph or 7 kph or 6 kph or 5 kph or 4 kph or 3 kph or 2 kph or 1 kph or 0 kph. When the braking condition requires that the vehicle speed is above a speed threshold, the control system may not request that the braking torque be made if the vehicle speed is less than or equal to the minimum speed threshold. In such situations, the processors may collectively identify that the braking condition is not satisfied and so the braking system is not requested to generate the braking torque by the torque request signal. This can avoid unnecessary intervention by the control system in certain scenarios, such as where the vehicle is at rest and therefore no braking torque is required to moderate the vehicle speed. The speed threshold may be configurable such that the speed threshold is changeable, for example via a user interface. Optionally, the one or more processors are collectively configured to determine if the active drive mode has changed to the driver selected drive mode, and in response to identifying that the active drive mode has changed to the driver selected drive mode modify or stop the braking torque request signal to reduce or stop the braking torque requested from the braking system. By modifying the braking torque there may be a more gradual reduction of torque rather than a step change braking torque dis-application. This gradual decrease in braking torque means that the vehicle may come to a more gradual stop. The braking torque request signal may be modified such that the braking torque requested is reduced gradually, or “tapered-off”. By reducing the braking torque gradually, abrupt or unexpected acceleration of the vehicle can be avoided. The one or more processors may be collectively configured to calculate the modified braking torque in dependence upon the input parameters. For example, a reduction in the vehicle speed and / or road gradient can result in a reduction in the requested braking torque. The modified braking torque may be determined by the one or more processors by providing a look-up table of modified braking torque demands paired with vehicle speeds and gradients the control system can quickly find the required modified braking torque to be utilised. Different modified braking torque demand values can be provided for a number of different values of vehicle speed or vehicle gradient enabling greater control of the braking potential of the vehicle for different driving scenarios. The reduced braking torque requested from the braking system may be pre-calibrated. The control system may further comprise at least one memory on which the look-up table is stored. The one or more processors may be configured to access the at least one memory and read the look-up table stored thereon to identify the modified braking torque demand from said look-up table. Optionally, the one or more processors are collectively configured to, in response to identifying that the braking condition is satisfied, modify the braking torque request signal to increase the braking torque from the braking system during a taper-on period. By tapering the braking torque there may be a more gradual application of torque rather than a step change braking torque application. This gradual increase in braking torque means that the vehicle may slow more gradually to a stop or below the speed threshold, this more gradual application of torque reduces or mitigates any disturbance that could be felt by the driver or their passengers should there be a sudden application of torque. Further, this may give more time for the driver of the vehicle to take corrective action, such as requesting further foundational braking by depressing the brake pedal, should the driver deem such action necessary to be undertaken. Optionally, the taper on period is between 0.1 seconds and 3.0 seconds. The taper on period may be greater than 0.2 second, greater than 0.5 second, or greater than 1 second. The taper on period may be 1.5 seconds. The one or more processors may be collectively configured to calculate the modified braking torque in dependence upon the input parameters. For example, a reduction in the vehicle speed and / or road gradient can result in a reduction in the requested braking torque. The modified braking torque may be determined by the one or more processors by providing a look-up table of modified braking torque demands paired with vehicle speeds and gradients the control system can quickly find the required modified braking torque to be utilised. Different modified braking torque demand values can be provided for a number of different values of vehicle speed or vehicle gradient enabling greater control of the braking potential of the vehicle for different driving scenarios. The braking torque requested from the braking system may be pre-calibrated. The control system may further comprise at least one memory on which the look-up table is stored. The one or more processors may be configured to access the at least one memory and read the look-up table stored thereon to identify the modified braking torque demand from said look-up table. Optionally, the input parameters further includes a vehicle speed signal indicative of a vehicle speed and / or a gradient signal indicative of a gradient of a surface on which the vehicle is located. By utilising a vehicle speed signal and / or vehicle gradient signal, more nuanced control of the vehicle may be achieved. Optionally, the braking torque request signal comprises a braking torque demand indicative of the braking torque requested from the braking system, and wherein the braking torque demand is dependent upon at least one of the vehicle speed and the gradient of the surface on which the vehicle is located. With this arrangement, for certain driving conditions, the braking torque demand may be different when compared to other driving conditions. For example, where the road is steep and the vehicle is travelling at a first vehicle speed there may be a first value of the braking torque demand. In comparison when the vehicle is traveling at the same vehicle speed but at a different, less steep gradient, the braking torque demand may be at a second value which is different to, e.g., lower than, the first value. Optionally, or additionally, the vehicle speed threshold may be dependent upon the gradient of the surface on which the vehicle is located. In such situations the control system may enable more reactive braking requested by the control system in situations where the vehicle is on a steep gradient and is more likely to accelerate under its own weight than for a second less steep gradient. In such a scenario the speed threshold may be lower when the gradient is steeper and where the gradient is less steep the speed threshold may be greater. Optionally, the braking torque demand varies linearly in relation to one or both of the vehicle speed and the gradient of the surface on which the vehicle is located. By linearly relating the braking torque demand to one or both of the vehicle speed and the road gradient, the torque demand can be varied in dependence upon the current road conditions and speeds. The relationship between the braking torque demand and the vehicle speed and road gradient can be calculated by the one or more processors based on appropriate formulae. Alternatively, the input parameters may comprise a look-up table defining the braking torque demand as a function of the road gradient and the vehicle speed. The one or more processors may be configured to select the braking torque demand from the look-up table based on the vehicle speed and the road gradient. The control system may further comprise at least one memory on which the look-up table is stored. The one or more processors may be configured to access the at least one memory and read the look-up table stored thereon to identify the braking torque demand from said look-up table. Optionally, the braking condition requires that the gradient of the surface on which the vehicle is supported has a magnitude which is greater than a gradient threshold, and wherein the gradient threshold is 1 % or 2% or 3% or 4% or 5%. When the braking condition requires that the vehicle is supported on a surface having a gradient with a magnitude which is less than a gradient threshold, i.e., where the vehicle is on a flat or relatively low gradient, then the control system does not request the braking torque. This can avoid the need for unnecessary interventions by the braking system when the vehicle is on the flat or on a gentle slope, since at low gradients the driver will generally have more time to react without control system intervention than for medium-to-high gradients (e.g., greater than 5% gradient) where the vehicle may accelerate more quickly under its own weight. Optionally, the one or more processors are collectively configured to ascertain an elapsed time following receipt of the drive mode signal and determine if the elapsed time is less than or equal to a permitted duration for outputting the drive mode change instruction signal, and output the drive mode change instruction signal in response to the determination that the elapsed time is less than or equal to the permitted duration. The drive mode change may be forced to be aborted at the end of the drive mode change period irrespective of any other condition being met. This is to ensure that the vehicle driver is not able to change direction of travel when falling foul of functional limitations that could give a poor response whilst driving of the vehicle. The drive mode change period may be 1 to 5 seconds from the initial receipt of the drive mode change signal. The drive mode change period may be 3 seconds or 1 second or 2 seconds or 3 seconds or 4 seconds or 5 seconds or 0.5 seconds. According to another aspect of the invention, there is provided a system comprising the control system of the control system aspect and a braking system. According to yet another aspect of the invention, there is provided a vehicle comprising the system of the system aspect or the control system according to the control system aspect. Optionally, the vehicle may comprise a drive mode selector. According to another aspect of the invention, there is provided a method for controlling a braking system of a vehicle. The method comprises receiving input parameters at least comprising a drive mode signal indicative of a driver selected drive mode of the vehicle, and an active drive mode signal indicative of an active drive mode of the vehicle. The method further comprises determining a braking condition is satisfied, wherein the braking condition requires at least that the received input parameters are indicative of: the driver selected drive mode is not a neutral drive mode, and the active drive mode is a neutral drive mode; and in response to determining that the braking condition is satisfied, outputting a braking torque request signal to the braking system to request a braking torque from the braking system. The method may optionally comprise any additional step, input parameter, condition, identification, determination and / or output of any one of the control system aspect, the system aspect and / or the vehicle aspect. According to another aspect of the invention, there is provided computer readable instructions which, when executed by one or more processors, cause the one or more processors to perform the method according to the method aspect. 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 One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 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 diagram of the vehicle of Figure 1; Figure 3 shows a schematic diagram of a control system in accordance with an embodiment of the invention; Figure 4 to 7 show flow charts in accordance with embodiments of the invention; and Figure 8 shows a graph of braking pressure against time according to an embodiment of the invention. DETAILED DESCRIPTION A control system 100 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figures 1 to 8. The control system 100 is suitable for controlling a braking system 60 of a vehicle 1 with at least one prime mover 26 (alternatively known as an actuator or torque source). As shown in Figure 2, the control system 100 is installed in a vehicle 1. The control system 100 is shown in more detail in Figure 3. The vehicle 1, in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figure 2. In some, but not necessarily all examples, the vehicle 1 is a passenger vehicle, also referred to as a passenger car or as an automobile. In other examples, embodiments of the invention can be implemented for other applications, such as commercial vehicles, vans or the like. Figure 2 schematically illustrates an example of at least part of a powertrain of the vehicle 1 with wheels 34. In this example, the vehicle 1 powertrain comprises a propulsion system 22 comprising the at least one prime mover 26. The prime mover 26 may be any one of an: internal combustion engine ‘ICE’, electric traction motor or alternatively the vehicle 1 may comprise a plurality of prime movers 26. Where a plurality of prime movers 26 are provided they may be one or more ICEs and an electric traction motor, or a plurality of electric traction motors. The prime mover(s) 26 are selectively operable for the purpose of providing drive torque for accelerating the vehicle 1. In alternative configurations with two prime movers 26, the first prime mover 26 may provide drive to a front axle and the second prime mover 26 provides drive to a rear axle, or vice versa. Where the at least one prime mover 26 comprises an electric traction motor this is an electric motor arranged to convert electrical energy into kinetic energy in the form of mechanical torque and may also be arranged to convert kinetic energy into electrical energy. The electric traction motor 26 may be an alternating current induction motor or a permanent magnet motor, or another type of suitable electric machine. The electric traction motor 26 is a traction motor configured to enable at least an electric mode comprising electric-only driving. That is, the electric traction motor 26 can drive the vehicle 1 by itself (without additional torque provided by a second torque source such as an engine). Another term for the electric traction motor 26 is an electric drive unit (EDU). In order to store electrical energy for the electric traction motor 26, the vehicle 1 comprises an electrical energy storage means. The electrical energy storage means can be a traction battery. The traction battery provides a nominal voltage required by electrical power users such as the electric traction motor 26. The traction battery may be a high voltage battery. The traction battery may have a voltage and capacity to support electric only driving for sustained distances. The traction battery may have a capacity of several kilowatt-hours, to maximise range. The capacity may be in the tens of kilowatt-hours, or even over a hundred kilowatt-hours. Although the traction battery is described as one entity, the function of the traction battery could be implemented using a plurality of small traction batteries in different locations on the vehicle 1. An inverter may be provided to convert between the DC output of the traction battery and the AC input required for the electric machine 26. The vehicle 1 comprises a transmission system 10 comprising a transmission 12, such as a single-speed gear reduction unit. The transmission system 10 is connected to the prime mover 26. The transmission 12 may be an automatic transmission comprising a fluid torque convertor or a manual transmission comprising a plurality of selectable gears. A transmission output shaft 20 from the transmission 12 is connected to a final set of gears 32, such as a pinion gear meshed with a ring gear, to transfer torque to the wheel axles and thus to vehicle wheels 34. The braking system 60 is shown schematically in Figure 2 by a dashed line 60. The braking system 60 comprises brakes 62. The brakes 62 include foundation brakes. It will be appreciated that foundation brakes include any braking 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. Examples of foundation brakes are friction brakes such as drum brakes or disc brakes 62. Disc brakes 62 comprise a brake disc and a calliper. In order to arrest movement of a vehicle 1 it will be appreciated that this means, in the example of disc brakes 62, that the application of a pressure from the calliper to the brake discs is used to slow vehicle 1 as is known in the art. Other examples of foundation brakes are eddy current brakes. The brakes 62 may also comprise a regenerative brake. The regenerative brakes, also referenced 62, are connected or connectable to the traction battery 28 such that when braking using the regenerative brakes 62 electrical energy is generated by the conversion of kinetic energy from braking. This electrical energy may then be stored in a traction battery to add battery charge from a braking event. 8 The vehicle further comprises a control system 100 for controlling the braking system 60, The control system 100 is shown located as part of the propulsion system 22, however the control system 100 may be located at any suitable location within the vehicle, for example within a transmission system 10 or as part of a braking system 60. The control system 100 is electrically connected to one or more sub-systems of the vehicle 1 including the braking system 60 to enable communication between the control system 100 and other components of the vehicle 1, such as a brake controller. The vehicle 1 has a number of drive modes which are selectable via a drive mode selector 70. The drive mode selector may be any suitable selector as is known in the art, such as a gesture sensor based drive mode selector, a lever or a rotary selector. For example, the drive mode selector may be the drive mode selector as described in WO2018130378A1, which describes a DRIVE MODE SELECTOR FOR A DRIVETRAIN, VEHICLE COMPRISING SUCH A DRIVE MODE SELECTOR, AND A METHOD OF SELECTING A DRIVE MODE OF A DRIVETRAIN, and this document is incorporated herein by reference. For reasons of clarity and to aid teaching the invention, the drive mode selector 70 shown in Figure 2 is a lever 70, however it is envisioned that the drive mode selector 70 may be any previously described device or device known within the art that is suitable for selection of a drive mode. The drive mode selector 70 comprises a controller 72. The controller 72 may be a separate computer, such as a microprocessor, or may be a software module running on a computer, such as a microprocessor, that is responsible for one or more other tasks within the vehicle. The controller 72 may form part of an electronic vehicle management system incorporating the control system 100 and / or communicate with the control system 100 as is shown in Figure 2. The controller 72 may include and / or communicate with other processors, sensors and outputs, as known to the skilled person and / or from WO2018130378A1. The vehicle 1 has a number of drive modes, including a park mode (‘P’), a reverse mode (‘R’), a neutral mode (‘N’) and a forward (“drive”) mode fD’). The vehicle 1 may have additional drive modes as is known in the art, such as a sport mode ‘S’ or manual mode ‘M’. In the reverse mode R, the driven wheels 34 (either front or rear axle for two-wheel drive or both front and rear axle for four-wheel drive) drive the car 100 rearwardly when the park brake and foot brake (not shown) are disengaged and the accelerator (not shown) is depressed. I n the drive mode D, the wheels 34 (either front or rear axle for two-wheel drive or both front and rear axle for four-wheel drive) move the vehicle 1 forwards when a park brake and foot brake are disengaged and an accelerator pedal is depressed. Selection of the drive mode of the automatic transmission conventionally involves moving the drive mode selector 70 between positions representing each of the various modes. A typical sequence (from forward / top to rear / bottom for a lever or clockwise for a rotary selector) is P, R, N, D. In view of the above description of the vehicle 1, it will be understood that the vehicle 1 may be a full hybrid electric vehicle (HEV) or a battery electric vehicle (BEV), a plug-in electric hybrid vehicle (PHEV), a mild hybrid electric vehicle (MHEV), an internal combustion engine vehicle (ICEV) or otherwise. It is envisioned that the present invention may work with any of these vehicle types. BEVs are an electric-only vehicle 1 which are propelled by an electric machine 26 that receives power from an on-board traction battery. The BEV may comprise a single electric machine, or both a first electric machine 26 and a second electric machine 26. The first and second electric machines 26 may provide power to the front and rear axles respectively. Alternatively, the BEV may have an electric machine 26 used to drive each wheel individually, as such a vehicle comprising four wheels may comprise four electric machines 26 with each electric machine driving a single wheel. MHEVs do not have an electric-only mode of propulsion, but the electric machine 26 may be configured to provide assistance such as boosting output torque of the engine 24. In such vehicles the electric machine 26 is not sufficiently powerful to drive the vehicle 1 under electric power alone. ICEV are propelled solely by an engine 24. Any on-board electric machine is used only as a starter-generator. 9 The vehicle 1 may be operable in a single pedal operating mode. The single pedal driving mode may be selected by the driver of the vehicle 1 via a setting on a graphical user interface or a push-button near the steering wheel, or alternatively the single pedal driving mode may be permanently on. The single pedal operating mode enables the vehicle 1 to be driven using the accelerator pedal with braking provided by the braking system, for example by one or more regenerative brakes 62, when the driver lifts pressure from the accelerator pedal. Additional braking may be provided by the driver actuating the brake pedal. In the single pedal driving mode, the regenerative braking enables the vehicle to slow down more quickly when the driver reduces or removes any actuation on the accelerator pedal. The regenerative brakes 62 provide a braking force to arrest or slow movement of the vehicle 1 without the need for the driver to actuate the brake pedal. At the same time, the regenerative braking enables the generation of electrical energy to charge the traction battery. The control system 100 will now be described with the aid of Figures 3 to 8. The control system 100 is configured to receive, at least one input parameter 310 from a drive mode selector sensor 74, which indicates a selected drive mode of the vehicle, and determine, if a braking condition is satisfied. If the braking condition is satisfied the control system 100 then outputs a control signal 155. The control system 100 as illustrated in Figure 3 comprises one controller 110, although it will be appreciated that this is merely illustrative. The controller 110 comprises processing means 120 and memory means 130. The processing means 120 may be one or more electronic processing device 120 which operably executes computer-readable instructions. The memory means 130 may be one or more memory device 130. The memory means 130 is electrically coupled to the processing means 120. The memory means 130 is configured to store instructions, and the processing means 120 is configured to access the memory means 130 and execute the instructions stored thereon. The controller 110 comprises an input means 140 and an output means 150. The input means 140 may comprise an electrical input 140 of the controller 110. The output means 150 may comprise an electrical output of the controller 110. The input 140 is arranged to receive input parameters 310 and determine if a braking condition is satisfied. The controller 110 is arranged to output a control signal 155 comprising a braking torque request signal 330 to the braking system 60 of the vehicle to request a braking torque. The at least one input parameter signal 310 comprises one or more electrical signals indicative of at least one input parameter. The output 150 is arranged to output the control signal 155. Figure 4 illustrates a flow chart 400 of control system logic carried out by the control system 100, the controller 110 and / or processor(s) 120. The flow chart 400 describes control system logic for controlling a braking system 60 of a vehicle 1, such as the vehicle 1 illustrated in Figure 1 and 2. The flow chart 400 concerns the determination of whether the braking condition is satisfied and in response application of a braking torque to arrest or slow movement of the vehicle 1. The flow chart 400 comprises a step S410 whereby the at least one input parameter 310 is received by the processors) 120. The input parameters 310 comprise a drive mode signal 320 and an active drive mode signal 326. The drive mode signal 320 is indicative of a selected drive mode of the vehicle 1, this may be a driver selected drive mode such as a forward drive mode D, or reverse drive mode R. Although described as a driver selected drive mode, it should be understood that an ADAS system may optionally select the drive mode (for example during a parking operation). As such, an ADAS selected drive mode may also be considered a “driver selected drive mode”. The active drive mode signal 326 is indicative of the actual current (active) drive mode of the vehicle. The active drive mode signal 326 may be obtained from a sensor or signal of the drive mode selector sensor 74, or another control system or sensor of vehicle 1. As will be apparent, the active drive mode signal 326 may in certain situations indicate a different drive mode to the driver selected drive mode. This may occur when, for example, the control system 100, or another control system in vehicle 1 requests a neutral drive mode N to be active due to some functional criterion which overrides the request of the driver, for example, due to the vehicle travelling above a threshold speed such that the driver selected drive mode cannot be affected. The method 400 is aimed at such a scenario and arresting vehicle motion when the vehicle is in the neutral drive mode N when the neutral drive mode N has not been selected by the driver (or by the ADAS system). Then, at step S420, represented by a decision box comprising two branches (a T branch and a ‘0’ branch), the processor(s) 120 is configured to determine if a braking condition has been satisfied. The condition is satisfied when the active drive mode is a neutral drive mode N and the driver selected drive mode is not the neutral drive mode N. If the condition is satisfied, then the flow chart 400 will move down the T branch to step S430 and the processor(s) 120 will output a braking torque request signal 330 to the braking system 60 to request a braking torque from the braking system 60. If the condition is not satisfied, for example because the neutral drive mode N was selected as a driver selected drive mode, then the flow chart 400 will move to step S440 and end the control system logic. The flow chart 400 and control system logic therein may become active each time a drive mode signal 320 indicates that a drive mode change has been requested. As such, each time the driver requests a drive mode change the control system 100 may check to see if the condition is met. The drive mode signal 320 may further comprise information indicative of a request to change from an initial drive mode to the driver selected drive mode. The initial drive mode is indicative of a first direction of travel and the driver selected drive mode is indicative of a second direction of travel opposite to the first direction of travel. For example, the vehicle may be in a reverse drive mode R and the driver may wish to put the vehicle into a forward drive mode D. In such a case, the determination of the braking condition at step S420 may further require that there is a request to change from an initial drive mode to the driver selected drive mode where the initial drive mode is indicative of a first direction of travel and the driver selected drive mode is indicative of a second direction of travel opposite to the first direction of travel. Additionally, or optionally, the processor(s) 120 are collectively configured to modify the braking torque request signal 330 to increase the braking torque from the braking system 60 during a taper on period. The ability to increase the torque requested over a taper on period prevents a step change in torque application from the braking system which may cause a driveline disturbance felt by the driver of the vehicle. The taper on period may be between 0.1 seconds and 3.0 seconds, or 0.1 seconds and 2.0 seconds, or 0.5 seconds and 2.0 seconds. Alternatively, the taper on period is 1.5 seconds. Figure 5 illustrates a flow chart 500 having additional or optional control system logic to flow chart 400 carried out by the control system 100, the controller 110 and / or processor(s) 120. Steps S510, S520, S530 and S540 are similar to steps S410, S420, S430, and S440 but with some additional logic. Flow chart 500 considers the vehicle speed as part of the braking condition and does not request a braking torque when the vehicle is moving at a speed below a speed threshold. This additional condition prevents potentially unnecessary braking where it is not required, e.g., when the vehicle is stationary. The flow chart 500 describes control system logic for control of a braking system 60 of a vehicle 1 whereby additional, or optional steps are undertaken. The braking condition comprises one or more operating requirements to be satisfied prior to intervention by the control system 100. In such a case, the input parameters further include a vehicle speed signal 322 indicative of the speed of the vehicle 1. The processor(s) 120 is further configured to compare the vehicle speed with a speed threshold as part of step S520. The braking condition requires the additional identification at S530 that the vehicle speed is above a vehicle speed threshold. Should the braking condition be met then the control system logic follows the normal route per step S520 discussed above in relation to S420. Additionally, at step S530, the processor(s) 120 may be configured to delay the output of a drive mode change instruction signal 332 until the vehicle speed is at or below the vehicle speed threshold. The drive mode change instruction signal 332 requests that the active drive mode be changed to the driver selected drive mode. The speed threshold may be 8 kph or 7 kph or 6 kph or 5 kph or 4 kph or 3 kph or 2 kph or 1 kph 0 kph, or any subset or range thereof. Where the speed of the vehicle 1 is below or equal to the vehicle speed threshold the condition is not met and the braking torque is not requested. As will be apparent the speed threshold is irrespective of direction, in other words if the speed threshold is, for example, 8 kph and the vehicle was traveling forward at 9 kph that would meet the additional condition of the braking condition. Likewise, if the vehicle were travelling in reverse at 9 kph for the same speed threshold of 8 kph the additional condition would also be met. Additionally, or optionally for either flow chart 400 or 500, the braking condition may comprise one or more operating requirements to be satisfied prior to intervention by the control system 100. In such a case, the input parameters 310 further include a gradient signal 324 indicative of a gradient of a surface on which the vehicle is travelling or located on. The processor(s) 120 may be further arranged to determine whether a magnitude of a gradient of the surface on which the vehicle is travelling is greater than a gradient threshold as part of step S430 / S530. Should the braking condition be met then the control system logic follows the normal route per step S420 / S520 discussed above. The gradient threshold is: 5%, or 4%, or 3, or 2%, or 1 %, or any subset or range thereof. Additionally, or optionally, where the input parameters further include one or both of the vehicle speed signal 322 indicative of a vehicle speed and the gradient signal 324 indicative of a gradient of a surface on which the vehicle is travelling, the braking torque demanded may be dependent upon one or both of the vehicle speed or gradient. Figure 6 illustrates a flow chart 600 having the additional or optional control system logic to flow chart 400 or 500 carried out by the control system 100, the controller 110 and / or processor(s) 120. The flow chart 600 describes control system logic for control of a braking system 60 of a vehicle 1 whereby the braking torque requested by the braking torque request signal 330 and is a torque demand Pd. The torque demand Pa is dependent upon one or both of the vehicle speed and the gradient of the surface on which the vehicle is located. The flow chart 600 concerns the determination of a torque demand Pd which is tailored to react to current vehicle 1 conditions. Steps S610, S620, S630 and S640 are similar to steps S510, S520, S530 and S540 orS410, S420, S430 and S440 but with some additional logic. The flow chart 600 comprises an additional step S625 between step S620 and S630. At this step the processor(s) 120 determine, in dependence upon one or both of the vehicle speed and / or the gradient of the surface on which the vehicle 1 is travelling, a torque demand Pd. The torque demand Pa is then output with the braking torque request signal 330. The torque demand Pd may be calculated by the processor(s) 120 enabling the vehicle 1 to adapt quickly to changing surface conditions or vehicle speeds. In such a case, the torque demand Pd may linearly vary in relation to one, or both, of the vehicle speed and the gradient of the surface on which the vehicle is travelling. Alternatively, or optionally, the torque demand Pd may be obtained from a look-up table. The look-up table comprises a plurality of vehicle speed-gradient pairings. The vehicle speed-gradient pairings all indicating a torque demand Pd to be utilised for a particular vehicle speed-gradient pairing. The processor(s) 120 can access the look-up table which is stored in the memory means 130 to select an appropriate torque demand Pd for the current driving conditions. An alternative, or optional, flow chart 700 is provided in Figure 7. Flow chart 700 provides additional steps in relation to flow chart 600 to modify the braking torque where the condition is no longer satisfied. The advantage of which is to prevent braking where it is no longer required by the control system 100. Flow chart 700 comprises additional steps S750 and S760 which come after step S730. After the braking torque request signal 330 is output at S730 the processors) 120 continue to monitor the input parameters 310 to check whether the braking condition is still met at step S760. For example, if the active drive mode signal 326 changes from neutral N to a forward drive mode D (where the driver has selected the forward drive mode D for example) then the braking condition is no longer met. As a result, the braking torque previously requested is no longer required. Steps S710, S720, S725, S730 and S740 are similar to steps S610, S620, S625, S630 and S640 but with some additional logic. After the braking condition is determined to no longer be required, the flow chart 700 moves onto step S760. At step S760 the braking torque request signal 330 is stopped to remove the braking torque requested from the braking system 60. Alternatively, following step S750 where the condition is no longer met the braking torque request signal 330 is modified to reduce the requested braking torque at step S760. For example, the requested braking torque may be modified in dependence upon the vehicle speed and / or gradient on which the vehicle 1 is currently travelling. Alternatively, the modification to the braking torque is determined by providing a look-up table of modified torque demands paired with vehicle speeds and gradients the control system can quickly find the required modified torque to be utilised. Different modified torque demand values can be provided for a number of different values of vehicle speed and / or vehicle gradient enabling greater control of the braking potential of the vehicle for different driving scenarios. The reduced braking torque requested from the braking system may be pre-calibrated and / or obtained from a look-up table stored in the memory means 130. Alternatively, at step S760 the braking torque may be reduced as part of a taper-off period. The taper-off period is substantially similar to the taper-on period described above however a reduction in braking torque to zero rather than an increase in braking torque from zero per the taper-on period. Optionally, according to any of the flow charts 400, 500, 600, 700 an additional step may be provided whereby the at least one input parameter 310 further comprises a vehicle operating mode signal 328 indicative of a current operating mode of the vehicle 1. The condition further requires determining that the current operating mode corresponds to one or more of a set of predefined vehicle operating modes. This enables the control system 100 to output the braking torque request signal 330 only when the vehicle 1 is operated in certain vehicle operating modes and to avoid requesting braking torque in other vehicle operating modes. This can help to avoid the braking torque being applied when the vehicle 1 is in a vehicle operating mode in which braking is not desired, such as when the vehicle 1 is being towed (in a ‘tow-mode’) or moving through a car wash, for example. The set of predefined vehicle operating modes may include a single pedal operating mode in which acceleration and braking functions are requested through a single pedal, typically the accelerator or gas pedal. Optionally, or additionally the input parameters 310 further comprise a driver detection signal as the vehicle operating mode signal 328. The driver detection signal is generated when the control system 100 or an alternative control system detects that a driver is present and seated in the driver seat. The detection of driver presence and the generation and output of a driver detection signal to the control system may be made by any one or more of: detecting that the driver side door has been opened and closed in dependence upon a driver side door sensor, that the driver seat belt is buckled in dependence upon a driver seatbelt buckle sensor, a weight is present in the driver seat in dependence upon a driver seat weight sensor. Optionally, or additionally, any of the flow charts 400, 500, 600, 700 may have an additional step whereby the control system checks if the drive mode change has been output within a permitted duration. This may be used to ensure that the driver does not fall foul of functional limitations that give a poor response when driving the vehicle 1. In such a case, the one or more processors 120 are collectively configured to ascertain an elapsed time following receipt of the selected drive mode signal 320 and determine if the elapsed time is less than or equal to a permitted duration for outputting the drive mode change instruction signal 332. If the elapsed time is less than or equal to the permitted duration then the control system 100 outputs the drive mode change instruction signal 332 in response to the determination that the elapsed time is less than or equal to the permitted duration. If the elapsed time is greater than the permitted duration then the drive mode change may not proceed. Figures 4 to 7 show flow charts 400,500, 600,700 which indicate methods for controlling a braking system 60 of a vehicle 1 according to an embodiment of the invention. The methods of flow charts 400, 500, 600, 700 may be performed by the braking system 60 and control system 100 illustrated in Figures 2 for vehicle 1. In particular, the memory means 130 may comprise computer-readable instructions which, when executed by the processor 120, perform the steps of any one of flow charts 400, 500, 600, 700 according to an embodiment of the invention. The method of applying and removing the braking torque as discussed above will be described with the aid of Figure 8 showing a graph 800. Figure 8 has time, t, on the x-axis and braking torque, Pd on the y-axis. At an initial time ti, which coincides with, or is shortly after, the output step S420, a braking torque Pd begins to be applied by the braking system 60. That is, once the braking condition has been satisfied and the braking torque request signal 330 has been sent to the braking system 60. At ti the braking torque begins to be applied by the braking system 60 until a maximum is reached at t2 as shown by the two curves 810 and 820. The braking torque may either increase at a constant rate, as indicated by the linear curve 810 or, the rate of braking torque may change during the taper-on period as indicated by curve 820. Alternatively, instead of a gradual increase the braking torque may be applied as a step change (not shown) where the requested torque may be a request for a first torque level without any taper-on as indicated in Figure 8 by curves 810 and 820. The torque level reached at time t2 may be dependent upon one or both of the gradient and vehicle speed as discussed above. After time b and up to time b, the braking torque may be maintained on for a time period equal to the difference between b and b. This time period may be 1 to 10 seconds or the time period may last until the condition is no longer satisfied as discussed above with relation to flow chart 700. Whilst the time period b to b is shown as a constant braking torque level, it will be appreciated that the torque level may vary in dependence upon the vehicle speed and / or gradient of the surface on which the vehicle 1 is travelling as discussed above. Subsequently at b a taper-off period may begin whereby the baking torque request signal is modified or stopped to reduce or stop the braking torque requested from the braking system 60 as discussed above with respect to flow chart 700. Alternatively, instead of a gradual decrease, or decrease in dependence upon vehicle speed and / or gradient, the braking torque may be removed as a step change, that is that the modified torque request may be a request for a zero braking torque level without any taper-off. As will be appreciated, the braking torque may not plateau and be maintained as indicated by the graph 800 between b and b. Instead, the braking torque Pd may be increased to a value at which point the drive mode change occurs, subsequently the braking torque Pd is then decreased. In other words, curves 810 and 820 would increase then decrease without a constant braking torque Pd being applied. 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 controlling a braking system of a vehicle, the control system comprising one or more processors collectively configured to:receive input parameters at least comprising:a drive mode signal indicative of a driver selected drive mode of the vehicle; andan active drive mode signal indicative of an active drive mode of the vehicle;determine a braking condition is satisfied, wherein the braking condition requires at least that the received input parameters are indicative of:the driver selected drive mode is not a neutral drive mode; andthe active drive mode is a neutral drive mode; andin response to determining that the braking condition is satisfied, output a braking torque request signal to the braking system to request a braking torque from the braking system.

2. A control system according to claim 1, wherein the drive mode signal further comprises information indicative of a request to change from an initial drive mode to the driver selected drive mode;wherein the initial drive mode is indicative of a first direction of travel and the driver selected drive mode is indicative of a second direction of travel opposite to the first direction of travel.

3. A control system according to claim 1 or 2, wherein the input parameters further comprise: a vehicle speed signal indicative of a vehicle speed;wherein the braking condition further at least requires that the vehicle speed is above a vehicle speed threshold; and wherein the one or more processors are collectively configured to:in response to identifying that the braking condition is satisfied, delay output of a drive mode change instruction signal to request the active drive mode change to the driver selected drive mode until the vehicle speed is at or below the speed threshold.

4. A control system according to claim 3, wherein the speed threshold is 8 kph or 7 kph or 6 kph or 5 kph or 4 kph or 3 kph or 2 kph or 1 kph or 0 kph.

5. The control system according to claim 3 or 4, wherein the one or more processors are collectively configured to determine if the active drive mode has changed to the driver selected drive mode, and in response to identifying that the active drive mode has changed to the driver selected drive mode modify or stop the braking torque request signal to reduce or stop the braking torque requested from the braking system.

6. A control system according to any preceding claim, wherein the one or more processors are collectively configured to, in response to identifying that the braking condition is satisfied, modify the braking torque request signal to increase the braking torque from the braking system during a taper-on period.

7. A control system of any preceding claim, wherein the input parameters further include a vehicle speed signal indicative of a vehicle speed and / or a gradient signal indicative of a gradient of a surface on which the vehicle is located.8, A control system according to claim 7, wherein:the braking torque request signal comprises a braking torque demand indicative of the braking torque requested from the braking system; andwherein the braking torque demand is dependent upon at least one of the vehicle speed and the gradient of the surface on which the vehicle is located.

9. The control system of claim 8, wherein, the braking torque demand varies linearly in relation to one or both of the vehicle speed and the gradient of the surface on which the vehicle is located.

10. The control system of any of claims 7, 8 or 9, wherein the braking condition requires that the gradient of the surface on which the vehicle is supported has a magnitude which is greater than a gradient threshold, and wherein the gradient threshold is 1 % or 2% or 3% or 4% or 5%.

11. A control system according to claim 3 or according to any of claims 4 to 10 when dependent upon claim 3, wherein the one or more processors are collectively configured to:ascertain an elapsed time following receipt of the drive mode signal and determine if the elapsed time is less than or equal to a permitted duration for outputting the drive mode change instruction signal; andoutput the drive mode change instruction signal in response to the determination that the elapsed time is less than or equal to the permitted duration.

12. A system comprising the control system of any preceding claim and a braking system.

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

14. A method for controlling a braking system of a vehicle, the method comprising:receiving input parameters at least comprising:a drive mode signal indicative of a driver selected drive mode of the vehicle; andan active drive mode signal indicative of an active drive mode of the vehicle;determining a braking condition is satisfied, wherein the braking condition requires at least that the received input parameters are indicative of:the driver selected drive mode is not a neutral drive mode; andthe active drive mode is a neutral drive mode; andin response to determining that the braking condition is satisfied, outputting a braking torque request signal to the braking system to request a braking torque from the braking system.

15. Computer readable instructions which, when executed by one or more processors, cause the one or more processors to perform the method according to claim 14.18

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