Control system for controlling a powertrain of a vehicle

Abstract

Aspects of the present invention relate to a control system (100), a system, a vehicle (1), a method and computer readable instructions. The control system is configured to receive (S410) a plurality

Description

TECHNICAL FIELD The present disclosure relates to a control system for controlling a powertrain of a vehicle. Aspects of the invention relate to a control system, a system, a vehicle, a method and computer readable instructions. BACKGROUND It is known to provide a vehicle with a powertrain having multiple drive modes in which the powertrain can be operated. These often include a forward drive mode ‘D’ and a reverse drive mode ‘R’. For example, in automatic transmission vehicles, the drive modes typically include two or more of: a forward drive mode ‘D’, a reverse drive mode ‘R’, a neutral drive mode ‘N’ and a park drive mode ‘P’. In some vehicles the drive modes are selectable using a drive mode gear lever or drive mode selector. The gear lever or selector may be a mechanical or electrical device used to select one of the specific drive modes. Selection of the drive mode conventionally involves moving a lever or rotary selector 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) for an automatic transmission is P, R, N, D. In such a case, the driver of the vehicle can move between the different drive modes by actuating the gear lever or selector. When undertaking a manoeuvre, such as a parking manoeuvre, a driver may wish to change the direction of the vehicle and so must move the drive mode from a forward drive mode ‘D’ to a reverse drive mode ‘R’, or vice versa. If, however, the vehicle is moving at speed there is the potential that changing the drive mode may cause a driveline disturbance which could be felt by the driver. The driveline disturbance may negatively impact the smoothness of vehicle travel causing a shuffle or shunt to be felt by the driver and / or their passengers when changing drive modes. Driveline disturbances may decrease the comfort of the driver and / or their passengers. 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, a system, a vehicle, a method 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 controlling a powertrain of a vehicle, the control system comprising one or more processors collectively configured to: receive a plurality of input parameters comprising: a vehicle speed signal indicative of a vehicle speed; and a drive mode change signal indicating that a drive mode change is required; determine, in dependence on the input parameters, whether the vehicle speed is greater than a speed threshold; in response to determining that the vehicle speed is greater than the speed threshold, delay outputting a drive mode change instruction signal until the vehicle speed is less than or equal to the speed threshold. According to an aspect of the present invention there is provided a control system for controlling a powertrain of a vehicle, the control system comprising one or more processors collectively configured to: receive a plurality of input parameters comprising: a vehicle speed signal indicative of a vehicle speed; and a drive mode change signal indicating that a drive mode change between a forward driving mode and a reverse driving mode is required; determine, in dependence on the input parameters, whether the vehicle speed is greater than a speed threshold when the drive mode change is required; in response to determining that the vehicle speed is greater than the speed threshold, delay outputting a drive mode change instruction signal until the vehicle speed is less than or equal to the speed threshold. The control system is configured to prevent change of drive mode change when a vehicle is moving and the driver wishes to change the vehicles intended direction of travel. By requesting the change of drive mode to be delayed this can reduce the magnitude of (or mitigate entirely) driveline disturbances that might otherwise be felt by the driver. For example, the disturbance is mitigated when the drive mode changes whilst the vehicle is at or below the minimum speed threshold in a forward direction (the Drive gear (D)) and the control system instructs the vehicle to travel in reverse (the Reverse gear (R)) or vice versa. The delayed drive mode change further can reduce wear on components of the powertrain as angular momentum will be reduced substantially when the vehicle is at or below the minimum speed threshold as compared to when the vehicle is moving above this threshold. 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 plurality of input parameters comprising: a vehicle speed signal indicative of a vehicle speed; and a drive mode change signal indicating that a drive mode change between a forward driving mode and a reverse driving mode is required; determine, in dependence on the input parameters, whether the vehicle speed is greater than a speed threshold when the drive mode change is required; in response to determining that the vehicle speed is greater than the speed threshold, delay outputting a drive mode change instruction signal until the vehicle speed is less than or equal to the speed threshold. In an embodiment, the input parameters comprise a torque demand signal indicating an amount of torque demanded of the powertrain of the vehicle; the one or more processors are collectively configured to determine whether the amount of torque demanded is higher than a permitted torque threshold, and in response to determining that the amount of torque demanded is higher than the permitted torque threshold, delay outputting the drive mode instruction signal until the amount of torque demanded is equal or below the permitted torque threshold. The torque demanded from the powertrain of the vehicle may be a driver torque demand or an ADAS (Advanced Driver Assistance System) torque demand. Where a driver demands a torque to be delivered by the torque generating devices, for example by depressing an accelerator pedal, the control system may determine if this demanded torque is permitted to be delivered at the same time as the drive mode change. For example, if a drive mode change is requested when the accelerator has been completely depressed, the increase in the demand for torque could negatively affect the powertrain of the vehicle if the drive mode change were to proceed at such a high torque demand. To address this, the control system may delay instructing the drive mode change until the torque is equal or below the permitted torque threshold. The control system may wait for the amount of torque demanded by the driver to be reduced to below the permitted torque threshold, i.e. the control system may take a passive role. Optionally, the one or more processors are collectively configured to output a modified torque demand signal to one or more torque generating devices of the powertrain to reduce the amount of torque demanded to be equal to or below the permitted torque threshold. By modifying the torque demand to reduce it to at or below the permitted threshold, the control system can actively decrease the time whereby the system is able to arrive at the permitted torque threshold without the need for driver input by modulating the accelerator pedal for example. The permitted torque threshold may be any suitable value. For example, the permitted torque threshold may be 0 Nm, 0.5 Nm, 2 Nm, 3 Nm, 4 Nm, 5 Nm, 6 Nm, 7 Nm, 8 Nm, 9 Nm, 10 Nm, 12 Nm, 15 Nm, or 20Nm. Optionally, the permitted torque threshold is 1 Nm. The permitted torque threshold is the threshold whereby the drive mode change can be permitted to proceed. The permitted torque threshold may be a relatively low torque so that there is a reduction in the of causing excess stress on the components of the powertrain. By causing the drive mode change to occur at or below a torque threshold of 1 Nm there is a mitigation or reduction in any driveline disturbances that may be felt by the driver, such as shuffles and or shunts, that could occur if the drive mode change happens at greater magnitudes of torque. As used herein, the term “permitted torque range” refers to the range of torque values which are equal to or less than the permitted torque threshold. In an embodiment, the input parameters comprise a gradient signal indicative of a gradient of a surface on which the vehicle is travelling, the one or more processors are collectively configured to determine whether the gradient meets a gradient braking condition, the gradient braking condition requiring at least that the gradient is greater in magnitude than a gradient threshold; and in response to determining the gradient meets the gradient braking condition, output a braking torque request signal to request a braking torque. The braking torque is the torque applied by the brakes to arrest motion of a wheel. For example, where the brake is a brake calliper, the braking torque is the torque applied by the calliper to the brake disc. Alternatively, the braking torque may be a braking force request signal to request a braking force applied by the calliper to the brake disc instead of a braking torque. Alternatively, the braking torque may be a braking pressure request signal to request a braking pressure applied by the calliper to the brake disc instead of a braking torque. Alternatively, or optionally, in response to determining the gradient is greater in magnitude than the gradient threshold output a braking force request signal to request a braking force. Alternatively, or optionally, in response to determining the gradient is greater in magnitude than the gradient threshold output a braking torque request signal to request a braking torque. Wherein the braking torque is dependent upon one or both of a braking force and braking pressure. Optionally or additionally, the gradient braking condition further requires that the gradient is negative. In such examples, the gradient threshold is a down slope gradient threshold. With this arrangement, when the vehicle is travelling downhill the control system may request a braking torque to arrest or slow movement of the vehicle. The braking torque reduces the potential for undesirable vehicle acceleration under its own weight. A negative gradient is defined as downhill in the current direction of travel. For example, the front of the vehicle is facing downhill with the vehicle in drive, or the front of the vehicle is facing uphill with the vehicle in reverse; in both examples the vehicle is intended to be driven downhill. The gradient threshold may be any suitable value. For example, the gradient threshold may be 0%, -1%, -2%, -3%, -4%, -5%, -6%, -7%, -8%, -9%, or -10%. Optionally or additionally, the gradient threshold is a 0% to -2% gradient. By requiring a negative gradient, the downhill only logic can avoid potentially unnecessary interventions when the vehicle is going uphill. Optionally or additionally, the one or more processors are collectively configured to output a compensatory braking torque demand signal to request a compensatory braking torque from a braking system to compensate for the reduction in the amount of torque from the one or more torque generating devices of the powertrain due to the modified torque demand signal. This can enable the overall torque provided by the combination of the powertrain and the braking system to may closely approximate the amount of torque demanded. Optionally or additionally, the compensatory braking torque demand signal is output only if the gradient is determined to be negative. Optionally or additionally, the one or more processors are collectively configured to: determine whether the gradient is positive and greater in magnitude than an uphill slope gradient threshold; and in response to determining the gradient is positive and greater in magnitude than the uphill slope gradient threshold, output an arresting torque request signal to from one or more torque generating devices of the powertrain of the vehicle to request an arresting torque from the one or more torque generating devices. When the vehicle is travelling uphill and powertrain torque output is reduced, the vehicle will naturally come to a rest more quickly due to the decelerating force of the vehicle’s own weight. By outputting an arresting torque request signal, the control system can cause the powertrain to provide an arresting torque to slow the vehicle as well. This arresting torque could be provided by a regenerative braking system in the vehicle, for example, and / or by operating an electric traction motor of the powertrain as a generator, for example as a crankshaft integrated motor generator. A positive gradient is defined as uphill in the current direction of travel. For example, the vehicle is facing uphill in drive, or the vehicle is facing downhill and in reverse; in both examples the vehicle is intended to be driven uphill and therefore to a ‘higher’ comparative elevation. The gradient threshold may be any suitable value. For example, the gradient threshold may be 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. The uphill slope gradient threshold is a gradient above 0% to 2%. In an embodiment, the input parameters comprise a drive mode change time limit indicating a time limit for the drive mode change to occur; and the one or more processors are collectively configured to: determine if the drive mode change instruction signal has been outputted within the drive mode change time limit; and in response to determining that the drive mode change instruction signal has not been outputted within the drive mode change time limit, output a drive mode change not completed signal. The drive mode change time limit signal is used to check that the gear change occurs within a set time limit. If the gear change does not progress before the time limit, then a further signal is output indicating that the drive mode change was not completed within the time required. The drive mode change time limit may be 1 to 5 seconds. The drive mode change time limit may be 3 seconds. If the gear change has not proceeded within the time limit set by the drive mode change time limit there may be an overriding reason for the drive mode change not to have progressed, for example alternative control systems have overridden the original drive mode change command. According to another aspect of the present invention there is provided a system. The system comprising the any control system of preceding aspect and a powertrain of a vehicle. According to an yet another aspect of the present invention there is provided a vehicle. The vehicle comprising the system of the preceding aspect or the control system of the control system aspect. According to further aspect of the present invention there is provided a method for controlling a powertrain of a vehicle. The method comprising: receiving a plurality of input parameters comprising: a vehicle speed signal indicative of a vehicle speed; and a drive mode change signal indicating that a drive mode change between a forward driving mode and a reverse driving mode is required; determining, in dependence on the input parameters, whether the vehicle speed is greater than a speed threshold when the drive mode change is required; and in response to determining that the vehicle speed is greater than the speed threshold, delay outputting a drive mode change instruction signal until the vehicle speed is less than or equal to the speed threshold. The method may comprise any further input parameters, determining steps and / or response steps of any other aspect or embodiment of the invention. According to an aspect of the present invention there is provided computer readable instructions which, when executed by a computer, are arranged to perform the method according to the previous 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: Figure 1 shows a vehicle in accordance with an embodiment of the invention; Figure 2 shows a schematic diagram of a system of the vehicle of Figure 1; Figure 3 shows a schematic diagram of a control system of the vehicle of Figure 1; Figure 4 is a flow chart of a first method in accordance with an embodiment of the invention; Figure 5 is a flow chart of a second method in accordance with an embodiment of the invention; Figure 6 is a flow chart of a third method in accordance with an embodiment of the invention; Figure 7 is a flow chart of a fourth method in accordance with an embodiment of the invention; and Figure 8 is a flow chart of a fifth method in accordance with 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 powertrain of a vehicle 1. 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. Figure 1 illustrates a vehicle 1 in accordance with an embodiment of the present invention. 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. The vehicle 1 comprises a control system 100 as illustrated in Figure 3. Figure 2 schematically illustrates a system 50 of the vehicle 1 of Figure 1. The system 50 comprises a powertrain 22 and a control system 100. The system 50 may optionally further comprise a braking system 60. The powertrain 22 comprises at least one prime mover 26. The at least one prime mover 26 is a torque source for the purpose of providing drive torque by which the vehicle 1 can be accelerated. In the illustrated embodiment, the at least one prime mover 26 is an electric traction motor 26. 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). Alternatively, the at least one prime mover 26 may comprise an internal combustion engine ‘ICE’ (not shown), or comprise a plurality of prime movers 26, for example a plurality of electric traction motors. The electric traction motor may provide drive to one or more of the wheels 34 in any suitable manner, such as via a transmission shaft and / or via one or more gears, differentials or transaxles, or directly. In the illustrated embodiment, the electric traction motor 26 provides torque to one or more of the wheels 34 via an optional transmission system 10 comprising a transmission 12, such as a single-speed gear reduction unit, an automatic transmission comprising a fluid torque convertor, or a manual transmission comprising a plurality of gears. Optionally, the transmission 12 may provide drive to the wheels 34 via one or more differentials 32. In alternative configurations with two prime movers 26, a first prime mover 26 may provide drive to a front axle with a second prime mover 26 providing drive to a rear axle, or vice versa. In other embodiments, the powertrain may comprise more than two electric traction motors, for example three or four electric traction motors, each arranged to drive one of the wheels 34 of the vehicle. Although the vehicle is illustrated as having two pairs of wheels 34, it will be appreciated that the vehicle may have any suitable number of wheels, for example two wheels, three wheels, or more than four wheels. In order to store electrical energy for the electric traction motor 26, the vehicle 1 comprises an electrical energy storage 28, such as a traction battery. The electrical energy storage 28 is configured to deliver electrical energy to the electric traction motor, and optionally to receive and store electrical energy generated by the electric traction motor (for example during regenerative braking). The electrical energy storage provides a nominal voltage required by electrical power users such as the electric traction motor 26. The electric traction motor 26 is electrically connected to the electrical energy storage 28, optionally by an inverter (not shown). In some embodiments, the electrical energy storage 28 is communicatively coupled to the control system. The electrical energy storage 28 is optionally a high voltage battery. The electrical energy storage 28 may have a voltage and capacity to support electric only driving for sustained distances. The electrical energy storage 28 may have a capacity of several kilowatt-hours, to increase range. The capacity may be in the tens of kilowatt-hours, or over a hundred kilowatt-hours. Although the electrical energy storage is illustrated and described as one entity, the function of the electrical energy storage could be implemented using a plurality of small electrical energy storages in different locations on the vehicle 1. The braking system 60 comprises brakes 62 configured to provide a braking force or torque to decelerate and / or prevent movement of one or more of the wheels 34. Optionally, the brakes 62 are foundation brakes. The term “foundation brake” is generally used herein to mean brakes which are located in or around the wheels of the vehicle. Example foundation brakes include frictional brakes, such as drum brakes or disc brakes, regenerative brakes and eddy current brakes. In the specific example, the foundation braking system 60 comprises a frictional braking system having disc brakes 62 which resist motion of the wheels 34 through the selective application of a braking pressure from a calliper to the brake discs, as is known in the art. The vehicle further composes a control system 100 for controlling the powertrain 22 and the braking system 60. The control system 100 is shown located as part of the powertrain 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. Optionally, the control system 100 is, or comprises, or is part of, a powertrain control module configured to control the operation of the prime mover(s) of the powertrain 22. 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 (not shown). 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, 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 with the art 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 drive modes include a forward (“drive”) mode (‘D’) and a reverse mode (‘R’). The vehicle 1 may have additional drive modes as is known in the art, such as a park mode (‘P’), a neutral mode (‘N’), a sport mode ‘S’ or a 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) are urged to rotate in a rearward direction by the prime mover 26. In 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) are urged to rotate in a forward direction by the prime mover 26. 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) ora 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. MHEvsdo 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 generally not sufficiently powerful to drive the vehicle 1 under electric power alone. ICEVs are propelled solely by an engine 24. 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 will now be described with the aid of Figures 3 to 8. With reference to Figure 3, there is illustrated the control system 100 for controlling the powertrain of the vehicle. The control system 100 comprises one or more controller 110. 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 152 of the controller 110. The controller 110 may have an interface the input means 140 and the output means 150. The input means 140 is arranged to receive a receive a plurality of input parameters 142 from one or more components of the vehicle. The plurality of input parameters 142 comprise electrical signals which indicate operational parameters or variables of the vehicle. The plurality of input parameters 142 includes a vehicle speed signal 143 indicative of a vehicle speed, and a drive mode change signal 144 indicating if a drive mode change between a between a forward driving mode and a reverse driving mode is required. The plurality of input parameters 142 may further comprise one or more additional input signals, such as a driver torque demand signal 145 indicating a powertrain torque demand made by a driver of the vehicle, for example as received from an accelerator pedal position sensor, and / or a gradient signal 146 indicative of a gradient of a surface on which the vehicle is travelling. The output means 150 is arranged to output one or more output signals 152. The one or more output signals includes a drive mode change instruction signal 153 to request the drive mode change from the forward driving mode to the reverse driving mode or vice versa. The one or more output signals 152 may further comprise one or more additional output signals, such as a braking request signal 154 for a braking system of the vehicle, and a modified powertrain torque demand signal 155 for the powertrain. Figure 4 illustrates a first method 400 according to an embodiment of the invention. The method 400 is a method for controlling the powertrain of a vehicle, such as the vehicle 1 in Figure 1. The method 400 may be performed by the system 100 illustrated in Figure 3. In particular, the memory 130 may comprise computer-readable instructions which, when executed by the processor 120, perform the method 400 according to an embodiment of the invention. With method 400, the control system can determine whether the drive mode change can proceed or should be delayed in dependence on the speed of the vehicle 1. This can reduce stress on components of the powertrain and can result in a smoother driving experience and / or vehicle behaviour. At step S410, the plurality of input parameters 142 are received by the control system 100. The plurality input parameters 142 comprises a vehicle speed signal 143 indicative of a vehicle speed. There are several ways in which the vehicle speed signal can be implemented, for example the vehicle speed signal may be received or derived from a speed sensor measurement, such as from a wheel speed sensor or a motor rotational speed sensor using means known in the art. The plurality of input parameters 142 further comprises a drive mode change signal 144 that indicates if a drive mode change between a forward driving mode ‘D’ and a reverse driving mode ‘R’ is required, for example based on a request from the driver of the vehicle 1. The drive mode change signal 144 may be obtained in dependence of a reading from a position sensor associated with a drive mode selector. The drive mode change signal may alternatively, or optionally, be obtained via other means, such as signal processing, as is known in the art. At S420, the control system 100 compares the vehicle speed to a speed threshold. At step S430, the control system 100 determines, in dependence on the plurality of input parameters 142, whether the vehicle speed is greater than a speed threshold when the drive mode change is required. If the vehicle speed is greater than the speed threshold, then the method moves to step S470 at which point the control system delays outputting a drive mode change instruction signal and instead returns to step S420 to again compare the vehicle speed to the speed threshold. This may happen immediately or after a predetermined time interval. For example, the time interval may be 0.1 to 10 ms. If the vehicle speed is less than or equal to the speed threshold, then the method moves to step S480 at which point the control system outputs a drive mode change instruction signal to permit the requested drive mode change to take place. In this manner, the control system delays outputting the drive mode change signal until the vehicle speed is less than or equal to the speed threshold. The speed threshold may be any suitable value. For example, the speed threshold may be 0 kph. The speed threshold may be from 2 to 10 kph (in a forward or reverse direction in dependence on the direction the front of the vehicle is facing). The speed threshold may be 2 kph, 3 kph, 4 kph, 5 kph, 6 kph, 7 kph, 8 kph, 9 kph, 10 kph, or any subset or range therein. Figure 5 illustrates a second method 500 according to an embodiment of the invention. The method 500 is a method for controlling the powertrain of a vehicle, such as the vehicle 1 in Figure 1. The method 500 may be performed by the system 100 illustrated in Figure 3. In particular, the memory 130 may comprise computer-readable instructions which, when executed by the processor 120, perform the method 500 according to an embodiment of the invention. With method 500, the control system can determine whether the drive mode change can proceed or should be delayed in dependence on the speed of the vehicle 1. This can reduce stress on components of the powertrain and can result in a smoother driving experience and / or vehicle behaviour. Method 500 is similar to method 400 illustrated in Figure 4. Steps S510, S520, S530, S570 and S580 of method 500 correspond to steps S410, S420, S430, S470 and S480 of method 400. At step S510, the control system again receives a plurality of input parameters 142. In method 500, the plurality of input parameters further comprises a torque demand signal 145. The torque demand signal 145 indicates the amount of torque demanded of the powertrain of the vehicle 1. The torque demand signal is an electrical signal which is indicative of a torque demand from a driver and / or ADAS request. There are several ways in which the torque demand signal can be implemented. For example, the torque demand signal may be based on driver input, for example driver input provided by a driver via an accelerator pedal / input. For example, the torque demand signal may be received or derived from an accelerator pedal position sensor signal. Alternatively, or in addition, the torque demand signal may be received from, or supplemented by, a torque demand from a vehicle control system, such as an ADAS controller. The torque demand signal may be a wheel level torque demand derived from an accelerator pedal position torque demand in combination with one or more further signals, such as a vehicle speed limiting signal from a stability control system, an ADAS torque demand modified signal, and / or a vehicle speed signal. At steps S520 and S530, the control system again compares the vehicle speed to a speed threshold and determines, in dependence on the plurality of input parameters 142, whether the vehicle speed is greater than a speed threshold when the drive mode change is required. As with method 400, if the vehicle speed is greater than the speed threshold, then the method moves to step S570 at which point the control system delays outputting a drive mode change instruction signal and instead returns to step S520 to again compare the vehicle speed to the speed threshold. Unlike method 400, method 500 has further steps S540 and S542. At step S540, the control system compares the amount of torque demanded to a permitted torque threshold. The permitted torque threshold may be any suitable value, as desired. For example, the permitted torque threshold may be from 0 Nm to 1 Nm, from 0 Nm to 2 Nm, from 0 Nm to 3 Nm, from 0 Nm to 4 Nm or from 0 Nm to 5 Nm. In one particular example, the permitted torque threshold is 1 Nm. At step S542, the control system determines whether the amount of torque demanded is higher than the permitted torque threshold. If the amount of torque demanded is greater than the permitted torque threshold, then the method moves to step S570 at which point the control system delays outputting a drive mode change instruction signal. From step S570, the method returns as shown to step S540 to again compare the torque demanded to the permitted torque threshold. This checking cycle may continue to repeat until the amount of torque demanded is within the limit defined by the permitted torque threshold. Alternatively, the method could return to step S520, as shown by the dashed line, to again compare the vehicle speed to the speed threshold. The return to prior comparison steps in the method may happen immediately or after a predetermined time interval. For example, the time interval may be 0.1 to 10 ms. If the amount of torque demanded is determined to be within the permitted torque range, as defined by the permitted torque threshold, then the method moves to step S580 at which point the control system outputs a drive mode change instruction signal to permit the requested drive mode change to take place. In this manner, the control system delays outputting the drive mode change signal until the vehicle speed is less than or equal to the speed threshold and the amount of torque demanded is less than or equal to the permitted torque threshold. As used herein, the phrase “within the permitted torque range” is used to mean that the amount of torque demand is no greater than the permitted torque threshold. Whilst the flow chart 500 shows a sequence of steps S520, S530, S540 and S542 in series, it will be apparent that to the skilled reader that the steps S520 and S542 may happen at the same time in parallel or alternatively with steps S540 and S542 occurring prior to S520 and S530. The order in Figure 5 has been provided for the purpose of teaching the invention alone and is not intended to limit the invention to this particular configuration. Figure 6 illustrates a third method 600 according to an embodiment of the invention. The method 600 is a method for controlling the powertrain of a vehicle, such as the vehicle 1 in Figure 1. The method 600 may be performed by the system 100 illustrated in Figure 3. In particular, the memory 130 may comprise computer-readable instructions which, when executed by the processor 120, perform the method 600 according to an embodiment of the invention. With method 600, the control system can determine whether the drive mode change can proceed or should be delayed in dependence on the speed of the vehicle 1. This can reduce stress on the powertrain and can result in a smoother driving experience and / or vehicle behaviour. Method 600 is broadly the same as method 500 illustrated in Figure 5. Steps S610, S620, S630, S640, S642, S670 and S680 of method 600 correspond to steps S510, S520, S530, S540, S542, S570 and S580 of method 500. Unlike method 500, method 600 has an additional step S644 and an optional additional step S690. At step S644, once the control system has determined that the amount of torque demanded is greater than the permitted torque threshold, and has delayed outputting the drive mode change instruction signal, the control system outputs a modified torque demand signal 155 for one or more torque generating devices of the powertrain to reduce the amount of torque demanded - that is, the magnitude of the amount of torque demanded - to within the permitted torque range. The modified torque demand signal 155 defines a modified powertrain torque demand which reduces in value from the powertrain torque demand to a reduced powertrain torque demand which is within the permitted torque range. In this manner, more responsive drive mode change can still be provided in situations where the driver is depressing the accelerator pedal and demanding an amount of torque which might otherwise cause unexpected vehicle behaviour in the event of a drive mode change. With this method, the control system actively reduces torque output and does not require the driver to lift off the accelerator pedal to enable the drive mode change. Consequently, the delay between the drive mode change request and the resulting drive mode change in situations in which the amount of torque demanded is initially outside of the permitted range can be reduced compared to method 500. The modified torque demand signal 155 may instruct the powertrain to provide a torque output which is reduced from the torque demand to within the permitted torque range as a step change. Alternatively, the modified torque demand signal 155 may be modulated by the control system to reduce the modified powertrain torque demand from the powertrain torque demand to the reduced powertrain torque demand gradually. For example, at a torque reduction rate, which may be constant or variable. For example, the torque reduction rate may be 1 to 500 Nm / s or 1 to 200 Nm / s or 1 to 100 Nm / s or 1 to 50 Nm / s. In this manner, the modified torque demand signal 155 can mitigate or reduce the likelihood of driveline disturbances such as shuffles or shunts which might otherwise occur if there were a step change in torque demand. Alternatively, the rate at which the torque is reduced may be different for each axle and may be based on the current torque request at that axle (including the effect of the reduction). A factor may then applied to adjust the reduction rates in dependence on the driver demanded torque - this allows the rates to be quicker and less refined if the driver tips in hard, i.e. rapidly increases the driver demanded torque, during the manoeuvre. The modified torque demand signal 155 may request a linear torque reduction rate, or a non-linear torque reduction rate. For example, the modified torque demand signal 155 may request a percentage reduction in torque demand per second. For example, a 1 to 50% reduction in torque demand every 0.01 to 1 seconds. The percentage reduction per second results in a tapering in the torque reduction rate until the torque demanded is no longer outside the permitted torque range. Once the control system has output the modified torque demand signal 155 for to reduce the amount of torque demanded to the permitted torque threshold or lower, the method 600 returns as shown to step S640 to again compare the amount of torque demanded to the permitted torque threshold to confirm that the modified torque demand signal has indeed reduced the amount of torque demanded to within the permitted torque range. Alternatively, the method 600 could return to step S620, as indicated by the dashed line. Optionally, the method 600 may proceed from step S644 to optional step S646. At optional step S646, the control system outputs a compensatory braking torque demand signal to request a compensatory braking torque from a braking system of the vehicle, for example a foundation brake system. The compensatory braking torque at least partly compensates for the reduction in the amount of torque provided by the torque generating device(s) due to the modified torque demand signal. This can be advantageous in situations in which the driver demands torque outside of the permitted range in the opposite direction to the current direction of travel. In such situations, the compensatory torque can “fill-in” at least some of the decelerative torque that would otherwise be provided by the torque generating device(s). The compensatory braking torque can be any suitable value above 0 Nm. For example, the compensatory braking torque could be a fixed value of, for example, 5 Nm, 10 Nm, 15 Nm or higher. Alternatively, the control system can determine the compensatory braking torque in dependence on a difference between the powertrain torque demand and the modified powertrain torque demand at any given point in time. For example, the compensatory braking torque required could vary in proportion to variations in the modified powertrain torque demand as defined by the modified torque demand signal 155. In some embodiments, the control system outputs the compensatory braking request signal such that the compensatory braking torque is equal to the difference between the powertrain torque demand and the modified powertrain torque demand. In this manner, the compensatory braking torque can completely compensate for the reduction in the amount of torque provided by the torque generating device(s) due to the modified torque demand signal. After optional step S646, the method can return to step S620 or to step S640. At optional step S690, the control system modulates the modified powertrain torque demand signal to increase the modified powertrain torque demand from the reduced powertrain torque demand back to the powertrain torque demand indicated by the torque demand signal. In other words, to return the torque back to the amount currently demanded by the driver and / or ADAS. The modified torque demand signal 155 may request or demand that the torque demand be increased from the reduced torque to the powertrain torque demand as a step change or gradually at a torque increase rate which may be constant or variable. For example, the torque increase rate may be 1 to 500 Nm / s or 1 to 200 Nm / s or 1 to 100 Nm / s or 1 to 50 Nm / s. By gradually increasing torque using a torque increase rate of the modified torque demand signal 155, the system can mitigate or reduce the likelihood of driveline disturbances that may be felt by the driver such as shuffles or shunts if there were a step change in torque demand. Alternatively, the rate at which the torque is increased may be different for each axle and may be based on the current torque request at that axle (including the effect of the increase). A factor may then be applied to adjust the increase rates in dependence on the driver demanded torque - this allows the rates to be quicker and less refined if the driver tips in hard during the manoeuvre. At optional step S695, the control system may be further configured to modulate the compensatory braking request signal to decrease the compensatory braking torque in dependence on the modulated modified torque demand signal 155. The modulation of the compensatory braking request signal may be made in dependence on a difference between the modified powertrain torque demand and the powertrain torque demand as the modified powertrain torque demand increases from the reduced powertrain torque demand to the powertrain torque demand. For example, the control system may output the compensatory braking request signal such that the compensatory braking torque is equal to the difference between the powertrain torque demand and the modified powertrain torque demand. In this manner, the compensatory braking torque can reduce in line with the increase in the amount of torque provided by the torque generating device(s) due to the modified torque demand signal and thereby provide an overall torque approximating the powertrain torque demand. Figure 7 illustrates a fourth method 700 according to an embodiment of the invention. The method 700 is a method for controlling the powertrain of a vehicle, such as the vehicle 1 in Figure 1. The method 700 may be performed by the system 100 illustrated in Figure 3. In particular, the memory 130 may comprise computer-readable instructions which, when executed by the processor 120, perform the method 700 according to an embodiment of the invention. With method 700, the control system can determine whether the drive mode change can proceed or should be delayed in dependence on the speed of the vehicle 1. This can reduce stress on components of the powertrain and can result in a smoother driving experience and / or vehicle behaviour. Method 700 is broadly the same as method 600 illustrated in Figure 6. Additional or optional steps, and any other differences, will be described below with reference to Figure 7. At step S710, the plurality of input parameters 142 further comprises a gradient signal 146 indicative of a gradient of a surface on which the vehicle is travelling or is currently stationary. There are several different ways in which the gradient signal may be implemented. For example, the gradient signal may be a direct measurement of the gradient from one or more sensors on the vehicle, for example from one or more inclinometers. Alternatively, or in addition, the gradient signal may be derived from one or more other signals or measurements, such as a vehicle speed signal and / or from an acceleration signal. In one example, the control system receives a longitudinal acceleration signal from an accelerometer (such as an accelerometer forming part of a restraint control system of the vehicle), and a vehicle speed signal from a speed sensor (such as an ABS sensor or a motor speed sensor), from which the control system calculates a linear acceleration. The control system then subtracts the linear acceleration from the longitudinal acceleration to determine the acceleration due to gravity and thereby estimate the gradient of the surface on which the vehicle is travelling. At step S712 the control system compares the gradient to a gradient threshold. The gradient threshold may be any suitable value of incline. The gradient threshold may be selected in dependence on one or more of: vehicle characteristics, vehicle operating mode, powertrain characteristics and driver characteristics. For example, the gradient threshold may be 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%,16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25% or more. The gradient threshold may be negative or positive, i.e. downhill or uphill, respectively. Thus, the above examples may also be expressed as negative values. At step S714, the control system determines whether the gradient meets a gradient braking condition. The gradient braking condition requires at least that the magnitude of the gradient is greater than the gradient threshold. If the magnitude of the gradient is less than the gradient threshold, such that the gradient braking condition is not met, the method 700 proceeds to step S720 to compare the vehicle speed to the speed threshold. If the gradient is greater in magnitude than the gradient threshold, and the gradient braking condition is met, then the method proceeds instead to step S770 to delay outputting the drive mode change instruction signal before proceeding to step S716. Optionally, at step S714, the gradient braking condition further requires that the gradient is negative, in which case the gradient threshold is a down slope gradient threshold. The down slope gradient threshold may be the same as the gradient threshold discussed above but in the negative domain. For example, a 0% to -2% gradient, or a 0% to -3% gradient, or a 0% to -4% gradient, or a 0% to -5% gradient. If the magnitude of the gradient is less than the gradient threshold and / or the gradient is positive, the control system determines that the gradient braking condition is not met and the method 700 proceeds to step S720 to compare the vehicle speed to the speed threshold, as shown and as discussed above. If the gradient is both negative and greater in magnitude than the down slope gradient threshold, then the control system determines that the gradient braking condition is met and the method proceeds to step S770 to delay outputting the drive mode change instruction signal before proceeding to step S716. At step S716 the control system outputs a braking torque request signal to request a braking torque from the braking system of the vehicle 1. For example, the braking torque request signal may be output to a brake controller of the vehicle to instruct the generation of the braking torque by the foundation brakes of the vehicle. In this manner, the braking system can prevent or reduce an increase in the vehicle speed due to the gradient and thereby provide more expected vehicle behaviour and reduce distance overshoot in the event of a delay to the drive mode change. Once the braking torque request signal has been output at step S716, the method continues to as shown to step S720. Figure 8 illustrates a fifth method 800 according to an embodiment of the invention. The method 800 is a method for controlling the powertrain of a vehicle, such as the vehicle 1 in Figure 1. The method 800 may be performed by the system 100 illustrated in Figure 3. In particular, the memory 130 may comprise computer-readable instructions which, when executed by the processor 120, perform the method 800 according to an embodiment of the invention. With method 800, the control system can determine whether the drive mode change can proceed or should be delayed in dependence on the speed of the vehicle 1. This can reduce stress on components of the powertrain and can result in a smoother driving experience and / or vehicle behaviour. For the sake of simplicity, method 800 is illustrated as a variation of method 400. However, it will be understood that the additional step or steps of method 800 could also apply to any of methods 400-700. Similarly, one or more of the flow charts 400, 500, 600, 700, and 800 may be combined such that the control system 100 undertakes any combination of the checks and determination steps therein. Method 800 is illustrated as similar to method 400 but with additional steps S872 and S874 after step S870. At step S872, the control system compares an elapsed time since the drive mode change signal indicating that a drive mode change between a forward driving mode (D) and a reverse driving mode (R) is required to a time limit for the drive mode change to occur. 5 At step S874, the control system determines whether the drive mode change instruction signal has been outputted within the time limit, i.e. whether the elapsed time is within the time limit. If the elapsed time is within the time limit, the method proceeds to step S820, whereby the checking cycle begins again. If the drive mode change instruction signal has not been outputted within the drive mode change time limit - i.e. if the elapsed time is greater than the time limit, the method proceeds to step S876 at which point the control system outputs 10 a “drive mode change not completed” signal. Optionally, the control system may at that point end the process without carrying out the requested drive mode change, or may force the drive mode change to occur by outputting the drive mode change instruction signal irrespective of any other control system logic. A method for controlling the powertrain of the vehicle 1 is also described. The method for controlling the 15 powertrain of vehicle 1 may comprise the steps of any of flow charts 400, 500, 500B, 600, 700 and / or 800. 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 powertrain of a vehicle, the control system comprising one or more processors collectively configured to:receive a plurality of input parameters comprising:a vehicle speed signal indicative of a vehicle speed; anda drive mode change signal indicating that a drive mode change between a forward driving mode (D) and a reverse driving mode is required;determine, in dependence on the input parameters , whether the vehicle speed is greater than a speed threshold when the drive mode change is required;in response to determining that the vehicle speed is greater than the speed threshold, delay outputting a drive mode change instruction signal until the vehicle speed is less than or equal to the speed threshold.

2. A control system of claim 1, wherein the input parameters comprise a torque demand signal indicating an amount of torque demanded of the powertrain of the vehicle;the one or more processors are collectively configured to determine whether the amount of torque demanded is higher than a permitted torque threshold, andin response to determining that the amount of torque demanded is higher than the permitted torque threshold, delay outputting the drive mode instruction signal until the amount of torque demanded is equal or below the permitted torque threshold.

3. A control system of claim 3, wherein the one or more processors are collectively configured to output a modified torque demand signal to one or more torque generating devices of the powertrain to reduce the amount of torque demanded to be equal to or below the permitted torque threshold.

4. A control system of claim 2 or 3, wherein the permitted torque threshold is 1 Nm.

5. A control system of any preceding claim, wherein the input parameters comprise a gradient signalindicative of a gradient of a surface on which the vehicle is travelling,the one or more processors are collectively configured to determine whether the gradient meets a gradient braking condition, the gradient braking condition requiring at least that the gradient is greater in magnitude than a gradient threshold; andin response to determining the gradient meets the gradient braking condition, output a braking torque request signal to request a braking torque.

6. A control system according to claim 5, wherein the gradient braking condition further requires that the gradient is negative and wherein the gradient threshold is a down slope gradient threshold.7, A control system of claim 5 or 6, wherein the down slope gradient threshold is from 0% to -2%.

8. A control system according to claim 3 or any of claims 4 to 7 when dependent upon claim 3, wherein the one or more processors are collectively configured to output a compensatory braking torque demand signal to request a compensatory braking torque from a braking system to compensate for the reduction in the amount of torque from the one or more torque generating devices of the powertrain due to the modified torque demand signal.

9. A control system according to claim 8 when dependent upon any one of claims 5 or 6 or 7, wherein the one or more processors are collectively configured to output the compensatory braking torque demand signal only if the gradient is determined to be negative.

10. A control system of any of claims 5 to 9, whereinthe one or more processors are collectively configured to determine whether the gradient is positive and greater in magnitude than an uphill slope gradient threshold;in response to determining the gradient is positive and greater in magnitude than the uphill slope gradient threshold output an arresting torque request signal to from one or more torque generating devices of the powertrain of the vehicle to request an arresting torque from the one or more torque generating devices.

11. A control system according to any preceding claim, wherein the input parameters comprise a drive mode change time limit indicating a time limit for the drive mode change to occur;the one or more processors are collectively configured to determine if the drive mode change instruction signal has been outputted within the drive mode change time limit; andin response to determining that the drive mode change instruction signal has not been outputted within the drive mode change time limit output a drive mode change not completed signal.

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

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

14. A method for controlling a powertrain of a vehicle, the method comprising: receiving a plurality of input parameters comprising:a vehicle speed signal indicative of a vehicle speed; anda drive mode change signal indicating that a drive mode change between a forward driving mode and a reverse driving mode is required;determining, in dependence on the input parameters, whether the vehicle speed is greater than a speed threshold when the drive mode change is required;in response to determining that the vehicle speed is greater than the speed threshold, delay outputting a drive mode change instruction signal until the vehicle speed is less than or equal to the speed threshold.

15. Computer readable instructions which, when executed by a computer, are arranged toperform a method according to any of claim 14.21

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