GB2587715A

GB2587715A - A controller for a vehicle

Info

Publication number: GB2587715A
Application number: GB2015888.7A
Authority: GB
Inventors: Jean Brice Roques Olivier; Meslot Pierre-Gwenael
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2018-02-26
Filing date: 2018-02-26
Publication date: 2021-04-07
Anticipated expiration: 2038-02-26
Also published as: GB202015888D0; GB2587715B

Abstract

A controller for a vehicle is configured to determine the position of the accelerator pedal with respect to a reference accelerator pedal position (aref); and either determine a torque output in dependence on an acceleration pedal map 60 if the position of the accelerator pedal is greater than the reference accelerator pedal position (aref); and, determine a torque output in dependence on a deceleration pedal map 62 if the position of the accelerator pedal is less than the reference accelerator pedal position (aref). The controller may further determine the pedal map based on a road load signal indicative of a torque output suitable for maintaining the current vehicle speed. The road load signal may be a function of at least one of: the vehicle speed, the gradient, the terrain response mode and/or the requested powertrain torque. The pedal map may further include high and low speed acceleration and deceleration maps.

Description

A CONTROLLER FOR A VEHICLE

TECHNICAL FIELD

The present disclosure relates to a controller for a vehicle. Aspects of the invention relate to a controller, a control system, a vehicle and to a method.

BACKGROUND

A conventional powertrain for a vehicle delivers a given amount of resistive torque due to the internal losses of an internal combustion engine (ICE) when the accelerator pedal is released. The level of restive torque or "overrun" provided by the ICE by can be increased by downshifting gears, which increases the frictional and pumping losses of the ICE. With electrification of the powertrain, it is now possible to offer a customisable level of resistive torque when the accelerator pedal is released by emulating the internal losses of an ICE to single-pedal driving. However, known emulations of these losses fail to reproduce accurately the experience that drivers expect from driving a vehicle comprising an ICE.

The present invention has been devised to mitigate or overcome the above-mentioned problem.

SUMMARY OF THE INVENTION

According to an aspect of the present invention there is provided a controller for a vehicle, the controller being configured to: determine the position of the accelerator pedal with respect to a reference accelerator pedal position; and, determine a torque output in dependence on an acceleration pedal map if the position of the accelerator pedal is greater than the reference accelerator pedal position; or, determine a torque output in dependence on a deceleration pedal map if the position of the accelerator pedal is less than the reference accelerator pedal position.

The controller may be configured to: receive a road load signal indicative of a torque value suitable for maintaining the current speed of the vehicle; determine a road load accelerator pedal position signal in dependence on the road load signal, the road load accelerator pedal position signal being indicative of the reference accelerator pedal position; receive an accelerator pedal position signal indicative of the current position of the accelerator pedal; and, compare the reference accelerator pedal position signal and the accelerator pedal position signal to determine the position of the accelerator pedal with respect to the reference accelerator pedal position.

The controller may be configured to: receive a maximum torque signal indicative of the maximum torque deliverable by the powertrain of the vehicle; and, determine the acceleration pedal map in dependence on the road load signal and the maximum torque signal.

The controller may be configured to: receive an overrun torque demand signal indicative of the level of overrun torque requested by a vehicle system; and, determine the deceleration pedal map in dependence on the road load signal and the overrun toque demand signal.

Optionally, the road load signal is a function of at least one of: the speed of the vehicle; the gradient of the surface the vehicle is traversing; the terrain response mode; and, the torque requested from the powertrain of the vehicle.

Optionally, the maximum torque signal is a function of at least one of: the speed of the vehicle; the gradient of the surface the vehicle is traversing; the terrain response mode; and, the torque requested from the powertrain of the vehicle.

Optionally, the overrun torque demand signal is a function of at least one of: the speed of the vehicle; the gradient of the surface the vehicle is traversing; the terrain response mode; and, the torque requested from the powertrain of the vehicle.

In an embodiment, the acceleration pedal map comprises a low-speed acceleration pedal map and a high-speed acceleration pedal map.

In an embodiment, the deceleration pedal map comprises a low-speed deceleration pedal map and a high-speed deceleration pedal map.

The controller may be configured to: receive a vehicle speed signal indicative of the speed of the vehicle; and, determine a torque output according to the low-speed acceleration pedal map if the position of the accelerator pedal is greater than the reference accelerator pedal position and the vehicle speed equals or is less than a low-speed limit; or, determine a torque output according to the high-speed acceleration pedal map if the position of the accelerator pedal is greater than the reference accelerator pedal position and the vehicle speed equals or is greater than a high-speed limit.

The controller may be configured to: receive a vehicle speed signal indicative of the speed of the vehicle; and, determine a torque output according to the low-speed deceleration pedal map if the position of the accelerator pedal is less than the reference accelerator pedal position and the vehicle speed equals or is less than a low-speed limit; or, determine a torque output according to the high-speed deceleration pedal map if the position of the accelerator pedal is less than the reference accelerator pedal position and the vehicle speed equals or is greater than a high-speed limit.

The controller may be configured to determine a torque output in dependence on the low-speed acceleration pedal map and the high-speed acceleration pedal map if the position of the accelerator pedal is greater than the reference accelerator pedal position and the vehicle speed is between the low-speed limit and the high-speed limit.

The controller may be configured to determine a torque output in dependence on the low-speed deceleration pedal map and the high-speed deceleration pedal map if the position of the accelerator pedal is less than the reference accelerator pedal position and the vehicle speed is between the low-speed limit and the high-speed limit.

The controller may be configured to determine the torque output in dependence on the vehicle speed.

According to a further aspect of the present invention there is provided a control system for an accelerator pedal of a vehicle, the control system comprising a controller according to the previous aspect.

According to a further aspect of the present invention there is provided a vehicle comprising a control system according to the previous aspect.

According to a further aspect of the present invention, the controller may be configured to selectively inhibit or modify the application of acceleration or deceleration pedal maps in dependence on the surface over which the vehicle is travelling.

The controller may be configured to selectively inhibit or modify the application of acceleration or deceleration pedal maps in dependence on a received or determined terrain mode, or a terrain type received from a further vehicle system or controller.

According to a further aspect of the invention is provided a method of controlling a vehicle, the method comprising: determining the position of the accelerator pedal with respect to a reference accelerator pedal position; and determining a torque output in dependence on an acceleration pedal map if the position of the accelerator pedal is greater than the reference accelerator pedal position; or determining a torque output in dependence on a deceleration pedal map if the position of the accelerator pedal is less than the reference accelerator pedal position.

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 schematic representation of a powertrain for use with an embodiment of this invention; Figure 2 shows a graph illustrating the torque output produced in response to an accelerator pedal position at road load conditions; Figure 3 shows a schematic representation of a controller according to an embodiment of this invention; Figure 4 shows a block diagram summarizing an example of a control method designed according to an embodiment of this invention; Figure 5 shows a graph illustrating the torque output produced in response to an accelerator pedal position according to the control method of Figure 4; Figure 6 shows a block diagram summarizing an example of a control method designed according to an embodiment of this invention; Figure 7 shows a graph illustrating the torque output produced in response to an accelerator pedal position according to the control method of Figure 6; and, Figure 8 shows a graph illustrating the torque output produced in response to an accelerator pedal position according to a control method designed according to an embodiment of this invention.

DETAILED DESCRIPTION

With reference to Figure 1, a powertrain, designated generally as 2, of an electric vehicle 4 is shown in plan view. The powertrain 2 comprises an energy storage means, in the form of a battery 5, operatively connected via an inverter 7 to an electric motor 6, which generates torque, and a drive transmission 8. The drive transmission 8 could take the form of a differential (no disconnection mechanism or gears). The torque is transferred through a driveline 10 to wheels 12 that generate a tractive force to move the vehicle 4. A controller 14 is operatively connected to the electric motor 6 by the inverter 7, and functions to control the generation of torque by converting an accelerator pedal position to a torque output using an accelerator pedal map. Although figure 1 only shows one motor 6 driving the wheels of a rear axle, it will apparent that the vehicle 1 may be arranged so that it has one motor driving the wheels of a front axle, or may have at least one additional motor to drive the wheels of both the front a and rear axles, or additional motors to drive individual wheels.

Figure 2 shows a graph 28, in the form of an accelerator pedal map, relating the torque requested from the electric motor 6 to the travel of the accelerator pedal. The skilled reader will understand that this is a simplified section through a map that may also incorporates vehicle speed or actuator speed. A full map would consist of a torque surface in the Z (vertical) axis based on the accelerator pedal position in one axis and the motor speed or vehicle speed in another axis. The required torque is the output.

Line 30 shows the road load plotted against the position of the accelerator pedal. For clarity, the term "road load' refers to the torque that opposes the movement of the vehicle 4 or, in other words, the torque necessary for maintaining the speed of the vehicle 4. Line 30 shows that the torque increases with respect to the accelerator pedal position to a maximum torque output relating to the maximum torque deliverable by the powertrain 2 when the accelerator pedal is fully pressed (100% accelerator pedal position). Conversely, the torque output decreases with respect to pedal position to a minimum when the accelerator pedal is fully released (0% accelerator pedal position), which relates to the maximum resistive torque or overrun torque requested from the electric motor 6 by a powertrain control unit 26. The relationship between the road load and the accelerator pedal position can be characterised generally as being constantly proportional. However, such a relationship cannot deliver a driving experience comparable to what the driver would expect from driving a vehicle comprising an ICE. To this end, the controller 14 functions to provide an intuitive driving experience.

With reference to Figure 3, in accordance with embodiments of the invention, the controller 14 is operable to receive input data regarding the operation of the vehicle 4 and to issue a torque request to the powertrain control unit 26 to achieve a control objective, such as an acceleration demand from the driver of the vehicle 4. The input data comprises a plurality of electrical signals relating to: the accelerator pedal position 17; the vehicle speed 18; the vehicle longitudinal inclination 20; a terrain response mode 22; the current torque 24 being delivered by the electric motor 6; the road load 25; optionally, the road load accelerator pedal position 27; the maximum torque 29 deliverable by the powertrain 2; the overrun torque 31 requested by the powertrain control unit 26; and, the state of charge 21 of the battery 5. In this instance, the vehicle longitudinal inclination 20 relates to the gradient of the surface the vehicle 4 is traversing. These electrical signals, together with the controller 14 and the powertrain control unit 26 form part of a control system 35. The controller 14 comprises a processor 32 configured to convert an accelerator pedal position to a torque output based on one or more accelerator pedal maps, which can be stored in and read from a memory module 34. Alternatively, the controller may be configured to determine the one or more accelerator pedal maps. The skilled reader will appreciate that Figure 3 is provided only to illustrate an example of a controller 14 architecture in which the invention may be implemented.

With reference to Figure 4, in accordance with an embodiment of the invention, the controller 14 incorporates software to implement the process 36 shown in the block diagram. The process 36 initiates at step 38, which may be when the vehicle 4 is operating under road load conditions. At step 40, the current position of the accelerator pedal is determined. The position of the accelerator pedal is then compared, at step 42, against a reference accelerator pedal position to determine if it is greater than the reference accelerator pedal position. The reference accelerator pedal position relates to the road load accelerator pedal position 27. If it is determined that the accelerator pedal position is greater than the reference accelerator pedal position, the process 36 progresses to step 44 where a torque output is determined using an acceleration pedal 54 map before the process 36 terminates at step 52. However, if at step 42 it is determined that the accelerator pedal position is not greater than the reference accelerator pedal position, the process 36 progresses to step 46 where it is determined if the accelerator pedal position equals or is less than the reference accelerator pedal position. If the accelerator pedal position equals the reference accelerator pedal position, the process 36 progresses to step 50 where the current torque output is maintained before the process 36 terminates at step 52.

However, if it is determined, at step 46, that the accelerator pedal position is less than the reference accelerator pedal position, the process 36 progresses to step 48 where a torque output is determined using a deceleration pedal map 56 before the process 36 terminates at step 52. It is envisaged that the process 36 could repeat continually (e.g. at every execution cycle of a given software task).

Figure 5 shows a graph 58, in the form of an accelerator pedal map, illustrating the operation carried out by the process 36. The relationship between the road load and the accelerator pedal position is shown by line 30. The controller 14 is configured to receive a road load signal 25, indicative of the road load (toRL), and determine a road load accelerator pedal position signal 27. The road load accelerator pedal position signal 27 is indicative of the reference accelerator pedal position (arei). In this example, the reference accelerator pedal position is the road load accelerator pedal position (aref), but for some implementations or circumstances, it may be desirable to determine the reference accelerator pedal position on the basis of other factors in addition to the road load accelerator pedal position. The controller 14 is further configured to receive an accelerator pedal position signal 17, which indicates the current accelerator pedal position, and compare the reference accelerator pedal position signal 27 and the accelerator pedal position signal 17 to determine the position of the accelerator pedal with respect to the reference accelerator pedal position (aro). If the accelerator pedal position is greater than the reference accelerator pedal position (ars), the controller 14 determines that an acceleration demand has been requested by the driver of the vehicle 4. In this case, a torque output is determined using an acceleration pedal map 60. On the other hand, if the accelerator pedal position is less than the reference accelerator pedal position (are), the controller 14 decides that a deceleration demand has been requested and determines a torque output using a deceleration pedal map 62. The lower and upper limits of the acceleration pedal map 60 are set by the road load (toRL) and the maximum torque deliverable by the powertrain 2, respectively. Whereas, the lower and upper limits of the deceleration pedal map 62 are set by the maximum resistive torque and the road load (toRL), respectively. The acceleration and deceleration pedal maps 60, 62 are customisable to provide an intuitive driving experience more akin to driving a vehicle comprising an ICE. For example, the acceleration and deceleration pedal maps 60, 62 could be customised according to the speed of the vehicle 4.

In an embodiment of the invention, the acceleration pedal map 60 comprises a low-speed acceleration pedal map and a high-speed acceleration pedal map. Similarly, the deceleration pedal map 62 comprises a low-speed deceleration pedal map and a high-speed deceleration pedal map. The controller 14 is configured to receive a vehicle speed signal 18, indicative of the speed of the vehicle 4, and determine a torque output in dependence on the vehicle speed signal 18. If the accelerator pedal position is greater than the reference accelerator pedal position (aref) and it is determined that the speed of the vehicle 4 is below a predetermined threshold speed the controller 14 determines a torque output using the low-speed acceleration pedal map. However, if the accelerator pedal position is greater than the reference accelerator pedal position (are) and the speed of the vehicle 4 is greater than the predetermined threshold speed, the controller 14 determines a torque output using the high-speed acceleration pedal map. Similarly, if the accelerator pedal position is less than the reference accelerator pedal position (are') and the speed of the vehicle 4 is below the predetermined threshold speed, the controller 14 determines a torque output using the low-speed deceleration pedal map. Moreover, if the accelerator pedal position is less than the reference accelerator pedal position (aro) and the speed of the vehicle 4 is greater than the predetermined threshold speed, the controller 14 determines a torque output using the high-speed deceleration pedal map.

Alternatively, selection of the low-speed and high-speed acceleration and deceleration pedal maps may be dependent on the vehicle speed relative to different speed limits. If the accelerator pedal position is greater than the reference accelerator pedal position (aref) and it is determined that the speed of the vehicle 4 equals or is below a predetermined low-speed limit, the controller 14 determines a torque output using the low-speed acceleration pedal map. However, if the accelerator pedal position is greater than the reference accelerator pedal position (are) and the speed of the vehicle 4 equals or is greater than a predetermined high-speed limit, the controller 14 determines a torque output using the high-speed acceleration pedal map. Similarly, if the accelerator pedal position is less than the reference accelerator pedal position (aref) and the speed of the vehicle 4 equals or is below a predetermined low-speed limit, the controller 14 determines a torque output using the low-speed deceleration pedal map. Moreover, if the accelerator pedal position is less than the reference accelerator pedal position (aref) and the speed of the vehicle 4 equals or is greater than a predetermined high-speed limit, the controller 14 determines a torque output using the high-speed deceleration pedal map. The controller 14 is further configured to determine a torque output based a combination of the low-speed and high-speed acceleration pedal maps if the accelerator pedal position is greater than the reference accelerator pedal position (aref), but the speed of the vehicle 4 is between the low-speed and high-speed limits.

Likewise, a torque output is determined based a combination of the low-speed and high-speed deceleration pedal maps when the accelerator pedal position is less than the reference accelerator pedal position (a,,,), but the speed of the vehicle 4 is between the low-speed and high-speed limits. Combining pedal maps may be done by interpolating between the low-speed and high-speed pedal maps in dependence on the vehicle speed.

In a further embodiment of the invention, the controller 14 may also be configured to modify the acceleration and deceleration pedal maps, or the low-speed and high-speed versions thereof, using a gradient modifier to take into account a gradient of the surface the vehicle 4 is traversing. The controller 14 determines the gradient modifier in dependence on the vehicle longitudinal inclination or gradient signal 20.

With reference to Figure 6, in accordance with an embodiment of the invention, the controller 14 incorporates software to implement the process 64 shown in the block diagram. The process 64 initiates at step 66 and progresses to step 68, where it is determined whether the vehicle 4 is traversing a gradient. This can be done using the vehicle longitudinal inclination or gradient signal 20. If it is determined that the vehicle 4 is traversing a gradient, the process 64 moves to step 70 where it is determined whether the gradient is a positive gradient or a negative gradient. If, at step 70, it is determined that the vehicle 4 is traversing a positive gradient, the process 64 moves to step 72 and a torque output is determined using a positive gradient pedal map.

However, if, at step 70, it is determined that the vehicle 4 is traversing a negative gradient, the process 64 moves to step 74 and a torque output is determined using a negative gradient pedal map. Following steps 72, 74, the process 64 terminates at step 76. Basing the torque output on accelerator pedal maps that have been modified to account for the gradient of the surface the vehicle 4 is traversing prevents the perceived performance reduction that occurs in electric vehicles, which do not have a traditional gearbox, and offers the opportunity to enhance an electrified powertrain capability feel over a conventional one.

Figure 7 shows a graph 78 illustrating the operation carried out by the process 64.

The graph 78 comprises three accelerator pedal maps. Line 30 shows an accelerator pedal map under road load conditions, and lines 80, 82 are the positive gradient and the negative gradient accelerator pedal maps respectively. That is, lines 80, 82 are accelerator pedal maps that have been altered to account for a positive gradient and a negative gradient respectively. The degree to which lines 80, 82 are altered may also be influenced by the terrain response mode selected by the driver of the vehicle 4, in addition to gradient. The controller 14 is configured to determine the selected terrain response mode using the terrain response mode signal 22. It can be seen from line 80 that the torque output is greater, for the same accelerator pedal position, when compared to road load conditions. Conversely, line 82 shows that the torque output is less when compared to road load conditions for the same accelerator pedal position.

The graph 78 comprises two additional accelerator pedal maps, lines 83, 84. These lines 83, 84 represent the torque output necessary for maintaining the speed of the vehicle 4 when going from road load conditions to traversing a positive gradient or a negative gradient respectively. Lines 83, 84 have been altered to account for the same gradients as lines 80, 82. When the vehicle 4 is traversing a positive gradient, the controller 14 functions to determine torque output using the positive gradient accelerator pedal map, line 80. It can be seen from comparing lines 80, 83 that, for the same accelerator pedal position (a1), the torque output (tol) from the positive gradient accelerator pedal map, line 80, is less than the torque (to2) necessary for maintaining the speed of the vehicle 4 while traversing the positive gradient. That is, the positive gradient accelerator pedal map, line 80, used by the controller 14 purposively under compensates for the positive gradient. In order to maintain the speed of the vehicle 4, the driver of the vehicle 4 is required to press the accelerator pedal to position (a2) to achieve the required torque output (to2). This situation is constructed by the controller 14 in order to provide an intuitive driving experience in which the driver would expect to have to press the accelerator pedal to some extent when traversing a positive gradient based on their experience of driving a vehicle comprising an ICE.

Similarly, the driver would expect to have to lift-off or release the accelerator pedal when going downhill. In view of that, the negative gradient accelerator pedal map, line 82, used by the controller 14 purposively over compensates for the negative gradient, and so the driver of the vehicle 4 is required to release the accelerator pedal in order to maintain the speed of the vehicle 4 when traversing a negative gradient.

It can be seen that the upper limit of the positive gradient accelerator pedal map, line 80, is offset from the road load accelerator pedal map, line 30, such that it exceeds the maximum torque deliverable by the powertrain 2. This is done in order to prevent the effect of the gradient modification from dissipating, as indicated by line 85, as the torque demand increases away from the road load and towards the maximum torque deliverable by the powertrain 2, which would be counter-intuitive for the driver of the vehicle 4.

In a further embodiment of the invention, the controller 14 may determine an accelerator pedal map on receiving the state of charge signal 21, which indicates that the state of charge of the battery 5 is below a predetermined threshold, and determine a torque output in dependence on the accelerator pedal map.

Figure 8 shows a graph 86 including an accelerator pedal map 87 in accordance with this embodiment of the invention. The graph 86 includes an additional accelerator pedal map 88. The additional accelerator pedal map 88 is an example of how known accelerator pedal maps are modified when the state of charge of an energy storage means on an electric vehicle falls below a threshold. In this example, it can be seen that the accelerator pedal map 88 initially increases with the accelerator pedal position, after which a torque limit is applied and the torque output remains constant as the accelerator pedal position increases. However, rather than applying a torque limit, the accelerator pedal map 87 is configured to deliver increasing amounts of torque with respect to pedal position up to a maximum which is less that the maximum torque deliverable by the powertrain 2. Although this results in an overall lower output torque, the behaviour of the vehicle 4 is made to be more intuitive for the driver when compared to simply applying a torque limit. In embodiments of the invention, the accelerator pedal map 87 is configured to maximise the range of the vehicle 4, increasing the likelihood of the vehicle 4 reaching its destination. Moreover, the accelerator pedal map 87 could be configured so that the torque delivered over the first part of the accelerator pedal range is delivered at a higher rate when compared to the torque delivered over the second part of the accelerator pedal range. This means that the driver is able to accelerate in city traffic conditions and maintain a high cruising speed, but the vehicle 4 will have a lower acceleration in the second part of the accelerator pedal range.

The controller may be configured to selectively inhibit or modify the application of acceleration or deceleration pedal maps in dependence on the surface over which the vehicle is travelling.

Any controller or controllers described herein may suitably comprise a control unit or computational device having one or more electronic processors. Thus the system may comprise a single control unit or electronic controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein the term "controller" or "control unit' will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide any stated control functionality. To configure a controller, a suitable set of instructions may be provided which, when executed, cause said control unit or computational device to implement the control techniques specified herein. The set of instructions may suitably be embedded in said one or more electronic processors. Alternatively, the set of instructions may be provided as software saved on one or more memory associated with said controller to be executed on said computational device. A first controller may be implemented in software run on one or more processors. One or more other controllers may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller. Other suitable arrangements may also be used.

Many modifications may be made to the above examples without departing from the scope of the present invention as defined in the accompanying claims.

Claims

CLAIMS1. A controller for a vehicle, the controller being configured to: receive a road load signal indicative of a torque output suitable for maintaining the current speed of the vehicle; determine a reference accelerator pedal position in dependence on the road load signal; determine a current accelerator pedal position; compare the reference accelerator pedal position and the current accelerator pedal position; and determine a torque output in dependence on an acceleration pedal map if the current accelerator pedal position is greater than the reference accelerator pedal position, or determine a torque output in dependence on a deceleration pedal map if the current accelerator pedal position is less than the reference accelerator pedal position. C\I
2. A controller according to claim 1, the controller being configured to: receive a maximum torque signal indicative of the maximum torque deliverable by the powertrain of the vehicle; and, determine the acceleration pedal map in dependence on the road load signal C\I and the maximum torque signal.
3. A controller according to claim 1 or claim 2, the controller being configured to: receive an overrun torque demand signal indicative of the level of overrun torque requested by a vehicle system; and, determine the deceleration pedal map in dependence on the road load signal and the overrun toque demand signal.
4. A controller according to any preceding claim, wherein the road load signal is a function of at least one of: the speed of the vehicle; the gradient of the surface the vehicle is traversing; the terrain response mode; and, the torque requested from the powertrain of the vehicle.
5. A controller according to claim 2 or either of claims 3 or 4 where dependent directly or indirectly on claim 2, wherein the maximum torque signal is a function of at least one of: the speed of the vehicle; the gradient of the surface the vehicle is traversing; the terrain response mode; and, the torque requested from the powertrain of the vehicle.
6. A controller according to claim 3 or either of claims 4 and 5 where dependent directly or indirectly on claim 3, wherein the overrun torque demand signal is a function of at least one of: the speed of the vehicle; the gradient of the surface the vehicle is traversing; the terrain response mode; and, CD the torque requested from the powertrain of the vehicle. C\I
7. A controller according to any preceding claim, wherein the acceleration pedal map comprises a low-speed acceleration pedal map and a high-speed acceleration pedal map. C\I
8. A controller according to any preceding claim, wherein the deceleration pedal map comprises a low-speed deceleration pedal map and a high-speed deceleration pedal map.
9. A controller according to claim 7, the controller being configured to: receive a vehicle speed signal indicative of the speed of the vehicle; and, determine a torque output according to the low-speed acceleration pedal map if the current accelerator pedal position is greater than the reference accelerator pedal position and the vehicle speed equals or is less than a low-speed limit; or, determine a torque output according to the high-speed acceleration pedal map if the current accelerator pedal position is greater than the reference accelerator pedal position and the vehicle speed equals or is greater than a high-speed limit.
10. A controller according to claim 8, the controller being configured to: receive a vehicle speed signal indicative of the speed of the vehicle; and, determine a torque output according to the low-speed deceleration pedal map if the current accelerator pedal position is less than the reference accelerator pedal position and the vehicle speed equals or is less than a low-speed limit; or, determine a torque output according to the high-speed deceleration pedal map if the current accelerator pedal position is less than the reference accelerator pedal position and the vehicle speed equals or is greater than a high-speed limit.
11. A controller according to claim 9, the controller being configured to determine a torque output in dependence on the low-speed acceleration pedal map and the highspeed acceleration pedal map if the current accelerator pedal position is greater than the reference accelerator pedal position and the vehicle speed is between the low-speed limit and the high-speed limit.
CD 12. A controller according to claim 10, the controller being configured to determine C\I a torque output in dependence on the low-speed deceleration pedal map and the high-speed deceleration pedal map if the current accelerator pedal position is less than the reference accelerator pedal position and the vehicle speed is between the low-speed limit and the high-speed limit. C\I
13. A controller according to claim 11 or 12, the controller being configured to determine the torque output in dependence on the vehicle speed.
14. A control system for a vehicle, the control system comprising a controller according to any preceding claim.
15. A vehicle comprising a control system according to claim 14.
16. A method of controlling a vehicle, the method comprising: receiving a road load signal indicative of a torque output suitable for maintaining the current speed of the vehicle; determining a reference accelerator pedal position in dependence on the road load signal; determining a current accelerator pedal position; comparing the reference accelerator pedal position and the current accelerator pedal position; and determining a torque output in dependence on an acceleration pedal map if the current accelerator pedal position is greater than the reference accelerator pedal position, or determining a torque output in dependence on a deceleration pedal map if the current accelerator pedal position is less than the reference accelerator pedal position.