Control system for an Anti-lock braking system

Abstract

Examples pertain to a control system for controlling an anti-lock braking system of a vehicle, the control system comprising one or more processors collectively configured to receive a surface signal indicative of a gravel driving surface, determine, in dependence on the received surface signal, an anti-lock braking system mode to be implemented, and output a signal to control the anti-lock braking system to implement the determined anti-lock braking system mode. The anti-lock braking system mode to be implemented is determined by selecting, in dependence on the received surface signal, an anti-lock braking system mode from a plurality of anti-lock braking system modes, wherein respective modes of the plurality of anti-lock braking system modes comprise different braking configurations. The anti-lock braking system mode determined to be implemented on the gravel driving surface permits a relatively higher level of wheel slip, as compared to an anti-lock braking system mode determined for use on a non-gravel driving surface.

Description

[0001] CONTROL SYSTEM FOR AN ANTI-LOCK BRAKING SYSTEM

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a control system for an anti-lock braking system. Aspects of the invention relate to a control system, to a system, to a vehicle and to a method.

[0004] BACKGROUND

[0005] It is known that during braking of a vehicle, an increasing braking torque may be applied to the wheels of a vehicle. As the braking torque increases, adhesion between the tyre of a wheel and the driving surface, e.g., the ground, may increase. However, as braking torque increases the wheel (or tyre of a wheel) may slip and beyond a critical braking torque, the wheel may lock, such that the adhesion between the tyre of the wheel and the driving surface may decrease. It is an aim of anti-lock braking systems to apply braking torque to most efficiently transfer a braking force from the tyres of the wheels of a vehicle to the driving surface to stop the vehicle. It is known for anti-lock braking systems to do so by preventing, or limiting, the case of wheel lock, so as to increase the braking force that is transferred between the tyre of a wheel and the driving surface. However, such anti- lock braking systems have primarily been developed for tarmac driving surfaces.

[0006] It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

[0007] SUMMARY OF THE INVENTION

[0008] Aspects and embodiments of the invention provide a control system, a system, a vehicle and a method as claimed in the appended claims.

[0009] According to an aspect of the present invention there is provided a control system for controlling an anti-lock braking system of a vehicle. The control system is configured to obtain an indication of a gravel driving surface, determine, in dependence on the indication, an anti-lock braking system mode to be implemented, and output a signal to control the anti-lock braking system to implement the determined anti-lock braking system mode. For example, the control system may be configured to obtain an indication of a gravel driving surface by receiving a surface signal indicative of a gravel driving surface. Advantageously, the anti-lock braking system (ABS) can be controlled to operate in one or more suitable modes of different available modes based on an indication of a gravel driving surface, which may improve the ability of the ABS to dynamically adapt to different driving surfaces.

[0010] According to an aspect of the present invention there is provided a control system for controlling an anti-lock braking system of a vehicle. 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 surface signal indicative of a gravel driving surface, determine, in dependence on the received surface signal, an anti-lock braking system mode to be implemented and output a signal to control the anti-lock braking system to implement the determined anti-lock braking system mode. The ABS mode to be implemented is determined by selecting, in dependence on the received surface signal, an ABS mode from a plurality of ABS modes, wherein respective modes of the plurality of ABS modes comprise different braking configurations. The anti-lock braking system mode determined to be implemented on the gravel driving surface permits a relatively higher level of wheel slip, as compared to an anti-lock braking system mode determined for use on a non-gravel driving surface. Advantageously, the ability to implement different braking configurations allows for different modes of the ABS to be tailored to different driving conditions or scenarios, for example, the driving of the vehicle on different surfaces. This may enable each mode to be specifically configured to better provide stopping in each of the respective driving conditions or scenarios. This may enable a more effective ABS mode to be implemented for a gravel driving surface.

[0011] According to an aspect of the present invention there is provided a control system for controlling an anti-lock braking system of a vehicle. The control system comprises one or more processors collectively configured to receive a surface signal indicative of a gravel driving surface, determine, in dependence on the received surface signal, an anti-lock braking system mode to be implemented and output a signal to control the anti-lock braking system to implement the determined anti-lock braking system mode. The ABS mode to be implemented is determined by selecting, in dependence on the received surface signal, an ABS mode from a plurality of ABS modes, wherein respective modes of the plurality of ABS modes comprise different braking configurations. The anti-lock braking system mode determined to be implemented on the gravel driving surface permits a relatively higher level of wheel slip, as compared to an anti-lock braking system mode determined for use on a non-gravel driving surface. Advantageously, in dependence on the indication of the gravel driving surface, an ABS mode can be determined and implemented that makes use of wheel slip and, in some cases wheel lock. Wheel slip for a vehicle driving on a gravel surface may cause displacement of the gravel, which may result in the displaced gravel piling up in front of the wheel of the vehicle. The displaced gravel may act to reduce the stopping distance of the vehicle.

[0012] The control system may determine the ABS mode to be implemented by selecting an ABS mode that is configured to implement a different braking configuration compared to an ABS mode for use on a non-gravel driving surface that causes a relatively higher level of wheel slip, and in some cases wheel lock, such that a stopping distance of the vehicle on the gravel driving surface implementing the selected ABS mode is reduced as compared to a stopping distance of the vehicle on the gravel driving surface implementing the ABS mode intended for use for a non-gravel driving surface.

[0013] Advantageously, the control system may be configured to determine the ABS mode to be implemented by selecting an ABS mode that comprises a braking configuration configured to cause an interaction between at least one wheel of the vehicle and a driving surface, as a result of wheel slip, or wheel lock, where the interaction is different from (e g., greater than) an interaction between the at least one wheel of the vehicle and the driving surface when a braking configuration of an ABS mode for use on a non-gravel driving surface is applied.

[0014] The different braking configurations may comprise different configurations of applied braking torque. Respective configurations of applied braking torque may include at least one of a braking torque, a maximum braking torque, a duration of an applied braking torque, a number of repetitions of an applied braking torque, and an interval between respective applications of at least one braking torque. Advantageously, the different implementations for configurations of applied braking torque enable flexibility for providing different braking configurations, which may allow respective ones of the different configurations to be tailored for different conditions.

[0015] It may be that respective braking configurations provide different respective stopping distances of a vehicle. For example, it may be that the selected ABS mode has a braking configuration configured to reduce a stopping distance of the vehicle. For example, the selected ABS mode may have a braking configuration configured to provide a stopping distance reduced in comparison to a stopping distance of the vehicle when a braking configuration of an ABS mode determined for use on a non-gravel driving surface is applied.

[0016] The control system may be configured to determine the ABS mode to be implemented by selecting an ABS mode that is configured to comprise at least one time period over which there is wheel slip for at least one wheel of the vehicle (i.e., at least one time period over which the at least one wheel slips, or is locked). It may be that at least one of: the time period has an increased duration as compared to each of one or more time periods of wheel slip of an anti-lock braking system mode determined for use on a non-gravel driving surface; the time period is an additional time period with respect to time periods of the anti-lock braking system mode determined for use on a non-gravel driving surface; and a maximum wheel slip value reached during the time period is higher (or a maximum wheel slip reached has a wheel slip value that is higher, or corresponds to a higher value) as compared to a maximum wheel slip value reached during each of one or more time periods of wheel slip of an anti-lock braking system mode determined for use on a non-gravel driving surface.

[0017] For example, the time period may have an increased duration with respect to each of one or more time periods of wheel slip of an ABS mode determined for use on a non-gravel driving surface, or the time period may have an additional time period with respect to time periods of the ABS mode determined for use on a non-gravel driving surface (for example, where the ABS mode determined for use on a non-gravel driving surface prevents wheel lock). Additionally, or alternatively, the maximum wheel slip value reached during the time period may be higher (or may correspond to a higher value) as compared to a maximum wheel slip value reached during each of one or more time periods of wheel slip of an anti-lock braking system mode determined for use on a non-gravel driving surface.

[0018] Advantageously, based on the indication of the gravel driving surface, the ABS can be controlled to implement a braking configuration that prolongs a period of wheel lock, or introduces a period of wheel lock if wheel lock was prevented in an ABS mode implemented for a non-gravel driving surface. The ABS may alternatively, or additionally, be controlled to increase a maximum wheel slip value reached during the period of wheel slip, and may, for example, enable wheel lock. This may enable the wheel of the vehicle to dig deeper into the gravel to reduce the stopping distance of the vehicle.

[0019] The control system may be configured to determine the ABS mode to be implemented by selecting an ABS mode that is configured to apply braking in a plurality of cycles and wherein for at least one cycle of the plurality of cycles a time period is present over which a braking torque at least sufficient to cause wheel slip of at least one wheel of the vehicle (or to cause the maximum wheel slip reached) is applied, wherein the time period has an increased duration with respect to each of one or more corresponding time periods of an ABS mode determined for use on a non-gravel driving surface, or the time period is an additional time period with respect to time periods of the ABS mode determined for use on a non-gravel driving surface. Alternatively, or additionally, the braking torque may be sufficient to cause a wheel slip value (e.g., a maximum wheel slip value) to be reached that is higher than a wheel slip value (e.g., a maximum wheel slip value) reached for an ABS mode determined for use on a non-gravel driving surface. For example, the braking torque may be sufficient to cause wheel lock.

[0020] Advantageously, based on the detected presence of the gravel driving surface, the braking torque applied in at least one of the braking cycles of an ABS mode can be controlled to at least one of prolong or introduce a period of wheel slip (or wheel lock), or increase a maximum wheel slip value reached to reduce the stopping distance of the vehicle, while maintaining composure of the vehicle and protecting the integrity of the tyres of the vehicle (e.g., protecting the surface of the tyres from wear) due to the cyclical application of braking.

[0021] The control system may be configured to determine the ABS mode to be implemented further based on an indication of at least one of: a reliability of an indication of the gravel driving surface, a velocity of the vehicle, a longitudinal acceleration of the vehicle, a driving direction of the vehicle and a steering angle of the vehicle.

[0022] Advantageously, the ABS mode can be controlled based on additional factors that affect the efficiency of the braking and the steering of the vehicle and / or the composure of the vehicle. This may enable the determined ABS mode to be more adaptive to a wider range of driving conditions of the vehicle, in addition to the driving surface. For example, an ABS mode with at least one of a longer period of prolonged or introduced wheel slip, or with a relatively higher value of maximum wheel slip value reached within the period of wheel slip may be implemented if it is indicated that the vehicle is travelling in a straight direction to further improve (e.g., reducing) a stopping distance of the vehicle while still maintaining the composure of the vehicle, or for example, preventing excessive wear on a specific portion of the tyres. Alternatively, an ABS mode with at least one of a shorter period of prolonger or introduced wheel slip or with a relatively lower value of maximum wheel slip value reached within the period of wheel slip may be implemented if it is indicated that the vehicle is turning. This may prioritise vehicle composure and tyre wear over stopping distance of the vehicle. In another example, it may be that in response to an indication that the vehicle is travelling above a predetermined speed, an ABS mode with a shorter or no period of wheel lock or wheel slip may be implemented to prioritise vehicle composure, steering or e.g., tyre wear. It may be that in response to an indication that the vehicle is travelling below a predetermined speed, an ABS mode with at least one of a longer period of wheel slip or a higher maximum value of wheel slip may be implemented, for example to decrease stopping distance without affecting vehicle composure.

[0023] The control system may be configured to select a first ABS mode as the ABS mode to be implemented in dependence on at least a comparison of a characteristic associated with an indication of the gravel driving surface with at least a first criterion, and to select a second ABS mode as the ABS mode to be implemented in dependence on at least a comparison of the characteristic associated with the indication of the gravel driving surface is detected with at least a second criterion.

[0024] Advantageously, an ABS mode can be selectively implemented based on additional information relating to the indication of the gravel driving surface, which allows an ABS mode better suited to the real or real-time driving conditions to be implemented.

[0025] It may be that the characteristic is at least one of a reliability of the indication of the gravel driving surface, or a period of time lapsed since the indication is received and / or determined (i.e., since a determination of the presence of the gravel driving surface was performed or completed). It may be that the indication is provided (e.g., received) in the surface signal or the indication corresponds to a determination of the presence of the gravel driving surface performed by the control system in dependence on the received signal. It may be that the surface signal further comprises the characteristic, or it may be that the characteristic is otherwise obtained by the control system (e.g., is received separately from the indication, or is determined by the control system in dependence on a determination of the presence of the gravel surface performed by the control system).

[0026] The first criterion may be associated with a first level of reliability of the indication of the gravel driving surface, the second criterion may be associated with a second level of reliability of the indication of the gravel driving surface, wherein the second level of reliability may be higher than the first level of reliability and wherein the second ABS mode may comprise a braking configuration configured to reduce a stopping distance of the vehicle on a gravel driving surface compared to a stopping distance of the vehicle on a gravel driving surface provided by the first ABS mode. For example, the second ABS mode may comprise a braking configuration configured to permit a relatively higher level of wheel slip, as compared to the first ABS mode.

[0027] Advantageously, an ABS mode can be selectively implemented based on the reliability of the indication of the gravel driving surface, such that an ABS mode with a higher level of wheel slip can be implemented when there is greater certainty that the vehicle is driving on a gravel driving surface, and an ABS mode with a lower level of wheel slip can be implemented when there is less certainty that the vehicle is driving on a gravel driving surface. This enables a trade-off between composure of the vehicle (and e.g., tyre wear) and the stopping distance achievable for the vehicle as it enables a higher level of (e.g., at least one of a prolonged period of, or higher maximum value of) wheel slip to be selectively implemented for a scenario where there is more certainty that the vehicle is driving on a gravel driving surface and reduces the likelihood of the use of a higher level of wheel slip, or in fact wheel lock, in a scenario of a false, or questionable detection of a gravel driving surface, where the use of wheel slip may not improve the stopping distance of the vehicle.

[0028] For example, it may be that the second ABS mode comprises at least one time period over which at least one wheel of the vehicle slips, wherein the time period has an increased duration with respect to each of a one or more time periods of wheel slip of the first ABS mode or wherein the time period is an additional time period with respect to time periods of the first ABS mode. It may be that the second ABS mode alternatively, or additionally comprises a maximum wheel slip value reached during the time period that is higher than a maximum wheel slip value reached by the first ABS mode.

[0029] It may be that the first ABS mode corresponds to an ABS mode implemented for a non-gravel driving surface. Alternatively, it may be that the first ABS mode comprises a a braking configuration configured to permit a relatively higher level of wheel slip, as compared to an ABS mode implemented for a non-gravel driving surface. For example, the first ABS mode may comprise at least one time period over which at least one wheel of the vehicle slips, and at least one of: the time period has an increased duration with respect to each of one or more time periods of wheel slip of an ABS mode implemented (or determined for use) for a non-gravel driving surface; the time period is an additional time period with respect to time periods of an ABS mode implemented for a non-gravel driving surface; and the maximum wheel slip value during the time period reaches (or corresponds to) a higher value as compared to a maximum wheel slip value reached during each of one or more time periods of wheel slip of an anti-lock braking system mode determined for use on a non-gravel driving surface.

[0030] Advantageously, it may be that a selection of ABS modes with graded levels of wheel slip may be enabled in response to the indication of the reliability of the indication of the gravel driving surface, which may prevent a higher level of wheel slip from being implemented when the true driving surface may be wet or dry tarmac, or ice. This may decrease the stopping distance of the vehicle and better maintain composure of the vehicle.

[0031] The surface signal indicative of the gravel driving surface may comprise at least one sensor signal indicative of the gravel driving surface, and the control system may be further configured to determine a presence of the gravel driving surface in dependence on the at least one sensor signal.

[0032] Advantageously, an ABS mode can be implemented based on a determination of the presence of a gravel driving surface performed by the control system itself, which may enable the implementation of the determined ABS mode to be more efficient and more responsive, for example by reducing the lag between a determination of a gravel driving surface and the determination and implementation of the determined ABS mode.

[0033] The at least one sensor signal may comprise at least one of: at least one sensor signal from at least one sensor of the ABS; and at least one sensor signal from at least one sensor of a suspension system of the vehicle. The control system may be configured to determine a presence of the gravel driving surface in dependence on at least one sensor signal from at least one sensor of the ABS and at least one sensor signal from at least one sensor of a suspension system of the vehicle.

[0034] Advantageously, the accuracy and / or reliability of the determination of the gravel driving surface can be improved by using the combination of sensor signals as measures of the movement of the vehicle from separate systems of the vehicle. The sensor signals from the different systems are less likely to be affected by the same underlying biases etc, which may otherwise give rise to a false or inaccurate detection of a gravel driving surface.

[0035] It may be that the at least one sensor signal comprises at least one of a yaw rate sensor signal, and a lateral acceleration sensor signal. For example, it may be that the at least one sensor of the ABS, comprises at least one of a yaw rate sensor signal, and a lateral acceleration sensor signal. The control system may be configured to receive at least a yaw rate sensor signal, and a lateral acceleration sensor signal and determine the presence of the gravel driving surface in dependence on the yaw rate sensor signal, and the lateral acceleration sensor signal.

[0036] Advantageously, the accuracy and / or reliability of the determination of the gravel driving surface can be improved when the determination is based on at least one of a yaw rate sensor signal and a lateral acceleration sensor signal as both a yaw rate sensor and a lateral acceleration sensor sense at least one direct effect of the gravel driving surface on the vehicle. For example, when the vehicle is driving on a gravel driving surface, the vehicle may experience displacement or movement, such as vibration, due to the interaction of the vehicle, or wheels thereof, and the gravel driving surface. Such displacement or movement may not correspond to the intended movement of the vehicle, such as the steering angle as a result of the uneven surface structure of the gravel driving surface. Such displacement or movement may be sensed by the yaw rate sensor and the lateral acceleration sensor.

[0037] For example, it may be that the control system is configured to determine the presence of the gravel driving surface in dependence on at least one of a yaw rate and / or lateral acceleration sensor signal from at least one sensor of the ABS, and a ride height and / or inertial measurement unit (IM U) sensor signal from a sensor of a suspension system of the vehicle, wherein the IMU may be a two sensor or three sensor IMU. It may be that the control system is configured to receive at least one of: a yaw rate and / or lateral acceleration sensor signal from at least one sensor of the ABS, and a ride height and / or inertial measurement unit sensor signal from a sensor of a suspension system of the vehicle via the surface signal, or via the surface signal and at least one additional signal. Advantageously, the combination of sensors provides a higher accuracy and more reliable determination of the gravel driving surface.

[0038] The control system may be configured to detect the presence of the gravel driving surface in dependence on at least a detection of a pre-determined characteristic in the at least one sensor signal. For example, the control system may be configured to determine the presence of the gravel driving surface in dependence on a comparison of a characteristic of the at least one sensor signal with at least one criterion. For example, the pre-determined characteristic may be noise in the signal. The criterion may be a threshold, for example, the threshold may be a pre-determined value, or a dynamic value such as a value associated with a running average.

[0039] Advantageously, the accuracy and / or reliability of the determination of the gravel driving surface can be further improved by detecting a predetermined characteristic (such as noise) in at least one of the yaw rate sensor signal and lateral acceleration sensor signal as a characteristic unique to, or with a higher likelihood of being associated with, the effects on the vehicle sensed by the respective sensors as a result of driving on the gravel driving surface may be used to mitigate against false detections or determinations of a gravel driving surface.

[0040] The control system may be configured to at least one of determine the ABS mode to be implemented, and output the signal, in response to obtaining an indication of a drive mode of the vehicle.

[0041] Advantageously, the operation of the control system may be made more efficient by performing at least one of the determining the ABS mode and outputting the signal to control the ABS in response to obtaining the indication of the drive mode. For example, it may be that a drive mode of the vehicle is selectable (e g., by a user), and that respective drive modes may enable greater or lesser driver or vehicle control of an ABS mode selection. As a result, it may be that the implementation of a determined ABS mode may only be enabled for specific drive modes, and for example, it may be that at least one drive mode selectable for the vehicle may disable the use of the ABS selection. Thus, the performing of at least one of determining the ABS mode and outputting the signal to control the ABS in response to the indication of the drive mode may therefore save processing power by reducing or preventing redundant processing when a drive mode selected for the vehicle does not enable a determined ABS mode to be implemented.

[0042] It may be that the ABS mode to be implemented is an ABS mode to be implemented with respect to wheels of the vehicle sharing a first common axle, and the control system is configured to output the signal to control the ABS to implement the determined ABS mode with respect to the wheels of the vehicle sharing the first common axle, and the control system may be further configured to control the ABS to implement a different ABS mode with respect to wheels of the vehicle sharing a second common axle different to the first axle.

[0043] For example, the control system may control the ABS to implement the different ABS mode with respect to wheels of the vehicle sharing the second common axle by way of the output signal, or by way of a further signal output by the control system.

[0044] Advantageously, wheels of a first axle, e.g., wheels of a driving direction leading axle, can be controlled to implement an ABS mode independently of wheels of a second axle, which may improve tyre wear, steerability and / or composure of the vehicle.

[0045] It may be that the ABS mode to be implemented is an ABS mode to be implemented with respect to wheels of the vehicle sharing a first common axle, and the control system is further configured to determine an ABS mode to be implemented with respect to wheels of the vehicle sharing a second common axle different to the first axle. The control system may be configured to determine the ABS mode to be implemented with respect to wheels of the vehicle sharing a second common axle according to any of the disclosures herein. For example, the control system may be configured to determine the ABS mode to be implemented with respect to wheels of the vehicle sharing a second common axle in dependence on an indication of the gravel driving surface associated with the wheels of the second axle. For example, it may be that the indication of the gravel driving surface (e.g., received in the surface signal, or determined in dependence on the one or more sensor signals) is associated with the wheels of the first axle, or wheels of the second axle and the determination for the respective ABS modes is in dependence on the relative indications. For example, it may be that the at least one sensor signal that the control system is configured to receive is associated with wheels of the first axle, or wheels of the second axle and the control system is configured to receive and / or determine the respective indications in dependence on the respective at least one sensor signals.

[0046] Advantageously, determining and implementing the determined ABS modes separately, and e.g., independently, for the wheels of a first axle and the wheels of a second axle may further improve tyre wear, steerability and / or composure of the vehicle.

[0047] According to an aspect of the present invention there is provided a system. The system comprises any control system disclosed herein and an anti- lock braking system, ABS, wherein the ABS is configured to operate in a plurality of ABS modes, wherein respective modes of the plurality of ABS modes provides a different braking configuration. Advantageously, the system can use input from the ABS or other sub-systems, which may indicate the gravel driving surface, to determine an ABS mode to be implemented and provide an output to control the ABS mode to be implemented.

[0048] According to an aspect of the present invention there is provided a vehicle. The vehicle comprises any system or any control system disclosed herein. Advantageously, a vehicle may be fitted with such systems and control systems to provide an improved vehicle able to dynamically adapt an ABS mode to be implemented to different driving surfaces.

[0049] According to an aspect of the present invention there is provided a method for controlling an anti-lock braking system, ABS of a vehicle. The method comprises receiving a surface signal indicative of a gravel driving surface, determining, in dependence on the received surface signal, an anti-lock braking system mode to be implemented, and outputting a signal to control the anti-lock braking system to implement the determined anti-lock braking system mode. The ABS mode to be implemented is determined by selecting, in dependence on the received surface signal, an ABS mode from a plurality of ABS modes, wherein respective modes of the plurality of ABS modes comprise different braking configurations. The anti-lock braking system mode determined to be implemented on the gravel driving surface permits a relatively higher level of wheel slip, as compared to an anti-lock braking system mode determined for use on a non-gravel driving surface. Advantageously, there is a way to use control the ABS of the vehicle to adapt braking of the vehicle based on an indication of a gravel driving surface.

[0050] According to an aspect of the present invention there are provided a computer readable instructions which, when executed by one or more processors, cause the one or more processors to perform any method disclosed herein. Advantageously, the method may be implemented as computer code, such as a computer on board the vehicle.

[0051] According to an aspect of the present invention there is provided a computer readable medium comprising computer readable instructions which, when executed by one or more processors, cause the one or more processors to perform any method disclosed herein. Advantageously, the method may be stored, transferred or transmitted as computer readable medium.

[0052] 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.

[0053] BRIEF DESCRIPTION OF THE DRAWINGS

[0054] 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 according to examples disclosed herein;

[0055] Figure 2 shows a control system according to examples disclosed herein;

[0056] Figure 3 shows a control system configured to perform methods according to examples disclosed herein;

[0057] Figure 4 shows a control system configured to perform methods according to examples disclosed herein;

[0058] Figures 5A, 5B and 5C show graphical representations of braking according to the implementation of examples disclosed herein;

[0059] Figure 6 shows a control system configured to perform a method according to examples disclosed herein;

[0060] Figure 7 shows a system according to examples disclosed herein; and

[0061] Figure 8 shows a method according to examples disclosed herein.

[0062] DETAILED DESCRIPTION

[0063] A vehicle 10 according to examples disclosed herein is shown in Figure 1. The vehicle 10 comprises the systems 700 or control systems 100 discussed below.

[0064] A control system 100 for controlling an anti-lock braking system (ABS) of a vehicle is illustrated in Figure 2. The control system 100 comprises one or more controllers 110.

[0065] The control system 100 is configured to receive a surface signal 165 indicative of a gravel driving surface, and determine, in dependence on the received signal indicative of a gravel driving surface, an anti-lock braking system mode to be implemented. The control system 100 is configured to output a signal 155 (e.g., a control signal) to control the anti-lock braking system 170 to implement the determined anti-lock braking system (ABS) mode. The ABS mode to be implemented is determined by selecting, in dependence on the received surface signal, an ABS mode from a plurality of ABS modes. Respective modes of the plurality of ABS modes comprise different braking configurations. The ABS mode determined to be implemented on the gravel driving surface permits a relatively higher level of wheel slip, as compared to an ABS mode determined for use (or intended for use or implementation) on a non-gravel driving surface.

[0066] The control system comprises one or more processors 120, collectively configured to receive the surface signal 165 indicative of a gravel driving surface; determine, in dependence on the received signal 165 indicative of a gravel driving surface, an anti-lock braking system mode to be implemented; and output the signal 155 to control the ABS 170 to implement the determined ABS mode. The ABS mode to be implemented is determined by selecting, in dependence on the received surface signal, an ABS mode from a plurality of ABS modes, wherein respective modes of the plurality of ABS modes comprise different braking configurations. The ABS mode determined to be implemented on the gravel driving surface permits a relatively higher level of wheel slip, as compared to an ABS mode determined for use on a non-gravel driving surface. Advantageously, the determination of the ABS mode to be implemented, enables an ABS mode to be determined and implemented that makes use of wheel slip, or in fact, wheel lock. The use of wheel slip for a vehicle driving on a gravel surface may reduce a stopping distance of the vehicle. For example, the wheel slip, or wheel lock, may cause displacement of the gravel of the driving surface, which may result in the displaced gravel piling up in front of the wheel of the vehicle. The displaced gravel may act to reduce the stopping distance of the vehicle.

[0067] The control system 100 may be configured to obtain the surface signal 165 by receiving at least one sensor signal, e.g., from a sensor 160, indicating the presence of the gravel driving surface. The control system 100 may be further configured to determine the presence of the gravel driving surface in dependence on at least the received at least one sensor signal. Alternatively, it may be that the control system 100 is configured to receive the surface signal 165 from a manual input 160 from a user. For example, by the activation by the user of an indicator, such as a button or touch sensitive input element on a dashboard or a user interface of the vehicle, indicating the presence of the gravel driving surface.

[0068] The control system 100 as illustrated in Figure 2 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.

[0069] 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 155 of the controller 110. The input 140 is arranged to receive a signal 165 from a sensor, such as a sensor of the anti-lock braking system 170 and / or a sensor of a suspension system (not shown), or a signal associated with a manual input from a user. The signal 165 is an electrical signal which is indicative of a gravel driving surface. The output 150 is arranged to output a control signal 155 indicative of a determined ABS mode to be implemented, for controlling the ABS 170 to implement the determined ABS mode.

[0070] Figure 3 illustrates a control system 100 such as that described above in relation to Figure 2 configured to perform a method 300 according to an embodiment of the invention. The control system 100 is for controlling an anti-lock braking system of a vehicle. The control system 100 is configured to receive 302 a surface signal 310 indicative of a gravel driving surface, determine 304 an ABS mode to be implemented and output 306 a signal to control the ABS to implement the determined ABS mode.

[0071] The ABS mode to be implemented is determined 304 by selecting, in dependence on the received surface signal 310, an ABS mode from a plurality of ABS modes, wherein respective modes of the plurality of ABS modes comprise different braking configurations. For example, it may be that different braking configurations provide different stopping distances of a vehicle by applying different configurations of braking torque. The respective configurations of applied braking torque may include at least one of: a braking torque, a maximum braking torque, a duration of an applied braking torque, a number of repetitions of an applied braking torque, and an interval between respective applications of at least one braking torque. By changing at least one of a braking torque, a maximum braking torque, a duration of an applied braking torque, a number of repetitions of an applied braking torque, and an interval between respective applications of at least one braking torque, different braking configurations can be implemented. The at least one of the plurality of ABS modes may comprise a braking configuration configured to reduce the stopping distance of the vehicle on a gravel driving surface, such as an off-road surface, e.g., a gravel track. For example, the stopping distance achieved when the ABS mode is implemented may be reduced with respect to a braking distance achieved when a braking configuration intended to be implemented on a non-gravel driving surface, such a wet or dry tarmac, or ice, is applied to the vehicle on the gravel driving surface.

[0072] The ABS mode determined to be implemented on the gravel driving surface may permit a relatively higher level of wheel slip, as compared to an ABS mode determined for use on a non-gravel driving surface. The control system 100 may be configured to select such an ABS mode to be implemented from among the plurality of ABS modes. Wheel slip is a scenario in which, as a result of an application a braking torque, there is a relative motion between a non-powered wheel of the vehicle and the driving surface. As braking torque is further increased a value of wheel slip may increase and beyond a critical value of braking torque a wheel of a vehicle may lock. The relative motion caused by wheel slip, or wheel lock, may be accompanied by a decrease in adhesion between the wheel (or a tyre of the wheel) and the driving surface. A vehicle driving on a gravel driving surface may make use of the gravel of the driving surface to reduce the stopping distance of the vehicle by implementing a braking configuration configured to increase a level of wheel slip, for example up to and including wheel lock, by at least one of introducing, or prolonging a period of wheel slip for at least one wheel of the vehicle, or increasing a maximum value of wheel slip that is reached. While wheel slip, or wheel lock for a vehicle on a non-gravel driving surface may increase the stopping distance of a vehicle, for example due to a decrease in the transfer of force through the wheel to the road resulting from reduced adhesion between the wheel (or a tyre of the wheel) and the road, wheel slip or wheel lock for a vehicle on a gravel driving surface may reduce the stopping distance. For example, the relative motion between the wheel and the surface during a period of wheel slip for a vehicle on a gravel driving surface may result in an interaction between the wheel and the gravel of the gravel surface (for example, as a result of a force applied from the wheel to the gravel) that causes the gravel to pile up in front of the wheel. This interaction between the wheel and the gravel, (or further between the wheel, the gravel and a hard sub-surface beneath the gravel) and the displacement of the gravel, may reduce the stopping distance of the vehicle. It may be that increasing the interaction between the wheel and the gravel, decreases the stopping distance of the vehicle, for example, by increasing the displacement of the gravel to in front of the wheel.

[0073] The control system 100 may be configured to determine 304 the ABS mode to be implemented by selecting an ABS mode that comprises a braking configuration configured to cause an interaction resulting from wheel slip, that is different from an interaction between at least one wheel of the vehicle and the driving surface when a braking configuration of an ABS mode implemented for (or intended for implementation for) a non-gravel driving surface is applied. For example, the control system 100 may be configured to select an ABS mode that comprises a braking configuration configured to cause a greater interaction between the wheel of the vehicle and the driving surface as a result of wheel slip.

[0074] The control system 100 may be configured to select an ABS mode configured to provide a prolonged, or introduced time period over which wheel slip occurs, for example, as compared to an ABS mode implemented (or intended to be implemented) for a vehicle on a non-gravel driving surface, such as a wet or dry tarmac road. For example, the control system 100 may be configured to select an ABS mode that is configured to comprise at least one time period over which there is wheel slip for at least one wheel of the vehicle, where the time period may have an increased duration with respect to each of one or more time periods of wheel slip of an ABS mode implemented for (or determined for used on) a non-gravel driving surface, or where the time period is an additional time period with respect to time periods of the ABS mode implemented for a non-gravel driving surface.

[0075] It may be that the at least one time period over which there is wheel slip has a duration of more than 0.15 seconds, for example, 0.2, 0.3, 0.4 or 0.5 seconds (plus or minus a predetermined tolerance, such as + / - 1 %, + / - 2%, + / - 5%, + / - 10%, etc.,). For example, the at least one time period over which there is wheel slip may have a duration of, of greater than 0.3 seconds (plus or minus a predetermined tolerance, such as + / - 1 %, + / - 2%, + / - 5%, + / - 10%, etc.,).

[0076] Alternatively, or in addition, control system 100 may be configured to select an ABS mode configured to provide a maximum wheel slip value, during the time period over which wheel slip is present, that is higher as compared to a maximum wheel slip value reached during each of one or more time periods of wheel slip of an anti-lock braking system mode determined for use on a non-gravel driving surface.

[0077] Advantageously, by selecting an ABS mode in which at least a period of wheel slip (or wheel lock) is prolonged or introduced, and / or in which a maximum wheel slip value permitted to be reached is increased, as compared to an ABS mode (intended to be) implemented for a non-gravel driving surface, the stopping distance of the vehicle on the gravel driving surface may be reduced.

[0078] It may be that the wheel slip value corresponds to a measure of wheel slip (e.g., an extent or degree of wheel slip). It may be that the wheel slip value corresponds to a measure of wheel slip (e.g., an extent or degree of wheel slip) up to and including wheel lock. For example the measure of wheel slip may range from relatively low wheel slip through to relatively high wheel slip, e.g., up to and including wheel lock. It may be that the wheel slip value corresponds a measure of wheel slip given in units of metres per second. It may be that the maximum wheel slip value reached is greater than 3 metres per second, for example, it may be 3.5, 4, 5, 10 or 12 metres per second (plus or minus a predetermined tolerance, such as + / - 1 %, + / - 2%, + / - 5%, + / - 10%, etc.,). For example, the maximum wheel slip value reached may be, or may be greater than 3.5 metres per second (plus or minus a predetermined tolerance, such as + / - 1 %, + / - 2%, + / - 5%, + / - 10%, etc.,). It may be that the maximum wheel slip value that is reached corresponds to locking of the wheel.

[0079] The control system 100 may be configured to select such an ABS mode by selecting an ABS mode with at least one of an introduced or prolonged time period over which a braking torque at least sufficient to cause wheel slip is applied, or with a time period over which a braking torque is applied that is at least sufficient to cause an increase in the maximum wheel slip value. It may be that the braking torque applied by the ABS is applied in a plurality of cycles, and the control system 100 is configured to select an ABS mode comprising a braking configuration configured to at least one of introduce or prolong wheel slip or increase a maximum value of wheel slip in at least one cycle, or in each cycle of the braking configuration.

[0080] For example, the control system 100 may be configured to determine 304 the ABS mode to be implemented by selecting an ABS mode that is configured to apply braking in a plurality of cycles and wherein for at least one cycle of the plurality of cycles a time period is present over which a braking torque at least sufficient to cause at least one wheel of the vehicle to slip is applied. The time period may have an increased duration with respect to each of one or more corresponding time periods of an ABS mode implemented for a non-gravel driving surface, or the time period may have an additional time period with respect to time periods of the ABS mode implemented for a non-gravel driving surface. The maximum wheel slip during the time period may reach (e g., may correspond to) a higher wheel slip value as compared to a maximum wheel slip value reached during each of one or more time periods of wheel slip of an anti-lock braking system mode determined for use on a non-gravel driving surface.

[0081] It may be that the introduced or prolonged time period is a continuous time period, i.e., one non-divided block of time. Alternatively, the time period may comprise a plurality of sub-periods, which may be either sequential or separated from each other in time. The duration of the period of wheel slip may be increased by increasing the duration of one or more of the sub-periods, or introducing at least one additional sub-period, and for example, reducing the time period between sub-periods (within or between cycles) of the application of a braking torque at least sufficient to cause wheel slip.

[0082] Figure 4 illustrates a control system 100 such as that described above in relation to Figure 2 and Figure 3 configured to perform a method 300 according to an embodiment of the invention, with additional possible functionality. As shown in Figure 4 the control system 100 may be configured to determine 304 the ABS mode to be implemented further based on an indication 400. Indication 400 may be an indication of at least one of: a reliability of an indication of the gravel driving surface 410, a velocity of the vehicle 420, a longitudinal acceleration of the vehicle 430, a driving direction of the vehicle 440 and a steering angle of the vehicle 450.

[0083] The determination 304 in dependence on the indication 400 may enable the determined ABS mode to be more adaptive to a wider range of driving conditions of the vehicle, in addition to being adaptive to the driving surface detected for the vehicle. For example, an ABS mode resulting in an increased interaction between the wheel of the vehicle and the gravel (e.g., a mode with a higher level of wheel slip, such as an additional or longer time period of wheel slip and / or a higher maximum value of wheel slip) may be implemented if it is indicated that the reliability 410 of the indication of the gravel driving surface is compared with at least one criterion, for example a threshold. Such a threshold may be a pre-determined or a dynamic threshold. The threshold may be associated with a level of likelihood that the indication is reliable, i.e., that the indication accurately indicates the presence of a gravel driving surface. For example, an ABS mode with an additional or prolonged period of wheel slip, and / or a higher maximum wheel slip value may be selected when the reliability 410 of the indication of the gravel surface is determined to be greater (or equal) to a predetermined probability threshold that the indication of the gravel surface corresponds to a true presence of a gravel driving surface (or conversely, to a false detection of a gravel driving surface). For example, the reliability 410 of the indication of the gravel driving surface may correspond to a probability that the indication of the gravel driving surface corresponds to a true presence of a gravel driving surface (or conversely, to a false detection of a gravel driving surface). The probability may be any value between zero and one. The probability threshold may correspond to a probability within the range of 0.1 to 1.0 (inclusive), or any value or sub-range therein, for example a value of (or rounded to) 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 etc., or a sub-range of 0.5 to 1 , 0.6 to 1 , 0.7 to 1 , 0.8 to 1 or 0.9 to 1 , that the indication of the gravel driving surface corresponds to a true (or false) presence of a gravel driving surface. It may be that the indication of the gravel driving surface is provided by (e g., received in) the surface signal 310, or the indication of the gravel driving surface corresponds to a determination of the presence of the gravel driving surface, such as a determination performed by the control system 100 , as will be discussed in more detail below.

[0084] The reliability 410 may correspond to whether the indication of the gravel driving surface is determined (e g., by the control system 100) from at least one sensor signal, or is received by the control system 100, for example, from a surface signal corresponding to a manual input from a user. For example, the reliability 410 of the indication of the gravel driving surface may be higher when the presence of the gravel driving surface is determined by way of at least one sensor input, as opposed to a manual input from a user, or vice versa.

[0085] Returning to the determination 302 of the ABS mode performed by the control system 100, an ABS mode with a higher level of wheel slip, e.g., at least one of an additional or longer period of wheel slip and a higher maximum value of wheel slip, may be selected in dependence on a comparison of the indication 400 of at least one of the velocity of the vehicle 420 and the longitudinal acceleration of the vehicle 430 with a criterion, such as a threshold. For example, it may be that such an ABS mode is selected if it is determined, by way of the indication of at least one of the velocity of the vehicle 420 and the longitudinal acceleration of the vehicle 430, that the vehicle is travelling below (or at) a predetermined speed, for example 160 kilometres per hour (plus or minus a predetermined tolerance, such as + / - 1 %, + / - 2%, + / - 5%,+ / - 10%, etc.,), or 150 kilometres per hour (plus or minus a predetermined tolerance, such as + / - 1 %, + / - 2%, + / - 5%,+ / - 10%, etc.,).

[0086] It may be that the ABS mode is selected such that the specific relatively higher level of wheel slip, e.g., at least one of the specific duration of the time period (i.e., specific duration of the prolonged or introduced time period) of wheel slip or maximum value of wheel slip, provided by the selected ABS mode is also in dependence on the indication 400 of at least one of the velocity of the vehicle 420 and the longitudinal acceleration of the vehicle 430. For example, an ABS mode providing a higher level of wheel slip, e.g., a prolonged time period of wheel slip compared to an ABS mode to be implemented for a non-gravel driving surface and with a relatively higher level of wheel slip (e.g., a longer duration of wheel slip) and / or a higher maximum wheel slip value compared to other ABS modes of the plurality of ABS modes implementable for a gravel driving surface may be selected in dependence on an indication that the vehicle is travelling at a speed below a first threshold, and an ABS mode providing a higher level of wheel slip (e.g., a prolonged time period of wheel slip) compared to an ABS mode to be implemented for a non-gravel driving surface and with a relatively lower level of wheel slip (e.g., shorter duration of wheel slip, and / or lower maximum wheel slip value) compared to other ABS modes of the plurality of ABS modes implementable for a gravel driving surface may be selected in dependence on an indication that the vehicle is travelling at speed equal to, or greater than the first threshold, and optionally also at a speed below a second threshold, where the second threshold is associated with a higher speed than the first threshold. For example the first threshold may be 30 kilometres per hour (plus or minus a predetermined tolerance, such as + / - 1 %, + / - 2%, + / - 5%, + / - 10%, etc.,), and the second threshold may be 160 kilometres per hour (plus or minus a predetermined tolerance, such as + / - 1 %, + / - 2%, + / - 5%, + / - 10%, etc.,).

[0087] It may be that the ABS mode providing a higher level of wheel slip compared to an ABS mode for a non-gravel driving surface (e.g., at least one of a prolonged period of wheel slip and a higher maximum wheel slip value) with a relatively lower level of wheel slip compared to other ABS modes for a gravel driving surface (e.g., at least one of a shorter duration of wheel slip and a lower maximum wheel slip value compared to other ABS modes for a gravel driving surface) is a first ABS mode and the ABS mode providing a higher level of wheel slip compared to an ABS mode for a non-gravel driving surface (e.g., at least one of a prolonged period of wheel slip and higher maximum wheel slip value) with a relatively higher level of wheel slip compared to other ABS modes for a gravel driving surface (e.g., at least one of a longer duration of wheel slip and a higher maximum wheel slip value compared to other ABS modes for a gravel driving surface) is a second ABS mode of the plurality of modes from which the ABS mode to be implemented is selectable, as will be discussed further below.

[0088] An ABS mode with a higher level of wheel slip (e.g., at least one of an additional or longer period of wheel slip and a higher maximum wheel slip value) compared to an ABS mode to be implemented (or determined for use for) a non-gravel driving surface may be determined in dependence on, e.g., selected in dependence on, a determination based on the indication 400 of the steering angle 450 that the vehicle is travelling in a straight direction, as opposed to a determination based on an indication of the steering angle 450 that the vehicle is turning, or being steered to turn. As described above, it may be that the ABS mode is selected such that the specific higher level of wheel slip (e.g. , at least one of the specific duration of the time period of wheel slip, i.e. , specific duration of the prolonged period of wheel slip, and the specific maximum wheel slip value) provided by the selected ABS mode is also in dependence on at least the indication 400 of the steering angle 450. For example, an ABS mode providing a higher level of wheel slip (e.g., at least one of a prolonged period of wheel slip and higher maximum wheel slip value) as compared to an ABS mode implemented for a non-gravel surface with a relatively lower level (e.g., a relatively shorter duration, and / or lower maximum wheel slip value) compared to other ABS modes of the plurality of ABS modes implementable for a gravel driving surface may be selected, as opposed to a higher level of wheel slip (e.g., a prolonged period of wheel slip with a relatively longer duration and / or higher maximum wheel slip value) compared to other ABS modes of the plurality of ABS modes implementable for a gravel driving surface, in dependence on an indication that the vehicle is turning, or vice versa.

[0089] An ABS mode with a higher level of wheel slip (e.g., an additional or longer period of wheel slip and / or a higher maximum wheel slip value reached) compared to an ABS mode determined for use for a non-gravel driving surface may be selected in dependence on, e.g., selected in dependence on a determination based on, the indication 400 of the driving direction of the vehicle 440. For example, the driving direction may be one of forward, or reverse. As above, it may also be that the ABS mode is selected such that the specific higher level of wheel slip (e.g., specific duration of the time period of wheel slip, i.e., specific duration of the prolonged period of wheel slip and / or the specific maximum wheel slip value) provided by the selected ABS mode is also in dependence on the indication 400 of the driving direction of the vehicle 440.

[0090] The ABS mode to be implemented may be an ABS mode to be implemented with respect to wheels of the vehicle sharing a first common axle, and the control system 100 may be configured to output the signal to control the ABS to implement the determined ABS mode with respect to the wheels of the vehicle sharing the first common axle. The control system 100 may be further configured to control the ABS to implement a different ABS mode with respect to wheels of the vehicle sharing a second common axle different to the first axle. The ABS mode to be implemented with respect to the wheels of the vehicle sharing the second common axle may be pre-determined, or may determined (e.g., selected) by the control system 100 according to any of the examples disclosed herein. The control system 100 may be configured to control the ABS to implement an ABS mode of wheels of a first axles independently of wheels of a second axle. For example, it may be that the ABS mode to be implemented with respect to the wheels of the vehicle sharing the first common axle and the ABS mode to be implemented with respect to the wheels of the vehicle sharing the second common axle are determined independently. For example, the ABS modes may be determined in dependence on respective sensor signals associated with the wheels of the respective axles. The control system 100 may be configured to select at least one of the ABS mode to be implemented with respect to wheels of the vehicle sharing a first common axle and the ABS mode to be implemented with respect to wheels of the vehicle sharing the second common axle in dependence on at least the indication 400 of the driving direction of the vehicle 440. It may be that the control system 100 is configured to control the ABS to implement the different ABS mode with respect to wheels of the vehicle sharing the second common axle by way of the signal 155, or by way of a further signal 480 output by the control system 100.

[0091] The first common axle may be a front axle of the vehicle (for example, in relation to a driving direction of the vehicle), and the second common axle may be a rear axle of the vehicle, or vice versa.

[0092] Although it is shown in Figure 4 that indication 400 is separate from the surface signal 310 indicative of a gravel driving surface, it may be that indication 400 is included in indication 310, or is determined from indication 310 by the control system 100.

[0093] As shown in Figure 4, the control system 100 may be configured to perform any one or more of steps 304 or 306 in response to obtaining an indication 460 of a drive mode 470 of the vehicle. A drive mode of the vehicle may relate to a level of automated control, as opposed to driver control, of at least one system of the car that controls the chassis, for example at least one of an anti-lock braking system, a suspension system and a steering control system of the vehicle. It may be that the drive mode is manually selectable by a user. In respective drive modes, it may be that implementation of an ABS mode determined in dependence on an indication of a gravel driving surface is limited, or prohibited. Advantageously, performing any one or more of steps 304 and 306 in response to the indication 460 of the drive mode 470 may reduce or prevent redundant processing by the control system 100. The control system 100 may be configured in step 304 to determine the ABS mode to be implemented by selecting a first ABS mode as the ABS mode to be implemented in dependence on at least a comparison of a characteristic associated with an indication of the gravel driving surface with at least a first criterion and selecting a second ABS mode as the ABS mode to be implemented in dependence on at least a comparison of the characteristic associated with the indication of the gravel driving surface with at least a second criterion.

[0094] The indication of the gravel driving surface may be as described and, for example, provided in or by the surface signal, or determined from the surface signal.

[0095] The first criterion and the second criterion may be thresholds. The second criterion may correspond to a higher threshold than the first criterion. The characteristic associated with the detection of the presence of the gravel driving surface may be at least one of a reliability of the indication or a time period lapsed since the indication was at least one of received, or determined. For example, the first criterion may correspond to a first reliability threshold and the second criterion may correspond to a second reliability threshold, for example, greater than the first reliability threshold. As described above, the reliability of the indication of the gravel driving surface may correspond to a probability that the indication of the gravel driving surface corresponds to a true presence of a gravel driving surface (or conversely, to a false detection of a gravel driving surface). The reliability threshold may correspond to (for example, may the same as) any of the probability thresholds discussed above.

[0096] Alternatively, or additionally the selection of the first or second ABS mode may be in dependence on at least one of a velocity of the vehicle 420, a longitudinal acceleration of the vehicle 430, a driving direction of the vehicle 440 and a steering angle of the vehicle 450, as described above.

[0097] The second ABS mode may comprise a braking configuration configured to reduce a stopping distance of the vehicle on a gravel driving surface with respect to a stopping distance of the vehicle on a gravel driving surface provided by the first ABS mode. For example, the second ABS mode may comprise a braking configuration configured to permit a relatively higher level of wheel slip, as compared to the first ABS mode. For example, the second ABS mode may comprise a braking configuration configured to provide at least one of an additional or prolonged period of wheel slip and a higher maximum value of wheel slip reached as compared to the braking configuration of the first ABS mode. For example, the second ABS mode may comprise a braking configuration configured to provide a time period over which there is wheel slip with a duration of greater than 0.15 seconds, and for example, of, or greater than 0.3 seconds (plus or minus a predetermined tolerance, such as + / - 1 %, + / - 2%, + / - 5%, + / - 10%, etc.,). The second ABS mode may comprise a braking configuration configured to provide a maximum wheel slip value of greater than 3 metres per second, for example, of , or greater than, 3.5 metres per second, such as 4, 5, 10 or 12 metres per second (plus or minus a predetermined tolerance, such as + / - 1 %, + / - 2%, + / - 5%,+ / - 10%, etc.,). For example, the second ABS mode may comprise a braking configuration configured to provide a time period over which there is wheel slip with a duration of 0.3 seconds and provide a maximum wheel slip value of 12 metres per second. It may be that the second ABS mode comprises a braking configuration configured to provide wheel lock. It may be that the wheel lock is provided over a time period with a shorter duration than time periods over which lower values of maximum wheel slip are provided, for example in the first ABS mode. Advantageously, this may further reduce the stopping distance of the vehicle on a gravel driving surface and improve vehicle composure.

[0098] The first ABS mode may comprise a braking configuration configured to reduce a stopping distance of the vehicle on a gravel driving surface with respect to a stopping distance of the vehicle on a gravel driving surface provided by an ABS mode intended for implementation on a non-gravel driving surface. For example, the first ABS mode may comprise a braking configuration configured to permit a relatively higher level of wheel slip, as compared to an ABS mode intended for implementation on a non-gravel driving surface. For example, the first ABS mode may comprise a braking configuration configured to provide at least one of an additional or prolonged period of wheel slip and a higher maximum value of wheel slip reached as compared to the braking configuration of an ABS mode implemented for a non-gravel driving surface. The first ABS mode may comprise a braking configuration configured to provide a time period over which there is wheel slip with a duration of greater than 0.15 seconds, and for example, of , or greater than 0.3 seconds, for example, 0.4 or 0.5 seconds (plus or minus a predetermined tolerance, such as + / - 1 %, + / - 2%, + / - 5%, + / - 10%, etc. The first ABS mode may comprise a braking configuration configured to provide a maximum wheel slip value of greater than 3 metres per second, for example, of 3.5, 4 or 5 metres per second (plus or minus a predetermined tolerance, such as + / - 1 %, + / - 2%, + / - 5%, + / - 10%, etc.,). For example, the second ABS mode may comprise a braking configuration configured to provide a time period over which there is wheel slip with a duration of 0.4 seconds and provide a maximum wheel slip value of 3.5 metres per second. Advantageously, the use of first and second reliability thresholds for determining which of the first and second ABS modes is to be selected may enable more reliable detections of the presence of the gravel driving surface to cause a braking configuration providing a higher level of wheel slip to be implemented. This may allow the stopping distance of a vehicle to be reduced and increase composure of the vehicle. The selection of the first and second modes may also prevent or avoid the use of a higher level of wheel slip in the case of a false positive detection of a gravel driving surface, where the providing of a higher level of wheel slip may not decrease the stopping distance of a vehicle on a wet or dry tarmac driving surface.

[0099] Figure 5A illustrates a graphical representation of braking 510 according to an ABS mode intended to be implemented for a non-gravel driving surface. Figure 5B illustrates a graphical representation of braking 520 implemented in dependence on the indication of the gravel driving surface, for example, according to the first ABS mode implemented for at least the wheels of the rear axle of the vehicle, where the first ABS mode has a relatively higher level of wheel slip as compared to the ABS mode intended for implementation on the non-gravel surface. Figure 5C illustrates a graphical representation of braking 530 implemented in dependence on the indication of the gravel driving surface, for example, according to the second ABS mode implemented for at least the wheels of the rear axle of the vehicle, where the second ABS mode has a relatively higher level of wheel slip as compared to the first ABS mode (e.g., configured for implementation on the gravel surface). Figures 5A, 5B and 5C illustrate values of wheel speed (for example in units of metres per second) on the vertical axis as a function of time (for example, in units of seconds) on the horizontal axis.

[0100] In Figure 5A, the braking of the wheels of the front axle of the vehicle is represented by lines 511 and 512 and the braking of the wheels of the rear axle of the vehicle is represented by lines 513 and 514. In Figure 5B, the braking of the wheels of the front axle is represented by lines 521 and 522 and the braking of the wheels of the rear axle is represented by lines 523 and 524. In Figure 5C, the braking of the wheels of the front axle is represented by lines 531 and 532 and the braking of the wheels of the rear axle is represented by lines 533 and 534.

[0101] As shown in Figure 5B, the first ABS mode is implemented for at least the wheels of the rear axle as per lines 523, 524, causing the wheels of the rear axle to have a higher level of wheel slip, e.g., at least one of a time period of wheel slip with a longer duration and a higher maximum wheel slip value reached, as compared to the rear wheels of the vehicle implementing the ABS mode for use on the non-gravel driving surface (e.g., lines 513 and 514 of Figure 5A).

[0102] As shown in Figure 5C, the second ABS mode is implemented for the wheels of the rear axle as per lines 533, 534, causing the wheels of the rear axle to have a higher level of wheel slip, e.g., at least one of a time period of wheel lock with a longer duration and a higher maximum wheel slip value reached, as compared to the rear wheels of the vehicle implementing the ABS mode for use on the non-gravel driving surface (e.g., lines 513 and 514 of Figure 5A) and the rear wheels of the vehicle implementing the first ABS mode (e.g., lines 523 and 524 of Figure 5B). It may also be that, as shown in Figure 5C, the braking of the wheels of the front axle as per lines 531 , 532 may have a different braking configuration as compared to the wheels of the rear axle. For example, as shown in Figure 5C, it may be that the ABS mode implemented for the wheels of the front axle is (or is similar to) the ABS mode implemented for the non-gravel driving surface.

[0103] Figure 6 illustrates a control system 100 such as that described above in relation to Figure 2, Figure 3 and Figure 4 configured to perform a method 300 according to an embodiment of the invention, with additional possible functionality.

[0104] As shown in Figure 6, the control system 100 may be configured to receive 302 a surface signal 310 indicative of a gravel driving surface. The surface signal 310 indicative of the gravel driving surface may comprise at least one sensor signal indicative of the gravel driving surface. The control system 100 may be further configured to determine 600 a presence of the gravel driving surface in dependence on the at least one sensor signal.

[0105] The at least one sensor signal may comprise at least one of: at least one sensor signal from at least one sensor of the anti-lock braking system; and at least one sensor signal from at least one sensor of a suspension system of the vehicle. The control system 100 may be configured to determine a presence of the gravel driving surface in dependence on at least one sensor signal from at least one sensor of the ABS and at least one sensor signal from at least one sensor of a suspension system of the vehicle. It may be that the control system 100 is configured to determine the presence of the gravel driving surface in dependence on both the at least one sensor signal from at least one sensor of the ABS and at least one sensor signal from at least one sensor of a suspension system of the vehicle in response to a comparison of an indicated speed of the vehicle with a criterion, such as a threshold. For example, the control system 100 may be configured to determine the presence of the gravel driving surface in dependence on the at least one sensor signal from at least one sensor of the ABS and at least one sensor signal from at least one sensor of a suspension system of the vehicle in response to a determination that the speed of the vehicle is greater than or equal to 30 kilometres per hour (plus or minus a predetermined tolerance, such as + / - 1 %, + / - 2%, + / - 5%,+ / - 10%, etc.,).

[0106] Advantageously, the accuracy and / or reliability of the determination of the gravel driving surface can be improved by using the combination of sensor signals from the separate anti-lock braking system and the suspension system as measures of the movement of the vehicle from separate systems of the vehicle. For example, it may be that the sensors of the separate systems are subjected to different biases etc, and the determination in dependence on the combination of sensors from the different systems may reduce the false-positive detection of a gravel driving surface.

[0107] The surface signal 310 may comprise both a sensor signal from at least one sensor of the ABS, and a sensor signal from at least one sensor of a suspension system of the vehicle, or the surface signal 310 may comprise a sensor signal from at least one sensor of the ABS, or a sensor signal from at least one sensor of a suspension system of the vehicle and the control system 100 may be configured to receive the additional signal separate from the surface signal 310, e.g., from either the anti-lock braking system or the suspension system.

[0108] The surface signal 310 may comprise at least one of a yaw rate sensor signal and a lateral acceleration sensor signal. For example, it may be that the at least one sensor signal comprises at least one of a yaw rate sensor signal, and a lateral acceleration sensor signal.

[0109] The control system 100 may be configured to receive at least one of a yaw rate sensor signal, and a lateral acceleration sensor signal and determine 600 the presence of the gravel driving surface in dependence on at least one of a yaw rate sensor signal, and a lateral acceleration sensor signal. For example, the control system 100 may be configured to determine 600 the presence of the gravel driving surface in dependence on both the yate rate sensor signal and the lateral acceleration sensor signal, which may improve the reliability of the determination. It may be that the control system 100 is configured to receive the yaw rate sensor signal and / or the lateral acceleration signal from the ABS. The control system 100 may configured to receive the yaw rate sensor signal and the lateral acceleration signal via (e.g., in) the surface signal 310, or via the surface signal 310 and at least one additional signal.

[0110] The control system 100 may be configured to determine the presence of the gravel driving surface in dependence on at least one of a yaw rate and / or lateral acceleration sensor signal from at least one sensor of the ABS, and a ride height and / or inertial measurement unit (IMU) sensor signal from a sensor of a suspension system of the vehicle. For example, it may be that the at least one sensor signal comprises at least one of a yaw rate and / or lateral acceleration sensor signal from at least one sensor of the ABS, and a ride height and / or an IMU sensor signal from a sensor of a suspension system of the vehicle. The IMU may be a two sensor or three sensor IMU. Advantageously, the combination of signals from the yaw rate and / or lateral acceleration sensors, and the ride height and / or IMU sensors may provide a more accurate and more reliable determination of the gravel driving surface.

[0111] It may be that the control system 100 is configured to receive at least one of: a yaw rate and / or lateral acceleration sensor signal from at least one sensor of the ABS, and a ride height and / or inertial measurement unit sensor signal from a sensor of a suspension system of the vehicle via the surface signal 310, or via the surface signal 310 and at least one additional signal.

[0112] The control system 100 may be configured to determine the presence of the gravel driving surface in dependence on at least a detection of a predetermined characteristic in the at least one sensor signal. For example, the control system 100 may be configured to determine 600 the presence of the gravel driving surface in dependence on a comparison of a characteristic of the at least one sensor signal with at least one criterion. The predetermined characteristic may be noise in the at least one sensor signal. The criterion may be a threshold, for example, the threshold may be a predetermined value, or a dynamic value such as a value associated with a running average. The control system 100 may be configured to receive the at least one sensor signal indicative of the gravel driving surface periodically or continuously, for example, based on a sampling rate of the at least one sensor. The control system 100 may be configured to determine the presence of the gravel driving surface in dependence on the at least one sensor signal periodically or continuously, and for example may be configured to determine the presence responsive to receiving the at least one sensor signal.

[0113] Figure 7 shows an example system 700 comprising an anti-lock braking system 710 and a control system 100 as disclosed herein. The anti-lock braking system 710, as shown, may be configured to receive a signal 155 indicative of a determined ABS mode to be implemented, for controlling the ABS to implement the determined ABS mode. As shown, the ABS 710 may also be configured to provide to control system 100 at least one sensor signal 720 indicative of the gravel driving surface.

[0114] Figure 8 illustrates a method 800 according to an embodiment of the invention. The method 800 is a method of controlling an ABS of a vehicle, such as the vehicle 10 illustrated in Figure 1 . In particular, the method 800 comprises receiving 802 a surface signal indicative of a gravel driving surface. The method further comprises determining 804, in dependence on the received surface signal, an anti-lock braking system mode to be implemented and outputting 806 a signal to control the anti-lock braking system to implement the determined anti-lock braking system mode. The ABS mode to be implemented is determined by selecting, in dependence on the received surface signal, an ABS mode from a plurality of ABS modes, wherein respective modes of the plurality of ABS modes comprise different braking configurations. The ABS mode determined to be implemented on the gravel driving surface permits a relatively higher level of wheel slip, as compared to an ABS mode determined for use on a non-gravel driving surface.

[0115] The method 800 may be performed by the control system 100 illustrated in Figure 2. 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.

[0116] 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

CLAIMS1 . A control system for controlling an anti-lock braking system of a vehicle, the control system comprising one or more processors collectively configured to: receive a surface signal indicative of a gravel driving surface; determine, in dependence on the received surface signal, an anti-lock braking system mode to be implemented; and output a signal to control the anti-lock braking system to implement the determined anti-lock braking system mode, wherein the anti-lock braking system mode to be implemented is determined by selecting, in dependence on the received surface signal, an anti-lock braking system mode from a plurality of anti-lock braking system modes, wherein respective modes of the plurality of anti-lock braking system modes comprise different braking configurations, wherein the anti-lock braking system mode determined to be implemented on the gravel driving surface permits a relatively higher level of wheel slip, as compared to an anti-lock braking system mode determined for use on a non-gravel driving surface.

2. The control system of claim 1 , wherein the different braking configurations comprise different configurations of applied braking torque, and wherein respective configurations of applied braking torque include at least one of: a braking torque, a maximum braking torque, a duration of an applied braking torque, a number of repetitions of an applied braking torque, and an interval between respective applications of at least one braking torque.

3. The control system of any preceding claim, wherein the control system is configured to determine the anti-lock braking system mode to be implemented by selecting an anti-lock braking system mode that is configured to comprise at least one time period over which there is wheel slip for at least one wheel of the vehicle and wherein at least one of: the time period has an increased duration as compared to each of one or more time periods of wheel slip of an anti-lock braking system mode determined for use on a non-gravel driving surface; the time period is an additional time period with respect to time periods of the anti-lock braking system mode determined for use on a non-gravel driving surface; and a maximum wheel slip value reached during the time period is higher as compared to a maximum wheel slip value reached during each of one or more time periods of wheel slip of an anti-lock braking system mode determined for use on a non-gravel driving surface.

4. The control system of any preceding claim, wherein the control system is configured to determine the anti-lock braking system mode to be implemented further based on an indication of at least one of: a reliability of an indication of the gravel driving surface, a velocity of the vehicle, a longitudinal acceleration of the vehicle, a driving direction of the vehicle and a steering angle of the vehicle.

5. The control system of any preceding claim, wherein the control system is configured to: select a first anti-lock braking system mode as the anti-lock braking system mode to be implemented in dependence on at least a comparison of a characteristic associated with an indication of the gravel driving surface with at least a first criterion; and select a second anti-lock braking system mode as the anti-lock braking system mode to be implemented in dependence on at least a comparison of the characteristic associated with the indication of the gravel driving surface with at least a second criterion.

6. The control system of claim 5, wherein: the first criterion is associated with a first level of reliability of the indication of the gravel driving surface; the second criterion is associated with a second level of reliability of the indication of the gravel driving surface, wherein the second level of reliability is higher than the first level of reliability, wherein the second anti-lock braking system mode comprises a braking configuration configured to permit a relatively higher level of wheel slip, as compared to the first anti-lock braking system mode.

7. The control system of any preceding claim, wherein the surface signal indicative of the gravel driving surface comprises at least one sensor signal indicative of the gravel driving surface, and the control system is further configured to determine a presence of the gravel driving surface in dependence on the at least one sensor signal.

8. The control system of claim 7, wherein the at least one sensor signal comprises at least one of: at least one sensor signal from at least one sensor of the anti-lock braking system; and at least one sensor signal from at least one sensor of a suspension system of the vehicle, and the control system is configured to determine a presence of the gravel driving surface in dependence on at least one sensor signal from at least one sensor of the anti-lock braking system and at least one sensor signal from at least one sensor of a suspension system of the vehicle.

9. The control system of claim 7 or claim 8, wherein the at least one sensor signal comprises at least one of: a yaw rate sensor signal; and a lateral acceleration sensor signal.

10. The control system of any preceding claim, wherein the control system is configured to at least one of: determine the anti-lock braking system mode to be implemented; and output the signal, as recited in claim 1 , in response to obtaining an indication of a drive mode of the vehicle.11 . The control system of any preceding claim, wherein the anti-lock braking system mode to be implemented is an anti-lock braking system mode to be implemented with respect to wheels of the vehicle sharing a first common axle, and the control system is configured to output the signal to control the anti-lock braking system to implement the determined anti-lock braking system mode with respect to the wheels of the vehicle sharing the first common axle; and the control system is further configured to control the anti-lock braking system to implement a different anti-lock braking system mode with respect to wheels of the vehicle sharing a second common axle different to the first axle.

12. The control system of any preceding claim, wherein the anti-lock braking system mode to be implemented is an anti-lock braking system mode to be implemented with respect to wheels of the vehicle sharing a first common axle, and the control system is further configured to determine an anti-lock braking system mode to be implemented with respect to wheels of the vehicle sharing a second common axle different to the first axle.

13. A system comprising the control system of any preceding claim and an anti-lock braking system, wherein the anti-lock braking system is configured to operate in a plurality of anti-lock braking system modes, wherein respective modes of the plurality of anti-lock braking system modes provide different braking configurations.

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

15. A method for controlling an anti-lock braking system of a vehicle, the method comprising: receiving a surface signal indicative of a gravel driving surface; determining, in dependence on the received surface signal, an anti-lock braking system mode to be implemented; and outputting a signal to control the anti-lock braking system to implement the determined anti-lock braking system mode, wherein the anti-lock braking system mode to be implemented is determined by selecting, in dependence on the received surface signal, an anti-lock braking system mode from a plurality of anti-lock braking system modes, wherein respective modes of the plurality of anti-lock braking system modes comprise different braking configurations, wherein the anti-lock braking system mode determined to be implemented on the gravel driving surface permits a relatively higher level of wheel slip, as compared to an anti-lock braking system mode determined for use on a non-gravel driving surface.

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