GB2630278A

GB2630278A - Vehicle control mode selection method and apparatus

Info

Publication number: GB2630278A
Application number: GB2307327.3A
Authority: GB
Inventors: Young Adrian; Lal Meghna; Frampton Tom; Walker Stuart
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2023-05-17
Filing date: 2023-05-17
Publication date: 2024-11-27
Also published as: GB202307327D0; WO2024235982A1

Abstract

A vehicle control system (100) for selecting one of a plurality of subsystem control modes to control operation of at least one vehicle subsystem (110) of a vehicle (200) comprising a plurality of wheels (W1-W4) each having a pneumatic tire (T1-T4). The subsystem control modes each correspond to one or more different terrain types for the vehicle. One or more processor (120) are collectively configured to receive one or more pressure indicator signal (TPS-n), the or each pressure indicator signal comprising at least one tire pressure indicator providing an indication of a pressure of one of the pneumatic tires. A plurality of terrain condition indicators (17) are determined. The plurality of terrain condition indicators include a first terrain condition indicator in the form of a sand terrain condition indicator; the first terrain condition indicator being determined in dependence on the at least one tire pressure indicator. One of the plurality of subsystem control modes is selected in dependence on the plurality of terrain condition indicators. The vehicle control system is configured to operate in the selected one of the plurality of subsystem control modes.

Description

VEHICLE CONTROL MODE SELECTION METHOD AND APPARATUS

TECHNICAL FIELD

The present disclosure relates to a vehicle control mode selection method and apparatus. More particularly, the disclosure relates to a method and apparatus for selection of one of a plurality of subsystem control modes.

Aspects of the invention relate to a vehicle control system, a vehicle, a method and computer readable instructions.

BACKGROUND

It is known to provide a plurality of control modes for controlling the subsystems of a vehicle. The subsystem control modes may be configured to provide an appropriate control strategy for operating on a particular terrain type. The subsystem control mode may be selected in dependence on different operating parameters. The terrain types for an off-road vehicle may include a sand terrain type. The accurate selection of a subsystem control mode for operation on sand terrain is especially desirable to assist the vehicle to avoid becoming bogged down or stuck in sand.

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

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a vehicle control system, a vehicle, a method and computer readable instructions as claimed in the appended claims.

According to an aspect of the present invention there is provided a vehicle control system for selecting one of a plurality of subsystem control modes to control operation of at least one vehicle subsystem of a vehicle comprising a plurality of wheels each comprising a pneumatic tire, each of the subsystem control modes corresponding to one or more different terrain types for the vehicle; the vehicle control system comprising one or more processor collectively configured to: receive one or more pressure indicator signal, the or each pressure indicator signal comprising at least one tire pressure indicator providing an indication of a pressure of one of the pneumatic tires; determine a plurality of terrain condition indicators, the plurality of terrain condition indicators comprising a first terrain condition indicator in the form of a sand terrain condition indicator; wherein the first terrain condition indicator is determined in dependence on the at least one tire pressure indicator; and select one of the plurality of subsystem control modes in dependence on the plurality of terrain condition indicators; wherein the vehicle control system is configured to operate in the selected one of the plurality of subsystem control modes. The tire pressure may be reduced manually or automatically for driving on sand. The vehicle control system utilises the indicated pressure of one or more of the pneumatic tires to assess the likelihood that the vehicle is travelling on sand, i.e. on a terrain predominantly composed of sand. The accuracy with which the vehicle control system can determine that the vehicle is travelling on sand can be improved.

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: determine a plurality of terrain condition indicators, the plurality of terrain condition indicators comprising a first terrain condition indicator in the form of a sand terrain condition indicator; wherein the first terrain condition indicator is determined in dependence on the at least one tire pressure indicator providing an indication of a tire pressure; select one of a plurality of subsystem control modes in dependence on the plurality of terrain condition indicators; and operate in the selected one of the plurality of subsystem control modes.

The vehicle control system is operable to determine which of the plurality of the subsystem control modes is appropriate for the prevailing conditions. At least in certain embodiments, the vehicle control system is configured to determine with improved accuracy that the vehicle is operating on a sand terrain. The appropriate subsystem control mode for operating on sand terrain may be selected with improved accuracy.

The one or more different terrain types may comprise a first terrain type corresponding to a sand terrain type.

The subsystem control modes may comprise a first subsystem control mode which corresponds to the first terrain type. The first subsystem control mode is a sand terrain subsystem control mode which is configured for travelling on the sand terrain. The one or more processor may be collectively configured to evaluate at least the first terrain condition indicator to determine a first combined probability value associated with the first subsystem control mode. The first combined probability value may be a sand combined probability value. The sand combined probability value provides an indication of the extent to which the sand terrain subsystem control mode is appropriate.

The first combined probability value may be determined in dependence on the at least one tire pressure indicator. The one or more processor may be collectively configured to increase the first combined probability value in dependence on a determination that the at least one tire pressure indicator indicates that the tire pressure of each of the pneumatic tires is less than a first pressure threshold. In dependence on a determination that the at least one tire pressure indicator indicates that the tire pressure of each of the pneumatic tires is less than the first pressure threshold, the first terrain condition indicator may be modified to increase the first combined probability value. The increase in the first combined probability value increases the likelihood that the first subsystem control mode is selected. At least in certain embodiments, the first subsystem control mode is selected for the operation on sand terrain.

The one or more pressure indicator signal may comprise a tire pressure indicator for each of the pneumatic tires. The one or more processor may be collectively configured to set the first combined probability value equal to a discrete sand terrain indicator in dependence on a determination that the at least one tire pressure indicators indicate that the tire pressure of each of the pneumatic tires is less than the first pressure threshold.

The first combined probability value is set to the discrete sand terrain indicator when all of the tire pressure of all of the pneumatic tires is less than the first pressure threshold. This provides improved control of the selection of the first subsystem control mode.

The discrete sand terrain indicator may be a fixed (i.e. static) value. In a variant, the terrain indicator may be dynamic or may have more than one value. For example, the terrain indicator may be selected in dependence on the indicated pressure of the or each pneumatic tires. The first combined probability value may be increased as the pressure of the pneumatic tires approaches a predetermined pressure threshold associated with operation of the vehicle on the first terrain type.

The one or more processor may be collectively configured to determine the first combined probability value without the sand terrain condition indicator in dependence on one or more of the following conditions: (a) a determination that the at least one tire pressure indicator indicates that a tire pressure of at least one of the pneumatic tires is greater than or equal to a second pressure threshold; and (b) a fault condition signal is received indicating a fault with the tire pressure monitoring system (TPMS) or a tire pressure sensor. The second pressure threshold may be greater than the first pressure threshold. The second pressure threshold may be a high pressure threshold. The first combined probability value is not changed by the first terrain condition indicator when one or more of these conditions is identified. At least in certain embodiments, the probability of selecting the first subsystem control mode may be reduced or prevented if a fault condition is detected or one or more of the tire pressures is greater than the second pressure threshold. The tire pressure monitoring system (TPMS) may comprise one or more of the tire pressure sensors. The fault condition signal may be associated with one of the tire pressure sensors.

The one or more processor may be collectively configured to evaluate the at least one terrain condition indicator to determine a second combined probability value associated with a second subsystem control mode.

The second system control mode may correspond to a second terrain type. The second subsystem control mode is a non-sand subsystem control mode. One of the first and second subsystem control modes may be selected in dependence on the first and second combined probability values.

The subsystem control mode may be selected in dependence on a change threshold. The change threshold is calibratable and may be defined to control the selection of one of the subsystem control modes. One of the first and second subsystem control modes may be selected in dependence on a change threshold. The vehicle control system is configured to operate in the selected one of the first and second subsystem control modes.

A request may be output to change the subsystem control mode in which the vehicle control system is currently operating. The request may be in the form of a subsystem control mode signal. The subsystem control mode signal may be output by the one or more processor.

When the vehicle control system is operating in the second subsystem control mode, the one or more processor may be collectively configured to determine if there is a positive difference between the second combined probability value and the first combined probability value. The positive difference may be integrated with respect to time to generate an integrated value. A subsystem control mode signal to request a change from the second subsystem control mode to the first subsystem control mode may be output in dependence on a determination that the integrated value is greater than the change threshold. By calibrating the change threshold, the change from the second subsystem control mode to the first subsystem control mode can be controlled. At least in certain embodiments, this provides improved selection of the first subsystem control mode.

When the vehicle control system is operating in the first subsystem control mode, the one or more processor may be collectively configured to determine if there is a positive difference between the first combined probability value and the second combined probability value. The positive difference may be integrated with respect to time to generate an integrated value. A subsystem control mode signal to request a change from the first subsystem control mode to the second subsystem control mode may be output in dependence on a determination that the integrated value is greater than the change threshold. By calibrating the change threshold, the change from the first subsystem control mode to the second subsystem control mode can be controlled. At least in certain embodiments, this provides an improved transition from the first subsystem control mode to another subsystem control mode.

The one or more processor may be collectively configured to determine a road roughness indicator. A subsystem control mode signal to request a change from the first subsystem control mode to the second subsystem control mode may be output in dependence on a determination that the road roughness indicator is greater than a sand terrain roughness threshold. The transition from the first subsystem control mode to another subsystem control mode may be controlled in dependence on the road roughness. At least in certain embodiments, this provides an improved transition from the first subsystem control mode to another subsystem control mode. Conversely, a subsystem control mode signal to request a change from the second subsystem control mode to the first subsystem control mode may be output in dependence on a determination that the road roughness indicator is less than a sand terrain roughness threshold.

The one or more processor may be collectively configured to determine a vehicle speed. A subsystem control mode signal to request a change from the first subsystem control mode to the second subsystem control mode may be output in dependence on a determination that the vehicle speed is greater than a sand terrain speed threshold. The sand terrain speed threshold may be calibratable. The transition from the first subsystem control mode to another subsystem control mode may be controlled in dependence on the vehicle speed. The change from the first subsystem control mode to the second subsystem control mode may be implemented only when the vehicle speed is greater than the sand terrain speed threshold. This may reduce or avoid unnecessary or unwanted changes from the first subsystem control mode to the second subsystem control mode. Conversely, a subsystem control mode signal to request a change from the second subsystem control mode to the first subsystem control mode may be output in dependence on a determination that the vehicle speed is less than a sand terrain speed threshold.

The one or more processor may be collectively configured to determine a surface rolling resistance of the vehicle. The one or more processor may be configured to output a subsystem control mode signal to request a change from the first subsystem control mode to the second subsystem control mode in dependence on a determination that the surface rolling resistance of the vehicle is less than a sand terrain rolling resistance threshold. The sand terrain rolling resistance threshold may be calibratable. The change from the first subsystem control mode to the second subsystem control mode may be implemented only when the determined surface rolling resistance is greater than the sand terrain rolling resistance threshold. This may reduce or avoid unnecessary or unwanted changes from the first subsystem control mode to the second subsystem control mode. Conversely, a subsystem control mode signal to request a change from the second subsystem control mode to the first subsystem control mode may be output in dependence on a determination that the surface rolling resistance of the vehicle is greater than the sand terrain rolling resistance threshold.

The one or more processor may be collectively configured to implement an exit timer in dependence on a determination that the surface rolling resistance of the vehicle is less than a first sand terrain rolling resistance threshold. The exit timer may be started the surface rolling resistance of the vehicle is less than a first sand terrain rolling resistance threshold. A subsystem control mode signal to request a change from the first subsystem control mode to the second subsystem control mode may be output upon expiry of the exit timer.

The exit timer may help to reduce or avoid erratic switching to and from the first subsystem control mode. At least in certain embodiments, the exit timer is operative to reduce or prevent changes away from the first subsystem control modes due to a localised change in the terrain type, for example a relatively small area of hard/compacted sand. The exit timer may, for example, avoid a change as the vehicle traverses a localised region of sand (for example, a region of compacted sand) or rock having a lower surface rolling resistance than the surrounding sand. The exit timer may be implemented more generally to control selection of the subsystem control modes. For example, the exit timer may be started in dependence on a determination that the second subsystem control mode is more appropriate than the first subsystem control mode.

The one or more processor may be configured to continue to monitor the determined combined probability while the exit timer is operating. The control strategy may be revised or modified if the subsystem control mode determined to be most appropriate changes while the exit timer is operating. For example, the one or more processor may determine that remaining in the current subsystem control mode is appropriate if the current subsystem control mode is determined to be most appropriate due to changes in the at least one terrain indicator. Alternatively, the one or more processor may determine that a change to a different subsystem control mode may be more appropriate while the exit timer is operating.

Alternatively, or in addition, the one or more processor may be collectively configured to implement a distance travelled monitor in dependence on a determination that the surface rolling resistance of the vehicle is less than a first sand terrain rolling resistance threshold. The distance travelled monitor may perform a check to determine if the vehicle has travelled at least a predetermined distance travelled threshold. After determining that the surface rolling resistance of the vehicle is less than a first sand terrain rolling resistance threshold, a subsystem control mode signal to request a change from the first subsystem control mode to the second subsystem control mode may be output only after the vehicle has travelled a distance which is greater than or equal to the distance travelled threshold. The distance travelled monitor may be implemented more generally to control selection of the subsystem control modes. For example, the distance travelled monitor may be applied in dependence on a determination that the second subsystem control mode is more appropriate than the first subsystem control mode.

The change threshold may be set to a sand change threshold in dependence on a determination that the surface rolling resistance of the vehicle is greater than the sand terrain rolling resistance threshold. The sand change threshold may be calibratable to provide improved change to or from the first subsystem control mode.

The one or more processor may be collectively configured to receive an ambient temperature signal indicating an ambient temperature. The vehicle control system may be configured to determine the first combined probability value in dependence on the ambient temperature. The first combined probability value may be increased in dependence on a determination that the ambient temperature is greater than a temperature threshold. The temperature threshold may, for example, be defined as 25°C.

The first and second subsystem control modes are different from each other. The second subsystem control mode may be one of the following: a grass/gravel/snow control mode (GGS mode) that is suitable for when the vehicle is travelling in grass, gravel or snow terrain; a mud/ruts control mode (MR mode) which is suitable for when the vehicle is travelling in mud and/or rutted terrain; a rock crawl/boulder mode (RB mode) which is suitable for when the vehicle is travelling across rocky terrain such as a boulder field; a special programs OFF mode (SP OFF mode) which is a suitable compromise mode; and a general control mode, for all terrain conditions and especially vehicle travel on motorways and regular roadways.

The first terrain condition indicator is determined in dependence on the at least one tire pressure indicator. It will be understood that one or more other terrain condition indicator may be determined in dependence on the at least one tire pressure indicator.

The one or more processor may be collectively configured to implement an entry timer. The entry timer may comprise a first entry time threshold corresponding to a minimum time required to manually reduce the tire pressure of each of the tires for driving on sand. The first entry time threshold may be a fixed time period or may be a dynamic time period, for example based on a previous measured tire pressure. The combined probability value for the sand subsystem control mode may be reduced in dependence on a determination that the elapsed time is less than the first entry time threshold. Alternatively, the selection of the sand subsystem control mode may be inhibited if the elapsed time is less than the first entry time threshold. The entry timer may be implemented between changes to the selected subsystem control mode. A change from a selected subsystem control mode to a different subsystem control mode may be delayed or inhibited until expiry of the first entry time threshold. The entry timer may be initiated after selection of a subsystem control mode. A change from the selected subsystem control mode to a different subsystem control mode, such as the first subsystem control mode, may be inhibited until expiry of the first entry time threshold.

Alternatively, or in addition, the at least one entry time threshold may comprise a second entry time threshold.

The tire pressure status may not be updated while the vehicle is stopped (or the vehicle ignition is off) and a delay in the updating of the tire pressure status may prevent accurate evaluation of the sand subsystem control mode. The second entry time threshold may correspond to a maximum time after the vehicle has stopped for the tire pressure status to be updated. The combined probability value for the sand subsystem control mode may be reduced in dependence on a determination that the elapsed time is less than the second entry time threshold. Alternatively, the selection of the sand subsystem control mode may be inhibited if the elapsed time is less than the second entry time threshold. The entry timer may be implemented when the vehicle stops or the ignition is switched off. A change from a selected subsystem control mode to a different subsystem control mode may be delayed or inhibited until expiry of the second entry time threshold.

According to an aspect of the present invention there is provided a vehicle control system for selecting one of a plurality of subsystem control modes to control operation of at least one vehicle subsystem of a vehicle comprising a plurality of wheels each comprising a pneumatic tire, each of the subsystem control modes corresponding to one or more different terrain types for the vehicle; the vehicle control system comprising one or more processor collectively configured to: receive one or more pressure indicator signal, the or each pressure indicator signal comprising at least one tire pressure indicator providing an indication of a pressure of one of the pneumatic tires; determine a plurality of terrain condition indicators, the plurality of terrain condition indicators comprising a first terrain condition indicator in the form of a sand terrain condition indicator; wherein the first terrain condition indicator is determined in dependence on the at least one tire pressure indicator; select one of the plurality of subsystem control modes in dependence on the plurality of terrain condition indicators; and output a subsystem control mode signal to indicate the selected one of the plurality of subsystem control modes.

According to a further aspect of the present invention there is provided a vehicle comprising the vehicle control system as described herein.

According to a further aspect of the present invention there is provided a method of selecting one of a plurality of subsystem control modes to control operation of at least one vehicle subsystem of a vehicle comprising a plurality of wheels each having a pneumatic tire, each of the subsystem control modes corresponding to one or more different terrain types for the vehicle; wherein the method comprises: receive one or more pressure indicator signal, the or each pressure indicator signal comprising at least one tire pressure indicator providing an indication of a pressure of one of the pneumatic tires; determining a plurality of terrain condition indicators, the plurality of terrain condition indicators comprising a first terrain condition indicator in the form of a sand terrain condition indicator, wherein the first terrain condition indicator is determined in dependence on the pressure of the at least one pneumatic tire indicated by the one or more pressure indicator signal; selecting one of the plurality of subsystem control modes in dependence on the plurality of terrain condition indicators; and operating in the selected one of the plurality of subsystem control modes.

The method facilitates determination of which of the plurality of the subsystem control modes is appropriate for the prevailing conditions. At least in certain embodiments, the method can determine with improved accuracy that the vehicle is operating on a sand terrain. The selection of an appropriate subsystem control mode for operating on a sand terrain may be provided with improved accuracy.

The one or more different terrain types may comprise a first terrain type corresponding to a sand terrain type. The subsystem control modes may comprise a first subsystem control mode which corresponds to the first terrain type. The method comprises evaluating at least the first terrain condition indicator to determine a first combined probability value associated with the first subsystem control mode.

According to a further aspect of the present invention there is provided a computer readable instructions which, when executed by a computer, are arranged to perform a method described herein.

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 vehicle comprising a vehicle control system in accordance with an embodiment of the present invention; Figure 2 shows a schematic representation of the vehicle subsystems in the vehicle shown in Figure 1; Figure 3 shows a schematic representation of the controller for the vehicle control system of the vehicle shown in Figure 1; Figure 4 shows a schematic representation of a vehicle control system for use in the control system; and Figure 5 shows a block diagram representing operation of the control system to select a sand subsystem control mode in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

A vehicle control system 100 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figures. As shown in Figure 1, the vehicle control system 100 is installed in a vehicle 200.

The vehicle 200 is described herein with reference to a reference frame comprising a longitudinal axis X, a transverse axis Y and a vertical axis Z. The reference signs herein include a suffix in the form of a whole number to differentiate between a plurality of like components on the vehicle 200. The same suffix is applied for components associated with each other, for example components forming part of the same sub-assembly of the vehicle 200.

The vehicle 200 is a road vehicle, such as an automobile, a sports utility vehicle (SUV) or a utility vehicle. As shown in Figures 1 and 2, the vehicle 200 in the present embodiment is an automobile. The vehicle 200 comprises one or more torque-generating machine, such as an internal combustion engine (ICE) and/or an electric traction motor. The vehicle 200 may be a battery electric vehicle (BEV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV) or an internal combustion engine (ICE) vehicle. The vehicle 200 comprises a plurality of vehicle subsystems (denoted generally by the reference numeral 210 and shown schematically in Figure 3). The vehicle subsystems 210 in the present embodiment include, but are not limited to, a traction control system 210A, a propulsion (or engine) management system 210B, a transmission system 210C, a steering system 210D, an anti-lock braking system (ABS) 210E, a suspension control system 210F and a differential control system 210G. Although six (6) subsystems are illustrated, the vehicle 200 may include additional vehicle subsystems 210.

The traction control system 210A is configured to control operation of a vehicle powertrain and/or the vehicle's brakes to maintain traction (grip), for example on a surface having a low surface friction. The propulsion (or engine) management system 210B is configured to control operation of the torque generating machine (denoted by the reference numeral 84 in Figure 2), such as an internal combustion engine or an electric traction motor. The transmission system 210C comprises a transmission 81 which is operable selectively to engage one of a plurality of drive ratios. The drive ratios typically comprise a plurality of forward drive ratios, a reverse drive ratio and a neutral (or disengaged) drive ratio. The transmission system 210C in the present embodiment also includes a transfer case 82 operable selectively to engage a low drive ratio. The transfer case 82 may be omitted from the transmission system 210C. The steering system 210D is configured to control operation of a power assisted steering system provided on the vehicle 200. The anti-lock braking system 210E is configured to control operation of one or more braking systems provided on the vehicle 200. The suspension control system 210F in the present embodiment comprises an adjustable-height suspension. The suspension control system 210F may, for example, be an air suspension or a mechanically adjustable suspension. The suspension control system 210F comprises a plurality of adjustable-height suspension units, the adjustable-height suspension units being associated with the respective wheels W1-W4 of the vehicle 200. The height of the suspension units may be controlled, for example by controllably inflating and deflating one or more air bladder, to raise or lower the vehicle body. The differential control system 210G comprises one or more lockable differential, for example one or more of a centre differential, a rear differential and a front differential. The differential control system 210G in the present embodiment comprises a centre differential (denoted by the reference numeral 83 in FIG. 2).

The vehicle 200 comprises four (4) wheels W1-W4. As shown in Figure 1, the wheels W1-W4 each comprise a pneumatic tire (tyre) T1-T4. The front wheels W1, W2 and/or the rear wheels W3, W4 may be driven by the one or more torque-generating machine. In the present embodiment, the vehicle 200 is four-wheel drive and each of the wheels W1-W4 is driven by the one or moretorque-generating machine. The vehicle 200 comprises a tire pressure monitoring system (TPMS) 215 for monitoring the tire pressure of each wheel W1-W4. The TPMS 215 comprises a tire pressure monitor 220 and a plurality of tire pressure sensors TPS-n configured to measure the pressure of each of the pneumatic tires T1-T4. The tire pressure sensors TPD-n output tire pressure signals TPS-n to the tire pressure monitor 220. The tire pressure sensors TPD-n indicate the measured pressure of each of the pneumatic tires T1-T4. The tire pressure monitor 220 is configured to output one or more pressure indicator signal SP1-SP4. The one or more pressure indicator signal SP1-SP4 in the present embodiment indicate the measured pressure of each of the pneumatic tires T1-T4. In a variant, the one or more pressure indicator signal SP1-SP4 may characterise the pressure of each of the pneumatic tires T1-T4. The one or more pressure indicator signal SP1-SP4 may characterise the pressure of the pneumatic tires T1-T4 as one of the following: a High pressure, a Medium (normal) pressure, and a Low pressure. A Low pressure is defined as a pressure less than a first threshold, for example less than 24 Psi. A High pressure is defined as a pressure greater than a second threshold, for example greater than 44 Psi. A Medium (normal) pressure is defined as a pressure greater than the first threshold and less than the second threshold, for example greater than 24 Psi and less than 44 Psi. The tire pressure monitor 220 in the present embodiment is configured to detect a fault condition, for example in one or more of the tire pressure sensors TPS-n or the TPMS 215. The tire pressure monitor 220 is configured to output a fault condition signal SFC to indicate the detection of a fault condition.

The vehicle control system 100 is configured to control operation of the vehicle subsystems 210. In particular, the vehicle control system 100 is configured to select one of a plurality of subsystem control modes. The subsystem control modes are defined for types of terrain on which the vehicle 200 is operating. The subsystem control modes each define a set of operating parameters of the vehicle subsystems 210. Each of the subsystem control modes define one or more operating parameter for the vehicle subsystems 210. The one or more operating parameter provide dynamic control of the vehicle 200 which is appropriate for the terrain conditions. As such, each of the subsystem control modes correspond to one or more different terrain type. As described herein, the vehicle control system 100 is configured to determine a plurality of terrain condition indicators to assess the terrain conditions. The vehicle control system 100 is configured to select one of the plurality of subsystem control modes in dependence on the plurality of terrain condition indicators. In particular, the vehicle control system 100 is configured to select the subsystem control mode which is determined to be most appropriate for the terrain conditions. The vehicle control system 100 is configured to operate in the selected subsystem control mode. The vehicle subsystems 210 are controlled in dependence on the operating parameters defined in the selected subsystem control mode.

As shown in Figure 3, the vehicle control system 100 comprises one or more controller 110. The one or more controller 110 is configured to select one of the plurality of subsystem control modes. The vehicle control system 100 as illustrated in Figure 3 comprises one controller 110, although it will be appreciated that this is merely illustrative. The controller 110 comprises processing means 120 and memory means 130. The processing means 120 may be one or more electronic processing device 120 which operably executes computer-readable instructions. The memory means 130 may be one or more memory device 130. The memory means 130 is electrically coupled to the processing means 120. The memory means 130 is configured to store instructions, and the processing means 120 is configured to access the memory means 130 and execute the instructions stored thereon.

The controller 110 comprises an input means 140 and an output means 150. The input means 140 may comprise an electrical input 140 of the controller 110. The output means 150 may comprise an electrical output 150 of the controller 110. The input 140 is arranged to receive a plurality of signals (denoted generally by the reference numerals 16 and 17) from a plurality of vehicle sensors (denoted generally as a vehicle sensor system VSS in FIG. 3) provided on the vehicle 200. The plurality of signals are representative of different parameters associated with the status and dynamic operation of the vehicle 200. The signals are electrical signals which are indicative of an operating state of the vehicle subsystems 210 and/or one or more measured parameter. The controller 110 is configured to generate a subsystem control mode signal 155 which is indicative of the selected one of the plurality of subsystem control modes. The subsystem control mode signal 155 functions as a request for the vehicle control system 100 to operate in the selected one of the plurality of subsystem control modes. The output 150 is arranged to output the subsystem control mode signal 155. The subsystem control mode signal 155 is output to control operation of one or more of the vehicle subsystems 210. The vehicle control system 100 is configured to operate in the selected one of the plurality of subsystem control modes. The subsystem control mode signal 155 is output to each of the vehicle subsystems 210 to control the vehicle subsystems in a manner appropriate to the driving condition, such as the terrain, on which the vehicle is travelling (referred to as the terrain condition).

As described in further detail herein, the signals 16, 17 provide, or are used to calculate, a plurality of driving condition indicators (also referred to as terrain indicators) which are indicative of the nature of the condition in which the vehicle 200 is travelling. The controller 110 determines the most appropriate subsystem control mode for the various vehicle subsystems 210 on the basis of the terrain indicators. The controller 110 then implements the subsystem control mode determined to be most appropriate.

The sensors on the vehicle include, but are not limited to, sensors which provide continuous sensor outputs 16 to the controller 110, including wheel speed sensors, an ambient temperature sensor, an atmospheric pressure sensor, tire pressure sensors, sensors, such as gyroscopic sensors, for measuring yaw, roll and pitch of the vehicle, a vehicle speed sensor VSP, a longitudinal acceleration sensor, an engine torque sensor (or engine torque estimator), a steering angle sensor, a steering wheel speed sensor, a gradient sensor (or gradient estimator), a lateral acceleration sensor on the stability control system (SCS), a brake pedal position sensor, an acceleration pedal position sensor and longitudinal, lateral, vertical motion sensors. The vehicle speed sensor VSP comprises an inertial measurement unit, for example including one or more accelerometer.

The vehicle speed sensor VSP in the present embodiment comprises an accelerometer configured to measure longitudinal acceleration of the vehicle 200. The vehicle speed sensor VSP is configured to output a vehicle speed signal SVS indicating the vehicle speed VLS. In the present embodiment the vehicle speed signal SVS indicates the longitudinal speed VLS of the vehicle 200. The vehicle speed signal SVS may indicate a magnitude of the longitudinal speed VLS of the vehicle.

The controller 110 also receives a signal from the electronic power assisted steering unit (ePAS unit) of the vehicle to indicate the steering force that is applied to the wheels (steering force applied by the driver combined with steering force applied by the ePAS system).

The vehicle 200 is also provided with a plurality of sensors which provide discrete sensor outputs 16 to the controller 110, including a cruise control status signal (ON/OFF), a transfer box status signal (whether the gear ratio is set to a HIGH range or a LOW range), a Hill Descent Control (HDC) status signal (ON/OFF), a trailer connect status signal (ON/OFF), a signal to indicate that the Stability Control System (SCS) has been activated (ON/OFF), a windscreen wiper signal (ON/OFF), air suspension status (Raised/High, Normal, or Low), and a Dynamic Stability Control (DSC) signal (ON/OFF).

The vehicle 200 may also be provided with one or more detection systems (denoted generally as a vehicle detection system VDS in FIG. 3) in the form of a camera system, a RADAR system or a LIDAR system. The camera system may, for example, include one or more camera sensors that form a part of a parking aid system on the vehicle. Alternatively, the cameras may be provided to give an indication of the nature of the terrain in the surrounding vicinity of the vehicle, but not necessarily the terrain immediately beneath the vehicle wheels. Further examples of the use of camera data in the present invention will be described in further detail below.

The electronic processing device 120 is configured to implement a subsystem controller 14, an estimator module 18 and a selector module 20, as shown schematically in Figure 4. The estimator module 18 comprises a controller having one or more electronic processor having at least one input and at least one output. The selector module 20 comprises a controller having one or more electronic processor having at least one input and at least one output. The subsystem controller 14, estimator module 18 and the selector module 20 may be implemented by the same electronic processing device 120 or by different electronic processing devices 120. The subsystem controller 14 provides output signals to Human Machine Interface (HMI) module (not shown). The subsystem controller 14 includes three functions; a validation, fault management and check function 14a, an algorithm 14b to allow switching between automatic operation and manual operation (as described in further detail below), and an interface algorithm 14c for the HMI module to support the automatic response mode of operation. A first output signal 35 provides a notification to the HMI module of whether the automatic response mode or the manual response mode is active. If the automatic response mode is active then a second output signal 36 is provided to notify the driver when the system is "optimizing" and a change in the subsystem control mode is taking place.

As shown schematically in FIG. 4, the estimator module 18 comprises a plurality of estimator modules dedicated to specific aspects of vehicle and vehicle sub-system behaviour. In the example shown, these modules comprise: wheel acceleration 18a; wheel inertia torque estimator 18b; vehicle longitudinal force 18c; aerodynamic drag estimator 18d; wheel longitudinal force estimator 18e; wheel slip detection 18f; lateral acceleration estimator 18g; vehicle yaw estimator 18h; wheel speed variation and corrugation detection 18i; surface rolling resistance 18j; wheel longitudinal slip or 'breakaway torque' 18k; surface friction or 'mu' plausibility check 181; lateral surface friction or 'mu' estimation/rut detection 18m; steering force estimator 18n; and corrugation detection estimation 180.

Within a first stage of the estimator module 18, various ones of the sensor outputs 16 are used to derive one or more terrain condition indicator 17. In a first stage of the estimator module 18, a vehicle speed is derived from the wheel speed sensors, wheel acceleration is derived from the wheel speed sensors, the longitudinal force on the wheels is derived from the vehicle longitudinal acceleration sensor, and the torque at which wheel slip occurs (if wheel slip occurs) is derived from the motion sensors to detect yaw, pitch and roll. Other calculations performed within the first stage of the estimator module 18 include the wheel inertia torque (the torque associated with accelerating or decelerating the rotating mass of the wheels), "continuity of progress" (the assessment of whether the vehicle is starting and stopping, for example as may be the case when the vehicle is travelling over rocky terrain), aerodynamic drag, yaw, and lateral vehicle acceleration.

The estimator module 18 also includes a second stage in which the following terrain indicators are calculated: surface rolling resistance (based on one or more of the wheel inertia torque, the longitudinal force on the vehicle, aerodynamic drag, and the longitudinal force on the wheels), the steering force on the steering wheel (based on the lateral acceleration and the output from the steering wheel sensor), the wheel longitudinal slip (based on the longitudinal force on the wheels, the wheel acceleration, SCS activity and a signal indicative of whether wheel slip has occurred), lateral friction (calculated from the measured lateral acceleration and the yaw versus the predicted lateral acceleration and yaw), and corrugation detection (high frequency, low amplitude wheel height excitement indicative of a washboard type surface).

The SCS activity signal is derived from several outputs from a Stability Control Systems (SCS) ECU (not shown), which contains the DSC (Dynamic Stability Control) function, the TC (Traction Control) function, ABS (anti-lock braking system) and HDC (hill descent control) algorithms, indicating DSC activity, TC activity, ABS activity, brake interventions on individual wheels, and engine torque reduction requests from the SCS ECU to the engine. All these indicate a slip event has occurred and the SCS ECU has taken action to control it. The estimator module 18 also uses the outputs from the wheel speed sensors 72a-d to determine a wheel speed variation and corrugation detection signal.

The controller 110 also includes a road roughness module 24 for calculating the terrain roughness/corrugation based on the air suspension sensors (the ride height sensors) and the wheel accelerometers. A terrain indicator signal in the form of a road roughness output 26 is output from the road roughness module 24. Additionally, or alternatively, wheel articulation data may be provided to the road roughness module 24 by appropriate sensing means, such as suspension stroke transducers, such as continuously variable damping (CVD) sensors.

The estimates for the wheel longitudinal slip and the lateral friction estimation are compared with one another within the estimator module 18 as a plausibility check.

Calculations for wheel speed variation and corrugation output, the surface rolling resistance estimation, the wheel longitudinal slip and the corrugation detection, together with the friction plausibility check, are output from the estimator module 18 and provide terrain indicator signals 22, indicative of the nature of the terrain in which the vehicle is travelling, for further processing within the controller 110.

The terrain indicator signals 22 from the estimator module 18 are provided to the selector module 20 for determining which of a plurality of vehicle subsystem control modes is most appropriate based on the indicators of the type of terrain in which the vehicle is travelling. The selector module 20 serves as an automatic special program selector (ASPS) and comprises an automatic special program selector (ASPS) algorithm, or probability algorithm 20a. The most appropriate subsystem control mode is determined by analyzing the probability that each of the different subsystem control modes is appropriate on the basis of the terrain indicator signals 22, 26 from the estimator module 18 and the road roughness module 24.

The vehicle subsystems 210 may be controlled automatically (referred to as the "automatic response mode") in response to an output 30 from the selector module 20 and without the need for driver input. Alternatively, the vehicle subsystems 210 may be operated in response to a manual driver input (referred to as "manual response mode") via a Human Machine Interface (HMI) module (not shown).

When operating in the automatic response mode, the selection of the most appropriate subsystem control mode is achieved by means of a three phase process: (1) for each type of subsystem control mode, a calculation is performed of the probability that the subsystem control mode is suitable for the terrain over which the vehicle 200 is travelling, based on the terrain indicators; (2) the integration of "positive differences" between the probability for the current subsystem control mode and the other subsystem control modes; and (3) the program request to the subsystem controller 14 when the integration value exceeds a pre-determined threshold or the current terrain subsystem control mode probability is zero.

The specific steps for phases (1), (2) and (3) will now be described in more detail.

In phase (1), the continuous terrain indicator signals in the form of the road roughness output 26 and the terrain indicator signals 22 from the estimator module 18 are provided to the selector module 20. The selector module also receives directly from various sensors on the vehicle, including the transfer box status signal (whether the discrete terrain condition indicators 17 gear ratio is set to a HIGH range or a LOW range), the DSC status signal, cruise control status (whether the vehicle's cruise control system is ON or OFF), and trailer connect status (whether or not a trailer is connected to the vehicle). Terrain indicator signals indicative of ambient temperature and atmospheric pressure are also provided to the selector module 20.

The probability algorithm 20a for calculating the most suitable subsystem control mode for the vehicle subsystems based on the discrete terrain condition indicators 17 received directly from the sensors and the continuous terrain condition indicators 22, 26 are calculated by the estimator module 18 and the road roughness module 24, respectively.

The subsystem control modes typically include a grass/gravel/snow control mode (GGS mode) that is suitable for when the vehicle is travelling in grass, gravel or snow terrain, a mud/ruts control mode (MR mode) which is suitable for when the vehicle is travelling in mud and/or rutted terrain, a rock crawl/boulder mode (RB mode) which is suitable for when the vehicle is travelling across rocky terrain such as a boulder field, a sand mode (Sand mode) which is suitable for when the vehicle is travelling in sand terrain (or deep soft snow) and a special programs OFF mode (SP OFF mode) which is a suitable compromise mode, or general mode, for all terrain conditions and especially vehicle travel on motorways and regular roadways.

The different terrain types are grouped according to the friction of the terrain and the roughness of the terrain.

For example, it is appropriate to group grass, gravel and snow together as terrains that provide a low friction and a relatively smooth surface, and it is appropriate to group rock and boulder terrains together as they tend to be characterized by relatively high friction and very high roughness.

For each subsystem control mode, the probability algorithm 20a within the selector module 20 performs a probability calculation, based on the terrain indicators, to determine a probability that each of the different subsystem control modes is appropriate. The selector module 20 includes a tuneable data map which relates the continuous terrain condition indicators 22, 26 (e.g. vehicle speed, road roughness, steering angle) to a probability that a particular subsystem control mode is appropriate. Each probability value takes a value of between 0 and 1. So, for example, the vehicle speed calculation may return a probability of 0.7 for the RB mode if the vehicle speed is relatively slow, whereas if the vehicle speed is relatively high the probability for the RB mode will be much lower (e.g. 0.2). This is because it is much less likely that a high vehicle speed is indicative that the vehicle is travelling over a rock or boulder terrain.

In addition, for each subsystem control mode, each of the discrete terrain condition indicators 17 (e.g. trailer connection status ON/OFF, cruise control status ON/OFF) is also used to calculate an associated probability for each of the subsystem control modes, GGS, RB, Sand, MR or SP OFF. So, for example, if cruise control is switched on by the driver of the vehicle, the probability that the SP OFF mode is appropriate is relatively high, whereas the probability that the MR subsystem control mode is appropriate will be lower.

For each of the different subsystem control modes, a combined probability value, Pb, is calculated based on the individual probabilities for that subsystem control mode, as described above, as derived from each of the continuous or discrete terrain condition indicators 17, 22, 26. In the following equation, for each subsystem control mode the individual probability as determined for each terrain indicator is represented by a, b, c, d... n. The combined probability value, Pb, for each subsystem control mode is then calculated as follows: Pb =(a.b.c.d... n)/((a.b.c.d... n)+(1-a).(1-b).(1-c).(1-d)... (1-n)) Any number of individual probabilities may be input to the probability algorithm 20a and any one probability value input to the probability algorithm may itself be the output of a combinational probability function.

Once the combined probability value for each subsystem control mode has been calculated, the subsystem control program corresponding to the subsystem control mode with the highest probability is selected within the selector module 20 and an output 30 providing an indication of this is provided in the form of a control signal to the subsystem controller 14. The benefit of using a combined probability function based on multiple terrain indicators is that certain indicators may make a subsystem control mode (e.g. GGS or MR) more or less likely when combined together, compared with basing the selection on just a single terrain indicator alone.

A further control signal 31 from the selector module 20 may optionally be provided to a driver advice system in the form of a driver tutoring (DT) or driver advice module 34, to initiate driver tutoring routines, as described in further detail below. The driver advice module 34 is fed with data from multiple vehicle sub-systems pertaining to the status and behaviour of the vehicle and comprises a plurality of elements dedicated to key features for example: auto response 34a; suspension ride height and/or pressure settings 34b; and transfer box ratio setting 34c.

In phase (2), an integration process is implemented continually within the selector module 20 to determine whether it is necessary to change from the current subsystem control mode to one of the alternative subsystem control modes.

The first step of the integration process is to determine whether there is a positive difference between the combined probability value for each of the alternative subsystem control modes compared with the combined probability value for the current subsystem control mode.

By way of example, assume the current subsystem control mode is GGS with a combined probability value of 0.5. If a combined probability value for the sand subsystem control mode is 0.7, a positive difference is calculated between the two probabilities (i.e. a positive difference value of 0.2). The positive difference value is integrated with respect to time. If the difference remains positive and the integrated value reaches a predetermined change threshold (referred to as the change threshold), or one of a plurality of predetermined change thresholds, the selector module 20 determines that the current terrain subsystem control mode (for GGS) is to be updated to a new, alternative subsystem control mode (in this example, the sand subsystem control mode). An output 30 in the form of a control signal is then output from the selector module 20 to the subsystem controller 14 to initiate the sand subsystem control mode for the vehicle subsystems.

In phase (3), the probability difference is monitored and if, at any point during the integration process, the probability difference changes from a positive value to a negative value, the integration process is cancelled and reset to zero. Similarly, if the integrated value for one of the other alternative subsystem control modes (i.e. other than sand), reaches the predetermined change threshold before the probability result for the sand subsystem control mode, the integration process for the sand subsystem control mode is cancelled and reset to zero and the other alternative subsystem control mode, with a higher probability difference, is selected.

The probability difference between the current subsystem control mode and all other subsystem control modes is monitored continually and the integrated value for each subsystem control mode is continually compared with the predetermined change threshold. The predetermined change threshold is calibrated offline, prior to vehicle running, and is stored in a memory of the selector module 20.

In an embodiment, one or more additional change thresholds may also be implemented for comparison with the integrated difference value, each of which is based on a different one of the terrain indicators. For example, another change threshold may be set dependent on vehicle rolling resistance. In this case the integrated difference value is compared with both thresholds (one for surface roughness and one for rolling resistance), and when a first one of the thresholds is crossed a change to the subsystem control mode is initiated.

The electronic processing device 120 is configured to determine the terrain condition indicators which are indicative of the nature or characteristics of the terrain on which the vehicle 200 is travelling. The vehicle 200 is operable on a first terrain type, the first terrain type is a terrain or surface which is predominantly composed of or at least substantially consists of sand. The terrain condition indicators comprise a first terrain condition indicator which is used to determine a first combined probability Pb that the vehicle 200 is operating on the first terrain type. The first terrain condition indicator is referred to herein as a sand terrain condition indicator.

A first subsystem control mode is defined to configure the vehicle subsystems 210 for operation on the first terrain type. The first subsystem control mode is referred to herein as a sand subsystem control mode.

The electronic processing device 120 calculates the combined probability value Pb for each of the different subsystem control modes. The combined probability values Pb are calculated in dependence on each of the terrain condition indicators 17, 22, 26, including the first terrain condition indicator. The selector module 20 is configured to select the first subsystem control mode in dependence on a determination that the first combined probability value Pb is the highest probability. The selector module 20 is configured to output a control signal to the subsystem controller 14 indicating that the first subsystem control mode is the most appropriate. The first subsystem control mode may, for example, configure the propulsion (or engine) management system 210B to provide a modified throttle map to adapt the throttle response. Alternatively, or in addition, the first subsystem control mode may configure the suspension control system 210F, for example to adjust the height of the adjustable suspension. The first subsystem control mode may re-configure other vehicle subsystems 210.

The sand terrain condition indicator provides an indication that the vehicle 200 is travelling on the first terrain type. The vehicle 200 is typically configured to drive on the first terrain type by reducing the pressure of the pneumatic tires of each of the wheels W1-W4. The reduced tire pressure enables the tire wall to adapt to the sand, thereby providing improved traction. The pressure of the pneumatic tires may, for example, be reduced by greater than or equal to 10%, 20% or 30% (compared to the tire pressure for on-road driving) to configure the vehicle 200 for driving on the first terrain type. In the present embodiment, the tire pressure is adjusted manually. In a variant, the tire pressure may be adjusted by a central tire inflation system (CTIS). The electronic processing device 120 is configured to identify that the tire pressure of one or more of the wheels W1-W4 is less than or equal to a first pressure threshold. The first pressure threshold corresponds to a tire pressure that would normally be associated with operating the vehicle on sand. The one or more tire pressure indicator is thereby used as the first terrain condition indicator to calculate the first combined probability value Pb indicating the probability that the vehicle 200 is operating on the first terrain type, i.e., that the vehicle 200 is traversing terrain which is predominantly composed of or at least substantially consists of sand. In the present embodiment, the first terrain condition indicator is determined in dependence on a determination that the tire pressure of each of the wheels W1-W4 is less than the first pressure threshold. The first pressure threshold in the present embodiment is defined as 24 Psi.

The electronic processing device 120 is configured to determine the first terrain condition indicator in dependence on the pressure indicator signals SP1-SP4 received from the TPMS 215. The pressure indicator signals SP1-SP4 represent the measured pressure of each of the pneumatic tires. The electronic processing device 120 is configured to compare the measured pressures to the first pressure threshold. The first pressure threshold may be defined as a value which corresponds to 90%, 80% or 70% of a tire pressure suitable for driving the vehicle 200 on-road (i.e., on a road or metalled surface). The electronic processing device 120 is configured to increase the first combined probability value Pb in dependence on a determination that the at least one pressure indicator signals SP1-SP4 indicates that the tire pressure of one or more of the pneumatic tires is less than the first pressure threshold. In the present embodiment, the electronic processing device 120 sets the first combined probability value to a discrete sand terrain indicator in dependence on a determination that the tire pressure of each of the pneumatic tires is less than the first pressure threshold. The discrete sand terrain indicator is a predefined value. The selector module 20 compares the first combined probability value to the combined probability value Pb calculated for each of the other subsystem control modes. The selector module 20 selects the first subsystem control mode in dependence on a determination that the first combined probability value is the highest of the combined probability values Pb.

Rather than indicate the measured pressure of each of the pneumatic tires, the pressure indicator signals SP1-SP4 may characterise each tire pressure as being in a predefined pressure range. The one or more pressure indicator signal SP1-SP4 may characterise the pressure of the pneumatic tires T1-T4 as being in one of a low-pressure range, a medium-pressure range and a high-pressure range. The first pressure threshold described herein may be defined as an upper threshold for the low-pressure range. A second pressure threshold may be defined as a lower threshold for the high-pressure range. The first and second pressure thresholds may define the lower and upper thresholds of the medium-pressure range. The TPMS 215 may characterise the tire pressure of each of the pneumatic tires as being in one of the low-pressure range and the high-pressure range.

The electronic processing device 120 may increase the first combined probability value Pb in dependence on a determination that the pressure indicator signals SP1-SP4 indicate that each of the pneumatic tires is in the low-pressure range. The first combined probability value Pb may be set to the discrete sand terrain indicator in dependence on a determination that the tire pressure of each of the pneumatic tires is in the low-pressure range. The first combined probability value is then compared to the combined probability value Pb calculated for each of the other subsystem control modes.

In the calculation of the first combined probability value Pb for the first subsystem control mode, the electronic processing device 120 is configured to disregard the sand terrain condition indicator under certain operating conditions. In the present embodiment, the sand terrain condition indicator is disregarded in the following conditions: (a) a determination that the at least one tire pressure indicator indicates that a tire pressure of one or more of the pneumatic tires is greater than or equal to a second pressure threshold; and (b) a fault condition signal SFC is received indicating a fault with the tire pressure monitoring system (TPMS) or one or more tire pressure sensor TPS-n.

Other conditions may be applied to determine the validity of the sand terrain condition indicator.

The operation of the electronic processing device 120 to select a subsystem control mode having a highest probability of being appropriate for the terrain type on which the vehicle 200 is travelling will now be described. The operation of the electronic processing device 120 will be described in relation to first and second terrain types which are different from each other. In the present embodiment, the first terrain type corresponds to sand terrain; and the second terrain type corresponds to grass, gravel or snow terrain. It will be understood that the second terrain type may be a different terrain type. The electronic processing device 120 is configured to calculate a first combined probability value Pb associated with the first subsystem control mode; and a second combined probability value Pb associated with the first subsystem control mode. The first and second combined probability values Pb are calculated in dependence on the terrain condition indicators 17. The terrain condition indicators 17 include the first terrain condition indicator determined in dependence on the pressure indicator signals SP1-SP4. The electronic processing device 120 is configured to select the subsystem control modes having the largest combined probability value Pb. The vehicle control system is configured to operate in the selected one of the first and second subsystem control modes.

In the present embodiment, the selection of one of the first and second subsystem control modes is performed in dependence on a change threshold. A transition from the first subsystem control mode to the second subsystem control mode, or from the second subsystem control mode to the first subsystem control mode is controlled in dependence on an integration of "positive differences" between the probability for the current subsystem control mode and the other (unselected) subsystem control mode. When the vehicle control system is operating in the second subsystem control mode, the electronic processing device 120 is configured to: determine if there is a positive difference between the second combined probability value and the first combined probability value. If there is a positive different, the positive difference is integrated with respect to time to generate an integrated value. The electronic processing device 120 is configured to output the subsystem control mode signal 155 to request a change from the second current subsystem control mode to the first subsystem control mode in dependence on a determination that the integrated value is greater than the change threshold. When the vehicle control system 100 is operating in the first subsystem control mode, the electronic processing device 120 is configured to determine if there is a positive difference between the first combined probability value and the second combined probability value. If there is a positive difference, the positive difference is integrated with respect to time to generate an integrated value. The electronic processing device 120 is configured to output the subsystem control mode signal 155 to request a change from the first current subsystem control mode to the second subsystem control mode in dependence on a determination that the integrated value is greater than the change threshold. The change threshold in the present embodiment is set to a sand change threshold in dependence on a determination that the surface rolling resistance of the vehicle is greater than a sand terrain rolling resistance threshold.

The road roughness module 24 calculates the terrain roughness/corrugation based on the air suspension sensors (the ride height sensors) and the wheel accelerometers. The road roughness module 24 may also receive one or more accelerometer signal from an Inertia Measurement Unit (IMU) to calculate one or more of a pitch road roughness, a roll road roughness and a heave road roughness The terrain indicator signal in the form of a road roughness output 26 is output from the road roughness module 24. A sand terrain roughness threshold is defined to control changes between the subsystem control modes. The sand terrain roughness threshold is defined as road roughness estimator value of 20%. The electronic processing device 120 is configured to compare the road roughness indicator to a sand terrain roughness threshold. The subsystem control mode signal 155 to request a change from the first subsystem control mode to the second subsystem control mode is output in dependence on a determination that the road roughness indicator is greater than the sand terrain roughness threshold.

In the present embodiment, a sand terrain speed threshold is defined. The sand terrain speed threshold is defined as 3 m/s in the present embodiment. The sand terrain speed threshold may be higher or lower than 3 m/s. The sand terrain speed threshold may, for example, be defined as 20kph, 25kph or 30kph. The subsystem control mode signal 155 is output to request a change from the second subsystem control mode to the first subsystem control mode in dependence on a determination that the vehicle speed is less than the sand terrain speed threshold. The subsystem control mode signal 155 is output to request a change from the first subsystem control mode to the second subsystem control mode in dependence on a determination that the vehicle speed is greater than the sand terrain speed threshold.

As described herein, the electronic processing device 120 may be configured to determine the (instantaneous) surface rolling resistance of the vehicle 200. In the present embodiment, the estimator module 18 calculates the surface rolling resistance based on one or more of the following: the wheel inertia torque, the longitudinal force on the vehicle, aerodynamic drag, and the longitudinal force on the wheels. When travelling on a terrain comprising sand, the surface rolling resistance of the vehicle 200 is typically higher than the surface rolling resistance when the vehicle 200 is travelling on other surfaces, such as a road or metalled (finished) surface. A sand terrain rolling resistance threshold is defined to control changes between different subsystem control modes. The sand terrain rolling resistance threshold is defined as 2200 Newtons in the present embodiment.

The sand terrain rolling resistance may be less than or greater than 2200 Newtons. A determined surface rolling resistance which is greater than the sand terrain rolling resistance threshold, is an indicator that the vehicle 200 is travelling on a sand terrain. The combined probability value Pb for the sand subsystem control mode may be increased in dependence on a determination that the determined surface rolling resistance is greater than the sand terrain rolling resistance threshold. The electronic processing device 120 is configured to compare the surface rolling resistance of the vehicle 200 to the sand terrain rolling resistance threshold.

The subsystem control mode signal 155 is output to request a change from the first subsystem control mode to the second subsystem control mode in dependence on a determination that the surface rolling resistance of the vehicle is less than the sand terrain rolling resistance threshold. A reduction in the surface rolling resistance is indicative of the vehicle having travelled from a sand terrain to a different terrain. The change from the first subsystem control mode to the second subsystem control mode may be executed in dependence on a determination that the surface rolling resistance of the vehicle 200 is less than the sand terrain rolling resistance threshold. If the surface rolling resistance of the vehicle 200 is greater than the sand terrain rolling resistance threshold, the electronic processing device 120 is configured to continue to operate in the first subsystem control mode. The switch from the first subsystem control mode to the second subsystem control mode is implemented in dependence on a determination that the surface rolling resistance of the vehicle 200 is less than the sand terrain rolling resistance threshold.

In a variant, the electronic processing device 120 may be configured to implement an exit timer. The exit timer implements an exit time threshold. The exit time threshold is defined as 10 seconds in the present embodiment. The exit time threshold may be less than or greater than 10 seconds. The exit timer is initiated in dependence on a determination that the surface rolling resistance of the vehicle is less than the sand terrain rolling resistance threshold. The output of the subsystem control mode signal 155 to request a change from the first subsystem control mode to the second (or other non-sand) subsystem control mode is delayed until expiry of the exit timer. The exit timer may help to reduce or avoid a premature or unnecessary switch from the first subsystem control mode to the second (or other non-sand) subsystem control mode, for example when the vehicle traverses a localised region of terrain having a different composition which results in a lower rolling resistance. The localised region of terrain may, for example, correspond to region of compacted sand. The subsystem control mode signal 155 to request a change from the first subsystem control mode to the second subsystem control mode may be output at least substantially in real time in dependence on a determination that the surface rolling resistance of the vehicle is greater than the first sand terrain rolling resistance threshold.

The electronic processing device 120 is configured to continue monitoring the combined probability values Pb while the exit timer is operating. If the comparison of the combined probability values Pb indicates that a different subsystem control mode would be more appropriate, the electronic processing device 120 is configured to update or revise the control strategy while the exit timer is operating. For example, the electronic processing device 120 compares the combined probability values Pb and, during the exit timer countdown, may determine that remaining in the first subsystem control mode is appropriate (rather than changing to the second subsystem control mode) due to changes in the at least one terrain indicator. The electronic processing device 120 is configured to output the subsystem control mode signal 155 to request that, during the exit timer countdown, the vehicle control system 100 remains in the first subsystem control mode. In a further example, the comparison of the combined probability values Pb during the exit timer countdown may determine that changing to a different subsystem control mode (for example to a third subsystem control mode rather than a second subsystem control mode) is appropriate due to changes in the at least one terrain indicator. The electronic processing device 120 is configured to output the subsystem control mode signal 155 to request, during the exit timer countdown, a change from the first subsystem control mode to the third subsystem control mode.

The vehicle control system 100 in the present embodiment controls changes to and from the first subsystem control mode in dependence on the indicated tire pressure(s). The changes may also be controlled in dependence on one or more of: the road roughness, vehicle speed and surface rolling resistance. The utilisation of one or more of these additional parameters provides improved accuracy, for example to differentiate between edge cases in which the tire pressures may have been reduced for purposes other than driving on a sand terrain. This may provide improved resolution when differentiating between the plurality of subsystem control modes. The selection of the subsystem control mode may also take account of system faults, for example identified in the fault condition signal SFC received from the tire pressure monitor 220.

A method 500 of selecting one of a plurality of the subsystem control modes to control operation of the at least one vehicle subsystem will now be described with reference to Figure 5. The method 500 is described with reference to a sand subsystem control mode and a comfort subsystem control mode. The comfort subsystem control mode is set as a default subsystem control mode. It will be understood that the method 500 is applicable in respect of other combinations of the subsystem control modes. The method 500 may be implemented for other subsystem control modes. A first tire pressure threshold is determined (BLOCK 505); and a second tire pressure threshold is determined (BLOCK 510). The first and second tire pressure thresholds may, for example be read from the one or more memory device 130. In the present embodiment, the first tire pressure threshold is a low pressure threshold; and the second tire pressure threshold is a high tire pressure threshold. A front left tire pressure is measured (BLOCK 515); a rear right tire pressure is measured (BLOCK 520); a rear right tire pressure is measured (BLOCK 525); and a front right tire pressure is measured (BLOCK 530). The tire pressures may, for example, be measured by the tire pressure sensors associated with each of the wheels W1-W4. The measured tire pressures are compared to the tire pressure thresholds (BLOCK 535) to determine if any of the following conditions are satisfied: (a) any of the tire pressures are low, i.e. one or more of the measured tire pressures is less than the low tire pressure threshold; (b) all of the tire pressures are low, i.e. all of the measured tire pressures are less than the low tire pressure threshold; and (c) any of the tire pressures are high, i.e. one or more of the measured tire pressures is greater than the high tire pressure threshold.

The method comprises detecting a fault condition with one or more of the tire pressure sensors and/or the TPMS 215 (BLOCK 540). A road roughness indicator is determined in respect of the surface on which the vehicle 200 is travelling (BLOCK 545). A road roughness threshold is determined (BLOCK 550). The road roughness threshold may, for example, be read from the one or more memory device 130. A vehicle speed is determined (BLOCK 555). A vehicle speed threshold is determined (BLOCK 560). The vehicle speed threshold may, for example, be read from the one or more memory device 130. An exit timer threshold is determined (BLOCK 570). The exit timer threshold may, for example, be read from the one or more memory device 130.

The exit timer threshold in the present embodiment is a sand exit timer threshold which is implemented to control an exit from the first subsystem control mode which is a sand subsystem control mode. A surface rolling resistance is determined in respect of the surface on which the vehicle 200 is travelling (BLOCK 575). A surface rolling resistance threshold is determined (BLOCK 580). The surface rolling resistance threshold may, for example, be read from the one or more memory device 130. An ambient temperature is determined (BLOCK 585). The ambient temperature may, for example, be measured by a temperature sensor provided on the vehicle 200. An ambient temperature threshold is determined (BLOCK 590). The ambient temperature threshold may, for example, be read from the one or more memory device 130. One or more additional timers and associated thresholds may be determined (BLOCK 595). Rather than reference the ambient temperature, the method may comprise determining a tire temperature. The control method(s) described herein may be performed in dependence on the determined tire temperature.

A tire pressure status is determined (BLOCK 600). The tire pressure status classifies the tire pressures as follows: (i) all tire pressures are normal (i.e., all tire pressures are between the low tire pressure threshold and the high tire pressure threshold); (ii) at least one tire pressure is low (i.e., at least one tire pressure is less than the low tire pressure threshold); (Hi) at least one tire pressure is high (i.e., at least one tire pressure is greater than the high tire pressure threshold); (iv) the tire pressures are low for operating on sand (i.e., all of the tire pressures are less than the low tire pressure threshold); and (v) a fault condition is detection. The tire pressure status is output.

The method comprises calculating a combined probability value Pb for the comfort subsystem control mode in dependence on the tire pressure status (BLOCK 605). A first comfort probability value is calculated in dependence on a tire pressure status indicating that all tire pressures are normal (BLOCK 610). A second comfort probability value is calculated in dependence on a tire pressure status indicating that at least one tire pressure is low (BLOCK 615). A third comfort probability value is calculated in dependence on a tire pressure status indicating that at least one tire pressure is high (BLOCK 620). A fourth comfort probability value is calculated in dependence on a tire pressure status indicating that all tire pressures are low for operating on sand (BLOCK 625). A fifth comfort probability value is calculated in dependence on a tire pressure status indicating a fault condition (BLOCK 630). A tire pressure comfort probability value is calculated in dependence on the tire pressure status (BLOCK 635). A supplementary comfort probability value is calculated in dependence on all other comfort indicators (BLOCK 640). A combined comfort probability value is calculated in dependence on the tire pressure comfort probability value and the supplementary comfort probability value (BLOCK 645). A combined probability value is output for the comfort subsystem control mode (BLOCK 650).

The method comprises calculating a combined probability value Pb for the sand subsystem control mode in dependence on the tire pressure status (BLOCK 705). A first sand probability value is calculated in dependence on a tire pressure status indicating that all tire pressures are normal (BLOCK 710). A second sand probability value is calculated in dependence on a tire pressure status indicating that at least one tire pressure is low (BLOCK 715). A third sand probability value is calculated in dependence on a tire pressure status indicating that at least one tire pressure is high (BLOCK 720). A fourth sand probability value is calculated in dependence on a tire pressure status indicating that all tire pressures are low for operating on sand (BLOCK 725). A fifth sand probability value is calculated in dependence on a tire pressure status indicating a fault condition (BLOCK 730). A tire pressure sand probability value is calculated in dependence on the tire pressure status (BLOCK 735). A supplementary sand probability value is calculated in dependence on all other sand indicators (BLOCK 740). A combined sand probability value is calculated in dependence on the tire pressure sand probability value and the supplementary sand probability value (BLOCK 745). A combined probability value is output for the sand subsystem control mode (BLOCK 750).

The method comprises comparing the combined probability values for the comfort subsystem control mode and the sand subsystem control mode. It will be understood that the method can compare the combined probability value of the sand subsystem control mode with one or more other subsystem control modes. The subsystem control mode having the largest combined probability value is selected. The vehicle control system is configured to operate in the selected subsystem control mode.

In a variant, the electronic processing device 120 may be configured to implement an entry timer. The entry timer implements at least one entry time threshold. The at least one entry time threshold may comprise a first entry time threshold. The first entry time threshold may correspond to a minimum time required to manually reduce the tire pressure of all of the tires T1-T4 of the vehicle 200 for driving on sand. For example, the first entry time threshold may represent a time required manually to reduce the pressure of each of the tires T1-T4 from a normal tire pressure or a high tire pressure to a low tire pressure. The combined probability value Pb for the sand subsystem control mode may be reduced in dependence on a determination that the elapsed time is less than the first entry time threshold. Alternatively, the selection of the sand subsystem control mode may be inhibited if the elapsed time is less than the first entry time threshold. The entry timer may be implemented between changes to the selected subsystem control mode. A change from a selected subsystem control mode to a different subsystem control mode may be delayed or inhibited until expiry of the first entry time threshold. The entry timer may be initiated after selection of a subsystem control mode. A change from the selected subsystem control mode to a different subsystem control mode, such as the first subsystem control mode, may be inhibited until expiry of the first entry time threshold.

Alternatively, or in addition, the at least one entry time threshold may comprise a second entry time threshold. The tire pressure status may not be updated while the vehicle 200 is stopped (or the vehicle ignition is off). A delay in the updating of the tire pressure status may prevent evaluation of the sand subsystem control mode.

The second entry time threshold corresponds to a maximum time after the vehicle has stopped for the tire pressure status to be updated. The combined probability value Pb for the sand subsystem control mode may be reduced in dependence on a determination that the elapsed time is less than the second entry time threshold. Alternatively, the selection of the sand subsystem control mode may be inhibited if the elapsed time is less than the second entry time threshold. The entry timer may be implemented when the vehicle 200 stops.

A change from a selected subsystem control mode to a different subsystem control mode may be delayed or inhibited until expiry of the second entry time threshold after the vehicle 200 stops. The first and second entry time thresholds may be the same as each other or may be different from each other.

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 vehicle control system for selecting one of a plurality of subsystem control modes to control operation of at least one vehicle subsystem of a vehicle comprising a plurality of wheels each having a pneumatic tire, each of the subsystem control modes corresponding to one or more different terrain types for the vehicle; the vehicle control system comprising one or more processor collectively configured to: receive one or more pressure indicator signal, the or each pressure indicator signal comprising at least one tire pressure indicator providing an indication of a pressure of one of the pneumatic tires; determine a plurality of terrain condition indicators, the plurality of terrain condition indicators comprising a first terrain condition indicator in the form of a sand terrain condition indicator; wherein the first terrain condition indicator is determined in dependence on the at least one tire pressure indicator; and select one of the plurality of subsystem control modes in dependence on the plurality of terrain condition indicators; wherein the vehicle control system is configured to operate in the selected one of the plurality of subsystem control modes.
2. A vehicle control system as claimed in claim 1, wherein the one or more different terrain types comprise a first terrain type corresponding to a sand terrain type; the subsystem control modes comprising a first subsystem control mode which corresponds to the first terrain type; wherein the one or more processor is collectively configured to evaluate at least the first terrain condition indicator to determine a first combined probability value associated with the first subsystem control mode.
3. A vehicle control system as claimed in claim 2, wherein the first combined probability value is determined in dependence on the at least one tire pressure indicator, wherein the one or more processor is collectively configured to increase the first combined probability value in dependence on a determination that the at least one tire pressure indicator indicates that the tire pressure of each of the pneumatic tires is less than a first pressure threshold.
4. A vehicle control system as claimed in claim 2 or claim 3, wherein the one or more pressure indicator signal comprise a tire pressure indicator for each of the pneumatic tires; wherein the one or more processor is collectively configured to set the first combined probability value equal to a discrete sand terrain indicator in dependence on a determination that the at least one tire pressure indicators indicate that the tire pressure of each of the pneumatic tires is less than the first pressure threshold.
5. A vehicle control system as claimed in any one of claims 2 to 4, wherein the one or more processor is collectively configured to: evaluate the at least one terrain condition indicator to determine a second combined probability value associated with a second subsystem control mode, the second system control mode corresponding to a second terrain type; select one of the first and second subsystem control modes in dependence on the first and second combined probability values and a change threshold; and operate in the selected one of the first and second subsystem control modes.
6. A vehicle control system as claimed in claim 5, wherein, when the vehicle control system is operating in one of the first and second subsystem control mode, the one or more processor is collectively configured to: determine if there is a difference between the first and second combined probability values and to integrate the difference with respect to time to generate an integrated value; and output a subsystem control mode signal to request a change from the one subsystem control mode to the other subsystem control mode in dependence on a determination that the integrated value is greater than the change threshold.
7. A vehicle control system as claimed in claim 6, wherein the one or more processor is collectively configured to: determine a road roughness indicator; and output a subsystem control mode signal to request a change from the first subsystem control mode to the second subsystem control mode in dependence on a determination that the road roughness indicator is greater than a sand terrain roughness threshold; and/or determine a vehicle speed; and output a subsystem control mode signal to request a change from the first subsystem control mode to the second subsystem control mode in dependence on a determination that the vehicle speed is greater than a sand terrain speed threshold.
8. A vehicle control system as claimed in any one of claims 5, 6 or 7, wherein the one or more processor is collectively configured to: determine a surface rolling resistance of the vehicle; and output a subsystem control mode signal to request a change from the first subsystem control mode to the second subsystem control mode in dependence on a determination that the surface rolling resistance of the vehicle is less than a sand terrain rolling resistance threshold.
9. A vehicle control system as claimed in claim 8, wherein the one or more processor is collectively configured to: implement an exit timer in dependence on a determination that the surface rolling resistance of the vehicle is less than a first sand terrain rolling resistance threshold; and output a subsystem control mode signal to request a change from the first subsystem control mode to the second subsystem control mode upon expiry of the exit timer.
10. A vehicle control system as claimed in claim 8 or claim 9, wherein the change threshold is set to a sand change threshold in dependence on a determination that the surface rolling resistance of the vehicle is greater than the sand terrain rolling resistance threshold.
11. A vehicle control system as claimed in any one of claims 2 to 10, wherein the one or more processor collectively is configured to receive an ambient temperature signal indicating an ambient temperature; wherein the vehicle control system is configured to determine the first combined probability value in dependence on the ambient temperature.
12. A vehicle comprising the vehicle control system as claimed in any one of the preceding claims.
13. A method of selecting one of a plurality of subsystem control modes to control operation of at least one vehicle subsystem of a vehicle comprising a plurality of wheels each having a pneumatic tire, each of the subsystem control modes corresponding to one or more different terrain types for the vehicle; wherein the method comprises: receive one or more pressure indicator signal, the or each pressure indicator signal comprising at least one tire pressure indicator providing an indication of a pressure of one of the pneumatic tires; determining a plurality of terrain condition indicators, the plurality of terrain condition indicators comprising a first terrain condition indicator in the form of a sand terrain condition indicator, wherein the first terrain condition indicator is determined in dependence on the pressure of the at least one pneumatic tire indicated by the one or more pressure indicator signal; selecting one of the plurality of subsystem control modes in dependence on the plurality of terrain condition indicators; and operating in the selected one of the plurality of subsystem control modes.
14. A method as claimed in claim 13, wherein the one or more different terrain types comprise a first terrain type corresponding to a sand terrain type; the subsystem control modes comprising a first subsystem control mode which corresponds to the first terrain type, the method comprising evaluating at least the first terrain condition indicator to determine a first combined probability value associated with the first subsystem control mode.
15. Computer readable instructions which, when executed by a computer, are arranged to perform a method according to claim 13 or claim 14.