System and method for detecting wheelspin

Abstract

Aspects of the present invention relate to a control system (1) for detecting a wheelspin event (WSE(n)) on a wheel (W1-W4) of a vehicle (5). The control system (1) includes one or more processor (120) collectively configured to receive a wheel speed signal (SLC(n) indicating a wheel speed of the wheel (W1-W4) and to determine an acceleration of the wheel (W1-W4) in dependence on the wheel speed signal (SLC(n). A moving average (ā(n)) of the acceleration (a(n)) of the wheel (W1-W4) is determined. A wheelspin event (WSE(n)) is detected in dependence on a determination that the moving average (ā(n)) of the acceleration (a(n)) of the wheel (W1-W4) is greater than or equal to a wheel acceleration threshold (TH1). A wheelspin event signal (SWS(n)) is output to indicate detection of a wheelspin event (WSE(n)) on the wheel (W1-W4). Aspects of the invention relate to the control system (1), a system (15), a vehicle (5) and a method (200).

Description

[0001] SYSTEM AND METHOD FOR DETECTING WHEELSPIN

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a system and method for detecting wheelspin. Aspects of the invention relate to a control system, a system, a vehicle and a method.

[0004] BACKGROUND

[0005] It is known to detect wheel slip in a road vehicle, such as an automobile, by comparing the wheel speeds. If a variance in the wheel speed exceeds a threshold value, a controller may detect a wheel slip event at one or more of the wheels. One or more vehicle systems may be controlled in dependence on the detection of the slip event. This approach may not be suitable for determining that there is wheelspin at one or more driving wheel of the vehicle (referred to herein as a wheelspin event). A different control strategy may be appropriate to control the vehicle subsystems when wheelspin occurs at one or more of the wheels.

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

[0007] SUMMARY OF THE INVENTION

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

[0009] According to an aspect of the present invention there is provided a control system for detecting a wheelspin event on a wheel of a vehicle; the control system comprising one or more processor collectively configured to:

[0010] receive a wheel speed signal indicating a wheel speed of the wheel;

[0011] determine an acceleration of the wheel in dependence on the wheel speed signal;

[0012] determine a moving average of the acceleration of the wheel;

[0013] detect a wheelspin event in dependence on a determination that the moving average of the acceleration of the wheel is greater than or equal to a wheel acceleration threshold; and

[0014] output a wheelspin event signal indicating detection of a wheelspin event on the wheel. The determination of the moving average of the acceleration may help to reduce signal noise, for example caused by short-term fluctuations in the wheel speed. At least in certain embodiments, the control system is configured to detect the wheelspin event at each wheel independently of the other wheels. This enables detection of the wheelspin event at each wheel. A braking (retardation) force may be applied to the wheel in dependence on detection of the wheelspin event. The application of a braking force may promote the delivery of torque to one or more other wheels on the vehicle. Moreover, at least in certain embodiments, the control system may differentiate between different combinations of wheelspin events occurring concurrently at two or more of the wheels. This may facilitate control of the vehicle, for example to select a vehicle drive mode in dependence on the wheelspin combination.

[0015] The control system comprises one or more controllers collectively comprising at least one electronic processor having an electrical input for receiving an input signal; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to: receive the wheel speed signal; determine the acceleration of the wheel in dependence on the wheel speed signal; and determine the moving average of the acceleration of the wheel . The at least one electronic processor is configured to compare the moving average to a wheel acceleration threshold. The at least one processor may beconfigured to detect a wheelspin event in dependence on a determination that the moving average of the acceleration of the wheel is greater than or equal to a wheel acceleration threshold. The at least one processor may output the wheelspin event signal indicating detection of a wheelspin event on the wheel.

[0016] The one or more processor may determine an absolute value of the acceleration. The moving average may be determined in dependence on the absolute value of the acceleration. The moving average may be referred to as an absolute average wheel acceleration.

[0017] The wheel acceleration threshold may be predefined. The wheel acceleration threshold may, for example, be determined in dependence on empirical data. The empirical data may represent at least one wheelspin event on one or more of the wheels of a vehicle. The wheel acceleration threshold may be defined so as to identify the at least one wheelspin event represented by the empirical data. The wheel acceleration threshold may be stored, for example on the at least one memory device. The at least one processor may access the wheel acceleration threshold stored on the at least one memory device.

[0018] The one or more processor may be collectively configured to determine a gradient of the surface on which the vehicle is operating. The gradient is represented by an angle relative to a horizontal plane. The gradient may be positive or negative. The one or more processor may determine an absolute value of the gradient. The one or more processor may receive a gradient signal indicating the gradient of the surface on which the vehicle is operating. Alternatively, the one or more processor may be configured to estimate the gradient of the surface on which the vehicle is operating. The one or more processor may be configured to correct the determined acceleration of the wheel in dependence on the determined gradient.

[0019] The determined gradient may be applied as an entry condition to detecting a wheelspin event. The detection of a wheelspin event may be inhibited in dependence on a determination that the gradient is greater than or equal to a gradient threshold. The one or more processor may be collectively configured to output the wheelspin event signal in dependence on a determination that the gradient is less than a gradient threshold. The one or more processor may be collectively configured to inhibit the output of the wheelspin event signal in dependence on a determination that the gradient is greater than the gradient threshold.

[0020] The vehicle typically comprises a plurality of the wheels. For example, the vehicle may comprise four (4) of the wheels. The one or more processor may be collectively configured to repeat the detection of the wheelspin event in respect of each of the plurality of wheels. The one or more processor may output the wheelspin event signal to indicate detection of the wheelspin event at one or more of the plurality of wheels. One or more of the plurality of wheels may be a driving wheel, i.e. drivingly connected to a torque-generating machine. The one or more processor may be collectively configured to repeat the detection of the wheelspin event in respect of each driving wheel of the vehicle.

[0021] The one or more processor may be collectively configured to identify the wheel(s) where the or each wheelspin event is detected. The wheelspin event signal may identify each wheel where the wheelspin event is detected.

[0022] The wheelspin event signal may indicate detection of the wheelspin event at two or more of the plurality of wheels. The one or more processor may be collectively configured to generate a wheelspin group indicator to identify the grouping of the detected wheelspin events. The wheelspin group indicator may, for example, identify the wheelspin events in dependence on the location of the affected wheel(s) on the vehicle, for example: front right (FR), front left (FL), rear right (RR) and rear left (RL). The wheelspin group indicatormay be output to a vehicle control unit. The vehicle control unit may be configured to control one or more vehicle subsystem in dependence on the wheelspin group indicator. The one or more processor may be configured to classify an operating condition of the vehicle in dependence on the grouping of the detected wheelspin events.

[0023] The wheelspin group indicator may identify the grouping of the wheelspin events as an all-wheel wheelspin event in dependence on the detection of the wheelspin event at each of the plurality of wheels. A vehicle control unit may be configured to engage (i.e. to lock) one or more differential lock in dependence on receipt of the wheelspin group indicator identifying the grouping of the wheelspin events as an all-wheel wheelspin event. The differential lock may comprise one or more of the following: a central differential lock, a front axle differential and a rear axle differential. A vehicle control unit may be configured to adjust a throttle mapping and / or a brake pedal mapping in dependence on receipt of the wheelspin group indicator identifying the grouping of the wheelspin events as an all-wheel wheelspin event.

[0024] The wheelspin group indicator may identify the grouping of the wheelspin events as a split-mu (split- .) wheelspin event in dependence on the detection of the wheelspin event on the wheels on only one side of the vehicle (either the left-hand side or the right-hand side of the vehicle). The split-mu wheelspin event is detected when wheelspin events are detected on the wheels on one side of the vehicle but not the other side of the vehicle. For example, wheelspin events may be detected on the wheels on the left-hand side of the vehicle but not on the right-hand side (or vice versa). A vehicle control unit may be configured to engage (i.e. to lock) one or more differential lock in dependence on receipt of the wheelspin group indicator identifying the grouping of the wheelspin events as a split-mu wheelspin event. The differential lock may comprise one or more of the following: a front axle differential and a rear axle differential. A vehicle control unit may be configured to adjust a throttle mapping and / or a brake pedal mapping in dependence on receipt of the wheelspin group indicator identifying the grouping of the wheelspin events as an all-wheel wheelspin event.

[0025] The wheelspin group indicator may identify the grouping of the wheelspin events as a cross-axle wheelspin event in dependence on the detection of wheelspin events on wheels disposed on different axles and on opposing sides of the vehicle. For example, wheelspin events may be detected on first and second wheels, the first and second wheels being disposed on different axles and on opposing sides of the vehicle. The wheelspin events are not detected on the other wheels during the cross-axle wheelspin event. A vehicle control unit may be configured to engage (i.e. to lock) one or more differential lock in dependence on receipt of the wheelspin group indicator identifying the grouping of the wheelspin events as a cross-axle wheelspin event. The differential lock may comprise a central differential lock provided on the vehicle.

[0026] The wheelspin group indicator may identify the grouping of the wheelspin events as a front-axle wheelspin event in dependence on the detection of the wheelspin events on each of the plurality of wheels on a front axle of the vehicle. The wheelspin events are not detected on the wheels on a rear axle of the vehicle during the front-axle wheelspin event. A vehicle control unit may be configured to engage (i.e. to lock) a differential lock in dependence on receipt of the wheelspin group indicator identifying the grouping of the wheelspin events as a front-axle wheelspin event. The differential lock may comprise a central differential lock provided on the vehicle.

[0027] The wheelspin group indicator may identify the grouping of the wheelspin events as a rear-axle wheelspin event in dependence on the detection of the wheelspin events on each of the plurality of wheels on a rear axle of the vehicle. The wheelspin events are not detected on the wheels on a front axle of the vehicle during the rear-axle wheelspin event. A vehicle control unit may be configured to engage (i.e. to lock) a differential lock in dependence on receipt of the wheelspin group indicator identifying the grouping of the wheelspin events as a rear-axle wheelspin event. The differential lock may comprise a central differential lock provided on the vehicle.The one or more processor may be collectively configured to detect the wheelspin event in dependence on one or more entry condition. The detection of the wheelspin event may be enabled in dependence on a determination that the one or more entry condition is satisfied. The detection of the wheelspin event may be inhibited or disabled in dependence on a determination that the one or more entry condition is not satisfied. The one or more processor may be collectively configured to detect the or each wheelspin event in dependence on a determination that one or more of the following entry conditions is satisfied:

[0028] a vehicle speed is less than a vehicle speed threshold value;

[0029] a vehicle longitudinal acceleration is less than a vehicle acceleration threshold value;

[0030] the wheel speed is less than a wheel speed threshold value;

[0031] a braking system is not actuated; and

[0032] a transmission system is in a drive gear.

[0033] According to a further aspect of the present invention there is provided a system comprising the control system described herein and at least one vehicle control unit for controlling at least one vehicle subsystem of the vehicle. The at least one vehicle control unit may be configured to modify the operation of the at least one vehicle subsystem in dependence on the wheelspin detected signal output from the control system.

[0034] According to a further aspect of the present invention there is provided a system comprising the control system as described herein and at least one vehicle control unit for selecting one of a plurality of vehicle drive modes. The vehicle drive modes may each define one or more operating parameter of at least one vehicle subsystem. The at least one vehicle control unit may be configured to select one of the plurality of vehicle drive modes in dependence on the wheelspin event signal from the control system.

[0035] According to a further aspect of the present invention there is provided a control system or a system as described herein.

[0036] According to a further aspect of the present invention there is provided a method of detecting a wheelspin event on a wheel of a vehicle; the method comprising:

[0037] determine an acceleration of the wheel;

[0038] determine a moving average of the acceleration of the wheel ;

[0039] compare the moving average of the acceleration of the wheel to a wheel acceleration threshold; and

[0040] detect the wheelspin event in dependence on a determination that the moving average of the acceleration of the wheel is greater than the wheel acceleration threshold.

[0041] The method may comprise modifying the operation of at least one vehicle subsystem in dependence on the detection of the wheelspin event.

[0042] The term wheelspin is used herein to refer to the spinning of a driving wheel of the vehicle due to a loss of traction or contact with the surface on which the vehicle is operating. The driving wheel spins freely relative to the surface. The spinning wheel is generally unsuitable for transmitting a tractive force to propel the vehicle.

[0043] According to a further aspect of the present invention there is provided computer readable instructions which, when executed by one or more processor, cause the one or more processor to perform the 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.

[0044] BRIEF DESCRIPTION OF THE DRAWINGS

[0045] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0046] Figure 1 shows a schematic representation of a vehicle comprising a control system in accordance with an embodiment of the present invention;

[0047] Figure 2 shows a schematic representation of the control system, the drive units and the subsystems of the vehicle shown in Figure 1;

[0048] Figure 3 shows a schematic representation of the controller of the control system shown in Figures 1 and 2;

[0049] Figure 4A is a first graph showing the signal noise in the measured wheel speed as the vehicle transitions from operating on-road to off-road;

[0050] Figure 4B is a second graph showing the acceleration of the individual wheels of the vehicle during a wheelspin event;

[0051] Figure 5 is a first block diagram representing a method of detecting a wheelspin event in accordance with an embodiment of the present invention;

[0052] Figure 6 is a second block diagram represent a method of determining a gradient of the surface on which the vehicle is operating; and Figures 7A and 7B are a third block diagram representing a method of generating a wheelspin group indicator to identify which wheel or combination of wheels is encountering a wheelspin event.

[0053] DETAILED DESCRIPTION

[0054] A control system 1 and a method 200 for detecting a wheelspin event WSE(n) in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figures.

[0055] The vehicle 5 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 5. The same suffix is applied for components associated with each other, for example components forming part of the same sub-assembly of the vehicle 5. The integer n is used herein to identify a signal or event relating to a corresponding one of a plurality of features of the vehicle 5.

[0056] As shown in Figure 1, the control system 1 is installed in a vehicle 5 comprising four (4) wheels W1-W4 (Front Right FR, Front Left FL, Rear Right RR and Rear Left RL). The vehicle 5 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 5 in the present embodiment is an automobile. The vehicle 5 comprises one or more torque-generating machine 11, such as an internal combustion engine (ICE) and / or an electric drive unit. The vehicle 5 may be a battery electric vehicle (BEV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PH EV) or an internal combustion engine (ICE) vehicle. The front wheels W1 , W2 are disposed on a front axle A1 ; and the rear wheels W3, W4 are disposed on a rear axle A2.The front wheels W1 , W2 and / or the rear wheels W3, W4 may be driven by the one or more torque-generating machine 11. In the present embodiment, the vehicle 5 is four-wheel drive. The wheels W1-W4 may each be referred to as a driving wheel W1-W4. The vehicle 5 comprises one or more torque-generating machine 11 (shown in Figure 2). In the present embodiment, the wheels W1-W4 are driven by first and second torque-generating machines in the form of an internal combustion engine 11-1 and an electric drive unit 11-2. The vehicle 5 may have permanent four-wheel drive. In the present embodiment the four-wheel drive is selectively engaged by engaging a centre differential.

[0057] The vehicle 5 comprises a plurality of wheel speed sensors WS1-WS4. Each of the wheel speed sensors WS1-WS4 is associated with one of the wheels W1-W4. The wheel speed sensors WS1-WS4 are configured to measure a rotational speed of the wheels W1-W4. The wheel speed sensors WS1-WS4 in the present embodiment are the wheel speed sensors WS1-WS4 used in an anti-lock brake system. The wheel speed sensors WS1-WS4 measure a rotational speed of the wheels W1-W4. The wheel speed sensors WS1-WS4 are calibrated to output signals SLC1-SCL4 indicating an instantaneous wheel speed of each of the wheels W1-W4. In the present embodiment, the output signals SLC1-SCL4 indicate a raw wheel speed, i.e. an unfiltered wheel speed. The wheel speed in the present embodiment comprises a linear (directional) velocity calculated by multiplying the wheel rotational angular speed with a nominal rolling radii of the wheels W1-W4. The output signals SLC1-SCL4 are in the form of wheel speed signals SLC1-SLC4. Each wheel speed signal SLC1-SLC4 is indicative of the linear velocity of a respective one of the wheels W1-W4. The wheel speed signals SLC1-SLC4 are output to the control system 1. The control system 1 in the present embodiment is configured to process the absolute linear velocity of each of the wheels W1-W4 (i.e., a non-negative value of the linear velocity). In a variant, the wheel speed may comprise the rotational speed of each of the wheels W1-W4. The output signals SLC1-SCL4 may comprise rotational velocity signals. It will be understood that the linear velocity and rotational speed are directly proportional to each other and may be used interchangeably.

[0058] The control system 1 is configured to detect a wheelspin event WSE(n) in one or more of the wheels W1-W4. In the present embodiment, the control system 1 is configured to detect a wheelspin event WSE(n) in each of the wheels W1-W4. The control system can detect a wheelspin event WSE(n) on each wheel W1 -W4 independent of the behaviour of the other wheels W1-W4. The wheelspin event WSE(n) is indicative of the wheel(s) W1-W4 spinning relative to the surface on which the vehicle 5 is operating. During the wheelspin event WSE(n), the wheel W1-W4 can rotate freely. The wheel W1-W4 may rotate continuously during the wheelspin event WSE(2), typically completing a plurality of rotations with little or no direct control. The wheelspin event WSE(n) may, for example, occur due to a loss of traction at a contact patch between the wheel W1-W4 and a surface on which the vehicle 5 is operating. The loss of traction allows the driving wheel(s) W1-W4 to rotate freely relative to the surface (i.e. the wheelspins). The wheelspin event WSE(n) may occur when the torque applied to the wheel W1-W4 exceeds the available traction. Alternatively, the wheelspin event WSE(n) may occur when the wheel W1-W4 is lifted off the surface, for example due to axle articulation when the vehicle 5 is off-roading. The wheelspin event WSE(n) relates to one or more driving wheel W1-W4 of the vehicle 5 spinning as a result of a torque applied by one or more of the first and second torque-generating machines 11-1, 11-2. The tractive force generated by the driven wheels W1-W4 to propel the vehicle 5 is reduced when one or more of the wheels W1-W4 spins. The available traction is dependent on the friction between the surface and each wheel W1-W4 of the vehicle 5. The friction is represented by a coefficient of friction (p) which varies depending on the properties of the surface on which the vehicle 5 is operating. The coefficient of friction (p) will, for example, vary depending on surface roughness. The rotational speed of the wheel W1-W4 increases as the wheel W1-W4 spins relative to the surface. The acceleration of the wheels W1-W4 can be determined in dependence on the output signals SLC1-SLC4 output from the wheel speed sensors WS1-WS4. As described herein, the control system 1 is configured to monitor the acceleration a(n) of the wheel s W1-W4 to detect a wheelspin event SVE(n) on each wheel.As illustrated in Figure 3, the control system 1 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 the wheel speed signals SLC1-SLC4 from the wheel speed sensors WS1-WS4. The wheel speed signals SLC1-SLC4 are electrical signals which are indicative of the wheel speed of each of the wheels W1-W4 of the vehicle 5. The wheel speed signals SLC1-SLC4 are measured with respect to time. The output 150 is arranged to output a wheelspin event signal SWS(1)-(4) which is indicative of the detection of a wheelspin event WSE(n). The wheelspin event signal SWS(1)-(4) identifies the or each wheel W1-W4 experiencing a wheelspin event WSE(n). As described herein, the wheelspin event signal SWS(1)-(4) is output to control operation of one or more vehicle subsystems (denoted herein generally by the reference numeral 21).

[0059] The control system 1 is incorporated into a system 15 provided on the vehicle 5. The system 15 comprises the control system 1 and at least one vehicle control unit VCU. The vehicle control unit(s) VCU is configured to control operation of one or more vehicle subsystems 21. As described herein, the control system 1 is in communication with the at least one vehicle control unit VCO. In particular, the control system 1 is configured to output the wheelspin detected signal to the at least one vehicle control unit(s) VCU. The at least one vehicle control unit(s) VCU is configured to control operation of the one or more vehicle subsystems 21 in dependence on the wheelspin event signal SWS(1)-(4). The or each vehicle control unit VCU comprises an electrical processor configured to receive the wheelspin detected signal(s) WSD(n) from the control system 1. The one or more vehicle control unit VCU controls operation of one or more of the vehicle subsystems 21 in dependence on the wheelspin event signal(s) SWS(1)-(4) generated by the control system 1. It will be understood that the vehicle control unit VCU and the control system 1 may be combined into the same control unit.

[0060] The vehicle 5 comprises a plurality of the vehicle subsystems (denoted generally by the reference numeral 21 and shown schematically in Figures 2 and 3). The vehicle subsystems 21 in the present embodiment include, but are not limited to, a traction control system 21 A, a propulsion (or engine) management system 21 B, a transmission system 21 C, a steering system 21 D, a braking system 21 E, a suspension system 21 F, and a differential system 21 G. The transmission system 21 C comprises a transmission control unit for monitoring a selected drive gear of the transmission. The differential system 21 G may comprise one or more locking differential, such as a centre differential lock and / or an electronic differential. The braking system 21 E is typically an anti-lock braking system (ABS) and comprises a plurality of friction brakes associated with respective wheels W1-W4. The braking system 21 E comprises a brake pedal sensor for determining a position of a brake pedal. The vehicle 5 may comprise less than or more than seven (7) vehicle subsystems 21. The vehicle control unit VCU is configured to control operation of the vehicle subsystems 21. In particular, the vehicle control unit VCU is configured to control or to modify the operation of the at least one vehicle subsystem in dependence on the wheelspin detected signal from the control system 1. The vehicle subsystems 21 may optionally comprise a regeneration system 21 H which may control retardation of the vehicle 5.

[0061] The vehicle control unit VCU may be configured to implement one or more vehicle drive mode 31 (n). The or each vehicle drive mode 31 (n) defines one or more operating parameter of at least one of the vehicle subsystems 21. Each vehicle drive mode configures the at least one of the vehicle subsystems 21 in dependence on the current or prevailing operating conditions. For example, the vehicledrive mode 31 (n) may configure the vehicle subsystems 21 in dependence on a determined (or estimated) surface friction. A first drive mode may be configured to control the vehicle subsystems 21 when the vehicle 5 is operating on a surface having a high coefficient of friction (such as a road); and a second drive mode may be configured to control the vehicle subsystems 21 when the vehicle 5 is operating on a surface having a low coefficient of friction (such as a wet grass or ice). At least in certain embodiments, the vehicle control unit VCU may select one of the vehicle drive modes in dependence on the wheelspin event signal SWS(1 )-(4) received from the control system 1.

[0062] The vehicle drive modes 31 (n) may be associated with a corresponding terrain classification. The vehicle drive modes in the present embodiment comprise: a general driving control mode 31(1); a Grass / Gravel / Snow (GGS) control mode 31(2); a mud and rut control mode 31(3); a sand control mode 31(4); and a rock crawl control mode 31(5). The general driving control mode 31(1) is appropriate for on-road driving and may, for example, configure the suspension to prioritise comfort. The Gass / Gravel / Snow (GGS) control mode 31(2); may adapt throttle response and configures the transmission to prioritise traction. The mud and ruts control mode 31(3) may allow increased wheel spin to enable traversal of muddy terrain. The sand control mode 31 (4) may map the throttle to response to help maintain momentum through sand. The rock crawl control mode 31(5) may comprise selecting a low transmission ratio (for example by engaging a transfer case) for performing rock-crawl manoeuvres and / or engaging four-wheel drive.

[0063] The control system 1 according to the present embodiment is configured to monitor the wheel speed of each of the wheels W1-W4 to detect a change which is indicative of a wheelspin event WSE(n). The controller 110 is configured to process the wheel speed signal SLC1-SLC4 received for each wheel W1- W4 to detect a wheelspin event WSE(n) on one or more of the wheels W1-W4. The processing is performed in respect of each of the wheels W1-W4. The processing of the wheel speed of each wheel W1-W4 is independent of the wheel speed of the other wheels W1-W4. The wheelspin event WSE(n) may be detected in respect of each wheel W1-W4 without reference to the wheel speed (or acceleration) of any of the other wheels W1-W4. The controller 110 is configured to perform the same operation in respect of each of the wheels W1 -W4 to detect a wheelspin event WSE(n) on one or more of the wheels W1-W4. The operation of the controller 110 to detect a wheelspin event WSE(n) on the first wheel W1 will now be described.

[0064] The controller 110 is configured to receive a first wheel speed signal SLC1 indicating the wheel speed of the first wheel W1. The controller 110 processes the first wheel speed signal SCL1 to determine a wheel acceleration of the first wheel W1 (referred to herein as the first wheel acceleration AC1). In particular, the controller 110 determines a derivative (i.e., an instantaneous rate of change) of the wheel speed of the first wheel W1. The controller 110 determines a moving average a(1) (also known as a rolling average) of the first wheel acceleration a(1) of the first wheel W1. The moving average a(1) of the first wheel acceleration a(1) is calculated over a predetermined time period. The time period is calibratable, for example in dependence on empirical data. A moving average a(1) of the first wheel acceleration a(1) is represented by the trace 75’(1) in Figure 4B. first wheel acceleration a(1). The calculation of the moving average a(1) is effective in filtering the first wheel acceleration a(1) to smooth out or reduce short-term fluctuations. Alternatively, or in addition, a low pass filter may be applied to reduce or remove noise from the first wheel acceleration a(1). An absolute value |a|(1) of the moving average a(1) of the first wheel acceleration a(1) is determined.

[0065] The controller 110 accesses a wheel acceleration threshold STH1. The wheel acceleration threshold STH1 may, for example, be stored in memory device 130. In the present embodiment the wheel acceleration threshold STH1 is predefined. The wheel acceleration threshold STH1 may, for example, be defined in dependence on empirical data. The wheel acceleration threshold STH1 may be calibratable, for example for a particular drivetrain. The wheel acceleration threshold STH1 defines an upper threshold for the moving average of the acceleration of the first wheel W1. The controller 110 is configured to compare the moving average a(1) of the firstwheel acceleration a(1) to the wheel acceleration threshold STH1. In dependence on a determination that the moving average a(1) of the first wheel acceleration a(1) is greater than the wheel acceleration threshold STH1, the controller 110 detects a wheelspin event WSE(1) on the first wheel W1. In other words, the controller 110 determines that the first wheel W1 is undergoing spin when the moving average a(1) of the wheel acceleration of the first wheel W1 is greater than the wheel acceleration threshold STH1. In dependence on a determination that the moving average a(1) of the first wheel acceleration a(1) is less than the wheel acceleration threshold STH1, the controller 110 determines that there is no wheelspin event WSE(1) on the first wheel W1 (or that a wheelspin event on the first wheel W1 is over). The controller 110 is configured to output a wheelspin event signal SWS(n) to indicate detection of a wheelspin event. The controller 110 is configured to output a first wheelspin event signal SWS(1) to indicate detection of a wheelspin event on the first wheel W1. The first wheelspin event signal SWS(1) functions as a flag to indicate detection of wheelspin on the first wheel W1.

[0066] As outlined above, the vehicle 5 comprises a plurality of the wheels W1-W4. The controller 110 is configured to detect a wheelspin event at each of the plurality of wheels W1-W4. In particular, the controller 110 calculates a moving average of the acceleration of each of the plurality of wheels W1-W4. The moving average a(n) of the acceleration a(n) of each of the plurality of wheels W1-W4 is compared to the wheel acceleration threshold STH1. The wheel acceleration threshold STH1 is the same for each of the wheels W1-W4 in the present embodiment.

[0067] A first graph 60 showing the measured wheel speed of each of the wheels W1-W4 of the vehicle 5 is shown in Figure 4A. The first graph 60 comprises four traces 65(1)-65(4) representing the measured speed of respective wheels W1-W4. The first graph 60 represents the measured wheel speed of the vehicle 5 which is initially operating on-road (i.e. on a road or a metalled surface) and then transitions to operating off-road. The vehicle 5 transitions from on-road to off-road terrain at time t1. This transition is represented by an increase in the noise in the wheel speed signals received from the wheel speed sensors WS1-WS4. The noise in the wheel speed signals would be reflected in short-term fluctuations in the acceleration of each of the wheels W1-W4. As described herein, a moving average a(n) of the acceleration of each wheel W1-W4 is calculated to reduce the short-term fluctuations.

[0068] A second graph 70 showing the moving average a(n) of the acceleration of each of the wheels W1-W4 is shown in Figure 4B. In the present embodiment, an absolute value |a|(1) of the moving average a(n) is plotted in the second graph 70. The second graph 70 comprises four traces 75(1)-75(4) representing the absolute moving average |a|(n) of the acceleration of respective wheels W1-W4. In the illustrated example, there is wheelspin at each of the wheels W1-W4. The wheelspin corresponds to a magnitude of the acceleration a(n) of each wheel W1-W4 being greater than or equal to an estimated longitudinal acceleration of the vehicle 5. In the illustrated scenario, the vehicle 5 is likely to be stuck (or becoming stuck) since all of the wheels W1-W4 are spinning. The wheel acceleration threshold STH1 is shown in Figure 4B by way of example. As described herein, a wheelspin event WSE(n) is detected when the absolute moving average |a|(n) of the acceleration a(n) exceeds the predefined wheel acceleration threshold STH1. By way of example, a series of wheelspin events WSE(1) on the first wheel W1 are illustrated in Figure 4B.

[0069] In the present embodiment, each of the plurality of wheels W1-W4 is a driving wheel (i.e. is driven by one or more of the first and second torque-generating machine 11-1, 11-2). As such, a wheelspin event WSE(n) of the type described herein may occur at each of the wheels W1-W4. In a variant, only some of the wheels W1-W4 may be driven, for example the vehicle 5 may be front-wheel drive or rear-wheel drive (either permanent or selectable). The controller 110 may be configured to detect a wheelspin event WSE(n) only on those wheels W1-W4 which are driven by the one or more torque-generating machine 11.The controller 110 is configured to output a wheelspin event signal SWS(n) to indicate detection of a wheelspin event WSE(n) on the or each wheel W1-W4. The controller 110 may optionally also determine a wheelspin group indicator GSI in dependence on detection of a wheelspin event WSE(n) more than one of the wheels W1-W4. The wheelspin group indicator GSI provide an indication of a dynamic operating state of the vehicle 5. One or more operating parameter of at least one the vehicle sub-system 21 may optionally be re-configured in dependence on the wheelspin group indicator GSI. The controller 110 may optionally output a control signal in dependence on the wheelspin group indicator GSI, for example to change a vehicle driving mode. The determination of the wheelspin group indicator GSI will now be described in more detail.

[0070] The controller 110 is configured to classify the wheelspin group indicator GSI as an all-wheel wheelspin event in dependence on detection of a wheelspin event WSE(1 )-(4) at each of the plurality of wheels W1-W4 (i.e., all of the wheels are experiencing spin). Detection of a wheelspin event WSE(n) at each of the wheels W1-W4 may indicate that the vehicle 5 is operating on a surface having a low coefficient of friction ( .), such as ice or wet grass. The controller 110 may configure the one or more vehicle subsystem 21 for operation on a surface having a low coefficient of friction (p) in dependence on a determination that the wheelspin group indicator GSI represents an all-wheel wheelspin event. For example, the controller 110 may select one of a plurality of driving modes configured for the detected conditions.

[0071] The controller 110 is configured to classify the wheelspin group indicator GSI as a split-mu (split-p) wheelspin event in dependence on the detection of a wheelspin event WSE(n) on either the left-hand side or the right-hand side of the vehicle 5 while no wheelwheelspin event WSE(n) is detected on the other side of the vehicle 5. The wheelspin group indicator GSI may indicate a split-mu (split-p) wheelspin event in dependence on the detection of wheelspin events WSE(1), WSE(3) on the front and rear wheels W1, W3 on the right-hand side of the vehicle 5 while there is no wheelspin event WSE(2), WSE(4) detected on the front and rear wheels W2, W4 on the left-hand side of the vehicle 5. Conversely, the wheelspin group indicator GSI may indicate a split-mu (split-p) wheelspin event in dependence on the detection of wheelspin events WSE( 1 ), WSE(3) on the front and rear wheels W2, W4 on the left-hand side of the vehicle 5 while there is no wheelspin event WSE(2), WSE(4) detected on the front and rear wheels W1, W3 on the right-hand side of the vehicle 5. The controller 110 may optionally determine the wheelspin group indicator GSI as being a left or right split-mu wheelspin event to identify those wheels W1-W4 which are experiencing spin. The determination of the wheelspin group indicator GSI as a split-mu wheelspin event may indicate that only one side of the vehicle 5 is operating on a surface having a low coefficient of friction (p). This may occur as the vehicle 5 transitions from a surface having a low coefficient of friction onto a surface having a high coefficient of friction, for example as the vehicle 5 pulls away from a grass verge onto a metalled road. The controller 110 may configure the one or more vehicle subsystem 21 for operation on a surface having a low coefficient of friction (p) in dependence on the determination that the wheelspin group indicator GSI is a split-mu wheelspin event. For example, the controller 110 may select one of a plurality of driving modes configured for the detected conditions. The controller 110 may engage a differential lock provided on one or more of the front and rear axles; and / or engage a central differential provided on the vehicle.

[0072] The controller 110 is configured to classify the wheelspin group indicator GSI as a cross-axle wheelspin event in dependence on the detection of a wheelspin event WSE(n) on wheels disposed on different axles on opposing sides of the vehicle 5 (while no wheelspin event WSE(n) is detected on the other wheels). The wheelspin group indicator GSI may indicate a cross-axle wheelspin event in dependence on the detection of wheelspin events WSE(1), WSE(4) on the right front wheel W1 and the left rear wheel W4 while there are no wheelspin events WSE(2), WSE(3) detected on the left front wheel W2 and the right rear wheel W3. Conversely, the wheelspin group indicator GSI may indicate a cross-axle wheelspin event in dependence on the detection of wheelspin events WSE(2), WSE(3) on the left front wheel W2 and the right rear wheel W3 while there are no wheelspin events WSE(1), WSE(4) detected on the rightfront wheel W1 and the left rear wheel W4. The determination of the wheelspin group indicator GSI as a cross-axle wheelspin event may indicate that the vehicle 5 is in a cross-axle situation where wheels on the opposing sides of the vehicle 5 on opposing axles are raised off the ground. The controller 110 may configure the one or more vehicle subsystem 21 in dependence on a determination that the wheelspin group indicator GSI represents a cross-axle wheelspin event. For example, the controller 110 may engage a differential lock to one or more of the front and rear axles; and / or may lock a central differential.

[0073] The controller 110 is configured to classify the wheelspin group indicator GSI as a front-axle wheelspin event in dependence on the detection of a wheelspin event WSE(n) on the front wheels W1 , W2 of the vehicle 5 (while no wheelspin event WSE(n) is detected on the rear wheels W3, W4). The wheelspin group indicator GSI may indicate a front-axle wheelspin event in dependence on the detection of wheelspin events WSE(1), WSE(2) on the right and left front wheels W1, W2 while there are no wheelspin events WSE(3), WSE(4) detected on the right and left rear wheels W3, W4. The determination of the wheelspin group indicator GSI as a front-axle wheelspin event may indicate that the front wheels W1, W2 are in contact with a surface having a low coefficient of friction. The controller 110 may configure the one or more vehicle subsystem 21 in dependence on a determination that the wheelspin group indicator GSI represents a front-axle wheelspin event. For example, the controller 110 may engage a central differential in dependence on a determination of the wheelspin group indicator GSI as a rear-axle wheelspin event.

[0074] The controller 110 is configured to classify the wheelspin group indicator GSI as a rear-axle wheelspin event in dependence on the detection of a wheelspin event WSE(n) on the rear wheels W3, W4 of the vehicle 5 (while no wheelspin event WSE(n) is detected on the front wheels W1 , W2). The wheelspin group indicator GSI may indicate a rear-axle wheelspin event in dependence on the detection of wheelspin events WSE(3), WSE(4) on the right and left rear wheels W3, W4 while there are no wheelspin events WSE(1 ), WSE(2) detected on the right and left front wheels W1, W2. The determination of the wheelspin group indicator GSI as a rear-axle wheelspin event may indicate that the rear wheels W3, W4 are in contact with a surface having a low coefficient of friction. The controller 110 may configure the one or more vehicle subsystem 21 in dependence on a determination that the wheelspin group indicator GSI represents a rear-axle wheelspin event. For example, the controller 110 may engage a central differential in dependence on a determination of the wheelspin group indicator GSI as a rear-axle wheelspin event.

[0075] The controller 110 is optionally configured to correct the determined acceleration of the or each wheel W1-W4 in dependence on a gradient a of a surface on which the vehicle 5 is operating. The gradient a corresponds to a pitch angle of a longitudinal axis X of the vehicle 5 relative to a (virtual) horizontal plane. In the present embodiment, the controller 110 is configured to implement a gradient estimator 160 to estimate the gradient a of the surface. An absolute value of the estimated gradient a is determined (referred to herein as the absolute gradient |a|). The absolute gradient |a| is then used to correct the determined acceleration of the or each wheel W1-W4. In a variant, the gradient estimator 160 may be implemented by a separate control unit. The operation of the gradient estimator 160 will now be described in more detail.

[0076] The gradient estimator 160 receives a longitudinal acceleration signal SLA(X) indicating a measured longitudinal acceleration LA(X) of the vehicle 5. The longitudinal acceleration signal SLA(X) represents the longitudinal acceleration LA(X) of the vehicle 5 measured along the longitudinal axis (x-axis). The longitudinal acceleration signal SLA(X) may be filtered to reduce noise. The vehicle longitudinal acceleration signal SLA(X) is received from an accelerometer 25 disposed on the longitudinal axis (x-axis) of the vehicle 5, as shown in Figure 2. The accelerometer 25 in the present embodiment is provided in an inertial measurement unit IMU of the vehicle 5. As described herein, the acceleration of each of the wheels W1-W4 is derived from the measured wheel speed of each of the wheels W1-W4. The gradient estimator 160 utilises the moving average a(n) of the wheel acceleration a(n) of each wheel W1-W4 to estimate thegradient a of the surface on which the vehicle 5 is operating. The graph 60 shown in Figure 4 shows traces 65A-D representing the wheel acceleration of each of the wheels W1-W4. A trace 65A’ represents the moving average a(1) of wheel acceleration of the first wheel W1.

[0077] The method 200 of detecting a wheelspin event SVE(n) will now be described with reference to a first block diagram shown in Figure 5. The method 200 will be described with reference to the detection of a wheelspin event SVE(1) on the first wheel W1. It will be understood that the method 200 is performed in respect of each of the wheels W1-W4.

[0078] The method 200 comprises receiving a wheel speed signal SLC(1) from the wheel speed sensor WS1 associated with the first wheel W1 (BLOCK 205). The wheel speed signal SLC(1) represents a measured wheel speed of the first wheel W1. A first derivative of the wheel speed is determined (BLOCK 210). The first derivative represents the instantaneous rate of change of the wheel speed of the first wheel W1 (i.e. the acceleration a(1) of the first wheel W1). The first derivative is calculated with a sample time of 10ms in the present embodiment. The sample time may be shorter than, or longer than 10ms. An absolute value |a|(1) of the first derivative is determined (BLOCK 215). The first derivative representing the acceleration of the first wheel W1 is output. As described herein, the acceleration of the first wheel W1 may optionally be corrected. A moving (rolling) average of the acceleration of the first wheel W1 is determined (BLOCK 220). The moving average a(1) represents the average of the acceleration of the first wheel W1 in a predetermined time period. A wheel acceleration threshold STH1 is obtained (BLOCK 225). The wheel acceleration threshold STH1 is predefined. The wheel acceleration threshold STH1 may, for example, be read from the storage device 130. The wheel acceleration threshold STH1 is calibratable. The wheel acceleration threshold STH1 defines an upper threshold for the moving average a(1) of the acceleration of the first wheel W1. A determination that the moving average a(1) of the acceleration of the first wheel W1 is greater than the wheel acceleration threshold STH1 indicates a wheelspin event WSE(1) at the first wheel W1. The method 200 comprises comparing the moving average a(1) of the acceleration of the first wheel W1 to the wheel acceleration threshold STH1 (BLOCK 230). The method 200 comprises detecting a wheelspin event SVE(1) at the first wheel W1 in dependence on a determination that the moving average a(1) of the acceleration is greater than or equal to (>) the wheel acceleration threshold STH1 (BLOCK 235). The method 200 may comprise detecting an absence of a wheelspin event SVE(1 ) at the first wheel W1 in dependence on a determination that the moving average a(1) of the acceleration is less than the wheel acceleration threshold STH1. The method 200 comprises outputting a first wheelspin event signal SWS(1) to indicate detection of a wheelspin event on the first wheel W1. The first wheelspin event signal SWS(1) functions as a flag or a marker to indicate detection of the wheelspin event WSE(1) on the first wheel W1.

[0079] The controller 110 may be configured to control the one or more vehicle subsystem 21 in dependence on the the detection of the wheelspin event WSE(1) on the first wheel W1. The controller 110 may select a different one of the plurality of drive modes 31 (n), for example to select a four-wheel drive mode. Alternatively, or in addition, the controller 110 may control the braking system 21 H to apply a braking (retardation) force to the first wheel W1 in dependence of detection of the wheelspin event WSE(1) at the first wheel W1. The application of a braking force to the or each spinning wheel W1-W4 promotes the delivery of torque to one or more of the other wheels W1-W4.

[0080] As outlined above, the method 200 may optionally comprise correcting the acceleration of the first wheel W1. The correction may, for example, be applied to account for gradient corruption. The gradient corruption occurs when the vehicle 5 is operating on a gradient, i.e. on a surface inclined at a positive (+ve) or negative (-ve) gradient a. The method 200 may comprise receiving a gradient signal indicating a gradient a of the surface on which the vehicle 5 is operating. Alternatively, the method 200 may comprise estimating thegradient a of the surface on which the vehicle 5 is operating (BLOCK 235). The gradient a may be represented as an absolute gradient H

[0081] A method 300 of determining the absolute gradient |a| of the vehicle 5 will now be described with reference to a second block diagram shown in Figure 6. The method 300 may be performed by the controller 110 or by a separate controller. The method 300 in the present embodiment is performed by a gradient estimator 160 implemented by the controller 110. The gradient estimator 160 outputs an estimate of the gradient a. The method 300 comprises receiving the wheel speed signals SWS(n) and determining a moving average a(n) of the wheel acceleration of each of the plurality of wheels W1-W4 (BLOCK 310). The controller 110 determines an absolute value of the moving average a(n) of each of the plurality of wheel accelerations (BLOCK 315). The method 300 comprises receiving the vehicle longitudinal acceleration signal SLA(X) indicating the longitudinal acceleration of the vehicle 5 (BLOCK 320). The vehicle longitudinal acceleration signal SLA(X) may, for example, be received from the longitudinal accelerometer 25 provided on the vehicle 5, for example in the inertial measurement unit IMU. The measured longitudinal acceleration LA(X) of the vehicle 5 is converted to an absolute vehicle longitudinal acceleration |a|(n) (BLOCK 325). The method 300 comprises comparing the absolute vehicle longitudinal acceleration and the absolute moving average |a|(n) of the acceleration a(n) of the wheels W1-W4 (BLOCK 330). Any difference (referred to herein as the “longitudinal acceleration difference”) between the absolute longitudinal acceleration and the absolute moving average |a|(n) of the acceleration a(n) of the wheels W1-W4 may be attributed to the gradient a of the surface on which the vehicle 5 is operating (when there is no wheelspin). The longitudinal acceleration difference can be used to estimate the gradient a of the surface. This could be performed using trigonometric inverse functions. In the present embodiment, however, the gradient a is estimated in terms of the percentage gravitational acceleration measured (Grav_A_Pt). Alternative techniques may utilise an angle or percentage height gain over distance. The controller 110 receives the percentage gravitational acceleration measured Grav_A_Pt (BLOCK 335). The longitudinal acceleration difference is multiplied by the percentage gravitational acceleration measured (Grav_A_Pt) (BLOCK 340). The product of the longitudinal acceleration difference and the percentage gravitational acceleration measured (Grav_A_Pt) is multiplied by a gain (K) to convert to a percentage value (BLOCK 345). Upper and lower limits are applied to restrict the percentage value to a predetermined operating range (BLOCK 450). The upper limit represents an upper saturation point for a positive gradient (+Ve) and the lower limit represents a lower saturation point for a negative gradient (-Ve). The upper and lower limits are defined to represent a realistic operating range for the vehicle 5. A low pass filter is applied to remove transient inputs (BLOCK 355). The transient inputs may, for example, occur as the vehicle 5 traverses a speed bump or a pothole. An absolute gradient value |cx| is determined in dependence on the gradient a(BLOCK 360). A saturation limit of one hundred (100) is applied to ensure that the determined absolute gradient |a| does not exceed 100% (BLOCK 365). The absolute gradient |a| is output (BLOCK 370).

[0082] The controller 110 is configured to correct the determined acceleration of each wheel W1-W4 in dependence on the absolute gradient |cx| determined by the gradient estimator 160.

[0083] A method 500 of generating a wheelspin group indicator will now be described with reference to a third block diagram shown in Figures 7A and 7B. The method 500 incorporates the method 200 of detecting a wheelspin event SVE(n) described herein. The method 500 may optionally comprise correcting the acceleration of the acceleration of the or each wheel W1-W4 for gradient corruption. The method 500 may, for example, utilise the method 300 described herein to determine the absolute gradient |a|.

[0084] The method 500 comprises determining a speed of each of the wheels W1-W4 (BLOCK 505). The wheel speeds are measured by the wheel speed sensors in the present embodiment. A derivative (i.e., an instantaneous rate of change) is determined for each wheelspeed. The derivative represents an acceleration of each wheel W1-W4 (referred to herein as the wheel acceleration). A moving average a(n) (or a rolling average) of each wheel acceleration is calculated to determine an absolute moving average |a|(n) of the acceleration a(n) of each wheel W1-W4 (BLOCK 510). The moving average a(n) is calculated over a predetermined time period. The determination of the moving average a(n) of each wheel acceleration helps to reduce or remove signal noise. Alternatively, or in addition, a low pass filter may be applied to reduce or remove noise from the wheel speed signals. In the present embodiment, the absolute moving average |a|(n) of the acceleration a(n) of each wheel W1-W4 is determined. The absolute moving average |a|(n) of the acceleration a(n) of each wheel W1-W4 is compared to a threshold TH1 (BLOCK 515). The threshold TH1 is calibratable, for example in dependence on empirical data. A wheelspin event WSE(n) is detected in dependence on a determination that the absolute moving average |a|(n) of the acceleration a(n) is greater than the threshold TH 1 (BLOCK 520). A wheelspin flag is generated to indicate detection of a wheelspin event WSE(n) on each wheel W1-W4. A comparator classifies a grouping of the detected wheelspin events WSE(n) (BLOCK 525). The comparator may, for example, classify the wheelspin events WSE(n) as representing one of the following: a cross-axle wheelspin event; a front-axle wheelspin event; a rear-axle wheelspin event; a four-wheelspin event; and a split-mu wheelspin event. The comparator outputs the wheelspin group indicator GSI (BLOCK 530).

[0085] The method 500 in the present embodiment comprises monitoring a dynamic operating state of the vehicle 5. The dynamic operating state may be characterised by one or more operating parameters. The dynamic operating state of the vehicle 5 in the present embodiment is characterised with respect to one or more of the following operating conditions: individual wheel speed(s) of the wheels W1-W4; an estimated velocity of the vehicle 5; and a longitudinal acceleration of the vehicle 5. The method 500 may optionally require that the, or each, operating parameter is within a predetermined operating range. This may define an entry condition for detecting a wheelspin event SVE(n). The monitoring of each of these operating parameters will now be described.

[0086] The measured wheel speed of each of the wheels W1-W4 is compared to a calibratable threshold (BLOCK 550). The comparison determines whether each wheel speed is within a predetermined wheel speed range. Each wheel speed is corrected for gradient corruption (BLOCK 555). The correction is performed in dependence on the gradient a of the surface on which the vehicle 5 is operating. The corrected wheel speeds are compared to one or more wheel speed threshold (BLOCK 560). The one or more wheel speed threshold may comprise an upper wheel speed threshold and / or a lower wheel speed threshold. The or each wheel speed threshold may be calibratable. In dependence on a determination that each wheel speed is within the wheel speed range, a flag is set to enable detection of a wheelspin event SVE(n) (BLOCK 565). The flag may function as an entry condition for detection of a wheelspin event SVE(n). The controller 110 is configured to detect a wheel speed event SVE(n) in dependence on a determination that the wheel speed is within a wheel speed range defined by the one or more wheel speed threshold. The detection of a wheel speed event SVE(n) may be enabled in dependence on a determination that each of the wheel speeds is less than the upper wheel speed threshold. The detection of a wheelspin event SVE(n) may be disabled or inhibited in dependence on a determination that one or more of the wheel speeds is outside the wheel speed range.

[0087] An absolute vehicle velocity Vref is determined (BLOCK 570). The absolute vehicle velocity Vref may, for example, be estimated in dependence on the measured wheel speeds. The absolute vehicle velocity is compared to one or more vehicle velocity threshold (BLOCK 575). The one or more vehicle velocity threshold may comprise a vehicle velocity upper threshold and / or a vehicle velocity lower threshold. The or each vehicle velocity threshold may be calibratable. In dependence on a determination that the vehicle velocity is within the vehicle velocity range, a flag is set to enable detection of a wheelspin event SVE(n) (BLOCK 565). The flag may function as an entry condition for detection of a wheelspin event SVE(n) . The controller 110 is configured to detect a wheel speed event SVE(n) in dependence on a determination that the vehicle velocity is within a vehicle velocity range defined by the one or more vehicle velocitythreshold. The detection of a wheel speed event SVE(n) may be enabled in dependence on a determination that the vehicle velocity is less than the vehicle velocity upper threshold. The detection of a wheelspin event SVE(n) may be disabled or inhibited in dependence on a determination that the vehicle velocity is outside the vehicle velocity range.

[0088] The longitudinal acceleration LA(X) of the vehicle 5 is measured by the accelerometer 25 disposed along a longitudinal axis (X-axis) of the vehicle 5 (BLOCK 580). An absolute value of the longitudinal acceleration LA(X) is determined (BLOCK 585). The longitudinal acceleration LA(X) is corrected for gradient corruption (BLOCK 555). The corrected longitudinal acceleration is compared to one or more longitudinal acceleration threshold (BLOCK 560). The one or more longitudinal acceleration threshold may comprise an upper longitudinal acceleration threshold and / or a lower longitudinal acceleration threshold. The or each longitudinal acceleration threshold may be calibratable. For example, a wheel speed event SVE(n) may be detected in dependence on a determination that the longitudinal acceleration is less than a lower longitudinal acceleration threshold. In dependence on a determination that the longitudinal acceleration is within the longitudinal acceleration range, a flag is set to enable detection of a wheelspin event SVE(n) (BLOCK 565). The flag may function as an entry condition for detection of a wheelspin event SVE(n). The controller 110 is configured to detect a wheel speed event SVE(n) in dependence on a determination that the longitudinal acceleration is within a longitudinal acceleration range defined by the one or more longitudinal acceleration threshold. The detection of a wheelspin event SVE(n) may be enabled in dependence on a determination that the longitudinal acceleration is within the predetermined longitudinal acceleration range. The detection of a wheelspin event SVE(n) may be disabled or inhibited in dependence on a determination that the longitudinal acceleration is outside the wheel speed range.

[0089] The boundary flag is generated in dependence on a determination that the wheel speeds, the vehicle velocity and the longitudinal acceleration are within the respective operating ranges. The boundary flag is supplied as an input to a wheelspin group indicator module 170 (BLOCK 600). A brake pedal signal SBP is received indicating a brake pedal position (BLOCK 605). The brake pedal signal SBP is received from a brake pedal sensor 27 for measuring a position of a brake pedal (not shown). A selected gear signal SGS is received indicating a current selected transmission gear (BLOCK 610). The selected gear signal SBP is received from a transmission controller 29 (shown schematically in Figure 3). A check is performed (BLOCK 615) to check that one or more of the following conditions is satisfied: (i) the boundary flag indicates that the wheel speeds, the vehicle velocity and the vehicle longitudinal acceleration are within the respective operating ranges; (ii) the brake pedal is not pressed; and (iii) the selected gear is not Park (i.e. a drive gear is selected). A calibratable delay is introduced (BLOCK 620). The wheelspin group indicator GSI is processed and the grouping of the wheels W1-W4 on which a wheelspin event SVE(n) is detected is evaluated (BLOCK 625). An entry / exit delay timer is introduced to control changes to the group spin indicator GSI (BLOCK 630). The entry / exit delay timer is calibratable for each of the wheelspin groupings. The wheelspin group indicator module sets the group spin indicator GSI (BLOCK 635). A wheelspin group indicator signal SGS is output indicated the wheelspin group indicator GSI (BLOCK 640).

[0090] The wheelspin group indicator module outputs the wheelspin group indicator signal to the gradient estimator 160 (BLOCK 650). A calibratable delay is optionally introduced (BLOCK 655). The absolute gradient |a| is estimated (BLOCK 660). The absolute gradient |cx| may, for example, be estimated using the method(s) described herein. The absolute gradient |a| may optionally be corrected in dependence on the operating state of the vehicle 5, as represented by the wheelspin group indicator GSI (BLOCK 665). The correction may be appropriate due to a corruption in the estimated gradient a. For example, when the wheel speed acceleration is greater than the measured longitudinal acceleration of the vehicle 5, the gradient estimation may become corrupted. The gradient estimator 160 may apply a gradient estimation correction (%) in dependence on detection of a wheelspin event SVE(n). The gradient estimation correction (%) may, for example, correspond to a value of the estimated gradient a determined before detection of the corruption. Independence on a determination that the wheelspin event SVE(n) is complete, the absolute gradient estimation (%) is used as a live (real-time) gradient estimator. A calibratable time delay may be applied after completion of the wheelspin event SVE(n) before changing to the absolute gradient estimation (%). A corrected absolute gradient |a| is output (BLOCK 670).

[0091] The corrected absolute gradient |a| is compared to one or more gradient threshold (BLOCK 675). The corrected absolute gradient |a| may, for example, be compared to an upper gradient threshold and / or a lower gradient threshold. The corrected absolute gradient |a| may be supplied as feedback for monitoring the operating state of the vehicle 5. The corrected absolute gradient |a| in the present embodiment is compared to a lower gradient threshold to determine if a correction of the longitudinal acceleration of the vehicle 5 is required. If the longitudinal acceleration is not corrected when the vehicle 5 is on a gradient, an incorrect (false) determination that the vehicle 5 is in a stuck condition may be generated. In the present embodiment, the corrected absolute gradient |a| is supplied to the operating state module to correct the wheel speeds and / or the longitudinal acceleration for gradient corruption (BLOCK 555).

[0092] The method 500 comprises outputting the wheelspin group indicator. The wheelspin group indicator may be output to the vehicle control unit VCU for controlling at least one vehicle subsystem 21 of the vehicle 5. For example, the vehicle control unit VCU may modify or control the operation of the at least one vehicle subsystem 21 in dependence on the wheelspin group indicator and / or detection of a wheelspin event SVE(n) at one or more wheel W1-W4.

[0093] The controller 110 is described herein as implementing the gradient estimator 160 to determine the gradient a. It will be understood that the gradient estimator 160 may be separate from the controller 110. For example, the gradient a may be estimated by another controller or subsystem provided on the vehicle 5. The gradient a may be estimated by an ABS braking system. The control system 1 described herein may be configured to receive a gradient signal indicating the gradient a.

[0094] One or more entry condition may be defined for detecting a wheel slip event WSE(n). The detection of the wheel slip event WSE(n) may be enabled / disabled in dependence on the one or more entry condition. The detection of a wheel slip event WSE(n) may be controlled in dependence on the entry condition(s) being satisfied. The output of the wheelspin event signal SWS(n) indicating detection of a wheelspin event WSE(n) may be inhibited in dependence on a determination that the one or more entry condition is not satisfied. One or more of the vehicle speed Vref and / or the vehicle longitudinal acceleration LA(X) may be used as an entry condition. For example, detection of the wheel slip event WSE(n) may be inhibited in dependence on a determination that the vehicle speed Vref is greater than a predetermined vehicle speed threshold. Alternatively, or in addition, detection of the wheel slip event WSE(n) may be inhibited in dependence on a determination that the vehicle longitudinal acceleration LA(X) is greater than a predetermined vehicle acceleration threshold.

[0095] The entry condition may also include an operating state of the transmission system 21 C and / or the braking system 21 E. Detection of the wheel slip event WSE(n) may be inhibited in dependence on a determination that the braking system 21 C is engaged, for example a parking brake or a friction brake is engaged. Alternatively, or in addition, detection of the wheel slip event WSE(n) may be inhibited in dependence on a determination that the transmission system 21 C is in a Park gear or Neutral. Detection of the wheel slip event WSE(n) may be enabled in dependence on a determination that the transmission system 21 C is in a driving gear.

[0096] It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

CLAIMS1. A control system for detecting a wheelspin event on a wheel of a vehicle; the control system comprising one or more processor collectively configured to:receive a wheel speed signal indicating a wheel speed of the wheel;determine an acceleration of the wheel in dependence on the wheel speed signal;determine a moving average of the acceleration of the wheel;detect a wheelspin event in dependence on a determination that the moving average of the acceleration of the wheel is greater than or equal to a wheel acceleration threshold; andoutput a wheelspin event signal indicating detection of a wheelspin event on the wheel.

2. A control system as claimed in claim 1 , wherein the wheel acceleration threshold is predefined.

3. A control system as claimed in claim 1 or claim 2, wherein the one or more processor is collectively configured to: determine a gradient of the surface on which the vehicle is operating; andcorrect the acceleration of the wheel in dependence on the determined gradient.

4. A control system as claimed in claim 3, wherein the one or more processor is collectively configured to output the wheelspin event signal in dependence on a determination that the gradient is less than a gradient threshold.

5. A control system as claimed in any one of claims 1 to 4, wherein the vehicle comprises a plurality of the wheels, the one or more processor being collectively configured to:repeat the detection of the wheelspin event in respect of each of the plurality of wheels; andoutput the wheelspin event signal to indicate detection of the wheelspin event at one or more of the plurality of wheels.

6. A control system as claimed in claim 5, wherein the one or more processor is collectively configured to:generate a wheelspin group indicator to identify a grouping of the or each wheel where the wheelspin event is detected.

7. A control system as claimed in claim 6, wherein the wheelspin group indicator identifies the grouping of the wheelspin events as an all-wheel wheelspin event in dependence on the detection of the wheelspin event) at each of the plurality of wheels.

8. A control system as claimed in claim 6 or claim 7, wherein the wheelspin group indicator identifies the grouping of the wheelspin events as a split-mu wheelspin event in dependence on the detection of the wheelspin event on the wheels on only one side of the vehicle.

9. A control system as claimed in any one of claims 6, 7 or 8, wherein the wheelspin group indicator identifies the grouping of the wheelspin events as a cross-axle wheelspin event in dependence on the detection of wheelspin events on wheels disposed on different axles and on opposing sides of the vehicle.

10. A control system as claimed in any one of claims 6 to 9, wherein the wheelspin group indicator identifies the grouping of the wheelspin events as at least one of the following:(i) a front-axle wheelspin event in dependence on the detection of the wheelspin events on each of the plurality of wheels on a front axle of the vehicle; and(ii) a rear-axle wheelspin event in dependence on the detection of the wheelspin events on each of the plurality of wheels on a rear axle of the vehicle.

11. A control system as claimed in any one of the preceding claims, wherein the one or more processor is collectively configured to detect the wheelspin event signal in dependence on a determination that one or more of the following entry conditions is satisfied:a vehicle speed is less than a vehicle speed threshold value;a vehicle longitudinal acceleration is less than a vehicle longitudinal acceleration threshold value;a braking system is not actuated; andtransmission system is in a drive gear.

12. A system comprising the control system of any one of the preceding claims and at least one vehicle control unit for controlling at least one vehicle subsystem of the vehicle, the at least one vehicle control unit being configured to modify the operation of the at least one vehicle subsystem in dependence on the wheelspin detected signal from the control system.

13. A system comprising the control system of any one of claims 1 to 11 and at least one vehicle control unit for selecting one of a plurality of vehicle drive modes, the vehicle drive modes each defining one or more operating parameter of at least one vehicle subsystem, wherein the at least one vehicle control unit is configured to select one of the plurality of vehicle drive modes in dependence on the wheelspin event signal from the control system.

14. A vehicle comprising a control system as claimed in any one of claims 1 to 11; ora system as claimed in claim 12 or claim 13.

15. A method of detecting a wheelspin event on a wheel of a vehicle; the method comprising:determine an acceleration of the wheel;determine a moving average of the acceleration of the wheel;compare the moving average of the acceleration of the wheel to a wheel acceleration threshold; anddetect the wheelspin event in dependence on a determination that the moving average of the acceleration of the wheel is greater than the wheel acceleration threshold.

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