WO2019134963A1

WO2019134963A1 - Controller and method

Info

Publication number: WO2019134963A1
Application number: PCT/EP2019/050151
Authority: WO
Inventors: David Armstrong; Elliot HEMES; William Burdock
Original assignee: Jaguar Land Rover Limited
Priority date: 2018-01-05
Filing date: 2019-01-04
Publication date: 2019-07-11
Also published as: GB201800159D0; GB2569974A; GB2569974B

Abstract

A vehicle controller configured to control a stiffness of a suspension system of a vehicle, the controller being configured to control the stiffness in dependence at least in part on the topology of terrain the vehicle is negotiating, the controller being configured to increase the stiffness of a portion of a suspension associated with a front wheel of the vehicle when it is determined that the following stiffness conditions are met: the vehicle is ascending a gradient in terrain; the controller determines that at least one off-road travel condition is met; and the controller determines that the vehicle has reached a crest in the terrain, the controller being configured to determine that the vehicle has reached a crest in the terrain when one or more crest conditions are met, the crest conditions including the condition that a portion of the suspension system associated with a front wheel of the vehicle has an extension of at least a predetermined amount of extension from the vehicle.

Description

CONTROLLER AND METHOD

TECHNICAL FIELD

The present disclosure relates to a controller and method. The present disclosure relates to a system for controlling a suspension system of a vehicle. In particular, but not exclusively, embodiments of the invention relate to a system for controlling a suspension system of a vehicle adapted for driving in an off-road environment.

Aspects of the invention relate to a vehicle controller, a vehicle, a method of controlling a suspension system of a vehicle, a non-transitory computer readable carrier medium, a computer program product and a processor.

BACKGROUND

When a user is driving off-road, variations in terrain height can be relatively abrupt and result in occupant discomfort as a vehicle negotiates the terrain. If the vehicle is travelling at too high a speed, damage to the vehicle may occur due for example to a suspension component such as a suspension arm abruptly reaching a limit of travel.

It is also known to provide a control system for a motor vehicle for controlling one or more vehicle subsystems. US7349776 discloses a vehicle control system comprising a plurality of subsystem controllers including an engine management system, a transmission controller, a steering controller, a brakes controller and a suspension controller. The subsystem controllers are each operable in a plurality of subsystem function or configuration modes. The subsystem controllers are connected to a vehicle mode controller which controls the subsystem controllers to assume a required function mode so as to provide a number of driving modes for the vehicle. Each of the driving modes corresponds to a particular driving condition or set of driving conditions, and in each mode each of the sub-systems is set to the function mode most appropriate to those conditions. Such conditions are linked to types of terrain over which the vehicle may be driven such as grass/gravel/snow, mud and ruts, rock crawl, sand and a highway mode known as‘special programs off (SPO). The vehicle mode controller may be referred to as a Terrain Response (TR) (RTM) System or controller. The driving modes may also be referred to as terrain modes, terrain response modes, or control modes.

GB2492655B discloses a control system for a motor vehicle in which the most appropriate terrain mode for the prevailing terrain over which the vehicle is driving is determined automatically by the control system. The control system then causes the vehicle to operate in the terrain mode determined to be the most appropriate.

It is against this background that the present invention has been conceived. Embodiments of the invention may provide an apparatus, a method or a vehicle which addresses the above problems. Other aims and advantages of the invention will become apparent from the following description, claims and drawings.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a vehicle controller, a vehicle, a method of controlling a suspension system of a vehicle, a non-transitory computer readable carrier medium, a computer program product and a processor as claimed in the appended claims.

In an aspect of the invention for which protection is sought there is provided a vehicle controller configured to control a stiffness of a suspension system of a vehicle, the controller being configured to control the stiffness in dependence at least in part on the topology of terrain the vehicle is negotiating, the controller being configured to increase the stiffness of a portion of a suspension associated with a front wheel of the vehicle when it is determined that the following stiffness conditions are met:

the vehicle is ascending a gradient in terrain;

the controller determines that at least one off-road travel condition is met; and the controller determines that the vehicle has reached a crest in the terrain, the controller being configured to determine that the vehicle has reached a crest in the terrain when one or more crest conditions are met, the crest conditions including the condition that a portion of the suspension system associated with a front wheel of the vehicle has an extension of at least a predetermined amount of extension from the vehicle.

It is to be understood that the predetermined amount may be a predetermined absolute amount, such as a position that corresponds to 50% of the amount of available travel of the wheel from a position of full upward travel. Alternatively the predetermined amount may be a predetermined amount in addition to the amount of extension prior to reaching the crest. Other arrangements may be useful in some alternative embodiments.

For example, in some embodiments the crest conditions for a head on approach may include the condition that a portion of the suspension system associated with each of the front wheels of the vehicle has an extension of at least a predetermined amount of extension relative to the rear wheels. In in some embodiments the crest conditions for a diagonal approach may include the condition that a portion of the suspension system associated with one front wheel of the vehicle has an extension of at least a predetermined amount of extension relative to the remaining wheels of the vehicle. Other arrangements may be useful.

Optionally, the stiffness conditions further include the condition that the vehicle speed exceeds a predetermined first speed value.

Optionally, the condition that the vehicle is ascending a gradient in terrain comprises the condition that the vehicle is ascending terrain having a gradient exceeding a first gradient value.

Optionally, the condition that at least one off-road travel condition is met includes the condition that terrain surface roughness is greater than a predetermined first roughness value.

Optionally, the condition that at least one off-road travel condition is met includes the condition that an off-road driving mode has been selected.

It is to be understood that the off-road driving mode may be a terrain response (TR) mode associated with off-road driving and not on-road driving. For example the vehicle may have one or more off-road driving modes such as a sand mode in which the vehicle is configured for driving over sand in addition to an‘on-highway’ or‘special programs off (SPO)’ driving mode, not being an off-road driving mode.

Optionally, the condition that at least one off-road travel condition is met includes the condition that an off-road driving mode has been selected in which the vehicle is configured for driving over sand.

Optionally, the controller is configured to determine that the one or more crest conditions further include the condition that a pitch attitude of the vehicle is changing in a direction from uphill to downhill as the portion of the suspension system associated with a front wheel extends to the predetermined amount of extension from the vehicle.

Optionally, the controller is configured to increase the stiffness of a portion of a suspension associated with a front wheel of the vehicle when, following the controller determining that the pitch attitude of the vehicle is changing in a direction from uphill to downhill as the portion of the suspension system associated with a front wheel extended to the predetermined amount of extension from the vehicle, the pitch rate of the vehicle in the direction from uphill to downhill exceeded a predetermined pitch rate.

The predetermined pitch rate may be 10 degrees per second in some embodiments.

Optionally, the controller may be configured to cause the amount of extension of the suspension of a front wheel to increase when the stiffness conditions are met.

Optionally, the controller may be further configured to determine whether the vehicle is negotiating a crest in terrain substantially head on, wherein if the controller determines that the vehicle is cresting substantially head on the controller increases the stiffness of the portion of the suspension associated with each front wheel of the vehicle.

Optionally, if the controller determines that the vehicle is cresting substantially head on the controller causes the amount of extension of the suspension of each front wheel to increase when the stiffness conditions are met.

This feature may be implemented in vehicles having suspension systems that allow positive extension by means of an actuator such as a motor or hydraulic fluid arrangement as opposed to passive systems which do not allow positive extension but do allow stiffness adjustment.

Optionally, the controller may be further configured to determine whether the vehicle is negotiating a crest in terrain substantially head on, wherein if the controller determines that the vehicle is not cresting the dune substantially head on, the controller increases the stiffness of the portion of the suspension associated with a leading front wheel of the vehicle and not a trailing front wheel.

It is to be understood that the leading front wheel is the higher of the front wheels, and therefore closest to the crest of the terrain.

Optionally, if the controller determines that the vehicle is cresting diagonally the controller causes the amount of extension of the suspension of the leading front wheel and not a trailing front wheel to increase when the stiffness conditions are met. Optionally, the controller may be configured to determine that the vehicle is cresting the terrain substantially head-on if the condition is met that a steering angle of the vehicle is within a predetermined angle of a straight-ahead condition, a time-averaged value of lateral acceleration is substantially zero and extension of the portions of the suspension system associated with left and right front wheels of the vehicle extend to at least the predetermined amount of extension within a predetermined distance of travel of the vehicle.

In some embodiments the predetermined steering angle is +/- 100 degrees of rotation of a steering wheel of the vehicle from a straight-ahead position and the predetermined distance of travel is 1 m. Other values of steering angle and distance of travel may be useful in some embodiments.

Optionally, the controller may comprise processing means, wherein the processing means comprises an electronic processor and an electronic memory device electrically coupled to the electronic processor and having instructions stored therein,

wherein the processor is configured to access the memory device and execute the instructions stored therein such that it is operable to control the stiffness of the suspension system of a vehicle, the controller being configured to control the stiffness in dependence at least in part on the topology of terrain the vehicle is negotiating, the controller being configured to increase the stiffness of a portion of a suspension associated with a front wheel of the vehicle when it is determined that the following stiffness conditions are met: the vehicle is ascending a gradient in terrain;

In an aspect of the invention for which protection is sought there is provided a vehicle comprising a controller according to another aspect.

In an aspect of the invention for which protection is sought there is provided a method of controlling a suspension system of a vehicle implemented by means of a controller,

the method comprising controlling the stiffness in dependence at least in part on the topology of terrain the vehicle is negotiating, the method comprising increasing the stiffness of a portion of a suspension associated with a front wheel of the vehicle when it is determined that the following stiffness conditions are met:

the vehicle is ascending a gradient in terrain;

the controller determines that at least one off-road travel condition is met; and the controller determines that the vehicle has reached a crest in the terrain, the method comprising determining that the vehicle has reached a crest in the terrain when one or more crest conditions are met, the crest conditions including the condition that a portion of the suspension system associated with a front wheel of the vehicle has an extension of at least a predetermined amount of extension from the vehicle.

In an aspect of the invention for which protection is sought there is provided a non-transitory computer readable carrier medium carrying computer readable code for controlling a vehicle to carry out the method of another aspect.

In an aspect of the invention for which protection is sought there is provided a computer program product executable on a processor so as to implement the method of another aspect.

In an aspect of the invention for which protection is sought there is provided a non-transitory computer readable medium loaded with the computer program product of another aspect.

In an aspect of the invention for which protection is sought there is provided a processor arranged to implement the method of another aspect, or the computer program product of another aspect.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF 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 is a schematic illustration of a vehicle according to an embodiment of the invention in plan view;

FIGURE 2 shows the vehicle of FIG. 1 in side view;

FIGURE 3 is a schematic illustration of a portion of a control system of the vehicle of FIG. 1 ;

FIGURE 4 is a schematic illustration of a steering wheel and pedals of the vehicle of FIG. 1 ;

FIGURE 5 is a schematic illustration of a vehicle negotiating a crest, showing (a) a vehicle approaching the crest of a dune approaching in the crest substantially‘head on’, i.e. along a path that is substantially normal to a crest line of the dune, and (b) a vehicle approaching the crest of the dune diagonal to the crest line of the dune; and

FIGURE 6 is a flow chart illustrating operation of a vehicle according to the embodiment of FIG. 1.

DETAILED DESCRIPTION

References herein to a block such as a function block are to be understood to include reference to software code for performing the function or action specified which may be an output that is provided responsive to or in dependence on one or more inputs. The code may be in the form of a software routine or function called by a main computer program, or may be code forming part of a flow of code not being a separate routine or function. Reference to function block is made for ease of explanation of the manner of operation of embodiments of the present invention.

FIG. 1 shows a vehicle 100 according to an embodiment of the present invention. The vehicle 100 has a powertrain 129 that includes an engine 121 that is connected to a driveline 130 having an automatic transmission 124. It is to be understood that embodiments of the present invention are also suitable for use in vehicles with manual transmissions, continuously variable transmissions or any other suitable transmission. In the embodiment of FIG. 1 the transmission 124 may be set to one of a plurality of transmission operating modes, being a park mode, a reverse mode, a neutral mode, a drive mode or a sport mode, by means of a transmission mode selector dial 124S. The selector dial 124S provides an output signal to a powertrain controller 1 1 in response to which the powertrain controller 1 1 causes the transmission 124 to operate in accordance with the selected transmission mode.

The driveline 130 is arranged to drive a pair of front vehicle wheels 1 1 1 ,1 12 by means of a front differential 137 and a pair of front drive shafts 1 18. The driveline 130 also comprises an auxiliary driveline portion 131 arranged to drive a pair of rear wheels 1 14, 1 15 by means of an auxiliary driveshaft or prop-shaft 132, a rear differential 135 and a pair of rear driveshafts 139.

Embodiments of the invention are suitable for use with vehicles in which the transmission 124 is arranged to drive only a pair of front wheels or only a pair of rear wheels (i.e. front wheel drive vehicles or rear wheel drive vehicles) or selectable two wheel drive/four wheel drive vehicles. In the embodiment of FIG. 1 the transmission 124 is releasably connectable to the auxiliary driveline portion 131 by means of a power transfer unit (PTU) 131 P, allowing operation in a two wheel drive mode or a four wheel drive mode. It is to be understood that embodiments of the invention may be suitable for vehicles having more than four wheels or where only two wheels are driven, for example two wheels of a three wheeled vehicle or four wheeled vehicle or a vehicle with more than four wheels.

As shown in FIG. 1 and FIG. 3, a control system for the vehicle 100 includes a central controller 10, referred to as a vehicle control unit (VCU) 10, the powertrain controller 1 1 , a brake controller 13 (in the form of an anti-lock braking system (ABS) controller), a steering controller 170C and a suspension system controller 191 C. The ABS controller 13 forms part of a braking system 22 (FIG. 3). The VCU 10 receives and outputs a plurality of signals to and from various sensors and subsystems (not shown) provided on the vehicle. The VCU 10 includes a low-speed progress (LSP) control system 12 shown in FIG. 3, a stability control system (SCS) 14, a cruise control system 16 and a hill descent control (HDC) system 12HD. The SCS 14 improves the safety of the vehicle 100 by detecting and managing loss of traction or steering control. When a reduction in traction or steering control is detected, the SCS 14 is operable automatically to command the ABS controller 13 to apply one or more brakes of the vehicle to help to steer the vehicle 100 in the direction the user wishes to travel. In the embodiment shown the SCS 14 is implemented by the VCU 10. In some alternative embodiments the SCS 14 may be implemented by the ABS controller 13. Although not shown in detail in FIG. 3, the VCU 10 further includes a Traction Control (TC) function block. The TC function block is implemented in software code run by a computing device of the VCU 10. The ABS controller 13 and TC function block provide outputs indicative of, for example, TC activity, ABS activity, brake interventions on individual wheels and engine torque requests from the VCU 10 to the engine 121 in the event a wheel slip event occurs. Each of the aforementioned events indicate that a wheel slip event has occurred. In some embodiments the ABS controller 13 implements the TC function block. Other vehicle sub-systems such as a roll stability control system or the like may also be included.

As noted above the vehicle 100 also includes a cruise control system 16 which is operable to automatically maintain vehicle speed at a selected speed when the vehicle is travelling at speeds in excess of 25 kph. The cruise control system 16 is provided with a cruise control HMI (human machine interface) 18 by which means the user can input a target vehicle speed to the cruise control system 16 in a known manner. In one embodiment of the invention, cruise control system input controls are mounted to a steering wheel 171 (FIG. 4). The cruise control system 16 may be switched on by pressing a cruise control system selector button 176. When the cruise control system 16 is switched on, depression of a‘set- speed’ control 173 sets the current value of a cruise control set-speed parameter, cruise_set-speed to the current vehicle speed. Depression of a V button 174 allows the value of cruise_set-speed to be increased whilst depression of a button 175 allows the value of cruise_set-speed to be decreased. A resume button 173R is provided that is operable to control the cruise control system 16 to resume speed control at the instant value of cruise_set-speed following driver over-ride. It is to be understood that known on-highway cruise control systems including the present system 16 are configured so that, in the event that the user depresses the brake or, in the case of vehicles with a manual transmission, a clutch pedal, control of vehicle speed by the cruise control system 16 is cancelled and the vehicle 100 reverts to a manual mode of operation which requires accelerator or brake pedal input by a user in order to maintain vehicle speed. In addition, detection of a wheel slip event, as may be initiated by a loss of traction, also has the effect of cancelling control of vehicle speed by the cruise control system 16. Speed control by the system 16 is resumed if the driver subsequently depresses the resume button 173R.

The cruise control system 16 monitors vehicle speed and any deviation from the target vehicle speed is adjusted automatically so that the vehicle speed is maintained at a substantially constant value, typically in excess of 25 kph. In other words, the cruise control system is ineffective at speeds lower than 25 kph. The cruise control HMI 18 may also be configured to provide an alert to the user about the status of the cruise control system 16 via a visual display of the HMI 18. In the present embodiment the cruise control system 16 is configured to allow the value of cruise_set-speed to be set to any value in the range 25- 150kph.

The LSP control system 12 also provides a speed-based control system for the user which enables the user to select a very low target speed at which the vehicle can progress without any pedal inputs being required by the user to maintain vehicle speed. Low-speed speed control (or progress control) functionality is not provided by the on-highway cruise control system 16 which operates only at speeds above 25 kph.

In the present embodiment, the LSP control system 12 is activated by pressing LSP control system selector button 178 mounted on steering wheel 171 . The system 12 is operable to apply selective powertrain, traction control and braking actions to one or more wheels of the vehicle 100, collectively or individually.

The LSP control system 12 is configured to allow a user to input a desired value of vehicle target speed in the form of a set-speed parameter, user set-speed, via a low-speed progress control HMI (LSP HMI) 20 (FIG. 1 , FIG. 3) which shares certain input buttons 173- 175 with the cruise control system 16 and HDC control system 12HD. Provided the vehicle speed is within the allowable range of operation of the LSP control system 12 (which is the range from 2 to 30kph in the present embodiment although other ranges are also useful) and no other constraint on vehicle speed exists whilst under the control of the LSP control system 12, the LSP control system 12 controls vehicle speed in accordance with a LSP control system set-speed value LSP_set-speed which is set substantially equal to userset- speed. Unlike the cruise control system 16, the LSP control system 12 is configured to operate independently of the occurrence of a traction event. That is, the LSP control system 12 does not cancel speed control upon detection of wheel slip. Rather, the LSP control system 12 actively manages vehicle behaviour when slip is detected.

The LSP control HMI 20 is provided in the vehicle cabin so as to be readily accessible to the user. The user of the vehicle 100 is able to input to the LSP control system 12, via the LSP HMI 20, the desired value of user set-speed as noted above by means of the‘set-speed’ button 173 and the‘+7 buttons 174, 175 in a similar manner to the cruise control system 16. The LSP HMI 20 also includes a visual display by means of which information and guidance can be provided to the user about the status of the LSP control system 12. The LSP control system 12 receives an input from the ABS controller 13 of the braking system 22 of the vehicle indicative of the extent to which the user has applied braking by means of the brake pedal 163. The LSP control system 12 also receives an input from an accelerator pedal 161 indicative of the extent to which the user has depressed the accelerator pedal 161 , and an input from the transmission or gearbox 124. This latter input may include signals representative of, for example, the speed of an output shaft of the gearbox 124, an amount of torque converter slip and a gear ratio request. Other inputs to the LSP control system 12 include an input from the cruise control HMI 18 which is representative of the status (ON/OFF) of the cruise control system 16, an input from the LSP control HMI 20, and an input from a gradient sensor 45 indicative of the gradient of the driving surface over which the vehicle 100 is driving. In the present embodiment the gradient sensor 45 is a gyroscopic sensor. In some alternative embodiments the LSP control system 12 receives a signal indicative of driving surface gradient from another controller such as the ABS controller 13. The ABS controller 13 may determine gradient based on a plurality of inputs, optionally based at least in part on signals indicative of vehicle longitudinal and lateral acceleration and a signal indicative of vehicle reference speed (v actual) being a signal indicative of actual vehicle speed over ground. Methods for the calculation of vehicle reference speed based for example on vehicle wheel speeds are well known. For example in some known vehicles the vehicle reference speed may be determined to be the speed of the second slowest turning wheel, or the average speed of all the wheels. Other ways of calculating vehicle reference speed may be useful in some embodiments, including by means of a camera device or radar sensor.

The HDC system 12HD is activated by depressing button 177 comprised by HDC system HMI 20HD and mounted on the steering wheel 171. When the HDC system 12HD is active, the system 12HD controls the braking system 22 in order to limit vehicle speed to a value corresponding to that of a HDC set-speed parameter HDC_set-speed which may be controlled by a user in a similar manner to the set-speed of the cruise control system 16 and LSP control system, using the same control buttons 173, 173R, 174, 175. The HDC system 12HD is operable to allow the value of HDC_set-speed to be set to any value in the range from 2-30kph. The HDC set-speed parameter may also be referred to as an HDC target speed. Provided the user does not override the HDC system 12HD by depressing the accelerator pedal 161 when the HDC system 12HD is active, the HDC system 12HD controls the braking system 22 (FIG. 3) to prevent vehicle speed from exceeding HDC_set-speed. In the present embodiment the HDC system 12HD is not operable to apply positive drive torque. Rather, the HDC system 12HD is only operable to cause negative brake torque to be applied, via the braking system 22.

It is to be understood that the VCU 10 is configured to implement a known Terrain Response (TR) (RTM) System of the kind described above in which the VCU 10 controls settings of one or more vehicle systems or sub-systems including the powertrain controller 1 1 in dependence on a selected driving mode. The driving mode may be selected by a user by means of a driving mode selector 141 S (FIG. 1 ). The driving modes may also be referred to as terrain modes, terrain response (TR) modes, or control modes. Further sub-systems under the control of the TR system include the suspension system controller 191 C, the SCS system and steering controller 170C. The suspension controller 191 C is configured to control an air suspension system 191 (FIG. 3) to allow vehicle ride height to be set to one of four settings corresponding to different heights of the vehicle 100 above level ground. It also allows a stiffness of the portion of the suspension system 191 associated with each wheel to be adjusted independently of one another by means of a magnetic ride control portion of the suspension system 191. Thus the suspension system 191 has a portion 191 FL configured to adjust the stiffness of the front left wheel 1 1 1 , a portion 191 FR configured to adjust the stiffness of the front right wheel 1 1 1 , a portion 191 RL configured to adjust the stiffness of the rear left wheel 1 14, and a portion 191 RR configured to adjust the stiffness of the rear right wheel 1 15. In each driving mode, the VCU 10 sets the value of ride height of the vehicle, and suspension stiffness of the front and rear portions 191 F, 191 R, to predetermined values associated with the selected driving mode.

In the embodiment of FIG. 1 four driving modes are provided: an‘on-highway’ driving mode suitable for driving on a relatively hard, smooth driving surface where a relatively high surface coefficient of friction exists between the driving surface and wheels of the vehicle; a ‘sand’ driving mode suitable for driving over sandy terrain, being terrain characterised at least in part by relatively high drag, relatively high deformability or compliance and relatively low surface coefficient of friction; a‘grass, gravel or snow’ (GGS) driving mode suitable for driving over grass, gravel or snow, being relatively slippery surfaces (i.e. having a relatively low coefficient of friction between surface and wheel and, typically, lower drag than sand); a ‘rock crawl’ (RC) driving mode suitable for driving slowly over a rocky surface; and a‘mud and ruts’ (MR) driving mode suitable for driving in muddy, rutted terrain. Other driving modes may be provided in addition or instead. In the present embodiment the selector 141 S also allows a user to select an‘automatic driving mode selection condition’ of operation in which the VCU 10 selects automatically the most appropriate driving mode as described in more detail below. The on-highway driving mode may be referred to as a‘special programs off (SPO) mode in some embodiments since it corresponds to a standard or default driving mode, and is not required to take account of special factors such as relatively low surface coefficient of friction, or surfaces of high roughness.

The LSP control system 12 causes the vehicle 100 to operate in accordance with the value of LSP_set-speed.

In order to cause application of the necessary positive or negative torque to the wheels, the VCU 10 may command that positive or negative torque is applied to the vehicle wheels by the powertrain 129 and/or that a braking force is applied to the vehicle wheels by the braking system 22, either or both of which may be used to implement the change in torque that is necessary to attain and maintain a required vehicle speed. In some embodiments torque is applied to the vehicle wheels individually, for example by powertrain torque vectoring, so as to maintain the vehicle at the required speed. Alternatively, in some embodiments torque may be applied to the wheels collectively to maintain the required speed, for example in vehicles having drivelines where torque vectoring is not possible. In some embodiments, the powertrain controller 1 1 may be operable to implement torque vectoring to control an amount of torque applied to one or more wheels by controlling a driveline component such as a rear drive unit, front drive unit, differential or any other suitable component. For example, one or more components of the driveline 130 may include one or more clutches operable to allow an amount of torque applied to one or more wheels to be varied. Other arrangements may also be useful.

Where a powertrain 129 includes one or more electric machines, for example one or more propulsion motors and/or generators, the powertrain controller 1 1 may be operable to modulate torque applied to one or more wheels in order to implement torque vectoring by means of the one or more electric machines.

In some embodiments the LSP control system 12 may receive a signal wheel_slip (also labelled 48 in FIG. 3) indicative of a wheel slip event having occurred. This signal 48 is also supplied to the on-highway cruise control system 16 of the vehicle, and which in the case of the latter triggers an override or inhibit mode of operation in the on-highway cruise control system 16 so that automatic control of vehicle speed by the on-highway cruise control system 16 is suspended or cancelled. However, the LSP control system 12 is not arranged to cancel or suspend operation on receipt of wheel_slip signal 48. Rather, the system 12 is arranged to monitor and subsequently manage wheel slip so as to reduce driver workload. During a slip event, the LSP control system 12 continues to compare the measured vehicle speed with the value of LSP_set-speed, and continues to control automatically the torque applied to the vehicle wheels (by the powertrain 129 and braking system 22) so as to maintain vehicle speed at the selected value. It is to be understood therefore that the LSP control system 12 is configured differently to the cruise control system 16, for which a wheel slip event has the effect of overriding the cruise control function so that manual operation of the vehicle must be resumed, or speed control by the cruise control system 16 resumed by pressing the resume button 173R or set-speed button 173.

The vehicle 100 is also provided with additional sensors (not shown) which are representative of a variety of different parameters associated with vehicle motion and status. These may be inertial systems unique to the LSP or HDC control systems 12, 12HD or part of an occupant restraint system or any other sub-system which may provide data from sensors such as gyros and/or accelerometers that may be indicative of vehicle body movement and may provide a useful input to the LSP and/or HDC control systems 12, 12HD. The signals from the sensors 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 terrain conditions over which the vehicle 100 is travelling.

The sensors (not shown) on the vehicle 100 include, but are not limited to, sensors which provide continuous sensor outputs to the VCU 10, including wheel speed sensors, as mentioned previously, suspension extension (i.e. the amount by which the suspension of each wheel is extended away from a reference position corresponding to an upper limit of travel of the wheel with respect to a body of the vehicle, the amount of extension also being referred to as wheel droop), an ambient temperature sensor, an atmospheric pressure sensor, tyre pressure sensors, wheel articulation sensors, gyroscopic sensors to detect vehicular yaw, roll and pitch angle and rate, a vehicle speed sensor, 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 which may be part of the SCS 14, a brake pedal position sensor, a brake pressure sensor, an accelerator pedal position sensor, longitudinal, lateral and vertical motion sensors, and water detection sensors forming part of a vehicle wading assistance system (not shown). In other embodiments, only a selection of the aforementioned sensors may be used.

The VCU 10 also receives a signal from the steering controller 170C. The steering controller 170C is in the form of an electronic power assisted steering unit (ePAS unit) 170C. The steering controller 170C provides a signal to the VCU 10 indicative of the steering force being applied to steerable road wheels 1 1 1 , 1 12 of the vehicle 100. This force corresponds to that applied by a user to the steering wheel 171 in combination with steering force generated by the ePAS unit 170C. The ePAS unit 170C also provides a signal indicative of steering wheel rotational position or angle.

In the present embodiment, the VCU 10 evaluates the various sensor inputs to determine the probability that each of the plurality of different TR modes (control modes or driving modes) for the vehicle subsystems is appropriate, with each control mode corresponding to a particular terrain type over which the vehicle is travelling (for example, mud and ruts, sand, grass/gravel/snow) as described above.

If the user has selected operation of the vehicle in the automatic driving mode selection condition, the VCU 10 then selects the most appropriate one of the control modes and is configured automatically to control the subsystems according to the selected mode. This aspect of the invention is described in further detail in our co-pending patent applications GB2492748, GB2492655 and GB2499279, the contents of each of which is incorporated herein by reference as noted above.

As indicated above, the nature of the terrain over which the vehicle is travelling (as determined by reference to the selected control mode) may also be utilised in the LSP control system 12 to determine an appropriate increase or decrease in vehicle speed. For example, if the user selects a value of user set-speed that is not suitable for the nature of the terrain over which the vehicle is travelling, the system 12 is operable to automatically adjust the value of LSP_set-speed to a value lower than user set-speed. In some cases, for example, the user selected speed may not be achievable or appropriate over certain terrain types, particularly in the case of uneven or rough surfaces. If the system 12 selects a set- speed (a value of LSP_set-speed) that differs from the user-selected set-speed userset- speed, a visual indication of the speed constraint is provided to the user via the LSP HMI 20 to indicate that an alternative speed has been adopted.

Other arrangements may be useful in some embodiments.

In the present embodiment, the VCU 10 is configured to detect cresting of a slope whilst travelling up a slope and to control suspension stiffness in response to the detection of cresting. In the present embodiment, the VCU 10 is configured to increase the stiffness of the portion of the suspension system 191 associated with one or both front wheels as the vehicle negotiates the crest of a slope, in dependence on whether the vehicle 100 is negotiating the crest head-on (perpendicular to the summit) or at an angle (diagonally) to the summit. Shown in fig. 5.

The VCU 10 is configured continually to check whether the following conditions are met in order to determine whether the vehicle 100 may be cresting a slope:

(1 ) the gradient of the driving surface exceeds a predetermined minimum gradient value, grad_min, which in the present embodiment is 20% although other values of grad_min may be useful such as 10%, 15%, 25% or any other suitable value;

(2) vehicle speed v actual has a value from a predetermined minimum speed value speed_min to a predetermined maximum speed value speed_max.

(3) terrain surface roughness has a value exceeding a predetermined minimum roughness value rough min, road roughness being determined by reference to suspension excitation (i.e.‘up and down’ movement of wheel suspension as the vehicle moves over a surface).

(4) the vehicle 100 is operating in a driving mode other than the‘SPO off or‘highway’ driving mode, indicating that the vehicle 100 is driving in an off-road environment. In some embodiments, the VCU 10 only checks whether the‘sand’ mode is selected; if the sand mode is not selected the VCU 10 determines that the vehicle 100 is not driving in an off road environment.

(5) a rapid change of direction of vehicle pitch is taking place from‘uphill’ pitch to‘downhill’ pitch, i.e. the vehicle is experiencing a net change in pitch attitude from an upward pitch attitude to a downward pitch attitude, at a rate exceeding a predetermined minimum rate rate_min. In the present embodiment the value of rate_min is 10 degrees per second although other values may be useful in some alternative embodiments.

(6) one or both front wheels of the vehicle are experiencing an amount of extension (droop) exceeding a predetermined minimum amount extension min. In the present embodiment extension min is 50% although other values may be useful.

(7) An error between lateral acceleration and vehicle steering angle exceeds a critical amount of steering error consistent with ascent of a slope at a diagonal angle. It is to be understood that conditions (5) and (6) are indicative that the vehicle 100 has reached a crest in the terrain. Condition (7) is indicative that the vehicle is negotiating the hill in a diagonal manner, i.e. not‘head on’. It is to be understood that diagonal negotiation may be preferred in some situations in order to enhance driver visibility of obstacles ahead of the vehicle 100 that may be obscured by the terrain. In addition diagonal negotiation may reduce the likelihood of the vehicle becoming“beached” (or“grounded”) on the crest of the hill, which may for example be a sand dune.

FIG. 6 shows ten traces of parameters associated with the vehicle 100 as a function of time before, during and after cresting a dune in a diagonal manner, i.e. not substantially head on.

Traces T1 to T10 are as follows: T1 - vehicle speed (kph); T2 - accelerator pedal position (percent of full travel); T3 - steering wheel angle; T4 - longitudinal acceleration (m/s/s); T5 - lateral acceleration (m/s/s); T7 - front left (FL) suspension height (distance of travel upwardly from a lowest allowable position); T8 - front right (FR) suspension height; and T9 - rear left (RL) suspension height; and T10 - rear right (RR) suspension height.

In the traces shown, the vehicle is ascending a slope with a diagonal approach to the left to the crest of the slope. That is, as the vehicle ascends the slope, the front right wheel is leading whilst the left-hand side of the vehicle is lower down the slope. At time t=5s (indicated t1 in FIG. 6) the vehicle passes over the crest of the slope. The direction of lateral acceleration (trace T5) reverses coincident with roll over the top of the crest. It can be seen that diagonally opposing front left (FL), and rear right wheels are aligned with respect to suspension travel (traces T7 and T10, respectively) prior to reaching the crest.

In the present embodiment, if conditions (1 ) to (6) are met and condition (7) is not met, with condition (6) including the condition that both front wheels of the vehicle 100 are experiencing amounts of extension exceeding extension min, the VCU 10 determines that the vehicle 100 is cresting a hill‘head on’. In response to these conditions being met, the VCU 10 causes the portions of the suspension system 191 controlling the stiffness of the front left and front right wheels, portions 191 FL and 191 FR, to increase the stiffness of the respective portions. This has the result that, once the vehicle 100 has negotiated the crest of the terrain and the amount of vehicle weight borne by the front wheels 1 1 1 , 1 12 increases again as the vehicle pitch attitude lowers, a risk of damage to the suspension system 191 due to the wheels abruptly reaching an upper limit of travel of the portion of the suspension system 191 associated with the front wheels 1 1 1 , 1 12 is reduced. Furthermore, a risk of damage to a portion of the vehicle 100 other than the suspension system 191 such as to a portion of the undercarriage of the vehicle 100, engine sump or front bumper may be reduced. It is to be understood that increasing suspension stiffness will tend to reduce the rate of travel of the suspension upwardly when the amount of weight on the corresponding wheel is increased, and potentially the total amount of upward travel depending on the subsequent steady state loading on the suspension system 191.

It is to be understood that if conditions (1 ) to (7) are met, the VCU 10 is configured to cause the portion of the suspension system 191 controlling the stiffness of the leading front wheel 1 1 1 , 1 12, i.e. the left portion 191 FL or right portion 191 FR, to increase the stiffness of that portion. Thus if the VCU 10 is ascending a hill diagonally to the left, the leading front wheel is the front right wheel. Conversely, if the VCU 10 is ascending a hill diagonally to the right, the leading front wheel is the front left wheel. This has the result that, once the vehicle 100 has negotiated the crest of the terrain and the amount of vehicle weight borne by the front leading wheel 1 1 1 , 1 12 increases as the vehicle pitch attitude lowers, there is a reduced risk of damage to the suspension system 191 due to the leading wheel (which will tend to bear a greater portion of the weight of the vehicle 100 as the loading on the suspension system 191 associated with the front wheels 1 1 1 , 1 12 increases following cresting) abruptly reaching an upper limit of travel of the portion of the suspension system 191 associated with that front wheel 1 1 1 , 1 12. Furthermore, a risk of damage to a portion of the vehicle 100 other than the suspension system 191 such as to a portion of the undercarriage of the vehicle 100, engine sump or front bumper may be reduced.

In some embodiments, the suspension system 191 may be a fully active suspension system 191 in which an actuator forms part of the portion of the suspension system 191 associated with each wheel and permits the amount of extension of each portion of the suspension system 191 to be increased (or decreased) as required.

In some embodiments having a fully active suspension system 191 , in addition to increasing the stiffness of one or both portions of the suspension system 191 associated with the front left and right wheels 1 1 1 , 1 12, the VCU 10 is configured to extend the suspension system to the maximum permitted extension amount and subsequently to increase the stiffness of the relevant portion(s) of the suspension system. Thus, in the event the vehicle 100 is negotiating a hill head-on and the VCU 10 determines that the conditions are met for negotiating a crest‘head on’ as described above, the VCU 10 causes the portion of the suspensions system 191 associated with each of the front wheels 1 1 1 , 1 12 to be extended and increased in stiffness. In the event the vehicle 100 is negotiating a hill diagonally and the VCU 100 determines that the conditions are met for negotiating a crest diagonally as described above, the VCU 10 causes the portion of the suspensions system 191 associated with only the leading front wheel 1 1 1 , 1 12 to be extended and increased in stiffness.

It is to be understood that other arrangements may be useful in some embodiments.

In some embodiments, the VCU 10 may monitor the rotational acceleration of each of the front wheels 1 1 1 , 1 12 and require that the condition is met that the rotational acceleration of both front wheels (in the case of negotiating a hill head on) or the leading wheel 1 1 1 , 1 12 (in the case of negotiating a hill diagonally) exceeds a predetermined value rot_acc_min relative to the other wheels of the vehicle in addition to the conditions described above, before triggering suspension stiffness adjustment (or stiffness and extension adjustment in the case of fully active suspension systems).

In some embodiments, the VCU 10 may receive information generated by one or more forward-looking sensor systems in order to confirm the profile (or topography) of terrain ahead of the vehicle 100. This may increase the probability that the VCU 10 adjusts the stiffness and optionally the extension of the portion of the suspension associated with one or both front wheels of the vehicle 100. For example, a crest detection system employing a video camera, radar or lidar-based sensor system may be employed to provide an input to the VCU 10, such as an input indicative of a distance of the vehicle 100 from the crest of a hill where a crest is detected. Other arrangements may be useful in some embodiments.

Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example“comprising” and“comprises”, means “including but not limited to”, and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims

1. A vehicle controller configured to control a stiffness of a suspension system of a vehicle, the controller being configured to control the stiffness in dependence at least in part on the topology of terrain the vehicle is negotiating, the controller being configured to increase the stiffness of a portion of a suspension associated with a front wheel of the vehicle when it is determined that the following stiffness conditions are met:

the vehicle is ascending a gradient in terrain;

2. A controller according to claim 1 wherein the stiffness conditions include the condition that the vehicle speed exceeds a predetermined first speed value.

3. A controller according to claim 1 or claim 2 wherein the condition that the vehicle is ascending a gradient in terrain comprises the condition that the vehicle is ascending terrain having a gradient exceeding a first gradient value.

4. A controller according to any preceding claim wherein the condition that at least one off-road travel condition is met includes the condition that terrain surface roughness is greater than a predetermined first roughness value.

5. A controller according to any preceding claim wherein the condition that at least one off-road travel condition is met includes the condition that an off-road driving mode has been selected.

6. A controller according to claim 5 wherein the condition that at least one off-road travel condition is met includes the condition that an off-road driving mode has been selected in which the vehicle is configured for driving over sand.

7. A controller according to any preceding claim wherein the controller is configured to determine that the one or more crest conditions include the condition that a pitch attitude of the vehicle is changing in a direction from uphill to downhill as the portion of the suspension system associated with a front wheel extends to the predetermined amount of extension from the vehicle.

8. A controller according to claim 7 wherein the controller is configured to increase the stiffness of a portion of a suspension associated with a front wheel of the vehicle when, following the controller determining that the pitch attitude of the vehicle is changing in a direction from uphill to downhill as the portion of the suspension system associated with a front wheel extended to the predetermined amount of extension from the vehicle, the pitch rate of the vehicle in the direction from uphill to downhill exceeded a predetermined pitch rate.

9. A controller according to any preceding claim configure to cause the amount of extension of the suspension of a front wheel to increase when the stiffness conditions are met.

10. A controller according to any preceding claim configured to determine whether the vehicle is negotiating a crest in terrain substantially head on, wherein if the controller determines that the vehicle is cresting substantially head on the controller increases the stiffness of the portion of the suspension associated with each front wheel of the vehicle.

1 1 . A controller according to claim 10 as dependent on claim 9 wherein if the controller determines that the vehicle is cresting substantially head on the controller causes the amount of extension of the suspension of each front wheel to increase when the stiffness conditions are met.

12. A controller according to any one of claims 1 to 9 configured to determine whether the vehicle is negotiating a crest in terrain substantially head on, wherein if the controller determines that the vehicle is not cresting the dune substantially head on, the controller increases the stiffness of the portion of the suspension associated with a leading front wheel of the vehicle and not a trailing front wheel.

13. A controller according to claim 12 as dependent on claim 9 wherein if the controller determines that the vehicle is cresting diagonally the controller causes the amount of extension of the suspension of the leading front wheel and not a trailing front wheel to increase when the stiffness conditions are met.

14. A controller according to any one of claims 10 to 13 wherein the controller is configured to determine that the vehicle is cresting the terrain substantially head-on if the condition is met that a steering angle of the vehicle is within a predetermined angle of a straight-ahead condition, a time-averaged value of lateral acceleration is substantially zero and extension of the portions of the suspension system associated with left and right front wheels of the vehicle extend to at least the predetermined amount of extension within a predetermined distance of travel of the vehicle.

15. A vehicle controller according to any preceding claim comprising processing means, wherein the processing means comprises an electronic processor and an electronic memory device electrically coupled to the electronic processor and having instructions stored therein, wherein the processor is configured to access the memory device and execute the instructions stored therein such that it is operable to control the stiffness of the suspension system of a vehicle, the controller being configured to control the stiffness in dependence at least in part on the topology of terrain the vehicle is negotiating, the controller being configured to increase the stiffness of a portion of a suspension associated with a front wheel of the vehicle when it is determined that the following stiffness conditions are met: the vehicle is ascending a gradient in terrain;

16. A vehicle comprising a controller according to any preceding claim.

17. A method of controlling a suspension system of a vehicle implemented by means of a controller,

the vehicle is ascending a gradient in terrain;

18. A non-transitory computer readable carrier medium carrying computer readable code for controlling a vehicle to carry out the method of claim 17.

19. A computer program product executable on a processor so as to implement the method of claim 17.

20. A non-transitory computer readable medium carrying computer readable code which when executed causes a vehicle to carry out the method of claim 17.

21 . A processor arranged to implement the method of claim 17, or the computer program product of claim 19.