GB2552661B

GB2552661B - Vehicle levelling method and apparatus

Info

Publication number: GB2552661B
Application number: GB1613217.7A
Authority: GB
Inventors: Spirine Pavel
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2016-08-01
Filing date: 2016-08-01
Publication date: 2019-08-28
Anticipated expiration: 2036-08-01
Also published as: GB201613217D0; GB2552661A

Description

VEHICLE LEVELLING METHOD AND APPARATUS

TECHNICAL FIELD

The present disclosure relates to vehicle levelling method and apparatus. Particularly, but not exclusively, the present disclosure relates to a vehicle which is self-levelling and to a related controller. The present disclosure also relates to a method of controlling a vehicle suspension to level the vehicle. Aspects of the invention relate to a vehicle, to a controller and to a method.

BACKGROUND A vehicle, such as an automobile, a sports utility vehicle (SUV) or an off-road vehicle, may occasionally be used as a temporary base, for example for a picnic or as a seating platform. Items, such as cups, plates and bottles, may be placed in a load bay or the vehicle, on a tailgate or on external surfaces (such as a bonnet or a roof). Individuals may also wish to sit on these portions of the vehicle. If the vehicle is parked on an uneven or an inclined surface, such as a field, the surfaces of the vehicle are likely also to be inclined and this may prove problematic due to an increased risk of toppling, spillage and general inconvenience. In certain scenarios, parking a vehicle on an incline may make loading/unloading of the vehicle more difficult. Furthermore, if the vehicle is a motorhome, an incline may make it more difficult or uncomfortable for anyone wishing to sleep in the vehicle.

It is known to provide vehicles with an adjustable suspension, for example an air suspension. The suspension can be controlled to level the load bay, for example to compensate for different loadings. Current systems level the load bay by adjustment of the rear axle in relation to the front axle, to reduce a pitch angle of the vehicle. The height or pressure in the air springs may be adjusted to maintain bump and rebound travel for dynamic conditions. The systems may, for example, measure wheel travel height at each corner. The suspension is adjusted such that the wheel travel height is substantially the same on the front and rear axles of the vehicle. Thus, the orientation of the load bay is adjusted so as to be substantially parallel to the road. This is appropriate when the vehicle is in motion, but does not overcome the aforementioned problems when the vehicle is parked on an uneven or an inclined surface.

It is against this backdrop that the present invention has been conceived. At least in certain embodiments, the present invention seeks to provide a self-levelling vehicle.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a vehicle, to a controller and to a method as claimed in the appended claims.

According to one embodiment there is provided a vehicle comprising: a body; a plurality of suspension units mounted to the body and associated with respective wheels of the vehicle, one or more of said suspension units comprising at least one adjustable actuator; means for sensing a pitch angle and/or a roll angle of the body relative to an absolute horizontal plane; a control unit comprising at least one processor configured to receive a pitch angle signal and/or a roll angle signal from said sensing means; and a memory device connected to the at least one processor; wherein, in dependence on said pitch signal and/or said roll signal, the at least one processor is configured to output a control signal to control one or more of said adjustable actuators to reduce the magnitude of the pitch angle and/or the magnitude of the roll angle of the body. The pitch angle and/or the roll angle are measured relative to said absolute horizontal plane. By controlling the actuators to reduce the magnitude of the pitch angle and/or the magnitude of the roll angle, the vehicle can be self-levelling such that the body is oriented substantially parallel to said absolute horizontal plane. The at least one adjustable actuator may controllably adjust the vertical extent of the suspension unit, thereby raising or lowering the suspension unit. The at least one adjustable actuator is operable to controllably adjust the height of the body relative to the associated wheel (which, in normal use, remains in contact with the ground). By adjusting the body height proximal to each said suspension unit, the pitch angle and/or the roll angle of the body may be controllably adjusted.

The body has a reference frame comprising a longitudinal axis, a transverse axis and a vertical axis. The pitch angle is the inclination angle of the longitudinal axis of the body relative to a horizontal plane. The roll angle is the inclination angle of the transverse axis of the body relative to a horizontal plane.

The at least one processor may be configured to output said control signal to control one or more of said adjustable actuators to reduce the magnitude of the pitch angle and/or the magnitude of the roll angle of the body at least substantially to zero. When the pitch angle is zero the longitudinal axis is disposed in the absolute horizontal plane. When the roll angle is zero, the transverse axis is disposed in the absolute horizontal plane. When the pitch angle and the roll angle are zero, the vertical axis of the body is disposed perpendicular to said absolute horizontal plane.

The control unit may be configured to implement self-levelling only while the vehicle is stationary or at low speeds, say less than 10km/h. The control unit may be configured to utilise at least substantially the full travel of the suspension units to level the vehicle. It has been recognised that the full extent of the bump/rebound travel may be used since the vehicle will be stationary.

The at least one processor may be configured to output said control signal to control one or more of said adjustable actuators only when the vehicle is stationary or the vehicle speed is below a predefined speed threshold. The at least one processor may be configured to receive a vehicle speed signal to determine the vehicle speed.

The at least one processor may be configured to output said control signal to control one or more of said adjustable actuators only when a vehicle parking brake is engaged.

The at least one processor may be configured to output said control signal in dependence on a level request signal. The level request signal may be user-generated. The level request signal may be generated when a control interface is operated. The control interface may, for example, comprise a button or a switch disposed in an occupant compartment and/or a load bay of the vehicle. Alternatively, or in addition, the level request signal may be generated by a remote transmitter, such as a cellular telephone or a remote access device, such as a keyfob.

The sensing means may comprise at least one pitch angle sensor and/or at least one roll angle sensor. The sensing means may comprise one or more accelerometer. Alternatively, or in addition, the sensing means may comprise one or more inclinometer.

The at least one processor may be configured to reduce the magnitude of the pitch angle by outputting said control signal to control one or more of said adjustable actuators to adjust the suspension unit(s) disposed at a front of the vehicle and / or at a rear of the vehicle. The at least one processor may be configured to reduce the magnitude of the pitch angle by outputting said control signal to control one or more of said adjustable actuators to raise the suspension unit(s) disposed at a front of the vehicle or at a rear of the vehicle. The at least one processor may be configured to reduce the magnitude of the pitch angle by outputting said control signal to control one or more of said adjustable actuators to raise the suspension unit(s) disposed at a front of the vehicle and to lower the suspension unit(s) disposed at a rear of the vehicle; or to lower the suspension unit(s) disposed at a front of the vehicle and to raise the suspension unit(s) disposed at a rear of the vehicle.

The at least one processor may be configured to reduce the magnitude of the roll angle by outputting said control signal to adjust the suspension unit(s) disposed on a left side of the vehicle and / or on a right side of the vehicle. The at least one processor may be configured to reduce the magnitude of the roll angle by outputting said control signal to raise the suspension unit(s) disposed on a left side of the vehicle or on a right side of the vehicle. The at least one processor may be configured to reduce the magnitude of the roll angle by outputting said control signal to lower the suspension unit(s) disposed on a left side of the vehicle and to raise the suspension unit(s) disposed on a right side of the vehicle.

The at least one processor may be configured to reduce the magnitude of the roll angle by outputting said control signal to raise the suspension unit(s) disposed on a left side of the vehicle and to lower the suspension unit(s) disposed on a right side of the vehicle.

The at least one processor may be configured to prioritise changes which lower one or more of the suspension unit over changes which raise one or more of the suspension unit. This control strategy may help to reduce operation of the at least one adjustable actuator associated with each suspension unit.

In alternative embodiments, the at least one processor may be configured to prioritise changes which raise one or more of the suspension unit over changes which lower one or more of the suspension unit. This control strategy may help to maintain ground clearance.

Each adjustable actuator may comprise a linear actuator. An extension of the linear actuator may be controllably adjusted to adjust the suspension unit. For example, the linear actuator may be extended to raise the suspension unit; and retracted to lower the suspension unit. It will be understood that this arrangement may be reversed depending on the mounting arrangement of the actuator.

Each adjustable actuator may comprise an air spring and at least one control valve. The at least one control valve is operable to control the supply of high pressure air to and from the air spring. The at least one control valve may be operable in dependence on said control signal to vent compressed air from the air spring to lower that suspension unit. The air spring may be connected to a high pressure air supply, for example comprising a compressor and/or a reservoir.

In alternate embodiments, the adjustable actuators may comprise hydraulic or electromechanical actuators. For example, the adjustable actuators could comprise a linear actuator, for example comprising a leadscrew.

According to a further embodiment there is provided a controller for controlling at least one suspension unit to reduce the magnitude of a pitch angle and/or the magnitude of a roll angle of a body of a vehicle, the controller comprising: at least one processor configured to receive a pitch angle signal comprising a pitch angle of the body relative to an absolute horizontal plane; and/or to receive a roll angle signal comprising a roll angle of the body relative to an absolute horizontal plane; and a memory device connected to the at least one processor; wherein, in dependence on said pitch signal and/or said roll signal, the at least one processor is configured to generate a control signal to control the at least one suspension unit to reduce the magnitude of the pitch angle and/or the magnitude of the roll angle of the body. The at least one processor may be configured to output said control signal to reduce the magnitude of the pitch angle and/or the magnitude of the roll angle of the body at least substantially to zero.

The at least one processor may be configured to output said control signal only when the vehicle is stationary or the vehicle speed is below a predefined speed threshold.

The at least one processor may be configured to output said control signal in dependence on a level request signal.

The at least one processor may be configured to receive said pitch angle signal from at least one pitch angle sensor; and/or to receive said roll angle signal from at least one roll angle sensor.

The at least one processor may be configured to receive said pitch angle signal and/or said roll angle signal from one or more inclinometer or accelerometer.

The at least one processor may be configured to reduce the magnitude of the pitch angle by outputting said control signal to control the suspension unit(s) disposed at a front of the vehicle or at a rear of the vehicle.

The at least one processor may be configured to reduce the magnitude of the roll angle by outputting said control signal to control the suspension unit(s) disposed on a left side of the vehicle or on a right side of the vehicle.

The at least one processor may be configured to prioritise changes which lower one or more of the suspension unit over changes which raise one or more of the suspension unit.

The at least one processor may be configured to output said control signal to control actuators associated with said suspension units.

According to a further embodiment there is provided a method of controlling at least one suspension unit to reduce the magnitude of a pitch angle and/or the magnitude of a roll angle of a body of a vehicle, the method comprising: measuring the pitch angle and/or the roll angle relative to an absolute horizontal plane; and adjusting the at least one suspension unit in dependence on the measured pitch angle and/or the measured roll angle to reduce the magnitude of the pitch angle and/or the magnitude of the roll angle of the body.

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

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

Figure 1 shows a schematic representation of a self-levelling vehicle in accordance with an embodiment of the present invention;

Figure 2 shows a schematic representation of a rear elevation of the self-levelling vehicle shown in Figure 1; and

Figure 3 shows a schematic representation of a side elevation of the self-levelling vehicle shown in Figure 1.

DETAILED DESCRIPTION A vehicle 1 in accordance with an embodiment of the present invention will now be described with reference to the accompanying figures. The vehicle 1 in the present embodiment is an automobile, but it will be understood that the present invention is applicable to other vehicle types. As described herein, the vehicle 1 comprises a controller 2 for levelling the vehicle 1.

With reference to Figure 1, the vehicle 1 comprises a body 3 and four wheels 4-n (where n is an integer from 1 to 4 inclusive to identify each wheel). The body 3 comprises an occupant compartment 5 and a load bay 6 having a tailgate 7. The vehicle 1 has two front wheels 4-1, 4-2; and two rear wheels 4-3, 4-4. In the present embodiment the wheels 4-n are all driven by an internal combustion engine (not shown). In alternate embodiments, either the front wheels 4-1,4-2 or the rear wheels 4-3,4-4 may be driven. The body 3 has a reference frame (denoted generally by the reference numeral 8) and the orientation of the body 3 is defined herein in terms of the angular orientation of the reference frame 8 relative to an absolute horizontal plane PXY. The reference frame 8 comprises a longitudinal axis X, a transverse axis Y and a vertical axis Z. It will be understood that the orientation of the body 3 is dependent on multiple factors, including vehicle loading and local topography, such as ground incline. The angular rotation of the body 3 about the longitudinal axis X is referred to herein as a “roll angle” (denoted generally by the symbol (β)); and the angular rotation of the body 3 about the transverse axis Y is referred to herein as a “pitch angle” (denoted generally by the symbol (a)).

The roll angle (β) of the body 3 is illustrated in Figure 2; and the pitch angle (a) is illustrated in Figure 3.

The vehicle 1 comprises a suspension (denoted generally by the reference numeral 9) having four suspension units 9-n mounted to the body 3. The suspension units 9-n are each associated with a respective one of said wheels 4-n of the vehicle 1. First and second suspension units 9-1, 9-2 are associated with the front wheels 4-1,4-2; and third and fourth suspension units 9-3, 9-4 are associated with the rear wheels 4-3, 4-4. The suspension units 9-n each comprise a controllable actuator 10-n. The actuators 10-n are each adjustable to raise or lower the associated suspension unit 9-n, thereby adjusting the height and/or orientation of the body 3. The suspension units 9-n may optionally each comprise a displacement sensor 11 -n operable to determine the current extension of the actuator 10-n. In the present embodiment the suspension 9 is an air suspension and each actuator 10 comprises a pneumatic spring (not shown) connected to a high pressure air supply 12, such as a compressor or a high pressure reservoir. A control valve 13-n is associated with each said adjustable actuator 10-n to control the supply of compressed air from said high pressure air supply 12 and/or to control the venting of air from each actuator 10-n. The control valves 13-n are operated to connect the high pressure air supply 12 to the actuators 10-n in order to raise the suspension units 9-n. Conversely, the control valves 13-n are operated to connect the actuators 10-n to atmosphere in order to lower the suspension units 9-n. The control valves 13-n may be operated independently of each other to provide independent control of the actuators 10-n. The control valves 13-n may be in the form of solenoid valves and may optionally be combined in a valve block (not shown). The high pressure air supply 12 may, for example, be connected to a high pressure gallery disposed in the valve block.

The controller 2 comprises an electronic processor 15 configured to execute a set of computational instructions stored on a non-transitory computer readable media. In the present embodiment, the computational instructions are stored in system memory 16 connected to the electronic processor 15. The system memory 16 may comprise a memory device. The controller 2 is configured to control the actuators 10 to reduce the magnitude of the pitch angle (a) and/or the magnitude of the roll angle (β) of the body 3 of the vehicle 1. At least in certain embodiments the controller 2 is operable to level the body 3 (i.e. to orient the body 3 such that the pitch angle (a) and the roll angle (β) are substantially zero). In use, the controller 2 is operable to control said adjustable actuators 10-n to reduce the magnitude of the pitch angle (a) and/or the magnitude of the roll angle (β) of the body 3. In particular, the electronic processor 15 is configured to output a control signal Sow) to open or close the control valves 13-n associated with each of the actuators 10, thereby extending or retracting the associated actuator 10-n and raising or lowering suspension units 9-n. By adjusting the suspension unit 9-n, there is a corresponding change in the height and/or pitch angle (a) and/or the roll angle (β) of the body 3. At least in certain embodiments, the controller 2 is configured selectively to control the actuators 9-n to raise or lower one or more of the suspension units 9-n in order to reduce the magnitude of the pitch angle (a) and/or the magnitude of the roll angle (β) at least substantially to zero. The relationship between the changes in the extension/retraction of the actuator(s) 10-n and the change in the magnitude of the pitch angle (a) and/or the magnitude of the roll angle (β) is dependent on the geometry of the vehicle 1, particularly a wheel base and a track width of the vehicle 1.

The vehicle 1 comprises means 17 for sensing the roll angle (β) and the pitch angle (a) of the body 3. It will be understood that the roll angle (β) and the pitch angle (a) may be positive or negative. In the present embodiment, the sensing means comprises a three-axis accelerometer 17 configured to output a roll signal SR and a pitch signal SP. The roll signal SR and the pitch signal SP are published to a communication network 18 and read by the electronic processor 15. The sensing means 17 is configured to determine the absolute pitch angle (a) and the absolute roll angle (β), i.e. the pitch and roll angles of the reference frame 8 in relation to a horizontal plane PXY (disposed parallel to the plane of the page in Figure 1). The roll signal SR comprises a roll angle (β) of the body 3 relative to the absolute horizontal plane PXY. The pitch signal SP comprises a pitch angle (a) of the body 3 relative to the absolute horizontal plane PXY. The roll signal SR and the pitch signal SP are output to the electronic processor 15 to establish a feedback loop. The electronic processor 15 is configured to generate said control signals Sow)in dependence on said pitch signal SP and said roll signal SR. The control signals Sow) control the actuators 10-n which adjust the suspension units 9-n. The electronic processor 15 is configured to continue monitoring the pitch angle (a) and the roll angle (β) of the body 3. The resulting feedback loop allows the electronic processor 15 to generate control signals Sow) to reduce the magnitude of the pitch angle (a) and the roll angle (β). The electronic processor 15 is configured to continue to output control signals Soutm until the measured pitch angle (a) and roll angle (β) are substantially zero. The electronic processor 15 is configured to close the control valves 13-n to inhibit changes when the desired pitch angle (a) and/or roll angle (β) is achieved. If multiple suspension units 9-n are to be adjusted, the electronic processor 15 may be configured to control the actuators 10-n sequentially or simultaneously.

The vehicle 1 comprises a control interface 19 which is operated by a user to generate a selflevel request signal RQ which is published to the communication network 18. The electronic processor 15 is configured to output said control signals Soutm in dependence on said self level request signal RQ. The control interface 19 may, for example, comprise a button, a capacitive sensor or a touch-screen disposed in the occupant compartment 5, for example in a centre console; or in the load bay 6. The vehicle 1 comprises a parking brake 20 which is engaged when the vehicle 1 is stationary. A parking signal SPK is published to the communications network 18 when the parking brake 20 is engaged. The electronic processor 15 is configured to read said parking signal SPK from the communications network 18. At least in certain embodiments, the electronic processor 15 is configured to output said control signals Soutm only when said parking brake 20 is engaged. The electronic processor 15 may be configured to inhibit the output of said control signals Sow) when said parking brake 20 is dis-engaged. Alternatively, or in addition, the control interface 19 may comprise voice control or remote control, for example via a key fob or an application running on a cellular telephone. Alternatively, or in addition, the electronic processor 15 could be configured automatically to generate the self-level request signal RQ, for example when predefined conditions are satisfied, for example the vehicle 1 comes to a stop and a user requests that the suspension 9 is lowered.

The operation of the controller 2 will now be described with reference to the accompanying figures. The vehicle 1 is stationary and the parking brake 20 is engaged. The control interface 19 is operated and the self-level request signal RQ is published to the communication network 18. The controller 2 reads the self-level request signal RQ and initiates the self-levelling in dependence on said self-level request signal RQ. The electronic processor 15 reads the roll signal SR and the pitch signal SP from the communication network 18 and determines the roll angle (β) and the pitch angle (a) of the body 3 relative to the absolute horizontal plane PXY. By selectively controlling the actuators 10-n, the controller 2 can reduce the magnitude of the pitch angle (a) and/or the magnitude of the roll angle (β) at least substantially to zero. The control valves 13-n are operated in dependence on said control signals Sow) to adjust one or more of the actuators 10-n. The sensing means 17 continue to measure the pitch angle (a) and the roll angle (β), providing substantially real-time feedback to the electronic processor 15. The suspension units 9-n are adjusted to reduce the roll angle (β) and/or the pitch angle (β) at least substantially to zero. The electronic processor 15 may be configured to output a control signal Sow) to close the control valves 13-n to hold the suspension units 9-n. If the parking brake 20 is released or the speed of the vehicle 1 increases above a predefined threshold, for example Okph or 10kph, the controller 2 may exit the self-levelling function.

It will be appreciated that the electronic processor 15 may control the actuators 10-n to raise one of the suspension units 9-n and to lower another one of the suspension units 9-n to provide the required change in the magnitude of the pitch angle (a) or the magnitude of the roll angle (β). For example, the electronic processor 15 may raise the first and second suspension units 9-1,9-2 and lower the third and fourth suspension units 9-3, 9-4 to adjust the pitch angle (a) of the vehicle 1. Similarly, the electronic processor 15 may raise the first and third suspension units 9-1,9-3 and lower the second and fourth suspension units 9-2, 9-4 to adjust the roll angle (β) of the vehicle 1.

The electronic processor 15 is configured to control the suspension 9 to level the body 3 when the vehicle 1 is stationary. As the vehicle is not moving, the full extent of the bump/rebound travel for each suspension unit 9-n may be used. In certain scenarios, for example if the vehicle is parked on a particularly steep incline, there may be insufficient suspension travel available to reduce the magnitude of the pitch angle (a) and/or the roll angle (β) to zero. The electronic processor 15 may be configured to control the actuators 10-n in order to reduce the magnitude of the pitch angle (a) and/or the magnitude of the roll angle (β) as much as possible. If there is no further suspension travel available, the electronic processor 15 may be configured to close the control valves 13-n to hold the suspension units 9-n.

The electronic processor 15 in the embodiment described herein could be modified to implement a control strategy which prioritises changes which will lower one or more of the suspension units 9-n over changes which will raise one or more of the suspension units 9-n. By way of example, the electronic processor 15 may determine that the pitch angle (a) of the vehicle 1 could be reduced by either raising the first and second suspension units 9-1,9-2 or lowering the third and fourth suspension units 9-3, 9-4 (or potentially a combination of both). The electronic processor 15 is configured to prioritise lowering the third and fourth suspension units 9-3, 9-4 to reduce the pitch angle (a). This prioritisation may help to reduce the supply of high pressure air to the actuators 10-n which may reduce or avoid the need to operate the high pressure air supply 12.

The electronic processor 15 may receive an end-of-travel signal from the suspension units 9-n when there is no further bump/rebound travel available. The end-of-travel signal could, for example, be generated by the displacement sensor 11-n. Alternatively, a micro-switch, a release valve or a hard-stop may be disposed at the end of the travel of the suspension units 9-n.

It will be appreciated that various modifications may be made to the embodiment(s) described herein without departing from the scope of the appended claims.

The suspension units 9-n may optionally each comprise a displacement sensor 11 -n operable to determine a current extension of the associated actuator 10-n. The electronic processor 15 may receive displacement signals SD(n) from the displacement sensors 11-n. A look-up table may be stored in the system memory 16 correlating the measured pitch angle (a) and/or the measured roll angle (β) to the required change in the extension/retraction of the actuators 10-n. In this arrangement, the electronic processor 15 may access the look-up table to determine the required change in the extension of the actuators 10-n. The electronic processor 15 may determine the required adjustment of each actuator 10-n to reduce the magnitude of the pitch angle (a) and/or the magnitude of the roll angle (β), preferably to zero. In dependence on the displacement signals Sdm, the electronic processor 15 determines the required adjustment to the actuators 10-n (for example to extend or retract each actuator 10-n) and generates the control signals Soutm- Alternatively, rather than access a look-up table, the electronic processor 15 may calculate the required change in the extension/retraction of one or more of the actuators 10-n to achieve the desired pitch angle (a) and/or roll angle (β).

The sensing means 17 is described herein as a three-axis accelerometer. In alternative implementations, a one (1) or two (2) axis accelerometer may be used. Other types of sensors may also be used, for example a tilt sensor or the like. For example, in alternative embodiments the sensing means 17 may comprise a plurality of single-axis inclinometers (tilt sensors) having sensing axes arranged substantially mutually perpendicular; or a single dualaxis inclinometer. Such an inclinometer may include, but is not limited to, a digital tilt-sensor, a Micro-Electro-Mechanical (MEMS) inclinometer, a liquid (electrolyte) level sensor or a pendulum type sensor.

Claims

CLAIMS:

1. A vehicle comprising: a body; a plurality of suspension units mounted to the body and associated with respective wheels of the vehicle, one or more of said suspension units comprising at least one adjustable actuator; means for sensing a pitch angle (a) and/or a roll angle (β) of the body relative to an absolute horizontal plane (PXY); a controller comprising at least one processor configured to receive a pitch angle signal and/or a roll angle signal from said sensing means; and a memory device connected to the at least one processor; wherein, in dependence on said pitch signal and/or said roll signal, the at least one processor is configured to output a control signal to control one or more of said adjustable actuators to reduce the magnitude of the pitch angle (a) and/or the magnitude of the roll angle (β) of the body; and wherein the at least one processor is configured to output said control signal to control one or more of said adjustable actuators only when the vehicle is stationary or the vehicle speed is below a predefined speed threshold..

2. A vehicle as claimed in claim 1, wherein the at least one processor is configured to output said control signal to control one or more of said adjustable actuators to reduce the magnitude of the pitch angle (a) and/or the magnitude of the roll angle (β) of the body substantially to zero.

3. A vehicle as claimed in any one of claim 1 or claim 2, wherein the at least one processor is configured to output said control signal to control one or more of said adjustable actuators only when a vehicle parking brake is engaged.

4. A vehicle as claimed in any one of claims 1 to 3, wherein the at least one processor is configured to output said control signal in dependence on a level request signal.

5. A vehicle as claimed in any one of the preceding claims, wherein the sensing means comprises at least one pitch angle sensor and/or at least one roll angle sensor.

6. A vehicle as claimed in any one of the preceding claims, wherein the sensing means comprises one or more inclinometer or accelerometer.

7. A vehicle as claimed in any one of the preceding claims, wherein the at least one processor is configured to reduce the magnitude of the pitch angle (a) by outputting said control signal to control the suspension unit(s) disposed at a front of the vehicle and / or at a rear of the vehicle.

8. A vehicle as claimed in any one of the preceding claims, wherein the at least one processor is configured to reduce the magnitude of the roll angle (β) by outputting said control signal to control the suspension unit(s) disposed on a left side of the vehicle and / or on a right side of the vehicle.

9. A vehicle as claimed in any one of the preceding claims, wherein the at least one processor is configured to prioritise changes which will lower the one or more of the suspension unit over changes which will raise the one or more of the suspension unit.

10. A vehicle as claimed in any one of the preceding claims, wherein each adjustable actuator comprises an air spring and at least one control valve; wherein the at least one control valve is operable in dependence on said control signal to vent compressed air from the air spring to lower that suspension unit.

11. A controller for controlling at least one suspension unit to reduce the magnitude of a pitch angle (a) and/or the magnitude of a roll angle (β) of a body of a vehicle, the controller comprising: at least one processor configured to receive a pitch angle signal comprising a pitch angle (a) of the body relative to an absolute horizontal plane (PXY); and/or to receive a roll angle signal comprising a roll angle (β) of the body relative to an absolute horizontal plane (PXY); and a memory device connected to the at least one processor; wherein, in dependence on said pitch signal and/or said roll signal, the at least one processor is configured to generate a control signal to control the at least one suspension unit to reduce the magnitude of the pitch angle (a) and/or the magnitude of the roll angle (β) of the body; and wherein the at least one processor is configured to output said control signal only when the vehicle is stationary or the vehicle speed is below a predefined speed threshold.

12. A controller as claimed in claim 11, wherein the at least one processor is configured to output said control signal to reduce the magnitude of the pitch angle (a) and/or the magnitude of the roll angle (β) of the body at least substantially to zero.

13. A controller as claimed in claim 11 or claim 12, wherein the at least one processor is configured to output said control signal to control the at least one suspension unit only when a vehicle parking brake is engaged.

14. A controller as claimed in any one of claims 11 to 13, wherein the at least one processor is configured to output said control signal in dependence on a level request signal.

15. A controller as claimed in any one of claims 11 to 14, wherein the at least one processor is configured to receive said pitch angle signal from at least one pitch angle sensor; and/or to receive said roll angle signal from at least one roll angle sensor.

16. A controller as claimed in any one of claims 11 to 15, wherein the at least one processor is configured to receive said pitch angle signal and/or said roll angle signal from one or more inclinometer or accelerometer.

17. A controller as claimed in any one of claims 11 to 16, wherein the at least one processor is configured to reduce the magnitude of the pitch angle (a) by outputting said control signal to control the suspension unit(s) disposed at a front of the vehicle and / or at a rear of the vehicle.

18. A controller as claimed in any one of claims 11 to 17, wherein the at least one processor is configured to reduce the magnitude of the roll angle (β) by outputting said control signal to control the suspension unit(s) disposed on a left side of the vehicle and / or on a right side of the vehicle.

19. A controller as claimed in any one of claims 11 to 18, wherein the at least one processor is configured to prioritise changes which lower the at least one suspension unit over changes which raise the at least one suspension unit.

20. A controller as claimed in any one of claims 11 to 19, wherein the at least one processor is configured to output said control signal to control an actuator associated with said at least one suspension unit.

21. A method of controlling at least one suspension unit to reduce the magnitude of a pitch angle (a) and/or a roll angle (β) of a body of a vehicle, the method comprising: measuring the pitch angle (a) and/or the roll angle (β) relative to an absolute horizontal plane (PXY); and adjusting the at least one suspension unit in dependence on the measured pitch angle (a) and/or the measured roll angle (β) to reduce the magnitude of the pitch angle (a) and/or the magnitude of the roll angle (β) of the body; wherein the step of adjusting is carried out only when the vehicle is stationary or the vehicle speed is below a predefined speed threshold.