Control system and method for a vehicle suspension

Abstract

A control system (100 fig 1) and method are provided for controlling a suspension system (310 fig 2) of a vehicle (300 fig 1) to adjust a height of a hitch connecting device 370 disposed on the vehicle. The suspension system (310) includes at least one front suspension unit (S1, S2 fig 2) and at least one rear suspension unit (S3, S4 fig 2). The front (S1, S2) and / or rear (S3, S4) suspension unit is / are height adjustable. The control system (100) is configured to receive a signal (415, 565 fig 5) indicative of a height (TZ1 fig 7A) of a trailer coupler 375 disposed on a trailer; and determine a first target height for the hitch connecting device 370 in dependence on the signal (415, 565). The control system (100) is configured to output at least one suspension control signal (170 fig 6) to adjust a height of the front (S1, S2) and / or rear (S3, S4) suspension unit to position the hitch connecting device 370 at the first target height. The invention facilitates trailer hitching without for example manual trailer jockey operation.

Description

TECHNICAL FIELD The present disclosure relates to a control system and method for a vehicle suspension. Aspects of the invention relate to a control system, a system, a vehicle and a method. The control system and method have particular application in controlling the vehicle suspension to configure a vehicle to facilitate hitching a trailer. BACKGROUND A trailer typically comprises a trailer tongue having a trailer coupler for connecting to a hitch connecting device provided on a tow vehicle. The hitch connecting device may be in the form of a tow ball which locates in an aperture formed in the trailer coupler to form an articulated connection. As the hitch connecting device is provided at the rear of the tow vehicle, repeated reversing manoeuvres may be required to position the tow ball in a position suitable for hitching the trailer to the towing vehicle. The tow vehicle is typically positioned to locate the tow ball in front of or alongside the trailer coupler. A user must then manually locate the trailer coupler over the tow ball by raising a trailer jockey wheel before hitching the trailer coupler onto the tow ball. The hitching of the trailer to the tow vehicle can be a laborious process. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a control system, a system, a vehicle and a method as claimed in the appended claims. According to an aspect of the present invention there is provided a control system for controlling a suspension system of a vehicle to adjust a height of a hitch connecting device disposed on the vehicle, the suspension system comprising at least one front suspension unit and at least one rear suspension unit , wherein the at least one front suspension unit and / or the at least one rear suspension unit is height adjustable; the control system comprising one or more controller, the control system being configured to: receive a signal indicative of a height of a trailer coupler disposed on a trailer; determine a first target height for the hitch connecting device in dependence on the signal indicating the trailer coupler height; and output at least one first suspension control signal to adjust a height of the at least one front suspension unit and / or the at least one rear suspension unit to position the hitch connecting device at the first target height. The control system is operative to control the suspension system to adjust the height of the hitch connecting device in dependence on the indicated height ofthe trailer coupler. At least in certain embodiments, the hitch connecting device is positioned at a height suitable for hitching the trailer to the vehicle. This may facilitate coupling ofthe trailer to the vehicle. The control system may be integrated with a camera tracking system which is operable to track the location ofthe trailer coupler. This may facilitate positioning ofthe hitch connecting device relative to the trailer coupler. The first target height for the hitch connecting device may be lower that the trailer coupler height. The control system is operable to adjust a height of the at least one front suspension unit and / or the at least one rear suspension unit to position the hitch connecting device at a height below that of the trailer coupler. The control system may enable the hight of the hitch connecting device to be adjusted automatically or partially automatically to facilitate hitching to a trailer. The vehicle suspension may be controlled to alter the relative pitch and / or the ride height of the vehicle to enable the hitch connecting device to be positioned lower than the target trailer coupler. In use, the vehicle can reverse towards the trailer coupler to position the hitch connecting device under the trailer coupler. The control system may control the suspension system such that the hitch connecting device performs a scooping motion to locate under the trailer coupler. Once the hitch connecting device is located under the trailer coupler, the suspension system may be controlled to raise the hitch connecting device (i.e., to increase the height of the hitch connecting device). The hitch connecting device may engage the trailer coupler. The control system may be configured to stop or pause changes in the height of the suspension system in dependence on a determination that the hitch connecting device has engaged the trailer coupler. The user is thereby allowed to latch the trailer coupler onto the hitch connecting device with relative ease. The at least one front suspension unit is associated with a front axle of the vehicle; and the at least one rear suspension unit associated with a rear axle of the vehicle. The hitch connecting device may, for example, comprise or consist of a tow ball. Other types of hitch connecting device are contemplated. The trailer coupler may be configured to engage the tow ball. The trailer coupler may comprise a locking mechanism. The locking mechanism may, for example, be actuated by a handle. Other types of trailer coupler are contemplated. The hitch connecting device forms part of a vehicle trailer hitch provided on the vehicle. The vehicle trailer hitch comprises a tow bar. The hitch connecting device is mounted to the tow bar. The tow bar and the hitch connecting device may be fixedly mounted to the vehicle. The tow bar may, for example, be fastened to a bracket or a beam provided at the rear of the vehicle. The trailer coupler may be in the form of a trailer hitch. A trailer typically comprises a trailer tongue which extends forward towards the front end. The trailer coupler may be disposed at the front end of the trailer tongue. The trailer coupler is configured to engage and releasably lock onto the hitch connecting device. This connects the trailer to the vehicle and allows the trailer to articulate about the coupler to hitch connection as the vehicle manoeuvres (left and right steering directions while travelling). The trailer may comprise a trailer jockey wheel to adjust the height of the trailer coupler. In a variant, the tow bar may be pivotally mounted to the vehicle, for example to enable the hitch connecting device to be selectively configured in a deployed position and a retracted position. The signal indicating the height of the trailer coupler may be received from a vehicle system, such as a hitching assistance system. The hitching assistance system may process image data received from one or more imaging sensor to identify the trailer coupler. The hitching assistance system may determine the height of the trailer coupler and output a trailer height signal to the control system. The trailer height signal may indicate the height of the trailer coupler. Alternatively, the control system may receive image data from one or more imaging sensor. The image data may be indicative of the height of the trailer coupler. The control system may process the image data to determine the height of the trailer coupler. The first target height for the hitch connecting device may be set relative to the indicated height of the trailer coupler. At least in certain embodiments, the height of the trailer coupler may be determined in dependence on the signal with reference to a reference height of the hitch connecting device, for example a centre of a tow ball. The control system may be configured to determine an absolute height of the trailer coupler and the hitch connecting device. For example, the absolute height of each of the trailer coupler and the hitch connecting device may be defined with respect to a reference plane. The reference plane may, for example, correspond to a ground plane on which the vehicle and the trailer are disposed. Alternatively, the control system may be configured to determine a height of the trailer coupler relative to the hitch connecting device. The control system comprises one or more controllers collectively comprising at least one electronic processor having an electrical input for receiving at least one input signal. The input signal comprises the signal indicative of the height of the trailer coupler. The at least one electronic processor is configured to determine the first target height for the hitch connecting device in dependence on the signal indicating the trailer coupler height. At least one memory device is electrically coupled to the at least one electronic processor and having instructions stored therein. The at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to determine the first target height. The at least one electronic processor has an electrical output for outputting at least one output signal. The at least one output signal comprises the at least one first suspension control signal to adjust a height of the at least one front suspension unit and / or the at least one rear suspension unit to position the hitch connecting device at the first target height. The control system may be configured to receive a signal indicating a location of the trailer coupler relative to the hitch connecting device. The trailer coupler location signal may be received from a vehicle system. The vehicle system may be configured to process image data received from one or more imaging sensorto identify the trailer coupler. The vehicle system may determine the location of the trailer coupler and output a trailer coupler location signal to the control system. The vehicle system may, for example, comprise a hitching assistance system. The hitching assistance system may perform image processing to identify the trailer coupler. The location of the trailer coupler may be identified in a horizontal plane. The trailer coupler location signal may facilitate positioning of the hitch connecting device in a predetermined position relative to the trailer coupler. At least in certain embodiments, this may facilitate coupling of the trailer coupler to the hitch connecting device. The hitch connecting device may, for example, be positioned below the trailer coupler. In certain embodiments, the control system may control the vehicle to position the hitch connecting device in the predetermined position relative to the trailer coupler in dependence on the trailer coupler location signal. The control of the vehicle may be autonomous or semi-autonomous. In a variant, the control system may be configured to determine a location of the trailer coupler relative to the hitch connecting device. For example, the control system may process image data received from one or more imaging sensor to determine the location of the trailer coupler. The control system may control the vehicle to position the hitch connecting device in the predetermined position relative to the trailer coupler in dependence on the determined location of the trailer coupler. If a trailer coupler is not detected, the control system may be configured to output a notification to advise that the trailer coupler is not present or has not been detected. The signal indicating the position of the trailer coupler may facilitate positioning of the vehicle to align the hitch connecting device with the trailer coupler. The hitch connecting device and the trailer coupler may be aligned with each other. The hitch connecting device and the trailer coupler may be aligned with each other along the vertical axis. When aligned with each other, the hitch connecting device may be located vertically below the trailer coupler. The hitch connecting device may be determined to be at least substantially aligned with the trailer coupler when a central vertical axis of the hitch connecting device is at least substantially coincident with a central vertical axis of the trailer coupler. The control system may be configured to output the at least one second suspension control signal to adjust the height of the at least one front suspension unit and / or the at least one rear suspension unit to raise the hitch connecting device when the hitch connecting device is at least substantially aligned with the trailer coupler. The changes in the height of the hitch connecting device may be initiated in dependence on a determination that the hitch connecting device and the trailer coupler are aligned with each other. The hitch connecting device may be raised to reduce the vertical separation between the hitch connecting device and the trailer coupler, thereby facilitating coupling. Alternatively, the hitch connecting device may be raised to initiate the mechanical coupling of the hitch connecting device and the trailer coupler. For example, the at least one second suspension control signal may adjust the height of the at least one front suspension unit and / or the at least one rear suspension unit to raise the hitch connecting device to engage the trailer coupler. The control system may be configured to determine that the hitch connecting device has engaged the trailer coupler. The control system may be configured to output a third suspension control signal to stop or pause changes in the height of the at least one front suspension unit and / or the at least one rear suspension unit in dependence on the determination that the hitch connecting device has engaged the trailer coupler. The third suspension control signal may be generated to stop or pause changes in the height of the at least one front suspension unit and / or the at least one rear suspension unit to hold or maintain the height of the hitch connecting device. This may help to reduce or prevent pre-loading of the trailer coupler which might otherwise hamper the coupling procedure. For example, the application of a load to the trailer coupler may restrict or prevent operation of a locking mechanism provided on the trailer coupler. The control system may be configured to receive a load signal from a load sensor configured to detect a load on the hitch connecting device. The control system may determine that the hitch connecting device has engaged the trailer coupler in dependence on the load signal. The load signal may facilitate detection of the engagement of the hitch connecting device and the trailer coupler. In a variant, the control system may be configured to output a suspension control signal to adjust the height of the at least one front suspension unit and / or the at least one rear suspension unit to lower the hitch connecting device in dependence on the determination that the hitch connecting device has engaged the trailer coupler. The hitch connecting device may be lowered to remove any load applied to the trailer coupler. The control system may be configured to adjust the height of the at least one front suspension unit and / or the at least one rear suspension unit to lower the hitch connecting device by a predetermined height, or until a detected load on the hitch connecting device is less than a threshold load value. The control system may be configured to output a steering control signal and / or a torque request signal to control the vehicle autonomously or semi-autonomously to align the hitch connecting device with the trailer coupler. Alternatively, or in addition, the control system may output a steering notification signal and / or a torque notification signal to advise a driver (or user) of appropriate steering inputs and / or torque inputs to control the vehicle so as to align the hitch connecting device with the trailer coupler. The control of the vehicle may be implemented in combination with a hitch assistance system. The first target height may be a predetermined distance below the height of the trailer coupler. The distance may be defined to enable the hitch connecting device to locate under trailer coupler. This reduces the likelihood of the hitch connecting device engaging the trailer coupler as the vehicle manoeuvres, for example as it reverses towards the trailer. The control system may be configured to determine a horizontal distance between the hitch connecting device and the trailer coupler. The control system may output the at least one first suspension control signal to adjust the height of the hitch connecting device when the determined horizontal distance is less than or equal to a predetermined horizontal distance threshold. The height of the hitch connecting device may be adjusted when the vehicle is spaced apart from the trailer by the horizontal distance. At least in certain embodiments, the height of the hitch connecting device may be adjusted while the vehicle is moving, for example as it approaches the trailer. This may expedite the performance of a hitching manoeuvre. The control system may determine the horizontal distance by processing image data received from one or more imaging sensor and / or one or more proximity signal received from one or more proximity sensor. Alternatively, the control system may determine the horizontal distance in dependence on a signal indicating a location of the trailer coupler. The trailer coupler location signal may be received from a vehicle system, such as the hitching assistance system. The control system may be configured to compare the first target height for the hitch connecting device to a hitch connecting device height upper limit. If the first target height for the hitch connecting device is greater than the hitch connecting device height upper limit, the control system may be configured to set the first target height to the hitch connecting device height upper limit. Alternatively, the control system may control the vehicle to position the hitch connecting device in a predetermined position relative to the trailer coupler. The control system may be configured to output a notification to advise that the trailer coupler is outside an operating range, for example to advise that the hitch connecting device is greater than the hitch connecting device height upper limit. The control system may be configured to compare the first target height for the hitch connecting device to a hitch connecting device height lower limit. If the first target height for the hitch connecting device is less than the hitch connecting device height lower limit, the control system may be configured to set the first target height to the hitch connecting device lower limit. Alternatively, the control system may control the vehicle to position the hitch connecting device in a predetermined position relative to the trailer coupler. The control system may be configured to output a notification to advise that the trailer coupler is outside an operating range, for example to advise that the hitch connecting device is less than the hitch connecting device height lower limit. The hitch connecting device may be a fixed device, i.e., having a fixed mounting position. Alternatively, the hitch connecting device may be moveable, i.e., having a movable mounting position. The hitch connecting device may, for example, comprise a retractable hitch connecting device selectively configurable in a retracted position and a deployed position. The control system may be configured to output the at least one first suspension control signal to adjust the height of the at least one front suspension unit and / or the at least one rear suspension unit so as to position the hitch connecting device at the first target height when the hitch connecting device is in the deployed position. When configured in the deployed position, the at least one front suspension unit and / orthe at least one rear suspension unit are controlled to locate the hitch connecting device at the target height. The control system may be configured to determine a configuration of the retractable hitch connecting device. In particular, the control system may be configured to determine if the retractable hitch connecting device is in the retracted position or the deployed position. In dependence on a determination that the retractable hitch connecting device is configured in the retracted position, the control system may be configured to output a hitch connecting device deployment signal to deploy the retractable hitch connecting device. At least in certain embodiments, the hitch connecting device may be deployed automatically. The hitch connecting device deployment signal may be output before the at least one first suspension control signal. The hitch connecting device deployment signal may be output when the horizontal distance between the hitch connecting device and the trailer coupler is less than or equal to a predetermined deployment threshold. According to a further aspect of the present invention there is provided a control system as described herein. According to a further aspect of the present invention there is provided a system comprising the control system described herein and a hitching assistance system. The hitching assistance system may be configured to control dynamic operation of the vehicle, for example to perform a hitching manoeuvre. The hitching assistance system may be configured to output the signal indicative of the height of the trailer coupler. Alternatively, or in addition, the hitching assistance system may be configured to output a signal indicative of a location of the trailer coupler. Alternatively, the control system described herein may be incorporated into the hitching assistance system. The system may comprise a suspension control system for controlling operation of the vehicle suspension. According to a further aspect of the present invention there is provided a vehicle comprising a system as described herein. According to a further aspect of the present invention there is provided a vehicle comprising a control system as described herein. According to a further aspect of the present invention there is provided a method for controlling a suspension system of a vehicle to adjust a height of a hitch connecting device disposed on the vehicle, the suspension system comprising at least one front suspension unit and at least one rear suspension unit, wherein the at least one front suspension unit and / or the at least one rear suspension unit is height adjustable; the method comprising: receive a signal indicative of the trailer coupler height indicating a height of a trailer coupler disposed on a trailer; determine a first target height for the hitch connecting device in dependence on the signal indicating the trailer coupler height; and outputting at least one first suspension control signal to adjust a height of the at least one front suspension unit and / or the at least one rear suspension unit to position the hitch connecting device at the first target height. According to a further aspect of the present invention there is provided a control system for controlling a suspension system of a vehicle to adjust a height of a hitch connecting device disposed on the vehicle, the suspension system comprising at least one front suspension unit and at least one rear suspension unit , wherein the at least one front suspension unit and / or the at least one rear suspension unit is height adjustable; the control system comprising one or more controller, the control system being configured to: determine a height of a trailer coupler disposed on a trailer; determine a first target height for the hitch connecting device in dependence on the signal indicating the trailer coupler height; and output at least one first suspension control signal to adjust a height of the at least one front suspension unit and / or the at least one rear suspension unit to position the hitch connecting device at the first target height. The height of the trailer coupler may be determined in dependence on a signal received from a hitching assistance system. The hitching assistance system may process image data received from one or more imaging sensor to identify the trailer coupler. The hitching assistance system may determine the height of the trailer coupler and output a trailer height signal to the control system. The trailer height signal may indicate the height of the trailer coupler. Alternatively, the control system may receive image data from one or more imaging sensor. The control system may process the image data to determine the height of the trailer coupler. The functionality described herein in relation to the hitching assistance system may be implemented by the control system. The control system may be configured to determine a location of the trailer coupler relative to the hitch connecting device. For example, the control system may process image data received from one or more imaging sensor to determine the location of the trailer coupler. The control system may control the vehicle to position the hitch connecting device in the predetermined position relative to the trailer coupler in dependence on the determined location of the trailer coupler. According to a further aspect of the present invention there is provided a method for controlling a suspension system of a vehicle to adjust a height of a hitch connecting device disposed on the vehicle, the suspension system comprising at least one front suspension unit and at least one rear suspension unit, wherein the at least one front suspension unit and / or the at least one rear suspension unit is height adjustable; the method comprising: determine a height of a trailer coupler disposed on a trailer; determine a first target height for the hitch connecting device in dependence on the signal indicating the trailer coupler height; and outputting at least one first suspension control signal to adjust a height of the at least one front suspension unit and / or the at least one rear suspension unit to position the hitch connecting device at the first target height. The at least one front suspension unit is associated with a front axle of the vehicle; and the at least one rear suspension unit is associated with a rear axle of the vehicle. According to a further aspect of the present invention there is provided a computer readable instructions which, when executed by a computer, are arranged to perform a method(s) as described herein. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in anyway and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic representation of a vehicle incorporating a control system in accordance with an embodiment of the present invention; Figure 2 shows a schematic representation of an adjustable-height suspension system of the vehicle shown in Figure 1; Figure 3 shows a side elevation of a hitch connecting device and a trailer coupler for connecting a trailer to the vehicle shown in Figure 1; Figure 4 shows a plan view of the trailer tongue on which the trailer coupler shown in Figure 3 is mounted; Figure 5 shows a schematic representation of a hitching assistance system for use in conjunction with the control system described herein; Figure 6 shows a schematic representation of the control system in accordance with an embodiment of the present invention; Figure 7A is a schematic representation of a hitching manoeuvre in which the vehicle according to an embodiment of the present invention approaches a trailer; Figure 7E3 is a schematic representation of the vehicle shown in Figure 7A with the vehicle suspension configured to lower the hitch connecting device below the trailer coupler; Figure 7C is a schematic representation of the vehicle shown in Figure 7B with the hitch connecting device aligned with the trailer coupler; Figure 7D is a schematic representation of the vehicle shown in Figure 7C with the vehicle suspension configured to raise the hitch connecting device to engage the trailer coupler; Figure 8 is a block diagram representing operation of the control system in accordance with an embodiment of the present invention; Figure 9A shows a further embodiment of the present invention comprising a retractable hitch connecting device, the hitch connecting device being shown in a retracted position in Figure 9A: and Figure 9B shows the retractable hitch connecting device shown in Figure 9A in a deployed position. DETAILED DESCRIPTION A control system 100 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figures. As shown in Figure 1, the control system 100 is installed in a vehicle 300. The vehicle 300 is a tow vehicle 300 and is configured to tow a trailer 350. The vehicle 300 is a road vehicle, such as an automobile, a sports utility vehicle (SUV) or a utility vehicle. The vehicle 300 in the present embodiment is an automobile. As shown in Figure 1, the vehicle 300 comprises a body 305 and four (4) wheels W1-4. In particular, the vehicle 300 two front wheels W1, W2 disposed at the front of the vehicle 300; and two rear wheels W3, W4 disposed at the rear of the vehicle 300. The vehicle 300 comprises a suspension system 310 which connect the body 305 to the wheels W1-W4. The suspension system 310 enables relative motion between the body 305 and the wheels W1-W4. As shown schematically in Figure 1, the suspension system 310 comprises a plurality of suspension units S1-S4, each of the suspension units S1-S4 being associated with a respective one of the wheels W1-W4. The front wheels W1, W2 are supported on respective front suspension units S1, S2; and the rear wheels W3, W4 are supported on respective rear suspension units S3, S4. A schematic representation of the suspension system 310 is shown in Figure 2. The suspension system 310 is height adjustable. The height of each of the front and rear suspension units S1-S4 can be controlled actively. The height of each of the suspension units S1-S4 can be controllably increased or decreased. As described herein, the suspension system 310 provides pitch control and / or height control. The pitch and / or the height of the body 305 can be changed by controlling the relative height of the suspension units S1-S4. The height of each of the suspension units S1-S4 can be controlled independently in the present embodiment. In a variant, the front suspension units S1, S2 may be controlled independently of the rear suspension units S3, S4. The suspension system 310 is an air suspension system 310. The suspension units S1-S4 each comprise an inflatable bladder 315 which can be selectively inflated and deflated to increase and decrease the height of the associated suspension unit S1-S4. The vehicle 300 comprises an air reservoir 320 for storing compressed air (i.e., air at a pressure greater than atmospheric pressure), a compressor 325 for supplying compressed air to the air reservoir 320, a suspension control system 335, and a pneumatic valve system 340 for controlling the supply of air to and from the suspension units S1-S4. The suspension control system 335 is an electronic control unit comprising at least one electronic processor configured to control operation of the pneumatic valve system 340. The pneumatic valve system 40 comprises one or more pneumatic valve for controlling the supply of airto and from the suspension units S1-S3. The height of each of the suspension units S1-S4 is controllable independently by the suspension control system 335. The suspension system 310 may utilise other mechanisms to adjust the height of the suspension units S1-S4. For example, one or more mechanical or hydraulic actuator may be provided to adjust the height of the suspension units S1-S4. The vehicle 300 is described herein with reference to a longitudinal axis X, a transverse axis Y and a vertical axis Z. As described herein, the suspension units S1-S4 are controlled to effect rotation and / or translation of the body 305 relative to the axes X, Y, Z. A rotational movement of the body 305 about the longitudinal axis X is referred to herein as a rolling motion and is measured by a roll angle. A rotational movement of the body 305 about the transverse axis X is referred to herein as a pitching motion and is measured by a pitch angle a. A translational movement of the body 305 along the vertical axis Z is referred to herein as raising or lowering the body 305. The rotation and / or translation of the body 305 are described herein with respect to a reference plane coincident with the ground. The description herein of changes in the height of the suspension units S1-S4 refer to the active control of the suspension height, rather than changes resulting from dynamic loading of the suspension S1-S4. The active control of the suspension height is achieved through controlling the pressure in the air bladders 315 associated with each of the suspension units S1-4 in the present embodiment. Other techniques are contemplated for actively controlling the suspension height. For example, the vehicle 300 may comprise one or more mechanical or hydraulic actuator operable to control the suspension height. The vehicle 300 is configured to tow the trailer 350. The vehicle 300 comprises a vehicle trailer hitch 355 for connection to the trailer 350. As shown in Figure 3, the vehicle trailer hitch 355 includes a tow bar 360 extending from a bracket 365 provided at the rear of the vehicle 300. The vehicle trailer hitch 355 comprises a hitch connecting device 370 such as a tow ball 370. As shown in Figure 4, the trailer 350 has a trailer tongue 380 for connection to the vehicle 300. The trailer tongue 380 is disposed at a front ofthe trailer 350 and extends in a forward direction. A trailer coupler 375 is provided at a front end of the trailer tongue 380. The trailer coupler 375 is configured to engage and releasably lock onto the hitch connecting device 370, such as the tow ball 370, on the vehicle trailer hitch 355. The trailer coupler 375 comprises a locating aperture 375A configured to receive the hitch connecting device 370. The trailer coupler 375 releasably locks the hitch connecting device 370 in the locating aperture. The trailer coupler 375 connects the trailer 350 to the vehicle 300 and allows the trailer 350 to articulate about the connection formed by the trailer coupler 375 and the hitch connecting device 370 as the vehicle 300 changes direction while travelling. The vehicle 300 comprises at least one imaging sensor 410 configured to capture an image representing a scene external to the vehicle 300. The or each imaging sensor 410 is configured to output an image data signal 415. The image data signal 415 represents image data captured by the at least one imaging sensor 410. The at least one imaging sensor 410 comprises a first optical sensor 410 in the present embodiment. The first imaging sensor 410 is provided for capturing a first scene to a rear of the vehicle 300. The first imaging sensor 410 is mounted in a rearward-facing orientation. The first imaging sensor 410 is mounted at the rear of the vehicle 300. In the present embodiment, the first imaging sensor 410 is disposed on a tailgate 420 mounted to the body 305 of the vehicle 300. Other mounting locations are contemplated for the first imaging sensor 410. The first imaging sensor 410 may comprise a mono or stereo optical sensor. Alternatively, or in addition, the at least one imaging sensor 410 may comprise a Light Detection and Ranging (LIDAR) sensor and / or a radar sensor. The vehicle 300 comprises at least one parking sensor 430 configured to output a proximity signal 435. The at least one parking sensor 430 comprises at least one first parking sensor 430 mounted at the rear of the vehicle 300. The or each parking sensor 430 comprises one or more proximity sensor configured to determine the proximity and position of an obstacle in relation to the vehicle 300. The or each parking sensor 430 comprises an ultrasonic (time-of-flight) sensor in the present embodiment. The vehicle 300 comprise a hitching assistance system 500 to facilitate hitching of the trailer 350 to the vehicle 300. The hitching assistance system 500 is configured to determine the location of the trailer 350. In dependence on the determined location of the trailer 350, the hitching assistance system 500 is configured to control the vehicle 300 to facilitate hitching of the trailer 350 to the vehicle 300. The hitching assistance system 500 is configured to determine a position of the hitch connecting device 370 relative to the trailer coupler 375 which would be suitable for hitching the trailer 350 to the vehicle 300. In the present embodiment, the position of the hitch connecting device 370 determined by the hitching assistance system 500 corresponds to a position in which the hitch connecting device 370 is positioned below and vertically aligned with the trailer coupler 375 The hitching assistance system 500 is configured to identify the trailer coupler 375 on the trailer tongue 380 and to control the vehicle 300 to align the hitch connecting device 370 with the trailer coupler 375. The hitch connecting device 370 and the trailer coupler 375 are aligned along a vertical axis Z1. The vertical axis Z1 corresponds to a vertical centreline of the trailer coupler 375. The hitching assistance system 500 is configured to control the vehicle 300 to align a vertical centreline of the hitch connecting device 370 with the vertical axis Z1 corresponding to the vertical centreline of the trailer coupler 375. The alignment is performed within operational tolerances. The control of the vehicle 300 to align the hitch connecting device 370 with the trailer coupler 375 is referred to herein as a hitching manoeuvre. As described herein, the suspension system 310 is controlled to position the hitch connecting device 370 below the trailer coupler 375. In particular, the suspension system 310 is controlled to locate the hitch connecting device 370 at a first target height HH1. The control of the suspension system 310 in the present embodiment is performed concurrently with the hitching manoeuvre. For example, the suspension system 310 may be controlled to locate the hitch connecting device 370 at the first target height HH1 when the horizontal distance between the vehicle 300 and the trailer 350 is less than or equal to a predetermined distance threshold. In a variant, the suspension system 310 may be controlled to locate the hitch connecting device 370 at the first target height HH1 before the hitching manoeuvre is initiated. The trailer coupler 375 is releasably locked onto the hitch connecting device 370 after the hitching manoeuvre has been completed. The locking of the trailer coupler 375 onto the hitch connecting device 370 typically comprises a manual locking operation, for example to operate the trailer coupler 375. The hitching assistance system 500 is operable to provide autonomous, semi-autonomous or remote control of the vehicle 300 to perform the hitching manoeuvre. The hitching assistance system 500 may optionally also identify the position and / or the orientation of the trailer tongue 380. The orientation of the trailer tongue 380 may enable the vehicle 300 to be controlled to achieve a predetermined orientation relative to the trailer 350, for example to facilitate towing after the trailer 350 is hitched to the vehicle 300. The hitching manoeuvre may comprise controlling the vehicle 300 to achieve a hitching angle (i.e., an articulation angle of the vehicle 300 and the trailer 350) within a predetermined range. The hitching assistance system 500 as illustrated in Figure 5 comprises one first controller 510, although it will be appreciated that this is merely illustrative. The first controller 510 comprises first processing means 520 and first memory means 530. The first processing means 520 may be one or more electronic processing device 520 which operably executes computer-readable instructions. The first memory means 530 may be one or more memory device 530. The first memory means 530 is electrically coupled to the first processing means 520. The first memory means 530 is configured to store instructions, and the first processing means 520 is configured to access the first memory means 530 and execute the instructions stored thereon. The first controller 510 comprises an input means 540 and an output means 550. The input means 540 may comprise an electrical input 540 of the first controller 510. The output means 550 may comprise an electrical output 550 of the first controller 510. The input 540 is arranged to receive the image data signal 415 from the at least one imaging sensor 410; and the proximity signal 435 from the at least one parking sensor 430. The image data signal 415 is an electrical signal which is indicative of the image captured by the at least one imaging sensor 410. The proximity signal 435 is an electrical signal which is indicative of the proximity and the position of an obstacle to the vehicle 300. The output 550 is arranged to output a trailer coupler location signal 560 and a trailer coupler height signal 565. The trailer coupler location signal 560 is an electrical signal which identifies the location of the trailer coupler 375 relative to the vehicle 300. A horizontal distance TX1 between the hitch connecting device 370 and the trailer coupler 375 is determined in dependence on the trailer coupler location signal 560. The trailer coupler height signal 565 is an electrical signal which identifies a height TZ1 (referred to herein as the trailer coupler height TZ1) of the trailer coupler 375. The trailer coupler height TZ1 may indicate a relative or an absolute trailer coupler height TZ1. For example, the trailer coupler height TZ1 may indicate the trailer coupler height TZ1 relative to the hitch connecting device 370. For example, the trailer coupler height TZ1 may indicate the trailer coupler height TZ1 relative to a geometric centre of the tow ball 370. In the present embodiment, the trailer coupler height TZ1 of the trailer coupler height TZ1 defines the trailer coupler height TZ1 relative to a datum plane or a ground level. The hitching assistance system 500 is operative to monitor the location and the trailer coupler height TZ1 during performance of a hitching manoeuvre. The trailer coupler location signal 560 and the trailer coupler height signal 565 are updated during the hitching manoeuvre to indicate the location and the trailer coupler height TZ1 at least substantially in real-time. The hitching assistance system 500 comprises a trailer coupler identifier 570 for identifying the trailer coupler 375. The trailer coupler identifier 570 is configured to determine the location and the trailer coupler height TZ1. The trailer coupler identifier 570 receives signals from the vehicle sensors and processes the signals to identify the location and the trailer coupler height TZ1. The input 540 comprises at least one of the image data signal 415 from the at least one imaging sensor 410; and optionally also the proximity signal 435 from the at least one parking sensor 430. The first processing means 520 processes the image data signal 415 to identify the trailer coupler 375. The image processing algorithm may, for example, utilise pattern matching to identify the trailer coupler 375 and / or the trailer tongue 380. The image data signal 415 and / or the proximity signal 435 may be processed to determine a horizontal distance (range) between the vehicle 300 and the trailer 350. Other signals may be used to identify the trailer coupler 375. The trailer coupler identifier 570 outputs the trailer coupler location signal 560 and the trailer coupler height signal 565. The trailer coupler location signal 560 is an electrical signal which identifies the location of the trailer coupler 375 relative to the vehicle 300. The trailer coupler height signal 565 is an electrical signal which identifies the trailer coupler height TZ1. The output 550 is arranged to output a plurality of vehicle control signals 580. The vehicle control signals 580 are electrical signals for controlling operation of one or more vehicle systems to control the dynamic operation of the vehicle 300. In particular, the vehicle control signals 580 are operative to position the vehicle 300 in relation to the trailer 350 to enable hitching to be performed. The vehicle control signals 580 may comprise one or more of the following: a steering control signal 580A output to a steering control system 585A, a torque request signal 580B output to an engine control system 585B, a transmission control signal 580C output to a transmission control system 585C and a braking control system 580D output to a braking control system 585D. The hitching assistance system 500 is configured to control the vehicle 300 to perform the hitching manoeuvre to align the hitch connecting device 370 with the trailer coupler 375. The hitching assistance system 500 may be configured to provide autonomous, semi-autonomous or remote control of the vehicle 300 to perform the hitching manoeuvre. Semi-autonomous control of the vehicle 300 requires one or more driver input to perform the hitching manoeuvre. Autonomous control of the vehicle 300 performs the hitching manoeuvre without driver inputs. Remote control allows the vehicle 300 to be controlled to perform the hitching manoeuvre with the driver outside of the vehicle 300. Alternatively, a driver may control the vehicle 300 to perform the hitching manoeuvre. The driver may operate vehicle controls, such as a steering wheel, an accelerator pedal, a transmission selector and a brake pedal, to control the vehicle 300 to perform the hitching manoeuvre. The control system 100 is arranged to control operation of the suspension system 310. The control system 100 is configured to generate at least one first suspension control signal 160 which is output to the suspension control system 335 to control the height of each of the suspension units S1-S4. The control system 100 as illustrated in Figure 6 comprises one second controller 110, although it will be appreciated that this is merely illustrative. The second controller 110 comprises second processing means 120 and second memory means 130. The second processing means 120 may be one or more electronic processing device 120 which operably executes computer-readable instructions. The second memory means 130 may be one or more memory device 130. The second memory means 130 is electrically coupled to the second processing means 120. The second memory means 130 is configured to store instructions, and the second processing means 120 is configured to access the second memory means 130 and execute the instructions stored thereon. The second controller 110 comprises an input means 140 and an output means 150. The input means 140 may comprise an electrical input 140 of the second controller 110. The output means 150 may comprise an electrical output 150 of the second controller 110. A human-machine-interface (HMI) 155 is provided for controlling operation of the control system 100. The HMI 155 comprises one or more input device for receiving a user input; and one or more output device for outputting information to a user. The one or more input device may, for example, comprise a button or a switch. The one or more output device may comprise a display screen. The HMI 155 in the present embodiment comprises a touch screen (for example, a resistive or capacitive touch screen) configured to output a graphical user interface (GUI). The input 140 is arranged to receive the trailer coupler location signal 560 and the trailer coupler height signal 565 from the trailer coupler identifier 570. As described herein, the trailer coupler location signal 560 identifies the location of the trailer coupler 375 relative to the vehicle 300; and the trailer coupler height signal 565 identifies the trailer coupler height TZ1. In a variant, the control system 100 may be configured to determine the location of the trailer coupler 375 and / or the trailer coupler height TZ1. For example, the input 140 may receive the image data signal 415 and / or the proximity signal 435 and determine the location and / or the trailer coupler height TZ1 using the techniques described herein. The output 150 is arranged to output at least one first suspension control signal 160. The at least one first suspension control signal 160 is an electrical signal which sets a height of the front suspension units S1, S2 and / or a height of the rear suspension units S3, S4. The at least one first suspension control signal 160 is output to the suspension system 310 to adjust the height of one or more of the suspension units S1-S4. The trailer coupler height signal 565 indicates the trailer coupler height TZ1. The control system 100 determines the first target height HH1 of the hitch connecting device 370 in dependence on the trailer coupler height TZ1 indicated by the trailer coupler height signal 565. The first target height HH1 is determined to enable the hitch connecting device 370 to be located directly below (i.e., underneath) the trailer coupler 375. Thus, the first target height HH1 is less than the indicated trailer coupler height TZ1. The first target height HH1 may comprise a predetermined vertical offset (for example 50mm or 100mmm) below the indicated trailer coupler height TZ1 to enable the hitch connecting device 370 to be located under the trailer coupler 375. The second controller 110 is configured to determine if the first target height HH1 of the trailer coupler 375 is within an operating range of the vehicle 300. The operating range may be defined with respect to the range of travel available in the front and rear suspension units S1-S4; and / or the layout of the vehicle 300, for example the wheelbase of the vehicle 300. A hitch connecting device upper limit HUP1 and / or a vehicle trailer hitch lower limit HLW1 are defined for the vehicle 300. The second controller 110 is configured to compare the first target height HH1 to the hitch connecting device upper limit HUP1 (i.e., the upper achievable height of the hitch connecting device 370) and / or the vehicle trailer hitch lower limit HLW1 (i.e., the upper achievable height of the hitch connecting device 370). If the first target height HH1 is greaterthan the hitch connecting device upper limit HUL1, the second controller 110 is configured to set the first target height HH1 to the hitch connecting device upper limit HUP1. If the first target height HH1 is less than the hitch connecting device lower limit HLL1, the second controller 110 is configured to set the first target height HH1 to the hitch connecting device lower limit HLW1. The second controller 110 is configured to determine a current height VZ1 (referred to herein as the hitch connecting device height VZ1) of the hitch connecting device 370, for example in dependence on a current height of the front and rear suspension units S1-S4. The second controller 110 determines a vertical offset between the hitch connecting device height VZ1 and the first target height HH1. The second controller 110 is configured to generate the at least one first suspension control signal 160 to control a height of the body 305 and / orthe pitch angle a of the body 305 to adjust the height of the hitch connecting device 370 from the current hitch connecting device height VA1 to the first target height HH1. The second controller 110 determines an appropriate height of the front suspension units S1, S2 and / or the rear suspension units S3, S4 to locate the hitch connecting device 370 at the first target height HH1. The appropriate heights of the front and rear suspension units S1-S4 may be accessed in a look-up table, for example defining appropriate offsets between the front and rear suspension units S1-S4 to achieve a predetermined change in the hitch connecting device height VZ1. Alternatively, the height of the front suspension units S1, S2 and / or the height of the rear suspension units S3, S4 may be determined dynamically by modelling the vehicle 300 and the trailer 350 in two-dimensions (in a vertical plane) or in three-dimensions. Terrain characteristics, such as a slope angle, may also be modelled. The orientation of the longitudinal axis of the vehicle 300 and the longitudinal axis of the trailer 350 may be modelled to determine the hitch connecting device height VZ1 and the trailer coupler height TZ1. The at least one first suspension control signal 160 may be generated to adjust at least one of the height of the front suspension units S1, S2 and the height of the rear suspension units S3, S4 to change a pitch angle a of the body 305, thereby varying the height of the hitch connecting device 370. By controlling the height of the front suspension units S1, S2 relative to the height of the rear suspension units S3, S4, the pitch angle a of the body 305 can be controlled to increase or decrease the hitch connecting device height VZ1. For example, the height of the rear suspension units S3, S4 may be lowered to reduce the hitch connecting device height VZ1. Alternatively, or in addition, the height of the front suspension units S1, S2 may be raised to increase the hitch connecting device height VZ1. In the present embodiment, the control system 100 is configured to adjust the height of the rear suspension units S3, S4 (to adjust the pitch angle a of the body 305) to locate the hitch connecting device 370 at a height substantially equal to the first target height HH1. In a variant, the control system 100 may increase or decrease the height of the front suspension units S1, S2 and the height of the rear suspension units S3, S4 to raise and lower the body 305, thereby lowering the hitch connecting device 370. The control system 100 is configured to output the at least one first suspension control signal 160 when the horizontal distance TX1 between the vehicle 300 and the trailer 350 is less than or equal to a trailer distance threshold value. The control system 100 determines the horizontal distance TX1 in dependence on the trailer coupler location signal 560 received from the hitching assistance system 500. In a variant, the control system 100 may determine the horizontal distance TX1 in dependence on the image data signal 415 and / or the proximity signal 435. In the present embodiment, the at least one first suspension control signal 160 is output as the vehicle 300 approaches the trailer 350. In a variant, the at least one first suspension control signal 160 while the vehicle 300 is stationary. The hitching assistance system 500 and the control system 100 control the vehicle 300 to locate the hitch connecting device 370 below the trailer coupler 375. The control system 100 is configured to identify when the hitch connecting device 370 and the trailer coupler 375 are aligned with each other. In particular, the control system 100 is configured to identify when the vertical axis of the hitch connecting device 370 and the trailer coupler 375 are aligned with each other. The alignment of the hitch connecting device 370 and the trailer coupler 375 may be within an operating tolerance. The operating tolerance may be predefined, for example as being less than or equal to a radius of the tow ball 370. The control system 100 determines that the hitch connecting device 370 and the trailer coupler 375 are aligned when their respective vertical axis are offset from each other in a horizontal plane by a distance with is less the operating tolerance. The control system 100 is configured to output at least one second suspension control 170 signal to raise the hitch connecting device 370 in dependence on a determination that the hitch connecting device 370 and the trailer coupler 375 are aligned with each other. The at least one second suspension control signal 170 is arranged to adjust at least one of the height of the front suspension units S1, S2 and the height of the rear suspension units S3, S4 to adjust a pitch angle a of the body 305 to increase the height of the hitch connecting device 370. By adjusting the height of the front suspension units S1, S2 and / or the rear suspension units S3, S4, the body 305 is rotated about the transverse axis Y, thereby adjusting the pitch angle a and increasing / decreasing the height of the hitch connecting device 370. For example, the height of the rear suspension units S3, S4 may be increased (relative to the height of the front suspension units S1, S2) to raise the hitch connecting device 370. Alternatively, or in addition, the height of the front suspension units S1, S2 may be decreased (relative to the height of the rear suspension units S3, S4) to raise the hitch connecting device 370. In the present embodiment, the control system 100 is configured to adjust the height of the rear suspension units S3, S4 to adjust the pitch angle a of the body 305 to raise the hitch connecting device 370. In particular, the control system 100 is configured to increase the height of the rear suspension units S3, S4 to reduce the pitch angle a of the body 305, thereby raising the hitch connecting device 370. In a variant, the control system 100 may increase both the height of the front suspension units S1, S2 and the height of the rear suspension units S3, S4 to raise the body 305, thereby raising the hitch connecting device 370. The control system 100 is configured to output at least one third suspension control signal 180 to pause or halt changes in the height of the hitch connecting device 370 in dependence on a determination that the hitch connecting device 370 has engaged (or contacted) the trailer coupler 375. The at least one third suspension control signal 180 being output to stop changes in the height of the front suspension unit S1, S2 and / or the rear suspension units S3, S4. When raising the hitch connecting device 370, the control system 100 determines a second target height HH2 for the hitch connecting device 370. The second target height HH2 is greater than the first target height HH1. The control system 100 is configured to control the suspension system 310 to increase the height of the hitch connecting device 370 from the first target height HH1 to the second target height HH2 in dependence on a determination that the hitch connecting device 370 and the trailer coupler 375 are aligned with each other. The second target height HH2 may be determined in dependence on the trailer coupler height TZ1 indicated by the trailer coupler height signal 565. The second target height HH2 may be substantially equal to the indicated trailer coupler height TZ1. Alternatively, the second target height HH2 may be defined at a predetermined vertical offset (for example 20mm, 30mm or 40mm) below the indicated trailer coupler height TZ1. The predetermined vertical offset is defined to reduce or prevent pre-loading of the trailer coupler 375 which may hinder or prevent operation of the trailer coupler 375, for example preventing operation of the locking device. In the present embodiment, the hitch connecting device 370 comprises a load sensor 390 configured to detect a load applied to the hitch connecting device 370. The load sensor 390 may, for example, comprise a strain gauge, fastened to the tow bar 360 or the bracket 365. The load sensor 390 detects an increased load when the hitch connecting device 370 engages (i.e., contacts) the trailer coupler 375. The load sensor 390 outputs a load signal 395 to the input 140 of the control system 100. In dependence on a determination that the hitch connecting device 370 has engaged the trailer coupler 375, the output 150 is configured to output the at least one third suspension control signal 180 to the suspension system 310 to stop or pause further changes in the height of the hitch connecting device 370. The at least one third suspension control signal 180 may request that the height of the rear suspension units S3, S4 and / or the height of the front suspension units S1, S2 are held constant to prevent the hitch connecting device 370 being raised. Alternatively, the at least one third suspension control signal 180 may request that the height ofthe rear suspension units S3, S4 and / orthe height of the front suspension units S1, S2 are controlled to lower the hitch connecting device 370 to reduce the load applied to the hitch connecting device 370, for example until the load signal 395 indicates a load applied which is less than a predetermined load threshold. In a variant, the control system 100 may process the image data received from the imaging sensor 410 to determine when the hitch connecting device 370 engages the trailer coupler 375. The control system 100 may process the image data to determine when the hitch connecting device 370 is at least partially received inside the trailer coupler 375. For example, the control system 100 may implement an image processing algorithm to determine when an upper portion ofthe hitch connecting device 370 is obscured from view. The control system 100 may determine that the hitch connecting device 370 has engaged the trailer coupler 375 when a predetermined portion of the hitch connecting device 370 is received inside the trailer coupler 375. In dependence on the determination, the output 150 is configured to output at least one third suspension control signal 180 to stop or pause further changes in the height ofthe front and / or rear suspension units S1-S4. The height ofthe hitch connecting device 370 is thereby held constant. The operation ofthe control system 100 to perform a hitching manoeuvre is illustrated in Figures 7A to 7D. The increases and decreases in the vertical height of the front and / or rear suspension units S1-S4 are represented in these figures by vertical arrows directed vertically upwardly and downwardly respectively. In the illustrated example, the vehicle 300 and the trailer 350 are disposed on a horizontal surface. It will be understood that the control system 100 may operate on an inclined surface or an irregular surface. As shown in Figure 7A, the hitching assistance system 500 determines the horizontal distance TX1 between the hitch connecting device 370 and the trailer coupler 375. The hitching assistance system 500 also determines the trailer coupler height TZ1. The front and rear suspension units S1-S4 are at the same height such that the pitch angle a of the body 305 is zero degrees (0°), as shown in Figure 7A. The control system 100 determines the hitch connecting device height VZ1 in dependence on the heights of the front and rear suspension units S1-S4. The hitching assistance system 500 outputs vehicle control signals 580 to reverse the vehicle 300 towards the trailer 350, as illustrated in Figures 7A and 7E3. It will be understood that the hitching assistance system 500 may output steering control signals to align the vehicle 300 and the trailer 350. The vehicle 300 is reversed at a first speed v1 which is less than a threshold speed VTH. The control system 100 monitors the horizontal distance TX1 between the hitch connecting device 370 and the trailer coupler 375. When the horizontal distance TX1 is less than a threshold value, the control system 100 outputs at least one first suspension control signal 160 to adjust the pitch angle a of the body 305 to raise or lower the hitch connecting device 370. In the present embodiment, the at least one first suspension control signal 160 is output to reduce the height of the rear suspension units S3, S4, as shown in Figure 7B. The resulting increase in the pitch angle a causes the hitch connecting device 370 to be lowered. The at least one first suspension control signal 160 controls the front and / or rear suspension units S1-S4 to locate the hitch connecting device 370 at a first target hitch height HH1 which is lowerthan the trailer coupler 375. The hitching assistance system 500 outputs control signals to reverse the vehicle 300 to locate the hitch connecting device 370 below trailer coupler 375, as illustrated in Figure 7C. The vehicle 300 is reversed at a second speed v2 which is less than the first speed v1 as the vehicle 300 approaches the trailer 350. The control system 100 monitors the position of the trailer coupler 375 relative to the hitch connecting device 370. The hitching assistance system 500 stops the vehicle 300 (i.e., v=0) in dependence on a determination that the hitch connecting device 370 and the trailer coupler 375 are aligned with each other vertically. The control system 100 outputs at least one second suspension control 170 signal to raise the hitch connecting device 370 to the second target height HH2. The second target height HH2 is above the first target height HH1. As illustrated in Figure 7D, the height of the rear suspension units S3, S4 are increased, thereby reducing the pitch angle a and raising the hitch connecting device 370 to the second target height HH2. The control system 100 is configured to detect an increased load in the hitch connecting device 370 indicative of the hitch connecting device 370 engaging the trailer coupler 375. The control system 100 halts further increases in the height of the hitch connecting device 370 in dependence on the detection of an increased load. The hitch connecting device 370 is thereby located in the trailer coupler 375. The control system 100 optionally outputs a user prompt to lock the trailer coupler 375. Figure 8 illustrates a method 200 according to an embodiment of the invention. The method 200 is a method of controlling a suspension system 310 of the vehicle 300, such as the vehicle 300 illustrated in Figure 1. In particular, the method 200 is a method of controlling the suspension system 310 to facilitate hitching the vehicle 300 to a trailer 350. The method 200 may be performed by the control system 100 described herein. In particular, the memory 130 may comprise computer-readable instructions which, when executed by the processor 120, perform the method 200 according to an embodiment of the invention. The operation of the method 200 will now be described with reference to a block diagram shown in Figure 8. A user of the vehicle 300 selects a reverse drive ratio for the vehicle 300 and enables the hitching assistance system 500 (BLOCK 202). The vehicle 300 begins to travel in reverse (BLOCK 204). The vehicle 300 may travel autonomously or under the control of a driver. A first check is performed to determine if the hitching assistance system 500 detects a trailer coupler 375 (BLOCK 206). If the hitching assistance system 500 does not detect a trailer coupler 375, a notification is output to the driver to advise that the trailer coupler 375 is not present or has not been detected (BLOCK 208). The vehicle 300 continues to perform the current reversing manoeuvre without affecting changes in the height of the front suspension units S1, S2 and / or the height of the rear suspension units S3, S4 (BLOCK 210). The vehicle 300 performs the reversing manoeuvre without varying the height of the front and rear suspension units S1-S4. The process ends (BLOCK 212). If the first check (BLOCK 206) determines that the trailer coupler 375 is detected, the hitching assistance system 500 determines the height and the location of the trailer coupler 375 (BLOCK 214). A horizontal distance TX1 between the hitch connecting device 370 and the trailer coupler 375 is determined. A height of the trailer coupler 375 relative to a reference plane is determined. The control system 100 determines a first target height HH1 of the hitch connecting device 370 in dependence on the determined trailer coupler height TZ1. The vehicle 300 is manoeuvred towards the trailer coupler 375 (BLOCK 216). The vehicle 300 may be manoeuvred towards the trailer coupler 375 either autonomously, semi-autonomously or under the control of the driver. A second check is performed to determine if the first target height HH1 is within the operating range of the vehicle 300 (BLOCK 218). In particular, the second check determines if the first target height HH1 is less than the hitch connecting device upper limit HUL1; and greater than the hitch connecting device lower limit HLW1. If the first target height HH1 is within the operating range, the control system 100 controls the vehicle suspension system 310 to adjust the height of the hitch connecting device 370 to a height below the determined trailer coupler height TZ1 (BLOCK 220). The vehicle 300 is controlled relative to the trailer 350 to position the hitch connecting device 370 below the determined trailer coupler height TZ1. Once the hitch connecting device 370 is positioned under the trailer coupler 375, the suspension system 310 is controlled to raise the hitch connecting device 370, for example to locate the tow ball 370 in the locating aperture formed in the trailer coupler 375 (BLOCK 222). When the hitch connecting device 370 reaches the second target height HH2 or a load is detected by the load sensor 390, the vehicle suspension system 310 is controlled to hold the height of the hitch connecting device 370 constant (BLOCK 224). A message is output to the driver of the vehicle 300 to inform them that the hitching manoeuvre is complete (BLOCK 260). The driver is responsible for locking the trailer coupler 375 to the hitch connecting device 370. The method ends (BLOCK 265). If the second check (BLOCK 218) determines that the first target height HH1 is outside of the operating range, the control system 100 performs a third check to determine if the first target height HH1 is too high (i.e., the first target height HH1 is greater than the hitch connecting device upper limit HUL1) or too low (i.e., the first target height HH1 is less than the hitch connecting device lower limit HLW1 (BLOCK 228). If the third check (BLOCK 228) determines that the first target height HH1 is greater than the hitch connecting device upper limit HUL1, a notification is output to the driver to advise that the trailer coupler 375 is outside of the operating range of the vehicle 300 (BLOCK 230). The suspension system 310 is controlled to adjust the height of the hitch connecting device 370 to an upper achievable height (BLOCK 232). The vehicle 300 is controlled to locate the hitch connecting device 370 below the trailer coupler 375. The method ends (BLOCK 265). If the third check (BLOCK 228) determines that the first target height HH1 is less than the hitch connecting device lower limit HLW1, a notification is output to the driver to advise that the trailer coupler 375 is outside of an operating range (BLOCK 234. The suspension system 310 is controlled to adjust the height of the hitch connecting device 370 to a lower achievable height (BLOCK 236). The hitching manoeuvre is then paused (BLOCK 238). The hitching manoeuvre is paused to enable the trailer coupler height TZ1 to be adjusted. A prompt may optionally be output to request a reduction in the trailer coupler height TZ1. If during the pause (BLOCK 238) the trailer coupler height TZ1 is not adjusted, the hitching assistance system 500 may control the vehicle 300 to position the hitch connecting device 370 to a predetermined position relative to the trailer coupler 375 (BLOCK 240). For example, the vehicle 300 may be controlled to position the hitch connecting device 370 in a predetermined position which is laterally offset from and / or located in front of the trailer coupler 375. The method ends (BLOCK 212). If during the pause (BLOCK 238) the trailer coupler height TZ1 is increased such that the first target height HH1 is within the operating range, the control system 100 controls the vehicle suspension system 310 to adjust the height of the hitch connecting device 370 to a height below the determined trailer coupler height TZ1 (BLOCK 242). The method then proceeds in accordance with the process described herein when the first target height HH1 is within the operating range. The vehicle trailer hitch 355 in the above embodiment is fixedly mounted to the vehicle 300. As such, the height of the hitch connecting device 370 is fixed. In a variant illustrated in Figures 9A and 9B, the vehicle trailer hitch 355A is a retractable vehicle trailer hitch 355A comprising a retractable hitch connecting device 370A. The retractable hitch connecting device 370A may be selectively deployed and retracted. The retractable hitch connecting device 370A is selectively configurable in a retracted (stowed) position (shown in Figure 9A) and a deployed position (shown in Figure 9B). In the illustrated example, the retractable hitch connecting device 370A is pivotable about a vertical axis. Other mechanisms are contemplated for the retractable hitch connecting device 370A. The height and / or the location of the retractable hitch connecting device 370A vary depending on whether it is in the retracted position or the deployed position. The control system 100 in accordance with this embodiment of the present invention is configured to output the at least one first suspension control signal 160 to adjust the height of the at least one front suspension unit S1, S2 and / or the at least one rear suspension unit S3, S4 so as to position the hitch connecting device 370 at the first target height HH1 when the hitch connecting device 370 is in the deployed position. The control system 100 is configured to determine if the retractable hitch connecting device 370A is configured in the retracted position or the deployed position. In dependence on a determination that the retractable hitch connecting device 370A is configured in the retracted position, the control system 100 is configured to output a hitch connecting device deployment signal HDS to deploy the retractable hitch connecting device 370A. The hitch connecting device deployment signal HDS is output before the at least one first suspension control signal 160. The control system 100 in this embodiment is configured to check that the retractable hitch connecting device 370A is in the deployed position before outputting the at least one first suspension control signal. In a variant, the hitch connecting device deployment signal may be output during performance of the hitching manoeuvre as the vehicle 300 approaches the trailer 350. For example, the hitch connecting device deployment signal may be output when there is a predetermined horizontal distance between the retractable hitch connecting device 370A (in the deployed position) and the trailer coupler 375. Rather than output vehicle control signals 580, the hitching assistance system 500 may be configured to output a series of driver instructions to prompt a driver of the vehicle 300 to make appropriate control inputs to perform the hitching manoeuvre. For example, the driver instructions may comprise one or more of the following: steering angle prompts; torque prompts; transmission prompts; and braking prompts. The hitching assistance system 500 may output driver instructions for controlling the vehicle 300 to position the hitch connecting device 370 in the predetermined position relative to the trailer coupler 375 for hitching the trailer 350 to the vehicle 300. The driver instructions may, for example, prompt the driver to control the vehicle 300 to align the hitch connecting device 370 vertically with the trailer coupler 375. The control system 100 may be configured to control operation of the suspension system 310 to position the hitch connecting device 370 at the first target height HH1 while the driver is controlling the vehicle 300. For example, the control system 100 may control the suspension system 310 to position the hitch connecting device 370 at the first target height HH1 when the horizontal distance TX1 between the vehicle 300 and the trailer 350 is less than or equal to a trailer distance threshold value. The suspension system 310 may be controlled automatically to position the hitch connecting device 370 at the first target height HH1 so that it can be located below the trailer coupler 375, thereby facilitating hitching of the trailer 350 to the vehicle 300. The control system 100 and the hitching assistance system 500 described herein are provided in system 600 for controlling operation of the vehicle 300. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

1. A control system for controlling a suspension system of a vehicle to adjust a height of a hitch connecting device disposed on the vehicle, the suspension system comprising at least one front suspension unit and at least one rear suspension unit, wherein the at least one front suspension unit and / or the at least one rear suspension unit is height adjustable; the control system comprising one or more controller, the control system being configured to:receive a signal indicative of a height of a trailer coupler disposed on a trailer;determine a first target height for the hitch connecting device in dependence on the signal indicating the trailer coupler height; andoutput at least one first suspension control signal to adjust a height of the at least one front suspension unit and / or the at least one rear suspension unit to position the hitch connecting device at the first target height.

2. A control system as claimed in claim 1, wherein the control system is configured to:receive a signal indicating a location of the trailer coupler relative to the hitch connecting device; and output at least one second suspension control signal to adjust the height of the at least one front suspension unit and / or the at least one rear suspension unit to raise the hitch connecting device when the hitch connecting device is at least substantially aligned with the trailer coupler.

3. A control system as claimed in claim 2, wherein the control system is configured to:determine that the hitch connecting device has engaged the trailer coupler and to output a third suspension control signal to stop changes in the height of the at least one front suspension unit and / or the at least one rear suspension unit.

4. A control system as claimed in claim 3, wherein the control system is configured to:receive a load signal from a load sensor configured to detect a load on the hitch connecting device; anddetermine that the hitch connecting device has engaged the trailer coupler in dependence on the load signal.

5. A control system as claimed in any one of claims 2, 3 or 4, wherein the control system is configured to:output a steering control signal and / or a torque request signal to control the vehicle autonomously or semi-autonomously to align the hitch connecting device with the trailer coupler; and / oroutput a steering notification signal and / or a torque notification signal to advise a driver of appropriate steering inputs and / or torque inputs to control the vehicle so as to align the hitch connecting device with the trailer coupler.

6. A control system as claimed in any one of the preceding claims, wherein the first target height is a predetermined distance below the height of the trailer coupler.

7. A control system as claimed in any one of the preceding claims, wherein the control system is configured to:determine a horizontal distance between the hitch connecting device and the trailer coupler; andoutput the at least one first suspension control signal to adjust the height of the hitch connecting device when the determined horizontal distance is less than or equal to a predetermined horizontal distance threshold.

8. A control system as claimed in any one of the preceding claims, wherein the control system is configured to:compare the first target height for the hitch connecting device to a hitch connecting device height upper limit; andif the first target height for the hitch connecting device is greater than the hitch connecting device height upper limit, set the first target height to the hitch connecting device height upper limit.

9. A control system as claimed in any one of the preceding claims, wherein the control system is configured to:compare the first target height for the hitch connecting device to a hitch connecting device height lower limit; andif the first target height for the hitch connecting device is less than the hitch connecting device height lower limit, set the first target height to the hitch connecting device height lower limit.

10. A control system as claimed in any one of the preceding claims, wherein the hitch connecting device is a retractable hitch connecting device selectively configurable in a retracted position and a deployed position;the control system being configured to output the at least one first suspension control signal to adjust the height of the at least one front suspension unit and / or the at least one rear suspension unit so as to position the hitch connecting device at the first target height when the hitch connecting device is in the deployed position.

11. A control system as claimed in claim 10, wherein the control system is configured to: determine a configuration of the retractable hitch connecting device;in dependence on a determination that the retractable hitch connecting device is configured in the retracted position, output a hitch connecting device deployment signal to deploy the retractable hitch connecting device;the hitch connecting device deployment signal being output before the at least one first suspension control signal.

12. A system comprising the control system of any preceding claim and a hitching assistance system that is configured to control dynamic operation of the vehicle, for example to perform a hitching manoeuvre.

13. A vehicle comprising the system of claim 12 or the control system of claims 1 to 11.

14. A method for controlling a suspension system of a vehicle to adjust a height of a hitch connecting device disposed on the vehicle, the suspension system comprising at least one front suspension unit and at least one rear suspension unit, wherein the at least one front suspension unit and / or the at least one rear5 suspension unit is height adjustable; the method comprising:receive a signal indicative of the trailer coupler height indicating a height of a trailer coupler disposed on a trailer;determine a first target height for the hitch connecting device in dependence on the signal indicating the trailer coupler height; and10                    outputting at least one first suspension control signal to adjust a height of the at least one frontsuspension unit and / or the at least one rear suspension unit to position the hitch connecting device at the first target height.

15. Computer readable instructions which, when executed by a computer, are arranged to perform a 15 method according to claim 14.

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