It is known to provide active vehicle suspensions which can vary the ride height of the vehicle so as to provide, for example, a normal ride height for driving on road, and an increased ride height for off road driving where greater ground clearance is required. It is also known to reduce the ride height at high speed where it can be assumed that the road is smooth and better aerodynamics are important, and also to provide an access level for the vehicle where the ride height is lower than is suitable for normal driving. This ride height is only maintained while the vehicle is stationary, or travelling at less than a predetermined low speed, and is designed to enable easy access to and exit from high off-road vehicles, for example.

According to the invention there is provided a suspension system for a vehicle, the system including a controller arranged to control the system so as to operate at at least a first lower ride height and a second higher ride height so as to provide a plurality of modes of operation of the system, wherein one of the modes is an access mode in which the controller maintains the ride height at the first level whilst the vehicle is stationary, but provides an increase to the second level if the vehicle drives off, at least

under some predetermined conditions, characterized in that another one of the modes is a crawl mode in which the suspension system is arranged to override said increase to the second level if the vehicle drives off under said predetermined conditions so that the vehicle can be driven at the first ride height level.

The increase in ride height from the first level is preferably triggered by the vehicle reaching a pre-determined speed which is preferably between about 10 and 20 kph, such as 16kph for example. Alternatively it could be triggered by some other condition or combination of conditions, such as all the vehicle doors being shut and the transmission being put into a gear suitable for driving off, such as first or second gear in a manual gearbox or drive in an automatic, or by a signal from an engine management system of the vehicle indicating that the vehicle is being driven off.

The invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a vehicle according to the invention; Figure 2 is a front view of a user interface of the vehicle in Figure 1; Figure 3 shows the form in which indicator symbols of the interface unit of Figure 2 are represented in the state diagrams of Figures 4 to 10;

Figure 4 is a state diagram showing the ride height functionality of the air suspension system of Figure 1; Figure 5 is a state diagram for the functionality of an off-road mode of the air suspension system of Figures 1 and 4, as represented by the off-road indicator symbol of Figures 2 and 3; Figure 6 is a state diagram for a combined off-road mode selection button and status indicator of the interface unit of Figure 2, which is associated with the off-road mode of Figures 4 and 5 and with the off-road indicator symbol of Figures 2 and 3; Figure 7 is a state diagram for the functionality of an access mode of the air suspension system of Figures 1 and 4, as represented by the access indicator symbol of Figures 2 and 3; Figure 8 is a state diagram for a combined access mode selection button and status indicator of the interface unit of Figure 2, which is associated with the access mode of Figures 4 and 7 and with the access indicator symbol of Figures 2 and 3;

Figure 9 is a state diagram for the functionality of a lock mode of the air suspension system of Figures 1 and 4, as represented by the lock indicator symbol of Figures 2 and 3; and Figure 10 is a state diagram for a combined lock mode selection button and status indicator of the interface unit of Figure 2, which is associated with the lock mode of Figures 4 and 9 and with the lock indicator symbol of Figures 2 and 3.

Referring to the figures, an off-road vehicle 10 includes an air suspension system having a suspension controller 12 which is arranged in use to be capable of altering the ride height of the vehicle 10 through variation of the setting of a set of air suspension modules 14, each of which is associated with a respective wheel 16 of the vehicle 10.

The suspension controller 12 is connected to an interface unit 18, which includes a set of push button switches 20,22,24 each of which is dedicated to the manual selection of an operating mode of the suspension system.

One switch comprises a combined off-road mode selection button and status indicator, referred to as the off-road button 20. A second switch comprises a combined access mode selection button and status indicator, referred to as the access button 22. A third switch comprises a combined

lock mode selection button and status indicator, referred to as the lock button 24. Although no integral lamp units are shown in the figures, the buttons 20,22,24 can be illuminated under the control of the suspension controller 12.

Also included in the display unit 18 and associated one with each push button 20,22,24 is a respective symbol 26,28,30, each of which symbols can be illuminated under the control of the suspension controller 12.

A wheel speed based belly-out/vehicle grounding detection unit 32 is integrated with the suspension controller 12 and is arranged to provide the controller 12 with a signal indicative of a grounded condition of the vehicle 10. The reader is referred to PCT/GB97/01393 for details of a suitable belly- out detection means of this type.

The symbols 26,28,30 remain"secret-until-lit", i. e. each symbol is substantially invisible to a user unless it has been illuminated. The symbols 26,28,30 each comprises a graphic icon which shows a user, when illuminated, which one or more of the suspension modes controlled by their associated button 20,22,24 is/are available for selection.

At any time, only the symbols 26,28,30 which represent the modes which are available to the user for selection are illuminated. If a mode is

entered in which one or more than one of the other modes is/are not available, once the selected mode has been entered the symbol or symbols 26,28,30 for the mode or modes which then become unavailable for selection is/are extinguished and their associated buttons 20,22,24 are operatively disconnected from the suspension controller 12 as appropriate.

The buttons 20,22,24 act as status indicators to show in which mode the system is operating or whether it is in the process of altering the ride height, e. g. so as to move between modes. If a mode is selected by pushing its button 20,22,24, the button 20,22,24 associated with that mode flashes while the suspension controller 12 adjusts the ride height to adopt the selected mode. When the ride height appropriate for the selected mode has been achieved, the suspension system has entered the selected mode and so the button 20,22,24 stops flashing and is constantly illuminated as the status indicator.

If, while the system is operating in a selected mode, the ride height leaves a predetermined tolerance band associated with that mode, the suspension controller 12 varies the ride height to bring it back within the tolerance band. While the ride height is outside the tolerance band and the suspension controller 12 is varying the ride height in this manner, the button 20,22,24 for the selected mode flashes which lets the user know that the ride height status is not that which has been selected and that it is

being adjusted so as to correct for the error between selected ride height and actual ride height.

When the vehicle 10 is powered down, the suspension controller 12 memorises the currently selected mode and on power-up adjusts (if necessary) the suspension ride height so as to remain in/re-adopt that mode.

For the sake of clarity of explanation of the state diagrams of Figures 4 to 10, it will be assumed that on power-up the vehicle 10 is in an on-road mode, in which the ride height is set at a suitable level for normal road use.

The on-road mode is also the default mode which the suspension controller 12 adopts when the vehicle 10 is first powered-up or powered up after the suspension controller's memory has been cleared, e. g. during servicing or a vehicle breakdown.

In the on-road mode, the modes which are available are a towing mode, the access mode and the off-road mode. The towing mode does not have a dedicated button and is entered by pressing the lock button 24, but only if the vehicle 10 is in the on-road mode. In the on-road mode, therefore, all three symbols 26,28,30 are illuminated. The off road symbol 26, however, is extinguished above a predetermined safety speed and this is described in greater detail below.

If the lock button 24 is used when the vehicle 10 is in the on-road mode, the suspension height is locked substantially at the on-road height, which state acts as a towing mode.

The towing mode can also be selected automatically by connection to the vehicle 10 of a trailer. Such a connection could be distinguished from a mere lighting board by, for example, use of a strain gauge on a towbar. In this manner, the system can be prevented from locking itself into the towing mode when connected to only a lighting board, e. g. when using a bicycle rack. Other forms of trailer detection means can be used, such as for example a parking aid transducer used to form a local area map or by configuring differently the wiring between a trailer plug and a lighting board plug.

Once in the towing mode, the suspension controller 12 will not allow the user to move to another mode without prior deselection of the towing mode by pressing the lock-button 24 again, i. e. performing an unlock function, so that the suspension controller 12 reverts to the on-road mode.

When the vehicle 10 is in the towing mode, therefore, the off-road symbol 26 and the access mode symbol 28 are secret and their respective buttons 20,22 are operatively disconnected from the suspension controller 12. The only symbol which is illuminated in the towing mode is the lock

symbol 30 and its associated button 24 is also illuminated so as to indicate that that function has been selected and is in use.

If the vehicle 10 is in the on-road mode and experiences difficulties through grounding, also referred to as belly-out, which are detected by the belly-out/grounding detection unit 32, the off-road button 20 flashes and the suspension controller 12 automatically starts to adopt the off-road mode in an attempt to clear whatever obstacle is causing the grounding. The automatic raising of the ride height to an over-ride ride height is performed progressively (up to the maximum of the off-road ride height) so that the vehicle 10 is raised only high enough to clear the obstacle. This feature is only implemented below the predetermined safety speed, as discussed below.

The off-road mode can be selected from the on-road mode or from the access mode and its availability is indicated by illumination of the off-road symbol 26. The off-road mode is selected by pressing the off-road button 20 but it should be noted that the off-road symbol 26 is illuminated (and therefore the off-road mode available) only if the vehicle speed is below a predetermined and pre-settable safety speed. The safety speed acts as an interlock to prevent use of the vehicle 10 with the suspension modules 14 at an off-road height at high speed, where the raised centre of gravity might reduce user safety. The safety speed chosen depends on the particular

vehicle 10 but may conveniently be set, for example, somewhere between 40 and 60 kph (25 and 37.5 mph).

If the vehicle speed exceeds the safety speed while in the off-road mode, the ride height is altered to the on-road mode. The off-road button 20 flashes during the transition to the on-road mode and is extinguished once that mode has been achieved, which means that the off-road mode must be re-selected if abandoned in this manner. The off-road symbol 26 remains extinguished above the safety speed because the off-road mode is not then available for selection but is illuminated once more when the vehicle speed falls below the safety speed.

When the off-road mode symbol 26 is illuminated and the mode is selected by pressing the off-road button 20, the button 20 flashes as the suspension controller 12 raises the ride height to the off-road height. Once at the off-road height, the off-road symbol 26 remains illuminated and the off-road button 20 stops flashing and is constantly illuminated so as to then act as the status indicator.

If the vehicle 10 is in the off-road mode and experiences difficulties through grounding, also referred to as belly-out, which are detected by the belly-out/grounding detection unit 32, the off-road button 20 flashes.

To deselect the off-road mode and return to the on-road mode, the user merely presses the off-road button 20 again. In similar fashion to the entry to the off-road mode, the off-road button 20 flashes while the suspension controller 12 lowers the ride height back down to the on-road ride height.

Once at the on-road mode ride height, the off-road button 20 stops flashing and its illumination is extinguished. The off-road symbol 26, however, remains illuminated so as to indicate that the off-road mode is still available for re-selection if so desired.

When in the off-road mode or while moving there, the access symbol 28 remains illuminated because the access mode is available directly from the off-road mode without having to go back through the on-road mode.

When in the off-road mode, however, the lock symbol 30 is extinguished and the lock button 24 is operatively disconnected from the suspension controller 12. This is because it is deemed undesirable to lock the ride height in the off-road mode so that the user cannot be caught unawares by forgetting he has raised the centre of gravity of the vehicle 10. Thus, in the off-road mode, only the off-road symbol 26, the off-road button 20 and the access symbol 28 are illuminated.

From either the on-road mode or the off-road mode, it is possible to select the access mode and its symbol 28 is therefore illuminated in both the

on-road and off-road modes. The ride height in the access mode is at its lowest, so as to allow easier occupant access and for easier loading and unloading of goods.

When the access symbol 28 is illuminated and the access button 22 is pressed, the suspension controller 12 lowers the ride height to its lowest setting and, while lowering the ride height, flashes the access button 22.

When the access ride height has been achieved, the access button 22 stops flashing and is illuminated constantly so as to act as the status indicator.

When entering the access mode from either the on-road mode or the off- road mode, the off-road symbol 26 remains illuminated, because it is possible to move directly from the access mode to either the on-road mode or the off-road mode. The lock symbol 30 is also illuminated in the access mode, as will be explained below.

To move to the on-road mode from the access mode, the user simply presses the access button 22, which deselects the access mode and the access button 22 flashes until the ride height has been altered to the on-road mode.

When the on-road mode has been achieved, the access button 22 stops flashing and its illumination is extinguished but the access symbol 28 remains illuminated because that mode is available for direct selection from the on-road mode.

If the vehicle 10 is in the access mode and the vehicle speed exceeds the drop-out speed, the suspension controller 12 alters the ride height to the on- road ride height, so as to reduce the likelihood of vehicle damage, which might be caused for example by high speeds with lowered ride height.

If the suspension controller 12 drops out of access mode in this manner, the access button 22 flashes until the on-road height has been achieved and is then extinguished. The access symbol 26 remains illuminated as that mode can still be directly selected/re-selected from the on-road mode.

To re-enter access mode when it has been abandoned by dropping-out, it is necessary to specifically re-select it using the access button 22. The access mode drop-out speed is pre-set in the suspension controller 12 and may, for example, be in the region of 16 kph (10 mph).

The access mode can only be entered if the vehicle 10 is substantially stationary or by pre-selecting the access mode from the either the on-road mode or the off-road mode, which is known as"access pre-select".

If the vehicle 10 is travelling above the access mode drop-out speed in either the off-road mode or the on-road mode, the suspension controller 12 will not allow entry to the access mode except through access pre-select.

Access pre-select is only available below a pre-set intermediate vehicle speed, which may for example be in the order of 40 to 80 kph (25 to 50 mph), so that there is a reasonable chance that the speed will have dropped to or below the drop-out speed within a predetermined time-out. If the vehicle speed does not fall below the drop-out speed within the time-out, access pre- select is cancelled but may be re-selected.

When the access mode is pre-selected and the vehicle speed is below the intermediate speed, the ride height is altered to adopt an intermediate position in between the on-road mode ride height and the access mode ride height, so that the access mode can be entered with a shorter delay than would be necessary if the suspension controller 12 had to lower the ride height the full distance in substantially one step.

If access mode is pre-selected above the intermediate speed, the ride height is not altered until the vehicle speed drops to or below the intermediate speed and only if this happens within a pre-set period of time after access pre-select has been selected. In an alternative embodiment, it would be possible to extinguish the access symbol 28 when the vehicle 10 is travelling above the intermediate speed so as to indicate that it is not possible to select the access mode, even through access pre-select, while travelling above the intermediate speed.

If a vehicle door (not shown) is opened, the ride-height is frozen regardless of the mode selected. Under such a door-open ride height freeze, if the access mode was pre-selected for example whilst operating in the off- road mode, the user can at least benefit from the reduction in ride height to the intermediate level.

Outside the door-open ride height freeze, when the vehicle 10 is next stationary or its speed reduces to below the drop-out speed, the ride height is altered and the access button 22 flashes until the access mode has been entered, after which it is illuminated constantly as the status indicator.

If the access mode is entered from the on-road mode, the lock symbol 30 remains illuminated. If the access mode is entered from the off-road mode, the lock symbol 30 is illuminated once the ride height has been altered to the access mode ride height. Thus, in the access mode all three symbols 26, 28,30 are illuminated, as is the access button 22.

A crawl mode is available, but only from the access mode. To enter the crawl mode, the lock button 30 is pressed while the suspension system is in the access mode. The crawl mode locks the vehicle 10 at the access mode ride height and may, for example, be found useful in areas with a height restriction such as in garaging.

Once locked in the crawl mode, the access symbol 28, the access button 22, the lock symbol 30 and the lock button 24 are all illuminated constantly.

In the crawl mode, the access mode drop-out speed is over-ridden, so as for example to prevent the ride height from rising unexpectedly if the user exceeds the drop-out speed in a multi-storey car-park with restricted headroom.

With respect to parking in areas of restricted headroom, it is advantageous that the suspension controller 12 memorises the mode settings on power-down. In this manner, when the vehicle 10 is next started, it remembers that it was in crawl mode when it was switched off and stays in that mode on power-up. This reduces the risk of vehicle and building damage in, for example, a garage having a relatively low roof.

From the crawl mode, it is not possible to move to the on-road mode or to the off-road mode without deselecting the crawl mode first. This means that the off-road mode is not directly available from crawl mode and, therefore, the off-road symbol 26 is extinguished while in the crawl mode.

The crawl mode is deselected by pressing the lock-button 24, whereupon the illumination of the lock button 14 is extinguished. The on-road mode and the off-road mode become available once more and the off-road symbol 26 is illuminated.

If a belly-out/grounded condition is detected while in the crawl mode, the suspension controller 12 does not automatically raise the ride height, in case the vehicle 10 is in an area with a low height restriction. Under these circumstances the user must make a conscious decision to allow the ride height to be raised. One way in which this can be implemented by the user is to press the lock button 24 so as to unlock the suspension controller 12 from the crawl mode. This puts the system back into access mode and the ride height will then be raised automatically in conformance with the normal belly-out procedure.

If the vehicle 10 is in the towing mode and a belly-out condition is detected, the suspension controller 12 temporarily suspends the towing mode so that the ride height can be raised automatically and the obstacle can be over-come.

If there is an air leak, the ride height will tend to drop over time and it will be necessary to adjust it so as to regain the set ride height. A similar situation occurs if compensation/adjustment is necessary for changes in the ambient temperature or through heavy loading. If the vehicle 10 is in the off-road mode, the access mode or the crawl mode and such adjustment to ride height is necessary, the off-road or access button 20,22 flashes as appropriate while the adjustment takes place.

The suspension controller 12 is arranged to limit functionality in the event of fault conditions. For example, if there is a fault with one of the suspension units 14 such that air cannot be exhausted, it would be undesirable to allow entry to the off-road mode because it might prove difficult to lower the ride height later, even if the safety speed were to be exceeded. Under these circumstances, the suspension controller 12 disables the off-road function and its symbol 26 is not illuminated beyond a bulb check on vehicle power-up, which indicates to a user that there is a fault as a mode (off-road) which should be available has been disabled.