GB2347125A

GB2347125A - Active rear and semi-active front anti-grounding vehicle suspension system

Info

Publication number: GB2347125A
Application number: GB0013851A
Authority: GB
Inventors: Michael John Gallery
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1996-05-22
Filing date: 1997-05-15
Publication date: 2000-08-30
Anticipated expiration: 2017-05-15
Also published as: GB2347125B; GB0013851D0

Abstract

A vehicle suspension system is described for a vehicle having two rear wheels on opposite sides, at least one front wheel (12), and a body (16). The system comprises rear wheel suspension for controlling vertical movement of the rear wheels relative to the body, a control unit (40) arranged to level the vehicle solely by controlling the rear wheel suspension, front wheel suspension (18) for controlling vertical movement of the front wheel (12) relative to the body (16), and grounding detection means (58) for detecting grounding of the vehicle body. The front wheel suspension (18) is arranged to operate passively during normal operation of the vehicle but actively to raise the vehicle body (16) relative to the front wheel (12) if grounding is detected.

Description

A VEHICLE SUSPENSION SYSTEM The invention relates to a motor vehicle and is particularly, but not exclusively, concerned with a suspension which can be controlled to minimise the risk of a multi-purpose vehicle becoming stuck as a result of grounding when being driven over rugged terrain.

Multi-purpose vehicles designed for on-road and offroad use are normally designed so that there is considerable clearance between the vehicle body and the ground in order to avoid grounding of the vehicle body wherever possible. Despite large ground clearances, it is well known that grounding can occasionally occur.

The present invention provides a vehicle suspension system for a vehicle having two rear wheels on opposite sides of the vehicle, at least one front wheel, and a body, the system comprising rear wheel suspension means for controlling vertical movement of the rear wheels relative to the body, control means arranged to level the vehicle solely by controlling the rear wheel suspension means, front wheel suspension means for controlling vertical movement of the front wheel relative to the body, and grounding detection means for detecting grounding of the vehicle body, the front wheel suspension means being arranged to operate passively during normal operation of the vehicle but actively to raise the vehicle body relative to the front wheel if grounding is detected.

A vehicle suspension and a method of controlling the same will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a diagrammatic view looking rearwardly of a vehicle and showing part of a front suspension of the vehicle and Figure 2 is a view similar to Figure 1 showing the suspension with the body raised to clear an obstruction on the ground.

A four wheel drive vehicle 10 has two front and two rear ground engageable wheels. The rear wheels are mounted on rear wheel suspensions which are actively controlled to provide self levelling of the vehicle. The front wheels are mounted on front wheel suspensions, one of which is shown in Figures 1 and 2. The wheel 12 is mounted for rotation at one end of a suspension arm 14 which is pivotally connected at its inner end to a body 16 of the vehicle 10.

A suspension strut 18 is arranged between the suspension arm 14 and the body 16 and comprises a damper 20 having a body 22 and a piston rod 24. The body 22 is pivotally attached to the suspension arm 14 and the upper end of the piston rod 24 is pivotally attached to the body 16. The piston rod 24 passes slidably through a plate 26 and a spring 28 is arranged in compression between the damper body 22 and the plate 26. The plate 26 abuts a projection 30 at the upper end of the piston rod 24. An air sleeve 32 is sealingly secured to the projection 30 and to the body 22 of the damper 20.

A pressure sensor 34 is provided on the sleeve 32 for sensing the pressure of air within a chamber 36 defined by the sleeve 32 and a suitable inlet/outlet 38 is provided on the sleeve to enable air to enter and leave the chamber 36.

Air pressure in the sleeve 32 partly supports the body 16 with the spring 28 providing additional support. If desired, the entire weight of the body 16 could be supported by an air spring instead of providing additional springing such as the spring 28.

A height sensor H such as a linear transducer is mounted between the projection 30 and the suspension arm 14. Instead of using a linear transducer H, a rotary transducer could be connected by a suitable linkage to the suspension arm 14.

The sensor 34 is connected to a control unit 40. The control unit 40 is connected to a valve 42 in a line 44 between the inlet/outlet 38 and a source 46 of compressed air. The source 46 of compressed air is arranged to maintain a pressure in the chamber 36 which is slightly above atmospheric pressure, for example 2 bar. The pressure is maintained substantially at that level during normal ride of the vehicle, preventing collapse of the sleeve.

The wheel 12 is. drivable in known manner from an engine and transmission 48 via a universal joint 50, a drive shaft 52 and a constant velocity joint 54. An anti-lock braking system (ABS) ring 56 is mounted on the wheel 12 and an ABS sensor 58 is suitably mounted adjacent the ring 56. The ABS sensor 58 is connected to the control unit 40.

Alternatively, the wheel spin signal could be obtained from what is known in the art as a sensor bearing where a speed sensor is contained within the bearing or a seal for the bearing.

Figure 1 shows the suspension in a typical position when driving along a normal road. If the vehicle is driven off the road on to a rugged terrain, there is a risk that the body 16 may occasionally make contact with an obstruction such as a large mound 60 on the ground. When the body makes contact with the mound 60, increased traction will be required at a contact patch 62 between the wheel 12 and the ground and increased torque applied to the wheel to overcome the resistance of the mound can result in wheel spin. The wheel spin is sensed by the ABS sensor 58 and a signal is transmitted to the control unit 40. The control unit 40 compares the signal via an algorithm with a predetermined threshold value. The algorithm and threshold value are determined by calculation and computer modelling and subsequently refined and validated by development on a vehicle.

If the wheel spin is accompanied by a reduction of load on the wheel 12 of the vehicle as sensed by the pressure sensor 38 and confirmed by a downward movement of the wheel 12 as detected by the height sensor H, the control unit 40 will deduce by the algorithm that the vehicle has grounded.

After the control unit has deduced that grounding has occurred, valve 42 is opened to allow air to be introduced into the chamber 36 thereby raising the piston rod 24 and lifting the body 16 clear of the mound 60. Body weight is then re-transferred to the wheels and traction at the contact patch 62 is restored to enable the vehicle to continue its progress.

A timer 64 in the control unit 40 ensures that the raised position of the body 16 is maintained only for a given period to enable the vehicle to move clear of the mound 60 before the body is allowed to return to its Figure 1 position. At the end of the period, the valve 42 is open to permit air to leave the chamber 36 until the body resumes its normal ride height dictated by the spring 28 and the pressure in chamber 36 returns to normal ride pressure.

As will be appreciated from Figure 2, the lifting of the body 16 to clear the mound 60 will result in increased angular displacement of the drive shaft 52. Whilst the increased angular displacement may easily be accommodated by the drive joints 50,54, it is desirable to resume normal ride height as soon as possible to minimise any strain in the joints due to the increased angular displacement. The use of the timer 64 ensures that the body 16 will be raised only for a specific period of time so that the driver cannot drive a vehicle with the body permanently in its raised position.

The control system 40 is set so that pressure reduction in chamber 36 due to relatively light contact between the body 16 and the mound 60 will produce a signal in the control unit 40 which then awaits the signals from the ABS sensor 58 and height sensor H. If the friction between the body 16 and mound 60 increases sufficiently to cause wheel spin and downward movement of the suspension arm 14, the control unit 40 then triggers the raising of the body 16 as described above. Hitherto, struts 18 similar to that shown in Figure 1 have been used on rear wheel suspensions of multi-purpose vehicles and reduced pressure due to grounding of the vehicle has been sensed to provide a signal which raises the body. However, a control unit used in such a case has to be set so that fluctuations in pressure which occur when driving the vehicle over rugged ground will not trigger raising of the body. Therefore, in order for the prior systems to operate, substantial grounding has to take place between the body and the ground so that considerable weight loss will be sensed at the wheel in order to trigger raising of the body. Normally that means prolonged wheel spin and substantial wearing away of the contact patch 62 to leave a deep rut which is undesirable from the point of view of tyre wear and environmental damage.

With the present invention, the onset of grounding can be sensed earlier and is advantageous over the prior systems.

By using signals from both the ABS sensor 58, the height sensor H and the pressure sensor 36, wheel spin resulting, say, from driving on icy roads will not trigger. the raising of the body 16.

It is also desirable to prevent inadvertent raising of the body in other situations where such raising of the body is inappropriate. In that respect, certain steps can be taken as follows: 1. Grounding is most likely to occur when a vehicle is being driven over rough terrain. Normally, the vehicle will be driven in a low drive ratio, for example first gear or reverse gear, when being driven over rough terrain. If the vehicle has a range change transmission, there is every possibility that"low range"will be selected when the vehicle is being driven over uneven ground. A suitable detector, for example a switch, may be used to detect selected ratios so that it becomes possible to raise the body only when the vehicle is being driven in a low ratio.

In that way, inadvertent raising of the body when the vehicle is being driven in high ratio would be prevented.

Drive ratios could be detected by using a switch similar to a reversing light switch or by comparing engine and wheel speeds.

2. The algorithm could be set to prevent raising of the body 16 above a set vehicle speed which could be detected by the ABS sensor 58. It is likely that a vehicle in danger of grounding is likely to be driven over rough terrain at a much lower speed than when the vehicle is being driven along the road.

3. Throttle pedal position could be sensed to provide an electronic signal for use by the control unit 40. In that way, the amount of torque being produced by the engine could be deduced and compared to a signal generated by wheel spin and, say, vehicle acceleration, thereby creating another plausibility check for grounding.

4. In order to ensure that the control unit 40 does not cause the vehicle to rise or fall at an inconvenient time, the control unit 40 may sense when the ignition circuit is switched on and the doors are closed. In that way, it will not be possible to raise the body when the ignition is switched off or if a door is open. A signal to indicate that the doors are closed can be obtained from the normal courtesy light switches of the vehicle.

The system may have provision for a manual override switch to enable the vehicle to be raised and lowered as required by the driver. Such an override arrangement could be useful if the timer 64 were to trip out too quickly before the vehicle has cleared the mound 60. The manual override would be associated with a suitable form of blocker to prevent raising of the body at high vehicle speeds.

Whilst specific reference has been made to sensing of parameters associated with one wheel 12, it will be appreciated that all of the wheels of the vehicle, both front and rear, could be arranged as shown in Figure 1 with a common control unit 40 and source 46 of compressed air.

The control unit would then receive signals relating to all four wheels and air would be introduced into the chambers 36 of all four struts 18 to raise the body.

As mentioned above, the embodiment described includes a known air-levelled suspension systems which is designed to keep the vehicle level irrespective of the distribution of load, and which operates on rear wheels only. The suspension for the front wheels is therefore arranged to provide an anti-grounding function according to this invention as described above. This provides an antigrounding system at little extra cost as components such as the control unit 40 and a source of compressed air 46 are already required for the active rear suspension system.

Claims

CLAIMS 1. A vehicle suspension system for a vehicle having two rear wheels on opposite sides of the vehicle, at least one front wheel, and a body, the system comprising rear wheel suspension means for controlling vertical movement of the rear wheels relative to the body, control means arranged to level the vehicle solely by controlling the rear wheel suspension means, front wheel suspension means for controlling vertical movement of the front wheel relative to the body, and grounding detection means for detecting grounding of the vehicle body, the front wheel suspension means being arranged to operate passively during normal operation of the vehicle but actively to raise the vehicle body relative to the front wheel if grounding is detected.
2. A system according to claim 1 wherein the front wheel suspension means is arranged to act passively unless grounding is detected.
3. A system according to claim 1 or claim 2 wherein the front wheel suspension means comprises a fluid operable member and the system further comprises a source of fluid pressure arranged to introduce fluid under pressure into the fluid operable member to raise the body relative to the front wheel in the event of grounding.
4. A system according to claim 3 wherein the front wheel suspension member comprises a strut which includes a sleeve into which fluid can be introduced to raise the body.
5. A system according to claim 3 or claim 4 arranged to maintain fluid in the fluid operable member at a pressure slightly above atmospheric pressure during normal operation of the vehicle.