GB2359527A

GB2359527A - Vehicle suspensions

Info

Publication number: GB2359527A
Application number: GB0004032A
Authority: GB
Inventors: Theodore Edmund Cooper Potter
Original assignee: MG Rover Group Ltd; Land Rover Group Ltd
Current assignee: MG Rover Group Ltd; Jaguar Land Rover Ltd
Priority date: 2000-02-22
Filing date: 2000-02-22
Publication date: 2001-08-29
Anticipated expiration: 2020-02-22
Also published as: GB2359527B; GB0004032D0

Abstract

A suspension for a four-wheeled vehicle has longitudinal linking of the front and rear wheels, 10, 16; 12,18, on each side of the vehicle and diagonal links linking the diagonally-opposite pairs of wheels, 10, 18;12,16. The links may be formed by torsion bars 30, 32, 36, 38, 40, 42 or by fluid connections between hydraulic suspension units (Fig.2). The longitudinal links resist vehicle bounce and roll, opposing vertical movement of the two wheels on one side in the same direction, and the diagonal links resist pitch and roll, opposing opposite movements of the two wheels of a diagonal pair. The suspension is thus stiff in roll and soft in cross articulation.

Description

2359527 Vehicle Susi)ensions The present invention relates to vehicle

suspensions, in particular but not exclusively to suspensions for off-road vehicles.

It is well known that to achieve good levels of traction in off-road vehicles it is desirable to have a suspension system that offers very low resistance to cross- articulation, but that, particularly for on-road driving, it is desirable to have a suspension which is stiff in roll. Various suspension systems have been proposed to meet these requirements.

The present invention provides a suspension for connecting two front wheels and two rear wheels to a sprung part of a vehicle the suspension comprising first and second longitudinal interconnection means each interconnecting the two wheels on a respective side of the vehicle and being arranged to resist movement of said two wheels in the same vertical direction more than that in opposite directions, and first and second diagonal interconnection means each interconnecting a respective diagonally opposite pair of said wheels and being arranged to resist movement of said two wheels in opposite vertical directions more than that in the same vertical direction.

The sprung part of the vehicle to which the suspension is attached may be a chassis, if the vehicle has a separate chassis, or part of the vehicle body.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a perspective view of a vehicle suspension according to a first embodiment of the invention, Figures 2 is a perspective view of a vehicle suspension according to a second embodiment of the invention.

Referring to Figure 1 a vehicle has two front wheels 10, 12 each connected to its chassis 8 by means of an independent suspension including a front suspension arm 13, 14, and two rear wheels 16, 18 connected to its chassis be means of a beam axle 20. The front suspension arms 13, 14 are pivotably mounted on the vehicle chassis so that they each rotate about an axis X X substantially parallel to the longitudinal centre line C - C of the vehicle to allow vertical wheel travel. Two reversing arms 22, 24 are also mounted at the rear of the vehicle, one associated with each rear wheel 16, 18. These reversing arms have an inboard end 26 connected by means of a vertical link 28 to the beam axle 20 at a point between the centre line of the vehicle and the respective rear wheel, and an outboard 29 end pivotably connected to the chassis. This means that as the beam axle 20 rotates in one direction relative to the chassis 8 as a result of vehicle roll or cross articulation, the reversing arms 22, 24 rotate in the opposite direction.

An outer torsion bar 30, 32 extends longitudinally down each side of the vehicle having one end connected to the base of the respective front suspension arm 13, 14 near its point of connection to the chassis 8, and the other end connected to the outboard end of the respective reversing arm, near its point of connection to the chassis. These torsion bars 30, 32 are shown as being in two parts joined together by a cranked section 34, but a single straight torsion bar would operate in the same manner and could equally be used. Each outer torsion bar 30, 32 and its respective reversing link 22, 24 therefore forms a longitudinal interconnection between the two wheels on one side of the vehicle. The torsion bar 30, 32 is put under torsion by movement of the two wheels 10, 16 or 14, 14 vertically in the same direction, but not, 6 r at least only to a much lesser extent, by movement of the two wheels vertically in opposite directions. The longitudinal interconnections therefore oppose bounce and roll type movements of the vehicle, but not pitch or cross axle articulation. It will be appreciated that the relationship between the amount of rotation of the front end of the torsion bars 30, 32 by movement of the front wheels, and the amount of rotation of the rear ends of the torsion bars 30, 32 by the same amount of vertical movement of the rear wheels can be controlled by varying various aspects of the suspension design. These aspects include the length of the reversing arms 22, 24, the distance of their point of connection to the beam axle from its centre point, and the length of the front suspension arms 13, 14. These aspects can therefore be controlled so that equal and opposite vertical movements of the two interconnected wheels results in no torsion in the torsion bars, or so that, with such movements, one end of the torsion bar 30, 32 is rotated more than the other so a low level of torsion is applied, and hence a low level of resistance to the wheel movement provided.

Four inner torsion bars 36, 38, 40, 42 are also provided, those 36, 36 at the front of the vehicle having their front end connected to the base of the respective suspension arm 13, 14, and those 40, 42 at the rear of the vehicle each having their rear end connected to the base of the respective reversing arm 22, 24. At the rear ends of the two front inner torsion bars 36, 38 and the front ends of the two rear inner torsion bars 40, 42 a crank portion 44 is provided which extends vertically downwards. The bottom end of each of these crank portions 44 is connected by a rigid diagonal link 46 to the diagonally opposite one. Therefore each diagonally opposite pair of wheels is interconnected by a diagonal interconnection comprising two of the inner torsion bars 36, 38, 40, 42, two of the depending crank portions 44 and one of the diagonal links 46. These diagonal interconnections oppose vertical movement of the two diagonally opposite wheels vertically in opposite directions, but not, or only to a much lesser extent their vertical movement in the same vertical direction. The diagonal interconnections therefore resist pitch and roll type movements, but not bounce or cross articulation. As with the longitudinal interconnections, the system can be tuned so that a low level of resistance to equal movements of the diagonal pair of wheels in the same direction is provided, if such resistance is required. However for the lowest resistance to cross articulation, this 5 resistance will be arranged to be zero.

The total effect of the system is therefore as follows. Vehicle roll is opposed by both the longitudinal 30, 32 and the diagonal 36, 46, 42; 38, 46, 40 interconnections, cross articulation is not opposed significantly by any of the interconnections, pitch is opposed solely by the diagonal interconnections and bounce is opposed solely by the longitudinal interconnections. This means that the suspension is very stiff in roll and very soft in cross articulation, and that the pitch, roll and bounce stiffliesses can all be controlled substantially independently by altering the absolute and relative stiffnesses of the longitudinal and diagonal interconnections.

In the embodiment shown the whole weight of the vehicle is supported by the longitudinal links, there being no separate springs other than those shown for supporting the vehicle. It will be appreciated that further springs could be added, for example coil springs at each corner, but that these would lead to some resistance to cross articulation which is usually undesirable, particularly in an off- road vehicle.

The interconnection system described above can also be used in an all independent suspension system. In this case the reversing links 22, 24 will need to be replaced by a suitable mechanism for converting rotation of the suspension arms at one end of the vehicle, into rotation in the opposite sense of the ends of the inner and outer torsion bars. This could be achieved by a variety of simple mechanical mechanisms.

Referring to Figure 2, a second embodiment of the invention uses a fully independent suspension with two front wheels 110, 112 each connected to the vehicle chassis by a respective suspension arm 113, 114 and two rear wheels 116, 118 each connected to the vehicle chassis by a respective suspension arm 119, 120.

Each of the suspension arms 113, 114, 119, 120 is pivotably mounted on the vehicle chassis so that it rotates about an axis X - X substantially parallel to the longitudinal centre line of the vehicle to allow vertical wheel travel.

Each of the suspension arms 113, 114, 119, 120 has a first hydraulic unit 122 connected to it comprising a piston 124 and a cylinder 126, the piston 124 being connected to the upper side of the respective suspension arm 113, 114, 119, 120 at a point outboard of its pivot axis X - X and the cylinder 126 being mounted on the vehicle chassis or body. The piston and cylinder therefore define a hydraulic chamber 128 the volume of which is decreased by vertically upward movement of the respective wheel and increased by downward movement of the wheel. Each hydraulic chamber is connected to a respective accumulator 130, and, by means of a hydraulic pipe 122a, to the hydraulic chamber of the first hydraulic unit 122 associated with the other wheel on the same side of the vehicle. This therefore forms two longitudinal interconnections, each between the two wheels on one side of the vehicle. Vertical movement of the two wheels in the same direction is resisted because the combined volume of the two hydraulic chambers 128 is reduced or increased and hydraulic fluid is urged into or out of the accumulators 130. Vertical movement of the two wheels in opposite directions is not resisted, or at least not to a significant extent, because fluid is simply transferred from one of the hydraulic chambers 128 to the other. These longitudinal interconnections therefore perform the same function as those in the first embodiment of the invention.

A second hydraulic unit 132 is also connected to each suspension arm 113, 114, 119, 120. These hydraulic units are the same as the first, the two at the front of the vehicle also being attached to the upper side of the front suspension arms 113, 114, but the two at the rear being attached to the under side of the two rear suspension arms 119, 120. Therefore the volume of the chambers in the rear second hydraulic units is decreased by downward vertical movement of the rear wheels and increased by upward vertical movement. As well as being connected to its respective accumulator, each hydraulic chamber of the second hydraulic units 132 is connected by means of a hydraulic pipe 132a to that associated with the diagonally opposite wheel. This therefore forms two diagonal interconnections 132, 132a, each between a respective pair of diagonally opposite wheels 110, 118; 112, 116. These diagonal interconnections 132, 132a resist vertical movement of the respective pair of diagonally opposite wheels 110, 118; 112, 116 in opposite directions, but not, or at least not significantly, their movement in the same vertical direction. These diagonal interconnections 132, 132a therefore perform the same function as the diagonal interconnections in the first embodiment of the invention.

Therefore, as with the first embodiment, vehicle bounce is resisted by the longitudinal interconnections 122, 122a, which also support the weight of the vehicle, pitch is resisted by the diagonal interconnections 132, 132a, roll is resisted by both the longitudinal and the diagonal interconnections, and cross articulation is not significantly resisted by any of the interconnections.

It will be appreciated that the packaging of the hydraulic units can be varied significantly to suit the particular vehicle. For example they could all lie substantially horizontally and be connected to the suspension arms by suitable crank arms. It will also be appreciated that the design of the longitudinal links is substantially independent from that of the diagonal ones. For example the longitudinal links could be formed from torsion bars as in Figure 1, and the diagonal ones by hydraulic links as in Figure 2.

Claims

A suspension for connecting two front wheels and two rear wheels to a sprung part of a vehicle the suspension comprising first and second longitudinal interconnection means each interconnecting the two wheels on a respective side of the vehicle and being arranged to resist movement of said two wheels in the same vertical direction more than that in opposite directions, and first and second diagonal interconnection means each interconnecting a respective diagonally opposite pair of said wheels and being arranged to resist movement of said two wheels in opposite vertical directions more than that in the same vertical direction.
2. A suspension according to claim 1 wherein the longitudinal interconnection means each comprise a torsion bar arranged to be put under torsion by vertical movement of the respective pair of wheels in the same vertical direction.
3. A suspension according to claim 2 wherein each of said torsion bars is arranged to be put under substantially no torsion by vertical movement of the respective pair of wheels in opposite vertical directions
4. A suspension according to any foregoing claim wherein each diagonal interconnection means each comprises a torsion bar arranged to be put under torsion by vertical movement of the respective pair of wheels in opposite vertical directions.
5. A suspension according to claim 4 wherein each of the torsion bars of the diagonal interconnection means is arranged to be put under substantially no torsion by vertical movement of the respective pair of wheels in the same vertical direction.
6. A suspension according to claim 1 wherein each of the longitudinal interconnection means comprises a hydraulic interconnection.
A suspension according to claim 1 or claim 6 wherein each of the diagonal interconnection means comprises a hydraulic interconnection.
8. A suspension according to any foregoing claim wherein the longitudinal interconnections support substantially all of the vehicle's weight.
9. A vehicle suspension substantially as hereinbefore described with reference to the accompanying drawings.