GB2298834A - Vehicle suspension system - Google Patents

Abstract

A suspension system 19 on a vehicle 12 having a body 14, a pair of front wheels 16 and a pair of rear wheels 18. Respective suspension arms 20, 32 are provided for the front and rear wheels 16, 18. Two torsion bars 30 are arranged one each side of the vehicle 12 with one end positioned adjacent the front suspension arm 20 on that side of the vehicle and the other end positioned adjacent the rear suspension arm 32 on the same side of the vehicle. Each torsion bar 30 is arranged to transmit torsional load resulting from movement of the suspension arm adjacent one of its ends to the suspension arm adjacent its other end, whereby the suspension arms 20, 32 will tend to move in opposite directions. The action of the suspension system is to move the body or chassis 14 so as to minimise pitching accelerations. A spring 42 acts as an attitude control and extends between the body 14 and a point M between the rear wheels 18. The spring 42 is arranged so that it acts on the body 14 in a vertical plane containing a roll axis R of the vehicle 12.

Description

VEHICLE SUSPENSION SYSTEM.

The invention relates to a vehicle suspension system, particularly for reducing pitching motion of a vehicle.

It is known that vehicle occupants are very sensitive to pitch accelerations. Reducing vehicle pitching motions results in a much better ride quality for the occupants of a vehicle and numerous systems exist to reduce pitch accelerations in vehicles. One such system known as the Hydragas system and produced by us has proved to be very effective over the years. Other systems have been proposed in a number of patent specifications referred to below.

U.K. Patent No. 1483172 discloses a suspension system for a four wheeled vehicle. When one wheel 13 encounters a bump, the wheel 13 moves up, as does the vehicle body adjacent the wheel 13. Load is transmitted from the wheel 13 via a torsion bar 2, mounted transversely with respect to the vehicle, to a link 34. The link 34, in turn, transmits load to a further transverse torsion bar 4 which pushes the wheel 19 against the ground forcing the body of the vehicle adjacent the wheel 19 to rise. In that way the pitching motion caused by the bump is reduced.

French Patent No. 837667 discloses a suspension system for reducing pitch motion similar to that of GB-A-1483 172.

In FR-A-837 667, a torsion bar is again arranged transversely of the vehicle between front and rear wheels.

The torsion bar transmits load from front to rear wheels and vice versa and raises the body to reduce pitch acceleration when one wheel is bumped.

Both of the above systems use multiple short torsion bars transverse of the vehicle. Short torsion bars must be of solid construction in order to withstand the stresses involved but solid torsion bars are heavy and add undue weight to the vehicle.

United States Patent No. 2099819 relates to a vehicle suspension system comprising front and rear wheels A,B each mounted on a pivotable arm 1 on the vehicle body. Each arm 1 is connected to a torsion bar 49,49' respectively. The torsion bars 49,49' extend longitudinally of the vehicle and are interconnected at adjacent ends by gears 51. As one wheel A encounters a bump the wheel rises, pivoting the arm 1 which twists the torsion bar 49. The torsion load is transmitted by means of the gears 51 from one bar 49 to the other 49' which, in turn, causes the wheel B to be pushed against the ground. Again the result is a lessening of pitching motion by lifting of one end of the vehicle body when the opposite end encounters a bump. US-A-2099819 requires a less complicated mechanical linkage than that used in the above mentioned prior art.However, it does employ two relatively short torsion bars, the drawbacks of which have been set out above.

It is an object of the present invention to provide an improved vehicle suspension system.

According to a first aspect of the invention there is provided a suspension system on a vehicle having a body or chassis, a first wheel on one side of the vehicle and a second wheel on the same side of the vehicle and spaced from the first wheel longitudinally of the vehicle, the suspension system comprising respective mountings for the wheels which permit substantially vertical movement of the wheels relative to the body or chassis and an elongate torsion member arranged with one end positioned adjacent the first wheel mounting and the other end positioned adjacent the second wheel mounting, the torsion member being arranged, in use, to transmit torsional load resulting from substantially vertical movement of the first wheel to the second wheel whereby the wheels will tend to move substantially vertically in opposite directions.

In that way load is transmitted along the torsion member to raise the vehicle body at its end spaced from a displaced wheel resulting in a reduction in pitching motion. Furthermore, use of a longer torsion bar which absorbs torsional load over a greater distance allows the use of lower grade material for the bar, as opposed to spring steel which is used on short torsion bars saving on cost. Also, the use of a lower grade material enables suspension members to be incorporated into the torsion bar rather than being connected thereto by splines. Such an arrangement will enable the low grade torsion bar/suspension member arrangement to cope well with stress reversal. Normal torsion bars must operate at a prestressed level as splined connections to suspension members tend to fret if subjected to stress reversal.Moreover, the longer bar does not need to be solid like the prior art torsion bars and so a weight saving can be achieved. A further advantage of using lower grade material is that it can be more easily manipulated into a convoluted shape to avoid obstructions on the underside of the vehicle. The system of the present invention is lighter, cheaper and simpler to produce than the prior systems. The present system may also eliminate the need for rear suspension coil springs which normally take up space in the rear of a vehicle. Eliminating the coil springs releases that space for other purposes.

In a preferred embodiment each torsion member is connected at one end directly to the wheel mounting associated with said one end. The torsion member may be integral with said wheel mounting at said one end.

Alternatively, the torsion member may be connected to the wheel mounting at said one end via a linkage. Each torsion member may be connected at its other end to the wheel mounting associated with the wheel at said other end via a linkage whereby movement of either wheel in one sense will tend to produce movement of the other wheel in the opposite sense.

The wheel mounting associated with the wheel at said other end may be mounted on the body at a pivot point and the linkage is preferably connected to part of the wheel mounting at a position inboard of the pivot point.

Each torsion member is preferably tubular.

A respective torsion member may be provided on each side of the vehicle.

If desired, a plurality of torsion members may be provided on each side of the vehicle, each torsion member extending from a point adjacent the front wheel on one side of the vehicle to a point adjacent the rear wheel on the same side of the vehicle.

The invention also includes a vehicle having a suspension system according to the said first aspect of the invention or any of the consistory clauses relating thereto.

Attitude control means may be provided for the body.

The attitude control means is preferably arranged to act on the vehicle body in a substantially vertical plane containing a roll axis of the vehicle. The attitude control means may be arranged adjacent a pair of the vehicle wheels, preferably rear wheels.

In a preferred embodiment, the attitude control means is mounted between the body of the vehicle and a mounting for the adjacent pair of wheels, the attitude control means preferably being positioned midway between those wheels.

The attitude control means preferably comprises a spring. Alternatively, it may comprise a controllable actuator, for example a hydraulic actuator.

According to a second aspect of the invention, there is provided a vehicle having a body, first and second wheels spaced apart longitudinally of the vehicle, wheel movement transmission means arranged whereby vertical movement of one of the wheels will be transmitted to. the other wheel and attitude control means for maintaining a desired attitude of the body during said transmission of movement, the attitude control means being arranged to act on the body in a vertical plane containing a roll axis of the vehicle.

In that way pitch stiffness and roll stiffness are determined independently by the attitude control means and wheel movement transmission means respectively. That allows the roll stiffness and pitch stiffness to be determined independently of one another, depending upon the vehicle requirements.

A vehicle suspension system in accordance with the invention will now be described in detail by way of example and with reference to the accompanying drawings in which: Fig.l is a schematic plan view of a suspension system in accordance with the invention, Fig.2a is a view of a front part of the suspension system shown in Fig.l looking in the direction of arrow A in Fig 1, Fig.2b is a similar view to that of Fig.2a with the suspension system shown in bump and rebound positions, the rebound position being shown in broken lines, Fig.3 is a view of a rear part of the suspension system shown in Fig.1 looking in the direction of arrow A in Fig 1 showing bump and rebound positions, the bump position being shown in chain-dotted lines and the rebound position being shown in broken lines, Fig.4 is a similar view to Fig.3 of another arrangement of the rear part of the suspension system, Figures 5a and Sb are schematic side and end elevations respectively of a vehicle having a suspension system in accordance with the invention, the vehicle being shown at rest, Figures 6a and 6b are similar views to Figs. 5a and 5b, showing the vehicle in pitch, Figures 7a and 7b are similar views to Figs. 5a and Sb, showing the vehicle in roll, Figures 8a and 8b are similar views to Figs 5a and 5b showing the vehicle in bounce, and Figures 9a and 9b are similar views to Figs 5a and 5b showing the vehicle in cross-axle articulation.

In Fig. 1, a vehicle 12 has a body or chassis 14 (hereinafter called a body), a pair of front wheels 16, a pair of rear wheels 18 and a suspension system 19.

The suspension system 19 has front parts 19a, l9b, the part 19a being shown in detail in Fig. 2a. The suspension part 19a includes a wheel mounting in the form of a suspension arm 20 having one end pivotally connected to an associated wheel 16, a pivot 22 by means of which the suspension arm is pivotally mounted on the vehicle body 14 and an extension 24 projecting inwardly of the vehicle from the pivot 22.

The extension 24 is pivotally connected at its inboard end to a linkage 25 comprising first and second links 26,28 (see Fig 2a). The first link 26 is connected at one end to the extension 24 and at its other end to one end of the link 28. The other end of the link 28 is rigidly connected to a torsion bar 30.

The torsion bar 30 extends from a point adjacent the front suspension part 19a to a point adjacent a rear suspension part 19c on the same side of the vehicle 12.

The suspension 19 has rear parts 19c, 19d and, as shown in Fig 3, a wheel mounting in the form of a rear suspension arm 32 of rear suspension part 19c is rigidly connected at its inner end 34 to the torsion bar 30 and is pivotally connected at its outer end 36 to the rear wheel 18. The torsion bar 30 and link 28 can be made as one piece, as can the torsion bar 30 and rear suspension arm 32. In a preferred embodiment, the link 28, torsion bar 30 and rear suspension arm 32 are formed in one piece.

The torsion bar 30 can be bent into a convoluted shape to avoid obstacles on the underside of the vehicle.

Each rear wheel 18 is pivotally connected to a brake reaction rod (not shown) of known kind which extends between the wheel 18 and the vehicle body 14.

Fig.4 shows an alternative arrangement of the rear suspension part 19c. In that arrangement, the rear suspension arm 32 extends from the rear wheel 18 and is pivotally mounted on the body 14. The torsion bar 30 is connected to the suspension arm 32 via links 31, 31a. The link 31a is pivotally attached to the arm 32 between the body 14 and the wheel 18, so that downward movement of the link 31a results in downward movement of the wheel 18. The link 31 is rigidly attached to the torsion bar 30 or is formed in one piece therewith.

When the vehicle pitches the torsion bars 30 provide no resistance to pitch and so a further system is required to provide the vehicle with pitch stiffness and attitude control. Accordingly, attitude control means is provided in the form of a spring 42 connected between the body 14 and a point M between the rear wheels 18. The point M represents the mean position between the rear wheels 18 and is in substantially the same vertical plane as a roll axis R of the body 14 or is adjacent thereto. In that way the spring 42 has no or no substantial effect on vehicle roll, roll stiffness being provided by the torsion bars 30 and pitch stiffness and attitude control being provided by the spring 42.

The operation of the suspension system will now be described initially with reference to Figures 1 to 3.

Normal wheel level is indicated at 40 in Fig 2b and the bounce and rebound levels are shown at 40a and 40b respectfully. As the front wheel 16 encounters a bump it moves vertically upwards. The suspension arm 20 pivots about pivot point 22 and the extension 24 moves downwardly.

The extension 24 pushes down the first and second links 26,28 causing the link 28 to rotate clockwise as indicated in Fig.2b and apply torsional load Tb to the torsion bar 30. The torsion load is transmitted along the bar 30 to the rear part 19c of the suspension 19. The effect on the rear part 19c of the suspension 19 is described below.

As the front wheel 16 rebounds, the suspension arm 20 pivots downwardly about pivot point 22 as shown in broken lines in Fig 2b. Therefore the extension 24 moves upwardly together with the links 26,28. The link 28 rotates anticlockwise as viewed in Fig.2b applying, torsional load Tr to the torsion bar 30. The torsional load is again transmitted along the torsion bar 30 to the rear part 19c of the suspension.

Referring to Fig 3, the rear part 19c of the suspension is shown in detail. The bounce position is shown in chain dotted lines and the rebound position is shown in broken lines.

As described above, front wheel bounce produces torsional load Tb in the torsion bar 30. In the system illustrated in Fig. 3 the torsional load Tb in the bar 30 tends to rotate the suspension arm 32 clockwise, forcing the rear wheel 18 against the ground. As the rear wheel 18 cannot descend, the load on the suspension arm 32 tends to lift the rear corner of body 14 adjacent the rear suspension part 19c. Thus as the front corner of the vehicle body adjacent front suspension part 19a lifts as a result of the front wheel 16 encountering a bump, the suspension system 19 causes the rear corner of the vehicle body 14 adjacent the rear suspension part 19c also to lift and in that way the pitching acceleration is reduced.

Conversely, as the front wheel 16 of front suspension part 19 drops into a rebound position by entering a hollow in the road thereby causing the adjacent corner of the body 14 to descend, torsional load Tr applied to the torsion bar 30 causes the corner of the body 14 adjacent the rear suspension part 19c also to descend. Therefore the pitching accelerations are once again reduced by the suspension system as the rear of the body drops with the front of the vehicle body.

It will be appreciated that movement of a rear wheel over a bump or into a hollow will result in torque transmission to the front wheel on the same side causing the body to rise and fall in the manner described above to reduce pitching accelerations.

The front and rear suspension parts 19b, 19d are substantially mirror images of the suspension parts 19a and 19c respectfully and operate in the same manner. Whilst the invention has been described in relation to a system having a single torsion bar it will be appreciated that a plurality of torsion bars could be used on each side of the vehicle, each torsion bar extending from a point adjacent the front wheel to a point adjacent the rear wheel on the same side.

Figures 5a to 9b show schematic side and end views of a vehicle having the suspension system preferably as set out above, in different ride situations. Therefore, in figures 5a-9b, the torsion bars will be arranged so that when, say, a wheel at the front of the vehicle is lifted, a wheel on the same of the vehicle at the rear and which is connected to the front wheel by the torsion bar will descend.

Figures 5a and 5b show the vehicle at rest. The weight of the vehicle is shared principally between the torsion bars 30 (some weight may be reacted by the attitude control means shown in the form of spring 42). The torsion bars 30, have an "at rest" torsion T and the spring 42 has a length D.

When the vehicle is subjected to pitch, as shown in Figs 6a and 6b, the torsion bars 30 maintain substantially the same torsion as they experience at rest, i.e. torsion T.

The spring 42 is extended to length D + dp as the body 14 pitches and acts to generate a restoring force on the body 14 tending to bring it back to its "at rest" position. The restoring force creates stiffness in pitch for the vehicle.

When the vehicle pitches in an opposite direction, the spring 42 compresses and again acts to restore the body 14 to its rest position.

Figures 7a and 7b show the vehicle subjected to roll.

The torsion bars 30 twist and create a restoring force therefore providing roll stiffness for the body 14. The spring 42 does not substantially extend or compress during roll as it lies substantially in the same vertical plane as the roll axis R.

When the vehicle is subjected to bounce, as shown in Figs 8a and 8b, the torsion bars 30 deflect beyond their "at rest" position and the spring 42 compresses. The bounce stiffness is thus generated by the torsion bars 30 and by the deflection of the spring 42 (D - db).

Figs. 9a and 9b show the vehicle subjected to cross axle articulation, i.e. when one axle is articulated in an opposite sense to the other. In this case, the front wheels 16 lie on a slope slanting downwardly from left to right in Fig 9b, while the rear wheels 18 lie on a slope slanting downwardly from right to left. During cross axle articulation the torsion bars 30 maintain their "at rest" torsion and the spring 42 does not lengthen or shorten.

Accordingly, the suspension system shown in Figures 1 to 9 exhibits no cross-axle articulation stiffness.

The lower the cross axle articulation stiffness, the better the traction of the vehicle in off-road or crosscountry driving conditions. Pressure changes exerted by the tyres of the vehicle on the ground are related to cross-axle articulation stiffness. Reducing that stiffness reduces such pressure changes, leading to better off-road performance.

A further advantage of the system described above is that the pitch stiffness of the vehicle is independent of the roll stiffness. The pitch stiffness is a function of the rate/stiffness of the spring 42 while the roll stiffness is related to the rate of the torsion bars 30.

Accordingly, a designer can select and tune the appropriate components to determine vehicle pitch and roll stiffness according to vehicle requirements.

Instead of using a spring 42, an actuator could be used (e.g. a hydraulic actuator) under the control of a suitable mechanism for providing attitude control. The actuator would be located at the same position as the spring 42.

The suspension of the present invention can be used in addition to conventional suspension systems. For instance a mixed suspension system could comprise a mixture of partially conventionally sprung, partially torsion bar sprung suspensions.

The system of the present invention is lighter, cheaper and simpler to produce than the Hydragas system and, does not require the high leverage ratios used in that system.

Such high leverage ratios increase stress on working parts, increase body, chassis or subframe loading and result in a lack of compliance and increase in stiction in suspension mountings.

The lower stresses experienced by the torsion bars should help to avoid sinkage problems often associated with such systems. Furthermore, the present system can replace conventional suspension systems which would lead to efficient use of vehicle space, i.e. improved packaging.

Whilst the terms "front" and "rear" have been used throughout the specific description, a person skilled in the art will appreciate that in this respect the terms are interchangeable and that systems specifically described herein as relating to the "front" of a vehicle could function equally well when applied to the "rear" or middle wheels of a vehicle and vice versa. Also, as mentioned above, the use of long torsion bars 30 enables a lower grade of material to be used as opposed to spring steel used with conventional short conversion bars. Moveover, the torsion bars 30 may be tubular thereby minimising weight.

The attitude control, e.g. through spring 42, may be used with suspension systems which do not utilise the torsion bar arrangements described with respect to Figs 1 to 9b but use a different system for transmitting movement from a wheel at one end of the vehicle to a wheel at the other end of the vehicle.

Claims (28)

1. A suspension system on a vehicle having a body or chassis, a first wheel on one side of the vehicle and a second wheel on the same side of the vehicle and spaced from the first wheel longitudinally of the vehicle, the suspension system comprising respective mountings for the wheels which permit substantially vertical movement of the wheels relative to the body or chassis and an elongate torsion member arranged with one end positioned adjacent the first wheel mounting and the other end positioned adjacent the second wheel mounting, the torsion member being arranged, in use, to transmit torsional load resulting from substantially vertical movement of the first wheel to the second wheel whereby the wheels will tend to move substantially vertically in opposite directions.

2. A suspension system according to claim 1 in which the torsion member is connected at one end directly to the wheel mounting associated with said one end.

3. A suspension system according to claim 2 in which the torsion member is integral with said wheel mounting at said one end.

4. A suspension system according to claim 1 in which the torsion member is connected to the wheel mounting at said one end via a linkage.

5. A suspension system according to any preceding claim in which the torsion member is connected at its other end to the assembled wheel mounting via a linkage.

6. A suspension system according to claim 5 in which the wheel mounting at the said other end is mounted on the vehicle body at a pivot point and the linkage is connected to part of the wheel mounting at a position spaced from the pivot point.

7. A suspension system according to claim 5 or 6 in which the linkage is mounted adjacent a front wheel.

8. A suspension system according to any preceding claim in which the torsion member is tubular.

9. A suspension system according to any preceding claim in which a torsion member is provided on each side of the vehicle.

10.A suspension system according to any preceding claim in which a plurality of torsion bars is provided on each side of the vehicle, each torsion bar extending from a point adjacent the associated first wheel to a point adjacent the associated second wheel.

11.A suspension system according to any preceding claim in which attitude control means is provided for the body.

12.A suspension system according to claim 11 in which the attitude control means is arranged to act on the body in a substantially vertical plane containing or adjacent a roll axis of the vehicle.

13.A suspension system according to claim 11 or 12 in which the attitude control means is arranged adjacent a pair of the vehicle wheels.

14.A suspension system according to claim 13 in which the attitude control means is arranged adjacent rear wheels of the vehicle.

15.A suspension system according to claim 13 or 14 in which the attitude control means is mounted between the body of the vehicle and a mounting for the adjacent pair of wheels.

16.A suspension system according to claim 15 in which the attitude control means is positioned at a point corresponding to a mean position between the wheels.

17.A suspension system according to any of claims 11 to 16 in which the attitude control means comprises a spring.

18.A suspension system according to any of claims 11 to 16 in which the attitude control means comprises a controllable actuator.

19.A suspension system according to claim 18 in which the actuator is a hydraulic actuator.

20.A vehicle having a suspension system according to any preceding claim.

21.A vehicle having a body, first and second wheels spaced apart longitudinally of the vehicle, wheel movement transmission means arranged whereby vertical movement of one of the wheels will be transmitted to the other wheel and attitude control means for maintaining a desired attitude of the body during said transmission of movement, the attitude control means being arranged to act on the body in a substantially vertical plane containing or adjacent a roll axis of the vehicle.

22.A vehicle according to claim 21 in which the wheel movement transmission means comprises a suspension system according to any of claims 1 to 10.

23.A vehicle according to claim 21 or 22 in which the attitude control means extends between the body of the vehicle and a point corresponding to a mean position between a pair of wheels spaced one each side of the vehicle.

24.A vehicle according to any of claims 21 to 23 in which the attitude control means comprises a spring.

25.A vehicle according to any of claims 21 to 23 in which the attitude control means comprises an actuator controllable from a control unit.

26.A vehicle according to claim 25 in which the actuator is a hydraulic actuator.

27.A suspension system on a vehicle constructed and arranged substantially as described herein with reference to the accompanying drawings.

28. A vehicle having attitude control means constructed and arranged substantially as described herein with reference to the accompanying drawings.