GB2296223A

GB2296223A - Vehicle suspension system

Info

Publication number: GB2296223A
Application number: GB9425537A
Authority: GB
Inventors: Edward Bruce Mclaurin
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1994-12-19
Filing date: 1994-12-19
Publication date: 1996-06-26
Anticipated expiration: 2014-12-19
Also published as: GB2296223B; GB9425537D0

Abstract

A vehicle suspension system for an opposed wheelset comprises a pair of wheel carriers 2 which are flexibly connected by a joint 4 towards opposite ends of a rigid cross link 1 to permit camber variations of the wheel 3 as it deflects. Suspension means 10 are provided proximal to each wheel carrier 2 to control the deflection of the wheel 3 towards a vehicle body and, in use, are flexibly connected at their upper ends to the vehicle body. The cross link 1 is flexibly connected by a joint 8 to a mounting means 5 which is used to secure the cross link to the vehicle body. In use, the flexible joint 8 must be arranged to lie intermediate of an axis through both upper ends of the suspension means and of an axis through both flexible joints 4 between the wheel carrier 2 and the cross link 1. This arrangement of the flexible joint 8 provides for a suspension system having semi-independent kinematics. <IMAGE>

Description

Vehicle Suspension Svstem The invention relates to a vehicle suspension system and particularly to a semi-independent suspension system for an opposed wheel wheelset of a vehicle.

Vehicle suspension systems may be classified as being one of three general types; the independent; the rigid (beam) axle; or the semi-independent type. With an independent suspension system each wheel of an opposed wheelset is provided with an unconnected suspension such that the vertical displacement of a wheel on one side of the vehicle body does not affect the displacement of the opposed wheel on the other side of the vehicle body and the camber (the inclination of the wheel plane to the vertical on a horizontal surface) of each wheel is dependent only on the vertical displacement of that wheel with relation to the body. The rigid axle suspension system has a rigid axle or a beam linking the suspension of each wheel which acts to maintain a generally constant spatial relationship between opposed wheels for all suspension displacements.This results in the camber of each wheel changing by equal amounts depending on the vertical displacement of the wheels. With a semi-independent suspension system the wheels do not maintain a generally constant spatial relationship with each other but are nevertheless linked so that the camber of each wheel is dependent on the displacement of the other.

Independent suspensions can use a wide choice of supporting linkages and wheel motion geometries, generally taking up less space than either of the other two systems and are best able to deal with differential wheel displacements over rough terrain. However vehicle body roll during cornering, which acts to cause differential wheel displacement, can result in the tyres adopting large and different camber angles. This tends to reduce the holding ability of the tyres to the terrain surface. Moreover, during straight ahead travel of the vehicle the constantly deflecting suspension may produce a constantly varying wheel tracking which can cause adverse steering reactions and increased tyre wear.

Rigid axle suspension systems generally offer the simplest wheel location and drive arrangements and are usually cheapest to implement.

This system is advantageous during cornering as it minimises camber angles produced by body roll but has the disadvantage that single or differential wheel displacements will produce a change in the camber angle of the displaced wheel which leads to undesirable gyroscopic effects on steered axles.

Semi-independent suspension systems have been developed which combine some features of both the independent and rigid axle systems.

One such linkage which can provide an appropriate semi-independent suspension interconnection is the trailing twist (torsion crank) axle.

This comprises two pivoted arms, one for each wheel, aligned longitudinal of the vehicle body and rigidly secured to a transverse beam which is generally situated between the arm pivots and the transverse axis connecting the two wheel centres of the wheelset.

This beam is usually an open section designed to be flexurally rigid in bending to prevent substantial camber and alignment movements of the wheels and torsionally flexible to permit differential suspension movement. The position of the torsional centre of this 'rigid' beam in relation to the pivot points of the arms determines the kinematic properties of the suspension system: if the torsional centre lies on the transverse axis through the wheel centres then the system will have the kinematic properties of a rigid system; if the torsional centre lies on the transverse axis connecting the chassis pivots of the arms then an independent system results; intermediate of these two extreme positions the system will act by varying degrees as a semi-independent system.

However, since the wheels are rigidly connected to the trailing arms one problem with the trailing twist system is that wheel deflections cause the castor angle (the angle, in side elevation, between the steering axis and the vertical) variations to occur, making it unsuitable for use with a steered wheel wheelset.

Furthermore, the arrangement of the beam and the need to maintain a straight torsional axis makes it difficult to accommodate a drive unit and so makes this system difficult to use for a driven wheel wheelset.

It is an aim of the present invention to provide a semi-independent suspension system which is readily adaptable to use with driven, undriven or steered wheelsets.

According to the present invention there is provided a vehicle suspension system for an opposed wheelset comprising a pair of wheel carriers, a cross link, mounting means flexibly connected to the cross link for securing the cross link to a vehicle body, and a pair of suspension means each having a first end secured proximal to an associated wheel carrier and a second end adapted for attachment to the vehicle body wherein each wheel carrier is flexibly connected towards opposite ends of the cross link so as to be capable of camber variations and wherein, in use, the flexible connection between the cross link and the mounting means lies intermediate of an axis through both second ends of the suspension means and of an axis through both flexible connections between each wheel carrier and the cross link.

The flexible connection between each wheel carrier and its respective end of the cross link permits the camber of each wheel to vary as the wheel deflects and may conveniently comprise a ball and socket joint, a hinge type joint or a bush arrangement. The flexible connection between the cross link and the mounting means is adapted to allow the cross link to pivot about that joint in response to vertical deflections of one or both wheels.This flexible joint may again be a ball and socket joint, a hinge type joint or a bush arrangement and may be connected to the cross link closer to one end of the cross link than the other whilst retaining the kinematics of a semi-independent suspension linkage provided that the mounting means is always arranged in use such that the flexible connection with the cross link lies between the transverse axis through the flexible connection of the wheel carriers with the cross link and the axis connecting the points of contact of the suspension means with the vehicle body.

The cross link may, for example, comprise a rigid beam designed to be flexurally rigid in bending but torsionally flexible or may include a relatively simple drive line when used for a driven wheelset. This latter arrangement removes the need for a chassis mounted differential used in the prior art trailing twist system.

Moreover, the present invention is readily adaptable for use with a steered wheelset because the wheels are flexibly connected to the cross link and the castor angle can be arranged to remain substantially constant as the wheel deflects. The suspension system according to the present invention therefore provides a greater flexibility of use than known systems.

The suspension means, which may be similar to that used in independent suspension systems, for example a telescopic strut or wishbone arrangement can be secured either close to wheel carriers on the cross link or on the wheel carriers themselves and permits essentially vertical deflections of the wheel carrier both towards and away from the vehicle body but provides resistance to those vertical deflections towards the vehicle body.

In use the cross link is mounted on a vehicle body using a mounting means which may be of a similar type to that used to secure a beam axle in a conventional rigid axle suspension system, for example an A frame or a panhard rod arrangement in flexible connection with the cross link, which is capable of preventing substantial sideways movement of the cross link with respect to the vehicle body.

Generally this type of mounting means is used in conjunction with with arms which are provided towards each end of the cross link and which extend approximately parallel to an axis running fore and aft of the vehicle body and generally perpendicular to the cross link. The arms are secured to the vehicle body so as to be capable of preventing substantial fore and aft movement of the cross link relative to the vehicle body.

Embodiments of the present invention will now be described, by way of example only, with reference to the enclosed drawings of which: Figure 1 is a part sectioned end elevation of a suspension system according to the present invention for an undriven wheelset.

Figure 2 is a part sectioned plan view in the region of one of the wheels of the wheelset of Figure 1.

Figure 3 is a part sectioned side elevation of the suspension system in the region of Figure 2.

Figure 4 is a part sectioned end elevation of a suspension system according to the present invention for an undriven but steered wheelset.

Figure 5 is a part sectioned plan view in the region of one of the wheels of the wheelset of Figure 4.

Figure 6 is a part sectioned side elevation of the suspension system in the region of Figure 5.

Figure 7 is a part sectioned end elevation of a suspension system according to the present invention for a driven wheelset with an incorporated drive unit.

Figure 8 is a part sectioned end elevation of a suspension system according to the present invention for a driven wheelset with the drive unit mounted on the vehicle frame.

The embodiment shown in Figures 1 to 3 is for an undriven wheelset and comprises a rigid cross beam 1 running substantially transversely of a vehicle body 26 (represented by the broken lines on Figure 3) at each end of which is pivotally connected a wheel carrier 2 for wheel 3 by means of a ball and socket joint 4 so as to allow for changes in the camber when the wheel 3 is deflected. It will be appreciated by those skilled in the art that generally an additional linkage (not shown) between the cross beam 1 and each of the wheel carriers 2 will also be required in order to inhibit steering alignment changes as the wheels 3 deflect.

The cross beam 1 secured to the underside of the vehicle body 26 by means of an A-frame 5 and a pair of arms 6 which are located between the cross beam 1 and the vehicle body frame 7. This vehicle body frame 7 may be integral with a vehicle body, as is usual in production cars, or may be a chassis separate from the vehicle body 26, as shown in all of the accompanying Figures and which is often the case with off road vehicles. The A-Frame 5 and the arms 6 act respectively to prevent substantial sideways and fore and aft movement of the cross beam 1 in a similar manner to conventional rigid axle arrangements.

A substantially vertical telescopic strut 9 is rigidly secured to each wheel carrier 2 and towards its upper end is flexibly located to the vehicle body frame 7 by means of rubber bushes (not shown) so as to be capable of providing resistance to deflections of the wheel carriers 2 towards the vehicle body 26. Additional resistance to such deflections of the wheel carriers 2 is provided by a helical spring 10 similar to that used in conventional independent suspension systems.

The A-Frame 5 is flexibly connected to the cross beam 1 with a ball and socket joint 8 positioned between the axis connecting the ball and socket joints 4 of the wheel carriers 2 and the axis connecting the upper ends of the telescopic struts 9. This enables the suspension system to act to varying degrees as a semi-independent suspension system depending on the exact position of the ball and socket joint 8 between the axes.

Referring now to the embodiment shown in Figures 4, 5 and 6 for an undriven, steered wheelset. The suspension system is essentially that of the previous embodiment but adapted to be steered as with a conventional steered wheelset.

As can be seen from the Figures 4 to 6 this embodiment additionally comprises a steering mechanism 11 and associated operating link 12 which is connected to one of the wheel carriers 2.

Operation of the mechanism 11 causes the operating link 12 to move to rotate the associate wheel 3 and effect steering of the vehicle. The steering movement of the one wheel connected to the link 12 is transmitted to the other wheel by means of a track rod 13. Since the telescopic struts 9 are mounted substantially vertically they act to allow only substantially vertical deflections of the wheel carriers 2, thereby ensuring that the castor angle of the steered wheels 3 remain substantially constant.

Referring now to Figure 7, which shows an embodiment of the invention adapted for use with a driven wheelset, the cross link is provided by an axle assembly which comprises a driven differential 14 and rotating axle and drive shafts (not shown) in axle housing 15.

The axle housing 15 is connected to the wheel carriers 16 towards its ends by means of a bushed revolute hinge joint 17 which allows for camber changes as the wheels 3 deflect.

The differential 14 and axle housing 15 arrangement is prevented from substantial sideways and fore and aft movements by means of respectively an A-Frame 5 and arm 6 arrangement similar to that used in the undriven systems of Figures 1 to 6. However, the mounting means comprises an additional support member 18 which is pivotally connected to the A-Frame 5 by a ball and socket joint 8 and the function of which is to displace the pivot point of this joint 8 above the transverse axis connecting the revolute joints 17 so as to provide semi-independent kinematics.

Figure 8 shows an alternative embodiment for a driven wheelset in which the drive unit 19 is secured to the vehicle frame 7 on a cross member 20. A rigid cross beam 21 is located to the vehicle frame 7 by means of a panhard rod 22. The panhard rod 22 replaces the A-Frame of the previous embodiments and acts together with the arms 6 to prevent substantial sideways and fore and aft displacements of the cross beam 21. The panhard rod 22 is pivotally hinged at both ends by means of bushed revolute joints 23,24 which permit the cross beam 21 to pivot about the joint 23 as the the wheel carriers 25 deflect. The revolute joint 23 is again arranged to be higher than the ball and socket joints 4 between the cross beam 21 and the wheel carriers 25, thereby providing semi-independent kinematics.

It will be well known to those skilled in the art that there exists circumstances in which a panhard rod or an A-Frame type mounting means may be used interchangeably similarly a conventional wishbone type wheel carrier suspension means might be used as a substitute for the telescopic strut and helical spring arrangement described herein without departing from the present invention.

Claims

1. A vehicle suspension system for an opposed wheelset comprising a pair of wheel carriers, a cross link, mounting means flexibly connected to the cross link for securing the cross link to a vehicle body, and a pair of suspension means each having a first end secured proximal to an associated wheel carrier and a second end adapted for attachment to the vehicle body wherein each wheel carrier is flexibly connected towards opposite ends of the cross link so as to be capable of camber variations and wherein, in use, the flexible connection between the cross link and the mounting means lies intermediate of an axis through both second ends of the suspension means and of an axis through both flexible connections between each wheel carrier and the cross link.

2. A vehicle suspension system as claimed in Claim 1 wherein the cross link comprises a rigid cross beam.

3. A vehicle suspension system as claimed in Claim 1 or Claim 2 wherein the wheel carriers are pivotally connected to the cross link by means of a ball and socket joint.

4. A vehicle suspension system as claimed in any preceding claim wherein the mounting means comprises an A-Frame.

5. A vehicle suspension system as claimed in Claim 4 wherein the A frame is pivotally connectable to the cross link by means of a ball and socket joint.

6. A vehicle suspension system as claimed in any one of the Claims 1 to 3 wherein the mounting means comprises a panhard rod having a first end adapted to be flexibly mountable on the vehicle body and a second end flexibly connected to the cross link.

7. A vehicle suspension system as claimed in Claim 6 wherein the panhard rod is pivotally connectable to the cross link by means of a revolute joint.

8. A vehicle suspension system as claimed in Claim 1 wherein the cross link comprises a driven differential and axle housing arrangement.

9. A vehicle suspension system as claimed in Claim 8 wherein the wheel carriers are connected towards opposite ends of the axle housing by means of a revolute joint.

10. A vehicle suspension system for an opposed wheelset substantially as hereinbefore described with reference to Figures 1 to 8 of the accompanying drawings.