GB2222987A

GB2222987A - Vehicle wheel suspension system

Info

Publication number: GB2222987A
Application number: GB8921424A
Authority: GB
Inventors: Alexander Eric Moulton
Original assignee: Moulton Developments Ltd
Current assignee: Moulton Developments Ltd
Priority date: 1988-09-23
Filing date: 1989-09-22
Publication date: 1990-03-28
Anticipated expiration: 2009-09-22
Also published as: GB2222987B; GB8822473D0; GB8921424D0

Abstract

A wheel suspension system for the rear wheels of a vehicle in which the wheels are carted by arms 10, 11 pivotally mounted by pivot bearing means 12 carried on the sprung structure of the vehicle, has the sprung structure being supported on each wheel by means of a respective hydropneumatic spring unit 15 operating against the respective wheel supporting arm 10, 11. The spring unit has a means resiliently deformed between two abutments, one acted upon by a strut 16 which moves with the wheel and transmits wheel loadings to the spring unit. The second abutment is constrained in its movement upwardly relative to the sprung structure of the vehicle. The suspension arm carries, at different vertical levels, two pivot mountings, one 19 for the strut 16 which transmits wheel loadings to the first mentioned abutment of the spring unit, and the other 18 for a non extensible link means 17 connected to, or integral with, the second abutment of the spring unit, these vertically spaced pivot mountings 19, 18 being displaced from the pivot bearing means 12 supporting the supporting arm as it swings when the wheel rises and falls relative to the sprung structure of the vehicle, said displacement being towards the end of said arm at which the wheel is carried. The wheels rotate about axes 2, 3 and the arms 10, 11 are interconnected by a torsionally resilient beam. <IMAGE>

Description

VEHICLE WHEEL SUSPENSION SYSTEM This invention relates to a vehicle wheel suspension system.

In its broadest aspect the present invention provides a wheel suspension system for a vehicle in which the wheel is carried by an arm pivotally mounted by pivot bearing means carried on the sprung structure of the vehicle, with the sprung structure being supported on the wheel by means of a spring unit operating against said wheel supporting arm, the spring unit being of the kind in which a means is resiliently deformed between two abutments, one acted upon by a strut which moves with the wheel and transmits wheel loadings to the spring unit, and with the second abutment being constrained in its movement upwardly relative to the sprung structure of the vehicle, and wherein the suspension arm carries, at different vertical levels, two pivot mountings, one for the strut which transmits wheel loadings to the first mentioned abutment of the spring unit, and the other for a non extensible link means connected to, or integral with, the second abutment of the spring unit; and wherein such vertically spaced pivot mounting are displaced from the pivot bearing means supporting the supporting arm as it swings when the wheel rises and falls relative to the sprung structure of the vehicle, said displacement being towards the end of said arm at which the wheel is carried.

Preferably, in such a system, said displacement is over a distance of between 50 and 150 mm.

Such a system is particularly advantageous, as will be apparent from what follows, when applied to a suspension system for the rear wheels of a four wheeled automotive vehicle of the kind in which the sprung structure of the vehicle is supported inter alia by hydraulic displacer units each operating against an associated road wheel at a leverage of between 1: 3 and 1 6.

Hydraulic displacer units incorporating gas springs are well-known in the art and so far as concems the units employed in this invention, one associated with each wheel, these comprise a piston member and a housing constituting a cylinder, with the piston and cylinder being hermetically sealed and bridged by a flexible diaphragm. The diaphragm thus bounds a displacer chamber and is acted upon directly by a liquid under pressure. The housing is appropriately located, with intervening resilient pad or bush means, on and relative to the sprung structure of the vehicle. The piston is arranged to move with a road wheel of the vehicle by acting at high leverage on a supporting arm for that wheel. The liquid bearing upon the diaphragm is maintained under the requisite pressure by a resilient gas spring forming part of the unit.

Rear suspension systems are well-known in which each rear wheel is carried at the rear end of a trailing or semi-trailing arm which is supported at its leading end for pivotal movement about an axis extending generally transversely of the vehicle.

An hydraulic displacer unit is arranged to control the pivotal movement of the suspension arm. Examples of such suspension systems have been described in prior British Patent Specifications Numbers 1,096,207; 1,151,391; 1,231,282 and 1,404,585. In these and other similar examples where an hydraulic displacer unit acts on a suspension arm at a relatively high leverage, which may range between 1:3 and 1:6 (spring lever / wheel lever), it is advantageous for the displacer units to be mounted to act more or less horizontally so that the penetration of passenger space is minimal.

However, the consequential high loadings generated by the high leverage necessitates low friction bearings of high radial stiffness. The wheel supporting arm requires adequate location to prevent unwanted steering consequences, while at the same time the arm requires to be resiliently mounted to provide two distinct types of controlled movement.

Of the two types of movement required in such suspension systems, the first of these we term in this Specification "pivotal movement" and the second we term "compliance movement".

By "pivotal movement" we mean the partial rotation which the wheel supporting arm performs about the mounting at its leading end, this occuring as the associated wheel rises or falls relative to the vehicle sprung structure.

By "compliance movement", we mean movement of the wheel supporting arm such that the axis of the aforementioned pivotal movement is itself displaced. When this occurs, the associated wheel may move fore and after longitudinally, relative to the sprung structure of the vehicle, or transversely thereof, or any combination of these. The amplitude of the deflections in compliance movement of a suspension arm are much smaller than those in pivotal movements.

This invention has for its object to provide a vehicle suspension system which satisfies in large measure the following different and often conflicting criteria: (i) The loadings fed into the sprung structure of the vehicle are of a low order; (ii) a controlled degree of pivotal and compliance movement is allowed to each wheel supporting arm while at the same time the arm is located to reduce or eliminate unwanted rear wheel steering consequences; (iii) the rear wheel suspension assembly is adequately insulated from the sprung structure of the vehicle, both as regards noise and vibration; (iv) the entire rear suspension system should as nearly as possible be capable of manufacture as a self-contained sub-assembly which can easily be mounted in the vehicle at a late stage of the latter's manufacture;; (v) the rear suspension system should intrude as little as possible into the passenger and luggage space of the vehicle and on the other hand the best possible ground clearance is desirable.

In the system described in the specification of patent No 1 404 585 means are shown of applying a levered spring suspension unit of the hydropneumatic type to a trailing arm. In that system, two wheel suspension arms trailed from pivotal mountings on a cross beam, the two rear wheel suspensions being truly independent.

A ball joint at the end of a push rod transmitted loading to and from the displacer unit of a hydropneumatic spring unit, these loadings being transmitted to and from the trailing arm of an associated wheel. The high levered loads were in part contained within structural links, but they were resolved in the very same dual concentric interleaved rubber bush pivot mountings by which the wheel supporting trailing arms were carried.

By the arrangement there described, the reaction loads from the spring unit were fed into the body structure at a zone which is located more or less vertically above the wheel spindle and as a result this loading was sensibly equivalent to wheel load; in particularly it was not multiplied. The horizontal disposition of the unit rendered occupation of useful space at a minimum. The compliance of the whole 'axle' assembly was provided by separate rubber shear pads at the ends of the cross beam or tube. That system has been successfully in use in road vehicles for some years.

In this present invention, much of the foregoing concept is retained but novel features are introduced which widen the application of a levered hydropneumatic spring suspension unit, to include the 'H' frame or flexing cross beam type of rear axle with its unrivalled simplicity, lightness and low cost. By "H" frame we refer to a system in which two trailing arms are bridged by a stiff but resiliently deformable cross beam which adjoins the trailing arms at locations intermediate their lengths.

The present invention, in its broadest aspect is defined in claim 1, further preferred advantageous features being defined in the subsidiary claims.

One embodiment of a suspension system for the two rear wheels of a four wheeled automotive vehicle according to this invention, is illustrated by way of example, in the accompanying drawings in which: Figure 1 is an exploded view of the various components constituting the essential elements of the suspension system, while Figure 2 is a diagrammatic side view of the system as applied to support a single wheel on one side of the vehicle (as illustrated the left rear wheel).

In the drawings, a rear wheel suspension system is shown in which: (i) Both rear wheels (whose centres of rotations are indicated at 2 and 3) are carried on a trailing 'H' frame generally designated 5. This "H" frame 5 has the leading ends of twin trailing arms 10 and 11 separately pivoted at 12 to the vehicle sprung structure at 13. A cross beam 14 bridges the two arms 10 and 11, adjoining each arm at a location intermediate the length of the arm. The cross beam 14 of the 'H' frame is a deformable beam allowing a limited controlled degree of independence to the pivotting of the arms 10 and 11 relative to one another about the pivots at 12. However the two rear wheels are not "independently suspended" in the true sense of this term.

(ii) Pivotal upwards movement of each arm 10 or 11 is resisted by a hydropneumatic spring suspension unit 15 incorporating an hydraulic displacer unit of the rolling diaphragm type, the diaphragm being acted upon by liquid which is maintained under pressure by virtue of the fact that it bears also upon a resiliently deformable gas spring incorporated within the unit. The liquid pressure acting on each diaphragm may be 100 to 300 psi. Each diaphragm is acted upon also by a push rod 16 which is connected by a thrust joint 19 to an associated trailing arm 10 or 11, at or near the location of the junction of that arm 10 or 11 with the cross-member 14 of the H-frame.

(iii) Reaction loads from the suspension unit 15 with its diaphragm type hydraulic displacer unit and spring are fed back to the arm 10 or 11 by a casing shroud 17 pivotally connected to the arm at 18 in a location adjacent and immediately above the thrust joint 19 and above the cross beam 14; (iv) Vertical loading from the hydropneumatic spring unit is transmitted to the sprung structure of the vehicle by way of a resilient buffer pad or mounting generally designated 20.

The invention also provides that the arrangement is such that as the arm 10 or 11 swings, the pivot point 18 and the thrust joint 19 move differentially to cause movement of the rolling diaphragm within the hydraulic displacer chamber of the spring unit 15, this causing loading or relaxing of the gas spring within the unit.

The unit 15 will, as is conventional, incorporate means for damping liquid flows to and from its hydraulic displacer chamber, bounded in part by the diaphragm, this serving to damp rising and falling movements of the associated wheel relative to the sprung structure of the vehicle.

The effective distance between the wheel centre at 2,3 and the pivot point 18 constitutes what we term in this specification an "equivalent" lever. The spring unit 15 acts upon its associated arm 10 or 11, at the thrust joint 19 and the effective distance of this joint from the pivot at 18, constitutes a further or counter lever. The ratios of the effective lengths of these two levers gives the leverage at which each unit 15 bears upon its associated wheel; and this leverage is conveniently between 1: 3 and 1: 6.

The system now proposed is to be compared with the system described in prior specification No 1,404,585, where wheel loads were transmitted to associated spring units by levers which equated to the full lengths of the arms supporting the wheels.

Thus the "equivalent" lever as now proposed is substantially shorter than the "actual" lever of the prior arrangement; and given that identical leverages are being compared, such an "equivalent" lever can be opposed by a counter lever (the distance between the thrust joint 19 and the pivot at 18) which is shorter than the counter lever of the prior system. This relative reduction of lever lengths promotes saving of space; this being relevant both as regards intrusion into the space available for vehicle equipment, passengers and luggage and as regards ground clearance.

The structural compatibility of the short "equivalent" lever with the 'H' frame is well shown in Figs 1 and 2 of the drawings and it will be noted that loads are conveniently fed into the arm at the junction of the arm with the crossbeam, without significant stress being imposed onto the flexing crossbeam itself.

The same principles can be applied to an independent suspension with a cross beam aligned with or close to the pivot axes of the trailing arms. However in such a case comparable reductions in the lengths of the levers will no longer be fully realised.

Referring to Figure 2 it will be appreciated that when the reaction pad 20 for the unit 15 is in the transverse vertical plane containing the wheel spindle 21, there will be no vertical reaction load at the pivots at 12 from which the arm 10 and 11 trail.

As this situation is departed from, either by design or in the displacement of the lever arm 10 or 11 in its arcuate path, so its pivot bearing 12 will take some load. Also the reaction pad 20 will suffer a small shear mode movement in accommodating the fore and aft shuffling of the spring unit 15.

As compared with the system described in prior specification No 1,404,585, the functions of the two pivots 12 which support the trailing arms 10 or 11 are separated from the functions of the pivots 18 which sustain high spring loadings. By this, the "actual" pivot at 12 can be better adapted to provide compliance, while the "equivalent" arm pivot at 18 is required to provide a bearing which is heavily loaded during the functioning of the hydro-pneumatic spring unit 15. Thus the pivot 12 of the trailing arm can be a rubber bush of sufficient radial flexibility to provide compliance. The highly loaded pivot 18 can be of the multileaf bonded rubber type having to contain the high radial loads and withstand a high wind-up angle without regard to torsional rates; or it can be any other appropriate type of bearing.

The whole "rear axle assembly" as hereby described is of low weight and simplicity while retaining the installation advantages of minimum intrusion into the useful space.

Claims

1. A wheel suspension system for a vehicle in which the wheel is carried by an arm pivotally mounted by pivot bearing means carried on the sprung structure of the vehicle, with the sprung structure being supported on the wheel by means of a spring unit operating against said wheel supporting arm, the spring unit being of the kind in which a means is resiliently deformed between two abutments, one acted upon by a strut which moves with the wheel and transmits wheel loadings to the spring unit, and with the second abutment being constrained in its movement upwardly relative to the sprung structure of the vehicle, and wherein the suspension arm carries, at different vertical levels, two pivot mountings, one for the strut which transmits wheel loadings to the first mentioned abutment of the spring unit, and the other for a non extensible link means connected to, or integral with, the second abutment of the spring unit; and wherein such vertically spaced pivot mountings are displaced from the pivot bearing means supporting the supporting arm as it swings when the wheel rises and falls relative to the sprung structure of the vehicle, said displacement being towards the end of said arm at which the wheel is carried.

2. A system according to claim 1, and in which said displacement is over a distance of between 50 and 150 mm.

3. A rear wheel suspension system in which: (i) Both rear wheels are carried on a trailing 'H' frame (5) which has the leading ends of twin trailing arms (10 and 11) separately pivoted (at 12) to the vehicle sprung structure, a cross-member (14) of the "H" frame bridging the two arms and adjoining each arm at a location intermediate the length of each arm.

(ii) Pivotal upwards movement of each arm (10 or 11) is resisted by a hydropneumatic spring suspension unit (15) incorporating an hydraulic displacer unit of the rolling diaphragm type, the diaphragm being acted upon by liquid which bears also upon a gas spring incorporated within the unit, with each diaphragm acting also upon an associated suspension arm (10 or 11) by way of a push rod (16) which is connected by a thrust joint (19) located at or near the location of the junction of that arm (10 or 1)1 with the cross-member (14) of the H-frame.

(iii) Reaction loads from the spring unit (15) with its diaphragm are fed back to the arm (10 or 11) by a casing shroud (17) pivotally connected to the arm at (18) in a location adjacent and immediately above the thrust joint (19) and above the cross-member (14); (iv) Vertical loading from the hydropneumatic spring unit (15) is transmitted to the sprung structure of the vehicle by way of a resilient buffer pad or mounting (20).

(vii) The arrangement is such that as the arm (10 or 11) swings, the pivot point (18) and the thrust joint (19) move differentially to cause movement of the rolling diaphragm within the spring unit (15), this causing loading or relaxing of the gas spring within the unit.

4. A rear wheel suspension system according to claim 3 and in which the distance between the wheel centre (2,3) and the pivot point (at 18) on the trailing arm (10 or 11) carrying that wheel, -through which pivot point (at 18) reaction loads from the spring unit (15) are fed to the arm-, is substantially shorter than the pivotal length of the arm as it swings during rising and falling wheel movements relative to the sprung structure of the vehicle; and in which the distance between said pivot point (at 18) and the thrust joint (19) of the diplacer unit push rod, is such in relation to the distance between the wheel centre (2,3) and the first mentioned pivot point (at 18), that the spring unit (15) operates against the wheel carried by its associated suspension arm (10 or 11) at an effective leverage of between 1: 3 and 1: 6.

5. A rear wheel suspension system according to either of claims 3 or 4 and in which, in terms of generally vertical planes extending transversely of the vehicle, the wheel centres (2, 3) and the reaction pads (20) by means of which the spring units (15) are supported against the vehicle sprung structure are all in a first plane, the reaction pivots (at 18) and the thrust joints (19) are in a second plane, said second plane being nearer to a plane containing the pivots(12) from which the wheel supporting arms trail, than it is to said first plane.

6. A wheel suspension system for a vehicle in which the wheel is carried by an arm pivotally mounted by pivot bearing means carried on the sprung structure of the vehicle, substantially as hereinbefore described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows 1. A wheel suspension system for a vehicle in which the wheel is carried by an arm pivotally mounted by pivot bearing means carried on the sprung structure of the vehicle, with the sprung structure being supported on the wheel by means of a spring unit operating against said wheel supporting arm, the spring unit being of the kind in which a means is resiliently deformed between two abutments, one acted upon by a strut which moves with the wheel and transmits wheel loadings to the spring unit, and with the second abutment being constrained in its movement upwardly relative to the sprung structure of the vehicle, and wherein the suspension arm carries, at different vertical levels, two pivot mountings, one for the strut which transmits wheel loadings to the first mentioned abutment of the spring unit, and the other for a non extensible link means connected to, or integral with, the second abutment of the spring unit; and wherein such vertically spaced pivot mountings are disposed spaced over a horizontal distance of between 50 and 150 mm from the pivot bearing means for the wheel supporting arm, which bearing supports the swinging movement of the arm when the wheel rises and falls relative to the sprung structure of the vehicle, said spacing being towards the end of said arm at which the wheel is carried.

2. A wheel suspension system according to claim 1 and in which, as the arm swings when the wheel rises and falls, said vertically spaced pivot mountings are moved differentially, in opposite horizontal directions relative to a vertical plane passing through the pivot bearing means for the supporting arm.

4. A rear wheel suspension system according to claim 3 and in which the distance between the wheel centre (2,3) and the pivot point (at 18) on the trailing arm (10 or 11) carrying that wheel, -through which pivot point (at 18) reaction loads from the spring unit (15) are fed to the arm-, is substantially shorter than the pivotal length of the arm as it swings during rising and falling wheel movements relative to the sprung structure of the vehicle; and in which the distance between said pivot point (at 18) and the thrust joint (19) of the diplacer unit push rod, is such in relation to the distance between the wheel centre (2,3) and the first mentioned pivot point (at 18), that the spring unit (15) operates against the wheel carried by its associated suspension arm (10 or 11) at an effective leverage of between 1 : 3 and 1 : 6.

5. A rear wheel suspension system according to either of claims 3 or 4 and in which, in terms of generally vertical planes extending transversely of the vehicle, the wheel centres (2, 3) and the reaction pads (20) by means of which the spring units (15) are supported against the vehicle sprung structure are all in a first plane, the reaction pivots (at 18) and the thrust joints (19) are in a second plane, said second plane being nearer to a plane containing the pivots(l2) from which the wheel supporting arms trail, than it is to said first plane.