WO1992014622A1

WO1992014622A1 - Multi-stage suspension assembly

Info

Publication number: WO1992014622A1
Application number: PCT/AU1992/000054
Authority: WO
Inventors: Warren Graham Fairweather
Original assignee: A.S.T. Pty. Ltd.
Priority date: 1991-02-15
Filing date: 1992-02-14
Publication date: 1992-09-03

Abstract

A multi-stage suspension for an axle of a vehicle comprises a first spring, for example a set of leaf springs (24), having a high stiffness which is linked to the axle via a connection which is inoperative at low loading. At low loading suspension is provided by a second spring, for example an air bar (50), having a low stiffness interposed between the first spring and a pivotal arm (38) which supports the axle. Light loads are thereby carried by the low stiffness second spring while high loads are carried by the high stiffness first spring. The mounting of the second spring between the first spring and the pivotal arm (38) results in full axle movement being maintained without restriction by the presence of the second spring whereby the axle is capable of movement over rough terrain.

Description

MULTI-STAGE SUSPENSION ASSEMBLY

This invention relates to a vehicle suspension assembly, and more particularly to a suspension assembly for a vehicle designed to carry heavy loads but which is also adapted to provide a relatively soft ride when the suspension is only lightly loaded.

Manufacturers of heavy vehicles, such as trucks which are designed to carry heavy payloads, usually fit suspension assemblies which include springs having high spring rates. These springs cause the vehicle to be hard riding so that when the vehicle is fully laden the payload is adequately protected from road vibration and shock loads. However when the vehicle is unladen or when the vehicle is relatively lightly loaded the stiffness of these springs result in the vehicle and its load being subjected to the destructive effects of shock loads, particularly when the vehicle is required to travel over uneven or rough terrain. This is a particular problem when these vehicles are used for military applications in which vehicles that are designed to carry very heavy loads, for example ordnance equipment and other heavy supplies, are often also used to transport relatively light loads, such as troops or fragile electronics equipment where injury or damage can result from shock loading which is not properly absorbed by the high stiffness suspension.

Proposals have been made to provide a suspension assembly for a vehicle which has a stiff suspension when the vehicle is fully laden and a soft suspension when the vehicle is unladen or lightly loaded. For example, U.S. Patent specification No. 3,031,179 proposes a suspension assembly comprising a set of leaf springs fixed to a single axle of a vehicle and an air bag disposed between a chassis of the vehicle and the axle so that the air bag is in series with the leaf spring. One end of the leaf spring is mounted to the chassis and the other end is spaced apart from the vehicle underside. When the vehicle is lightly loaded the air bag supports the load and when the vehicle is more heavily loaded the air bag is sufficiently decreased in height by the weight of the load to allow the chassis to engage the other end of the leaf spring whereby the leaf spring assists the air bag in supporting the additional load. This additional loading is thus carried by both the air bag and the leaf spring. Such an assembly may be unsuitable for both single and dual axle vehicles as the air bag must carry an increasing amount of the additional loading following engagement of the chassis with the other end of the leaf spring. Further, the operational stroke length of the overall suspension assembly is limited by the height of the air bag which may severely restrict the vehicle in respect of the degree of difficulty of the terrain over which it can travel. High profile air bags have been proposed in the past for use alone on single and dual axle vehicles but a major disadvantage in using high profile air bags is that if an air bag on one side of the vehicle collapses the vehicle and its load may overturn.

There is proposed in U.S. Patent specification No. 3,970,293 a suspension assembly which includes a two-stage suspension arrangement in which a spring having a low spring rate supports the weight of the vehicle and any load up to a predetermined level of loading with any further loading in excess of the predetermined level of loading being wholly carried by another spring means having a high spring rate. In this proposal the air-bag which operates as the low rate spring means is engaged directly with the chassis which precludes its use in a configuration in which the axle is required to pivot vertically through a substantial distance relative to the chassis, for example a vertical swing of 460 mm as is currently required by the Australian Army for certain trucks with an off-road capability.

According to the present invention there is provided a vehicle suspension assembly associated with an axle of the vehicle, said suspension assembly comprising a pivotal member extending generally lengthwise of the chassis of the vehicle, the pivotal member being pivotally supported at one end relative to the chassis whereby the member can swing upwardly and downwardly relative to the chassis and the pivotal member being engaged with the axle at a position remote from said one end, first spring means having a relatively high spring rate interposed between the chassis and the axle, means for providing a releasable load-transmitting connection between the first spring means and the axle, and second spring means having a relatively low spring rate interposed between the first spring means and the pivotal member, the arrangement being such that when a load up to a predetermined level of loading is applied to the suspension assembly the connection between the first spring means and the axle is inoperative whereby the load is carried by the second spring means and at said predetermined level of loading the connection between the first spring means and the axle becomes operative whereby further loading is wholly carried by the second spring means, and the first spring means moves with the axle and pivotal member during movement of die axle relative to the chassis.

The pivotal member preferably comprises an arm and the second spring means may comprise, for example, a helical compression spring or a rubber spring or, in a preferred embodiment, an air bag assembly.

It is preferred that the releasable load-transmitting connection comprises an arrangement in which the first spring means is located relative to the axle in a lost motion assembly with the lost motion being taken up when the predetermined level of loading has been achieved. The lost motion assembly may comprise a bracket carried by the axle through which the first spring means extends from its chassis connection to a free end, the bracket having a surface which is engaged by the first spring means when the lost motion is taken up. The first spring means may engage a spaced opposed surface of the bracket when the vehicle is unladen. Alternatively, or in addition, the releasable load-transmitting connection may comprise a stop for limiting deflection of the second spring means relative to the arm whereby the first spring means then acts on the axle via the arm.

The first spring means may take any suitable form including, for example, a torsion beam and trailing arm system, but in a preferred embodiment the first spring means comprises a set of leaf springs. The first spring means may extend either above or beneath the axle.

The predetermined level of loading is advantageously adjustable and may be controlled by the releasable connection. However, preferably it is adjusted by varying the spring rate of the second spring means, for example in the case of the air bag assembly by regulating the air pressure within the air bag. Advantageously, when plural vehicle suspension assemblies in accordance with the invention are provided on the vehicle and the second spring means of each comprises an air bag assembly, the pressurised air supply is common to all of the air bag assemblies so that should one of the air bags suffer a catastrophic failure all of the air bags will collapse uniformly so that the vehicle chassis lowers evenly until it is supported by the first spring means.

Where the suspension assembly of the present invention is used on a single axle, the connection of the first spring means with the chassis must be rigid in order to prevent collapse of the suspension assembly. However, in a dual axle arrangement, comprising two parallel axles in adjacent spaced array, the arm associated with each of the axles and the first spring means may be connected to a portion of the chassis between the axles which is supported for pivotal movement relative to the remainder of the chassis about an axis substantially parallel to the axles. By this means, the dual axles are oppositely pivotable about the intermediate axis without affecting the function of the suspension assembly associated with each axle. In a preferred embodiment in which the first spring means is a set of leaf springs, a common set of leaf springs is supported by the relatively pivotable portion of the chassis and has opposed free ends which are disposed to the side of the respective axle remote from the connection with said chassis portion. The pivotal portion of the chassis may comprise a trunnion saddle carried by a trunnion shaft fixedly carried by the remainder of the chassis. Alternatively, a rotatable shaft may be carried by fixed bearing means supported on the chassis, the rotatable shaft carrying the first spring means and the one end of each arm means.

It will be appreciated that in, for example, a truck a suspension assembly in accordance with the present invention will be associated with each side of the vehicle. In this case, the arms of the two suspension assemblies associated with the axle conveniently have a common pivotal mounting at the one end thereof with the chassis.

An embodiment of a vehicle suspension assembly in accordance with the invention will now be described by way of example only with reference to the accompanying drawings in which:

Fig. 1 is a partial sectional side view corresponding of the embodiment;

Fig. 2 is a partial sectional plan view of the embodiment of Figure 1;

Fig. 3 is a view similar to Figure 1 but showing a modification; and

Fig. 4 is a view similar to Figure 2 but also showing the modification of Figure 3.

In some drawings certain parts of the suspension assembly have been omitted for clarity.

Referring to Figures 1 and 2, a suspension arrangement, generally indicated by the numeral 10, is mounted to one side of a vehicle chassis 12 comprising longitudinally extending spaced chassis members 13. A corresponding suspension arrangement 10' is mounted to the other side of the chassis 12 and includes mirror image but otherwise identical parts. Accordingly, for convenience, only the suspension arrangement 10 will be described. The vehicle includes a pair of parallel axles 14, each having wheels 15 and 15' mounted for rotation therewith at each end. The wheels 15 and 15' are associated with the suspension arrangements 10 and 10' respectively. The chassis 12 includes a trunnion 16 supported by a structure 18 (not shown in Figure 2) which depends from the associated chassis member 13 between the axles 14, the trunnion 16 having its axis substantially parallel to the axles 14. A trunnion saddle 20 is mounted on the trunnion 16 for rotation about the axis of the trunnion.

The suspension arrangement 10 comprises a set of leaf springs 24 centrally mounted on the trunnion saddle 20 and clamped to it by a pair of U- bolts 26 to enable the set of leaf springs 24 to rotate with the saddle 20 about the axis of the trunnion 16. The set of leaf springs 24 has opposite outer end portions 28 which project through openings 30 in respective brackets 32 fixed to the axles 14. The suspension arrangement 10 is associated with both axles 14 in mirror image fashion so that the parts of the suspension arrangement 10 associated with one axle 14 are identical to the parts thereof associated with the other axle except that in the one case they are disposed or extend to the right (in the drawings) from the trunnion 16 whereas in the other case they are disposed or extend to the left (in die drawings) from the trunnion. For convenience, therefore only those parts associated with the right hand axle 14 (in the drawings) will be described in detail. Part of the leaf spring set 24 and bracket 32 to the left of the trunnion 16 has been omitted for clarity.

An A-frame 34, more clearly shown in Figure 2 having an apex 36 and arms 38 and 38' extending generally lengthwise of the chassis from the apex, is mounted to the trunnion 16 and to the axles 14 in rubber bushes 39 and 40. Each of the arms 38 and 38' is associated with the respective suspension arrangement 10 and 10' and also extends axially outwardly from the apex 36. In an alternative configuration, the two arms 38 and 38' could be separate and extend from independent mounting points on the trunnion 16. Only the arm 38 will be described hereinafter. The apex 36 of the frame 34 is pivotally mounted to the trunnion 16 and the arm 38 is fixedly mounted at an intermediate portion 42 to the axle 14 via the bracket 32 which supports the bush 40. The arm 38 extends longitudinally to a distal end 48 to the side of the axle remote from the trunnion. The A-frame 34, optionally with either single or double parallel longitudinal radius rods (not shown) mounted above the axle 14 from the trunnion 16, locates the axle 14 both longitudinally and laterally of the chassis. Such radius rods may ensure that the axles do not alter in their rotational angle when the spring assembly 10 pivots about the axis of the trunnion 16 so that all drive components, for example universal joint faces, remain parallel at all times.

Referring to Figure 1, the set of leaf springs 24 has a free end 44, which in this embodiment comprises an extended single bottom-most leaf spring 46, to the side of the opening 30 remote from the trunnion. The free end 44 of the leaf spring 46 is kinked or offset to enable an air bag 50 of an air spring to be mounted between the free end 44 of the leaf spring 46 and the distal end 48 of the arm 38 which is angled to underlie said free end 44. The air bag 50 is mounted thereon by bolts (not shown) at respective upper and lower mounting surfaces 52 and 54 of the air bag 50. In the modification depicted in Figures 3 and 4, the set of leaf springs 24 has, instead of the offset free end 44, a free end 58 which includes a generally C-shaped bracket 60 which is mounted by bolts at its bottom 62 onto two bottom-most leaf springs 63 and 64 which project straight through the opening 30 in the bracket 32. The distal end 65 of the arm 38 in Figures 3 and 4 extends lengthwise from the intermediate portion 42 substantially parallel to the longitudinal axis of the chassis 12 to underlie the C-shaped bracket 60. This contrasts with the angled distal end 48 in Figures 1 and 2. In all other respects the suspension arrangements of Figures 3 and 4 is identical to that of Figures 1 and 2 and will not be described further. The bracket 32 defines lower and upper faces 30a and 30b of the opening 30 which are spaced by a greater distance than the height of the outer end portion 28 of the leaf-spring set 24 which projects through the opemng 30, with the lower face 30a being spaced beneath the outer end portion 28 under zero or relative light loading of the chassis 12. A lost-motion coupling is thereby defined, with the lower face 30a acting as a limit stop of the lost motion coupling. An anti-rattle leaf 56 is fitted between the trunnion 16 and the spring pack 24 to engage the lower face 30a of the bracket 32.

The air bag 50, which has a relatively low spring rate compared to the set of leaf springs, is thus not supported or engaged directly by the chassis. Instead it is compressible between the free end 44 or 58 of the leaf spring set 24 and the distal end of the arm 38 or 65 which are capable of moving towards each other with initial increasing loading of the chassis due to the lost motion arrangement provided by opening 30 and the location of the air bag to the side of the axle remote from the trunnion.

In use, when the chassis is unladen or lightly loaded the tare weight of the vehicle and any load is transmitted vertically downwards through the trunnion 16 and transferred through the set of leaf spring set 24 to the free end 44 or 58 thereof. This force is transmitted downwardly through the top surface 52 of the air bag 50 to the distal end 48 or 58 of the arm 38 to the axle 14 where it is counteracted by the reactive force from the road surface which acts upwardly through the axle 14. During this light loading situation, due to the lost motion coupling loading will not be transmitted direcύy from the spring set 24 to the axle via the bracket 30. The weight in this lightiy loaded situation is thereby carried by the air bag 50 due to the relative stiffness of the spring set 24, and the vehicle and its payload is cushioned by the air bag 50 from the destructive effects of shock loads which would be experienced by a vehicle sprung with only a leaf spring set when it is similarly loaded. As the level of loading is progressively increased the weight acting on the air bag 50 causes it to compress thereby resulting in a progressive narrowing of the space between the outer end portion 28 of the leaf spring set and the lower face 30a of the bracket 32 as the leaf spring set moves downwardly with the chassis. Depending on the internal pressure of the air bag 50 and the size of the space, a predetermined level of loading will result in the leaf spring set 24 engaging the lower face 30a of the bracket 32 so that any excess loading above the predetermined level is wholly carried by the set of leaf springs 24.

As the air bags 50 are not connected directly to the chassis 12, the suspension arrangement 10 is able to rotate about the axis of the trunnion 16 without restriction by the air bags, such rotation being counterbalanced by the connection of both axles 14 with the trunnion saddle 20 through the respective suspension arrangements 10. A vehicle incorporating the suspension arrangement 10 on dual axles is not limited by the air bags in respect of the difficulty of the terrain over which it can travel as the air bags will pivot with the axles and the arms, the only limitation imposed being the amount of clearance available for the wheels and the suspension assembly as they oscillate about the trunnion axis. Further, the fitting of a relatively low profile air bag, as is permitted by the present invention, gives an additional advantage in that if the air bag is damaged catastrophically then the consequent sudden relatively small decrease in height of the chassis relative to the road surface will lessen the likelihood of the vehicle and its load overturning as can occur with conventional high profile air bags. This likelihood may be reduced even further if the air bags on the same axle but on opposite sides of the chassis are pneumatically connected together whereby both bags will deflate if one of the two bags is damaged. The air bags on the axles 14 on the same side of the chassis may be pneumatically connected together or not.

Manually adjustable air regulator valves (not shown) may be installed to vary the air bag pressure and, consequently, the predetermined level of loading which the air bag 50 can carry. Alternatively, height control valves (not shown) may be mounted between the arms 38 of the A-frame 34 and the spring pack 24.

Existing suspension systems utilizing leaf springs and arms as described may be converted into a system in accordance with the invention by incorporating a lower heat spring modified to carry the air bag, by replacing the arm with an arm modified to carry the air bag, and by incorporating a lost motion coupling between the heat spring and the axle. Accordingly, many of the existing suspension components can be retained in the conversion. Existing leaf spring suspensions without arms can also be readily converted t incorporating arms and the additional components specified.

The invention has been described by way of example only and various modifications are possible within the scope of the invention. For example, the suspension assembly 10 may be modified for fitment to a single axle vehicle to provide a two-stage suspension arrangement by rigidly fixing the trunnion saddle 20 or other chassis connection points relative to the chassis 12 to prevent pivotal movement of the set of leaf springs 24. Furthermore, while the opening 30 has been described as beneath the axle 14, it may be provided above the axle with the leaf spring set 24 being modified to suit. Further the lost motion coupling provided by the bracket 32 may be replaced by lost motion coupling comprising a stop designed to limit the relative displacement of the free end of the leaf spring towards the free end of the arm 38 under compression of the air bag whereby loading is then transferred between the leaf spring set and axle via the arm and the increasing loading is taken up by flexing of the leaf spring set. Such a stop may be provided within the air bag. Either of the leaf spring set and air bag may be replaced by suitable spring means such as, in the case of the air bag, a coil spring.

Claims

CLAIMS:

1. A vehicle suspension assembly associated with an axle of the vehicle, said suspension assembly comprising a pivotal member extending generally lengthwise of the chassis of the vehicle, the pivotal member being pivotally supported at one end relative to the chassis whereby the member can swing upwardly and downwardly relative to the chassis and the pivotal member being engaged with the axle at a position remote from said one end, first spring means having a relatively high spring rate interposed between the chassis and the axle, means for providing a releasable load-transmitting connection between the first spring means and the axle, and second spring means having a relatively low spring rate interposed between the first spring means and the pivotal member, the arrangement being such that when a load up to a predetermined level of loading is applied to the suspension assembly the connection between the first spring means and the axle is inoperative whereby the load is carried by the second spring means and at said predetermined level of loading the connection between the first spring means and the axle becomes operative whereby further loading is wholly carried by the second spring means, and the first spring means moves with the axle and pivotal member during movement of the axle relative to the chassis.

2. A suspension assembly according to claim 1, wherein the pivotal member is an arm, the axle is connected to the arm at a position intermediate the ends of the arm, and the second spring means is associated with the end of the arm remote from said one end whereby the second spring means lies to a side of the axle remote from the said one end of the arm.

3. A suspension assembly according to claim 2, wherein the first spring means comprises a set of leaf springs extending generally longitudinally of the chassis and the second spring means is operatively associated with a free end of the leaf spring set.

4. A suspension assembly according to claim 3, wherein the means for providing a releasable load-transmitting connection comprises a lost motion coupling between the leaf spring set and the axle, said lost motion coupling providing a load-transmitting surface which is spaced from an opposed load-transmitting surface associated with the leaf spring set at loading up to said predetermined loading, the spacing between said surfaces progressively reducing as the loading increases whereby at said predetermined loading said surfaces engage to cause direct load transmission between the leaf spring set and axle.

5. A suspension assembly according to claim 4, wherein the lost motion coupling comprises a bracket attached to the axle, the leaf spring set passes through a passage in the bracket, said passage being of a depth to permit relative vertical motion between the bracket and the leaf spring set, and a wall of the passage providing the load-transmitting surface.

6. A suspension assembly according to any one of claims 1 to 5, wherein there is a respective said first spring means, arm, releasable connection and second spring means associated with each end portion of the axle, and the two second spring means each comprise an air bag, the two air bags being pneumatically connected whereby deflation of one bag as a result of damage to that bag will also result in deflation of the other bag.

7. A suspension assembly according to any one of claims 1 to 6, wherein the vehicle has a dual axle and the suspension assembly is associated with both axles, one of said axles being located forwardly of a mounting zone on the chassis and the other of said axles being located rearwardly of said mounting zone, the said one axle being mounted on a first said pivotal member which extends forwardly from said mounting zone and the said other axle being mounted on a second said pivotal member which extends rearwardly from said mounting zone, the leaf spring set extends forwardly and rearwardly from said mounting zone and is attached to the chassis at the mounting zone and a respective said second spring means and releasable connection is associated with each of the two axles.

8. A suspension assembly according to claim 7, wherein the leaf spring set is pivotally attached to the chassis at the mounting zone for pivotal movement about an axis substantially parallel to the axes of the axles.

9. A suspension assembly according to any one claims 1 to 5, wherein the second spring means comprises an air bag