This invention relates to the suspension system of vehicles having at least one rigid transverse axle with a ground engaging wheel assembly at each end thereof. It is normal practice in vehicles to provide a resilient suspension mechanism between the vehicle body and the transverse axle or axels which includes a pivot mechanism to control relative vertical movement between the axle and the body of the vehicle and shock loads, arising from irregularities on the surface traversed. In vehicles carrying heavy loads, such as used in the mining industry, the weight transferred between the vehicle body and the wheels through the suspension mechanism is particularly high, and in currently used suspension constructions, is subject to high rates of wear. This results in a need for frequent maintenance and hence substantial non-operational periods of the vehicle. This is a substantial cost burden having regard to the fact that such vehicle can have a total load capacity of several hundred tons.

One of the major areas of wear is in the pivotal connection between the vehicle body and the suspension system, that is necessary to accommodate vertical movement between the vehicle wheels and the load carrying body. This problem arises because known constructions only permit the provision of relatively limited bearing areas between the components forming the principal pivot connection between the body and the suspension system. This limitation is in part due to the same bearing area being provided to perform the functions of locating the wheels relative to the body, and also effecting the weight transfer from the body through the suspension to the wheels. It is therefore the principle object of the present invention to provide a vehicle suspension system arranged to effect both the load transfer and wheel location function in a manner that will enhance the effective operating life thereof, and is economic to construct and of substantially improved working life.

With this object in view, there is provided a load carrying vehicle suspension system comprising a vehicle body and at least one axle assembly having a wheel assembly at each end thereof, and mounting means adjacent each wheel assembly attaching said axle assembly to said vehicle body at

laterally spaced locations, each said mounting means being arranged to provide a pivot connection between the axle assembly and the vehicle body and an at least partially independent load transfer between the vehicle body and the axle assembly. The providing of the connection between the vehicle body and the wheel assemblies of a construction that effects the transfer of at least some of the load therebetween independent of the pivotal connection therebetween, results in the bearing load on the relatively moving components of the pivotal connection, being substantially reduced. Hence, the effective working life thereof is greatly increased.

Preferably, the load transfer means is adapted to enable the degree of independent load transfer to the axle assembly to be adjusted such as to suit differing loads being carried by the vehicle. In view of constructional and operational considerations, in known vehicles, the dimensions of the bearing area of the pivotal connections is restricted and thus previous bearing constructions were highly loaded, and frequently overloaded, in severe conditions, and hence had a very short working life. However, by separating all or a substantial portion of the load transfer function from the pivotal bearing function, greatly enhances the effective life of the bearing. In a preferred embodiment, the load transfer is effected by a substantially non-compressable fluid, preferably a liquid such as water, filled chamber, preferably in the form of a variable volume chamber. The chamber can comprise inner and outer chamber wall sections, one of which is fixed and the other movable relative thereto in a guided linear sliding movement. One of the chamber wall sections is secured to the vehicle body and the other engages the axle assembly, whereby the vehicle weight can be transferred through the fluid in the chamber to the axle assembly.

In one embodiment, the member connecting the wheel assembly to the body includes an arm rigidly connected to the axle assembly at one end and connected at the other end to the vehicle body for angular movement relative thereto about an axis parallel to the axle. The arm is made of two parts having respective axially aligned portions interconnected to permit limited angular

movement therebetween about the common axis of said parts of the arm, and again resilient restraint means.

The incorporation of this construction in the members, connecting the respective ends of a wheel assembly to the vehicle body, permits limited lateral roll of the vehicle body relative to the axle. This permitted limited movement reduces tortional stress in the axle and/or axle mounting when the vehicle is traversing uneven terrain. This construction is particularly applicable to vehicles incorporating air or gas bag suspension systems.

The invention will be better understood from the following description of a practical arrangement of the suspension system as illustrated in the accompanying drawings.

In the drawings :-

Figure 1 is a side view of a typical multi-axle trailer suspension to which the present invention is applicable; Figure 2 is a longitudinal section view through one of the intermediate suspension hangers shown in Figure 1 along the line 2-2;

Figure 3 is a transverse sectional view along the line 3-3 in Figure 2;

Figure 4 is a side view partly in section of the invention applied to an alternative construction of vehicle axle assembly. Figure 5 is a transverse sectional view along the line 5-5 in Figure 4.

Referring now to Figure 1 of the drawings, there is shown diagrammatically a two axle (A, B) vehicle body support assembly comprising a forward and rear spring support unit 1 and 2. The front and rear spring support units are anchored to respective fixed hangers 5 and 6 by draw rods 7 and 8 respectively, whilst the free ends of each spring is captive in a rocker box 9, which is pivotally supported in the spring hangers 11 secured by the upper end plate 14 to the vehicle chassis 15. The layout of the spring assemblies 1 and 3, the fixed hangers 5 and 6 and the rocker box 9 are of generally known construction and shall not be described in further detail. The present invention resides in the modified form of the hanger 11 which is shown in detail in Figures 2 and 3 of the drawings.

Referring now to Figures 2 and 3, the hanger 11 comprises a pair of spaced side plates 16, 17 secured at the upper end to the cross plate 18 which in turn in use is welded or otherwise rigidly attached to the vehicle body 15. The respective side plates 16, 17 of the hanger are spaced apart a distance to receive therebetween the rocker box 9, the respective opposite walls thereof being shown in cross-section in Figure 3.

The rocker box has a centrally located aperture 21 extending through the opposite walls to receive the respective ends of the bush 22 and through which the anchor bolt 23 passes. The anchor bolt 23 also passing through the opposing side plates 16 and 17 of the hanger 11. The rocker box 9 is secured between the opposite walls of the hanger and may rotate to a limited degree about the anchor bolt 23.

The construction of the hanger 1 1 and the attachment thereto of the rocker box 9 and bush 22 are of known conventional construction. Under high load conditions it has in the past been experienced that the bush 22 wears at a high rate on the lower side, creating a need for frequent replacement of the bush, hence significant losses of operating time of the vehicle are experienced. This is primarily due to the load transferred between the hanger 11 and the rocker box 9 being effected solely through the lower side of bushes 22, below the axis of the anchor bolt 23.

In order to deal with this problem, there is provided in the upper portion of the hanger 11 a cylindrical chamber 25 in which is slidably located a piston member 26. The piston member 26 has a part circular lower face 27 which is complementary to and seated on the upper peripheral portion of the bush 22 mounted on the anchor pin 23.

The upper face 28 of the piston 26 provides a somewhat part-spherical seat for the lower end of the inflatable bag 30 located in the cylinder 25. The upper side of the bag 30 is seated in the locating ring 31 to engage the hanger end plate 14. The bag is thereby captive between the end plate 14 and the piston 26. A valve member 32, secured in a conventional manner to the bag 30, extends through an appropriate opening in the end plate 14 of the hanger to permit the inflating of the bag with a gas, liquid or combination thereof.

Normally the bag is inflated with a liquid, so as to be substantially non resilient, but in some applications, an amount of gas can be included as a simple and convenient way of adjusting the pressure in the bag to the level appropriate to the weight supported through the rocker box 9. With the above described construction, and the appropriate pressurising in the bag 30, a downward force is applied to the underside of the bush 22 through the piston member 26 to the upper side of the bush 22 counteracting the upward force applied through the rocker box 10. The downward force is transferred to the bush through a relatively large area of contact between the piston 26 and the bush 22 thereby reducing the rate of wear of the bush.

In this way, the transfer of the weight of the vehicle load through the hanger to the vehicle springs is distributed over the upper and lower surfaces of the bush 22 and anchor bolt 23 representing a reduced load per unit area. Accordingly, the wear rate on the bushing and the anchor bolt is reduced to a level which will provide a substantial useful working life of the bushing, resulting in substantial savings in down time of the vehicle for the purposes of maintenance of the bushing.

There is shown in Figures 4 and 5 of the drawings an alternative form of the present invention as applicable to a vehicle suspension wherein the suspension medium is a pressurised bag or bags 33 as an alternative resilient means to the conventional laminated leaf springs 1 as used in the embodiment shown in Figure 1. The trailing suspension arm 35 is secured to the axle 36 of the vehicle in the conventional manner, and one or a plurality of air or gas bags 33 are located between the arm 35 and the vehicle body 34 in the conventional manner.

The forward end 40 of the arm 35 is attached to a hanger 44 of the same basic construction as previously described with respect to Figures 2 and 3, except that in this situation the forward end 40 of the arm 35 is connected directly to the bush 32 and anchor bolt 23 supported in the hanger 34 in the same manner as previously described with respect to the connection of the rocker box 10 to the hanger 6 as shown in Figure 2. The hanger 34 also incorporates a piston 26 and bag 25 that is constructed and operated in the

same manner as previously described with reference to Figures 1 and 2. Thus again, the loading and hence the wear, on the bush 32, is substantially reduced or eliminated, with the corresponding advantage in the reduction of down time for maintenance. As seen in Figures 4 and 5, the trailing suspension arm 35 is of a two part construction having a front portion 40 and a rear portion 41, the latter having a portion thereof received within the front portion 40.

The rear part of the front portion 40 of the suspension arm receives therein the forward part of the rear portion 41, with a rubber sleeve 45 therebetween. The internal dimensions of the front portion 40 are chosen relative to the external dimensions of the rear portion 41 of the arm 35 so that the rear portion can roll about the axis thereof to a limited degree within the forward portion. The two inter-filling portions 40, 41 of the arm are secured together by a plurality of transverse bolts 43 with a rubber bushing being provided between each bolt and the internally located portion of the trailing arm.

This construction, when provided on the respective opposite ends of a transverse axle 36, enables a degree of relative vertical displacement of one end of the axle to the other. This results in a reduction in the stress generated in the axle when the vehicle is traversing uneven surfaces, thereby substantially reducing the stresses created within the axle assembly, and prolonging the effective life thereof and/or reducing the risk of failure of the axle and/or the locating arms.