GB2145985A - Tractor auxiliary suspension arrangement - Google Patents

Abstract

The suspension system particularly for a tractor 10 having an overhanging load 15 includes a pair of road wheels 23 each supported via a castor arrangement 22 on a separate arm 17. The arms 17 are pivotally connected at their front ends to laterally spaced locations on the tractor and at their rear ends with a pair of laterally extending links 19 which are also pivotally connected with the overhanging load to form a parallel motion mechanism. Double-acting hydraulic rams 24 act as a biassing means to urge the road wheel into contact with the ground thus supporting at least part of the weight of the overhanging load and hence enhancing the stability of the tractor. The ram 24 can also be used to raise the arms 17 when the tractor is reversed. <IMAGE>

Description

SPECIFICATION Tractor auxiliary suspension arrangement This invention relates to an auxiliary suspension system for a tractor or other unsprung vehicle. The term "tractor" is used hereinafter to refer to all kinds of vehicles having unsprung axles, as well as agricultural tractors. The invention is particularly suitable for use on a tractor carrying an overhanging load, such as a trenching machine, a bucket or other loader, or the like.

Agricultural tractors are frquently modified so as to be able to perform functions other than the simple drawing of agricultural implements. For example, a bucket excavator is frequently attached to the rear of a tractor, so as to project rearwardly thereof to a considerable extent. Similarly, a trenching machine may be attached to the rear of a tractor. Other earth-working equipment may be connected to a tractor, to overhang either the rear of the tractor or the front thereof -- such as a front bucket loader, or a bulldozer attachment.

All of the foregoing equipment adds a considerable load to the tractor, which overhangs the adjacent front or rear axle thereof. Both when the equipment is in use and when the tractor is being moved from place to place, this overhanging load can cause problems with the stability of the tractor.

Particularly when the overhanging load is relatively massive, the problems of stability are exacerbated by the fact that very few tractors have any form of axle suspension system, neither on the front nor on the rear axles, though of course the use of tyres of relatively large sections do provide limited cushioning from severe shocks. As a result, it is found that though the movement of a tractor with a relatively massive overhanging load may cause no particular problem at fairly low speeds, the problems become greater as the speed of movement of the tractor rises. Moreover, as the quality of the terrain over which the tractor is driven becomes worse, so do the stability problems -- and the problems are compounded with a massive overhanging load.When both the speed of movement of the tractor is high and the terrain is rough, the tractor may become unstable to such an extent that it becomes uncontrollable, or even turns over.

It is a principal object of this invention to provide an auxiliary suspension system for a tractor (as hereinbefore defined), especially when carrying an overhanging load, which system serves at least to offer a degree of damping of pitching motion when being moved, but also largely to eliminate the above-described problems of instability when the tractor is carrying an overhanging load.

Accordingly, this invention provides an auxialiary suspension system for a tractor (as defined herein), which system comprises an arm pivotally connected to the tractor and projecting generally parallel to the longitudinal axis of the tractor, a road wheel rotatably mounted on a castor arrangement supported by the arm, and biassing means suitably disposed to urge the road wheel downwardly relative to the tractor.

Though a viable construction of the suspension system may have but one arm and one road wheel, most preferably the auxiliary suspension system comprises a pair of arms spaced laterally of the tractor and each disposed as just-described, each arm being provided with a castor arrangement and road wheel and with biassing means, whereby the auxiliary suspension system includes two laterally-spaced road wheels, one to each side of the tractor. In the following, all references will be to such a preferred form of the suspension system, though it will be understood that certain of the following features are applicable to a simple form of the suspension system, having but one arm and road wheel.

A prime intention of this invention is to enhance the stability of a tractor (as defined herein) carrying an overhanging load, and in the following reference will mostly be made to such a vehicle. The auxialiary suspension system may instead be used on vehicles having unsprung axles merely to damp such pitching motion, as occurs when an unsprung vehicle is driven rapidly. In such an arrangement, the arms could for example simply project rearwardly of the vehicle from the front axle thereof, so to damp the resilience of the vehicle tyres.

It will be appreciated that when used with a tractor having an overhanging load, the auxiliary suspension system of this invention carries at least a part of the weight of the overhanging load, through the road wheels of the suspension system.

Moreover, the suspension system serves greatly to reduce the turning moment applied to the tractor by the overhanging load and which is centred on the adjacent tractor axle, and this leads to great enhancement of the stability of the tractor, particularly when the tractor is being driven at relatively high speeds or is being driven over rough terrain.

The greater the projection of the arms of the suspension system in the direction of overhanging of the load, the greater is the enhancement of the tractor stability. However, too great a projection may lead to problems in the physical construction of the suspension system and also may interfere with the operation of the overhanging load; it is however preferred for the suspension system to be arranged such that the centre of gravity of the overhanging load, at least when in its position for transport from place to place, lies over the axis of the road wheels of the suspension system, or lies between the axis of those road wheels and the adjacent axle of the tractor.

The provision of a castor arrangement for each road wheel ensures that the auxiliary suspension system does not in any way interfere with normal steering of the tractor, for such a castor arrangement will ensure that each road wheel takes up an appropriate angular position with respect to the longitudinal axis of the tractor as the tractor is steered, so obviating the need to provide complex steering mechanisms for the road wheels of the auxiliary suspension system.However, though a castor arrangement permitting 360" of castoring action could be provided, it is nevertheless preferred for the auxiliary suspension system to be provided with means to effect lifting of the road wheels clear of the ground, whenever reverse gear is engaged in the tractor This then simplifies the construction of the castor mechanism, in that a castoring action of less than 360 (and typically only 1800 need be provided. Such lifting means may for example comprise one or more hydraulic rams adapted to lift the arms when fluid under pressure is supplied to the rams, the control of the supply of such fluid under pressure being under the control of a valve interconnected to the gear selection mechanism of the tractor.

Preliminary tests have shown that most advantageous results can be obtained from an auxiliary suspension system of this invention by damping relatively heavily the movement of the arm downwardly, but damping only lightly the movement of the arm upwardly. This serves to ensure that shock loads imparted to the suspension system are minimised while still providing a highlevel of control over the stability of the tractor The biassing means could comprise a conventional spring assembly employing for example leaf springs or coil springs. It is however preferred for the biassing means to comprise, for each arm, a double-acting hydraulic ram connected between the arm and a mounting point on the tractor, there being an appropriate source of hydraulic fluid under pressure and a control arrangement for the supply of that fluid to the hydraulic rams.An advantage of such hydraulic biassing means is that the biassing force imparted to the arms may be substantially constant, irrespective of the angular positions of the two arms. Moreover, it is relatively easy to incorporate appropriate valves in the control arrangement for the supply of hydraulic fluid, to impart the required damping characteristics to the suspension system. A further advantage is that where the suspension system is to provide automatic lifting of the arms when reverse gear is selected on the tractor, the double-acting rams of the biassing means may serve the function of the lifting means for the arms.

In a preferred embodiment of this invention, adapted for use with an overhanging load projecting rearwardly from the tractor, each arm is pivotted to the rear axle assembly of the tractor, so as to project both rearwardly and laterally therefrom, such that the road wheel carried thereby is generally in line with the rear wheel of the tractor. Control of the position and movement of the rear end of each arm is advantageously achieved by means of a pair of links pivotally connected both to a strut attached to the arm and to appropriate mounting points provided on the overhanging load, each link extending generally laterally and the links being disposed to form a parallel motion mechanism.

The castor arrangement may then conveniently be mounted on said strut, to carry the road wheel rearwardly thereof and to permit that wheel to perform a castoring function.

This invention extends to a tractor whenever fitted with an auxiliary suspension system of this invention, as described above. Moreover, the invention further extends to the combination of a tractor having a trenching machine attached thereto in the form of an overhanging load projecting rearwardly of the tractor, and an auxiliary suspension system of this invention as described above, disposed to support a portion of the load of the trenching machine and to enhance the stability of the tractor and trenching machine combination.

By way of example only, one specific embodiment of the invention will now be described in detail, reference being made to the accompanying drawings, in which: Figure I is a diagrammatic side view of the rear part of a conventional unsprung agricultural tractor having an overhanging trenching machine attached to the rear thereof and fitted with an auxiliary suspension system of this invention; Figure 2 is a rear view of the assembly illustrated in Figure 1; Figure 3 is a plan view of the assembly illustrated in Figures 1 and 2; and Figure 4 is a perspective view of the principal parts of the suspension systems of this invention.

Referring to the drawings, there is shown diagrammatically at 10 the rear part of a conventional agricultural tractor including a rear axle assembly 11 fitted with road wheels 12. Attached to the conventional connection points at the rear of the tractor is a frame 13 of a trenching machine shown diagrammatically at 14, the trenching machine including a trenching boom 15 coupled to the frame 13 by means of a pair of pivotal links 16. The links permit the movement of the boom 15 to and from the illustrated transport position thereof. However, it will be appreciated that even when the boom is in this transport position, the tractor is subjected to a most considerable load, overhanging rearwardly and which leads to problems of stability when the tractor is driven at high speed, particularly over rough terrain.

In order to improve the stability characteristics and to relieve the tractor of much of the turning moment imparted by the overhanging load, the tractor is fitted with an auxiliary suspension system which comprises a pair of arms 17 pivotally connected at their forward ends to brackets 18 mounted on the rear axle assembly 11 of the tractor. Each arm 17 projects both rearwardly (Figure 1) and laterally (Figure 3) such that the end of each arm remote from its pivotal connection to the axle assembly 11 lies substantially aligned with the adjacent tractor rear wheel 12.

Attached to the rear end of each arm 17 is a strut 18, to which are pivotally connected a pair of links 19, each link 19 at its inner end being pivotally connected to an appropriate mounting 20 provided on the frame 13 of the trenching machine 14. The links 19 in conjunction with the strut 18 and the trenching machine frame 13 approximate to a pareilel motion linkage, to control the movement of the rear end of the associated arm 17.

Each strut 18 also has attached thereto a pair of brackets 21 (Figure 4) which pivotally support a Ushaped carrier 22 within which is rotatably mounted a road wheel 23. The carrier 22 may pivot about a substantially vertical axis through an angle of about 180 , so providing a castor arrangement for the carried road wheel 23.

A double-acting hydraulic ram 24 has the free end of its piston rod 25 pivotted to a lug 26 mounted on the arm 17, part-way between the ends thereof, and has the free end of its cylinder pivotted to the frame 13 of the trenching machine 14. Hydraulic fluid under pressure may be supplied to the ram to cause the expansion thereof, so as to bias the associated road wheel 23 downwardly, firmly into engagement with the ground and so relieving the tractor of a part of the weight of the trenching machine 14. This also relieves the tractor of much of the turning moment which the trenching machine imparts thereto.

The hydraulic supply arrangement for each hydraulic ram 24 is illustrated in Figure 4, and comprises a source 30 of hyraulic fluid under pressure, which source normally is provided as a part of the agricultural tractor. Control valves 31 and 32 serve to control the supply of fluid under pressure to the hydraulic ram 24, respectively for the expansion and for the contraction of the ram. Down-stream of control valve 31 is a accumulator 33, and fluid is supplied to the top of the ram 24 through a pair of throttling valves 34 and 35, respectively for flow to and from the ram. Similarly, two throttling valves 36 and 37 are provided to control the flow of fluid respectively to and from the lower end of the ram.

In operation, the hydraulics are arranged to supply fluid under a predetermined pressure to the ram 24, such that the associated road wheel 23 is biassed into contact with the ground with the appropriate force, irrespective of the angular position of the arm 17, relative to the tractor. The valves 34, 35, 36 and 37 should all be adjusted such that there is only light damping of the arms when performing upward movement, but such that the downward movement of the arms is relatively heavily damped.

When the tractor is to be driven in reverse, the selection of reverse gear on the tractor serves automatically to set valves 31 and 32 appropriately, whereby the rams 24 are contracted, so lifting the two arms 17 and raising the road wheels 23 clear of the ground.

Claims (14)

1. An auxiliary suspension system for a tractor (as defined herein), said system comprising an arm pivotally connected to the tractor and projecting generally parallel to the longitudinal axis of the tractor, a road wheel rotatably mounted on a castor arrangement supported by the arm, and biassing means suitably disposed to urge the road wheel downwardly relative to the tractor.

2. A suspension system according to claim 1 comprising two road wheels laterally spaced of the tractor one to each side of the tractor, each road wheel being supported via a castor arrangement on a separate arm, the arms being pivotally connected to the tractor at laterally spaced locations on the tractor and each provided with a biassing means to urge the associated road wheel downwardly.

3. A suspension system according to claim 1 or claim 2 for a tractor having any overhanging load projecting rearwardly of a rear axle assembly of the tractor in which the or each arm is pivotted at its forward end on the tractor and projects rearwardly and laterally therefrom and in which a pair of laterally extending links are pivotally connected between the overhanging load and the rear end of the or each arm to form a parallel motion mechanism.

4. A suspension system according to claim 2 and 3 in which each road wheel is generally in line with a respective one of the rear wheels of the tractor.

5. A suspension system according to claim 3 constructed such that the centre of gravity of the overhanging load, at least when in a position for transport from place to place, lies over the axis of rotataion of the or each road wheel of the suspension system, or lies between said axis of the or each road wheel and the rear axle of the tractor.

6. A suspension system according to any one of claims 1 to 5 in which the or each biassing means comprises a double-acting hydraulic ram acting between the associated arm and the tractor, a source of hydraulic fluid under pressure and valve means for controlling the supply of pressurised fluid to the or each ram to urge the or each road wheel downwardly.

7. A suspension system according to any one of claims 1 to 6 in which the downward movement of the or each arm is damped relatively heavily whilst the upward movement of the or each arm is damped only relatively lightly.

8. A suspension system according to claim 6 and 7 in which the valve means is arranged to control the supply of fluid to and exhaust of fluid from the or each ram to give the required damping characteristics.

9. A suspension system according to any one of claims 1 to 8 in which lifting means are provided for lifting the road wheels clear of the ground to facilitate reversing of the tractor.

10. A suspension system according to claim 9 in which the lifting means is arranged to be interconnected with a gear selection means of the tractor so that the lifting means is actuated whenever a reverse gear is selected.

11. A suspension system according to claim 9 or claim 10 in which the lifting means comprises hydraulic ram means connected with the or each arm and arranged to lift the or each arm when fluid under pressure is supplied to the or each ram means.

12. A suspension system according to claim 6 and claim 11 in which the hydraulic ram means is provided by part of the or each double-acting hy drauiic ram so that the biassing means also provides the lifting function.

13. A tractor provided with an auxiliary suspension system in accordance with any one of claims 1 to 12.

14. An auxiliary suspension system for a tractor, said suspension system being constructed and arranged substantially as hereinbefore described with reference to and as shown in the accompanying drawings.