GB2303775A

GB2303775A - Drawbar suspension unit

Info

Publication number: GB2303775A
Application number: GB9616072A
Authority: GB
Inventors: James Daniel White; Malcolm White
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-07-31
Filing date: 1996-07-31
Publication date: 1997-03-05
Also published as: GB9616072D0

Abstract

A drawbar suspension unit comprises a connection member 14 for connecting together towing and towable vehicle. Member 14 is mounted on one of said vehicles and for limited vertical pivotal movement relative thereto. The unit includes damping means 42 secured to said one of said vehicles and to said connecting member to dampen said pivotal movement.

Description

DRAWBAR SUSPENSION UNIT This invention relates to drawbar suspension units, and the invention is particularly but not exclusively concerned with drawbar suspension units on agricultural trailers.

In the use of an agricultural trailer, in conjunction for example with a tractor, it is found that during towing of the trailer by the tractor there is a tremendous amount of load surge caused by the vertical up and down movement of the trailer during transverse of the tractor and trailer on the ground.

This load surge can be so great that the front wheels of the tractor will leave the ground which has the effect of making the tractor very unstable and impossible to steer. In addition, this up an down movement makes it very uncomfortable for the driver of the tractor.

The present invention seeks to provide an improved drawbar suspension unit which will mitigate the surge loads on the tractor or other towing vehicle.

According to the present invention there is provided a drawbar suspension unit comprising a connection member for connecting together towing and towable vehicles and being mounted for limited vertical pivotal movement relative thereto.

The unit includes damping means secured to one of said vehicles and to said connecting member to dampen said pivotal movement The connection member may be a rigid member secured to or forming part of the drawbar of a towable vehicle such as a trailer. The damping means may be a unit carried by said rigid member and being adapted during movement of the towable vehicle by a towing vehicle to eliminate or substantially reduce surge loads from the towable vehicle to the towing vehicle.

Preferably, the drawbar suspension unit will be attached to an original drawbar of a towable vehicle, the connection member carrying an auxiliary drawbar.

The damping means will preferably be in the form of a rubber spring whose damping effect is variable so as to cater for varying surge loads.

In order that the invention may be more readily understood, an embodiment thereof will now be described, by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section of a drawbar suspension unit in accordance with the invention; Figure 2 is a plan view of the auxiliary drawbar of the suspension unit in Figure 1; Figure 3 is a side view, partly in section, of the auxiliary drawbar of Figure 2; Figure 4 is a view on the line XX of the suspension unit at Figure 1 with the auxiliary drawbar removed; Figure 5 is a view on arrow W of the suspension unit of Figure 1 with the damping unit and auxiliary drawbar removed; and Figure 6 is a view on YY of the suspension unit of Figure 1.

Referring to the accompanying drawings, a drawbar suspension unit 1 is attached to the original drawbar 2 of a towable vehicle (not shown) such as an agricultural trailer.

Drawbar 2 is shown as having had its towing eye removed by reducing the length of said drawbar. Drawbar suspension unit 1 is secured to the shortened drawbar 2 by, for example, welding or in any other suitable way. Suspension unit 1 includes vertical plate 6 and horizontal plate 8 which are connected together and both of which are connected to the original drawbar 2, plate 6 being connected to the end of drawbar 2 and plate 8 to the underneath of said drawbar. Extending forwardly to the right hand side (as seen in Figure 1) of, and attached to vertical plate 6 is a further plate 10 which is of generally inverted U cross-section having a horizontal bight portion 10A and, connected thereto by curved corner portions lOB, downwardly depending limb portions lOC.

Connected to and extending downwardly from the rear underside of plate 8 is a hinge box 12 which is closed on all sides except for an open front. Hinge box 12 is provided with aligned bushes located in opposite side walls and between which extends an axle (not shown). Mounted on the axle within hinge box 12 for vertical pivotal movement relative thereto is an auxiliary drawbar 14 which is made of square-section metal tube.

At its rear end, drawbar 14 is provided with bushes 16 which are aligned with the above-mentioned bushes 13 of hinge box 12 and through which the axle (not shown) passes.

At its front end, auxiliary drawbar 14 is angled downwardly and rearwardly (see figure 1) and the upper wall of the drawbar has secured to its under surface a plate 18 which extends forwardly from the drawbar. Close to its forward end, plate 18 is provided with a towing eye 20 by means of which the towable vehicle may be attached to a towing vehicle such as a tractor.

The forward end of auxiliary drawbar 14 is closed by means of a capping plate 22.

Extending downwardly from the area of connection of plates 6 and 8 is a guide bracket 24 through which auxiliary drawbar 14 passes. The detail of guide bracket 24 is shown in Figure 4, the bracket including vertical plates 26 and 28 between which auxiliary drawbar 14 extends and through which passes a round section rod 29 (not shown in Figure 4). Rod 28 extends through bushes 30 and 32, said bushes extending outwardly from respective plates 26 and 28. The ends of rod 29 are threaded and the rod is secured in position by means of nuts 34 and 36.

Figure 1 shows auxiliary drawbar 14 in its lowermost position with its bottom wall resting on rod 29. Lateral movement is restricted by means of plates 26 and 28.

Located between plate 10 and the upper surface of auxiliary drawbar 14 is a damper unit 40 in the form of a rubber spring 42 which extends from the under surface of plate 10 to the upper surface of octagonal plate 44. Rubber spring 42 is of generally cylindrical shape having an axial bore running therethrough.

The ends of the axial bore are located on a spigot 46 which depends downwardly from plate 10 and an opposed spigot 48 which extends upwardly from octagonal plate 44. As shown in figures 1 and 3, plate 44 is attached at its forward edge to a bar 50 located on the upper surface of auxiliary drawbar 14 and at its rear edge directly to drawbar 14. As a result, plate 44 is parallel to plate 10 when auxiliary drawbar 14 is in its lowermost position.

The rubber spring which forms damper unit 22 has a damping effect which is variable so as to accommodate varying surge loads between the towable vehicle and the towing vehicle. Such variation is achieved by varying the amount of or the resilience factor of the rubber forming the damper unit 22.

The vertically upward movement of auxiliary drawbar 14 about its rear pivot is limited by the engagement of the upper surface of drawbar 14 with the lower surface of plate 6 lying between plates 26 and 28. Accordingly, it will be appreciated that auxiliary drawbar 14 is constrained laterally between plates 26 and 28 and vertically to a limited angular movement between the limits defined by rod 29 and plate 6. Such vertical movement is dampened by the damper unit 22.

In use, when the towable vehicle is attached to the towing vehicle through the intermediary of the eye 20 of auxiliary drawbar 14 and the two vehicles are traversed along the ground, the presence of the damper unit 22 will cushion the transmission of load surges from the towed vehicle to the towing vehicle.

It will be appreciated that the damping unit may take a form other than a rubber spring and that a different way of attaching the rigid member to the original drawbar of the towable vehicle may be used. For example, the damping unit may take the form of a coil spring, or a hydraulic or pneumatic ram, each preferably being variable in their damping effect.

Finally, a suspension unit in accordance with the present invention may form an integral part of a towable vehicle instead of the unit being an add-on unit.

Claims

1. A drawbar suspension unit comprising a connection member for connecting together towing and towable vehicles and being mounted for limited vertical pivotal movement relative thereto.

The unit includes damping means secured to one of said vehicles and to said connecting member to dampen said pivotal movement.

2. A unit according to Claim 1 wherein the connection member and damping means are secured to the towable vehicle.

3. A unit according to Claim 1 or Claim 2 which is attached to the original drawbar of a towable vehicle, the connection member being an auxiliary drawbar.

4. A unit according to any of the preceding claims wherein the damping means is in the form of a rubber spring.

5. A unit according to any of the preceding claims wherein the damping effect of the damping means is variable so as to cater for varying surge loads.

6. A unit according to Claim 1 and substantially as herein described.

7. A drawbar suspension unit substantially as described with reference to the accompanying drawings.