GB2252276A

GB2252276A - Tandem axle vehicle suspension

Info

Publication number: GB2252276A
Application number: GB9101913A
Authority: GB
Inventors: Bernard Ashton; Gallais Raymond Le
Original assignee: GKN Tadchurch Ltd
Current assignee: GKN Tadchurch Ltd
Priority date: 1991-01-29
Filing date: 1991-01-29
Publication date: 1992-08-05
Also published as: GB9101913D0

Abstract

A suspension system for a pair of axles of a vehicle, generally of the type disclosed in GB 1498403, has pair of axles pivotally connected at the ends of a pair of longitudinal beams (10) of which the centres are connected to the vehicle structure by respective pairs of spring members, each spring member (15) comprising rigid plates (16) in a sandwich structure with blocks (17) of resilient material secured to the plates, the axes of the spring members of each pair being equally and oppositely inclined to the vertical. The suspension system has resilient bump stops (18, 19) for limiting movement of the beams, and the spring members are arranged to give the suspension a natural frequency of about 2Hz. <IMAGE>

Description

VEHICLE SUSPENSIONS This invention relates to vehicle suspensions.

More particularly, it relates to a suspension system for a pair of axles of a vehicle, generally of the type disclosed in British Patent Specification No. 1 498 403.

Such a suspension system comprises a pair of axles mounted parallel to one another adjacent the ends of a pair of longitudinal beams and pivotally connected thereto by brackets. The centres of the longitudinal beams are connected to the vehicle structure by respective pairs of spring members, each spring member comprising a plurality of rigid plates separated in a sandwich structure by blocks of resilient material secured to each adjacent plate, each spring member being so arranged that its axis extends transversely to the direction of movement of the vehicle and the axes of each pair of spring members being inclined relative to each other at equal and opposite angles to the vertical. The axles are located longitudinally of the vehicle by torque rods and A-frames connected between the axles and the vehicle frame structure.Such a suspension system will hereafter be referred to as a suspension system of the kind specified.

Such a suspension performs satisfactorily, but it is the object of the present invention to provide an improved performance in respect of minimising road damage due to the passage of a heavy vehicle thereover, whilst maintaining vehicle roll stiffness.

This object is achieved by providing spring members which are arranged to provide a reduced spring rate in respect of upward movement of the longitudinal beams relative to the vehicle frame structure, compared with the spring rate which has usually been provided hitherto in such suspensions, together with resilient bump stop means for each longitudinal beam at the spring members thereof, the bump stop means being engaged by the longitudinal beams after a predetermined amount of upward movement of the beams relative to the frame structure to provide an increased spring rate in respect of said vertical movement.

The vertical rate of the spring members preferably is chosen so that the suspension has a natural frequency of approximately 2 Hz. This has been found to be advantageous in minimising road damage from heavy vehicles.

In a suspension system according to the invention, the lower rate of the spring members in respect of vertical movement of the longitudinal beams relative to the frame structure may firstly be obtained by reducing the angle of inclination of the plates of the spring members to the vertical to about 17 , i.e. the lower end of the range disclosed in GB 1 498 403. The result of this is that the vertical movement produces more shear in the spring members relative to compression thereof, which with suitable selection of the characteristics of the sandwiched rubber blocks can produce the required lower rate. An increased number of sandwiched rubber blocks may then be required in each spring member.

At the same time, the resistance of the spring members to compression is not significantly altered, so that vehicle roll remains effectively countered, with the roll stiffness remaining high.

The spring members are preferably arranged so that for a fully laden vehicle, static, the longitudinal beams do not reach the positions in which the bump stop means are engaged. When the vehicle is being driven, a substantial amount of suspension movement takes place in the range wherein the bump stop means are not engaged.

When the pump stop means are engaged to provide the increased spring rate, the fact that the suspension system includes the longitudinal beams which are able to pivot about the spring members has the effect that the wheels are still able to follow road surface irregularities without being constrained by the increased spring rate provided by the bump stop means. Therefore, in use, the suspension system provides the required ability for the wheels to follow the road surface without causing excessive damage thereto.

The accompanying drawing shows diagrammatically the spring members supporting one of the longitudinal beams of a suspension system according to the invention. Other details of the suspension system are generally as described in GB 1 498 403.

In the drawing, the longitudinal beam is indicated at 10, the beam extending perpendicularly to the plane of the drawing. Between its ends, the beam is provided on opposite sides with support plates 11 which are equally and oppositely inclined to the vertical at an angle of about 17 thereto.

A vehicle chassis member extending longitudinally thereof, in the form of a C-section member, is indicated at 12. To this is secured a fabricated support structure 13 which includes parts 14 facing the support plates 11 and spaced therefrom. Respective spring members 15 are interposed therebetween, each spring member comprising a plurality of plates 16 in a sandwiched structure with rubber blocks 17 which are bonded to the plates 16.

It will thus be appreciated that upward movement of the beam 10 relative to the vehicle chassis member 12 produces a combination of shear and compression in the rubber blocks 17, with shear predominating. Any attempted roll of the vehicle, however, produces primarily compression of the rubber blocks of one of the spring members, so that such roll is effectively resisted.

Adjacent the spring members 15, the beam 10 carries a resilient bump stop 18 in the form of a rubber block, engageable with an abutment 19 secured to the structure 13 after a predetermined amount of upward movement of the beam 10 relative to the vehicle chassis. When the bump stop engages the abutment 19, the spring rate in respect of the upward movement of the beam 10 is greatly increased.

Claims

1. A suspension system of the kind specified wherein the spring members provide a spring rate in respect of upward movement of the longitudinal beams relative to the vehicle frame structure such that the suspension has a natural frequency of approximately 2 Hz, and further comprising resilient bump stop means for each longitudinal beam at the spring members thereof, the bump stop means being engaged after a predetermined amount of upward movement of the beams relative to the frame structure to provide an increased spring rate in respect of said vertical movement.

2. A suspension system according to Claim 1 wherein the plates of the spring members are inclined to the vertical at about 17".

3. A suspension system substantially as hereinbefore described with reference to the accompanying drawings.