GB2220175A

GB2220175A - Vehicle rear suspension unit

Info

Publication number: GB2220175A
Application number: GB8815803A
Authority: GB
Inventors: Brian Ronald Haylock
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1988-07-02
Filing date: 1988-07-02
Publication date: 1990-01-04
Also published as: GB8815803D0

Abstract

In a twist-beam suspension 10, a transverse beam 26 connects two trailing arms 12, 14 and is rigidly secured to the arms. The beam is stressed in torsion while the suspension is operative and the beam twists. The beam has a C-shaped cross section, with the open part of the C preferably facing downwards. <IMAGE>

Description

Vehicle rear suspension unit This invention relates to a vehicle rear suspension unit for non-driven rear wheels of the type commonly referred to as a "twist beam suspension".

In a twist beam suspension, the two rear wheels of a vehicle are mounted at the ends of trailing arms with the front ends of the trailing arms hinged to the vehicle body about a common horizontal axis. Each arm has an associated spring and damper unit adjacent the wheel, and a transverse beam interconnects the two trailing arms between their ends. When one wheel is forced to rise higher than the other, the transverse beam twists, and this has been found to produce a desirable interconnection between the motion of the two wheels.

The cross sectional shape of the transverse beam itself has been found to be significant. Examples of twist beam suspensions are to be found in DE-PS 2 430 048, DE-PS 2 103 399 and in US-PS 4 165 099.

According to the present invention, there is provided a vehicle rear suspension unit comprising two trailing arms each adapted to be mounted at one end to the vehicle body for pivoting movement about a generally horizontal axis and each having means at the other end for supporting a road wheel, the two arms being interconnected by a transverse beam rigidly fixed to each arm and having a C-shaped cross section.

The use of a C-shaped cross section provides greater stiffness than is available from prior art beam sections.

Thus the beam can be lighter in weight than has been the case hitherto.

The C-shaped section is preferably cylindrical with a longitudinal opening along its length. The opening preferably occupies an arc of between 30 & and 60 & with a preferred arc subtending an angle of 40 & at the centre of the cylinder.

The ends of the beam are preferably shaped so that they butt up against the sides of the arms, surround half of the cross section of the arms, and are welded to the arms.

A reinforcing bracket may also be welded to the arm and to the adjacent end of the beam to increase the rigidity of the joint.

The beam itself is preferably of a slightly larger diameter than the arm.

The longitudinal slit in the beam is preferably underneath.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic plan view of a suspension unit in accordance with the invention; Figure 2 is a section through the beam of the suspension in Figure 1, on the lines II-II; and Figure 3 is a perspective view of the joint between the beam and one arm, with a stiffening bracket omitted for clarity.

The suspension unit 10 has two trailing arms 12 and 14 carrying respectively wheels 16 and 18 at their trailing ends. A suspension strut (not shown) will be connected between the ends of the arms at 20 and 22 and an appropriate part of the vehicle body which is not shown in Figure 1.

At their inboard ends the arms 12, 14 are mounted for pivoting movement about an axis 24 in a body structure 26.

The arms are also connected to one another by a beam 28 which is rigidly secured at each end to the arms 12, 14 with stiffening brackets 30, 32 adding to the rigidity of the beam/arm joints.

The theory of operation of this type of suspension is discussed at some length in the prior art references mentioned above and will not be further explained here.

It is important however that the arms 12, 14 should be stiff in bending and resistant to torsion whilst the beam 28 should be capable of twisting in torsion.

Figure 2 shows the beam 28 in cross section showing the Csection with the open part of the C at the bottom. The beam is of relatively thin-walled material, for example 2.75mm thickness. This thickness has been found to have equivalent stiffness to 6mm thick material in a configuration in accordance with DE-PS 2 430 048.

It is necessary for the beam to be able to twist in torsion, and a continuous cylindrical tubular section has been found to be too stiff. The size of the opening in the C-section, (as measured by the angle subtended by the arc at the centre of the section) is limited at its lower end by the necessity to prevent the two edges of the opening from rubbing against each other and producing undesirable noise when twisting takes place. A suitable lower figure is 30 & The maximum size of the opening will be determined by the torsional stiffness of the beam which will reduce as the opening gets larger, and a maximum opening size of 60 & is suggested with a preferred opening size of 40 &

The beam is shaped at its ends as shown in Figure 3 so that it embraces the tubular arms 12, 14 and can be welded to the arms. The joint between the beam and each arm needs to be as stiff as possible and thus not only are the ends of the beam welded to the arms, but also reinforcing plates 30,32 are provided and welded to both components.

The beam 28 is preferably manufactured by rolling a flat sheet into a C-shaped cross section. Because of the location of the edges on either side of the slit 34 in a low stress area, it is not necessary to take special care to finish these edges in a non stress-raising manner. As a result the beam can be produced from cropped edge material rather than the as-rolled edge material previously needed.

The invention thus provides a light and cheap beam for use in a twist beam suspension.

Claims

1. A vehicle rear suspension unit comprising two trailing arms each adapted to be mounted at one end to the vehicle body for pivoting movement about a generally horizontal axis and each having means at the other end for supporting a road wheel, the two arms being interconnected by a transverse beam rigidly fixed to each arm and having a C-shaped cross section.

2. A suspension unit as claimed in Claim 1, wherein the C-shaped section is preferably cylindrical with a longitudinal opening along its length.

3. x suspension unit as claimed in Claim 1 or Claim 2, wherein the gap between the two arms of the C occupies an arc of between 30 & and 60 &

4. A suspension unit as claimed in Claim 3, wherein the gap is an arc which subtends an angle of 40 & at the centre of the section.

5. A suspension unit as claimed in any preceding claim, wherein the ends of the beam are shaped so that they butt up against the sides of the arms, surround half of the cross section of the arms, and are welded to the arms.

6. A suspension unit as claimed in any preceding claim, wherein a reinforcing bracket is welded to each arm and to each adjacent end of the beam to increase the rigidity of the beam/arm joints.

7. A suspension unit as claimed in any preceding claim, wherein the beam itself is of a slightly larger diameter than the arm.

8. A suspension unit as claimed in any preceding claim, wherein the longitudinal slit between the arms of the Cshaped section of the beam is underneath.

9. 9 vehicle rear suspension unit substantially as herein described with reference to the accompanying drawings.