GB2124984A

GB2124984A - Rear axle for a vehicle particularly a motor vehicle

Info

Publication number: GB2124984A
Application number: GB08321127A
Authority: GB
Inventors: Helmut Kaltwasser
Original assignee: Adam Opel GmbH
Current assignee: Adam Opel GmbH
Priority date: 1982-08-13
Filing date: 1983-08-05
Publication date: 1984-02-29
Also published as: DE3230114C2; GB8321127D0; GB2124984B; DE3230114A1

Abstract

A rear axle for a vehicle, specifically a non-driven rear axle of a motor vehicle, is formed from two flexurally and torsionally rigid longitudinal guide arms 21, 22, on which the wheels 15 are rotatably mounted, and a flexurally rigid but torsionally resilient transverse beam 14 which interconnects the longitudinal guide arms and is connected to the respective longitudinal guide arms in an angularly rigid manner by welding. The transverse beam has an open cross-section which has its plane of symmetry disposed horizontally. In its central region between the longitudinal guide arms the transverse beam has a V-shaped cross-section, whereas in the region of its connections to the respective longitudinal guide arms the transverse beam has a U-shaped cross- section. The two cross-sectional shapes merge into each other gradually. The beam is thereby relatively free from deformation under torsional forces whilst its U-shaped ends are more adapted for connections to the guide arms. <IMAGE>

Description

SPECIFICATION Rear axle for a vehicle, particularly a motor vehicle This invention relates to a rear axle for a vehicle, particularly a motor vehicle.

German patent specification 2,430,048 (Volkswagenwerke) discloses a rear axle having flexurally and torsionally rigid longitudinal guide arms on which respective ones of a pair of rear wheels are rotatable mounted, and having a flexurally rigid but torsionally resilient transverse beam which interconnects the longitudinal guide arms and is connected to the two longitudinal guide arms in an angularly rigid manner by welding.

For achieving sufficient torsional and flexural rigidity it is desirable to construct the longitudinal guide arms of such rear axles as a box section, but for the transverse beam interconnecting the longitudinal guide arms the need for sufficient torsional resilience allied with adequate flexural rigidity can be met only by the use of an open cross-section. For this purpose it is known for the transverse beams to have a U-shaped, V-shaped, Z-shaped or angular profile.

Such a transverse beam has to be so configured that the maximum bending forces acting upon it in two planes are completely absorbed. In the vertical plane of the transverse beam these bending moments are derived from the vertical forces acting on the wheels, eccentrically to the longitudinal guide arm axis, and in the horizontal plane such bending moments are produced by the lateral forces occuring during cornering.

On the other hand, the open cross-sections provide sufficient torsional resilience for the independent up-and-down suspension movement of the two rearwheels not to be unduly pejudiced. However, the resulting torque resistance can at the same time be used in an advantageous manner simultaneously to provide a stabilising effect, and in many cases the fitting of an additional transverse stabiliser (in other words, a Pan hard rod) is completely unnecessary.

However, for the reasons mentioned above, when the transverse beam is subjected to torsional forces the open cross-sections exclusively utilised for the transverse beam of this rear axle do exhibit a more or less strong tendency to deformation of their cross-sectional shape, in that the free arms thereof become displaced relative to each other, or alternatively, if they are prevented from doing this by the use of a special type of connection, the resulting restriction on deformation produces correspondingly high stess peaks at the connections to the longitudinal guide arms.Because of the specific properties of the open cross-sections, the interconnection between the transverse beam and the torsionally and flexurally rigid longitudinal guide arms becomes especially uncertain, since the danger of cracking as a result of locally exceeding the permissible stress values is correspondingly high.

In order to place a limit on the stress peaks at the connections between the transverse beam and the longitudinal guide arms, it is known from the said German specification 2,430,048 to utilise a transverse beam having a V-shaped cross-section, which is known to exhibit little deformation of its crosssectional shape when the beam is subjected to torsional forces. To the extent that the relative displacement of the free arms of this cross-sectional shape is less than for another open cross-sectional shape, the stresses at the connections to the longitudinal guide arms will also be less.On the other hand, this particular cross-sectional shape does have the disadvantage that its geometrical configuration renders it unfavourable for providing a connection to the longitudinal guide arms, and therefore, despite the inherently low tendency of the V-shaped crosssectional shape to deform in response to torsional forces, increased stresses appear at the connections to the longitudinal guide arms.

By welding-in further components, for example appropriately formed gussets and other reinforcing elements, attempts have been made to reduce the stress peaks and to distribte the forces over a larger transfer surface or more suitably arranged welding seams.

By the present invention there is provided a rear axle for a vehicle, particularly a motor vehicle, in which a pair of rear wheels are rotatably mounted on respective ones of a pair of flexurally and torsionally rigid longitudinal guide arms, a flexurally rigid but torsionally resilient transverse beam interconnects the longitudinal guide arms and is connected to the two longitudinal guide arms in an angularly rigid manner by welding, in its central region the transverse beam has a cross-sectional shape that exhibits little deformation when the beam is subjected to torsional forces, and in the lateral directions the cross-sectional shape of the beam merges gradually by way of respective transition regions into a cross-sectional shape that is particularly suitable for providing the connections to the respective longitudinal guide arms inasmuch as thrust and normal forces occu ring particularly during torsional stressing of the transverse beam can thereby be absorbed and transmitted without giving rise to inadmissibly high stress values.

With such a construction, not only is the crosssectional shape of the transverse beam relatively free from deformation under the influence of torsional forces, but also the cross-sectional shape is particularly favourable for the establishment of connections to the longitudinal guide arms, especially with regard to the absorption and transmission of the thrust and normal forces corresponding to the normal torsional response of the transverse beam.

In a preferred form of rear axle in accordance with the invention, the transverse beam has a V-shaped cross-section and is mounted in the rear axle with the plane of symmetry of the V-shaped cross-section arranged horizontally, and the V-shaped crosssection of the beam merges in both lateral directions into a U-shaped cross-section by means of which the transverse beam is connected to the respective longitudinal guide arms.

This specific configuration of the transverse beam on the one hand permits a further reduction in the deformation of the cross-section of the beam in the transition regions in response to torsional forces, as a result of the resistance of the V-shaped crosssectional shape to deformation by the torsional forces, and on the other hand makes it possible for deformation forces arising at the connections to the longitudinal guide arms to be transmitted to the longitudinal guide arms, or to be absorbed by the guide arms, substantially without the incidence of unacceptably high stress values.

Tests have confirmed this, in that on torsional stressing of the transverse beam of the rear axle there is, as compared with a beam having a continuous V-shaped or U-shaped cross-section, a significant increase in the long-term durability, or of vibrations withstood before a first crack appeared in the weld seam.

A further advantage of the transition from a V-shaped cross-section into a U-shaped crosssection in the region of the connections is that the connections between the transverse beam and the longitudinal guide arms are simpler with a U-shaped cross-section purely from a geometrical point of view, and these connections can be made more cheaply than with a V-shaped cross-section.

In order to derive full benefit from the inherent resistance of a V-shaped cross-section to deformation in response to torsional forces, in accordance with an important further preferred feature of the invention it is proposed that the transition regions between the U-section outer regions of the transverse beam and the V-section central region be provided directly adjacent the connections to the respective longitudinal guide arms.

Further, and more specifically as regards the cross-sectional shapes, it is proposed that the Ushaped cross-section of the transverse beam include a web portion of generally arcuate shape, and that at each of the transition regions the U-shaped crosssection merge smoothly into the V-shaped crosssection (thus, without any kinking). In the transition regions, stresses arising from torsional forces are reduced as a result of displacement of metal in the arms of the cross-sections.

With retention of the spacing between the arms of the U-shaped cross-section at the outermost regions of the transverse beam, for maintaining sufficient flexural rigidity in the plane of symmetry of the V-shaped cross-section it is proposed that the arms of the V-shaped cross-section include end portions which are bent over towards each other so that these bent-over end portions extend approximately parallel to each other. This bending-over not only increases the resistance moment to bending, but also reduces the structural height and results in a substantial resistance of the arms to bending when subjected to strong torsional forces.

Finally, it is proposed that the longitudinal guide arms, which are preferably constructed as a box section, enclose the U-section portions of the transverse beam, and that the transverse beam penetrate the entire width of the longitudinal guide arms.

Preferably with this construction the arms of the U-shaped cross-section engage both sides of the inner wall surface of the longitudinal guide arms over a large area, to thereby permit a long welding seam along the edge of a cut-out in the respective longitudinal guide arm.

In the drawing: Figure 1 is a plan view of the left-hand half of a rear axle in accordance with the present invention; and Figures 2 to 4 are sections on the lines Il-Il, Ill-Ill and IV-IV respectively of Figure 1, in the direction of the arrows.

The embodiment of a rear axle in accordance with the present invention which is shown in the drawing essentially comprises two longitudinal guide arms 10 which at their respective front ends are resiliently connected to a vehicle body (not shown) by way of respective bearing eyes 11, and at their rear ends rotatablysupportthe rear wheels 15 by means of respective stub axles 13 fixed to respective wheel carriers 12, with a transverse beam 14 interconnecting the two longitudinal guide arms at a location somewhat behind the bearing eyes 11. The rear wheels 15 are provided with tyres 16 on wheel rims designated 17, and with respective brake drums 19 to which the respective rear wheels 15 are secured by means of wheel nuts 18.

To allow a telescopic shock absorber (not shown) to be connected, the wheel carrier 12 includes an extension 20.

For providing a high degree of torsional and flexural rigidity the longitudinal guide arms 10 are each constructed as a box section comprising upper and lower half shells 21 and 22 of U-shaped cross-section which are interconnected along their flanges 23 and 24 by spot welding, at welding points 25.

A pair of coil springs (not shown) provide suspension support for the vehicle superstructure, and are supported by the longitudinal guide arms 10 by means of respective spring seats 26.

The transverse beam 14 interconnecting the longitudinal guide arms 10 is arranged between the bearing axes of the longitudinal guide arms 10 and the common axis of the rear wheel axles. In the region between the longitudinal guide arms 10 the transverse beam 14 has essentially a V-shaped cross-section, and the beam is so arranged that its arms 14a and 14b extend at about the same angles diagonally forwardly in a downward direction and diagonally forwardly in an upward direction, respectively, as shown in Figure 2. The free end portions of the arms are bent over symmetrically so as to extend approximately parallel to each other.

In a transition region 27 at each side of the vehicle centre line the V-shaped cross-section of the transverse beam merges smoothly into a U-shaped cross-section comprising a pair of parallel arms 14a' and 14b' interconnected by a web portion 14c' of semi-circular cross-section.

The transverse beam 14with its U-section end regions 28 extends into corresponding respective lateral openings in the longitudinal guide arms 10 and penetrates the entire width of the longitudinal guide arms, namely as far as the otuer flanges 23 of the guide arms. In the region of the connections to the transverse beam 14, the longitudinal guide arms 10 each have an inwardly directed wedge-shaped projection 29 whose point makes contact with an apex line of the U-section 28. The attendant increase in the width of the longitudinal guide arm 10 provides a wide base for the connection with the transverse beam 14, this gives the favourable result of a very long weld seam 30 which extends over the apex of the transverse beam 14, and is only briefly interrupted at point 31.

The spacing between the two arms 14a' and 14b' of the U-shaped cross-section 28 of the transverse beam 14 is designed to be such that the arms rest squarely on the inside of the respective longitudinal guide arm half shells 21 and 22. This provides the possibility of forming further weld seams, in addition to the weld seam 30, along the edges of cut-outs on the upper and lower sides of the longitudinal guide arms 10. With this configuration each longitudinal guide arm 10 has circular cut-outs 31a and 31b in which annular beads 32a and 32b are formed by raising the edge of the aperture. Along the edge of the aperture the arms of the cross-section of the transverse beam, which at this point is a U-section, are welded to the upper and lower half shells of the longitudinal guide arms 10. The weld seams are designated 33a and 33b. With these annular beads, on the one hand the distortions caused by weld stresses are avoided, and on the other hand the weld connection is provided in an advantageous manner with a certain amount of resilience.

The rear axle in accordance with the present invention provides the advantage of reducing the forces occurring at the connections between the transverse beam 14 and the longitudinal guide arms 10 and tending to produce deformation of the cross-sectional shape of the transverse beam in consequence of the torsional forces to which the transverse beam is subjected during differing upand-down suspension movements of the respective rear wheels 15, with the residual forces being very well absorbed by the longitudinal guide arms, so resulting in a considerable improvement in the fatigue strength.

Claims

1. A rear axle for a vehicle, particularly a motor vehicle, in which a pair of rear wheels are rotatably mounted on respective ones of a pairofflexurally and torsionally rigid longitudinal guide arms, a flexurally rigid but torsionally resilient transverse beam interconnects the longitudinal guide arms and is connected to the two longitudinal guide arms in an angularly rigid manner by welding, in its central region the transverse beam has a cross-sectional shape that exhibits little deformation when the beam is subjected to torsional forces, and in the lateral directions the cross-sectional shape of the beam merges gradually by way of respective transition regions into a cross-sectional shape that is particularly suitable for providing the connections to the respective longitudinal guide arms inasmuch as thrust and normal forces occurring particularly during torsional stressing of the transverse beam can thereby be absorbed and transmitted without giving rise to inadmissibly high stress values.

2. A rear axle according to claim 1, in which the transverse beam has a V-shaped cross-section and is mounted in the rear axle with the plane of symmetry of the V-shaped cross-section arranged horizontally, and the V-shaped cross-section of the beam merges in both lateral directions into a U-shaped crosssection by means of which the transverse beam is connected to the respective longitudinal guide arms.

3. A rear axle according to claim 2, in which the U-shaped cross-section of the transverse beam includes a web portion of generally arcuate shape, and at each of the transition regions the U-shaped cross-section merges smoothly into the V-shaped cross-section.

4. A rear axle according to claim 2 or 3, in which the V-shaped cross-section of the transverse beam includes bent-over free end portions that extend approximately parallel to each other.

5. A rear axle according to any one of claims 2 to 4, in which the U-section portions of the transverse beam are enclosed by the longitudinal guide arms, with the transverse beam penetrating the entire width of the guide arms.

6. A rear axle according to any one of claims 1 to 5, in which the two cross-sectional shapes of the transverse beam have an apex line which extends in a straight line.

7. A rear axle according to any one of claims 1 to 6, in which the transverse beam is mounted in the rear axle with the cross-section of the beam open in the direction of travel.

8. A rear axle according to any one of claims 1 to 7, in which the transition regions between the respective cross-sectional shapes of the transverse beam are disposed adjacent the connections to the respective longitudinal guide arms.

9. A rear axle according to any one of claims 1 to 8, in which the transverse beam is formed from strip material.

10. A rear axle according to any one of claims 1 to 9, in which the respective cross-sectional shapes of the transverse beam are formed from strips of identical width.

11. A rear axle for a vehicle, particularly a motor vehicle, substantially as hereinbefore particularly described and as shown in the accompanying drawing.