DE29915351U1 - Cross member as part of a twist beam rear axle - Google Patents

Description

FILE No.

Your sign

P ? T E N T ? N W &Lgr; L.T" &Ggr;

452/38514-001

ROLF BOCKERMANN DIPL-ING.

PETER KSOLL DR.-ING. DIPL-ING.

ADMITTED TO THE EUROPEAN PATENT OFFICE EUROPEAN PATENT ATTORNEYS MANDATAIRES AGREES EUROPEEN

Bergstrasse 159 44791 BOCHUM

PO Box 102450 44724 BOCHUM

02.09.1999 XR/Mon

Benteler AG, Residenzstrasse 1, 33104 Paderborn Cross member as part of a twist beam rear axle

Various proposals have been made as to how the cross member of a torsion beam rear axle of a passenger car should be designed in order to make it flexurally rigid on the one hand, but also sufficiently torsionally flexible on the other. These include, for example, the proposals in EP 0 249 537 Bl, EP 0 681 932 A2, EP 0 752 332 Bl, DE-GM's 297 20 207 and US-PS 2,069,911.

However, all of these cross members have the characteristic that their production is complex and therefore the production costs for a complete twist beam rear axle are high. In particular, it is disadvantageous in the known cases that the steels used for the starting tubes require heat treatment in several steps. It is therefore necessary to first anneal the cold-formed tube profiles, then harden them and then temper them again.

Telephone (0234) 51957/58/59 ■ Fax (02 34) 51 0512 ■ e-mail: bochumpatent@t-online.de

Commerzbank AG Bochum, account no. 3864 782 (bank code 43040O36) ■ Postbank Essen, account no. 7447-431 (bank code 360 10043)

VAT ID No.: DE 124146411

in order to then feed them into further configuration to complete a twist beam rear axle. All of these process steps require special equipment and the provision of various energy sources so that a usable tube profile can be made available.

Based on the prior art, the invention is based on the object of creating a cross member as a component of a twist-beam rear axle of a passenger car, which can be manufactured using a significantly simpler process.

According to the invention, this object is achieved by the features of claim 1.

An essential part of the invention is the fact that a starting tube provided for cold forming, regardless of its cross-section, is now made of a micro-alloyed, high-strength steel. Such a steel meets the requirements that are placed on a cross member as a component of a torsion beam rear axle of a passenger car. By eliminating heat treatments with the associated energy sources and devices, including the time required, a high economic output is guaranteed within the scope of the invention, in particular due to the significantly shorter production time. A more economical output inevitably leads to more cost-effective production, with the result that a torsion beam rear axle can also be manufactured more cost-effectively, which ultimately affects the cost of a passenger car.

According to the features of claim 2, the starting tube for the cross member can consist of a cold- or hot-rolled micro-alloyed high-strength steel.

In particular, in this context, according to claim 3, the tube is formed from a steel of material quality S420NC.

The configuration of the cold-formed tube profile can vary depending on the respective requirements. For example, according to the features of claim 4, it is possible for the end sections to have a circular cross-section.

According to claim 5, the end sections can also have a cross-section that deviates from the circular shape. Such a cross-section can be oval or shoe-shaped. This means that even with a shoe-shaped end section, the cross-section is U-shaped and double-walled. It is simply designed to be larger for connection to a trailing arm.

Furthermore, regardless of the design of the end sections, it is possible for the tube profile to be provided with stiffening beads, particularly at the transition from the U-shaped middle length section to the torsionally rigid end sections, which can be formed inwards or outwards.

Furthermore, according to the features of claim 6, it is possible that at least the outer surface of the tubular profile can be subjected to a surface hardening, in particular a mechanical one. If necessary, the inner surface can also be hardened.

Such surface hardening is preferably carried out according to claim 7 by at least the outer

The surface of the pipe profile is irradiated with balls, especially steel balls.

The invention is explained in more detail below using an embodiment shown in the drawings.

Figure 1 shows a top view of a tubular profile as a cross member for a twist beam rear axle of a passenger car and

characters

2 to 5 various cross sections through the pipe profile of the

Figure 1 along lines II-II, III-III, IV-IV and V-V.

In Figure 1, 1 denotes a tubular profile as a cross member for a torsion beam rear axle of a passenger car (not otherwise shown in detail). The tubular profile 1 is made from an originally round tube R (Figure 5) which consists of a micro-alloyed high-strength steel, for example the material quality S420NC.

During non-cutting cold forming, the cross-section of the tube R is maintained in the end sections a of the tube profile 1. However, this circular cross-section at the ends 2 continuously changes in the transition sections b into a U-shaped double-walled cross-section which extends over the middle longitudinal section c of the tube profile 1 (Figures 1 to 5).

Assuming that the tubular profile 1 according to Figure 1 is shown in plan view, i.e. in the installation position in the passenger car, the legs extend

3 of the middle U-shaped length section c (Figures 2

and 3) from an arched web 4 with slight divergence with respect to the horizontal median longitudinal plane MLE of the tubular profile 1 passing through the longitudinal axis LA in the direction of travel FR (Figure 3).

The tubular profile 1 is provided at the end of the central U-shaped longitudinal section c with bead-like impressions 5 extending in the transverse direction of the tubular profile 1. Figure 3 shows that the impressions 5 have their greatest depth at the apex S of the U-shaped longitudinal section c lying in the horizontal central longitudinal plane MLE. Their depth decreases in the direction of the free ends 6 of the legs 3 until they run evenly into the outer surface 7 of the legs 3. Seen in longitudinal section, the impressions 5 therefore have a sickle-shaped configuration.

The edges 8 of the impressions 5 are rounded (Figure 1).

After cold forming a circular tube R made of a micro-alloyed high-strength steel of material quality S420NC, the tube profile 1 does not need to be subjected to any further heat treatment. It is only blasted with steel balls on its outer surface 9 and finally fed to further configuration to complete a twist beam rear axle.

Reference symbol list

1 - Pipe profile

2 - ends &ngr;. 1

3 - Leg &ngr;. c

4 - Bridge

5 - Imprints

6 - Ends of 3

7 - Surface of

8 - margins &ngr;.

9 - Surface of

a - end sections v.

b - Transitional sections v. 1

c - middle length section v. 1

FR - Direction of travel

LA - longitudinal axis of

MLE - mid-longitudinal plane of

R - Pipe

S - vertex v. c

Claims (7)

1. Cross member as a component of a twist beam rear axle of a passenger car, which consists of a rigid, torsionally soft tubular profile ( 1 ) which is formed by cold forming a tube (R) made of a micro-alloyed high-strength steel and has a torsionally soft middle longitudinal section (c) with a double-walled U-shaped cross section and torsionally stiff end sections (a). 2. Cross member according to claim 1, wherein the tube (R) consists of a cold- or hot-rolled micro-alloyed high-strength steel. 3. Cross member according to claim 1 or 2, wherein the tube (R) consists of a steel of material quality S420NC. 4. Cross member according to one of claims 1 to 3, wherein the end portions (a) have a circular cross-section. 5. Cross member according to one of claims 1 to 3, in which the end sections (a) have a cross-section deviating from the circular shape. 6. Cross member according to one of claims 1 to 5, in which at least the outer surface ( 9 ) of the tubular profile ( 1 ) is solidified. 7. Cross member according to one of claims 1 to 6, in which at least the outer surface ( 9 ) of the tubular profile ( 1 ) is hardened by irradiation with balls, in particular steel balls.