Expanded tube for a motor vehicle crash box and manufacturing method for it

Abstract

The present invention relates to a motor vehicle crash box with a working direction in vehicle's longitudinal axis manufactured out of a tube which is expanded into different zones, wherein the zones are different in strength and diameter by using steel after forming a homogenous austenitic microstructure with a strain hardening effect. The present invention further relates to the manufacturing method of such a component.

Claims

1. A motor vehicle crash box with a working direction in a vehicle's longitudinal axis, wherein the component is manufactured out of a tube which is made of an austenitic steel which has a homogeneous austenitic microstructure with a strain hardening effect even after forming, which is expanded by a forming process into an expanded tube having at least three zones, each zone having a different material strength and a different diameter; wherein a center of the expanded tube in longitudinal direction works as a mirror axis and the zones are characterized in a way that starting from the outer-sides to the center, the diameter of each respective zone of the at least three zones decreases towards the center.

2. The motor vehicle crash box according to claim 1, wherein the zones have a strength [N/mm.sup.2] to diameter [mm] ratio of 6.0-9.0 N/mm.sup.3.

3. The motor vehicle crash box according to claim 1, wherein between the different zones is a minimum strength delta of Rm75 MPa.

4. The motor vehicle crash box according to claim 1, wherein the zones have a foldability which is inversely proportional to the diameter of the zone.

5. The motor vehicle crash box according to claim 1, wherein the expanded tube is configured to provide a residual safety area by reaching a block length of the system, preferably L.sub.80 mm after impact.

6. A method for manufacturing the motor vehicle crash box according to claim 1, wherein the tube is manufactured as a longitudinal-welded tube.

7. The method according to claim 6, wherein the tube is expanded by a mechanical drift expanding process in a mechanical drift expanding process machine.

8. The method according to claim 7, wherein the mechanical drift expanding process machine uses at least two different expanding mandrels for at least two different zones of the crash box.

9. The method according to claim 7, wherein the mechanical drift expanding process machine has a mirrored longitudinal axis to create a symmetrical crash box.

10. The method according to claim 6, wherein the tube is manufactured out of strain-hardenable austenitic stainless steels, having an initial yield strength R.sub.p0.2380 MPa and an initial elongation A.sub.8040%.

11. The motor vehicle crash box according to claim 1, wherein at least one end of the expanded tube is widened to provide a flange around the circumference of the end of the tube, the flange being essentially perpendicular to the longitudinal axis of the tube crash box and its working direction, said flange providing a surface for attaching the crash box to a neighboring vehicle part.

12. The method according to claim 6, wherein the tube has an initial thickness of 0.8 mmt2.5 mm and the ratio of the initial diameter to the thickness is 24r.sub.d/t125.

13. The motor vehicle crash box according to claim 1, wherein the motor vehicle in which the crash box is integrated is a passenger car, a truck, a bus or an agricultural vehicle.

14. The motor vehicle crash box according to claim 1, wherein the crash box is an energy absorbing element in a crash barrier, guardrail or inside a railway vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is illustrated in more detail referring to the attached drawings.

(2) FIG. 1 shows one embodiment of the invention schematically seen from the side view,

(3) FIG. 2 shows the relation of the component strength depending to the longitudinal length of the component,

(4) FIG. 3 shows from the side view the situation from the initial in the vehicle installed component geometry (left side) and the forming behavior during an impact situation (right side),

(5) FIG. 4 shows from the side view the behavior of the component during an impact reaching the block length,

(6) FIG. 5 shows from the side view the welding connection of the expanded tube to the neighboring vehicle parts.

EMBODIMENTS ILLUSTRATING THE INVENTION

(7) FIG. 1 illustrates from the side view the expanded tube crash box after manufacturing. The dotted line demonstrates the longitudinal symmetry axis. In this embodiment of the present invention, there are three zones (1), (2), (3) symmetrical in transverse direction whereby the zone 1 (1) with the smallest diameter d.sub.1 is located in the central zone. From the central to the longitudinal outsides, the zones increase in their diameter, demonstrated with the zone 2 (2) and zone 3 (3).

(8) FIG. 2 illustrates for the component showed in FIG. 1 the relation of strength in longitudinal direction of the component with the different zones whereby transition zones (4) are located between the main zones (1), (2) and (3) from FIG. 1. The transversal dotted lines (5) demonstrate the starting points where a change of the zone and therefore a change in diameter and strength proceed. The zone 1 with the smallest diameter d.sub.1 has the lowest strength level. With an increased diameter, the strength level increases, too. For the embodiment of FIG. 1 results that there exist two differences in strength named Rm (6). The difference in strength between each diameter is essentially the same

(9) FIG. 3 illustrates the forming behavior of the component during an impact situation from the longitudinal side whereby the zone with the lowest diameter, (1) from FIG. 1, and therefore the lowest strength level fold. The zones with the higher diameter will slide over the ones with the lower diameter depending on the particular strength levels.

(10) FIG. 4 illustrates the ongoing impact from FIG. 3 at its ending position called block length L.sub.B (7) where the energy absorption of the component is exhausted. The block length L.sub.B (7) is further equal with a residual safety area where other components can be located and will not be influenced by the impact.

(11) FIG. 5 illustrates one preferred embodiment of the present invention where at least one end of the expanded tube is widened in a way that the end (8) is bent across the longitudinal axis of the tube crash box and its working direction to enable joining on the lap joint (9) to the neighboring vehicle parts (10). The joining can be executed as welding as a fillet or like mechanical joining as a lap joint like screwing.