GAS PRESSURE CONTAINER AND TUBE ELEMENT FOR AN AIRBAG SYSTEM, AND METHOD FOR PRODUCING SAME

Abstract

A gas pressure container for an airbag system of a motor vehicle is disclosed having a tube element with a high bursting resistance when internal pressure is being applied. The tube element includes a steel alloy and a first longitudinal portion of the tube element has a tensile strength Rm,.sub.11 higher than (>) 800 MPa, a transition temperature Tu,.sub.11 of at least −40° C., and an outer circumference U1. The tube element also includes at least one second longitudinal portion and/or additional longitudinal portions, which extend axially from the first longitudinal portion. The second longitudinal portion or the additional longitudinal portions and the first longitudinal portion are formed from a seamless or welded single-piece tube made of a uniform material, and more specifically from a hot-rolled or cold-drawn tube.

Claims

1. A gas pressure container for an airbag system of a motor vehicle, comprising: a tube element with high bursting resistance when internal pressure is applied, wherein the tube element consists of a steel alloy and in a first longitudinal portion comprises a tensile strength (Rm,.sub.11) which is greater than (>) 800 MPa, a transition temperature (Tu,.sub.11) of lower than −40° C. and an outer circumference (U.sub.1), wherein the tube element includes a second longitudinal portion which extends axially from the first longitudinal portion, wherein the second longitudinal portion and the first longitudinal portion are realized in one piece and in one material from a seamless or welded tube, wherein the second longitudinal portion comprises an outer circumference (U.sub.12) which is reduced compared to the outer circumference (U.sub.11) of the first longitudinal portion, wherein in the second longitudinal portion, the tube element comprises a transition temperature (Tu,.sub.12) of lower than (<) −50° C. and lower than (<) the transition temperature (Tu,.sub.11) of the first longitudinal portion.

2. The gas pressure container as claimed in claim 1, wherein the tube element includes at least one further longitudinal portion which extends axially from the first longitudinal portion, wherein the further longitudinal portion and the first longitudinal portion are realized in one piece and in one material from a seamless or welded tube, wherein the further longitudinal portion comprises an outer circumference (U.sub.13, U.sub.16) which is reduced compared to the outer circumference (U.sub.11) of the first longitudinal portion and a transition temperature (Tu,.sub.13, Tu,.sub.16) of the further longitudinal portion is lower than (<) −50° C. and lower than (<) the transition temperature (Tu,.sub.11) of the first longitudinal portion.

3. The gas pressure container as claimed in claim 1, wherein the following correlation applies to the outer circumferences (U.sub.11, U.sub.12, U.sub.13, U.sub.16): U.sub.12=(0.6−0.9)×U.sub.11, in particular U.sub.12=(0.7−0.8)×U.sub.11, and/or U.sub.13=(0.6−0.9)×U.sub.11, in particular U.sub.13=(0.7−0.8)×U.sub.11, and/or U.sub.16=(0.65−0.95)×U.sub.11, in particular U.sub.16=(0.75−0.85)×U.sub.11.

4. The gas pressure container as claimed in claim 1, wherein the wall thickness (WD.sub.2) of the second longitudinal portion and/or of the further longitudinal portion is greater than the wall thickness (WD.sub.1) in the first longitudinal portion.

5. The gas pressure container as claimed in claim 4, wherein the wall thickness (WD.sub.2) of the second longitudinal portion and/or of the further longitudinal portion is at least 5% greater than the wall thickness (WD.sub.1) in the first longitudinal portion.

6. The gas pressure container as claimed in claim 1, wherein the wall thickness (WD.sub.2) of the second longitudinal portion and/or of the further longitudinal portion is less than or equal to the wall thickness (WD.sub.1) of the first longitudinal portion.

7. The gas pressure container as claimed in claim 1, wherein the second longitudinal portion is realized on an end (E.sub.1) of the tube element.

8. The gas pressure container as claimed in claim 1, wherein the second longitudinal portion is realized on one end (E.sub.1) and a third longitudinal portion on the other end (E.sub.2) of the tube element and the first longitudinal portion is realized as a center portion.

9. The gas pressure container as claimed in claim 1, wherein the second longitudinal portion and/or a further longitudinal portion with a reduced outer circumference (U.sub.12, U.sub.13, U.sub.16) extends between two first longitudinal portions with a greater outer circumference (U.sub.11, U.sub.11′) of the tube element.

10. The gas pressure container as claimed in claim 1, wherein at least the second longitudinal portion with the reduced outer circumference (U.sub.12) of the tube element comprises increased plastic deformability in the circumferential direction compared to the first longitudinal portion, wherein the following applies: deformability,.sub.12>1.05×deformability,.sub.11.

11. The gas pressure container as claimed in claim 1, wherein the first longitudinal portion and/or the second longitudinal portion comprises/comprise a metallic microstructure with a surface portion of at least 70 percent tempered martensite.

12. The gas pressure container as claimed in claim 1, wherein the second longitudinal portion comprises a reduced tensile strength (Rm,.sub.12) compared to the tensile strength (Rm,.sub.11) of the first longitudinal portion, wherein the following applies: Rm,.sub.12<0.9×Rm,.sub.11.

13. The gas pressure container as claimed in claim 1, wherein a transition region, in which the tensile strength (Rm,.sub.14) continuously increases, is arranged between the second longitudinal portion and the first longitudinal portion, wherein the transition region comprises a width (B.sub.14) which is between 10 and 100 mm, in a preferred manner between 15 and 40 mm.

14. The gas pressure container as claimed in claim 1, wherein a transition portion, in which the outer circumference (U.sub.15) increases continuously in the direction of the first longitudinal portion, is arranged between the second longitudinal portion and the first longitudinal portion and/or between the third longitudinal portion and the first longitudinal portion.

15. The gas pressure container as claimed in claim 1, wherein the transition region is located in the transition portion, wherein the transition portion comprises a width (B.sub.15) which is greater than the width (B.sub.14) of the transition region.

16. The gas pressure container as claimed in claim 1, wherein the second longitudinal portion of the tube element comprises a mixed ferrite-perlite microstructure with a surface portion of at least 70 percent.

17. The gas pressure container as claimed in claim 1, wherein the second longitudinal portion or the further longitudinal portion is realized as a local predetermined breaking point (S) when internal pressure is applied in the gas pressure container, in a preferred manner the predetermined breaking point (S) is arranged in the center (M) of the gas pressure container.

18. The gas pressure container as claimed in claim 1, wherein a longitudinal portion comprises a notch in the lateral surface of the tube element and the outer circumference (U.sub.19) with notch is enlarged compared to the outer circumference (U.sub.11) of the first longitudinal portion.

19. A tube element with high bursting resistance when internal pressure is applied, in particular for use in a gas pressure container according to claim 1, wherein the tube element is a seamless or welded, in particular cold-drawn steel tube with a constant outer circumference (U), wherein the tube element comprises a first longitudinal portion with a tensile strength (Rm,.sub.11) which is greater than (>) 800 MPa and at least one second longitudinal portion and, as an option, further longitudinal portions, and the longitudinal portions are realized in one piece and in one material, wherein the second longitudinal portion, which is to be processed in particular by means of cold forming, and, as an option, further longitudinal portions of the tube element comprises/comprise an increased tube expanding capacity to DIN ISO 8495-2004 compared to the first longitudinal portion, wherein the following applies: tube expanding capacity,.sub.12>1.1* tube expanding capacity,.sub.11 and/or tube expanding capacity,.sub.13>1.1* tube expanding capacity,.sub.11 and/or tube expanding capacity,.sub.16>1.1* tube expanding capacity,.sub.11.

20. The tube element as claimed in claim 19, wherein in the second longitudinal portion to be processed, the tube element comprises a hardness (HV.sub.12) and/or in a further longitudinal portion a hardness (HV.sub.13, HV.sub.16) as well as in the first longitudinal portion a hardness (HV.sub.11), and the second and/or further longitudinal portion to be processed comprises a reduced hardness (HV.sub.12, HV.sub.13, HV.sub.16) compared to the first longitudinal portion, wherein the following applies: HV.sub.12/HV.sub.11=0.4 to 0.99 and/or HV.sub.13/HV.sub.11=0.4 to 0.99 and/or HV.sub.16/HV.sub.11=0.4 to 0.99.

21. The tube element as claimed in claim 19, wherein the tube element consists of a composition of the following alloy elements in percent by weight along with iron and contaminants necessary to the smelting process: C between 0.07 and 0.29; Si 0.1 to 0.55; Mn 0.2 to 1.6; P <0.025; S <0.02; Cr <2; Ti <0.03; Mo <0.6; Ni <0.6; Al 0.001 to 0.05; V <0.2; Nb <0.05.

22. A method for producing a gas pressure container including a tube element with high bursting resistance when internal pressure is applied, which, proceeding from a seamless or welded steel tube, comprising: a) hardening and then tempering the tube, in a preferred manner prior to cold drawing, b) cold drawing the tube as an option, c) cutting the tube element to length, d) heating the tube element partially in a second longitudinal portion and/or a further longitudinal portion to heating temperature (Tw), for a maximum of 120s, in a preferred manner a maximum of 30s, wherein a first longitudinal portion is not heated at the same time, e) optionally holding at the temperature (Tw) for a maximum of 120s, in a preferred manner 30s, f) forming the second longitudinal portion and/or the further longitudinal portion by reducing its outer circumference (U.sub.12, U.sub.13, U.sub.16), in a preferred manner directly after partially heating or holding process, wherein the tube element comprises a first longitudinal portion with a transition temperature (Tu,.sub.11) and a second longitudinal portion with a transition temperature (Tu,.sub.12) and/or a further longitudinal portion with a transition temperature (Tu,.sub.13, Tu,.sub.16), wherein the following applies: Tu,.sub.12<Tu,.sub.11 and Tu,.sub.12<−50° C. and/or Tu,.sub.13<Tu,.sub.11 and Tu,.sub.13<−50° C. and/or Tu,.sub.16<Tu,.sub.11 and Tu,.sub.16<−50° C., g) cool the second longitudinal portion and/or the further longitudinal portion prior to or after the forming.

23. The method as claimed in claim 22, wherein the second longitudinal portion and/or the further longitudinal portion is/are heated and warm-formed in one single production step.

24. The method as claimed in claim 22, wherein during cooling of the second longitudinal portion and/or of the further longitudinal portion from the heating temperature (Tw) to lower than (<) 150° C. advantageous tangential internal stresses are set.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0061] FIGS. 1a to 1c show a first embodiment of the gas pressure container according to the invention;

[0062] FIG. 2 shows a second embodiment of the gas pressure container according to the invention;

[0063] FIG. 3 shows a third embodiment of the gas pressure container according to the invention;

[0064] FIG. 4 shows a fourth embodiment of the gas pressure container according to the invention;

[0065] FIG. 5 shows hardness progression on the tube element prior to reduction of the outer circumference in the second longitudinal portion;

[0066] FIGS. 6a to 6c show a side view and two sectional views of the embodiment according to FIG. 4;

[0067] FIGS. 7a to 7c show a side view and two sectional views of an alternative design variant with a notch; and,

[0068] FIG. 8 shows a schematic side view of a gas pressure container with closure plates welded on.

[0069] In the Figures, the same reference designations are used for identical or similar components, even if a repeated description is omitted for reasons of simplicity.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

[0070] FIG. 1a shows a gas pressure container 1 which includes a tube element 10 having a second longitudinal portion 12 with a wall thickness WD.sub.12 and a third longitudinal portion 13 and a wall thickness WD.sub.13 at the corresponding ends E.sub.1, E.sub.2 of the tube element 10 and includes a first longitudinal portion 11 which is arranged between the second longitudinal portion 12 and third longitudinal portion 13. The second and third longitudinal portions 12, 13 comprise a smaller outer circumference U.sub.12, U.sub.13 compared to the outer circumference U.sub.11 of the first longitudinal portion 11, as can be seen in FIGS. 1b and 1c, the outer circumference U.sub.15 merging continuously in each case in a transition portion 15 from the first longitudinal portion 11 into the second or rather into the third longitudinal portion 12, 13. The first longitudinal portion 11 comprises a constant outer circumference U.sub.11. The second and third longitudinal portions 12, 13 comprise a transition temperature Tu,.sub.12, Tu,.sub.13 of lower than −50° C. which is also lower than the transition temperature Tu,.sub.11 of the first longitudinal portion 11. The first longitudinal portion 11 comprises a tensile strength of at least 800 MPa and a metallurgical microstructure with a surface portion of at least 70% tempered martensite. In the transition region 14 (shown by the broken line) between first longitudinal portion 11 and second longitudinal portion 12 or rather first longitudinal portion 11 and third longitudinal portion 13, a rather undefined mixed microstructure and/or undefined mechanical characteristic values is/are present, which is why the width B.sub.14 of the transition portion 14 is smaller than the width B.sub.12 of the second longitudinal portion 12 and B.sub.13 of the third longitudinal portion 13. In a preferred manner, the width B.sub.14 is also smaller than the width B.sub.15 of the transition region 15. FIGS. 1b and 1c show in each case a frontal view of the tube element 10. The respective outer circumferences U.sub.11, U.sub.12 and U.sub.11, U.sub.13 as well as the circumference U.sub.15 of the transition portion 15 which extends in between in each case can easily be seen. The transition temperatures T.sub.u,10, T.sub.u,11, T.sub.u,11′, T.sub.u,12, T.sub.u,13, T.sub.u,15, T.sub.u,16, are named in the description, but are not shown in the figures.

[0071] FIG. 2 shows a second embodiment of the gas pressure container 1 according to the invention, which includes a tube element 10 having a second longitudinal portion 12 and a third longitudinal portion 13 and a first longitudinal portion 11 which is arranged between the second longitudinal portion 12 and the third longitudinal portion 13. The second and third longitudinal portions 12,13 comprise a smaller outer circumference U.sub.12, U.sub.13 compared to the outer circumference U.sub.11 of the first longitudinal portion 11, the outer circumference U.sub.15 merging continuously in each case in a transition portion 15 from the first longitudinal portion 11 into the second and third longitudinal portions 12, 13. In longitudinal extension, the first longitudinal portion 11 comprises an outer circumference U.sub.11 which is arched slightly radially outward, the outer circumference as the outer diameter being consequently shown to be circular in this embodiment too. The second and third longitudinal portions 12,13 comprise a transition temperature Tu,.sub.12, Tu,.sub.13 of lower than −50° C. which is also lower than the transition temperature Tu,.sub.11 of the first longitudinal portion 11. The first longitudinal portion 11 comprises a tensile strength of at least 800 MPa and a metallurgical microstructure with a surface portion of at least 70% tempered martensite. In the transition region 14 (shown by the broken line) between first longitudinal portion 11 and second longitudinal portion 12 or rather first longitudinal portion 11 and third longitudinal portion 13, a rather undefined mixed microstructure and/or undefined mechanical characteristic values is/are present, which is why the width B.sub.14 of the transition portion 14 is smaller than the width B.sub.12 of the second and B.sub.13 of the third longitudinal portions 12, 13. In a preferred manner, the width B.sub.14 is also smaller than the width B.sub.15 of the transition region 15. The transition region 14 is consequently located in the transition region 15.

[0072] FIG. 3 shows a third embodiment of the gas pressure container 1 according to the invention which includes a tube element 10 having a second longitudinal portion 12 at a first end E.sub.1 of the tube element 10 and a third longitudinal portion 13 at the second end E.sub.2 of the tube element 10 as well as two first longitudinal portions 11, 11′ which are arranged in the region between the ends E.sub.1, E.sub.2. The second and third longitudinal portions 12,13 comprise a smaller outer circumference U.sub.12, U.sub.13 compared to the first longitudinal portions 11, 11′, the outer circumference U.sub.15 merging continuously in each case in a transition portion 15 from the first longitudinal portions 11, 11′ into the second or rather third longitudinal portions 12, 13. In addition, the two first longitudinal portions 11, 11′ enclose a further longitudinal portion 16 which is realized in a reduced manner in the outer circumference U.sub.16 compared to the first longitudinal portions 11, 11′. The outer circumferences U.sub.16, U.sub.12 and U.sub.13 can be different to one another, the dimension of the further longitudinal portion 16 being adaptable in particular to mounting parts, such as a bursting disk (not shown), which are to be joined thereto or are supported thereon inside the tube element. In contrast, the dimension of the second and third longitudinal portions 12,13 are measured such that closure plates, as shown in FIG. 7, or the like are attachable, in particular are weldable to the ends E.sub.1, E.sub.2 of the tube element 10. The second and third longitudinal portions 12,13 comprise a transition temperature Tu,12, Tu,13 of lower than −50° C. which is also lower than the transition temperature Tu,11, Tu,.sub.11′ of the first longitudinal portions 11, 11′. The first longitudinal portions 11, 11′ comprise a tensile strength of at least 800 MPa and a metallurgical microstructure with a surface portion of at least 70% tempered martensite. In the transition regions 14 between first longitudinal portion 11 and second longitudinal portion 12 or rather first longitudinal portions 11, 11′ and third longitudinal portion 13 as well as first longitudinal portions 11, 11′ and further longitudinal portion 16, a rather undefined mixed microstructure and/or undefined mechanical characteristic values is/are present, which is why the width B.sub.14 of the transition portions 14 (shown by the broken line) is smaller than the width B.sub.12 of the second and B.sub.13 of the third longitudinal portions 12, 13. In a preferred manner, the width B.sub.14 is also smaller than the width B is of the transition portions 15. In addition, there is a wall thickness WD.sub.16 in the further longitudinal portion 16. The wall thickness WD.sub.16 can be greater or smaller than the wall thickness WD.sub.11, WD.sub.11′.

[0073] FIG. 4 shows a fourth embodiment of the gas pressure container 1 according to the invention which includes a tube element 10 having a further longitudinal portion 16 with a smaller outer circumference U.sub.16 compared to the two first longitudinal portions 11, 11′, which extend axially therefrom to the ends E.sub.1, E.sub.2 of the tube element 10 and have an outer circumference U.sub.11, U.sub.11′.

[0074] The outer circumference U.sub.16 is adapted in particular to mounting parts, such as a bursting ring, which are to be joined thereto inside the tube element or are supported thereon. At the ends E.sub.1 and E.sub.2 of the tube element 10 are a second and a third longitudinal portion 12, 13 which, with reference to the longitudinal direction, are very short and which have the outer circumferences U.sub.12, U.sub.13 which are smaller than the non-reduced outer circumference of the first longitudinal portions U.sub.11, U.sub.11′ but greater than the reduced outer circumference U.sub.16 of the further longitudinal portion 16 in a central longitudinal portion. The second and third longitudinal portions 12,13 comprise a transition temperature Tu,12, Tu,13 of lower than −50° C. which is also lower than the transition temperature Tu,11 of the first longitudinal portion 11, 11′. The first longitudinal portion 11, 11′ comprises a tensile strength of at least 800 MPa and a metallurgical microstructure with a surface portion of at least 70% tempered martensite. In the transition region 14 between first and further longitudinal portions 11, 11′, 16, a rather undefined mixed microstructure and/or undefined mechanical characteristic values is/are present. FIG. 5 shows the hardness progression on a tube element 10 according to the invention prior to reduction of the outer circumference, proceeding from the first end E1 in the axial direction via a second longitudinal portion 12 to the first longitudinal portion 11. It is possible to see the lower hardness and consequently tensile strength in the second longitudinal portion and a transition region 14 with increasing hardness values up to a maximum which then remain constant in the first longitudinal portion 11.

[0075] FIGS. 6a to 6c once again show a design variant according to FIG. 4. FIG. 6b shows a cutting line b-b from FIG. 6a. The constant circular outer circumference U.sub.11 of the first longitudinal portion 11 can be seen. FIG. 6c shows a cutting line c-c from FIG. 6a through the further longitudinal portion 16. It can be seen that this too comprises a circular outer circumference U.sub.16 which is, however, smaller than the outer circumference U.sub.11′ of the first longitudinal portion 11′ which is located behind it in the viewing direction according to FIG. 6c.

[0076] FIGS. 7a to 7c show an alternative design variant to this. According to FIG. 7b, which shows a sectional representation b-b from FIG. 7a, a constant outer circumference U.sub.11 of the first longitudinal portion 11 is shown once again. In a central region with reference to the longitudinal direction, this latter comprises a notch 19 or rather cavity. The outer circumference U.sub.19 produced by the notch 19 is enlarged compared to the outer circumference U.sub.11 which is located behind it in the viewing direction according to FIG. 7c. The notch 19 can be introduced into the lateral surface of the tube element 10 in any arbitrary geometric form. In particular, the further longitudinal portion produced with the notch 19 can be applied to any arbitrary exemplary embodiment in said publication.

[0077] FIG. 8 shows a schematic view of the tube element 10 with closure plates 17. The closure plates 17 are seal welded to the tube element by way of a circumferential weld seam 18. The closure plates can be welded to the ends E1 and E2 on all previously described exemplary embodiments.

[0078] The foregoing description of some embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The specifically described embodiments explain the principles and practical applications to enable one ordinarily skilled in the art to utilize various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents. Further, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as described by the appended claims.