DE20301941U1 - Seat belt reel unit with torsion element for limitation of unwinding forces, comprising coated torsion bar - Google Patents

Abstract

The seat belt reel unit (10) comprises a reel (12), rotating within a frame (14) joined to the vehicle. A torsion element (16) is inserted transversally into the hollow space in the center of the reel (12), protrudes with one end from the opposite side and is fixed to the frame (14). The locking wheel (22) and the torsion bar (18), which is coated with a layer of die cast aluminum or magnesium (20), are made all in a piece. No additional torsion pipe is required.

Description

PRINCE & PARTNER·^ ···"···

PATENT ATTORNEYS

EUROPEAN PATENT ATTORNEYS

EUROPEAN TRADEMARK ATTORNEYS if ^f^?^ ⁸ 1

D-81241 Munich

Phone: + 49 89 89 69 8-0
Fax: +49 89 89 69 8-211
Email: info@prinzundpartner.de

TRW Occupant Restraint Systems GmbH & Co. KG
Industriestrasse 20
D-73553 Alfdorf

Tl0266 EN

JS /se/Hc 7 February 2003

Torsion unit for force limitation in a belt retractor

The invention relates to a torsion unit for force limitation in a belt retractor, wherein the torsion unit comprises at least two torsion elements which can contribute to force limitation by plastic deformation.

Such a torsion unit, which can be integrated into a reel of a belt retractor, is known from EP-A-O 962 366. In the event of an accident, the torsion unit allows a limited belt webbing withdrawal against a resistance force provided by the torsion unit despite the seat belt being blocked, in order to reduce the peak loads in the seat belt to protect the vehicle occupant. In order to adapt the characteristic curve of the torsion unit, which results from the resistance force depending on the length of belt webbing withdrawn, to the respective requirements, the inner diameter of a torsion tube in the known torsion unit is selected so that a torsion bar arranged inside the torsion tube is supported on the torsion tube in the twisted state.

The invention provides a torsion unit for a belt retractor with which different force levels can be specifically achieved when deforming the torsion unit.

According to the invention, in a torsion device of the type mentioned at the outset, it is provided that the second torsion element has a shape adapted to the first torsion

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T10266 EN -2/6- February 7, 2003

sion element is an injection-molded or cast torsion element. The torsion unit according to the invention allows a compact design of the belt retractor, whereby the second torsion element can be formed cost-effectively with different geometries thanks to the production by injection or casting. This results in a wide range of possible variations for the resulting force characteristic of the torsion unit according to the invention.

Advantageous embodiments of the torsion unit according to the invention are specified in the subclaims.

Further features and advantages of the invention will become apparent from the following description and from the accompanying drawings, to which reference is made. In the drawings:

- Figure 1 is a sectional view of a belt retractor with a torsion unit according to a first embodiment;

- Figure 2 is a sectional view of a belt retractor with a torsion unit according to a second embodiment; and

- Figures 3a to 3e show side views of torsion units according to different design variants.

The belt retractor 10 shown in Figure 1 comprises a belt reel 12 which is rotatably mounted in a frame 14 which can be fastened in a vehicle. A belt strap can be accommodated on the belt reel 12 which serves to restrain a vehicle occupant in the event of an accident so that he or she participates in the deceleration of the vehicle. A torsion unit 16 is arranged inside the belt reel 12 and is connected to the belt reel 12 in a rotationally fixed manner at the right-hand end with respect to Figure 1. The other end of the torsion unit 16 is selectively connected to the load-bearing frame 14 of the belt retractor 10 in a rotationally fixed manner.

If, in the event of an accident, after the belt reel 12 has been blocked, a tensile force acts in the belt webbing which exerts a torque on the belt reel 12 which

Prince & Partners *··* · " ""

T10266 EN - 3/6 - February 7, 2003

is greater than a resistance torque that can be applied by the torsion unit 16 without deformation, the belt webbing is pulled off the belt spool 12, whereby the torsion unit 16 is twisted between its end firmly connected to the belt spool 12 and its end held in a rotationally fixed manner by the frame 14.

The torsion unit 16 essentially consists of a solid torsion bar 18 which is surrounded by a layer 20 which is formed by overmolding or casting the torsion bar 18 with a material. For example, the torsion bar 18 can be surrounded by a magnesium or aluminum die cast. The layer 20 surrounding the torsion bar 18 serves in this case as a torsion tube which can be coupled in a known manner to the internal torsion bar 18 and/or to the belt reel 12 and/or to the load-bearing frame 14 in order to implement a desired force characteristic of the torsion unit 16 depending on the requirement or depending on the given situation.

In the embodiment shown in Figure 1, a locking wheel 22 is made in one piece with the layer 20, i.e. the torsion tube and the locking wheel 22 are manufactured in one step by overmolding or casting the torsion bar 18. The locking wheel 22 can also be subsequently injected or cast onto the torsion bar 18 and the layer 20. Finally, an embodiment is also provided in which the locking wheel 22 is injected or cast onto the torsion bar 18 without a layer 20 being provided.

In the embodiment shown in Figure 2, the ratchet wheel 22 is again made in one piece with the layer 20 and is cast or injected in such a way that it surrounds the belt reel 12 at its left end with respect to Figure 2. This means that an additional part that would otherwise be required for coupling the torsion unit 16 to the belt reel 12 and the corresponding assembly step can be omitted. The design also has the advantage that the fastening is more precise and stable. Likewise

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As in the embodiment of Figure 1, a fixing pin 24 for positioning the torsion unit 16 is cast into the ratchet wheel 22.

It is also possible to control the individual torsion elements (torsion bar 18 and surrounding torsion tube) separately. The externally molded torsion bar 18 can also be hollow on the inside if it is only intended to contribute a relatively low section modulus.

By overmolding or casting, a wide variety of torsion tube geometries can be produced in a simple manner, some of which are shown as examples in Figures 3a to 3e. The torsion tubes 20 have recesses 26 at certain points, which influence the torsional behavior of the torsion tube 20 and thus the force level of the torsion unit 16. Thus, by suitable selection of the geometry of the torsion tubes 20, various desired force characteristics can be realized cost-effectively.

The torsion unit 16 according to the invention can also consist of a torsion tube that is "overmolded" or completely cast with a suitable material from the inside so that the injected or cast insert has a different force level than the torsion tube. As described above, the force characteristic of the torsion unit 16 can be varied by appropriate coupling of the individual torsion elements (torsion tube and insert).

Suitable plastics can also be used as materials for injection molding or casting, whereby the materials should generally have a deformation energy that is as constant as possible over a temperature range of -30 ⁰ C to +8O ⁰ C.

Claims (11)

1. Torsion unit for force limitation in a belt retractor, wherein the torsion unit ( 16 ) comprises at least two torsion elements which can contribute to force limitation by plastic deformation, characterized in that the second torsion element is an injection-molded or cast torsion element adapted to the shape of the first torsion element. 2. Torsion unit according to claim 1, characterized in that the first torsion element is a torsion bar ( 18 ) and the second torsion element is a torsion tube ( 20 ) surrounding the torsion bar ( 18 ). 3. Torsion unit according to claim 2, characterized in that an injection-molded or cast ratchet wheel ( 22 ) is formed on the torsion bar ( 18 ) and/or on the torsion tube ( 20 ). 4. Torsion unit according to claim 3, characterized in that a fixing pin ( 24 ) is cast into the ratchet wheel ( 22 ). 5. Torsion unit according to one of claims 2 to 4, characterized in that the torsion tube ( 20 ) is not rotationally symmetrical. 6. Torsion unit according to one of claims 2 to 5, characterized in that the torsion bar ( 18 ) is hollow on the inside. 7. Torsion unit according to claim 1, characterized in that the first torsion element is a torsion tube and the second torsion element is an insert injected or cast into the interior of the torsion tube. 8. Torsion unit according to one of the preceding claims, characterized in that the injection-molded or cast torsion element is a magnesium or aluminum die-cast part. 9. Torsion unit according to one of claims 1 to 7, characterized in that the injection-molded or cast torsion element is made of a plastic. 10. Belt retractor for a vehicle safety belt, with a torsion unit ( 16 ) according to one of the preceding claims. 11. Belt retractor according to claim 10 with a torsion unit according to claim 3 or 4, characterized in that the injection-molded or cast ratchet wheel ( 22 ) surrounds at least part of a belt spool ( 12 ) of the belt retractor ( 10 ).