DE20301940U1 - Torsion unit for seat belt, comprising torsion bar and torsion bar accommodating pipe, both made of different materials - Google Patents

Abstract

The unit (10) is assembled of a hollow pipe (12) with teeth (14, 16) engaging with the teeth at the reel in case of an impact, located at one end and a torsion bar (18), accommodated inside the pipe (12) and also provided with teeth (20) at one end. Both parts (12, 18) are connected with a joint element (22) at the opposite end. A separating element (24) is positioned between pipe (12) and bar (18) in order to avoid stuck welding. The main components (12, 18) are made of materials differing in density and facilitating the variation of the particular properties of the torsion resistance.

Description

PRINZ & PARTNER dlk"" '"''""

PATENT ATTORNEYS

EUROPEAN PATENT ATTORNEYS

EUROPEAN TRADEMARK ATTORNEYS JiJ^??™ ⁸ 7

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

Tl 0265 EN

JS /se/Hc 7 February 2003

Torsion unit for force limitation in a belt retractor

The invention relates to a torsion unit for limiting the force in a belt retractor, with a torsion tube and a torsion bar arranged inside the torsion tube.

Such a torsion unit, which can be integrated into a reel of a belt retractor, is known from EP-A-0 962 366. In the event of an accident, the torsion unit allows a limited belt webbing withdrawal against a predetermined resistance force 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curve of the torsion unit, which results from the resistance force depending on the length of belt webbing withdrawn, to the respective requirements, the inner diameter of the torsion tube in the known torsion unit is selected so that the torsion bar rests on the torsion tube in the twisted state.

The invention provides a torsion unit for a belt retractor in which the torsional resistance moment provided by the torsion tube and the torsion bar can be further varied.

According to the invention, in a torsion unit of the type mentioned above, it is provided that the torsion tube and the torsion bar are made of materials

Prince & Partners

T10265 EN - 2/6 - FEBRUARY 7, 2003

different strengths. This results in additional parameters with which the torsional resistance moment provided by the torsion tube and torsion bar can be varied. Since the strength of a material is largely responsible for the deformation behavior of a component made from it, the torsional behavior of a torsion tube or torsion bar can be specifically influenced by the choice of material. The combination of a torsion tube and a torsion bar made of different materials thus opens up even more diverse variation options for setting the desired characteristic curve of the torsion unit, particularly when certain geometric specifications exist. For example, in the case of a torsion unit with a torsion tube that must have a certain minimum wall thickness due to the required number of torsion turns, a material of particularly low strength can be selected in order to achieve a low force level despite the large wall thickness of the torsion tube.

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 side view of a torsion unit according to a first embodiment;

- Figure 2 is a sectional side view of part of a torsion unit according to a second embodiment;

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

The torsion unit 10 for a belt retractor shown in Figure 1 comprises a torsion tube 12, which has a toothing 14, 16 at each of its ends, which engage in a locking toothing of the belt retractor for blocking the

Prince & Partners

t10265 en - 3/6 - February 7, 2003

Torsion tube 12 can engage. A torsion bar 18 is arranged inside the torsion tube 12. The first end of the torsion bar 18 protrudes from the torsion tube 12 and also has a toothing 20 which can engage in another locking toothing of the belt retractor. At their second ends, the torsion tube 12 and the torsion bar 18 are connected to one another in a force-fitting manner via a coupling piece 22.

The torsion tube 12 and the torsion bar 18 are made of different

materials, ie the material of the torsion bar 18 has either a higher or a lower strength than the material of the torsion tube 12. However, the energy required for the deformation is largely constant for both materials over a temperature range of -30 ⁰ C to +80 ⁰ C.

The interaction of material and wall thickness determines the torsional moment of resistance and thus the force level of the torsion tube 12. In the case of a torsion tube 12 with a large wall thickness, which would generally lead to a high moment of resistance, a torsion tube with a relatively low force level can still be produced by choosing a material of low strength, e.g. aluminum.

To prevent cold welding of the torsion tube 12 with the torsion bar 18, a separating element 24 and/or a separating layer is provided in the region in which a relative movement between the torsion tube 12 and the torsion bar 18 is to take place.

If the torsion bar 18 is only intended to contribute a small torsional resistance moment, the torsion bar 18 can also be designed hollow.

The alternative embodiment shown in Figure 2 differs from the previously described embodiment in that the torsion tube 12 and the torsion bar 18 are pressed together at their second ends in a force-fitting manner. The two ends can also be welded together to ensure the transmission of force.

Prince & Partners

T10265EN -4/6- 7 FEBRUARY2003

Figures 3 a to 3 e show various differently shaped torsion tubes 12 for torsion units 10 according to the invention, which are not rotationally symmetrical. The cylinder walls of the torsion tubes 12 have recesses 26 at certain points, which influence the torsional behavior of the torsion tube 12 and thus the force level of the torsion unit 10. A desired characteristic curve of the torsion unit 10 can thus be achieved by suitable selection of the geometry of the torsion tube 12.

Claims (11)

1. Torsion unit for limiting the force in a belt retractor, with a torsion tube ( 12 ) and a torsion bar ( 18 ) arranged inside the torsion tube ( 12 ), characterized in that the torsion tube ( 12 ) and the torsion bar ( 18 ) are made of materials of different strengths. 2. Torsion unit according to claim 1, characterized in that the torsion bar ( 18 ) is formed from a material of higher strength than the material of the torsion tube ( 12 ). 3. Torsion unit according to claim 1, characterized in that the torsion bar ( 18 ) is formed from a material of lower strength than the material of the torsion tube ( 12 ). 4. Torsion unit according to one of the preceding claims, characterized in that the torsion tube ( 12 ) and the torsion bar ( 18 ) are each non-positively connected to one another at one end. 5. Torsion unit according to claim 4, characterized in that the ends of the torsion tube ( 12 ) and the torsion bar ( 18 ) are connected to one another by means of a coupling piece ( 22 ). 6. Torsion unit according to claim 4, characterized in that the ends of the torsion tube ( 12 ) and the torsion bar ( 18 ) are pressed together. 7. Torsion unit according to claim 4, characterized in that the ends of the torsion tube ( 12 ) and the torsion bar ( 18 ) are welded together. 8. Torsion unit according to one of the preceding claims, characterized in that a separating element ( 24 ) and/or a separating layer is provided at least in regions between the torsion tube ( 12 ) and the torsion bar ( 18 ). 9. Torsion unit according to one of the preceding claims, characterized in that the torsion bar ( 18 ) is hollow. 10. Torsion unit according to one of the preceding claims, characterized in that the torsion tube ( 12 ) is not rotationally symmetrical. 11. Belt retractor for a vehicle safety belt, with a torsion unit ( 10 ) according to one of the preceding claims.