Clamping ring for fastening a gas generating cartridge

A clamping ring is used to mount an air bag gas generator cartridge on a support plate. A tensioning ear is formed in the clamping ring. Further, a wave is formed in the ring to increase the holding force between the ring and the cartridge. The wave consists of two convex arches projecting outward from the ring and an inward convex arch therebetween, the apex of the inward arch being at least tangential to the circle defined by the remaining portions of the ring in the initial condition of the ring. This type of clamping ring mounting is capable of withstanding torques between the cartridge and the support plate of well above 10 Nm.

PRIOR ART

Gas generator cartridges for vehicle airbags, specifically airbags for restraining the head, are often mounted on a support plate by means of two clamping rings, the support plate being mounted on the vehicle body. In view of the substantial forces which occur when the cartridge is triggered, it is required that the mounting of the cartridge on the support plate withstands a torque of at least 10 Nm.

This requirement can be met by means of screw clamps. Screw clamps, however, are expensive in manufacture and, moreover, time consuming in assembly, specifically because care must be taken that the screws are fastened with a predetermined torque to ensure the required holding force. Moreover, it has been found with screw clamps that the elasticity, which is essential for safely holding the gas generator cartridge, decreases with time.

Tests made with stepless ear clamps such as known from U.S. Pat. No. 5,305,499 have shown that a torque of up to only 3.5 Nm is achieved when the metal cartridge is directly fastened by means of a metal clamp, even if the clamp is made sufficiently heavy. Using an additional insert of rubber or plastics will achieve torques of up to about 9 Nm. Stepless ear clamps having an integrated wave-shaped elasticity reserve, such as described in WO 02/077509 A1 and corresponding U.S. Pat. No. 7,093,326, achieve values of 5 to 6 Nm in a metal/metal fastening.

DE 103 29 008 A1 and corresponding Canadian published patent application 2,488,110 discloses an open ear clamp made from band material for gas generator cartridges. This clamp is provided with a number of outward curved waves to improve its elasticity. The inner surface of the clamping ring is roughened to increase the holding force.

SUMMARY OF THE INVENTION

It is an object of the invention to avoid at least part of the disadvantages which occur with comparable clamping rings of the prior art. A more specific object resides in the provision of a clamping ring, particularly for mounting gas generator cartridges, which ensures a high torque and which is as easy to fix as possible.

This object is met by a clamping ring further including a wave formed in the ring for increasing the holding force between the ring and the object, the wave having two convex arches projecting outward from the ring and an inward convex arch therebetween, the apex of the inward arch being situated substantially on a circle defined by the remaining portions of the ring. The configuration of the clamping ring profile results in a surprisingly high holding force, which may be caused by the elastic cooperation between the tensioning ear and the wave and also by the pressure by which the inward convex arch existing between the two outward arches of the wave engage the object to be mounted, i.e., the gas generator cartridge. The tests referred to above have shown that the clamping ring according to the invention withstands torques of up to 13 Nm with a direct metal/metal engagement. At the same time, the clamping ring, which is tensioned by merely narrowing the ear, has the advantage of being easy to mount.

The inward arch having a larger radius than the outward arches is of advantage for achieving a suitable elasticity and a defined pressure between the inward arch and the cartridge. The wave being positioned diametrically opposite the tensioning ear is beneficial because of the elastic interaction between the integrated wave and the tensioning ear.

The forming the clamping ring from tubular material results in a clamping ring which is stable in shape and easy to manufacture.

The disclosed and claimed dimensions have proven suitable in clamping rings for mounting commonly available gas generator cartridges.

The reinforcing bead in the web of the tensioning ear is advantageous in terms of holding force.

The integration of part of the support plate carrying the gas generator cartridge into the clamping ring is of advantage concerning the holding force and safety of the mounting.

DETAILED DESCRIPTION OF AN EMBODIMENT

The closed clamping ring10shown inFIG. 1consists of a tube section made of zinc galvanised steel which has a width of 10 mm in the axial direction, a wall thickness of 1.5 mm, and an inner diameter of 28.5 mm in the non-tensioned condition shown.

For tensioning the clamping ring10about an object to be mounted (not shown inFIG. 1), the clamping ring has a so-called “Oetiker ear”11which includes two outward extending legs12interconnected by a web13. A reinforcing bead14is stamped into the web13. In the embodiment shown, the inner distance between the legs, which are parallel in the non-tensioned condition, is 8 mm. The ear11is tensioned by being narrowed to a predetermined degree by means of a pliers-type special tool with jaws which engage the legs12near their inner ends.

A wave generally identified by15is formed in the clamping ring10diametrically opposite the ear11. The wave15includes two outward arches16which extend outward from the ring10and an inward convex arch17therebetween. The outward arches16project 2 to 3 mm from the undeformed ring. The radius length of the overall wave15corresponds approximately to the width of the ear11in the non-tensioned condition.

The inward arch17is so dimensioned that its apex is at least tangential to the inner circle defined by the remaining parts of the ring. For increasing the clamping action, the inward arch17may be shaped such that its apex, in the initial condition, projects slightly inward beyond the above-mentioned circle. The radius of the inward arch17is substantially greater than that of the outward arches16so that the latter are comparatively stiff whereas the inward arch17engages the object to be clamped with a correspondingly higher elasticity.

As schematically shown inFIGS. 2 and 3, a gas generator cartridge20for a vehicle air bag is mounted on a support plate25near either one or its cylindrical ends21by means of a clamping ring10according toFIG. 1. At the left-hand end according toFIG. 2, the cartridge20has a nipple22for connection to an air bag (not shown). The support plate25has lateral lugs26for mounting on a vehicle body.

As shown inFIG. 3, the two terminal portions27of the support plate25are curved along an arc of about 120° corresponding to the outer diameter of the cylindrical ends21of the cartridge20. In the assembled condition, the terminal portions27lie between the cartridge20and the respective clamping ring10.

For mounting the gas generator cartridge20on the support plate25, the cylindrical ends21of the cartridge are placed in the pre-bent terminal portions27of the support plate25, whereupon the clamping rings10are slid onto the cartridge20and the support plate25. By narrowing the clamping ring ears11by means of a pliers-type tool, which has been set to a predetermined force or predetermined distance, the metallic cartridge20and the metallic support plate25may be clamped directly into the metallic clamping ring10so as to achieve a torque between the cartridge20and the support plate25well above the required value of 10 Nm.

The dimensions given in the above description relate to the preferred embodiment in which a gas generator cartridge20to be mounted has cylindrical ends21of a given outer diameter (about 27 mm). With differently dimensioned objects, the clamping ring would have to be dimensioned differently, possibly also in its wall thickness and axial width.

Accordingly, it will be understood that the preferred embodiment of the present invention has been disclosed by way of example and that other modifications and alterations may occur to those skilled in the art.