Gas generator

Abstract

A gas generator, especially for a vehicle safety system, has a pyrotechnical igniter unit (22) and a holder (14) for the igniter unit (22). The igniter unit (22) is attached to the holder (14) in that the igniter unit (22) and the holder (14) are encapsulated together by one of injection molding and foaming of a plastic. The holder (14) has at least one passage opening (30, 38) for the plastic during the encapsulation by one of injection molding and foaming, the at least one opening being configured in such a way as to create a form-fitting anti-twist protection between the plastic (34) and the holder (14).

Description

TECHNICAL FIELD

The present invention relates to a gas generator, especially for a vehicle safety system, having a pyrotechnical igniter unit and a holder for the igniter unit, the igniter unit being attached to the holder in that the igniter unit and the holder are encapsulated together by injection molding or foaming.

BACKGROUND OF THE INVENTION

Gas generators are used especially for vehicle occupant restraint systems in the form of airbags or belt tensioners. Various types of gas generators exist, namely, purely pyrotechnical generators, compressed gas generators in which the pressurized gas is released by the igniter unit, or else hybrid gas generators. The igniter unit is a hermetically sealed, prefabricated unit and it has to be directly or indirectly coupled to the outer housing of the gas generator in a fixed position. Normally, a section of the outer housing is used as the holder, that is to say, the part to which the igniter unit is directly attached. Igniter contacts and also the plastic used for the encapsulation by injection molding and/or foaming protrude through a passage opening in the holder, as a result of which sections of the igniter unit and, at the same time, the holder are embedded in the plastic. The plastic is intended to attach the igniter unit to the holder and also to seal the passage opening so that it is gas-tight as well as moisture-tight.

The object of the invention is to make a gas generator of the above-mentioned type even more gas-tight in the area of the transition from the holder to the igniter unit.

BRIEF SUMMARY OF THE INVENTION

This is achieved in a gas generator, especially for a vehicle safety system, having a pyrotechnical igniter unit and a holder for the igniter unit. The igniter unit is attached to the holder in that the igniter unit and the holder are encapsulated together by one of injection molding and foaming of a plastic. The holder has at least one passage opening for the plastic during the encapsulation by one of injection molding and foaming, the at least one opening being configured in such a way as to create a form-fitting anti-twist protection between the plastic and the holder. For gas generators employed so far, a centered, circular passage opening was provided in the holder, which has the drawback that the plastic and the holder only established an adhesive connection in the twisting direction, that is to say, around the axis of the opening. Therefore, this connection has to be handled relatively carefully so that it does not become detached, allowing moisture to penetrate into the gas generator. In contrast, with the invention, in addition to the adhesive connection in the twisting direction, a form-fitting connection is also created between the plastic and the holder, this form-fitting connection preventing such a detachment. The form-fitting connection between the plastic and the igniter unit in the twisting direction is normally established in that several igniter contacts on the back of the igniter unit protrude into the plastic.

According to a preferred embodiment, the passage opening is out-of-round.

Another possible configuration for the passage opening is that it is provided with a notch protruding laterally outwards relative to the passage opening, the notch acting as an anti-twist protection.

As an alternative, of course, several passage openings can be provided.

As already mentioned above, the holder is especially a section of an outer housing of the gas generator.

The igniter contacts preferably protrude through the holder and especially are part of the igniter unit and form a prefabricated unit together with said igniter unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross section through an embodiment of the gas generator according to the invention,

FIG. 2 shows a top view of the holder used in the embodiment of FIG. 1 and

FIG. 3 shows a top view of an alternative holder that can be used in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a pyrotechnical gas generator that has a two-shell outer housing 10 being constituted of a pot-shaped upper part 12 and a pot-shaped lower part 14. The pot-shaped lower part 14 has an indentation 16 shaped by deep-drawing that serves to accommodate an igniter connector (not shown here). A combustion chamber 20 filled with pyrotechnical propellant 18 is provided inside the gas generator 10. In order to ignite the propellant 18, a prefabricated igniter unit 22 is used, which is situated in the center of the combustion chamber 20 and which has a cylindrical head 23 filled with pyrotechnical means as well as igniter contacts 24 that form part of the igniter unit and that protrude from a backside of said igniter unit. A lid-shaped housing 26 surrounding the head 23 of the igniter unit 22 receives a booster charge 28.

The lower part 14 of the housing 10 is shown in FIG. 2 in a slightly enlarged depiction. It is a deep-drawn metal part that has a centered passage opening 30 through which the two igniter contacts 24 can protrude. The passage opening 30 is out-of-round since it has four lateral notches 32 protruding outwards. Although a circular bore was made in the center of the passage opening, the passage opening becomes out-of-round because of the notches 32. Of course, it is also possible to have a passage opening 30 that is oval, angular or delimited by flat sides.

The igniter unit 22 is connected to the holder 14 through encapsulation by injection molding or foaming in that these two parts are placed into an injection molding or foaming tool. The inserted liquid plastic 34 penetrates into and fills up an annular interstice between the tool—which simulates what will later be the housing 26—and the head 23. The plastic also fills up the interstice in the vertical direction from the head 23 to the plateau-like elevation of the holder 14, as well as the entire passage opening 30 along with the notches 32 and finally also the lower indentation 16 in the holder 14, except for a receptacle for the igniter connector that will later be connected to the igniter contacts 24.

As a result, the igniter unit 22 and the holder 14 are embedded in the plastic 34 so that the igniter unit 22 is connected to the holder 14 in a fixed position.

Subsequently, the booster charge 28 is filled into the lid 26 and the unit created by injection molding and/or foaming is inserted into the lid 26.

Consequently, in the area of the out-of-round passage opening 30 that is provided with the notches 32 and that is completely filled with plastic 34, a mechanical anti-twist protection is created between the cured plastic 34 and the holder 14, this anti-twist protection preventing the plastic 34 from being loosened or detached from the holder 14 when excessive force is exerted from the outside.

In the embodiment according to FIG. 3, in addition to the circular central passage opening 30, four additional passage openings 38 are provided that are likewise filled with plastic 34 so that these passage openings 38 with their smaller cross section create the anti-twist protection.

Claims

1. A gas generator, especially for a vehicle safety system, having

a pyrotechnical igniter unit (22) and

a holder (14) for said igniter unit (22),

said igniter unit (22) being attached to said holder (14) in that said igniter unit (22) and said holder (14) are encapsulated together by one of injection molding and foaming of a plastic,

said holder (14) having at least one passage opening (30, 38) for said plastic during said encapsulation by one of injection molding and foaming, said at least one opening being configured in such a way as to create a form-fitting anti-twist protection between said plastic (34) and said holder (14).

2. The gas generator according to claim 1, wherein said passage opening (30) is out-of-round.

3. The gas generator according to claim 1, wherein said passage opening (30) has a notch (32) protruding laterally outwards.

4. The gas generator according to claim 1, wherein several passage openings (30, 38) are provided.

5. The gas generator according to claim 1, wherein a central passage opening (30) is provided.

6. The gas generator according to claim 1, wherein said holder (14) is a section of an outer housing (10) of said gas generator.

7. The gas generator according to claim 1, wherein igniter contacts (24) of said igniter unit (22) protrude through said holder (14).

8. The gas generator according to claim 7, wherein said igniter contacts (24) are part of said igniter unit (22) and form a prefabricated unit together with said igniter unit (22).