GB2279442A

GB2279442A - Gas generator for an airbag

Info

Publication number: GB2279442A
Application number: GB9411246A
Authority: GB
Inventors: Akira Kokeguchi; Yoshikazu Nakayama
Original assignee: Takata Corp
Current assignee: Takata Corp
Priority date: 1993-06-08
Filing date: 1994-06-06
Publication date: 1995-01-04
Anticipated expiration: 2014-06-06
Also published as: GB9411246D0; JPH06344855A; GB2279442B; DE4419519A1

Description

1 1 - INFLATOR FOR AIR BAG DEVICE 2279442

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an inflator for use in an air bag device, particularly, to an inflator of a cylindrical type. More particularly, the present invention relates to an inflator of which temperature dependency of the gas blowout characteristics is decreased or annulled.

Description of Prior Art

An inflator of cvlindrical type comprises a cylindrical casing havinc, oas outlet holes disposed on the peripheral surface thereof, a cylindrical booster tube inserted coaxially into the casing and having a plurality of gas passing holes communicating the inside with the outside of the tube. an ignition cord inserted into the booster tube in the axial direction, an ignitor for igniting the ignition cord. booster propellant filled up between the ignition cord and the booster tube, and main propellant filled up between the booster tube and the casing. The holes of the casing are sealed with a film adhered to an Z:! inner surface of the casinq.

When a vehicle having an air bag device comprising an air bag and the above inflator collides, the ignitor is turned on the electricity to fire the booster propellant in the booster tube, the main propellant is fired to generate gas, and the gas breaks the film to blow out outside of the casing 1.

An onset rate, which indicates rapidly of a pressure increase of the gas blown out of the casing immediately after ignition of the igniter, influences extension of the air bag.

Because the propellant reacts more actively as the ambient temperature (atmospheric temperature) becomes higher, the onset rate of the gas pressure in the conventional inflator is influenced by the ambient temperature.

SUNINIARY OF THE I-NVE'NTION It is an object of the present invention to provide an inflator of which temperature dependency of the onset rate of the gas pressure is decreased or annulled.

An in-flator for an air ba(y device according to the present invention comprises a cylindrical casing having gas outlet holes disposed on the peripheral surface thereof, a film adhered to the inner surface of the casinsz and sealina the aas outlet holes, a cvlindrical booster tube inserted coaxialiv into the casing and havina a plurality of gas passing holes communicating the inside with the outside of the cylindrical member, booster propellant filled up in the booster tube, and main propellant filled up between the booster tube and the casin2, the film is a synthetic resin film of which the tensile strength is increased as the temperature thereof becomes lower.

In the inflator for the air bag according to the present invention, the booster propellant is fired by the ignitor and the main propellant is then fired to generate gas so that the gas is spouted out of the inflator. The propellant reacts more rapidly as the gas pressure in the casing becomes higher.

The film seals the holes and has the tensile strength which increases as the temperature of the film becomes lower, thereby gas pressure becomes r :Y higher in the casing during the reaction of the propellant and before breaking of the film, so that the propellant in the casing reacts more rapidly as the temperature becomes lower. In this manner, the decrease of the reaction rate of the propellant due to the drop of the ambient temperature is canceled by the increase of reaction rate due to the rise of the gas pressure in the casing. When the gas pressure in the casing exceeds the tensile strength of the film, the film is broken.

When the temperature rises, the reaction rate of the propellant is increased, and the tensile strenoth of the film is lowered. As a result, the film is broken before the pressure in the casing goes up so I In hiah. Therefore. the increase of the reaction rate of the propellant due to the temperature rise is canceled by decrease of the reaction rate of the propellant due to the drop of the gas pressure in the casing,.

BRIEF DESCRIPTION OF THE DR.AWINGS

Fis!. 1 is a lon2itudinal cross-sectional view showing an inflator according to an embodiment of the present invention; Fig. 2 is a cross-sectional view showincy the inflator accordina to the embodiment., 3 is a plan view showing the inflator according to the F i aty. 3 embodiment; Fig. 4 is a side view showina the inflator accordincy to the embodiment, and Ficy. 5 is a diagram of operating characteristics of the inflator according to the embodiment.

4 An embodiment of the present invention will now be described with reference to attached drawin2s.

A casing 1 is cylindrical and has a plurality of gas outlet holes 2 disposed on the peripheral surface thereof. The casing I is made of aluminum or aluminum base allov. A synthetic resin film 10 is adhered to the inner surface of the casing 1 to seal the gas outlet holes 2. As shown in Fia. 5, the synthetic resin film 10 has characteristics that the tensile strength thereof is increased as the temperature becomes lower.

A booster tube 3 is coaxially inserted into the casing 1. An ignition cord 4 is inserted into the booster tube 33 at the axial position n thereof. Booster propellant --5 is filled between the ignition cord 4 and the booster tube -3). -XIain propellant 6 is filled between the booster tube 35 and the casing 1. A plurality of gas passing holes 3a are disposed on the booster tube 3.

A filter 7 for collecting particulate in the gas is disposed along the inner surface of the casing 1. An ignitor 8 for i2niting the ignition cord 4 is disposed on one end face of the casing 1. The auto ignition material 9 is disposed on the other end face portion in the casina 1. The auto ionition material 9 is fired bv heat of fire in case of fi re.

When the ionitor 8 is turned on the electricity, the ignition cord 4 is ignited. Soon after this. the booster propellant 5 and main propellant 6 are ignited so that the gas breaks the film 10 and is spouted through the gas outlet holes 2.

The gas outlet holes 2 are sealed bv the svnthetic resin film 10 of which the tensile strength is increased as the temperature becomes lower. When the ambient temperature is low, the gas pressure in the casing I immediately after the operation of the inflator (before the g film 10 is broken) is high. This high pressure cancels the reduction of the reaction rate of the propellants 5. 6 corresponding to the drop of the ambient temperature.

When the ambient temperature is hiCFh, the reaction rate of the propellant 5,6 is increased. However, the tensile strength of the synthetic resin film 10 is decreased. Accordingly, the film 10 is broken before the gas pressure in the casing I is raised sufficiently. That is, the gas pressure in the casing I is lowered when the ambient temperature is high. This is one of factors for reducing the reaction rate of the propellant. As a result of this, even if the ambient temperature is high, the reaction rate of the propellant for generating gas is substantially equal to the reaction rate at a low temperature.

In the present invention. the synthetic resin film is preferably made of polvethylene tereplithalate (PET), particularly biaxial oriented PET, nylon, polypropylene. urethane or the like. The synthetic resin film may be a film laminated a plurality of films.

When it is defined that the tensile stren(2th of the film at the room temperature (22 "Q is T-1-) and the tensile strength of the film at -30 OC is T-o, the film has preferably a ratio of T--)O/T22 between 1.2 and 1. 35, more preferably between 1.25 and 1.3. The film is preferable to have tensile strength which is increased linearly from a room temperature to 30 'C. The ratio T-30/T22 of the urethane film is approximately 1.3. The ratio T-30/T22 of the biaxial oriented PET film is approximately 1.25.

As the mentioned above, in the inflator for the air bac, device according to the present invention, the onset rate is substantially constant even if an ambient temperature is changed, so that an air bag is always extended in a predetermined manner.

6 WHAT IS CLAEMED IS:

1. An inflator for an air bag device comprising; a cylindrical casing having gas outlet holes disposed on the peripheral surface thereof., a film adhered to the inner surface of said casino and sealing said gas outlet holes..

a cylindrical booster tube inserted coaxially into said casing and having a plurality of gas passing holes communicating the inside with the outside of said tube; booster propellant filled up in said booster tube; and, main propellant filled up between said booster tube and said casing, said film being a synthetic resin film of which the tensile strength _lDecomes higher as a temperature thereof becomes lower.

2. An inflator as claimed in claim 1. wherein said synthetic resin is polyethylene terephthalate. nylon. polypropylene or urethane.

3. An inflator as claimed in claim 1. wherein said film is a biaxially oriented polyethylene terephthalate film.

4. An inflator as claimed in claim 1. wherein the tensile strength T11 of said film at a room temperature and the tensile I -- strength T-30 of said film at -30 C ar,- in a range such that the ratio T- 30/T22 is between 1.2 and L')5, and the tensile strength of the film is increased linearly from the room temperature to -30 'C.

5. An inflator as claimed in claim 4, wherein said ratio T30/T221 is between 1.25 and 1.35.

6. An inflator substantially as hereinbefore described with reference to the accompanying description and Figures 1 to 5 of the drawings.