Airbag inflator

Abstract: To provide an airbag inflator which can manufactured at a low coat and enables a bag to be held in the deployed state for a relatively long period of time. A body 2 of an airbag inflator 1 is divided into first and second gas chambers 1A, 1B. The inflator starts to discharge gas by breaking the seal of the first gas chamber 1A. As the pressure difference between the first gas chamber 1A and the second gas chamber 1B is increased, a disk closure 5 is torn so that gas is discharged also from the second gas chamber 1B.

Description: The present invention relates to an inflator which generates gas for inflating and deploying an airbag for protecting a vehicle occupant. More concretely, the present invention relates to an airbag inflator of a type suitable for an airbag for protecting the side of an occupant in a seat, which is improved to enable the bag to be held in its deployed state for a relatively long period of time by virtue of a plurality of high-pressure gas chambers. Such an airbag inflator having a plurality of combustion chambers containing gas generant therein is known through disclosures in US-A-5,219,178, US-A-3 966 228 and JP-A-HO9-136604. In the airbag inflators disclosed in these publications, the volume of gas to be generated can be controlled into several modes thereby enabling the preferred deployment of the airbag to suitably correspond to the severity of the collision and the condition of the occupant. An airbag inflator having a plurality of separate and sealed high-pressure gas chambers is also known (e.g., JP-A-H07-156741). However, there is a strong demand for an airbag inflator which can be manufactured at low cost and enables the bag to be held in its deployed state for a relatively long period of time. The present invention is made in order to correspond to the aforementioned demand and the object of the present invention is to provide an airbag system which can provide improved performability of protecting an occupant. This object is achieved with the features of the claims. In order to solve the above-described problems, the present invention provides an airbag inflator for discharging gas for deploying an airbag comprising: a plurality of high-pressure gas chambers which are divided and sealed; an initiator for starting to discharge gas by breaking the seal of a first high-pressure gas chamber; a means for detecting a pressure difference between the first high-pressure gas chamber and the other high-pressure gas chamber and for discharging gas sequentially from the other high-pressure gas chamber by breaking the seal of the other high-pressure gas chamber due to the pressure difference. In the initial stage of the deployment of the airbag, bag is deployed by gas from the first high-pressure gas chamber. As the gas is discharged from the first high-pressure gas chamber, the inner pressure in the first high-pressure gas chamber falls. At this point, by using the means, for example, a disk closure which is disposed between the first high-pressure gas chamber and the other high-pressure gas chamber and can be torn when subjected to a predetermined pressure difference, gas is additionally discharged from the other high-pressure gas chamber sequentially. Therefore, the shrinkage of a bag, which is caused by the temperature fall of gas discharged from a first high-pressure gas chamber and/or air vent through a vent hole, can be compensated by supplying another gas so that the deployment pressure (e.g. 0.3-0.6 kgf/cm 2 ) of the bag can be held for a long period of time (e.g. 5-7 seconds). This can improve the performability of, for example, a side airbag, for protecting the occupant. According to the present invention, the aforementioned means is a disk closure which is disposed between the first high-pressure gas chamber and the other gas chamber and is torn when subjected to a predetermined pressure difference. This is because the means can be actualized by quite simple structure and a mechanism for delayed operation between the high-pressure gas chambers, which are divided, can be achieved at a low cost. Hereinafter, the present invention will be described with reference to the attached drawings. Fig. 1 is a sectional view of an airbag inflator of piston-less type according to the first embodiment of the present invention; and Fig. 2 is a sectional view of an airbag inflator of piston type according to the second embodiment of the present invention. Fig. 1 is a sectional view of an airbag inflator 1 of piston-less type as a first embodiment of the present invention. The airbag inflator 1 comprises a body 2 having a space formed therein in which gas is filled and sealed. The body 2 has a cylindrical profile. The body 2 comprises three parts 2X, 2Y, and 2Z, arranged in the longitudinal direction. The left part 2X is a cylinder formed integrally with a bottom which is a left end wall of the body. The middle part 2Y and the right part 2Z are both open tubular cylinders. These three parts are arranged so that the ends of the middle part 2Y are in contact with the ends of the adjacent parts and are connected by welding the ends along the outer peripheries. Each welded portion has a flange portion projecting inwardly. A base 4 is screwed in the right end of the body 2 via a gasket 3 so that the body 2 is sealingly closed by the gasket 3 and the base 4. Disc closures 5, 6 are disposed between the left part 2X and the middle part 2Y, and between the middle part 2Y and the right part 2Z, respectively inside the body 2. The disc closures 5, 6 are thin metal (stainless steel) sheets (for example, the thickness of 0.4 mm), are sandwiched between the ends of the parts of the body 2, and are fixed by a well-known means such as welding. The inside of the body 2 is divided in three chambers by the disc closures 5, 6. Among the three chambers, gas is filled and sealed in a first gas chamber 1A positioned in the middle and in a second gas chamber 1B positioned on the left side of the first gas chamber 1A via the disc closure 5. The gas is inert gas such as argon, nitrogen or helium, having high pressure (in the order of 200-300 kgf/cm 2 ). The body 2 is provided with injection holes 2a, 2b allowing the communication between the outside of the body 2 and the first and second gas chambers 1A, 1B, respectively. The high-pressure gas is injected through the injection holes 2a, 2b. Practically, the gas is injected at the same time in order not to cause pressure difference between the first gas chamber 1A and the second gas chamber 1B. Fitted in the injection holes 2a, 2b are steel balls 7, 8. After filling the gas, the steel balls 7, 8 are fitted in the injection holes 2a, 2b so as to close the injection holes 2a, 2b to seal the gas. A chamber 1C positioned on the right side of the first gas chamber 1A via the disk closure 6 has an initiator assembly 10 disposed therein. When a vehicle comes into collision, the initiator assembly 10 receives an electric signal from a sensor (not shown) to ignite. The initiator assembly 10 is integrally fixed to an inner surface of the base 4 (the surface facing the first gas chamber 1A when screwed). Therefore, when the base 4 is screwed in the right end of the body 2, the initiator assembly 10 is disposed inside the chamber 1C. An enhancer cap 11 is fitted to an end (the left end in Fig. 1) of the initiator assembly 10. The enhancer cap 11 includes enhancer (gas generant) 12 held inside thereof. Inside the first gas chamber 1A, a screen 15 is disposed near the left-hand-side disk closure 5. The screen 15 is made by forming metal mesh material into a disk-like configuration having a predetermined thickness. The screen 15 is used for capturing cinders of the enhancer 12 and fragments of the disc closures 5, 6. The outer periphery of the screen 15 is fitted in a groove 2c formed along the inner periphery of the first gas chamber 1A. More particularly, projections 2d, 2e are formed on the both sides of the groove 2c to project from the inner surface of the first gas chamber 1A. The width of the groove 2c between the projections 2d, 2e is set to correspond to the thickness of the screen 15. The screen 15 is fitted in or engaged with the groove 2c. Since the screen 15 is flexible, the screen 15 is slightly deformed in the radial direction during the screen 15 is installed in the groove 2c. Communication holes 2f are formed between the bottom of the groove 2c and the outer surface of the body 2. Four of the communication holes 2f are formed at predetermined intervals in the circumferential direction of the body 2. Though the communication holes 2f allow the communication between the inside of the first gas chamber 1A and the outside of the body 2, the communication holes 2f are normally closed by disc closures 16 disposed on the bottom of the groove 2c. Each disc closure 16 is a circular sheet made of metal such as stainless steel and having hemispherical convex portions at the middle thereof projecting toward the inside of the communication holes 2f. Each disc closure 16 is in contact with the bottom of the groove 2c in such a manner that the surface having the convex portions is directed to the communication holes 2f. The sealing between the disc closure 16 and the body 2 is accomplished by adhesion. The description will now be made as regard to the works of the airbag inflator 1 of piston-less type structured as mentioned above. When the vehicle comes into collision, the sensor not shown senses the collision and outputs an electric signal to the initiator assembly 10. Because of this electric signal, initiator assembly 10 operates. The operation of the initiator assembly 10 ignites the enhancer (gas generant) 12 to generate high temperature and high pressure gas. The pressure of the generated gas destroys or blows away the enhancer cap 11. The impact pressure of the gas generated from the enhancer 12 tears the disc closure 6 in the first gas chamber 1A. As the disc closure 6 is torn, the gas filled and sealed in the first gas chamber 1A at a high pressure expands due to the heat from the enhancer 12 and the gas pressure from the enhancer 12 is also added whereby the inner pressure of the first gas chamber 1A is increased. By the increased inner pressure, the disc closures 16 disposed in the groove to close the communication holes 2f are torn. As the disc closures 16 are thus torn, the communication holes 2f are in the communicating state so that gas of high temperature about 150-200 °C is discharged into the bag. Accordingly, the bag (its capacity is about 5-15 litters) is immediately inflated with this high temperature gas. As the gas is discharged from the inside of the first gas chamber 1A, pressure difference is generated between the inside of the first gas chamber 1A and the inside of the second gas chamber 1B, in which gas is filled and sealed, adjacent to the first gas chamber 1A via the left-hand-side disc closure 5. When this pressure difference exceeds the predetermined value, the disc closure 5 is torn. As the disc closure 5 is torn, the gas within the second gas chamber 1B is discharged into the bag through the communication holes 2f which have been opened already. As mentioned above, the bag is inflated with gas of high temperature about 150-200 °C discharged from the first gas chamber 1A first. The temperature of the gas falls because of the temperature difference between the gas and the air in the cabin, so the bag shrinks gradually. This phenomenon should be caused whether gas leaks from the bag or not. In the airbag inflator 1 according to the first embodiment, after the gas is discharged from the first gas chamber 1A, the shrinkage of the bag is compensated by the gas from the second gas chamber 1B. From experiments, wherein the capacity of the first gas chamber 1A was 50 cc, the capacity of the second gas chamber 1B was 30 cc, the start of gas discharge from the second gas chamber 1B was after 0.1 second from the ignition of the initiator assembly 10, and the capacity of the bag was 15 liters, it was found that the inner pressure of the bag can be held at 0.3-0.6 kgf/cm 2 for about 5-7 seconds. Therefore, the performability of protecting the occupant can be improved. Fig. 2 is a sectional view of an airbag inflator 21 of piston type as a second embodiment of the present invention. The airbag inflator 21 comprises a body 22 having a space formed therein in which gas is filled and sealed. The body 22 has a cylindrical profile. The body 22 comprises three parts 22X, 22Y, and 22Z, arranged in the longitudinal direction. The left part 22X is a cylinder formed integrally with a bottom which is a left end wall of the body 22. The middle part 22Y and the right part 22Z are both open tubular cylinders. These three parts are arranged so that the ends of the middle part 22Y are in contact with the ends of the adjacent parts and are connected by welding the ends along the outer peripheries. Each welded portion has a flange portion projecting inwardly. The right end of the body 22 is open and a sleeve 23 is inserted into the right end. The sleeve 23 is formed in a cylindrical shape and has an initiator assembly 24 fixed to the inside thereof. As mentioned above in the first embodiment, when a vehicle comes into collision, the initiator assembly 24 receives an electric signal from a sensor (not shown) to ignite. Assembled into the initiator assembly 24 is a piston 25 having a cone-shaped end, which is disposed in such a manner that the piston 25 can slide in the leftward direction in this drawing. Though the piston 25 normally stays in a right position in the sleeve 23, the piston 25 is pressed by high pressure gas, that is generated because of the ignition of the initiator assembly 24, so as to project toward the left of the body 22. The body 22 is sealingly closed by the sleeve 23 and the initiator assembly 24. Disc closures 26, 27 are disposed between the left part 22X and the middle part 22Y, and between the middle part 22Y and the right part 22Z, respectively inside the body 22. The disc closures 26, 27 are thin metal (stainless steel) sheets (for example, the thickness of 0.4 mm), are sandwiched between the ends of the parts of the body 22, and fixed by a well-known means such as welding. The inside of the body 22 is divided in three chambers by the disc closures 26, 27 Among the three chambers, gas is filled and sealed in a first gas chamber 21A positioned in the middle and in a second gas chamber 21B positioned on the left side of the first gas chamber 21A via the disc closure 26. The gas is inert gas such as argon, nitrogen or helium, having high pressure (in the order of 200-300 kgf/cm 2 ). The body 22 is provided with injection holes 22a, 22b allowing the communication between the outside of the body 22 and the first and second gas chambers 21A, 21B, respectively. The high-pressure gas is injected through the injection holes 22a, 22b. Practically, the gas is injected at the same time in order not to cause pressure difference between the first gas chamber 21A and the second gas chamber 21B. Fitted in the injection holes 22a, 22b are steel balls 28, 29. After filling the gas, the steel balls 28, 29 are fitted in the injection holes 22a, 22b so as to close the injection holes 22a, 22b to seal the gas. The aforementioned sleeve 23 is disposed in a chamber 21C adjacent to the first gas chamber 21A via the disc closure 27. Communication holes 22c are formed in the peripheral wall of the chamber 21C to allow the communication between the outside of the body 22 and the chamber 21C. Four of the communication holes 22c are formed at predetermined intervals in the circumferential direction of the body 22. A screen 30 which is made by forming metal mesh material is disposed between the outer surface of the sleeve 23 and the inner surface of the body 22. As well as the screen 15 mentioned above, the screen 30 is used for capturing cinders of the enhancer and fragments of the disc closures. In the first gas chamber 21A, an enhancer holder 32, of which axial section is groove-like shape, is disposed near the disk closure 27. The enhancer holder 32 has a flange 32a which is fixed integrally to the body 22 by a well-known means such as welding. In this fixed state, the enhancer holder 32 is open toward the chamber 21C. Communication holes 32b are formed in the wall of the enhancer holder 32 in such a manner as to extend radially. Four of the communication holes 32b are formed at predetermined intervals in the circumferential direction of the enhancer holder 32. Three through holes 32c are formed in the bottom (the left-hand-side wall in Fig. 2) of the enhancer holder 32 in such a manner as to extend in the axial direction. Disposed on a bottom side of the enhancer holder 32 is an enhancer unit 33 which includes an enhancer (gas generant) 34 therein. On the both sides of the enhancer 34, arc holders 35 are disposed to be in contact with the inner surface of the enhancer holder 32. A spring 36 is fixed between the arc holders 35, 35 in its tensioned state. An actuator 37 is attached to the spring 36 so that the actuator 37 is normally biased toward the right of this drawing in a direction apart from the enhancer 34 because of the elasticity of the spring 36. The actuator 37 is pressed by the piston 25 which projects by the ignition of the initiator assembly 24 and thus collides with the enhancer 34. By the impact of this collision, the enhancer 34 is ignited. The description will now be made as regard to the works of the airbag inflator 21 of piston type structured as mentioned above. When the vehicle comes into collision, the sensor not shown senses the collision and outputs an electric signal to the initiator assembly 24. Because of this electric signal, initiator assembly 24 operates. The operation of the initiator assembly 24 applies thrust on the piston 25. The piston 25 subjected to the thrust slides in the direction apart from the initiator assembly 24 and then collides with the disc closure 27. Because of the collision of the piston 25, the disc closure 27 is torn. As the disc closure 27 is torn, the gas filled and sealed in the first gas chamber 21A at high pressure is introduced into the enhancer holder 32 through the communication holes 32b. The gas is then discharged into the airbag via the screen 30 through the communication holes 22c formed in the body 22 so as to deploy the airbag. After the disc closure 27 is torn, the piston 25 further moves toward the left apart from the sleeve 23 and then collides with the actuator 37. Because of this collision, the spring 36 is elastically deformed to bring the actuator 37 into collision with the enhancer 34. The enhancer 34 is ignited due to the collision and the high temperature gas is generated and introduced into the first gas chamber 21A via the holes 32c. Therefore, the residual gas in the first gas chamber 21A is increased in its temperature and expands. Since the residual gas in the first gas chamber 21A is increased in its temperature and expands, the gas is also discharged into the bag through the communication holes 32b in the wall of the enhancer holders 32 and the communication holes 22c of the body 22. As the gas is discharged from the inside of the first gas chamber 21A, pressure difference is generated between the inside of the first gas chamber 21A and the inside of the second gas chamber 21B, in which gas is filled and sealed, adjacent to the first gas chamber 21A. When this pressure difference exceeds the predetermined value, the disc closure 26 is torn. As the disc closure 26 is torn, the gas within the second gas chamber 21B is discharged into the bag through the communication holes 32b in the wall of the enhancer holder 32 and the communication holes 22c of the body 22. Therefore, the shrinkage of the bag is compensated by the gas from the second gas chamber 21B. In this manner, in the airbag inflator 21 of piston type according to the second embodiment, after the gas in the first gas chamber 21A is discharged, the shrinkage of the bag can be compensated by the gas in the second gas chamber 21B. In this case also, the inner pressure of the bag can be held at 03-0.6 kgf/cm 2 for about 5-7 seconds. As described above, according to the present invention, the shrinkage of a bag, which is caused by the temperature fall of gas discharged from a first high-pressure gas chamber and/or air vent through a vent hole, can be compensate by supplying another gas so that the deployment pressure (e.g. 0.3-0.6 kgf/cm 2 ) of the bag can be held for a long period of time (e.g. 5-7 seconds). This can improve the performability of, for example, a side airbag, for protecting the occupant.

Claims: An airbag inflator for discharging gas for deploying an airbag comprising: a plurality of high-pressure gas chambers (1A, 1B; 21A, 21B, 21C) which are divided and separately sealed and arranged in the longitudinal direction; an initiator (10, 24) for starting to discharge gas by breaking the disc closure (16, 27), of a first hight-pressure gas chamber (1A; 21A); a disc closure means (5; 26) for detecting a pressure difference between said first high-pressure gas chamber (1A; 21A) and the other high-pressure gas chamber (1B; 21B) and for discharging gas sequentially from the other high-pressure gas chamber (1B; 21B) by breaking the disc closure means (5; 26) of the other high-pressure gas chamber due to the pressure difference. The airbag inflator as claimed in claim 1, wherein said disc closure means (5; 26) which is disposed between said first high-pressure gas chamber (1A; 21A) and the other gas chamber (1B, 21B) and is torn when subjected to a predetermined pressure difference. The airbag as claimed in claims 1 or 2, comprising communication holes (2f), which allow communication between the gas chambers (1A, 1B) and the airbag and which are positioned between the first gas chamber (1A) and the second gas chamber (1B).

Inventors: KOKEGUCHI AKIRA, KOKEGUCHI, AKIRA, Kokeguchi, Akira c/o Takata Corporation
Applicants: TAKATA CORP, TAKATA CORPORATION
Application year: 1999
Main classification: B60R21
IPC codes: B60R21