Abstract:
An air bag inflator is divided into first and second gas chambers. The inflator starts to discharge gas by breaking a seal of the first gas chamber. As the pressure difference between the first gas chamber and the second gas chamber is increased, a disk closure situated between the first and second gas chambers is torn, so that gas is discharged also from the second gas chamber. The air bag inflator can be manufactured at a low cost and enables the air bag to be held in the deployed state for a relatively long period of time.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to an inflator which generates gas for inflating and deploying an air bag for protecting a vehicle occupant. In particular, the present invention relates to an air bag inflator suitable for an air bag for protecting a side of an occupant on a seat, which is improved in allowing the air 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. 
     An air bag inflator having a plurality of combustion chambers containing gas generating agents therein is known in U.S. Pat. No. 5,219,178 and Japanese Patent Unexamined Publication (KOKAI) No. H09-136604. In the air bag inflators disclosed in these publications, the volume of gas to be generated can be controlled in several modes thereby enabling the preferred deployment of the air bag to suitably correspond to the severity of the collision and the condition of the occupant. 
     An air bag inflator having a plurality of separate and sealed high-pressure gas chambers is also known, e.g. Japanese Patent Unexamined Publication (KOKAI) No. H07-156741. 
     However, there is a strong demand for an air bag inflator which can be manufactured at a low cost and enables the air bag to be held in its deployed state for a relatively long period of time. 
     The present invention has been made in order to satisfy the aforementioned demand, and an object of the present invention is to provide an air bag inflator, which can provide improved ability in protecting an occupant. 
     Another object of the invention is to provide an air bag inflator which can inflate the air bag quickly and keep the inflated condition of the air bag for a relatively long period of time. 
     Further objects and advantages of the invention will be apparent from the following description of the invention. 
     SUMMARY OF THE INVENTION 
     In order to solve the above-described problems, the present invention provides an air bag inflator for discharging gas for deploying an air bag. The inflator comprises a plurality of high-pressure gas chambers which are sealed; an initiator for staring to discharge gas by breaking the seal of the first high-pressure gas chamber; 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 air bag, the air bag is deployed by gas ejected 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 it is subjected to a predetermined pressure difference, gas is additionally discharged from the other high-pressure gas chamber sequentially. Therefore, the shrinkage of the air bag, which is caused by 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 the additional gas, so that the deployment pressure, e.g. 0.3-0.6 kgf/cir, of the air bag can be held for a long period of time, e.g. 5-7 seconds. This can improve the performing ability of, for example a side air bag, 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 it is subjected to a predetermined pressure difference. This is because the means can be made by a 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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of an air bag inflator of a pistonless type according to a first embodiment of the present invention; and 
     FIG. 2 is a sectional view of an air bag inflator of a piston type according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, the present invention will be described with reference to the attached drawings. 
     FIG. 1 is a sectional view of an air bag inflator  1  of a piston-less type as a first embodiment of the present invention. The air bag inflator  1  comprises a body  2  having a space therein in which gas is filled and sealed. The body  2  has a cylindrical profile, and comprises three parts  2 X,  2 Y and  2 Z arranged in the longitudinal direction. The left part  2 X is a cylinder integrally formed with a bottom which is a left end wall of the body. The middle part  2 Y and the right part  2 Z are both hollow tubular cylinders. These three parts are arranged such that the ends of the middle part  2 Y are in contact with the ends of the adjacent parts and are connected together by welding the ends along the outer peripheries. Each welded portion has a flange portion projecting inwardly. A base  4  is screwed into 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 . 
     Disk closures  5 ,  6  are disposed between the left part  2 X and the middle part  2 Y, and between the middle part  2 Y and the right part  2 Z, respectively, inside the body  2 . The disk closures  5 ,  6  are thin metal sheets, i.e. stainless steel with the thickness of 0.4 mm. The disk closures  5 ,  6  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 disk closures  5 ,  6 . Among the three chambers, gas is filled and sealed in a first gas chamber  1 A positioned in the middle and in a second gas chamber  1 B positioned on the left side of the first gas chamber  1 A via the disk closure  5 . The gas is an inert gas, such as argon and helium, having high pressure about 200-300 kgf/cm 2 . 
     The body  2  is provided with injection holes  2   a ,  2   b  allowing the outside of the body  2  to communicate with the first and second gas chambers  1 A,  1 B, respectively. The high-pressure gas is injected through the injection holes  2   a ,  2   b . Practically, the gas is injected at the same time in order not to cause pressure difference between the first gas chamber  1 A and the second gas chamber  1 B. Fitted in the injection holes  2   a ,  2   b  are steel balls  7 ,  8 . After filling the gas, the steel balls  7 ,  8  are fitted in the injection holes  2   a ,  2   b  so as to close the injection holes  2   a ,  2   b  to seal the gas. 
     A chamber  1 C positioned on the right side of the first gas chamber  1 A 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 the inner surface of the base  4  at a side facing the first gas chamber  1 A when screwed. Therefore, when the base  4  is screwed into the right end of the body  2 , the initiator assembly  10  is disposed inside the chamber  1 C. An enhancer cap  11  is fitted to an end (left end in FIG. 1) of the initiator assembly  10 . The enhancer cap  11  includes an enhancer, i.e. gas generating agent,  12  held inside thereof. 
     Inside the first gas chamber  1 A, a screen  15  is disposed near the disk closure  5  at the left side. The screen  15  is made by forming a 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 disk closures  5 ,  6 . The outer periphery of the screen  15  is fitted in a groove  2   c  formed along the inner periphery of the first gas chamber  1 A. More particularly, projections  2   d ,  2   e  are formed on both sides of the groove  2   c  to project from the inner surface of the first gas chamber  1 A. The width of the groove  2   c  between the projections  2   d ,  2   e  is set to correspond to the thickness of the screen  15 . The screen  15  is fitted in or engaged with the groove  2 C. Since the screen  15  is flexible, the screen  15  can be slightly deformed in the radial direction when the screen  15  is installed in the groove  2   c.    
     Communication or discharge holes  2   f  are formed between the bottom of the groove  2   c  and the outer surface of the body  2 . Four communication holes  2   f  are formed at predetermined intervals in the circumferential direction of the body  2 . Although the communication holes  2   f  allow communication between the inside of the first gas chamber  1 A and the outside of the body  2 , the communication holes  2   f  are normally closed by disk closures  16  disposed on the bottom of the groove  2   c . Each disk closure  16  is a circular sheet made of metal, such as stainless steel, and having a hemispherical convex portion at the middle thereof projecting toward the inside of the communication hole  2   f . Each disk closure  16  contacts the bottom of the groove  2   c  in such a manner that the surface having the convex portion is directed to the communication hole  2   f . The sealing between the disk closure  16  and the body  2  is accomplished by adhesion. 
     The description will now be made as regard to the operation of the air bag inflator  1  of the 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 . By this electric signal, the initiator assembly  10  operates. The operation of the initiator assembly  10  ignites the enhancer (gas generating agent)  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 disk closure  6  in the first gas chamber  1 A. 
     As the disk closure  6  is torn, the gas filled and sealed in the first gas chamber  1 A 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  1 A is increased. By the increased inner pressure, the disk closures  16  disposed in the groove  2   c  to close the communication holes  2   f  are torn. As the disk closures  16  are thus torn, the communication holes  2   f  become the communicating state, so that the gas with high temperature about 150-200° C. is discharged into the air bag. Accordingly, the air bag, which has a capacity of about 5-15 liters, is immediately inflated with this high temperature gas. 
     As the gas is discharged from the inside of the first gas chamber  1 A, pressure difference occurs between the inside of the first gas chamber  1 A and the inside of the second gas chamber  1 B, in which gas is filled and sealed, adjacent to the first gas chamber  1 A via the disk closure  5  at the left side. When this pressure difference exceeds a predetermined value, the disk closure  5  is torn. As the disk closure  5  is torn, the gas within the second gas chamber  1 B is discharged into the air bag through the communication holes  2   f  which have been opened already. 
     As mentioned above, the air bag is inflated with the gas of high temperature about 150-200° C. discharged from the first gas chamber  1 A first. The temperature of the gas falls because of the temperature difference between the gas and air in the cabin, so that the inflated air bag shrinks gradually. This phenomenon occurs regardless of the gas leak from the air bag. 
     In the air bag inflator  1  according to the first embodiment, after the gas is discharged from the first gas chamber  1 A, the shrinkage of the air bag is compensated by the gas from the second gas chamber  1 B. 
     In experiments, wherein the capacity of the first gas chamber  1 A was 50 cc; the capacity of the second gas chamber  1 B was 30 cc; the start of gas discharge from the second gas chamber  1 B was after 0.1 second from the ignition of the initiator assembly  10 ; and the capacity of the air bag was 15 liters, it was found that the inner pressure of the air bag can be held at 0.3-0.6 kgf/cm 2  for about 5-7 seconds. Therefore, the ability for protecting the occupant can be improved. 
     FIG. 2 is a sectional view of an air bag inflator  21  of a piston type as a second embodiment of the present invention. The air bag 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, and comprises three parts  22 X,  22 Y and  22 Z arranged in the longitudinal direction. The left part  22 X is a cylinder integrally formed with a bottom which is a left end wall of the body  22 . The middle part  22 Y and the right part  22 Z are both open tubular cylinders. These three parts are arranged such that the ends of the middle part  22 Y contact the ends of the adjacent parts, and are connected by welding along the outer peripheries. Each welded portion has flange portions 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 in 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 to Although the piston  25  normally stays in a right position in the sleeve  23 , the piston  25  can be pressed by a high pressure gas generated at the time of ignition of the initiator assembly  24 , so as to project toward the left of the body  22 . The body  22  is sealingly closed at the right side by the sleeve  23  and the initiator assembly  24 . 
     Disk closures  26 ,  27  are disposed between the left part  22 X and the middle part  22 Y, and between the middle part  22 Y and the right part  22 Z, respectively, inside the body  22 . The disk closures  26 ,  27  are thin metal sheets, i.e. stainless steel with the thickness of 0.4 mm. The disk closures  26 ,  27  are sandwiched between the ends of the parts of the body  22 , and fixed by well-known means, such as welding. The inside of the body  22  is divided in three chambers by the disk closures  26 ,  27 . Among the three chambers, gas is filled and sealed in a first gas chamber  21 A positioned in the middle and in a second gas chamber  21 B positioned on the left side of the first gas chamber  21 A via the disk closure  26 . The gas is an inert gas, such as argon and helium, having high pressure in about 200-300 kgf/cm 2 . 
     The body  22  is provided with injection holes  22   a ,  22   b  allowing the outside of the body  22  to communicate with the first and second gas chambers  21 A,  21 B, respectively. The high-pressure gas is injected through the injection holes  22   a ,  22   b . Practically, the gas is injected at the same time in order not to cause pressure difference between the first gas chamber  21 A and the second gas chamber  21 B. Fitted in the injection holes  22   a ,  22   b  are steel balls  28 ,  29 . After filling the gas, the steel balls  28 ,  29  are fitted in the injection holes  22   a ,  22   b  so as to close the injection holes  22   a ,  22   b  to seal the gas. 
     The aforementioned sleeve  23  is disposed in a chamber  21 C adjacent the first gas chamber  21 A via the disk closure  27 . Communication or discharge holes  22   c  are formed in the peripheral wall of the chamber  21 C to communicate between the outside of the body  22  and the chamber  21 C. Four communication holes  22   c  are formed at predetermined intervals in the circumferential direction of the body  22 . A screen  30  which is made of a metal mesh material is disposed between the outer surface of the sleeve  23  and the inner surface of the body  22 . Similar to the screen  15  mentioned above, the screen  30  is used for capturing cinders of the enhancer and fragments of the disk closures. 
     In the first gas chamber  21 A, an enhancer holder  32 , an axial section of which has a groove-like shape, is disposed near the disk closure  27 . The enhancer holder  32  has a flange  32   a  integrally fixed to the body  22  by well-known means, such as welding. In this fixed state, the enhancer holder  32  is open toward the chamber  21 C. Communication holes  32   b  are formed in the wall of the enhancer holder  32  to extend radially. Four communication holes  32   b  are formed at predetermined intervals in the circumferential direction of the enhancer holder  32 . Three through holes  32   c  are formed in the bottom, i.e. left side wall in FIG. 2, of the enhancer holder  32  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 generating agent)  34  therein. On both sides of the enhancer  34 , holders  35  are disposed to contact the inner surface of the enhancer holder  32 . A spring  36  is disposed between the holders  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 away 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 operation of the air bag inflator  21  of the 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, the initiator assembly  24  operates. The operation of the initiator assembly  24  applies thrust force on the piston  25 . The piston  25  subjected to the thrust force slides in the direction away from the initiator assembly  24  and then collides with the disk closure  27 . Because of the collision of the piston  25 , the disk closure  27  is torn. 
     As the disk closure  27  is torn, the gas filled and sealed in the first gas chamber  21 A at high pressure is introduced into the enhancer holder  32  through the communication holes  32   b . The gas is then discharged into the air bag via the screen  30  through the communication holes  22   c  formed in the body  22  so as to deploy the air bag. 
     After the disk closure  27  is torn, the piston  25  further moves toward the left away from the sleeve  23  and then collides with the actuator  37 . Because of this collision, the spring  36  is elastically deformed to allow the actuator  37  to collide 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  21 A via the holes  32   c . Therefore, the residual gas in the first gas chamber  21 A is increased in its temperature and expands. 
     Since the residual gas in the first gas chamber  21 A is increased in its temperature and expands, the gas is also discharged into the air bag through the communication holes  32   b  in the wall of the enhancer holder  32  and the communication holes  22   c  of the body  22 . As the gas is discharged from the inside of the first gas chamber  21 A, pressure difference occurs between the inside of the first gas chamber  21 A and the inside of the second gas chamber  21 B, in which gas is filled and sealed, adjacent the first gas chamber  21 A. When this pressure difference exceeds a predetermined value, the disk closure  26  is torn. As the disk closure  26  is torn, the gas within the second gas chamber  21 B is discharged into the air bag through the communication holes  32   b  in the wall of the enhancer holder  32  and the communication holes  22   c  of the body  22 . Therefore, the shrinkage of the air bag is compensated by the gas from the second gas chamber  21 B. 
     In this manner, in the air bag inflator  21  of the piston type according to the second embodiment, after the gas in the first gas chamber  21 A is discharged, the shrinkage of the air bag can be compensated by the gas in the second gas chamber  21 B. In this case also, the inner pressure of the air bag can be held at 0.3-0.6 kgf/cm 2  for about 5-7 seconds. 
     In the above embodiments, two gas chambers are formed in the air bag inflator. However, it is possible to form more than two gas chambers sequentially discharging a gas. 
     As described above, according to the present invention, the shrinkage of the air bag, which is caused by the temperature fall of the gas discharged from the 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 air bag can be held for a long period of time, e.g. 5-7 seconds. This can improve the performing ability of, for example, a side air bag, for protecting the occupant. 
     While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.