Abstract:
A stored gas inflator is formed by a pressure vessel including a gas port, a small chamber facing the gas port, and a main chamber situated adjacent to the small chamber and having a capacity larger than that of the small chamber. A high pressure gas is filled in the small chamber and the main chamber. A first partition closes the gas port, and a second partition separates the small chamber and the main chamber so that a burst pressure of the second partition is set to be lower than a stored gas pressure in the main chamber. A gas blasting initiator is mounted to the small chamber for applying burst pressure to at least one of the first and second partitions to allow the main chamber to eject the gas.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT  
         [0001]    The present invention relates to a stored gas inflator which has a pressure vessel filled with high-pressure gas to eject the gas through a gas port, and more particularly, to a stored gas inflator comprising a burst shim for closing the gas port, and an initiator for applying burst pressure to the burst shim, wherein the burst shim is ruptured by the burst pressure from the initiator to open the gas port.  
           [0002]    One known form of a gas supply unit for inflation of an airbag is a stored gas inflator which releases pressurized gas stored in a pressure vessel through a gas port. It should be noted that such an airbag is a safety device mounted in a vehicle such as an automobile and designed to be inflated to protect an occupant in the event of an emergency.  
           [0003]    [0003]FIG. 4 is a sectional view showing a conventional example of such a stored gas inflator. The stored gas inflator  100  shown in FIG. 4 comprises a pressure vessel  102  which is filled with high-pressure gas. The pressure vessel  102  is provided with gas ports  104  for allowing the high-pressure gas filled therein to be released. Normally, the gas ports  104  are air-tightly closed by a thin-plate-like burst shim  106  which is disposed to overlay an inner surface of the pressure vessel  102 . The burst shim  106  is ruptured to open the gas ports  104  when a predetermined pressure (burst pressure) is applied from the outside of the pressure vessel  102 .  
           [0004]    Near the gas ports  104  of the pressure vessel  102 , an initiator (detonator)  108  for applying burst pressure to the burst shim  106  is disposed. The initiator  108  has a base portion  108   a  fixed to the outer surface of the pressure vessel  102 , and a detonating portion  108   b  extending from the tip of the base portion  108   a.  The detonating portion  108   b  explodes in response to a detonation signal from a controller (not shown).  
           [0005]    The pressure vessel  102  is provided, near the gas ports  104  thereof, with a burst pressure inlet  110  into which the detonating portion  108   b  is inserted. The aforementioned burst shim  106  also air-tightly closes the burst pressure inlet  110 .  
           [0006]    As the initiator  108  receives a detonation signal from the controller (not shown), the detonating portion  108   b  explodes in the burst pressure inlet  110  so as to apply burst pressure to the burst shim  106  facing the burst pressure inlet  110 . As a result, the burst shim  106  is ruptured so as to open the gas ports  104 , whereby the gas is released through the gas ports  104 .  
           [0007]    In the stored gas inflator  100  having the aforementioned structure, the burst shim  106  closing the gas ports  104  is always subjected to the stored gas pressure from the inside of the pressure vessel  102 . On the other hand, the initiator  108  applies the burst pressure to the burst shim  106  from the outside of the pressure vessel  102  under a condition at a pressure (atmospheric pressure) significantly lower than the aforementioned stored gas pressure.  
           [0008]    Therefore, to rupture the burst shim  106  against the stored gas pressure from the inside of the pressure vessel  102 , the initiator  108  must apply burst pressure which is higher twice or more than the stored gas pressure of the pressure vessel  102 , so that the required power (explosion power) of the initiator  108  should be extremely high.  
           [0009]    It is an object of the present invention to provide a stored gas inflator which is triggered for gas releasing operation even with a relatively low power initiator.  
           [0010]    Further objects and advantages of the invention will be apparent from the following description of the invention.  
         SUMMARY OF THE INVENTION  
         [0011]    A stored gas inflator of the present invention comprises: a pressure vessel filled with high-pressure gas and having a gas port, a burst shim for closing the gas port; and a gas blasting initiator for applying burst pressure to the burst shim. The pressure vessel is divided into a small chamber facing the gas port and a main chamber having a capacity larger than that of the small chamber. The burst shim is composed of a first burst shim, and a second burst shim, wherein the small chamber and the gas port are partitioned from each other by the first burst shim, and the small chamber and the main chamber are partitioned from each other by the second burst shim. The small chamber and the main chamber are filled with high pressure gas, respectively, and the initiator is mounted to the small chamber. The burst pressure of the second burst shim is set to be lower than the stored gas pressure of the main chamber.  
           [0012]    According to the stored gas inflator as mentioned above, the initiator explodes inside the small chamber filled with the high-pressure gas. The first burst shim closing the gas port is always subjected to the stored gas pressure from the inside of the small chamber. As the initiator explodes inside the small chamber, gas blasted by the initiator rapidly increases the inner pressure of the small chamber. When the inner pressure of the small chamber reaches the burst pressure of the first burst shim, the first burst shim is ruptured.  
           [0013]    In the stored gas inflator of the present invention, the initiator increases the stored gas pressure in the small chamber, and the increased pressure ruptures the first burst shim. Therefore, the initiator may have such power capable of increasing the stored gas pressure in the small chamber to the burst pressure of the first burst shim. That is, even a relatively low power initiator can easily rupture the first burst shim.  
           [0014]    In the stored gas inflator of the present invention, it is preferable that, in the pressure vessel, the small chamber and the main chamber communicate with each other through a small hole.  
           [0015]    According to this structure as mentioned above, the small chamber and the main chamber are always at the same pressure in the normal state before the actuation of the initiator. The second burst shim is subjected to the same pressure from the both sides. Therefore, a member which can be ruptured when subjected to a relatively low gas pressure can be employed as the second burst shim. This can eliminate the need of another process of filling gas into the small chamber besides the process for the main chamber. Filling of gas into both of the small chamber and the main chamber can be achieved by only one filling process, thereby facilitating the assembly of the stored gas inflator.  
           [0016]    In one embodiment of the present invention, the gas pressure in the small chamber is increased according to the detonation of the initiator, thereby rupturing both the first burst shim and the second burst shim and thus releasing the gas.  
           [0017]    In another embodiment of the present invention, the gas pressure in the small chamber is increased according to the detonation of the initiator, thereby first rupturing the first burst shim and thus releasing gas from the small chamber. Then, the second burst shim is ruptured when the difference between the gas pressure in the small chamber and the gas pressure in the main chamber exceeds the burst pressure of the second burst shim, thereby releasing the gas filled in the main chamber. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    FIGS.  1 ( a ) and  1 ( b ) are explanatory views showing the structure of a stored gas inflator according to an embodiment of the present invention;  
         [0019]    [0019]FIG. 2 is an enlarged sectional view of a portion  2  in FIG. 1( b );  
         [0020]    [0020]FIG. 3 is a sectional view of a main part of a stored gas inflator according to another embodiment of the present invention; and  
         [0021]    [0021]FIG. 4 is a sectional view of a stored gas inflator according to prior art. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0022]    Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. FIGS.  1 ( a ) and  1 ( b ) show the structure of a stored gas inflator according to an embodiment of the present invention, wherein FIG. 1( a ) is a perspective view of the stored gas inflator, and FIG. 1( b ) is a perspective sectional view taken along line  1 ( b )- 1 ( b ) of FIG. 1( a ). FIG. 2 is an enlarged sectional view of a portion  2  of FIG. 1( b ).  
         [0023]    The stored gas inflator  10  comprises a pressure vessel  12  which has an elongated cylindrical profile, and is filled with high-pressure gas. The gas in the stored gas inflator  10  is pressurized at a predetermined inner pressure Pm. The pressure vessel  12  is provided, at one end in the longitudinal direction, with a gas port  14 .  
         [0024]    The gas port  14  is closed by a first burst shim  16 . The first burst shim  16  is designed to be ruptured to open the gas port  14  when subjected to a pressure equal to or higher than a predetermined pressure value P 1  from the inside of the pressure vessel  12 . The pressure value P 1  is higher than the pressure Pm of the stored gas. Hereinafter, this pressure value P 1  is called as “burst pressure P 1 ” of the first burst shim  16 .  
         [0025]    The inside of the pressure vessel  12  filled with high-pressure gas is divided, by a second burst shim  22  and a partition  24 , into a small chamber  18  facing the gas port  14  and a main chamber  20  having a capacity larger than that of the small chamber  18 . At the boundary between the small chamber  18  and the main chamber  20  of the pressure vessel  12 , the partition  24  is formed to stand in the centripetal direction from an inner surface of the pressure vessel  12 . The partition  24  is provided at its center with a gas introduction opening  26 . The second burst shim  22  is disposed to close the gas introduction opening  26  and to divide the small chamber  18  and the main chamber  20 , and is connected to the partition  24  around the peripheral edge thereof.  
         [0026]    The partition  24  is provided with a small hole  28  for allowing fluid communication between the small chamber  18  and the main chamber  20 . The small hole  28  always allows the fluid communication between the small chamber  18  and the main chamber  20 , whereby the gas stored in the small chamber  18  and the gas stored in the main chamber  20  are pressurized always at the same pressure (the aforementioned predetermined pressure Pm). In this state, the second burst shim  22  is subjected to the same gas pressure Pm at the both sides, i.e. from the small chamber  18  and the main chamber  20 .  
         [0027]    The second burst shim  22  is designed to be ruptured to open the introduction opening  26  when subjected to a pressure equal to or higher than a predetermined pressure value P 2 . Hereinafter, this pressure value P 2  is called as “burst pressure P 2 ” of the second burst shim  22 . The burst pressure P 2  of the second burst shim  22  is lower than the pressure Pm of gas stored in the small chamber  18  and the main chamber  20 .  
         [0028]    As will be described later, in a first embodiment of the present invention, the burst pressure P 2  is substantially equal to or slightly lower than (P 1 −Pm).  
         [0029]    The small chamber  18  is provided with an initiator mounting portion  32 . Mounted to the mounting portion  32  is an initiator  30  for applying burst pressure to the first and second burst shims  16  and  22 .  
         [0030]    The initiator  30  has a large-diameter base portion  30   a  and a detonating portion  30   b  extending from the tip of the base portion  30   a.  The initiator  30  has a connector  30   c  at the bottom of the base portion  30   a,  and is connected to an initiator controller (not shown) via the connector  30   c.  The detonating portion  30   b  explodes in response to a detonation signal from the initiator controller.  
         [0031]    The initiator mounting portion  32  has a mounting hole  34  for the insertion of the detonating portion  30   b  into the small chamber  18 . To mount the initiator  30  to the mounting portion  32 , the detonating portion  30   b  is inserted into the small chamber  18  through the mounting hole  34  while the base portion  30   a  is air-tightly fitted in and strongly fixed to the mounting portion  32 .  
         [0032]    In this embodiment, the stored gas inflator  10  is provided with a tubular male threaded joint portion  40  continuously formed from the gas port  14 . The male threaded joint portion  40  has external thread  40   a  formed on the outer surface thereof. Though there is no illustration, the male threaded joint portion  40  is screwed into a female threaded joint portion of a gas supply pipe for a passenger protection airbag mounted on a vehicle, such as an automobile, whereby the stored gas inflator  10  is air-tightly connected to the supply pipe for supplying gas to the airbag.  
         [0033]    The small chamber  18  of the pressure vessel  12  is substantially rectangular in section taken along a direction perpendicular to the longitudinal direction. That is, in the small chamber  18 , each pair of the opposite faces is flat and parallel to each other. By clamping such a pair of opposite faces with a tool, such as a wrench, the pressure vessel  12  can be rotated with a large torque, thereby securely screwing the male threaded joint portion  40  into the female threaded joint portion.  
         [0034]    Inside the male threaded joint portion  40 , a filter  42  is arranged for preventing fragments of the ruptured burst shims  16 ,  22  from entering together with gas stream into the aforementioned gas supply pipe during the gas releasing operation of the stored gas inflator  10 .  
         [0035]    Hereinafter, the operation of the stored gas inflator  10  having the aforementioned structure will be described.  
         [0036]    The pressure vessel  12  which is divided into the small chamber  18  and the main chamber  20  is filled with high-pressure gas having inner pressure Pm. Because the small chamber  18  and the main chamber  20  communicate with each other through the small hole  28 , the inside of the small chamber  18  and the inside of the main chamber  20  are both at the inner pressure Pm.  
         [0037]    The first burst shim  16  closing the gas port  14  for providing communication between the small chamber  18  and the outside of the stored gas inflator is subjected to the stored gas pressure Pm from the inside of the small chamber  18 . The second burst shim  22  dividing the vessel into the small chamber  18  and the main chamber  20  is subjected to the gas pressure Pm from the both sides, i.e. from the small chamber  18  and the main chamber  20 .  
         [0038]    In the event of an emergency, such as a vehicle collision, the initiator  30  receives a detonation signal from the initiator controller (not shown), whereby the detonating portion  30   b  exposed to the inside of the small chamber  18  explodes. This explosion rapidly increases the inner pressure of the small chamber  18 .  
         [0039]    In the first embodiment, by this rapid increase in the inner pressure of the small chamber  18 , the first and second burst shims  16 ,  18  are ruptured substantially simultaneously or with some time difference so as to open the gas port  14  and the gas introduction opening  26 . Therefore, the communication between the main chamber  20  and the gas port  14  is ensured, thereby releasing a large amount of gas from the gas port  14  into the airbag through the gas supply pipe.  
         [0040]    In the stored gas inflator  10 , the initiator  30  is mounted to the small chamber  18  which is filled with high-pressure gas, and is designed to increase the inner pressure of the small chamber  18  to the burst pressure of the first burst shim  16 , thereby rupturing the first burst shim  16 . Therefore, the initiator  30  is enough to have such power (explosion power) capable of increasing the stored gas pressure Pm in the small chamber  18  to the burst pressure P 1  of the first burst shim  16 . That is, a low power initiator may be employed as the initiator  30 .  
         [0041]    In this first embodiment, the first burst shim  16  is ruptured when the gas pressure in the small chamber  18  is increased from Pm by (P 1 −Pm). The second burst shim  22  is ruptured when the gas pressure in the small chamber  18  is increased from Pm by P 2 . P 2  may be substantially equal to (P 1 −Pm) or slightly smaller than (P 1 −Pm). In either case, the gas pressure in the small chamber  18  is increased by (P 1 −Pm) and by P 2  so as to rupture the burst shims  16 ,  22 . In this first embodiment, it is preferable that the burst pressure P 2  for the second burst shim  22  is set as lower as possible within a range where the first burst shim  16  can be ruptured.  
         [0042]    In a second embodiment of the present invention, first, the first burst shim  16  is ruptured without rupturing the second burst shim  22  when the gas pressure in the small chamber  18  is increased by detonation of the initiator  30 , whereby gas inside the small chamber  18  is released through the gas port  14 . This gas release results in reduction in gas pressure in the small chamber  18 . At a point when the gas is released from the small chamber  18  until the difference (Pm−P′) between the gas pressure Pm exerted by the inner pressure of the main chamber  20  and the pressure P′ exerted by the inner pressure of the small chamber  18  exceeds P 2 , the second burst shim  22  is ruptured, whereby the gas stored in the main chamber  20  is released through the gas port  14 .  
         [0043]    In this second embodiment, the burst timing of the second burst shim  22  can be adjusted by selecting the burst pressure P 2  of the second burst shim  22  within a range lower than Pm. In this manner, the stored gas inflator  10  is operable as a dual stage stored gas inflator.  
         [0044]    In the aforementioned embodiments, the stored gas inflator  10  has the pressure vessel  12  in which the small chamber  18  and the main chamber  20  communicate with each other through the small hole  28 , whereby the high-pressure gas is filled in the small chamber  18  and the main chamber  20  simultaneously. In addition, the stored gas inflator  10  can be quite simply assembled. According to the design specification of the pressure vessel and/or the initiator, the small hole  26  may be eliminated and the small chamber  18  and the main chamber  20  may be air-tightly separated from each other. In this case, the small chamber  18  and the main chamber  20  are filled with high-pressure gas, respectively.  
         [0045]    In the aforementioned embodiments, the burst shims  16 ,  22  may be separate thin disc members to close the gas port  14  and introduction opening  26 , respectively. Alternatively, the burst shims  16 ,  22  may be fragile areas of extensions integrally formed with and extending from the peripheries of the gas port  14  and the introduction opening  26  to close the gas port  14  and introduction opening  26 , respectively. The fragile areas are ruptured when subjected to the predetermined pressures.  
         [0046]    The stored gas inflator of the present invention may have an initiator  300  which is mounted to the small chamber  18  in such a manner that the gas blasting direction of the initiator  300  is directed toward the first burst shim  16  as shown in FIG. 3. FIG. 3 is a sectional view similar to FIG. 2 but showing an example of the initiator according to another embodiment.  
         [0047]    The initiator  300  has the same structure as in the initiator  30  mentioned above, that is, having a large-diameter base portion  300   a  and a detonating portion  300   b  extending from the tip of the base portion  300   a.  The initiator  300  has a connector  300   c  at the bottom of the base portion  300   a,  and is connected to an initiator controller (not shown) via the connector  300   c.  The detonating portion  300   b  explodes in response to a detonation signal from the initiator controller to blast high-pressure gas along the central axial line L of the initiator  300  extending through the base  300   a  and the detonating portion  300   b.    
         [0048]    An initiator mounting portion  320  to which the initiator  300  is mounted is formed in such a manner that the central axial line L of the initiator  300  is inclined toward the first burst shim  16 , and, thereby, holds the base portion  300   a  such that the gas blasting direction of the detonating portion  300   b  which is exposed to the inside of the small chamber  18  through the mounting hole  340  is oriented toward the first burst shim  16 .  
         [0049]    According to this structure as mentioned above, as the detonating portion  300   b  of the initiator  300  explodes inside the small chamber  18 , gas is blasted toward the first burst shim  16  so that the blast pressure directly acts as power for rupturing the burst shim  16 , thus promoting the rupture of the burst shim  16 . As a result, an initiator having further lower power can be employed as the initiator  300 . Further, according to the second embodiment of the present invention, the initiator is arranged such that its axis is inclined toward the first burst shim as mentioned above, thereby ensuring the rupture of the first burst shim prior to the rupture of the second burst shim.  
         [0050]    As described above in detail, a stored gas inflator of the present invention ensures its gas releasing operation even with a low power initiator.  
         [0051]    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.