Abstract:
The present invention provides a small, high-output gas generator for an air bag. A filter  30  is disposed between a first gas generator  11  and a second gas generator  21 . Gas discharged from the first gas generator  11  and gas discharged from the second gas generator  21  pass through the same filter  30 , and are then discharged from a second gas discharge port  36  to inflate the air bag.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a multi-stage gas generator used in an air bag system for protecting passengers during a collision.  
       BACKGROUND ART  
       [0002]     Air bags installed in vehicles such as automobiles have a wide range of applications such as bags for protecting the head region, chest, waist, and knees of a passenger, curtain bags provided on the side window, and so on. However, the space inside a vehicle is limited, and hence it is often impossible to install a gas generator for each application. Therefore, it is important to reduce the size of the gas generator so that a bag for use in a variety of applications can be inflated effectively in a limited space.  
         [0003]     Furthermore, in recent years larger air bags than those of the past are used in lateral collision applications, and a gas generator having a large output is necessary to inflate such an air bag within the required time period.  
         [0004]     In response to these two demands, ideas such as increasing the size of a conventional gas generator without altering its basic constitution, or simply combining a plurality of conventional gas generators, have been considered. With these methods, however, the required space-saving cannot be achieved.  
         [0005]     JP-A 11-139241 discloses arranging a plurality of gas generators in parallel inside the steering wheel. U.S. Pat. No. 5,658,010 discloses arranging two cylindrical inflators in parallel. JP-A No. 10-181517 discloses a module in which a filter is disposed on the exterior of a filterless inflator. JP-A 03-175298 discloses an inflator in which two combustion chambers and a filter chamber are provided independently of each other.  
       DISCLOSURE OF THE INVENTION  
       [0006]     The present invention provides a multi-stage gas generator for an air bag which is small, light, has a high output, and can be applied as a gas generator for use with various types of air bags.  
         [0007]     As means for achieving this object, the present invention provides a multi-stage gas generator for an air bag, comprising a combination of a plurality of filterless gas generators, each having a first gas discharge port, and an external filter,  
         [0008]     a space, which includes the filter and a plurality of the first gas discharge ports provided in each of the plurality of gas generators, being surrounded by a housing having a second gas discharge port, and  
         [0009]     gas, that is discharged from the first gas discharge ports of the plurality of gas generators, passing through the filter, then being discharged from the second gas discharge port to inflate the air bag.  
         [0010]     By combining a plurality of gas generators, a high overall output can be achieved, and by using a single filter for the plurality of gas generators, a reduction in the overall size can be achieved. As a result, the gas generator can be disposed in a small space in the interior of the vehicle, and can also be applied to an air bag that requires a high output (an air bag for lateral collisions or the like).  
         [0011]     The multi-stage gas generator for an air bag according to the present invention may comprise a combination of two cylindrical, filterless gas generators, each having a first gas discharge port, and an external filter,  
         [0012]     the two cylindrical gas generators having a plurality of the first gas discharge ports which are arranged in an axial direction in the respective peripheral surfaces thereof, and the respective first gas discharge ports being arranged parallel to face each other,  
         [0013]     a filter, which has a substantially V-shaped cross-section in the width direction and a length equal to or greater than the axial length of at least the plurality of first gas discharge ports, being disposed between the two gas generators, and  
         [0014]     a housing, which has a second gas discharge port, being provided to surround all of the plurality of first gas discharge ports in the two gas generators and the filter.  
         [0015]     The length of this multi-stage gas generator is greater than the width, and similarly to the invention described above, a single filter is used for the plurality of gas generators. Therefore, a high output can be achieved, and overall reductions in size and weight can be achieved in relation to the output.  
         [0016]     The multi-stage gas generator for an air bag according to the present invention may comprise a combination of two disk-form, filterless gas generators, each having a first gas discharge port, and an external filter,  
         [0017]     the two disk-form gas generators each having a plurality of the first gas discharge ports which are arranged in a circumferential direction in the respective peripheral surfaces thereof, and the respective first gas discharge ports being arranged parallel to face each other,  
         [0018]     a cylindrical filter being disposed between the two gas generators, and  
         [0019]     a housing, which has a second gas discharge port, being provided to surround all of the plurality of first gas discharge ports in the two gas generators and the filter.  
         [0020]     In the present invention, the term “disk-form” signifies a low columnar form having a certain degree of thickness, rather than a disk form having no thickness.  
         [0021]     The width of this multi-stage gas generator is greater than the height, and similarly to the invention described above, a single filter is used for the plurality of gas generators. Therefore, a high output can be achieved, and overall reductions in size and weight can be achieved in relation to the output.  
         [0022]     In the multi-stage gas generator for an air bag according to the present invention, air bag inflating means may use only the combustion gas of a gas generating agent (i.e. a pyrotechnic inflator), only gas (argon, helium, nitrogen gas, or similar) charged at high pressure (i.e. a hybrid inflator), or both combustion gas and gas charged at high pressure.  
         [0023]     Well-known substances may be used as the gas generating agent and gas. Moreover, an inflator (gas generator) which uses either type of inflating means comprises an electric igniter (comprising an ignition charge) as means for igniting the gas generating agent or to rupture a rupturable plate behind which the high-pressure gas is charged densely.  
         [0024]     The multi-stage gas generator of the present invention is small and light in relation to the magnitude of its output, and is therefore suitable for application to an air bag (a lateral collision air bag or the like) which is disposed in a small space in the interior of a vehicle but requires a high output. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1 ( a ) is a schematic plan view of a multi-stage gas generator, and  FIG. 1 ( b ) is a front view of  FIG. 1 ( a ); and  
         [0026]      FIG. 2 ( a ) is a plan view of a multi-stage gas generator, and  FIG. 2 ( b ) is a front view of  FIG. 2 ( a ). 
     
    
     REFERENCE NUMERALS OF THE DRAWINGS ARE  
       [0000]    
       
           10 ,  50  gas generator (inflator)  
           11 ,  51  first gas generator  
           12 ,  62  second gas generator  
           12   a ,  51   a    1   a  gas discharge port  
           22   a ,  52   a    1   b  gas discharge port  
           30 ,  70  filter  
           35 ,  75  housing  
           36 ,  76  second gas discharge port  
       
     
       DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     (1) First Embodiment  
       [0035]     A first embodiment will be described using  FIG. 1 .  FIG. 1 ( a ) is a schematic plan view of a multi-stage gas generator, in which the dot-dot-dash line is an imaginary line and the broken lines indicate parts that cannot be seen.  FIG. 1 ( b ) is a front view of the multi-stage gas generator, in which the broken lines indicate parts that cannot be seen. In  FIG. 1 ( b ), a filter  30  and a housing  35  alone are illustrated in sectional form.  
         [0036]     As shown in  FIG. 1 ( b ), gas discharge ports are provided with opening holes in a wall, but in  FIG. 1 ( a ), for convenience and to clearly illustrate formation positions, the gas discharge ports are illustrated in a slightly modified form.  
         [0037]     A multi-stage gas generator  10  comprises a first gas generator  11  and a second gas generator  21 . The first gas generator  11  and second gas generator  21  themselves are well-known apparatuses accommodating a desired means for inflating an air bag. The outer shell container thereof (usually referred to as a housing, shell, or the like) is selected according to the air bag inflating means, and is made of metal (aluminum, stainless steel, steel, or similar).  
         [0038]     The first gas generator  11  has a plurality of  1   a  gas discharge ports  12  ( 12   a  etc.) disposed at fixed intervals in the axial direction of the peripheral surface of the first gas generator  11 , and a first electric igniter  13  is mounted on one end face of the first gas generator  11 . The second gas generator  21  has a plurality of  1   b  gas discharge ports  22  ( 22   a  etc.) disposed at fixed intervals in the axial direction of the peripheral surface of the second gas generator  21 , and a second electric igniter  23  is mounted on one end face of the second gas generator  21 . The  1   a  gas discharge ports  12  and  1   b  gas discharge ports  22  may be sealed with aluminum or stainless steel tape.  
         [0039]     The first gas generator  11  and second gas generator  21  are arranged parallel to each other such that the  1   a  gas discharge ports  12  and  1   b  gas discharge ports  22  face each other directly, and such that the length range of the respective gas discharge ports in the axial direction match each other (in other words, such that the  1   a  gas discharge port  12   a  directly faces the  1   b  gas discharge port  22   a , and the  1   a  gas discharge port  12   d  directly faces the  1   b  gas discharge port  22   d ).  
         [0040]     The filter  30  is disposed between the two gas generators  11 ,  21 . A well-known filter can be used as the filter  30 . In the case of a pyrotechnic inflator, the filter  30  functions as a coolant/filter having functions of cooling and filtering combustion gas, and in the case of a hybrid inflator, the filter  30  traps pieces of broken rupturable plate.  
         [0041]     The filter  30  has a substantially V-shaped cross-section in the widthwise direction, and the length thereof is equal to or greater than the axial length of at least the plurality of first gas discharge ports  12 ,  22  (i.e. the length from the  1   a  gas discharge port  12   a  to the  1   a  gas discharge port  12   d , or the length from the  1   a  gas discharge port  22   a  to the  1   a  gas discharge port  22   d ).  
         [0042]     A housing  35  is provided to surround all of the plurality of  1   a  gas discharge ports  12  and  1   b  gas discharge ports  22  of the two gas generators  11 ,  21 , and the filter  30 . The interior of the housing  35  does not communicate with the external atmosphere.  
         [0043]     The housing  35  has a plurality of second gas discharge ports  36 . The second gas discharge ports  36  may be sealed by aluminum or stainless steel tape. An air bag is attached to cover at least the second gas discharge ports  36 .  
         [0044]     The housing  35  and the two gas generators  11 ,  21  are fixed to each other by welding together respective contact surfaces thereof. The filter  30  is held by the housing  35  to be clamped from above and below.  
         [0045]     A member (short pass prevention member) for preventing “short pass”, in which gas leaks out from a contact portion between the filter  30  and housing  35  and is discharged from the second gas discharge ports  36  without passing through the filter  30 , may be disposed in this contact portion. The short pass prevention member may employ a typical member used in known inflators.  
         [0046]     Next, an operation of the multi-stage gas generator will be described. The two igniters  13 ,  23  may be activated simultaneously, at a time difference, or singularly (note, however, that in this case, the other igniter is activated at a time difference that does not contribute to inflation of the air bag to ensure operational safety when dismantling the gas generator) In the following, however, a case in which the two igniters  13 ,  23  are activated at a time difference will be described.  
         [0047]     First, upon activation of the first igniter  13 , gas serving as an air bag inflating medium is discharged from the  1   a  gas discharge ports  12  of the first gas generator  11 . The gas passes through the filter  30 , flows into a space  31 , and is then discharged from the second gas discharge ports  36  to inflate the air bag. By means of the space  31 , the filter  30  does not contact the second gas discharge ports  36 , and the gas is discharged after initially flowing into the space  31 . As a result, the gas is discharged evenly from the plurality of second gas discharge ports  36 .  
         [0048]     After a slight delay, the second igniter  23  is activated, whereby gas serving as an air bag inflating medium is discharged from the  1   b  gas discharge ports  22  of the second gas generator  21 . The gas passes through the filter  30 , flows into the space  31 , and is then discharged from the second gas discharge ports  36  to further inflate the air bag.  
         [0049]     Since the multi-stage gas generator  10  comprises the two gas generators  11 ,  21 , its output can be increased greatly, and since the two gas generators  11 ,  21  share the single filter  30 , the overall size and weight of the multi-stage gas generator  10  can be reduced.  
       (2) Second Embodiment  
       [0050]     A second embodiment will be described using FIG.  2 .  FIG. 2 ( a ) is a schematic plan view of a multi-stage gas generator in which the dot-dot-dash line is an imaginary line.  FIG. 2 ( b ) is a front view of the multi-stage gas generator in which the broken lines indicate parts that cannot be seen.  
         [0051]     As shown in  FIG. 1 ( b ), gas discharge ports are formed by opening holes in a wall, but in FIGS.  2 ( a ) and  2 ( b ), for convenience and to clearly illustrate formation positions, the gas discharge ports are illustrated in a slightly modified form.  
         [0052]     A multi-stage gas generator  50  comprises a first gas generator  51  and a second gas generator  61 . The first gas generator  51  and second gas generator  61  themselves are well-known apparatuses accommodating desired means for inflating an air bag. The outer shell container thereof (usually referred to as a housing, shell, or the like) is selected according to the air bag inflating means, and is made of metal (aluminum, stainless steel, steel, or similar).  
         [0053]     The first gas generator  51  has a plurality of  1   a  gas discharge ports  52  ( 52   a  etc.) in the circumferential direction of the peripheral surface of the first gas generator  51 , and a first electric igniter ( 53  denotes a connector connected to the igniter) is mounted on a bottom face side of the first gas generator  51 . The second gas generator  61  has a plurality of  1   b  gas discharge ports  62  ( 62   a  etc.) in the circumferential direction of the peripheral surface of the second gas generator  61 , and a second electric igniter ( 63  denotes a connector connected to the igniter) is mounted on a bottom face of the second gas generator  61 . The  1   a  gas discharge ports  52  and  1   b  gas discharge ports  62  may be sealed with aluminum or stainless steel tape.  
         [0054]     The first gas generator  51  and second gas generator  61  are arranged parallel to each other such that the  1   a  gas discharge ports  52  and  1   b  gas discharge ports  62  face each other, and such that the length range of the respective gas discharge ports in the circumferential direction match each other (in other words, such that the  1   a  gas discharge port  52   a  faces the  1   b  gas discharge port  62   a , and the  1   a  gas discharge port  52   f  faces the  1   b  gas discharge port  62   f ).  
         [0055]     A cylindrical filter  70  is disposed between the two gas generators  51 ,  61 . A well-known filter can be used as the filter  70 . In the case of a pyrotechnic inflator, the filter  70  functions as a coolant/filter having functions of cooling and filtering combustion gas, and in the case of a hybrid inflator, the filter  70  traps pieces of broken rupturable plate.  
         [0056]     A housing  75  is provided to surround all of the plurality of  1   a  gas discharge ports  52  and  1   b  gas discharge ports  62  of the two gas generators  51 ,  61 , and the filter  70 . The interior of the housing  75  does not communicate with the external atmosphere.  
         [0057]     The housing  75  has a second gas discharge port  76 . The second gas discharge port  76  is provided in a position directly facing a hollow portion of the cylindrical filter  70  in the housing  75 , and may be provided singularly or in a plurality. The second gas discharge port  76  may be sealed by aluminum or stainless steel tape. An air bag is attached to cover at least the second gas discharge port  76 .  
         [0058]     The housing  75  and the two gas generators  51 ,  61  are fixed to each other by welding together respective contact surfaces thereof. The filter  70  is held by the housing  75  so as to be clamped from above and below.  
         [0059]     A member (short pass prevention member) for preventing “short pass”, in which gas leaks out from a contact portion between the filter  70  and housing  75  and is discharged from the second gas discharge port  76  without passing through the filter  70 , may be disposed in this contact portion. The short pass prevention member may employ a typical member used in known inflators.  
         [0060]     Next, similarly to the first embodiment, a case in which the two igniters are activated at a time difference will be described.  
         [0061]     First, upon activation of the first igniter, gas serving as an air bag inflating medium is discharged from the  1   a  gas discharge ports  52  of the first gas generator  51 . The gas passes through the filter  70 , flows into a space (the hollow portion of the filter  70 )  71 , and is then discharged from the second gas discharge port  76  to inflate the air bag. By means of the space  71 , the filter  70  does not contact the second gas discharge port  76 , and the gas is discharged after initially flowing into the space  71 . As a result, the gas is discharged evenly from the plurality of second gas discharge ports  76 .  
         [0062]     After a slight delay, the second igniter is activated, whereby gas serving as an air bag inflating medium is discharged from the  1   b  gas discharge ports  62  of the second gas generator  61 . The gas passes through the filter  70 , flows into the space  71 , and is then discharged from the second gas discharge port  76  to further inflate the air bag.  
         [0063]     Since the multi-stage gas generator  50  comprises the two gas generators  51 ,  61 , its output can be increased greatly, and since the two gas generators  51 ,  61  share the single filter  70 , the overall size and weight of the multi-stage gas generator  50  can be reduced.