Abstract:
A gas generator for an airbag is provided which is small and lightweight and enables an efficient use of the filter. This gas generator includes: a first member with one end open; a second member closing the open end of the first member; an ignition unit and a gas generating unit, both installed in a container formed by the first and second members; a filter arranged along an outer circumference of the container to enclose gas passing ports formed in the container; and a strip plate member arranged along an outer circumference of the filter, having a width smaller than the width of the filter and adapted to prevent a radial expansion of the filter, or a mesh member covering the filter.

Description:
This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/JP96/03166 which has an International filing date of Oct. 29, 1996 which designated the United States of America. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an airbag gas generator for protecting an occupant from an impact and more specifically to a gas generator which can be reduced in size and weight and can make an efficient use of a filter. 
     2. Description of the Related Art 
     An example of a conventional airbag gas generator is illustrated in FIG.  4 . The gas generator includes: a housing  31  having gas discharge ports  30 ; an ignition means accommodating chamber  32  formed in a central part of the housing  31 ; a combustion chamber  33  formed on the outer side of the ignition means accommodating chamber  32 ; a coolant filter chamber  34  formed on the outer side of the combustion chamber  33 ; ignition means, i.e., an igniter  35  and a transfer charge  36 , disposed in the ignition means accommodating chamber  32 ; gas generating means i.e. a canister  38  filled with a gas generating agent  37 , disposed in the combustion chamber  33  and to be ignited by the ignition means to generate a gas; a coolant  39  for cooling a combustion gas generated in the combustion chamber  33  and cleaning means for cleaning or purifying the combustion gas, i.e., a filter  40 , both disposed in the coolant filter chamber  34 . 
     A plurality of gas discharge ports  30  are formed in the housing  31  in a circumferential direction at predetermined intervals. 
     The coolant filter chamber  34  is divided by a retainer  42  into an upper tier chamber and a lower tier chamber, the upper tier chamber accommodating the filter  40  and the lower tier chamber accommodating the coolant  39 . 
     When a sensor (not shown) senses an impact, its signal is sent to the igniter  35 , which is then activated to ignite the transfer charge  36 . The transfer charge  36  when ignited generates high-temperature and high-pressure flames, which pass through openings  41 , fractures the wall of the canister  38  and then ignites the gas generating agent  37  contained therein. Then, the gas generating agent  37  burns to generate a gas, which then passes through gas passing ports  44  of a combustor cup  43  and passes through the coolant  39 , during which period the gas is cooled and removed of combustion residues. Further as the gas passes through the filter  40 , the remaining combustion residues are removed. The cooled and cleaned gas flows through the gas discharge ports  30  into an airbag (not shown). The inflow-gas inflates the airbag, forming a cushion between an occupant and a hard structure to protect the occupant against an impact. 
     In the conventional gas generator described above, the gas discharge ports are disposed downstream of the filter with respect to the gas flow direction and are formed intermittently at predetermined intervals. Hence, the gas flow that enter and pass through the filter and move out of the housing tend to concentrate toward the gas discharge ports and therefore do not reach the portions of the filter between the adjacent gas discharge ports. As a result, these filter portions are not used effectively. In other words, an efficient utilization cannot be made of the entire area of the filter. 
     In the above conventional gas generator, the coolant filter chamber where the filter is installed is formed outside the combustion chamber. This construction increases the diameter of the gas generator, which causes a problem of increased size and weight of the gas generator. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a novel gas generator that solves problems experienced in the prior art described above. 
     This invention provides an airbag gas generator which comprises: a first member with one end thereof open; a second member closing the open end of the first member; an ignition units and a gas generating agent, both disposed in a container formed by the first and second members; a filter arranged around an outer circumference of the container to enclose gas passing ports formed in the container; and (1) a strip plate member having a width smaller than the width of the filter and adapted to prevent a radial expansion of the filter, or (2) a mesh member covering the filter, both arranged around an outer circumference of the filter. 
     In the gas generator including the container, the gas passing ports and the filter, (1) the strip plate member or (2) the mesh member is also provided. 
     The filter is held between the first member and the second member. The filter is arranged along the outer circumference of the container to enclose the gas passing ports formed in the container. The first member and the second member together form the gas discharge port outside the filter. An outer side surface  20  of the filter faces the gas discharge port. 
     The gas passing through the gas passing ports enters the filter and is then introduced from the gas discharge port into the airbag. 
     The strip plate member is preferably installed at the gas discharge port, which is therefore defined by the first member, the second member, and the strip plate member. The gas passing ports are preferably disposed not to oppose the gas discharge port in radial direction so that the gas does not flow out straight in radial direction but flows out in a curved path. In other words, the flow path in the filter is preferably extended. 
     It is preferred that the strip plate member and the mesh member be preferably made of a stainless steel material and that the mesh member has a stainless steel wire mesh covering the entire surface thereof. 
     (1) The strip plate member is arranged along the outer circumference of the filter and has a width smaller than that of the filter. Hence, there is an uncovered portion of the filter which is not covered by the strip plate member. This uncovered portion functions as a continuous window to allow the gas to pass through the filter when it has entered the filter. This continuous window eliminates a problem that the gas flows tend to concentrate toward gas discharge ports used in the conventional gas generator. 
     When the gas applies a force to the filter, the filter tends to expand outwardly in radial direction. This tendency is restricted by the strip plate member. 
     (2) The mesh member is arranged along the outer circumference of the filter to cover the filter. The mesh member allows passage of gas through its entire area. This eliminates the problem of the conventional gas generator in which the gas flow tends to concentrate toward gas discharge ports. The gas flow passing through the filter do not concentrate but passes through the entire area of the mesh member located adjacent to the filter before flowing out into the airbag. 
     The mesh member may be formed of, for example, laminated layers of stainless steel wire mesh. 
     With the gas generator of this invention constructed as described above, the gas can pass through the entire area of the filter, thus realizing an efficient use of the filter. 
     The gas generator of this invention obviates the need for the coolant filter chamber provided in the conventional gas generator. This not only simplifies the construction of the gas generator but reduces the diameter of the gas generator. As a result, the gas generator can be reduced in size and weight. 
    
    
     FIG. 1 is a cross-sectional view of one embodiment of a gas generator; 
     FIG. 1 a  is a cross-sectional view of one embodiment of a gas generator; 
     FIG. 2 is a cross-sectional view of another embodiment of a gas generator; 
     FIG. 3 is a cross-sectional view of still another embodiment of another embodiment of a gas generator; and 
     FIG. 4 is a partial cross-sectional view of a conventional gas generator. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Now one embodiment of this invention will be described with reference to the drawings. 
     FIG. 1 is a cross-sectional view of one embodiment of the gas generator according to this invention. The gas generator includes a first member  1 , a second member  3 , ignition means  5 , gas generating means  6 , a filter  8 , and a strip plate member  9 . The first member  1  and the second member  3  are formed by press working. 
     The first member  1  is cylindrical in shape and has one end open and the other end closed. The first member  1  has an open end portion  2 , a circular portion  10 , and a circumferential wall portion  11  formed around the periphery of the circular portion  10 . The circumferential wall portion  11  is formed with a plurality of gas passing ports  7  arranged in a circumferential direction. 
     The second member  3  has a dish shape and closes the open end portion  2  of the first member  1 . The second member  3  has a circular portion  12 , a circumferential wall portion  13  formed around the periphery of the circular portion  12 , and a flange portion  14  formed at the front end portion of the circumferential wall portion  13 . The circumferential wall portion  13  has an inner diameter such that it can receive the circumferential wall portion  11  therein. The front end portion of the circumferential wall portion  11  fits into the inner side of the circumferential wall portion  13 , and a weld portion  15  is formed in a circumferential direction along an engagement portion between the circumferential wall portion  11  and the circumferential wall portion  13 . The first member  1  and the second member  3  are welded together at the weld portion  15  to form a container  4  having a space therein. 
     Installed in the container  4  are the ignition means  5  and the gas generating means  6 . The ignition means  5  comprises a squib (igniter)  16  and an enhancer (transfer charge)  17 . The enhancer  17  is accommodated in a container which is in contact with the squib  16 . The gas generating means  6  comprises a canister  18 , which is an annular thin aluminum container filled with a gas generating agent. 
     Around the container  4  is arranged the filter  8 , which comprises several laminated layers of intertwined fiber body arranged at the center of the filter and several layers of wire mesh surrounding the inner and outer sides, with respect to a radial direction, of the laminated fiber body. This filter  8  is rectangular in cross section and has an upper end surface  19 , an outer side surface  20 , a lower end surface  21 , and an inner side surface  23 . The upper end surface  19  hermetically contacts the inner surface of a support member  22 , have a L-shaped in cross section which secured to the circumferential wall portion  11 . The lower end surface  21  hermetically contacts the upper surface of the flange portion  14  of the second member. In this way, the filter  8  is supported restricted in the vertical direction and in the radial direction. The inner side surface  23  encloses the gas passing ports  7  with a predetermined clearance therebetween. 
     The strip plate member  9  is made of a strip of stainless steel plate. The strip plate member  9  surrounds the filter along the outer side surface  20  of the filter and has a width about half that of the filter. The strip plate member  9  is located at the lower half of the filter  8  and opposed to the gas passing ports  7 . The strip plate member  9  forms a circumferentially continuous window  24  between it and the support member  22 , which allows the gas to pass through its entire area. 
     In the gas generator of the above construction, when a sensor (not shown) detects an impact and sends an electric signal to the squib  16 , the squib  16  is activated to ignite the enhancer  17  that produces high-temperature and high-pressure flames. The flames break the wall of the container that accommodates the enhancer  17  and ignites the gas generating agent inside the canister. A gas produced by the combustion of the gas generating agent passes through the gas passing ports  7  into the filter  8 . After entering the filter  8 , the gas diffuses in the filter  8  and strikes the strip plate member  9 . The gas that has struck the strip plate member  9  changes its course along the strip plate member  9 . The gas that has diffused in the filter  8  flows in a diffuse state into an airbag (not shown) through the window  24 . In the mean time the combustion gas is cooled and cleared of combustion residues. The combustion gas that has flowed into the airbag inflates the airbag to form a cushion between an occupant and a hard structure, protecting the occupant from impacts. 
     FIG. 1 a  shows a mesh member  59  instead of the strip plate member shown in FIG.  1 . The front end portion of the circumferential wall portion  11  fits inside the circumferential wall portion  13 , with the front end surface of the circumferential wall portion  11  in contact with the inner surface of the circular portion  12 . The filter  8  has a vertical end surface  70 , an inclined curved portion  71 , and a horizontal end surface  69 . The vertical end surface  70  hermetically contacts the outer circumferential surface of the circumferential wall portion  11  of the first member, and the horizontal end surface  69  hermetically contacts the upper surface of the flange portion  14  of the second member. The inclined curved portion  71  encloses the gas passing ports  7  with a predetermined clearance therebetween. 
     The mesh member  59  is made by laminating layers of stainless steel wire mesh. The mesh member  59  wholly covers the container  4  from above. That is, it covers the outer surface of the circular portion  10  of the first member, the outer circumferential surface of the inclined curved portion  71  of the filter, and the upper surface of the flange portion  14  of the second member. The mesh member  59  is clamped at its outer periphery between a fixing ring  72  and the flange portion  14  and secured to the container  4 . An area  73  of the mesh member  59  that opposes the gas passing ports  7  maybe provided with a plate member for diffusing gas. 
     The mesh member  59  allows the gas to pass through its entire area. The mesh member  59  secures the filter  8  to the container  4 . 
     The gas that has entered the filter  8  diffuses in the filter  8  and, in the diffuse state, flows through the mesh member  59  adjacent to the filter into the airbag (not shown). 
     FIG. 2 shows another embodiment of the gas generator of this invention. Members identical to the corresponding members shown in FIG. 1 are assigned like reference numbers and their explanations are omitted. This gas generator is intended for a further improvement in the filtering action. 
     A first member  1 ′ has an open end portion  2 ′ and a support portion  22 ′ formed integral with the open end portion  2 ′. A second member  3 ′ closes the open end portion  2 ′ and, along with the first member  1 ′, forms the container  4 . The first member  1 ′ has a flange member  14 ′ secured to the circumferential portion thereof. A filter  8 ′ is held between the support portion  22 ′ and the flange member  14 ′ and arranged along the outer circumference of the container  4  so that it is restricted in the vertical and radial directions. The filter  8 ′ is wider than the filter  8  shown in FIG. 1. A strip plate member  9 ′ has a width slightly larger than one-half the filter width. 
     This gas generator has a combustion ring  25  that forms a combustion chamber  26 . The combustion ring  25  is formed with a plurality of gas passing nozzles  27  at one end side portion thereof. The gas passing nozzles  27  are vertically deviated from the gas passing ports  7  so that the gas flow from the combustion chamber  26  follows a bent path as indicated by the arrow of FIG.  2 . As a result, a gas energy loss occurs, reducing the speed of the gas flow, which in turn assures effective cooling of gas and arresting of combustion residues by the filter. 
     The gas generator shown in FIG. 3 is also intended for a further improvement in the filtering action as in the case of FIG.  2 . 
     A first member  1 ″ has an open end portion  2 ″ and a flange portion  14 ″ formed integral with the open end portion  2 ″. A second member  3 ″ closes the open end portion  2 ″ and, along with the first member  1 ″, forms the container  4 . The first member  1 ″ has a support member  22 ″ secured to the circumferential portion thereof. A filter  8 ″ is held between the support portion  22 ″ and the flange member  14 ″ and arranged along the outer circumference of the container  4  so that it is restricted in the vertical and radial directions. The filter  8 ″ is thicker than the filters shown in FIGS. 1 and 2. 
     A combustion ring  25 ′ in this gas generator has gas passing nozzles  27 ′ formed in the other end side portion thereof which is opposite to the one end side portion in FIG.  2 . These gas passing nozzles  27 ′ are vertically deviated from the gas passing ports  7  so that the gas-flow from the combustion chamber  26  follows a bent path as indicated by the arrow of FIG.  3 . As a result, a gas energy loss occurs, reducing the speed of the gas-flow, which in turn assures effective cooling of gas and arresting of combustion residues by the filter.