Abstract:
A hybrid inflator having a structure permitting easy and reliable mounting to an airbag module, facilitating welding during manufacture, and improving in gas sealability and reduced in weight, is provided. The hybrid inflator is for use in an inflation type safety system for a motor vehicle equipped with an airbag, and includes an inflator housing, pressurized gas contained at least in the inflator housing, a gas generator housing connected to the inflator housing and provided with at least one gas generator outlet, a gas generating agent contained in the gas generator housing and ignited by an initiator, and an inflator operation assembly containing the initiator for operating the inflator. The inflator operation assembly comprises a boss welded to an end portion of the inflator housing to hermetically seal the housing, and the boss has an edge of flange shape to be mounted to an airbag module.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an inflation type safety system for motor vehicles, and more particularly, to a hybrid inflator capable of quickly inflating an airbag. 
     BACKGROUND OF INVENTION 
     In recent years, with development of inflator for use in an inflation type safety system for motor vehicles, hybrid inflator which utilizes pressurized gas and solid gas generating agent in combination is attracting attention. A primary requirement for the design of such hybrid inflator is to inflate the airbag by a given amount in a given time to make the airbag operate effectively, and various structures therefor have been proposed hitherto (see Unexamined JP-A No. 8-282427, for example). Since the hybrid inflator is applied to a motor vehicle, the weight of the motor vehicle constitutes an important design requirement, so that the weight and dimensions of the inflator are important factors in the design. Also, there is a demand for inflators that can be manufactured easily, can be easily and reliably mounted to motor vehicles, can be easily filled with gas, and free of gas leak. 
     SUMMARY OF THE INVENTION 
     The present invention was created to fulfill the above requirements, and an object thereof is to provide a hybrid inflator which has a structure permitting the inflator to be easily and reliably mounted to an airbag module, compared to conventional inflators, easily welded during the manufacture, and improved in gas sealability and reduced in weight. 
     The present invention provides a hybrid inflator for an inflation type safety system for a motor vehicle equipped with an airbag, comprising an inflator housing, pressurized gas contained in the inflator housing, a gas generator housing connected to the inflator housing and provided with at least one gas generator outlet, a solid gas generating agent contained in the gas generator housing, and an initiator adapter for igniting the gas generating agent to produce propellant gas, wherein the hybrid inflator is characterized in that the adapter comprises a boss welded to an edge portion of the inflator housing, and that an outer end portion of the boss has a flange shape for mounting an airbag module. The outer surface of the flange portion of the boss is formed as a planar surface and a pressurized gas charging hole is bored so as to extend from the surface to the interior of the inflator housing. The charging hole is sealed by a pin inserted therein as a sealing member after the gas is charged. 
     The present invention also provides an airbag device production method applied to a hybrid inflator for an inflation type safety system for a motor vehicle equipped with an airbag, the hybrid inflator comprising an inflator housing, pressurized gas contained at least in the inflator housing, a gas generator housing connected to the inflator housing and provided with at least one gas generator outlet, a gas generating agent contained in the gas generator housing and ignited by an initiator, and an inflator operation assembly containing the initiator for operating the inflator, wherein the method is characterized in that the inflator operation assembly comprises a boss welded to an end portion of the inflator housing to hermetically seal the housing, an edge of the boss having a flange shape, and the hybrid inflator being mounted to a module via the flange of the boss. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal sectional view of a hybrid inflator according to one embodiment of the present invention; 
     FIG. 2 is an enlarged longitudinal sectional view of a boss of the hybrid inflator according to the present invention; 
     FIG. 3 is a longitudinal sectional view showing the boss with a connector and a connector cover attached thereto; 
     FIG. 4 is an exploded perspective view schematically illustrating how the connector and the connector cover are attached to the boss; and 
     FIG. 5 is an end view showing the boss with the connector and the connector cover attached thereto. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention will be hereinafter described in detail with reference to the drawings illustrating an embodiment thereof. 
     FIG. 1 is a longitudinal sectional view of a hybrid inflator according to one embodiment of the present invention. 
     As shown in FIG. 1, a hybrid inflator  102  has a cylindrical gas generator  108  and a cylindrical inflator housing, that is, a high-pressure gas housing  104 . The high-pressure gas housing  104  surrounds the gas generator  108  and is arranged coaxially therewith to have a common center axis  120 . The high-pressure gas housing  104  contains a suitable gas under pressure, and the gas generator  108  contains grains  158  of a suitable gas generating agent. 
     The gas generator  108  has a cylindrical gas generator housing  112  comprising a first housing  116  and a second housing  178  axially coupled thereto. The first housing  116  has one end thereof coupled to an initiator adapter  124 , for example, by welding at a weld  148  for hermetic sealing. The initiator adapter  124  includes a suitable initiator  128  (e.g., an electric igniter tube) which is used to ignite the grains  158  of the gas generating agent. In order to separate the initiator  128  from the gas under pressure contained in the gas generator  108 , a secondary closing disk  136  is fixed between the end of the first housing  116  and a corresponding end of the initiator adapter  124 , to form a hermetic seal in cooperation with the weld  148 . 
     The first housing  116  of the gas generator housing  112  defines a first chamber  154  therein. The first chamber  154  adjoins the initiator  128  and is axially aligned therewith. The first chamber  154  of the gas generator housing  112  mainly contains therein the grains  158  of gas generating agent which, when ignited, produce a propellant gas that augments the gas flow toward an airbag. The first chamber  154  can thus be characterized as a propellant chamber or a combustion chamber. A suitable igniting agent  140  for assisting the ignition of the propellant grains  158  may be arranged between the initiator  128  and the propellant grains  158  at a location corresponding to the discharge from the initiator. Gas product formed by the ignition of the igniting agent  140  can chemically react with the pressurized gas to further enhance the characteristic of initiation of flow by means of rapid pressurization of the inflator  102 . A suitable booster cup  144  contains therein the igniting agent  140  (generally, in the form of powder or obtained by drying slurry) and is fixed to at least one end of the initiator adapter  124  (e.g., held between the adapter  124  and the housing  116  via the weld  148 ). The first chamber  154  may include a screen  166  or a like member so that while the propellant gas is discharged toward a second chamber  224  in the second housing  178 , granular matter of specified size may be retained therein. The high-pressure gas housing  104  of the inflator  102  has a volume greater than that of the second chamber  224 . 
     The first chamber  154  communicates with the high-pressure gas housing  104  through at least one bleed orifice (bleed hole)  162 . In the figure, two bleed holes are formed. Consequently, in a static state, the first chamber  154  contains a large amount of gas under pressure. The bleed holes  162  extend in a radius direction, that is, they have a starting point thereof located on the center axis  120  and extend along a radius extending in a direction perpendicular to the center axis  120 . The size and/or number of the bleed holes  162  may be selected to correctly adjust the performance of the inflator  102 . 
     Since at least one bleed hole  162  is formed, a specified amount of the propellant gas flow, created due to the ignition of the propellant grains  158 , is guided into the high-pressure gas housing  104  as a gas flow  400  shown in FIG.  1 . Where the propellant of the aforementioned type (e.g., gun type propellant, hybrid propellant) and pressurized gas (e.g., mixture of oxygen and inert gas) are used, second combustion, that is, additional combustion of the propellant gas takes place in the high-pressure gas housing. Generally, an amount smaller than half the propellant gas produced to attain desired results (e.g., about 40% or less, more generally, about 30% or less of the propellant gas) flows into the high-pressure gas housing  104  during operation. 
     A main flow of the propellant gas produced in the first chamber  154  (e.g., at least about 50%, more generally, at least about 70% of the total flow of the propellant gas) is guided, as a gas flow  401  shown in FIG. 1, into the second chamber  224  (afterburner chamber) defined by the second housing  178  of the gas generator housing  112 . At least one afterburner nozzle or aspirator  174  (first communication hole) guides the gas flow  401  (chiefly the propellant gas) from the first chamber  154  into the second chamber  224 , whereby a desired communication is established. The afterburner nozzle  174  is engaged with a shoulder  170  formed in the inside of the first housing  116  to be situated inward of the first housing  116  before the first housing  116  is suitably connected to the second housing  178  (e.g., by welding connection at a weld  150 ). 
     The second housing  178  of the gas generator housing  112  has one end thereof engaged with an inner surface of an afterburner adapter  182  having at least one gas generator outlet  186  formed therein. An O-ring  228  is interposed between the second housing  178  and the adapter  182  to provide suitable sealing. The afterburner adapter  182  is suitably fixed to a boss  194 , for example, by welding at a weld  208 , and the boss  194  is fixed to the high-pressure gas housing  104 , for example, by welding at a weld  212 . These members are fixed together to provide hermetic sealing because in the static state the second chamber  224  contains a large amount of gas under pressure. To keep the gas under pressure appropriately within the inflator  102  until necessity arises, a main closing disk  190  is arranged between the end of the afterburner adapter  182  and the boss  194  and is retained by the weld  208 . 
     Owing to the communication between the first chamber  154  and the second chamber  224 , at least part of the propellant gas produced by the combustion of the propellant grains  158  and of the gas produced by the combustion of the igniting agent  140  is guided into the second chamber (afterburner chamber)  224 . A rapid increase of pressure in the second chamber  224 , which is controlled by a method described in detail later, opens the main closing disk  190  at a suitable time, so that the gas flow from the inflator  102  is guided to a diffuser  198  and then into an airbag (not shown). The diffuser  198  has a plurality of diffuser ports  200  to provide output to the airbag. In order to keep specified granular matter within the inflator  102  and to attain at least one of mixing and further accelerated reaction of the propellant gas with the pressurized gas before these gases move to the airbag, the diffuser  198  may include a diffuser screen  204 . 
     The second chamber  224  further communicates with the high-pressure gas housing  104 . At least one, preferably, a plurality of gas generator inlets  216  establish communication between the high-pressure gas housing  104  and the second chamber  224 . Consequently, the pressurized gas in the high-pressure gas housing  104  can flow, as a gas flow  403  shown in FIG. 1, into the second chamber  224  at a suitable time. Namely, the direction of this specified gas flow can be controlled. Specifically, a valve  220  may be arranged adjacent to at least one, preferably, all of the gas generator inlets  216 . In the static state, the valve  220  in this region need not actually separate the high-pressure gas housing  104  from the second chamber  224 . In fact, a large amount of pressurized gas should preferably be kept within the second chamber  224  in the static state, and this permits the use of connection not associated with sealing. As one structure of the valve  220  not separating the second chamber  224  from the high-pressure gas housing on the gas generator inlets  216 , a metallic insert material comprising a substantially cylindrical roll may be used. Cantilever connection may be employed between the valve  220  and the inner wall of the second housing  178 . In this case, a rear portion (i.e., portion sufficiently spaced from the inlet  216 ) of the valve  220  is connected to the second housing  178 , while front and intermediate portions of the valve  220  are not connected. As a result, the valve  220  is freely displaceable or deflectable. 
     From the above, it will be understood that in the static state the pressure prevailing in the interiors of the high-pressure gas housing  104  and the gas generator housing  112  is substantially uniform. However, in a dynamic state, that is, after the ignition of the propellant grains  158 , the pressures in the respective chambers of the inflator  102  differ from each other to attain desired performance. When the propellant grains  158  are ignited, the propellant gas produced starts to flow into at least the second chamber  224  to increase the pressure therein. Since the inflator  102  has at least one bleed hole  162 , part of the propellant gas flows into the high-pressure gas housing  104  and brings about a slight increase of the pressure in the high-pressure gas housing. The rate of increase in the pressure within the second chamber  224  is preferably higher than that within the high-pressure gas housing  104 . The difference of pressure increase rate is produced because the propellant gas flows into each of the second chamber  224  and the high-pressure gas housing  104  and due to their relative volume difference. Because of this pressure difference, the valve  220  is pressed against the gas generator housing  112 , or more specifically, against the inner wall of that portion of the second housing  178  which corresponds to the valve  220 . As a result, the gas generator inlets  216  are shut off by the valve  220 , so that the high-pressure gas housing  104  is separated from the second chamber  224 . The aforementioned cantilever connection of the valve  220  permits displacement of the valve  220 . When the pressure in the second chamber  224  has reached a predetermined pressure value, the fluid pressure directly acting upon the main closing disk  190  opens, breaks, or destroys the disk  190 . Consequently, the disk  190  opens, creating a gas flow from the gas generator  108  to the diffuser  198  and the airbag. 
     After the main closing disk  190  opens to produce the gas flow to the airbag, the valve  220  maintains its position and thereby keeps shutting off the gas generator inlets  216  for a specified time. However, when a specified pressure difference is created between the high-pressure gas housing  104  and the second chamber  224 , the valve  220  is displaced by an urging force induced by the pressure difference, to open the gas generator inlets  216 . Where the valve  220  is formed in the manner described above, the free end of the valve  220  is displaced radially inward toward the center axis  120  or the valve is depressed in regions radially corresponding to at least the gas generator inlets  216 , thereby admitting desired gas flows through the gas generator inlets  216 . The valve  220  is, however, retained since it is connected to the second housing  178 . When the gas generator inlets  216  are opened, the gas starts to flow from the high-pressure gas housing  104  into the second chamber  224 . The valve  220  is movable from its first to second position. Namely, the valve  220  is, when in use, situated at the first position and substantially blocks the aforesaid flow. When the pressure in the high-pressure gas housing  104  has exceeded the pressure in the gas generator housing  112  by a predetermined amount, the valve  220  moves to the second position to admit the flow, the second position being located more radially inward than the first position. 
     In this embodiment, the initiator  128  is fitted in the initiator adapter  124  as mentioned above, and an outer periphery thereof can be brought to engagement along the inner periphery of an O-ring  132  for providing suitable sealing. The secondary closing disk  136  is provided to separate the initiator  128  from the pressurized gas contained in the gas generator  108 . 
     When a suitable signal indicative of the need to expand the airbag is detected by a detector (sensor), the initiator  128  is activated. Activation of the initiator  128  ruptures the secondary closing disk  136  and ignites the igniting agent (booster agent)  140 , which in turn ignites the propellant grains  158 , and the combustion of the propellant grains  158  produces propellant gas within the first chamber  154 , then activates the inflator  102  as mentioned above to break the main closing disk  190 , so that the gas flow delivers required gas to the airbag through the diffuser ports  200  of the diffuser  198  as indicated by the arrow in FIG.  1 . 
     According to the present invention, the aforementioned initiator adapter  124  is formed of a boss  101  having a flange  100  and an end face of planer shape. The flange  100  facilitates the mounting of the inflator  102  to an airbag module  300 . A pressurized gas charging hole  103  is formed in a planar end face  101   a  of the boss  101 , and a seal pin  105  is inserted into the charging hole  103  and welded thereto after the gas is charged. With this structure, the pin can be reliably inserted into the charging hole before the gas charging, whereby gas leak is prevented from being caused due to displacement. 
     FIG. 2 is an enlarged longitudinal sectional view of the initiator adapter  124 . The flange  100  is attached to the airbag module  300 , and since the airbag module has a whirl-stop and positioning mechanism and also the flange  100  is provided, the mountability improves. The gas charging hole  103  is provided with a planar gas seal, so that gas sealing is facilitated at the time of charging. Also, since welding is performed on a plane with the inflator  102  set upright, welding in the process is easy and welding reliability improves. 
     The boss  101  shown in FIG. 2 incorporates the O-ring  132  fitted in an insertion hole for the initiator  128 , and after the O-ring  132  is incorporated in the boss  101 , the initiator  128  is inserted. That is, there is a gap provided between the inner diameter of the O-ring and the outer diameter of the initiator to facilitate the insertion, and sealing is achieved by depressing the O-ring on the initiator flange surface. This lessens the possibility of the O-ring  132  being twisted and also facilitates automatic mounting. 
     Referring now to FIGS. 3 to  5 , an embodiment constructed such that a connector protection cover is fitted on the flange of the boss  101  characterizing the inflator  102  of the present invention will be described. 
     In FIG. 3, a connector  400  is connected to the initiator  128 , which is fitted in the initiator insertion hole of the boss  101  and fixed thereto by crimping, and a connector cover  401  is fitted over the connector  400 . The connector cover  401  deforms to receive the flange of the boss  101  and has connector cover hooks  402  thereof that hook  100  onto the edge of the flange  100  for engaging therewith, as shown in FIG. 4, thus eliminating the need for separate members such as screws. 
     Also, the flange  100  has a notch  100   b  cut in part thereof and protuberances  301  are formed on a corresponding portion of the module case  300 , so that they serve as positioning means for the inflator  102  when the inflator is fastened by nuts. The connector cover  401  is mounted on the end flange  100  of the boss  101  of the inflator  102 , as shown in FIG. 5, wherein  402  denotes connector cover hooks and  403  denotes a connector cover whirl-stop fitted in a groove  103  of the flange  100 . 
     The connector cover described above prevents the connector section from touching the mounting section when the inflator is mounted on a vehicle, and thus resulting contact failure or conduction failure can be eliminated. Also, since dust can be kept from the vicinities of the connector for a long period of time, conduction failure does not occur. 
     When the inflator is mounted to the module case and fastened thereto by nuts, the notch cut in part of the flange and the protuberances formed on the corresponding portion of the module case engage with each other, so that the inflator does not rotate but can be fixed in a predetermined oriented position.