Patent Publication Number: US-2006006632-A1

Title: Gas generator for air bag

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims priority on U.S. Provisional Application No. 60/579,681 filed on Jun. 16, 2004, and Japanese Patent Application No. 2004-166306 filed in Japan on Jun. 3, 2004, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a gas generator suitable for use in an air bag system installed in an automotive vehicle.  
      2. Description of the Related Arts  
      An air bag system is known as a device for protecting passengers from impact when a vehicle collides. In an air bag system, a gas is introduced into an air bag instantaneously so that the air bag inflates, and hence the air bag system functions as buffering means between the passenger and the constitutional components of the vehicle (the steering wheel, for example).  
      In recent years, air bag systems for the driver side, the front passenger side, side collisions, a vehicle roll, and so on have been proposed with the aim of improving passenger safety against the impact that is generated during a vehicle collision. A gas generator used in these air bag systems should satisfy a condition of being able to generate gas instantaneously, but with respect to the system for side collisions in particular, the gap between the constitutional components of the vehicle and the passenger is narrow, and hence the period from perception of the impact to the start of gas discharge into the air bag has to be short. Moreover, the gas generator should have a thin structure in the width direction due to problems regarding the mounting space for the gas generator. Likewise in air bag systems for use during vehicle roll (curtain air bags), the gas generator requires a thin structure in the width direction due to problems regarding mounting space.  
      U.S.-A No. 2002/0109339 may be cited as background art relating to the present invention.  
     SUMMARY OF THE INVENTION  
      To solve these problems, an aspect of the present invention is to provide a gas generator for an air bag, in particular a gas generator for a side (side collision protection) air bag, a gas generator for a curtain air bag, or another small gas generator or the like, which has a simple structure and is suitable for mounting in particularly small spaces.  
      The present invention is described as being used in a gas generator for an air bag for side collisions or a gas generator for a curtain air bag, in which the period from perception of the collision to the start of gas discharge should be short. However, the present invention is not necessarily limited thereto, and may be used in gas generators for air bags for a driver side, a front passenger side, or a knee-bolster.  
      An aspect of the present invention is to provide a gas generator for an air bag wherein, in an inflator housing comprising a bottle portion storing a pressurized medium and a diffuser attached to one end portion of the bottle portion and formed, in an axial direction thereof, with a gas outlet being closed by a rupturable plate, an ignition means for rupturing the rupturable plate is fixed to an igniter collar to face the rupturable plate, and attached to the diffuser, a first gas discharge hole is formed in the igniter collar such that the pressurized medium discharged through the gas outlet is discharged in a substantially axial direction of the inflator housing, and the ignition means and first gas discharge hole are off-center respectively from the center of the igniter collar.  
      Gas generators include those using only pressurized gas (stored gas generators), those using a solid gas generating agent (pyrotechnic gas generators), and those using both pressurized gas and a solid gas generating agent (hybrid gas generators). Stored gas generators and hybrid gas generators comprise a rupturable plate for sealing the pressurized medium in the interior of the housing. When the rupturable plate is ruptured, discharge of the gas (ejection of the gas into the air bag) begins. By means of this mechanism, the period from perception of an impact to the start of gas discharge is short, which is advantageous for the aforementioned hybrid gas generator or stored gas generator. It is therefore assumed that the present invention relates to stored gas generators and hybrid gas generators.  
      The pressurized medium is sealed inside the bottle portion. One end of the bottle portion is closed, and the diffuser is attached to the opposite end portion, thus forming the inflator housing. Here, the term “one end side of the bottle is closed” signifies that a component which is open prior to assembly of the gas generator is closed by a spinning method or Mannesmann method, or by attaching a separate member. Alternatively, a commercially available component having one closed end portion prior to assembly of the gas generator may be used.  
      The opposite end portion of the bottle is open, and in this case, the diffuser is attached thereto. A gas outlet for discharging the pressurized medium in the bottle is formed in the diffuser, and preferably disposed to open in the axial direction of the bottle. The gas outlet is blocked by the rupturable plate prior to an operation of the gas generator. Instead of blocking the gas outlet in the diffuser with the rupturable plate, a part of the opposite end portion of the bottle may be opened and then closed by the rupturable plate.  
      Further, the igniter collar to which the ignition means for rupturing the rupturable plate are attached is incorporated into the diffuser. At this time, the ignition means is disposed to face the rupturable plate. The first gas discharge hole is formed in the igniter collar. The first gas discharge hole is formed in the igniter collar such that when the igniter collar is attached to the diffuser, the pressurized medium is discharged in the substantially axial direction of the housing. The first gas discharge hole may be formed in the thickness direction of the igniter collar, for example. Note that the ignition means and the first gas discharge hole are off-center from the center of the igniter collar. By disposing the ignition means and first gas discharge hole in this manner, the width of the gas generator in the radial direction can be reduced, and hence the gas generator can be mounted even in the narrow spaces of the vehicle. Here, the term “substantially axial direction” indicates that the axis of the housing and the axial direction of the first gas discharge hole are essentially parallel, but as long as the pressurized medium flows substantially in the axial direction of the housing, these two axes may intersect and still be included in the term “substantially axial direction” in the present invention.  
      Hence, the gas outlet is formed to open in the axial direction of the housing and closed by the rupturable plate, while the ignition means is disposed to face the rupturable plate, and therefore the ignition means is attached from the substantially axial direction of the housing. As a result, no components protrude in the width direction (radial direction) of the gas generator, and hence the gas generator is released from mounting space restrictions.  
      Moreover, since the first gas discharge hole is formed in the igniter collar and opened such that the gas is discharged in the substantially axial direction of the housing, no components in the gas discharging part protrude in the width direction of the housing, and therefore the gas generator can be mounted easily in a comparatively narrow mounting space.  
      Note that the attachment orientation of the ignition means facing the rupturable plate is preferably set such that the central axis of the ignition means is parallel to the axial direction of the inflator housing. However, there are no particular limitations on the orientation of the ignition means as long as the ignition means is capable of rupturing the rupturable plate, and as long as no protrusions are formed in the width direction of the housing.  
      Further, in the gas generator of the present invention, the ignition means is preferably constituted only by an electric igniter which activates upon reception of an ignition signal, the electric igniter is preferably formed integrally with the igniter collar using a resin, and the igniter collar is preferably attached to the diffuser by crimping.  
      By constituting the ignition means only by an electric igniter, the constitution of the gas generator is simplified. Further, by fixing the igniter to the igniter collar with resin, the igniter assembly (a combination of the igniter collar and igniter) can be produced easily.  
      Moreover, by fixing the igniter collar to the diffuser by crimping, welding heat and the like are not used, and hence construction can be performed safely. Particularly in cases where the electric igniter and the joining locations are in close proximity, welding heat may cause inadvertent ignition or melting of the resin. With a crimping method, however, such problems do not arise.  
      Also in the gas generator of the present invention, positioning means is preferably formed on at least one of the igniter collar and the diffuser so that the electric igniter and the rupturable plate are oriented to face each other.  
      In so doing, the igniter collar and diffuser can be assembled and positioned easily. The positioning means may be constituted by forming a convex portion (or concave portion) in the igniter collar and forming a corresponding concave portion (or convex portion) in the diffuser such that the igniter collar can be set in only one orientation in relation to the diffuser, or by forming the entire igniter collar in a gourd shape, a deformed elliptical shape, a non-symmetrical shape, and so on, and forming the diffuser in a corresponding shape.  
      Further, in the gas generator of the present invention, a tubular gas discharge port having one closed end portion is preferably also attached to the part of the igniter collar in which the first gas discharge hole is formed, and a large number of second gas discharge holes is preferably formed in the peripheral wall surface of the gas discharge port near to this closed end portion at equal intervals in the circumferential direction.  
      By using the tubular gas discharge port, connection to the air bag is simplified. The second gas discharge holes formed in the peripheral wall surface of one end portion of the gas discharge port are preferably disposed to counterbalance thrust. In so doing, the gas generator can be prevented from shooting forward like a rocket even when operated unintentionally during conveyance. Note that when the gas discharge port is fixed to the igniter collar, this fixing operation may be performed using welding (a well-known welding method such as resistance welding), a method of forming a screw on the gas discharge port and screwing the gas discharge port to the igniter collar, or a method of providing an outward-facing flange on the open end portion of the gas discharge port, providing an annular protrusion on the igniter collar, and fixing the two together by crimping.  
      The entirety or part of the gas discharge port and the igniter collar may be formed from an integral component. For example, such a structure may be employed that the peripheral wall portion including an open tip end is provided in the igniter collar such that the peripheral wall portion surrounds the first gas discharge hole, and the gas discharge port which has one end closed portion and formed with second gas discharge holes on the peripheral wall portion is fixed to it by using the method described above.  
      Alternatively, such a structure may be employed that the tip end of the peripheral wall portion thereof, extending from the first gas discharge hole, is open, the second gas discharge holes are formed in the peripheral wall portion toward this open end portion, and the open end is blocked at the closure of a separate member.  
      Also in the gas generator of the present invention, a preferable structure of the electric igniter is that an ignition charge is disposed in the electric igniter on a header portion carrying a heat generating portion which is caused to generate heat by an ignition current, the ignition charge being disposed in contact with the heat generating portion, and that the electric igniter is preferably closed tightly by a bottomed cup attached to the header portion, the bottom of the bottomed cup serving as a fragile site.  
      The heat generating portion that is caused to generate heat by an ignition current is formed in the header portion of the igniter, and the ignition charge is disposed on the header portion in contact with the heat generating portion and sealed tightly by the bottomed cup. The fragile portion ruptures and breaks at least initially during an activation of the electric igniter, but it is preferable that parts other than the fragile portion do not rupture and break even after the igniter activation. To form the fragile site, at least part of the bottom of the cup may be formed more thinly than the peripheral wall part so that only the bottom part breaks easily, or a notch may be formed in the bottom of a cup having a constant thickness. Substantially identical effects to those of a cup having a thicker peripheral wall part are exhibited when the cup thickness is constant and an annular reinforcement is disposed on the inside of the cup (on the header).  
      By providing the fragile site on at least part, or the entirety, of the cup bottom, the generation direction of the flame, impact wave, and high-temperature gas produced when the ignition charge is ignited can be restricted. By placing the rupturable plate in this direction, the energy generated by the igniter can be concentrated on the rupturable plate, and therefore the inflator can be operated reliably.  
      By means of the present invention, problems relating to the mounting space of a gas generator can be solved effectively. Even when mounting space is restricted, particularly in the case of a gas generator for a side collision or curtain air bag system, the gas generator can be mounted and fixed securely. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a cross-sectional view of a gas generator for an air bag of the present invention;  
       FIG. 2  is an enlarged cross-sectional view of an igniter collar part of the present invention;  
       FIG. 3  is an enlarged view of the igniter collar part of the present invention; and  
       FIG. 4  is an enlarged view showing another aspect of the igniter collar part of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present invention will be described in detail below using the drawings which illustrate an embodiment of the present invention.  FIG. 1  is a cross-sectional view showing an embodiment of a gas generator  100  of the present invention.  
      In the gas generator  100  of the present invention, a bottle  10  storing a pressurized medium  11  for inflating an air bag has an opening portion  12  on one end, the other end thereof is closed, and the pressurized medium, constituted by an inert gas such as argon or helium, nitrogen gas, or carbon dioxide, is charged into an interior space  16  at a charging pressure of approximately 30,000 to 70,000 kPa. The bottle  10  has a circular cross section in the width direction, and the opening portion  12  takes a similar circle form. However, there are no particular limitations on the forms thereof, and hence these cross sectional forms may be polygonal. The shape of the housing is preferably symmetrical with respect to a central axis  13 .  
      A known gas cylinder may be used as the bottle  10 , or the bottle  10  may be produced by subjecting a pipe to swaging, spinning, or Mannesmann processing to close one end (the end portion on the left side of  FIG. 1 ) thereof.  
      A diffuser  20  is attached to the opening portion  12  of the bottle  10 . In the diffuser  20 , a gas outlet  21  for discharging the pressurized medium in the interior of the bottle  10  is blocked by a rupturable plate  22 . The rupturable plate  22  is fixed to an inwardly protruding part  23  formed on the gas outlet  21  of the diffuser  20  by a welding method such as resistance welding, and a central portion of the rupturable plate  22  is caused to expand outward by the pressure of the pressurized medium  11  in the interior of the bottle  10 .  
      Further, a charging nozzle  24  for charging the pressurized medium into the interior of the bottle is formed in the diffuser  20 . Following charging of the pressurized medium, the charging nozzle  24  is sealed with a pin  25 . The pin  25  is fixed to the diffuser  20  by welding. As a result, the pressurized medium  11  is tightly sealed in the interior (interior space  16 ) of the bottle  10 .  
      Alternatively, the charging nozzle  24  may be provided on the bottle  10  and sealed by the pin  25  in the same manner. Alternatively, a structure is possible in which the charging nozzle  24  is not provided in either the bottle  10  or the diffuser  20  and the pressurized medium is charged through the opening portion  12  of the bottle  10 . In this case, the gas outlet  21  is sealed in advance by the rupturable plate  22 , the diffuser  20  is placed in the vicinity of the opening portion  12 , the pressurized medium  11  is charged, and once a predetermined amount of the pressurized medium  11  has been charged, the opening portion  12  is closed by the diffuser  20 . In the gas generator  100  of  FIG. 1 , the diffuser portion  20  (with the gas outlet  21  blocked by the rupturable plate  22 ) is connected to the bottle  10 , whereupon the pressurized medium  11  is charged through the gap for the pin  25  attached to the charging nozzle  24  (the gap formed between the pin  25  and the charging nozzle  24 ), and then the pin  25  is welded to the diffuser  20  to close the nozzle completely.  
      The bottle  10  and diffuser  20  may be connected by welding, or by providing a male screw portion on the outer peripheral surface of the end portion of the bottle  10 , providing a female screw portion on the inner peripheral surface of the end portion of the diffuser portion  20 , and screwing the male screw portion and female screw portion together.  
      An igniter  26  having an ignition charge is provided in the diffuser portion  20  as rupturing means for rupturing the rupturable plate  22 . The igniter  26  is fitted into and attached to the diffuser  20 . When attaching the igniter  26  to the diffuser  20 , the igniter  26  is first attached to an igniter collar  27 , and then the igniter collar  27  is attached to an opening portion  28  formed in the diffuser  20 . At this time, the igniter  26  is attached to face the rupturable plate  22 . An annular protruding portion  29  is formed on a peripheral wall portion of the igniter collar  27 . The annular protruding portion  29  is disposed to abut against a stepped portion  31  of the diffuser  20 , and then fixed thereto by crimping  30 . In  FIG. 1 , the igniter  26  is disposed in an off-center position from the center of the igniter collar  27 . This is to enable the igniter  26  to be attached in a position facing the rupturable plate  22  (gas outlet  21 ), which is disposed in an off-center position from the center of the diffuser  20 . In so doing, the energy generated by the igniter  26  impinges on the rupturable plate  22  efficiently, and hence the rupturable plate  22  can be ruptured reliably. Note, however, that as long as the rupturable plate  22  is ruptured reliably by the igniter  26 , the igniter  26  may be disposed at an incline to the rupturable plate  22 , or the respective centers of the rupturable plate  22  and igniter  26  may be slightly offset.  
      When the igniter collar  27  is attached to the diffuser  20 , the attachment operation should be performed such that the igniter  26  faces the rupturable plate  22 , and it is therefore preferable that positioning means be formed. The positioning means serve to restrict the attachment orientation of the igniter collar  27  to the diffuser  20 , and is obtained, for example, by forming a convex portion (or concave portion) on the periphery of the igniter collar  27  and forming a corresponding concave portion (or convex portion) on the diffuser  20 . Alternatively, by forming the entire igniter collar  27  in a non-symmetrical shape and forming the opening portion  28  of the diffuser  20  in a corresponding shape, the igniter collar  27  can be attached to the diffuser  20  in a fixed orientation. These positioning means will be described later.  
      A first gas discharge hole  32  is also formed in the igniter collar  27  to discharge the pressurized medium that passes through the gas outlet  21  to the exterior of the gas generator. The first gas discharge hole  32  is also disposed in an off-center position from the center of the igniter collar  27 . More specifically, the igniter collar  27  is attached with the igniter  26  for rupturing the rupturable plate  22 , and formed with the first gas discharge hole  32  for discharging the pressurized medium from the interior of the bottle  10  to the outside, and by disposing the igniter  26  and first gas discharge hole  32  in this manner, the dimension of the gas generator  100  in the height direction (the vertical direction in  FIG. 1 ) can be suppressed. As a result, the entire gas generator  100  is reduced in size (reduced in thickness) such that the gas generator can be mounted on parts of the vehicle interior which have a restricted gas generator mounting space. The outer form of the diffuser  20  is preferably smaller than the maximum outer diameter of the bottle.  
      Due to the disposal relationships of the gas outlet  21  and rupturable plate  22  with the first gas discharge hole  32 , the flow of pressurized medium through the interior of the diffuser  20  is complicated (zigzag). Hence, even if fragments of the rupturable plate or the like flow together with the pressurized medium, these fragments can be trapped easily in the interior of the diffuser  20 .  
      Further, a gas discharge port  40  having one closed end  41  is connected to the igniter collar  27 , and a plurality of second gas discharge holes  42  is formed on the peripheral wall portion on the end portion side of the closed end  41 . By connecting the air bag (not shown) to this part, the pressurized medium can be discharged from the gas generator  100  into the interior of the air bag. The gas discharge port  40  is fixed and connected to the igniter collar  27  at an open end portion  43  thereof by a welding method such as resistance welding. Note that a convex portion  44  is formed on the gas discharge port  40 , and by attaching the air bag to engage with this convex portion  44  and fixing the air bag around the peripheral wall portion of the gas discharge port  40  using a band, the air bag can be prevented from become disengaged from the gas discharge port during an operation.  
      Note that a sealing member such as an O-ring may be disposed on the contact surface between the igniter collar  27  and diffuser  20  (between the protruding portion  29  and stepped portion  31 ), for example, to ensure that all of the pressurized medium inside the bottle  10  is discharged through the first gas discharge hole  32  (and supplied only to the air bag) during an operation of the gas generator  100 .  
      The gas discharge port  40  is attached such that the central axis of the bottle  10  (shown by the dot/dash line in  FIG. 1 ) and the central axis of the gas discharge port  40  are parallel.  
      The gas discharge port  40  also functions as a filter for removing foreign matter (for example, fragments of the rupturable plate  22 ) by means of the second gas discharge holes  42  formed on the other end side thereof. Alternatively, the opening diameter of the second gas discharge holes  42  may be formed to be larger, and punched metal, expanded metal, wire mesh, or the like formed with a large amount of small holes may be disposed on the inside of the second gas discharge holes  42  to serve as a filter. There are no particular limitations on the location of the filter as long as foreign matter in the flowing pressurized medium can be removed.  
      The second gas discharge holes  42  are preferably provided uniformly around the peripheral wall portion of the gas discharge port  40 . In so doing, thrust generated when the gas generator  100  is operated unintentionally during transport or conveyance is counterbalanced, and hence the gas generator can be prevented from shooting forward like a rocket.  
      Note that in the embodiment shown in  FIG. 1 , the total opening area of the second gas discharge holes  42  is set to be larger than the opening area of the first gas discharge hole  32 . Moreover, the first gas discharge hole  32  is set to be smaller than the gas outlet  21 , and thus the outflow amount of the pressurized medium is regulated by the first gas discharge hole  32 .  
      Also in the embodiment of  FIG. 1 , by forming the second gas discharge holes  42  at a remove from the end  41  of the gas discharge port  40  (preferably, at a distance equal to or greater than the radius of the rupturable plate  22 ), the end  41  part functions as a pocket for trapping foreign matter (fragments of the rupturable plate  22 , for example), and hence this is preferable.  
      To enhance the rupturability of the rupturable plate  22  in the gas generator  100  of this embodiment, an annular portion  37  is provided to envelop the ignition charge  36  from the periphery thereof as shown in  FIG. 2 , and the side of the annular portion  37  which faces the rupturable plate  22  is left open. The annular portion  37  is formed from the same material as a metallic header  39 , or may be formed integrally with the header  39 . A bridge wire (not shown) for generating heat by means of the ignition current is attached to the header  39 , and the ignition charge  36  is ignited by this bridge wire. The annular portion  37  provides directivity to a detonation wave generated by combustion of the ignition charge. Note that the reference numeral  38  denotes a cup for closing the opening of the annular portion  37 . To ensure that the part closing the opening portion of the annular portion  37  ruptures easily during an activation of the igniter  26 , the thickness of the cup may be adjusted (by making the bottom part of the cup thinner than the peripheral wall part), or a notch may be provided in the bottom part of the cup.  
       FIGS. 3 and 4  show examples in which positioning means are formed on the igniter collar  27  so that when the igniter collar  27  is attached to the diffuser  20 , the igniter  26  and rupturable plate  22  are disposed facing each other at all times. Both  FIG. 3  and  FIG. 4  show an outline of the structure shown in  FIG. 2  when seen from the right side of  FIG. 2 .  
      In the structure shown in  FIG. 3 , the igniter  26  and the first gas discharge hole  32  are formed on the circular igniter collar  27  on the upper side and lower side, respectively. Note that the reference numeral  26 ′ denotes an electroconductive pin for transmitting the ignition current to the igniter.  
      In  FIG. 3 , the protruding portion  29  is formed around the peripheral surface of the igniter collar  27 , and a positioning portion  40  is formed to protrude further than the protruding portion  29 . Meanwhile, a concave portion (not shown) corresponding to the protrusion of the positioning portion  50  is formed in the part of the diffuser  20  in which the igniter collar  27  is incorporated, and by disposing the igniter collar  27  in the interior of the diffuser  20  such that the positioning portion  50  fits to the concave portion, the igniter  26  and rupturable plate  22  are disposed to face each other at all times.  
      In  FIG. 4 , a part of the protrusion  29  formed around the peripheral surface of the igniter collar  27  is cut away, and this part acts as a positioning portion  51 . More specifically, a convex portion (not shown) corresponding to the cut-away portion of the positioning portion  51  is formed in the part of the diffuser  20  in which the igniter collar  27  is incorporated, and by disposing the igniter collar  27  in the interior of the diffuser  20  such that the positioning portion  51  fits to the convex portion, the igniter  26  and rupturable plate  22  are disposed to face each other at all times.  
      Next, an operation of the gas generator  100  of the present invention will be described. When installed in a vehicle, the gas generator  100  is installed as a system combining operating signal output means constituted by an impact sensor, a control unit, a module case accommodating the gas generator  100  and an air bag, and so on. The air bag is connected at the second gas discharge holes  42  part of the gas discharge port  40 .  
      First, when the vehicle receives an impact, an impact sensor receives the signal from the system, thereby operating the igniter  26  to ignite and burn the ignition charge such that the rupturable plate  22  is ruptured.  
      When the rupturable plate  22  ruptures, the gas outlet  21  opens, and hence the pressurized medium in the interior space  16  flows out through the first gas discharge hole  32 , into the gas discharge port  40 , and through the second gas discharge holes  42  to inflate the air bag.  
      The gas generator of the present invention may be used as a gas generator in an air bag system for use in side collisions, a curtain air bag system, and so on, or as a gas generator for a driver side air bag system, a front passenger side air bag system, a knee-bolster system, or an inflatable seat belt.  
      Note that the gas generator shown in  FIG. 1  uses only a pressurized medium, but the present invention may be applied to a hybrid type gas generator which also uses a solid gas generating agent.  
      The invention thus being described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.