Abstract:
An inflator for an airbag includes a container defining and outer surface and an inner compartment. A plurality of igniters are disposed within the inner compartment and are operably associated with a gas-generating unit. Each gas-generating unit is formed by a pair of matched stamped housings. Bushing separate and secure the gas-generating units in place along the outer surface of the container. Each gas-generating unit defines an annular chamber filled with gas generating material. Each of the igniters within the container are independently ignitable and are mechanically isolated from each other to prevent actuation of one igniter in response to the actuation of an adjacent igniter. The igniters are independently actuated to control the magnitude of inflation force of the airbag.

Description:
RELATED APPLICATIONS  
       [0001]    This application claims priority to U.S. Provisional Application Serial No. 60/367,644; filed on Mar. 26, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates to an airbag assembly for a motor vehicle and specifically to a variable inflation force inflator for an airbag assembly.  
           [0003]    Typically, an airbag assembly includes an airbag cushion and an inflator. Conventional inflator assemblies include a detonator to trigger a gas-producing chemical. Triggering the gas-producing chemical produces a large quantity of rapidly expanding gas that inflates the airbag cushion. The inflator is typically triggered electrically by way of an electronic control module positioned within a motor vehicle. The rapidly expanding gas that inflates the airbag cushion exerts a large force in a relatively short duration of time. This large force is a product of the speed in which an airbag must fully inflate in order to provide impact prevention to occupants of the vehicle during a collision.  
           [0004]    The force of inflation is set at a level such that an occupant of normal size and weight will not be injured. The required force to inflate an airbag cushion varies depending on the specific size and weight of the occupant. Injury to occupants is a design consideration taken into account when determining the magnitude of airbag inflation force.  
           [0005]    Warnings, along with devices that simply turn the air bag off upon sensing specific conditions are currently in use to warn and protect against possible injury. In some instances a simply switch is installed to turn off the airbag. Other devices sense the size or weight of the occupant and activate the airbag only under a predefined set of conditions. It is well proven that airbag cushions provide an additional level of safety to an occupant during a collision. Devices that disable the airbag remove this level of safety to the possible detriment of smaller occupants.  
           [0006]    For this reason, it is desirable to develop an airbag assembly that can inflate at various force levels such that the safety benefits of an airbag cushion can be used for occupants of all sizes.  
         SUMMARY OF THE INVENTION  
         [0007]    An embodiment of this invention is an inflator for an airbag assembly including a plurality of independently actuatable gas generating units to vary inflation force of an airbag cushion.  
           [0008]    An embodiment of this invention includes a plurality of gas generating units mounted to an igniter holder. Each gas-generating unit includes an outer periphery including a plurality of gas output openings. The igniter holder is generally a cylinder defining an outer surface and an inner cavity. Igniters are disposed within the inner cavity at discrete locations along an axis. Each of the igniters are electrically connected to a control unit by way of electrical leads. The igniters are mechanically isolated from each other to prevent actuation of one igniter in response to the actuation of an adjacent igniter.  
           [0009]    In one embodiment, the igniters are isolated by a hardenable compound packed into the igniter holder. Alternatively, interior walls are disposed within the cavity and between the igniters to separate the igniters and prevent actuation of one igniter from setting off an adjoining igniter.  
           [0010]    Each gas-generating unit is formed from a first and second stamped metal housing. The first and second stamped housings include overlapping tab sections at the contact point therebetween. The overlapping tab sections seal a compartment formed between the first and second metal housings. The tab sections are not mechanically attached to each other. Instead, the housings are forced into contact and remain in contact by way of pressure applied from a securing member attached to the end of the igniter holder.  
           [0011]    The compartment formed between the first and second metal housings includes the pyrotechnic compound and a gas filter. The compartment includes an angle alpha between the first and second metal housings, such that the width decreases as the perpendicular distance from the axis increases so that gas generated by the pyrotechnic compound will be forced through the gas filter. To minimize heat from one gas-generating unit from igniting an adjacent gas-generating unit a thermal screen is disposed between each gas-generating unit.  
           [0012]    The inflator of this invention preferably includes three gas-generating units of differing size and power. The power correlates to the amount of pyrotechnic material disposed in each compartment. A controller is used to selectively ignite each gas-generating unit based on various parameters sensed within the motor vehicle  
           [0013]    The inflator assembly of this invention includes multiple gas-generating units or chambers including an individually actuated igniter that allows control over inflation of the airbag cushion to vary the magnitude of force exerted by the airbag cushion during inflation. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:  
         [0015]    [0015]FIG. 1 is a perspective view of an inflator for an airbag;  
         [0016]    [0016]FIG. 2 is a cross sectional view of one embodiment of the inflator;  
         [0017]    [0017]FIG. 3 is a cross sectional view of another embodiment of the inflator;  
         [0018]    [0018]FIG. 4, is a cross sectional view of one embodiment of mounting an igniter  
         [0019]    [0019]FIG. 5A is a schematic view of one configuration of the gas generating units;  
         [0020]    [0020]FIG. 5B is a schematic view of another configuration of the gas generating units; and  
         [0021]    [0021]FIG. 5C is a schematic view of another configuration of the gas generating units. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, an inflator for an airbag assembly is generally indicated at  10  in FIG. 1. The inflator  10  includes a plurality of gas generating units  18  mounted to an igniter holder  14 . Preferably, the gas generating units  18  are disposed annularly about an axis  32 . Each of the gas generating units  18  includes an outer periphery including a plurality of gas output openings  24 . Although preferably each gas generating unit  18  extends about the entire circumference of the igniter holder  14 , it is within the contemplation of this invention that the gas generating units extend about only a portion of the igniter holder  14 .  
         [0023]    Referring to FIG. 2, the gas-generating unit  18  is shown in cross section. The igniter holder  14  is generally a cylinder defining an outer surface  64  and an inner cavity  66 . Igniters  12  are disposed within the inner cavity  66  at discrete locations along the axis  32 . Each of the igniters  12  are electrically connected to a control unit  76  by way of electrical leads  52 . The igniters  12  are mechanically isolated from each other to prevent actuation of one igniter  12  in response to the actuation of an adjacent igniter  12 . Preferably, the igniters  12  are isolated mechanically by way of a self-hardening compound  44  within the cavity  66  of the igniter holder  14 .  
         [0024]    Referring to FIG. 3, an alternate method of mechanically isolating the igniters  12  includes a plurality of inner walls  56  disposed between adjacent igniters  12 . Each of the inner walls  56  includes an opening for the electrical leads  52 . As appreciated, the use of the inner walls  56  can be used in combination with the use of the self-hardening compound  44 . Further, the inner walls  56  provide additional reinforcement of the igniter holder  14 .  
         [0025]    Referring to FIG. 4, another alternate method of isolating the igniters  12  is shown and includes a housing  58 . Each of the igniters  12  are built into the housing  58  and embedded into the igniter holder  14  at an igniter opening  22 . The housing  58  can be mounted by any means known by one skilled in the art to the igniter holder  14 . Installation of the igniter housings  58  allows for replacement of a specific igniter independent of other igniters contained with the igniter holder.  14 .  
         [0026]    Referring to FIG. 2, the gas generating units  18  are secured to the outer surface of the igniter holder  14  by sealing bushings  42 . The sealing bushings  42  provide for the assembly and construction of each of the gas generating units  18  without the use of any type of heat generating securing means such as spot welding or the like beside the pyrotechnical material  26 . It is desirable to minimize the use of heat producing assembly processes to prevent unwanted ignition of the pyrotechnic material  26 . Each of the gas generating units  18  includes a quantity of pyrotechnic material  26  that generates the explosive gas to immediately inflate the airbag. Each sealing bushing  42  includes an opening  62  corresponding to one of the igniter openings  22  and first opening  20 .  
         [0027]    The gas generating units  18  include first and second stamped metal housings  38 , 40 . Each stamped housing  38 , 40  includes a length  36  and a width  34 . The width  34  of each metal housing  38 , 40  is positioned generally parallel to the axis  32  and the length  36  is generally positioned transverse to the axis  32 . The first and second metal housings  38 , 40  include overlapping tab sections  60  at a contact point therebetween. The overlapping tab sections  60  provide a seal to prevent gas from discharging between the first and second housings  38 , 40 . Note that the tab sections  60  may or may not be mechanically attached to each other, the contact point between the first and second metal housings  38 , 40  are held together by the sealing bushings  42 , if bushing of sufficient strength are used.  
         [0028]    A fastening member  68  secures the metal housings  38 , 40  and the sealing bushings  42  to the outer surface  64  of the igniter holder  14 . Preferably, each of the sealing bushings  42  slides onto the outer surface  64  of the igniter holder  14  and are secured by a fastening member  68 . Preferably, the fastening member includes threads that engage a threaded portion of the igniter holder  14 . Alternatively, each sealing bushing  42  may include threads that engage threads disposed on the outer surface of the igniter holder  14 . It is within the contemplation of this invention to use any type and amount of fastening member as known to one skilled in the art.  
         [0029]    Referring to FIG. 5C, another embodiment of the gas generator  18  is shown including an igniter  70  with a stepped outer surface  72 . The stepped outer surface  72  provides an alternate means of securing of the metal housing sections  38 , 40  to the igniter holder  70  (See FIG. 3). In this embodiment, the metal housing sections  38 , 40  are constrained between a shoulder  74  and an adjacent gas-generating unit  18 . One gas generating unit abuts the shoulder, a second gas generating unit abuts the second shoulder and the first generating unit, and subsequent gas generating unit would abut the adjacent gas generating unit and finally be secured by a securing member that fastens to the igniter holder.  
         [0030]    Referring to FIG. 2, a compartment  30  formed between the first and second metal housings includes the pyrotechnic compound  26  and a gas filter  28 . The compartment  30  is annularly shaped about the axis  32 . Preferably, the compartment  30  includes an angle alpha between the first and second metal housings  38 , 40  such that the width  34  decreases as the perpendicular distance from the axis  32  increases. Configuring the compartment of the gas generator  18  in this manner ensures that gas generated by the pyrotechnic material  26  will be forced through the gas filter  28 . As gas is generated and pushes outward toward the gas output openings  24 , the gas filter  28  is compressed to prevent gas from blowing by the gas filter  28 .  
         [0031]    To minimize heat from one gas-generating unit  18  from igniting an adjacent gas-generating unit  18  a thermal screen  48  is disposed between each gas-generating unit  18 . Preferably, each thermal screen  48  is disk shaped and formed from a material capable of shielding enough heat emitted from one gas-generating unit  18  such that an adjacent heat generating unit  18  is not ignited.  
         [0032]    The gas generating units  18  shown in FIG. 2 are hyperbolic shapes rotated about the axis  32 . Referring to FIGS.  5 A-C, other generally hyperbolic shapes are schematically shown. FIG. 5A illustrates an alternate shape for the gas-generating units including a modified hyperbolic shape having a curved surface.  
         [0033]    [0033]FIG. 5B illustrates another embodiment of the gas-generating unit  18  of a different configuration. In this configuration, gas-generating units  18  of differing size are arranged to control inflation of the airbag. The size of each gas-generating unit  18  correlates to the inflation force derived from gas expelled through the gas output openings  24 . The largest and most powerful gas-generating unit  18  is positioned between two gas-generating units  18  of lesser size and power. Placement of gas-generating units  18  of a specific power level allow for control of the inflation force of the air bag. It should be understood that it is within the contemplation of this invention to use any shape known to one skilled in the art for the gas generating units  18 .  
         [0034]    Referring to FIG. 2, the inflator of this invention preferably includes three gas-generating units  18  of differing size and power. The power correlates to the amount of pyrotechnic material disposed in each compartment. Preferably, the relationship between each of the gas-generating units  18  is 1:2:4. This combination provides eight possible levels of power to deploy an airbag cushion. As appreciated, any combination of relationship between gas-generating units  18  as would be known to a worker skilled in the art.  
         [0035]    The controller  76  is used to selectively ignite each gas-generating unit  18  based on various parameters sensed within the motor vehicle. Some of the parameters may include occupant weight, position and severity of collision. The controller  76  tailors actuation of the igniters  12  and thereby deployment of the airbag cushion to specific vehicle and occupant conditions in order to optimize protection obtained from the airbag. Further, it is possible to sequentially activate the gas generating units  18  to provide sequential ramping up of air bag inflation force to compensate for specific vehicle and occupant characteristics. It is within the contemplation of this invention to use gas-generating units  18  of various power and combinations as required to optimize airbag inflation depending on specific vehicle conditions.  
         [0036]    The foregoing description is exemplary and not just a material specification. The invention has been described in an illustrative manner, and should be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications are within the scope of this invention. It is understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.