Abstract:
The present invention provides an inflator for an inflatable restraint system in an automobile. The inflator includes an elongate inflator body containing a baffle tube that cools gases as they are shunted therethrough upon gas generator activation.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates generally to inflators for use in inflatable occupant restraint systems in motor vehicles and, more particularly, to baffle systems for replacing filters used in inflators to remove particulates from combustion gases and to cool the gases.  
         [0002]     Installation of inflatable occupant restraint systems, such as airbags, as standard equipment in all new vehicles has intensified the search for smaller, lighter and less expensive restraint systems. Accordingly, since the inflator used in such systems tends to be the heaviest and most expensive component, there is a need for a lighter and less expensive inflator.  
         [0003]     A typical inflator includes cylindrical steel or aluminum housing having a diameter and length related to the vehicle application and characteristics of a gas generant propellant contained therein. Inhalation by a vehicle occupant of particulates generated by propellant combustion-during airbag-activation can be hazardous. Thus, the inflator is generally provided with an internal, more rarely external, filter comprising one or more layers of steel screen of varying mesh and wire diameter. Gas produced upon combustion of the propellant passes through the filter before exiting the inflator. Particulate material, or slag, produced during combustion of the propellant in a conventional system is substantially removed as the gas passes through the filter. In addition, heat from combustion gases is transferred to the material of the filter as the gases flow through the filter. Thus, as well as filtering particulates from the gases, the filter acts to cool the combustion gases prior to dispersal into the airbag.  
         [0004]     However, the wire mesh filter assembly increases the weight and expense of the inflator. In addition, due to factors such as spatial constraints within the gas generator/inflator and/or the type of gas generant used, combustion of the gas generant may be incomplete when combustion products exit the combustion chamber, resulting in flaming of the combustion products as the gases exit the combustion chamber and enter the wire mesh filter. The porous structure of the wire mesh filter may be unable to contain the flaming combustion products.  
       SUMMARY OF THE INVENTION  
       [0005]     Various gas generant formulations have been developed in which the particulates resulting from combustion of the gas generant are substantially eliminated or significantly reduced. To solve the problems of reducing airbag inflator size, weight, cost and efficiency, the present invention obviates the need for a conventional filter by appropriate selection of a state of the art gas generant, or a smokeless gas generant if desired, and by incorporation of a baffle tube which cools the combustion gases prior to dispersal of the gases into an airbag. Obviating the need for a filter in an inflator allows the inflator to be simpler, lighter, less expensive and easier to manufacture.  
         [0006]     The baffle tube includes an inner annulus and an outer annulus exterior of and spaced apart from the inner annulus to define a baffle between the inner and outer annuli. A plurality of walls extends between the inner annulus and the outer annulus to connect the outer annulus to the inner annulus, partitioning the baffle into a series of adjacent baffle chambers.  
         [0007]     The baffle tube also provides an extended travel path for combustion gases flowing from the propellant chamber to discharge nozzles in the inflator, thereby allowing time for complete combustion of the gas generant in the inflator.  
         [0008]     In another embodiment, the present invention provides orifices formed in the inner annulus, the outer annulus, and the walls. The walls and the orifices formed in the walls divide the baffle into a series of adjacent fluidly-communicating baffle chambers. Gases flow out of the inner annulus orifice, then sequentially through the fluidly-communication baffle chambers, the out of the baffle via the outer annulus orifice. This arrangement enables the degree of cooling of the gases to be controlled. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is cross-sectional side view of an inflator incorporating a baffle member in accordance with the present invention;  
         [0010]      FIG. 2  is an end view of the baffle member incorporated into the inflator of  FIG. 1 ;  
         [0011]      FIG. 3  is a cross-sectional side view of the baffle member shown in  FIGS. 1 and 2  taken along section line  3 - 3  of  FIG. 2 ;  
         [0012]      FIG. 4  is an end view of a second embodiment of a baffle member in accordance with the present invention;  
         [0013]      FIG. 5  is a partial cross-sectional view of the baffle tube shown in  FIG. 4  taken along section line  5 - 5 ;  
         [0014]      FIG. 6  is a partial cross-sectional view of the baffle tube shown in  FIG. 4  taken along section line  6 - 6 ;  
         [0015]      FIG. 7  is a partial cross-sectional view of the baffle tube shown in  FIG. 4  taken along section line  7 - 7 ;  
         [0016]      FIG. 8  is a partial cross-sectional view of the baffle tube shown in  FIG. 4  taken along section line  8 - 8 ;  
         [0017]      FIG. 9  is cross-sectional side view of an inflator incorporating the embodiment of the baffle member shown in  FIG. 4 ; and  
         [0018]      FIG. 10  is a schematic representation of an exemplary vehicle occupant restraint system incorporating an inflator including a baffle tube in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0019]      FIG. 1  shows a gas generator or inflator  10 , in accordance with one embodiment of the invention. Inflator  10  includes a housing  12 , for example, an aluminum forging. In this embodiment, housing  12  is provided with at least one gas discharge nozzle  14 , or a plurality of gas discharge nozzles  14  arranged in at least one circumferentially and homolaterally extending row. Nozzles  14  may be circumferentially spaced apart substantially evenly. Housing  12  has an integral end closure  16  at one end and an end closure  20  at the opposite end that is crimped in place. A perforated propellant chamber  22  is centrally and longitudinally disposed within housing  12  for containment of propellant grains  24 . Propellant chamber  22  has a longitudinal axis L.  
         [0020]     The inside of the propellant chamber  22  may be provided with a burst foil covering perforations  11  of chamber  22  to facilitate pressure buildup and flame front propagation through propellant grains  24 . End closure  20  accepts an electrical squib  26  in fluid communication with propellant chamber  22  facilitating electric ignition of propellant grains  24 .  
         [0021]     A cap  90  abuts an end portion of propellant chamber  22  and an end portion of a baffle tube  30  (described in greater detail below) to aid in positioning and securing chamber  22  and tube  30  within housing  12 . Cap  90  is shaped so as to form an annular void  91  when seated with respect to chamber  22  and baffle tube  30 . Void  91  allows the passage of combustion gases between plenum  40  and a baffle formed in baffle tube  30 .  
         [0022]     The propellant  24  residing in propellant chamber  22  may be any known smokeless gas generant composition useful for airbag application and is exemplified by, but not limited to, compositions and processes described in U.S. Pat. Nos. 5,872,329, 6,074,502, 6,287,400, 6,306,232 and 6,475,312 incorporated herein by reference. As used herein, the term “smokeless” should be generally understood to mean such propellants as are capable of combustion yielding at least about 90% gaseous products based on a total product mass; and, as a corollary, less than about 10% solid products based on a total product mass. It has been generally found that filters as used in other inflator designs can be eliminated by using compositions having the described combustion characteristics. Other suitable compositions are set forth in the U.S. patent application Ser. Nos. 10/407,300 and 60/369,775, incorporated herein by reference.  
         [0023]     Referring again to  FIGS. 1, 2 , and  3 , a baffle tube  30  encloses propellant chamber  22  in a radially spaced relationship to propellant chamber  22 , thereby defining an annular plenum  40  extending between propellant chamber  22  and baffle tube  30 . In the embodiment shown, baffle tube  30  is arranged concentrically with propellant chamber  22 .  
         [0024]     Baffle tube  30  has an inner annulus  32  and an outer annulus  34  exterior of and spaced apart from inner annulus  32  to define a baffle extending between the inner and outer annuli. Inner annulus  32  has a first length D 1  and outer annulus  34  has a second length D 2 . First length D 1  is greater than the second length D 2 . At least one wall  38  extends between inner annulus  32  and outer annulus  34  to connect the outer annulus to the inner annulus. In the embodiment shown, a plurality of circumferentially spaced-apart walls  38  is formed to connect outer annulus  34  to inner annulus  32 . Also, as seen in  FIG. 3 , walls  38  are coextensive with a length D 2  of outer annulus  34 . In addition, as shown in  FIG. 2 , walls  38  partition baffle tube  30  into a series of parallel baffle chambers  41  extending along a length D 2  of baffle tube  30  between inner annulus  32  and outer annulus  34 .  
         [0025]     In the embodiment shown in  FIGS. 1-3 , baffle tube  30  is extruded from an aluminum alloy, although other, alternative materials and fabrication methods are also contemplated. Propellant chamber  22  and baffle tube  30  each have a substantially cylindrical cross-section. However, a wide variety of alternative cross-sectional shapes may be used in accordance with the design criteria and spatial constraints relating to a particular application. For example, propellant chamber  22  and/or baffle tube  30  may have rectangular cross-sections.  
         [0026]     In operation of the gas generator, and referring again to  FIGS. 1-3 , upon activation of squib  26 , combustion gases exit propellant chamber  22  through perforations  11  in the propellant chamber. The gases proceed through plenum  40  along the circumference of propellant chamber  22  toward-first end  80  of inner annulus  32 . The gases pass out of plenum  40 , transit annular void  91  extending between plenum  40  and baffle tube  30 , and proceed into baffle chambers  41 . The gases then flow through baffle chambers  41  along length D 2  of outer annulus  34  to exit the inflator via discharge nozzles  14 . Combustion gases exiting propellant chamber  22  are volumetrically expanded and cooled by passing along baffle tube  30 , prior to entering an airbag via discharge nozzles  14 . In addition, passage of the gases through baffle tube  30  allows extra time for full combustion of the gases prior to exiting the inflator, thereby minimizing flaming of the combustion products exiting discharge nozzles  14 .  
         [0027]      FIGS. 4-9  show another embodiment of the baffle tube of the present invention.  
         [0028]     Referring to  FIG. 4 , a baffle tube  130  includes the same basic features set forth in the above description of baffle tube  30 , including an inner annulus  132  and an outer annulus  134  exterior of and spaced apart from inner annulus  132  to define a baffle extending between the inner and outer annuli. In addition, a plurality of walls  138  extend between inner annulus  132  and outer annulus  134  to connect the outer annulus and the inner annulus. As shown in  FIG. 4 , walls  138  partition baffle tube  130  into a series of parallel baffle chambers  141  extending along the length of baffle tube  130  between inner annulus  132  and outer annulus  134 . However, it may be seen from  FIG. 9  that outer annulus  134  in this embodiment is substantially coextensive with inner annulus  132 .  
         [0029]     Also, referring to  FIGS. 4-9 , an orifice  160  is formed in each of walls  138  proximate an end of outer annulus  134  for passage of an inflation fluid therethrough. More specifically, referring to  FIGS. 4 and 5 , a first orifice  160 - 1  in a first wall  138 - 1  is formed proximate a first end  170  of outer annulus  134 . Referring to  FIGS. 4 and 6 , a second orifice  160 - 2  is formed in a second wall  138 - 2  adjacent first wall  138 -l. However, second orifice  160 - 2  is formed proximate a second end  172  of outer annulus  134 , opposite the first end  170  of the outer annulus. This pattern of orifices formed in adjacent walls proximate alternating ends of outer annulus  134  is continued around the circumference of baffle tube  130 . It may also be seen that orifices  160 - 1  and  160 - 2  enable fluid communication between adjacent baffle chambers  141 .  
         [0030]     Referring to  FIG. 7 , in addition to orifices formed in walls  138 , an orifice  180  is formed in inner annulus  132  proximate an end portion of the annulus to enable fluid communication between an interior of inner annulus  132  and an associated baffle chamber  141 . Also, referring to  FIG. 8 , another orifice  182  is formed in outer annulus  134  proximate an end of the outer annulus to enable fluid communication between a baffle chamber  141  and an exterior of outer annulus  134 .  
         [0031]     Operation of the embodiment shown in  FIGS. 4-9  is substantially the same as described above for baffle tube  30 . Referring to  FIGS. 4-9 , upon activation of squib  26 , combustion gases exit propellant chamber through perforations  11  in propellant chamber  22 . The gases proceed through plenum  40  along the circumference of propellant chamber  22  toward first end  181  of inner annulus  132 . However, in this embodiment, rather than passing out of plenum  40  along the entire circumference of propellant chamber  22 , the gases exit plenum  40  via orifice  180  formed in first annulus  132  ( FIGS. 4 and 7 ). Gases exiting orifice  180  flow into a baffle chamber  141 - 3  bounded by adjacent walls  138 - 2  and  138 - 3  and outer annulus  134 , then proceed along the length of baffle chamber  141 - 3  until they reach orifice  160 - 3  formed in wall  138 - 3 . At this point, the gases flow through orifice  160 - 3  into the next, adjacent baffle chamber  141 - 4 . The gases then flow along the length of this baffle chamber until the orifice in the next wall  138 - 4  is reached. Thus, the gases flow sequentially from one baffle chamber to another around the circumference of inner annulus  134  until baffle chamber  141 -F is reached. Gases then exit baffle tube  130  via orifice  182  ( FIG. 8 ) formed in outer annulus  134 . An outer plenum  135  fluidly communicates with orifice  182  to provide fluid communication with nozzles  14 . The gases then exit the inflator via discharge nozzles  14 , as previously described.  
         [0032]     In sum, the embodiment shown in  FIGS. 4-9  facilitates alternating and sequential fluid flow through each of the channels within the baffle plenum, whereby alternating longitudinal flow of the gas as it proceeds circumferentially about the baffle provides for slag deposition and excellent cooling of the gases.  
         [0033]     As in the previously described embodiment, passage of the gases through the baffle chambers allows extra time for full combustion of the gases prior to exiting the inflator, thereby minimizing flaming of the combustion products exiting discharge nozzles  14 . In addition, combustion gases exiting propellant chamber  22  are volumetrically expanded and cooled by passing along baffle chambers  141 , prior to entering an airbag via discharge nozzles  14 . In this embodiment, the gases are forced through a series of sequential baffle chambers  141  formed in baffle tube  130  to affect the residence time of combustion gases in the baffle tube. This is done to ensure that the gases reside in the baffle for a length of time sufficient to cool the gases to a temperature within a predetermined temperature range prior to the gases exiting inflator  10 . The degree of gas cooling may be controlled by controlling the number of baffle passages  141  formed along baffle tube  130 . In addition, more than one pathway through sequential fluidly-communicating passages may be formed by forming multiple exit orifices in inner annulus  132  and outer annulus  134 , with an appropriate arrangement of walls  138  and orifices formed therein being positioned between an inner annulus orifice  180  and a respective outer annulus orifice  182 .  
         [0034]     Referring to  FIG. 10 , any of the baffle tube embodiments described herein may be incorporated into an inflator  10  used in an inflatable vehicle occupant protection system, such as an airbag assembly  200 . Airbag assembly  200  includes at least one airbag  204  and an inflator  10  as described herein coupled to airbag  204  so as to enable fluid communication with an interior of the airbag. Airbag assembly  150  may also be in communication with a crash event sensor  210  including a known crash sensor algorithm that signals actuation of airbag assembly  200  via, for example, activation of airbag inflator  10  in the event of a collision.  
         [0035]     Referring again to  FIG. 10 , airbag assembly  200  may also be incorporated into a broader, more comprehensive vehicle occupant restraint system  280  including additional elements such as a safety belt assembly  150 .  FIG. 10  shows a schematic diagram of one exemplary embodiment of such a restraint system. Safety belt assembly  150  includes a safety belt housing  152  and a safety belt  151  extending from housing  152 . A safety belt retractor mechanism  154  (for example, a spring-loaded mechanism) may be coupled to an end portion  153  of the belt. In addition, a safety belt pretensioner  156  may be coupled to belt retractor mechanism  154  to actuate the retractor mechanism in the event of a collision. Typical seat belt retractor mechanisms which may be used in conjunction with the safety belt embodiments of the present invention are described in U.S. Pat. Nos. 5,743,480, 5,553,803, 5,667,161, 5,451,008, 4,558,832 and 4,597,546, incorporated herein by reference. Illustrative examples of typical pretensioners which may be used in system  280  are described in U.S. Pat. Nos. 6,505,790 and 6,419,177, incorporated herein by reference.  
         [0036]     Safety belt system  150  may be in communication with a crash event sensor  158  (for example, an inertia sensor or an accelerometer) including a known crash sensor algorithm that signals actuation of belt pretensioner  156  via, for example, activation of a pyrotechnic igniter (not shown) incorporated into the pretensioner. U.S. Pat. Nos. 6,505,790 and 6,419,177, previously incorporated herein by reference, provide illustrative examples of pretensioners actuated in such a manner.  
         [0037]     It should be understood that the preceding is merely a detailed description of various embodiments of this invention and that numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the spirit or scope of the invention. The scope of the invention should not therefore be limited by the preceding description, but should be given its broadest interpretation as stated in the claims appended hereto.