Abstract:
An inflator for an air bag-type passenger restraint system for a motor vehicle includes two cup-shaped members which are joined to form chambers for a gas generator and activating devices for activating the gas generator. The two members are coupled by threads which do not increase the weight of the inflator. The inflator also includes a filter for filtering particulate matter from the gas generator.

Description:
BACKGROUND OF THE INVENTION 
     A. Field of Invention 
     This invention pertains to an air bag passenger restraint system, and more particularly to a housing for the components used to inflate the air bag in such a system. 
     B. Description of the Prior Art 
     Active passenger restraint systems and more particularly, restraint systems with air bags have proved to be very effective in preventing serious injury and even death in motor vehicles involved in crashes. Typically, these systems include an inflator housing containing chemical agents which may be triggered, for example by a crash, to generate a large volume of gas. The housing is arranged and constructed so that the gas is channeled to a bag which inflates. Thus, the big cushions the body of the passengers. 
     Early gas generator or inflator designs comprised two metal cups which were held together on their circumference to form a pressure chamber. As pressures typically reach 2000 psi within a gas generator, the wall thickness of these cups had to be sufficient to withstand this pressure typically with a safety factor of 2. These cups were typically held together by welding, threads, or by mechanically bending one cup around the other. 
     In an effort to reduce the overall weight of the gas generator by reducing the wall thickness of the cups, means were sought to provide a physical attachment of the two cup halves at some inner diameter. In one prior art configuration, in addition to the peripheral attachment, an inner bolt circle of rivets was used to provide this additional attachment as well as a separate two-piece threaded member that served both to hold the electric squib as well as provide mechanical attachment of the upper and lower half. The outer periphery of this type of inflator was welded. 
     Another configuration utilized a butt welding technique wherein the two cup halves were friction-welded together at both the peripheral diameter as well as an inner diameter. Yet other configurations utilized several interconnecting cup members which were laser or electron-beam welded together to form the desired multi-attachments of the gas generator pressure chamber. Some prior art inflator housings are shown in U.S. Pat. No. 4,711,466; and 4,561,675. However, it has been found that assembling inflator housings by welding is undesirable because it increases their cost of manufacture and weight. Moreover, in some instances it may be advantageous to be able to disassemble a completed housing, for example for quality control, or to replace defective or old chemical agents. However, a welded housing is difficult to take apart. 
     OBJECTIVES AND SUMMARY OF THE INVENTION 
     In view of these disadvantages of the prior art, an objective of the present invention is to provide in inflator housing which can be assembled inexpensively. 
     A further objective is to provide an inflator housing which is assembled without any increase in weight. 
     A further objective is to provide an inflator housing which can be easily disassembled when required. 
     Other objectives and advantages of the invention shall become apparent from the following description. An inflator housing is constructed in accordance with this invention from two cup members which cooperate to form chambers for holding a primer, and the chemical agents which can be activated to generated a gas. Each of the cups is formed with mating means for threadedly engaging the other cup. 
     Advancements over the last ten years in production machine tool technology has made it possible to machine concentric threads on two different diameters which start at the same point, thus permitting such a machined member to be attached to a second machined member having also two mating machine threads starting at the same point. This technique is thus ideally suited for attaching two inflator cups to form a pressure chamber for the physical attachment occurring at both the outer diameter as well as a second inner diameter. This double attachment technique permits reducing the wall thickness of the inflator halves thereby reducing the inflator weight for the same internal pressure requirements, as well as providing the necessary two pressure chambers within the inflator --one to hold the enhancer or primer material and the second to hold the primary gas generate material. For maximum pressure holding capability a buttress thread design is used for all threads. 
     The double threaded housing can be made of aluminum. To achieve even reductions in weight and manufacturing costs plastic housings have also been molded. It is believed that this screwed together inflator technique is probably the only practical means of attaching plastic housings. 
     This screwed together inflator configuration is both applicable to electric squib initiation wherein an external crash sensor closes an electrical circuit across the squib to initiate gas generation when an air bag is needed, as well as a completely self-contained sensor initiator incorporation a stab primer contained within the gas generator. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 shows an elevational view of an inflator housing constructed in accordance with this invention; 
     FIG. 2 shows a top view of the lower cup of the housing of FIG. 1; 
     FIG. 3 shows an exploded view of the housing of FIGS. 1 and 2. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the Figures, an inflator housing 10 is composed of two cups, a lower cup 12 and an upper cup 14 made, for example, of aluminum or an aluminum alloy. alternatively, the cups may be molded of a plastic material. The lower cup includes a substantially square base 16 with several mounting holes 18. Base 16 permits the housing 10 to be mounted on a surface 20. which may for example be part of the steering wheel or the glove compartment of a motor vehicle. The housing is also secured to an air bag, a portion of which is shown in FIG. 1 as at 22. The air bag surrounds the housing so that gases generated therein can inflate the air bag. 
     As shown in more detail in FIG. 3, extending upwardly from base 16, lower cup 12 has an outer cylindrical wall 24. Wall 24 may rise for a distance which is about half the thickness of the housing 10. Lower cup 12 also is provided with an inner cylindrical wall 26 disposed concentrically with outer wall 24. Inner wall 26 extends substantially through the whole thickness of the housing. Also formed in base 16 is a tubular wall 28 extending through the base to hold a rubber grommet 30. 
     Wall 26 is formed with a plurality of holes 32. Preferably these holes are angled at about 45°. At least the upper portion of wall 26 has threads 34 on its outer surface 27. Similarly wall 24 has an upper section with threads 36 on its outer surface 25. At the top, wall 26 is formed with an annular thin web 38. 
     Upper cup 14 is formed with a substantially circular plate 40. An outer cylindrical wall 42 extends downwardly from plate 40 as shown in FIG. 3. This wall 42 is formed with a plurality of venting holes 44. The inner surface 46 of wall 42 is formed with threads 48 at a pitch matching the pitch of the threads 36 on wall 24. Upper cup 14 also has an inner cylindrical wall 50 disposed concentrically with respect to outer wall 42. Inner wall 50 has an inner surface 52 which also has threads 54 at a pitch which matches the pitch of the threads 34 on wall 26. The two cups 12, 14 are sized and shaped so that they can be joined together to form the inflator housing 10 by placing the upper cup 14 over the lower 12 and turning one or both to engage the threads. Importantly the two sets of threads 36/48 and 34/54 engage simultaneously. When assembled, the two cups form two chambers: a central cylindrical chamber 56, and an annular chamber 58 disposed concentrically around chamber 56. Chamber 58 is partitioned into an upper section 60 and a lower section 61 by a ring 62. As shown in FIG. 3, preferably, ring 62 consists of flat portion 64 extending substantially radially and joined to a tubular section 66 extending substantially axially. In other words, ring 62 has a generally L-shaped cross-section. 
     An acceleration sensor 68 is disposed in central chamber 56. Sensor 68 may be either a mechanical sensor or an electrical sensor. The electrical sensor may be provided with an electrical cable 70 passing through grommet 30 to provide power to the sensor if required. As shown in FIG. 1, sensor 68 sits in the upper part of chamber 56. If necessary, one or more primer capsules 72 may also be provided in a lower annular section 74 of the chamber 56 defined between the upper section of cylindrical wall 28 and wall 26. Primer 72 is disposed on top of a BKNO 3  powder mix 73. The lower section 61 of chamber 58 is used to hold a plurality of capsules 76 which when ignited generate a gas. The upper section 60 of chamber 58 is used to hold a filter assembly 78. 
     The inflator housing 10 is assembled as follows. First, the primer 72, mix 73 and the acceleration sensor 68 are positioned within wall 26. Cable 70 (if provided) is passed through the grommet 30 for later connection to a power supply and (optionally) to a sensor monitoring means not shown. In order to keep the sensor in place, the web 38 on wall 26 is bent radially inwardly to the position shown in FIG. 1. Capsules 76 are installed in the annular space between walls 24 and 26. Next, ring 62 is placed so that it sits on top of wall 24. Importantly, in this position, a narrow annular passage 80 is formed between portion 66 of ring 62 and wall 26. Finally, a filter assembly consisting of a primary slag filter 77 and a secondary filter mesh 78 is placed on top ring 62. The upper cup 14 is then placed over the lower cup 12 and one or both cups 12, 14 are twisted to engage the threads. This action is continued until the two cups are firmly interlocked, as shown in FIG. 1. The inflator housing is then installed into a motor vehicle as described above. 
     The inflator housing operates as follows. When the motor vehicle is involved in a crash, it undergoes a deceleration. If this deceleration exceeds a certain preset level, the acceleration sensor 68 activates primer 72. The primer ignites BKNO 3  powder 73 which in turn initiates capsules 76 through holes 32. The ignited capsules 76 generate chemically a large volume of gases, as well as particulate matter which is a byproduct of the chemical reactions resulting from the burning of the capsules. The gases flow through passageway 80 and then out through primary and secondary filters 77, 78 and holes 44. The particulate matter entrained in the gases is picked up by the primary slag filter 77. The generation of gas takes place at a high temperature and pressure relative to ambient conditions. One skilled in the art will recognize that the two sets of threads perform two functions in the inflator housing: they are used as a pressure resistant coupling between the two cups so that they do not fly apart as a result of the high pressure; and they insure that the chambers within the housing are hermetically sealed so that gas generated within the outer chamber 58 does not interfere with the operation of sensor 68. 
     Obviously numerous modifications can be made to the invention without departing from its scope as defined in the appended claims.