Inflator assembly

An inflator includes a housing formed by two cups interlocked to provide a tamper-proof enclosure with at least one of the cups formed with indentations for grasping by a tool to facilitate assembly of the cups. In a chamber of the housing is an initiator secured in place by a snap-fit. A canister containing tablets of gas generating material is held in the chamber by an interference fit. A filter is held in place in the housing by a ring-shaped retainer member. Passages within the housing direct gases from the initiator to the canister through the filter out of the housing into an air bag with the path of travel changing direction by at least 90.degree. to create turbulent flow for enhanced inflator gas production.

BACKGROUND OF THE INVENTION 
A. Field of Invention 
This invention pertains to an improved inflator assembly, and more 
particularly to an improved inflator assembly for inflating an air bag 
used for protecting passengers in a motor vehicle during a crash. 
B. Description of the Prior Art 
Air bag systems have become accepted as the primary means of protecting 
motor vehicle passengers from injury during crashes. It has been estimated 
that within five years all passenger vehicles sold in the United States 
will be equipped with such systems. An important part of the air bag 
system is its inflator assembly, the component which provides the 
pressurized gas necessary to inflate the bag. Because it plays such a 
crucial role in the system, the inflator assembly must meet several 
important criteria. It must be sturdy and robust so that it operates 
flawlessly years after its original installation without any servicing. It 
must be strong so that it can withstand the internal pressures resulting 
from the rapid gas generation process. It must be tamper proof so that it 
cannot be easily dismantled and tampered by unskilled personnel. It must 
be relatively small and light weight, especially if it is to be installed 
in the steering wheel for the protection of the driver. It must be 
inexpensive to keep down the overall price of the motor vehicles. 
While there are several inflator assemblies presently available on the 
market, none of them meet all of the criteria set forth above. 
OBJECTIVES AND SUMMARY OF THE INVENTION 
It is an objective of the present invention to provide an improved inflator 
assembly which is sturdy and resistant to long-term wear and tear in an 
automobile so that it remains functional over long time periods without 
the need for servicing. 
A further objective is to provide an inflator assembly which is made 
tamper-proof after assembly. 
Yet a further objective is to provide an inflator assembly which provides a 
tortuous path for gases generated within to insure the expulsion of clean 
gas to the air bag. 
Other objectives and advantages of the invention shall be described below. 
Briefly, an inflator assembly constructed in accordance with this 
invention includes a housing formed by two cups positioned and 
interengaged to define two chambers therein. After assembly the two cups 
are interlocked to provide a tamper-proof enclosure. At least one of the 
cups is formed with several indentations arranged to permit the cup to be 
grasped with a tool during assembly so that the cups can be rotated 
relative to each other. 
Inside one of the chambers there is provided an initiator which sets off 
the inflator assembly. Advantageously the initiator is snap fit within the 
housing to insure that it is initially positioned and remains at a 
predetermined location. 
Also provided in the chamber is a canister of tablets made of a gas 
generating material. The canister is held in an interference fit within 
the housing to prevent it from moving either radially or axially therein. 
Also disposed in the housing is a ring-shaped retainer member and a filter 
held in place by the retainer member. The retainer member is inserted into 
the housing to support the filter so that the filter does not fall out 
during assembly. 
Within the housing there are passages provided for gases to flow from the 
initiator to the canister and from the canister through the filter and out 
of the assembly formed by the interengagement of two cups into the air 
bag. These passages are arranged to insure that the gases change direction 
by at least 90.degree. from the initiator to the filter. In this manner a 
turbulent flow is created to provide sufficient contact between the 
initiator gases and the tablets for a fast inflator gas production.

DETAILED DESCRIPTION OF THE INVENTION 
In the following directional terms such up, down, top, bottom and so forth 
are used in conjunction with the orientation of the drawings for the sake 
of clarity. It should be understood that the assembly described below may 
have a different orientation once it is installed in a motor vehicle. 
Referring now to the Figures, an inflator assembly 10 constructed in 
accordance with this invention consists of a housing 12 formed of two cups 
14, 16. Upper cup 14 is formed of two concentric cylindrical walls, an 
outer wall 18, and an inner wall 20, both walls extending normally from a 
base plate 22. Similarly bottom cup 16 is formed of two cylindrical walls 
24, 26 extending normally from a base plate 28. A peripheral flange 30 on 
cup 14 is used for mounting the assembly to an air bag module. 
As described in commonly assigned U.S. Pat. No. 5,201,542, the two cups are 
secured together by a double threaded arrangement. More particularly, the 
inner surfaces of walls 18, 20 are threaded and engage the threads formed 
on the outer surfaces of walls 24, 26 respectively. In this manner, when 
the housing 10 is closed the two cups are engaged by the threaded co-axial 
annular couplings 32, 34. 
Importantly, wall 24 of cup 16 is formed with an annular rib 36 disposed 
below the threads. In addition, wall 18 of cup 14 is formed with an 
axially extending annular lip 38 extending below rib 36 when the two cups 
are threadedly engaged as described above and as illustrated by letter A 
in dotted lines in FIG. 3. After the two cups have been engaged, this lip 
38 is rolled over rib 36 to mechanically interlock the cups together, as 
shown in solid lines in FIG. 3 by letter B. This mechanical interlock is 
provided to insure that after the two cups have been assembled, they 
cannot be opened and tampered with by unauthorized personnel. In addition, 
the mechanical interlock provides some mechanical strength for the housing 
12. Alternatively, or in addition to the rib and lip arrangement described 
above, the two cups may also be interlocked by providing holes in the cups 
and driving spikes 40 through the holes as shown in FIG. 3. Spikes 40 are 
preferably flush with the outer surface of wall 18 to insure that once 
they are driven in they cannot be removed. 
As it can be best seen in FIG. 3, after the housing 10 is assembled, a 
substantial portion of the bottom cup 16 is disposed inside, or at least 
covered by the top cup 14. Hence it is difficult to grasp the bottom cup 
16 properly to allow the two cups to be screwed together. In order to 
solve this problem, bottom plate 28, which is substantially circular in 
shape, is provided peripherally with a plurality of scallops or notches 
42. The purpose of these notches is discussed below. 
The two cups 14, 16 cooperate to form two chambers within housing 12, a 
central chamber 44, and annular chamber 46 disposed coaxially about 
chamber 44. Chamber 44 is used to hold an initiator 48. Preferably, 
initiator 48 has a cylindrical body 50 having a diameter slightly smaller 
than the diameter of hole 52 defined by wall 26 of cup 16. Near the top, 
initiator 48 has an annular enlarged portion 54 with a downwardly pointed 
shoulder 56. Below portion 54, initiator 48 is provided with a plurality 
of flexing fingers 58 arranged annularly about body 50. Each of these 
fingers 58 extends upwardly toward portion 54 and radially outwardly and 
are slightly flexible radially. 
Hole 52 is formed with an inner annular groove 60 defined by a wall portion 
62 extending upward and toward a radially inwardly oriented shoulder 64. 
The distance between shoulder 64 and the top surface 66 of wall 26 is 
slightly smaller than the distance between the tips of fingers 58 and 
shoulder 56 on portion 54. 
The initiator includes wires 68, 70 used to send an electrical signal to 
the initiator 48 for detonation. Wires 68, 70 are connected to an 
acceleration sensor disposed elsewhere in the system. Alternatively, 
initiator 48 may include a mechanical acceleration sensor in which case 
the wires 68, 70 are omitted. 
The wall 26 is thus arranged and constructed to engage with the initiator 
48 and hold the same in a preselected position inside the chamber 44. For 
this purpose, initiator 48 may be inserted into opening 52 from the top 
downward. As the body 50 is moving inward into hole 52, fingers 58 are 
flexed radially inward. When the tip of the fingers 58 reach groove 60 
they snap radially outward thereby locking the initiator 48 into the 
position shown in FIG. 3. In this position, wires 68, 70 extend outwardly 
of hole 52 while the portion of initiator 48 disposed above top surface 66 
of wall 26 is disposed inside chamber 44. To insure that the initiator 48 
remains in this position and does not move or fall out, a resilient O-ring 
72 is placed between top surface 56 and shoulder 66. When the initiator is 
in place the O-ring 72 is squeezed in the axial direction thereby 
providing an axial biasing force between the initiator portion 54 and 
surface 66. In this manner O-ring 72 is pulling the fingers 58 upward to 
remain in engagement with shoulder 64. Additionally, the O-ring 72 also 
forms a seal around body 50 to insure that the chamber 44 is sealed off 
from ambient atmosphere. 
Above initiator 48, chamber 44 is provided with a pellet 74 made of an 
auto-ignition material. 
Chamber 44 communicates with chamber 46 through a plurality of holes 76. 
Preferably holes 76 are sloped downwardly at an angle of about 45.degree.. 
Chamber 46 is used to hold a canister 78 and a filter assembly discussed 
more fully below. Canister 78 is generally annular in shape and has a 
generally L-shaped cross section. The canister 78 is formed of two 
members, a wall member 80 which defines an annular cavity and a 
ring-shaped cover member 82. The inner and outer edges of the cover member 
is rolled together with the inner and outer edges of the wall member to 
form two annular seals 84, 86. These seals are also covered with a potting 
material as at 88, 90. In this manner the two members 80, 82 form a 
hermetically sealed canister 78. Canister 78 is used to hold a plurality 
of tablets 92 which when heated above a preset temperature release a gas 
very rapidly. A disk shaped member 94 is used to keep the tablets 92 above 
cover 82. Cover 82 is formed with a circular groove 96. This groove 96 is 
in contact with a circular ridge 98 formed on the inner surface of base 
plate 28. 
Radially outwardly of canister 78, base plate 22 is provided with a 
downwardly extending annular wall 100 extending for a short distance 
inside chamber 46. 
Chamber 46 further holds a retaining ring 102. This ring 102 has two 
annular portions, a substantially horizontal portion 104 and a vertical 
portion 106. Portion 104 is provided with a plurality of holes 107. 
Vertical porion 106 is sized so that it forms an interference fit with 
wall 100 as the ring 102 is inserted into cup 14. 
As shown in FIG. 3, above the horizontal portion 104, there are provided 
two concentric annular filters, 108, 110. Filter 108 is a slag filter and 
it forms an annular space 112 with the vertical portion 106 of ring 102. 
Filter 110 is disposed radially outwardly of filter 108 and is constructed 
and arranged to pick up fine particles from the gas flow. For example, 
filter 110 may be made of several layers of a fine filtration material 
made of paper, cloth, ceramic, and/or other filter media. Preferably the 
filter media is embedded at the two axial ends in a graphite seal 114, 116 
used to insure that gases exiting the chamber 46 do not by-pass the filter 
110, however, other means of sealing can be used. As shown in the Figures, 
the outer wall 18 of upper cup 14 is provided with a plurality of 
peripheral holes 118 for venting gasses through the filter 110. 
The inflator assembly 10 is constructed as follows. The canister 78 is 
installed into the lower cup 16 and the initiator 48 is snapped into hole 
52 from the top. The auto-ignition disk 74 is installed in the upper cup 
14, inside wall 20. Filters 108 and 110 are pressed into the upper cup 14 
in an inverted position and the retaining ring 102 is pressed on top of 
filters 108 and 110. Ring 102 may be positioned such that its holes 107 
are angularly offset from holes 118 in cup 14. 
The filters 108, 110 and ring 102 are maintained in this position by the 
interference fit between ring wall 106 and wall 100. Therefore cup 14 can 
be turned to the position shown in FIGS. 3 and 5 without the filters 108, 
110 and the ring 102 falling out therefrom. 
Cups 14 and 16 are then placed into an abutting relationship and one or 
both cups are turned so that they become threadedly engaged. During this 
process the bottom cup 16 is grasped with a tool (not shown) having 
engaging means for engaging the cup 16 by notches 42. Cup 14 and/or 16 is 
turned until a torque in a preselected range is reached. For example, the 
cups can be turned until they are torqued at about 35 ft. - lbs. 
Once the housing 10 is completed the inflator assembly is ready to be 
installed. As shown in FIG. 3, as the two cups 14, 16 are screwed together 
an upper edge 120 of lower cup 16 presses ring 102 upward thereby 
squeezing the filters 108, 110 and the graphite seals 114, 116 between the 
horizontal ring portion 104 and base plate 22. At the same time the 
portion of the canister 78 disposed under ring portion 104 is also 
captured between ring 104 and base plate 28 of lower cup 16. In this 
manner the filters 108, 110 and canister 78 are effectively trapped 
between the base plates 22, 28 and ring 102 to prevent them from movement. 
The registration between ridge 98 and groove 96 further insures that the 
canister 78 does not shift in the radial or lateral direction. Thus, the 
canister is prevented from rattling. This is important because if the 
canister rattles, the tablets contained therein may pulverize and thereby 
lose their effectiveness. 
The inflator assembly operates as follows. The inflator assembly is 
normally installed in the passenger compartment of a motor vehicle, for 
example in the steering wheel. Initiator 48 is connected by wires 68, 70 
to a crash detector (not shown). When a crash is sensed by the detector, 
an electrical signal is received over wires 68, 70 which signal sets off 
the initiator 48. The initiator 48 acts as a primer to generate a 
relatively small amount of gases. These gases quickly fill up chamber 44 
and flow through holes 76 toward chamber 46. The wall 80 of canister 78 is 
constructed and arranged so that its wall section disposed in the 
immediate vicinity of holes 76 is ruptured by the gases from the initiator 
48. The gases from the initiator then enter into the canister and set off 
tablets 92. The tablets 92 then generate gases very rapidly and at a 
relatively high pressure. These gases rupture the portion of wall 80 
disposed adjacent to holes 107 allowing gases to escape into space 112. 
From this space, the gases exit through the filters 108, 110 and holes 
118. Importantly, holes 107 are positioned in such a manner that the gas 
flow through these holes is oriented at better than 90.degree. with 
respect to the flow of gases through holes 76. In fact holes 107 are 
oriented upwardly in an axial direction, i.e. in parallel with respect to 
the axis X--X of inflator 10, while holes 76 are oriented at 45.degree. 
downwardly with respect to the axis, therefore the gas flow through these 
holes are oriented at a respective angle of 135.degree.. This feature is 
important because it allows causes the gases to flow turbulently through 
the canister 78 and provide extended contact between the initiator gases 
and the tablets 92 to insure that tablets 92 are set off rapidly and 
uniformly. Otherwise the initiator gases could cause the canister wall 80 
to rupture prematurely allowing the initiator gases to escape through 
holes 107 before the tablets are fully set off. 
The angular offset between holes 107 and 118 insure a turbulent flow of 
gases from chamber 46 to the outside. In this manner as theses gases flow 
through the filters 108, 110, they are cleaned better of particulate 
mater. 
If the inflator assembly overheats, for example in case of fire, the pellet 
74 ignites causing the tablets 92 to set off at a preselected temperature. 
Without the pellet 74, the assembly 10 could overheat to a very high 
temperature to set off tablets 92. By the time this high temperature is 
reached, the housing 10 may be weakened and therefore when the tablets 92 
are set off the gases generated may cause structural distress. 
Obviously numerous modifications may be made to the invention without 
departing from its scope as defined in the appended claims.