Steering wheel with air bag module

A vehicle steering wheel assembly (20) includes an air bag module (24) connected with a frame (42) of a vehicle steering wheel (22). The module (24) includes an inflator (62), an air bag (64), and a mounting hub (66). An internal groove (184) in the mounting hub (66) receives resiliently deflectable tabs (208) on the inflator (62) to secure the inflator to the mounting hub. A mounting portion (240) of the air bag (64) is received in one section of an external groove (182) on the mounting hub (66). A base portion (262) of a guide ring (260) is received in another section of the external groove (182). A wall portion (266) of the guide ring retains the mounting portion (240) of the air bag (64) in the groove, to secure the air bag to the mounting hub. The steering wheel frame (42) has a plurality of tabs (164) which are deformed into slots (162) in the mounting hub to secure the module (24) to the frame. A single fastener (40) secures the mounting hub (66) and thereby the module (24) to the vehicle steering shaft (26).

BACKGROUND OF THE INVENTION 
1. Technical Field 
The present invention relates to an apparatus for helping to protect an 
occupant of a vehicle and to a method of assembling the apparatus. In 
particular, the present invention relates to an apparatus which includes 
an air bag module connected with a vehicle steering wheel, and to a method 
of assembling the air bag module and the vehicle steering wheel. 
2. Description of the Prior Art 
An inflatable vehicle occupant protection device, such as an air bag, is 
inflated to help protect an occupant of a vehicle. The air bag is inflated 
by inflation fluid from an inflator. The inflated air bag is located 
between the occupant and a vehicle part to help protect the vehicle 
occupant from forcefully striking or being struck by the vehicle part. 
The air bag and the inflator are typically connected with each other and 
thereafter mounted as a unit, commonly known as an air bag module, on the 
vehicle. An air bag module for helping to protect a driver of a vehicle is 
typically mounted in or on the steering wheel of the vehicle. 
An air bag module for helping to protect a driver of a vehicle is typically 
attached to the steering wheel after the steering wheel is mounted on a 
steering shaft of the vehicle. Attaching the module to the steering wheel 
in this manner, that is, after the steering wheel has already been mounted 
on the vehicle, requires assembly steps which can be cumbersome. 
In a typical air bag module, the air bag and the inflator are supported on 
a module plate with fasteners and a retainer. The fasteners extend through 
openings in the air bag, the inflator, the module plate and the retainer. 
During assembly of the module, at least some of the openings in these 
components must be aligned with each other for insertion of the fasteners. 
SUMMARY OF THE INVENTION 
The present invention is a module comprising an inflatable vehicle occupant 
protection device and an actuatable inflator which, upon actuation, 
provides inflation fluid to inflate the inflatable device. The module 
includes a mounting hub for connection with a steering shaft of a vehicle. 
First means for attaching the inflator to the mounting hub at a first 
location on the mounting hub includes means for defining a first groove in 
one of the mounting hub and the inflator. The first means for attaching 
also includes a resiliently deflectable tab on the other of the mounting 
hub and the inflator, which is receivable in the first groove. Second 
means for attaching the inflatable device to the mounting hub at a second 
location on the mounting hub includes a member and means for defining a 
second groove in the mounting hub. A mounting portion of the inflatable 
device is receivable in a first section of the second groove. The member 
has a base portion receivable in a second section of the second groove and 
a wall portion retaining the mounting portion of the inflatable device in 
the first section of the second groove. 
In a preferred embodiment, the means for attaching the inflator to the 
mounting hub comprises a plurality of resiliently deflectable tabs which 
deflect from an initial position upon relative movement of the inflator 
and the mounting hub toward a predetermined relative position. The tabs 
return toward the initial position in the groove upon movement of the 
inflator and the mounting hub into the predetermined relative position 
thereby to maintain the inflator and the mounting hub in the predetermined 
relative position. 
The module is receivable in a tubular portion of a steering wheel frame. An 
end portion of a first one of the mounting hub and the tubular portion of 
the frame is deformable into engagement with an end portion of a second 
one of the mounting hub and the tubular portion of the frame to secure the 
mounting hub for movement with the frame. 
The present invention also is a method of assembling a vehicle steering 
wheel and an air bag module. The method includes the steps of: providing a 
vehicle steering wheel including a frame having a tubular portion; 
providing a mounting hub which is connectable with a vehicle steering 
shaft and which includes a tubular portion; attaching an inflator within 
the tubular portion of the mounting hub; attaching an air bag to the 
tubular portion of the mounting hub; positioning the mounting hub in the 
tubular portion of the steering wheel frame; and retaining the mounting 
hub in the steering wheel frame by deforming an end portion of a first one 
of the tubular portion of the frame and the tubular portion of the 
mounting hub against an end portion of a second one of the tubular portion 
of the frame and the tubular portion of the mounting hub.

DESCRIPTION OF A PREFERRED EMBODIMENT 
A vehicle steering wheel assembly 20 (FIGS. 1 and 6) which is constructed 
in accordance with the present invention includes a steering wheel 22 and 
an air bag module 24. The steering wheel assembly 20 is connected to a 
steering shaft 26 (FIG. 1) which is located within a steering column 28 of 
the vehicle. 
The steering wheel assembly 20 is provided as a unit for connection to the 
steering shaft 26. The steering wheel assembly 20 is secured to the 
steering shaft 26 by a fastener 40 (best seen in FIG. 6), in a manner 
described below. The steering wheel assembly 20, including the steering 
wheel 22, is rotatable with the steering shaft 26 about a longitudinal 
central axis A of the steering shaft to control the direction of vehicle 
travel. 
The steering wheel 22 includes a frame 42. The frame 42 is a metal 
structure and includes a tubular central portion 44 which is welded to a 
ring 45. A cylindrical cavity 86 (FIG. 6) is defined by the tubular 
central portion 44 of the frame 42. A plurality of spokes 46 extend 
outward from the ring 45 and are welded to a rim 48 of the steering wheel 
22. The rim 48 is substantially circular in shape and is centered on the 
axis A. 
The steering wheel frame 42 includes a plurality of circumferentially 
spaced tabs 164 (FIG. 6) disposed in a circular array extending around the 
lower end portion of the ring 45 of the steering wheel frame 42. The tabs 
164 extend axially downward (as viewed in FIG. 6) prior to assembly of the 
air bag module 24 with the steering wheel frame 42. 
The steering wheel 22 also includes a plastic cover 60 encapsulating a 
majority of the exterior of the frame 42. The cover 60 includes a pair of 
centrally located deployment door panels 80. The deployment door panels 80 
are held in initially closed positions, as shown in FIG. 1, by a 
rupturable central section 82 of the cover 60. The deployment door panels 
80 are pivotable outward at hinge portions 84. 
The air bag module 24 includes an inflator 62 (best seen in FIG. 4) and an 
inflatable vehicle occupant protection device 64 of the type commonly 
referred to as an air bag. The inflator 62 and the air bag 64 are attached 
to a mounting hub 66 of the air bag module 24. The air bag module 24 is 
attached to the steering wheel 22 by the mounting hub 66, in a manner 
described below, to form the steering wheel assembly 20. 
The mounting hub 66 includes a substantially tubular portion 68 and a 
radially spaced apart central portion 100 (FIGS. 2 and 3). Four connector 
arms 140 (FIGS. 2-5) extend radially and axially between the central 
portion 100 and the tubular portion 68 of the mounting hub 66. The 
connector arms 140 interconnect the central portion 100 and the tubular 
portion 68 of the mounting hub 66. The central portion 100 has an axially 
extending opening 102 (FIGS. 4 and 5) and a fastener opening 106 which 
extends transversely through the opening 102. The fastener opening 106 is 
defined at one end by a threaded surface portion 108. 
The tubular portion 68 of the mounting hub 66 defines within its lower end 
portion a chamber 142 in which the central portion 100 is located. The 
chamber 142 in the mounting hub 66 is in fluid communication with a 
chamber 144 (FIG. 1) defined by the steering column 28 when the mounting 
hub is connected with the steering shaft 26 as described below. The 
chambers 142 and 144 store a volume of ambient air that may be aspirated 
into the air bag 64 during inflation of the air bag. A plurality of vents 
146 (FIGS. 3 and 4) extend longitudinally through the material of the 
tubular portion 68 of the mounting hub 66. The vents 146 are in fluid 
communication with the chamber 142. 
An inner shoulder flange 148 (FIG. 4) on the mounting hub 66 extends 
radially inward from the tubular portion 68 in an axially central region 
of the mounting hub 66. A deflector portion 210 of the mounting hub 66 
extends axially upward from the inner shoulder flange 148. The mounting 
hub 66 also has an outer shoulder flange 160 at its lower end portion (as 
viewed in FIGS. 4 and 5). The outer shoulder flange 160 extends 
circumferentially around the tubular portion 68 of the mounting hub 66. 
A plurality of axially extending slots 162 (FIGS. 4 and 5) are disposed in 
a circular array extending around the lower end portion of the tubular 
portion 68 of the mounting hub 66. Each slot 162 is circumferentially 
spaced from adjacent slots 162 and is at least partially defined by a 
radially extending upper end surface 166. 
An external groove 182 is formed near an upper end (as viewed in FIG. 4) of 
the tubular portion 68 of the mounting hub 66. The external groove 182 is 
continuous and extends circumferentially around an outer cylindrical 
surface of the mounting hub 66. 
The mounting hub 66 also includes an internal groove 184 (FIG. 4) which is 
spaced axially downward from the external groove 182 at a location 
slightly above the inner shoulder flange 148, as viewed in FIG. 4. The 
internal groove 184 is substantially continuous and extends 
circumferentially around an inner cylindrical surface of the mounting hub 
66. The internal groove 184 passes through and is discontinuous at a view 
port 168 (FIG. 4) in the mounting hub 66. The view port 168 is provided so 
that a person or robot may determine, during assembly of the steering 
wheel assembly 20, the presence or absence of the inflator 62 in the 
mounting hub and whether the inflator is in a proper position relative to 
the mounting hub 66. 
The inflator 62 is actuatable as described below to provide inflation fluid 
for inflating the air bag 64. The inflator 62 contains an ignitable gas 
generating material 200 (FIG. 4) for generating, upon ignition, a large 
volume of inflation fluid in the form of gas for inflating the air bag 64. 
The gas generating material 200 may have any suitable composition and 
configuration known in the art. The inflator 62 may alternatively contain 
a quantity of pressurized inflation fluid, a combination of pressurized 
inflation fluid and ignitable material for heating the inflation fluid, or 
a mixture of gases in which at least one of the mixture of gases is 
combustible. 
The inflator 62 has a relatively short, generally cylindrical housing 202 
centered on the axis A. The housing 202 contains the ignitable gas 
generating material 200. The housing 202 has a plurality of gas outlet 
openings 204. 
A mounting flange 206 is located on the housing 202 of the inflator 62 near 
one end of the housing. The mounting flange 206 includes a plurality of 
discrete resiliently deflectable tabs 208. The tabs 208 are disposed in a 
circular array extending around the outer periphery of the mounting flange 
206 and project radially outward from the housing 202. 
The inflator 26 includes an electrically actuatable initiator 220 which has 
an elongate cylindrical casing 222 extending axially within the housing 
202. The initiator 220 includes a pair of electrodes (not shown) external 
to the lower end of the housing 202. A pyrotechnic material in the casing 
222 is ignitable in a known manner upon the flow of electric current 
between the electrodes. The pyrotechnic material in the initiator 220 may 
have any suitable composition and configuration known in the art. When the 
pyrotechnic material is ignited, it produces hot combustion products which 
rupture and emerge from the casing 222 to ignite the gas generating 
material 200. 
The air bag 64 (FIGS. 4 and 5) has a relatively large inflatable portion 
242. An inlet portion 244 of the air bag 64 includes a molded bead 240 for 
securing the air bag to the mounting hub 66 in a manner described below. 
The air bag 64 is preferably made from a fabric material such as woven 
nylon. The air bag 64 can alternatively be made from non-woven material, 
such as plastic film. The use of plastic film, in particular, would 
require inflation fluid vents to be formed in the air bag 64, as is known 
in the art. 
The air bag module 24 also includes a guide ring 260 (FIG. 4) for securing 
the air bag 64 to the mounting hub 66 and for guiding movement of the 
mounting hub into the steering wheel frame 42 during assembly of the 
steering wheel assembly 20. The guide ring 260 is an annular member having 
a split-ring configuration including an opening 268 that allows 
circumferential and diametrical expansion for attaching the guide ring 
around the mounting hub 66. The guide ring 260 is preferably made from a 
relatively low friction material, such as polytetrafluoroethylene. The 
guide ring 260 has an L-shaped cross-sectional configuration, as seen in a 
plane extending along and radially from the axis A, including a base 
portion 262 and a wall portion 266. The wall portion 266 of the guide ring 
260 has a chamfered upper or leading edge 264. 
In assembly of the air bag module 24, the inflator 62 is placed at least 
partially into the tubular portion 68 of the mounting hub 66. The mounting 
flange 206 of the inflator 62 engages an upper end surface of the 
deflector portion 210 of the mounting hub 66. The inflator 62 is moved 
axially into the tubular portion 68 of the mounting hub 66, in a downward 
direction as viewed in FIGS. 4 and 5. The tabs 208 on the mounting flange 
206 on the inflator 62 deflect radially inward and axially backward 
relative to the direction of movement of the inflator, as the tabs slide 
axially along the inner periphery of the deflector portion 210 of the 
mounting hub 66. 
When the inflator 62 is in a predetermined position within the tubular 
portion 68 of the mounting hub 66, the bottom of the inflator housing 202 
engages the inner shoulder flange 148 on the mounting hub 66. This 
engagement blocks further axial movement of the inflator 62 relative to 
the mounting hub 66, in a downward direction as viewed in FIGS. 4 and 5. 
When the inflator 62 is in the predetermined position within the tubular 
portion 68 of the mounting hub 66, at least one and preferably all of the 
tabs 208 resiliently expand radially outward into the internal groove 184 
in the mounting hub. The resilience of the tabs 208 prevents the tabs from 
coming out of the groove 184 and retains the housing 202 of the inflator 
62 against the inner shoulder flange 148 of the mounting hub 66. The 
engagement of the tabs 208 on the inflator 62 in the groove 184 on the 
mounting hub 66 blocks axial movement of the inflator relative to the 
mounting hub in an upward direction as viewed in FIGS. 4 and 5. 
The air bag 64 is then attached to the mounting hub 66 by placing the 
mounting bead 240 of the air bag over the upper end of the mounting hub, 
as viewed in FIG. 4. The mounting bead 240 of the air bag 64 is received 
in a first or upper section of the external groove 182 in the mounting hub 
66. The wall portion 266 of the guide ring 260 is, thereafter, placed 
around the mounting bead 240 of the air bag 64. The base portion 262 of 
the guide ring 260 is received in a second or lower section of the outer 
groove 182. The resilience of the guide ring 260 retains the mounting bead 
240 of the air bag 64 in the groove 182. 
The assembled air bag module 24 is then inserted into the cavity 86 (FIG. 
6) in the tubular central portion 44 of the frame 42 of the steering wheel 
22. Specifically, the air bag module 24 is moved axially in an upward 
direction as viewed in FIG. 6 into the steering wheel frame 42. The 
chamfered leading edge 264 of the wall portion 266 of the guide ring 260 
centers and guides the air bag module 24 as it moves into the tubular 
central portion 44 of the steering wheel frame 42. 
The mounting hub 66 and the guide ring 260 are sized to have substantially 
the same outside diameter, when assembled together, and to fit closely 
within the tubular central portion 44 of the steering wheel frame 42. This 
close fit forces the wall portion 266 of the guide ring 260 radially 
inward against the mounting bead 240 of the air bag 64. The tubular 
central portion 44 of the steering wheel frame 42 thus clamps the wall 
portion 266 of the guide ring 260 and the mounting bead 240 of the air bag 
64 against the tubular portion 68 of the mounting hub 66. This clamping 
retains the mounting bead 240 in the groove 182 in the mounting hub 66. 
When the air bag module 24 is thus disposed in the steering wheel frame 42, 
the outer shoulder flange 160 on the mounting hub 66 engages a lower end 
portion 340 (FIG. 6) of the tubular central portion 44 of the steering 
wheel frame. This engagement limits axial upward movement (as viewed in 
FIG. 1) of the mounting hub 66, and thereby the air bag module 24, 
relative to the steering wheel frame 42. 
The air bag module 24 is then secured to the steering wheel 22 by bending 
the tabs 164 on the steering wheel frame 42 radially inward into the slots 
162 in the mounting hub 66. The tabs 164 engage the radially extending end 
surfaces 166 of the slots 162. The engagement of the tabs 164 in the slots 
162 blocks rotational movement of the air bag module 24 relative to the 
steering wheel frame 42. The engagement of the tabs 164 in the slots 162 
also blocks axial movement of the air bag module 24 relative to the 
steering wheel frame 42, in a downward direction as viewed in FIGS. 1 and 
4-6. 
The steering wheel assembly 20, including the air bag module 24, is then 
secured to the steering shaft 26. A mounting portion 104 (FIG. 1) of the 
steering shaft 26 is inserted axially into the opening 102 in the central 
portion 100 of the mounting hub 66. The mounting hub 66 and the steering 
wheel frame 42 include respective access ports 170 and 180 through which 
the fastener 40 is inserted in a right to left direction as viewed in 
FIGS. 1 and 6. The fastener opening 106 in the central portion 100 of the 
mounting hub 66 receives a body portion 120 (FIG. 6) of the fastener 40. 
An externally threaded portion 122 of the fastener 40 is screwed into the 
internally threaded portion 108 of the fastener opening 106. The body 
portion 120 of the fastener 40 fits into a recess 124 (FIG. 2) in the 
mounting portion 104 of the steering shaft 26 to retain the mounting hub 
66 and the steering wheel 22 on the steering shaft 26. A port cover 181 
(FIG. 1) on the steering wheel 22, which normally hides the access ports 
170 and 180, is deflectable during assembly to permit insertion of the 
fastener 40. 
When the steering wheel assembly 20 is attached to the steering shaft 26 in 
the vehicle, the inflator 62 is connected with an electric circuit 280 
(FIG. 1) of the vehicle. A wire bundle 284 having lead wires 286, 288 and 
an electrical connector 282 extends between the initiator 220 and the 
circuit 280. The circuit 280 includes a power source 300 and a normally 
open switch 302. The power source 300 is preferably the vehicle battery 
but may be a capacitor. The switch 302 is part of a sensor 304 which 
senses a vehicle situation, such as a collision, in which inflation of the 
air bag 64 is desired. 
When the sensor 304 detects a vehicle situation in which inflation of the 
air bag 64 is desired, the switch 302 closes. Electrical energy is 
directed to the initiator 220 over the wire bundle 284. The pyrotechnic 
material contained in the casing 222 of the initiator 220 ignites. 
Ignition of the pyrotechnic material produces combustion products which 
rupture the casing 222 of the initiator 220. The combustion products 
ignite the gas generating material 200 located in the housing 202 of the 
inflator 62. 
The gas-generating material, when ignited, generates inflation fluid which 
flows radially outward through the openings 204 of the inflator 62. The 
inflation fluid impinges on the deflector portion 210 of the mounting hub 
66. The deflector portion 210 of the mounting hub 66 shields the inlet 
portion of the air bag 64 from the hot inflation fluid flowing from the 
openings 204 in the inflator 62. The deflector portion 210 of the mounting 
hub 66 also deflects the inflation fluid to flow axially into the inlet 
portion 244 of the air bag 64. 
The inflation fluid then flows into the inflatable portion 242 of the air 
bag 64. The air bag 64 inflates and is forced against the cover 60. The 
inflating air bag 64 ruptures the central section 82 of the cover 60 and 
moves the deployment door panels 80 to pivot outward about the hinge 
portions 84. The air bag 64 expands outward from the steering wheel 22 
past the deployment door panels 80. 
The air bag 64 inflates from a folded, uninflated condition, as illustrated 
in FIG. 1 to a position between the steering wheel 22 and an occupant of 
the vehicle, such as the driver of the vehicle. The inflated air bag 64 
helps to protect the occupant from forcefully striking the steering wheel 
22 or other parts of the vehicle. 
During inflation of the air bag 64, the vents 146 allow aspiration of 
ambient air into the air bag from the steering column chamber 144. This 
aspiration is created by the rapid flow of inflation fluid from the 
inflator 62 which creates a negative pressure or vacuum within the vents 
146. This negative pressure draws ambient air from within the steering 
column chamber 144 and the mounting hub chamber 142. The ambient air is 
aspirated into the air bag 64 through the vents to help inflate the air 
bag 64. 
After the air bag 64 is fully inflated and inflation of the air bag is no 
longer desired, the air bag deflates in a known manner. Part of the 
inflation fluid from the deflating air bag may flow through the vents 146 
in the mounting hub 66 into the mounting hub chamber 142 and steering 
column chamber 144. 
It should be apparent that no fasteners, such as rivets, screws or bolts, 
or welds are required to attach the air bag 64 or the inflator 62 to the 
mounting hub 66. Also, no fasteners, such as rivets, screws or bolts, or 
welds are required to attach the air bag module 24 to the steering wheel 
22. Furthermore, no alignment of fastener openings is required since the 
air bag 64 and the mounting hub 66 have no openings for fasteners such as 
rivets, screws or bolts to extend through. This feature makes the air bag 
module 24 particularly suitable for assembly by a robot. 
The mounting hub 66 of the air bag module 24 supports both the module and 
the steering wheel 22 on the steering shaft 26. The steering wheel 
assembly 20 is secured to the steering shaft 26 with the single fastener 
40. Thus, the steering wheel 22 and the air bag module 24 can be installed 
in a vehicle, as a unit, with minimal assembly steps and associated costs. 
After assembly of the air bag module 24, it is relatively difficult to 
remove the inflator 62 from the mounting hub 66, without using special 
tools to remove the tabs 208 from the internal groove 184 in the mounting 
hub 66. Since the air bag 64 hides the manner in which the inflator is 
attached to the mounting hub 66, theft of the inflator 62 is made 
difficult. 
It is also relatively difficult to remove the steering wheel assembly 20 
and/or the air bag module 24 from the steering shaft 26, because the 
fastener 40 (FIG. 6) has theft or removal resistant features. The fastener 
40 includes the body portion 120, the threaded portion 122, a drive head 
320 and a frangible portion 322 connecting the body to the drive head. The 
drive head 320 receives a driving force to screw and unscrew the threaded 
portion 122 of the fastener 40 from the threaded portion 108 of the 
fastener opening 106 in the mounting hub 66. The frangible portion 322 
breaks to separate the drive head 320 from the body portion 120 upon the 
application of a driving force above a predetermined driving force. The 
body portion 120 which remains in the fastener opening 106 engages the 
surface defining the recess 124 in the steering shaft 26 to retain the 
steering wheel assembly 20 on the steering shaft. The threaded portion 122 
of the fastener 40 is difficult to remove from the threaded portion 108 of 
the fastener opening 106 in the mounting hub 66 after the frangible 
portion 322 is broken. 
The internal groove 184 for attaching the inflator 62 to the mounting hub 
66 is spaced axially downward and radially inward from the external groove 
182 of the mounting hub where the air bag 64 is attached to the mounting 
hub. As a result, during actuation of the inflator 62, the forces applied 
to the attachment between the inflator and the mounting hub 66 have 
minimal or no effect on the attachment between the air bag 64 and the 
mounting hub. Also, during inflation of the air bag 64, the forces 
transmitted from the air bag to the mounting hub 66 have minimal or no 
effect on the attachment between the inflator 62 and the mounting hub. 
The method of assembling the air bag module 24 of the present invention 
includes the following steps. A tubular shaped mounting hub 66 is provided 
to connect the air bag module 24 to a vehicle steering wheel frame 42 and 
to a vehicle steering shaft 26. An inflator 62 has a housing 202 with a 
flange 206. The flange 206 includes transversely extending tabs 208 for 
attaching the inflator 62 to the mounting hub 66. 
The inflator 62 is attached to the mounting hub 66 by first placing the 
inflator at least partially into the tubular portion 68 of the mounting 
hub. The flange 206 of the inflator 62 engages an upper end surface of the 
deflector portion 210 of the mounting hub 66, as viewed in FIG. 4. The 
inflator 62 is moved within the tubular portion 68 of the mounting hub 66 
to deflect the tabs 208 on the flange 206 radially inward and axially 
backward relative to the direction of movement of the inflator. When the 
inflator 62 is moved to a predetermined position within the tubular 
portion 68 of the mounting hub 66, such as against the inner shoulder 
flange 148, at least one of the tabs 208 resiliently expands radially 
outward into the inner groove 184 in the mounting hub. 
The air bag 64 is then attached to the mounting hub 66 by placing a 
mounting bead 240 of the air bag 64 over the upper end of the mounting hub 
66, as viewed in FIG. 4. The bead 240 of the air bag 64 is positioned in 
an upper section of the outer groove 182 in the mounting hub 66. A wall 
portion 266 of a guide ring 260 is placed around the bead 240 of the air 
bag 64 and a base 262 of the guide ring is placed into a lower section of 
the outer groove 182. 
The attaching steps are performed without rotatably aligning the inflator 
62 and the air bag 64 relative to the mounting hub 66. Specifically, the 
parts are merely moved axially relative to each other during assembly. The 
method of assembly is particularly suitable for robotic assembly because 
there are no mounting holes or fasteners which would otherwise have to be 
aligned. 
The method also includes the step of determining if the inflator 62 is 
present and properly positioned within the mounting hub 66. This is done 
preferably by a robot "looking" with a camera or sensor into the view port 
168. If the inflator 62 is not in the mounting hub 66 or if the inflator 
is not in the predetermined position in the mounting hub, the mounting hub 
is discarded so that it is not placed in the steering wheel 22. 
The method of assembling the air bag module 24 into the steering wheel 22 
includes providing a steering wheel frame 42. The mounting hub 66 which 
connects the steering wheel frame 42 to the steering shaft 26 is provided 
as part of the air bag module 24. The air bag module 24 is centered in the 
cavity 86 in steering wheel frame 42 by the leading edge 264 of the guide 
ring 260. The guide ring 260 guides movement of the air bag module 24 into 
the cavity 86. The outer shoulder flange 160 of the mounting hub 66 
engages a lower end portion 340 (FIG. 6) of the tubular central portion 44 
of the frame 42 of the steering wheel 22. The mounting hub 66 is retained 
in the frame 42 of the steering wheel 22 by deforming tabs 164 on a ring 
45 of the frame into the slots 162 in the mounting hub and against end 
surfaces 166 of the slots. 
The central portion 100 of the mounting hub 66 is connected to the steering 
shaft 26 of the vehicle with a removal resistant fastener 40. The opening 
102 in the central portion 100 of the mounting hub 66 receives a portion 
104 of the steering shaft 26. The recess 124 in the steering shaft 26 is 
aligned with the fastener opening 106 in the central portion 100 of the 
mounting hub 66. The fastener 40 is screwed into the central portion 100 
of the mounting hub 66 so a body 120 of the fastener engages a surface of 
the recess 124 to block relative rotational movement and relative axial 
movement between the mounting hub 66 and the steering shaft 26. 
A drive head 320 is connected to the body 120 at a frangible portion 322. 
The frangible portion 322 breaks upon a torsional driving force of a 
predetermined magnitude being applied to the drive head 320 of the 
fastener 40 when the threaded portion 122 and body 120 can no longer 
rotate. Applying a driving force to the fastener 40 which is at least as 
great as the predetermined magnitude breaks the frangible portion 322 and 
separates the drive head 320 from the body 120. Removal of the portion of 
the fastener 40 in the central portion 100 of the mounting hub 66 is 
relatively difficult since the drive head 320 is no longer attached. 
From the above description of the invention, those skilled in the art will 
perceive improvements, changes and modifications in the invention. Such 
improvements, changes and modifications within the skill of the art are 
intended to be covered by the appended claims.