Steering wheel assembly

A steering wheel assembly (10) mounts on a vehicle steering shaft (14) which has a threaded end portion (18). The steering wheel assembly (10) comprises a steering wheel armature (20), an inflatable vehicle occupant protection device (80) supported on the steering wheel armature (20), an inflator (90) for providing inflation fluid for inflating the inflatable vehicle occupant protection device (80), a hub (160) fixedly attached to the steering wheel armature (20) and for non-rotatable attachment to the steering shaft (14), and a rotatable fastener (180) rotatably supported on the hub (160) for axially forcing the hub onto the steering shaft (14) upon rotation of the fastener in a first direction. The fastener (180) has a first end portion (182) including gearing (190) for rotating the fastener and a second end portion (184) for threadedly engaging the threaded end portion (18) of the steering shaft (14) upon rotation of the fastener. A retainer plate (200) spaced from the inflator (90) is fixedly attached with the steering wheel armature (20). The retainer plate (200) overlies the first end portion (182) of the fastener (180) and retains the fastener on the steering wheel armature (20).

TECHNICAL FIELD
 The present invention is related to a steering wheel assembly which is
 mounted on a steering shaft of a vehicle and which is rotatable to steer
 the vehicle.
 BACKGROUND OF THE INVENTION
 A vehicle steering wheel is typically attached to a vehicle steering shaft
 by a splined connection. The splined connection non-rotatably attaches the
 steering wheel to the steering shaft and transmits torque from the
 steering wheel, namely, torque generated during turning of the steering
 wheel, to the steering shaft. The steering wheel is additionally secured
 to the steering wheel by a nut to prevent relative axial movement between
 the steering wheel and the steering shaft. The nut is screwed onto a
 threaded extension located on the end of the steering shaft which extends
 into the passenger compartment of the vehicle. Usually, the nut is
 accessed by an installer through the center of the steering wheel once the
 steering wheel has been placed onto the steering shaft. An air bag module
 is then typically mounted in the center of the steering wheel and covers
 the nut.
 Another type of connection for connecting a vehicle steering wheel to the
 steering shaft utilizes tapered surfaces on the steering shaft and inside
 a hub portion of the steering wheel. A gear-headed bolt is used to bring
 the tapered surfaces into non-rotatable engagement. Threads on the bolt
 engage an internally threaded surface on the steering shaft to pull the
 steering wheel onto the steering shaft. The gear head of the bolt is
 driven by a tool which is inserted into the steering wheel from the side
 (i.e., perpendicular to the axis of rotation).
 SUMMARY OF THE INVENTION
 The present invention is a steering wheel assembly to be mounted on a
 vehicle steering shaft which rotates about an axis to steer a vehicle and
 which has a threaded end portion. The steering wheel assembly comprises a
 steering wheel armature, an inflatable vehicle occupant protection device
 supported on the steering wheel armature, an inflator for providing
 inflation fluid for inflating the inflatable vehicle occupant protection
 device, a hub fixedly attached to the steering wheel armature and for
 non-rotatable attachment to the steering shaft, and a rotatable fastener
 rotatably supported on the hub for axially forcing the hub onto the
 steering shaft upon rotation of the fastener in a first direction. The
 fastener has a first end portion including gear means for rotating the
 fastener and a second end portion for threadedly engaging the threaded end
 portion of the steering shaft upon rotation of the fastener. A retainer
 plate spaced from the inflator is fixedly attached with the steering wheel
 armature. The retainer plate overlies the first end portion of the
 fastener and retains the fastener on the steering wheel armature.

DESCRIPTION OF PREFERRED EMBODIMENTS
 An exploded perspective view of a steering wheel assembly 10 constructed in
 accordance with the present invention is shown in FIG. 1. The steering
 wheel assembly 10 is to be mounted on an end portion 12 of a vehicle
 steering shaft 14 (shown in phantom lines in FIG. 2). The end portion 12
 of the steering shaft 14 is hollow and has a tapered outer surface 16
 which includes diametrically opposed flats (not shown). The end portion 12
 has an inner surface 18 which is threaded.
 The steering wheel assembly 10 includes a steering wheel armature 20 (FIG.
 1). The steering wheel armature 20 is preferably constructed in accordance
 with the invention described in Applicant's co-pending application U.S.
 Ser. No. 09/004,244, entitled "Steering Wheel Armature", filed Jan. 8,
 1998, Attorney Docket No. TRW(AP)3788. The armature 20 is preferably made
 of cast magnesium. The armature 20 has a circular outer rim portion 22 and
 an inner ring portion 24 connected by a plurality of radially and axially
 extending spokes 26. The ring portion 24 defines a central opening 28 in
 the armature 20. The ring portion 28 includes three axially extending
 apertures 30 spaced about the ring portion.
 The steering wheel assembly 10 further includes a plastic insert 40 located
 in the central opening 28 in the armature 20. The insert 40 is preferably
 made of a thermoplastic material. The insert 40 has four side walls 42 and
 front wall 44 which is connected to one of the side walls in a hinge area
 46. The side walls 42 and the front wall 44 together define a cavity 48 in
 the insert 40. A generally U-shaped gap 50 separates the front wall 44
 from three of the four side walls 42. The front wall 44 includes a
 plurality of openings 52.
 An integral one-piece cover 54 is molded about the steering wheel armature
 20 and the insert 40. The cover 54 covers the outer rim portion 22, the
 inner ring portion 24 and the spokes 26 of the steering wheel armature 20.
 Further, the cover 54 has a continuous outer surface 56 which extends
 uninterruptedly over the insert 40. The cover 54 is preferably made of a
 homogenous urethane material. As the cover 54 is molded about the insert
 40, portions of the material of the cover 54 fill the gap 50 defined in
 the insert to form a generally U-shaped tear seam 58 which is preferably
 not visible in the outer surface 56. Additional portions of the cover
 material fill the openings 52 in the front wall 44 of the insert 40 to
 form a composite deployment door 60. The tear seam 58 outlines the
 boundaries of the deployment door 60.
 It is contemplated that the cover 54 could alternatively be made of several
 cover portions rather than the one-piece cover shown. For example, an
 alternate cover construction could comprise a first cover portion covering
 the outer rim portion 22 and the spokes 26 of the armature 20, while a
 second cover portion covers the inner ring portion 24 of the armature and
 the insert 40.
 The steering wheel assembly 10 includes a horn switch 70 and an associated
 backing plate 72 for the horn switch. The horn switch 70 is preferably a
 membrane type switch known in the art. The backing plate 72 is a
 semi-rigid part preferably made of a plastic material. The horn switch 70
 and backing plate 72 are generally rectangular in shape and are located in
 the cavity 48 in the insert 40. The horn switch 70 is located between the
 deployment door 60 and the backing plate 72. The horn switch 70 is
 actuatable by exerting manual pressure on the outer surface 56 of the
 cover 54 covering the deployment door 60. Both the horn switch 70 and the
 backing plate 72 have an elongated slot 74. A fabric tether 76 having an
 hourglass shape and a pair of openings 78 at each end extends through the
 slots 74 in the horn switch 70 and the backing plate 72, respectively, and
 is folded over so that the openings 78 at both ends of the tether 76 are
 aligned.
 An inflatable vehicle occupant protection device, such as an air bag 80, is
 located in the cavity 48 in the insert 40 of the steering wheel assembly
 10. The air bag 80, shown schematically in the drawings, is folded inside
 the cavity 48 and abuts the backing plate 72 as well as the four side
 walls 42 of the insert 40. The air bag 80 is of known construction and
 includes a generally ring-shaped air bag retainer 82 (FIGS. 1 and 2)
 having four equally spaced mounting apertures (not numbered). The air bag
 retainer 82 is located inside the air bag 80 and encircles a mouth 84 of
 the air bag. A stud 86 extends through each of the four apertures in the
 air bag retainer 82 and through corresponding apertures (not numbered) in
 the air bag 80. Two of the studs 86 also extend through the openings 78 in
 the tether 76.
 The steering wheel assembly 10 further includes an air bag inflator 90 and
 a reaction plate 100. The air bag inflator 90 is electrically actuatable
 to provide inflation fluid to inflate the air bag 80. The inflator 90
 includes a cylindrical body portion 92 and a flange portion 94 extending
 radially from the body portion. The body portion 92 of the inflator 90
 includes a plurality of circumferentially spaced fluid exit ports 96 and
 is located inside the air bag 80. The flange portion 94 of the inflator 90
 is circular and extends beyond the mouth 84 of the air bag 80.
 The reaction plate 100 is a generally rectangular part preferably made of
 hardened steel. The reaction plate 100 includes a generally circular first
 depression 102 (FIG. 1) for receiving the flange portion 94 of the
 inflator 90. A generally circular second depression 104 (FIGS. 1 and 2) in
 the reaction plate 100 is formed radially inward of the first depression
 102 and accommodates wiring from the inflator 90. Four openings 106 (FIG.
 1) are spaced around the first depression 102 in the reaction plate 100
 and are located so as to align with the studs 86 projecting from the air
 bag retainer 82. Nuts 108 are screwed on the studs 86 to secure the air
 bag 80 and the inflator 90 to the reaction plate 100. The reaction plate
 100 further includes three openings 110 spaced and located identically to
 the three openings 30 in the ring portion 24 of the steering wheel
 armature 20.
 The steering wheel assembly 10 further comprises a mounting bracket 120
 commonly referred to as a spider or spider member. The mounting bracket
 120 is preferably made of cast magnesium. The mounting bracket 120 has
 three leg portions 122 which extend radially and axially from a base
 portion 124 (FIG. 3). Each leg portion 122 includes a foot portion 126
 located at a terminal end of the leg portion 122. The foot portions 126
 are axially offset from the base portion 124. Each foot portion 126 has an
 opening 128 which aligns with a respective one of the three openings 110
 in the reaction plate 100 and a respective one of the three openings 30 in
 the ring portion 24. Fasteners, such as self-tapping screws 130 (FIGS. 1
 and 2), extend through the openings 128 in the foot portions 126, through
 the openings 110 in the reaction plate 100, and into the openings 30 in
 the ring portion 24 to secure the mounting bracket 120 in the steering
 wheel assembly 10. The connection of the mounting bracket 120 to the ring
 portion 30 also secures the reaction plate 100, to which the air bag 80
 and the inflator 90 are attached, in the steering wheel assembly 10. The
 mounting bracket 120 further includes three openings 132 (FIG. 3) for
 receiving fasteners 134 which secure a back cover 240 to be described
 later.
 The base portion 124 of the mounting bracket 120 has a base surface 136
 facing the reaction plate 100 and an axially extending surface 138 (FIG.
 4) which extends perpendicularly from the base surface. The axially
 extending surface 138 defines a central passage 140 through the base
 portion 124 of the mounting bracket 120. The passage 140 is centered on an
 axis A. An annular ridge 142 extends from the axially extending surface
 138 radially inwardly into the passage 140. Two spaced apart holes 144 are
 located in the base portion 124 of the mounting bracket 120 surrounding
 the passage 140. Each of the holes 144 is threaded to receive a screw 146.
 The base portion 124 of the mounting bracket 120 further includes two
 radially and axially extending ridges 148. The ridges 148 define a
 generally rectangular channel 150 in the base portion 124 extending
 radially inward from a perimeter edge 152 of the mounting bracket 120 to
 the passage 140.
 A metal hub 160 is partially located in the passage 140 in the base portion
 124 of the mounting bracket 120. The hub 160 is generally tubular in shape
 and is centered on the axis A. The hub 160 is preferably cast into the
 mounting bracket 120 and is thus fixed to the bracket. The annular ridge
 142 of the mounting bracket 120 extends into the material of the hub 160
 to attach the hub to the mounting bracket non-rotatably during casting.
 Alternatively, it should be understood that the hub 160 could be formed
 integrally with the mounting bracket 120 as a one-piece cast part.
 The hub 160 includes radially extending first and second end surfaces 162
 and 164. The first end surface 162 faces toward the reaction plate 100 and
 is recessed from the base surface 136 of the mounting bracket 120 by a
 distance S1. An axially extending surface 166 defines a bore 168 extending
 from the first end surface 162 to the second end surface 164 of the hub
 160. The bore 168 is centered on the axis A. The surface 166 defining the
 bore 168 is tapered to have an interference fit with the tapered outer
 surface 16 of the steering shaft 14. The surface 166 inside the hub 160
 further includes diametrically opposed flats (not shown) for mating with
 the corresponding flats on the outer surface 16 of the steering shaft 14.
 The steering wheel assembly 10 includes a rotatable fastener 180 centered
 on the axis A. The fastener 180 has a first end portion 182 and a second
 end portion 184 which extends from the first end portion. The first and
 second end portions of the fastener 180 are fixed together and rotate
 together. Preferably, the fastener 180 is made from one piece of a
 metallic material.
 The first end portion 182 of the fastener 180 is disk-shaped and includes
 parallel, radially extending first and second surfaces 186 and 188,
 respectively (FIGS. 4 and 5). The first and second surfaces 186 and 188
 are separated by a distance S2 which is the axial thickness of the first
 end portion 182 of the fastener 180. The first end portion 182 of the
 fastener 180 is configured as a spur gear and thus has axially extending
 gear teeth 190 which are circumferentially disposed about the perimeter of
 the first end portion 182.
 The second end portion 184 of the fastener 190 extends axially from the
 second surface 188 of the first end portion 182 of the fastener. A
 cylindrical projection 192 extends axially from the first surface 186 of
 the first end portion 182 in a direction opposite the direction in which
 the second end portion 184 extends. The cylindrical projection 192 is
 centered on the axis A.
 The second end portion 184 of the fastener 180 includes an externally
 threaded portion 194 and an anti-cross-threading tip 196 adjacent the
 terminal end of the fastener. The threaded portion 194 of the second end
 portion 184 of the fastener 180 is threaded to mate with the threaded
 inner surface 18 in the end portion 12 of the steering shaft 14.
 The first end portion 182 of the fastener 190 rests on and is supported for
 rotation by the first end surface 162 of the hub 160. The second end
 portion 184 of the fastener 190 is located within and rotatable in the
 bore 168 through the hub 160. The fastener 190 is rotatable about the axis
 A which is coaxial with the axis of rotation of the vehicle steering shaft
 14.
 The steering wheel assembly 10 further includes a retainer plate 200 (FIGS.
 3 and 4). The retainer plate 200 is preferably made of hardened steel. The
 retainer plate 200 has a generally square central portion 202 partially
 encircled by a peripheral portion 204 of the retainer plate. Both the
 central portion 202 and the peripheral portion 204 of the retainer plate
 200 are planar. The peripheral portion 204 of the retainer plate 200 abuts
 the base surface 136 of the mounting bracket 120. The central portion 202
 of the retainer plate 200 is axially offset from the peripheral portion
 204 by a distance S3.
 The perimeter of the retainer plate 200 is defined by three side surfaces.
 First and second side surfaces 206 and 208 are planar and are
 perpendicular to one another. A third side surface 210 connects the first
 and second side surfaces 206 and 208 and is arcuate. Both the first and
 second side surfaces 206 and 208 extend along the peripheral portion 202
 and the central portion 204 of the retainer plate 200. The third side
 surface 210 extends only along the peripheral portion 204 of the retainer
 plate 200.
 The central portion 202 of the reaction plate 200 includes a circular
 opening 212. The cylindrical projection 192 on the fastener 180 is
 received in the opening 212 with sufficient clearance around the
 projection to allow for unrestricted rotation of the fastener in the
 opening. The central portion 202 of the retainer plate 200 further
 includes a reaction surface 214 surrounding the opening 212 and facing the
 fastener 180.
 The peripheral portion 204 of the retainer plate 200 includes two spaced
 apart clearance holes 216. The clearance holes 216 in the retainer plate
 200 align with the holes 144 in the base portion 124 of the mounting
 bracket 120. The screws 146 extend through the holes 216 in the retainer
 plate 200 and into the threaded holes 144 in the base portion 124 of the
 mounting bracket 120 to attach the retainer plate to the mounting bracket.
 With the retainer plate 200 attached to the mounting bracket 120, an axial
 space 220 is formed between first end surface 162 of the hub 160 and the
 central portion 202 of the retainer plate 200. The axial space 220 has a
 height S4 which is equal to the sum of the distance S1 (between the first
 end surface 162 of the hub 160 and the base surface 136 of the mounting
 bracket 120) and the distance S3 (the axial offset of the retainer plate
 200). The height S4 of the axial space 220 is greater than the axial
 thickness S2 of the first end portion 182 of the fastener 180. The height
 S4 of the axial space 220 permits limited axial movement of the first end
 portion 182 of the fastener 180 in the axial space while retaining the
 first end portion 182 of the fastener 180 in the space and thereby
 retaining the second end portion 184 of the fastener in the bore 168 in
 the hub 160.
 The back cover 240 (FIG. 5) for the steering wheel assembly 10 encloses the
 back side of the steering wheel assembly facing the vehicle steering shaft
 14. The back cover 240 is preferably made of ABS molded plastic but could
 be made of another plastic material. The back cover 240 has a large
 opening 242 for encircling a vehicle steering column (not shown). The
 opening 242 is defined by an axially extending cylindrical inner wall 244
 and an outer wall 246 which is connected to the inner wall by a back face
 248. The back cover 240 includes three radially extending flanges spaced
 about the opening 242 which serve as mount locations 250 for the back
 cover 240. Each mount location 250 has a hole 252 for receiving a
 respective one of the fasteners 134. The back cover 240 is attached to the
 mounting bracket 120 by the three fasteners 134 which extend through the
 holes 252 in the mount locations 250.
 The outer wall 246 includes first and second wing portions 254 and 256
 (FIGS. 1 and 5) located opposite one another. A lower wall 258 extends
 between the first and second wing portions 254 and 256 and also connects
 with the back face 248 of the back cover 240. Each of the wing portions
 254 and 256 has an ear tab 260 for engaging a surface (not shown) in the
 back side (i.e., facing away from the vehicle occupant) of the molded
 cover 54 between adjacent spokes 26 of the steering wheel assembly 10.
 The lower wall 258 of the back cover 240 includes a hinged trap door 262.
 The trap door 262 is generally square in shape and is attached to the
 lower wall 258 by a living hinge 264 formed in the material of the lower
 wall. One or more tabs 266 on the trap door 262 hold the trap door flush
 with the lower wall 258. A groove 268 is formed in the lower wall 258
 immediately above the trap door 262. The groove 268 allows a tool such as
 a screwdriver to be inserted underneath the trap door 262 in order to pry
 the trap door open. The living hinge 264 permits the trap door 262 to fold
 out away from the steering wheel assembly 10 so that an attachment tool
 (not shown) can be inserted inside the steering wheel assembly 10 to
 rotate the fastener 180.
 To attach the steering wheel assembly 10 to the steering shaft 14, the hub
 160 in the mounting brackeft 120 is located coaxial with the steering
 shaft. The hub 160 is placed oaver the end 12 of the steering shaft 14
 such that the end of the steering shaft is received in the bore 168 in the
 hub. The corresponding flats on the outer surface 16 of the steering shaft
 14 and in the bore 168 are aligned. By manually pushing the steering wheel
 assembly 10 toward the steering shaft 14, the tapered outer surface 16 of
 the steering shaft is brought into contact with the tapered surface 166
 inside the bore 168 in the hub 160. The anti-cross-threading portion 196
 of the second end portion 184 of the fastener 180 extends down inside the
 steering shaft 14 and the threaded portion 194 of the fastener engages the
 threaded inner surface 18 of the steering shaft. The trap door 262 in the
 back cover 240 of the steering wheel assembly 10 is then opened.
 An attachment tool (not shown) for rotating the fastener 180 is inserted
 through the trap door 262. The attachment tool slides into the channel 150
 formed in the base portion 124 of the mounting bracket 120 until gear
 teeth on the attachment tool meshingly engage the gear teeth 190 on the
 first end portion 182 of the fastener 180. The gear teeth on the
 attachment tool are rotated in a direction causing the fastener 180 to
 rotate in a tightening direction and to begin screwing itself into the end
 12 of the steering shaft 14. The retainer plate 200 overlying the first
 end portion 182 of the fastener 180 stabilizes the fastener during
 rotation and prevents the fastener from being tilted due to axial forces
 exerted on the fastener by the attachment tool or due to torque resulting
 from the rotation of the gears.
 The rotation of the fastener 180 in the tightening direction moves the
 second surface 188 in the first end portion 182 of the fastener into
 contact with the first end surface 162 of the hub 160 and exerts an axial
 force on the hub which causes the steering wheel assembly 10 to be pulled
 downward (to the right as viewed in FIG. 2) onto the steering shaft 14. As
 the steering wheel assembly 10 is forced onto steering shaft 14, the
 tapered surfaces 166 and 16 in the hub 160 and on the steering shaft 14,
 respectively, are pressed together to secure the steering wheel assembly
 to the steering shaft.
 The diametrically opposed flats on the surface 16 of the steering shaft 14
 and in the bore 168 in the hub 160 provide an alignment of the steering
 wheel assembly 10 and the steering shaft as well as a means for
 transmitting torque from the steering wheel assembly to the steering
 shaft. Torque which is produced by turning the steering wheel assembly 10
 (i.e., steering the vehicle) is transmitted through the steering wheel
 armature 20 and the mounting bracket 120 to the hub 160 which is now
 non-rotatably attached to the steering shaft 14.
 The steering wheel assembly 10 is removed from the steering shaft 14 by
 opening the trap door 262 and inserting the attachment tool so that its
 gear teeth are engaged with the gear teeth 190 on the fastener 180. The
 fastener 180 is then rotated in an untightening direction opposite the
 tightening direction. Rotation in the untightening direction causes the
 fastener 180 to move axially and relatively away from the steering shaft
 14. The second surface 188 in the first end portion 182 of the fastener
 180 comes out of contact with the first end surface 162 of the hub 160.
 Continued rotation of the fastener 180 in the untightening direction
 brings the first surface 186 in the first end portion 182 of the fastener
 180 into contact with the reaction surface 214 in the central portion 202
 of the retainer plate 200. With the surface 186 of the fastener 180
 abutting the reaction surface 214 of the retainer plate 200, rotation of
 the fastener applies an axial force on the steering wheel assembly 10 in a
 direction away from the steering shaft 14 and causes the hub 160 to
 disengage from the steering shaft.
 FIG. 6 illustrates a second embodiment of the present invention. In the
 embodiment of FIG. 6, identical structure to that of the previous
 embodiment is identified with the same reference numerals. FIG. 6
 illustrates a retainer plate 270 having a slightly modified structure from
 the retainer plate 200 of the previous embodiment.
 The retainer plate 270 has a larger central portion 272 than the retainer
 plate 200. The central portion 272 extends completely over the first end
 portion of the fastener 180 and covers a portion of the channel 150 formed
 in the mounting bracket 120 by ridges 148. A small square-shaped opening
 274 is located in the portion of the central portion 272 covering the
 channel 150. Further, the central portion 272 of the retainer plate 270
 includes an extension 280 which extends in the direction of one of the leg
 portions 122 of the mounting bracket 120 and which provides the central
 portion with an L-shaped configuration. The extension 280 of the central
 portion 272 has an additional opening (not shown) for receiving a third
 fastener 146 for securing the retainer plate 270 to the mounting bracket
 120.
 The retainer plate 270 functions identically to the retainer plate 200
 described in the previous embodiment, but has additional advantages. By
 virtue of its larger size and its three mounting locations, the retainer
 plate 270 is able to withstand larger forces than the retainer plate 200
 on its reaction surface 214 (not shown) during untightening of the
 fastener 180. Because a portion of the channel 150 which guides the
 attachment tool to the fastener 180 is covered by the retainer plate 270,
 the retainer plate stabilizes the end of the attachment tool during
 tightening and/or untightening of the fastener 180. Finally, the
 square-shaped opening 274 in the central portion 272 of the retainer plate
 270 overlying the channel 150 accommodates a retention feature on the
 attachment tool to further stabilize the tool during tightening and/or
 untightening of the fastener 180.
 FIGS. 7 and 8 illustrate a steering wheel assembly 300 constructed in
 accordance with a third embodiment of the present invention. The steering
 wheel assembly 300 includes a steering wheel armature 310 having a rim
 portion (not shown) and a central mounting plate 312 connected to the rim
 portion by spokes 314. The mounting plate 312 includes a hub portion 316
 with a bore 318 defined by a tapered surface 320. The hub portion 316 may
 be formed in one piece with the mounting plate 312 or may be a separate
 part which is cast into the mounting plate. A plurality of bosses 322
 extend from the mounting plate 312 in a direction away from the hub
 portion 316. A clearance hole 324 extends through each of the bosses 322
 and through the mounting plate 312.
 A rotatable fastener 330 identical to the fastener 180 described in the
 first embodiment is supported for rotation by the hub portion 316. A first
 end portion 332 of the fastener 330 comprises a spur gear with a
 cylindrical projection 334 extending axially away from the hub portion
 316. A second end portion 336 of the fastener 330 includes a threaded
 outer surface 338 for engaging the threaded inner surface 18 of the
 vehicle steering shaft 14.
 The steering wheel assembly 300 includes a retainer plate 340 overlying the
 first end portion 332 of the fastener 330. The retainer plate 340 is
 generally rectangular in shape and has a central portion 342 partially
 encircled by a peripheral portion 344. The central portion 342 is axially
 offset from the peripheral portion 344 and has an opening 346 for
 receiving the projection 334 on the first end portion 332 of the fastener
 330. The peripheral portion 344 has a plurality of openings 348 which
 align with a plurality of threaded openings 350 in the mounting plate 312
 and which receive fasteners 352 to secure the peripheral portion of the
 retainer plate 340 to the mounting plate.
 The steering wheel assembly 300 further includes an inflatable vehicle
 occupant protection device in the form of an air bag module 360 which is
 secured to the mounting plate 312. The air bag module 360 includes a
 folded air bag 362, an air bag retainer 364, an air bag inflator 366, and
 a reaction plate 368. The reaction plate 368 is supported by the bosses
 322. A plurality of studs 370 extend through the air bag retainer 364, the
 air bag 362, and the reaction plate 368. Each of the studs 370 further
 extends through a respective one of the clearance holes 324 in the bosses
 322 and the mounting plate 312. Nuts 372 are screwed onto the studs 370 to
 secure the air bag module 360 in the steering wheel assembly 300.
 The steering wheel assembly 300 is attached to and removed from the
 steering shaft 14 by rotating the fastener 330 as described above in the
 first embodiment regarding the fastener 180. The reaction plate 340
 functions identically to the reaction plate 200 described above.
 FIG. 9 illustrates a steering wheel assembly 400 constructed in accordance
 with a fourth embodiment of the present invention. In the embodiment of
 FIG. 9, identical structure to that of the third embodiment of FIGS. 7 and
 8 is identified with same reference numerals. S1 Similar structure to that
 of the third embodiment is also identified with the same reference
 numerals, but with a prime added.
 The steering wheel assembly 400 includes an air bag module 360' and a
 mounting bracket 410. The air bag module 360' includes a reaction plate
 430 with a recessed wall portion 432 which is located axially adjacent the
 first end portion 332 of the fastener 330.
 The mounting bracket 410 has a base portion 412 and a flange portion 414
 connected by a radially and axially extending connecting portion 416. The
 base portion 412 has a centrally located opening 418 for receiving a
 portion of the rotatable fastener 330. The fastener 330 is supported for
 rotation by the base portion 412 of the mounting bracket 410. The flange
 portion 414 of the mounting bracket 410 has a plurality of spaced apart
 openings 420 for receiving bolts 422 for securing the air bag module 360'.
 The steering wheel assembly 400 is attached to and removed from the
 steering shaft 14 by rotating the fastener 330 substantially as described
 above in the first embodiment. In the fourth embodiment of FIG. 9, the
 recessed wall portion 432 of the reaction plate 430 functions as a
 retainer plate to axially retain the fastener 330, stabilize the fastener
 during rotation, and provide a reaction surface during rotation of the
 fastener in the untightening direction. Further, the steering wheel
 assembly 400 eliminates bolts which are typically used to attach the air
 bag module 360' to the mounting plate 312' of the steering wheel armature
 310' because the fastener 330 secures the air bag module to the steering
 wheel armature in addition to securing the steering wheel assembly to the
 steering shaft 14.
 From the above description of the invention, those skilled in the art will
 perceive improvements, changes and modifications. Such improvements,
 changes and modifications within the skill of the art are intended to be
 covered by the appended claims.