STEERING WHEEL ASSEMBLY

Abstract: A simplified integrated steering wheel assembly (20) has a one-piece steering wheel armature (30) and an airbag scrim (24). A cover (22) is molded over a portion of the steering wheel armature and a portion of the airbag scrim. The airbag scrim forms a cavity (90) for containing an airbag (50) and an airbag inflator (46) between the airbag scrim and a hub portion (32) of the steering wheel armature.

Description: STEERING WHEEL ASSEMBLY This invention relates to steering wheel assemblies having airbags integral therewith. Steering wheel assemblies have been proposed wherein the steering wheel and airbag are attached to the vehicle as a modular unit. An integrated steering wheel assembly includes a cover, a steering wheel armature, and an airbag. Most covers are formed of a synthetic plastic material that is molded over a portion of the steering wheel armature and the airbag. The airbag is generally installed after the cover has been molded onto the steering wheel armature and may be installed by a manufacturer other than the manufacturer of the steering wheel armature. Thus, it is generally required that the molding process for the cover provide a cavity between the cover and a portion of the steering wheel armature to accommodate installation of the airbag. Currently, there are two general methods used to provide the cavity for the airbag. The first method is to use a steering wheel assembly that has a two- piece steering wheel armature. In such a system, the cover is molded over the first piece of the armature. Then, the second piece of the armature is secured to the first piece of the armature and a cavity for the airbag is formed between the two pieces of the armature. The second method is to provide a steering wheel armature that includes a support ring. When the cover is molded over such an armature, the support ring supports the cover and creates a cavity for the airbag. Both methods require a lifter mechanism in the cover mold. Both of these methods have several disadvantages. First, both require a large amount of material to form either the two-piece armature or the armature and hoop. Material cost can be significant because these parts are often formed from magnesium. Second, both methods require that the steering wheel assembly be relatively thick to accommodate the airbag module. Third, adaptability of these methods to changes in the styling of the cover is very low. Generally, changes in the styling of the cover will require modification of the armature tooling, which causes delays and can be expensive. Fourth, both of these methods frequently suffer from the defect of the lifter mechanism in the cover mold producing a read-through line in the cover material. Finally, with the prior methods, it has proven difficult to control the thickness of the cover forwardly of the airbag. Thus, it is desirable to produce a method and design for an integrated steering wheel assembly that is simpler and that eliminates the additional elements of either a two-piece armature or an armature with a hoop There is provided in accordance with the present invention a simplified integrated steering wheel assembly. The integrated steering wheel assembly includes fewer parts than a typical steering wheel assembly and is readily adaptable to changes in styling of the steering wheel assembly. Brief Description of the Drawings Fig. 1 is a perspective view of an integrated steering wheel assembly, with an airbag scrim shown in phantom, according to the present invention. Fig. 2 is a cross-sectional view of the integrated steering wheel assembly. Fig. 3 is an exploded perspective view of the airbag scrim, a steering wheel armature, and a pair of positioning pins. Fig. 4 is a partial cross-sectional view of the steering wheel armature and the airbag scrim in a cover mold. Fig. 5 is an enlarged view of a portion of the airbag scrim and a hub portion of the steering wheel armature. Fig. β is an enlarged cross-sectional view of a tear seam on the airbag scrim. Fig. 7 is a perspective view of a portion of the steering wheel armature. Detailed Description of the Invention In Fig. 1, an integrated steering wheel assembly is shown generally at 20. A cover 22 covers the majority of the integrated steering wheel assembly 20. An airbag scrim 24 is shown in phantom. The airbag scrim 24 includes a tear seam 26 and a pair of pockets 28, only one of which is shown. Fig. 2 is a cross-sectional view of the integrated steering wheel assembly 20. The integrated steering wheel assembly 20 includes a steering wheel armature 30 having a hub portion 32 and an outer rim portion 34. A pair of support tabs 36 and a pair of bosses 38 are located on the hub portion 32. An aperture 40 for the steering column (not shown) is also located on the hub portion 32. A mounting hole 42 is located in each of the bosses 38. Each of the pockets 28 on the airbag scrim 24 fit over one of the support tabs 36. An airbag inflator 46 mounted on a airbag inflator bracket 48 and an airbag 50, all shown in phantom, are located between the airbag scrim 24 and the hub portion 32. The airbag inflator bracket 48 is secured to the hub portion 32 by means of mounting bolts (not shown) that extend through mounting holes 42. The airbag inflator 46 and the airbag 50 are known in the art and form no portion of the present invention. As will be understood by one having ordinary skill in the art, the thickness of the cover 22 over the tear seam 26 would desirably be uniform and thin in order for the airbag inflator 46 to operate properly. The prior art has had difficulty in properly positioning the scrim during molding, and thus has had difficulty achieving uniform thickness. Fig. 3 is an exploded perspective view of the airbag scrim 24 and the steering wheel armature 30. A plurality of spokes 52 connect the hub portion 32 to the outer rim portion 34. The shape of the spokes 52 and their location may be varied. The hub portion 32 includes a number of tooling apertures 54. Two apertures 56 are located on the airbag scrim 24. The apertures 56 are shaped to fit over the bosses 38. Two positioning pins 58 are used to position the airbag scrim 24 relative to the hub portion 32 when the cover 22 is being molded. The positioning pins 58 include a first end 60 and a boss 62 located on the first end 60. Two vacuum channels 64 extend through each positioning pin 58 to the first end 60. Fig. 4 is a partial cross-sectional view of the steering wheel armature 30 and the airbag scrim 24 in a cover mold 70 prior to molding of the cover 22. The cover mold 70 includes a cavity 72 having a contour that is the same as the contour of the outer surface of the cover 22. A vacuum line 74 connects each vacuum channel 64 to a vacuum source 76. The vacuum source 76 is of a conventional type known in the art. The boss 62 of each positioning pin 58 preferably extends into the tear seam 26 of the airbag scrim 24. The positioning pins 58 are located in the cover mold 70 to hold the airbag scrim 24 at the appropriate distance from the hub portion 32. When a vacuum from the vacuum source 76 is applied through the vacuum channels 64, the positioning pins 58 hold the airbag scrim 24 against the hub portion 32 while a cover material is added to the cover mold 70. The positioning pins 58 are shown as extending through aperture 40 and tooling aperture 54. If desired, the positioning pins 58 could extend through other parts of the hub portion 32. As shown in Fig. 5, the apertures 56 in the airbag scrim 24 fit over the bosses 38 of the hub portion 32. Fig. 6 is an enlarged view of the tear seam 26. The tear seam 26 includes a first wall 80, a second wall 82 and a third wall 84. The second wall 82 is oriented perpendicularly to the first wall 80 and the third wall 84. A substantially 90 • joint 86 joins the second wall 82 to the first wall 80. A radiused joint 88 joins the second wall 82 to the third wall 84. The first, second and third walls 80, 82 and 84 define a cavity 90. The substantially 90 degree joint 86 between the first wall 80 and the second wall 82 creates a more fragile joint than the radiused joint 88. Thus, the tear seam 26 is designed such that when the airbag inflator 46 inflates the airbag 50 the tear seam 26 ruptures along the substantially 90 degree joint 86. When the steering wheel armature 30 is positioned in the cover mold 70, the bosses 62 of the positioning pins 58 are located in the cavity 90. Fig. 7 is a perspective view of a portion of the steering wheel armature 30. Fig. 7 shows the relationship between the hub portion 32, boss 38, support tab 36, spokes 52, and outer rim portion 34. If desired, the cover 22 could be formed from a wide variety of materials. It is most preferable that the cover 22 be formed from class A urethane. The steering wheel armature 30 is most preferably formed from magnesium, but could also be formed of other materials such as die cast aluminum.

Claims: Claims : 1. A steering wheel assembly (20) comprising: a steering wheel armature (30) having a hub portion (32), an outer rim portion (34) and a plurality of spokes (52) extending between said hub portion and said outer rim portion; an airbag scrim (24) having an elongated continuous tear seam (26) , said airbag scrim secured to said hub portion, said tear seam spaced apart from said hub portion and extending from said airbag scrim toward a cover (22); and said cover integrally covering a portion of said steering wheel armature and a portion of said airbag scrim including said tear seam. 2. The steering wheel assembly (20) of Claim 1 wherein said hub portion (32) includes one of a plurality of support tabs (36) and pockets (28) and said airbag scrim (24) includes a plurality of the other support tabs and pockets, each of said pockets receiving one of said support tabs when said airbag scrim is secured to said hub portion, and said support tabs not being movable within said pockets. 3. The steering wheel assembly (20) of Claim 2 wherein said support tabs (36) comprises two upwardly extending support tabs located on said hub portion and said plurality of pockets (28) comprises two downwardly extending pockets, said tear seam (26) positioned between said two pockets. 4. The steering wheel assembly (20) of Claim 1 wherein said hub portion (32) includes a plurality of bosses (38) and said airbag scrim includes a plurality of apertures (56), each of said apertures surrounding one of said bosses when said airbag scrim (24) is secured to said hub portion. 5. The steering wheel assembly (20) of Claim 4 wherein said plurality of bosses comprises a pair of oval shaped bosses (38) located on said hub portion and said plurality of apertures (56) comprises a pair of oval shaped apertures, said tear seam (26) positioned between said pair of apertures. 6. The steering wheel assembly (20) of Claim 1 wherein said cover (22) comprises urethane. 7. The steering wheel assembly (20) of Claim 1 further comprising an airbag (50) and an airbag inflator (46) , said airbag and said airbag inflator located between said airbag scrim (24) and said hub portion (32) and secured to said hub portion.

Inventors: LUO GUANHONG JASON, MUSE BOB G, LUO, GUANHONG (JASON), MUSE, BOB, G.
Applicants: BREED AUTOMOTIVE TECH, LUO GUANHONG JASON, MUSE BOB G, BREED AUTOMOTIVE TECHNOLOGY, INC., LUO, GUANHONG (JASON), MUSE, BOB, G.
Application year: 1999
Main classification: B60R21
IPC codes: B60R21