DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] Referring to FIG. 1, a vehicle steering wheel 10 includes a central hub portion 12 , a generally circular outer rim portion 14 , and a plurality of spokes 16 extending between the hub portion 12 and the rim portion 14 . An air bag module 18 is mounted within the hub portion 12 of the steering wheel 10 . The air bag module 18 includes an air bag cushion (not shown) and an inflator (not shown) for generating gas to inflate the air bag cushion. The air bag module 18 also includes an air bag cover assembly generally designated as 20 .

[0021] As best illustrated in FIGS. 1, 3 , 4 and 6 , the air bag cover assembly 20 includes a cover element 22 including an upper edge 21 and a lower edge 23 , a membrane horn switch 24 , and a reaction plate 26 . It is contemplated that the reaction plate 26 may be of a multi-piece construction if desired so as to facilitate outward deployment of the underlying air bag cushion. Due to the very thin nature of the membrane horn switch 24 , the membrane horn switch may be of either a single piece or a multi-piece construction. However, a single piece construction may be preferred to minimize complexity during the assembly process.

[0022] In accordance with one aspect of the present invention, the cover element 22 includes a contoured outer show surface 30 ( FIG. 4 ) and a corresponding contoured inner surface 32 . A plurality of mounting posts 34 arranged in pairs extend away from locations at the inner surface 32 for insertion through complimentary aligned openings within the membrane horn switch 24 and the reaction plate 26 . According to a potentially preferred configuration, both mounting posts 34 in each pair pass through a single opening 60 within the membrane horn switch 24 ( FIG. 6 ) while each of the mounting posts 34 thereafter passes through an aligned discrete reaction plate post acceptance aperture 36 within the reaction plate 26 . As illustrated in FIG. 3 , the reaction plate post acceptance apertures 36 are preferably arranged in complementary pairs predominantly around the periphery of the reaction plate 26 . Following insertion of the mounting posts 34 through the aligned openings within the membrane horn switch 24 and reaction plate 26 , the distal ends of the mounting posts 34 may be fused together by heat so as to maintain their assembled positional relationship.

[0023] Referring to FIG. 2, a typical prior art air bag cover assembly 20 ′ is illustrated wherein the cover element 22 ′ is of a substantially contoured geometry curved along an surface between the upper edge 21 and a lower edge 23 ′. In such prior art air bag cover assembly 20 ′, the reaction plate 26 ′ typically has been substantially planar in configuration thereby causing the membrane horn switch 24 ′ to adopt a similar planar orientation. As illustrated, the use of such a substantially flat reaction plate 26 ′ in combination with a curved cover element 22 ′ gives rise to a varying distance between the membrane horn switch 24 ′ and the inner surface 32 ′ of the cover element 22 ′. This variation in distance between the inner surface 32 ′ and the membrane horn switch 24 ′ may be particularly pronounced in so called “single shot” cover elements which incorporate only a single layer of material. As will be appreciated, a variation in the distance between the membrane horn switch 24 ′ and the cover element 22 ′ may give rise to varying levels of force being required to effect activating contact between the inner surface 32 ′ and the membrane horn switch.

[0024] As illustrated in FIGS. 3, 4 , and 7 , the present invention addresses the deficiencies of the prior art designs through incorporation of an improved reaction plate 26 of a generally contoured curved construction substantially corresponding to the curvature of the inner surface 32 of the cover element 22 across the operative region supporting the membrane horn switch 24 . The improved reaction plate 26 further provides enhanced features to facilitate the efficient and effective attachment of the curved construction to the cover element 22 .

[0025] As best illustrated in FIG. 3 , the reaction plate 26 is preferably of a two piece construction having a general plan geometry substantially corresponding to the desired activation area for the membrane horn switch 24 . Accordingly, the reaction plate 26 preferably includes an upper plate edge 41 and a lower plate edge 43 for disposition adjacent the upper edge 21 and the lower edge 23 of the cover element 22 .

[0026] As illustrated, the reaction plate 26 is preferably of a two piece construction including a first segment 50 and a second segment 52 matable to one another at an interior location beneath the cover element 22 such as beneath a central tear seam 54 ( FIG. 1 ) disposed across the cover element 22 . Such a segmented construction may reduce the force required to effect outward deployment of an underlined air bag cushion (not shown) while at the same time providing a substantially uniform support surface for the membrane horn switch. Of course, a single piece reaction plate may also be utilized if desired.

[0027] In accordance with the present invention, the reaction plate is preferably curved so as to form a generally convex surface between the upper plate edge 41 and the lower plate edge 43 . As illustrated, this curvature preferably corresponds substantially to the degree of curvature across the inner surface 32 of the cover element 22 such that upon assembly a substantially uniform distance is maintained between the membrane horn switch 24 and the cover element 22 . If desired, the reaction plate 26 may also be slightly curved in the dimension extending between lateral sides 44 , 46 . However it is believed that such curvature should not be excessive so as to avoid placing undue stress upon the membrane horn switch 24 .

[0028] According to the potentially preferred embodiment, the membrane horn switch 24 is held in place atop the reaction plate 26 by a plurality of clip elements 56 disposed at the periphery of the reaction plate 26 . In assembly, the horn switch may be slid between the clip elements 56 and standoff elements 58 disposed across the surface of the reaction plate 26 in surrounding relation to the clip elements 56 . The clip elements 56 and standoff elements 58 thus serve to hold the membrane horn switch 24 at a desired height relative to the surface of the reaction plate.

[0029] In addition to the relative height control provided by the clip elements 56 and standoff elements 58 , the membrane horn switch 24 is secured against slipping out of position by passing one or both mounting posts 34 through aligned apertures 60 ( FIG. 6 ) at the perimeter of the membrane horn switch 24 in a manner as will be well known to those of skill in the art.

[0030] As illustrated in FIGS. 3, 4 and 7 , in the illustrated and potentially preferred embodiment the reaction plate 26 preferably includes a plurality of rounded force concentrating projections 45 arranged across the upper surface of the reaction plate 26 and beneath the operative portions of the membrane horn switch 24 . As will be appreciated, such projections provide for the concentration of force at substantially discrete points across the membrane horn switch upon the application of pressure. Such force concentration may facilitate the ability to maintain the requisite contact between opposing surfaces in the horn switch even if force is applied across a relatively broad surface by the operator.

[0031] One potentially preferred configuration for the membrane horn switch is illustrated in FIG. 6 . As shown, in this configuration the membrane horn switch 24 incorporates a plurality of horn switch post acceptance apertures 60 . The horn switch post acceptance apertures 60 preferably each except two mounting posts 34 and are positioned for alignment substantially over the reaction plate post acceptance apertures 36 so as to permit the substantially unobstructed insertion of the mounting posts 34 through both the membrane horn switch 24 and the reaction plate 26 during assembly.

[0032] As shown in FIG. 5 , the mounting posts 34 preferably include a proximal shoulder portion 64 of enhanced width extending away from the inner surface 32 of the cover element 22 . The mounting posts 34 thereafter narrow to a reduced operative width distal portion 65 corresponding substantially to the dimensions of the reaction plate post acceptance apertures 36 . Thus, the mounting posts 34 may be inserted through the reaction plate post acceptance apertures 36 until reaching the shoulder portion 64 at which point further insertion is prevented. Conversely, the horn switch post acceptance apertures 60 are of sufficient dimension to permit the complete insertion of all portions of the mounting posts 34 therethrough.

[0033] As illustrated, according to the potentially preferred embodiment the reaction plate post acceptance apertures 36 are surrounded by a substantially flat surface zone 66 forming a shoulder stop surface. This substantially flat surface zone 66 is preferably formed as a depression of variable depth across the upper surface of the reaction plate 26 with depth of the depression increasing towards the interior of the reaction plate 26 . Such a variable depth depression has been found to be an effective and efficient mechanism to provide a substantially uniform support surface for the shoulder portions 64 of the mounting posts 34 . This, in turn, promotes the ability of the shoulder portions 64 to be held in stable supported contact with the substantially flat surface zone 66 . The stable interface between the shoulder portions and the substantially flat surface zones 66 promotes the establishment and maintenance of proper relative positioning between the cover element 22 and the reaction plate 26 . In addition, the walls of the depression which surround the shoulder portions 64 assist in establishing proper positioning of the cover element 22 relative to the reaction plate 26 and provide further support against undesired lateral slippage once insertion of the mounting posts 34 has taken place.

[0034] As illustrated in FIGS. 4 and 7 , the reaction plate 26 preferably also includes a plurality of protuberant boss elements 68 arranged across the lower surface of the reaction plate 26 . As shown, these boss elements 68 preferably surround the reaction plate post acceptance apertures 36 . The boss elements are preferably substantially flat on their underside and provide a substantially uniform surface for the fusion of the distal ends of the mounting posts 34 thereby locking the elements of the air bag cover assembly 20 in place. In addition, the boss elements 68 also serve to provide an enhanced mass heat sink to absorb excess energy during the fusion of the mounting posts 34 to one another.

[0035] It is believed that the present invention provides a new and useful air bag cover assembly useful in applications requiring the use of contoured air bag covers. While specific embodiments of the present invention have been illustrated and described, it is to be understood that the invention is in no way to be limited to such illustrated and described embodiments since modifications may be made and other embodiments of the principles of this invention may occur to those of skill in the art to which this invention pertains. Therefore, it is intended by the appended claims to cover all such modifications and other embodiments as may incorporate the broad principles of this invention within the true spirit and scope thereof.