Airbag cover

An airbag cover includes a tear seam formed by a groove in the front side of the airbag cover as well as the groove in the back side of the airbag cover. These grooves are separated by a transverse layer. The transverse layer has a length, thickness and angle or orientation with respect to the airbag cover. This length, thickness, and angle vary at different locations along the tear seam. These variations permit control over the speed at which the deployment door opens as well as the order in which different portions of the tear seam tear.

BACKGROUND OF THE INVENTION 
 This invention pertains to the field of airbag covers, such as are used in 
 automobile steering wheels, and more specifically to tear seams, 
 deployment doors and hinges in airbag covers. 
 Tear seams in airbag covers tear upon the deployment of an airbag. 
 Conventional airbag covers feature tear seams which consist of a groove in
 the airbag cover. The groove provides a weakened place in the airbag cover
 wherein the deploying airbag can easily break through. Generally, the 
 groove has a thickness less than that of the other portions of the airbag 
 cover. This reduced thickness weakens the tear seam such that it ruptures 
 upon deployment of the airbag. 
 Because the tear seam is of a reduced thickness, the tear seam can be 
 visible as an indented line in the airbag cover. Conversely, tear seams 
 may be hidden from view by being embodied in the reverse side of the 
 airbag cover such that it is not visible to an occupant of the vehicle. 
 The grooves which create conventional tear seams have substantially 
 constant depths. Because these depths do not vary, the tensile strength of
 the tear seam remains substantially the same throughout the tear seam. 
 While this tensile strength is weaker than that of the remaining area of 
 the airbag cover such that the tear seam tears before any other part of 
 the airbag cover, the tearing of the tear seam is not easily controllable.
 Neither the rate of tearing of the tear seam nor the location along the 
 tear seam wherein the tear seam first tears is easily controllable. Thus, 
 for example, if an end of the tear seam tears before the center of the 
 tear seam, the airbag will not deploy evenly. Rather, the airbag will 
 deploy through the end of the tear seam, which tears first, and then push 
 its way through the remainder of the tear seam. This could result in less 
 than optimal deployment of the airbag. 
 SUMMARY OF THE INVENTION 
 According to one aspect of the present invention, an airbag cover is 
 provided which has a novel tear seam. The tear seam is a groove formed in 
 the front of the airbag cover as well as a groove formed in the back of 
 the airbag cover. These front and back grooves are slightly out of 
 alignment, being separated by a thin transverse layer of the airbag cover.
 The transverse layer has a length and width, both of which vary at 
 different locations along the tear seam. The centerline of the transverse 
 layer is oriented at an angle with respect to the airbag cover. Like the 
 transverse layer's length and width, this angle varies at different 
 locations along the tear seam. 
 According to another aspect of the present invention, the tear seam defines
 a pair of deployment doors in the airbag cover. The deployment doors are 
 formed in the airbag cover and open by rotating around hinges upon the 
 deployment of the airbag. The hinges may be formed in the airbag cover by 
 removing a portion of the back side of the airbag cover. The airbag cover 
 may also comprise reinforcing means to strengthen the hinges. 
 According to another aspect of the present invention, the airbag cover has 
 an essentially circular configuration. This differs from conventional 
 airbag covers that have substantially square or rectangular 
 configurations. 
 One advantage of the present invention is that variation of the transverse 
 layer's length, width and angle permits the tearing of the tear seam to be
 controllable. The speed at which the tear seam tears and the speed at 
 which the deployment doors open, as well as which part of the tear seam 
 tears first can, be controlled. Additionally, fatigue failure can be 
 prevented at locations along the tear seam, which receive considerable 
 stress. For example, in designs where the vehicle horn is activated by 
 depressing the airbag cover, the portion of the tear seam running through 
 the section of the airbag cover that is depressed when the driver 
 activates the horn can be configured to have a greater integrity. 
 Another advantage of the present invention is the reduction in material 
 mass in a portion of the back side of the airbag cover. The removal of 
 some material forms hinges within the airbag cover to permit the 
 deployment doors to pivot open to a greater degree without tearing the 
 hinges. The reinforcing means also aids in preventing the deployment doors
 from completely detaching from the airbag cover during airbag deployment. 
 Another advantage of the present invention is that the tear seam, unlike 
 conventional tear seams, enables an emblem to be mounted on the front side
 of the airbag cover. For example, a portion of the tear seam may be 
 configured to follow a portion of the outline of the emblem. Such design 
 is shown herein as a semi-circle in the middle of the airbag cover. This 
 would permit a round emblem to be mounted onto the front of the airbag 
 cover. Upon deployment of the airbag, the tear seam would tear forming two
 doors out of the airbag cover. The doors would open and the airbag would 
 deploy through the airbag cover. The round emblem, outlined by the 
 semi-circular tear seam prior to the deployment of the airbag, would then 
 be retained on one of the doors of the airbag cover after the 
 semi-circular tear seam tears and the airbag deploys through the airbag 
 cover. 
 Still other benefits and advantages of the invention will become apparent 
 to those skilled in the art to which it pertains upon a reading and 
 understanding of the following detailed specification.

DETAILED DESCRIPTION OF THE INVENTION 
 Referring now to the drawings wherein the showings are for purposes of 
 illustrating a preferred embodiment of the invention only and not for 
 purposes of limiting the same, an airbag cover 10 embodying a tear seam 12
 is illustrated in FIGS. 1, 2, 6, and 7. The tear seam 12 is more clearly 
 shown in FIGS. 3, 4, 5, 8, 9 and 10. 
 With reference now to FIGS. 1-7, the airbag cover 10 has a tear seam 12 
 therein. Referring to FIGS. 1, 2, 6 and 7, the tear seam 12 defines first 
 and second deployment doors 70, 74 in the airbag cover 10. Upon the 
 deployment of the airbag 16 the tear seam 12 tears and deployment doors 
 70, 74 open. The airbag 16 is thus deployed through the airbag cover 10. 
 With reference to FIGS. 2 and 7, the airbag cover 10 and deployment doors 
 70, 74 are in a plane 18 that has a high radius of curvature or is 
 essentially flat prior to the deployment of the airbag 16. 
 With references to FIGS. 1, 2, 6, 7 and 11 the airbag cover 10 further 
 comprises first and second hinges 48, 50 about which the deployment doors 
 pivot open upon the deployment of the airbag 16. In addition to permitting
 the deployment doors 70, 74 to open, the hinges prevent the deployment 
 doors 70, 74 from completely detaching from the airbag cover. 
 Referring to FIGS. 3, 4, and 5 the airbag cover 10 has front and back sides
 22, 24. As used herein and in the claims the term "front" refers to a side
 or surface of an airbag cover that faces towards a vehicle occupant when 
 the airbag cover is installed in its operative location in a vehicle. As 
 used herein and in the claims the term "back" refers to a side or surface 
 of an airbag cover that faces away from a vehicle occupant when the airbag
 cover is installed in its operative location in a vehicle. 
 The tear seam 12 has a front groove 26 in the front side 22 of the airbag 
 cover 10. The front groove 26 has a front open top 28 and a front closed 
 bottom 30. The tear seam 12 also has a back groove 32 in the back side 24 
 of the airbag cover 10. The back groove 32 has a back open top 34 and a 
 back closed bottom 36. 
 With continuing reference to FIGS. 3, 4, and 5, the tear seam 12 has a 
 transverse layer 38 separating the front 26 and back 32 grooves. The 
 transverse layer 38 traverses from the closed bottom of one of the grooves
 to the closed bottom of the other groove. 
 Referring to FIGS. 4,5,8,9 and 10, the transverse layer 38 has a length 
 that is measured from the closed bottom of one of the grooves to the 
 closed bottom of the other groove, as shown at reference character 40. The
 transverse layer 38 has a thickness 42 which varies along the length 40 of
 the transverse layer 38. The transverse layer 38 of the tear seam 12 tears
 upon the deployment of the airbag 16 at a point along the length of the 
 transverse layer 38 where the thickness 42 is at minimum. 
 With reference to FIGS. 3, 4, and 5, the transverse layer 38 of the tear 
 seam 12 in the airbag cover forms an angle 46 with respect to the flat 
 plane 18. The angle 46 is less than or equal to 90.degree. and greater 
 than or equal to 0.degree.. In the preferred embodiment the angle 46 is 
 equal to 72 degrees. 
 Referring now to FIGS. 8, 9 and 10, according to one embodiment of the 
 present invention, the depths of the front 26 and back 32 grooves of the 
 tear seam 12 vary at different locations along the tear seam. This 
 variation correspondingly slightly varies the length 40 of the transverse 
 layer 38. 
 Referring now to FIGS. 1, 2, 6, 7 and 11, an important aspect of the 
 invention is that the airbag cover 10 may have a non-rectangular 
 configuration, such as an essentially circular configuration as is 
 illustrated. The related art only discloses rectangular or square airbag 
 covers. 
 As shown in FIG. 11, The airbag cover 10 has first and second hinges 48, 
 50. The first and second hinges are situated diametrically opposite from 
 each other along the perimeter of the circular airbag cover 10. Thus, the 
 first and second hinges are separated by an angle 52 of 180.degree. as 
 shown in FIGS. 6, 7 and 11. 
 With reference to FIGS. 6 and 7, the tear seam 12 preferably comprises a 
 first tear seam segment 54 within the circular airbag cover 10. This first
 tear seam segment 54 extends across the diameter of the circular airbag 
 cover 10 such that it is parallel to the first and second hinges 48, 50. 
 Thus, the first tear seam segment 54 forms an angle 56 with respect to the
 first and second hinges. In the preferred embodiment, the angle 56 is 
 equal to zero degrees. 
 With continuing reference to FIGS. 6 and 7, the tear seam 12 also comprises
 a second tear seam segment 58 along one half of the perimeter of the 
 circular airbag cover between the first and second hinges 48, 50. The 
 second tear seam segment 58 is bisected by the first tear seam segment 54.
 The second tear seam segment 58 thereby comprises an upper 60 second tear 
 seam segment half and a lower 62 second tear seam segment half. 
 The tear seam 12 further comprises a third tear seam segment 64 along the 
 remaining one half the perimeter circular airbag cover. The third tear 
 seam segment 64 extends between the first and second hinges 48, 50. The 
 third tear seam segment 64 is situated opposite the second tear seam 
 segment 58 along the perimeter of the circular airbag cover 10. The third 
 tear seam segment 64 is bisected by the first tear seam segment 54 thereby
 comprising an upper 66 third tear seam segment half and a lower 68 third 
 tear seam segment half. 
 Referring now to FIGS. 1, 2, 6, 7 and 11, the first tear seam segment 54, 
 upper second tear seam segment half 60 and upper third tear seam segment 
 half 66 form a first deployment door 70 in the circular airbag cover 10. 
 The first deployment door 70 pivots open on said first hinge 48 upon the 
 deployment of the airbag 16 and the tearing of first tear seam segment 54,
 upper second tear seam segment half 60 and upper third tear seam segment 
 half 66. Upon opening, the first deployment door 70 forms an angle 72 with
 respect to the substantially flat plane 18. The angle 72 is less than or 
 equal to 270.degree.. 
 With continuing reference to FIGS. 1, 2, 6, 7 and 11 the first tear seam 
 segment 54, lower second tear seam segment half 62 and lower third tear 
 seam segment half 68 form a second deployment door 74 in the circular 
 airbag cover 10. The second deployment door pivots open on the second 
 hinge 50 upon the deployment of the airbag 16 and the tearing of the first
 tear seam segment 54, lower second tear seam segment half 62 and lower 
 third tear seam segment half 68. Upon opening, the second deployment door 
 74 forms an angle 76 with respect flat plane 18. The angle 76 is less than
 or equal to 270.degree.. 
 With reference to FIGS. 3-11, the minimum thickness 44 of the transverse 
 layer 38 along the length 40 of the transverse layer has different values 
 at different locations along the tear seam 12. 
 As shown in FIGS. 6, 7, 8 and 11, the minimum thickness 44 has its minimum 
 value 78 along the first tear seam segment 54 and near a point 79 where 
 the first tear seam segment 54 bisects the second 58 and third 64 tear 
 seams. 
 With reference to FIGS. 3-11, the minimum thickness 44 of the transverse 
 layer 38 along the length 40 of the transverse layer has different values 
 at different locations along the tear seam 12. 
 With reference to FIGS. 6, 7, 10 and 11, the minimum thickness 44 has its 
 maximum value 80 at the point 81 on the upper second 60 and upper third 66
 tear seam halves near the first hinge 48 and at the point 81 on the lower 
 second 62 and lower third 68 tear seam halves near the second hinge 50. 
 Preferably, the minimum thickness 44 of the transverse layer 38 along the 
 length 40 of the transverse layer 38 gradually transitions between 
 thicknesses 78 and 80 along the upper second 60, upper third 66, lower 
 second 62 and lower third 68 tear seam halves. A transitioning transverse 
 layer is shown in FIG. 9, which is a cross sectional view of the 
 transverse layer along lines 9--9 of FIGS. 6 and 7. 
 With reference to FIGS. 6, 7, 8 and 11, the length 40 of the transverse 
 layer 38 is preferably a minimum 82 along the first tear seam segment 54 
 and near the locations 79 wherein the first tear seam segment 54 bisects 
 the second 58 and third 64 tear seams. 
 Referring now to FIGS. 6, 7, 10 and 11, the length 40 of the transverse 
 layer 38 is at a maximum length 84 near the locations 81 on the upper 
 second 60 and upper third 66 tear seam halves near the first hinge 48 as 
 well as the locations 81 on the lower second 62 and lower third 68 tear 
 seams halves near the second hinge 50. 
 Referring now to FIGS. 5 and 6, preferably, the length 40 of the transverse
 layer 38 of the tear seam 12 gradually transitions between lengths 84 and 
 82 along the upper second 60, upper third 66, lower second 62 and lower 
 third 68 tear seam halves. 
 The varying lengths and thicknesses of the transverse layer 38 of the tear 
 seam 12 enable controllable operation of the airbag cover 10. The minimum 
 thickness 78 which is preferably located along the first tear seam segment
 provides that the first tear seam segment will tear first upon deployment 
 of the airbag 16. The thickness of the transverse layer 38 of the tear 
 seam 12 increases as one moves from that point along the perimeter of the 
 airbag cover 10 towards the first and second hinges 48, 50. This feature 
 helps control the rate at which the first 70 and second 74 deployment 
 doors pivot open upon deployment of the airbag 16. 
 The decreased length 40 of the transverse layer 38 at the first tear seam 
 segment 54 provides sufficient strength and rigidity of the tear seam 12 
 such that the airbag cover 10 will not fail due to fatigue failure at the 
 first tear seam segment 54 when the center of the airbag cover 10 is 
 depressed, for example when the operator of the motor vehicle operates the
 motor vehicle's horn. 
 Referring now to FIGS. 3-11, the angle 46 of the transverse layer 38 
 relative to the substantially flat plane 18 has preferred values at 
 particular locations along the tear seam 12 in order to obtain the desired
 strength and rigidity and to prevent fatigue failure of the transverse 
 layer of the tear seam. 
 Referring to FIGS. 6, 7, 8 and 11, angle 46 is at a minimum 86 along the 
 first tear seam segment 54 and near the locations 79 wherein the first 
 tear seam segment 54 bisects the second 58 and third 64 tear seams. 
 Referring to FIGS. 6, 7, 10 and 11, the angle 46 has a maximum value 88 
 near the locations 81 on the upper second 60 and upper third 66 tear seam 
 halves near the first hinge 48 and near the locations on the lower second 
 62 and lower third 68 tear seam halves near the second hinge 50. 
 With reference to FIG. 9, preferably, the angle 46 of the transverse layer 
 38 of the tear seam 12 gradually transitions between angles 88 and 86 
 along the upper second 60, upper third 66, lower second 62, and lower 
 third 68 tear seam halves. In the preferred embodiments, the angle 86 is 
 zero degrees and the angle 88 is seventy-two degrees. 
 According to another aspect of the current invention, the ratio of the 
 maximum thickness 78 to the minimum thickness 80 is less than or equal to 
 2. This ensures that the aforementioned desired characteristics of the 
 current invention are obtained. Preferably, the minimum thickness 78 has a
 value of about 0.5 mm and the maximum thickness 80 has a value of about 
 0.75 mm. 
 With reference to FIG. 11, the hinges 48, 50 may be formed within the 
 airbag cover 10 by molding the back side 24 of the airbag cover 10 
 corresponding to the locations of the first and second hinges 48, 50. The 
 hinges pivot on generally linear hinge lines. The lengths of the hinge 
 lines, as indicated at 90 and 92, may be between about 0.5 and about 3.0 
 inches but is preferably about 1.25 inches. 
 With continuing reference to FIG. 11, the airbag cover 10 also has 
 reinforcing means 94. The reinforcing means 94 is connected to the hinges 
 48, 50 and prevents the deployment doors 70, 74 from completing detaching 
 from the airbag cover 10 upon the tearing the tear seam 12, opening of the
 deployment doors and deployment of the airbag 16. Preferably there are 
 first 100 and second 102 upper reinforcing means for the first hinge 48 as
 well as first 104 and second 106 lower reinforcing means for the second 
 hinge 50. These reinforcing means help to prevent injury to the occupant 
 of the motor vehicle upon the deployment of the airbag. 
 Preferably the reinforcing means as well as the airbag cover, hinges, 
 deployment doors and tear seam are all cast or molded out of an elastic 
 polymer having somewhat rigid properties. The preferred material is a 
 polymer available from Dupont and designated by their product code 
 "DYM-350." 
 Another important advantage of the invention is that a decorative emblem 
 can be incorporated into the tear seam design. Many vehicle owners take 
 great pride in their vehicles. It can be important to them to be reminded 
 of their purchase whenever they look down at the steering wheel. Vehicle 
 manufacturers also benefit by encouraging brand loyalty and pride by 
 prominently portraying the vehicle logo. With reference to FIGS. 6 and 7, 
 the present invention contemplates a tear seam 12 configured within the 
 airbag cover 10 such that an emblem 96 can be mounted anywhere on the 
 front side 22 of the airbag cover 10 and remain safely attached to the 
 airbag cover 10 during and throughout the deployment of the airbag 16. The
 emblem 96 can be mounted by any fastening method chosen with sound 
 engineering judgment. 
 With continuing reference to FIGS. 6 and 7, in such a configuration, the 
 tear seam 12 and a portion of the emblem 96 are adjacent to each other. 
 The tear seam 12 essentially follows a portion of the perimeter of the 
 emblem 96. Such design encourages the emblem 96 to remain affixed to the 
 airbag cover 10 during deployment of the airbag 10. The tear seam 12 tears
 around the emblem 96 without affecting the emblem's fixation to the airbag
 cover 10. After the airbag 16 deploys and the tear seam 12 tears, the 
 emblem remains attached to the first deployment door 70 which pivots back.
 The emblem 96 represented in FIGS. 6 and 7 is illustrated as circular and 
 mounted in the center of the airbag cover 10. However, the present 
 invention contemplates mounting an emblem of any shape onto any location 
 of any shaped airbag cover. 
 While the invention has been described in connection with specific 
 embodiments and applications, no intention to restrict the invention to 
 the examples shown is contemplated. It will be apparent to those skilled 
 in the art that the above methods may incorporate changes and 
 modifications without departing from the general scope of this invention. 
 It is intended to include all such modifications and alterations in so far
 as they come within the scope of the appended claims or the equivalents 
 thereof.