Abstract:
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.

Description:
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&#39;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&#39;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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein: 
     FIG. 1 a front view of the airbag cover mounted to a steering wheel, with the airbag shown in a partially deployed condition; 
     FIG. 2 is a perspective view of the cover mounted to a steering wheel, shown with the cover being opened as when the airbag has deployed; 
     FIG. 3 is a cross-sectional view of the airbag cover showing the tear seam; 
     FIG. 4 is a magnified cross-section of the airbag cover showing the tear seam; 
     FIG. 5 is a magnified cross-section of another embodiment of the airbag cover showing the tear seam; 
     FIG. 6 is a front view of the airbag cover shown with airbag cover being closed as before the airbag deploys. 
     FIG. 7 is a perspective view of the airbag cover shown in a closed position; 
     FIG. 8 is a cross-sectional view of the tear seam along lines  8 — 8  of FIGS. 6 and 7; 
     FIG. 9 is a cross sectional view of the tear seam along lines  9 — 9  of FIGS. 6 and 7; 
     FIG. 10 is a cross sectional view of the tear seam along lines  10 — 10  of FIGS. 6 and 7; and, 
     FIG. 11 is a back view of the airbag cover showing the tear seam, hinges and reinforcing means. This is the view that the airbag sees before deploying through the airbag cover. 
    
    
     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° and greater than or equal to 0°. 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° 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°. 
     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°. 
     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&#39;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&#39;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.