Abstract:
An apparatus ( 10 ) for covering an inflatable vehicle occupant protection device ( 40 ) comprises a cover ( 70 ) including first and second portions ( 100, 110 ). The cover ( 70 ) is movable from a closed condition to an open condition upon inflation of the inflatable device ( 40 ). The cover ( 70 ) has a cover tear seam ( 90, 92 ) defining the first and second portions ( 100, 110 ) of the cover. The apparatus ( 10 ) includes a switch ( 130 ) in an electric circuit for actuating an electrically actuatable device ( 131 ) of the vehicle. The switch ( 130 ) includes a first switch portion ( 132 ) underlying the first cover portion ( 100 ) and a second switch portion ( 134 ) underlying the second cover portion ( 100 ). The first cover portion ( 100 ) is manually depressible to operate the first switch portion ( 132 ) and thereby to actuate the electrically actuatable device ( 131 ). The second cover portion ( 110 ) is manually depressible to operate the second switch portion ( 134 ) and thereby to actuate the electrically actuatable device ( 131 ). The switch ( 130 ) has a bridge portion ( 136 ) underlying and extending across the cover tear seam ( 90, 92 ). The bridge portion ( 136 ) of the switch ( 132 ) electrically interconnects the first switch portion ( 132 ) and the second switch portion ( 134 ) when the cover portions ( 100, 110 ) are in the closed condition. The bridge portion ( 136 ) is rupturable upon movement of the cover ( 70 ) from the closed condition to the open condition. One of the bridge portion ( 136 ) and the first and second switch portions ( 132, 134 ) has a switch actuator portion ( 172 ) underlying and extending across the cover tear seam ( 92 ). The switch actuator portion ( 172 ), when manually depressed, actuates the electrically actuatable device ( 131 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a switch for mounting on a portion of a vehicle as part of a vehicle safety apparatus. In particular, the present invention relates to a horn switch that is part of an air bag module mounted on a vehicle steering wheel. 
     2. Description of the Prior Art 
     It is known to mount an air bag module on a steering wheel of a vehicle to help protect the driver of the vehicle. The air bag module includes an air bag and an inflator. In the event of sudden vehicle deceleration of a magnitude which requires protection of the driver, the inflator is actuated to inflate the air bag into a position to help protect the driver of the vehicle. 
     It is known to provide a horn switch that is operable by pressing on a cover of an air bag module mounted on a vehicle steering wheel. U.S. Pat. No. 5,585,606 discloses a membrane type horn switch which is connected with an air bag module cover. The horn switch includes two active parts, each secured for movement with a respective movable part of the cover. The cover has a tear seam which releasably joins the movable parts of the cover. When the air bag inflates, a rupturable portion of the switch tears to enable the movable cover parts to open so that the air bag can inflate out of the cover. The rupturable portion of the switch underlies the tear seam in the module cover. 
     SUMMARY OF THE INVENTION 
     The present invention is an apparatus for covering an inflatable vehicle occupant protection device. The apparatus comprises a cover including first and second portions. The cover is movable from a closed condition to an open condition upon inflation of the inflatable device. The cover has a cover tear seam defining the first and second portions of the cover. The apparatus includes a switch in an electric circuit for actuating an electrically actuatable device of the vehicle. The switch includes a first switch portion underlying the first cover portion and a second switch portion underlying the second cover portion. The first cover portion is manually depressible to operate the first switch portion and thereby to actuate the electrically actuatable device. The second cover portion is manually depressible to operate the second switch portion and thereby to actuate the electrically actuatable device. The switch has a bridge portion underlying and extending across the cover tear seam. The bridge portion of the switch electrically interconnects the first switch portion and the second switch portion when the cover portions are in the closed condition. The bridge portion is rupturable upon movement of the cover from the closed condition to the open condition. One of the bridge portion and the first and second switch portions has a switch actuator portion underlying and extending across the cover tear seam. The switch actuator portion when manually depressed actuates the electrically actuatable device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features of the present invention will become apparent to one skilled in the art to which the present invention relates upon consideration of the following description of the invention with reference to the accompanying drawings, wherein: 
     FIG. 1 is a schematic view, partially in section, showing a horn switch as part of an air bag module mounted on a vehicle steering wheel; 
     FIG. 2 is a schematic plan view of portions of the air bag module of FIG. 1 including the horn switch; 
     FIG. 3 is a plan view similar to FIG. 2 of a horn switch in accordance with a second embodiment of the present invention; and 
     FIG. 4 is a schematic plan view of a horn switch in accordance with a third embodiment of the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention relates to a vehicle safety apparatus including a switch. In particular, the present invention relates to an air bag module which includes a switch for an electrically actuatable device of the vehicle, such as a vehicle horn. As representative of the present invention, FIG. 1 illustrates an air bag module  10 . The air bag module  10  is mounted on a vehicle steering wheel (not shown) which is supported on a steering shaft or steering column of the vehicle. 
     The air bag module  10  includes an inflator shown schematically at  30 . The inflator  30  has one or more fluid outlets for directing inflation fluid into an air bag  40  upon actuation of the inflator. The inflator may be a pyrotechnic inflator which uses the combustion of gas-generating material to generate inflation fluid in the form of gas to inflate the air bag  40 . The module  10  alternatively could include an inflator which contains a stored quantity of pressurized inflation fluid, or a combination of pressurized inflation fluid and ignitable material for heating the inflation fluid. 
     The air bag  40  is illustrated schematically in a deflated, packed condition in FIG.  1 . The air bag  40  is preferably made from a fabric material such as woven nylon. The air bag  40  can alternatively be made from non-woven material, such as plastic film. The use of plastic film, in particular, would require inflation fluid vents to be formed in the air bag  40 , as is known in the art. 
     The module  10  includes a retaining ring  50  from which extend a plurality of fasteners  52 , such as weld studs. The fasteners  52  on the retaining ring  50  extend through openings in an end portion  54  of the air bag  40 . The retaining ring  50  is secured to a portion of the module such as a base plate (not shown) by nuts (not shown) screwed onto the fasteners  52 . The end portion  54  of the air bag  40  is clamped between the base plate and the retaining ring  50 , and the base plate is fastened to the vehicle steering wheel. As a result, the air bag  40  is secured in position on the vehicle steering wheel, adjacent to the inflator  30 . 
     The vehicle includes known means (not shown) for sensing a collision involving the vehicle and for actuating the inflator  30  in response to the sensing of a collision. The means may include a deceleration sensor and vehicle electric circuitry for actuating the inflator  30  in response to sensing a vehicle deceleration indicative of a vehicle collision having a severity greater than a predetermined threshold value. As discussed below, the means provides an electric signal over lead wires to the inflator  30 , when the inflator is to be actuated. 
     The air bag module  10  includes a cover  70  for enclosing the air bag  40  and the inflator  30 . The cover  70  is made from a material which is strong enough to protect the parts of the air bag module  10  which are enclosed within the cover. The material of the cover  70  is sufficiently flexible or deformable that it can be resiliently deformed or depressed inwardly (that is, in a downward direction as viewed in FIG. 1) by pressure from an occupant of the vehicle, so as to actuate an electrical device of the vehicle such as the vehicle horn. 
     The cover  70  has a main body portion  72  which has inner and outer side surfaces  74  and  76 . The main body portion  72  of the cover  70  includes a fixed part  80  of the cover. A mounting flange or mounting portion  82  of the cover  70  extends from the main body portion  72  in a direction toward the base plate  20 . A plurality of first fastener openings  84  are formed in the mounting portion  82  of the cover  70 . Fasteners (not shown) such as rivets extend through the fastener openings  84  in the mounting portion  82  of the cover  70  to secure the cover to the vehicle. 
     An I-shaped tear seam  90  (FIG. 2) is formed in the main body portion  72  of the cover  70 . The tear seam  90  includes a linear central or base section  92  and four side sections  94 ,  96 ,  98  and  102 . The tear seam  90  constitutes a weakened portion of the cover  70  which is rupturable under the force of the inflating air bag  40  to enable the air bag to inflate out of the cover. 
     The tear seam  90  partially defines first and second movable parts  100  and  110  of the cover. Each one of the first and second movable cover parts  100  and  110  has a generally rectangular configuration. The base section  92  and the side sections  94  and  96  of the tear seam  90  extend along three sides of the first movable cover part  100 . A first hinge portion  112  of the cover  70  extends along the fourth side of the first movable cover part  100 , between the two side sections  94  and  96  of the tear seam  90 . The first hinge portion  112  connects the first movable cover part  100  to the fixed cover part  80  for pivotal movement relative to the fixed cover part. 
     The base  92  and the other two side sections  98  and  102  of the tear seam  90  extend along three sides of the second movable cover part  110 . A second hinge portion  114  of the cover  70  extends along the fourth side of the second movable cover part  110 , between the two side sections  98  and  102  of the tear seam  90 . The second hinge portion  114  connects the second movable cover part  110  to the fixed cover part  80  for pivotal movement relative to the fixed cover part. 
     The air bag module  10  includes a switch  130  for actuating an electrically actuatable device of the vehicle, such as a vehicle horn indicated schematically at  131  (FIG.  1 ). In the preferred embodiment, the switch  130  is a membrane switch of a known type which includes first and second layers of electrically conductive material (not shown) normally separated by a dielectric material. The layers of conductive material are supported on a non-conducting substrate material. The layers of conductive material are engageable with each other, in response to the application of force to the switch  130 , to complete a circuit in the switch. 
     The switch  130  includes first and second switch portions  132  and  134  located on opposite sides of an intermediate portion or bridge portion  136 . The first and second switch portions  132  and  134  are physically and electrically interconnected by the bridge portion  136 , as described below. 
     The first switch portion  132  underlies the first cover part  100 . Four fastener openings  140  are formed in the first switch portion  132 . The first switch portion  132  has an active area  142 , indicated by dashed lines, which encompasses most of the area of the first switch portion, save for the outer edge portion and the fastener openings  140 . The first and second layers of conductive material of the switch  130 , as well as the substrate material, extend continuously over the active area  142  of the first switch portion  132 . 
     A rigid first back plate  150  is located at a position underlying the first switch portion  132 . (The spacing between the first movable cover part  100 , and the first switch portion  132  is exaggerated, for clarity, in FIG. 1.) Four fastener openings (not shown) are formed in the first back plate  150  and underlie the first switch portion. 
     Four fasteners  154  (FIG. 1) in the form of pins extend inward from the first movable cover part  100 . The pins  154  extend through the fastener openings  140  in the first switch portion  132  and into the fastener openings in the first back plate  150 . The pins  154  have a press fit in the fastener openings in the first back plate  150  and securely fasten the first back plate to the first movable cover part  100 . The pins  154  maintain the first switch portion  132  in position between the first back plate  150  and the inner side surface of the first movable cover part  100 . 
     The first back plate  150  provides a relatively rigid support for the first switch portion  132 , so that force applied to the first cover part  100  can result in operation of the first switch portion of the switch  130 . The first back plate  150  and the first switch portion  132  are movable with the first movable cover part  100  upon opening of the cover  70 . 
     The second switch portion  134  underlies the second movable cover part  110 . Four fastener openings  156  are formed in the second switch portion  140 . The second switch portion  134  has an active area  158 , indicated by the dashed lines, which encompasses most of the area of the second switch portion, save for the outer edge portion and the fastener openings  156 . The first and second layers of conductive material of the switch  130 , as well as the substrate material, extend continuously over the active area  158  of the second switch portion  134 . 
     A rigid second back plate  160  is located at a position underlying the second switch portion  134 . (The spacing between the second movable cover part  110 , and the second switch portion  134  is exaggerated, for clarity in FIG. 1.) Four fastener openings (not shown) are formed in the second back plate  160  and underlie the second switch portion  134 . 
     Four fasteners  164  (FIG. 1) in the form of pins extend inward from the second movable cover part  110 . The pins  164  extend through the fastener openings  156  in the second switch portion  134  and into the fastener openings in the second back plate  160 . The pins  164  have a press fit in the fastener openings in the second back plate  160  and securely fasten the second back plate to the second movable cover part  110 . The pins  164  maintain the second switch portion  134  in position between the second back plate  160  and the inner side surface of the second movable cover part  110 . 
     The second back plate  160  provides a relatively rigid support for the second switch portion  134 , so that force applied to the second cover part  110  can result in operation of the second switch portion of the switch  130 . The second back plate  160  and the second switch portion  134  are movable with the second movable cover part  110  upon opening of the cover  70 . 
     The bridge portion  136  (FIG. 2) of the switch  130  extends between the first and second switch portions  132  and  134 , and underlies or extends across the base section  92  of the tear seam  90 . The bridge portion  136  includes a first part  170  and a second part  172 . 
     The first part  170  of the bridge portion  136  extends from the first switch portion  132  and across the base section  92  of the cover tear seam  90 . An end portion  171  of the first part  170  overlies the second back plate  160 , adjacent to the second switch portion  134 . The end portion  171  of the first part  170  of the bridge portion  136  is connected with the second part  172  of the bridge portion. 
     The second part  172  of the bridge portion  136  of the switch is substantially wider than the first part  170  of the bridge portion, as measured in the direction along the length of the base section  92  of the cover tear seam  90 . The first part  170  of the bridge portion  136  is very narrow compared to either the second part  172  or the first and second switch portions  132  and  134 . As a result, the first part  170  of the bridge portion, as discussed below, is rupturable upon movement of the cover  70  to the open condition. 
     The second part  172  of the bridge portion  136  is contiguous with and is connected for movement with the second switch portion  134 . The second part  172  of the bridge portion  136  extends from the second switch portion  134  across the base section  92  of the cover tear seam  90  and thus extends across the gap between the two back plates  150  and  160 . 
     The second part  172  of the bridge portion  136  of the switch has an active area  174 . The active area  174  on the bridge portion  136  is electrically connected, in a manner not shown, with the active area  142  on the first switch portion  132 . The active area  174  is contiguous with and extends from the active area  158  of the second switch portion  134 . The active area  174  extends across and underlies the base section  92  of the cover tear seam  90  and is located generally equidistant between the side sections  94 ,  96 ,  98  and  102  of the cover tear seam  90 . Thus, the active area  174  on the bridge portion  136  of the switch  130  is located generally under the center of the cover  70 . 
     A lead assembly  180  extends from the first switch portion  132 , across the side section  96  of the cover tear seam  90 , and into a position underlying the fixed portion  80  of the cover. The lead assembly  180  connects the switch  130  with the vehicle horn  131  (FIG.  1 ), with a power source  182  such as the vehicle battery, and with other vehicle electric circuitry indicated schematically at  184 . 
     To effect operation of the vehicle horn  131 , the driver of the vehicle presses on the cover  70  of the air bag module  10  in a downward direction as viewed in FIG.  1 . The force applied to the cover  70  of the air bag module  10  is transmitted through the cover to the switch  130 . Specifically, force applied to the first movable cover part  100  is transmitted to the first switch portion  132 . The first switch portion  132  is operated, and the vehicle horn  131  is energized. When force is applied to the second movable cover part  110 , the force is transmitted to the second switch portion  134 , the second switch portion is operated, and the vehicle horn  131  is energized. 
     When force is applied to the base section  92  of the cover tear seam  90 , the force is transmitted to the bridge portion  136  of the switch  130 . The active area  174  of the bridge portion  136  of the switch  130  is operated, and the vehicle horn  131  is energized. 
     When the force on the cover  70  of the air bag module  10  is released, the resilience of the cover causes it to move away from the air bag  40 . As this movement occurs, the switch  130  returns to its original condition, and the vehicle horn  131  is de-energized. 
     Depending on the configuration of the bridge portion  136  of the switch  130 , the horn  131  can be energized by depressing various portions of the cover  70  along the base section  92  of the cover tear seam  90 . For example, the active area  174  of the bridge portion  136  extends for about 40% of the length of the first and second switch portions  132  and  134  (measured vertically as viewed in FIG.  2 ). The relative dimensions and locations of the bridge portion parts  170  and  172  can be varied from the configuration shown to provide for horn energization by pressing on more, or different, areas of the cover  70  along the length of the base section  92  of the cover tear seam  90 . 
     In the event of an impact to the vehicle of a magnitude greater than the predetermined threshold value, the sensing means provides an electrical signal over lead wires to the inflator  30 . The inflator  30  is actuated in a known manner. Inflation fluid flows out of the inflator  30  and into the air bag  40 . The rapidly flowing inflation fluid causes the air bag  40  to inflate in an upward direction as viewed in FIG.  1 . 
     The force of the inflating air bag  40  is applied toward the inside of the switch  130  and the cover  70 . Specifically, the inflating air bag  40  pushes outward against the first and second back plates  150  and  160  and against the inner side surface  74  of the cover  70 . The cover  70  opens along the I-shaped tear seam  90 , which is the predetermined weakened portion of the cover. The first and second movable cover parts  100  and  110  move away from each other, pivoting about the hinge portions  112  and  114 , respectively, to an open condition. 
     When the cover  70  opens, the first movable cover portion  100  moves away from the second movable cover portion  110 . The first switch portion  132  moves with the first movable cover part  100 . The second switch portion  134  moves with the second movable cover part  110 , relative to the first switch portion  132 . As this movement occurs, force is transmitted to the bridge portion  136  of the switch  130 . The bridge portion  136  of the switch  130  ruptures along the narrow first part  170 . The electrical connection between the first and second switch portions  132  and  134  is broken. The cover  70  opens sufficiently that the air bag  40  inflates between the first and second movable cover parts  100  and  110  into a position to help protect the vehicle occupant. 
     The switch  130  can be used to actuate an electrically actuatable device of the vehicle other than the vehicle horn  131 . For example, the switch  130  could be used to actuate or control the vehicle radio, speed control, etc. Alternatively, the switch  130  could have a plurality of electrically independent active areas for controlling a plurality of electrically actuatable devices including the vehicle horn  131 . 
     FIG. 3 illustrates an air bag module  10   a  in accordance with a second embodiment of the present invention. The air bag module  10   a  is generally similar in construction and operation to the air bag module  10  (FIGS. 1 and 2) and parts which are the same or similar are given the same reference numerals with the suffix “a” added. 
     The air bag module  10   a  includes a horn switch  130   a . The horn switch  130   a  includes first and second switch portions  132   a  and  134   a . In the air bag module  10   a , the base section  92   a  of the cover tear seam  90   a  is not linear but instead is diverted around an emblem  210  located on the outside of the cover  70   a . The emblem  210  is a decorative emblem, such as one containing the logo of the vehicle manufacturer. 
     The base section  92   a  of the cover tear seam  90   a  includes a first part  221  extending generally perpendicular to the side sections  94   a  and  98   a . A second part  222  of the base section  92   a  extends perpendicular to the first part  221  in a direction toward the first switch portion  132   a . A third part  223  of the base section  92   a  extends parallel to the first part  221 , and a fourth part  224  extends parallel to the second part  222  in a direction toward the second switch portion  134   a . A fifth part  225  of the base section  92   a  is collinear with the first part  221  and extends to the side sections  96   a  and  102   a.    
     The second, third and fourth parts  222 - 224  of the base section  92   a  of the cover tear seam  90   a  partially define a generally rectangular central area  230  of the cover  70   a . The emblem  210  is located in the central area  230  of the cover  70   a . The first and fifth parts  221  and  225  of the base section  92  lie on an imaginary line which extends through the central area  230  of the cover  70   a.    
     The horn switch  130   a  includes a third switch portion  240  which extends from the second switch portion  134   a . The third switch portion  240  underlies the emblem  210  and the central area  230  of the cover  70   a . A rupturable bridge portion  170   a  of the horn switch  130   a  electrically and mechanically interconnects the third switch portion  240  and the first switch portion  132   a.    
     The third switch portion  240  has an active area  242 . The active area  242  is contiguous with and extends from the active area  158   a  of the second switch portion  134   a . The active area  242  underlies the emblem  210  and the central area  230  of the cover  70   a . An imaginary line along the first and fifth parts  221  and  225  of the base section  92   a  of the cover tear seam  90   a  extends through the active area  242  of the third switch portion  240 . As a result, the active area  242  of the third switch portion  240  is likely to be operated if the driver of the vehicle presses on the emblem  210 , which is typically centrally located for decorative reasons. 
     FIG. 4 illustrates schematically an air bag module  10   b  in accordance with a third embodiment of the present invention. The air bag module  10   b  is generally similar in construction and operation to the air bag module  10   a  (FIG. 3) and parts which are the same or similar are given the same reference numerals with the suffix “b” added. 
     The air bag module  10   b  includes a horn switch  130   b . The horn switch  130   b  includes a bridge portion  136   b  which comprises two rupturable bridge sections  170   b . Each one of the bridge sections  170   b  extends between and electrically interconnects the first switch portion  132   b  and the second switch portion  134   b . The bridge sections  170   b  are spaced apart along the length of the base section  92   b  of the cover tear seam  90   b . Disposed between the bridge sections  170   b  is an third portion  240   b  of the horn switch  130   b.    
     The third switch portion  240   b  extends from the second switch portion  134   b . The third switch portion  240  underlies the central area  230   b  of the cover  70   b . The third switch portion  240   b  has an active area  242   b . The active area  242   b  is contiguous with and extends from the active area  158   b  of the second switch portion  134   b . The active area  242   b  underlies the central area  230   b  of the cover  70   a . An imaginary line extending vertically (as viewed in FIG. 4) through the center of the cover  70   b  extends through the active area  242   b  of the third switch portion  240   b . As a result, the active area  242   b  of the third switch portion  240   b  is likely to be operated if the driver of the vehicle presses on the central area  230   b  of the cover  70   b.    
     From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, the present invention is not limited to an air bag module which is mounted on a vehicle steering wheel. The present invention can be used with an air bag module mounted on a vehicle instrument panel, a vehicle seat or door panel, or other portion of the vehicle. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.