Abstract:
A horn switch device includes a retractable body, an unmoving body, first and second biasing members for biasing the retractable body in a restoring direction, and first and second contact members. The contact members are attached to, and move with, the retractable body, and are capable of contacting each other by movement of the retractable body. The first biasing member pushes the first contact member and the second contact member apart. The second biasing member pushes the second contact member toward the first contact member. When a module cover is depressed, the biasing members are compressed to bring the contact members into contact with each other, thereby sounding the horn. Since the biasing members are arranged in series, vehicle vibration can be absorbed, thereby preventing accidental contact of the contact members. The device facilitates positioning of the contact members, thereby simplifying assembly of a steering wheel and an airbag system.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT  
       [0001]     The present invention relates to a horn switch, and in particular, it relates to a horn switch device provided in an airbag system and constructed such that, when depressed, a module cover is retracted to turn on a horn switch. The invention also relates to an airbag system and a steering wheel that include the horn switch device.  
         [0002]     Driver-seat airbag systems mounted to car steering wheels are known in which when the module covers of the airbag systems are depressed, horn switches are turned on to sound horns. For example, Japanese Unexamined Patent Application Publication No. 10-100832 and Japanese Unexamined Patent Application Publication No. 2001-114057 describe airbag systems in which, when depressed, a module cover is retracted against the repulsive force of a spring to turn on a horn switch.  
         [0003]     In the conventional horn switch devices, the spring has a single stage, so that the reaction force of the module cover is proportional to the pushing stroke of the module cover.  
         [0004]     Accordingly, it is an object of the present invention to provide a horn switch device in which multistage (i.e., two-stage) springs arranged in series bias a retractable body such as a module cover to offer the advantage of improving operability.  
         [0005]     It is also an object of the present invention to provide an airbag system and a steering wheel that include the horn switch device.  
         [0006]     Further objects and advantages of the invention will be apparent from the following description of the invention and the associated drawings.  
       SUMMARY OF THE INVENTION  
       [0007]     A horn switch device according to the present invention includes a retractable body that is retracted by depression by an occupant; an unmoving body that faces the retractable body; a biasing member interposed between the retractable body and the unmoving body, for biasing the retractable body in the restoring direction; and a pair of contact members capable of coming into or out of contact with each other by the movement of the retractable body. Both of the pair of contact members move together with the retractable body. The contact members include a first contact member located toward the retractable body and a second contact member located toward the unmoving body. The biasing member includes a first biasing member that pushes the first contact member and the second contact member in a separating direction, and a second biasing member that pushes the second contact member toward the first contact member.  
         [0008]     According to the invention, the first biasing member and the second biasing member are springs, each having a different spring constant.  
         [0009]     According to a first embodiment of the horn switch device, the retractable body is a module cover of an airbag system.  
         [0010]     In the first embodiment of the invention, the unmoving body is a member extending from a retainer of the airbag system.  
         [0011]     According to a second embodiment of the horn switch device, the retractable body is an airbag system.  
         [0012]     In the second embodiment of the invention, the unmoving body is a steering wheel or a member extending from the steering wheel.  
         [0013]     In another embodiment of the invention, an airbag system includes a horn switch device according to one of the first and second embodiments of the invention.  
         [0014]     In another embodiment of the invention, a steering wheel includes a horn switch device according to one of the first and second embodiments of the invention.  
         [0015]     In still another embodiment of the invention, a steering wheel is equipped with an airbag system that includes a horn switch device according to one of the first and second embodiments of the invention.  
         [0016]     In the horn switch device according to the invention, the contact members are apart from each other when the retractable body such as a module cover or an airbag system is in a restored position (undepressed state). When the retractable body is depressed, the contact members come into contact with each other, thereby sounding the horn.  
         [0017]     The horn switch device of the invention is constructed in such a manner that a retractable body such as a module cover or an airbag generates a repulsive force against depression by first and second biasing members arranged in series. Accordingly, vibration from the vehicle body can easily be absorbed. This prevents any accidental contact of the contact members from the vibration even if the distance between the contact members is small.  
         [0018]     When the spring constants of the biasing members are different, the spring having a smaller spring constant is first compressed when the retractable body is depressed, offering good operability. Briefly, the retractable body starts retraction only by slight depression.  
         [0019]     According to the invention, the retractable body may be either a module cover or an airbag system. When the retractable body is a module cover, the unmoving body is preferably a member extending from a retainer. When the retractable body is an airbag system, the unmoving member is preferably a steering wheel or a member extending from the steering wheel. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a cross-sectional view of a steering wheel equipped with an airbag system including a horn switch device according to a first embodiment of the invention.  
         [0021]     FIGS.  2 ( a ) and  2 ( b ) are cross-sectional views of the horn switch device depicted in  FIG. 1 .  
         [0022]      FIG. 3  is a cross-sectional view of a steering wheel equipped with an airbag system including a horn switch device according to a second embodiment of the invention.  
         [0023]     FIGS.  4 ( a ) and  4 ( b ) are cross-sectional views of the horn switch device depicted in  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     Embodiments of the present invention will be specifically described hereinafter with reference to the drawings.  
         [0025]      FIG. 1  is a cross-sectional view of a steering wheel equipped with an airbag system including a horn switch device according to a first embodiment of the invention.  
         [0026]     FIGS.  2 ( a ) and  2 ( b ) are enlarged views of the horn switch device depicted in  FIG. 1 .  FIG. 2 ( a ) shows “an undepressed” state in which a module cover  40  is not depressed, and  FIG. 2 ( b ) shows “a module-cover depressed state” in which the module cover  40  is depressed to sound a horn.  
         [0027]     The airbag system  1  is a driver-seat airbag system disposed in the center (a base  101 ) of a steering wheel  100 . The airbag system  1  includes a metal retainer  10 , an airbag  20  mounted to the retainer  10  with an airbag-fixing ring  24 , an inflator  30  for inflating the airbag  20 , a synthetic-resin module cover  40  that covers the folded airbag  20 , and a horn switch device  70 .  
         [0028]     According to the first embodiment of the invention, the module cover  40  is a retractable body. The module cover  40  has a groove-like tear line  40   a . When the airbag  20  is inflated by the inflator  30 , the module cover  40  is cleaved along the tear line  40   a.    
         [0029]     The retainer  10  has a substantially rectangular main plate  11 . The main plate  11  has an opening  12  for the inflator  30  to pass through. Around the opening  12  are provided through holes for stud bolts  25  extending from the airbag-fixing ring  24 .  
         [0030]     An anchor piece  14  extends downward (i.e., in  FIG. 1 , in the direction opposite to the occupant of the vehicle) from the outer rim of the main plate  11  of the retainer  10 . The anchor piece  14  is used to fix the airbag system  1  to the steering wheel  100 . The anchor piece  14  has openings  14   a  for bolts or rivets to pass through. The steering wheel  100  has an airbag-system mounting piece  102  rising from the base  101  thereof. The mounting piece  102  also has an opening  102   a  for a bolt or a rivet to pass through.  
         [0031]     In mounting the airbag system  1  to the steering wheel  100 , the anchor piece  14  is placed on the mounting piece  102 , and they are joined with a bolt or a rivet  103  through the openings  14   a  and  102   a . The openings  14   a  and  102   a  may be screw sections for bolts.  
         [0032]     An enclosure  15  extends upward (i.e., in  FIG. 1 , toward the occupant) from the outer rim of the main plate  11  of the retainer  10 . An extension  16  extends laterally (to the side of the airbag system  1 ) from the distal end of the enclosure  15  in the standing direction. In this embodiment, the extension  16  is an unmoving body.  
         [0033]     To the extension  16  is fixed a nut  17 , to which the lower end of a guide shaft  50  is threaded.  
         [0034]     The airbag  20  has a structure in which the periphery of an inflator insertion hole  22  thereof is placed on the periphery of the inflator opening  12  of the retainer main plate  11 , on which the airbag-fixing ring  24  is placed. The stud bolts  25  are passed through the bolt insertion holes provided around the inflator insertion hole  22  of the airbag  20 . Each stud bolt  25  is then passed through a bolt insertion hole of the retainer  10 . The stud bolt  25  is then passed through a bolt insertion hole of a flange  31  of the inflator  30 , on which a nut  26  is tightened. The airbag  20  and the inflator  30  are thus fixed to the retainer  10 .  
         [0035]     The module cover  40  has a main surface  41  that faces the occupant and a leg  42  extending from the back of the main surface  41 . The leg  42  is molded integrally with the main surface  41  by injection molding of synthetic resin, and has a substantially rectangular frame shape similar to the enclosure  15  of the retainer  10 . The periphery  41   a  of the main surface  41  overhangs outward from the leg  42 .  
         [0036]     The leg  42  provides a mount for an overhang  45 . The overhang  45  extends outward in the direction perpendicular to the direction in which the module cover  40  retracts. The overhang  45  has an opening  45   a  for the guide shaft  50  to pass through.  
         [0037]     As shown in FIGS.  2 ( a ) and  2 ( b ), the lower end of the guide shaft  50  is threaded into the nut  17  of the extension  16  to be fixed to the extension  16 , and extends from the extension  16  toward the occupant. The upper end of the guide shaft  50  projects upward relative to the overhang  45  through the opening  45   a , and has a flange  51  at the upper end as a stopper. Between the flange  51  and the overhang  45  is interposed a washer  52  made of an electrical insulation material such as rubber.  
         [0038]     A first slider  61  on the side of the overhang  45  and a second slider  62  on the side of the extension  16  are slidably fitted around the outer circumference of the guide shaft  50 . Both of the sliders  61  and  62  are made of an electrically insulating material such as synthetic resin.  
         [0039]     A first contact member  71  is fitted on the slider  61 ; a second contact member  72  is fitted on the slider  62 .  
         [0040]     The first contact member  71  has a cylindrical part  71   c , an inward collar  71   a  extending inward from one end of the cylindrical part  71   c , and an outward collar  71   b  extending outward from the other end of the cylindrical part  71   c . The second contact member  72  has a cylindrical part  72   c , an inward collar  72   a  extending inward from one end of the cylindrical part  72   c , and an outward collar  72   b  extending outward from the other end of the cylindrical part  72   c.    
         [0041]     The inward collar  71   a  of the first contact member  71  is disposed along the lower surface of the slider  61 , and the inward collar  72   a  of the second contact member  72  is disposed along the upper surface of the slider  62 ; the collars  71   a  and  72   a  are disposed to face each other.  
         [0042]     The outward collar  71   b  of the first contact member  71  overlaps with the overhang  45 . A first bracket  81  is disposed so as to retain the collar  71   b . The first bracket  81  has a guide slit  81   a  extending in parallel with the axis of the guide shaft  50 .  
         [0043]     A second bracket  82  overlaps with the outward collar  72   b  of the second contact member  72  from the side opposite to the extension  16 . The bracket  82  has a projection  82   a  that is in engagement with the guide slit  81   a.    
         [0044]     A first coil spring  91  is interposed between the brackets  81  and  82  to push the brackets  81  and  82  in a separating direction. A second coil spring  92  is interposed between the outward collar  72   b  of the second contact member  72  and the extension  16  to push the outward collar  72   b  and the extension  16  in a separating direction. In this embodiment, the first coil spring  91  has a spring constant larger than that of the second coil spring  92 .  
         [0045]     The horn-sounding action of the steering wheel  100  equipped with the airbag system  1  including the horn switch device  70  will now be described.  
         [0046]     As shown in  FIG. 2 ( a ), before the module cover  40  is depressed, the contact members  71  and  72  are apart from each other.  
         [0047]     When the module cover  40  is depressed, the sliders  61  and  62  slide along the guide shaft  50 , so that the first and second contact members  71  and  72  descend. With the descent, the second coil spring  92 , which has a smaller spring constant, is first compressed, and then the first coil spring  91  is compressed.  
         [0048]     The extension  16  extends from the retainer  10  fixed to the steering wheel  100 , so that the extension  16  is not displaced even if the module cover  40  is depressed. Also, the guide shaft  50  fixed to the extension  16  is not displaced.  
         [0049]     As the first and second contact members  71  and  72  are pushed down, the contact members  71  and  72  are finally brought into contact with each other, as shown in  FIG. 2 ( b ), to sound the horn.  
         [0050]     On release from the module cover  40 , the first and second contact members  71  and  72  and the module cover  40  are pushed up by the repulsive force of the coil springs  91  and  92  to return to the state shown in  FIG. 2 ( a ). The contact members  71  and  72  are thus pushed apart to stop sounding the horn.  
         [0051]     In the horn switch device  70 , as described above, when the module cover  40  is depressed, the coil spring  92 , which has a smaller spring constant, is first compressed to allow the module cover  40  to be pushed lightly, thereby providing preferable operability. Since the two coil springs  91  and  92  are employed, vibration from the vehicle body can easily be absorbed. Accordingly, even if the distance between the contact members  71  and  72  is small, the contact members  71  and  72  are not brought into contact with each other by the vibration.  
         [0052]     In the first embodiment, both of the first and second contact members  71  and  72  are mounted to or supported by the module cover  40 , so that they can be positioned easily and accurately. This reduces the difficulty in assembling the horn switch device  70  or the airbag system  1 .  
         [0053]     While in the above-described embodiment the spring constant of the first coil spring  91  is larger than that of the second coil spring  92 , the spring constant values may be reversed.  
         [0054]     While the above-described embodiment has a structure in which only the module cover is retracted by depression, the invention can also be applied to an airbag system in which the module cover and the retainer move vertically together.  FIG. 3  is a cross-sectional view of a steering wheel  100 A equipped with an airbag system  1 A with such a structure according to a second embodiment of the invention.  
         [0055]     FIGS.  4 ( a ) and  4 ( b ) are enlarged views of the horn switch device depicted in  FIG. 3 .  FIG. 4 ( a ) shows “an undepressed” state in which a module cover is not depressed, and  FIG. 4 ( b ) shows “a module-cover depressed state” in which the module cover is depressed to sound a horn.  
         [0056]     The airbag system  1 A also includes a retainer  10 A, an airbag  20  mounted to the retainer  10 A with a ring  24 , an inflator  30  for inflating the airbag  20 , a module cover  40 A that covers the folded airbag  20 , and a horn switch device  70 .  
         [0057]     The retainer  10 A of this embodiment also has a substantially rectangular main plate  11 . The airbag  20  and the inflator  3   b  are mounted to the main plate  11 , whose mounting structure is the same as that of the airbag system  1  depicted in  FIG. 1 .  
         [0058]     An enclosure  15 A extends upward (i.e., in  FIG. 3 , toward the occupant) from the outer rim of the main plate  11  of the retainer  10 A. An extension  16 A extends laterally (to the side of the airbag system  1 A or in the direction perpendicular to the direction in which the airbag system  1 A retracts (vertically in  FIG. 3 )), from the distal end of the enclosure  15 A in the standing direction.  
         [0059]     The module cover  40 A has a main surface  41  that faces the occupant and a leg  42 A extending downward (i.e., in  FIG. 3 , in the direction opposite to the occupant) along the inner wall of the enclosure  15 A from the back of the main surface  41 . The leg  42 A is fixed to the enclosure  15 A with a fixing member (not shown) such as a rivet.  
         [0060]     In this second embodiment, airbag-system supporting pieces  104  extend from the steering wheel  100 A along the outer wall of the enclosure  15 A. The supporting pieces  104  are provided in a number equal to the number of extensions  16 A, and are disposed such that the respective ends face the extensions  16 A from below. At the end of each supporting piece  104  is provided a facing part  105  that extends to the side of the airbag system  1 A (in parallel with the direction in which the extension  16 A extends) and faces the lower surface of the extension  16 A. In this embodiment, the facing part  105  is an unmoving body. To the facing part  105 , a nut  106  for fixing a guide shaft is fixed.  
         [0061]     In this second embodiment, the extension  16 A has an opening  45   a ′ (see FIGS.  4 ( a ) and  4 ( b )), through which the guide shaft  50  passes. The lower end of the guide shaft  50  is threaded into the nut  106  at the facing part  105  to be fixed to the facing part  105 , and extends upward from the facing part  105 . Also in this embodiment, a flange  51  is provided as a stopper at the upper end of the guide shaft  50 . Between the flange  51  and the extension  16 A is interposed an electrically insulating washer  52  made of rubber or the like.  
         [0062]     Accordingly, in the second embodiment of the invention, the entire airbag system  1 A moves along the guide shaft  50 .  
         [0063]     Also in the second embodiment, the horn switch device  70  is disposed between the extension  16 A and the facing part  105  such that it is fitted around the guide shaft  50 . The horn switch device  70  is substantially the same as that shown in FIGS.  2 ( a ) and  2 ( b ). In this embodiment, the overhang  45  in FIGS.  2 ( a ) and  2 ( b ) is replaced with the extension  16 A, and the extension  16  is replaced with the facing part  105 . Specifically, in this second embodiment, the first slider  61  is disposed on the side of the extension  16 A, and the second slider  62  is disposed on the side of the facing part  105 , as shown in FIGS.  4 ( a ) and  4 ( b ). The outward collar  71   b  of the first contact member  71  overlaps with the extension  16 A. The second coil spring  92  is interposed between the outward collar  72   b  of the second contact member  72  and the facing part  105 .  
         [0064]     Also in the horn switch device  70  of this second embodiment, the first coil spring  91  has a spring constant larger than that of the second coil spring  92 .  
         [0065]     The remaining structure of this second embodiment is the same as that of the first embodiment depicted in  FIGS. 1 and 2 ( a ) and  2 ( b ). The same reference numbers of  FIGS. 3 and 4 ( a ) and  4 ( b ) as those of  FIGS. 1 and 2 ( a ) and  2 ( b ) indicate the same components;  
         [0066]     The horn-sounding action of the steering wheel  100 A equipped with the airbag system  1 A having the horn switch device  70  will be described.  
         [0067]     As shown in  FIG. 4 ( a ), before the module cover  40 A is depressed, the contact members  71  and  72  are apart from each other.  
         [0068]     When the module cover  40 A is depressed, the entire airbag system  1 A moves downward. Along with that, the sliders  61  and  62  slide along the guide shaft  50 , so that the first and second contact members  71  and  72  descend. With the descent, the second coil spring  92 , which has a smaller spring constant, is first compressed, and then the first coil spring  91  is compressed.  
         [0069]     The facing part  105  (extending from supporting piece  104 ) is integrated with the steering wheel  10 A, so that it is not displaced even if the module cover  40 A is depressed. Also the guide shaft  50  fixed to the facing part  105  is not displaced.  
         [0070]     As the first and second contact members  71  and  72  are pushed down, the contact members  71  and  72  come into contact with each other, as shown in  FIG. 4 ( b ), to sound the horn.  
         [0071]     On release from the module cover  40 A, the first and second contact members  71  and  72  and the extension  16 A are pushed up by the repulsive force of the coil springs  91  and  92 , so that the entire airbag system  1 A returns to the state shown in  FIG. 4 ( a ). This separates the contact members  71  and  72  so as to stop sounding the horn.  
         [0072]     While the spring constant of the first coil spring  91  of this second embodiment is also larger than that of the second coil spring  92 , the spring constant values may be reversed.  
         [0073]     The above-described embodiments are only examples of the invention. The invention is not necessarily limited to the embodiments described herein.  
         [0074]     The disclosures of Japanese Patent Application Nos. 2004-366356 filed on Dec. 17, 2004; 2005-11775 filed on Jan. 19, 2005; and 2005-183679 filed on Jun. 23, 2005, are incorporated herein.