Abstract:
A horn switch gear includes a backward moving body, a stationary body, a biasing member, and a pair of contact members. The backward moving body, which is configured to move backward, faces the stationary body. The biasing member, which is interposed between the backward moving body and the stationary body, biases the backward moving body in a restoring direction. The contact members, which are brought into or out of contact with each other by a forward or backward movement of the backward moving body, are moved together with the backward moving body. The stationary body includes an interposition which is interposed between the contact members for separating the contact members while the backward moving body is in a restored position, and which moves away from between the contact members to bring the contact members into contact with each other while the backward moving body is in a backward position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part of U.S. application Ser. No. 10/798,645, filed Mar. 12, 2004 now U.S. Pat. No. 6,881,911, which is incorporated by reference in its entirety. 

   BACKGROUND 
   The present invention relates to a horn switch and, more preferably, to a horn switch gear provided to an airbag system such that a module cover or an airbag system moves backward by pressure applied by an occupant. The present invention also relates to an airbag system including the horn switch gear. 
   Driver-seat airbag systems mounted on steering wheels of cars include one in which when a module cover of the airbag system is pushed, a horn switch is turned on to blow a horn. For example, Japanese Unexamined Patent Application Publication Nos. 10-100832 and 2001-114057 describe driver-seat airbag systems in which when an airbag system is pushed, a module cover moves backward to turn on a horn switch. 
   In known horn switch gears, one of the contact members is mounted to a module cover and the other is attached to a retainer. However, providing separate contact members increases the difficulty of assembly work which must be done with high accuracy. 
   Accordingly, it is an object of the present invention to provide a horn switch gear having a pair of contact members at only one of a backward moving body such as a module cover and a stationary body such as a retainer to facilitate the positioning of the contact members and an airbag system including the horn switch gear. 
   SUMMARY 
   According to an embodiment of the invention, a horn switch gear is provided. The gear includes a backward moving body configure to move backward by pressure applied by an occupant; a stationary body facing the backward moving body; a biasing member interposed between the backward moving body and the stationary body for biasing the backward moving body in a restoring direction; and a pair of contact members that are brought into or out of contact with each other by a forward or the backward movement of the backward moving body. The contact members are moved forward or backward together with the backward moving body. The stationary body includes an interposition which is interposed between the contact members for separating the contact members from each other while the backward moving body is in a restored position and which is configured to bring the contact members into contact with each other while the backward moving body is in a backward position. 
   In an embodiment of a horn switch gear, the stationary body may include a guide for guiding at least one of the contact members to bring the contact members into contact with each other when the backward moving body is moved backward from the restored position. 
   An embodiment of a horn switch gear according to the invention includes: a backward moving body configured to move backward by pressure applied by an occupant; a stationary body facing the backward moving body; n biasing member interposed between the backward moving body and the stationary body for biasing the backward moving body in the restoring direction; and a pair of contact members that are brought into or out of contact with each other by a forward or backward movement of the backward moving body. The contact members are retained by the stationary body. The backward moving body includes an interposition which is interposed between the contact members for separating the contact members from each other while the backward moving body is in a restored position and which moves away from between the contact members to bring the contact members into contact with each other while the backward moving body is in a backward position. 
   In an embodiment of a horn switch gear, the backward moving body may include a guide for guiding at least one of the contact members by coming into contact with it to bring the contact members into contact with each other when the backward moving body is moved backward from the restored position. 
   An embodiment of a horn switch gear according to the invention includes: a backward moving body configured to move backward by pressure applied by an occupant; a stationary body facing the backward moving body; a biasing member interposed between the backward moving body and the stationary body for biasing the backward moving body in a restoring direction; and a pair of contact members that are brought into or out of contact with each other by a forward or backward movement of the backward moving body. The contact members are separated from each other while the backward moving body is in a restored position. The contact members are moved forward or backward together with the backward moving body. The stationary body includes a guide for guiding at least one of the contact members by coming into contact with it to bring the contact members into contact with each other when the backward moving body is moved backward from the restored position. 
   An embodiment of a horn switch gear according to the invention includes: a backward moving body configured to move backward by pressure applied by an occupant; a stationary body facing the backward moving body; a biasing member interposed between the backward moving body and the stationary body for biasing the backward moving body in a restoring direction; and a pair of contact members that are brought into or out of contact with each other by a forward or backward movement of the backward moving body. The contact members are separated from each other while the backward moving body is in a restored position. The contact members are retained by the stationary body. The backward moving body includes a guide for guiding at least one of the contact members by coming into contact with it to bring the contact members into contact with each other when the backward moving body is moved backward from the restored position. 
   An embodiment of a horn switch gear according to the invention includes: a backward moving body configured to move backward by pressure applied by an occupant; a stationary body facing the backward moving body; a biasing member interposed between the backward moving body and the stationary body for biasing the backward moving body in a restoring direction; and a pair of contact members that is brought into or out of contact with each other by a forward or backward movement of the backward moving body. The contact members are moved forward or backward together with the backward moving body. The stationary body includes an interposition which moves away from between the contact members to bring the contact members into contact with each other while the backward moving body is in a restored position and which is interposed between the contact members for separating the contact members from each other while the backward moving body is in a backward position. 
   An embodiment of a horn switch gear according to the invention includes: a backward moving body configured to move backward by pressure applied by an occupant; a stationary body facing the backward moving body; a biasing member interposed between the backward moving body and the stationary body for biasing the backward moving body in a restoring direction; and a pair of contact members that are brought into or out of contact with each other by a forward or backward movement of the backward moving body. The contact members are retained by the stationary body. The backward moving body includes an interposition which moves away from between the contact members to bring the contact members into contact with each other while the backward moving body is in a restored position and which is interposed between the contact members for separating the contact members from each other while the backward moving body is in a backward position. 
   In an embodiment of a horn switch gear according to the invention, the backward moving body may be an airbag system, a module cover, or a module cover of an airbag system. 
   In an embodiment of a horn switch gear, while the backward moving body (which may be, for example, a module cover or an airbag system) is in a restored position (i.e., in an unpushed condition), the contact members may be separated from each other. When the backward moving body is pushed, the interposition may move away from between the contact members to bring the contact members into contact with each other, thereby blowing a horn. 
   In an embodiment of a horn switch gear, it is also possible to include a guide for guiding at least one of the contact members which comes into contact with it to bring the contact members into contact with each other when the backward moving body is moved backward from the restored position. With such a structure, the contact members may be forced by the guide to come into contact with each other, increasing the contact pressure of the contact members. 
   In an embodiment of a horn switch gear, when the backward moving body moves backward, the contact members may be guided by a guide to come into contact with each other to blow the horn. 
   In an embodiment of a horn switch gear, while the backward moving body (which may be, for example, a module cover or an airbag) is in a restored position, the contact members may be in contact with each other. A horn control circuit may be constructed not to bring the horn into conduction with the contact members in a closed condition. 
   In an embodiment of a horn switch gear, when the backward moving body moves backward, the interposition may enter the contact members to separate them from each other, i.e., to open the contact members. A horn control circuit may bring the horn into conduction to blow the horn. 
   In an embodiment of a horn switch gear, the horn switch gear may have contact members at only one of the backward moving body and the stationary body. As a result, the positioning of the contact members may be easy, making it easy to assemble the airbag system and so on. 
   An embodiment of a horn switch gear according to the present invention includes: a moving body configured to move backward by pressure applied by an occupant; a stationary body facing the backward moving body; a biasing member interposed between the moving body and the stationary body; a pair of contact members that are configured to be brought into or out of contact with each other by a forward or backward movement of the moving body; and an interposition which: is interposed between the contact members when the moving member is in a first position, and is not interposed between the contact members when the moving member is in a second position. The contact members either are retained by the stationary body or are moved together with the moving body. 
   In an embodiment of a horn switch according to the present invention, the first position may a restored position and the second position is a backward position. Similarly, the first position may be a backward position and the second position may be a restored position. 
   In an embodiment of a horn switch according to the present invention, the interposition may be part of the stationary body or part of the moving body. 
   In another embodiment according to the present invention, a horn switch is provided that comprises a backward moving body configured to move backward by pressure applied by an occupant, wherein the backward moving body includes an airbag retainer, a stationary body facing the backward moving body, a biasing member interposed between the backward moving body and the stationary body for biasing the backward moving body in a restoring direction, a pair of contact members that are configured to be brought into or out of contact with each other by a forward or backward movement of the backward moving body, and an interposition which is interposed between the contact members for separating the contact members from each other while the backward moving body is in a restored position, and is configured to bring the contact members into contact with each other while the backward moving body is in a backward position. The contact members are positioned below the retainer. 
   In another embodiment according to the present invention, a driver side airbag system comprises an airbag module including a gas generator, an airbag, a cover and an airbag retainer configured to move backward in response to a force applied by an occupant; a horn switch positioned between the airbag module and a stationary body. The horn switch comprises a biasing member interposed between the airbag module and the stationary body for biasing the airbag module in a restoring direction, and a pair of contact members that are configured to be brought into or out of contact from each other by a forward or backward movement of the airbag module. 
   In another embodiment of the present invention, an airbag system is provided. The airbag system comprises a movable airbag module including a gas generator, an airbag, a cover and an airbag retainer; and a horn switch positioned between the airbag retainer and a fixed vehicle structure. The horn switch includes a biasing member interposed between the airbag retainer and the vehicle structure for biasing the airbag module in a restoring direction, a pair of contact members that are configured to be brought into or out of contact with each other by a forward or backward movement of the airbag module, and a guide for contacting and guiding at least one of the contact members to bring the contact members into contact with each other when the airbag module is moved backward from the restored position. 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects, and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below. 
       FIG. 1  is a sectional view of an embodiment of an airbag system including an embodiment of a horn switch gear according to the present invention; 
       FIGS. 2A and 2B  are sectional views the horn switch gear of  FIG. 1  in which  FIG. 2A  is a non-contact (i.e., a restored position) view and  FIG. 2B  is an in-contact (i.e., a backward position) view; 
       FIG. 3  is an exploded perspective view of the horn switch gear of  FIG. 1 ; 
       FIG. 4  is an exploded perspective view of the horn switch gear of  FIG. 1 ; 
       FIG. 5  is an exploded perspective view of the airbag system of  FIG. 1 ; 
       FIGS. 6A and 6B  are sectional views of a second embodiment of a horn switch gear according to the present invention; 
       FIG. 7  is an exploded perspective view of the horn switch gear of  FIGS. 6A and 6B ; 
       FIG. 8  is an exploded perspective view of the horn switch gear of  FIGS. 6A and 6B ; 
       FIGS. 9A and 9B  are sectional views of a third embodiment of a horn switch gear according to the present invention; 
       FIG. 10  is an exploded perspective view of the horn switch gear of  FIGS. 9A and 9B ; 
       FIG. 11  is an exploded perspective view of the horn switch gear of  FIGS. 9A and 9B ; 
       FIGS. 12A and 12B  are sectional views of a fourth embodiment of a horn switch gear according to the present invention; 
       FIGS. 13A and 13B  are sectional views of a fifth embodiment of a horn switch gear according to the present invention; 
       FIG. 14  is a sectional view of a sixth embodiment of a horn switch gear according to the present invention; 
       FIG. 15  is a sectional view of the horn switch gear of  FIG. 14 ; 
       FIG. 16  is an exploded perspective view of the horn switch gear of  FIG. 14 ; 
       FIG. 17  is a sectional view of an embodiment of an airbag system including an embodiment of a horn switch gear according to the present invention; 
       FIG. 18  is a sectional view of an embodiment of an airbag system including an embodiment of a horn switch gear according to the present invention; and 
       FIG. 19  is a sectional view of another embodiment of an airbag system including an embodiment of a horn switch gear according to the present invention. 
   

   DETAILED DESCRIPTION 
   Embodiments of the present invention will be described hereinafter with reference to the drawings.  FIG. 1  shows an airbag system  1  having a horn switch gear  70  according to an embodiment of the invention in sectional view.  FIGS. 2A and 2B  show the horn switch section of  FIG. 1  in enlarged view.  FIGS. 3 and 4  shows the horn switch gear  70  in exploded view, viewed from opposite directions from each other. And,  FIG. 5  shows the airbag system  1  in exploded perspective view.  FIG. 2A  shows an “unpushed” state in which a module cover  40  is not pushed.  FIG. 2B  shows a “module-cover pushed state” in which the module cover  40  is pushed to blow a horn. 
   The airbag system  1  is a driver-seat airbag system mounted in the center of a steering wheel. The airbag system  1  includes a metal retainer  10 , an airbag  20  mounted to the retainer  10  with an airbag-mounting ring  24 , an inflator  30  for inflating the airbag  20 , a synthetic-resin module cover  40  which covers the folded airbag  20 , and a horn switch gear  70 . 
   The module cover  40  has a grooved tear line  40   a . The module cover  40  is torn open along the tear line  40   a  when the airbag  20  is inflated by the inflator  30 . The airbag  20  is not shown in  FIG. 5 . 
   As clearly shown in  FIGS. 1 and 5 , the retainer  10  includes a substantially rectangular main plate  11 . The main plate  11  has an opening  12  for the inflator  30  to be inserted. Around the opening  12  is provided an insertion hole  13  for a stud bolt  25  rising from the airbag-mounting ring  24 . 
   An anchor piece  14  rises from the outer periphery of the main plate  11  of the retainer  10  toward the lower part in the drawing (opposite to an occupant). The anchor piece  14  is for mounting the airbag system  1  to a steering wheel. The anchor piece  14  has an opening  14   a  for a bolt or the like to be inserted. The opening  14   a  may be a bolting screw hole. 
   A peripheral wall  15  rises from substantially the whole outer circumference of the main plate  11  (except the part of the anchor piece  14 ) upward in the drawing (toward the occupant). Extensions  16  extend sideward (laterally from the airbag system  1 ) from the rising end of the peripheral wall  15 . 
   To each extension  16 , a metal nut  17  into which a metal guide shaft  50  is screwed is firmly fixed by welding, caulking, or integral molding. 
   The periphery of an inflator insertion hole  22  of the airbag  20  is superposed on the periphery of the inflator opening  12  of the retainer main plate  11 , on which the airbag-mounting ring  24  is superposed. A stud bolt  25  is inserted into a bolt insertion hole formed around the periphery of the inflator insertion hole  22  of the airbag  20 . The stud bolt  25  is inserted into the bolt insertion hole  13  of the retainer  10 . The stud bolt  25  is further inserted into a bolt insertion hole  32  of a flange  31  of the inflator  30  and tightened with a nut  26  ( FIG. 1 ). Thus, the airbag  20  and the inflator  30  are fixed to the retainer  10 . 
   The module cover  40  includes a main surface  41  facing the occupant and a leg piece  42  rising from the back of the main surface  41 . The leg piece  42  is integrated with the main surface  41  by synthetic-resin injection molding into a nearly rectangular frame shape similar to the peripheral wall  15  of the retainer  10 . The peripheral side  41   a  of the main surface  41  extends outward from the leg piece  42 . 
   The nearly rectangular-frame-shaped leg piece  42  has cutaway portions  43  cut from the rising end of the leg piece  42 . The cutaway portions  43  are constructed to receive the extensions  16  of the retainer  10 . The leg piece  42  also has rivet holes  44 . 
   The leg piece  42  has a metal frame  60  mounted thereto. The frame  60  includes a frame body  61  surrounding the outer surface of the leg piece  42  and overhangs  63  extending laterally from the frame body  61 . 
   The frame body  61  has rivet holes  64  ( FIG. 5 ). The rivet holes  64  and the leg piece  42  are interposed on each other, which are riveted (not shown) through the rivet holes  44  and  64 , and so the frame  60  is fixed to the leg piece  42 . 
   The frame body  61  has cutaway portions  62  having a size and an arrangement corresponding to the rim of the cutaway portions  43  of the leg piece  42 . The cutaway portions  43  and  62  receive the extensions  16  of the retainer  10 . 
   Each overhang  63  has an insertion hole  68  for the guide shaft  50 . 
   Referring to  FIG. 2 , the lower end of the guide shaft  50  is screwed into the nut  17  of each extension  16  to be fixed to the extension  16 , rising from the extension  16  toward the occupant. The guide shaft  50  has a flange  51  serving as a stopper at the upper rim. The horn switch gear  70  is provided so as to be fitted on the guide shaft  50 . 
   The structure of the horn switch gear  70  will be described mainly with reference to  FIGS. 2 to 4 . 
   The horn switch gear  70  includes an anode  80 , a slide cylinder  90 , a cathode  100 , a coil spring  110 , an insulation ring  120 , and a washer  130 , as shown in  FIGS. 3 and 4 . 
   The anode  80  includes a washer-shaped ring flange  81  and a plurality of (three in this embodiment) tongue-shaped contacts  82  rising from the inner periphery of the flange  81  in the same directions. 
   The slide cylinder  90  includes a tubular cylinder body  91 , a flange  92  extending from one end of the cylinder body  91  along the axial center, and pawls  93  ( FIG. 4 ) extending from the end of the cylinder body  91  in parallel to the axial center. The flange  92  has three arc-shaped slits  94  extending along the outer periphery of the cylinder body  91  around the inner periphery thereof. 
   The cathode  100  includes a flange  101  and three tongue-shaped contacts circumferentially rising from the inner periphery of the flange  101 . As shown in  FIG. 2 , the lower end of each contact  102  is curved toward the center of the cathode  100 . 
   The insulation ring  120  includes a flange  121 , a nearly cylindrical inner wall  122  rising from the flange  121 , and three outer walls  123  rising along the outer periphery of the inner wall  122 . The part of the inner wall  122  facing the outer walls  123  has windows (also referred to as “window openings”)  124 . Each window  124  extends from the inner periphery of the flange  121  toward the rising end of the inner wall  122 . The upper rim of the windows  124  is located slightly lower than the upper end of the outer wall  123  (adjacent to the flange  121 ). 
   As shown in  FIG. 2 , the upper rim of the windows  124  forms an inclined surface  124   a  that is closer to the outer wall  123  at the upper part. The upper end of the outer wall  123  forms an inclined surface  123   a  that is closer to the inner wall  122  at the lower part. The inclined surface  123   a  serves as guide for guiding the contact  102  to bring it into contact with the contact  82 . 
   Each contact  102  of the cathode  100  is slidably superposed on the outer circumference of the inner wall  122 . When the module cover  40  is in restored (i.e., in an unpushed, non-contact condition), the lower end of the contact  102  is in contact with the inner-wall inclined surface  124   a  ( FIG. 2A ). When the module cover  40  is pushed into a backward position, the lower end of the contact  102  is separated from the inclined surface  124   a  but is brought into contact with the inclined surface  123   a  at the upper end of the outer wall  123  and the contact  82  of the anode  80  ( FIG. 2B ). The outer circumference of the inner wall  122  and the inner circumference of the outer wall  123  are in an approximately equal radius relative to the central axis of the insulation ring  120 . 
   The inner wall  122  has cutaway portions  126  at three locations of the upper end thereof. The flange  121  of the insulation ring  120  has cutaway portions  127  at three locations of the outer periphery thereof. 
   The washer  130  has three protrusions  131  to be cut in the cutaway portions  127 . The protrusions  131  have a rising height larger than the thickness of the flange  121 , projecting upward from the upper surface of the flange  121  with the horn switch gear  70  in an assembled condition ( FIG. 2 ). 
   The coil spring  110  has a diameter so as to be fitted on the outer wall  123  and brought into contact with the flange  121  and the flange  101  of the cathode  100 . 
   As shown in  FIG. 2 , each contact  82  of the anode  80  is inserted into the slit  94  of the slide cylinder  90  and superposed on the outer circumference of the cylinder body  91 . The flange  81  of the anode  80  is superposed on the flange  92  of the slide cylinder  90 , which are fixed together with an adhesive or the like as necessary. 
   The flange  101  of the cathode  100  is superposed on the flange  92 , which are fixed together with an adhesive or the like as necessary. The cathode  100  and the slide cylinder  90  may be fixed together by engagement or the like. 
   The coil spring  110  is fitted on the outer circumference of the outer walls  123  of the insulation ring  120 . The insulation ring  120  is coaxially arranged around the outer circumference of the cylinder body  91  such that the inner wall  122  is inserted between the contacts  82  and  102 . The pawls  93  of the slide cylinder  90  are inserted and locked into the guide-shaft insertion hole  68  of the frame  60 . 
   The flange  121  located at the lower end of the horn switch gear  70  is superposed on the extension  16  through the washer  130 . The lower end of the coil spring  110  is in contact with the protrusions  131  of the washer  130 , while the upper end of the coil spring  110  is in contact with the flange  101  of the cathode  100 . Thus, the cathode  100  is brought into conduction with the retainer  10  through the coil spring  110  and the washer  130 . Since the retainer  10  is mounted to a steering wheel (not shown), the cathode  100  is brought into conduction with the cathode of a battery of a vehicle. The anode  80  is in close contact with the overhangs  63  to be brought into contact with the anode of the battery through a lead wire (not shown) connecting to the overhangs  63 . 
   In the airbag system  1  including the horn switch gear  70  with such a structure, the upper part of each window  124  of the insulation ring  120  interposes between the contacts  82  and  102 , thus separating the contacts  82  and  102  from each other ( FIG. 2A ) until the module cover  40  is pushed. Thus, the upper part of the windows  124  of the inner wall  122  serves as interposition (i.e., a separating element) for separating the contacts  82  and  102  from each other. 
   The module cover  40  is pushed upward toward a restored position ( FIG. 2A ) by the coil spring  110 . The pawls  93  are brought into contact with the flange  51  of the guide shaft  50  by the pressure of the coil spring  110 . 
   Referring to  FIG. 2B , when the module cover  40  is pushed by an occupant, the frame  60  integrated with the module cover  40  moves back downward to contract the coil spring  110  by pressure, thereby moving the slide cylinder  90 , the anode  80 , and the cathode  100  downward. Accordingly, the contacts  82  and  102  also move downward together therewith, the contacts  102  being pushed inward by the inclined surfaces  123   a , so that the contacts  82  and  102  are brought into contact with each other to blow the horn. 
   When the occupant releases the pressure applied to the module cover  40 , the module cover  40  is moved back into the restored position of  FIG. 2A  by the repulsive force of the coil spring  110 , thereby stopping the horn. 
   As previously described, both of the anode  80  and the cathode  100  of the horn switch gear  70  are arranged to the module cover  40 , improving the positioning accuracy of the anode  80  and the cathode  100  when assembled to the module cover  40 . 
   Referring to  FIGS. 6 to 8 , a horn switch gear  70 A according to a second embodiment will be described. 
   In this embodiment, an anode  140  includes a flange  141  and three contacts  142  rising from the outer periphery of the flange  141 . 
   A slide cylinder  150  has an inner wall  151  and outer walls  153  rising from the inner and the outer peripheries of a flange  152 , respectively. The flange  152  has slits  154  for the contacts  142  to pass through. From the inner periphery of the flange  152 , pawls  155  project in the direction opposite to the inner wall  151 . 
   A cathode  160  has a cylindrical contact  161  and a collar  162  projecting inwardly from the upper periphery of the cylindrical contact  161 . 
   An insulation ring  170  has an inner cylinder  171 , an outer cylinder  172 , a bottom  174  connecting them together, windows (also referred to as “window openings”)  173  shaped to cut the intersection between the bottom  174  and the outer cylinder  172 , and inclined surfaces  172   a  formed at the upper rims of the windows  173 . The inclined surfaces  172   a  are each tapered so as to be reduced in diameter at the lower part. 
   The upper parts of the windows  173  of the outer cylinder  172  serve as interposition (i.e., a separating element) for separating the contacts  142  and  161  from each other. 
   A washer  180  has protrusions  181  which come into the windows  173  for supporting the lower end of the coil spring  110 . 
   The contact  161  of the cathode  160  is superposed on the outer surface of the inner wall  151  of the slide cylinder  150 , as shown in  FIG. 6 , and the collar  162  is brought into contact with the upper end of the coil spring  110 . Thus, the contact  161  of the cathode  160  is brought into conduction with the vehicle body through the coil spring  110  and the washer  180 . The collar  162  overlaps with the flange  152  of the slide cylinder  150 . 
   The lower part of the contact  161  is arranged between the outer cylinder  172  of the insulation ring  170  and the inner wall  151  of the slide cylinder  150 . The contacts  142  of the anode  140  are arranged outside the outer cylinder  172 . 
   The other arrangement in  FIGS. 6 to 8  is similar to that of the first embodiment. 
   As shown in  FIG. 6A , the outer cylinder  172  is interposed between the contacts  142  and  161 , thereby separating the contacts  142  and  161  from each other when the module cover  40  is in unpushed (i.e., restored) position. 
   When the module cover  40  is pushed by an occupant, the anode  140  and the cathode  160  are pushed down together with the slide cylinder  150 , thereby letting the contacts  142  of the anode  140  move into the windows  173  under the force of an inward elasticity of the contacts  142 . When the anode contacts  142  enter the windows  173 , they come into contact with the contact  161  of the cathode  160  ( FIG. 6B ), thereby blowing the horn. When the occupant releases the pressure applied to the module cover  40 , the module cover  40  is pushed back to the restored position of  FIG. 6A  by the coil spring  110 . At that time, the upper parts of the windows  173  of the outer cylinder  172  enter the contacts  142  and  161  and separate them from each other, thereby stopping the horn. 
   Referring to  FIGS. 9 to 11 , a horn switch gear  70 B according to a third embodiment will be described. 
   This embodiment includes a truncated-cone shaped tapered section  16 A on the upper surface of the extension  16  of the retainer  10 , the guide shaft  50  being arranged coaxially with the tapered section  16 A. 
   In this embodiment, an anode  200  includes a flange  201  and three contacts  202  rising from the inner periphery of the flange  201 . 
   An insulation ring  210  includes a flange  211 , inner walls  212  and outer walls  214  rising from the inner and the outer peripheries of the flange  211 , respectively, elastic deformation sections  213  extending from the ends of the inner walls  212  in parallel with the outer walls  214 , pawls  215  projecting from the flange  211  in the opposite direction to the inner walls  212 , and slits  216  provided in the flange  211  between the inner walls  212  and the outer walls  214 . 
   A cathode  220  includes a cylindrical contact  221  and collars  222  projecting outward from one end of the contact  221 . 
   As shown in  FIGS. 9A and 9B , the contacts  202  and  221  are inserted between the inner walls  212  and the outer walls  214  of the insulation ring  210 . The contacts  202  of the anode  200  pass through the slits  216  and overlap with the outer surfaces of the inner walls  212  and the elastic deformation sections  213 , while the contact  221  of the cathode  220  overlaps with the inner surfaces of the outer walls  214 . 
   The cathode collars  222  overlap with the flange  211  of the insulation ring  210 , with which the upper end of the coil spring  110  is brought into contact. The lower end of the coil spring  110  is brought into contact with the upper surface of the extension  16 . Thus, the cathode  220  comes into conduction with the vehicle body through the coil spring  110 . 
   As shown in a restored position shown in  FIG. 9A , the elastic deformation sections  213  overlap with the outer surface of the tapered section  16 A or is slightly separated therefrom until the module cover  40  is pushed. When the module cover  40  is pushed into a backward position by an occupant, the elastic deformation sections  213  are pushed down along the tapered section  16 A to expand like straddle legs, as shown in  FIG. 9B . Thus, the contacts  202  of the anode  200  overlapping with the outer surfaces of the elastic deformation sections  213  are brought into contact with the contact  221  of the cathode  220  to blow the horn. 
   When the occupant releases the pressure applied to the module cover  40 , the module cover  40  moves back to the restored position ( FIG. 9A ) by means of the coil spring  110 , thereby stopping the horn. 
   In the previously described embodiments, the contacts of the horn switch gear are closed to thereby blow the horn. It is also possible, however, to have a horn control circuit which supplies no power to the horn while the contacts are closed but which, upon opening the contacts, supplies power to the horn.  FIGS. 12A and 12B  show an example of such the horn switch gear. The horn switch gear  70 C is constructed such that, in the horn switch gear  70  shown in  FIGS. 1 to 5 , contacts  102 A and contacts  82  are in contact with each other ( FIG. 12A ) until the module cover  40  is pushed into a backward position by an occupant ( FIG. 12B ). When the module cover  40  is pushed, the inner walls  122 A of the insulation ring enter the contacts  82  and  102 A and separate them from each other. Reference numeral  123 A indicates an insulation-ring outer wall. The other arrangement of  FIGS. 12A and 12B  is the same as that of  FIG. 2 . Similarly, the embodiments of  FIGS. 6 to 11  may also be constructed to blow the horn by opening the contacts. 
   The above embodiments are merely examples of the present invention. The invention may employ other arrangements different from those in the drawings. For example, in the above embodiments, the contacts may not be fixed to the module cover  40  but rather to the extension  16  such as, for example, as shown in the embodiment shown in  FIGS. 13A and 13B . 
     FIGS. 13A and 13B  show an embodiment of a horn switch gear  70 ′ in which the horn switch gear  70  of  FIG. 2  is essentially flipped vertically. In this embodiment, however, the pawls  93 ′ rise from the inner periphery of the flange  121  of the insulation ring. The remain portions of the horn switch gear  70 ′ are the same as that of the horn switch gear  70 , wherein the same numerals indicate the same components. 
   As shown in  FIG. 13A , while the module cover  40  is not pushed (i.e., the module  40  is in a restored position), the contacts  82  and  102  are separated from each other, whereas when the module cover  40  is pushed into a backward position ( FIG. 13B ) by an occupant, the contacts  82  and  102  are brought into contact with each other, thereby blowing the horn in a manner substantially similar to the horn switch gear  70  shown in  FIG. 2 . 
     FIG. 14  is a sectional view of a horn switch gear  70 D according to another embodiment with a module cover in an unpushed condition (i.e., in a restored position).  FIG. 15  is a sectional view of the horn switch gear  70 D with the module cover in a pushed condition (i.e., in a backward position). And,  FIG. 16  is an exploded perspective view of the horn switch gear  70 D. 
   Referring to  FIG. 16 , the horn switch gear  70 D includes an anode  240 , a slide cylinder  250 , a cathode  260 , the coil spring  110 , an insulation ring  270 , and a washer  280 . 
   The anode  240  includes a washer-shaped ring flange  241  and two tongue-shaped contacts  242  rising from the outer periphery of the flange  241  in the same direction and around the axial center of the flange  241  at regular intervals. 
   The slide cylinder  250  includes a tubular cylinder body  251 , two first collars  252  extending radially from one end of the cylinder body  251  along the axial center, two second collars  253  which extending radially outward from the outer circumference of the cylinder body  251  at even intervals from one end of the first collars  252  toward the other end of the first collars  252  along the axial center (hereinafter, the other end is lower and the one end is upper), outer walls  254  rising downward along the outer circumference of the cylinder body  251  from the distal ends of the extensions of the second collars  253 , and a pair of facing pieces  255  projecting from the outer circumference of the cylinder body  251  so as to face the lower surfaces of the first collars  252 . 
   An upper part of the cylinder body  251  (in the axial direction) is larger in diameter than a lower part of the cylinder body  251 ; a step  251   a  is formed between the upper and lower parts. The step  251   a  is flush with the lower surface of the second collars  253 . 
   The first collars  252  and  252  are arranged around the axial center of the cylinder body  251  at even intervals. The second collars  253  and  253  are arranged around the axial center of the cylinder body  251  at even intervals with a phase difference of 90° from the first collars  252 . 
   The outer walls  254  each have a guide hole  254   a  for a later-described guide projection  275  to be fitted. The guide hole  254   a  extends downward (toward the distal end) from the base end of the outer wall  254  so as to cut out the end rim of the second collar  253 . 
   Each facing piece  255  can be elastically displaced from the lower surface of the first collar  252  substantially in the direction toward and away therefrom. The facing pieces  255  and the first collars  252  elastically clamp the periphery of the guide-shaft insertion hole  68  provided in the overhang  63  of the frame  60  that supports the upper part of the horn switch gear  70 D. 
   The interval between the lower surface of the first collar  252  and the upper surface of the second collar  253  is substantially the same as the total thickness of the periphery of the guide-shaft insertion hole  68  and the flange  241  of the anode  240 . 
   The slide cylinder  250  is constructed of an insulative synthetic resin or the like. 
   The cathode  260  includes a ring-shaped flange  261  and two tongue-shaped contacts  262  rising downward from the outer periphery of the flange  261 . The contacts  262  and  262  are arranged around the axial center of the flange  261  at even intervals. The interval between the contacts  262  and  262  is larger than the outer diameter of the coil spring  110  and smaller than the interval between the contacts  242  and  242  of the anode  240 . 
   The insulation ring  270  includes a ring-shaped flange  271  and a cylindrical peripheral wall  272  rising from the outer periphery of the flange  271 . The outer diameter of the peripheral wall  272  is equal to or slightly smaller than the interval between the inner surfaces of the outer walls  254  and  254  of the slide cylinder  150  and equal to or slightly larger than the space between the contacts  242  and  242  of the anode  240 . 
   The peripheral wall  272  has two windows (also referred to as “window openings”)  273  having a size for each contact  262  of the cathode  260  to pass through. The inner circumference of the peripheral wall  272  has guide grooves  274  ( FIGS. 14 and 15 ), from the upper rim to the windows  273 , for guiding the contacts  262  into the windows  273 . The lower rim of each window  273  forms an inclined surface  273   a  which is inclined downward and outwardly (radially) from the peripheral wall  272  such that a lower part of the inclined surface  273   a  is separated from the center of the peripheral wall  272 , as shown in  FIGS. 14 and 15 . The windows  273  and  273  are arranged around the axial center of the peripheral wall  272  at even intervals. 
   Two guide projections  275 , which project from the outer circumference of the peripheral wall  272 , come into engagement with the guide holes  254   a  of the outer walls  254  of the slide cylinder  250 . The guide projections  275  are arranged with a phase difference of 90° from the windows  273 . 
   The flange  271  of the insulation ring  270  has four cutaway portions  276  at regular intervals around the inner periphery thereof. The washer  280  includes four projections  281  arranged at regular intervals from the lower surface to enter the cutaway portions  276 . Each projection  281  has a rising height larger than the thickness of the flange  271 , thus projecting downward from the lower surface of the flange  271 , with the horn switch gear  70 D assembled ( FIGS. 14 and 15 ). 
   In assembling the horn switch gear  70 D, the anode  240  is first fitted on the upper end (between the first collars  252  and the second collars  253 ) of the cylinder body  251  of the slide cylinder  250  to superpose the flange  241  of the anode  240  on the upper surfaces of the second collars  253 . The cathode  260  is fitted on the lower ends of the cylinder body  251  to superpose the flange  261  of the cathode  260  on the lower surfaces of the second collars  253 . At that time, they are arranged so that the contacts  242  of the anode  240  and the contacts  262  of the cathode  260  are positioned in the same phase around the axial center of the cylinder body  251  (briefly, the contacts  242  of the anode  240  face the outer sides of the contacts  262  of the cathode  260 ) and are arranged with a phase difference of 90° from the second collars  253 . The anode  240  and the cathode  260  are fixed to the second collars  253  with an adhesive or the like as necessary. 
   The upper end of the cylinder body  251  is inserted into the guide-shaft insertion hole  68  of the overhang  63 . The first collars  252  are arranged on the upper surface of the overhang  63 , while the second collars  253  are arranged on the lower surface of the overhang  63 . At that time, the periphery of the guide-shaft insertion hole  68  is clamped by the facing pieces  255  and the first collars  252 . Thus, the slide cylinder  250  is fixed to the overhang  63 . The flange  241  of the anode  240  is clamped between the overhang  63  and the second collars  253 , through which the contacts  242  are brought into conduction with the overhang  63 . 
   The coil spring  110  is then fitted on the lower end of the cylinder body  251  of the slide cylinder  250 . The respective contacts  242  and  262  of the anode  240  and the cathode  260  are arranged outside the coil spring  110 . 
   The washer  280  is next superposed on the upper surface of the flange  271  of the insulation ring  270 . At that time, the projections  281  of the washer  280  are fitted in the cutaway portions  276  of the flange  271 . The peripheral wall  272  of the insulation ring  270  is fitted on the lower end of the coil spring  110 . At that time, the upper end of the coil spring  110  is brought into contact with the flange  261  of the cathode  260 , while the lower end is brought into contact with the washer  280 . The peripheral wall  272  is then inserted between the outer walls  254  and  254  of the slide cylinder  250  while the coil spring  110  is contracted by pressure to bring the guide projections  275  into engagement with the respective guide holes  254   a  of the outer walls  254 . At that time, the contacts  262  of the cathode  260  are arranged in the guide grooves  274  to the windows  273  of the inner circumference of the peripheral wall  272 , while the contacts  242  of the anode  240  are arranged along the outer circumference of the peripheral wall  272 . 
   Thereafter, the guide shaft  50  is inserted into the cylinder body  251  of the slide cylinder  250  and the end of the guide shaft  50  is screwed into the nut  17  of the extension  16 . Thus, the projections  281  of the washer  280  which project lower than the flange  271  of the insulation ring  270  through the cutaway portions  276  are brought into contact with the extension  16 , so that the contacts  262  of the cathode  260  are brought into conduction with the extension  16  through the washer  280 , the coil spring  110 , and the flange  261 . The flange  51  of the guide shaft  50  and the overhang  63  are insulated from each other by the first collars  252  of the slide cylinder  250  which are arranged on the upper surface of the overhang  63 . 
   As shown in  FIG. 14 , when a horn switch gear  70 D with such a structure is in a restored position, the upper parts of the windows  273  of the peripheral wall  272  interpose between the contacts  242  and  262  to separate the contacts  242  and  262  from each other, until the module cover  40  is pushed. Thus, the upper parts of the windows  273  of the peripheral wall  272  serve as interpositions which separate the contacts  242  and  262  from each other. 
   As shown in  FIG. 15 , when the module cover  40  is pushed into a backward position by an occupant, the frame  60  integrated with the module cover  40  moves back downwardly to move the slide cylinder  250 , the anode  240 , and the cathode  260  downward while contracting the coil spring  110  by pressure. Thus, the contacts  242  and  262  also move downward integrally therewith, so that the contacts  262  are pushed outward by the inclined surfaces  273   a  at the lower rims of the windows  273 . As a result, the contacts  242  and  262  are brought into contact with each other, thereby blowing the horn. 
   When the pressured applied by the occupant on the module cover  40  is released, the module cover  40  moves back into the restored position ( FIG. 14 ) by the repulsive force of the coil spring  110 , thereby stopping the horn. 
   The above embodiments are constructed so that only the module cover  40  moves backward when pushed. It is also possible, however, to construct the module cover and the retainer such that they move backward integrally. Thus, the entire airbag system may be pushed backward to close (or open) the contacts of the horn switch gear, thereby blowing (or stopping) the horn. 
   As shown in  FIGS. 17-19 , the module cover  40  and retainer  10  both move backward integrally when the cover  40  is pushed by a vehicle occupant. In these embodiments, the contacts  82 ,  102  of the horn switch  70  are positioned below the retainer  10 . In all other respects, the airbag module  200  is similar to the embodiments above. A bracket  214  is positioned on the rear of the airbag module, including the cover  40  and the retainer  10 . The bracket  214  includes a mounting hole  214   a  for receiving a bolt to be inserted for mounting the airbag module to a steering wheel. A portion  214   b  of the bracket  214  supports the bottom of the horn switch  70 . 
   In the embodiment shown in  FIG. 17 , the horn switch  70  is positioned under an extension  16  of the airbag retainer  10  at an outer peripheral edge of the airbag module. The horn switch  70  can be mounted to the airbag module below the main surface  41  and on the outer peripheral edge of the airbag module, outside of the leg piece  42 . 
   The horn switch gear  70  is provided so as to be fitted on the guide shaft  50 . As can be seen in  FIG. 17 , the lower end of the guide shaft  50  is screwed into the nut  17  of each portion  214   b  of the bracket  214  to be fixed to the portion  214   b . The guide shaft  50  extends below the retainer  16  and the bracket  214 , away from a vehicle occupant. The guide shaft  50  has a flange  51  serving as a stopper. The flange  51  is positioned above an extension of the airbag retainer, towards a vehicle occupant. 
   In the airbag system  200  shown in  FIG. 18 , the guide shaft  50  is inserted from the bracket  214  side so as to make assembling of the components easier. In this embodiment, the flange  51  is positioned below the portion  214   b  of the bracket  214  and the guide shaft  50  extends above an extension  16  of the airbag retainer  10 . 
   As can be seen in  FIG. 19 , the horn switch  70  of the airbag system  200  is mounted under the main plate  11  of the retainer  15 . The horn switch  70  can be mounted to the airbag module below the main surface  41  of the cover  40  and on an inner side of the leg piece  42 . Thus, the horn switch  70  is positioned laterally closer to the inflator  30  than the embodiments shown above. 
   The stud bolt  50  is projected downwardly from the bottom of the retainer main plate  11 . A nut  251 ′ is positioned on the stud bolt  50  to secure the stud bolt  50  to the horn gear  70 . The horn switch  70  is mounted around the stud bolt  50  and is supported from a portion  214   b  of the bracket  214 . The stud bolt  50  is position below the airbag module. The stud bolt  50  is also positioned to extend below the bracket  214 . 
   The priority applications, Japanese Application 2003-187870 (filed Jun. 30, 2003) and Japanese Application 2004-002217 (filed Jan. 7, 2004) are incorporated herein by reference in their entireties. 
   Given the disclosure of the present invention, one versed in the art would appreciate that there may be other embodiments and modifications within the scope and spirit of the invention. Accordingly, all modifications attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is to be defined as set forth in the following claims.