Steering wheel

Abstract: There is disclosed an automotive steering wheel W1 including a heavy air bag system 30. This air bag system 30 is held by a horn-switching mechanism 40. Although the air bag system 30 is heavy, the operator has a good feel for the operation of the horn-switching mechanism 40. This horn-switching mechanism 40 comprises a stationary member 41, a movable member 48, a switch main body 50, coil springs 55, and a jawed bolt 56. The switch main body 50 comprises a stationary contact 52 mounted on the stationary member 41 and a movable contact 54 mounted on the movable member 48. The coil springs 55 bias the movable member 48 upward. The jawed bolt 56 permits the movable member 48 to be moved toward the stationary member 41 and limits the distance of the movable member 48 from the stationary member 41. At least one of the coil springs 55 is located at a height substantially equal to the height of the resultant center of gravity G of all components biased upward by all the coil springs 55.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering wheel mounted in a vehicle and, particularly, to a steering wheel equipped with an air bag system. More particularly, the invention relates to a steering wheel including an air bag system supported by a horn-switching mechanism. 2. Description of the Related Art A known steering wheel of this kind is described, for example, in document JP-U-143734/1990 and shown in Fig. 1. This steering wheel, generally indicated by WO, has a wheel main body 1. An air bag system 4 is mounted at the top of the central portion of the wheel main body 1. Each horn-switching mechanism 10 is located between the wheel main body 1 and the air bag system 4. The wheel main body 1 includes part of the steering wheel WO and excludes the air bag system 4 and the horn-switching mechanisms 10. The air bag system 4 is composed of an air bag 5, an inflator 6, a pad 7, and a bag holder 8. The air bag 5 is folded so that it is capable of inflating. The inflator 6 supplies a gas used to inflate the air bag 5. The pad 7 covers the folded air bag 5. The bag holder 8 holds the air bag 5, the inflator 6, and the pad 7. The horn-switching mechanisms 10 are located under the bag holder 8 at opposite sides, respectively, of the holder 8. Fig. 1 is a cross-sectional view of the steering wheel WO, taken in the longitudinal direction and in the front and rear direction. Each horn-switching mechanism 10 comprises a stationary member 11, a movable member 12, a coil spring 16, and a jawed bolt 19. The stationary member 11 consists of a metal plate and is connected with a metal core 2 forming the steering wheel main body 1. Fixed contacts 14 are mounted to the front and rear ends, respectively, of the stationary member 11. The movable member 12 is made of a metal plate and located above the stationary member 11. Movable contacts 15 are positioned at the front and rear ends, respectively, of the movable member 12. The coil spring 16 is positioned between the movable member 12 and the stationary member 11 and forms a means for biasing the movable member 12 upward. The jawed bolt 19 forms a means for limiting the distance by which the movable member 12 is spaced from the stationary member 11. The jawed bolt 19 is screwed to the metal core 2 from above the movable member 12. A lead wire (not shown) is connected with the movable member 12 of the horn-switching mechanisms 10 so that the movable member 12 is electrically connected with the positive side of a horn-activating circuit. The stationary member 11 is electrically connected with the negative side of the horn-activating circuit via the metal core 2. The fixed contact 14 and the movable contact 15 together form a switch main body 13. Insulating spacers 17, 18 and rubber rings 20 electrically insulate the movable member 12 from the stationary member 11 when they are in contact with both the coil springs 16 and the jawed bolts 19. The movable member 12 has a mounting member (not shown) attached thereto permitting the bag holder 8 to be secured with bolts. In the prior art steering wheel WO, the horn-switching mechanisms 10 are located on opposite sides of, and under, the heavy air bag system 4. That is, the air bag system 4 of the prior art steering wheel WO is swingably supported by the coil springs 16 of the horn-switching mechanisms 10 that are at opposite sides of, and under, the air bag system 4. When the coil springs 16, used to bias the horn-switching mechanisms 10 of the prior art steering wheel WO, have a low spring constant, the horn-switching mechanisms 10 may be inadvertently activated because the heavy air bag system 4 can easily tilt or swing horizontally due to vibrations of the vehicle. More specifically, in the prior art steering wheel WO, the air bag system 4 and the movable member 12 are held upwardly by all the coil springs 16. In the illustrated example, four coil springs are used. The position of the resultant center of gravity G of these supported members (the air bag system 4 and the movable member 12) is higher than the coil springs 16 by as much as 30 mm. With the forward coil spring 16(F) placed at the center of a rotation moment, a rotation moment, P x L, acts on the rear coil spring 16(B), where P is the force of a rearward swinging movement at the side of the center of gravity G and L is the distance between the center of gravity G and the coil spring 16(F) in the direction of height. The rotation moment, P x L, compresses the coil spring 16(B) and brings the rear movable contact 15(B) into contact with the fixed contact 14(B). As a result, the switch main body 13(B) is electrically activated. Accordingly, the coil springs 16 biasing the horn-switching mechanisms 10 have high spring constants. However, when coil springs having high spring constants are used, as in the coil springs 16, a larger load must be applied to manually activate the horn-switching mechanisms 10. This deteriorates the feel for the horn-switching mechanisms experienced by the driver when the horn-switching mechanisms 10 are operated. A steering wheel comprising the features summarized in the pre-characterizing clause of claim 1 is known from document GB-A-2 270 657. The stationary member of the horn-switching mechanism of this known steering wheel is formed by a portion of the steering wheel main body. This results in that it is quite complicated to assemble the known steering wheel. SUMMARY OF THE INVENTION It is an object of the present invention to further develop the steering wheel comprising the features of the pre-characterizing clause of claim 1 such that it can easily be assembled. This object is achieved by the steering wheel according to claim 1. According to the invention, the stationary member comprises a support plate which is arranged and designed as is defined in the characterizing clause of claim 1. Moreover, according to the invention, the air bag system and the horn-switching mechanism including the support plate are assembled into a sub-assembly which is mounted to the steering wheel main body. As a consequence of the design according to the invention, the sub-assembly can easily be mounted to the steering wheel main body, and assembling the steering wheel is simplified. Moreover, in the steering wheel according to the invention, at least one biasing means is arranged substantially at an equal level in the direction of movement of the movable member as the resultant center of gravity of all the components collectively which are biased towards the upper side of the biasing means. Therefore, if one biasing means is not disposed around the height of the resultant center of gravity but is located at the center of the rotation moment, the rotation moment, P x L, acts on the biasing means located near the height of the resultant center of gravity, where P is the force of a horizontal swinging movement acting on the resultant center of gravity G of the air bag system and L is the distance between the center of gravity G and the biasing means located near the height of the center of gravity. This rotation moment, P x L, barely compresses the biasing means located near the height of the center of gravity because L is close to zero. Therefore, inadvertent activation of the switch main bodies to operate the horn can be prevented. In addition, the load needed to manually operate the horn-switching mechanisms is reduced because biasing means with lower spring constants may be used or the number of the biasing means may be reduced. Accordingly, in the steering wheel in accordance with the invention, if a heavy air bag system is mounted to the horn-switching mechanism, the load applied to manually operate the horn-switching mechanism may be reduced. This can improve the feel experienced by the operator when the horn-switching mechanisms are operated. The center of the biasing means is located near the height of the center of gravity of the air bag system. The above-described distance L can become close to zero by placing this center of the biasing means at the height of the center of gravity. Consequently, the load required to operate the horn-switching mechanisms may be reduced further by using biasing means having lower spring constants. When all the biasing means are located near the height of the center of gravity of the air bag system, all the rotation moments produced about the biasing means can be reduced to nearly zero. In consequence, the load required to manually operate the horn-switching mechanisms may be decreased further by using biasing means of lower spring constants. This may contribute to further improvement of the feel experienced by the operation when operating the horn-switching mechanisms. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view of the prior art steering wheel; Fig. 2 is a cross-sectional view of a steering wheel in accordance with the invention, taken along line II-II of Fig. 4; Fig. 3 is a cross-sectional view of the steering wheel shown in Fig. 2, taken along line III-III of Fig. 4; Fig. 4 is a plan view of the steering wheel shown in Fig. 2; Fig. 5 is a plan view of a support plate forming part of a stationary member used in the steering wheel shown in Fig. 4; Fig. 6 is an exploded perspective view of a switch subassembly used in the steering wheel shown in Fig. 4; and Fig. 7 is a partial cutaway of the front elevation of the switch subassembly shown in Fig. 6. DESCRIPTION OF THE PREFERRED EMBODIMENTS While the preferred embodiments of the invention are hereafter described with reference to the accompanying drawings, it should be understood that the invention is not limited thereto but rather various changes and modifications are possible within the scope of the invention that is delineated by the accompanying claims. Referring to Figs. 2-4, there is shown a steering wheel embodying the concept of the present invention. This steering wheel, generally indicated by Wl, comprises an annular portion R, a boss portion B located in the center of the annular portion R, and three spoke portions S connecting the annular portion R with the boss portion B. In terms of Components, the steering wheel W 1 is composed of a steering wheel main body 21, an air bag system 30, and a horn-switching mechanism 40 comprising a plurality of individual switch main bodies 50. The air bag system 30 is located on top of the boss portion B. The horn-switching mechanism 40 is connected to the main body 21 of the steering wheel and holds the air bag system 30. The steering wheel main body 21 is part of the steering wheel W1 excluding the air bag system 30 and the horn-switching mechanism 40. The main body 21 of the steering wheel has a metal core 22 that connects the annular Portion R, the boss portion B, and the spoke portions S. The metal core 22 has a core portion 23 located at the annular portion and core portions 25 that are located at the spoke portions and at the side of the core portion 23. These core portions 23 and 25 are coated with a coating layer 26 of a synthetic resin. A metal core 24 at the location of the boss portion B is composed of a boss 24a and a coating portion 24b. The boss 24a is made of steel and connected to the steering shaft (not shown). The coating portion 24b is made of an aluminum alloy or the like and surrounds the boss 24a. The coating portion 24b is formed integrally with the core portions 23 and 25. A rear core portion 25(B) at the spoke locations bifurcates and connects to the coating portion 24b of the metal core 24 of the boss portion. The main body 21 of the steering wheel has a lower cover 27 that covers the bottom of the boss portion B. The lower cover 27 is screwed to the metal core 22. The air bag system 30 comprises an air bag 31, an inflator 33, a pad 34, and a bag holder 35. The air bag 31 is folded so as to be inflatable. The inflator 33 supplies a gas used for inflation into the air bag 31. The pad 34 covers the folded air bag 31. The bag holder 35 holds the air bag 31, the inflator 33, and the pad 34. The inflator 33 comprises a substantially cylindrical body 33a and a flange 33c. A gas discharge port 33b is formed at the top of the body 33a. The flange 33c protrudes from the outer surface of the body 33a. The pad 34 is made of a synthetic resin and comprises a top wall portion 34a and a side wall portion 34b. When the air bag 31 inflates, the top wall portion 34a breaks at a given location. The side wall portion 34b is substantially hexagonally shaped at its perimeter and extends downwardly from around the outer surface of the top wall portion 34a. The side wall portion 34b has an engaging groove 34c formed at a given position in the inner surface. The bag holder 35 has side wall portions 37 provided with engaging claws 37a (described later). These claws 37a engage the fringes of the engaging groove 34c. Ribs (bearing no reference numeral) are formed on the bottom surface of the top wall portion 34a. These ribs bear against mounting portions 39 (described later) of the bag holder 35. The bag holder 35 holds the air bag 31 and the inflator 33 by using an annular retainer 32, which has a plurality of bolts (not shown) extending downward. These bolts pass through the air bag 31, the bag holder 35, and the flange 33c of the inflator 33. Nuts are screwed to the bolts so that the air bag 31 and the inflator 33 are held by the bag holder 35. The side wall portion 34b is mounted with rivets so that the pad 34 is held by the bag holder 35. The bag holder 35 is a made of metal plate and comprises a lateral plate portion 36, side wall portions 37, and three interconnecting plate portions 38. The lateral plate portion 36 has a centrally provided insertion hole 36a into which the body 33a of the inflator can be inserted from below. The side wall portions 37 extend from the front fringe and from both sides of the rear fringe, respectively, of the lateral plate portion 36 and take a V-shaped form in cross section. The three interconnecting plate portions 38 extend upward from right and left side fringes and from the rear fringe, respectively. Each side wall portion 37 is provided with an engaging claw 37a interlocked in the groove 34c located in the pad side wall portion 34b. Each side wall portion 37 is formed with mounting holes (not shown) used to mount the pad side wall portion 34b with rivets. The mounting portions 39 extending outwardly and laterally are formed at the top ends of the interconnecting plate portions 38. Nuts 39b are welded to the mounting portions 39, which are provided with mounting holes 39a. At the positions of the mounting portions 39, the air bag system 30 is connected to the horn-switching mechanism 40. These mounting portions 39 form parts of a movable member 48 of the horn-switching mechanism 40. Lead wires (not shown) are connected with the bag holder 35 to electrically connect the holder with the positive side of a horn-activating circuit. The horn-switching mechanism 40, a switch subassembly H of which is shown in exploded form in Fig. 6, comprises a stationary member 41, the movable member 48, switch main bodies 50, coil springs 55, and jawed bolts 56. The stationary member 41 is connected to the metal core portions 25 in the spoke portions. The movable member 48 is located above the stationary member 41. Each switch main body 50 comprises a stationary contact member 51 and a movable contact member 53 which include a stationary contact 52 and a movable contact 54, respectively. One of the coil springs 55 is disposed between the stationary member 41 and the movable member 48 and biases the movable member 48 upwardly. Each jawed bolt 56 allows the movable member 48 to move toward the stationary member 41 and acts as a means for limiting the distance of the movable member 48 from the stationary member 41. In the illustrated embodiment, the stationary member 41 comprises a support plate 42 and support grommets 47. The support plate 42 is mounted to a left spoke portion metal core portion 25(L) and a right spoke portion metal core portion 25(R) with bolts 58. The support plate 42 is made of a metal plate and comprises a connecting rod portion 43, shown in Fig. 5, and support base portions 44, as shown in Figs. 2, 3, and 5. The connecting rod portion 43 has a U-shaped form in a plane view (see Fig. 5). The support base portions 44 extend upwardly from the left fringe, the right fringe, and the rear fringe, respectively, of the connecting rod portion 43 and extend outwardly from their top ends. Each support base portion 44 comprises a vertical plate portion 44a and a base body portion 44b. The vertical plate portions 44a extend upwardly from the connecting rod portion 43. The base body portions 44b extend outwardly from the top ends of the vertical plate portion 44a. Each base body portion 44b has centrally provided mounting hole 44c. This hole 44c consists principally of a circular hole with the inclines of right-angled triangles attached to its opposite fringes that are in symmetrical positions. Each base body portion 44b has small circular engaging holes 44d on opposite sides of the mounting hole 44c. Connecting portions 45 descend obliquely from around the vertical plate portions 44a of the right and left support base portions 44. Nuts 46 are firmly secured to the connecting portions 45 to mount the support slate 42 to the left spoke portion metal core portion 25(L) and the right spoke portion metal core portion 25(R) with the bolts 58. As shown in Figs. 6 and 7, the support grommet 47 is substantially cylindrical in shape and made of an insulating synthetic resin such as polyacetal. An engaging plate portion 47a conforming to the shape of the opening in the mounting hole 44c in each support base portion 44 is mounted to the bottom of the support grommet 47. This grommet 47 has a recess 47c corresponding to the arc-shaped portion of the mounting hole 44c, the recess 47c being located over the engaging plate portion 47a. A protrusion 47b is formed on the top surface of the engaging plate portion 47a and is inserted in the engaging hole 44d. A pair of engaging step portions 47d and a pair of recesses 47e are formed at symmetrical positions in the outer surface of the support grommet 47. The stationary contact members 51 (described further below) is engaged at the positions of the engaging step portions 47d. Each of a plurality of insulating spacers 49 has engaging claws 49b which are placed in the recesses 47e, respectively, so as to be movable downwardly. The stationary contact member 51 is made of spring steel and includes the stationary contact 52, engaging portions 51a, and spring portions 51c. The stationary contact 52 is preferably annular in shape. The engaging portions 51a extend downwardly from symmetrical positions on the outer fringe of the stationary contact 52. Each spring portion 51c extends downward from the bottom end of the corresponding engaging portion 51a and is curved. The engaging portions 51a have inwardly protruding engaging claws 51b that engage the engaging step portions 47d, respectively, of the support grommet 47. When the support grommet 47 is mounted to the support base portion 44 with a bayonet-type fitting, the spring portions 51c of the stationary contact member 51 push against the fringes of the mounting hole 44c on the top surface of the base body portion 44b of the support base portion 44. When the support grommet 47 is mounted with the bayonet fitting, the engaging plate portions 47a are inserted into the mounting hole 44c in the support base portion 44 from above. Then, the grommet 47 is rotated through 90°. The protrusions 47b on the engaging plate portions 47a are inserted into the engaging holes 44d in the support base portion 44. When the engaging claws 51b of the stationary contact member 51 are engaged with the engaging step portions 47d of the support grommet 47, the stationary contact 52 rests on the top end surface of the grommet 47. When the support plate 42 is mounted to the left spoke portion metal core portion 25(L) and the right spoke portion metal core portion 25(R) with the bolts 58, the stationary contact 52 of the stationary contact member 51 is electrically connected with the negative side of the horn-activating circuit through the spring portion 51c of the stationary contact member 51, the support plate 42, and the metal core portions 25(R), 25(L). In the illustrated embodiment, the movable member 48 comprises the mounting portions 39 of the bag holder 35 and the insulating spacers 49. These insulating spacers 49 are substantially cylindrical in shape and made of a synthetic resin, having insulation qualities, such as polyacetal. As shown in Figs. 6 and 7, each insulating spacer 49 comprises a spring seat 49a, two engaging claws 49b, and three engaging step portions 49c. The spring seat 49a protrudes like a jaw from the top outer surface. The engaging claws 49b protrude downward from the bottom of the spring seat 49a. The engaging step portions 49c are formed on the inner surfaces of the spring seat 49a. The engaging claws 49b are placed in the recesses 47e formed in the support grommet 47, allowed to move downwardly in the recesses 47e toward, and engage with the annular stationary contact 52 of the stationary contact member 51. The engaging step portions 49c inhibit movement of the movable contact member 53. The movable contact member 53 is made of spring steel and comprises an annular base portion 53a, three engaging portions 53b, and movable contacts 54. The engaging portions 53b extend downward from the outer surface of the base portion 53a. The movable contacts 54 extend outwardly from the bottom ends of the engaging portions 53b. Engaging claws 53c, for engaging the engaging step portions 49c of the insulating spacer 49, protrude outwardly from the engaging portions 53b. When the engaging claws 53c of the movable contact member 53 are anchored to the engaging step portions 49c of the insulating spacers 49, the movable contacts 54 are placed on the bottom surfaces of the insulating spacers 49. In the illustrated embodiment, the support grommet 47, the insulating spacer 49, and the coil spring 55, together with the stationary contact 52 and the movable contact 54 forming the switch main body 50, are pre-assembled into the switch subassembly H shown in Fig. 7. This subassembly H is fabricated in a manner described below. First, the stationary contact member 51 is mounted to the support grommet 47, and the movable contact member 53 is mounted to the insulating spacer 49. Then, the lower end of the coil spring 55 is made to bear against the engaging plate portions 47a of the grommet 47. The top end of the coil spring 55 is abutted against the spring seat 49a of the insulating spacer 49. The engaging claws 49b of the spacer 49 are then inserted into the recesses 47e in the grommet 47 and are engaged to the stationary contact 52 of the stationary contact member 51. Thus, the switch subassembly H is completed. Since the subassembly H is easy to handle, the horn-switching mechanisms 40 can be easily assembled. In this embodiment, the switch subassemblies H are assembled to form the horn-switching mechanism 40 which in turn support the air bag system 30. First, the engaging plate portions 47a of the support grommet 47 of each switch subassembly H are inserted into the mounting holes 44c in the base body portions 44b of the support base portions 44 of the support plate 42 and mounted with a bayonet fitting. The mounting portions 39 of the bag holder 35 of the air bag system 30 assembled previously are placed above each switch subassembly H. The jawed bolts 56 are inserted into the switch subassemblies H from below and screwed to the nuts 39c of the mounting portions 39, thus forming the horn-switching mechanism 40. This horn-switching mechanism 40 supports the air bag system 30. The horn-switching mechanism 40 and the air bag system 30 are assembled into a subassembly which can be easily mounted to the main body 21 of the steering wheel. The air bag system 30 is assembled in the manner described below. The retainer 32 is placed in the air bag 31. The air bag 31 is then folded. Bolts (not shown), extending from the retainer, are passed through the bag holder 35 and through the flange 33c of the inflator and secured there with nuts. The engaging claws 37a of the side wall portions 37 of the bag holder are engaged in the engaging grooves 34c in the pad side wall portions 34b. The pad side wall portions 34b are riveted to the side wall portions 37 of the bag holder, thus completing the air bag system 30. After supporting the air bag system 30 on the horn-switching mechanisms 40, the connecting portions 45 of the support plate 42 of the horn-switching mechanism 40 are made to bear against the left spoke portion metal core portion 25(L) and the right spoke portion metal core portion 25(R). From the rear side of the metal core portion 25(L) and 25(R), the bolts 58 are screwed to the nuts 46 of the connecting portions 45. Thus, the horn-switching mechanism 40 can be connected to the main body 21 of the steering wheel. Consequently, the steering wheel W1 may be assembled. The boss 24a of the boss portion metal core 24 of the steering wheel main body 21 has been previously connected to the steering shaft of the vehicle. When the jawed bolt 56 is screwed to the nut 39b, the movable contact 53 of each switch subassembly H is pushed by an enlarged portion 56a of the bolt 56, so that the base portion 53a of the movable contact member 53 is pressed against the fringe of the mounting hole 39a of the mounting portion 39 of the bag holder 35. As a result, the movable contact 53 of each switch subassembly H is electrically connected with the positive side of the horn-activating circuit through the lead wires (not shown). When the support plate 42 is secured to the metal core portions 25(L) and 25(R), of the spoke portions with the bolts 58, the stationary contact 52 of each switch subassembly H is electrically connected with the negative side of the horn-activating circuit through the spring portions 51c of the stationary contact member 51, the support plate 42 and the metal core portions 25(L) and 25(R). In the present embodiment, when the horn-switching mechanism 40 is connected with the main body 21 of the steering wheel in this manner, the outwardly extending front end portions of the base body portions 44b of the support base portions 44 of the support plate 42 forming the stationary member 41 bear against the coating layer 26 on the metal core portions 25 of the spoke portions of the wheel main body. Thus, the base body portions are supported. In the illustrated embodiment, the base body portions 44b of the support base portions 44 of the support plate 42 and the mounting portions 39 of the bag holder 35 are placed close to the coating layer 26 of each spoke portion S. Consequently, the coil springs 55 of each switch subassembly H are so positioned that the vertical center of each coil spring 55 is coincident with the height of the resultant center of gravity G of the components biased upwardly by all the coil springs 55. The components biased upwardly by all the coil springs 55 are the air bag system 30 (air bag 31, retainer 32, inflator 33, pad 34, bag holder 35, lead wires, etc.), the movable member 48 (mounting portions 39, insulating spacer 49, and movable contact member 53), and the jawed bolts 56. Therefore, in the steering wheel W 1 of the present embodiment, if one coil spring 55(B) is placed at the center of a rotation moment as shown in Fig. 2, a rotation moment, P x L, acts on the coil spring 55(A), where P is the force of a horizontal swinging movement acting at the center of gravity G (such as of the air bag system 30) and L is the distance between the height of the center of gravity G and the height of the coil spring 55(A) located at the center of gravity G. Since the distance L is nearly zero, the rotation moment, P x L, barely compresses the coil spring 55(A) For this reason, even if the coil spring 55(A) does not have a high spring constant, the switch main body 50 is prevented from being inadvertently activated. In addition, coil springs with lower spring constants can be used at the other coil springs 55(B) and 55(C), because the rotation moment due to swinging movement of the air bag system 30 is small. Accordingly, in the case of the steering wheel W1 of the present embodiment, if the heavy air bag system 30 is held by the horn-switching mechanism 40, a coil spring of a low spring constant can be used as the coil spring 55. This can improve the driver's feel for the horn-switching mechanism 40 when operated. In this embodiment, if the air bag system 30 is as heavy as the prior art air bag system, the load that needs to be applied to manually operate the horn may be reduced to two thirds of the load required in the prior art bag systems. Usually, the horn is operated by depressing the top wall portion 34a of the pad 34 of the air bag system 30. At this time, the coil spring 55 of each switch subassembly H is compressed, bringing the movable contact 54 of the movable contact member 53 of the switch main body 50 into contact with the stationary contact 52 of the stationary contact member 51, thus activating the horn. In the embodiment described above, the vertical center of all the coil springs 55 of the horn-switching mechanism 40 is made coincident with the height of the center of gravity G of the components biased upwardly by all the coil springs 55. The height of each switch subassembly H may be shifted so that the center of gravity G lies within the limits defined by the upper and lower ends of each coil springs 55. This structure yields less advantages than the above-described embodiment but the load that must be applied to operate the horn-switching mechanism 40 can be made smaller than in conventional systems. Furthermore, the center of gravity G may be placed between the upper and lower ends of at least one coil spring 55; the center of gravity G is not placed between the upper and lower ends of any other coil spring 55. In this way, the produced advantages are less conspicuous than in the above-described embodiment, but the load that must be applied to operate the horn-switching mechanism 40 can be smaller than before. If at least one coil spring 55 is placed at a height substantially equal to the height of the center of gravity G (in other words, at least one coil spring 55 is placed within the steering wheel, and the distance of the height of the center of gravity G separated from the upper or lower end of the coil spring 55 is within approximately half of the vertical length of the spring 55), the aforementioned rotation moment, P x L, can be reduced. Consequently, the load that must be applied to operate the horn-switching mechanism can be made smaller than heretofore. Of course, if the above-described range is exceeded, unwanted operation of the horn due to swinging movement of the air bag system cannot be prevented unless springs of higher spring constants are used. Hence, less advantages will be produced. In the above-described embodiments, the coil springs 55 are used as examples of the biasing means. Leaf springs may be employed instead.

Claims: A steering wheel (W1), including a steering wheel main body (21) having a central boss portion (B), a horn-switching mechanism (40), and an air bag system (30) held by said horn-switching mechanism (40), wherein said steering wheel has an upper side where said air bag system (30) is located and a lower side where said central boss portion (B) is located, said air bag system (30) comprising a folded air bag (31), an inflator (33) for supplying a gas into said air bag (31), a pad (34) covering the folded air bag (31), and a bag holder (35) holding said air bag (31), said inflator (33) and said pad (34), said horn-switching mechanism (40) comprising a stationary member (41), a movable member (48) positioned at a distance from said stationary member (41), a plurality of switch main bodies (50), a plurality of biasing means (55), and a plurality of limiting members (56), wherein said movable member (48) comprises a plurality of mounting portions (39) formed on said bag holder (35) and extending from lateral sides of said air bag system (30), each of said switch main bodies (50) comprising a stationary contact (52) mounted on said stationary member (41) and a movable contact (54) mounted on one of said mounting portions (39), said plurality of biasing means (55) being mounted between said stationary member (41) and one of said mounting portions (39) and biasing said movable member (48) towards said upper side, said plurality of limiting members (56) interconnecting, said stationary member (41) with said mounting portions (39) of said movable member (48) such that said movable member (48) can move towards said stationary member (41) and such that the distance said movable member (48) can move away from said stationary member (41) is limited, wherein at least one of said biasing means (55) is arranged substantially at an equal height, that is at substantially an equal level in the direction of movement of said movable member (48), as the resultant center of gravity (G) of all the components collectively which are biased upwards towards said upper side by said biasing means (55), characterized in that said stationary member (41) comprises a support plate (42) mounted to said steering wheel main body (21), in that said support plate (42) comprises a plurality of base body portions (44b) arranged below said mounting portions (39), said base body portions (44b) supporting said biasing means (55) and said limiting members (56) at their lower ends, in that said support plate (42) further comprises a plurality of connecting portions (45) for mounting said support plate (42) to said steering wheel main body (21), said connecting portions (45) being arranged below said base body portions (44b), and in that said air bag system (40) and said horn-switching mechanism (40) including said support plate (42) are assembled into a subassembly which is mounted to the steering wheel main body (21). The steering wheel according to claim 1, wherein the center of at least one of said biasing means (55) is arranged substantially at an equal level in the direction of movement of said movable member (48) as the resultant center of gravity (G) of all the components collectively which are biased towards said upper side by said biasing means (55). The steering wheel according to claim 1, wherein each of said biasing means (55) is arranged substantially at an equal level in the direction of movement of said movable member (48) as the resultant center of gravity (G) of all the components collectively which are biased towards said upper side by said biasing means (55). The steering wheel according to one of claims 1 to 3, wherein said connecting portions (45) are arranged closer to said central boss portion (B) than said biasing means (55). The steering wheel according to one of claims 1 to 4, wherein each of said base body portions (44b) abuts on and is supported by a spoke portion (S) of said steering wheel main body (21). The steering wheel according to one of claims 1 to 5, wherein said pad (34) comprises a top wall portion (34a) having a portion that brakes when the inflator (33) supplies the gas into the air bag (31) and a side wall portion (34b) extending downwardly from the periphery of said top wall portion (34a), and wherein each of said mounting portions (39) is disposed below said top wall portion (34a). The steering wheel according to one of claims 1 to 6, wherein one of said stationary contacts (52) is mounted on each of said base body portions (44b) and wherein one of said movable contacts (54) is mounted on each of said mounting portions (39). The steering wheel according to one of claims 1 to 7, wherein said support plate (42) comprises a connecting rod portion (43) interconnecting said plurality of base body portions (44b). The steering wheel according to one of claims 1 to 8, wherein said bag holder (35) comprises a lateral plate portion (36) with an insertion hole (36a) into which said inflator (33) is inserted and interconnecting plate portions (38) extending upwardly from the edges of said lateral plate portion (36), and wherein said mounting portions (39) are formed at the upper ends of said interconnecting plate portions (38).

Inventors: FUJITA YOSHIYUKI, FUJITA, YOSHIYUKI
Applicants: TOYODA GOSEI KK, TOYODA GOSEI CO., LTD.
Application year: 1997
Main classification: B62D1
IPC codes: B60R21, B60R16, B60Q5