Steering wheel

Abstract: First and second spoke cores (33a,33b) are arranged linearly through the boss plate (31) so that most of the lower ends of the first and second spoke cores (33a,33b) are located above a middle line (m). A third spoke core (33c) is arranged in a direction perpendicular to the first and second spoke cores (33a,33b). A pair of tine portions (34) are provided in the third spoke core (33c) so as to be connected to the first and second spoke cores (33a,33b), thereby the tine portions (34) and the first and second spoke cores (33a,33b) intersect each other obliquely. In the tine portions (34), through holes (35) and reception seats (36) are provided so that the air bag module is fixed with screws and the through holes (35) while the air bag module abuts on the reception seats (36).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering wheel and particularly to a steering wheel provided with an air bag apparatus. The present application is based on Japanese Patent Application No. 2000-308860, which is incorporated herein by reference. 2. Description of Related Art Conventionally, a steering wheel of this type is formed by a core member, as a base material, covered with resin or the like. As the core member, for example, one shown in Fig. 5 is used. This core member 100 is constituted by a boss plate 101 connected to a steering shaft not shown, an annular rim 102 with the boss plate 101 as a center, and a plurality of spokes 103 connecting the boss plate 101 and the rim 102. In the case where the spokes 103 are provided by three, for example, these spokes may be provided in the following mode. That is, of these three spokes 103, a first spoke 103a and a second spoke 103b are disposed to be arranged substantially linearly through the boss plate 101 when those spokes are viewed from the front of the steering wheel. On the other hand, the third spoke 103c is provided in such a position that, with the boss plate 101 as a center of rotation, the first and second spokes 103a and 103b are respectively rotated by about 90 degrees counterclockwise and clockwise respectively. The end portion of the third spoke 103c at the boss plate 101 side is made to branch off into two tines the ends of which are connected to the first and second spokes 103a and 103b respectively. Further, an air bag module 104 provided with a not-shown inflator, an air bag, or the like, is disposed above the boss plate 101 of the core member 100 configured thus. Here, in a steering shaft in a neutral state where rotating operation is not carried out, a middle line m which passes a center axis line of the steering shaft so as to divide the steering wheel into two, upper and lower portions is defined as follows. The air bag module 104 in the steering wheel is fixed by means of screws and through holes 105. The through holes 105 are formed in the first and second spokes 103a and 103b and are substantially on the above-mentioned middle line m . When an impact exceeding a predetermined range acts on the vehicle, the air bag accommodated in the air bag module 104 is developed to receive a crew. In the conventional steering wheel, however, as shown Figs. 6A and 6B, a large load in the vehicle forward direction as indicated by an arrow in the drawing may act on the lower end portion of the rim 102 of the core member 100 due to a change in posture of the crew or the like. If such a large load acts on the rim 102 of the steering wheel, the rim 102 may be deformed. However, the air bag module 104 is attached to the first and second spokes 103a and 103b and on the middle line m of the steering wheel as described above. Here, for example, consideration is made about a case where a large load acts on the lower side of the steering wheel in the neutral state in which the steering wheel is not rotated. In such a case, because the first and second spokes 103a and 103b of the core member 100 are large in rigidity, the steering wheel is deformed and bent with respect to the axial line of first and second spokes 103a and 103b. Hence, there might occur a situation that the air bag module 104 was not displaced in accordance with the deformation of the rim 102 and the lower end of air bag module 104 floated up from the steering wheel. This situation resulted in displacement of the direction of developing the air bag with respect to the advancing direction of the crew and there was a fear that the impact absorption effect was lowered. JP 11198818 refers to a stress absorbing structure for a steering wheel. The steering wheel main body is provided with a ring part and a pad and four strokes. A connection part is formed at the boss and is constituted by a material whose main component is an iron. The end edge part of the connection part are buried in the core metal of the spoke. A bent part is provided on the way of the connection part. When a prescribed load acts upon the steering wheel, the connection part is deformed at the bent part and a stress can be absorbed surely. EP 0 488 618 A1 discloses a steering wheel structure comprising three spoke cores connected with a core of the wheel ring. The center spoke core as well as the side cores are formed with holes through which the airbag module is mounted thereon. US 6,109,646 discloses a steering wheel comprising three spokes connecting a ring with a pad. The spoke cores extend between the ring core and the center of the core. Two spoke cores are coupled to the third spoke core (on the driver side). In an accommodating space defined below a pad an airbag device is mounted. The airbag device is mounted by means of a bag holder on three leaves located on the same plane. Two of the leaves are formed at a tine portion of the central spoke, respectively, wherein the tine portion is formed by bifurcating the third spoke at the connecting side to the other two spoke portions. The third leaf branches from the central spokes, i.e. the first and second spoke core and is disposed in a central position. SUMMARY OF THE INVENTION The present invention has been achieved by paying the attention to such a problem in the background art. It is an object of the present invention to provide a steering wheel in which the development direction of the air bag is changed in accordance with deformation of the steering wheel. This object is solved by a steering wheel comprising the features of claim 1. A preferred embodiment is defined by claim 2. In the invention, even if the steering wheel is deformed due to large load acting on the steering wheel, the air bag module is easily displaced in accordance with the deformation of the steering wheel. Further, in accordance with the displacement of the air bag module, the direction of developing the air bag received in the air bag module is changed. In the invention, lower ends of the first and second spoke cores are located substantially above a middle line which passes on a center axis of the steering shaft so as to divide the steering wheel into the upper and lower portions, in the neutral state of the steering wheel. By the above structure, the difference in rigidity between respective portions of the rim portion becomes small, so that the difference in displacement between rotation positions of the steering wheel can be reduced. In the invention, a branch portion bifurcated to provide two tines is formed at an end of the third spoke core in a manner so that forward ends of said two tines are connected respectively to said first and second spoke cores and so that, when said steering wheel is viewed from the front side thereof, said two tines and said first and second spoke cores intersect each other obliquely in plane view. By the above structure, the difference in rigidity between respective portions of the rim portion can be reduced, and the quantity of material for the third spoke core can be reduced so that the weight of the steering wheel can be reduced. In the invention, the air bag module is fixed to the branch portion in the third spoke core. The air bag module can be displaced surely in accordance with the deformation of the steering wheel. In the invention, in an air bag module fixing portion in the spoke cores, a reception seat on which the air bag module abuts partly may be provided. In the above structure, when the air bag module is attached to the spokes, the air bag module abuts on the reception seat so that the air bag module can be attached stably. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of a steering wheel according to an embodiment of the present invention; Fig. 2 is a sectional view taken on the line II-II in Fig. 1; Fig. 3 is a sectional view taken on the line III-III in Fig. 1; Fig. 4 is a plan view of a core member adopted in the steering wheel; Fig. 5 is a plan view of a core member adopted in a related art steering wheel; and Figs. 6A and 6B are sectional views taken on the line VI-VI in Fig. 5, Fig. 6A shows a non-deformed state, Fig. 6B shows a deformed state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereunder, an embodiment of the steering wheel according to the present invention will be described by referring to Figs. 1 to 4. As shown in Fig. 1, the steering wheel is constituted by an annular rim 11, a pad 12 disposed at the center of the rim 11, and three spokes 13a, 13b and 13c extending from the rim 11 to the pad 12. The rim 11 is connected to the forward end of a steering shaft 15 through spoke cores 33a to 33c in the spokes 13a to 13c which will be described later and through a not-shown gear mechanism. Thus, rotating operation of the steering wheel is transmitted to the steering shaft 15. Further, this steering wheel is provided with an air bag module 20 at the portion of the pad 12. As shown in Fig. 2 which is a sectional structure of the steering wheel taken on the line II-II in Fig. 1, the air bag module 20 is disposed in a reception recess 12a on a back side of the pad 12. The air bag module 20 is constituted by an air bag 21 folded and received like a bag, an inflator 22 for supplying the air bag 21 with a gas for expansion, and a bag holder 23 for holding and fixing the air bag 21 and the inflator 23. The bag holder 23 is fixed to the pad 12 by screws. The air bag module 20 is provided as described above so that the pad 12 serves also as a cover to cover the air bag module 20. A tear line 12b, for example, H shaped, is formed by recess lines in the center of the back of the pad 12 so that the tear line 12b is pressed and broken when the air bag 21 is expanded and developed. Further, as shown in Fig. 3 which is a sectional structure of the steering wheel taken on the line III-III in Fig. 1, in the bag holder 23 of the air bag module 20, the flanges of the bag holder 23 are partially expanded and bent downward to form fittings 24. The fittings 24 are fixed by screws to a core member 30 which will be described later. In the steering wheel configured thus, such a core member 30 as shown in Fig. 4 is used. The core member 30 is provided with a boss plate 31 as a boss portion connected to the forward end of the steering shaft 15, an annular rim core 32 corresponding to the rim 11 of the steering wheel, and first to three spoke cores 33a to 33c corresponding to the three spokes 13a to 13c. The rim core 32 is disposed with the boss plate 31 as a center, that is, to surround the boss plate 31. Further, of the three spokes, the first and second spoke cores 33a and 33b are formed linearly through the boss plate 31 so as to continue uninterruptedly with each other when viewed from the front side of the steering wheel. The opposite ends of the thus formed first and second spoke cores 33a and 33b are connected to the rim core 32. On the other hand, an end of the third spoke core 33c is connected to the rim core 32 in the direction substantially perpendicular to the extending direction of the first and second spoke cores 33a and 33b. The end of the third spoke core 33c at the rim core 32 side has a substantially Y-shape and the other end of third spoke core 33c at the boss plate 31 side is made to branch off into two tine portions 34. The two tine portions 34 made to branch off thus are bent at their longitudinal centers and connected, at their forward ends, to the first and second spoke cores 33a and 33b respectively so that the tine portions 34 and the spoke cores 33a and 33b intersect each other obliquely when the steering wheel is viewed from the front side. In this embodiment, as shown in Figs. 3 and 4, a pair of through holes 35 as a fixing portion of the air bag module 20 are formed in the two tine portions 34 of the third spoke core 33c so as to be substantially opposite to each other. Further, reception seats 36 are provided under the through holes 35, so that the fittings 24 of the bag holder 23 abut on the seats 36 respectively. The air bag module 20 is fixed to the core member 30 by screws in the through holes 35. That is, the air bag module 20 is configured so that the air bag module 20 is fixed to the steering wheel in a position apart from the center line CL extending in longitudinal direction of the first and second spoke cores 33a and 33b. Specifically, in this embodiment, the fittings 24 of the air bag module 20 and the through holes 35 and the seats 36 formed on the third spoke core 33c are provided at a position under a center line CL of the first and second spoke cores 33a and 33b when the steering wheel is set in the neutral state where the steering wheel is not subjected to rotating operation position. In the steering wheel according to this embodiment, for example, in the neutral state in which the steering wheel is not subjected to rotating operation, if a large load acts on a lower side of the steering wheel so that the lower side portion of the rim core 32 is deformed toward the boss plate 31 side, the third spoke core 33c is also deformed in accordance with the deformation of the rim core 32. Hence, following the deformation of the third spoke core 33c, the air bag module 20 is also displaced. In accordance with the displacement of the air bag module 20, the direction of developing the air bag 21 in the air bag module 20 is also changed. As a result, generation of displacement between the direction of developing the air bag 21 and the direction of advancing the vehicle crew to the air bag 21 is lowered, and the impact absorption effect is improved. Further, in this embodiment, the first and second spoke cores 33a and 33b are arranged such that, in the neutral state where the steering wheel is not subjected to rotating operation, most of the lower ends 331 of the first and second spoke cores 33a and 33b are located above a middle line m which passes through the center of the steering wheel and divides the steering wheel into two, upper and lower, portions. Further, the forward ends of the two tine portions 34 of the third spoke core 33c are connected obliquely to the first and second spoke cores 33a and 33b, as stated above. Hence, the difference in rigidity among positions in the rim 11 between the spokes 13a, 13b and 13c becomes small. Accordingly, the difference in quantity of displacement between rotation positions of the steering wheel can be made small. According to the steering wheel of this embodiment, therefore, the following effects can be obtained. (a) The air bag module 20 is fixed in a position apart from the center line CL of the first and second spoke cores 33a and 33b. As a result, generation of displacement between the direction of developing the air bag 21 and the direction of advancing the vehicle crew to the air bag 21 is lowered, and the impact absorption effect is improved. (b) The first and second spoke cores 33a and 33b are arranged such that most of the lower ends of the first and second spoke cores 33a and 33b are located above the middle line m . Hence, the difference in rigidity between portions of the rim 11 becomes small, and the difference in quantity of displacement between rotation positions of the steering wheel can be made small. (c) The forward ends of the two tine portions 34 of the third spoke core 33c are connected obliquely to the first and second spoke cores 33a and 33b, as stated above. Hence, the difference in rigidity between portions of the rim 11 can be made smaller, and while the necessary rigidity is kept surely, the quantity of the material to be used can be reduced to thereby reduce the weight of the steering wheel. (d) The attachment position of the air bag module 20 is provided at the two tine portions 34 of the third spoke core 33c. Accordingly, the air bag module 20 can be displaced surely in accordance with the displacement of the third spoke core 33c. (e) The reception seats 36 are provided in the third spoke core 33c. Hence, when the air bag module 20 is attached to the third spoke core 33c, the fittings 24 of the bag holder 23 abut on the reception seats 36 so that the air bag module 20 becomes stable. (Modification) The embodiment of the present invention may be changed as follows. In the embodiment described above, the two tine portions 34 of the third spoke core 33c are bent at their substantially longitudinal centers, and are connected to the first and second spoke cores 33a and 33b in this bent condition. On the other hand, in the modification, the tine portions 34 may be formed into straight or curved line shapes and connected to the first and second spoke cores 33a and 33b. In the embodiment described above, the reception seats 36 are provided on the tine portions 34 of the third spoke core 33c. In the modification, no reception seats 36 may be provided. In the embodiment described above, the air bag module 20 is fixed to the tine portions 34 of the third spoke core 33c. In the modification, for example, fittings are provided at a base portion of the third spoke core 33c and through holes are formed in the fittings so that the air bag module 20 is fixed by means of screws and the through holes. In the embodiment described above, the tine portions 34 of the third spoke core 33c are connected to the first and second spoke cores 33a and 33b so that the first and second spoke cores 33a and 33b and the two tine portions 34 intersect each other obliquely when the steering wheel is viewed from the front side. In the modification, the tine portions 34 of the third spoke core 33c may be connected to the first and second spoke cores 33a and 33b so that the tine portions 34 and the first and second spoke cores 33a and 33b intersect perpendicularly to each other when the steering wheel is viewed from the front side. In the embodiment described above, most part of the lower ends of the first and second spoke cores 33a and 33b are made to be located above the middle line m . In the modification, the first and second spoke cores 33a and 33b are arranged so that the center line CL of first and second spoke cores 33a and 33b approaches the middle line m . As described above in detail, according to the present invention, generation of displacement between the direction of developing the air bag and the direction of advancing the vehicle crew to the air bag is lowered, and the impact absorption effect is improved. Further, the difference in quantity of displacement between rotation positions of the steering wheel can be made small. Further, while the necessary rigidity is kept surely, the weight of the steering wheel can be reduced. Further, the air bag module can be displaced surely in accordance with the displacement of the third spoke core. Further, the air bag module can be attached to the third spoke core stably.

Claims: A steering wheel comprising: a boss portion (12) connectable to a steering shaft; a rim portion (11) provided to surround said boss portion; a spoke portion (13a, 13b, 13c) connecting said boss portion (12) and said rim portion (11) to each other, said spoke portion (13a, 13b, 13c) including a first spoke core (33a), a second spoke core (33b) and a third spoke core (33c), said first and second spoke cores (33a, 33b) being arranged substantially linearly through said boss portion (12) so as to continue uninterruptedly with each other when said steering wheel is viewed from a front side thereof, said third spoke core (33c) being arranged so as to connect said first and second spoke cores (33a, 33b) to said rim portion (11) in a direction substantially perpendicular to an extending direction of said first and second spoke cores (33a, 33b); and an air bag module (20) mounted on said steering wheel; wherein a fixing portion 35 of said air bag module to said steering wheel is provided at a position apart from a center line (CL) extending in the longitudinal direction of said first and second spoke cores; wherein the respective inner ends of said first and second spoke cores (33b, 33c) are located substantially above a middle line (m) which intersects a center axis of said steering shaft to divide said steering wheel into the upper and lower portions when said steering wheel is set in a neutral state in which the steering wheel is not rotated; wherein a branch portion bifurcated to provide two tines (34) is formed at an end of said third spoke core (33c) in a manner so that forward ends of said two tines (34) are connected respectively to said first and second spoke cores (33a, 33b) and so that, when said steering wheel is viewed from the front side thereof, said two tines (34) and said first and second spoke cores (33a, 33b) intersect each other obliquely in plane view; characterised by fixing said air bag module (20) only to the two tines (34) of said third spoke core (33c). A steering wheel according to Claim 1, further comprising, a reception seat (36) provided in at least one of said spoke cores (33a, 33b, 33c), wherein said air bag module (20) abuts partly with said reception seat.

Inventors: SHIGA ICHIZO, SONOBE AKIHIKO, SHIGA, ICHIZO, SONOBE, AKIHIKO, Shiga, Ichizo, c/o Toyoda Gosei Co., Ltd., Sonobe, Akihiko, c/o Toyoda Gosei Co., Ltd.
Applicants: TOYODA GOSEI KK, TOYODA GOSEI CO., LTD.
Application year: 2001
Main classification: B62D1
IPC codes: B62D1, B60R21