Steering wheel with air bag device

Abstract: A steering wheel main body comprises cover members for covering a metal ring core (5) and metal spoke cores (6A,6B,6C), respectively, and a pad, situated substantially in a central upper portion of the steering wheel which is formed integrally with such cover members. A boss (8) is connected through a connecting part (21) with the metal spoke cores (6B,6C), which are arranged on opposite sides of the steering wheel and formed into a united body. The boss (8) is situated below the metal ring core (5) and the metal spoke cores (6B,6C) are connected to the boss (8) and to the other metal spoke core (6A) through sub-connecting parts (22) to thereby form an opening (23), and an air bag device is mounted through the opening. This permits completion of the assembling operation of the steering wheel with ease. After completion of the assembling of the steering wheel, that completed assembly is mounted onto the top end portion of a steering shaft.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering wheel with an air bag device, and especially to a steering wheel in which assembly efficiency can be improved together with a more stable air bag device. 2. Description of the Related Art A steering wheel includes an annular ring, a pad disposed in the central portion of the ring, and two or more spokes respectively extending from the ring. A metal core is embedded in the ring and core metals are also respectively embedded in the spokes. In such cases, the metal cores, in both the ring and spokes, are respectively covered with polyurethane foam or the like cover members. Also, below the pad, the leading end portions of the spokes metal cores are connected to a boss plate, hereafter referenced as a boss. This boss is normally mounted on the leading end portion of a steering shaft in such a manner that it is fastened with a nut. In a steering wheel structured in this manner, not only the metal spoke cores but also the boss formed integrally with a steering wheel main body are mounted on the steering shaft by fastening them with a nut, an air bag device and the like are mounted on the metal spoke cores and the boss, and the pad is then mounted on the air bag device. On the other hand, in recent years, there has been proposed a steering wheel in which the boundary lines between the cover members and pad are eliminated by forming them integrally with each other (for example, Japanese Utility Model Publication No. Hei. 2-133955). According to this steering wheel, the integral formation of the cover members and pad can improve the design of the steering wheel. As described above, in the steering wheel in which the cover members and pad are formed integrally with each other, the design thereof can be improved and, at the same time, the outer appearance of the steering wheel can be diversified. However, when the steering wheel is assembled, there arises the following problem. That is, in the above-mentioned steering wheel, since the air bag device cannot be mounted from above or from the bottom of the cover members for covering the metal ring core and metal spoke cores, it is necessary to have previously separated the boss from the metal spoke cores. Therefore, in the above-mentioned conventional technique, the steering wheel comprises a steering wheel main body including the spoke metal cores, the boss, and the air bag device, and these three parts must be assembled to one another. For this reason, the assembling operation is quite complicated, and operationability can be adversely affected. Also, since the boss must be connected to the spoke metal cores with high reliability, there is required a further complicated operation. Generally a bag holder, which holds and fixes an air bag and its inflator, is structured such that the peripheral side wall portion thereof is fixed to a rib extending downwardly from the pad with a rivet or the like, thereby stabilizing the operation of the air bag device when the air bag is inflated. According to the above-mentioned steering wheel in which the cover members and pad are formed integrally with each other, when mounting the air bag device onto the steering wheel, it is difficult to fix the periphery of the bag holder to the rib of the pad with a rivet. For this reason, the periphery of the bag holder is not fixed by any means, or, as disclosed in the above mentioned utility model publication, the upper portion of the periphery of the bag holder is simply contacted with the rib. In the inflated state of the air bag of the above-mentioned steering wheel, there is a fear that, when it receives a stress from the air bag, the bag holder can be deformed easily in an outward direction thereof. Therefore, when the air bag is in an inflated state, there is a fear that the air bag can escape in the lateral direction thereof through a clearance generated due to the deformed bag holder. That is, there arises a possibility that the operation stability of the air bag device can be impaired. US-5,243,877 which is the basis of the preamble of enclosed claim 1, discloses a steering wheel with an armature consisting of a rim supported by two arms, which from the viewpoint of the driver angle downwardly towards the center of the rim to a hub. The arms are broadly joined about the hub on a plane parallel to the plane of the rim. The plane of the hub provides support for an airbag container. The arms are preferably stepped to provide top plane surfaces where the arms flow into the rim. Furthermore, there is provided a flat bar connecting the arms at their lower joints with the rim. The surface of the hub is provided with an upwardly rising retaining member and two lugs adapted to receive an airbag container. US-5,470,099 discloses a steering wheel with a rim section, a center section and a spoke section joining said rim and center sections. The steering wheel is provided with a continuous integral molded material on at least the driver's side and has a mounting side opposite to the driver's side for mounting airbag module in the center section of the mounting side. It is an object of the invention to provide a steering wheel, in which cover members respectively for covering the metal rim core and the metal spoke cores are formed integrally with a pad and which includes an airbag device, wherein the assembly operation and the operation stability of the airbag device is improved. A solution on this object has been achieved by a steering wheel according to appended claim 1. A big opening for inserting the airbag device is defined by the sub-connecting part, which connects the first and second part core metals, the boss and the connecting parts. The airbag device can be easily mounted. Furthermore, by the cylindrical portion of the bag holder, provided at a peripheral portion of the bag holder and extending upwardly with an upper end portion of said peripheral portion being disposed on an inside of said sub-connecting part, said sub-connecting part prevents said airbag holder from being deformed upon inflation of said airbag. By this means a stable operation of the airbag device is ensured. Claims 2 to 5 are directed towards advantageous further details of the structure of the steering wheel. Claim 6 is directed towards an advantageous fixing of the bag holder to the steering wheel, whereby the bag holder may be simply mounted from below after being inserted into the opening as mentioned above. When a given deceleration is detected, the airbag is inflated and the pad is spread out. In this case, as the airbag is inflated, the bag holder receives a given stress from the expanding airbag. However, according to the present invention, due to the fact that the core metal connecting parts (the sub-connecting part or the like) for connecting together the metal spoke cores, are provided, and also that the bag holder can be supported by the core metal connecting parts when the airbag is inflated, the deformation of the bag holder can be minimized to thereby prevent the airbag from escaping there from in a lateral direction. This assures a stabilized spreading out of the bag as well as the desired inflation of the airbag. Other objects, features, and characteristics of the invention will become apparent upon consideration of the following description and the appended claims with reference to the accompany drawings, all of which form a part of this specification. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 is a perspective view of a metal core structure of a steering wheel according to an embodiment of the invention; Fig. 2 is a sectional view taken along the line B-B shown in Fig. 3; Fig. 3 is a rear view of a steering wheel; Fig. 4 is a plane section view of an adapter employed in the steering wheel; Fig. 5 is a sectional view of a steering wheel main body showing the air bag device mounting operation; Fig. 6 is a sectional view of the steering wheel and a steering shaft showing the mounting operation for connecting the steering wheel onto the steering shaft; Fig. 7 is a sectional view taken along the line A-A shown in Fig. 3; Fig. 8 is a sectional view of a steering wheel, showing the operation to inflate an air bag; and Fig. 9 is a perspective view of a metal core structure employed in another embodiment of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Now, description will be given below in detail of an embodiment of a steering wheel according to the present invention with reference to the accompanying drawings. As shown in these drawings, the steering wheel W comprises a steering wheel main body 1 which includes an annular ring 2, a pad 3 disposed in the central portion of the ring 2, and three spokes 4 respectively extending from the ring 2. Also, ring 2 comprises a metal ring core 5 formed of a steel pipe or the like and a cover member 7a for covering the metal ring core 5. The spoke parts 4 respectively comprises metal spoke cores 6A, 6B, 6C, each of which is formed of a light die-cast metal such as aluminum alloy or the like. A cover member 7b covers the three metal spoke cores 6A-6C. The cover members 7a, 7b and pad 3 are formed of a soft synthetic resin material, such as polyurethane foam, in a united or integral body. The steering wheel main body 1 is assembled and fixed to a boss 8. The structure for assembling the steering wheel main body 1 will be discussed later in detail. A storage recess 11 is formed below the pad 3, which is enclosed by the cover member 7b. In the storage recess 11 are disposed a membrane switch (not shown) and an air bag device 13. The membrane switch includes two upper and lower thin plates which form part of a conventional horn switch circuit (not shown). Accordingly, if the pad 3 is pressed, the two thin plates are brought into contact with each other, so that a horn can be actuated. The air bag device 13 includes a bag-like air bag 14 that is stored in a folded manner, an inflator 15 for supplying gas for inflation to the air bag 14, and a bag holder 16 for holding and fixing the air bag 14 and inflator 15. The bag holder 16, as shown in Fig. 2, is fixed by a screw 17 to the metal spoke core 6A. The method for fixing the bag holder 16 to the metal spoke core will be described later. Also, the bag holder 16 according to the present embodiment is mainly comprised of an annular plate 16a having an opening formed in the central portion thereof for storing the inflator 15, and a cylindrical portion 16b formed integrally with the outer peripheral edge of the plate 16a and extending upwardly therefrom. Next, description will be given below of the details of the structure of the steering wheel W. At first, description will be given of a structure for mounting or assembling the boss 8. As shown in Fig. 6, in the top end portion of a steering shaft 30, there are formed two serrated portions 31 and, in the central or intermediate portion of the serrated portions 31, in the vertical direction thereof, there is formed an annular groove 32. In each of the two serrated portions 31 of the steering shaft 30, there are formed a given number of teeth 31a, generally about 30 pieces. Also, in the central portion of the boss 8, there is formed a through hole 9 and an adapter 10, formed of steel, is inserted into and welded to the inner periphery of the through hole 9. This adapter 10 is structured such that the lower portion thereof is formed in a substantially cylindrical shape and the adaptor 10 has a yoke portion 10a at the upper portion thereof so as to be formed in a substantially C shape when it is viewed from top. A bolt hole 18, having a female screw is formed adjacent the top end portion of the yoke portion 10a. Further, on the inner peripheral surface of the adapter 10, there are formed two serrated portions 19 which correspond to the two serrated portions 31 of the steering shaft 30, respectively. The adapter 10 is fitted with the top end portion of the steering shaft 30 while the serrated portions 19 mesh with the serrated portion 31. Also, a tapered bolt 33 is fastened to the bolt hole 18 in such a manner that part of the tapered bolt 33 is inserted into the annular groove 32. Due to this, not only the adapter 10 but also the boss 8 are strongly fixed to the top end of steering shaft 30. On the other hand, in the present embodiment, the boss 8 is formed integrally with the steering wheel main body 1. That is, as shown in Fig. 1, boss 8 is connected through a connecting part 21 to the two left and right metal spoke cores 6B and 6C. However, boss 8 is situated below both of the metal ring core 5 and the metal spoke cores 6B and 6C. Also, the metal spoke cores 6B and 6C are connected through a sub-connecting part 22 to the remaining (the driver's side) spoke part core metal 6A, respectively. Due to this structure, the respective metal spoke cores 6A - 6C, metal ring core 5 and boss 8 are connected together strongly and, at the same time, the boss 8, connecting part 21 and sub-connecting part 22 cooperate in forming a relatively large opening 23 on the driver's seat side of boss 8. Also, the metal spoke cores 6B and 6C are connected to each other by a support bar 24, which assures the stability of the air bag 14 when it is inflated. Incidentally, the reference numeral 40 designates bag holder fixing protrusions in which threaded holes 41 are formed for fixing the bag holder 16 by bolts. Further, in the present embodiment, a lower cover (not shown) formed of resin is arranged in such a manner that it encloses the lower side of the steering wheel main body 1. Next, description will be given of the procedure for mounting the steering wheel W onto the steering shaft 30. At first, as shown in Fig. 5, the membrane switch and air bag device 13 are inserted from the opening 23 defined by the boss 8, connecting part 21 and sub-connecting part 22. Bag holder 16 of the air bag device 13 is fixed to the metal spoke core 6A with a screw 17. In this operation, since the opening 23 is formed comparatively large, the air bag device 13 can be easily inserted through the opening 23 and mounted onto the interior of the steering wheel main body 1. Next, as shown in Fig. 6, the boss 8, adapter 10, together with the steering wheel main body 1 united integrally therewith are inserted onto the top end of the steering shaft 30. At the same time, the serrated portions 31 of the steering shaft 30 are brought into meshed engagement with the serrated portions 19 formed in the adapter 10. Then, the bolt 33 is threadedly engaged into the bolt hole 18 formed in the adapter 10, thereby fixing the boss 8 to the steering shaft 30. Because the steering wheel main body 1, via metal spoke cores 6B and 6C, is connected to the boss 8 through the connecting parts 21, by fixing the boss 8 to the steering shaft 30, the steering wheel main body 1 including the air bag device 13 can also be fixed at the same time. As has been described heretofore, according to the present embodiment, as shown in Fig. 1, the metal spoke cores 6B and 6C are integrally connected to the boss 8 through the connecting part 21. Also, the boss 8 is structured such that it is situated below both the metal ring core 5A and metal spoke cores 6A - 6C, while the metal spoke cores 6B and 6C are connected to the boss 8 via connecting parts 21, as well as to the remaining spoke part core metal 6A by use of the sub-connecting parts 22 to thereby form the opening 23, respectively. Hereupon, as shown in Figs. 2 and 7, adjacent to and outside the upper portion of the cylindrical portion 16b of the bag holder 16 according to the present embodiment, there are provided sub-connecting parts 22 and a support bar 24. Next, description will be given below of the operation and effects of a steering wheel W having the above-mentioned structure. Due to this structure, since the air bag device 13 can be inserted through the opening 23, the air bag device 13 can be easily interposed between the pad 3 and boss 8. That is, according to the present embodiment, the air bag device 13 can be moved into position through the opening 23 which has a relatively wide area, the assembling operation of the steering wheel W can be completed. Therefore, in assembling the steering wheel W, the operation efficiency is greatly enhanced. Even when the steering wheel is structured such that it has the opening 23 formed in the above-mentioned manner, not only can the boss 8 can be strongly connected to the two left and right metal spoke cores 6B and 6C through the connecting part 21, but also the respective metal spoke cores 6B and 6C can be strongly connected to the remaining (driver's side) metal spoke core 6A through the sub-connecting part 22. Thanks to this, the metal spoke cores 6A - 6C, metal ring core 5 and boss 8 are strongly connected to one another. Therefore, the steering wheel W can be assembled with sufficient stability as a whole. Further, according to the present embodiment, the two metal spoke cores 6B and 6C, respectively, extend from the two sides of the steering wheel and are connected to the boss 8 by use of the connecting part 21. Due to this, the metal spoke core 6B, 6C, connecting part 21 and boss 8, when they are viewed from top, are situated substantially on the same straight line, which increases the structural strength of the steering wheel. When a given deceleration is detected, gas is generated instantaneously from the inflator 15 and is supplied into the air bag 14. As a result of this, as shown in Fig. 8, the air bag 14 is inflated to thereby spread out the pad 3. At the same time, while the base end portion of the air bag 14 is held by the bag holder 16, the cylindrical portion 16b of the bag holder 16 receives from the air bag 14 an outwardly directed stress when the air bag 14 is inflated. However, according to the present embodiment, there are provided the sub-connecting part 22 and support bar 24 which connect the metal spoke cores 6A, 6B, 6C to one another adjacent to and outside the upper end portion of the cylindrical portion 16b. Due to this, the upper end portion of the cylindrical portion 16b of the bag holder 16 is supported by the respective central portions of the side surfaces of the sub-connecting part 22 and support bar 24, which prevents the cylindrical portion 16b of the bag holder 16 from being deformed any further. Therefore, the deformation of the bag holder 16, and cylindrical portion 16b, can be minimized to thereby eliminate the possibility that the air bag 14 can escape in the lateral direction. This assures the stabilized spreading-out of the air pad 3 as well as the inflation of the air bag 14. As a result of this, the operation stability of the air bag device can be enhanced further. In particular, according to the present embodiment, the sub-connecting part 22 and support bar 24 are situated adjacent to and outside that portion of the bag holder 16 which gives the largest amount of displacement when the air bag 14 is inflated (e.g., the upper end portion of the cylindrical portion 16b). Thanks to this, the deformation of the bag holder 16 can be decreased further, so that the above-mentioned effect can be obtained more positively. The invention is not limited to the above-mentioned embodiment and the following embodiments are also possible. In the above-mentioned embodiment, the invention is embodied as the steering wheel W which includes the three spoke parts 4 and the metal spoke cores 6A - 6C. However, the invention can also be embodied as another type of steering wheel which, for example; as shown in Fig. 9, includes four metal spoke cores 34A, 34B, 34C and 34D. In this embodiment, for example, the boss 8 is connected to left and right metal spoke cores 34C and 34D respectively through connecting parts 35. However, similarly to the previously mentioned embodiment, the boss 8 is situated below the metal ring core 5 as well as the metal spoke cores 34A - 34D. Also, the metal spoke cores 34C and 34D are connected to the remaining (driver's side) metal spoke cores 34A and 34B through sub-connecting parts 36, respectively. Thanks to this, not only the metal spoke cores 34A - 34D, metal ring core 5 and boss 8 are strongly connected together, but also a relatively large opening 37 is created on the driver's side of the boss 8 by the connecting parts 35 and sub-connecting parts 36. As a result of this, there can be provided effects which are equivalent to the above-mentioned embodiment. Furthermore, it is possible to further modify the embodiments of the present invention as follows. The number of the spoke parts (metal spoke cores) is not limited to any special number but it may be 2 or more than 5, provided that the number is two or more. In the illustrated embodiment, the air bag device 13 is fixed to the steering wheel main body 1 by use of the screw 17. Alternatively, however, it is also possible to use other types of fixing means such as a rivet, a clip or the like. In the illustrated embodiment, the boss 8, which is united together with steering wheel main body 1, is fixed to the steering shaft 30 using the adapter 10, and bolt 33. However, the invention is not limited to this arrangement but, similar to a conventional steering wheel, the boss 8 can also be fixed using a nut. In the illustrated embodiment, there are provided the sub-connecting part 22 and support bar 24 which connect the respective metal spoke cores 6A - 6C to one another, and they are disposed in the neighborhood of the cylindrical portion 16b of the bag holder 16. However, it is not always necessary that all of the metal core connecting parts are disposed in this manner. Also, the support bar 24 can be omitted. The cross sectional shape of the sub-connecting part 22 and support bar 24 is not limited to the any specified shapes. However, it is preferable to adopt such a shape that it can support the bag holder 16 (the cylindrical portion 16b) with as large an area as possible. In addition, various other modifications or variations may be made by those of ordinary skill in the art without departing from the scope of this invention which is defined by the appended claims.

Claims: A steering wheel with an air bag device, said steering wheel comprising a boss (8) to be fixed to a steering shaft (30); a ring part core metal (5); at least two first spoke part core metals (6B, 6C; 34C, 34D) which are connected to said ring part core directly and to said boss through respective connecting parts (21;35); an air bag device (13) including an airbag (14), an inflator (15), and an airbag holder (16) for supporting and fixing said airbag and said airbag inflator; a cover member (7a, 7b) for covering said ring part core metal (5), spoke part core metals and a pad part (3) situated substantially in a central upper portion of said ring part and formed integral with said cover member. characterized by at least one second spoke part core metal (6A, 34A, 34B) which is not directly connected to said boss (8); a sub-connecting part (22;36) which connects said first and second spoke part core metals (6A, 6B; 34A-D), so that an opening (23) is being defined by said boss (8), connecting parts (21) and sub-connecting part (22) for said air bag device (13) as to be inserted from said opening; and said bag holder (16) including a cylindrical portion (16b) provided at a peripheral portion thereof and extending upwardly with an upper end portion of said peripheral portion being disposed on an inside of said sub-connecting part (22; 36), whereby said sub-connecting part (22; 36) prevents said bag holder (16) from being deformed upon inflation of said airbag (14). The steering wheel with an air bag device according to claim 1, characterized in that : said two first spoke part core metals (6B, 6C, 34C, 34D), said two connecting parts (21; 35) and said boss (8) are situated on one straight line. The steering wheel with an air bag device according to claim 1 or 2, characterized by a support bar (24; 38) which connects said two first spoke part core metals (6B, 6C; 34C, 34D) with each other directly and is located adjacent to and outside the upper end of the cylindrical portion (16b) of said bag holder (16). The steering wheel with an air bag device according to one of claims 1to 3, characterized in that : said sub-connecting part (22; 36) and support bar (24; 38) are disposed on an outside of a portion of said bag holder (16) which shows a largest displacement amount upon inflation of said air bag (14). The steering wheel with an air bag device according to one of claims 1 to 4, characterized in that : two second spoke part core metals (34A, 34B) are provided, which are connected by said sub-connecting part (36) to said first spoke part core metals and to each other. The steering wheel according to any of claims 1 to 5, wherein said holder (16) is fixed to a spoke part core metal (6A; 34A; 34B)

Inventors: HOSOI AKIO, NAGATA ATSUSHI, SAKANE KATSUNOBU, HOSOI, AKIO, NAGATA, ATSUSHI, SAKANE, KATSUNOBU
Applicants: TOYODA GOSEI KK, TOYODA GOSEI CO., LTD.
Application year: 1996
Main classification: B60R21
IPC codes: B62D1, B60R21