STEERING WHEEL CORE MATERIAL

Abstract: A steering wheel core material of continuous filament FRP for vehicles is made up of a ring, a boss positioned at the center of the ring, and spokes connecting the boss to the ring, said boss being integrally joined to a boss metal fitting (10). It is formed by winding resin-impregnated continuous filaments (17) in layer around the ring and spoke-forming mold and the body of the boss metal fitting, with an elastic material (16) interposed between the body of the boss metal fitting (10) and the FRP (17).

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a steering wheel which is produced from FRP (fiber reinforced plastics). Description of the Prior Art: For the purpose of weight reduction and strengthening, a new type of automobile steering wheel has recently been developed. It is made up of a core reinforced with continuous filament rovings, a cushioning material covering the core, and a surface layer of leather or the like. It is now in practical use. The core is made of continuous filaments such as glass fiber and carbon fiber impregnated with epoxy resin, polyester resin, or the like. To make the core, the resin-impregnated continuous filaments are wound in layers around a jig and the resin is cured by heating. This FRP core is light in weight and very strong. It is used to produce a steering wheel which is very little subject to the vibrations of the automobile during driving. This type of steering wheel core has a structure as shown in Fig. 11. The steering wheel core 1 of FRP is made up of a ring 2, a boss 3 positioned at the center of the ring 2, and spokes 4 which connect the ring 2 to the boss 3. The boss 3 is provided with a metal fitting 9 to which the steering shaft is connected. The metal fitting is integrally jointed to the FRP core when the continuous filaments are laminated. The steering wheel core 1 is produced by using an apparatus shown in Figs. 12 and 13. The apparatus 5 is made up of a main shaft 6, a lower mold 7 fixed to the shaft 6, and an upper mold 8 which mates with the lower mold 7. The upper and lower molds 7 and 8 have grooves 7a and 8a, respectively, formed on their circumference. When the upper and lower molds 7 and 8 are closed, these grooves 7a and 8a form a groove having a semi circular cross-section in which the ring 2 is made. The core 1 is produced in the following manner. At first, a boss metal fitting 9 is attached to the shaft 6, and the upper mold 8 is mated to the lower mold 7. Resin-impregnated continuous filaments are wound around the groove by turning the shaft 6 so that the ring 2 is formed, and they are bent at the notches 8b formed on the circumference of the upper mold 8 and led to the boss metal fitting 9 and wound around its body 9a so that the boss 3 and spokes 4 are formed. After winding, the assembly is heated to cure the resin. Thus there is obtained the steering wheel core 1 of continuous filament roving FRP. A disadvantage of the steering wheel core 1 produced as mentioned above is that it has such a light weight and a small inertia moment that it is poor in performance to prevent the steering wheel from vibrating in the circumferential direction (flutter characteristics). One way to improve the flutter characteristics is to increase the weight of the ring 2 by attaching weights to the ring 2 or by increasing the amount of continuous filaments wound in the ring 2. However, attaching weights leads to low productivity and high production cost because it takes more time and labour to place weights at accurate positions on the apparatus 5 for the well-balanced steering wheel. On the other hand, increasing the amount of continuous filaments results in an extremely thick ring 2 because they have a low specific gravity. A steering wheel with a thick ring is awkward to handle. Unfortunately, improving the flutter characteristics by increasing the weight of the ring aggravates the shake characteristics because it increases the total weight of the steering wheel. FR-A-2,418,487 (Corresponding to the preamable of claim 1) discloses a method of manufacturing a fiber reinforced plastics steering wheel as described above. FR-A-970,444 discloses a steering wheel including cooperating metal hub parts having vibration damping pads provided therebetween, which parts are fitted between the steering wheel and steering column. SUMMARY OF THE INVENTION The present invention was completed to eliminate the above-mentioned disadvantages involved in the conventional steering wheel core material. It is an object of the present invention to provide an FRP steering wheel which is improved in flutter characteristics without the addition of weight to the ring which adversely affects the shake characteristics. The invention provides a laminated FRP steering wheel formed by winding resin-impregnated continuous filaments in a layer around a ring- and spoke-forming mould and the body of a boss metal fitting positioned at the center of the ring, characterized in that the body of the boss metal fitting is made up of an inner member for connection to a steering shaft and an outer member surrounding the inner member with an elastic material interposed therebetween, the resin-impregnated continuous filaments being wound to engage the outer peripheral surface of the outer member and in that said inner member has a radially outwardly projecting flange at one end thereof, and said outer member has a radially outwardly projecting flange at its end remote from said one end of the inner member with said resin-impregnated continuous filaments engaged with the outer peripheral surface of the outer member being contained between said flanges. In some embodiments, the inner member may have at least one flat portion on its outer periphery, the outer member having at least one flat portion on its inner periphery which is opposed to said flat portion on the inner member with said elastic material interposed therebetween. In other embodiments, one of said inner member and said outer member may have at least one projecting portion, with the other of said inner and outer members having at least one recessed portion which loosely mates with said projecting portion, said elastic material being interposed therebetween. Said inner member may have a radially outwardly projecting flange at one end thereof, with said outer member having a radially outwardly projecting flange at its end remote from said one end of the inner member, said resin-impregnated continuous filaments wound engaged with the outer peripheral surface of the outer member being contained between said flanges. The elastic material may have a torsional rigidity of 30 to 300 N.m/rad. The elastic material, boss metal fitting, and resin-impregnated continuous filaments are integrally joined together in the production of the steering wheel. The process comprises attaching the elastic material to the boss metal fitting, mounting the boss metal fitting on the molding apparatus, and winding the resin-impregnated continuous filaments. Thus the process is simple and can be run efficiently at low cost. The elastic material is not specifically limited; it includes, for example, rubber, synthetic resin, air, and oil. According to the present invention, it is possible to easily improve the flutter characteristics, while keeping good shake characteristics, simply by interposing an elastic material between the FRP and the boss metal fitting. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a longitudinal sectional view of a boss metal fitting used in a steering wheel according to a first example of the invention; Fig. 2 is a disassembled perspective view of the boss metal fitting of Fig. 1; Figs. 3 and 4 are transverse sectional views showing the steering wheel and the elastic material in a first example of the invention; Fig. 5 is a graph showing the relation between the torque and torsion angle observed in the operation of a steering wheel produced from the steering wheel in the first example; Fig. 6 is a longitudinal sectional view of the boss metal fitting used in the steering wheel in the second example of the invention; Fig. 7 is a disassembly perspective view of the boss metal fitting as shown in Fig. 6; Fig. 8 is a transverse sectional view of the boss metal fitting as shown in Fig. 6; Fig. 9 is a graph showing the relation between the torque and torsion angle observed in the operation of a steering wheel produced from the steering wheel in the second example; Fig. 10 is a transverse sectional view of the boss metal fitting used in the steering wheel in the third example of the invention; Fig. 11 is a perspective view showing an example of a known FRP steering wheel; Fig. 12 is a disassembly perspective view showing an example of the apparatus for producing the steering wheel; and Fig. 13 is a front view showing the apparatus as shown in Fig. 12 which is in operation. DETAILED DESCRIPTION OF THE INVENTION The examples in the invention will be explained with reference to the drawings. The first example is explained with reference to Figs. 1 and 2. The steering wheel core in this example has a boss metal fitting 28 made up of an inner member 29 and a surrounding outer member 30. The inner member 29 has a flange 29a at its lower end and also has at its center a serrated through hole 31 into which the steering shaft (not shown) is fitted. In addition, on the periphery of the body 29b of the inner member are formed a pair of parallel flat surfaces 29c. On the other hand, the outer member 30 has a flange 30a at its upper end. On the internal periphery of the body 30b are formed a pair of parallel flat surfaces 30c. The inner member loosely fits into the outer member so that the body 29b of the inner member 29 loosely fits into the outer member so that the body 29b of the inner member 29 turns to come into contact with the flat surface 30c of the outer member 30. When the inner member 29 is fitted into the outer member 30, a gap is formed between them. This gap is filled with an elastic material 32 such as rubber, synthetic resin, air, and oil to complete the boss metal fitting 28. Three kinds of elastic materials each having a torsional rigidity of 75 (sample 1), 100 (sample 2), and 250 (sample 3) N.m/rad were selected to produce three kinds of boss metal fittings. The boss metal fitting 28 was mounted on the above-mentioned manufacturing apparatus 5, and the steering wheel core as shown in Fig. 1, was formed by winding the continuous filaments FRP 33. The steering wheel core was fabricated into a steering wheel. The thus produced steering wheel was examined for flutter level. The flutter level was obtained by measuring the acceleration applied in the circumferential direction of the steering wheel (S) when a car with an unbalanced tyre is run. The amount of unbalance is 40 g. The peak acceleration is regarded as the flutter level of the steering wheel. The smaller the flutter level, the better the flutter characteristics. The results are shown in the following table. For comparison, the same experiment was carried out with a steering wheel in which the boss metal fitting is filled with an elastic material having a torsional rigidity of 750 N.m/rad (in Comparative Example 1) and a steel-cored steering wheel (in Comparative Example 2). Measurements of Flutter Level Flutter Level (G) Sample 1 0.6 Sample 2 0.75 Sample 3 1.0 Comparative Example 1 1.2 Comparative Example 2 0.6 It is noted from the table above that the steering wheel provided with the boss metal fitting of Sample 1 has almost the same flutter level as the conventional steel-cored steering wheel. It is also noted that Sample 2 and Sample 3 also have good flutter characteristics, although they are not so good as Sample 1. The improvement in flutter characteristics achieved in the present invention may be elucidated as follows: while the force applied to the steering wheel has a low torque, the elastic material 32 remains almost undeformed as shown in Fig. 3 and absorbs vibrations in the circumferential direction of the steering wheel. This leads to the improved flutter characteristics. As the torque applied to the steering wheel increases, the elastic material 32 deforms and the edges of the flat surfaces 29c of the inner member 29 come into contact with the flat surface 30c of the outer member 30, as shown in Fig. 4, so that the torque applied to the steering wheel is efficiently transmitted to the steering wheel (not shown). Fig. 5 shows the relationship between the torque applied to the steering wheel and the torsional angle. While a torque is applied to the steering wheel but the inner member 29 is not yet in contact with the outer member 30, the torque is transmitted to the steering shaft through the elastic material 32. Therefore, in the case of a steering wheel provided with an elastic material having a comparatively small torsional rigidity (samples 1 to 3), the torsional angle increases more than the torque increases. This characteristic can be controlled by changing the gap between the inner member 29 and the outer member 30, or the density and pressure of the elastic material. The second example will be explained with reference to Figs. 6 - 9. The boss metal fitting 34 is made up of an inner member 35 and a cylindrical outer member 36 as shown in Fig. 6. The inner member 35 has a flange 35a formed at its lower end and also has at its center a serrated through hole 37 into which the steering shaft (not shown) is fitted. In addition, on the periphery of the inner member 35 are formed recessed parts 35b. On the other hand, the cylindrical outer member 36 has a flange 36a formed at its upper end. On the internal periphery of the body 36 are formed projecting parts 36b which loosely fit into the recessed parts 35b, so that they come into contact with each other when the outer member is turned. When the inner member 35 is fitted into the outer member 36, a gap is formed between them. The gap is filled with an elastic material 38 such as rubber, synthetic resin, air, and oil to complete the boss metal fitting 34. The FRP 39 of continuous filaments is joined to the boss metal fitting 34 to complete the steering wheel core. The thus produced steering wheel core is processed into a steering wheel which has characteristics as shown in Figs. 8 and 9. While the force applied to the steering wheel has a low torque, the elastic material 38 remains almost undeformed as shown in Fig. 8 and absorbs vibrations in the circumferential direction of the steering wheel . This leads to the improved flutter characteristics. As the torque applied to the steering wheel increases, the elastic material 38 deforms and the projecting part 36b of the outer member 36 comes into contact with the recessed parts 35b of the inner member 35, so that the torque applied to the steering wheel is efficiently transmitted to the steering wheel (not shown). Fig. 9 shows the relationship between the torque applied to the steering wheel and the torsional angle. While a low torque is applied to the steering wheel, it is transmitted to the steering shaft through the elastic material 38. As the result, the torsional angle increases more than the torque increases, and the torsional rigidity decreases, as indicated by the section I. This characteristic can be controlled by changing the gap between the inner member 35 and the outer member 36, or the density and pressure of the elastic material 38. After the torque has reached a certain level, the elastic material 38 deforms, permitting the inner member 35 to come into contact with the outer member 36. In this stage, the torque is transmitted from the steering wheel directly to the steering shaft. Thus the torsional angle increases less than the torque increases and the torsional rigidity increases. In the third example as shown in Fig. 10, the boss metal fitting 40 is made up of an inner member 41 and an outer member 42, with the gap (in the radial direction) between them entirely filled with an elastic material 43. The projecting part 42b formed on the outer member 42 faces the recessed part 41b of the inner member 41. They have such dimensions that they come into contact with each other when the outer member turns. By joining the inner member 41 and the outer member 42 together through the elastic material 43, it is possible to improve the flutter characteristics.

Claims: A laminated FRP steering wheel (1) formed by winding resin-impregnated continuous filaments in a layer around a ring- and spoke-forming mold (5) and the body of a boss metal fitting (28) positioned at the center of the ring, the body of the boss metal fitting (28) being for connection to a steering shaft the resin-impregnated continuous filaments being wound to engage the outer peripheral surface of the body of the boss metal fitting (28) said body of the boss metal fitting (28) having a radially outwardly projecting flange (29a) at one end thereof, and a radially outwardly projecting flange (30a) at its end remote from said one end, with said resin-impregnated continuous filaments engaged with the outer peripheral surface of the body of the boss metal fitting (28) being contained between said flanges (29a, 30a), characterized in that said body of the boss metal fitting (28) consists of an inner member (29) and an outer member (30) surrounding the inner member (29) with an elastic material (32) interposed therebetween, and that each of said inner and outer members has one of said flanges (29a, 30a). A steering wheel according to Claim 1 wherein the inner member (29) has at least one flat portion (29c) on its outer periphery and the outer member (30) has at least one flat portion (30a) on its inner periphery which is opposed to said flat portion on the inner member (29) with said elastic material (32) interposed therebetween. A steering wheel according to Claim 1 wherein one of said inner members (35) and said outer member (36) has at least one projecting portion (36b) and the other of said inner and outer members has at least one recessed portion (35b) which loosely mated with said projecting portion (36b), with elastic material (32) interposed therebetween. A steering wheel as claimed in any of Claims 1 to 3 wherein the elastic material has a torsional rigidity of 30 to 300 N.m/rad.

Inventors: KOIKE, SHINJI, KONDO, KATSUMI, TERADA, MASAKI, TSUCHIYA, TASUHIRO, YAMAZAWA, YASUSHI
Applicants: TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1987
Main classification: B62D1
IPC codes: B62D1