Wheel for an automobile and a manufacturing method therefor

Abstract: A wheel for an automobile and a manufacturing method therefor wherein, in manufacturing a disc material portion (41) from a substantially flat square plate (40), a length of the side of the substantially flat square plate (40) is selected so that, after the subsequently formed disc (10) is pressed into a rim (20), a most recessed portion (12) of a ventilation (11) is located axially outside a center of curvature (24) of a well radius (23) of the rim (20).

Description: The present invention relates to a wheel for a vehicle, such as an automobile, and a manufacturing method therefor. By the invention it is possible to lighten the wheel to a great extent without decreasing its fatigue strength. As illustrated in FIGS. 8 and 9, an automobile wheel includes a disc 1 and a rim 2 connected to each other by spot welding 3. The spot welding 3 necessarily includes a stress concentrated portion 5 (FIG. 10) which tends to weaken the wheel. To compensate, the rim 2 and the disc 1 are engaged with each other axially over a relatively large length m' (FIG. 9). Clearance between the rim and the disc 1 is kept as small as possible because a tight engagement increases the strength of the wheel and decreases automobile vibration. Disc 1 is manufactured, as generally illustrated by two dotted lines in FIG. 3, by die-cutting a substantially square flat plate having a side of length L' along a circle having a diameter D' greater than L', thereby obtaining a disc material portion 4. Disc material portion 4 is then formed into a disc shape to obtain a disc. In this instance, an arcuate portion 4a of the disc material portion 4 is formed into an axial end 4a of the disc flange shown in FIG. 9. Straight portion 4b of the disc material is formed into an arcuate recessed portion (or ventilation) 4b of the disc of FIG. 9. To increase the strength at the weld portion and to suppress radial displacements of the rim wall from a true circle, as described above, a most recessed portion 4c of the ventilation 4b is located axially inside a center of curvature 6 of the well radius between a rim well 8 and a rim side wall 9 so that a disc flange 7 contacts the rim well 8 at all circumferential portions of the disc flange 7. It has been thought from past experiences that if the most recessed portion 4c of the ventilation 4b were located axially outside the center of curvature 6 of the well radius, the strength of the welding portion would be greatly decreased and radial displacements of the rim from a true circle would increase. As a result, the length L' of the side of the disc material portion 4 is determined from the position of the most recessed portion of the ventilation when the disc 1 is pressed into the rim 2. More particularly, an axial length m' of 5 to 7 mm remains for engagement between the rim 2 and the disc 1 at the most recessed portion of the ventilation. Despite that, there are two cases where the most recessed portion of a ventilation is located axially outside the center of well radius of a rim: one is a case where a periphery of the ventilation is bent to reinforce the ventilation, as illustrated in FIGS. 11 and 12, and another is a case where a specially shaped blank is used as a disc material as illustrated in FIGS. 13 and 14. These two cases have particular problems described below. More particularly, in the case of the disc shown in FIGS. 11 and 12, the ventilation has an axially bent portion or rib G. Rib G is defined as a portion having a cross section of a different shape from that of a portion of the disc, other than the most recessed portion and located on the same radius as the most recessed portion with respect to a center of the disc. The bent portion G extends also circumferentially, and at each circumferential end the bent portion G of each ventilation has two curved portions having respective curvatures R 1 and R 2 opposite to each other. Because of this bent portion G: (1) A volume inside the wheel is reduced by Δ R in radius so that the space available for mounting a brake is decreased. (2) Rigidity of the disc becomes large relative to that of the rim, so that relatively large radial displacements are caused in the rim, which lower the fatigue strength and life of the weld portion. Increased rigidity of the circumferential ends of the ventilation also increases rim deformation, which increases the radial displacements of the rim. (3) It is necessary to increase a size of the disc material portion in proportion to an axial length L of the bent portion. Further, in the case of the disc shown in FIGS.13 and 14, since the disc material has an angularly cut portion K, the disk also has an angular portion K' in the ventilation which shortens the fatigue life of the wheel. Use of this type of disk in automobiles is therefore restricted. However, in the case of a wheel of the type generally shown in FIG.9, the rim and the disc are frequently welded to each other by a weld which is continuous, at least locally, in a circumferential direction of the wheel. As a result, excess strength and rigidity of the wheel is created. GB-A-754725 shows a wheel composed of a wheel rim and a wheel disc, in which the wheel rim has radially inwardly directed indentations which support the rim on the disc. These indentations and the wheel disc portions which engage them are profiled so that the rim and disc can be introduced axially one into the other, and then rotated into the final position. Between these engaging portions, the disc edge defines recesses which are axially outwardly of the engaging portions. The rim and disc may be locked together by their shape, or welded or rivetted. An object of the present invention is to provide a wheel for a vehicle such as an automobile and a manufacturing method therefor where the above-described surplus of strength and rigidity is used to enable downsizing of the disc material portion so as to lighten the disc without shortening the life of the wheel. A method for manufacturing a wheel in accordance with the present invention is set out in claim 4. The features and advantages of the present invention will become more apparent and will be more readily appreciated from the following detailed description of the preferred embodiment of the present invention, in conjunction with the accompanying drawings, in which: FIG. 1 is a front elevational view of a wheel for an automobile in accordance with one embodiment of the present invention; FIG. 2 is a cross-sectional view of the wheel of FIG. 1 taken along line 2-2; FIG. 3 is a plan view of a flat plate for use in manufacturing the disc of FIG. 1; FIG. 4 is a plan view of a disc material portion manufactured by eliminating four corners of the flat plate of FIG. 3; FIG. 5 is a perspective view of a disc manufactured by forming the disc material portion of FIG. 4 into the shape of a disc; FIG. 6 is a graph illustrating a relationship between a radial displacements of a rim from a true circle and a distance h (mm) between a most recessed portion of a ventilation and a center of curvature of a well radius of a rim; FIG. 7 is a graph illustrating a relationship among h, a distance between an axial end of a disc flange and the center of curvature of the well radius of the rim, and a life of the wheel; FIG. 8 is a front elevational view of a conventional wheel for an automobile; FIG. 9 is a cross-sectional view of the conventional wheel of FIG. 8 taken along line 9-9; FIG. 10 is an enlarged cross-sectional view of a spot-welded portion and an adjacent area of the conventional wheel of FIG. 8; FIG. 11 is a partial, front elevational view of a conventional disc of the type where a periphery of a ventilation is bent; FIG. 12 is a cross-sectional view of a portion of the disc close to the ventilation of FIG. 11 taken along line 12-12; FIG. 13 is a partial plan view of a special type blank for a conventional disc; and FIG. 14 is a plan view of a portion of a disc made from the blank of FIG. 13, manufactured by drawing. As illustrated in FIGS. 1 and 2, a wheel for an automobile is composed of a disc 10, made, for example, by drawing and a rim 20 which are welded to each other. More particularly, the disc 10 includes a central portion, four disc flanges (axially raised portions or flange portions) 13 protruding from a periphery of the central portion and four ventilations (flange openings or recessed spaces or recesses) 11. The rim 20 includes a well (a drop portion or a well portion) 21, a side wall 22, a well radius (a curved portion or a curved radius portion) 23 connecting the well 21 and the side wall 22. The well radius 23 has a center of curvature 24. The disc 10 is welded to the rim 20 at the disc flanges 13 and the rim well 21 using welding other than spot welding. The welding may be arc welding, laser welding, fillet welding, or a through welding. The weld portion is denoted by reference numeral 30. Each disc flange 13 includes an axial end. Each ventilation 11 is positioned between adjacent disc flanges 13. Each ventilation 11 includes a substantially arcuate periphery recessed axially outwardly from the axial end of the disc flange 13. Because of the substantially arcuate periphery of each ventilation 11, the disc 10 does not have the shape of the ventilation shown in FIG. 14. Each ventilation 11 includes a most recessed portion 12 (or a radially inwardly-directed extremum) which is located axially outside of the center of curvature 24 of the well radius 23 of the rim 20. The most recessed portion 12 of each ventilation 11 has a cross section of the same shape as a portion of the disc 10 other than the most recessed portion 12 and located on the same radius as the most recessed portion 12 with respect to a center of the disc 10 after the disc 10 is pressed into the rim 20. Therefore, the ventilation 11 does not include a bent portion G, as shown in FIGS. 11 and 12. In a method for manufacturing a wheel for an automobile in accordance with one embodiment of the present invention, as illustrated in FIGS. 3 and 4, a disc material portion (or a first portion) 41 is manufactured by eliminating four corners from a substantially square flat plate 40 along a circle having a diameter D greater than a length L of a side of the substantially square flat plate 40. Then, the disc material portion 41 is formed by drawing into a disc 10, as shown in FIG. 5. The disc 10 includes four disc flanges 13 and four ventilations 11. An arcuate portion 41a at each of the four corners of the disc material portion 41 is formed into the axial end of the disc flanges 13 which are located in a plane perpendicular to an axis of the disc. A straight side 41b of the disc material 41 is formed into the periphery of the ventilation 11 in FIG. 5. On the other hand, the rim 20 is manufactured, independently, by curvingly bending a flat plate, butt-welding abutted portions of the curved plate to produce a cylindrical element, and forming the cylindrical element into the shape of a disc. The rim 20 includes a well 21, a side wall 22, and a well radius 23 connecting the well 21 and the side wall 22. The disc 10 is welded to the rim 20 at the disc flanges 13 and at the rim well 21. Welding is not conducted at the ventilations 11. In manufacturing the disc material portion 41, the length L of the side of the substantially square flat plate 40 is selected so that the most recessed portions 12 of the ventilations 11 are located axially outside the center of curvature 24 of the well radius 23 of the rim 20 by at least 5 mm. More particularly, if the length L' of the side of flat plate 4 is relatively long in FIG. 3, the axial depth of the ventilation 11 will be small in FIG. 5. As a result, the most recessed portion 4c of the ventilation will be at a position axially inside the center of curvature 6 of the well radius, as shown in FIG. 9. In contrast, when the length L of the flat plate 40 is relatively short, an axial depth of the ventilation 11 will be large. As a result, the most recessed portion 12 of the ventilation is at a position axially outside the center of curvature 6 of the well radius, as shown in FIG. 2. Thus, in the conventional wheel, as shown in FIGS. 8 and 9, the rim 2 and the disc 1 contact each other over an entire circumferences thereof. In the wheel according to the present invention, however, as shown in FIGS. 1 and 2, the rim 20 and the disc 10 contact each other at only portions other than the ventilations 11. As a result, when manufacturing the substantially square flat plate 40, length L' of the side of the plate 40 is shortened to length L, so that the amount of material and the weight thereof are decreased at a rate of (L) 2 /(L') 2 , which becomes very significant. For example, in the case of a disc for an automobile, the length of a side of the substantially square flat plate can be reduced by about 14 to 17%, so that the amount of material and the weight thereof are reduced by as much as 20 to 30%. In forming the disc 10, the ventilations 11 of the disc 10 are formed so as to have a substantially arcuate periphery axially recessed from the axial end of the disc flanges 13, after the disc 10 is pressed into the rim 20. Therefore, the conventional ventilations of FIG. 14, having an angular portion K', are not included within the ventilations of the illustrated disc of the invention. However, ventilations which have configurations P and P' shown in FIGS. 13 and 14 having shallow arcuate peripheries may be included within the present invention. Further, in forming the disc 10, the most recessed portion 12 of each ventilation 11 is formed so as to have a cross section of the same shape as a cross section of a portion of the disc other than the most recessed portion 12 and located on the same radius as the most recessed portion 12 with respect to the center of the disc. Therefore, the ventilations of FIG. 12 having a bent portion G are not included within the ventilations of the disc of the present invention. In welding the disc 10 to the rim 20, the disc 10 is welded to the rim 20 at each disc flange 13 (more particularly, at the axial end of each disc flange 13) by a weld which is at least locally continuous over a length at least 30 mm in a circumferential direction of the disc. In the wheel and the manufacturing method therefor, the following conditions should be preferably satisfied so that a good torque transmittance characteristic is sufficiently maintained and so that radial dimensional deviation and a fatigue strength are not degraded. First, to maintain sufficient torque transmitting strength (shear strength), in the disc material manufacturing step, length L of the side of the substantially square flat plate 40 and diameter D at which the corners of the substantially square flat plate 40 are eliminated are selected so that the circumferential length C (FIG. 2) of the axial end of each disc flange 13 is equal to or greater than 30 mm. Therefore, in the subsequent welding step, each disc flange 13 is welded to the well 21 over a circumferential length equal to or greater than 30 mm. A total weld length of the welds at the four disc flanges 13 is 120 mm (4 × 30 mm) or more, so that the torque transmitting strength is not smaller than that obtained in the conventional weld structure including eight spot welds (8 × nugget diameter 15 mm = 120 mm). With respect to radial displacement of the rim from a true circle, a variance in axial position of the most recessed portion of each ventilation greatly affects the radial displacements of the rim. More particularly, in a case where the axial positions of the most recessed portions of the four ventilations are coincident with one another, no problem occurs. However, since such a positional coincidence cannot be expected in drawing, a variance in position necessarily occurs. In a case where the most recessed portions of the four ventilations are axially close to the center of curvature 24 of the well radius 23, some of the most recessed portions may be located axially inside the center of curvature 24 of the well radius 23, causing an increase in the rigidity of the wheel. Other most recessed portions may be located axially outside the center of curvature 24 of the well radius 23, causing a decrease in the rigidity of the wheel. As a result, a relatively large imbalance in the rigidity of the wheel is caused so that the disc 10 is easily inclined relative to the rim 20 to thereby increase radial displacements of the rim 20. FIG. 6 illustrates the radial displacements at the rim bead seat which were measured in tests conducted using automobile wheels (wheels having rim bead seat diameters of 12 - 16 inches and wheel widths of 4 - 7 inches). As seen from FIG. 6, the radial displacement is amplified in the range of h of ± 1 mm on opposite sides of the center of 1 mm. The radial displacement is relatively small in the range of h equal to or greater than 2 mm, and is stably small in the range of h equal to or greater than 5 mm. Therefore, the conventional concept that the radial displacement would be amplified if the most recessed portion of the ventilation were spaced axially outwardly from the rim radius can be dissipated by selecting h to be 2 mm or more, and more preferably, 5 mm or more. There is an upper limit to h of selecting C (a circumferential length of the axial end of each disc flange 13) of 30 mm or more. With respect to a fatigue strength, it is conceived that an axial distance m between the axial end of each disc flange 13 and the center of curvature 24 of the well radius 23 (an axial length of engagement between the rim 20 and the disc 10) also affects the fatigue strength of the weld portion of the wheel. Thus, life tests on a drum were conducted by adding parameter m to parameter h (an axial distance between the most recessed portion 12 of the ventilation and the center of curvature 24 of the well radius 23). FIG. 7 shows the test results wherein the fatigue strength of the wheel is shown in terms of a number of rotations of the wheel drum before cracking starts at the weld portion. As understood from FIG. 7, the life span of a wheel can be controlled by selecting an optimum combination of h and m. More particularly, as seen in FIG. 7, too small or too large a value of m shortens the wheel life. This is because a value of m which is too small decreases the rigidity of the disc 10 relative to the rim 20, thereby increasing deformations in the disc 10 such that stresses are concentrated on the disc 10. On the other hand, a value of m which is too large increases deformations in the rim 20 so that stresses are concentrated on the rim. Since the life of the wheel is extended when m is such that the deformation of the disc and the deformation of the rim are balanced with each other, such value of m should be selected. In this instance, if the value of h is 30 mm or less, an ideal combination of m and h as can satisfy a life span of about 800,000 cycles can be found in FIG. 7 by selecting a value of m in the range of 3 mm to 40 mm. With the illustrated wheel in accordance with the present invention, the following advantages can be obtained: First, because the most recessed portion 12 of each ventilation 11 is located axially outside the center of curvature 24 of the well radius 23 of the rim 20, a substantially square flat plate having a size smaller than a conventional plate can be used as a plate material for the disc material portion 41, so that the size of the plate material portion and the weight of the disc 10 can be greatly decreased. Further, because the periphery of each ventilation 11 is not bent axially, unlike the conventional disc, problems such as interference between the bent portion and a brake, decrease in the life of the weld portion due to excessive disc rigidity of the disc, and decrease in the material utilization rate due to the up-sizing of the substantially square flat plate by an axial length of the bent portion do not occur. Second, in a case where a circumferential length C of the axial end of each disc flange 13 is selected to be about 30 mm or more and a circumferential length of the weld at each disc flange 13 is selected to be 30 mm or more, torque transmitting strength substantially equal to or greater than that of the conventional wheel can be obtained. Third, where the most recessed portion 12 of each ventilation 11 is axially spaced from the center of curvature 24 of the well radius 23 of the rim 20 by a distance equal to or more than 5 mm, radial displacements of the rim 20 are suppressed, and the life span of the wheel is not shortened. Further, vibrational characteristics of an automobile are not degraded. Fourth, in a case where the axial end of the disc flange 13 is axially inwardly spaced from the curvature center 24 of the well radius 23 by a distance equal to or more than 30 mm, an optimum combination of h and m can be found with h being equal to or less than 30 mm. Further, with the illustrated method for manufacuring a wheel in accordance with the present invention, the following advantages can be obtained. First, because the length L of the substantially square flat plate 41 is determined so that the most recessed portion 12 of each ventilation 11 is located axially outside the center of curvature 24 of the well radius 23, a substantially square flat plate smaller than a conventional one can be used to manufacture the disc material portion 41, so that the amount of the plate material and the weight of the resultant disc 10 can be greatly decreased. Further, because the periphery of each ventilation 11 is not bent axially, unlike the conventional disc, problems such as interference between a bent portion and a brake, decrease in the life of the weld portion of the wheel due to excessive rigidity of the disc, and decrease in the material utilization rate due to the up-sizing of the substantially square flat plate by an axial length of a bent portion do not occur. Second, in the disc material portion manufacturing, when the length L of the side of the substantially square flat plate and the diameter D at which corners of the substantially square flat plate are eliminated are determined so that the circumferential length C of the axial end of each disc flange 13 is 30 mm or more, and, during welding, each disc flange 13 is welded to the well of the rim over a circumferential length equal to or greater than 30 mm, torque transmitting strength substantially equal to or greater than that of the conventional wheel can be obtained. Third, in manufacturing the disc material portion, if the length L of the side of the substantially square flat plate and the diameter D at which the corners are eliminated are selected so that the most recessed portion 12 of each ventilation 11 is axially outwardly spaced from the center of curvature 24 by 5 mm or more, radial displacements of the rim 20 are suppressed, and life span is not shortened. Further, vibrational characteristics of an automobile are not degraded. Fourth, when the length L of the side of the substantially square flat plate and the diameter D at which the corners are eliminated are selected so that the axial end of the disc flanges 13 are axially inwardly spaced from the center of curvature 24 of the well radius 23 by a distance at least 3 mm and no greater than 40 mm, an optimum combination of h and m can be found where h is equal to or less than 30 mm.

Claims: A vehicle wheel having a central axis, the wheel having an axially inward side facing inwardly with respect to the vehicle in use and an axially outward side in use facing outwards, said wheel comprising: a rim (20) including: a well portion having a base wall (21) extending substantially parallel to the central axis; a radially extending side wall (22) provided adjacent to the axially outward edge of said well base wall; a curved radius portion (23) joining said well base wall and said side wall (22), said curved radius portion (23) having a center of curvature (24); a bead seat portion extending axially from the outer periphery of said side wall (22); and a bead-retaining flange at the axially outer end of said bead seat portion; and a central disc (10) disposed so as to be substantially surrounded by said rim (20), said disc (10) including a central portion and a plurality of flange portions (13) each protruding from a periphery of said central portion, said plurality of flange portions (13) being joined to said well base wall (21) of said rim by continuous welding, i.e other than spot welding, of the axially innermost end edge of each said flange portion to said well base wall (21); wherein each adjacent pair of said flange portions (13) defines between them a recessed space where the edge of the central disc lies axially outwardly with respect to the axially innermost end edges of said flange portions (13) ; wherein each said recessed space (11) has a radially inwardly-directed extremum (12) located axially outward of said center of curvature (24) by 5mm or more; and wherein the radius from the center axis of said disc (10) to each said extremum (12) is the same as the radius from the center axis of said disc to a point on each said flange portion (13) having the same axial position along the central axis as each said extremum (12). A wheel according to claim 1, wherein said end edge of each flange portion (13) has a circumferential length of 30mm or more and each flange portion (13) is joined to said well base wall (21) by a weld 30 mm or more long. A wheel according to claim 1 or 2, wherein said end edge of each flange portion (13) is axially inward of said center of curvature (24) by a distance between 3mm and 40mm. A method for manufacturing a vehicle wheel having an axially outward side facing outwardly with respect to the vehicle in use and an axially inward side, the method comprising the steps of: (i) forming a first portion (41) by truncating the corners of a substantially square flat plate (40) along a circle having a diameter greater than the side length of the substantially square flat plate (40); (ii) drawing the first portion (41) so as to obtain a disc (10) having a central portion, a central axis, and four flange portions (13) corresponding to the truncated corners of the first portion (41) and defining four recesses (11) between adjacent pairs of said flange portions (13), each recess (11) having an inwardly directed extremum (12), the radius from the central axis to each said extremum being the same as the radius from the central axis to a point on each of the flange portions (13) having the same axial position as each said extremum (12); (iii) providing a rim (20) having a central axis and including: a well base wall (21) extending substantially parallel to the central axis; a radially extending side wall (22) adjacent to the axially outward edge of the well base wall (21); a curved radius portion (23) joining the well base wall (21) and the side wall (22), the curved radius portion (23) having a center of curvature (24); a bead seat portion extending axially from the outer periphery of said side wall (22); and a bead-retaining flange at the axially outer end of said bead seat portion; and (iv) joining each flange portion (13) to the well base wall (21) by continuous welding of the axially innermost end edge of each said flange portion to said well base wall (21); wherein said step (i) of forming the first portion (41) includes selecting the length of the side of the substantially square flat plate (40) and the diameter of the circle along which the corners of the substantially square flat plate (40) are truncated such that each extremum of each recess is located 5mm or more axially outward of said center of curvature (24) of said curved radius portion (23) where each flange portion (13) is joined to the well base wall (21). The method according to claim 4, wherein said welding step includes any one of arc welding, laser welding, fillet welding, and through welding. The method according to claim 4 or 5, wherein said step (i), of forming the first portion (41) includes selecting the length of the side of the substantially square flat plate (40) and the diameter of the circle along which the corners of the substantially square flat plate (40) are truncated such that the circumferential length of said end edge of each flange portion (13) is 30mm or more. The method according to claim 6, wherein said welding comprises forming a weld between each flange portion (13) and the well portion (21) 30mm or more long. The method according to any one of claims 4 to 7, wherein said step (i) of forming the first portion (41) includes selecting the length of the side of the substantially square flat plate (40) and the diameter of the circle along which the corners of the substantially square flat plate (40) are truncated such that said end edge of each flange portion (13) is located between 3mm and 40mm axially inward of said center of curvature (24) of said curved radius portion, after said step (iv) of joining.

Inventors: ABE KISHIRO, MARUYAMA SABURO, SAITO TAKANORI, SAKUMA JUN, SUGAWARA MITSUNORI, ABE, KISHIRO, MARUYAMA, SABURO, SAITO, TAKANORI, SAKUMA, JUN, SUGAWARA, MITSUNORI, Abe, Kishiro, c/ Topy Kogyo K.K., Maruyama, Saburo, Copy Kogyo K.K., Saito, Takanori, Topy Kogyo K.K., Sakuma, Jun, c/o Topy Kogyo K.K., Sugawara, Mitsunori, c/o Topy Kogyo K.K.
Applicants: TOPY IND, TOPY KOGYO KABUSHIKI KAISHA
Application year: 1995
Main classification: B60B3
IPC codes: B23K9, B21D53, B60B3, B23K26