VEHICLE WHEEL DISC, VEHICLE WHEEL INCLUDING SUCH A WHEEL DISC AND METHOD FOR PRODUCING SUCH A WHEEL DISC AND VEHICLE WHEEL

Abstract

A wheel disc including a hub located centrally within the wheel disc and defining a wheel axis. The hub has a plurality of bolt holes formed therein. The wheel disc further including an outer circumferential edge and a transition portion radially extending between the hub and the outer circumferential edge. The transition portion has a plurality of vent holes formed therein. The transition portion has a front surface and a rear surface defining a thickness therebetween such that the thickness of the transition portion varies in the radial direction.

Claims

1. A wheel disc comprising: a hub located centrally within the wheel disc and defining a wheel axis, the hub having a plurality of bolt holes formed therein; an outer circumferential edge; and a transition portion radially extending between the hub and the outer circumferential edge, wherein the transition portion has a plurality of vent holes formed therein, and wherein the transition portion has a front surface and a rear surface defining a thickness therebetween such that the thickness of the transition portion varies in the radial direction.

2. The wheel disc of claim 1, wherein the thickness of the transition portion decreases in the radial outwardly direction.

3. The wheel disc of claim 2, wherein the change in thickness of the transition portion has a constant rate of change.

4. The wheel disc of claim 1, wherein the transition portion is subdivided into a plurality of concentric segments.

5. The wheel disc of claim 4, wherein the transition portion is divided into first, second, third, fourth, and fifth sequential segments extending radially outwardly from the wheel axis.

6. The wheel disc of claim 5, wherein only the third segment of the transition portion varies in thickness in the radial outwardly direction.

7. The wheel disc of claim 6, wherein the vent holes are formed only in the third segment.

8. The wheel disc of claim 6, wherein the thickness of the third segment decreases in the radial outwardly direction.

9. The wheel disc of claim 5, wherein the third segment has a maximum thinning of 60% of the thickness of the hub, the fourth segment has a maximum thinning of 60% of the thickness of the hub, and/or the fifth segment has a maximum thinning of 60% of the thickness of the hub.

10. The wheel disc of claim 5, wherein the first and fourth segments have a constant thickness.

11. The wheel disc of claim 5, wherein the second and fourth segments have a constant thickness.

12. The wheel disc of claim 5, wherein the first segment is adjacent an outer edge of the hub.

13. The wheel disc of claim 12, wherein the first segment has a front surface having a generally frustoconical shape sloped at a first angle relative to the wheel axis.

14. The wheel disc of claim 13, wherein the third segment has a radial length of about between 50 percent to about 70 percent of the radial length of the transition portion.

15. The wheel disc of claim 13, wherein the second segment joins the first and third segments together with a curvature that smoothly blends in with the first and third segments.

16. The wheel disc of claim 15, wherein the front and rear surfaces of the fifth segment are generally planar and perpendicular to the wheel axis.

17. The wheel disc of claim 16, wherein the fourth segment joins the third and fifth segments together with a curvature that smoothly blends in with the third and fifth segments.

18. The wheel disc of claim 12, wherein the fifth segment has a thickness which is less than the thickness of the first segment.

19. The wheel disc of claim 1 produced by a flow forming process by flow forming a metallic blank, during elongation of a preformed marginal region adjoining the clamped hub.

20. The wheel disc of claim 19, wherein the metallic blank is a steel blank.

21. A vehicle wheel having a wheel rim which is configured to be secured to the wheel disc of claim 1.

22. A method of forming the wheel disc of claim 1, wherein the wheel disc is formed into a final desired shape by a flow forming process.

23. A method of forming a vehicle wheel having a wheel rim which is configured to be secured to the wheel disc of claim 1.

24. A method of manufacturing a vehicle wheel disc including the steps of: (a) providing a metallic preform; (b) positioning the preform on a mandrel of a flow forming machine; and (c) flow forming the preform against the mandrel by a rolling tool to form a wheel disc having: a hub located centrally within the wheel disc and defining a wheel axis, the hub having a plurality of bolt holes formed therein; an outer circumferential edge; and a transition portion radially extending between the hub and the outer circumferential edge, wherein the transition portion has a front surface and a rear surface defining a thickness therebetween such that the thickness of the transition portion varies in the radial direction produced during flow-forming by displacement of the rolling tool.

25. The method of claim 24 including the step of forming a plurality of vent holes in the transition portion such as by a piercing, punching or cutting operation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is a front elevational view of an embodiment of a vehicle wheel in accordance with the present invention.

[0028] FIG. 2 is a cross-sectional view of the wheel taken along lines 2-2 of FIG. 1.

[0029] FIG. 3 is a front perspective view of the wheel of FIG. 1.

[0030] FIG. 4 is a rear perspective view of the wheel of FIG. 1.

[0031] FIG. 5 is an enlarged sectional view of a portion of the wheel disc of the wheel of FIG. 1 illustrating the profile details of the front and rear surfaces of the wheel disc.

[0032] FIG. 6 is a sectional view showing a blank which can be used to produce the wheel disc shown in FIGS. 1-5.

[0033] FIG. 7 is a schematic illustration of a flow forming machine schematically illustrating the process of flow forming a wheel disc preform.

[0034] FIG. 8 is a schematic cross-sectional view of a portion of the transition portion of the wheel disc of FIG. 1.

[0035] FIG. 9 is a schematic cross-sectional view of a first alternate embodiment of a portion of a transition portion of a wheel disc.

[0036] FIG. 10 is a schematic cross-sectional view of a second alternate embodiment of a portion of a transition portion of a wheel disc.

[0037] FIG. 11 is a schematic cross-sectional view of a third alternate embodiment of a portion of a transition portion of a wheel disc.

[0038] FIG. 12 is a schematic cross-sectional view of a fourth alternate embodiment of a portion of a transition portion of a wheel disc.

[0039] FIG. 13 is a schematic cross-sectional view of a fifth alternate embodiment of a portion of a transition portion of a wheel disc.

[0040] FIG. 14 is a schematic cross-sectional view of a sixth alternate embodiment of a portion of a transition portion of a wheel disc.

[0041] FIG. 15 is a schematic cross-sectional view of a seventh alternate embodiment of a portion of a transition portion of a wheel disc.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Referring now to the drawings, there is illustrated in FIGS. 1 through 5 a “full face” vehicle wheel, indicated generally at 10. The vehicle wheel 10 generally incudes an inner “full face” wheel disc, indicated generally at 12, and an annular outer “partial” wheel rim 14. Although the invention is illustrated and described in conjunction with the particular vehicle wheel construction disclosed herein, it will be appreciated that the invention can be used in conjunction with other types of “full face” vehicle wheel constructions.

[0043] In a preferred embodiment (and as illustrated herein), the wheel disc 12 and the wheel rim 14 are produced separately and then joined together by any suitable means, such as by welding, to produce a fabricated full face vehicle wheel 10. In a preferred embodiment, the wheel disc 12 and the wheel rim 14 are made from steel and are then welded together at 16 (shown in FIG. 2), to form the wheel 10. Of course, the wheel disc 12 and/or the wheel rim 14 may be made of any suitable materials such as for example, aluminum, magnesium, titanium or alloys thereof, carbon fiber and/or composite materials and/or may be secured together by other suitable means, if so desired.

[0044] The combination of the wheel disc 12 and the wheel rim 14 defines a wheel axis W for the wheel 10. The wheel rim 14 can have any suitable annular shape for receiving and supporting a tire (not shown). The wheel rim 14 preferably has a continuous annular shape relative to the wheel axis W for accommodating a vehicle tire (not shown) mounted thereon. It should be appreciated that the wheel rim 14 can have any desired diameter and/or shape. In a preferred embodiment, the wheel rim 14 has an outer diameter or a wheel diameter within the range of about 405 millimeters (about 16 inches), to about 560 millimeters (about 22 inches).

[0045] In a preferred embodiment (and as illustrated herein), the steel wheel rim 14 is formed by a rolling and forming process to obtain the desired annular shape, as shown in FIGS. 1 through 4. The wheel rim 14 includes a front circumferential edge 20, and a rear facing circumferential edge 22. The wheel rim 14 further includes a generally tubular or cylindrical central wall 24 extending between the edges 20 and 22. The central wall 24 may have any suitable shape for receiving the tire as well as providing rigidity to the annular shaped outer rim 14. Thus, the central wall 24 is preferably not perfectly tubular or cylindrical but includes curvatures or bends therein.

[0046] As best shown in FIG. 2, the rear edge 22 of the wheel rim 14 defines a curled lip portion 26 for contacting and sealing against a wall of the tire when mounted on the finished wheel 10. The front edge 20 is formed to provide a joining welding edge with the rear of the wheel disc 12. It is noted that in the illustrated embodiment as best shown in FIG. 2, the outer circumferential edge of the wheel disc 12 defines a curled lip portion 28 for contacting and sealing against a wall of the tire when mounted on the wheel 10. Of course, the wheel disc 12 and the wheel rim 14 could be alternatively formed such that the curled lip portion 28 is formed on the wheel rim 14 instead. In this situation, the outer circumferential edge of the wheel disc would have a smaller diameter and would be welded to an interior wall of the central wall 24.

[0047] When the wheel 10 is formed by joining the wheel disc 12 to the outer rim 14, the wheel 10 defines a centerline C or center-plane that is approximately located equally spaced axially from the curled lip portions 26 and 28 of the wheel 10, as shown in FIG. 2. The wheel 10 includes circular bead seats 30 and 32 where the tire contacts and seals against the wheel 10. The bead seats 30 and 32 may be located generally adjacent to the curled lip portions 28 and 26, respectfully. Broken lines, indicated generally by BS, schematically represent the bead seat or inner diameter portion of a tire that is mounted on the wheel 10. The conventionally known “rim width” may be determined as the axial distance between the bead seats 30 and 32. The wheel diameter is generally the radial diameter of the bead seats 30 and 32.

[0048] The wheel disc 12 is generally comprised of or defined by three portions: a central hub, indicated generally at 40, an outer circumferential edge 42, and an annular transition portion, indicated generally at 44. The hub 40 is preferably circular and is generally defined as the central portion of the wheel disc 12 and functions as a wheel mounting portion or center mounting portion of the wheel 10. Note that the outer circumferential edge 42 includes the curled lip portion 28. The transition portion 44 is generally annulus or ring-shaped and radially extends between the hub 40 and the outer circumferential edge 42. The transition portion 44 generally encircles the hub 40. As will be described in detail below, the transition portion 44 is preferably subdivided into a plurality of segments passing into or adjacent one another or into the hub 40 and the circumferential edge 42.

[0049] In a preferred embodiment, the wheel disc 12 is preferably produced from a single steel blank which is then formed by suitable means to form the wheel disc 12. The blank may be first provided as a smooth, flat annular or ring-shaped steel disc blank B (shown in FIG. 6), and then preferably shaped by flow forming into the final wheel disc shape. Alternatively, the blank B may be formed by any suitable means, such as stamping and/or flow forming, into a wheel disc “preform” (such as the preform 48 shown in FIG. 7) having a particular partially formed wheel disc shape before it is formed into the final wheel disc shape, preferably by flow forming.

[0050] It is known to produce wheel discs by a flow forming or flow turning process. However, as will be explained in detail below, the present invention relates to the manufacture of a wheel disc 12 by a flow forming process that provides for varying thicknesses in the transition portion 44. In the flow forming process, a flow forming machine is used to form the wheel disc preform into the desired shape of the wheel disc 12. For example, there is schematically illustrated in FIG. 7 a flow forming machine, indicated generally at 46, having a mandrel 47 which receives a wheel disc preform 48. The mandrel 47 may have a profiled surface 47a corresponding to the desired profile shape of the final formed wheel disc. The wheel disc preform 48 may be clamped at a central region such as the hub 40. The material of the wheel disc preform extending radially outwardly from the hub 40 is pressed and elongated by means of flow forming under rotation of a roller 49 (or other tools) against wheel disc preform mounted on the mandrel 47 (or other tools) in order to obtain the desired contour. Note that the mandrel 47 and the rollers 49 are drawn very schematically and generic. Thus, the cross-sectional profile of the transition portion 44 can be produced to provide for a desired varying thickness of the transition portion 44. This is unlike conventional wheel discs which are made by flow forming or flow turning having generally uniform surfaces on their inner and outer sides of the wheel disc.

[0051] In the illustrated embodiment, the hub 40 has a front face or surface 50, as seen in FIGS. 1, 2, 3, and 5, and a rear face or surface 52, as seen in FIGS. 2, 4, and 5. The front surface 50 is located on the outboard side of the wheel 10 when mounted on a vehicle. The rear surface 52 is located on the inboard side of the wheel 10 when mounted on a vehicle. The hub 40 functions as a wheel mounting portion or center mounting portion of the wheel 10 for connecting with an axle (not shown) via a plurality of lug bolts (not shown) and lug nuts (not shown).

[0052] The hub 40 includes a circular outer edge portion, indicated generally at 54, which generally defines the edge of the hub 40 which joins or connects with the transition portion 44 of the wheel disc. The hub 40 has a diameter H.sub.D (see FIG. 5). Although the hub 40 includes a plurality of apertures formed therein, as will be discussed in detail below, the hub 40 may be formed with a relatively constant thickness H.sub.t (see FIG. 5) between the front and rear surfaces 50 and 52. In fact, the thickness H.sub.t of the hub 40 may coincide with the thickness of the initial blank from which the wheel disc 12 is formed. Of course, the hub 40 may be formed with a varying thickness if so desired. In a preferred embodiment, the thickness H.sub.t is within a range of about 3.0 millimeters to about 7.0 millimeters. In a more preferred embodiment, the thickness H.sub.t is within a range of about 3.5 millimeters to about 6.8 millimeters.

[0053] The hub 40 includes a centrally located pilot aperture or hub hole 56. The hub hole 56 extends along the wheel axis W. The hub hole 56 may accommodate a portion of the axle and/or receive a protective/decorative cap (not shown). The hub hole 56 may have any suitable diameter. The hub hole 56 may be formed by a stamping process performed on the blank.

[0054] A plurality of lug bolt receiving holes 58 are formed in the hub 40 and are circumferentially spaced around the hub hole 56 and the wheel axis W. In the illustrated embodiment, the hub 40 includes five lug bolt receiving holes 58. Alternatively, the number and/or location of the lug bolt receiving holes 58 may be other than illustrated if so desired. The lug bolt receiving holes 58 receive the lug bolts (not shown) for securing the vehicle wheel 10 with lug nuts (not shown) on the axle of an associated vehicle. The lug bolt receiving holes 58 may also be used to secure the blank for the flow forming machine during production of the wheel disc 12.

[0055] The details of the transition portion 44 will now be discussed. The transition portion 44 defines a front face or surface 60, as seen in FIGS. 1, 2, 3, and 5, and a rear face or surface 62, as seen in FIGS. 2, 4, and 5. The front surface 60 is located on the outboard side of the wheel 10 when mounted on a vehicle. The rear surface 62 is located on the inboard side of the wheel 10 when mounted on a vehicle. As stated above, it is preferred to form the majority of the transition portion 44 with varying thickness between the front and rear surfaces 60 and 62. This varying thickness optimizes the material usage of the wheel disc 12 which may reduce the overall mass of the wheel disc 12.

[0056] The transition portion 44 preferably includes a plurality of vent holes formed therethrough. In the illustrated embodiment, the transition portion 44 includes a set of five large vent holes 70, and a set of five smaller outer vent holes 72. The vent holes 70 and 72 not only provide ventilation to wheel brakes (not shown) positioned adjacent to the wheel 10 when the wheel 10 is mounted on a vehicle but also provide for a reduction in material of the transition portion 44, thereby reducing the overall mass of the wheel disc 12. The number of vent holes 70 and 72 in the illustrated embodiment corresponds to the five-bolt hole pattern of the lug bolt receiving holes 58 for an aesthetically pleasing appearance.

[0057] The vent holes 70 are preferably circumferentially spaced around the transition portion 44 about the wheel axis W equidistant from one another. Similarly, the vent holes 72 are preferably circumferentially spaced around the transition portion 44 about the wheel axis W equidistant from one another although offset from the vent holes 70. Of course, it should be understood that the transition portion 44 may have any number of vent holes having any suitable shape and positioned at any suitable location within the transition portion 44.

[0058] Referring now to FIG. 1, in the illustrated embodiment of the wheel disc 12, the vent holes 70 each have a generally trapezoidal shape with curved corners formed therein. Each of the vent holes 70 is similar in shape and size. The vent holes 70 extend a relatively large amount in the radial direction, as shown in the cross-section of FIG. 2, thereby removing a fair amount of material. Referring back to FIG. 1, the vent holes 70 have an inner wall 74, an outer wall 76, and a pair of sloping walls 78. The inner wall 74 has a general width 70a. The outer wall 76 has a general width 70b. The vent hole 70 has a general radial length 70c. As can be understood, the shape, number and/or location of the vent holes 70 can be other than illustrated and described if so desired.

[0059] In a preferred embodiment, the width 70a of the inner wall 74 may range from about 30 millimeters to about 120 millimeters. In a more preferred embodiment, the width 70a of the inner wall 74 may range from about 30 millimeters to about 100 millimeters. Consequently, in a preferred embodiment, the width 70b of the outer wall 76 may range from about 50 millimeters to about 150 millimeters. In a more preferred embodiment, the width 70b of the outer wall 76 may range from about 80 millimeters to about 130 millimeters. In a preferred embodiment, the radial length 70c may range from about 50 millimeters to about 160 millimeters. In a more preferred embodiment, the radial length 70c may range from about 50 millimeters to about 150 millimeters.

[0060] In the illustrated embodiment of the wheel disc 12, the vent holes 72 each have a generally triangular shape with curved corners formed therein. Each of the vent holes 72 is similar in shape and size. The vent holes 72 have an outer wall 80 and a pair of sloped walls 82. The vent hole 72 has a general width 72a. The vent hole 72 has a general radial length 72b. In a preferred embodiment, the width 72a may range from about 30 millimeters to about 100 millimeters. In a more preferred embodiment, the width 72a may range from about 30 millimeters to about 90 millimeters. Consequently, in a preferred embodiment, the length 72b may range from about 30 millimeters to about 90 millimeters. In a more preferred embodiment, the length 72b may range from about 40 millimeters to about 85 millimeters.

[0061] The formation of the vent holes 70 and 72 removes a relatively substantial portion of the material from the transition portion 44. It is preferred that the design of the wheel disc 12, and in particular the transition portion 44, be designed such that the presence of the vent holes 70 and 72 are considered when designing the varying thickness of the transition portion 44. Thus, the lack of material being removed from the areas at the vent holes 70 and 72 determines the design aspects and geometry of the transition portion 44. Of course, other factors should be considered such as the weight target of the wheel 10, the design intent of the wheel 10, and the performance intent of the wheel 10. The ventilation holes 70 and 72 may be formed by any suitable method, such as with a piercing, punching or cutting operation.

[0062] Stress levels at critical points within the wheel disc 12 should be discovered and considered in determining the shape of the front and rear surfaces 60 and 62 of the transition portion 44. Thus, the shape of the vent holes 70 and 72 can affect the optimization results in order to achieve the performance requirements. The design implications for the desired thickness differences within the transition portion 44 will generally correlate to the location and the lack of material from the vent holes 70 and 72.

[0063] It should also be understood that the illustration of the wheel disc 12 shown in cross-section in FIG. 5 lacks cross-sectional lines to help with clarity and understanding of the drawing in FIG. 5. Lastly, the details of the drawing in FIG. 5 (as well as the other Figures) is not necessarily to scale and may have exaggerated dimensions to assist in clarity and understanding of the drawings.

[0064] For descriptive purposes, the transition portion 44 is subdivided into a plurality of concentric radial or annular segments. In the illustrated embodiment as shown in FIG. 5, there are generally five segments, indicated generally at A, B, C, D and E. The segments A, B, C, D and E are separated from one another at transition points 100, 102, 104, 106, 108, and 110. The transition points 100, 102, 104, 106, and 108 are radially spaced from one another and refer to a radial dimension or distance relative to the wheel axis W. The segments A, B, C, D and E generally pass into each other or into the hub 40 or the outer circumferential edge 42 of the wheel disc 12. Each of the segments A, B, C, D and E generally includes an inner end situated closer to the wheel axis W, and an outer end situated farther away from the wheel axis W. More specifically, the segment A extends between transition points 100 and 102. The transition point 100 generally corresponds to the outer edge of the circular outer edge portion 54 of the hub 40. The curved segment B extends between the transition points 102 and 104. The segment C extends between the transition points 104 and 106. In a preferred embodiment, the vent holes 70 and 72 are formed only in segment C. Thus, the segments A, B, D, and E preferably do not include vent holes formed therein. The curved segment D extends between the transition points 106 and 108. The segment E extends between the transition points 108 and 110. The transition point 110 is generally positioned adjacent the outer circumferential edge 42 of the wheel disc 12.

[0065] As can be seen in FIG. 5, the transition points 100, 102, 104, 106, 108, and 110 generally correspond to major bends or curvature changes of the wheel disc 12. It should be understood that the transition portion 44 may be formed other than what is shown in FIG. 5.

[0066] As shown in FIG. 5, the inner end of the segment A connects with the circular outer edge portion 54 of the hub 40. The outer end of the segment A connects with the inner end of the curved segment B. The segment A has a generally frustoconical shape and is generally sloped at an angle S.sub.1 relative to the wheel axis W. In the illustrative embodiment, the angle S.sub.1 is about 43 degrees relative to the wheel axis W. In a preferred embodiment, the angle S.sub.1 may range from about 15 degrees to about 60 degrees. In a more preferred embodiment, the angle S.sub.1 may range from about 20 degrees to about 60 degrees.

[0067] The segment C also has a generally frustoconical shape. As will be explained in detail below, the segment C preferably has a varying thickness defined between a front surface 64 of the segment C and a rear surface 66 of the segment C. In the illustrated embodiment, the thickness of segment C of the transition portion varies in the radial direction, and more specifically the thickness decreases from the transition point 104 to the transition point 106.

[0068] As shown in FIG. 5, segment B (between transition points 102 and 104) joins the segments A and C together with a curvature that preferably smoothly blends in with both of the segments A and C. In a similar manner, the curved segment D (between the transition points 106 and 108) blends the sloped frustoconical segment C with the segment E (between the transition points 108 and 110). It is noted that the segment E is preferably generally planar and perpendicular to the wheel axis W. Of course, the segment E could be formed with a frustoconical shape if so desired.

[0069] The wheel 10 can be manufactured to any size suitable size for mounting a tire thereon. Tire sizes for conventional vehicles are generally within the range of about 16 inches (406 mm) to about 22 inches (560 mm), for example. With respect to FIGS. 5 and 6 and for descriptive purposes, the illustrated embodiment of the wheel disc 12 relates to a wheel 10 having a 22 inch or about 560 mm “wheel diameter” as conventionally understood as the diameter of the bead seats 30 and 32. Note that the outermost diameter W.sub.D for the illustrated embodiment is about 600 mm. The rear surface 62 at the segment E is spaced by a depth D.sub.d taken in an axial direction generally from the rear surface 52 of the hub 40.

[0070] In the illustrative embodiment, the depth D.sub.d is about 89 mm. In a preferred embodiment, the depth D.sub.d may range from about 25 millimeters to about 120 millimeters. In a more preferred embodiment, the depth D.sub.d may range from about 30 millimeters to about 110 millimeters. In general, the dimensions of the depth D.sub.d, the slopes of the segments A and C, and the dimensions of the segments A, B, C, D, and E will be generally determined by the requirements for accommodating a brake caliper (not shown) adjacent thereto when the wheel 10 is mounted on the vehicle.

[0071] A stated above, the transition portion 44 may be formed to any suitable size and shape. Referring to the illustrated embodiment of FIG. 5, the transition portion 44 is dimensionally defined by an outer radius R.sub.O and an inner radius R.sub.I from the wheel axis W. The radial length or distance of the transition portion 44 is defined by the radial length R.sub.T (R.sub.O minus R.sub.t). In a preferred embodiment, the radial length R.sub.T may range from about 110 millimeters to about 220 millimeters. In a more preferred embodiment, the radial length R.sub.T may range from about 120 millimeters to about 200 millimeters.

[0072] As shown in FIG. 5, the segment A has a radial length R.sub.1. The segment B has a radial length R.sub.2. The segment C has a radial length R.sub.3. The segment D has a radial length R.sub.4. The segment E has a radial length R.sub.5. In the illustrated embodiment, the radial length R.sub.t is about 8% of the radial length R.sub.T. The radial length R.sub.2 is about 6% of the radial length R.sub.T. The radial length R.sub.3 is about 61% of the radial length R.sub.T. In one preferred embodiment, the radial length R.sub.3 ranges from about 50% to about 70% of the radial length R.sub.T. The radial length R.sub.4 is about 6% of the radial length R.sub.T. The radial length R.sub.5 is about 19% of the radial length R.sub.T. In a preferred embodiment, the radial length R.sub.t may range from about 5% to about 30% of the radial length R.sub.T. The radial length R.sub.2 may range from about 5% to about 30% of the radial length R.sub.T. The radial length R.sub.3 may range from about 60% to about 80% of the radial length R.sub.T. The radial length R.sub.4 may range from about 5% to about 15% of the radial length Rr. The radial length R.sub.5 may range from about 10% to about 30% of the radial length R.sub.T.

[0073] As stated above, the segment C preferably has a varying thickness defined between its front and rear surfaces 64 and 66. In the illustrated embodiment, the thickness of segment C of the transition portion varies in the radial direction, and more specifically the thickness decreases from the transition point 104 to the transition point 106 in a radial outwardly direction. It should be understood that the segment C may be formed with a varying thickness other than what is shown and described herein. In a preferred embodiment, the front and rear surfaces 64 and 66 remain relatively smooth each having a generally frustoconical shape relative to the wheel axis W. Also, in a preferred embodiment, the change in thickness of the segment C has a constant rate of change or a linear rate. Thus, the front and rear surfaces 64 and 66 illustrated in the cross-sectional drawing of FIG. 5 are shown as straight lines. Due to the nature of the varying and decreasing thickness, the front surface 64 is sloped at a slightly different angle than the rear surface 66. The frustoconical shaped front surface 64 has a sloped angle S.sub.2 relative to 90 degrees from the wheel axis, as indicated in FIG. 5. The frustoconical shaped rear surface 66 has a sloped angle S.sub.3 relative to 90 degrees from the wheel axis. The angle S.sub.3 is slightly greater than the angle S.sub.2.

[0074] In the illustrative embodiment shown in FIG. 5, the angle S.sub.2 is about 16 degrees (about 74 degrees (90-16) relative to the wheel axis W), and the angle S.sub.3 is about 17 degrees. In a preferred embodiment, the angle S.sub.2 may range from about 10 degrees to about 50 degrees. In a more preferred embodiment, the angle S.sub.2 may range from about 12 degrees to about 45 degrees. In a preferred embodiment, the angle S.sub.3 may range from about 12 degrees to about 52 degrees. In a more preferred embodiment, the angle S.sub.3 may range from about 14 degrees to about 47 degrees.

[0075] In the illustrative embodiment shown in FIG. 5, the segment A preferably has a constant thickness t.sub.1 extending between transition points 100 and 102. The thickness t.sub.1 may be the same thickness H.sub.t of the hub 40. The thicknesses t.sub.1 and H.sub.t may be the same thickness as the blank B used in forming the wheel disc 12. The segment B may also generally have the same thickness t.sub.1. Although the segment C may have a varying thickness anywhere along its length, in a preferred embodiment generally the entire length of the segment C varies in thickness, as shown in FIG. 5. The segment C has a thickness t.sub.2 adjacent the transition point 104. The thickness t.sub.2 may be the same as the thickness t.sub.1. Preferably, the segment C decreases in thickness at a constant rate in a radial outwardly direction to the transition point 106. The segment C has a thickness t.sub.3 adjacent to the transition point 106, wherein the thickness t.sub.3 is less than the thickness t.sub.2.

[0076] In a preferred embodiment, the thickness t.sub.2 may range from about 3.0 millimeters to about 7.0 millimeters. In a more preferred embodiment, the thickness t.sub.2 may range from about 3.5 millimeters to about 6.8 millimeters. In a preferred embodiment, the thickness t.sub.3 may range from about 3.0 millimeters to about 6.0 millimeters. In a more preferred embodiment, the thickness t.sub.3 may range from about 3.5 millimeters to about 5.0 millimeters.

[0077] In a preferred embodiment, the thicknesses of the segments D and E are about the same as the thickness t.sub.3. Thus, thickness t.sub.4 of the segment E, as shown in FIG. 5, is about the same as the thickness t.sub.3. In a preferred embodiment, only the segment C has a varying thickness such that thicknesses of the segments A, B, D, and E are constant throughout their radial length.

[0078] The blank B or wheel disc preform which is used to form the wheel disc 12 may be formed with a constant thickness that corresponds to the thickness H.sub.t of the hub 40. During formation of the transition portion 44, the thickness at the segments C, D, and E may be reduced. In a preferred embodiment, the segment C has a maximum thinning of 60% of the thickness HR of the hub 40. In a preferred embodiment, the segment D has a maximum thinning of 60% of the thickness H.sub.t of the hub 40. In a preferred embodiment, the segment E has a maximum thinning of 60% the thickness H.sub.t of the hub 40.

[0079] As stated above, the thickness of segment C between the transition points 104 and 106 of the transition portion 44 may vary in the radial direction. In the embodiment shown in FIG. 5, the thickness decreases from the transition point 104 toward the transition point 106 in a radial outwardly direction. This configuration is also schematically illustrated and represented in FIG. 8. There are schematically illustrated in FIGS. 9 through 15 alternate embodiments of transition portions illustrating different configurations of the section C, for example, wherein there is a varying thickness between the transition points 104 and 106. FIGS. 9 through 15 are schematical representations similar to, but different, from the illustration of FIG. 8. For example, there is schematically illustrated in FIG. 9 a transition portion 111 in which the thickness increases from the transition point 104 to the transition point 106 in a radially outwardly direction. Front and rear surfaces 112 and 113 of the transition portion 111 may remain relatively smooth each having a generally frustoconical shape relative to the wheel axis W. Smooth surfaces may also be configured in the embodiment illustrated in FIGS. 10 through 15.

[0080] There is illustrated in FIG. 10 a transition portion 114 wherein the thickness decreases from the transition point 104 in a direction towards the transition point 106 to an intermediate point 115, wherein the thickness then increases in the direction towards the transition point 106. A front surface 116 may remain smooth, wherein a rear surface 117 includes the intermediate point 115 such that the rear surface 117 has two sloped surfaces 117a and 117b. There is illustrated in FIG. 11 a transition portion 120 similar to the transition portion 110 of FIG. 10 except that a front surface 122 is formed with an intermediate point 124 forming two sloped surfaces 122a and 122b. A rear surface 126 may be smooth.

[0081] There is illustrated in FIG. 12 a transition portion 130 wherein the thickness increases from the transition point 104 in a direction towards the transition point 106 to an intermediate point 132, wherein the thickness then decreases in the direction towards the transition point 106. A front surface 134 may remain smooth, wherein a rear surface 136 includes the intermediate point 132 such that the rear surface 136 has two sloped surfaces 136a and 136b. There is illustrated in FIG. 13 a transition portion 140 similar to the transition portion 130 of FIG. 12 except that a front surface 142 is formed with an intermediate point 144 forming two sloped surfaces 142a and 142b. A rear surface 146 may be smooth.

[0082] FIGS. 14 and 15 represent embodiments having transition portions 150 and 160, respectively, wherein the thickness between the transition points 104 and 106 are relatively large such that the thickness at the transition point 104 is at least doubled or halved compared to the thickness at the transition point 106.

[0083] As can be understood, the specific numbers, ranges, dimensions and/or percentages disclosed herein can be other than illustrated and described if so desired.

[0084] The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.