WO2004074010A2 - Light weight and high performance braking composite bicycle wheel rim - Google Patents

Abstract

A fiber reinforced plastic bicycle wheel rim is formed of six segments per side and formed in a section having precisely formed, machinable brake surfaces and preferably combining inner high modulus fiber reinforced plastic lamination and an outer lamination of improved frictional coefficient materials at the braking surfaces.

Description

Light Weight and High Performance Braking Composite Bicycle Wheel Rim

BACKGROUND OF THE INVENTION [0001] Priority is claimed based on US Provisional Application filed 2/14/2003

Serial No. 60/447,642 and having the same title and inventors as this application.

FIELD OF THE INVENTION [0002] The invention is an improved one-piece, hollow bicycle wheel rim having improved sectional shape and surface for high performance caliper braking and composite layup providing lighter weight and increased strength in an economical manner.

DESCRIPTION OF RELATED ART [0003] Basic principles of optimum compaction low void composite molding the bicycle industry are described in U.S. Patents 5,624,519 and 6,270,104, sharing a common assignee with this application. The disclosures in U.S. Patents Nos. 5,624,519 and 6,270,104 are incorporated by reference as if fully set forth herein. It will be noted that the fiber/resin areal ratios taught in those patents correspond to a fiber to resin ratio of about 65/35 by weight. [0004] Metal wheel rims have long been made by bending a straight extrusion, bar or other shape to a circular form and then joining the ends to make a closed circle. It is also known to machine a brake surface, particularly after welding an aluminum rim, as in European Patent Office Publication No. 0579525A1. These patents are incorporated by reference as fully set forth herein. [0005] Owing to the different strength, and coefficient of friction properties of composite fiber reinforced plastics, particularly the high tensile strength and high stiffness of materials such as carbon fiber, the base material is formed to shape prior to curing However there has long been a concern about the performance of such structurally sound rims under high performance caliper braking conditions, such as in a long, fast descent on a mountain road.

[0006] Three typical methods of forming a wheel or wheel rim from carbon fiber reinforced plastic are know. These include a cord composite in which the high strength skin surrounds a core such a foam core, U.S. Patent 5,061,013, a solid composite such as U.S. Patent 6,347,839 BI in which composite laminations have no designed end openings or different density materials between interior and exterior surfaces and a partially hollow but plugged construction such as U.S. Patent 6,398,313 BI where two hollow halves have interior inserts and exterior reinforcements at joining ends. The disclosures in these three patents are incorporated by reference as if fully set forth herein. A copending application, Serial No. 10/632,727 filed 7/31/2003 discloses use of optimum compaction, low void manufacturing for an aerodynamic section, two piece rim. The disclosure therein is incorporated by reference herein

[0007] The invention herein avoids the drawbacks of the prior art such as Lew

Patent 6,347,839 and 6,398,313 by using general principles of optimum compaction low void composite construction specially adapted to the unique shape and structural requirements of high braking performance and light weight wheel rims using a combination of laminates incorporating fibers at different angles relative to one another. [0008] Notably, unlike prior art carbon fiber wheel or rim forming techniques, the instant rims are formed from a plurality of prepreg segments, tabbed to overlap to result in a solid wall, but hollow rim. Preferably six segments per side, for a total of twelve, are formed surrounding a bladder, with overlapping tabs on each side and at the center plane, such that under curing pressure and temperature there is a continuous chemical bond in the preferred epoxy matrix. Six segments per side better aligns the fibers with expected loads when the preferred 0 - 45 - 90 degree oriented fiber layups are used. The segments are staggered from side to side so that seams on one side do not line up transversely across from seams on the other side. [0009] The molds contain plugs or projections to form spoke nipple access holes and enabling precise alignment of the spoke hole finishing tools. The valve stem hole can also be provided for in this manner.

[00010] After forming the uncured skin, the unit is placed in a mold, the mold closed, the bladder pressurized while the mold is heated. When fully cured, the rim is removed from an opened mold and the bladder removed. Finishing of the access holes and spoke holes is accomplished and, if desired, the brake walls may be further machined.

[00011] The preferred carbon fiber reinforced epoxy laminate structure has a tough, high performance braking surface, which may also be made machinable.

BRIEF DESCRIPTION OF THE DRAWINGS [00012] Fig. 1 is a sectional view showing the sectional shape and a tire.

[00013] Fig. 2 is a fragmentary side elevational view of a portion of the rim.

[00014] Fig. 3 is a side elevational view of the rim.

[00015] Fig. 4 is a fragmentary bottom plan view of a portion of the rim.

[00016] Fig. 5 is a schematic view showing prior art fiber alignment. [00017] Fig. 6 is a schematic view showing fiber alignment in the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[00018] A wheel rim 10 is formed of fiber reinforced plastic resin. Preferably this is formed predominantly of a high modulus fiber, such as carbon fiber, in an epoxy matrix, with special structural locations containing other fibers commensurate with needs in areas having unique performance and/or manufacturing requirements, such as brake surfaces. Thus, strong, but more easily machinable fibers, such as glass can be used in certain areas, and tougher fibers, such as Kevlar, can be used in high impact areas.

[00019] The fibers in the individual segments are aligned in laminations such as taught in U.S. Patents Nos. 5,624,519 and 6,270,104 sharing a common assignee with this application. By using a series of 0 - 45 - 90 degree alignments, the high strength and high modulus properties of carbon fiber can be used to advantage to produce a shape of complex curvature having substantially uniform strength in the needed directions in the finished structure, while the optimum compaction and low void methods, as improved for wheel rims as taught herein, produces the finished structure having a substantially uniform density.

[00020] It will be apparent that when 0 - 45 - 90 degree aligned fibers are formed in a circular rim die cut from a continuous flat layup, an individual fiber line, tangent at a first point on the rim, is skewed at 45 degrees from the tangent at a second point, spaced 45 degrees circumferentially. At the second point, fibers in an adjacent layer are tangent. Thus, for a 45 degree arc of the rim, fibers diverge from the tangent, to a third point half the 45 degree arc, at which point the fibers in the adjacent layer converge to the second point of tangency. Because carbon fiber is extremely strong at certain load orientations, it is desirable to keep the fiber orientation in line with the loads - mainly circumferentially and radially. By dividing the overall structure into six layups, spaced around 60 degree arcs, much closer alignment of fibers is maintained.

[00021] Optimum fiber to resin ratios substantially above the industry standards are also permitted by the product and process taught herein.

[00022] Rim 10 as shown as a high performance road racing rim adapted to receive a conventional glued-on "tubular" or "sew-up" tire 11 in which the tire and tube are formed together as a unit and this unit is adhesively affixed to the tire well 12 and further mechanically held in place by virtue of the inflation pressure in the tube, compressing the unit around the rim 10. As shown in Fig. 1, tire well 12 extends between left and right apexes 14, 16.

[00023] Depending downwardly from apexes 14, 16 are bevels 18, 20. Bevels

18, 20 space brake surfaces 22, 24 radially inwardly (toward the axle of the wheel relative to apexes 14, 16 and well 12) and transversely outwardly (away from the center plane of the rim) from apexes 14, 16. Well 12 is smoothly curved with a dimension corresponding to that needed to receive a high performance "sew-up" tire 11 with a diameter of around one inch, typically 21 to 28 mm.

[00024] Sharp changes in curvature in tire well 12 are avoided to maximize utilization of standard tires and to maximize their adhesion and other performance, however bevels 18, 20 form a significant spacing between apexes 14, 16 and brake surfaces 22, 24. Because bevels 18, 20 shown in section in Fig. 1 are formed in a three dimensional, circular rim, the form, in actuality, a conical segment at an angle from the central axis (corresponding to the axis of the axle of the wheel) of about 20 degrees from the horizontal.

[00025] Extending downwardly from apexes 14, 16 are braking surfaces 22, 24 which join left and right inwardly angled interior walls 26, 28. Inwardly angled interior walls 26, 28 join walls 22, 24 at concavities 30, 32. Concavities 30, 32 provide lateral spacing of brake walls 22, 24 away from the center plane of the wheel, inwardly angled interior walls 26, 28 meet spoke bed 34.

[00026] The relative dimensions of the section disclosed approximate a structure that is 'square' in that distance from spoke bed 34 to tire well is almost equal to the distance across the brake walls 22, 24.

[00027] Braking surfaces 22, 24 are substantially flat and preferably 19 to 22 mm across for a high performance road tire of a nominal width of about the same nominal width. This width is considered a high performance, light weight, high speed tire having minimal weight and friction. As rim and tire systems use compatible ranges of sizes, wider rims could be designed for wider tires, such as 24 or 25 mm rims for tires of those nominal dimensions for wheel specially designed for rough road races, such as races historically run on cobblestones, or races in weather conditions requiring wider tires.

[00028] Keeping in mind that specific lamination schedules are generally in accordance with the teachings of the aforementioned Patents Nos. 5,624,519 and 6,270,104, certain wheel rim advantages are shown in the schematic arrangements of laminations. The individual laminations of each segment are each comprised of component unidirectional fiber layers arranged at 0 - 45 - 90 degrees relative to one another. [00029] A number of unique attributes are present in the wheel rim of this invention, compared to other carbon fiber reinforced plastic wheel rims.

[00030] This rim is made from a one piece mold, having no joints. As such, it is different from several alternative rims, such as those using a pair of mating arc segments, or a pair of arc segments joined with special joint pieces. Unlike other one piece wheels ~ such as disc wheels — using all fiber reinforced plastic rim, spokes and hub assemblies, the instant rim uses separate components of rim, spoke and hub assembly to obtain maximum lightness and performance

[00031] The preforms used to make the one piece rim disclosed herein differ from other attempts to form wheels from fiber reinforce plastics in that other methods typically attempt to maximize the size and continuity of the preforms by using the largest preforms suitable to molding. In the rim disclosed herein, preferably six segmented preforms per side are used. The use of segmented preforms enables the alignment of fibers that more closely follow the lines of stress in the structure.

[00032] While the quasi-isotropic nature of the 0 - 45 - 90 degree fiber oriented preforms provides an excellent strength to weight relationship, in a round structure, like a bicycle wheel rim, it has been discovered that aligning six segments around the circumference of a rim provides better fiber alignment. Using a zero degree bundle or "tape" such as in application serial number 10/632,727 in the apexes and spoke bed further strengthens the rim.

[00033] As shown in Fig. 5, in the prior art rim 100 comprised of a semicircular lamination 102, an individual fiber line 104, is tangent at a first point 106 on the rim. A parallel fiber line 110, is skewed at 45 degrees from the tangent at a second point, 108, spaced 45 degrees circumferentially from the first point 106. Thus, for a 45 degree arc of the rim, fiber lines 104, 108 angularly diverge from the tangent. Because carbon fiber is extremely strong at certain load orientations, it is desirable to keep the fiber orientation in line with the loads - mainly circumferentially and radially.

[00034] As shown in Fig. 6, by dividing the overall structure 10 into six segments 200, 202, 204, 206, 208, 210, spaced around 60 degree arcs, much closer aligmnent of fibers is maintained. At the point of tangency 212 of segment 202 fiber line 214 is parallel to the tangent. At point of tangency 216 displaced 45 degrees from point 212, The fiber line 218 closest to parallel to the tangent is only is only 15 degrees from parallel to the tangent. Because segment 202 is where point 212 is located and segment 204 is where point 216 is located, the overall rim 10 is stronger, stiffer and lighter than prior art carbon rims formed from a single circular layup or semicircular layup. The aforementioned relationships are for illustration, and from the benefits of this teaching, and that in the references incorporated herein, the person of ordinary skill will be able to practice the invention using the parameters taught herein.

[00035] An added benefit of the use of overlapping segments, compared to circular or semicircular layups is that much less waste of materials results and cutting patterns are more simple.

[00036] Each side of the rim is layed up of six segments, each abutting or with a slight over lap at seams 220, 222, 224, 226, 228, 230. The reverse side is layed up in a similar fashion. The segments from side to side are staggered, as shown in Fig. 4, so that a seam, such as 220, will be aligned with the center of the reverse side segment 200R, and the seams between reverse side segments will be aligned opposite the center of a segment, such as 200. When compacted and curved, a seamless rim will be formed. The tirewell preform consists of 5-6 segments with circumferentially overlapping tabs to form a seamless overlapping continuous surface. The tirewell preforms also overlap to structurally tie the two braking sidewalls together forming one continuous structure. Reinforcing the apexes and spoke bed with continuous unidirectional carbon fiber bundles or ropes also contributes to strength. In this manner, strength, stiffness and mass are balanced rather than concentrated at certain points.

[00037] The overlapping ends of the tire well preforms provide junctions between adjacent fiber orientations, with more fibers at the junction. Of course the compression of the molding process coupled with effective curing of the plastic resin results in a solid structure, even with the junctions, seams and overlaps.

[00038] The rim of this invention relies primarily on an inner layer of high modulus fiber reinforcement in a thermoset plastic matrix. Excellent structural performance is obtained with carbon fiber in an epoxy matrix, although other combinations are not intended to be excluded.

[00039] In keeping with the high performance molding techniques used, and a high fiber areal weight, the structural and mechanical characteristics of carbon fiber bear significantly on the mechanical properties of the braking surface, should the braking surface be comprised of the same fiber reinforced plastic as the structural layer. The high modulus, extremely hard and stiff carbon has a low coefficient of friction when exposed to elastomeric caliper brake pads such as those used on bicycles. As the carbon comprises about 60 to 70 percent or more of the structure, (preferably 65/35 carbon to resin by weight) brake surfaces have been an inherent problem for carbon fiber bicycle wheel rims. In the invention herein, the entire exterior surface of the wheel is a separate lamination formed of a glass fiber scrim in an epoxy matrix. The glass provides some structural strength, but it is negligible when compared to the carbon fiber structural base laminations. The major structural effect is mainly to maintain the outer layer intact. The glass fiber scrim, however provides a superior braking surface. Because the outer layer and the inner base laminations are fibers in an epoxy resin matrix applied one over another prior to compression and curing, in the curing process, the epoxy forms a continuous matrix of chemically cross linked molecules. The outer, glass reinforced layer has the additional advantage of being easily machinable, as compared to a layer of carbon fiber reinforcing fibers. Carbon fiber machining causes substantial wear on tools.

In keeping with the adaptation of the instant rim to wheels used in demanding 'climbing' conditions - such as road races in mountain areas having thousands of feet of vertical changes - the completed wheel can be formed having complementary components with the traits of the rim. By comparison to 'aerodynamic' wheels, more spokes can be used. Mass in the rim can be reduced, with load being borne by spokes. Reduced mass helps the rider to devote power to greater speed on uphill climbs, while aerodynamic drag is not a substantial factor in speed riding downhill, and in fact distributing load over more spokes may assist in reducing wheel 'shimmy.¹ Thus, an all carbon wheel with integral hub spokes and rims may have only three large spokes, at a weight penalty. Even a high performance aerodynamic carbon rim wheel with separate hub, spokes and carbon fiber rim may have sixteen spokes. The instant rim can be advantageously built into a wheel having twenty front spokes and twenty four rear spokes. An offset spoke bed as taught in Patent No. 6,679,561 could be used.

[00042] In ordinary wheels, a standard sporting goods grade epoxy can be used for the prepreg materials from which the various layers are formed into prepregs. Because of the demands on the rims caused by braking, it has been discovered that a high temperature epoxy performs better. This insures that the structural integrity of the rim is maintained even on long downhill rides with extensive braking resulting frictionally created heat.

[00043] Bicycle wheel rims formed of a hollow section have typically been machined, such as by drilling, to provide access holes for spoke attachment. Spoke attachment typically involves lacing wire (or other elongate structure) spokes from hub to rim, and fastening a spoke nipple to the end of the spoke, threaded thereto, for tightening and adjustment or 'truing.' Point loads on the rim at the location of the nipple are substantial, so the load can typically be spread by use of a washer or eyelet. The size of the washer is limited by the size of the access hole, as is the ease of manipulation of the nipple, or, when automatically assembled, the size of the tools used for automatic wheel assembly.

[00044] Drilling access holes in a hollow carbon fiber reinforced plastic rim is a difficult operation given the size of the holes and the strength, stiffness and hardness of the carbon. Some breakage of the fibers at the edge of the hole also results in abrupt changes in strength and stress paths in the material. Further, these edges provide manipulation difficulty for the wheel assembler. In the instant invention, the molding and preform arrangement used utilizes molded access apertures. This could be and preferably will be expanded to include the valve hole and spoke holes. By forming these in the mold, superior manufacturing efficiency, tool utilization, ease of manipulation and assembly and improved structural integrity over drilled holes is gained.

[00045] The spoke bed 34 formed herein uses the strength properties of carbon fiber reinforced plastic, and the design utility in molding to have a spoke bed thinner than in other carbon fiber rims. Although thinner, the spoke bed is formed with sufficient width to enable spoke drilling at a 2.75 degree drill angle. The spoke holes, aligned with the aforementioned access apertures can also be formed with 0.100" stagger. This will provide greater lateral stability in the wheel, with the designed number of spokes, such that a lower wheel weight, particularly at the rim, will permit good high speed, downhill performance.

[00046] A bladder is used to mold this one piece, monocoque rim consistent with the teachings of Patent Nos. 5,624,519 and 6,270,104 and could be as simple as an inner tube or as complex as a specially formed conforming bladder.

Rim 10 is formed of an inner lamination 300 and an outer lamination 320. Lamination 320 overlies the entire rim, including tire well 12, apexes 14, 16 and extend under braking surfaces 22, 24 to walls 26, 28 and spoke bed 34. This will extend to a second bladder used in conjunction with the trapped rubber thermally expandable flexible insert which is used to form the tire well and hook bead shape in the clincher style rim. All bladders and insert are removable.

[00047] Braking surface laminations particularly advantageously use glass fibers having properties much different from high strength, high modulus carbon in the inner lamination 300. Braking surfaces 22, 24 perform best when used in conjunction with the highly developed bicycle caliper brakes, when surfaces 22, 24 are either formed in a precise mold or machined to a high level of smoothness and trueness. The carbon itself, however, provides a less desirably hard surface and generally does not perform optimally in demanding conditions such as long, fast mountain road downhill rides.

[00048] Brake surfaces 22, 24 are also subject to wear and damage when in use, particularly as a result of contamination by foreign objects such as sand, stones, road tar and the like.

[00049] The glass scrim has a more optimum coefficient of friction with typical elastomeric caliper brake shoes, thus the combination of materials provides a performance advantage. Glass reinforced plastic has improved thermal, frictional, and machinability properties

[00050] While the present invention has been disclosed and described with reference to a single embodiment thereof, it will be apparent, as noted above that variations and modifications may be made therein. It is, thus, intended in the following claims to cover each variation and modification that falls within the true spirit and scope of the present invention.

Claims

We claim:

1. A one-piece, hollow bicycle wheel rim formed of fiber reinforced plastic having first structural reinforcing fibers in a thermoset plastic matrix; said rim having a generally pentagonal sectional shape defined by a spoke bed, angled side walls, braking surface walls and a tire well; said braking surface walls being formed of second structural reinforcing fibers in a thermoset plastic matrix such that the braking surfaces of said braking surface walls provide for a higher coefficient of friction when subject to application caliper brake pads than is the coefficient of friction of walls reinforced solely with said first reinforcing fibers; said first reinforcing fibers being aligned in a composite layup in which a nominal line of substantially straight fibers in six layups, is spaced around the rim at substantially 60 degree arcs, so that the nominal line of fibers does not substantially deviate from parallel to a tangent to a circle defined by the outer edges of the rim; said rim is formed from a plurality of prepreg segments, with tire well pieces of said preforms tabbed to overlap to result in a solid wall, but hollow rim; said rim being formed from six prepreg segments per side, for a total of twelve, are formed surrounding a bladder, abutting or with slight overlap on each side and at the center plane, such that under curing pressure and temperature there is a continuous chemical bond in the preferred epoxy matrix; said six aligning the fibers with expected loads when the preferred 0 - 45 - 90 degree oriented fiber layups are used; said segments are staggered from side to side so that seams on one side do not line up transversely across from seams on the other side.

2. A one-piece, hollow bicycle wheel rim formed of fiber reinforced plastic having first structural reinforcing fibers in a thermoset plastic matrix; said rim having a generally pentagonal sectional shape defined by a spoke bed, angled walls, braking surface walls and a tire bed; said braking surface walls being formed of second structural reinforcing fibers in a thermoset plastic matrix such that the braking surfaces of said braking surface walls provide for a higher coefficient of friction when subject to application caliper brake pads than is the coefficient of friction of walls reinforced solely with said first reinforcing fibers; said first reinforcing fibers being aligned in a composite layup in which a nominal line of substantially straight fibers in six layups, is spaced around the rim at substantially 60 degree arcs, so that the nominal line of fibers does not substantially deviate from parallel to a tangent to a circle defined by the outer edges of the rim.

3. The rim of claim 2 further comprising:

Said rim is formed from a plurality of prepreg segments, tabbed to overlap to result in a solid wall, but hollow rim.

4. The rim of claim 2 further comprising:

Said rim being formed from six prepreg segments per side, for a total of twelve, are formed surrounding a bladder, abutting or with slight overlap on each side and at the center plane, such that under curing pressure and temperature there is a continuous chemical bond in the preferred epoxy matrix.

5. The rim of claim 4 further comprising: said six segments substantially aligning the fibers with expected loads when the preferred 0 - 45 - 90 degree oriented fiber layups are used.

6. The rim of claim 5 further comprising: said segments are staggered from side to side so that seams on one side do not line up transversely across from seams on the other side.

7. The rim of claim 2 further comprising: said tire well is formed and arranged to receive a tubular tire.

8. The rim of claim 2 further comprising: said tire well is formed and arranged to have outwardly extending flanges ate the apexes adapted to receive a clincher tire.

9. A fiber reinforced composite circular wheel rim for supporting a tire comprising: a hollow sectional shape defined by a spoke bed with angled walls extending outwardly therefrom, said walls merging into concavities; brake surfaces extending outwardly from said concavities and said brake surfaces ending in apexes; said apexes having a tire well extending therebetween; said rim formed and arranged in a one piece hollow fiber reinforced composite structure from a plurality of laminated segments joined and overlapped to form said structure; said segments being formed of straight, unidirectional fibers; each of said segments having a reference fiber line parallel to said fibers; said rim having a circular perimeter; said segments all having said reference fiber line diverging from any tangent to said perimeter by less than about 15 degrees.

10. The rim of claim 9 further comprising: said rim is formed of a plurality of high modulus fibers in a thermoset plastic matrix;

said fibers are formed in multiple laminations of unidirectional fibers, each of said laminations having its fibers aligned in crossing relation to each adjacent lamination.

11. The rim of claim 10 further comprising: said fibers in said multiple laminations having its fibers aligned in crossing relation to each adjacent lamination in a relationship of about 45 degrees.

12. The rim of claim 11 further comprising: said rim has an exterior surface; the seams between said six segments and said staggered six segments being arranged so seams between them are nonaligned.

16. The rim of claim 15 further comprising:

said rim being formed of a hollow optimum compaction, low void structure wherein the fiber to resin ratio is greater than 65/35 by weight. said laminations being compacted one against the other and cured to provide a structure having multiple overlapping fibers in a substantially monolithic thermoplastic matrix.

17. The rim of claim 9 further comprising:

said rim having a center plane defining a first half and a second half;

said segments being six in number forming a first uncured portion of said rim in said first half;

said second half having a corresponding, but staggered six segments;

the seams between said six segments and said staggered six segments being arranged so seams between them are nonaligned.

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