Background of the invention Typical bicycle wheels consist of a hub supported by spokes within a circular rim. Spokes are the connecting rods between the bicycle hub and the rim. Spokes support the weight of the bike and rider and are used in tension to connect the hub and the outer part of the rim. As the wheel rotates, the spokes are continuously subjected to compressive (at the bottom) and tensile (at the top) stresses. These cyclical stresses cause problems both in the structural portion of the spoke as well as in the fittings, which attach the spoke to the rim and hub.

Consequently, the mechanical properties of the, spoke, in particular its elastic resistance and tractional rigidity, are critical elements for the structural strength of the wheel. Other critical elements include the number of spokes and the weight of each spoke that are necessary to give adequate structural strength to the wheel. The assembly of spokes within the wheel system also forms the critical elements of the support structure for the wheel and is primarily responsible for the strength and performance characteristics of the wheel.

In prior art devices, the spokes were generally fabricated from steel or some other metal alloy, and their composition has been dictated by the fact that spokes represent stress concentration points along the circumference of the rim. Generally the number of metal spokes were deliberately minimized to reduce the weight of the wheel while maintaining its structural strength. This approach increased the distance between adjacent spokes and creates a high stress along the axis of the spoke. As a result the spokes may break or have to be strengthened by adding any variety of mechanisms to the wheel. The latter alternative frustrates the initial objective of weight reduction. Another problem of metal alloy spokes is that under too great an amount of stress they may fail and this is often exacerbated by the inflexibility of metal spokes.

In recent times, in an effort to decrease the weight of bicycle wheels, spokes have been made of different material such as composite polymers. US Pat. No. 6,036, 281 described a bicycle wheel system having spokes, wherein the body of said spokes are constructed from a bundle of liquid crystals fibers surrounded by an extruded plastic jacket. In the process of making said known spoke, the plastic jacket is stripped and cut at both ends of said spoke body, exposing the fibers at said ends, which are further immersed in a thermosetting adhesive.

Said process of cutting or stripping the plastic jacket is not easy to implement and is a delicate process which can provide with weakened points in the spoke described and even damage the inner liquid crystal fibers.

A main object of this invention is to provide with improved spokes for bicycle wheels, which are light and strong enough to provide a durable support element for hub and rim wheels.

Another object is to provide with spokes wherein the connecting ends to the rim and hub are strong and resistant. A further object is to provide with an improved method for making spokes having the above-mentioned qualities.

Summary of the invention The present invention therefore relates in a first aspect to spokes which are made essentially of reinforced carbon fibers or a combination of reinforced carbon fibers with other fibers which are pultruded to form a longitudinal axis having a first and second end. In a second aspect the invention relates to spokes for use in a bicycle wheel, said wheel consisting of a hub, a rim and a set of spokes. In a third aspect the invention relates to a method for the preparation of a spoke joining a plurality of fibers or filaments of which at least one is a reinforced carbon fiber, forming a spoke body by pultruding said fibers or filaments, said body consisting of a first end, a second end and an intermediate body part. The spoke is further provided with an axially displaceable rim fitting and hub fitting for the attachment of said spoke to the hub and the rim respectively. Said fittings are provided concentrically and axially around the spoke body, with a degree of freedom such that they can shift in the longitudinal direction along the axis of the body for a suitable fixation to the rim and hub. Once the end parts of the spoke have their final shape, the fittings will be shifted up to a position wherein they can attach the spoke to the rim and the hub. The spokes according to the invention have the advantage of being lighter with respect to conventional spokes and nevertheless have the same ability of

being adjusted as any conventional metal spokes. A further advantage of said spokes is that the spoke body may be shaped into conventional cylindrical shape, but also into any suitable aerodynamic shape.

The main advantage of carbon fibers in the spokes is their strength and ability to compensate the compressive and tensile stresses.

The carbon composite material is preferably a matrix material which is typically a thermoset or thermoplast such as epoxy, polyester, polypropylene, polyurethane, polyamides, polyvinylester, etc likely to comprise strands of carbon fibers. In an embodiment of the present invention, said composite material is a carbon based or a metal based matrix material.

In another embodiment of the present invention, said composite material is a polymer impregnated fiber material. The polymer may comprise either a thermoset polymer or a thermoplastic polymer, as desired. The crank is preferably comprised of composite material made of a thermoplastic impregnated fiber material, or a polymer impregnated carbon fiber material. The primary choices are carbon or carbon composite materials. Aramids (aromatic nylons) may be used in combination with carbon. Aramide filaments are prepared by condensation of a diamine and terephthalic acid, a carboxylic acid that contains a hexagonal benzene ring in its molecules. Other reinforced materials as filaments such as carbon nanotubes can also be used. The close packing of the aromatic polymer chains produced a strong, tough, stiff, high-melting fiber for radial tires, heat-or flame-resistant fabrics, bulletproof clothing, and fiber-reinforced composite materials. Examples are Nomex 6D and Kevlar @ (both own by Dupont).

In a preferred embodiment filaments are joined by twisting prior to the pultrusion. In a yet more preferred embodiment the central filament is a reinforced carbon filament on which Kevlar0 filaments are winded. Parallel alignment of the fibers or the filaments is also an alternative.

The present invention relates further to a method for constructing a spoke for a high performance bicycle wheel, said wheel consisting of a hub supported by spokes from a rim, comprising the steps of: joining a plurality of fibers of which at least one is a reinforced carbon

fiber pultruding said strand into a tubular shape to form a spoke body, cutting or sawing said spoke body into predetermined lengths suitable for use as a spoke, said spoke having a first end, a second end and an intermediate body part, and feeding the spoke around a rim fitting and a hub fitting suitable for connecting the spoke body to the rim and hub respectively and processing said first and second end to obtain outward conical alike shaped first and second end.

The main step in the invention is the incorporation of carbon reinforced fibers in the spokes. A suitable method is pultrusion. Pultrusion is known in the art. Conventional pultrusion is a continuous process of producing composite materials of constant cross-sectional area and is a relatively automated process. The pultrusion equipment consists in general of a fiber or filament delivery system, a resin bath, preform fixtures, a heated die, synchronized pullers and a cut-off saw. The fibers or filaments are passed from a creel and pulled through a resin bath where they are impregnated with the resin. Since polyesters, vinyl esters and epoxy resins possess desirable electrical, chemical and thermal properties, they are a natural choice for many pultruders. Some of the most commonly used filaments or fibers in pultrusion are fiberglass, graphite, aramid fibers and carbon fibers. The resin-embedded fibers are then pulled through the preform fixtures which contour the fiber/resin combination to the desirable shape and align the fibers. In the present invention pultrusion is performed on a plurality of filaments of which at least one filament is a carbon filament. This plurality of filaments might be joined in a parallel alignment or they might be partially or completely twisted. The most preferred embodiment according to the present invention is a straight aligned carbon filament on which several KevlarO filaments are winded.

After passing through the preforms, the fibers and uncured resin then pass through a heated e. g. chrome-plated tool steel die. The entrance area of the die is sometimes water cooled to prevent premature resin coagulation at the die entrance. Multiple sets of heaters in direct contact with the die are used to heat the die to the desired temperature profile. The heater temperatures can be controlled to achieve a desired temperature profile along the length of the die. The heat from the die wall initiates an exothermic chemical reaction in the resin, thereby causing the matrix to gel. As the exothermic chemical reaction continues to release heat, the interior of the composite can attain a temperature that is greater than the die wall temperature. The finished product exiting the die is a highly cured product that requires

minimal post-fabrication processing. The cured product is extracted from the die by a set of pullers and directed towards a saw to be cut into useable segments.

It is important to understand that many processing parameters can influence the integrity of a finished composite. Proper choice of pull speed, correct die wall temperatures, optimum fiber volume, selection and compatibility of fibers and matrix, good packing of fibers, kinetic properties of the resin and proper resin impregnation play instrumental roles in terms of product quality. These finished composites may be thermoset or thermoplast.

The primary choice for the filaments are carbon or carbon composite filaments. Aramids (aromatic nylons) may be used in combination with carbon. Aramide filaments are prepared by condensation of a diamine and terephthalic acid, a carboxylic acid that contains a hexagonal benzene ring in its molecules. The close packing of the aromatic polymer chains produced a strong, tough, stiff, high-melting fiber for radial tires, heat-or flame-resistant fabrics, bulletproof clothing, and fiber-reinforced composite materials. Examples are Nomex @ and Kevlar @ (both by Dupont).

It is known that carbon filaments are high-strength materials that are used as reinforcing agents in composites. Carbon fibers are produced by using heat to chemically change rayon or acrylic fibers. Carbonization occurs at temperatures of 1000°C to 2500°C (1832° to 4532°F) in an inert atmosphere. Carbon fibers are converted to graphite at temperatures above 2500°C. Carbon and graphite fibers can also be made from pitch, a residual petroleum product. Products that use carbon fibers include heat-shielding materials, aircraft fuselages and wings, spacecraft structures, and sports equipment. High-strength fibers such as aramid and polyethylene are also used in armor applications such as bullet-resistant garments, car doors, and crew seats for military helicopters and aircraft. Once the spoke body is (pre) formed the two end parts will be reshaped such that they will be provided with a conical or V-shaped end portion. A thermoset spoke body will preferably be reshaped by a second moulding operation. A part of the ends will be enlarged in the surface area for providing anchoring points to the extra fibers provided conically around the end parts. A thermoplast spoke will preferably be reshaped by a heating step in which the end part will be reformed into a conical hollow part. The hollow cavity, when existent, will then be refilled with a suitable filler, such as thermoset or thermoplastic material.

The present invention also relates to bicycle wheel, comprising a set of spokes according to the invention.

In the following detailed description, reference is made to the accompanying figures, in which is shown by way of illustration, specific embodiments in which the invention may be practiced.

Brief description of the drawings Figure 1 represents a cross-sectional side view of a spoke according to a preferred embodiment, showing the fittings in section and the connections between the spokes, fittings, hub, and rim; Figure 2 represents a frontal view of a plurality of reinforced carbon fiber forming a strand in their mold ; Figure 3 represents a cross-sectional view taken along the line 1-1 in figure 2; Figure 4 represents a frontal view of a spoke body according to a preferred embodiment, with its mold for modifying first and second ends of said spoke into a threaded like structure; Figure 5 represents a frontal view of a molding process of said spoke according to a preferred embodiment; Figure 6 represents a frontal view of a molding process of said spoke according to another embodiment; Figure 7 represents a frontal view of a cross-sectional side view of a molding process of said spoke according to a preferred embodiment.

Detailed description The present invention relates to a spoke for bicycle wheel wherein said spoke comprises a plurality reinforced carbon fibers twisted in a single strand forming the spoke body. Figure 1 represents a preferred embodiment according to the invention and for clarity of illustration, the relative dimensions of said figure are exaggerated. As shown figure 1, the present invention relates preferably to a spoke (1) which is constructed of a plurality reinforced carbon fibers (2) twisted into a single strand, forming a spoke body having a first end (4), a second end (5) and an intermediate body part (3). Said spoke is further provided with a rim fitting (6) and hub fitting (7) for the attachment of said spoke to the hub (8) and the rim (9) respectively. These fittings (6,7) are concentrically shifted around the body (3) prior to the final deformation of the end parts (4,5).

The rim fitting (6) and hub fitting (7) have an internal passage extending axially through the fitting, with a conical portion (10) and a tubular portion (11) and wherein said first (4) and second ends (5) have an outward conical shape fitting into the conical portion (10) of said fittings.

According to a preferred embodiment of the invention the spoke (1) is essentially constructed of reinforced carbon fibers (2) which are thermoplastic or thermoset. The specific consequences of the use of thermoplastic or thermoset and their typical advantages are known by the skilled man and will not be further illustrated in the present application.

The present invention further relates to a method for constructing said spoke wherein preferred embodiments are illustrated Figures 2-7.

In a first step of said method, as shown Figure 2, a plurality of reinforced carbon fibers (2) are twisted into a single strand (12) which is further extruded in a tubular shape in a known molding process (13) to form a spoke body using a tubular mold (14). The molding process is done according to techniques known in the art. The present molding process allows the production of a tubular shaped strand. The choice of the shape and more in particular the cross-sectional shape of the spoke is function of the aerodynamic properties which are desired for the spoke, such as cylindrical or ellipsoidal and may vary along the strand. Any form, using an appropriate mold is possible.

The next step in said method consists of cutting said tubular body into predetermined lengths suitable for use as spokes, having a first end (4), a second end (5) and an intermediate body part (3).

The next step consists of providing concentrically around the spoke body (3) a rim fitting (6) and a hub fitting (7) for connecting the spoke body to the rim (9) and hub (8) respectively wherein said fittings have an internal passage extending axially through the fitting, with a conical portion (10) and a tubular portion (11). In the process of sliding said fittings (6) and (7), the spoke body is inserted through the fitting passage with the conical portion (10) of said passage oriented facing outwards towards said first (4) and second ends (5).

In a further step in said method, said first end (4) and second end (5) are processed to obtain outward conically shaped first (4) and second ends (5) which can then fit into the conical portion (10) of said fittings. In said process, said first (4) and second ends (5) are modified and further provided with reinforced carbon fibers in a manner as to obtain outward conical ends to fit in the conical portion (10) of said rim (9) and hub fittings (8).

According to a preferred embodiment, said first (4) and second ends (5), are modified by applying locally a radial pressure (15) to said ends molding them into a threaded like structure (16), as shown Figure 4. These corrugations are obtained because the resin has been tinned out. The surface of these portions is extended due to the corrugations which act as a suitable anchor for further reinforced carbon fibers. The next step consists of winding around the threaded or corrugated ends (16) reinforced carbon fibers (17) in a conical fashion and further molding (18) into a conical shape said processed first (4) and second ends (5) as shown Figure 5.

According to another embodiment, said first (4) and second ends (5), are modified by applying an axial pressure (19) to said ends, such that these ends disperse for example by a pressure mold, molding them into a hollow conical shape (20) as shown Figure 6. A specific mold is introduced, for example by a rotational movement in the end parts. In particular, the thermoplastic filaments will then due to an increase in temperature tend to form a conical deformation. The formed cavity will then be filled. In a later step, said processed ends (20) are provided in the cavity with for example reinforced carbon fibers filling (21) said outward hollow conical shape. Other filling materials may be resins, PU-polymers, adhesives, etc.

The thus obtained spokes have superior characteristics due to the properties of reinforced carbon fibers, such as being very light, but at the same time very strong and having ends which are able to endure tensile and compressive forces. A spoke constructed in the manner of the present invention will have many advantages even when employed in prior art wheel systems, but these advantages are optimized when employed in the wheel system of this invention. The obtained wheel system provides increased lateral stability, higher overall strength, reduced weight and superior performance by employing intertwined or intertwisted aligned fibers connected to receive a straight pull without torsional stress.

The present invention further relates to a high performance bicycle wheel system having radially inner and outer elements comprising: an outer circular rim constructed of high strength, low weight material, having a transverse cross section, constructed with a plurality of eyelets located on the inner portion of the cross section and spaced about the circumference of the rim, an inner cylindrical hub mounted on an axle for concentric rotation with the rim about the axis of the axle, said hub constructed with attachment means for connection to a spoke, a plurality of spokes, having a longitudinal axis, extending substantially radially outward from the hub to the rim, said spokes being connected to the rim through said eyelets and to said hub by said attachment means, said spokes comprising: a plurality of twisted reinforced carbon fibers, and a rim fitting and hub fitting to connect fitting said spoke to the hub and rim respectively and conical shaped ends fitting in said rim fitting and hub fitting.