Wheel spoke

A wheel spoke includes a shaft, a head at an axial end of the shaft, and a head rear surface on the face of the head which faces towards the shaft; the head rear surface has a plurality of alternating raised portions and recesses which can define a discontinuous contact surface.

CLAIM FOR PRIORITY

This application is a U.S. National Stage Application of PCT/EP2010/062683 filed on Aug. 31, 2010, claiming priority to Italian application PD2009A000253 filed Sep. 7, 2009, the contents of both of which are incorporated herein by reference.

DESCRIPTION

The subject of the present invention is a wheel spoke, a method of producing the spoke, and an open-matrix mould usable for the production thereof.

It is well known that a wheel spoke includes a shaft, a head at an axial end of the shaft, and a head rear surface on the face of the head which faces towards the shaft. Owing to manufacturing requirements and, in particular, to requirements for removal from the mould, the head of the spoke is moulded with a so-called open-matrix mould, that is, a mould which is composed of two or more parts that can be moved towards one another to an operative, closure position and moved apart to facilitate the removal of the spoke from the mould.

However accurate the coupling surfaces between the parts of the mould may be, they almost inevitably leave small amounts of flash or indentations on the head rear surface, in relief relative to the surface itself.

This flash may be particularly harmful when both the spoke and the wheel hub in which the seats for housing the heads are formed are made of relatively brittle and undeformable materials. In fact, in that case, the flash, which constitutes the sole point of support of the head rear surface in the hub seat, may produce stress peaks such as to damage the spoke to the extent of causing possible fracture thereof.

The current approach to solving this problem is to limit, flatten or somehow reduce the formation of flash during moulding to improve the distribution of the working load between the head rear surface and the seat which houses it. On the other hand, the way to eliminate the flash completely would be to use a closed-matrix mould which, since it would not have discontinuities, would enable a perfectly smooth head rear surface to be obtained.

However, the use of a closed-matrix mould conflicts with the practicality of removing the spoke from the mould. In fact, whereas removal is generally possible when moulding the spoke nipples which, since they are very short, can easily be removed from a closed-matrix mould by means of pin extractors or the like, the considerable length of the spoke shaft does not allow the same method to be used.

It is therefore almost unavoidable to use open-matrix moulds for the spokes and to accept any flash and its harmful consequences.

The problem underlying the invention is to minimize the adverse effects of any flash formed on the head rear surface during the moulding of the spoke.

Within the scope of this problem, an important objective of the invention is to improve the strength of the spokes in the head region.

Another objective of the invention, which is useful particularly for straight pull spokes (that is, spokes with the head coaxial with the shaft) or slightly elbowed spokes, is that of preventing rotation between the head of the spoke and the seat in which it is fitted when the spoke is under tension.

This problem is solved and these objectives and others which will be explained further below are achieved by the invention by means of a spoke formed in accordance with the appended claims.

InFIG. 1, a wheel spoke, generally indicated1, is of the type including a shaft2having a conventionally threaded end (not shown) and an opposite end having an enlarged head3. The head3is produced by the moulding of the spoke in an open-matrix mould, that is, a mould composed of two or more parts which can be moved towards one another to an operative, closure position and moved apart to facilitate the removal of the spoke from the mould.

Opposed faces5,6are defined on the head3. The face5that faces towards the shaft has a conical, so-called “head rear surface” on which flash7is inevitably though undesirably produced, owing to the unavoidably imprecise closure of the coupling surfaces of the mould parts.

When the spoke is fitted on the wheel, the head3is restrained in a hub (which is not shown since it is conventional per se) with the head rear surface5nested in a seat of the hub. In this condition, as a result of the substantially pulsating working load to which the spoke is subjected during the rotation of the wheel, overloads may be produced, which are caused by the projection of the flash7and which, in the long term, may cause fatigue fracture of the spoke and/or in any case stressing of the material.

A spoke according to a first embodiment of the invention is generally indicated20inFIG. 2. Details similar to those of the preceding drawing are indicated by the same reference numerals. The spoke20is of the straight pull type, that is with a shaft2that is coaxial with the head33, but the invention is also suitable for application to spokes with elbowed or partially elbowed spokes.

The spoke20differs from the spoke1substantially in that the head rear surface35bears a plurality of alternating raised portions and recesses21,22which can define a discontinuous surface (limited to the ridges of the raised portions) for contact with the juxtaposed surface of the hub seat in which it is nested. Although, in this case, the area of contact between the head rear surface35and the housing hub seat is reduced it has been found that the spoke thus produced has improved strength and reliability in comparison with spokes with conventional head rear surfaces.

The raised portions21and the resulting recesses22preferably extend radially (along the generatrices of the head rear surface, which is generally conical) with uniform thickness and rounded ridges of uniform radius (FIG. 2). They may also have a pitch which is smaller than the depth of the recesses42(a so-called “millerighe” profile—FIG. 3,FIG. 3also shows raised portions41, head43and head rear surface45), or the raised portions51may be formed with sharp edges with a uniform cross-section along their radial extent (FIG. 4, also showing recesses52, a head53and head rear surface55), or with a shape that is tapered from the shaft2towards the outer edge of the head63rear surface (FIG. 5, also showing recesses62and raised portions61).

In all cases it is necessary or at least preferable that any flash and/or consequent indentations at the closure lines of the matrix for the moulding of the spoke be concealed in respective recesses72moulded in the head73rear surface75in the region of each flash (FIG. 6). Raised portions are designated71inFIG. 6.

In a further embodiment of the invention, raised portions86and recesses87have a concentric, annular shape (FIG. 7, also showing head83) in combination with the recesses ofFIG. 6and/or in combination with the multiple raised portions and recesses of the embodiments ofFIGS. 2 to 5. In this case (FIG. 8), the raised portions96adopt the configuration of projections98distributed variously on the head93rear surface, the recesses inFIG. 8being designated97.

It has been found that, as well as resisting brittle fracture of the spoke shaft, the modification of the head rear surface in accordance with the teachings of the invention also effectively prevents rotation of the spoke relative to the seat in the hub; this is particularly advantageous with straight pull spokes, that is, spokes in which the shaft is entirely straight and coaxial with the head.

A further subject of the invention is a method of producing a spoke according to the embodiments described above, that is, a spoke produced by moulding with an open-matrix mould30a,30bwhich is potentially liable to form flash and/or indentations in the region of the matrix closure lines. The spoke is produced, as shown inFIG. 9, with the formation on the rear head surface105, of a plurality of alternating raised portions and recesses in which the said flash and/or indentations are concealed.

Finally, a subject of the invention is an open-matrix mould30a,30bfor spokes of the type including a shaft, a head at an axial end of the shaft, and a head rear surface on the face of the head which faces towards the shaft, wherein the mould comprises at least two opposed closure lines31a,31band at least one raised portion32in the region of each closure line, for imparting a corresponding recess22to the rear surface105of the spoke head.

The invention thus solves the problem posed and at the same time affords many advantages. In particular, as well as considerably reducing the risk of brittle fracture of the spoke in the head region, it also achieves the advantageous effect of preventing rotation of the spoke relative to the hub seat.