A spoke for wire wheels, method of construction of said wheel and wheel thus obtained

DESCRIPTION Technical field of the invention The subject of the present invention is a spoke for a wire wheel of the type including the characteristics mentioned in the preamble of claim 1. Spokes including such characteristics are known from the production of the same Applicant and from the following documents: DE 4212094A1, EP 0860301, WO 2005/058613, DE 20319177 Ul, DE 20320152 Ul. State of the art

Recently, a marked interest has been shown in the market for wire wheels, in particular in the motorcycling sector, for wheels suitable for the fitting of tyres without inner tube (so-called tubeless) . Such tyres in fact have undoubted advantages of safety and lightness compared with conventional tyres with inner tube. They are therefore preferred for high speed use and for competitions .

However, the wheels suitable for such fitting present a problem, which is not easily solved, with regard to the need for a perfect air seal in the region of union between each spoke and the rim. The seal is complicated by the dynamic effects on the spoke inasmuch as the spoke is subjected to possible radial sliding, although of limited magnitude, relative to its mounting seat in the rim, owing to the localised deformation occurring on the rim under load.

The same Applicant has perfected a technical solution for mounting between rim and spokes which solves the aforesaid problem. This system is based on the fact that the end portion of the spoke, which is received in a through-hole in the rim (where a radial bulge towards the

inside of the rim is customarily arranged) has a circumferential seal between its outer cylindrical wall and the wall of the hole such as to guarantee the air seal even in the present of limited axial displacements of the spoke with respect to the rim. The axial displacements are also limited by a snap ring mounted on the end portion of the spoke (or nipple) outside the rim. However, some problems remain unsolved with regard to any drilling inaccuracies of the rim or variations in the thickness of same as a result of which interference could occur between the snap ring and the rim.

Typically, it is possible for a hole significantly misaligned with respect to the centre of the bulge to impede the seating of the snap ring in its natural seat with the spoke (or nipple) fitted.

Moreover, the aforesaid technique requires accurate machining of the holes in the rim, and also optional prolongation of same by means of special processing

(fusion bit) . Taking into account the fact that any machining faults, even of a single hole, have an adverse effect on the sealing capacity of the entire wheel, it is clear that the construction of the wheel is tricky and subject to many critical factors. Description of the invention The problem underlying the present invention is that of providing a spoke for wheels that is structurally and functionally designed so as to allow all the drawbacks mentioned with reference to the prior art cited to be remedied. This problem is solved by the invention by means of a spoke produced according to claims 1 to 10.

Advantageously, the invention proposes to allow pre- assembly of spokes and seats which must receive them in a sealed manner on the rim. In addition, it is proposed to simplify this assembly and make it available without requiring complex equipment. This is achieved with the method of claims 11 to 15. Brief description of the drawings

The characteristics and advantages of the invention will become clearer from the following detailed description of a preferred, but not exclusive, exemplary embodiment thereof, illustrated by way of non-limiting example with reference to the appended drawings, in which :

Figure 1 is a view in longitudinal section of a spoke according to the present invention;

Figure 2 is a sectional view of a rim in which is embedded a bush arranged to receive an end portion of the spoke of the preceding figure;

Figure 3 is a sectional view of the assembled spoke and rim.

Preferred embodiment of the invention

In the drawings, the reference 1 indicates as a whole a wire wheel of the type including a rim 2 and a hub (not shown) interconnected with one another by a plurality of spokes 3 produced according to the present invention. Each spoke 3 includes an end portion 4 which may be produced integrally with the spoke itself, or separately therefrom (preferred example) . When the end portion 4 is produced separately from the stem 5 of the spoke, the end portion is screwed adjustably onto a threaded section 6 of the stem 5 by means of a threaded blind hole 6 thereof. In this second example, the end

portion 4 of the spoke is also designated by the term "nipple" .

A bush 7 is arranged to be inserted (or embedded) in a through-hole 8 of the rim 2. The bush is associated with the corresponding spoke such that the bush can be arranged directly on the end portion 4 (Fig. 1) or previously embedded in the rim (Fig. 2) in order to arrange for the fitting of the spoke 3.

In the bush 7 a seat 10 is defined in which the end portion 4 of the spoke is received with the capability of limited axial sliding between a first and a second shoulder 11, 12, axially spaced and capable of abutting against corresponding axially opposed abutment surfaces 13, 14 on the bush 7. The first shoulder 11 is constituted by a hemispherical ball-type surface defined on a flange 15 located in proximity to an operating head 16 of the portion 4; the second shoulder 12 is defined by a snap ring (Sieger ring) received in a corresponding annular depression 17 of the part of the portion 4 nearest the stem 5.

The abutment surface 13 is configured in a cup-shape to receive the ball-type configuration of the shoulder 11. The second abutment surface 14 is the opposed flat end face of the bush 7. The distance between the first and second shoulder on the end portion 4 is greater than the distance between the abutment surfaces on the bush so that the end portion 4 can move axially in the bush in the event of deformation of the rim. In this way, deformations or breakages in the corresponding spoke 3 under dynamic load are avoided.

Between the bush 7 and a section 18 of cylindrical wall of the end portion 4 a sealing gasket 19 of the 0- ring type is interposed, preferably received in an annular depression 20 of the bush. The gasket 19 may also be received in a depression on the portion 4. Between the bush 7 and the corresponding hole 8 in the rim a second gasket 25 is interposed, received in a depression 21 of the bush. In this way a complete air seal is produced between spoke, bush and rim. The bush 7 also has in proximity to the abutment surface 14 a tapered (conical) section 22 capable of cooperating with a corresponding conical section 23 of the portion 4 in order to deform radially a lip 24 of the bush 7 and facilitate the retention thereof in the hole 8. Provision is also made for the bush 7 to be retained otherwise in the hole 8 by forcing, adhesive securing, mechanical deformation, rivetting, screwing or by some other means .

On the opposite side from the lip 24 the bush has a collar 25 such that, once embedded in the rim 2, the bush is held in two directions.

In order to construct a wire wheel according to the invention, a rim and a hub are interconnected with one another by a plurality of spokes 3 as indicated above. The bushes 7 may be pre-assembled on the end portions 4 of the spoke or slipped separately into the holes 8 of the rim 2. The bushes are then locked in the holes in the rim by plastic deformation of the lip 24. This deformation may be brought about by screwing the end portion 4 onto the stem of the spoke so that, as a result of the traction exerted, the deformation means and complememtary means constituted by the conical sections

22, 23, by interfering with one another, cause the lip 24 to be deformed radially towards the outside, thus locking the bush.

The invention described solves the problem posed, obtaining numerous advantages, including that of permitting greater tolerances in the machining of the holes 8 on the rim 2, both as far as the positioning of each hole with respect to the corresponding bulge on the rim is concerned, and as far as the dimensions of the hole itself are concerned. Furthermore, prolongation by means of the use of special processing, of the holes to be made, is not required.

The present invention therefore solves the problems mentioned above with respect to the prior art cited.