Abstract:
A clamp for fixing a seat post to a seat tube provided with a slit in a longitudinal vertical plane. The clamp has a pair of deformable branches defining a through hole having a cylindrical inner surface; a slit between the elastically deformable branches; and a tightening screw that draws up the two facing surfaces and reduces the diameter of the cylindrical inner surface.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a clamp for fixing a seat post to a seat tube of a bicycle. 
     As is known, the saddle of a bicycle is carried by a tubular element (seat post) which is slidably inserted inside a vertical tube, namely, the seat tube, of the bicycle frame. The seat tube carrying the seat post is provided with a through slit made in an end portion of the tube, which bestows on said end portion characteristics of elastic deformability in the radial direction. The end portion of the seat tube is tightened against the outer surface of the seat post by means of a clamp having a slit which is set aligned to the slit of the seat tube and which is radially compressed by means of a screw which brings two elastically deformable branches of the clamp up to one another. For aesthetic reasons, the tightening screw is set on the side of the seat tube that faces the rear part of the bicycle. 
     Recently there have been introduced on the market seat posts made of carbon fiber, which consist of a fiber fabric embedded in a matrix of plastic material. A seat post made of carbon fiber makes it possible to obtain a reduction in weight as compared to a component having the same characteristics which is made, for instance, of an aluminium alloy or similar light alloys. 
     The traditional solution described previously for fixing the seat post to the seat tube presents a serious drawback in the case where the seat post is made of a carbon-fiber fabric embedded in a matrix of plastic material. The present applicant has found that, when a clamp of a traditional type is tightened around the end portion of the seat tube, the two internal edges defined by the through slit of the seat tube are deformed inwards and tend to cut into the outer surface of the seat post. These incisions form points of initiation of failure, which in certain cases may lead to failure of the seat post. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to overcome the aforesaid drawback by providing a simple and effective solution that does not entail the need to modify the seat tubes with respect to current solutions and that makes it possible to keep the tightening screw set in the rear part of the seat tube. 
     According to the present invention, the above purpose is achieved by a clamp having the characteristics specified in claim  1 . 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described in detail with reference to the attached drawings, provided purely by way of non-limiting example, in which: 
     FIG. 1 is a schematic perspective view illustrating a seat-post assembly provided with a clamp according to the present invention; 
     FIG. 2 is a cross-sectional view according to the line II—II of FIG. 1; 
     FIG. 3 is an elevation according to the arrow III of FIG. 2; 
     FIG. 4 is a cross-sectional view similar to that of FIG.  2  and illustrating a second embodiment of the present invention; and 
     FIG. 5 is an elevation according to the arrow V of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 1, number  10  designates, as a whole, a seat-post assembly for a bicycle, comprising a seat tube  12 , a seat post  14  and a clamp  16 . 
     With reference to FIG. 2, the seat tube  12  has, in a traditional way, a through slit  18  which extends as far as the top end of the seat tube  12 . The through slit  18  is set in a longitudinal vertical plane the trace of which, in the plane of representation of FIG. 2, is indicated by the axis A. The slit  18  is situated on the side of the seat tube  12  that faces the rear part of the bicycle. 
     The clamp  16  is made of metal material, such as aluminium or one of its alloys, and has a cylindrical surface  20  designed to compress from outside the top end portion of the seat tube  12 . The clamp  16  has a through slit  22  which defines two elastically deformable branches  24   a ,  24   b . The two deformable branches  24   a ,  24   b  are elastically brought up to one another so as to reduce the diameter of the cylindrical surface  20  by tightening a screw  26 . According to the present invention, the clamp  16  is configured in such a way that, in an assembled configuration in which the screw  26  is set in a position corresponding to the slit  18 , the slit  22  opens out onto the cylindrical surface  20  in a position that is displaced with respect to the slit  18  of the seat tube  12 . Tests carried out by the present applicant have shown that the misalignment between the slits  22  and  18  guarantees that, during tightening of the screw  26 , the end portion of the seat tube  12  will close radially without producing a deformation inwards of the edges  28 . 
     In the embodiment illustrated in FIG. 2, the slit  22  of the clamp  16  has two surfaces  30   a ,  30   b  facing one another, which are plane, parallel to one another and inclined with respect to a plane orthogonal to the longitudinal axis A of the tightening screw  36 . The direction of the screw  36  is determined in such a way that the surfaces  30   a ,  30   b  facing one another of the slit  22  remain constantly parallel to one another during tightening of the screw  26 . Thanks to the configuration of the clamp  16 , the mutual approach of the two facing surfaces  30   a ,  30   b  takes place without producing a concentration of forces on the edges of the seat tube  12  that are adjacent to the slit  28 . This makes it possible to obtain radial closing of the seat tube  12  with a mutual approach in the tangential direction of the edges facing one another of the slit  18 , without any deformation inwards of the edges  18 . In this way, the risk is eliminated of producing incisions on the outer surface of the seat post  14 , which could lead to initiation of failure. 
     FIG. 4 illustrates a variant of the clamp according to the present invention. The items corresponding to the ones previously described are designated by the same reference numbers. Unlike in the embodiment previously described, the screw  26  extends according to an axis transverse to the longitudinal axis A. Also in this variant embodiment, the slit  22  of the clamp is displaced in the tangential direction with respect to the slit  18  of the seat tube  12 . Also in this case, the mutual approach between the two surfaces  30   a    30   b  facing one another of the slit  22  is along a direction tangential to the tube and in a position that does not entail a concentration of forces on the edges  28  of the seat tube  12 . The main difference with respect to the embodiment described previously is that in the present case the surfaces  30   a ,  30   b  facing one another of the slit  22  are step-like surfaces with respective end portions which are parallel to one another. The end portions that open out onto the inner cylindrical surface are substantially orthogonal to the axis of the screw  26 , i.e., they are substantially parallel to a plane orthogonal to the axis of the screw, but could also be inclined with respect to said plane. 
     Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to what is described and illustrated herein, without thereby departing from the scope of the present invention as defined in the ensuing claims.