Hollow crank arm for a bicycle and process for manufacturing the same

Abstract

A hollow crank arm for a bicycle comprising a body of elongated shape, at the ends of which are formed, respectively, an area for connection of the bottom bracket spindle and an area for connection of the pedal. The body includes a cavity of elongated shape and two solid end portions which are the aforesaid connection areas for the bottom bracket spindle and for the pedal. The crank arm is preferably formed through a forging process.

1 . A process for the production of a hollow crank arm for a bicycle having an area for connection to the bottom bracket spindle and an area for connection of the pedal, wherein it forms a cavity and two solid end portions containing said areas located on opposite sides of said cavity.  
   
   
       2 . A process according to  claim 1 , wherein it comprises the step of forming the cavity with an opening that opens onto the area between the solid portions.  
   
   
       3 . A process according to  claim 1 , wherein it comprises the steps of forming holes for fixing the bottom bracket spindle and the pedal which do not communicate with the cavity.  
   
   
       4 . A process according to  claim 2 , wherein it comprises the step of closing the opening.  
   
   
       5 . A process according to  claim 4 , wherein it comprises the steps of forming a flap for integral closing which extends in the proximity of said opening and of fixing said flap along at least one part of an edge of the opening.  
   
   
       6 . A process according to  claim 5 , wherein the fixing of said flap is carried out by welding or bonding.  
   
   
       7 . A process according to  claim 6 , wherein it comprises the steps of: providing a separate closing element having a shape suited for fitting to the opening and fixing said closing element to the body.  
   
   
       8 . A process according to  claim 1 , wherein the cavity is obtained by means of hot drawing with a punch.  
   
   
       9 . A process according to  claim 1 , wherein the cavity is formed by fixing a closing element to a body in which a lowered area has been formed.  
   
   
       10 . A process according to  claim 9 , wherein the closing element is fixed to the crank arm body by means of welding or bonding.  
   
   
       11 . A process according to  claim 9 , wherein the lowered area is formed by machining with removal of material or plastic deformation.  
   
   
       12 . A process according to  claim 1 , wherein the body is formed by casting in a die and in that the cavity is formed by a filling element positioned in the die prior to casting of the molten material.  
   
   
       13 . A process according to  claim 12 , wherein the filling element is a core of porous material which remains inserted in the crank arm body.  
   
   
       14 . A process according to  claim 12 , wherein the filling element is extracted from the body of the crank arm after solidification of the molten material.  
   
   
       15 . A process according to  claim 1 , wherein the body is formed by the crosslinking, in a die, of a structural-fibre-based fabric embedded in a matrix of plastic material, in which the fibres are chosen in the group comprising carbon fibres, glass fibres, aramidic fibres, boron fibres, ceramic fibres, or any combination thereof.  
   
   
       16 . A process according to  claim 15 , wherein the cavity is formed by providing an extractable expandable core.  
   
   
       17 . A process according to  claim 16 , wherein the expandable core is made of thermally dilatable material.  
   
   
       18 . A process according to  claim 16 , wherein the cavity is formed by providing an inflatable element.