Trunnion for half-toroidal-type continuously variable transmission and method for working same

Abstract

While rotating a spindle 34 , the circular hole 15 is worked using a cutting tool 39 . Before or after the working operation of the circular hole 15 , a chuck 36 is translated in a direction perpendicular to the rotation center axis of the spindle 34 by a slider 35 . And, the flat surface 29 as well as the stepped surfaces 31, 31 and inner surfaces 38, 38 , which are respectively composed of partially tubular surfaces, are cut or worked.

What is claimed is:  
     
         1 . A trunnion of a half-toroidal-type continuously variable transmission, comprising: 
 a middle portion having a flat surface on an inner surface thereof; and    a pair of pivot shafts respectively disposed on the both end portions of said trunnion and being concentric with each other,    wherein a circular hole is formed in a part of said flat surface, with one end thereof opened,    wherein, in said flat surface, there are formed stepped surfaces in the boundary portions between the peripheral edge portions of said flat surface and the remaining portion thereof,    said stepped surfaces respectively define partially tubular surfaces having a single center axis, and    wherein said single center axis of said partially tubular surfaces is located at a position offset from a center axis of said circular hole in a direction in which said pair of pivot shafts are arranged.    
     
     
         2 . A trunnion for a half-toroidal-type continuously variable transmission according to  claim 1 , further including: 
 a pair of bent portions respectively formed in the both end portions of said trunnion in the longitudinal direction thereof,    wherein the inner surfaces of said pair of bent portions respectively define partially tubular surfaces having the same center axis as said stepped surfaces of said flat surface.    
     
     
         3 . A trunnion for a half-toroidal-type continuously variable transmission according to  claim 1 , wherein the center axis of said stepped surfaces of said flat surface and said inner surfaces of said bent portions and the center axis of said circular hole are respectively perpendicular to the center axis of said pair of pivot shafts.  
     
     
         4 . A trunnion for a half-toroidal-type continuously variable transmission, comprising: 
 a middle portion having a flat surface formed in an inner surface thereof, for mounting thereon thrust bearings, said thrust bearings allowing said power rollers forming a part of said half-toroidal-type continuously variable transmission to be swiningly shifted, while supporting a thrust load applied to power rollers; and    a pair of pivot shafts respectively disposed on the both end portions of said trunnion and being concentric with each other, for supporting said power rollers in such a manner as to be swingingly shiftable and rotatable,    wherein a circular hole is formed in part of said flat surface, with one end thereof opened,    wherein, in said flat surface, there are formed stepped surfaces in the boundary portions between the peripheral edge portions of said flat surface and the remaining portion thereof,    said stepped surfaces respectively define partially tubular surfaces having a single center axis, and    wherein said single center axis of said partially tubular surfaces is located at a position offset from a center axis of said circular hole in a direction in which said pair of pivot shafts are arranged.    
     
     
         5 . A method for working a trunnion for a half-toroidal-type continuously variable transmission, said trunnion comprising: 
 a middle portion having a flat surface formed on an inner surface thereof; and    a pair of pivot shafts respectively disposed on the two end portions of said trunnion and being concentric with each other,    wherein a circular hole is formed in a part of said flat surface, with one end thereof opened,    wherein, in said flat surface, there are formed stepped surfaces in the boundary portions between the peripheral edge portions of said flat surface and the remaining portion thereof,    said stepped surfaces respectively define partially tubular surfaces having a single center axis, and    wherein said single center axis of said partially tubular surfaces is located at a position offset from a center axis of said circular hole in a direction in which said pair of pivot shafts are arranged,    said method, comprising the steps of: 
 holding said trunnion by a chuck supported on the leading end portion of a spindle of a machine tool performing a cutting operation in such a manner that the center axis of one of said circular hole and said partially tubular surfaces is coincident with or parallel to the center axis of said spindle;  
 working one of said circular hole, said partially tubular surfaces and said flat surface of said held trunnion, while rotating said spindle;  
 moving said chuck in a direction which is perpendicular to the center axis of said spindle and is parallel with the arranged direction of said pivot shafts of said trunnion; and,  
 working the other of said circular hole, said partially tubular surfaces and said flat surface of said trunnion, while rotating said spindle.