Patent Publication Number: US-2013239400-A1

Title: Method of Manufacturing Continuously Variable Transmission Variator Component and Chuck Apparatus for Manufacturing Variator Component

Description:
TECHNICAL FIELD 
     The present invention relates to a method of manufacturing a component of an automotive continuously variable transmission variator and to a chuck apparatus for manufacturing the variator component. 
     BACKGROUND ART 
     As shown in  FIG. 12 , ball splines are provided between a power transmission shaft  2  for transmitting rotation from an engine and an input disk  1  that is a component of the variator of a toroidal continuously variable transmission. These ball splines enable the input disk  1  to rotate in synchronization with the power transmission shaft  2  and also move relative to the axial direction of the power transmission shaft  2 . 
     As shown in  FIG. 13 , cylindrical portions  3   a  and ball spline grooves  3   b  are alternately formed in the circumferential direction on a cylindrical inner diameter portion  3  of the input disk  1 . Further, around the outer periphery of the input disk  1  are formed a traction surface  4  that is a power transmission surface opposing power rollers (not shown), a first back surface  5  for countering the thrust load that is a surface on the opposite side in the axial direction from the traction surface  4  and a second back surface  6  for countering the thrust load that is a surface on the opposite side in the axial direction from the traction surface  4  and located at the rim of the cylindrical inner diameter portion  3 . 
     Further, multiple ball spline grooves  2   a  are formed around the power transmission shaft  2  at a prescribed gap in the circumferential direction. 
     Then, the ball spline grooves  2   a  of the power transmission shaft  2  and the ball spline grooves  3   b  of the input disk  1  are opposite to each other, so that balls  7  are accommodated between the paired ball spline grooves  2   a  and  3   b  to configure ball splines that engage the input disk  1  and the power transmission shaft  2 . 
     Here, as shown in  FIG. 13 , gaps  8  are formed between the cylindrical portions  3   a  of the input disk  1  and an outer diameter portion of the power transmission shaft  2 , and since the radial position of the input disk  1  is therefore constrained solely by the ball splines, the traction surface  4  of the input disk  1  has to be machined to have high coaxial and perpendicular properties with respect to the ball spline grooves  3   b . Further, the first and second back surfaces  5  and  6  of the input disk  1  have to be machined to have a high perpendicular property with respect to the ball spline grooves  3   b.    
     As methods of manufacturing a variator component of a continuously variable transmission, for example, the techniques described in Patent Documents 1 to 3 are known. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     
         
         Patent Document 1: JP 2002-28818 A 
         Patent Document 2: JP 2000-61494 A 
         Patent Document 3: JP 2001-347443 A 
       
    
     SUMMARY OF THE INVENTION 
     Problem to be Solved 
     Patent Document 1 describes machining of the traction surface using spline tooth surfaces formed on the cylindrical inner diameter portion of the disk, as the machining reference. However, Patent Document 1 does not disclose any concrete technique regarding how the spline tooth surfaces are engaged and the coaxial and perpendicular properties of the traction surface is enhanced Therefore, the coaxial and perpendicular properties of the traction surface with respect to the spline tooth surfaces cannot be ensured. 
     Besides, Patent Document 2 describes the use of a hard broaching tool to alternately form cylindrical portions and ball spline grooves in the circumferential direction of the disk inner diameter portion and enhancement of the coaxiality and perpendicularity of the traction surface using the cylindrical portion as the machining reference. However, Patent Document 2 needs a hard broaching tool formed coaxially at high accuracy with forming teeth for forming the cylindrical portion of the disk inner diameter portion and forming teeth for forming the ball spline grooves, so that disk manufacturing cost may be increased owing to additional processes. 
     In addition, Patent Document 3 describes that a chuck mechanism is mounted for centering by engaging ball spline grooves formed in the disk inner diameter portion with balls and machining of the traction surface is performed via the chuck mechanism using the ball spline grooves as the machining reference. However, Patent Document 2 also fails to disclose any concrete technique regarding how the chuck mechanism holds the ball spline grooves and the coaxial and perpendicular properties of the traction surface is enhanced. Therefore, the coaxial and perpendicular properties of the functional surface with respect to the ball spline grooves cannot be ensured. 
     The present invention has been made in the light of the foregoing circumstances and has an object to provide a method of manufacturing a component of a continuously variable transmission variator and a chuck apparatus for manufacturing the variator component, so that the power transmission surface can be machined with enhanced coaxial and perpendicular properties with respect to finish-machined spline grooves in the central inner diameter portion and working cost can be reduced. 
     Solution to the Problem 
     In order to achieve the aforesaid object, according to an embodiment of the present invention, there is provided a method of manufacturing a continuously variable transmission variator component, the method comprising the steps of: performing, on a workpiece of the continuously variable transmission variator component, pre-machining of a power transmission surface on one side surface while leaving a machining allowance and pre-machining of spline holes for engaging a power transmission shaft in a central inner diameter portion while leaving machining allowance; performing a thermal hardening process on the workpiece; finish-machining of a plurality of spline grooves constituting the workpiece spline holes; snugly abutting a part of a chuck mounted on a lathe or a grinder into the plurality of spline grooves and clamping the workpiece to make a rotational axis of the chuck and centers of the plurality of spline grooves of the workpiece coaxial; and finish-machining of the power transmission surface of the workpiece using the spline grooves of the workpiece clamped by the chuck as a machining reference. 
     Here, each of the centers of the plurality of spline grooves denotes the center of the spline groove inner diameter (BBD): Between Ball Diameter). 
     By the method of manufacturing the continuously variable transmission variator component according to the present embodiment, it is possible to produce a variator component whose power transmission surface is enhanced in coaxial and perpendicular properties with respect to the spline grooves. Further, there is no increase in the number of processing steps in order to enhance the coaxial and perpendicular properties of the power transmission surface with respect to the spline grooves. 
     Further, according to an aspect of the present invention, the method of producing the continuously variable transmission variator component may further comprising finish-machining of another side surface of the workpiece using the spline grooves of the workpiece clamped by the chuck as the machining reference. 
     By the method of manufacturing the continuously variable transmission variator component according to an aspect of the present invention, it is possible to produce a variator component having another side surface enhanced in the perpendicular property with respect to the spline grooves. 
     Further, according to an aspect of the present invention, the method of producing the continuously variable transmission variator component may further comprise finish-machining of an end face of the workpiece using the spline grooves of the workpiece clamped by the chuck as the machining reference. 
     By the method of manufacturing the continuously variable transmission variator component according to an aspect of the present invention, it is possible to produce a variator component having an end face enhanced in the coaxial property with respect to the spline grooves. 
     Further, according to an aspect of the present invention, in the method of producing the continuously variable transmission variator component, the chuck may comprise: a plurality of radially expandable pieces formed by circumferentially dividing a hollow cylindrical member; a plurality of clamp ridges formed on the outer peripheries of prescribed radially expandable pieces corresponding to the plurality of spline grooves to be projected into contact with groove surfaces of the spline grooves: and a radial expansion shaft snugly abutted on the plurality of spline grooves respectively corresponding to the plurality of clamp ridges. 
     By the method of manufacturing the continuously variable transmission variator component according to an aspect of the present invention, owing to the provision of the chuck expands and holds the multiple radially expandable pieces to abut the individual multiple clamp ridges snugly in the individual associated spline grooves, by insertion of the radial expansion shaft within the multiple radially expandable pieces, it is possible to mount the workpiece on a lathe or a grinder with the enhanced coaxial property. 
     Further, according to an aspect of the present invention, in the method of manufacturing the continuously variable transmission variator component, the chuck may comprise: a radially expandable section provided with a plurality of radially expandable pieces formed by circumferentially dividing a hollow cylindrical member provided with a fluid passage at an axial position; and a plurality of clamp ridges formed on the outer peripheries of prescribed radially expandable pieces corresponding to the plurality of spline grooves to be projected into contact with groove surfaces of the spline grooves, and the plurality of radially expandable pieces expand and hold the plurality of radially expandable pieces to abut the plurality of clamp ridges snugly in the spline grooves, respectively, upon supply of a fluid into the fluid passage. 
     By the method of manufacturing a continuously variable transmission variator component according to an aspect of the present invention, owing to the provision of the chuck whereby supply of a fluid into the fluid passage expands and holds the multiple radially expandable pieces to abut the multiple clamp ridges snugly in the spline grooves, respectively, it is possible to mount the workpiece on a lathe or a grinder with the enhanced coaxial property. 
     Further, according to an aspect of the present invention, in the method of manufacturing a continuously variable transmission variator component, the chuck may comprises: a shaft portion having a tapered outer peripheral surface: and a plurality of clamp ridges formed on the tapered outer peripheral surface at a prescribed gap in a circumferential direction at positions respectively corresponding to the plurality of spline grooves to project into contact with the groove surfaces of the spline grooves, and the plurality of clamp ridges are respectively abutted snugly in the spline groves by insertion of the tapered outer peripheral surface of the shaft portion into the central inner diameter portion. 
     By the method of manufacturing the continuously variable transmission variator component according to an aspect of the present invention, owing to the provision of the chuck that abuts the multiple clamp ridges snugly in the individual associated spline groves upon insertion of the tapered outer peripheral surface of the shaft portion into the central inner diameter portion, it is possible to mount the workpiece on a lathe or a grinder with the enhanced coaxial property. 
     Further, according to an aspect of the present invention, there is provided a method of manufacturing a continuously variable transmission variator component the method comprising: performing, on a workpiece of the continuously variable transmission variator component, pre-machining of a power transmission surface on one side surface while leaving a machining allowance and pre-machining of spline holes for engaging a power transmission shaft in a central inner diameter portion while leaving the machining allowance; performing a thermal hardening process on the workpiece; finish-machining of a plurality of spline grooves constituting the workpiece spline holes; snugly abutting a part of a chuck mounted on a lathe or a grinder against the plurality of spline grooves and clamping the workpiece to make a rotational axis of the chuck and centers of the plurality of spline grooves of the workpiece coaxial; finish-machining of another side surface of the workpiece using the spline grooves of the workpiece clamped by the chuck as a machining reference; and finish-machining of a power transmission surface of the workpiece using the another side surface of the workpiece as the machining reference. 
     By the method of manufacturing the continuously variable transmission variator component according to an aspect of the present invention, it is possible to produce a variator component whose power transmission surface is enhanced in coaxial and perpendicular properties with respect to the spline grooves by finish-machining of the other side surface of the work using the spline grooves of the work clamped by the chuck as the working surface and finish-machining of the power transmission surface of the work using this other side surface of the work as the working reference. 
     On the other hand, according to an aspect of the present invention, there is provided a chuck apparatus for manufacturing a variator component, the chuck apparatus comprising: a plurality of radially expandable pieces formed by circumferentially dividing a hollow cylindrical member; a plurality of clamp ridges that project outward from the outer peripheries of the plurality of radially expandable pieces; and a radial expansion shaft that expands and holds the plurality of radially expandable pieces by insertion within the plurality of radially expandable pieces, wherein, at the time of mounting on a lathe or a grinder the workpiece of a continuously variable transmission variator component, in which a plurality of spline groove holes to be engaged with a power transmission shaft in a circumferential direction of a central inner diameter portion have been finish-machined, and performing finish-machining of a part other than the plurality of spline grooves of the workpiece, the plurality of clamp ridges are snugly abutted in the plurality of spline grooves of the workpiece, respectively, by inserting the radial expansion shaft mounted at a rotational center of the lathe or the grinder in the plurality of radially expandable pieces. 
     By the chuck apparatus for manufacturing a variator component according to an aspect of the present invention, it is possible to mount the workpiece on a lathe or a grinder with the enhanced coaxial property. 
     Further, according to an aspect of the present invention, there is provided a chuck apparatus for manufacturing a variator component, the chuck apparatus comprising: a radially expandable section provided with a plurality of radially expandable pieces formed by circumferentially dividing a hollow cylindrical member provided with a fluid passage at an axial center position; and a plurality of clamp ridges that project outward from the outer peripheries of the plurality of radially expandable pieces, wherein, at the time of mounting on a lathe or a grinder the workpiece of a continuously variable transmission variator component, in which a plurality of spline groove holes to be engaged with a power transmission shaft in a circumferential direction of a central inner diameter portion have been finish-machined, and performing finish-machining of a part other than the spline grooves of the workpiece, the plurality of clamp ridges are snugly abutted in the plurality of spline grooves of the workpiece, respectively, by mounting the radially expandable section at the rotational center of the lathe or the grinder and supplying a fluid into the fluid passage to expand and hold the plurality of radially expandable pieces. 
     By the chuck apparatus for manufacturing a variator component according to an aspect of the present invention, it is possible to mount the workpiece on a lathe or a grinder with the enhanced coaxial property. 
     Further, according to an aspect of the present invention, there is provided a chuck apparatus for manufacturing a variator component, the chuck apparatus comprising: a shaft portion having a tapered outer peripheral surface; and a plurality of clamp ridges that project at a prescribed gap in a circumferential direction of the tapered outer peripheral surface, wherein, at the time of mounting on a lathe or a grinder the workpiece of a continuously variable transmission variator component, in which a plurality of spline groove holes to be engaged with a power transmission shaft in a circumferential direction of a central inner diameter portion have been finish-machined, and performing finish-machining of apart other than the plurality of spline grooves of the workpiece, the plurality of clamp ridges are snugly abutted in the plurality of spline grooves of the workpiece, respectively, by inserting the shaft portion mounted at the rotational center of the lathe or the grinder into the centeral inner diameter portion. 
     By the chuck apparatus for manufacturing the variator component according to the present embodiment, it is possible to mount the workpiece on a lathe or a grinder with the enhanced coaxial property. 
     Advantageous Effects of the Invention 
     By the method of manufacturing a continuously variable transmission variator component according to the present invention, it is possible to produce a variator component whose power transmission surface is enhanced in coaxial and perpendicular properties with respect to the spline grooves. Further, as there is no increase in the number of processing steps in order to enhance the coaxial and perpendicular properties of the power transmission surface with respect to the spline grooves, it is possible to reduce the manufacturing cost of the variator component. 
     Further, by the chuck apparatus for manufacturing a variator component according to the present invention, it is possible to mount a workpiece on a lathe or a grinder with the enhanced coaxial property. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  to  FIG. 1D  are diagrams showing processing steps of a method of manufacturing a continuously variable transmission variator component according to a first embodiment of the present invention; 
         FIG. 2  is a diagram schematically illustrating a chuck (collet chuck) used in the method of the first embodiment; 
         FIG. 3  is a diagram showing the state of the chuck snugly abutted in workpiece spline grooves in the method of the first embodiment; 
         FIG. 4  is diagram showing a master cylinder for correcting swing of multiple radially expandable pieces of the chuck in the first embodiment; 
         FIG. 5A  and  FIG. 5B  are diagrams showing another way of using the first embodiment; 
         FIG. 6A  and  FIG. 6B  are diagrams showing a method of manufacturing a continuously variable transmission variator component according to a second embodiment differing in the structure of the chuck; 
         FIG. 7A  and  FIG. 7B  are diagrams showing a method of manufacturing a continuously variable transmission variator component according to a third embodiment differing in the structure of the chuck; 
         FIG. 8  is a diagram showing an upstream processing step of a method of manufacturing a component of the variator of a toroidal continuously variable transmission according to a fourth embodiment; 
         FIG. 9A  and  FIG. 9B  are diagrams showing a downstream processing step of the method of manufacturing a component of the variator of a toroidal continuously variable transmission according to the fourth embodiment; 
         FIG. 10  is a diagram showing an upstream processing step of a method of manufacturing a component of the variator of a belt-type continuously variable transmission according to the fourth embodiment; 
         FIG. 11A  and  FIG. 11B  are diagrams showing a downstream processing step of the method of manufacturing a component of the variator of a belt-type continuously variable transmission according to the fourth embodiment; 
         FIG. 12  is a diagram showing the state of engagement between a continuously variable transmission variator component and a ball spline of a power transmission shaft; and 
         FIG. 13  is a diagram showing the ball spline engagement state in a sectional view. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Modes of implementing the present invention (hereinafter called embodiments) are explained in detail below with reference to the drawings. Note that constituent portions the same as the constituents shown in  FIG. 8  and  FIG. 9  are assigned like symbols and explanation thereof is omitted. 
       FIG. 1A  to  FIG. 1D  show an embodiment of a method of manufacturing an input disk that is a component of the variator of a toroidal continuously variable transmission, according to the present invention.  FIG. 2  to  FIG. 4  show a structure of a collet chuck  12  used in the present embodiment. 
     In the method of manufacturing an input disk of the present embodiment, pre-working and heat treatment are firstly performed in  FIG. 1A . In the pre-working, a workpiece  10  is formed by hot forging to an approximate shape with a machining allowance with respect to the finished dimensions. Next, cutting is performed to machine the outer shape of the workpiece  10  to a shape with an optimum machining allowance in consideration of the heat treatment strain. Next, the cylindrical inner diameter portion  10   a  of the workpiece  10  is formed to a shape of prescribed dimensions by broach machining. Then, the workpiece  10  formed by the cutting and broach machining is hardened by heat treatment. 
     Next, as shown in  FIG. 1B , a hard broach tool  11  is used for finish-machining of multiple ball spline grooves  3   b  at prescribed intervals in the circumferential direction of the cylindrical inner diameter portion  10   a  of the workpiece  10 . It should be noted that the hard broach tool  11  can be used to simultaneously finish-machine the ball spline grooves  3   b  and cylindrical portions  3   a.    
     Next, as shown in  FIG. 1C , the workpiece  10  is clamped by a collet chuck  12  mounted on a lathe drive section  13 , with a large diameter portion (the first back surface  5  side) facing outward. The lathe drive section  13  is rotationally driven to finish-machine the first back surface  5  and second back surface  6  of the workpiece  10  to have a high perpendicular property with respect to the ball spline grooves  3   b  using the ball spline grooves  3   b  formed in the cylindrical inner diameter portion  10   a  of the workpiece  10 , as the machining reference. 
     The structure of the collet chuck  12  will be explained next. 
     As shown in  FIG. 1C , the collet chuck  12  is provided with a chuck body  14  mounted on the lathe drive section  13 , a radially expandable clamp section  15  of hollow cylindrical shape projecting from the side surface of the chuck body  14  and capable of radial expansion for engagement with the cylindrical inner diameter portion  10   a  of the workpiece  10 , and a radial expansion shaft  16  for expanding the radially expandable clamp section  15 . 
     As shown in  FIG. 2  and  FIG. 3 , the radially expandable clamp section  15  includes radially expandable pieces  15   a  to  15   f  multi-divided in the circumferential direction, and the outer peripheries of prescribed radially expandable pieces  15   a ,  15   c  and  15   e  are formed with clamp ridges  17  whose crest shape is the same as the shape of the multiple ball spline grooves  3   b  formed in the cylindrical inner diameter portion  10   a  of the workpiece  10 . 
     As shown in  FIG. 1C , the radial expansion shaft  16  is formed with a tapered portion  16   a  that abuts on the inner diameter portion of the radially expandable pieces  15   a  to  15   f.    
     Note that the chuck of the present invention corresponds to the collet chuck  12 . 
     The cylindrical inner diameter portion  10   a  of the workpiece  10  is fitted onto the radially expandable clamp section  15  of the collet chuck  12  of the aforesaid structure with the large diameter portion (the first back surface  5  side) facing outward. The chuck body  14  of the collet chuck  12  united with the workpiece  10  is mounted coaxially with the rotational center of the lathe drive section  13 , and the tip portion of the radial expansion shaft  16  inserted into the radially expandable clamp section  15  is engaged with the axis position of the lathe drive section  13 . Then, the tapered portion  16  of the radial expansion shaft  16  radially expands the radially expandable pieces  15   a  to  15   f  to snugly fit the clamp ridges  17  of the radially expandable pieces  15   a ,  15   c  and  15   e  in the multiple ball spline grooves  3   b  of the workpiece  10 , so that the workpiece  10  is clamped coaxially with the rotational center P of the lathe drive section  13 , and the multiple ball spline grooves  3   b  of the workpiece  10  assume a state of extending in parallel with the rotational center P of the lathe drive section  13 . 
     With perpendicularity thus having been enhanced with respect to the ball spline grooves  3   b  extended in parallel at the rotational center of the lathe drive section  13 , finish-machining of the first back surface  5  and second back surface  6  of the workpiece  10  is performed. 
     Next, as shown in  FIG. 1D , the workpiece  10  is clamped on the lathe drive section  13  via the collet chuck  12  with the large diameter portion (the first back surface  5  side) facing the lathe drive section  13  side. 
     Also in this case, as regards the structure of the collet chuck  12  and its method of use, the procedure is the same as shown in  FIG. 1C . The clamp ridges  17  of the radially expandable pieces  15   a ,  15   c  and  15   e  of the collet chuck  12  clamping the workpiece  10  with the large diameter portion facing the lathe drive section  13  side are snugly fit into the multiple ball spline grooves  3   b  of the workpiece  10 . Accordingly, the multiple ball spline grooves  3   b  extend in parallel with the rotational center P of the lathe drive section  13 , and the rotational center P and the center of the inner diameter (BBD) of the ball spline grooves  3   b  become coaxial. 
     With coaxial and perpendicular properties thus having been enhanced with respect to the ball spline grooves  3   b  extended in parallel at the rotational center of the lathe drive section  13 , finish-machining of the traction surface  4  of the workpiece  10  is performed. 
     Therefore, with the collet chuck  12  of the present embodiment, by snugly fitting into the ball spline grooves  3   b  formed in the cylindrical inner diameter portion  10   a  the clamp ridges  17  formed on the radially expandable clamp section  15  in the same shape as the ball spline grooves  3   b . Thus, the workpiece  10  is clamped to extend in parallel with the rotational center P of the lathe drive section  13 . It is therefore possible to produce an input disk  1  formed with a traction surface  4 , the first back surface  5  and the second back surface  6  that are enhanced in coaxial and perpendicular properties with respect to the ball spline grooves  3   b.    
     Further, the coaxial and perpendicular properties of the traction surface  4 , the first back surface  5  and the second back surface  6  can be enhanced without need to machine a reference surface for the inner and outer diameters, the first back surface  5 , and the second back surface  6  before the hard broach machining and without increasing the number of processing steps, so that the manufacturing cost of the input disk  1  can be reduced. 
     It should be noted that a method of manufacturing an input disk  1  formed with the traction surface  4 , the first back surface  5  and the second back surface  6  has been explained in the present embodiment. However, even in a case where the end face of the input disk  1  is to be formed using the ball spline grooves  3   b  as a machining reference, it is possible also to enhance the perpendicularity of the end face with respect to the ball spline grooves. 
     Further, the circumferentially multi-divided radially expandable pieces  15   a  to  15   f  constituting the radially expandable clamp section  15  of the collet chuck  12  may swing in the circumferential direction. Hence, as shown in  FIG. 4 , the circumferential swing of the radially expandable pieces  15   a  to  15   f  can be corrected by fitting on the radially expandable clamp section  15 , a master cylinder  18  having an internal diameter configuration of the same design as the cylindrical inner diameter portion  3  finish-machined in the cylindrical inner diameter portion  10   a  (same center of pitch, center of outer diameter, etc. as the ball spline grooves  3   b ). 
     Further, a method of manufacturing an input disk  1  that is a toroidal continuously variable transmission variator component has been explained in the present embodiment. As shown in  FIG. 5A  and  FIG. 5B , however, the collet chuck  12  of the present embodiment is applicable to a pulley  22  that is a belt-type continuously variable transmission variator component having ball spline grooves  20  formed in a cylindrical inner diameter portion and provided on a side surface with a pulley surface  21   a  as a functional surface and on the opposite side from the pulley surface  21   a  with a back surface  21   b  as a functional surface. Specifically, the clamp ridges  17  formed on the radially expandable clamp section  15  are snugly fit into the ball spline grooves  20  formed in the cylindrical inner diameter portion, so that the blank (pulley  22 ) is clamped to extend in parallel with the rotational center P of the lathe drive section  13 , thus enabling manufacturing of a pulley  22  with a pulley surface  21   a  and back surface  21   b  enhanced in coaxial and perpendicular properties with respect to the ball spline grooves  20 . 
     Next, shown in  FIG. 6A  is a chuck of a different structure from the collet chuck  12  shown in  FIG. 1  to  FIG. 5 . Note that component parts the same as those shown in  FIG. 1  to  FIG. 5  are assigned like symbols and explanation thereof will be omitted. 
     The chuck  23  according to the present embodiment clamps the workpiece  10  on which the pre-working and heat treatment shown in  FIG. 1A  have been completed and the hard broach machining shown  FIG. 1B  has been completed. Further, the chuck  23  according to the present embodiment is rotated around the rotational center P by the lathe drive section  13 . 
     The chuck  23  is provided with a radially expandable clamp section  24  equipped with multiple radially expandable pieces formed by circumferentially dividing a hollow cylindrical member including a fluid passage (not shown) at the axial position. The radially expandable pieces are of substantially the same shape as the radially expandable pieces  15   a  to  15   f  shown in  FIG. 3 . The prescribed radially expandable pieces are formed with clamp ridges of the same shape as in  FIG. 3  to project in the same shape as the groove shape of the ball spline grooves  3   b.    
     In the radially expandable clamp section  24  of the chuck  23  of the present embodiment, a fluid is supplied to the fluid passage to expand and hold the multiple radially expandable pieces and snugly fit the clamp ridges formed on the prescribed radially expandable pieces in the ball spline grooves  3   b  formed in the cylindrical inner diameter portion  10   a . Hence, the workpiece  10  is clamped to extend in parallel with the rotational center P of the lathe drive section  13 . This enables manufacturing of an input disk  1  formed with a traction surface  4 , the first back surface  5  and the second back surface  6  that are enhanced in coaxial and perpendicular properties with respect to the ball spline grooves  3   b.    
     It should be noted that as shown in  FIG. 6B , also with respect to the pulley  22  that is a component of the variator of a belt-type continuously variable transmission, the chuck  23  according to the present embodiment snugly fits the clamp ridges formed on the prescribed radially expandable pieces according to the present embodiment in the ball spline grooves  20  of the pulley  22 . This make it possible to form a pulley surface  21   a  and back surface  21   b  that are enhanced in coaxial and perpendicular properties with respect to ball spline grooves  20 . 
     Further, shown in  FIG. 7A  is a chuck of another different structure. 
     The chuck  25  according to the present embodiment is formed with a tapered outer peripheral surface  26 . Multiple clamp ridges that project in the same shape as the shape of as the groove shape of the ball spline grooves  3   b  are formed on the tapered outer peripheral surface  26  at a prescribed gap in the circumferential direction. These clamp ridges are regions of the same shape as in  FIG. 3 . 
     And with the chuck  25  according to the present embodiment, when the tapered outer peripheral surface  26  is inserted into the cylindrical inner diameter portion  10   a , the clamp ridges formed on the tapered outer peripheral surface  26  snugly fit in the ball spline grooves  3   b  formed in the cylindrical inner diameter portion  10   a , whereby the workpiece  10  is clamped to extend in parallel with the rotational center P of the lathe drive section  13 . This enables manufacturing of an input disk  1  formed with a traction surface  4 , the first back surface  5  and the second back surface  6  that are enhanced in coaxial and perpendicular properties with respect to the ball spline grooves  3   b.    
     It should be noted that as shown in  FIG. 7B , also with respect to the pulley  22  that is a component of the variator of a belt-type continuously variable transmission, the chuck  25  according to the present embodiment snugly fits the clamp ridges formed on the tapered outer peripheral surface  26  according to the present embodiment in the ball spline grooves  20  of the pulley  22 . This makes it possible to form a pulley surface  21   a  and back surface  21   b  that are enhanced in coaxial and perpendicular properties with respect to ball spline grooves  20 . 
     In addition, shown in  FIG. 8  to  FIG. 9B  is a different method from the method shown in  FIG. 1A  to  FIG. 1D  of manufacturing an input disk that is a component of the variator of a toroidal continuously variable transmission. 
     In the method of manufacturing an input disk according to the present embodiment, firstly, the pre-working and heat treatment shown in  FIG. 1A  and the finish-machining of the ball spline grooves  3   b  shown in  FIG. 1B  are performed. 
     Next, as shown in  FIG. 8 , the workpiece  10  is clamped by the collet chuck  12  mounted on the lathe drive section  13 , with the large diameter portion (the first back surface  5  side) facing outward, By using the ball spline grooves  3   b  formed in the cylindrical inner diameter portion  10   a  of the workpiece  10  as the machining reference, the lathe drive section  13  is rotationally driven to finish-machine the first back surface  5 , the second back surface  6 , and the outer surface of the workpiece  10  to have a high perpendicular property with respect to the ball spline grooves  3   b.    
     Next, as shown in  FIG. 9A , the workpiece  10  is clamped on the lathe drive section  13  via the chuck (not shown) with the large diameter portion (the first back surface  5  side) facing the lathe drive section  13  side. 
     Here, an annular backing plate  30  is interposed between the lathe drive section  13  and the first back surface  5 , and multiple shoes  32  supported by a shoe bracket  31  supported by the lathe body (not shown) are abutted on the outer peripheral surface of the workpiece  10 . As shown in  FIG. 9B , the rotational center P 1  of the backing plate  30  is positioned at an offset from the rotational center of the workpiece  10  (rotational center P of the lathe drive section  13 ). 
     In the above configuration, when the lathe drive section  13  rotates, a force of pushing the workpiece  10  positioned at an offset relative to the backing plate  30  against the shoes  32  is exerted to enhance the perpendicular property of the first back surface  5  of the workpiece  10  with respect to the rotational center of the workpiece  10  (rotational center P of the lathe drive section  13 ). 
     This makes it possible to perform finish-machining of the traction surface  4  of the workpiece  10  with enhanced coaxial and perpendicular properties by using the first back surface  5  of the workpiece  10 , as the machining reference. 
     Further, the method shown in  FIG. 8  and  FIG. 9  is applicable to the pulley  22 , shown in  FIG. 10  to  FIG. 11B , which is a component of a belt-type continuously variable transmission variator. 
     Also in the method of manufacturing an input disk according to the present embodiment, firstly, the pre-working and heat treatment shown in  FIG. 1A  and the finish-machining of the ball spline grooves  3   b  shown in  FIG. 1B  are performed. 
     Next, as shown in  FIG. 10 , the pulley  22  is clamped via the collet chuck  12  on the lathe drive section  13  so that the pulley surface  21   a  faces the lathe drive section  13  side. By using the ball spline grooves  20  formed in the cylindrical inner diameter portion of the pulley  22 , as the machining reference, the lathe drive section  13  is rotationally driven to finish-machining of the back surface  21   b  of the pulley  22  to have a high perpendicular property with respect to the ball spline grooves  20 . 
     Next, as shown in  FIG. 11A , the pulley  22  is clamped on the lathe drive section  13  via a chuck (not shown) with the back surface  21   b  side facing the lathe drive section  13  side. 
     Also in the present embodiment, at least two circumferentially spaced backing plates  30  are interposed between the lathe drive section  13  and the back surface  21   b , and multiple shoes  32  supported by a shoe bracket  31  supported by the lathe body (not shown) are abutted on the outer peripheral surface of the workpiece  10 . Further, as shown in  FIG. 11B , the rotational center P 1  of the backing plates  30  is positioned at an offset from the rotational center of the workpiece  10  (the rotational center P of the lathe drive section  13 ). 
     In the above configuration, when the lathe drive section  13  rotates, a force of pushing the pulley  22  positioned at an offset relative to the backing plates  30  against the shoes  32  is exerted to enhance the perpendicular property of the back surface  21   b  of the pulley  22  with respect to the rotational center of the pulley  22  (the rotational center P of the lathe drive section  13 ). 
     This makes it possible to perform finish-machining of the pulley surface  21   a  of the pulley  22  with enhanced coaxial and perpendicular properties by using the back surface  21   b  of the pulley  22 , as the machining reference. 
     Here, although the ball spline grooves  3   b ,  20  are formed in the workpiece  10  (the input disk  1 , the pulley  22 ) in the embodiments set out above, the spirit of the present invention is not limited thereto. Involute spline grooves may be formed, and in the power transmission shaft, involute spline grooves may be formed to match these involute spline grooves. 
     Further, although the collet chuck  12  or chuck  23  is mounted on the lathe drive section  13  in each of the embodiments set out above, the same effect can also be produced by mounting the collet chuck  12  or chuck  23  on the drive section of a grinder (not shown). 
     INDUSTRIAL APPLICABILITY 
     As in the foregoing, the method of manufacturing a continuously variable transmission variator component according to the present invention is useful for enhancing the coaxial and perpendicular properties of the power transmission surface with respect to the spline grooves without increasing the number of processing steps and thereby lowering the manufacturing costs of the variator components. 
     REFERENCE SIGNS LIST 
     
         
           1  . . . Input disk,  3   b  . . . Ball spline groove,  4  . . . Traction surface,  5  . . . First back surface,  6  . . . Second back surface,  10  . . . Workpiece,  10   a  . . . Cylindrical inner diameter portion,  12  . . . Collet chuck,  13  . . . Lathe drive section,  14  . . . Chuck body,  15  . . . Radially expandable clamp section,  15   a  to  15   f  . . . Radially expandable pieces,  16  . . . Radial expansion shaft,  16   a  . . . Tapered portion,  17  . . . Clamp ridges,  18  . . . Master cylinder,  20  . . . Ball spline groove,  21   a  . . . Pulley surface,  21   b  . . . Back surface,  22  . . . Pulley,  23  . . . Chuck,  24  . . . Radially expandable clamp section,  25  . . . Chuck,  26  . . . Tapered outer peripheral surface,  30  . . . Backing plate,  31  . . . Shoe bracket,  32  . . . Shoe