Abstract:
A trunnion ( 3 ) of a toroidal continuously variable transmission comprises a pulley ( 38 ) having a pulley groove ( 30 ) and a notch ( 37 ) crossing the pulley groove ( 38 ). The trunnion ( 3 ) rotates in synchronism with another trunnion by looping an endless wire around the pulley groove of each trunnion ( 3 ) and by engaging a large diameter part of the endless wire with the notch ( 37 ). After the trunnion ( 3 ) is formed by die forging, a rotary tool ( 90 ) is first aligned with a boundary interface ( 31 ′A,  31 ′B) between the pulley groove ( 30 ) and notch ( 37 ). The tool ( 90 ) is then rotated while it is moved forward in the axial direction of the tool ( 90 ), and the boundary interface ( 31 ′A,  31 ′B) is cut to a predetermined position.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a trunnion of a toroidal continuously variable transmission for vehicles and a manufacturing process for the trunnion. 
     BACKGROUND OF THE INVENTION 
     Tokkai Hei 4-366049 published by the Japanese Patent Office in 1992 discloses a toroidal continuously variable transmission for vehicles wherein the ration of the rotation speed of an input disk to the rotation speed of an output disk, i.e., a speed ratio, is continuously varied by varying the gyration angle of a pair of power rollers gripped between the input disk and output disk. The power rollers are respectively supported by trunnions at a position facing each other. 
     These trunnions must be rotated synchronously. In this context, Tokkai Hei 7-253145 published by the Japanese Patent Office in 1995 discloses a technique wherein a pulley is formed in the trunnions, and the trunnions are synchronously rotated by looping an endless wire around a pulley groove of the pulley. The slipping of the endless wire in the circumferential direction is prevented by engaging a large diameter part of the endless wire with a notch formed in a pulley groove. Therefore, in order to accurately synchronize the gyration angle of the trunnions, the notch must be formed precisely in the circumferential direction. 
     However, when the trunnions are formed by forging, casting or sintering, the precision of the notch is poor. 
     Therefore, the notch has to be machined after forming, but if the notch is machined by driving a tool in the axial direction while the trunnion is rotated around its rotation axis as the notch runs in a circumferential direction, the number of indexing steps of machining positions and positioning steps increases and the productivity declines. 
     It is therefore an object of this invention to machine the notch which engages with the large diameter part of the endless wire to a high precision without reducing productivity. 
     In order to achieve the above object, this invention provides a trunnion of a toroidal continuously variable transmission and a manufacturing process for the trunnion. The trunnion comprises a support having a hole therethrough comprising a pulley with a pulley groove and a notch crossing the pulley groove, a first shaft on the top of the support, and a second shaft part on the bottom of the support that is coaxial with the first shaft part, the notch comprising an arc portion and two straight portions, one of the straight portion being formed on one side of the arc portion and the other of the straight portion being formed on the other side of the arc portion. The process comprises forming said pulley groove and said notch by forging, casting or sintering, aligning a rotary tool for machining a flat surface by a blade provided on an end face so as to face a boundary interface between the pulley groove and notch, and rotating the tool while moving the tool forward in the axial direction of the tool so as to cut the boundary interface to a predetermined position. 
     The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a trunnion and a power roller of a toroidal continuously variable transmission according to this invention. 
     FIG. 2 is a front view of the trunnion. 
     FIG. 3 is a side view of the trunnion. 
     FIG. 4 is a base plan view of the trunnion, showing a state before machining. 
     FIG. 5 is a base plan view of the trunnion, showing a state after machining. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 of the drawings, a trunnion  3  comprises a support  3 C which supports a power roller  1  such that it is free to rotate, and shaft parts  3 A and  3 B formed on the top and bottom of the support  3 C. The support  3 C and shaft parts  3 A,  3 B are formed in one piece by die forging. 
     A through-hole  34  is formed in the support  3 C. One end of a pivot shaft  2  is inserted in the through-hole  34 , and the pivot shaft  2  pivots around an axis C. The power roller  1  is supported at the other end of the pivot shaft  2  via a radial bearing  19 . An outer ring  18  and ball bearing  16  are interposed between the support  3 C and power roller  1 , and support a thrust load. 
     When the trunnion  3  displaces in the direction of an axis  3 Z, the power roller  1  gyrates between the input disk and output disk, not shown, and the ratio of the rotation speed of the input disk to the rotation speed of the output disk, i.e., the speed ratio, varies continuously. 
     The shaft part  3 B is formed in a cylindrical shape, as shown in FIG. 2. A rod  6  of a hydraulic actuator, not shown, is inserted into the shaft part  3 B. The rod  6  and trunnion  3  are joined by pressing a pin  36  into a pinhole  33  formed in the support  3 C and a pinhole  35  formed in the rod  6  which are formed in the support  3 C. 
     A pulley  38  is formed in the lower part of the support  3 C, as shown in FIG.  3 . The pulley  38  comprises a pulley groove  30  and a notch  37  which crosses the pulley groove  30 . An endless wire, not shown, is looped around the pulley groove  30  and notch  37  in order to synchronize the gyration angle of the trunnion  3 , and the gyration angle of another trunnion, not shown, which is disposed facing the trunnion  3 . The endless wire is provided with a large diameter part having a diameter larger than the wire gage, and this large diameter part engages with the notch  37  so that the endless wire does not slide in a circumferential direction relative to the trunnion  3 . 
     The pulley groove  30  and the notch  37  are formed in one piece with the support  3 C when the trunnion  3  is formed by die forging. 
     After forging, the angles β formed by axis C of the pivot  2  and boundary interfaces  31 ′A,  31 ′B between the notch  37  and the pulley groove  30  are less than 45 degrees, as shown in FIG.  4 . The angles β are for example 39 degrees. 
     Next, machining described later is performed, and the angles between the axis C of the pivot shaft  2  and the boundary interfaces  31 A,  31 B become α 1 , α 2  as show in FIG.  5 . Here, the angles α 1 , α 2  are 45 degrees. Consequently, the angle of the notch  37  is enlarged from 2β to 90 degrees after forging, and the extension of the boundary interfaces  31 A,  31 B intersects perpendicularly on the axis  3 Z of the trunnion  3 . 
     The machining of the boundary interfaces  31 A,  31 B will now be described further referring to FIG.  4 . 
     The rotary tool  90  can machine a flat surface by a blade provided on the tip surface. The tool  90  may be an end mill, for example. 
     First, the boundary interface  31 ′A on the right-hand side of the figure and the tool  90  are aligned, and the angle between the axis of the tool  90  and the axis C of the pivot shaft  2  is adjusted to a first angle. The first angle is 45 degrees. 
     The tool  90  is then rotated while moving if forward in the axial direction, and cutting of the boundary interface  31 ′A is started. When the tip of the tool  90  reaches a line L 1  which is at an angle 45 degrees relative to the axis C of the pivot shaft  2 , this line extending from the axis  3 Z of the trunnion  3 , cutting of the boundary interface  31 ′A is terminated. 
     Next, the tool  90  is retracted in the axial direction to prevent interference with the trunnion, the trunnion  3  is rotated counterclockwise in the figure, and the angle made by the axis of the tool  90  and the axis C of the point shaft  2  is adjusted to a second angle. The second angle is −45 degrees. Furthermore, the trunnion  3  is displaced parallel so as to face the tool  90 . 
     The tool  90  is then rotated while moving if forward in the axial direction, and cutting of the boundary interface  31 ′B on the left-hand side of the figure is started. When the tip of the tool  90  reaches a line L 2  which makes an angle of 45 degrees relative to the axis C, this line L 2  extending from the axis  3 Z of the trunnion  3 , cutting of the boundary interface  31 ′B is terminated. 
     Therefore, the angle made by the boundary interfaces  31 A,  31 B is precisely 90 degrees as shown in FIG. 5 due to the aforesaid double cutting by the tool  90 . The shaded portions  32 A,  32 B in the figure are machining allowances removed by cutting. Accordingly, the shaded portions are formed to be straight. 
     Therefore, the notch  37  includes an arc portion  37 C and two straight portions ( 37 A,  37 B) where the arc portion  37 C and the two straight portions ( 37 A,  37 B) are divided by first boundary surfaces ( 31 ′A,  31 ′B). The notch  37  and the pulley grooves  30  are divided by second boundary surfaces ( 31 A,  31 B). The axis C intersects a first imaginary line ( 40 A or  40 B) at a first angle B on a sectional plane perpendicular to the axis of the first shaft part. The axis C intersects a second imaginary line ( 41 A or  41 B) at a second angle (α 1  or α 2 . 
     As the relative rotation angle of the trunnion  3  and the tool  90  is 90 degrees, the numerical values used for indexing the cutting position are 45 degrees and 90 degrees, and the work piece can be set easily and quickly. 
     Moreover, since the tool  90  moves only in the axial direction, the setting of a machine tool, not shown, which drives the tool  90  is easy and accurate. 
     If the rotary too  90  with a large diameter is used and the offset amount from the center of the pulley groove  30  of the tool  90  is made large, no cutting residues remain below the boundary interfaces  31 A,  31 B as shown in FIG.  3 . Hence, it is possible to prevent the endless wire from being caught on the cutting residues when the endless wire is attached, and it is easy to attach it to the notch  37  precisely and rapidly. 
     Further, as the machining allowances  32 A,  32 B are small, the machining time can be reduced. If two of the rotary tools  90  are available, the boundary interfaces  31 ′A,  31 ′B can be cut separately at the same time, in which case the machining time may be further reduced. 
     In the above embodiment, the angles α 1 , α 2  formed by the axis C of the pivot shaft  2  and the boundary interfaces  31 A,  31 B are arranged to be 45 degrees, but these angles may be different values. For example, if the angle α 1  is set to 30 degrees and the angle α 2  is set to 50 degrees, the first and second angles during positioning may be set at respectively 30 degrees and 50 degrees relative to the axis C. 
     In addition, although the trunnion is formed by die forging in the aforesaid embodiment, it may be molded by casting or sintering instead. 
     The entire contents of Japanese Patent Application P10-227073 (filed Aug. 11, 1998) are incorporated herein by reference. 
     Although the invention has been described above by reference to a certain embodiment of the invention, the invention is not limited to the embodiment described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings. The scope of the invention is defined with reference to the following claims.