Abstract:
A toroidal-type continuously variable transmission has a casing; an input disk and an output disk rotatably supported concentrically with each other; a plurality of power rollers each held between the input and output disks; a plurality of trunnions disposed at position twisted with respect to a center axis; a drive device for shifting the trunnions in the axial directions or the pivot shafts; a pair of yokes for supporting the pivot shafts of each of the trunnions so as to be swung and shifted in the axial direction thereof, the yokes being swingable according to the shifting movement of the associated trunnion; and, a pair of opposing members each disposed to be opposed to the associated yoke, wherein the yokes each includes projection portion contacted with the associated opposing member, the projection portion being the fulcrum of the swinging movements of the yokes.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field or the Invention  
           [0002]    The present invention relates to a toroidal-type continuously variable transmission which is used, for example, as a transmission for a vehicle.  
           [0003]    2. Description of the Related Art  
           [0004]    A toroidal-type continuously variable transmission of a double cavity type used, for example, an a transmission for a vehicle is structured as shown in FIGS. 16 and 17.  
           [0005]    As shown in FIG. 16, inside a casing  50 , an input shaft (center shaft)  1  is rotatably supported and, on the outer periphery of the input shaft  1 , two input disks  2 ,  2  and two output disks  3 ,  3  are mounted. Also, on the outer periphery of the middle portion of the input shaft  1 , an output gear  4  is rotatably supported. In the central portion of the output gear  4 , cylindrical-shaped flange portions  4   a ,  4   a  are formed; and, the output disks  3 ,  3  are connected by splint connection to the flange portions  4   a ,  4   a  respectively.  
           [0006]    The input shaft  1  can be driven and rotated by a drive shaft  22  through a loading-cam-typo pressing device  12  disposed between the input disk  2  situated on the left in FIG. 16 and a cam plate  7 . Also, the output gear  4  is supported within the casing  50  through a partition wall  13  composed of two members connected together, whereby the output gear  4  can be rotated about the axis O of the input shaft  1  but is prevented from shifting in the direction of the axis O.  
           [0007]    The output disks  3 ,  3  are supported by needle roller bearings  5 ,  5  each interposed between the input shaft  1  and themselves in such a manner that they can be rotated about the axis O of the input shaft  1 .  
           [0008]    Also, the input disk  2  situated on the left side in FIG. 16 is supported on the input shaft  1  through a ball spline  6  while the input disk  2  on the right side in FIG. 16 is spline connected to the input shaft  1 ; and, the two input disks  2  can be rotated together with the input shaft  1 . And, between the inner surfaces  2   a ,  2   a  (concave-shaped surfaces) of the input disks  2 ,  2  and the inner surfaces  3   a ,  3   a  (concave-shaped surfaces) of the output disks  3 ,  3 , power rollers  11  (see FIG. 17) are held in such a manner that they can be rotated.  
           [0009]    In the inner peripheral surface  2   c  of the input disk  2  situated on the right side in FIG. 16, there is formed a stepped portion  2   b ; and, a stepped portion  1   b  formed in the outer peripheral surface  1   a  of the input shaft  1  is butted against the stepped portion  2   b , while the back surface (in FIG. 16, the right surface) of the input disk  2  is butted against a loading nut  9 . Due to this, the input disk  2  is substantially prevented from shifting in the axis O direction with respect to the input shaft  1 . Also, between the cam plate  7  and the flange portion  1   b  of the input shaft  1 , a countersunk spring B is interposed; and, the countersunk spring  8  applies a pressing force to the respective contact portions between the concave-shaped surfaces  2   a ,  2   a ,  3   a ,  3   a  of each disks  2 ,  2 ,  3 ,  3  and the peripheral surfaces  11   a ,  11   a  of the power rollers  11 ,  11 .  
           [0010]    Now, FIG. 17 is a section view taken along the line A-A shown in FIG. 16. As shown in. FIG. 17, inside the casing  50 , there are disposed a pair of trunnions  15 ,  15  each of which can be swung about a pair of pivot shafts  14 ,  14  disposed at positions twisted with respect to the input shaft  1 . By the way, in FIG. 17, illustration of the input shaft  1  is omitted.  
           [0011]    The two trunnions  15 ,  15  respectively include, in their respective two end portions which are situated in the longitudinal-direction (in FIG. 17, vertical-direction) of a support plate portion  16 , a pair of bent wall portions  20 ,  20  which are formed to be bent on the inner surface side of the support plate portion  16 . And, these bent wall portions  20 ,  20  form recess-shaped pocket portions P respectively for storing their associated power rollers  11  therein. Also, on the outer surfaces of the bent wall portions  20 ,  20 , the pivot shafts  14 ,  14  are disposed in such a manner that they are concentric with each other.  
           [0012]    A circular hole  21  is formed in the central portion of each of the support plate portions  16  and the base end portion  23   a  of a displacement shaft  23  is supported in the Circular hole  21 . And, in case where the trunnions  15 ,  15  are respectively swung about their associated pivot shafts  14 ,  14 , the inclination angles of the displacement shafts  23  supported on the central portions of the trunnions  15 ,  15  can be adjusted. Also, on the peripheries of the leading end portions  23   b  of the displacement shafts  23  projecting from the inner surfaces of the trunnions  15 ,  15 , there are rotatably supported the power rollers  11 ; and, the power rollers  11 ,  11  are interposed between the input disks  2 ,  2  and output disks  3 ,  3 . By the way, the base end portions  23   a  and leading end portions  23   b  of the respective displacement shafts  23 ,  23  are eccentric to each other.  
           [0013]    Also, the pivot shafts  14 ,  14  of the trunnions  15 ,  15  are respectively supported in such a manner that they can be swung and shifted in the axial direction thereof (in FIG. 16, in the front and back direction; and, in FIG. 17, in the vertical direction) with respect to a pair of yokes  23 A,  23 B; and, the yokes  23 A,  23 B prevent the trunnions  15 ,  15  from moving in the horizontal direction thereof.  
           [0014]    As shown in FIG. 18, each of the yokes  23 A,  23 B is formed into a rectangular shape by press working or forging a blank member made of metal ouch as steel. In the four corners of the respective yokes  23 A,  23 B, there are formed four circular-shaped support holes  18 , while the pivot shafts  14  disposed on the two end portions of the trunnion  15  are swingably supported on the support holes  18  through radial needle roller bearings  30 .  
           [0015]    Also, in the width-direction (in FIGS. 17 and 18, the right-and-left direction) central portion of each of the yokes  23 A,  23 B, there are formed circular-shaped engaging holes  19 , while the inner peripheral surfaces of the engaging holes  19  are formed as spherical-shaped concave surfaces; and, Spherical-shaped surface posts  64 ,  68  are respectively fitted into the engaging holes  19 . That is, the yoke  23 A situated on the upper side is swingably supported by the spherical-shaped surface post  64  which is supported on the casing  50  through a fixing member  52 , while the lower-side yoke  23 B is swingably supported by the spherical-shaped surface post  68  and the upper valve body  61  of a cylinder  31  supporting the spherical-shaped surface post  68 .  
           [0016]    By the way, the displacement shafts  23 ,  23  disposed on the trunnions  15 ,  15  are disposed at positions which are opposite by 180° to each other with respect to the input shaft  1 . Also, the direction, in which the leading end portions  23   b  of the respective displacement shafts  23 ,  23  are eccentric to the base end portions  23   a  thereof, is the same direction (in FIG. 17, the reversed upward and downward direction) to the rotation direction of the two kinds of disks  2 ,  2 ,  3 ,  3 . Also, the eccentric direction is a direction which is substantially perpendicular to the mounting direction of the input shaft  1 . Therefore, the power rollers  11 ,  11  are supported in such a manner that they can be shifted slightly in the longitudinal direction of the input shaft  1 . As a result of this, due to elastic deformation of each components based on thrust load generated by the pressing device  12 , even when the power rollers  11 ,  11  tend to shift in the axial direction of the input shaft  1 , an unreasonable force can be prevented from being applied to the respective composing parts of the toroidal-type continuously variable transmission and thus the shifting movements of the power rollers  11 ,  11  can be absorbed.  
           [0017]    Also, between the outer surface of the power roller  11  and the inner surface of the support plate portion  16  so the trunnion  15 , there are interposed a thrust ball bearing  24  and a thrust needle roller bearing  25 , in this order, starting from the outer surface of the power roller  11  which are both thrust rolling bearings, Of these bearings, each of the thrust ball bearings  24  is structured such that, while supporting a thrust-direction load applied to the power roller  11 , it allows the power roller  11  to rotate. Each of the thrust ball bearings  24  comprises a plurality of balls  26 ,  26 , a circular-ring-shaped retainer  27  for holding the balls  26 ,  26  in such a manner that the balls  26  are allowed to roll, and a circular-ring-shaped outer race  28 . Also, the inner race raceway of each thrust ball bearing  24  is formed in the outer surface of the power roller  11 , whereas the outer race raceway thereof is formed in the inner surface of the outer race  28 .  
           [0018]    Also, the thrust needle roller bearing  25  is held by and between the inner surface of the support plate portion  16  of the trunnion  15  and the outer surface of the outer race  28 . And, the thrust needle roller bearing  25  is structured such that, while supporting a thrust load applied to the outer race  28  from the power roller  11 , it allows the power roller  11  and outer race  28  to swing about the base end portion  23   a  of their associated displacement shaft  23 .  
           [0019]    Further, on the one-end portions (in FIG. 17, the lower end portions) of the trunnions  15 ,  15 , there are disposed drive rods (trunnion shafts)  29 ,  29  and, on the outer peripheral surfaces of the middle portions of the drive rods  29 ,  29 , there are fixedly mounted drive pistons (oil-pressure pistons)  33 ,  33 . And, these drive pistons  33 ,  33  are respectively oil-tight fitted into the drive cylinder  31  composed of the upper and lower valve bodies  61 ,  62 . The drive pistons  33 ,  33  and drive cylinder  31  cooperate together in constituting a drive device  32  which can shift the trunnions  15 ,  15  in the axial directions of the pivot shafts  14 ,  14  of the trunnions  15 ,  15 .  
           [0020]    In the case of the thus-structured toroidal-type continuously variable transmission, the rotational movement of the input shaft  1  is transmitted through the pressing device  12  to the respective input disks  2 ,  2 . And, the rotational movements of the input disks  2 ,  2  are transmitted through the pair of power rollers  11 ,  11  to the output disks  3 ,  3  and further the rotational movements of the output disks  3 ,  3  are taken out from the output gear  4 .  
           [0021]    To change a rotation speed ratio between the input shaft  1  and output gear  4 , the pair of drive pistons  33 ,  33  may be shifted in the mutually opposite directions. With the shifting movements of the drive pistons  33 ,  33 , the pair of trunnions  15 ,  15  are shifted in the mutually opposite directions, For example, the power roller  11  on the left side in FIG. 17 is shifted downwardly, whereas the power roller  11  on the right side is shifted upwardly. This changes the directions of tangential-direction forces acting on the contact portions between the peripheral surfaces  11   a ,  11   a  of the power rollers  11 ,  11  and the inner surfaces  2   a ,  2   a ,  3   a ,  3   a  of the input and output disks  2 ,  2 ,  3 ,  3 . And, due to such change in the directions of these forces, the trunnions  15 ,  15  are swung in the mutually opposite directions about the pivot shafts  14 ,  14  pivotally supported on the yokes  23 A,  23 B.  
           [0022]    This changes the contact positions between the peripheral surfaces  11   a ,  11   a  of the power rollers  11 ,  11  and the inner surfaces  2   a ,  3   a  of the input and output disks  2 ,  3  to thereby change a rotation speed ratio between the input shaft  1  and output gear  4 . Also, in case where a torque to be transmitted between the input shaft  1  and output gear  4  varies and the elastic deformation quantities of the respective composing parts vary, the power rollers  11 ,  11  and cuter races  2 E,  28  belonging to these power rollers  11 ,  11  are slightly rotated about the base end portions  23   a ,  23   a  of the displacement shafts  23 ,  23  since the thrust needle roller bearings  25 ,  25  are interposed between the outer surfaces of the outer races  28 ,  28  and the inner surfaces of the support plate portions  16  respectively constituting their associated trunnions  15 ,  15 , the slight rotational movements of the power rollers  11  and outer races  28  can be carried out smoothly. Therefore, the force necessary to change the inclination angles of the displacement shafts  23 ,  23  in the above-mentioned manner can be reduced down to a small level.  
           [0023]    By the way, the yokes  23 A,  23 B, which support the pivot shafts  14 ,  14  of the trunnions  15 ,  15  swingably and shiftably in the axial direction, are structured such that, as described above, they can be swung about the spherical-shaped surface posts  64 ,  68  (for example, see U.S. Pat. No. 6,117,043). However, conventionally, there has been desired the development of a structure that can swing the yokes  23 A,  23 B more smoothly.  
           [0024]    In attaining this desire, in JP-A-9-291997, there is disclosed a technique which can swing the yokes  23 A,  233  about pins inserted into pin holes formed in the yokes  23 A,  23 B.  
           [0025]    However, in this technique, when forming the pin holes in the yokes  23 A,  23 B, the formation positions of the pin holes must be at with high accuracy. This not only makes it difficult to manufacture the yokes  23 A,  23 B but also makes it necessary to provide the pins specially, which results in the increased number of parts used in the toroidal-type continuously variable transmission and in the increased manufacturing cost thereof.  
         SUMMARY OF THE INVENTION  
         [0026]    The present invention aims at eliminating the above drawbacks found in the conventional toroidal-type continuously variable transmission. Accordingly, it is an object of the present invention to provide a toroidal-type continuously variable transmission which not only can facilitate the manufacturing of the yokes but also can reduce the manufacturing cost of the yokes and thus the toroidal-type continuously variable transmission.  
           [0027]    In attaining the above object, according to a first aspect to the present invention, there is provided a toroidal-type continuously variable transmission, having a casing; an input disk and an output disk having inner surfaces respectively and rotatably supported concentrically with each other in the casing in such a manner that the inner surfaces are opposed to each other; a plurality of power rollers each held between the input and output disks; a plurality of trunnions each having a pair of pivot shafts disposed at positions twisted with respect to a center axis of the input and output disks and concentric with each other, the trunnion supporting the associated power roller so as to be rotated; a drive device for shifting the trunnions in the axial directions of the pivot shafts; a pair of yokes for supporting the pivot shafts of each of the trunnions so as to be swung and shifted in the axial direction thereof, the yokes being swingable according to the shifting movement of the associated trunnion, and, a pair of opposing members each disposed to he opposed to the associated yoke, wherein the yokes each includes projection portion contacted with the associated opposing member, the projection portion being the fulcrum of the swinging movements of the yokes.  
           [0028]    According to the present invention, the projection portions of the yokes are contacted with their associated opposing members (such as a casing or a cylinder for storing therein a piston for shifting the trunnion), whereby the yokes can be swung about these projection portions to thereby synchronize the shifting movements of the trunnions supported on the yokes.  
           [0029]    In this manner, since the yokes swing about the projection portions contacted with the opposing members, the yokes are allowed to swing smoothly. Therefore, the shifting movements of the trunnions supported on the yokes can be synchronized stably, thereby being able to stabilize the transmission performance of the toroidal-type continuously variable transmission.  
           [0030]    Also, because the structure can be obtained by forming the projection portions in the yokes, the manufacture of the yokes is easy and also there is eliminated the need for special provision or pins, thereby being able to reduce the manufacturing cost of the toroidal-type continuously variable transmission.  
           [0031]    According to a second aspect of the present invention, there is provided a toroidal-type continuously variable transmission, having a casing; an input disk and an output disk It having inner surfaces respectively and rotatably supported concentrically with each other in the casing in such a manner that the inner surfaces are opposed to each other; a plurality of power rollers each held between the input and output disks; a plurality of trunnions each having a pair of pivot shafts disposed at positions twisted with respect to a center axis of the input and output disks and concentric with each other, the trunnion supporting the associated power roller so as to be rotated; a drive device for shifting the trunnions in the axial directions of the pivot shafts; a pair of yokes for supporting the pivot shafts of each of the trunnions so as to be swung and shifted in the axial direction thereof, the yokes being swingable according to the shifting movement of the associated trunnion; and, a pair of opposing members each disposed to be opposed to the associated yoke, wherein the opposing members each includes projection portion contacted with the associated yoke, the projection portion being the fulcrum of the swinging movements of the yokes.  
           [0032]    According to the second aspect of the present invention, the projection portions of the opposing members are contacted with their associated yokes, whereby the yokes can be swung about these projection portions to thereby synchronize the shifting movements of the trunnions supported on the yokes.  
           [0033]    In this manner, since the yokes are structured so as to swing about the projection portions formed in the opposing members and contacted with the yokes, the yokes are allowed to swing smoothly. Therefore, the shifting movements of the trunnions supported on the yokes can be synchronized stably, thereby being able to stabilize the transmission performance of the toroidal-type continuously variable transmission.  
           [0034]    Also, because the structure can be obtained by forming the projection portions in the opposing members, the manufacture of the yokes is easy and also there is eliminated the need for special provision of pins, thereby being able to reduce the manufacturing cost of the yokes and thus the toroidal-type continuously variable transmission.  
           [0035]    According to the present invention, the toroidal-type continuously variable transmission as set forth in the first or second aspect, wherein each of the yokes forms a penetration hole therein, the toroidal-type continuously variable transmission further includes a restricting member inserted into the penetration hole of the yoke and restricting the movement of the yoke in the horizontal direction, and a clearance is formed between the restricting member and the penetration hole.  
           [0036]    According to the present structure, since there is formed a clearance between the restricting member and the penetration hole of the yoke, the yoke is allowed to move in the horizontal direction only by the amount corresponding to this clearance. Therefore, even in case where the positions of the contact portions between the peripheral surfaces of the power rollers and the inner surfaces of the input and output disks are caused to vary in the respective power rollers due to the shifted position of the yokes within the casing or due to variations in the assembling positions of the power rollers with respect to the trunnions. The yokes are allowed to move in the horizontal direction to thereby correct the variations in the positions of the contact portions between the peripheral surfaces of the power rollers and the inner surfaces Of the input and output disks. Thanks to this, loads to be applied to the respective power rollers can be made uniform, so that the durability of the power rollers is not lowered but the lives of the power rollers can be extended.  
           [0037]    Also, because there is eliminated the need to set the positions of the yokes within the casing and the assembling positions of the power rollers with respect the trunnions with accuracy so as to be able to prevent the durability of the power rollers from being lowered, the operation for assembling these composing parts is easy.  
           [0038]    Further, according to the present invention, the toroidal-type continuously variable transmission as set forth in the first aspect of the present invention, wherein, in each of the opposing members, a recess portion into which a leading end portion of the projection portion of each of the yoke is inserted is formed.  
           [0039]    That is, according to the present structure, by inserting the leading end portions of the projection portions of the yokes into the recess portions formed in the opposing members, the yokes can be swingably supported in the recess portions of the opposing members. Thanks to this, the centers of the swinging movements of the yokes can be made always constant, which makes it possible to stabilize the swinging movements of the yokes.  
           [0040]    Also, since there is eliminated the need for provision of posts and pins which are used to support the yokes swingably, there can be avoided not only the operation to form holes in the yokes for insertion of the posts and pins but also the operation to assemble the pins to the yokes, which makes it further easier to manufacture the yokes. Further, no need for provision of the posts and pins can reduce the number or parts and the manufacturing cost of the toroidal-type continuously variable transmission.  
           [0041]    In addition, according to the present invention, the toroidal-type continuously variable transmission as set forth in the second aspect of the present invention, wherein, in each of the yokes, a recess portion into which a leading end portion of the projection portion of each of the opposing members is inserted is formed.  
           [0042]    That is, by inserting the leading end portions of the projection portions of the opposing members into the recess portions formed in the yokes, the yokes can be swingably supported on the projection portions of the yokes. Thanks to this, the centers of the swinging movements of the yokes can be made always constant, which can stabilize the swinging movements of the yokes.  
           [0043]    Also, since there is eliminated the need for provision of posts and pins which are used to support the yokes swingably, there can be avoided not only the operation to form holes in the yokes for insertion of the posts and pins but also the operation to assemble the pins to the yokes, which makes it further easier to manufacture the yokes. Further, no need for provision of the posts and pins can reduce the number of parts and the manufacturing cost of the toroidal-type continuously variable transmission. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0044]    [0044]FIG. 1 is a section view of a toroidal-type continuously variable transmission according to a first embodiment of t he present invention;  
         [0045]    [0045]FIG. 2 is a section view taken along the line A-A shown in FIG. 1;  
         [0046]    [0046]FIGS. 3A and 3B each shows a yoke shown in FIG. 1; specifically, FIG. 3A is a plan view of the yoke, and FIG. 3B is a side view of the yoke;  
         [0047]    [0047]FIGS. 4A and 4B are explanatory views of the yoke, showing how the yoke swings in varying the speed ratio;  
         [0048]    [0048]FIG. 5 is a section view of a toroidal-type continuously variable transmission according to a second embodiment of t he present invention;  
         [0049]    [0049]FIGS. 6A and 6B each shows the yoke shown in FIG. 5; specifically, FIG. 6A is a plan view of the yoke, end FIG. 6B is a side view of the yoke;  
         [0050]    [0050]FIGS. 7A and 7B are explanatory views of the yoke, showing how the yoke swings in varying the speed ratio;  
         [0051]    [0051]FIG. 8 is a section view of a toroidal-type continuously variable transmission according to a third embodiment of t he present invention;  
         [0052]    [0052]FIG. 9 is a section view taken along the line A-A shown in FIG. 8;  
         [0053]    [0053]FIG. 10 is a plan view of the yoke shown in FIG. 8;  
         [0054]    [0054]FIGS. 11A and 11B are explanatory views of the yoke, showing how the yoke swings in varying the speed ratio;  
         [0055]    [0055]FIG. 12 is a section view of a toroidal-type continuously variable transmission according to a fourth embodiment of the present invention;  
         [0056]    [0056]FIG. 13 is a section view taken along the line A-A shown in FIG. 12;  
         [0057]    [0057]FIGS. 14A and 14B each shows the yoke shown in FIG. 12; specifically, FIG. 14A is a plan view of the yoke, and FIG. 143 is a side view of the yoke;  
         [0058]    [0058]FIGS. 15A and 15B are explanatory views of the yoke, showing how the yoke swings in varying the speed ratio;  
         [0059]    [0059]FIG. 16 is a section view of an example of a concrete structure of a conventional toroidal-type continuously variable transmission;  
         [0060]    [0060]FIG. 17 is a section view taken along the line A-A shown in FIG. 16; and,  
         [0061]    [0061]FIG. 18 is a plan view of the yoke shown in FIG. 16. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0062]    Now, description will be given below of the mode for carrying out the present invention with reference to the accompanying drawings. By the way, in the following drawings, like composing elements as in FIGS.  16  to  18 , the same designations are given and thus the description thereof is simplified.  
         [0063]    FIGS.  1  to  3  show a first embodiment of a toroidal-type continuously variable transmission according to the present invention. As shown in FIGS.  1  to  3 , in the width-direction (in FIG. 1, in the front and back direction; and, in FIGS.  2  and  3 , in the right and left direction) middle portions of each of yokes  23 A,  23 B that exist between support holes  18 ,  18 , there are formed elongated-hole-shaped penetration holes  69 ,  69  through which spherical-shaped surface posts (restricting elements)  64 ,  68  can be inserted. The penetration holes  69 ,  69  are formed larger than the outside diameter of the spherical-shaped surface post  64 ,  68  in the width direction of the yokes  23 A,  23 B and, therefore, as shown in FIG. 2, between the penetration holes  69 ,  69  and spherical-shaped surface posts  64 ,  68 , there are formed given clearances S, so that the yokes  23 A,  23 B can play in the width direction. That is, the width-direction movements of the yokes  23 A,  23 B are restricted by the spherical-shaped surface posts  64 ,  68  and the yokes  23 A,  23 B can be moved by an amount corresponding to the clearance S.  
         [0064]    As shown in FIGS. 1 and 3, in the longitudinal-direction (in FIG. 1, in the right and left direction; and, in FIG. 3A, in the vertical direction) outer portions of the penetration holes  69 ,  69  of the yoke  23 A, there are formed bow-shaped plate-like projection portions  70 ,  70  projecting toward the fixing member  52  of a casing  50 , that is an opposing member to the yoke  23 A; and the projection portions  70 ,  70  provide the fulcrums of the swinging movement of the yoke  23 A.  
         [0065]    Similarly, in the longitudinal-direction outer portions of the penetration holes  69 ,  69  of the yoke  23 B as well, there are formed bow-shaped-plate-like projection portions  71 ,  71  projecting toward the upper valve body  61  of the cylinder  31 , that is the opposing member of the yoke  23 B, while the projection portions  71 ,  71  provide the fulcrums of the swinging movement of the yoke  23 B.  
         [0066]    Also, as shown in FIG. 1, the projection portions  70 ,  70  of the yoke  23 A are contacted with the fixing member  52  of the casing  50  and the projection portions  71 ,  71  of the yoke  23 B are contacted with the upper valve body  61 , so that the yokes  23 A,  23 B can be respectively swung about their associated projection portions  70 ,  70 ,  71 ,  71 .  
         [0067]    In the above-structured toroidal-type continuously variable transmission, when the contact positions between the disks and the power rollers are changed, for example, a drive piston  33  situated on the left side in FIG. 2 is shifted downwardly in FIG. 2, while a drive piston  33  on the right side is shifted upwardly in FIG. 2. With the shifting movements of the drive pistons  33 ,  33 , the trunnions  15 ,  15  connected to the drive pistons  33 ,  33  are shifted in the mutually opposite directions: that is, the left trunnion  15  is shifted upwardly in FIG. 2, while the right trunnion  15  is shifted downwardly in FIG. 2.  
         [0068]    Due to this, as shown in FIG. 4A, the yoke  23 A is inclined in a direction, where the right side of the yoke  23 A in FIG. 4A is situated on the upper side, about the projection portions  70 ,  70  contacted with the fixing member  52  of the casing  50 . Similarly, the yoke  23 B is also inclined in the same direction of the yoke  23 A about the projection portions  71 ,  71  contacted with the upper valve body  61  of the cylinder  31 .  
         [0069]    Also, in case where the left drive piston  33  shifts upwardly in FIG. 2 and the right drive piston  33  shifts downwardly in FIG. 2, as shown in FIG. 4B, the yoke  23 A is inclined in a direction where the left side of the yoke  23 A in FIG. 4B is situated on the upper side; and, the yoke  23 B is also inclined in the same direction of the yoke  23 A.  
         [0070]    And, due to the swinging movements of the yokes  23 A,  235 , the shifting movements of the trunnions  15 ,  15  supported by the yokes  23 A,  23 B can be synchronized with each other.  
         [0071]    As described above, since the yokes  23 A,  23 B are swung about the bow-shaped-plate-like projection portions  70 ,  70 ,  71 ,  71  contacted with the fixing member  52  of the casing  50  and upper valve body  61 , the swinging movements of the yokes  23 A,  23 B can be made smooth. This can synchronize the shifting movements of the trunnions  15 ,  15  supported on the yokes  23 A,  23 B with each other stably, which in turn can stabilize the transmission performance of the toroidal-type continuously variable transmission.  
         [0072]    Also, because the present structure can be obtained by forming the projection portions  70 ,  70 ,  71 ,  71  in the yokes  23 A,  23 B, the manufacture of the yokes can be facilitated. Also, since there is eliminated the need for special provision of a pin or the like, the manufacturing cost of the yokes and thus the toroidal-type continuously variable transmission can be reduced.  
         [0073]    And, because the clearances are formed between the yokes  23 A,  23 B and spherical-shaped surface posts  64 ,  68 , the yokes  23 A,  23 B can be moved by an amount corresponding to the clearance S. Thanks to this, even in case where the positions of the yokes  23 A,  23 B inside the casing  50  vary, or oven in case where the positions of the contact portions between the peripheral surface  11   a  of the power roller  11  and disks  2 ,  3  vary according to the power rollers  11  due to variations in the assembling positions of the power rollers  11  with respect to the trunnions  15 , the yokes  23 A,  23 B are allowed to move in the horizontal direction, thereby being able to correct the variations in the positions Of the contact portions.  
         [0074]    Therefore, loads applied to the respective power rollers  11  can be made substantially uniform, which makes it possible to prevent the durability of the power rollers  11  from lowering, thereby being able to extend the lives of the power rollers  11 .  
         [0075]    Also, in order not to descend the durability of the power roller  11 , since it is not necessary to set the positions of the yokes  23 A,  23 B inside the casing  50  and the assembling positions of the power rollers  11  with respect to the trunnions  15  with high accuracy, the assembling operations of these parts can be facilitated.  
         [0076]    Now, FIGS.  5  to  7  show a second embodiment of a toroidal-type continuously variable transmission according to the present invention. By the way, in the present embodiment, the composing elements thereof similar to those of the first embodiment are given the same designations and thus the description thereof is simplified here.  
         [0077]    As shown in FIG. 5, in the fixing member  52  of the casing  50  that is an opposing member to the yoke  23 A, there are formed bow-shaped-plate-like projection portions  72 ,  72  which project toward the yoke  23 A; and, in the upper valve body  61  of the cylinder  31  that is an opposing member to the yoke  23 B, there are formed bow-shaped-plate-like projection portions  73 ,  73  which project toward the yoke  23 B.  
         [0078]    As shown in FIGS. 6A and 6B, the projection portions  72 ,  72  of the fixing member  52  of the casing  50  are contacted with the middle portions A of the yoke  23 A that are situated between the two end portions of the yoke  23 A crossing each other in the width direction of the yoke  23 A; and, the projection portions  73 ,  73  of the upper valve body  61  are contacted with the middle portions B of the yoke  23 B that are situated between the two end portions of the yoke  23 B crossing each other in the width direction of the yoke  23 B. Thus, the yokes  23 A,  23 B can be respectively swung about their associated projection portions  72 ,  72 ,  73 ,  73 .  
         [0079]    In the above-structured toroidal-type continuously variable transmission, as shown in FIG. 7A and FIG. 7B, when the contact positions between the disks and the power rollers are changed, the yoke  23 A contacted with the projection portions  72 ,  72  formed in the fixing member  52  of the casing  50  is swung about these projection portions  72 ,  72  Similarly, the yoke  23 B contacted with the projection portions  73 ,  73  formed in the upper valve body  61  of the cylinder  31  is also swung about these projection portions  73 ,  73 . Therefore, in the present embodiment, there can be obtained similar effects to the first embodiment.  
         [0080]    Now, FIGS.  8  to  11  show a third embodiment of a toroidal-type continuously variable transmission according to the present invention. By the way, in the present embodiment, the same composing elements thereof as the first embodiment are given the same designations and thus the description thereof is simplified here.  
         [0081]    As shown in FIGS. 8 and 9, in the fixing member  52  of the casing  50 , there are formed bow-shaped-plate-like recess portions  74 ,  74  with which the leading end portions of the projection portions  70 ,  70  of the yoke  23 A can be fitted respectively. In case where the leading end portions of the projection portions  70 ,  70  of the yoke  23 A are respectively fitted with the recess portions  74 ,  74  of the fixing member  52  of the casing  50 , the yoke  23 A is swingably supported by the recess portions  74 ,  74 .  
         [0082]    Also, in the upper valve body  61  of the cylinder  31 , there are formed bow-shaped-plate-like recess portions  75 ,  75  with which the leading end portions of the projection portions  71 ,  71  of the yoke  23 B can be fitted respectively. In case where the leading and portions of the projection portions  71 ,  71  of the yoke  23 B are respectively fitted with the recess portions  75 ,  75  of the upper valve body  61 , the yoke  23 B is swingably supported by the recess portions  75 ,  75 .  
         [0083]    That is, according to the present embodiment, as shown in FIGS.  8  end  9 , there are omitted the spherical-shaped surface posts  64 ,  68  (see FIGS. 1 and 2) which are used to support the yokes  23 A,  23 B in a swingable manner. Therefore, as shown in FIG. 10, in the yokes  23 A,  23 B, there are not formed penetration holes through which the spherical-shaped surface posts  64 ,  68  are inserted.  
         [0084]    In the above-structured toroidal-type continuously variable transmission, as shown in FIGS. 11A and 11B, when the contact positions between the disks and the power rollers are changed, the yoke  23 A is swung about the projection portions  70 ,  70  that are fitted with the recess portions  74 ,  74  formed in the fixing member  52  of the casing  50 . Similarly, the yoke  23 B is also swung about the projection portions  71 ,  71  fitted with the recess portions  75 ,  75  formed in the upper valve body  61  of the cylinder  31 .  
         [0085]    Therefore, according to the present embodiment, not only there can be obtained similar effects to the first embodiment but also the swinging centers of the yokes  23 A,  23 B are always constant to thereby be able to stabilize the swinging movements of the yokes  23 A,  23 B.  
         [0086]    Also, because there is eliminated the need for provision of spherical-shaped surface posts and pins which are used to support the yokes  23 A,  23 B in a swingable manner, there can be eliminated not only the operation to form holes in the yokes  23 A,  23 B for insertion of the spherical-shaped surface posts and pins but also the operation to assemble the pins to the yokes  23 A,  23 B, thereby being able to facilitate further the manufacture or the yokes  23 A,  23 B, And, since it is not necessary to use the spherical-shaped surface posts and pins, the number of parts can be reduced and thus the manufacturing cost of the toroidal-type continuously variable transmission can be reduced further.  
         [0087]    Now, FIGS.  12  to  15  show a fourth embodiment of a toroidal-type continuously variable transmission according to the present invention, By the way, in the present embodiment, the similar composing elements thereof to the first embodiment are given the same designations and thus the description thereof is simplified here.  
         [0088]    As shown in FIGS. 12 and 13, in the fixing member  52  of the casing  50 , there formed integrally therewith bow-shaped-plate-like projection portions  76 ,  76  which project toward the yoke  23 A. Also, in the upper valve body  61  of the cylinder  31 , there are formed bow-shaped-plate-like projection portions  77 ,  77  which project toward the yoke  23 B  
         [0089]    Also, as shown in FIGS. 14A and 14B, in the middle portions of the longitudinal-direction two end portions of the yokes  23 A,  23 B, there are formed bow-shaped-plate-like recess portions  78 ,  78 ,  79 ,  79  with which the leading and portions of the projection portions  76 ,  76 ,  77 ,  77  can be fitted respectively.  
         [0090]    In case where the leading end portions of the projection portions  76 ,  76 ,  77 ,  77  are respectively fitted with the recess portions  78 ,  78 ,  79 ,  79 , the yokes  23 A,  23 B are swingably supported by the projection portions  76 ,  76 ,  77 ,  77 .  
         [0091]    That is, according to the present embodiment, as shown in FIGS. 12 and 13, there are not formed the spherical-shaped surface posts  64 ,  68  (see FIGS. 1 and 2) which are used to support the yokes  23 A,  23 B in a swingable manner. Therefore, as shown in FIGS. 14A and 14B, in the yokes  23 A,  23 D, there are not formed penetration holes through which the spherical-shaped surface posts  64 ,  66  are inserted.  
         [0092]    In the above-structured toroidal-type continuously variable transmission, as shown in FIGS. 15A and 15B, when the contact positions between the disks and the power rollers are changed, the yoke  23 A is swung about the recess portions  78 ,  78  fitted with the leading end portions of the projection portions  76 ,  76  formed in the fixing member  52  of the casing  50 . Similarly, the yoke  23 B is also swung about the recess portions  78 ,  78  fitted with the leading end portions of the projection portions  77 ,  77  formed in the upper valve body  61  or the cylinder  31 .  
         [0093]    Therefore, according to the present embodiment, not only there can be obtained similar effects to the first embodiment but also the swinging centers of the yokes  23 A,  23 B can be always kept constant to thereby be able to stabilize the swinging movements of the yokes  23 A,  23 B.  
         [0094]    Also, since there is eliminated the need for provision of the spherical-shaped surface posts and pins which are used to support the yokes  23 A,  23 B in a swingable manner, there can be eliminated not only the operation to form holes through which the spherical-shaped surface posts and pins are inserted but also the operation to assemble the pins to the yokes  23 A,  23 B, which makes it possible to facilitate further the manufacture of the yokes  23 A,  235 . Further, because it is not necessary to use the spherical-shaped surface posts and pins, the number of parts can be reduced and thus the manufacturing cost of the toroidal-type continuously variable transmission can be reduced further.  
         [0095]    By the way, the present invention is not limited to the above-described embodiments but various modifications are possible without departing from the gist of the present invention.  
         [0096]    For example, in the first and third embodiments, in the yokes  23 A,  23 B, there are formed the projection portions  70 ,  70 ,  71 ,  71  integrally with them. However, the projection portions  70 ,  70 ,  71 ,  71  may also be formed separately from the yokes  23 A,  23 B.  
         [0097]    Similarly, in the second embodiment as well, the projection portions  72 ,  72  or the fixing member  52  of the casing  50  and the projection portions  73 ,  73  of the upper valve body  61  of the cylinder  31  may also be formed separately from the fixing member  52  of the casing  50  and the upper valve body  61  of the cylinder  31 .  
         [0098]    Further, in the fourth embodiment as well, the projection portions  76 ,  76  of the fixing member  52  of the casing  50  and the projection portions  77 ,  77  of the upper valve body  61  or the cylinder  31  may also be formed separately from the fixing member  52  of the casing  50  and the upper valve body  61  of the cylinder  31 .  
         [0099]    Also, in the first and third embodiments, the projection portions  70 ,  71  of the yokes  23 A,  23 B are formed in a bow-shaped-plate-like shape. However, the shape of the projection portions  70 ,  71  is not limited to this but, for example, they may have a shape the leading end portion of which is rounded like a semi-spherical shape or a substantially triangular shape. This applies similarly to the projection portions  72 ,  73  in the second embodiment as well as to the projection portions  76 ,  77  in the fourth embodiment.  
         [0100]    By the way, in case where the leading end portions of the projection portions  70 ,  71 ,  72 ,  73 ,  76 ,  77  are rounded, the swinging movements of the yokes  23 A,  23 B can be made further smoother.  
         [0101]    Also, in the above-mentioned respective embodiments, as the opposing members to the yokes, there are used the fixing member  52  of the casing  50  and the upper valve body  61  of the cylinder  31 ; however, instead of them, the casing  50  may be used as the opposing member.  
         [0102]    As has been described heretofore, according to the toroidal-type continuously variable transmission of the present invention, not only the manufacture of a yoke can be facilitated but also the manufacturing cost of the yoke and thus the toroidal-type continuously variable transmission can be reduced.