Abstract:
A toroidal-type continuously variable transmission has an input disk, an output disk, a pressing device for pressing said first disk toward said second disk, a plurality of trunnions having a pair of first support shafts for supporting a plurality of power rollers, a pair of support plates for supporting the first pivot shafts of each of the trunnions; and a pair of swing brackets each including a second pivot shaft parallel to the first pivot shaft of the trunnion, the swing brackets being respectively supported so as to be swingable about the second pivot shafts with respect to the support plates. The first pivot shafts of the trunnion are respectively supported so as to be swingable with respect to the support plates through the swing brackets.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     A toroidal-type continuously variable transmission according to the invention is used as a transmission unit forming as an automatic transmission for a car or as a transmission for controlling the operating speeds of various industrial machines such as a pump. Especially, the invention relates to an improvement in a so called half-toroidal-type continuously variable transmission in which the peripheral surfaces of a plurality of power rollers and the inner surfaces of a pair of disks holding the power rollers between them are not present on the diameter-direction opposite sides of the centers of the inclined rotation of the power rollers. 
     As an example of a transmission unit forming a transmission for a car, there is known such a half-toroidal-type continuously variable transmission as shown in  FIGS. 3 and 4  schematically. In this toroidal-type continuously variable transmission, as disclosed in JP-A-62-71465U, an input side disk  2  is supported concentrically with an input shaft  1  and an output side disk  4  is fixed to the end portion of an output shaft  3  which is disposed concentrically with the input shaft  1 . In the interior of a casing  5  (see  FIG. 6  which will be discussed later) in which a toroidal-type continuously variable transmission, there are disposed trunnions  7 ,  7  which can be swung about pivot shafts  6 ,  6  disposed at positions twisted with respect to the input shaft  1  and output shaft  3 . 
     Specifically, a pair of pivot shafts  6 ,  6  are disposed on the outer surfaces of the two end portions of each trunnion  7  in such a manner that the two pivot shafts  6 ,  6  are concentric with each other. The center axes of the pivot shafts  6 ,  6  are present at twisted positions which do not intersect with the center axes of the input side and output side disks  2 ,  4  but exist in directions at right angles or almost at right angles to the directions of the center axes of the input side and output side disks  2 ,  4 . Also, on the central portions of the respective trunnions  7 ,  7 , there are supported the base half sections of displacement shafts  8 ,  8 ; and, in case where the trunnions  7 ,  7  are swung about the pivot shafts  6 ,  6 , the inclination angles of the shifts shafts  8 ,  8  can be adjusted. On the peripheries of the front half sections of the displacement shafts  8 ,  8  supported on the trunnions  7 ,  7 , there are supported power rollers  9 ,  9  in such a manner that they can be rotated. And, the power rollers  9 ,  9  are held by and between the inner surfaces  2   a,    4   a  of the input side and output side disks  2 ,  4 . 
     The sections of the mutually opposing inner surfaces  2   a,    4   a  of the input side and output side disks  2 ,  4  are respectively formed in a concave surface having an arc-shaped section, while the concave surface can be obtained by rotating an arc having the pivot shaft  6  as a center thereof or by rotating a curved line close to such arc. And, the peripheral surfaces  9   a,    9   a  of the power rollers  9 ,  9  each formed in a spherically convex surface are respectively contacted with the inner surfaces  2   a,    4   a  of the input side and output side disks  2 ,  4 . Also, between the input shaft  1  and input side disk  2 , there is interposed a driving/pressing device  10  such as a loading cam device; and, the input side disk  2  can be rotated by the driving/pressing device  10  while it is elastically pressed toward the output side  4  by the driving/pressing device  10 . By the way, the driving/pressing device  10  may also be composed of a combination of an oil-pressure type pressing device and a power transmission portion such as a spline engagement portion. 
     When the above-structured toroidal-type continuously variable transmission is in use, as the input shaft  1  is rotated, the driving/pressing device  10  rotates the input side disk  2  while pressing the input side disk  2  against the plurality of power rollers  9 ,  9 . And, the rotational movement of the input side disk  2  is transmitted through the plurality of power rollers  9 ,  9  to the output side disk  4 , so that the output shaft  3  fixed to the output side disk  4  can be rotated. When changing the rotation speed between the input shaft  1  and output shaft  3 , firstly, to reduce the rotation speed between the input shaft  1  and output shaft  3 , the trunnions  7 ,  7  may be swung about the pivot shafts  6 ,  6  and the displacement shaft  8 ,  8  may be inclined in such a manner that the peripheral surfaces  9   a,    9   a  of the power rollers  9 ,  9 , as shown in  FIG. 3 , can be respectively contacted with the near-to-center portion of the inner surface  2   a  of the input side disk  2  and the near-to-outer-periphery portion of the inner surface  4   a  of the output side disk  4 . On the other hand, to increase the rotation speed between the input shaft  1  and output shaft  3 , the trunnions  7 ,  7  may be swung and the displacement shaft  8 ,  8  may be inclined in such a manner that the peripheral surfaces  9   a,    9   a  of the power rollers  9 ,  9 , as shown in  FIG. 4 , can be respectively contacted with the near-to-outer-periphery portion of the inner surface  2   a  of the input side disk  2  and the near-to-center portion of the inner surface  4   a  of the output side disk  4 . In case where the inclination angles of the displacement shafts  8 ,  8  are set intermediate between  FIGS. 3 and 4 , an intermediate transmission ratio can be obtained between the input shaft  1  and output shaft  3 . 
     Further,  FIGS. 5 and 6  show a more specified toroidal-type continuously variable transmission which is disclosed in JP-A-1-173552U. In this toroidal-type continuously variable transmission, an input side disk  2  and an output side disk  4  are respectively supported on the periphery of a circular-pipe-shaped input side rotary shaft  11  in such a manner that they can be rotated. Also, between the end portion of the input side rotary shaft  11  and input side disk  2 , there is interposed a driving/pressing device  10  such as a loading cam device. On the other hand, an output gear  12  is coupled to the output side disk  4  in such a manner that the output side disk  4  and output gear  12  can be rotated synchronously. 
     Pivot shafts  6 ,  6 , which are disposed on the two end portions of each of a pair of trunnions  7 ,  7  in such a manner that the pivots  6 ,  6  are concentric with each other, are supported on their associated pair of support plates  13 ,  13  in such a manner that they can be swung as well as can be shifted in the axial direction thereof (that is, in  FIG. 5 , in the front and back direction of the figure sheet; and, in  FIG. 6 , in the vertical direction). And, on the intermediate portions of the respective trunnions  7 ,  7 , there are supported the base half sections of the displacement shafts  8 ,  8 . Each of the displacement shafts  8 ,  8  is structured such that a support shaft portion  14  forming the base half section thereof and a pivot support shaft portion  15  forming the front half section thereof are eccentric to each other. And, the support shaft portions  14  are rotatably supported on intermediate portions of their associated trunnions  7 ,  7 , while power rollers  9 ,  9  are rotatably supported on the peripheries of the pivot support shaft portions  15 . 
     Also, between the outer surfaces of the power rollers  9 ,  9  and the inner surfaces of the intermediate portions of the trunnions  7 ,  7 , there are disposed thrust ball bearings  16 ,  16  and thrust needle roller bearings  17 ,  17  in the order starting from the outer surfaces of the power rollers  9 ,  9 . The thrust ball bearings  16 ,  16 , while supporting thrust-direction loads applied to the power rollers  9 ,  9 , allow the power roller  9 ,  9  to rotate. Also, the thrust needle roller bearings  17 ,  17 , while supporting thrust loads applied from the power rollers  9 ,  9  to outer races  18 ,  18  forming the thrust ball bearings  16 ,  16 , allow the pivot support shaft portions  15 ,  15  of the displacement shafts  8 ,  8  and the outer races  18 ,  18  to be swung about the support shaft portions  14 ,  14  of the displacement shafts  8 ,  8 . Further, the trunnions  7 ,  7  can be shifted in the axial direction thereof by actuators  19 ,  19  of an oil pressure type. By the way, in the present specification, the expression “the axial direction of a trunnion” means the axial directions of a pair of pivot shafts respectively disposed on the two end portions of the present trunnion. 
     In the case of the above-structured toroidal-type continuously variable transmission, the rotational movement of the input side rotary shaft  11  is transmitted through the driving/pressing device  10  to the input side disk  2 . And, the rotational movement of the input side disk  2  is transmitted through a pair of power rollers  9 ,  9  to the output side disk  4  and further the rotational movement of the output side disk  4  is taken out from the output gear  12 . To change the rotation speed ratio between the input side rotary shaft  11  and output gear  12 , the pair of trunnions  7 ,  7  may be respectively shifted by their associated actuators  19 ,  19  in the mutually opposite directions, for example, in such a manner that the power roller  9  shown on the right side in  FIG. 6  is shifted upwardly in  FIG. 6 , whereas the power roller  9  shown on the left side in  FIG. 6  is shifted downwardly in FIG.  6 . This changes the direction of a tangential-direction force acting on the contact portions between the peripheral surfaces  9   a,    9   a  of the power rollers  9 ,  9  and the inner surfaces  2   a,    4   a  of the input side and output side disks  2 ,  4 . And, due to the change in the direction of the tangential-direction force, the trunnions  7 ,  7  are swung in the mutually opposite directions about the pivot shafts  6 ,  6  which are pivotally supported on the support plates  13 ,  13 . This changes the contact positions between the peripheral surfaces  9   a,    9   a  of the power rollers  9 ,  9  and the inner surfaces  2   a,    4   a  of the input side and output side disks  2 ,  4 , as shown in  FIGS. 3 and 4 , with the result that the rotation speed ratio between the input side rotary shaft  11  and output gear  12  is changed. 
     In the power transmission by the toroidal-type continuously variable transmission, the power rollers  9 ,  9  are shifted in the axial direction of the input side rotary shaft  11  in accordance with the elastic deformation of the respective components of the toroidal-type continuously variable transmission. And, the displacement shafts  8 ,  8  supporting the power rollers  9 ,  9  are slightly rotated about their associated support shaft portions  14 . Due to this slight rotation, the outer surfaces of the outer races  18 ,  18  of the thrust ball bearings  16 ,  16  and the inner surfaces of the trunnions  7 ,  7  are shifted relative to each other. Between these outer and inner surfaces, there are interposed the thrust needle roller bearings  17 ,  17  and, therefore, such relative shift can be attained with a small force. 
     Also, in order to be able to increase the power that can be transmitted by the toroidal-type continuously variable transmission, as a structure capable of increasing the number of power rollers  9 ,  9 , conventionally, there is also known a structure of a so called double-cavity type in which, as shown in  FIG. 7 , input side disks  2 A,  2 B and output side disks  4 A,  4 B are disposed by twos on the periphery of an input side rotary shaft  11   a  and these input side disks  2 A,  2 B and output side disks  4 A,  4 B are arranged in parallel to each other in the transmission direction of the power. In the structure shown in  FIG. 7 , an output gear  12   a  is supported on the periphery of the intermediate portion of the input side rotary shaft  11   a  in such a manner that it can be rotated with respect to the input side rotary shaft  11   a  while it is prevented against movement in the axial direction thereof. That is, a sleeve  22 , which is disposed on the central portion of the output gear  12   a,  is rotatably supported on the middle wall  21  of the housing  5  by a pair of rolling bearings  23 ,  23  such as angular contact ball bearings. And, the output side disks  4 ,  4  are spline engaged with the two end portions of the sleeve  22 . 
     Also, the input side disks  2 A,  2 B are supported on the two end portions of the input side rotary shaft  11   a  through ball splines  24 ,  24  in such a manner that they can be shifted in the axial direction thereof as well as can be rotated together with the input side rotary shaft  11   a.  This input side rotary shaft  11   a  can be driven or rotated by a drive shaft  20  through the driving/pressing device  10 . Of the pair of input side disks  2 A,  2 B, the input side disk  2 A situated on the driving/pressing device  10  side can be moved in the axial direction thereof along the input side rotary shaft  11   a  as the driving/pressing device  10  operates. On the other hand, the input side disk  2 B is butted against a loading nut  25  through a countersunk spring  26  having large elasticity to limit (substantially prevent) the movement of the input side rotary shaft  11   a  in the axial direction thereof. In the case of the thus structured toroidal-type continuously variable transmission, the transmission of the power from the input side rotary shaft  11   a  to the output gear  12   a  is carried out through two routes, that is, one route between one input side disk  2 A and output side disk  4  and the other route between the other input side disk  2 B and output side disk  4 . Thanks to this, great power can be transmitted. 
     By the way, the support plates  13 ,  13  (see FIG.  6 ), which are used to support the two end portions of trunnions  7 ,  7  to be incorporated into a half toroidal-type continuously variable transmission in such a manner that they can be swung as well as can be shifted in the axial direction thereof, as shown in  FIG. 6 , are supported on support posts  27   a,    27   b  fixedly disposed within the casing  5  in such a manner that they can be swung as well as can be shifted in the axial direction of the irrespective support posts  27   a,    27   b  (in  FIG. 6 , in the vertical direction). And, since the pivot shafts  6 ,  6  disposed on the two end portions of the respective trunnions  7 ,  7  are supported on the end portions of the thus arranged support plates  13 ,  13 , the trunnions  7 ,  7  can be swung and can be shifted in the axial direction thereof. It is the gist of the invention to improve the structure of this portion and, therefore, description will be given below in more detail of the structure and operation of this portion with reference to FIG.  8 . 
     A pair of pivot shafts  6 ,  6 , which are concentrically disposed on the two end portions of a trunnion  7 , are supported inside circular holes  28 ,  28  formed in the end portions of a pair of support plates  13 ,  13  which are disposed so as to hold the trunnion  7  from both sides in the axial direction of the trunnion  7 . Therefore, radial needle roller bearings  29  are disposed on the peripheries of the respective pivot shafts  6 ,  6 . Each of outer races  30  forming the respective radial needle roller bearings  29  has an outer peripheral surface which is formed in a spherically convex surface. Each of the outer races  30  is fitted with the inner surface of the circular hole  28  with no play in such a manner that it can be moved in the axial direction and can be swung. 
     In case where a rod  31  connected to one end portion (in  FIG. 8 , the lower end portion) of the trunnion  7  is pushed and pulled by the actuator  19  (see FIG.  6 ), the outer races  30  of the respective radial needle roller bearings  29 ,  29  are slightly swung as well as (while the center axes of the outer races  30  and the center axes of the circular holes  28  are kept not coincident with each other) are shifted in the axial direction inside the respective circular holes  28 ,  28 . Not only such movements of the respective outer races  30 ,  30  within the circular holes  28 ,  28  but also the axial-direction shifting movements of the respective pivot shafts  6 ,  6  with respect to their associated radial needle roller bearings  29 ,  29  allow the trunnion  7  to shift in the axial direction thereof. This changes the direction of a force acting on the peripheral surface  9   a  of a power roller  9  (which will be discussed below) and, when the inclination angle of the trunnion  7  supporting the power roller  9  is changed, the pivot shafts  6 ,  6 , based on the operations of the respective radial needle roller bearings  29 ,  29  are swung in the twisted rotation direction inside the respective circular holes  28 ,  28 . 
     A support shaft portion  14  forming a displacement shaft  8  for supporting the power roller  9  on the trunnion  7  is supported in the interior of a circular-shaped support hole  32  formed in the axial-direction middle portion of the trunnion  7  supported between the pair of support plates  13 ,  13  in the above-mentioned manner by another radial needle roller bearing  33  in such a manner that the support shaft portion  14  can be swung and shifted in the twisted rotation direction. Also, the power roller  9  is rotatably supported on the periphery of a pivot support shaft portion  15  also forming the displacement shaft  8  by still another radial needle roller bearing  34 . Between the outer surface of the power roller  9  and the inner surface of the trunnion  7 , there are interposed a thrust ball bearing  16  and a thrust needle roller bearing  17  in the order starting from the power roller  9  side. Thanks to this structure, not only the power roller  9  can be rotatably supported while supporting a large thrust load applied to the power roller  9 , but also, when torque varies, the power roller  9  is allowed to shift in the axial direction of the respective input side and output side disks  2 ,  2 A,  2 B,  4  (see  FIGS. 3 ,  4 ,  5  and  7 ). 
     In the case of the conventional structure in which the trunnion  7  is supported between the pair of support plates  13 ,  13  in the above-mentioned manner and the power roller  9  is supported on the present trunnion  7 , the cost thereof is expensive and it is difficult to realize a structure capable of transmitting greater torque. The reasons for these drawbacks are as follows: 
     Firstly, the reason for the expensive cost is that, between the trunnion  7  and power roller  9 , there are interposed the displacement shaft  8 , the pair of radial needle roller bearings  33 ,  34 , thrust ball bearing  16  and thrust needle roller bearing  17  in such a manner that they are combined together in a complicated manner. Also, each of the bearings  33 ,  34 ,  16 ,  17  is constructed by a plurality of parts combined together. Due to this, the number of parts is increased and the assembling operation is troublesome, which gives rise to the expensive cost. Also, since the radial needle roller bearing  34  interposed between the displacement shaft  8  and power roller  9  is operated at a high speed, it is necessary to supply a sufficient amount of lubricating oil to the radial needle roller bearing  34 . Such supply of the lubricating oil is executed through lubricating oil passages formed in the interiors of the trunnion  7  and displacement shaft  8 . However, it is troublesome to form such lubricating oil passages, with the result that the cost of the structure is inevitably increased. 
     Also, the reason why it is difficult to realize a structure capable of transmitting greater torque is that, in order to connect together the trunnion  7  and power roller  9  through the displacement shaft  8  and the pair of radial needle roller bearings  33 ,  34 , the support hole  32  is formed in the axial-direction middle portion of the trunnion  7  and the power roller  9  is formed in a hollow annular shape. That is, when the toroidal-type continuously variable transmission is in operation, large radial loads and thrust loads are applied to the two diameter-direction opposite positions of the peripheral surface  9   a  of the power roller  9  from the inner surfaces  2   a,    4   a  of the input side and output side disks  2 ,  2 A,  2 B,  4  (see  FIGS. 3 ,  4 ,  5  and  7 ). Also, a large thrust load which is applied to the power roller  9  is applied to the inner surface of the trunnion  7 . 
     When the toroidal-type continuously variable transmission is in operation, the trunnion  7  and power roller  9  are elastically deformed due to these large loads. That is, the trunnion  7  with the two end portions thereof supported is elastically deformed in the direction in which the inner surface of the axial-direction middle portion thereof is turned into a concave surface, whereas the power roller  9  is elastically deformed into an oval shape in which the contact portions thereof with respect to the two inner surfaces  2   a,    4   a  provide a short diameter. And, due to such elastic deformation, there are generated large stresses respectively in the interiors of the trunnion  7  and power roller  9 . The thus-generated stresses concentrate not only on the portion of the trunnion  7  that is situated in the periphery of the support hole  32  but also on the near-to-inside-diameter portion of the power roller  9  (the peripheral portion of the center hole thereof). In case where the torque to be transmitted by the toroidal-type continuously variable transmission increases and the above stresses increase further, the durability of the trunnion  7  and power roller  9  cannot be fully secured. To eliminate the durability shortage due to the above causes, the trunnion  7  and power roller  9  may be formed so as to be increased in the thickness. However, in this case, the weights of the trunnion  7  and power roller  9  increase greatly Therefore, to increase the thickness of the trunnion  7  and power roller  9  is not always a proper measure. 
     SUMMARY OF THE INVENTION 
     The present invention aims at eliminating the above-mentioned drawbacks found in the conventional toroidal-type continuously variable transmission. Accordingly, it is an object of the invention to provide a toroidal-type continuously variable transmission which not only can secure the durability of the trunnion and power roller without increasing the weights thereof but also can reduce the cost thereof as the need arises. 
     In attaining the above object, according to a first aspect of the invention, there is provided a toroidal-type continuously variable transmission, including: 
     a first disk including an inner surface and supported in such a manner as to be rotatable and shiftable in the axial direction thereof; 
     a second disk including an inner surface and supported concentrically with the first disk in such a manner that, with the inner surface thereof opposed to the inner surface of the first disk, the second disk is rotatable independently of the first disk but is prevented from shifting in the axial direction thereof; 
     a pressing device for pressing the first disk toward the second disk; 
     a plurality of trunnions each including in the two end portions thereof two first pivot shafts respectively situated at twisted positions with respect to the center axes of the first and second disks, each of the trunnions being swingable about the first pivot shafts; 
     a pair of support plates for supporting the first pivot shafts of each of the trunnions; 
     a plurality of power rollers interposed between the inner surfaces of the first and second disks in such a manner as to be rotatably supported on the trunnions; and, 
     a pair of swing brackets each including a second pivot shaft parallel to the first pivot shaft of each of the trunnions, the swing brackets being respectively supported so as to be swingable about the second pivot shafts with respect to the support plates, 
     wherein the first pivot shafts of each of the trunnions are respectively supported so as to be swingable with respect to the support plates through the swing brackets. 
     Further, according to a second aspect of the invention, in the toroidal-type continuously variable transmission according to the first aspect, the trunnions are respectively supported on the pair of swing brackets by the first radial needle roller bearings so as to be swingable, and 
     the swing brackets are respectively supported on the support plates by the second radial needle roller bearings so as to be swingable. 
     Moreover, according to a third aspect of the invention, in the toroidal-type continuously variable transmission according to the first aspect, the trunnions are made of solid members without holes in the axial-direction middle portions thereof, and the power rollers are made of solid members without center holes. 
     According to a fourth aspect of the invention, there is provided a toroidal-type continuously variable transmission, comprising: 
     a first disk including an inner surface and supported in such a manner as to be rotatable and shiftable in the axial direction thereof; 
     a second disk including an inner surface and supported concentrically with the first disk in such a manner that, with the inner surface thereof opposed to the inner surface of the first disk, the second disk is rotatable independently of the first disk but is prevented from shifting in the axial direction thereof; 
     a pressing device for pressing the first disk toward the second disk; 
     a plurality of trunnions each including in the two end portions thereof two first pivot shafts respectively situated at twisted positions with respect to the center axes of the first and second disks, each of the trunnions being swingable about the first pivot shafts; 
     a plurality of power rollers interposed between the inner surfaces of the first and second disks in such a manner as to be rotatably supported on the trunnions; and, 
     a plurality of thrust ball bearings each for allowing the rotation of the power roller while supporting thrust-direction load applied to the power roller, each of the thrust ball bearing comprising:
         an inner race raceway formed in the inner surface of the power roller;   an outer race raceway formed in the inner surface of the trunnion;   a plurality of balls rollably interposed between the inner race raceway and the outer race raceway; and,   a retainer for holding the balls therein.       

     According to a fifth aspect of the invention, in the toroidal-type continuously variable transmission according to the fourth aspect, further including: 
     a pair of support plates for supporting the first pivot shafts of each of the trunnions; and, 
     a pair of swing brackets each including a second pivot shaft parallel to the first pivot shaft of each of the trunnions, the swing brackets being respectively supported so as to be swingable about the second pivot shafts with respect to the support plates, 
     wherein the first pivot shafts of each of the trunnions are respectively supported so as to be swingable with respect to the support plates through the swing brackets. 
     According to a sixth aspect of the invention, in the toroidal-type continuously variable transmission according to the fifth aspect, the trunnions are respectively supported on the pair of swing brackets by the first radial needle roller bearings so as to be swingable, and 
     the swing brackets are respectively supported on the support plates by the second radial needle roller bearings so as to be swingable. 
     In addition, according to a seventh aspect of the invention, there is provided a toroidal-type continuously variable transmission, comprising: 
     a first disk including an inner surface and supported in such a manner as to be rotatable and shiftable in the axial direction thereof; 
     a second disk including an inner surface and supported concentrically with the first disk in such a manner that, with the inner surface thereof opposed to the inner surface of the first disk, the second disk is rotatable independently of the first disk but is prevented from shifting in the axial direction thereof; 
     a pressing device for pressing the first disk toward the second disk; 
     a plurality of trunnions each including in the two end portions thereof two first pivot shafts respectively situated at twisted positions with respect to the center axes of the first and second disks, each of the trunnions being swingable about the first pivot shafts; 
     a plurality of power rollers interposed between the inner surfaces of the first and second disks in such a manner as to be rotatably supported on the trunnions; and, 
     a plurality of thrust ball bearings each for allowing the rotation of the power roller while supporting thrust-direction load applied to the power roller, each of the thrust ball bearing comprising:
         an inner race raceway formed in the inner surface of the power roller;   an outer race raceway formed in an outer race fitted with the inner surface of the trunnion;   a plurality of balls rollably interposed between the inner race raceway and the outer race raceway; and,   a retainer for holding the balls therein.       

     In the case of the above-structured toroidal-type continuously variable transmission according to the invention, the operation to transmit the rotational power between the first and second disks and change the transmission ratio between the first and second disks is similar to the conventional structure which is shown in  FIGS. 5  to  7 . 
     Especially, in the toroidal-type continuously variable transmission according to the invention, in case where the components of the transmission such as the first and second disks are elastically deformed when the present transmission is in operation, the swing brackets are respectively swung with respect to their associated support plates to thereby cause the peripheral surfaces of the power rollers to follow the inner surfaces of the first and second disks. 
     In the case of the structure of the toroidal-type continuously variable transmission according to the invention, there are eliminated not only the need for provision of the displacement shaft, radial needle roller bearings and thrust needle roller bearing but also the lubricating oil passage used to supply lubricating oil to the radial needle roller bearing interposed between the power roller and displacement shaft, which are necessary in the conventional structure. This can decrease the number of parts and the number of working steps and, therefore, the cost of the toroidal-type continuously variable transmission can be reduced. 
     Also, there is further eliminated the need for formation of the center holes and support holes in the axial-direction middle portions of the power rollers and trunnions. Even in case where there are formed the center holes and support holes in order to reduce the weight of the toroidal-type continuously variable transmission and secure the lubricating oil passage, the center holes and support holes may be formed so as to be smaller in diameter than those formed in the conventional toroidal-type continuously variable transmission. This can relieve the concentration of stresses involved with the power rollers and trunnions, thereby being able to secure the durability of the power rollers and trunnions without increasing the weights thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view (similar to  FIG. 8 ) of the main portions of a first embodiment of a toroidal-type continuously variable transmission according to the invention; 
         FIG. 2  is a section view of the main portions of a second embodiment of a toroidal-type continuously variable transmission according to the invention; 
         FIG. 3  is a schematic side view of the basic structure of a toroidal-type continuously variable transmission, showing a state in which the rotation speed thereof is reduced down to the maximum; 
         FIG. 4  is a schematic side view of the basic structure of a toroidal-type continuously variable transmission, showing a state in which the rotation speed thereof is increased up to the maximum; 
         FIG. 5  is a section view of the main portions of the structure of a conventional toroidal-type continuously variable transmission; 
         FIG. 6  is a section view taken along the line A—A shown in  FIG. 5 ; 
         FIG. 7  is a section view of the main portions of the structure of a conventional toroidal-type continuously variable transmission of a double cavity type; and, 
         FIG. 8  is a section view of the main portions of a toroidal-type continuously variable transmission used to explain the problems to be solved by the invention, corresponding to the upper right portion of FIG.  6 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now,  FIG. 1  shows an embodiment of a toroidal-type continuously variable transmission according to the invention. By the way, a toroidal-type continuously variable transmission according to the invention is characterized by the structure of a portion where first pivot shafts  6 ,  6  respectively disposed on the two end portions of each trunnion  7   a  are supported on a pair of support plates  13 ,  13 . The structures and operations of the remaining portions of the present embodiment are similar to those of the toroidal-type continuously variable transmission of a single cavity type shown in  FIGS. 5 and 6  or the toroidal-type continuously variable transmission of a double cavity type shown in FIG.  7 . Therefore, the illustration and description of the same parts are omitted here and thus description will be given below mainly of the characteristic portion of the invention. 
     In the toroidal-type continuously variable transmission according to the present embodiment, the first pivot shafts  6 ,  6  are supported on the support plates  13 ,  13  through swing brackets  35 ,  35 . These support plates  13 ,  13  are respectively supported within the casing  5  (see  FIGS. 6 and 7 ) in such a manner that they can be swung and can be shifted in the axial direction of the trunnion  7   a.  Also, each of the swing brackets  35 ,  35  includes a support plate portion  36  and a second pivot shaft  37  projectedly provided on the outer surface of the base end portion (the opposite surface) of the support plate portion  36 . A second circular hole  38  is formed in the front half section of the support plate portion  36 . The center axis of the second circular hole  38  and the center axis of the second pivot shaft  37  are parallel to each other. 
     The second pivot shafts  37  forming the swing brackets  35 ,  35  each having the above structure are supported in the interiors of the circular holes  28  formed in the end portions of the support plates  13 ,  13  by second radial needle roller bearings  39  in such a manner that they can be rotated and can be shifted in the axial direction thereof. On the other hand, the first pivot shafts  6 ,  6  disposed on the two end portions of the trunnion  7   a  are supported in the second circular holes  38  formed in the front half sections of the support plate portions  36  of the swing brackets  35 ,  35  by first radial needle roller bearings  29 ,  29 . And, outer races  30  forming the first radial needle roller bearings  29 ,  29  are respectively arranged such that their respective outer surfaces are formed in a spherically convex surface. The thus formed outer races  30  are fitted into the second circular holes  38  with no play in such a manner that they can be moved in the axial direction thereof and can be swung. 
     In the present embodiment, the trunnion  7   a  is made of a solid member which does not include a support hole in the axial-direction middle portion thereof, while a power roller  9 A is also made of a solid member which does not have a center hole. And, a plurality of balls  42 ,  42  are rollably interposed between an inner race raceway  40  formed in the inner surface of the power roller  9 A and an outer race raceway  41  formed directly in the inner surface of the trunnion  7   a,  while they are held by a retainer  43 , thereby constituting a thrust ball bearing  16   a.  Thanks to this structure, the power roller  9 A is rotatably supported on the inner surface of the trunnion  7   a  while supporting a thrust-direction load applied to the power roller  9 A. By the way, to the thrust ball bearing  16   a,  there can be supplied lubricating oil through a hollow pipe-shaped rod  31  and an oil supply passage (not shown) formed in the interior of the trunnion  7   a.    
     In the case of the above-structured toroidal-type continuously variable transmission according to the present embodiment, when in operation, in case where the components such as the input side and output side disks  2 ,  2 A,  2 B,  4  are elastically deformed to thereby shift the axial-direction positions of the inner surfaces  2   a,    4   a  of the input side and output side disks  2 ,  2 A,  2 B,  4  (see  FIGS. 3 ,  4 ,  5  and  7 ), the swing brackets  35 ,  35  are swung with respect to the support plates  13 ,  13 , respectively. That is, the swing brackets  35 ,  35  are swung about the second pivot shafts  37  and are thereby shifted in the front and back direction of the sheet of  FIG. 1 , thereby causing the whole trunnion  7   a  to shift in the front and back direction of the sheet of FIG.  1 . This changes the position of the power roller  9 A supported on the inner surface portion of the trunnion  7   a  with respect to the axial direction of the input side and output side disks  2 ,  2 A,  2 B,  4 , thereby causing the peripheral surface  9   a  of the power roller  9 A to follow the inner surfaces  2   a,    4   a  of the input side and output side disks  2 ,  2 A,  2 B,  4 . 
     Due to the engagement between the inner surfaces  2   a,    4   a  and the peripheral surface  9   a  of the power roller  9 A, a radial load based on a large thrust load which is applied to the power roller  9 A is applied to the oscillatory support portions of the second pivot shafts  37 ,  37  with respect to the support plates  13 ,  13 . However, since the second radial needle roller bearings  39  are disposed on the above-mentioned oscillatory support portions, the following operation of the peripheral surface  9   a  with respect to the inner surfaces  2   a,    4   a  can be performed smoothly. Therefore, in the traction portion in which the inner surfaces  2   a,    4   a  are contacted with the peripheral surface  9   a  to transmit the power between them, there can be secured a sufficient contact pressure, which can restrict an increase in the degree of slippage of the traction portion, thereby being able to prevent the power transmission efficiency from lowering and gross slippage from occurring. 
     According to the above-structured toroidal-type continuously variable transmission according to the present embodiment, there are eliminated not only the need for provision of the displacement shaft  8 , radial needle roller bearings  33 ,  34  and thrust needle roller bearing  17  but also the need for formation of the lubricating oil passage used to supply lubricating oil to the radial needle roller bearing  33  interposed between the power roller  9  and displacement shaft  8 , which have been necessary in the conventional structure shown in FIG.  7 . Also, there is eliminated the need for the operation to form the center holes and support holes  32  with the inside diameter dimensions thereof regulated severely in the power roller  9  and trunnion  7 . This can decrease the number of parts and the number of working steps to thereby be able to reduce the cost of the toroidal-type continuously variable transmission. Especially, the mechanism for forming the lubricating oil passage in the interior of the displacement shaft  8  made of hard material as well as the mechanism for feeding the lubricating oil from the trunnion  7  into the lubricating oil passage side formed in the interior of the displacement shaft  8  which can be swung with respect to the trunnion  7  are both complicated, which gives rise to the expensive cost of the toroidal-type continuously variable transmission. However, according to the present embodiment, since both of these mechanisms can be omitted, the cost of the toroidal-type continuously variable transmission can be reduced sufficiently. By the way, even in the present embodiment as well, the lubricating oil passage for supplying the lubricating oil to the thrust ball bearing  16   a  must be formed in the interior of the trunnion  7   a.  However, in the case of the lubricating oil passage, the downstream end portion thereof may be only formed so as to be open to the inner surface of the middle portion of the trunnion  7   a,  which does not make troublesome the lubricating oil passage forming operation or the components assembling operation. 
     Also, in the case of the toroidal-type continuously variable transmission according to the present embodiment, no center hole or support hole is formed in the axial-direction middle portions of the power roller  9 A and trunnion  7   a,  but the power roller  9 A and trunnion  7   a  are respectively made of solid members This can relieve the concentration of the stresses involved with the power roller  9 A and trunnion  7   a  and, therefore, the durability of the power roller  9 A and trunnion  7   a  can be secured without increasing the weights of the power roller  9 A and trunnion  7   a.  That is, omission of the center hole and support hole not only can enhance the rigidity of the power roller  9 A and trunnion  7   a  to thereby make it difficult for the power roller  9 A and trunnion  7   a  to be deformed elastically but also can eliminate the stress-easy-to-concentrate portions from the power roller  9 A and trunnion  7   a,  which makes it possible to enhance the durability of the power roller  9 A and trunnion  7   a.    
     By the way, in the present embodiment, the outer race raceway  41  forming the thrust ball bearing  16   a  is formed directly in the inner surface of the trunnion  7   a.  However, alternatively, as shown in  FIG. 2 , the outer race raceway  41  can also be formed in an outer race  44  which is produced separately from the main body portion of the trunnion  7   b  and, after then, the outer race  44  can be fitted with and fixed to the main body portion of the trunnion  7   b.  This structure not only can facilitate the execution of a quenching effect treatment on the surface portion of the outer race raceway  41   a  but also can facilitate the heat treatment on the main body portion of the trunnion  7   b  under the optimum conditions. Also, in the case of the second radial needle roller bearings  39  interposed between the circular holes  28  formed in the end portions of the support plates  13 ,  13  and the second pivot shafts  37  of the swing brackets  35 , outer races each having an outer peripheral surface formed in a spherically convex surface can also be incorporated into the second radial needle roller bearings  39 . 
     While only certain embodiments of the invention have been specifically described herein, it will apparent that numerous modifications may be made thereto without departing from the spirit and scope of the invention. 
     Since the invention is structured and operates in the above-mentioned manner, the invention is able to realize a toroidal-type continuously variable transmission which can secure sufficient durability even when transmitting large torque and also can be structured light in weight at a low cost.