Patent Publication Number: US-2011070996-A1

Title: Conical friction wheel type continuously variable transmission device

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2009-218122 filed on Sep. 18, 2009 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a conical friction wheel type continuously variable transmission device that includes: a pair of conical friction wheels disposed parallel to each other and disposed such that large diameter portions and small diameter portions of the friction wheels are respectively disposed opposite to each other in an axial direction; and a ring interposed between opposing inclined surfaces of the friction wheels, wherein speed is steplessly changed by moving the ring in the axial direction. Specifically, the present invention relates to the configuration of the ring. 
     DESCRIPTION OF THE RELATED ART 
     As shown in  FIG. 4A , in the related art, a conical friction wheel type continuously variable transmission device (cone ring type continuously variable transmission device)  101  is known that includes an input-side conical friction wheel  22 , an output-side conical friction wheel  23 , and a metal ring  125  interposed between opposing inclined surfaces of the friction wheels, so as to surround the input-side friction wheel  22 . In the cone ring type continuously variable transmission device  101 , respective axes of the friction wheels are parallel to each other, and large diameter portions and small diameter portions of the friction wheels are respectively disposed opposite to each other in an axial direction. With this configuration, the cone ring type continuously variable transmission  101  steplessly changes speed by moving the ring  125  in the axial direction. 
     In the cone ring type continuously variable transmission  101 , a large axial force corresponding to transferred torque and the like are applied in an oil environment, such as with traction oil, and a large contact pressure is applied in the state where an oil film exists between the ring  125  and the friction wheels  22 ,  23  at contact portions thereof, whereby power is transmitted. 
     As shown in  FIG. 4B , in the related art, an inner contact surface  126  of the ring  125  contacts the input-side friction wheel  22  and includes a linear portion  126   a  positioned in a center region, and curved portions  126   b ,  126   e  that are provided on both sides of the center region and have relatively large curvatures. An outer contact surface  127  of the ring  125  also contacts the output-side friction wheel  23  and includes a curved portion  127   a  having a relatively large radius R (center O) (refer to Published Japanese Translation of PCT Application No. JP-A-2009-506279, paragraphs [0181] to [0184],  FIG. 7 ). With this configuration, vibration of the ring is suppressed through linear contact between the input-side friction wheel  22  and the linear portion  126   a  on the inner contact surface  126  of the ring  125 , and the speed can be smoothly changed as the outer contact surface  127  contacts the output-side friction wheel  23  at a point (contact point P) on the curved portion  127   a.    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     The ring  125  is set so that a centerline of curvature (radius) R of the outer surface curved portion  127   a  passing through a width-direction center point Q of the inner surface linear portion  126   a  is positioned at the width-direction center of the curved portion  127   a . That is, the width-direction center portion P of the ring outer contact surface  127  is positioned at a point farthest from the inner surface linear portion  126   a , and a peak point is set to the contact point P at which the outer contact surface  127  contacts the output-side friction wheel  23 . With this configuration, when the inner surface contact portion center Q and the outer surface contact portion P are positioned at the width-direction center of the ring  125 , a large clamping force F is applied from the friction wheels  22 ,  23  to the ring  125  in the direction of the same line (R). Consequently, a moment occurring on the ring  125  can be suppressed and power transmission loss can be reduced, which is preferable in terms of transmission efficiency. 
     However, in the cone ring type continuously variable transmission device  101 , a large contact pressure is applied to the contact portions between the ring  125  and the friction wheels  22 ,  23 , and power is transmitted through a shear force of the oil film in an extreme pressure condition. Therefore, a large load is applied to the friction wheels  22 ,  23  in a direction separating the friction wheels  22 ,  23  from each other. When the continuously variable transmission device  101  is used for driving a vehicle and a large load is applied, and particularly when the cone ring type continuously variable transmission device  101  is used in a low speed condition (underdrive condition), deformation of the input-side friction wheel, especially, deformation of the small diameter portion thereof, is large because of the large transferred torque and low rigidity in the small diameter portion of the input-side friction wheel  22  (see an axis line l to an axis line l′ shown in  FIG. 4A ). 
     Thus, as shown in  FIG. 4C , the input-side friction wheel  22  deforms in a direction that separates the small diameter portion side of the input-side friction wheel  22  from the output-side friction wheel  23 , that is, in a direction that increases an angle of inclination α formed by a contact inclination surface  22   e  of the input-side friction wheel  22 . The ring  125  also inclines in accordance with the deformation described above when the inner surface linear portion  126   a  contacts the input-side friction wheel  22 , and an outer surface contact point P 1  formed on the curved portion  127   a  is moved to the small diameter portion side of the output-side friction wheel  23 . This moves the outer surface contact point P 1  of the ring  125  closer to a corner portion, and a local surface pressure is generated at the corner portion, resulting in a reduction of durability of the ring  125 , and by extension, the cone ring type continuously variable transmission device  101 , thus reducing transmission efficiency. 
     In consideration of the foregoing, it is an object of the present invention to provide a conical friction wheel type continuously variable transmission device that solves the above problems by setting a movable range of an outer surface contact point of a ring longer in a moving direction when the friction wheel deforms as described above. 
     According to a first aspect of the present invention, a curved portion of a second-side contact surface is disposed such that a point (referred to as a contact point) on the curved portion, which is farthest from a linear portion, is positioned offset to a large diameter portion side of another friction wheel that the curved portion contacts. Therefore, even when one friction wheel, especially, a small diameter portion side of the one friction wheel, deforms due to a contact pressure, and a contact point is moved to the small diameter portion side, a local surface pressure is prevented from occurring on an edge (corner) portion due to the long distance to the edge portion on the small diameter portion side. This improves the durability of a ring, and by extension, the durability of the continuously variable transmission device, and also improves transmission efficiency without applying an unusual force to the ring. 
     According to a second aspect of the present invention, an inner contact surface of the ring is the linear portion, and an outer contact surface is the curved portion. Accordingly, even when the one friction wheel deforms on the small diameter portion side, and the contact point is moved to the small diameter portion side, the distance to the edge portion on the small diameter portion side is long, and thus a local surface pressure is prevented from occurring on the edge (corner) portion. Consequently, the durability of the ring can be improved. 
     According to a third aspect of the present invention, because the curved portion is formed of an arc about a single point, the second-side contact surface of the ring is smoothly moved even with the deformation of the friction wheel. Further, the first-side contact surface is formed of the linear portion to suppress rotation vibration of the ring. Good transmission efficiency can be thus maintained through the combination of these features. 
     According to a fourth aspect of the present invention, a force applied to the first-side contact surface of the ring and a force applied to the second-side contact surface of the ring are on the same line, and thus a moment is suppressed from acting on the ring so as to prevent reduced durability due to movement of the contact point on the second-side contact surface. Moreover, it is also possible to prevent a reduction in the transmission efficiency by stabilizing the rotation of the ring. 
     According to a fifth aspect of the present invention, a plane of rotation of the ring is set at an angle that is raised toward a direction perpendicular to axes, and thus an unusual force is not generated when the ring rotates, thereby improving the transmission efficiency. 
     According to a sixth aspect of the present invention, a side surface of the ring is formed of a plane perpendicular to the axes. Therefore, even if the contact point is positioned offset, the entire ring forms a natural parallelogram, and the plane of rotation of the ring is perpendicular to the axes. This achieves compact configuration with a short diameter. 
     According to a seventh aspect of the present invention, because the second-side contact surface is entirely formed of the curved portion, the contact point is movable in a maximum range when the friction wheel deforms, and this allows improvement of the durability of the ring. 
     According to an eighth aspect of the present invention, because the one friction wheel surrounded by the ring is an input member, the durability of the ring can be improved when the friction wheel deforms in a decelerating (underdrive) state where a transferred torque is large. 
     According to a ninth aspect of the present invention, when the second-side axial portions of the friction wheels are supported by a case such as a partition, the one friction wheel must be supported by a bearing to provide play when assembled. Even if the one friction wheel deforms in the state of shaft support with play, such deformation can be absorbed by expanding a movable range of the contact point using the configuration of the ring described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front cross-sectional view showing a hybrid drive system to which the present invention is applied; 
         FIG. 2  is a front cross-sectional view showing a conical friction wheel (cone ring) type continuously variable transmission device in the hybrid vehicle; 
         FIGS. 3A and 3B  show lateral cross-sectional views of a ring of the conical friction wheel type continuously variable transmission device according to the present invention, in which  FIG. 3A  shows a state where no load is applied (i.e., a friction wheel does not deform), and  FIG. 3B  shows a state where a load is applied (i.e., the friction wheel deforms); and 
         FIGS. 4A to 4C  show related art, in which  FIG. 4A  is a cross-sectional view showing an outline of a conical friction wheel type continuously variable transmission device,  FIG. 4B  is a lateral cross-sectional view showing a ring when no load is applied, and  FIG. 4C  is a lateral cross-sectional view showing the ring when a load is applied. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     A hybrid drive system to which the present invention is applied will be described below with reference to the attached drawings. As shown in  FIGS. 1 and 2 , a hybrid drive system  1  includes an electric motor  2 , a cone ring type continuously variable transmission device (conical friction wheel type continuously variable transmission device)  3 , a differential device  5 , an input shaft  6  that moves in accordance with an output shaft of an engine (not shown), and a gear transmission device  7 . The above devices and shafts are housed in a case  11  that is formed by two case members, that is, a case member  9  and a case member  10 . Further, the case  11  includes a first space A and a second space B divided by a partition  12  in an oil-tight manner. 
     The electric motor  2  includes a stator  2   a  fixed to the first case member  9 , and a rotor  2   b  provided on an output shaft  4 . A first end portion of the output shaft  4  is rotatably supported by the first case member  9  through a bearing  13 , and a second end portion of the output shaft  4  is rotatably supported by the second case member  10  through a bearing  15 . An output gear  16  consisting of a toothed gear (pinion) is formed on a first side of the output shaft  4 , and meshes with an intermediate gear (toothed gear)  19  provided on the input shaft  6  through a toothed idler gear  17 . 
     A shaft  17   a  of the toothed idler gear  17  includes a first end portion that is rotatably supported by the partition  12  through a bearing  20 , and a second end portion that is rotatably supported by the second case member  10  through a bearing  21 . The toothed idler gear  17  is disposed partially overlapping with the electric motor  2  in a radial direction when viewed from the side (that is, when viewed in an axial direction). 
     The cone ring type continuously variable transmission device  3  includes a conical friction wheel  22  serving as an input member, a conical friction wheel  23  serving as an output member, and a ring  25  made of metal. The friction wheels  22 ,  23  are disposed so that respective axes of the friction wheels  22 ,  23  are parallel to each other, and a small diameter portion and a large diameter portion of the friction wheel  22  are disposed axially opposite to a small diameter portion and a large diameter portion of the friction wheel  23 . The ring  25  is interposed between opposing inclined surfaces of the friction wheels  22 ,  23 , and surrounds one of the friction wheels, for example, the input-side friction wheel  22 . A large thrust force is applied to at least one of the friction wheels, and therefore the ring  25  is interposed between the inclined surfaces by a relatively large clamping force based on the above thrust force. Specifically, an axial force application unit (not shown) formed of a cam mechanism is formed between the output-side friction wheel  23  and an output shaft  24  of the continuously variable transmission device, on opposing surfaces in the axial direction. The thrust force in a direction shown by an arrow D in the drawing is generated in accordance with the transferred torque, and a large clamping force is generated to act on the ring  25  between the output-side friction wheel  23  and the input-side friction wheel  22  that is supported in a direction that counters the thrust force. 
     The input-side friction wheel  22  includes a first end portion (large diameter portion) supported by the first case member  9  through a roller bearing  26 , and a second end portion (small diameter portion) supported by the partition  12  through a tapered roller bearing  27 . The output-side friction wheel  23  includes a first end portion (small diameter portion) supported by the first case member  9  through a roller (radial) bearing  29 , and a second end portion (large diameter portion) supported by the partition  12  through a roller (radial) bearing  30 . The output shaft  24 , which applies to the output-side friction wheel  23  the thrust force acting in the direction shown by the arrow D as described above, includes a second end portion supported by the second case member  10  through a tapered roller bearing  31 . An inner race of the bearing  27  is interposed between a step portion and a nut  32  on the second end portion of the input-side friction wheel  22 , and the thrust force that acts on the input-side friction wheel  22  through the ring  25  in the direction shown by the arrow D from the output-side friction wheel  23  is supported by the tapered roller bearing  27 . On the other hand, a reaction force of the thrust force acting the output-side friction wheel  23  acts on the output shaft  24  in a direction opposite to the direction shown by the arrow D, and the reaction force of the thrust force is supported by the tapered roller bearing  31 . 
     The ring  25  moves in the axial direction by an axial moving unit, such as a ball screw, and changes the positions of contact between the ring  25  and the input-side friction wheel  22  and between the ring  25  and the output-side friction wheel  23 , so as to steplessly change speed by steplessly changing a rotation ratio between the input member  22  and the output member  23 . The thrust force D in accordance with the transferred torque and the reaction force of the thrust force are canceled out by the tapered roller bearings  27 ,  31  in the integrated case  11 , and an equilibrant force as an external force such as a hydraulic pressure is not required. 
     The differential device  5  includes a differential case  33 , and the differential case  33  includes a first end portion supported by the first case member  9  through a bearing  35 , and a second end portion supported by the second case member  10  through a bearing  36 . A shaft that is perpendicular to the axial direction is attached to the inside of the differential case  33 , and bevel gears  37 ,  37 , which serve as differential carriers, are engaged with the shaft. Left and right axle shafts  39   l ,  39   r  are supported by the shaft, and bevel gears  40 ,  40  that mesh with the differential carriers are fixed to the axle shafts. Further, a differential ring gear (toothed gear)  41  having a large diameter is attached to the outside of the differential case  33 . 
     The output shaft  24  of the continuously variable transmission device is formed with a gear (pinion)  44 , and the gear  44  meshes with the differential ring gear  41 . The motor output gear (pinion)  16 , the toothed idler gear  17 , the intermediate gear  19 , the output gear (pinion)  44  of the continuously variable transmission device, and the differential ring gear  41  constitute the gear transmission device  5 . The motor output gear  16  and the differential ring gear  41  are disposed overlapping each other in the axial direction, and the intermediate gear  19  and the output gear  44  of the continuously variable transmission device are disposed overlapping the motor output gear  16  and the differential ring gear in the axial direction. Note that, a gear  45 , which is engaged with the output shaft  24  of the continuously variable transmission device through a spline, is a parking gear that locks the output shaft when a shift lever is in a parking position. Further, the term “gear” refers to a meshing rotary transmission unit including toothed gears and sprockets. In this embodiment, however, the gear transmission device refers to a toothed gear transmission device that is formed by toothed gears only. 
     The input shaft  6  is supported by the second case member  10  through a roller bearing  48 . The input shaft  6  is engaged (drivingly connected) with the input member  22  of the continuously variable transmission device  3  at a first end thereof through a spline S, and a second end of the input shaft  6  is linked with the output shaft of the engine through a clutch (not shown) housed in a third space C defined by the second case member  10 , so that the input shaft  6  moves in accordance with the output shaft of the engine. The second case member  10  is open and connected to the engine (not shown) on a third space C side. 
     The gear transmission device  7  is housed in the second space B. The second space B is a space between the third space C, and the electric motor  2  and the first space A, in the axial direction. The second space B is defined by the second case member  10  and the partition  12 . The shaft-supporting portions ( 27 ,  30 ) of the partition  12  are placed in an oil-tight state by oil seals  47 ,  49 , respectively, and the shaft-supporting portions of the second case member  10  and the first case member  9  are shaft-sealed by oil seals  50 ,  51 ,  52 . The second space B is configured to be oil-tight, and is filled with a predetermined amount of lubricant oil such as ATF. The first space A defined by the first case member  9  and the partition  12  is similarly configured to be oil-tight, and is filled with a predetermined amount of traction oil having a shear force, and a large shear force under an extreme pressure condition in particular. 
     Next, the operation of the hybrid drive system  1  as described above will be explained. The hybrid drive system  1  is connected to an internal combustion engine on the third space C side of the case  11 , and the output shaft of the engine is connected to the input shaft  6  through a clutch. The power from the engine is transmitted to the input shaft  6 , and the rotation of the input shaft  6  is transmitted to the input-side friction wheel  22  in the cone ring type continuously variable transmission device  3  through the spline S. The power is further transmitted to the output-side friction wheel  23  through the ring  25 . 
     During this transmission, a large contact pressure acts between the friction wheels  22 ,  23  and the ring  25  due to the thrust force acting on the output-side friction wheel  23  in the direction shown by the arrow D. Because the first space A is filled with the traction oil, an oil film of the traction oil is formed between the friction wheels and the ring, bringing about the extreme pressure condition. In this condition, the traction oil has a large shear force, and thus the power is transmitted between the friction wheels and the ring by the shear force of the oil film. This allows the transfer of a predetermined torque in a non-slip manner without causing wear on the friction wheels and the ring, even though the torque transfer is made through contact between metal members. Moreover, the ring  25  slips in the axial direction smoothly to change the positions of contact between the friction wheels and the ring, whereby the speed is steplessly changed. 
     The rotation of the output-side friction wheel  23  whose speed has been steplessly changed is transmitted to the differential case  33  of the differential device  5  through the output shaft  24 , the output gear  44 , and the differential ring gear  41 . The power is then distributed to the left and right axle shafts  39   l ,  39   r  so as to drive the vehicle wheels (front wheels). 
     On the other hand, the power from the electric motor  2  is transmitted to the input shaft  6  through the output gear  16 , the toothed idler gear  17 , and the intermediate gear  19 . Similar to the description above, the speed of the rotation of the input shaft  6  is steplessly changed by the cone ring type continuously variable transmission device  3 , and the rotation is transmitted to the differential device  5  through the output gear  44  and the differential ring gear  41 . The gear transmission device  7  formed by the gears  16 ,  17 ,  19 ,  44 ,  41 ,  37 ,  40  is housed in the second space B filled with the lubricant oil, and therefore the power is smoothly transmitted through the lubricant oil when the gears mesh. At such time, because the differential ring gear  41  (see  FIG. 2 ) disposed at a lower position in the second space B is formed of a large diameter gear, the differential ring gear  41  scoops up the lubricant oil so that a sufficient amount of lubricant oil is reliably supplied to the other gears  16 ,  17 ,  19 ,  44  and the bearings  27 ,  30 ,  20 ,  21 ,  31 ,  48 . 
     Various operation modes of the engine and the electric motor, that is, operation modes as the hybrid drive system  1 , may be employed as necessary. As an example, when the vehicle starts off, the clutch is disconnected and the engine is stopped so that the vehicle is started using only the torque from the electric motor  2 . Once the vehicle speed reaches a predetermined speed, the engine is started and the vehicle is accelerated by the power from the engine and the electric motor. When the vehicle speed becomes a cruising speed, the electric motor goes into a free rotation or is placed in a regeneration mode, and the vehicle travels using only the power from the engine. During deceleration or braking, the electric motor regenerates to charge a battery. Further, the vehicle may be started by the power from the engine using the clutch as a starting clutch, with the torque from the motor used as an assisting power. 
     Next, with reference to  FIGS. 2 and 3 , the conical friction wheel (cone ring) type continuously variable transmission device  3  according to the present invention will be described. The continuously variable transmission device  3  includes the input-side friction wheel  22 , the output-side friction wheel  23 , and the ring  25  as described above, and the friction wheels  22 ,  23  and the ring  25  are made of metal such as steel. The friction wheels  22 ,  23  are disposed so that axes l-l, n-n of the friction wheels  22 ,  23  are parallel to each other, and formed in a conical shape so that inclined surfaces are linearly formed. The ring  25  is interposed between opposing inclined surfaces  22   e ,  23   e . The ring  25  is disposed so as to surround one of the friction wheels, specifically, the input-side friction wheel  22 , and a cross-section taken along a plane perpendicular to a circumferential direction of the ring  25  is substantially a parallelogram shape. A plane of rotation m-m of the ring  25  is set substantially perpendicular to the axis l-l. 
     The cone ring type continuously variable transmission device  3  is assembled by inserting the partition  12  into second-side axial portions  22   b ,  23   b  of the friction wheels  22 ,  23 , in the state where first-side axial portions  22   a ,  23   a  are supported by the first case member  9  through bearings  26 ,  29 , respectively. During this assembling, it is difficult in terms of axial accuracy to press-fit the inner races of the bearings  27 ,  30 , and thus the inner race of one of the bearings  27 ,  30  is fit to the corresponding axial portion with play therebetween. Specifically, the axial portion  22   b  of the input-side friction wheel  22  is fit to the bearing  27  with play therebetween and supported by the bearing  27 . An outer race of the roller bearing  30  is press-fit to and retained by the partition, and the inner race is press-fit to and retained on the axial portion, between the second-side axial portion  23   b  of the output-side friction wheel  23  and the partition  12  to attach the roller bearing  30 . 
     The tapered roller bearing  27  that supports the second-side axial portion  22   b  of the input-side friction wheel  22  is attached to the partition  12  by press-fitting the outer race of the tapered roller bearing  27  to the partition  12 , as well as the roller and the inner race thereof. A sleeve  60  is press-fit to an inner diameter side of an inner race  27   a , and integrally fixed to the inner race  27   a . The sleeve  60  forms a flange portion  60   a  of which one end side (a conical side) extends in an outer diameter direction. A large diameter dowel portion  60   b , a spline portion  60   e , and a small diameter dowel portion  60   d  are sequentially formed on an inner diameter side of the flange portion  60   a  from the conical side to a tip end side of the sleeve  60 . 
     On the other hand, the second-side axial portion  22   b  of the input-side friction wheel  22  is sequentially formed with a stepped portion a, a large diameter support portion b, a spline portion c, a small diameter support portion d, and an external thread portion e from a conical side of the second-side axial portion  22   b  to a tip end thereof. The partition  12  is assembled so that the second-side axial portion  22   b  is inserted into the sleeve  60  that is integrally press-fit to the bearing  27 . During such assembling, the large diameter dowel portion  60   b  of the sleeve  60  and the large diameter support portion b of the axial portion  22   b  are fit to each other with play therebetween, and the small diameter dowel portion  60   d  and the small diameter support portion d are fit to each other with play therebetween. Further, the spline portions  60   c, c  are engaged with each other. With this configuration, the second-side axial portion  23   b  of the output-side friction wheel  23  is supported by the roller bearing  30  in a state where the inner race of the roller bearing  30  is press-fit to the second-side axial portion  23   b , and the partition  12  can be inserted with the second-side axial portion  22   b  of the input-side friction wheel  22  because there is play between the sleeve  60  and the second-side axial portion  22   b . Further, the external thread portion e is screwed into the nut  32  so as to abut the flange portion  60   a  of the sleeve  60  against the stepped portion a. The nut  32  is pressed against an outer side face of the inner race  27   a , so that the axial portion  22   b  is tightened to restrict its movement in the axial direction with respect to the bearing  27 . 
       FIGS. 3A and 3B  show cross-sectional views taken along a plane (a plane including the axes l-l, n-n of the friction wheels) perpendicular to the rotating direction of the ring.  FIG. 3A  shows a natural state where the friction wheel does not deform with no load or a light load applied to the continuously variable transmission device  3 .  FIG. 3B  shows a state where the friction wheel deforms with a load applied to the continuously variable transmission device. In this state, as described above, the input-side friction wheel  22  is supported by the partition  12  having play with the axial portion  22   b  on the small diameter portion G side thereof. The small diameter portion G has a small diameter and thus low rigidity, and the rotation speed of the input-side friction wheel  22  is faster at cruising speeds that are often used for long periods of time. Thus, the deformation of the input-side friction wheel  22  on the small diameter portion G side has a significant effect on the ring  25 . 
     As shown in  FIG. 3A , the ring  25  according to the present invention includes: an inner (first-side) contact surface  70  that contacts the inclined surface  22   e  of the input-side friction wheel  22 ; an outer (second-side) contact surface  71  that contacts the inclined surface  23   e  of the output-side friction wheel  23 ; and left and right side surfaces  73 ,  75 , each of which is formed of a plane perpendicular to the rotating direction of the ring, that is, the axis l-l of the friction wheel. The inner contact surface  70  includes a linear portion  70   a  of a predetermined length p when viewed in a cross-section taken perpendicular to the rotating direction of the ring. Curved surface portions  70   b ,  70   c , which have relatively large curvatures, are formed on the left and right sides of the linear portion, respectively. The outer contact surface  71  is formed of a curved portion  71   a  that is continuous in a cross-section taken perpendicular to the rotating direction of the ring, and is preferably formed of an arc having a relatively large radius R about a single center point O. 
     The linear portion  70   a  of the inner contact surface  70  is positioned closer (offset) to a large diameter portion H side of the input-side friction wheel  22  which the linear portion  70   a  contacts, and the curved portion  70   c  on the small diameter portion G side is set longer than the curved portion  70   b  on the large diameter portion side. A point P on the outer surface curved portion  71   a  passing through the center point Q of the linear portion  70   a  is a point farthest from the linear portion  70   a . That is, the inner contact surface  70  contacts the input-side friction wheel  22  at the linear portion  70   a , and the outer contact surface  71  contacts the output-side friction wheel  23  at the point P farthest from the linear portion  70   a  (more precisely, from the center point Q of the linear portion  70   a ), whereby the point serves as the contact point P. The contact point P is positioned offset with respect to a center o in a width direction of the curved portion  71   a  toward a side that is opposite to the side toward which the center point Q is offset. 
     In other words, the center O of the radius R of the curved portion  71   a  formed of the above arc is positioned on the large diameter portion H side of the input-side friction wheel  22 , and the radius R passing through the center point Q of the linear portion  70   a  serves as a perpendicular bisector of the linear portion  70   a . The contact point P, which is an intersection point on the curved portion  71   a  with the radius R passing the center point Q, is positioned offset to a small diameter portion J side of the output-side friction wheel  23  which the curved portion (the outer contact surface  71 ) contacts, with respect to the center point o in the width direction of the curved portion. Therefore, the distance from the contact point P to an edge portion t on a small diameter portion K side of the curved portion  71   a  is set longer than the distance from the contact point P to an edge portion u on the large diameter portion J side. Note that, the curved portion  71   a  is entirely formed across the outer contact surface  71  in the width direction, and this configuration is preferable because the movable range of the contact point P due to deformation of the friction wheel, which will be described later, is expanded. However, the present invention is not limited to the configuration in which the curved portion  71   a  extends entirely across in the width direction, and a portion close to the side surface may be formed as another curved surface or an inclined surface. 
     The plane of rotation m-m of the ring  25  (see  FIG. 2 ) is set at an angle that is raised toward the direction perpendicular to the axes of the friction wheels with respect to the angles perpendicular to the incline surfaces  22   e ,  23   e  of the friction wheels  22 ,  23  on which the ring  25  contacts. Preferably, the plane of rotation m-m of the ring is formed of a plane perpendicular to the axes l-l, n-n, and the side surfaces  73 ,  75  are formed of planes perpendicular to the axes. 
     The cone ring type continuously variable transmission device  3  transmits power such that the friction wheels  22 ,  23  hold the ring  25  therebetween at a contact pressure in accordance with the transferred torque. In the decelerating (underdrive) state where no load or a light load is applied, or where the ring is positioned on the large diameter portion H side of the input-side friction wheel  22 , the deformation of the friction wheel is small and the state of the ring  25  is as shown in  FIG. 3A . In this state, the linear portion  70   a  of the inner contact surface  70  of the ring  25  contacts the input-side friction wheel  22 , and the outer contact surface  71  contacts the output-side friction wheel  23  near the contact point P on the curved portion  71   a . In the state where vibration of the ring is suppressed with the force F applied to the linear portion  70   a  (center point Q) from the input-side friction wheel  22  and the force F applied to the contact point P of the curved portion  71   a  from the output-side friction wheel  23  acting on the same line (R), the ring  25  rotates smoothly on the plane of rotation m-m without application of a moment, and transmits the power with high transmission efficiency. 
     In the state where a large load is applied to the cone ring type continuously variable transmission device  3 , and particularly, in the decelerating (underdrive) state where the ring  25  is positioned on the small diameter portion G side on which the input-side friction wheel  22  is likely to be deformed, the state of the ring  25  is as shown in  FIG. 3B . That is, the input-side friction wheel  22  deforms in a direction that increases the angle of inclination α on the contact-side inclined surface  22   e  of the input-side friction wheel  22 , and the ring  25  linearly contacting the linear portion  70   a  is also inclined in accordance with the deformation. Consequently, the contact point P on the curved portion  71   a  of the outer contact surface  71  at which the ring  25  contacts the output-side friction wheel  23  is moved to the small diameter portion K side of the friction wheel  23  (P→P 1 ). 
     The contact point P on the curved portion  71   a  in the no-load state is positioned offset to the large diameter portion J side in advance. Therefore, even if the contact point P 1  is moved in accordance with the deformation of the friction wheel as described above, the contact point P 1  is kept from moving up to the edge (corner) portion t of the curved portion because the length on the small diameter K side is set longer. Thus, the contact point P 1  settles at the middle position of the curved portion  71   a . This prevents a local surface pressure from acting on the corner portion t of the outer contact surface  71 , whereby fatigue fracturing of the ring  25  is reduced. The durability of the ring  25 , and by extension, the durability of the cone ring type continuously variable transmission device  3  is thus improved, making it possible to maintain the power transmission with high transmission efficiency for a long time. 
     The above description concerns an embodiment in which the continuously variable transmission device is applied to a hybrid drive system. However, the present invention is not limited to this, and may be applied to a drive device other than the hybrid drive system as another type of gear transmission device, such as a gear transmission device that serves as a reverse gear transmission device, or uses a planetary gear that separates and transfers a part of torque and combines the torque with an output from the continuously variable transmission device, so as to expand the shift range of the continuously variable transmission device or distribute a part of the transferred torque. Further, the present invention may be singly used as a continuously variable transmission device. In this case, it is preferable that the present invention be applied to a transport machine, such as an automobile. However, the present invention may be applied to other power transmission apparatuses, such as an industrial machine. 
     The present invention relates to a conical friction wheel type continuously variable transmission device (cone ring type CVT), and can be used in any and all power transmission apparatuses, including a transport machine such as a hybrid drive system, and an industrial machine.