Abstract:
A continuously variable transmission device including a guiding cover rotating about a first axis, a guided cover rotating about a second axis, a planet gear including a first belt in contact with an inner surface of the guiding cover and a second belt in contact with an inner surface of the guided cover, contact areas between the belts and the inner surfaces of the covers being defined in a single first radial plane relative to the first axis, wherein the planet gear rotates about a third axis contained in the first radial plane, the angular orientation relative to the first axis defining the transmission ratio of the device, and wherein the planet gear pivots about a fourth axis perpendicular to the first radial plane and nonintersecting with the first axis, and pivots about a fifth axis parallel to the first radial plane and perpendicular to the third axis.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit under 35 USC §371 of PCT Application No. PCT/EP2013/062939 entitled CONTINUOUSLY VARIABLE TRANSMISSION DEVICE and filed on Jun. 20, 2013 by inventors Pierre Chevalier and Adrien Panzuti. PCT Application No. PCT/EP2013/062939 claims priority of French Patent Application No. 12 55867 entitled DISPOSITIF DE TRANSMISSION CONTINÛMENT VARIABLE and filed on Jun. 21, 2012 by inventors Pierre Chevalier and Adrien Panzuti. 
     FIELD OF THE INVENTION 
     The invention relates to a continuously variable transmission device for transmitting a rotational movement. 
     Such a device may for example be used in the motor or pump industry as well as in the automobile field or, more generally, the mobility field. 
     In these different fields, continuously variable transmission devices (CVD), sometimes called “variable speed transmissions”, have the particular advantage of being able to control the speed of rotation of the output shaft continuously, which has an advantage over transmissions with fixed reduction ratios. 
     BACKGROUND OF THE INVENTION 
     It is known to use the ratio of two diameters between an input and an output to produce a CVT-type transmission. The motion transmission between the input and the output occurs by friction. 
     Thus, DE-A-10 2006 016 955 and FR-A-2,173,528 disclose variable speed drives in which two bells cooperate with a planet gear that bears against the inner surfaces of those bells and whose angular position around an axis perpendicular to and not intersecting the axis of rotation of the bells makes it possible to adjust the transmission ratio of that variable speed transmission. The position of the planet gear relative to the inner surfaces of the bells is adjusted by sliding the planet gear relative to those surfaces, perpendicular to its direction of rotation. During that sliding, the means for controlling the position of the planet gear must overcome a frictional force between the planet gear and the inner surfaces of the bells. To avoid excessive stress on those control means, that frictional force should therefore be relatively low. Furthermore, for effective transmission of the movement within the variable speed transmission, it is important to limit the slipping between the input and output elements, i.e., to work with a relatively high friction coefficient between the planet gear and those surfaces. 
     There are therefore two opposite constraints relative to the friction coefficient between the planet gear and the inner surfaces of the bells, which requires compromises and is detrimental either to the lifetime of the variable speed transmission or to its efficiency. Furthermore, in these known variable speed transmissions, adjusting the angular position of the planet gear is relatively time-consuming, since it is necessary to account for the slipping to be done between the planet gear and the inner surface of the bells, that slipping not being able to be immediate in light of the friction between those parts. Furthermore, this slipping of the planet gear, perpendicular to its direction of rotation when its position is being adjusted, tends to wear the planet gear and/or the inner surface of the bells out. 
     SUMMARY OF THE DESCRIPTION 
     The invention more particularly aims to resolve these drawbacks and this dual constraint by proposing a new continuously variable transmission device whose transmission ratio can be adjusted quickly, with less force and less wear than in the known materials, while limiting the number of parts of the device. 
     To that end, the invention relates to a continuously variable transmission device for transmitting a rotational movement comprising a driving bell rotating around a first axis, a driven bell rotating around a second axis aligned with the first axis, and a planet gear provided with a first belt in contact with an inner surface of the driving bell and a second belt in contact with the inner surface of the driven bell, contact zones between said belts and the inner surfaces of the bells being defined in a same first radial plane relative to the first axis, while the planet gear rotates around a third axis included in the first radial plane and the angular orientation of which relative to the first axis defines the transmission ratio of the device and while the planet gear pivots around a fourth axis perpendicular to the first radial plane and not intersecting the first axis. According to the invention, the planet gear pivots around a fifth axis parallel to the first radial plane and perpendicular to the third axis. 
     Owing to the invention, the input and output speed ratio of the device can be changed by changing the angular position of the planet gear resulting not from direct slipping of the planet gear on the inner surfaces of the driving and driven bells, but rather by pivoting around the fifth axis. Thus, the control force necessary to change the speed ratio of the device according to the invention is lower than that necessary in the variable speed transmissions known from DE-A-10 2006 016 955 and FR-2,173,528. As a result, the wear of the device is lower and speed ratio changes are faster than with these known variable speed transmissions. 
     According to advantageous, but optional aspects of the invention, such a device may incorporate one or more of the following features, considered in any technically allowable combination:
         The angular position of the planet gear around the fourth axis is adjustable by primary tilting of the planet gear around the fifth axis, said primary tilting causing secondary tilting of the planet gear around the fourth axis.   The secondary tilting of the planet gear is brought about by its primary tilting creating resultant forces, producing a pivoting torque, and by the fact that the inner surfaces of the bells are warped and the bells rotate.   Means for controlling the angular position of the planet gear around the fifth axis act on the planet gear by making it pivot around a fifth axis, by orienting the belts of the planet gear relative to the inner surfaces of the bells by primary tilting, causing secondary tilting of the planet gear around the fourth axis. Alternatively, the planet gear rotates freely around the fourth axis and the fifth axis, while a differential torque created between the driving bell and the driven bell act on the planet gear by causing it to pivot around the fifth axis, by orienting the belts of the planet gear relative to the inner surfaces of the bells by primary tilting that causes secondary tilting of the planet gear around the fourth axis.   The two bells are rotatably mounted on a same fixed shaft, a longitudinal axis of which is parallel to the first axis, while the planet gear is mounted pivoting on the shaft, around the fourth axis.   The driving bell is secured to a driving shaft, while the driven bell is secured to a driven shaft, and the device comprises a housing for maintaining and guiding the rotation of the driving bell, the driven bell and the planet gear. The device then advantageously comprises a planet gear carrier that defines the position of the third axis and is mounted pivotably around the fourth axis and around the fifth axis, relative to the housing. This planet gear carrier can be mounted in the housing by a Cardan joint with control finger. In that case, it is possible to provide that a control finger of the Cardan joint is translated in a plane perpendicular to the fifth axis and including the third axis. Alternatively, the planet gear carrier is mounted in the housing by a double pivot link comprising a first pivot link around the fourth axis, that first pivot link being freely rotated, and a second pivot link around the fifth axis, that second pivot link being steered in rotation.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood and other advantages thereof will appear more clearly in light of the following description of four embodiments of a device according to its principle, provided solely as an example and done in reference to the appended drawings, in which: 
         FIG. 1  is an axial cross-section of a transmission device according to the invention in a first usage configuration; 
         FIG. 2  is a cross-section along line II-II in  FIG. 1 ; in this figure, I-I designates the cutting plane of  FIG. 1 ; 
         FIGS. 3 and 4  are cross-sections respectively similar to  FIGS. 1 and 2  in a second usage configuration of the device; in these figures, and IV-IV indicates the corresponding cutting planes; 
         FIG. 5  is a cross-section similar to  FIG. 3  when the planet gear has reached an offset position relative to that of  FIG. 3 ; 
         FIGS. 6 and 7  are cross-sections respectively similar to  FIGS. 1 and 2  in a third usage configuration of the device; in these figures, V-V and VI-VI indicate the corresponding cutting planes; 
         FIG. 8  is a cross-section similar to  FIG. 6  when the planet gear has reached an offset position relative to that of  FIG. 6 ; 
         FIG. 9  is a cross-section similar to  FIG. 1  for a device according to a second embodiment of the invention; 
         FIG. 10  is a cross-section along plane X-X of  FIG. 9 ; in this figure, IX-IX indicates the cutting plane of  FIG. 9 ; 
         FIGS. 11 and 12  are cross-sections similar to  FIGS. 9 and 10 , respectively, in a second usage configuration of the device; in these figures, XI-XI and XII-XII indicate the corresponding cutting planes; 
         FIGS. 13 and 14  are cutting planes similar to  FIGS. 9 and 10 , respectively, in a third usage configuration of the device; in these figures, XIII-XIII and XIV-XIV indicate the corresponding cutting planes; 
         FIGS. 15 and 16  are cross-sections respectively similar to  FIGS. 9 and 10  in the fourth usage configuration of the device; in these figures, XV-XV and XVI-XVI indicate the corresponding cutting planes; 
         FIGS. 17 and 18  are cross-sections respectively similar to  FIGS. 9 and 10  in a fifth usage configuration of the device; in these figures, XVII-XVII and XVIII-XVIII indicate the corresponding cutting planes; 
         FIG. 19  is a cross-section similar to  FIG. 1  for a device according to a third embodiment of the invention; 
         FIG. 20  is a cross-section along plane X-X of  FIG. 19 ; in this figure, XIX-XIX indicates the cutting plane of  FIG. 19 ; and 
         FIG. 21  is a view similar to  FIG. 6  for a device according to a fourth embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The continuously variable transmission device  2  shown in  FIGS. 1 to 8  is designed to transmit a rotational movement between a driving bell  4  and a driven bell  6 . In the example, the driving bell is secured in rotation with a pinion  8  designed to mesh with a chain (not shown), while the driven bell  6  is provided with two outer flanges  62  and  64  provided with orifices  66  for attaching spokes of a cycle wheel. Thus, the device  2  can be used to drive the back wheel of a cycle, using a chain engaged with the pinion  8 . 
     Reference X 4  denotes the axis of rotation of the bell  4  and X 6  denotes the axis of rotation of the bell  6 . The axes X 4  and X 6  are parallel and aligned. 
     The bells  4  and  6  are rotatably mounted around a fixed shaft  10 , a longitudinal and central axis X 10  of which is parallel to the axes X 4  and X 6 . The axis X 10  is an axis of symmetry for the shaft  10 . In practice, the axes X 4 , X 6  and X 10  are combined. Bearings  12 ,  14  and  16  make it possible to support the bells  4  and  6  on the shaft  10  with a possibility of rotation. A bearing  18  is mounted between the outer surface of the bell  4  and the inner surface of the bell  6 , allowing a differentiated rotational movement of those bells around the axes X 4  and X 6 , respectively. 
     References S 4  and S 6  respectively denote the inner surfaces of the bells  4  and  6 , those surfaces respectively being centered on the axes X 4  and X 6 . 
     The device  2  also comprises a planet gear  20  mounted on the shaft  10  with the possibility of rotating around an axis X 20 . When the axes X 20  and X 10  are parallel, the axis X 20  is offset relative to the axis X 10  in a radial direction relative to the axis X 10 , by a non-zero distance d 1 . 
     The planet gear  20  comprises two rings  204  and  206  respectively positioned in the inner volume V 4  or V 6  of a bell  4  or  6  and each provided with a belt  205  or  207  designed to be in contact with the inner surface S 4  or S 6  of the adjacent bell. 
     Thus, in the plane of  FIG. 1 , which is radial relative to the axes X 4 , X 6  and X 10 , a first contact zone Z 4  is defined between the belt  205  and the surface S 4 , while a second contact zone Z 6  is defined in that same plane between the belt  207  and the surface S 6 . 
     The speed transmission ratio of the device  2  depends on the ratio of the distance between the zone Z 4  and the axis X 10  on the one hand, and the distance between the zone Z 6  and the axis X 10  on the other hand. The higher the ratio is, i.e., the further the zone Z 4  is from the axis X 10 , the higher the speed transmission ratio is. 
     As shown by  FIGS. 4 and 7 , the belt  207  is immobilized on the ring  206  using slugs  208 . Similar slugs, not shown in the figures, are used to secure the elements  204  and  205  in rotation. Alternatively, the elements  207  and  206 , and the elements  204  and  205 , respectively, can be in a single piece. 
     A bearing  209  is engaged in the inner volume of the rings  204  and  206 . 
     References  214  and  216  respectively denote the surfaces of the rings  204  and  206  that are radial relative to the axis X 20  and oriented toward the other ring. The surface  216  is provided with hollow housings  217  in which balls  218  and springs  219  are partially accommodated. The surface  214  is also provided with hollow housings  220  for partially receiving balls  218 . Thus, in the mounted configuration of the device  2 , the balls are positioned between the surfaces  214  and  216  and partially engaged in the housings  217  and  220 . Springs  219  are positioned near the balls  218  and accommodated in housings adjacent to the housings  217 . 
     Based on the resisting torque of the driven bell  6  relative to the driving bell  4 , the relative angular position of the rings  204  and  206  around the axis X 20  can vary, in a direction such that the balls  218  move in the housings  217  toward the springs  219 . In light of the geometry of the housings  217 , the depth of which relative to the surface  216  decreases coming closer to the adjacent housings that receive the springs  219 , this relative angular movement of the rings  204  and  206  results in axially expanding the planet gear  20 , i.e., axially separating the rings  204  and  206  from each other and increasing the intensity of the contact force between the belt  205  and the surface S 4  and between the belt  207  and the surface S 6 . At the end of travel of the balls  218  in the housings  217 , the springs  219  exert a return force in a direction opposite the relative angular movement between the rings  204  and  206 . Thus, the elements  217  to  220  constitute a pre-stress mechanism that makes it possible to adjust the contact force between the belts  205  and  207  and the inner surfaces of the bells, based on the resisting torque of the driven bell  6  relative to the driving bell  4 . 
     Alternatively, the balls  218  can be replaced by other rolling elements, such as rollers or needles. In that case, the geometry of the housings  217  and the position of the springs  218  are adapted accordingly. 
     The planet gear  20  also comprises a sleeve  222  positioned radially inside the bearing  209  and a first part of a ball joint  223  immobilized inside the sleeve  222 . 
     Furthermore, a second ball joint part  123  is immobilized on the shaft  10  using a screw  124 . 
     A needle cage makes up the bearing  209  with rolling bodies and allows the rotation of the planet gear  20  around the axis X 20 , while the shaft  10  and the ball joint are fixed in rotation relative to the axis X 10 . 
     The offset between the axes X 10  and X 20  comes from the geometry of the inner part  123  of the ball joint which, in the plane of  FIG. 1 , is not symmetrical relative to the axis X 10 . 
     In practice, the outer part  223  of the ball joint is made up of two half-shells that are attached around the part  123  once the latter is immobilized on the shaft  10  by the screw  124 . The two half-shells are then kept in place by the sleeve  222 , which acts as a binding band. 
     The part  123  is provided with a notch  125  in which a slug  30  emerges, the tail of which  302  is immobilized in the part  223  of the ball joint, for example screwed into that part. The head  304  of the slug  30 , which is provided with a piercing  306 , is engaged in the notch  125 , which guides it in translation in a motion parallel to the plane of  FIGS. 2, 4 and 7 . 
     A spring  40  is attached in the piercing  306  by a first end  402 , and on the shaft  10  by a second end  404 . This spring forms an elastically deformable element for returning the slug  30  to its position. 
     A cable  50  is attached, by a first end  502 , in the piercing  306  and extends as far as the outside of the device  2 . In practice, the cable  50  passes through a groove  102  arranged in the outer surface of the shaft  10 , in a direction parallel to the axis X 10 . In  FIG. 7 , the depiction of the cable  50  is interrupted to make it possible to view the groove  102 . Said groove is positioned radially inside bearings  12  and  14 , which allows the cable  10  to emerge outside the inner volume of the device  2 , i.e., the sum of the volumes V 4  and V 6 . Outside that volume, the cable  50  passes through a stopper  60  via an orifice  602  that emerges radially outward. 
     Thus, the slug  30  is subjected to antagonistic forces, i.e., an elastic attraction force E 40  exerted by the spring  40 , which tends to move it to the left in  FIG. 2 , and a traction force E 50  transmitted by the cable  50  when it is pulled. The forces E 40  and E 50  are exerted in the two main directions of the spring and the cable, near their ends  402  and  502 . For clarity of the drawing, the arrows showing these forces are laterally offset in  FIGS. 2, 4 and 7 . 
     The planet gear  20  pivots freely around an axis Y 20  perpendicular to the plane of  FIG. 1 , i.e., a radial plane relative to the axis X 4  that contains the contact zones Z 4  and Z 6 . The planet gear can thus the planet gear can assume the positions shown in  FIGS. 1, 5 and 8 , respectively, relative to the bells  4  and  6 . 
     In the configuration of  FIGS. 1 and 2 , the zones Z 4  and Z 6  extend at a same radial distance from the axes X 4  and X 6 . Thus, the transmission ratio of the rotational movement between the bells  4  and  6  is equal to 1. 
     In the configuration of  FIG. 5 , the zone Z 4  is radially further from the axis X 4  than the zone Z 6  is from the axis X 6 . 
     In this configuration, the reduction ratio of the device  2  is maximal. Thus, the bell  6  rotates faster than the bell  4 . The speed transmission ratio of the rotational movement between the bells  4  and  6  is greater than 1. 
     Intermediate configurations between those of  FIGS. 1 and 2  on the one hand, and  5  on the other hand, may be achieved as explained below. 
     In the configuration of  FIG. 5 , the axis X 20  forms a non-zero angle α with the axis X 10  in the plane of that figure. 
     In the configuration of  FIG. 8 , the planet gear  20  is tilted in the direction opposite the configuration of  FIG. 5 . The axis X 20  forms an angle β with the axis X 10  oriented in the opposite direction relative to the angle α and having practically the same value. In that case, the zone Z 4  is radially closer to the axis X 4  than the zone Z 6  is to the axis X 6 , such that the transmission ratio of the device  2  is less than 1, in practice minimal in the configuration shown in  FIG. 8 . The bell  6  rotates more slowly than the bell  4 . 
     Intermediate configurations between those of  FIGS. 1 and 2  on the one hand, and  8  on the other hand, can be reached as explained below. 
     The planet gear  20  is also rotatable, i.e., pivotable, around a fifth axis Z 20  that extends perpendicular to the axis X 20  in the plane of  FIGS. 1, 3, 5, 6 and 8 . 
     The position of the planet gear  20  relative to the driving and driven bells  4  and  6  is controlled not in the plane of  FIGS. 1, 3, 5, 6 and 8  that contains the contact zones Z 4  and Z 6  between that planet gear and said bells, but in a perpendicular plane shown in  FIGS. 2, 4 and 7 . 
     In the configuration of  FIGS. 1 and 2 , the traction force E 50  exerted via the cable  50  balances the elastic traction force E 40  exerted by the spring  40  stretched between the head  304  and the fixed shaft  10 . Under these conditions, the planet gear  20  does not tend to change positions relative to the bells  4  and  6 . In other words, the position of the zones Z 4  and Z 6  relative to the axes X 4  and X 6  is stable. 
     In the configuration of  FIGS. 3 and 4 , the elastic force E 40  overcomes the traction force E 50 , which creates primary pivoting or tilting of the planet gear  20  in the trigonometric direction, as shown by arrow F 1 , in the plane of  FIG. 4  around the axis Z 20 . 
     In the plane of  FIG. 4 , the axis of the planet gear X 20  not being parallel to the axis X 10 , traction forces F Y10  of the bells and traction forces F Y20  of the planet gear do not have the same direction and thus create resultant forces F R  at the origin of a pivoting torque M Y20  visible in  FIG. 3 . This primary tilting F 1  of the planet gear  20  around the axis Z 20 , combined with the fact that the inner surfaces S 4  and S 6  of the bells are warped and the bells are rotating, generates secondary tilting around the axis Y 20  in the direction of arrow F 2  in  FIG. 3 , i.e., in a direction increasing the transmission ratio of the device  2 . 
     This tilting of the planet gear  20  continues as long as the elastic force E 40  is greater than the traction force E 50 . 
     As long as the elastic force E 40  overcomes the traction force E 50 , the planet gear  20  remains in the configuration of  FIG. 4 , to the point that it continues its secondary tilting movement in the direction of arrow F 2 , which causes it to go from the configuration of  FIG. 3  to the configuration of  FIG. 5 . 
     On the contrary, in the configuration of  FIGS. 6 and 7 , the force D 50  exerted via the cable  50  is greater than the elastic force E 40  exerted by the cable  40 , such that the planet gear  20  tilts in the clockwise direction around the axis Z 20  in the plane of  FIG. 7 , as shown by arrow F 1 ′, which causes secondary tilting of that planet gear around the axis Y 20  in the direction of arrow F 3 , in the plane of  FIG. 6 , the forces F R  then in  FIG. 7  having a direction opposite the direction of  FIG. 4 . This results in decreasing the transmission ratio of the device  2 . 
     As long as the force E 50  is greater than the elastic force E 40 , the planet gear  20  is kept in the configuration of  FIG. 7 , to the point that the secondary tilting of the planet gear  20  around the axis Y 20  continues in the direction of arrow F 3 , which results in causing the planet gear to go from the configuration of  FIG. 6  to that of  FIG. 8 . 
     Thus, indirect control is obtained inasmuch as the control of the tilting of the planet gear  20  takes place in the radial plane of  FIGS. 2, 4 and 7 , which is perpendicular to that which contains the zones Z 4  and Z 6  and that is that of  FIGS. 1, 3, 5, 6 and 8 . 
     In the second, third and fourth embodiments respectively shown in  FIGS. 9 to 18, 19 and 20, and 21 , the elements similar to those of the first embodiment bear the same references and work in the same way. Hereinafter, one only describes what distinguishes these other embodiments from the first embodiment. 
     In the second embodiment shown in  FIGS. 9 to 18 , the driving bell  4  of the continuously variable transmission device  2  is secured to a first shaft  104  that is a driving shaft and centered on a first axis X 4 . Likewise, the driven bell  6  is secured to a second shaft  106  centered on a second axis X 6 . The axes X 4  and X 6  respectively form axes of rotation for the bells  4  and  6 . A planet gear  20  rotates around a third axis X 20  included in the plane of  FIG. 9 , when it is driven by the driving bell  4 . Said planet gear  20  comprises two rings  204  and  206  mounted together on a bearing  209 . The rings  204  and  206  can form a single piece. A ball joint part  223  has a spherical outer surface S 223  that is not coaxial with the axis X 20  and that constitutes the central axis of the planet gear X 20 , and a cylindrical inner surface S′ 223  coaxial with the axis X 20 . The bearing  209  is radially accommodated inside the surface S′ 223 . The bearing  209  and the ball joint part  223  together constitute a planet gear carrier for the planet gear  20  and define the position of the axis X 20  relative to the bells  4  and  6 . 
     The axes X 4  and X 6 , which are aligned, are radially offset relative to the axis X 20  by a non-zero distance d 1 , as in the first embodiment. The rings  204  and  206  respectively bear contact belts  205  and  207  with the inner surfaces S 4  and S 6  of the bells  4  and  6 . 
     A housing  150  is provided around the bells  4  and  6  of the planet gear  20 . That housing  150  is made up of two flanges  154  and  156  that are respectively provided with passage orifices for the shafts  104  and  106 , and a cylindrical body  158  secured to the two flanges. A ball joint part  153  is immobilized on the inner radial surface of the body  158  and cooperates with the ball joint part  223  to allow pivoting of the elements  209  and  223  and of the planet gear  20  around a fourth axis Y 20  perpendicular to the plane of  FIGS. 9, 11, 13, 15 and 17  and intersecting the axis Y 20 . 
     Since the surfaces of the ball joint parts  153  and  223  bearing on one another in slipping contact are in the form of a sphere portion, the elements  209  and  223  and the planet gear  20  can also pivot around a fifth axis Z 20  comprised in the plane of  FIGS. 9, 11, 13, 15 and 17  and perpendicular to the axis X 20 . 
     The bell  4  is supported by the housing  150  using a circular bearing  124  and an axial bearing  134 . These bearings are respectively positioned between an outer radial surface  42  of the bell  4  and the cylindrical body  158  and between an axial surface  44  of the bell  4  and the flange  154 . The bearings  124  and  134  each guide the rotation of the bell  4  around the axis X 4 . Likewise, two bearings  126  and  136  guide the rotation of the bell  6  around the axis X 6 , relative to the housing  150 . 
     As more particularly shown by  FIGS. 10, 12, 14, 16 and 18 , the ball joint formed by the elements  153  and  223  is a Cardan joint with a control finger. More particularly, this ball joint comprises a finger or slug  30  engaged in a housing  224  of the part  223  and is secured to a piston  42  belonging to a control subassembly  40 . This therefore procures free rotation of the elements  153  and  223  relative to one another around the axis Y 20 , locked rotation around the axis X 20 , and rotation indexed by the finger  30  around the axis Z 20 . The indexing of the rotation around the axis Z 20  is induced by the translation of the finger  30 , parallel to the axis X 10 . The control subassembly  40  also comprises a body  44  fastened on the housing  150 , in which the piston  42  is positioned and which defines two chambers  46  and  48  each connected to a hose  52  or  54  supplied with a control fluid, such as oil. Alternatively, air or water can be used as control fluid. 
     The control subassembly  40  can also be produced via other technical solutions for translating a part such as a rack, a cam, a cable and other power means such as an electric motor, an electromagnetic, or a mechanical actuator. 
     In the configuration of  FIGS. 9 and 10 , the piston  42  is in the median position inasmuch as the chambers  46  and  48  have the same volume. In this configuration, which is comparable to that of  FIGS. 1 and 2  for the first embodiment, contact zones Z 4  and Z 6  defined between the belts  205  and  207  on the one hand, and the inner surfaces S 4  and S 6  of the bells  4  and  6  on the other hand, are situated substantially at the same radial distance from the axes X 4  and X 6 . In that case, the transmission ratio of the device  2  of the second embodiment is equal to 1. 
     When the transmission ratio of the device  2  needs to be increased, the piston  42  is moved toward the bell  6  in the plane of  FIG. 12 . This is obtained by supplying the chamber  46  with oil at a pressure higher than that present in the chamber  48 . This movement of the piston  42  in the direction of arrow F 11  drives the finger  30  toward the bell  6 , which causes the part  223  of the ball joint to pivot around the axis Z 20 . This creates primary pivoting or tilting of the planet gear  20  in the trigonometric direction, as shown by arrow F 1 , in the plane of  FIG. 12  around the axis Z 20 . 
     In the plane of  FIG. 12 , the axis of the planet gear X 20  being non-parallel to the axes X 4  and X 6 , traction forces F Y10  of the bells and traction forces F Y20  of the planet gear do not have the same direction and thereby create resultant forces F R  at the origin of a pivot torque M Y20  shown in  FIG. 11 . This primary tilting F 1  of the planet gear  20  around the axis Z 20 , combined with the fact that the inner surfaces S 4 , S 6  of the bells are warped and the bells are rotating, generates secondary tilting around the axis Y 20  in the direction of arrow F 2  in  FIG. 11 , i.e., in a direction increasing the transmission ratio. 
     The secondary tilting of the planet gear  20  around the axis Y 20  continues as long as the planet gear  20  is kept in the tilted position shown in  FIG. 12 . This makes it possible to reach the configuration of  FIG. 13 , where the transmission ratio of the device  2  is maximal, while the planet gear  20  is in a stable configuration, pivoting around the axis Y 20 , since the piston  42  has been brought back to a median configuration, relative to the subassembly  40  body  44 , balancing the oil pressures in the chambers  46  and  48 . The planet gear  20  remains in that configuration as long as the piston  42  is not moved relative to the body  44 . 
     In this configuration, the axes X 20  and X 4  define a non-zero angle α between them. 
     Conversely, when the transmission ratio of the speeds of the device  2  needs to be decreased, the piston  42  is moved toward the bell  4 , in the direction of arrow F 11 ′ in  FIG. 16 , while supplying the chamber  48  with oil at a pressure greater than that present in the chamber  46 . This results in moving the fingers  30  toward the bell  4  and causing the planet gear  20  to pivot in the direction of the arrow Ft around the axis Z 20 . This primary pivoting or tilting causes, for the same reasons as previously stated, secondary tilting of the planet gear  20  around the axis Y 20 , as shown by arrow F 3  in  FIG. 15 , the forces F R  then, in  FIG. 16 , being oriented in the direction opposite the direction in  FIG. 12 . 
     As before, this secondary tilting continues as long as the finger  30  is kept in the configuration of  FIG. 16  until reaching the position of  FIGS. 17 and 18 , where the piston  42  is brought back to a central position relative to the body  44 , which causes the position of  FIG. 17  to be stable, in rotation around the axis Y 20 , for the planet gear  20 . 
     In this configuration, the axes X 20  and X 4  define a non-zero angle β between them oriented in the direction opposite the angle α and having substantially the same value. 
     Thus, in this second embodiment as well, an indirect control of the pivoting of the planet gear  20  is obtained, owing to the fact that said planet gear pivots around the axis Z 20  and is controlled in a plane perpendicular to the axis, using the subassembly  40 . 
     According to an alternative of the second embodiment, instead of a Cardan joint with control finger between the planet gear carrier formed by the elements  209  and  223  on the one hand, and the housing  150  on the other hand, a double pivot link can be used. In this alternative, the planet gear carrier is made up of a first cradle where the bearing  209  is accommodated. This first cradle is connected to a second cradle by a pivot link with axis Y 20 . The rotation around the axis Y 20  is free. The second cradle is connected to the casing  150  by a pivot link with axis Z 20 . The rotation around the axis Z 20  is indexed by a control unit similar to the subassembly  40 . 
     According to another alternative of this second embodiment, the bells  4  and  6  are respectively in a single piece with the shafts  104  and  106 . 
     In the third embodiment illustrated in  FIGS. 19 and 20 , a steering mode similar to that of the first embodiment is used for the continuously variable transmission device  2 , with an action in a radial plane perpendicular to a radial plane containing the contact zones Z 4  and Z 6  between the planet gear  20  and the driving and driven bells  4  and  6 . This embodiment differs from the first one in that the axes of rotation X 10  and X 20  are combined when they are parallel, while the axes of rotation X 4  and X 6  are axially offset relative to the axes X 10  and X 20  by a non-zero radial distance d 2 . 
     In the examples described in reference to the first and third embodiments, the cable  50  passes between the shaft and the bell  4 . Alternatively, said cable can pass between the shaft and the bell  6 . According to another alternative, the cable  50  can pass inside the shaft  10 . 
     In the fourth embodiment of the invention shown in  FIG. 21 , no cable or piston is used to control the movement of the planet gear  20  in the inner volumes V 4  and V 6  of the bells  4  and  6 . In this embodiment, the pivoting control of the planet gear  20 , to adjust the transmission ratio of the continuously variable transmission device  2 , is done in a radial plane containing contact zones Z 4  and Z 6  respectively defined between the belts  205  and  207  of the planet gear  20  and the inner surfaces S 4  and S 6  of the bells  4  and  6 . 
     An elastically deformable element, i.e., a spiral spring  40 , is fastened between the head  304  of the slug  30 , to which it is fastened by a first end  402 , and an axially movable part  70 , to which it is fastened by a second end  404 . The spring  40  therefore exerts an elastic force E 40  on the slug  30  comparable to that mentioned regarding the first two embodiments. 
     The part  70  is accommodated inside the housing  103  of the fixed shaft  10 , that housing being centered on the axis X 10 . Said housing allows the translation along the axis X 10  of the part  70 , but locks its rotation around the axis X 10 . A control rod  72  connects the part  70  to a crank  74  situated outside the inner volume of the device  2 , which is the sum of the inner volumes V 4  and V 6  of the bells  4  and  6 , via a helical link. It is thus possible, by rotating the crank  74  around the axis X 10 , as shown by the double arrow F 5 , to move the part  70  axially along the axis X 10 . This movement makes it possible to vary the stiffness constant of the spring  40 , and consequently the intensity of the force E 40 . 
     The planet gear  20  is mounted freely rotating around the axes Y 20  and Z 20 , which are defined as in the first embodiment. 
     The operation is as follows: in the configuration of  FIG. 21 , the speed transmission ratio is maximal. As long as the bells  4  and  6  rotate at a stabilized speed, the planet gear  20  keeps the position shown in  FIG. 21 . 
     If the user wishes to decrease the transmission ratio of the device  2 , he increases the driving torque of the driving bell  4 . As a result, the input torque on the driving bell  4  is higher than the output torque on the driven bell  6 . A differential torque is thus created between the bells  4  and  6 . The planet gear is no longer statically balanced. The tangential contact force between the belt  205  and the surface S 4  is higher than the tangential force between the belt  207  and the surface S 6 . Momentum is created around the axis Z 20 , which causes the planet gear  20  to tilt clockwise around the axis Z 20 , in the direction of arrow F 6  in  FIG. 21 . As in the second embodiment, this primary tilting causes secondary tilting around the axis Y 20 , in the direction of arrow F 7   FIG. 21 , which decreases the radial distance between the zone Z 4  and the axis of rotation X 4  of the bell  4  and increases the radial distance between the zone Z 6  and the axis of rotation X 6  of the bell  6 . Thus, the transmission ratio of the device  2  decreases. 
     If the planet gear  20  is in another configuration, in particular in a configuration where the transmission ratio is minimal, it is possible to increase the transmission ratio using an inverse phenomenon, while decreasing the torque exerted on the driving bell  4 . 
     The aforementioned secondary tilting takes place against the elastic force E 40 . It is possible to modify the value of the differential torque from which this tilting can occur by playing on the stiffness constant of the spring  40 , i.e., by moving the part  70  along the axis X 10 , inside the housing  104 . The crank  74 , the connecting rod  72  and the part  70  therefore constitute, with the spring  40 , means for controlling the angular position of the planet gear  20  around the axis Y 20 , in the inner volume of the device  2  made up of the respective inner volumes V 4  and V 6  of the bells  4  and  6 . 
     The invention is explained above and shown in the context of its use in the cycling field. It is, however, applicable in other fields, in particular those of motors or pumps as well as in the automobile field, and more generally in the field of mobility. 
     The technical features of the embodiments and alternatives considered above may be combined.