Abstract:
A continuously variable transmission having a variator ( 5 ) comprising input discs ( 2 ) coupled to an input shaft ( 12 ) and an output disc ( 3 ) providing a rotary variator output. The input and output discs are mounted for rotation about a common axis and at last one roller ( 4 ) is arranged between the discs to transfer drive from one to the other at a continuously variable variator drive ratio. The roller is mounted in a carrier ( 30 ) in a manner which permits it to spin about its own axis and to tilt relative to the disks to vary the variator drive ratio. A hydraulic actuator ( 22 ) is arranged to apply to the carrier ( 30 ) a reaction force determined by a hydraulic pressure difference acting on the actuator. The reaction force opposes a traction force applied to the roller ( 4 ) by the action of the discs ( 2, 3 ). Power-recirculation gearing ( 6 ), preferably in the form of planetary gearing, receives as inputs the rotation of the input shaft ( 12 ) and the rotary variator output, and produces an output speed which is a function of both its inputs.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is the U.S. national phase of PCT application no. PCT/GB2009/051758 filed 22 Dec. 2009 which claims priority to Japanese application JP 2008-325767 filed 22 Dec. 2008. 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a continuously variable transmission, which is particularly, but not exclusively, suited to use in motor vehicles including automobiles. More specifically, the invention relates to a multi-regime continuously variable transmission which has improved responsiveness during regime switching. 
     (2) Description of Related Art 
     WO 03/100295 (Torotrak (Development) Limited et al) discloses a continuously variable transmission which employs a toroidal race variator and in which various members are disposed coaxially. This continuously variable transmission provides forward and reverse gears suitable for a vehicle, including geared neutral, by combining the variator with a planetary gear device whose output speed is determined by both (a) the variator&#39;s output speed and (b) the speed of the transmission&#39;s input shaft. The transmission employs torque recirculation. 
     The variator of WO 03/100295 comprises: two input disks each having semi-toroidally recessed surfaces; one output disk which is positioned between the input disks, and each side surface of which has a semi-toroidally recessed surface; and rollers which make contact with the facing recessed surfaces of the input disks and the output disk. The input disk on the input side (engine side) is secured to an input shaft, while the output disk is linked to a sleeve forming a rotary output which is positioned around the input shaft. A boss part on one of the input disks is inserted into the sleeve, the input shaft and the input-disk boss being linked to the same element (a carrier) of a planetary gear device, and the sleeve shaft being linked to another element (a sun gear) of the planetary gear device. 
     WO 07/003657 (Torotrak (Development) Limited et al) discloses a continuously variable transmission in which an “end stop” function is provided, to prevent the variator from going beyond the end of its intended ratio range, by means of one-way clutches which prevent the speed of a first shaft, which drives the transmission output in low regime, from exceeding the speed of a second output shaft, which drives the transmission output in high regime. 
     Japanese patent application 2006-292079 describes a continuously variable transmission which comprises a full-toroidal continuously-variable transmission device (a “variator”), a planetary gear mechanism, a reverse-rotation gear mechanism, and a low/high switching mechanism. The planetary gear mechanism has a carrier coupled to an input disk of the full-toroidal continuously-variable gearing device and to an input shaft, a first sun gear coupled to an output disk of the full-toroidal continuously-variable gearing device, a rear carrier constituting an output element in a low regime, and a second sun gear constituting an output element in a high regime. In the low regime rotation of the rear carrier is transmitted via the reverse-rotation gear mechanism to the output shaft. In the high regime the rotation of the second sun gear is transmitted via a high clutch to the output shaft. In low regime power is recirculated through the planetary gear mechanism, whose output speed is determined both by the speed of the input disk and that of the output disk. The transmission has a low/high switching mechanism for switching between (a) the low regime, involving the engagement of a low clutch, in which rotary drive is transmitted via the planetary gear mechanism, with power recirculation, to the output shaft, and (b) the high regime, involving the engagement of a high clutch, in which the rotary output of the continuously-variable gearing device is transmitted to the output shaft. The transmission has a hydraulic actuator for controlling the movement of the rollers. A pressure difference applied to the hydraulic servo determines the force it applies. The hydraulic actuator acts upon a rotation and inclination support part, providing a reaction force opposing the force of traction occurring at the rollers. The direction of the reaction force output by the hydraulic actuator is switched whenever switching takes place between the low regime and the high regime. 
     The switching timing for the clutch and other elements is normally as follows for configurational reasons.  FIG. 5(   a ) is a graph of transmission ratio during regime change in a continuously variable transmission of the type under discussion; ( b ) is a graph illustrating changes in the state of engagement (contact) and disengagement of the low clutch used in the low regime; ( c ) is a graph illustrating changes in the state of engagement and disengagement of the high clutch used in the high regime; and ( d ) is a graph illustrating switching of the direction of the reaction force (the direction of the servo pressure difference) output by the hydraulic actuator used in roller position control. 
     In a vehicle equipped with this continuously variable transmission, regime switching will take place if, for instance, kick-down occurs while in the high regime in which the high clutch is engaged. In such situations, the system (at time t 11 ) starts engagement of the low clutch which had previously been disengaged, and, once the engagement of the low clutch has been completed (time t 12 ), it switches the direction of the reaction force (the direction of the pressure difference) of the hydraulic actuator (e.g. from 1 (MPa) towards −1 (MPa), although the magnitude of the force will typically be changed as well as its direction. Once the switching of the reaction force direction has been completed (time t 13 ), the system starts disengagement of the high clutch which had until then been engaged. The transmission ratio is fixed at the “synchronous” ratio (−0.3 in the present example) while both clutches are engaged. After release of the old clutch (t 14 ) changing of the transmission ratio resumes. 
     Because the gearing ratio is fixed during the regime switching between times t 11  and t 14  it follows that, despite the requirement for rapid gear changing across regimes at times such as kick-down, sluggish gear changes are liable to occur. Hence there is a pressing demand for regime switching to proceed more rapidly in order to achieve a prompt response to driver demands. 
     SUMMARY OF THE INVENTION 
     The present invention aims to provide a continuously variable transmission having improve responsiveness when rapid regime-switching is required, such as during kick-down. 
     In accordance with a first aspect of the present invention, there is a continuously variable transmission comprising
         a variator comprising an input disk coupled to an input shaft, an output disk providing a rotary variator output, the input and output disks being mounted for rotation about a common axis, at least one roller arranged between the two disks to transfer drive from one disk to the other at a continuously variable variator drive ratio, the roller being mounted in a carrier in a manner which permits it to spin about its own axis and to tilt relative to the disks to vary the variator drive ratio, and a hydraulic actuator arranged to apply to the carrier a reaction force determined by a hydraulic pressure difference acting on the actuator, the reaction force opposing a traction force applied to the roller by the action of the disks;   power-recirculation gearing which receives as inputs the rotation of the input shaft and the rotary variator output, and which produces an output speed which is a function of both its inputs;   a low/high switching mechanism which comprises a low clutch and a high clutch and which serves to switch between (a) a low regime in which the low clutch is engaged and the output of the power-recirculation gearing is transmitted to an output shaft, and (b) a high regime in which the high clutch is engaged and rotation of the variator output is transmitted to the output shaft, and wherein   the direction of the reaction force of the hydraulic actuator is reversed during switching between low regime and high regime, the transmission being characterised in that it further comprises:   an engagement control which starts to engage the disengaged clutch (which may be the low clutch or the high clutch) when the transmission reaches a condition at which regime change is to be initiated; and   a reaction force switching control which starts the reversal of the reaction force direction while the disengaged clutch is being engaged.       

     In accordance with a preferred embodiment of the invention, there is a continuously variable transmission, wherein the reaction force switching control completes the reversal of the direction of the reaction force before the complete engagement of the disengaged clutch. 
     According to a further preferred embodiment of the present invention, there is a continuously variable transmission, comprising a disengagement control which, once the reaction force direction has been reversed and the previously disengaged clutch is completely engaged, starts to disengage the clutch which had been engaged prior to the regime switch. 
     According to a further preferred embodiment of the present invention, there is a continuously variable transmission, further comprising a one-way clutch which is provided between the input-side member of the high clutch and an input-side member of the low clutch, and which prevents the rotational speed of the input-side member of the high clutch from becoming lower than the rotation speed of the input-side member of the low clutch. 
     According to a further preferred embodiment of the present invention, there is a continuously variable transmission, comprising a mechanism for reversing the rotational direction of the variator&#39;s rotary output before it is transmitted to the input-side member of the high clutch. 
     According to a further aspect of the present invention there is a continuously variable transmission ( 1 ) which comprises:
         input disks ( 2   1  and  2   2 ) coupled to an input shaft ( 12 ), an output disk ( 3 ) for outputting continuously variable geared rotation, rollers ( 4  and  4 ) sandwiched between the two disks ( 2   1 ,  2   2  and  3 ), (respective} rotation and inclination support parts ( 30 ) for supporting the rotational centre ( 4   a ) of each roller in a freely rotatable fashion and also for supporting the said roller with freedom to incline relative to the two disks ( 2   1 ,  2   2  and  3 ), and a full-toroidal continuously-variable gearing device ( 5 ) for autonomously changing the angle of inclination of the rollers by controlling the movement of the rollers ( 4  and  4 ) relative to the surface direction of the two disks ( 2   1 ,  2   2  and  3 ) via the rotation and inclination support parts;   a hydraulic actuator ( 22 ) for controlling the movement of the rollers ( 4  and  4 ) between the two disks ( 2   1 ,  2   2  and  3 ) by pressing and driving the rotation and inclination support part ( 30 ) on the basis of supplied hydraulic pressure;   a power-recirculation mechanism ( 6 ) which performs a power-recirculation operation in which the rotation of the input shaft ( 12 ) is synthesised with the continuously variable geared rotation; and   a low/high switching mechanism ( 10 ) which is able to switch regimes between a low regime entailing the engagement of a low clutch (L) whereby rotation received via the power-recirculation mechanism ( 6 ) is freely transmitted to an output shaft ( 16 ), and a high regime entailing the engagement of a high clutch (H) whereby the continuously-variable geared rotation of the continuously-variable gearing device ( 5 ) is freely transmitted to the output shaft ( 16 ),   and, in this said continuously variable transmission, a reaction force to traction produced by the rollers ( 4  and  4 ) is output by the hydraulic pressure of the hydraulic actuator ( 22 ) via the rotation and inclination support part ( 30 ), and also the direction of the reaction force output by the hydraulic actuator ( 22 ) is switched when the system switches between the low regime and the high regime,   characterised in that the said continuously  35  variable transmission ( 1 ) comprises:   an engagement control means ( 37 ) which starts engagement control for engagement of the disengaged clutch (which may be the high clutch (H) or the low clutch (L)) when the system reaches a switching point at which the regime should be switched; and   a reaction force-switching control means ( 38 ) which controls the hydraulic pressure supplied to the hydraulic actuator ( 22 ) during the engagement control by means of the engagement control means ( 37 ), and thus starts reaction force-switching control for switching the direction of the reaction force.       

     Preferably, the reaction force—switching control means ( 38 ) completes the reaction force-switching control before completion of the engagement control by means of the engagement control means ( 37 ). 
     Preferably, the transmission further comprises a disengagement control means ( 43 ) which, once the reaction force-switching control and the engagement control have both been completed, starts disengagement control for disengaging the clutch which had been engaged prior to the regime switching. 
     Preferably, the transmission further comprises a reverse-rotation mechanism ( 7 ) for transmitting the continuously-variable geared rotation of the continuously-variable gearing device ( 5 ) to the input-side member ( 19 ) of the high clutch (H) after having first reversed the said rotation; and
         a one-way clutch ( 20 ) which is provided between the input-side member ( 19 ) of the high clutch (H) and an input-s member ( 17 ) of the low clutch (L), and which regulates the rotation of the input-side member ( 19 ) of the high clutch (H) becoming a lower rotation than the rotation of the input-side member ( 17 ) of the low clutch (L). It should be appreciated that the reference numbers in brackets above are for cross-referencing with the figures and are for convenience to facilitate understanding of the invention, and they do not in any way have any bearing on the scope of the claims.       

     Because the engagement control means starts engagement control for engagement of the disengaged clutch (the clutch on the disengaged side—which may be the high clutch or the low clutch) when the system reaches a switching point at which the regime should be switched, and the reaction force-switching control means controls the hydraulic pressure supplied to the hydraulic actuator during the engagement control by means of the engagement control means, and thus starts reaction force-switching control for switching the direction of the reaction force. Consequently (in contrast to the situation which pertains with the prior art technique in which the direction of the reaction force of the hydraulic actuator is switched only upon completing engagement of the previously disengaged clutch, which necessitates a lengthy period of time since control is carried out in such a way that the hitherto engaged clutch (clutch on the engaged side) is disengaged only after completing switching of the reaction force direction), when the present invention is employed, because the direction of the reaction force produced by the hydraulic actuator is switched during the engagement control of the clutch on the disengaged side, it is possible to rapidly start the process of disengaging the clutch on the engaged side following on from the switching of the direction of the reaction force, thereby improving responsiveness when rapid regime-switching is required, such as during kick-down. 
     Where the reaction force-switching control means completes the reaction force-switching control before completion of the engagement control by means of the engagement control means, and thus, subsequently, even if the clutch which had been engaged prior to the regime switching is disengaged, smooth gear changing without any shocks is achieved since reaction force-switching control has reliably been completed at that time. 
     Where the disengagement control means starts disengagement control for disengaging the clutch on the engaged side after the switching of the direction of the reaction force due to the hydraulic actuator and the engagement of the clutch on the disengaged side, and thus smooth and stable gear changing without any shocks is achieved. 
     Where the transmission comprises a reverse-rotation mechanism for transmitting the continuously-variable geared rotation of the continuously-variable gearing device to the input-side member of the high clutch after having first reversed the said rotation; and a one-way clutch which is provided between the input-side member of the high clutch and an input-side member of the low clutch, and which regulates the rotation of the input-side member of the high clutch becoming a lower rotation than the rotation of the input-side member of the low clutch, and it follows from this that, when the gearing ratio of the continuously-variable gearing device reaches the optimum value for regime switching, the system can start switching of the direction of the reaction force (orientation of the pressure difference) due to the hydraulic actuator and start engagement of the clutch on the previously disengaged side, and hence regime switching can be carried out both promptly and smoothly without producing any shock. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1(   a ) is a schematic representation of a continuously variable transmission (CVT) comprising a full-toroidal continuously-variable gearing device according to the present invention; 
         FIG. 1(   b ) is a velocity diagram for parts of the  FIG. 1   a  transmission; 
         FIG. 2  represents certain working parts of the same transmission in a highly diagrammatic form; 
         FIG. 3(   a ) is a graph of changes in the gearing ratio of the continuously variable transmission; 
         FIG. 3(   b ) is a graph of changes in the state of engagement (contact) and disengagement of the low clutch used in low regime; 
         FIG. 3(   c ) is a graph of changes in the state of engagement and disengagement of the high clutch used in the high regime; 
         FIG. 3(   d ) is a graph illustrating the situation on switching the direction of the reaction force (direction of the differential pressure) output by the hydraulic actuator  22 ; 
         FIG. 4  is a flow diagram of operations upon regime change; 
         FIG. 5(   a ) is a graph of transmission ratio during regime change in a known continuously variable transmission; 
         FIG. 5(   b ) is a graph illustrating changes in the state of engagement (contact) and disengagement of the low clutch used in the low regime; 
         FIG. 5(   c ) is a graph illustrating changes in the state of engagement and disengagement of the high clutch used in the high regime; and 
         FIG. 5(   d ) is a graph illustrating switching of the direction of the reaction force (orientation of the pressure difference) output by the hydraulic actuator used in roller position control. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in  FIG. 1(   a ), a continuously variable transmission  1  comprises: a full-toroidal continuously-variable gearing device (also referred to hereinbelow as a variator)  5 ; a planetary gear device U comprising a power-recirculation mechanism  6  and a reverse-rotation gear mechanism  7 ; and a low/high switching mechanism  10 . A traction produced by rollers  4  and  4  is reacted through hydraulic actuator  22  acting through a carriage  30 , and determined by hydraulic pressure in the actuator. The direction of the reaction force exerted by the hydraulic actuator  22  is switched when the system switches between low regime and high regime. 
     The continuously-variable gearing device  5  has: two input disks  2   1  and  2   2  coupled to an input shaft  12 ; a single output disk  3  located between the two input disks  2   1  and  2   2  for outputting continuously variable geared rotation; and rollers  4  and  4  sandwiched between the two disks  2   1 ,  2   2  and  3 . 
     It should be noted that the input disks  2   1  and  2   2  are also collectively referred to hereinbelow as the input disk or input disks  2 . The input disks  2   1  and  2   2  and the output disk  3  have facing semi-toroidal recesses  2   a  and  3   a  forming a pair of toroidal cavities containing the two sets of rollers  4  and  4 . The rollers  4  transmit drive from the input disks to the output disks (or from the output disks to the input disks, since power can flow through the variator in either direction) at a continuously variable drive ratio (the ratio of input disk speed to output disk speed). The rollers are able to tilt, changing their inclination, when moved in a direction at right angles to their axes, thereby altering their contact radii with the input disks  2   1  and  2   2  and the output disk  3 , and so altering the drive ratio. A drum-shaped output transmission shaft  13  is coupled to the circumferentially outermost portion of the output disk  3 , and the said output transmission shaft  13  extends to the rear of the variator, surrounding the rear input disk  2   2 . 
     The power-recirculation mechanism  6  performs a power-recirculation operation in which the rotation of the input shaft  12  is combined with the continuously variable rotation output from the output disk  3 , and it comprises, in a dual planetary gear arrangement, a carrier C 1  for supporting a first pinion P 1   a  and a second pinion P 1   b  which mesh with each other, a ring gear R 1  which meshes with the first pinion P 1   a , and a sun gear S 1  which meshes with the second pinion P 1   b.    
     The carrier C 1 , which is linked to the input shaft  12  which is itself linked to the output shaft  8   a  (see  FIG. 2 ) of an engine  8  via a torque converter  9 , is used for the transmission of the output of the engine  8 . The sun gear S 1 , which is linked to the abovementioned drum-shaped output transmission shaft  13 , is used for the transmission of the continuously-variable output rotation output of the variator  5 . The ring gear R 1  outputs power to the low clutch L of the low/high switching mechanism  10 . 
     The reverse-rotation gear mechanism  7  is used to transmit the continuously-variable geared rotation of the variator  5  to the high transmission shaft  19  of the high clutch H after having first reversed the said rotation. It comprises two pinions P 2  and P 3 , one large and the other small, which are secured to a shaft  24  rotatably supported on a securing member  15 , in a step pinion arrangement. The large pinion P 2 , which meshes with a ring gear R 2  secured to the output transmission shaft  13 , is used to transmit the output rotation of the variator  5 , while the small pinion P 3 , which meshes with a sun gear S 3 , outputs power to the high clutch H of the low/high switching mechanism  10 . The reverse-rotation gear mechanism  7  is effectively a planetary gear whose carrier C 2  is fixed. 
     The low/high switching mechanism  10  is configured in such a way as to be able to switch regimes between:
         (a) a low regime in which the low clutch L is engaged and rotation received via the power—recirculation mechanism  6  is transmitted to an output shaft  16 , and   (b) a high regime in which the high clutch H is engaged and the continuously-variable output of the variator  5  is transmitted to the output shaft  16 .       

     In other words, the low/high switching mechanism  10  comprises the low clutch L whereby output rotation from the power-recirculation mechanism  6  is transmitted via a low-transmission shaft (input-side member of the low clutch L)  17 , and the high clutch H whereby output rotation from the reverse-rotation gear mechanism  7  is transmitted via a sleeve-shaped high-transmission shaft (input-side member of the high clutch H)  19 . The variator  5 , planetary-gear device U and low/high switching mechanism  10  and also the input shaft  12  and output shaft  16  are coaxial. 
     A one-way clutch  20  is provided between the high-transmission shaft  19  of the high clutch H and the low-transmission shaft  17  of the low clutch L. This one-way clutch  20  prevents the rotation of the high-transmission shaft  19  from becoming slower than the rotation of the low-transmission shaft  17 , and so limits the gearing ratio of the variator  5 . The one-way clutch freewheels whilst the high-transmission shaft  19  is turning faster than the low-transmission shaft  17 , but locks to prevent the low-transmission shaft  17  from turning faster than the high-transmission shaft  19 . It may for example be formed as a sprag clutch. 
     As shown in  FIG. 2 , the variator  5  has: a carriage (rotation and inclination support part) for supporting the roller  4 , permitting the roller to spin about its own axis, and also to incline relative to the two disks  2   1  and  2   2  and  3 ; and a hydraulic actuator  22  for applying a controllable force to the carriage  30  on the basis of hydraulic pressure supplied from a hydraulic-pressure control device which is not depicted. The hydraulic actuator  22  has opposed hydraulic chambers  22   c  and  22   d  which are partitioned from each other by a piston  22   a , and has a piston rod  22   b  which is linked via the carriage  30  to the axis  4   a  of the roller  4 . The angle of inclination of the rollers  4  and  4  is autonomously changed by controlling the movement of the rollers  4  and  4  relative to the surface direction of the two disks  2   1 ,  2   2  and  3  via the carriage  30 . Reference number  18  in  FIG. 2  denotes a driven vehicle wheel which is turned by the drive force which is transmitted from the continuously variable transmission  1 , via the output shaft  16  and a differential gear (which is not depicted). 
     During torque transmission from the input disk  2  to the output disk  3  due to engagement of the high clutch H, a pressure—regulating valve (not depicted) is connected via a hydraulic pathway  33  to the hydraulic chamber  22   c  in such a way that the hydraulic chamber  22   c  can output, via the carriage  30 , a reaction force (a force urging the roller  4  downwards in  FIG. 2 ) against a traction force F 1  (see  FIG. 2 ) which acts on each roller  4  under such conditions. During torque transmission from the output disk  3  to the input disk  2  via the power-recirculation mechanism  6  due to engagement of the low clutch L, a pressure-regulating valve (not depicted) is connected via a hydraulic pathway  34  to the hydraulic chamber  22   d  in such a way that the hydraulic chamber  22   d  can output, via the carriage  30 , a reaction force (a force urging the roller  4  upwards in  FIG. 2 ) against a traction force F 2  (see  FIG. 2 ) which acts on each roller  4  under such conditions. 
     As shown in  FIG. 1(   a ), a control unit  11  for controlling the continuously variable transmission  1  has a decision-making means  28 , an engagement control means  37 , a reaction force-switching control means  38 ,  30  and a disengagement control means  43 . 
     The decision-making means  28  monitors the drive ratio of the variator  5  and makes a decision as to whether the said drive ratio has reached a regime-switching optimum value (i.e. a point at which the regime should be switched), and also determines whether the low clutch L is currently connected. When a decision has been made by the decision-making means  28  that the system has reached a point at which the regime should be switched, the engagement control means  37  starts to engage the disengaged clutch (which may be the high clutch H or the low clutch L). Engagement of the clutch is carried out by supplying hydraulic pressure to a hydraulic actuator (not depicted) acting on the clutch to be engaged (which may be the high clutch H or the low clutch L), by controlling a hydraulic-pressure control device (not depicted) by means of the engagement control means  37 . 
     While the clutch is being engaged by the engagement control means  37 , the reaction force-switching control means  38  controls the hydraulic pressure supplied to the hydraulic actuator  22 , through a hydraulic-pressure control device which is not depicted, and thus starts the process of switching the direction (differential pressure direction) of the reaction force which is output by the hydraulic actuator  22 . Switching of the direction of the reaction force is completed before the oncoming clutch is fully engaged. When the switching of the reaction force and the engagement of the oncoming clutch have been completed, the disengagement control means  43  exhausts hydraulic pressure from a hydraulic actuator (not depicted) of the old clutch which was engaged before the regime switching (which may be the high clutch H or the low clutch L), and thus starts to disengage the said clutch. 
     As shown in  FIG. 1(   a ), a one-way clutch  21  for preventing backward rotation is provided between the input shaft  12  and a sun gear shaft  13 ′ which is integral with the drum-shaped output transmission shaft  13 . The input shaft  12  which is coupled with the input disk  2  ( 2   1  and  2   2 ), and the sun gear shaft  13 ′ which is coupled to the output disk  3  always rotate in the opposite direction to each other whatever the drive ratio of the variator  5 . Since the direction of rotation of the engine  8  is fixed (by way of example, being assumed here to be clockwise), the one-way clutch  21  is set so as to rotate idly when the input shaft  12  turns clockwise and the sun gear shaft  13 ′ turns anticlockwise. 
     Upon launch (moving away from rest) of the vehicle, or while reversing, the continuously variable transmission  1  is put into the low-regime state by engaging the low clutch L by means of the engagement control means  37  and disengaging the high clutch H by means of the disengagement control means  43  under control by the  20  low/high switching mechanism  10 , based on hydraulic control by means of elements including a shift lever and the hydraulic-pressure control device which are not depicted. Thereupon, as shown in  FIGS. 1(   a ) and ( b ), the rotation of the input shaft  12  coupled to the output shaft  8   a  of the engine  8  is transmitted to the input discs  2   1  and  2   2  of the variator  5  and the carrier C 1  of the power-recirculation mechanism  6 . The rotation of the input shaft  12 , which is input to the input discs  2   1  and  2   2 , undergoes a speed change in the variator  5 , and the variator output rotation Vout is output by means of the output disk  3  and passes via the output transmission shaft  13  to the sun gear S 1  and the ring gear R 2 . 
     When the variator output rotation Vout is input to the sun gear S 1 , a combination takes place in the power-recirculation mechanism  6 , in the form of torque recirculation of the rotation of the input shaft  12  input to the carrier C 1  and the abovementioned variator output rotation Vout of the sun gear S 1 , and the result is output from the ring gear R 1 . The output rotation of the ring gear R 1  constitutes an output rotation OutL. It is variable through a range extending from stepped-down reverse rotation, via a neutral position (the Geared Neutral point, GN), to stepped-down forward rotation, in accordance with the drive ratio of the variator  5 . The output rotation OutL of the ring gear R 1  is output, in the form of output rotation in the low-regime state, via the low transmission shaft  17  and the low clutch L, to the output shaft  16 . 
     In low regime power is recirculated through the power-recirculation mechanism  6 . When the variator output rotation Vout (drive ratio of the variator  5 ) is in the geared-neutral state GN illustrated in  FIG. 1(   b ) by the single dot and chain line, and the transmission is in low regime, the ring gear R 1  is stationary. The output rotation OutL is zero. The vehicle can be brought to a halt and subsequently launched without disengaging the low clutch L and a launch device such as a torque converter can be dispensed with. 
     Selection of reverse (R) and forward drive (D) may be made using a shift lever (not shown). In reverse (which is available in low regime only), the output speed OutL of the output shaft  16  is increased (faster reverse rotation) when the drive ratio of the variator  5  is increased (if, in  FIG. 1(   b ), the variator output rotation Vout is slowed). 
     In the drive (D) range, in low regime, the output speed OutL of the output shaft  16  is increased when the drive ratio of the variator  5  is reduced (if, in  FIG. 1(   b ), the variator output rotation Vout is speeded up). 
     As the vehicle accelerates forwards from rest, the output speed OutL of the output shaft  16  in low-regime is increased while the drive ratio of the variator  5  is reduced. When the variator  5  reaches the gearing ratio for a synchronous regime change (Sc in  FIG. 1   b ) and a regime-change decision is taken, the low/high switching mechanism  10  is controlled on the basis of hydraulic-pressure control by means of the hydraulic-pressure control device which is not depicted. The high clutch H is engaged by means of the engagement control means  37  and the low clutch L is disengaged by means of the disengagement control means  43 , whereupon the toroidal continuously variable transmission  1  is put into the high-regime state. 
     At this juncture, as shown in  FIGS. 1(   a ) and ( b ), in high-regime, the variator output rotation Vout is input to the ring gear R 2  of the reverse-rotation gear mechanism  7 , and the rotation which has been input to the ring gear R 2  passes via the large and small pinions P 2  and P 3 . Due to the gear ratios R 2 /P 2  and S 3 /P 3 , the variator output rotation Vout is changed to slightly stepped up rotation and is reversed before being output from the sun gear S 3 . The rotation of the sun gear S 3  is output via the high-transmission shaft  19  and the high clutch H to the output shaft  16 , providing the transmission&#39;s output in high-regime. The transmission operates without power-recirculation, its output speed being determined by the variator output rotation Vout. The power-recirculation mechanism  6  is removed from the power transmission path. 
     The synchronous change from low-regime to high-regime during the abovementioned synchronous regime change is carried out when the drive ratio of the variator  5  (the variator output rotation Vout) is at its minimum. 
     Situations can arise where the variator tends to go beyond the synchronous ratio. Note that synchronous ratio is the variator drive ratio at which a regime change produces no change in the transmission&#39;s output speed. That is, at synchronous ratio the high-transmission shaft  19  and the low-transmission shaft  17  rotate at the same speed. At all other permissible variator ratios the high-transmission shaft  19  rotates faster than the low-transmission shaft  17 . External causes, such as the vehicle running on sloping roads, or rapid braking, can tend to cause the speed of the low-transmission shaft to exceed that of the high-transmission shaft. 
     For example, in low regime, if the ratio of the speed of the output shaft  16  to that of the input shaft  12  (the ratio of the speed of the vehicle&#39;s drive wheel  18 ,  20  to the engine speed) becomes large and attempts to become larger in the positive direction than the upper end of the range OutL shown in  FIG. 1(   b ), then the low-transmission shaft  17  and the high-transmission shaft  19 , which are coupled through the power-recirculation mechanism  6  and the reverse-rotation gear mechanism  7 , enter a state in which their rotations approach each other and, once they have reached the same speed, the one-way clutch  20  is engaged. 
     When the one-way clutch  20  is engaged in low regime in this way, the speed of the high-transmission shaft  19  is prevented from becoming lower than that of the low-transmission shaft  17 , and thus the drive ratio of the variator  5  is prevented from exceeding the abovementioned synchronous ratio Sc. Consequently the rollers  4  and  4  are prevented from becoming excessively inclined, thereby preventing problems such as the rollers flying off the two discs  2  and  3 . 
     Similarly in high regime if the ratio of the speed of the output shaft  16  to that of the input shaft  12  (the ratio of the speed of the vehicle&#39;s driven wheel to the engine speed) becomes small and attempts to become smaller in the positive direction than the lower end of the output range OutH shown in  FIG. 1(   b ), then the low-transmission shaft  17  and the high-transmission shaft  19 , which are coupled through the power-recirculation mechanism  6  and the reverse-rotation gear mechanism  7 , enter a state in which their rotations approach each other and, once they have reached the same speed, the one-way clutch  20  is engaged. This similarly prevents problems such as the rollers  4  and  4  flying off the two discs  2  and  3 . 
     The present invention can thus prevent situations such as dropout of a roller  4  as the speed of the low-transmission shaft  17  exceeds that of the high-transmission shaft  19  during regime switching, due to the presence of the one-way clutch  20 . Hence when the gearing ratio of the variator  5  reaches the optimum value for regime switching, the system can start switching the direction of the reaction force (orientation of the pressure difference) of the hydraulic actuator  22  and start engagement of the clutch on the previously disengaged side (which may be the high clutch H or the low clutch L). In this way, regime switching can be carried out both promptly and smoothly without creating any shock. 
     Further, whatever the variator drive ratio may be, when the input discs  2   1  and  2   2  of the variator  5  rotate in the forward-rotation direction (e.g. clockwise) and the roller  4  is driven in rotation in response, the sun gear shaft  13 ′ coupled to the output disk  3  does not rotate in the forward-rotation direction (e.g. clockwise) faster than the input shaft  12  linked to the input disk  2 , but rather the one-way clutch  21  located between the two shafts  12  and  13 ′ rotates idly. By way of example, if the roller  4  is driven in rotation in the reverse direction, for example upon input of reverse torque to the variator  5  from the vehicle drive wheel  18  when the vehicle is at a halt on an uphill slope or upon backward rotation of the engine  8  (slight backward rotation when the engine  8  is stopped), then the sun gear shaft  13 ′ rotates fast in the forward-rotation direction (clockwise) relative to the input shaft  12 , and the one-way clutch  21  is locked such that backward rotation of the input disk  2  is inhibited. In this way, the roller  4  is driven in rotation in the backward direction, the fraction force of the roller is relieved, and situations where the roller drops out are prevented before they can arise. 
     The switching timing of elements such as the clutch are detailed hereinbelow.  FIG. 3(   a ) is a graph illustrating changes in the drive ratio of the continuously variable transmission  1 ; ( b ) is a graph illustrating changes in the state of engagement (contact) and disengagement of the low clutch used in the low regime; ( c ) is a graph illustrating changes in the state of engagement and disengagement of the high clutch used in the high regime; and ( d ) is a graph illustrating the situation on switching the direction of the reaction force (direction of the differential pressure) output by the hydraulic actuator  22 . Further,  FIG. 4  is a flow chart explaining the operation of the present embodiment. 
     In a vehicle equipped with the present continuously variable transmission  1 , in Step S 1 , if the decision-making means  28  makes a decision that the drive ratio of the variator  5  has reached a switching point at which the regime should be switched (S 1 : YES), then, in Step S 2 , it determines whether the low clutch L is currently connected. If it determines that the low clutch L is connected (S 2 : YES), then the engagement control means  37  supplies hydraulic pressure to a corresponding hydraulic actuator (not depicted) and, in Step S 3 , it starts engagement of the high clutch H which had been disconnected and, in Step S 5 , it starts switching the reaction force direction (differential pressure direction) of the hydraulic actuator  22 . Then, in Step S 6 , the engagement control means  37  determines whether engagement of the high clutch H has been completed, and, once it has determined that the connection has been completed (S 6 : YES), the reaction force-switching control means  38  determines, in Step S 7 , whether or not the switching of the reaction force direction (which was started in Step S 5 ) has been completed. If it determines that the switching of the reaction force direction has been completed (S 7 : YES), then the disengagement control means  43  starts (S 8 ) disengagement of the low clutch L by exhausting hydraulic pressure from the corresponding hydraulic actuator (not depicted), and the process is completed at the time when the disengagement takes place. 
     On the other hand when, by way of example, kick-down takes place during running using the high clutch H, then if, in Step S 1 , the decision-making means  28  makes the decision that a switching point has been reached (S 1 : YES) and, in Step S 2 , it determines that the high clutch H is connected rather than the low clutch L being connected (S 2 : No), then the engagement control means  37  supplies hydraulic pressure to the corresponding hydraulic actuator (not depicted) and, in Step S 4 , it starts engagement (at the time t 1  in  FIG. 3 ) of the low clutch L which had been disengaged and, in Step S 9 , it starts switching (time t 1 ) of the reaction force direction of the hydraulic actuator  22  (e.g. from 1 [MPa] towards −1 [MPa]). 
     Also, the engagement control means  37  determines in Step S 10  whether the connection of the low clutch L has been completed and, if it determines that the connection has been completed (S 10 : YES) (time t 2 ), the reaction force-switching control means  38  determines, in Step S 11 , whether or not the switching of the reaction force direction (which was started in Step S 9 ) has been completed. If it determines that the switching of the reaction force direction has been completed (S 11 : YES), then, in Step S 12 , the disengagement control means  43  carries out (time t 2 ) a process for starting disengagement of the high clutch H by exhausting hydraulic pressure from the corresponding hydraulic actuator (not depicted). Upon completion (time t 3 ) of disengagement of the high clutch H, the transmission ratio can once more be increased from the state at times t 1  to t 3  when the gearing ratio had been fixed at a constant (−0.3). 
     As described hereinabove, the present embodiment is configured in such a way that, when the engagement control means  37  decides that the system has reached a switching point at which the regime should be switched, it starts engagement control for engaging the previously disengaged clutch (which may be the high clutch H or the low clutch L), and the reaction force switching control means  38  starts reaction force-switching control whereby the hydraulic pressure supplied to the hydraulic actuator  22  is controlled and the direction of the reaction force is switched during the engagement control by means of the engagement control means  37 . Consequently (in contrast to the situation which pertains when the direction of the reaction force of the hydraulic actuator  22  is switched only upon completing engagement of the previously disengaged clutch, which requires a lengthy period of time since control is carried out in such a way that the hitherto engaged clutch is disengaged only after completing switching of the reaction force direction), when the present mode of embodiment is employed, the reaction force switching means  38  is used to switch the direction of the reaction force produced by the hydraulic actuator  22  during the engagement control of the clutch on the disengaged side by means of the engagement-control means  37 , and thus it is possible to rapidly start the process of disengaging the clutch on the engaged side following the switching of the direction of the reaction force. This improves responsiveness when rapid regime-switching is required, such as during kick-down. 
     Further, in the present embodiment, because the reaction force switching control means  38  completes the reaction force-switching control before completion of the engagement control by means of the engagement control means  37 , it follows that, subsequently, when disengaging the clutch which had been engaged prior to the regime switching, smooth gear changing without any shocks is achieved since reaction force-switching control has reliably been completed at that time. Further, because the disengagement control means  43  starts disengagement control for disengaging the clutch on the engaged side after the switching of the direction of the reaction force due to the hydraulic actuator  22  and the engagement of the clutch on the disengaged side, it follows that smooth and stable gear changing without any shocks is achieved.