Belt-drive continuously variable transmission

A belt-drive continuously variable transmission including a lock mechanism for locking a primary moveable sheave of a primary pulley in a highest transmission ratio position. The lock mechanism includes a fixed side axial groove extending on an outer circumferential surface of a primary fixed sheave shaft, a moveable side axial groove extending on an inner circumferential surface of a primary moveable sheave sleeve, an intervening member disposed between the axial grooves, an axial tapered groove formed as a part of at least one of the axial grooves which is disposed corresponding to a highest transmission ratio, and an intervening member displacement limiting member arranged to limit an amount of displacement of the intervening member relative to the primary fixed sheave shaft along the fixed side axial groove or the moveable side axial groove.

BACKGROUND OF THE INVENTION

The present invention relates to a belt-drive continuously variable transmission including a primary pulley and a secondary pulley each having a pair of opposed sheave surfaces, and a belt wound on the pairs of opposed sheave surfaces to connect the primary pulley and the secondary pulley with each other.

The belt-drive continuously variable transmission is operative to ensure a necessary belt clamping force by applying a hydraulic pressure to the primary pulley during high speed running and maintain a highest transmission ratio against variation in transmission torque. In this condition, a primary pressure applied to the primary pulley becomes maximum within a transmission unit, and therefore, a line pressure to be regulated on the basis of a pump discharge pressure from an oil pump must be increased to at least the primary pressure. For this reason, during high speed cruising in which the high speed running is maintained for a long period of time, torque for driving the oil pump cannot be reduced. Accordingly, in an engine-equipped vehicle in which the torque for driving the oil pump is obtained from an engine, it is not possible to enhance fuel economy.

In order to solve the above problem, there have been proposed transmission ratio lock mechanisms for a belt-drive continuously variable transmission which is adapted to lock a primary moveable sheave relative to a primary fixed sheave in a position where a predetermined transmission ratio is attained. Japanese Patent Application Unexamined Publication No. 2008-51154 discloses a hydraulically operated transmission ratio lock mechanism that is adapted to lock a primary moveable sheave relative to a primary fixed sheave in a position where a predetermined transmission ratio is attained, by sealing a hydraulic pressure in a primary pressure chamber of the primary pulley. Japanese Patent Application Unexamined Publication No. 2006-170387 discloses a meshing transmission ratio lock mechanism that is adapted to lock a primary moveable sheave relative to a primary fixed sheave in a position where a predetermined transmission ratio is attained, by using meshing engagement of the primary moveable sheave.

SUMMARY OF THE INVENTION

However, the conventional belt-drive continuously variable transmission equipped with the above-described hydraulically operated transmission ratio lock mechanism must be additionally provided with a valve construction for sealing a hydraulic pressure in the primary pressure chamber. Further, the conventional belt-drive continuously variable transmission equipped with the meshing transmission ratio lock mechanism must be additionally provided with a hydraulic motor and a meshing pawl construction for establishing the meshing engagement of the primary moveable sheave. Therefore, even in either the conventional belt-drive continuously variable transmission equipped with the hydraulically operated transmission ratio lock mechanism or the conventional belt-drive continuously variable transmission equipped with the meshing transmission ratio lock mechanism, there exists such a problem that the number of components is increased to thereby cause an increased cost.

The present invention has been made to solve the problem of the conventional arts. An object of the present invention is to provide a belt-drive continuously variable transmission that can perform a transmission ratio lock function without causing an increase in cost, by utilizing a force acting on an existing component and a moveable sheave.

In one aspect of the present invention, there is provided a belt-drive continuously variable transmission including:a primary pulley including a primary fixed sheave having a primary fixed sheave shaft and a primary moveable sheave having a primary moveable sheave sleeve, the primary moveable sheave sleeve being fitted onto the primary fixed sheave shaft and slidably moveable relative to the primary fixed sheave shaft in an axial direction of the primary pulley,a secondary pulley including a secondary fixed sheave having a secondary fixed sheave shaft and a secondary moveable sheave having a secondary moveable sheave sleeve, the secondary moveable sheave sleeve being fitted onto the secondary fixed sheave shaft and slidably moveable relative to the secondary fixed sheave shaft in an axial direction of the secondary pulley,a belt wound on the primary pulley and the secondary pulley to transmit a driving force from a drive source to the primary pulley and the secondary pulley;a first fixed side axial groove extending on an outer circumferential surface of the primary fixed sheave shaft in the axial direction of the primary pulley;a first moveable side axial groove extending on an inner circumferential surface of the primary moveable sheave sleeve in the axial direction of the primary pulley so as to be opposed to the first fixed side axial groove;a first intervening member disposed between the first fixed side axial groove and the first moveable side axial groove, the first intervening member serving to reduce slide resistance that is caused when the primary moveable sheave sleeve makes an axial slide motion in a transmission range between a low transmission ratio and a high transmission ratio,a first axial tapered groove formed as a part of at least one of the first fixed side axial groove and the first moveable side axial groove which is disposed corresponding to a highest transmission ratio range, the first axial tapered groove being formed such that a depth defined between the first fixed side axial groove and the first moveable side axial groove is gradually reduced toward a side of a highest transmission ratio, anda first intervening member displacement limiting member arranged to limit an amount of displacement of the first intervening member relative to the primary fixed sheave shaft or the primary moveable sheave sleeve along the first fixed side axial groove or the first moveable side axial groove,wherein when the primary moveable sheave sleeve is moved toward a lock position in which the primary moveable sheave sleeve is to be locked in a position corresponding to the highest transmission ratio, the first intervening member displacement limiting member serves to input an engagement force produced by a hydraulic thrust acting on the primary moveable sheave to the first intervening member, andwherein when the primary moveable sheave sleeve is moved apart from the lock position thereof, the first intervening member displacement limiting member serves to input a disengagement force produced by a belt reaction force acting on the primary moveable sheave to the first intervening member.

EFFECT OF THE INVENTION

When the primary moveable sheave shaft is moved toward the lock position corresponding to the highest transmission ratio, an engagement force produced by the hydraulic thrust acting on the primary moveable sheave is inputted to the primary intervening member through the primary intervening member displacement limiting member. The primary intervening member to which the engagement force is inputted is pushed into and engaged in the axial tapered groove that is tapered such that the depth between the axial grooves is gradually reduced. As a result, a frictional resistance force generated on mutual contact surfaces of the primary intervening member and each of the primary fixed sheave shaft and the primary moveable sheave sleeve is increased. Thus, the primary intervening member serves as a lock member that locks the primary moveable sheave in the lock position corresponding to the highest transmission ratio. On the other hand, when the primary moveable sheave sleeve is moved apart from the lock position, a disengagement force produced by the belt reaction force acting on the primary moveable sheave is inputted to the primary intervening member through the primary intervening member displacement limiting member. As a result, the primary intervening member is disengaged from the axial tapered groove by the disengagement force inputted thereto, so that the primary moveable sheave is unlocked and released from the lock position. Meanwhile, the primary intervening member (for instance, a ball, a roller, etc.) used as the lock member serving to lock the primary moveable sheave relative to the primary fixed sheave is an existing component to reduce slide resistance that is caused when the primary moveable sheave sleeve makes an axial slide motion in a transmission range between a low transmission ratio and a high transmission ratio. With this construction, it is possible to perform a transmission ratio lock function by utilizing the force exerted on the existing component and the primary moveable sheave without causing increase in cost.

DETAILED DESCRIPTION OF THE INVENTION

In the followings, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1is a general system diagram showing a drive system and a control system of an engine vehicle equipped with a belt-drive continuously variable transmission according to a first embodiment of the present invention. Referring toFIG. 1, a construction of the general system will be explained hereinafter.

As shown inFIG. 1, the drive system of the engine vehicle equipped with the belt-drive continuously variable transmission according to the first embodiment includes engine1, torque converter2, forward/reverse changeover mechanism3, belt-drive continuously variable transmission mechanism4, final reduction gear mechanism5and driving wheels6,6.

In engine1, an output torque can be controlled by an accelerator operation of a vehicle driver, and also an engine speed (i.e., an engine rotation number) and a fuel injection amount can be controlled on the basis of an engine control signal outputted from an external device. Engine1includes output torque control actuator10that controls the output torque by a throttle valve opening and closing operation and a fuel cut operation.

Torque converter2is a fluid transmission device having a torque increasing function. Torque converter2includes lockup clutch20that can directly couple engine output shaft (i.e., torque converter input shaft)11and torque converter output shaft21with each other when the torque increasing function is not required. Lockup clutch20is brought into hydraulic engagement by a lockup pressure to hold the direct coupling between engine output shaft11and torque converter output shaft21, when lockup is requested. Torque converter2also includes turbine runner23connected to engine output shaft11through converter housing22, pump impeller24connected to torque converter output shaft21, and stator26disposed through one-way clutch25.

Forward/reverse changeover mechanism3serves to make changeover of a direction of rotation inputted to belt-drive continuously variable transmission4between a positive direction during forward running and a reverse direction during reverse running. Forward/reverse changeover mechanism3includes double-pinion planetary gear set30, forward clutch31and reverse brake32. Double-pinion planetary gear set30includes a sun gear connected to torque converter output shaft21, and a carrier connected to transmission input shaft40. Forward clutch31is brought into engagement by a clutch pressure during forward running, thereby attaining direct connection between the sun gear of double-pinion planetary gear set30and the carrier thereof. Reverse brake32is brought into engagement by a brake fluid pressure during reverse running, thereby fixing a ring gear of double-pinion planetary gear set30to a transmission case.

Belt-drive continuously variable transmission mechanism4includes primary pulley42, secondary pulley43and belt44. Belt-drive continuously variable transmission mechanism4has a continuously variable function of making stepless change of a transmission ratio that is a ratio between input speed (input rotation number) of transmission input shaft40and output speed (output rotation number) of transmission output shaft41by changing a contact radius of belt44contacted with primary pulley42and secondary pulley43.

Primary pulley42includes primary fixed sheave42aand primary moveable sheave42b. Primary fixed sheave42ahas primary fixed sheave shaft42eintegrally formed with primary fixed sheave42a. Primary moveable sheave42bhas primary moveable sheave sleeve42fintegrally formed with primary moveable sheave42b. Primary moveable sheave sleeve42fis disposed concentrically with primary fixed sheave shaft42e, and has a hollow cylindrical shape. Primary moveable sheave sleeve42fis fitted onto primary fixed sheave shaft42e, and slidably moved relative to primary fixed sheave shaft42ein an axial direction of primary pulley42by primary hydraulic pressure (hereinafter referred to as primary pressure) Ppri introduced into primary pulley hydraulic pressure chamber45. Primary pulley42also includes highest transmission ratio lock mechanism A that serves to lock primary moveable sheave42bin a specific axial position relative to primary fixed sheave42ain which a highest transmission ratio is attained.

Secondary pulley43includes secondary fixed sheave43aand secondary moveable sheave43b. Secondary fixed sheave43ahas secondary fixed sheave shaft43eintegrally formed with secondary fixed sheave43a.Secondary moveable sheave43bhas secondary moveable sheave sleeve43fintegrally formed with secondary moveable sheave43b. Secondary moveable sheave sleeve43fis disposed concentrically with secondary fixed sheave shaft43e, and has a hollow cylindrical shape. Secondary moveable sheave sleeve43fis fitted onto secondary fixed sheave shaft43e, and slidably moved relative to secondary fixed sheave shaft43ein an axial direction of secondary pulley43by secondary hydraulic pressure (hereinafter referred to secondary pressure) Psec introduced into secondary pulley hydraulic pressure chamber46.

Belt44is wound on primary pulley42and secondary pulley43to transmit a driving force from engine1to primary pulley42and secondary pulley43. Specifically, belt44is wound on primary sheave surfaces42c,42dof primary fixed sheave42aand primary moveable sheave42bwhich are opposed to each other in the axial direction of primary pulley42to form a V-shaped groove therebetween, and secondary sheave surfaces43c,42dof secondary fixed sheave43aand secondary moveable sheave43bwhich are opposed to each other in the axial direction of secondary pulley43to form a V-shaped groove therebetween. Belt44includes two pairs of stacked rings each including multiple rings stacked on one another in a radial direction thereof, and multiple elements that are stamped plates sandwiched between the two pairs of stacked rings and connected and contacted with each other to form a loop shape.

Final reduction gear mechanism5serves to reduce transmission output rotation transmitted from transmission output shaft41of belt-drive continuously variable transmission mechanism4and transmit the transmission output rotation to left and right drive wheels6,6with a differential function. Final reduction gear mechanism5includes first gear52, second gear53, third gear54and fourth gear55with a reduction function and differential gear56with a differential function which are disposed between transmission output shaft41, idler shaft50and left and right drive axles51,51.

As shown inFIG. 1, the control system of the engine vehicle equipped with the belt-drive continuously variable transmission according to the first embodiment includes transmission hydraulic control unit7as a hydraulic control unit of a primary pressure and secondary pressure-regulating type, and CVT control unit (CVTCU)8as an electronic control unit.

Transmission hydraulic control unit7serves to produce primary pressure Ppri that is introduced into primary pulley hydraulic pressure chamber45, and secondary pressure Psec that is introduced into secondary pulley hydraulic pressure chamber46. Transmission hydraulic control unit7includes oil pump70, pressure regulator valve71, line pressure solenoid72, first pressure reducing valve73, first solenoid74, second pressure reducing valve75and second solenoid76.

Pressure regulator valve71serves to regulate line pressure PL on the basis of a discharge pressure as an original pressure which is discharged from oil pump70. Pressure regulator valve71has line pressure solenoid72, and serves to regulate a pressure of a pressurized oil fed from oil pump70, to line pressure PL having a predetermined value in accordance with a command outputted from CVTCU8and then introduce line pressure PL to line pressure passage77. Oil pump70is driven by engine drive torque transmitted through torque converter output shaft21.

First pressure reducing valve73is a normally high spool valve that serves to regulate primary pressure Ppri to be introduced into primary pulley hydraulic pressure chamber45by pressure reducing control on the basis of line pressure PL as an original pressure which is produced by pressure regulator valve71. First pressure reducing valve73includes first solenoid74that is actuated by a current command outputted from CVTCU8.

Second pressure reducing valve75is a normally high spool valve that serves to regulate secondary pressure Psec to be introduced into secondary pulley hydraulic pressure chamber46by pressure reducing control on the basis of line pressure PL as an original pressure which is produced by pressure regulator valve71. Second pressure reducing valve75includes second solenoid76that is actuated by a current command outputted from CVTCU8.

CVTCU8executes transmission ratio control, line pressure control, forward/reverse changeover control, lockup control, and the like. CVTCU8receives information from sensors and switches such as primary pulley speed sensor80, secondary pulley speed sensor81, secondary hydraulic pressure sensor82, oil temperature sensor83, inhibitor switch84, brake switch85, accelerator opening sensor86, vehicle speed sensor87, and turbine speed sensor88. CVTCU8also receives necessary information such as engine speed information obtained by engine speed sensor91from engine control unit (ECU)90, and outputs an engine speed control command, a fuel cut command, a fuel cut recover command and the like to ECU90. The transmission ratio control, the line pressure control, the forward/reverse changeover control, the lockup control which are executed in CVTCU8will be schematically explained hereinafter.

In the transmission ratio control, primary pressure Ppri to be applied to primary pulley hydraulic pressure chamber45and secondary pressure Psec to be applied to secondary pulley hydraulic pressure chamber46are set in order to attain a target transmission ratio that is determined in accordance with a transmission input speed, an accelerator opening, etc. Further, current commands that are provided to obtain the primary pressure Pri set and the secondary pressure Psec set, respectively, are outputted to first solenoid74and second solenoid76, respectively.

In the line pressure control, a maximum hydraulic pressure among necessary hydraulic pressures in the respective hydraulic elements (i.e., lockup clutch20, forward clutch31, reverse brake32, primary pulley42, secondary pulley43) of the belt-drive continuously variable transmission is set as a target line pressure. Further, a current command that is provided to obtain the target line pressure set is outputted to line pressure solenoid72.

In the forward/reverse changeover control, changeover between engagement and disengagement of forward clutch31and reverse brake32are performed in accordance with a drive range position selected. In the lockup control, changeover between engagement and disengagement of lockup clutch20is performed in accordance with judgment as to whether or not a running condition lies within a lockup range.

FIG. 2toFIG. 6show details of highest transmission ratio lock mechanism A used in primary pulley42of the belt-drive continuously variable transmission according to the first embodiment. Referring toFIG. 2toFIG. 4, the construction of highest transmission ratio lock mechanism A will be explained hereinafter.

As shown inFIG. 2toFIG. 6, highest transmission ratio lock mechanism A includes fixed side axial groove12, moveable side axial groove13, balls (i.e., intervening member)14,14, cut-raised arcuate groove (i.e., axial tapered groove)15, lock snap ring (i.e., intervening member displacement limiting member)16, and unlock snap ring (i.e., intervening member displacement limiting member)17.

Fixed side axial groove12is formed in a suitable position on an outer circumferential surface of primary fixed sheave shaft42e(for instance, in one to three positions thereon). Fixed side axial groove12is a groove having a semi-circular shape in section, and extends in an axial direction of primary fixed sheave shaft42e.

Moveable side axial groove13is formed on an inner radial side of primary moveable sheave sleeve42f.Specifically, moveable side axial groove13is formed in a suitable position on an inner circumferential surface of primary moveable sheave sleeve42fwhich corresponds to the position of fixed side axial groove12. That is, moveable side axial groove13is opposed to fixed side axial groove12in a radial direction of primary moveable sheave42b. Moveable side axial groove13is a groove having a semi-circular shape in section, and extends in an axial direction of primary moveable sheave sleeve42fin a parallel relation to fixed side axial groove12.

Balls14,14are disposed in a cylindrical space defined between fixed side axial groove12and moveable side axial groove13which are located opposed to each other. Respective balls14,14are provided as an intervening member that serves to reduce slide resistance that is caused when primary moveable sheave sleeve42fmakes an axial slide motion in a transmission range from a low transmission ratio to a high transmission ratio.

Cut-raised arcuate groove15has an arcuate shape in section, and is formed as a part of fixed side axial groove12(i.e., as one end portion of fixed side axial groove12) which is disposed corresponding to a highest transmission ratio range. Specifically, cut-raised arcuate groove15is a tapered groove that remains in a terminal position where a cutting and grooving operation for forming fixed side axial groove12with a circular grooving cutter is ended. Cut-raised arcuate groove15extends in the axial direction of primary fixed sheave shaft42e, and is formed such that a depth thereof is gradually reduced toward a side of primary sheave surface42cof primary fixed sheave42a.Cut-raised arcuate groove15serves as an axial tapered groove that is formed such that a depth defined between fixed side axial groove12and moveable side axial groove13is gradually reduced toward a side of the highest transmission ratio.

Lock snap ring16is an intervening member displacement limiting member disposed in a ring groove formed in an end portion of moveable side axial groove13. As shown inFIG. 4, when primary moveable sheave sleeve42fis urged to move toward a lock position in which primary moveable sheave sleeve42fis to be locked in an axial position corresponding to the highest transmission ratio, lock snap ring16having a circular section serves to input engagement force B produced by a hydraulic thrust acting on primary moveable sheave42b, to balls14,14. In this embodiment, the engagement force B acts in a same direction as that of the hydraulic thrust. The term “hydraulic thrust” means a force that is obtained by multiplying primary pressure Ppri to attain the highest transmission ratio and a pressure applying area of primary moveable sheave42bto which primary pressure Ppri is applied (seeFIG. 3).

Unlock snap ring17is an intervening member displacement limiting member disposed in a ring groove formed in a middle portion of moveable side axial groove13which is spaced and distant from lock snap ring16in the axial direction of primary moveable sheave sleeve42f. Lock snap ring16and unlock snap ring17are arranged to limit and allow a degree of freedom of displacement of balls14,14relative to primary fixed sheave shaft42eor primary moveable sheave sleeve42falong fixed side axial groove12or moveable side axial groove13to a slight extent. That is, lock snap ring16and unlock snap ring17are arranged with an axial limit distance therebetween such that balls14,14are disposed between lock snap ring16and unlock snap ring17with an axial clearance between balls14,14and the snap rings16,17opposed to respective balls14,14. The axial limit distance is set such that a predetermined amount of displacement of balls14,14in the axial direction of primary pulley42can be ensured. As shown inFIG. 6, when primary moveable sheave sleeve42fof primary moveable sheave42bis urged to move apart from the lock position corresponding to the highest transmission ratio, unlock snap ring17having a circular section serves to input disengagement force F to balls14,14which is produced by a belt reaction force that acts on primary moveable sheave42b. In this embodiment, the disengagement force F acts in a same direction as that of the belt reaction force. The term “belt reaction force” means force E as shown inFIG. 5, which is exerted on primary moveable sheave42bby belt44when belt44is displaced in a direction as indicated by arrow D so as to reduce a contact radius thereof with respect to primary pulley42as secondary pressure Psec is increased upon shifting from the highest transmission ratio toward a side of a low transmission ratio.

FIG. 7shows a logic flow of unit element pressure control that is executed by CVTCU8of the belt-drive continuously variable transmission according to the first embodiment. Referring toFIG. 7, a routine of the unit element pressure control will be explained hereinafter.

As shown inFIG. 7, the logic flow starts, and goes to step S1in which input torque Tin to be inputted to the belt-drive continuously variable transmission is calculated on the basis of information such as engine speed, accelerator opening, etc. The logic flow then goes to step S2.

In step S2, subsequent to the calculation of input torque Tin in step S1, secondary pressure Psec to be applied to secondary pulley hydraulic pressure chamber46is calculated so as to attain a target transmission ratio which is determined in accordance with transmission input speed, accelerator opening, etc., by input torque Tin. The logic flow then goes to step S3.

In step S3, subsequent to the calculation of secondary pressure Psec in step S2, primary pressure Ppri to be applied to primary pulley hydraulic pressure chamber45is calculated so as to attain the target transmission ratio which is determined in accordance with transmission input speed, accelerator opening, etc., by input torque Tin. The logic flow then goes to step S4.

In step S4, subsequent to the calculation of primary pressure Ppri in step S3, clutch pressure Pc to be applied to forward clutch31or reverse brake32is calculated on the basis of input torque Tin calculated in step S1such that there occurs no slippage of forward clutch31or reverse brake32due to the input torque Tin calculated. The logic flow then goes to step S5.

In step S5, subsequent to the calculation of clutch pressure Pc in step S4, lockup pressure PLU to be applied to lockup clutch20is calculated on the basis of input torque Tin calculated in step S1such that there occurs no slippage of lockup clutch20due to the input torque Tin calculated. The logic flow then goes to step S6.

In step S6, subsequent to the calculation of lockup pressure PLU in step S5, it is judged whether or not the primary pressure Ppri calculated exceeds other element pressures (i.e., secondary pressure Psec, clutch pressure Pc and lockup pressure PLU). The term “element pressures” means necessary hydraulic pressures in respective hydraulic elements that are used in a unit of the belt-drive continuously variable transmission. When the answer in step S6is YES, indicating that the primary pressure Ppri calculated is larger than the other element pressures, the logic flow goes to step S8. When the answer in step S6is NO, indicating that the primary pressure Ppri calculated is not larger than the other element pressures, the logic flow goes to step S7as explained later.

In step S8, subsequent to the judgment that the primary pressure Ppri calculated is larger than the other element pressures in step S6, it is judged whether or not a transmission ratio command to be outputted is a highest transmission ratio command. When the answer in step S8is YES, indicating that the transmission ratio command to be outputted is the highest transmission ratio command, the logic flow goes to step S11. When the answer in step S8is NO, indicating that the transmission ratio command to be outputted is not the highest transmission ratio command (i.e., other transmission ratio command), the logic flow goes to step S9.

In step S9, subsequent to the judgment that the transmission ratio command to be outputted is not the highest transmission ratio command in step S8, it is judged whether or not highest transmission ratio continuing timer value T is larger than 0. When the answer in step S9is YES, indicative of T>0, the logic flow goes to step S10. When the answer in step S9is NO, indicative of T=0, the logic flow goes to step S7.

In step S10, subsequent to the judgment indicative of T>0, the highest transmission ratio continuing timer value T is reset to 0. The logic flow then goes to step S7.

In step S11, subsequent to the judgment that the transmission ratio command to be outputted is the highest transmission ratio command in step S8, the highest transmission ratio continuing timer value T is increased every time the judgment that the transmission ratio command to be outputted is the highest transmission ratio command is made, and it is judged whether or not the highest transmission ratio continuing timer value T increased is not smaller than timer value Ts preset in order to check that primary moveable sheave42bis held in the lock position corresponding to the highest transmission ratio. When the answer in step S11is YES, indicative of T≧Ts, the logic flow goes to step S12. When the answer in step S11is NO, indicative of T<Ts, the logic flow goes to step S7.

In step S7, subsequent to the judgment that the primary pressure Ppri calculated is not larger than the other element pressures in step S6, the judgment indicative of T=0 in step S9, the reset of the highest transmission ratio continuing timer value T, or the judgment indicative of T<Ts, normal target line pressure PL* is calculated by selecting a maximum hydraulic pressure from all the element pressures (i.e., secondary pressure Psec, primary pressure Ppri, clutch pressure Pc and lockup pressure PLU) calculated in step S2to step S5. The logic flow then goes to step S14.

In step S12, subsequent to the judgment indicative of T≧Ts in step S11, corrected primary pressure Ppri′ is calculated by subtracting primary pressure drop amount ΔPpri from the primary pressure Ppri calculated in step S3. Primary pressure drop amount ΔPpri is an amount of drop of primary pressure Ppri which is allowed on the basis of a locking force upon locking at the highest transmission ratio. In order to carry out calculation of corrected primary pressure Ppri′, a hydraulic pressure drop amount that is dropped per one control cycle is previously determined. Subsequent to the judgment indicative of T≧Ts, the hydraulic pressure is allowed to gradually and slowly drop from the primary pressure Ppri calculated in step S3and finally reach the corrected primary pressure Ppri′. The logic flow then goes to step S13.

In step S13, subsequent to the calculation of corrected primary pressure Ppri′ in step S12, lock-time target line pressure (i.e., target line pressure upon locking) PL* is calculated by selecting a maximum hydraulic pressure from the secondary pressure Psec calculated in step S2, the corrected primary pressure Ppri′ calculated in step S12, the clutch pressure Pc calculated in step S4, and the lockup pressure PLU calculated in step S5. The logic flow then goes to step S14.

In step S14, subsequent to the calculation of normal target line pressure PL* in step S7or the calculation of lock-time target line pressure PL* in step S13, a line pressure command to obtain the target line pressure PL* calculated in step S7or the target line pressure PL* calculated in step S13is outputted, and a hydraulic pressure command to obtain all the calculated element pressures (i.e., secondary pressure Psec, primary pressure Ppri, clutch pressure Pc and lockup pressure PLU) is outputted. The logic flow then goes to return.

Next, an operation of the belt-drive continuously variable transmission according to the first embodiment will be explained. The operation includes “a locking operation of the highest transmission ratio lock mechanism A”, “a unlocking operation of the highest transmission ratio lock mechanism A”, “a unit element pressure control operation” and “a fuel economy enhancing operation by combination of highest transmission ratio lock and hydraulic pressure control”.

[Locking Operation of Highest Transmission Ratio Lock Mechanism A]

When primary moveable sheave42bin an unlock condition is moved to and locked in the axial position corresponding to the highest transmission ratio (hereinafter referred to also as a highest transmission ratio position), lockability (fixability) to smoothly shift primary moveable sheave42bto a lock condition is required. Referring toFIG. 2to FIG.4, the locking operation of the highest transmission ratio lock mechanism A which is capable of realizing the above lockability is explained hereinafter.

Balls14,14each serving as the intervening member disposed between primary fixed sheave shaft42eand primary moveable sheave sleeve42fare disposed between lock snap ring16and unlock snap ring17arranged with the axial limit distance therebetween as explained above. With this arrangement, when primary moveable sheave sleeve42fis in an axial position relative to primary fixed sheave shaft42ewhich corresponds to a lowest transmission ratio (hereinafter referred to as a lowest transmission ratio position) as shown inFIG. 2, the predetermined amount of displacement of balls14,14in the axial direction of primary pulley42(i.e., movement of balls14,14in a left-and-right direction inFIG. 2) can be ensured within the axial limit distance. However, displacement of balls14,14in the axial direction of primary pulley42beyond the axial limit distance is restrained by lock snap ring16and unlock snap ring17.

Accordingly, for instance, during a shift stroke in which primary moveable sheave sleeve42fof primary moveable sheave42bis moved from the lowest transmission ratio position as shown inFIG. 2toward the highest transmission ratio position as the lock position as shown inFIG. 3, primary pressure Ppri having a high pressure value is introduced into primary pulley hydraulic pressure chamber45to thereby urge primary moveable sheave42bby a hydraulic thrust. At this time, an amount of displacement of balls14,14with respect to primary moveable sheave42bis limited by lock snap ring16and unlock snap ring17, and therefore, balls14,14are allowed to move along fixed side axial groove12and moveable side axial groove13in a rightward direction inFIG. 2.

When primary moveable sheave42bis urged to the highest transmission ratio position together with balls14,14as shown inFIG. 3, balls14,14are engaged in cut-raised arcuate groove15having the gradually reduced depth. At this time, as shown inFIG. 4, engagement force B produced by the hydraulic thrust that acts on primary moveable sheave42bis inputted to balls14,14through lock snap ring16. Balls14,14thus undergo the engagement force B in the same direction as the hydraulic thrust, and are pushed into cut-raised arcuate groove15. As shown inFIG. 4, force C then acts on opposed circumferential surfaces of primary moveable sheave sleeve42fand primary fixed sheave shaft42ethrough ball14on the side of cut-raised arcuate groove15such that a radial clearance between an inner circumferential surface of primary moveable sheave sleeve42fand an outer circumferential surface of primary fixed sheave shaft42eis expanded. As the hydraulic thrust is increased, the force C that presses primary fixed sheave shaft42eand primary moveable sheave sleeve42fthrough ball14on the side of cut-raised arcuate groove15becomes larger to thereby increase a frictional resistance generated on mutual contact surfaces of ball14on the side of cut-raised arcuate groove15and each of primary fixed sheave shaft42eand primary moveable sheave sleeve42f.

Ball14on the side of cut-raised arcuate groove15which undergoes the increased frictional resistance by wedge effect serves as a lock member, so that primary moveable sheave42bis locked or fixed to the highest transmission ratio position. Meanwhile, each of balls14,14which is used as the lock member for locking primary moveable sheave42bin the axial position relative to primary fixed sheave shaft42eis an existing component for reducing slide resistance that is generated when primary moveable sheave sleeve42fslides in the axial direction in a transmission range from a low transmission ratio to a high transmission ratio.

As explained above, in the belt-drive continuously variable transmission according to the first embodiment, the highest transmission ratio lock mechanism A is constructed such that primary moveable sheave42bis locked in the highest transmission ratio position by utilizing the hydraulic thrust that acts on primary moveable sheave42band balls14,14each being the existing component. With the provision of the highest transmission ratio lock mechanism A, it is possible to attain a function of smoothly locking primary moveable sheave42bin the highest transmission ratio position without causing an increase in cost.

[Unlock Operation of Highest Transmission Ratio Lock Mechanism A]

When primary moveable sheave42bis unlocked and released from the highest transmission ratio position, unlockability to smoothly shift primary moveable sheave42bto an unlock condition is required. Referring toFIG. 5andFIG. 6, an unlock operation of the highest transmission ratio lock mechanism A will be explained hereinafter.

When a shift command to shift to a low-side transmission ratio as a target transmission ratio is outputted under a condition that primary moveable sheave42bis locked in the highest transmission ratio position, shift hydraulic pressure control to reduce primary pressure Ppri and increase secondary pressure Psec is executed. Under the shift hydraulic pressure control, secondary pressure Psec is increased to pull belt44on the side of secondary pulley43in order to suppress slippage of belt44on the side of primary pulley42. As secondary pressure Psec is increased, belt44is downwardly urged on the side of primary pulley42such that a contact radius of belt44is reduced as indicated by arrow D inFIG. 5. Reaction force of belt44downwardly urged acts on primary moveable sheave42bin the axial direction (i.e., in the leftward direction inFIG. 5) as indicated arrow E inFIG. 5, so that primary moveable sheave42bis urged to slightly move toward a side of the low transmission ratio by the reaction force of belt44.

When unlock snap ring17is brought into contact with ball14on the side of cut-raised arcuate groove15by slight displacement of primary moveable sheave42b, disengagement force F produced by the reaction force of belt44which acts on primary moveable sheave42bin a same direction as that of the reaction force of belt44is inputted to ball14on the side of cut-raised arcuate groove15through unlock snap ring17. When the disengagement force F exceeds a locking force produced by the frictional resistance, ball14on the side of cut-raised arcuate groove15is disengaged from cut-raised arcuate groove15so that primary moveable sheave42bis unlocked and released from the highest transmission ratio position.

As explained above, in the belt-drive continuously variable transmission according to the first embodiment, the highest transmission ratio lock mechanism A is constructed such that primary moveable sheave42bis unlocked and released from the highest transmission ratio position by utilizing the reaction force of belt44which acts on primary moveable sheave42band balls14,14each being the existing component. With the provision of the highest transmission ratio lock mechanism A, it is possible to attain a function of smoothly unlocking and releasing primary moveable sheave42bfrom the highest transmission ratio position without causing an increase in cost.

[Unit Element Pressure Control Operation]

The aim of providing the belt-drive continuously variable transmission with the highest transmission ratio lock function resides in reducing the line pressure as an original pressure for a unit element pressure by reducing the primary pressure. An operation of controlling the unit element pressure in such a manner will be explained hereinafter by referring toFIG. 7.

In a case where the transmission ratio is lower than 1 and primary pressure Ppri is equal to or lower than other element pressures (i.e., secondary pressure Psec, clutch pressure Pc and lockup pressure PLU), the logic flow proceeding from step S1through step S2, step S3, step S4, step S5, step S6, step S7to step S14as shown inFIG. 7is repeatedly executed.

In a case where primary pressure Ppri exceeds the other element pressures but the highest transmission ratio command is not outputted, the logic flow proceeding from step S1through step S2, step S3, step S4, step S5, step S6, step S8, step S9, step S7to step S14as shown inFIG. 7is repeatedly executed.

In a case where primary pressure Ppri exceeds the other element pressures and the highest transmission ratio command is outputted but the condition of time is not satisfied, the logic flow proceeding from step S1through step S2, step S3, step S4, step S5, step S6, step S8, step S11, step S7to step S14as shown inFIG. 7is repeatedly executed.

Even in any of the above cases, normal control of primary pressure Ppri and line pressure PL is carried out in accordance with the judgment that primary moveable sheave42bis not held in the lock position corresponding to the highest transmission ratio. Specifically, in step S7, normal target line pressure PL* is calculated by selecting the maximum hydraulic pressure from all element pressures (i.e., secondary pressure Psec, primary pressure Ppri, clutch pressure Pc and lockup pressure PLU) calculated in respective steps S2, S3, S4and S5. In step S14subsequent to step S7, a primary pressure command to obtain the primary pressure Ppri calculated in step S3is outputted, and a line pressure command to obtain the normal target line pressure PL* calculated in step S7is outputted.

On the other hand, in a case where primary pressure Ppri exceeds the other element pressures, the highest transmission ratio command is outputted and the condition of time is satisfied, the logic flow proceeding from step S1through step S2, step S3, step S4, step S5, step S6, step S8, step S11, step S12, step S13to step S14as shown inFIG. 7is repeatedly executed.

Thus, in a case where the condition of the highest transmission ratio command and the condition of time are satisfied when primary pressure Ppri is the maximum hydraulic pressure among multiple unit element pressures, it is judged that primary moveable sheave42bis held in the lock position corresponding to the highest transmission ratio. Further, control of reducing primary pressure Ppri to be introduced into primary pulley hydraulic pressure chamber45of primary pulley42and control of reducing line pressure PL are executed in accordance with the judgment that primary moveable sheave42bis held in the lock position corresponding to the highest transmission ratio. Specifically, in step S12, corrected primary pressure Ppri′ is calculated by subtracting primary pressure drop amount ΔPpri from the primary pressure Ppri calculated in step S3. In the next step S13, lock-time target line pressure PL* is calculated by selecting the maximum hydraulic pressure from the corrected primary pressure Ppri′ calculated in step S12and the other element pressures calculated. In the next step S14, a primary pressure command to obtain the corrected primary pressure Ppri′ calculated in step S12is outputted, and a line pressure command to obtain the target line pressure PL* calculated in step S13is outputted.

In a case where the transmission ratio command is changed from the highest transmission ratio command to the low-side transmission ratio command during execution of the unit element pressure control to reduce primary pressure Ppri and line pressure PL, the logic flow proceeding from step S1through step S2, step S3, step S4, step S5, step S6, step S8, step S9, step S10, step S7to step S14as shown inFIG. 7is repeatedly executed. Specifically, in step S10, the highest transmission ratio continuing timer value T is reset to 0, and then return to normal control of primary pressure Ppri and line pressure PL is executed.

[Operation of Enhancing Fuel Economy by Combination of Highest Transmission Ratio Lock and Hydraulic Pressure Control]

An engine vehicle necessitates fuel economy enhancing ability to enhance fuel economy utilizing the highest transmission ratio lock function. Referring toFIG. 8toFIG. 10, an operation of enhancing fuel economy by combination of highest transmission ratio lock and hydraulic pressure control will be explained hereinafter.

First, an engine vehicle equipped with a belt-drive continuously variable transmission that is not provided with the highest transmission ratio lock mechanism is explained as a comparative example. In this comparative example, during high speed running, a necessary belt clamping force is ensured by the primary pulley to thereby retain a highest transmission ratio with respect to variation in transmission torque. At this time, a primary pressure supplied to a primary pulley becomes a maximum hydraulic pressure within the unit. Therefore, it is necessary to increase a line pressure that is regulated on the basis of a pump discharge pressure discharged from an oil pump, to at least the primary pressure.

For this reason, during high speed cruising in which the high speed running is maintained for a long period of time, as shown inFIG. 8, a relationship between line pressure P1, primary pressure Ppri and secondary pressure Psec as indicated by the expression: line pressure PL>primary pressure Ppri>secondary pressure Psec is to be maintained, while keeping the highest transmission ratio. That is, it is necessary to continuously maintain line pressure PL higher than primary pressure Ppri. Thus, an increase in necessary hydraulic pressure is caused during high speed cruising in which the highest transmission ratio is used with high frequency. As a result, torque for driving the oil pump cannot be reduced during the high speed cruising in which the highest transmission ratio is used for a long period of time. In the engine-equipped vehicle that obtains the torque for driving the oil pump from the engine, it is not possible to enhance fuel economy.

In contrast, the belt-drive continuously variable transmission according to the first embodiment includes the highest transmission ratio lock mechanism A serving for locking primary moveable sheave42bin the highest transmission ratio position, and performs the unit element pressure control in accordance with the flow chart as shown inFIG. 7.

Specifically, as shown inFIG. 9, in the highest transmission ratio position in which primary moveable sheave42bis to he locked, primary pressure Ppri becomes reduced to a hydraulic pressure obtained by subtracting primary pressure drop amount ΔPpri from normal primary pressure Ppri, and line pressure PL also becomes reduced to a hydraulic pressure obtained by subtracting line pressure drop amount ΔPL from normal target line pressure PL*.

For example, as shown inFIG. 10, acceleration is carried out from time t0to time t1, and at time t1, the acceleration is shifted to high speed cruising. Subsequently, in a case where it is judged that primary moveable sheave42bis locked in the highest transmission ratio position at time t2when a predetermined time has elapsed from time t1, reduction in both primary pressure Ppri and line pressure PL is started at time t2. At time t3, the reduction in both primary pressure Ppri and line pressure PL is completed. During cruising from time t3, a relationship between line pressure Pl, primary pressure Ppri and secondary pressure Psec as indicated by the expression: line pressure PL>secondary pressure Psec>primary pressure Ppri is maintained, while keeping the highest transmission ratio. That is, during high speed cruising in which the high speed running is maintained for a long period of time, it is enough only to ensure the line pressure PL higher than secondary pressure Psec that becomes the maximum hydraulic pressure as primary pressure Ppri is reduced. Therefore, it is possible to reduce a necessary hydraulic pressure at the highest transmission ratio which is used with high frequency during high speed cruising, as indicated by hatching inFIG. 10.

Accordingly, torque for driving oil pump70can be reduced during high speed cruising in which the high speed running is maintained for a long period of time. As a result, the engine vehicle which obtains the torque for driving oil pump70from engine1, can serve for enhancing fuel economy.

The present invention is not limited to the first embodiment as described above, and can be modified as follows.

In the first embodiment, highest transmission ratio lock mechanism A is provided on the side of primary pulley42, in which primary moveable sheave42bis locked in the highest transmission ratio position. However, in the present invention, a lowest transmission ratio lock mechanism can also be provided on the side of secondary pulley43, in which secondary moveable sheave43bis locked in a lowest transmission ratio position corresponding to a lowest transmission ratio. Further, both the highest transmission ratio lock mechanism A and the lowest transmission ratio lock mechanism can be provided such that primary moveable sheave42bis locked in the highest transmission ratio position, and secondary moveable sheave43bis locked in the lowest transmission ratio position. Meanwhile, the lowest transmission ratio lock mechanism is useful, for instance, in such an electric-powered vehicle that performs control of maintaining the lowest transmission ratio in a normal running range.

Although in the first embodiment, balls14,14are used as the intervening members, rollers or any other rolling components can be used as the intervening members. That is, any other components can be used as the intervening members as long as the components are disposed between the fixed side axial groove and the moveable side axial groove and serve to reduce slide resistance that is generated when the moveable sheave slides on the fixed sheave in the axial direction in a transmission range between a low transmission ratio and a high transmission ratio.

In the first embodiment, the axial tapered groove (i.e., cut-raised arcuate groove15) is formed as one end portion of fixed side axial groove12. However, the axial tapered groove can be formed as one end portion of moveable side axial groove13, or can be formed as both the one end portion of fixed side axial groove12and the one end portion of moveable side axial groove13. Further, a sectional shape of the axial tapered groove can be a shape other than the arcuate shape used in the first embodiment. That is, the axial tapered groove can be formed at least one of the end of fixed side axial groove12and the end of moveable side axial groove13, and can be arranged corresponding to a highest transmission ratio range or a lowest transmission ratio range such that a depth of cut-raised arcuate groove15which is formed between fixed side axial groove12and moveable side axial groove13is gradually reduced toward a side of a limit at the transmission ratio.

Referring toFIG. 11, there is shown a belt-drive continuously variable transmission according to a second embodiment of the present invention. The second embodiment differs from the first embodiment in construction of the highest transmission ratio lock mechanism. As shown inFIG. 11, the belt-drive continuously variable transmission according to the second embodiment includes highest transmission ratio lock mechanism A′ in which roller18serves as the intervening member and roller retainer plate19serves as the intervening member displacement limiting member. Roller retainer plate19has roller retaining hole19ais disposed between fixed side axial groove12and moveable side axial groove13, and extends in the axial direction of primary pulley42. Roller18is moveably disposed in roller retaining hole19awith an axial clearance between both axial ends of roller18and peripheral edges of roller retaining hole19aopposed to the axial ends of roller18. Roller18is retained by roller retainer plate19such that an amount of displacement of roller18in the axial direction of primary pulley42is limited to a predetermined value. Cut-raised arcuate groove15is formed such that the depth thereof is gradually reduced toward a side opposite to primary sheave surface42dof primary moveable sheave42b. Cut-raised arcuate groove15is formed as one end portion of moveable side axial groove13which is disposed corresponding to the highest transmission ratio range. Further, cut-raised arcuate groove15is formed such that the depth defined between fixed side axial groove12and moveable side axial groove13is gradually reduced toward the side of the highest transmission ratio. With this arrangement of cut-raised arcuate groove15, a direction of the engagement force inputted to roller18is opposite to a direction of the hydraulic thrust acting on primary moveable sheave42b, and a direction of the disengagement force inputted to roller18is opposite to a direction of the reaction force of belt44.

The intervening member displacement limiting member is not limited to roller retainer plate19used in the second embodiment, and may be any other member that is constructed and arranged as follows. That is, the intervening member displacement limiting member is disposed in a position where the intervening member displacement limiting member can limit a degree of freedom of displacement of the intervening member which is allowed in accordance with a slide movement of primary moveable sheave42b. Further, when primary moveable sheave sleeve42fis moved toward the lock position corresponding to the highest transmission ratio, the intervening member displacement limiting member serves to input an engagement force produced by the hydraulic thrust acting on primary moveable sheave42bto the intervening member. On the other hand, when primary moveable sheave sleeve42fis moved apart from the lock position corresponding to the highest transmission ratio, the intervening member displacement limiting member serves to input a disengagement force produced by the belt reaction force acting on primary moveable sheave42bto the intervening member. A direction of the engagement force may be the same as that of the hydraulic thrust as explained in the first embodiment, or in contrast, may be opposite thereto as explained in the second embodiment. Similarly, a direction of the disengagement force may be the same as that of the belt reaction force as explained in the first embodiment, or in contrast, may be opposite thereto as explained in the second embodiment.

In the first and second embodiments, the belt-drive continuously variable transmission of the present invention is applied to an engine vehicle, serving to enhance fuel economy by locking the primary pulley in the highest transmission ratio position. However, the belt-drive continuously variable transmission of the present invention is not limited to the first and second embodiments and can be applied to a drive system of other vehicles such as a hybrid vehicle, an electric vehicle, a fuel cell vehicle, etc. For example, in a case where the belt-drive continuously variable transmission of the present invention is applied to the hybrid vehicle using an engine and a motor as drive sources, both fuel economy and electricity economy can be enhanced. In a case where the belt-drive continuously variable transmission of the present invention is applied to the electric vehicle or the fuel cell vehicle which uses a motor as a drive source, electricity economy can be enhanced.

The belt-drive continuously variable transmission according to the above embodiments can attain the following functions and effects.

(1) The belt-drive continuously variable transmission according to the first and second embodiments includes primary pulley42, secondary pulley43, belt44, fixed side axial groove12, moveable side axial groove13, an intervening member (i.e., balls14, roller18), an axial tapered groove (i.e., cut-raised arcuate groove15), and an intervening member displacement limiting member (i.e., lock snap ring16, unlock snap ring17, roller retainer plate19). Primary pulley42includes primary fixed sheave42ahaving primary fixed sheave shaft42eand primary moveable sheave42bhaving primary moveable sheave sleeve42f. Primary moveable sheave sleeve42fis fitted onto primary fixed sheave shaft42e, and slidably moved relative to primary fixed sheave shaft42ein the axial direction of primary pulley42. Secondary pulley43includes secondary fixed sheave43ahaving secondary fixed sheave shaft43eand secondary moveable sheave43bhaving secondary moveable sheave sleeve43f. Secondary moveable sheave sleeve43fis fitted onto secondary fixed sheave shaft43e, and slidably moved relative to secondary fixed sheave shaft43ein the axial direction of secondary pulley43. Belt44is wound on primary pulley42and secondary pulley43to transmit a driving force from a drive source (i.e., engine1). Fixed side axial groove12extends on an outer circumferential surface of primary fixed sheave shaft42ein the axial direction of primary pulley42. Moveable side axial groove13extends on an inner circumferential surface of primary moveable sheave sleeve42fin the axial direction of primary pulley42so as to be opposed to fixed side axial groove12. The intervening member is disposed between fixed side axial groove12and moveable side axial groove13. The intervening member serves to reduce slide resistance that is caused when primary moveable sheave sleeve42fmakes an axial slide motion in a transmission range between a low transmission ratio and a high transmission ratio. The axial tapered groove is formed as a part of at least one of fixed side axial groove12and moveable side axial groove13which is disposed corresponding to a highest transmission ratio range. The axial tapered groove is formed such that a depth defined between fixed side axial groove12and moveable side axial groove13is gradually reduced toward a side of a highest transmission ratio. The intervening member displacement limiting member is arranged to limit an amount of displacement of the intervening member relative to primary fixed sheave shaft42ealong fixed side axial groove12or moveable side axial groove13. When primary moveable sheave sleeve42fis moved toward a lock position in which primary moveable sheave sleeve42fis to be locked in the highest transmission ratio position, the intervening member displacement limiting member serves to input an engagement force produced by a hydraulic thrust acting on primary moveable sheave42bto the intervening member. When primary moveable sheave sleeve42fis moved apart from the lock position, the intervening member displacement limiting member serves to input a disengagement force produced by a belt reaction force acting on primary moveable sheave42bto the intervening member.

With this construction, it is possible to perform a transmission ratio lock function (i.e., highest transmission ratio lock function) by utilizing the force (i.e., the hydraulic thrust and the belt reaction force) exerted on the existing component (i.e., balls14, roller18) and primary moveable sheave42bwithout causing increase in cost.

(2) The axial tapered groove (i.e., cut-raised arcuate groove15) has an arcuate shape in section, and is formed as one end portion of the at least one of fixed side axial groove12and moveable side axial groove13. With this construction, the axial tapered groove can be readily formed only by subjecting the at least one of fixed side axial groove12and moveable side axial groove13to grooving. Thus, it is possible to readily form the axial tapered groove without need of any additional machining.

(3) Fixed side axial groove12and moveable side axial groove13are parallel to each other. The intervening member displacement limiting member is an element component (i.e., lock snap ring16, unlock snap ring17, roller retainer plate19) which is disposed together with the intervening member (i.e., balls14, roller18) with an axial clearance therebetween within a region between fixed side axial groove12and moveable side axial groove13such that the amount of displacement of the intervening member in the axial direction of primary pulley24is limited.

With this construction, it is possible to readily provide the intervening member displacement limiting member by using the element component (for instance, two snap rings16,17) which serves as a member that limits a degree of freedom of displacement of the intervening member (i.e., balls14).

(4) The belt-drive continuously variable transmission according to the first and second embodiments further includes a unit element pressure control means for executing control of reducing primary pressure Ppri to be introduced into primary pulley hydraulic pressure chamber45of primary pulley42and executing control of reducing line pressure PL in a case where it is judged that primary moveable sheave42bis held in the lock position corresponding to the highest transmission ratio (seeFIG. 7).

With this construction, when primary moveable sheave42bis locked at the highest transmission ratio which is used with a high frequency during high speed cruising, torque for driving oil pump70by engine1can be reduced as long as the highest transmission ratio is maintained with reduction of primary pressure Ppri and line pressure PL. Accordingly, it is possible to attain enhancement in fuel economy by continuing reduction of the torque for driving oil pump70.

This application is based on prior Japanese Patent Application No. 2011-063630 filed on Mar. 23, 2011. The entire contents of the Japanese Patent Application No. 2011-063630 is hereby incorporated by reference.