Abstract:
Disclosed is a hydraulic control device for a continuously variable transmission which changes the transmission gear ratio by changing the hydraulic pressure supplied to hydraulic pressure chambers for pulleys in the continuously variable transmission via control valves is changed. In this hydraulic control device, line pressure regulation hydraulic pressure which corresponds to the magnitudes of the oil pressure supplied to the hydraulic pressure chambers is introduced into a regulator valve, and line pressure which is input into the control valves according to the magnitudes of the oil pressure is subjected to feedback regulation. In the hydraulic control device for the continuously variable transmission, after the valve element of the control valve is driven in the valve opening direction, a vibration restriction control operation which temporarily restricts the displacement of the valve element is executed.

Description:
FIELD OF DISCLOSURE 
     The present invention relates to hydraulic pressure controllers for a continuously variable transmission that controls the hydraulic pressure supplied to each pulley of a belt type continuously variable transmission, and in particular, to a hydraulic pressure controller for a continuously variable transmission that feedback-adjusts a line pressure, which is an originating pressure of the hydraulic pressure supplied to each pulley, in accordance with the level of the hydraulic pressure supplied to each pulley. 
     BACKGROUND OF THE DISCLOSURE 
     A belt type continuously variable transmission is a known transmission mounted on a vehicle or the like. The belt type continuously variable transmission includes a first pulley that receives driving force from an internal combustion engine, a second pulley coupled to a vehicle wheel, and a belt running around the two pulleys. The continuously variable transmission changes the winding radius of the belt at each pulley to change the gear ratio in a continuous and stepless manner. 
     Such a belt type continuously variable transmission changes the hydraulic pressure of a hydraulic pressure chamber arranged in each pulley to change the balance of thrusts, which is the force that sandwiches the belt. This changes the winding ratio of the belt at each pulley and controls the gear ratio. 
     To this end, such a continuously variable transmission includes a hydraulic pressure controller that controls the hydraulic pressure supplied to each pulley. The hydraulic pressure controller includes a plurality of solenoid valves, which are driven based on an electrical drive command, and a plurality of control valves, which are driven by a driving hydraulic pressure output from the solenoid valves. The hydraulic pressure controller drives the control valves based on drive commands output from an electronic control unit to supply hydraulic oil to the hydraulic pressure chamber of each pulley or discharge hydraulic oil from the hydraulic pressure chamber of each pulley thereby controlling the hydraulic pressure of the hydraulic pressure chamber in each pulley. 
     In the hydraulic pressure controller for the continuously variable transmission, a regulator valve adjusts the hydraulic pressure of the hydraulic oil discharged from an oil pump and generates line pressure, which is the originating pressure of the hydraulic pressure to output from the control valves. The line pressure is input to the control valves, and the line pressure is adjusted by the control valves to generate the hydraulic pressure supplied to each pulley. 
     In the hydraulic pressure controller described above, a drive load of the oil pump becomes high when the line pressure becomes high. Thus, a hydraulic pressure controller for a continuously variable transmission that is described in patent document 1 feedback-adjusts the line pressure in accordance with the level of the hydraulic pressure supplied to each pulley. 
     Specifically, hydraulic pressure corresponding to the level of the hydraulic pressure supplied to each pulley is input to the regulator valve. The line pressure is increased when the hydraulic pressure supplied to each pulley is high, and the line pressure is decreased when the hydraulic pressure supplied to each pulley is low. 
     In this manner, by feedback adjusting the line pressure in accordance with the level of the hydraulic pressure supplied to each pulley, an excessive increase in the drive load of the oil pump when the line pressure increases more than necessary is suppressed. 
     PRIOR ART DOCUMENT 
     Patent Documents 
     Patent document 1: Japanese Laid-Open Patent Publication No. 2009-156413 
     DISCLOSURE OF THE INVENTION 
     Problems that are to be Solved by the Invention 
     When changing the hydraulic pressure supplied to each pulley, valve bodies of the control valves that control the hydraulic pressure supplied to the pulleys are driven, and a valve body of the regulator valve adjusts the line pressure. However, immediately after starting the driving of the valve bodies, inertia may excessively move the valve bodies and thereby oscillate the valve bodies. 
     If a valve body oscillates, the hydraulic pressure adjusted by the control valves and the regulator valve oscillates over a target hydraulic pressure. When the hydraulic pressure supplied to each pulley oscillates, the tension on the belt repetitively increases and decreases. This may result in slipping of the belt on each pulley or excessive load being applied to the belt and thereby lower the durability of the continuously variable transmission. 
     Further, once the hydraulic pressure supplied to each pulley starts to oscillate, the oscillating hydraulic pressure is fed back to the regulator valve and the line pressure is adjusted based on the fed back hydraulic pressure. As a result, the line pressure adjusted through the regulator valve is also oscillated. This may produce an adverse cycle in which the line pressure is feedback adjusted based on the oscillating hydraulic pressure, the oscillation is propagated to the line pressure, and the hydraulic pressure supplied to each pulley is adjusted based on the oscillating line pressure. As a result, a state in which the hydraulic pressure supply to each pulley oscillates may continue over a long period of time. 
     It is an object of the present invention to provide a hydraulic pressure controller for a continuously variable transmission capable of feedback adjusting the line pressure in accordance with the level of the hydraulic pressure supplied to each pulley and suppressing oscillation of the hydraulic pressure supplied to each pulley and the line pressure when changing the hydraulic pressure supplied to each pulley, while suppressing the drive load of the oil pump from becoming excessively large. 
     Means for Solving the Problems 
     To achieve the above object, after driving a valve body of the control valve in a valve opening direction, a hydraulic pressure controller according to the present invention executes oscillation suppression control that temporarily suppresses movement of the valve body. 
     Thus, oscillation of the valve body when the valve body is driven in the valve opening direction can be suppressed, and repetitive increase and decrease of the hydraulic pressure supplied to a pulley over a target hydraulic pressure is suppressed. Further, by suppressing such oscillation of the valve body and suppressing the oscillation of the hydraulic pressure supplied to the pulley, oscillation of the line pressure, which is feedback adjusted based on the hydraulic pressure supplied to the pulley, can be suppressed. 
     This can suppress the occurrence of an adverse cycle in which the line pressure is adjusted based on the oscillating hydraulic pressure and the hydraulic pressure supplied to each pulley is adjusted based on the oscillating line pressure. 
     In this manner, a hydraulic pressure controller for a continuously variable transmission according to the present invention feedback adjusts the line pressure in accordance with the level of the hydraulic pressure supplied to each pulley, suppresses excessive increases in the drive load applied to an oil pump, and suppresses oscillation of the hydraulic pressure, which is supplied to each pulley, and the line pressure when the hydraulic pressure supplied to each pulley is changed. This consequently suppresses repetitive increasing and decreasing of tension on a belt when the hydraulic pressure of the pulleys is changed and suppresses a decrease in the durability of the continuously variable transmission. 
     When the control valve uses a driving hydraulic pressure input to the control valve to drive the valve body in a valve opening direction, specifically, it is preferred that after starting to output the driving hydraulic pressure to the control valve to drive the valve body in the valve opening direction, oscillation suppression control is executed to further change the driving hydraulic pressure to suppress movement of the valve body in a valve closing direction when the valve body oscillates as the output of the driving hydraulic pressure starts. 
     More specifically, when the control valve moves the valve body in the valve opening direction as the driving hydraulic pressure increases, after starting the output of the driving hydraulic pressure to drive the valve body in the valve opening direction, the oscillation suppression control further increases the driving hydraulic pressure in accordance with a timing at which the valve body starts to move in the valve closing direction. The employment of such a configuration further increases the driving hydraulic pressure and offsets force that acts to move the valve body in the valve opening direction, suppresses movement of the valve body in the valve closing direction, and suppresses oscillation of the valve body. 
     After starting the output of the driving hydraulic pressure to the control valve to drive the valve body in the valve opening direction, the timing at which the valve body starts to move in the valve closing direction changes in accordance with the responsiveness or the like of the actual movement of the valve body relative to changes in the driving hydraulic pressure. When the temperature of the hydraulic oil is high, the viscosity of the hydraulic oil decreases. Thus, the responsiveness of the actual movement of the valve body relative to changes in the driving hydraulic pressure increases as the temperature of the hydraulic oil changes. That is, the valve body moves more readily when the driving hydraulic pressure is output as the temperature of the hydraulic oil increases. Further, after the driving hydraulic pressure is output, the timing at which the valve body starts to move in the valve closing direction is advanced as the temperature of the hydraulic oil increases. 
     Thus, after starting the output of the driving hydraulic pressure to the control valve to drive the valve body in the valve opening direction, it is preferred that a timing for further changing the driving hydraulic pressure be advanced as the temperature of the hydraulic oil increases. The employment of such a configuration allows for the timing for changing the hydraulic pressure to be set in accordance with changes in the responsiveness of the actual movement of the valve body relative to changes in the driving hydraulic pressure as the temperature of the hydraulic oil changes. 
     Further, as the hydraulic pressure output to the control valve to drive the valve body in the valve opening direction increases, the valve opening speed of the valve body when the driving hydraulic pressure is output increases. That is, as the hydraulic pressure output to drive the valve body in the valve opening direction increases, the valve body moves more readily when the valve body starts to move in the valve closing direction. Thus, as the hydraulic pressure output to the control valve to drive the valve body in the valve opening direction increases, after starting the output of the driving hydraulic pressure to the control valve to drive the valve body in the valve opening direction, the timing for further changing the driving hydraulic pressure may be advanced. When employing such a configuration, the timing for changing the driving hydraulic pressure may be set in accordance with changes in the valve opening speed of the valve body when the driving hydraulic pressure is output. 
     When the hydraulic pressure controller for a continuously variable transmission includes a control valve provided with a first pressure chamber and a second pressure chamber located on opposite sides of the valve body, and the control valve changes a level of the driving hydraulic pressure supplied to the first pressure chamber to drive the valve body, the movement of the valve body may be suppressed by prohibiting discharge of the hydraulic oil from the second pressure chamber and supply of the hydraulic oil to the second pressure chamber. 
     The oscillation of the valve body is apt to occur when the driving hydraulic oil acts on the valve body to drive the valve body in the valve opening direction. 
     Thus, when the hydraulic pressure controller for a continuously variable transmission feedback adjusts the line pressure in correspondence with a change in a larger one of a hydraulic pressure supplied to a first pulley, which is coupled to an internal combustion engine, and a hydraulic pressure supplied to a second pulley, which is coupled to a vehicle wheel, it is preferred that the execution conditions for executing oscillation suppression control be set so that when increasing the hydraulic pressure supplied to the first pulley, the oscillation suppression control is executed when the hydraulic pressure supplied to the first pulley becomes greater than the hydraulic pressure supplied to the second pulley. 
     The employment of such a configuration executes the oscillation suppression control under a situation that may result in an adverse cycle in which the hydraulic pressure supplied to each pulley oscillates continuously over a long period of time such as when the line pressure is feedback adjusted in correspondence with changes in the hydraulic pressure supplied to the first pulley when increasing the hydraulic pressure supplied to the first pulley. 
     Thus, a state in which the hydraulic pressure supplied to each pulley oscillates continuously over a long period of time is suppressed in a preferred manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing a continuously variable transmission that is a control subject of a hydraulic pressure controller according to a first embodiment of the present invention. 
         FIG. 2  is a schematic diagram showing the structure of a hydraulic pressure control unit in the hydraulic pressure controller of the first embodiment. 
         FIG. 3  is a time chart showing the relationship of a change in the drive duty of a first solenoid valve and a change in the hydraulic pressure supplied to a first pulley in a gear shift control of the prior art. 
         FIG. 4  is a time chart showing the relationship of a change in the drive duty of a first solenoid valve and a change in the hydraulic pressure supplied to the first pulley when a oscillation suppression control of the first embodiment is executed. 
         FIG. 5  is a flowchart showing a flow of a series of processes related to the execution of the oscillation suppression control of the first embodiment. 
         FIG. 6  is a flowchart showing a flow of processes in the oscillation suppression control of the first embodiment. 
         FIG. 7  is a schematic diagram showing the structure of a hydraulic pressure control unit in a hydraulic pressure controller according to a second embodiment. 
         FIG. 8  is a flowchart showing a flow of processes in the oscillation suppression control of the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     One embodiment of a hydraulic pressure controller for a continuously variable transmission according to the present invention applied to an electronic control unit  300  that controls a continuously variable transmission  100 , which is installed in a vehicle, and a hydraulic pressure control unit  200  will now be described with reference to  FIGS. 1 to 6 .  FIG. 1  is a schematic diagram showing the structure of the continuously variable transmission  100 , which is a control subject of the hydraulic pressure controller of the present invention. 
     As shown in  FIG. 1 , an input shaft of a torque converter  110  in the continuously variable transmission  100  is connected to an output shaft of an internal combustion engine  400 . An output shaft of the torque converter  110  is connected to an input shaft of a switching mechanism  120 . 
     The switching mechanism  120  is a double-pinion planet gear mechanism and includes a forward clutch  121  and a reverse brake  122 . An output shaft of the switching mechanism  120  is connected to a first pulley  130 . 
     When the forward clutch  121  is engaged and the reverse brake  122  is released, the driving force of the internal combustion engine  400 , which is input through the torque converter  110 , is directly transmitted to the first pulley  130 . In contrast, when the forward clutch  121  is released and the reverse brake  122  is engaged, the driving force of the internal combustion engine  400 , which is input through the torque converter  110 , is reversed and transmitted to the first pulley  130  as a driving force of a reversed rotation. 
     In the switching mechanism  120 , if the forward clutch  121  and the reverse brake  122  are both released, the transmission of the driving force between the internal combustion engine  400  and the first pulley  130  is cut off. 
     The first pulley  130 , which is coupled to the internal combustion engine  400  by the torque converter  110  and the switching mechanism  120 , is coupled to a second pulley  150 , which is an output side pulley, by a belt  140 . More specifically, a single belt  140  runs around the first pulley  130  and the second pulley  150  arranged in parallel as shown at the lower left side in  FIG. 1 . Driving force is transmitted between the first pulley  130  and the second pulley  150  by the belt  140 . 
     The second pulley  150  is coupled to a differential through a reduction gear (not shown). Thus, the rotation of the second pulley  150  is transmitted to the differential via the reduction gear, and the rotation is transmitted to left and right drive wheels via the differential. 
     The first pulley  130  is formed by combining a fixed sheave and a movable sheave. A hydraulic pressure chamber  134  is defined and formed in the first pulley  130  as shown by broken lines in  FIG. 1 . 
     The second pulley  150  is also formed by combining a fixed sheave and a movable sheave. A hydraulic pressure chamber  154  is also defined and formed in the second pulley  150  as shown by broken lines in  FIG. 1 . 
     The belt  140  runs around the first pulley  130  and the second pulley  150 , as described above. The belt  140  is sandwiched between the fixed sheave and the movable sheave of the first pulley  130  and sandwiched between the fixed sheave and the movable sheave of the second pulley  150 . 
     Thus, when a hydraulic pressure Pin of the hydraulic pressure chamber  134  in the first pulley  130  is changed, the distance between the fixed sheave and the movable sheave of the first pulley  130  changes, and thrust Wpri acting on the belt  140  at the first pulley  130  changes. Further, when a hydraulic pressure Pout of the hydraulic pressure chamber  154  in the second pulley  150  changes, the distance between the fixed sheave and the movable sheave of the second pulley  150  changes, and thrust Wsec acting on the belt  140  at the second pulley  150  changes. 
     As shown in  FIG. 1 , each of the pulleys  130  and  150  includes a gradient at a portion that contacts the belt  140 . Thus, when changing the thrust Wpri at the first pulley  130  and the thrust Wsec at the second pulley  150 , winding radii Rin and Rout of the belt  140  at the pulleys  130  and  150  are changed. 
     More specifically, when increasing the hydraulic pressure Pin in the first pulley  130  to increase the thrust Wpri and decreasing the hydraulic pressure Pout in the second pulley  150  to decrease the thrust Wsec, the winding radius Rin of the belt  140  at the first pulley  130  is increased and the winding radius Rout of the belt  140  at the second pulley  150  is decreased. When decreasing the hydraulic pressure Pin in the first pulley  130  to decrease the thrust Wpri and increasing the hydraulic pressure Pout in the second pulley  150  to increase the thrust Wsec, the winding radius Rin of the belt  140  at the first pulley  130  is decreased and the winding radius Rout of the belt  140  at the second pulley  150  is increased. 
     In the continuously variable transmission  100 , the hydraulic pressures Pin and Pout of the pulleys  130  and  150  are changed to change the thrusts Wpri and Wsec and change the winding radii Rin and Rout of the belt  140  at the pulleys  130  and  15 . This controls a gear ratio γ. 
     More specifically, when performing upshifting and decreasing the gear ratio γ, the hydraulic pressure Pin of the hydraulic pressure chamber  134  in the first pulley  130  is increased to increase the thrust Wpri at the first pulley  130 , and the hydraulic pressure Pout of the hydraulic pressure chamber  154  in the second pulley  150  is decreased to decrease the thrust Wsec at the second pulley  150 . This increases the winding radius Rin of the belt  140  at the first pulley  130 , decreases the winding radius Rout of the belt  140  at the second pulley  150 , and decreases the gear ratio γ. 
     When performing downshifting and increasing the gear ratio γ, the hydraulic pressure Pin of the hydraulic pressure chamber  134  in the first pulley  130  is decreased to decrease the thrust Wpri at the first pulley  130 , and the hydraulic pressure Pout of the hydraulic pressure chamber  154  in the second pulley  150  is increased to increase the thrust Wsec at the second pulley  150 . This decreases the winding radius Rin of the belt  140  at the first pulley  130 , increases the winding radius Rout of the belt  140  at the second pulley  150 , and increases the gear ratio γ. 
     As shown in  FIG. 1 , the hydraulic pressure chambers  134  and  154  of the pulleys  130  and  150  are connected to the hydraulic pressure control unit  200 . The hydraulic pressure control unit  200  is a hydraulic pressure circuit including a plurality of solenoid valves, which are driven based on a drive command output from the electronic control unit  300 , and a control valve, which is driven by the drive hydraulic pressure output from the solenoid valves. The hydraulic pressure of the hydraulic oil is adjusted by operating the control valve to supply the hydraulic oil to the hydraulic pressure chambers  134  and  154  or discharge the hydraulic oil from the hydraulic pressure chambers  134  and  154  thereby adjusting the hydraulic pressures Pin and Pout of the hydraulic pressure chambers  134  and  154 . 
     The electronic control unit  300  includes a central processing unit (CPU) that executes calculations related to the control of the internal combustion engine  400 , calculations related to the control of the continuously variable transmission  100  through the hydraulic pressure control unit  200 , and the like. Further, the electronic control unit  300  includes a read-out only memory (ROM), which stores calculation programs and calculation maps for the calculations in addition to various types of data, a random access memory (RAM) that temporarily stores calculation results, and the like. 
     As shown in  FIG. 1 , the electronic control unit  300  is connected to the sensors described below. 
     An accelerator position sensor  301  detects the amount of an accelerator pedal depressed by a driver. An air flow meter  302  detects the amount and temperature of the air drawn into the internal combustion engine  400 . A crank angle sensor  303  detects the engine speed NE based on a rotation angle of a crankshaft, which is an output shaft of the internal combustion engine  400 . A turbine rotation number sensor  304  is arranged in the vicinity of the switching mechanism  120  and detects the rotation speed of a turbine of the torque converter  110 . A first pulley rotation speed sensor  305  is arranged in the vicinity of the first pulley  130  and detects the rotation speed Nin of the first pulley  130 . A second pulley rotation speed sensor  306  is arranged in the vicinity of the second pulley  150  and detects the rotation speed Nout of the second pulley  150 . Wheel speed sensors  307  are respectively arranged in the vicinity of the vehicle wheels and detect the rotation speed of the corresponding vehicle wheels. A temperature sensor  308  detects the temperature of the hydraulic oil supplied to the hydraulic pressure chambers  134  and  154  by the hydraulic pressure control unit  200 . 
     Based on output signals from the various sensors  301  to  308 , the electronic control unit  300  entirely controls the internal combustion engine  400  and the continuously variable transmission  100 . For example, a vehicle speed SPD is calculated based on the rotation speed Nout of the second pulley  150 , which is detected by the second pulley rotation speed sensor  306 . A required torque is calculated based on the current vehicle speed SPD and the depression amount of the accelerator pedal detected by the accelerator position sensor  301 . An opening degree Th of a throttle valve  411 , which is arranged in an intake passage  410  of the internal combustion engine  400 , is adjusted to adjust intake air amount GA and realize the required torque. 
     Further, when adjusting the intake air amount GA, the electronic control unit  300  calculates a target gear ratio γtrg as the gear ratio γ that most efficiently generates the request torque. The electronic control unit  300  also executes gear shift control that controls the hydraulic pressure control unit  200  so that the actual gear ratio γ conforms to the calculated target gear ratio γtrg. In other words, in the present embodiment, the electronic control unit  300  and the hydraulic pressure control unit  200  form the hydraulic pressure controller for the continuously variable transmission  100 . 
     In the gear shift control, the current gear ratio γ is calculated based on the rotation speed Nin of the first pulley  130  and the rotation speed Nout of the second pulley  150 . Further, to bring the gear ratio γ closer to the target gear ratio γtrg, the hydraulic pressure Pin in the first pulley  130  is changed to change the thrust Wpri. The thrust Wpri at the first pulley  130  is changed, and the hydraulic pressure Pout in the second pulley  150  is changed to change the thrust Wsec so that the belt  140  does not slip on the pulleys  130  and  150 . 
     A structure of the hydraulic pressure control unit  200  will now be described in detail with reference to  FIG. 2 .  FIG. 2  is a schematic diagram showing the structure of the hydraulic pressure control unit  200  in the hydraulic pressure controller according to the present embodiment. 
     As shown at the left side in  FIG. 2 , the hydraulic pressure control unit  200  includes a regulator valve  212  that adjusts the pressure of the hydraulic oil discharged from the oil pump  211  to generate line pressure Pl, which becomes the originating pressure of the hydraulic pressures Pin and Pout. The regulator valve  212  sends some of the hydraulic oil discharged from the oil pump  211  to another regulator valve (not shown) based on the level of the line pressure Pl. The hydraulic oil send from the regulator valve  212  to another regulator valve is supplied to the torque converter  110  and the switching mechanism  120  as a hydraulic pressure Psec. The regulator valve  212  adjusts the line pressure Pl by discharging some of the hydraulic oil discharged from the oil pump  211  based on the level of the line pressure Pl. 
     The hydraulic pressure control unit  200  includes a modulator valve  214  that further depressurizes the line pressure Pl and generates a fixed modulator pressure Pm. The modulator pressure Pm output from the modulator valve  214  is supplied to a first solenoid valve  215  and a second solenoid valve  216 . 
     The first solenoid valve  215 , which is electrically driven by a drive command output from the electronic control unit  300 , adjusts the modulator pressure Pm to generate a first solenoid pressure Pslp, which is the driving hydraulic pressure of a first control valve  217 . More specifically, the first solenoid valve  215 , which is a normally open type solenoid valve that closes when supplied with power, outputs a larger first solenoid pressure Pslp as the drive duty decreases in accordance with the level of the drive duty output as the drive command from the electronic control unit  300 . 
     The second solenoid valve  216 , which is electrically driven by a drive command output from the electronic control unit  300 , adjusts the modulator pressure Pm to generate a second solenoid pressure Psls, which is the driving hydraulic pressure of a second control valve  218 . The second solenoid valve  216 , which is also a normally open type solenoid valve like the first solenoid valve  215 , outputs a larger second solenoid pressure Psls as the drive duty decreases in accordance with the level of the drive duty output as the drive command from the electronic control unit  300 . 
     The first solenoid pressure Pslp, which is output from the first solenoid valve  215 , is input to the first control valve  217 . The first control valve  217  adjusts the line pressure Pl in accordance with the first solenoid pressure Pslp. This adjusts the level of the hydraulic pressure supplied to the hydraulic pressure chamber  134  in the first pulley  130  and controls the hydraulic pressure Pin of the hydraulic pressure chamber  134 . 
     The first control valve  217  includes three input ports  217   d ,  217   e , and  217   f . The first solenoid pressure Pslp is input to the second input port  217   e . The line pressure Pl is input to the first input port  217   d , and the solenoid modulator pressure Psolmod is input to the third input port  217   f.    
     The first control valve  217  accommodates a valve body  217   a  that is movable in the axial direction. A first pressure chamber  217   b  and a second pressure chamber  217   c  are defined and formed in the first control valve  217  so as to sandwich the valve body  217   a . The second input port  217   e  is connected to the first pressure chamber  217   b , and the third input port  217   f  is connected to the second pressure chamber  217   c.    
     As a result, the first solenoid pressure Pslp supplied to the first pressure chamber  217   b  through the second input port  217   e  and the solenoid modulator pressure Psolmod supplied to the second pressure chamber  217   c  through the third input port  217   f  act from opposite directions on the valve body  217   a  of the first control valve  217 . A spring  217   g  is accommodated in the first pressure chamber  217   b  in a compressed state as a biasing member for biasing the valve body  217   a  toward the second pressure chamber  217   c.    
     The solenoid modulator pressure Psolmod supplied to the second pressure chamber  217   c  through the third input port  217   f  is adjusted to a certain level by a pressure adjustment valve  230 , as will be described later. Thus, the balance of the forces acting on the valve body  217   a  of the first control valve  217  changes in accordance with the level of the first solenoid pressure Pslp supplied to the first pressure chamber  217   b  through the second input port  217   e . The valve body  217   a  is moved in the axial direction in accordance with changes in the balance of the forces. 
     The first control valve  217  further includes an output port  217   h  connected to the hydraulic pressure chamber  134  in the first pulley  130  through a failsafe valve  219 , which will be described later, a discharge port  217   i  connected to a discharge passage, and a feedback port  217   j.    
     The first control valve  217  moves the valve body  217   a  in accordance with the balance of the forces acting on the valve body  217   a . Further, the first control valve  217  moves the valve body  217   a  toward the second pressure chamber  217   c  when the first solenoid pressure Pslp become high and the pressure in the first pressure chamber  217   b  becomes high. Thus, in the first control valve  217 , when the first solenoid pressure Pslp becomes high, the first input port  217   d  opens and communicates the first input port  217   d  and the output port  217   h.    
     As a result, when the first solenoid pressure Pslp becomes high, some of the hydraulic oil input through the first input port  217   d  is supplied to the hydraulic pressure chamber  134  in the first pulley  130  through the output port  217   h.    
     The first control valve  217  is formed so that the driving force toward the second pressure chamber  217   c , that is, the driving force in the valve opening direction, increases as the input first solenoid pressure Pslp increases. Thus, as the first solenoid pressure Pslp increases, the hydraulic pressure output from the first control valve  217  increases and the hydraulic pressure Pin of the hydraulic pressure chamber  134  increases. 
     Further, as shown in  FIG. 2 , some of the hydraulic pressure supplied to the hydraulic pressure chamber  134  is fed back to act on the valve body  217   a  through the feedback port  217   j . Thus, when the hydraulic pressure Pin increases and approaches the hydraulic pressure corresponding to the level of the first solenoid pressure Pslp, the valve body  217   a  moves toward the first pressure chamber  217   b . When the hydraulic pressure Pin becomes equal to the hydraulic pressure corresponding to the level of the first solenoid pressure Pslp, the valve body  217   a  closes the first input port  217   d.    
     When the hydraulic pressure Pin becomes higher than the hydraulic pressure corresponding to the level of the first solenoid pressure Pslp, the valve body  217   a  further moves toward the first pressure chamber  217   b , and the discharge port  217   i  opens and communicates the output port  217   h  and the discharge port  217   i . This discharges the hydraulic oil from the hydraulic pressure chamber  134  to the discharge passage through the output port  217   h  and the discharge port  217   i , and the hydraulic pressure Pin of the hydraulic pressure chamber  134  is adjusted to the hydraulic pressure corresponding to the level of the first solenoid pressure Pslp. 
     The hydraulic oil discharged through the discharge passage is collected in an oil pan (not shown) and supplied again to each part by the oil pump  211 . 
     The second solenoid pressure Psls output from the second solenoid valve  216  is input to the second control valve  218 . The second control valve  218  adjusts the line pressure Pl in accordance with the second solenoid pressure Psls to adjust the level of the hydraulic pressure supplied to the hydraulic pressure chamber  154  in the second pulley  150  and control the hydraulic pressure Pout of the hydraulic pressure chamber  154 . 
     The second control valve  218  includes three input ports  218   d ,  218   e , and  218   f  like the first control valve  217 . The second solenoid pressure Psls is input to the second input port  218   e . The line pressure Pl is input to the first input port  218   d , and the solenoid modulator pressure Psolmod is input to the third input port  218   f.    
     The second control valve  218  accommodates a valve body  218   a , which is movable in the axial direction. A first pressure chamber  218   b  and a second pressure chamber  218   c  are defined and formed in the second control valve  218  so as to sandwich the valve body  218   a . The second input port  218   e  is connected to the first pressure chamber  218   b , and the third input port  218   f  is connected to the second pressure chamber  218   c.    
     As a result, the second solenoid pressure Psls supplied to the first pressure chamber  218   b  through the second input port  218   e  and the solenoid modulator pressure Psolmod supplied to the second pressure chamber  218   c  through the third input port  218   f  act from opposite directions on the valve body  218   a  of the second control valve  218 . A spring  218   g  is accommodated in the first pressure chamber  218   b  in a compressed state as a biasing member for biasing the valve body  218   a  toward the second pressure chamber  218   c.    
     The solenoid modulator pressure Psolmod supplied to the second pressure chamber  218   c  through the third input port  218   f  is adjusted to a certain level by the pressure adjustment valve  230 , as will be described later. Thus, the balance of the forces acting on the valve body  218   a  of the second control valve  218  changes in accordance with the level of the second solenoid pressure Psls supplied to the first pressure chamber  218   b  through the second input port  218   e . The valve body  218   a  is moved in the axial direction in accordance with such change in balance of the forces. 
     The second control valve  218  further includes an output port  218   h  connected to the hydraulic pressure chamber  154  in the second pulley  150 , a discharge port  218   i  connected to the discharge passage, and a feedback port  218   j.    
     The second control valve  218  moves the valve body  217   a  in accordance with the balance of forces acting on the valve body  218   a . When the second solenoid pressure Psls increases and the pressure in the first pressure chamber  218   b  increases, the valve body  218   a  is moved toward the second pressure chamber  218   c . Thus, in the second control valve  218 , when the second solenoid pressure Psls becomes high, the first input port  218   d  opens and communicates the first input port  218   d  and the output port  218   h.    
     Thus, when the second solenoid pressure Psls becomes high, some of the hydraulic oil input through the first input port  218   d  is supplied to the hydraulic pressure chamber  154  in the second pulley  150  through the output port  218   h.    
     The second control valve  218  is formed so that the driving force toward the second pressure chamber  218   c , that is, the driving force in the valve opening direction increases as the input second solenoid pressure Psls increases. Thus, as the second solenoid pressure Psls increases, the hydraulic pressure output from the second control valve  218  increases and the hydraulic pressure Pout of the hydraulic pressure chamber  154  increases. 
     Further, as shown in  FIG. 2 , some of the hydraulic pressure supplied to the hydraulic pressure chamber  154  is fed back to act on the valve body  218   a  through the feedback port  218   j . Thus, when the hydraulic pressure Pout increases and approaches the hydraulic pressure corresponding to the level of the second solenoid pressure Psls, the valve body  218   a  moves toward the first pressure chamber  218   b . When the hydraulic pressure Pout becomes equal to the hydraulic pressure corresponding to the level of the second solenoid pressure Psls, the valve body  218   a  closes the first input port  218   d.    
     When the hydraulic pressure Pout becomes higher than the hydraulic pressure corresponding to the level of the second solenoid pressure Psls, the valve body  218   a  is further moved toward the first pressure chamber  218   b , and the discharge port  218   i  opens thereby communicating the output port  218   h  and the discharge port  218   i . This discharges the hydraulic oil in the hydraulic pressure chamber  154  to the discharge passage through the output port  218   h  and the discharge port  218   i , and the hydraulic pressure Pout of the hydraulic pressure chamber  154  is adjusted to the hydraulic pressure corresponding to the level of the second solenoid pressure Psls. 
     The solenoid modulator pressure Psolmod is adjusted to a certain level through the pressure adjustment valve  230  shown at the upper part of  FIG. 2 . 
     The pressure adjustment valve  230  includes an input port  230   b , an output port  230   c , and a discharge port  230   d . The pressure adjustment valve  230  accommodates a valve body  230   a , which is movable in an axial direction. 
     A spring  230   e  is accommodated in the pressure adjustment valve  230  in a compressed state as a biasing member for biasing the valve body  230   a  in one direction. Thus, the valve body  230   a  is always biased in the same direction by the spring  230   e  so as to communicate the input port  230   b  and the output port  230   c  as shown in  FIG. 2 . 
     Hydraulic pressure further depressurized from the line pressure Pl is input to the input port  230   b  of the pressure adjustment valve  230 . The output port  230   c  of the pressure adjustment valve  230  is connected to the third input port  217   f  of the first control valve  217  and the third input port  218   f  of the second control valve  218  as shown in  FIG. 2 . 
     Some of the hydraulic oil output from the output port  230   c  is fed back to the valve body  230   a  through a feedback port  230   f.    
     Thus, when the solenoid modulator pressure Psolmod, which is the hydraulic pressure of the hydraulic oil output from the output port  230   c , becomes excessively high, the valve body  230   a  is moved against the biasing force of the spring  230   e  by the hydraulic pressure fed back through the feedback port  230   f.    
     In this manner, when the valve body  230   a  is moved in the valve opening direction against the biasing force of the spring  230   e , the valve body  230   a  closes the input port  230   b  and opens the discharge port  230   d  thereby communicating the output port  230   c  and the discharge port  230   d . As a result, some of the hydraulic oil supplied to the second pressure chamber  217   c  of the first control valve  217  and the second pressure chamber  218   c  of the second control valve  218  is discharged through the output port  230   c  and the discharge port  230   d.    
     When some of the hydraulic oil supplied to the second pressure chambers  217   c  and  218   c  through the discharge port  230   d  of the pressure adjustment valve  230  is discharged in such a manner, the solenoid module pressure Psolmod decreases and adjusts the solenoid modulator pressure Psolmod to a certain level. 
     The hydraulic oil discharged from the discharge port  230   d  is collected in the oil pan (not illustrated) through the discharge passage and supplied to each part again by the oil pump  211 . 
     The electronic control unit  300  executes gear shift control to change the drive duty output to the first solenoid valve  215  and the second solenoid valve  216  and control the first solenoid pressure Pslp and the second solenoid pressure Psls. 
     The electronic control unit  300  controls the hydraulic pressure control unit  200  to adjust the hydraulic pressures Pin and Pout of the hydraulic pressure chambers  134  and  154  in the pulleys  130  and  150  so that the gear ratio γ conforms to the target gear ratio γtrg. 
     When an abnormality occurs in the first control valve  217  or the first solenoid valve  215 , the hydraulic pressure Pin cannot be properly controlled and the hydraulic pressure Pin may increase one-sidedly or decrease one-sidedly. 
     For instance, when a foreign matter or the like is caught in the first control valve  217  and the necessary amount of hydraulic oil cannot be supplied to the hydraulic pressure chamber  134 , the hydraulic pressure Pin becomes insufficient and imbalances the thrusts Wpri and Wsec in the pulleys  130  and  150 , and the tension of the belt  140  pushes and opens the first pulley  130 . As a result, the gear ratio γ becomes high in a one-sided manner and the engine speed NE increases. 
     In this regard, the hydraulic pressure control unit  200  includes the failsafe valve  219 , which switches the supply path of the hydraulic oil supplied to the first pulley  130 . 
     The hydraulic oil output from the output port  217   h  of the first control valve  217  is supplied to the hydraulic pressure chamber  134  in the first pulley  130  through the failsafe valve  219  as shown at the lower right side of  FIG. 2 . In the first pulley  130 , the movable sheave moves in accordance with the hydraulic pressure Pin in the hydraulic pressure chamber  134  as described above. This changes the distance between the fixed sheave and the movable sheave. 
     The hydraulic oil output from the output port  218   h  of the second control valve  218  and supplied to the hydraulic pressure chamber  154  in the second pulley  150  is directly supplied to the hydraulic pressure chamber  154  in the second pulley  150  without passing the failsafe valve  219 . In the second pulley  150 , the movable sheave is moved in accordance with the hydraulic pressure Pout in the hydraulic pressure chamber  154  as described above. This changes the distance between the fixed sheave and the movable sheave. 
     The failsafe valve  219  arranged between the first control valve  217  and the first pulley  130  includes a first input port  219   a  to which the hydraulic oil output from the output port  217   h  of the first control valve  217  is introduced and a second input port  219   b  into which the hydraulic oil output from the output port  218   h  of the second control valve  218  is drawn as shown in  FIG. 2 . The failsafe valve  219  is formed to selectively communicate one of the first input port  219   a  and the second input port  219   b  to the output port  219   c  in accordance with the position of the valve body driven by the driving hydraulic pressure output from a switching solenoid valve  220 . 
     More specifically, in a normal state in which the switching solenoid valve  220  is in the “OFF” state and the driving hydraulic pressure is not output from the switching solenoid valve  220 , the first input port  219   a  is in communication with the output port  219   c . In a fail state in which the switching solenoid valve  220  is in the “ON” state and the driving hydraulic pressure is output from the switching solenoid valve  220 , the second input port  219   b  is in communication with the output port  219   c . In other words, the failsafe valve  219  is formed to select one of the hydraulic oil adjusted through the first control valve  217  and the hydraulic oil adjusted through the second control valve  218  and output the selected one to the first pulley  130 . 
     The electronic control unit  300  switches the switching solenoid valve  220  to the “ON” state when the hydraulic pressure Pin in the first pulley  130  cannot be properly controlled by the first control valve  217 . This switches the supply path of the hydraulic oil so that the hydraulic oil adjusted by the second control valve  218  is also supplied to the first pulley  130 . The hydraulic pressures Pin and Pout of the pulleys  130  and  150  thus become equal, and the gear ratio γ can be suppressed from increasing in a one-sided manner. 
     As shown in the right side of  FIG. 2 , the oil path for drawing hydraulic oil into the hydraulic pressure chamber  134  of the first pulley  130  and the oil path for drawing the hydraulic oil into the hydraulic pressure chamber  154  of the second pulley  150  each include an orifice. These orifices are used so that the hydraulic oil in the hydraulic pressure chambers  134  and  154  is not rapidly discharged and the hydraulic pressures Pin and Pout are not rapidly decreased to prevent slipping of the belt  140  on the pulleys  130  and  150 . 
     In the hydraulic pressure controller of the present embodiment, the line pressure Pl is maintained at the minimum required level, and the feedback adjustment of the line pressure Pl is performed to minimize the drive load on the oil pump  211 . 
     More specifically, the hydraulic pressure Pin of the hydraulic pressure chamber  134  in the first pulley  130  and the second solenoid pressure Psls output by the second solenoid valve  216  are each conveyed to a reduction valve  213  to feedback adjust the line pressure Pl. The reduction valve  213  adjusts the modulator pressure Pm in accordance with the conveyed hydraulic pressure Pin and the second solenoid pressure Psls to generate a line pressure adjustment hydraulic pressure Psrv. The line pressure adjustment hydraulic pressure Psrv is conveyed to the regulator valve  212  and used to adjust the line pressure Pl in the regulator valve  212 . 
     In other words, in the hydraulic pressure control unit  200  of the present embodiment, the line pressure Pl is feedback adjusted in accordance with the line pressure adjustment hydraulic pressure Psrv that changes in accordance with the levels of the hydraulic pressures Pin and Pout in the pulleys  130  and  150 . 
     Through such feedback adjustment with the reduction valve  213 , the line pressure Pl is adjusted to be slightly higher than the higher one of the hydraulic pressure Pin and the hydraulic pressure Pout. 
     The feedback adjustment of the line pressure Pl in accordance with the levels of the hydraulic pressures Pin and Pout supplied to the pulleys  130  and  150  prevents the line pressure Pl from increasing more than necessary and prevents the drive load of the oil pump  211  from becoming excessively high. 
     When changing the hydraulic pressures Pin and Pout, the valve bodies  217   a  and  218   a  of the control valves  217  and  218  are driven and the valve body of the regulator valve  212  is driven. However, inertia may excessively move the valve body immediately after starting to drive the valve body. This may oscillate the valve body. 
     For instance, immediately after decreasing the drive duty of the first solenoid valve  215  and increasing the first solenoid pressure Pslp, which is the driving hydraulic pressure, to increase the hydraulic pressure Pin as shown in  FIG. 3 , inertia excessively moves the valve body  217   a  in the valve opening direction and oscillates the valve body  217   a . When the valve body  217   a  is oscillated, the oscillation of the valve body  217   a  may also oscillate the hydraulic pressure Pin adjusted through the control valve  217  over the target hydraulic pressure Ptrg as shown in  FIG. 3 . 
     When the hydraulic pressure Pin is oscillated in such a manner, the tension on the belt  140  repetitively increases and decreases therewith. This may result in the belt  140  slipping on the pulleys  130  and  150  or excessive load being applied to the belt  140  thereby lowering the durability of the continuously variable transmission  100 . 
     Once the hydraulic pressure Pin is oscillated as shown in  FIG. 3  when the hydraulic pressure Pin is greater than the hydraulic pressure Pout, the line pressure adjustment hydraulic pressure Psrv that changes in accordance with the oscillating hydraulic pressure Pin is input to the regulator valve  212 . Thus, the line pressure Pl is feedback adjusted in accordance with changes in the oscillating hydraulic pressure Pin, and the line pressure Pl adjusted by the regulator valve  212  is oscillated. In other words, an adverse cycle in which the oscillation is propagated to the line pressure Pl, and the hydraulic pressures Pin and Pout supplied to the pulleys  130  and  150  are adjusted in accordance with the oscillating line pressure Pl occurs. 
     As a result, the oscillation of the hydraulic pressure Pin resists attenuation, and a state in which the hydraulic pressures Pin and Pout supplied to the pulleys  130  and  150  oscillate is continued for a long period of time. 
     In the electronic control unit  300  of the present embodiment, oscillation suppression control is executed to suppressing the oscillation of the hydraulic pressure Pin by decreasing the drive duty and increasing the first solenoid pressure Pslp and then further decreasing the drive duty and increasing the first solenoid pressure Pslp as shown in  FIG. 4 . 
     When the drive duty is decreased at time t 1  as shown in  FIG. 3  to increase the hydraulic pressure Pin, the hydraulic pressure Pin exceeds and overshoots the target hydraulic pressure Ptrg. As shown in  FIG. 3 , the hydraulic pressure Pin starts to decrease from time t 3  and starts to increase again at time t 4 . In the oscillation suppression control, as shown in  FIG. 4 , the drive duty is decreased at time t 1 . Then, at time t 2 , the drive duty is further decreased and the first solenoid pressure Pslp is further increased so that the valve body  217   a  can be biased in the valve opening direction from time t 3  to time t 4 . 
     In this manner, by further increasing the first solenoid pressure Pslp at time t 2 , the valve body  217   a  excessively moved in the valve opening direction as the first solenoid pressure Pslp increases at time t 1  offsets the portion of the force acting to move the valve body  217   a  in the valve closing direction and suppresses oscillation of the valve body  217   a.    
     This suppresses undershooting of the hydraulic pressure Pin at time t 4  and suppresses oscillation of the hydraulic pressure Pin as show in  FIG. 4 . 
     The flow of processes related to the oscillation suppression control will now be specifically described with reference to  FIGS. 5 and 6 .  FIG. 5  is a flowchart showing the flow of a series of processes related to the oscillation suppression control, and  FIG. 6  is a flowchart showing the flow of a process of the oscillation suppression control. The series of processes shown in  FIG. 5  are repeatedly executed in predetermined control cycles in the electronic control unit  300  when the engine is running. 
     When the series of processes shown in  FIG. 5  is started, the electronic control unit  300  first determines in step S 10  whether or not to increase the hydraulic pressure Pin. For instance, if the target gear ratio γtrg is less than the current gear ratio γ and the hydraulic pressure Pin needs to be increased for upshifting, it is determined that the hydraulic pressure Pin should be increased. If the target gear ratio γtrg and the current gear ratio γ are in conformance or if the target gear ratio γtrg is greater than the current gear ratio γ, it is determined that the hydraulic pressure Pin should not be increased. 
     When determined in step S 10  that the hydraulic pressure Pin should be increased (step S 10 : YES), the electronic control unit  300  proceeds to step S 20  and determines whether or not the hydraulic pressure Pin is greater than the hydraulic pressure Pout. 
     When determined in step S 20  that the hydraulic pressure Pin is greater than the hydraulic pressure Pout (step S 20 : YES), the electronic control unit  300  proceeds to step S 100  and executes the oscillation suppression control shown in  FIG. 6 . 
     When the oscillation suppression control is started, as shown in  FIG. 6 , in step S 110 , the electronic control unit  300  first sets the timing for further increasing the first solenoid pressure Pslp based on the drive duty of the first solenoid valve  215  and the temperature of hydraulic oil detected by the oil temperature sensor  308 . 
     After the output of the first solenoid pressure Pslp for increasing the hydraulic pressure Pin is started and the valve body  217   a  is driven in the valve opening direction, the timing for starting movement of the valve body  217   a  in the valve closing direction, that is, the timing of time t 3  in  FIG. 3  changes in accordance with the responsiveness or the like of the actual movement of the valve body  217   a  with respect to changes in the first solenoid pressure Pslp. 
     When the temperature of the hydraulic oil is high, the viscosity of the hydraulic oil decreases. Thus, the responsiveness of the actual movement of the valve body  217   a  with respect to changes in the first solenoid pressure Pslp increases as the temperature of the hydraulic oil increases. That is, as the temperature of the hydraulic oil increases, the valve body  217   a  moves more rapidly when the first solenoid pressure Pslp is changed. Further, after the first solenoid pressure Pslp is output, the timing at which the valve body  217   a  starts to move in the valve closing direction is also advanced as the temperature of the hydraulic oil increases. 
     As the first solenoid pressure Pslp increase to increase the hydraulic pressure Pin, the valve opening speed of the valve body  217   a  increases when the first solenoid pressure Pslp is output. That is, as the first solenoid pressure Pslp increases to increase the hydraulic pressure Pin, the valve body  217   a  moves more rapidly, and the timing at which the valve body  217   a  starts to move in the valve closing direction is also advanced. 
     Here, the time (time Tint in  FIG. 4 ) from when output of the first solenoid pressure Pslp starts to when the first solenoid pressure Pslp is further increased is set based on the temperature of the hydraulic oil and the level of the drive duty when output of the first solenoid pressure Pslp is started to increase the hydraulic pressure Pin. The time Tint is set to be shorter as the temperature of the hydraulic oil increases and the drive duty decreases when output of the first solenoid pressure Pslp for increasing the hydraulic pressure Pin is started. 
     By setting the length of the time Tint in this manner, the timing at which the first solenoid pressure Pslp is further increased is advanced as the temperature of the hydraulic oil increases and the first solenoid pressure Pslp increases to increase the hydraulic pressure Pin. 
     After setting the timing for further increasing the first solenoid pressure Pslp in step S 110 , the electronic control unit  300  proceeds to step S 120  and further increases the first solenoid pressure Pslp when the set timing is reached. Specifically, the drive duty is further decreased when the set timing is reached. This further increases the first solenoid pressure Pslp. 
     When the oscillation suppression control is executed through step S 110  and step S 120  in this manner, the electronic control unit  300  temporarily terminates the series of processes. 
     If determined in step S 10  of  FIG. 5  that the hydraulic pressure Pin should not be increased (step S 10 : NO), the electronic control unit  300  skips step S 20  and step S 100  and terminates the series of processes without executing the oscillation suppression control. 
     If determined in step S 20  that the hydraulic pressure Pin is less than or equal to the hydraulic pressure Pout (step S 20 : NO), the electronic control unit  300  skips step S 100  and terminates the series of processes without executing the oscillation suppression control. 
     In this manner, after increasing the first solenoid pressure Pslp to increase the hydraulic pressure Pin, the oscillation suppression control further temporarily increases the first solenoid pressure Pslp to offset the portion of the force that acts to move the valve body  217   a , which has been excessively moved in the valve opening direction, in the valve closing direction. This suppresses movement of the valve body  217   a . Thus, as shown in  FIG. 4 , undershooting of the hydraulic pressure Pin can be suppressed, and oscillation of the hydraulic pressure Pin can be suppressed. 
     The first embodiment has the advantages described below. 
     (1) In the hydraulic pressure controller according to the present embodiment, after driving the valve body  217   a  of the first control valve  217  that controls the hydraulic pressure Pin in the valve opening direction, the oscillation suppression control is executed to temporarily suppress the movement of the valve body  217   a.    
     Thus, oscillation of the valve body  217   a  when the valve body  217   a  is driven in the valve opening direction is suppressed, and repetitive increasing and decreasing of the hydraulic pressure Pin supplied to the first pulley  130  over the target hydraulic pressure Ptrg is suppressed. Further, oscillation of the valve body  217   a  is suppressed in this manner, and oscillation of the hydraulic pressure Pin supplied to the first pulley  130  is suppressed. This suppresses oscillation of the line pressure Pl, which is feedback adjusted based on the hydraulic pressure Pin. 
     As a result, the occurrence of an adverse cycle is suppressed in which the line pressure Pl is adjusted based on the oscillating hydraulic pressure Pin, and the hydraulic pressures Pin and Pout supplied to the pulleys  130  and  150  are adjusted based on the oscillating line pressure Pl. 
     In other words, the line pressure Pl is feedback adjusted in accordance with the levels of the hydraulic pressures Pin and Pout, excessive increase of the drive load of the oil pump  211  is suppressed, and oscillation of the hydraulic pressures Pin and Pout and the line pressure Pl when the hydraulic pressure Pin changes is suppressed. 
     Further, as a result, when the hydraulic pressure Pin of the first pulley  130  changes, repetitive increase and decrease of the tension on the belt  140  is suppressed, and a decrease in the durability of the continuously variable transmission  100  is suppressed. 
     (2) As described above, after the first solenoid pressure Pslp is output to increase the hydraulic pressure Pin and the valve body  217   a  is driven in the valve opening direction, the timing at which the valve body  217   a  starts to move in the valve closing direction changes in accordance with the responsiveness or the like of the actual movement of the valve body  217   a  with respect to changes in the first solenoid pressure Pslp. When the temperature of the hydraulic oil is high, the viscosity of the hydraulic oil decreases. Thus, the responsiveness of the actual movement of the valve body  217   a  with respect to changes in the first solenoid pressure Pslp increases as the temperature of the hydraulic oil increases. In other words, as the temperature of the hydraulic oil increases, the valve body  217   a  moves more readily when the first solenoid pressure Pslp. Further, as the temperature of the hydraulic oil increases, the timing at which the valve body  217   a  starts to move in the valve closing operation becomes earlier. 
     In the first embodiment, after starting the output of the first solenoid pressure Pslp to drive the valve body  217   a  in the valve opening direction thereby increasing the hydraulic pressure Pin, the timing for further increasing the first solenoid pressure Pslp is advanced as the temperature of the hydraulic oil increases. Thus, the first solenoid pressure Pslp can be changed in accordance with changes in the responsiveness of the actual movement of the valve body  217   a  with respect to the changes in the first solenoid pressure Pslp when the temperature of the hydraulic oil changes. Accordingly, the oscillation of the valve body  217   a  is accurately suppressed, and the oscillation of the hydraulic pressure Pin is properly suppressed. 
     (3) The valve opening speed of the valve body  217   a  when the first solenoid pressure Pslp increases as the first solenoid pressure Pslp increases to increase the hydraulic pressure Pin. In other words, as the first solenoid pressure Pslp output to drive the valve body  217   a  in the valve opening direction increases, the valve body  217   a  is moved more readily when the first solenoid pressure Pslp is output. This advances the timing at which the valve body  217   a  starts to move in the valve closing direction. In this regard, in the first embodiment, the timing for further increasing the first solenoid pressure Pslp is set based on the level of the drive duty output to increase the hydraulic pressure Pin. As the duty ratio output to increase the hydraulic pressure Pin decreases and the first solenoid pressure Pslp output to increase the hydraulic pressure Pin increases, the timing for changing the drive duty to further increase the first solenoid pressure Pslp is advanced. 
     Thus, the timing for changing the first solenoid pressure Pslp can be set in accordance with changes in the valve opening speed of the valve body  217   a  when the first solenoid pressure Pslp is output, and oscillation of the valve body  217   a  can be effectively suppressed. 
     (4) The oscillation of the valve body  217   a  is apt to occurring when the first solenoid pressure Pslp is output to increase the hydraulic pressure Pin supplied to the first pulley  130 , and the first solenoid pressure Pslp acts on the valve body  217   a  to drive the valve body  217   a  in the valve opening direction. In this regard, in the first embodiment, the oscillation suppression control is executed when the hydraulic pressure Pin increases and when the hydraulic pressure Pin is greater than the hydraulic pressure Pout. 
     Thus, when increasing the hydraulic pressure Pin supplied to the first pulley  130 , the oscillation suppression control is executed under a situation that may result in an adverse cycle in which the hydraulic pressures Pin and Pout supplied to the pulley  130  and  150  are oscillated continues for a long period of time due to feedback adjustment of the line pressure P 1  performed in accordance with changes in the hydraulic pressure Pin supplied to the first pulley  130 . 
     Accordingly, a state in which the hydraulic pressures Pin and Pout supplied to the pulleys  130  and  150  oscillate continuously over a long period of time is suppressed in a preferred manner. 
     The first embodiment may be modified in the forms described below. 
     The first embodiment is configured to set the timing that further increases the first solenoid pressure Pslp based on the temperature of the hydraulic oil and the drive duty for increasing the hydraulic pressure Pin. The timing for further increasing the first solenoid pressure Pslp may also be set based on only one of the temperature of the hydraulic oil and the drive duty. 
     The method for setting the timing to further increase the first solenoid pressure Pslp in the first embodiment is one example of a method for setting the timing for further increasing the first solenoid pressure Pslp, and the present invention is not limited to the setting shown illustrated in the first embodiment. In other words, as long as movement of the valve body  217   a  in the valve closing direction can be suppressed after the first solenoid pressure Pslp is output to increase the hydraulic pressure Pin, the method for setting the timing for further increasing the first solenoid pressure Pslp can be changed as required. 
     In the first embodiment, the oscillation suppression control increases the first solenoid pressure Pslp only once after the output of the first solenoid pressure Pslp is started to increase the hydraulic pressure Pin. However, the oscillation suppression control may increase the first solenoid pressure Pslp over a number of times. In other words, the oscillation suppression control may cyclically increase in accordance with the cycle of the oscillation of the hydraulic pressure Pin to suppress movement of the valve body  217   a  and suppress oscillation of the hydraulic pressure Pin. 
     In the first embodiment, the drive duty is changed to further increase the first solenoid pressure Pslp and thereby suppress undershooting in which the hydraulic pressure Pin becomes lower than the target hydraulic pressure Ptrg. In this regard, after increasing the first solenoid pressure Pslp to increase the hydraulic pressure Pin, the drive duty may be temporarily changed to decrease the first solenoid pressure Pslp and suppress overshooting in which the hydraulic pressure Pin becomes greater than the target hydraulic pressure Ptrg by suppressing movement of the valve body  217   a . This suppresses oscillation of the hydraulic pressure Pin. 
     In addition, after increasing the first solenoid pressure Pslp to increase the hydraulic pressure Pin, the first solenoid pressure Pslp may be alternately and repetitively increased and decreased in accordance with the oscillation cycle of the hydraulic pressure Pin to temporarily suppress movement of the valve body  217   a  and suppress oscillation of the hydraulic pressure Pin. 
     Second Embodiment 
     A second embodiment of a hydraulic pressure controller for a continuously variable transmission according to the present invention applied to an electronic control unit  300  that controls a continuously variable transmission  100 , which is installed in a vehicle, and a hydraulic pressure control unit  200  will now be described with reference to  FIGS. 7 and 8 . The present embodiment differs from the first embodiment in that a closing valve  240  and a switching solenoid valve  241 , which drives the closing valve  240 , are added to the hydraulic pressure control unit  200 , as shown in  FIG. 7 . Otherwise, the present embodiment is the same as the first embodiment. Thus, in the description hereafter, components that are the same as the first embodiment will not be described, and components differing from the first embodiment will be described in detail. 
     The hydraulic pressure control unit  200  of the present embodiment includes the closing valve  240  on the discharge passage through which the hydraulic oil discharged from the discharge port  230   d  of the pressure adjustment valve  230  flows, as shown in  FIG. 7 . The closing valve  240  can switch between states closing and opening the discharge passage. 
     Further, the hydraulic pressure control unit  200  of the present embodiment includes the switching solenoid valve  241  that drives the closing valve  240 . The switching solenoid valve  241  is a solenoid valve electrically driven based on a drive command from the electronic control unit  300  and switched between an “ON” state, in which the driving hydraulic pressure is output to the closing valve  240 , and an “OFF” state, in which the driving hydraulic pressure is not output. 
     When the switching solenoid valve  241  is switched to the “ON” state, the driving hydraulic pressure is output, and the driving hydraulic pressure switches the closing valve  240  to the state closing the discharge passage, that is, a valve closing state. 
     When the switching solenoid valve  241  is switched to the “OFF” state, the drive hydraulic pressure is not output, and the closing valve  240  is switched to the state opening the discharge passage, that is, the valve opening state. 
     In the present embodiment, the discharge passage is closed by closing the closing valve  240  to prohibit the discharge of hydraulic oil from the second pressure chamber  217   c  of the first control valve  217  and the supply of hydraulic oil to the second pressure chamber  217   c  and execute oscillation suppression control that suppresses movement of the valve body  217   a.    
     More specifically, the series of processes shown in  FIG. 5  are repetitively executed while the engine is running in the same manner as the first embodiment. When determined that the hydraulic pressure Pin should be increased (step S 10 : YES) and that the hydraulic pressure Pin is greater than the hydraulic pressure Pout (step S 20 : YES), the process proceeds to step S 100  to execute the oscillation suppression control. 
     In the present embodiment, the oscillation suppression control shown in  FIG. 8  is executed. As shown in  FIG. 8 , when the oscillation suppression control is started, in step S 130 , the electronic control unit  300  sets the switching solenoid valve  241  to the “ON” state and switches the closing valve  240  to the valve closing state. 
     When closing the closing valve  240  in step S 130  and executing the oscillation suppression control, the electronic control unit  300  temporarily terminates the series of processes. 
     In this manner, when the closing valve  240  is closed in step S 130  and the oscillation suppression control is executed, the discharge of hydraulic oil from the discharge port  230   d  of the pressure adjustment valve  230  is prohibited. When the discharge of the hydraulic oil from the discharge port  230   d  of the pressure adjustment valve  230  is prohibited, the hydraulic oil in the second pressure chamber  217   c  is not discharged even if the solenoid modulator pressure Psolmod supplied to the second pressure chamber  217   c  of the first control valve  217  becomes high. When the hydraulic oil in the second pressure chamber  217   c  is no longer discharged, the solenoid modulator pressure Psolmod increases and the input port  230   b  is closed by the valve body  230   a . This prohibits the supply of hydraulic oil to the second pressure chamber  217   c.    
     Thus, the execution of the oscillation suppression control prohibits the discharge of hydraulic oil from the second pressure chamber  217   c  and the supply of hydraulic oil to the second pressure chamber  217   c . As a result, the volume of the second pressure chamber  217   c  barely changes, and the valve body  217   a  barely moves. 
     Accordingly, when the output of the first solenoid pressure Pslp for increasing the hydraulic pressure Pin is started and the valve body  217   a  is driven in the valve opening direction, excessive movement of the valve body  217   a  in the valve opening direction can be suppressed. Further, subsequent movement of the valve body  217   a  can also be suppressed. 
     Thus, oscillation of the valve body  217   a  can be suppressed, and oscillation of the hydraulic pressure Pin can be suppressed when the valve body  217   a  is oscillated. 
     In this manner, the second embodiment has advantages (1) and (4) of the first embodiment. 
     The second embodiment may be modified in the forms described below. 
     In the second embodiment, the closing valve  240  is arranged in the discharge passage through which the hydraulic oil discharged from the discharge port  230   d  of the pressure adjustment valve  230  flows. The closing valve  240  only needs to be arranged at a position at which the discharge of hydraulic oil from the second pressure chamber  217   c  of the first control valve  217  and the supply of the hydraulic oil to the second pressure chamber  217   c  can be prohibited. Thus, the closing valve  240  may be arranged in a passage connecting the third input port  217   f  of the first control valve  217  and the output port  230   c  of the pressure adjustment valve  230 . 
     The closing valve  240  is driven by the driving hydraulic pressure output from the switching solenoid valve  241 . However, the closing valve  240  may be formed by an electrically driven solenoid valve, and the closing valve  240  may be directly driven by the electronic control unit  300 . 
     Elements that can be changed in each embodiment described include the following. 
     In the embodiments described above, the second solenoid pressure Psls is conveyed to the reduction valve  213 . In the reduction valve  213 , the line pressure adjustment hydraulic pressure Psrv is set based on the hydraulic pressure Pin and the second solenoid pressure Psls, and output to the regulator valve  212 . However, the hydraulic pressure Pout supplied to the hydraulic pressure chamber  154  in the second pulley  150  may be conveyed to the reduction valve  213  instead of the second solenoid pressure Psls, and the line pressure Pl may be feedback adjusted based on the hydraulic pressure Pin and the hydraulic pressure Pout. 
     The present invention may be applied even to a hydraulic pressure controller that feedback adjusts the line pressure Pl based on the hydraulic pressure Pin and the hydraulic pressure Pout. 
     When the line pressure Pl is feedback adjusted based on the hydraulic pressure Pin and the hydraulic pressure Pout, oscillation of the hydraulic pressure Pout as a result of the oscillation of the valve body  218   a  produces an advertent cycle in which the oscillation is propagated to the line pressure Pl and the hydraulic pressures Pin and Pout are adjusted based on the oscillating line pressure Pl. 
     Thus, when employing such a configuration, it is preferred that the oscillation suppression control be executed to further increase the second solenoid pressure Psls after increasing the second solenoid pressure Psls to increase the hydraulic pressure Pout. 
     When employing a configuration executing the oscillation suppression control that closes the closing valve  240  like in the second embodiment, the discharge of the hydraulic oil from the second pressure chamber  218   c  of the second control valve  218  and the supply of the hydraulic oil to the second pressure chamber  218   c  are prohibited during execution of the oscillation suppression control. Thus, oscillation of the valve body  218   a  of the second control valve  218  can be suppressed by executing oscillation suppression control that closes the closing valve  240  like in the second embodiment. 
     Thus, if the line pressure Pl is feedback adjusted based on the hydraulic pressure Pin and the hydraulic pressure Pout, it is preferred that the conditions for executing of the oscillation suppression control in the second embodiment be changed so that the oscillation suppression control is executed even when the hydraulic pressure Pout is increased. 
     The executing conditions of the oscillation suppression control are not limited to the executing conditions of the embodiments described above. Thus, the executing conditions of the oscillation suppression control can be changed as required in accordance with the configuration of the hydraulic pressure control unit  200  to which the present invention is applied. 
     In the embodiment described above, the hydraulic pressure controller for the continuously variable transmission according to the present invention is embodied as the hydraulic pressure controller for controlling the continuously variable transmission  100  that is installed in a vehicle. However, the present invention is not limited to a hydraulic pressure controller that controls a continuously variable transmission installed in a vehicle. That is, the present invention can be applied as a hydraulic pressure controller that controls a continuously variable transmission other than one installed in a vehicle. 
     In the embodiments described above, the oil temperature sensor  308  is used as an estimating means for estimating the temperature of the hydraulic oil, and the temperature of the hydraulic oil is detected by the oil temperature sensor  308 . However, the structure of the estimating means may be changed as long as the temperature of the hydraulic oil can be estimated. For instance, a structure that estimates a heat generation amount of the internal combustion engine  400  based on an integrated value of the intake air amount GA and estimates the temperature of the hydraulic oil based on the heat generation amount or a structure that estimates the temperature of the hydraulic oil based on the temperature of an engine coolant, which cools the internal combustion engine  400 , may be employed as the estimating means. 
     The structures of the continuously variable transmission  100 , the hydraulic pressure control unit  200 , and the electronic control unit  300  in the above embodiments are examples embodying the present invention. These structures may be changed as required. 
     In other words, the present invention is not limited to the continuously variable transmission  100 , the hydraulic pressure control unit  200 , and the electronic control unit  300  configured like in the embodiments described above. The present invention may be applied to a hydraulic pressure controller that feedback adjusts the line pressure Pl based on the hydraulic pressures Pin and Pout supplied to the pulleys  130  and  150   
     DESCRIPTION OF THE REFERENCE CHARACTERS 
       100 : continuously variable transmission 
       110 : torque converter 
       120 : switching mechanism 
       121 : forward clutch 
       122 : reverse brake 
       130 : first pulley 
       134 : hydraulic pressure chamber 
       140 : belt 
       150 : second pulley 
       154 : hydraulic pressure chamber 
       200 : hydraulic pressure control unit 
       211 : oil pump 
       212 : regulator valve 
       213 : reduction valve 
       214 : modulator valve 
       215 : first solenoid valve 
       216 : second solenoid valve 
       217 : first control valve 
       217   a : valve body 
       217   b : first pressure chamber 
       217   c : second pressure chamber 
       217   d : first input port 
       217   e : second input port 
       217   f : third input port 
       217   g : spring 
       217   h : output port 
       217   i : discharge port 
       217   j : feedback port 
       218 : second control valve 
       218   a : valve body 
       218   b : first pressure chamber 
       218   c : second pressure chamber 
       218   d : first input port 
       218   e : second input port 
       218   f : third input port 
       218   g : spring 
       218   h : output port 
       218   i : discharge port 
       218   j : feedback port 
       219 : failsafe valve 
       219   a : first input port 
       219   b : second input port 
       219   c : output port 
       220 : switching solenoid valve 
       230 : pressure adjustment valve 
       230   a : valve body 
       230   b : input port 
       230   c : output port 
       230   d : discharge port 
       230   e : spring 
       230   f : feedback port 
       240 : closing valve 
       241 : switching solenoid valve 
       300 : electronic control unit 
       301 : acceleration position sensor 
       302 : airflow meter 
       303 : crank angle sensor 
       304 : turbine rotation speed sensor 
       305 : first pulley rotation speed sensor 
       306 : second pulley rotation speed sensor 
       307 : wheel speed sensor 
       308 : oil temperature sensor 
       400 : internal combustion engine 
       410 : intake passage 
       411 : throttle valve