JPH0721310B2 - Line pressure controller for continuously variable transmission - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a line pressure control device for a continuously variable transmission,
In particular, the target line pressure for open loop control can be corrected by a simple program, which simplifies the logic and reduces the memory capacity and calculation processing time, resulting in changes over time and machine differences during production. The present invention relates to a line pressure control device for a continuously variable transmission that can ensure an appropriate line pressure even when a change occurs in hydraulic characteristics.

[Prior Art] In vehicles such as automobiles, a transmission is interposed between an internal combustion engine and driving wheels. The transmission changes the driving force transmitted from the internal combustion engine to the drive wheels and the traveling speed in conformity with the traveling condition of the vehicle that changes over a wide range, so that the performance of the internal combustion engine is sufficiently exhibited.

This transmission is a gear type transmission that selectively changes the meshing state of a plurality of gear trains to change the gear ratio (gear ratio) stepwise to transmit driving force, and is also fixed to a rotating shaft. A groove width formed between the pulley parts of the driving side pulley and the driven side pulley having a fixed pulley part piece and a movable pulley part piece mounted on the rotary shaft so as to be able to come into contact with and separate from the fixed pulley part piece. There is a continuously variable transmission or the like in which the radius of rotation of a belt wound around a pulley is increased or decreased to continuously change a gear ratio (belt ratio) to transmit a driving force. A line pressure control device for controlling the line pressure that changes the gear ratio of such a continuously variable transmission is disclosed in, for example, Japanese Patent Laid-Open No. 61-233256.

[Problems to be solved by the invention]

By the way, in the continuously variable transmission, when the line pressure for changing the gear ratio is controlled to the target line pressure, it is controlled by the closed loop control and the open loop control. Closed loop control sets a target line pressure from a map of throttle opening, gear ratio, engine speed, etc., integrates the difference between this target line pressure and the actual line pressure, and calculates the integrated value. The target line pressure is corrected by the obtained integral value, and the line pressure is fed back and controlled so as to become the target line pressure. In the open loop control, the line pressure is controlled without feedback so that the line pressure becomes the target line pressure. Further, the line pressure is corrected when the clutch pressure immediately before the lockup of the hydraulic clutch that interrupts the driving force of the continuously variable transmission is relatively high. By correcting this line pressure, if the hydraulic characteristics change due to changes over time or machine differences during production, etc., the target line pressure for open loop control is corrected to ensure an appropriate line pressure, and This prevents inconveniences such as abnormal deterioration.

However, in the conventional correction of the line pressure, the difference between the average value of the clutch pressure immediately before the hydraulic clutch locks up (at this time, the clutch pressure is equal to the line pressure) and the target line pressure is used as the correction value. The target line pressure was corrected with this correction value. However, the program for calculating the average value and the program for correcting the target line pressure is complicated, the logic is complicated, the memory capacity is large, and the calculation processing time is long.

[Object of the Invention]

Therefore, an object of the present invention is to correct the target line pressure of the open loop control by a simple program, which simplifies the logic and can reduce the memory capacity and the calculation processing time. An object of the present invention is to realize a line pressure control device for a continuously variable transmission that can secure an appropriate line pressure even when the hydraulic characteristic changes due to the above.

[Means for solving problems]

In order to achieve this object, the present invention relates to both the above-mentioned pulleys of a driving side pulley and a driven side pulley, each of which has a fixed pulley piece and a movable pulley piece which is attached to and detachable from the fixed pulley piece. In a continuously variable transmission that increases or decreases the groove width between the pieces to increase or decrease the radius of gyration of the belt wound around the pulleys and changes the gear ratio, a hydraulic clutch that disconnects the driving force from the continuously variable transmission is used. A line is provided for detecting the oil pressure of the clutch pressure acting on the hydraulic clutch as a line pressure when the hydraulic clutch is completely engaged, and a line for changing the speed ratio detected by the pressure sensor. Stores the integrated value calculated when controlling by closed loop control so that the pressure becomes the target line pressure, and switches from closed loop control to open loop control. If so, the target line pressure is corrected using the stored integrated value in the previous closed loop control as the correction value in the present open loop control, and the line pressure is controlled by the open loop control so as to become the corrected target line pressure. A control means is provided.

[Action]

According to the configuration of the present invention, when the closed loop control is changed to the open loop control by the control means, the target line pressure is corrected using the stored integrated value in the previous closed loop control as the correction value in the current open loop control. By controlling the line pressure to the corrected target line pressure by the open loop control, the target line pressure of the open loop control can be corrected by a simple program.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

1 to 3 show an embodiment of the present invention.

In FIG. 1, 2 is, for example, a belt drive type continuously variable transmission, 2A is a belt, 4 is a drive side pulley, 6 is a drive side fixed pulley, 8 is a drive side movable pulley part, 10 is a driven side pulley, Reference numeral 12 is a driven side fixed pulley section piece, and 14 is a driven side movable pulley section piece.

The drive side pulley 4 includes a drive side fixed pulley portion piece 6 fixed to a rotary shaft 16 as an input shaft, and a drive side fixed to the rotary shaft 16 so as to be movable and non-rotatable in the axial direction of the rotary shaft 16. And a movable pulley piece 8. The driven pulley 10 also has a rotary shaft 17, which is an output shaft, a driven fixed pulley portion 12, and a driven movable pulley portion 14, like the driving pulley 4.

The drive side movable pulley part 8 and the driven side movable pulley part
First and second housings 18 and 20 are attached to 14 respectively, and first and second hydraulic chambers 22 and 24 are formed respectively. The hydraulic pressure receiving area of the drive side movable pulley part 8 of the first hydraulic chamber 22 is set to be larger than the hydraulic pressure receiving area of the driven pulley part 14 of the second hydraulic chamber 24. As a result, the belt ratio, which is a gear ratio, is changed by controlling the hydraulic pressure used in the first hydraulic chamber 22. Further, in the second hydraulic chamber 24 on the driven side,
Driven side fixed pulley part 12 and driven side movable pulley part 14
An urging means 26 including a spring or the like for urging the driven-side movable pulley portion 14 is provided in a direction in which the groove width between and is reduced.
The biasing means 26 prevents slippage by maintaining a large gear ratio on the full low side and maintaining the holding force of the belt 2A when the hydraulic pressure is low as at the time of starting.

An oil pump 28 is provided on the rotary shaft 16, and the oil pump 28 is connected to the first and second hydraulic chambers 22 and 24 by the first and second oil passages 30 and 32, respectively. A primary pressure control valve 34, which is a shift control valve that controls the primary pressure that is the sheave pressure of the input shaft, is provided midway.
This, the first oil passage 30 of the oil pump 28 side of the primary pressure control valve 34, the line pressure by the third oil passage 36 (typically 5~25kg / cm ²⁾ to a constant pressure (3-4 kg / cm ²⁾
A constant pressure control valve 38 which is controlled to the control oil pressure and is taken out is communicated with the primary pressure control valve 34 is communicated with a first three-way solenoid valve 42 for primary pressure control through a fourth oil passage 40.

Further, a line pressure control valve 44 having a relief valve function for controlling the line pressure which is a pump pressure is connected in the middle of the second oil passage 32 by a fifth oil passage 46, and a line pressure control valve 44 is provided with a sixth valve. Second line pressure control by oil passage 48
Connect the three-way solenoid valve 50.

Further, the line pressure control valve 44 has a second position
In the middle of the second oil passage 32 on the hydraulic chamber 24 side, a clutch pressure control valve 52 for controlling a clutch pressure which is a hydraulic pressure acting on a hydraulic clutch 62 described later is communicated with a seventh oil passage 54, and the clutch pressure control valve 52 An eighth oil passage 56 communicates with a third three-way solenoid valve 58 for clutch pressure control.

Further, the constant control oil pressure taken out from the constant pressure control valve 38 is supplied to the primary pressure control valve 34, the primary pressure control first three-way solenoid valve 42, the line pressure control valve 44, and the line pressure control second three-way solenoid valve 50. Then, these valves 38, 34, 42, 44, 50, 52 are connected by a ninth oil passage 60 so as to supply them to the clutch pressure control valve 52 and the clutch pressure control third three-way solenoid valve 58, respectively.

The clutch pressure control valve 52 communicates with the clutch hydraulic chamber 72 of the hydraulic clutch 62 via a tenth oil passage 64, and a pressure sensor 68 communicates with the eleventh oil passage 66 in the middle of the tenth oil passage 64. The pressure sensor 68 can directly detect the hydraulic pressure when controlling the clutch pressure in the hold mode, the start mode, etc., and contributes to commanding the detected hydraulic pressure to be the target clutch pressure.
Further, since the clutch pressure becomes equal to the line pressure in the drive mode, it also contributes to the line pressure control.

The hydraulic clutch 62 includes a casing 70 of an input shaft attached to the rotating shaft 17, a clutch hydraulic chamber 72 provided in the casing 70, and a piston 74 pushed by hydraulic pressure acting on the clutch hydraulic chamber 72. An annular spring 76 for urging the piston 74 in the retreat direction, a first pressure plate 78 movably provided by a pushing force of the piston 74 and an urging force of the annular spring 76, and an output side. Friction plate 80 and the second fixed to the casing 70
And a pressure plate 82.

When the hydraulic clutch 62 raises the clutch pressure, which is the hydraulic pressure applied to the clutch hydraulic chamber 72, the piston 74 pushes forward to move the first pressure.
The pressure plate 78 and the second pressure plate 82 are brought into close contact with the friction plate 80 to be in a so-called combined state. On the other hand, when the clutch pressure, which is the hydraulic pressure applied to the clutch hydraulic chamber 72, is lowered, the piston is retracted by the urging force of the annular spring 76 and the first plate 78 and the second pressure plate 82 are separated from the friction plate 80, so-called. The clutch will be released. The driving force output from the continuously variable transmission 2 is interrupted by the engagement and disengagement of the hydraulic clutch 62.

An input shaft rotation detection gear 84 is provided outside the first housing 18, and a first rotation detector 86 on the input shaft side is provided in the vicinity of an outer peripheral portion of the input shaft rotation detection gear 84. An output shaft rotation detection gear 88 is provided outside the second housing 20, and a second rotation detector 90 on the output shaft side is provided near the outer peripheral portion of the output shaft rotation detection gear 88. The number of revolutions of the engine and the belt ratio are grasped from the number of revolutions detected by the first revolution detector 86 and the second revolution detector 90.

Further, the hydraulic clutch 62 is provided with an output transmission gear 92. The output transmission gear 92 is composed of a forward output transmission gear 92F and a reverse output transmission gear 92R, and a third rotation detection for detecting the rotation speed of the final output shaft 94 in the vicinity of the outer peripheral portion of the reverse output transmission gear 92R. A container 96 is provided. The third rotation detector 96 detects the number of rotations of the final output shaft 94 that communicates with a wheel (not shown), and can detect the vehicle speed. Further, the number of rotations between the input side and the output side before and after the hydraulic clutch 62 can be detected by the number of rotations detected by the second rotation detector 90 and the third rotation detector 96, and the clutch slip amount can be detected. Contribute to.

The pressure sensor 68 and the first to third rotation detectors 86, 90,
In addition to various signals from 96, carburetor throttle opening, carburetor idle position, accelerator pedal signal, brake signal, power mode option signal, shift lever position, etc. Set up. The controller 98 controls the primary pressure control first three-way solenoid valve 42, the line pressure control second three-way solenoid valve 50, and the clutch in order to control the belt ratio and the clutch disengagement state in various control modes by various input signals. The opening / closing operation of the pressure control third three-way solenoid valve 58 is controlled.

Reference numeral 100 is an oil pan, and reference numeral 102 is an oil filter.

The function of the input signal input to the control unit 98 will be described in detail. The detection signal of the shift lever position ... The line pressure required for each range by each range signal such as P, R, N, D and L. / Ratio, clutch control, carburetor throttle opening detection signal ...... Engine torque is detected from the memory input in advance in the program, target ratio or target engine speed is determined, carburetor idle position detection signal ... Carburetor throttle opening Accuracy in correction and control of the degree sensor, accelerator pedal signal ...... The driver's intention is detected based on the accelerator pedal depression state, and the control direction during traveling or starting is determined. Brake signal ...... Brake pedal depression operation Is detected and the control direction such as clutch disengagement is determined, and the power mode option signal is detected. No. …… The performance of the vehicle is sports (or economy)
Use as an option for

The line pressure control valve 44 has a shift control characteristic that changes the line pressure in a full low state, a full over top state, and a fixed ratio state to perform three-stage control.

As with the line pressure control valve 44, the operation of the primary pressure control valve 34 for controlling the primary pressure for gear shift control is controlled by a dedicated primary pressure control first three-way solenoid valve 42. This primary pressure control first three-way solenoid valve 42
Is used to control the operation of the primary pressure control valve 34 to bring the primary pressure into the first oil passage 30 or to bring the primary pressure into the atmosphere. The primary pressure control valve 34 transfers the line pressure to the first oil passage 30 to shift the belt ratio to the full overdrive side, or to the atmosphere side to shift it to the full low side.

The clutch pressure control valve 52 for controlling the clutch pressure conducts the line pressure to the tenth oil passage 64 side when the maximum clutch pressure is required, and to the atmosphere side when the minimum clutch pressure is set. is there. The clutch pressure control valve 52, like the line pressure control valve 44 and the primary pressure control valve 34,
The operation is controlled by the third clutch pressure controlling third three-way solenoid valve 58, and the description thereof will be omitted.

The clutch pressure varies within a range from the lowest atmospheric pressure (zero) to the highest line pressure. There are four basic patterns for controlling the clutch pressure. The basic pattern is (1), neutral mode .............. When the shift position is N or P and the clutch is completely disengaged, the clutch pressure is the minimum pressure (zero). (2) Hold mode: If the shift position is D or R and the throttle is released and there is no intention to run, or if you want to decelerate and cut the engine torque while running, the clutch pressure is low enough to contact the clutch ( 3) Normal start mode (special start mode) ...... When starting the vehicle (normal start) or when trying to re-engage the clutch after the clutch is disengaged (special start), the clutch pressure is prevented from rising and the vehicle Engine generated torque that can operate smoothly (clutch input torque) Depending was appropriate level (4), when the migrated clutch in the drive mode ...... complete running state is completely coupled, high levels of There are four clutch pressure having a margin to withstand sufficiently the engine torque.

The four basic patterns (1) are performed by a dedicated switching valve (not shown) that is interlocked with the shift operation. The other (2), (3) and (4) are the first to the first by the control unit 98.
This is performed by controlling the duty value of the third three-way solenoid valves 42, 50, 58. Particularly in the state of (4), the seventh oil passage 54 and the tenth oil passage 54 are controlled by the clutch pressure control valve 52.
The maximum pressure is generated by communicating with 64, and the clutch pressure is the same as the line pressure.

Further, the primary pressure control valve 34 and the line pressure control valve 44,
The clutch pressure control valve 52 is the first to third three-way solenoid valve 4
It is controlled by the output hydraulic pressure from 2, 50 and 58 respectively. The control hydraulic pressure for controlling these first to third three-way solenoid valves 42, 50, 58 is a constant control hydraulic pressure taken out by the constant pressure control valve 38. This control oil pressure is always lower than the line pressure, but is a stable and constant pressure. In addition, the control oil pressure
It has also been introduced into 34, 44 and 52 to stabilize these control valves 34, 44 and 52.

In such a continuously variable transmission 2, a hydraulic clutch 62 for connecting and disconnecting the driving force from the continuously variable transmission 2 is also provided,
A pressure sensor 68 for detecting the hydraulic pressure of the clutch pressure acting on the hydraulic clutch 62 as a line pressure when the hydraulic clutch 62 is completely engaged is provided, and the control unit 98 detects the pressure sensor 68. The integrated value calculated when the line pressure for changing the gear ratio is controlled by the closed loop control so as to become the target line pressure is stored, and when the closed loop control is changed to the open loop control, the stored previous value is stored. The target line pressure is corrected using the integrated value in the closed loop control as a correction value in the present open loop control, and the line pressure is controlled by the open loop control so that the line pressure becomes the target line pressure.

The control by the control unit 98 will be described with reference to FIGS.

In the figure, PLINSP: Target line pressure PCLU: Clutch pressure OPWLIN: Line pressure duty value LPFF: Map of target line and line pressure output duty value LCLMOD: Line pressure = PCLU (clutch pressure at clutch lockup in drive mode) ) And feed back this PCLU Closed loop control mode LOLMOD: OPWLIN (line pressure duty value) is set and output by LPFF in start mode Open loop control mode LHOMOD: OPWLIN is set and output similarly to LOLMOD in hold mode Open loop control mode LDIMOD: Open loop control mode that outputs OPWLIN = 0 in neutral mode.

In the line pressure control mode by the control unit 98, as shown in FIG. 2, in LCLMOD, the first switching unit 104, the second switching unit 106, and the third switching unit 108 are switched as shown by the solid line.
In this LCLMOD, PLINSP is read from the map set by the throttle opening and the belt ratio (20
0), U1P which is the line pressure output duty value is calculated from LPFF by this PLINSP (201). Further, the actual line pressure (here, the hydraulic clutch 62 is locked up, so the line pressure = the clutch pressure (PCLU).)
Is fed back (202), and E2P which is a correction value as an integrated value is calculated from the difference and obtained (203). This E2P is added to the U1P (204) and output as OPWLIN which is the line pressure output duty value (205), and the line pressure is fed back and controlled so as to become the target line pressure.

The correction value E2P, which is the integral value calculated each time by this LCLMOD, is obtained by the integration control with PLINSP-PCLU = 0 (202), and therefore the difference from LPFF which is an open loop map is actually obtained. Become.

Therefore, as learning control for correcting the line pressure, the line pressure control mode shifts to the closed loop LCLMOD, and the hydraulic clutch 62 is locked up (line pressure = clutch pressure (PCLU) and PCLU> 10 kg / cm ² ( This is corrected by correcting on the high pressure side where the clutch pressure becomes equal to the line pressure,
This is to improve control accuracy. ), And the correction value E2P that is the integral value obtained by the integration control is stored. The correction by the correction value E2P is performed only by the positive direction as the safety side of the line pressure (this is to prevent the line pressure from decreasing due to a malfunction of the hydraulic circuit). The correction value E3P is obtained (206).

In this way, the correction value E3P, which is the integral value obtained when controlling by LCLMOD of closed loop control, is stored in the backup memory.

When the closed loop control LCLMOD is changed to the open loop control LHOMOD or LOLMOD, the first switching unit 104 and the second switching unit 106 are switched as shown by the broken line and the third switching unit 108 is switched as shown by the solid line. . As a result, the correction value E3P (206), which is the stored integral value obtained by the previous LCLMOD, is added to the line pressure output duty value U1P from LPFF (201) for correction, and output as OPWLIN.
5) Then, control by open loop control so that the line pressure becomes the target line pressure. As a result, it is possible to secure an appropriate line pressure even when the hydraulic characteristics change due to changes over time. Moreover, the program is simple, and the memory capacity and the calculation processing time can be reduced.

When LDIMOD is reached, the third switching unit 108 switches as indicated by the broken line, and outputs OPWLIN as 0.

Next, the control of the line pressure will be described with reference to FIG. In addition,
The line pressure control mode determination is determined according to the operating state of the vehicle by the same logic as the conventional one, and the description thereof will be omitted.

When the control starts (300), it is judged whether it is LCLMOD (3
01) to do. In the case of YES, the line pressure output duty value U1P is calculated from LPFF (302), and the actual line pressure due to the closed loop (here, since the hydraulic clutch 62 is locked up, line pressure = clutch pressure (PCLU ) Is fed back to obtain E2P which is a correction value which is an integral value from the difference.

Next, it is judged whether the PCLU is less than or equal to 10 kg / cm ² or more (304), and if PLCU> 10 kg / cm ² , the E2P is limited and E3P is newly obtained as a correction value and backed up. Store in memory and update the previous E3P (305).

If PCLU ≦ 10 kg / cm ² in the judgment of step 304, E2P is added to U1P obtained in step 302 to correct the OPW.
Get LIN (306). The upper and lower limit processing of this OPWLIN is performed at 5 to 95% (307), OPWLIN is output (308), and return (30
9) This OPWLIN controls the line pressure to the target line pressure by closed loop control.

On the other hand, if NO in the determination in step 301, LOL
It is judged whether it is a MOD (310). If YES, LPFF to U
1P is calculated (311), and E3P stored in step 306 is added to this U1P for correction to obtain OPWLIN (31
2). The obtained OPWLIN is from 5 to 95 by the above step 307.
% Upper and lower limit processing is performed, OPWLIN is output in step 308, and the process returns (309). This OPWLIN controls the line pressure to the target line pressure by open loop control.

If NO in step 310, LHO
It is judged whether it is MOD (313). If YES, LPFF to U
1P is calculated (314), and E3P stored in step 305 is added to this U1P for correction to obtain OPWLIN (31
Five). The obtained OPWLIN is from 5 to 95 by the above step 307.
% Upper and lower limit processing is performed, OPWLIN is output and return (309) in step 308. This OPWIN controls the line pressure to the target line pressure by open loop control.

Furthermore, if the determination in step 313 is NO, L
It is judged whether it is DIMOD (316). If YES, OPWLIN
To 0 (OPWLIN = 0) (317) and return (309). If NO, return (309).

In this way, when the closed loop control LCLMOD changes to the open loop control LHOMOD or LOLMOD, the correction value E3P, which is the stored integral value obtained by the previous LCLMOD, is the line pressure output duty value from the LPFF. U
It is added to 1P, corrected, output as OPWLIN, and controlled by open loop control so that the line pressure becomes the target line pressure. As a result, it is possible to secure an appropriate line pressure even when the correction characteristic changes due to changes over time. Moreover, the program is simple, and the memory capacity and the calculation processing time can be reduced.

In this embodiment, the line pressure is corrected only in the positive direction, but the basic idea is that the integrated value E2P calculated by the closed loop control is the open loop map LPF.
Since it is obtained from the difference between the duty value output at F and the line pressure controlled by that duty value, the integral value E2P is the conversion value of the change amount of the hydraulic circuit with respect to the target hydraulic pressure into the duty value. . Therefore, as a correction of this hydraulic circuit, if this integrated value E2P is used not only in the positive direction but also in the negative direction as in this embodiment, a more accurate line pressure with respect to the target line pressure can be obtained. That is clear.

〔The invention's effect〕

As described in detail above, according to the present invention, when the closed loop control is changed to the open loop control by the control means, the stored integral value in the previous closed loop control is set as the correction value in the open loop control this time. By correcting the line pressure and controlling the line pressure to the corrected target line pressure by the open loop control, the target line pressure of the open loop control can be corrected by a simple program.

This simplifies the logic and reduces the memory capacity and calculation processing time.In addition, even if the hydraulic characteristics change due to changes over time or machine differences during production, etc. Even if a change occurs in the hydraulic circuit for pressure, it is possible to secure an appropriate line pressure.

Furthermore, there is no need to add new hardware,
It can be dealt with only by changing the software, the program can be easily executed and the function can be easily confirmed, and most of the conventional programs can be used.
It is possible to reduce the amount of increase in the memory of the control unit and prevent the cost from being excessively increased, which is economically advantageous.

[Brief description of drawings]

1 to 3 show an embodiment of the present invention, FIG. 1 is a block diagram of a continuously variable transmission, FIG. 2 is a control block diagram, and FIG.
The figure is a control flowchart. In the figure, 2 is a belt drive type continuously variable transmission, 2A is a belt, 4 is a drive side pulley, 10 is a driven side pulley, 34 is a primary pressure control valve, 38 is a constant pressure control valve, and 42 is a primary pressure control valve. , 38 is a constant pressure control valve, 42 is a first three-way solenoid valve for primary pressure control, 44 is a line pressure control valve, 50 is a second three-way solenoid valve for line pressure control, 52 is a clutch pressure control valve, 58 is a clutch pressure control Third three-way solenoid valve, 62 is a hydraulic starting clutch, 68 is a pressure sensor, 84 is an input shaft rotation detection gear, 90 is a second rotation detector, 96 is an output transmission gear, 98 is a control unit, 104
Is a first switching unit, 106 is a second switching unit, and 108 is a third switching unit.

Front page continuation (72) Inventor Tatsumi Takumi 840 Chiyoda-cho, Himeji-shi, Hyogo Prefecture Mitsubishi Electric Co., Ltd. Himeji Plant (72) Inventor Hiroaki Yamamoto 1-13 13 Sadamoto-cho, Himeji-shi, Hyogo Mitsubishi Electric Control Software Himeji Corporation Inside the office

Claims (1)

[Claims] 1. A groove width between the two pulley part pieces of each of a driving side pulley and a driven side pulley having a fixed pulley part piece and a movable pulley part piece attached to the fixed pulley part piece so as to be able to come into contact with and separate from the fixed pulley part piece. In a continuously variable transmission that changes the gear ratio by increasing or decreasing the radius of gyration of the belt wound around the pulleys, a hydraulic clutch for connecting and disconnecting the driving force from the continuously variable transmission is provided. A pressure sensor that detects the hydraulic pressure of the clutch pressure acting on this hydraulic clutch when completely connected is provided as a line pressure, and the line pressure that changes the gear ratio detected by this pressure sensor becomes the target line pressure. The integrated value calculated when controlling by closed-loop control is stored so that it is stored when the closed-loop control is changed to open-loop control. The target line pressure is corrected by using the integrated value in the closed loop control as a correction value in the present open loop control, and the control means is provided to perform the open loop control so that the line pressure becomes the corrected target line pressure. Line pressure control device for continuously variable transmission.