JPH11210873A - Hydraulic control device for continuously variable transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve operability of a line pressure controlling solenoid and suppress shift shock due to abrupt shift by reducing line pressure by means of the line pressure controlling solenoid valve when abrupt transmission occurs, and increasing heat quantity of the solenoid valve under the low oil temperature. SOLUTION: Shifting of a continuously variable transmission 10 is carried out by driving a transmission control valve by means of a step motor 152 according to command of a transmission controller 1. Line pressure PL is controlled by a line pressure solenoid valve 528. In such a case, the controller 1 to which output signals from input and output shaft rotational sensors 2, 3 and a temperature sensor 50 are input senses abrupt shifting state of the continuously variable transmission 10. When the abrupt shifting state is sensed, the line pressure controlling solenoid 528 is duty-controlled so as to reduce the line pressure. When the sensed oil temperature or outside temperature is lower than the specified value, driving current for the line pressure controlling solenoid valve 528 is increased for promoting heating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control device for a continuously variable transmission employed in a vehicle or the like.

[0002]

2. Description of the Related Art As a hydraulic control device for a continuously variable transmission used in a vehicle, for example, a hydraulic control device disclosed in Japanese Patent Application Laid-Open No. 8-233308 is known.

In a continuously variable transmission, transmission control and torque transmission are performed by hydraulic pressure applied to a hydraulic servo cylinder. If a normal hydraulic pressure cannot be obtained due to damage to a hydraulic system or the like, Shift control cannot be performed. Therefore, if the target gear ratio cannot be maintained due to the failure of the hydraulic system to obtain a normal oil pressure, the gear mode is forcibly switched to set the gear ratio to the maximum Lo gear ratio (= maximum gear ratio). This allows the vehicle to run.

[0004]

However, in such a conventional example, it is determined that the target gear ratio cannot be maintained even if the control valve of the hydraulic circuit is stuck or a control program malfunctions, and the gear ratio is forcibly reduced. Is set to the lowest Lo, there is a possibility that a sudden shift occurs during normal running and a large shift shock occurs.

[0005] As a countermeasure, when a sudden shift state of the continuously variable transmission is detected, the line pressure is reduced through a line pressure control valve for controlling the line pressure of the continuously variable transmission, thereby transmitting the continuously variable transmission. A system in which the capacity is reduced to prevent a shift shock during a sudden shift has been proposed by the present applicant (Japanese Patent Application No. 9-255113).

However, the duty solenoid used in the line pressure control valve is difficult to operate quickly when the outside air temperature is low. That is, since the viscous resistance increases due to the decrease in the oil temperature, the responsiveness of the solenoid decreases.
Therefore, in such a case, even if a sudden shift is detected and an attempt is made to reduce the line pressure, the line pressure does not decrease quickly.
The shift shock cannot be sufficiently reduced.

An object of the present invention is to solve such a problem by a method of driving a duty solenoid for line pressure control.

[0008]

According to a first aspect of the present invention, there is provided a speed change mechanism of a hydraulically driven continuously variable transmission, and a hydraulic pressure applied to the speed change mechanism such that a target speed ratio determined according to a driving state of a vehicle is obtained. And a line pressure control unit for supplying a line pressure adjusted to a predetermined pressure by duty-controlling a line pressure control solenoid to the shift control unit. A rapid shift detecting means for detecting a rapid shift state of the continuously variable transmission, a temperature detecting means for detecting an oil temperature or an outside air temperature, and reducing the line pressure based on a signal for detecting the rapid shift state. A line pressure for controlling the duty of the line pressure control solenoid and increasing the drive power of the line pressure control solenoid when the detected oil temperature or the outside air temperature is lower than a predetermined temperature; A lower control means, the providing.

In a second aspect based on the first aspect, the line pressure reduction control means increases the drive voltage of the solenoid.

In a third aspect based on the first aspect, the line pressure reduction control means increases a ratio of an over-excitation time to a drive cycle of the solenoid.

According to a fourth aspect of the present invention, there is provided a speed change mechanism of a hydraulically driven continuously variable transmission, and a speed change control means for controlling a hydraulic pressure applied to the speed change mechanism so as to attain a target speed ratio determined according to a driving state of the vehicle. A line pressure control means for supplying a line pressure adjusted to a predetermined pressure by duty-controlling a line pressure control solenoid to the speed change control means. A rapid shift detecting means for detecting a rapid shift state, a temperature detecting means for detecting an oil temperature or an outside air temperature, and a signal for detecting the rapid shift state,
A line pressure for increasing the drive frequency of the line pressure control solenoid when the detected oil temperature or the outside air temperature is lower than a predetermined temperature while duty controlling the line pressure control solenoid to reduce the line pressure. Reduction control means.

According to a fifth aspect of the present invention, in the first and fourth aspects, the line pressure reduction control means is provided when the oil temperature or the outside air temperature is lower than a predetermined temperature during normal line pressure control of the line pressure control solenoid. The control is performed such that the drive power of the solenoid is increased for a predetermined period.

[0013]

According to the first to third aspects of the present invention, when there is a sudden shift abnormality, the line pressure is reduced by the line pressure control solenoid to prevent the sudden shift, etc. When the temperature or outside temperature is low, more power is supplied to the solenoid for line pressure control than necessary to increase the calorific value,
Since the operability of the line pressure control solenoid is improved by increasing the temperature, even when the oil temperature or the outside air temperature is low,
The line pressure can be quickly reduced, and shift shocks associated with sudden shifts can be reduced.

According to the fourth aspect of the invention, by increasing the drive frequency of the line pressure control solenoid, it is possible to increase the amount of heat generated by setting the line pressure control solenoid to apply more power than necessary. .

According to the fifth aspect of the present invention, the operability of the line pressure control solenoid can be maintained in good condition by raising the temperature of the line pressure control solenoid during normal line pressure control in advance. If there is a gear change,
Rapid shifting can be accurately prevented, and shifting shock can be reduced.

[0016]

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

1 to 3 show an example in which the present invention is applied to a toroidal type continuously variable transmission 10. FIG. 1 is a schematic diagram of the continuously variable transmission 10, and FIGS. FIG.

In the continuously variable transmission 10, the input shaft 20 is connected to the engine 11 via a torque converter 12 having a lock-up mechanism L / U, while the output shaft 21 is connected to driving wheels (not shown). The speed change mechanism is shifted by the step motor 152 driving the speed change control valve 150 in response to a command from the speed change controller 1, and the line pressure PL supplied to the speed change mechanism is changed by the speed change controller 1.
Is controlled by a line pressure solenoid valve 528 in response to the

The shift control controller 1 is mainly composed of a microcomputer, and controls the throttle opening TVO from a throttle opening sensor 4 for detecting the throttle opening of the engine 11 and the output shaft 21 of the continuously variable transmission 10. Each signal such as an output shaft rotation speed No from the output shaft rotation sensor 3 for detecting the rotation speed, an input shaft rotation speed Nt from the input shaft rotation sensor 2 for detecting the rotation speed of the input shaft 20 of the continuously variable transmission 10, And a temperature sensor 50 for detecting the oil temperature of the continuously variable transmission 10 or the outside air temperature (for example, the temperature of the engine room).
Is input.

The shift control controller 1 includes a throttle opening TVO detected by the throttle opening sensor 4 and an output shaft rotation speed N of the continuously variable transmission 10 detected by the output shaft rotation sensor 3.
o, based on the input shaft rotation speed Nt of the continuously variable transmission 10 detected by the input shaft rotation sensor 2, a target gear ratio corresponding to the driving state of the vehicle is calculated, and the actual gear ratio of the continuously variable transmission 10 is A command is issued to the step motor 152 for a control amount STP (number of steps) that matches the target gear ratio.
A line pressure PL of a hydraulic control unit, which will be described later, is determined based on operating conditions such as the vehicle speed VSP and the input shaft rotation speed Nt, and a line pressure solenoid valve 528 is driven by duty control or the like, and a line pressure corresponding to the operating condition is determined. Control is performed to achieve PL. In this embodiment, a value obtained by multiplying the output shaft rotation speed No by a predetermined constant is used as the vehicle speed VSP.

Next, the hydraulic control unit shown in FIGS. 2 and 3 will be described.

The hydraulic pump 15 driven by the engine 11
Is controlled by a pressure regulator valve 502 disposed in a line pressure circuit 534 to a predetermined line pressure P.
L, the shift control valve 150, the forward / reverse switching valve 524
The drive of the transmission mechanism of the continuously variable transmission 10 is performed via the. The line pressure PL of the line pressure circuit 534 is
Is set so as not to exceed a predetermined upper limit.

The pressure regulator valve 502 is
The line pressure PL of the line pressure circuit 534 is regulated in accordance with the signal pressure PLsol from the line pressure solenoid valve 528 that is duty-controlled by the shift control controller 1, and the line pressure circuit 534 is drained to the torque converter pressure circuit 535. Thus, the line pressure PL is adjusted.

The signal pressure PLsol corresponding to the duty ratio of the line pressure solenoid valve 528 is input to the accumulator control valve 514 via the oil passage 601, and the accumulation control valve 514 causes the oil passage 54 to respond to the signal pressure PLsol.
By adjusting the oil pressure of 2, the pressure regulator 5
02 is controlled to set the line pressure PL to a predetermined value.

The pressure oil supplied to the torque converter pressure circuit 535 is supplied to the lock-up control valve 508 via a relief valve 512 for controlling the supplied oil pressure so as not to exceed the withstand pressure upper limit value of the torque converter 12.
The lubricating oil passage 38 of the transmission mechanism is formed downstream of the lock-up control valve 508 via a cooler 530. The lock-up control valve 5
08 is controlled based on the signal pressure from the lock-up solenoid valve 526 that is duty-controlled by the shift control controller 1, and engages or releases the lock-up clutch of the torque converter 12.

On the other hand, the line pressure PL of the line pressure circuit 534
Denotes a forward shift control valve 150 and a reverse shift control valve 522
The hydraulic oil is supplied from the transmission control valve 150 or the reverse transmission control valve 522 to the Hi-side oil passage 4 of the transmission mechanism in accordance with the traveling direction of the vehicle selected by the forward / reverse switching valve 524.
0 and supply to the Lo side oil passage 41.

As shown in FIGS. 1 and 3, the transmission mechanism of the continuously variable transmission 10 is composed of a half toroidal type first toroidal transmission section 22 and a second toroidal transmission section 24, and is composed of two sets. I / O disks 28, 32 and 29, 33
The pair of power rollers 30, 31 sandwiched between the input disk 28 and the output disk 29 of the first toroidal transmission unit 22 are in opposite directions to each other by a hydraulic servo cylinder provided at the base end. And are supported by trunnions 83 and 85 that can be rotated about an axis.

Hydraulic servo cylinders 87 and 89 for driving the trunnions 83 and 85 include a Hi-side oil chamber 516 (increased-side oil chamber) and a Lo-side oil chamber 518 defined on the left and right sides of the piston in the figure.
(Deceleration-side oil chambers), and the trunnions 83 and 85 are displaced in the axial direction according to the pressure difference between these oil chambers, and the tilt angles (tilt angles) of the power rollers 30 and 31 are changed according to the axial displacement. The gear ratio is continuously changed by changing the gear ratio.

For this reason, the hydraulic servo cylinders 87, 89
Are connected to the Hi-side oil chamber 516 communicating with the Hi-side oil passage 40 and Lo.
The arrangement of the Lo side oil chamber 518 communicating with the side oil passage 41 is reversed, and the trunnion 8 is moved in the direction in which the gear ratio becomes Hi.
The Hi-side oil chamber 516 that drives 3, 85
The hydraulic servo cylinder 87 of No. 3 is disposed on the right side of the piston in the figure, whereas the hydraulic servo cylinder 89 of the opposing trunnion 85 is disposed on the left side of the piston in the figure.

At the time of gear shifting, the hydraulic pressure in the Hi-side oil passage 40 and the Lo-side oil passage 41 is relatively changed, so that the pressure difference between the pistons of the hydraulic servo cylinders 87 and 89 (hereinafter referred to as differential pressure), Hi-side oil chamber 516 and Lo-side oil chamber 518
The trunnions 83, 85 are displaced synchronously in opposite axial directions by changing the differential pressure of the trunnions 83, 8
The power rollers 30, 31 tilt (turn around the trunnion axis) in response to the axial displacement of No. 5 so that the gear ratio can be continuously changed. Then, after reaching the predetermined gear ratio, the force applied to the piston in accordance with the pressure difference between the front and rear of the Hi-side oil chamber 516 and the Lo-side oil chamber 518 is applied to the trunnion 8.
3, 85 to support the torque reaction force (traction force) of the power rollers 30, 31 applied to them.

Therefore, the torque transmission capacity of the power rollers 30, 31 is determined based on the differential pressure between the hydraulic servo cylinders 87, 89 supporting the trunnions 83, 83. Note that the second toroidal transmission unit 24 is similarly configured.

In such a continuously variable transmission 10, the step motor 152, the shift control valve 150, and the precess cam 13
6, the gear ratio is controlled while operating the hydraulic servo, and the gear change control valve 150 is connected to the rack and pinion 1
The spool 158 is composed of a sleeve 156 connected to the stepping motor 152 via 52a and 154c, and a spool 158 that can be relatively displaced on the inner periphery of the sleeve 156.
Is driven by a precess cam 136 provided on any one of the trunnions 83, 85 of the first or second toroidal transmission units 22, 24, and a feedback link 142 following the precess cam 136.

For example, in the forward state, the forward / reverse switching valve 524 communicates the Hi-side oil passage 166 of the transmission control valve 152 with the Hi-side oil passage 40 of the transmission mechanism, while the transmission control valve 1
52 communicates with the Lo-side oil passage 168 of the transmission mechanism 52 and the Lo-side oil passage 41 of the transmission mechanism. At this time, when the target gear ratio is on the Hi side,
The step motor 152 drives the sleeve 156 downward in FIG. 3 to transfer the pressure oil of the line pressure circuit 534 to the Hi-side oil passage 16.
6 and 40, while connecting the Lo side oil passage 168 to the tank to drive the trunnion 83 to the left in the figure.
The opposing trunnion 85 is displaced rightward in the figure.

When the target gear ratio coincides with the actual gear ratio, the feedback link 142 oscillated in accordance with the rotation of the precess cam 136 drives the spool 158 downward, and the Hi-side oil passage 166 and the Lo-side oil passage 168 , The target gear ratio is maintained. At this time, the torque capacity that can be transmitted by the power rollers 30, 31, and 36, 37 is determined by the differential pressure between the Hi-side oil chamber 516 and the Lo-side oil chamber 518 of the hydraulic servo cylinders 87, 89.

The normal shift control performed by the shift controller 1 calculates a target gear ratio based on a map preset according to the throttle opening TVO (or the amount of depression of an accelerator pedal) and the vehicle speed VSP. In addition, feedback control is performed by predetermined PI control in addition to the above-described hydraulic servo.

On the other hand, in the transmission control controller 1, the target transmission ratio cannot be maintained due to damage to the hydraulic system, sticking of the valve, malfunction of the control program, etc., and the transmission ratio starts to rapidly change to the Lo side or the Hi side. In such a case, control as shown in FIG. 4 is performed to suppress the sudden shift and the shift shock.

The flowchart shown in FIG. 4 is executed every predetermined time, for example, every 10 msec.

First, in step S1, the input shaft speed N
t and the output shaft speed No. are read, and in step S2,
It is determined from the input shaft rotation speed Nt and the output shaft rotation speed No whether or not a rapid shift state has occurred.

In this case, the actual speed ratio RRTO is calculated from the ratio between the input shaft speed Nt and the output shaft speed No, and the amount of change in the actual speed ratio RRTO per unit time (for example, the control cycle dt) is determined by the actual speed ratio. The speed is calculated as φ, and when the absolute value of the actual speed φ exceeds a predetermined value, it is determined that the rapid shift state has occurred.

When it is determined that the rapid shift state has occurred, the process proceeds to step S3, and the line pressure PL of the line pressure circuit 534 is reduced to a predetermined minimum value PLmin in order to suppress the rapid shift.
Set to.

Next, in step S4, the continuously variable transmission 10
The oil temperature (or the outside air temperature) is read. If the oil temperature is equal to or higher than the predetermined temperature, the process proceeds to step S6, and if the oil temperature is equal to or lower than the predetermined low temperature, the process proceeds to step S7.

In step S6, the line pressure solenoid valve 528 is driven so that the line pressure PL of the line pressure circuit 534 becomes the minimum value PLmin. In this case, the line pressure solenoid valve 528 is driven by a driving method at a normal temperature. I do.

That is, the line pressure solenoid valve 528 is duty-driven by a signal of a reference duty value (valve opening time ratio) for obtaining the minimum value PLmin. FIG. 5 shows a voltage waveform of the duty signal, which is a waveform of a predetermined excitation time including an initial overexcitation time t1 (for facilitating initial operation) having a high voltage with respect to the driving cycle t0. The line pressure PL is reduced from the normal line pressure PL0 to the minimum value PLmin by the duty driving of the line pressure solenoid valve 528 as shown in FIG.

On the other hand, in step S7, the line pressure solenoid valve 528 is driven to set the line pressure PL of the line pressure circuit 534 to the minimum value PLmin. In this case, the line pressure solenoid valve 528 is turned on at the normal temperature in step S6. In contrast to the driving method at the time, the driving is performed by a driving method at a low temperature in which the driving power of the solenoid is increased.

That is, the driving frequency of the duty signal is changed as shown in FIG.
The line pressure solenoid valve 528 is switched to a frequency X1 which is increased by a predetermined amount with respect to the reference frequency X0 as shown in FIG. Drive.

With this configuration, the target gear ratio cannot be maintained due to damage to the hydraulic system, sticking of the valve, malfunction of the control program, and the like, and the actual gear ratio starts to change rapidly to the Lo or Hi side. When it is detected that the oil temperature (or the outside air temperature) is equal to or higher than a predetermined temperature, the line pressure PL of the line pressure circuit 534 is set to a predetermined minimum value PLmin by a duty signal at the normal temperature as shown in FIG. Thus, the line pressure solenoid valve 528 is driven. Therefore, the line pressure PL of the line pressure circuit 534 is changed from the line pressure PL0 during normal running to a predetermined minimum value PL as shown in FIG.
It will quickly drop to min.

The shift of the toroidal type continuously variable transmission is started based on the axial displacement of the trunnions 83 and 85 as described above. Also in the case, the Hi-side oil passage 40 and the Lo-side oil passage 4
1 communicates with the line pressure circuit 534 and the tank via the shift control valve 150 to change the speed.

Therefore, at this time, the line pressure circuit 534
Is reduced to a predetermined minimum value PLmin, the maximum value of the hydraulic pressure that can be applied to the pistons of the hydraulic servo cylinders 87 and 89 is limited, and a sudden shift can be prevented.

Further, as described above, the torque transmission capacity of the continuously variable transmission is determined by the differential pressure between the pistons opposing the traction force of the power rollers 30, 31, and is therefore applied to the pistons of the hydraulic servo cylinders 87, 89. By limiting the maximum value of the hydraulic pressure that can be applied, the torque transmission capacity of the continuously variable transmission is also reduced. For example, when performing a rapid shift (downshift) to the Lo side, if the torque transmission capacity of the continuously variable transmission is sufficiently large, the shift speed -φ to the Lo side is expressed by:
The magnitude of the shift shock (deceleration shock) is determined according to the magnitude of the inertia moment of the input system.

Accordingly, the torque transmission capacity of the continuously variable transmission is also reduced, so that the generated shift shock can be reduced. Also, the minimum line pressure PLmin at the time of sudden shifting
Is set so as to have the minimum torque transmission capacity that allows travel, so that even if an abnormality occurs in the hydraulic system or the shift control controller 1 that disables shifting, the necessary minimum torque is transmitted. By doing so, traveling can be enabled.

On the other hand, it was detected that the target gear ratio could not be maintained due to an abnormality in the hydraulic system or a malfunction of the control program, and that the actual gear ratio started to rapidly change to the Lo or Hi side. When the oil temperature (or outside temperature)
Is below a predetermined low temperature, the line pressure PL of the line pressure circuit 534 is generated by the duty signal at the time of low temperature as shown in FIG.
Is set to a predetermined minimum value PLmin, the line pressure solenoid valve 528 is driven.

When the oil temperature or the like is low, the temperature of the line pressure solenoid valve 528 is also low, and the line pressure solenoid valve 528
Because it is difficult to obtain a quick operation of the line pressure, if the line pressure solenoid valve 528 is driven in the same manner as at the normal temperature,
The response of the line pressure solenoid valve 528 is delayed (in this case, the reduction of the line pressure PL of the line pressure circuit 534 is delayed as shown in FIG. 8). , It is possible to ensure good operability of the line pressure solenoid valve 528.

That is, by increasing the drive frequency of the line pressure solenoid valve 528 and the ratio of the overexcitation time of the high voltage to the drive cycle, unnecessary power is given to increase the heat generation amount of the solenoid, and the line pressure solenoid is increased. The operability of the line pressure solenoid valve 528 is improved by increasing the temperature of the valve 528.

Therefore, the line pressure PL of the line pressure circuit 534 rapidly decreases from the line pressure PL0 during normal running to a predetermined minimum value PLmin as shown in FIG. Therefore, when the oil temperature or the like is low, the reduction of the line pressure PL is not delayed, and the shift shock generated in response to the sudden shift can be reduced, and as a result, fail-safe of the vehicle can be ensured.

FIG. 9 shows a second embodiment, in which the line pressure circuit 5 is operated when the oil temperature (or outside air temperature) is lower than a predetermined low temperature.
As a driving method of the line pressure solenoid valve 528 for lowering the line pressure PL of FIG.
4 is driven by a duty signal having 4 increased.

That is, as shown in FIG. 9, the line pressure solenoid valve 5 is driven by a duty signal in which the ratio of the overexcitation time t4 to the reference drive cycle t0 of the duty signal is sufficiently increased.
28 is duty-driven.

According to this, similarly to the first embodiment, when the oil temperature or the like is low, the line pressure PL of the line pressure circuit 534 is quickly reduced to the predetermined minimum value PLmin, and the shift shock is reduced. Can be reduced.

FIGS. 10 and 11 show a third embodiment.
As a driving method of the line pressure solenoid valve 528 for reducing the line pressure PL of the line pressure circuit 534 to the minimum value PLmin when the oil temperature (or the outside air temperature) is lower than a predetermined low temperature,
The drive voltage is increased, that is, the drive is performed by a duty signal supplied by turning on / off the overexcitation voltage.

In this case, as shown in FIG. 10, the drive circuit 60 is formed of a simple switch circuit, and the switch 61 is turned on and off at a predetermined frequency to generate a duty signal having a high drive voltage. The duty value can be set by the ratio of the ON time. In addition, as shown in FIG.
For non-overexcitation at normal temperature (normal drive voltage)
Alternatively, a predetermined frequency signal may be used only during non-excitation.

According to this, the shift shock can be reduced as in the first and second embodiments.

FIG. 12 shows a fourth embodiment. this is,
If the oil temperature (or the outside air temperature) is equal to or lower than a predetermined low temperature, the line pressure solenoid valve 528 is driven in advance by a low temperature driving method during normal line pressure control, that is, the driving power of the line pressure solenoid valve 528 is increased by a predetermined amount. Drive.

As shown in FIG. 12, in step S11, the oil temperature (or outside temperature) of the continuously variable transmission 10 is read, and in step S12, it is determined whether the oil temperature is equal to or lower than a predetermined temperature.

If the oil temperature is equal to or lower than the predetermined temperature, step S1
Proceeding to 3, the ratio of the over-excitation time of the duty signal of the line pressure solenoid valve 528 during normal line pressure control is changed.

In this case, the ratio of the over-excitation time to the non-over-excitation time is increased without changing the duty value for obtaining the normal line pressure PLO.

When the predetermined time has elapsed, in step S16, the duty signal is returned to the overexcitation time of the original duty signal, that is, the duty signal during normal line pressure control.

On the other hand, before the lapse of the predetermined time and when the oil temperature is equal to or higher than the predetermined temperature, the process proceeds to steps S17 and S18,
It is determined from the input shaft rotation speed Nt and the output shaft rotation speed No whether or not a rapid shift state has occurred.

If it is determined that the rapid shift state has occurred, control is performed in step S19 so that the line pressure PL of the line pressure circuit 534 is reduced to a predetermined minimum value PLmin.

In this case, the line pressure solenoid valve 528 may be driven by the driving method at the normal temperature in each of the above embodiments.

As described above, if the driving power of the line pressure solenoid valve 528 is increased in advance during normal line pressure control, the line pressure solenoid valve 528 can be driven even when the oil temperature (or outside temperature) is low. By raising the temperature of the valve 528, the operability of the line pressure solenoid valve 528 can be kept good, and therefore, a shift shock generated in response to a sudden shift can be reduced.

The control for changing the ratio of the overexcitation time of the duty signal may be returned to the original ratio of the overexcitation time when the oil temperature becomes equal to or higher than a predetermined temperature.

Each of the embodiments has been described with reference to an example in which the present invention is applied to a toroidal type continuously variable transmission. However, it is needless to say that the present invention can be applied to a belt type continuously variable transmission.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a continuously variable transmission according to an embodiment of the present invention.

FIG. 2 is a first half of a circuit diagram showing a hydraulic control unit of the continuously variable transmission.

FIG. 3 is a second half of a circuit diagram illustrating a hydraulic control unit of the continuously variable transmission.

FIG. 4 is a flowchart illustrating an example of control performed by a shift control controller.

FIG. 5 is a waveform diagram showing an example of a duty signal at a normal temperature.

FIG. 6 is a characteristic diagram of a line pressure.

FIG. 7 is a waveform diagram showing an example of a duty signal at a low temperature.

FIG. 8 is a characteristic diagram showing a delay in line pressure.

FIG. 9 is a waveform diagram illustrating an example of a duty signal at a low temperature according to the second embodiment.

FIG. 10 is a schematic circuit diagram of a third embodiment.

FIG. 11 is a waveform diagram illustrating an example of a duty signal at a low temperature.

FIG. 12 is a flowchart illustrating an example of control according to the fourth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Shift control controller 2 Input shaft rotation sensor 3 Output shaft rotation sensor 4 Throttle opening sensor 10 Continuously variable transmission 11 Engine 12 Torque converter 15 Hydraulic pump 20 Input shaft 21 Output shaft 22 First toroidal transmission section 24 Second toroidal transmission section 28, 32 Input disk 29, 33 Output disk 30, 31, 36, 37 Power roller 40, 166 Hi-side oil passage 41, 168 Lo-side oil passage 50 Temperature sensor 60 Drive circuit 83, 85 Trunnion 87, 89 Hydraulic servo cylinder 136 Precess cam 142 Feedback link 152 Step motor 150 Shift control valve 502 Pressure regulator valve 516 Hi-side oil chamber 518 Lo-side oil chamber 522 Reverse shift control valve 524 Forward / reverse switching valve 528 Line pressure solenoid valve 534 L Down pressure circuit

Claims (5)

[Claims] 1. A transmission mechanism of a hydraulically driven continuously variable transmission, transmission control means for controlling a hydraulic pressure applied to the transmission mechanism so as to attain a target transmission ratio determined according to an operation state of a vehicle, and line pressure control. And a line pressure control means for supplying a line pressure adjusted to a predetermined pressure by duty-controlling a solenoid for the transmission to the speed change control means. A rapid shift detecting means for detecting, a temperature detecting means for detecting oil temperature or outside air temperature, and a duty control of the line pressure control solenoid so as to reduce the line pressure based on a signal detecting the rapid shift state. And line pressure reduction control means for increasing drive power of the line pressure control solenoid when the detected oil temperature or outside air temperature is lower than a predetermined temperature. Hydraulic control device for a continuously variable transmission according to claim. 2. The hydraulic control device for a continuously variable transmission according to claim 1, wherein said line pressure reduction control means increases a drive voltage of a solenoid. 3. The hydraulic control device for a continuously variable transmission according to claim 1, wherein said line pressure decrease control means increases a ratio of an over-excitation time to a drive cycle of a solenoid. 4. A transmission mechanism for a hydraulically driven continuously variable transmission, transmission control means for controlling a hydraulic pressure applied to the transmission mechanism so as to attain a target transmission ratio determined according to a driving state of a vehicle, and line pressure control. And a line pressure control means for supplying a line pressure adjusted to a predetermined pressure by duty-controlling a solenoid for the transmission to the speed change control means. A rapid shift detecting means for detecting, a temperature detecting means for detecting oil temperature or outside air temperature, and a duty control of the line pressure control solenoid so as to reduce the line pressure based on a signal detecting the rapid shift state. And a line pressure decrease control means for increasing a drive frequency of the line pressure control solenoid when the detected oil temperature or the outside air temperature is lower than a predetermined temperature. Hydraulic control device for a continuously variable transmission, wherein the door. 5. The line pressure reduction control means controls to increase the drive power of the solenoid for a predetermined period when the oil temperature or the outside air temperature is lower than a predetermined temperature during normal line pressure control of the line pressure control solenoid. The hydraulic control device for a continuously variable transmission according to claim 1 or 4, wherein