JPH0564261B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a control device that electronically controls the speed change in a belt-type continuously variable transmission for a vehicle. Related to speed change control during driving.

[Conventional technology]

Regarding the speed change control of this type of continuously variable transmission, for example, there is a basic one shown in Japanese Patent Application Laid-Open No. 55-65755. It is shown that the speed change is controlled mechanically. However, in this shift control method, the shift speed, that is, the rate of change of the gear ratio, is mechanically determined by each gear ratio, primary pressure, etc., and the shift speed cannot be directly controlled, so there is a limit to responsiveness during transients, and it is difficult to converge. Overshoot and hunting are likely to occur. Therefore, in recent years,
It has been proposed to electrically process various information and requirements and electronically control the speed change of a continuously variable transmission by controlling the speed change.

Conventionally, regarding speed change control during coasting with the throttle fully closed in the above-mentioned continuously variable transmission, for example, Japanese Patent Application Laid-Open No. 1983
There is a prior art in Japanese Patent No. 208254, which states that in order to optimize the effectiveness of engine braking during deceleration, the speed change speed in this case is made a decreasing function of the vehicle speed.

[Problem to be solved by the invention]

By the way, since the above-mentioned prior art is intended for engine braking, it is naturally applicable only to a state where the engine and a drive system including a continuously variable transmission are connected by a clutch. Therefore, it cannot be applied to extremely low-speed driving after the clutch is disengaged to prevent engine stalling.

In the drive system of a continuously variable transmission, the clutch is disengaged to prevent engine stalling when the vehicle speed is below the set speed just before stopping, and the forward/reverse switching device is set to the neutral position. controlled to separate. When the vehicle runs at an extremely low speed after the clutch is disengaged, the primary pulley, which has a large moment of inertia, is rotated near the maximum gear ratio by the reverse driving force on the wheel side, producing a large torque reaction force.

That is, the moment of inertia of the primary pulley is Ip,
If the angular velocity is ω and the total gear ratio is n, then the torque reaction force is
T _B is calculated as T _B =Ip・ω・n. This torque reaction force T _B acts as a braking force, so when the throttle is repeatedly opened and closed, a large negative braking force acts next to the positive driving force as shown in Figure 4b, causing the vehicle to move forward and backward. This causes problems such as rocking and vibration.

In view of these points, the present invention provides a continuously variable transmission that electronically performs gear change control using simple open-loop control with the gear shift speed as the control target, and that can suppress back-and-forth rocking of the vehicle when driving at extremely low speeds. The purpose is to provide a control device for.

[Means to solve the problem]

In order to achieve this object, the present invention has a variable speed control valve 23 having control ports 23a, 23b and a spring 23c that operate to switch between an oil supply position and an oil drain position, and a flow rate restriction means 32 from a line pressure oil path 21.
The oil passage 26 that branches through the solenoid valve 28
The control unit 40 generates a signal hydraulic pressure according to an electric signal from the control unit 40, and this signal hydraulic pressure is introduced into the control port 23a of the speed change control valve 23 through an oil passage 34 to control the speed change.

The control unit 40 also includes means 45 for calculating the actual gear ratio based on the primary pulley rotation speed and secondary pulley rotation speed, and means 46 for determining the target gear ratio based on the throttle opening and the secondary pulley rotation speed.
, means 63 for determining extremely low speed running after clutch disengagement based on the secondary pulley rotation speed, throttle opening degree and engine rotation speed; and means 64 for reducing the target gear ratio by a predetermined time during extremely low speed driving.
, a means 48 for calculating a target gear change speed from the deviation between the corrected target gear ratio and the actual gear ratio, and a means 48 for determining a manipulated variable based on the relationship between the target gear change speed and the actual gear ratio, and generating an electrical signal of this manipulated variable. It is characterized by comprising a means 49 for outputting.

[Effect]

In the present invention having the above configuration, the continuously variable transmission basically converts an electric signal from the control unit 40 into a signal oil pressure by the solenoid valve 28, and introduces this signal oil pressure into the control port 23a of the variable speed control valve 23. It operates repeatedly in two positions: oil supply and oil drain. Then, the primary pressure is increased or decreased while changing the speed change speed according to the manipulated variable of the electric signal, and the speed change is controlled electronically.

In the control unit 40, a target gear ratio is set according to driving and running conditions, a target gear shift speed is calculated from the deviation between the target gear ratio and the actual gear ratio, and whether to shift up or down is determined based on the sign of the gear shift speed. be done. Then, the manipulated variables for upshifting and downshifting are set based on the target shift speed and actual gear ratio, respectively, and electrical signals of these manipulated variables are output for open-loop control.

Therefore, the shift is down or up depending on the operating amount of the electric signal, and at this time, the actual gear ratio quickly follows the target gear ratio while changing the gear shift speed with a slope according to the shift speed of the deviation between the two.
Moreover, it is smoothly converged. In this way, the shift speed is controlled in a stepless manner with good response over the entire shift range.

In addition, if the clutch is disengaged just before stopping during deceleration, and the drive system after the continuously variable transmission is disconnected from the engine, and the vehicle runs at an extremely low speed, the target gear ratio can be corrected by decreasing it for a predetermined period of time. , the gear is temporarily controlled to shift to a higher gear. Therefore, the braking force associated with the torque reaction force when the primary pulley is rotated by the wheels is reduced, and the back-and-forth rocking of the vehicle is suppressed, making it possible to improve ride comfort.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

Referring to FIG. 1, an outline of a continuously variable transmission and a hydraulic control system to which the present invention is applied will be explained. First, the drive system will be described. An engine 1 is connected to a main shaft 5 of a continuously variable transmission 4 via an electromagnetic clutch 2 and a forward/reverse switching device 3.

In the continuously variable transmission 4, a subshaft 6 is arranged parallel to a main shaft 5, a primary pulley 7 is provided on the main shaft 5, a secondary pulley 8 is provided on the subshaft 6, and a drive belt 11 is provided on both pulleys 7, 8. is wrapped.
Both pulleys 7 and 8 are connected to the fixed side and the hydraulic cylinders 9 and 1.
0 and a movable side that is movable in the axial direction, the pulley interval is variable, and the primary cylinder 9 has a larger pressure receiving area than the secondary cylinder 10. The belt is appropriately clamped by the line pressure of the secondary cylinder 10, and the ratio of the winding diameter of the drive belt 11 to the pulleys 7 and 8 is changed by the primary pressure of the primary cylinder 9, thereby continuously changing the speed.

Further, the subshaft 6 is connected to an output shaft 13 via a set of reduction gears 12 . and output shaft 1
3 is configured to be transmitted to drive wheels 16 via a final gear 14 and a differential gear 15.

Next, the hydraulic control system of the continuously variable transmission 4 will be explained. First, it has an oil pump 20 driven by an engine 1, and a line pressure oil passage 21 on the discharge side of the oil pump 20 is connected to a secondary cylinder 10,
It communicates with a line pressure control valve 22 and a speed change control valve 23 , and the speed change control valve 23 communicates with the primary cylinder 9 via an oil passage 24 .

The line pressure oil passage 21 further communicates with an oil passage 26 via an orifice 32a that restricts the flow rate, and a portion of the line pressure is taken out. The oil passage 26 is connected to the regulator valve 2
5, a constant regulator pressure PR is generated,
The oil passage 26 for this regulator pressure PR is connected to the line pressure control solenoid valve 27 via the orifice 32b.
will be communicated to. Also, the oil passage 26 has an orifice 32c.
The oil passage 35 has an orifice 32d.
The solenoid valve 28 is connected to the solenoid valve 28 for controlling the speed change speed.

The solenoid valve 27 is configured to drain oil when the duty signal from the control unit 40 is on, and the pulsed duty pressure Pd generated by the solenoid valve 27 is smoothed by the accumulator 30, and the line pressure is restored by the oil path 33. It is supplied to the control valve 22. The solenoid valve 28 has a similar configuration, and the pulsed duty pressure Pd generated by the solenoid valve 28 is directly supplied to the speed change control valve 23 through the oil passage 34.

The line pressure control valve 22 is configured to control the line pressure PL by a function of the initially set spring and the duty pressure Pd of the oil passage 33.

The speed change control valve 23 has one control port 23
A constant regulator pressure PR of the oil passage 35 acts on b, and a spring 23c acts on the other control port 23a.
is energized, and the duty pressure Pd of the oil passage 34 acts. Then, by turning on and off the duty pressure Pd, the line pressure oil passage 21 is repeatedly switched between an oil supply position where the line pressure oil passage 21 is connected to the oil passage 24 and an oil drain position where the oil passage 24 is connected to the drain oil passage 29. Therefore, it is possible to change the operating time of the two positions using the duty ratio D to change the flow rate of oil supply or drainage to the primary cylinder, and to control the speed change using the speed change speed di/dt.

Here, increase the duty ratio D to increase the duty pressure.
When the zero time of Pd is increased, the amount of oil supplied is greater than the amount of oil drained, and the shift is increased. On the other hand, if the duty ratio D is decreased and the constant pressure time of the duty pressure Pd is lengthened, the relationship of oil supply amount < oil displacement amount will be established, resulting in a downshift.

Referring to FIG. 2, the electronic control system will be explained.

First, the primary pulley rotation speed sensor 41 detects the primary pulley rotation speed Np, the secondary pulley rotation speed sensor 42 detects the secondary pulley rotation speed Ns, the engine rotation speed sensor 43 detects the engine rotation speed Ne, and the throttle opening θ.
It has a throttle opening sensor 44 that detects.
These sensor signals are input to a control unit 40.

The transmission speed control system in the control unit 40 will be explained. It has an actual gear ratio calculation means 45 which inputs the primary pulley rotation speed Np and the secondary pulley rotation speed Ns, and calculates the actual gear ratio i by i=Np/
Calculated by Ns. Further, the secondary pulley rotation speed Ns and the throttle opening θ are input to the target gear ratio search means 46, and the target gear ratio is is searched by a table of Ns-θ based on the shift pattern.

On the other hand, the throttle opening degree θ is input to the acceleration detecting means 51, and a change in the throttle opening degree is calculated by dθ/dt. This throttle opening change dθ/dt is input to the coefficient setting means 47, and a coefficient k is set as an increasing function of the throttle opening change dθ/dt.

The actual gear ratio i, the target gear ratio is at steady state, and the coefficient k are input to the gear shifting speed calculation means 48, and the target shifting speed di/dt is calculated by di/dt=k(is-i). do. Further, if the sign of the shift speed di/dt is positive, it is determined to be a downshift, and if it is negative, it is determined to be a shift up.

The target speed change speed di/dt and the actual speed change ratio i are further input into the duty ratio search means 49, and di/dt-
Duty ratio D as the manipulated variable from the table of i
Search for.

Here, the duty ratio D is D=f(di/dt,i)
Since the relationship is as follows, a table of ±di/dt and i is provided. The duty ratio D at which oil supply and oil drain are balanced is set to D=50%. Therefore, in the shift-up table of -di/dt and i, the duty ratio D is set at a value of 50% or more, for example, in an increasing relationship with respect to the absolute value of -di/dt. Further, in the table of di/dt and i for downshifting, the duty ratio D is set as a decreasing function with respect to di/dt at a value of 50% or less.

On the other hand, D with respect to i ensures an appropriate amount of primary oil at each gear ratio. In other words, the amount of primary oil supplied is small at low speeds, and the amount of primary oil supplied is larger at higher speeds. Therefore, when shifting up or down by the same gear ratio, the amount of oil supplied or drained is required to be larger as the speed increases.

Therefore, in the shift-up table, the duty ratio D is set as a decreasing function with respect to i, and in the shift-down table, the duty ratio D is set as an increasing function with respect to i. In both upshifting and downshifting, the higher the speed, the greater the amount of oil supplied and discharged according to the duty ratio D. Thus ±di/dt,i
The duty ratio D necessary for the speed change control and the primary oil amount is searched using the three-dimensional table of and D.

Then, the electric signal of the duty ratio D searched by the duty ratio search means 49 is outputted to the solenoid valve 28 via the drive means 50.

Next, the line pressure control system will be explained. First, the throttle opening θ and the engine speed Ne are input to the engine torque setting means 52, and θ−Ne
Determine the engine torque T from the table. In addition, the actual gear ratio i is input to the required line pressure setting means 53, and the required line pressure per unit torque is determined at each gear ratio.
Configure PLu. These engine torque T and required line pressure PLu per unit torque are input to the target line pressure calculation means 54, and the target line pressure PLt is calculated as follows:
Calculated by PLt=PLu・T.

This target line pressure PLt is input to the duty ratio setting means 55, and a duty ratio D corresponding to the target line pressure PLt is set. Then, this electric signal with the duty ratio D is outputted to the solenoid valve 27 via the driving means 56.

In the above control system, as a shift control system during extremely low speed travel, there is provided extremely low speed travel determining means 60 to which the secondary pulley rotation speed Ns is input. and the fourth
As shown in Figure a, the disconnection vehicle speed of electromagnetic clutch 2 is
Extremely low speed driving is determined when the vehicle speed is V2 or lower and the vehicle speed at which the maximum gear ratio is reached is V1 or higher. Also, throttle opening θ
The engine has coasting determining means 61 for determining that the engine speed Ne is small, and deceleration determining means 62 for determining that the engine speed Ne has decreased. These judgment signals are input to the shift-up judgment means 63, and if it is judged that the vehicle is running at an extremely low speed after the clutch is disengaged due to the clutch being disengaged, the throttle opening is small, and the engine speed is decreasing, the shift-up is corrected.

Further, target gear ratio correction means 46 is attached to the output side of the target gear ratio search means 46, and the coefficient setting means 4
Coefficient correction means 65 is attached to the output side of 7.
Then, the target gear ratio IS is determined by the shift up correction signal.
and coefficient k are each corrected by a predetermined time t.

That is, regarding the correction of the target gear ratio is, the product of a constant α determined as a function of line pressure in the case of the maximum gear ratio iLOW and the vehicle speed V at that time is determined. Then, the target gear ratio is is corrected to decrease by is=iLOW-α·V. Further, the correction time t is determined as an increasing function of the vehicle speed V.

Regarding the correction of the coefficient k, a constant β (β<1) is used, and the correction is performed to decrease it by k·β. Further, β is determined as a decreasing function of the vehicle speed V.

Next, the operation of this embodiment will be explained.

First, the oil pump 2 is activated by the operation of the engine 1.
1 is driven, the line pressure PL of the oil passage 21 is supplied only to the secondary cylinder 10, and the gear ratio is set to the maximum low gear. At this time, the oil at the line pressure PL is taken out into the oil passage 26 with the flow rate restricted by the orifice 32a, and the pressure is regulated by the regulator valve 25 to generate the regulator pressure PR.
is guided to solenoid valves 27, 28, etc., making it possible to electronically control line pressure and speed change.

Further, signals of the primary pulley rotation speed Np, the secondary pulley rotation speed Ns, the throttle opening θ, and the engine rotation speed Ne are input to the control unit 40 and processed.

Therefore, in the line pressure control system, the actual gear ratio i is calculated from the primary pulley rotation speed Np and the secondary pulley rotation speed Ns, and the engine torque T is set based on the engine rotation speed Ne and the throttle opening θ. Further, the required line pressure PLu per unit torque is set according to the actual speed ratio i, the target line pressure PLt is calculated from these, and the duty ratio D is set according to this target line pressure PLt.

Therefore, if the engine torque T increases during starting or acceleration, the target line pressure PLt will be calculated to be large.
A signal with a large duty ratio D is sent to the solenoid valve 27.
Output to. Therefore, the amount of oil discharged from the solenoid valve 27 increases and is converted to a lower duty pressure Pd.
This duty pressure Pd is introduced into the line pressure control valve 22, and the line pressure PL is controlled to be high.

Furthermore, as the vehicle speed increases, shift control is started and the actual gear ratio i becomes smaller, and when the engine torque T also becomes smaller, the duty ratio D becomes smaller. Therefore, in the solenoid valve 27, the duty pressure Pd increases as the amount of discharged oil decreases, and in the line pressure control valve 22, the line pressure PL is sequentially controlled to be lower.

In this way, the line pressure PL is continuously electronically controlled to be lower as the actual gear ratio i is smaller, and higher as the engine torque T is larger. By constantly introducing this line pressure PL into the secondary cylinder 10 and acting on it, the minimum necessary pulley pressing force that does not cause belt slip is always applied.

On the other hand, in the speed change control system, the throttle opening θ
The target gear ratio is determined by the and secondary pulley rotation speed Ns.
is is set. Then, the target gear speed di/
dt is calculated, and the duty ratio D is set based on the relationship between the target speed change speed di/dt and the actual speed change ratio i.
The electric signal of the duty ratio D is output to the solenoid valve 28 and converted into duty pressure Pd, and this duty pressure Pd is introduced into the control port 23a of the speed change control valve 23, and lubrication is performed by turning on and off the duty pressure Pd. Operates repeatedly in two positions for draining oil.

At this point, by decreasing the vehicle speed or stepping on the accelerator,
When it reaches i, the duty ratio D is set to D<50%. For this reason, the shift speed control valve 23 operates for a longer time in the oil draining position, and the primary cylinder 9 is drained of more oil than it is filled with oil, and the primary pressure Pp decreases, resulting in a downshift.

At this time, the greater the shift speed di/dt resulting from the deviation between the target gear ratio is and the actual gear ratio i, the smaller the value of the duty ratio D is set, and the amount of oil discharged is varied by the duty ratio D. Therefore, the actual gear ratio i, which is smaller than the target gear ratio is, which is set to a larger value, follows the target gear ratio is with a slope according to the gear shift speed di/dt. In other words, if the initial deviation is large, the actual gear ratio i will quickly follow the shifting speed with a large slope, and as the deviation gradually decreases, the slope will become smaller, and the shifting speed will slow down and shift smoothly so that overshoot does not occur. Converge.

Conversely, if is<i due to an increase in vehicle speed or release of the accelerator, the duty ratio D is set to D>50%. Therefore, the shift speed control valve 23 operates for a longer time in the refueling position, and the primary cylinder 9
is filled with more oil than the drained oil, increasing the primary pressure Pp and shifting up. In this case, the greater the absolute value of -di/dt, the greater the value of the duty ratio D is set, and the amount of oil supplied is varied by the duty ratio D. Then, the actual gear ratio i, which is larger than the target gear ratio is set to a smaller value, quickly follows the gear change speed by changing the gear change speed and converges smoothly, as described above.

Also, both upshifting and downshifting,
According to the duty ratio D according to the actual gear ratio i, the higher the speed, the more oil is supplied and drained, and the primary cylinder 9 is always maintained.
becomes the oil amount commensurate with the actual gear ratio i.

In this way, the target shift speed di/dt is calculated according to the driving and running conditions, and an electric signal with a duty ratio D based on the shift speed di/dt and the actual speed ratio i is output to perform open loop control. Then, the shift speed di/dt is varied as a control target by the duty signal, and the shift is controlled by shifting up or down over the entire shift range.

Next, the shift control during extremely low speed running after the clutch is disengaged will be explained using the flowchart shown in FIG.

First, when the accelerator is depressed while the vehicle is substantially stationary, the electromagnetic clutch 2 is automatically connected by the clutch current, and the power from the engine 1 is input to the continuously variable transmission 4, causing the vehicle to travel. And set vehicle speed V2 just before stopping
If the following conditions occur, the system will automatically disconnect to prevent engine stalling. In addition, after the clutch is disengaged, the vehicle will start with engine 1.
Meanwhile, the drive system after the continuously variable transmission 4 is disconnected, and the vehicle further coasts at an extremely low speed. At this time, the continuously variable transmission 4 is still in the process of shifting, so as the vehicle speed decreases, downshift control is performed to further move toward the maximum gear ratio LOW.

Therefore, in step S1, the vehicle speed V according to the rotation speed of the secondary pulley is checked, and when the electromagnetic clutch 2 is disengaged when the vehicle speed is below the set vehicle speed V2, the throttle opening degree θ is checked in step S2, and if the accelerator is fully closed, the engine is stopped in step S3. The engine speed Ne is checked, and if the engine speed Ne decreases, it is determined that the engine is running at a very low speed after the clutch is disengaged. Then, the process proceeds to step S4, where the target gear ratio IS is corrected to decrease.
In step S5, the coefficient k is also corrected to decrease. Thereafter, in step S6, the corrected target gear ratio (iLOW-
α·V) and coefficients k·β to calculate the shift speed di/dt and perform shift control.

For this reason, the shift speed di/
The sign of dt becomes negative and its value also becomes small,
Shift-up control is performed at a slow speed change as shown by the broken line in FIG. 4a. Therefore, the total gear ratio n when the primary pulley 7, which has a large moment of inertia, is rotated by the wheel becomes small, and therefore the braking force T _B accompanying the torque reaction force decreases as shown by the broken line in Fig. 4b. The back and forth rocking of the vehicle is suppressed.

At this time, the time is checked in step S7, and when the predetermined time t has elapsed, the process proceeds to step S8, where the target gear ratio is is fixed at the maximum gear ratio iLOW. Therefore, after the predetermined time t, the speed change is controlled to reliably return to the maximum speed ratio iLOW. Note that if any one of the three conditions is no longer satisfied even within the predetermined time t, the maximum gear ratio ratio iLOW is returned to.

Here, the constants α, β, and time t are set in relation to the vehicle speed V, so that the larger the vehicle speed V is, the longer the time is corrected, and the shift is gradually increased at a slower speed. Further, as α·V increases, the gear ratio is changed to a smaller one.

Although one embodiment of the present invention has been described above,
It can also be applied when the forward/reverse switching device is provided with a neutral position and the drive system is disconnected.

〔Effect of the invention〕

As explained above, according to the present invention, in a control device that electronically controls speed change in a continuously variable transmission,
The control unit is configured to calculate a target gear shift speed based on the deviation between the target gear ratio and the actual gear ratio, and to perform open loop control by setting the manipulated variable of the electrical signal based on the target gear shift speed and the actual gear ratio. Therefore, it is possible to directly control the speed change so that it follows quickly and converges smoothly. This improves responsiveness during transients and reduces overshoot. Control is also much easier.

Since the signal oil pressure generated by the electric signal is introduced into the control port of the speed change control valve and operates repeatedly between the two positions of oil supply and oil drain, the primary pressure can be increased or decreased while changing the speed change depending on the amount of operation of the electric signal. Therefore, the speed change speed can be controlled accurately.

When the vehicle is running at very low speed after the clutch is disengaged, the gear ratio is controlled to be temporarily reduced, so that the braking force required when the wheels rotate the primary pulley, which has a large moment of inertia, can be effectively reduced.
Therefore, the longitudinal vibration of the vehicle is reduced, and ride comfort is improved.

Since various correction factors are set in relation to the vehicle speed, the braking force can be reduced appropriately depending on the driving condition.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the hydraulic control system of the continuously variable transmission and control device of the present invention, and FIG. 2 is a block diagram showing an embodiment of the electrical control system of the control device of the continuously variable transmission of the present invention. 3 is a flowchart showing shift control during extremely low speed running after clutch disengagement, FIG. 4a shows the shift characteristics, and FIG. 4b shows torque fluctuations. 2...Electromagnetic clutch, 4...Continuously variable transmission, 5
... Main shaft, 11 ... Drive belt, 6 ... Subshaft, 7
...Primary pulley, 8...Secondary pulley, 9...Primary cylinder, 10...Secondary cylinder, 21, 26...Oil passage, 22...Line pressure control valve, 23...Shift speed control valve, 23
a, 23b... Control port, 23c... Spring, 32a... Orifice, 28... Solenoid valve, 40... Control unit, 45... Actual gear ratio calculating means, 46... Target gear ratio searching means, 48... …
Shift speed calculation means, 49... Duty ratio search means, 63... Shift up determination means, 64... Target gear ratio correction means.

Claims (1)

[Claims] 1. The engine is connected to the main shaft via a clutch that automatically connects and disconnects depending on the running condition, and the main shaft is provided with a primary pulley with variable pulley spacing,
A secondary pulley with variable pulley spacing is installed on the sub-shaft on the wheel side, which is arranged parallel to the main shaft. A drive belt is wound between both pulleys, and the line pressure is controlled by controlling the line pressure in the oil path from the hydraulic source. A line pressure control valve is provided that supplies pressure to the cylinder of the secondary pulley to apply a pulley pressing force, and a variable speed control valve that supplies and drains line pressure to the oil path to the cylinder of the primary pulley to change the primary pressure. In a continuously variable transmission which changes the ratio of the winding diameter of the drive belt to both pulleys using the primary pressure and continuously changes the speed, the speed change control valve 23 is controlled to switch between an oil supply position and an oil drain position. An oil passage 26, which has ports 23a, 23b and a spring 23c, and branches from the line pressure oil passage 21 via a flow rate restriction means 32a, communicates with a solenoid valve 28 and outputs a signal oil pressure according to an electric signal from a control unit 40. This signal oil pressure is introduced into the control port 23a of the speed change control valve 23 through the oil path 34 to control the speed change, and the control unit 40 controls the actual speed change based on the primary pulley rotation speed and the secondary pulley rotation speed. Means 45 for calculating the ratio, and means 46 for determining the target gear ratio based on the throttle opening and the rotation speed of the secondary pulley.
, means 63 for determining extremely low speed running after clutch disengagement based on the secondary pulley rotational speed, throttle opening degree and engine rotational speed, and means 64 for reducing and correcting the target gear ratio by a predetermined time during extremely low speed driving.
, a means 48 for calculating a target gear change speed from the deviation between the corrected target gear ratio and the actual gear ratio, and a means 48 for determining a manipulated variable based on the relationship between the target gear change speed and the actual gear ratio, and generating an electrical signal of this manipulated variable. 1. A control device for a continuously variable transmission, comprising: means 49 for outputting.