JP2575029B2 - Clutch control method for continuously variable transmission - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clutch control method for a continuously variable transmission, and in particular, initializes a filter in a normal start mode when a specific limitation condition is satisfied, and controls a clutch pressure. The present invention relates to a clutch control method for a continuously variable transmission, in which the clutch switching operation is smoothly performed at a low temperature by smoothly reducing the engine speed to prevent engine stall.

[Conventional technology]

In a vehicle, a transmission is interposed between an internal combustion engine and drive wheels. This transmission changes the driving force of the drive wheels and the traveling speed in accordance with the traveling conditions of the vehicle that vary over a wide range, thereby sufficiently exhibiting the performance of the internal combustion engine. The transmission is formed between both pulley parts of a pulley having a fixed pulley part fixed to the rotating shaft and a movable pulley part attached to the rotating shaft so as to be able to approach and separate from the fixed pulley part. There is a continuously variable transmission that changes the radius of rotation of a belt wound around a pulley by reducing and increasing the width of a groove portion, transmits power, and changes a gear ratio (belt ratio). Examples of this continuously variable transmission include, for example, JP-A-57-186656, JP-A-59-43249, JP-A-59-77159, and JP-A-59-77159.
No. 61-233256.

[Problems to be solved by the invention]

By the way, in the conventional clutch control method of the continuously variable transmission, the engine torque (TRQEN) is determined from the first table based on the throttle opening in the normal start mode, and the engine torque (TRQEN) is first-ordered by a feedforward filter. Find the filter engine torque (TRQENF) in addition to the delay element. Then, RATC (belt ratio) is added to the filter engine torque (TRQENF).
XKA (proportional gain) is multiplied to calculate a feedforward amount that is converted into a clutch pressure value at which the clutch can transmit a predetermined torque.

However, when the throttle opening is suddenly closed in the normal start mode, a response delay occurs in the filter engine torque (TRQENF), and when the engine torque decreases, the feedforward amount remains, and the remaining feedforward amount Is controlled to increase the clutch pressure.

For this reason, when the oil temperature of the continuously variable transmission is low and the viscosity of the oil is high and low, the clutch pressure is released slowly even if the throttle opening is suddenly closed.

[Object of the invention]

Therefore, an object of the present invention is to eliminate the above-mentioned disadvantages and to initialize the feedforward filter by the control unit in the normal start mode when the continuously variable transmission satisfies a specific limitation condition, and to set the clutch based on the feedforward amount. By controlling to reduce the pressure rapidly, the clutch pressure is rapidly reduced by initializing the filter, the clutch switching operation can be performed smoothly at low temperature, and the occurrence of engine stall can be reliably prevented. An object of the present invention is to realize a clutch control method for a variable transmission.

[Means for solving the problem]

In order to achieve this object, the present invention relates to a method for reducing the width of a groove between a fixed pulley portion and a movable pulley portion attached to and detachable from the fixed pulley portion by reducing the groove width between the two pulley portions. In a clutch control method for a continuously variable transmission that performs speed change control to reduce or increase the radius of rotation of a belt wound around a vehicle and change gear ratio, a request for multiplying an engine torque value determined by a throttle opening detection signal by a proportional gain is made. A control unit for calculating a feedforward amount for clutch pressure is provided, and in a normal start mode when the continuously variable transmission satisfies a specific limitation condition, the control unit initializes a feedforward filter during the normal start mode, It is characterized in that control is performed so as to sharply reduce the clutch pressure due to the forward amount.

[Action]

According to the above-described invention, in the normal start mode when the continuously variable transmission satisfies a specific limitation condition, the control unit initializes the feedforward filter,
Control is performed to rapidly reduce the clutch pressure due to the feedforward amount, smoothly performing the clutch switching operation at low temperatures, and reliably preventing the occurrence of engine stall.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1 to 5 show an embodiment of the present invention. 4 and 5, reference numeral 2 denotes a belt-driven continuously variable transmission.
2A is a belt, 4 is a driving pulley, 6 is a driving fixed pulley piece, 8 is a driving movable pulley piece, 10 is a driven pulley, 12 is a driven fixed pulley piece, and 14 is a driven pulley. It is a movable pulley piece. As shown in FIG. 4, the drive-side pulley 4 is a drive-side fixed pulley piece 6 that is fixed to a rotating shaft 16.
And a drive-side movable pulley piece 8 attached to the rotary shaft 16 so as to be movable and non-rotatable in the axial direction of the rotary shaft 16. The driven pulley 10 also has a driven-side fixed pulley piece 12 and a driven-side movable pulley piece 14, similarly to the drive-side pulley 4.

First and second housings 18 and 20 are mounted on the driving-side movable pulley piece 8 and the driven-side movable pulley piece 14, respectively, and first and second hydraulic chambers 22 and 24 are formed respectively. You. At this time, the second hydraulic chamber 24 is provided in the second hydraulic chamber 24 on the driven side.
An urging means 26 comprising a spring or the like for urging the second housing 20 in the direction in which the second housing 20 is enlarged is provided.

An oil pump 28 is provided on the rotating shaft 16. The oil pump 28 communicates with the first and second hydraulic chambers 22 and 24 via first and second oil passages 30 and 32, respectively. Is provided with a primary pressure control valve 34 as a shift control valve for controlling a primary pressure as an input shaft sheave pressure. Further, a line pressure (generally 5 to 25 kg / cm ² ) is applied to the first oil passage 30 on the oil pump 28 side of the primary pressure control valve 34 by a third oil passage 36 at a constant pressure (4.0 to 5.0 kg / c).
m ² ), a primary pressure control first three-way solenoid valve 42 is connected to the primary pressure control valve 34 via a fourth oil passage 40.

In the middle of the second oil passage 32, a line pressure control valve 44 having a relief valve function for controlling a line pressure as a pump pressure is provided.
Through a fifth oil passage 46, and the line pressure control valve
The second oil passage 48 communicates with a second three-way solenoid valve 50 for line pressure control through a sixth oil passage 48.

Further, a clutch pressure control valve 52 for controlling a clutch pressure is communicated with a seventh oil passage 54 in the middle of the second oil passage 32 on the second hydraulic chamber 24 side of the portion where the line pressure control valve 44 communicates. An eighth oil passage 56 communicates with the clutch pressure control valve 52 with a third three-way solenoid valve 58 for clutch pressure control.

The primary pressure control valve 34, the primary pressure control first solenoid valve 42, the constant pressure control valve 38, the sixth oil passage 4
8. The second solenoid valve 50 for line pressure control and the clutch pressure control valve 52 are connected to each other by a ninth oil passage 60.

The clutch pressure control valve 52 is connected to the hydraulic
While communicating with the oil passage 64, a pressure sensor 68 is provided in the middle of the tenth oil passage 64 by an eleventh oil passage 66.
To communicate. The pressure sensor 68 can directly detect the hydraulic pressure when controlling the clutch pressure in the hold and start modes and the like, and contributes when instructing the detected hydraulic pressure to be the target clutch pressure. In the drive mode, the clutch pressure becomes equal to the line pressure, which also contributes to line pressure control.

An input shaft rotation detection gear 70 is provided outside the first housing 18, and a first rotation detector 72 on the input shaft side is provided near an outer peripheral portion of the input shaft rotation detection gear 70. Further, an output shaft rotation detection gear 74 is provided outside the second housing 20, and a second rotation detector 76 on the output shaft side is provided near an outer peripheral portion of the output shaft rotation detection gear 74. Then, detection signals from the first rotation detector 72 and the second rotation detector 76 are output to a control unit 82, which will be described later, to grasp the engine speed and the belt ratio.

The hydraulic starting clutch 62 is provided with an output transmission gear 78, and a third rotation detector 80 for detecting the rotation of the final output shaft is provided near the outer periphery of the gear 78. That is, the third rotation detector 80 detects the rotation of the reduction gear, the differential, the drive shaft, and the final output shaft directly connected to the tire, and can detect the vehicle speed. Further, the second rotation detector 76 and the third
The rotation detector 80 can also detect rotation around the hydraulic start clutch 62, which contributes to the detection of the clutch slip amount.

Further, control for inputting various conditions such as the throttle opening of a carburetor (not shown) of the vehicle and the engine rotation and the vehicle speed from the first to third rotation detectors 72, 76, 80, and changing the duty ratio to perform shift control. The control unit 82 controls the first three-way solenoid valve 42 for primary pressure control and the constant pressure control valve 38, the second three-way solenoid valve 50 for line pressure control, and the third three-way solenoid valve 58 for clutch pressure control. It is configured to control the pressure sensor 68 while controlling the opening / closing operation. The various signals input to the control unit 82 and the functions of the input signals will be described in detail. The following signals can be obtained: a shift lever position detection signal... P, R, N, D, L, etc. Required line pressure, ratio, clutch control, carburetor throttle opening detection signal …… Detects engine torque from memory previously input into the program, determines target ratio or target engine speed, carburetor idle position detection signal Accuracy in correction and control of the carburetor throttle opening sensor and accelerator pedal signal Accelerator pedal signal Detects the driver's will based on the depression of the accelerator pedal, and determines the control direction when driving or starting, and a brake signal. Detects whether the brake pedal has been depressed, determines the control direction, such as disengaging the clutch. Mode option signal …… Sports (or economy) performance of the vehicle
There is an option to use it.

84 is a piston of the hydraulic start clutch 62, 86 is an annular spring, 88 is a first pressure plate, 90 is a friction plate, 92 is a second pressure plate, 94 is an oil pan, and 96 is an oil filter.

The control unit 82 generally multiplies an engine torque value determined by a throttle opening detection signal in a normal start mode by a proportional gain to calculate a feedforward amount for a required clutch pressure.

Further, the control unit 82 initializes a feedforward first filter (204), which will be described later, in a normal start mode when the continuously variable transmission 2 satisfies a specific limitation condition, and controls the clutch pressure based on the feedforward amount. Is controlled so as to sharply decrease. As the specific limiting condition, for example, a condition that the oil temperature of the continuously variable transmission 2 is 30 degrees or less, the throttle opening is 20% or less, and the amount of change in the throttle opening is greater than -5%. Is set.

The formula of the feedforward first filter (204) for actually performing the process of initializing the feedforward first filter (204) is given by: TRQENF (n + 1) = − BFFC ×× TRQEN (n) −TRQENF (N)｝ + TRQEN (n). By setting TRQENF (0) = 0, the first filter (204) is initialized. Further, the first filter (204) has a first-order lag element, and as shown in FIG. 3, the filter engine torque (TRQEN) changes with the step change of the engine torque (TRQEN).
F). This response speed is determined by the coefficient of BFFC.

The response of the step of the first filter (204) is TRQENF (n) = − BFFC × {TRQEN (n−1) −TRQENF (n−1)} + TRQEN (n−
1) where TRQENF (n) = NF (n) TRQEN (n) = N (n) If BFFC = B, then when n = 1, NF (1) = − B · {N (0) −NF (0)} + N (0) = B · NF (0) + (1−B) N (0) When n = 2, NF (2) = − B · {N (1) ) −NF (1)｝ + N (1) = B {B · NF (0) + (1−B) N (0)} + (1−B) N (1) = B ² · NF (0) + (1−B) ｛B ・ N (0) + N (1)｝ When n = 3, NF (3) = − B ｛{N (1) -NF (1)｝ + N (1) = B ｛B · NF (0) + (1 -B) N (0)} + (1-B) N (1) = B 3 · NF (0) + (1-B) {B 2 · N (0) + B · N (1) + N (2)｝ When n = n, NF (n) = B ⁿ · NF (0) + (1-B)） B ⁿ⁻¹ · N (0) + B ⁿ⁻² · N (1) +... B · N (n−2) + The (n-1)}.

here, NF (0) = 0, N (0) = 0, N
Assuming that (1) = N (n) =... = N (n−1) = 1, NF (n) = (1-B) {B ⁿ⁻¹ + B ⁿ⁻² +. , B <1, NF (n) = (1−B) × 1 / (1−B) = 1 (∵n = ∞) Therefore, NF (n) converges to 1.

Also, NF (0) = 0, N (0) = 0, N
If (1) = N (2) =... = N (n−1) = 1, then NF (n) = (1−B) · B ⁿ⁻¹ , and if B <1, NF ( n) = 0 (∵n = ∞) Therefore, NF (n) converges to 0.

 Next, the operation will be described.

As shown in FIG. 5, the belt-driven continuously variable transmission 2 includes an oil pump 28 located on the rotating shaft 16 and a rotating shaft 16.
The oil is absorbed through an oil filter 96 from an oil pan 94 at the bottom of the transmission. The line pressure, which is the pump pressure, is controlled by the line pressure control valve 44.If the amount of leakage from the line pressure control valve 44, that is, the escape amount of the line pressure control valve 44, is large, the line pressure becomes low,
Conversely, if it is less, the line pressure will be higher.

Further, the line pressure control valve 44 has a shift control characteristic of changing the line pressure in each of a full low state, a full overtop state, and a fixed ratio state to perform three-stage control.

The operation of the line pressure control valve 44 is a dedicated second three-way solenoid valve.
The second three-way solenoid valve 50
The line pressure control valve 44 operates following the above operation, and the second three-way solenoid valve 50 is controlled at a constant frequency duty ratio. That is, when the duty ratio is 0%, the second three-way solenoid valve 50 does not operate at all, the output side is connected to the atmosphere side, and the output oil pressure becomes zero. Also, duty ratio 100
% Means that the second three-way solenoid valve 50 is operated, the output side is connected to the atmosphere side, the maximum output oil pressure is the same as the control pressure, and the output oil pressure is varied according to the duty ratio. Therefore, the fifth
As shown in the figure, the characteristics of the second three-way solenoid valve 50 are substantially linear, and the line pressure control valve 44 can be operated in an analog manner, and the duty ratio of the second three-way solenoid valve 50 can be arbitrarily set. It can be varied to control the line pressure.
The operation of the second three-way solenoid valve 50 is controlled by the control unit 82.

The primary pressure for shifting control is the primary pressure control valve.
The operation of the primary pressure control valve 34 is controlled by a dedicated first three-way solenoid valve 42, similarly to the line pressure control valve 44. This first three-way solenoid valve 42
Is used to conduct the primary pressure to the line pressure or to conduct the primary pressure to the atmosphere side, and to conduct the line pressure to shift the belt ratio to the full overdrive side, or to conduct to the atmosphere side to the full low side. It is to shift to.

The clutch pressure control valve 52 for controlling the clutch pressure is connected to the line pressure side when the maximum clutch pressure is required, and is connected to the atmosphere side when the minimum clutch pressure is required. The clutch pressure control valve 52 is also connected to the line pressure control valve 44.
Like the primary pressure control valve 34 and the primary pressure control valve 34, the operation is controlled by a dedicated third three-way solenoid valve 58, and the description is omitted.
The clutch pressure varies within a range from a minimum atmospheric pressure (zero) to a maximum line pressure.

There are four basic patterns for controlling the clutch pressure, which will be described later. These basic patterns are as follows: (1) Neutral mode When the shift position is N or P and the clutch is completely disengaged, the clutch pressure becomes the minimum pressure (zero). (2) Hold mode: When the shift position is D or R and the throttle is released and there is no driving intention, or when it is desired to decelerate during running and cut off the engine torque, the clutch pressure is low enough to make the clutch contact ( 3), start mode: When the clutch is to be engaged again at the time of starting or after the clutch is disengaged, the clutch pressure is adjusted according to the engine generated torque (clutch input torque) that prevents the engine from rising and allows the vehicle to operate smoothly. Appropriate level (4), drive mode ..... If the fully coupled, There are four high-level clutch pressure having a margin to withstand sufficiently the engine torque. The basic pattern (1) is performed by a dedicated switching valve (not shown) interlocked with the shift operation, and the other (2), (3), and (4) are first to third three-way solenoid valves by the control unit 82. It is performed by the duty ratio control of 42, 50 and 58. Particularly in the state (4), the seventh oil passage 54 and the tenth oil passage 64 are operated by the clutch pressure control valve 52.
To make the maximum pressure generation state, and the clutch pressure becomes the same as the line pressure.

Further, the primary pressure control valve 34 and the line pressure control valve 4
4, and the clutch pressure control valve 52 is controlled by the output hydraulic pressure from the first to third three-way solenoid valves 42, 50, 58, respectively. The control oil pressure to be controlled is a constant oil pressure generated 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. The control oil pressure is also introduced into the control valves 34, 44, and 52 to stabilize the control valves 34, 44, and 52.

Next, the electronic control of the belt-driven continuously variable transmission 2 will be described.

The continuously variable transmission 2 is hydraulically controlled, and in accordance with a command from the control unit 82, an appropriate line pressure for belt holding and torque transmission, a primary pressure for gear ratio change, and a clutch are securely connected. The clutch pressures required for the operation are secured.

The general clutch control of the belt-driven continuously variable transmission 2 will be described with reference to FIG.

First, a signal is extracted from the first table (200) and the second table (202) based on the detection signal of the carburetor throttle opening.

Then, from the first table (200), the engine torque (T
RQEN), and the signal of the engine torque (TEQEN) passes through a first filter for feedforward (204), and a filter engine torque (TRQENF) is obtained by a first-order lag element of the first filter (204). RATC x KA (proportional gain) (20) for engine torque (TRQENF)
6) to calculate the feed forward amount. RATC is
This is a value obtained by dividing the engine speed by the clutch input shaft speed in a calculation unit (not shown). Similarly, the signal from the second table (202) is supplied to the second filter (2
08), and also acts on the engine speed (210) R
ATC × KB (proportional gain) (212). The signals from RATC × KA (proportional gain) (206) and RATC × KB (proportional gain) (212) are merged (214) and passed as a Pcst signal via switch (216) to clutch engagement pressure and clutch pressure. Actuated (218) and sent to the pressure loop controller (220). The signal processed by the pressure loop controller (220) is output as a PWM signal to the clutch pressure controlling third three-way solenoid valve 68 via the duty output generator (222).

Next, the clutch control of the continuously variable transmission 2 by the control unit 82 in the start mode control will be described with reference to the flowchart of FIG.

For example, start in normal start mode (300)
It is determined whether the oil temperature of the continuously variable transmission 2 is equal to or lower than 30 degrees (302). If NO, FFCNT is set to 0, and the throttle opening (LSTHER
T) is set as the throttle opening (THRT) (304), and the calculated value, that is, the filter engine torque (TRQENF) is calculated by performing the calculation by the first filter 204 for feedforward (306), and the process proceeds to the end (322). . If the determination (302) is YES, it is determined whether the throttle opening is equal to or less than 20% (308), and if NO, the above processing (3) is performed.
The process proceeds to 04), and in the case of YES, it is determined (310) whether or not the amount of change in the throttle opening is greater than -5%.
If this determination (310) is NO, it is determined whether or not FFCNT = 0 (312), and if the determination (312) is YES, the above processing (3) is performed.
The process proceeds to 04), and in the case of NO, it is determined whether or not THRT + 3 is not less than LSTHRT (314). If the determination (314) is YES, the process proceeds to the above-described process (304). If the determination is NO, the calculation by the feedforward first filter 204 is performed to calculate the calculated value, that is, the filter engine torque (TRQENF). The process proceeds to the calculation process (306).

Further, if it is determined whether or not the change amount of the throttle opening is larger than -5% (310), if FFCNT + 1 → F
FCNT (316) and judges whether or not FFCNT is 3 (31
8) is performed, and in the case of NO, the process proceeds to the process (306) of calculating the calculated value, that is, the filter engine torque (TRQENF) by performing the calculation by the first feedforward filter 204. If the determination (318) is YES, FFCNT is set to 0, and the throttle opening (LS
THRT) is set to the throttle opening (THRT), and the filter engine torque (TRQENF) is changed to the engine torque (TRQE) in order to initialize the first feedforward filter 204.
N) (320), the first feedforward filter 204 is initialized in order to sharply reduce the clutch pressure due to the feedforward amount, and the process proceeds to end (322).

This allows the continuously variable transmission to meet certain limiting conditions,
That is, when the oil temperature of the continuously variable transmission is 30 degrees or less, the throttle opening is 20% or less, and the variation of the throttle opening is -5%.
In the normal start mode when a larger condition is satisfied, the control unit can initialize the feedforward filter, the clutch pressure due to the feedforward amount is rapidly reduced, and the clutch switching operation at low temperature is performed. It can be performed smoothly and the occurrence of a worst-case engine stall can be reliably prevented.

In addition, when starting on a slope, even if the throttle opening is slightly loosened, the specific limiting condition is not satisfied, the feedforward filter is not initialized, and the clutch pressure decreases sharply and the vehicle goes backward. Can be prevented.

Furthermore, even if the accelerator is loosened against the will due to vibration during driving the vehicle and the throttle opening is slightly changed,
It is possible to reliably prevent a malfunction such that the feedforward filter is initialized without satisfying a specific limitation condition.

Note that the present invention is not limited to the above-described embodiment, and various application modifications are possible.

For example, in the embodiment of the present invention, the specific limiting condition for initializing the feedforward filter is that the oil temperature of the continuously variable transmission is 30 degrees or less, the throttle opening is 20% or less, and the throttle opening is 20% or less. -5% change
Although the condition is set to be larger than the above, it is also possible to use the numerical value of each condition by slightly changing it as desired.

〔The invention's effect〕

As described above in detail, according to the present invention, in the normal start mode when the continuously variable transmission satisfies a specific limitation condition, the control unit initializes the feedforward filter by the control unit and reduces the clutch pressure based on the feedforward amount. Since the control is performed to reduce the pressure suddenly, the clutch pressure can be reduced rapidly by initializing the feedforward filter, and the clutch switching operation can be performed smoothly at low temperatures, and the occurrence of engine stall is reliably prevented. I can do it. Also, even if the throttle opening is changed slightly when the vehicle is driven or when the vehicle starts moving up a hill, specific limiting conditions are not satisfied, and the malfunction that the feedforward filter is initialized is reliably prevented. Can be done.

[Brief description of the drawings]

1 to 5 show an embodiment of the present invention, FIG. 1 is a flowchart of a clutch control method for a belt-driven continuously variable transmission, and FIG. 2 is an explanatory diagram of a start mode control of the belt-driven continuously variable transmission. FIG. 3 shows the filter engine torque (TRQE) in the clutch control of the continuously variable transmission.
NF) and engine torque (TRQEN), FIG. 4 is a schematic sectional view of a belt-driven continuously variable transmission, and FIG. 5 is a block diagram of the belt-driven continuously variable transmission. In the figure, 2 is a belt-driven continuously variable transmission, 2A is a belt, 4 is a driving pulley, 10 is a driven pulley, 30 is a first oil passage, 32 is a second oil passage, and 34 is a primary pressure control valve. , 36 is a third oil passage, 38 is a constant pressure control valve, 40 is a fourth oil passage, 42 is a first three-way solenoid valve, 44 is a line pressure control valve, 46 is a fifth oil passage, 48 is a sixth oil passage, 50 is a second three-way solenoid valve, 52 is a clutch pressure control valve, 54 is a seventh oil passage, 56 is an eighth oil passage, 58 is a third three-way solenoid valve, 60 is a ninth oil passage, 62 is a hydraulic starting clutch, 64 is a tenth oil passage, 66 is an eleventh oil passage, 68 is a pressure sensor, 72 is a first rotation detector, 76 is a second rotation detector, 80 is a third rotation detector, 82 is a control unit, 94 is An oil pan 96 is an oil filter.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takumi Tatsumi 840 Chiyoda-cho, Himeji-shi, Hyogo Mitsubishi Electric Corporation Himeji Works (72) Inventor Hiroaki Yamamoto 13-1, Sadamotocho, Himeji-shi, Hyogo Mitsubishi Electric Control Software Co., Ltd. Himeji Office (56) References JP-A-63-315337 (JP, A) JP-A-61-233256 (JP, A) JP-A-61-132432 (JP, A) −238129 (JP, A)

Claims (2)

(57) [Claims] 1. A belt which is wound around a pair of fixed pulley portions and a movable pulley portion which is detachably mounted on the fixed pulley portions, the width between the two pulley portions being reduced. In a clutch control method for a continuously variable transmission that performs speed change control to reduce or increase a turning radius and change a speed ratio, a feed for clutch pressure required by multiplying an engine torque value determined by a throttle opening detection signal by a proportional gain is provided. A control unit for calculating a forward amount is provided, and in a normal start mode when the continuously variable transmission satisfies a specific limitation condition, the control unit initializes a feedforward filter in the normal start mode, and controls a clutch pressure based on the feedforward amount. A clutch control method for a continuously variable transmission, characterized in that control is performed so as to sharply decrease the clutch. 2. The specific limiting condition is that the oil temperature of the continuously variable transmission is 30 degrees or less, the throttle opening is 20% or less, and the variation of the throttle opening is greater than -5%. The clutch control method for a continuously variable transmission according to claim 1, which is a specific limiting condition.