JP3013073B2 - Control device for continuously variable transmission - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a continuously variable transmission (CVT) provided between an engine and a drive shaft in a vehicle.

[0002]

2. Description of the Related Art With regard to speed change control of a continuously variable transmission, a technology for feedback-controlling a speed ratio so that a target input speed (or a target speed ratio) matches an actual input speed (or an actual speed ratio), and A technique for stopping feedback control when these differences are within a predetermined dead zone width is disclosed in
161346, JP-A-61-233253, JP-A-1-15564 and the like.

Here, an input-side rotation sensor that generates a pulse signal in synchronization with the rotation of the input side of the continuously variable transmission is used to detect the actual input rotation speed. Since the actual speed ratio is the actual input rotational speed / the actual output rotational speed, a pulse signal is generated in synchronization with the input-side rotation sensor and the output-side rotation of the continuously variable transmission. An output rotation sensor is used.

In general, there are the following two types of methods for calculating the number of rotations based on a signal from a rotation sensor, which are widely used (see FIG. 12). (1) Period measurement method Period of pulse signal from rotation sensor (time from rising of pulse signal to rising of next pulse signal) Tsen
(sec), and based on this, the rotation speed N (r
pm).

N = 60 / (Tsen × P) P: Number of pulses per rotation of rotation sensor (number of teeth) (2) Frequency measurement method Frequency of pulse signal from rotation sensor (number of pulses within predetermined window time) ) The CT is measured, and based on this, the rotational speed N (rpm) is calculated by the following equation.

N = (60 × CT) / (Twin × P) Twin: Window time (sec) P: Number of pulses per rotation of rotation sensor (number of teeth) The number of pulses per rotation of rotation sensor ( Number of teeth) P
Is generally set to be larger in the frequency measurement method than in the period measurement method.

[0007]

By the way, comparing the above-mentioned period measurement method and frequency measurement method, the detection accuracy tends to deteriorate in the period measurement method because the measurement time becomes shorter as the number of rotations increases. Yes (see Figure 13)
In the frequency measurement method, as the number of rotations decreases, the number of input pulses decreases, so that the detection accuracy tends to deteriorate (see FIG. 14).

Therefore, in a system in which the speed ratio is feedback-controlled so that the target input speed (or the target speed ratio) and the actual input speed (or the actual speed ratio) match, in a region where the speed detection accuracy is deteriorated. If the control is performed within the variation range of the rotation speed or the speed ratio, the measured deviation does not coincide with the true deviation, and a minute hunting may be caused near the control target value.

In addition, since the actuator operates continuously near the control target value, there is a concern that the durability of the actuator may be degraded, and the fuel consumption may be degraded due to an increase in power consumption.
The present invention has been made in view of such conventional problems, and has as its object to appropriately prevent a hunting operation in a region where rotation speed measurement accuracy in a period measurement method or a frequency measurement method is deteriorated.

[0010]

Therefore, according to the first aspect of the present invention, as shown in FIG. 1, a target input speed setting means for setting a target input speed of a continuously variable transmission, and a continuously variable transmission. An actual input rotational speed detecting means for detecting an actual input rotational speed of the continuously variable transmission based on a cycle of a pulse signal from an input-side rotational sensor that generates a pulse signal in synchronization with the input-side rotation of the transmission; Speed ratio feedback control means for feedback-controlling the speed ratio of the continuously variable transmission such that the speed and the actual input speed match, and a difference between the target input speed and the actual input speed within a predetermined dead band width. And a control stopping means for stopping the feedback control at the time of (i), wherein a dead band width varying means for setting the width of the dead band to be larger as the actual input rotation speed becomes larger is provided. Toss .

In the invention according to claim 2, in FIG.
The actual input rotation speed detecting means does not detect the actual input rotation speed of the continuously variable transmission based on the cycle of the pulse signal from the rotation sensor (period measurement method), but based on the frequency of the pulse signal from the rotation sensor. It is assumed that the actual input rotation speed of the continuously variable transmission is detected (frequency measurement method), and the dead zone width varying means is set so that the width of the dead zone becomes larger as the actual input rotation speed becomes smaller.

According to the third aspect of the present invention, as shown in FIG. 2, target speed ratio setting means for setting a target speed ratio of the continuously variable transmission, and a pulse synchronized with the rotation of the input side of the continuously variable transmission. An actual input speed detecting means for detecting an actual input speed of the continuously variable transmission based on a cycle of a pulse signal from an input side rotation sensor for generating a signal; and in synchronization with a rotation of an output side of the continuously variable transmission. An actual output speed detecting means for detecting the actual output speed of the continuously variable transmission based on the cycle of the pulse signal from the output side revolution sensor for generating the pulse signal; Actual speed ratio calculating means for calculating the speed ratio, speed ratio feedback control means for feedback controlling the speed ratio of the continuously variable transmission so that the target speed ratio and the actual speed ratio match, a target speed ratio and the actual speed ratio When the difference between the A control stop means for stopping the feedback control, the control device for a continuously variable transmission comprising,
A dead zone width varying means is provided for setting the width of the dead zone to be larger as the actual input rotation speed and the actual output rotation speed become larger.

The dead zone width varying means here has means for calculating the product of the actual input rotational speed and the actual output rotational speed, and any device which sets the width of the dead zone to be larger as the product becomes larger ( Claim 4). In the invention according to claim 5, FIG.
Wherein the actual input rotational speed detecting means and the actual output rotational speed detecting means detect the actual input rotational speed and the actual output rotational speed of the continuously variable transmission based on the period of the pulse signal from the rotation sensor (period measurement method). ), Rather than detecting the actual input rotation speed and the actual output rotation speed of the continuously variable transmission based on the frequency of the pulse signal from the rotation sensor (frequency measurement method). The width of the dead zone is set to be larger as the actual input rotational speed and the actual output rotational speed become smaller.

The dead zone width varying means here has means for calculating the product of the actual input rotation speed and the actual output rotation speed, and any device which sets the width of the dead zone larger as the product becomes smaller ( Claim 6).

[0015]

According to the first aspect of the present invention, while setting the target input rotation speed of the continuously variable transmission, the actual input rotation speed is detected and the target input rotation speed is set to match the actual input rotation speed. The gear ratio of the step transmission is feedback-controlled. In the case where the actual input rotation speed detecting means is of the cycle measurement type, the higher the actual input rotation speed, the worse the rotation speed detection accuracy. Therefore, the width of the dead zone is increased as the actual input rotational speed increases, and the feedback control near the target input rotational speed is stopped, thereby preventing a hunting operation.

According to the second aspect of the present invention, since the actual input rotational speed detecting means is a frequency measuring method, the smaller the actual input rotational speed, the worse the rotational speed detection accuracy. Therefore, the width of the dead zone is increased as the actual input rotational speed decreases, and the feedback control near the target input rotational speed is stopped, thereby preventing the hunting operation. In the invention according to claim 3, while setting the target speed ratio of the continuously variable transmission, the actual speed ratio is calculated by detecting the actual input speed and the actual output speed, and the target speed ratio and the actual speed ratio are calculated. The feedback control of the speed ratio of the continuously variable transmission is performed so that the values of.

In the case where the actual input rotational speed detecting means and the actual output rotational speed detecting means are of a period measurement type, the higher the rotational speed, the worse the rotational speed detection accuracy. Therefore, as the rotation speed increases, the width of the dead zone is increased, and the feedback control near the target gear ratio is stopped, thereby preventing the hunting operation. Here, both the actual input rotational speed and the actual output rotational speed are considered by calculating the product of the actual input rotational speed and the actual output rotational speed, and by setting the width of the dead zone larger as the product increases. (Claim 4).

In the invention according to claim 5, since the actual input rotational speed detecting means and the actual output rotational speed detecting means are of the frequency measurement type, the lower the rotational speed, the worse the rotational speed detection accuracy. Therefore, as the rotation speed decreases, the width of the dead zone is increased, and the feedback control near the target speed ratio is stopped, thereby preventing the hunting operation. here,
By calculating the product of the actual input rotational speed and the actual output rotational speed, and by setting the width of the dead zone larger as the product becomes smaller, both the actual input rotational speed and the actual output rotational speed can be considered. (Claim 6).

[0019]

Embodiments of the present invention will be described below. FIG. 3 shows a system configuration. A long travel damper (spring type damper for absorbing rotation fluctuation) 2 is provided on the output side of the engine 1.
, A continuously variable transmission (CVT) 3 is provided.

The continuously variable transmission 3 includes a primary pulley 4 on the engine side and a secondary pulley 5 on the drive shaft (diff) side.
And a belt 6 wound between them, the pulley ratio is changed by adjusting the shift pressure to the primary pulley-side actuator 4a and the line pressure to the secondary pulley-side actuator 5a, thereby changing the gear ratio. It can be changed steplessly. However, another CVT such as a toroidal type may be used.

The shift pressure and the line pressure are adjusted by controlling the hydraulic pressure of a hydraulic circuit 8 connected to an oil pump 7 by solenoid valves (duty solenoids) 9 and 10 having a relief function. Controlled by 11. Therefore, by controlling the solenoid valves 9 and 10 by the controller 11 to control the shift pressure and the line pressure,
The gear ratio can be controlled.

In order to control the gear ratio, the controller 11 has an input side for generating a pulse signal in synchronization with the rotation of the input side (primary pulley 4) to detect the actual input rotation speed Nin of the continuously variable transmission 3. A rotation sensor 12, an output rotation sensor 13 for generating a pulse signal in synchronization with the rotation of the output side (secondary pulley 5) to detect the actual output rotation speed Nout of the continuously variable transmission 3, and opening of a throttle valve of the engine 1. Detection signals are input from a potentiometer type throttle sensor 14 that generates a voltage signal corresponding to the degree (throttle opening) TVO. Note that an engine rotation sensor can be used as the input rotation sensor 12 and a vehicle speed sensor can be used as the output rotation sensor 13.

Based on these signals, the controller 11 sets the gear ratio by a built-in microcomputer, and controls the electromagnetic valves 9 and 10 to obtain the gear ratio to perform gear control. The starting clutch 15 is provided between the output side (secondary pulley 5) of the continuously variable transmission 3 and the drive shaft (diff).
The clutch pressure applied to the starting clutch 15 is controlled by an electromagnetic valve 16, and the electromagnetic valve 16 is also controlled by the controller 11.

FIG. 4 is a flowchart of a shift control routine. This routine is executed every unit time. In step 1 (indicated as S1 in the figure, the same applies hereinafter)
The actual input rotation speed Nin of the continuously variable transmission calculated by another routine is read. Here, in the case of the period measurement method, FIG.
The actual input rotation speed Nin is calculated by the routine of FIG. 6. In the case of the frequency measurement method, the actual input rotation speed Nin is calculated by the routine of FIG.

The routine of FIG. 5 in the case of the period measurement method will be described. This routine is started in synchronization with the rise of the pulse signal from the input side rotation sensor 12. Steps
In step 101, the value of a timer (clock pulse counter) is read, and the pulse signal period (the time from the rise of a pulse signal to the rise of the next pulse signal) Tsen (sec) is measured. In step 102, the timer is reset to 0 for the next pulse signal period measurement.

In step 103, based on the measured pulse signal period Tsen, the actual input rotation speed Nin (r
pm). Nin = 60 / (Tsen × P) P: Number of pulses (number of teeth) per rotation of rotation sensor The routine of FIG. 6 in the case of the frequency measurement method will be described.

In step 201, for initialization, the timer for measuring the window time is reset to start 0, and the count value CT of the number of pulses is cleared.
In step 202, it is determined whether or not a pulse signal has been input from the input-side rotation sensor 12.
3 increments the count value CT. Step 20
In step 4, it is determined whether the value of the timer has reached a predetermined window time Twin, and the process returns to step 202 until the window time Twin elapses.

When the window time Twin elapses, the process proceeds from step 204 to step 205, where the count value Ccount, that is, the frequency of the pulse signal from the input side rotation sensor 12 (the number of pulses within the predetermined window time Twin) CT And the actual input rotational speed Nin (r
pm). After the calculation, the process returns to step 201. Nin = (60 × CT) / (Twin × P) Twin: Window time (sec) P: Number of pulses per rotation of rotation sensor (number of teeth) Returning to FIG.

In step 2, at least the vehicle speed VSP
(Actual output speed Nout), more specifically,
Referring to a map as shown in FIG. 7, a target input rotation speed Ninset of the continuously variable transmission is set from the vehicle speed VSP (actual output rotation speed Nout) and the throttle opening TVO. When the actual output speed Nout of the continuously variable transmission is used, the actual output speed Nout calculated by another routine is read and used.

In the case of the period measuring method, the actual output rotational speed Nout is calculated by a routine similar to that shown in FIG. That is, by starting the same routine as in FIG. 5 in synchronization with the rise of the pulse signal from the output-side rotation sensor 13, Nou is started.
It is calculated as t = 60 / (Tsen × P). In the case of the frequency measurement method, the actual output rotation speed Nout is calculated by a routine similar to that of FIG. That is, Nout = (60 × CT) / (Twin × P) is calculated by counting the pulse signals from the output side rotation sensor 13 in the same routine as in FIG.

In step 3, the target input rotational speed Ninset
(Control deviation) between the actual output rotational speed Nin and Er = Ninset
Calculate Nin. In step 4, refer to the map,
The dead zone width DNO is set based on the actual input rotation speed Nin. Here, in the case of the period measurement method, as shown in (1) of FIG. 8, the dead zone width DNO is set to increase as the actual input rotation speed Nin increases. For the frequency measurement method,
As shown in FIG. 8 (2), the width DNO of the dead zone is set to be larger as the actual input rotation speed Nin becomes smaller.

In step 5, the absolute value of the control error Er is compared with the dead zone width DNO. As a result of comparison, | Er
In the case of | ≦ DNO, the control deviation Er is within the width of the dead zone. Therefore, the process proceeds to step 6 to substantially stop the feedback control, and sets the control deviation Er = 0. In step 7, a gear ratio control amount is calculated by well-known PID (proportional / integral / differential) control based on the control deviation Er (see FIG. 9).

In step 8, a duty signal is output to the solenoid valves 9 and 10 based on the calculated gear ratio control amount. Thus, the gear ratio is feedback-controlled so that the target input rotation speed Ninset and the actual input rotation speed Nin match. Here, in the case of the period measurement method, as the actual input rotational speed Nin increases, the rotational speed detection accuracy deteriorates. However, as the actual input rotational speed Nin increases, the width of the dead zone increases and the vicinity of the target input rotational speed Ninset increases. The hunting operation can be prevented because the feedback control is stopped.

In the case of the frequency measurement method, the smaller the actual input rotational speed Nin, the lower the rotational speed detection accuracy becomes.
As the actual input rotational speed Nin decreases, the width of the dead zone is increased, and the feedback control near the target input rotational speed Ninset is stopped, so that the hunting operation can be prevented.
In this embodiment, step 1 corresponds to the actual input rotational speed detecting means together with another routine, step 2 corresponds to the target input rotational speed setting means,
Steps 7 and 8 correspond to the speed ratio feedback control means, step 4 corresponds to the dead zone width varying means, and steps 5 and 6 correspond to the control stopping means.

Next, another embodiment will be described. In this embodiment, the speed ratio is feedback-controlled so that the target speed ratio and the actual speed ratio match. FIG. 10 is a flowchart of the shift control routine. In step 11, the actual input rotation speed Nin of the continuously variable transmission calculated by another routine is read.

Here, in the case of the period measuring method, the actual input rotational speed Nin is calculated by the routine of FIG. 5, and in the case of the frequency measuring method, the actual input rotational speed Nin is calculated by the routine of FIG.
Is calculated. In step 12, the actual output speed Nout of the continuously variable transmission calculated by another routine is read.

In the case of the period measuring method, the actual output rotational speed Nout is calculated by a routine similar to that shown in FIG. That is, by starting the same routine as in FIG. 5 in synchronization with the rise of the pulse signal from the output-side rotation sensor 13, Nou is started.
It is calculated as t = 60 / (Tsen × P). In the case of the frequency measurement method, the actual output rotation speed Nout is calculated by a routine similar to that of FIG. That is, Nout = (60 × CT) / (Twin × P) is calculated by counting the pulse signals from the output side rotation sensor 13 in the same routine as in FIG.

In step 13, the actual speed ratio R = Nin / Nout is calculated from the actual input rotational speed Nin and the actual output rotational speed Nout. In step 14, referring to the map, the vehicle speed VS
A target speed ratio Rset of the continuously variable transmission is set from P (actual output speed Nout) and the throttle opening TVO. In step 15, a difference (control deviation) Er = Rset-R between the target speed ratio Rset and the actual speed ratio R is calculated.

In step 16, referring to the map, the product of the actual input rotational speed Nin and the actual output rotational speed Nout (Nin × Nout)
), The dead zone width DNO is set. here,
In the case of the period measurement method, as shown in FIG. 11A, the product of the actual input rotational speed Nin and the actual output rotational speed Nout (Nin × N)
out), the dead zone width DNO is set to be larger. In the case of the frequency measurement method, as shown in (2) of FIG. 11, the smaller the product (Nin × Nout), the larger the width DNO of the dead zone is set.

In step 17, the absolute value of the control error Er is compared with the dead zone width DNO. As a result of comparison, | Er
In the case of | ≦ DNO, the control deviation Er is within the width of the dead zone. Therefore, the process proceeds to step 18 to substantially stop the feedback control, and the control deviation Er = 0. Steps
In step 19, a gear ratio control amount is calculated by well-known PID (proportional / integral / differential) control based on the control deviation Er.

In step 20, a duty signal is output to the solenoid valves 9 and 10 based on the calculated gear ratio control amount. Thus, the gear ratio is feedback-controlled so that the target gear ratio Rset and the actual gear ratio Rin match.
Here, in the case of the period measurement method, the actual input rotation speed N
As the in and the actual output rotational speed Nout increase, the rotational speed detection accuracy deteriorates. However, as Nin × Nout increases, the width of the dead zone is increased, and the feedback control near the target speed ratio Rset is stopped. Can be prevented.

In the case of the frequency measurement method, as the actual input rotation speed Nin and the actual output rotation speed Nout are smaller, the rotation speed detection accuracy is deteriorated. However, as Nin × Nout becomes smaller, the width of the dead zone is increased. Since the feedback control near the target speed ratio Rset is stopped, the hunting operation can be prevented. In this embodiment, step 11 corresponds to an actual input rotation speed detecting means together with another routine, step 12 corresponds to an actual output rotation detecting means together with another routine, and step 13 corresponds to an actual output rotation speed detecting means. Step 14 corresponds to target gear ratio setting means, steps 15, 19, and 20 correspond to gear ratio feedback control means, and step 16 corresponds to dead zone width varying means. Steps 17 and 18 correspond to control stopping means.

[0043]

As described above, according to the first aspect of the present invention, in the case where the actual input rotational speed detecting means of the period measuring method is provided, in the high rotational speed region where the rotational speed detection accuracy is deteriorated,
By increasing the width of the dead zone, feedback control in the vicinity of the target input rotation speed is stopped, thereby obtaining an effect of preventing hunting operation.

According to the second aspect of the present invention, when the actual input rotational speed detecting means of the frequency measuring method is provided, the width of the dead zone is increased in the low rotational speed region where the rotational speed detection accuracy is deteriorated. The feedback control in the vicinity of the input rotation speed is stopped, thereby obtaining an effect that the hunting operation can be prevented. According to the third aspect of the present invention, the width of the dead zone is increased in the high rotation region where the rotation speed detection accuracy is deteriorated when the actual input rotation speed detection unit and the actual output rotation speed detection unit of the cycle measurement method are provided. Then, the feedback control in the vicinity of the target speed ratio is stopped, whereby the effect of preventing the hunting operation can be obtained.

Further, according to the fourth aspect of the present invention, the width of the dead zone is set to be larger as the product of the actual input rotational speed and the actual output rotational speed becomes larger, so that the difference between the actual input rotational speed and the actual output rotational speed is obtained. Both can be considered appropriately. According to the invention according to claim 5, when the actual input rotation speed detecting means and the actual output rotation speed detecting means of the frequency measurement method are provided, the width of the dead zone is increased in the low rotation region where the rotation speed detection accuracy is deteriorated. Then, the feedback control in the vicinity of the target speed ratio is stopped, whereby the effect of preventing the hunting operation can be obtained.

According to the present invention, the width of the dead zone is set to be larger as the product of the actual input rotational speed and the actual output rotational speed becomes smaller. Both can be considered appropriately. Also,
By preventing the hunting operation as described above, it is possible to obtain the effect that the durability of the actuator can be improved and the fuel consumption can be improved by saving power consumption.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a configuration of the present invention (part 1).

FIG. 2 is a functional block diagram showing a configuration of the present invention (part 2);

FIG. 3 is a system diagram showing an embodiment of the present invention.

FIG. 4 is a flowchart of a shift control routine.

FIG. 5 is a flowchart of a rotation speed detection routine of a cycle measurement method.

FIG. 6 is a flowchart of a rotation speed detection routine of a frequency measurement method.

FIG. 7 is a view showing a target input rotation speed setting map;

FIG. 8 is a diagram showing a dead zone width setting map;

FIG. 9 is a block diagram of a PID operation unit.

FIG. 10 is a flowchart of a shift control routine according to another embodiment of the present invention.

FIG. 11 is a diagram showing a dead zone width setting map.

FIG. 12 is an explanatory diagram of a period measurement method and a frequency measurement method.

FIG. 13 is a diagram illustrating a measurement error rate of the cycle measurement method.

FIG. 14 is a diagram illustrating a measurement error rate of the frequency measurement method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 3 Continuously variable transmission 4 Primary pulley 5 Secondary pulley 6 Belt 9,10 Solenoid valve 11 Controller 12 Input rotation sensor 13 Output rotation sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FIF16H 59:70 (56) References JP-A-57-161346 (JP, A) JP-A-61-233253 (JP, A) JP-A-64-15564 (JP, A) JP-A-62-93562 (JP, A) JP-A-63-31835 (JP, A) JP-A-61-214751 (JP, A) JP-A-62-179142 (JP, A) JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F16H 9/00 F16H 59/00-63/48 G05B 11/36

Claims (6)

(57) [Claims] 1. A target input speed setting means for setting a target input speed of a continuously variable transmission, and a pulse from an input side rotation sensor for generating a pulse signal in synchronization with the input side rotation of the continuously variable transmission. An actual input rotational speed detecting means for detecting an actual input rotational speed of the continuously variable transmission based on a signal cycle; and a feedback of a speed ratio of the continuously variable transmission so that the target input rotational speed and the actual input rotational speed match. Control of a continuously variable transmission, comprising: a speed ratio feedback control means for controlling; and a control stop means for stopping the feedback control when a difference between a target input rotation speed and an actual input rotation speed is within a predetermined dead zone width. The control device for a continuously variable transmission, further comprising: a dead zone width varying unit that sets the width of the dead zone as the actual input rotation speed increases. 2. A target input rotation speed setting means for setting a target input rotation speed of a continuously variable transmission, and a pulse from an input side rotation sensor for generating a pulse signal in synchronization with the input side rotation of the continuously variable transmission. An actual input speed detecting means for detecting the actual input speed of the continuously variable transmission based on the frequency of the signal; and a feedback of the speed ratio of the continuously variable transmission so that the target input speed and the actual input speed match. Control of a continuously variable transmission, comprising: a speed ratio feedback control means for controlling; and a control stop means for stopping the feedback control when a difference between a target input rotation speed and an actual input rotation speed is within a predetermined dead zone width. The control device for a continuously variable transmission, further comprising: a dead zone width varying unit that sets the width of the dead zone to be larger as the actual input rotation speed becomes smaller. A target speed ratio setting means for setting a target speed ratio of the continuously variable transmission; and a pulse signal from an input side rotation sensor for generating a pulse signal in synchronization with the input side rotation of the continuously variable transmission. An actual input rotational speed detecting means for detecting an actual input rotational speed of the continuously variable transmission based on a cycle, and a pulse signal from an output side rotation sensor for generating a pulse signal in synchronization with the output side rotation of the continuously variable transmission An actual output rotational speed detecting means for detecting an actual output rotational speed of the continuously variable transmission based on the cycle of; a real gear ratio calculating means for calculating an actual gear ratio from the actual input rotational speed and the actual output rotational speed; Speed ratio feedback control means for feedback-controlling the speed ratio of the continuously variable transmission so that the speed ratio and the actual speed ratio coincide with each other; and when a difference between the target speed ratio and the actual speed ratio is within a predetermined dead zone width. Control stop to stop the feedback control A continuously variable transmission control device comprising: a stepless variable width control means for setting the width of the deadband larger as the actual input rotational speed and the actual output rotational speed increase. Control device. 4. The dead band width varying means has means for calculating a product of an actual input rotation speed and an actual output rotation speed, and the width of the dead band is set to be larger as the product becomes larger. The control device for a continuously variable transmission according to claim 3, wherein 5. A target speed ratio setting means for setting a target speed ratio of a continuously variable transmission, and a pulse signal from an input side rotation sensor for generating a pulse signal in synchronization with the input side rotation of the continuously variable transmission. An actual input rotational speed detecting means for detecting an actual input rotational speed of the continuously variable transmission based on the frequency; and a pulse signal from an output side rotation sensor for generating a pulse signal in synchronization with the output side rotation of the continuously variable transmission. An actual output speed detecting means for detecting an actual output speed of the continuously variable transmission based on the frequency of the actual transmission speed; an actual speed ratio calculating means for calculating an actual speed ratio from the actual input speed and the actual output speed; Speed ratio feedback control means for feedback-controlling the speed ratio of the continuously variable transmission so that the speed ratio and the actual speed ratio coincide with each other; and when a difference between the target speed ratio and the actual speed ratio is within a predetermined dead zone width. Control for stopping the feedback control A continuously variable transmission control device, comprising: a dead zone width varying device that sets the width of the dead zone to be larger as the actual input rotation speed and the actual output rotation speed become smaller. Machine control device. 6. The dead band width varying means includes means for calculating a product of an actual input rotational speed and an actual output rotational speed, and the width of the dead band is set to be larger as the product becomes smaller. The control device for a continuously variable transmission according to claim 5, wherein