JP2004293654A - Control device for power transmission mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for a power transmission mechanism for correctly detecting slip limit pressure of belt nipping pressure without causing excessive slip. <P>SOLUTION: The control device for a power transmission mechanism detects the slip in a case that one of at least two controllable physical quantities is changed. The control device comprises: a condition satisfaction determining means (step S1) for determining whether or not a predetermined condition is satisfied; and a selecting means for selecting the physical quantity to be changed, based on the content of the condition that is determined to be satisfied. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control device for a power transmission mechanism such as a continuously variable transmission, and more particularly to a control device for detecting a slip state thereof.
[0002]
[Prior art]
Driving torque in a vehicle such as an automobile is generated by a power source such as an engine and transmitted to wheels via a transmission mechanism such as a clutch or a transmission. If the transmission torque capacity of the transmission mechanism is increased, the torque input from the power source can be transmitted to the output side such as the drive wheels, but if the transmission torque capacity is increased more than necessary, the power consumed for that also increases. The fuel efficiency of the vehicle as a whole deteriorates. For this reason, conventionally, in general, a control device is set in advance so that a hydraulic pressure for setting a transmission torque capacity of a power transmission mechanism is determined in advance in correspondence with an output of a power source, or the output of the power source is reflected in a pressure regulation level of the hydraulic pressure. Make up.
[0003]
In particular, in a continuously variable transmission for a vehicle, when the clamping pressure for sandwiching a belt, a power roller, and the like is increased, the transmission torque capacity is increased, but the transmission efficiency of power in the continuously variable transmission is reduced. Since it is necessary to reliably prevent damage such as wear due to slippage, high precision is required for controlling the clamping force. However, since the running state or driving state of the vehicle is not always constant, a large torque may temporarily act on a transmission mechanism such as a continuously variable transmission, and as a result, slippage may occur. In addition, in order to find a critical pressure at which slippage occurs, a minute slippage may be intentionally caused.
[0004]
One example is a slip detection method for a continuously variable transmission that transmits power by frictional contact or a transmission system for the same, which involves lowering a crimping force (that is, a clamping pressure or an engagement pressure). Patent Literature 1 discloses a method of determining slip by detecting an increase in friction efficiency. In the method described in Patent Document 1, the pressing force is gradually reduced while the transmitting force, speed, or transmission ratio is almost constant, and the pressing force is reduced stepwise when a slip is detected due to an increase in oil temperature. And then set the pressure to a higher level of pressure than during slip. Further, Non-Patent Document 1 describes a method for detecting slippage of a belt by periodically changing a belt clamping pressure.
[0005]
[Patent Document 1]
JP 2001-12593 A (paragraphs (0012), (0018) to (0020), and (0026))
[Non-patent document 1]
7. 7th Luk Symposium (7th Luke Symposium) / 12. April 2002 Handouts [0006]
[Problems to be solved by the invention]
In the method described in Patent Literature 1, slip when the pressure is reduced is detected by an increase in friction efficiency. Since a time delay inevitably occurs between the time when the rise is detected, even if the pressing force is increased stepwise by the establishment of the slip determination, slippage may be excessive. In addition, since the crimping force is increased when the increase in friction efficiency is detected, if the increase in friction efficiency is not detected for some reason, the crimping force is further reduced. As a result, there is a possibility that excessive slippage may occur due to an increase in the reduction width of the pressing force.
[0007]
Furthermore, when the pressure force is gradually reduced to cause a slip, if the decrease gradient is small, it takes a long time to detect the slip, and in the process, the operating state changes and the detection of the slip must be stopped. May be lost. On the other hand, if the gradient of the decrease in the pressing force is increased, excessive slip may occur due to overshoot, which may result in damage such as abrasion.
[0008]
The present invention has been made in view of the technical problem described above, and a pressure for setting a transmission torque capacity by adding to a transmission member causes excessive slippage between the transmission members and control delay. It is an object of the present invention to provide a control device that can be optimized without using a control device.
[0009]
Means for Solving the Problems and Their Functions
In order to achieve the above object, an invention according to claim 1 is a control apparatus for a power transmission mechanism that detects slippage when one of at least two controllable physical quantities is changed. A control device for a power transmission mechanism, comprising: a condition satisfaction determination unit for determining whether a condition is satisfied; and a selection unit for selecting the physical quantity to be changed based on the content of the condition for which the condition is determined. .
[0010]
Therefore, according to the first aspect of the present invention, a predetermined condition is determined, a physical quantity to be changed is selected in accordance with the condition, and as a result, control meeting the condition is performed.
[0011]
According to a second aspect of the present invention, in the first aspect of the present invention, in the process of changing the selected physical quantity, the physical quantity to be changed when the condition determined by the condition satisfaction determining means is not satisfied. Is a control device for a power transmission mechanism, further comprising control target changing means for changing the parameter to another physical quantity not selected.
[0012]
Therefore, according to the second aspect of the present invention, when the condition is not satisfied for some reason, the physical quantity to be changed is changed to another one, and the control for detecting the slip is continued.
[0013]
A third aspect of the present invention is the control device for a power transmission mechanism according to the first or second aspect of the invention, wherein the physical quantity is periodically changed when the slip is detected. .
[0014]
Therefore, according to the third aspect of the present invention, since the physical quantity is added with a periodic fluctuation, even if the value reaches an excessive slippage momentarily at a valley or a peak of the fluctuation component, the next moment. Since the value of the physical quantity rises or falls, the slip is detected without excessive slip.
[0015]
According to a fourth aspect of the present invention, in any one of the first to third aspects of the invention, the physical quantity is a clamping force for clamping a torque transmission member constituting the power transmission mechanism and a torque input to the power transmission mechanism. A control device for a power transmission mechanism, wherein the condition is a lower limit value of the clamping pressure.
[0016]
Therefore, in the invention of claim 4, when the clamping pressure is likely to reach the preset lower limit value, the input torque is to be controlled in addition to or instead of controlling the clamping pressure. Further, by controlling the torque, the occurrence of overshoot due to poor response of the hydraulic circuit used for controlling the clamping pressure and the occurrence of excessive slip due to the overshoot are avoided.
[0017]
According to a fifth aspect of the present invention, there is provided the control device for a power transmission mechanism according to the fourth aspect of the present invention, wherein the clamping force is initially changed to detect the slip state. .
[0018]
Therefore, in the invention of claim 5, in order to detect the slip state at first, only the clamping force is changed, and after the slip state is detected, a new clamping force is set based on the state. When the squeezing pressure reaches the lower limit, the input torque is changed in addition to or instead of the squeezing pressure, and a slip state is detected.
[0019]
According to a sixth aspect of the present invention, in any one of the first to third aspects of the invention, the physical quantity includes a clamping force for clamping a torque transmission member constituting the power transmission mechanism and a torque input to the power transmission mechanism. The condition includes a condition that enables the torque to be changed periodically, and the selecting unit determines that the cycle is set when the condition that allows the torque to be changed is not satisfied. And detecting the slipping state based on the rotational speed of the power transmission mechanism when the holding pressure is periodically changed. It is a control device of a power transmission mechanism characterized by comprising means.
[0020]
Therefore, in the invention of claim 6, when the periodic change of the input torque cannot be continued for some reason, the control is switched to the clamping force which is another physical quantity, and the control for the detection is continued. .
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described based on specific examples. First, an example of a transmission system including a power transmission mechanism according to the present invention will be described. FIG. 2 schematically illustrates a drive mechanism including a belt-type continuously variable transmission 1 as a power transmission mechanism. The step transmission 1 is connected to a power source 5 via a forward / reverse switching mechanism 2 and a fluid transmission mechanism 4 having a lock-up clutch 3.
[0022]
The power source 5 includes an internal combustion engine, an internal combustion engine and an electric motor, or an electric motor. In the following description, the power source 5 is referred to as an engine 5. The fluid transmission mechanism 4 has, for example, a configuration similar to that of a conventional torque converter, and includes a pump impeller rotated by an engine 5, a turbine runner disposed opposite to the pump impeller, and a stator disposed therebetween. It is configured to supply a spiral flow of fluid generated by a pump impeller to the turbine runner to rotate the turbine runner and transmit torque.
[0023]
In the transmission of torque through such a fluid, inevitable slippage occurs between the pump impeller and the turbine runner, which causes a reduction in power transmission efficiency. And a lock-up clutch 3 for directly connecting to an output-side member such as The lock-up clutch 3 is configured to be controlled by hydraulic pressure, is controlled to a fully engaged state, a completely released state, and a slip state that is an intermediate state between these states, and can appropriately control the slip rotation speed. It has become.
[0024]
The forward / reverse switching mechanism 2 is a mechanism that is employed in accordance with the fact that the rotation direction of the engine 5 is limited to one direction, and outputs the input torque as it is, and outputs it in reverse. It is configured. In the example shown in FIG. 2, a double pinion type planetary gear mechanism is employed as the forward / reverse switching mechanism 2. That is, the ring gear 7 is arranged concentrically with the sun gear 6, and between the sun gear 6 and the ring gear 7, a pinion gear 8 meshed with the sun gear 6 and another pinion gear 9 meshed with the pinion gear 8 and the ring gear 7 are arranged. The pinion gears 8 and 9 are held by the carrier 10 so as to rotate and revolve. Further, a forward clutch 11 for integrally connecting the two rotating elements (specifically, the sun gear 6 and the carrier 10) is provided, and by selectively fixing the ring gear 7, the direction of the output torque is provided. Is provided.
[0025]
The continuously variable transmission 1 has the same configuration as a conventionally known belt-type continuously variable transmission, and each of a drive pulley 13 and a driven pulley 14 arranged in parallel with each other includes a fixed sheave and a hydraulic pulley. And a movable sheave that is moved back and forth in the axial direction by actuators 15 and 16. Therefore, the groove width of each of the pulleys 13 and 14 changes by moving the movable sheave in the axial direction, and accordingly, the winding radius of the belt 17 wound around each of the pulleys 13 and 14 (the effective diameter of the pulleys 13 and 14). ) Changes continuously, and the gear ratio changes steplessly. The drive pulley 13 is connected to the carrier 10 which is an output element of the forward / reverse switching mechanism 2.
[0026]
A hydraulic pressure (line pressure or its correction pressure) corresponding to the torque input to the continuously variable transmission 1 is supplied to the hydraulic actuator 16 of the driven pulley 14 via a hydraulic pump and a hydraulic control device (not shown). I have. Therefore, when each sheave of the driven pulley 14 sandwiches the belt 17, tension is applied to the belt 17, and a clamping pressure (contact pressure) between each pulley 13, 14 and the belt 17 is secured. . On the other hand, pressure oil corresponding to the gear ratio to be set is supplied to the hydraulic actuator 15 in the drive pulley 13 so that the groove width (effective diameter) according to the target gear ratio is set. .
[0027]
The driven pulley 14 is connected to a differential 19 via a gear pair 18, and outputs torque from the differential 19 to driving wheels 20. Therefore, in the above drive mechanism, the lock-up clutch 3 and the continuously variable transmission 1 are arranged in series between the engine 5 and the drive wheels 20.
[0028]
Various sensors are provided to detect the operation state (running state) of the vehicle equipped with the above-described continuously variable transmission 1 and the engine 5. That is, a turbine speed sensor 21 that detects an input speed (speed of the turbine runner) to the continuously variable transmission 1 and outputs a signal, and an input speed that detects a speed of the drive pulley 13 and outputs a signal. A sensor 22, an output rotation speed sensor 23 that detects the rotation speed of the driven pulley 14 and outputs a signal, and a hydraulic sensor 24 that detects the pressure of the hydraulic actuator 16 on the driven pulley 14 side for setting the belt clamping pressure are provided. ing. Although not particularly shown, an accelerator opening sensor that detects the amount of depression of the accelerator pedal and outputs a signal, a throttle opening sensor that detects the opening of the throttle valve and outputs a signal, and a brake pedal are depressed. A brake sensor or the like that outputs a signal in the case is provided.
[0029]
In order to control the engagement / disengagement of the forward clutch 11 and the reverse brake 12, control the squeezing force of the belt 17, control the gear ratio, and control the lock-up clutch 3, the transmission Electronic control unit (CVT-ECU) 25 is provided. The electronic control unit 25 is configured mainly by a microcomputer as an example, performs calculations in accordance with a predetermined program based on input data and data stored in advance, and various states such as forward, reverse or neutral, It is configured to execute setting of a required clamping force, setting of a gear ratio, engagement / disengagement of the lock-up clutch 3, and control of a slip rotation speed and the like.
[0030]
Here, as an example of data (signal) input to the transmission electronic control unit 25, a signal of an input rotation speed (input rotation speed) Nin of the continuously variable transmission 1 and an output of the continuously variable transmission 1 will be described. The signal of the rotation speed (output rotation speed) No is input from the corresponding sensor. An engine electronic control unit (E / G-ECU) 26 for controlling the engine 5 outputs a signal of an engine speed Ne, a signal of an engine (E / G) load, a throttle opening signal, and an accelerator pedal (not shown). ) Is input.
[0031]
A request for changing the engine torque is input from the transmission electronic control unit 25 to the engine electronic control unit 26. The engine torque fluctuation request includes the fluctuation width of the engine torque, that is, the amplitude, the fluctuation frequency, that is, the cycle, and the like. The engine torque fluctuation request causes the continuously variable transmission 1 to change a slip state (for example, a slip ratio) in accordance with the fluctuation of the engine torque, and the squeezing pressure is determined based on the squeezing pressure in the state. It is output for correction or for obtaining a map value of the clamping pressure. Details will be described later.
[0032]
According to the continuously variable transmission 1, the engine speed, which is the input speed, can be controlled steplessly (in other words, continuously), so that the fuel efficiency of a vehicle equipped with the same can be improved. For example, a target driving force is determined based on a required driving amount and a vehicle speed represented by an accelerator opening, and a target output required to obtain the target driving force is determined based on the target driving force and the vehicle speed. The engine speed for obtaining the target output at the optimum fuel efficiency is obtained based on a prepared map, and the gear ratio is controlled so as to become the engine speed.
[0033]
In order not to impair such an advantage of improving fuel efficiency, power transmission efficiency in the continuously variable transmission 1 is controlled to a favorable state. Specifically, the torque capacity of the continuously variable transmission 1, that is, the belt clamping pressure is set to a value as low as possible within a range where the target torque determined based on the engine torque can be transmitted and the belt 17 does not slip. Controlled. The control is executed by detecting a mutual relationship between the squeezing pressure and the input torque, for example, a state where the squeezing pressure is excessive or insufficient with respect to the input torque, and correcting the squeezing pressure based on the detection result.
[0034]
The control device according to the present invention is configured to perform the control of the decrease and the fluctuation of the clamping pressure, the detection of the slipping state, and the fluctuation control of the input torque. FIG. 1 is a flowchart for explaining an example of the control.
[0035]
In FIG. 1, first, it is determined whether a control precondition is satisfied (step S1). The control preconditions are, for example, that the warm-up is completed, the oil temperature is equal to or higher than a predetermined value, and that the vehicle is in a quasi-steady running state on a flat road.
[0036]
If an affirmative determination is made in step S1, it is next determined whether or not the correction of the belt clamping pressure has been completed (step S2). Here, the correction of the belt squeezing pressure is to correct the squeezing pressure value given in advance by learning based on the squeezing pressure value when the slip state is detected. That is, this determination is to avoid performing the same control repeatedly.
[0037]
If the determination is affirmative in step S2, the process exits this routine. If the determination is negative, the flag F is determined (step S3). As will be described later, this flag F indicates whether torque fluctuation is occurring or necessary, and is set to “0” or “1” according to the execution state of the control. I have. Since this flag F is set to "0" at the beginning of the routine, a signal is output which gradually lowers the average value (average clamping pressure) while changing the clamping pressure periodically, that is, in a wavy manner ( Step S4 and step S5).
[0038]
Next, after the rotational speed calculated from the input rotational speed is subjected to band-pass processing, a moving average S of the rotational speed subjected to the band-pass filter processing is calculated. Further, a deviation ΔS from a value before a predetermined time, that is, a value in a state immediately before that time is calculated (step S6). Such signal processing is performed to remove a signal component or the like due to a shift.
[0039]
Next, it is determined whether or not the change in the sliding state caused by reducing the belt clamping pressure as described above is large. That is, it is determined whether or not the state is immediately before the macro slip (step S7). When the deviation ΔS is larger than the preset reference value ΔS1, that is, when it is determined that the rate of change of the rotation speed S is large, the rotation speed is rapidly changing. That is, it is considered that the state is immediately before the macro slip.
[0040]
Here, the macro slip refers to the distance between the belt 17 and the pulleys 13 and 14 due to the expansion and contraction of the belt 17 and the relative movement of the metal pieces (sometimes referred to as pieces or blocks) constituting the belt 17. This is a slip state that exceeds the inevitable micro-slip, and is a so-called excessive slip which causes factors such as wear and adhesion.
[0041]
If the determination is affirmative in step S7, that is, if it is determined that the state is immediately before the macro slip, the clamping pressure fluctuation / decrease command issued up to that point is stopped (step S8). Thereafter, the map value of the squeezing pressure is changed based on the average squeezing pressure at the time of making a positive determination in step S7 and the fluctuation width thereof (step S9), and the process exits from this routine.
[0042]
On the other hand, if it is determined in step S7 to be negative, that is, it is not in the state immediately before the macro slip, the valley of the fluctuating component of the squeezing pressure that is fluctuated and applied reaches the predetermined hydraulic pressure lower limit value. It is determined whether or not it has been performed (step S10). The lower limit of the hydraulic pressure is a pressure value determined due to a centrifugal force or a pressure value artificially determined in advance from the viewpoint of fail-safe.
[0043]
If a negative determination is made in step S10, this routine is exited. Conversely, if a positive determination is made, the slip state may be determined and detected depending on the fluctuation / decrease of the clamping pressure. Therefore, the fluctuation / decrease in the clamping pressure is temporarily stopped (step S11). Thereafter, the flag F is changed from "0" to "1" (step S12). During this time, the average clamping pressure is maintained at the value at the time of suspension.
[0044]
Next, the control for changing the input torque, specifically, the ignition timing retard control is used to further reduce the clamping pressure while periodically changing the input torque. However, the squeezing pressure is set to an average squeezing pressure without any periodic fluctuation, and the inclination of the squeezing pressure to be lower than before is made gentler (step S13). This is because even if the valley portion of the periodic fluctuation component reaches the set lower limit, the applied average clamping force does not reach the set lower limit, and there is still room for reduction. is there. This process is performed in the same manner when the flag F is "1" in step S3.
[0045]
Then, the determination of the slip state (for example, whether or not the state is immediately before the occurrence of the macro slip) is performed in the same manner as in step S7 (step S14). If the determination is affirmative in step S14, that is, in the state immediately before the occurrence of macro slip, the map value is changed based on the clamping pressure value and the torque fluctuation width determined in step S14 (step S15). ).
[0046]
If negative in step S14, that is, if the state is not immediately before the occurrence of macro slip, it is determined whether the average clamping pressure has reached the hydraulic pressure lower limit value (step S16).
If the result is negative, this routine is exited. On the other hand, in the case of affirmative, it is considered that the state is not immediately before the occurrence of macroslip over the entire range of the settable clamping pressure. Therefore, the map value is changed based on the lower limit value of the clamping pressure and the fluctuation range of the currently applied torque (step S17). That is, the map value is updated by effectively utilizing the data obtained at that time.
[0047]
After the map values are changed in steps S15 and S17, the change in torque is stopped, the flag F is returned to "0", and the routine exits (step S18).
[0048]
With the above-described control, the clamping pressure is reduced with a periodic wave-like variation, so that an increase in slip at the time of the reduction and a state immediately before the macro slip as an integrated value are detected. Therefore, even if the value instantaneously reaches the value of macroslip, the clamping force immediately increases at the next moment, and the slip state can be detected without macroslip.
[0049]
Since the input torque is also applied by a periodic wave-like fluctuation, an increase in slip at the time of the increase and a state immediately before the macro slip are detected as an integrated value thereof. Therefore, even if the value reaches the macroslip momentarily, the torque immediately drops at the next moment, and the slip state can be detected without reaching the macroslip.
[0050]
If the clamping pressure is likely to reach a preset lower limit of hydraulic pressure, slip detection is performed by changing the input torque in addition to controlling the clamping pressure. Therefore, by changing the input torque, it is possible to avoid the occurrence of overshoot due to poor response of the hydraulic circuit used for controlling the clamping pressure and the macroslip due to the overshoot.
[0051]
In the above specific example, the retard control is performed as a method of changing the input torque. However, even when the retard control has to be interrupted such as a rise in the exhaust gas temperature, only the clamping pressure is changed. , The slip detection can be continued.
[0052]
Here, the relationship between the above specific example and the present invention will be briefly described. The functional means of step S1 described above corresponds to the condition satisfaction determination means of the present invention, and the functional means of step S4 corresponds to the selection means. Further, the functional means of steps S10 and S13 described above correspond to the control target switching means of the present invention. Further, the functional means of steps S7 and S14 correspond to the slip detecting means of the present invention.
[0053]
Note that the present invention is not limited to the above specific examples, and the continuously variable transmission targeted by the present invention may be a toroidal-type continuously variable transmission in addition to the above-described belt-type continuously variable transmission. Further, the power transmission mechanism to which the present invention is applied may be a power transmission means by frictional contact such as a clutch other than the continuously variable transmission.
[0054]
【The invention's effect】
As described above, according to the first aspect of the present invention, a predetermined condition is determined, a physical quantity to be changed is selected in accordance with the condition, and as a result, control meeting the condition can be performed.
[0055]
According to the second aspect of the present invention, when the condition is not satisfied for some reason, the physical quantity to be changed can be changed to another one, and the control for detecting the slip can be continued.
[0056]
Furthermore, according to the third aspect of the present invention, since the physical quantity is added with a periodic fluctuation, even if the value reaches an excessive slippage momentarily at the valley or the peak of the fluctuation component, At the moment, the value of the physical quantity rises or falls, so that the slip can be detected without excessive slip.
[0057]
In addition, according to the fourth aspect of the invention, when the squeezing pressure is likely to reach the preset lower limit, the input torque is to be controlled in addition to or instead of the squeezing pressure control. Further, by controlling the torque, it is possible to avoid the occurrence of overshoot due to poor response of the hydraulic circuit used for controlling the clamping pressure and the occurrence of excessive slip due to the overshoot. .
[0058]
According to the fifth aspect of the present invention, only the clamping force is changed to detect the slip state at first, and after detecting the slip state, the clamping force is newly set based on the state. When the squeezing pressure reaches the lower limit value, the input torque is changed in addition to the squeezing pressure, or alternatively, the slip state can be detected.
[0059]
Therefore, in the invention according to claim 6, when the periodic change of the input torque cannot be continued for some reason, the control is switched to another physical quantity, the clamping pressure, and the control for detection is continued. Can be.
[Brief description of the drawings]
FIG. 1 is a flowchart illustrating an example of control by a control device according to the present invention.
FIG. 2 is a diagram schematically illustrating an example of a transmission system including a power transmission mechanism according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Continuously variable transmission, 3 ... Lock-up clutch, 5 ... Engine (power source), 13 ... Drive pulley, 14 ... Driven pulley, 15, 16 ... Actuator, 17 ... Belt, 20 ... Drive wheel, 25 ... Transmission Electronic control unit (CVT-ECU).

Claims (6)

In a control device of a power transmission mechanism that detects a slip state when one of at least two controllable physical quantities is changed,
Condition satisfaction determining means for determining whether a predetermined condition is satisfied,
A control unit for controlling the power transmission mechanism, comprising: selecting means for selecting the physical quantity to be changed based on the content of the condition determined to be satisfied. In the process of changing the selected physical quantity, when the condition determined by the condition satisfaction determining means is not satisfied, the control target switching means for changing the physical quantity to be changed to another unselected physical quantity. The control device for a power transmission mechanism according to claim 1, further comprising: The control device for a power transmission mechanism according to claim 1, wherein the physical quantity is periodically changed when the slip state is detected. The physical quantity includes a clamping force for clamping a torque transmission member constituting the power transmission mechanism and a torque input to the power transmission mechanism,
The control device for a power transmission mechanism according to any one of claims 1 to 3, wherein the condition is a lower limit value of the clamping force. The control device for a power transmission mechanism according to claim 4, wherein the squeezing force is initially changed to detect the slip state. The physical quantity includes a clamping force for clamping a torque transmission member constituting the power transmission mechanism and a torque input to the power transmission mechanism,
Said conditions include conditions that allow said torque to be varied periodically,
The selecting means is configured to select the squeezing pressure as a physical quantity to be periodically changed when a condition that allows the torque to be periodically changed is not satisfied. The power transmission according to any one of claims 1 to 3, further comprising a slip state detection unit that detects the slip state based on a rotation speed of the power transmission mechanism when the power transmission mechanism is periodically changed. Mechanism control device.

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