JP2008025724A - Controller for automatic transmission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect fastening start of a friction engagement element when performing select operation from a neutral range to a traveling range. <P>SOLUTION: In the automatic transmission connected with an engine via a torque converter, the time from completing selection from the neutral range to the travelling range to detection of fastening start of the friction engagement element is measured and a line pressure is learned based on the time, wherein fastening start of the friction engagement element is judged based on a changing speed of a ratio (Nt/Ne) of a turbine rotation speed Nt and an engine speed Ne. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control device for an automatic transmission, and more particularly to a technique for fastening a friction engagement element in accordance with switching from a neutral range to a travel range.

Patent Document 1 discloses the start of engagement of a friction engagement element associated with switching from a neutral range to a travel range based on whether or not the turbine rotation speed of the torque converter has decreased by a predetermined rotation speed from the rotation speed in the neutral range. Automatic shift to measure the time from when the selection operation to the travel range is performed until the engagement of the friction engagement element is started, and to correct the precharge pressure in the engagement control according to the measurement time A machine control device is disclosed.
JP-A-6-011026

By the way, when the accelerator operation is performed simultaneously with the selection operation to the travel range and the engine rotation speed is changed, the turbine rotation speed is changed by the change of the engine rotation speed.
For this reason, when it is determined that the engagement of the friction engagement element is started based on the turbine rotational speed as in the conventional case, the engagement of the friction engagement element is started when the accelerator operation is performed simultaneously with the selection operation to the travel range. There was a possibility of misjudging.

If the start of engagement of the frictional engagement element is erroneously determined, the precharge pressure is erroneously corrected, thereby causing a problem that a shock occurs due to the selection operation or the shift is delayed.
The present invention has been made in view of the above problems, and even when the accelerator operation is performed simultaneously with the selection operation from the neutral range to the traveling range, the engagement start of the friction engagement element can be accurately detected. Therefore, an object of the present invention is to provide an automatic transmission control device capable of appropriately correcting the engagement control of the friction engagement element.

Therefore, the invention according to claim 1 determines the fastening start of the friction engagement element accompanying the switching from the neutral range to the travel range based on the ratio between the input shaft rotational speed and the output shaft rotational speed of the torque converter, Based on the determination of the engagement start, the engagement of the frictional engagement element accompanying the switching from the neutral range to the travel range is controlled.
According to the above-described invention, the engagement start of the friction engagement element accompanying the switching from the neutral range to the travel range is determined by the ratio of the input shaft rotational speed (engine rotational speed) and the output shaft rotational speed (turbine rotational speed) of the torque converter. Detect based on change.

In the neutral state of the transmission, the output shaft rotational speed Nt of the torque converter varies with the input shaft rotational speed Ne (engine rotational speed) due to the action of the fluid inside the torque converter, and the input shaft rotational speed Ne is steady. For example, the rotational speed ratio Nt / Ne can be regarded as Nt / Ne = 1 × f (f is an energy loss coefficient).
On the other hand, when the friction engagement element is engaged with the selection operation to the travel range, the output shaft rotational speed Nt of the torque converter is directed to a value obtained by multiplying the output shaft rotational speed Nout of the transmission by the speed ratio. Since switching from the neutral range to the travel range is generally performed when the vehicle is stopped, the output shaft rotational speed Nt of the torque converter changes in the decreasing direction, and (Nt / Ne) also changes in the decreasing direction. Therefore, the start of engagement of the friction engagement element is detected based on the change in the decreasing direction of Nt / Ne.

Therefore, even if the accelerator operation is performed at the same time as the select operation, it is possible to avoid erroneously detecting the engagement start of the friction engagement element due to a change in the input shaft rotational speed (engine rotational speed) of the torque converter, and the friction The fastening control of the engagement element can be appropriately corrected.
According to a second aspect of the present invention, when the fluctuation of the input shaft rotation speed of the torque converter is large, the fastening start determination based on the rotation speed ratio is prohibited.

According to the above invention, if the fluctuation of the input shaft rotation speed of the torque converter is large, this affects the rotation speed ratio, and the detection accuracy of the engagement start of the friction engagement element is lowered.
Accordingly, it is possible to avoid erroneously detecting the start of engagement of the friction engagement element when the accelerator is greatly depressed in accordance with the selection operation to the travel range and the engine speed rapidly increases.

According to the third aspect of the present invention, the detected value of the input shaft rotational speed of the torque converter is subjected to a smoothing process, and the friction engagement is performed based on the ratio between the input shaft rotational speed and the output shaft rotational speed after the smoothing process. It is characterized by determining the start of element fastening.
According to the above invention, since the change in the output shaft rotational speed is delayed with respect to the change in the input shaft rotational speed of the torque converter, the smoothing process corresponding to the delay characteristic with respect to the detected value of the input shaft rotational speed. To prevent the rotation speed ratio from changing due to the change in the output shaft rotation speed corresponding to the change in the input rotation speed.

Therefore, the change in the rotation speed ratio when the input shaft rotation speed changes can be suppressed, and the change in the rotation speed ratio accompanying the start of the engagement of the friction engagement element can be detected with higher accuracy.
According to a fourth aspect of the present invention, the speed of change of the rotational speed ratio is compared with a threshold that is variably set based on at least one of the engine rotational speed, the oil temperature, and the accelerator operation speed. It is characterized by determining the start of fastening of the joint element.

According to the above invention, the change speed of the ratio between the input shaft rotational speed and the output shaft rotational speed of the torque converter is compared with a threshold value to detect the engagement start of the friction engagement element. It is variably set based on at least one of speed, oil temperature, and accelerator operation speed.
Accordingly, it is possible to accurately detect the engagement start of the friction engagement element in response to the change speed of the rotation speed ratio being affected by the engine rotation speed, the oil temperature, and the accelerator operation speed.

In the neutral range, the peak value of the change speed of the rotation speed ratio is obtained, and the peak value and the change speed of the rotation speed ratio after the change from the neutral range to the travel range is performed. To determine the start of the fastening.
According to the above invention, when a change exceeding the change in the neutral range occurs after shifting to the travel range after obtaining the change in the rotation speed ratio caused by the fluctuation of the engine rotation speed in the neutral range. It is determined that this is due to a change in the output shaft rotation speed due to the start of engagement of the friction engagement element, and the engagement start of the friction engagement element is detected.

  Therefore, even if there are variations in individual automatic transmissions or changes with time, it is possible to accurately detect the engagement start of the friction engagement element after switching from the neutral range to the travel range.

Embodiments of the present invention will be described below.
FIG. 1 shows a power train system for a vehicle including a control device for an automatic transmission according to the present invention.
In FIG. 1, the output of the engine (internal combustion engine) 20 is transmitted to the transmission mechanism 2 via the torque converter 1.

As shown in FIG. 2, the transmission mechanism 2 includes two sets of planetary gears G1, G2, three sets of multi-plate clutches H / C, R / C, L / C, one set of brake bands 2 & 4 / B, It consists of a set of multi-plate brakes L & R / B and a set of one-way clutches L / OWC.
The two sets of planetary gears G1 and G2 are simple planetary gears composed of sun gears S1 and S2, ring gears r1 and r2, and carriers c1 and c2, respectively.

The sun gear S1 of the planetary gear set G1 is configured to be connectable to the input shaft IN by a reverse clutch R / C, and is configured to be fixed by a brake band 2 & 4 / B.
The sun gear S2 of the planetary gear set G2 is directly connected to the input shaft IN.
A carrier c1 of the planetary gear set G1 is configured to be connectable to the input shaft I by a high clutch H / C, while a ring gear r2 of the planetary gear set G2 is a carrier of the planetary gear set G1 by a low clutch L / C. The carrier c1 of the planetary gear set G1 can be fixed by a low & reverse brake L & R / B.

A ring gear r1 of the planetary gear set G1 and a carrier c2 of the planetary gear set G2 are directly and integrally connected to the output shaft OUT.
In the speed change mechanism 2 configured as described above, the first to fourth speeds and the reverse speed are realized by a combination of engagement states of the respective clutches and brakes (friction engagement elements).
Each clutch / brake (friction engagement element) is operated by a supply hydraulic pressure, and the supply hydraulic pressure for each clutch / brake is adjusted by various solenoid valves included in the solenoid valve unit 11 shown in FIG. The

  An A / T controller 12 for controlling various solenoid valves of the solenoid valve unit 11 detects an oil temperature sensor 13 for detecting the temperature of an ATF (automatic transmission fluid), and an opening degree of an accelerator operated by a driver. An accelerator opening sensor 14, a vehicle speed sensor 15 that detects the traveling speed (vehicle speed) of the vehicle, a turbine rotation sensor 16 that detects a turbine rotation speed Nt that is an output shaft rotation speed of the torque converter 1, and an input shaft rotation speed of the torque converter 1. The engine rotation sensor 17 for detecting the rotational speed Ne of the engine 20, the air flow meter 18 for detecting the intake air amount of the engine 20, the inhibitor switch 19 for detecting the shift position of the shift lever 21 operated by the driver, and the engine 20 Detecting throttle opening TVO Liters detection signal from the opening sensor 22 etc. are input, based on these detection results, controls the engagement oil pressure of each frictional engagement element.

As the ranges selected by the shift lever 21, a parking range P, a reverse range R, a neutral range N, a drive range D, and a low range L are provided.
The A / T controller 12 determines a target gear position from the range selected by the shift lever 21, the vehicle speed, the accelerator opening, etc., and if the target gear position differs from the actual gear position, the solenoid valve unit By controlling the various solenoid valves 11, the clutch / brake (friction engagement element) is controlled to be engaged / released to shift to the target shift stage.

  Further, as a characteristic control in the present application, when the A / T controller 12 is switched from the neutral range N to the travel range such as the reverse range R or the drive range D, the friction engagement element starts to be engaged from the switching of the range. And has a function of learning the line hydraulic pressure (precharge hydraulic pressure) when the friction engagement element is fastened so that the time approaches the target time. Will be described with reference to the flowcharts of FIGS.

The routines shown in the flowcharts of FIGS. 3 to 5 are executed every predetermined minute time (for example, 10 ms). First, in step S100, the turbine rotational speed Nt and the engine rotational speed Ne are detected.
In step S101, the engine rotation speed Ne detected in step S100 is subjected to a smoothing process, and the processed value is set to Ne ′.

As the annealing process, a known process that can delay the transient response to the detected value of the engine rotational speed Ne, such as a signal process using a low-pass filter and a moving average calculation, can be adopted as appropriate, and the annealing process is performed. The phase is matched with the turbine rotational speed Nt that changes with a delay with respect to the change in the engine rotational speed Ne.
In step S102, it is determined whether or not the current shift position is in the neutral range N.

When it is in the neutral range N, the process proceeds to step S103, and it is determined whether or not the absolute value of the difference ΔTVO between the current value of the throttle opening TVO and the previous value is smaller than a predetermined value ε. It is determined whether or not the throttle opening TVO is stable in a state where it is shifted to, in other words, whether or not the accelerator is operated.
Note that it is possible to determine whether or not the accelerator opening is stable instead of the throttle opening TVO.

When it is determined that the absolute value of ΔTVO is smaller than the predetermined value ε and the throttle opening TVO is stable, the process proceeds to step S104, and it is determined whether or not a certain time has passed since the shift to the neutral range N. to decide.
If a predetermined time or more has elapsed since the shift to the neutral range N, the process proceeds to step S105, and a difference Δ (Nt / Ne ′) between the current value of Nt / Ne ′ and the previous value is calculated (Δ ( Nt / Ne ′) = current value of Nt / Ne′−previous value of Nt / Ne ′).

Δ (Nt / Ne ′) indicates the changing speed of the rotational speed ratio between the input shaft rotational speed and the output shaft rotational speed of the torque converter 1.
In the next step S106, the negative value of Δ (Nt / Ne ′) is peak-held, and the negative peak value is stored as α.
In step S107, an update permission flag for an ND learning value to be described later is set.

In step S108, line pressure control in the neutral range N is executed.
On the other hand, if it is determined in step S102 that the current shift position is not in the neutral range N, the process proceeds to step S109.
In step S109, it is determined whether or not the line pressure control (ND selection line pressure control) is being performed at the time of switching from the neutral range N to the drive range D.

The ND select line pressure control is performed for a certain period of time after switching from the neutral range N to the drive range D in order to reduce the clutch engagement shock when switching from the neutral range N to the drive range D. It has become.
If it is determined in step S109 that the ND select line pressure is being controlled, the process proceeds to step S110.

In step S110, after switching from the neutral range N to the drive range D, it is determined whether or not the clutch engagement start is determined.
If the start of fastening is not determined, the process proceeds to step S111, and a counter for measuring the elapsed time after switching from the neutral range N to the drive range D is counted up.

In the next step S112, the difference ΔNe ′ between the current value and the previous value of the engine speed Ne ′ after the annealing process, and the difference Δ (Nt / Ne ′) between the current value and the previous value of Nt / Ne ′. Are calculated respectively.
In step S113, it is determined whether or not the absolute value of ΔNe ′ is larger than a threshold value γ (> 0) stored in advance.

When the absolute value of ΔNe ′ is larger than the threshold value γ, it is assumed that the accelerator operation is performed almost simultaneously with switching from the neutral range N to the drive range D. In such a case, Δ (Nt / Ne ') The clutch engagement start cannot be detected accurately.
Therefore, when the absolute value of ΔNe ′ is larger than the threshold value γ, the process proceeds to step S118, and the update is prohibited by clearing the update permission flag for the ND learning value.

On the other hand, if the absolute value of ΔNe ′ is equal to or smaller than the threshold value γ, the process proceeds to step S114, and it is determined whether or not Δ (Nt / Ne ′) is larger than a previously stored threshold value β (> 0).
For example, when the operation of returning the accelerator (throttle) is performed in accordance with the selection operation from the neutral range N to the drive range D and the engine rotation speed Ne decreases, the turbine rotation speed Nt also decreases accordingly. Become.

However, if the decrease in the engine rotation speed Ne is large and the follow-up of the turbine rotation speed Nt is delayed more than the specified value, the turbine rotation speed Nt and the decrease due to the engagement of the clutch and the decrease in the turbine rotation speed Nt following the engine rotation speed Ne There is a possibility that the clutch engagement start timing may be erroneously detected because the distinction cannot be clearly made.
Therefore, it is determined whether Δ (Nt / Ne ′) is larger than the threshold value β whether or not the follow-up of the turbine rotational speed Nt is delayed more than a specified amount with respect to the decrease in the engine rotational speed Ne.

If Δ (Nt / Ne ′) is larger than the threshold value β, the process proceeds to step S119, and the update is prohibited by clearing the update permission flag for the ND learning value.
If Δ (Nt / Ne ′) is equal to or smaller than the threshold value β, the process proceeds to step S115, and it is determined whether Δ (Nt / Ne ′) is smaller than the peak value α.
The peak value α is a negative peak value of Δ (Nt / Ne ′) obtained in a state where the peak value α is shifted to the neutral range N and the throttle is stable. When Nt / Ne ′) becomes smaller, it is determined that the turbine rotational speed Nt has decreased due to the start of clutch engagement associated with switching from the neutral range N to the drive range D.

Accordingly, if it is determined that Δ (Nt / Ne ′) is smaller than the peak value α, the process proceeds to step S116, and it is determined whether or not the clutch is engaged according to switching from the neutral range N to the drive range D.
In addition, instead of comparing Δ (Nt / Ne ′) with a threshold value α which is a negative peak value when shifted to the neutral range N, the Δ (Nt / Ne ′) may be compared with a predetermined value (<0) stored in advance. Further, it can be compared with a threshold value α (<0) that is variably set according to the operation condition at that time.

When the threshold value α to be compared with Δ (Nt / Ne ′) is variably set according to the driving condition, at least one of the engine speed Ne, the ATF temperature, and the throttle (accelerator) opening change is set as the driving condition. One can be included.
When the threshold value α is variably set according to the engine rotational speed Ne, as shown in FIG. 6, the threshold value α is made smaller as the engine rotational speed Ne is higher.

As a result, when Δ (Nt / Ne ′) does not change more rapidly during high rotation, the clutch engagement start is not judged, and due to the response delay of the turbine rotation speed Nt to the change in the engine rotation speed Ne, It is possible to prevent erroneous determination of the clutch engagement start.
When the threshold value α is variably set according to the ATF temperature, the higher the oil temperature, the longer the response delay of the turbine rotation speed Nt with respect to the change in the engine rotation speed Ne, and the larger the steady rotation speed difference. Therefore, as shown in FIG. 7, the higher the oil temperature, the smaller the threshold α.

Further, when the threshold value α is variably set according to the throttle (accelerator) opening degree change, as shown in FIG. 8, the threshold value α is set as the change in the opening degree is large and the engine speed Ne changes more greatly. Set a smaller value.
In step S117, ND select line pressure control is executed.
When the clutch is engaged, the hydraulic pressure is rapidly increased to the precharge pressure, and then the hydraulic pressure is gradually increased from the precharge pressure to start the clutch engagement. The learning value is set as the line pressure that is the pressure.

In the learning of the line pressure, as described later, the time from when the shift operation from the neutral range N to the drive range D is performed until the start of engagement of the clutch that is engaged with the shift operation is detected is detected. The line pressure (precharge pressure) is increased or decreased so that the measured time becomes the target time.
If it is determined in step S116 that the clutch engagement start is determined, it is determined in step S110 that the clutch engagement start is detected, and the process proceeds to step S120.

In step S120, since the clutch engagement is started, the hydraulic pressure supplied to the clutch is reduced by lowering the line pressure than before the engagement is started in order to prevent the occurrence of a shock due to the rapid engagement of the clutch. Lower the clutch so that the clutch is gradually fully engaged.
On the other hand, when the period for performing the ND select line pressure control elapses, the process proceeds from step S109 to step S121.

In step S121, it is determined whether or not an ND learning value update permission flag is set.
If the ND learning value update permission flag is set, the process proceeds to step S122, where the ND learning value (line pressure in ND select line pressure control) is updated.
Specifically, the time from when the neutral range N is switched to the drive range D to when the clutch engagement start is detected is compared with the target time.

  Here, if the actual time is shorter than the target time, it is determined that the hydraulic pressure (precharge pressure) is too high and a shock may occur, and the line pressure in the ND select line pressure control is reduced. Conversely, when the actual time is longer than the target time, it is determined that the hydraulic pressure (precharge pressure) is too low and the shift is delayed, and the line pressure in the ND select line pressure control is determined. Learn to update.

Note that instead of learning the line pressure based on the time until the start of engagement is detected, the precharge command pressure can be learned, or the hydraulic pressure increase speed can be changed.
In step S123, the update is prohibited by clearing the update permission flag of the ND learning value.
Further, in step S124, the value of the counter that measures the time from when the neutral range N is switched to the drive range D to when the clutch engagement start is detected is cleared.

In step S125, normal line pressure control is performed.
According to the above embodiment, since the clutch engagement start associated with the switching from the neutral range N to the drive range D is determined based on the ratio between the turbine rotational speed Nt and the engine rotational speed Ne, the fluctuation effect of the engine rotational speed Ne. Accordingly, it is possible to avoid erroneous detection of the start of fastening.

Accordingly, the clutch hydraulic pressure (precharge pressure) to be engaged when switching from the neutral range N to the drive range D is appropriately set to prevent the occurrence of a shock, and the clutch engagement can be completed quickly to accelerate acceleration. Can be maintained.
For example, when the clutch engagement start is determined based on the turbine rotation speed Nt, the turbine rotation speed Nt changes due to the influence of the engine rotation speed Ne. The decrease in the turbine rotational speed Nt following the decrease in Ne cannot be separated, and the start of clutch engagement may be erroneously detected (see FIG. 9).

  On the other hand, the ratio of the turbine rotation speed Nt to the engine rotation speed Ne changes at a substantially constant value when the turbine rotation speed Nt changes following the fluctuation of the engine rotation speed Ne. On the other hand, when the turbine rotation speed Nt changes due to the start of clutch engagement, the turbine rotation speed Nt decreases accordingly. Therefore, the turbine rotation speed Nt decreases due to the clutch engagement, and the engine rotation speed Ne decreases. The decrease in the turbine rotation speed Nt following the above can be separated, and the start of clutch engagement can be detected with high accuracy (see FIG. 9).

  Further, since the change in the turbine rotation speed Nt following the change in the engine rotation speed Ne causes a delay, the engine rotation speed Ne is subjected to a smoothing process, and the engine rotation speed Ne ′ and the turbine rotation speed after the annealing process are performed. If the ratio to Nt is obtained, the influence of the delay is eliminated, and the decrease in the turbine rotation speed Nt due to the engagement of the clutch and the decrease in the turbine rotation speed Nt following the decrease in the engine rotation speed Ne are further increased. Separation with high accuracy.

Further, if the negative peak value when the neutral range N is selected is used as the threshold value α to be compared with Δ (Nt / Ne ′), Nt / Ne that can occur when the engine speed Ne changes following the engine speed Ne. A decrease in Nt / Ne accompanying a decrease in turbine rotational speed Nt can be determined on the basis of the decrease in '.
Therefore, even if there are variations in individual automatic transmissions or changes with time, it is possible to accurately detect the engagement start of the clutch after switching from the neutral range N to the drive range D.

In the above-described embodiment, the control at the time of switching from the neutral range N to the drive range D is shown. However, at the time of switching from the neutral range N to the reverse range R, the start of clutch engagement is similarly detected. The hydraulic pressure can be learned, and the travel range is not limited to the drive range D.
In addition, on the condition that the vehicle speed is 0, it is possible to detect the start of engagement and perform hydraulic pressure learning.

Next, inventions other than those described in the claims that can be grasped from the above-described embodiment will be described together with the effects thereof.
(A) The automatic transmission according to any one of claims 1 to 3, wherein the engagement start of the friction engagement element is determined based on a comparison between a change speed of the rotation speed ratio and a threshold value. Control device.
According to the above invention, since the rotational speed ratio changes as the output shaft rotational speed of the torque converter decreases as the friction engagement element starts to be engaged, it is based on whether the rotational speed ratio change speed exceeds the threshold value. The start of fastening of the friction engagement element is determined.

Therefore, it is possible to accurately determine the start of engagement of the friction engagement element by accurately capturing the change in the rotation speed ratio due to the decrease in the output shaft rotation speed of the torque converter.
(B) A control device for an automatic transmission according to claim 5, wherein a peak value of the change speed of the rotational speed ratio is obtained after a predetermined time has elapsed since switching to the neutral range.

According to the above invention, when there is a large rotational speed difference between the input shaft and the output shaft of the torque converter immediately after switching to the neutral range, it is avoided to sample this as a peak value. .
Therefore, the change in the rotation speed ratio affected by the change in the engine rotation speed can be sampled with high accuracy, and the detection accuracy of the engagement start of the friction engagement element can be maintained.

The system diagram which shows the control system of the automatic transmission in embodiment. The figure which shows the transmission mechanism of the automatic transmission in embodiment. The flowchart which shows the oil pressure learning control at the time of ND selection in embodiment. The flowchart which shows the oil pressure learning control at the time of ND selection in embodiment. The flowchart which shows the oil pressure learning control at the time of ND selection in embodiment. The diagram which shows the correlation with the engine rotational speed and threshold value in embodiment. The diagram which shows the correlation with the oil temperature and threshold value in embodiment. The diagram which shows the correlation with the throttle opening change in embodiment, and a threshold value. The time chart which shows the mode of the detection of the fastening start timing in embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Torque converter, 2 ... Transmission mechanism, 11 ... Solenoid valve unit, 12 ... A / T controller, 13 ... A / T oil temperature sensor, 14 ... Accelerator opening sensor, 15 ... Vehicle speed sensor, 16 ... Turbine rotation sensor, 17 ... Engine rotation sensor, 18 ... Air flow meter, 19 ... Inhibitor switch, 20 ... Engine, 21 ... Shift lever, 22 ... Throttle opening sensor, G1, G2 ... Planetary gear, H / C ... High clutch, R / C ... Reverse clutch, L / C ... Low clutch, 2 & 4 / B ... 2-speed / 4-speed band brake, L & R / B ... Low & reverse brake

Claims (5)

In an automatic transmission that is connected to an engine via a torque converter and performs a shift by controlling engagement / release of a friction engagement element,
Determination of the engagement start of the friction engagement element associated with switching from the neutral range to the travel range is made based on the ratio of the input shaft rotation speed and the output shaft rotation speed of the torque converter, and based on the determination of the engagement start, A control device for an automatic transmission that controls fastening of a friction engagement element in association with switching from the neutral range to a travel range. 2. The control device for an automatic transmission according to claim 1, wherein when the fluctuation of the input shaft rotational speed is large, the fastening start determination based on the rotational speed ratio is prohibited. The detected value of the input shaft rotational speed is subjected to a smoothing process, and the fastening start is determined based on a ratio between the input shaft rotational speed and the output shaft rotational speed after the smoothing process. 3. A control device for an automatic transmission according to 1 or 2. Comparing the change speed of the rotation speed ratio with a threshold value variably set based on at least one of an engine rotation speed, an oil temperature, and an accelerator operation speed, and determining the fastening start. The control device for an automatic transmission according to any one of claims 1 to 3. Obtain the peak value of the change speed of the rotation speed ratio in the neutral range, compare the peak value with the change speed of the rotation speed ratio after switching from the neutral range to the travel range, and start the fastening The control device for an automatic transmission according to any one of claims 1 to 3, wherein:

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