JP3628228B2 - Control method of automatic transmission - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control method for an automatic transmission, and more particularly to a shift control method from a low speed to a high speed.
[0002]
[Prior art]
Conventionally, shifting from a low speed to a high speed (for example, shifting from 2nd speed to 3rd speed, 3rd speed to 4th speed) is performed by engaging one engagement element and releasing another engagement element. There is an automatic transmission. In this case, it is difficult to smoothly switch the torque transmission path from the disengagement-side engagement element to the engagement-side engagement element, and there is a problem that the shift time becomes long and a shift shock occurs.
[0003]
In order to solve such a problem, the hydraulic pressure of the engagement element on the disengagement side is reduced, and feedback control is performed so that the input rotation speed is higher than the input rotation speed at the low speed stage by a constant value, and this feedback control is maintained. An automatic transmission has been proposed in which the input rotation speed is reduced by increasing the hydraulic pressure of the engagement element on the engagement side to perform a smooth shift (Japanese Patent Publication No. 7-51984).
[0004]
FIG. 9 is an example of a conventional shift control method, and shows temporal changes in the hydraulic pressure of the engaging element, the input rotation speed (turbine rotation speed), and the output shaft torque during a shift transition from the low speed stage to the high speed stage.
As is apparent from the figure, first, as shown in the region (1), the hydraulic pressure of the engagement element on the disengagement side is reduced to reduce the input rotational speed V at the low speed stage.₂  More constant value r₁  Feedback control is performed so that the target value is as high as possible.
Then, while maintaining the feedback control as in (2), the hydraulic pressure of the engagement element on the engagement side is increased to decrease the input rotational speed. Eventually, as shown in (3), a region called a torque phase where the vehicle acceleration decreases appears, and the rate of decrease of the input rotational speed becomes gentle. Thereafter, since the input rotational speed deviates from the initial target rotational speed, the disengagement-side engagement element is further depressurized to increase the input rotational speed, exits the torque phase, ends the feedback control, and releases the engagement on the disengagement side. The element is completely freed. And time t₁  And the input speed is V₃  To complete the shift.
[0005]
[Problems to be solved by the invention]
Performing the control as described above has the effect of shortening the shift time and reducing the shift shock as compared with the conventional case, but there is a problem that an uncomfortable feeling of deceleration remains because the period of the torque phase becomes relatively long.
[0006]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an automatic transmission control method capable of shortening a shift time and reducing a shift shock, shortening a torque phase period, and improving a feeling of deceleration.
[0007]
[Means for Solving the Problems]
To achieve the above objective,The present invention, An automatic transmission having first and second engagement elements and shifting from a low speed stage to a high speed stage by engaging the first engagement element and releasing the second engagement element , The hydraulic pressure of the second engagement element is reduced and the input rotational speed is higher than the input rotational speed at the low speed stage by a certain valueFirstFeedback control to achieve the target valueFirstProcess and aboveOf the second engagement element using the first target valueWhile maintaining the feedback control, the hydraulic pressure of the first engagement element is increased to reduce the input rotational speed.SecondProcess,By performing feedback control using a second target value that is higher than the first target value after the time when the input rotational speed falls below the input rotational speed at the low speed stage,The pressure reduction gradient of the second engagement element is made larger than the previous pressure reduction gradientThirdProcess,A fourth step of ending feedback control using the second target value and releasing the second engagement element when the input rotational speed is lower than the input rotational speed at a low speed by a predetermined value or more;A method for controlling an automatic transmission having the above is provided.
[0008]
When shifting from the low speed stage to the high speed stage, first, the hydraulic pressure of the second engagement element is reduced, and feedback control is performed so that the input rotational speed becomes a target value higher than the input rotational speed at the low speed stage by a certain value. Then, while maintaining the feedback control, the hydraulic pressure of the first engagement element is increased to reduce the input rotational speed. These steps are the same as in the prior art.
When the input rotational speed falls below the input rotational speed at the low speed stage, a deceleration region called a torque phase is generated. In the present invention, the decompression gradient of the second engagement element in this torque phase is set to be greater than the decompression gradient before the torque phase. It is getting bigger. Therefore, the period of the torque phase can be shortened, and the feeling of deceleration in the torque phase is improved.
[0009]
As a method for making the pressure reduction gradient of the second engagement element in the torque phase larger than the pressure reduction gradient before the torque phase,In the present invention, The feedback target value after the time when the input speed falls below the input speed at the low speed stage is higher than the previous feedback target value.doing. That is, the feedback target value in the torque phase is set higher than the feedback target value before the torque phase.
As a method of making the pressure reduction gradient of the second engagement element in the torque phase larger than the pressure reduction gradient before the torque phase, there is a method of increasing the feedback gain in addition to the method of increasing the target value. Is erroneously determined, there is a risk that the input rotational speed may be increased due to feedback hunting. In contrast,The present inventionIf the target value is increased as described above, the hunting is smaller than that when the feedback gain is increased, and at least the target value is not increased. It is.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an example of an automatic transmission for a vehicle according to the present invention.
This automatic transmission includes a torque converter 1, an input shaft 2 to which engine power is transmitted via the torque converter 1, three clutches C1 to C3, two brakes B1 and B2, a one-way clutch F, and a Ravigneaux type planetary gear. A mechanism 4, an output gear 5, an output shaft 7, a differential device 8 and the like are provided.
In this embodiment, the first engagement element that is engaged when shifting from the low speed stage to the high speed stage in the present invention refers to the C3 clutch, and the second engagement element that is released refers to the B1 brake.
[0011]
The forward sun gear 4a of the planetary gear mechanism 4 is connected to the input shaft 2 via a C1 clutch, and the forward sun gear 4a is connected to the transmission case 6 via a B1 brake. The rear sun gear 4b is connected to the input shaft 2 via a C2 clutch. The carrier 4c is connected to the input shaft 2 via the intermediate shaft 3 and the C3 clutch. The carrier 4c is connected to the transmission case 6 via a B2 brake and a one-way clutch F that allows only forward rotation (in the engine rotation direction) of the carrier 4c. The carrier 4c supports two types of pinion gears 4d and 4e, the forward sun gear 4a meshes with a long pinion 4d having a long shaft length, and the rear sun gear 4b meshes with a long pinion 4d via a short pinion 4e having a short shaft length. . A ring gear 4f that meshes only with the long pinion 4d is coupled to the output gear 5. The output gear 5 is connected to the differential device 8 via the output shaft 7.
[0012]
The automatic transmission realizes four forward speeds and one reverse speed as shown in FIG. 2 by operating the clutches C1, C2, C3, the brakes B1, B2 and the one-way clutch F. In FIG. 2, ● represents the action state of hydraulic pressure. The B2 brake is engaged at the time of reverse and the first speed, but is engaged at the first speed only in the L range.
FIG. 2 also shows operating states of first to fourth solenoid valves (SOL1 to SOL4) 22 to 25 described later. ○ indicates an energized state, x indicates a non-energized state, and Δ indicates a temporarily energized state. This operation table shows the operation in a steady state.
[0013]
FIG. 3 shows an example of a hydraulic control device used in the automatic transmission.
This hydraulic control device includes an oil pump 10, a regulator valve 11, a manual valve 12, a solenoid modulator valve 13, a sequence valve 15, a fail safe valve 16, a B1 pressure control valve 17, a C2 pressure control valve 18, a C2 lock valve 19, and a C3. The pressure control valve 20, the B2 pressure control valve 21, the first to fourth solenoid valves 22 to 25, the electronic control device 30, etc. The electronic control device 30 is input with signals relating to the driving state of the vehicle such as the throttle opening, the vehicle speed, the rotational speed of the input shaft 2 (turbine rotational speed), and the shift position for detecting the position of the shift lever. Accordingly, the first to fourth solenoid valves 22 to 25 are controlled.
[0014]
The first solenoid valve 22 is for B1 brake control, the second solenoid valve 23 is for C2 clutch control, and the third solenoid valve 24 is for both C3 clutch control and B2 brake control. The reason why the third solenoid valve 24 is used for both C3 clutch control and B2 brake control is that the B2 brake does not operate in the D and 2 ranges but is used only in the engine brake control in the L range and the transient control in the R range. This is because it does not interfere with the C3 clutch operated in the D range. The fourth solenoid valve 25 is a valve for switching the sequence valve 15 at the transition between the L range (first speed) and the R range. As described above, since the first to third solenoid valves 22 to 24 need to perform delicate hydraulic control, a duty solenoid valve or a linear solenoid valve is used, and an ON / OFF switching valve is used for the fourth solenoid valve 25. Good.
[0015]
The regulator valve 11 changes the discharge pressure of the oil pump 10 to a predetermined line pressure P._L  To the manual valve 12, solenoid modulator valve 13, B2 pressure control valve 21 and the line pressure P_L  Supply. As shown in FIG. 4, the regulator valve 11 includes a spool 11b urged rightward by a spring 11a, and a plug 11c separate from the spool 11b is provided at the left end. The discharge pressure of the oil pump 10 is input to the port 11d, and the port 11e is connected to the suction side of the oil pump 10. Line pressure P is applied to the rightmost port 11f._L  Has been fed back. C1 clutch pressure P at left end port 11h only during reverse (R)_C1Is input, and the line pressure at the time of backward movement is regulated higher than that at the time of forward movement.
[0016]
In the manual valve 12, the spool 12a is switched to each of L, 2, D, N, R, and P ranges according to manual operation of the shift lever. The line pressure P input from the input port 12b_L  Are selectively output from the forward output port 12c or the reverse output 12d.
[0017]
The solenoid modulator valve 13 is a valve that supplies a constant source pressure to each of the solenoid valves 22 to 25, and includes a spool 13b that is biased leftward by a spring 13a as shown in FIG. The input port 13c is connected to the line pressure P from the regulator valve 11._L  The solenoid modulator pressure Psm is output from the output port 13d to the solenoid valves 22 to 25 and the right end signal port 19c of the C2 lock valve 19. The port 13e is a drain port. The output pressure Psm is fed back to the left end port 13f, whereby the solenoid modulator pressure Psm is adjusted to a hydraulic pressure corresponding to the load of the spring 13a.
[0018]
B1 pressure control valve 17 is B1 brake pressure P_B1As shown in FIG. 5, the pressure regulating valve includes a spool 17b urged to the left by a spring 17a, and a signal pressure P from the first solenoid valve 22 is provided to the left end port 17c._s1Is entered. The port 17d is a drain port. The output port 17e is connected to the B1 brake, and the input port 17f is connected to a port 16i of the failsafe valve 16 described later. Furthermore, the output pressure P is applied to the right end port 17h._B1Has been fed back. Therefore, the output pressure P_B1Is the signal pressure P_s1The pressure is adjusted to a proportional hydraulic pressure.
[0019]
The fail-safe valve 16 is a valve for preventing multiple engagement (interlock) in which the C2, C3 clutch and B1 brake are simultaneously engaged during traveling in the D range. Specifically, when the hydraulic pressure is simultaneously supplied to the three engagement elements C2, C3, B1 due to malfunction of the solenoid valves 22 to 25, failure of the electronic control circuit, sticks of various valves, etc., the hydraulic pressure of the B1 brake P_B1The 3rd speed state is forcibly established by removing The fail-safe valve 16 includes a spool 16b urged to the right by a spring 16a as shown in FIG. 5. Normally, the spool 16b is in the right position as shown in the upper side of the drawing, and is moved to the R range. Only at the time of switching transition and interlock, it switches to the left as shown in the lower part of the drawing. Right end port 16c has C3 clutch pressure P_c3Or R range pressure P_R  Is selectively input, and the C2 clutch pressure P is applied to the port 16d._C2Is input and the B1 brake pressure P is applied to the port 16e._B1And the spool 16b is pushed to the left by these hydraulic pressures. The port 16j at the left end containing the spring 16a has a line pressure P during forward movement._D  Is always input, and the line pressure P at the time of forward movement is also input to the port 16h._D  Is input via the sequence valve 15. Therefore, the spool 16b is pushed rightward by these hydraulic pressures. The port 16 i is connected to the input port 17 f of the B1 pressure control valve 17. The port 16l is a drain port.
In addition to the above ports, the fail safe valve 16 has a reverse hydraulic pressure, that is, a C1 clutch pressure P as shown in FIG._C116f, a port 16g connected to the drain port 21d of the B2 pressure control valve 21, a drain port 16k, and the like.
[0020]
The sequence valve 15 has a function of ensuring the first speed when the second solenoid valve 23 or the C2 pressure control valve 18 is malfunctioning. In addition, since the third solenoid valve 24 is used for both the control of the C3 clutch and the B2 brake, the function of switching the original pressure of the B2 pressure control valve 21 and the C3 pressure control valve 20, R range pressure P to right end port 16c_R  And a function of draining the original pressures of the B1 brake pressure and the C3 clutch pressure when the B2 brake pressure is applied. As shown in FIG. 6, the valve 15 includes a spool 15b biased leftward by a spring 15a, and the signal pressure P of the fourth solenoid valve 25 input to the signal port 15c at the left end._S4To the right. That is, the spool 15b is switched to the right only at the time of the first speed in the L range and the transition to the R range as shown in the lower side of the drawing. The C2 clutch pressure P is supplied from the C2 pressure control valve 18 to the port 15d._C2Is input, and the port 15e is connected to the C2 clutch. The port 15f has a line pressure P from the manual valve 12 when moving forward._D  Is entered. The port 15g is connected to the port 16h of the fail-safe valve 16, and the line pressure P during forward movement_D  Is output. The port 15h is a drain port. The port 15i has a B2 pressure control valve 21 to a B2 brake pressure P._B2Is input, and the port 15j is connected to the B2 brake. Port 15k has a line pressure P during retraction._R  Is input and is directly connected to the C1 clutch. The port 151 is connected to the right end port 16c of the fail safe valve 16, and the port 15m is connected to the C3 clutch.
[0021]
B2 pressure control valve 21 is B2 brake pressure P_B2And a spool 21b biased leftward by a spring 21a. The left end port 21c has a signal pressure P from the third solenoid valve 24 in the R range._S3Is input, and the port 21 d is connected to the port 16 g of the fail-safe valve 16. Further, the port 21e is connected to the B2 brake via the sequence valve 15, and the hydraulic pressure P is supplied to the B2 brake at the time of transition to the 1st speed in the L range and the transition to the R range._B2Has a role to supply. Line pressure P at port 21f_L  , And the output pressure P is applied to the right end port 21g containing the spring 21a._B2Has been fed back.
[0022]
The port 21d is drained because it is connected to the C1 clutch via the failsafe valve 16 during forward travel. Further, the signal pressure P of the third solenoid valve 24 input to the left end port 21c._S3Since the drain is also drained, the spool 21b is in the left end position as shown in the lower side of FIG. Therefore, the hydraulic pressure P to the B2 brake_B2Will also be drained.
[0023]
On the other hand, when the transition from the P, N range to the R range is transitioned, the fourth solenoid valve 25 is temporarily turned on, so that the sequence valve 15 is temporarily switched to the right side and is high at the right end port 16c of the fail safe valve 16. Reverse hydraulic pressure P_R  Is input, the fail-safe valve 16 is also temporarily switched to the left, and the port 21d of the B2 pressure control valve 21 is drained. Further, the signal pressure P from the third solenoid valve 24 to the left end port 21c._S3Therefore, the spool 21b is held at the position shown on the upper side of FIG._B2Is the signal pressure P_S3Proportional to the line pressure P_L  The pressure is adjusted to a lower hydraulic pressure.
In this way, the B2 pressure control valve 21 is configured so that the hydraulic pressure P applied to the B2 brake at the time of transition to the R range._B2Is switched off slowly, in other words, the engagement is delayed from the C1 clutch, thereby reducing the switching shock.
[0024]
C2 pressure control valve 18 is C2 clutch pressure P_C27 and includes a spool 18b biased leftward by a spring 18a as shown in FIG. The input port 18c has a line pressure P during forward travel._D  Is input and the C2 clutch pressure P is output from the output port 18d._C2Is output. A signal pressure P of the second solenoid valve 23 is connected to the left end port 18e via a C2 lock valve 19._s2Or the line pressure P when moving forward_D  Is entered. Reference numeral 18f denotes a drain port. Output pressure P_C2Is fed back to the right end port 18g in which the spring 18a is accommodated, and the output pressure P_C2Is the signal pressure P_s2The pressure is adjusted to a proportional hydraulic pressure.
[0025]
The C2 lock valve 19 has a signal pressure P of the second solenoid valve 23 with respect to the left end port 18e of the C2 pressure control valve 18 at the time of a start transient._s2And the maximum hydraulic pressure P during driving (1st to 3rd speed)_D  It is a valve which switches so that it may supply. As shown in FIG. 7, the lock valve 19 includes a spool 19b biased rightward by a spring 19a, and is pushed leftward by a solenoid modulator pressure Psm input to a signal port 19c at the right end. The input port 19d has a forward line pressure P_D  The output port 19e is connected to the left end port 18e of the C2 pressure control valve 18. The left two ports 19f and 19g are connected to the signal pressure P of the second solenoid valve 23._s2Is entered. At the start of starting, the signal pressure P of the second solenoid valve 23_s2Is lower than the solenoid modulator pressure Psm, the spool 19b is in the left position, and the signal pressure P is applied to the left end port 18e of the C2 pressure control valve 18 via the ports 19g and 19e._s2To control the slippage of the C2 clutch and start slowly. On the other hand, when the start is completed and the vehicle enters the running state, P_s2= Psm, the spool 19b is switched to the right position by the spring 19a, and the line pressure P during forward movement_D  To the left end port 18e of the C2 pressure control valve 18 to securely engage the C2 clutch. Further, when the fourth speed state is reached, the signal pressure P of the second solenoid valve 23 is_s2Is drained, the spool 19b is in the left position, the left end port 18e of the C2 pressure control valve 18 is drained through the ports 19g and 19e, and the C2 clutch is released.
[0026]
The C3 pressure control valve 20 has a C3 clutch pressure P_C37 and includes a spool 20b biased leftward by a spring 20a as shown in FIG. The left end port 20c is connected to the third solenoid valve 24, and its signal pressure P_s3Is entered. Therefore, the spool 20b is in the lower position in FIG. 7 at the 1st and 2nd speeds, and the spool 20b is in the upper position in FIG. 7 at the 3rd and 4th speeds. The port 20d is a drain port, the port 20e is an output port connected to the C3 clutch, and the port 20f has a line pressure P during forward travel._D  Is entered. An output pressure P is applied to the right end port 20g where the spring 20a is disposed._C3Has been fed back.
[0027]
Next, hydraulic control of the C3 clutch (first engagement element) and the B1 brake (second engagement element) at the time of shifting from the second speed to the third speed will be described with reference to FIG.
In FIG. 8, the control of the areas (1) and (2) is the same as in FIG. That is, in the area (1), the hydraulic pressure of the B1 brake on the release side is reduced to reduce the input rotational speed V at the second speed.₂  More constant value r₁  Target value (initial target value R) that is high (for example, about 50 rpm)₁  The feedback control is performed so that
Next, while maintaining feedback control as in (2), the hydraulic pressure of the C3 clutch on the engagement side is increased to decrease the input rotational speed. Eventually, as shown in (3) ', a region called a torque phase where the vehicle acceleration decreases appears, and the rate of decrease of the input rotational speed becomes gentle.
In the torque phase, as indicated by a broken line, the feedback target value of the torque phase (second target value R₂  Is called the initial target value R before the torque phase.₁  Set higher. That is, the input rotation speed V at the second speed stage₂  More constant value r₂  Just make it higher. At this time, the input rotational speed and the second target value R₂  Therefore, the release-side B1 brake is depressurized with a larger gradient than the depressurization gradient in (3) of FIG. 9 in an attempt to increase the input rotational speed as in (3) '. As a result, it is possible to exit the torque phase in a short time and to improve the feeling of deceleration.
Note that the end of the torque phase indicates that the input speed is V at the second speed.₂  What is necessary is just to determine that it is complete | finished when it becomes lower than more than a predetermined value (for example, about 30 rpm).
At the end of the torque phase, the feedback control is terminated, the hydraulic pressure of the disengagement side B1 brake is released, and the hydraulic pressure of the engagement side C3 clutch rises.₁  And the input speed is the input speed V at the third gear.₃  To complete the shift.
In FIG. 8, in order to make the feedback target value higher than the initial target value, it is increased stepwise. However, it may be gradually increased by providing an ascending gradient, or may be increased stepwise in multiple steps. .
[0028]
Although FIG. 8 illustrates the hydraulic control of the C3 clutch and the B1 brake at the time of the shift transition from the second speed to the third speed, the present invention is applied to the hydraulic control of the C2 clutch and the B1 brake at the time of the shift transition from the third speed to the fourth speed. Is also applicable. That is, as is apparent from FIG. 2, when shifting from the 3rd speed to the 4th speed, the C2 clutch is released and the B1 brake is engaged. In this case, the B1 brake becomes the first engagement element. , C2 clutch is the second engagement element.
[0029]
In the automatic transmission of this embodiment, the operation of the one-way clutch F is used at the time of shifting from the first speed to the second speed, and the engagement element is not engaged and released, but the shifting from the first speed to the second speed is performed. The present invention can be applied to an automatic transmission that sometimes engages and disengages two engaging elements.
[0030]
In the above-described embodiment, the automatic transmission having the three clutches C1 to C3 and the two brakes B1 and B2 has been described. However, the present invention is not limited to this. Any automatic transmission that engages one engaging element and releases the other engaging element at the time of shifting to a high speed stage can be applied.
Although the hydraulic control valves for the B1 brake and the C3 clutch are configured by the combination of the spool valves 17 and 20 and the solenoid valves 22 and 24, they may be configured by a single solenoid valve. As the solenoid valve in this case, a known solenoid valve such as a duty solenoid valve or a linear solenoid valve can be used.
[0031]
【The invention's effect】
As apparent from the above description, according to the present invention, when shifting from the low speed stage to the high speed stage, the hydraulic pressure of the engagement element on the disengagement side is reduced to make the input rotational speed constant from the input rotational speed at the low speed stage. Since the feedback control is performed so that the target value is higher by the value, and the feedback control is maintained, the hydraulic pressure of the engagement element on the engagement side is increased to reduce the input rotation speed, so the shift time can be shortened. At the same time, the shift shock can be reduced.
In addition, since the decompression gradient of the disengagement element on the disengagement side in the torque phase is made larger than the decompression gradient before the torque phase, the torque phase period can be shortened, and the feeling of deceleration during shifting can be improved. .
Furthermore, since the target value in the torque phase is set higher than before the torque phase, the hunting is small and does not blow up at least above the target value.
[Brief description of the drawings]
FIG. 1 is a schematic mechanism diagram of an example of a vehicle automatic transmission according to the present invention.
FIG. 2 is an operation table of each engagement element and solenoid valve of the automatic transmission of FIG. 1;
FIG. 3 is an overall circuit diagram of a hydraulic control device for the automatic transmission shown in FIG. 1;
4 is a circuit diagram of a regulator valve, a manual valve, and a solenoid modulator valve in the hydraulic control device of FIG. 3;
5 is a circuit diagram of a B1 pressure control valve and a failsafe valve in the hydraulic control device of FIG. 3. FIG.
6 is a circuit diagram of a fail-safe valve, a sequence valve, and a B2 pressure control valve in the hydraulic control device of FIG. 3. FIG.
7 is a circuit diagram of a C2 pressure control valve, a C2 lock valve, and a C3 pressure control valve in the hydraulic control device of FIG. 3. FIG.
FIG. 8 is a time change diagram of hydraulic pressure, input rotation speed, and output shaft torque of the C3 clutch and B1 brake at the time of shifting from the second speed to the third speed according to the present invention.
FIG. 9 is a time change diagram of the hydraulic pressure, input rotation speed, and output shaft torque of the engagement element at the time of shifting from the conventional low speed stage to the high speed stage.
[Explanation of symbols]
C3 clutch (first engaging element)
B1 Brake (second engagement element)
17 B1 pressure control valve
20 C3 pressure control valve
22, 24 Solenoid valve
30 Electronic control unit

Claims (1)

In an automatic transmission having first and second engagement elements, wherein the first engagement element is engaged and the second engagement element is released to shift from a low speed to a high speed. ,
A first step of performing feedback control so that the input rotation speed hydraulic and vacuum of the second engagement element is a first target value higher by a predetermined value than the input speed for the low speed stage,
A second step of increasing the hydraulic pressure of the first engagement element to reduce the input rotational speed while maintaining feedback control of the second engagement element using the first target value ;
After the time when the input rotational speed falls below the input rotational speed at the low speed stage, feedback control using the second target value higher than the first target value is performed , thereby reducing the pressure reduction gradient of the second engagement element. A third step of making it greater than the previous vacuum gradient;
A fourth step of ending feedback control using the second target value and releasing the second engagement element when the input rotational speed is lower than the input rotational speed at a low speed by a predetermined value or more; A control method for an automatic transmission having

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