KR19980040245A - Hydraulic control system for automatic transmission and its control method - Google Patents

Abstract

It provides automatic transmission that can achieve the 4th forward speed and 1st reverse speed, but the friction element with small inertia change is given priority by controlling the operation of the friction element with large change of inertia during shifting from driving range to neutral range. In order to reduce the shift shock and improve the shifting feeling by the operation of the friction element having a large inertia change after the operation is performed, the oil pump for generating hydraulic pressure by the drive gear rotating together when the engine is driven, the oil Pressure control means for adjusting the hydraulic pressure generated from the pump to the appropriate line pressure when the vehicle is moving forward or backward, a torque converter for transmitting the driving force of the engine to the input shaft of the transmission, and a damper clutch for increasing the power transmission efficiency of the torque converter With converter clutch regulator valve to supply the working pressure of A converter feed valve that receives oil discharged from a pump and supplies oil of a constant pressure to the converter clutch regulator valve, and a line pressure from the pressure control means in conjunction with a shift lever to drive range, reverse range, two range, A manual valve selectively discharged to an L-range pipeline and a transmission control unit connected to a plurality of pipelines connected to the manual valve to be turned on and off by a transmission control unit so as to block or penetrate hydraulic pressure, A plurality of solenoid valves that independently supply the hydraulic pressure according to the capacity and are independently controlled, a plurality of switch valves for selectively supplying the hydraulic pressure supplied to the solenoid valve to a plurality of friction elements, and the hydraulic pressure supplied to the switch valve. Common to each gear, or optional In a hydraulic control system for an automatic transmission comprising a plurality of friction elements actuating, branch line pressure lines from the oil pump are branched to control the friction elements that operate at four speeds in the drive-on driving range and are inactive at other transmission stages. Connected to one side of the valve body to move the valve spool of the fail-safe valve; Friction elements that are non-operated in parking ranges and travel ranges and operated in other ranges by branching the conduit, and run at speeds 3, 4 and 3 in the drive range with drive-off with reverse range drive on And moveably connect the valve spool of the switch valve to selectively control another friction element which is inoperative at another shift stage; It is connected to the L-range pipe connected from the above-mentioned pipe line and the manual valve, but it is made through the direction switching means to move the valve spool of the switch valve by selectively supplying the L-range pipe or line pressure to the connection part. It provides a hydraulic control system for an automatic transmission.

Description

Hydraulic control system for automatic transmission and its control method

The present invention relates to a hydraulic control system for an automatic transmission and a control method thereof, and more particularly, a hydraulic control system for an automatic transmission, which reduces shift shock when shifting from a driving range 1 speed to a neutral range, thereby improving shifting feeling. The control method is related.

In general, the automatic transmission has a torque converter and a multistage shifting mechanism connected to the torque converter, and a hydraulically operated friction element for selecting one of the gear stages of the transmission gear mechanism according to the driving condition of the vehicle. It is included. The hydraulic control system of the automatic transmission for a vehicle operates the hydraulic pressure generated from the oil pump through a control valve to select and operate a friction element so that an appropriate shift can be automatically performed according to the driving state of the vehicle. The hydraulic control system is a pressure control means for regulating the hydraulic pressure generated from the oil pump, manual and automatic shift control means that can form a shift mode, and shifting speed and response to form a smooth shift mode during shifting Hydraulic control means, damper clutch control means for actuating the damper clutch of the torque converter, and hydraulic distribution means for distributing a proper hydraulic supply to each friction element. And the automatic transmission for automobiles that are commonly used includes a pump impeller connected to the output shaft of the engine to drive together, a turbine runner connected to the input shaft of the transmission to operate together, and a stator disposed between the impeller and the turbine runner It has a fluid torque converter.

This configuration causes the fluid to circulate by the pump impeller driven by the engine with the aid of the stator, which causes the fluid to flow in a direction that does not interfere with the rotation of the pump impeller when the fluid enters the impeller from the turbine runner. Automatic shifting is achieved by changing the speed ratio in the planetary gear system by the operation of a friction element such as a clutch or a kick-down brake at each shift stage. In addition, the friction element is selectively operated by changing the flow direction of the hydraulic pressure by a plurality of valves of the hydraulic control device, the manual valve is a port conversion to the selected position of the driver's shift lever to the fluid pressure from the oil pump It is intended to be supplied and is connected to a pipeline to supply this fluid pressure to the shift control valve.

The hydraulic control system for an automatic transmission is an example in which a friction element that operates in common when shifting from the parking and the neutral range to the driving range or the reverse range is used to reduce the static shock during shifting. However, this also has a disadvantage in that the shift shock is increased due to the operation of the large frictional inertia during the shift from the driving range to the neutral range. Therefore, there is a problem that the shift feeling is reduced.

An object of the present invention for solving the problems of the prior art is to provide an automatic transmission that can obtain a shift stage of the battery 4 speed and reverse 1 speed, the friction element having a large inertia change when shifting from the driving range to the neutral range. By controlling the operation of momentarily, the friction element with small inertia change is preferentially operated, and then the friction element with large inertia change is performed to reduce the shift shock to improve the feeling of shift.

Therefore, in order to achieve the object of the present invention, the oil pump for generating oil pressure by the drive gear rotates together when the engine is driven, and the oil pressure generated from the oil pump is adjusted to the appropriate line pressure when the vehicle is moving forward or backward A pressure regulating means, a torque converter for transmitting the driving force of the engine to the input shaft of the transmission, a converter clutch regulator valve for supplying an operating pressure of a damper clutch for increasing the power transmission efficiency of the torque converter, and oil discharged from the oil pump. A converter feed valve for supplying a constant pressure oil to the converter clutch regulator valve and the converter clutch is connected to a shift lever, and the line pressure from the pressure regulating means is selectively selected as a traveling range, a reverse range, a second range, and an L range pipeline. A manual valve to be discharged to the manual valve A plurality of solenoid valves connected to a plurality of pipes connected to each other to be controlled on and off by the transmission control unit to block or penetrate the hydraulic pressure, supply hydraulic pressure according to the capacity of the clutch corresponding to each friction element, and independently control the valves. And a plurality of switch valves selectively supplying the hydraulic pressure supplied to the solenoid valve to the plurality of friction elements, and a plurality of friction elements commonly acting or selectively acting on each shift stage by the hydraulic pressure supplied to the switch valve. A hydraulic control system for an automatic transmission comprising: a valve of a fail-safe valve which operates at a speed of four driving ranges in a drive-on state and controls a non-operating friction element at another shift stage by branching a line pressure line coming from an oil pump. Open with one side of the valve body to move the spool Is determined; Wagon elements that are not operated at the parking range and travel range and operated at other ranges by branching the conduit, and operate at speed 3, 4 at the drive range with the reverse range drive on, and at speed 3 with the drive off. And moveably connect the valve spool of the switch valve to selectively control another friction element which is inoperative at another shift stage; It is connected to the L-range pipeline connected from the above-mentioned pipeline and the manual valve, but is made through the direction switching means so that the valve spool of the switch valve can be moved by selectively supplying the L-range pipeline or line pressure to the connection portion. A hydraulic control system for an automatic transmission is provided.

The hydraulic control system for an automatic transmission is characterized in that a fail-safe solenoid valve is provided on the line connecting the line pressure pipeline from the oil pump to the fail-safe valve.

The direction change means provides a hydraulic control system for an automatic transmission, characterized in that the check valve is interposed to move the valve spool of the switch valve by selectively opening and closing the L range pipeline from the line pressure pipeline and the manual valve.

A friction element self-poring through a connected conduit leading through a line pressure conduit at a parking and neutral range; It also provides another friction element actuated through the conduit, but when shifting from the driving range to the neutral range, the another friction element is controlled by a solenoid valve which is duty controlled by the transmission control unit (TCU). Provided is a control method of a hydraulic control system for an automatic transmission.

The friction element controlled by the solenoid valve when shifting from the driving range to the neutral range is duty-controlled by the transmission control unit (TCU) when the neutral range operation is completed, and is momentarily controlled to the non-operation state and then returned to the operating state. It provides a control method of the hydraulic control system for an automatic transmission, characterized in that to be controlled.

The friction element controlled by the solenoid valve when shifting from the driving range to the neutral range is fail-safe when the neutral range operation is completed, and the solenoid valve is opened to supply hydraulic pressure to the friction element to control the automatic transmission. To provide a control method for a hydraulic control system for a vehicle.

1 is a hydraulic circuit diagram in a parking and neutral range state according to an embodiment of the present invention;

2 is a hydraulic circuit diagram showing a driving range 1 speed state according to the embodiment of the present invention;

3 is a hydraulic circuit diagram illustrating a shift state from a driving range 1 speed to a neutral range according to an exemplary embodiment of the present invention.

The configuration and operation of the most preferred embodiment according to the present invention will be described in more detail below with reference to the accompanying drawings.

1 is a view schematically showing a hydraulic circuit diagram according to an embodiment of the present invention, showing a hydraulic control system with a shift lever selected to a neutral range.

The hydraulic control system includes a torque converter (2) located between the crankshaft of the engine and the transmission to transmit power; An oil pump (4) installed in the pump drive hub of the torque converter and having a drive gear that rotates together and a driven gear geared to the drive gear; A pressure adjusting unit (A) for converting the hydraulic pressure generated by the oil pump (4) to a constant pressure to control the friction element; A damper clutch control unit (B) for operating / deactivating the damper clutch of the torque converter (2) by varying the oil pressure generated by the oil pump (4); Manual valve (C) for receiving the hydraulic pressure of the pressure adjusting unit in conjunction with the shift lever in order to implement a predetermined shift stage at the driver's will to deliver to each friction element; A friction element part (D) which is selectively operated by hydraulic pressure supplied through the hydraulic pressure and a manual valve controlled by the pressure regulating part; The friction element controller E for selectively supplying the friction element portion D with the line pressure coming from the oil pump 4 or the drive pressure coming from the manual valve by the transmission control unit to the friction element selectively. Wow; It comprises a shift control unit (F) consisting of a plurality of switch valves for selectively supplying the pressure controlled by the friction element control unit (E) to the friction element.

The discharge port side of the oil pump 4 has a structure in which a pressure control valve 6 capable of appropriately varying the line pressure when the mode is changed to the neutral range, the reverse range and the reverse range is connected. The pressure regulating valve 6 is connected by a clutch regulator valve 8 for supplying hydraulic pressure to the torque converter 2 through the hydraulic conduit and another hydraulic conduit, which can supply or shut off the hydraulic condenser on the hydraulic conduit. Feed valve 10 is disposed. The clutch regulator valve 8 is controlled by a transmission control unit (TCU) and is connected to a pipeline from the oil pump 4 to selectively convert the hydraulic pressure supplied through the pipeline to the converter clutch regulator valve 8. By varying the position of the bar spool by supplying, the pipeline connected to the torque converter 2 is selectively communicated to enable / disable the damper clutch.

The pressure regulating valve 6 has a structure in which the fifth solenoid valve S5 controlled by the transmission control unit TCU is connected to the hydraulic line. The fifth solenoid valve S5 is connected to the line pressure line from the oil pump to receive hydraulic pressure. Further, the line pressure line from the oil pump 4 is further extended to be connected to the manual valve 12 to supply hydraulic pressure, and the line pressure is introduced into the manual valve 12 so that the drive pressure and the reverse pressure line adjust the pressure. It is made of a structure that is connected to the valve (6).

The pressure regulating valve 6 maintains an appropriate pressure at each shift of the line pressure and the reverse pressure introduced into the manual valve 12, which is controlled by the transmission control unit TCU. While S5) is duty controlled, the pressure of the hydraulic pressure flowing into the manual valve 12 is always kept constant.

And a friction element that is directly controlled by the line pressure coming from the oil pump 6 and the drive pressure passing through the manual valve 12 or operated by each shift stage by the control of the friction element control unit E and the shift control unit F. The addition is connected by a predetermined pipeline. These friction elements are operated in driving range 1 speed, 2 speed, 3 speed, 4 speed and drive range with driving range 1 speed, 2 speed, 3 speed, 2 range 1 speed, 2 speed, L range. A first friction element C1 which is non-operating in the parking range, the neutral range and the reverse range; Parking Range, Neutral Range, and Reverse Range Drive Range 1, 2, 3, Drive Off, Drive Range Drive 1, 2, 3, 2, 1, 2, L Range A second friction element B4 which is non-operational in the driving range 4 speed in the drive on state and the driving range 2 speed in the drive off state; Running range 2 speed, 3 speed, 4 speed with drive on, 2 speed, 3 speed with drive off, 2 speed with 2 speed, parking range and driving range with neutral and reverse range drive on 1 A third friction element B2 which is inoperative in the first speed, the second range, the first speed, and the L range of the speed, drive-off state; The system operates only in the 2-range 2-speed, and operates in the parking range, neutral range, reverse range and driving range 4 speed, except for the parking range, neutral range, and reverse range and driving range. 4 friction element B3; A fifth friction element C3 which is operated in the driving range 4 speed in the drive-on state and is inoperative in the parking range, the neutral range, and the shift range before the reverse range and the driving range except for this; Operation is carried out in the 3rd, 4th speed with the reverse range and drive on, and 3rd speed with the drive off, parking speed and neutral range, 1st speed, 2nd speed with the drive on and 1st speed with the drive off, A sixth friction element C2 which is inoperative in the second speed and the second range, the first speed, the second speed, and the L range; A seventh friction element B1 which is operated in the parking range, the neutral range, and the L range, and which is inoperative in the driving ranges of the drive-on and off-states and in the entire shift stages of the second range; Is being done.

The friction element controller E is composed of a plurality of solenoid valves controlled by a transmission control unit TCU.

The solenoid valve is connected to the drive pressure line of the manual valve and the first solenoid valve (S1) to selectively activate or deactivate the first and second friction elements (C1) (B4) by the duty control of the transmission control unit ; A second solenoid valve S2, which is also connected to the drive pressure line of the manual valve 12 to selectively activate or deactivate the third friction element B2 by the duty control of the transmission control unit TCU; Fourth connected to the line pressure line from the oil pump 4 to selectively activate or deactivate the fourth friction element (B3) and the fifth friction element (C3) by the duty control of the transmission control unit (TCU) A solenoid valve S4; It is connected to the line pressure line from the oil pump (4) to selectively activate or deactivate the sixth friction element (C2) and the seventh friction element (B1) by the duty control of the transmission control unit (TCU) 3 solenoid valve S3; Is being done.

In addition, the shift control unit (F) receives the hydraulic pressure from the first solenoid valve (S1) to supply the hydraulic pressure to selectively control the first and second friction elements (C1) (B4), oil The hydraulic pressure is also supplied through the line pressure line from the pump 4 to selectively supply the hydraulic pressure to the second friction element B4 and the seventh friction element B1, and the drive pressure line of the manual valve 12 is opened. An ND control valve 100 configured to selectively receive the hydraulic pressure and selectively control the first friction element C1; The valve spool can be interlocked by receiving the hydraulic pressure from the fourth solenoid valve S4 and receiving the two-range pressure from the manual valve 12 so that the hydraulic pressure can selectively control the fourth friction element B3. A first switch valve (102) to make; It is connected to another hydraulic line coming out of the first switch valve 102 to control the fifth friction element (C3), the line pressure coming from the branch by branching one side of the line pressure line connected to the oil pump (4) A fail-safe valve 104 for interlocking the valve spool to selectively activate and deactivate the fifth friction element C3; By receiving the hydraulic pressure from the fourth solenoid valve (S4) and selectively operating and deactivating the sixth and seventh friction elements (C2) (B1), the hydraulic pressure coming out through the L range conduit of the manual valve 12 and the A second switch valve 106 for actuating and deactivating by selectively interlocking the valve spool by hydraulic pressure through a line pressure line for moving the valve spool of the fail-safe valve 104; It is made, including.

Meanwhile, in order to vary the valve spool of the fail-safe valve 104, the fail-safe solenoid valve 108 is interposed on the line pressure line connected to the oil pump.

And it is configured by connecting the hydraulic pipe for interlocking the valve spool of the fail-safe valve 104 and the L range pressure pipeline from the manual valve 12, the connection portion is the hydraulic pressure of the line pressure pipeline and the hydraulic pressure of the L range pipeline It is made of a structure in which the direction switching means which is installed so as to selectively flow through the valve spool of the second switch valve 106 is interposed. The direction switching means is composed of a check valve to selectively open and close the hydraulic pressure of the line pressure line and the L range line to be drawn to the second switch valve side.

In the hydraulic control system for an automatic transmission according to the present invention made as described above, when the engine starts to drive, the driving gear of the oil pump 4 rotates to suck the oil in the oil pan to start discharging. At this time, the discharged oil is discharged to the line pressure through the pipeline, a part of the line pressure is introduced to the regulator valve side, another part of the hydraulic pressure is introduced to the manual valve 12, and another part of the hydraulic pressure is converted to the converter clutch regulator valve (8) ) Is introduced into the sixth solenoid valve (S6) side for varying the valve spool. Another part of the line pressure is drawn to the sixth solenoid valve side for varying the valve spool of the pressure regulating valve 6. Accordingly, the fifth solenoid valve S5 is duty controlled by the transmission control unit TCU, and the line pressure is changed by changing the pressure to an appropriate pressure corresponding to each shift stage. The line pressure converted as described above is input to the converter clutch regulator valve 8 through the converter feed valve 10 and is controlled by the sixth solenoid valve S6 controlled by the transmission control unit TCU. The damper clutch in (2) is activated or deactivated. On the other hand, when the pressure of the hydraulic pressure transmitted to the converter feed valve side is greater than the prescribed value, the return to the oil tank is made through the oil filter.

As described above, the oil pump 4 is converted to a constant pressure to control the friction element through the manual valve 12 or the direct switch valve, and the like. In particular, the vehicle is neutral in the parking and the neutral range, the driving range 1 speed, and the driving range 1 speed. When shifting to a range, it demonstrates in detail below.

Parking Range and Neutral Range

As shown in FIG. 1, the valve spool is fixed to the manual valve 12 in a neutral or parking state, and the line pressure drawn into the manual valve 12 has no effect as shown in FIG. Will not. The line pressure pipe discharged from the oil pump 4 is branched to be connected to the ND control valve 100, and the line pressure is introduced therethrough. The hydraulic pressure is a port 150 for controlling the second friction element B4. ) And a port 152 for controlling the seventh friction element. At this time, the valve spool of the ND control valve 100 is formed to move to the left in the figure fixed to the elastic force of the elastic member holding it so that the port 150 for controlling the second friction element (B4) is opened A port 152 for controlling the second friction element B4 and also for controlling the seventh friction element B1 is opened to operate the seventh friction element B1 while the hydraulic pressure is drawn in. Therefore, the parking and the neutral range are enabled by the operation of the second and seventh friction elements B4 and B1.

Travel range 1 speed

When the shift lever is moved to the traveling range, as shown in FIG. 2, the valve spool of the manual valve 12 linked thereto is moved to convert the line pressure drawn from the oil pump 4 into drive pressure. To the first solenoid valve S1 and the ND control valve 100 through the conduit. At this time, after moving the valve spool of the ND control valve 100 to the right in the drawing through the drive pressure pipe connected to the ND control valve 100 side, the first friction element (C1) is drawn into the first friction element (C1) side ) Will be activated. In addition, the first solenoid valve S1 controlled by the transmission control unit TCU is controlled to be in an off state to distribute the hydraulic pressure, and the hydraulic pressure introduced therethrough passes through the ND control valve 100 to the second friction element B4. It is pulled to the side to operate it. Therefore, in the driving range 1 speed, the first and second friction elements C1 and B4 operate to shift the vehicle to a driving state.

And the line pressure from the oil pump (4) is drawn to the third, fourth solenoid valve (S3) (S4) side controlled by the transmission control unit (TCU) to enter the standby state and to the fail-safe valve 104 side The fail-safe solenoid valve 108 is turned on so that no pressure is applied to the valve spools of the fail-safe valve 104 and the second switch valve 106.

Neutral range at speed 1

When the shift lever is moved to shift from the running range to the neutral range state while driving, the valve spool of the manual valve 4 linked thereto is moved to move to the neutral range state. Then, since the first friction element C1 is in a state where the operation is not performed in the neutral state, the hydraulic pressure is released, and the hydraulic pressure is discharged to the exhaust port side formed in the valve spool of the manual valve 12. . At the same time, the first solenoid valve S1 controlled by the transmission control unit TCU is duty-controlled in an on state, and the oil pressure in the pipeline between the first solenoid valve S1 and the ND control valve 100 is controlled. Discharge is made through the discharge port formed on the ND control valve 100 side. At this time, while the hydraulic pressure that is pressurizing the valve spool of the N-D control valve 100 is released, the valve spool is moved to the left in the figure by the elastic member holding the valve spool.

On the other hand, the transmission control unit TCU duty-controls the third solenoid valve S3 in the off state to distribute the line pressure drawn to the third solenoid valve S3 side, and this hydraulic pressure causes the second switch valve 106 to flow. It controls the seventh friction element (B1) through. However, at this time, since the inertia change of the seventh friction element B1 is large, the control tempo of the third solenoid valve S3 controlled by the transmission control unit TCU is controlled a little later, that is, the transmission control unit TCU. By the control of the fail-safe solenoid valve 108 is turned off, the line pressure discharged from this pressurizes the valve spool of the fail-safe valve 104 and the second switch valve 106 to the right in the drawing When the position is set to, the operation of the seventh friction element B1 is temporarily stopped and then restarted. Then, if the N-D control valve 100 is completely moved to the left side, the hydraulic pressure is introduced into the seventh friction element (B1) to operate the seventh friction element (B1). Therefore, the second and seventh friction elements B4 and B1 operate in the neutral range.

The hydraulic control system and control method for an automatic transmission according to the present invention, by using a fail-safe valve for the seventh friction element which is one of the friction elements operating in the neutral range when the shift is made from the neutral range to the traveling range. It is possible to reduce the change of inertia by controlling the operation to be stopped after the operation stops and thus improving the feeling of shift by reducing the shift shock.

Claims (6)

An oil pump for generating oil pressure by a drive gear rotating together when the engine is driven, pressure adjusting means for adjusting the oil pressure generated from the oil pump to an appropriate line pressure when the vehicle is moved forward or backward, and driving force of the engine A torque converter that transmits to the input shaft of the transmission, a converter clutch regulator valve for supplying an operating pressure of a damper clutch for increasing power transmission efficiency of the torque converter, and an oil discharged from an oil pump to the converter clutch regulator valve. A converter feed valve for supplying a constant pressure oil, a manual valve which is linked to the shift lever and selectively discharges the line pressure from the pressure regulating means to a traveling range, a reverse range, a two range, an L range pipe, and the manual valve. Connected to a number of pipelines connected to the A plurality of solenoid valves on and off controlled by the transmission control unit to shut off or penetrate, supply hydraulic pressure according to the capacity of the clutch in response to each friction element, and independently control the hydraulic pressure supplied to the solenoid valve. In the hydraulic control system for an automatic transmission comprising a plurality of switch valves for selectively supplying a plurality of friction elements, and a plurality of friction elements acting in common or selectively acting for each shift stage by the hydraulic pressure supplied to the switch valve. In order to move the valve spool of the fail-safe valve which operates in the driving range 4 speed of the drive-on state and controls the non-operating friction element at the other shifting stage, the line pressure line from the oil pump is branched. Connected; Friction elements that are non-operated in parking ranges and travel ranges and operated in other ranges by branching the conduit, and 3 or 4 speeds in the travel range with the reverse range drive on and 3 speeds in the drive range with the drive off And movably connect the valve spool of the switch valve to selectively control another friction element which is inoperative at another shift stage; It is connected to the L-range pipe connected from the above-mentioned pipe line and the manual valve, but it is made through the direction switching means to move the valve spool of the switch valve by selectively supplying the L-range pipe or line pressure to the connection part. Hydraulic control system for automatic transmission. The hydraulic control system for an automatic transmission according to claim 1, wherein a fail-safe solenoid valve is interposed on the line pressure line from the oil pump and the line connecting the fail-safe valve. The hydraulic control system for an automatic transmission according to claim 1, wherein the direction switching means includes a check valve so as to move the valve spool of the switch valve by selectively opening the L range pipe from the line pressure pipe and the manual valve. . A first friction element actuated through a connected conduit leading through the line pressure conduit at the parking and neutral ranges; Also providing a second friction element that is actuated through the conduit, when the shift range from the driving range to the neutral range is said another friction element is controlled by a solenoid valve duty controlled by the transmission control unit (TCU) A control method for a hydraulic control system for an automatic transmission, characterized in that. 5. The method of claim 4, wherein the first friction element controlled by the solenoid valve when shifting from the traveling range to the neutral range is duty controlled by the transmission control unit (TCU) in an inactive state momentarily when the neutral range is in operation. The control method of the hydraulic control system for an automatic transmission, characterized in that to be controlled again in the operating state after being controlled. The friction element controlled by the solenoid valve when shifting from the driving range to the driving range is fail-safe when the neutral range operation is completed, and the solenoid valve is turned off to supply hydraulic pressure to the friction element. A control method for a hydraulic control system for an automatic transmission, characterized in that.