KR19990059844A - Hydraulic Control System for Automatic Transmission - Google Patents

Abstract

The hydraulic control system for an automatic transmission according to the present invention provides a hydraulic control system for an automatic transmission to indirectly control the friction elements indirectly to improve a feeling of shifting.

The hydraulic control system for an automatic transmission according to the present invention includes a regulator valve for controlling the oil pressure generated in the oil pump to a line pressure having a constant pressure amplitude, and supplying oil pressure to the transmission lubrication unit including a torque converter;

A reducing valve controlling the line pressure supplied from the regulator valve to a reducing pressure to supply each solenoid valve;

A manual valve for supplying and discharging the line pressure supplied from the regulator valve to a pipeline corresponding to each range;

Since the first, second, third, and fourth solenoid valves control the reducing pressure supplied from the reducing valve, the hydraulic pressure supplied from the manual valve is indirectly controlled to independently control the rear clutch, the end clutch, the low-reverse brake, First, second, third and fourth pressure control valves for selectively supplying and discharging the front clutch and the second brake;

When the hydraulic pressure is supplied to the end clutch in the L range state to operate it, a fail-safe valve is configured to discharge the hydraulic pressure that operated the low-reverse brake to control the speed in three speeds.

Description

Hydraulic Control System for Automatic Transmission

The present invention relates to a hydraulic control system for an automatic transmission, and more particularly, to realize a forward 4 speed and a reverse 1 speed by indirectly and independently controlling the rear clutch, the end clutch, the low-reverse brake, the front clutch, and the second brake. A hydraulic control system for a transmission.

In general, the hydraulic control system for controlling the automatic transmission is configured in various ways depending on the friction elements constituting the gear train.

Here, the hydraulic control system for an automatic transmission that achieves four forward speeds and one reverse speed by selectively controlling the rear type planetary gears of the rear clutch, end clutch, low-reverse brake, front clutch, and second brake is described.

Such hydraulic control systems are well known in the art, and in most cases, one or two pressure control valves are controlled by solenoid valves so that the pressure-controlled hydraulic pressure is supplied to the friction elements in a mutually correlated manner via several shift valves and clutch valves. It is structured.

However, the hydraulic control system for an automatic transmission as described above has a disadvantage of lowering the feeling of shifting because the friction elements are controlled to be related to each other.

Therefore, the present invention was created to solve the above disadvantages, the hydraulic control system for an automatic transmission according to the present invention provides a hydraulic control system for an automatic transmission to indirectly control the friction elements to improve the feeling of shift.

1 is a hydraulic circuit diagram formed in the N range of the hydraulic control system for an automatic transmission according to the present invention.

2 is a hydraulic circuit diagram formed at the R range of the hydraulic control system for an automatic transmission according to the present invention.

3 is a hydraulic circuit diagram formed at the D range 1 speed of the hydraulic control system for an automatic transmission according to the present invention.

4 is a hydraulic circuit diagram formed at the D range 2 speed of the hydraulic control system for an automatic transmission according to the present invention.

5 is a hydraulic circuit diagram formed at the D range 3 speed of the hydraulic control system for an automatic transmission according to the present invention.

6 is a hydraulic circuit diagram formed at the D range 4 speed of the hydraulic control system for an automatic transmission according to the present invention.

7 is a hydraulic circuit diagram formed in the L range of the hydraulic control system for an automatic transmission according to the present invention.

8 is a hydraulic circuit diagram formed when the L range fails in the hydraulic control system for an automatic transmission according to the present invention.

<Explanation of symbols for the main parts of the drawings>

3: Regulator valve 13: Torque converter control valve 15: Damper clutch control valve 17: Reducing valve 21: Manual valve 23, 24, 25, 27, 28, 29, 31: Pipe line 33, 35, 37, 39: First 2, 3, 4 pressure control valve 47: fail-safe valve 49: switch valves S1, S2, S3, S4: 1, 2, 3, 4 solenoid valve R / C: rear clutch E / C: end clutch LR / B: Low reverse brake F / C: Front clutch 2ND / B: Second brake S / A: Servo application S / R: Servo release

In order to realize this, the hydraulic control system for an automatic transmission according to the present invention includes a line pressure control means for controlling the oil pressure generated in the oil pump to a line pressure having a constant pressure amplitude and supplying hydraulic pressure to the transmission lubrication unit including a torque converter;

Reducing pressure control means for controlling the line pressure supplied from the line pressure control means to a reducing pressure to supply each solenoid valve;

Range control means for supplying and discharging the line pressure supplied from said line pressure control means to a pipeline corresponding to each range;

Since the reducing pressure supplied from the reducing pressure control means is controlled, the hydraulic pressure supplied from the range control means is indirectly controlled to supply the rear clutch, the end clutch, the low-reverse brake, the front clutch, and the second brake selectively. And hydraulic control means for discharging;

When the hydraulic pressure is supplied to the end clutch in the L range state to operate it, it includes a fail-safe means for discharging the hydraulic pressure to operate the low-reverse brake to control to a three speed state.

The hydraulic control system for an automatic transmission configured as described above controls the oil pressure supplied from the reducing pressure control means so that the oil pressure supplied from the range control means is indirectly pressure-controlled by the hydraulic control means to independently supply and discharge each friction element. 4 forward speed and 1 reverse speed are realized.

In the L range, the fail-safe fail-safe means discharges the hydraulic pressure for operating the low-reverse brake to control the driving speed in three speeds.

BEST MODE Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a hydraulic circuit diagram formed in the N range of the hydraulic control system for an automatic transmission according to the present invention, including rear clutch (R / C), end clutch (E / C), low-reverse brake (LR / B), It is configured to independently control the front clutch F / C and the second brake 2ND / B.

That is, the regulator valve 3 is connected to the oil pump 1 to the conduit 5 so that the oil pressure generated in the oil pump 1 is controlled to the line pressure having a constant pressure amplitude in the regulator valve 3 of the line pressure control means. Connected.

The regulator valve 3 is a torque converter control valve 13 and a damper clutch control valve 15 to supply the hydraulic pressure supplied from the oil pump 1 to the torque converter 7 and the transmission lubrication parts 9 and 11. Leads to.

The damper clutch control valve 15 controls the damper clutch control valve 15 as the solenoid valve S controls the reducing pressure supplied from the reducing valve 17, which is a reducing pressure control means, thereby controlling the torque converter control valve. The hydraulic pressure supplied from (13) is configured to pass through the torque converter 7 or not via it.

The reducing valve 17 receives the reducing pressure supplied to the line 5 to reduce the reducing pressure of the solenoid valve S and the first, second, third, and fourth solenoid valves S1, S2, and S3 of the hydraulic control means. It is connected to the pipeline 19 to supply to, S4.

And the manual valve 21 of the range control means that is supplied with the line pressure to the conduit 5 connected to the regulator valve 3 supplies the hydraulic pressure to the conduits 23, 24, 25, 27, 28 corresponding to each range. And to discharge.

That is, the manual valve 21 is configured to control the communication of the conduits 23, 24, 25, 27, 28 and the conduits 5 according to the operation of the shift lever, and the regulator valve 3 corresponds to each range. It is connected to the pipe (29, 31) to control the line pressure.

The hydraulic pressure supplied to the conduits 23, 24, 25, 27 and 28 connected to the manual valve 21 is pressure-controlled, so that the rear clutch R / C, the end clutch E / C, and the low-reverse brake ( Hydraulic control means are provided to selectively supply and discharge the servo applications (S / A) and the servo release (S / R) of the LR / B), the front clutch (F / C) and the second brake (2ND / B). This hydraulic control means is provided with first, second, third and fourth solenoid valves S1, S2, S3, S4 and the first, second, third and fourth pressure control valves 33, 35, 37 controlled thereby. 39).

In the above, the front clutch F / C is connected to the pipeline 27 so as to be directly released by the hydraulic pressure supplied from the manual valve 21.

The first pressure control valve 33 is installed on the pipeline 41 so as to independently supply and discharge the hydraulic pressure supplied from the pipeline 23 connected to the manual valve 21 to the rear clutch R / C.

The second pressure control valve 35 is installed on the conduit 43 to supply and discharge the hydraulic pressure supplied from the conduit 23 connected to the manual valve 21 independently to the end clutch E / C.

The third pressure control valve 37 supplies and discharges the hydraulic pressure supplied from the conduit 25 connected to the manual valve 21 independently to the servo release S / R of the second brake 2ND / B. Installed on the

The fourth pressure control valve 39 supplies the hydraulic pressure supplied from the conduit 25 connected to the manual valve 21 to the servo application S / A and the low-reverse brake LR / B of the second brake 2ND / B. Fail-safe valve 47 and switch valve 49 of the fail-safe means is installed on the conduit 50 to be selectively supplied to the hydraulic pressure.

The switch valve 49 is connected to the conduits 23, 25, 28 so as to be controlled by the hydraulic pressure supplied from the manual valve 21.

On the other hand, the fail-safe valve 47 has the second solenoid valve S2 sticked off in the L range state in which the rear clutch R / C and the low-reverse brake LR / B operate, and the end clutch E / C When the hydraulic pressure is supplied to and actuated, it is configured to discharge the hydraulic pressure used to operate the low-reverse brake (LR / B) to control at the 3-speed state.

That is, the fail-safe valve 47 includes first, second, third, fourth, fifth, and sixth ports 51, 53, 55, 57, 59, and 61, and a valve spool supported by the elastic member 63 to control it. 65).

The first port 51 is connected to receive the hydraulic pressure from the fourth pressure control valve 39, the second port 53 is a low-reverse brake (LR / B) for the hydraulic pressure supplied to the first port 51 ) Is connected to supply to the switch valve 49 connected to the servo application (S / A), the third port 55 is formed to discharge the hydraulic pressure that was supplied to the second port 53, and the fourth , 5, 6 ports 57, 59, 61 are manual valves 21 such that the valve spool 65 controls the communication between the first, second ports 52, 53 and the second, third ports 53, 55. Drive pressure, rear clutch control pressure, and end clutch control pressure are supplied to the conduits 67, 41 and 43, respectively.

The valve spool 65 has first, second, third, fourth, fifth and sixth lands 69, 71, 73, 75, 77, 79 having hydraulically acting surfaces of different sizes.

The first land 69 has a hydraulically acting surface on which the drive pressure supplied to the fourth port 57 acts, and the second land 71 has a larger hydraulically acting surface on the adjacent side of the first land 69. The third land (73) is formed with a smaller hydraulic action surface on the adjacent side of the second land (71) to communicate the first and second ports (51, 53) with the second land (71). And to control.

In addition, the fourth land 75 is formed with a smaller hydraulic action surface on the adjacent side of the third land 73 to control the communication between the second and third ports 53 and 55 together with the third land 73. The hydraulic pressure supplied to the six ports 61 acts, and the fifth land 77 is formed with a smaller hydraulic action surface on the adjacent side of the fourth land 75 so that the hydraulic pressure supplied to the fifth port 59 acts. In addition, the sixth land 79 is formed to have a smaller hydraulic action surface on the adjacent side of the fifth land 77 and is configured to be supported by the elastic member 63.

When the engine of the vehicle having the hydraulic control system for an automatic transmission configured as described above is started, the oil pump 1 generates hydraulic pressure, and the regulator valve 3 controls the hydraulic pressure to a line pressure so that the pipeline 5 At the same time, the hydraulic pressure is supplied to the torque converter 7 and the transmission lubrication parts 9 and 11 via the torque converter control valve 13 and the damper clutch control valve 15, and the reducing valve 17 The line pressure is controlled by the reducing pressure and supplied to the conduit 19.

(N range)

In this state, when the N range is selected by the shift lever, the transmission control unit TCU controls the solenoid valve S to be off to release the damper clutch (not shown).

The damper clutch control is omitted because the transmission control unit TCU controls the solenoid valve S in accordance with a predetermined logic.

In addition, when the shift lever is selected to N, the manual valve 21 is controlled in the state of FIG. 1 to communicate the conduit 5 with the conduit 25.

At this time, the transmission control unit TCU controls all of the first, second, third and fourth solenoid valves S1, S2, S3, and S4 to be on.

Therefore, the reducing pressure supplied to the conduit 19 controls the first, second, third and fourth pressure control valves 33, 35, 37 and 39 so that the line pressure supplied to the conduit 25 is the third and fourth pressures. It is blocked by the control valves 37 and 39 and does not activate any friction elements. Therefore, the N range is realized.

(R range)

When the shift lever is selected to R in the above N range, the manual valve 21 is controlled in the state of FIG. 2, thereby communicating the conduit 5 to the conduits 25, 27, and 31. The hydraulic pressure supplied to this conduit 31 acts so that the regulator valve 3 controls the line pressure corresponding to the R range.

At this time, the transmission control unit TCU controls the first, second, third and fourth solenoid valves S1, S2, S3 and S4 to ON, ON, ON and OFF.

Therefore, the reducing pressure supplied to the conduit 19 controls the first, second, third and fourth pressure control valves 33, 35, 37 and 39.

The reverse pressure supplied to the conduit 27 is supplied to the front clutch F / C to operate the same, and at the same time, the fourth port 57 of the fail-safe valve 47 is provided through the conduit 67 connected to the conduit 27. ) And acts on the first land 69 thereof to move the valve spool 65 to the left as shown in FIG. 2 to communicate the first and second ports 51 and 53.

The line pressure supplied to the conduit 25 is low via the second and second ports 51 and 53 and the switch valve 49 of the fourth pressure control valve 39 and the fail-safe valve 47 connected thereto. It is supplied to the reverse brake (LR / B) to activate it. Therefore, the R range is realized.

(D range 1 speed)

In addition, if the shift lever is selected as D and the throttle opening degree is increased in the above N range, the manual valve 21 is controlled in the state shown in FIG. 3 to thereby connect the conduit 5 to the conduits 23, 24, 25, 29. ). The hydraulic pressure supplied to this conduit 29 acts so that the regulator valve 3 controls the line pressure corresponding to the D range.

At this time, the transmission control unit TCU controls the first, second, third and fourth solenoid valves S1, S2, S3 and S4 to off, on, on and on, respectively.

Therefore, the reducing pressure supplied to the conduit 19 controls the first, second, third and fourth pressure control valves 33, 35, 37 and 39, so that the drive pressure supplied to the conduit 23 is the switch valve 49. 3 is controlled in the state of FIG. 3 together with the hydraulic pressure supplied to the conduit 25, and is supplied to the rear clutch R / C via the first pressure control valve 33 to operate it. Therefore, D range 1 speed is realized.

The drive pressure supplied to the conduits 24 and 67 is supplied to the fourth port 57 of the fail safe valve 47 and acts on the first land 69 thereof.

In addition, the hydraulic pressure for operating the rear clutch R / C is supplied to the fifth port 59 of the fail-safe valve 47 and acts on the fifth land 77 thereof to supply the pipe lines 24 and 67. While overcoming the hydraulic pressure, the valve spool 65 is moved to the right as shown in FIG. 3 to communicate the second and third ports 53 and 55.

(D-range 2 speed)

When the throttle opening degree is increased in the D range 1 speed state as described above, the manual valve 21 continues to communicate the conduits 23, 24, 25, and 29 accordingly. The hydraulic pressure supplied to this pipe line 29 is used for line pressure control as in the D range 1 speed.

At this time, the transmission control unit TCU controls all of the first, second, third and fourth solenoid valves S1, S2, S3 and S4 to off, on, on and off.

Therefore, the reducing pressure supplied to the conduit 19 controls the first, second, third and fourth pressure control valves 33, 35, 37 and 39 so that the drive pressure supplied to the conduit 23 is in the D range 1 speed. As described above, the rear clutch R / C and the fail-safe valve 47 are operated to control the switch valve 49.

The drive pressure supplied to the conduits 24 and 67 is supplied to the fourth port 57 of the fail safe valve 47 as in the D range 1 speed.

In addition, the line pressure supplied to the conduit 25 controls the switch valve 49 as in the D-range 1, and the fail-safe valve controlled in the state of FIG. 4 connected to the fourth pressure control valve 39 ( The first and second ports 51 and 53 of 47 are supplied to the servo application S / A via the switch valve 49 to operate the second brake 2ND / B. Thus, the D range second speed is realized.

(D-range 3 speed)

When the throttle opening degree is increased in the D range 2 speed state as described above, the manual valve 21 continues to communicate the conduits 23, 24, 25, and 29 accordingly. The hydraulic pressure supplied to this conduit 29 is used for line pressure control as in the D-range 2 speed.

At this time, the transmission control unit TCU controls all of the first, second, third and fourth solenoid valves S1, S2, S3 and S4 to be off.

Therefore, the reducing pressure supplied to the conduit 19 controls the first, second, third, and fourth pressure control valves 33, 35, 37, and 39, so that the drive pressure supplied to the conduit 23 at the second speed D range. As shown in FIG. 5, the rear clutch R / C is operated and the switch valve 49 is controlled in the state of FIG. 5 together with the line pressure supplied to the conduit 25. At the same time as the end clutch (E / C) is supplied to the sixth port 61 of the fail-safe valve 47 to act on its fourth land (75).

The drive pressure supplied to the conduits 24 and 67 is supplied to the fourth port 57 of the fail-safe valve 47 as in the second range D.

In addition, the line pressure supplied to the pipe line 25 is supplied from the fourth pressure control valve 39 to the first port 51 of the fail-safe valve 47, but the third land 73 thereof is connected to the first and second ports ( Since the communication of 51 and 53 is interrupted | blocked, it cuts out here and is supplied to the servo release S / R via the 3rd pressure control valve 37, and releases the 2nd brake 2ND / B. Thus, the D range third speed is realized.

In particular, when the power supply to the first, second, third and fourth solenoid valves S1, S2, S3 and S4 is cut off while driving in the D-range, the rear clutch R / C and the end clutch E / C are all turned off. It is possible to drive D range 3 speeds by supplying hydraulic pressure to).

(D-range 4 speed)

When the throttle opening degree is increased in the D range 3 speed state as described above, the manual valve 21 continues to communicate the conduits 23, 24, 25, and 29 accordingly. The hydraulic pressure supplied to this conduit 29 is used for line pressure control as in the third range D speed.

At this time, the transmission control unit TCU controls the first, second, third and fourth solenoid valves S1, S2, S3 and S4 on, off, on and off, respectively.

Therefore, the reducing pressure supplied to the conduit 19 controls the first, second, third and fourth pressure control valves 33, 35, 37 and 39, so that the drive pressure supplied to the conduit 23 at the third speed D range. As well as operating the end clutch (E / C) and at the same time as the hydraulic pressure supplied to the conduit 25 to control the switch valve 49 in the state of Figure 6, the hydraulic pressure for operating the rear clutch (R / C) It is discharged via the first pressure control valve 33 to release it.

The drive pressure supplied to the conduits 24 and 67 is supplied to the fourth port 57 of the fail safe valve 47 as in the third range D speed.

Therefore, the valve spool 65 of the fail-safe valve 47 is moved to the left side as shown in FIG. 6 to communicate the first and second ports 51 and 53 thereof.

In this state, the line pressure supplied to the conduit 25 is controlled via the first and second ports 51 and 53 and the switch valve 49 of the fourth pressure control valve 39 and the fail-safe valve 47. The hydraulic pressure supplied to the ply S / A and operating the servo release S / R is discharged via the third pressure control valve 37 to operate the second brake 2ND / B. Thus, the D range four speeds are realized.

(L range)

On the other hand, if the shift lever is selected to L and the throttle opening degree is increased in the above-mentioned D range state, the manual valve 21 is controlled in the state of FIG. 7 accordingly, and thus the pipeline 5 is connected to the pipeline 23, 24, 25, 28. (29). The hydraulic pressure supplied to this conduit 29 acts so that the regulator valve 3 controls the line pressure corresponding to the L range.

At this time, the transmission control unit TCU controls all of the first, second, third and fourth solenoid valves S1, S2, S3 and S4 to off, on, on and off.

Therefore, the reducing pressure supplied to the conduit 19 controls the first, second, third and fourth pressure control valves 33, 35, 37 and 39, so that the drive pressure and the line supplied to the conduits 23, 25 and 28 are provided. The low pressure and the low pressure control the switch valve 49 in the state of FIG. 7, and the drive pressure supplied to the conduit 23 is transferred to the rear clutch R / C via the first pressure control valve 33. Supplied to activate it.

The drive pressure supplied to the conduits 24 and 67 is supplied to the fourth port 57 of the fail safe valve 47 as in the D range.

The line pressure supplied to the conduit 25 is the low-reverse brake via the first and second ports 51 and 53 and the switch valve 49 of the fourth pressure control valve 39 and the fail-safe valve 47. Supplied to (LR / B) to activate it. Therefore, the L range is realized.

(L range fail time)

On the other hand, if the off-stick of the second solenoid valve (S2) occurs while driving in the L range state, the reducing pressure supplied to the conduit 19 in the state of Figure 7 controls the second pressure control valve (35).

Therefore, the drive pressure supplied from the conduit 23 connected to the manual valve 21 is supplied to the end clutch E / C to operate it.

At the same time, the drive pressure for operating the end clutch E / C is supplied to the sixth port 61 of the fail-safe valve 47 and acts on the fourth land 45 to be supplied to the fifth port 59. The first land (69) is supplied to the fourth port (57) by the force of the rear clutch (R / C) control pressure acting on the fifth land (77) and the elastic member (63) acting on the sixth land (79). The valve spool 65 is moved to the right as shown in FIG.

Therefore, the line pressure supplied from the fourth pressure control valve 39 is cut off at the first port 51 of the fail-safe valve 47, and the hydraulic pressure used to operate the low-reverse brake LR / B is switched to the switch valve 49. ) And the second and third ports 53 and 55 of the fail-safe valve 47 are discharged.

Therefore, the hydraulic control system is controlled in the third speed driving state.

As described in the R, D, L range angular speed, the hydraulic control system for an automatic transmission indirectly controls each friction element indirectly.

As described above, the hydraulic control system for an automatic transmission according to the present invention controls the oil pressure supplied from the reducing pressure control means so that the oil pressure supplied from the range control means is indirectly pressure-controlled by the hydraulic control means to independently supply each friction element. And discharge to realize forward 4 speed and reverse 1 speed; In the L range, the fail-safe means for discharging the hydraulic pressure used to operate the low-reverse brake can be controlled in the 3-speed driving state.

Therefore, the present invention can improve the shifting feeling while indirectly and independently controlling the friction element.

Claims (11)

A line pressure control means for controlling the oil pressure generated by the oil pump to a line pressure having a constant pressure amplitude and supplying oil pressure to the transmission lubrication part including a torque converter; Reducing pressure control means for controlling the line pressure supplied from the line pressure control means to a reducing pressure to supply each solenoid valve; Range control means for supplying and discharging the line pressure supplied from said line pressure control means to a pipeline corresponding to each range; Since the reducing pressure supplied from the reducing pressure control means is controlled, the hydraulic pressure supplied from the range control means is indirectly controlled to supply the rear clutch, the end clutch, the low-reverse brake, the front clutch, and the second brake selectively. And hydraulic control means for discharging; When the hydraulic pressure is supplied to the end clutch in the L range state to operate it, a fail-safe means for discharging the hydraulic pressure for operating the low-reverse brake to control it at three speeds is included. -When the second solenoid valve of the hydraulic control means is sticked off in the L range state where the reverse brake is operated, and the hydraulic pressure is supplied to the end clutch, the hydraulic pressure used to operate the low-reverse brake is discharged to the third speed state. Hydraulic control system for automatic transmission characterized by consisting of a fail-safe valve to control The apparatus of claim 1, wherein the line pressure control means comprises: a regulator valve controlled by the oil pressure supplied from the range control means to control the oil pressure supplied from the oil pump to the line pressure; A torque converter control valve connected to the regulator valve; And a damper clutch control valve for supplying hydraulic pressure to the transmission lubrication unit by operating and releasing the damper clutch hydraulically from the torque converter control valve while passing the hydraulic pressure to and from the torque converter. The hydraulic control system for an automatic transmission as set forth in claim 1, wherein the reducing pressure control means is configured by a reducing valve which is controlled by the hydraulic pressure supplied from the line pressure control means to reduce the line pressure to the reducing pressure. . The hydraulic control system for an automatic transmission according to claim 1, wherein the range control means comprises a manual valve for controlling communication of the conduit according to the operation of the shift lever. The method of claim 1, wherein the hydraulic control means comprises: first, second, third, fourth solenoid valves for controlling the reducing pressure supplied from the reducing pressure control means; A rear clutch and an end clutch, respectively controlled by the control pressures of the first, second, third and fourth solenoid valves to control the pressure of the hydraulic pressure supplied from the range control means. A hydraulic control system for an automatic transmission comprising first, second, third and fourth pressure control valves for supplying and discharging independently of the low-reverse brake, the front clutch and the second brake. The hydraulic control system for an automatic transmission according to claim 5, wherein the front clutch forms a hydraulic circuit so as to be directly released by the hydraulic pressure supplied from the range control means. The hydraulic control system for an automatic transmission according to claim 5, wherein the third pressure control valve forms a hydraulic circuit so as to supply and discharge hydraulic pressure to the servo release of the second brake. The hydraulic pressure control valve of claim 5, wherein the fourth pressure control valve includes a hydraulic circuit connected to the fail safe means and the switch valve to selectively supply and discharge hydraulic pressure to the servo application and the low-reverse brake of the second brake via the fail safe means. Hydraulic control system for an automatic transmission characterized in that the forming. 9. The hydraulic control system according to claim 8, wherein the switch valve is configured to select a flow path supplied to and discharged from the servo application and the low-reverse brake by the hydraulic pressure supplied from the range control means. The failsafe valve of claim 1, further comprising: a first port configured to receive hydraulic pressure from a fourth pressure control valve of the hydraulic control means; A second port for supplying hydraulic pressure supplied to the first port to a low reverse brake and a servo application; A third port for discharging the hydraulic pressure supplied to the second port; A valve spool supported by an elastic member at one side to enable the control as described above and having a plurality of lands; And fourth, fifth and sixth ports to which the drive pressure from the range control means, the rear clutch control pressure and the end clutch control pressure are respectively supplied such that the valve spool controls communication between the first, second and second and third ports. Hydraulic control system for automatic transmission. 11. The valve assembly of claim 10, wherein the valve spool comprises: a first land having a hydraulically acting surface on which drive pressure supplied to the fourth port acts; A second land formed on a side of the first land with a larger hydraulic action surface; A third land formed on the adjacent side of the second land with a smaller hydraulic action surface to control communication between the first and second ports together with the second land; A fourth land formed with a smaller hydraulic action surface on an adjacent side of the third land, intermittently communicating the second and third ports with the third land, and acting on the hydraulic pressure supplied to the sixth port; A fifth land formed with a smaller hydraulic action surface on an adjacent side of the fourth land, and having a hydraulic pressure supplied to the fifth port; And a sixth land formed on the adjacent side of the fifth land with a smaller hydraulic action surface and supported by the elastic member.