Hydraulic control system for automatic transmission

A hydraulic control system for an automatic transmission, the hydraulic control system controlling an automatic transmission power train that includes:

• first, second, third, and fourth clutches operating respectively when in first, second, and third speeds, when in third and fourth speeds, when in a reverse R range, and when an engine brake is required;
• a first brake operating when the engine brake in the first speed is required or in the reverse R range;
• and a second brake operating in the second and fourth speeds, the hydraulic control system comprising:
• a manual valve including an R range port for exhausting hydraulic pressure in the reverse R range, an N range port for exhausting hydraulic pressure in all shift ranges except the reverse R range, a D range port for exhausting hydraulic pressure in all forward driving ranges, and an L range port for exhausting hydraulic pressure in low range;
• a first switch valve for selectively supplying a first pressure, which is controlled by a first solenoid valve, to the first clutch and the fourth clutch;
• a second switch valve for selectively supplying a second pressure, which is controlled by a second solenoid valve, to the second clutch and the first brake;
• a third-clutch control valve for controlling hydraulic pressure received from the R range port of the manual valve and supplying the hydraulic pressure to the third clutch;
• a second-brake control valve for controlling hydraulic pressure supplied from the D range port of the manual valve and supplying the hydraulic pressure to the second brake;
• and
• a third solenoid valve for simultaneously controlling the third-clutch control valve and the second-brake control valve.