Patent ID: 6942591

Claim:
A hydraulic control system of a six-speed automatic transmission for a vehicle comprising: a line pressure control portion stably maintaining hydraulic pressure supplied from an oil pump and varying a line pressure according to driving conditions; a launch control portion for controlling torque increase of a torque converter and for controlling a damper clutch; a pressure reduction control portion for reducing line pressure and for outputting the reduced line pressure as control pressure; a switch valve control portion comprising a manual valve for changing hydraulic lines according to a manual operation, a first switch valve controlled by the line pressure and a first on/off solenoid valve, a second switch valve controlled by the line pressure and a second on/off solenoid valve, and third and fourth switch valves being controlled by the line pressure and control pressure from the second switch valve; a first clutch control portion comprising a first clutch side switch valve and a first clutch side pressure control valve that are controlled by a first duty control solenoid valve such that the first clutch control portion controls an operating pressure of the first clutch; a B 1 /C 3 control portion comprising a third clutch side switch valve and a third clutch side pressure control valve that are controlled by a second duty control solenoid valve, a control valve for switching hydraulic lines for hydraulic pressure supplied from the third clutch side pressure control valve, and a first brake side fail-safe valve for supplying hydraulic pressure received from the control valve to the first brake and for executing a fail-safe function; a second clutch control portion comprising a second clutch side switch valve and a second clutch side pressure control valve that are controlled by a third duty control solenoid valve, and a second clutch side fail-safe valve for transmitting hydraulic pressure received from the second clutch side pressure control valve to the second clutch and for executing a fail-safe function; a B 2 control portion comprising a second brake side switch valve and a second brake side pressure control valve that are controlled by a fourth duty control solenoid valve, a sixth-speed-related switch valve for supplying, under the control of the operating pressure of the third clutch, hydraulic pressure received from the fourth duty control solenoid valve to the second brake side pressure control valve as a control pressure, and a second brake side fail-safe valve for transmitting hydraulic pressure received from the second brake side pressure control valve to the second brake and for executing a fail-safe function.