Patent ID: 6986724

Claim:
A hydraulic control system of a six-speed automatic transmission for a vehicle, the automatic transmission including first, second, and third clutches and first and second brakes, the hydraulic control system 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 a 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 shift control portion for distributing a plurality of range pressures of a manual valve to the clutches and the brakes; a fail safe control portion for controlling hydraulic supply from the shift control portion to the clutches and the brakes; wherein the shift control portion comprises first, second, third, and fourth pressure control valves respectively controlled by a reduced pressure of a reducing valve and controlled pressures of first, second, third, and fourth solenoid valves, for controlling at least one of the forward and reverse range pressures of the manual valve and thereby for supplying the controlled pressure to at least one frictional element; wherein the fail safe control portion includes: a switch valve controlled by a control pressure of a solenoid valve and a plurality of control pressures selectively supplied from the manual valve, for selectively supplying hydraulic pressure received through an input port to a plurality of output ports; a first fail safe valve controlled by hydraulic pressure supplied from the second pressure control valve and the forward range pressure supplied from the manual valve, for selectively transmitting a hydraulic pressure from the third pressure control valve; and a second fail safe valve controlled by line pressure and hydraulic pressures from the second pressure control valve and the first fail safe valve, for selectively transmitting a hydraulic pressure from the switch valve.