Patent ID: 7878934

Claim:
A hydraulic control system of an eight-speed automatic transmission for a vehicle for controlling a first clutch operated at first, third, fifth, sixth, and seventh forward speeds, a second clutch operated at fourth, fifth, sixth, seventh, and eighth forward speeds and a reverse speed, a third clutch operated at second, third, fourth, sixth, and eighth forward speeds and a reverse speed, a first brake operated at first, second, seventh, and eighth forward speeds and a reverse speed, and a second brake operated at first, second, third, fourth, and fifth forward speeds and a reverse speed, the hydraulic control system comprising: a first clutch control portion that supplies an output pressure of a first pressure control valve to the first clutch, the first pressure control valve being, controlled by output pressures of a first proportional control solenoid valve and a first pressure switching valve; a second clutch control portion that supplies an output pressure of a second pressure control valve to the second clutch, the second pressure control valve being controlled by output pressures of a second proportional control solenoid valve and a second pressure switching valve; a third clutch control portion that supplies an output pressure of a third pressure control valve to the third clutch, the third pressure control valve being controlled by output pressures of a third proportional control solenoid valve and a third pressure switching valve; a first brake control portion that supplies an output pressure of a fourth pressure control valve to the first brake at the first, second, seventh, and eighth forward speeds and a reverse range pressure of a manual valve to the first brake at the reverse speed, the fourth pressure control valve being controlled by output pressures of a fourth proportional control solenoid valve and a fourth pressure switching valve; and a second brake control portion that supplies an output pressure of a fifth pressure control valve to the second brake, the fifth pressure control valve being controlled by output pressures of a fifth proportional control solenoid valve and a filth pressure switching valve.