Patent ID: 7341133

Claim:
A hydraulic circuit of a hydraulic power transmission having a pump impeller, a turbine runner, a lock-up clutch and a hydraulic power transmission chamber (R 1 ) housing the pump impeller and the turbine runner, said hydraulic circuit comprising: a servo oil chamber for operation of the lock-up clutch isolated from the hydraulic power transmission chamber; a lock-up oil passage (L 1 a ) that supplies hydraulic pressure for lock-up to the servo oil chamber and is connected to a common hydraulic pressure supply circuit (L 1 ); and a circulation oil passage (L 1 b ) that supplies hydraulic pressure for circulation to the hydraulic power transmission chamber and is connected in common with said lock-up oil passage to said common hydraulic pressure supply circuit through a first orifice and through a check valve in parallel with said first orifice, said check valve preventing flow from the common hydraulic pressure supply circuit to the hydraulic power transmission chamber.