Lock-up apparatus in torque converter

A hydraulic power transmission for driving a vehicle with power received from an engine crankshaft, said hydraulic power transmission comprising:

• an outlet shaft having an exterior cylindrical surface and a central passage defining an interior cylindrical surface;
• a driving member connected to the engine crankshaft;
• a pump impeller connected to the driving member;
• a turbine hub mounted on said output shaft and fixed against rotation relative to said output shaft;
• a turbine impeller hydraulically driven by the pump impeller, said turbine impeller being rigidly fixed to said turbine hub;
• a lock-up clutch including a clutch plate extending radially from said turbine hub and a clutch facing fixed to said clutch plate, said clutch plate being slidably mounted for axial movement between (1) a lock-up position wherein said clutch facing is frictionally engaged with said driving member to establish a direct mechanical coupling between said driving member and said output shaft and (2) a disengaged position wherein said clutch facing is separated from said driving member;
• a release chamber provided between the driving member and the lock-up clutch for supplying and draining a hydraulic fluid;
• a central chamber provided between the pump impeller and the turbine for supplying and draining the hydraulic fluid;
• hydraulic fluid supply means for supplying the hydraulic fluid;
• hydraulic fluid changeover means for supplying the hydraulic fluid from the hydraulic fluid supply means either to the release chamber to disengage said lock-up clutch or to the central chamber to engage said lock-up clutch while draining the release chamber;
• a first oil passage including said central passage in the center of the output shaft and providing fluid ;communication between said hydraulic changeover means and said release chamber;
• a second oil passage providing fluid communication between said central chamber and said hydraulic fluid changeover means;
• and
• orifice means for providing direct constant communication between said first oil passage and said central chamber, said orifice means comprising a first conduit formed in said turbine hub and opening to said central chamber at a point on a surface of said turbine hub radially inward of said lock-up clutch and said turbine impeller;
• whereby said lock-up clutch is engaged and disengaged to or from the driving member in response to a difference in hydraulic fluid pressure between said release chamber and said central chamber.