Viscous coupling by-pass element having variable drive capability

A viscous coupling adapted for use as a by-pass element for a torque converter including a torque converter housing and an output shaft;

• said viscous coupling being of the type including an annular housing assembly adapted to be positioned within the torque converter housing and having first and second axially spaced, radially-extending, annular side wall members defining an annular viscous shear chamber therebetween, containing viscous fluid to define a wetted surface within said shear chamber, and have an effective drive factor;
• said annular housing assembly defining a clutch surface adapted for clutching co-action with a confronting surface of the torque converter housing, in response to the presence of pressurized fluid in an apply chamber;
• an annular clutch assembly disposed within said viscous shear chamber and including an annular, radially-extending clutch portion cooperating with one of said side wall members to define a viscous shear chamber and a reservoir, and a hub portion adapted to be drivingly associated with the output shaft of the torque converter;
• characterized by:
• (a) one of said clutch portion and said one of said side wall members defining generally radially-extending fill passage means providing fluid communication from said reservoir to said viscous shear chamber;
• (b) one of said first and second side wall members defining discharge passage means, including pump means, providing fluid communication from said viscous shear chamber to said reservoir;
• and
• (c) valve means operable in response to variations in the fluid pressure in said apply chamber to vary the fluid communication through one of said fill passage means and said discharge passage means, thereby varying the wetted surface of said viscous shear chamber and varying the effective drive factor of said viscous coupling.