Fluid power transmission system with lock-up clutch

A fluid power transmission system including a pump impeller, a first member integrated with said pump impeller, a turbine runner, a second member integrated with said turbine runner, a lock-up clutch, an annular drive member and an annular driven member, wherein fluid flow established by said pump impeller is fed to rotate said turbine runner, wherein said lock-up clutch is selectively engageable with said first member and is connected to said annular drive member, and wherein said annular driven member is arranged to face said drive member and made rotatable relative to said drive member and is connected to said second member whereby torque is transmitted between said drive member and said driven member, said fluid power transmission system comprising:

• a plurality of first projections arranged at a circumferentially constant clearance on a first surface of said drive member, wherein said first surface faces a second surface of said driven member and wherein each of said first projections has a predetermined circumferential length;
• a plurality of second projections arranged at a circumferentially constant clearance on the second surface of said driven member and wherein each of said second projections has a predetermined circumferential length for meshing with said first projections at a radially slight clearance;
• a plurality of damper springs arranged between a plurality of projections selected from the group including said plurality of first projections and said plurality of second projections and wherein each of said damper springs is adapted to be compressed by said first projections and said second projections;
• and
• a viscous fluid confined between said first projections and said second projections.