Patent ID: 7284645

Claim:
A fluid transmission device comprising: a turbine impeller; a pump impeller which is opposed to the turbine impeller so as to define a circulation circuit of a working oil between the pump impeller and the turbine impeller, and which has a pump shell including a diameter-expanded portion along a peripheral end portion; and a cylindrical transmission cover which defines an oil chamber in communication with the circulation circuit between the transmission cover and a back surface of the turbine impeller, a male fitting surface of a periphery of the diameter-expanded portion being fitted to a female fitting surface of an inner circumference of a peripheral wall portion of the cylindrical transmission cover, a fillet weld being formed between an end surface of the peripheral wall portion and a peripheral surface of the diameter-expanded portion along an entire circumference thereby connecting together the pump shell and the transmission cover, wherein an annular recess is formed in an inner circumferential surface of the peripheral wall portion to adjoin the female fitting surface on the side opposite from the fillet weld, and wherein a portion of the transmission cover corresponding to the recess constitutes an annular thin-walled portion which has a thickness smaller than that of the portions of the transmission cover on the opposite sides of the annular thin-walled portion.