Patent ID: 7614487

Claim:
A frictional engagement apparatus comprising: a first frictional engagement unit including plural first friction plates, a second frictional engagement unit including plural second friction plates and being disposed axially spaced from the first frictional engagement unit, one case that supports the first frictional engagement unit and the second frictional engagement unit non-rotatable circumferentially but shiftable axially relative to the one case, and one retaining ring fitted to the case so as to be located between the first frictional engagement unit and the second frictional engagement unit, the retaining ring being abutted to a nearest first friction plate and/or a nearest second friction plate to stop an approaching shift of the first frictional engagement unit and/or the second frictional engagement unit, wherein the retaining ring includes a u-shaped cross section defined by an annular recess that extends in a circumferential direction of the retaining ring at a radially interior portion of the retaining ring, and wherein the annular recess allows the radially interior portion of the retaining ring to elastically deform in an axial direction of the case such that the radially interior portion of the retaining ring decreases in thickness when the first frictional engagement unit and the second frictional engagement unit approach each other.