Transmission device

A transmission device comprising:

• a first clutch that includes a first clutch drum, a first piston, and a first engagement oil chamber;
• and
• a second clutch that includes a second clutch drum directly fixed to an outer circumferential portion of the first clutch drum, a second piston, and a second engagement oil chamber, wherein:
• the first clutch drum includes a first outer cylinder portion that extends in an axial direction and is fitted with an outer circumferential portion of a first friction engagement plate, a first inner cylinder portion that extends in the axial direction inside the first outer cylinder portion and movably supports an inner circumferential portion of the first piston, a first intermediate cylinder portion that extends in the axial direction between the first outer cylinder portion and the first inner cylinder portion in a radial direction, a first outer annular wall portion that extends in the radial direction between the first intermediate cylinder portion and the first outer cylinder portion, and a first inner annular wall portion that extends in the radial direction between the first inner cylinder portion and the first intermediate cylinder portion;
• the first outer cylinder portion, the first inner cylinder portion, the first intermediate cylinder portion, the first outer annular wall portion, and the first inner annular wall portion are integrally formed with one another;
• a cancel oil chamber defining portion defining a second cancel oil chamber for canceling centrifugal hydraulic pressure produced in the second engagement oil chamber of the second clutch is integrally formed with the first clutch drum as a one-piece unitary structure so as to extend outward from an outer circumferential surface of the first outer cylinder portion;
• an end surface of the cancel oil chamber defining portion is located closer to an open end surface of the first clutch drum than an end surface of the first outer annular wall portion, and the second cancel oil chamber is formed by the cancel oil chamber defining portion;
• and
• a radial surface of the cancel oil chamber defining portion on a side of the second cancel oil chamber axially overlaps the first outer annular wall portion.