Automatic transmission

An automatic transmission, comprising:

• a brake including:
• a hub member coupled to a transmission case;
• a drum member coupled to a given rotating member;
• a plurality of friction plates disposed between the hub member and the drum member;
• a piston configured to engage the plurality of friction plates;
• an engagement hydraulic chamber to which hydraulic fluid is supplied to bias the piston in an engaging direction;
• and
• a disengagement hydraulic chamber to which hydraulic fluid is supplied to bias the piston in a disengaging direction,
• wherein the piston extends radially inward of the plurality of friction plates,
• wherein the engagement hydraulic chamber and the disengagement hydraulic chamber are disposed radially inward of the plurality of friction plates,
• wherein the hub member includes:
• a first hub member having a cylindrical part spline-engaged with the friction plates, spline-engaged with the transmission case, and forming the disengagement hydraulic chamber;
• a second hub member disposed at one side of the first hub member in the axial direction, fitted into the transmission case, and coupled to the one side of the first hub member in the axial direction by a first coupling member;
• and
• a third hub member disposed at the other side of the first hub member in the axial direction, coupled to the other side of the first hub member in the axial direction by a second coupling member, and forming the engagement hydraulic chamber, and
• wherein the first coupling member and the second coupling member are disposed radially inward of the disengagement hydraulic chamber.