Patent ID: 7896145

Claim:
An automatic transmission including a first clutch and a second clutch, comprising: a first drum in which a first piston of said first clutch is axially slidably received and which cooperates with said first piston to define a first oil chamber therebetween; a second drum which is disposed coaxially with said first drum, so as to accommodate said first drum, and in which a second piston of said second clutch is axially slidably received, said second drum cooperating with said second piston to define a second oil chamber therebetween; a first fluid supply portion for feeding a working fluid into said first oil chamber through said first drum and said second drum, to operate said first piston; and a second fluid supply portion for feeding the working fluid into said second oil chamber through said second drum, to operate said second piston, wherein said second fluid supply portion is located radially outwardly of said first fluid supply portion, said second drum includes a second inner cylindrical wall and a second outer cylindrical wall which are coaxial with each other, and further includes a second bottom wall connecting corresponding axial end portions of said second inner and outer cylindrical walls, said second drum further including a second annular protrusion extending from a radially intermediate part of said second bottom wall in an axial direction thereof toward said first drum, said second inner cylindrical wall and said second annular protrusion of said second drum being rotatably supported by a housing of said automatic transmission, said second piston being axially slidably received in a second annular recess formed between said second annular protrusion and said second outer cylindrical wall, said second oil chamber being defined by said second piston, said second outer cylindrical wall, said second bottom wall and said second annular protrusion, said second fluid supply portion communicating with said second oil chamber through a second through-hole formed through said second annular protrusion, and said first fluid supply portion communicating with said first oil chamber through a third through-hole formed through said second inner cylindrical wall and a first through-hole formed through a first inner cylindrical wall.