Clutch unit for automatic transmission

A clutch unit for an automatic transmission having a first rotation element and a second rotation element, the clutch unit comprising:

• a spline gear fixedly connected to the first rotation element and including spline teeth at an external circumference of the spline gear;
• a clutch drum having an internal circumference spline-engaged with the spline teeth of the spline gear to be movable in an axial direction of the clutch drum;
• a clutch hub fixedly connected to the second rotation element;
• a plurality of clutch plates spline-engaged with an internal circumference of the clutch drum;
• a plurality of clutch disks alternatingly mounted between the plurality of clutch plates and spline-engaged with an external circumference of the clutch hub;
• a supporting portion fixed to a transmission housing of the automatic transmission and having an end portion to support the plurality of clutch plates;
• and
• a piston mounted in an interior of the transmission housing to form a hydraulic pressure chamber with the transmission housing, configured to have a rolling contact with the clutch drum in which a first bearing is mounted between the piston and the clutch drum, and configured to transmit a pressurizing force to the plurality of clutch plates and the clutch disks through the clutch drum.