Clutch device for automatic transmission

A clutching device of an automatic transmission, comprising:

• a clutch drum connected with a first rotation element;
• a clutch connected with the clutch drum and also connected with a second rotation element, and configured to connect and disconnect torque delivery between the first and second rotation elements;
• and
• a piston unit to operate the clutch to connect the torque delivery between the first and second rotation elements,
• wherein the piston unit includes:
• a first piston forming a first sealed space with the first rotation element and the clutch drum and moving toward the clutch by a hydraulic pressure supplied to the first sealed space through a first hydraulic line formed in the first rotation element;
• a spring retainer forming a second sealed space with the first rotation element and the first piston and arranged on the first rotation element;
• a support drum arranged in the first piston, wherein a first end of the support drum is supported by the first rotation element in a sealed state and a second end of the support drum is supported by the spring retainer in a sealed state;
• a second piston forming a third sealed space with the first rotation element and the spring retainer, arranged in the support drum, and moving in an axial direction of the first rotation element when a hydraulic pressure is supplied to the third sealed space through a second hydraulic line formed in the first rotation element;
• a first return spring stored in the second sealed space and applying restoring force to the first piston;
• a second return spring disposed between the second piston and the support drum and applying restoring force to the second piston;
• a latch spring inserted in an insert groove formed in the first piston and applying pressure to the clutch when the first piston moves toward the clutch;
• and
• a latch device selectively limiting bidirectional movement of the first piston by a cam operation between a stopper ring and the second piston.