Abstract: Disclosed is a power transmission device. The power transmission device includes power transmission device includes a drive motor comprising a motor housing, a rear cover, a stator, and a rotor. A motor shaft coupled to the rotor penetrates the front surface and rear cover, with a driving gear at one end protruding outside the motor housing. A drum surrounds the drive motor, featuring a drum circular plate portion and a cylindrical portion extending in the wheel axis direction. A drum cover is coupled to the drum and includes an outer-diameter portion with a driven gear that engages the driving gear. A wheel hub on which a tire is mounted is coupled to the drum to rotate together with it.

Abstract: A power transmission device including two or more pistons is disclosed The power transmission device includes: a housing arranged to form a mounting space by connecting a clutch housing, a clutch connecting portion, a clutch hub and a disk housing to each other; a power transmission hub selectively and operably connected to the housing; first friction disks splined to an interior circumference of the disk housing; second friction disks splined to an exterior circumference of the power transmission hub and disposed alternately with the first friction disks; a piston module including two or more pistons respectively having a corresponding piston chamber, and selectively and frictionally coupling the first friction disks with the second friction disks; and at least one return spring or at least one separating spring supplying a spring load counteracting against an axial force, wherein friction material is attached to any surface of first or second friction disks.

Abstract: The present invention relates to a dual clutch which can transmit rotational power of a first clutch housing to a second clutch housing through a first piston for operating the first clutch, thereby reducing the number of parts and reducing production cost.

Abstract: A method of determining a return spring load in a power transmission device including two or more pistons is disclosed. The power transmission device may include: a housing configured to form a mounting space; a clutch pack configured to include a plurality of separate plates splined to the housing, and a plurality of friction disks alternately disposed with the separate plates, the separate plates and the friction disks being selectively coupled to each other by friction; a power transmission plate configured to be splined to the friction disks; two or more pistons operatively connecting the housing to the power transmission plate by selectively applying an axial force to the clutch pack by an operating hydraulic pressure supplied to the piston chamber; and at least one return spring configured to provide a return spring load against an axial force caused by the operating hydraulic pressure.