The drive motor 1 reciprocates the piston 633 of the compression mechanism 630 and uses the interior permanent magnet motor 1 according to an embodiment of the disclosure as described above. Therefore, a detailed description of the interior permanent magnet motor 1 is omitted.

The rotation shaft 640 is provided to transmit the rotational force of the interior permanent magnet motor 1 to the compression mechanism 630. In other words, the rotation shaft 640 is coupled to the rotor 20 of the interior permanent magnet motor 1 and rotates together with the rotor 20 to operate the compression mechanism 630. The rotation shaft 640 is rotatably supported by a shaft supporter 622 fixed to the frame 620.

The rotation shaft 640 may include an eccentric portion 641 provided at an upper portion of the rotation shaft 640 and a cavity 643 provided at a lower portion thereof.

The eccentric portion 641 is eccentric with respect to the rotational center axis of the rotation shaft 640. The eccentric portion 641 is connected to the piston 633 of the compression mechanism 630 by a connecting rod 635.

Therefore, when the rotation shaft 640 rotates, the piston 633 may performs a linear reciprocating motion with respect to the cylinder 631. In other words, the rotational motion of the rotation shaft 640 may be converted into the linear reciprocating motion of the piston 633 by the eccentric portion 641 of the rotation shaft 640 and the connecting rod 635.