PURPOSE: To make compact an electric motor for driving a displacer piston, and reduce the power consumption of the electric motor by adding a spring mechanism to a rod for restricting the neutral position of the displacer piston.
CONSTITUTION: Coil springs 41 and 42, and a gas spring 43 are provided in a crank chamber for restricting the central position of a displacer piston 12. As a result, an inertia force and another force against the slide resistance of seal members 23 and 25, a yoke cam 25 and the like, works on the displacer piston 12, as the displacer piston 12 moves toward top dead center or bottom dead center. The power consumption of an electric motor 22 at a speed equal to or above a certain level can be reduced and the motor 22 can be made com pact. Furthermore, even when the weight of the displacer piston 12 and the like cannot be made sufficiently light, the spring constant of an added spring mechanism is made large, thereby ensuring the compact size of the electric motor 22.
ISHIKAWA HIRONORI
HAMASHIMA TAKANORI
