Patent ID: 7464799

Claim:
A hydraulic device, comprising: a cylindrical housing; a free piston accommodated in the housing so as to be free to slide axially, the free piston separating a gas chamber axially from a liquid chamber in the housing, the free piston comprising: a hollow main body which is in contact with an inner circumference of the housing; a metal bellows having an open end which is secured to an end of the main body, and elongating and contracting according to a pressure balance between the gas chamber and the liquid chamber to vary a ratio of a capacity of the gas chamber and a capacity of the liquid chamber; and a stopper which prevents the metal bellows from elongating beyond a predetermined length, the stopper comprising a cap shaped member which is fixed to the main body and covers the metal bellows, the cap shaped member having a communicating hole allowing communication between an inside and an outside of the cap shaped member; and a hydraulic damper which comprises a piston which reciprocates in the housing and separates the liquid chamber into a first operating chamber and a second operating chamber, and a piston rod which is fixed to the piston and projects through the first operating chamber and outward from the housing, whereby the free piston separates the gas chamber axially from the second operating chamber in the housing.