A vibration isolator, comprising:
- an outer cylinder member connected to one of a vibration source and a vibration reception portion;
- a mount member arranged on an inner peripheral side of the outer cylinder member and connected to the other of the vibration source and the vibration reception portion;
- an elastic body arranged between the outer cylinder member and the mount member;
- a main liquid chamber filled with a liquid and having partition walls, a part of which is formed partly by the elastic body so that the main liquid chamber has an inner volume that changes as the elastic body deforms;
- an auxiliary liquid chamber filled with a liquid and having partition walls, a part of which is formed partly by a diaphragm so that the auxiliary liquid chamber is expandable/contractible;
- a first restriction passage for communicating the main liquid chamber and the auxiliary liquid chamber with each other;
- a second restriction passage for communicating the main liquid chamber and the auxiliary liquid chamber with each other, the second restriction passage being different in flow resistance from the first restriction passage;
- a film-like membrane forming another part of the partition walls of the main liquid chamber, and being elastically deformable in an expanding/contracting direction for increasing/decreasing the inner volume of the main liquid chamber;
- a negative pressure chamber provided on an outer side of the main liquid chamber through the membrane, for attracting the membrane to an inner wall when supplied with a negative pressure, to thereby restrain the membrane from deformation in the expanding/contracting direction, and releasing the membrane from the inner wall when supplied with an atmospheric pressure;
- a valve mechanism including a valve body supported movably between an open position for opening the second restriction passage and a closed position for closing the second restriction passage, and a valve chamber having walls, a part of which is formed by a movable wall that is movable along an opening/closing direction of the valve body, said movable wall causing the valve body to be moved into the open position when the valve chamber is supplied with the negative pressure, and into the closed position when the valve chamber is supplied with the atmospheric pressure;
- an internal passage arranged on the inner peripheral side of the outer cylinder member and communicating the negative pressure chamber and the valve chamber with each other;
- and
- an operating pressure supply passage for communicating one of the negative pressure chamber and the valve chamber with an operating pressure supply source for selectively supplying one of the negative pressure and the atmospheric pressure from the outer side of the vibration isolator,
- wherein said internal passage extends through said valve body and said movable wall.