Patent attributes
A relief valve is provided in a central part of an elastic diaphragm. A relief hole is provided in the central part of the relief valve. The relief valve is formed thinner than a main body section on an outer circumferential side thereof. Pressing projections protrude from the relief valve upper surface at predetermined intervals in the circumferential direction. The pressing projections contact a projection support section, and a central opening of a central section is located above the relief hole. During excessive deformation on a negative pressure side, the hydraulic liquid of a secondary liquid chamber allows an inner peripheral portion of the relief valve to cause such a preceding deformation as to be lifted up, and the relief valve is rapidly brought out of contact with the seal section, so that the hydraulic liquid leaks rapidly from the central opening to a primary liquid chamber.
