Liquid-sealed vibration-proof device

A liquid-sealed vibration-proof device comprising

• a first coupling member to be mounted to a vibratory body;
• a second coupling member to be mounted to a car body member or the like;
• an insulator absorbing and insulating vibrations from the vibratory body and interposed between the first coupling member and the second coupling member;
• a main chamber, whose wall is formed by a part of the insulator and in which liquid is sealed, a subsidiary chamber connected to the main chamber through a first orifice and partly formed by a first diaphragm, a third liquid chamber connected to the main chamber through a second orifice and formed so that the liquid within the main chamber may be introduced therein, and a balance chamber partitioned through a second diaphragm to the third liquid chamber and formed so that either of a negative pressure and atmospheric pressure may be introduced therein;
• wherein the balance chamber is provided with changeover means actuating to change over to either of the negative pressure and the atmospheric pressure continuously or alternately at a specified frequency, and control means controlling the changeover actuation of the changeover means,
• the control means being operated under the condition that an idling revolution range of an engine is divided into a low revolution number range and a high revolution number range on the basis of a predetermined conversion point, the control means performing a control action so as to vibrate the second diaphragm in a state synchronized to the vibration frequencies of other orders than a first-order frequency of engine explosive vibrations in said high revolution number range and so as to vibrate the second diaphragm in a state synchronized to the vibration frequencies of other orders than the first-order frequency of the engine explosive vibrations in said low revolution number range.