U.S. Pat. No. 4,789,142 describes an engine mount in which the partition wall has a bypass opening in addition to the duct through which the hydraulic fluid can flow back and forth between the working chamber and the compensation chamber. In the bypass opening there is situated a ferromagnetic diaphragm which has an upper and a lower stop as viewed in the longitudinal direction of the engine mount. Below the diaphragm and below the compensation chamber there is arranged an electromagnetic switching actuator in the form of an electrically conductive coil, via which the diaphragm can be controlled. It is thus possible for the coil to be energized in such a way that the diaphragm is situated either in its lower stop position or in its upper stop position, in which the bypass opening is closed in each case.
Furthermore, it is possible for the coil to be energized in such a way that the diaphragm assumes any desired position between the lower stop position and the upper stop position. The diaphragm then opens up the bypass opening such that hydraulic fluid can flow back and forth between the working chamber and the compensation chamber. Through targeted adjustment of the position of the diaphragm between the upper and the lower stop by means of the coil, it is furthermore possible for the volume of the working chamber to be adapted to the present demands on the engine mount.
With the hydraulic mount known from U.S. Pat. No. 4,789,142, it is possible for low-frequency vibrations to be damped by virtue of hydraulic fluid flowing back and forth via the duct between the working chamber and the compensation chamber of the engine mount. Furthermore, high-frequency vibrations which are introduced into the engine mount can thereby be kept away from the body of the motor vehicle by virtue of the bypass being opened by the ferromagnetic diaphragm and the diaphragm being actuated by the coil in such a manner that the volume of the working chamber remains approximately constant. It is however noted that the coil of the electromagnetic switching actuator must be constantly energized in order to control the diaphragm. This applies both in the situation wherein the diaphragm is to be held in the upper or the lower stop position and also in the situation wherein the diaphragm is to be held between these positions. This leads to a high electrical consumption of the electromagnetic switching actuator. It is also noted that large forces are required for the control of the diaphragm because the diaphragm is acted on by the hydraulic fluid in the working chamber. This makes it necessary to use a switching actuator which can generate large forces and which therefore takes up a large amount of installation space, which is not always available in modern motor vehicles.