Such mounts are known per se and are frequently used in motor vehicles, in particular as engine mounts. Mounts of this type have proven very successful in damping both low-frequency vibrations and high-frequency vibrations. If the through-opening in the partition wall is closed, high-frequency vibrations with small amplitudes are isolated well by the configuration of the throttle plate and the membrane arranged therein. As soon as the bypass in the throttle plate is open, low-frequency vibrations, for example during idling, are isolated even better. The bypass in the throttle plate can be closed by a closure device.
For resiliently elastic support, for example of the engine in a motor vehicle, such a hydraulic mount usually has a supporting body of elastomeric material. The supporting body is located between fastening means arranged at a variable distance from each other. The interior space of the mount is divided by a rigid plate or throttle plate into two chambers of variable volume—a working chamber and an equalizing chamber. For damping low-frequency vibrations, the two chambers are connected to each other by way of a damping channel, also known as a throttle channel. Further developments of hydraulic mounts of the type in question have not only an elastic supporting body and a damping channel but usually also a decoupling membrane for isolating higher-frequency vibrations and may also have a controllable bypass.
Such a hydraulic mount with a controllable bypass is disclosed in U.S. Pat. No. 4,660,812. Here, the bypass can be closed by a closure plate and an adjusting device. In the case of mounts of this type of construction, pressure surges in the working chamber can in unfavorable cases act on the closure device in such a way that the bypass opens unintentionally. This can be avoided by a configuration of the closure device in which the opening direction of the closure device is opposed to the force effect of the pressure surges. Such a mount is disclosed, for example, in EP 0 852 304 B1.
To improve the vibrational behavior, mounts of the type in question have not only the mentioned throttle channel and the bypass but also usually a decoupling membrane arranged in the throttle plate. When there are higher frequency vibrations with small amplitudes, the membrane can vibrate at the same time correspondingly.
Such a mount is disclosed, for example, in U.S. Pat. No. 5,344,127. In the case of such an embodiment, however, the main effect that can be achieved by opening the bypass, that is lowering the spring rate at higher frequencies, is worsened. It is thus desirable to render the decoupling membrane ineffective when the bypass is open.
In EP 1 426 651 A1 there is disclosed a mount in which both the bypass can be opened and the decoupling membrane can be firmly clamped by way of an electromagnetically actuated slide. However, the slide acts transversely to the direction of effect of the mount and causes additional effort in terms of reducing the frictional forces and compensating for the fluid to be displaced.