1. Field of the Invention
This invention relates to a vibration isolating device suitable for use in automobile and other vehicles, machinery and the like, which serves to not only sufficiently damp low frequency, large amplitude vibrations but also effectively insulate high frequency, small amplitude vibrations from a vibration source.
2. Related Art Statement
The vibration isolating device generally called as a rubber vibration isolator is used, for instance, as an engine mount for automobile vehicles, whereby vibrations from an internal combustion engine are absorbed so as not to be transmitted to a vehicle chassis.
The vibration isolating device of this type comprises a frame body connected to a vehicle chassis, a frame body connected to an engine, an elastic member disposed between these frame bodies and contributing to the formation of a closed chamber, an incompressible liquid such as water or the like filled in the closed chamber, a partition member secured at its peripheral edge to one of the above two frame bodies and dividing the closed chamber into two small chambers, and a restricted passage arranged in the partition member and communicating the two small chambers with each other.
When vibrations from the engine are transmitted to the vibration isolating device, they can be damped by a flow resistance subjected to the liquid when the liquid flows from the one small chamber to the other through the restricted passage, a viscosity resistance of the liquid itself, an internal friction of the elastic member and the like.
In this vibration isolating device, however, when the vibration transmitted to the device is, for example, high frequency, small amplitude vibrations of not less than 50 Hz, the restricted passage is rendered into a clogged state under influences of viscosity resistance and inertia force of the liquid, friction force between the liquid and the restricted passage and the like. As a result, the rapid increase of dynamic spring rate in the device deteriorates considerably the ride comfortability on the vehicle.