1. Field of the Invention
This invention relates to a self-expanding mount for supporting a vibration source, such as an engine, on a base such as a chassis of a vehicle, and more particularly to a self-expanding mount of this kind, which has a liquid chamber filled with liquid, the pressure of which is varied in response to vibration transmitted from the vibration source to cause contraction and expansion of a resilient member thereof fixed to the vibration source, to thereby control transmission of the vibration to the base.
2. Prior Art
Conventionally, self-expanding mounts of this kind, which are so-called active mounts, have been proposed e.g. by Japanese Provisional Patent Publication (Kokai) No. 60-8540 and U.S. Pat. No. 4,638,983.
The former discloses a vibration-absorbing device comprising a fluid chamber provided between a vibrating body or engine and a vibrated body or a chassis of a vehicle, which is filled with fluid and adapted to expand and contract in response to vibration transmitted from the vibrating body, and pulsating pressure-generating means which imparts pulsating pressure to the fluid within the fluid chamber in opposite phase to a pulsation caused by the vibration transmitted from the vibrating body to thereby prevent transmission of vibration from the vibrating body to the vibrated body, wherein the pulsating pressure-generating means is comprised of a vibrating element which is formed of a generally flat plate made of a magnetic material and forming part of walls defining the fluid chamber, the vibrating element being capable of vibrating to thereby impart pulsation to the fluid within the fluid chamber, and a pair of solenoids which, when energized, cause vibration of the vibrating element. In the proposed vibration-absorbing device, the vibrating element in the form of a generally flat plate is vertically vibrated by an electromagnetic force generated by the solenoids to impart vibration to the fluid within the fluid chamber in opposite phase to pulsation caused by vibration of the engine, to thereby prevent the vibration of the engine from being transmitted to the chassis.
The latter discloses an apparatus for the resilient mounting of a vibrating body, including a mounting bracket and a pedestal which are interconnected through a resilient element that contains a liquid-filled hollow space (main liquid chamber), a compensating baffle associated with a positioning element being provided whose adjustment permits compensation of the pressure variations in the liquid caused by disturbing vibrations, wherein the compensating baffle faces the liquid-filled space, the positioning element is adapted to be actuated by a primary element which detects disturbing vibrations of the vibrating body, and the primary element and the positioning element are interconnected through a freely programmable control unit. Further, an equalizing space (auxiliary liquid chamber) is connected to the working space or liquid-filled space through a throttle opening. According to this prior art, when the liquid-filled space is compressed by downward movement of the engine, for example, the compensating baffle is displaced upward to thereby prevent vibration of the engine from being transmitted to the chassis or frame of a vehicle.
Thus, according to the prior art devices described above, the vibrating element or the compensating baffle as a driven member is displaced in an oscillating manner within the liquid chamber to vary liquid pressure within the liquid chamber, which causes expansion and contraction of the resilient member defining the liquid chamber and fixed to the engine to thereby prevent the vibration of the engine from being transmitted to the chassis.
In the former prior art, the vibrating element in the form of a generally flat plate is disposed to be reciprocally displaced within a space between the two solenoids which are arranged at opposite ends of the vibrating element. However, the distance between the solenoids should be short in view of the fact that the output from the solenoids, i.e. the driving force for vibrating the vibrating element is inversely proportionate to the square of the distance between the solenoids. Therefore, the amount of displacement of the vibrating element cannot be set to a large value. Consequently, the fluid pressure within the fluid chamber cannot be varied with a large amplitude and hence the resilient member fixed to the engine cannot be contracted and expanded with a large amplitude. Thus, according to this prior art, low frequency engine vibration components, which are large in amplitude, cannot be accurately and effectively controlled.
On the other hand, in the latter prior art, the compensating baffle associated with the positioning element is supported, via a resilient rubber membrane which seals against the liquid-filled hollow space, in a core fitted in a central portion of the resilient element disposed on the engine side. Therefore, to obtain large displacement of the compensating baffle, the resilient rubber membrance has to be large in surface area. However, if such a rubber membrance with a large surface area is used, a variation in the liquid pressure caused by displacement of the compensating baffle is absorbed by the rubber membrance which is more flexible than the resilient element. Therefore, the rubber membrance should have a smaller surface area, which results in smaller displacement of the compensating baffle. Accordingly, a large amplitude of variation in the liquid pressure within the hollow space cannot be obtained, and hence the resilient element cannot be contracted and expanded with a large amplitude. Thus, also this prior art cannot accurately and effectively control low frequency vibrations of the engine, which are large in amplitude.