Electricity: motive power systems – Impact – mechanical shock – or vibration-producing motors
Patent
1983-12-19
1986-07-15
Duggan, Donovan F.
Electricity: motive power systems
Impact, mechanical shock, or vibration-producing motors
2671401, 381 71, 310 51, H02K 3300
Patent
active
046008632
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to the reduction of vibration transmission from a source of vibration to a mounting of that source, by the use of vibration actuators (e.g. interposed between the mounting and the source) energised in such wise that the transmission of source vibration to the mounting is at least reduced and at best prevented.
The active control of noise and other vibration has recently become commercially important and this invention relates to the reduction or prevention of vibration transmission from a source of vibration such as a reciprocating engine (e.g. a marine propulsion plant) to the mounting means of that source (e.g. the chassis of a vehicle or the hull of a craft carrying the source).
The invention can be applied to the reduction of vibration transmissions from both repetitive and nonrepetitive sources but, in general, is expected to find its most important commercial applications in the attenuation of vibrations emanating from a repetitive source.
DISCUSSION OF PRIOR ART
Methods for the active attenuation of vibration are disclosed in U.S. Pat. Nos. 4,122,303 and 4,153,815, the former being concerned with the control of random vibrations and the latter with the control of repetitive vibrations. The techniques disclosed in these U.S. patent specifications are applicable to the control of the actuators described herein and the following disclosure will concentrate on the design of the actuators, it being assumed that the energising of the same will be clear from the above-noted specifications whose entire disclosure is herein incorporated by reference.
The active cancellation of vibration transmitted through machinery mounts conventionally requires the use of actuators operating in three mutually perpendicular directions at each mounting point because the source of vibration is usually multi-directional. Furthermore, the vibrational modes of the machinery mount couple vibration from one axis to another.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a method of reducing the transmission of vibration from a source of vibration to a mounting of the source, comprises the employment of at least one vibration actuator and the energisation of the or each actuator to reduce the effect of source-derived vibration on said mounting, is characterised in that a shear decoupling means is provided in series with the source of vibration.
Conveniently the shear decoupling means is incorporated in the actuator whereby the or each actuator has substantial stiffness along a force-applying axis but is substantially compliant in the shear directions with a ratio of compliance in shear and axial directions of at least 15:1.
By ensuring that the vibration to be reduced can couple to the mounting through the vibration actuator along a single axis only, and applying the active opposing vibration along that axis, it is possible to operate satisfactorily with a single actuator at each mounting.
DECOUPLING MECHANISMS
Any or a combination of the following can be used to decouple the shear vibration at each actuator: known technology. substantially greater in shear than in compression, e.g. using a multi-layer elastomer-metal shim sandwich. a hollow mounting. material, e.g. steel, instead of shims. filled with a suitable fluid, such as water, to increase the stiffness in compression, whilst still retaining compliance in shear. ball or roller bearings. In the case of roller bearings, only one of the tangential axes is decoupled and a second similar bearing is required at right angles. Planar ball bearings, however, have a quite limited load-bearing capacity. the mounting and a suspension attached to the source.
BRIEF DESCRIPTION OF DRAWINGS
The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a prior art arrangement in which three actuators are required at each mounting,
FIG. 2 is a schematic indication of how shear isolation of the mounting permits a single actuator to be used,
FIG. 3 shows a s
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patent: 2876979 (1959-03-01), Barbera
patent: 2919883 (1960-01-01), Murphy
patent: 2964272 (1960-12-01), Olson
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patent: 3721417 (1973-03-01), Skala
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patent: 4005858 (1977-02-01), Lochner
patent: 4153815 (1979-05-01), Chaplin et al.
patent: 4509730 (1985-04-01), Shtarkman
Chaplin George B. B.
Smith Roderick A.
Duggan Donovan F.
Sound Attenuators Limited
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