Device for providing a rigid mechanical link with frequency cut-

Details Device for providing a rigid mechanical link with frequency cut- Device for providing a rigid mechanical link with frequency cut-

1994-10-05

1996-10-29

Young, Lee W.

Brakes

Internal-resistance motion retarder

Having a thrust member with a variable volume chamber

18832219, F16F 500

Patent

active

055688470

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a device for providing a rigid mechanical link between two structures.
Mechanical linking devices which are used in particular for suspending or supporting one structure by another structure, generally comprise a linking member of more or less high stiffness, for example a spring or a block of elastomeric material, associated with a "dashpot" type means for damping movements between the two structures and for filtering vibrations. Such devices are used in the automotive industry, for suspending the body and the engine assembly of an automotive vehicle. They are characterized essentially in that they dissipate energy and transmit forces, the forces transmitted being proportional to the vibratory speeds.
Hydraulic devices for filtering low frequency vibrations are also known, these being used in particular in the automotive industry and comprising two chambers with resiliently deformable walls which are filled with liquid and connected together via a narrow passage, vibrations of a predetermined low frequency being attenuated by resonance of the mass of liquid being driven along the narrow passage. The low value of the frequency attenuated by these devices is related to the relatively low stiffness of the block or blocks of elastomeric material in which the aforementioned chambers are formed. This low stiffness leads to deformation of the walls of the chambers, which results in the forces at the frequency to be attenuated nevertheless being transmitted in part.
By contrast, when it is required to use mechanical connections of high or very high stiffness, as for example in the case where a helicopter fuselage is to be suspended from a main gearbox mounted between a turbine and a rotor, known devices are not suitable and it has been proposed to balance the vibratory forces generated by the rotor and transmitted by the gearbox, by providing inertial opposing forces of equal value and opposite direction which are produced by masses connected by means of levers to the suspension arms of the main gearbox. The levers provide amplification which allows the weight of the on-board masses to be reduced. Despite this, the weight is still significant and there is insufficient filtering of the low frequency excitation generated by the rotor.
A particular object of the invention is to avoid those disadvantages of the prior art.
The invention provides a device which makes it possible to provide a rigid mechanical link between two structures, whilst cancelling, or at least reducing to a very great extent, the transmission of a low frequency of a given value, and without absorbing energy.
The invention also provides a device of this type which is reliable, lightweight and compact.
To this end, the invention proposes a device for providing a rigid mechanical link with frequency cut-off between two structures, the device comprising a member for transmitting static forces between the two structures and a cylinder-piston assembly, the piston of which is secured to one structure and the cylinder of which is secured to the other structure, the device being characterized in that the member for transmitting static forces is a tie-rod of high stiffness, the ends of which are secured to said structures, and in that the device comprises means for generating inertia instantaneously opposing the displacement of the piston in the cylinder in response to an impulsive or quasi-impulsive acceleration, these means comprising a duct of small cross-section relative to that of the piston, the duct interconnecting the two chambers formed in the cylinder on either side of the piston, and a substantially non-viscous liquid which completely fills the cylinder and the duct, so that the transmission to one of the structures of an impulsive or quasi-impulsive acceleration applied to the other structure, which causes displacement of the piston in the cylinder in one direction, is opposed by the inertia of the liquid displaced in the opposite direction in the duct, this inertia as seen at the piston being equal to the mass of the

REFERENCES:
patent: 3477665 (1969-11-01), Legrand
patent: 4872649 (1989-10-01), Kawamata
patent: 5000299 (1991-03-01), Goto et al.
patent: 5316240 (1994-05-01), Girard et al.

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