In the transport field, it is known that a moving motor-driven vehicle is subjected to vibration. More particularly with aircraft, such as rotorcraft or analogous aircraft, the vibration generated by the moving vehicle is particularly severe and at high frequency. As an indication, the frequencies generated usually lie in the range about 10 hertz (Hz) to about 25 Hz, with motion at an amplitude that is small compared with overall movements caused by effects of the aircraft itself moving.
Such vibration is transmitted to equipment installed in the aircraft and it is harmful. For example, transmission of such vibration to seats installed in the cabin of the aircraft gives rise to discomfort for the passengers subjected thereto. Seats commonly incorporate suspension means that are designed to damp large amplitude movements that are generally caused by the effects of the aircraft moving, but such suspension means are not suitable for filtering the low-amplitude and high-frequency vibration. Also by way of example, other pieces of equipment in an aircraft may be sensitive to vibration and run the risk of malfunctioning and/or of needing to be protected from such vibration for safety reasons. Also for example, vibration transmitted to the equipment can give rise to noise nuisance. In general, it is useful, or indeed essential, to break any rigid connection between a main structure or fuselage of an aircraft and equipment on board the aircraft in order to avoid transmitting the vibration from one to the other.
In order to establish a frame of reference useful for understanding the prior art and the present invention, it is necessary to take the following directions and orientations into consideration, e.g. relative to the position at which a seat is installed in the cabin of the aircraft and the position of the passenger sitting on the seat. These directions and orientations can readily be transposed for any other piece of equipment, given the vibration to be filtered along the directions and orientations:
a transverse direction along a Y axis corresponds to an orientation about which the equipment is to be protected from pitching vibration. For a seat, for example, the direction extends between the passenger's right and left sides;
a longitudinal direction along an X axis corresponds to an orientation about which the equipment is to be protected from vibration in roll. For a seat for example, this direction extends from in front of to behind the passenger;
sliding corresponds to the equipment moving in the XY plane. This plane corresponds to the plane on which the equipment is supported in the aircraft; and
a height-wise direction along a Z axis corresponds to an orientation in which the equipment needs to be protected from pumping vibration. This orientation extends orthogonally to the XY plane.
Solutions have been proposed that in general terms consist in interposing deformable means between the equipment and the fuselage of the aircraft. On the basis of their opposition to being deformed, use is made of the elasticity of the deformable means to absorb relative movements at high frequency and of low amplitude between the fuselage and the equipment. More particularly, the flexibility of the deformable means is used to filter such relative movements.
One known solution consists in interposing the deformable means between the equipment and a carrier structure secured to the fuselage, such that the elasticity of the means absorbs vibration on the basis of the deformation of the means caused directly by the relative movements between the structure and the equipment.
Document FR2863966 describes a seat provided with such resilient means. Such a solution presents the advantage of being inexpensive, compact, and easily integrated in a piece of equipment, in particular a seat. Nevertheless, relying exclusively on the resilience of the deformable means is not completely satisfactory in terms of the filtering that needs to be achieved in order to absorb nearly all of the vibration coming from the fuselage of the aircraft, particularly for any piece of equipment of a weight that is likely to vary, such as a seat that is likely to receive passengers having respective different weights.
Another known solution that is more complex consists in interposing between the equipment and the fuselage of the aircraft a mechanism that associates deformable means and a weighted lever arm. The lever arm allows relative movements to take place between the equipment and the fuselage, and the deformable means absorb the movements of the lever arm that generates force that is amplified by its weighting. Such a mechanism is consequently suitable for filtering the vibration to which the fuselage is subjected in order to avoid transmitting it to the equipment.
Document EP1719700 describes a device for supporting a rotorcraft battery. The spring stiffness is selected so that the resonant frequency of the suspension receiving the battery lies in the range about 20 Hz to about 30 Hz. One or more supports are secured to the rotorcraft so that the battery rests on the device interposed between the support and the battery. The height to the device is less than the height of the battery so as to limit overall size. The springs comprise a plurality of elastically deformable blades, and stiffness adjustment means modify the length of their active portions, using an abutment that is movable between a first position and a second position. Some of the spring blades deform in twisting under the effect of the weight of the battery and others deform in bending under the effect of the weight of the battery.
Document U.S. Pat. No. 4,311,213 describes a mechanism suitable for filtering the vibration to which a rotorcraft is subjected, and in particular the seat fitted thereto. That mechanism is organized as an array of link members, each interposed between the rotorcraft fuselage and a suspended seat-carrying platform. The link members are oriented substantially in crossed directions, and with hinge engagement on the fuselage, serving to carry the platform via resulting means in order to suspend it. Two link members are connected to each other by a torsion shaft or arm. Each link member comprises a deformable member that is interposed between the platform and the fuselage, and a lever arm for operating the deformable member carrying a weighting weight. The weight is carried by the lever arm at its free end opposite from its end anchored to the fuselage. The torsion shaft engages hinge bearings via which the lever arms of the corresponding link members are hinged to the fuselage at their anchor ends. Although that mechanism provides effective filtering, it is complex, expensive, bulky, and requires a specific arrangement and organization of the array of link members depending on the implantation. The arrangement of the array of link members and the ways in which they are interposed, need to be determined specifically.
Document U.S. Pat. No. 4,088,042 describes a vibration isolating system that is compact, of nodal type, filtering multiple frequencies and fitted to a helicopter. In FIG. 2, it can be seen that the system forms a four-branched cross, with four dampers at the ends of the branches.