PASSIVE VIBRATION DAMPING DEVICE FOR AIRCRAFT

Abstract

A passive multi-frequency damping device for damping vibrations of an aircraft has a support structure, a plurality of N metal damping masses, each having a respective n-th mass, N being a natural number greater than or equal to 2, and n being a natural number from 1 to N, a plurality of N elastic elements each having a respective n-th stiffness, and each being glued to both the support structure and a respective n-th damping mass to support the respective n-th damping mass on the support structure so that the respective n-th damping mass is free to vibrate relative to the support structure. For each n from 2 to N, each n-th damping mass is arranged to at least partially surround an n1-th damping mass. The first damping mass has a solid semi-cylindrical shape, and the remaining damping masses have a hollow semi-cylindrical shape.

Claims

1. A passive multi-frequency damping device for damping vibrations of an aircraft, the passive multi-frequency damping device comprising: a support structure; a plurality of N damping masses of a metallic material, each having a respective n-th mass, wherein N is a natural number greater than or equal to 2, and n is a natural number from 1 to N; a plurality of N elastic elements each having a respective n-th stiffness; wherein each n-th elastic element is glued to both the support structure and a respective n-th damping mass to support said respective n-th damping mass on the support structure so that the respective n-th damping mass is free to vibrate relative to the support structure; wherein, for each n from 2 to N, each n-th damping mass of said plurality of N damping masses is arranged to at least partially surround an n1-th damping mass of said plurality of N damping masses, and wherein a first damping mass has a cylindrical shape with a first height and a semi-circular cross section, or has a solid semi-cylindrical shape, and wherein each remaining N1 damping mass of said plurality of N damping masses has a cylindrical shape with a respective height and with a cross-section of arc of, or sector of, annulus, or has a hollow, semi-cylindrical shape.

2. The passive multi-frequency damping device of claim 1, wherein for each n from 2 to N, the cross-section of arc of, or sector of, annulus of the n-th damping mass has an inner radius substantially equal to, or slightly greater than, an outer radius of the n1-th damping mass.

3. The passive multi-frequency damping device of claim 2, wherein the first height of the first damping mass and respective heights of remaining N1 damping masses of the plurality of N damping masses are all equal.

4. The passive multi-frequency damping device of claim 1, wherein, for each n from 2 to N, each n-th elastic element adapted to support a respective n-th damping mass of said plurality of N damping masses comprises separate portions shaped as plates.

5. The passive multi-frequency damping device of claim 1, wherein, for each n from 2 to N, the n-th mass of each damping mass of said plurality of N damping masses is a multiple of a mass of the first damping mass.

6. The passive multi-frequency damping device of claim 1, wherein the damping masses are made of tungsten.

7. An aircraft comprising: an engine component, comprising a plurality of blades and adapted to rotate about an axis of rotation to provide thrust to said aircraft; and a passive multi-frequency damping device comprising: a support structure; a plurality of N damping masses of a metallic material, each having a respective n-th mass, wherein N is a natural number greater than or equal to 2, and n is a natural number from 1 to N; a plurality of N elastic elements each having a respective n-th stiffness; wherein each n-th elastic element is glued to both the support structure and a respective n-th damping mass to support said respective n-th damping mass on the support structure so that the respective n-th damping mass is free to vibrate relative to the support structure; wherein, for each n from 2 to N, each n-th damping mass of said plurality of N damping masses is arranged to at least partially surround an n1-th damping mass of said plurality of N damping masses, and wherein a first damping mass has a cylindrical shape with a first height and a semi-circular cross section, or has a solid semi-cylindrical shape, and wherein each remaining N1 damping mass of said plurality of N damping masses has a cylindrical shape with a respective height and with a cross-section of arc of, or sector of, annulus, or has a hollow, semi-cylindrical shape; wherein, for each n from 1 to N, the n-th mass of the n-th damping mass and the n-th stiffness of a respective n-th elastic element supporting said n-th damping mass on the support structure are such that the square root of the ratio of said n-th stiffness to said n-th mass is proportional to a different blade passing frequency of said engine component.

8. The aircraft of claim 7, wherein for each n from 1 to N, the n-th mass of the n-th damping mass and the n-th stiffness of the respective n-th elastic element supporting said damping mass on the support structure are such that a square root of the ratio of said n-th stiffness to said n-th mass is proportional to Nn+1-th blade passing frequency.

9. The aircraft of claim 7, wherein the engine component is a rotor, a propeller or a compressor.

10. The passive multi-frequency damping device of claim 4, wherein said separate portions are two equal separate portions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The features and advantages of this invention will be clarified by the following detailed description, given purely by way of non-limiting example and with reference to the accompanying drawings, in which:

[0033] FIG. 1 is an axonometric view of a damping device according to a first embodiment of the invention;

[0034] FIG. 2 is an exploded view of the damping device in FIG. 1; and

[0035] FIG. 3 is an axonometric view of a damping device according to a further embodiment of the invention.

DETAILED DESCRIPTION

[0036] In general, in the present description and in the accompanying claims, terms such as lower, outer, inner, radial, radially, transverse, transversely and the like are used with the usual meaning in the relevant technical field.

[0037] With reference to FIGS. 1 to 3, the passive multi-frequency damping device for damping vibrations of an aircraft according to the invention is generally indicated by reference sign 10.

[0038] The damping device 10 is particularly adapted to absorb said vibrations to be damped from the air present in the cabin of an aircraft, and essentially comprises a support structure 12, a plurality of damping masses 14, and a plurality of elastic elements 16.

[0039] In particular, the damping device 10 comprises a number N of damping masses 14, where N is a natural number greater than or equal to 2, for example 2, 3, 4 or 5, etc., and the same number N of elastic elements 16. As may be seen in FIGS. 1 and 2, the damping device 10 may comprise two damping masses 14 and two respective elastic elements 16, for example. As may be seen in FIG. 3, it is also possible for the damping device 10 to comprise three damping masses 12 and three respective elastic elements 16, for example.

[0040] The support structure 12 is designed such that it may be connected to the core of a structural element, for example a frame, a floor beam or an intercostal of the aircraft, and such that it may support or uphold said damping masses 14 such that they are free to vibrate or oscillate with respect to said support structure 12. The support structure 12 is preferably in the form of a metal plate which has two respective side wings 18 and 20, on each of which a respective circular through hole 22 and 24 is provided. In this way, by using known threaded or non-threaded mechanical connection means such as screws, rivets, Hi-Lok fasteners and/or bolts, it is possible to fix the support structure 12 to an inner wall of the interior compartment or the cabin of the aircraft or to a structural element as described above.

[0041] The damping masses 14 are made of a metal material, preferably a high-density metal material so as to be able to provide a large mass without necessarily occupying a large space. The damping masses 14 are preferably made of a metal having a high specific weight, for example tungsten.

[0042] According to the invention, the damping masses 14 are shaped such that, for each n from 2 to N, each n-th damping mass 14 of said plurality of damping masses 14 is arranged to at least partially surround an n1-th damping mass 14 of said plurality of damping masses 14. Indeed, as may be seen in FIGS. 1 and 2, a second damping mass 14 laterally or radially surrounds a first damping mass 14, and, as may be seen in FIG. 3, not only a second damping mass 14 laterally or radially surrounds a first damping mass 14 but also a third damping mass 14 radially or laterally surrounds the second damping mass 14. Essentially, with the exception of a first damping mass 14, each following damping mass 14 is arranged telescopically with respect to the previous damping mass, so as to reduce the radial dimensions of the damping device 10 to a minimum.

[0043] According to the invention, the damping masses 14 all have a cylindrical shape, or a three-dimensional shape which may be obtained by extruding a base cross section in space; in the embodiment shown in the figures, these are orthogonal cylinders. In particular, it is possible to use a solid or hollow semi-cylindrical shape.

[0044] As mentioned above, the first damping mass 14 has a cylindrical shape with a first height hi and with a semi-circular cross section, or substantially has a solid semi-cylindrical shape, and each one of the remaining damping masses 14 has a cylindrical shape with a respective height h.sub.n and with a cross section of a arc of, or sector of, annulus, i.e. they have substantially a hollow semi-cylindrical shape.

[0045] In a preferable embodiment, each damping mass 14 has the same height as the other damping masses 14.

[0046] Furthermore, for each n from 2 to N, the cross section of arc of, or of sector of, annulus of the n-th damping mass 14 preferably has an inner radius r.sub.n substantially equal to or slightly greater than an outer radius r.sub.n1 of the n1-th damping mass 14. Substantially, therefore, as shown in FIGS. 1 and 2 (for the case where N=2) and in FIG. 3 (for the case where N=3), the circular sector cross section of the second damping mass 14 has an inner radius r.sub.2 substantially equal to or slightly greater than an outer radius r.sub.1 of the first damping mass 14, and the circular sector cross section of the third damping mass 14 has an inner radius substantially equal to or slightly greater than an outer radius of the second damping mass 14.

[0047] Each damping mass 14 has a respective n-th mass m.sub.n, and each elastic element 16 likewise has a respective n-th elastic stiffness k.sub.n.

[0048] The elastic elements 16 are glued to both the support structure 12 and a respective damping mass 14; therefore, the first elastic element 16 is glued to both the support structure 12 and the first damping mass 14, the second elastic element 16 is glued to both the support structure 12 and the second damping mass 14, the third elastic element 16 is glued to both the support structure 12 and the third damping mass 14, and so on. In so doing, each elastic element 16 supports a respective damping mass 14 on the support structure 12, so as to keep said mass free to vibrate or oscillate freely with respect to the support structure 12.

[0049] For this purpose, the elastic elements 16 are made of a polymeric material.

[0050] In a preferable embodiment shown in the figures, the elastic elements 16 are made as a parallelepiped, or a plate, or a layer of elastic material which may be glued to the two opposite faces in order to be connected on one side to a particular damping mass 14 and on the other side to the support structure 12.

[0051] Even more preferably, for each n from 2 to N (where N is the number of damping masses 14 or elastic elements 16), each n-th elastic element 16 comprises separate portions in the form of a parallelepiped, or of a plate, preferably two separate portions 16a and 16b, even more preferably two equal separate portions 16a and 16b.

[0052] Clearly, depending on the required shape and on the shape of the support structure 12, different shapes are possible for the damping masses 14 and for the elastic elements 16, but the relative arrangement of the damping masses 14 and the respective elastic elements 16 is always such that, except for the first damping mass 14, the successive damping masses 14 are arranged telescopically, or at least partially surrounding a preceding damping mass 14 in a radial or lateral or transverse direction, and always such that the elastic connection between the damping mass 14 and the support structure 12 is ensured by a respective elastic element 16 (optionally provided in the form of various separate elastic element portions 16a 16b) which is arranged therebetween and glued to both in order to allow the respective damping mass 14 to vibrate or oscillate freely with respect to the support structure 12.

[0053] The mass m.sub.n of each damping mass 14 and the stiffness k.sub.n of each respective elastic element 16 are determined during the design phase such that the system formed by a damping mass 14 and by the particular elastic element 16 is adapted to damp a specific frequency. In particular, when f.sub.i, is the frequency which vibrations are intended to be damped by a respective pair formed by the n-th damping mass 14 and by the respective n-th elastic element 16, the respective mass m.sub.n and the respective stiffness k.sub.n are selected such that the following formula is satisfied:

[00002]$f_i={\mathrm{BPF}}_i=\frac{1}{2}\sqrt{\frac{k_n}{m_n}}$

[0054] In this way, each respective pair formed by the n-th damping mass 14 and by the respective n-th elastic element 16 will be adapted to damp a respective frequency f.sub.i.

[0055] For example, if an elastic stiffness k common to all the elastic elements 16 is fixed, for each n from 2 to N, the n-th mass m.sub.n of each damping mass 14 of said plurality of damping masses 14 may be provided as a multiple of the mass m.sub.1 of the first damping mass 14, for example an increasing multiple. The damping masses 14 are preferably such that the mass m.sub.n of each n-th damping mass 14 arranged further inward with respect to the N-th damping mass is inversely proportional to the square of the i-th order of the blade passing frequency BPF.sub.i, the vibrations of which said n-th damping mass 14 is intended to damp.

[0056] The damping device 10 according to the invention may be applied in particular to an aircraft comprising an engine component that comprises a plurality of blades and is adapted to rotate about an axis of rotation thereof to provide thrust to said aircraft.

[0057] In the context of the invention, engine component is understood to include propellers, even of turboprops, rotors, propulsion rotors for helicopters or drones, compressors, in particular parts of turbojet or turboprop engines, and more generally any component comprising a plurality of blades or vanes which rotate at a predetermined rotational frequency in a manner that may cause noise.

[0058] In this case, the damping device 10 is characterized in that, for each n from 1 to N, the n-th mass m.sub.n of each damping mass 14 and the n-th stiffness k.sub.n of the respective elastic element 16 supporting this damping mass 14 on the support structure 12 are such that the square root of the ratio of said n-th stiffness to said n-th mass is proportional to a different blade passing frequency (BPF.sub.1, BPF.sub.2, BPF.sub.3, . . . , BPF.sub.i) of said engine component.

[0059] Substantially, therefore, each damping mass 14elastic element 16 pair has a ratio between the stiffness and the mass that is selected according to a different blade passing frequency (BPF), a component of the vibration to be damped.

[0060] In particular, preferably, for each n from 1 to N, the n-th mass m.sub.n of each damping mass 14 and the n-th stiffness k.sub.n of the respective elastic element 16 supporting this damping mass 14 on the support structure 12 are such that the square root of the ratio of said n-th stiffness to said n-th mass is proportional to the Nn+1-th (N minus n plus 1) blade passing frequency (BPF.sub.Nn+1). Therefore, for example, in the case where N=2, or in the case where the device comprises only two damping masses 14 and two respective elastic elements 16, the mass m.sub.1 of the first damping mass 14 and the stiffness k.sub.1 of the first elastic element 16 supporting the first damping mass 14 on the support structure 12 are such that the square root of the ratio of said first stiffness k.sub.1 and said first mass m.sub.1 is proportional to the second blade passing frequency BPF.sub.2, and the second damping mass 14 and the stiffness k.sub.2 of the second elastic element 16 supporting the second damping mass 14 on the support structure 12 are such that the square root of the ratio of said second stiffness k.sub.2 and said second mass m.sub.2 is proportional to the first blade passing frequency BPF.sub.1.

[0061] For example, if the damping device 10 according to the invention having three (N=3) damping masses 14, as is shown for example in FIG. 3, is used, the masses m.sub.n and the stiffnesses k.sub.n are selected such that the square root of the ratio of the stiffness k.sub.1 of the first elastic element 16 and the mass m.sub.1 of the first damping mass m.sub.1 is proportional to the third BPF (BPF.sub.3), and that the square root of the ratio of the stiffness k.sub.2 of the second elastic element 16 and the mass m.sub.2 of the second damping mass m.sub.2 is proportional to the second BPF (BPF.sub.2), and that the square root of the ratio of the stiffness k.sub.3 of the third elastic element 16 and the mass m.sub.3 of the third damping mass m.sub.3 is proportional to the first BPF (BPF.sub.1). In a manner which is obvious per se, a person skilled in the art will be able to determine the masses and the stiffnesses required for damping vibrations at other frequencies, using a greater number of damping masses 14 and of respective elastic elements 16.

[0062] Clearly, this teaching may also be applied to different engine components such as those set out above.

[0063] As may be seen from the preceding description, by virtue of the damping device according to the invention, the objects of the above-described invention may be fully achieved, resulting in several advantages.

[0064] In particular, the invention provides an improved passive damping device relative to the prior art.

[0065] Firstly, by virtue of using a plurality of damping masses and a plurality of respective elastic elements which are independent of one another, it is possible to damp vibrations at various frequencies simultaneously, and it is no longer necessary to select which frequency to damp.

[0066] Moreover, as a result of the telescopic arrangement of the damping masses, the damping device according to the invention is particularly suitable for aeronautical applications where the requirement for small dimensions is of maximum importance.

[0067] Without prejudice to the principle of the invention, the embodiments and the details of construction may vary widely with respect to that which has been described and illustrated purely by way of non-limiting example, without thereby departing from the scope of protection of the invention as defined in the appended claims.