SE538004C2

SE538004C2 - A vibration absorbing device for reducing vibrations and sounds in a structure

Info

Publication number: SE538004C2
Application number: SE1451045A
Authority: SE
Inventors: Mats Gustavsson
Original assignee: A2 Vibcon Ab
Priority date: 2014-09-09
Filing date: 2014-09-09
Publication date: 2016-02-09
Also published as: WO2016037933A1; SE1451045A1; EP3191734A1; EP3191734B1

Description

20 25 30 35 538 004 ln various aircraft contexts, for instance propeller-driven aircraft, two or several motor speeds are typically used during flight to optimize performance, fuel consumption or comfort at various flight states. These various motor speeds result in vibrations and sounds with two or several relatively well defined fundamental frequencies. The known passive vibration absorbing devices only give the desired reduction of vibrations and sounds at one of the motor speeds and related frequency.

At the other motor speeds the influence of a passive vibration absorbing device may be an increase of the vibrations and sounds.

This problem has been addressed in WO 2006/083223 showing a vibration absorbing device, which thanks to the rotatable spring element will be adaptive. The spring element will adjust itself to such a rotary position that a maximum vibration amplitude is achieved for the oscillating mass of the spring element at vibration excitation at, or in the proximity of, one of the resonance frequencies of the device. The known device may thus, without any actuating members, absorb two different vibration frequencies. WO 2006/083222 shows another similar adaptive vibration absorbing device.

SUMMARY OF THE INVENTION One problem which could occur with the known vibration absorbing devices is that the dynamic element may be in a disadvantageous position when a vibration is excited in the structure. Such a disadvantageous position is when the vibration direction of the vibration in the structure is perpendicular to the desired oscillation direction of the dynamic element for a specific frequency. Thus, the dynamic element may be prevented from rotating to the one of the first rotary position and the second rotary position in which the oscillation direction is parallel with the vibration direction, or the adaptation will be so 10 15 20 25 30 35 538 004 slow that the function of the vibration absorbing device is significantly reduced.

This problem is solved by the device initially defined, which is characterized in that the device comprises a positioning mechanism configured to position the dynamic element in a neutral rotary position, different from the first rotary position and the second rotary position, when the structure does not vibrate.

Such a positioning mechanism will thus prevent the dynamic element from reaching a rotary position in which its desired oscillation direction is perpendicular to the vibration direction of the excited vibration of the structure. lt is to be noted that the vibration direction of the vibration of the structure is normally known. The positioning mechanism may thus be easily adjusted to a preferred neutral rotary position in a non-vibrating state of the structure when mounting the vibration absorbing device to the structure.

The dynamic element will adjust itself from the neutral rotary position to one of the first rotary position and the second rotary position so that a maximum vibration amplitude is achieved for the oscillating mass of the dynamic element at vibration excitation at, or in the proximity of, one of the resonance frequencies of the vibration absorbing device. ln some cases, for example when the vibration amplitude is very low, the adjusting may be slow. Energy absorption is however, acquired also for intermediate rotary positions between the first rotary position and the second rotary position.

The positioning mechanism may be designed to have a very specific relation between the rotation relative to the neutral rotary position and the moment (torque) given by the positioning mechanism. Such specific relations between rotary position of 10 15 20 25 30 35 538 004 the dynamic element and the moment may thus include a progressive behavior with a low moment for low rotation and a significant increase of the moment at a certain rotation.

According to an embodiment of the invention, the dynamic element comprises an elastic element extending along the axis of rotation.

The oscillation of the elastic element may be obtained through an energy-absorbing bending of the elastic element.

Alternatively, or supplementary, the oscillation of the elastic element may be obtained through an energy-absorbing shearing of the elastic element.

According to a further embodiment of the invention, the elastic element provides said different rigidity of the dynamic element.

According to a further embodiment of the invention, the dynamic element has a mass element provided on the elastic element and forming a dynamic mass.

According to a further embodiment of the invention, the mass element provides said different rigidity.

The different rigidity of the dynamic element may be obtained through a geometric design of the dynamic element, i.e. the elastic element or the mass element, with a different geometric shape along the two main axes, e.g. the dimension along the first main axis may be different from the dimension along the second main axis. The different rigidity of the dynamic element may also be obtained through an orthotropic material of the dynamic element, i.e. the elastic element or the mass element.

According to a further embodiment of the invention, the elastic element comprises an intermediate segment, a first outer segment and a second outer segment, which extend along the 10 15 20 25 30 35 538 004 axis of rotation and are rotatable in relation to each other and the attachment. Advantageously, the intermediate segment, the first outer segment and the second outer segment may provide said different rigidity. By such an elastic element, the vibration absorbing device may adapt itself to possibly eight different angular resonance frequencies.

According to a further embodiment of the invention, the first outer segment and the second outer segment are mechanically coupled to each outer. With such a coupling, a symmetric elastic element is obtained, which may adapt itself to four different angular resonance frequencies.

According to a further embodiment of the invention, the vibration absorbing device comprises two rotary bearings, which are mounted to the attachment and thus are mechanically connected to the structure, wherein the dynamic element at a respective end thereof is journalled in the two rotary bearings to be rotatable around the axis of rotation.

With such a double support of the dynamic element, two elastic elements are formed, one on each side of the mass element or on each side of a central position of the dynamic element, which elastic elements will act as a combined spring and thus reduce the required accuracy of the mounting of the dynamic element.

This will allow for proper functioning of the vibration absorbing device even if there is a small difference in properties for the two elastic elements.

Advantageously, at least one of the rotary bearings comprises a pin bearing.

According to a further embodiment of the invention, the positioning mechanism comprises a weight provided on the dynamic element to rotate the dynamic element to the neutral 10 15 20 25 30 35 538 004 rotary position by means of the gravity force when the structure does not vibrate.

According to a first variant of this embodiment, the weight is attached to the elastic element.

According to a second variant of this embodiment, the weight is attached to the mass element.

According to a further embodiment of the invention, the positioning mechanism comprises a spring arrangement acting on the dynamic element to rotate the dynamic element to the neutral rotary position when the structure does not vibrate.

Advantageously, the spring arrangement may comprise at least one spring connected to the dynamic element.

According to a first variant of this embodiment, the at least one spring is attached to the elastic element.

According to a second variant of this embodiment, the at least one spring is attached to the mass element.

According to a further embodiment of the invention, the at least one spring comprises a spring having a non-linear characteristic and a progressive behavior with a low moment for low rotation of the dynamic element and a significantly higher moment at a certain rotation of the dynamic element.

With such a non-linear spring, the spring arrangement may thus be designed to have the very specific relation between the rotation relative to the neutral rotary position and the moment (torque) given by the spring arrangement.

According to a further embodiment of the invention, the positioning mechanism comprises a magnet arrangement acting 10 15 20 25 30 35 538 004 on the dynamic element to rotate the dynamic element to the neutral rotary position when the structure does not vibrate.

Advantageously, the magnet arrangement comprises a first magnet connected to the dynamic element and a second magnet connected to the attachment.

According to a second variant of this embodiment, the first magnet is attached to the mass element.

According to a first variant of this embodiment, the first magnet is attached to the elastic element.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is now to be explained more closely through a description of various embodiments and with reference to the drawings attached hereto.

Fig1 discloses schematically a side view of a vibration absorbing device according a first embodiment of the present invention. discloses schematically a cross-section through the vibration absorbing device in a first rotary position. discloses schematically a cross-section through the vibration absorbing device in a second rotary position. discloses schematically a cross-section through the vibration absorbing device in a neutral rotary position. discloses schematically a cross-section through the vibration absorbing device according to a second embodiment of the present invention. discloses schematically a cross-section through the vibration absorbing device according to a third embodiment of the present invention.

Fig 2 Fig 3 Fig 4 Fig 5 Fig 6 10 15 20 25 30 35 538 004 Fig 7 discloses schematically a cross-section through the vibration absorbing device according to a fourth embodiment of the present invention.

Fig 8 discloses schematically a cross-section through the vibration absorbing device according to a fifth embodiment of the present invention.

Fig 9 discloses schematically a side view of a vibration absorbing device according to a sixth embodiment of the invention.

Fig 10 discloses schematically a side view of a vibration absorbing device according to a seventh embodiment of the invention.

Fig 11 discloses schematically a side view of a vibration absorbing device according to a eight embodiment of the invention.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS Fig 1 discloses a first embodiment of a vibration absorbing device for reducing vibrations and sounds in a structure 1. The structure 1 may be a vehicle, for instance an aircraft, a car, or a ship, or any stationary structure, for instance a building, a machine tool or any other stationary installation, where it is desirable to reduce sounds or vibrations.

The vibration absorbing device comprises an attachment 2, which is configured to be attached to the structure 1 in any suitable manner, for instance by means of one or more screw joints 3, schematically indicated.

Furthermore, the vibration absorbing device comprises a dynamic element 4. The dynamic element 4 has two opposite ends. ln the first embodiment, the two ends are supported by and journalled in a respective one of two rotary bearings 5 to be rotatable around an axis x of rotation. The dynamic element 4 is at least partly elastic and has a spring constant k. 10 15 20 25 30 35 538 004 The two rotary bearings 5 are mounted to the attachment 2. The rotary bearings 5 are thus mechanically connected to the structure 1. One, or possibly both, of the two rotary bearings 5 comprises a pin bearing. ln the first embodiment, the dynamic element 4 comprises an elastic element 6 extending along the axis x of rotation. The elastic rod 6 may be made of any suitable elastic material, for instance spring steel, composite material, etc., to provide elastic properties with said spring constant k permitting the elastic rod 6 to flex and oscillate. ln the embodiments disclosed, the elastic element 6 is in the form of an elastic rod.

The oscillation of the elastic element 6 may be obtained through an energy-absorbing bending of the elastic element 6.

Alternatively, or supplementary, the oscillation of the elastic element 6 may be obtained through an energy-absorbing shearing of the elastic element 6. ln this case, the elastic element 6, may have a smaller longitudinal extension along the axis x of rotation than in the embodiments disclosed.

As has been indicated in Fig 1, the two ends held by the rotary bearings 5 are comprised by the elastic element 6. ln the first embodiment, the dynamic element 4 also comprises a mass element 7 provided on the elastic element 6 at a central position of the elastic element 6. The mass element 7 forms a dynamic mass of the dynamic element 4. lt should be noted that it is possible to dispense with the mass element 7. The dynamic mass of the dynamic element 4 may then be provided by the elastic element 6.

The dynamic element 4 has at least partly a cross-section, see Fig 2, which defines a first main axis y, perpendicular to the axis 10 15 20 25 30 35 538 004 x of rotation, and a second main axis z, perpendicular to the first main axis y and to the axis x of rotation. The dynamic element 4 has a different rigidity with respect to the first main axis y and the second main axis z. ln the first embodiment, the elastic element 6 provides the different rigidity of the dynamic element 4 along the first main axis y and the second main axis z. Fig 2 discloses a cross- section through the elastic element 6.

The different rigidity of the dynamic element 4 may be obtained through a geometric design of the dynamic element 4, i.e. the elastic element 6 and/or the mass element 7. ln Figs 2 and 3, the cross-sectional dimension of the elastic element 6 is longer along the first main axis y than along the second main axis z.

The different rigidity of the dynamic element 4 may also be obtained through an orthotropic material of the dynamic element 4, i.e. the elastic element 6 and/or the mass element 7. ln case of a vibration in the structure 1, the dynamic element 4 is brought to take a first rotary position, in which the dynamic element 4 will oscillate along the first main axis y, or a second rotary position, in which the dynamic element 4 will oscillate along the second main axis z. ln Fig 2, the dynamic element 4 is adjusted to the first rotary position, in which the first main axis y is parallel to the vibration direction v. The structure 1 then vibrates with an angular resonance frequency wy = (ky/m)'/= of the vibration absorbing device, wherein ky corresponds to the spring constant of the dynamic element 4 with respect to the first main axis y and m is the effective modal mass. The dynamic element 4 will oscillate in the direction of the first main axis y. 10 10 15 20 25 30 35 538 004 ln Fig 3, the dynamic element 4 is rotated 90° and has thus adjusted itself to the second rotary direction in which the second main axis z is parallel to the vibration direction v. The structure 1 then vibrates with an angular resonance frequency wz = (kZ/mY/Z of the vibration absorbing device, wherein k: corresponds to the spring constant of the dynamic element 4 with respect to the second main axis z. The dynamic element 4 will oscillate in the direction of the second main axis z. lf the structure 1 vibrates with the angular frequency wz and the dynamic element 4 is in the first rotary position, the dynamic element 4 may not rotate to the second rotary position in which the oscillation direction is parallel with the vibration direction v. ln the same way, if the structure 1 vibrates with the angular frequency wy and the dynamic element 4 is in the second rotary position, the dynamic element 4 may not rotate to the first rotary position in which the oscillation direction is parallel with the vibration direction v. ln order to prevent the dynamic element 4 from being locked in such a disadvantageous position, the vibration absorbing device comprises a positioning mechanism configured to position the dynamic element 4 in a neutral rotary position, different from the first rotary position and the second rotary position, when the structure 1 does not vibrate.

Consequently, in case of a vibration in the structure 1, the dynamic element 4 is brought to take the first rotary position, in which the dynamic element 4 will oscillate along the first main axis y, or the second rotary position, in which the dynamic element 4 will oscillate along the second main axis z, if the frequency of the vibration is such that it matches one of the angular resonance frequencies wz, wy of the vibration absorbing device. 11 10 15 20 25 30 35 538 004 The vibration absorbing device is thus self-adaptable to achieve maximum vibrations absorption of two different vibration frequencies.

According to the first embodiment, the positioning mechanism comprises a weight 11 provided on the dynamic element 4. The weight 11 will rotate the dynamic element 4 to the neutral rotary position, see Fig 4, by means of the gravity force when the structure 1 does not vibrate. The weight 11 is attached to the mass element 7 as can be seen in Figs 2-4. lt should be noted, that the weight 11 alternatively could be attached to the elastic element 6.

According to a second embodiment, the positioning mechanism comprises a spring arrangement acting on the dynamic element 4 to rotate the dynamic element 4 to the neutral rotary position when the structure 1 does not vibrate, see Fig 5. In the second embodiment, the spring arrangement comprise two springs 12, which are connected to the dynamic element 4. The two springs 12 are attached to the mass element 7 at a respective first end and are attached to the attachment 2 at a respective second end.

Fig 6 discloses a third embodiment, which differs from the fourth embodiment in that the spring arrangement comprises only one spring 12 holding the dynamic element 4 in the neutral rotary position. The springs 12 is attached to the mass element 7 at a first end and to the attachment 2 at a second end. lt should be noted, that the springs 12, or said one spring 12, instead of being attached to the mass element 7, alternatively, could be attached to the elastic element 6.

The spring or springs 13 may have a non-linear characteristic. ln particular, the spring or springs 13 may have a progressive 12 10 15 20 25 30 35 538 004 behavior with a low moment (torque) for low rotation of the dynamic element 4 and a significantly higher moment (torque) at a certain higher rotation of the dynamic element 4.

According to a fourth embodiment, the positioning mechanism comprises a magnet arrangement 14 acting on the dynamic element 4 to rotate the dynamic element 4 to the neutral rotary position, see Fig 7, when the structure 1 does not vibrate. The magnet arrangement 14 comprises a first magnet 15 attached to the mass element 7 and two second magnets 16 attached to the attachment 2. The first and second magnets 15 and 16 have the same polarity, positive or negative, i.e. they are repelling each other.

Fig 8 discloses a fifth embodiment, which differs from the fourth embodiment in that the second magnets 16 have been replaced by one magnet 17. ln this embodiment, the first magnet 15 and the second magnet 17 have different polarity, i.e. they are attracting each other.

The sounds and vibrations may emanate directly from an engine, transmission or the like of a vehicle or a stationary installation. However, the vibration absorbing device may also be used to alter and reduce the peak of a resonance in the structure 1, for instance squeal from brakes. This as a result of the inherent energy absorption capability for the two angular resonance frequencies my and oaz.

Excitation of both the two angular resonance frequencies my and oaz of the vibration absorbing device will result unless the rotary position is such that the vibration direction is exactly in one of the main axes.

The positioning mechanism assures that the vibration absorbing device is forced towards the neutral rotary position when no vibrations are present. The neutral rotary position can be 13 10 15 20 25 30 35 538 004 selected for each specific structure in order to adapt for specific structural resonances and specific excitation frequencies. For example the neutral position me be selected to improve the adaptation to a frequency of vibration that normally is first in an operating cycle like a flight envelope. Similarly the neutral position may be selected to improve the adaptation to reduce the statistically most likely resonance while the adaptation to less likely resonances thus becomes slower.

Fig 9 discloses a sixth embodiment, which differs from the previous embodiments in that the dynamic element 4 is supported by one rotary bearing 5 only. ln a first variant, the rotary bearing 5 engages one end of the dynamic element 4, i.e. the elastic element 6, whereas the other end of the dynamic element 4 is free. A mass element 6 may be provided at the other free end of the elastic element 6. ln a second variant, not disclosed, the rotary bearing 5 engages the dynamic element 4, i.e. the elastic element 6, at a central position thereof, wherein both ends of the dynamic element 4 are free. A mass elements 7 may be provided at a respective one of the free ends of the elastic element 6.

These variants are explained more closely in WO 2006/083223 discussed above, which is incorporated herein by reference.

Fig 10 discloses a seventh embodiment, which differs from the previous embodiments in that the elastic element 6 comprises three elastic segments, namely an intermediate segment 6a, a first outer segment 6b and a second outer segment 6c, which extend along the axis x of rotation and are rotatable in relation to each other and the attachment 2. The intermediate segment 6a is connected to the first outer segment 6b by means of a rotary bearing 5b and to the second outer segment 6b by means of a rotary bearing 5b. All of the segments 6a-6b provides the different rigidity as the elastic element 6 of the previous 14 10 15 20 25 30 538 004 embodiments. The independently rotatable segments 6a-6c may permit the vibration absorbing device to adapt itself to possibly eight different angular resonance frequencies. ln the seventh embodiment, the intermediate segment 6a is provided with a mass element 7. A positioning mechanism comprising a weight 11 is provided on the intermediate segment 6a. Also the positioning mechanisms discussed above in the second to fifth embodiments may be employed. lt is also to be noted that also the first and second outer segments 6b, 6c may, but do not have to, comprise a positioning mechanism as indicated in Fig 10.

Fig 11 discloses an eight embodiment, which differs from the seventh embodiment in that the first outer segment 6b and the second outer segment 6c are coupled to each outer by means of a suitable mechanical element 18, schematically indicated as a dashed line. Thanks to the mechanical element 18, symmetry is achieved. The first outer segment 6b and the second outer segment 6c will act as one elastic element, which, together with the intermediate segment 6a, permits the vibration absorbing device to adapt itself to four different angular resonance frequencies. lt should be understood, the dynamic element 4 may comprise another number of elastic elements than disclosed above in order to create symmetry and/or to permit the vibration absorbing device to adapt itself to several different angular frequencies.

The present invention is not limited to the embodiments disclosed but may be varied or modified within the scope of the following claims. 15 538 004 lt should be noted that the progressive behavior mentioned above may also be achieved with a positioning mechanism comprising the magnet arrangement 14, or the weight 11. 16

Claims

538 004 Den svenska patentansokningen nr 1451045-7 Benamning: En vibrationsabsorptionsanordning f6r reduce-ring av vibrationer och ljud i en struktur Patentkrav

1. En vibrationsabsorptionsanordning far reducering av vibrat- ioner och ljud i en struktur (1), innefattande ett faste (2), som är utformat att fastas pa strukturen (1), atminstone ett rotationslager (5), som är monterat pa fastet (2) och saledes mekaniskt forbundet med strukturen (1), och ett dynamiskt element (4) lagrat i rotationslagret (5) for att vara roterbart runt en rotationsaxel (x), varvid det dynamiska elementet (4) är atminstone delvis elastiskt, varvid det dynamiska elementet (4) atminstone delvis har ett tvarsnitt, som definierar en forsta huvudaxel (y), som är vinkelrat mot rotationsaxeln (x), och en andra huvudaxel (z), som är vinkelrat mot den forsta huvudaxeln (y) och mot rotationsaxeln (x), varvid det dynamiska elementet (4) har olika rorelsemotstand med avseende pa den forsta huvudaxeln (y) och den andra huvudaxeln (z), och varvid en vibration i en vibrationsriktning (v) i strukturen (1) kommer att bringa det dynamiska elementet (4) till att inta en forsta rotationsposition, i vilken det dynamiska elementet (4) kommer att oscillera langs den forsta huvudaxeln (y), eller en andra rotationsposition, i vilken det dynamiska elementet (4) kommer att oscillera langs den andra huvudaxeln (z), beroende pa vibration-ens frekvens, kannetecknad av att anordningen innefattar en positionerings- mekanism som är utformad att positionera det dynamiska elementet i en neutral rotationsposition, som skiljer sig fran den forsta rotationspositionen och den andra rotationspositionen, nar strukturen inte vibrerar. 538 004

2. En vibrationsabsorptionsanordning enligt krav 1, varvid det dynamiska elementet (4) innefattar ett elastiskt element (6) som stracker sig langs rotationsaxeln (x).

3. En vibrationsabsorptionsanordning enligt krav 2, varvid det elastiska elementet (6) tillhandahaller namnda olika rorelsemotstand.

4. En vibrationsabsorptionsanordning enligt nagot av kraven 2 och 3, varvid det dynamiska elementet (4) har ett masselement (7), som är anordnat pa det elastiska elementet (6) och bildar en dynamisk massa.

5. En vibrationsabsorptionsanordning enligt krav 4, varvid masselementet (7) tillhandahaller namnda olika rorelsemotstand.

6. En vibrationsabsorptionsanordning enligt nagot av kraven 2 till 5, varvid det elastiska elementet (6) innefattar ett mellanliggande segment (6a), ett forsta yttre segment (6b) och ett andra yttre segment (6c), vilka stracker sig langs rotationsaxeln (x) och är roterbara i forhallande till varandra och till fastet (2).

7. En vibrationsabsorptionsanordning enligt krav 6, varvid det forsta yttre segmentet (6b) och det andra yttre segmentet (6c) at-mekaniskt kopplade med varandra.

8. En vibrationsabsorptionsanordning enligt nagot av de fore- gaende kraven, varvid vibrationsabsorptionsanordningen innefattar tva rotationslager (5), vilka är monterade pa fastet (2) och sa- ledes är mekaniskt forbundna med strukturen (1), och varvid det dynamiska elementet (4) vid respektive ande av detsamma är lag-rat i de tva rotationslagren (5) for att vara roterbart runt rotationsaxeln (x).

9. En vibrationsabsorptionsanordning enligt krav 8, varvid at- minstone ett av rotationslagren (5) innefattar ett spetslager. 538 004

10. En vibrationsabsorptionsanordning enligt nagot av de faregbende kraven, varvid positioneringsmekanismen innefattar en vikt (11) anordnad pa det dynamiska elementet (4) for att rotera det dynamiska elementet (4) till den neutrala rotationspositionen nar strukturen (1) inte vibrerar.

11. En vibrationsabsorptionsanordning enligt nagot av de foregaende kraven, varvid positioneringsmekanismen innefattar ett fjaderarrangemang (12) som verkar pa det dynamiska elementet (4) for att rotera det dynamiska elementet (4) till den neutrala rotationspositionen nar strukturen (1) inte vibrerar.

12. En vibrationsabsorptionsanordning enligt krav 11, varvid fja- derarrangemanget (12) innefattar atminstone en fjader (13) for- bunden med det dynamiska elementet (4).

13. En vibrationsabsorptionsanordning enligt krav 12, varvid namnda atminstone en fjader (13) innefattar en fjader som har en icke-linjar karaktaristik och ett progressivt beteende med ett lagt moment for lag rotation hos det dynamiska elementet (4) och ett vasentligt hogre moment vid en viss rotation hos det dynamiska elementet (4).

14. En vibrationsabsorptionsanordning enligt nagot av de fore- gaende kraven, varvid positioneringsmekanismen innefattar ett magnetarrangemang (14) som verkar pa det dynamiska elementet (4) for att rotera det dynamiska elementet (4) till den neutrala rotationspositionen nar strukturen (1) inte vibrerar.

15. En vibrationsabsorptionsanordning enligt krav 14, varvid magnetarrangemanget (14) innefattar en forsta magnet (15) forbunden med det dynamiska elementet (4) och en andra magnet (16, 17) forbunden med fastet (2). 538 004 1/4