Aircraft provided with a device for reducing vibration, and a method therefor

A method of minimizing vibration in a cabin of an aircraft, said aircraft being provided with a load-bearing structure and with a main gearbox for driving a rotary wing in rotation, the main gearbox being fastened to said load-bearing structure via at least three suspension bars, wherein, with said aircraft having a vibration reduction system provided with an active vibration absorber fastened to each suspension bar, each vibration absorber being provided with a first mass and with a second mass between which a force generator is arranged, the first mass having an upper mass element and a lower mass element, the second mass having an intermediate mass element, the method comprising:

• fastening the intermediate mass element to the upper mass element via a first resilient member and fastening the intermediate mass element to the lower mass element via a second resilient member such that the intermediate mass element is positioned between the upper and lower mass elements and is configured to move along an associated suspension bar of the at least three suspension bars;
• estimating a control force per force generator for minimizing a vibration level relating to the vibration level present in said cabin with a control unit;
• putting a bound on said control forces with the control unit so as to obtain a bounded force per force generator as a function of the forces currently passing through each suspension bar so that each current force does not exceed a predetermined threshold;
• and
• sending an instruction from the control unit to said force generators so that said force generators generate said bounded forces.

An aircraft comprising:

• a load-bearing structure;
• a main gearbox driving a rotary wing in rotation;
• at least three suspension bars fastening the main gearbox to the load-bearing structure;
• and
• a vibration reduction system having an active vibration absorber fastened around each suspension bar, each vibration absorber comprising:
• a first mass having a lower mass element and an upper mass element, an upper mass element positioned between the lower mass element and the rotary wing, the lower mass element connected to an associated suspension bar of the at least three suspension bars via a first spring configured to allow the lower mass element to move along the associated suspension bar, the upper mass element connected to the associated suspension bar via a second spring configured to allow the upper mass element to move along the associated suspension bar,
• a second mass having an intermediate mass element positioned between the upper mass element and the lower mass element, the intermediate mass element fastened to the lower mass element via a first resilient member and fastened to the upper mass element via a second resilient member such that the intermediate mass element is configured to move along the associated suspension bar, and
• a force generator having a lower electromagnetic actuator and an upper electromagnetic actuator, the lower electromagnetic actuator positioned between the intermediate mass element and the lower mass element, and the upper electromagnetic actuator positioned between the intermediate mass element and the upper mass element;
• and
• a control unit;
• wherein the force generator is configured to input a control force on being instructed by the control unit as a function of information coming from at least one first measurement sensor for sensing monitoring parameters for monitoring the associated suspension bar;
• wherein the lower mass element, the upper mass element, and the intermediate mass element each surround the associated suspension bar;
• and
• wherein the lower mass element, the upper mass element, and the intermediate mass element are configured to induce vibration absorption along an absorption axis (AX) coinciding with the extension axis along which the associated suspension bar extends.