Patent ID: 6680554
Filing Date: 2004-01-20
Classification: B64C,F16C,F16F,Y10T

Abstract:
A transmission system for a helicopter equipped with a main gearbox and with a rear gearbox, said transmission system comprising:a single rotary transmission tube, for connecting said main and rear gearboxes of said helicopter, which is of a supercritical type such that at least one natural frequency of said transmission tube is below its nominal rotational speed; and an active and controllable magnetic damper that is operable to generate a magnetic force for acting on said transmission tube and controllable to reduce the vibration of said transmission tube when a speed of said transmission tube is within a predetermined range of frequencies defined about said natural frequency, wherein said magnetic damper comprises: a stator which comprises at least one electromagnet for generating said magnetic force; a rotor which is mounted on said transmission tube and which is situated in a zone of action of said magnetic force; an electric currant generator for producing an electric current flowing through said electromagnet; and control means for controlling said electric current flowing through said electromagnet so as to control said magnetic force which acts on the rotor and therefore on the transmission tube, and wherein the control means comprise a control loop which automatically controls a variation in strength of said electric current flowing through the electromagnet and which includes: means for determining an actual lateral position of the transmission tube; means for containing a theoretical position of the transmission tube; means for calculating a difference between said theoretical and actual positions; a correction unit that determines a correction to be applied by the electromagnet in the form of a corrective magnetic force that needs to be exerted on the transmission tubes; means for summing the corrective magnetic force and a disturbing external force; and a calculation unit which is linked to said means for summing and which determines the theoretical position of the tube from modeling of the transmission system, taking into account a transfer function and matrices of state of the transmission system, and which transmits the theoretical position to said means for containing a theoretical position.