The Dynamics Of An Aircraft Engine Transmission And Vibration Control

Transmission, playing an important role in aero-engine, is a typical complex gear rotor system with multi-level, multi-offshoot and unparallel axes. Because of the gear meshing effect, the lateral vibration and torsion vibration of system couple each other, so the system could not be studied only according to every rotors separately. The lateral-torsional coupling vibration equations of system should be built and then the vibration of system could be analyzed. In order to improve the vibration performance, it is necessary to set up a effective control system to hold the vibration in a given scope, thus the stability and reliability will be assured.Firstly, the linear dynamics models of helix gear and vertical bevel gear are set up, the calculation method of the meshing stiff and meshing damping are introduced, and the coupling stiffness matrix and coupling damping matrix are deduced. Then the method to analyze the vibration of complex gear-rotor system is proposed. The vibrations of the only one rotor are built, and the dynamic meshing forces are expressed with the coupling stiffness matrix and coupling damping matrix. The meshing forces are considered as the exciting forces of the gear nodes on the rotors. The vibrations of all the rotors are synthesized to the lateral-torsional coupling vibration equations of complex gear-rotor system. Solving these equations, the natural modes and dynamic response are acquired.Secondly, The vibration characteristics of a gear transmission in an aero-engine are analyzed with the method proposed. The results indicate that, except the only one rotor modes and coupling modes being similar to an only one rotor, system derive many new modes sensitive to the gear meshing. Therefore, the gear transmission effect to the these modes must be pay attention to when the system is designed. For the gear meshing, the exciting forces on a rotor of system would be passed to other rotors. When one rotor is excited, the vibration response usually occurred on many rotors at the same time. So the dynamic balance precision of rotors, especially the high speed rotors, should be improved, in order to reduce the unbalanced exciting and improve the dynamic quality of the whole system.Lastly, the change curve between the amplitude of the gear node directly connected with the aero-engine and the supporting stiff of the bear near the gear node. BP artificial neural network are used to simulate the change curve. According to the need of system, the fuzzy logic controller is designed to control the vibration of system, and then, the control arithmetic is simulated with the simulation tool of Matlab. The results indicate that, through regulate the input and output scale constants of controller, some ideal controlling purpose could be reached.