Study On Dynamic And Fatigue Characteristics Of The Accessory Drive System Under Shock Loads

As an important power transmission device for the fighter plane,the accessory drive system will bear heavy shock load frequently due to working state instantaneous changes of aeroengine under combat condition.It would cause the transmission shaft fatigue failure fracture easily and serious will make the fighter plane lost combat capability.Therefore,it is important to study the dynamic response characteristics and fatigue characteristics of the transmission shaft in the accessory drive system under shock load,which has great military value to improve the stability and combat capability of our fighter plane.Based on the structural characteristics of the accessory drive system,the dynamic model and equation of the tri-parallel transmission shaft-gear drive system was established by using the partial analysis method.The natural frequency,critical speed and principle mode of the system were obtained under certain parameters,and found that transmission shaft was more prone to shock torsional vibration damage due to the smaller stiffness.Based on the Newmark-? algorithm,the Matlab calculation program of the torsional vibration response of the drive system under shock load was written to solve the dynamic equation.The angle of twist per unit length was used as the measure of the torsional vibration response of transmission shaft,and the influence of different shock load forms on the vibration response of transmission shaft in the system were calculated and analyzed.And found that the shock waveform and the shock pulse width have little effect on the peak value of torsional vibration response of the system,the most influence factor was the peak value of shock load,but when the shock pulse width was the same or close to the second order natural frequency of system,the system will bear a severe shock resonance response.And then,the influence of parameters such as the torsional stiffness of transmission shafts,the moment of inertia of input rotor,loads and gears,the transmission ratio on the peak value of shock response and its transitivity of the transmission shafts in the drive system were studied.The results show that by increasing the torsional stiffness of transmission shafts,changing structural layout of loads and increasing transmission ratio could reduce the peak value of shock response of the transmission shafts.The torsional stiffness and torsional strength damage of the transmission shaft material under frequent shock load were obtained through the fatigue test,and the mathematical model of torsional stiffness and torsional strength degradation were established.Based on the study of the static and dynamic characteristics of accessory drive system under different operating conditions,and based on the method of reducing the peak value of shock response of transmission shafts obtained by the parallel shaft-gear system,the position of each accessory was adjusted and the transmission ratio of system was optimized,then the structure of the accessory drive system was improved and the peak value of shock response of transmission shafts which had larger damage potential in original system were reduced.Moreover,the method of monitoring and calculating the damage state of transmission shafts was put forward based on the torsional stiffness and torsional strength degradation model.The paper provided a theoretical basis for the design and state monitoring of accessory drive system under frequent and complex shock load.