Noise Mechanism Of The Pressure Servo Valve

The pressure servo valve is the key component of the aircraft brake servo control system and plays a vital role in ensuring aircraft landing.However,noise is generated in the servo valve affect its working performance seriously during its working.The working principle and characteristics of the pressure servo valve are analyzed in this thesis.The characteristics and mechanism of noise of the servo valve are studied in several ways,some improvement methods are brought forward to reduce the noise.The thesis mainly includes the follow parts:Chapter 1:Introduction.The key role of the pressure servo valve in the aircraft brake system and necessity of analyzing the noise mechanism of the pressure servo valve are introduced.The characteristics and the preliminary reasons of the servo valve noise are discussed,Literature review of the servo valve noise at home and abroad is given,the objectives,significance and contents of the thesis are outlined.Chapter2:Characteristic analysis and of the pressure servo valve.The structure and working principle of the pressure servo valve are introduced.According to the established mathematical model,dynamic and static characteristics of the pressure servo valve are studied,which provide the theoretical basis for further analysis.Chapter3:Torque motor vibration characteristics analysis and noise experiments.The modal and harmonic mathematical model of the torque motor armature assembly is built,which is based on the ANSYS Workbench.The mode shapes and frequencies of the first 6 orders are obtained.Under the action of the jet force and the electromagnetic force,the harmonic response curves and the resonance law of the key points in different directions are analyzed.The test-rig of noise frequency measurement is designed and the resonant frequency of the noise is measured for validating the model,the results show that the simulation results are consistent with the test,and the high-frequency(around 4000Hz)dominates the servo valve noise.Chapter4:Investigation into the noise reasons of the pressure servo valve.Models of the torque motor,the nozzle and the slide valve are built respectively in the AMESim platform.While model of the armature components is integrating the self-developed C language program into the AMESet platform.The experimental results of the dynamic and static characteristics of the pressure servo valve have a good agreement with the simulation.The influence of the internal and external factors such as valve geometric parameters,slide valve gain,cavitation,dead volume bubble and pressure pulsation of pressure servo valve are analyzed and summarized,and corresponding improvement are proposed.Chapter5:The flow cavitation analysis in the pre-stage of the servo valve.The relationship between the cavitation occurred in the pre-stage and the noise of the pressure servo valve is analyzed.Based on the cavitation theory,the 3-D simulation model of the nozzle flapper fluid field is established.The simulations considering turbulence,multiphase flow and cavitation models are carried out by Fluent software.The influence of the flapper shape,the outlet pressure on cavitation are analyzed.According to the summarized mechanism and the cavitation rules in the pre-stage flow field,suggestions of reducing the cavitation and of noise are proposed.Chapter6:The research progress and results of the noise mechanism of the pressure servo valve are summarized,and the further research work and directions are put forward.