Prediction Of Vibro-acoustic Characteristics And Structure Optimization For Noise Reduction Of Axial Piston Pumps

Axial piston pumps are widely used in mobile,industrial and aerospace areas due to their advantages of high power-to-weight density and high reliability.Axial piston pumps are the main power sources in fluid power systems,as well as the main noise sources.With the development of society,our people pay increasing demand on environmental protection,and stricter regulations are issued to regulate the allowable sound power levels of mechanical machinery.Therefore,the requirement of quieter axial piston pumps is essential to reduce the sound power level of machinery.In this thesis,a vibro-acoustic model is developed to predict the vibro-acoustic characteristics of axial piston pumps in the design stage.The vibro-acoustic model includes two sub-models,(1)the lumped parameters(LP)model,and(2)the finite element and boundary element(FE/BE)model.The LP model is used to calculate the excitation sources,and the FE/BE model is used to calculate the vibration on the pump surface and the noise emitted from the pump using the excitation sources from the LP model.In order to validate the LP model,the source flow ripples of an axial piston pump are measured in some operating conditions.The comparisons of the simulated and measured flow ripples indicated that the error in the amplitudes of flow ripples are smaller than 3%.In order to validate the vibro-acoustic model,the vibration at specific points on the pump surface and the sound pressure levels in the sound fields are measured.Comparisons of the simulated and measured results indicate that the vibro-acoustic model is capable of predicting the vibrations and sound pressure levels at integer multiples of the pumping frequency,and the simulated and measured vibration velocities are of the same order of magnitudes and the error of the simulated and measured sound pressure level is only 1.3 dB(A)and 1.4 dB(A)at the 9th order at two different pressure levels.Two key components which have great influences on the vibro-acoustic characteristics of axial piston pumps are optimized.(1)The multi-objective optimization method is developed for the optimization of the valve plate structure.The noise of the axial piston pump using the original and optimized valve plates are measured,and the results show that the sound pressure level at the 9th order is reduced by 2.4 dB(A)at the specified operating condition.(2)The topology optimization method is developed for the optimization of the housing structure.The vibration and noise of the axial piston pump using the original and optimized housings are measured at different pressure levels.The results show that the average sound pressure level at the 18th order are reduced by 1.2-2.1 dB(A)when the optimized housing is used.The thesis is organized as follows:Chapter 1 presents the research background,and introduces the state of the art in noise reduction of axial piston pumps.The limitations of the current studies are pointed out,and the research subject and the challenges of the thesis are given.In chapter 2,the LP model of the axial piston pump are developed.In the LP model,the leakages across three main friction pairs are considered,which are of great effects on the piston chamber pressure build-up.The density and bulk modulus of hydraulic oil are analyzed and modeled at a wide range of pressure,with special consideration on the occurrence of air bubble and vaporization of fluid.At last,the source flow ripples of the axial piston pump are measured to further validate the LP model.In chapter 3,the vibro-acoustic model of the axial piston pump is established to predict the vibro-acoustic chracteristics of the axial piston pump at the design stage,by combing the finite element and boundary element methods.Details of the finite element model and its updating using experimental modal analysis are presented.The linearization of the friction pairs are presented in the FE model.The theory of sound calculation using boundary element method and the details of the BE model are presented.At last,the vibration and noise of the axial piston pump are measured in a hemi-anechoic room to validate the vibro-acoustic model.In chapter 4,the valve plate structural parameters of an axial piston pump are optimized using multi-objective optimization method.Firstly,the vibro-acoustic characteristics of the axial piston pump are measured,and the dominant causes of vibration and noise level are identified.The multi-objective optimization method is used to optimize the valve plate structure,and the optimal solution is obtained.The measured sound pressure level using the original and optimized valve plates validates the effectiveness of the proposed method.In chapter 5,the housing structure of an axial piston pump is optimized using topology optimization method.The effects of the thickness of housing on the frequency response function are analyzed,and the results reveal that the frequency response function can be reduced by increasing the thickness.The theory of topology optimization and the procedure to build the model are presented,and the optimized housing is obtained from the optimization result.The vibration and noise of the axial piston pump using the original and optimized housings are measured,and the effectiveness of the method is validated.In chapter 6,the conclusions of the current study,and the outlook of future study are presented.