Investigation On Test Method And Noise Reduction Structure With Large Operating Conditions For Piston Pump Flow Rate

Noise pollution has become one of the most serious environmental problems in the world, especially in industry. Axial piston pump is one of the main noise sources in hydraulic system, and the air-borne noise of the whole hydraulic system is aggravated by the pump fluid-borne noise. The pump output flow, which is characterized by high frequency, is the main source of the fluid-borne noise, and it is impossible to measure this high frequency flow ripple with traditional flow meters, so some indirect methods have been developed. The Secondary Source Method is a well-known indirect method to measure the pump source flow rate, which is of high precision in most case and can be used for many types of hydraulic pumps. However, the test system is complicated and the accuracy of the measured source flow rate is low when the test pipe length is multiple of the pressure wave length. A new test method, which is simpler and more accurate than traditional ones, has been proposed and discussed in this paper, so that those weaknesses mentioned above have been overcome.A numerical simulation model has been developed based on the operating principle of the axial piston pump, and the influence of the pressure and temperature as well as the movement of the oil film has been considered simultaneously in the model. Then this simulation model was validated by the test results obtained with the Secondary Source method. According to experimental test, when the pump output pressure was15MPa, the pump speed1000rpm and the swash plate angle13deg, the computational accuracy was improved22.7%compared to the traditional model. So this numerical simulation model can be used to analyze the source flow rate and optimize the structure of the axial piston pump. A new estimation algorithm of the pump source impedance has been designed to deal with the case when the test pipe length is multiple of the pressure wave length, a new computational algorithm to solve the problem of the source flow rate with unequal diameter discharge pipe has also been developed. It can be seen from the results that the pump source impedance can be obtained with the new estimation algorithm over following operating conditions:the pump output pressure was between5MPa and22MPa, the pump speed was between400rpm and1500rpm. In addition, the92%test accuracy of source flow rate has been reached by the modified Practical Approximate Method with the computational algorithm. So the application of the current test method is expanded. The parameter selection criteria of the pre-compression volume and the swash plate cross angle with relief groove has been developed, the ratio of the non-uniformity grade difference of flow ripple and the volume difference of the pre-compression volume is used to determine the size of pre-compression volume, the position of the sensitive zone of the port plate where the peak value of the source flow rate and cylinder pressure occur was used to choose degrees of both the angle connecting the port plate and the pre-compression volume and the swash plate cross angle. It can be seen from the simulation result that the optimization procedure for the pre-compression volume and the swash plate cross angle with relief groove has been greatly simplified by adopting the developed parameter selection criteria. The results given in this paper help potential researchers to better understand both the development of flow ripple model and the procedure of performing flow ripple test for piston pump, structure optimization criteria for obtaining quieter piston pump are also proposed and validated by simulation, nevertheless, further experiments are required to approve its effectiveness. The structure of this thesis is illustrated in the following:In chapter1, the research purpose and the research significance of this thesis are discussed. The research content and the technical route are given, and the technical issues are presented accordingly.In chapter2, a newly built numerical simulation model for axial piston pump which is based on the operation principle of the axial piston pump is presented. The computation for the leakage flow rate from all three key oil films is modified, and the calculation accuracy is improved compared to the traditional ones. The energy equation is introduced, and the pressure field and temperature field of the three oil films can be computed simultaneously. The simulation model of the whole hydraulic system connected to the axial piston pump is also built.In chapter3, the testing principle of the pump source flow rate is depicted in detail, and problems which are met in building the test apparatus are provided. Because the current test method is difficult to test the source flow rate of the pump with complicated pump discharge pipe, the finite element method and the dynamic boundary condition is used to compute the characteristic of the discharge pipe. Then according to the different test principle, the relationship between the characteristic of the discharge pipe and the source flow rate is presented, and the corresponding test method is modified.In chapter4, the signal processing of the Secondary Source Method is presented, the precise test results are obtained, and the simulation model built in chapter2is validated. It can be seen from the test results that the new estimation algorithm of the pump source impedance can get the result over the whole operating conditions and the accuracy increased20%over the following operating conditions:pump delivery pressure is5MPa,15MPa and22MPa, the pump speed is400rpm,1000rpm and1500rpm. The signal processing for the Practical Approximate Method is simplified with the high precision. Therefore, the application of the test method is extending. In chapter5, the effect of operating conditions and the fluid characteristic on flow ripple is analyzed, and their influencing degree is concluded, which is the guideline for optimization of the axial piston pump. The parallel solution is used to obtain the simulation result as fast as possible. The dynamic boundary condition is used to define the time-depended pump delivery pressure and pump speed, and the effect of transient operating condition is also provided.In chapter6, the structure of the pre-compression volume and the swash plate cross angle with relief groove have been optimized with the built simulation method. The selection criteria of the Pre-compression volume and the swash plate cross angle with relief groove is presented.In chapter7, the conclusion of this thesis is provided and the further research is analyzed.