Study On Flow Ripple And Valve Plate Optimization Of Axial Piston Pump

Axial piston pump, the most important component in hydraulic systems, is widely used in industrial and construction machinery. Noise level, one of the three important performances of piston pump, becomes increasingly influential with the ever-increasing working performance and environmental concerns. The vast majority of piston pump noise is known as fluid-born noise, which is influenced by many factors with complex principles. The fluid-born noise of piston pump, which has been regarded as a challenge up to now, is responsible to decreasing reliability and lifecycle of pump. Therefore, it is necessary to study the mechanism of fluid-born noise generation and the corresponding noise control methods.In this thesis, the mechanism of fluid-born noise generation in axial piston pump was studied. The mathematical model of flow characteristics from piston pump was developed with distributed-parameter method. Wave propagation theory has been employed in this model, hence pressure pulsation characteristics can be evaluated in detail. The calculated results at pump discharge port using this model are more accurate than those using lamped-parameter model in pressure pulsation analysis. The errors of flow ripple and pressure pulsation can be controlled within 5% compared with experimental results, which is acceptable for theoretical analysis of flow characteristics. The influences of working pressure and temperature on fluid bulk modulus were examined by experimental results to improve the accuracy of simulation. Three-dimension (3D) dynamic simulation was adapted using compressible fluid model to obtain the flow field within the piston pump body. It was shown in simulation that the flow ripple rate of piston pump increased from 5.8% to 17.8% at the same boundary conditions, as a comparison with the experimental result of 18.6%. Thus the simulation accuracy has been significantly improved using the developed compressible fluid model. The influencing factors of flow ripple, including compression ripple together with leakage ripple and geometrical ripple, were analyzed in simulation using the compressible fluid model. It can be seen from simulation study that the compression ripple is the main part of flow ripple which accounts to 88% of the total. The remainder leakage flow ripple has the lowest proportion of 4%, and geometrical flow ripple takes the rest of 8%. In order to reduce the fluid-born noise level of piston pump, the optimization of valve plate structure was investigated. Based upon the theoretical and experimental analysis, the optimization ranges of the structure size were proposed, which could be used as a reference to design low noise level piston pump.In chapter 1, the aim and significance of the study in the thesis were discussed. The current research progresses on noise control of piston pump were reviewed. The main research subjects were presented.In chapter 2, the theoretical study of fluid-born noise was carried out. The mathematical model of flow characteristics of piston pump was developed, and important parameters in the model were modified based on the simulation and experimental analysis. Besides, theory on measurement of high frequency flow ripple was discussed. The impedance connection of piston pump being in series and in parallel was analyzed, and the accuracy of source impedance model was improved using first-order square approximation model.In chapter 3, 3D dynamic calculations have been preformed to obtain the flow field within the piston pump body. Both the compressible fluid model and viscidity fluid model were used in the simulation. It was shown in experimental results that the accuracy of flow ripple simulation increased greatly with the compressible fluid model. Among the three forms of flow ripple, including compression ripple together with leakage ripple and geometrical ripple, the compression ripple accounts to 88% of the total. Besides, cavitation of piston pump was investigated using full cavitation model, and it can be seen in simulation that the cavitational wear is most likely to be located on the valve plate surface around the top end of the damping groove connecting from low pressure kidney to high pressure kidney.In chapter 4, the flow ripple test rig of hydraulic pump was built, which was used for experimental study as compared with theoretical study using proposed mathematical model and flow field simulation.In chapter 5, fluid-born noise characteristics, including fluid bulk modulus, pressure pulsation and flow ripple, were measured. With the experimental results, it can be seen that the accuracy of mathematical model and flow field simulation was both acceptable. The influences of flow ripple amplitude and flow ripple rate were analyzed by employing mathematical evaluation, simulation study and experimental measurement separately. Besides, the method of cross-correlation function was used to measure the fluid bulk modulus, which was affected both by working pressure and temperature.In chapter 6, the relationship between the structure of valve plate and the fluid-born noise parameters was analyzed. The optimization ranges of the structure size were proposed, which could be used as a reference to design the low noise level piston pump.In chapter 7, conclusions in this thesis were summarized and future research proposals were suggested.