Study On Valve Plate And Flow-Distribution Method For Noise Reduction Of Axial Piston Pump

Axial piston pump, the most important driving component of hydraulic transmission system, is widely applied in large-size electromechanical and military equipment. Meanwhile, it constitutes the main source of noise. With the growing attention on the environmental protection, the equipment puts forward increasingly strict demands for components on noise emission, making research on noise reduction of axial piston pump important. An axial piston pump is the most complicated hydraulic component whose research involves several disciplines. The generation mechanisms of noise excitation sources in axial piston pump are complex due to the presence of transitions and coupling transmissions among them. Moreover, the noise reduction is related to the service life of pump, as well as reliability and efficiency. Therefore, noise reduction of axial piston pump is always a great challenge in the hydraulic transmission filed. This thesis focuses on the noise-generation mechanisms of axial piston pump and effective design methods for low-noise axial piston pump.Three new noise reduction methods for axial piston pump were proposed in this thesis, which includes the low-flow-ripple valve plate, the tandem axial piston pump with indexing angle and the energy-recuperated pressure equalization unit. The simulation and experimental results showed that all of these methods could reduce both the fluid-born and structural noise. Thus, these methods can be applied in the optimization of existing axial piston pumps and development of new low-noise axial piston pumps. The first design method, a low-flow-ripple valve plate, was designed inventively considering the influence of peak backflow position on outflow ripple. A mathematical model of the flow area calculation of damping grooves was developed, which could realize a smooth pressure transition and a diminishing backflow in the piston chamber. This novel method avoids the repeated simulation, data processing and selection in the traditional ones based on flow characteristics simulation models. It can be applied in the design of valve plate with different damping grooves since the section shape of damping groove is not defined. The experimental comparisons between pumps with and without optimization show that the proposed method is effective in reducing outflow ripple and pressure overshoot in the piston chamber. The second one, a tandem axial piston pump with indexing angle, was innovatively designed to replace the signal rotary unit with two tandem rotary units for axial piston pump with one suction and delivery port. The outflows of these two rotary units have an optimal phase difference. The outflow ripple, swash-plate and shaft torque pulsations can be reduced by more than60%,40%and80%respectively due to the superposition of wave crests and troughs when two flows converge at the delivery port. The superposition effect is only determined by the indexing angle, so the noise reduction effect of this method is insensitive to the pump’s working parameters. The third method, the pressure equalization unit composed of two check valves and one-way-flow pressure chamber was creatively proposed, which utilized the hydraulic energy stored in the high-pressure piston chamber at the inner dead center to pressurize the low-pressure piston chamber at the outer dead center. The hydraulic energy stored in the high-pressure piston chamber can be partly recuperated. The amount and peak valve of backflow between the piston chamber and the kidney slot are reduced. Simulation results show that the recuperated energy is proportional to the energy stored in the piston chamber, so the pressure equalization effect is more evident when the pump works at high pressure and small displacement. Compared with traditional pump, the flow ripple and swash-plate torque pulsation can be reduced by more than40%and30%respectively, and the volumetric efficiency can be improved by more than3%.In chapter1, the aim and significance of the studies in the dissertation were discussed. Then, the research on axial piston pump at home and abroad was investigated, and the current research progresses and trends on noise reduction of axial piston pump were reviewed. At last, the main research subjects in this dissertation were presented.In chapter2, a simulation model of noise excitation sources for axial piston pump was developed. Besides the mathematical model of flow characteristics of axial piston pump, the micro parameters of friction pairs were optimized by a dynamic lubrication oil-film model. The accuracy of simulation model was verified by the comparisons between experimental and simulation results of flow ripple and volumetric efficiency at different working conditions.In chapter3, a design method of low-flow-ripple valve plate was discussed. Firstly, the coupling generation mechanisms of fluid-born and structural noises were analyzed, and the influence of the peak backflow on the flow ripple was discussed. Then, the mathematical models for calculations of damping grooves, damping orifices and kidney slots were developed. The influences of design parameters on the noise reduction effect were discussed. The effects of this method on reducing pressure overshoot in the piston chamber, flow ripple at the delivery port and cross flow at the transitional region are analyzed. It was pointed out that the noise reduction effect of valve plate was sensitive to working parameters.Lastly, the valve plate of one domestic axial piston pump was optimized employing this design method, and the noise reduction effect was verified by the comparative experiments.In chapter4, a noise reduction method based on a tandem axial piston pump utilizing indexing angle was discussed. Firstly, the working principle of this design method was introduced. Secondly, the indexing angle was optimized to realize better noise reduction effect. The flow ripple, swash-plate and shaft torque pulsation of the tandem pump with indexing angle were compared with the traditional pump. The sensitivity of noise reduction effect to working parameters was also analyzed. Lastly, a model pump was designed.In chapter5, a noise reduction method based on pressure equalization mechanism is discussed. Firstly, the variations of pressure and flow in the piston chamber during the transitional region of valve plate are analyzed. The pressure equalization structure composed of two high-speed check valves and a pressure recuperation chamber was designed. Then, the working principle and effects of this method on reducing flow ripple and swash-plate torque pulsation were analyzed. Lastly, the model pump was designed based on the parameters optimization of the check valve and pressure chamber.In chapter6, conclusions in this dissertation were summarized and future research proposals were suggested.