Research On Flow Characteristics Of Integrated Piston Bent-axis Piston Pump Under Elasto-hydrodynamic And Cavitation Effects

As the key technology of power-by-wire technology of advanced large aircraft,the electrohydrostatic actuator(EHA)is turning towards larger power,higher power-to-weight ratio,higher efficiency and higher reliability,which is higher demands on the power density and reliability of hydraulic pump in EHA.The integrated piston bent-axis piston pump has become an ideal structure type to achieve high power-to-weight ratio and high reliability of hydraulic pumps for EHA,due to its advantages of high power density and reliability.Howerver,the swing of the piston,elastic deformation of the piston ring and cavitation of oil restrict the adaptation of the integrated piston bent-axis piston pump for EHA to high-speed and high-pressure operating conditions.This dissertation focused on the flow characteristics of the integrated piston bent-axis piston pump under the elasto-hydrodynamic and cavitation effects were investigated by theoretical analysis,numerical calculation and experimental testing.The research aims to reveal the flow characteristics of the integrated piston bent-axis piston pump under high-speed and high-pressure conditions.The main contents of this dissertation are as follows:(1)The effect of the piston swing on the kinematics and dynamic parameters of the the integrated piston bent-axis piston pump was analyzed.Based on the space coordinate method,the dynamic model of the integrated piston bent-axis piston pump was established,and the displacements of the pump under different structural parameters were compared to verify the dynamic model.The analysis results show the piston swing significantly affects the circumferential force of the pistonr ring and its clearance distribution,but has little effect on the kinematic parameters such as the displacement and velocity of the piston.(2)The flowrate model for the integrated piston bent-axis piston pump considering the elastic deformation of the piston ring and oil cavitation was presented.Based on elastohydrodynamic lubrication theory,the leakage model of the integrated piston bent-axis piston pump considering the elastic deformation of thepiston ring was established.The dynamic rate equation of the oil gas content and the oil effective bulk elastic modulus model were established by the cavitation theory.The compressive loss displacement was derived,and a theoretical model for the flowrate characteristic analysis of the integrated piston bent-axis piston pump under high-speed and high-pressure operating conditions was proposed.(3)The effect of the elastic deformation of the piston ring on the leakage of the integrated piston bent-axis piston pump was revealed.Based on the finite difference method and the continuous distribution pressure discretization method,the pressure and thickness distribution characteristics of oil film between the piston ring and the cylinder block were calculated,which verifies its theoretical model and researched the leakage characteristics of the integrated piston bent-axis piston pump under different operating conditions.The research results shown the elastic deformation of the piston ring reduced the pump leakage,and the pump leakage has a negative value range(oil suction effect)and a positive value range(oil discharge effect),and the fundamental reason is that the elastic deformation of the piston ring in the oil discharge area affects the Couette flow more than the Poiseuille flow.(4)The mechanism of oil cavitation on the compression flowrate loss of the integrated piston bent-axis piston pump was revealed.According to the pressure model and dynamic volume elastic modulus model of the oil,the effect of the rotational speed on the oil volume elastic modulus in the oil suction stroke was analyzed.Then,based on the compression loss model,the compression loss characteristics under different operating conditions were investigated.The results shown the dynamic change of gas content,effective bulk elastic modulus of the oil under the cavitation effect were the fundamental reasons for the flowrate loss and volumetric efficiency decline of the pump.The smaller the initial value of the effective bulk elastic modulus of the oil,the larger the nonlinear range of the low pressure stage,and the larger the compression flowrate loss of the integrated piston bent-axis piston pump.(5)An experimental system for the flow characteristics of the F12-80 integrated piston bent-axis piston pump was developed.The rationality of the flow loss mechanism analysis and the accuracy of the flow model under the elasto-hydrodynamic and cavitation effects were verified by comparing and analyzing theoretical calculation results and experimental results.The results shown the simulation results were in good agreement with the experimental results under different operating conditions,and tts relative error was less than 1.3%.When the rotational speed was higher than 800r/min and the load pressure was higher than 6MPa,the compression flowrate loss of the pump accounts for more than 60%,which was the main source of its volume loss.The research results of this paper systematically revealed the mechanism of the piston swing,elastic deformation of the piston ring,oil cavitation on the flowrate loss of integrated piston bent-axis piston pump,and enrich and improve the design method and theoretical system of bent-axis piston pump,which can provide theoretical basis and design method for the development of high power-to-weight ratio,high reliability,and high performance of integrated piston bent-axis piston pump for EHA.