| The travel motor is the key actuator used to implement the walking function in engineering machinery, and its performance directly affects the work efficiency of overall machine. There are phenomena such as pressure impact when high/low speed switching, flow pulsation, fluid noise, eccentric wear leakage and cavitation during the process of flow-distribution, etc. in the working of travel motor. These issues become more prominent especially under the condition of high speed and high pressure, and directly affect the performance of travel motor. Then the variable displacement mechanism and flow-distribution mechanism are one of main reasons for these issues, and also are the hot topics of researchers all the time.Aiming at above issues, this thesis combined with the major special project of Fujian province, and took travel motor of 21t hydraulic excavator as the research object. This paper made the comprehensive research and improvement to the variable displacement mechanism and flow-distribution characteristics of travel motor. The main work contents are as bellow:Firstly, the variable displacement mechanism was researched based on MATLAB. The two step variables was redesigned to stepless variable controlled by servo valve, and its performances were analyzed. The paper designed the swashplate position control circuit and established the corresponding mathematical model of elements, and used state space method to express the mathematical model of control system of motor variable mechanism. Based on Simulink, the simulation model of nonlinear system of variable mechanism was built. It was shown that system existed disadvantages such as slow response, large rise and adjust time. The dynamic characteristics of the control system were improved by adding correct element of PID.Secondly, the flow-distribution characteristics of motor were researched based on computational fluid dynamics (CFD) method. The thesis took the properties of fluid in high speed and pressure (such as compressibility, visco-temperature and visco-pressure characteristics) into account, and established the mathematical and physical model of complex flow field in the flow-distribution process of motor. The fluid states of each position in unsteady flow field during flow-distribution process were calculated, and then turbulence was selected as calculation model of CFD. Visible observation of two fields of oil film pressure and velocity, as well as the analysis of leakage in port plate pair and eccentric wear phenomenon, were carried on. The region of cavitation occurred (in the front of valve-plate damping groove) was predicted. The thesis compared and analyzed the influences of different structural damping grooves and the same structural damping groove with different parameters on flow-distribution characteristics of motor. The influences of different working conditions on flow-distribution characteristics of axial piston motor were analyzed in detail.Finally, relevant condition tests of motor were carried out and the noise, outlet flux, leakage and position of cavitation in different conditions were tested. The tested results were compared with simulation results, and verified the correctness of simulation results.The main contributions of this paper are that the variable displacement mechanism was redesigned based on servo-control, which can adapt to the complex walking conditions of stepless variable speed. The flow-distribution characteristics of motor were researched in micro level first time by pump CFD software (PumpLinx), and verified by test. The results are more intuitive and accurate. The research results of paper have certain guiding significance for the design and engineering application of motor. |
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