Full Coupled Dynamic Modeling And Performance Degradation Mechanism Analysis Of Axial Piston Pump/Motor

In the national economic construction priority areas of the manufacturing,metallurgy,mining and construction,the heavy equipment of high power and high energy consumption,such as mining machinery,rolling machine,injection molding machine,large shield machine,almost be the multi energy domain coupling electro hydraulic systems with the machine,electricity,liquid and control.As the key power and implementation components of the system,the problem of axial piston pump /motor under the extreme condition,such as the efficiency decrease,performance degradation and nonlinear dynamic characteristics,limit the development of the equipment of high pressure,high speed and high precision seriously.Based on the the full coupling dynamic model of the axial piston pump/motor proposed in this paper,the mechanism analysis of the performance degradation,such as the increase of pressure fluctuation and the decrease of efficiency were conducted.The research meet the urgent needs of the basic theory and engineering practice,the main works are as follows:Due to the assumptions of constant pressure and speed,the traditional dynamic models have no ability to analyze the coupling characteristics of piston machines comprehensively.The array bond graph modeling method was presented to establish the full coupling dynamic model of piston machine.From the array bond graph model of piston machine,the coupling relationship between the subsystems are clear.Then the decoupling analysis of the tribological and dynamic of the piston-slipper subsystem was conducted and the energy loss factor was defined.The results show that the Coulomb friction forces produced by the piston inertia forces do not consume energy in general.The energy loss factor represents the degree of energy loss during the energy conversionprocess of the piston-slipper subsystem.In order to reduce the stiffness ratio and improve the calculation efficiency,the full coupling model was dealt with dimensionless method.Then the simulation model was establish to reveal the full coupling characteristics of piston machines.The results show that the reverse flow and jet flow of the piston chambers are the main cause of flow pulsation intensified.The flow pulsation becomes obvious with the increase of high pressure and high speed.And the impact of the piston pressure and the change of the Coulomb friction forces of the piston pair are intensified at the same time.At last the full coupling model are verified by a comparison of the simulation results with the previous results.According to the variations of the inner discharge and the flow shock with the operating parameters,the mechanism of the flow and pressure pulsation was revealed.The results show that with the increase of rotation speed,the flow pulsation increases and the pressure fluctuation decreases,and both of them increase with pressure.The simulation results are in good agreement with the experimental results.The rationality of the mechanism analysis and the accuracy of the model were verified.A simplified method was put forward based on the power composition analysis to reduce the dimension the full coupling model and refine the energy loss estimation model for parameter identification.The method regard the piston chamber subsystem as the pure energy consumption unit.The full coupling model validates the reduced order model by the comparison of step responses.The system parameters identified by the energy loss estimation model are reasonable.The experimental results show that impacted by the oil compressibility and Coulomb friction,energy losses get obvious with the increase of the speed and pressure.A semi-empirical parametric modeling method based on mechanical forward and backward inference for the piston machine efficiency characteristics was proposed.Firstly,the flow and torque loss mechanism models were established.Secondly,the nonlinear changing regularity of the system parameters contained in the composite parameters of mechanism models were analyzed.Thirdly,the empirical formula of composite parameters were established.Finally,the semi-empirical parametric model of piston pump efficiency characteristics was obtained.The results show that the empiricalformula of composite parameters reflects the nonlinear variation of the system parameters effectively,such as the Coulomb friction coefficient and the oil effective bulk modulus.The rapid changes of system parameters are the fundamental reasons of volumetric efficiency and mechanical efficiency unable to upgrade again and the piston pump efficiency decreased under extreme conditions.The theoretical analysis and experimental results show that the performance degradation phenomenon of the normal piston machines under extreme conditions is the dynamical internal cause of the failure initiation and propagation,and the nature of the performance degradation and fault initiation is the changes of the system parameters and structure parameters under the influences of the environment and condition factors.The full coupling dynamic models of the piston machines provide fundamental theories for the thorough analysis and evaluation of the comprehensive performance,and the effective use of the running state information,such as the pressure pulsation and energy consumption,provides the theoretical support for the quantitative analysis of the performance degradation and failure evolution based on mechanical forward and backward inference.