| As an important hydraulic control component in electro hydraulic control systems,the electro-hydraulic servo-valve is widely used in industrial fields such as robotics,aerospace,manufacturing,and chemical engineering.Due to the small structure size and fast response speed,the flapper-nozzle servo-valve has become one of the most widely used servo-valve types in hydraulic servo system.However,due to the complicated structure of the flapper-nozzle servo-valve and the complex exrternal force which are electromagnetic force,flow force and feedback force,the servo-valve often produces blocking and resonance during its working process.These phenomenon seriously affects the stability of the servo-valve which has also become one of the main causes induced the self-excited oscillation of the servo-valve and even leads to the failure of the entire servo system.To solve the self-excited oscillation phenomenon of the servo-valve armature assembly,this paper establishes a dynamic mathematical model for the armature assembly of the flapper-nozzle servo-valve based on distributed parameter.The mode information and vibration mode of the armature assembly flexible part are studied by the methods of experiment and simulation,and the dynamic response characteristics of armature components under different external loads are analyzed.By establishing fluid-structure interaction dynamic model of the servo-valve pilot stage,the advanced distribution parameter model of the armature assembly is derived which considers the influence of the electromagnetic force and the flow force together.Meanwhile,the effect of the flow force on the armature assembly is also studied,which provide a theoretical basis for the researches of the servo-valve self-excited oscillation.According to the structural characteristics and external load distribution of the spring tube,the distribution parameter model of the spring tube based on the tangential and axial vibration is proposed respectively.According to the mode information of the spring tube,the mass normalized eigenfunction of different spring tube vibration modes are derived to construct a complete mathematical model of the spring tube based on distributed parameters.With this mathematical model of spring tube and the parameters of other armature components,a distributed parameters mathematical model of the complete armature assembly is proposed and the corresponding numerical simulation program is established.The dynamic response of the armature assembly at different positions under different loads is analyzed.For verified the mode information of the spring tube obtained by distributed parameters method,the finite element method is used to analyze the mode information of different spring tube vibration modes.The comparison between the prediction results of distributed parameters and finite element methods are studied which can verify the validity of the distributed parameters model.In order to verify the distributed parameter mathematical model of the armature assembly and the vibration mode of the spring tube,the dynamic response of the armature assembly under different external loads are analyzed using the finite element simulation,experiment and classical model respectively.The prediction results of these three methods and the distributed parameter model are compared to determine the way of spring tube vibration and the calculation method of the distributed parameters model.In order to further improve the distributed parameters mathematical model of the armature assembly,a fluid-structure interaction numerical simulation model of the pilot stage flow field in the servo-valve is established based on the finite element method,which can analyze the flow force induced by fluid-structure interaction.The flow characteristics,cavitation distribution and flow force of the pilot stage flow field under different boundary conditions are simulated and the relationship between the three factors is established and analyzed.Based on this corresponding relationship,a distributed parameters mathematical model of the armature assembly including the flow force is derived,and the influence of the flow force on the movement of the armature assembly is analyzed.Meanwhile,according to the experiment and semi-empirical formula methods,the cavitation distribution and flow force of the pilot stage flow field are measured.The comparison between the experiment and simulation results is analyzed,which can also verify the numerical simulation model of fluid-structure interaction.Based on the distributed parameter mathematical model of the armature assembly,a feedforward vibration suppression method for the armature assembly is proposed.The vibration suppression effects of different feedforward signals on the armature assembly are simulated and compared.At the same time,the finite element and experiment methods are used to measure and analyze the dynamic characteristics of the armature assembly which is affected by the feedforward signal.The comparison between the results of the distributed parameter model,finite element method and experiment are analyzed to verify the feedforward vibration suppression method. |
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