A new tamping device which is driven by an electrohydraulic exciter was proposed to overcome the limitations of mechanically driven devices.The double-rod oscillation cylinder drives the tamping arm to realize vibration.A new spin valve was designed in order to fulfill dynamic state requirements of the oscillation cylinder.Parametric analysis was carried out by establishing mathematic model.Then,the relationships among the structure of valve port and the frequency,amplitude,output shock force of the cylinder were researched.An experimental device of the electrohydraulic exciter was established to validate the theoretical results.The signals were acquired by AVANT dynamic signal analyser of vibration.The results show that new tamping device can satisfy all kinds of complex working conditions with the flexible adjustment of frequency and amplitude.
The steady state and dynamic characteristics of pressure output of a hydraulic power unit are important to the hydraulic system behavior.Because of the compact structure,the B-half bridge resistance network is widely used in the pilot controlled pressure relief valves.However the steady-state pressure error might be unacceptably big in those pressure control systems.A constant pressure power unit is typically assumed in analysis of steady state and dynamic behavior of hydraulic systems.The flow-pressure relationship seems to be much complex,in particular when big flow variation takes place.In this paper,the π bridge hydraulic resistance network pilot stage is designed in order to get better flow-pressure characteristics.Based on the similarity of electrical circuits,the main factors influencing flow-pressure characteristics are analyzed.Moreover,the optimum diameters of both constant hydraulic resistor and dynamic resistor are proposed.Flow-pressure characteristics are compared with different constant hydraulic resistors,dynamic resistor and spring stiffness by simulations and experiments.Results of simulations and experiments show that flow-pressure characteristics depend very little on the spring stiffness in whole flow range.Good controlled pressure characteristics can be achieved with suitable constant resistors.Overshoot can be reduced with the small diameter of the dynamic resistor.Flow-pressure characteristics of pressure relief valve can be improved with a π bridge pilot stage.The proposed pressure control method will provide some positive guidelines and be helpful to design a high performance hydraulic system with large flow.
