Research On Monitoring Method Of Hydraulic System Operation Status Based On Motor’s Speed Fluctuation Analysis

The hydraulic system is widely used in many modern industrial fields,such as ships and engineering machinery,because it has the advantages of high-power density and strong adaptiveness to complex conditions and its operating status can reflect the quality of the work in the actual project.However,in the hydraulic system,the transmission process of information is becoming more and more complicated with the improvement of automation and intelligence,and signals such as flow,pressure,temperature are susceptible to noise and delayed to conditions.Therefore,effective condition monitoring is important to ensure the equipments safe and smooth operating in the hydraulic system.The methods of theory-simulation-experiment were combined in this paper,and the studying of condition monitoring was based on the mechanism of motor’s speed fluctuation and characteristic fluctuation was taken as the indicator.The main research contents were as follows:1、Analysis the Relationship between Motor’s Speed Fluctuation and Internal Parameters of the SystemDue to the multi-parameter,nonlinear and strong coupling of the hydraulic system,on the motor-load subsystem dynamics model,oil’s bulk modulus,viscosity and friction torque extracted from inherent properties were main dynamic parameters which caused motor’s speed wave;And the global coupled mathematical model of the whole system had been established to analyze the interaction mechanism of motor’s speed fluctuation,and the results showed that the uninterrupted coupling between the internal multi-parameter and new equilibrium states caused motor’s speed wave;Finally,according to the kinematics characteristics and working principle of the cam plate type axial piston motor,AMESim motor model had been built.The simulation analysis of temperature changing,oil content changing,loading and motor’s speed changing had been carried out on the model.The results showed that the increase of oil’s temperature,oil’s gas content and load would increase the fluctuation from the motor’s output,while the increase of electric motor’s speed could reduce the fluctuation from the motor’s output.2、Research on Monitoring Method of Hydraulic System Operation Status Based on the signal of Motor’s Speed FluctuationThe dynamic history of fluctuations’ amplitude in the instantaneous speed signal was used as a new reliable indicator for condition monitoring of the hydraulic system.For this phenomenon,the accurate measurement method of motor’s instantaneous speed was studied;The equal-angle resampling and order spectrum analysis were used to look for the roots of each speed fluctuation’s components and to track amplitudes of steady-state speed fluctuation components;The equal-angle resampling and short-time Fourier transform were used to track the dynamic amplitudes of the unsteady-state speed fluctuation components.The motor’s speed fluctuations and operating state of system were analyzed relevancely:the 1X fluctuation component was caused by the fluctuation form of the motor speed and the nonlinear parameters which transferred by oil,thus it could reflect the instantaneous flow fluctuation;the 0.33 X fluctuation component was caused by the fluctuation form of load which transferred by gearbox and coupling,thus it could reflect the system loading status.And the experimental results showed that the amplitude of 1X fluctuation component and the extreme difference of instantaneous flow fluctuation、 the amplitude of 0.33 X fluctuation component and the load pressure had the same trend under the different working conditions.