Research On And Application Of Instantaneous Speed Characteristic Of Variable Speed Pump-controlled Hydraulic Motor System

As an energy-saving hydraulic transmission system,variable speed pump-control hydraulic motor system(VSPMS)has been widely applied to industrial equipment,engineering machineries,ship machineries and other fields.As an important means to ensure the safe and reliable operation of the equipment,the system performance evaluation and state monitoring have become the research focus in recent years.Considering that the instantaneous speed(IS)is not only the kinematic parameter but also the monitoring signal of the VSPMS.In this paper,dynamic theory is used to analyze the characterization process of operating parameters on the characteristics of the IS.The essential relation between the IS and changes in system operating performance is revealed.This provides a new idea and method for system performance evaluation and condition monitoring.The main research contents of this paper are as follows:The characterization process of operating parameters on the characteristics of the IS was explored.By using the dynamic model of the VSPMS,the influence of temperature,motor displacement,load moment of inertia,motor speed and load on the IS have been revealed.The relationship between the IS of the motor and the system dynamics as well as running state was studied.The measurement and characteristic extraction of the IS for the VSPMS were studied.Firstly,a measurement method of the IS based on A/D conversion and sampling point software counter was proposed.The source of measurement error has been analyzed and the conclusion is drawn that the measurement accuracy of the IS can be improved by increasing sampling frequency and rotational speed ratio.Secondly,considering that the speed measuring gear disk and magnetoelectric sensor can divide the source signal equally,the IS signal collected in this paper is essentially a stationary signal sampled from an equal angle and also a quasi-harmonic signal.Based on this,a feature extraction method for the trend term and fluctuation term of instantaneous rotational speed was proposed.The trend term of the IS was extracted accurately by EMD method.And the real-time frequency and amplitude characteristics of instantaneous speed fluctuation(ISF)were extracted by normal time-frequency transform and the inaction method.The speed stiffness characteristics of the VSPMS were studied.Based on the study of the influence mechanism of multi-parameter on speed stiffness,a quantification method of speed stiffness has been defined.The experimental verification of the characteristics of speed stiffness was completed.Theoretical research and experimental results show that displacement of hydraulic motor and leakage coefficient of hydraulic system are the most important factors affecting the speed stiffness characteristics.On the basis of theoretical research,the speed stiffness has been applied to the wear condition monitoring of an axial piston pump.The results show that the speed stiffness can identify the wear state of the pump.Moreover,the speed stiffness is positively correlated with the volumetric efficiency of the system.Causes analysis of the ISF for the hydraulic system was conducted.The system operation law was revealed through dynamic analysis.The results show that the internal excitation generated by the working mechanism of the axial piston motor and the external excitation generated by the misalignment of the shaft system are the most important internal and external sources of the ISF.The correctness of the dynamic analysis was verified on the test bench of electromechanical hydraulic system.The experimental results show that the characteristic frequency of the excitation source corresponding to the ISF can be accurately presented in the standard time-spectrum diagram under the typical variable working conditions(variable speed,variable load).The amplitude variation of each ISF component extracted by the no-action method can well identify the change of system operating conditions.The results are consistent with the theoretical analysis.In addition,the correlation between the amplitude of the ISF and system efficiency has been revealed by experiment.The results show that the fluctuation amplitude of the IS is opposite to the change of system efficiency.The IS provides a new method for performance evaluation and operation status monitoring of the VSPMS.