Research On The Characteristics Of High-Frequency Electrohydraulic Exciter

As a key component of the vibration test apparatus, electro hydraulic exciter is widely applied to many important engineering fields, such as the simulated environment of missiles, rockets, satellites, the fatigue test of engineering materials, or the seismic test of some large constructions and so on. As a result, the improvement of performances of the electrohydraulic exciter will directly affect the development of various industrial areas. Therefore the study on the characteristics of the electrohydraulic exciter is an important fundamental research.Upon the background of National Foundation of Natural Sciences,"Research on a New Electrohydraulic Exciting methods and Separate Control Strategy" and a major project of Zhejiang Provincial Natural Science Foundation of China,"Basic Research on the Electrohydraulic Excitation Technique of Heavy load and High frequency", the parallel design of a two-dimensional valve (here within defined as a2D valve) and a standard servo valve is adopted to control an electrohydraulic exciter so that the frequency bandwidth is greatly extended and the precision control of the vibration characteristic variables. The research significance includes not only engineering value, but also certain complement to the control theory of the electrohydraulic system, and establishes theoretical foundation for the exciting technique of the high frequency electrohydraulic exciter. The main research works and results of this paper are as follows:1) The frequency bandwidth of conventional electrohydraulic exciter is always limited to a rather narrow range. This restriction is attributed not only to the limited response capability of the servo valve but also to the electrohydraulic servo system itself, the bandwidth of which is unable to be extended. Thus,2D valve is adopted as a main control component of this system, of which structure and control mode is improved. The measured results and the theoretical analysis showed that proposed multiple control mechanism not only achieves higher working frequency, but also realized control precision for the vibration characteristic variables.2) The mathematical model of hydraulic actuation mechanism is build, and then by defining multiple parameters the output vibration waveform of high-frequency electrohydraulic exciter is solved in using the subsection integration method. Based on the analytical results, the vibration boundary positions and the relationships exist between working states and the control parameters are finally derived. The measured results are consistent well with the theoretical analysis. The established mathematical model is not only suitable for high-frequency electrohydraulic exciter controlled by parallel mechanisms, but also applied to various electrohydraulic excitation systems upon the background of the fatigue test.3) In low frequency section, the expressions of regulating relationships between the characteristic variables of the vibration (working frequency, vibration amplitude and vibration bias) and the control parameters (the rotary speed and axial displacement of the spool of2D valve and fixed opening area of standard servo valve in parallel) are derived in analytical method. In order to control characteristics variables of vibration conveniently, the mathematical model of hydraulic actuation mechanism is simplified and the effective work area is obtain. As a result, the characteristics variables of vibration are controlled accurately by the model in the experiment.4) The resonance mechanism of fluid power system could not be described by the classical theory of fluid dynamics because it is developed on basis of linear theory. Thus, a way of the resonance analysis of electrohydraulic excitation system is presented. The block diagram of electrohydraulic excitation system is established by extracting nonlinear parts from the traditional linearization analysis, as a result the resonant frequency is obtained. According to input energy from oil source equals to the reverse energy to oil source, load pressure and load flow are solved analytically as the working frequency reaches to the natural frequency. The analytical expression of resonance peak is also derived without damping. Finally, the measured results are compared with theoretical analysis in the resonant frequency subsetion. The initial research on resonance mechanism will lay a theoretical foundation for resonance phenomena of classical fluid theory in hydraulic system.