Design And Study Of The Online Measuring Device For Hydraulic Oil Bulk Modulus

In the dynamic research of hydraulic systems and hydraulic components, oil bulk modulus directly affects natural frequency and damping ratio which are correlated to the stability and dynamic quality of hydraulic systems. Therefore it is essential to obtain the value of the oil bulk modulus. In this thesis, we study on the measuring device for the oil bulk modulus. After analyzing the defects of the previous measuring devices, we design an online measuring device for the oil bulk modulus for a large-scale hydraulic test rig with six degrees of freedom, and fulfill the demand of researching oil bulk modulus. This device can measure the oil bulk modulus automatically and multifunctionally, which is also with on-line ability and high repeated measuring precision.This thesis combines theoretical analysis and computer simulation with experimental verification. The principle design, structural design and hydraulic system design and control system design for the whole measure device are shown in this thesis. Meanwhile the analysis of error, finite element simulation and hydraulic system simulation are completed, which is accord with the experimental results. The primary research on the relationship between the hydraulic oil bulk modulus and oil pressure, temperature and gas content is done, which can provide a reference for the further study in this area. The main research work of this paper is as follows:In the first chapter, the basic theory of oil bulk modulus is introduced, and the influencing factors are analyzed. It also elaborates on the common measuring method of oil bulk modulus, expatiates the research history and status about oil bulk modulus and its measure technology at home and oversea. Then expatiates on practical background of the project, in the end, puts forward the research significance and primary research content.In the second chapter, according to the design requests of oil bulk modulus measuring device, in the base of theory analysis on oil bulk modulus, the measuring scheme which is defined by oil bulk modulus is brought up. Then go on with the principle design, explain its design key points. After the main structure and hydraulic system design, controlling system design of measuring device is finally finished.In the third chapter, the measuring error of the device was analyzed by theoretical computation and finite element simulation with Pro/E software. The measuring error is acceptable. Measures to reduce the error are suggested. The simulation model of the device hydraulic system is completed by AMESim software. It can be shown that, the structure parameters, measuring method and hydraulic system parameters are designed in reason.In the fourth chapter, it gives a brief introduction about design of oil temperature control subsystem and vacuum pumping subsystem, together with the single and repetitive experiment on oil bulk modulus, and the experiment with the change of oil parameters. The results show that the oil bulk modulus measuring can proceed automatically by the device with high repetitive measuring accuracy. With the increase of oil pressure, the value of oil bulk modulus has an approximative linear enlargement under low pressure when the enlargement tends to be gently under high pressure. It also diminishes with the increase of oil temperature, but not linearly. However, it will increase remarkably with decrease of gas content.In the fifth chapter, the main research work and production of this paper is summed up. The further research work and direction are in expectation.