Internal leakage is the most common failure of hydraulic cylinder; when it increases, it decreases volumetric efficiency, pressure and speed of the hydraulic cylinder, and can seriously affect the normal operation of the hydraulic cylinder, so it is important to measure it, especially to measure it online. Firstly, the principle of internal leakage online measurement is proposed, including the online measurement system, the fixed mode of the strain gauge and the mathematical model of the flow-strain signal conversion. Secondly, an experimental system is established to collect internal leakages and strain values, and the data is processed. Finally, the convolutional neural network (CNN), BP neural network (BPNN), Radial Basis Function Network (RBF), and Support Vector Regression (SVR) are used to predict the hydraulic cylinder leakage; the comparison of experimental results show that the CNN has high accuracy and high efficiency. This study provides a new idea for online measurement of small flow on other hydraulic components.
Hydraulic cylinder is the most typical hydraulic actuator. The traditional sealing ring used in hydraulic cylinder produces the friction which greatly affects the high speed performance of the hydraulic cylinder. Researchers tried to improve the situation by improving sealing material and structure. But the problem between friction and leakage is not solved radically. Then a kind of high speed hydraulic cylinder with low friction was developed. The constant clearance seal technology was employed in this hydraulic cylinder. This hydraulic cylinder with constant clearance seal has the characteristics of low friction and fast speed. However, the internal leakage always exists, and the hydraulic cylinder volume efficiency is obviously decreased with the working pressure increasing. There is a contradiction between the sealing performance and working pressure in the hydraulic cylinder. To solve the above problems, we propose a kind of self-compensation variable-clearance sealing hydraulic cylinder. The compensation mechanism, compensation effect and adaptability of variable clearance seal are studied. The load analysis model of the piston lip in flow field is established. These provide theoretical basis and technical support for design and manufacture. Then the optimization method of the piston structure of variable clearance hydraulic cylinder is studied. Three different types of piston structures are proposed. And the piston structure with the best sealing effect is determined by the comparison of the study. The test platform is developed. Measure methods are adopted to measure the static and dynamic internal leakage respectively. The validity of the theoretical research is verified through tests.
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