High-pressure Bi-directional Positive Displacement Meter For Tiny Flow

Flow rate is one of the most important parameters in industrial automation, and positive displacement meter is a common flowmeter with high accuracy and good robustness, which can also be used for the measurement of high viscosity fluids, rotating flow and pulsating flow. So, it takes up a large proportion in all kinds of flowmeters, and is used in many areas, especially applicable for hydraulic system. Recently, with the population of high pressure hydraulic system and the increasing requirements for the efficient and automatic control, the measure of tiny flow under the high pressure condition is more and more important. But there still aren’t relevant domestic products. Therefore, the research of PD meters for tiny flow with high accuracy and pressure resistance can not only improve the performance of electro-hydraulic control system, but also has great importance for the development of domestic flow meters industry.This dissertation presents the design of an oval gear flowmeter with abundant literature reviews, which uses a pair of low-eccentricity oval gears as the core components and uses hall sensors for the non-contact signal-detection. The designed flowmeter is with a lower displacement in order to measure tiny flow. A rally closed measurement volume was built so that the flowmeter can endure high pressure. A complete digitization modelling theory is established for the CNC machining of oval gear in order to ensure the high accuracy. And the dissertation also researches the metrological characteristics of flowmeter deeply through theoretical analyses and experiments. Results show the flowmeter is with a relative error less than 0.5% over a flow range of 0.05-3L/min. The flowmeter has the characteristics of high accuracy, enduring high pressure of 31.5Mpa, simple structure, and can measure bi-directional flows.This dissertation consists the following six chapters:Chapter 1 introduces the development of flow measurement and the classification of flowmeters, especially details the research progress of oval gear flowmeter. This chapter also introduces the application of P.D. meter for the measurement of tiny flow. A brief summary of the significances and contents of the dissertation research is described.Chapter 2 presents the design of an oval gear flowmeter, introduces the structure, working principles and characteristics, and highlights the realization of tiny flow measurement under the high pressure condition. This chapter also elaborates the derivation of the pitch curve equation and the solution of tooth profile. Then, a complete digitization modelling theory of oval gear is established.Chapter 3 presents the non-contact signal-detection structure, elaborates the principle of magnetic circuit design and components selection. Then, a finite element simulation is made to analyze the influence of key structure parameters and validate the design.Chapter 4 performs the theoretical analyses of the flowmeter’s metrological characteristics, including pressure loss, pulsation and relative error. The chapter lays a strong emphasis on the study of the internal leakage mechanism and the change of actual flow coefficient, and also explores the relation between flow coefficient and relative error.Chapter 5 introduces the made prototype of flowmeter and the experiments system. Experiments are performed for the research of flowmeter’s metrological characteristics. The results validate the correctness of the design and theoretical analyses of flowmeter. This chapter also proposes a modification method of actual flow coefficient and obtains the measuring accuracy and measuring range of the flowmeter.Chapter 6 summarizes the main research work and achievements of the dissertation. And the further research work and directions are put forward.