| Magneto-rheological fluid damper(MRFD) has become an important development direction because of its advantages such as controllable damping, large adjustment range, fast response, low energy consumption. Aiming at addressing the problems in research such as the unstable magnetic field when the cylinder working as a part of magnetic circuit, the distortion of dynamometer curve, the non-smooth transition when the piston reverses its direction. A novel MRFD with parallel annular channel and bypass orifice was designed and fabricated in this paper, and which has been studied in the aspects of structure design, theoretical study, sample fabricating and testing, the specific contents of work are as follow:(1) The purpose and significance of studying MRFD were raised as the unique advantages of the MR semi-active automobile suspension were analyzed through the comparison among different vehicle suspension. And the current researches of MR technology were introduced at home and abroad.(2) Overall structural design of the MRFD: Combining automobile shock absorber damping characteristic and suspension technical requirements for the installation, the damper of the single cylinder single rod type structure was chose to solve the blocking problem of the double cylinder valve structure. The structure of a double coil electromagnetic piston head assembly with parallel annual channel and bypass orifice was designed. A bypass orifice was designed in the electromagnetic iron core to improve the non-smooth transition of damping force when the piston reverses its moving direction. A cascade dual coil was wounded on the core inversely in order to prevent electromagnetic material prematurely magnetic saturation and increase the effective length of the annular damping channel. A sleeve outside the iron core was designed to improve the stability and the controllability of the magnetic field in the channel. In addition, the floating piston was designed and the air pressure in gas compensating cavity was defined, the material of each part was selected from the aspect of cost and performance of the device.(3) Theoretical study of MRFD: A simplified electromagnetic piston head magnetic circuit model was established according to the design standards. The range of the key parameters of the magnetic piston was calculated according to the magnetic saturation conditions of magnetic material, magnetic induction intensity in the annular damping channel was analyzed and obtained its solution, and the results were verified by finite element method. The apparent slip boundary conditions was considered in the mechanical analysis of MRFD, which was introduced in the selected constitutive model of Herschel-Bulkley to form a new mode, and the flow field in the channel were analyzed under this model, then the damping force expression of the piston head was obtained, and the formulas of output damping force was worked out by combining the force of the floating piston and the friction between the moving components. finally comparing with the damping force without considering apparent slip, the apparent slip effect on damping force was analyzed quantitatively in theory?(4) Fabrication and test of sample: The machining process of MRFD were introduced, a prototype was developed and a test about damping-displacement characteristic of the damper was finished on a hydraulic vibration table of WTDS following the test standard of automobile vibration damper, The test results shown that the damper has a wide controllable range and can meet the regulation requirements. The round and full dynamometer curve shown that bypass orifice realized the function that the piston can reverse its moving direction smooth, at the same time the high-pressure gas compensation cavity solved the damper air path effectively. And through comparison, the experimental test results were in good agreement with the theoretical simulation ones. |
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