The Vibration Isolation Performance And Control Method Research Of MRF Semi-active Engine Mount

In recent years as a result of the improvement of road conditions and the application of high-power engine, lightweight body and consumer's high demand for comfortableness, the NVH problems caused by engine vibration are becoming more and more serious. Therefore, the demand for isolation performance of engine mount is on an increase. Because the traditional engine mount cannot satisfy the complex characteristics of ideal vibration isolation within the broadband section, the semi-active/active engine mount emerges. On the other hand, the vigorous development of intelligent materials provid broad prospects for the vibration isolation technology.The semi-active MRF (Magneto-rheological Fluid) engine mount studied in this thesis is a combination of the magneto-rheological fluid and vibration isolation technology and belongs to a typical semi-active control mount. Intelligent control MRF engine mount can change the strength of applied magnetic field through controlling the current and then change the fluidity of MRF and finally realize theinstant controls of dynamic chatacteristics. This thesis analyzes the MR effect principle, yield shearing stress and mechanical characteristics of MRF; designs structure of a MRF and builds bond graph model and mathematic model to study characteristics of MRF mount; I also compare the isolation characteristics of two degree MRF mount using two different intelligent methods. This thesis is aiming to do the exploratory research of MRF engine mount's development.The main contents are as follows:The first part is discussing the ideal vibration isolation characteristics of engine mount, reviewing the development and commercial applications of magneto-rheological fluid technology, and the semi-active control strategy and then analyzing the MR effect principle, yield shearing stress and mechanical characteristics of MRF. Then I propose the idea toapply magneto-rheological fluid to the performance improvement of traditional hydraulic mount and analyze the structure and working principle of typical MRF mount. An expression of liquid damping with the current change under the valve mode model is derived. After that, I design a MRF engine mount on the basis of existing hydraulic mount.In part three, bond graph modeling of MRF mount is built up based on its physical model. Frequency changing expression of MRF mount's dynamic stiffness and damping lagging angle is deduced. Then I simulate the dynamic characteristics within low frequency using MATLAB and do the parametric research. Especially, the influence of current intensity upon dynamic characteristics is analyzed.At last, considering stiffness and damping of MRF mount and suspension, the two degree system mechanical model of engine and body is built, whose simulated model is constructed using Simulink module of MATLAB software. Then applying Fuzzy control and Fuzzy-PID control separately to control the MRF mount system and develops the force and acceleration time domain curves of body in different working conditions. After comparing with the passive engine mount, we find that the isolation effects are improved a lot under applicable methods, in which the Fuzzy-PID control method is better.