| Engines are one of the most critical sources of noise and vibration in vehicles such as automotive vehicles, ships, and airplanes. An engine mount system, which can decrease the transmission of engine vibration energy in a broader frequency range, can improve the noise, vibration, and harshness (NVH) factors of vehicles. Passive rubber or hydraulic mounts have been widely used in engine vibration isolation. However, it is very difficult for engines adopting passive mounts to effectively achieve isolation performance in a wider operation frequency range. In recent years, a semi-active mount based on magnetorheological fluid (MRF) with controllable damping characteristics in time, wide bandwidth, rapid response, low energy consumption, and simple structure has become one of the most important developments in engine vibration isolation. However, there exists few research reports on the structure design and isolation characteristics analysis of MRF mounts. Moreover, the design of isolation control strategy is very challenging due to the complex nonlinearity and uncertainty of an MRF mount system. Some semi-active (or active) control methodologies can achieve good isolation performances at certain vibration directions, but they have some limitations as the coupling and harmony of full engine vibration model with multi-direction and multi-main frequency excitations have rarely been considered. In this dissertation, the vibration isolation challenges of a typical four-cylinder, four-cycle in-line engine via an MRF mount system are addressed. The theoretical analysis, numerical simulations, and experiments are applied to study the dynamic characteristics of an engine vibration isolation system, the engine parameter identification methodologies, the test and modeling methodologies of an MRF mount, the isolation control methodologies, the simulation of engine isolation system, as well as the design of the multifunction laboratory platform and the realization of the engine isolation system. The main contributions of the dissertation include the following:(1) The significance of the engine vibration isolation via MRF mount system is explained. The engine mounts, engine vibration isolation dynamic models, engine parameters identification, and isolation control methodologies are reviewed. Moreover, the main research works aimed at the problems in engine vibration isolation via MRF mounts are addressed.(2) A dynamic model and a kinematics equation are built, which can reflect the heave, roll, and pitch vibration of the main vibration states of a four-cylinder engine after the analysis of engine excitation resource. Nowadays, the identification methodologies of engine inertia parameters and excitation parameters are different in test modes, which are often very complex and cannot reflect real engine performance in actual operation conditions. Therefore, an engine multi-parameter identification methodology under actual operation condition is proposed and studied based on the analysis of engine vibration dynamic action. This can concurrently identify the inertia parameters and the excitation parameters based on the proposed engine vibration isolation model. The errors of parameters identification are later analyzed. Moreover, a single-layer isolation principle is applied to discuss engine isolation performance through engine excitation, mount damping, and stiffness. These provide the basis for the design of the vibration isolation controller.(3) After the analysis of the structure and operation principle of an MR fluid-elastic mount in the squeeze mode, an MRF mount performance test methodology is proposed under a broader excitation frequency range, millimeter-sized displacement, and adjustable drive current according to the mechanical relations of forced vibration.The static and dynamic characteristics of rubber mounts and MRF mounts are analyzed through an electric liquid servo testing system. To solve the difficulties of modeling for MRF dampers, a simple and accurate damping control model of an engine MRF mount is developed.(4) A sky-hook damping isolation controller and a fuzzy isolation controller are designed in order to isolate the main vertical vibration of an engine. A frequency-weighted fuzzy adaptive control (FWFAC) methodology is proposed to solve the vibration isolation difficulties derived from the broader multi-frequency excitation and heave-roll coupling vibration of a four-cylinder four-cycle engine, as well as the nonlinearity of MRF mounts. It adopts order analysis technology to achieve different order excitation states of an engine, after which a damping-weighted fuzzy control is designed to restrain vibration states with larger energy in vertical vibration and roll vibration. Moreover, the last damping outputs of engine MRF mounts are calculated by an adaptive algorithm via particle swarm optimization (PSO) to achieve the minimum heave-roll vibration isolation performance index.(5) A simulation platform of engine MRF mount isolation system based on Matlab/Simulink is set up. The engine excitation parameters identification is simulated under steady operation conditions. Their simulation identification values are in good accordance with the theoretical values. The isolation results of the engine without mounts, the engine via passive rubber mounts, the hydraulic mounts, and the MRF mounts with different control methodologies (sky-hook control, fuzzy control, and FWFAC) are compared under the same steady or unsteady operation conditions. The simulation results indicate that the MRF mounts using the FWFAC methodology have the most effective isolation performance in a broader excitation frequency range, through which the absolute transmissibility ratio of force and torque can be decreased to lower than 20%.(6) To validate the proposed engine multi-parameter identification methodology and isolation control methodologies, an engine multifunction single-layer isolation structure is designed. Based on the integration of key software and hardware systems, a new multifunction test and control platform for engine vibration isolation via MRF mounts is designed with virtual instrument technology. An experiment methodology that can adopt the proposed test bench to realize engine parameters identification, vibration isolation test and control, is developed and validated. The following steps describe the procedure: (1) The engine excitation parameters identification and inertia parameter identification are validated under steady operation conditions. The error analysis indicates that the maximum relative errors of estimation values and theoretical values of the different parameters are around 3%-7%. (2) The actual isolation results of the engine without mounts, the engine via passive (rubber, hydraulic) mounts, and the MRF mounts using different control algorithm are all studied under the same steady or unsteady operation conditions. Test results show that the MRF mounts have better vibration isolation performance than passive mounts and engine without mounts, especially in a lower operation excitation frequency range. The MRF mount system with FWFAC controller in actual complex excitation achieves the best performance in all proposed isolation methodologies. It can decrease the absolute force transmissibility ratio to 5%-20% and decrease absolute torque transmissibility ratio to 10%-25% in broader excitation frequency range. This is a very significant improvement in the NVH of vehicles.
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