An engine isolation system via tuneable damping mounts can contribute to enhanced automobile performance. In this study, a magnetorheological fluids (MRF) mount in squeeze mode for engine isolation is proposed and its damping characteristics are analysed. Based on an engine isolation dynamic model with three degrees of freedom, a hierarchical fuzzy control (HFC) system is proposed to decrease the vertical vibration force and roll moment transmitted from an engine to a foundation. On the control level, a fuzzy controller is designed to isolate the engine vertical vibration. On the coordination level, fuzzy reasoning is adopted to realize a coordination strategy for tuning the damping of each MRF mount in order to minimize the transmitted torque. The simulation is developed in MATLAB, and the experimental isolation system for an actual engine is built in the laboratory. With wide excitation frequency inputs under different operation conditions, studies on different engine mount isolation systems are carried out. Simulation results indicate that MRF mounts using the HFC strategy have more advantages than passive elastomeric mounts or hydraulic mounts, especially in the low-frequency range. Laboratory results confirm that the engine HFC system via MRF mounts performs markedly better than the passive mount system. The absolute force transmissibility ratio and torque transmissibility ratio are reduced to lower than 0.3 in actual complex excitation, which is very significant for an improvement in noise, vibration, and harshness.
Reducing the vibration of an automotive magnetorheological (MR) suspension system can contribute greatly to enhancing vehicle performance. However, it is difficult to design a control system that depends on a complicated whole-vehicle vibration model. This paper proposes a hierarchical controller that consists of a control level and a coordination level for heave, roll, and pitch vibration control of a vehicle with an MR suspension system. On the control level, a local fuzzy controller is designed for each quarter-vehicle MR suspension system, based on a hybrid control strategy of skyhook control and groundhook control. On the coordination level, a coordination controller is designed to tune four local independent fuzzy controllers by adjusting their output parameters on the basis of system feedback. A test and control system for MR suspensions is set up and implemented on a minibus equipped with four controllable MR dampers. The results on random rough roads confirm that the hierarchical controller can reduce automotive vertical vibration, roll motion, and pitch motion more effectively than a passive suspension or an MR suspension using a hybrid control strategy. It achieves better ride comfort and automobile handling stability, although data for bump input indicate that the hierarchical controller does not decrease automotive vertical vibration more effectively than hybrid control or a passive system. However, it yields better results in decreasing pitch and roll motions.
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