Development of an Electromagnetic Active Engine Mount

Abstract

Engine mounts need to satisfy three design requirements: (1) firmly support engine weight, (2) isolate structure from the engine’s noise and vibration, and (3) control engine motion when large shocks or engine resonances are present. In addition to these three criteria, which are common for designing all types of engine mounts (passive, semi-active, and active), two more design requirements need to be satisfied for active engine mounts. First, they should be designed such that if there is any malfunction with the actuator, the controller, or the sensors, the active engine mount should still safely operate as a passive mount. Second, the power consumption, the size and weight of the required actuator and its controller should be kept as low as possible. The current paper aims to present an active hydraulic (or fluid) engine mount design by using an electromagnetic actuator and capacitive circuit such that it is able to act as a passive mount, semi-active mount, and an active mount. In addition, the presented design has the capability to be converted to a damper as and when needed. The multi-functional capability of the proposed engine mount design (passive, semi-active, active, and damper) distinguishes the current design from the previously designed active engine mounting systems, and this multi-functional capability is explained in the paper. The proposed design consists of a conventional passive hydraulic (fluid) mount, an electromagnetic actuator (voice coil) and a capacitive circuit. The voice coil is placed in the lower chamber of the passive hydraulic mount and it can change the volumetric stiffness of the bottom chamber actively such that the engine mount has low dynamic stiffness in a wide range of frequencies. The capacitive circuit is paralleled with the voice coil and in situations when large shock inputs are present; it adds capacitance to the electromagnetic circuit and changes the characteristics of the mount from an isolator to a damper. Since the active engine mount design of this paper involves several energy domains, bond graph modeling technique is used for mathematical modeling. MATLAB simulation results are shown for an automotive application and the performance of the proposed active engine mount design is evaluated as an isolator and as a damper. Finally, an adaptive controller, based on Filtered-X LMS algorithm, is proposed and its performance is investigated. The proposed design can eliminate transmitted force from the engine to the structure in a frequency range of 15 Hz to 125 Hz.