Analysis on Irreversible Demagnetization Condition of Linear Oscillatory Actuator with Moving Magnets

In this paper, a linear oscillatory actuator (LOA) with moving magnets used in active engine mount is modeled and theoretically analyzed considering its performance decline at high temperature. Firstly, a finite element model (FEM) of the LOA with moving magnets is established. The actuator force is decomposed to ampere force and cogging force through formation mechanism analysis. By using the FEM, ampere forces and cogging forces of the LOA with moving magnets under different current loads and different mover positions are calculated. The FEM and calculation method are validated by bench level test. The voice coil constant and cogging coefficient at normal temperature are identified, which indicates the actuator force is a linear model related to the current and the mover position. Then, considering temperature-dependent magnetic hysteresis curve (B-H curve) of permanent magnet (PM) material used in the LOA with moving magnets, thermal demagnetization analysis and actuator force decay analysis are carried out. The magnetic density distribution of PMs and actuator forces at different temperatures are obtained. Finally, according to magnetic density distribution in PMs under different working conditions, critical conditions for irreversible demagnetization of the LOA with moving magnets are determined. A nonlinear actuator force prediction model of the LOA with moving magnets under thermal demagnetization is established, which includes three independent variables: temperature, current and mover position. The model proposed in this paper can provide convenience for the active control of LOA with moving magnets considering temperature variation in engine vibration reduction.