Virtual Evaluation of PM Rotor Failure Modes and Magnet Adhesive Debonding with Cohesive Interface Approach

The modern luxurious electric vehicle (EV) demands high torque and high-speed requirements with increased range. Fulfilling these requirements gives rise to the need for increased efficiency and power density of the motors in the Electric Drive Unit (EDU). Internal Permanent Magnet (IPM) motor is one of the best suited options in such scenarios because of its primary advantages of higher efficiency and precise control over torque and speed. In the IPM motor, permanent magnets are mounted within the rotor body to produce a resultant rotating magnetic field with the 3-phase AC current supply in the stator. IPM configuration provides structural integrity and high dynamic performance as the magnets are inserted within the rotor body. Adhesive glue is used to install the magnets within the laminated stack of rotor. High rotational speed of rotor introduces centrifugal loading on the magnets which can result in multiple failure modes such as the debonding of the magnet, and high radial deflection of rotor which in turn reduces the rotor-stator air gap. In this paper, we are exploring the effect of modelling the magnet-to-lamination bonding with the cohesive interface approach. Also, we are exploring the effect of various parameters of the cohesive interface on the debonding nature of magnet glue, radial deformation of the rotor, and durability over standard duty cycles. Predicted outputs with this analysis approach is found to be in good agreement with the tested data points. Hence, the simulation methodology described in this paper can be used a decision-making tool in the initial design phases of IPM rotors to come up with the appropriate adhesive selection and robust designing.