Electromagnetic-Thermal-Stress Efforts of Stator-Casing Grease Buffers for Permanent Magnet Driving Motors

Driving motors are one of the most critical components in modern electrified transportation systems, deciding directly the system's working reliability and controllability. To extend the life-cycle of the driving motors while operating them with enough torque output, the temperature rise maintenance techniques have attracted extensive research attention. This paper presents a novel stator-casing fitting approach by filling grease materials into the assembly gap between the dovetail-groove-fitted stator core and motor shell of PMSMs. The grease-filled dovetail-groove-fitted structure can reduce effectively the thermal resistance between the machine's internal components and the external coolants, and can also relieve the stress-caused magnetic performance regressions of the electrical steel sheets laminating the stator core. In addition, due to both the thermal conduction enhancement and the stress-buffering effect, the deformation occurring in stator cores can also be reduced, which is helpful to guarantee the machine's precision. Therefore, the electromagnetic, thermal, and stress-deformation performances in the PMSM can all be improved by using grease buffers filled between stator cores and motor casings. To validate the electromagnetic-thermal-stress efforts of the buffers on the prototype together with the simulation methodologies, a 44-kW 6000-rpm line-started PMSM is taken as the reference machine, and a multi-physical coupled model of the problem is numerically calculated. The influences of the grease properties on the machine's working performances and temperature rises are investigated through comparative analyses. Finally, the numerical calculation results are compared with experimental ones to validate their effectiveness.