Optimization of tangential interior brushless DC motor rotor for hybrid vehicles

Abstract To address performance degradation and demagnetization risks in hybrid electric vehicle oil pump motors under high-temperature conditions, this article proposes a novel rare-earth-free interior tangential brushless DC motor. Leveraging the negative temperature coefficient characteristics of ferrite materials, the design enhances the motor’s high-temperature performance and stability. Simultaneously, by improving the flux concentration capability, it effectively reduces magnetic leakage and lowers motor costs.Firstly, the impact of leakage flux coefficient on the mechanical characteristics of brushless DC motors was investigated, leading to the proposal of a novel air-isolated injection-molded rotor structure for interior tangential motors. Through finite element modeling and magnetic circuit integration method analysis, the quantitative correlation between magnetic bridge width and leakage flux coefficient was determined. While satisfying mechanical strength requirements, the new air-isolated injection-molded structure demonstrated 25.3% reduction in leakage flux coefficient compared to conventional magnetic bridge structure configurations accompanied by 21.7% enhancement in electromagnetic torque, 43% increase in viscous damping coefficient, and 10% improvement in power density.The mechanical characteristic curve exhibited greater stiffness, with the structural reliability of the rotor’s air-isolated flux barrier design being further validated through simulation studies.Secondly, a new ‘mirror image’ segmented rotor structure is proposed, which can reduce the motor cogging torque by 75.4% and significantly suppress the oil pump pressure fluctuation and noise; Finally, the effectiveness of the new rotor structure and the accuracy of the optimisation method are verified through prototype tests, and the test prototype has an increase in output power by 11%, while the cogging torque is effectively reduced by 73.5%.This article pioneers the integrated design combining non-rare-earth material applications, optimized air-isolated injection-molded rotor structures, and a novel “mirror-image” segmented configuration, meeting hybrid electric vehicles’ requirements for cost-effectiveness, performance, and operational reliability.