Design of a Slotless Structure for Minimizing Cogging Torque and Torque Ripple in a Column Type EPS Motor for Vehicles

Currently, the automotive market is undergoing a vibrant transition toward component electrification driven by the widespread adoption of electric vehicles. The steering system, electric power steering (EPS), has evolved gradually from traditional hydraulic systems (HPSs) to electric systems. The current state sees the majority of commercial vehicles equipped with electric EPS systems. EPS reduces the steering effort applied to the steering wheel during low-speed driving, enhancing driving convenience. It is widely adopted in most commercial vehicles due to numerous advantages such as system simplification, speed-dependent steering control, and vehicle weight reduction compared to traditional HPSs. EPS can achieve a 3%-5% improvement in fuel efficiency compared to traditional HPSs because it operates only when the driver manipulates the steering wheel. However, what matters most in EPS is vibration and noise. Drivers are directly exposed to the vibration and noise of EPS. Therefore, it is crucial to implement electromagnetic designs that reduce cogging torque and torque ripple, which are the causes of vibrations and noise in electric motors. However, due to the inherent characteristics of electric motors, in structures designed for winding coil windings, such as fixed stator slots and teeth, the variation in reluctance during operation is not consistent. Consequently, this leads to an increase in the occurrence of cogging torque and torque ripple. However, if an EPS motor is designed with a structure lacking stator teeth, the change in reluctance during rotor rotation remains constant. In theory, this would significantly reduce cogging torque and torque ripple when the rotor is in motion. Therefore, in this article, the conventional EPS motor, designed with a structure containing stator teeth resulting in cogging torque and torque ripple, is targeted for reduction. This article designed a slotless motor structure with the goal of significantly minimizing these effects. In this article, pursued a design to achieve the target output of the EPS slotless motor and enhance the overall output density. Ultimately, this motor designed, fabricated, and analyzed a motor for the automotive EPS system with the capability to reduce vibrations and noise while achieving weight reduction.