Airgapless Electric Motors With an External Rotor

Abstract

This paper proposes a new family of electric motors based on the concept of an airgapless device. In this type of device, the rotor is allowed to touch the stator at a contact point, which maximizes the internal flux and, therefore, the electromagnetic torque. A higher torque density motor is proposed in this paper due to a reduced reluctance caused by zero airgap situation. A comparison with other high-torque-density electric motors demonstrates the advantages of the proposed airgapless motors. The proposed motor will maximize the generated torque, allowing these types of motors to be competitive in applications where hydraulic motors are prevalent, i.e., low-speed and high-torque requirements. Hydraulic motor systems face two major problems with their braking system and with low efficiency due to a large number of energy conversion stages (i.e., a motor pump, hydraulic connections, and the hydraulic motor itself). The proposed electric motor, unlike hydraulic motors, converts electrical energy directly to mechanical energy with no extra braking system necessary and with higher efficiency. The modeling of this machine with a minimum number of poles is discussed before a generalization is presented. A proof-of-concept electric motor with nine magnetic bipoles is built to validate the theoretical assumptions proposed in this paper.