Low-speed, high-torque drives require both high torque density and strong overload capability. Permanent-magnet vernier machines (PMVMs) are promising for this purpose owing to the magnetic-gear effect. The dual-stator spoke-type PMVM (DS-PMVM) achieves high torque density at light load but suffers from yoke saturation and weak overload capability at heavy load. This paper proposes a dual-rotor spoke-type PM vernier machine (DR-PMVM) that achieves both high torque density and strong overload capability. The machine employs an open-slot stator, a low-speed spoke-type PM rotor, and a high-speed salient-pole PM rotor. The spoke-type PM rotor concentrates magnetic flux and enhances high-pole-pair working PM flux density harmonics, while the salient-pole PM rotor strengthens the low-pole-pair PM working harmonics along its d-axis and suppresses non-working armature harmonics along its q-axis. These effects jointly increase the PM flux linkage and reduce iron saturation, leading to improved torque density and overload performance. Finite-element analysis (FEA) verifies the proposed mechanism and performance advantages. Compared with the DS-PMVM, the DR-PMVM achieves 25% higher torque at 5 A/mm² and 71% higher torque at 10 A/mm², with a 24% improvement in overload capability. The proposed design demonstrates an effective approach to balance high torque density and overload robustness in high-gear-ratio PMVMs for low-speed, high-torque applications.

vernier machine,dual-rotor,torque density,overload capability,working harmonic