An Integrated Design Approach of Rotor Assembly for Radial Flux Surface-Mounted Permanent Magnet Synchronous Motors

Abstract

Enhancing the dependability and power density of a SPMSMs is crucial for its extensive utilization in the automotive and aerospace sectors. One major concern regarding these machines is the significant thermo-mechanical loads experienced by the overall rotating assembly due to high rotational speeds and a wide operational temperature range from $50^\circ C$ to $150^\circ C$. This poses a considerable challenge in maintaining structural integrity among the components. Redesigning components to reduce assembly complexity and weight necessitates careful consideration of boundary conditions and contact modeling to prevent catastrophic failures like magnet fly-by conditions. To reduce model complexity, a simplified approach involves integrating the hub and shaft; both machined from AISI 4340. Additionally, the application of a carbon fiber sleeve is investigated through 3-dimensional composite modeling to enhance structural integrity. The primary objective of this thesis is to scientifically justify the design and validation of an integrated rotor hub and shaft using efficient FEM and integration strategies, with the aim of maximizing the durability of a $150kW$ radial flux SPMSMs spinning at $20,000 rpm$. The integrated topology optimization is evaluated using a multiphysics platform alongside studies on motor assembly eigenfrequency. By employing the integrated approach and utilizing AISI 4340 for both the shaft and rotor hub, a weight reduction of $1.84kg$ is achieved, eliminating the need for standard components such as balancing end clamp plates, locknuts, and washers. Furthermore, introducing a carbon fiber sleeve enhances structural integrity, thereby reducing adhesive stress. The design and optimization of the rotating components ensure that the maximum von Mises stress is $50\%$ lower than the material's yield strength. Reduced masses lead to lower centrifugal forces, thereby diminishing radial stress and promoting component and assembly stiffness.