Axially Offset Rotor Units With Surface Relief for Cogging Torque
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Solution Overview
Problem
Magnet-embedded rotors in rotating electric machines experience significant cogging torque, which affects efficiency and performance, and existing solutions have not adequately addressed this issue.
Innovation Solution
The rotor design includes multiple rotor units with embedded permanent magnets and a skew structure, where the magnetic pole centers of adjacent units are offset in the circumferential direction, and the outer rotor core surface features displacement portions radially inward from magnetic pole centers to magnetic pole bordering sections, reducing cogging torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a magnet-embedded rotor with permanent magnets is used to generate both magnet torque and reluctance torque, then the torque output is improved, but the cogging torque increases significantly
Solution Approach 1:
The rotor is divided into multiple rotor units (first rotor unit, second rotor unit, etc.) disposed side by side in the axial direction. Each rotor unit contains its own permanent magnets and magnetic pole sections. This segmentation allows the cogging torque from each unit to be phase-shifted relative to others, enabling cancellation of harmful cogging torque components while maintaining the beneficial torque output from all units.
Solution Approach 2:
The magnetic pole centers of adjacent rotor units are intentionally offset in the circumferential direction by a predetermined angle. This asymmetric arrangement creates phase differences in the cogging torque generated by each rotor unit, allowing the harmful cogging torque components to interfere destructively and reduce overall cogging torque, while the torque production capability is maintained through the combined effect of all units.
2Object-generated harmful factors
If the magnetic pole centers of rotor units are offset in the circumferential direction, then the cogging torque is reduced through phase interference, but the structural complexity increases
Solution Approach 1:
The rotor is divided into multiple rotor units (first rotor unit, second rotor unit, etc.) disposed side by side in the axial direction. Each rotor unit contains its own permanent magnets and magnetic pole sections. This segmentation allows the cogging torque from each unit to be phase-shifted relative to others, enabling cancellation of harmful cogging torque components while maintaining the beneficial torque output from all units.
Solution Approach 2:
The magnetic pole centers of adjacent rotor units are intentionally offset in the circumferential direction by a predetermined angle. This asymmetric arrangement creates phase differences in the cogging torque generated by each rotor unit, allowing the harmful cogging torque components to interfere destructively and reduce overall cogging torque, while the torque production capability is maintained through the combined effect of all units.
3Object-generated harmful factors
If displacement portions are added to the outer circumferential surface of the rotor core, then the cogging torque is reduced through geometric modification, but the manufacturing complexity increases
Solution Approach 1:
Displacement portions are formed on the outer circumferential surface of the rotor core at the magnetic pole bordering sections. These displacement portions create local geometric modifications that alter the air gap distribution and magnetic flux density distribution. The curved or stepped geometry of the displacement portions helps to smooth out the variations in magnetic reluctance that cause cogging torque, thereby reducing the harmful effects while maintaining manufacturability through standard machining or molding processes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively reduces cogging torque by interfering with the phases of cogging torque generated in each rotor unit, resulting in a significant decrease to levels that are difficult to achieve with conventional designs, while maintaining or improving torque output.
Implementation Method 1
a magnet-embedded rotor includes a permanent magnet embedded within a rotor core and obtains not only a magnet torque from the permanent magnet but also a reluctance torque
Implementation Method 2
a rotating electric machine including a magnet-embedded rotor
Data Source
AI summary
A rotor includes a plurality of rotor units disposed side by side in an axial direction. The plurality of rotor units each include a rotor core, a plurality of permanent magnets, a plurality of magnetic pole sections and a plurality of magnetic pole bordering sections. At least one of the rotor units has a displacement portion in an outer circumferential surface of the rotor core. The displacement portion is displaced radially inward from respective magnetic pole centers of a circumferentially adjacent pair of the magnetic pole sections toward the magnetic pole bordering section between the pair of the magnetic pole sections. The displacement portion is disposed corresponding to at least one of the magnetic pole bordering sections. The magnetic pole centers of at least one of the rotor units are offset in the circumferential direction with respect to the magnetic pole centers of another of the rotor units.