Segmented Rotor Magnets Reduce Cogging Torque
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Solution Overview
Problem
Conventional motors face challenges in reducing cogging torque and torque ripple simultaneously, as methods to mitigate cogging torque often result in torque reduction, and there is a trade-off relationship between the two when applying skew angles.
Innovation Solution
A rotor design featuring a shaft with a rotor core, circumferentially and axially arrayed magnets, and sheet-shaped magnetic portions on the radial outside surfaces, where first and second magnets with magnetic portions are alternately arranged in different axial portions to generate opposite phases, reducing cogging torque without torque reduction and minimizing torque ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a skew is applied to reduce cogging torque, then cogging torque is reduced, but torque is reduced
Solution Approach 1:
The rotor is divided into multiple magnetic pole pairs with different skew angles. Each pole pair has magnets with specific skew angles arranged in a segmented pattern around the rotor circumference. This segmentation allows different regions to contribute differently to cogging torque cancellation while maintaining overall torque output.
Solution Approach 2:
Different local regions of the rotor have different skew angle characteristics. Specifically, certain pole pairs have magnets with larger skew angles to generate opposite-phase cogging torque, while other pole pairs have smaller or zero skew angles to maintain torque output. This local differentiation resolves the contradiction between cogging torque reduction and torque maintenance.
2Object-generated harmful factors
If a skew angle is increased to reduce cogging torque, then cogging torque is reduced, but torque ripple increases
Solution Approach 1:
The rotor employs multiple pole pairs with differentiated skew angle assignments. By segmenting the magnetic poles into groups with different skew characteristics, the patent achieves cogging torque reduction through phase inversion while preventing excessive torque ripple that would result from uniform high skew angles across all poles.
Solution Approach 2:
The skew angle is varied as a parameter across different pole pairs rather than being uniform. Specific pole pairs have skew angles optimized for cogging torque cancellation, while others have skew angles optimized for smooth torque characteristics. This parameter variation allows simultaneous optimization of both cogging torque and torque ripple.
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 design effectively reduces cogging torque and torque ripple, minimizing vibration and noise in motors while maintaining torque levels, by canceling out opposing phases of cogging torque and torque ripple waveforms.
Implementation Method 1
The rotor includes at least one magnet... the magnets include first magnets with the magnetic portions being provided on at least a circumferential portion in a radial outside surface of the first magnets and second magnets in which none of the magnetic portions are on a radial outside surface of the second magnets
Data Source
AI summary
A rotor includes a shaft, a rotor core, magnets on a radial outside surface of the rotor core, and sheet-shaped magnetic portions provided on radial outside surfaces of some of the magnets. The magnets include first magnets in which the magnetic portions are on a circumferential portion in a radial outside surface of the first magnets and second magnets in which the magnetic portions are not on a radial outside surface of the second magnets. The first magnets and the second magnets are alternately arranged in the circumferential direction in each of a first portion and a second portion along the axial direction in the radial outside surface of the rotor core. The first magnets of the first portion and the second magnets of the second portion overlap each other, and the second magnets of the first portion and the first magnets of the second portion overlap each other.