Permanent Magnet Motor Rotor Barriers Reduce Torque Ripple
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Solution Overview
Problem
Permanent magnet motors suffer from torque ripple due to inherent harmonics in flux linkage and cogging, which are undesirable, especially at low speeds, and result in stress to the rotor assembly.
Innovation Solution
The design incorporates a rotor assembly with magnet retention slots featuring angled or curved slot surfaces forming barriers around the magnets, and additional barriers positioned along the mid-axis between magnet retention slots, which reduce torque ripple and stress by guiding magnetic flux and distributing forces asymmetrically or symmetrically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional magnet retention slots are used in permanent magnet motors, then the motor structure is simple and easy to manufacture, but torque ripple increases and stress on the rotor assembly increases
Solution Approach 1:
The patent applies curved slot surfaces instead of straight surfaces in the magnet retention slots. The curved surfaces are designed with specific radii of curvature to optimize magnetic flux distribution and reduce torque ripple while maintaining manufacturing feasibility. This curvature modification directly addresses the harmful torque ripple effect without significantly complicating the manufacturing process.
Solution Approach 2:
The patent modifies geometric parameters of the magnet retention slots, including slot width, slot depth, and slot surface angles. By optimizing these parameters, the magnetic flux density distribution is improved, which reduces torque ripple and stress on the rotor assembly while maintaining a relatively simple overall structure that remains easy to manufacture.
2Ease of manufacture
If conventional magnet retention slots are used in permanent magnet motors, then the motor structure is simple and easy to manufacture, but stress on the rotor assembly increases
Solution Approach 1:
The curved slot surfaces distribute mechanical stresses more evenly across the rotor assembly compared to straight slot surfaces. The curvature radius is specifically selected to reduce stress concentration points, thereby lowering overall stress on the rotor assembly while keeping the structural complexity and manufacturing difficulty at acceptable levels.
Solution Approach 2:
By optimizing slot geometric parameters such as width, depth, and angular orientation, the patent reduces stress concentrations in the rotor assembly. These parameter modifications allow the rotor to withstand operational loads with reduced stress, improving durability without requiring major structural changes that would complicate manufacturing.
3Object-generated harmful factors
If barriers are added around magnet corners in magnet retention slots, then torque ripple and stress are reduced, but device complexity increases
Solution Approach 1:
The magnet retention slot is segmented into multiple surfaces (first slot surface, second slot surface, third slot surface, etc.) with different orientations and curvatures. Each segment serves a specific function in guiding magnetic flux and reducing torque ripple. This segmentation achieves the desired performance improvement while keeping each individual segment relatively simple to manufacture.
Solution Approach 2:
Different regions of the magnet retention slot are given different geometric properties. For example, certain slot surfaces have specific curvature radii while others are straight, and some surfaces are positioned at specific angles. This local differentiation optimizes flux distribution and reduces torque ripple without requiring the entire slot structure to be complex.
4Object-generated harmful factors
If multiple barriers are positioned around mid-axis between magnet retention slots, then torque ripple is reduced, but device complexity increases
Solution Approach 1:
The region around the mid-axis between magnet retention slots is divided into multiple barriers or segments. These segmented barriers create a more controlled magnetic flux path, reducing torque ripple. The segmentation allows for optimized flux distribution while maintaining a manageable structural complexity through systematic arrangement of the segments.
Solution Approach 2:
The barriers positioned around the mid-axis are arranged asymmetrically to optimize magnetic flux distribution. This asymmetric arrangement helps balance the magnetic forces and reduce torque ripple that would otherwise occur due to symmetric flux patterns. The asymmetric design achieves performance improvement without requiring excessive structural complexity.
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 decreases torque ripple and stress on the rotor assembly, improving motor performance and maintaining or increasing output torque and power without compromising efficiency.
Implementation Method 1
The plurality of angled or curved slot surfaces forming the first barrier around the corner of the magnet positioned closest to an outer surface of the rotor assembly may be configured to reduce torque ripple of the permanent magnet motor and stress to the rotor assembly
Data Source
AI summary
A permanent magnet motor comprises: a stator comprising teeth; and a rotor rotatable relative to the stator, the rotor having a plurality of poles, wherein each pole of the rotor comprises a pair of magnet retention slots, each magnet retention slot accommodating a magnet. Surfaces of the teeth of the stator facing the rotor are flat or have an arc shape. Each magnet retention slot may have a plurality of angled slot surfaces forming a first barrier around a corner of the magnet positioned closest to an outer surface of the rotor. At least three second barriers are positioned around a mid-axis extending along between the pair of the magnet retention slots. Each magnet retention slot comprises a slot surface slanted or curved relative to a second side surface of the magnet facing an inner surface of the rotor to form a third barrier around an end of the second side surface of the magnet.