Interior Permanent Magnet Rotor Slits for Low-Noise Ferrite Motors
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Solution Overview
Problem
Interior permanent magnet motors using sintered ferrite magnets face issues with increased vibration and noise due to eccentric assembly, as the existing designs either reduce magnetic flux density or fail to effectively counteract the radial electromagnetic exciting force.
Innovation Solution
The motor design incorporates arc-shaped permanent magnets with specific slit configurations, where the slits between the rotor outer peripheral surface and magnet insertion holes satisfy a ratio of 0.35≤Ss/Si≤0.5, including a magnetic pole center slit and side slits, to balance magnetic flux and torque while reducing radial exciting forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sintered ferrite magnets are used instead of rare-earth permanent magnets, then cost is reduced, but residual flux density is reduced to about 1/3
Solution Approach 1:
The patent changes the geometric parameters of the magnet insertion holes (making them non-circular with specific width-to-depth ratios) and adjusts the arrangement parameters of multiple holes per pole to compensate for the lower residual flux density of ferrite magnets, thereby maintaining sufficient magnetic flux while using cost-effective materials
Solution Approach 2:
The patent divides each magnetic pole into multiple magnet insertion holes (two or more per pole) arranged in the radial direction, segmenting the magnetic flux path to increase the total effective magnetic flux area and compensate for the lower density of ferrite magnets
2Force
If the surface area of permanent magnets is increased to compensate for lack of torque, then torque is maintained, but the area of magnet insertion holes is increased leading to reduced magnetic path resistance
Solution Approach 1:
The patent applies different geometric characteristics to different parts of the magnet insertion holes: the width is optimized for magnetic flux capacity while the depth is controlled to maintain mechanical stability, and the non-circular shape is specifically designed to balance flux area with magnetic path resistance
Solution Approach 2:
The patent uses non-circular (arc-shaped) magnet insertion holes with specific curvature characteristics to optimize the magnetic flux distribution and path resistance, improving the efficiency of magnetic flux utilization while maintaining structural integrity
3Object-affected harmful factors
If slits are formed in the rotor core to reduce electromagnetic exciting force, then vibration and noise are reduced, but magnetic flux resistance is increased
Solution Approach 1:
The patent optimizes the parameters of the magnet insertion holes (width-to-depth ratio, non-circular shape) to achieve a balance where sufficient magnetic flux is maintained while the structural design inherently reduces the need for additional slits, minimizing magnetic path resistance while controlling vibration and noise
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 suppresses vibration and noise caused by assembly fluctuations while maintaining motor efficiency and reducing costs by using ferrite magnets, ensuring sufficient torque and magnetic flux.
Implementation Method 1
a current flowing through a coil of the stator attracts the rotor core so that the electromagnetic exciting force in the radial direction is increased
Implementation Method 2
the magnetic flux generated by a current flowing through a coil of the stator attracts the rotor core
Implementation Method 3
in order to increase the magnetic-path resistance against a reaction magnetic flux from a stator, in a portion of the core, which is located at an outer periphery of each of the permanent magnets, a plurality of elongated slits extending substantially in a normal direction are formed
Data Source
AI summary
In an interior permanent magnet motor, a plurality of slits are formed between a rotor outer peripheral surface of a rotor and a radially-outer insertion hole contour surface of a magnet insertion hole. Assuming that a total area of the plurality of slits per magnetic pole is represented by Ss, and an area of a region in a rotor core on a radially outer side with respect to the corresponding one magnet insertion hole is represented by Si, the plurality of slits are formed so as to satisfy a relationship of 0.35≤Ss/Si≤0.5.