Interior Permanent Magnet Motor Rotor Slit Design for Torque Ripple Reduction
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Solution Overview
Problem
Conventional interior permanent magnet motors experience torque ripple and noise due to unoptimized slit shapes and positions, which do not adequately reduce harmonics of the induced voltage.
Innovation Solution
The rotor design includes a rotor core with permanent magnet insertion holes, permanent-magnet end-portion air gaps, and slits arranged such that their widths between the air gaps and adjacent slits increase towards the magnetic pole center, with three or more slits in an angular range of 360/(number of poles × 3) degrees between magnetic poles, optimizing magnetic flux distribution to reduce harmonics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional slit configurations are used, then manufacturing is simplified, but torque ripple and noise reduction is insufficient
Solution Approach 1:
The patent applies local quality by differentiating the slit configuration in different angular regions. Specifically, the number of slits, their widths, and spacing are locally optimized: in the interpolar region (angular range of 360/(number of poles × 3) degrees from interpolar line), three or more slits are provided with specific width ratios to reduce harmonics, while in other regions different slit configurations are used. This localized differentiation allows simultaneous reduction of both harmonics and torque ripple that cannot be achieved with uniform conventional slit designs.
Solution Approach 2:
The patent employs parameter changes by precisely controlling the number of slits (three or more in specific angular range), the widths of slits and core portions, and the angular distribution of slits. The width ratio between core portions and slits is specifically optimized in the interpolar region, and the angular range 360/(number of poles × 3) degrees is carefully selected. These parameter optimizations collectively reduce both harmonics of induced voltage and torque ripple more effectively than conventional designs.
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 torque ripple and noise by minimizing harmonics of the induced voltage, leading to a more efficient and low-noise rotor.
Implementation Method 1
optimizing magnetic flux distribution to reduce harmonics
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A rotor of an interior permanent magnet motor includes a rotor core 2; permanent magnet insertion holes 5 formed in an outer circumferential portion of the rotor core 2 along a circumferential direction; a permanent-magnet end-portion air gap 8 formed in each of both end portions of each permanent magnet insertion hole 5; a permanent magnet 3 inserted in each permanent magnet insertion hole 5; and slits 7 formed in an outer circumferential core portion on an outer side in a radial direction with respect to each permanent magnet insertion hole, wherein three or more of the slits 7 are present in an angular range of 360/(number of poles × 3) degrees from an interpolar line 9, and a width of a core present between the permanent-magnet end-portion air gap 8 and the slit 7 and a width of a core present between the slits 7 are such that a width of a core gradually increases as the core is closer to a magnet pole center 10 from the interpolar line 9.