Embedded Permanent Magnet Rotor Core with Circular Arc Surfaces
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Solution Overview
Problem
Conventional embedded permanent magnet rotary electric machines face issues such as cogging torque, torque ripples, voltage saturation, dimensional tolerances leading to gaps and demagnetization due to cylindrical rotor core shapes and similar internal and external magnet housing aperture dimensions.
Innovation Solution
The design features a rotor core with circular arc-shaped surfaces, radially convex permanent magnets, and air gap portions in magnet housing apertures to reduce harmonics, separate q-axis magnetic flux from the stator, and increase magnetic saturation, preventing demagnetization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the outer circumferential surface of the rotor core is a cylindrical surface, then the structure is simple and easy to manufacture, but harmonics are present in the magnetomotive force waveforms causing cogging torque and torque ripples
Solution Approach 1:
The rotor core outer circumferential surface is designed with circular arc-shaped curved surfaces instead of a cylindrical surface. This curvature modification reduces harmonics in the magnetomotive force waveform, thereby suppressing cogging torque and torque ripples while maintaining manufacturing feasibility.
2Device complexity
If the outer circumferential surface of the rotor core is a cylindrical surface, then the structure is simple, but the core portion subjected to q-axis magnetic flux is in close proximity to the stator increasing q-axis inductance and causing voltage saturation
Solution Approach 1:
The circular arc-shaped curved surfaces on the rotor core increase the air gap distance between the core portion subjected to q-axis magnetic flux and the stator. This geometric modification reduces q-axis inductance and prevents voltage saturation during high-speed rotation.
3Ease of manufacture
If the internal shapes of magnet housing apertures and external shapes of the magnets are similar shapes, then the manufacturing process is simplified, but gaps are more likely to arise between radially inner end portions of the magnets and the magnet housing apertures
Solution Approach 1:
The magnet housing aperture is designed with air gap portions at the radially inner end portions, creating local dimensional differences. This allows the aperture shape to differ from the magnet shape in critical areas, eliminating gaps between the magnet and aperture while maintaining overall manufacturing simplicity.
4Ease of manufacture
If the two circumferential side portions of the permanent magnets are flat surfaces inclined relative to the magnetic pole center, then the manufacturing process is simplified, but the thicknesses of the side portions are thinner parallel to the magnetic pole center causing lower operating points
Solution Approach 1:
The air gap portions in the magnet housing aperture increase the effective thickness of the permanent magnet side portions parallel to the magnetic pole center. This parameter change raises the operating points of the side portions, suppressing demagnetization while maintaining the simplified flat surface geometry.
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 cogging torque and torque ripples, expands the operating range, securely fixes magnets without clearances, and reduces demagnetization risks by minimizing magnetic leakage and enhancing magnetic saturation.
Implementation Method 1
an external shape in which a plurality of circular arc-shaped curved surfaces 13 that are convex radially outward are arranged circumferentially
Implementation Method 2
B2>B1 is satisfied, where B1 is a thickness of a core portion of the rotor core between the circular arc-shaped curved surfaces and the magnet housing apertures at the magnetic pole center, and B2 is a thickness of a circumferential end portion of the core portion
Data Source
AI summary
R1>R2>R3 is satisfied, where R1 is a radius of curvature of a cylindrical surface that contacts circular arc-shaped curved surfaces arranged circumferentially, R2 is a radius of curvature of the circular arc-shaped curved surfaces, and R3 is a radius of curvature of an upper surface of permanent magnets, air gaps are formed on radially outer portions of two circumferential side portions of magnet housing apertures, surfaces that contact two circumferential side surfaces of the permanent magnets so as to be parallel to a radial direction are disposed on radially inner portions of the two circumferential end portions, and B2>B1 is satisfied, where B1 is a thickness of a core portion of the rotor core between the circular arc-shaped curved surfaces and the magnet housing apertures at a magnetic pole center, and B2 is a thickness of a circumferential end portion of the core portion.