Rotor Slot Arc Surface for Demagnetization Resistance
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Solution Overview
Problem
Permanent magnets in rotating electrical machines are susceptible to demagnetization due to strong demagnetizing fields from the stator, requiring increased thickness and number of magnets to prevent demagnetization, which is inefficient.
Innovation Solution
A rotor design with a gap between the second corner part of the permanent magnet and the inner circumference of the slot, featuring an arc surface that disperses the magnetic flux, reducing the peak intensity of the demagnetizing field and allowing for a thinner magnet configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the permanent magnet in the magnetization direction is increased to prevent demagnetization, then the reliability of the permanent magnet is improved, but the quantity of substance (amount of magnets) increases
Solution Approach 1:
The invention applies different structural characteristics to different regions of the slot. Specifically, the inner circumferential surface of the slot has an arc surface with a center on the inner circumference side, creating a gap between the permanent magnet's second corner part and the slot. This local structural modification concentrates the magnetic flux through the arc surface region, providing enhanced magnetic resistance exactly where needed to prevent demagnetization, rather than uniformly increasing magnet thickness throughout.
Solution Approach 2:
The invention employs an arc surface on the inner circumferential surface of the slot, replacing a flat surface with a curved one. The arc surface has its center on the inner circumference side of the slot, and this curvature concentrates the magnetic flux passing through the slot, thereby enhancing the magnetic resistance at the critical region near the second corner part of the permanent magnet without requiring increased magnet thickness.
2Reliability
If the thickness of the permanent magnet is increased to reduce peak demagnetizing field intensity, then the reliability is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
Instead of uniformly increasing magnet thickness, the invention modifies only the slot structure at the critical region. The arc surface on the inner circumferential surface of the slot creates a gap that concentrates magnetic flux locally, providing enhanced protection against demagnetization only where the demagnetizing field is strongest, thus avoiding unnecessary complexity in other regions.
Solution Approach 2:
The invention changes the geometric parameters of the slot rather than the magnet. By modifying the inner circumferential surface to have an arc shape with a specific center location, the magnetic flux distribution is altered, concentrating flux through the arc surface and reducing peak demagnetizing field intensity without changing magnet dimensions.
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
The design neutralizes the demagnetizing field, reducing the thickness of the permanent magnets and the number required, while maintaining effective magnetic performance.
Implementation Method 1
The magnetic flux from the stator side tends to pass along the rotor core near the second corner part, and tends to short-cut to the rotor core near the first corner part
Implementation Method 2
there is a possibility that the demagnetizing field concentrates on the second corner part 103b may arise
Data Source
AI summary
When a corner part that is most distant from a perimeter surface of a rotor core is defined as a first corner part and a corner part in a position that faces the first corner part in a magnetization direction of a permanent magnet is defined as a second corner part, a gap is formed between the second corner part and an inner circumference side of a slot, and the inner circumference side of the slot that forms the gap has an arc surface that has a point X as a center on the inner circumference side of the slot that faces the first corner part. Therefore, the demagnetizing field by the magnetic flux from the stator side does not act intensively on the second corner part of the permanent magnet, and the demagnetizing field instead affects in a wide range of the permanent magnet equally.