Variable Axial Air Gap Design for Permanent Magnet Motor Cogging Torque Reduction
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Solution Overview
Problem
Permanent magnet motors experience undesirable cogging torque, which causes jerkiness and torque ripple, especially at lower speeds, due to variations in magnetic interaction between the rotor and stator.
Innovation Solution
A variable gap width is implemented between the rotor and stator, with the gap width varying as a function of axial position, effectively reducing cogging torque by adjusting the outer diameter of the rotor and inner diameter of the stator, thereby minimizing the undesirable torque ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a constant gap width is used between rotor and stator, then the motor structure is simple and easy to manufacture, but the cogging torque is high causing jerkiness and torque ripple
Solution Approach 1:
The patent applies local quality by making the gap width vary at different axial positions along the rotor-stator assembly. Specifically, the gap width is adjusted locally at different sections (e.g., first section has different gap width than second section) to reduce cogging torque in specific regions where it is most problematic, while maintaining simpler construction in other areas.
Solution Approach 2:
The patent changes the geometric parameter of the gap width from a constant value to a variable value that changes along the axial direction. This parameter change allows the magnetic interaction between rotor and stator to be optimized at different positions, reducing the harmful cogging torque effect while maintaining manufacturability through controlled variations in gap dimensions.
2Object-generated harmful factors
If a variable gap width is implemented to reduce cogging torque, then torque ripple is reduced and operation becomes smoother, but the manufacturing complexity increases
Solution Approach 1:
The patent segments the rotor-stator assembly into distinct axial sections (first section, second section, etc.), with each section having a specific gap width configuration. This segmentation allows the complex variable gap structure to be broken down into manageable segments that can be manufactured and assembled separately, reducing overall manufacturing complexity while still achieving the torque ripple reduction benefit.
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 variable gap design significantly reduces cogging torque compared to motors with constant gap widths, leading to smoother operation and reduced torque ripple, while also offering manufacturing advantages and consistent performance.
Implementation Method 1
operate by way of a rotor rotating in relation to stator under the influence of magnetic interaction between components of the rotor and the stator
Implementation Method 2
Cogging torque can be understood as a torque due to the interaction between magnets (e.g. permanent magnets) and slotting
Data Source
AI summary
A permanent magnet motor (and associated rotor and stator) are described. The motor includes: a rotor having: an outer surface disposed radially from a central axis; and a plurality of permanent magnets located on the outer surface of or within pockets located between the outer surface and the central axis of the rotor; a stator having an inner surface in a spaced apart relationship to the outer surface or the plurality of permanent magnets with a gap there between that varies as a function of axial position along the central axis, and a first gap width at a first axial position is different from a second gap width at a second axial position, and the first and second gap widths are sized and configured to reduce the coping torque of the IPM motor as compared to an IPM motor having a constant gap width of the first or second width.