Permanent Magnet Motor Air Gap Layout for Lower Torque Ripple
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Solution Overview
Problem
Conventional permanent magnet motors suffer from asymmetry of magnetic flux density amplitudes in air gaps and torque ripples due to the different materials and structures of adjacent magnetic poles, leading to higher costs and inefficiencies.
Innovation Solution
A permanent magnet motor design with alternating poles and permanent magnet poles arranged circumferentially, featuring varying air gaps and specific geometric configurations to optimize magnetic flux distribution, ensuring a ratio of 0.4 ≤ δ2 / δ1 ≤ 0.9 and a thickness of permanent magnets that satisfies t / (δ2 + δ1) ≥ 1.5, which reduces magnetic resistance and enhances magnetic flux density symmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional permanent magnet motor design with identical air gaps is used, then manufacturing is simplified, but magnetic flux density asymmetry and torque ripples occur
Solution Approach 1:
The patent applies asymmetry by deliberately designing different air gap thicknesses for permanent magnet poles (δ1) and alternating poles (δ2), where δ2/δ1 is controlled within 0.4-0.9. This asymmetric air gap configuration compensates for the inherent magnetic flux density asymmetry caused by different pole structures, thereby reducing torque ripples while maintaining manufacturing feasibility through precise air gap control.
2Power
If permanent magnets are arranged with different magnetization directions, then magnetic poles are formed, but magnetic flux density asymmetry occurs
Solution Approach 1:
The patent changes the air gap thickness parameter to compensate for magnetic flux density asymmetry. By controlling the ratio δ2/δ1 within 0.4-0.9 and satisfying t/(δ1+δ2)≥1.5, the patent adjusts magnetic circuit parameters to balance the magnetic flux density amplitudes between permanent magnet poles and alternating poles, thereby reducing torque ripples while maintaining effective magnetic pole formation.
3Quantity of substance
If conventional alternating pole design is used, then material cost is reduced, but torque ripples increase
Solution Approach 1:
The patent applies local quality by creating different air gap characteristics at different locations: smaller air gaps (δ2) at alternating poles and larger air gaps (δ1) at permanent magnet poles. This localized air gap differentiation compensates for the reduced magnetic flux density at alternating poles caused by material reduction, thereby suppressing torque ripples while maintaining cost-effective material usage.
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 design reduces asymmetry in magnetic flux density amplitudes and torque ripples, improving motor efficiency and reducing costs by optimizing air gap thickness and magnetic flux distribution.
Implementation Method 1
The magnetic line from the N pole of one permanent magnet passes through the stator core to the S pole of an adjacent permanent magnet
Implementation Method 2
the soft magnetic material between two permanent magnet mounting slots is magnetized by the permanent magnets
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
Provided is a permanent magnet motor, comprising a rotor component (1) and a stator component (2). The rotor component (1) comprises alternating poles (4) and permanent magnet poles (3) alternately arranged in a circumferential direction. The stator component (2) comprises stator teeth portions (5) arranged and spaced apart in a circumferential direction on an inner circumferential side of the stator component. A first air gap (6) is formed between an inner circumferential side of the stator teeth portion (5) and an outer circumferential side of the permanent magnet pole (3). A second air gap (7) is formed between the inner circumferential side of the stator teeth portion (5) and an outer circumferential side of the alternating pole (4). An average thickness of the first air gap (6) is δ1, and an average thickness of the second air gap (7) is δ2, wherein 0.4 ≤ δ2 / δ1 ≤ 0.9. The permanent magnet motor of the present application can reduce asymmetry of flux density amplitudes of air gaps corresponding to the permanent magnet pole and the alternating pole, and thereby reducing torque ripples.