Brushless Motor Stator Geometry for Cogging Torque Reduction
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Solution Overview
Problem
Conventional brushless motors with permanent magnets suffer from torque ripple and cogging torque, leading to vibration and noise issues, while also lacking in efficiency and being costly due to the need for thick magnets and inefficient magnet utilization, especially in applications like fan motors for air conditioners.
Innovation Solution
A brushless motor design with a rotor having 10 magnet poles and 12 teeth, where the teeth tip width to stator inside diameter ratio is between 0.18 and 0.25, and an integrated stator core structure without divided cores, optimizing the magnetic flux and winding efficiency to reduce cogging torque and enhance motor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the number of magnet poles and teeth are optimized to reduce cogging torque, then vibration and noise are reduced, but motor efficiency is not sufficiently improved
Solution Approach 1:
The patent applies parameter changes by establishing specific mathematical relationships between the number of magnet poles (P) and teeth (M), and between teeth tip width (t1) and stator inside diameter (Ds). The formulas P/M=0.833±0.083 and 0.18<t1/Ds<0.25 optimize the magnetic flux distribution to simultaneously reduce cogging torque and improve motor efficiency through precise dimensional control
2Object-affected harmful factors
If the shape of the magnet is made thicker toward the center to increase magnetic flux density, then cogging torque is reduced, but the usage amount of magnet increases and cost increases
Solution Approach 1:
Instead of changing magnet shape to reduce cogging torque, the patent changes the stator tooth geometry parameters - specifically the teeth tip width ratio (t1/Ds between 0.18 and 0.25) and the P/M ratio. This approach achieves cogging torque reduction through stator design optimization rather than increasing magnet quantity or changing magnet shape
3Productivity
If divided cores are linked together to enhance motor efficiency, then production efficiency increases, but dimensional differences and uneven gap distribution cause magnetic variation and vibration
Solution Approach 1:
The patent maintains the divided core structure for production efficiency but compensates for assembly errors through precise parameter control of the teeth tip width ratio (t1/Ds). This parameter optimization ensures uniform magnetic flux distribution even with dimensional variations in assembled cores, reducing vibration while maintaining manufacturing advantages
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 solution effectively reduces cogging torque, achieves low vibration and noise, and maintains high efficiency without increasing costs, while ensuring optimal magnetic flux utilization and minimizing production errors.
Implementation Method 1
A permanent magnet brushless motor in which a concentrated winding wire is made on every tooth thereof is widely used
Implementation Method 2
torque ripple or cogging torque occurs with magnetic attraction exerting over permanent magnet and teeth
Data Source
AI summary
A motor of this invention comprises a rotor having a permanent magnet, the number of which magnet poles is P, and a stator including M pcs of teeth, the teeth arranged in a circumferential direction in a manner to face the permanent magnet through a spatial gap, wherein the stator includes stator core having the number M of the teeth, and a winding wire wound about each of the tooth, wherein the number P of the magnet poles and the number M of the teeth have a relation defined by formulae (2/3)M<P<(4/3)M, and M≠P, and wherein ratio (t1/Ds) of teeth tip width t1 to stator inside diameter Ds is given by a formula 0.18<(t1/Ds)<0.25.