Tapered Stator Tooth Tips Reduce Cogging Torque
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Solution Overview
Problem
Electric machines, particularly those with interior permanent magnet rotors, face challenges in reducing cogging torque, which leads to vibrations and noise due to the interaction between rotor magnets and stator teeth, and existing solutions like skewed magnetic fields or resilient rotors either increase costs or introduce new failure mechanisms.
Innovation Solution
The design involves a stator with radially inward extending teeth having tapered tips that create a graded air gap when assembled with the rotor, reducing the amplitude of cogging torque at key frequencies and minimizing leakage flux, thereby reducing noise and maintaining motor efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a skewed magnetic field is used to reduce cogging torque, then cogging torque is reduced, but it is difficult to apply in motors with interior permanent magnet rotors
Solution Approach 1:
The patent applies local quality by modifying only the stator tooth tip geometry rather than the entire magnetic field structure. The tooth tip is shaped with a specific profile (curved or angled surface) that locally alters the air gap and magnetic flux distribution at the critical interface between stator and rotor, achieving cogging torque reduction without requiring global magnetic field skewing
Solution Approach 2:
The patent replaces the mechanical/structural approach of skewed magnetic fields with a geometric modification approach. Instead of physically skewing the magnetic field structure, the invention uses a specifically shaped stator tooth tip geometry to achieve the same effect of reducing cogging torque through optimized magnetic flux paths
2Object-generated harmful factors
If a resilient rotor construction is used to reduce cogging torque, then cogging torque is reduced, but the cost of the motor significantly increases and a potential failure mechanism is added
Solution Approach 1:
The patent employs a cost-effective stator-side geometric modification instead of expensive resilient rotor materials or complex rotor constructions. The stator tooth tip shaping can be achieved through standard manufacturing processes, providing an economical solution that avoids the high costs and reliability concerns of resilient rotor constructions
Solution Approach 2:
The patent segments the problem-solving approach by focusing modification efforts specifically on the stator tooth tip region rather than requiring modification of the entire rotor structure. This localized approach reduces manufacturing complexity and cost compared to resilient rotor constructions that require modifying the entire rotor assembly
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 approach effectively reduces noise and motor vibrations while maintaining efficiency and cost-effectiveness, without increasing manufacturing complexity or cost, and minimizes adverse effects on motor performance.
Implementation Method 1
Cogging torque is present because the rotor magnets prefer to line up with the stator teeth
Implementation Method 2
efficiency of BLDC and BLAC motors with permanent magnets embedded in the rotor (e.g., an interior permanent magnet rotor) is typically limited due to leakage flux of individual permanent magnets through the rotor core
Data Source
AI summary
An interior permanent magnet machine is described. The machine includes a rotor rotatable about a central machine axis. The rotor includes a plurality of permanent magnet openings and a plurality of permanent magnets disposed therein. The permanent magnet openings are separated by rotor webs configured to facilitate reducing leakage flux through the rotor webs. The machine also includes a stator disposed coaxially with the rotor and separated from the rotor by a circumferential air gap. The stator includes a plurality of stator teeth that define a plurality of stator slots therebetween. The stator teeth include a stator tooth tip configured to facilitate reducing cogging torque and torque ripple.