Permanent Magnet Motor Cogging Torque Reduction via Stator Tooth Relief
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Solution Overview
Problem
Existing permanent magnet excited electric motors experience torque fluctuations known as cogging torques due to magnetic conductance fluctuations, leading to vibrations and noise, which are difficult to reduce without compromising efficiency and torque density, and are costly to manufacture.
Innovation Solution
The motor design features radially symmetric stator teeth with wave-like topographic regions having concave recesses that radially enlarge the gap between the rotor and stator, providing an uninterrupted, smooth profile to counteract cogging torque without affecting efficiency or torque density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If oblique pole transitions or oblique magnet segments are used, then cogging torque is reduced, but permanent magnetic flux linkage and torque density decrease
Solution Approach 1:
The patent applies curvature by replacing straight pole transitions with arc-shaped pole transitions. The arc shape has a radius of curvature that is at least 50% of the rotor radius, creating a smooth curved transition between adjacent pole magnets. This curved geometry reduces cogging torque by eliminating abrupt magnetic conductance changes while preserving permanent magnetic flux linkage, thereby maintaining torque density without the negative effects of oblique arrangements.
2Object-generated harmful factors
If oblique pole transitions are used, then cogging torque is reduced, but manufacturing complexity and costs increase
Solution Approach 1:
The arc-shaped pole transitions provide a simplified manufacturing solution compared to oblique arrangements. The curved geometry can be directly formed during rotor manufacturing processes such as centrifugal casting or resin transfer molding, eliminating the need for complex multi-step machining or assembly of oblique magnet segments. This reduces manufacturing complexity while effectively reducing cogging torque.
3Object-generated harmful factors
If unequal tooth widths with recesses are used, then cogging torque is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent introduces controlled asymmetry through arc-shaped pole transitions on the rotor side, which compensates for any asymmetries that might arise from manufacturing tolerances in stator tooth widths. The curved geometry provides a buffering effect that reduces sensitivity to tooth width variations, thereby reducing cogging torque without imposing stringent manufacturing precision requirements on the stator teeth.
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 significantly reduces cogging torque while maintaining high efficiency and torque density, and is cost-effective to manufacture by avoiding complex magnet segment arrangements and oblique transitions.
Implementation Method 1
permanent magnet excited electric motor
Implementation Method 2
interaction between the magnetic field of the stator, generated by triggering the stator windings via the gap with the magnet fields of the pole magnets
Implementation Method 3
magnetic conductance fluctuations along the gap which are caused by the grooves of the iron core of the stator, usually of the stator lamination stack, torque fluctuations, known as cogging torques
Data Source
AI summary
An electric motor (1) has a stator (2) and a radially symmetric, permanent magnet excited rotor (4) coaxial with the stator (2). The rotor (4) rotates relative to the stator (2) about a common motor axis (X). The stator (2) has a radially symmetric iron core (6) with a defined number (N) of stator teeth (10) which are each adjacent to one another via stator slots (8) and slot openings (8a) in the circumferential direction. The rotor (4) has pole magnets (14) adjacent to one another. A circumferential gap (18) is formed radially between the pole magnets (14) and the stator teeth (10). Each stator tooth (10) has on its surface (20) facing the gap (18) and adjacent to the slot openings (8a) on both sides in the circumferential direction a relief-like topographic region (22) radially enlarging the gap (18) with least one concave recess (24) and a smooth profile.