Asymmetric Rotor Laminations for DC Motor Cogging Torque Reduction
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Solution Overview
Problem
Wound rotor motors with commutators face challenges in reducing axial length and wire usage due to overlapping winding heads, which also result in noticeable cogging torque, especially with asymmetric lamination designs like the 20 slot configuration.
Innovation Solution
The design incorporates a rotor core with asymmetric laminations and strategically placed grooves on the pole faces to create a higher fundamental cogging torque order, reducing axial length and wire usage while minimizing cogging torque by adjusting the phase difference between the groove and pole cogging torques, typically achieving a cogging torque order of 28, 36, or 44 with 4 stator poles and 14, 18, or 22 rotor poles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If asymmetric lamination design is used to reduce winding head overlap, then axial length is reduced, but cogging torque increases
Solution Approach 1:
The patent applies asymmetric lamination design where slots are arranged non-uniformly around the rotor circumference, creating asymmetric pole configurations. This asymmetry allows winding heads to lay alongside adjacent heads without crossing, reducing axial length while the specific asymmetric pattern is designed to control cogging torque characteristics
Solution Approach 2:
The patent changes the slot arrangement parameters and pole configurations to achieve different cogging torque orders. By selecting specific numbers of rotor poles (14, 18, or 22) with corresponding asymmetric slot patterns, the fundamental cogging torque order is increased to 28, 36, or 44 respectively, reducing the effective cogging torque magnitude
2Ease of manufacture
If conventional symmetric lamination is used, then manufacturing is easier, but winding heads must cross over increasing axial length
Solution Approach 1:
The patent deliberately introduces asymmetry in the lamination slot arrangement to enable compact winding head positioning. The asymmetric configuration allows all winding heads to be contained within a shorter axial space by eliminating the need for heads to cross over previously wound heads, accepting increased manufacturing complexity as a trade-off for compactness
3Object-generated harmful factors
If more rotor poles are added to increase cogging torque order, then effective cogging torque is reduced, but device complexity increases
Solution Approach 1:
The patent changes the number of rotor poles to specific values (14, 18, or 22) that, when combined with a 4-pole stator, produce high fundamental cogging torque orders (28, 36, or 44). This parameter optimization reduces effective cogging torque while the asymmetric slot patterns are designed to facilitate practical manufacturing despite the increased pole count
Data Source
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AI summary
A DC motor, has a stator housing accommodating a permanent magnet stator; a rotor, rotatably mounted confronting the stator, the rotor having a shaft, a rotor core fitted to the shaft and having asymmetric laminations, a commutator fitted to the shaft adjacent one end of the rotor core, and windings wound about poles of the rotor core and terminated on the commutator; and brush gear comprising brushes in sliding contact with the commutator for transferring electrical power to the windings, wherein the cogging torque order for the motor is greater than twenty. Preferably, the cogging torque order is 28, 36 or 44.