Permanent Magnet Rotor Offset for Low-Cogging Torque Pulsation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Electrified vehicle traction motors, particularly permanent magnet motors, experience pulsing and vibrating torque at certain speed ranges and torque levels, leading to passenger discomfort and accelerated wear of components.
Innovation Solution
The electric motor system incorporates a permanent magnet motor with a hollow cylindrical stator and a cylindrical rotor, where at least one pair of permanent magnets is asymmetrically staggered or offset relative to a symmetric N pole positioning, and a controller is used to mitigate or eliminate magnetic cogging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional solutions (skew configurations, harmonic current injection, current modification) are used to reduce torque pulsation, then vibration and noise are partially reduced, but motor efficiency is drastically reduced
Solution Approach 1:
The patent applies asymmetry by offsetting the angular positions of permanent magnets within pole pairs. Specifically, in a four-pole motor, the two north magnets and two south magnets are positioned at different angular offsets from their symmetric positions, creating an asymmetric magnetic field distribution that reduces cogging torque and torque pulsation without requiring skew configurations or current modifications that would reduce efficiency
2Ease of manufacture
If symmetric N pole positioning is used, then motor structure is simple and manufacturing is easy, but magnetic cogging causes pulsing torque and vibration
Solution Approach 1:
The patent maintains the simple symmetric N-pole structure for ease of manufacturing, then introduces controlled asymmetry by offsetting individual permanent magnets within pole pairs. This hybrid approach preserves the overall symmetric structure while adding local asymmetric elements that cancel magnetic cogging effects, achieving both manufacturing simplicity and reduced vibration
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 configuration effectively reduces magnetic cogging and torque pulsation, enhancing passenger comfort and extending the reliability and durability of the motor system without significantly reducing efficiency.
Implementation Method 1
a permanent magnet motor (PMM) including a hollow cylindrical stator defining a circular inner portion with a plurality of slots, defined between a respective plurality of ferromagnetic teeth, and having a plurality of electromagnetic coils arranged in the plurality of slots, respectively, and a cylindrical rotor disposed within the stator and defining a circular outer portion having N pairs of permanent magnets arranged thereabout
Implementation Method 2
at least one pair of the N pairs of permanent magnets is asymmetrically staggered or offset relative a symmetric N pole positioning... the magnetic cogging is caused by the rotor poles passing under the ferromagnetic stator teeth and is mitigated or eliminated due to the asymmetric staggering or offsetting of the at least one pair of the N pairs of permanent magnets
Data Source
AI summary
An electric motor system, such as for an electrified vehicle, includes a permanent magnet motor (PMM) including a hollow cylindrical stator defining a circular inner portion with a plurality of slots, defined between a respective plurality of ferromagnetic teeth, and having a plurality of electromagnetic coils arranged in the plurality of slots, respectively, and a cylindrical rotor disposed within the stator and defining a circular outer portion having N pairs of permanent magnets arranged thereabout to define N rotor poles, respectively, wherein at least one pair of the N pairs of permanent magnets is asymmetrically staggered or offset relative a symmetric N pole positioning, and wherein N is an even integer greater than or equal to four, and a controller configured to control the PMM to mitigate or eliminate magnetic cogging.