Electric Machine Slot Closers for Torque Ripple Reduction
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Solution Overview
Problem
Existing electric machine designs with open slots suffer from torque ripple and other negative characteristics due to the lack of effective slot closure methods, which previous solutions like metal wedges fail to adequately address, especially at low-torque operating conditions.
Innovation Solution
The introduction of slot closers with a nonmagnetic case encapsulating ferromagnetic flux bridges creates nonmagnetic gaps between the flux bridges and the stator teeth, reducing torque ripple by providing a high permeability path for magnetizing flux while preventing excessive leakage at both high and low-torque operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If open slots are used in the stator, then the manufacturing process is simpler, but torque ripple increases and performance deteriorates at low-torque conditions
Solution Approach 1:
A slot closer component is introduced as an intermediary element placed within the open slot. This slot closer includes a nonmagnetic case and a ferromagnetic flux bridge, acting as a mediator between the stator teeth to provide effective slot closure without requiring complex manufacturing processes for the stator itself.
Solution Approach 2:
The slot closer employs composite construction combining nonmagnetic material (case) and ferromagnetic material (flux bridge). This composite structure allows the nonmagnetic case to provide mechanical support and slot closure while the ferromagnetic flux bridge provides the necessary magnetic path, resolving the contradiction between simple manufacturing and torque ripple reduction.
2Ease of manufacture
If metal wedges are used to close slots, then slot closure is achieved, but excessive leakage flux occurs at low-torque operations
Solution Approach 1:
The slot closer provides localized magnetic properties within the slot region. The ferromagnetic flux bridge is positioned specifically to provide a high-permeability path for magnetizing flux where needed, while the nonmagnetic case prevents excessive leakage. This local differentiation of magnetic properties resolves the energy loss issue without sacrificing slot closure capability.
Solution Approach 2:
The invention changes the magnetic parameter (permeability) by introducing materials with different magnetic properties into the slot. The ferromagnetic flux bridge provides high permeability for the desired magnetic path, while the nonmagnetic case provides low permeability to prevent leakage, thereby optimizing flux distribution and reducing energy loss at low-torque conditions.
3Reliability
If slot closers with nonmagnetic case and flux bridge are used, then torque ripple is reduced and performance improves, but device complexity increases
Solution Approach 1:
The slot closer is segmented into distinct functional components: a nonmagnetic case providing mechanical support and slot closure, and a ferromagnetic flux bridge providing the magnetic path. This segmentation allows each component to be optimized for its specific function while maintaining overall simplicity and manufacturability despite the improved performance.
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 torque ripple and improves torque generation characteristics across the operating range by maintaining a high permeability path for magnetizing flux and minimizing leakage, outperforming previous metal wedge designs.
Implementation Method 1
Each slot closers includes a flux bridge surrounded by a nonmagnetic case
Implementation Method 2
providing a high permeability path for magnetizing flux
Implementation Method 3
The case forms nonmagnetic gaps between the flux bridge and the adjacent teeth, respectively, to reduce potential for torque ripple
Data Source
AI summary
An electric machine includes a stator having teeth that define open slots and slot closers disposed in the slots. Each slot closers includes a flux bridge surrounded by a nonmagnetic case. The slot closer is disposed between adjacent ones of the teeth with the case engaging and spanning the adjacent teeth. The case forms nonmagnetic gaps between the flux bridge and the adjacent teeth, respectively, to reduce potential for torque ripple.