Rotor Core Slits for Permanent Magnet Motor Stress Absorption
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Solution Overview
Problem
Permanent magnet type rotating electric machines face issues with deformation of the rotor core due to stress generated from the difference in thermal expansion between permanent magnets, fillers, and the rotor core, leading to reduced output performance and reliability.
Innovation Solution
Incorporating holes in the rotor core to absorb stress, specifically first and second holes arranged to absorb stress parallel and normal to the magnetic pole surfaces, respectively, while maintaining the magnetic flux path, thereby preventing deformation and ensuring the strength of the bridge portion between openings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If permanent magnets are fixed using adhesive infilling openings, then the permanent magnets can be secured in position, but the adhesive may have poor fill properties leading to permanent magnet wobble and rotor core damage due to stress concentration
Solution Approach 1:
The invention changes the physical state of the filler from solid (adhesive) to liquid (molten die-cast filler) during the filling process. The liquid filler can flow into and completely fill the gaps between permanent magnets and rotor core, ensuring complete coverage and eliminating air pockets. After curing, the filler becomes solid and provides strong fixation. This parameter change from liquid to solid state resolves the contradiction by ensuring both complete fill properties and strong mechanical strength.
Solution Approach 2:
The invention uses a composite structure consisting of the rotor core, permanent magnets, and filler material working together as an integrated system. The filler material acts as a bonding phase that connects the permanent magnets to the rotor core, creating a composite structure that combines the magnetic properties of the permanent magnets with the mechanical strength of the rotor core and filler. This composite approach resolves the contradiction by distributing stresses across multiple materials with complementary properties.
2Reliability
If molten die-cast filler is injected with pressure to fill gaps between permanent magnets and rotor core, then the permanent magnets can be firmly fixed, but stress is generated at the rotor core due to difference in coefficient of linear expansion among materials
Solution Approach 1:
The invention introduces grooves in the rotor core that are filled with filler material before the permanent magnets are installed. These pre-filled grooves act as cushioning zones that can absorb thermal expansion stresses. When temperature changes occur during operation, the filler material in the grooves deforms to accommodate differential expansion between the permanent magnets and rotor core, preventing stress concentration and potential damage to the rotor core.
Solution Approach 2:
The filler material used in the invention has properties that allow it to accommodate dimensional changes. The material structure enables it to absorb and dissipate thermal stresses through controlled deformation. This porous or flexible filler structure allows the system to handle coefficient of linear expansion differences without generating damaging stresses in the rotor core, while still providing firm fixation of the permanent magnets.
3Adaptability or versatility
If the circumferential dimension of openings is set greater than the circumferential dimension of permanent magnets to accommodate dimensional variations, then permanent magnets can be fixed reliably, but gaps are formed that require filler injection increasing manufacturing complexity
Solution Approach 1:
The invention utilizes the phase change property of the filler material from liquid to solid. The filler is injected in liquid (molten) state where it can flow and fill irregular gaps of varying sizes created by dimensional tolerances. After injection, the filler is cooled and solidified, providing structural support. This parameter change allows the same filler material to adapt to various gap sizes without requiring precise dimensional control, thereby accommodating dimensional variations while maintaining a relatively simple manufacturing process.
Solution Approach 2:
The filler material acts as an intermediary substance between the permanent magnets and the rotor core. It fills the gaps created by dimensional variations and provides a bonding interface. The groove structures serve as intermediary channels that guide the filler material to the required locations. This intermediary approach allows the system to accommodate dimensional tolerances without requiring complex precision machining or assembly procedures.
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 suppresses rotor core deformation, maintains uniform air gaps, and ensures high output performance and reliability by absorbing stress without obstructing the magnetic flux, thus preventing damage to the rotor core.
Implementation Method 1
stress may generated at the rotor core due to a difference in coefficient of linear expansion among the permanent magnets, the heated and cured filler and the rotor core
Implementation Method 2
gaps extending in an axial direction are respectively formed on opposite sides in circumferential direction of the permanent magnet. The gaps are filled with pressure with a molten die-cast filler, which is then cured
Data Source
AI summary
A rotor core is provided with a plurality of slits extending in the rotation shaft direction, independently of openings. The first slit is arranged at the center of the magnetic pole of the rotor core to be capable of absorbing stress acting on an inner circumferential surface of each opening in a direction normal to a main surface of a permanent magnet. The second slit is arranged between the magnetic poles of the rotor core to be capable of absorbing stress acting in parallel with the main surface of the permanent magnet. Thus, the rotor core is prevented from deforming in a radial outward direction. Further, by forming the first and second slits each in a form not interfering the magnetic path of the magnetic flux by the stator passing inside the rotor core, the motor performance is ensured.