Rotor Core Inserts for Centrifugal Stability
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Solution Overview
Problem
Current rotor cores for electric machines face challenges in withstanding centrifugal forces without reducing torque due to increased flux leakage, which is costly to address through traditional methods like thickening or altering the rotor core's geometry.
Innovation Solution
A rotor core design featuring a core stack of lamination plates with axial apertures for magnets and radially extending inserts made from ferrous or austenitic materials to provide structural stability and prevent flexing, while minimizing flux leakage by using non-ferrous or bi-phase inserts to support the lamination plates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of the web or bridge is increased to reduce stress from centrifugal force, then structural strength is improved, but torque is reduced due to increased flux leakage
Solution Approach 1:
The patent applies selective heat treatment (austenitic transformation) to specific local regions of the rotor core - specifically the web and bridge portions - to create zones of enhanced mechanical strength exactly where centrifugal stresses are highest. This localized material property modification allows the rotor core to withstand centrifugal forces without requiring a global increase in thickness that would cause flux leakage.
2Strength
If the arc radius of the slot is increased to reduce stress, then structural strength is improved, but torque is reduced due to increased flux leakage
Solution Approach 1:
The selective heat treatment is applied to the bridge regions adjacent to the magnet slots, strengthening these specific areas to bear the centrifugal loads without requiring an increase in the slot arc radius. This maintains the original slot geometry and magnetic flux paths while providing the necessary mechanical support.
3Strength
If selective heat treatment is applied to strengthen the rotor core, then structural strength is improved without increasing flux leakage, but manufacturing cost increases significantly
Solution Approach 1:
The selective heat treatment process targets only the specific regions (web and bridges) that require enhanced strength, rather than treating the entire rotor core. This localized approach reduces the overall heat treatment time, energy consumption, and process complexity, thereby lowering manufacturing costs compared to full-core heat treatment while still achieving the necessary mechanical properties.
4Strength
If the cross section is increased to provide strength, then structural strength is improved, but torque is reduced due to increased flux leakage
Solution Approach 1:
The patent changes the material parameters (microstructure and magnetic properties) of specific rotor core regions through selective heat treatment. By transforming the steel microstructure to austenitic phases in the web and bridge areas, the material achieves enhanced mechanical strength without increasing the physical cross-sectional area, thereby avoiding any increase in flux leakage.
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 design enhances structural integrity to withstand centrifugal forces without reducing torque, allowing for smaller magnets or increased motor torque and speed, thus improving cost and packaging efficiency.
Implementation Method 1
each of the at least one insert includes portions formed from a ferrous material and portions formed from an austenitic material
Implementation Method 2
radial forces exerted on the plurality of lamination plates during operation of the electric motor
Data Source
AI summary
A rotor core for an electric motor includes a core stack including a plurality of lamination plates, each lamination plate including a plurality of apertures formed therein, the plurality of apertures of each of the lamination plates axially aligned and defining a plurality of axial magnet slots extending through the core stack and adapted to support a plurality of permanent magnets therein, and at least one insert extending axially through the core stack and adapted to provide radial structural stability to the plurality of lamination plates to prevent portions of the plurality of lamination plates adjacent the plurality of magnet slots from flexing due to radial forces exerted on the plurality of lamination plates during operation of the electric motor.