Rotary Electric Machine Rotor Bridge Design for Centrifugal Force Resistance
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Solution Overview
Problem
High-speed rotation in electric-drive vehicles generates excessive heat and centrifugal stress in permanent magnets, which existing cooling methods fail to adequately address, especially in motors with large shaft sizes.
Innovation Solution
A rotary electric machine design featuring a stator with an annular core and teeth portions, a rotor with magnetic material and V-shaped permanent magnets, flux barriers, and strategically placed bridge parts to manage magnetic flux and reduce eddy-current loss and centrifugal force resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high speed rotation is achieved, then motor output is improved, but heat generation in permanent magnet increases
Solution Approach 1:
The rotor core is segmented into multiple regions: permanent magnet regions, flux barrier regions, first bridge parts, and second bridge parts. This segmentation creates distinct functional zones that control magnetic flux paths and reduce eddy-current loss while maintaining structural integrity during high-speed rotation
Solution Approach 2:
Different regions of the rotor core are given different magnetic properties and structural characteristics. The flux barriers provide magnetic isolation, the first bridge parts provide mechanical support, and the second bridge parts provide magnetic flux paths. This local differentiation optimizes both heat management and centrifugal force resistance
2Temperature
If cooling structure is added to permanent magnet, then heat exchange is improved, but centrifugal force resistance deteriorates
Solution Approach 1:
The cooling function is merged with the structural support function. The first bridge parts serve dual purposes: providing mechanical support against centrifugal forces and creating magnetic flux paths that reduce eddy-current loss. The flux barriers simultaneously provide magnetic isolation and structural framework for heat management
Solution Approach 2:
The flux barriers and bridge parts act as intermediary structures between the permanent magnets and the rotor core. These intermediaries manage both thermal and mechanical loads, transferring heat away from magnets while distributing centrifugal stresses throughout the rotor structure
3Loss of energy
If flux barrier is provided at both ends of permanent magnet, then magnetic flux leakage is reduced, but device complexity increases
Solution Approach 1:
The flux barriers serve multiple functions simultaneously: they provide magnetic isolation to reduce flux leakage, create structural support frameworks, define cooling passage geometries, and contribute to the overall rotor mechanical strength. This multi-functionality reduces the need for separate dedicated components
4Loss of energy
If bridge part width is reduced to decrease eddy-current loss, then eddy-current loss is reduced, but centrifugal force resistance deteriorates
Solution Approach 1:
The solution moves from considering only the radial dimension to incorporating circumferential and axial dimensions. The bridge parts are optimized in three dimensions, with specific width ratios in different directions. The first bridge parts extend axially to provide structural support while the second bridge parts are optimized circumferentially for magnetic flux management
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 effectively reduces magnetic flux leakage, minimizes eddy-current loss, and enhances centrifugal force resistance, maintaining magnetic strength and torque efficiency during high-speed rotation.
Implementation Method 1
a magnetic flux leaked from the permanent magnet mostly passes the first bridge from an N-pole, enters an S-pole, and returns to the N-pole from the inner peripheral part of the rotor
Implementation Method 2
permanent magnets supported on the rotor core... a stator winding wound therearound
Implementation Method 3
heat generation in the magnet during high speed rotation can be a disadvantage... securing centrifugal force resistance for the permanent magnet
Data Source
AI summary
A rotary electric machine, in which α>β is established when the teeth portion has a width α in a circumferential direction thereof, a rotation center of the rotor and one of corners, which is on a rotor surface side, on both ends of each of the permanent magnets are connected by a straight line, a center between an N-pole and an S-pole of the permanent magnets is on a q-axis, and an angle formed by two straight lines on the q-axis side is β, a first bridge part is provided between a flux barrier provided at the rotor core and the rotor surface, and γ>δ is established when the first bridge part has a minimum width γ, and the flux barrier has a minimum width δ on the q-axis.