Rotor Magnetic Path Entrance Width Variation for Reluctance Torque
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Solution Overview
Problem
Conventional rotary electric machine rotors experience a drop in torque generation efficiency during high-load operations due to significant reduction in q-axis inductance and reluctance torque, primarily because of the design features that lead to unequal reductions in d-axis and q-axis inductance.
Innovation Solution
The rotor design incorporates a central magnet with a pair of circumferential-direction magnets and low permeability regions near the magnet ends, where the width of the magnetic path entrance portions narrows towards the outer peripheral face, allowing for greater reduction in d-axis inductance compared to q-axis inductance, thereby enhancing reluctance torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the magnetic path entrance portions have constant width (conventional design), then the structure is simple and easy to manufacture, but the q-axis inductance drops significantly during high-load operation, reducing torque generation efficiency
Solution Approach 1:
The magnetic path entrance portions are designed with non-uniform width, being narrower at the outer peripheral face and wider at the inner peripheral face. This local variation in geometry creates different magnetic reluctance characteristics at different radial positions, preventing excessive concentration of magnetic flux and maintaining q-axis inductance during high-load operation, thereby improving torque generation efficiency
Solution Approach 2:
The magnetic path entrance portions are designed with asymmetric width distribution in the radial direction. By making the width narrower at the outer periphery and wider at the inner periphery, the design creates an asymmetric magnetic circuit that optimizes flux distribution and maintains inductance characteristics under high-load conditions
2Productivity
If the width of magnetic path entrance portions narrows towards the outer peripheral face, then reluctance torque increases during high-load operation, but the manufacturing precision requirements increase
Solution Approach 1:
The design changes the geometric parameter of the magnetic path entrance portions by varying the width in the radial direction. This parameter variation optimizes the magnetic circuit characteristics to maintain higher q-axis inductance during high-load operation, thereby increasing reluctance torque while managing manufacturing complexity
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 design increases reluctance torque during high-load operations, improving torque generation efficiency by maintaining a higher difference between d-axis and q-axis inductance, thus addressing the inefficiencies in conventional rotor designs.
Implementation Method 1
a low permeability region provided in the vicinity of each of end portions of the central magnet in the circumferential direction, and having a permeability lower than that of a magnetic material, of which the rotor core is made
Implementation Method 2
each of the magnetic poles includes a central magnet provided in the vicinity of an outer peripheral face of the rotor core, a pair of circumferential-direction magnets disposed on both sides of the central magnet in the circumferential direction
Implementation Method 3
a width of a magnetic path entrance portion that is formed between a magnetic-pole inward side face, which is an inward side face of each of the circumferential-direction magnets in the circumferential direction of the magnetic pole, and the low permeability region adjacent to the magnetic-pole inward side face becomes narrower towards the outer peripheral face of the rotor core
Data Source
AI summary
A rotor for a rotary electric machine has a plurality of magnetic poles provided at intervals in a circumferential direction of a rotor core, at an outer periphery of the rotor core. Each of the magnetic poles includes a central magnet, a pair of circumferential-direction magnets disposed on both sides of the central magnet in the circumferential direction such that a spacing between the pair widens towards an outer periphery of the rotor core, and low permeability regions provided in the vicinity of end portions of the central magnet in the circumferential direction, and having a permeability lower than a magnetic material of the rotor core. The rotor core is formed such that a width of a magnetic path entrance portion that is formed between a magnetic-pole inward side face of the circumferential-direction magnet and the adjacent low permeability region decreases towards an outer peripheral face of the rotor core.