IPM Rotor Arc Profile for Cogging Torque Suppression
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Solution Overview
Problem
Existing rotating electric machines with Interior Permanent Magnet (IPM) rotors face challenges in reducing cogging torque, which affects their efficiency and performance.
Innovation Solution
The design incorporates a rotor core with permanent magnets and outer core portions arranged in a specific arc shape, where the radially outer surface of the outer core portions is closer to the rotation axis, reducing the displacement from a reference circle, and includes protruding portions of the permanent magnets to enhance magnetic flux utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the radially outer surface of the outer core portions is designed with a large arc shape extending far inward, then cogging torque is reduced, but the displacement amount becomes excessively large which may affect manufacturing precision and structural integrity
Solution Approach 1:
The patent applies parameter changes by optimizing the arc shape parameters of the radially outer surface of the outer core portions. Specifically, it defines that the displacement amount from the reference circle should be smaller than the maximum thickness of the permanent magnets, transforming the geometric parameters to achieve both cogging torque reduction and manufacturing feasibility. This parameter optimization resolves the contradiction by finding the optimal range that balances torque reduction with structural and manufacturing requirements.
2Stability of the object's composition
If the arc shape of the radially outer surface extends far inward to reduce cogging torque, then magnetic pole switching becomes smoother, but the structural complexity of the rotor core increases
Solution Approach 1:
The patent applies spheroidality by designing the radially outer surface of the outer core portions with a specific arc shape that is convex in the circumferential direction. This curved geometry smooths the magnetic pole switching by creating a gradual transition between adjacent magnetic poles, reducing abrupt changes in magnetic flux. The arc shape continuously transitions from the magnetic pole center toward both sides, providing smooth magnetic field distribution while maintaining a relatively simple overall rotor core structure.
3Object-generated harmful factors
If the displacement amount of the arc-shaped surface is increased to reduce cogging torque, then magnetic flux distribution improves, but the volume of the rotor core decreases which may affect strength
Solution Approach 1:
The patent applies parameter changes by establishing a specific constraint on the displacement amount: it should be smaller than the maximum thickness of the permanent magnets in an axial view. This parameter constraint ensures that while the arc shape is sufficient to reduce cogging torque and improve magnetic flux distribution, the rotor core maintains adequate volume and structural strength. The parameter optimization balances magnetic performance with mechanical strength requirements.
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 configuration effectively suppresses cogging torque and increases magnet torque, leading to improved efficiency and reduced energy losses in the rotating electric machine.
Implementation Method 1
permanent magnets embedded in the rotor core
Implementation Method 2
magnet torque generated by the permanent magnets
Implementation Method 3
reluctance torque generated by outer core portions located radially outside the permanent magnets
Data Source
AI summary
A rotor has a plurality of magnetic poles each including one of permanent magnets and one of outer core portions. Each of the outer core portions has a radially outer surface that has an arc shape such that the radially outer surface becomes closer to a rotation axis of the rotor as it extends from a magnetic-pole center of the magnetic pole toward both sides in a circumferential direction. A reference circle is defined which has a diameter equal to a maximum diameter of the rotor core and centers on the rotation axis. An outer circumferential surface of the rotor core has, at intersections between the arc-shaped radially outer surfaces of the outer core portions, maximum displacement portions that are most displaced from the reference circle radially inward. A displacement amount of the maximum displacement portions from the reference circle is smaller than a maximum thickness of the permanent magnets.