Rotor Core Protrusions Reduce Cogging Torque
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Solution Overview
Problem
Existing electric motors in automotive auxiliary systems, such as EPS devices, face challenges in reducing cogging torque and torque ripple, which contribute to vehicle interior vibrations and noise, while also seeking to minimize magnet cost and simplify manufacturing.
Innovation Solution
A rotor core design featuring laminated plates with a magnetic pole structure that includes protrusions on both sides of the outer periphery, forming a storage space for permanent magnets, which reduces cogging torque by moderating magnetic flux distribution and minimizing changes in magnetic flux with magnetic pole width variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If rectangular magnets with uniform magnetization are arranged in the circumferential direction in an annular integral rotor core, then magnet cost can be reduced and manufacturing can be simplified, but the magnetic flux distribution becomes non-sinusoidal, causing increased torque ripple and cogging torque
Solution Approach 1:
The invention applies asymmetry by providing protrusions at specific positions on the magnetic pole outer peripheral surface. These protrusions create an asymmetric geometry that modifies the magnetic flux distribution in the air gap, making it more sinusoidal despite using simple rectangular magnets. This asymmetric design allows the use of cost-effective rectangular magnets while suppressing torque ripple and cogging torque.
Solution Approach 2:
The invention changes geometric parameters of the magnetic pole by adding protrusions with specific dimensions. The protrusions have defined heights, widths, and positions relative to the magnetic pole base, which alters the magnetic flux distribution characteristics. By optimizing these geometric parameters, the patent achieves sinusoidal flux distribution and reduced torque fluctuations without changing the magnet shape or material.
2Object-generated harmful factors
If the magnetic pole is designed with protrusions to achieve sinusoidal magnetic flux distribution, then torque ripple and cogging torque are reduced, but the magnetic pole width increases, requiring larger rotor core dimensions
Solution Approach 1:
The invention addresses the width increase issue by utilizing the axial dimension (depth of the rotor core) to compensate for the radial dimension (magnetic pole width). The protrusions extend in the axial direction, allowing the magnetic flux distribution to be controlled through axial geometry rather than requiring increased radial width. This dimensional transition maintains a compact rotor core while achieving the desired magnetic characteristics.
3Power
If the air gap length is reduced to compensate for torque loss in interior permanent magnet type motors, then torque can be maintained, but manufacturing precision requirements increase and the risk of magnetic flux leakage at the magnet storage space bridge increases
Solution Approach 1:
The invention converts the potential harm of magnetic flux leakage at the magnet storage space bridge into a benefit by designing the protrusions to strategically guide and control the magnetic flux paths. The protrusions act as flux concentrators that direct the magnetic flux through desired paths, reducing unwanted leakage while maintaining torque output. This allows for a relaxed air gap design that is more tolerant of manufacturing variations.
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 cogging torque and torque ripple, enhancing manufacturing efficiency and reducing the required dimensional accuracy and magnet usage, thereby suppressing vibrations and noise in vehicle interiors.
Implementation Method 1
the magnetic flux distribution will not be sinusoidal shape, and the torque ripple and cogging torque cannot be sufficiently reduced
Implementation Method 2
an electromagnetic excitation force generated between the stator and the rotor of the electric motor
Data Source
AI summary
A cogging torque in a rotary electric machine is sufficiently reduced. The rotor core includes a magnetic pole having the base formed on the outer peripheral side of the storage space. A plurality of magnetic poles are provided in the circumferential direction, and include the first protrusion protruding from the base in one circumferential direction along the outer periphery of the rotor core, and the second protrusion which is provided on the opposite side to with the base interposed and protrudes from the base along the outer periphery of the rotor core in the other circumferential direction. At least one of the first protrusion and the second protrusion is located on the outer peripheral side from the first line segment which is a virtual line connecting the end of the first protrusion and the end of the second protrusion, and is provided such that the space is provided with respect to the first line segment.