Trapezoidal Permanent Magnet Motor for Low Cogging Torque
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Solution Overview
Problem
Existing permanent magnet electric motors suffer from significant cogging torque ripple, leading to vibration, noise, and speed fluctuations, which affect smooth operation and performance, especially in variable speed drives and high-precision positioning systems.
Innovation Solution
The design features a stator and rotor with isosceles trapezoidal permanent magnets symmetrically aligned, forming 90° angles with the central line, reducing cogging torque ripple by optimizing magnetic flux distribution and minimizing magnetic flux leakage through trapezoidal slots and air gaps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If rectangular permanent magnets are used in the rotor, then the motor structure is simple and easy to manufacture, but the cogging torque ripple is large causing vibration and noise
Solution Approach 1:
The patent applies asymmetry by changing the permanent magnet cross-section from a symmetric rectangular shape to an asymmetric isosceles trapezoidal shape. The trapezoidal magnet has different width dimensions at the top and bottom, creating an asymmetric magnetic field distribution that reduces cogging torque ripple. The magnetic lines of force are designed to form 90° angles with the side faces, and the side faces form specific included angles (5-20°, preferably 8°) with the central line, optimizing the magnetic flux distribution to minimize harmful cogging effects while maintaining manufacturing feasibility.
2Ease of manufacture
If rectangular permanent magnets are used, then the manufacturing process is simple, but the motor produces vibration and noise due to large cogging torque
Solution Approach 1:
The asymmetric isosceles trapezoidal magnet design modifies the magnetic field distribution in the air gap, reducing the periodic fluctuations that cause cogging torque. This asymmetry in magnet geometry leads to smoother torque output, thereby reducing vibration and noise during motor operation, while the standardized trapezoidal shape remains compatible with conventional manufacturing processes.
3Device complexity
If conventional rectangular magnets are used, then the motor structure is straightforward, but speed fluctuation occurs affecting smooth operation
Solution Approach 1:
The isosceles trapezoidal magnet configuration creates a more uniform magnetic flux distribution in the air gap compared to rectangular magnets. The asymmetric geometry with optimized included angles (5-20°) between the side faces and central line ensures that magnetic lines of force intersect the air gap at 90°, reducing magnetic reluctance variations and resulting in more stable rotational speed with reduced fluctuations.
4Reliability
If rectangular permanent magnets are used, then the motor can operate, but cogging torque ripple amplifies vibration and noise at mechanical resonance frequencies
Solution Approach 1:
The asymmetric isosceles trapezoidal magnet design reduces the magnitude and frequency components of cogging torque ripple that would otherwise excite mechanical resonance in the motor structure. By optimizing the magnet geometry with specific included angles (5-20°), the patent minimizes the harmonic content of cogging torque, preventing resonance amplification and reducing vibration and noise even during variable speed operation.
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 significantly reduces cogging torque ripple by 81.55%, minimizing vibration and noise, enhancing smooth operation and high-precision positioning capabilities in speed control systems.
Implementation Method 1
the magnetic lines of the permanent magnet are symmetric with reference to the central line of the permanent magnet and form included angles of 90° with a left side face of the trapezoid or a right side face of the trapezoid of the permanent magnet
Implementation Method 2
an air gap is formed between an outer circumferential surface of the rotor component and an inner cambered surface of the stator component
Data Source
AI summary
A permanent magnet electric motor having reduced cogging torque ripple, comprising a stator component, permanent magnets and a rotor component, wherein the rotor component is mounted in the center of the stator component, and an air gap is formed between an outer circumferential surface of the rotor component and an inner cambered surface of the stator component. Each permanent magnet has a cross-section of an isosceles trapezoid, and the magnetic lines of the permanent magnet are symmetric relative to the center line of the magnet and orthogonal to the trapezoid faces. According to the present disclosure, by means of changing the shape of the permanent magnet, the cogging torque ripple of the permanent magnet electric motor can be reduced in order to reduce the vibration and noise caused by the cogging torque ripple and the fluctuation in speed, so that the permanent magnet electric motor runs stably.