Displaced Magnet Pole Arrangement for Cogging Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Permanent-magnet based AC rotating electrical machines experience significant cogging torque due to the interaction between rotor and stator geometry, leading to efficiency, reliability, vibration, and noise issues, with existing solutions either being costly, complex, or compromising other design considerations.
Innovation Solution
The displacement of magnet poles from their conventional positions, with specific angular displacement patterns determined by the formula D = 2p - 1N, where D is the angular displacement, p is the magnet pole number, and N is the number of magnet poles, to reduce cogging torque while maintaining mechanical balance and flexibility in design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If magnet poles are uniformly spaced around the rotor circumference, then the machine structure is simple and easy to manufacture, but cogging torque is significant causing vibration and noise
Solution Approach 1:
The patent applies asymmetry by displacing magnet poles from their conventional uniform positions. The displacement follows a specific pattern where the angular position of each magnet pole is shifted by an amount proportional to its pole number, creating an asymmetric distribution that eliminates the symmetry causing cogging while maintaining manufacturability
Solution Approach 2:
The patent changes the angular position parameter of magnet poles from uniform spacing to a displaced pattern. The displacement amount is calculated based on the formula involving the number of magnet poles and their individual pole numbers, transforming the geometric parameter to reduce cogging torque
2Loss of information
If the number of winding slots is an integral multiple of the number of magnet poles, then the magneto-motive force contains minimized harmonics, but cogging is pronounced
Solution Approach 1:
The patent breaks the symmetry between winding slots and magnet poles by displacing the magnet poles. This asymmetric arrangement disrupts the direct alignment that causes cogging when the slot number is an integral multiple of pole number, while preserving the harmonic benefits of the integral multiple relationship
3Object-generated harmful factors
If magnet poles are displaced to reduce cogging, then cogging torque is minimized, but mechanical balance may be affected
Solution Approach 1:
The patent carefully controls the displacement parameter to achieve cogging reduction while maintaining mechanical balance. The displacement follows a specific mathematical pattern that ensures the center of gravity remains at the rotor axis, preventing mechanical imbalance despite the asymmetric magnet pole positions
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 approach effectively reduces cogging torque by altering the potential energy positions of the rotor relative to the stator, minimizing unwanted vibrations and noise, and allows for simpler construction and analysis, while maintaining mechanical balance and reducing harmonic content.
Implementation Method 1
permanent-magnet based, alternating current (AC), rotating electrical machines
Implementation Method 2
the attraction between the rotor and the stator is at a maximum
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The present invention provides an electrical machine (1) with reduced cogging. The magnet poles (3) of the electrical machine are comprised of at least two separate groups of at least two circumferentially adjacent magnet poles. One of the circumferentially outer magnet poles (3a, 3h) in one of the groups of magnet poles is defined as being in its reference position. The reference position of each other magnet pole (3b to 3g) is defined as the position each other magnet pole would occupy if all the magnet poles were equally circumferentially spaced around the first or second body and the one circumferentially outer pole was in its reference position. At least one of the circumferentially outer magnet poles (3a, 3h) in each group is sited in its reference position. At least one magnet pole (3a to 3g) in each group is a displaced magnet pole and is sited in a position that is displaced from its reference position by an amount that is not equal to an integral multiple of the reference angular pitch of the winding slots. The displacement of the magnet poles (3) provides a pronounced reduction in cogging.