Permanent Magnet Rotor Positional Shifts for Cogging Torque Reduction
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Solution Overview
Problem
Conventional methods for reducing cogging torque in permanent magnet type rotating electric machines, such as those used in electric power steering devices, are inefficient and unsuitable for mass production due to the need for precise positioning and symmetry of permanent magnets, which can result in large cogging torque variations.
Innovation Solution
The solution involves controlling the circumferential positional shifts of permanent magnets to align either in the same direction or in opposite directions, canceling out the order component of the cogging torque equal to the number of slots, thereby reducing the overall cogging torque without requiring precise symmetry or shape control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the positions of permanent magnets are randomly shifted and shapes deviate randomly, then manufacturing is easier and productivity is improved, but the cogging torque becomes extremely large
Solution Approach 1:
The invention changes the parameter control approach from requiring precise positional accuracy and shape symmetry to controlling the direction and amount of positional shifts. By specifying that all permanent magnets should be shifted in the same circumferential direction by amounts within a predetermined range, the patent transforms an precision-critical parameter into a range-based parameter, thereby improving manufacturing efficiency while controlling cogging torque.
Solution Approach 2:
The invention intentionally introduces controlled asymmetry by allowing permanent magnets to be shifted in the same circumferential direction rather than maintaining perfect symmetry. This controlled asymmetric positioning, when combined with specific shift amount ranges, actually reduces the cogging torque compared to perfectly symmetric positioning with random variations, thus resolving the contradiction between manufacturing ease and harmful factor reduction.
2Object-generated harmful factors
If precise positioning and symmetry control of permanent magnets is implemented, then cogging torque is reduced, but manufacturing complexity increases and productivity decreases
Solution Approach 1:
The patent transforms the control parameters from precise positional coordinates and shape dimensions to simpler directional shifts and amount ranges. This parameter transformation simplifies the manufacturing process while achieving the same cogging torque reduction effect, thereby resolving the contradiction between harmful factor reduction and productivity maintenance.
Solution Approach 2:
The invention applies different control requirements to different aspects of permanent magnet positioning: it controls the circumferential shift direction and amount within specific ranges, but does not control radial position or shape details. This selective local quality control approach reduces manufacturing complexity while effectively controlling cogging torque.
3Ease of manufacture
If permanent magnets are positioned with random shifts and shape deviations, then manufacturing is simpler, but the order component of cogging torque equal to the number of slots increases
Solution Approach 1:
The patent changes the positioning parameter from random variation to controlled directional shift within a specific range. By specifying that all magnets should shift in the same circumferential direction by amounts within a predetermined range (rather than random shifts), the invention simplifies manufacturing while specifically targeting the reduction of the order component of cogging torque equal to the number of slots.
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 the cogging torque component equal to the number of slots, improving productivity and enabling mass production by simplifying the positional shift patterns and reducing the impact of shape deviations, while maintaining motor characteristics.
Implementation Method 1
a rotor (10) including a rotor core (11) and a plurality of permanent magnets (15) arranged on a periphery of the rotor core (11)
Data Source
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AI summary
A permanent magnet type rotating electric machine includes: a rotor including a rotor core having a polygonal shape and a plurality of permanent magnets; and a stator including a stator core and armature windings, in which, when the number of poles is M, the number of slots is N, M permanent magnets are sequentially numbered from first to M-th in a circumferential direction, and a positional shift amount in the circumferential direction from a corresponding one of equiangularly arranged reference positions, each being at the same radial distance from a center of a rotating shaft, for an i-th (i=1, 2, ..., M) permanent magnet is hi, M unit vectors in total, each being in an angular direction of 2πN(i-1)/M (rad), are defined, and a sum of M vectors obtained by multiplying the unit vectors respectively by the positional shift amount hi is smaller than a maximum value of an absolute value of the positional shift amount hi.