Rotor Grooves and Slits for Stable Cogging Torque
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Solution Overview
Problem
Permanent magnet-embedded type rotary electric machines experience unstable cogging torque fluctuations due to manufacturing errors affecting the dimensions of slits that limit magnetic flux passage, leading to increased manufacturing steps and torque disturbances.
Innovation Solution
The implementation of magnetic flux short-circuit preventing slits and pairs of grooves on the rotor's outer surface, strategically positioned to limit magnetic flux passage and reduce cogging torque, with design angles calculated to minimize manufacturing error impacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If slits are provided in end portions of each magnetic pole to limit magnetic flux passage, then cogging torque is reduced, but manufacturing precision becomes critical and cogging torque fluctuates unstably when dimensions deviate from design
Solution Approach 1:
The invention divides the single flux-limiting function into two segments: internal slits within the rotor and external grooves on the rotor surface. This segmentation allows each element to contribute partially to flux limitation, reducing the sensitivity to dimensional deviations in any single element and stabilizing cogging torque reduction.
Solution Approach 2:
The invention applies different structural features at different locations: internal slits are positioned within the rotor body while external grooves are positioned on the rotor surface. Each location provides a different mechanism for limiting magnetic flux, creating local quality variations that collectively reduce cogging torque more stably than a single uniform structure.
2Object-generated harmful factors
If oblique skew is applied to stator or stepwise skew is applied to rotor to reduce cogging torque, then cogging torque is reduced, but the number of manufacturing steps increases
Solution Approach 1:
Instead of applying skew to the stator or rotor structure (conventional approach), the invention inverts the approach by using radial slits and grooves that limit magnetic flux passage directly. This alternative method achieves cogging torque reduction without requiring complex skewing manufacturing processes.
Solution Approach 2:
The invention extracts the flux-limiting function from the overall rotor structure and implements it through specific slit and groove features. This extraction allows cogging torque reduction to be achieved through simple radial cutting operations rather than complex skewing procedures, reducing manufacturing complexity.
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 stabilizes cogging torque reduction by controlling magnetic flux passage, reducing manufacturing error influences, and enhancing reluctance torque while preventing steel plate damage.
Implementation Method 1
magnetic flux can pass between the rotor and the stator is limited properly even in a situation where a manufacturing error occurs
Data Source
AI summary
Magnetic flux short-circuit preventing slits extend from opposite ends of two permanent magnets in an outer circumferential surface of a rotor toward a center of a magnetic pole. Grooves formed in the outer circumferential surface can be located at a distance from each other symmetrically with respect to the center of the magnetic pole and at a distance from a groove of an adjacent magnetic pole in the outer circumferential surface. Relations are established as θf=n×τs and θs=n×τs where τs designates a pitch of stator winding slots, which pitch is converted into an angle around a rotation center, θf designates an angle between the magnetic flux short-circuit preventing slits, θs designates an angle between the grooves, and n designates a predetermined integer. Thereby, a permanent magnet-embedded type rotary electric machine in which the influence of a manufacturing error can be minimized so that cogging torque can be reduced stably.