Motor Case Arc Supports for Low-Load Stator Press-Fit Assembly
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Solution Overview
Problem
Conventional inner-rotor type brushless motors face issues with increased press-fit load and decreased assembling accuracy due to the gapless accommodation of the stator core in the motor case, leading to variations in rotational resistance.
Innovation Solution
The brushless motor design incorporates a case with multiple flat and arced parts in the circumferential direction, supporting the stator only by inner circumferential surfaces with arc-shaped connections, reducing press-fit load and ensuring accurate alignment of the stator and rotor units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the stator core is gaplessly accommodated in the motor case, then the structural compactness is improved, but the press-fit load increases and assembling accuracy decreases
Solution Approach 1:
The case is segmented into multiple flat parts and connection parts, with the stator supported only at specific inner circumferential surfaces of the connection parts. This segmentation approach allows the stator to be accommodated compactly while limiting contact points to maintain positioning accuracy and reduce press-fit load.
Solution Approach 2:
The inner circumferential surfaces of the connection parts are formed with arc-shaped cross-sections having the case center as the radius center. This local quality modification at the support points ensures accurate radial positioning of the stator while maintaining overall structural compactness.
2Stability of the object's composition
If the stator core is gaplessly accommodated in the motor case, then the structural compactness is improved, but the press-fit load increases
Solution Approach 1:
The case is divided into flat parts and connection parts, with the stator supported only at the inner circumferential surfaces of the connection parts. This segmentation reduces the contact area and distributes the press-fit load to specific locations, thereby reducing the overall press-fit load while maintaining compact structure.
Solution Approach 2:
The inner circumferential surfaces of the connection parts are formed with arc-shaped cross-sections. This curved surface design allows the stator to be supported at optimal points, reducing the press-fit load while maintaining structural compactness and accurate positioning.
3Force
If adhesive is used to fill the gap between stator core and motor case, then the press-fit load is reduced, but the centers of stator core and motor case may be displaced
Solution Approach 1:
The adhesive filling approach is replaced by a structural design where the stator is supported only by the inner circumferential surfaces of the connection parts. This extraction of the adhesive function eliminates the risk of center displacement while still reducing press-fit load through the arc-shaped support surfaces.
Solution Approach 2:
The arc-shaped inner circumferential surfaces of the connection parts serve as an intermediary structure between the stator and case. This intermediary design provides precise radial positioning and supports the stator without requiring adhesive, thereby maintaining assembling accuracy while reducing press-fit load.
Data Source
AI summary
A case 31 has a total of first to sixth flat parts 32A to 32F arranged in a circumferential direction of the case 31 and a total of first to sixth arced parts 32a to 32f connecting adjacent flat parts with each other. When viewed in an axial direction of a shaft 44, inner circumferential surfaces CF of the first to sixth arced parts 32a to 32f are each formed in an arced shape having a radius R1 and a center AC of the case 31 as the center. In addition, since the stator 35 is only supported by the inner circumferential surfaces CF (six in total), the press-fit load of the stator 35 with respect to the case 31 can be reduced, and it is possible to increase the assembling accuracy.