Overmolded BLDC Rotor Core With Radial Projections for Magnet Alignment
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Solution Overview
Problem
Power tools, such as impact drivers and wrenches, face challenges in reducing the size of brushless direct-current motors without compromising power performance, particularly in retaining and securely mounting permanent magnets on the rotor surface.
Innovation Solution
A brushless direct-current motor design featuring a rotor core with radial projections and a mold structure that secures a magnet ring with arcuate and flat inner surfaces, providing axial and rotational support for the permanent magnet, allowing for efficient retention and alignment without adhesives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the rotor size is reduced to decrease motor length and girth, then the motor size is reduced, but the retention and secure mounting of permanent magnets on the rotor surface becomes difficult
Solution Approach 1:
The rotor core is segmented into multiple radial projections that extend outwardly, creating distinct mounting zones for permanent magnets. Each projection provides a dedicated surface for magnet attachment, allowing secure retention even in a compact rotor configuration. This segmentation enables reliable magnet mounting while maintaining reduced rotor dimensions.
Solution Approach 2:
The mold structure is received within the axial channels formed between radial projections, creating a nested configuration where the mold structure fits into the spaces between projections. This nesting approach allows the mold structure to be integrated within the compact rotor geometry without increasing overall rotor size, while still providing secure magnet retention.
2Device complexity
If conventional motor designs are used, then the motor structure is simple, but the motor size is large and power density is reduced
Solution Approach 1:
The design transitions from conventional two-dimensional magnet placement on a flat rotor surface to a three-dimensional configuration using radial projections that extend outwardly. This dimensional change allows magnets to be positioned at multiple radial distances from the rotor center, optimizing magnetic field distribution and increasing power density within a compact volume.
Solution Approach 2:
The mold structure serves as an intermediary component that facilitates secure magnet retention on the rotor core. It is formed in contact with the radial projections and provides a mounting interface for permanent magnets, enabling reliable attachment while maintaining the compact rotor design. This intermediary structure resolves the conflict between simple construction and high power density.
3Area of moving object
If the rotor is made compact to reduce motor girth, then the motor girth is reduced, but the alignment and retention features for magnets become more difficult to implement
Solution Approach 1:
The radial projections are designed with asymmetric geometries, including arcuate inner surfaces and flat inner surfaces at different angles. This asymmetry provides built-in alignment features that guide magnet placement during manufacturing, ensuring proper orientation even in the compact rotor configuration. The varying surface angles create natural positioning references that simplify magnet alignment.
Solution Approach 2:
The radial projections and mold structure are pre-formed with integrated alignment features before magnet assembly. The arcuate and flat surfaces are predetermined during rotor manufacturing, providing ready-made alignment references that guide magnet placement. This preliminary preparation of alignment features simplifies the subsequent magnet assembly process despite the compact rotor geometry.
Data Source
AI summary
A brushless direct-current (BLDC) motor is provided. The motor includes a stator including a stator core, stator teeth, and windings; a rotor shaft disposed within the stator and extending along a longitudinal axis; and a rotor. The rotor includes a rotor core including an inner body mounted on the rotor shaft and radial projections projecting outwardly from the inner body, a permanent magnet mounted on an outer end of the radial projections, and a mold structure formed in contact with the radial projections and configured to secure the permanent magnet to the rotor core.