BLDC Rotor Magnet Sleeve Structure for Compact Motor Retention
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Solution Overview
Problem
Power tools, such as impact drivers and impact wrenches, face challenges in reducing the size of brushless direct-current motors without compromising power performance, particularly in retaining and securely positioning permanent magnets on the rotor's outer surface to minimize size while maintaining efficiency.
Innovation Solution
The design incorporates a rotor core with surface-mounted permanent magnets, a sleeve for radial constraint, and a fan for axial constraint, along with a support plate that nests bearings within the stator assembly, reducing the motor's length and improving power density by optimizing the placement and retention of magnets and bearings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the rotor size is reduced to minimize motor girth, then the motor fits better in tight spaces, but the permanent magnets become difficult to retain securely on the rotor surface
Solution Approach 1:
The rotor magnet retention structure is divided into multiple functional segments: the rotor core with outer surface, the sleeve that fits over the rotor core, the flange at one end, and the fan at the other end. This segmentation allows each component to perform its specific retention function independently, ensuring secure magnet placement even in a compact rotor design.
Solution Approach 2:
The sleeve is nested over the rotor core, creating a layered structure where the sleeve contains the magnets on its inner surface, which in turn contains the rotor core. This nesting approach maximizes space utilization and provides multiple retention mechanisms within a compact volume, addressing both size reduction and magnet retention requirements.
2Reliability
If conventional motor designs are used, then magnet retention is straightforward, but the motor size and girth increase
Solution Approach 1:
The sleeve serves multiple functions simultaneously: it provides radial containment for the magnets through its cylindrical shape, axial constraint at one end via the flange, and structural support for the rotor assembly. The fan also contributes to axial constraint. This multi-functionality eliminates the need for separate retention components, reducing overall motor size while maintaining reliable magnet retention.
Solution Approach 2:
Instead of relying solely on radial embedding of magnets in the rotor core, the design adds axial dimensionality to magnet retention through the flange and fan structures. This three-dimensional retention approach (radial + axial constraints) provides secure magnet placement without increasing the rotor's radial dimensions, thus maintaining compact motor size.
3Length of moving object
If the motor assembly is compacted to reduce length, then the power tool fits in tighter locations, but the placement and retention of magnets becomes more challenging
Solution Approach 1:
The sleeve is pre-formed with the flange at one end and the fan at the other end, creating a ready-to-assemble retention structure. The magnets are then placed on the sleeve's inner surface during assembly, where their position is automatically constrained by the sleeve's geometry. This preliminary structuring of the retention mechanism simplifies the magnet placement process despite the compact motor length.
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 allows for a compact motor assembly that maintains power performance while reducing the overall size of the power tool, enhancing its fit in tight spaces without sacrificing power delivery.
Implementation Method 1
the fan comprises a radial body having a plurality of blades for generating airflow through the motor
Implementation Method 2
a brushless direct-current (BLDC) motor is provided... a stator including a stator core and a plurality of windings... at least one permanent magnet mounted on an outer surface of the rotor core
Data Source
AI summary
A brushless direct-current (BLDC) motor is provided. The motor includes a stator including a stator core and windings; a rotor shaft disposed within the stator and extending along a longitudinal axis; and a rotor including a rotor core fixedly mounted on the rotor shaft and at least one permanent magnet mounted on an outer surface of the rotor core. A sleeve is provided including a substantially cylindrical body mounted on the at least one permanent magnet and a flange that engages a first axial end of the at least one permanent magnet to constrain the at least one permanent magnet radially and along a first axial direction. Further, a fan is mounted on the rotor shaft and engaging a second axial end of the at least one permanent magnet to constrain the at least one permanent magnet along a second axial direction.