Outer-Rotor String Trimmer Motor With Adhesive-Free Magnet Retention
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Solution Overview
Problem
Existing string trimmers face challenges in using outer-rotor motors due to complexity and cost, which can affect efficiency and durability, particularly in holding permanent magnets and managing heat generated by the motor.
Innovation Solution
The string trimmer incorporates an outer-rotor motor with a rotor assembly that includes a magnet base with teeth and an outer ring to hold permanent magnets in place without adhesives, and a heat sink with a plate-like shape and fins to absorb and dissipate heat, while sealing the motor housing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an outer-rotor motor is used in a string trimmer, then torque and efficiency are improved, but device complexity and cost increase
Solution Approach 1:
The patent combines multiple functions into the heat sink component: it serves as both a thermal management device and a structural support element that seals the motor housing. This merging reduces the overall number of parts needed, thereby reducing device complexity while maintaining the torque advantages of the outer-rotor motor configuration
Solution Approach 2:
The heat sink is designed with multi-functionality, acting simultaneously as a heat dissipation device, a structural support, and a sealing element for the motor housing. This universal component approach reduces complexity by eliminating the need for separate sealing components and support structures
2Power
If an outer-rotor motor is used in a string trimmer, then torque and efficiency are improved, but manufacturing cost increases
Solution Approach 1:
The patent combines multiple functions into the heat sink component: it serves as both a thermal management device and a structural support element that seals the motor housing. This merging reduces the overall number of parts needed, thereby reducing device complexity while maintaining the torque advantages of the outer-rotor motor configuration
Solution Approach 2:
The heat sink structure provides self-sealing of the motor housing through its integrated design, eliminating the need for additional sealing components. This self-service approach reduces manufacturing steps and assembly complexity, thereby reducing overall manufacturing cost
3Power
If permanent magnets are held in the rotor assembly, then magnetic flux and torque are maximized, but complexity increases due to holding mechanisms
Solution Approach 1:
The patent integrates the permanent magnet holding function into the rotor assembly structure itself, combining magnetic retention with rotational support. This merging eliminates separate holding mechanisms while maintaining maximum magnetic flux for optimal torque production
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 design enhances the efficiency and durability of the string trimmer by maximizing magnetic flux, reducing complexity, and effectively managing heat, thus extending the tool's operating life and usability.
Implementation Method 1
a heat sink attached to the motor housing, the heat sink configured to: support and position the stator assembly inside the interior chamber and within the rotor assembly; absorb heat generated by the stator assembly
Implementation Method 2
the exterior surface includes: fins configured to dissipate the heat absorbed by the heat sink to an environment
Implementation Method 3
The plurality of windings may be energized electronically in a sequence (i.e., electronically commutated) to induce magnetic poles in the stator, which interact with the fixed magnetic poles of the permanent magnets to turn the rotor
Data Source
AI summary
A tool such as a string trimmer having an outer-rotor motor is disclosed. The tool includes a motor housing configured to align a rotor assembly, a stator assembly, a bearing support structure that fully pilots and supports the rotor assembly on one side of the motor housing, and a heat sink that fully supports the stator assembly on another side of the motor housing. The heat sink seals the motor housing from debris and is configured to absorb heat generated by the outer-rotor motor without added airflow from a fan or from openings. The disclosed outer-rotor motor requires no adhesives to hold magnets, thereby simplifying fabrication and improving magnet performance.