Canned BLDC Motor Cooling for Compact Power Tools
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Solution Overview
Problem
There is a need for a compact outer-rotor brushless motor with high power density suitable for portable power tool applications.
Innovation Solution
The design includes a brushless direct-current (BLDC) motor with a rotor shaft, motor can, stator assembly, stator mount, outer rotor, and a fan that generates airflow through the motor can for cooling, without the need for additional fans.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a compact outer-rotor BLDC motor is used, then the motor size is reduced, but the cooling efficiency deteriorates
Solution Approach 1:
The fan is integrated directly into the rotor assembly, merging the cooling function with the rotating component. This eliminates the need for separate cooling mechanisms that would increase motor size, while still providing effective cooling through the strategically positioned fan blades that draw air through intake openings and expel it through exhaust openings.
Solution Approach 2:
The cooling approach transitions from axial to radial airflow configuration. Air is drawn in through radial intake openings and expelled through radial exhaust openings, creating a radial cooling flow pattern that optimizes heat dissipation within the compact motor structure without requiring additional axial space.
2Temperature
If the fan diameter is increased to improve cooling, then the motor size increases
Solution Approach 1:
The fan blades are positioned strategically within the rotor structure to create effective airflow channels. The fan diameter is optimized to be smaller than the rotor core diameter, with blades positioned to maximize air movement through the motor can while maintaining a compact overall motor size. The cooling effectiveness is achieved through local optimization of airflow paths rather than increasing overall fan size.
Solution Approach 2:
The fan is nested within the rotor assembly, with the fan diameter being smaller than the rotor core diameter. This nested configuration allows the cooling function to be integrated within the existing rotor structure without adding external dimensions, effectively hiding the cooling mechanism within the motor's internal volume.
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 achieves efficient cooling and high power density in a compact form, suitable for portable power tools, without requiring a larger fan diameter than the rotor core.
Implementation Method 1
a fan mounted on the rotor shaft inside the motor can to generate an airflow through the motor can
Implementation Method 2
a brushless direct-current (BLDC) motor disposed within the housing
Data Source
AI summary
A power tool includes a housing having a clamshell structure. An electric motor is provided including a motor can, a stator fixedly supported within the motor can, and a rotor mounted on a rotor shaft, where the motor can is partially contained within the housing and includes a front annular portion that projects out of a front end of the housing and includes a first threaded exterior surface. A head assembly is provided including an output member driven by the electric motor, and a rear annular portion with a diameter similar to the front annular portion of the motor can and that includes a second threaded exterior surface. A nut is mounted onto the first threaded exterior surface and the second threaded exterior surface proximate the front end of the motor case to securely fasten the head assembly to the motor can.