Outer-Rotor BLDC Stator Mount for Compact Cooling and Debris Control
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Solution Overview
Problem
Conventional brushless direct-current (BLDC) motors face challenges in compact and efficient placement in power tools, particularly in outdoor products like lawn mowers and impact tools, due to size constraints and the need for protection against debris and contamination.
Innovation Solution
A brushless direct-current (BLDC) motor design featuring a stator with radially extending teeth and windings, a rotor with permanent magnets and an inner annular member forming a fan for airflow, and end caps with sloped surfaces to guide airflow and expel debris, ensuring efficient cooling and protection from contaminants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an outer-rotor motor design is used to increase power output and reduce vibration, then the motor produces higher torque and lower vibration, but the motor size increases making compact placement difficult
Solution Approach 1:
The motor is divided into modular components including a stator assembly, rotor assembly, end caps, and mounting bracket that can be separately manufactured and assembled. This segmentation allows for optimized design of each component while maintaining overall compact dimensions.
Solution Approach 2:
The mounting bracket is integrated with the motor housing to combine structural support and motor mounting functions in a single component. The end caps are designed to simultaneously seal the motor, provide mounting surfaces, and guide airflow, merging multiple functions into unified structures.
2Volume of moving object
If the motor is placed in a compact configuration for space efficiency, then the overall tool size is reduced, but protection against debris and contamination becomes more difficult
Solution Approach 1:
The end caps are designed as sealed structures that form protective barriers around the motor components. These end caps create a sealed environment while maintaining compact motor dimensions, preventing debris and contamination from entering the motor interior.
Solution Approach 2:
The mounting bracket serves as an intermediary structure between the motor and the tool housing, providing both mechanical support and additional protection. The bracket creates a buffer zone that helps shield the motor from direct exposure to debris while maintaining compact overall dimensions.
3Ease of manufacture
If conventional motor designs are used for simplicity, then manufacturing is easier, but cooling efficiency and debris management are insufficient
Solution Approach 1:
The end caps incorporate sloped and curved surfaces that naturally guide airflow around the rotor and stator components. These curved surfaces efficiently direct cooling air through the motor windings and magnetic components, enhancing heat dissipation while maintaining relatively simple manufacturing processes.
Solution Approach 2:
The end caps are designed to perform multiple functions simultaneously: sealing the motor, guiding airflow for cooling, providing mounting surfaces, and directing debris away from sensitive components. This multi-functionality improves cooling efficiency without significantly increasing manufacturing complexity.
4Power
If the motor is designed for high power output, then torque is increased, but the motor becomes more susceptible to torque ripple and vibration
Solution Approach 1:
The rotor design incorporates asymmetric magnet placement and the end caps feature asymmetric airflow channels that help balance electromagnetic forces. This asymmetric design compensates for inherent torque ripple in outer-rotor motors, reducing vibration while maintaining high torque output.
Solution Approach 2:
The motor design incorporates dynamic balancing features in the rotor and stator assemblies, allowing the system to adapt to varying load conditions. The flexible mounting bracket provides dynamic isolation that reduces the transmission of vibrations to the tool housing while maintaining stable high-torque operation.
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
The design allows for high-power output in a compact form, effectively managing airflow to prevent contamination and enhance cooling, thus improving the performance and reliability of BLDC motors in outdoor power tools.
Implementation Method 1
The radial back plate of the first end cap includes at least one sloped surface forming at least one air gap such that the airflow generated by the fan is centrifugally guided within the first end cap by the sloped surface and caused to exit the first end cap through the air gap.
Data Source
AI summary
A power tool or a mower is provided including brushless direct-current motor having an inner stator and an outer rotor. A rotor shaft extends through a stator core of the inner stator. The motor includes a first end cap disposed on a first side of the stator and supporting the rotor shaft via a front bearing and a second end cap disposed on a second side of the stator and supporting the rotor shaft via a rear bearing. The front end cap is mounted on a housing of the power tool or a deck of the mower while the rear end cap is located fully outside the housing or the deck.