Outer-Rotor BLDC Motor End-Cap Airflow for Debris Exclusion
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Solution Overview
Problem
Existing brushless direct-current (BLDC) motors for outdoor power tools face challenges in compact and efficient placement, particularly in preventing debris and contamination, especially in high-dust environments like lawns, and in balancing the weight distribution of battery packs within the tool.
Innovation Solution
The design incorporates a brushless direct-current (BLDC) motor with a unique end cap configuration that includes radial back plates and annular bodies for airflow management, securing the rotor shaft via front and rear bearings, and integrating a sensor board and deflection limiting members to absorb impacts, while ensuring airflow is expelled radially to prevent contamination and balance the tool's weight distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an outer-rotor brushless motor is used to provide high power output, then the motor can produce high torque and reduce vibration, but the motor increases the overall length and diameter of the tool housing
Solution Approach 1:
The end cap integrates multiple functions: it seals the motor housing, supports the rotor shaft via bearings, provides airflow management channels, and incorporates deflection limiting members. This consolidation of functions into a single component achieves compact design while maintaining high power output capability
Solution Approach 2:
The motor is oriented with the rotor shaft extending perpendicular to the longitudinal axis of the transmission mechanism, placing the motor housing below the transmission mechanism rather than in-line. This spatial reconfiguration reduces the overall length of the tool while accommodating the larger outer-rotor motor
2Volume of moving object
If the motor is placed in a compact manner to reduce tool size, then the overall length is reduced, but protection against debris entry and contamination becomes more difficult
Solution Approach 1:
The end cap acts as a sealed barrier protecting the motor components from debris and contamination. It incorporates bearing supports that seal around the rotor shaft, preventing particulate ingress while allowing rotational motion. The integrated airflow channels are contained within the sealed housing structure
Solution Approach 2:
The motor housing is divided into sealed compartments with the end cap forming a protective barrier. The airflow management system is segmented into separate channels that are contained within the housing, preventing uncontrolled airflow that could draw debris into the motor
3Use of energy by moving object
If battery packs are added to provide power, then the motor can operate, but the weight distribution and balance of the tool becomes unbalanced
Solution Approach 1:
The motor housing is positioned below the transmission mechanism, creating a counterbalancing weight distribution. This placement of the motor assembly acts as a counterweight to the battery pack and other components, improving the overall balance and handling characteristics of the tool
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, efficient, and durable motor placement that prevents debris entry, maintains high performance, and balances the tool's weight, ensuring effective operation in harsh outdoor conditions.
Implementation Method 1
The airflow generated by the fan is centrifugally guided within the first end cap by the at least one sloped surface and caused to exit the first end cap through the at least one air gap
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A brushless direct-current motor is provided which includes an inner stator and an outer rotor. The rotor includes a rotor core disposed around the stator, an inner annular member mounted on a rotor shaft, and a plurality of radial blades extending angularly from the rotor core to the inner annular member forming a fan. A first end cap is provided including a radial back plate proximate the fan and a center opening in the radial back plate through which the rotor shaft extends. A second end cap is provided including a main body disposed adjacent the stator opposite the fan. 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 through the air gap.