Slim BLDC Motor Layout for High-Power Body-Grip Tools
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Solution Overview
Problem
Existing brushless DC motors for power tools are too large in diameter to fit within the gripping portion of a power tool handle while providing high power output, and existing AC-powered motors with segmented stators are expensive and prone to noise and vibration.
Innovation Solution
A compact brushless DC motor with a single-piece stator and small diameter rotor, featuring a series of permanent magnet rings and a stepped rotor shaft, integrated with a circuit board and bearing system to achieve high power output within a small grip circumference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a brushless DC motor is designed to output high power (at least 450 watts), then the power output is improved, but the motor diameter becomes greater than or equal to 40 mm making it unsuitable for placement in a gripping handle
Solution Approach 1:
The motor design transitions from a conventional short-and-fat configuration to a long-and-slim configuration by increasing the axial length while reducing the diameter. This dimensional change allows the motor to fit within the gripping handle's diameter constraint (≤40 mm) while compensating for the reduced radial space by extending axially, thereby maintaining the required power output of at least 450 watts.
Solution Approach 2:
The motor design changes key geometric parameters: reducing the diameter to ≤40 mm and increasing the axial length to at least 1.4 times the diameter (length-to-diameter ratio ≥ 1.4:1). These parameter changes enable the motor to meet both the power output requirement (≥450 watts) and the size constraint for gripping handle placement.
2Length of moving object
If an AC-powered motor with segmented stator design is used, then the motor can be sized for gripping portion placement, but the motor is expensive and prone to high noise and vibration in high torque applications
Solution Approach 1:
The design extracts and eliminates the segmented stator structure from the motor, replacing it with a single-piece stator. This removal of the segmented design eliminates the sources of high noise and vibration associated with segmented constructors while maintaining the compact size suitable for gripping handle placement.
Solution Approach 2:
The stator is designed as a single integrated piece rather than multiple segmented parts. This merging of the stator into one continuous structure reduces noise and vibration in high torque applications while maintaining the compact motor dimensions for gripping portion placement.
3Length of moving object
If an AC-powered motor is used, then the motor can be compact, but it is incapable of producing the same output levels from a smaller-voltage DC power source
Solution Approach 1:
The motor is specifically optimized for DC power source operation with parameters tuned for smaller-voltage DC input. The single-piece stator design, combined with appropriate winding configurations and magnetic circuit design, enables the motor to achieve high power output (at least 450 watts) from DC power sources while maintaining a compact diameter suitable for gripping handle placement.
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 motor achieves a maximum power output of at least 450 watts within a grip circumference of 120 mm or less, reducing size and noise while maintaining high power efficiency and reliability.
Implementation Method 1
a brushless direct-current (BLDC) motor at least partially disposed within the grip portion of the housing and configured to output a maximum power output of at least 450 watts. The motor includes a stator including a stator core and stator windings; and a rotor rotatably received within the stator and including a rotor shaft extending along a longitudinal axis and a series of permanent magnet rings mounted sequentially along the longitudinal axis and surrounding the rotor shaft, each permanent magnet including a plurality of magnetic poles.
Data Source
AI summary
A brushless direct-current (BLDC) motor for a power tool outputs a maximum power output in the range of approximately 450 to 950 watts and a continuous power output in the range of approximately 400 to 730 watts over a discharge cycle of the battery pack when the battery pack has a maximum voltage of approximately 20 volts and a capacity of approximately 5 amp·hours. The motor includes a rotor with an outer diameter that is less than or equal to approximately 16 mm. A ratio of the maximum power output of the motor to a length of the motor is in the range of approximately 8.5 to 17.5 W/mm.