Compact BLDC Motor Layout for Body-Grip Tool Power Density
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Solution Overview
Problem
Existing brushless DC motors for power tools are too large for placement in a gripping handle due to their diameter being greater than 40 mm, and previous designs using AC power sources or segmented stators are inefficient and prone to noise and vibration.
Innovation Solution
A compact brushless DC motor with a non-segmented stator core and a diameter of less than 34 mm, powered by a DC battery pack, featuring a rotor with permanent magnets and a circuit board for interconnecting stator windings, allowing for high power output while minimizing noise and vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a brushless DC motor is designed to output high power for power tool applications, then the power output is improved, but the motor diameter becomes greater than 40 mm making it unsuitable for placement in a gripping handle
Solution Approach 1:
The patent changes key design parameters including reducing the stator diameter to 34 mm or less, optimizing the motor size constant Km to 0.39-0.59 (Nmm/√W)/mm, and achieving a power-to-diameter ratio of at least 16.7 W/mm. These parameter changes enable the motor to fit in gripping handles while maintaining high power output capability
Solution Approach 2:
The patent employs composite construction with a non-segmented stator core made from magnetic material, permanent magnets on the rotor, and optimized winding configurations. This composite approach allows maximum power density within the constrained 34 mm diameter while maintaining structural integrity and magnetic efficiency
2Length of stationary object
If an AC power source is used in a motor for a gripping tool, then the motor can be sized for the gripping portion, but it is incapable of producing the same output levels from a DC power source
Solution Approach 1:
The patent optimizes the motor design specifically for DC power source operation by configuring the stator windings and magnetic circuit to maximize efficiency with DC input. The motor achieves high power output from DC battery packs while maintaining the compact size needed for gripping handles, resolving the limitation of AC-only designs
3Ease of manufacture
If a segmented stator design is used to form stator windings, then the motor can be manufactured, but it is expensive and prone to high noise and vibration in high torque applications
Solution Approach 1:
The patent merges the stator core into a single non-segmented piece with integrated windings, eliminating the gaps and misalignments between segmented parts. This unified construction reduces magnetic irregularities, minimizes noise and vibration during high torque operation, and simplifies the manufacturing process while maintaining ease of production
Solution Approach 2:
The non-segmented stator design creates a homogeneous magnetic structure throughout the stator assembly, ensuring uniform magnetic flux distribution. This homogeneity reduces magnetic imbalances that cause vibration and noise, while the integrated construction maintains manufacturing efficiency
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 compact motor design achieves a high power-to-volume ratio, enabling efficient power tool operation with reduced noise and vibration, and is capable of producing up to 16.7 W/mm of power output from a battery pack with a nominal voltage of less than 20 volts.
Implementation Method 1
The motor includes a stator including a stator core and stator windings; a rotor rotatably received within the stator and including a rotor shaft extending along a longitudinal axis and permanent magnets
Data Source
AI summary
A power tool is provided including a housing including a grip portion; and a brushless direct-current (BLDC) motor at least partially disposed within the grip portion of the housing. The motor includes a stator having a rotor core, a rotor, and front and rear bearing support structures. The stator core includes a non-segmented construction with a maximum diameter of approximately smaller than or equal to 34 mm, and a ratio of a motor size (Km) constant of the motor to a length of the motor is in the range of approximately 0.39 to 0.59 (Nmm/√W)/mm. When powered by a 20 V battery pack, a ratio of a maximum power output of the motor to a volume of the motor is at least approximately 0.0106 W/mm{circumflex over ( )}3.