Outer-Rotor BLDC Motor Assembly for High Power in Tight Spaces
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Solution Overview
Problem
Conventional power tools, such as impact drivers and impact wrenches, face challenges with insufficient power and excessive size, making them unfit for certain applications due to their length or girth, particularly when using inner-rotor motors.
Innovation Solution
The development of a compact outer-rotor brushless direct-current (BLDC) motor assembly with a stator core, stator windings, a cylindrical rotor core supporting permanent magnets, and a rotor shaft, integrated with a transmission system that includes a planetary gear set, allowing for a reduced overall length and increased power output without sacrificing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an inner-rotor motor is used, then the motor structure is compact, but the power output is insufficient and the tool size is excessive
Solution Approach 1:
The patent inverts the conventional motor configuration by using an outer-rotor design instead of an inner-rotor design. This inversion allows the rotor to be positioned outside the stator, creating a different spatial arrangement that enables both compact overall dimensions and high power output capability. The outer rotor configuration with integrated transmission components achieves 620 watts power output while maintaining a length of less than 11.3 mm.
Solution Approach 2:
The patent merges the transmission system components directly into the motor assembly, integrating the planetary gear set with the outer rotor structure. This merging eliminates the need for separate transmission housings and reduces the overall motor length while maintaining power transmission efficiency. The stator mount and transmission housing are combined into a unified structure that supports both the stator and transmission components.
2Power
If an outer-rotor motor is used, then the power output and magnetic flux are higher, but the motor diameter increases
Solution Approach 1:
The patent employs a nested arrangement where the stator is positioned inside the outer rotor, and the transmission components are nested within the motor assembly. The stator core with windings is contained within the outer rotor structure, and the planetary gear set is integrated within the available space. This nesting allows the motor to achieve 620 watts power output with a compact diameter of less than 52 mm by efficiently utilizing the radial space.
Solution Approach 2:
The patent optimizes the motor design by emphasizing axial compactness over radial expansion. The outer-rotor configuration with integrated transmission achieves high power output primarily through axial length optimization (less than 11.3 mm) rather than radial growth. The stator mount and transmission housing are arranged to minimize the radial footprint while maintaining the necessary magnetic flux path and mechanical strength.
3Length of moving object
If the motor length is reduced to fit tight spaces, then the fitment in tight spaces is improved, but the power output may be compromised
Solution Approach 1:
The patent changes the fundamental configuration parameters of the motor by adopting an outer-rotor design with integrated transmission, rather than simply scaling down a conventional inner-rotor motor. This parameter change enables the motor to achieve exceptional compactness (length less than 11.3 mm) while maintaining high power output (620 watts) through optimized magnetic flux paths and efficient torque transmission via the planetary gear set.
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 outer-rotor BLDC motor assembly achieves a maximum power output of at least 620 watts from a 20V battery pack while reducing the motor's diameter to less than 52 mm and length to less than 11.3 mm, enhancing power and fitment in tight spaces.
Implementation Method 1
brushless direct-current (BLDC) motor assembly
Implementation Method 2
stator windings wound in various patterns on the stator teeth
Implementation Method 3
transmission includes a planetary gear set
Data Source
AI summary
A brushless direct-current (BLDC) motor is provided including: a stator including a stator core having an aperture extending therethrough and a series of stator windings; and a rotor including a rotor core having a substantially cylindrical body, permanent magnets secured to an inner surface of the rotor core, a rotor shaft extending through the stator, and an overmold structure. The overmold structure includes: a radially body extending adjacent an axial end of the stator and coupled to the rotor shaft via a bushing, and a peripheral body formed around an outer surface and axial end surfaces of the rotor core and structurally securing the permanent magnets to the inner surface of the rotor core.