Brushless Motor Stator Bus Bar Assembly for Compact Power Tools
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Solution Overview
Problem
Conventional brushed motors in cordless power tools are less durable and less efficient due to brush wear and mechanical commutation, which limits their performance and size efficiency, especially in compact handheld applications.
Innovation Solution
A brushless DC motor with a stator assembly featuring a lamination stack, field windings, and a bus bar system with conductive terminals and end insulators, which allows for efficient electronic commutation and reduced motor length, enhancing durability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a brushed motor is used in cordless power tools, then the motor can be simpler in structure and easier to manufacture, but the durability decreases due to brush wear and mechanical commutation failures
Solution Approach 1:
The patent replaces the mechanical brush-commutator system with an electronic commutation system using Hall effect sensors and a control circuit. This substitution eliminates the wear-prone mechanical contacts while maintaining the motor's ability to convert electrical energy to mechanical energy, thereby improving durability without significantly complicating the manufacturing process
Solution Approach 2:
The patent changes the commutation method from mechanical to electronic by modifying the control parameters and signal processing. Hall effect sensors detect rotor position and generate commutation signals that control the timing of stator winding activation, replacing the physical brush-commutator interaction with electronically controlled current switching
2Device complexity
If a brushed motor is used in cordless power tools, then the motor structure can be simpler, but the energy efficiency decreases leading to shorter operation time between charges
Solution Approach 1:
The patent replaces the mechanically commutated system with an electronically commutated brushless DC motor system. This substitution reduces energy losses associated with brush friction and mechanical contact, improving overall energy efficiency and extending battery operation time between charges
Solution Approach 2:
The patent incorporates Hall effect sensors that provide feedback on rotor position to a control circuit. This feedback mechanism enables precise timing of stator winding activation, optimizing the magnetic field interaction and improving energy conversion efficiency while reducing unnecessary energy consumption
3Reliability
If a brushless DC motor is used to improve durability and efficiency, then the motor length increases which is problematic for compact handheld power tools
Solution Approach 1:
The patent integrates the Hall effect sensors, control circuit, and stator windings into a compact nested arrangement within the motor housing. The sensors are mounted on the stator core, the control circuit is positioned adjacent to the windings, and all components are arranged in a space-efficient configuration that minimizes the overall motor length while maintaining the brushless design
Solution Approach 2:
The patent optimizes the motor layout by arranging components in a radial and axial configuration that maximizes space utilization. The stator windings are arranged radially around the rotor, and the Hall effect sensors are positioned at strategic angular locations, allowing compact packaging in the dimensional space available in handheld tools
4Reliability
If electronic commutation is implemented in a brushless DC motor, then the motor achieves better durability and efficiency, but the device complexity increases due to additional sensors and control circuits
Solution Approach 1:
The patent designs the control circuit to perform multiple functions: it processes signals from the Hall effect sensors, determines rotor position, generates commutation signals for the stator windings, and provides protection functions. This multi-functionality reduces the need for separate dedicated components, thereby limiting the increase in overall device complexity while achieving reliable electronic commutation
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 brushless DC motor design improves durability and energy efficiency, reducing motor length for compact power tools and minimizing mechanical failures, thus extending tool operation time and enhancing performance under heavy loads.
Implementation Method 1
The magnetic field associated with the PM in the rotor assembly attempts to align itself with the stator generated magnetic field resulting in rotational movement of the rotor
Implementation Method 2
When power is applied to a winding, the resulting current in the winding generates a magnetic field that couples to the rotor
Implementation Method 3
A set of sense magnets coupled to the PMs in the rotor assembly are sensed by a sensor, such as a Hall Effect sensor, to identify the current position of the rotor assembly
Data Source
AI summary
A stator assembly for a brushless DC motor includes a stator core including stator poles and an outer surface, at least one magnet wire wound on the poles forming stator windings, and a bus bar including a non-conductive mount and conductive terminals. Each conductive terminal includes: a main portion and a tang portion extending from a first longitudinal end of the main portion. At least a contact portion of the at least one magnet wire is wrapped around the tang portion and fused to make an electric connection to the conductive terminal. The tang portion has a smaller lateral width than the main portion and is folded over the main portion to capture the contact portion of the at least one magnet wire. A power wire supply electric power to the motor is coupled to the conductive terminal proximate the second longitudinal end of the main portion.