Brushless Motor Stator Winding Torque Control
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Solution Overview
Problem
Existing brushless motors in power tools face challenges in controlling the output characteristic due to variations in the number of turns of stator winding coils, leading to torque imbalances and vibration issues, and require additional space for subsidiary windings to adjust motor characteristics.
Innovation Solution
A brushless motor design with three-phase stator windings where the number of turns in each phase is adjusted to minimize imbalances, allowing for balanced coil turns and even heat generation without the need for a subsidiary winding, ensuring efficient torque control and reduced vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If all coils are wound with the same number of turns to simplify manufacturing, then manufacturing precision is improved, but the torque output characteristic cannot reach the desired level or may exceed it
Solution Approach 1:
The patent applies local quality by differentiating the number of turns in specific coils (U1, V1, W1) from other coils. Instead of uniform winding, selected coils have different turn counts (n-1, n, or n+1) to locally adjust magnetic field strength and achieve precise torque control while maintaining overall manufacturing simplicity.
Solution Approach 2:
The patent changes the parameter of coil turns from a uniform value to varied values across different coils. By adjusting the number of turns in specific coils relative to the base number n, the patent fine-tunes the motor's torque output characteristic to match desired specifications without requiring complete redesign of the winding system.
2Adaptability or versatility
If a subsidiary stator winding is added to control motor characteristic, then adaptability of motor output is improved, but device complexity and space requirements increase
Solution Approach 1:
The patent merges the motor characteristic control function directly into the main stator winding structure. Instead of adding a separate subsidiary winding system, the control is achieved by varying turns within the existing three-phase coils, thereby integrating multiple functions into a single unified structure and reducing overall device complexity.
Solution Approach 2:
The main stator winding is given multi-functionality by making it capable of both generating the primary magnetic field and providing torque characteristic control through varied turn counts. This eliminates the need for dedicated subsidiary windings, as the same winding structure performs dual roles, thereby reducing device complexity while maintaining adaptability.
3Power
If different number of turns are used in each coil to control output characteristic, then power control precision is improved, but torque balance deteriorates causing vibration
Solution Approach 1:
The patent deliberately introduces asymmetry in the form of slight variations in coil turns (n-1, n, n+1) to achieve precise torque control. This controlled asymmetry allows fine-tuning of the magnetic field to match desired output characteristics while the variations are kept minimal to prevent significant torque imbalance and vibration.
Solution Approach 2:
The patent applies partial action by varying turns in only specific coils (U1, V1, W1) rather than all coils uniformly. This selective modification allows precise control of output characteristics with minimal disruption to overall torque balance, as the variations are localized to specific phases rather than applied universally.
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 design allows for precise control of the motor's output characteristic, minimizing torque imbalances and vibration, while optimizing the use of space within the motor housing.
Implementation Method 1
When driving current of the motor is supplied to the coils of the stator winding, a magnetic field is generated around the coils and the magnetic field interacts with the field generated by the permanent magnet, so that a rotor is driven.
Data Source
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AI summary
It is an object of the invention to provide a technique for easily controlling the output characteristic of a brushless motor in a power tool by adjusting the number of turns of a coil that forms a stator winding. A power tool has a brushless motor which includes a rotor 133 having a permanent magnet, a cylindrical stator, and three-phase stator windings which are installed on an inner circumferential side of the stator and rotationally drive the rotor. A plurality of slots are formed in an inside surface of the stator at predetermined intervals in a circumferential direction. Each of the three stator windings is formed by a plurality of coils wound through the slots of the stator and connected to each other. The total number of turns of the coils wound through the slots in each phase is the same in the three phases and not a multiple of the number of the slots in each phase.