Brush Teeth Geometry for Commutator Noise Reduction
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Solution Overview
Problem
Conventional brushes for electric motors experience noise due to initial misfit contact surfaces with the commutator, leading to vibrations during operation.
Innovation Solution
A brush design with a protruding portion featuring obtuse angles and multiple teeth that gradually wear to increase contact area, reducing noise by initially engaging only the teeth tops and later the surfaces, thus minimizing sharp contact changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional square brush with arc contact surface is used, then the brush can be easily manufactured and mounted, but the contact surface does not fit well with the commutator during initial operation, causing vibration and noise
Solution Approach 1:
The brush contact surface is segmented into multiple teeth (typically 3-7 teeth) along the axial direction, with each tooth having a specific height and spacing. This segmentation allows the brush to initially contact the commutator at discrete points (tooth tops), reducing vibration and noise, while gradually wearing to increase contact area over time.
Solution Approach 2:
The brush design incorporates a dynamic contact evolution process where the contact area between brush and commutator changes over time. Initially, only the tops of the teeth contact the commutator, providing stable point contact. As the brush wears, the contact area gradually increases to include the full tooth surfaces, adapting the contact characteristics during the brush lifecycle.
2Area of stationary object
If the brush contact surface is designed to match the commutator arc, then the theoretical contact area is maximized, but manufacturing tolerances prevent proper fitting during initial operation
Solution Approach 1:
Different parts of the brush contact surface have different functional qualities. The tooth tops are designed with specific curvature and height to provide initial point contact, while the tooth surfaces are designed to gradually wear and expand the contact area. This local differentiation of contact characteristics allows the brush to accommodate manufacturing tolerances while achieving proper contact evolution.
Solution Approach 2:
The brush teeth are pre-formed with specific geometries (height, spacing, curvature) before installation that anticipate the wear process. The tooth tops are positioned to make initial contact with the commutator, and the tooth dimensions are calculated to ensure proper contact area development as wear occurs, eliminating the need for precise initial fitting.
3Object-affected harmful factors
If the brush uses a larger contact area from the beginning, then noise and vibration are reduced, but the contact area changes sharply during operation, causing instability
Solution Approach 1:
The brush contact area is designed to evolve dynamically during operation rather than remaining static. The segmented tooth structure enables a controlled transition from point contact at tooth tops to surface contact across full tooth areas, providing stability during the transition period while reducing noise and vibration throughout the brush lifecycle.
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 design significantly reduces noise during motor operation by maintaining a consistent and increasing contact area between the brush and commutator, suppressing commutation sparks and vibrations.
Implementation Method 1
With continuous wearing between the the commutator and the teeth, the teeth are worn out and the first surface and the second surface of the protruding portion start to contact with the commutator
Implementation Method 2
stays in tight contact with the commutator due to the elastic pushing force of a spring
Implementation Method 3
the brush slides with respect to the commutator
Data Source
AI summary
A brush used to contact with a commutator, includes a brush body which includes two opposite axial end faces and a protruding portion projecting from the brush body toward the commutator. The protruding portion includes a first surface, a second surface and at least two teeth. The first surface and the second surface are respectively adjacent to the two axial end faces. Angles formed between the first surface and the second surface and corresponding adjacent axial end faces are obtuse. The teeth is located between the first surface and the second surface, and extends generally along a circumferential direction of the commutator. The ratio of a total width of the at least two teeth in an axial direction of the brush to an axial height of the brush body is in the range of 0.25-0.75. An electric motor including the brush is also provided.