Brush Apparatus Pigtail Embedding for DC Motor Wear Management
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Solution Overview
Problem
Existing brush apparatuses for high-power DC electric motors face challenges in maintaining brush life and contact stability due to increased lead wire thickness, which reduces flexibility and leads to voltage drops and premature wear, while using multiple lead wires complicates brush holder design and reduces holding stability.
Innovation Solution
A brush apparatus with a rectangular solid brush and a pigtail composed of tightly bonded lead wires, embedded at the center of the brush, allowing for parallel extension with the commutator surface, and a brush holder with a notch for downward movement as the brush wears, ensuring flexibility and stable contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the thickness of the lead wire is increased to reduce internal electric resistance, then the current density and voltage drop are reduced, but the finished outer diameter of the pigtail increases, which decreases the permissible wear dimension and shortens brush life
Solution Approach 1:
The lead wire is segmented into multiple thin wires (e.g., 3-5 wires) bundled together to form the pigtail. This segmentation allows achieving the required current capacity through increased wire count rather than individual wire thickness, maintaining flexibility while reducing voltage drop. The segmented structure enables the pigtail to accommodate brush wear movement without causing contact failure.
2Loss of energy
If the thickness of the lead wire is increased to reduce internal electric resistance, then the current density is reduced, but the flexibility of the pigtail deteriorates, which hinders downward movement of the brush and causes contact failure
Solution Approach 1:
Multiple thin lead wires are segmented and bundled to form the pigtail. This segmentation maintains flexibility because each individual thin wire can bend independently, allowing the pigtail to accommodate the downward movement of the brush during wear without causing contact failure, while collectively providing sufficient current capacity.
Solution Approach 2:
The parameter of wire thickness is changed from thick to thin, while compensating for current capacity by increasing the number of wires. This parameter change maintains flexibility for brush movement while achieving the required electrical performance through increased wire count rather than individual wire thickness.
3Loss of energy
If two lead wires are embedded at different positions to reduce internal electric resistance, then the current density is reduced, but the shape of the brush holder is constrained, which decreases the holding contact surface and lowers holding stability
Solution Approach 1:
The electrical function is segmented across multiple thin wires rather than requiring two separate thick wires at different positions. This allows both wires to be embedded at the same optimal position on the brush, maintaining the brush holder's simple structure and large holding contact surface while achieving reduced current density through the segmented wire bundle.
4Reliability
If the lead wire is embedded on the opposite side of the commutator contact surface to improve holding reliability, then the brush is reliably held by the brush holder, but interference with the bracket occurs, requiring reduction of brush height and shortening brush life
Solution Approach 1:
Instead of positioning the pigtail at the opposite side of the brush (one-dimensional positioning), the pigtail is positioned at the widthwise center of the wider side, extending in parallel with the commutator contact surface. This dimensional change in positioning allows the pigtail to clear external brackets while maintaining adequate embedding depth for reliable holding, preventing the need to reduce brush height.
Data Source
AI summary
A brush apparatus includes a brush and a brush holder. The brush includes a pigtail embedded in a wider side thereof so that the longitudinal side in cross-section of the pigtail extends in parallel with a surface of the brush coming into contact with a commutator. The brush holder includes a brush holding member, a brush spring for pressing the brush against the commutator for sliding contact, a base for holding the brush holding member and electrically connecting the same to an earth circuit, and a connection lug on the base. The brush holding member is formed with a notch on a wider side from an upper end thereof for allowing a downward movement of the pigtail when the brush wears and hence is pressed downward. A distal end of the pigtail is connected to the connection lug.