Asymmetrical Carbon Brush Arrangement for Starter Motor Wear
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Solution Overview
Problem
In starter motors with automatic start-stop systems, the uneven load distribution and higher switching cycles lead to differential wear rates of carbon brushes, reducing the service life due to asymmetrical load profiles and peak loads, necessitating a solution to evenly distribute current load and reduce wear.
Innovation Solution
An asymmetrical arrangement of carbon brushes is achieved using a uniform brush plate with offset receiving parts on the brush holders, allowing for optimal load distribution without requiring multiple brush plates and holders, by adjusting the position of the receiving part relative to the rotor axis based on rotation direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If carbon brushes are arranged with equidistant angular spacing (180° offset for pairs) on the commutator circumference, then the structure is simple and manufacturing is easy, but the load distribution becomes uneven and wear rates differ, reducing service life
Solution Approach 1:
The patent applies asymmetry by deviating the angular spacing of at least one carbon brush pair from the standard 180° offset. Specifically, the plus and minus brushes in at least one pair are positioned at an angle different from 180°, creating an asymmetrical arrangement that optimizes load distribution across all brush pairs. This asymmetrical positioning ensures that load peaks are evenly distributed, preventing differential wear and extending service life, while maintaining a single uniform brush plate design for manufacturing simplicity.
2Reliability
If an asymmetrical arrangement of carbon brushes is implemented to optimize load distribution, then service life is extended, but multiple variations of brush plates and holders are required, increasing device complexity
Solution Approach 1:
The patent applies local quality by implementing asymmetry only where needed - specifically in the angular positioning of carbon brush pairs rather than in the overall brush plate structure. The brush plate itself remains uniform and symmetrical, requiring only one design variant. The asymmetrical arrangement is achieved through localized adjustment of brush holder positions on the commutator circumference, allowing optimal load distribution without proliferating brush plate variations and maintaining manufacturing simplicity.
3Power
If the number of commutator segments is selected to reduce torque ripple, then motor performance is improved, but the load on individual carbon brushes becomes more uneven, increasing wear peaks
Solution Approach 1:
The patent compensates for the uneven load distribution caused by non-divisible segment numbers (used for torque ripple reduction) by applying asymmetrical positioning to the carbon brush pairs. By deviating the angular spacing of brush pairs from standard symmetrical arrangements, the invention balances the load peaks across all brushes, ensuring uniform wear rates even when the commutator segment count creates inherently uneven loading patterns.
Data Source
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AI summary
The invention relates to an electric machine comprising at least two pairs of carbon brushes (16) consisting of one positive and one negative carbon brush which cooperate with a commutator (15) to supply the rotor with current, the carbon brushes being mounted by means of their brush holders in a retainer on a brush plate and the retainers on said brush plate lying opposite one another at an angle of 180°. The aim of the invention is to achieve a longer service life for the machine and the smallest possible variety of parts. To achieve this, on at least one brush holder (17a) the retainer part (21b) is offset from the centre, in particular the axis of symmetry (y) of the brush holder (17a), at an angle (a) in relation to the rotor axis (x), to obtain an asymmetrical arrangement of the carbon brush, and the retainer part (21b) on the remaining brush holders is arranged on the axis of symmetry (y) of said holders.