DC Motor Rotor Assembly Solderless Varistor Fixing
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Solution Overview
Problem
Brushed DC motors experience voltage peaks and electromagnetic interference due to back EMF spikes, and existing solutions using solder-joined varistors are mechanically unstable at high temperatures, leading to potential electrical shorts and reduced operational life, with soldering processes being environmentally hazardous and costly.
Innovation Solution
A rotor assembly for DC motors featuring a varistor connected to the commutator via an electrically-conductive solderless fixing means, such as adhesive or an electrically-conductive casing, which provides thermal stability and mechanical strength, reducing the risk of mechanical failure and electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solder-joined varistor is used to protect against voltage peaks, then electromagnetic interference is suppressed, but the connection becomes mechanically unstable at high temperatures
Solution Approach 1:
The invention extracts the harmful solder material from the connection between the varistor and commutator segments, replacing it with a solderless fixing means such as adhesive or mechanical fixation. This eliminates the dissolution reactions that occur between solder and metallized electrodes at high temperatures, while maintaining the varistor's protective function against electromagnetic interference.
Solution Approach 2:
The invention changes the material parameters of the fixing means from solder (with low melting point and susceptibility to dissolution) to alternative materials such as adhesive or electrically-conductive epoxy resin that maintain mechanical stability and electrical conductivity at high operating temperatures, preventing connection failure.
2Reliability
If soldering process is used to join varistor to commutator, then electrical connection is achieved, but residual flux causes environmental hazards and increased manufacturing cost
Solution Approach 1:
The invention extracts and eliminates the soldering process and associated flux materials from the manufacturing process, replacing them with solderless fixing means that do not generate harmful residual flux, thereby reducing environmental hazards and simplifying manufacturing cleanup requirements.
Solution Approach 2:
The invention replaces expensive and environmentally problematic soldering materials (solder and flux) with simpler, cleaner alternative fixing materials such as adhesive or electrically-conductive epoxy resin that do not require costly solvent cleaning processes and are easier to dispose of safely.
3Reliability
If solder is used to connect varistor to commutator, then electrical connection is established, but dissolution reaction occurs at high temperature reducing operational life
Solution Approach 1:
The invention extracts the solder material from the connection system, eliminating the source of dissolution reactions between solder and metallized electrodes on the varistor. This prevents progressive degradation of the electrical connection and maintains structural integrity throughout the motor's operational life at high temperatures.
Solution Approach 2:
The invention uses composite fixing materials such as electrically-conductive epoxy resin or adhesive that combine mechanical bonding properties with electrical conductivity, replacing the homogeneous solder material. These composite materials resist high-temperature dissolution and maintain connection stability throughout the motor's operational lifespan.
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 solution significantly enhances the operational life of DC motors by eliminating thermal degradation and mechanical instability, while simplifying the construction and reducing environmental hazards associated with soldering processes.
Implementation Method 1
The varistor has a non-linear current-voltage characteristic, and is capable of protecting against excessive transient voltages, by deviation of the current generated by the transient voltages therethrough.
Implementation Method 2
the electrically-conductive solderless fixing means can be formed so as to be thermally stable to a much greater temperature than solder alone
Data Source
AI summary
A rotor assembly for a DC motor is provided which includes a rotor having a rotor shaft, a commutator mounted to the rotor shaft, and a varistor which is connected to the commutator via an electrically-conductive solderless fixing means, such as an electrically-conductive adhesive.