Molded Motor Bracket Equipotentiality via Conductive Tape
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Solution Overview
Problem
Molded motors using brushless DC motors experience electrical erosion due to potential differences between metal brackets supporting ball bearings, leading to circulation currents and premature wear, especially under high-frequency PWM control.
Innovation Solution
The integration of electrically conductive members, such as tape, wire, or plates, to short-circuit brackets on both ends of the motor frame, ensuring equal potentials and preventing circulation currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PWM control is used to control brushless DC motor, then motor control precision is improved, but electrical erosion occurs due to potential difference between brackets
Solution Approach 1:
The patent applies the equipotentiality principle by providing an electrically conductive member that electrically connects both brackets to each other, ensuring that both brackets are at the same electrical potential. This eliminates the potential difference between brackets that causes circulation current and electrical erosion during PWM control, while maintaining the precision of motor control.
Solution Approach 2:
The patent introduces an electrically conductive member as an intermediary element between the two brackets. This conductive member acts as a mediator to equalize the electrical potential between brackets, preventing the generation of circulation current and protecting the ball bearings from electrical erosion while allowing PWM control to function properly.
2Strength
If metal brackets are used to support ball bearings, then mechanical strength is improved, but circulation current flows through bearings causing wear
Solution Approach 1:
The patent uses the equipotentiality principle by electrically connecting both metal brackets through an electrically conductive member. This ensures that both brackets remain at the same electrical potential, preventing circulation current from flowing through the ball bearings and shaft, thereby eliminating electrical erosion and extending bearing lifespan while maintaining the mechanical strength benefits of metal brackets.
3Reliability
If insulation resin is used to form motor frame, then electrical insulation is improved, but bracket potential becomes unstable
Solution Approach 1:
The patent introduces an electrically conductive member as an intermediary that bridges the gap between the insulated motor frame and the metal brackets. This conductive member provides a stable electrical connection between brackets, ensuring potential stability despite the insulating resin, while the resin itself maintains its electrical insulation function between different electrical components.
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 solution eliminates electrical erosion and extends the lifespan of ball bearings by maintaining equal potentials across brackets, preventing abnormal sounds and wear, even under PWM control.
Implementation Method 1
The motor frame is provided with an electrically conductive member arranged to electrically connect the brackets to each other. That is, the electrically conductive member short-circuits the brackets to each other.
Data Source
AI summary
An inner rotor type molded motor controlled by pulse width modulation using an inverter circuit includes a pair of electrically conductive brackets attached to a load-side portion and an anti-load-side portion of a motor frame. An electrically conductive tape is attached on the outside of the motor frame to extend between the brackets, thereby short-circuiting the brackets to each other. In this manner, electrical erosion in the molded motor can be prevented.