Conductive Sheet Diverts Bearing Current in Inverter Motors
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Solution Overview
Problem
Motors driven by inverters experience electric corrosion in rolling bearings due to high carrier frequencies and source voltages, leading to durability degradation and noise issues, as electric current flows through the bearings, causing corrosion and abnormal abrasion.
Innovation Solution
A motor design featuring a stator with an insulating part, a rotor assembly with a rolling bearing, a printed wiring board with a drive circuit, and a conductive sheet electrically connected to the stator core using a connecting pin, which reduces electric current flow through the bearings by routing it through the conductive sheet and stator core, thereby minimizing corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If high carrier frequency and high source voltage are used to reduce motor noise, then motor noise is reduced, but electric current flows through the bearing causing electric corrosion
Solution Approach 1:
A conductive sheet is introduced as an intermediary component between the drive circuit and the bearing. This conductive sheet provides an alternative current path that diverts electric current away from the bearing, thereby preventing electric corrosion while allowing the motor to operate at high carrier frequencies for noise reduction
Solution Approach 2:
The harmful electric current path through the bearing is extracted and redirected through a dedicated conductive sheet. By separating the current path from the bearing, the bearing is protected from electric corrosion while the drive circuit continues to operate at high frequencies
2Reliability
If a conductive member is used to short-circuit the stator core and metal bracket, then electric corrosion is reduced, but electric current flows from the drive circuit to the bearing through the metal bracket
Solution Approach 1:
The conductive sheet serves as an intermediary that blocks the harmful current path through the metal bracket and bearing. It provides a controlled current diversion path that prevents current from flowing through the bearing while maintaining electrical connectivity where needed
3Reliability
If a conductive tape is used to short-circuit brackets, then electric corrosion is reduced, but electric current still flows through the bearing when electric potential is generated in the rotor
Solution Approach 1:
The conductive sheet acts as a more effective intermediary than conductive tape, providing comprehensive current diversion. It is positioned and configured to intercept all harmful current paths, including those generated by rotor electric potential, preventing current flow through the bearing
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 effectively reduces electric current through the bearings by up to 97%, preventing abnormal abrasion and noise, while maintaining productivity and quality, and is particularly effective when driving motors with high carrier frequencies and source voltages.
Implementation Method 1
a conductive sheet provided between the printed wiring board and the bracket... the conductive sheet and the stator core are electrically connected
Data Source
AI summary
In a motor driven by a drive circuit such as an inverter, there is a problem that electric current flowing through a bearing causes electric corrosion, which impairs the durability of the bearing. A motor of the invention includes: a stator in which a winding is applied through an insulating part to a stator core formed by laminating a predetermined number of electromagnetic steel plates which have been punched into a predetermined shape; a rotor assembly in which a rotor and bearings and formed by rolling bearings are fitted to a shaft; a printed wiring board which is arranged at an end part of the stator in an axial direction and to which a drive circuit is mounted; a bracket imposed to at least the end part of the stator in the axial direction to which the printed wiring board is arranged; and a conductive sheet provided between the printed wiring board and the bracket.