Shaft Ground Assembly for Motor Endshield

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Solution Overview

Problem

Vertically mounted electric motors experience amplified vibrations and premature bearing failure due to resonance frequency matching and induced electrical currents in the output shaft bearings, leading to arcing and pitting.

Innovation Solution

A method and grounding kit that electrically ground the rotor shaft by replacing the lockplate fastener with a mounting plate fastener and securing a conductive shaft ground assembly to the motor endshield, providing a path for electrical charges to ground and reducing vibrations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If variable frequency drives are used on electric motors, then motor control flexibility is improved, but electrical currents are induced in the output shaft bearings causing arcing and pitting

Engineering Contradiction:

Improvemotor control flexibilityVSAvoidelectrical currents in bearings

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

A shaft ground assembly is introduced as an intermediary component between the rotor shaft and the motor endshield. This assembly provides a dedicated electrical path that intercepts induced currents before they reach the bearings, using a conductive element in direct contact with the rotor shaft to channel currents safely to ground through the motor housing.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The harmful electrical currents are extracted from the bearing path by providing an alternative ground path through the shaft ground assembly. The conductive element captures the induced currents on the rotor shaft and redirects them through the mounting plate and fastener assembly to the motor endshield, removing the current flow from the bearing circuit.

Inventive Principle:

Principle #2Taking out (Extraction)

2Productivity

If vertically mounted electric motors operate at resonance frequency, then motor functionality is maintained, but vibrations are amplified causing bearing displacement and failure

Engineering Contradiction:

Improvemotor functionalityVSAvoidbearing stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The mounting plate fastener assembly serves multiple functions simultaneously: it mechanically secures the shaft ground assembly to the motor endshield, electrically grounds the rotor shaft through the conductive fastener, and provides structural support for the bearing lockplate. This multi-functionality allows vibration mitigation without adding separate components.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The resonance-induced vibrations and electrical currents that would normally harm the bearings are converted into a beneficial grounding path. The shaft ground assembly utilizes the electrical potential created by VFD operation to establish a controlled current path through the mounting structure, transforming the harmful electrical energy into a protective function.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 electrical currents in the bearings, minimizing arcing, pitting, and premature failure, thereby enhancing the operational stability and longevity of the motor.

Implementation Method 1

The shaft ground includes a conductive element configured to electrically couple to the rotor shaft

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 2

replacing the first lockplate fastener with a first mounting plate fastener coupled to the mounting plate, motor endshield, and bearing lockplate

Methodology Applied

Scientific EffectMechanical fastening: Mechanical Fastener

Data Source

PatentUS11699941B2Method and apparatus for providing motor with shaft ground

Publication Date: 2023.07.11 NIDEC MOTOR CORP

AI summary

A method of electrically grounding a rotor shaft of an electric motor includes removing a first lockplate fastener from a motor endshield and an internal bearing lockplate. A second lockplate fastener remains coupled to the motor endshield and internal bearing lockplate such that the internal bearing lockplate stays secured along an interior side of the motor endshield. A mounting plate of a shaft ground assembly is positioned along an exterior side of the motor endshield. The mounting plate supports a shaft ground that includes a conductive element configured to electrically couple to the rotor shaft. The first lockplate fastener is replaced with a first mounting plate fastener coupled to the mounting plate, motor endshield, and bearing lockplate to secure the mounting plate to the endshield and to secure the bearing lockplate along the interior side of the motor endshield.