# US 8,771,891 B2 · Diagnostic system for unbalanced motor shafts for high speed compressor

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- Number: US 8,771,891 B2
- Document ID: US8771891B2
- Status: Granted
- Kind: B2
- Application number: 11/464,540
- Filed: 2006-08-15
- Published: 2008-02-21
- Granted: 2014-07-08
- Earliest claimed: 2006-08-15
- Assignees: GM Global Technology Operations LLC
- Applicants: Oliver Maier; Bernd Peter Elgas; Ulrich Dumke; Peter Willimowski
- Inventors: Oliver Maier; Bernd Peter Elgas; Ulrich Dumke; Peter Willimowski
- Web page: https://patentgrep.com/patent/US8771891B2

## CPC

- H01M 8/04686: {of auxiliary devices, e.g. batteries, capacitors}
- F04D 27/001: {Testing thereof; Determination or simulation of flow characteristics; Stall or surge detection, e.g. condition monitoring}
- F04D 29/662: {Balancing of rotors (compensating imbalance G01M1/36)}
- H01M 8/04089: of gaseous reactants
- H02H 7/09: against over-voltage; against reduction of voltage; against phase interruption
- F04C 2240/50: Bearings
- F04C 2270/80: Diagnostics
- Y02E 60/50: Fuel cells
- Y02P 70/50: Manufacturing or production processes characterised by the final manufactured product
- H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- F04D: NON-POSITIVE-DISPLACEMENT PUMPS (engine fuel-injection pumps F02M; ion pumps H01J41/12; electrodynamic pumps H02K44/02)
- H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H)
- F04C: ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS (engines F03C); ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

A diagnostic system for determining whether a rotor shaft of a compressor is unbalanced. The compressor includes a displacement sensor that measures the displacement of the rotor shaft as it is rotating. The sensor dynamic frequency signal is sent to a bandpass filter that filters out an eigen-frequency frequency that is a function of shaft elasticity and rotor dynamics. The filtered frequency signal is then rectified by a rectifier to make the filtered frequency signal positive. The rectified signal is then passed through a low pass filter that converts the rectified signal to a DC signal. The DC signal is then sent to a controller that determines if the amplitude of the signal is above a predetermined threshold, which indicates a problem with the balance of the compressor.

## Claims

### Claim 1

A method for determining whether a rotor shaft of a compressor is unbalanced, said method comprising:
determining a distance between an end of a displacement sensor and the rotor shaft as it rotates;
providing a frequency signal representing the distance between the end of the displacement sensor and the rotor shaft wherein the frequency signal is indicative of the balance of the rotor shaft;
bandpass filtering the frequency signal to provide a single unbalance frequency signal;
rectifying the bandpass filter signal to provide a positive unbalance frequency signal;
low pass filtering the positive unbalance frequency signal to convert the unbalance frequency signal to a DC signal whose amplitude is indicative of the balance of the rotor shaft; and
comparing the amplitude of the DC signal to at least one threshold to determine whether the rotor shaft is unbalanced, wherein comparing the amplitude of the DC signal to at least one threshold includes comparing the amplitude of the DC signal to a low threshold and a high threshold, and wherein if the amplitude of the DC signal is greater than the low threshold and less than the high threshold, a warning signal is provided and if the amplitude of the DC signal is greater than the high threshold, the system is shut-down and/or its performance is reduced.

### Claim 2 (depends on 1)

The method according to claim 1 wherein bandpass filtering the frequency signal includes filtering an eigen-frequency signal from the frequency signal that is a function of the rotor shaft elasticity and rotor dynamics.