WO1990007645A1 - A method of monitoring machine vibrations - Google Patents

A method of monitoring machine vibrations Download PDF

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Publication number
WO1990007645A1
WO1990007645A1 PCT/SE1989/000706 SE8900706W WO9007645A1 WO 1990007645 A1 WO1990007645 A1 WO 1990007645A1 SE 8900706 W SE8900706 W SE 8900706W WO 9007645 A1 WO9007645 A1 WO 9007645A1
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WO
WIPO (PCT)
Prior art keywords
vibration
sequence
engine
characteristic
time
Prior art date
Application number
PCT/SE1989/000706
Other languages
French (fr)
Inventor
Ludwik Jan Liszka
Original Assignee
Ludwik Jan Liszka
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ludwik Jan Liszka filed Critical Ludwik Jan Liszka
Publication of WO1990007645A1 publication Critical patent/WO1990007645A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H1/00—Measuring characteristics of vibrations in solids by using direct conduction to the detector
    • G01H1/003—Measuring characteristics of vibrations in solids by using direct conduction to the detector of rotating machines
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02P—IGNITION, OTHER THAN COMPRESSION IGNITION, FOR INTERNAL-COMBUSTION ENGINES; TESTING OF IGNITION TIMING IN COMPRESSION-IGNITION ENGINES
    • F02P17/00—Testing of ignition installations, e.g. in combination with adjusting; Testing of ignition timing in compression-ignition engines
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B3/00—Engines characterised by air compression and subsequent fuel addition
    • F02B3/06—Engines characterised by air compression and subsequent fuel addition with compression ignition

Definitions

  • the invention relates to a method of monitoring periodic vibrations of machine equipment with a number of machine components which generate vibrations, wherein a vibration signal from a vibration sensor is sampled and digitized to form a plurality of time series, each corresponding to at least one period, and wherein time mean values are calculated on the basis of said time series for determining a characteristic vibration sequence for one period.
  • the background of the invention is a desire to reliably monitor the ignition sequence of marine diesel engines connected with a respective engine axle to a joint gear box. It has turned out that the moment of ignition for each cylinder in a number of subsequent ignition sequences varies and that the pressure variations are complicated. Consequently, it is difficult to reliably determine a characteristic vibration sequence by the generally known method indicated above.
  • the characteristic vibration sequence can be fine-corrected in that the vibration signal and/or the time series, in parallel to the calculation of the time mean values, is/are additionally transformed from the time domain to the frequency domain so as to form a characteristic frequency spectrum, the peaks of which correspond to the time intervals between different time moments in said characteristic vibration sequence, and in that this characteristic frequency spectrum is compared to the characteristic vibration sequence for identifying the peaks of the frequency spectrum, with regard to their origin from said vibration generating machine components, and for achieving a fine-correction of said characteristic vibration sequence.
  • FIG. 2 is a block diagram of the essential method steps according to the invention.
  • FIG. 1 there are shown very schematically a number of parallel, multiple cylinder marine diesel engines D1 ,....,DN, which have their motor axles M1, Vietnamese,MN connected to a joint gear box VX with a common output shaft UA.
  • a first vibration sensor A1,....,AN is disposed on the joint gear box VX at a location on the extension of the respective motor axle
  • This sensor A1, Vietnamese,MN is used, on the one hand, for monitoring the associated bearings and gears in the joint gear box and, on the other hand, for monitoring and analyzing the ignition sequence in the associated diesel engine during two engine revolutions corresponding to one period.
  • a further sensor is used, on the one hand, for monitoring the associated bearings and gears in the joint gear box and, on the other hand, for monitoring and analyzing the ignition sequence in the associated diesel engine during two engine revolutions corresponding to one period.
  • B1, Vietnamese,BN is disposed on the engine block at the respective diesel engine, i.e. on the cylinder, which is first in order in the ignition sequence.
  • This sensor B1,....,BN is utilized as a trigger sensor.
  • the sensor which is used for monitoring of the ignition sequence, is thus located at a distance from the engine block, although an a machine part (the joint gear box VX) vibrationally coupled thereto, which has turned out to be advantageous when analyzing the ignition sequence in that certain disturbing signal components are hereby eliminated.
  • the two sensors A1, Vietnamese,AN and B1, Vietnamese,BN, respectively, are each connected to an input of a microprocessor 1 via a respective amplifier 2A and 2B, respectively, and an A/D converter 3A and a pulse former 3B, respectively.
  • An indication device 4 e.g. a viewing screen, is connected to an output of the microprocessor 1.
  • a computer terminal or a personal, computer can of course be used for bidirectional communication with the microprocessor 1.
  • the vibration signal from the respective sensor A1,....,AN is sampled, the sampling being started upon obtaining a trigger signal from the sensor B1, Vietnamese,BN, and each sampled, digitized amplitude value being fed to the microprocessor 1 for conventional forming of a plurality of time series (cf Figure 2, to the right).
  • Each such time series corresponds to two engine revolutions (one period) or a multiple thereof.
  • a time mean value is calculated for the ignition moment of each cylinder in the ignition sequence.
  • the characteristic vibration sequence can be substantially improved by additional conversion of the vibration signal from the time domain to the frequency domain (cf the left part of Figure 2).
  • FFT Fast Fourier Transform
  • a frequency region is used which substantially corresponds to the engine speed (number of revolutions) multiplied with the number of cylinders in each engine, thus about 10-15 times the engine speed for a
  • Time intervals between different ignitions in the ignition sequence correspond to peaks of the frequency spectrum.
  • the frequency spectrum only contains one or two peaks. If the ignition moments deviate periodically from the theoretical ones, the frequency spectrum will contain more peaks. In the extreme case, where all time intervals between the ignitions are different, there will be as many peaks as the number of cylinders, i.e. 10 peaks for a 10-cylinder engine.
  • peaks corresponding to the time intervals between ignitions which do not strictly follow one another i.e. t i+2 -t i , will be included in the frequency spectrum, although at lower frequencies.
  • the peaks of the frequency spectrum which have been calculated as indicated above, are reconverted into ignition intervals expressed in portions of the engine period or working cycle, or in degrees. Such a reconversion can be made with high accuracy, if the engine speed is measured simultaneously, preferably with a separate sensor C on the associated engine axle.
  • the less accurate measurements obtained by mean value calculation of the triggered time series can be used for identifying the various cylinders in the time intervals being reconverted from the frequency spectrum, so that a corrected, characteristic ignition sequence can be determined.
  • This corrected ignition sequence, for each of the diesel engines, may be continuously displayed on the viewing screen 4, e.g. in the form of a polar diagram.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)
  • Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)

Abstract

A method of monitoring periodic vibrations of machine equipment with a number of machine components which generate vibrations, in particular for monitoring the periodically repeated ignition sequence in a multiple cylinder combustion engine, in particular a number of diesel engines connected in parallel in a ship. Vibration signals (A) from sensors, which are disposed on a joint gear box on the extension of the respective engine axle, are sampled upontriggering (B) from a trigger sensor, which is disposed on the cylinder which is first in the ignition sequence of the respective engine, and are digitized to form time series, whereupon mean values are calculated on the basis of a plurality of such time series so as to form a characteristic ignition sequence. According to the invention the vibration signals (A) are additionally converted (FFT) to the frequency domain, and the peaks in the frequency spectrum are reconverted to time intervals for fine-correction of the respective characteristic ignition sequence.

Description

A METHOD OF MONITORING MACHINE VIBRATIONS.
The invention relates to a method of monitoring periodic vibrations of machine equipment with a number of machine components which generate vibrations, wherein a vibration signal from a vibration sensor is sampled and digitized to form a plurality of time series, each corresponding to at least one period, and wherein time mean values are calculated on the basis of said time series for determining a characteristic vibration sequence for one period.
The background of the invention is a desire to reliably monitor the ignition sequence of marine diesel engines connected with a respective engine axle to a joint gear box. It has turned out that the moment of ignition for each cylinder in a number of subsequent ignition sequences varies and that the pressure variations are complicated. Consequently, it is difficult to reliably determine a characteristic vibration sequence by the generally known method indicated above.
According to the invention, the characteristic vibration sequence can be fine-corrected in that the vibration signal and/or the time series, in parallel to the calculation of the time mean values, is/are additionally transformed from the time domain to the frequency domain so as to form a characteristic frequency spectrum, the peaks of which correspond to the time intervals between different time moments in said characteristic vibration sequence, and in that this characteristic frequency spectrum is compared to the characteristic vibration sequence for identifying the peaks of the frequency spectrum, with regard to their origin from said vibration generating machine components, and for achieving a fine-correction of said characteristic vibration sequence. Suitable further features are stated in the dependent claims The invention and its advantages are explained further below with reference to the appended drawings, which schematically illustrate an exemplary embodiment. Figure 1 shows schematically a number of marine diesel engines, a joint gear box and a monitoring system for carrying out the method according to the invention; and
Figure 2 is a block diagram of the essential method steps according to the invention.
In Figure 1, there are shown very schematically a number of parallel, multiple cylinder marine diesel engines D1 ,....,DN, which have their motor axles M1,.....,MN connected to a joint gear box VX with a common output shaft UA. A first vibration sensor A1,....,AN is disposed on the joint gear box VX at a location on the extension of the respective motor axle
M1,....,MN. This sensor A1,.....,AN is used, on the one hand, for monitoring the associated bearings and gears in the joint gear box and, on the other hand, for monitoring and analyzing the ignition sequence in the associated diesel engine during two engine revolutions corresponding to one period. A further sensor
B1,.....,BN is disposed on the engine block at the respective diesel engine, i.e. on the cylinder, which is first in order in the ignition sequence. This sensor B1,....,BN is utilized as a trigger sensor.
The sensor, which is used for monitoring of the ignition sequence, is thus located at a distance from the engine block, although an a machine part (the joint gear box VX) vibrationally coupled thereto, which has turned out to be advantageous when analyzing the ignition sequence in that certain disturbing signal components are hereby eliminated. The two sensors A1,.....,AN and B1,.....,BN, respectively, are each connected to an input of a microprocessor 1 via a respective amplifier 2A and 2B, respectively, and an A/D converter 3A and a pulse former 3B, respectively. An indication device 4, e.g. a viewing screen, is connected to an output of the microprocessor 1. Instead of only a viewing screen or some other indication device, a computer terminal or a personal, computer can of course be used for bidirectional communication with the microprocessor 1.
The vibration signal from the respective sensor A1,....,AN is sampled, the sampling being started upon obtaining a trigger signal from the sensor B1,.....,BN, and each sampled, digitized amplitude value being fed to the microprocessor 1 for conventional forming of a plurality of time series (cf Figure 2, to the right). Each such time series corresponds to two engine revolutions (one period) or a multiple thereof. On the basis of these time series, a time mean value is calculated for the ignition moment of each cylinder in the ignition sequence. These time mean values form together a characteristic vibration or ignition sequence for one period.
However, the moments of ignition for each diesel engine cylinder vary relatively widely, and it is therefore difficult to obtain a representative characteristic vibration sequence in this way.
According to the invention, the characteristic vibration sequence can be substantially improved by additional conversion of the vibration signal from the time domain to the frequency domain (cf the left part of Figure 2). Thus, in this case, the sampling is effected without any trigger pulse so as to form time series, and these time series are converted by Fourier-transformation (FFT = Fast Fourier Transform) for obtaining a characteristic frequency spectrum. Here, a frequency region is used which substantially corresponds to the engine speed (number of revolutions) multiplied with the number of cylinders in each engine, thus about 10-15 times the engine speed for a
10-cylinder engine.
Time intervals between different ignitions in the ignition sequence correspond to peaks of the frequency spectrum. A peak at the frequency f has a momentary level, which is proportional to the amplitude of the ignitions corresponding to the time interval ti+1-ti = 1/f, where ti and ti+1 are two subsequent ignition moments.
In an ideal case, where only one or two time intervals occur between the ignitions, the frequency spectrum only contains one or two peaks. If the ignition moments deviate periodically from the theoretical ones, the frequency spectrum will contain more peaks. In the extreme case, where all time intervals between the ignitions are different, there will be as many peaks as the number of cylinders, i.e. 10 peaks for a 10-cylinder engine.
Moreover, peaks corresponding to the time intervals between ignitions which do not strictly follow one another, i.e. ti+2-ti, will be included in the frequency spectrum, although at lower frequencies. The peaks of the frequency spectrum, which have been calculated as indicated above, are reconverted into ignition intervals expressed in portions of the engine period or working cycle, or in degrees. Such a reconversion can be made with high accuracy, if the engine speed is measured simultaneously, preferably with a separate sensor C on the associated engine axle.
The less accurate measurements obtained by mean value calculation of the triggered time series can be used for identifying the various cylinders in the time intervals being reconverted from the frequency spectrum, so that a corrected, characteristic ignition sequence can be determined. This corrected ignition sequence, for each of the diesel engines, may be continuously displayed on the viewing screen 4, e.g. in the form of a polar diagram.

Claims

1. A method of monitoring periodic vibrations of machine equipment with a number of machine components which generate vibrations, in particular for monitoring the periodically repeated ignition sequence of at least one combustion engine with a plurality of cylinders, in particular a marine diesel engine (D1,...,DN), wherein
- a vibration signal from a vibration sensor (A1,...,AN) is sampled and digitized to form a plurality of time series, each corresponding to at least one period, and
- time mean values are calculated on the basis of said
time series for determining a characteristic vibration sequence for one period,
c h a r a c t e r i z e d in that
- said vibration signal and/or said time series, in parallel to said calculation of time mean values, is/are additionally transformed from the time domain to the frequency domain so as to form a characteristic frequency spectrum, the peaks of which correspond to the time intervals between different time moments in said characteristic vibration sequence, and
- said characteristic frequency spectrum is compared to
said characteristic vibration sequence for identifying the peaks of the frequency spectrum, with regard to their origin from said vibration generating machine components, and for achieving a fine-correction of said characteristic vibration sequence.
2. A method as defined in claim 1, c h a r a c t e r i z e d in that the sampling is started upon receipt of a trigger signal from a separate trigger sensor (B1,...,BN) located at a certain vibration generating machine component.
3. A method as defined in claim 1 or 2, wherein said machine equipment comprises at least one multiple cylinder combustion engine, in particular a diesel engine (D1,...,DN), c h a r a c t e r i z e d in that said vibration signal is obtained from a vibration sensor (A1,...,AN.) located at a distance from the engine block on a machine part (VX) vibrationally coupled thereto.
4. A method as defined in claims 2 and 3, c h a r a c t e r- i z e d in that said trigger signal is obtained from a trigger sensor (B1,...,BN) located on the engine block adjacent to the cylinder being first in the ignition sequence.
5. A method as defined in claim 4, wherein said machine equipment comprises a plurality of combustion engines (D1,...,DN) having their respective engine axles (M1,...,MN) connected to a joint gear box (VX) with at least one output shaft (UA), c h a r a c t e r i z e d in that the vibration signal is obtained from a vibration sensor (A) disposed on the joint gear box (VX).
6. A method as defined in claim 5, c h a r a c t e r i z e d in that the vibration signal is obtained from a vibration sensor (A1,...,AN) located on the extension of the engine axle
(M1,...,MN) of the combustion engine (D1,...,DN), the ignition sequence of which is to be monitored. 7. A method as defined in claim 5 or 6, c h a r a c t e r i z e d in that in order to obtain said vibration signal the same vibration sensor (A1,...,AN) is used as the one used for monitoring of bearings and gears in the joint gear box (VX). θ. A method as defined in any one of claims 3 to 7, c h a r a c t e r i z e d in that said frequency spectrum lies in a frequency region approximately corresponding to the engine speed multiplied by the number of cylinders.
9. A method as defined in any one of claims 3 to 8, c h a r a c t e r i z e d in that the deviations of the frequency peaks from frequency values, which are calculated theoretically or on the basis of said characteristic vibration sequence, are
converted to time differences in said ignition sequence.
10. A method as defined in claim 9, c h a r a c t e r i z e d in that said time intervals are continuously calculated and indicated, e.g. in a polar diagram.
11. A method as defined in any one of claims 3 to 10, c h a r a c t e r i z e d in that the engine speed (n) is continuously measured for the respective combustion engine for a more
accurate reconversion of the frequency spectrum to time
intervals in said characteristic vibration sequence.
PCT/SE1989/000706 1988-12-27 1989-11-30 A method of monitoring machine vibrations WO1990007645A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE8804663A SE461291B (en) 1988-12-27 1988-12-27 MADE TO MONITOR PERIODIC VIBRATIONS OF A MACHINE EQUIPMENT
SE8804663-6 1988-12-27

Publications (1)

Publication Number Publication Date
WO1990007645A1 true WO1990007645A1 (en) 1990-07-12

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PCT/SE1989/000706 WO1990007645A1 (en) 1988-12-27 1989-11-30 A method of monitoring machine vibrations

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SE (1) SE461291B (en)
WO (1) WO1990007645A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000055583A1 (en) * 1999-03-13 2000-09-21 Textron Systems Corporation Sensor plug and method and apparatus for determining an amount of oil in a device

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2190198A (en) * 1986-04-28 1987-11-11 Vipac Pty Ltd Vibrational analysis system for a machine

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2190198A (en) * 1986-04-28 1987-11-11 Vipac Pty Ltd Vibrational analysis system for a machine

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000055583A1 (en) * 1999-03-13 2000-09-21 Textron Systems Corporation Sensor plug and method and apparatus for determining an amount of oil in a device

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Publication number Publication date
AU4819290A (en) 1990-08-01
SE461291B (en) 1990-01-29
SE8804663D0 (en) 1988-12-27

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