RU1784851C - Method for turbo-compressor bearing defects revealing - Google Patents

Abstract

Usage: turbocompressor engineering, in particular in the field of vibration diagnostics of plain bearings. SUMMARY OF THE INVENTION: A method for detecting defects in a bearing of a turbocharger is to further determine a cepstrum of a vibration signal, 7 i.e. they resort to nonlinear transformations of vibration in the form of a logarithmic spectrum, followed by the inverse Fourier transform and separation of the second rotor cepstrum rothmonics. And rotor auto-oscillations are judged by exceeding the level of the second rotor rachmonics of the normalized value. If rotor auto-oscillations are detected, a vibrational signal is synchronously averaged over time with a synchronization frequency equal to 1/2 of the rotor harmonic, and then 1/2 level of the rotor harmonic is extracted by direct Fourier transform and the size of the clearance of the bearing judged by the excess of 1/2 of the rotor harmonic of the synchronized normalized value. 4 ill. (L C

Description

The invention relates to turbocompressor engineering, in particular to vibration diagnostics of plain bearings without stopping and disassembling a turbocompressor, and can be used in all areas of the economy where turbocompressors with plain bearings are used.

The purpose of the invention is to increase reliability and durability by increasing the reliability of defect detection.

In FIG. 1 shows the low-frequency spectrum (AUTO SPEC) and the cepstrum (CEPSRUM) of the vibration of a turbocharger of a ZTEYUM diesel locomotive No. 1087. Frequency values with a maximum scale length of 400 Tz are plotted in the spectrum along the abscissa axis; along the ordinate axis, the rms value of vibration velocity (RMS) with a maximum length of 1.79 mm / s, time values with a maximum scale length of 1 s are plotted in the spectrum along the abscissa axis; on oci4 ordinates, the level of the cepstrum with a maximum scale length of 8.66 dB; in FIG. 2 - vibration cepstrum of a ZTEYUM diesel locomotive with a maximum scale along the abscissa axis, respectively, 31.3 ms and 125 ms; in FIG. 3 - low-frequency spectrum after synchronous averaging (ENH SPEC) and power spectrum (AUTOSPEC) of a turbocharger vibration in a frequency range up to 400 Hz; in FIG. 4 is a block diagram of a device for implementing the proposed method.

It was found that if the spectrogram contains periodic components (harmonics), then there is a dependence

4. About © SL

between the harmonics of the spectrum f and the rachmonic and cepstrum T, as well as the distance between the individual harmonics Af and the line frequency of the cepstrum AT: f 1 / t; Af 1 / AT.

The presented ratio is demonstrated by the example of a spectrum and a cepstrum of vibration velocity of bearing housings of the TK-34 urban compressor. In the spectrum, dyelonic harmonics fg 14 Hz, Afg 14 Hz, and BtfkericTpe the corresponding diesel rhmonics TD 71.3 ms ATD 71.3 ms are observed.

In order to iden tify rotor and half rotor harmonics (bearing frequencies), the vibrations of a turbocompressor need to reduce the time resolution of the cepstrum.

On the cepstrogram, the first, 3 ms and second 2TP 8.54 ms rahmonics were found, corresponding to the rotor harmonic fp

232 Hz and a half rotor harmonic of 1 / 2fp 116 Hz of the spectrum (Fig. 2). In addition, a known diesel turbocharger TD 71.3 ms was detected. So using

the second cepstrum rhmonics identified rotor and half rotor harmonics of the turbocharger vibration, overlapping sources of strong extraneous noise (diesel harmonics),

By turbocharger with cylindrical plain bearings, rotor harmonics fp 232 were identified

Hz and half rotor harmonic 1 / 2fp 116 Hz, significantly exceeding the amplitude of the rotor harmonic (Fig. 1). For example, the half rotor harmonic is 7.63 mm / s and the rotor harmonic is 1.6 mm / s. Self-oscillating modes of rotation of the rotor are detected on all turbochargers tested. The amplitude of the half-rotor harmonic of the 1 / 2fp 136 Hz vibration spectrum is 6.67 mm / s and is comparable with the diesel harmonic amplitude of 6.82 mm / s (Fig. 3). The rotor harmonic of the turbocharger is 1.7 mm / s.

Thus, a bearing frequency (half rotor harmonic) was detected in the low-frequency vibration spectrum of the turbocharger and a connection was found between the detected diagnostic features and defects in the sliding bearings, in particular rotor auto-oscillations. The threshold level of the second rotary cepstrum rahmonics is set for each type of turbocharger and determines the Goth level, the excess of which under operating conditions allows us to identify the initial stage of bearing failure, i.e. determine the deviation of the technical condition of the controlled turbocharger from the defect-free one.

The detection of rotor harmonics and bearing frequencies associated with signal extraction is generally carried out by increasing the signal-to-noise ratio by synchronous time averaging. Isolation of signals in the above

0 sense effective in terms of eliminating uncorrelated noise superimposed. repeated signals (periodic), and contribute to a significant increase in the signal-to-noise ratio. However, to apply the time averaging process, knowledge of the clock frequency is necessary.

When processing vibration signals of turbochargers, after the detection of rotor harmonics and bearing frequencies, synchronous averaging is performed in the time domain using an additional filter. Synchronization of rotor harmonic fp 273 Hz and bearing

5 frequencies (Fig. 3) made it possible to increase the noise level by more than two times and to distinguish more clearly the amplitudes of the studied frequencies in the spectrum. For example, the amplitude of the rotor harmonic decreased from a value of 9; 78

0 mm / s to 4.78 mm / s, and the amplitude of the bearing frequency from 6.67 mm / s to 2.62 mm / s.

The threshold value of the synchronized level of vibration velocity in the frequency range corresponding to one second

5 of the rotor harmonic is set for each type of turbocharger and determines the level, exceeding which under operating conditions allows us to identify a further stage of bearing failure and to determine significant deviations of the clearances in the bearings of the controlled turbomachine from the defect-free.

To implement the detection method

5 defects in a turbocompressor bearing, a device is proposed (Fig. 4), comprising a vibration sensor 5, which is attached to the housing of a turbocharger 1 by means of a horseshoe-shaped magnet 4. An electrical signal from sensor 5 is supplied and amplified in a logarithmic amplifier 6. An amplified electrical signal (voltage), proportional to the magnitude of the vibration velocity of the turbomachine

5 on a logarithmic scale enters the next band-pass filter 7, tuned to half the rotor speed fp / 2, where fp is the rotor speed. Filter bandwidth Af fM3Kc is ft-imi, where fM3Kc frnviH is the maximum and minimum filter frequency selected from the condition: f max fnnH 1.26; Af / fp, 26,. the bandwidth does not exceed 1/3 octave.

The maximum and minimum values of the filter frequency are Tmax (fp + Dt) / 2; fMMH (fp- Af) /2,T.e. the filter is set to half the rotor speed. Such a frequency range makes it possible to use the necessary resolution in frequency and time.

The filtered electrical signal, proportional to the rms value of the vibration velocity on a logarithmic scale in the frequency range corresponding to half the rotational speed of the rotor from the filter 7, is fed to a specialized digital device 8 by a microprocessor, where it is converted into a cepstrum value and is extracted as a second rotary rahmoniki. The level of the second rotor rachmonica capra is supplied to a comparator 9 (comparator) containing a demultiplier.

The result of comparing with the normalized level of the second cepstrum rachmonica through the demultiplier and analog-to-digital converter 10 is supplied to the indicating device 11, where the cepstrum level is displayed. If the level of calculation of the cepstrum value in the microprocessor 8 exceeds the normalized value in the comparison device 9, then the filtered electrical signal is sent through the demultiplier of the comparison device to the specialized digital device microprocessor 8, where the signal is averaged synchronously, and then one second rotor harmonic is calculated. The frequency of the synchronized one second rotary harmonic of the spectrum is supplied to the comparison device 9. The results of the comparison with the normalized level of one second harmonic of the spectrum through the demultiplier and analog-to-digital converter 10 are supplied to the indicating device 11, where the level of the synchronized bearing frequency is displayed and the final diagnosis is identified. The circuit is powered from the power unit 12. The built-in calibrator 13 and switch 14 provide self-control of the device.

Claims (1)

SUMMARY OF THE INVENTION A method for detecting defects in turbocharger bearings by measuring the level of one second rotor harmonic of the vibration spectrum of a turbocharger, determining self-oscillations of the rotor and clearances in plain bearings, and determining the clearance in bearings and self-oscillations of the rotor by exceeding the level of one second rotor harmonic of the normalized value so that in order to increase accuracy when using the method for a turbocharger of internal combustion engines, divide the cepstrum of the vibration signal by non-linear transformation of vibrations in the form of a logarithm of the spectrum with subsequent inverse Fourier transforms and extract it as the second rotary cepstrum of the cepstrum, then additionally synchronously average the vibration signal over time with a synchronization frequency equal to one second rotor harmonic, and then the level of one second rotor harmonic is extracted by the direct Fourier transform and the clearance in the rotor bearings is determined by exceeding the level of one th second rotor harmonic of synchronized normalized values. I Gcha WITH Ci (/ {1 ЕКН SPEC С ./) VAT Vi UJSrtH / c «MbLIN X O. 0Н% 40ЈШ LIN YOGUR Г STOBED K T "G" " HH; O.OHz v “Y / y (/ S 1 S4Wpfcrf - ii “th ™ w4 iiv Ph.Z Sf fsJf sSJ