DE102011104271B3 - Method for monitoring quality and aging of lubricants by dissipation factor measurements for e.g. aircraft, involves utilizing differences between dissipation factors in unused and aged states of lubricants for rating of state changes - Google Patents

Abstract

The method involves determining a dissipation factor of a test object from basic shrinkage of a measurement signal and a reference signal from a phase shift. Polarization losses are determined for quality and aging of lubricants from portions of guidance losses. Differences between the measured dissipation factors in the unused state of lubricants and the measured dissipation factors in an aged state of lubricants is used for rating of the state changes of quality and/or the aging of lubricants. A scheduling for state-oriented maintenance is performed. An independent claim is also included for a measuring system for monitoring quality and aging of lubricants.

Description

The present invention relates to a method and apparatus for monitoring the quality and aging of lubricants using loss factor measurements.

The quality and the aging of lubricants are significant influencing factors for availability and reliability in plant construction and mechanical engineering, as well as in driving and aircraft technology, marine engineering and other components to be lubricated. Even more important is the safety of the entire drive technology.

In this context, oil-soluble active ingredients such as additives for mineral oils, mineral oil products or synthetic oils should be mentioned in order to improve the physical and chemical properties and thus the lubricating effect and to minimize the effects of aging. Nevertheless, lubricants and lubricating oils age by thermal action, oxidation and moisture.

It is known that oil quality is performed with resonant and oscillator circuits operating at resonant frequencies between 10 MHz and 300 MHz ( DE 698 10 288 T2 )/1/. At these frequencies, the dipoles in the oil can no longer sufficiently follow the adjacent alternating field. The output signals of this circuit for evaluating the oil quality at a temperature of 50 ° C are 3.8 V for new oil and 2.8 V for very heavily aged oil.

It is further known, method and apparatus for monitoring the quality of lubricating oil by ion mobility spectroscopy ( EP 1 387 165 A1 ) / 2 /. In this case, a lubricating oil sample or exiting steam of this lubricating oil is taken from a transmission. The sample is fed to an ion mobility spectrometer and analyzed for existing substances and evaluated.

Also known is a method for diagnosing the dielectric aging of individual components of electrical installations and devices by means of loss factor measurements with frequencies smaller than the frequency of the public, electrical supply systems ( DE 10 2005 050 112 B4 ) / 3 /. This method relates to electrical insulating materials and operates in a lower frequency range than the public electrical supply systems.

Moreover, loss factor measurement methods for electrical insulating materials by means of Schering bridge circuits or computer-based measuring systems which operate on the principle of a vector impedance measurement are known / 4 /.

In addition, it is known that medium-voltage loss factor measurements were made on electric materials from generator bars both with the Schering bridge and with the computer-based loss factor measurement / 5 /.

Furthermore, a method for the production of dielectric cable impregnating oils and loss factor measurements of these oils for checking and optimizing the applicability are known (US Pat. DE 1 050 48 216 B ) / 6 /.

The indicated in the claims invention is based on the problem of monitoring the quality and aging of lubricants with the help of loss factor measurements in plant and machinery and in lubricating drive systems sensitive and cost-effective online with and without remote access and offline to perform time-scheduled lubricant Change intervals to state-dependent lubricant change intervals or if necessary, for safety reasons shutdowns.

This problem is solved by the features specified in the claims.

The advantages achieved by the invention are in particular that, instead of resonant and oscillator circuits (frequency range 10 MHz to 300 MHz) with Schering bridge circuits or computer-based measuring systems that operate on the principle of vectorial impedance measurement in the frequency ranges from 1 Hz to 10 kHz , is measured.

For resonance and oscillator circuits, the loss factors (at 50 ° C oil temperature), d. H. the measurement differences between new and very aged lubricating oils at 26% (decrease) / 1 /, d. H. it gives a change factor (multiplication factor) of 0.74 for the evaluation. At higher temperatures up to 120 ° C this factor becomes even less favorable.

The inventor is based on the finding that due to the lower frequency range of 1 Hz to 10 kHz, the dipoles, ions and charge carriers can better follow the applied electric field both in unused (new) and especially in aged lubricants. This significantly increases the loss factor values. As described in the embodiment, resulting advantageously at 50 ° C oil temperature between new and very heavily aged lubricating oils for the corresponding measurement differences in the loss factors, a change factor of 7.1 (increase). At higher oil temperatures, the corresponding change factors are even higher.

This makes the quality and aging of lubricants in plants, in machines and assemblies, in engines, as well as in vehicles and aircraft, in marine propulsion systems and in wind turbines more sensitive and thus more accurately measurable. This means that the influences on the quality level and the degree of aging due to chemical and physical reactions, caused by heat, moisture, acidity, foreign particles, oxidation, as well as the influences of additives, cracking products and catalysts, can be more accurately recorded and evaluated.

This makes it possible to move from time-planned lubricant change intervals to state-oriented lubricant change intervals.

In addition, by means of Schering bridge circuits or computer-aided measuring systems with the help of capacitive probes and temperature sensors on-site measurements can be carried out with or without remote access with little technical and financial effort.

The figures show:

U

Prüfwechselspannung

R

Referenzzweig

M

Messzweig

C₀

Referenzkapazität

C_x

Prüflingskapazität

S₀

Stromsensor

S_x

Stromsensor

T

Temperatursensor

LWL

Lichtwellenleiter

DSP

digitaler Signalprozessor

1 : Schematic diagram of the computer-based loss factor measurement

U

test voltage

R

reference branch

M

measuring branch

C ₀

reference capacity

C _x

Prüflingskapazität

S ₀

current sensor

S _x

current sensor

T

temperature sensor

LWL

optical fiber

DSP

digital signal processor

2 : Graphical representation of the phase shift φ of the reference signal (RS) and of the measuring signal (MS)

3 : Determination of the quality and / or aging of lubricating oils by means of loss factor measurements at 22 ° C

4 : Determination of the quality and / or aging of lubricating oils by means of loss factor measurements as a function of the temperature

5 : Determination of the quality and / or aging of lubricating oils by means of loss factor measurements as a function of the temperature.

An embodiment of the invention will be described in more detail below. Schering bridge circuits consist of capacitors and resistors and form an AC bridge. The adjustment elements to be operated are housed in a grounded, separate housing. The test object and a lossless Vergeichskondensator are at the test voltage. Using the adjustment elements and a zero indicator, the bridge is adjusted.

A corresponding further development, which is preferably used here, is the computer-based loss factor measurement ( 1 ) consisting of the reference branch (R) with the capacitance (C _o ) and the current sensor (S _o ) and the measuring branch (M) with the Prüflingskapazität (C _x ) and the current sensor (S _x ). This measuring system works on the principle of vector impedance measurement. The current signals measured in the branches are digitized and transmitted by means of optical waveguides (LWL) to a digital signal processor (DSP) and further processed in a Fourier transformation. In this case, the phase position and the amplitude are determined for the currents of the reference branch and the measuring branch. From the respective fundamental oscillations of the measuring signal (MS) and the reference signal (RS), the loss factor tan δ of the test object is determined from the phase shift φ ( 2 ): δ = 90 ° - φ tan δ = tan (π / 2 - t · φ / T · 2π).

In this case, T is the period duration for the reference and measurement signal and t is the current time coordinate. The loss factor tan δ of the test object is composed of the proportions, the conduction losses and the polarization losses: tan δ = tan δ _conduct + tan δ _pol .

These are decisive for the quality and aging of lubricants.

Loss factor values of lubricating oils are measured by means of probes which are measured as cylinder or pot capacitors in the frequency range from 1 Hz to 10 kHz. In the exemplary embodiment, the loss factor values were determined, preferably with the parameters 100 Hz and 100 V. The oil temperature is measured by a temperature sensor (T) ( 1 ).

in the 3 The loss factor values for a new oil and for different aged oils are shown. From this graph, which holds for a temperature of 22 ° C, it can be seen that the difference between the loss factor 0.05 of the new oil and the loss factor 0.9 of the very much aged oil corresponds to an increase factor of 18.

In 4 For lubricating oils, the temperature dependence of the loss factor is given. The state changes and / or the aging of lubricants, the lubricating oils at an oil temperature of 50 ° C is the difference between the measured loss factor 1.02 when new and the measured loss factor 7.2 in the very aged condition. This corresponds to an increase factor of 7.1.

The difference at an oil temperature of 100 ° C between the measured dissipation factor 4.5 in the new state and the measured dissipation factor 65 in the very strongly aged state results in an increase factor of 14 ( 5 ).

This means that the measuring method described in this invention has a very high measuring sensitivity and thus different quality and aging conditions can be determined very well in practice.

bibliography

• /1/ DE 698 10 288 T2
• / 2 / EP 1 387 165 A1
• / 3 / DE 10 2005 050 112 B4
• / 4 / T. Strehl, A. Engelmann, Mobile Test System for the Isolation Diagnosis of Electrical Equipment, etz, Issue 18/2003
• / 5 / M. Muhr, R. Schwarz, C. Sumereger, G. Knollseisen, Comparison of Loss Factor Measurement Methods and the Partial Discharge Behavior of Generator Bar Models, n / a VDE Verlag GmbH, pp. 339-344, 2006
• / 6 / DE 1 050 48 216 B

Claims (13)

Method for monitoring the quality and the aging of lubricants by means of loss factor measurements, wherein the computer-based loss vector measuring system operates according to the vector-method or the Schering-bridge circuit principle, wherein the current signals measured in the branches are digitized and sent to a digital signal processor ( DSP) and further processed in a Fourier transformation, wherein from the respective basic shrinkages of the measurement signal (MS) and the reference signal (RS) from the phase shift φ the loss factor tan δ of the test object at 1 Hz to 10 kHz is determined, the Dissipation factor tan δ of the test object is made up of the proportions of the conductive losses and the polarization losses, which are decisive for the quality and the aging of lubricants, whereby the differences between the state changes of the quality and / or the aging of lubricants respectively n the measured loss factors in the new state (target state) and the measured loss factors in the aged state (actual state) are used and wherein the method has a very high sensitivity, so that small different quality and aging state changes are displayed very accurate practice. The method of claim 1, wherein after evaluation of the detected measurement results by comparison with predetermined limit values in addition in a further process step improving active ingredients are added. The method of claim 1, wherein scheduling for condition-based maintenance is performed. The method of claim 1, wherein after evaluation of the detected measurement results by comparison with predetermined limits, a classification is made. The method of claim 1, wherein after evaluation of the detected measurement results by comparison with predetermined limits, the lubricant is changed. The method of claim 1, wherein after the evaluation of the detected measurement results in case of exceeding of predetermined limits for safety reasons, a shutdown is made. The method of claim 1, wherein after evaluation of the detected measurement results by comparison with predetermined limits decision support for investment planning and / or new purchases arise. The method of claim 1, wherein the method is performed in online mode with or without remote access or in offline mode or in the laboratory. Measuring system for monitoring the quality and the aging of lubricants consisting of a reference branch (R) with the capacity (C ₀ ) and the current sensor (S ₀ ) and a measuring branch (M) with the Prüflingskapazitat (C _x ) and the current sensor (S _x ), wherein applied to both branches with the capacitive probes an AC voltage in the frequency range of 1 Hz to 10 kHz and wherein a measuring method according to one of claims 1 to 8 is carried out during operation. Measuring system according to claim 9, having a temperature sensor for determining the oil temperature. A measuring system according to claim 10, wherein the voltage applied to the probes is 100V at a frequency of 100Hz. Measuring system according to claim 9, wherein means for online operation with and without remote inquiry or for offline operation are installed. Measuring system according to claim 9 with an optical waveguide for transmitting the measuring signals to the digital signal processor (DSP).

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