EP0095037A2 - Lubricant watching device at a piston compressor - Google Patents

Abstract

The lubricant monitoring system comprises an element which absorbs a liquid lubricant on the piston rod between a lubricant wiper assembly surrounding the same and a seal which surrounds the piston rod where the rod enters the compressor cylinder and an electrode of a measuring capacitor (CM) near the element. The lubricant absorbent element acts as the dielectric of the measuring capacitor. In the event of a fault on the lubricant wiper assembly, liquid lubricant is absorbed by the absorbent element so that the dielectric constant changes. This can be utilized for an alarm.

Description

The invention relates to a lubricant monitoring arrangement on a piston compressor, in particular for compressing oxygen.

In piston compressors for compressing gases that cause fire, for example oxygen, a lantern-like housing part with observation openings is provided between the crankcase and the housing containing the cylinders. At the transition from the crankcase to the lantern housing, a partition is provided which also has lubricant rings for the piston rod. At the transition from the lantern housing to the cylinder housing, a seal is provided which surrounds the piston rod and prevents the escape of oxygen from the cylinder into the lantern chamber. Between the lubricant wiper rings on the one hand and the seal on the other hand, a ring is clamped onto the piston rod, which prevents the wafer-thin film of lubricant from spreading Forms crankcase on the piston rod, reaches the area of the seal on the cylinder housing. As long as the lubricant wiper rings are intact, the wafer-thin lubricant film on the piston rod does not pose any risk of fire, since the lubricant film does not move relative to the piston rod and cannot exceed the ring attached to it. If, however, the lubricant scraper rings are no longer intact or worn, lubricant can be dragged from the crankcase in such an amount that the lubricant gradually exceeds the clamped ring and then reaches the seal on the cylinder housing, where there is contact between oxygen and lubricant Fire could arise.

In some countries, therefore, to protect the operating personnel, it has been recommended that protective walls, e.g. made of concrete. However, such protective walls hinder access to the compressor by the operating personnel. If this personnel wants to observe the compressor from outside the protective wall, the observer can miss details, especially if the protective wall is a large distance away from the compressor due to the space required for maintenance and repair work.

The invention has for its object to provide a lubricant monitoring arrangement that detects any penetration of large amounts of lubricant on the piston rod and can then turn off the piston compressor and / or give an alarm.

According to the invention, this object is achieved in that on the piston rod between an oil wiper pack and a seal which the piston rod penetrates at their penetration closing level surrounding the compressor cylinder, at least one liquid lubricant The absorbent body and in the region of an electrode of a measurement capacitor prior ^g are e-view, wherein the absorbent body is used as the dielectric of the measuring capacitor. When larger amounts of lubricant appear on the piston rod, the dielectric constant of the absorbent body changes, which is reflected in a change in the signals from the measuring capacitor. This signal change can then be used to switch off the compressor and / or to trigger an alarm. It is therefore unnecessary to determine the effectiveness of the oil scraper pack from outside or inside any protective walls by observation or possibly to set up protective walls and the like in the area of the compressor.

According to a further development of the invention, the electrode of the measuring capacitor is connected to a further electrode which, together with an electrode which is arranged at rest while leaving an air gap free, forms a coupling capacitor to which a capacitance measuring device is connected. This avoids connecting the connections of the non-moving capacitance measuring device to the moving electrode or moving this measuring device with the piston rod.

In order to also keep away any thermal influences that could have an unfavorable effect on the capacitance measurement, according to a further embodiment of the invention, in addition to the electrode of the measuring capacitor, a second electrode of the same dimension and shape as the electrode of the measuring capacitor is attached to the piston rod between the lubricant-absorbing body and the seal provided that, together with an air space, which is located as a dielectric between the second electrode and the piston rod, forms a comparison capacitor. The comparative capacitor and the measuring capacitor are therefore subject to approximately the same heat influences that occur during the Operation of the compressor can occur. Since both the capacitance of the measuring capacitor and that of the comparative capacitor are recorded with each stroke of the piston rod, changes in capacitance caused by the effects of heat are thus compensated for.

• Fig. l einen Axialschnitt durch einen Kompressor im Bereich des Laternengehäuses,
• Fig. 2 die Anordnung eines Messkondensators an der Kolbenstange,
• Fig. 3 die Anordnung von zwei Kondensatoren an der Kolbenstange,
• Fig. 4 ein Blockschaltschema einer elektronischen Schaltung zur Anordnung nach Fig. 3 für einen Kompressor mit mehreren Kolbenstangen,
• Fig. 5 ein Schaltschema der elektronischen Auswerteeinheit in Fig. 4 und
• Fig. 6 ein Zeitdiagramm mit dem Kurvenverlauf verschiedener im Blockschaltschema nach Fig. 4 auftretender Grössen.

Some embodiments of the invention are explained in more detail in the following description with reference to the drawing. Show it:

• 1 shows an axial section through a compressor in the area of the lantern housing,
• 2 shows the arrangement of a measuring capacitor on the piston rod,
• 3 shows the arrangement of two capacitors on the piston rod,
• 4 shows a block circuit diagram of an electronic circuit for the arrangement according to FIG. 3 for a compressor with a plurality of piston rods,
• Fig. 5 is a circuit diagram of the electronic evaluation unit in Fig. 4 and
• FIG. 6 shows a time diagram with the course of the curve of various sizes occurring in the block circuit diagram according to FIG. 4.

1, the piston compressor has a cylinder housing 1 and a crankcase 2, which is connected to the cylinder housing 1 via a lantern-like housing part 3. In the lantern housing part 3, two observation openings 4 are provided opposite one another. From the crankcase 2 extends through the lantern-like Housing 3 is a piston rod 5, which is extended into the cylinder housing 1 and carries a piston at its upper end in FIG. 1 in a manner not shown. At the point where the piston rod 5 penetrates the cylinder housing 1, a seal 6 of a known type is provided. In a partition 7 between the crankcase 2 and the lantern-like housing part 3, a piston rod guide bearing 8 of a known type with three oil scraper rings 9 is provided. The oil scraper rings 9 ensure that lubricating oil from the crankcase 2 can at most spread as a wafer-thin film on the vertical piston rod 5, at most up to an oil trapping device 10 which is clamped on the piston rod 5. A lubricating oil monitoring device 11 is arranged on the upper end of the guide bearing 8 in FIG. 1, to which parts of the oil trapping device 10 also belong and which is shown in more detail in FIG. 2.

The oil trap 10 is composed of a ring 12 made of cotton or felt, an axially split sleeve 13 made of insulating material, for example Delrin (registered trademark) and an O-ring 14. The two-part sleeve 13 is held on the piston rod 5 by screws, not shown. In order to prevent the device from slipping axially on the piston rod 5, the latter is provided with a weak constriction 16 which is filled by the sleeve 13 and against which the O-ring 14 also bears. The ring 12, which can suck up lubricating oil, forms the dielectric of a measuring capacitor CM, the electrodes of which consist of the piston rod 5 and an annular metal coating 15 attached in the sleeve 13. The annular metal covering 15, which consists, for example, of an electroplated copper layer, is connected via a radial conductor 17 to an annular metal covering 18 which is arranged on the outer surface of the sleeve 13 and extends over the same height as the covering 15. The metal covering 18 also expediently consists of an electroplated copper layer.

The annular coating 18 forms an electrode of a coupling capacitor CK, the second electrode of which is formed by an annular metal coating 19 which e.g. in the form of an electroplated copper layer on the inner peripheral surface of an annular insulating body 20. The insulating body 20 can also consist of Delrin and is contained in an annular electrode holder 21 which is fastened on the housing of the piston rod guide bearing 8. The electrode 19 of the coupling capacitor is thus stationary and arranged relative to the electrode 18 such that it is opposite the piston rod of the electrode 19 at bottom dead center (UTP). This position corresponds to the position shown in FIG. 2. The electrode 19 is connected to a capacitance measuring device in a manner not shown here.

When lubricating oil is sucked up by the absorbent ring 12, its dielectric constant E changes from a value of approximately 1 to a value of approximately 2. This changes the capacitance of the measuring capacitor CM, all of which influences the capacitance of the coupling capacitor CK. During the dwell time of the piston rod in the UTP, a resulting capacitance C is measured, which results from the series connection of the two capacitors according to the formula:

This resulting capacity is recorded by the capacity measuring device mentioned and gives the operating personnel a clue as to how much oil has already penetrated from the crankcase into the oil trapping device 10. The measuring device can be connected to an alarm transmitter or can directly switch off the drive of the compressor.

Compared to this very simple embodiment of the lubricant monitoring, FIG. 3 shows a further developed embodiment in which any influence of temperature on the capacitance measurement is compensated for. 3, in addition to the measuring capacitor CM and the coupling capacitor CK, a comparative capacitor CV is provided in the oil trap 10 '. The comparative capacitor CV consists of an air space 22, the dimensions and shape of which are the same as the dimensions or the shape of the space of the measuring capacitor CM that receives the cotton or felt ring 12. Corresponding to the size and shape of the electrode 15 of the measuring capacitor, the comparison capacitor also has an electrode 25 of the same size and shape, which is formed as an annular metal coating on the cylindrical boundary surface of the space 22 in the sleeve 13. The electrode 25 is connected via a radial conductor 27 to an annular metal coating 28 which, like the electrode 18, is attached to the outer surface of the sleeve 13. The fixed electrode 19 of the coupling capacitor CK is of the same design as in the exemplary embodiment according to FIG. 2. The comparative capacitor CV is arranged on the piston rod 5 such that it faces the piston rod of the electrode 19 of the coupling capacitor in the UTP. In comparison to the arrangement according to FIG. 2, the measuring capacitor CM is therefore mounted at a lower point on the piston rod, so that when the piston rod 5 moves downward, the measuring capacitor first moves past the electrode 19.

4, the fixed part of the coupling capacitor CK, in addition to the electrode 19, has a potential control electrode 29 which is embedded in the insulating material 20, the whole being built into the housing of the electrode holder 21 on light metal. The radial distance between the movable electrodes 18 and 28 on the one hand and the fixed electrode 19 on the other is kept as small as possible. Between these electrodes, the capacitance of the coupling capacitor for the two movable electrodes 18 and 28 is approximately the same. Assuming that the oil trap 10 'expands evenly due to temperature influences, the capacitance of the coupling capacitor CK experiences the same change for both electrodes 18 and 28. The capacity of the _K opplungskondensators CK is connected with the capacity of the measurement capacitor CM and the comparison capacitor CV in series; the two capacitance values are thus detected at the connection of the electrode 19

The electrodes 19 and 29 are connected to an electronics unit 31 via a triax cable 30. Since it is assumed that the compressor has four cylinders, there are accordingly four piston rods and four identical capacitor arrangements with four triax cable connections I to IV.

In a regular cycle, the electronics unit 31 connects one of the four coupling capacitors via the respective connection I to IV to a high-frequency oscillator (not shown) in the unit 31. The RF potential of the first screen of the cable 30 and thus also of the control electrode is connected via a voltage follower 29 exactly tracked the potential of the cable core and the fixed electrode 19, so that the dead capacity is neutral. is. The capacitances CM ^* and CV ^* detected by the electrode 19 form part of the capacitance of the oscillating circuit of the oscillator, the frequency of which is therefore changed by the changes in these values.

The RF signal of the oscillator is fed via a coaxial cable 32 to a unit 33, which is a discriminator contains circuit that converts the frequency changes into voltage changes. In addition, the unit 33 contains a cyclic clock generator, which effects the switching of the four coupling capacitors via a cable 34. The input of an evaluation unit 35, which receives a voltage signal via a line 36, is connected to the output of the unit 33. This signal contains information about the increase in the capacitance of the measuring capacitor CM caused by the oil compared to the capacitance of the comparative capacitor CV which remains dry, in a cyclical sequence for each of the four piston rods.

From these changes, the evaluation unit 35 forms a measurement signal that is proportional to the accumulated oil quantity, which is displayed by a measuring device 37 and can be used to actuate an alarm device 38. Four lamps 39 indicate the switching cycle of the four coupling capacitors, which are every 15 seconds. switch.

6, a shows the time profile of the voltage signal u _D (t) fed via the line 36 to the evaluation unit 35, which can be displayed with an oscilloscope (not shown here) connected to this unit. The curve point 51 corresponds to the position of the oil trap 10 'far above the UTP. Here the electrode 19 has a very small capacity against the piston rod 5; the frequency of the oscillator in unit 31 is high and the voltage at the output of the discriminator in unit 33 is at its negative saturation.

When the piston rod 5 moves downward, the electrode 18 of the measuring capacitor CM first immerses in the coupling capacitor CK. The voltage quickly rises positively to the apex 53, which is higher the more oil has accumulated in the ring 12. The bottom 54 results when the electrode 19 is between the electrodes 18 and 28. In the UTP, the electrode 28 comes to stand in front of the electrode 19; this results in the peak 55 corresponding to the capacitance of the comparison capacitor CV, which remains at a constant level in the first approximation. When the piston rod 5 moves up again, the mirror-image continuation of the curve with the points 56, 57, 59 results.

5, the discriminator voltage u _{D is} initially present at the input of a comparator Kl. As soon as this voltage has risen slightly above the negative saturation value 51 in accordance with the point 52 of the curve in FIG. 6a, the comparator Kl tilts in the positive direction (FIG. 6b). This triggers a monoflop MF1. The short pulse L1 generated in this way erases the CM voltage value stored in the previous piston stroke in a peak value detector PD. If the signal voltage u rises to the apex 53, this new value remains stored in the peak value detector PD; this value is designated û _DM .

In the UTP (point 55), the electrode 28 of the comparative capacitor CV is in front of the electrode 19. Here the signal reaches the lower peak value û _DV . This value is also recorded and saved for the duration of the next stroke. For this purpose, according to FIG. 5, a differentiation stage Q is provided, in which the signal u _{D (t) is} differentiated electronically. The output voltage of the differentiating stage Q goes from u _D to zero at every vertex (point 5?, 55, 57) or valley (point 54, 56) (FIG. 6e). As this figure shows, the output voltage changes the sign from minus to plus at the peaks (points 53, 55, 57) and from plus to minus at the valleys (points 54, 56). A comparator F2 (FIG. 5) is controlled with these changes. The circuit logic following this comparator ensures that a sample-and-hold circuit SH is one Receives sample command only in the UTP (point 55 in Fig. 6a), with which the value ü _{DV is} recorded and stored. The circuit logic contains three monoflops MF2, MF3 and MF4, which are first activated by the comparator Kl as soon as its output signal at point 52 becomes larger (FIGS. 6g, i, l). Thus, these monoflops can only act during the measurement phase, which extends from points 51 to 59, corresponding to the movement of the oil trap 10 'in the area of the UTP.

At the first peak of u _D (point 53), the output signal of the comparator K2 (FIG. 6f) rises and triggers the monoflops MF2 and MF4 (FIG. 6g, 1), the monoflop MF2 setting the flip-flop FF1 with a short pulse (Fig. 6h).

At the first valley of u _D (point 54), the output signal of the comparator K2 (FIG. 6f) drops and triggers the monoflop MF3 (FIG. 6i), which in turn sets the flip-flop FF2 (FIG. 6k) with a short pulse; this flip-flop blocks the monoflop MF2 against further triggering. At the second peak of u (point 55), the output signal of the comparator K2 (FIG. 6f) rises again and triggers the monoflop MF4 again (FIG. 61). The short pulse of the monoflop MF 4 now passes through the AND gate A opened by the flip-flops FF1 and FF2 to the sample-and-hold circuit SH (FIG. 5) and effects a detection of the peak value û _DV , which then remains saved.

At the second valley of u (point 56), the output signal of the comparator K2 (FIG. 6f) drops again, triggers the monoflop MF3 (FIG. 6i) again, which resets the flip-flop FF2 (FIG. 6k). This closes the AND gate A and protects the sample-and-hold circuit SH from the following pulse of the monoflop MF4, which is triggered when ü _DM (point 57) is reached again. Resetting flip-flop FF2 also releases monoflop MF2, so that at the second peak of u _D (point 57), the output signal of comparator K2 (FIG. 6f), which triggers monoflop MF 2 (FIG. 6g), rises and thus causes a reset of the flip-flop FF1 (Fig. 6h).

With the further upward movement of the piston rod 5, u _D drops again to the negative saturation level (point 59).

When crossing the threshold of the comparator Kl (point 58 corresponding to point 52), its output signal drops again and blocks the monoflops MF2, MF3 and MF4 again. The circuit logic is thus reset to the initial state.

According to the above description, the new peak values of u _{D ',} which correspond to the capacitances of the measuring capacitor CM or the comparison capacitor CV, are stored in the UTP in the peak value detector PD or in the sample-and-hold circuit SH. A differential amplifier DV (Fig. 5) forms the difference u _B. Each time the felt ring 12 is renewed in the oil trap 10 ', this difference is adjusted to zero for each of the four piston rods with the aid of an adjustable auxiliary voltage u. The individual u _o values are switched electronically by the same clock generator; which switches over the four coupling capacitors.

To the extent that oil accumulates in the felt rings 12, the capacitance of the relevant measuring capacitor CM, ie û _DM , increases positively. From one stroke to the next, û _DM and û _{DV change} very little, and with it the differential voltage u _B. A low-pass filter TPF (FIG. 5) smoothes the by refreshing the voltage values in the peak value detector PD or in the sample-and-hold circuit SH conditional voltage jumps. The signal is displayed with the instrument 36 via a power amplifier EV connected to the low-pass filter TPF. With a comparator K3 with an adjustable threshold, which is also connected to the low-pass filter TPF, the alarm device 38 can be switched on via a relay R when a certain limit value of u _{B is} reached.

The average frequency of the HF oscillator contained in the unit 31 can shift over a longer period of time due to thermal changes in the capacitances of the measuring capacitor CM, the comparative capacitor CV and the coupling capacitor CK as well as changes in the elements of the oscillator itself. Although the circuit in the evaluation unit 35 forms the difference between the capacitances of the measuring and comparison capacitors, it is expedient to track the frequency discriminator in the unit 33 to the drift of the oscillator frequency. For this purpose, the peak voltage u _DV formed by the sample-and-hold circuit SH is fed back to the unit 33 via a line 40 (FIG. 4) and used to correct the basic level of the signal u _{D (t)} . This level is thus corrected so that the voltage value ü _DV remains at a constant level.

Instead of tracking the discriminator in unit 33 of the drift of the oscillator, the oscillator itself can be corrected by feeding the voltage u _DV back to unit 31 via cable 32 or 34 and using it to regulate the frequency, for example by means of a capacitance diode.

The circuit described has the advantage that it detects the point in time at which the peak value (point 55 in FIG. 6a) occurs without detecting the UTP on the compressor by other means.

Deviating from the examples described, it is also possible to use the monitoring arrangement for compressors which do not have a piston rod guide bearing, but only a package of oil scraper rings in the region of the partition 7; these rings also seal the space of the crankcase against the space of the lantern housing part. The two halves of the axially divided sleeve 13 can also be held together instead of by screws by means of exciting rings placed around the sleeve.

Claims (13)

1. Lubricant monitoring arrangement on a piston compressor, in particular for compressing oxygen, characterized in that at least on the piston rod between a lubricant wiper package at the exit of the piston rod from the crankcase of the compressor and a seal that surrounds the piston rod at its penetration point in the compressor cylinder a liquid lubricant absorbing body and in the area of which an electrode of a measuring capacitor is provided, the absorbing body serving as the dielectric of the measuring capacitor. 2. Arrangement according to claim 1, characterized in that the electrode of the measuring capacitor is connected to a further electrode which, together with an electrode arranged at rest while leaving an air gap, forms a coupling capacitor which is connected to a capacitance measuring device. 3. Arrangement according to claims 1 and 2, characterized in that the fixed electrode of the coupling capacitor is arranged in such a position that it faces the further electrode when the piston rod is at bottom dead center. 4. Arrangement according to claims 1 and 2, characterized in that on the piston rod between the lubricant-absorbing body and the seal in addition to the electrode of the measuring capacitor, a second electrode same dimension and shape as the electrode of the measuring capacitor is provided, which together with an air space, which is located as a dielectric between the second electrode and the piston rod, forms a comparison capacitor. 5. Arrangement according to claim 4, characterized in that the electrode of the comparison capacitor is connected to a further electrode which cooperates as a movable electrode with the electrode of the coupling capacitor arranged at rest. 6. Arrangement according to claim 5, characterized in that the fixed electrode of the coupling capacitor is arranged in such a position that it faces the movable electrode of the comparative capacitor when the piston rod is in bottom dead center. 7. Arrangement according to one of claims 1 to 6, characterized in that the absorbent body surrounds the piston rod in a ring and said electrodes are designed as ring-shaped metal coatings surrounding the piston rod. 8. Arrangement according to claim 7, characterized in that the metal coverings in the form of electroplated copper layers are attached to an insulating body attached to the piston rod or to an insulating body surrounding the piston rod and supported on the crankcase of the compressor. 9. The arrangement according to claim 8, characterized in that the insulating body attached to the piston rod has the shape of an axially divided sleeve. 10. Arrangement according to claims 4 to 9, characterized in that an electronic circuit is provided which is designed such that it detects, stores and compares the sizes of the capacitances of the measuring and comparative capacitors in the region of the bottom dead center of the piston rod and from the increase in the capacitance of the measuring capacitor relative to the capacitance of the comparative capacitor forms a difference signal which corresponds to the amount of lubricant absorbed by the absorbent body. 11. The arrangement according to claim 10, characterized in that the electronic circuit has a high-frequency oscillator and is designed such that the sizes of the individual capacitances are measured by frequency modulation of the high-frequency oscillator and by subsequent demodulation. 12. Arrangement according to claims 10 and 11, characterized in that the electronic circuit contains an evaluation unit with a peak value detector and a sample-and-hold circuit. 13. Arrangement according to one of claims 10 to 12, characterized in that an alarm transmitter and / or recording device is connected to the output of the electronic circuit.

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