EP4311937A1 - Method for automatically monitoring a piston machine, piston machine which can be monitored according to the method, and computer program comprising an implementation of the method - Google Patents

Abstract

A method for automatically monitoring a piston machine (10) and a piston machine (10) operating according to the method are specified, wherein during operation of the piston machine (10) a suction and pressure valve (16) enclosed by the piston machine (10) is opened. 18) a time value (30, 32) is determined or can be determined, wherein a difference (40) is formed or can be formed from the determined time values (30, 32) and the difference (40) with a predetermined, predeterminable or determined setpoint (46) is compared or is comparable and a signal (48, 48 ') is or can be generated when the setpoint (46) is exceeded or undershot.

Description

Method for automatically monitoring a piston engine, piston engine that can be monitored according to the method and computer program with an implementation of the method

The innovation proposed here relates to the technical field of automatic monitoring of a piston or rotary machine, collectively referred to below as a piston machine, in particular a piston compressor, or at least a machine comprising a piston machine, in particular a piston compressor. Examples of piston machines are piston compressors, piston engines, compressors, pumps, hypercompressors, piston pumps, and the like.

If a piston machine is spoken of as an example below, this represents one of the aforementioned machines and groups of such machines, which include at least one piston machine, in particular a piston compressor, and is therefore not to be interpreted in a restrictive manner.

One task of the innovation proposed here is to specify a criterion that is, on the one hand, suitable for monitoring the condition of a piston engine and, on the other hand, is also a particularly simple criterion. Proceeding from this, a further task of the innovation proposed here is to provide a method for automatically monitoring a piston engine based on this criterion.

The task of automatically monitoring a piston engine is achieved according to the invention by means of a method with the features of claim 1. This requires a method for automatic monitoring, in particular automatic online monitoring or for continuous automatic monitoring, a piston machine is provided with the following:

The piston engine comprises at least one suction valve and at least one pressure valve, possibly also in the form of a so-called central valve comprising at least one or at least one suction and pressure valve. During operation of the piston engine, a time value (opening time value) is determined for opening the at least one suction valve and for opening the at least one pressure valve. If there are several suction or pressure valves, this applies to one suction valve and one pressure valve from the group of suction or pressure valves. A time value for such an event is, for example, related to a respective rotational position of a crankshaft that may be included in the piston engine. Such a time value is then given in “degrees of crankshaft” and describes the rotational position at the time of the respective event, i.e. at the time of opening of the respective valve. As part of the method, it is then further provided that a difference is formed from the determined time values and the difference is compared with a predetermined, predefinable or determined target value, in particular with a target value determined in the course of the method and possibly updated repeatedly. Finally, as part of the method, a signal, in particular an error notification signal, is generated if the setpoint value is exceeded or fallen short of.

The innovation proposed here is based on the knowledge that the times of opening of the suction and pressure valves included in the piston engine (each at least one suction valve and one pressure valve) are important parameters for the operation of the piston engine. In addition to such characteristic values, other characteristic values are known, for example pressure, in particular pressure values such as suction pressure and/or final/delivery pressure, temperature, capacity control values, vibration, power, etc. It is customary to monitor such characteristic values as part of the operation of a piston engine and based on Changes in such parameters to close a given or impending exception or error situation.

As part of a patent search based on the invention, extensive prior art was identified. From the DE 10 2013 109 410 A1 a calculation of a pressure-displacement diagram for a positive displacement pump is known. The prospect of detecting valve openings is only theoretical. There is no use. At the EP 3 486 482 A1 Valve opening times are determined and used to calculate/estimate a final pressure and, if necessary, to switch off if a maximum value is exceeded, but not for monitoring purposes and there is no qualification of valve damage. In the WO 2005/108765 A1 The times at which a valve opens or closes are not considered, but rather the period in which an actuator for a valve opens. So it's about how long the actuation activity of the valve lasts. At the DE 102 09 545 A1 The drive pressure of a valve control is measured and used to assess the condition of the control valve. Opening times do not apply. From the WO 2020/007923 A1 In connection with the present invention, the only result is that a diagnostic method can be carried out automatically using a computer. In the DE 10 2015 225 999 A1 Problems with control valves are recorded through a statistical valve position frequency analysis. At the WO 2006/000483 A1 The opening and closing times of exactly one valve and a period of time between these times are recorded. If the period becomes too long, the cylinder and combustion will be switched off. It's about the time at which a valve opens and closes and the time between the two events, i.e. different events at exactly one valve. The invention, on the other hand, is about the time difference between the opening of a suction valve and the opening of a pressure valve, i.e. the consideration of the opening event at different valves. With the approach of WO 2004/102052 A1 Leaks should be detectable on a valve. To do this, the sound/vibration is measured and processed in both the tight and leaky states. If the sound exceeds a limit value, this should indicate a leak. Also at the EP 1 477 678 B2 it's about structure-borne sound measurement and level comparison. At the EP 1 015 800 B1 In contrast to the approach proposed here, a closing time of motor-driven valves is determined. These are valves that are actively closed and the time for closing is determined. From the AT 402 090 B a method for flow control is known. The closing time of a suction valve is used as a control variable to regulate the flow rate of the compressor. There is no provision for detecting damage. The closing time is determined using vibration measurement. In the DE 32 44 738 C2 The period between opening and closing of a suction valve is considered. Changes should make it possible to identify a malfunction. However, by only considering the intersection of the dynamic pressure line with the suction pressure line, the behavior of the pressure valve is not taken into account. The opening of the pressure valve is used exclusively to calculate the steepness of the compression, which is not linear for compressible gases. This means that the methodology cannot be used universally and is only suitable for incompressible media.

An advantage of the innovation proposed here is, in addition to the possibility of deriving a qualitatively well-founded statement about the condition of the respective piston engine, also the ability to combine several individually meaningful characteristic values into a new characteristic value, namely in the form of the difference mentioned above. It has turned out that monitoring and, above all, properly evaluating a large number of parameters is complex and requires a certain level of specialist knowledge. The difference determined as part of the innovation proposed here can, for example, be displayed continuously or regularly to an operator when the piston engine is in operation, and the operator can thus quickly and easily assess the condition of the piston engine, in particular the condition of the sealing components - for example valves, piston rings, (Stuffing box) packing, valve and dead space controls - of each active compression chamber (compression space) judge. Furthermore, the difference determined can be used for automatic leak detection. In addition, the state of the piston engine and a change in the state can optionally also be based on a development of the difference, namely a development of the difference over a longer period of time, for example one hour, several hours, one day, several days, several weeks, several months, etc .up to several years.

The above-mentioned object is also achieved by means of a piston machine, which can be monitored according to the method proposed here and possibly an advantageous embodiment and which includes means for carrying out the method as described here and below or to which such means are assigned. Such means are summarized below under terms such as sensors, evaluation unit and monitoring unit and the monitoring unit is preferably a programmable monitoring unit in the form of or in the manner of a microprocessor system or the like. The method proposed here, possibly supplemented by individual or several advantageous embodiments described below, is preferably implemented in the form of a computer program for automatic execution (the computer program is an implementation of the method in question for monitoring a piston engine). The innovation proposed here is, on the one hand, also a computer program with program code instructions that can be executed by a monitoring unit and, on the other hand, a storage medium with such a computer program, i.e. a computer program product with program code means, and finally also a monitoring unit or a system which includes a piston engine and a monitoring unit, whereby in such a computer program is loaded or loadable in a memory of the monitoring unit as a means for carrying out the method and its configurations.

If procedural steps or sequences of procedural steps are described below, this refers to actions that take place due to the computer program or under the control of the computer program.

For the further description, in order to avoid unnecessary repetitions, features and details that are described in connection with the mentioned method for automatic monitoring of a piston engine, of course also in connection with and with regard to a monitoring unit set up to carry out the method or for carrying out System set up according to the method, comprising a piston engine or at least one piston engine and a monitoring unit or at least one monitoring unit - individually and collectively also referred to as a device - and vice versa. Accordingly, the method can also be developed by means of individual or multiple method features that relate to method steps carried out by the device, and the device can accordingly also be developed by means for carrying out method steps carried out as part of the method. Consequently, features and details that are described in connection with the method in question and possible configurations naturally also apply in connection with and with regard to the device intended to carry out the method and vice versa, so that the disclosure relates to the individual aspects of the invention is or can always be referred to mutually.

Advantageous embodiments of the invention are the subject of the subclaims. The relationships used within the claims indicate the further development of the subject matter of the referenced claim through the features of the respective dependent claim. They are not to be understood as a waiver of the achievement of independent, objective protection for the features or combinations of features of a dependent claim. Furthermore, with regard to an interpretation of the claims and the Description in a more detailed specification of a feature in a dependent claim, it can be assumed that such a restriction is not present in the respective preceding claims or in a more general embodiment of the subject method/device for automatic monitoring of a piston engine. Any reference in the description to aspects of dependent claims is therefore to be read expressly as a description of optional features, even without any special reference. Ultimately, the patent claims filed with the application presented here are merely suggestions for wording without prejudice to achieving further patent protection. Since the features of the dependent claims in particular can form separate and independent inventions with regard to the prior art on the priority date, the applicant reserves the right to make these or further combinations of features previously only disclosed in the description and/or drawings the subject of independent claims or to make declarations of division. They can also contain independent inventions that have a design that is independent of the subject matter of the claims referred to in each case.

It is preferably provided that in a method as described here and below and in a piston machine operating according to the method, in the event of the setpoint being exceeded on the one hand and in the event of the setpoint being undershot on the other hand, specific signals are provided, for example a first signal in the case of a If the limit is exceeded and a second signal is generated if the limit is exceeded. This also makes qualitative monitoring of the piston engine and even a respective compression chamber possible, and as a result a signal specific to the detected status, exception or error situation can be output. For example, exceeding the setpoint indicates an existing or impending so-called low pressure leak and if the setpoint is exceeded, a corresponding signal can be output and is output in the preferred embodiment (the term signal is sufficient in its meaning from a specific level on a signal line or a signal on exactly one signal line up to, for example, a text transmitted electronically and/or displayed in a suitable, fundamentally known manner, a text combined with image elements or a graphics). On the other hand, falling below the setpoint indicates an existing or impending so-called high-pressure leak and if the setpoint falls below the setpoint, a corresponding signal can be output and is output in the preferred embodiment (a signal with the scope of meaning outlined above). For an operator of the piston machine, such a specific status or error message makes maintenance and, if necessary, troubleshooting/troubleshooting much easier.

It is advantageously provided that in a method as described here and below and in a piston machine operating according to the method, the difference is formed for each working cycle of a piston included in the piston machine or at least for equidistantly spaced working cycles and the comparison with the target value for each working cycle or for each work cycle for which a difference was determined. Monitoring the difference in each work cycle or in equidistantly spaced work cycles ensures permanent or sufficiently long-lasting and, above all, meaningful monitoring of the piston engine and the regularity also ensures data that can be evaluated in terms of its tendency, for example to evaluate a change in the determined difference over time .

In the case of driving the piston of the piston engine by means of a crankshaft, the working cycle of the piston corresponds to a crankshaft cycle and then it is advantageously provided that the difference is formed for each crankshaft cycle or at least for equidistantly spaced crankshaft cycles and the comparison with the target value for each crankshaft cycle or for every crankshaft cycle for which a difference was determined.

It is particularly preferably provided that in a method as described here and below or in a piston machine operating according to the method in a piston machine in which an (additional) opening duration of at least one valve is influenced during operation, an opening time control value-dependent setpoint is used as the setpoint or . can be used. Influencing an opening duration of at least one valve (for example as in the AT 402 090 B described) acts on the valves in addition to the pressure conditions in the respective compression chamber and changes the opening time and thus the opening duration of the respective valve compared to conditions (opening time, opening duration) that arise without such an influence, i.e. without such an additional influence would.

Such (additional) influencing of an opening duration of at least one valve takes place, for example, in the form of an active influencing of the opening duration of at least one valve or in the form of a passive influencing of the opening duration of at least one valve. Actively influencing the opening duration of at least one valve has a direct effect on the respective valve, for example by actively keeping the valve open, for example mechanically or electromechanically by means of a corresponding actuator. A passive influence on the opening duration of at least one valve has an indirect effect on the respective valve, for example by changing the volume of the compression chamber as part of a so-called dead space control.

An opening duration of at least one valve is influenced, for example, by means of a control, in particular as part of a control by means of a control system or by means of a so-called active power control system or as part of a dead space control or as part of a speed control or as part of a combination of at least two such controls.

The result of influencing an opening duration of at least one valve is a control value, the application of which influences the opening duration of at least one valve during operation of the piston engine. The setpoint used to monitor the piston engine depends on this control value, which influences the opening duration/opening time of the respective valve. In general, the setpoint used is a function of this control value. Therefore, the setpoint set in the case of operation of a piston engine with an influence on the opening duration of at least one valve is referred to as the opening time control value-dependent setpoint. To the extent that the influencing of the opening duration of at least one valve is based on a regulation, the control value is dependent on a setpoint that is effective there. The opening time control value-dependent setpoint is therefore dependent not only on the respective control value, but also on the setpoint on which it is based. The designation of the setpoint used in the context of the method proposed here as being dependent on the opening time control value should therefore not be interpreted in a restrictive manner and also includes, for example, a dependence on a further setpoint, provided that this influences the opening time of at least one valve of the piston engine.

In the event that an opening duration of at least one valve is influenced during the operation of a piston engine, monitoring according to the approach proposed here can continue to be carried out by means of such a setpoint, namely an opening time control value-dependent setpoint, even in the case of changing time values (opening time values) due to the influence on the opening duration of at least one valve possible. Here too - in a fundamentally optional manner - a distinction between falling below or exceeding the setpoint, namely the opening time setting value-dependent setpoint, comes into consideration and in this respect what has already been said above applies accordingly and to avoid repetition, reference is made to it here without further ado.

It is also advantageous - additionally or alternatively - to monitor a respective regulation, for example a regulation in form a performance or damage area control. For this purpose, a temporal change in the determined difference (the difference from the determined time values) is considered. In principle, it is expected that the determined difference does not change or changes only slightly, in other words: It is checked whether a change in the determined difference during a predetermined or predeterminable period of time remains within a framework determined by a predetermined or predeterminable limit value. Exceeding the limit is an indication of faulty control or a faulty component of the control loop. Additionally or alternatively, the time course of the control value is also considered in relation to the time course of the determined difference (both during the same period of time). If during the period under consideration the difference determined remains the same or at least essentially the same in the sense outlined above and the control value increases, this is also an indication of a faulty control or a faulty component of the control loop. The components of the control circuit that may be identified as faulty in this sense include, in particular, the sensors, the controller and the actuator. Such a review of a respective regulation is a preferred, but nevertheless optional addition to the method proposed here and an implementation of such a review of a respective regulation comes accordingly as a supplement to an implementation of the method proposed here for automatic monitoring of a piston engine, in particular an implementation in the form of a computer program , into consideration.

An exemplary embodiment of the innovation proposed here is explained in more detail below using the drawing. Corresponding objects or elements are provided with the same reference numbers in all figures.

The or each exemplary embodiment is not to be construed as limiting. Rather, within the scope of the present disclosure, additions and modifications are also possible, in particular those that are, for example, by combining or modifying individual ones in conjunction with the general or Features or method steps described in a special part of the description and contained in the claims and/or the drawing can be found by the person skilled in the art with a view to solving the problem and, through combinable features, lead to a new object or to new method steps or sequences of method steps.

Show it

Fig. 1

a piston machine with a monitoring unit,

Fig. 2

a pressure curve recorded on a piston engine over a crankshaft cycle,

Fig. 3

a schematically simplified representation of a computer program as an example of an implementation of the method proposed here,

Fig. 4

a schematically simplified representation of a process flow within the framework of the method proposed here and

Fig. 5

a graphical representation of a control value-dependent setpoint.

The representation Figure 1 shows a piston engine 10 in a schematically simplified manner and with only a few details.

A piston engine 10, for example a piston engine 10 in the form of a piston compressor or the like, and its functionality is basically known per se. The following description therefore does not claim to be complete and is only intended to introduce basic terms:

A piston engine 10 is a device intended for conveying a gas or fluid, generally referred to below as a medium. A piston engine 10 comprises at least one cylinder 12. There is at least one compression chamber 13 in the cylinder 12. At least one piston 14 is guided within the cylinder 12 (one piston 14 for each cylinder 12). The or each piston 14 is movable in the cylinder 12 in a manner known per se by means of an external drive (not shown). A crankshaft, for example, acts as an external drive. Other external drives, for example a hydraulic drive, are also possible. The or each piston 14 moves oscillating in the cylinder 12.

The further description is continued in the sense of simple conditions based on a piston engine 10 with exactly one cylinder 12, exactly one compression chamber 13 in the cylinder 12 and, accordingly, exactly one piston 14. The number of these components is not important for the innovation proposed here and accordingly, a majority of the respective components must always be read and are, with this note, considered to be included in the description presented here.

As part of the oscillating movement of the piston 14, there is a cyclical and alternating forward movement, hereinafter referred to as the pre-stroke, and a subsequent backward movement of the piston 14, hereinafter referred to as the return stroke, and generally a position of the piston 14 in the cylinder 12, hereinafter referred to as the piston position. This respective medium is compressed in the compression chamber 13 (the compression chamber 13 is the area in the cylinder 12 in which the medium changes its pressure state) and the volume of the compression chamber 13 changes during the forward and return strokes of the piston 14 (the volume of the compression chamber 13 changes /decreases/increases due to the movement of the piston 14 and the piston 14 compresses the medium in the compression chamber 13 up to the desired delivery pressure; volume reduction during the forward stroke; volume increase during the return stroke). As part of the oscillating movement, the piston 14 exerts pressure on the respective medium during the pre-stroke.

A certain amount of the respective medium is sucked into the compression chamber 13 and expelled from it due to the cyclic movement of the piston 14 and the opening of at least one respective valve 16, 18. For this purpose, in a manner known per se, at least one valve 16, 18 (at least one so-called suction valve 16; at least one so-called pressure valve 18) is fluidly coupled to the compression chamber 13.

Here too, the further description is continued in the sense of simple conditions based on a piston engine 10 with exactly one suction valve 16 and exactly one pressure valve 18. The number of these valves 16, 18 and/or a possible combination in the form of a so-called central valve or possibly several central valves (a central valve includes at least one suction valve 16 and at least one pressure valve 18) is not important for the innovation proposed here and is accordingly a plurality of such valves 16, 18 (two or more suction valves 16 and/or two or more pressure valves 18) should always be read and with this reference should be considered to be included in the description presented here.

The work of the piston 14 is cyclical - a forward stroke and a return stroke of the piston 14 (each translationally) take place alternately and immediately after one another - and the piston 14 is driven by means of a drive, for example by means of a continuously rotating crankshaft. A forward stroke of the piston 14 and a subsequent return stroke of the piston 14 are collectively referred to as a compression cycle or a duty cycle for short (both terms refer to the same thing and are interchangeable). When the piston 14 in the cylinder 12 retracts (return stroke), the volume above the piston 14 in the cylinder 12 increases (the volume of the compression chamber 13) and the respective medium is sucked into the compression chamber 13 via the suction valve 16 (inlet valve). Following the return stroke of the piston 14 and after passing through a bottom dead center of the piston stroke, an advance takes place of the piston 14 in the cylinder 12 (pre-stroke). This leads to a reduction in the volume of the compression chamber 13 and the medium previously sucked into the compression chamber 13 is finally expelled from the compression chamber 13 via the pressure valve 18 (exhaust valve). When the piston stroke passes through a top dead center, the forward stroke of the piston 14 ends and is followed by another return stroke and so on.

The forward stroke and return stroke of the piston 14 alternately and cyclically follow each other directly, so that due to the suction of the respective medium during the return stroke and the expulsion of the sucked-in medium during the forward stroke, a delivery of the respective medium and possibly also a change in the pressure conditions between a suction side (downstream of the suction valve 16) on the one hand and a pressure side (upstream of the pressure valve 18) on the other hand.

The representation in Figure 1 shows - assigned to the piston engine 10 - a sensor system 20 which is at least temporarily assigned to the piston engine 10 by measurement technology. The illustration in Figure 1 further shows - also at least temporarily assigned to the piston engine 10 - a monitoring unit 22 and an evaluation unit 24 shown as being included in the monitoring unit 22. The terms sensor system 20, monitoring unit 22 and evaluation unit 24 are functional identifiers and do not imply any necessary spatial or device-related separation. For example, sensors 20 and evaluation unit 24 can be combined into one unit. Likewise, monitoring unit 22 and evaluation unit 24 or sensors 20, monitoring unit 22 and evaluation unit 24 can be combined into one unit or sensors 20, evaluation unit 24 and monitoring unit 22 can be spatially and device-technically separated.

The sensor system 20 comprises at least one measuring instrument and this takes measured values or data resulting from a simulation - hereinafter referred to individually or collectively as raw data 26 - in a manner known per se on the piston engine 10 or in relation to the Piston engine 10 on. The respective measuring instrument is used to record raw data 26 and the at least one measuring instrument records the valve activity (activity of the suction or pressure valve 16, 18; possibly a measuring instrument for recording the valve activity of the suction and pressure valve 16, 18) by recording such raw data 26 ) or a variable representative of valve activity.

An example of a measuring instrument included in the sensor system 20 is a pressure sensor which measures the dynamic pressure in the compression chamber 13, namely the dynamic pressure which arises in the compression chamber 13 due to the oscillating movement of the piston 14 within the compression chamber 13. Other measuring instruments that can provide raw data, which can be used to detect the opening of a valve 16, 18 (suction or pressure valve 16, 18), are also possible. An example of such a different measuring instrument is a vibration sensor, which detects the vibration in connection with a so-called opening stroke of the respective valve 16, 18, or a proximity sensor, by means of which the opening of the respective valve 16, 18 can be recognized by direct measurement.

The evaluation unit 24 receives the raw data 26 recorded by the sensor system 20 from the sensor system 20 and evaluates it. As part of this evaluation, the evaluation unit 24 determines a time or a measure for a time at which the suction valve 16 opens, and a time or a measure for one work cycle (compression cycle; the terms work cycle and compression cycle are interchangeable) of the piston 14 Time at which the pressure valve 18 opens, hereinafter referred to collectively as the opening time value 30, 32 or briefly as the time value 30, 32 (time value 30, 32 for the opening of the suction and pressure valve 16, 18 encompassed by the piston engine 10).

The result of the evaluation by the evaluation unit 24 is a pair of values per work cycle and this includes a first time value 30 for opening of the suction valve 16 comprised by the piston engine 10 and a second time value 32 for opening the pressure valve 18 comprised by the piston engine 10. The evaluation unit 24 determines such pairs of values, for example, for each work cycle or for regularly spaced work cycles, for example for every second work cycle third work cycle or every nth work cycle with, for example, n = [1 .. 1,000].

The valves 16, 18 (suction valve 16, pressure valve 18) open when a certain pressure level in the cylinder 12 is reached. They are kept closed for this long by the counterpressure in a respective supply line (suction-side supply line, pressure-side supply line) and, for example, by springs or the like until the pressure in the compression chamber 13 has reached a level to burp it. The suction valve 16 opens when the suction pressure level falls below. Open the pressure valve 18 when the final pressure/delivery pressure level is exceeded. The time values 30, 32 are therefore dependent on the dynamic pressure level in the compression chamber 13. If these change, this indicates possible leaks or mechanical damage to a valve 16, 18; on the cylinder 12, in the compression chamber 13 or the like.

A time value 30, 32 is, for example, the rotational position of the crankshaft, i.e. the respective rotational position at the time the respective valve 16, 18 is opened. The use of the rotational position of the crankshaft as a time value 30, 32 is quite common in practice. The consideration of the rotational position of the crankshaft as a time value 30, 32 is also understandable because the duration of a full revolution of the crankshaft (the duration of a working cycle of the piston 14) can be viewed as a unit of time and the current rotational position of the crankshaft is then a fraction of this time unit . Alternatively, a time measured in milliseconds, for example, at which the respective valve 16, 18 opens can also be recorded as the time value 30, 32. The time then starts, for example, at every work cycle or every nth work cycle, with, for example, n = [1 .. 1,000], of the piston 14 at zero.

In the interests of simple conditions, it is assumed for the further description that the piston 14 of the piston engine 10 is driven by means of a crankshaft and the rotational position of the crankshaft at the time of opening of the suction valve 16 and the rotational position of the crankshaft at the time of opening of the pressure valve 18 as Time values 30, 32 for opening the suction or pressure valve 16, 18 are considered. The respective rotational position of the crankshaft is detected by means of a suitable measuring instrument belonging to the sensor system 20, for example by means of an incremental encoder assigned to the crankshaft, and the recorded data on the rotational position belongs to the raw data 26 transmitted to the evaluation unit 24. The raw data 26 can be in the form of each a pair of values (pressure value, rotational position) are immediately transmitted to the evaluation unit 24. Alternatively, the raw data 26 can also be transmitted to the evaluation unit 24 in the form of a data set with, for example, all pressure values recorded during a working cycle of the piston 14 and the associated rotational position.

The representation in Figure 2 shows a pressure curve 34 in the compression chamber 13 of the piston engine 10. The pressure curve 34 is a graphical representation of raw data 26 recorded by means of the sensor system 20 in the case of a pressure sensor as a measuring instrument, transmitted to the evaluation unit 24 and subsequently evaluated.

In the exemplary underlying situation, a crankshaft acts as a drive for the piston 14 and the pressure curve 34 is accordingly Figure 2 plotted over a full revolution of the crankshaft [0° .. 360°]. In addition to the pressure curve 34 (dynamic pressure in the compression chamber 13), the illustration in Figure 2 also two so-called static - static for at least one working cycle - pressure values, namely a static suction pressure 36 and a static delivery pressure 38. These two static pressure values 36, 38 are characteristic values of the respective piston engine 10 and result from the dimension of the respective compression chamber 13 and due to the process in which the piston engine 10 is used. They are determined by measurement (each on the inlet and outlet pipes of the compression chamber 13) at the beginning and at the end of a work cycle or for a plurality of work cycles, for example in every nth work cycle with, for example, n = [1 .. 1,000] ) is determined or determined mathematically, for example by determining a moving average from a predetermined or predeterminable number of such measured values.

To determine a pair of values as described above, the evaluation unit 24 receives and processes the raw data 26 recorded by the sensor system 20, for example raw data 26 on the dynamic pressure in the compression chamber, as well as data on the static suction pressure 36 and the static delivery pressure 38.

By means of the evaluation unit 24, the raw data 26 are measured during one work cycle (but not necessarily during each work cycle; for example in every nth work cycle with, for example, n = [1 .. 1,000]) with the static suction pressure 36 and the static delivery pressure 38 compared. When the level of the raw data 26 reaches or falls below the value of the static suction pressure 36 for the first time in the working cycle, i.e. when the data under consideration (the value under consideration) of the raw data 26 reaches or falls below the value of the static suction pressure 36 for the first time in the working cycle, this represents that Opening the suction valve 16. When the level of the raw data 26 reaches or exceeds the value of the static delivery pressure 38 for the first time in the working cycle, i.e. when the data under consideration (the value under consideration) of the raw data 26 reaches the value of the static delivery pressure 38 for the first time in the working cycle or exceeds, this represents the opening of the pressure valve 18.

In short, as part of the comparison and by means of the evaluation unit 24, it is determined when the curve of the pressure curve 34 (the curve of the dynamic Pressure) reaches or falls below the static suction pressure 36 and when the curve of the pressure curve 34 reaches or exceeds the static delivery pressure 38. The opening time values 30, 32 associated with these points are referred to as break through points. These are transition points 30, 32 of the dynamic pressure through the values of the static pressures (static suction pressure 36, static delivery pressure 38).

In other words, to determine the time values/step-through points 30, 32, the dynamic pressure resulting from the operation of the piston engine 10 in its compression chamber 13 and the static suction pressure 36 as well as the static delivery pressure 38 are considered. The time value 30 for opening the suction valve 16 results from the dynamic pressure falling below the static suction pressure 36, i.e. when the dynamic pressure or the curve of the pressure curve 34 reaches or falls below the static suction pressure 36 and the piston engine 10 includes at least temporarily Means, for example the evaluation unit 24, by means of which the piston engine 10 can be determined during operation if and when the dynamic pressure falls below the static suction pressure 36.

The time value 32 for opening the pressure valve 18 results from the dynamic pressure exceeding the static delivery pressure 38, i.e. when the dynamic pressure or the curve of the pressure curve 34 reaches or exceeds the static delivery pressure 38 and the piston engine 10 includes at least temporarily Means, for example the evaluation unit 24, by means of which the piston engine 10 can be determined during operation if and when the dynamic pressure exceeds the static delivery pressure 38.

In the representation in Figure 2 The entry points 30, 32 are designated on the curve of the pressure curve 34 and their time values can each be read in “degrees of crankshaft”. The break-through point 30 associated with the event of opening the suction valve 16 is called "Break Through Suction Pressure" - BTSP for short - and The break through point 32 associated with the event of opening of the pressure valve 18 is referred to as “Break Through Discharge Pressure” - BTDP for short. As part of the method proposed here, the evaluation unit 24 determines these entry points 30, 32, i.e. the opening time values (time values in the sense described above) 30, 32 of the respective event (event of opening of the respective valve 16, 18).

The comparison carried out for this purpose by means of the evaluation unit 24 can take place instantaneously with respect to exactly one date of the raw data 26 then received by the evaluation unit 24 and synchronously with the operation of the piston engine 10. Alternatively, the comparison can also take place asynchronously to the operation of the piston engine 10 with respect to a total of raw data 26 received from the evaluation unit 24 during a period of time, for example during a work cycle, and each date included therein.

The innovation proposed here is based on the knowledge that a difference Δ = BTDP - BTSP is largely constant in a properly functioning piston engine 10, even over a long period of operation. This results in the further insight that a deviation in the value of the difference Δ can be an indication of a possible or impending exceptional situation, for example an indication of wear on a component included in the piston engine 10.

The difference Δ is formed, for example, by means of the monitoring unit 22, in particular continuously, i.e. for every working cycle or every nth working cycle of the piston 14 with, for example, n = [1 ... 1,000]. In the representation in Figure 1 (as well as in Figure 4 ), the difference Δ is designated by the reference number 40. The reference number 40 designates in particular the result of the difference formation, for example a date resulting from the difference formation or a memory location with the result of the difference formation. - The formula symbol used here in the description is not used in the patent claims, but the reference number is used; the terms "difference Δ" and "difference (40)" mean the same thing and are interchangeable.

The monitoring unit 22 includes a difference calculator 42 (or an implementation of a difference calculator 42 in the form of a difference calculation functionality) for the difference formation and a difference evaluator 44 (or an implementation of a difference evaluator 44 in the form of a difference assessment functionality) for further evaluation of the difference Δ.

The difference generator 42 forms the difference Δ from the determined opening time values 30, 32. The difference generator 42 therefore determines the current value of the difference Δ as Δ = BTDP - BTSP.

The difference evaluator 44 carries out a comparison of the difference Δ with a target value 46, in particular a comparison of the difference Δ with an expected value for the difference as a target value 46, and / or a comparison of a change in the difference Δ over time (in particular during a predetermined or predetermined number of Working cycles) with a corresponding predetermined or predefinable (further) setpoint 46.

As a result of the evaluation of the determined difference Δ in relation to the target value 46 by means of the difference evaluator 44, a signal 48 may be generated, which is, for example, an indication of an existing or impending error or exceptional situation, so that it is then the signal 48 is an error notification.

It is clear to the person skilled in the art that an implementation of the generation of such a signal 48 can take place in a variety of forms and, in some cases, can also include the generation of different signals. A result may be encoded by a specific level of signal 48. Without the respective result, the signal 48 then has a different level. The result can be achieved in the same way through the generation a signal 48 can be coded and without the result this signal 48 is not generated and/or another signal is generated. Finally, a signal 48 can also include at least one date. The respective result is then encoded by the date transmitted using signal 48. At least all of this should be considered to be included in the description presented here if we speak here and below of a signal 48 generated by means of the difference evaluator 44 and based on the difference Δ determined in each case.

The functionality of the monitoring unit 22 is preferably implemented in software (computer program 50 with program code instructions; see Figure 3 ) and accordingly loaded in a manner known per se into a memory (not shown separately) which is, for example, comprised by the monitoring unit 22 or assigned to the monitoring unit 22. To execute the program code instructions included in each case, a processing unit (not shown separately) included in the monitoring unit 22 or assigned to the monitoring unit 22 is provided in a manner known per se in the form of or in the manner of a microprocessor or the like. When operating the piston engine 10, these program code instructions are executed for automatic monitoring.

The representation in Figure 3 shows, in a highly simplified schematic form, the evaluation unit 24 and the monitoring unit 22 as part of a computer program 50 executed as part of a method for automatic monitoring of a piston engine 10, as well as function blocks 52, 54, 56, 58 included therein, which represent an implementation of the method for automatic monitoring Represent piston engine 10.

As part of the method (first functional block 52), a time value 30, 32 for the opening of a suction and pressure valve 16, 18 included in the piston engine 10 is recorded during operation of the piston engine 10. A difference is then formed from the determined opening time values 30, 32 (second function block 54). The difference Δ = BTDP - BTSP is therefore formed (BTDP = "Break Through Discharge Pressure" = passage through the delivery pressure = time of the pressure valve opening; BTSP = "Break Through Suction Pressure" = passage through the suction pressure = time of the suction valve opening). This difference Δ is then compared, for example, with an expected value for the difference as a setpoint 46 for the difference (third function block 56). Finally, depending on the result of the comparison, a corresponding signal 48 is generated (fourth function block 58). The process is repeated cyclically by repeatedly executing the function blocks 52-58 mentioned. The method is not necessarily carried out for the entire duration of operation of the piston engine 10. A time-limited execution (for example for diagnostic purposes), for example a time-limited execution using a temporarily installed monitoring unit 22 (or a temporarily installed sensor system 20 and monitoring unit 22), is also possible.

Instead of a computer program 50 with individual program code instructions, the method described here can also be implemented, or at least partially, in the form of firmware. It is clear to the person skilled in the art that instead of implementing a method in software, an implementation in firmware or in firmware and software or in firmware and hardware is always possible. This also applies in the case of an implementation of the method proposed here for automatic monitoring of a piston engine 10. It should therefore apply to the description presented here that the term software or the term computer program also includes other implementation options, namely in particular an implementation in firmware or in firmware. and software or in firmware and hardware.

The representation in Figure 4 shows in a schematically simplified form and in comparison to the representation in Figure 3 in yet another way the process flow within the framework of the procedure proposed here:
In a first step 60 (corresponds to the functionality of the first function block 52), the evaluation unit 24 is used to determine the opening time values 30, 32 (valve opening times) of a respective compression chamber 13 under consideration (in the case of a piston engine 10 with more than one compression chamber 13, this can and is advantageous entire process is carried out individually for each compression chamber 13). For this purpose, suitable raw data 26 are recorded using at least one corresponding measuring instrument of the sensor system 20 and these are evaluated using the evaluation unit 24 as described above. The raw data 26 or a raw data and the static pressure values (static suction pressure 36, static delivery pressure 38) are included in the determination of the valve opening times. The result of the evaluation by means of the evaluation unit 24 is a pair of values, each with a time value 30, 32 for the event of opening of the suction and pressure valve 16, 18 (two opening time values 30, 32; the two entry points 30, 32; BTDP, BTSP).

In a second step 62 (corresponds to the functionality of the second function block 54), a difference Δ between the opening time value 30 of the pressure valve 16 (BTDP) and the opening time value 32 is determined using the difference former 42 based on the two opening time values 30, 32 determined previously (first step 60). of the suction valve 18 (BTSP): Δ = BTDP - BTSP. Depending on the form in which the opening time values 30, 32 were determined (for example in ° crankshaft angle or for example in milliseconds), the determined difference Δ results in a corresponding unit. However, the difference Δ is at least indirectly a time value.

In a third step 64 (corresponds to the functionality of the third and fourth function blocks 56, 58), the difference Δ determined in the second step 62 is compared with a predetermined or predeterminable or alternatively a calculated or empirically determined setpoint 46, in particular a setpoint 46, by means of the difference evaluator 44 Expected value for the difference as target value 46, compared.

If the determined difference Δ exceeds or falls below the expected value for the difference, an exceptional situation is recognized. As part of the method, a corresponding signal 48 is then preferably generated. There are different options for such a signal 48 and, regardless of this, the options already mentioned above still apply: If the expected value for the difference is exceeded or undershot, exactly one signal 48 can be generated. This then simply indicates the existence of the exceptional situation. Likewise, a first signal 48 can be generated in the event that the expected value for the difference is exceeded and another, second signal 48 'can be generated in the event that the expected value for the difference is undershot. The respective signal (first or second signal 48, 48') then characterizes the present exceptional situation. A signal generated in the event that the expected value for the difference is exceeded (first signal 48) shows an existing or impending so-called low-pressure leak (for example a leak in the suction valve 16, a leak in the stuffing box packing, a leak in the area of at least one piston ring or another in the compression chamber 13 sealing components). A signal (second signal 48 ') generated in the event of a fall below the expected value for the difference shows an existing or impending so-called high-pressure leak (for example a leak in the pressure valve 18, a leak in the stuffing box packing, a leak in the area of at least one piston ring or another in the compression chamber 13 sealing components).

Preferably, at least one threshold value (not shown graphically; the or each threshold value is supplied/made available to the difference evaluator 44 as well as a target value 46) is taken into account for the detection of an excess or fall below the expected value for the difference. This means that a respective signal (individual signal 48 or first or second signal 48, 48') is only generated if the excess or undershoot is above the threshold value. By choosing a suitable threshold value (predetermined or predeterminable Threshold value) the detection sensitivity of the method can be adjusted. Optionally, a (predetermined or predeterminable) first threshold value can be taken into account for the detection of an exceedance of the expected value for the difference and a (predetermined or predeterminable) second threshold value can be taken into account for the detection of a fall below the expected value for the difference. The detection sensitivity can then be adjusted individually for each of the two recognizable exceptional situations (low-pressure leak, high-pressure leak).

Additionally or alternatively, a plurality of threshold values or a plurality of first and second threshold values can be provided. Then, depending on whether the respective threshold value is exceeded, a classification of the relevance of the recognized exceptional situation is possible, whereby a ratification of such relevance can range, for example, from mere information to an indication of an immediate or imminent need for action.

The expected value for the difference can be determined mathematically as a setpoint 46 based on data specific to the respective piston engine 10, in particular based on dimensional data of the piston engine 10 or depending on manipulated variables, for example manipulated variables for the valve control and/or manipulated variables for a so-called dead space control. The expected value for the difference is then determined, for example, before the piston engine 10 is put into operation, for example calculated on the basis of the mechanical dimensions of the piston engine 10 or taken from a performance calculation of the piston engine 10, and is within the scope of the method as a constant value and thus as a predetermined one Setpoint 46 available. A calculated expected value for the difference can also be entered during operation of the respective piston engine 10 and, if necessary, updated regularly (for example after maintenance). As part of the method, such an expected value for the difference is then taken into account as a predeterminable target value 46, because within the framework of the method the respective target value 46 is then one Variables and their values can be adjusted as needed. Finally, an empirical determination of an expected value for the difference is also possible. For example, a difference Δ determined after commissioning (or after maintenance) of the piston engine 10 (a difference Δ determined as described above) can be used as an expected value for the difference. It is also possible to use an average value of several differences Δ determined after commissioning (or after maintenance) of the piston engine 10 as an expected value for the difference and thus as a setpoint 46.

Particularly preferably, it is provided that a possible influence on an opening duration of at least one valve 16, 18 and a resulting shift of at least the opening time value 32 of the pressure valve 18 is also taken into account. Such an influence on an opening duration of at least one valve 16, 18 changes the opening duration of the or each respective valve 16, 18 compared to conditions that would arise without such an influence (see above: "The valves 16, 18 (suction valve 16, pressure valve 18 ) open due to reaching a certain pressure level in the cylinder 12.").

Such an influence on an opening duration takes place, for example, within the framework of a regulation, for example within the framework of a regulation by means of a control system or by means of a so-called power regulation system or within the framework of a so-called dead space regulation or within the framework of a speed regulation or within the framework of a combination of at least two such regulations.

Such an influence on an opening duration causes, for example, that the suction valve 16 is open longer. This means that compression starts later. Given the situation in Figure 2 (no such influence takes place there) compression begins at 180° crankshaft because at this point the suction valve 16 is closed again. When the opening duration of the suction valve 16 is influenced, the start of compression shifts towards greater Values as 180° crankshaft. This results in the pressure valve 18 also opening correspondingly later, so that a correspondingly shifted/later opening time value 32 of the pressure valve 18 results. When an opening duration is influenced as part of a dead space control, the opening duration of the suction valve 16 and/or the opening duration of the pressure valve 18 shift, so that correspondingly changed opening time values 30, 32 result.

Influencing the opening duration of at least one valve 16, 18, in particular the suction valve 16, is basically known per se. An influence on an opening duration of at least one valve 16, 18 takes place, for example, in the form of an active influence on the opening duration or in the form of a passive influence on the opening duration as explained above in the general description part or in the form of a combined active and passive influence. Due to or within the scope of influencing the opening duration of at least one valve 16, 18, a control value results first and foremost, namely a control value for the changed, in particular extended, opening duration of the respective valve 16, 18 or a changed, in particular extended, opening duration of the respective valve 16, 18 effective control value, and then a changed, in particular later, opening time value 30, 32 of the respective valve 16, 18 resulting from the changed, in particular extended opening duration. This control value is referred to below as the opening time control value for easier reference.

A later opening time value 32 of the pressure valve 18 leads to a change in a difference Δ determined as described above. To take into account any such influence on an opening duration of at least one valve 16, 18, a difference Δ determined as described above is compared with a setpoint 46 that is dependent on a respective opening time control value. An opening time control value x, for example, leads to an opening time value 32: k + x, where k is the opening time value 32 without influence; generally to an opening time value 32: k(x) that depends on the opening time control value. Influencing the opening time For example, the expected difference Δ = BTDP - BTSP is larger than without influence. This is taken into account by means of an opening time control value-dependent setpoint 46 - in short: by means of a control value-dependent setpoint 46 - (the setpoint 46 is a function of the opening time control value).

A control value-dependent setpoint 46, a group of control value-dependent setpoints 46 or the entirety of the control value-dependent setpoints 46 can be determined, for example, empirically or by machine learning. In machine learning, for example, 10 different opening time control values are applied while the piston engine is in operation and the resulting difference Δ is determined. The difference Δ determined in this way for a specific opening time control value is the control value-dependent setpoint 46 applicable to this opening time control value. In machine learning, it is generally possible to determine several differences Δ for one and the same opening time control value one after the other or at a time interval. The control value-dependent setpoint 46 can then be determined, for example, by averaging (averaging for a group of the determined differences Δ). Additionally or alternatively, statistical values belonging to the group of determined differences Δ, such as a standard deviation, can be included in a possible application of at least one threshold value (see below).

A graphical representation of the control value-dependent setpoint 46 leads to a curve 70 as in Figure 5 shown. The opening time control value is shown on the abscissa and the resulting (control value-dependent) setpoint 46 is shown on the ordinate. In the situation shown as an example, the opening time control value can generally assume values between 0 and 100. A value range from 0 to 100 can mean, for example, a value range from 0% to 100%, which is the basis for a power control. However, a value range from 0 to 100 can also be the result of normalization of any other value range. Each opening time control value has exactly one control value-dependent setpoint 46.

An opening time control value of, for example, 80 belongs to the in Figure 5 In the situation shown, the value 228 is as a control value-dependent setpoint 46.

Instead of a previously fixed setpoint 46, a setpoint-dependent setpoint 46 is used in the event of an influence on the opening duration of at least one valve 16, 18 of the piston engine 10. The data on which the graphical representation in the form of a curve 70 is based are stored, for example, in a look-up table and, based on the example chosen above, in such a look-up table in a row or column with the ordinal number 80 is the associated control value-dependent setpoint 46 can be read, here the value is 228. In this case, this value is the control value-dependent setpoint 46 and is shown accordingly in the illustration Figure 5 denoted by the reference number for the control value-dependent setpoint 46.

The evaluation of a respective determined difference Δ in relation to a respective control value-dependent setpoint 46 is carried out as described above, namely as described above for the case of a "simple" setpoint 46.

In the representation in Figure 5 The markings above and below the curve 70 are examples of differences Δ determined during operation for a respective opening time control value. A determined difference Δ "in the vicinity" of the control value-dependent setpoint 46 associated with the respective opening time control value is "okay". If the distance is too large - as described above - a signal 48 (or either a first signal 48 or a second signal 48 '; for example a first signal 48 in the case of a difference Δ above the curve 70 to signal a fault situation on the suction side or an impending suction-side error situation and a second signal 48 'in the case of a difference Δ lying below the curve 70 for signaling a pressure-side error situation or an impending pressure-side error situation). To take into account whether a determined difference Δ is sufficiently close to the control value-dependent setpoint 46 associated with the respective opening time control value, As described above, the use of at least one threshold value comes into consideration and to this extent what was said above applies accordingly. In the representation in Figure 5 For example, two determined differences Δ are highlighted by a border 72, which are not sufficiently close to the control value-dependent setpoint 46 belonging to the respective opening time control value.

Although the innovation proposed here has been illustrated and described in more detail by the exemplary embodiment, it is not limited by the example(s) disclosed and other variations can be derived from this by the person skilled in the art without departing from the scope of the invention.

Individual aspects of the description presented here that are in the foreground can be briefly summarized as follows: A method for automatically monitoring a piston engine 10 and a piston engine 10 operating according to the method are specified. When operating the piston engine 10, a time value 30, 32 is determined for opening a suction and pressure valve 16, 18 included in the piston engine 10, or a time value 30, 32 is determined for opening a suction and pressure valve 16, 18 included in the piston engine 10 Time value 30, 32 can be determined. A difference Δ is formed from the determined time values 30, 32 or a difference Δ can be determined (formed) from the determined time values 30, 32. The difference Δ is compared with a predetermined, predeterminable or determined target value 46 or the difference Δ is subjected to a comparison with a predetermined, predeterminable or determined target value 46 (is comparable to a predetermined, predeterminable or determined target value 46). If the setpoint 46 is exceeded or not reached, a signal 48, 48' is generated or a signal 48, 48' can be generated.

Reference symbol list

10

Piston engine

12

cylinder

13

Compression chamber

14

Pistons

16

valve, suction valve

18

valve, pressure valve

20

Sensor technology

22

Monitoring unit

24

Evaluation unit

26

Raw data

28

(free)

30

(Opening) time value, entry point, break through point

32

(Opening) time value, entry point, break through point

34

Pressure history (pressure history of dynamic pressure)

36

static suction pressure

38

static delivery pressure

40

Difference Δ

42

Difference makers

44

Difference evaluator

46

Setpoint

48, 48'

signal

50

Computer program

52-58

Function block

60, 62, 64

Step (in the process flow)

70

Curve (representation of the control value-dependent setpoint)

72

Border

Claims (15)

Method for automatically monitoring a piston machine (10) comprising at least one suction valve (16) and one pressure valve (18), wherein during operation of the piston engine (10) a time value (30, 32) is determined for opening the suction valve (16) and opening the pressure valve (18), wherein a difference (40) is formed from the determined time values (30, 32) and the difference (40) is compared with a predetermined, predeterminable or determined target value (46) and whereby a signal (48, 48') is generated when the setpoint (46) is exceeded or fallen short of. Method according to claim 1, wherein to determine the time values (30, 32), a dynamic pressure resulting from the operation of the piston engine (10) in a compression chamber (13) of the piston engine (10) and a static suction pressure (36) as well as a static delivery pressure (38) are considered, wherein the time value (30) for opening the suction valve (16) results from the dynamic pressure falling below the static suction pressure (36) and wherein the time value (32) for opening the pressure valve (18) results from the dynamic pressure exceeding the static delivery pressure (38). Method according to claim 1 or 2,
wherein in the case of influencing an opening duration of at least one valve (16, 18), an opening time control value-dependent setpoint (46) is used as the setpoint (46). Method according to claim 3, wherein the active influencing of an opening duration of at least one valve (16, 18) takes place as part of a control system that is effective during operation of the piston engine (10) and the result of the control is a control value and wherein a time course of the determined difference (40) and/or a time course of the control value resulting from the control is evaluated to assess the control. Method according to one of the preceding claims,
wherein if the setpoint (46) is exceeded, a first signal (48) is generated and if the setpoint (46) is undershot, a second signal (48') is generated. Method according to one of the preceding claims, wherein the difference (40) is formed for equidistantly spaced working cycles of a piston (14) encompassed by the piston engine (10) and the comparison with the target value (46) is carried out for each work cycle for which a difference (40) was determined. Method according to one of the preceding claims, wherein the piston is driven by means of a crankshaft and the working cycle of the piston (14) corresponds to a crankshaft cycle, wherein the difference (40) is formed for equidistantly spaced crankshaft cycles and the comparison with the target value (46) is carried out for each crankshaft cycle for which a difference (40) was determined. Piston machine (10) with means (20, 22, 24, 50) for carrying out a method according to one of claims 1 to 7. Piston engine (10) according to claim 8, wherein during operation of the piston engine (10) a time value (30, 32) can be determined for opening a suction and pressure valve (16, 18) included in the piston engine (10), wherein a difference (40) can be determined from the determined time values (30, 32) and the difference (40) is comparable to a predetermined, predeterminable or determined target value (46) and whereby a signal (48, 48') can be generated if the setpoint (46) is exceeded or fallen below. Piston engine (10) according to claim 9, wherein to determine the time values (30, 32), a dynamic pressure resulting from the operation of the piston engine (10) in a compression chamber (13) of the piston engine (10) and a static suction pressure (36) as well as a static delivery pressure (38) are considered, wherein the time value (30) for opening the suction valve (16) can be determined by determining if and when the dynamic pressure falls below the static suction pressure (36) and wherein the time value (32) for opening the pressure valve (18) can be determined by determining if and when the dynamic pressure exceeds the static delivery pressure (38). Piston machine (10) according to claim 8 or 9,
wherein in the case of a piston engine (10) with an influence on an opening duration of at least one valve (16, 18), an opening time control value-dependent setpoint (46) can be used as the setpoint (46). Digital storage medium with electronically readable control signals which can interact with a programmable monitoring unit (22) for a piston engine (10) in such a way that a method according to one of claims 1 to 7 is carried out. System with a piston engine (10), in particular a piston engine (10) according to one of claims 8 to 11, and a monitoring unit (22) assigned to the piston engine (10) and a computer program (50) with an implementation that can be executed by means of the monitoring unit (22). the method according to one of claims 1 to 7. Computer program (50), comprising commands which, when executed by a computer, in particular a computer functioning as a programmable monitoring unit (22) of a piston engine (10), in particular a piston engine (10) according to one of claims 8 to 11, cause the computer to to carry out the method according to one of claims 1 to 7. Computer-readable storage medium, comprising commands which, when executed by a computer, in particular a computer functioning as a programmable monitoring unit (22) of a piston engine (10), in particular a piston engine (10) according to one of claims 8 to 11, cause the computer to carry out the method to be carried out according to one of claims 1 to 7.

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