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

Abstract

A method for automatically monitoring a piston engine (10) and a piston engine (10) operating according to the method are specified, wherein, during operation of the piston engine (10), a time value (30, 32) is determined or can be determined for each opening of a suction and pressure valve (16, 18) encompassed by the piston engine (10), wherein a difference (40) is formed or can be formed from the determined time values ​​(30, 32) and the difference (40) is compared or comparable with a predetermined, predeterminable or determined setpoint value (46) and wherein, if the setpoint value (46) is exceeded or not reached, a signal (48, 48') is generated or can be generated.

Description

[0001] The innovation proposed here concerns the technical field of automatic monitoring of a piston or rotary machine, hereinafter collectively referred to 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.

[0002] When, in the following, a piston machine is mentioned as an example, this stands in for 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 restrictively.

[0003] One objective of the proposed innovation is to specify a criterion that is suitable for monitoring the condition of a piston engine and is also a particularly simple criterion. Building on this, a further objective of the proposed innovation is to specify a method for automatically monitoring a piston engine based on this criterion.

[0004] The object of automatically monitoring a piston engine is solved according to the invention by means of a method with the features of claim 1. For this purpose, the following is provided for a method for automatically monitoring, in particular for automatic online monitoring or continuous automatic monitoring, of a piston engine: The piston engine comprises at least one suction valve and at least one pressure valve, optionally also in the form of at least one so-called central valve comprising one or at least one suction and pressure valve. During operation of the piston engine, a time value (opening time value) is determined for each opening of the at least one suction valve and each opening of the at least one pressure valve. In the case of several suction or pressure valves, this applies to each suction valve and each pressure valve from the group of suction or pressure valves. A time value for such an event is, for example, based on a respective rotational position of a possiblyThe crankshaft of the piston engine is referenced. Such a time value is then specified in "degrees of crankshaft" and denotes the rotational position at the time of the respective event, i.e., at the time the respective valve opens. The process further provides that a difference is calculated from the determined time values ​​and this difference is compared with a predetermined, predefinable, or determined target value, in particular with a target value determined during the process and, if necessary, repeatedly updated. Finally, if the target value is exceeded or not reached, a signal, in particular an error notification signal, is generated as part of the process.

[0005] The proposed innovation is based on the understanding that the opening times of the suction and discharge valves (at least one suction valve and one discharge valve) within the piston engine are important parameters for its operation. In addition to these parameters, other parameters are known, such as pressure, particularly pressure values ​​like suction pressure and / or discharge pressure, temperature, capacity settings, vibration, power, etc. It is common practice to monitor such parameters during the operation of a piston engine and to infer an existing or impending exceptional or fault situation from changes in these parameters.

[0006] WO 2018 / 052398 A1 discloses an approach for preventing cavitation (the formation and dissolution of vapor-filled cavities in the fluid pumped by the pump). This involves determining the valve opening and closing times. These are compared with reference points by calculating the respective differences. This results in a response delay for opening or closing the respective valve. Cavitation is then prevented by adjusting the pressure based on this response delay.

[0007] Extensive prior art was identified during a patent search based on the invention. DE 10 2013 109 410 A1 discloses a calculation of a pressure-displacement diagram for a positive displacement pump. The detection of valve openings is only theoretically considered; no practical application is demonstrated. EP 3 486 482 A1 determines valve opening times and uses them to calculate / estimate a final pressure and, if necessary, to shut down the pump when a maximum value is exceeded, but not for monitoring purposes, and no qualification of valve damage is performed. WO 2005 / 108765 A1 does not consider the times of opening or closing a valve, but rather the period during which an actuator for a valve opens. The focus is therefore on the duration of the valve's actuation activity. In 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 are not relevant here. WO 2020 / 007923 A1, in connection with the present invention, only indicates that a diagnostic procedure can be carried out automatically using a computer. DE 10 2015 225 999 A1 identifies problems with control valves through a statistical valve position frequency analysis. WO 2006 / 000483 A1 identifies the opening and closing times of exactly one valve and the time interval between these times. If the interval becomes too long, the cylinder and combustion are shut down. Thus, this concerns the time of opening and closing of a valve and the time span between these events, i.e., different events at exactly one valve. In contrast, the invention concerns 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.The approach described in WO 2004 / 102052 A1 is intended to detect leaks in a valve. For this purpose, the sound / vibration is measured and processed in both sealed and leaking states. If the sound exceeds a threshold value, this is supposed to indicate a leak. EP 1 477 678 B2 also deals with structure-borne sound measurement and level comparison. EP 1 015 800 B1, unlike the approach proposed here, determines the closing time of motor-driven valves. These are actively closed valves, and the closing time is measured. AT 402 090 B discloses a method for flow control. The closing time of a suction valve is used as the control variable for regulating the compressor's flow rate. Damage detection is not included. The closing time is determined by vibration measurement.German patent DE 32 44 738 C2 examines the time period between the opening and closing of a suction valve. Changes in this period are intended to indicate a malfunction. However, solely considering the intersection of the dynamic pressure line with the suction pressure line fails to account for the behavior of the pressure valve. The opening of the pressure valve serves only to calculate the gradient of compression, which is non-linear for compressible gases. Therefore, this method is not universally applicable and is only suitable for incompressible media.

[0008] One advantage of the proposed innovation, besides the possibility of deriving a well-founded assessment of the condition of the respective piston engine, is the ability to combine several individually limited parameters into a single new parameter, namely the difference mentioned above. It has become apparent that monitoring and, above all, properly evaluating a large number of parameters is complex and requires a certain level of expertise.The difference determined by the proposed innovation can be continuously or regularly displayed to an operator during operation of the piston engine, allowing them to quickly and easily assess the engine's condition, particularly the condition of the sealing components—such as valves, piston rings, packing glands, and valve and void space controls—of each active compression chamber. Furthermore, the determined difference can be used for automatic leak detection. Optionally, the condition of the piston engine, as well as any changes in its condition, can also be assessed by tracking the development of the difference over an extended period, such as one hour, several hours, one day, several days, several weeks, several months, and so on, up to several years.

[0009] The aforementioned problem is also solved by means of a piston engine, which, according to the method proposed here and optionally an advantageous embodiment, can be monitored and for this purpose includes means for carrying out the method as described here and below, or to which such means are assigned. Such means are referred to below as sensors, evaluation unit, and monitoring unit, and the monitoring unit is preferably a programmable monitoring unit in the form of, or similar to, a microprocessor system or the like. The method proposed here, optionally supplemented by one or more advantageous embodiments described below, is preferably implemented automatically in the form of a computer program (the computer program is an implementation of the present method for monitoring a piston engine).The innovation proposed here is therefore, on the one hand, a computer program with program code instructions executable 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 comprising a piston engine and a monitoring unit, wherein such a computer program is loaded or loadable into a memory of the monitoring unit as a means of carrying out the method and its embodiments.

[0010] When procedural steps or sequences of procedural steps are described below, this refers to actions that are carried out as a result of the computer program or under the control of the computer program.

[0011] For the purposes of this description, to avoid unnecessary repetition, it should be noted that features and details described in connection with the aforementioned method for the automatic monitoring of a piston engine also apply, of course, to and with regard to a monitoring unit or system designed to carry out 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 further developed by means of one or more method features relating to method steps performed by the device, and the device can accordingly also be further developed by means of performing method steps carried out within the framework of the method.Consequently, features and details described in connection with the present method and any embodiments naturally also apply in connection with and with regard to the device intended for carrying out the method, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, mutual reference is always made or can be made.

[0012] Advantageous embodiments of the invention are the subject of the dependent claims. References within the claims indicate the further development of the subject matter of the referenced claim by the features of the respective dependent claim. They are not to be understood as a waiver of the right to obtain independent, specific protection for the features or combinations of features of a dependent claim. Furthermore, with regard to the interpretation of the claims and the description, when specifying a feature in a dependent claim in more detail, it should be assumed that such a limitation does not exist in the preceding claims or in a more general embodiment of the method / device for the automatic monitoring of a piston engine.Any reference in the description to aspects of dependent claims is therefore to be read as a description of optional features, even without specific indication to the contrary. Finally, the patent claims filed with this application are merely suggested formulations without prejudice to obtaining further patent protection. Since the features of the dependent claims, in particular, may constitute 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 disclosed only in the description and / or drawings, the subject matter of independent claims or divisional declarations. These may also include independent inventions that have a design independent of the subject matter of the respective referenced claims.

[0013] Preferably, in a method as described here and below, and in a piston engine operating according to this method, specific signals are generated in the event of both exceeding and falling below the setpoint. For example, a first signal is generated in the event of an exceedance and a second signal in the event of a fall below the setpoint. This enables qualitative monitoring of the piston engine and even of individual compression chambers, and ultimately allows for the output of a signal specific to the detected condition, exception, or error situation.For example, exceeding the setpoint indicates an existing or impending so-called low-pressure leak, and in the event of exceeding the setpoint, a corresponding signal can be output and is output in the preferred embodiment (the term signal ranges in meaning from a specific level on a signal line or a signal on exactly one signal line to, for example, text transmitted electronically and / or displayed in a suitable, generally known manner, text combined with image elements or a graphic).Conversely, a deviation below the setpoint indicates an existing or impending high-pressure leak, and in the event of such a deviation, a corresponding signal can be output, as is done in the preferred embodiment (a signal with the meaning outlined above). For an operator or manager of the piston engine, such a specific status or error message greatly simplifies maintenance and, if necessary, troubleshooting / repair.

[0014] Advantageously, in a method as described here and below, and in a piston engine operating according to this method, the difference is calculated for each working cycle of a piston encompassed by the piston engine, or at least for equidistantly spaced working cycles, and a comparison with the target value is performed for each working cycle, or for each working cycle for which a difference has been determined. Monitoring the difference in each working cycle, or in equidistantly spaced working cycles, ensures continuous or sufficiently continuous and, above all, meaningful monitoring of the piston engine, and the regularity of the monitoring provides data that can also be evaluated in terms of its trends, for example, to assess changes in the calculated difference over time.

[0015] In the case of a piston drive of the piston engine by means of a crankshaft, the working cycle of the piston corresponds to a crankshaft cycle, and it is then advantageously provided that the difference is calculated for each crankshaft cycle or at least for equidistantly spaced crankshaft cycles, and the comparison with the target value is carried out for each crankshaft cycle or for each crankshaft cycle for which a difference has been determined.

[0016] It is particularly preferred that, in a method as described here and below, or in a piston engine operating according to the method, in a piston engine where the opening duration of at least one valve is (additionally) influenced during operation, an opening-time-dependent setpoint is used or can be used as the setpoint. Influencing the opening duration of at least one valve (for example, as described in AT 402 090 B) 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 the conditions (opening time, opening duration) that would result without such influence, i.e., without such additional influence.

[0017] Such (additional) influence on the opening duration of at least one valve can be achieved, for example, through active or passive manipulation. Active manipulation acts directly on the valve, for example, by actively holding it open, either mechanically or electromechanically using a suitable actuator. Passive manipulation acts indirectly on the valve, for example, by changing the volume of the compression chamber as part of a so-called displacement control system.

[0018] The opening duration of at least one valve can be influenced, for example, by means of a control system, in particular within the framework of a control system or a so-called active power control system, or within the framework of a clearance control system, or within the framework of a speed control system, or within the framework of a combination of at least two such controls.

[0019] The result of influencing the opening duration of at least one valve is a control value, the application of which, during the operation of the piston engine, affects the opening duration of at least one valve. The setpoint used for monitoring the piston engine depends on this control value, which influences the opening duration / opening time of the respective valve. Generally, the setpoint is a function of this control value. Therefore, the setpoint used when operating a piston engine and influencing the opening duration of at least one valve is referred to as an opening-time-dependent setpoint. If the influencing of the opening duration of at least one valve is based on a control system, the control value depends on a setpoint effective within that system. Thus, the opening-time-dependent setpoint is dependent not only on the respective control value but also on the setpoint to which it is based.The designation of the setpoint used in the proposed procedure as opening time dependent should therefore not be interpreted restrictively and also includes, for example, a dependence on another setpoint if this influences the opening time of at least one valve of the piston engine.

[0020] In the event that the opening duration of at least one valve is affected during the operation of a piston engine, monitoring according to the approach proposed here is still possible using such a setpoint, namely an opening-time-dependent setpoint, even in the case of changing time values ​​(opening times) due to the effect on the opening duration of at least one valve. Here, too, a distinction between undershooting and exceeding the setpoint, namely the opening-time-dependent setpoint, is possible – albeit in a fundamentally optional manner – and in this respect, what has already been said above applies accordingly, and to avoid repetition, we refer to it briefly here.

[0021] Furthermore, it is advantageous – either additionally or alternatively – to monitor the respective control system, for example, a power or damage control system. This involves observing changes over time in the calculated difference (the difference between the calculated time values). Generally, it is expected that the calculated difference will remain unchanged or change only slightly; in other words, it is checked whether a change in the calculated difference during a given or predefinable time period remains within a range defined by a given or predefinable limit. Exceeding a limit indicates a faulty control system or a faulty component of the control loop. Additionally or alternatively, the temporal progression of the manipulated value is also considered in relation to the temporal progression of the calculated difference (both during the same time period).If, during the observed time period, the determined difference remains constant or at least substantially constant in the sense outlined above, and the manipulated value increases, this also indicates a faulty control system or a faulty component of the control loop. Components of the control loop that may be identifiable as potentially faulty in this sense include, in particular, the sensors, the controller, and the actuator. Such a check of a given control system is a preferred, but nevertheless optional, supplement to the procedure proposed here, and an implementation of such a check of a given control system is accordingly a possible supplement to an implementation of the procedure proposed here for the automatic monitoring of a piston engine, especially an implementation in the form of a computer program.

[0022] An embodiment of the proposed innovation is explained in more detail below with reference to the drawing. Corresponding objects or elements are designated with the same reference numerals in all figures.

[0023] The embodiment or embodiments described are not to be interpreted as restrictive. Rather, additions and modifications are entirely possible within the scope of the present disclosure, in particular those which, for example, can be deduced by a person skilled in the art from the solution of the problem by combining or modifying individual features in conjunction with those described in the general or specific descriptive part and contained in the claims and / or the drawing, and which, through combinable features, lead to a new subject matter or to new process steps or sequences of process steps.

[0024] They show Fig. 1 a piston engine with a monitoring unit, Fig. 2 a pressure profile 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 sequence within the framework of the method proposed here, and Fig. 5 a graphical representation of a setpoint-dependent setpoint.

[0025] The presentation Figure 1 shows a piston engine 10 in a schematically simplified manner and with only a few details.

[0026] A piston machine 10, for example a piston machine 10 in the form of a piston compressor or the like, and its operating principle are generally known. The following description therefore makes no claim to completeness and is intended only to introduce basic concepts: A piston machine 10 is a device designed for conveying a gas or fluid, hereinafter generally referred to as the medium. A piston machine 10 comprises at least one cylinder 12. At least one compression chamber 13 is located in the cylinder 12. At least one piston 14 is guided within the cylinder 12 (one piston 14 for each cylinder 12). The piston(s) 14 are movable within the cylinder 12 by means of an external drive (not shown) in a manner known per se. A crankshaft, for example, serves as the external drive. Other external drives, such as a hydraulic drive, are also possible.Each piston 14 moves in an oscillating motion within cylinder 12.

[0027] The following description, for the sake of simplicity, is 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 irrelevant for the proposed innovation; therefore, a plurality of the respective components should always be considered included in the description presented here.

[0028] During the oscillating movement of piston 14, a forward movement, referred to below as the forward stroke, and a subsequent backward movement, referred to below as the return stroke, occur cyclically and alternately. This also results in a position of piston 14 within cylinder 12, referred to below as the piston position. The respective medium is compressed in the compression chamber 13 (the compression chamber 13 is the area in cylinder 12 where the medium changes its pressure state), and the volume of the compression chamber 13 changes during the forward and return strokes of piston 14 (the volume of the compression chamber 13 changes / decreases / increases due to the movement of piston 14, and the piston 14 compresses the medium in the compression chamber 13 until the desired delivery pressure is reached; volume decreases during the forward stroke; volume increases during the return stroke). During the forward stroke, piston 14 exerts pressure on the respective medium.

[0029] A certain quantity of the respective medium is drawn into and expelled from the compression chamber 13 by the cyclical movement of the piston 14 and the opening of at least one valve 16, 18. For this purpose, at least one valve 16, 18 (at least one so-called suction valve 16; at least one so-called pressure valve 18) is fluidically coupled to the compression chamber 13 in a manner known per se.

[0030] Here too, the further description continues in the sense of simplified 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 any possible combination in the form of a so-called central valve or possibly several central valves (a central valve comprises at least one suction valve 16 and at least one pressure valve 18) is irrelevant for the innovation proposed here. Accordingly, a plurality of such valves 16, 18 (two or more suction valves 16 and / or two or more pressure valves 18) is always implied and is hereby considered to be included in the description presented here.

[0031] The operation of piston 14 is cyclical – an extension stroke and a return stroke of piston 14 (each translational) occur alternately and immediately following one another – and piston 14 is driven by a drive, for example, a continuously rotating crankshaft. An extension stroke of piston 14 and a subsequent return stroke of piston 14 are collectively referred to as a compression cycle or, more simply, a working cycle (both terms denote the same thing and are interchangeable). When piston 14 retracts in cylinder 12 (return stroke), the volume above piston 14 in cylinder 12 (the volume of the compression chamber 13) increases, and the respective medium is drawn into the compression chamber 13 via the intake valve 16. Following the return stroke of piston 14 and after passing through bottom dead center, piston 14 is advanced in cylinder 12 (extension stroke).This leads to a reduction in the volume of the compression chamber 13, and the medium previously drawn into the compression chamber 13 is finally expelled from the compression chamber 13 via the pressure valve 18 (exhaust valve). Upon passing through top dead center of the piston stroke, the forward stroke of the piston 14 ends, and a return stroke begins, and so on.

[0032] The forward stroke and return stroke of the piston 14 alternate and cyclically follow each other directly, so that due to the suction of the respective medium during the return stroke and the discharge of the suctioned medium during the forward stroke, a conveyance 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 results.

[0033] The representation in Figure 1The diagram shows – assigned to the piston engine 10 – a sensor system 20 that is at least temporarily assigned to the piston engine 10 for metrological purposes. The representation in Figure 1 Figure 10 further shows a monitoring unit 22 and an evaluation unit 24, which is shown to be encompassed by the monitoring unit 22, also at least temporarily assigned to the piston engine 10. The terms sensor 20, monitoring unit 22, and evaluation unit 24 are functional identifiers and do not imply a necessary spatial or technical separation. For example, sensor 20 and evaluation unit 24 can be combined into a single unit. Likewise, monitoring unit 22 and evaluation unit 24, or sensor 20, monitoring unit 22, and evaluation unit 24, can be combined into a single unit, or sensor 20, evaluation unit 24, and monitoring unit 22 can be spatially and technically separated.

[0034] The sensor system 20 comprises at least one measuring instrument, which records measured values ​​or data resulting from a simulation – hereinafter referred to individually or collectively as raw data 26 – at or in relation to the piston engine 10 in a manner that is generally known per se. The respective measuring instrument serves 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; optionally, one measuring instrument each for recording the valve activity of the suction and pressure valve 16, 18) or a quantity representative of the valve activity by recording such raw data 26.

[0035] An example of a measuring instrument encompassed by the sensor system 20 is a pressure sensor that measures the dynamic pressure in the compression chamber 13, namely the dynamic pressure that results 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 from which the opening of a valve 16, 18 (suction or pressure valve 16, 18) can be detected are also possible. An example of such an alternative measuring instrument is a vibration sensor that detects the vibration associated with the so-called opening action of the respective valve 16, 18, or a proximity sensor that allows the opening of the respective valve 16, 18 to be detected by direct measurement.

[0036] The evaluation unit 24 receives the raw data 26 recorded by the sensor 20 and evaluates it. As part of this evaluation, the evaluation unit 24 determines, for each working cycle (compression cycle; the terms working cycle and compression cycle are interchangeable) of the piston 14, a time or a measure of a time at which the suction valve 16 opens and a time or a measure of a time at which the pressure valve 18 opens, hereinafter collectively referred to as the opening time value 30, 32 or simply 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 machine 10).

[0037] The result of the evaluation by the evaluation unit 24 is one pair of values ​​per work cycle, comprising a first time value 30 for the opening of the suction valve 16 encompassed by the piston machine 10 and a second time value 32 for the opening of the pressure valve 18 encompassed by the piston machine 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, every third work cycle, or every nth work cycle, where, for example, n = [1 .. 1,000].

[0038] Valves 16 and 18 (suction valve 16 and pressure valve 18) open when a certain pressure level is reached in cylinder 12. They are held closed by back pressure in their respective supply lines (suction-side supply line, pressure-side supply line) and, for example, by springs or similar devices, until the pressure in the compression chamber 13 reaches a level sufficient to vent it. The suction valve 16 opens when the suction pressure falls below a certain level. The pressure valve 18 opens when the final / delivery pressure level is exceeded. Therefore, the time values ​​30 and 32 depend on the dynamic pressure level in the compression chamber 13. Changes in these values ​​indicate potential leaks or mechanical damage to a valve 16 or 18, to the cylinder 12, to the compression chamber 13, or similar components.

[0039] A time value 30, 32, for example, represents the rotational position of the crankshaft, i.e., the respective rotational position at the moment each valve 16, 18 opens. Using the rotational position of the crankshaft as a time value 30, 32 is quite common in practice. Considering the rotational position of the crankshaft as a time value 30, 32 is also understandable because the duration of one full revolution of the crankshaft (the duration of one working cycle of piston 14) can be viewed as a unit of time, and the instantaneous rotational position of the crankshaft is then a fraction of this unit of time. Alternatively, a time value 30, 32 can also be recorded as a time, measured, for example, in milliseconds, at which the respective valve 16, 18 opens. This time then starts at zero, for example, at each working cycle or at each nth working cycle, where n = [1 .. 1000], of piston 14.

[0040] For the sake of simplicity, it is assumed for the following description that the piston 14 of the piston engine 10 is driven by a crankshaft, and that the rotational position of the crankshaft at the time the suction valve 16 opens and the rotational position of the crankshaft at the time the pressure valve 18 opens are considered time values ​​30, 32 for the opening of the suction and pressure valves 16 and 18, respectively. The respective rotational position of the crankshaft is recorded 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 are among the raw data 26 transmitted to the evaluation unit 24. The raw data 26 can be transmitted instantaneously to the evaluation unit 24 in the form of a pair of values ​​(pressure value, rotational position).Alternatively, the raw data 26 can also be transmitted to the evaluation unit 24 in the form of a data set containing, for example, all pressure values ​​recorded during a working cycle of the piston 14 and the respective associated rotation position.

[0041] The representation in Figure 2 Figure 34 shows a pressure curve in the compression chamber 13 of the piston engine 10. The pressure curve 34 is a graphical representation of raw data 26, which, in the case of a pressure sensor as a measuring instrument, were recorded by means of the sensor 20, transmitted to the evaluation unit 24 and subsequently evaluated.

[0042] In the exemplary situation, a crankshaft acts as the drive for the piston 14, and accordingly the pressure curve 34 is in Figure 2 plotted over one full revolution of the crankshaft [0° .. 360°]. In addition to the pressure curve 34 (dynamic pressure in the compression chamber 13), the representation in Figure 2Two so-called static pressure values ​​– static for at least one operating cycle each – are also defined: a static suction pressure 36 and a static discharge pressure 38. These two static pressure values ​​36 and 38 are characteristic values ​​of the respective piston machine 10 and result from the dimensions of the respective compression chamber 13 and from the process in which the piston machine 10 is used. They are determined by measurement (at the inlet and outlet pipes of the compression chamber 13) at the beginning and end of each operating cycle or for a plurality of operating cycles (for example, in every nth operating cycle, where n = [1 .. 1,000]), or computationally, for example, by calculating a moving average from a predetermined or predeterminable number of such measured values.

[0043] To determine each pair of values ​​as described above, the evaluation unit 24 receives and processes the raw data 26 recorded by the sensor 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.

[0044] Using the evaluation unit 24, the raw data 26 are compared with the static suction pressure 36 and the static discharge pressure 38 during each work cycle (but not necessarily during every work cycle; for example, in every nth work cycle with, for example, n = [1 .. 1,000]). When the level of the raw data 26 first reaches or falls below the value of the static suction pressure 36 in the work cycle, i.e., when the respective data (the respective value) of the raw data 26 first reaches or falls below the value of the static suction pressure 36 in the work cycle, this represents the opening of the suction valve 16.When the level of the raw data 26 first reaches or exceeds the value of the static delivery pressure 38 in the operating cycle, i.e., when the respective data (the respective value) of the raw data 26 first reaches or exceeds the value of the static delivery pressure 38 in the operating cycle, this represents the opening of the pressure valve 18.

[0045] In short, the comparison process, using evaluation unit 24, determines when the pressure curve 34 (the dynamic pressure curve) reaches or falls below the static suction pressure 36 and when it reaches or exceeds the static delivery pressure 38. The corresponding opening time values ​​30 and 32 are referred to as break-through points 30 and 32. These are the points where the dynamic pressure crosses the static pressure values ​​(static suction pressure 36 and static delivery pressure 38).

[0046] In other words, to determine the time values / transition points 30, 32, the dynamic pressure resulting in the compression chamber 13 of the piston engine 10 during its operation, the static suction pressure 36, and 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 pressure curve 34 reaches or falls below the static suction pressure 36. The piston engine 10 includes, at least temporarily, means, for example, the evaluation unit 24, by means of which it can be determined, and during operation the piston engine 10 is determined, when and if the dynamic pressure falls below the static suction pressure 36.

[0047] The time value 32 for opening the pressure valve 18 results from an exceedance of the static delivery pressure 38 by the dynamic pressure, i.e. when the dynamic pressure or the curve of the pressure profile 34 reaches or exceeds the static delivery pressure 38 and the piston machine 10 includes at least temporarily means, for example the evaluation unit 24, by means of which it can be determined and during operation the piston machine 10 is determined when and when the dynamic pressure exceeds the static delivery pressure 38.

[0048] In the representation in Figure 2The breakthrough points 30 and 32 on the pressure curve 34 are designated, and their time values ​​can each be read in "degrees of crankshaft rotation". Breakthrough point 30, corresponding to the opening of the suction valve 16, is designated as "Break Through Suction Pressure" (BTSP), and breakthrough point 32, corresponding to the opening of the discharge valve 18, is designated as "Break Through Discharge Pressure" (BTDP). Within the framework of the procedure proposed here, the evaluation unit 24 determines these breakthrough points 30 and 32, i.e., the opening time values ​​(time values ​​in the sense described above) 30 and 32 of the respective event (the opening of the respective valve 16 or 18).

[0049] The comparison performed by the evaluation unit 24 can be instantaneous with respect to exactly one raw data 26 date received by the evaluation unit 24 and synchronously with the operation of the piston machine 10. Alternatively, the comparison can also be performed asynchronously with respect to the operation of the piston machine 10 with respect to the entirety of raw data 26 received by the evaluation unit 24 during a period of time, for example during a work cycle, and each date included therein.

[0050] The proposed innovation is based on the finding that the difference Δ = BTDP - BTSP remains largely constant in a properly functioning piston engine 10, even over a long operating period. This leads to the further finding 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 in a component of the piston engine 10.

[0051] The difference Δ is calculated, for example, using the monitoring unit 22, in particular continuously, i.e., for each work cycle or each nth work cycle of the piston 14 with, for example, n = [1 ... 1,000]. In the illustration in Figure 1 (as well as in Figure 4The difference Δ is denoted by the reference numeral 40. The reference numeral 40 specifically denotes the result of the difference calculation, for example, a date resulting from the difference calculation or a storage location containing the result of the difference calculation. In the patent claims, the symbol used here in the description is not used; the terms "difference Δ" and "difference (40)" mean the same thing and are interchangeable.

[0052] The monitoring unit 22 includes a difference generator 42 (or an implementation of a difference generator 42 in the form of a difference generation functionality) for the difference formation and a difference evaluator 44 (or an implementation of a difference evaluator 44 in the form of a difference evaluation functionality) for further evaluation of the difference Δ.

[0053] The difference generator 42 calculates the difference Δ from the determined opening time values ​​30 and 32. The difference generator 42 therefore determines the current value of the difference Δ as Δ = BTDP - BTSP.

[0054] The difference evaluator 44 performs 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 target value 46, and / or a comparison of a change in the difference Δ over time (in particular during a given or predetermined number of work cycles) with a corresponding given or predetermined (further) target value 46.

[0055] 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 the signal 48 is then accordingly an error notification.

[0056] It is clear to those skilled in the art that the implementation of generating such a signal 48 can take many forms and may, in some cases, involve the generation of different signals. A result can be encoded by a specific level of the signal 48. Without the respective result, the signal 48 then has a different level. Likewise, the result can be encoded by the generation of a signal 48, and without the result, this signal 48 is not generated and / or a different signal is generated. Finally, a signal 48 can also include at least some data. The respective result is then encoded by the data transmitted by means of the signal 48. At least all of this is to be considered as encompassed by the description presented here, when, in the following, we refer to a signal 48 generated by means of the difference evaluator 44 and based on the respective difference Δ determined.

[0057] 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, for example, encompassed by or assigned to the monitoring unit 22 (not shown separately). For the execution of the program code instructions contained therein, a processing unit encompassed by or assigned to the monitoring unit 22 (not shown separately) in the form of a microprocessor or the like is provided in a manner known per se. During operation of the piston engine 10, these program code instructions are executed for its automatic monitoring.

[0058] The representation in Figure 3The figure shows, in a highly simplified schematic form, the evaluation unit 24 and the monitoring unit 22 as part of a computer program 50 executed within the framework of a method for the automatic monitoring of a piston engine 10, as well as the functional blocks 52, 54, 56, 58 included therein, which represent an implementation of the method for the automatic monitoring of a piston engine 10.

[0059] As part of the process (first functional block 52), a time value 30, 32 is recorded for the opening of a suction and a pressure valve 16, 18 encompassed by the piston engine 10 during operation. A difference is then calculated between the determined opening time values ​​30, 32 (second functional block 54). Thus, the difference Δ = BTDP - BTSP is calculated (BTDP = "Break Through Discharge Pressure" = time of pressure valve opening; BTSP = "Break Through Suction Pressure" = time of 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 functional block 56). Finally, a corresponding signal 48 is generated depending on the result of the comparison (fourth functional block 58). The process is repeated cyclically by repeatedly executing the aforementioned functional blocks 52-58.The procedure is not necessarily carried out for the entire duration of the 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 20 and monitoring unit 22), is also possible.

[0060] Instead of a computer program 50 with individual program code instructions, the implementation of the method described here can also be, or at least partially, carried out in the form of firmware. It is clear to those skilled in the art that, instead of implementing a method in software, implementation in firmware, in firmware and software, or in firmware and hardware is always possible. This also applies to the implementation of the method proposed here for the automatic monitoring of a piston engine 10. Therefore, for the purposes of this description, the terms "software" and "computer program" shall be understood to encompass other implementation possibilities, namely, in particular, implementation in firmware, in firmware and software, or in firmware and hardware.

[0061] The representation in Figure 4 shows in a schematically simplified form and in comparison to the representation in Figure 3The process flow within the framework of the proposed procedure is described in a different way: In a first step 60 (corresponding to the functionality of the first functional block 52), the opening time values ​​30, 32 (valve opening times) of each compression chamber 13 under consideration are determined using the evaluation unit 24 (in a piston engine 10 with more than one compression chamber 13, the entire procedure can and advantageously 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 evaluated using the evaluation unit 24 as described above. The raw data 26, or one raw data point each, and the static pressure values ​​(static suction pressure 36, static discharge pressure 38) are included in the determination of the valve opening times.The result of the evaluation using the evaluation unit 24 is a pair of values ​​with a time value 30, 32 each for the event of the opening of the suction and pressure valve 16, 18 (two opening time values ​​30, 32; the two penetration points 30, 32; BTDP, BTSP).

[0062] In a second step 62 (corresponding to the functionality of the second functional block 54), a difference Δ between the opening time value 30, 32 of the pressure valve 16 (BTDP) and the opening time value 32 of the suction valve 18 (BTSP) is determined using the difference generator 42, based on the two opening time values ​​30, 32 determined previously (first step 60): Δ = BTDP - BTSP. Depending on how the opening time values ​​30, 32 were determined (for example, in ° crankshaft angle or for example in milliseconds), the determined difference Δ has a corresponding unit. However, the difference Δ is at least indirectly a time value.

[0063] In a third step 64 (corresponding 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, for example, a specified or specifiable target value 46, in particular an expected value for the difference as target value 46, using the difference evaluator 44.

[0064] If the calculated difference Δ exceeds or falls below the expected value for the difference, an exceptional situation is detected. Within the procedure, a corresponding signal 48 is then preferably generated. There are various possibilities for such a signal 48, and regardless of this, the possibilities already mentioned above still apply: If the expected value for the difference is exceeded or fallen below, exactly one signal 48 can be generated. This then simply indicates the presence of the exceptional situation. Similarly, a first signal 48 can be generated if the expected value for the difference is exceeded, and a second signal 48' if the expected value for the difference is fallen below. The respective signal (first or second signal 48, 48') then characterizes the existing exceptional situation.A signal generated when the expected value for the difference is exceeded (first signal 48) indicates an existing or impending low-pressure leak (for example, a leak from the suction valve 16, a leak from the stuffing box packing, a leak in the area of ​​at least one piston ring or other components sealing the compression chamber 13). A signal generated when the expected value for the difference is not reached (second signal 48') indicates an existing or impending high-pressure leak (for example, a leak from the pressure valve 18, a leak from the stuffing box packing, a leak in the area of ​​at least one piston ring or other components sealing the compression chamber 13).

[0065] Preferably, at least one threshold value (not shown graphically; the threshold value(s) is supplied to / provided to the difference evaluator 44, as is a target value 46) is considered for detecting whether the expected value for the difference has been exceeded or fallen below. This means that a respective signal (individual signal 48 or first or second signal 48, 48') is only generated if the exceedance or fall below the threshold value is above the threshold value. The detection sensitivity of the method can be adjusted by choosing a suitable threshold value (predefined or configurable threshold value). Optionally, a (predefined or configurable) first threshold value can be considered for detecting whether the expected value for the difference has been exceeded, and a (predefined or configurable) second threshold value can be considered for detecting whether the expected value for the difference has fallen below the threshold value.Then, for each of the two identifiable exceptional situations (low-pressure leakage, high-pressure leakage), the detection sensitivity can be set individually.

[0066] Additionally or alternatively, multiple thresholds or multiple first and second thresholds can be provided. Depending on whether the respective threshold is exceeded, the relevance of the identified exceptional situation can then be classified, with the ratification of such relevance ranging, for example, from mere information to an indication of an immediate or imminent need for action.

[0067] The expected value for the difference can be calculated 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 valve control and / or manipulated variables for a so-called displacement control. The expected value for the difference is then determined, for example, before the piston engine 10 is commissioned, calculated based on the mechanical dimensions of the piston engine 10 or taken from a performance calculation of the piston engine 10, and is available within the procedure as a constant value and thus as a predefined setpoint 46. A calculated expected value for the difference can also be entered during the operation of the respective piston engine 10 and updated regularly if necessary (for example, after maintenance).Within the procedure, such an expected value for the difference is then considered as a predefinable target value 46, because within the procedure, the respective target value 46 is a variable and its value 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 each maintenance) of the piston engine 10 (a difference Δ determined as described above) can be used as the expected value for the difference. Likewise, the use of an average of several differences Δ determined after commissioning (or after each maintenance) of the piston engine 10 as the expected value for the difference, and thus as the target value 46, is possible.

[0068] Particularly preferred is the consideration of any potential influence on the opening duration of at least one valve 16, 18 and a resulting shift in at least the opening time value 32 of the pressure valve 18. Such an influence on the opening duration of at least one valve 16, 18 changes the opening duration of the respective valve(s) 16, 18 compared to the conditions that would result 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.").

[0069] Such an influence on the opening duration occurs, for example, within the framework of a control system, for example, within the framework of a control system or within the framework of a so-called performance control system or within the framework of a so-called clearance control or within the framework of a speed control or within the framework of a combination of at least two such controls.

[0070] Such an influence on the opening duration causes, for example, the suction valve 16 to remain open longer. As a result, compression begins correspondingly later. In the situation in Figure 2(No such influence occurs there) Compression begins at 180° crankshaft rotation because the intake valve 16 is closed again at this point. If the opening duration of the intake valve 16 is influenced, the start of compression shifts to a value greater than 180° crankshaft rotation. This causes the pressure valve 18 to open correspondingly later, resulting in a correspondingly shifted / later opening time value 32 for the pressure valve 18. If the opening duration is influenced as part of a displacement control system, the opening duration of the intake valve 16 and / or the opening duration of the pressure valve 18 are shifted, resulting in correspondingly changed opening time values ​​30 and 32.

[0071] Influencing the opening duration of at least one valve 16, 18, in particular the suction valve 16, is generally known. Influencing the opening duration of at least one valve 16, 18 can be achieved, for example, by actively influencing the opening duration, by passively influencing the opening duration as explained above in the general description section, or by a combined active and passive influence.As a result of or within the context of influencing the opening duration of at least one valve 16, 18, a control value is generated firstly, namely a control value for the changed, in particular extended, opening duration of the respective valve 16, 18 or a control value that causes the changed, in particular extended, opening duration of the respective valve 16, 18, 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 ease of reference.

[0072] A later opening time value 32 of the pressure valve 18 leads to a change in a difference Δ determined as described above. To account for any such influence on the opening duration of at least one valve 16, 18, a difference Δ determined as described above is compared with a setpoint 46 that depends on a respective opening time control value. For example, an opening time control value x leads to an opening time value 32: k + x, where k is the opening time value 32 without influence; more generally, to an opening time value 32 dependent on the opening time control value: k(x). With an influence on the opening duration, the expected difference Δ = BTDP - BTSP is therefore, for example, 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).

[0073] A position-dependent setpoint 46, a group of position-dependent setpoints 46, or the entirety of position-dependent setpoints 46 can be determined, for example, empirically or through machine learning. In machine learning, for instance, 10 different opening time position values ​​are applied during the operation of the piston engine, and the resulting difference Δ is determined in each case. The difference Δ determined in this way for a specific opening time position value is the position-dependent setpoint 46 applicable to that opening time position value. In principle, machine learning allows for the sequential determination of several differences Δ for one and the same opening time position value, either consecutively or at time intervals. The position-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).

[0074] A graphical representation of the setpoint-dependent target value 46 leads to a curve 70 as in Figure 5 The graph is shown. The x-axis represents the opening time setpoint, and the y-axis represents the resulting (setpoint-dependent) target value 46. In the example shown, the opening time setpoint can generally take values ​​between 0 and 100. A value range of 0 to 100 can, for example, represent a power control range of 0% to 100%. However, a value range of 0 to 100 can also be the result of normalizing any other value range. Each opening time setpoint corresponds to exactly one setpoint-dependent target value 46.

[0075] For example, an opening time setting of 80 corresponds to the following in the Figure 5 In the situation shown, the setpoint-dependent target value 46 is the value 228.

[0076] Instead of a previously fixed setpoint 46, a position-dependent setpoint 46 is used in the case of an influence on the opening duration of at least one valve 16, 18 of the piston engine 10. The data underlying the graphical representation in the form of a curve 70 are stored, for example, in a lookup table, and based on the example chosen above, the corresponding position-dependent setpoint 46 can be read in a row or column with the ordinal number 80 in such a lookup table, here the value 228. This value is the position-dependent setpoint 46 for this case and is accordingly represented in the graph. Figure 5 designated with the reference number for the position-dependent setpoint 46.

[0077] The evaluation of each determined difference Δ in relation to a respective position-dependent setpoint 46 is carried out as described above, namely as described above for the case of a "simple" setpoint 46.

[0078] In the representation in Figure 5The markings above and below curve 70 are examples of differences Δ determined during operation for a respective opening time setpoint. A determined difference Δ "close" to the setpoint-dependent target value 46 corresponding to the respective opening time setpoint is "OK". If the difference is too large, 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 curve 70 to signal a suction-side fault or an impending suction-side fault, and a second signal 48' in the case of a difference Δ below curve 70 to signal a pressure-side fault or an impending pressure-side fault) is generated, as described above.To determine whether a calculated difference Δ is sufficiently close to the setpoint-dependent target value 46 corresponding to the respective opening time setpoint, the use of at least one threshold value is considered – as described above – and the above applies accordingly. In the representation in . Figure 5 Two determined differences Δ are highlighted by a border 72 as examples, which are not sufficiently close to the setpoint-dependent target value 46 belonging to the respective opening time setpoint.

[0079] Although the innovation proposed here has been illustrated and described in detail by the exemplary embodiment, it is not limited by the disclosed example(s) and other variations can be derived from it by a person skilled in the art without leaving the scope of protection of the invention.

[0080] The key aspects of the description presented here can be summarized as follows: A method for the automatic monitoring of a piston engine 10 and a piston engine 10 operating according to this method are described. During operation of the piston engine 10, a time value 30, 32 is determined for each opening of a suction and pressure valve 16, 18 encompassed by the piston engine 10, respectively. A difference Δ is calculated from the determined time values ​​30, 32, or a difference Δ can be calculated from the determined time values ​​30, 32. The difference Δ is compared with a predetermined, predefinable, or determined setpoint value 46.The difference Δ is compared to a predetermined, predefinable, or determined target value 46 (is comparable to a predetermined, predefinable, or determined target value 46). If the target value 46 is exceeded or not reached, a signal 48, 48' is generated, or a signal 48, 48' can be generated. Reference symbol list

[0081] 10 Piston machine 12 Cylinder 13 Compression chamber 14 Piston 16 Valve, suction valve 18 Valve, pressure valve 20 Sensors 22 Monitoring unit 24 Evaluation unit 26 Raw data 28 (free) 30 (Opening) time value, break-through point 32 (Opening) time value, break-through point 34 Pressure curve (pressure curve of the dynamic pressure) 36 Static suction pressure 38 Static delivery pressure 40 Difference Δ 42 Difference generator 44 Difference evaluator 46 Setpoint 48, 48' Signal 50 Computer program 52-58 Function block 60, 62, 64 Step (in the process sequence) 70 Curve (representation of the manipulated setpoint) 72 Border

Claims

1. A method for automatically monitoring a piston machine (10) comprising, in each case, at least one intake valve (16) and a discharge valve (18), a time value (30, 32) being ascertained both for opening of the intake valve (16) and opening of the discharge valve (18) during operation of the piston machine (10), characterized in that a difference (40) is formed from the ascertained time values (30, 32) and the difference (40) is compared with a predetermined, predeterminable, or ascertained target value (46) and in that a signal (48, 48') is generated when the target value (46) is exceeded or fallen below.

2. The method according to claim 1, wherein, for ascertaining the time values (30, 32), a dynamic pressure resulting during operation of the piston machine (10) in a compression chamber (13) of the piston machine (10), a static intake pressure (36), and a static delivery pressure (38) are taken into consideration, wherein the time value (30) for the opening of the intake valve (16) results if the dynamic pressure falls below the static intake pressure (36) and wherein the time value (32) for the opening of the discharge valve (18) results if the dynamic pressure exceeds the static delivery pressure (38).

3. The method according to claim 1 or 2, wherein, if an opening duration of at least one valve (16, 18) is influenced, a target value (46) which is dependent on the opening-time manipulated value is used as the target value (46).

4. The method according to claim 3, wherein an opening duration of at least one valve (16, 18) is actively influenced as part of control that takes effect during operation of the piston machine (10) and the result of the control is a manipulated value, and wherein a time course of the ascertained difference (40) and / or a time course of the manipulated value resulting from the control is evaluated in order to assess the control.

5. The method according to any of the preceding claims, wherein, if the target value (46) is exceeded, a first signal (48) is generated, and, if the target value (46) is fallen below, a second signal (48') is generated.

6. The method according to any of the preceding claims, wherein the difference (40) is formed for equidistantly spaced work cycles of a piston (14) comprised by the piston machine (10) and the comparison with the target value (46) is carried out for each work cycle for which a difference (40) has been ascertained.

7. The method according to any of the preceding claims, wherein the piston is driven by means of a crankshaft and the work cycle of the piston (14) corresponds to one 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) has been ascertained.

8. A piston machine (10) comprising means (20, 22, 24, 50) for carrying out a method according to any of claims 1 to 7.

9. The piston machine (10) according to claim 8, wherein a time value (30, 32) can be ascertained both for opening of an intake valve and discharge valve (16, 18) comprised by the piston machine (10) during operation of the piston machine (10), wherein a difference (40) can be ascertained from the ascertained time values (30, 32) and the difference (40) can be compared with a predetermined, predeterminable, or ascertained target value (46) and wherein a signal (48, 48') can be generated when the target value (46) is exceeded or fallen below.

10. The piston machine (10) according to claim 9, wherein, for ascertaining the time values (30, 32), a dynamic pressure resulting during operation of the piston machine (10) in a compression chamber (13) of the piston machine (10), a static intake pressure (36), and a static delivery pressure (38) are taken into consideration, wherein the time value (30) for the opening of the intake valve (16) can be ascertained by it being possible to ascertain if and when the dynamic pressure falls below the static intake pressure (36) and wherein the time value (32) for the opening of the discharge valve (18) can be ascertained by it being possible to ascertain if and when the dynamic pressure exceeds the static delivery pressure (38).

11. The piston machine (10) according to claim 8 or 9, wherein, if, in a piston machine (10), an opening duration of at least one valve (16, 18) is influenced, a target value (46) which is dependent on the opening-time manipulated value can be used as the target value (46).

12. A digital storage medium comprising electronically readable control signals, which can interact with a programmable monitoring unit (22) for a piston machine (10) such that a method according to any of claims 1 to 7 is carried out.

13. A system comprising a piston machine (10), in particular a piston machine (10) according to any of claims 8 to 11, and a monitoring unit (22) assigned to the piston machine (10) and a computer program (50) which can be executed by means of the monitoring unit (22) and has an implementation of the method according to any of claims 1 to 7.

14. A computer program (50) comprising commands which, when executed by a computer, in particular a computer which functions as a programmable monitoring unit (22) of a piston machine (10), in particular a piston machine (10) according to any of claims 8 to 11, cause said computer to carry out the method according to any of claims 1 to 7.

15. A computer-readable storage medium comprising commands which, when executed by a computer, in particular a computer which functions as a programmable monitoring unit (22) of a piston machine (10), in particular a piston machine (10) according to any of claims 8 to 11, cause said computer to carry out the method according to any of claims 1 to 7.

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