DE102020119802B4 - Diagnosis of a compression behavior of an internal combustion engine - Google Patents

Abstract

Method for diagnosing a compression behavior of an internal combustion engine (1) in a motor vehicle with multiple cylinders (Z1-Z4), comprising the steps: - determining a diagnostic time window (112) within a torque gap (12) of one of the clocks of the internal combustion engine (1), independent of the operating point during driving operation of the motor vehicle,- identifying at least one cylinder (Z1-Z4), which is in a compression stroke at the beginning of the diagnosis time window,- determining a cylinder pressure curve of the identified cylinder (Z1-Z4) during the diagnosis time window as a function from a determined speed development (100) of the internal combustion engine (1) during the diagnosis time window (112), and assigning a deviation type to the identified cylinder (Z1-Z4) depending on a polytropic coefficient (N), which depends on the determined Cylinder pressure curve is determined for the diagnosis time window.

Description

The invention relates to a method and a diagnostic means for diagnosing a compression behavior of an internal combustion engine, and an internal combustion engine with multiple cylinders with such a diagnostic means.

Rough engine running and combustion misfires are a fundamental problem in combustion engines, which can at least lead to an incorrect build-up of the propulsion torque. The fact that there is a faulty torque build-up can be regularly read from the output variable of the engine speed - i.e. the speed development of the crankshaft.

However, the mere knowledge of the existence of an error is usually not enough to remedy the situation. A clear diagnosis of the malfunction is necessary to rectify the fault, whereby the causes of combustion misfires and/or rough engine running can be extremely different.

From the DE 10 2017 108 285 A1 an internal combustion engine is known, having a monitoring device for monitoring operation of the internal combustion engine, a cylinder pressure sensor of the monitoring device being arranged for each cylinder and being designed to measure a cylinder pressure of the cylinder, to determine cylinder pressure data corresponding to the cylinder pressure and to output a respective cylinder pressure signal indicating the cylinder pressure data . The monitoring device has an analysis unit that is designed to receive the respective cylinder pressure signal and, from a time profile of the cylinder pressure data of the respective cylinder, to determine for each cylinder individually for each cylinder whether there is an anomaly in the cylinder pressure, in particular whether there is an anomaly in the cylinder pressure during a compression phase of the respective cylinder during operation of the engine, to assign the anomaly to the respective cylinder of the engine.

Due to the expensive cylinder pressure sensors, however, this method is not suitable for series use in passenger vehicles.

An accurate diagnosis is very complex with current diagnostic systems and requires various information from different subsystems of the combustion engine. Even distinguishing between mechanical problems in the cylinder (e.g. in the sliding couple) on the one hand and problems in the gas filling (charge exchange) or in the air path on the other hand is difficult when the customer visits the workshop with the functionally impaired engine.

A visit to the workshop with an engine that is not running smoothly can therefore be unpleasant for the customer with regard to the probability of a correct initial diagnosis being successful.

In order to avoid such things better and better, options for predictive maintenance (also known as “health functions”) for combustion engines are becoming increasingly important. These are intended to quantify the current performance status - and thus the maintenance requirement - in particular with regard to the required scope of maintenance and with regard to an advantageous timeline.

From the DE 10 2017 115 876 A1 there is known an abnormality diagnosis for a mechanism for varying a compression ratio, which is described without a special hardware configuration for determining a compression ratio. To this end, the abnormality diagnosis apparatus includes: a speed difference calculation unit configured to calculate a predetermined speed difference, that is, a speed difference between an engine speed at a predetermined crank angle before or after compression top dead center and an engine speed near compression top dead center for a given cylinder during execution of the fuel cut processing; a setting unit configured to set a reference range of the predetermined speed difference; and a diagnosis unit configured to diagnose that an abnormality has occurred in the compression ratio varying mechanism when the predetermined rotational speed difference is out of the reference range.

However, this method can only be carried out when the engine is overrun and is therefore not suitable for complete on-board diagnostics.

Against this background, it is an object of the invention to enable improved identification of a fault cause for rough engine running and/or combustion misfires, and in particular to provide improved diagnosis of a compression behavior of an internal combustion engine with multiple cylinders.

This object is achieved by a method for diagnosing a compression behavior of an internal combustion engine having the features of claim 1, a diagnostic means for diagnosing a compression behavior of an internal combustion engine having the features of claim 12, and an internal combustion engine having the features of claim 14. Advantageous embodiments are the subject of the dependent Expectations.

1. a) Bestimmen eines Diagnose-Zeitfensters innerhalb eines Drehmomentlochs eines der Takte des Verbrennungsmotors während eines Fahrbetriebs des Kraftfahrzeugs. Unter einem Diagnose-Zeitfenster ist insbesondere ein zusammenhängender Zeitraum als Anteil eines Taktes (beispielsweise einer der Takte eines Viertakt-Verbrennung) der Verbrennung in dem Verbrennungsmotor zu verstehen. Unter einem Drehmomentenloch ist vorliegend insbesondere ein Kurbelwinkelbereich zu verstehen, in welchem der betrachteten Zylinder und/oder alle Zylinder des Motors keinen im Kontext relevanten Beitrag zu einem Vortriebs-Drehmoment leisten.
2. b) Identifizieren wenigstens eines Zylinders, welcher sich zu Beginn des Diagnose-Zeitfensters in einem Kompressionstakt befindet. Die Identifikation dieses/dieser Zylinder kann insbesondere durch ein Auslesen vorhandener Informationen aus einem Betriebsmodell, insbesondere der Motorsteuerung, erfolgen. Insbesondere wird bei einem Viertakter-Motor mit vier Zylindern der eine Zylinder identifiziert, welcher sich zu Beginn des Diagnose-Zeitfensters in einem Kompressionstakt befindet.
3. c) Ermitteln eines Zylinderdruckverlaufs des identifizierten Zylinders während des Diagnose-Zeitfensters, und
4. d) Zuordnen eines Abweichungstyps zu dem identifizierten Zylinder in Abhängigkeit von einem Polytropenkoeffizienten, der in Abhängigkeit von dem ermittelten Zylinderdruckverlauf für das Diagnose-Zeitfenster ermittelt wird. Unter einem Abweichungstyp ist vorliegend eine vorbestimmte Ausprägung des Polytropenkoeffizienten zu verstehen, die einem bestimmten Fehlertyp zugeordnet ist, der zu unrundem Motorlauf und/oder Verbrennungsaussetzern führt.

According to one aspect, a method for diagnosing a compression behavior of an internal combustion engine with multiple cylinders is provided, having at least one, several or all of the following method steps - in the specified order or another order that makes sense in the art:

1. a) Determination of a diagnosis time window within a torque gap of one of the cycles of the internal combustion engine while the motor vehicle is being driven. A diagnosis time window is to be understood in particular as a continuous period of time as a portion of a cycle (for example one of the cycles of a four-stroke combustion engine) of the combustion in the internal combustion engine. In the present case, a torque hole is to be understood in particular as a crank angle range in which the cylinder under consideration and/or all cylinders of the engine do not make any contribution to a propulsion torque that is relevant in the context.
2. b) Identifying at least one cylinder which is in a compression stroke at the beginning of the diagnosis time window. This/these cylinders can be identified in particular by reading out existing information from an operating model, in particular the engine control. In particular, in the case of a four-stroke engine with four cylinders, the one cylinder which is in a compression stroke at the start of the diagnosis time window is identified.
3. c) determining a cylinder pressure profile of the identified cylinder during the diagnosis time window, and
4. d) Assigning a deviation type to the identified cylinder as a function of a polytropic coefficient, which is determined as a function of the determined cylinder pressure profile for the diagnosis time window. In the present case, a type of deviation is to be understood as meaning a predetermined characteristic of the polytropic coefficient, which is assigned to a specific type of error that leads to uneven engine operation and/or combustion misfires.

• d1) Ermitteln des Zylinderdruckverlaufs auf Basis der ermittelten Ausprägung der Druckkennzahl jeweils für wenigstens zwei Zeitintervalle im Diagnose-Zeitfenster, und/oder
• d2) Ermitteln des Polytropenkoeffizienten auf Basis der ermittelten Ausprägung der Druckkennzahl und der zu den Zeitintervallen ermittelten Zylindervolumina, und/oder
• d3) Vergleich des ermittelten Polytropenkoeffizienten mit vorbestimmten Ausprägungen des Polytropenkoeffizienten, die verschiedenen Abweichungstypen zugeordnet sind, und/oder
• d4) Zuordnen eines Abweichungstyps für den untersuchten Zylinder zu dem bestimmten Diagnose-Zeitfenster entsprechend dem Ergebnis des Vergleichs.

According to one embodiment, several or all of the following method steps are carried out - in the specified order or in another order that makes sense for the person skilled in the art - to assign the deviation type:

• d1) determining the cylinder pressure profile on the basis of the determined expression of the pressure index for at least two time intervals in the diagnosis time window, and/or
• d2) determining the polytrope coefficient on the basis of the determined form of the pressure index and the cylinder volumes determined at the time intervals, and/or
• d3) comparison of the determined polytrope coefficient with predetermined forms of the polytrope coefficient, which are assigned to different types of deviation, and/or
• d4) Assigning a deviation type for the examined cylinder to the determined diagnosis time window according to the result of the comparison.

• i) eine Drehzahl-Erfassungseinheit, die dazu eingerichtet ist, eine Drehzahl einer Kurbelwelle des Verbrennungsmotors zu erfassen, und gemäß einer Ausführung die erfassten Werte in einer Samplingzeit von wenigstens in der Größenordnung von zehn Millisekunden bereitzustellen, und/oder
• ii) eine Zylindervolumen-Ermittlungseinheit, die dazu eingerichtet ist, ein Zylindervolumen in Abhängigkeit von einer Winkelstellung der Kurbelwelle zu ermitteln, und/oder
• iii) eine Recheneinheit, die dazu eingerichtet ist, die Drehzahl-Erfassungseinheit und/oder die Zylindervolumen-Ermittlungseinheit zu steuern und/oder damit erfasste bzw. ermittelte Werte zu verarbeiten. Die Recheneinheit ist insbesondere dazu eingerichtet, ein Diagnose-Zeitfenster innerhalb eines Drehmomentlochs eines der Takte des Verbrennungsmotors während eines Fahrbetriebs des Kraftfahrzeugs zu bestimmen, und wenigstens einen Zylinder (Z1-Z4) zu identifizieren, welcher sich zu Beginn des Diagnose-Zeitfensters in einem Kompressionstakt befindet, und/oder
• iv) eine Zylinderdruck-Ermittlungseinheit, die dazu eingerichtet ist, einen Zylinderdruckverlauf in Abhängigkeit von, insbesondere mittels der Drehzahl-Erfassungseinheit, erfassten Drehzahlen und/oder einer, insbesondere mittels der Recheneinheit aus den erfassten Drehzahlen ermittelten, Drehzahlentwicklung der Kurbelwelle im Diagnosezeitfenster zu ermitteln. Die Recheneinheit ist insbesondere dazu eingerichtet, die Zylinderdruck-Ermittlungseinheit zu steuern und/oder damit erfasste bzw. ermittelte Werte zu verarbeiten, und in Abhängigkeit von dem ermittelten Zylinderdruckverlauf des identifizierten Zylinders in dem Diagnose-Zeitfenster einen Abweichungstyp zu dem identifizierten Zylinder zuzuordnen.

According to a further aspect, a diagnostic means for diagnosing a compression behavior of an internal combustion engine with multiple cylinders is provided, which is set up in particular for a method according to one embodiment of the invention. The diagnostic agent has at least:

• i) a rotational speed detection unit that is set up to detect a rotational speed of a crankshaft of the internal combustion engine and, according to one embodiment, to provide the detected values in a sampling time of at least in the order of ten milliseconds, and/or
• ii) a cylinder volume determination unit that is set up to determine a cylinder volume as a function of an angular position of the crankshaft, and/or
• iii) a computing unit which is set up to control the rotational speed detection unit and/or the cylinder volume determination unit and/or to process values detected or determined therewith. The computing unit is set up in particular to determine a diagnostic time window within a torque gap of one of the strokes of the internal combustion engine while the motor vehicle is being driven, and to identify at least one cylinder (Z1-Z4) which is in a compression stroke at the beginning of the diagnostic time window located, and/or
• iv) a cylinder pressure determination unit, which is set up to determine a cylinder pressure profile as a function of speeds detected, in particular by means of the speed detection unit, and/or a speed development of the crankshaft in the diagnostic time window, determined in particular by means of the computing unit from the detected speeds. The arithmetic unit is set up in particular to control the cylinder pressure determination unit and/or to process values recorded or determined with it, and to assign a deviation type to the identified cylinder in the diagnosis time window depending on the determined cylinder pressure profile of the identified cylinder.

According to a further aspect, an internal combustion engine with several cylinders is provided, having a diagnostic means according to one embodiment of the invention, the internal combustion engine having in particular one, two, three, four, six or eight cylinders and/or as a four-stroke Otto or diesel engine or Wankel engine is formed. A typical area of application for the invention is, for example, four-cylinder petrol or diesel engines.

The invention is based, among other things, on the consideration that the cylinder compression can only be measured using known methods in the workshop, for which a mechanic must be employed; and the car first has to come to the workshop. The problem is already there, no advance statement can be made in terms of predictive maintenance. The diagnostic workshop work results in wages, even if the diagnosis remains without a result. It is not possible to continuously predict the mechanical failure behavior of the internal combustion engine with manual measurements of the cylinder compression. Since the cylinder compression is an elementary parameter for the mechanical condition of a drive, it must be recorded while driving if you want to continuously monitor the performance of the combustion engine (without having to visit a workshop with special equipment).

The invention is now based, among other things, on the idea of enabling such a continuous measurement while driving. For this purpose, according to one embodiment, a diagnosis time window is determined in the compression phase of a cylinder in which no heat is released in the engine, typically between 660° crank angle and 690° crank angle (relative to the ignition top dead center of the affected cylinder at 720°); Such a crank angle range without heat release is also referred to here as a torque hole, because in such a crank angle range, at most a propulsion torque that is negligible for the purposes of the invention is transmitted to the crankshaft.

However, another torque gap can also be flexibly selected during driving operation, for example during cylinder deactivation. According to one embodiment, a diagnostic cylinder pressure value is determined for this diagnostic time window at two time intervals depending on a speed development continuously recorded during driving operation. In addition, according to one embodiment, a mean cylinder volume of the individual cylinder is determined for each of the time intervals using a table lookup. According to one embodiment, the polytropic equation for the cylinder pressure curve during compression is set up with these pressure and volume values for the two time intervals within the diagnosis time window. According to one embodiment, the polytropic coefficient of the polytropic equation is determined by taking the logarithm and is compared with a reference coefficient. If the determined coefficient is lower than the reference, then there is a compression problem in the diagnosed cylinder. This diagnosis can then be carried out equally for all cylinders, so that higher-level deviation types can also be diagnosed for the entire engine while driving.

Because of the simultaneous changeover between the individual strokes of the different cylinders, the invention can be implemented in a particularly simple manner in an internal combustion engine with four cylinders, in particular designed as a four-stroke engine. Of course, other numbers of cylinders are also possible according to other designs.

One embodiment of the invention is now based, among other things, on the idea of determining the cylinder compression as an elementary parameter for the mechanical condition of the internal combustion engine while driving, in order to monitor the performance of the internal combustion engine continuously and without having to visit the workshop with special equipment. For this it is necessary to increase the cylinder compression - for example derive a cylinder pressure profile within the diagnosis time window using a driving operation high-frequency and continuously determinable characteristic variable, for example the speed development of the crankshaft, in particular in the diagnosis time window.

The method steps described below for determining the speed development of the crankshaft while driving is based, among other things, on the consideration that the cycles of a four-stroke combustion engine (intake, compression, work cycle, exhaust) overlap in time between the individual cylinders - they occur parallel to each other in different cylinders on.

According to the embodiment, to determine the speed development of the crankshaft, a time window must be identified directly before the ignition in the cycles, which does not include any significant build-up of propulsion torque, i.e. the crankshaft then continues to rotate essentially solely through inertia. In this time window, for example, the drop in engine speed (for example the start of the time window vs. the end of the time window) is then identified. This is made up of friction losses in the mechanics and piston braking due to gas compression.

If exactly the cylinder that is currently in its compression stroke is diagnosed in this time window, its influence on the speed curve can best be examined: because in the compression phase, a cylinder has the greatest influence on the speed curve, since it is affected by the compression the gas spring brakes the mechanism the hardest; brakes significantly more than the other bars.

The approach of determining the torque development during the - essentially - torque-free diagnosis time window, makes it possible to carry out a comparison with previously determined error-typical characteristics of the respective gas exchange parameters - possibly stored in an operating model - using various gas exchange parameters that can be combined if necessary .

With the speed detection, existing sensors (speed detection) with extended functions are used in particular. The capabilities of the existing speed measurement on the engine, especially on the crankshaft, have not been used to date to derive a statement about the compression behavior of a cylinder.

The invention makes it much easier to find the cause of rough-running problems, including combustion misfires, in particular by identifying the problem in the gas filling (charge exchange) or by excluding the air path.

According to one embodiment, online data acquisition of the diagnostic results while driving allows the workshop access to real driving situations and thus in particular a more targeted processing of service scopes and/or faster maintenance. Ultimately, this results in lower warranty costs, higher customer satisfaction and/or fewer repeat repairs.

According to one embodiment, the cylinder pressure profile is determined as a function of at least two characteristics of a pressure index, which is determined at least two time intervals in the diagnosis time window. This enables a diagnosis of the compression behavior of the cylinder as a function of a high-frequency, continuously determined rotational speed of the crankshaft.

The cylinder pressure curve is determined as a function of a determined speed development of the internal combustion engine during the diagnosis time window. As a result, the method can be carried out as a function of measured values determined during driving operation.

According to one embodiment, the polytrope coefficient is determined as a function of one, in particular average, cylinder volume for each of the two time intervals. Fast processing in the control unit is supported by the averaging assumed for simplification.

According to one embodiment, a reference polytropic coefficient range of 1.38 to 1.42 for regularly operating cylinders is defined as a predetermined value of the polytropic coefficient. Surprisingly, in the applicant's tests, this proved to be the case despite the significant deviation from the Polytro pen coefficient for air of about 1.36 as an advantageous range for the polytropic coefficient of compression in the cylinders.

According to one embodiment, the polytropic coefficient is determined for several or all cylinders of the internal combustion engine and a deviation type is assigned, and a higher-level deviation type is assigned by means of a comparison with predetermined combinations of deviation types for several or all cylinders. As a result, a higher-level deviation status can also be determined, which, for example, depicts problematic influences on the compression behavior that apply to all cylinders.

According to one embodiment, a mechanical damage and/or a wall heat transfer problem is assigned as a deviation type and/or as a higher-level deviation type (1) if the or several (for different cylinders) or all (for each cylinder) determined polytrope values are less than 1.38 . This means that a problem in the heat transfer of the cylinders can be assumed, especially in the low-load range.; and/or (2) assigned deposits in the cylinder if the determined polytrope value(s) is greater than 1.42.

According to one embodiment, a first time interval for determining the pressure index ranges from a beginning to a middle of the diagnostic time window, and a second time interval ranges from the middle to an end of the diagnostic time window. Fast processing in the control unit is supported by the averaging assumed for simplification.

According to one embodiment, a polytropic equation for the compression in the cylinder during the diagnosis time window is set up with the determined characteristics for the pressure index and an averaged cylinder volume, each for the first time interval and the second time interval. This simplification is possible due to the small crank angle range of the time intervals within the diagnosis time window with sufficient accuracy when determining the polytropic coefficient.

According to one embodiment, to determine the speed development, a continuous speed curve is recorded during the diagnosis time window and the recorded values are made available in a sampling quality of at least the order of ten milliseconds, in particular in the control unit. This allows the pressure index to be determined while driving, i. H. determined as a function of the determined speed development.

According to one embodiment, a determined deviation of the determined polytropic coefficient from the predetermined characteristic of the polytropic coefficient and/or the assigned deviation type (1) is stored in a fault memory, in particular a diagnostic tool for carrying out the method, and/or (2) in an engine condition monitoring system , stored in particular as a flag in the sense of a "health indicator". In this way, the maintenance personnel in the workshop can be given an adequate picture of the state of the internal combustion engine with regard to the compression behavior even without on-site diagnostic measures. According to one embodiment, the data stored in the fault memory can also be evaluated cumulatively over time, and measures can be recommended, in particular for predictive maintenance, if a predetermined fault pattern from individual entries emerges over time or can be extrapolated.

Additionally or alternatively, according to one embodiment, a determined deviation of the determined polytropic coefficient from the predetermined expression of the polytropic coefficient and/or the assigned deviation type (3) is displayed as a control message for a vehicle occupant. In this way, for example, urgent consequences from the determination of the type of deviation (e.g. "Visit a workshop") can be made immediately available to the vehicle driver.

According to one embodiment, the diagnostic means is set up to assign the deviation type (d1) to determine a cylinder pressure curve based on the determined characteristic of the pressure index for each of the time intervals in the diagnosis time window, (d2) a polytropic coefficient based on the determined characteristic of the pressure index and the to determine the cylinder volumes determined at the time intervals, (d3) to compare the determined polytropic coefficient with predetermined characteristics of the polytropic coefficient, which are assigned to different deviation types, and (d4) to compare a deviation type for the cylinder examined for the specific diagnosis time window according to the result of the comparison to assign.

The steps to be carried out according to one embodiment for determining the pressure index for the various time intervals within the diagnosis time window are described below and detailed in connection with the figures using an exemplary embodiment.

In order to support the most computationally efficient implementation of the method, according to one embodiment for determining the speed development, a speed difference is calculated from a speed value at the start of the diagnosis time window and a speed value at the end of the diagnosis time window.

In particular, a pressure index calculated on the basis of the rotational speed difference determined, in particular in the compression cycle, is then used as the charge exchange parameter.

For this purpose, according to one embodiment, it is sufficient to balance the drop in rotational speed with the aid of mechanical equations. This balancing allows conclusions to be drawn about the compression pressure before ignition. The compression pressure is directly related to the cylinder filling and thus the trapped air mass in the individual cylinder. Deviation detection can thus relate errors in running roughness to the gas exchange or exclude this as the cause.

This execution of an analytical method using a set of formulas in the time domain can be used particularly well from average engine load and up to average speeds, especially with smooth and constant speed curves, and is based in particular on a calculation of a pressure index in the cylinder during compression from the speed curve. An exemplary application is shown in the first exemplary embodiment of the description of the figures.

According to one embodiment, the diagnostic means is set up to determine a manifestation of a gas exchange parameter on the basis of the determined speed development in order to assign the type of deviation; to compare the determined characteristic with predetermined characteristics of the gas exchange parameter, which are assigned to different types of deviation; and assign a deviation type to the determined diagnosis time window according to the result of the comparison.

In order to be able to carry out the various presented embodiments of a method according to the invention with suitable hardware, according to one embodiment the diagnostic means is set up to carry out methods according to any embodiments of the invention.

• 1 a-c in schematischen Ansichten einen Verbrennungsmotor mit einem Diagnosemittel nach einer beispielhaften Ausführung der Erfindung, wobei in 1a die Einbauumgebung des Verbrennungsmotors, in 1b relevante Parameter sowie in 1c Drehmomentbeiträge an dem Kurbeltrieb des Verbrennungsmotors über die Zeit dargestellt sind;
• 2 ein Schaubild mit einem Diagramm einer Drehzahlentwicklung eines Arbeitszyklus des Verbrennungsmotors nach 1 und einer Darstellung der Takte der einzelnen Zylinder;
• 3 ein vergrößertes Detail aus dem Diagramm nach 2;
• 4 ein Schaubild mit einem Diagramm einer Zylinderdruckentwicklung über den Kurbelwellenwinkel in einer Kompressionsphase eines diagnostizierten Zylinders des Verbrennungsmotors nach 1 ;
• 5 ein Schaubild mit einem Diagramm einer Zylindervolumenentwicklung über den Kurbelwellenwinkel in der Kompressionsphase des diagnostizierten Zylinders von 4; und
• 6 ein Schaubild mit einem Diagramm einer für die Kompression des Zylinders von 4 und 5 aufgestellte Polytropengleichung; und
• 7 ein Schaubild der Zuordnung von Abweichungstypen mittels eines Vergleichs eines ermittelten Polytropenkoeffizienten und den Abweichungstypen zugeordneten Referenzwerten.

Further features, advantages and possible applications of the invention result from the following description in connection with the figures. Show it,

• 1ac in schematic views an internal combustion engine with a diagnostic means according to an exemplary embodiment of the invention, wherein in 1a the installation environment of the internal combustion engine, in 1b relevant parameters as well as in 1c Torque contributions to the crank mechanism of the internal combustion engine are shown over time;
• 2 a diagram with a diagram of a speed development of a working cycle of the internal combustion engine 1 and a representation of the strokes of the individual cylinders;
• 3 an enlarged detail from the diagram 2 ;
• 4 a diagram with a diagram of a cylinder pressure development over the crankshaft angle in a compression phase of a diagnosed cylinder of the internal combustion engine 1 ;
• 5 a graph with a diagram of a cylinder volume development over the crankshaft angle in the compression phase of the diagnosed cylinder of 4 ; and
• 6 a diagram with a diagram for the compression of the cylinder of 4 and 5 established polytrope equation; and
• 7 a diagram of the assignment of deviation types by means of a comparison of a determined polytropic coefficient and the reference values assigned to the deviation types.

In 1a an internal combustion engine 1 is shown in its installation environment, the internal combustion engine 1 in the exemplary embodiment being a four-stroke engine with 4 cylinders Z1, Z2, Z3 and Z4.

In the representation of 1a From the installation environment, in particular the intake system 9 with the air filter LF at the air inlet, the exhaust gas turbocharger ATL as well as an intercooler and the air collector LS shown toward cylinders Z. Potential leakage areas L on the pipelines between the various components can also be seen.

A potential mechanical failure R on the piston and/or on the inner wall of the cylinder is signaled as an example on cylinder Z1, which would potentially lead to greatly increased friction.

In 1b the internal combustion engine 1 is shown in a more detailed schematic view. The internal combustion engine 1 has the cylinders Z1, Z2, Z3 and Z4, with all cylinders Z providing their torque contribution M to the crank mechanism KT detection unit 6 and a cylinder pressure determination unit 7 for the reference pressures from the environment and air collector or crankcase, as well as for determining a cylinder pressure curve p13-p32 as a function of speeds n detected by means of the speed detection unit 6 and one by means of the computing unit 4 from the speeds detected n determined speed development 101 of the crankshaft KT in the diagnosis time window 12 has.

Of the 1b It can be seen, among other things, that depending on the respective cylinder pressure p, each cylinder Z can cyclically apply a torque contribution M to the crank mechanism KT. The totality of the torque contributions results in a rotational speed n of a crankshaft of the crank mechanism KT that varies over time.

The reference pressure p can be used by the pressure detection unit 7 , the instantaneous speed n can be used by the speed detection unit 6 and the arithmetic unit 4 can be used by the diagnostic means 2 .

In 1c a diagram of a torque development 100 with an exemplary torque curve 10 on the crank drive KT during normal operation over the crank angle KW is shown. It can be seen that the torque contribution M comes from different cylinders Z in alternation. A torque limit value 14 is shown in the illustration, which is set arbitrarily and determines below which torque a torque contribution of a cylinder is considered insignificant. As a result, a torque hole 12 can be identified within the meaning of the invention if the torque contributions of each cylinder are below the limit value 14 at a specific time interval.

In the representation of 1 c torque holes 12.1, 12.2, 12.3 and 12.4 of slightly different lengths result. In particular, a diagnosis time window 112 can be defined within each of these torque gaps 12, which can (but does not have to) include the entire period of the torque gap. The end time of the diagnosis time window 112 can be determined in particular by the ignition time or the time of a first noticeable release of heat after compression.

the 2 until 7 explain an exemplary embodiment of the method according to the invention for operating-point-independent compression testing of an internal combustion engine 1 while driving using the crankshaft speed n of the crankshaft drive KT. The method carried out in the exemplary embodiment is initially described in summary in the following paragraph.

In the exemplary embodiment, the vehicle is being driven, in particular a stationary operation of the internal combustion engine 1. During driving, a live engine control function continuously reads speed values n for the crankshaft KT (due to friction delay, in a compression phase of a cylinder, there is an increased drop in speed from one to one to be expected at the following point in time) and determines a speed development from this - cf. 1-3 . Diagnostic cylinder pressures p _{diag are} calculated for specific points in time P1, P3, P2 (cf. 4 ) and the volume functions V are averaged (cf. 5 ). With the help of these values, the diagnostic polytropic exponent N is calculated thermodynamically (cf. 6 ). The calculated polytrope value is compared with a reference value Nref (cf. 7 ). If the calculated value N falls significantly below the reference value Nref for one or a few cylinders Z (and possibly at several operating points of the driving operation), then a compression problem in the mechanics can be assumed. If all the calculated polytrope values N fall significantly below the reference value Nref, and particularly in the low-load range, then a problem in the heat transfer of the cylinder can be assumed. The deviation of the calculated values N from the reference Nref is made visible or accessible for further processing via error memory, CC message and/or with a "health indicator". The values calculated while driving are stored on the control unit and thus made accessible for extrapolation (prediction of compression performance).

The determination of the polytrope coefficient with detailed steps is shown below for a cylinder as an example.

First, a diagnosis time window 12 is defined for one, several or all cylinders.

In the four-stroke process of an internal combustion engine, there are areas on the degree-crank angle scale (abscissa axis of torque curve 10) in which there is no significant torque conversion (in particular below limit value 14). In these periods of time, the crankshaft is decelerated by the applied friction and load resistance. The decisive decelerating resistances are, among other things, the corresponding load requirement, the friction of the mechanics R and, above all, the compression of the gas filling of the next igniting cylinder.

By stationary balancing of the decelerating resistances by measuring the rotational speed of the crankshaft KT in the correct time window 12, it is possible to draw conclusions about the cylinder filling in order to allow better differentiation of the causes in the event of a fault.

In 2 is a sketch of an exemplary diagram 100 of a speed development 101 of a four-stroke cycle (= one working cycle (ASP): top dead center gas exchange (LOT) → intake → bottom dead center (UT) → compression → top dead center ignition (ZOT) → expand → UT → Outlet) of the internal combustion engine 1 shown.

Flowchart 100 shows curve 101 of engine speed n over one working cycle (ASP) of a 4-cylinder gasoline engine. The ignition times (ZZP) and an exemplary possible diagnosis time window 112 for the cylinder Z1 to be diagnosed in the compression are marked. The associated work cycles of the physical cylinders Z1-Z4 are shown below.

This example of a four-cylinder shows which area 112 of the crank angle scale can be used for gas exchange diagnosis. The diagnosis time window 112 for the cylinder Z1 to be diagnosed lies at the end of compression, directly before the ignition of the mixture; for cylinder Z3 at the end of the intake stroke; for cylinder Z4 at the end of the exhaust stroke; and for cylinder Z2 at the end of the power stroke, with no relevant torque being released in any of the cylinders Z (cf. limit value 14 in 1c ).

In particular, the diagnosis time window 112 must be selected in such a way that the last cylinder performing work no longer accelerates the crankshaft and the next cylinder performing work has not yet ignited.

In the exemplary embodiment, the basic requirements for defining the diagnosis time window 112 are: 1) no dominant release of heat (differential build-up of torque disappears since before ignition in the compression or after the pressure pulse in the working cycle); and/or 2) exhaust valve open (otherwise the piston brake must be included); and/or 3) Intake valve open & de-throttled (VVT), otherwise the piston brake must be taken into account by throttling and gas spring.

In the embodiment according to FIG 1 the diagnosis time window 112 for cylinder Z1 is defined from 30° before ZZP1 to ZZP1 (regarding the crank angle KW). The limits depend on an existing engine operating point and can be flexibly adapted to this, provided that the basic requirements 1-3 mentioned in the previous paragraph are not violated. The dynamic adjustment of the limits of the diagnosis time window 112 is also possible for dynamic driving depending on boundary conditions such as an ignition angle and the cylinder pressure curve.

• 660°KW - 690°KW, wie insbesondere aus den 4 und 5 ersichtlich ist.

In the exemplary embodiment, the diagnosis time window 12 is defined as:

• 660 ° KW - 690 ° KW, as in particular from the 4 and 5 is evident.

Three points in time P1, P3, P2 are then determined within the calculation window, for example P1=660°CA, P3=675°CA and P2=690°CA, with which the diagnosis time window 12 is divided into two sub-intervals t13 and t32, here in particular halved , becomes.

Diagnostic cylinder pressure values p13=p _diag,13 and p32=p _diag, 32 are determined for both partial intervals t13 and t32 by means of mechanical calculation.

How these diagnostic cylinder pressure values p _diag,13 and p _diag, 32 can be determined from the measured speed development 101 in the diagnosed cylinder Z is described below in the statements on equations (1)-(16):

A power balance should - based on a measured speed difference - allow a comparison between a target cylinder pressure and an actual state: $$\frac{\mathrm{i.e}}{\mathrm{i.e}t}\left(\frac{1}{2}\cdot {\mathrm{<figure-callout\; id="0"\; label="J"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">J</figure-callout>}}_0\cdot {\omega }^2\right)=\left(M_{tan}-M_R-M_L\right)\cdot \omega$$

J0, J

Allg. / anteiliges Massenträgheitsmoment

φ

Winkelstellung der Kurbelwelle

ω

Winkelgeschwindigkeit

Mtan

Moment durch Gaskraft im Zylinder und oszillierender Massenkraft

MR

Moment durch Reibungsverluste

ML

Moment durch Lastanforderung

MM

Anteiliges Moment durch rotatorische Massenträgheit

nmot

Aktuell anliegende Motordrehzahl

symbol meaning

J0, J

General / proportional mass moment of inertia

φ

Angular position of the crankshaft

ω

angular velocity

Mtan

Moment due to gas force in the cylinder and oscillating mass force

MR

moment due to friction losses

ML

moment by load request

mm

Partial moment due to rotational mass inertia

nmot

Current engine speed

Differentiation, substitution and introduction of a moment of inertia (division of the inertia components) results in the equation: $$J\cdot \dot{\omega }={\displaystyle \sum _i{M}_i=M_{tan}-M_{tan}}-M_R-M_L-M_M$$

If the equation is meaningfully divided into a "direct component" and an "alternating component", the following sub-equations are obtained:
"Constant proportion": $$\overline{M_{tan}}=\overline{M_R}-\overline{M_L}$$

The balancing of the direct component is based on a stationary operating point. The average torque provided keeps the average speed constant because it corresponds to the torque requirements from load and friction.
“Change share”: $$J\cdot \dot{\omega }=\widetilde{M_{tan}}-\widetilde{M_R}-\widetilde{M_M}$$

A conversion from time-based derivation to crank angle-based difference formation takes place with the help of the relationship $$\begin{array}{l}\omega =\frac{\mathrm{i.e}\phi }{\mathrm{i.e}t}=\pi \cdot \frac{n_{mOt}}{30}\text{by}\\ \dot{\omega }\approx {\left(\frac{\pi }{30}\right)}^2\cdot nmOt\cdot \frac{\Delta nmOt}{\Delta \phi }\end{array}$$

The decisive variables from equation (1) are further detailed for the evaluation. The relationship for the resulting moment from the inner-cylindrical gas force and results in: $$\widetilde{M_{tan}}=\left[A_K\cdot \left[p_{\mathrm{e.g}yt}\left(\phi \right)-p_0\right]-m_{Os\mathrm{e.g}}\cdot \ddot{s}\left(\phi \right)\right]\cdot {\mathrm{right}}_K\cdot \frac{\text{sin}\left(\phi +\beta \right)}{cOs\beta }$$

AK

Kolbendeckfläche = const.

rK

Wirkradius der Kurbelwelle entspricht halben Hub = const.

lPl

Pleuellänge = const.

mosz

Oszillatorische Massenteil entspricht Kolbenbaugruppe und anteiliger Pleuelmasse = const.

pzyl

Im Zylinder vorherrschender Druck

p0

Referenzdruck, Kurbelgehäusedruck

β(φ)

Pleuelschwenkwinkel in Abhängigkeit der Kurbelwinkelstellung

s̈(φ)

Kolbenbeschleunigung in Abhängigkeit von der Kolbenstellung

symbol meaning

AK

Piston top area = const.

rK

Effective radius of the crankshaft corresponds to half the stroke = const.

lPl

connecting rod length = const.

mosz

Oscillating mass part corresponds to piston assembly and proportionate connecting rod mass = const.

pcyl

Pressure prevailing in the cylinder

p0

Reference pressure, crankcase pressure

β(φ)

Connecting rod swivel angle depending on the crank angle position

s̈(φ)

Piston acceleration as a function of piston position

Further detailing the variable factors from Equation (3) yields: $$\ddot{s}\left(\phi ,\dot{\phi },\ddot{\phi }\right)={\mathrm{right}}_K\cdot \ddot{\phi }\cdot \text{sin}\phi +{\mathrm{right}}_K\cdot {\dot{\phi }}^2\cdot \text{cos}\phi {+}^{{\mathrm{right}}_K}{\text{/}}_2\cdot \ddot{\phi }\cdot {\lambda }_{Pl}\cdot \text{sin}\left(2\cdot \phi \right)+{\mathrm{right}}_K\cdot {\dot{\phi }}^2\cdot {\lambda }_{Pl}\cdot \text{cos}\left(2\cdot \phi \right)$$

Assuming a constant mean speed nmot, the relationship for the piston acceleration is simplified to: $${\ddot{s}}_{\mathrm{right}eat}\left(\phi ,\dot{\phi }\right)={\mathrm{right}}_K\cdot {\dot{\phi }}^2\cdot \left(cOs\phi +{\mathrm{\lambda }}_{\text{Pl}}\cdot \text{cos}\left(2\phi \right)\right)$$

Schubstangenverhältnis $${\lambda }_{Pl}{=}^{r_K}{\text{/}}_{l_{Pl}}$$

$$p_{zyl}={\overline{p}}_{zyl}$$

Bezug zum Umgebungsdruck $$p_0=p_{ung}$$

oder wie im weiteren auch genutzt der
Bezug zum Kurbelgehäusedruck $$p_0=p_{KurbGeh}=p_{umg}-DPS$$

wobei DPS für den Unterdruck im Saugrohr steht.The assumption leads to an error that can be neglected. The influence of the angular acceleration results in a negligibly small deviation over the entire map. $$\beta \left(\phi \right)=\text{arcsin}\left({\lambda }_{Pl}\cdot sin\phi \right)$$

push rod ratio $${\lambda }_{Pl}{=}^{{\mathrm{right}}_K}{\text{/}}_{l_{Pl}}$$

$$p_{\mathrm{e.g}yl}={\overline{p}}_{\mathrm{e.g}yl}$$

relation to the ambient pressure $$p_{}$$$${}_0=p_{\mathrm{and}nG}$$

or as further also used the
relation to crankcase pressure $$p_{}$$$${}_0=p_{K\mathrm{and}\mathrm{right}bGeH}=p_{\mathrm{and}mG}-DPS$$

where DPS stands for the vacuum in the intake manifold.

The friction torque from Equation (1) can be represented in different ways. Either a model can be introduced which reflects measurement data for a specific operating point of the diagnosis. A goal-oriented approach here would be a functional linking of the term with the speed, the load and the oil temperature.

In the following, however, it is assumed that the diagnosis is carried out at firmly defined steady-state load points. As a result, the friction torque for this load point can be assumed to be constant. $$\widetilde{M_R}=cOnst$$

$$J=const.$$

The same approach is also used for the proportional moment due to rotational mass inertia and the mass moment of inertia. $$\widetilde{M_M}=cOnst.$$

$$J=cOnst.$$

A suitable choice of diagnosis constants in the stationary operating point allows a simple application of the parameters afterwards.

Solving equation (1) for the gas moment gives: $$\widetilde{M_{tan}}=J\cdot \dot{\omega }+\widetilde{M_R}+\widetilde{M_M}$$

After inserting the relationships from equations (9) to (11), one can conclude the following simplification with the application constant KRM: $$\widetilde{M_{tan}}=J\cdot \dot{\omega }+K_{RM}$$

• In 3 ist das Detail X aus 2, also die Drehzahlentwicklung 101 über den Kurbelwinkel KW während des Diagnose-Zeitfensters 112 mit den Messpunkten P1 und P2 in der Kompression von Zylinder Z1 eingetragen. Für den Zylinderdruck p_P1 im Zylinder Z1 gilt zum Messpunkt P1 p_P1(t₁, n₁), für den Zylinderdruck p_P2 zum Messpunkt P2 p_P2(t₂, n₂). Ersichtlich sinkt während des Diagnose-Zeitfensters 112 die gemessene Drehzahl n, sodass gilt n₁ > n₂.

Application of the diagnosis:

• In 3 the detail X is off 2 , ie the speed development 101 via the crank angle KW during the diagnosis time window 112 with the measuring points P1 and P2 in the compression of cylinder Z1. The cylinder pressure p _P1 in the cylinder Z1 is p _P1 (t ₁ , n ₁ ) at the measuring point P1, and p _P2 (t ₂ , n ₂ ) for the cylinder pressure p _P2 at the measuring point P2. It can be seen that the measured rotational speed n falls during the diagnosis time window 112, so that n ₁ >n ₂ applies.

The angular velocity gradient from Equation (2) is expanded. The speed to be determined must be averaged and constants are marked again. $$\begin{array}{l}\dot{\omega }\approx {\left(\frac{\pi }{30}\right)}^2\cdot \frac{}{n_{mOt}}\cdot \frac{\Delta n_{mOt}}{\Delta \phi }\\ \dot{\omega }\approx {\left(\frac{\pi }{30}\right)}^2\cdot \frac{n_{m\mathrm{<figure-callout\; id="2"\; label="O\; t"\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_2}+n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}}{2}\cdot \frac{n_{m\mathrm{<figure-callout\; id="2"\; label="O\; t"\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_2}-n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}}{{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1}\\ \dot{\omega }\approx \frac{1}{2}\cdot {\left(\frac{\pi }{30}\right)}^2\cdot \frac{n_{m\mathrm{<figure-callout\; id="2"\; label="O\; t"\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_2}{}^2-n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}{}^2}{{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1}\\ \dot{\omega }\approx K_{\omega }\cdot \frac{n_{m\mathrm{<figure-callout\; id="2"\; label="O\; t"\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}t}{}^2-n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}{}^2}{{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1}\end{array}$$

mit einer Kinematikkonstanten für den Stationärpunkt, in welchem die Diagnose stattfindet $$K_K=r_K\cdot \frac{\text{sin}\left(\phi +\beta \right)}{cos\beta }$$

The term for the tangential moment from equation (3) is subsequently expanded to include the relationships from equations (4) to (8) and constants are identified. $$\begin{array}{l}\widetilde{M_{tan}}=\left[\frac{\left({\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">p</figure-callout>}}_1+{\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">p</figure-callout>}}_1-2\cdot p_{\mathrm{and}mG}+2\cdot DPS\right)}{2}\cdot A_K-m_{Os\mathrm{e.g}}\cdot \ddot{s}\left(\phi \right)\right]\cdot {\mathrm{right}}_K\cdot \frac{\text{sin}\left(\phi +\beta \right)}{cOs\beta }\\ \widetilde{M_{tan}}=\left[\frac{\left({\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">p</figure-callout>}}_1+{\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">p</figure-callout>}}_1-2\cdot p_{\mathrm{and}mG}+2\cdot DPS\right)}{2}\cdot A_K-m_{Os\mathrm{e.g}}\cdot \ddot{s}\left(\phi \right)\right]\cdot K_K\end{array}$$

with a kinematic constant for the stationary point in which the diagnosis takes place $$K_K={\mathrm{right}}_K\cdot \frac{\text{sin}\left(\phi +\beta \right)}{cOs\beta }$$

After inserting equations (14) and (13) into equation (12), solving for the cylinder pressures and combining all constants, the result is: $$\begin{array}{l}\left[\frac{\left({\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">p</figure-callout>}}_1+{\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">p</figure-callout>}}_1-2\cdot p_{\mathrm{and}mG}+2\cdot DPS\right)}{2}\cdot A_K-m_{Os\mathrm{e.g}}\cdot \ddot{s}\left(\phi \right)\right]\cdot K_K=J\cdot K_{\omega }\cdot \frac{N_{\mathrm{<figure-callout\; id="2"\; label="m\; O\; t"\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">m</figure-callout>}O{t}_{}{}_2}{}^2-n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}{}^2}{{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1}+K_{\mathrm{<figure-callout\; id="1"\; label="R\; M\; p"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">R</figure-callout>}M}& \\ \frac{p_{}}{}\frac{{}_1+{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">p</figure-callout>}}_2}{2}=\frac{J\cdot K_{\omega }}{K_K\cdot A_K}\cdot J\cdot K_{\omega }\cdot \frac{n_{m\mathrm{<figure-callout\; id="2"\; label="O\; t"\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_2}{}^2-n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}{}^2}{{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1}+\frac{K_{RM}}{K_K\cdot A_K}+\frac{m_{Os\mathrm{e.g}}\ddot{s}\left(\phi \right)}{A_K}+p_{\mathrm{and}mG}-D\mathrm{<figure-callout\; id="1"\; label="P\; S\; p"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">P</figure-callout>}S& \\ \frac{p_{}}{}\frac{{}_1+{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">p</figure-callout>}}_2}{2}=\frac{n_{m\mathrm{<figure-callout\; id="2"\; label="O\; t"\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_2}{}^2-n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}{}^2}{{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1}+{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">K</figure-callout>}}_2+\frac{m_{Os\mathrm{e.g}}\cdot \ddot{s}\left(\phi \right)}{A_K}+p_{\mathrm{and}mG}-DPS\end{array}$$

All pressure variables and speeds in equation (15) can be measured at points in time P1 and P2. A suitable indicator measurement technique known per se resolves the necessary physical variables based on the crank angle or at least averaged over several working cycles. In addition or as an alternative to the indication measurement technology, data from a suitable operating model, for example the engine control, can be accessed. The kinematic constant K _K can be tabulated and used depending on the piston position.

The influence of the speed nmot with regard to the oscillatory masses can, for example, be calculated in real time or stored on the control unit in the form of a lookup table of a suitably stored operating model with regard to speed and load.

The reduced piston acceleration (4) can be formulated for the two discrete points: $${\ddot{s}}_{\mathrm{right}e\mathrm{i.e}}\left(\phi ,\dot{\phi }\right)={\mathrm{right}}_K{\left[\frac{\frac{\pi }{30}\left(n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}+n_{mO{t}_2}\right)}{2}\right]}^2\cdot \left[cOs\left(\frac{{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2}{2}\right)+cOs\left({\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1+{\phi }_2\right)\right]$$

The constants K ₁ and K ₂ can be determined using reference measurements (engine function or gas exchange OK).

Diagnosis process:

After determining the application constants K ₁ and K ₂ , Equation (15) can be used to determine the diagnostic cylinder pressure from the speed change in compression: $${\overline{p}}_{\mathrm{e.g}yl,\mathrm{i.e}iaG}={\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">K</figure-callout>}}_1\cdot \frac{n_{m\mathrm{<figure-callout\; id="2"\; label="O\; t"\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_2}{}^2+n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}{}^2}{{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020119802B4\_0027.png,DE102020119802B4\_0028.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1}+{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102020119802B4\_0028.png"\; state="\{\{state\}\}">K</figure-callout>}}_2+\frac{m_{Os\mathrm{e.g}}\cdot {\ddot{s}}_{\mathrm{right}e\mathrm{i.e}}\left(\phi ,n_{mOt}\right)}{A_K}+p_{\mathrm{and}mG}-DPS$$

The diagnostic cylinder pressure p̅ _zyl,diag is an indication of the pressure profile during compression of the cylinder.

In this way, the diagnostic cylinder pressures p13=p _diag,13 for the time interval t13 and p32=p _diag,32 for the time interval t32 can be determined while driving for the diagnosis time window 12 of the diagnosed cylinder Z.

In addition, for both time intervals t13 and t32 in the diagnosis time window 12, an average cylinder volume V13 or V32 of the diagnosed cylinder Z is determined for the corresponding crank angle positions °KW, here for example using a table lookup at points P1, P3 and P2.

With the diagnostic pressure values determined in this way (=characteristics of a pressure index of the diagnosed cylinder Z) and volume values (=characteristics of a cylinder volume of the diagnosed cylinder), the polytropic equation for the cylinder pressure curve during compression (more precisely: in the diagnosis time window 12) is then drawn up : $${\mathrm{<figure-callout\; id="13"\; label="p"\; filenames="DE102020119802B4\_0029.png"\; state="\{\{state\}\}">p</figure-callout>}}_{13}\cdot V_{13}{}^N={\mathrm{<figure-callout\; id="32"\; label="p"\; filenames="DE102020119802B4\_0029.png"\; state="\{\{state\}\}">p</figure-callout>}}_{32}\cdot V_{32}{}^N$$

From the polytrope equation (17) given in 6 shown graphically for a high reference coefficient N _ref,h and a low reference coefficient N _ref,t , the polytrope coefficient N can be determined by taking the logarithm to: $$N=-\frac{lO{G}_{10}{\mathrm{<figure-callout\; id="13"\; label="p"\; filenames="DE102020119802B4\_0029.png"\; state="\{\{state\}\}">p</figure-callout>}}_{13}-lO{G}_{10}{p}_{31}}{lO{G}_{10}{\mathrm{<figure-callout\; id="13"\; label="V"\; filenames="DE102020119802B4\_0029.png"\; state="\{\{state\}\}">V</figure-callout>}}_{13}-lO{G}_{10}{\mathrm{<figure-callout\; id="32"\; label="V"\; filenames="DE102020119802B4\_0029.png"\; state="\{\{state\}\}">V</figure-callout>}}_{32}}$$

In a next step, the calculated polytropic coefficient N is compared with a reference polytropic coefficient range Nref of 1.38 to 1.42 for regularly working cylinders. Deviation types are assigned according to the following table: Relation N to Nref number of cylinders Error pattern (= deviation type or higher-level deviation type) code too small one or few Compression problem of the diagnosed cylinder(s). K1 too small Everyone Cylinder heat transfer problem (includes abnormal increase in friction) K2 too large Deposits in the diagnosed cylinder(s) G

If the relation is “too small”, a deviation that is all the more maintenance-relevant can be assumed - the more load cases/operating states this deviation is determined in, and/or - the more the deviation was determined in a low-load range of the engine.

If the relation is "too large", then this diagnostic indication can be used in further troubleshooting of complex fault patterns such as a rough-running engine in order to subsequently identify corresponding work steps.

The relation is preferably determined for all cylinders of the engine, in which case the deviation types specified in the table can then be assigned as higher-level deviation types. For example, if all the calculated polytrope values fall significantly below the reference value, particularly in the low-load range, then a problem in the heat transfer of the cylinder can be assumed.

The relationships in the table shown are also the same 7 refer to. There are to a variety of operating states a, b. c determined polytropic coefficients N for each of the cylinders Z1-Z4 of the internal combustion engine 1 entered. The deviation type K1 to be assigned therefore results for each cylinder Z, and the higher-level deviation type K2 to be assigned for the entire internal combustion engine 1, because all determined coefficients N are clearly below the reference range Nref.

Reference List

1

combustion engine

2

diagnostic tools

4

unit of account

6

Crankshaft speed acquisition unit

7

Cylinder pressure determination unit

9

intake system

10

Torque curve of the combustion engine over one engine cycle

12

torque holes

14

predetermined limit for relevant torque contribution

100

Speed development diagram

101

speed curve

112

diagnostic time window

ATL

exhaust gas turbocharger

G

deviation type

K1

deviation type

K2

deviation type

KT

crank drive

week

crank angle

L

potential leaks

LF

air filter

LS

air collector

M

Torque of a cylinder in 1

n

rotational speed

N

polytropic coefficient

noref

Reference polytrope coefficient (also given as range)

p

cylinder pressure

pdiag

Pressure index, here diagnostic cylinder pressure

P

Measurement times at the beginning, in the middle and at the end of the diagnosis time window

R

potential mechanical failure due to piston/cylinder friction

t

Time interval in the diagnosis time window

V

cylinder volume

Z

cylinder

ZZP

ignition timing of a cylinder

Claims (14)

Method for diagnosing a compression behavior of an internal combustion engine (1) in a motor vehicle with multiple cylinders (Z1-Z4), having the steps: - Determining a diagnosis time window (112) within a torque gap (12) of one of the cycles of the internal combustion engine (1), independent of the operating point while the motor vehicle is being driven, - Identifying at least one cylinder (Z1-Z4), which is in a compression stroke at the beginning of the diagnosis time window, - Determining a cylinder pressure profile of the identified cylinder (Z1-Z4) during the diagnosis time window as a function of a determined speed development (100) of the internal combustion engine (1) during the diagnosis time window (112), and - Allocation of a deviation type to the identified cylinder (Z1-Z4) as a function of a polytropic coefficient (N), which is determined as a function of the determined cylinder pressure profile for the diagnosis time window. procedure according to claim 1 , characterized in that the cylinder pressure profile is determined as a function of at least two expressions of a pressure index (p _diag ), which is determined at least at two time intervals (t13, t32) in the diagnosis time window. procedure according to claim 2 , characterized in that the polytrope coefficient (N) is determined as a function of one, in particular mean, cylinder volume (V13, V32) for each of the two time intervals (t13, t32). procedure according to claim 3 , characterized in that the following steps are carried out to assign the deviation type: - determining the cylinder pressure curve (p13-p32) on the basis of the determined characteristic of the pressure index for each of the time intervals (t13, t32) in the diagnosis time window, and/or - determining the Polytrope coefficients (N) on the basis of the determined characteristic of the pressure index and the cylinder volumes (V13, V32) determined at the time intervals, and/or - comparison of the determined polytropic coefficient (N) with predetermined characteristics of the polytrope coefficients (Nref) assigned to different types of deviations, and/or - assignment of a type of deviation for the examined cylinder to the specific diagnostic time window (112) according to the result of the comparison. procedure according to claim 4 , characterized in that a reference polytropic coefficient range of 1.38 to 1.42 for regularly working cylinders is defined as a predetermined expression of the polytropic coefficient (Nref). procedure according to claim 4 or 5 , characterized in that the polytropic coefficient is determined for several or all cylinders of the internal combustion engine and a deviation type is assigned, and a higher-level deviation type is assigned by means of a comparison with predetermined combinations of deviation types of several or all cylinders. Method according to one of the preceding claims, characterized in that as a type of deviation and/or as a superordinate type of deviation - a mechanical damage and/or a wall heat transfer problem is assigned if the or several or all determined polytropic values (N) are less than 1.38, - Deposits in the cylinder are assigned if the or several or all determined polytrope values (N) are greater than 1.42. Method according to any of the preceding claims 2 until 7 , characterized in that a first time interval (t13) for determining the pressure index from a beginning (P1) to a middle (P3) of the diagnosis time window (112) and a second time interval (t32) from the middle (P3) up to an end (P2) of the diagnosis time window (112). procedure according to claim 8 , characterized in that a polytropic equation for the compression in the cylinder during the diagnosis time window with the determined expression for the pressure index and an averaged cylinder volume, each for the first time interval (t13) and the second time interval (t32) is set up. Method according to one of the preceding claims, characterized in that to determine the speed development (100), a continuous speed curve (101) is recorded during the diagnosis time window (112) and the recorded values with a resolution of at least in the order of ten milliseconds, in particular in the control unit. Method according to one of the preceding claims, characterized in that a determined deviation of the determined polytropic coefficient from the predetermined characteristic of the polytropic coefficient (Nref) and/or the associated deviation type - is stored in a fault memory, and/or - is stored in an engine condition monitoring system , and/or - are displayed as a control message for a vehicle occupant. Diagnostic means (2) for diagnosing a compression behavior of an internal combustion engine (1) with a plurality of cylinders (Z), which is set up to use a method according to one of Claims 1 until 11 and wherein the diagnostic means (2) has: - a computing unit (4) which is set up to control a rotational speed detection unit (6) and/or a cylinder volume determination unit, the computing unit (4) being set up to to determine a diagnosis time window (112) within a torque gap (12) of one of the cycles of the internal combustion engine (1) while the motor vehicle is being driven, and to identify at least one cylinder (Z1-Z4) which is at the beginning of the diagnosis time window in a compression stroke, characterized by a cylinder pressure determination unit (7) which is set up to determine a cylinder pressure curve as a function of detected speeds and/or a speed development of the crankshaft in the diagnosis time window, the computing unit (4) being set up to calculate the cylinder pressure -Determination unit to control, and depending on the determined cylinder pressure curve of the identified Cylinder (Z1-Z4) in the diagnosis time window (112) to assign a deviation type to the identified cylinder (Z1-Z4). Diagnostic means (2) according to claim 12 , characterized in that the diagnostic means (2) is set up to assign the deviation type - a cylinder pressure curve (p) on the basis of the determined expression of the pressure index for each of the time to determine intervals (t13, t32) in the diagnosis time window, - to determine a polytropic coefficient (N) on the basis of the determined characteristic of the pressure index and the cylinder volumes (V13, V32) determined for the time intervals, - to determine the determined polytropic coefficient (N) with predetermined to compare characteristics of the polytrope coefficient (Nref) which are assigned to different types of deviation, and - to assign a type of deviation for the examined cylinder to the specific diagnosis time window (112) according to the result of the comparison. Internal combustion engine (1) with several cylinders (Z), characterized by a diagnostic means (2) according to one of Claims 12 or 13 .

Images