DE102020126770A1 - Determination of a combustion delay in a cylinder of an internal combustion engine - Google Patents

Abstract

The invention relates to a method for determining a combustion delay in a cylinder of an internal combustion engine in a motor vehicle, having the steps: determining a diagnostic time window within a torque gap of one of the cycles of the internal combustion engine while the motor vehicle is being driven, identifying a cylinder which is at the beginning of the Diagnosis time window is in a compression stroke, determining a speed development of the internal combustion engine during the diagnosis time window, in particular with a real-time capable sampling quality, and determining a combustion delay characteristic (BV) in the identified cylinder.

Description

The invention relates to a method for determining a combustion delay in a cylinder of an internal combustion engine, an engine control unit for an internal combustion engine, and an internal combustion engine with a plurality of cylinders and an engine control unit.

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.

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.

Against the background of the problems described, 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 determination of combustion delay in a cylinder of an internal combustion engine.

This object is achieved by a method for determining a combustion delay in a cylinder of an internal combustion engine having the features of claim 1, an engine control unit for an internal combustion engine having the features of claim 9, and an internal combustion engine having the features of claim 12. Advantageous versions are the subject of dependent claims.

1. (a) Bestimmen eines Diagnose-Zeitfensters innerhalb eines Drehmomentlochs eines der Takte des Verbrennungsmotors während eines Fahrbetriebs des Kraftfahrzeugs. Unter einem Diagnose-Zeitfenster ist speziell ein zusammenhängender Zeitraum als Anteil eines Kompressionstakts und/oder eines Arbeitstakts in dem Verbrennungsmotor (beispielsweise einer der Takte einer Viertakt-Verbrennung in einem Viertaktmotor) zu verstehen. Unter einem Diagnose-Zeitpunkt ist insbesondere ein Zeitpunkt innerhalb des Diagnose-Zeitfensters zu verstehen, für welchen eine, mehrere oder alle Bestimmungsgrößen einer zu ermittelnden Zielgröße ermittelt werden. Unter einem Drehmomentloch ist vorliegend insbesondere ein Kurbelwinkelbereich zu verstehen, in welchem der betrachtete Zylinder und/oder mehrere oder alle anderen Zylinder des Motors keinen im Kontext relevanten Beitrag zu einem Vortriebs-Drehmoment leisten (d.h. im Kontext eines Brennverzugs kann auch nach der Zündung während des Brennverzugs noch von einem Drehmomentloch gesprochen werden, da ja quasi aus der Definition des Brennverzugs schon resultiert, dass in dieser Zeit kein relevanter Vortriebs-Drehmomentbeitrag an die Kurbelwelle geliefert wird).
2. (b) Identifizieren eines Zylinders, welcher sich zu Beginn des Diagnose-Zeitfensters in einem Kompressionstakt (sprich in einem Kurbelwinkel-Bereich von einem unteren Totpunkt (UT) zum Zündungs-oberen Totpunkt (ZOT)) oder in einem Arbeitstakt (sprich in einem Kurbelwinkel-Bereich von einem Zündungs-oberen Totpunkt (ZOT) zum unteren Totpunkt (UT)) 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 derjenige Zylinder identifiziert, welcher sich zu Beginn des Diagnose-Zeitfensters in einem Kompressionstakt oder in einem Arbeitstakt befindet.
3. (c) Ermitteln einer Drehzahlentwicklung des Verbrennungsmotors während des Diagnose-Zeitfensters, insbesondere mit einer echtzeitfähigen Samplingqualität, Unter einer Drehzahlentwicklung ist vorliegend insbesondere zu verstehen, wie sich eine an der Kurbelwelle des Verbrennungsmotors anliegende Drehzahl während des Diagnose-Zeitfensters entwickelt. Dazu können Werte für die Drehzahl mit einem geringen Samplingintervall, beispielsweise im Bereich von einer Millisekunde (ms) oder kleiner, zwischen zeitlich benachbarten Werten, (also insbesondere mit einer echtzeitfähigen Samplingqualität) verwendet werden.
4. (d) Ermitteln eines Brennverzugskennwerts im identifizierten Zylinder, insbesondere während des Diagnose-Zeitfensters, in Abhängigkeit von der ermittelten Drehzahlentwicklung, insbesondere im Diagnose-Zeitfenster.

According to one aspect, a method for determining a combustion delay in one, in particular several, cylinders of an internal combustion engine in a motor vehicle is specified, having at least one, several or all of the following method steps - in the specified order or in another technically reasonable order:

1. (a) Determining 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 specifically as a continuous period of time as a portion of a compression stroke and/or a power stroke in the internal combustion engine (for example one of the strokes of four-stroke combustion in a four-stroke engine). A diagnosis point in time is to be understood in particular as a point in time within the diagnosis time window for which one, several or all parameters of a target variable to be determined are determined. 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 several or all other cylinders of the engine do not make any contribution to a propulsion torque that is relevant in the context (i.e. in the context of a combustion delay, even after ignition during the combustion delay can still be referred to as a torque hole, since the definition of combustion delay already means that no relevant propulsion torque contribution is delivered to the crankshaft during this time).
2. (b) Identifying a cylinder which is at the beginning of the diagnosis time window in a compression stroke (i.e. in a crank angle range from bottom dead center (UT) to ignition top dead center (ZOT)) or in a power stroke (i.e. in a crank angle -Range from an ignition top dead center (ZOT) to bottom dead center (UT)). 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, that cylinder which is in a compression stroke or in a power stroke at the beginning of the diagnosis time window is identified.
3. (c) Determining a speed development of the internal combustion engine during the diagnosis time window, in particular with a real-time capable sampling quality. In the present case, a speed development is to be understood in particular as how a speed applied to the crankshaft of the internal combustion engine develops during the diagnosis time window. For this purpose, values for the rotational speed with a small sampling interval, for example in the range of one millisecond (ms) or less, between adjacent values (ie in particular with a real-time capable sampling quality) can be used.
4. (d) Determination of a combustion delay characteristic in the identified cylinder, in particular during the diagnosis time window, as a function of the determined speed development, in particular in the diagnosis time window.

According to a further aspect, an engine control unit for an internal combustion engine is specified, which is set up to transfer, in particular by means of a method according to an embodiment of the invention, characteristics of a combustion delay characteristic determined and/or stored in a memory, in particular a non-volatile memory ( I) to a diagnostic component of the engine control unit for further onboard diagnostic functions, and/or (II) to a control component of the engine control unit for real-time regulation of functions of the internal combustion engine as a function of the determined combustion delay characteristic.

1. (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, insbesondere von ca. 0,5 oder 0,75 oder 1 ms bereitzustellen und/oder an eine Recheneinheit zu übermitteln, und/oder
2. (ii) eine Zylindervolumen-Ermittlungseinheit, die dazu eingerichtet ist, ein Zylindervolumen in Abhängigkeit von einer Winkelstellung der Kurbelwelle zu ermitteln und/oder an eine Recheneinheit zu übermitteln, und/oder
3. (iii) Zylindertemperatur-Ermittlungseinheit, die dazu eingerichtet ist, eine Zylindertemperatur in Abhängigkeit von einem Lastfall und/oder einer Drehzahl der Kurbelwelle zu ermitteln und/oder an eine Recheneinheit zu übermitteln, und/oder
4. (iv) eine Restgasanteil-Ermittlungseinheit, die dazu eingerichtet ist, einen Restgasanteil in Abhängigkeit von erfassten Drehzahlen und/oder einer Drehzahlentwicklung der Kurbelwelle im Diagnosezeitfenster zu ermitteln und/oder an eine Recheneinheit zu übermitteln, und/oder
5. (v) wenigstens eine Lambdasonde, die dazu eingerichtet ist, ein Verbrennungsluftverhältnis von in den Zylinder eingeführtem Luft-Kraftstoff-Gemisch zu ermitteln und/oder an eine Recheneinheit zu übermitteln, und/oder
6. (vi) eine Brennverzugs-Ermittlungseinheit, die dazu eingerichtet ist, eine Ausprägung eines Brennverzugskennwert in Abhängigkeit von erfassten Drehzahlen und/oder einer Drehzahlentwicklung der Kurbelwelle im Diagnosezeitfenster zu ermitteln und/oder an eine Recheneinheit zu übermitteln

According to a further aspect, a device is specified for determining a combustion delay parameter in a cylinder of an internal combustion engine in a motor vehicle with multiple cylinders, the device being implemented in particular in an engine control unit according to one embodiment of the invention, and/or being set up to implement a method according to a carrying out the invention, and wherein the device comprises at least one, more or all of the following:

1. (i) a speed detection unit that is set up to detect a speed of a crankshaft of the internal combustion engine and, according to one embodiment, to provide the detected values in a sampling time, in particular of approximately 0.5 or 0.75 or 1 ms and/ or to transmit to a processing unit, and/or
2. (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 to transmit it to a computing unit, and/or
3. (iii) Cylinder temperature determination unit, which is set up to determine a cylinder temperature as a function of a load case and/or a rotational speed of the crankshaft and/or to transmit it to a computing unit, and/or
4. (iv) a residual gas portion determination unit that is set up to determine a residual gas portion as a function of detected speeds and/or a speed development of the crankshaft in the diagnostic time window and/or to transmit it to a computing unit, and/or
5. (v) at least one lambda probe, which is set up to determine and/or to transmit to a computing unit a combustion air ratio of the air-fuel mixture introduced into the cylinder, and/or
6. (vi) a combustion delay determination unit, which is set up to determine and/or to transmit to a computing unit a characteristic of a combustion delay characteristic value as a function of detected speeds and/or a speed development of the crankshaft in the diagnosis time window

Furthermore, according to one embodiment, the device has (vii) a computing unit which is set up to determine the speed detection unit and/or the residual gas percentage determination unit and/or the cylinder volume determination unit and/or the cylinder temperature determination unit and/or at least one lambda probe and/or to control a combustion delay determination unit and/or measured values recorded there or to have the characteristics determined there and/or the data stored there transmitted. The processing unit is set up in particular to determine a diagnosis 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 which is in a compression stroke or a power stroke at the beginning of the diagnosis time window.

According to a further aspect, an internal combustion engine with multiple cylinders is specified, having an engine control unit 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 Otto or diesel engines.

The invention is based, among other things, on the consideration that the combustion delay in the individual cylinders is an elementary parameter for the combustion efficiency, but cannot be measured directly. However, if the performance of the combustion engine is to be continuously monitored (without visiting a workshop with special equipment), it must be recorded while the vehicle is being driven.

The combustion chamber in the cylinder (also referred to simply as "the cylinder") contains an aerosol with an air mass and a fuel mass for combustion. Typically and so also in the present case, the term combustion delay is defined, in particular in the case of Otto engines, by a range (normally and in the present case specified in crank angle degrees - °KW) between the ignition of the mixture present in the combustion chamber and the first noticeable heat release at the 5% conversion point; i.e. when 5% of the aerosol is chemically converted during combustion.

The length of the combustion delay determines the combustion quality, consumption, driving comfort and emissions to a very large extent. Combustion delays cannot be measured directly in the car/on the test bench. This means that no diagnosis can be made on the basis of combustion distortions. Regulations based on the target combustion delay cannot be implemented either.

The invention is based, among other things, on the idea of determining a real combustion delay or at least one characteristic value for a real combustion delay, in particular during driving operation and/or on the engine control unit, and using assumptions as well as measurement and map values in such a way that a sufficiently good approximation of the real combustion delay can be determined in order to enable further diagnostic functionalities (onboard and/or offboard) and/or interventions in the engine control with the purpose of an optimized operation of the internal combustion engine on this basis. For this purpose, according to one embodiment, the characteristics of the combustion delay characteristic that are determined are made available to the diagnoses and controls in real time during engine operation.

According to one embodiment, an energy balance of the cylinder is calculated in the area of the combustion delay that occurs (between the ignition point and the first lift of the pressure curve). With suitable assumptions for the calculation, a so-called "rapid heating curve calculation" for control unit applications is implemented - the assumptions are used to simplify the calculation, so that a real-time capability of the calculation is also possible with the limited calculation capacities of the engine control and/or other vehicle control units used. The heating curve calculation is carried out using the diagnostic characteristics of a cylinder pressure that are associated with the operating range (calculation, for example, as in WO 2019/238338 A1 described) merged. This allows the 5% conversion point to be determined via a delta iteration and the duration of the combustion delay to be derived from this.

The combustion delays determined can then be used for online diagnostics on the vehicle (in particular with regard to ignition components and the injection system). However, the determined combustion delays can also be used to operate compensatory control processes to optimize the combustion center of gravity achieved during operation. This can subsequently enable lower emission levels, increased driving comfort and optimal consumption.

According to one embodiment, the energy balance in the cylinder is first established. The wall heat losses and the enthalpy losses can be approximately set to zero without bringing too much inaccuracy into the calculation. Because of the small crank angle range considered, the internal energy content can be linearly interpolated. The heat work considered can be related to the definition of the start of combustion at 5% combustion conversion. The lower calorific value can be regarded as constant and possibly also as identical for diesel or petrol fuel with sufficient accuracy and expertly be determined accordingly. Because, by definition, no significant heat release takes place between ignition and the start of combustion, a polytropic temperature change can be assumed for the combustion delay calculation. The required pressure data can be determined from a high-resolution speed signal, for example as in WO 2019/238338 A1 described. The crankshaft angle at the point of ignition is known. The crankshaft angle at the start of combustion can then be determined iteratively directly and/or by interpolation. The calculation of the combustion delay characteristic value can thus be determined in a simple manner using variables typically available in motor vehicles.

According to one embodiment, the combustion delay characteristic is determined as a function of a crank angle difference between an ignition crank angle position at an ignition point of the identified cylinder and a combustion start crank angle position at a defined start of combustion of the identified cylinder. In this way, a direct connection can be established between the speed development and the combustion behavior in the cylinder, which simplifies the determination of the combustion delay using a directly measurable variable.

According to one embodiment, the start of combustion crank angle position is determined iteratively. In this case, in particular, a starting value for the crank angle position at the start of combustion is selected as a function of the ignition point. In the subsequent iteration steps, the starting value on both sides of the equations is adjusted until the difference between the two sides of a calculation equation falls below a certain deviation criterion. The iteration is then aborted and the expression of the crank angle position at the start of combustion is therefore considered to be determined iteratively. This type of determination is precise, but resource-intensive and therefore not suitable, or only suitable to a limited extent, for real-time use. It is therefore primarily applicable away from the vehicle, where, for example, a series of measurements can be processed using the speed signal and the combustion delay can be evaluated offboard.

According to an additional or alternative embodiment, the crank angle position at the start of combustion is determined by interpolation. Two starting values for the start of combustion crank angle position are selected: a first close to the ignition point, e.g. 30° CA before ITDC, and a second further away from the ignition point, e.g. 20° CA later, here corresponding to 10°CA before ITDC. The two sides of a calculation equation are calculated for both start values and the remaining difference of the results for the two sides is evaluated. With the two residual differences, a linear interpolation of the delta function is carried out in this selected evaluation window in order to determine the crank angle with the minimum delta (typically a zero crossing). In this way, the start-of-combustion crank angle position is determined as being interpolated. This type of determination is fast and requires fewer iterations; but is less accurate due to further linearization. It can therefore primarily be used "onboard" on the vehicle, for example for online diagnostic purposes.

According to one embodiment, the determination of a temperature in the identified cylinder at a diagnosis point in time in the diagnosis time window is provided, and the determination of the combustion delay characteristic as a function of the determined temperature. As a result, the combustion delay parameter can be determined via fluid-physical relationships, in particular the energy balance in the cylinder.

According to one embodiment, the temperature is determined by being predetermined as an estimated constant for one, several or all operating cases of the internal combustion engine. This simplifies the calculation effort when determining the combustion delay parameter without causing the results to be too falsified.

Alternatively, according to one embodiment, the temperature is determined by being read out from a pre-filled characteristic diagram as a function of an engine load and the engine speed. This results in a more precise calculation result than when a constant is assumed.

According to one embodiment, the combustion delay characteristic value is determined as a function of a cylinder volume at a diagnosis time in (i.e. during) the diagnosis time window/s in order to take into account the volume-related conditions of the cylinder, with the cylinder volume being determined from a pre-filled characteristic map as a function of a crank angle position and /or a geometry of the crank mechanism and the cylinder is read out.

In order to be able to trace the determination of the combustion delay parameter back to variables that are already present in the engine control system, one embodiment provides for the determination of a combustion air delay ratio in the identified cylinder at a diagnosis point in time in the diagnosis time window, and determining the combustion delay characteristic as a function of the determined combustion air ratio.

In order to be able to trace the determination of the combustion delay parameter back to variables that are already present in the engine controller, one embodiment provides that the combustion delay parameter is determined as a function of a fuel mass present in the diagnosed cylinder at the time of diagnosis.

In order to be able to use the energy balance in the diagnosed cylinder to determine the combustion delay, according to one embodiment the combustion delay characteristic value is determined as a function of an internal energy of the gas mixture in the diagnosed cylinder at the time of diagnosis.

According to one embodiment, for further processing of the determined combustion delay parameters, the residual gas content determined at the time of diagnosis is stored, in particular regularly clocked, in a non-volatile memory of an engine control unit of the internal combustion engine, in particular together with the operating point values determined for determining the combustion delay parameter, so that the operating situation of the internal combustion engine can be assigned .

For this purpose, according to one embodiment, the engine control unit is set up to store one or more characteristics of the combustion delay characteristic determined at one or different diagnosis times, in particular, in the non-volatile memory.

• - insbesondere im Fahrbetrieb, an eine Diagnosekomponente des Motorsteuergeräts für weitere Onboard-Diagnosefunktionen, und/oder
• - insbesondere im Fahrbetrieb, an eine Steuerkomponente des Motorsteuergeräts für eine Echtzeitregelung von Funktionen des Verbrennungsmotors in Abhängigkeit von dem ermittelten Restgasgehalt, und/oder
• - an einen Offboardrechner für Offline-Diagnosefunktionen z.B. im Serviceumfeld.

According to one embodiment, the characteristics of the combustion delay parameter that are determined and/or stored in the memory can be transferred for further processing. According to one embodiment, the memory content is transferred, in particular regularly clocked

• - In particular when driving, to a diagnostic component of the engine control unit for further onboard diagnostic functions, and/or
• - In particular when driving, to a control component of the engine control unit for real-time regulation of functions of the internal combustion engine depending on the determined residual gas content, and / or
• - to an offboard computer for offline diagnostic functions, for example in the service environment.

According to one embodiment, the computing unit has a cylinder volume determination unit and/or a cylinder temperature determination unit and/or can access measured values from one, several or all lambda probes of the internal combustion engine, in particular in real time and/or during driving operation.

For this purpose, according to one embodiment, the engine control unit is set up to transfer forms of the combustion delay characteristic value stored in the memory to an offboard computer for offline diagnostic functions.

According to one embodiment, to determine the combustion delay characteristic, a diagnostic time window is determined in the compression phase or in the working phase, in any case in the low-torque range of a cylinder in which no relevant heat release occurs in the engine, typically between 690° crank angle and 710° crank angle (in relation to the firing 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.

Because of the simultaneous change 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, according to other designs, other numbers of cylinders or working methods are also possible.

One embodiment of the invention is based, among other things, on the idea of determining the combustion delay parameter in the cylinder while driving in order to continuously monitor the performance of the internal combustion engine with special equipment without having to visit the workshop. To do this, it is necessary to determine the combustion delay parameter in the cylinder using a high-frequency and continuous measurement during driving derive ren characteristic of the driving operation, for example the speed development of the crankshaft, especially 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 drop in speed results from the friction losses of the mechanics and the piston braking due to the gas compression.

If exactly that cylinder is diagnosed in this time window that is currently in its compression stroke or a power stroke, its influence on the speed curve can best be examined: because a cylinder has the greatest influence in the compression phase and in the work phase before the end of the combustion delay on the course of the speed, as it has the greatest influence on the mechanics through the gas spring dynamics; significantly stronger than the other strokes or cylinders.

In addition, however, other torque-free phases can also be used to analyze the cylinder outside of the compression stroke or the power stroke.

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 - with various gas exchange parameters that can be combined if necessary .

In particular, existing sensors (for speed detection) with extended functions are used with the speed detection. 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 a combustion delay parameter in the cylinder.

With the invention, it is much easier to find the cause of rough-running problems, including combustion misfires, in particular by identifying any undesirable combustion delay time that may be present.

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.

In order to be able to detect the small deviations related to the average speed of the crankshaft due to rotational irregularities of the internal combustion engine with sufficient accuracy, according to one embodiment, the development of the speed is determined with a real-time sampling quality. In particular, in the present case we are talking about a real-time capable sampling quality if the variable—in this case the speed—is determined with a sampling time of approximately 1 ms or less, in particular continuously and/or without a break.

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 beginning 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 stroke and/or in the power stroke, is then used as the gas 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 implementation of an analytical method using a set of formulas in the time domain can be used particularly well from a medium engine load and up to medium engine speeds, especially in the case of smooth and constant engine speed curves. An exemplary application is shown in the first exemplary embodiment of the description of the figures.

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 device is set up to carry out methods according to any embodiments of the invention.

• 1a-c in schematischen Ansichten einen Verbrennungsmotor mit einer Einrichtung 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 zur Verdeutlichung der linearen Interpolation einer inneren Energie im Zylinder in Abhängigkeit von der Temperatur im Diagnose-Zeitfenster;
• 5 ein Kennfeld einer Zylindertemperatur in dem zu diagnostizierenden Zylinder in Abhängigkeit von der Motorlast und der Motordrehzahl;
• 6 ein Flussdiagramm verschiedener Möglichkeiten zur Nutzung der Information zu dem ermittelten Brennverzugskennwert;
• 7 ein Schaubild zur Verdeutlichung der linearen Interpolation einer Kurbelwellenstellung zum Brennbeginn im Zylinder in Abhängigkeit von einer Ergebnisdifferenz der beiden Seiten einer Berechnungsgleichung für die Kurbelwellenstellung zum Brennbeginn; und
• 8 ein Flussdiagramm zur groben Darstellung von Verfahrensschritten eines beispielhaften Verfahrens.

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

• 1a-c in schematic views an internal combustion engine with a device 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 to illustrate the linear interpolation of an internal energy in the cylinder as a function of the temperature in the diagnosis time window;
• 5 a map of a cylinder temperature in the cylinder to be diagnosed as a function of engine load and engine speed;
• 6 a flowchart of various options for using the information on the determined combustion delay characteristic;
• 7 a diagram to illustrate the linear interpolation of a crankshaft position at the start of combustion in the cylinder as a function of a result difference between the two sides of a calculation equation for the crankshaft position at the start of combustion; and
• 8th a flowchart for the rough representation of method steps of an exemplary method.

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 shows the installation environment, in particular the intake system 9 with the air filter LF at the air inlet, the exhaust gas turbocharger ATL and an intercooler and the air collector LS towards the cylinders Z.

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. The computing unit 4 also has a cylinder volume determination unit, a cylinder temperature determination unit and a combustion delay determination unit and can access measured values of all lambda probes of the internal combustion engine.

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 device 2 by means of the pressure detection unit 7 , the instantaneous speed n by means of the speed detection unit 6 and the arithmetic unit 4 .

In 1c a diagram 100 of a torque development with an exemplary torque curve 10 on the crank drive KT is shown during normal operation over the crank angle KW. is evident, that the torque contribution M comes from different cylinders Z in alternation. A torque limit value 14 is drawn in the illustration, which is in particular arbitrarily set and determines below which torque a torque contribution of a cylinder is considered insignificant, so that there is then a torque gap within the meaning of the invention. Consequently, a torque hole 12 according to the invention can be identified if the torque contributions of each cylinder are below the limit value 14 at a certain time interval. In the representation of 1 c torque holes 12.1, 12.2, 12.3 and 12.4 of slightly different lengths result.

As in 2 shown, a diagnosis time window 112 can be defined within each of these torque holes 12, which can also include the entire period of the torque hole (but does not have to, and does not include it in the exemplary embodiment described). The start time of the diagnosis time window 112 can be determined in particular by the ignition time ZZP1 or P1, the end time in particular by a time of a defined start of combustion P2 - in this case the time at which 5% of the fuel-air mixture in the cylinder has been converted by combustion. This can correspond, for example, to the point in time at which heat is first noticeably released after compression.

• Es wird ein Diagnose-Zeitfenster 112 innerhalb eines Drehmomentlochs 12 eines der Takte des Verbrennungsmotors 1 während eines Fahrbetriebs des Kraftfahrzeugs bestimmt. Darauf aufbauend wird ein Zylinder Z1 identifiziert, welcher sich zu Beginn des Diagnose-Zeitfensters 112 in einem Kompressionstakt befindet, innerhalb welchem im Ausführungsbeispiel der Zündzeitpunkt ZZP1 liegt.

the 2 until 8th explain an exemplary embodiment of the method according to the invention for determining a combustion delay characteristic value BV in a cylinder Z of the internal combustion engine 1 while driving with the aid of the crankshaft speed n of the crankshaft drive KT. In the following paragraph, the method carried out in the exemplary embodiment is initially described in summary:

• A diagnostic time window 112 is determined within a torque gap 12 of one of the cycles of internal combustion engine 1 while the motor vehicle is being driven. Based on this, a cylinder Z1 is identified which is in a compression cycle at the beginning of the diagnosis time window 112, within which the ignition point ZZP1 lies in the exemplary embodiment.

An energy balance is drawn up for this cylinder Z1. The wall heat losses dQw and the enthalpy losses Σ h _m · m _m can be approximately set to zero. Due to the small crank angle range considered, the internal energy content dU can be interpolated linearly. The considered thermal work dQc can be related to the definition of the start of combustion at 5% combustion conversion. The lower calorific value Hu can be viewed with sufficient accuracy as constant and possibly also as identical for diesel or Otto fuel or can be determined accordingly by a specialist. Because, by definition, no significant heat release takes place between ignition ZZP1 or P1 and the start of combustion P2, a polytropic temperature change can be assumed for the combustion delay calculation. The required pressure data p can be determined from a high-resolution speed signal n. The crankshaft angle φ ₁ at the ignition point ZZP1 is known. The crankshaft angle φ ₂ at the start of combustion can then be determined using a direct iteration method 210 and/or using an interpolation method 212 . The calculation of the combustion delay characteristic value BV can thus be determined in a simple manner using variables that are typically available in motor vehicles.

In the exemplary embodiment, the vehicle is being driven, but in particular not necessarily stationary operation of the internal combustion engine 1. A live function of the engine controller 2 continuously reads speed values n for the crankshaft KT while the vehicle is being driven (due to friction delay, in a compression phase of a cylinder there is an increased drop in speed from one to be expected at a later point in time) and determines a speed development from this - cf. 1-3 .

The combustion delay characteristic value BV is determined in the cylinder Z1 during the diagnosis time window 112 as a function of the determined speed development 101 and of a temperature T in the identified cylinder Z1 at a diagnosis point in time P2 in the diagnosis time window 112 . The speed development 101 is determined with a real-time capable sampling quality during the operation of the internal combustion engine 1 .

The determined characteristic of the combustion delay characteristic value BV and possibly also other characteristics of this or other cylinders Z determined sooner or later in rapid succession are stored in a non-volatile memory of engine control unit 2 in control unit 200 and are used for further diagnostic steps and/or control or Control tasks, if necessary in real time, made accessible.

The determination of the combustion delay parameter is shown below with detailed steps for cylinder Z1 as an example.

First, a diagnosis time window 112 is determined 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 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.

The cylinder Z1 which is in a compression stroke at the beginning of the diagnosis time window 112 is then identified.

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.

Flow chart 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 underneath.

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 ).

The diagnosis time window 112 must in particular be selected in such a way that the last cylinder performing work no longer achieves any significant acceleration of the crankshaft and the next cylinder performing work has not yet fired through.

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 would have to 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.

An example is in the execution according to 1 defines the diagnosis time window 112 for cylinder Z1 from ZZP1 (=P1) to 20°KW after ZZP1 (degrees relating to the crank angle KW). The limits depend on an existing engine operating point and can be flexibly adapted to this, in particular if 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.

In the exemplary embodiment, the diagnosis time window 112 is therefore defined as: 690° CA - 710° CA, based on a crank angle specification for cylinder Z1. In the representation of 1c and 2 - which refers to the entire internal combustion engine with four cylinders, this crank angle value corresponds to 30° to 10° before top dead center of ignition (TDC). In the following, only 690°KW - 710°KW is mentioned.

A diagnosis point in time 113 within the diagnosis time window 112 is determined at 690° CA. The cylinder temperature, for example, is determined for this point in time. In contrast, a time window like the diagnosis time window 112 is required for determining the diagnostic cylinder pressure p _zyl,diag from the speed development, because the determination is based on a difference consideration.

• Grundgleichung ist die Energiebilanz im Zylinder eines Verbrennungsmotors: $$-\text{pdV}+{\text{dQ}}_{\text{C}}-{\text{dQ}}_{\text{W}}\pm {\text{h}}_{\text{m}}\cdot {\text{m}}_{\text{m}}=\text{dU}$$
  

The determination of the combustion delay characteristic value BV in the cylinder Z1 is based on an energy balance calculation, which can be used in the cylinder, at least approximately:

• The basic equation is the energy balance in the cylinder of an internal combustion engine: $$-\text{pdV}+{\text{dQ}}_{\text{C}}-{\text{dQ}}_{\text{W}}\pm {\text{H}}_{\text{m}}\cdot {\text{m}}_{\text{m}}=\text{you}$$
  

To do this, track multiple acceptance, multiple assumptions are made.

Assumption 1: in the relatively short °CA evaluation range of the speed signal n, there is no significant heat transfer to the wall: $${\text{dQ}}_{\text{w}}\approx 0$$

Assumption 2: The °CA evaluation range of the speed signal n does not include any mass flows via the valves at the inlet/outlet and also no significant blow-by enthalpy losses: $${\displaystyle \sum {\text{H}}_{\text{m}}}\cdot {\text{m}}_{\text{m}}\approx 0$$

Introducing these first two assumptions into Equation (1), we get: $$-\text{pdV}+{\text{dQ}}_{\text{C}}=\text{you}$$

Assumption 3: Within the grdKW evaluation range, the temperature (and thus the internal energy U) of the gas mixture changes so little that U(T) can be interpolated linearly (cf. the representation of the 4 ): $$\text{you}={\text{u}}_2\left({\text{T}}_2\right)-{\text{u}}_1\left({\text{T}}_1\right)=\text{u}\left({\text{<figure-callout id="2" label="T" filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png" state="{{state}}">T</figure-callout>}}_2-{\text{T}}_1\right)$$

m_F ist dabei die Kraftstoffmasse, welche im Zylinder aktuell vorhanden ist. Diese Größe kann den stets aktualisierten Rechnungen der Motorsteuerung 2 entnommen werden (Kraftstofffüllung bzw. Lasterfassung).In addition, the start of combustion φ ₂ in cylinder Z1 is defined: The start of combustion φ ₂ is defined for the crank angle position (°CA) after ignition ZZP, at which 5% of the fuel mass in the combustion chamber has been converted (from there a clear lift of the cylinder pressure can be observed from the mere compression curve): $${\text{dQ}}_{\text{c}}=0.05\cdot {\text{m}}_{\text{f}}\cdot {\text{H}}_{\text{u}}$$

m _F is the fuel mass that is currently present in the cylinder. This variable can be taken from the constantly updated calculations of engine control 2 (fuel filling or load detection).

Assumption 4: the specific lower calorific value H _U from equation (4) is defined by the fuel used and is to be regarded as sufficiently constant for the purposes of the invention (assumption for gasoline and diesel is 42-45MJ/kg each).

Assumption 5: The term -pdV in equation (1) can be interpreted using the volume difference dV between two °CA positions and the average pressure p̅ between these two angular positions: $$-\text{pdV}=\overline{\text{p}}\cdot \left({\text{<figure-callout id="2" label="V" filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png" state="{{state}}">V</figure-callout>}}_2-{\text{V}}_1\right)$$

Inserted into equation (2), the result is now: $$\text{u}\left({\text{<figure-callout id="2" label="T" filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png" state="{{state}}">T</figure-callout>}}_2-{\text{T}}_1\right)=0.05\cdot {\text{m}}_{\text{f}}\cdot {\text{H}}_{\text{u}}-\overline{\text{p}}\cdot \left({\text{<figure-callout id="2" label="V" filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png" state="{{state}}">V</figure-callout>}}_2-{\text{V}}_1\right)$$

Assumption 6: There is still no significant heat release within the °KW evaluation range; this is inherently the case in the combustion delay window. Accordingly, from a thermodynamic point of view, a polytropic temperature change is assumed: $${\text{<figure-callout id="2" label="T" filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png" state="{{state}}">T</figure-callout>}}_2={\text{<figure-callout id="1" label="T" filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png" state="{{state}}">T</figure-callout>}}_1\cdot {\left(\frac{{\text{V}}_1}{{\text{V}}_2}\right)}^{\text{<figure-callout id="1" label="N −" filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png" state="{{state}}">N</figure-callout>}-1}$$

Together with the application of Assumption 6 and Assumption 3 in Equation (6), an iteration rule for the calculation of the combustion delay using the diagnostic cylinder pressure p̅ = p _{zyl,diag results} : $$\text{u}\left({\text{<figure-callout id="1" label="T" filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png" state="{{state}}">T</figure-callout>}}_1\cdot {\left(\frac{{\text{V}}_1}{{\text{V}}_2\left({\mathrm{\phi }}_2\right)}\right)}^{\text{N}-1}\right)=0.05\cdot {\text{m}}_{\text{f}}\cdot {\text{H}}_{\text{u}}-{\text{p}}_{\text{cyl},\text{diag}}\left({\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1,{\mathrm{\phi }}_2\right)\cdot \left({\text{V}}_2\left({\mathrm{\phi }}_2\right)-{\text{V}}_1\right)+\text{u}\left({\text{T}}_1\right)$$

The start of combustion crank angle position φ ₂ is the iteration parameter here.

Assumption 7: The temperature at the point of ignition (ZZP1) can either be estimated as constant (e.g. T690 = 600K) or taken from a pre-calculated map. Such maps can be created with the help of gas exchange calculations during the development time away from control unit 2 and then made available in control unit 2 for live calculations.

An example map for 690° crank angle is in the form of an estimate on a four-cylinder engine 5 shown.

In order to calculate the partial terms of equation (8), the following definitions are made in the exemplary embodiment: determination explanation constant values: T1 ≅ 600K Approximation of the temperature near the ignition point , see assumption 7 N =1.36 Polytropic exponent analogous to literature data H _U = 43MJ/kg rounded specification for petrol/diesel Operating point parameters: φ ₁ = φ _ZZP1 = 690°K W Crank angle position at the ignition point of cylinder Z1; the variable ignition angle (Otto) or injection angle (diesel) from the control unit specifies the exact angular position in each cycle V ₁ = V(φ ₁ ) Volume function value close to the ignition point, can be taken from a look-up function of the geometry data of the crank mechanism V ₂ (φ ₂ ) = V(φ ₂ ) Volume function value at the end of combustion, can be taken from a look-up function of the crank mechanism geometry data m _F The fuel mass currently in the cylinder can be taken from the control unit during operation U(x) the internal energy is a chemical constant for the gas mixture and is taken from a stored table lookup Calculation values: p _{cyl, diag} Mean cylinder pressure value from engine speed measurement at times φ ₁ before ignition and φ ₂ after ignition

In the iteration specification of equation (8), all values for determining the crankshaft angle position at the start of combustion are now known, except for a mean cylinder pressure value p _cyl,diag = f([P1; P2]) = p _{cyl,diag,690-710} .

nor in order to estimate the residual gas content x during operation from the high-resolution speed signal 101 of the internal combustion engine 1.

How the diagnostic cylinder pressure p _{zyl,diag,690-710} is determined in the exemplary embodiment can be found in the following description of equations (9) to (24), where φ ₁ is the crank angle KW=690° of P1 and φ ₂ is the approximate corresponds to crank angle KW=710° of P2, and p̅ _zyl,diag = p _{zyl,diag,690-710} applies.

Formelzeichen Bedeutung J₀, J Allg. / anteiliges Massenträgheitsmoment φ Winkelstellung der Kurbelwelle ω Winkelgeschwindigkeit M_tan Moment durch Gaskraft im Zylinder und oszillierender Massenkraft M_R Moment durch Reibungsverluste M_L Moment durch effektive Lastabnahme M_M Anteiliges Moment durch rotatorische Massenträgheit n_mot Aktuell anliegende Motordrehzahl The determination is based on a pressure balance of the diagnosed cylinder based on the measured speed curve: $$\frac{\mathrm{i.e}}{\mathrm{i.e}t}\left(\frac{1}{2}\cdot {\mathrm{<figure-callout\; id="0"\; label="J"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">J</figure-callout>}}_0\cdot {\omega }^2\right)=\left(M_{tan}-M_R-M_L\right)\cdot \omega$$

symbol meaning J ₀ , J General / proportional mass moment of inertia φ Angular position of the crankshaft ω angular velocity M _tan Moment due to gas force in the cylinder and oscillating mass force _MR moment due to friction losses M _L Moment through effective load reduction M _M Partial moment due to rotational mass inertia n _engine Current engine speed

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

• „Gleichanteil“: $$\overline{M_{tan}}=\overline{M_R}-\overline{M_L}$$
  

If the equation is meaningfully divided into a "direct component" and an "alternating component", the following sub-equations are obtained:

• "Constant proportion": $$\overline{M_{tan}}=\overline{M_R}-\overline{M_L}$$
  

• „Wechselanteil“: $$J\cdot \dot{\omega }=\widetilde{M_{tan}}-\widetilde{M_R}-\widetilde{M_M}$$
  

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 $$\begin{array}{l}\omega =\frac{\mathrm{i.e}\phi }{\mathrm{i.e}t}=\pi \cdot \frac{n_{mOt}}{30}pe\mathrm{right}\hfill \\ \dot{\omega }\approx {\left(\frac{\pi }{30}\right)}^2\cdot nmOt\cdot \frac{\mathrm{\Delta }nmOt}{\mathrm{\Delta }\phi }\hfill \end{array}$$

Formelzeichen Bedeutung A_K Kolbendeckfläche = const. r_K Wirkradius der Kurbelwelle entspricht halben Hub = const. l_Pl Pleuellänge = const. m_osz Oszillatorische Massenteil entspricht Kolbenbaugruppe und anteiliger Pleuelmasse = const. p_zyl Im Zylinder vorherrschender Druck p₀ Referenzdruck, Kurbelgehäusedruck β(φ) Pleuelschwenkwinkel in Abhängigkeit der Kurbelwinkelstellung s̈(φ) Kolbenbeschleunigung in Abhängigkeit von der Kolbenstellung The decisive variables from equation (9) are further detailed for the evaluation. The relationship for the resulting moment from the inner-cylindrical gas force and results in: $$\widetilde{M_{tan}}=\left[A_K\cdot \left[p_{\mathrm{e.g}yl}\left(\phi \right)-p_0\right]-m_{Os\mathrm{e.g}}\cdot \ddot{s}\left(\phi \right)\right]\cdot {\mathrm{right}}_K\cdot \frac{\text{sin}\left(\phi +\beta \right)}{\text{cos}\beta }$$

symbol meaning A _K Piston top area = const. r _K Effective radius of the crankshaft corresponds to half the stroke = const. l _pl connecting rod length = const. m _osc Oscillatory mass part corresponds to piston assembly and proportionate connecting rod mass = const. p _cyl 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 (11) yields: $$\ddot{s}\left(\phi ,\dot{\phi },\ddot{\phi }\right)={\mathrm{right}}_K\cdot {\dot{\phi }}^2\cdot \text{sin}\phi +{\mathrm{right}}_K\cdot {\dot{\phi }}^2\cdot \text{cos}\phi +\raisebox{1ex}{${\mathrm{<figure-callout\; id="2"\; label="right\; K"\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">right</figure-callout>}}_K$}\!\left/ \!\raisebox{-1ex}{$2$}\right.\cdot \ddot{\phi }\cdot {\lambda }_{Pl}\cdot \text{sin}\left(2\cdot \phi \right)+{\mathrm{right}}_K\cdot {\dot{\phi }}^2\cdot {\lambda }_{Pl}\cdot \text{cos}\left(2\cdot \phi \right)$$

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

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. $$\beta \left(\phi \right)=\text{arcsin}\left({\lambda }_{Pl}\cdot \text{sin}\phi \right)$$

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

push rod ratio $${\lambda }_{Pl}=\raisebox{1ex}{${\mathrm{right}}_K$}\!\left/ \!\raisebox{-1ex}{$l_{Pl}$}\right.$$

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

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

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

After inserting the relationships from equations (17) to (19), one can conclude the following simplification with the application constant KRM: $$\widetilde{M_{tan}}=J\cdot \dot{\omega }+K_{RM}$$

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 (14) is expanded. The speed to be determined must be averaged and constants are marked again. $$\begin{array}{c}\dot{\omega }\approx {\left(\frac{\pi }{30}\right)}^2\cdot \overline{n_{mOt}}\cdot \frac{\mathrm{\Delta }{n}_{mOt}}{\mathrm{\Delta }\phi }\\ \dot{\omega }\approx {\left(\frac{\pi }{30}\right)}^2\cdot \frac{n_{m\mathrm{<figure-callout\; id="2"\; label="O\; t"\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_2}+n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}}{2}\cdot \frac{n_{m\mathrm{<figure-callout\; id="2"\; label="O\; t"\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_2}-n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}}{{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.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="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_2}{}^2-n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}{}^2}{{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.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="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">O</figure-callout>}t}{}^2-n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}{}^2}{{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1}\end{array}$$

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

The term for the tangential moment from equation (11) is subsequently expanded to include the relationships from equations (12) to (16) and constants are identified. $$\begin{array}{c}\widetilde{M_{tan}}=\left[\frac{\left({\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">p</figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">p</figure-callout>}}_2-2\cdot p_{\mathrm{and}mG}+2\cdot DPS\right)}{2}\cdot A_K-m_{Os\mathrm{e.g}}\cdot \ddot{s}\left(\phi \right)\right]\cdot {\mathrm{right}}_K\cdot \frac{\text{sin}\left(\phi +\beta \right)}{\text{cos}\beta }\\ \widetilde{M_{tan}}=\left[\frac{\left({\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">p</figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">p</figure-callout>}}_2-2\cdot p_{\mathrm{and}mG}+2\cdot DPS\right)}{2}\cdot A_K-m_{Os\mathrm{e.g}}\cdot \ddot{s}\left(\phi \right)\right]\cdot K_K\end{array}$$

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

After inserting equations (22) and (21) into equation (20), solving for the cylinder pressures and combining all constants, the result is: $$\begin{array}{c}\left[\frac{\left({\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">p</figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">p</figure-callout>}}_2-2\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_{m\mathrm{<figure-callout\; id="2"\; label="O\; t"\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_2}{}^2-n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}{}^2}{{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1}+K_{\mathrm{<figure-callout\; id="1"\; label="R\; M\; p"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">R</figure-callout>}M}& \\ \frac{p_{}}{}\frac{{}_1+{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">p</figure-callout>}}_2}{2}=\frac{J\cdot K_{\omega }}{K_K\cdot A_K}\cdot \frac{n_{m\mathrm{<figure-callout\; id="2"\; label="O\; t"\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_2}{}^2-n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}{}^2}{{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1}+\frac{K_{RM}}{K_K\cdot A_K}+\frac{m_{Os\mathrm{e.g}}\cdot \ddot{s}\left(\phi \right)}{A_K}+p_{\mathrm{and}mG}-D\mathrm{<figure-callout\; id="1"\; label="P\; S\; p"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">P</figure-callout>}S& \\ \frac{p_{}}{}\frac{{}_1+{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">p</figure-callout>}}_2}{2}={\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">K</figure-callout>}}_1\cdot \frac{n_{m\mathrm{<figure-callout\; id="2"\; label="O\; t"\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_2}{}^2-n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}{}^2}{{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1}+{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.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 (23) can be measured at points in time P1 and P2. Data from a suitable operating model, for example the motor controller, 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, in particular according to equation (12), can be formulated for the two discrete points: $${\ddot{s}}_{\mathrm{right}e\mathrm{i.e}}\left(\phi ,\dot{\phi }\right)={\mathrm{right}}_K\cdot {\left[\frac{\frac{\pi }{30}\left(n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}+n_{mO{t}_2}\right)}{2}\right]}^2\cdot \left[\text{cos}\left(\frac{{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2}{2}\right)+\text{cos}\left({\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1+{\phi }_2\right)\right]$$

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

After determining the application constants K ₁ and K ₂ , Equation (23) can be used to determine the diagnostic cylinder pressure from the speed change in compression: $${\overline{p}}_{\mathrm{e.g}yl,\mathrm{i.e}iaG}={\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">K</figure-callout>}}_1\cdot \frac{n_{m\mathrm{<figure-callout\; id="2"\; label="O\; t"\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_2}{}^2-n_{m\mathrm{<figure-callout\; id="1"\; label="O\; t"\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">O</figure-callout>}{t}_{}{}_1}{}^2}{{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_2-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1}+{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102020126770A1\_0037.png,DE102020126770A1\_0038.png"\; state="\{\{state\}\}">K</figure-callout>}}_2+\frac{m_{Os\mathrm{e.g}}\cdot {\ddot{s}}_{\mathrm{right}e\mathrm{i.e}}\left(\phi ,n_{mOt}\right)}{A_K}+p_{\mathrm{and}mG}-DPS$$

The diagnostic cylinder pressure p̅ _zyl,diag is an indication of the pressure profile during the compression stroke and possibly the subsequent crank angle ranges in the power stroke of the cylinder and can subsequently be used to determine the combustion delay BV.

In this way, the diagnostic cylinder pressure p - _cyl,diag =p _{cyl,diag,690-710} at the time interval t12=t[P1;P2] can be determined while driving for the diagnosis time window 112 of the diagnosed cylinder Z1.

By using the determined diagnostic cylinder pressure p - _cyl,diag in equation (8), the iteration rule is complete.

1. a) Iterativ direkt: Es wird ein Startwert für den Parameter φ₂ = φ₁ + x₀ in Abhängigkeit von dem Zündzeitpunkt ZZP1 gewählt. In den folgenden Iterationsschritten wird der Wert des Parameters φ₂ auf beiden Seiten der Gleichung solange verstellt, bis die Differenz der Gleichungsseiten ein gewisses Abweichungskriterium unterschreitet. Dann wird die Iteration abgebrochen und φ₂ gilt somit als iterativ bestimmt. Vorteil: Genauigkeitsgewinne bei der Bestimmung. Nachteile: Ressourcenintensive Rechnung, nicht für Echtzeitanwendung. Anwendungsbeispiel: abseits des Fahrzeugs wird eine Messreihe anhand des Drehzahlsignals aufbereitet und der Brennverzug „offboard“ ausgewertet.
2. b) Interpolierend: Es werden zwei Startwerte für den Parameter φ_2a = φ₁ + x_min (nah am Zündzeitpunkt, z.B. x_min = 2°KW) und φ_2b = φ₁ + x_max (entfernt vom Zündzeitpunkt ZZP1, z.B. x_max = 20°KW) gewählt. Für beide Startwerte werden die Seiten der Gleichung (8) berechnet und ihre Restdifferenz Δ(φ₂) ausgewertet. Es wird im Folgenden davon ausgegangen, dass in diesem gewählten Auswertefenster eine lineare Interpolation der Δ-Fkt. ohne größere Genauigkeitsverluste geschehen kann. φ₂ gilt somit als interpoliert bestimmt. Diese Ermittlungsmethode ist in 7 anhand eines Diagramms dargestellt.

In order for equation (8) to be satisfied, the left and right sides must be iteratively reconciled. There are two methods for this, with the start of combustion crank angle position φ ₂ serving as the iteration parameter:

1. a) Directly iterative: A starting value for the parameter φ ₂ =φ ₁ +x ₀ is selected as a function of the ignition point ZZP1. In the following iteration steps, the value of the parameter φ ₂ on both sides of the equation is adjusted until the difference between the sides of the equation falls below a certain deviation criterion. The iteration is then aborted and φ ₂ is thus considered to be determined iteratively. Advantage: Accuracy gains in determination. Disadvantages: Resource-intensive calculation, not for real-time use. Application example: away from the vehicle, a series of measurements is processed using the speed signal and the combustion delay is evaluated "offboard".
2. b) Interpolating: Two starting values for the parameter φ _2a = φ ₁ + x _min (close to the ignition point, e.g. x _min = 2°KW) and φ _2b = φ ₁ + x _max (distant from the ignition point ZZP1, e.g. x _max = 20°KW) selected. The sides of equation (8) are calculated for both starting values and their remainder difference Δ(φ ₂ ) is evaluated. In the following it is assumed that in this selected evaluation window a linear interpolation of the Δ-Fct. can be done without major loss of accuracy. φ ₂ is thus determined as interpolated. This determination method is in 7 represented by a diagram.

Advantages: Gain in computing time; fewer iteration steps necessary. Disadvantages: Loss of accuracy due to further linearization. Application example: Calculation of the combustion delay "onboard" on the vehicle (diagnosis).

The goal of the described method from Equation (8) consists—regardless of the selected iteration method 210 or interpolation method 212—in the determination of φ ₂ . The combustion delay then results from: $${\text{B.V}}_{0-5\%}={\mathrm{\phi }}_2-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020126770A1\_0036.png,DE102020126770A1\_0037.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1$$

• Der errechnete Brennverzug BV wird dazu beispielsweise mit einem betriebspunktspezifischen Referenzwert verglichen, um anhand von Brennverzugsabweichungen eine Brennverzugsdiagnose durchzuführen. Insbesondere bei verlängerten Brennverzügen (Ist-BV > Referenz-BV), kann die Diagnose auf folgende Probleme für die weiterführende manuelle Fehlersuche verweisen:

Fehlerbild Mögliche Ursachen Brennverzug auf einzelnen Zylinder zu lang, dauerhaft Zündung am Zylinder fehlerhaft, Gemischbildung fehlerhaft Brennverzug auf allen Zylindern zu lang, dauerhaft Energiequelle (z.B. Batterie) bzw. Energieverteilung (z.B. Leitungen, Widerstände) für Zündsystem fehlerhaft Brennverzug bei hohen Lasten problematisch, Brennverzug im Leerlauf problematisch Abnutzung Zündung (Zündkerze) am Zylinder The determined characteristics of the combustion delay characteristic value BV can be used for diagnostic purposes:

• For this purpose, the calculated combustion delay BV is compared, for example, with an operating-point-specific reference value in order to carry out a combustion delay diagnosis on the basis of combustion delay deviations. In the case of prolonged combustion delays in particular (actual BV > reference BV), the diagnosis can refer to the following problems for further manual troubleshooting:

error image Possible causes Combustion delay on individual cylinders too long, permanent Faulty ignition on the cylinder, faulty mixture formation Combustion delay on all cylinders too long, permanent Energy source (e.g. battery) or energy distribution (e.g. cables, resistors) for ignition system faulty Combustion delay at high loads problematic, combustion delay at idle problematic Ignition (spark plug) wear on the cylinder

• Denn der Brennverzug BV kann als Indiz für die Verschiebung der effizienzrelevanten Schwerpunktlage (Kurbelwellenstellung (°KW) bei 50% Kraftstoffmassenumsatz) gesehen werden.

In addition or as an alternative, the characteristic of the combustion delay characteristic value BV determined can also be used for control purposes:

• Because the combustion delay BV can be seen as an indication of the shift in the efficiency-relevant center of gravity (crankshaft position (°KW) at 50% fuel mass conversion).

Thus, with a longer combustion delay time BV, compensatory control measures can lead engine operation back to more efficient combustion (short combustion delays, controlled center of gravity). In particular, turbulence-controlling measures (valve train) and an adapted mixture distribution (injection system) can enable regular operation again.

In 6 a flowchart of various options for using the determined combustion delay characteristic value BV for onboard diagnosis 204 and/or offboard diagnosis 208 and/or control tasks 206 using engine control 2 is shown.

First, the iteration specification given in Equation (8) for the crank angle position φ ₂ at the start of combustion is filled from, among other things, measured values for the speed n with high temporal resolution, a characteristic value for a crank angle position φ ₁ at the ignition point ZZP1=P1, characteristic values for the cylinder volume V and characteristic values for the temperature T _P1 at the time of diagnosis P1, as well as characteristic values for the specific lower calorific value Hu , the internal energy U(Px) and the fuel mass m _F currently present in the cylinder.

The crank angle position φ ₂ at the start of combustion is then determined from Equation 8 either by means of a more computationally intensive but more accurate direct iteration method 210 or by means of a faster but less precise interpolation method 212 .

The expression of the combustion delay characteristic value BV can be determined from the crank angle position φ ₂ at the start of combustion and stored in a non-volatile memory 202 of the engine controller 200 . If, for example, combustion delay characteristic values BV are determined with a sampling time of 1 ms or less, a new value BV—in particular with a time stamp and/or initial values for the determination—is stored in memory 202 for each ignition.

The stored values BV can be made available in real time, i.e. immediately during driving operation, for example to an online diagnostic component 204 and/or an engine control system 206 of the engine controller 2. The BV values can also be made available to an offboard diagnostic computer 208 at a later point in time, for example in the workshop.

1. (S10) Erfassen einer Drehzahl n der Kurbelwelle KT.
2. (S20) Bestimmen eines Diagnose-Zeitfensters 112 innerhalb eines Drehmomentlochs 12 eines der Takte des Verbrennungsmotors 1 während eines Fahrbetriebs des Kraftfahrzeugs,
3. (S30) Ermitteln einer Drehzahlentwicklung 101 des Verbrennungsmotors 1 daraus während des Diagnose-Zeitfensters 112, insbesondere mit einer echtzeitfähigen Samplingqualität, aus der erfassten Drehzahl n.
4. (S40) Identifizieren eines Zylinders Z1, welcher sich zu Beginn des Diagnose-Zeitfensters in einem Kompressionstakt oder in einem Arbeitstakt befindet.
5. (S50) Ermitteln eines Drucksignals p̅_zyl,diag im identifizierten Zylinder Z1 aus der Drehzahlentwicklung 101.
6. (S61) Ermitteln eines Brennbeginns φ₂ im identifizierten Zylinder Z1 mittels einer Iterationsmethode 210 in Abhängigkeit von dem ermittelten Drucksignal p̅_zyl,diag , oder
7. (S62) Ermitteln eines Brennbeginns φ₂ im identifizierten Zylinder Z1 mittels einer Interpolationsmethode 212 im identifizierten Zylinder in Abhängigkeit von dem ermittelten Drucksignal p̅_zyl,diag .
8. (S70) Ermitteln der Ausprägung des Brennverzugskennwerts BV in Abhängigkeit von dem ermittelten Brennbeginn φ₂ im identifizierten Zylinder Z1.
9. (S80) Brennverzugsabweichungen diagnostizieren.

In 8th a flowchart for the rough representation of method steps of an exemplary method is shown. The process steps shown are as follows:

1. (S10) detecting a speed n of the crankshaft KT.
2. (S20) determining 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,
3. (S30) determining a speed development 101 of the internal combustion engine 1 therefrom during the diagnosis time window 112, in particular with a real-time capable sampling quality, from the detected speed n.
4. (S40) Identification of a cylinder Z1 which is in a compression stroke or in a power stroke at the beginning of the diagnosis time window.
5. (S50) Determination of a pressure signal p̅ _zyl,diag in the identified cylinder Z1 from the speed development 101.
6. (S61) determining a start of combustion φ ₂ in the identified cylinder Z1 using an iteration method 210 as a function of the determined pressure signal p _{- zyl,diag} , or
7. (S62) Determining a start of combustion φ ₂ in the identified cylinder Z1 using an interpolation method 212 in the identified cylinder as a function of the determined pressure signal p _{- cyl,diag} .
8. (S70) Determining the characteristics of the combustion delay characteristic value BV as a function of the determined start of combustion φ ₂ in the identified cylinder Z1.
9. (S80) Diagnose combustion delay deviations.

Reference List

1

combustion engine

2

engine control

4

unit of account

6

Crankshaft speed acquisition unit

7

Cylinder pressure determination unit

(8th)

iteration rule

9

intake system

10

Torque curve of the combustion engine over one engine cycle

12

torque holes

14

predetermined limit for relevant torque contribution

16

Cylinder temperature determination unit

18

lambda probe

100

Speed development diagram

101

speed curve

112

diagnostic time window

200

engine control unit

202

Storage

204

Diagnostic component of an engine control

206

Control component of an engine control

208

Offboard diagnostic calculator

210

direct iteration method

212

interpolation method

(Sxx)

process steps

ATL

exhaust gas turbocharger

B.V

combustion delay

whoa

specific lower calorific value

KT

crank drive

week

crank angle

KT

crankshaft

LF

air filter

LS

air collector

M

Torque of a cylinder in 1

mF

current mass of fuel in a cylinder

n

rotation speed

p

cylinder pressure

pcyl, diag

Pressure index, here diagnostic cylinder pressure

P1, P2

Measurement times at the beginning and end of the diagnosis time window

p0

Atmospheric pressure under standard conditions (1013hPa)

R

ideal gas constant

rf

relative air filling of the cylinder in %

t

Time interval in the diagnosis time window

T

mean temperature of the gas mixture

T0

Ambient temperature under standard conditions (293K)

u

inner energy

V

cylinder volume

V max

maximum cylinder volume near bottom dead center of the crankshaft

Z

cylinder

ZZP

ignition timing of a cylinder

φ1

Crank angle position at ignition timing

φ2

Crank angle position at the start of combustion

QUOTES INCLUDED IN DESCRIPTION

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Patent Literature Cited

• WO 2019/238338 A1 [0018, 0020]

Claims (12)

Method for determining a combustion delay (BV) in a cylinder (Z1, Z2, Z3, Z4) of an internal combustion engine (1) in a motor vehicle, comprising the steps: - Determining a diagnostic time window (112) within a torque hole (12) of one of the Cycles of the internal combustion engine (1) while the motor vehicle is being driven, - identifying a cylinder (Z1) which is in a compression stroke or in a power stroke at the beginning of the diagnosis time window, - determining a speed development (101) of the internal combustion engine (1) during of the diagnosis time window, in particular with a real-time capable sampling quality, characterized by the step: - determining a combustion delay characteristic value (BV) in the identified cylinder as a function of the determined speed development. procedure according to claim 1 , characterized in that the combustion delay parameter (BV) as a function of a crank angle difference between an ignition crank angle position (φ ₁ ) at an ignition point (ZZP1, P1) of the identified cylinder and a combustion start crank angle position (φ ₂ ) at a defined start of combustion (P2 ) of the identified cylinder is determined. procedure according to claim 2 , characterized in that the start of combustion crank angle position is determined iteratively. procedure according to claim 2 , characterized in that the start of combustion crank angle position is determined by interpolation. Method according to one of the preceding claims, characterized by the steps: - determining a temperature (T) in the identified cylinder at a diagnosis point in time (P1) in the diagnosis time window, and - determining the combustion delay characteristic value (BV) as a function of the determined temperature. Method according to one of the preceding claims, characterized in that the combustion delay parameter (BV) is determined as a function of a cylinder volume (V) at a diagnosis point in time (P1) in the diagnosis time window. Method according to one of the preceding claims, characterized in that the combustion delay parameter (BV) is determined as a function of a fuel mass present in the diagnosed cylinder at the time of diagnosis (P1). Method according to one of the preceding claims, characterized in that the combustion delay parameter (BV) is determined as a function of an internal energy (U) of the gas mixture in the diagnosed cylinder at the time of diagnosis (P1). Engine control unit (2) for an internal combustion engine, set up to transfer combustion delay characteristic values (BV) determined and/or stored in the memory, in particular by means of a method according to one of the preceding claims - to a diagnostic component (204) of the engine control unit for further onboard diagnostic functions, and/or - To a control component (206) of the engine control unit for real-time regulation of functions of the internal combustion engine as a function of the determined combustion delay characteristic (BV). according to the engine control unit claim 9 Having a non-volatile memory (202), characterized in that the engine control unit is set up to store one or more characteristics of the combustion delay characteristic value (BV) determined at one or different diagnosis times in the non-volatile memory (202). according to the engine control unit claim 10 , set up to transfer forms of the combustion delay characteristic value stored in the memory to an offboard computer (208) for offline diagnostic functions. Internal combustion engine (1) with several cylinders (Z), characterized by an engine control unit (2) according to one of claims 9 until 11 .

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