DE102018200810B4 - Method for determining cylinder-specific lambda values and electronic control unit - Google Patents

Abstract

Method for determining the cylinder-specific lambda values of the individual cylinders of an internal combustion engine having several cylinders, with the following steps: - keeping the total lambda value of all cylinders in the lean or rich range; - abruptly stronger leaning or enriching of the air-fuel mixture supplied to an individual cylinder than that to the other cylinders supplied mixture;- Enrichment or leaning of the air-fuel mixture supplied to the other cylinders to compensate for the additional leaning or enrichment carried out while maintaining the total lambda value of all cylinders in the lean or rich range;- After leaning or enriching the air-fuel mixture supplied to the individual cylinder mixture measuring the reaction in the rough running of this cylinder;- checking all other cylinders accordingly in sequence and determining the respective rough running values; and- after the adjustment of all cylinders, deriving the cylinder-specific original lambda value from the rough-running values.

Description

The present invention relates to a method for determining the cylinder-specific lambda values of the individual cylinders of an internal combustion engine having a plurality of cylinders.

Due to the current emissions legislation, it has been necessary for some time to monitor the cylinder-specific air-fuel ratio of an internal combustion engine. For cost reasons, monitoring the air-fuel ratio of the individual cylinders using individual lambda sensors is either not possible or too expensive. Other methods have therefore been developed.

From the DE 10 2006 026 390 A1 and the DE 10 2006 044 073 A1 it is known to carry out the determination of the individual lambda values by targeted leaning of the combustion mixture as part of an adaptation process. In this method, the cylinder-specific lambda value is determined by targeted leaning of individual cylinders and by observing the extent of the intervention (CYBL-HOM method).

the DE 10 2009 027 822 A1 describes a method for determining an imbalance of at least one cylinder of an internal combustion engine, the at least one cylinder being operated in succession in at least one lean phase and at least one rich phase in order to produce exhaust gas neutrality on average, with a rough-running signal being evaluated in a lean phase in order to determine a cylinder-specific characteristic regarding the trimming.

In the DE 10 2010 035 365 A1 describes a method for determining the oxygen storage capacity of a catalytic converter and a method for determining an oxygen sensor inherent time lag. This procedure involves varying the air-fuel ratio to perform a pre-cat oxygen sensor test, a post-cat oxygen sensor test, and a catalytic converter's oxygen storage capability.

the DE 10 2007 043 734 A1 discloses a method in which at least two cylinders are operated with a lambda value and the associated rough-running value is determined here. The cylinders are then operated with a different lambda value and the associated rough-running value is determined again. The difference in the rough-running values is used to determine the lambda value of the individual cylinders.

The so-called CTG method (close-the-gap) is described in the specialist article “Catalyst properties for diagnosability” (Motortechnische Zeitung/Issue 1/2016).

WO 2016/041 742 A1 discloses a method for detecting defective injectors for feeding fuel into the combustion chambers of an internal combustion engine, in particular in a motor vehicle, and a corresponding engine test device for detecting defective injectors.

The present invention is based on the object of providing a method for determining the cylinder-specific lambda values of the individual cylinders of an internal combustion engine having a plurality of cylinders, which method can be carried out in a particularly efficient manner.

• - Halten des Gesamtlambdawertes aller Zylinder im mageren oder fetten Bereich;
• - sprunghaftes stärkeres Abmagern oder Anfetten des einem Einzelzylinder zugeführten Luft-Kraftstoff-Gemisches als das den anderen Zylindern zugeführten Gemisches;
• - Anfetten oder Abmagern des den anderen Zylindern zugeführten Luft-Kraftstoff-Gemisches zur Kompensation der durchgeführten zusätzlichen Abmagerung oder Anfettung unter Aufrechterhaltung des Gesamtlambdawertes aller Zylinder im mageren oder fetten Bereich;
• - nach Abmagern oder Anfetten des dem Einzelzylinder zugeführten Luft-Kraftstoff-Gemisches Messen der Reaktion in der Laufunruhe dieses Zylinders;
• - Prüfen aller anderen Zylinder entsprechend der Reihe nach und Ermitteln der jeweiligen Laufunruhewerte; und
• - nach der Verstellung aller Zylinder Ableiten des zylinderindividuellen ursprünglichen Lambdawertes aus den Laufunruhewerten.

According to the invention, this object is achieved by a method of the type specified, which comprises the following steps:

• - Keeping the total lambda value of all cylinders in the lean or rich area;
• - Suddenly more leaning or richening of the air-fuel mixture supplied to an individual cylinder than the mixture supplied to the other cylinders;
• - Enriching or leaning the air-fuel mixture supplied to the other cylinders to compensate for the additional leaning or enriching carried out while maintaining the total lambda value of all cylinders in the lean or rich range;
• - After leaning or enriching the air-fuel mixture supplied to the individual cylinder, measuring the reaction in the uneven running of this cylinder;
• - Checking all other cylinders one after the other and determining the respective rough-running values; and
• - after the adjustment of all cylinders, deriving the cylinder-specific original lambda value from the rough-running values.

The need for correction of the cylinder-specific lambda value can be determined from the difference between the determined rough-running values and the current operating point.

The current operating point is usually determined by the load (torque or air mass) and the engine speed, with the above relationship usually being read from a characteristic map.

In the method according to the invention, the total lambda value of all cylinders is preferably kept in the lean range and the individual cylinders are subjected to a more lean air-fuel mixture. The mixture fed to the other cylinders is enriched to compensate.

One advantage of the method according to the invention is that it can be combined with a diagnosis for the pre-cat probe, post-cat probe and/or oxygen storage capacity. With such a diagnosis (CTG method or "close-the-gap method"), the corresponding lambda target value is trimmed several times to "lean" or "rich" in order to evaluate the dynamics of the pre-cat probe. In addition, switching from lean to rich and vice versa is carried out on the basis of the post-cat sensor signal. Here, the breakthrough of the catalytic converter is evaluated using the binary lambda probe signal.

With such a diagnosis (CTG method), the lean or rich phase can last for several seconds. According to the invention, such a phase is preferably used for an evaluation of the cylinder-specific lambda values of the individual cylinders. The method according to the invention is preferably used in the lean phase of such a diagnosis. For this purpose, one cylinder is suddenly leaner more than other cylinders. Enriching the mixture in the other cylinders compensates for this additional sudden leaning. However, the total lambda is still in the lean range, as is required for the diagnosis (CTG diagnosis) that was carried out.

According to the invention, the air-fuel mixture fed to an individual cylinder is made leaner or richer by leaps and bounds than the mixture fed to the other cylinders.

The overall leaning or enriching required for this (lambda setpoint + additional leaning or enriching) of an individual cylinder is stored, preferably in an intermediate buffer, and the adjustment of all cylinders is determined, it being possible, as mentioned, to draw conclusions about the respective original lambda value from the corresponding adjustment range.

In the method according to the invention, all other cylinders are checked one after the other, and the rough-running value is preferably stored in each case. After all cylinders have been adjusted, the rough-running values allow conclusions to be drawn about the original lambda value.

According to the invention, a CYBL_HOM method is therefore preferably combined with a CTG diagnosis, so that it is no longer necessary to separate the two methods.

The present invention also relates to an electronic control unit for controlling an internal combustion engine with a rough-running determination unit and an injection quantity correction unit, a lambda probe being assigned to a group of cylinders of the internal combustion engine. According to the invention, the control unit is characterized in that it is designed to carry out the method described above.

In particular, the electronic control unit is designed in such a way that it uses a lean or rich phase of a diagnosis for a pre-cat probe, post-cat probe and/or oxygen storage capacity to determine the cylinder-specific lambda values of the individual cylinders, in particular to carry out a correspondingly modified CTG diagnosis with determination of the cylinder-specific lambda values of the individual cylinders.

The electronic control unit is designed in such a way that it makes the mixture supplied to an individual cylinder significantly leaner or richer than in other cylinders and, after the test cylinder has become leaner, measures the reaction in the uneven running for this cylinder. Furthermore, it is preferably set up to store the respectively determined rough-running values.

• 1 ein Diagramm, das den typischen Verlauf des Lambdasollwertes einer CTG-Diagnose zeigt;
• 2 ein Diagramm, das die Durchführung des erfindungsgemäßen Verfahrens wiedergibt, wobei oben die Abmagerung und unten der Laufunruhewert eines Einzelzylinders dargestellt ist; und
• 3 ein Diagramm, das den Lambda-Unterschied in Abhängigkeit vom Laufunruhe-Zielwertunterschied für verschiedene Arbeitspunkte zeigt.

The invention is explained in detail below using an exemplary embodiment in conjunction with the drawing. Show it:

• 1 a diagram that shows the typical course of the lambda target value of a CTG diagnosis;
• 2 a diagram that reproduces the implementation of the method according to the invention, the leaning being shown at the top and the rough-running value of an individual cylinder at the bottom; and
• 3 a diagram that shows the lambda difference as a function of the rough-running target value difference for various operating points.

The diagram of 1 represents the upstream lambda value on the ordinate as a function of time on the abscissa. The solid line shows the typical course of the diagnosis for a pre-cat probe, post-cat probe and oxygen storage capacity, with the lambda target value shown changing several times from lambda = 1 (middle dashed line) to "lean" (upper dashed line) and "rich" (lower dashed line) has been trimmed.

This course of the lambda value serves as the basis for carrying out the method according to the invention, which is shown in the diagram in FIG 2 is shown, the case of leaning being shown at the top and the corresponding rough-running value at the bottom. The illustration above shows how, in the lean phase, a test cylinder 1 is suddenly leaner more than other cylinders. A second test cylinder 2 is also shown. It also shows how the other cylinders 3 compensate for this additional leaning by enrichment. However, the total lambda is still in the lean range, as is required for the CTG diagnosis.

The corresponding overall leaning (lambda target point + additional leaning) marked with 4 corresponds to the length of the straight line from the dashed line corresponding to lambda=1 to the highest point.

The bottom diagram from 2 shows the corresponding rough-running value of the test cylinder 1 and the test cylinder 2. The corresponding rough-running difference 5 corresponds to the distance indicated by arrows.

When all the individual cylinders have been leaned out in order to achieve the corresponding rough-running difference, the respective cylinder-specific original lambda values are derived from the corresponding adjustment ranges.

By combining the test procedure for the cylinder-specific lambda values of the individual cylinders with the CTG diagnosis, a faster run through of the "imbalance monitoring" can be achieved. A chronological separation of both procedures is no longer necessary.

3 shows the lambda difference as a function of the uneven-running target value difference for various operating points in a diagram.

Claims (6)

Method for determining the cylinder-specific lambda values of the individual cylinders of an internal combustion engine having several cylinders, with the following steps: - Keeping the total lambda value of all cylinders in the lean or rich area; - Suddenly more leaning or richening of the air-fuel mixture supplied to an individual cylinder than the mixture supplied to the other cylinders; - Enriching or leaning the air-fuel mixture supplied to the other cylinders to compensate for the additional leaning or enriching carried out while maintaining the total lambda value of all cylinders in the lean or rich range; - After leaning or enriching the air-fuel mixture supplied to the individual cylinder, measuring the reaction in the uneven running of this cylinder; - Checking all other cylinders one after the other and determining the respective rough-running values; and - after the adjustment of all cylinders, deriving the cylinder-specific original lambda value from the rough-running values. procedure after claim 1 , characterized in that the need for correction of the cylinder-specific lambda value is determined from the difference between the determined rough-running values and the current operating point. procedure after claim 1 or 2 , characterized in that the total lambda value of all cylinders is kept lean and the individual cylinder is subjected to a more lean air-fuel mixture. Method according to one of the preceding claims, characterized in that the lean or rich phase of a diagnosis for the pre-cat probe, post-cat probe and/or oxygen storage capacity is used to determine the cylinder-specific lambda values of the individual cylinders. Method according to one of the preceding claims, characterized in that the required overall leaning or overall enrichment of an individual cylinder is stored in an intermediate buffer. Electronic control unit for controlling an internal combustion engine with a rough-running determination unit and an injection quantity correction unit, a lambda probe being assigned to a group of cylinders of the internal combustion engine, characterized in that the control unit for carrying out the method according to one of Claims 1 until 5 is trained.

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