DE102020206798A1 - Method for the automated measurement of a characteristic map of an internal combustion engine on a test bench and a control device for controlling a test bench - Google Patents

Abstract

The invention relates to a method for the automated measurement of a characteristic map of an internal combustion engine (3) on a test stand (1), whereby a) a map to be measured is spanned by a combustion focal point and a combustion air / fuel ratio, i.e. a lambda value (λ) Starting value pair (7) for the combustion center of gravity and the lambda value (λ) is determined in an estimated map center of the characteristic map at a predetermined pollutant concentration in the exhaust gas of the internal combustion engine (3), whereby the combustion focus is gradually adjusted based on the starting value pair (7) late and the lambda value (λ) can be changed to lower values under the condition that the predetermined pollutant concentration is maintained, corresponding values for the center of combustion and the lambda value (λ) being stored until c) a first limit (11) is reached, whereby ) proceeding from the start value pair (7) step by step the combustion sc The emphasis is on early and the lambda value (λ) is changed to higher values under the condition that the predetermined pollutant concentration is maintained, with corresponding values for the combustion focus and the lambda value (λ) being stored until a second limit (13) is reached , wherein the combustion focus at the second limit (13) is stored as the limit combustion focus (15), wherebyif) the lambda value (λ) is gradually increased until a third limit (17) in a first limit value pair (19) from the Combustion center of gravity and the lambda value (λ) is reached, whereby) starting from the first limit value pair (19) at the third limit (17) gradually the combustion center of gravity towards late and the lambda value (λ) to lower values along the third limit (17) can be changed, corresponding values for the center of combustion and the lambda value (λ) are stored until the first limit (11) is reached, with h) along of the first limit (11), the lambda value (λ) is gradually changed to lower values and, if there is a deviation from the first limit (11), the combustion focus is varied in order to remain at the first limit (11), with corresponding values of the combustion focus and the lambda value (λ) are stored until the second limit (13) is reached in a second limit value pair (21) from the combustion center of gravity and the lambda value (λ), i) starting from the second limit value pair (21) gradually following the combustion center of gravity early and the lambda value (λ) can be changed to higher values along the second limit (13), with corresponding values of the center of combustion and the lambda value (λ) being stored until the third limit (17) is reached, with the third limit ( 17) the combustion center of gravity and the lambda value (λ) are gradually changed to lower values, with corresponding values of the combustion center of gravity and de s lambda value (λ) are stored until the combustion center of gravity on the third limit (17) is equal to the limit combustion center of gravity (15).

Description

The invention relates to a method for the automated measurement of a characteristic diagram of an internal combustion engine on a test bench and a control device for controlling a test bench of an internal combustion engine.

Test stands for measuring engine characteristics are typically operated manually by what is known as a test stand driver. The test bench driver tries, on the one hand, on the basis of previous knowledge of the expected behavior of the internal combustion engine and, on the other hand, on the basis of his or her intuition acquired through experience or instruction, to probe the limits of the characteristic diagram. However, the quality of the data collected is therefore directly dependent on the cognitive abilities and the daily form of the test bench driver.

The invention is based on the object of creating a method for the automated measurement of a characteristic map of an internal combustion engine and a control device for controlling a test bench for an internal combustion engine, the disadvantages mentioned occurring at most to a reduced extent, preferably not at all.

The object is achieved in that the present technical teaching is provided, in particular the teaching of the independent claims and the embodiments disclosed in the dependent claims and the description.

The object is achieved in particular by creating a method for the automated measurement of a map of an internal combustion engine on a test bench, in which a) a start is made for the map to be measured by a combustion center of gravity and a combustion air-fuel ratio, hereinafter referred to as lambda value -Value pair, comprising a start value for the center of combustion and a start value for the lambda value, is determined in an estimated map center of the map in such a way that when the internal combustion engine is operated with the start value pair, a predetermined pollutant concentration is present in the exhaust gas of the internal combustion engine. The internal combustion engine is operated with the start value pair. Starting from the starting values - during operation of the internal combustion engine - the combustion center of gravity is gradually changed to a late stage and the lambda value is changed to lower values in such a way that the predetermined pollutant concentration is maintained. Values for the center of combustion and the lambda value for which this condition is met are saved.

This step-by-step change in the center of combustion and the lambda value according to b) is repeated until c) a first limit is reached in the characteristic diagram to be measured.

Then, d) proceeding from the start value pair, the combustion center of gravity is gradually changed towards the early stage and the lambda value is changed to higher values in such a way that the predetermined pollutant concentration is maintained. Again, those values for the center of combustion and the lambda value are stored for which this condition is met.

The step-by-step change in the combustion focus and the lambda value according to d) is repeated until e) a second limit is reached in the map to be measured, the combustion focus at the second limit being stored as the limit combustion focus.

The map is therefore initially scanned in a central range along the predetermined pollutant concentration starting from the starting value pair, initially in step b) in a first direction and then in step d) in a second, opposite direction until a predetermined limit is reached in each case is.

Starting from the value pair at which the second limit has been reached and which includes the limit combustion focus, f) the lambda value is now gradually increased until a third limit in a first limit value pair, comprising a value for the combustion focus and a value for the lambda value is reached. In particular, the combustion center of gravity is kept constant at the value of the limit combustion center of gravity.

The first limit value pair thus includes in particular the limit combustion center of gravity as a value for the combustion center of gravity.

Starting from the first limit value pair at the third limit, the combustion center of gravity is now gradually changed to late and the lambda value to lower values along the third limit, with corresponding values for the combustion center of gravity and the lambda value being stored. This means, in particular, that when the combustion focus and the lambda value are varied, care is taken to ensure that the map is scanned along the third limit, with only those values being stored for the combustion focus and the lambda value that are actually on the third limit. The change in the The combustion center of gravity and the lambda value according to g) is continued until the first limit is reached again - at the level of the third limit. In particular, a limit value pair is achieved in which the third limit and the first limit intersect.

Now h) the lambda value is gradually changed to lower values along the first limit. If the operating point of the internal combustion engine deviates from the first limit, the center of combustion is varied in order to remain at the first limit. The map is therefore scanned along the first limit. Corresponding values of the center of combustion and the lambda value, which lie on the first limit, are stored. The corresponding change in the lambda value and possibly the combustion center of gravity according to h) is repeated until the second limit is reached in a second limit value pair, comprising a value for the combustion center of gravity and a value for the lambda value. In the second limit value pair, the first limit and the second limit in particular now cross each other.

Now i) starting from the second limit value pair, the combustion center of gravity is gradually changed towards the early stage and the lambda value is changed to higher values along the second limit. The change is made in such a way that the map is scanned along the second limit. Those values of the center of combustion and the lambda value that lie on the second limit are stored. The corresponding change in the center of combustion and the lambda value according to i) is repeated until the third limit is reached.

The third limit is reached in particular in a limit value pair in which the second limit and the third limit intersect.

Then - in particular on the basis of this limit value pair - j) along the third limit, the combustion center of gravity is changed step by step towards late and the lambda value is changed to lower values. The characteristic map is therefore in turn scanned along the third limit, albeit beyond the limit combustion center of gravity. Those values of the center of combustion and of the lambda value which lie on the third limit are stored. The corresponding change in the combustion center of gravity and the lambda value according to j) is repeated until the combustion center of gravity is again - on the third limit - the same as the limit combustion center of gravity.

As a result, the map is scanned once, starting from the start value pair, along a map line defined by the predetermined pollutant concentration, in a central area, and once rounded along its boundaries. The map is limited by the first limit, the second limit and the third limit, the second limit having a first intersection with the first limit and a second intersection with the third limit, and the first limit and the third Cut the border at another intersection. The map thus has an enclosed inner area which is delimited on all sides by the first limit, the second limit and the third limit. In particular, the second border has a course that is more strongly curved or kinked in some areas, while the first border and the third border run essentially along straight lines or lines that are less curved over the entire course.

The method proposed here particularly advantageously enables automated measurement of the characteristic diagram on the basis of a standardized, rational procedure. In this case, the method can advantageously be carried out without intervention by the test stand driver on the control unit of the test stand. Thus, with a view to the measurement of the characteristic map, the result is no longer dependent on the subjective characteristics of the test bench driver. In particular, the result is reproducible.

The combustion center of gravity is understood to mean, in particular, a point in time or a crankshaft angle at which 50% of the fuel mass used or 50% of the chemical energy introduced into a combustion chamber of the internal combustion engine in the form of the fuel is converted. The fact that the combustion center of gravity is changed towards an early stage means in particular that it moves towards an earlier point in time relative to a top dead center position of a piston of the internal combustion engine, which is preferably designed as a reciprocating piston engine, which separates a compression stroke from an operating stroke and which is also referred to as ignition TDC or an earlier crankshaft angle is changed, in particular it is moved closer to the ignition TDC if the focus of combustion is after the ignition TDC. Correspondingly, a change in the center of combustion to late means that the center of combustion is shifted relative to ignition TDC in the direction of a later point in time or later crankshaft angle, in particular being further removed from ignition TDC if the combustion focus is after ignition TDC lies. The center of combustion is typically associated with an ignition point, in particular it can be specified by selecting the ignition point. An adjustment of the focus of the burn early or late can in particular by Change in the ignition timing can be effected. In this case, a change in the ignition point early or late corresponds in an analogous manner to a change in the center of combustion towards early or late, although the ignition point is typically before ignition TDC. Thus, a change in the ignition point early means an increase in the distance of the ignition point from the ignition TDC, a change in the ignition point late means an approach of the ignition point to the ignition TDC.

A change in the lambda value towards higher values means a leaning of a combustion air-fuel mixture in the combustion chamber of the internal combustion engine. A change in the lambda value towards lower values means that the combustion air-fuel mixture is enriched. Leaning means a change in the combustion air / fuel ratio in favor of the combustion air mass. Enrichment means a change in the combustion air / fuel ratio in favor of the fuel mass.

The fact that the lambda value is increased in step f) means that the lambda value is changed to higher values.

A step-by-step change in the lambda value and / or the combustion center of gravity means, in particular, a change by a respective predetermined change value, in particular a respective predetermined increment or decrement.

The internal combustion engine is preferably designed as a single-cylinder engine, in particular a single-cylinder test engine. But it can also have a plurality of combustion chambers.

According to a further development of the invention, it is provided that the internal combustion engine is operated after step a) and before step b) for the start value pair for a predetermined time interval under constant conditions. The internal combustion engine is additionally operated after step c) and before step d) for the start value pair for a predetermined time interval under constant conditions. The internal combustion engine is preferably additionally operated after step e) and before step f) at the limit combustion center of gravity at the second limit for a predetermined time interval under constant conditions. The operation of the internal combustion engine under constant conditions enables the operation of the internal combustion engine to be stabilized under the respective operating conditions, so that it is ensured that meaningful values for the characteristic map can be obtained with the exclusion of transient effects.

Constant operation of the internal combustion engine means in particular that all parameters, in particular at least all parameters that can be influenced, are kept constant during operation of the internal combustion engine.

According to a further development of the invention, it is provided that the first limit is selected from a predetermined exhaust gas temperature limit and a predetermined latest limit for the center of combustion. The first limit can therefore in particular be defined as a predetermined maximum temperature for the exhaust gas from the internal combustion engine, which should not or must not be exceeded. On the other hand, however, it can also be defined as a predetermined latest limit for the combustion center of gravity, that is to say a latest point in time or the latest crankshaft angle at which the combustion center of gravity should or may be. Compliance with these conditions ensures, in particular, damage-free operation of the internal combustion engine.

According to a further development of the invention, it is provided that the second limit is selected from a group consisting of a predetermined knock limit, a predetermined spark plug temperature limit, and a predetermined earliest limit for the center of combustion. Compliance with these conditions also ensures damage-free operation of the internal combustion engine.

The predetermined knock limit is preferably defined as a predetermined limit value for a knock index, which is preferably determined from a particularly high-resolution combustion chamber pressure signal. The combustion chamber pressure signal is preferably filtered beforehand. In particular, a mean value of all amplitudes of individual work cycles of the internal combustion engine can be used as a value for the knock index that is preferably available in real time.

The predetermined spark plug temperature limit is in particular a predetermined maximum temperature, measured on a spark plug of the internal combustion engine or in the vicinity of the spark plug.

The predetermined earliest limit for the center of combustion is - analogously to the predetermined latest limit for the center of combustion - a predetermined earliest point in time or earliest crankshaft angle that the center of combustion is allowed to assume.

According to a further development of the invention, it is provided that the third limit is a predetermined dropout limit. Compliance with the corresponding limit enables the internal combustion engine to run smoothly and without misfires. Combustion stability is preferably assessed to determine the predetermined misfire limit. For this purpose, in particular a coefficient of variation (COV) of the indicated mean pressure p _{mi is} determined, this value also being referred to for short as PMI_COV. This coefficient of variation is preferably determined as follows: An indicating system uses a combustion chamber pressure sensor, in particular a piezo pressure quartz, to record the combustion chamber pressure curve in the combustion chamber over time or the crankshaft angle. The indicated mean effective pressure p _mi corresponds to the indicated work related to the stroke volume V _h : $$p_{mi}=\frac{\oint p\left(V\right)dv}{V_H}.$$

Here p (V) is the combustion chamber pressure as a function of the current combustion chamber volume V.

wobei n die Anzahl der durchgeführten Messungen, i ein Laufindex über die einzelnen Messungen, p_mi,i der bei der durch den Laufindex i gekennzeichneten Messung erfasste Wert des indizierten Mitteldrucks p_mi, und $\overline{p_{mi}}$

der Mittelwert des indizierten Mitteldrucks p_mi ist.The coefficient of variation PMI_COV is now defined as the quotient of the standard deviation p _{mi, s} and the expected value - or, in the case of an existing series of measurements, the mean value of the indicated mean pressure p _mi . The standard deviation p _{mi, s} is defined as: $$p_{mi,s}=\sqrt{\frac{1}{1-n}{\displaystyle \sum {}_{i=1}^n\left(p_{mi,i}-\overline{p_{mi}}\right)}},$$

where n is the number of measurements carried out, i is a running index over the individual measurements, p _{mi, i is the value of the indicated mean pressure p mi} recorded in the measurement identified by the running index i, and $\overline{p_{mi}}$

is the mean value of the indicated mean pressure p _mi .

Accordingly, the coefficient of variation PMI_COV is now defined according to the following equation (3): $$\text{PMI\_COV =}\frac{p_{mi,s}}{\overline{p_{mi}}}.$$

The predetermined dropout limit is preferably defined by a predetermined limit value for the coefficient of variation PMI_COV defined in this way.

According to a development of the invention, it is provided that the predetermined pollutant concentration is a predetermined nitrogen oxide concentration, in particular a total nitrogen oxide concentration. The predetermined pollutant concentration is preferably 500 mg / m _n ³ (mg per standard cubic meter). In this way, it is particularly advantageous to define a characteristic diagram line along which the characteristic diagram can be scanned at least approximately in the middle of the characteristic diagram.

According to a development of the invention it is provided that the lambda value and the combustion center of gravity are varied under the additional condition that a combustion chamber pressure gradient does not exceed a predetermined combustion chamber pressure gradient limit value. This also ensures safe operation of the internal combustion engine. The combustion chamber pressure gradient is in particular a time derivative of the combustion chamber pressure curve or - equivalently - a derivative according to the crankshaft angle.

According to a further development of the invention, it is provided that the lambda value and the combustion center of gravity are varied under the additional condition that a combustion chamber peak pressure does not exceed a predetermined combustion chamber peak pressure limit value. This also advantageously ensures safe operation of the internal combustion engine, in particular without mechanical damage to the combustion chamber. The peak combustion chamber pressure is a pressure maximum of the combustion chamber pressure curve in the combustion chamber.

According to a further development of the invention, it is provided that the lambda value is varied by changing the combustion air mass supplied to the combustion chamber of the internal combustion engine. Alternatively or additionally, the lambda value is preferably varied by changing the fuel mass supplied to the combustion chamber. In particular, it is possible for both the supplied combustion air mass and the supplied fuel mass to be changed. Both variables can typically be easily adjusted on a test stand.

Alternatively or additionally, it is preferably provided that the center of combustion is varied by changing the ignition point. This is also easily possible on a test stand, in particular if the internal combustion engine is designed as a spark ignition internal combustion engine, in particular by means of electrical spark ignition, corona ignition, laser ignition, pilot jet ignition, or some other suitable spark ignition. The ignition point at least essentially determines the focus of combustion.

The object is finally also achieved by creating a control device for controlling a test bench for an internal combustion engine, the control device being set up to carry out a method according to the invention or a method according to one of the previously described ones Embodiments. In connection with the control device, the advantages already mentioned are realized in particular.

The pollutant concentration in the exhaust gas is measured in particular. In this way it can easily be determined whether the predetermined pollutant concentration has been maintained.

The conditions for the first limit, the second limit and the third limit are measured accordingly. In particular, at least one parameter is preferably measured, selected from a group consisting of the combustion air mass, the fuel mass, the combustion chamber pressure curve, the exhaust gas temperature, the spark plug temperature, and a pollutant concentration, in particular nitrogen oxide concentration, in particular total nitrogen oxide concentration. The center of combustion is determined in particular on the basis of the combustion chamber pressure curve.

• 1 eine schematische Darstellung eines Ausführungsbeispiels eines Prüfstands für eine Brennkraftmaschine mit einem Ausführungsbeispiel eines Steuergeräts, und
• 2 eine schematische Darstellung eines im Rahmen einer Ausführungsform des Verfahrens zu vermessenden Kennfelds.

The invention is explained in more detail below with reference to the drawing. Show:

• 1 a schematic representation of an embodiment of a test stand for an internal combustion engine with an embodiment of a control device, and
• 2 a schematic representation of a map to be measured in the context of an embodiment of the method.

1 shows a schematic representation of an exemplary embodiment of a test stand 1 on which an internal combustion engine 3 is arranged. The test bench 1 is set up to map the internal combustion engine 3 to measure. In particular, the test bench 1 a control unit 5 which is set up to include an embodiment of a method for the automated measurement of the engine characteristics map, which will be explained in more detail below 3 perform. The internal combustion engine 3 has at least one combustion chamber 4th on. It is preferably designed as a single-cylinder test engine.

2 shows a schematic representation of a map of the internal combustion engine 3 , which is spanned by a combustion center of gravity, which is represented here by an ignition point ZZP as a variable by which the combustion center of gravity is determined. The map is also spanned by a combustion air / fuel ratio, which is also referred to as the lambda value λ.

As part of the method, a starting value pair is used for the characteristic diagram 7th determined from a start value for the center of combustion or ignition time ZZP and a start value for the lambda value λ, this starting value pair 7th approximately in an estimated map center of the map based on a predetermined pollutant concentration in the exhaust gas of the internal combustion engine 3 defined characteristic curve 9 lies.

Based on the start value pair 7th Now - see b) - the combustion center of gravity, i.e. the ignition point ZZP, is gradually changed to retard and the lambda value λ to lower values, under the condition that the predetermined pollutant concentration is along the characteristic curve 9 is retained. Adjusting the focus of the burn late means that an in 2 The interval between the ignition time ZZP and an ignition TDC of the internal combustion engine, plotted on the abscissa, or measured in degrees crankshaft angle (° CA) 3 is decreased.

Corresponding values for the center of combustion and the lambda value λ along the characteristic curve defined by the predetermined pollutant concentration 9 are saved. The change in the center of combustion and the lambda value λ is repeated until a first limit is reached 11th is reached.

Then - see d) - proceeding from the start value pair 7th gradually the combustion center of gravity changes to early and the lambda value λ to higher values under the condition that the predetermined pollutant concentration along the characteristic curve 9 is retained. An early adjustment of the combustion center of gravity means here that the ignition time ZZP is at greater distances from the ignition TDC of the internal combustion engine 3 is changed. Corresponding values for the center of combustion and the lambda value λ on the characteristic curve defined by the predetermined pollutant concentration 9 are saved. The corresponding changes in the center of combustion and the lambda value λ are repeated until a second limit is reached 13th is reached, with the focus of combustion at the second limit 13th as borderline combustion focus 15th , here in particular determined by a first specific ignition time ZZP1, is stored.

The lambda value λ is now - see f) - increased gradually until a third limit 17th in a first limit value pair 19th is reached from the center of combustion and the lambda value λ. The first limit value pair has the limit combustion center of gravity 15th as a value for the center of combustion.

Based on the first limit value pair 19th is now - see g) - at the third border 17th the combustion center of gravity gradually decreases and the lambda value λ decreases along the third limit 17th changed, with corresponding values for the combustion threshold point and the lambda value λ stored until the first limit 11th is achieved.

Now - see h) - along the first boundary 11th the lambda value λ is gradually changed to lower values, and when there is a deviation from the first limit 11th the center of combustion is varied to at the first limit 11th to stay. Corresponding values of the center of combustion and the lambda value λ are saved. This is carried out until the second limit 13th in a second limit value pair 21 is reached from the center of combustion and the lambda value λ.

Now - see i) - proceeding from the second limit value pair 21 the combustion center of gravity gradually increases and the lambda value λ increases along the second limit 13th changed, corresponding values of the center of combustion and the lambda value λ are stored until the third limit 17th in an intersection 23 is reached in which the second limit 13th and the third limit 17th cut.

Now - see j) - starting from the point of intersection 23 gradually along the third border 17th the combustion center of gravity changes to late and the lambda value λ changes to lower values, with corresponding values of the combustion center of gravity and of the lambda value λ being stored until the combustion center of gravity is at the third limit 17th equal to the limit combustion center of gravity 15th is what is in turn in the first limit value pair 19th the case is.

The internal combustion engine 3 is preferred after determining the starting value pair 7th and before the step-by-step change in the combustion center of gravity and the lambda value λ to lower values for the start value pair 7th operated under constant conditions for a predetermined time interval. Constant conditions mean in particular that all parameters of the operation of the internal combustion engine 3 , at least all parameters that can be influenced, are kept constant. The internal combustion engine 3 will also after the first limit has been reached 11th - based on the start value pair 7th - and before the step-by-step change in the combustion center of gravity towards early and the lambda value λ to higher values - according to d) - again with the start value pair 7th operated under constant conditions for a predetermined time interval.

The internal combustion engine 3 is also preferred after first reaching the second limit 13th - based on the start value pair 7th - and before the step-by-step increase in accordance with f) of the lambda value λ while keeping the combustion center of gravity constant at the limit combustion center of gravity 15th -at the second border 13th operated under constant conditions for a predetermined time interval.

The first frontier 11th is preferably selected from a predetermined exhaust gas temperature limit and a predetermined latest limit for the focus of combustion.

The second limit 13th is preferably selected from a group consisting of a predetermined knock limit, a predetermined spark plug temperature limit, and a predetermined earliest limit for the center of combustion.

The third frontier 17th is preferably a predetermined dropout limit.

The predetermined pollutant concentration is preferably a predetermined nitrogen oxide concentration, total total nitrogen oxide concentration, preferably 500 mg / m _n ³ .

The lambda value λ and the center of combustion are preferably varied under the additional condition that a combustion chamber pressure gradient does not exceed a predetermined combustion chamber pressure gradient limit value.

The lambda value λ and the center of combustion are preferably varied under the additional condition - in particular in addition to the aforementioned additional condition - that a combustion chamber peak pressure does not exceed a predetermined combustion chamber peak pressure limit value.

The lambda value is preferably varied by adding one to the combustion chamber 4th the internal combustion engine 3 supplied combustion air mass and / or a combustion chamber 4th supplied fuel mass is / are changed.

Alternatively or additionally, the center of combustion is preferably varied by changing the ignition point ZZP.

Claims (10)

A method for the automated measurement of a map of an internal combustion engine (3) on a test stand (1), with a) a start value pair for the map to be measured by a combustion focus and a combustion air / fuel ratio, i.e. a lambda value (λ) (7) for the The center of combustion and the lambda value (λ) are determined in an estimated middle of the characteristic diagram at a predetermined pollutant concentration in the exhaust gas of the internal combustion engine (3), with b) starting from the start value pair (7), the combustion center of gravity towards the late stage and the lambda value (λ) step by step. can be changed to lower values under the condition that the predetermined pollutant concentration is maintained, corresponding values for the combustion focus and the lambda value (λ) are stored until c) a first limit (11) is reached, d) starting from the start -Value pair (7) the combustion center of gravity towards the early stage and the lambda value (λ) is changed to higher values under the condition that the predetermined pollutant concentration is maintained, with corresponding values for the combustion center of gravity and the lambda value (λ) being stored until e) a second limit (13) is reached, the burn severity point at the second limit (13) is stored as the limit combustion focus (15), where f) the lambda value (λ) is gradually increased until a third limit (17) in a first limit value pair (19) from the combustion focus and the lambda value (λ) is reached, whereby g) starting from the first limit value pair (19) at the third limit (17) gradually changes the center of combustion to a late stage and the lambda value (λ) changes to lower values along the third limit (17) corresponding values for the center of combustion and the lambda value (λ) are stored until the first limit (11) is reached, where h) the lambda value (λ) gradually changes to lower values along the first limit (11) and if there is a deviation the combustion center of gravity is varied from the first limit (11) in order to remain at the first limit (11), corresponding values of the combustion center of gravity and the lambda value (λ) being stored until the second size nze (13) is achieved in a second limit value pair (21) from the combustion center of gravity and the lambda value (λ), i) starting from the second limit value pair (21), the combustion focus early and the lambda value (λ) gradually increasing higher values are changed along the second limit (13), with corresponding values of the combustion center of gravity and the lambda value (λ) being stored until the third limit (17) is reached, with j) gradually following the combustion center of gravity along the third limit (17) late and the lambda value (λ) can be changed to lower values, with corresponding values of the combustion focus and the lambda value (λ) being stored until the combustion focus on the third limit (17) is equal to the limit combustion focus (15). Procedure according to Claim 1 , characterized in that the internal combustion engine (3) - after step a) and before step b), as well as after step c) and before step d), in each case at the start value pair (7), and preferably - after step e) and before step f) at the limit combustion center of gravity (15) at the second limit (13) is operated for a predetermined time interval under constant conditions. Method according to one of the preceding claims, characterized in that the first limit (11) is selected from a predetermined exhaust gas temperature limit and a predetermined latest limit for the center of combustion. Method according to one of the preceding claims, characterized in that the second limit (13) is selected from a group consisting of a predetermined knock limit, a predetermined spark plug temperature limit, and a predetermined earliest limit for the center of combustion. Method according to one of the preceding claims, characterized in that the third limit (17) is a predetermined dropout limit. Method according to one of the preceding claims, characterized in that the predetermined pollutant concentration is a predetermined nitrogen oxide concentration, in particular total nitrogen oxide concentration, preferably 500 mg per standard cubic meter. Method according to one of the preceding claims, characterized in that the lambda value (λ) and the combustion center of gravity are varied under the additional condition that a combustion chamber pressure gradient does not exceed a predetermined combustion chamber pressure gradient limit value. Method according to one of the preceding claims, characterized in that the lambda value (λ) and the combustion center of gravity are varied under the additional condition that a combustion chamber peak pressure does not exceed a predetermined combustion chamber peak pressure limit value. Method according to one of the preceding claims, characterized in that - the lambda value (λ) is varied by changing a combustion air mass fed to a combustion chamber (4) of the internal combustion engine (3) and / or a fuel mass fed to the combustion chamber (4) is / are changed, and / or that - the center of combustion is varied by changing an ignition point (ZZP). Control device (5) for controlling a test stand (1) for an internal combustion engine (3), the control device (5) being set up to carry out a method according to one of the Claims 1 until 9 .

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