DE102008005881B4 - Method and device for operating an internal combustion engine - Google Patents

Abstract

Method for operating an internal combustion engine having a plurality of cylinders (Z1 to Z4) and the injection valves (18) assigned to the cylinders (Z1 to Z4), which meter fuel, and an exhaust tract (4) in which an exhaust gas catalyst (21) and an exhaust gas probe (43 ) disposed in or downstream of the catalytic converter (21), in which
A characteristic variable (EMI) for pollutant emission in the region of the exhaust gas probe (43) is determined as a function of its measuring signals (MS2),
- a quality value (GW) for pollutant emission is determined as a function of a chronological course of the characteristic (EMI), and
- If the quality value (GW) exceeds a predetermined threshold (THD), first a diagnosis (CAT_DIAG) of the catalytic converter (21) is performed and if within the diagnosis (CAT_DIAG) of the catalytic converter (21) is recognized as properly functioning, a setpoint (LAM_SP) for an air / fuel ratio cylinder-individually relative to the respective cylinders (Z1 to Z4) is changed stepwise until, by means of an error indicator (ERR_IND) at least one for exceeding the ...

Description

The The invention relates to a method and an apparatus for operating An internal combustion engine according to claims 1 to 10th

Increasingly stricter legal regulations regarding permissible pollutant emissions in motor vehicles, in which internal combustion engines are arranged, make it necessary to pollutant emissions in one operation Keep the internal combustion engine as low as possible. This can be for one in that the pollutant emissions are reduced be that while the combustion of the air / fuel mixture in the respective cylinder the internal combustion engine arise. On the other hand are in internal combustion engines Exhaust aftertreatment systems in use, the pollutant emissions, the while the combustion process of the air / fuel mixture in the respective cylinder be generated in harmless Convert substances. In particular, in gasoline engines come to this than Catalytic converters, for example, three-way catalysts in use. A high one Conversion efficiency of pollutant emissions, such as carbon monoxide, Hydrocarbons and nitrogen oxides, sets a precisely adjusted air / fuel ratio in ahead of the cylinders. Furthermore, the mixture must also be upstream of the catalytic converter have a predetermined variation, such as an alternating one Operation of the internal combustion engine in excess of air and lack of air, to a filling and to effect emptying of the oxygen storage of the catalytic converter. at The storage of oxygen in particular the nitrogen oxides reduced while in the emptying the oxidation is supported and further prevented is that embedded oxygen molecules portions of the catalytic converter deactivate.

From the textbook "Manual combustion engines", published by Richard van Basshuyssen / Fred Schäfer, 2nd edition, June 2002, Friedrich Vieweg & Sohn Verlagsgesellschaft mbH, Braunschweig / Wiesbaden, pages 559-561, a lambda control for a linear probe with an additional trim control is known , As part of the lambda control, a control deviation is determined depending on a measurement signal of the linear lambda probe and a target value of the air / fuel ratio, which is supplied to a PII ² D controller whose controller output contributes to an injection quantity correction. By means of a downstream of the catalytic converter arranged further lambda sensor is determined by means of a PI trim controller, a characteristic shift and corrected taking into account this characteristic shift, the measurement signal of the linear lambda probe.

For different Pollutant emissions, such as hydrocarbons, carbon monoxide, nitrogen oxides and particles exist legal regulations, which the permissible emission of pollutants during the Restrict operation of the internal combustion engine. With increasing sharpness at legal Requirements regarding Pollutant emissions of limited pollutants it is necessary a low tolerance in the air-fuel ratio between the individual Allow cylinders of the internal combustion engine. In case of a big imbalance and lack of compensation, this can lead to a very strong deterioration pollutant emissions or even noticeable drivability problems to lead.

Out For this reason, legal regulations exist, for example in the United States of America, a cylinder-selective imbalance in the air / fuel ratio, the to an overrun predetermined pollutant emission limits leads to detect future in all vehicles.

From the DE 10 2006 002 257 A1 It is known, depending on a measurement signal of a lambda probe downstream of an exhaust gas catalyst, to determine a characteristic value that is representative of a nitrogen oxide emission or a hydrocarbon concentration. Depending on this or these values, an evaluation factor for the hydrocarbon concentration and also for a nitrogen oxide concentration is determined and used to correct an oxygen storage capacity based catalyst diagnosis.

From the DE 10 2004 036 034 B3 a method for controlling internal combustion engines having a plurality of cylinders is known in which a lambda signal of a lambda probe in the exhaust gas of the internal combustion engine is determined. The lambda probe is arranged in an exhaust manifold. In order to enable an assignment of the signals of the lambda probe to the individual cylinders, at least two combustion periods of a single cylinder are evaluated. In this case, the filling with air or fuel in the direction of increasing the lambda value and once in the direction of lowering the lambda value is influenced once with respect to a cylinder. This is intended to ensure that the measured lambda signals are assigned to the corresponding cylinders and are used to control the lambda value of the individual cylinder.

The post-published DE 10 2007 002 740 A1 discloses an internal combustion engine with an exhaust system in which an exhaust gas purification system designed as a three-way catalytic converter is arranged, and a lambda probe is arranged upstream of the exhaust gas purification system. The signal of the Lamb The probe is detected time-dependent and evaluated without consideration of the phase to the working cycle of the internal combustion engine. The evaluation may be a detection of the minimum values and the maximum values over a predetermined number of operating cycles of the internal combustion engine, from which a subtraction of the mean value of the minimum values from the mean value of the maximum values takes place. An equality factor of filling equality obtained in this way can be used in the individual cylinders in order to evaluate to what extent the equality of the filling has been improved after a specific change of the fuel-air mixture in a cylinder.

From the DE 10 2006 037 752 B3 a cylinder-individual lambda controller is known, to which the measured signal of the lambda probe arranged upstream of the catalytic converter is supplied as a controlled variable.

The The object underlying the invention is a method and to provide an apparatus for operating an internal combustion engine, the one or the low-emission operation of the internal combustion engine contributes.

The Task is solved by the characteristics of the independent Claims. Advantageous embodiments of the invention are characterized in the subclaims.

The Invention is characterized by a method and a corresponding Apparatus for operating an internal combustion engine with several Cylinders and the cylinders associated injectors, the Metering fuel, and with an exhaust tract in which an exhaust gas catalyst and an exhaust gas probe located in or downstream of the Catalytic converter are arranged. A parameter for pollutant emissions in the area the exhaust gas probe becomes dependent determined by the measured signal of the exhaust gas probe. A quality value for pollutant emission becomes dependent determined by a time course of the parameter for pollutant emission. If the quality value exceeds a predetermined threshold, is first a Diagnosis of catalytic converters carried out and if under the Diagnosis of the catalytic converter detected as properly functioning is a setpoint for an air / fuel ratio cylinder individually based on the respective cylinders, in particular rotating, step by step changed until by means of an error indicator at least one for the exceeding the threshold value by the quality value responsible cylinder is identified. That way is it is possible even with a relatively small cylinder-selective inequality in the air / fuel ratio to recognize these in the individual cylinders of the internal combustion engine and especially the one for each to identify responsible cylinders.

It has been surprising shown that way for Pollutant emission responsible cylinders are identified can, even if this with a pure review, for example by means of a rough running function or a misfire monitoring, regularly not more reliable possible is. The exhaust gas probe may be, for example, a lambda probe. The Pollutant emission can be particularly advantageous nitrogen oxides and / or Hydrocarbons and / or carbon monoxide.

Especially the cylinder-specific incremental change takes place to the respective cylinders associated with a respective exhaust bank. By the cylinder-specific increase of the air / fuel ratio can in each case by means of the error indicator of the respective cylinder be rated. In the context of gradual change, in particular Increase or decreasing the air-fuel ratio setpoint one cylinder, in particular per working cycle of the internal combustion engine, can even at low disturbances the one or the other for that responsible cylinders are identified particularly reliably.

On this way can be particularly effectively excluded that the crossing of the quality value indeed on a not working properly Catalytic converter is due.

According to one Further advantageous embodiment, if the exhaust gas catalyst recognized as properly functioning will, at first Trim controller intervention performed and only if the quality value continues to exceed the threshold level after the trim controller intervention, the setpoint for an air / fuel ratio cylinder-individually increased gradually relative to the respective cylinder until by means of the error indicator at least one for exceeding the threshold by the quality value responsible cylinder is identified. That way is it effectively possible, minor corresponding Compensating errors attributable to cylinders and thus corresponding pollutant emission so far lower that further identifying the for each Error responsible cylinder is not essential.

According to a further advantageous embodiment of the error indicator is represented by a rough running value, which can thus be easily determined in the context of a Laufunruheermittlung and that in particular without additional effort, since such a function regularly to operate the internal combustion engine is provided.

According to one Another advantageous embodiment of the error indicator is through represents a pollutant emission value. Also in this way can preferably existing functions for determining the pollutant emission be used in this context.

According to one Another advantageous embodiment, the parameter for pollutant emissions depends on a slope and / or an absolute value of the measuring signal of the Exhaust probe in the course of a breakdown operation of the catalytic converter downstream of Exhaust gas detected. In this way, the parameter for pollutant emissions can be particularly simple, such as using a given and be determined in advance determined map, this preferably means Kennfeldinterpolation.

According to one In another advantageous embodiment, the quality value depends on an integral of Characteristic for pollutant emission determined. In this way, a particularly simple and reliable determination of the quality value possible.

According to one In another advantageous embodiment, the integral is in each case via a determined time duration determined. In this way, specifications regarding the permissible Pollutant emissions particularly reliable and easy maintainable. The time duration may be the same, for example.

embodiments The invention are explained in more detail below with reference to the schematic drawings. It demonstrate:

1 an internal combustion engine with a control device,

2 and 3 a flowchart of a program for operating the internal combustion engine.

elements same construction or function are cross-figurative with the same Reference number marked.

An internal combustion engine ( 1 ) comprises an intake tract 1 , an engine block 2 , a cylinder head 3 and an exhaust tract 4 , The intake tract preferably comprises a throttle flap 5 and a collector 6 and a suction tube 7 leading to a cylinder Z1 via an inlet passage in the engine block 2 is guided. The engine block 2 further comprises a crankshaft 8th , which has a connecting rod 10 with the piston 11 of the cylinder Z1 is coupled.

The cylinder head includes a valvetrain 14 . 15 with a gas inlet valve 12 and a gas outlet valve 13 ,

The cylinder head 3 further comprises an injection valve 18 and a spark plug 19 , Alternatively, the injection valve 18 also in a suction tube 7 be arranged.

In the exhaust tract 4 is an exhaust gas catalyst 21 arranged, which is formed for example as a three-way catalyst. Furthermore, in the exhaust tract 4 also additionally or alternatively, for example, designed as a NOX catalyst exhaust gas catalyst 23 be arranged.

A control device 25 is provided, the sensors are assigned, which detect different parameters and each determine the value of the measured variable. Operating variables include variables determined in addition to the measured variables as a function of the measured quantities. The control device 25 is designed to determine, depending on at least one of the operating variables manipulated variables, which are then converted into one or more actuating signals for controlling the actuators by means of corresponding actuators. The control device may also be referred to as a device for operating the internal combustion engine.

The sensors are as a pedal position transmitter 26 formed, which an accelerator pedal position as an accelerator pedal 27 detected, an air mass sensor 28 , which is an air mass flow upstream of the throttle 5 detected, a first temperature sensor 32 , which detects an intake air temperature, an intake manifold pressure sensor 34 , which is an intake manifold pressure in the collector 6 detected, a crankshaft angle sensor 36 which detects a crankshaft angle, which is then assigned a speed and another temperature sensor 38 which detects a coolant temperature.

Furthermore, a first exhaust gas probe 42 provided upstream of the catalytic converter 21 is arranged and which detects a residual oxygen content of the exhaust gas and whose measurement signal MS1 is characteristic of the air / fuel ratio in the combustion chamber of the cylinder Z1 and upstream of the first exhaust gas probe 42 before the oxidation of the fuel, hereinafter referred to as the air / fuel ratio in the cylinders Z1 to Z4. Furthermore, a second exhaust gas probe 43 provided in either the catalytic converter 21 or downstream of the catalytic converter 21 is arranged and which detects a residual oxygen content of the exhaust gas and whose measurement signal MS2 is characteristic of the air / fuel ratio in the combustion chamber of the cylinder Z1 and upstream of the second exhaust gas probe 43 before the oxidation of the fuel, in Hereinafter referred to as the air / fuel ratio downstream of the catalytic converter 21 ,

The first exhaust gas probe 42 is preferably a linear lambda probe. The second exhaust gas probe 43 is preferably a binary lambda probe. However, it can also be a linear lambda probe.

ever according to embodiment There may be any subset of said sensors or it can also additional Sensors be present.

The actuators are, for example, the throttle 5 , the gas inlet and outlet valves 12 . 13 , the injection valve 18 or the spark plug 19 , In addition to the cylinder Z1 also further cylinders Z2 to Z4 are provided, which are then associated with corresponding actuators and sensors. For example, four, six, eight, twelve or any other number of cylinders Z1 to Z4 may be provided.

A program is a program memory of the control device 25 stored and can be processed during operation of the internal combustion engine. The program is described below with reference to the flowchart of 2 and 3 explained in more detail.

The Program is started in a step S1, where appropriate Variables are initialized.

In a step S2, a parameter EMI for pollutant emissions in the region of the second exhaust gas probe 43 determined depending on their measurement signal. The parameter is preferably representative of nitrogen oxide and / or hydrocarbons and / or carbon monoxide and in particular for their concentration. The characteristic variable for pollutant emission may preferably depend on a gradient and / or an absolute value of the measurement signal MS2 of the second exhaust gas probe 43 in the course of a breakdown of the catalyst downstream of the second exhaust gas probe 43 be determined. In this case, a breakthrough occurs when the area of the catalytic converter 21 upstream of the second exhaust gas probe 43 is either completely saturated with oxygen or the oxygen almost completely by corresponding reduction reactions from the exhaust gas catalyst 21 is cleared out. In this case, in particular the pollutant emissions emitted by the individual cylinders of the internal combustion engine reach the region of the second exhaust gas probe 43 , The determination of the characteristic variable EMI for pollutant emission may depend, for example, on a given characteristic map, preferably by means of map interpolation, depending on the slope and / or the absolute value of the measuring signal MS2 of the second exhaust gas probe 43 in the course of the breakthrough of the catalytic converter 21 upstream of the second exhaust gas probe 43 be determined.

An exemplary possibility of determining the characteristic EMI is in the DE 10 2006 002 257 A1 discloses, in which the characteristic is for example referred to as NOX factor or HC factor and the content of which is hereby incorporated in this regard.

Depending on the parameter EMI for pollutant emission becomes a quality value GW for Pollutant emission dependent determined by a time course of the characteristic EMI. "I" denotes in this context prefers a relative to the current one Time determined value, so for example the parameter EMI or of the quality value GW. The quality value GW is preferably determined by means of integration INT of the parameter EMI. In this connection can also prefers, for example, other operating variables such as a Considered air mass flow become. Such further operating variables, such as the Air mass flow can however basically already taken into account when determining the parameter EMI for pollutant emission become. Preferably, the determination of the quality value by appropriate Integration INT over a predetermined period of time, for example, in the case of performing a represents numerical integration may be predefinable by a corresponding to the period Number of assigned values of the parameter EMI, for example by the difference of the two counters i and l can be given. K represents a respective one Index related to the integration INT.

Determining the parameter EMI and preferably also the quality value GW for pollutant emission preferably takes place cyclically, wherein, for example, a periodicity of determining the parameter EMI and also the quality value GW independently of the execution of further steps of the program according to 2 and 3 can be.

In a step S4 is checked whether the quality value GW is larger as a predetermined threshold. The threshold THD may be, for example with regard to statutory or other regulations be firmly established with regard to pollutant emissions.

If the condition of step S4 is not fulfilled, the processing, if appropriate after a predefinable delay time period, is continued again in step S2. If, on the other hand, the condition of step S4 is fulfilled, then in a step S6 a catalyst ordinance CAT_DIAG is carried out. This is done, for example, depending on egg ner review of an oxygen storage capacity OSC of the catalytic converter 21 , The determination of the oxygen storage capacity value OSC can, for example, take place in such a way that the exhaust gas catalyst 21 is charged with oxygen until it is saturated, a predetermined first rich air / fuel ratio is set in the combustion chamber of the cylinder and the oxygen storage capacity value is determined depending on the measurement signals MS1, MS2 of the first and second exhaust gas probe. The oxygen capacity value can also be determined alternatively or additionally by substantially completely discharging the oxygen stored in the exhaust gas catalytic converter, setting a predetermined first lean air / fuel ratio into the combustion chamber of the respective cylinders and determining the oxygen storage capacity value depending on the measurement signals MS1 , MS2 of the first and second exhaust probes 42 . 43 , In addition, further procedures familiar to the skilled person are generally possible for determining the oxygen storage capacity value. If performing catalytic converter diagnosis CAT_DIAG in step S6 indicates that the exhaust gas catalyst 21 is not functioning properly, the program is stopped in a step S8, for example, a corresponding error entry with regard to the catalytic converter 21 can be done.

is On the other hand, if the condition of step S6 is satisfied, then in one step S10 preferably performs a trim controller intervention TRIM. Of the Trim control intervention TRIM can for example be carried out in such a way that, in comparison to before surgery either a fatter or a leaner air / fuel mixture. So, for example in the case of a slightly rich air / fuel mixture in one first number of cylinders Z1-Z4 and one stronger lean air / fuel mixture in a second number of cylinders Z1-Z4, wherein a total stoichiometric mixture results before the procedure, by an enrichment, caused by the trim controller intervention TRIM, a reduction in pollutant emissions are effected. The first number is greater than the second number, for example, the first number is 3 and the second number 1 in an internal combustion engine with a total of four Cylinders Z1-Z4.

So For example, in the case of a slightly lean air / fuel mixture in the first number of cylinders Z1-Z4 and a more richer air / fuel mixture in the second number of cylinders Z1-Z4, taking before the intervention a total stoichiometric Mixture results, by a leaning, caused by the Trim control intervention TRIM, reducing pollutant emission be effected.

In a step S12 is checked whether the trim controller intervention TRIM in a predetermined allowable range for the Trim controller is located. If this is the case, the determination of the Characteristic EMI and also the quality value GW in a step S14 according to the procedure of the step S2. Subsequently, it is then checked in a step S16 whether the quality value GW is larger as the predetermined threshold THD. Is this still the case? so the processing is continued again in step S10. is if this is not the case, then the processing in the step S8 and the absence of a pollutant relevant Error detected.

is on the other hand, does not satisfy the condition of step S12, then In a step S18, an identification process is started, the The goal is to be the one or the other the crossing the threshold THD by the quality value GW responsible To identify cylinders Z1 to Z4. This can be obtained, for example take place on the cylinders of the respective exhaust bank, by way of example in step S18 the procedure for an exhaust bank with three cylinders Z1, Z2, Z3 closer explained is. Step S18 is preferred for the respectively assigned ones Cycle Z1, Z2, Z3, so that in steps S20 to S28 closer explained Program sequence separately for each respective cylinder Z1-Z3 is going through. In step S18, a factor m with a Value 1 initialized.

In Step S20 is input to an identification target value LAM_SP_PP predetermined setpoint of the air / fuel ratio LAM_SP, for example, approximately equal to the stoichiometric air / fuel ratio can, changed, associated with a product of the factor m and a change value DELTA. Basically the value m in the step S18 also with a corresponding negative Value -1 are initialized and then incremented instead of in step S28 be decremented.

In a step S22 is checked whether the identification setpoint LAM_SP_PP of the air / fuel ratio in a given permissible Range of values is. If this is not the case, then the processing is in the step S18, until the flow for all the respective cylinders was run through and then the program ended. Is the condition on the other hand, of step S22, thus, in a step S24, the air / fuel ratio in the each with respect to of the step S18 current cylinder Z1 to Z3 according to the Identification setpoint of the air / fuel ratio LAM_SP_PP set while in terms of the other cylinder, the setpoint LAM_SP the air / fuel ratio is set.

In a step S26 becomes an error indicator ERR_IND determined. This can be done, for example, as shown in a step S30, depending on a rough running LU, which can be determined by means of appropriate functionality. Corresponding functions for determining the uneven running are regularly in the control device anyway 25 implemented. Determining the rolling noise LU is preferably carried out by appropriately evaluating the speed curve, specifically with regard to torque contributions of the respective cylinders. In this case, for example, a first or second derivative of the speed within a given crankshaft angle window, which is assigned to the respective cylinder, are evaluated, this crankshaft angle window can for example korrit pondieren to a so-called cylinder segment, for example, in a four-stroke internal combustion engine with a working cycle of 720 ° 180 ° and thus is given by the crankshaft angle of the working cycle divided by the number of cylinders.

In In this context, for example, the value that depends on the speed is determined, be proportioned to an average value all cylinders and so the running noise LU be determined.

For example may alternatively or additionally the error indicator also based on a pollutant emission value be determined, for example, of a control signal component a control signal or control signal output of a lambda controller or also one dependent can be done by this determined adaptation value or in principle dependent on another known procedure for determining the pollutant emission.

is the error indicator ERR_IND is representative for one Error ERR of the respective cylinder, then the respective cylinder as responsible for the crossing of the threshold value THD identified by the quality value as responsible. In this case, for example, a corresponding entry in a fault memory of the control device, which then for example can lead to an ad on a warning display or as an input for further Functions can serve.

is on the other hand, does not satisfy the condition of step S26, then In step S28, the factor m is incremented. alternative or additionally the sequence of steps S18 to S30 may also be so provided that the factor M is -1 is occupied in the step S18 and decrementing in the step S28 of the factor. This may for example depend on whether the parameter EMI for nitrogen oxides or on the other hand for Hydrocarbons or carbon monoxide is representative.

is the program sequence following step S18 for all corresponding Cylinder Z1 to Z3 completely through, the program is preferably terminated in step S8.

Claims (10)

Method for operating an internal combustion engine having a plurality of cylinders (Z1 to Z4) and injection valves assigned to the cylinders (Z1 to Z4) ( 18 ), which meter fuel, and an exhaust tract ( 4 ), in which an exhaust gas catalyst ( 21 ) and an exhaust gas probe ( 43 ) located in or downstream of the catalytic converter ( 21 ), in which - a parameter (EMI) for pollutant emission in the region of the exhaust gas probe ( 43 ) is determined as a function of their measurement signals (MS2), - a quality value (GW) for pollutant emission is determined as a function of a chronological course of the parameter (EMI) and - if the quality value (GW) exceeds a predetermined threshold value (THD), first a diagnosis (CAT_DIAG) of the catalytic converter ( 21 ) and if, in the context of the diagnosis (CAT_DIAG), the catalytic converter ( 21 ) is recognized as functioning properly, a setpoint value (LAM_SP) for an air / fuel ratio cylinder-individually relative to the respective cylinders (Z1 to Z4) is changed stepwise until at least one for exceeding the threshold value (THD) by means of an error indicator (ERR_IND) ) is identified by the quality value (GW) of responsible cylinders (Z1 to Z4). Process according to Claim 1, in which, if the catalytic converter ( 21 ) is recognized as properly functioning, first a trim controller intervention (TRIM) is carried out and only, if the quality value (GW) continues to exceed the threshold value even after the trim controller intervention (TRIM), the desired value (LAM_SP) for the air / fuel ratio related cylinder individually is rotationally changed to the respective cylinders (Z1 to Z4) until at least one cylinder (Z1 to Z4) responsible for exceeding the threshold value by the quality value (GW) is identified by means of the error indicator (ERR_IND). Method according to one of the preceding claims, in which, if the catalytic converter ( 21 ) is detected to be functioning properly, first a trim control (TRIM) is performed and only if the quality value (GW) continues to exceed the threshold (THD) even after the trim control intervention (TRIM), the setpoint (LAM_SP) for the air / fuel ratio Ratio cylinder-individually relative to the respective cylinder (Z1 to Z4) is gradually increased until by means of the error indicator (ERR_IND) at least one for the Exceeding the threshold value (THD) by the quality value (GW) of responsible cylinders (Z1 to Z4) is identified. Method according to one of the preceding claims, in the error indicator (ERR_IND) by a rough running value (LU) represents is. Method according to one of the preceding claims, in the error indicator (ERR_IND) by a pollutant emission value is represented. Method according to one of the preceding claims, in which the parameter (EMI) for pollutant emission depends on a slope and / or an absolute value of the measuring signal (MS2) of the exhaust gas probe ( 43 ) in the course of a breakthrough of the catalytic converter ( 21 ) downstream of the exhaust gas probe ( 43 ) is determined. Method according to one of the preceding claims, in the pollutant emission nitrogen oxide and / or hydrocarbon and / or carbon monoxide. Method according to one of the preceding claims, in the quality value (GW) is determined by an integral (INT) of the parameter (EMI). Method according to Claim 8, in which the integral (INT) each over a predetermined period of time is determined. Device for operating an internal combustion engine having a plurality of cylinders (Z1 to Z4) and injectors (Z1 to Z4) associated with injectors ( 18 ), which meter fuel, and an exhaust tract ( 4 ), in which an exhaust gas catalyst ( 21 ) and an exhaust gas probe ( 43 ) located in or downstream of the catalytic converter ( 21 ), wherein the device is designed to - a characteristic (EMI) for pollutant emission in the region of the exhaust gas probe ( 43 ) to determine depending on their measurement signal (MS2), - to determine a quality value (GW) for pollutant emission depending on a time course of the characteristic (EMI), - if the quality value (GW) exceeds a predetermined threshold (THD), first a diagnosis (CAT_DIAG) of the catalytic converter ( 21 ) and if, in the context of the diagnosis (CAT_DIAG), the catalytic converter ( 21 ) is recognized as properly functioning, stepwise to change a target value (LAM_SP) for an air / fuel ratio cylinder-specific based on the respective cylinders (Z1 to Z4) until at least one for exceeding the threshold value (THD) by means of an error indicator (ERR_IND) ) is identified by the quality value (GW) of responsible cylinders (Z1 to Z4).