DE10239258A1 - Internal combustion engine and method for operating an internal combustion engine with a fuel control device - Google Patents

Abstract

The invention relates to an internal combustion engine (1) with an exhaust system, which has a pre-catalyst device (3) and a main catalyst device (4) arranged downstream of the pre-catalyst device (3), and at least with a fuel control device (11) for mixture control as a function of the signal an oxygen sensor arranged in the exhaust gas. According to the invention, a first oxygen sensor (5) is arranged downstream of the pre-catalyst device (3) and upstream of the main catalyst device (4), the signal of which is fed to the fuel control device (11) for mixture control. DOLLAR A The invention further comprises a method for operating an internal combustion engine according to the invention.

Description

The invention relates to an internal combustion engine and a method for operating an internal combustion engine according to the preambles the independent Claims.

Internal combustion engines are from the prior art known with exhaust systems that have at least one pre-catalyst close to the engine and include at least one downstream main catalyst. To control the exhaust gas composition, there is usually one upstream of the pre-catalyst Lambda probe and another lambda probe downstream of the main catalytic converter or a NOx sensor with an oxygen measuring device.

Usually will be a broadband lambda probe in front of the pre-catalyst and a Step response lambda sensor installed behind the main catalytic converter. With Such a probe configuration is a mixture control and regulation possible in such a way that via the front probe a deviation of the actual mixture composition from a target mixture composition is detected and the recognized Deviation converted into a control intervention of a mixture pre-control becomes. The front probe is comparatively close to the internal combustion engine arranged so that deviations from the target composition quickly can be recognized and corrected. For one Fine control, the signal is arranged downstream of the main catalytic converter another lambda sensor or the NOx sensor with oxygen measuring device used. In particular, the calibration of the Lambda = 1 point of the front probe by the signal of the rear Probe in lambda = 1 mode. The control deviation to achieve a target lambda value is included in the regulation of the mixture deviation via the front probe.

A disadvantage of the usual Probe configuration is that the upstream of the pre-catalyst is close to the engine arranged probe of a high thermal and mechanical load exposed to high exhaust gas temperatures and pulsating exhaust gas flows is. The exhaust gas flow leads beyond to inaccuracies in the measurement of the mixed exhaust gas composition all engine cylinders, so that an increased effort in positioning the probe upstream of the pre-catalyst is required. That I the flow conditions dependent upstream of the pre-catalyst of the exhaust gas mass flow and the exhaust gas temperature it about it beyond just a compromise design.

A separate pre-catalyst diagnosis is with the described probe configuration according to the state the technology and the usual Method of measuring the oxygen storage capacity (OSC) of the pre-catalyst not possible, because the oxygen storage capacity of the entire system is tested. For a differentiated diagnosis of the exhaust system including a separate pre-catalytic converter diagnosis, such as that used to meet sharp Exhaust limit values are required, is an additional state of the art Lambda probe between the primary and the main catalytic converter, which results in increased costs and higher Application effort necessary.

Object of the present invention is therefore the creation of an internal combustion engine with at least one a pre-catalyst device and at least one downstream of the pre-catalyst device arranged exhaust gas system arranged main catalyst device, wherein a mixture control depending on a signal of a arranged in the exhaust gas oxygen sensor, in which the probe arrangement-specific Disadvantages of the prior art can be avoided. It is also a Object of the present invention, a method for operating a to create such an internal combustion engine. According to the invention the tasks set by the features of the independent claims.

According to the invention is a first oxygen sensor for example downstream of the first relative to the internal combustion engine Pre-catalyst and arranged upstream of the main catalyst, the Signal of the fuel control device for mixture control is supplied. Such an installation position of the first oxygen sensor results significant advantages over the conventional sensor arrangement. For the mixed exhaust gas of everyone Improved probe flow is ensured in the cylinder. Further is a lower effective cross sensitivity of the oxygen sensor against hydrocarbons, hydrogen and ammonia due to a downstream of the pre-catalytic converter to record a lower pollutant concentration. The pollutant conversion on the pre-catalyst leads to an increase in temperature of Catalytic converter and exhaust gas, since the exhaust system at least in this area but is not adiabatic, at least the additional energy generated partially removed again, so overall with one at most comparable high thermal load compared to an arrangement of the oxygen sensor upstream of the pre-catalyst is to be expected.

According to the invention, the exhaust system is also controlled to comply with specified pollutant emissions or regulated depending from the signal of a downstream of the pre-catalyst device Sensor, preferably an oxygen or NOx sensor. Opposite the usual Sensor configuration where the first oxygen sensor is upstream of the first precatalyst is arranged in the probe configuration according to the invention an improved probe flow and lower cross sensitivity of the first oxygen sensor and thus a higher one Functional reliability of the exhaust system achieved.

Furthermore, according to the invention, the separate Determination of a damage state of the pre-catalyst device as a function of the signal of the first oxygen sensor determines an oxygen storage capacity of the pre-catalyst device, the value of an oxygen concentration calculated upstream of the pre-catalyst device being used. In addition to the advantages already mentioned resulting from the installation position of the first oxygen sensor downstream of the pre-catalyst device, there is a decisive advantage in the possibility of separately determining the damage state of the pre-catalyst device without installing an additional second sensor.

According to the invention, it is also provided that to determine an oxygen storage capacity of the pre-catalyst device upstream of the pre-catalyst, a predetermined lambda value excitation takes place in the exhaust gas and an associated reaction downstream of the pre-catalyst is detected by means of the first oxygen sensor. Compared to that from the prior art, for example the DE 43 389 17 A1 , known method for determining the oxygen storage capacity of a catalytic converter, the lambda value excitation in the exhaust gas is not regulated but controlled according to the invention, so that an additional oxygen sensor upstream of the pre-catalytic converter device can be dispensed with.

Other features and advantages of Invention arise not only from the associated claims - by themselves or in combination - but also from the description below preferred embodiments in conjunction with the associated Drawings.

The drawings show:

1 a representation of sensor configurations in exhaust systems

2 a schematic diagram of the guide control known from the prior art

3 a schematic diagram of a management scheme according to the invention

4 a representation of the mixture control according to the prior art with a lambda sensor arranged upstream of a pre-catalyst

5 a representation of a mixture control in a lambda sensor arranged downstream of a pre-catalyst

6 a representation of a mixture control according to the invention

7 a representation of another mixture control according to the invention with a premature lean breakthrough downstream of a pre-catalyst

8th a representation of a mixture control according to the invention with an extended fat phase downstream of a pre-catalyst

9 a representation of a lambda value excitation and an assigned lambda reaction for determining an oxygen storage capacity according to the invention

10 a representation of a further lambda value excitation and an assigned lambda reaction

11 a representation of a further lambda value excitation and an assigned lambda reaction

12 a representation of known from the prior art sensor configurations for two-pipe exhaust systems

13 a representation of sensor configurations according to the invention for double-flow exhaust systems.

In the 1 The given representation of sensor configurations in exhaust systems shows an internal combustion engine for sensor configurations A, B and C. 1 . 1A . 1B with a downstream exhaust system 2 . 2A . 2 B which is a pre-catalyst 3 . 3A . 3B and a main catalyst 4 . 4A . 4B includes.

In configuration A known from the prior art, there is a first oxygen sensor 5A upstream of the pre-catalyst 3A and a second sensor 6A , for example an oxygen sensor or a NOx sensor, arranged downstream of the main catalyst. With configuration B the 1 is used to carry out a separate diagnosis of the pre-catalyst 3B another oxygen sensor 7B downstream of the pre-catalyst 3B arranged.

In configuration C is an internal combustion engine according to the invention 1 with an exhaust system 2 shown in which a first oxygen sensor 5 downstream of the pre-catalyst device 3 is arranged. With the internal combustion engine 1 it is preferably a direct injection gasoline engine or a diesel engine. The internal combustion engine is preferred 1 stratified charge capable. The pre-catalyst device 3 is designed as a 3-way catalytic converter or as an oxidation catalytic converter and can also comprise several individual catalytic converters. According to the invention downstream of the pre-catalyst device 3 arranged first oxygen sensor 5 is preferably a broadband lambda probe, which enables a relatively quick, but generally only rough, detection of the oxygen concentration or the lambda value of the exhaust gas.

The downstream of the oxygen sensor 5 arranged main catalyst device 4 can be a 3-way catalytic converter, a NOx storage catalytic converter or an oxidation catalytic converter and can also comprise a plurality of individual catalytic converters. The downstream de main catalyst device 4 arranged sensor 6 is preferably designed as a step response lambda probe, as a NOx sensor with an oxygen measuring device or as a multifunction sensor.

The installation position of the oxygen sensor 5 upstream of the pre-catalyst has some disadvantages, as already explained above.

The configuration C of the 1 has an optimized installation position of the first oxygen probe compared to the prior art, which is subject to lower loads there and also in right allows a separate determination of a damage state of the pre-catalyst device in a relatively simple manner. For optimized operation of the internal combustion engine according to the invention, however, it is advisable to take into account that the changed installation location of the first oxygen sensor downstream of the pre-catalytic converter device results in a longer exhaust gas run length and thus causes the control system of the mixture control to be possibly too long.

In 2 is one of the sensor configurations 1A corresponding representation of the principle of the guide control known from the prior art is shown. The signal from the oxygen sensor 5A , preferably a broadband lambda probe, is used to detect deviations of an actual lambda value from a by a fuel control device 11 predetermined target lambda value used.

Since, due to the construction, such broadband probes react relatively quickly, but also have relatively high error deviations and, in particular, accurate detection of the lambda = 1 point is difficult, the control intervention of the oxygen sensor is corrected 5A by the amount of the downstream of the main catalyst device 4A arranged sensor 6A , Around the lambda = 1 point, an accuracy in the alcohol range can be achieved with a step response probe in particular. The signal corrected by the amount of the step response probe is sent to a control unit 8th supplied, which in particular injectors 9 and / or a throttle valve 10 controls. Since the exhaust gas run length is short in the control section belonging to the first control loop, fast, stable control can be achieved with little effort. The control unit comprises for controlling or regulating the exhaust system 8th an exhaust gas control device.

In 3 is one of the sensor configuration C in the 1 Corresponding schematic representation of the control system for an internal combustion engine according to the invention is shown. Corresponding modules are provided with the same reference numerals as in 2 , Because the first oxygen sensor 5 downstream of the pre-catalyst device 3 is arranged, there is an increased inertia of the controlled system of the first control loop and thus a lower stability. In contrast to the guide control known from the prior art, the precatalyst device is also able to store oxygen 3 given a contribution to the inertia of the controlled system.

According to the invention, the volume of the pre-catalyst device is limited in order to reduce the activity of the controlled system and to achieve a predetermined stability limit for the mixture control. The relative volume of the pre-catalyst device is preferred 3 limited to a value between 0.7 and 0.3 of the engine displacement. Values of 0.6, 0.45 and 0.35 for the relative volume are particularly preferred.

Additionally or alternatively, a maximum volume-independent oxygen storage capacity of the pre-catalyst device is achieved to achieve a predetermined stability limit of the mixture control 3 selected. The maximum oxygen storage capacity is preferably limited to a value between 2.1 grams and 0.4 grams. Values of 2 grams, 1 gram and 0.5 grams of oxygen are particularly preferred. Such values are preferred especially for a pre-catalyst device 3 , which was conditioned for 4 hours at 600 degrees Celsius and a lambda value = 0.98. Includes the pre-catalyst device 3 If there are several catalysts, the corresponding maximum values apply for the totality of the catalysts, ie for the total catalyst volume or the total oxygen storage capacity of the individual catalysts.

Regardless of a limitation of the relative volume or the maximum oxygen storage capacity of a pre-catalyst device 3 can be expected in stoichiometrically driven operating states without large load and speed fluctuations that the control interventions via the first oxygen sensor are only slight and that in the pre-catalyst device 3 stored oxygen is only slightly loaded and unloaded. In such operating states, as is known in the prior art, continuous lambda control via one of the main catalyst devices 5 downstream probe 6 respectively. In dynamic operating states, such as a start-up phase, simple strategies for mixture control can be used with an oxygen sensor, which is arranged upstream of the pre-catalyst, as in the prior art. A deviation between an actual and a target lambda value is converted into a possibly filtered control intervention.

In 4 such a control strategy is illustrated for such a system with a low inertia of the controlled system. The upper curve shows a lambda value measured in front of a pre-catalytic converter, while the lower curve describes a control intervention depending on the deviation from the target value. A positive control intervention leads to an enrichment, a negative control intervention leads to a leaner exhaust gas. At a time T0, a starting process begins with a resulting enrichment of the exhaust gas. At time T1, the fuel control device intervenes for the first time through a lean-out control intervention, since there is an excessive deviation of the actual lambda value from the target lambda value over an excessively long period of time. At the point in time T2, the control intervention is intensified since there is no discernible tendency to lean the exhaust gas. Only at the later point in time T3 does the measured enrichment of the exhaust gas decrease, so that the intervention of the controller can be withdrawn. At the time T4, the control intervention is ended because the actual lambda value and the target lambda value match.

In 5 is a comparable scenario in an internal combustion engine according to the invention 1 with an upstream of a pre-catalyst device 3 arranged oxygen sensor 5 shown. The lambda value that can be measured in this sensor configuration downstream of the pre-catalyst device 3 is the heavily drawn curve, the non-measurable lambda value upstream of the pre-catalyst device 3 shown as a thin curve. Again at time T1, a start-up phase begins, which is accompanied by a longer enrichment of the lambda value upstream of the pre-catalyst device, which leads to a control intervention only at a time T1. However, the control loop here is not based on the extended exhaust gas runtime and the oxygen storage capacity of the pre-catalyst device 3 tuned so that the controller intervenes too weakly and then on the delayed following of the downstream of the pre-catalyst device 3 measured lambda value reacts with increased control interventions that cause the system to vibrate. These vibrations are only corrected at a time T2.

According to the invention, in order to avoid this behavior, which does not allow a favorable exhaust gas quality to be expected, the extended exhaust gas runtime and the oxygen storage capacity of the pre-catalyst device 3 taken into account in the form of rule intervention. According to the invention, the control intervention is shown in the form of a decreasing enrichment or emaciation of the exhaust gas. The maximum value and decay speed are dependent on the size of the measured lambda value deviation, ie the difference between a desired lambda value and an actual lambda value determined from the oxygen signal of the first oxygen sensor. There is also a dependency on the leaning or enrichment speed of the downstream of the pre-catalyst device 3 measured exhaust gas, the engine operating point, in particular the exhaust gas mass flow and an exhaust gas recirculation rate, and parameters such as the exhaust gas or catalyst temperature and the respective oxygen storage capacity of the catalyst device 3 , The oxygen storage capacity can be modeled or determined according to a method described below. This means that a certain amount of oxygen remains in the pre-catalyst device as far as possible even in dynamic operation 3 and compensates for the buffering of the controlled system by the oxygen storage capacity of the catalyst device.

In 6 is a too 5 analog scenario illustrated. The curve designation is the same as in 4 , however, the control intervention is modified according to the above. If mixture enrichment takes place from a point in time T0, this does not initially lead to any change in the lambda value of the exhaust gas downstream of the pre-catalyst device, since the enrichment is buffered by an oxygen release due to the stored oxygen. However, the lambda value of the exhaust gas upstream of the pre-catalyst device shows a deviation immediately after the time T0. Downstream of the pre-catalyst device, enrichment is measured from time T1 and, according to the invention, at time T2 the lambda value is trimmed towards the lean by a predetermined amount. The size of this amount is preferably selected as a function of the exhaust gas leaning rate in the time interval T1 to T2. The exhaust gas is then further leaned out at a predeterminable leaning rate, which takes into account the engine operating point, the exhaust gas mass flow, the catalyst temperature and / or the detected oxygen storage capacity, until a maximum deviation from the target value is measured at the oxygen sensor at time T4. Compared to the measured thinning rate, the decay rate of thinning is slower, linear or degressive.

In 7 A scenario is illustrated in which, during the lessening of the lean out of the control intervention, downstream of the pre-catalytic converter device 3 lean exhaust gas is measured. In this case, the emaciation is discontinued at time T6 and replaced by a fading enrichment. In 8th A scenario is illustrated in which the measured lambda value downstream of the pre-catalyst device during the decay of a lean-out control intervention 3 runs insufficiently or not at all towards lean. In this case, the leaning of the exhaust gas is continued with a constant lean control intervention until the measured lambda value falls below a predetermined deviation threshold from the setpoint lambda by the time T7. After time T7, the lean-out rule intervention is withdrawn. The lambda value in advance of the pre-catalyst device 3 goes back from the time T8 to the setpoint. The control intervention is ended at time T9.

Because the gastric breakthrough on a reduced oxygen storage capacity of the pre-catalyst device 3 indicates that the oxygen storage capacity entering into the form of the control intervention can be reduced by an amount dependent on the time and the amount of the lean breakthrough and can be used in subsequent control interventions. Furthermore, it can generally be assumed that increased control interventions are associated with a reduced oxygen storage capacity, since then the buffering is reduced by the oxygen storage capacity. Accordingly, a change in the oxygen storage capacity of the pre-catalyst device can be made from the average amount of the control intervention 3 be determined. A change in the oxygen storage capacity can also be derived from inadequate emaciation of the exhaust gas.

The arrangement of the first th oxygen sensor downstream of the pre-catalyst device 3 allows a separate determination of a damage state of the pre-catalyst device 3 without additional sensor effort. For this purpose, a calculated value of an oxygen concentration upstream of the pre-catalyst device 3 is compared with the value determined from the signal of the first oxygen sensor and an oxygen storage capacity is determined therefrom, which is correlated in a manner known per se with a damage state of the pre-catalyst device. The control unit 8th expediently comprises a diagnostic device for this purpose.

As is also known per se from the prior art, in particular upstream of the pre-catalyst device is used to determine an oxygen storage capacity 3 generates a lambda value excitation in the exhaust gas and detects an associated reaction downstream of the pre-catalyst device. In contrast to the prior art, for example DE 43 389 17 A1 , the lambda value excitation is upstream of the pre-catalyst device 3 not regulated, but controlled.

A lambda wobble with a predetermined amplitude and frequency is preferably generated as lambda excitation. In 9 are the controlled lambda value upstream of the pre-catalyst device 3 (dotted line), the lambda value downstream of the pre-catalyst device 3 with a high oxygen storage capacity of the pre-catalyst device 3 (solid line) and the lambda value downstream of the pre-catalyst device 3 for a pre-catalyst device 3 shown with a low oxygen storage capacity (dashed line). As in 9 can be seen in a pre-catalyst device 3 With a low oxygen storage capacity, the assigned reaction is faster and the curve is more similar to the stimulating wobble.

In 10 an alternative or additional method is shown in which the wobble frequency is reduced over a predetermined period of time. It is evident that the assigned reaction is downstream of the pre-catalyst device 3 with a low oxygen storage capacity (dashed line) occurs at relatively high wobble frequencies and reach the maximum possible amplitude. In contrast, with a high oxygen storage capacity (solid line), assigned reactions are only achieved at a relatively low wobble frequency, with their amplitude increasing only slowly.

In the embodiment of the method according to 11 with a constant wobble frequency, the wobble amplitude is increased over time. The lambda value follows downstream of the pre-catalyst device 3 with a high oxygen storage capacity delayed and with a relatively low amplitude (solid line), while a high oxygen storage capacity leads to a rapid subsequent reaction with a relatively high amplitude (dashed line).

All of the wobble methods shown can the wobble parameters can be varied continuously or narrowly. Furthermore, the response times of the first oxygen sensor can be evaluated a jump excitation from a slightly rich lambda value, for example Lambda = 0.96, to a slightly lean lambda value, for example lambda = 1.04, or vice versa. A high oxygen storage capacity corresponds to a long response time, while a low oxygen storage capacity corresponds to a short response time.

Combustion engines with exhaust systems with a plurality of exhaust lines are also known from the prior art, in which pairs of probes are arranged upstream of the pre-catalysts of each exhaust line and, if appropriate, further pairs of probes downstream of the main catalysts of each exhaust line. In 12A Such a sensor configuration is shown for a double-flow exhaust system without the possibility of a separate diagnosis of the pre-catalyst. In the 12B a sensor configuration is also shown for a double-flow exhaust system, in which a separate diagnosis of the pre-catalysts can be carried out by means of a third pair of probes.

The method according to the invention can also be used for exhaust systems which have a plurality of exhaust lines. This is in 13A a sensor configuration in an internal combustion engine 1 shown with an exhaust system, which two exhaust lines 12 . 13 having. Every exhaust line 12 . 13 has a pre-catalyst 14 and a downstream of the pre-catalyst 14 arranged main catalyst 15 on. Downstream of every pre-catalyst 14 and upstream of each main catalyst 15 is an oxygen sensor 16 . 17 arranged so that downstream of the pre-catalysts 14 one pair of sensors is arranged. Downstream of every main catalytic converter 15 is also a sensor 17 arranged so that downstream of the main catalysts 15 a pair of sensors is also arranged. The determination of a damage condition of a pre-catalytic converter can be carried out separately for each exhaust line.

In 13B is a sensor configuration for an exhaust system with an exhaust gas junction 18 downstream of the pre-catalysts 14 shown. Upstream of the exhaust gas junction 18 and downstream of the pre-catalysts 14 are the first oxygen sensors 19 arranged. Downstream of the exhaust gas junction 18 is a main catalyst 20 arranged. Downstream of the main catalytic converter 20 again is an oxygen sensor 21 arranged. In this case, too, a separate determination of the damage status of the individual pre-catalysts can be carried out 14 respectively. Just as in the exemplary embodiments described above, the pre-catalysts and main catalysts can also be used here with pre-catalyst devices and main catalyst devices more than one catalyst can be replaced without departing from the scope of the invention. This also applies to the sensors used.

Claims (33)

Internal combustion engine ( 1 ) with an exhaust system, which a pre-catalyst device ( 3 ) and one downstream of the pre-catalyst device ( 3 ) arranged main catalyst device ( 4 ), and with a fuel control device ( 11 ) for mixture control as a function of the signal from at least one oxygen sensor arranged in the exhaust gas, characterized in that a first oxygen sensor ( 5 ) downstream of the pre-catalyst device ( 3 ) and upstream of the main catalyst device ( 4 ) is arranged, the signal of the fuel control device ( 11 ) is fed to the mixture control. Internal combustion engine according to claim 1, characterized in that an exhaust gas control device for controlling or regulating the exhaust system for maintaining predetermined pollutant emission limits as a function of the signal of the first oxygen sensor ( 5 ) is provided. Internal combustion engine according to claim 1 or 2, characterized in that a diagnostic device for determining a damage state of the pre-catalyst device ( 3 ) is provided, of which depending on the signal of the first oxygen sensor ( 5 ) and a calculated value of an oxygen concentration upstream of the pre-catalyst device ( 3 ) an oxygen storage capacity of the pre-catalyst device ( 3 ) determined and the determined oxygen storage capacity with a damage state of the pre-catalyst device ( 3 ) is correlated. Internal combustion engine according to one of the preceding claims, characterized in that downstream of the main catalyst device ( 4 ) a sensor ( 6 ), in particular a step response lambda probe or a NOx sensor with an oxygen measuring device, the signal of the fuel control device ( 11 ), the exhaust gas control device and / or the diagnostic device can be supplied. Method of operating an internal combustion engine ( 1 ) with an exhaust system, which has at least one pre-catalyst device ( 3 ) and at least one downstream of the pre-catalyst device ( 3 ) arranged main catalyst device ( 4 ), and with a fuel control device ( 11 ) for mixture control as a function of the signal from an oxygen sensor arranged in the exhaust gas, characterized in that a first oxygen sensor ( 5 ) downstream of the pre-catalyst device ( 3 ) and upstream of the main catalyst device ( 4 ) is arranged, the signal of the fuel control device ( 11 ) is fed to the mixture control. A method according to claim 5, characterized in that to achieve a predetermined stability limit of the mixture control, the relative volume of the pre-catalyst device ( 3 ) is selected to be smaller than a predetermined maximum relative volume, in each case based on the engine displacement. A method according to claim 6, characterized in that the maximum relative volume in a range between 0.3 and 0.7, in particular at 0.6, 0.45 or 0.35. Method according to at least one of claims 5 to 7, characterized in that in order to achieve a predetermined stability limit of the mixture control, a maximum volume-independent oxygen storage capacity of the pre-catalyst device ( 3 ), preferably in a range between 2.1 grams and 0.4 grams. Method according to at least one of claims 5 to 8, characterized in that that for mixture control, a difference between a lambda setpoint and one from the oxygen signal of the first oxygen sensor determined actual lambda value is determined and as a function of this actual setpoint difference a control intervention from an additive and / or multiplicative immediate correction value and optionally a subsequent post-correction value that decays in time is formed. A method according to claim 9, characterized in that the Immediate correction value and / or possibly the post-correction value depending from an engine operating point, an exhaust gas mass flow, a pre-catalyst device temperature or an oxygen storage capacity the pre-catalyst device is selected. A method according to claim 9 or 10, characterized in that If necessary, the post-correction value depending on the actual setpoint difference is chosen. Method according to at least one of claims 9 to 11, characterized in that that an expected value of the actual setpoint difference is calculated and that a sign reversal of the immediate correction value and possibly the After correction value is carried out if the actual setpoint difference is faster than determined by the expected value decreases. Method according to at least one of claims 9 to 12, characterized in that an expected value of the actual-target value difference is calculated and, if the actual-target value difference decreases more slowly than determined by the expected value, the value of the immediate and / or possibly post-correction value is frozen. Method according to at least one of Claims 9 to 13, characterized in that the precatalyst device ( 3 ) is determined from the time course of the actual setpoint difference of the sensor signal within a predetermined time interval. Method according to at least one of claims 9 to 14, characterized in that the average amount of the control intervention determines and from this an oxygen storage capacity of the pre-catalyst device ( 3 ) is determined. Method according to at least one of Claims 5 to 15, characterized in that the signal from the first oxygen sensor (to control or regulate the exhaust system in order to comply with predetermined pollutant emission limits ( 5 ) is used. Method according to at least one of Claims 5 to 16, characterized in that the signal from the first oxygen sensor (to control or regulate the exhaust system in order to comply with predetermined pollutant emission limits ( 5 ) is used. Method according to at least one of claims 5 to 16, characterized in that the pre-catalyst device ( 3 ) comprises at least one 3-way catalyst. Method according to at least one of the preceding claims 5 to 18, characterized in that the pre-catalyst device ( 3 ) comprises at least one oxidation catalyst. Method according to at least one of the preceding claims 5 to 19, characterized in that the main catalyst device ( 4 ) comprises at least one NOx storage catalytic converter. Method according to at least one of the preceding claims 5 to 20, characterized in that the main catalyst device ( 4 ) comprises at least one 3-way catalyst. Method according to at least one of claims 5 to 21, characterized in that the first oxygen sensor ( 5 ) is a broadband lambda sensor. Method according to at least one of claims 5 to 22, characterized in that at least one second sensor downstream of the main catalyst ( 4 ) is arranged, the signal of which is used to regulate the mixture or to regulate or control the exhaust system. A method according to claim 23, characterized in that the second sensor ( 6 ) is a step response lambda probe. A method according to claim 23, characterized in that the second sensor ( 6 ) is a NOx sensor with an oxygen measuring device. Method according to at least one of claims 5 to 25, characterized in that for the separate determination of a damage state of the pre-catalyst device ( 3 ) depending on the signal from the first oxygen sensor ( 5 ) and a calculated value of an oxygen concentration upstream of the pre-catalyst device ( 3 ) an oxygen storage capacity of the pre-catalyst device ( 3 ) determined and the determined oxygen storage capacity with a damage state of the pre-catalyst device ( 3 ) is correlated. Method according to at least one of claims 5 to 25, characterized in that for determining the oxygen storage capacity of the pre-catalyst device ( 3 ) upstream of the pre-catalyst device ( 3 ) a predetermined controlled lambda value excitation takes place in the exhaust gas and an assigned reaction in the exhaust gas downstream of the pre-catalyst device ( 3 ) is detected by means of the first oxygen sensor. A method according to claim 27, characterized in that the lambda excitation is generated by a lambda wobble with a predetermined amplitude and frequency, and that an amplitude of the lambda value is determined from the assigned reaction in the exhaust gas and the oxygen storage capacity from the ratio of the two amplitudes the pre-catalyst device ( 3 ) is calculated. A method according to claim 27, characterized in that the frequency of the lambda value wobble is increased continuously or narrowly and the oxygen storage capacity of the pre-catalyst device ( 3 ) is determined as a function of the amplitude of the oxygen sensor signal. A method according to claim 27, characterized in that the amplitude of the lambda value wobble is increased continuously or narrowly and from the amplitude peak of the oxygen sensor to the oxygen storage capacity of the pre-catalyst device ( 3 ) is closed. The method according to claim 27, characterized in that a jump from a slightly rich lambda value, in particular lambda = 0.96, to a slightly lean lambda value, in particular lambda = 1.04, is carried out, and that a The response times of the first oxygen sensor are evaluated. Method according to one of claims 5 to 31, characterized in that the exhaust system a plurality of exhaust lines ( 12 . 13 ), and each exhaust line has at least one pre-catalyst device ( 14 ), downstream of the pre-catalyst devices ( 14 ) at least one main catalyst device ( 15 . 20 ) is arranged that an exhaust gas merging ( 18 ) downstream of the pre-catalyst devices ( 14 ) is provided and that downstream of each pre-catalyst device ( 14 ) a first oxygen sensor ( 16 ), possibly upstream before the exhaust gas merging ( 18 ), is provided. A method according to claim 33, characterized in that downstream of each main catalyst device ( 15 . 20 ) a sensor ( 17 . 21 ), preferably a step response lambda probe or a NOx sensor with an oxygen measuring device, is provided.