DE10257059B4 - Method and device for diagnosing catalyst units - Google Patents

Abstract

Method for diagnosing a catalyst unit of a catalytic system of an exhaust system with N-exhaust lines of an internal combustion engine, wherein the N-exhaust lines are each equipped with a catalyst unit and combine downstream of the catalyst units in a common exhaust pipe and a control of a lambda value of the exhaust gas in the N Exhaust passages upstream of the catalyst units is possible, characterized in that the following steps are carried out: (a) the catalyst units of N-1 exhaust strands are maintained in an oxygen-free state by exposure to a stoichiometric or rich exhaust gas for a predetermined time interval T; (b) for the catalyst units of the Nth exhaust gas train, a value of an oxygen storage capacity is determined by applying the lambda value excitation of the exhaust gas during the time interval T and evaluating an associated lambda value reaction of the exhaust gas downstream of the exhaust gas recombination in a region of the common exhaust gas line and determining a catalyst diagnostic value in dependence on this value.

Description

The invention relates to a method and a device for the diagnosis of catalytic converter units of a catalytic converter system of an exhaust system with N-exhaust gas trains of an internal combustion engine according to the preambles of the independent claims.

Internal combustion engines with an exhaust system with N exhaust system are known from the prior art. Each exhaust gas line can be equipped with a catalyst unit, which in turn consists of one or more catalysts, for example a precatalyst or a main catalyst. In this case, one or more cylinders, which are combined into cylinder groups, can be assigned to one exhaust gas line. To comply with legal exhaust emission regulations, an on-board monitoring of the catalysts is required. One known method for the diagnosis of catalysts in exhaust systems is the determination of the oxygen storage capacity (OSC). A reduction of the OSC is used as an early indicator for a catalyst deactivation, since often thermal aging of the catalyst leads to an OSC slump before deactivation of the noble metal components incorporated in such catalysts. The OSC is usually determined by a lambda value of the exhaust gas upstream the catalyst to be monitored is subjected to a cyclic fluctuation between a rich (lambda <1) and a lean (lambda> 1) phase around the value 1.0 and the lambda signal downstream of the catalytic converter is compared with the lambda signal upstream of the catalytic converter , When the OSC is high, the oxygen stored in the catalyst can largely process the reductant supply in fat phases of lambda fluctuation. Therefore, the fluctuations of the lambda signal downstream of the catalyst are relatively low.

If the OSC is low, the amount of stored oxygen is insufficient to fully implement the supply of reducing agent. In this case, the lambda signal follows with relatively high amplitude the lambda signal upstream of the catalytic converter

If the OSC falls below a predetermined limit value-recognizable by the exceeding of a limit value of the amplitude of the lambda signal downstream of the catalytic converter relative to the amplitude of the lambda signal upstream of the catalytic converter-the relevant catalytic converter is identified as defective and error information is output. Alternatively, the voltage signal of step response lambda probes, which are arranged upstream and downstream of the catalytic converter to be monitored, can also be evaluated for the comparison of lambda values. Although such probes do not allow the measurement of lambda values, an evaluation of lambda jumps in the case of a lean → fat or fat → lean transition is possible. The lambda jumps correspond to voltage jumps of the probe signal. If the voltage jumps of these probes before and after the catalyst are close in time, the OSC is low. If the voltage jumps are far apart in time, the OSC is high. Furthermore, an arrangement of a broadband lambda probe for measuring the lambda value in front of the catalyst and a step response lambda probe behind the catalyst for determining the OSC is known.

In the known methods, it is necessary for an accurate determination of the OSC that at least one probe is arranged upstream and downstream of the catalyst to be monitored. In an exhaust system with N-exhaust lines and a Abgaszusammenführung downstream of the catalysts can be detected with a probe downstream of the Abgaszusammenführungseinrichtung only the composition of the mixed gas from the various exhaust strands An individual monitoring of the catalysts is thus not readily possible On the other hand, the use of probes in each Exhaust line downstream of the catalysts associated with high costs.

From the DE 196 20 417 C2 a diagnostic method for a catalyst system is already known, in which a pilot and a main catalyst are arranged one after the other in an exhaust pipe About the main catalyst, a bypass valve is connected upstream and downstream of the catalyst system probes are arranged. For diagnosis, exhaust gas is passed through the primary and the main catalytic converter or only through the primary catalytic converter and the composition of the exhaust gas is detected in each case. Thus, the condition of each catalyst as well as that of the entire plant can be diagnosed. Instead of additional probes a bypass flap is needed.

It is also from the EP 0 595 044 B1 a device for operationally detecting a deterioration of a catalytic three-way converter of an internal combustion engine, wherein two exhaust pipes, which are connected to groups of cylinders, unite into a common exhaust pipe. The three-way catalytic converter is disposed in the common exhaust pipe or in each of the individual exhaust pipes or in all. In order to achieve an improved diagnosis of the condition of the entire catalyst system, synchronization detection means are provided for determining whether certain conditions are fulfilled or not met. In this case, a diagnosis is carried out with one probe each upstream of two precatalysts and one probe downstream of a main catalytic converter.

Furthermore, from the EP 1 057 989 A2 an air-fuel control system for engines is known, wherein an exhaust system with multiple exhaust gas lines, which unite electricity from catalysts to a common exhaust pipe, is monitored. During a catalytic converter diagnosis, all exhaust gas trains are subjected to a synchronous Lambda value excitation.

Object of the present invention is to provide a method and an apparatus with which a diagnosis of catalyst units of a catalyst system for an exhaust system with N-exhaust gas lines of an internal combustion engine can be done, which is accurate and at the same time can be realized inexpensively and structurally simple.

According to the invention the object is achieved by the features of the independent claims.

• (a) die Katalysatoreinheiten von zumindest N – 1 Abgassträngen werden durch Beaufschlagung mit einem stöchiometrischen oder fetten Abgas für ein vorgegebenes Zeitintervall T in einem sauerstofffreien Zustand gehalten;
• (b) für die Katalysatoreinheit des N-ten Abgasstranges wird durch Beaufschlagung der Katalysatoreinheiten mit einer Lambdawert-Anregung des Abgases während des Zeitintervalls T und Auswertung einer zugeordneten Lambdawert-Reaktion des Abgases stromab der Abgaszusammenführung in einem Bereich der gemeinsamen Abgasleitung ein Wert einer Sauerstoffspeicherfähigkeit ermittelt und in Abhängigkeit von diesem Wert ein Katalysatordiagnosewert bestimmt.

According to the invention, the following steps are carried out in a generic method:

• (a) the catalyst units of at least N-1 exhaust strands are maintained in an oxygen-free state for a predetermined time interval T by exposure to a stoichiometric or rich exhaust gas;
• (b) for the catalyst unit of the N-th exhaust gas line, a value of an oxygen storage capacity is determined by applying the lambda value excitation of the exhaust gas during the time interval T and evaluating an associated lambda value reaction of the exhaust gas downstream of the exhaust gas recombination in a region of the common exhaust gas line and determining a catalyst diagnostic value in dependence on this value.

The inventive method also allows an accurate diagnosis of a group of K catalyst units with only one arranged in a region of the common exhaust pipe sensor for evaluating the lambda reaction of the exhaust gas, as by the application of K exhaust strands with a stoichiometric or rich exhaust gas, these catalyst units no contribution bring to lambda value reaction in the mixed exhaust gas. This makes it possible to save both sensors and, based on the exact diagnosis, identify and replace defective catalyst units

Preference is given to a method in which exactly N-1 catalyst units are kept free of oxygen, and steps (a) and (b) are provided for determining the catalyst diagnosis value of the catalyst unit of the N-th exhaust line. This makes it possible to carry out an individual diagnosis of the catalytic converter unit of the N th exhaust branch independently of the catalyst units of the other exhaust branches.

The catalyst units can expediently each have a precatalyst, a main catalyst or a combination of precatalyst and main catalyst. It is understood that in a combination of the precatalyst and the main catalyst without further action an OSC and a catalyst diagnosis value of this combination is determined.

In order to carry out an individual diagnosis of all catalytic converter units of the N exhaust gas lines, steps (a) and (b) are carried out successively successively for all exhaust gas trains.

According to the invention, a diagnosis of the entire catalyst system which does not differentiate between the individual catalyst units can first of all be carried out, and an individual test of the individual catalyst units can only be carried out if there has been a detected damage to the overall system. In the case of a properly functioning system, the individual test can be dispensed with.

In order to avoid superfluous tests of a catalyst unit identified as being defective, it can be provided according to the invention that only a predetermined number of repetitions of steps (a) and (b) are provided for such a catalyst unit.

It is expedient to use a known lambda sweep with predetermined amplitude and frequency as lambda value excitation of the exhaust gas.

• (a) die Katalysatoreinheiten von zumindest N – 1 Abgasstrangen werden durch Beaufschlagung mit einem stöchiometrischen oder fetten Abgas für ein vorgegebenes Zeitintervall T in einem sauerstofffreien Zustand gehalten;
• (b) für die Katalysatoreinheiten des N-ten Abgasstranges wird durch Beaufschlagung der Katalysatoreinheiten mit einer Lambdawert-Anregung des Abgases während des Zeitintervalls T und Auswertung einer zugeordneten Lambdawert-Reaktion des Abgases stromab der Abgaszusammenführung in einem Bereich der gemeinsamen Abgasleitung ein Wert einer Sauerstoffspeicherfähigkeit ermittelt und in Abhängigkeit von diesem Wert ein Katalysatordiagnosewert bestimmt

The device according to the invention for the diagnosis of catalytic converter units of a catalytic converter system of an exhaust system with N-exhaust lines of an internal combustion engine, has a mixture control device for controlling a lambda value in the N-exhaust lines upstream of the catalyst units in each of the N-exhaust lines upstream of each catalyst unit and in an oxygen sensor arranged a region of the common exhaust pipe. A control device is provided which processes the signals of the oxygen sensors, can influence the lambda value of the exhaust gas in the N exhaust gas strands via adjusting means and causes the following steps:

• (a) the catalyst units of at least N-1 exhaust gas trains are maintained in an oxygen-free state by exposure to a stoichiometric or rich exhaust gas for a predetermined time interval T;
• (B) for the catalyst units of the N-th Abgasstranges is by applying the Catalyst units with a lambda value excitation of the exhaust gas during the time interval T and evaluation of an associated lambda value reaction of the exhaust gas downstream of the exhaust gas combination in a region of the common exhaust pipe determines a value of oxygen storage capability and determines a catalyst diagnosis value in dependence on this value

The device according to the invention allows an accurate diagnosis of selected catalyst units with only one arranged in the region of the common exhaust pipe oxygen sensor.

Other features and advantages of the invention will become apparent not only from the claims - alone or in combination - but also from the following description of preferred embodiments in conjunction with the accompanying drawings.

The drawings show a schematic representation:

1 an internal combustion engine with an exhaust system with two exhaust gas lines;

2 a flow diagram of the diagnostic method according to the invention;

3 the time course of a lambda signal of a probe arranged downstream of a catalytic converter during a determination of the oxygen storage capacity in a non-damaged catalytic converter,

4 the time course of a lambda signal of a sensor arranged downstream of a catalyst during a determination of the oxygen storage capacity in a damaged catalyst;

5 the time profile of the lambda signal from upstream or downstream of two catalysts arranged probes in a determination of the oxygen storage capacity according to the inventive method.

The representation in 1 shows a known internal combustion engine 1 with four cylinders. The internal combustion engine 1 may be a preferably direct injection gasoline engine or a diesel engine. Two cylinders each are combined into one group and one exhaust system 5A respectively. 5B assigned The exhaust strands 5A respectively. 5B each with a catalyst unit 2A respectively. 2 B stocked. Each catalyst unit 2A . 2 B may be a precatalyst, a main catalyst or a combination of primary and main catalyst, in the present case, the catalyst unit 2A from a precatalyst V and a main catalyst H arranged downstream of it. The catalysts may each be a three-way catalyst or a NOx storage catalyst. Upstream of the catalyst units are each sensors 3A respectively. 3B in the exhaust pipes 5A respectively. 5B arranged. The exhaust pipes 5A and 5B lead into a common exhaust pipe 6 and together with this form the exhaust system of the internal combustion engine 1 , At the point of discharge is an exhaust gas recombining unit 6A arranged. In an area of the common exhaust pipe 6 downstream of the catalyst units 2A and 2 B and the exhaust gas recombining unit 6A is a sensor 4 for the mixed exhaust gas at the exhaust gas lines 2A and 2 B arranged.

The sensors 3A . 3B and 4 are designed as a broadband lambda probe, as a step response lambda probe or as a NOx sensor with a lambda value signal output. The signals of the sensors 3A . 3B and 4 be from a control unit 7 recorded and evaluated. The control unit 7 Depending on the composition of the exhaust gas in the exhaust lines 5A . 5B and the exhaust pipe 6 Signals to a mixture control device 8th further. The mixture control device 8th regulates or controls via adjusting means 10 , for example via a throttle valve 9 , the fuel mixture that is fed to the cylinders.

Preferably, a sweep having a predetermined frequency and amplitude is used as lambda value excitation of the exhaust gas.

• (a) die Katalysatoreinheiten von N – 1 Abgassträngen werden durch Beaufschlagung mit einem stöchiometrischen oder fetten Abgas für ein vorgegebenes Zeitintervall T in einem sauerstofffreien Zustand gehalten;
• (b) für die Katalysatoreinheiten des N-ten Abgasstranges wird durch Beaufschlagung der Katalysatoreinheiten mit einer Lambdawert-Anregung des Abgases während des Zeitintervalls T und Auswertung einer zugeordneten Lambdawert-Reaktion des Abgases stromab der Abgaszusammenführung in einem Bereich der gemeinsamen Abgasleitung ein Wert einer Sauerstoffspeicherfähigkeit ermittelt und in Abhängigkeit von diesem Wert ein Katalysatordiagnosewert bestimmt

According to the invention, the following steps are carried out

• (a) the catalyst units of N-1 exhaust strands are maintained in an oxygen-free state by exposure to a stoichiometric or rich exhaust gas for a predetermined time interval T;
• (b) for the catalyst units of the Nth exhaust gas train, a value of an oxygen storage capacity is determined by applying the lambda value excitation of the exhaust gas during the time interval T and evaluating an associated lambda value reaction of the exhaust gas downstream of the exhaust gas recombination in a region of the common exhaust gas line and determining a catalyst diagnostic value in dependence on this value

The execution of steps (a) and (b) is performed by the control and evaluation unit 7 causes.

It goes without saying that the method according to the invention can also be used in an exhaust gas system with more than two, generally with N exhaust gas strands. Furthermore, the exhaust system in addition to the N-exhaust strands have further exhaust strands, which are not included in the inventive method. In particular, the common exhaust pipe 6 further downstream of the exhaust gas recombiner 6A arranged catalyst units exhaust gas supply. Further, a group of K catalyst units may also be diagnosed together by applying the method to a group of K exhaust trains.

In order to put all catalyst units in a defined state, all N catalyst units can also be put in an oxygen-free state for a time interval T1 before the time interval T. Preferably, individual control of the lambda value of the exhaust gas in each exhaust line upstream of the catalyst units is possible.

In 2 preferred sequence steps of the diagnostic method according to the invention are compiled in a flow chart. In step S1, by means of the sensor 4 a measurement of the mixed gas in the common exhaust pipe 6 performed and the oxygen storage capacity of the catalyst units of all exhaust gas trains or a catalyst diagnosis value determined. In step S2, a branch is made in dependence on the result of step S1. In the event that the value of the oxygen storage capacity of the catalyst system formed from the catalyst units of the individual exhaust lines shows that this is not defective overall, a return to step S1. The method used in the diagnosis of the catalyst system is based on the evaluation of the reaction of the exhaust gas to a lambda value excitation and is already known per se from the prior art. If the diagnosis of step S1 indicates that the oxygen storage capacity of the catalyst system is below a predetermined value, the exhaust gas is adjusted in step S3 in order to render all catalyst units oxygen-free. In the case of 1 these are the catalyst units 2A and 2 B ,

In a following step S4, a catalyst unit, for example 2 B during a predetermined time interval T with stoichiometric or slightly rich exhaust gas, while a diagnosis of the catalyst unit 2A he follows. For this purpose, for example, via the mixture control device 8th the exhaust gas in the exhaust system 5A controlled or regulated between rich and lean. Preferably, the internal combustion engine 1 during the diagnosis of the catalyst unit 2A operated so that the oxygen-free held catalyst unit 2 B under constant conditions, preferably with exhaust gas having a constant lambda value. During the execution of step S4, the comparison of the lambda signals of the sensors is performed in a manner known per se 3A and 4 the oxygen storage capacity of the catalyst unit 2A and in response thereto, a catalyst diagnostic value for the catalyst unit 2A certainly. Following step 4, a diagnosis of the catalyst unit takes place in step S5 2 B analogous to the diagnosis in step S.

In step S6, the catalyst diagnosis values of the catalyst unit become 2A and 2 B saved. In step S7, depending on the result in step S6, a branch occurs. Are the catalyst units 2A and 2 B is recognized as not defective due to the previous diagnosis, it is branched to step S9 and determined that a faulty measurement has taken place. In this case, a re-diagnosis is made in step S1. Is at least one of the catalyst units 2A or 2 B defective, a branch is made to step S8 and a display or storage that and optionally which of the catalyst units 2A or 2 B are defective. It is understood that the implementation of steps (a) and (b) according to the invention can also be carried out as a function of other conditions. In order to avoid superfluous diagnostic steps, it is also possible to exclude a catalytic converter unit which was detected as defective or which has been repeatedly identified as defective from the test.

In 3 the time profile of lambda signals of a broadband lambda probe upstream and downstream of a catalyst unit according to a known method for determining the oxygen storage capacity is shown.

In this case, the catalyst unit is subjected to a lambda value excitation of the exhaust gas; in this case, a sweep excitation with given frequency and amplitude. 3 shows the course of a non-damaged catalyst unit, in which there is a sufficiently large Sauerstaffspeicherfähigkeit. The lambda signal downstream of the catalyst unit therefore fluctuates only slightly by the value lambda = 1.

In 4 is appropriate 3 the time course of lambda signals in front of and behind a damaged catalyst unit shown with low oxygen storage capacity. The lambda signal of the probe arranged downstream of the catalyst unit follows with a slight phase shift the lambda signal of the probe arranged upstream of the catalyst device.

5 shows the time course of lambda signals before and after the catalyst units 2A and 2 B in a diagnosis of the catalyst unit according to the invention 2A , Here, reference is made to a configuration as in FIG 1 shown. The catalyst unit 2 B is supplied with a slightly rich exhaust gas (lambda <1), Notwithstanding the illustration in 5 can the catalyst unit 2 B be acted upon with very rich or stoichiometric exhaust gas. The catalyst unit 2A is subjected to a cyclically fluctuating fat-lean excitation. As the catalyst unit 2 B is kept oxygen-free, are the variations of the lambda signal in the common exhaust pipe 6 arranged sensor 4 solely on the fluctuations of the lambda value before the catalyst unit 2A DECLINES. To determine the oxygen storage capacity of the catalyst unit 2A can therefore essentially the lambda signals of the sensors 3A and 4 be used in a conventional manner. However, the amplitude of the fluctuation of the lambda signal is at the downstream of the catalyst units 2A and 2 B lying lower, since the exhaust gas mass flow in the common exhaust pipe 6 is greater than in the individual exhaust gas lines 5A respectively. 5B , This reduction must be taken into account in the evaluation of the lambda signals and in the specification of limit values from which a catalytic converter unit is recognized as being defective.

Alternatively to using a broadband lambda probe, as in the 3 to 5 The diagnosis of the catalyst units can also be carried out with a step response lambda probe, a NOx sensor with a lambda value signal output or a combination of such probes.

The method according to the invention is preferably used for the individual diagnosis of one or more catalyst units, which are each arranged in one of the N exhaust lines. However, a collective diagnosis of groups of K catalyst units arranged in a corresponding group of K exhaust passages is also possible with the method according to the invention

Claims (16)

Method for diagnosing a catalyst unit of a catalytic system of an exhaust system with N-exhaust lines of an internal combustion engine, wherein the N-exhaust lines are each equipped with a catalyst unit and combine downstream of the catalyst units in a common exhaust pipe and controlling a lambda value of the exhaust gas in the N Exhaust passages upstream of the catalyst units is possible, characterized in that the following steps are carried out: (a) the catalyst units of N-1 exhaust strands are maintained in an oxygen-free state by exposure to a stoichiometric or rich exhaust gas for a predetermined time interval T; (b) for the catalyst units of the Nth exhaust gas train, a value of an oxygen storage capacity is determined by applying the lambda value excitation of the exhaust gas during the time interval T and evaluating an associated lambda value reaction of the exhaust gas downstream of the exhaust gas recombination in a region of the common exhaust gas line and determining a catalyst diagnostic value in dependence on this value. Method for diagnosing a group of K catalyst units of a catalytic converter system of an exhaust system with N-exhaust lines of an internal combustion engine with K <N, wherein the N-exhaust lines are each equipped with a catalyst unit and combine downstream of the catalyst units in a common exhaust pipe and control a Lambda Value of the exhaust gas in the N-exhaust strands upstream of the catalyst units is possible, characterized in that the following steps are carried out: (a) the catalyst units of N - K exhaust strands are maintained in an oxygen-free state by exposure to a stoichiometric or rich exhaust gas for a predetermined time interval T; (b) for the catalyst units of the K other exhaust gas strands, a value of an oxygen storage capacity is determined by applying the lambda value excitation of the exhaust gas during the time interval T and evaluating an associated lambda value reaction of the exhaust gas downstream of the exhaust gas recombination in a region of the common exhaust gas line, and a catalyst diagnostic value is determined depending on this value. A method according to claim 1 or 2, characterized in that the oxygen-free held catalyst units are operated under constant conditions. Method according to at least one of the preceding claims, characterized in that for a catalyst unit identified as defective, steps (a) and (b) are repeated a predetermined number of times. Method according to at least one of the preceding claims, characterized in that the exhaust system has, in addition to the N-exhaust strands, further exhaust strands for which steps (a) and (b) are not performed. Method according to at least one of the preceding claims, characterized in that the steps (a) and (b) are carried out successively successively for a predetermined group of the N-exhaust strands. Method according to at least one of the preceding claims, characterized in that a value of an oxygen storage capability of the catalyst system is determined by applying the lambda excitation of the exhaust gas to the N catalyst units and evaluating an associated lambda value reaction of the exhaust gas in a region of the common exhaust gas line from this value, a catalyst system diagnosis value is determined and that, depending on this catalyst system diagnosis value, steps (a) and (b) are performed. Method according to at least one of the preceding claims, characterized in that a lambda sweep of predetermined amplitude and frequency is provided as lambda value excitation of the exhaust gas. Method according to at least one of the preceding claims, characterized in that the catalyst units are each formed as a precatalyst, main catalyst or a combination of precatalyst and main catalyst. Method according to at least one of the preceding claims, characterized in that in each case oxygen sensors are arranged upstream of the catalyst units of the N exhaust gas lines and in a region of the common exhaust gas line for determining the oxygen storage capacity. Method according to at least one of the preceding claims, characterized in that at least one of the upstream of the catalyst units arranged sensors is a broadband lambda probe, a step response lambda probe or a NOx sensor with a lambda value signal output. A method according to claim 10, characterized in that arranged in a region of the common exhaust pipe sensor is a broadband lambda probe, a step response lambda probe or a NOx sensor with a lambda value signal output. Device for diagnosing a catalyst unit of a catalytic converter system of an exhaust system with N-exhaust lines of an internal combustion engine, wherein the N-exhaust trains are each equipped with a catalyst unit and combine downstream of the catalyst device units in a common exhaust pipe, and with a mixture control device for controlling a lambda value of the exhaust gas in the N exhaust lines upstream of the catalyst units, characterized in that in each of the N exhaust lines upstream of the catalyst unit, an oxygen sensor and in one area an oxygen sensor is arranged in each case for the common exhaust gas line, and a control and evaluation device is provided which processes signals of the oxygen sensors, can influence the lambda value of the exhaust gas in the N exhaust gas strands by means of a fall-off device and can initiate the following steps: (a) the catalyst units of N-1 exhaust strands are maintained in an oxygen-free state by exposure to a stoichiometric or rich exhaust gas for a predetermined time interval T; (b) for the catalyst unit of the N-th exhaust gas line, a value of an oxygen storage capacity is determined by applying the lambda value excitation of the exhaust gas during the time interval T and evaluating an associated lambda value reaction of the exhaust gas downstream of the exhaust gas recombination in a region of the common exhaust gas line and determining a catalyst diagnostic value in dependence on this value. Apparatus according to claim 13, characterized in that the exhaust system in addition to the N-exhaust strands further exhaust strands, for which steps (a) and (b) are not provided. Apparatus according to claim 13 or 14, characterized in that the catalyst units are formed as a pre-catalyst, main catalyst or combination of pre- and main catalyst. Device according to at least one of claims 13 to 15, characterized in that the oxygen sensors are designed as a broadband lambda probe, as a step response lambda probe or as a NOx sensor with a lambda value signal output.

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