DE102018205452B4 - Method and arrangement for providing stable operating conditions for checking the functionality of an LNT catalytic converter - Google Patents

Abstract

Method for providing stable operating conditions for checking the functionality of an LNT catalytic converter (2) arranged in the exhaust line (6) of an internal combustion engine (5) forming part of a drive train (3), comprising the following steps: - decoupling the internal combustion engine (5) from remaining drive train (3), - ensuring a coupling of the internal combustion engine (5) with an electric machine (8), which is designed to drive the internal combustion engine (5), - determining the temperature of the LNT catalyst (2), - comparing the temperature of the LNT catalyst (2) with a minimum temperature and a maximum temperature, - if the temperature of the LNT catalyst (2) is between the minimum temperature and the maximum temperature, formation of stable operating conditions by means of driving the internal combustion engine (5) at an engine speed until reaching one Target motor speed by means of the electric machine (8), o keeping the motor speed constant at de r target engine speed by means of the electric machine (8), o performing a combustion process in the internal combustion engine (5) until an engine torque of the internal combustion engine (5) reaches a target engine torque and o keeping the engine torque constant at the target engine torque.

Description

The present invention relates to a method, a control and processing unit and an arrangement for providing stable operating conditions for checking the functionality of an LNT catalytic converter and a motor vehicle.

Exhaust gas aftertreatment devices are used to treat combustion gases (exhaust gases) after they have left the combustion chamber or the combustion chamber of an internal combustion engine, for example an internal combustion engine driving a motor vehicle. The treatment is usually carried out physically and chemically, sometimes using catalysts to influence chemical reactions.

For example, harmful nitrogen oxides (NO _x ) contained in a lean exhaust gas (λ> 1) can be temporarily stored in a so-called LNT catalytic converter (Lean NO _x trap), also referred to as NO _x storage catalytic converters, and then periodically reduced, according to a common process. by z. B. the internal combustion engine is operated with a substoichiometric, ie rich, air-fuel mixture (λ <1), so that the exhaust gas with reducing products having incompletely burned hydrocarbons, eg. B. carbon monoxide is enriched. An enrichment of the exhaust gas can also be done by post-injection of fuel, e.g. B. in a cylinder of the internal combustion engine or directly into the exhaust line.

However, the functionality of the LNT catalyst decreases with increasing operating time, which can be attributed, among other things, to contamination of the LNT catalyst with sulfur contained in the exhaust gas and to thermal aging as a result of high temperatures, such as occur, for example, when a particle filter is regularly regenerated or desulfurized is. If the functionality of the LNT catalyst is no longer sufficient, nitrogen oxides are no longer sufficiently removed from the exhaust gas and are instead released into the environment. In addition, further exhaust gas aftertreatment devices arranged downstream of the LNT catalytic converter can be adversely affected by the nitrogen oxides.

It is therefore necessary to regularly check the functionality of an LNT catalytic converter provided in the exhaust system. H. to monitor.

Most monitoring methods use a direct or indirect evaluation of the oxygen storage capacity during regeneration under rich conditions, since the oxygen storage capacity of the LNT catalyst decreases with increasing aging. Measurement data from lambda sensors arranged upstream and downstream of the LNT catalytic converter can be used for this. The result of such an evaluation is compared with a limit value or known measurement data in order to infer an aging condition of the LNT catalyst and to decide whether maintenance, repair, etc. of the LNT catalyst is required.

From the DE 10 2012 218 728 A1 a monitoring method is known which is based on the determination of a reducing agent slip, ie on a change in the reducing agent concentration downstream of the LNT catalytic converter. In order to determine the aging state of the LNT catalytic converter, the internal combustion engine is operated with a rich air / fuel mixture for a short period of time and the time profile of the signal of a lambda probe arranged downstream of the LNT catalytic converter is evaluated. This method requires an easily controllable, ie a slightly fluctuating, stable, lambda signal upstream of the LNT catalyst to be monitored.

That in the DE 10 2016 200 155 A1 The monitoring method disclosed uses the fact that, in addition to nitrogen oxides, oxygen is also stored in the LNT catalytic converter, which also reacts with the incompletely burned hydrocarbons contained therein during operation with a rich air / fuel mixture. Oxygen is stored, in particular, directly after switching from operation with a rich air / fuel mixture to operation with a lean air / fuel mixture. Based on the amount of oxygen stored or the course of a signal of a lambda probe arranged downstream of the LNT catalytic converter which correlates with the oxygen storage, conclusions can be drawn about the aging condition of the LNT catalytic converter.

The DE 10 2011 001 045 A1 discloses a method for diagnosing exhaust gas probes and / or catalytic converters, the diagnosis being carried out during sailing operation, ie when the internal combustion engine is decoupled.

From the DE 10 2015 200 769 A1 a method for monitoring an exhaust gas aftertreatment system with a NO _x storage catalytic converter in a hybrid electric motor vehicle is known. Here, the internal combustion engine is operated at a constant load point. The internal combustion engine and the electric motor are used together to provide a requested wheel torque. The torque generated by the internal combustion engine deviates from the requested wheel torque because the internal combustion engine is reached a value range of operating parameters of the NO _x storage catalytic converter is operated, the electric motor compensates for this difference. In other words, the internal combustion engine is coupled to the drive train during the monitoring of the NO _x storage catalytic converter and generates a torque which is transmitted to the wheels.

The DE 10 2017 201 643 A1 discloses a method for performing a reference measurement on a gas sensor arranged in an intake tract or an exhaust tract of an internal combustion engine of a hybrid electric drive of a motor vehicle. It is provided to decouple the internal combustion engine from the rest of the drive train during the reference measurement and to drive it by means of an electric motor of the hybrid electric drive. The fuel supply to the internal combustion engine is interrupted.

All monitoring procedures have in common that they must comply with the prescribed monitoring procedures (In-Use Performance Requirements, IUPR), which may a. specify a frequency of checking the functionality of the LNT catalytic converter. Since the behavior of an LNT catalyst depends to a large extent on its temperature, the known monitoring methods only provide reliable information about the functionality of the LNT catalyst in a relatively narrow temperature range, so that the required frequency of the check can often not be guaranteed.

The analysis of the oxygen storage capacity of the LNT catalyst is usually carried out under normal operating conditions, e.g. B. during normal driving of a vehicle when regeneration of the LNT catalyst is requested using a rich exhaust gas. In order to achieve the required accuracy, however, a certain stability of the lambda signal upstream of the LNT catalytic converter is required during the analysis of the oxygen storage capacity.

However, since the conditions in most regeneration processes are not sufficiently stable, the oxygen storage capacity can often not be analyzed with the required frequency. In addition, the results of the analysis of the oxygen storage capacity are strongly influenced by other factors, such as B. the temperature and space velocity, depending.

It is also known to provide an electrically operated clutch in a vehicle to separate the internal combustion engine from the wheels, e.g. B. during phases of a sailing operation (so-called coasting). As a result, the resistance in sailing operation can be reduced since entrainment of the internal combustion engine is avoided, which can save fuel. During the sailing operation, the internal combustion engine can be operated at idle or switched off.

The object of the present invention is therefore to specify possibilities with which the functionality of an LNT catalyst can be checked with sufficient frequency and accuracy.

This object is achieved by the subject matter of the independent claims. Advantageous developments of the invention are specified in the subclaims.

The basic idea of the invention is to drive the internal combustion engine at least by means of an electric machine in order to provide stable operating conditions under which an analysis of the oxygen storage capacity of the LNT catalyst can then take place. For example, the electric machine of a hybrid electric motor vehicle can be used to provide and maintain stable operating conditions during the analysis of the oxygen storage capacity. Here, the electric machine can be used to maintain a constant speed and a constant torque of the internal combustion engine.

A method according to the invention for providing stable operating conditions for checking the functionality of an LNT catalytic converter arranged in the exhaust line of an internal combustion engine forming part of a drive train has the following steps: decoupling the internal combustion engine from the rest of the drive train, ensuring coupling of the internal combustion engine with an electric machine, which is used for Driving the internal combustion engine is formed, determining the temperature of the LNT catalyst and comparing the temperature of the LNT catalyst with a minimum temperature and a maximum temperature.

An internal combustion engine, sometimes also referred to as an internal combustion engine, is to be understood as an internal combustion engine for converting chemical energy contained in the fuel into mechanical work. The internal combustion engine can be designed, for example, as a self-igniting or spark-ignited internal combustion engine. For example, motor gasoline or diesel can be used as fuel. Stated flow directions relate to the flow direction of the exhaust gas flow from the internal combustion engine in the direction of the exhaust.

The exhaust gas line is formed by an exhaust gas line through which the exhaust gas flow flows and in the catalysts and sensors are arranged so that the catalysts can also flow through the exhaust gas flow and the properties of the exhaust gas flow, for. B. its composition, temperature, etc., can be determined by means of the sensors. Stated flow directions relate to the flow direction of the exhaust gas flow from the internal combustion engine in the direction of the exhaust.

The internal combustion engine can by means of a clutch from the remaining drive train, that is, for. B. the wheels can be separated. The clutch can preferably be designed as an electrically operated clutch.

The electric machine may, for example, be the electric machine of a hybrid electric drive train, e.g. B. a hybrid electric motor vehicle. The electric machine can be provided at different positions of the hybrid electric drive train, e.g. B. at the P0 position, e.g. B. as a so-called belt integrated starter generator, BISG, at the P1 position, e.g. B. as a so-called crank integrated starter generator, CISG or at the P2 position.

If the electric machine is arranged in the P2 position, both clutches, i. H. the clutch between the internal combustion engine and the electric machine and the clutch between the electric machine and the transmission can be designed as electrically operated clutches. Here, the clutch between the electric machine and the transmission is opened during the sailing operation, i. H. the internal combustion engine is separated from the rest of the drive train by opening the clutch between the electric machine and the transmission, while the clutch between the electric machine and the internal combustion engine is or will be closed in order to ensure the coupling of the internal combustion engine to the electric machine.

Ensuring a coupling of the internal combustion engine to the electric machine means that the internal combustion engine and the electric machine are left in a coupled state, i. H. are operatively connected to one another, or, if this is not the case, are coupled to one another, for example likewise by means of a clutch, preferably an electrically operated clutch. There is also the possibility that the internal combustion engine and the electric machine are always coupled to each other, e.g. B. in a hybrid electric powertrain of the P0 or P1 configuration. In this case, the procedural step “ensuring a coupling of the internal combustion engine to the electric machine” is already fulfilled by providing an appropriately designed drive train.

Determining the temperature of the LNT catalyst can e.g. B. done by means of a temperature sensor. This can be arranged in the exhaust line, for example immediately upstream of the LNT catalytic converter, and can determine the temperature of the exhaust stream. The temperature of the LNT catalytic converter can then be derived from the temperature of the exhaust gas stream. Alternatively, the temperature of the LNT catalyst can be determined directly, e.g. B. by means of a temperature sensor arranged in the LNT catalyst.

The temperature of the LNT catalyst is then compared with a minimum and a maximum temperature. The minimum and maximum temperature can be set in such a way that an analysis of the oxygen storage capacity of the LNT catalytic converter can be carried out in the temperature range between the minimum and the maximum temperature. The minimum temperature can be, for example, 250 ° C, the maximum temperature, for example, 500 ° C.

If the temperature of the LNT catalyst is between the minimum temperature and the maximum temperature, stable operating conditions are formed in a next process step.

For this purpose, the internal combustion engine is driven by the electric machine until the engine speed reaches a target engine speed. This motor speed is then kept constant at the target motor speed by means of the electric machine. The setpoint engine speed is preferably in a range between 1500 and 2000 rpm. The setpoint engine torque should be selected so that stable control of the combustion air ratio is possible.

In addition, a combustion process is carried out in the internal combustion engine to increase the engine torque until a target engine torque is reached. The target engine torque can preferably be set so that a stable combustion air ratio λ is achieved. The engine torque is then kept constant at the target engine torque.

The coupling of the internal combustion engine to the electric machine enables, in comparison to an internal combustion engine without a coupled electric machine, a particularly precise setting of the engine speed and the engine torque as well as keeping the engine speed and the engine torque constant with little or no fluctuations. In other words, the electric machine drives the internal combustion engine and regulates the engine speed of the internal combustion engine. The internal combustion engine, on the other hand, is used to adjust the combustion air ratio, while the electric machine absorbs the engine torque of the internal combustion engine and keeps the engine speed of the internal combustion engine constant.

The measures described make it possible to provide stable operating conditions, in particular an accurate lambda signal upstream of the LNT catalytic converter which is subject to no or only slight fluctuations. These stable operating conditions make it possible to determine the oxygen storage capacity of the LNT catalytic converter with high accuracy and thus to test the functionality of the LNT catalytic converter. In addition, the stable operating conditions can be set largely independently of the current driving conditions, so that the oxygen storage capacity can also be determined with the required frequency. The driving behavior of a vehicle with which the described method is carried out is advantageously not influenced, or at least only slightly.

After the stable operating conditions have been established, the oxygen storage capacity of the LNT catalytic converter can be determined. For this purpose, the following steps can be carried out, for example: Applying a variable combustion air ratio to the LNT catalytic converter λ , Determine the time course of the combustion air ratio λ upstream and downstream of the LNT catalytic converter and determining the oxygen storage capacity of the LNT catalytic converter on the basis of the time profiles of the combustion air ratio λ upstream and downstream of the LNT catalyst.

To the LNT catalyst with a variable combustion air ratio λ to apply, the LNT catalyst can an exhaust gas stream with varying combustion air ratio λ be fed. For example, the exhaust gas stream can typically have a combustion air ratio λ have greater than 1. To create a combustion air ratio λ less than 1, either the internal combustion engine can already be operated with a rich air / fuel mixture or fuel is supplied to the exhaust gas stream. For the rest, reference is made to the introductory remarks on the determination of the oxygen storage capacity.

According to various design variants, the determined oxygen capacity can be compared with a minimum oxygen storage capacity. If the minimum oxygen storage capacity is undershot, a signal, for example an optical or acoustic signal, can then be output in order, for. B. to notify a driver of an insufficient oxygen storage capacity and necessary maintenance, repair, etc. of the LNT catalyst. As a result, a restricted function of the LNT catalytic converter can be recognized quickly, so that appropriate countermeasures can be initiated in order to avoid an undesired release of nitrogen oxides into the environment.

According to further embodiment variants, the oxygen storage capacity can be determined several times and an average oxygen storage capacity can be formed. The mean oxygen storage capacity can be compared to the minimum oxygen storage capacity. As a result, the oxygen storage capacity can advantageously be determined with a higher degree of accuracy, so that a statement about the functionality of the LNT catalytic converter can be made with greater reliability.

The number of determinations of the oxygen storage capacity can be individual or z. B. depending on the deviation of the individual values of the oxygen storage capacity from each other. A statistical evaluation of the measured values can be used here.

According to further embodiment variants, the oxygen storage capacity can be determined several times under different stable operating conditions with different target engine speeds and / or target engine torques. A combination of the described embodiment variants is also possible, in which the operating conditions are varied and the oxygen storage capacity is determined several times for each specific operating condition.

The determination of the oxygen storage capacity under different operating conditions enables the generation of a curve or area which represents the current functionality of the LNT catalyst or its aging condition. This can make it easy to identify outliers, so that more precise statements about the functionality of the LNT catalyst can be made.

According to further embodiment variants, the kinetic energy generated by the internal combustion engine can be recuperated, e.g. B. by the electric machine acting as a generator. The electrical energy generated in this way can be used, for example, to charge a rechargeable battery connected to the electric machine.

The kinetic energy that arises when the combustion process is carried out in the internal combustion engine can thus advantageously be used further by converting it into electrical energy. This can improve the overall energy balance.

A control and processing unit according to the invention for providing stable operating conditions for checking the functionality of an LNT catalytic converter arranged in the exhaust line of an internal combustion engine forming part of a drive line is designed to output a control signal for decoupling the internal combustion engine from the remaining drive line and a temperature of the LNT line. Compare catalyst with a minimum temperature and a maximum temperature.

In addition, the control and processing unit is designed to output a control signal to an electric machine for driving the internal combustion engine until an engine speed of the internal combustion engine reaches a target engine speed and for keeping the engine speed constant at the target engine speed, and a control signal to the internal combustion engine for performing a combustion process in the internal combustion engine until an engine torque of the internal combustion engine reaches a target engine torque, and to keep the engine torque constant at the target engine torque if the temperature of the LNT catalyst is between the minimum temperature and the maximum temperature.

The control and processing unit according to the invention can be used, for example, to carry out the method according to the invention explained above. Therefore, the above explanations serve to explain the method according to the invention also to describe the control and processing unit according to the invention. The advantages of the control and processing unit according to the invention correspond to those of the method according to the invention.

The control and processing unit can receive signals from lambda sensors and / or temperature sensors as input data, process these input data and control signals at actuators, e.g. B. output the internal combustion engine and the electric machine in response to the processed input data based on instructions or a programmed code according to one or more routines.

By means of the control and processing unit, the provision of the stable operating conditions can be carried out largely automatically.

The control and processing unit can be implemented in hardware and / or software and can be physically constructed in one or more parts. In particular, the control and processing unit can be part of an engine control or can be integrated into it. In a typical embodiment, the engine control of a motor vehicle functions as a control and processing unit.

According to various design variants, the control and processing unit can be designed to output a control signal for coupling the internal combustion engine to the electric machine.

Such a control signal can be output, for example, to an electronically actuated clutch, so that the provision of the stable operating conditions can be carried out completely automatically and no manual intervention, e.g. B. on the part of the driver, are required.

According to further embodiment variants, the control and processing unit can be designed to generate a control signal for changing the time profile of the combustion air ratio λ output an exhaust gas mixture leaving the internal combustion engine and an oxygen storage capacity of the LNT catalytic converter on the basis of time profiles of the combustion air ratio λ to determine upstream and downstream of the LNT catalyst.

Following the provision of stable operating conditions, this enables an automated check of the functionality of the LNT catalytic converter.

An arrangement according to the invention for providing stable operating conditions for checking the functionality of an LNT catalytic converter has a drive train with a clutch and an internal combustion engine, the internal combustion engine being able to be decoupled from the rest of the drive train by means of the clutch. In addition, the arrangement has an exhaust line connected to the internal combustion engine for receiving an exhaust gas mixture generated by the internal combustion engine, the LNT catalyst arranged in the exhaust line, an electric machine designed to drive the internal combustion engine, means for determining the temperature of the LNT catalyst and a control and processing unit, as described above.

The arrangement according to the invention can be used, for example, to carry out the method according to the invention explained above. Therefore, the above explanations serve to explain the method according to the invention also to describe the arrangement according to the invention. The advantages of the arrangement according to the invention correspond to those of the method according to the invention and its corresponding design variants.

A lambda sensor can be arranged upstream and downstream of the LNT catalytic converter.

A lambda sensor is to be understood as a sensor that delivers measurement signals from which the combustion air ratio λ , ie the ratio of the air mass actually available for combustion to the at least necessary stoichiometric air mass required for complete combustion is determined. The lambda sensor can be designed, for example, as a lambda sensor, which compares the residual oxygen content in the exhaust gas with the oxygen content of the current atmospheric air, from which the combustion air ratio can be determined. The lambda sensor can also be designed as a nitrogen oxide sensor, since such nitrogen oxide sensors can also output the combustion air ratio in addition to determining the nitrogen oxide content.

The combustion air ratios upstream or downstream of the LNT catalytic converter can be determined by means of the lambda sensor, the courses of which can be used to determine the oxygen storage capacity of the LNT catalytic converter. The functionality of the LNT catalytic converter can be checked on the basis of the oxygen storage capacity determined.

According to further design variants, the clutch can be designed as an electrically actuated clutch (e-clutch, e-clutch).

The internal combustion engine can thus be decoupled from the rest of the drive train by means of an electrically operated clutch. Such an E-clutch can, for example, replace a manual clutch of a manual transmission or be provided as an additional clutch in order, for. B. to enable a separation from an automatic transmission.

An electrically operated clutch usually has an electric actuator, which is controlled by an electronic control device of the arrangement, e.g. B. the described control and processing unit can be operated. The electrically operated clutch makes it possible to automatically, e.g. B. without driver intervention.

According to further embodiment variants, the electric machine can be designed to recuperate kinetic energy generated by the internal combustion engine. In other words, the electric machine can act as a generator that serves to convert kinetic energy generated by the internal combustion engine into electrical energy. This electrical energy can be used, for example, to charge a rechargeable battery connected to the electric machine. The energy balance can be improved by reusing the electrical energy.

Optionally, additional exhaust gas aftertreatment devices, e.g. B. an SCR catalyst may be arranged. Such an SCR catalytic converter is preferably arranged downstream of the LNT catalytic converter.

In addition, the arrangement can optionally have a high-pressure and / or a low-pressure exhaust gas recirculation.

A motor vehicle according to the invention has an arrangement with the features described above. Under a motor vehicle is a motor driven vehicle, e.g. B. to understand a land, air or water vehicle. The vehicle can be used as a hybrid electric vehicle, e.g. B. be designed as a mild hybrid electric vehicle or full hybrid electric vehicle.

• - Im Vergleich zu einer Überprüfung der Funktionsfähigkeit des LNT-Katalysators unter normalen Betriebsbedingungen werden die Bedingungen, z. B. das Verbrennungsluftverhältnis λ, stromaufwärts des LNT-Katalysators nicht durch den Fahrzeugführer und dessen Vorgaben beeinflusst.
• - Das Motordrehmoment des Verbrennungsmotors kann so gesteuert werden, z. B. auf ein Sollmotordrehmoment eingestellt werden, bei dem stabile Betriebsbedingungen einfach erreichbar sind und über eine ausreichend lange Zeitdauer aufrechterhalten werden können.
• - Die Sollmotordrehzahl und das Sollmotordrehmoment des Verbrennungsmotors können immer gleich gewählt werden, so dass die Streubreite der Messergebnisse abnimmt.
• - Die Überprüfung der Funktionsfähigkeit des LNT-Katalysators kann für mehrere vordefinierte Sollmotordrehzahlen und Sollmotordrehmomente des Verbrennungsmotors evaluiert werden, so dass eine Kurve oder Fläche erhalten werden kann, die den aktuellen Alterungszustand des LNT-Katalysators beschreibt. Die Verwendung der Kurve bzw. Fläche ermöglicht eine einfache Identifizierung von Ausreißern. Die Genauigkeit Aussagen über die Funktionsfähigkeit des LNT-Katalysators kann dadurch erhöht werden.

In summary, the following advantages can be realized with the described invention:

• - In comparison to a check of the functionality of the LNT catalyst under normal operating conditions, the conditions, e.g. B. the combustion air ratio λ , upstream of the LNT catalytic converter is not influenced by the driver and his specifications.
• - The engine torque of the internal combustion engine can be controlled, for. B. can be set to a target engine torque in which stable operating conditions are easily accessible and can be maintained over a sufficiently long period of time.
• - The target engine speed and the target engine torque of the internal combustion engine can always be selected the same, so that the spread of the measurement results decreases.
• - The check of the functionality of the LNT catalytic converter can be evaluated for several predefined target engine speeds and target engine torques of the internal combustion engine, so that a curve or area can be obtained which describes the current aging state of the LNT catalytic converter. The use of the curve or surface enables easy identification of outliers. This can increase the accuracy of statements about the functionality of the LNT catalytic converter.

• 1 eine schematische Darstellung eines beispielhaften Kraftfahrzeugs;
• 2 eine schematische Darstellung eines weiteren beispielhaften Kraftfahrzeugs; und
• 3 ein Flussdiagramm einer Ausführungsform eines Verfahrens.

Further advantages of the present invention are evident from the detailed description and the figures. The invention is based on the Illustrations and the following description explained in more detail. Show it:

• 1 a schematic representation of an exemplary motor vehicle;
• 2 a schematic representation of another exemplary motor vehicle; and
• 3 a flowchart of an embodiment of a method.

1 schematically shows an embodiment of a motor vehicle 1 , which is designed as a hybrid electric motor vehicle with a parallel hybrid drive train, with an arrangement according to the invention. The car 1 has a powertrain 3 for moving the wheels 16 with an internal combustion engine 5 that has four cylinders 15 has a clutch 4 , which is designed as an electrically operated clutch, and a transmission 17 on. It should be noted that the number of cylinders 15 is in no way restrictive and also internal combustion engines 5 with a different number of cylinders 15 , e.g. B. with six or eight cylinders 15 can be used. With the transmission 17 it can be an automatic transmission or a manual transmission.

The internal combustion engine 5 can be designed as a commercially available diesel or gasoline engine. The internal combustion engine 5 can be designed to carry out various combustion and mixture preparation processes and can be operated with different fuels. The present invention is of particular relevance for internal combustion engines 5 , which are operated at least temporarily in lean operation (with excess air) and with fuels from hydrocarbon compounds. Such internal combustion engines 5 encounter an exhaust gas mixture 7 which contains nitrogen oxides. Examples of this are commercially available car and truck diesel engines.

In the exemplary embodiment is the internal combustion engine 5 also an exhaust gas turbocharger assigned to an exhaust gas turbine 18 and a compressor 19 having. The presence of an exhaust gas turbocharger is only optional, ie the invention is not restricted to this.

There is also a supply air duct 13 for supply air 14 or one using the supply air 14 formed air-fuel mixture to the combustion chamber of the internal combustion engine 5 intended. In addition, the motor vehicle has 1 according to 1 via an exhaust line 6 to remove the from the internal combustion engine 5 formed exhaust gas mixture 7 ,

In the exhaust line 6 is an LNT catalyst 2 arranged. To the temperature of the LNT catalyst 2 can be determined on or in the LNT catalyst 2 medium 9 to determine the temperature of the LNT catalyst 2 , for example in the form of a temperature sensor. In addition, are in the exhaust system 6 upstream and downstream of the LNT catalyst 2 lambda sensors 11a . 11b to determine the combustion air ratio λ arranged.

Optionally, in the exhaust line 6 further exhaust gas aftertreatment devices, e.g. B. an SCR catalyst, may be arranged (not shown). For example, an SCR catalytic converter in the exhaust system 6 downstream of the LNT catalyst 2 be arranged.

It is also an electric machine 8th available, which is a so-called belt integrated starter generator (BISG), e.g. B. is with a nominal voltage of 12 V or 48 V, and which is arranged at the P0 position. Alternatively, the electric machine 8th be designed as a P1 or P2 electric machine and possibly with another, for. B. a P3 or P4 electric machine can be combined.

The electric machine 8th is for driving the internal combustion engine 5 educated. The electric machine also serves 8th the conversion of the internal combustion engine 2 generated kinetic energy into electrical energy. The electric machine 8th comes with a rechargeable battery 12 connected, which is designed to store the electrical energy.

The car 1 also has a control and processing unit 10 on that signaling with the means 9 to determine the temperature of the LNT catalyst, the lambda sensors 11a . 11b , the electric machine 8th , the internal combustion engine 5 and the clutch 4 connected is. The control and processing unit 10 can be formed as part of an engine control system or integrated into it.

Another embodiment of a motor vehicle according to the representation of the 2 differs from the embodiment shown in FIG 1 just that the means 9 to determine the temperature of the LNT catalyst 2 not on or in the LNT catalytic converter 2 , but as a temperature sensor in the exhaust system 6 immediately upstream of the LNT catalyst 2 is arranged. So it becomes the temperature of the exhaust gas mixture 7 immediately upstream of the LNT catalyst 2 determines what the temperature of the LNT catalyst 2 can be derived.

An exemplary method is referenced below 3 described. The method according to the invention can, for example, the steps S1 to S9 have and by means of motor vehicle 1 according to 1 or 2 be performed.

In one step S1 becomes the internal combustion engine 5 decoupled from the rest of the drive train, so that the motor vehicle 1 is in sailing mode. The decoupling can be done, for example, by releasing the coupling 4 take place by sending a corresponding control signal from the control and processing unit 10 is issued.

In addition, in the step S2 the coupling of the internal combustion engine 5 with the electric machine 8th ensured. Is it z. B. a hybrid electric motor vehicle with an arrangement of the electric machine 8th in the P0- (see 1 or 2 ) or P1 position, this is the electric machine 8th always with the internal combustion engine 5 coupled so that the coupling is always ensured. Is the electric machine 8th z. B. arranged in the P2 position of a hybrid electric motor vehicle, the coupling of the internal combustion engine 5 with the electric machine 8th ensured by the between electrical machine 8th and internal combustion engine 5 Arranged clutch is closed or remains closed.

In the next step S3 becomes the temperature of the LNT catalyst 2 determined. Then in one step S4 the temperature of the LNT catalyst 2 compared with a minimum temperature and a maximum temperature. Is the temperature of the LNT catalyst 2 between the minimum and maximum temperature, the procedure is then followed by step S5 continued. If not, the process goes back to step S3 ,

In step S5 becomes the internal combustion engine 5 by means of the electric machine 8th driven until the engine speed of the internal combustion engine 5 reached a target engine speed. The engine speed is kept constant at the target engine speed.

In step S6 becomes a combustion process in the internal combustion engine 5 carried out until the engine torque of the internal combustion engine reaches a target engine torque. The engine torque is kept constant at the target engine torque. At the end of the step S6 stable operating conditions are established.

In step 7 begins to determine the oxygen storage capacity of the LNT catalyst 2 by the LNT catalyst 2 with a variable combustion air ratio λ is applied. For this purpose, a corresponding control signal can be sent to the internal combustion engine 5 from the control and processing unit 10 be issued.

In step S8 is the time course of the combustion air ratio λ determined upstream and downstream of the LNT catalyst, e.g. B. by means of the lambda sensors 11a . 11b ,

Finally, in step S9 the determination of the oxygen storage capacity of the LNT catalyst 2 based on the time course of the combustion air ratio λ upstream and downstream of the LNT catalyst 2 based on which a statement about the functionality of the LNT catalyst 2 can be hit. The oxygen storage capacity can be determined by means of the control and processing unit 10 done by these sensor signals from the lambda sensors 11a . 11b receives and evaluates.

For example, the determined oxygen capacity can be compared with a minimum oxygen storage capacity. If the minimum oxygen storage capacity is not reached, a signal, e.g. B. an optical or acoustic signal, are output to indicate inadequate functionality of the LNT catalyst 2 to point. Optionally, the oxygen storage capacity can be repeated several times, e.g. B. can be determined several times in different stable operating conditions with different target engine speeds and / or target engine torques.

In the course of the entire process, the internal combustion engine can also 5 generated kinetic energy is converted into electrical energy and stored, ie recuperated. The electric machine can do this 8th accordingly designed as a generator and with a rechargeable battery 12 be connected.

LIST OF REFERENCE NUMBERS

1

motor vehicle

2

LNT catalyst

3

powertrain

4

clutch

5

internal combustion engine

6

exhaust gas line

7

Exhaust emissions

8th

electric machine

9

Means for determining the temperature

10

Control and processing unit

11a, 11b

lambda sensor

12

rechargeable battery

13

Zuluftstrang

14

supply air

15

cylinder

16

wheel

17

transmission

18

exhaust turbine

19

compressor

λ

Combustion air ratio

Claims (16)

Method for providing stable operating conditions for checking the functionality of an LNT catalytic converter (2) arranged in the exhaust line (6) of an internal combustion engine (5) forming part of a drive train (3), comprising the following steps: - decoupling the internal combustion engine (5) from the rest of the drive train (3), Ensuring a coupling of the internal combustion engine (5) to an electric machine (8) which is designed to drive the internal combustion engine (5), - determining the temperature of the LNT catalyst (2), Comparing the temperature of the LNT catalyst (2) with a minimum temperature and a maximum temperature, - If the temperature of the LNT catalyst (2) is between the minimum temperature and the maximum temperature, forming stable operating conditions using o driving the internal combustion engine (5) at an engine speed until a target engine speed is reached by means of the electric machine (8), o keeping the engine speed constant at the target engine speed by means of the electric machine (8), o Performing a combustion process in the internal combustion engine (5) until an engine torque of the internal combustion engine (5) reaches a target engine torque and o Keeping the engine torque constant at the target engine torque. Procedure according to Claim 1 , After the formation of the stable operating conditions, the oxygen storage capacity of the LNT catalyst (2) is determined. Procedure according to Claim 2 , the oxygen storage capacity being determined by performing the following steps: - applying a variable combustion air ratio λ to the LNT catalytic converter (2), - determining the time course of the combustion air ratio λ upstream and downstream of the LNT catalytic converter (2) and - determining the oxygen storage capacity of the LNT catalytic converter (2) on the basis of the time profiles of the combustion air ratio λ upstream and downstream of the LNT catalytic converter (2). Procedure according to Claim 2 or 3 , wherein the determined oxygen capacity is compared with a minimum oxygen storage capacity and a signal is output when the minimum oxygen storage capacity is undershot. Procedure according to one of the Claims 2 to 4 , wherein the oxygen storage capacity is determined several times and an oxygen storage capacity average is formed, and wherein the oxygen storage capacity average is compared with the minimum oxygen storage capacity. Procedure according to one of the Claims 2 to 5 , wherein the oxygen storage capacity is determined several times under different stable operating conditions with differing target engine speeds and / or target engine torques. Method according to one of the preceding claims, wherein kinetic energy generated by the internal combustion engine (5) is recuperated. Control and processing unit (10) for providing stable operating conditions for checking the functionality of an LNT catalytic converter (2) arranged in the exhaust line (6) of an internal combustion engine (5) forming part of a drive train (3), which is designed for this purpose - To output a control signal for decoupling the internal combustion engine (5) from the rest of the drive train (3), - To compare a temperature of the LNT catalyst (2) with a minimum temperature and a maximum temperature and - if the temperature of the LNT catalyst (2) is between the minimum temperature and the maximum temperature, ◯ a control signal to an electric machine (8) for driving the internal combustion engine (5) until an engine speed of the internal combustion engine (5) reaches a target engine speed and for keeping the engine speed constant at the target engine speed and ◯ to output a control signal to the internal combustion engine (5) for performing a combustion process in the internal combustion engine (5) until an engine torque of the internal combustion engine (5) reaches a target engine torque and for keeping the engine torque constant at the target engine torque. Control and processing unit (10) after Claim 8 , which is designed to - output a control signal for coupling the internal combustion engine (5) to the electric machine (8). Control and processing unit (10) after Claim 8 or 9 which is designed to - output a control signal for changing the time profile of the combustion air ratio λ of an exhaust gas mixture (7) leaving the internal combustion engine (5) and - an oxygen storage capacity of the LNT catalytic converter (2) on the basis of time profiles of the combustion air ratio λ upstream and downstream to determine the LNT catalyst (2). Arrangement for providing stable operating conditions for checking the functionality of an LNT catalytic converter (2), comprising: - a drive train (3) with a clutch (4) and an internal combustion engine (5), the internal combustion engine (5) by means of the clutch (4 ) can be decoupled from the rest of the drive train (3), - an exhaust line (6) adjoining the internal combustion engine (5) for receiving an exhaust gas mixture (7) generated by the internal combustion engine (5), - the LNT arranged in the exhaust line (6) Catalyst (2), - an electric machine (8), designed to drive the internal combustion engine (5), - means (9) for determining the temperature of the LNT catalyst (2) and - a control and processing unit (10) according to one of the Claims 8 to 10 , Arrangement after Claim 11 , comprising: - a lambda sensor (11 a) arranged upstream of the LNT catalytic converter (2) and - a lambda sensor (11b) arranged downstream of the LNT catalytic converter (2). Arrangement after Claim 11 or 12 , wherein the clutch (4) is designed as an electrically operated clutch. Arrangement according to one of the Claims 11 to 13 The electrical machine (8) is designed to recuperate kinetic energy generated by the internal combustion engine (5). Motor vehicle (1) with an arrangement according to one of the Claims 11 to 14 , Motor vehicle (1) after Claim 15 , trained as a hybrid electric motor vehicle.

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