DE102018205452A1 - Method and arrangement for providing stable operating conditions for checking the operability of an LNT catalyst - Google Patents

Abstract

A method is provided for providing stable operating conditions for checking the operability 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. The method comprises the following steps: decoupling of the internal combustion engine 5 from the rest of the 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 LNT catalyst 2 having 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 by driving the engine 5 at an engine speed until reaching a target engine speed by the electric machine 8, keeping constant the engine speed at the target engine speed by means of the electric machine 8, performing a combustion operation in the internal combustion engine 5 to a motor torque of the internal combustion engine 5 reaches a target engine torque and keeping the engine torque at the target engine constant In addition, a control and processing unit 10 and an arrangement with such a control and processing unit 10 and a motor vehicle 1 are specified.

Description

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

Exhaust 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 mostly carried out by physicochemical means, partly by using catalysts to influence chemical reactions.

For example, in a lean exhaust gas (λ> 1) contained harmful nitrogen oxides (NO _x ) according to a common method first in so-called LNT catalysts (Lean NO _x trap), also referred to as NO _x storage catalysts, cached and then periodically reduced, by z. B. the internal combustion engine with a substoichiometric, ie fat, air-fuel mixture (λ <1) is operated, so that the exhaust gas with reducing acting products incompletely burned hydrocarbons, eg. As carbon monoxide enriched. An enrichment of the exhaust gas can also by means of post injection of fuel, for. B. in a cylinder of the engine or directly into the exhaust system, done.

However, the functionality of the LNT catalyst decreases with increasing operating time, which is due, inter alia, to contamination of the LNT catalyst with sulfur contained in the exhaust gas as well as to thermal aging as a result of high temperatures, such as occur in a regularly scheduled particle filter regeneration or desulfurization is. If the functionality of the LNT catalyst is no longer sufficient, nitrogen oxides are no longer sufficiently removed from the exhaust gas and released into the environment instead. In addition, downstream of the LNT catalyst arranged further exhaust aftertreatment devices can be affected by the nitrogen oxides.

It is therefore necessary to regularly check the operability of an LNT catalyst provided in the exhaust system, d. H. to monitor.

Most monitoring methods use a direct or indirect evaluation of oxygen storage capacity during regeneration under rich conditions as the oxygen storage capacity of the LNT catalyst decreases with aging. For this purpose, measurement data from upstream and downstream of the LNT catalyst arranged lambda sensors can be used. The result of such evaluation is compared with a threshold or known measurement data to infer an aging condition of the LNT catalyst and decide whether maintenance, repair, etc. of the LNT catalyst is required.

From the DE 10 2012 218 728 A1 For example, a monitoring method is known that relies on the determination of a reductant slip, ie, a change in reductant concentration downstream of the LNT catalyst. In order to determine the aging state of the LNT catalyst, the internal combustion engine is operated for a short period of time with a rich air-fuel mixture and the time profile of the signal of a lambda probe arranged downstream of the LNT catalytic converter is evaluated. This method requires a well controllable, ie, a small, steady, lambda signal upstream of the LNT catalyst to be monitored.

That in the DE 10 2016 200 155 A1 The disclosed monitoring method utilizes the fact that in addition to nitrogen oxides, oxygen is also stored in the LNT catalyst, which also reacts with the incompletely burned hydrocarbons contained therein during operation with a rich air-fuel mixture. Specifically, the storage of oxygen occurs immediately after switching from a rich air-fuel mixture operation to a lean air-fuel mixture operation. On the basis of the amount of stored oxygen or correlated with the oxygen storage course of a signal downstream of the LNT catalyst arranged lambda probe conclusions about the aging state of the LNT catalyst can be drawn.

Common to all monitoring procedures is that they must comply with mandatory in-use performance requirements (IUPRs), which may include: a. specify a frequency of checking the functionality of the LNT catalyst. Since the behavior of an LNT catalyst is highly dependent on its temperature, however, the known monitoring methods provide reliable information about the functionality of the LNT catalyst only 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, eg. B. during a normal driving operation of a vehicle when a regeneration of the LNT catalyst is requested by means of a rich exhaust gas. However, to achieve the required accuracy, some stability of the lambda signal upstream of the LNT catalyst is required during the oxygen storage capacity analysis.

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

It is also known to provide an electrically operated clutch in a vehicle to separate the engine from the wheels, for. B. during phases of a sailing operation (so-called coasting). As a result, the resistance in the sailing mode can be reduced because entrainment of the internal combustion engine is avoided, whereby fuel can be saved. During sailing operation, the engine may be idled or shut down.

It is therefore an object of the present invention to specify ways in which the functionality of an LNT catalyst can be tested with sufficient frequency and accuracy.

This object is achieved by the subject matters 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 catalytic converter can take place. For example, the electric machine of a hybrid electric vehicle can be used to provide and maintain stable operating conditions during the analysis of the oxygen storage capacity. In this case, 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 operability of an LNT catalytic converter arranged in the exhaust line of an internal combustion engine forming part of a drive train comprises the following steps: decoupling of the internal combustion engine from the remaining drive train, ensuring a coupling of the internal combustion engine with an electric machine that 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 understood to mean 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 externally ignited internal combustion engine. As fuel, for example, motor gasoline or diesel can be used. Specified flow directions refer to the flow direction of the exhaust gas flow from the engine in the direction of the exhaust.

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

The internal combustion engine can by means of a clutch from the rest of the drive train, ie z. As the wheels are separated. The coupling may preferably be formed as an electrically actuated clutch.

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

In the case of an arrangement of the electric machine in the P2 position, both clutches, ie the clutch between the internal combustion engine and the electric machine as well as the clutch between the electric machine and the transmission can be designed as electrically operated clutches. In this case, the clutch between the electric machine and transmission is opened during the sailing operation, ie the internal combustion engine is separated by opening the coupling between the electric machine and transmission from the rest of the drive train, while the clutch is closed between electric motor and internal combustion engine or is to ensure the coupling of the internal combustion engine with the electric machine.

Ensuring a coupling of the internal combustion engine with the electric machine means that the internal combustion engine and the electric machine are left in a coupled state, i. H. are drivingly connected to each other, or, if this is not the case, are coupled together, for example, also by means of a clutch, preferably an electrically actuated clutch. There is also the possibility that the internal combustion engine and the electric machine are always coupled together, for. In a hybrid electric powertrain of the P0 or P1 configuration. In this case, the method step "ensuring a coupling of the internal combustion engine with the electric machine" is already fulfilled by the provision of a suitably designed drive train.

Determining the temperature of the LNT catalyst may, for. B. by means of a temperature sensor. This can be arranged in the exhaust gas line, for example immediately upstream of the LNT catalyst, and determine the temperature of the exhaust gas flow. Based on the temperature of the exhaust gas stream, the temperature of the LNT catalyst can then be derived. 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 to a minimum and a maximum temperature. The minimum and maximum temperatures may be set or may be such that an analysis of the oxygen storage capacity of the LNT catalyst may be performed in the temperature range between the minimum and maximum temperatures. The minimum temperature may for example be 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. Subsequently, this engine speed is kept constant at the target engine speed by means of the electric machine. Preferably, the target engine speed is in a range between 1500 and 2000 rpm. The target engine torque should be selected so that a stable control of the combustion air ratio is possible.

In addition, a combustion operation is performed in the internal combustion engine to increase the engine torque until a target engine torque is reached. The target engine torque may preferably be set so as to have a stable combustion air ratio λ is reached. Subsequently, the engine torque is kept constant at the target engine torque.

The coupling of the internal combustion engine with the electric machine allows in comparison to an internal combustion engine without a coupled electric machine, a particularly accurate adjustment of the engine speed and the engine torque and keeping the engine speed and the engine torque with at most slight fluctuations. In other words, the electric machine drives the engine and regulates the engine speed of the engine. The internal combustion engine, on the other hand, serves to adjust the combustion air ratio during which the electric machine receives the engine torque of the internal combustion engine and keeps the engine speed of the internal combustion engine constant.

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

After forming the stable operating conditions, the oxygen storage capacity of the LNT catalyst can be determined. For this purpose, for example, the following steps can be performed: applying the LNT catalyst with a variable combustion air ratio λ , Determining the time course of the combustion air ratio λ upstream and downstream of the LNT catalyst and determining the oxygen storage capacity of the LNT catalyst based on the timing of the combustion air ratio λ upstream and downstream of the LNT catalyst.

To the LNT catalyst with a variable combustion air ratio λ can apply to the LNT catalyst Exhaust gas flow with varying combustion air ratio λ be supplied. For example, the exhaust gas stream usually has a combustion air ratio λ greater than 1. For generating a combustion air ratio λ smaller than 1, either the internal combustion engine can already be operated with a rich air-fuel mixture or the exhaust gas flow is supplied with fuel. Incidentally, reference is made to the introductory statements for determining the oxygen storage capacity.

According to various embodiments, the determined oxygen capacity can be compared with a minimum oxygen storage capacity. If the minimum oxygen storage capacity is undershot, then a signal, for example an optical or acoustic signal, can be output in order, for. As a driver to a low oxygen storage capacity and a required maintenance, repair, etc. of the LNT catalyst point out. As a result, a limited function of the LNT catalyst can be detected quickly, so that appropriate countermeasures can be initiated in order to avoid an undesirable release of nitrogen oxides into the environment.

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

The number of oxygen storage capacity determinations may be individual or z. B. depending on the deviation of the individual values of the oxygen storage capacity of each other or be set. Here, a statistical evaluation of the measured values can be used.

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

The determination of the oxygen storage capacity under different operating conditions makes it possible to generate a curve or area which represents the current functionality of the LNT catalyst or its aging state. This can allow for easy identification of outliers so that more accurate statements about the functionality of the LNT catalyst are possible.

According to further embodiments, the kinetic energy generated by the internal combustion engine can be recuperated, z. B. by the electric machine acts as a generator. The electrical energy generated in this case can be used, for example, to charge a rechargeable battery connected to the electric machine.

The resulting in the implementation of the combustion process in the engine kinetic energy can thus be advantageously used by being converted into electrical energy. The energy balance can be improved as a whole.

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 a part of a drive train is designed to output a control signal for decoupling the internal combustion engine from the rest of the drive train and to set a temperature of the LNT. Catalyst with a minimum temperature and a maximum temperature to compare.

In addition, the control and processing unit is configured 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 to keep the engine speed constant at the target engine speed and a control signal to the internal combustion engine to perform a combustion operation in the internal combustion engine until an engine torque of the internal combustion engine reaches a target engine torque, and outputting the engine torque 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 for the description of 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 send control signals to actuators, e.g. The engine and the electric machine, in response to the processed input data based on instructions or a programmed code corresponding to one or more routines.

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

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

According to various embodiments, the control and processing unit may be configured to output a control signal for coupling the internal combustion engine with the electric machine.

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

According to further embodiments, the control and processing unit may be configured to provide a control signal for changing the time profile of the combustion air ratio λ output of the internal combustion engine leaving exhaust gas mixture and an oxygen storage capacity of the LNT catalyst based on temporal profiles of the combustion air ratio λ upstream and downstream of the LNT catalyst.

This allows an automated check of the functionality of the LNT catalyst following the provision of stable operating conditions.

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, wherein the internal combustion engine can be decoupled from the rest of the drive train by means of the clutch. In addition, the arrangement has an exhaust gas line adjoining the internal combustion engine for receiving an exhaust gas mixture produced by the internal combustion engine, the LNT catalytic converter arranged in the exhaust gas line, an electric machine designed to drive the internal combustion engine, means for determining the temperature of the LNT catalytic converter 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 for the description of 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 variants.

Upstream and downstream of the LNT catalyst, a lambda sensor may be arranged in each case.

A lambda sensor is to be understood as meaning a sensor which delivers measurement signals which make up the combustion air ratio λ ie, the ratio of the actual air mass available for combustion to the minimum necessary stoichiometric air mass required for complete combustion. The lambda sensor can be designed, for example, as a lambda probe, which compares the residual oxygen content in the exhaust gas with the oxygen content of the instantaneous 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 the determination of the nitrogen oxide content.

By means of the lambda sensor, the combustion air conditions upstream or downstream of the LNT catalyst can be determined, from the progress of which the oxygen storage capacity of the LNT catalyst can be determined. On the basis of the determined oxygen storage capacity, the functionality of the LNT catalyst can be checked.

According to further embodiments, the clutch may be formed 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 actuated clutch. Such an E-clutch can for example replace a manual clutch of a manual transmission or as be provided additional coupling to z. B. to allow a separation of an automatic transmission.

An electrically actuated clutch usually has an electric actuator which is controlled by an electronic control device of the arrangement, for. B. the described control and processing unit, can be operated. The electrically operated clutch allows the engine from the drive train automatically, z. B. without intervention of the driver to decouple.

According to further embodiments, the electric machine may 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 engine into electrical energy. This electrical energy can be used, for example, to charge a rechargeable battery connected to the electric machine. By further use of electrical energy, the energy balance can be improved.

Optionally, in the exhaust system further exhaust aftertreatment devices, eg. As an SCR catalyst can be arranged. Such an SCR catalyst is preferably arranged downstream of the LNT catalyst.

In addition, the arrangement may 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 driven by a motor vehicle, for. B. to understand a land, air or water craft. The vehicle may be used as a hybrid electric vehicle, e.g. B. as Mildhybridelelektrofahrzeug or Vollhybridelelektrofahrzeug, be formed.

• - 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:

• - Compared to a review of the functionality of the LNT catalyst under normal operating conditions, the conditions, eg. B. the combustion air ratio λ , upstream of the LNT catalyst is not affected by the vehicle operator and its specifications.
• - The engine torque of the engine can be controlled, for. B. can be set to a desired engine torque at the 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 engine can always be chosen the same, so that the spread of the measurement results decreases.
• The LNT catalytic converter capability test can be evaluated for a plurality of predefined engine target engine speeds and engine target torques so that a curve or area describing the current aging condition of the LNT catalyst can be obtained. The use of the curve or surface allows easy identification of outliers. The accuracy statements about the functionality of the LNT catalyst can be increased thereby.

• 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 will become apparent from the detailed description and the drawings. The invention will be explained in more detail with reference to the figures and the description below. 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 vehicle with a parallel hybrid drive train, with an inventive arrangement. The car 1 has a drive train 3 to move the wheels 16 with an internal combustion engine 5 that has four cylinders 15 has a clutch 4 , which is designed as an electrically actuated clutch, and a transmission 17 on. It should be noted that the number of cylinders 15 is in no way limiting and also combustion engines 5 with a different number of cylinders 15 , z. B. with six or eight cylinders 15 can be used. In the transmission 17 it can be an automatic transmission or a manual transmission.

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

In the embodiment, the internal combustion engine 5 also associated with an exhaust gas turbocharger, which is an exhaust gas turbine 18 and a compressor 19 having. The presence of an exhaust gas turbocharger is merely optional, that is, the invention is not limited thereto.

Furthermore, there is a Zuluftstrang 13 for supplying supply air 14 or one by means of 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 system 6 for discharging the engine 5 formed exhaust gas mixture 7 ,

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

Optionally, in the exhaust system 6 further exhaust aftertreatment devices, eg. As 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.

In addition, an electric machine 8th existing, which is a so-called belt integrated starter generator (BISG), z. B. with a rated 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, z. As a P3 or P4 electric machine combined.

The electric machine 8th is for driving the internal combustion engine 5 educated. In addition, the electric machine is used 8th the conversion of the combustion engine 2 generated kinetic energy into electrical energy. The electric machine 8th is 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, the signal technically with the means 9 for determining the temperature of the LNT catalyst, the lambda sensors 11a . 11b , the electric machine 8th , the internal combustion engine 5 as well as the clutch 4 connected is. The control and processing unit 10 may be formed as part of a motor control or integrated into this.

A further embodiment of a motor vehicle according to the representation of 2 differs from the embodiment according to the illustration of 1 only in that the means 9 for determining the temperature of the LNT catalyst 2 not on or in the LNT catalyst 2 , but as a temperature sensor in the exhaust system 6 immediately upstream of the LNT catalyst 2 is arranged. It is therefore the temperature of the exhaust gas mixture 7 immediately upstream of the LNT catalyst 2 determines the temperature of the LNT catalyst 2 can be derived.

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

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

In addition, in step S2 the coupling of the internal combustion engine 5 with the electric machine 8th ensured. Is it z. B. to a hybrid electric 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 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 vehicle, the coupling of the internal combustion engine 5 with the electric machine 8th ensured by the between electric machine 8th and internal combustion engine 5 arranged clutch is closed or remains closed.

In the following 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 the maximum temperature, the procedure is subsequently followed by step S5 continued. If not, the procedure 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 reaches 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 performed 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 formed.

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

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

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

For example, the determined oxygen capacity can be compared to a minimum oxygen storage capacity. If the minimum oxygen storage capacity falls below a signal, z. As an optical or acoustic signal, issued to an insufficient functionality of the LNT catalyst 2 to point. Optionally, the oxygen storage capacity may be repeated several times, e.g. B. several times at different stable operating conditions with different target engine speeds and / or target engine torque can be determined.

In the course of the entire process can also by the internal combustion engine 5 generated kinetic energy is converted into electrical energy and stored, ie recuperated be. For this purpose, the electric machine 8th designed accordingly 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 gas mixture

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

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102012218728 A1 [0007]
• DE 102016200155 A1 [0008]

Claims (16)

Method for providing stable operating conditions for checking the operability 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 remaining drive train (3), Ensuring a coupling of the internal combustion engine (5) with an electric machine (8) 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 by means of o driving the internal combustion engine (5) with an engine speed until reaching a target engine speed by means of the electric machine (8), o Keeping constant the engine speed 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 Constant maintenance of the engine torque at the target engine torque. Method according to Claim 1 wherein, after forming the stable operating conditions, the oxygen storage capacity of the LNT catalyst (2) is determined. Method according to Claim 2 in which the oxygen storage capacity is determined by performing the following steps: - charging the LNT catalyst (2) with a variable combustion air ratio λ, - determining the time profile of the combustion air ratio λ upstream and downstream of the LNT catalyst (2) and - determining the oxygen storage capacity of the LNT catalyst (2) based on the timing of the combustion air ratio λ upstream and downstream of the LNT catalyst (2). Method 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 falling below the minimum oxygen storage capacity. Method according to one of Claims 2 to 4 wherein the oxygen storage capacity is determined multiple times and an oxygen storage capacity average is formed and wherein the oxygen storage capacity average is compared to the minimum oxygen storage capacity. Method according to one of Claims 2 to 5 wherein the oxygen storage capacity is determined several times at different stable operating conditions with different target engine speeds and / or target engine torques. Method according to one of the preceding claims, wherein the kinetic energy generated by the internal combustion engine (5) is recuperated. Control and processing unit (10) for providing stable operating conditions for checking the operability of a in the exhaust line (6) of a part of a drive train (3) forming the internal combustion engine (5) arranged LNT catalyst (2), which is designed 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 to keep the engine speed constant at the target engine speed and ◯ a control signal to the internal combustion engine (5) for performing a combustion operation in the internal combustion engine (5) until an engine torque of the internal combustion engine (5) reaches a target engine torque, and to output the engine torque at the target engine torque. Control and processing unit (10) according to Claim 8 adapted to output a control signal for coupling the internal combustion engine (5) to the electric machine (8). Control and processing unit (10) according to 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 leaving the internal combustion engine, and an oxygen storage capacity of the LNT catalytic converter based on 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 operability 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) being operated by means of the clutch (4 ) can be decoupled from the remaining 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 system 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 Claims 8 to 10 , Arrangement according to 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 according to Claim 11 or 12 , wherein the clutch (4) is designed as an electrically operated clutch. Arrangement according to one of Claims 11 to 13 wherein the electric machine (8) is designed for recuperation of kinetic energy generated by the internal combustion engine (5). Motor vehicle (1) with an arrangement according to one of Claims 11 to 14 , Motor vehicle (1) according to Claim 15 , designed as a hybrid electric vehicle.

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