Method for determining nitrogen oxide and / or ammonia content in exhaust gas of internal combustion engine and exhaust system

Abstract

The invention relates to a method for determining a nitrogen oxide content and / or ammonia content in the exhaust gas of an internal combustion engine, the internal combustion engine having a catalytic converter (100), preferably a three-way catalytic converter, arranged in the exhaust gas system (10) of the internal combustion engine, and an exhaust gas sensor (110) arranged downstream of the catalytic converter (100). The method according to the invention comprises: determining an operating state of the internal combustion engine, which indicates lean operation or rich operation of the internal combustion engine; generating at least one signal by means of the exhaust gas sensor (110); and determining the nitrogen oxide content and / or ammonia content in the exhaust gas of the internal combustion engine at least partially based on the determined operating state of the internal combustion engine and at least partially based on at least one signal of the exhaust gas sensor (110).

Description

Technical Field

[0001] The present invention relates to a method for determining the nitrogen oxide content and / or ammonia content in the exhaust gas of an internal combustion engine and an exhaust system, in particular to a method for evaluating the nitrogen oxide content and / or ammonia content in the exhaust gas of an internal combustion engine, a signal of an exhaust gas sensor arranged in the exhaust system of an internal combustion engine downstream of a catalytic converter, preferably a three-way catalytic converter. Background Art

[0002] Catalytic converters are used for exhaust gas aftertreatment in vehicles in order to convert air pollutants and prevent them from being discharged into the surrounding environment. In exhaust gas aftertreatment with the aid of a three-way catalytic converter, carbon monoxide (CO), nitrogen oxides (NOx) and unburned hydrocarbons (HC) are converted into carbon dioxide (CO2), nitrogen (N2) and water (H2O).

[0003] The control or regulation of the air-fuel mixture for the internal combustion engine is carried out by means of a cascade control, which consists of an inner control loop, which regulates the lambda value upstream of the catalyst, and an outer control loop, which regulates the lambda value downstream of the catalyst. The catalyst should be kept in an optimal conversion window in particular. For this purpose, it is desirable to control or regulate the oxygen loading of the catalyst, in particular of the three-way catalyst, in such a way that the catalyst is saturated or loaded with about 50% oxygen. This ensures sufficient safety against possible failures of the system in the lean or rich direction. Summary of the invention

[0004] The object of the present invention is to provide a method and an exhaust system with which the nitrogen oxide content and / or the ammonia content in the exhaust gas of an internal combustion engine can be determined as simply and accurately as possible.

[0005] This task is solved by the method according to the present invention and the exhaust system according to the present invention. The preferred design scheme includes: determining the lambda threshold value based on the temperature of the exhaust gas, the temperature of the catalyst, the exhaust mass flow, the exhaust volume flow, the exhaust speed and / or the aging state of the catalyst, or predetermining the lambda threshold value as a fixed value; determining the exhaust mass flow, wherein, when the determined exhaust mass flow is greater than the predetermined exhaust mass flow threshold value, the nitrogen oxide content and / or the ammonia content in the exhaust gas of the internal combustion engine is also determined at least partially based on the mass flow factor; wherein the mass flow factor is determined based on the temperature of the exhaust gas, the temperature of the catalyst, the exhaust mass flow, the exhaust volume flow, the exhaust speed and / or the aging state of the catalyst; determining the sensitivity of the exhaust gas sensor to ammonia, wherein, when determining the internal The method comprises the steps of: taking into account the determined sensitivity of the exhaust gas sensor to ammonia when determining the ammonia content in the exhaust gas of the internal combustion engine; determining the carbon monoxide content in the exhaust gas of the internal combustion engine at least partially based on the determined ammonia content in the exhaust gas of the internal combustion engine and at least partially based on a carbon monoxide-related factor, and / or determining the hydrocarbon content in the exhaust gas of the internal combustion engine at least partially based on the determined ammonia content in the exhaust gas of the internal combustion engine and at least partially based on a hydrocarbon-related factor; wherein the carbon monoxide-related factor and / or the hydrocarbon-related factor are determined based on the temperature of the exhaust gas, the temperature of the catalyst, the exhaust mass flow, the exhaust volume flow, the exhaust velocity and / or the aging state of the catalyst.

[0006] The invention is essentially based on the idea that in a catalytic converter, in particular a three-way catalytic converter, when there is a lack of oxygen in the exhaust gas, that is, in rich exhaust gas, ammonia is produced, but the nitrogen oxides in the exhaust gas are almost completely reduced in the catalytic converter. When there is an excess of oxygen, that is, in lean exhaust gas, the catalytic converter can only incompletely reduce the nitrogen oxides in the exhaust gas. Therefore, when the lambda value is known, the nitrogen oxide content and / or the ammonia content in the exhaust gas downstream of the catalytic converter can be determined. In addition, the invention also uses the fact that an exhaust gas sensor, such as a nitrogen oxide sensor, indicates the sum of the nitrogen oxide content and the ammonia content based on its (transverse) sensitivity to ammonia, and the two contents can be determined by determining the operating state of the internal combustion engine. Of course, if the operating state of the internal combustion engine is known, that is, it is known whether the internal combustion engine is running lean or rich, then the ammonia content and / or the nitrogen oxide content in the exhaust gas can be determined from the signal of the exhaust gas sensor.

[0007] Therefore, according to one aspect of the present invention, a method for determining the nitrogen oxide content and / or ammonia content in the exhaust gas of an internal combustion engine is disclosed, the internal combustion engine having a catalytic converter, preferably a three-way catalytic converter, arranged in the exhaust gas system of the internal combustion engine and an exhaust gas sensor arranged downstream of the catalytic converter. The method according to the present invention comprises: determining an operating state of the internal combustion engine, which operating state can indicate whether it is lean operation or rich operation; generating at least one signal by means of the exhaust gas sensor; and determining the nitrogen oxide content and / or ammonia content in the exhaust gas of the internal combustion engine at least partially based on the determined operating state of the internal combustion engine and at least partially based on at least one signal of the exhaust gas sensor.

[0008] With knowledge of the operating state of the internal combustion engine, the nitrogen oxide content and / or the ammonia content can be determined from the signal of the exhaust gas sensor, as already mentioned above. If, for example, the internal combustion engine is running rich, then almost all the nitrogen oxides are reduced in the catalytic converter. In addition, ammonia is produced in the catalytic converter due to the lack of oxygen, and the signal of the exhaust gas sensor therefore almost completely indicates the ammonia content in the exhaust gas. Furthermore, the signal of the exhaust gas sensor can be evaluated to distinguish between the nitrogen oxide content and the ammonia content while taking into account the operating state of the internal combustion engine.

[0009] In a preferred embodiment, the method according to the invention further comprises: determining a lambda value by means of an exhaust gas sensor. Here, the operating state of the internal combustion engine is determined at least partially based on the determined lambda value. In particular, it can be determined from the determined lambda value whether the operating state of the internal combustion engine involves lean operation or rich operation, wherein it can be inferred from this in turn to what extent ammonia is generated or not generated in the catalytic converter, preferably in a three-way catalytic converter.

[0010] When the determined lambda value is greater than the lambda threshold, the signal generated by at least one of the exhaust gas sensors preferably indicates the nitrogen oxide content in the exhaust gas. In addition, when the determined lambda value is less than the lambda threshold, the signal generated by at least one of the exhaust gas sensors indicates the ammonia content in the exhaust gas.

[0011] This is based in particular on the fact that when the lambda threshold is exceeded, there is lean exhaust gas in the exhaust gas, that is to say an excess of oxygen, and the signal of the exhaust gas sensor therefore indicates the nitrogen oxide content in the exhaust gas. In contrast, when the lambda threshold is exceeded, there is rich exhaust gas, that is to say a lack of oxygen in the exhaust gas, and the signal of the exhaust gas sensor therefore essentially indicates the ammonia content in the exhaust gas.

[0012] In a preferred design of the method according to the present invention, the lambda threshold is predetermined as a fixed value, for example 1.0 or 200 mV, or the lambda threshold is dynamically determined based on the temperature of the exhaust gas, the temperature of the catalyst, the exhaust mass flow, the exhaust volume flow, the exhaust speed and / or the aging state of the catalyst and is thus variably adapted according to operating parameters of the internal combustion engine and / or the exhaust system.

[0013] In another preferred embodiment, the method according to the present invention further comprises: determining the exhaust gas mass flow. Here, when the determined exhaust gas mass flow is greater than a predetermined mass flow threshold, the nitrogen oxide content and / or ammonia content in the exhaust gas of the internal combustion engine is also determined at least partially based on the mass flow factor.

[0014] In particular, even under rich exhaust gas conditions, incomplete conversion of nitrogen oxides may still occur at high exhaust gas mass flows due to insufficient residence time of the exhaust gas in the catalyst. Therefore, in this state, both nitrogen oxides and ammonia may be present in the exhaust gas downstream of the catalyst. Therefore, in this preferred embodiment of the invention, it is provided that a mass flow factor is taken into account when a predetermined exhaust gas mass flow threshold is exceeded, from which the ammonia content and the nitrogen oxide content in the exhaust gas can then be determined simultaneously from the signal of the exhaust gas sensor. The mass flow factor is particularly designed to separate the signal of the exhaust gas sensor into a nitrogen oxide signal indicating the nitrogen oxide content and an ammonia signal indicating the ammonia content.

[0015] The mass flow factor is preferably determined based on the temperature of the exhaust gas, the temperature of the catalyst, the exhaust mass flow, the exhaust volume flow, the exhaust velocity and / or the catalyst aging state. The mass flow factor can therefore be a factor dynamically adapted to the operating parameters of the internal combustion engine and / or the exhaust system.

[0016] In another advantageous embodiment, the method according to the invention further comprises: determining the sensitivity of the exhaust gas sensor to ammonia, wherein the determined sensitivity of the exhaust gas sensor to ammonia is taken into account when determining the ammonia content in the exhaust gas of the internal combustion engine. The sensitivity can be, for example, a previously determined value or can be adapted during operation as a function of the aging state of the exhaust gas sensor.

[0017] The method according to the present invention preferably also includes: determining the carbon monoxide content in the exhaust gas of the internal combustion engine at least partially based on the determined ammonia content in the exhaust gas of the internal combustion engine and at least partially based on the carbon monoxide-related factor and / or determining the hydrocarbon content in the exhaust gas of the internal combustion engine at least partially based on the determined ammonia content in the exhaust gas of the internal combustion engine and at least partially based on the hydrocarbon-related factor.

[0018] In this case, the carbon monoxide-dependent factor and / or the hydrocarbon-dependent factor is preferably determined based on the temperature of the exhaust gas, the temperature of the catalytic converter, the exhaust gas mass flow, the exhaust gas volume flow, the exhaust gas velocity and / or the aging state of the catalytic converter.

[0019] In particular, the ammonia content can be a suitable indicator of the carbon monoxide and hydrocarbon content in the exhaust gas downstream of the catalytic converter, preferably downstream of the three-way catalytic converter. By using the carbon monoxide correlation factor or the hydrocarbon correlation factor, the corresponding carbon monoxide content or hydrocarbon content in the exhaust gas can be determined based on the ammonia content.

[0020] According to another aspect of the present invention, an exhaust system for an internal combustion engine is disclosed, the exhaust system comprising: a catalyst for after-treating the exhaust gas of the internal combustion engine; an exhaust gas sensor arranged downstream of the catalyst, the exhaust gas sensor being configured to generate a signal indicating the content of nitrogen oxides and / or ammonia in the exhaust gas; and a control unit, which receives the signal of the exhaust gas sensor and is configured to implement the method according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Those skilled in the art will be able to understand other tasks and features of the present invention by implementing the current teachings and observing the accompanying drawings, in which:

[0022] Figure 1 shows an exhaust system of an internal combustion engine with a catalyst and an exhaust gas sensor; and

[0023] Figure 2 It is shown that the Figure 1 Flow chart of an exemplary embodiment of the method according to the invention for determining the nitrogen oxide content and / or ammonia content in the exhaust gas of an exhaust gas train. DETAILED DESCRIPTION

[0024] Within the scope of the present disclosure, the term "lean exhaust gas" describes exhaust gas with an excess of oxygen, while the term "rich exhaust gas" describes exhaust gas with an excess of oxygen and partially underburned fuel.

[0025] Furthermore, within the scope of the present disclosure, the term "linear lambda signal" describes the profile of a dimensionless lambda value that indicates the air-fuel ratio of the combustion. In contrast, within the scope of the present disclosure, the term "binary lambda signal" describes the profile of a lambda value (with the unit [mV]) as a signal of an exhaust gas sensor.

[0026] Figure 1 An exemplary catalytic converter 100 is shown, which can be used in the exhaust system 10 of an internal combustion engine (not shown), preferably a gasoline engine, in order to convert air pollutants in the exhaust gas. The catalytic converter 100 is preferably a three-way catalytic converter for converting carbon monoxide (CO), nitrogen oxides (NOx) and unburned hydrocarbons (HC) into carbon dioxide (CO2), nitrogen (N2) and water (H2O).

[0027] It is self-evident to a person skilled in the art that further units or devices, such as a particle filter or a muffler, may be present in the exhaust gas tract 10 .

[0028] An exhaust gas sensor 110 is arranged downstream of the catalytic converter 100 and is designed to determine the nitrogen oxide and / or ammonia content in the exhaust gas downstream of the catalytic converter 100. The exhaust gas sensor 110 sensitive to nitrogen oxide and / or ammonia is, for example, a mixed potential sensor with a mixed potential electrode and / or a reference electrode. The exhaust gas sensor 110 is preferably a nitrogen oxide sensor that is cross-sensitive to ammonia.

[0029] The internal combustion engine is also equipped with a control unit 120, which is connected to the exhaust gas sensor 110 for communication and is designed to detect and evaluate the signal of the exhaust gas sensor and control the operation of the internal combustion engine. The control unit 120 is therefore designed to receive the sensor signal emitted by the exhaust gas sensor 110 and to determine therefrom the nitrogen oxide and / or ammonia content in the exhaust gas downstream of the catalytic converter 100, which is referred to below as Figure 2 It will be explained more precisely.

[0030] refer to Figure 2 It shows the method for finding Figure 1 An exemplary flow chart of the method according to the present invention for determining the nitrogen oxide content and / or ammonia content in the exhaust gas downstream of catalytic converter 100 .

[0031] Figure 2 The method starts in step 200 and then reaches step 210, in which the operating state of the internal combustion engine is determined. The operating state of the internal combustion engine shows in particular the lean operation or rich operation of the internal combustion engine. The rich operation of the internal combustion engine is characterized by the presence of an excess of fuel and thus an exhaust gas with an excess of fuel and a lack of oxygen, compared to the stoichiometric ratio of oxygen and fuel, in which all fuel and oxygen are completely burned. This is therefore a rich exhaust gas. In contrast, the lean operation of the internal combustion engine describes an operation with an excess of oxygen relative to the fuel. This results in an excess of oxygen in the exhaust gas, which is therefore a lean exhaust gas.

[0032] In particular, the lambda value can be determined by means of exhaust gas sensor 110 in order to determine the operating state of the internal combustion engine in step 210. In addition to a main signal indicating the nitrogen oxide content and / or the ammonia content, the exhaust gas sensor also generates a linear and / or binary lambda signal, from which a lambda value characterizing the operating state of the internal combustion engine can be determined.

[0033] In a further step 220 , at least one (main) signal is generated by means of exhaust gas sensor 110 , which signal indicates the sum of the nitrogen oxide and ammonia contents in the exhaust gas of the internal combustion engine downstream of catalytic converter 100 .

[0034] In a subsequent step 230 , a nitrogen oxide content and / or an ammonia content in the exhaust gas of the internal combustion engine is determined at least partially based on the determined operating state of the internal combustion engine and at least partially based on the at least one (main) signal of exhaust gas sensor 110 .

[0035] In step 230, it may be particularly preferred that the signal generated by at least one of the exhaust gas sensors 110 indicates the nitrogen oxide content in the exhaust gas when the determined lambda value is greater than the lambda threshold value. When the determined lambda value is less than the lambda threshold value, the signal generated by at least one of the exhaust gas sensors 110 alternatively indicates the ammonia content in the exhaust gas. This is particularly preferred when the determined lambda value is determined based on a binary lambda signal of the exhaust gas sensor 110.

[0036] In this case, it is particularly utilized that in rich exhaust gas, three-way catalytic converter 100 produces ammonia and the nitrogen oxides are almost completely reduced in three-way catalytic converter 100. This means that in such an operating state of the internal combustion engine in which rich exhaust gas is present, almost only ammonia and no nitrogen oxides are present downstream of catalytic converter 100. For this reason, the signal of exhaust gas sensor 110 can be interpreted as indicating a complete ammonia content, wherein the nitrogen oxide content is zero.

[0037] The lambda threshold value may be a fixed value, for example 200 mV. Alternatively, the lambda threshold value may be dynamically set during operation according to operating parameters of the internal combustion engine and / or the exhaust system 10. For example, the lambda threshold value may be determined based on the temperature of the exhaust gas, the temperature of the catalyst, the exhaust mass flow, the exhaust volume flow, the exhaust velocity and / or the aging state of the catalyst and may be dynamically adapted.

[0038] It may also be advantageous to determine the exhaust gas mass flow in step 230. The exhaust gas mass flow may be derived, for example, from the signal of a pressure sensor or a mass flow sensor arranged in the intake tract of the internal combustion engine and / or may be determined via operating parameters of the internal combustion engine.

[0039] When the determined exhaust mass flow is greater than a predetermined exhaust mass flow threshold value, the nitrogen oxide content and / or ammonia content in the exhaust gas of the internal combustion engine is also determined at least partially based on the mass flow factor. In particular, at very large exhaust mass flow values ​​(even in the case of rich exhaust gas), an incomplete conversion of nitrogen oxides can occur due to insufficient residence time in the catalyst 100, so that in this state both nitrogen oxides and ammonia can be present downstream of the catalyst 100. For this reason, it is preferred that the mass flow factor is taken into account when determining the nitrogen oxide content and / or ammonia content when the determined exhaust mass flow is greater than a predetermined exhaust mass flow threshold value. The mass flow factor is designed in particular to separate the signal of the exhaust gas sensor 110 into a nitrogen oxide signal indicating the nitrogen oxide content and an ammonia signal indicating the ammonia content, wherein the nitrogen oxide content in the exhaust gas of the internal combustion engine can be determined from the nitrogen oxide content signal and the ammonia content in the exhaust gas of the internal combustion engine can be determined from the ammonia content signal.

[0040] The mass flow factor can also be a predetermined factor or can be dynamically adjusted according to operating parameters of the internal combustion engine and / or the exhaust system. Here, the temperature of the exhaust gas, the temperature of the catalyst, the exhaust gas mass flow, the exhaust gas volume flow, the exhaust gas velocity and / or the catalyst aging state can be cited as operating parameters.

[0041] Furthermore, it is also preferred in step 230 that the (transverse) sensitivity of the exhaust gas sensor to ammonia is also taken into account when determining the ammonia content in the exhaust gas of the internal combustion engine. The main signal of the exhaust gas sensor 110 can in particular represent the sum of nitrogen oxides and ammonia, wherein a sensitivity factor is stored in the ammonia content. This sensitivity factor can be adapted as a function of the aging of the exhaust gas sensor 110. The sensitivity factor can alternatively be determined by the factory as a predetermined value. It may therefore be preferred that in step 230 the current transverse sensitivity of the exhaust gas sensor 100 is also determined or used and taken into account when determining the ammonia content in the exhaust gas of the internal combustion engine.

[0042] The sensitive factor can also be a predetermined factor or can be adjusted dynamically according to operating parameters of the internal combustion engine and / or the exhaust system. Here, the temperature of the exhaust gas, the temperature of the catalyst, the exhaust gas mass flow, the exhaust gas volume flow, the exhaust gas velocity and / or the aging state of the catalyst can be cited as operating parameters.

[0043] Furthermore, the present invention utilizes the fact that the ammonia content can be a suitable indicator for the carbon monoxide and hydrocarbon content in the exhaust gas of the internal combustion engine downstream of the catalytic converter 100. In particular, the carbon monoxide content in the exhaust gas of the internal combustion engine can be determined from the determined ammonia content in the exhaust gas of the internal combustion engine at least partially based on the carbon monoxide correlation factor. Alternatively or additionally, the hydrocarbon content in the exhaust gas of the internal combustion engine can also be determined from the determined ammonia content in the exhaust gas of the internal combustion engine at least partially based on the hydrocarbon correlation factor.

[0044] Therefore, exhaust gas sensor 100 may be used to determine not only the nitrogen oxide content, the ammonia content, the carbon monoxide content, but also the hydrocarbon content in the exhaust gas of the internal combustion engine downstream of catalytic converter 100 .

Claims

1. A method for determining a nitrogen oxide content and / or ammonia content in the exhaust gas of an internal combustion engine, the internal combustion engine comprising a catalytic converter (100) arranged in an exhaust gas system (10) of the internal combustion engine and an exhaust gas sensor (110) arranged downstream of the catalytic converter (100), wherein: This method has: - determining an operating state of the internal combustion engine, which indicates whether the internal combustion engine is operating lean or rich; - generating at least one signal by means of an exhaust gas sensor (110) which, due to its sensitivity to ammonia, indicates the sum of the nitrogen oxide content and the ammonia content; - determining a nitrogen oxide content and / or an ammonia content in the exhaust gas of the internal combustion engine at least partially based on the determined operating state of the internal combustion engine and at least partially based on at least one signal of an exhaust gas sensor (110); - determining a lambda value with the aid of the exhaust gas sensor (110), wherein an operating state of the internal combustion engine is determined at least partially based on the determined lambda value, and wherein: When the determined lambda value is greater than a lambda threshold value, the signal generated by at least one of the exhaust gas sensors (110) indicates the nitrogen oxide content in the exhaust gas, and / or If the determined lambda value is less than a lambda threshold value, the signal generated by at least one of the exhaust gas sensors (110) indicates the ammonia content in the exhaust gas.

2. The method according to claim 1, wherein the catalytic converter (100) is a three-way catalytic converter.

3. The method according to claim 1, wherein: The lambda threshold value is determined based on the temperature of the exhaust gas, the temperature of the catalytic converter, the exhaust gas mass flow, the exhaust gas volume flow, the exhaust gas velocity and / or the aging state of the catalytic converter, or The lambda threshold is predetermined as a fixed value.

4. The method according to any one of the preceding claims 1 to 3, further comprising: - determine the exhaust mass flow rate, in, If the determined exhaust gas mass flow is greater than a predetermined exhaust gas mass flow threshold value, a nitrogen oxide content and / or an ammonia content in the exhaust gas of the internal combustion engine is also determined at least partially based on the mass flow factor.

5. The method according to claim 4, wherein: The mass flow factor is determined based on the temperature of the exhaust gas, the temperature of the catalytic converter, the exhaust gas mass flow, the exhaust gas volume flow, the exhaust gas velocity and / or the aging state of the catalytic converter.

6. The method according to any one of the preceding claims 1 to 3, further comprising: - determining the sensitivity of the exhaust gas sensor to ammonia, in, When determining the ammonia content in the exhaust gas of an internal combustion engine, the determined sensitivity of the exhaust gas sensor (110) to ammonia is taken into account.

7. The method according to any one of the preceding claims 1 to 3, further comprising: - determining a carbon monoxide content in the exhaust gas of the internal combustion engine at least partially based on the determined ammonia content in the exhaust gas of the internal combustion engine and at least partially based on a carbon monoxide correlation factor, and / or - determining a hydrocarbon content in the exhaust gas of the internal combustion engine at least partially based on the determined ammonia content in the exhaust gas of the internal combustion engine and at least partially based on a hydrocarbon-related factor.

8. The method according to claim 7, wherein: The carbon monoxide-dependent factor and / or the hydrocarbon-dependent factor are determined based on the temperature of the exhaust gas, the temperature of the catalytic converter, the exhaust gas mass flow, the exhaust gas volume flow, the exhaust gas velocity and / or the catalytic converter aging state.

9. An exhaust system (10) for an internal combustion engine, comprising: - a catalytic converter (100) for after-treating exhaust gas of an internal combustion engine, an exhaust gas sensor (110) arranged downstream of the catalytic converter (100), which is designed to generate a signal which indicates the nitrogen oxide and / or ammonia content in the exhaust gas, and A control unit (120) which receives signals from the exhaust gas sensor (110) and is designed to carry out the method according to one of the preceding claims.

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