DE102016119816A1 - Method and device for monitoring a secondary air system - Google Patents

Abstract

The invention relates to a method for monitoring a secondary air system on an exhaust system of an internal combustion engine. For this purpose, a lambda probe arranged in the exhaust gas duct downstream of a three-way catalytic converter is heated to an operating temperature and a residual oxygen content in the exhaust gas duct is determined by means of the lambda probe. It is concluded on the basis of the determined residual oxygen content in the exhaust duct on a correct functioning of the secondary air system. In the case of a deviation of the determined residual oxygen content in the exhaust gas channel from the residual oxygen content to be expected in the case of correct function, an error in the secondary air system is concluded and a corresponding error signal is output.
The invention further relates to a device for carrying out such a method

Description

The invention relates to a method for monitoring a secondary air system on an exhaust system of an internal combustion engine, and to an apparatus for carrying out such a method.

For Niedrigstemission concepts a secondary air injection is used in the exhaust system of an internal combustion engine, in particular in a cold start phase to heat a catalyst to an operating temperature, in which an efficient conversion of the pollutants contained in the exhaust gas is possible. In this case, the internal combustion engine is operated with a substoichiometric, rich combustion mixture, the unburned components of this combustion mixture in the exhaust system downstream of the Einblasstelle for secondary air react exothermically with the secondary air and thus allow a very rapid heating of the catalyst to a light-off temperature. The light-off temperature is defined as the temperature at which the catalyst has 50% of its maximum conversion rate. In order to monitor emission limits and system functionality, the secondary air system must be diagnosed, as only in a scheduled function can the unburned components of the rich combustion mixture in the exhaust passage be implemented and otherwise increase in emissions, especially unburned hydrocarbon (HC) and carbon monoxide emissions (CO), comes. This topic is in connection with an increasing use of hybrid drive concepts of increasing importance, since the phases in which an internal combustion engine is operated in unfired thrust or towing, increase in hybrid drives and thus the risk of cooling of catalysts in the operation of the motor vehicle under the Light-off temperature increases.

From the DE 43 43 639 A1 a method for monitoring a secondary air system in conjunction with the exhaust system of a motor vehicle is known in which an oxygen content in the exhaust duct is determined in dependence on a determined by an air flow mass or volume flow through the intake passage and the fuel-air ratio of the internal combustion engine and from it a key figure is formed. If the key figure lies within a defined interval, it is concluded that the secondary air system is functioning correctly.

From the DE 100 47 809 A1 For example, an internal combustion engine having a secondary air system is known in which secondary air is introduced into the exhaust passage downstream of a NOx storage catalyst and upstream of a three-way catalyst. The secondary air is used to oxidize sulfur-containing compounds downstream of the NOx storage catalyst.

From the DE 199 57 184 A1 a method for operating an exhaust gas purification system of an internal combustion engine is known, wherein in the exhaust system, a twin catalyst with a reduction catalyst and an oxidation catalyst is arranged, wherein the secondary air is introduced downstream of the reduction catalyst and upstream of the oxidation catalyst in the twin-catalyst.

A disadvantage of the method known from the prior art, however, is that either no analysis of the functionality of the secondary air system is provided, or an analysis is performed via a sensor which is exposed to strong disturbances, so that the analysis is inaccurate.

The invention is now based on the object to propose a method for analyzing the functionality of a secondary air system, which is characterized by a high reliability and accuracy.

• - Beheizen einer in einem Abgaskanal des Verbrennungsmotors stromabwärts eines ersten Drei-Wege-Katalysators angeordneten Lambdasonde,
• - Einleiten von Sekundärluft an einer Einleitstelle stromaufwärts des ersten Drei-Wege-Katalysators in den Abgaskanal des Verbrennungsmotors,
• - Leiten der Sekundärluft durch den ersten Drei-Wege-Katalysator,
• - Ermitteln eines Sauerstoffgehalts im Abgas stromabwärts des ersten Drei-Wege-Katalysators,
• - Vergleich des ermittelten Sauerstoffgehalts im Abgas mit einem bei korrekter Funktion des Sekundärluftsystems zu erwartenden Sauerstoffgehalt,
• - Ausgabe einer Fehlerinformation, falls der ermittelte Sauerstoffgehalt von dem bei korrekter Funktion des Sekundärluftsystems zu erwartenden Sauerstoffgehalt abweicht.

The object is achieved according to the invention by a method for monitoring a secondary air system on an exhaust system of an internal combustion engine, which comprises the following steps:

• Heating a lambda probe arranged in an exhaust passage of the internal combustion engine downstream of a first three-way catalytic converter,
• Introducing secondary air at a point of introduction upstream of the first three-way catalytic converter into the exhaust gas passage of the internal combustion engine,
• Passing the secondary air through the first three-way catalyst,
• Determining an oxygen content in the exhaust gas downstream of the first three-way catalyst,
• Comparison of the determined oxygen content in the exhaust gas with an oxygen content to be expected in the case of correct functioning of the secondary air system,
• - Issue of an error information, if the determined oxygen content deviates from the expected with the correct function of the secondary air system oxygen content.

As an analysis of the oxygen content upstream of the first three-way catalyst is flawed, since the oxygen from the secondary air system has not yet sufficiently mixed with the exhaust gas of the internal combustion engine and also already carried out a conversion of the unburned components of the fuel through the supplied via the secondary air line oxygen, it is advantageous to the oxygen content of the exhaust gas downstream of the first To determine three-way catalyst, since at this point the exhaust gas and the secondary air have largely mixed together and the unburned exhaust gas components have been exothermic reacted by the secondary air. Thus, by a lambda probe downstream of the first three-way catalyst a much more accurate determination of the oxygen content in the exhaust passage and thus a review of the function of the secondary air system possible.

By the features listed in the dependent claims, advantageous developments and improvements of the method specified in the independent claim are possible.

In a preferred embodiment of the invention it is provided that the secondary air is supplied to the exhaust duct upstream of a turbine of an exhaust gas turbocharger. If the secondary air is supplied upstream of the turbine of the exhaust gas turbocharger, the turbine can act as a mixer and mix the stoichiometric exhaust gas with the secondary air, so that a reaction of the unburned components of the exhaust gas is facilitated by the secondary air. Thus, the heating of the first three-way catalyst can be facilitated and accelerated.

In a further preferred embodiment of the invention, it is provided that the lambda probe is heated electrically by means of a heating resistor. Resistance heating allows a particularly simple and rapid heating of the lambda probe to an operating temperature. In addition, modern lambda sensors have a good water hammer resistance, so that they can be heated directly after the engine is started and thus reach their operating temperature in a very short time.

It is particularly preferred if the lambda probe is heated to a temperature of at least 500 ° C, preferably of at least 600 ° C. In principle, the electrical resistance of the lambda probe and thus the probe signal is dependent on the temperature. The resistance increases with increasing temperature. The physical effect of oxygen transport in the lambda probe is also temperature-dependent, with the zirconium dioxide membrane used being capable of electrolytic conduction of oxygen ions above approx. 300 ° C. and thus being able to determine an oxygen content in the exhaust gas. Lambda probes operate particularly efficiently in a temperature range above 600 ° C., so it is preferable to heat the probes as quickly as possible to this operating temperature by means of resistance heating.

According to an advantageous embodiment of the method, it is provided that the lambda probe detects a substantially stoichiometric exhaust gas with the correct function of the secondary air system. In order to ensure the best possible emission control, and to keep the proportion of unburned hydrocarbon and carbon monoxide emissions low, it is advantageous if the unburned hydrocarbons and the carbon monoxide are converted substantially by the secondary air to carbon dioxide and water vapor. Therefore, if the secondary air system functions properly downstream of the first three-way catalyst, there should be a stoichiometric exhaust.

It is particularly preferred if the delivery rate of a secondary air pump of the secondary air system is increased when downstream of the first three-way catalyst, a substoichiometric, rich exhaust gas is detected. By increasing the delivery rate, a slight leak in the secondary air system can be compensated so that a highly efficient exhaust gas purification and heating of the three-way catalytic converters is achieved despite a leak.

According to an advantageous further development of the method, it is provided that a secondary air valve of the secondary air system is closed when a different operating state from a correct functioning of the secondary air system is detected. If there is a (major) defect in the secondary air system or a failure of the secondary air pump, then it is provided that the secondary air valve is closed in order to prevent an uncontrolled outflow of exhaust gas via the defective secondary air line.

• - einen Abgaskanal, in dem ein erster Drei-Wege-Katalysator und stromabwärts des ersten Drei-Wege-Katalysators eine Lambdasonde angeordnet ist,
• - wobei am Abgaskanal stromaufwärts des ersten Drei-Wege-Katalysators eine Einleitstelle für von dem Sekundärluftsystem bereitgestellte Sekundärluft vorgesehen ist,
• - wobei an der Lambdasonde eine Heizvorrichtung zur Beheizung der Lambdasonde vorgesehen ist, und wobei
• - die Vorrichtung ein Steuergerät umfasst, mit welchem ein erfindungsgemäßes Verfahren durchgeführt werden kann, wenn ein maschinenlesbarer Programmcode auf dem Steuergerät ausgeführt wird.

According to the invention, an apparatus for monitoring a secondary air system on an exhaust system of an internal combustion engine is proposed, which comprises:

• an exhaust gas passage in which a first three-way catalyst and downstream of the first three-way catalyst a lambda probe is arranged,
• wherein a discharge point for secondary air provided by the secondary air system is provided on the exhaust gas passage upstream of the first three-way catalyst,
• - Wherein a heater for heating the lambda probe is provided at the lambda probe, and wherein
• - the device comprises a control device with which a method according to the invention can be carried out when a machine-readable program code is executed on the control device.

By a device according to the invention for monitoring the secondary air system, a method according to the invention can be carried out in a simple manner.

In a preferred embodiment of the invention, it is provided that the exhaust system comprises a first three-way catalytic converter and a second three-way catalytic converter, wherein a first lambda probe upstream of the first three-way catalytic converter and a second lambda probe downstream of the first three Pathway catalyst and upstream of the second three-way catalyst are arranged. By a first, near-engine three-way catalyst, which is also referred to as a pre-catalyst or starting catalyst, shortly after a cold start of the engine, a three-way functionality of the exhaust gas purification can be provided, as this catalyst heat up very quickly to an operating temperature leaves. By a second catalyst, a sufficient conversion performance in the exhaust gas purification can be made available even with high amounts of exhaust gas. In this case, the heating of the second catalyst with respect to the heating of the first catalyst is delayed.

According to a preferred embodiment of the invention it is provided that the point of introduction of the secondary air upstream of a turbine of an exhaust gas turbocharger is arranged, wherein the first three-way catalyst is arranged downstream of the turbine. By introducing the secondary air upstream of the turbine, an improved mixing of the substoichiometric exhaust gas and the secondary air is possible, whereby an improved and faster conversion of the unburned components of the exhaust gas with the oxygen from the secondary air is possible.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other.

• 1 einen Verbrennungsmotor mit einem Frischluftsystem, einem Abgassystem, sowie einem Sekundärluftsystem, welcher dazu eingerichtet ist, ein erfindungsgemäßes Verfahren zur Überwachung einer ordnungsgemäßen Funktion des Sekundärluftsystems durchzuführen.
• 2 ein Verfahrensschaubild zur Durchführung eines erfindungsgemäßen Verfahrens zur Überwachung einer korrekten Funktion des Sekundärluftsystems.

The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

• 1 an internal combustion engine having a fresh air system, an exhaust system, and a secondary air system, which is adapted to perform a method according to the invention for monitoring a proper function of the secondary air system.
• 2 a process diagram for carrying out a method according to the invention for monitoring a correct function of the secondary air system.

1 shows an internal combustion engine 10 with a fresh air system 20 and an exhaust system 30 with which a method according to the invention for monitoring a correct function of a secondary air system 50 of the internal combustion engine 10 can be carried out. The internal combustion engine 10 has at least one combustion chamber 12 , preferably as in 1 presented four combustion chambers 12 on which about the fresh air system 20 can be supplied with ambient air. At the internal combustion engine 10 is an inlet 14 arranged, with which the fresh air from the fresh air system 20 on the individual combustion chambers 12 of the internal combustion engine 10 can be distributed. Further, on the internal combustion engine 10 a fuel injection system 18 provided over which the combustion chambers 12 of the internal combustion engine 10 can be supplied with fuel. At the internal combustion engine 10 is an exhaust manifold 16 arranged, which the internal combustion engine 10 with an exhaust system 30 for the aftertreatment of the exhaust gases of the internal combustion engine 10 combines.

The fresh air system 20 includes an air filter 22 which of the internal combustion engine 10 sucked fresh air filters. The fresh air system 20 further comprises a fresh air line 28 which the air filter 22 with the inlet 14 of the internal combustion engine 10 combines. Downstream of the air filter 22 is a compressor 24 an exhaust gas turbocharger 32 arranged, which over the air filter 22 sucked fresh air compressed. Downstream of the compressor 24 and upstream of the inlet is in the fresh air line 28 a throttle 26 arranged, with which the combustion chambers 12 of the internal combustion engine 10 supplied amount of fresh air can be regulated. Furthermore, the fresh air system 10 comprise an air mass or air flow meter, not shown, which preferably between the air filter 22 and the compressor 24 the exhaust gas turbocharger 32 is arranged.

The exhaust system 30 includes an exhaust passage 36 , which the exhaust manifold 16 of the internal combustion engine 10 connects with the environment. In the exhaust duct 36 is a turbine in the flow direction of an exhaust gas 34 the exhaust gas turbocharger 32 arranged, which with the compressor 24 in the fresh air system 20 connected via a shaft and drives this. Downstream of the turbine 34 is a first three-way catalyst 38 arranged, which preferably as a close-coupled pre-catalyst 38 is trained. This is under a near-engine arrangement of the first three-way catalyst 38 a Abgaslauflänge of a maximum of 50 cm, preferably of a maximum of 30 cm from the exhaust manifold 16 of the internal combustion engine 10 considered. Downstream of the first three-way catalyst 38 is in the exhaust duct 36 a second three-way catalyst 40 arranged, which preferably as the main catalyst 40 is arranged in a bottom layer of a motor vehicle. In the exhaust duct 36 is downstream of the turbine 34 and upstream of the first three-way catalyst 38 a first lambda probe 42 arranged, which is preferably designed as a broadband probe. Downstream of the first three-way catalyst 38 and upstream of the second three-way catalyst 40 is a second lambda probe 44 arranged, which is preferably designed as a jump probe. Alternatively or in addition to the second catalyst 40 can the exhaust system 30 one in 1 Particulate filters, not shown, which preferably downstream of the first three-way catalyst 38 is arranged.

The internal combustion engine 10 also has a secondary air system 50 on which a secondary air line 54 and a secondary air pump 52 includes. The secondary air line 54 connects the fresh air line 28 downstream of the air filter 22 and upstream of the compressor 24 with the exhaust duct 36 downstream of the exhaust valves in the cylinder head of the internal combustion engine 10 and upstream of the turbine 34 , The secondary air line 54 ends at a discharge point 58 in the exhaust duct 36 , The secondary air pump sucks 52 Air from the fresh air line 28 and leads them to the exhaust duct 36 to. In the secondary air line 54 is downstream of the secondary air pump 52 and upstream of the discharge point 58 a secondary air valve 56 arranged, with which the exhaust duct 36 supplied amount of secondary air can be controlled.

After a cold start of the internal combustion engine 10 is via the secondary air system 50 Secondary air into the exhaust duct 36 of the internal combustion engine 10 blown in to heat the first three-way catalyst 38 to accelerate and thus the first three-way catalyst 38 to heat to an operating temperature at which an effective conversion of pollutants contained in the exhaust gas through the first three-way catalyst 38 is possible. For diagnosis and monitoring of the secondary air system 50 In a first method step <100>, the second lambda probe is used 44 downstream of the first three-way catalyst 38 heated to an operating temperature of about 600 ° C. In a second method step <110>, the secondary air is at the discharge point 58 downstream of the exhaust manifold 16 and upstream of the turbine 34 in the exhaust duct 36 initiated in a warm-up phase, the first three-way catalyst 38 to an operating temperature above the light-off temperature of the first three-way catalyst 38 bring to. For this purpose, in a process step <120> the internal combustion engine 10 operated with a superstoichiometric, rich combustion mixture. In the process, the unburned fuel constituents and the fuel via the discharge point mix 58 supplied secondary air when flowing through the turbine 34 , where in the exhaust duct 36 present unburned fuel components are exothermally reacted with the oxygen from the secondary air, so that the first three-way catalyst 38 heated to its operating temperature. In a further method step <130> is at the second lambda probe 44 downstream of the first three-way catalyst 38 an oxygen content in the exhaust duct 36 determined. Detects the second lambda probe 44 a substantially stoichiometric exhaust gas (λ ~ 1), so may be a correct function of the secondary air system 50 be assumed. Under a substantially stoichiometric exhaust gas, an exhaust gas with lambda between 0.98 and 1.02 is considered.

Fault pictures like a clamping secondary air valve 56 or leaks in the secondary air system 50 lead to a shift in the oxygen content in the exhaust duct 36 , This can be done via the second lambda probe 44 downstream of the first three-way catalyst 38 be detected.

Detects the second lambda probe 44 one of a with the correct function of the secondary air system deviating oxygen content in the exhaust gas, so may at a low oxygen content in a process step <140> the delivery rate of the secondary air system 50 increase. Thus, even small leaks in the secondary air system 50 be compensated.

If a compensation of the error is not possible, the secondary air valve will be used in a process step <150> 56 closed and the secondary air system 50 switched off. Thus, it can be ensured that, at least during normal operation of the internal combustion engine 10 no exhaust due to leakage of the secondary air system 50 escapes and is emitted unpolluted into the environment.

In a method step <160>, an error signal is transmitted to the control unit and / or a display unit in the vehicle, which causes the driver to drive the motor vehicle while driving the motor vehicle and / or a mechanic during read-out of the control unit during servicing of the motor vehicle fails the secondary air system 50 displays. Preferably, a direct information to the driver with the request, since a failure of the secondary air system can lead to exceeding the emission limit values and thus is not acceptable.

The first lambda probe 43 is due to strandiness, mixing and reaction of secondary air and rich, superstoichiometric exhaust gas for Determination of the residual oxygen content in the exhaust duct 36 less well suited, since here depending on the operating point of the internal combustion engine 10 can give rise to strong fluctuations. Only after flowing through the first three-way catalyst 38 lies in the exhaust duct 36 downstream of the first three-way catalyst 38 a substantially homogeneous exhaust gas, so that at this point based on the second lambda probe 44 a much more reliable statement about the oxygen content in the exhaust duct 36 to meet.

In general, the period for the operation of the secondary air system 50 limited. For this purpose, the secondary air system 50 especially in a cold start phase of the internal combustion engine 10 for heating the three-way catalysts 38 . 40 used or after a prolonged push or tow operation of the internal combustion engine 10 in which there is a strong cooling of the exhaust duct 36 and the components for exhaust aftertreatment 38 . 40 can come. In this case, the secondary air system is usually on reaching an operating temperature, in particular the light-off temperature of the components for exhaust aftertreatment 38 . 40 , in a process step <170> deactivated again, the secondary air pump 52 shut off and the secondary air valve 56 is closed.

In addition, the secondary air system 50 be connected to the regeneration of a particulate filter in the exhaust passage to the necessary for the regeneration of the particulate filter oxygen at preferably stoichiometric operation of the internal combustion engine 10 to deliver.

LIST OF REFERENCE NUMBERS

10

internal combustion engine

12

combustion chamber

14

inlet

16

exhaust manifold

18

Fuel injection system

20

Fresh air system

22

air filter

24

compressor

26

throttle

28

Fresh air line

30

exhaust system

32

turbocharger

34

turbine

36

exhaust duct

38

first three-way catalyst / precatalyst

40

second three-way catalyst / main catalyst

42

first lambda probe / broadband probe

44

second lambda probe / jump probe

50

Secondary air system

52

Secondary pump air

54

Secondary air line

56

Secondary air valve

58

inlet point

60

Heater / heating resistor

62

control unit

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 4343639 A1 [0003]
• DE 10047809 A1 [0004]
• DE 19957184 A1 [0005]

Claims (10)

Method for monitoring a secondary air system (50) on an exhaust system (30) of an internal combustion engine (10), comprising the following steps: Heating a lambda probe (44) arranged in an exhaust gas duct (36) of the internal combustion engine (10) downstream of a first three-way catalytic converter (38), Introducing secondary air at an introduction point (58) upstream of the first three-way catalyst (38) into the exhaust passage (36) of the internal combustion engine (10), Passing the secondary air through the first three-way catalyst (38), Determining an oxygen content in the exhaust gas downstream of the first three-way catalyst (38), Comparison of the determined oxygen content in the exhaust gas with an oxygen content to be expected in the case of correct functioning of the secondary air system (50), - Output of error information, if the determined oxygen content of the expected difference in the correct function of the secondary air system (50) oxygen content. Method according to Claim 1 , characterized in that the secondary air is supplied to the exhaust passage (36) upstream of a turbine (34) of an exhaust gas turbocharger (32). Method according to Claim 1 or 2 , characterized in that the lambda probe (44) is electrically heated by means of a heating resistor (60). Method according to Claim 3 , characterized in that the lambda probe (44) to a temperature of at least 500 ° C, preferably of at least 600 ° C, heated. Method according to one of Claims 1 to 4 , characterized in that the lambda probe (44) detects a substantially stoichiometric exhaust gas with correct function of the secondary air system (50). Method according to Claim 5 characterized in that the delivery rate of a secondary air pump (52) of the secondary air system (50) is increased when a substoichiometric exhaust gas is detected downstream of the first three-way catalyst (38). Method according to one of Claims 1 to 6 , characterized in that a secondary air valve (54) is closed when a different operating state of a correct operation of the secondary air system (50) is detected. Apparatus for monitoring a secondary air system (50) on an exhaust system (30) of an internal combustion engine (10) comprising: - an exhaust passage (36) containing a first three-way catalyst (38) and downstream of the first three-way catalyst 38) a lambda probe (44) is arranged, - wherein at the exhaust passage (36) upstream of the first three-way catalyst (38) a discharge point (58) is provided for by the secondary air system (50) provided secondary air, - wherein at the lambda probe (44) a heating device (60) for heating the lambda probe (44) is provided, and wherein - the device comprises a control device (62), with which a method according to one of Claims 1 to 7 can be performed when a machine-readable program code is executed on the controller (62). Device after Claim 8 characterized in that the exhaust system (30) comprises a first three-way catalyst (38) and a second three-way catalyst (40), wherein a first lambda probe (42) upstream of the first three-way catalyst (38 ) and a second lambda probe (44) are disposed downstream of the first three-way catalyst (38) and upstream of the second three-way catalyst (40). Device after Claim 8 or 9 characterized in that the point of introduction (58) is located downstream of an exhaust manifold (16) of the internal combustion engine (10) and upstream of a turbine (34) of an exhaust gas turbocharger (32), the first three-way catalyst (38) downstream of the turbine (34) is arranged.

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