DE102016211595A1 - Method and device for controlling and / or monitoring the function of a secondary air supply in an emission control system - Google Patents

Abstract

The invention relates to a method and a device for controlling and / or monitoring the function of a secondary air supply in an exhaust gas purification system of an internal combustion engine having at least two in an exhaust passage successively arranged catalysts, wherein the second catalyst can be designed as a combination catalyst / particle filter. It is provided that for a secondary air diagnosis and the secondary air control, a two-point lambda probe is used in the flow direction of the exhaust gas behind the first catalyst and for this particular measures to compensate for tolerance and aging effects are applied. This results in particular cost advantages in emission control systems to meet stricter emission requirements. In particular, so that the particle filter can be operated optimally.

Description

State of the art

The invention relates to a method for controlling and / or monitoring the function of a secondary air supply in an exhaust gas purification system of an internal combustion engine, which has in its central portion at least two successively arranged in an exhaust duct catalysts and before / or behind this central portion still further exhaust gas cleaning components can be arranged , wherein in the flow direction of the exhaust gas after an engine block and before the first catalyst, a lambda probe is arranged and before another catalyst another exhaust gas probe is arranged, between the first and the further catalyst by means of the secondary air supply air is introduced for optimal operation of the further catalyst.

The invention further relates to a device, in particular a motor control unit, for carrying out the method.

In today's engine control systems lambda probes are used to detect the oxygen concentration in the exhaust gas and the lambda control of the engine. Broadband lambda probes and two-point lambda probes are used.

With a broadband lambda probe, the exhaust lambda can be controlled continuously in a wide lambda range. By linearizing the probe characteristic, a steady lambda control is possible even with a less expensive two-point lambda probe, albeit in a limited lambda range.

Compared to a broadband lambda probe, a two-point lambda probe has a significantly higher accuracy in a narrow range around lambda = 1 because of its jump-shaped probe characteristic. Outside of this narrow range around lambda = 1 with rich or lean lambda, the accuracy of a two-point lambda probe is generally lower than that of a broadband lambda probe due to tolerance and aging effects.

As a rule, broadband lambda probes are therefore used in engine control systems where rich or lean lambda values are to be measured accurately, or where a measurement in the range around lambda = 1 with limited accuracy is sufficient. Two-point lambda probes are used where the exhaust lambda in the range around lambda = 1 is to be measured with high accuracy.

Typical applications for a broadband lambda probe are lambda control in front of the catalytic converter and balancing of the oxygen input and output in the diagnosis of the catalytic converter. Typical applications of a two-point lambda probe are the very accurate lambda = 1 control behind the catalytic converter and the detection of the breakthrough of rich or lean exhaust gas in the diagnosis of the catalytic converter.

A typical exhaust system of a gasoline system for today's stringent emission and diagnostic requirements, e.g. SULEV consists of a broadband lambda probe, a first three-way catalytic converter, a two-point lambda probe and a second unmonitored three-way catalytic converter.

Future even stricter emission and diagnostic requirements (e.g., China 6 expected) will require exhaust systems that not only monitor the second catalyst but also limit the number of particulates in the exhaust gas. The second three-way catalyst must therefore be combined with a particulate filter or replaced with a coated particulate filter, also referred to as a four-way catalyst.

For optimal operation of the particulate filter, in particular with regard to a quick reaching the operating temperature and with respect to the regeneration, a secondary air introduction before the particulate filter may be necessary. This also applies to other components of the exhaust gas purifier (e.g., NCS or SCR catalyst).

Such a secondary air introduction is for example from the DE 102009043087 A1 known. It describes an internal combustion engine, in particular a diesel engine, with a catalyst and a particulate filter in the exhaust system, wherein at least one secondary air line for supplying secondary air into the exhaust system is designed and arranged such that the secondary air line opens downstream of the catalyst and upstream of the particulate filter in the exhaust system , wherein at least one secondary air line is designed and arranged such that it branches off from a combustion air system. For regeneration of the particulate filter, the amount of secondary air introduced into the exhaust system is selected such that a lambda value for the air-fuel ratio in the particulate filter λ _{DPF has} a value of 1 <λ _DPF <x, where 1.4 ≥ x ≥ 1, in particular 1.4 ≥ x ≥ 1.05. This ensures that the regeneration runs safely without falling below an exhaust gas temperature of 600 ° C in the particulate filter.

From the point of view of an optimal operating strategy of the particulate filter, it makes sense to use a broadband lambda probe to control the introduced secondary air quantity before the secondary air introduction and the particulate filter instead of a two-point lambda probe.

• • Erste Breitband-Lambdasonde
• • Erster Katalysator (als Dreiwegekatalysator ausgeführt)
• • Zweite Breitband-Lambdasonde
• • Zweiter Katalysator mit Partikelfilter (z.B. als beschichteter Partikelfilter ausgeführt)
• • Zweipunkt-Lambdasonde,

wobei die erste Breitband-Lambdasonde für die Lambdaregelung sowie zur Bilanzierung für die Diagnose des ersten Katalysators dient. Die zweite Breitband-Lambdasonde dient zur Führungsregelung sowie zur Durchbrucherkennung bei der Diagnose des ersten Katalysators sowie zur Bilanzierung für die Diagnose des zweiten Katalysators. Dazu kommt noch die Aufgabe der Regelung bei Sekundärluft-Einleitung. Die Zweipunkt-Lambdasonde nach dem zweiten Katalysator mit dem Partikelfilter dient zur Durchbrucherkennung für die Diagnose des zweiten Katalysators. Die zweite Breitband-Lambdasonde hat in dieser Anordnung allerdings funktionale Nachteile gegenüber einer Zweipunkt-Lambdasonde an dieser Einbauposition. Diese sind einerseits eine geringere Genauigkeit der Führungsregelung im Bereich um Lambda = 1 und andererseits eine weniger gute Eignung für die Erkennung von Lambdadurchbrüchen für die Diagnose des ersten Katalysators.Currently, in this context, exhaust systems with the following structure in conversation (arranged in the flow direction of the exhaust gas in the exhaust duct after the engine block), which in principle also from the DE 102013226063 A1 are known:

• • First broadband lambda probe
• First catalyst (designed as a three-way catalyst)
• • Second broadband lambda probe
• Second catalyst with particle filter (eg as coated particle filter)
• • two-point lambda probe,

wherein the first broadband lambda probe is used for the lambda control as well as for the balancing for the diagnosis of the first catalyst. The second broadband lambda probe is used for command control and for breakthrough detection in the diagnosis of the first catalyst and for balancing the diagnosis of the second catalyst. In addition, there is the task of regulating secondary air induction. The two-point lambda probe after the second catalyst with the particle filter is used for breakthrough detection for the diagnosis of the second catalyst. However, the second broadband lambda probe in this arrangement has functional disadvantages compared to a two-point lambda probe at this installation position. These are on the one hand a lower accuracy of the control of lambda = 1 and on the other hand less suitable for the detection of lambda breakthroughs for the diagnosis of the first catalyst.

It is therefore the object of the invention to provide a method which makes it possible in an exhaust gas purification system having at least two catalysts and a particle filter or a first catalyst and a coated particle filter as the second catalyst in combination with a particle filter and with a secondary air filter. Introduction behind the first catalyst to allow the use of a lower-cost two-point lambda probe in the flow direction of the exhaust gas behind the first catalyst instead of a second broadband lambda probe. This is to allow a lambda control to a setpoint of λ = 1 and λ> 1 with active secondary air operation to operate the particulate filter optimally. In addition, with this two-point lambda probe instead of a second broadband lambda probe, a diagnosis of the secondary air pump or of the secondary air system should also be made possible. At the same time a more accurate control of the range in the range of λ = 1, a more accurate diagnosis of the first catalyst and, if necessary, a sufficiently accurate diagnosis of the second catalyst to be achieved, but this is the task of a separate parallel application of the Applicant.

It is a further object of the invention to provide a corresponding device for carrying out the method.

Disclosure of the invention

The object relating to the method is achieved by using a two-point lambda probe for secondary air diagnosis and / or for secondary air control after the first catalyst and the secondary air supply and for this purpose certain measures for compensating for tolerance and aging effects are used.

A variant of the method also provides that at least one particle filter is arranged after the first catalyst and the secondary air feed or the particle filter is part of the further catalyst and the secondary air diagnosis and / or the secondary air control is carried out with the secondary air feed and the two-point lambda probe for the particle filter.

Thus, a comparatively simple and inexpensive exhaust gas purification system can be provided. In general, an engine control unit for an exhaust bank does not offer the possibility of operating a second broadband lambda probe with it. By contrast, the possibility of operating a broadband lambda probe and two two-point lambda probes is usually already present, so that no change to the control unit hardware is necessary. However, the use of a two-point lambda probe for lambda control with secondary air at λ = 1 and lean exhaust lambda (λ> 1) requires that there is a clear relationship between the probe voltage and the exhaust lambda. This relationship must be particularly unambiguous over the lifetime of the probe, otherwise a wrong lambda value is adjusted, which can lead to an unnecessarily slow Rußabbrand by unnecessarily slow heating of the particulate filter or its damage and increased emissions. This condition is usually not met. Instead, the actual probe characteristic may be offset by tolerance and aging effects from a reference probe characteristic. Therefore, applying certain measures to compensate for tolerance and aging effects is particularly important. With the help of such a corrected lambda signal are a lambda control with active secondary air operation and a diagnosis of a secondary air pump or the Secondary air system with sufficiently high accuracy allows.

The use of the first two-point lambda probe in this installation position for balancing the storage capacity of oxygen or fat gas of the second catalyst is described in an unpublished parallel application of the applicant with the internal file number R.366298. The requirements for the accuracy of the control and the diagnosis of the first catalyst can be better met by the exhaust system according to the invention than with the aforementioned exhaust system. The accuracy of the diagnosis of the second catalyst is sufficient in the exhaust gas system according to the invention to allow a reliable distinction between a still good and a defective catalyst. For the lambda control with secondary air at lambda ≠ 1 and for a diagnosis of the secondary air pump or the secondary air system, the accuracy is also considered sufficient. With the exhaust system according to the invention, therefore, the fulfillment of stricter emission and diagnostic requirements is possible cost-effectively.

• • Breitband-Lambdasonde /1. Katalysator/ Breitband-Lambdasonde / 2. Katalysator / Zweipunkt-Lambdasonde / 3. Katalysator / Zweipunkt-Lambdasonde oder
• • Breitband-Lambdasonde /1. Katalysator/ Zweipunkt-Lambdasonde / 2. Katalysator / NO_x-Katalysator / Zweipunkt-Lambdasonde oder
• • Breitband-Lambdasonde /1. Katalysator/ Zweipunkt-Lambdasonde / 2. Katalysator / Breitband-lambdasonde / 3. Katalysator / Zweipunkt-Lambdasonde / 4. Katalysator / Zweipunkt-Lambdasonde

It goes without saying that this central section of the exhaust gas purification system can be part of a more complex emission control system in which further exhaust gas-cleaning components can be installed in front of or behind this central section. For example, the following arrangements are conceivable:

• • Broadband lambda probe / 1. Catalyst / broadband lambda probe / 2. Catalyst / two-point lambda probe / 3. Catalyst / two-point lambda probe or
• • Broadband lambda probe / 1. Catalyst / two-point lambda probe / 2. Catalyst / NO _x catalyst / two-point lambda probe or
• • Broadband lambda probe / 1. Catalyst / two-point lambda probe / 2nd catalyst / broadband lambda probe / 3rd catalyst / 2-point lambda probe / 4th catalyst / 2-point lambda probe

A particularly preferred variant of the method provides that, in order to compensate for tolerance and aging effects, an offset of the probe characteristic of the first two-point lambda probe is adapted by balancing with high excess air when the internal combustion engine is running or stationary. This makes it particularly cost-effective to adapt a two-point lambda probe for the aforementioned measurement tasks.

To increase the accuracy of the secondary air diagnosis and / or the secondary air control, it can be provided that for the adaptation of an offset compensation in addition by a shift of the lambda-one point of the probe characteristic of the first two-point lambda probe is performed via a guide control of the second two-point lambda probe ,

An extended compensation of tolerance and aging effects can be achieved if a correction of a temperature-induced shift of the probe characteristic is used with the aid of an active measurement of the sensor element temperature with the engine running or stationary.

In addition, it can be provided that a correction of the calculation of the lambda value is used to adapt an offset taking into account a current exhaust gas composition and a different cross-sensitivity to different exhaust gas components.

Depending on the required accuracy, provision may also be made for the previously described corrective measures to be used in combination.

A particularly preferred use of the method with its method variants described above provides for the use of vehicles with at least two successively arranged catalysts in an exhaust gas purification system. which is about compliance with particularly stringent exhaust gas regulations. By applying the method according to the invention with the method variants for compensating the tolerance and aging effects, in particular the particle emission can be significantly reduced, since the particle filter can be operated in an optimal range for secondary air introduction.

The object relating to the device is achieved by arranging a first two-point lambda probe for secondary air diagnosis and / or secondary air control downstream of the first catalytic converter and secondary air supply, and an engine control unit is provided for carrying out the method according to the invention, to which the signals of the different lambda probes are switched on, and having these facilities, such as storage and / or comparison units, in addition to a catalyst diagnosis, a secondary air diagnosis and / or secondary air control and measures to compensate for tolerance and aging effects of the first two-point lambda probe according to the method variants described above allow. The functionality of these functions may be at least partially software-based, e.g. in the form of a control software, which may be provided as a separate unit or as part of a higher-level control unit.

To reduce the particle emission, a particle filter may be arranged after the first catalyst and the secondary air supply, or the particle filter may be designed as part of the further catalyst. These can be designed as catalytically coated particle filters.

The invention will be explained in more detail below with reference to an embodiment shown in the figure. It shows:

1 a schematic representation of an internal combustion engine with an emission control system, with which the inventive method can be applied.

1 shows a schematic representation of an internal combustion engine 1 consisting of an engine block 10 and an exhaust duct 20 , in which in the flow direction of the exhaust gas behind the engine block 10 a designed as a broadband lambda probe lambda probe 30 and behind it a first catalyst 40 are arranged. The lambda probe 30 allows the lambda control 100 and serves for the first accounting 110 for the diagnosis of the storage capacity of the first catalyst. It is usually designed as a broadband lambda probe.

Behind the first catalyst 40 is a first two-point lambda probe according to the invention 50 arranged for the catalyst diagnosis guide control and for breakthrough detection for the diagnosis of the first catalyst 40 serves. This first two-point lambda probe 50 In addition to balancing the storage capacity of the subsequent further catalyst 60 used. The further catalyst 60 can be designed as a combination block of catalyst and particle filter or as a coated particle filter. Likewise, a separate particle filter is conceivable.

After the further catalyst 60 is a second two-point lambda probe 70 for breakthrough detection for catalyst diagnosis 140 the further catalyst 60 intended. The lambda probes 30 . 50 and 70 are with a motor control unit 80 connected in the one hand, the lambda control and on the other hand, the diagnostic methods with regard to the monitoring of the functionality of the emission control system hardware or software implemented.

In addition, in this arrangement, a secondary air supply 90 in the exhaust duct 20 between the first catalyst 40 and first two-point lambda probe 50 intended. The first two-point lambda probe 50 Here, according to the invention, in addition to the secondary air diagnosis and the supply air control (in the combination: command control / secondary air diagnosis 120 as well as second balancing / secondary air control 130 ).

For faster heating of the catalyst 60 with particle filter function to its operating temperature is in the case of a rich combustion chamber mixture by secondary air introduction via the secondary air supply 90 caused an exothermic reaction in the coated particle filter before the particle filter. In order to avoid unnecessary emissions, a mean exhaust lambda of at least 1 must be maintained in front of the particulate filter. At sufficiently high temperature of the particulate filter can be achieved by excess oxygen combustion of the soot loading and thus the regeneration of the particulate filter. For this purpose, a defined lean exhaust lambda must be maintained before the particulate filter.

A lambda probe is then suitable as a probe in front of the coated particle filter for regulating the lambda in secondary air introduction and for a diagnosis of the secondary air pump or the secondary air system, if it has a sufficiently accurate lambda signal in a wide lambda range (typically at least between λ = 1 and λ = 1.2). A two-point lambda probe 50 . 70 does not fulfill this requirement without further measures.

This restriction also applies if the two-point lambda probe 50 , as described in the applicant's co-pending application R.366298, is to be used as a probe in front of the catalyst for adjusting the lambda value in rich preconditioning and adjusting the lean lambda value and for balancing the amount of oxygen introduced when measuring the oxygen storage capacity of the catalyst. In particular, a sufficiently accurate lambda signal in a lambda range of typically between λ = 0.95 and λ = 1.05 is required here.

The use of an in 1 first two-point lambda probe 50 for the lambda control with secondary air or for their diagnosis sets the compensation of tolerance and aging effects, which leads to a shift of the actual probe characteristic with respect to the control unit or the engine control unit 80 stored reference probe characteristic. Only then does the lambda signal of this first two-point lambda probe fulfill 50 the specified accuracy requirements.

• • Adaption eines konstanten Offsets der Sondenkennlinie durch einen Abgleich bei hohem Luftüberschuss bei laufendem Motor oder bei stehendem Motor.
• • Kompensation der Verschiebung des Lambda-Eins-Punktes der Sondenkennlinie über eine Führungsregelung mit der zweiten Zweipunkt-Lambdasonde 50,
• • Kompensation einer temperaturbedingten Verschiebung der Sondenkennlinie mit Hilfe einer aktiven Messung der Sensorelementtemperatur bei laufendem oder stehendem Motor.
• • Berücksichtigung der aktuellen Abgaszusammensetzung und von unterschiedlichen Querempfindlichkeiten der Sonde gegenüber verschiedenen Abgaskomponenten bei der Umrechnung der Sondenspannung zu einem Lambdawert.

By the applicant are under the file number DE102012211687A1 . DE102012211683A1 . DE102013216595A1 . DE102014210442A1 . DE102012221549A1 Methods have already been filed which provide for a compensation of tolerance and / or aging effects that result in such Characteristic curve shift, allow. The methods described there are used individually or in combination in the context of this invention to the first two-point lambda probe 50 applied:

• • Adaptation of a constant offset of the probe characteristic curve by adjustment with high excess air with the engine running or with the engine stopped.
• • Compensation of the shift of the lambda one point of the probe characteristic via a master control with the second two-point lambda probe 50 .
• • Compensation of a temperature-related shift of the probe characteristic with the aid of an active measurement of the sensor element temperature with the engine running or stopped.
• • Consideration of the current exhaust gas composition and of different cross-sensitivities of the probe compared to different exhaust gas components in the conversion of the probe voltage to a lambda value.

In a particularly preferred variant of the method of the invention, only a constant offset of the probe characteristic is adapted. This is comparatively easy by a balance at high excess air possible, as it exists for example during overrun fuel cutoff, and in many cases already leads to a sufficient accuracy of the lambda signal to it for the balancing of the oxygen input and output for the diagnosis of the catalyst 60 to use. At the same time, this adaptation improves the accuracy of the breakthrough detection in the diagnosis of the first catalyst 40 and the accuracy of the guidance regulation 120 with the help of the first two-point lambda probe 50 ,

By combining the adaptation of a constant offset of the probe characteristic with one or more of the above-mentioned methods, the accuracy of the lambda signal of the first two-point lambda probe 50 behind the first catalyst 40 be further improved if even higher demands are placed on the accuracy of this lambda signal.

After compensation, the lambda signal becomes the first two-point lambda probe 50 as described above for the lambda control with secondary air used to operate the particulate filter optimally. In addition, a corresponding diagnosis of a secondary air pump or the secondary air system can take place.

The process according to the invention can also be transferred analogously to exhaust gas purification plants with more than two monitored catalysts or coated particle filters.

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 102009043087 A1 [0011]
• DE 102013226063 A1 [0013]
• DE 102012211687 A1 [0039]
• DE 102012211683 A1 [0039]
• DE 102013216595 A1 [0039]
• DE 102014210442 A1 [0039]
• DE 102012221549 A1 [0039]

Claims (10)

Method for controlling and / or monitoring the function of a secondary air supply ( 90 ) in an exhaust gas purification system of an internal combustion engine ( 1 ), which in its central section at least two in an exhaust passage ( 20 ) successively arranged catalysts ( 40 . 60 ) and in front of or behind this central section, further exhaust-gas-cleaning components may be arranged, wherein in the flow direction of the exhaust gas after an engine block ( 10 ) and before the first catalyst ( 40 ) a lambda probe ( 30 ) and in front of another catalyst ( 60 ) a further exhaust gas probe is arranged, wherein between the first and the further catalyst ( 60 ) by means of the secondary air supply ( 90 ) Air for optimal operation of the further catalyst ( 60 ), characterized in that after the first catalyst ( 40 ) and the secondary air supply ( 90 ) a two-point lambda probe ( 50 ) is used for secondary air diagnosis and / or for the secondary air control and for this particular measures for the compensation of tolerance and aging effects are used. Process according to claim 1, characterized in that after the first catalyst ( 40 ) and the secondary air supply ( 90 ) at least one particle filter is arranged or the particle filter is part of the further catalyst ( 60 ) and with the secondary air supply ( 90 ) and the two-point lambda probe ( 50 ) for the particulate filter, the secondary air diagnosis and / or the secondary air control is performed. A method according to claim 1 or 2, characterized in that to compensate for tolerance and aging effects, an offset of the probe characteristic of the first two-point lambda probe ( 50 ) by an adjustment at high excess air with running or stationary internal combustion engine ( 1 ) is adapted. Method according to one of claims 1 to 3, characterized in that to compensate for tolerance and aging effects compensation by a shift of the lambda one-point of the probe characteristic of the first two-point lambda probe ( 50 ) via a guide control of the second two-point lambda probe ( 70 ) is carried out. A method according to claim 3 or 4, characterized in that for the compensation of tolerance and aging effects, a correction of a temperature-induced shift of the probe characteristic by means of an active measurement of the sensor element temperature with running or stationary internal combustion engine ( 1 ) is applied. A method according to claim 3, characterized in that for the consideration of a current exhaust gas composition and a different cross sensitivity to different exhaust gas components, a correction of the calculation of the lambda value is applied. Method according to one of claims 3 to 6, characterized in that the corrective measures are applied in combination. Use of the method according to claims 1 to 7 for vehicles with at least two successively arranged catalysts in an emission control system for compliance with particularly stringent exhaust gas regulations. Device for controlling and / or monitoring the function of a secondary air supply ( 90 ) an exhaust gas purification system of an internal combustion engine ( 1 ), which in its central section at least two in an exhaust passage ( 20 ) successively arranged catalysts ( 40 . 60 ) and in front of or behind this central section, further exhaust-gas-cleaning components may be arranged, wherein in the flow direction of the exhaust gas after an engine block ( 10 ) and before the first catalyst ( 40 ) a lambda probe ( 30 ) and after the first and after the further catalyst ( 60 ) a further exhaust gas probe is arranged, wherein between the first and further catalyst ( 40 . 60 ) by means of the secondary air supply ( 90 ) Air for optimal operation of the further catalyst ( 60 ), wherein the signals of the various lambda probes ( 30 . 70 ) an engine control unit ( 80 ), characterized in that after the first catalyst ( 40 ) and the secondary air supply ( 90 ) a first two-point lambda probe ( 50 ), which is also connected to the engine control unit ( 80 ) and the engine control unit ( 80 ) Devices, such as storage and / or comparison units, in addition to a catalyst diagnosis, a secondary air diagnosis and / or secondary air control and measures to compensate for tolerance and aging effects of the first two-point lambda probe ( 50 ) according to the method claims 3 to 7 allow. Device according to claim 9, characterized in that after the first catalyst ( 40 ) and the secondary air supply ( 90 ) a particle filter is arranged or the particle filter as part of the further catalyst ( 60 ) is executed.

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