DE102012221567A1 - Method for operating exhaust gas after-treatment device of e.g. commercial vehicle, involves forming and storing adaptation factor based on parameters of engine for adjusting actually determined model value to actual nitrogen oxide-value - Google Patents

Abstract

The method involves determining actual nitrogen oxide-value in an exhaust gas pipe (5) of an internal combustion engine (1) by a nitrogen oxide-pre-treatment emission model and/or nitrogen oxide-sensor (24). The oxide-value is compared with actually determined model value of the emission model, and an adaptation factor is formed and stored based on operating parameters e.g. exhaust gas temperature and rotational speed, of the engine for adjusting the model value to the actual nitrogen oxide-value. The sensor is switched-off after reaching age-conditioned reduction of function of the sensor. Independent claims are also included for the following: (1) a control device for operating an exhaust gas after-treatment device (2) a computer program for executing a method for operating an exhaust gas after-treatment device.

Description

The present invention relates to a method for operating an exhaust aftertreatment device of a motor vehicle according to the preamble of claim 1. Furthermore, the subject of the invention is a control device and a computer program according to the preambles of the respective independent claims.

State of the art

When operating motor vehicles with an exhaust aftertreatment device with a selective catalytic reduction (SCR) from a storage tank, a liquid reducing agent - usually a urea-water solution (so-called AdBlue) - under pressure in an exhaust pipe of the internal combustion engine in the flow direction upstream of an SCR Catalyst injected. This method is known from the prior art.

The amount of einzudüsenden liquid reducing agent depends on a nitrogen oxide content of the exhaust gas. To determine the nitrogen oxide content in the exhaust gas, nitrogen oxide sensors and nitrogen oxide raw emission models are known. The DE 10 2009 028 873 A1 and the DE 10 2009 055 058 A1 describe methods for determining the nitrogen oxide content in the exhaust gas with the aid of raw emission models of the internal combustion engine.

For commercial vehicles (commercial vehicles), the internal combustion engines and their exhaust aftertreatment devices are usually required to have high mileage levels of more than 1 million kilometers. To operate such commercial vehicle internal combustion engines or their exhaust aftertreatment devices, for example, the known SCR systems are used for nitrogen oxide reduction of the exhaust gas. In order to operate such a system, usually a nitrogen oxide sensor is arranged upstream and downstream of the SCR catalyst. Concepts are also known in which the nitrogen oxide sensor arranged upstream of the SCR catalytic converter is dispensed with. Since the available nitric oxide sensors on the market have a limited life, they usually have to be replaced after a certain time or mileage (eg after 400 000 km), which is associated with costs.

Disclosure of the invention

The invention is characterized in that a nitrogen oxide value currently determined by the nitrogen oxide sensor in the exhaust pipe is compared with a currently determined model value of the nitrogen oxide raw emission model and an adaptation factor is formed to approximate the model value to the value determined by the nitrogen oxide sensor is stored.

The determination and storage of the adaptation factor is a very simple method step, which requires little computing power in the control unit of the internal combustion engine and can be realized very inexpensively. The adaptation factor is preferably stored in a memory area of the control unit for operating the exhaust gas aftertreatment device.

A major advantage of the determination according to the invention of the nitrogen oxide value is that only one single emission model is required for all variants of an internal combustion engine which differ, for example, with regard to the intake air routing or the installation position of the nitrogen oxide sensor in the exhaust pipe, since the engine according to the invention Adaptation factor adjusts the model value to the determined value of the nitrogen oxide sensor. Thus, it is possible, without deteriorating the control of the internal combustion engine to replace the nitrogen oxide value determined by the nitrogen oxide sensor by the model value of the raw emission model, which is preferably multiplied by the adaptation factor.

The method according to the invention independently recognizes the no longer tolerable reduction in the function of the nitrogen oxide sensor and then automatically switches over to a modified method for the proper operation of the exhaust gas aftertreatment device.

The cost-replacing exchange of the nitrogen oxide sensor after reaching its lifetime can thus be avoided by the method according to the invention.

It can also be dispensed with costly design changes to extend the life of the nitric oxide or sensors. The adaptation factor determined over the entire lifetime of the nitrogen oxide sensor for simulating the real nitrogen oxide value on the basis of the modeled nitrogen oxide value Is sufficiently accurate to operate the exhaust aftertreatment system over the entire life of the internal combustion engine within the limits required by law.

The DE 10 2009 028 873 A1 and the DE 10 2009 055 058 A1 For example, nitrogen oxide raw emission models, which can already very accurately determine the nitrogen oxide content in the exhaust gas from operating variables of the internal combustion engine. The determined adaptation factor is determined empirically in order to be able to take into account the large number of variants in the operation of the internal combustion engine (eg the many variants of the fresh air ducts in commercial vehicles) and later - after switching off the nitrogen oxide sensor - to determine the current nitrogen oxide value as an adaptation factor , It avoids to adapt for each variant of the operation of the internal combustion engine, the applied nitrogen oxide raw emission model by software. When using the method according to the invention in commercial vehicles, it is also possible to use less expensive nitrogen oxide sensors or exhaust aftertreatment devices, which are provided, for example, for passenger cars.

Since the inventive method is preferably used in motor vehicles, which are designed for high mileage, and thus the life of the motor vehicle exceeds the usual life of a nitric oxide sensor, it is further proposed that after determining an age-related and no longer tolerable reduction in the function the nitrogen oxide sensor is switched off or shut down the nitrogen oxide sensor. After the decommissioning of the nitrogen oxide sensor, the exhaust aftertreatment device is operated exclusively with the model value of the nitrogen oxide raw emission model and the previously stored adaptation factor.

In an alternative method, it is also possible that a temporal trend is determined from a multiplicity of adaptation factors stored over time and the trend is updated after switching off the nitrogen oxide sensor or sensors, so that changes over time in operation of the internal combustion engine and the exhaust aftertreatment device can be considered.

There are several possibilities for determining a no longer tolerable reduction in the function of the nitrogen oxide sensor. The simplest option is to set a lifetime based on empirical values for the general lifetime of the nitric oxide sensor. It is assumed that the nitrogen oxide sensor provides reliable values during this time. After reaching the lifetime of the nitrogen oxide sensor is turned off without further testing.

However, it is also possible that the reduction in the function of the nitrogen oxide sensor during operation is determined by e.g. In the coasting operation of the motor vehicle, a deviation of the determined values of the nitrogen oxide sensor from a tolerated value range or limit value of a nitrogen oxide content and / or an oxygen content in the exhaust gas is ascertained. If the values determined are outside the limit value, an unacceptable reduction in the function of the nitrogen oxide sensor is assumed. Comparable investigations are, for example, even at idle the internal combustion engine possible. Basically, all operating states of the internal combustion engine are suitable, in which a strongly delimited, tolerable nitrogen oxide and / or oxygen content in the exhaust gas can be predetermined during proper operation. The oxygen content can be used to check the nitrogen oxide sensor, because these sensors can also determine the oxygen content in the exhaust gas.

As an alternative to this method step, it is also possible for the reduction in the function of the nitrogen oxide sensor to be determined by exceeding a signal rise time during a defined operating state of the internal combustion engine. In particular, the transitions from operation under load to overrun operation and vice versa are suitable for this alternative. It is e.g. during such transitions determines the amount of time that elapses until z. B. 63% of the expected signal end value are reached. If this time longer than expected, a no longer tolerable reduction in the function of the nitrogen oxide sensor is assumed.

If such aging of the nitrogen oxide sensor is determined, the nitrogen oxide sensor is shut down. On the one hand, this can happen because the value of the nitrogen oxide sensor in the control unit for operating the exhaust gas aftertreatment device is no longer taken into account. In this case, corresponding sensor monitoring functions can be shut down. On the other hand, the nitrogen oxide sensor can also be switched off completely and no longer be supplied with power. A heating of the nitrogen oxide sensor is no longer necessary. This leads to a reduction of the required electrical power in the motor vehicle.

In a development of the method according to the invention, it is possible for a plurality of adaptation factors to be determined and stored as a function of at least one operating variable of the internal combustion engine. Thus, for example, a first adaptation factor for small exhaust gas volume flows and a second adaptation factor be determined and stored for large exhaust gas flow rates. The aim here is to determine and store respectively a possible very precise adaptation factor for different operating ranges of the internal combustion engine, so that later, after switching off the nitrogen oxide sensor, the nitrogen oxide contents are calculated with sufficient accuracy in all operating points. The number of generatable adaptation factors is basically arbitrary. Only for practical reasons will one limit the number.

Instead of the exhaust gas volume flow, alternatively or additionally, many other operating variables of the internal combustion engine or of the exhaust gas aftertreatment device can be evaluated. It is possible, for example, an exhaust gas temperature, a speed of the internal combustion engine, a load of the internal combustion engine, a nitrogen oxide concentration in the exhaust gas, a nitrogen oxide mass flow, an exhaust gas recirculation rate, an outside temperature, an intake air temperature, an ambient pressure, an operating mode of the internal combustion engine and / or the oxygen content in a suction pipe of the internal combustion engine.

Further advantages of the invention are the following drawings, the description and the claims can be removed. In each case, in schematic form:

1 the environment of the invention; and

2 a flow chart with the start of the method according to the invention.

In 1 is an internal combustion engine 1 with an exhaust aftertreatment device 3 greatly simplified and shown schematically and shows the environment of the invention. The exhaust aftertreatment device 3 includes an exhaust pipe 5 , an oxidation catalyst 7 and an SCR catalyst 11 , Not shown is a particulate filter, which is usually downstream of the oxidation catalyst 7 is arranged. The flow direction of the exhaust gas through the exhaust pipe 5 is indicated by arrows (without reference numerals).

To the SCR catalyst 11 with a liquid reducing agent, for example a urea-water solution (so-called AdBlue) or another liquid reducing agent is upstream of the SCR catalyst 11 at the exhaust pipe 5 a metering device 13 arranged for the urea-water solution. The metering device 13 injected after determination of a nitrogen oxide content in the exhaust gas, a certain amount of urea-water solution via an injection valve 15 upstream of the SCR catalyst 11 in the exhaust pipe 5 to get into the SCR catalyst 11 to reduce the toxic nitrogen oxide into harmless water and nitrogen.

The entire dosing system includes beside the dosing device 13 a metering pump 17 , as well as a storage tank 19 for the urea-water solution. Between the dosing pump 17 and the metering device 13 is a first line (reducing agent supply line) 21 intended. Between the storage tank 19 and the dosing pump 17 is a second line as a suction line 22 intended for the urea-water solution. The wires 21 and 22 may be at least partially designed as a hose.

In the exhaust pipe 5 are also in the flow direction of the exhaust gas in front of and behind the SCR catalyst 11 Nitrogen oxide sensors 24 and 25 arranged. The nitric oxide sensor 24 is optional because the exhaust aftertreatment device 3 in a modified process even without the nitrogen oxide sensor 24 can be operated. The nitric oxide sensors 24 and 25 have a limited life, which become unusable, especially when installed in a commercial vehicle (commercial vehicle) with a very high mileage expected before the commercial vehicle has reached the end of its life.

Furthermore, the exhaust pipe comprises 5 a temperature sensor 27 ,

The sensors 24 . 25 and 27 are via signal lines (no reference numeral) with a first control device 29 the internal combustion engine 1 connected. The first controller 29 controls the internal combustion engine 1 and sends and receives data from a second controller 26 for controlling the dosing system. The first controller 29 includes a program memory 31 in which a computer program of a method according to the invention is stored and executable. The program memory 31 can with a data store 33 , which is designed as an EEPROM, communicate. The signal lines from and to the second control unit 26 of the dosing system are in 1 represented by dotted lines.

The functions of the two control units 26 and 29 can also be integrated in a single controller (not shown).

2 shows an exemplary sequence of the method according to the invention 100 , With the aid of the method according to the invention, it is possible that even after a no longer tolerable aging of the nitrogen oxide sensors 24 and or 25 the exhaust aftertreatment device 3 of the motor vehicle, in particular of the commercial vehicle, can continue to be operated properly without, for example, the nitrogen oxide sensor 24 must be replaced.

First, the exhaust aftertreatment device 3 with the properly working nitrogen oxide sensor 24 operated in a conventional manner. In step 110 of the method according to the invention is in each case a current nitrogen oxide content NOx _mess in the exhaust pipe 5 through the nitrogen oxide sensors 24 and 25 determined. If only one nitric oxide sensor 24 or 25 in the exhaust pipe 5 is arranged, only a single value NOx _{mess is} determined.

At the same time is about one in the program memory 31 stored nitrogen oxide raw emission model calculated a nitrogen oxide content NOx _mod calculated. Efficient and suitable for the process according to the invention nitrogen oxide Rohemissions models are for example from DE 10 2009 028 873 A1 or the DE 10 2009 055 058 A1 to which reference is hereby made.

To the determined via the nitrogen oxide raw emission model value NOx _mod to that of the nitrogen oxide sensor 24 adjusted value to adjust NOx _mess , is in step 120 for the nitric oxide sensor 24 an adaptation _factor F _adap determined and in the data memory 33 saved.

NOx_adap:

ein adaptierter NOx-Wert im Abgas

F_adap:

ein Adaptionsfaktor

NOx_mod:

ein vom Rohemissionsmodell berechneter NOx-Wert

The determination of the adaptation _factor F _adap is preferably done in two steps. Initially, an adapted nitrogen oxide value NOx _adap for the nitrogen oxide sensor 24 determined. This happens according to the formula: NOx _adap = F _adap · NOx _mod (Eq. 1) With:

NOx _adap :

an adapted NOx value in the exhaust gas

_Fadap :

an adaptation factor

NOx _mod :

an NOx value calculated by the raw emission model

The Gl. 1 requires the knowledge of the adaptation _factor F _adap .

Mit:

K:

Verstärkungsfaktor oder Integrationsbeiwert.

NOx_mess:

ein vom Stickoxid-Sensor 24 ermittelter NOx-Wert

The adaptation _factor F _adap is determined according to the following formula:

With:

K:

Gain factor or integration coefficient.

NOx _measurement :

one from the nitric oxide sensor 24 determined NOx value

This integral element matches the modeled values and the measured values. Once this is achieved, the adaptation _factor F _{adap remains} constant.

The gain factor K, for example, takes into account the variances due to different intake tracts in different commercial vehicles in which the same internal combustion engine 1 is installed.

The amplification factor K also depends, inter alia, on an exhaust gas volume flow, an exhaust gas mass flow and / or a nitrogen oxide concentration.

The practical implementation in a control unit can be carried out so that the Adpationsfaktor F _{adap is} stored in the EEPROM. After the start of the internal combustion engine 1 the adpation factor F _{adap is} initialized and then always during operation with the adapted nitrogen oxide value determined according to the above equations NOx _{adap is} updated. That is, the adaptation _factor F _adap regularly during the operation of the internal combustion engine 1 determined as long as the nitric oxide sensor 24 still working properly.

The adaptation _factor F _{adap usually} assumes values between 0.7 and 1.5. Values outside of this range are likely to be incorrect and therefore not used.

Parallel to the determination of the current adaptation _factor F _adap is in the process step 130 by means of a diagnostic routine the nitric oxide sensor 24 tested for an intolerable aging. As long as no aging is detected, the process steps run 110 . 120 and 130 according to the above description in a loop in predetermined cycles from.

If an intolerable aging of the nitric oxide sensor 24 has been determined, by the nitric oxide sensor 24 delivered measured values are no longer processed, but only the results of the raw emission model using the current value of the adaptation _factor F _adap are used. This means that an aged or defective nitric oxide sensor 24 does not need to be replaced, but simply shut down or shut down.

To establish an intolerable aging of the nitrogen oxide sensor 24 There are several options.

A first possibility is to use empirical values to specify the lifetime of a nitrogen oxide sensor of the type used. Here is is assumed that the nitrogen oxide sensor within the lifetime provides more reliable and sufficiently accurate measurement values _measured NOx. With reaching the lifetime it is assumed that the nitric oxide sensor 24 no longer works properly.

A second possibility is the actual aging of the nitric oxide sensor 24 from time to time to check. This can be z. B. during a push operation (or a similar suitable operating state) of the motor vehicle.

In overrun combustion does not take place, so that no nitrogen oxide, but, inter alia, oxygen in the exhaust gas is present. So if the nitric oxide sensor 24 During the overrun operation, nitrogen oxide values that are above a specified limit value are determined, then the aging of the nitrogen oxide sensor 24 so far advanced that its readings are no longer usable.

Because the nitric oxide sensor 24 can also measure the oxygen content in the exhaust gas, a similar diagnosis can be carried out with the oxygen content in the exhaust gas.

A third possibility is that the reduction in the function of the nitric oxide sensor 24 by exceeding a signal rise time during a defined operating state of the internal combustion engine 1 is determined. In particular, the transitions from load operation to overrun operation and from overrun operation to load operation are suitable for this alternative.

For example, during such transitions, a period of time is determined which elapses until, for example, 63% of the expected signal end value has been reached. If this period of time is longer than a predetermined limit value, aging of the nitrogen oxide sensor becomes intolerable 24 accepted.

When the nitric oxide sensor 24 has an intolerable aging, so is the known method for operating the exhaust aftertreatment device 3 changed. For this purpose, in the process step 140 the nitric oxide sensor 24 shut down by the measured values of the nitrogen oxide sensor 24 no longer in the control unit 29 be taken into account. Additionally or alternatively, it is also possible that the nitrogen oxide sensor 24 no longer supplied with electricity.

To the exhaust aftertreatment device 3 to be able to continue operating properly is in the process step 150 the currently required nitrogen oxide content NOx _adap in the exhaust gas is determined by the nitrogen oxide raw emission model determining a nitrogen oxide content NOx _mod and multiplying this by the last stored adaptation factor adaptation factor F _adap .

The current nitrogen oxide content is at the installation position of the nitrogen oxide sensor 24 in the exhaust pipe 5 that is, according to Eq. 1 calculated. Thereafter, the known method for operating the exhaust aftertreatment device 3 continued, the previous from the nitric oxide sensor 24 determined nitrogen oxide content in the exhaust pipe 5 due to the adapted nitrogen oxide content NOx _adap according to Eq. 1 is replaced.

In a further development of the method according to the invention, it is possible that, depending on at least one operating variable of the internal combustion engine 1 several adaptation _factors F _adap1 , F _adap2 , etc. are determined and stored.

Thus, for example, a first adaptation _factor F _adap1 can be determined and stored for small exhaust gas volume flows. A second adaptation _factor F _adap2 is determined and stored for large exhaust gas volume flows.

The goal here is for different operating ranges of the internal combustion engine 1 in each case an adaptation _factor F _{adap, i} to determine and store, so later, after switching off the nitrogen oxide sensor 24 , an individually determined for all operating _ranges adaptation _factor F _{adap, i can be applied} to determine the current nitrogen oxide content NOx _adap in the exhaust gas. The number of usable adaptation _factors F _{adap, i} is not limited.

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 2009028873 A1 [0003]
• DE 102009055058 A1 [0003, 0011, 0032]
• DE 102009028873 A1 [0011, 0032]

Claims (11)

Method for operating an exhaust aftertreatment device ( 3 ) of a motor vehicle, wherein by a nitrogen oxide raw emission model and / or by a nitrogen oxide sensor ( 24 ) a nitrogen oxide value in an exhaust pipe ( 5 ) an internal combustion engine ( 1 ), characterized in that a through the nitrogen oxide sensor ( 24 ) in the exhaust pipe ( 5 ) currently determined nitrogen oxide value (NOx _mess ) with a currently determined model value (NOx _mod ) of the nitrogen oxide raw emission model is compared and for the approximation of the model value (NOx _mod ) to the by the nitrogen oxide sensor ( 24 ) determined value (NOx _mess ) an adaptation _factor (F _adap ) is formed and stored. A method according to claim 1, characterized in that the adaptation _factor (F _adap ) according to a formula

is determined. A method according to claim 1 or 2, characterized in that after reaching an age-related reduction of the function of the nitrogen oxide sensor ( 24 ) the nitrogen oxide sensor ( 24 ) and the exhaust aftertreatment device ( 3 ) is operated exclusively with a calculated nitrogen oxide value (NOx _adap ), wherein the adaptive nitrogen oxide value (NOx _adap ) from the model value (NOx _mod ) of the nitrogen oxide raw emission model and the one or more stored adaptation _factors (F _adap ) is determined. A method according to claim 3, characterized in that the nitrogen oxide value (NOx _adap ) according to the formula NOx _adap = F _adap · NOx _mod is determined A method according to claim 3 or 4, characterized in that the reduction in the function of the nitrogen oxide sensor ( 24 ) is defined after the expiry of a predetermined life. Method according to one of claims 3 to 5, characterized in that the reduction of the function of the nitrogen oxide sensor ( 24 ) is determined by during a coasting operation of the internal combustion engine ( 1 ) the determined values (NOx _mess ) of the nitrogen oxide sensor ( 24 ) exceed a predetermined limit. Method according to one of claims 3 to 6, characterized in that the reduction of the function of the nitrogen oxide sensor ( 24 ) by exceeding a signal rise time during a change of the operating state of the internal combustion engine ( 1 ) is determined. Method according to one of the preceding claims, characterized in that, depending on at least one operating variable of the internal combustion engine ( 1 ) several adaptation _factors (F _adap1 , F _adap2 ) are determined and stored. A method according to claim 8, characterized in that the at least one operating variable is an exhaust gas volume flow, an exhaust gas temperature, a rotational speed of the internal combustion engine ( 1 ), a load of the internal combustion engine ( 1 ), a nitrogen oxide concentration in the exhaust gas, a nitrogen oxide mass flow, an exhaust gas recirculation rate, an outside temperature, an intake air temperature, an ambient pressure, an operating mode of the internal combustion engine ( 1 ) and / or the oxygen content in an intake manifold of the internal combustion engine ( 1 ). Control unit ( 29 ) for operating an exhaust aftertreatment device ( 3 ) of a motor vehicle, characterized in that the control unit ( 29 ) is arranged to control the flow of a method according to one of claims 1 to 9. Computer program, characterized in that it is programmed to use a method according to one of claims 1 to 9.

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