DE102010028852B4 - Method and device for diagnosing an exhaust gas purification system for an internal combustion engine - Google Patents

Abstract

Method for diagnosing an exhaust gas cleaning system (33) for removing pollutants from the exhaust gas of an internal combustion engine (31), with at least one measure for the amount of a component of the exhaust gas is determined and a performance, a speed or a load of the internal combustion engine (31), an injection quantity or a driving speed (10) are determined as parameters, with driving cycle classes being formed, for which driving cycle classes Limit values for the measure of the content of the exhaust gas are set, with the current driving cycle class being determined during operation of the internal combustion engine (31), with the measure of the content of the exhaust gas formed during operation of the internal combustion engine (31) being compared with the current driving cycle class specified limit value is compared, the exhaust gas purification system (33) being identified as faulty if a maximum limit value is exceeded or if a minimum limit value is not reached, the driving cycle class being based on a frequency or an intensity of changes in at least one of the parameters or determined from a combination of these values.

Description

The invention relates to a method for diagnosing an exhaust gas cleaning system for removing pollutants from the exhaust gas of an internal combustion engine, wherein at least one measure for the amount of a component of the exhaust gas is determined in the direction of flow of the exhaust gas after the exhaust gas cleaning system by means of an exhaust gas sensor during operation of the internal combustion engine and wherein Parameters a performance, a speed or a load of the internal combustion engine, an injection quantity or a driving speed are determined.

The invention also relates to a device for diagnosing an exhaust gas cleaning system for removing pollutants from the exhaust gas of an internal combustion engine, with an exhaust gas sensor being arranged downstream of the exhaust gas cleaning system in the flow direction of the exhaust gas, with the exhaust gas sensor being connected to a control unit of the internal combustion engine and with a program sequence in the control unit is provided to form a measure for the quantity of at least one component of the exhaust gas from the signal from the exhaust gas sensor, and the control unit has information about a power, a speed or a load of the internal combustion engine, an injection quantity or a driving speed as parameters.

State of the art

Compliance with and monitoring of emission limit values is increasingly being required by law while a vehicle is in operation. Based on a standardized driving cycle, a mass for a pollutant such as solid particles, hydrocarbons or nitrous oxide is specified for the route, and if this is exceeded, the vehicle driver must be informed of the emission problem. The violation must be detected in practical driving with any driving cycles, while the definition of a vehicle to be regarded as intact or defective is evaluated according to the standardized driving cycle. The distinction between intact and defective vehicles is made more difficult, since the difference between emissions that are still permissible and a vehicle that is to be regarded as defective is only small. For example, US legislation stipulates that a defect is only 1.5 times the permissible certification limit value for exhaust gas limit value monitoring. At the same time, it must be prevented that the monitoring classifies intact vehicles as defective in some driving situations. For this reason, using a fixed limit value that is independent of the driving situation is not a viable option. If the vehicle is operated under full load, emissions can be so high that a fixed limit value would be exceeded, although the vehicle can be considered healthy according to the standard driving cycle. The opposite case is also conceivable with a fixed limit. A defective vehicle operated with low emissions through appropriate driving behavior could go undetected for a long time while failing to withstand official inspection.

In order to reduce particle emissions from diesel engines, particle filters are used in the exhaust gas duct of internal combustion engines. The exhaust gas from the internal combustion engine is routed through the particle filter, which separates the solid particles in the exhaust gas and retains them in a filter substrate. Due to the soot masses stored in the filter substrate, the particle filter becomes clogged over time, which is noticeable in an increase in exhaust back pressure with a negative effect on engine performance and fuel consumption. For this reason, the stored soot mass has to be discharged from time to time. This filter regeneration takes place during separate regeneration phases via an oxidative burn-off of the particles, which takes place automatically as an exothermic reaction if the exhaust gas temperature is at least 580° C. and the oxygen concentration in the exhaust gas is sufficiently high. If such a filter is defective, uncleaned exhaust gas with solid particles undesirably reaches the outside world. It is therefore proposed to arrange a particle sensor after the particle filter as part of an on-board diagnosis in order to monitor its function. Furthermore, the loading status of the particle filter can be predicted by means of a particle sensor in front of the particle filter.

In Scripture DE 102005034247 A1 describes a method for monitoring an exhaust gas limit value of an internal combustion engine by means of an engine controller, the engine controller having at least one exhaust gas sensor and an error signal being emitted when the exhaust gas limit value is exceeded. The emissions predicted for the current driving situation are determined with the help of an engine model and compared with the signal from the exhaust gas sensor or a comparative value for the emissions derived from it. The exhaust gas sensor can be a collecting particle sensor. The method enables exhaust gas monitoring in the case of combustion engine operating conditions that deviate from standardized driving cycles for which the exhaust gas limit values are specified.

The DE 102006018956 A1 describes a method for determining a mass of particles or a particle mass flow in an exhaust system of an internal combustion engine, wherein in the exhaust system of the internal combustion engine at least at least one resistive particle sensor is arranged, the measured signal change of which is compared with a predicted signal change of the particle sensor determined from an engine model. Provision is made here for the measured signal change of the particle sensor and/or the predicted signal change of the particle sensor to be corrected, taking into account variables influencing cross-sensitivities of the particle sensor.

The procedures enable a distinction to be made between a defective particle filter and one that can still be considered intact. The disadvantage here is that both methods require a high level of software complexity in the engine control unit, in particular for the application of a particle raw emission model.

It is therefore the object of the invention to provide a device and a method which enable improved diagnosis of a defective particle filter with reduced software application complexity.

Other methods and devices are in the DE 195 37 788 A1 and the DE 10 2007 061 468 A1 disclosed.

Disclosure of Invention

The object of the invention relating to the method is achieved in that driving cycle classes are formed, that limit values for the measure of the content of the exhaust gas are specified for the driving cycle classes, that the current driving cycle class is determined during operation of the internal combustion engine, that the measure formed during operation of the internal combustion engine for the content of the exhaust gas is compared with the limit value specified for the current driving cycle class and that the exhaust gas cleaning system is recognized as faulty if a maximum limit value is exceeded or if a minimum limit value is not reached. The emission of the ingredient to be monitored can fluctuate depending on the operating parameters of the internal combustion engine, and thus depending on the driving conditions. As a result, different quantity flows of the ingredient can occur after a properly working emission control system. The applicable limit value must therefore be adapted to the situation. The invention proposes deriving driving cycle classes from the operating parameters present in the control unit of the internal combustion engine as a particularly simple choice of limit value, with the emissions having a known value within a driving cycle class. The determination of the appropriate limit value is possible without additional information or additional sensors and is therefore very cost-effective.

A particularly advantageous implementation of the method provides that the driving cycle class is considered individually as a parameter from the power, the speed or the load of the internal combustion engine, the injection quantity or the driving speed or is determined in combination with several of these parameters. Only parameters that are already present in the control unit of the internal combustion engine and whose effect on the untreated emissions of the internal combustion engine are taken into account when forming the limit value are used.

According to the invention, the driving cycle class is determined from a frequency or strength of changes in at least one of the parameters or from a combination of these values. Driving situations with low raw emissions can thus be separated from those with strong fluctuations in the parameters and thus typically high raw emissions by driving at a constant low load. By averaging the effect of parameters, several characteristics can be linked when forming the limit value.

An alternative embodiment provides that the driving cycle class is determined via a characteristic curve from the mean value of at least one of the parameters or from a frequency or strength of changes in at least one of the parameters or from a combination of these values. In this case it can be provided that no discrete driving cycle classes are generated, but rather that the driving cycle classes can assume continuous values.

An embodiment that is particularly easy to implement provides that a quantity of particles and/or nitrogen oxides and/or hydrocarbons determined at the exhaust gas sensor or a variable derived from this is determined over a specified measurement period as a measure of a constituent of the exhaust gas and is used with the current driving cycle Class associated limit is compared. In this case, the measurement duration can be adapted to the typical duration of a driving cycle class, such as a city trip, a cross-country trip or a freeway trip. The measurement duration can advantageously also be selected in such a way that the measurement accuracy of the exhaust gas sensor, for example a collecting particle sensor, is particularly high.

The erroneous classification of a correctly working emission control system as faulty can largely be avoided by inferring a defective emission control system, if a faulty emission control system was diagnosed in at least two consecutive measurement cycles.

An advantageous embodiment of the method provides that the limit values for the various driving cycle classes are defined during operation of an internal combustion engine with an exhaust gas purification system that has been damaged at certain points.

The object relating to the device is achieved in that limit values for the measure of the ingredient are stored in the control unit as a function of specified driving cycle classes, that a program sequence for recognizing driving cycle classes from parameters during operation of the internal combustion engine or of a vehicle operated therewith and that a comparison of the measure for the amount of the substance in the exhaust gas with a limit value specified for the driving cycle class is provided. With little additional effort, the raw emissions of the internal combustion engine can be predicted with high accuracy as a function of the operating situation.

If the exhaust gas cleaning system is designed as a particle filter, as a catalytic converter for selective catalytic reduction (SCR) or as a three-way catalytic converter, its correct function can be monitored particularly easily within the device described.

If the exhaust gas sensor is designed as a collecting resistive particle sensor, the correct function of a particle filter can be monitored by integrating the expected emissions over time in the driving cycle classes formed.

character list

• 1 eine Brennkraftmaschine mit einem Abgasreinigungssystem in schematischer Darstellung,
• 2 ein Ablaufdiagramm zur Diagnose eines Abgasreinigungssystems.

The invention is explained below using an exemplary embodiment illustrated in the figures. Show it:

• 1 an internal combustion engine with an exhaust gas cleaning system in a schematic representation,
• 2 a flowchart for diagnosing an emission control system.

1 shows an internal combustion engine 30 with an exhaust gas purification system 33 in a schematic representation. The illustration is limited to the components that are essential to the invention.

A fuel-air mixture is supplied to an internal combustion engine 31 via a fuel-air supply 30 . An exhaust gas cleaning system 33 and an exhaust gas sensor 34 are arranged in an exhaust gas duct 32 of the internal combustion engine 31 in the flow direction of the exhaust gas. A sensor signal 20 and a driving speed 10 determined by a speedometer (not shown) are fed to a control unit 35 .

The exhaust gas cleaning system 33 cleans the exhaust gas of the internal combustion engine 31 from at least one component of the exhaust gas. In this case, the exhaust gas sensor 34 measures the concentration or the quantity of at least one ingredient.

2 shows a flowchart for diagnosing an exhaust gas cleaning system 33 of an internal combustion engine 31, which describes the sequence of a program sequence stored in a control unit of the internal combustion engine 31. In the 1 introduced driving speed 10 is supplied as a parameter of a first averaging stage 11 and an alternating frequency stage 12. The first averaging stage 11 is followed by a first driving cycle class formation 13, the alternating frequency stage 12 is followed by a second driving cycle class formation 14. The first driving cycle class formation 13 and the second driving cycle class formation 14 follow a second averaging stage 15 and a comparison stage 16.

In a second branch of the flowchart, the in 1 sensor signal 20 of the exhaust gas sensor 34 shown is supplied to an integration stage 21, which is followed by the comparison stage 16. After the comparison stage 16, a block for a display 22 is provided.

The driving speed 10 describes the speed of a motor vehicle driven by the internal combustion engine 31 . In the first averaging stage 11, an average driving speed is formed from this over a predetermined period of time. At the same time, the frequency and strength of changes in the driving speed 10 in the predetermined period of time are recorded in the alternating frequency stage 12 .

Depending on the average driving speed, in the first driving cycle class formation 13 the route driven in the predetermined period of time is assigned to a stored driving cycle class. A signal change expected for a limit exhaust gas aftertreatment system for an exhaust gas sensor 34 downstream of the exhaust gas cleaning system 33 of the internal combustion engine 31 is assigned to each driving cycle class. In this case, an exhaust gas aftertreatment system that just barely meets the legal requirements with regard to filter properties for a respective exhaust gas component detected by the exhaust gas sensor 34 is considered to be a limit exhaust gas aftertreatment system. The expected sig nal change is fed to the second averaging stage 15 .

Based on the frequency and strength of the change in driving speed 10 in the predetermined time period, the second driving cycle class formation 14 is used to further assign the route covered in the predetermined time period to a driving cycle class and, derived from this, to an expected signal change of the dem Exhaust gas cleaning system 33 of the internal combustion engine 31 downstream exhaust gas sensor 34 on the assumption of a borderline damaged exhaust gas cleaning system 33. The signal change determined in this way can differ from the signal change determined from the average driving speed, since, for example, with the same average driving speed and the same exhaust gas cleaning system 33, the driving speed 10 changes frequently higher exhaust emissions than driving at a constant driving speed 10.

In the second averaging stage 15, the signal changes determined in the first averaging stage 11 and the alternating frequency stage 12 are averaged. The averaging can be arithmetic or weighted. The mean signal change obtained in this way is compared in the comparison stage 16 with the signal change actually shown by the exhaust gas sensor 34 . The signal change actually shown by the exhaust gas sensor 34 is obtained by integrating the sensor signal 20 in the integration stage 21 .

In the case of accumulating exhaust gas sensors 34, for example in the case of particle sensors, the integration stage 21 can be omitted, since the accumulating principle includes integration over the quantity of exhaust gas components that occur.

By comparing the signal change actually shown by the exhaust gas sensor 34 with a signal change specified for the driven driving cycle for an exhaust gas cleaning system 33 with borderline damage, the functionality of the exhaust gas cleaning system 33 can be determined after or during almost any operating conditions of the internal combustion engine 31. If the comparison in comparison stage 16 shows that exhaust gas cleaning system 33 allows a larger quantity of the respective exhaust gas component to pass through than is intended for the driving cycle determined for an exhaust gas cleaning system 33 with borderline damage, exhaust gas cleaning system 33 is identified as defective and the operator of internal combustion engine 31 is notified of the Display 22 informed accordingly.

In addition to driving speed 10 or in addition to driving speed 10, further parameters, for example the power, speed or load of internal combustion engine 31 or the fuel injection quantity supplied to internal combustion engine 31, can be used to classify the driving cycle.

The comparison can be made directly with the sensor signals or the integrals of the sensor signals with the sensor signals expected for an exhaust gas cleaning system 33 with borderline damage. However, variables derived from the sensor signals can also be compared. It can be provided that the concentration of an exhaust gas component currently measured by the exhaust gas sensor 34 is multiplied by the current exhaust gas volume flow and the resulting mass flow of the exhaust gas components is integrated to form a total mass. In the first driving cycle class formation 13 and the second driving cycle class formation 14, a total mass for the exhaust gas component is then output on the basis of the determined driving cycle, as is expected for the driving cycle for an exhaust gas cleaning system 33 with borderline damage, in which second averaging stage 15 averaged and the comparison stage 16 fed.

Claims (10)

Method for diagnosing an exhaust gas cleaning system (33) for removing pollutants from the exhaust gas of an internal combustion engine (31), with at least one measure for the amount of a component of the exhaust gas is determined and a performance, a speed or a load of the internal combustion engine (31), an injection quantity or a driving speed (10) are determined as parameters, with driving cycle classes being formed, for which driving cycle classes Limit values for the measure of the content of the exhaust gas are set, with the current driving cycle class being determined during operation of the internal combustion engine (31), with the measure of the content of the exhaust gas formed during operation of the internal combustion engine (31) being compared with the current driving cycle class specified limit value is compared, the exhaust gas purification system (33) being identified as faulty if a maximum limit value is exceeded or if a minimum limit value is not reached, the driving cycle class being based on a frequency or an intensity of changes in at least one of the parameters or determined from a combination of these values. procedure after claim 1 , characterized in that the driving cycle class from the power, the speed or the load of the internal combustion engine (31), the injection quantity or the driving speed (10) as a parameter, each considered individually or determined in combination with several of these parameters. procedure after claim 1 or 2 , characterized in that the driving cycle class is additionally determined from the mean value of at least one of the parameters. Procedure according to one of Claims 1 until 3 , characterized in that the driving cycle class is determined via a characteristic curve from the mean value of at least one of the parameters or from a frequency or strength of changes in at least one of the parameters or from a combination of these values. Procedure according to one of Claims 1 until 4 , characterized in that a quantity of particles and/or nitrogen oxides and/or hydrocarbons determined at the exhaust gas sensor (34) or a variable derived therefrom is determined as a measure for a constituent of the exhaust gas over a predetermined measurement period and with the assigned to the current driving cycle class Limit is compared. Procedure according to one of Claims 1 until 5 , characterized in that a defective exhaust gas cleaning system (33) is concluded if a faulty exhaust gas cleaning system (33) was diagnosed in at least two consecutive measurement cycles. Procedure according to one of Claims 1 until 6 , characterized in that the limit values for the various driving cycle classes are defined during operation of an internal combustion engine (31) with an exhaust gas purification system (33) that is damaged at the boundary. Device for diagnosing an exhaust gas cleaning system (33) for removing pollutants from the exhaust gas of an internal combustion engine (31), an exhaust gas sensor (34) being arranged downstream of the exhaust gas cleaning system (33) in the flow direction of the exhaust gas, the exhaust gas sensor (34) having a control unit ( 35) of the internal combustion engine (31) and wherein a program sequence is provided in the control unit (35) to form a measure for the quantity of at least one component of the exhaust gas from the signal from the exhaust gas sensor (34) and the control unit (35) as parameters Information on a power, a speed or a load of the internal combustion engine, an injection quantity or a driving speed (10) is available, with limit values for the measure for the ingredient depending on specified driving cycle classes being stored in the control unit (35), with the control unit (35) a program sequence for recognizing driving cycle classes from parameters during operation of the internal combustion engine (31) or a vehicle operated with it is provided, with a comparison of the measure for the quantity of the substance in the exhaust gas being provided with a limit value specified for the driving cycle class and wherein the driving cycle class is determined from a frequency or strength of changes in at least one of the parameters or from a combination of these values. device after claim 8 , characterized in that the exhaust gas cleaning system (33) is designed as a particle filter, as a catalytic converter for selective catalytic reduction (SCR) or as a three-way catalytic converter. device after claim 8 or 9 , characterized in that the exhaust gas sensor (34) is designed as a collecting resistive particle sensor.

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