Method for operating an internal combustion engine and device for executing the method

Abstract

A method for operating an internal combustion engine and a device for executing the method provide for diagnostics of the exhaust system in which an exhaust-gas treatment device for converting at least one undesirable exhaust gas component is situated. A measure for the conversion is determined from the exhaust gas component, ascertained upstream from the exhaust-gas treatment-device and measured downstream from the exhaust-gas treatment device and compared to a predefinable threshold value. An error signal is issued when the threshold is not met. The approach makes it possible in particular to detect a manipulation in the exhaust system such as the use of a dummy in the exhaust-gas treatment device or, for example, a deliberately defective lining of a component situated in the exhaust-gas treatment device.

Description

FIELD OF THE INVENTION

The present invention is directed to a method for operating an internal combustion engine, which provides for diagnostics of an exhaust system in which an exhaust-gas treatment device for converting at least one undesirable exhaust gas component is situated, and to a device for executing the method.

BACKGROUND INFORMATION

German Patent Application No. DE 44 26 020 describes a method in which the operational performance of a catalytic converter situated in an exhaust system of an internal combustion engine is monitored. Monitoring is carried out based on the temperature increase which occurs as a result of the exothermal conversion of oxidizable exhaust gas components in the catalytic converter. Two temperature signals are ascertained, the first temperature signal being based on a temperature measurement downstream from the catalytic converter and the second temperature signal being calculated using a model.

German Patent Application No. DE 103 58 195 describes a method for monitoring a component situated in an exhaust system of an internal combustion engine in which the low pass performance, which is determined by the heat capacity of the component, is checked by analyzing a measure of a first exhaust gas temperature which occurs upstream from the component to be monitored and a second exhaust gas temperature which is detected by a temperature sensor situated downstream from the component to be monitored. The described method enables monitoring of the component for a change which may have occurred in the event of improper manipulation. In the extreme case, the component to be monitored, e.g., a catalytic converter and/or a particle filter, may have been removed completely. Monitoring takes place either during inspections, which must be conducted in connection with the maintenance of emission standards, or during regular operation of the internal combustion engine.

A method for operating a catalytic converter used for exhaust emission control in an internal combustion engine and a device for executing the method, which provide control or regulation of a reagent fill level in the catalytic converter to a predefined storage setpoint value, are described in German Patent Application No. DE 10 2004 031 624 (not previously published). The targeted pre-definition of the storage setpoint value ensures that a sufficient reagent quantity is available in non-stationary operating states of the internal combustion engine for the preferably complete removal of at least one undesirable exhaust component and that a reagent slip is avoided. Described is a model of the catalytic converter which ascertains the reagent fill level in the catalytic converter based on the reagent flow flowing into the catalytic converter, possibly based on the NO_x mass flow flowing into the catalytic converter, possibly based on the NO_x mass flow exiting the catalytic converter, and possibly based on a reagent slip.

An object of the present invention is to provide a method for operating an internal combustion engine which provides for diagnostics of an exhaust system in which an exhaust-gas treatment device for converting at least one undesirable exhaust gas component is situated, and a device for executing the method.

SUMMARY OF THE INVENTION

The method according to the present invention for operating an internal combustion engine provides for diagnostics of the exhaust system in which an exhaust-gas treatment device for converting at least one undesirable exhaust gas component is situated. From the exhaust gas component, ascertained upstream from the exhaust-gas treatment device and measured downstream from the exhaust-gas treatment device, a measure for the conversion is determined and compared to a predefinable threshold value. An error signal is issued when the threshold is not met.

The method according to the present invention enables diagnostics of the entire exhaust system. Mechanical defects are detected, for example, which result in the fact that the entire exhaust gas flow does not flow through the exhaust-gas treatment device. As long as the exhaust-gas treatment device contains a catalytic converter, it is possible to draw a conclusion about the operational performance of the lining of the catalytic converter. The approach according to the present invention makes it possible in particular to detect a manipulation in the exhaust system such as the use of a dummy in the exhaust-gas treatment device or, for example, a deliberately defective lining of a component situated in the exhaust-gas treatment device. Moreover, the complete absence of the exhaust-gas treatment device may also be detected.

In the simplest case, the threshold value may be fixedly predefined. The threshold value may be set to a value of, for example, 50% of the measure for the conversion which is expected under normal operating conditions of the exhaust-gas treatment device. The threshold value is preferably variable.

In order to localize the error, further diagnostics may be carried out based on the error signal issued in the event of a threshold shortfall. Furthermore, the error signal may be displayed to prompt a motor vehicle driver to seek a repair shop.

The at least one exhaust gas component, which is detected upstream from the exhaust-gas treatment device, e.g., at the intake of the exhaust system, may be calculated or measured.

According to one embodiment, the degree of efficiency of the exhaust-gas treatment device is ascertained as a measure for the conversion. The degree of efficiency results from the difference between the inflowing and the outflowing exhaust gas component divided by the inflowing exhaust gas component. The concentration of the exhaust gas component in the exhaust may be used as the basis. Moreover, the mass flow or the volume flow of the exhaust gas component may be used. The degree of efficiency of the exhaust-gas treatment device is independent of absolute values of the underlying variables.

According to another embodiment, the decrease in the concentration or in the mass flow/volume flow of the exhaust gas component is ascertained as a measure for the conversion.

According to one embodiment, a measure for the exhaust gas component upstream from the exhaust-gas treatment device is ascertained from at least one performance characteristic of the internal combustion engine. A sensor or a mechanical exhaust-gas flap for redirecting exhaust gas flows is no longer necessary due to this measure. The speed of the internal combustion engine and/or a fuel signal which corresponds to a torque and/or the coolant temperature of the internal combustion engine and/or an exhaust gas recirculation rate and/or other performance characteristics may be taken into account as the performance characteristic, for example.

According to a corresponding embodiment, the threshold value, to which the measure for the conversion is compared, is set based on the operating conditions prevailing in the exhaust system. For example, the temperature of the exhaust-gas treatment device and/or the metered amount of a reagent introduced into the exhaust system and/or the exhaust gas mass flow may be taken into account. If the exhaust-gas treatment device contains at least one catalytic converter, the conversion of the undesirable exhaust gas component depends on the temperature of the catalytic surfaces, for example. If the reagent, introduced into the exhaust system, is provided for the conversion of the undesirable exhaust gas component, the reagent quantity stored in the catalytic converter and thus the degree of efficiency may be estimated from the metered amount of reagent. Ammonia or, e.g., a urea/water solution as a pre-stage, is provided as the reagent, for example. In an SCR catalytic converter (selective catalytic reduction), the ammonia converts the NOx emissions of the internal combustion engine.

According to one embodiment, a time delay is provided for delaying the exhaust gas component, measured downstream from the exhaust-gas treatment device, in order to be able to take into account the transfer time of the exhaust gas component in the exhaust system prior to the comparison with the exhaust gas component ascertained upstream from the exhaust-gas treatment device.

According to one embodiment, the error signal is issued only when the threshold shortfall lasts at least a predefined period of time. Sporadically occurring errors or errors caused by interference signals are suppressed using this measure.

The device according to the present invention for operating an internal combustion engine relates to a control unit which is designed for executing the method. The control unit preferably contains at least one electrical memory in which the method steps are stored as a computer program.

According to a refinement of the device according to the present invention, a preferably electrically operable exhaust-gas flap is provided which applies the exhaust gas component, occurring either upstream or downstream from the exhaust-gas treatment device, to a sensor for detecting the at least one undesirable exhaust gas component.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a technical environment in which a method according to the present invention proceeds.

FIG. 2 shows a flow chart of a method according to the present invention.

DETAILED DESCRIPTION

FIG. 1 shows an internal combustion engine 10, an air detection module 12 being situated in its intake area 11 and a reagent metering module 14 as well as an exhaust-gas treatment device 15 being situated in its exhaust system 13. A temperature sensor 16 is assigned to exhaust-gas treatment device 15. An exhaust-gas flap 17 having a first and a second exhaust gas feed 18, 19 is also situated in exhaust system 13. First exhaust gas feed 18 removes exhaust gas upstream from exhaust-gas treatment device 15 and second exhaust gas feed 19 removes exhaust gas downstream from treatment device 15 and supplies the exhaust gas to an NOx sensor 20. An exhaust gas mass flow msabg occurs in exhaust system 13.

Air detection module 12 supplies an air signal msL, internal combustion engine 10 supplies a speed N, temperature sensor 16 supplies a temperature signal TKat, and NOx sensor 20 supplies an NOx signal NOx to a control unit 30.

Control unit 30 supplies a fuel signal mK to a fuel metering device 31 which is assigned to internal combustion engine 10. A metering signal ascertainment module 32 supplies a reagent metering signal msRea to reagent metering module 14. A conversion ascertainment module 33 supplies an actuating signal 34 to exhaust-gas flap 17.

Air signal msL is supplied to conversion ascertainment module 33. Speed signal N is supplied to an NOx ascertainment module 35 which in turn supplies an NOx untreated-emission signal NOxvK to metering signal ascertainment module 32 as well as to conversion ascertainment module 33. Furthermore, a torque signal mi, an exhaust gas recirculation rate agr and a coolant temperature TW are supplied to NOx ascertainment module 35.

Furthermore, reagent metering signal msRea is supplied to an integrator 40 which in turn supplies a reagent quantity mRea to metering signal ascertainment module 32 and to a threshold value setting module 41.

Temperature signal TKat, provided by temperature sensor 16, is supplied to metering signal ascertainment module 32 as well as to threshold value setting module 41. NOx signal NOx, provided by NOx sensor 20, is supplied to metering signal ascertainment module 32, to conversion ascertainment module 33 and to a sensor error ascertainment module 42.

Conversion ascertainment module 33 supplies an actual conversion eta_actual and threshold value setting module 41 supplies a threshold value etaS to a comparator 43. Comparator 43 supplies a switching signal 44 to a timer t which provides a first error signal F1. Sensor error ascertainment module 42 provides a second error signal F2.

FIG. 2 shows a flow chart of the method according to the present invention. The method starts with a first function block 50 in which NOx signal NOx is ascertained. NOx ascertainment module 35 ascertains NOx untreated-emission signal NOxvK in a second function block 51. Conversion ascertainment module 33 ascertains actual conversion eta_actual in a third function block 52. Threshold value setting module 41 ascertains threshold value etaS in a fourth function block 53.

In a first query 54, which symbolizes comparator 43, it is determined whether actual conversion eta_actual is greater than or at least equal to threshold value etaS. If this is the case, the system jumps back to first function block 50. If this not the case, timer t is started in fifth function block 55.

In a second query 56, it is checked whether switching signal 44 is still present during the period of time predefined by timer t. If this is not the case, the system jumps back to first function block 50. If this is the case, first error signal F1 is provided in a sixth function block 56. The possibly present second error signal F2 is subsequently taken into account in a seventh function block 57.

The method according to the present invention proceeds as follows:

Control unit 30 ascertains fuel signal mK which is supplied to fuel metering device 31, as a function of speed N of internal combustion engine 10 and the position of an accelerator pedal of a motor vehicle (not shown in greater detail) or possibly as a function of air signal msL provided by air detection module 12. Fuel signal mK corresponds to torque mi which internal combustion engine 10 should provide or provides already.

The exhaust gas of internal combustion engine 10 contains at least one undesirable exhaust gas component which should be reduced by exhaust-gas treatment device 15. As an example, it is assumed in the following that the NOx emission of internal combustion engine 10 is the undesirable exhaust gas component.

A catalytic converter, for example, in particular an NOx storage catalytic converter, which is situated in exhaust-gas treatment device 15, is suitable for reducing the NOx emissions of internal combustion engine 10. It is assumed in the exemplary embodiment that the catalytic converter situated in exhaust-gas treatment device 15 is an SCR catalytic converter (selective catalytic reduction) which uses a reagent to convert the NOx contained in the exhaust gas. Ammonia may be provided as the reagent which may be obtained from a urea/water solution which is inserted into exhaust system 13 by reagent metering module 14.

The reagent flow is set via reagent metering signal msRea which is set by metering signal ascertainment module 32 as a function of NOx untreated-emission signal NOxvK, for example, which is provided by NOx ascertainment module 35. Via this measure, the reagent flow is adjusted to the NOx, and inserted into exhaust system 13 by internal combustion engine 10. NOx signal Nox, provided by NOx sensor 20 as a function of the NOx concentration downstream from exhaust-gas treatment device 15, may be used additionally or alternatively for setting reagent metering signal msRea. Furthermore, the reagent quantity, which is ascertained by integrator 40 via variable integration of reagent metering signal msRea, may be taken into account. Moreover, the temperature of the SCR catalytic converter which is detected by temperature sensor 16 which provides temperature signal Tkat may be taken into account in particular.

Temperature sensor 16 preferably detects the exhaust gas temperature directly upstream from exhaust-gas treatment device 15. If needed, temperature sensor 16 may be situated inside of exhaust-gas treatment device 15.

NOx sensor 20, which provides NOx signal NOx, detects at least the NOx concentration in the exhaust gas downstream from exhaust-gas treatment device 15. The shown exemplary embodiment provides exhaust-gas flap 17 which applies to NOx sensor 20 either exhaust gas from downstream from exhaust-gas treatment device 15 or exhaust gas from upstream from exhaust-gas treatment device 15. Exhaust-gas flap 17, actuated as a function of actuating signal 34 which is provided by conversion ascertainment module 33, establishes a connection between the exhaust gas and NOx sensor 20 either via first exhaust gas feed 18 or via second exhaust gas feed 19. Therefore, with the aid of exhaust-gas flap 17, NOx sensor 20 is able to detect the NOx concentration in the exhaust gas either upstream or downstream from exhaust-gas treatment device 15.

The NOx emissions of internal combustion engine 10 may be ascertained by NOx ascertainment module 35 from performance characteristics of internal combustion engine 10 and provided as NOx untreated-emission signal NOxvK. The NOx concentration may alternatively or additionally be measured upstream from exhaust-gas treatment device 15. As described above, an additional NOx sensor may be avoided due to the use of exhaust-gas flap 17. A plausibility check of the detected values may be performed by ascertaining the NOx emissions of internal combustion engine 10 in multiple ways.

For executing the method according to the present invention, it is provided to ascertain the at least one undesirable exhaust gas component upstream and downstream from exhaust-gas treatment device 15 according to the first two function blocks 50, 51. At least one measure for actual conversion eta_actual of the exhaust gas component is subsequently ascertained in conversion ascertainment module 33.

Conversion ascertainment module 33 preferably ascertains the degree of efficiency of the conversion of the exhaust gas component. The degree of efficiency results from the difference between the exhaust gas component flowing into exhaust-gas treatment device 15 and the exhaust gas component flowing out of exhaust-gas treatment device 15 divided by the inflowing exhaust gas component. This may be based on the concentration of the exhaust gas component or on the absolute values such as the mass flow or the volume flow of the exhaust gas component.

Instead of ascertaining the degree of efficiency, conversion ascertainment module 33 may base the ascertainment of at least one measure for the conversion of the at least one undesirable exhaust gas component on absolute variables such as the difference of the mass flow or the volume flow.

Conversion ascertainment module 33 preferably contains a time delay for delaying the exhaust gas component, measured downstream from exhaust-gas treatment device 15, in order to be able to take into account the transfer time of the exhaust gas component in exhaust system 13 prior to the comparison in comparator 43 with the exhaust gas component ascertained upstream from exhaust-gas treatment device 15.

According to fourth function block 53, threshold value etaS is set in threshold value setting module 41. In a simple embodiment, threshold value etaS may be set as a fixed value, e.g., 50% of a minimally expected actual conversion eta_actual. Threshold value etaS is preferably set as a function of operating conditions of internal combustion engine 10 and in particular as a function of operating conditions in exhaust system 13.

Threshold value etaS may initially depend on the temperature of exhaust-gas treatment device 15 which may be estimated or which is preferably measured by temperature sensor 16, at least approximately. In particular when exhaust-gas treatment device 15 contains an SCR catalytic converter, threshold value etaS is preferably set by the reagent stored in the SCR catalytic converter, the temperature of the SCR catalytic converter preferably also being taken into account, since the storage capability of an SCR catalytic converter with respect to the reagent depends on the temperature. In particular, exhaust gas mass flow msabg which is preferably calculated from performance characteristics of internal combustion engine 10 such as speed N and/or fuel signal mK and/or air signal msL may be additionally or alternatively taken into account.

Actual conversion eta_actual and threshold value etaS are supplied to comparator 43. According to first query 54, comparator 43 determines whether the measure for the actual conversion corresponds at least equally to threshold value etaS. If this is the case, the system jumps back to first function block 50 since the diagnostics did not yield an unusual result. However, if this is the case, comparator 43 provides switching signal 44 which is supplied to timer t.

According to fifth function block 55, switching signal 44 starts timer t. Second query 56 checks in timer t whether switching signal 44 is still present within the period of time predefined by timer t. If this is not the case, the system jumps back to first function block 50 since the diagnostics yielded only a sporadically occurring error or responded due to incidentally present interference signals. If switching signal 44 is still present after the period of time predefined by timer t has elapsed, first error signal F1 is provided according to sixth function block 56.

First error signal F1 may be displayed, for example, to signal to a driver of a motor vehicle that a stop at a repair shop is necessary. First error signal F1 is preferably stored in an error memory (not shown in greater detail) and/or is used preferably to start further diagnostic procedures.

First error signal F1 states that an error has occurred in exhaust system 13. An error may be caused, for example, when the exhaust gas flow in exhaust system 13 through exhaust-gas treatment device 15 is at least partially interrupted. This may occur, for example, due to a defective exhaust pipe between internal combustion engine 10 and exhaust-gas treatment device 15. Another error possibility may be present in exhaust-gas treatment device 15. A cleaning effect of exhaust-gas treatment device 15 with respect to the at least one undesirable exhaust gas component may have deteriorated over time, for example. Another possibility, which the method according to the present invention detects with great reliability, is based upon illegal tampering with exhaust system 13 which may mean, for example, that, instead of a proper exhaust-gas treatment device 15, a dummy has been installed, or that a lining of a catalytic converter, situated in exhaust-gas treatment device 15, has deliberately been completed in a shoddy manner.

Another error possibility is that NOx signal NOx, provided by NOx sensor 20, is erroneous. In the shown exemplary embodiment, an occurring error in NOx sensor 20 may be specifically searched for in sensor error ascertainment module 42. Due to the possibility of multiple error causes, an advantageous refinement of the approach according to the present invention provides that after the occurrence of first error signal F1, further measures are initially taken to localize the error.

Claims

1. A method for operating an internal combustion engine which provides for diagnostics of an exhaust system of the internal combustion engine, in which an exhaust-gas treatment device for converting at least one undesirable exhaust gas component is situated, the method comprising:

determining a measure for the conversion from the exhaust gas component, ascertained upstream from the exhaust-gas treatment device and measured downstream from the exhaust-gas treatment device;

comparing the measure to a predefined threshold value; and

providing an error signal when the threshold value is not met.

2. The method according to claim 1, wherein a degree of efficiency of the exhaust-gas treatment device is ascertained as a measure for the conversion.

3. The method according to claim 1, wherein a reduction of a concentration of the exhaust gas component is ascertained as a measure for the conversion.

4. The method according to claim 1, wherein a measure for the exhaust gas component upstream from the exhaust-gas treatment device is calculated from performance characteristics of the internal combustion engine.

5. The method according to claim 1, wherein the threshold value is set based upon at least one of (a) operating conditions in the exhaust system and (b) operating conditions of the internal combustion engine.

6. The method according to claim 5, wherein at least one of a temperature of the exhaust-gas treatment device and a metering of a reagent introduced into the exhaust system is taken into account.

7. The method according to claim 1, wherein a delay time for delaying the exhaust gas component measured downstream from the exhaust-gas treatment device is provided in order to take into account a transit time of the exhaust gas component in the exhaust system.

8. The method according to claim 1, wherein the error signal is provided when a threshold shortfall lasts at least a predefined period of time.

9. The method according to claim 1, wherein the exhaust gs component includes NOx emissions of the internal combustion engine.

10. The method according to claim 1, further comprising carrying out further diagnostic procedures after the error signal occurs.

11. A device for operating an internal combustion engine, which provides for diagnostics of an exhaust system of the internal combustion engine, in which an exhaust-gas treatment device for converting at least one undesirable exhaust gas component is situated, the device comprising at least one control unit for performing the following:

determining a measure for the conversion from the exhaust gas component, ascertained upstream from the exhaust-gas treatment device and measured downstream from the exhaust-gas treatment device;

comparing the measure to a predefined threshold value; and

providing an error signal when the threshold value is not met.

12. The device according to claim 11, further comprising a sensor for detecting the at least one undesirable exhaust gas component, and wherein an exhaust-gas flap applies the exhaust gas component occurring one of upstream and downstream from the exhaust-gas treatment device to the sensor.