FR2876149A1 - METHOD AND DEVICE FOR DIAGNOSING A NOX NITROGEN OXIDE SENSOR INSTALLED IN AN EXHAUST GAS AREA OF AN INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

Method for diagnosing a nitrogen oxides NOx sensor (16) installed in an exhaust gas zone (13) of an internal combustion engine (10). The diagnosis (50) is carried out after stopping the internal combustion engine (10) during continued operation of a control unit (30).

Description

Field of the invention

  The present invention relates to a method of diagnosing a NOx nitrogen oxide sensor installed in an exhaust zone of an internal combustion engine.

  The invention also relates to a device for implementing the method.

  State of the art DE 196 36 415 A1 describes a method and a device for monitoring the operation of a hydrocarbon sensor in an internal combustion engine which allows a diagnosis of a sensor heating device. of hydrocarbons and secondly a diagnosis of the sensor element. The diagnosis of the heating device is made by comparing the heating power to be supplied and a predefined power threshold.

  The sensor element is diagnosed by comparing the captured sensor signal when the heater is switched off and for predefined operating conditions with predictable internal combustion engine emission values for these operating conditions. As particular operating conditions, there is for example the operation of the internal combustion engine in thrust mode (inertial thrust) operating mode in which the internal combustion engine produces no raw emission. The signal provided by the hydrocarbon sensor is checked under its operating conditions if it is below a threshold.

  EP 979 441 A discloses a heating circuit of a component which predefines an observation interval within which it is intended to determine the average of the energy supplying the heating device to detect that the component to be heated. has reached the operating temperature.

  It has been found that a diagnosis of nitrogen oxides NOx sensor under different operating conditions results in variable diagnostic results. NOx nitrogen oxide sensors currently known may in particular have a drift fault depending on the operating conditions. The NOx nitrogen oxide sensor signal is used as needed to diagnose a NOx nitrogen oxide storage catalyst installed in an exhaust zone of the internal combustion engine. An undetected NOx nitrogen oxide sensor defect would challenge the diagnosis of the catalyst. For example, an undetected NOx nitrogen oxide sensor error could be misinterpreted as a catalyst failure.

  OBJECT OF THE INVENTION The object of the present invention is to develop a method for diagnosing a NOx nitrogen oxide sensor installed in an exhaust zone of an internal combustion engine as well as a device for the implementation of the method, allowing a very high diagnostic reliability.

  DESCRIPTION AND ADVANTAGES OF THE INVENTION For this purpose the invention relates to a method of the type defined above, characterized in that the diagnosis is made after stopping the internal combustion engine during the continued operation of a control apparatus.

  The method according to the invention provides for the diagnosis of a NOx nitrogen oxide sensor installed in the exhaust gas zone of an internal combustion engine after the internal combustion engine has been shut down and during the continued operation of a control unit.

  The diagnosis is based at least on one measurement of the NOx nitrogen oxide signal provided by the NOx nitrogen oxide sensor and a characteristic quantity of the NOx nitrogen oxide signal. For example, the measurement and / or the characteristic quantity can be compared with a threshold and if the threshold is exceeded, the NOx nitrogen oxide sensor will be considered as defective. The measurement and / or the characteristic quantity can also be used in particular to determine a shift of the NOx nitrogen oxides signal.

  With the help of tests, it has been possible to show that in particular a diagnosis during the continued operation of a control device after the shutdown of the internal combustion engine was much more reliable than a diagnosis during the operation of the combustion engine. internal.

  One development is to maintain the nitrogen oxide sensor NOx at least substantially at its operating temperature by operating a heater during continued operation. This measurement ensures that the NOx nitrogen oxide signal at the base of the diagnosis was obtained at least approximately at the operating temperature of the NOx nitrogen oxide sensor.

  It is a development that the heating device should only be operated if, in particular in the NOx nitrogen oxide sensor range, it is not below the dew point. Such a downward overflow of the dew point could damage the NOx nitrogen oxide sensor if the heating device was operating particularly if this NOx nitrogen oxide sensor is ceramic.

  A development plans to perform the diagnosis only if the temperature of the exhaust gas, at least at the beginning of the continued operation of the control unit, exceeds a predefined minimum temperature. By fulfilling this condition, it is ensured that the NOx nitrogen oxides signal supplied by the NOx nitrogen oxide sensor has not been influenced by a too low temperature of the exhaust gas. In addition, by pre-defining the minimum temperature at least in part, it is ensured that there is no overflow towards the bottom of the dew point.

  A particularly advantageous development is to perform the diagnosis if the Lambda air coefficient of the exhaust gas exceeds a predefined threshold of the Lambda coefficient. It can then be assumed that there has been sufficient rinsing of the exhaust gases discharged from the exhaust gas zone. This means ensures that the nitrogen oxide sensor NOx is no longer at least approximately exposed to the NOx nitrogen oxides so that the NOx nitrogen oxides signal only represents the signal shift.

  A development plans to predefine a measurement time interval. This limits the measurement time. In addition, during the measurement time interval, it is possible to determine the minimum of the NOx nitrogen oxide signal supplied by the nitrogen oxide sensor NOx which is, for example, a signal characteristic variable. nitrogen oxides NOx.

  A development plans to determine the measurement of the exhaust gas temperature from the average heating power of the heating device NOx nitrogen oxide sensor. It is thus possible to delete a temperature sensor.

  The device according to the invention relates first of all to a control apparatus for implementing the method.

  The control device comprises in particular at least one diagnostic command controlled by an operation tracking signal and a nitrogen oxide sensor heating command NOx controlled by the operation tracking signal. The control apparatus preferably comprises at least one electrical memory in which the steps of the method are recorded in the form of a computer program.

  Drawings The present invention will be described in more detail below with reference to an embodiment diagrammatically shown in the accompanying drawings, in which: FIG. 1 shows the technical environment in which a process is carried out; according to the invention for diagnosing a NOx nitrogen oxide sensor installed in the zone of the exhaust gases of an internal combustion engine; FIG. 2 shows a flowchart of an exemplary embodiment of the method.

Description of the embodiment

  FIG. 1 shows an internal combustion engine 10 whose intake zone 11 comprises an air sensor 12 and whose exhaust gas zone 13 comprises a temperature sensor 14 as well as downstream after a catalyst 15. There is a NOx 16 nitrogen oxide sensor.

  The NOx nitrogen oxide sensor 16 has a first sensor zone 17 which provides a NOx nitrogen oxide signal and a second sensor zone 18 which provides a signal, lam. The NOx nitrogen oxide sensor 16 further comprises a heating device 19 controlled by a heating device control signal 20.

  Upstream of the catalyst 15 is a crude mass flow rate of nitrogen oxides msNOxvK and a mass flow rate of the exhaust gas msabg.

  The air sensor 12 provides an msL air signal to a control apparatus 30; the internal combustion engine 10 provides a speed n rotation speed signal and the temperature sensor 14 provides an exhaust gas temperature signal Tabg. The NOx nitrogen oxide signal and the X lam signal are also supplied to the control apparatus 30. The control apparatus 30 provides a fuel signal to the fuel metering device 31.

  The control apparatus 30 generates an operation continuation signal 32 supplied to both a heating control 33 of the NOx nitrogen oxide sensor and to a first diagnostic control 34. The heating control 33 of the The nitrogen oxide sensor NOx further receives a release signal 36 provided by a dew-point determination means 35. The nitrogen oxide sensor control NOx 33 provides the control signal of the heating device as well as a measurement 37 of the available heating power for the operating means of the heating power 38.

  The heating power operating means 38 provides a measurement 39 of the exhaust gas temperature applied to a first diagnostic control 34 as well as a second diagnostic control 40 and a third diagnostic control 41.

  The first diagnostic command 34 comprises a first clock t1 and a second clock t2 and further receives the signal lam.

  The second diagnostic command 40 furthermore receives the NOx nitrogen oxide mass flow rate signal 43 supplied by the NOx nitrogen oxide mass flow rate determination means 42 and a mass oxide signal. nitrogen NOx 44 provided by means for determining the mass of nitrogen oxides NOx 43; the signal 44 is also provided to a third diagnostic control 41 which further receives a thrust cut-off signal 46 from a thrust cutoff determining means 45.

  The first diagnostic command 33 provides a first diagnostic control signal 51 at a first diagnosis 50; the second diagnostic command 40 provides a second diagnostic 52 with a second diagnostic control signal 53; a third diagnostic command 41 provides a third diagnostic control signal 55 with a third diagnosis 54. The first and second and third diagnostics 50, 52, 54 receive the NOx nitrogen oxide signal.

  The first diagnosis 50 has a first threshold S3; the second diagnosis 52 has a second threshold S2 and the third diagnosis 54 has a third threshold S3.

  The first diagnosis 50 provides a first diagnostic result D 1 to a first diagnostic operation means 60; the second diagnosis 52 provides a second diagnostic result D2 and the third diagnosis 54 provides a third diagnostic result D3.

  The diagnostic operating means 60 provides both a release signal 61 and an offset signal 62.

  Figure 2 shows an example of possible realization of a diagnosis.

  During a first request or interrogation 70, it is determined whether the operation continuation signal 32 has arrived. If this is the case, it is determined in a second request 71 whether the boundary conditions are met. If at least one limit condition is not fulfilled, the diagnosis is stopped.

  If the limiting conditions are fulfilled, in the first functional block 72, the control signal 20 is provided for the first control device 19.

  Then, according to a second functional block 73, the first clock t1 is started. In a third interrogation 74, it is checked whether the signal lam has exceeded a threshold of the Lambda coefficient. If this is not the case, a fourth poll 75 checks whether the time predefined by the first clock t1 has elapsed. If this is the case, the diagnosis is stopped. If this is not the case, the third interrogation 74 is executed.

  If the signal lam exceeds the threshold of the Lambda coefficient, a third functional block 76 launches the second clock t2. Then, in a fourth functional block 77, the NOx nitrogen oxide signal is taken and operated.

  In a fifth interrogation 78, it is checked whether the time predefined by the second clock t2 is complete. If this is not the case, the NOx nitrogen oxide signal is continued and exploited.

  If the time is up, in a sixth interrogation 79, it is checked whether the NOx nitrogen oxide signal or if a characteristic quantity of NOx nitrogen oxide signal has exceeded a threshold. If this is not the case, according to the fifth functional block 80, the shift signal 62 is transmitted.

  If the threshold has been exceeded, a sixth functional block 80 executes, if necessary, a plausibility check of the diagnosis. Then, according to a seventh functional block 82, the error signal 61 is emitted.

  The process according to the invention proceeds as follows: The NOx nitrogen oxide sensor 16 installed in the exhaust zone 13 of the internal combustion engine 10 downstream of the catalyst 15 and which is preferably an accumulator catalyst NOx nitrogen oxides, is provided to capture the concentrations of nitrogen oxides NOx in the exhaust gas downstream of the catalyst 15.

  The NOx nitrogen oxides signal may be used by the control apparatus 30 which controls the internal combustion engine 10 by the fuel signal. The internal combustion engine 10 is for example a direct injection internal combustion engine 10 which can operate in different modes of operation; in a first mode of operation, we will have a gross mass flow of nitrogen oxides msNOxvK increased and in another operating mode we will have a gross mass flow rate of nitrogen oxides NOx 9 lower. The crude mass flow rate of nitrogen oxides msNOxvK contained in the mass flow rate of the exhaust gas msabg is converted either directly by the catalyst 15 or combined in a storage phase. The nitrogen oxides NOx signal supplied by the NOx nitrogen oxide sensor 16 may be used to select the appropriate operating mode and secondly to diagnose the catalyst 15.

  The NOx nitrogen oxide sensor 16 may have a defect which may range from a zero offset of the NOx nitrogen oxide signal, a slope fault or a linearity defect to a total failure. In the event of a NOx 16 nitrogen oxide sensor fault, it is no longer possible to reliably select one of the operating modes and / or perform a reliable diagnosis of the catalyst 15.

  The second and third diagnostic commands 40, 41 as well as the second and third diagnostics 52, 54 provide for a diagnosis of the nitrogen oxide sensor NOx 16 during the operation of the internal combustion engine 10.

  The second diagnostic command 40 provides the second diagnostic control signal 53 as a function of the gross NOx nitrogen mass flow rate signal 43, the measurement of the exhaust gas temperature and the exhaust gas mass signal. nitrogen oxides NOx 44.

  The means for determining the crude mass flow rate of NOx nitrogen oxides 42 determines the crude mass flow rate of nitrogen oxides msNOxvK of the internal combustion engine 10 preferably by means of a model which can for example be used for the calculation, the speed of rotation signal n, the fuel signal which represents the load of the internal combustion engine 10, the air signal msL and, if appropriate, other operating parameters of the internal combustion engine 10.

  For the diagnosis, the level of NOx nitrogen oxide filling of the catalyst 15 is advantageously taken into account, which is determined by means of the NOx nitrogen oxide mass determination means 43. The second control signal and diagnosis 53 releases on the one hand the diagnosis to be performed in the second diagnosis 52 and on the other hand influences the second predefined threshold S2 as a function of input parameters of the second diagnostic command 40. The second diagnosis 52 supplies the second diagnostic result D2 to the diagnostic operation 60.

  The third diagnostic control 41 provides the third diagnostic control signal 55 in an operating state of the internal combustion engine 10 for which there is substantially no raw mass flow rate of msNOxvK nitrogen oxides. Such an operating state exists in particular during a thrust mode that is found by the means for determining the thrust cut-off 45. The thrust breaking determination means 45 can determine the thrust cut-off, for example using the speed or speed signal n and the fuel signal. In addition, the third diagnostic control 41 may optionally take into account the mass of nitrogen oxides NOx in the catalyst 15, mass determined by the means of determination of the mass of NOx nitrogen oxides 43. third diagnostic control signal 55 provided by the third diagnostic command 41 requires firstly the third diagnosis 54 to perform the diagnosis and also influences the third predefined threshold S3. The third diagnostic result D3 provided by the third diagnosis 54 is applied to the diagnostic operation 60.

  Since the diagnostic operating means 60 ascertains with the aid of the third diagnostic result D3 that, for example, the signal shift 62 of the NOx nitrogen oxide signal exceeds a predefined threshold, the d diagnostic operation 60 can, without any further control, issue the fault or error signal 61. Tests have shown that, despite the increase in the signal offset 62, the nitrogen oxide sensor NOx 16 can if necessary continue to operate taking into account only the increase of the signal offset 62. But it has also been found that the nitrogen oxide sensor NOx 16 can also have a fault if the operation of diagnosis 60 concludes for example from the second and / or third diagnostic result D2, D3 that NOx nitrogen oxide sensor 16 is in order.

  The first diagnostic result D 1 can be used both to perform independent diagnosis and / or to determine the signal offset 62 but also to check and / or verify the plausibility of the second and / or third diagnostic result D2, D3 .

  The first diagnostic command 34 only becomes active if the first interrogation 70 has found the presence of the motion tracking signal 32. The motion tracking signal 32 occurs after the stop of the internal combustion engine 10 during the further operation of the control apparatus 30, during which time the control unit 30 may for example perform other diagnoses.

  In the presence of the motion tracking signal 32, the heating control 33 of the nitrogen oxide sensor NOx can transfer the control signal 20 of the heating device to the heating dis-positive 19 of the nitrogen oxide sensor. NOx 16. Preferably, however, the dew point determination means 35 is additionally checked by a second interrogation 71 if the dew point has been exceeded, particularly in the zone of the nitrogen oxide sensor. NOx 16.

  The means for determining the dew point 35 can determine a downward overflow of the dew point, for example by means of a model of the zone of the exhaust gases 13 with which, for example, the temperature of the exhaust gases is taken into account. exhaust gas, the ambient air temperature, the exhaust mass flow rate msabg, the volume of the exhaust gas zone 13 and for example known thermal capacities.

  Preferably, it is verified by a second interrogation 71 whether the temperature of the exhaust gas or at least the measurement 39 of the temperature of the exhaust gas has exceeded a predefined temperature threshold. The temperature of the exhaust gases can be grasped for example by means of an exhaust gas temperature sensor 14 which supplies the temperature of the exhaust gases Tabg to the control unit 30.

  According to an advantageous development, the measurement 39 of the temperature of the exhaust gases is determined by the means for operating the heating power 38 from the measurement 37 supplied by the heating control of the nitrogen oxide sensor. NOx 33 for heating power. The means for evaluating the heating power 38 takes into account that the power demand of the heating device 19 decreases when the operating temperature of the NOx nitrogen oxide sensor 16 is reached.

  If the limiting conditions according to the second request 71 are fulfilled and if the nitrogen oxide sensor NOx 16 is heated in further motion, according to the second functional block 73, the first clock t1 of the first diagnostic command is started. 34.

  The third interrogation 74 checks whether the signal X lam has exceeded a predefined threshold of the Lambda coefficient. Exceeding the Lambda coefficient threshold means that the exhaust zone 13 has already been sufficiently rinsed during the tracking of the control apparatus 30 and thus contains at least substantially more NOx hydrocarbons or nitrogen oxides. .

  The first clock t1 is preferably designed to limit in time the execution of the third interrogation or request 73. The control of the end of the period is done in the fourth interrogation 75. If a timeout is found, the diagnosis is advantageously cut off and a fault signal not shown in detail is emitted.

  Insofar as the threshold of the Lambda coefficient has been exceeded, a fourth functional block 77 captures the NOx nitrogen oxide signal and operates it.

  The operation can be done for example by comparing the signal NOx nitrogen oxides at a threshold. Exceeding the threshold found in the sixth interrogation 79 causes the diagnostic operating means 60 to directly transmit the fault signal 61.

  The second clock 2, which is started according to the third functional block 76, is preferably provided. The input of the NOx nitrogen oxide signal according to the fourth functional block 78 continues until the time predefined by the second clock t2 has elapsed. The end of the period is found in the fifth functional block 78. The second clock t2 can observe and limit the duration of the measurement.

  According to an advantageous development, during the time predefined by the second clock t2, the NOx nitrogen oxide signal is exploited so that, for example, it will be possible to determine the signal minimum, which is, for example, the characteristic quantity of the signal. nitrogen oxides NOx signal.

  If the diagnostic operating means 60 comes to conclusion with the aid of the first diagnostic result D 1 provided by the first diagnosis 50 that no threshold has been exceeded, the diagnostic operating means 60 can provide the signal offset 62 which will be taken into account for the further exploitation of the NOx nitrogen oxide signal.

  Exceedance found by the sixth interrogation 79 of a threshold is used according to the sixth functional block 81 preferably to verify and / or make plausible at least one of the diagnostic results D2, D3 already existing.

  The NOx nitrogen oxide sensor 16 shown in FIG. 1 contains, because of its production, for example, the first and the second sensor zone 17, 18; the second sensor zone 18 provides the signal lam. Where appropriate, a separate Lambda or Lambda sensor may be provided in the exhaust zone 13.

Claims (10)

  1) A method for diagnosing an NOx nitrogen oxide sensor (16) installed in an exhaust zone (13) of an internal combustion engine (10), characterized in that the diagnosis (50) ) is performed after stopping the internal combustion engine (10) during the continued operation of a control apparatus (30).   2) Method according to claim 1, characterized in that the NOx nitrogen oxide sensor (16) is maintained at least approximately at the operating temperature by a heater (19) during further operation.   3) Method according to claim 2, characterized in that the heating device (19) is implemented only if there is no overflow of the dew point temperature.   4) Method according to claim 1, characterized in that the diagnosis (50) is carried out if the temperature of the exhaust gas (39, Tabg) exceeds at least at the beginning of the continuation of operation a predefined minimum temperature .   5) Method according to claim 1, characterized in that the diagnosis (50) is performed if the Lambda air coefficient of the exhaust gas exceeds a predefined Lambda coefficient threshold.   Process according to Claim 1, characterized in that a measurement time interval is provided and at least approximately the minimum produced in the measuring range is determined by the nitrogen oxide (NOx) signal supplied. by the NOx nitrogen oxide sensor (16).   7) Process according to any one of claims 2 or 4, characterized in that at least one measurement (39) of the temperature of the exhaust gas is determined from the average heating power of the heating device (19). ) of NOx nitrogen oxide sensor (16).   Method according to Claim 1, characterized in that, after the diagnostic result (D 1) obtained in the further operation of the control device (30), at least one diagnostic result (D2, D3) is verified. ) determined during operation of the internal combustion engine (10).   9) Device for diagnosing NOx nitrogen oxide sensor (16) installed in an exhaust zone (13) of an internal combustion engine (10), characterized in that at least one control apparatus (30) is provided for carrying out the method according to any one of claims 1 to 8.   10) Device according to claim 9, characterized in that the control device (30) comprises at least one diagnostic command (34) controlled by a function-tracking signal (32) and a heating control NOx nitrogen oxide sensor (33) controlled by the operation continuation signal (32).