DE102009055076A1 - Exhaust gas sensor e.g. nitrogen oxide sensor, calibration method for internal combustion engine of motor vehicle, involves providing pre-set value for signal, and calibrating exhaust sensor by comparison of signal with pre-set value - Google Patents

Abstract

The method involves providing a pre-set value for a signal delivered by an exhaust gas sensor e.g. broadband-lambda sensor, or a characteristic value derived from the signal for a predetermined operating point (10) of an internal combustion engine. The engine is not operated in a thrust operation. A exhaust sensor is calibrated by comparison of the signal of the exhaust gas sensor or the characteristic value with the pre-set value, where the signal is delivered in the predetermined operating point during operation of the internal combustion engine. An independent claim is also included for a device for calibrating an exhaust gas sensor in exhaust gas of an internal combustion engine.

Description

The invention relates to a method for calibrating an exhaust gas sensor in the exhaust gas of an internal combustion engine.

The invention further relates to a device for calibrating an exhaust gas sensor in the exhaust gas of an internal combustion engine, wherein the internal combustion engine is assigned a control unit.

State of the art

Legal regulations prescribe the monitoring of the composition of the exhaust gas of internal combustion engines for compliance with limit values. For this purpose, provided in the exhaust ducts of the internal combustion engine exhaust gas sensors, for example in the form of lambda sensors and NO _x sensors used.

In order to increase the accuracy of such exhaust gas sensors and compensate for their drift, calibration operations are known, which are performed in certain, sometimes undefined and dependent on the operating condition of the internal combustion engine time intervals.

For planar broadband lambda probes and NO _x sensors, it is known to perform the calibration in the overrun of the internal combustion engine, if the exhaust gas sensors, no combustion products, but only air is supplied. So is out of the DE 198 42 425 C2 a method for correcting the characteristic of a linear lambda probe, which is arranged upstream of a catalyst in an exhaust gas purification system for an internal combustion engine known. It is provided that in a fuel cut-off phase of the internal combustion engine, a throttle valve and / or at least one gas exchange valve is opened, so that a certain minimum pressure in the cylinder / cylinders of the internal combustion engine is reached, then the signal of the lambda probe to the oxygen concentration of the ambient air corresponding lambda value is assigned and corrected by means of this signal, the slope of the characteristic.

A disadvantage of this method is that the internal combustion engine must be operated for a predetermined period in the overrun to ensure that in the exhaust duct combustion products are no longer included. In particular, internal combustion engines, which are provided in vehicles and machines for so-called off-highway use, for example in construction vehicles, are not or only rarely operated in overrun operation.

It is therefore an object of the invention to provide a method which allows the calibration of broadband lambda probes and NO _x sensors outside a coasting operation of the internal combustion engine.

It is a further object of the invention to provide a corresponding device.

Disclosure of the invention

The object of the invention relating to the method is achieved in that at least for a given operating point of the internal combustion engine, in which the internal combustion engine is not operated in overrun mode, a default value for a signal output by the exhaust gas sensor or a characteristic derived therefrom is given and that via a Comparison of the output of the internal combustion engine at the predetermined operating point signal of the exhaust gas sensor or the characteristic derived therefrom with the default value of the exhaust gas sensor is calibrated. The exhaust gas sensor can thus be calibrated in any operating point of the internal combustion engine, the calibration is no longer bound to a coasting operation of the internal combustion engine. This is particularly advantageous for internal combustion engines, which are not or rarely operated in overrun mode, as is often the case in so-called off-highway applications. Preferably, an operating point is provided, which is often approached in the map of the internal combustion engine and which is held at least approximately for a certain period of time. The operating point can be defined, for example, via the specific work and the rotational speed and, in the case of an exhaust gas sensor designed as a broadband lambda probe, can be assigned to a corresponding lambda value via a lambda map. This lambda value can then be used as the default value for the calibration of the exhaust gas sensor.

The accuracy of the calibration can be improved by detecting an operating state of the internal combustion engine in which the internal combustion engine is operated at the predetermined operating point for a predetermined period of time or over a predetermined number of measurements of the signal output by the exhaust gas sensor, during the period or the measurements are used to repeatedly determine the signal output by the exhaust gas sensor or the characteristic quantity derived therefrom, and the exhaust gas sensor calibrates the reference value by comparing the mean value over the signals determined in the period or by the measurements or the mean over the parameters derived therefrom becomes.

According to a preferred embodiment variant of the invention, it can be provided be that for several predetermined operating points of the internal combustion engine in which the internal combustion engine is not operated in overrun default values for the signal output by the exhaust gas sensor or the characteristic derived therefrom are specified that the operating point 10 the internal combustion engine is determined during operation of the internal combustion engine and is assigned within a predetermined tolerance to a predetermined operating point, that the period of time that the internal combustion engine is operated at the predetermined operating point is detected that repeatedly determined during the period, the sensor signal or the characteristic derived therefrom and an average value is formed from the sensor signals or the characteristic quantities derived therefrom and that after a predetermined period of time or after the presence of a predetermined number of measured values for the sensor signal or the parameter derived therefrom, the exhaust gas sensor is calibrated by comparing the mean value with the default value. This makes it possible that the calibration of the exhaust gas sensor can be carried out in various operating points of the internal combustion engine, which increases the likelihood that the internal combustion engine is operated at an operating point which is provided for the calibration of the exhaust gas sensor. In particular, when using the internal combustion engine in various off-highway applications, this is preferably operated depending on the vehicle type in different operating points. The possibility of calibration at various predetermined operating points makes it possible for the exhaust gas sensor to be calibrated for different fields of application of the internal combustion engine.

A very accurate calibration of the exhaust gas sensor is made possible by the fact that for a given number of predetermined operating points calibration data are determined by comparing the output of the internal combustion engine in a given operating point signal of the exhaust gas sensor or the characteristic derived therefrom with the respective default value and that the calibration the exhaust gas sensor takes place on the basis of the calibration data when the calibration data are available for a predetermined number of predetermined operating points or when a predetermined period of time has expired. The calibration data associated with the given operating points can also be determined by comparing the mean value of the sensor signal or the mean value of the characteristic variable derived from the sensor signal from repeated measurements at the same operating point with the respective default values. The calibration of the exhaust gas sensor now no longer takes place solely on the basis of the comparison data determined at an operating point, but taking into account comparisons made between the measured signals or the parameters derived therefrom and the respective default values at different operating points. The calibration is preferably carried out when all calibration data for the given operating points are present. If one or more of the predetermined operating points are not approached over a longer period of time defined by the predetermined period of time, which makes calibration of the exhaust gas sensor necessary, the calibration of the exhaust gas sensor can be carried out on the basis of the previously available calibration data.

The object of the invention relating to the device is achieved in that default values for the signal emitted by the exhaust gas sensor or for parameters derived therefrom are stored in the control unit for at least one predetermined operating point in which the internal combustion engine is not operated in overrun mode and in that Control unit is provided a program sequence, which the operating point 10 detects the internal combustion engine and assigns a predetermined operating point, the signal output from the exhaust gas sensor or the characteristic derived therefrom and calibrated by comparing the signal output by the exhaust gas sensor or the derived characteristic with the default value for the predetermined operating point, the exhaust gas sensor. The device makes it possible to calibrate the exhaust gas sensor outside a coasting operation during operation of the internal combustion engine under load. The implementation can be based on existing components by a software extension within the engine associated control unit and is therefore inexpensive to implement.

The method and the device can preferably be used for calibrating an exhaust gas sensor designed as a broadband lambda probe or as an NO _x sensor in the exhaust gas of an internal combustion engine.

Brief description of the drawings

The invention will be explained in more detail below with reference to an embodiment shown in FIGS. Show it:

1 a load spectrum for an internal combustion engine in an off-highway application,

2 a lambda map of an internal combustion engine,

3 a flowchart for calibration of an exhaust gas sensor.

1 shows a typical load spectrum for an internal combustion engine in an off-highway Application using the example of a small excavator. These are operating points 10 in which the internal combustion engine is operated in use, depending on a normalized load 11 and a normalized speed 12 the internal combustion engine shown.

It turns out that the internal combustion engine is only very seldom operated in a push operation, which is necessary for the calibration of pumped oxygen reference operated exhaust gas sensors according to known methods. Such exhaust gas sensors are, for example, planar broadband lambda probes and NO _x probes.

The core of the present invention is the calibration of the exhaust gas probes in at least one operating point 10 , in which the internal combustion engine is operated under load and thus not in overrun operation. The illustrated load collective shows that a general definition of an operating point 10 is not possible for the calibration of the exhaust gas sensors. This is especially true because the load spectrum of internal combustion engines differ significantly in different off-highway applications.

2 shows a lambda map of an internal combustion engine. Depicted are those depending on a specific work 21 and from a speed 22 and thus from the operating point 10 the internal combustion engine adjusting lambda values 20 the exhaust gas. The illustrated lines run along the same lambda values 20 in the lambda map.

The lambda characteristic makes it possible for every operating point 10 attributable to the internal combustion engine a lambda value.

It turns out that high lambda values 20 mostly associated with steep gradients, which is a general definition of an operating point 10 for the calibration of the exhaust gas sensors further difficult. For the calibration of the exhaust gas sensors are high lambda values 20 in principle advantageous. However, the mass drifts of the internal combustion engine supplied air and the fuel supplied are to be considered.

3 shows a possible flowchart for calibration of an exhaust gas sensor at an operating point 10 , in which the internal combustion engine is operated under load and not in overrun mode.

A starting block 30 follows a first function block 31 for determining the operating point 10 the internal combustion engine. In a first query 42 it is decided whether the internal combustion engine in a same operating point 10 as previously operated. If this is not the case, first in a second function block 33 reset a counter. This is followed by the sequence divided according to that in the first function block 31 certain operating point 10 on a first branch 34 or a second branch 35 or a third branch 36 or a fourth branch 37 , Every branch 34 . 35 . 36 . 37 is one in four function blocks 40 each associated with a predetermined tolerance predetermined operating point. The method is not limited to the four predetermined operating points shown in the embodiment and can with any number of predetermined operating points with the associated branches 34 . 35 . 36 . 37 be carried out in the process.

Corresponds to the one in the first function block 31 certain current operating point 10 none of those in the fourth function blocks 40 predetermined operating points, the assignment is made to a third function block 39 for non-predetermined operating points and the process returns to the first function block 31 to determine the next operating point 10 the internal combustion engine.

The fourth function blocks 40 follow second queries 41 , Here it is checked whether the output signal of the exhaust gas sensor within a predetermined tolerance one for the respective operating point 10 predetermined default value for the output signal corresponds. If the output signal of the exhaust gas sensor is within the specified tolerance, no calibration of the exhaust gas sensor is necessary and the sequence jumps back before the first function block 31 , If the sensor signal is outside the tolerance, it is first in fifth function blocks 42 set a counter high by one.

In the following sixth function blocks 43 an averaging takes place via the sensor signals from repeated passes through the respective branch 34 . 35 . 36 . 37 on the number of passes during which the operating point of the internal combustion engine has not been changed. This is followed in third queries 44 a query whether the counter has exceeded a predetermined setpoint. This checks whether the internal combustion engine has a sufficiently long time in the respective operating point 10 was operated to perform a calibration of the exhaust gas sensor can. If this is not the case, the process returns to the first function block 31 , Will then be in the function block 31 and the subsequent first query 32 found that the operating point 10 the engine has not changed, the process returns to the same branch 34 . 35 . 36 . 37 as before and the counter is again increased by one. If the counter has exceeded such a predetermined desired value, there are sufficient measurement data for a comparison of the averaged over the consecutive pass sensor signal with the default value for the output signal of the exhaust gas sensor for the respective operating point 10 in front. Accordingly, in seventh function blocks 45 Calibration data for the exhaust gas sensor for the respective operating point 10 can be determined by comparing the mean value of the sensor signal with the default value for the output signal of the exhaust gas sensor.

After the seventh function blocks 45 the branches are running 34 . 35 . 36 . 37 back together and are a fourth query 46 fed. In the fourth query 46 It is checked whether the calibration data for all predetermined operating points of the four branches 34 . 35 . 36 . 37 available. If this is the case, it takes place in an eighth function block 47 the calibration of the exhaust gas sensor with the calibration data for all predetermined operating points.

If not all calibration data is available yet, it will be displayed in a fifth query 48 checks whether a predetermined time has elapsed, which makes a calibration of the exhaust gas sensor necessary. If this is the case, it takes place in a ninth function block 49 a calibration of the exhaust gas sensor with the existing calibration data. If the specified period of time has not expired, the process returns to the first function block 31 ,

The process allows pumped oxygen reference exhaust gas sensors to operate out of coasting during operation of the engine 10 to calibrate at predetermined operating points. The calibration can be carried out at a predetermined operating point, however, any number of operating points can also be predetermined. If, in this case, the internal combustion engine is not operated in all given operating points for a sufficiently long period in a critical time range, a forced calibration of the exhaust gas sensor with the calibration data of at least one predetermined operating point is carried out.

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 19842425 C2 [0005]

Claims (6)

A method for calibrating an exhaust gas sensor in the exhaust gas of an internal combustion engine, characterized in that at least for a predetermined operating point of the internal combustion engine, in which the internal combustion engine is not operated in overrun, a default value for a signal output from the exhaust gas sensor or a characteristic derived therefrom is specified and is calibrated by a comparison of the output of the internal combustion engine at the predetermined operating point signal of the exhaust gas sensor or the characteristic derived therefrom with the default value of the exhaust gas sensor. A method according to claim 1, characterized in that an operating state of the internal combustion engine in which the internal combustion engine is operated for a predetermined period or over a predetermined number of measurements of the signal output from the exhaust gas sensor at the predetermined operating point is detected, that during the period or by the measurements, the signal output by the exhaust gas sensor or the characteristic quantity derived therefrom is determined repeatedly, and the exhaust gas sensor is calibrated by a comparison of the mean value over the signals determined in the time period or by the measurements or the mean value over the parameters derived therefrom with the default value , A method according to claim 1 or 2, characterized in that for a plurality of predetermined operating points of the internal combustion engine, in which the internal combustion engine is not operated in overrun default values for the signal output by the exhaust gas sensor or the characteristic derived therefrom are specified that the operating point 10 the internal combustion engine is determined during operation of the internal combustion engine and is assigned within a predetermined tolerance to a predetermined operating point, that the period of time that the internal combustion engine is operated at the predetermined operating point is detected that repeatedly determined during the period, the sensor signal or the characteristic derived therefrom and an average value is formed from the sensor signals or the characteristic quantities derived therefrom and that after a predetermined period of time or after the presence of a predetermined number of measured values for the sensor signal or the parameter derived therefrom, the exhaust gas sensor is calibrated by comparing the mean value with the default value. Method according to one of claims 1 to 3, characterized in that for a predetermined number of predetermined operating points calibration data are determined by comparing the signal emitted during operation of the internal combustion engine in a given operating point signal of the exhaust gas sensor or the characteristic derived therefrom with the respective default value and that the calibration of the exhaust gas sensor on the basis of the calibration data is carried out when the calibration data is available for a predetermined number of predetermined operating points or when a predetermined period of time has expired. Device for calibrating an exhaust gas sensor in the exhaust gas of an internal combustion engine, wherein the internal combustion engine is assigned a control unit, characterized in that in the control unit default values for the signal output by the exhaust gas sensor or for derived parameters for at least one predetermined operating point, in which the internal combustion engine is not in Push operation is operated, are deposited and that in the control unit, a program sequence is provided which the operating point 10 detects the internal combustion engine and assigns a predetermined operating point, the signal output from the exhaust gas sensor or the characteristic derived therefrom and calibrated by comparing the signal output by the exhaust gas sensor or the derived characteristic with the default value for the predetermined operating point, the exhaust gas sensor. Application of the method or the device for calibrating an exhaust gas sensor designed as a broadband lambda probe or as an NO _x sensor in the exhaust gas of an internal combustion engine.

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