WO2018010901A1

WO2018010901A1 - Method for detecting a voltage offset in at least one section of a voltage lamda characteristic curve

Info

Publication number: WO2018010901A1
Application number: PCT/EP2017/064185
Authority: WO
Inventors: Michael Fey
Original assignee: Robert Bosch Gmbh
Priority date: 2016-07-14
Filing date: 2017-06-09
Publication date: 2018-01-18
Also published as: KR102316667B1; KR20190025908A; CN109477441B; DE102016212920A1; CN109477441A

Abstract

The invention relates to a method for detecting a voltage offset in at least one section of a voltage lamda characteristic curve (18) of a two-point lamda probe arranged in an exhaust gas channel of an internal combustion engine with respect to a reference voltage lamda characteristic curve (12) of the two-point lamda probe. Information on current operating conditions of the internal combustion engine and information on operating conditions which are expected with a specified degree of probability are obtained, wherein the expected operating conditions are obtained for a period of time which corresponds at least to the duration of the detection process. The composition of the air/fuel mixture supplied to the internal combustion engine is then changed only if the information on current operating conditions corresponds to a target value and the information on the expected operating conditions corresponds to the target value with a specified probability threshold.

Description

Description title

Method for detecting a voltage offset, at least in a region of a voltage lambda characteristic

State of the art

The invention relates to a method for detecting a voltage offset, at least in a region of a voltage lambda characteristic curve of a two-point lambda probe arranged in an exhaust passage of an internal combustion engine relative to a reference voltage lambda characteristic of the two-point lambda probe, wherein the two-point lambda probe is part of a Controlled system for adjusting an internal combustion engine supplied air / fuel mixture, wherein a characteristic deviation of the voltage-lambda characteristic is corrected to the reference voltage lambda characteristic at lambda = 1, wherein, starting from a value pair to be checked on the reference Voltage lambda characteristic with a lambda to be checked and a voltage to be tested, a change in the composition of the internal combustion engine supplied air / fuel mixture to lambda = 1 is carried out and wherein from the change in the composition of the air / fuel mixture until reaching Lambda = 1 on d the actual value of lambda is closed.

In order to optimize pollutant emissions and exhaust aftertreatment lambda probes are used in modern internal combustion engines for determining the composition of the exhaust gas and for controlling the internal combustion engine. Lambda sensors are basically known from, for example:

Konrad Reif (ed.): Sensors in the motor vehicle, 1st edition, 2010, pages 160-165. Lambda sensors determine the oxygen content of the exhaust gas, resulting in

Control of the internal combustion engine supplied air / fuel mixture and thus the Abgaslambda is used in front of a catalyst. In this case, via a lambda control loop, the air and fuel supply of the

Internal combustion engine regulated such that a provided for the exhaust aftertreatment by provided in the exhaust passage of the internal combustion engine catalysts optimal composition of the exhaust gas is achieved. In gasoline engines is usually on a lambda of 1, ie a stoichiometric ratio of air to fuel regulated. The pollutant emission of the internal combustion engine can be minimized. There are various forms of lambda probes in use.

In a two-point lambda probe, also referred to as a jump probe or Nernst probe, the voltage lambda curve at lambda = 1 has a sudden drop. It therefore essentially permits the distinction between rich exhaust gas (λ <1) during operation of the internal combustion engine

Excess fuel and lean exhaust gas (λ> 1) when operating with excess air and allows the exhaust gas to be regulated to a lambda of 1.

A broadband lambda probe, also referred to as a continuous or linear lambda probe, makes it possible to measure the lambda value in the exhaust gas in a wide range around lambda = 1. Thus, for example, a

Internal combustion engine can also be regulated to a lean operation with excess air. By linearizing the probe characteristic is also limited with a lower-cost two-point lambda probe in a

Lambda range a continuous lambda control before catalyst possible.

The prerequisite for this is that between the probe voltage of the two-point

Lambda probe and lambda is a clear connection. This relationship must exist over the entire life of the two-point lambda probe, since otherwise the accuracy of the control is not sufficient and unacceptably high emissions may occur. Due to manufacturing tolerances and aging effects of the two-point

Lambda probe this requirement is not met. Therefore, two-point lambda probes before catalyst are usually used with a two-point control. This has the disadvantage that in operating modes for which a lean or rich air fuel mixture is necessary ge, for example

Catalyst diagnosis or component protection, the target lambda set only pilot-operated, but can not be regulated. Various methods are known for calibrating the voltage lambda characteristic of two-point lambda probes.

DE 10 2012 211 687 A1 discloses a method with which displacements of the actual probe characteristic relative to the reference probe characteristic can be detected and compensated. This makes a continuous lambda control possible with a two-point lambda probe upstream of the catalytic converter. To detect temperature-related characteristic shifts, this method uses a change in the air / fuel mixture from one to

Checking value pair on the reference voltage lambda characteristic of the two-point lambda probe to lambda = 1. From the change of

Composition of the air / fuel mixture until reaching lambda = 1 is closed to the actual value of lambda before the change.

Despite the advantages of known from the prior art method for detecting a voltage offset at least in a range of

Voltage lambda characteristic include this still room for improvement. Thus, in DE 10 2012 211 687 Al, the change in the air / fuel mixture generally lasts several seconds and can lead to increased emissions because the emission-optimal operating point is temporarily left at lambda = 1. That is why it is only suitable for

Switching conditions performed, which can be expected to successfully detect temperature-induced characteristic shifts. These

Switch-on conditions used so far only information about current and past operating conditions. It therefore happens again and again that a change of the air / fuel mixture is started, because the current operating conditions are suitable, but then stopped because the operating conditions change and no longer allow reliable detection of temperature-related characteristic shifts. In this case, you will not get a measurement result, but the increased emissions that you have taken to get a measurement result, nevertheless, arise.

Revelation of the invention Therefore, a method is proposed for detecting a voltage offset, at least in a region of a voltage-lambda characteristic, which at least substantially avoids the disadvantages of known methods for detecting a voltage offset, at least in one region of a voltage-lambda characteristic, and which is particularly unsuccessful To avoid changes in the air / fuel mixture without measuring results.

According to the invention, therefore, a method for detecting a

Voltage offsets proposed at least in an area of a voltage-lambda characteristic of a two-point lambda probe arranged in an exhaust passage of an internal combustion engine with respect to a reference voltage-lambda characteristic of the two-point lambda probe. In the process, information about current operating conditions of the

Internal combustion engine and information about with a predetermined

Probability of expected operating conditions won. The expected operating conditions are obtained for a period corresponding to at least one duration of detection. The change of

Composition of the internal combustion engine supplied air / fuel mixture takes place only if the information about current operating conditions correspond to a desired value and the information about the expected operating conditions with a predetermined threshold value of the probability corresponding to the desired value.

The two-point lambda probe may be part of a controlled system for adjusting an air / fuel mixture supplied to the internal combustion engine. A

Characteristic deviation of the voltage lambda characteristic to the reference voltage lambda characteristic is corrected at lambda = 1. Starting from a pair of values to be checked on the reference voltage-lambda characteristic curve with a lambda to be checked and a voltage to be checked, a change in the composition of the

From the change in the composition of the air / fuel mixture to the achievement of lambda = 1 is closed to the actual value of lambda from the internal combustion engine supplied air / fuel mixture. The set point may be constant operating conditions or a predetermined deviation from constant operating conditions. In other words, the method is feasible even if there are certain deviations from the desired value, but these are still tolerable, for example because they are so slight.

The information about at least for the duration of the detection of future operating conditions can be obtained from at least one sensor, which are arranged outside of the internal combustion engine and the exhaust duct. For example, the sensor is a GPS sensor, a distance radar or a camera.

The operating conditions may be selected based on at least one of the group consisting of, for example: operating point of

Internal combustion engine, exhaust gas mass flow, temperature in the exhaust duct,

Injection time, pressure in an intake port of the internal combustion engine, operating mode of the internal combustion engine.

In addition, information about a time course of

Operating conditions for the threshold.

The threshold may take into account a predetermined value for a change over time in the operating conditions. For example, the predetermined value is 0. In other words, the predetermined value is constant and does not change with time.

The threshold can be variable. This can be changed according to certain criteria. The threshold value can be varied as a function of a time interval to an immediately preceding recognition. For example, if no detection was performed for a long time, the threshold is lowered. Conversely, if the detection is recent, the threshold can be increased.

In addition to the expected operating conditions, these dependent variables can be taken into account. In the method for detecting the voltage offset, a delay time of the controlled system is determined in a first method step, wherein in a second method step, starting from the one to be checked

Pair of values, the change of the composition of the air / fuel mixture towards lambda = l takes place, the change of the composition with the

Delay time of the controlled system is corrected, wherein the actual value of lambda in the value pair from the corrected change of

Composition of the air / fuel mixture is determined and wherein a deviation of the actual value of lambda from the

lambda, a voltage offset of the voltage lambda

Characteristic is detected.

The method makes it possible to detect a deviation of the actual lambda value from the lambda value expected and to be checked on the basis of the output signal of the two-point lambda probe. In this case, dynamic effects which lead to a delay of the lambda signal in the case of a lambda change are taken into account. Tolerance and

Aging-related voltage offsets of the voltage lambda characteristic curve with respect to the reference voltage lambda characteristic curve of the two-point lambda probe can be detected quickly and accurately, at the same time compensating for dynamic effects that would falsify detection. The reference voltage lambda characteristic gives the

Relationship between the output voltage and the lambda value for an intact two-point lambda probe with standardized operating parameters. To correct the voltage offset, the voltage of the

be assigned a new lambda value for the valid value pair.

Prerequisite for the implementation of the method is that any existing shift of the lambda-l-point is compensated.

The method takes into account a change in the dynamics of the two-point lambda probe compared with the new condition. It can do this

be provided that in the first method step, starting from the pair of values to be checked, a sudden change of

Composition of the air / fuel mixture is performed beyond lambda = 1 and that the delay time from the time difference between the abrupt change in the composition of the air / fuel mixture and the achievement of the lambda = 1 corresponding

Output voltage of the two-point lambda probe is determined. Due to the sudden change in the air / fuel mixture over lambda = 1, the time of the lambda jump is precisely defined. The time which, starting from the lambda jump, elapses until the output signal of the two-point lambda probe signals the passage through lambda = 1 corresponds to the delay time of the controlled system and can be taken into account in the second method step in the correction of the composition change. The abrupt change in the composition of the air / fuel mixture results in a precisely timed passage through lambda = 1, but other forms of lambda change can alternatively be used.

According to a particularly preferred embodiment variant of

It can be provided that in the second method step, starting from the value pair to be checked, a change in the

Composition of the air / fuel mixture above lambda = 1 is performed with a second ramp change in the composition of the air / fuel mixture at least in the range around lambda = 1 and that the actual lambda in the pair of values to be checked from the change in the composition of the air / Fuel mixture until the lambda = 1 corresponding output voltage of the two-point lambda probe minus the change in the composition of the air / fuel mixture is determined during the delay time of the controlled system.

From the known temporal change in the composition of the air / fuel mixture and the measured time until the output signal of the two-point lambda probe lambda = 1 signals, a lambda change of the pair of values to be tested up to lambda = 1 can be determined. The measured time and thus the specific lambda change can

For example, be determined too large due to a reduced dynamics of the two-point lambda probe. By correcting with the delay time of the controlled system determined in the first method step, the measured time and thus the determined lambda change can be corrected. The thus corrected lambda change then corresponds to the actual value of lambda in the value pair to be checked.

The change in the composition of the air / fuel mixture, starting from the value pair to be checked, take place with a constant ramp. Alternatively, other forms of lambda modification can be used. For example, a defined jump of the composition and a subsequent ramp-shaped change in the range at lambda = 1 can be provided first. The jump must not exceed the value of lambda = 1.

According to a particularly preferred embodiment variant of

It can be provided that a detected voltage offset of the voltage lambda characteristic is corrected with the actual value of lambda and / or that one or more causes for the voltage offset is inferred depending on the detected voltage offset, and

Measures to prevent or reduce the causes are taken. The correction can be effected for the one value pair or preferably for a predetermined range of the voltage lambda characteristic or the entire voltage lambda characteristic.

The accuracy in determining the actual value of lambda can be increased by providing in the first method step a first ramp-shaped change of the composition of the air / fuel mixture for determining the delay time of the controlled system and the slope of the second ramped change to the operating point the internal combustion engine is adjusted and / or that in the second

Process step, the slope of the second ramp-shaped change in the composition of the air / fuel mixture is adapted to the operating point of the internal combustion engine.

A further improvement in the accuracy of the method can be achieved in that the composition of the air / fuel mixture in the value pair to be checked for a stabilization period of

Output signal of the two-point lambda probe is kept constant. there the stabilization duration can be predetermined as a function of the operating point of the internal combustion engine.

A characteristic curve offset can be pronounced to different degrees in different ranges of the voltage-lambda characteristic. This is especially the case

Case if there are multiple causes for the characteristic offset. Therefore, it can be provided that the voltage offset is detected for different lambda ranges, in particular for a rich and a lean lambda range. An adapted correction of the characteristic offset can then be provided for the different lambda ranges.

If it is provided that pairs of values to be checked are selected in such a way that a predetermined desired lambda is maintained over the time average, then a voltage offset without increased emissions of the internal combustion engine can be detected and, if necessary, corrected. For example, at a desired lambda of one following a measurement at a rich one

Exhaust gas composition a measurement on a lean

Exhaust gas composition take place so that the required lambda of one is present on average over time.

Errors in the determination of a voltage offset can be avoided by the recognition of the voltage offset by repeated

Measurements are made plausible for the same pair of values or measurements for different value pairs. By averaging and filtering the

Measurement results can improve the accuracy in detecting a

Voltage offsets are further improved.

In internal combustion engines, which are operated at times with fuel cut, it may be provided that the detection of the voltage offset is plausibility in a fuel cut of the internal combustion engine. This provides an additional and independent way to check the voltage offset detected.

The detection and any correction of a

Voltage offsets can occur in different ranges of the voltage-lambda characteristic and thus starting from different to be checked Value pairs are performed. For this purpose, it can be provided that the value pair to be checked is set specifically and / or that the detection of the voltage offset at a during operation of the internal combustion engine

occurring value pair takes place. In the latter case, system-related active lambda changes, as used, for example, for catalyst diagnostics,

Dynamic diagnostics of exhaust probes or in phases with a two-point lambda control are made for the detection of a

Voltage offsets are used without making an active lambda change.

The accuracy in the detection of a voltage offset can be improved by performing the detection of the voltage offset during a constant operating point of the internal combustion engine for the duration of the detection. This can be done by performing the detection

be coupled corresponding switch-on.

A change in a voltage offset of a two-point lambda probe is generally comparatively slow. So at the start of the

Internal combustion engine already has a sufficiently well corrected voltage lambda characteristic, it can be provided that before a renewed

Detecting the voltage offset, the correction of the voltage offset from a previous operating cycle of the internal combustion engine is used.

A basic idea of the present invention is a triggering criterion for the change of the air / fuel mixture for the detection of

Characteristic shifts, which uses vehicle information that allows a statement about the expected development of operating conditions during this change in the air / fuel mixture. Such

Vehicle information may be, for example, navigation data or data from vehicle sensors.

The advantage of this method is that a change in the air / fuel mixture is only triggered when the detection of

Characteristic shifts with a high probability can be completed successfully. Unsuccessful changes to the air / Fuel mixture and associated increased emissions are avoided or at least reduced.

The invention provides, the change of the air / fuel mixture for

Detection of characteristic shifts can only be triggered if not only the current operating conditions and, if applicable, their development in the recent past are suitable for the detection, but also the operating conditions to be expected within the duration for the detection.

Quantities that can be evaluated to make a decision as to whether or not a change in the air-fuel mixture is successful are, for example, engine operating point (engine speed / load), exhaust gas mass flow,

Temperatures in the exhaust system, injection time, intake manifold pressure. It is advantageous to evaluate not only the values of these quantities but also their stability.

In addition, it is advisable to include various engine operating modes in the decision, such as fuel cut, sailing, engine operation or electric motor operation, cylinder or

Bank shutdown or semi-motor operation, single or multiple injection. Up-to-date information about these quantities and operating modes is usually available in the engine management system. An assessment of the stability is possible by comparing several successive values. From this, however, it is difficult to deduce statements about the future development of these quantities or operating modes, namely only in the form that with a certain probability stable conditions will continue to exist if stable conditions were present within a previously determined time of, for example, several seconds. Therefore, the invention provides to evaluate additional predictive vehicle information in order to make more reliable statements as to how these variables and

Operating modes, and whether this development is expected to bring about a successful completion of the air / fuel mixture change.

Since the total change in the air / fuel mixture typically takes 3-5 seconds, for example, to detect temperature-related characteristic shifts, a forecast of just a few seconds is sufficient. Such Additional information can come from the following sources, for example: navigation device, distance radar, camera.

Using navigation data, the most probable route can be determined, even if route guidance is not active. This can be done again

Derive predictions about the quantities exemplified above, e.g. how much they are likely to change in the next few seconds or whether the engine's operating mode is likely to change in the next few seconds. With additional sensor data, the environment of the vehicle can be taken into account and thus the prediction accuracy can be further increased. For example, the data from the distance radar or cameras can be used to determine the likelihood of an impending brake or

Derive acceleration process that would directly affect the above sizes.

It is intended to respond to the predictive vehicle information in the form that a change in the air / fuel mixture is activated only if the probability that the above-exemplified quantities remain stable in a predetermined time, and / or that the engine operating mode does not change, exceeds a certain threshold.

It is further provided that the threshold for the probability from which the change of the air / fuel mixture is activated to make of the urgency of detection of characteristic shifts. If, for example, a recognition has already been carried out shortly before, the threshold can be set high because a characteristic shift usually changes only slowly. If the last successful recognition is a long time ago or if no successful detection has yet occurred ("Uradaption"), it makes sense to lower the threshold because the emissions generated by the as yet uncompensated characteristic shift are of greater importance than those caused by the detection for a short time generated emissions.

As a further embodiment, it is provided to derive not only predictions about the directly relevant influencing variables mentioned above by way of example from the forward-looking vehicle information, but also via variables dependent on these quantities and their development, such as, for example, the sensor element temperature. For example, it may be the case that the directly relevant input variables themselves are a successful one

Detecting would be, but so dynamic that it is expected that the heating control will not be able to keep the sensor element temperature in the relatively narrow temperature range suitable for detection. In this case too, an unsuccessful activation of the change of the air / fuel mixture can be avoided with the help of the predictive vehicle information.

According to the invention, a computer program is proposed, which is set up to carry out each step of the method.

According to the invention is also an electronic storage medium

proposed on which such a computer program is stored.

According to the invention, an electronic control unit is furthermore proposed which comprises such an electronic storage medium. Brief description of the drawings

Further optional details and features of the invention will become apparent from the following description of preferred embodiments, which are shown schematically in the figures.

Show it:

1 shows a block diagram of an internal combustion engine, FIG. 2 shows a voltage-lambda characteristic curve of a two-point lambda probe with a voltage offset relative to a reference voltage-lambda characteristic curve, and

3 shows a temporal lambda curve for detecting a voltage offset. Embodiments of the invention Fig. 1 shows a block diagram of an internal combustion engine 10. The

Internal combustion engine 10 has at least one inlet channel 12 and at least one exhaust gas channel 14. In the exhaust passage 14, a two-point lambda probe 16 is arranged.

FIG. 2 shows a voltage lambda characteristic curve 18 of a two-point lambda probe 16 with a voltage offset with respect to a reference voltage lambda characteristic curve 20. The characteristic curves 18, 20 are plotted against an axis probe voltage 22 and with respect to an axis lambda 24.

The illustrated lambda range is indicated by a mark 26 at lambda = 1 in a rich lambda region 28 with lambda <1 and in a lean

Lambda range 30 with Lambda> 1 divided.

A value pair 32 to be checked is shown at the intersection of two dashed lines on the reference voltage lambda curve 20 by a voltage 32.1 to be checked and a lambda 32.2 to be checked. An actual value of lambda 34 is marked for the voltage 32.1 to be tested on the voltage lambda characteristic curve 18. A lambda change 36 due to a change of the air-fuel mixture supplied to the internal combustion engine and thus from lambda until reaching lambda = 1 is shown by a double-headed arrow.

The reference voltage lambda characteristic curve 20 corresponds to the profile of the output signal of an intact, unaged two-point lambda probe in the exhaust gas passage of an internal combustion engine during a change in the

Exhaust gas composition. It has its maximum slope at lambda = 1. The jump from a high output voltage to a low one

Output voltage takes place in a comparatively small lambda window. By aging, by manufacturing tolerances or by changes

Operating conditions of the two-point lambda probe may be the

Shift output voltage by a voltage offset relative to the reference voltage lambda curve 20. In the present exemplary embodiment, the voltage lambda characteristic curve 18 is shifted by a positive voltage offset with respect to the reference voltage lambda characteristic curve 20. In this case, the voltage offset in the lean lambda region 30 is more pronounced than in the rich lambda region 28. Such a course of the voltage offset is, for example, operated too hot

Two-point lambda probes known to be at the same time a constant

Have voltage offset over the entire characteristic curve.

The use of a two-point lambda probe for a steady-state lambda control in front of the catalytic converter presupposes that a specific exhaust gas lambda can be unambiguously assigned to a specific probe voltage. This is true in the case of the reference voltage lambda characteristic 20. Lies a

Voltage offset of the actual voltage lambda characteristic 18 with respect to the reference voltage lambda characteristic 20 before, this assignment is no longer correct. At a voltage offset towards higher probe voltages, as shown in the illustrated embodiment, a given probe voltage will set at too lean a lambda. At an offset towards lower probe voltages, the same will occur

Probe voltage at too rich lambda. A lambda control with a voltage lambda shifted by a positive voltage offset

Characteristic curve 18 therefore leads to a lean exhaust gas, while a voltage-lambda characteristic curve shifted by a negative voltage offset leads to a too rich exhaust gas, which in each case results in increased pollutant emissions of the internal combustion engine.

A voltage offset of the voltage lambda characteristic curve 18 can be recognized by the fact that the actual value of lambda 34 at a voltage to be tested 32.1 of the two-point lambda probe from a deliberately carried out change in the air / fuel ratio supplied to the internal combustion engine until reaching Lambda = 1 and determines with the to be checked

Lambda 32.2 is compared. In the event of a deviation, the actual value of lambda 34 can be assigned to the voltage to be tested 32.1 and the voltage lambda characteristic curve 18 thereby corrected. In this case, the voltage lambda characteristic curve 18 is preferably corrected in a larger range, for example in the rich lambda region 28. According to the invention, it is provided that in determining the actual value of Lambda 34 possible dynamic effects of the two-point lambda probe are taken into account. The dynamic effects may be due to an aging dynamic loss of the two-point lambda probe and their influence must be determined prior to determining the actual value of lambda 34.

Alternatively or in addition to the correction of the voltage lambda characteristic curve 18, the voltage offset or the profile of the voltage offset can be used

Voltage offsets on the cause of the voltage offset closed and measures are taken to avoid or reduce the influence of the causes. In the exemplary embodiment shown, the constant voltage offset can first be corrected, for example, and then the temperature of the two-point lambda probe can be reduced in order to adapt the voltage lambda characteristic curve 18 to the reference voltage lambda characteristic curve 20.

A prerequisite for the described detection of a temperature-related characteristic shift is that any existing shift of the lambda-l-point and a constant offset of the voltage-lambda curve 18 has been previously compensated by known methods, so that the voltage-lambda curve 18 in Lambda l point with the reference voltage lambda curve 20 matches.

The correction and the cause compensation can be done in different ways

Regions of the voltage lambda characteristic 18 are performed separately. With complete compensation, the voltage lambda characteristic curve 18 is congruent with the reference voltage lambda characteristic curve 20. This makes it possible, even with an aged two-point lambda probe to obtain a clear relationship between the probe voltage and lambda. This can also be compared to a broadband lambda probe

inexpensive two-point lambda probe in a restricted

Lambda a steady lambda control before catalyst can be performed.

3 shows, in one exemplary embodiment, a temporal lambda curve 38 for detecting a voltage offset in the case of a delayed-response two-point signal. Lambda probe. The lambda curve 38 is plotted against an axis of desired lambda 40 and a time axis 42. A lean lambda 44, a desired lambda = 1 46 and the lambda 32.2 to be checked shown in FIG. 2 are marked by dotted lines with respect to the axis of desired lambda 40.

Accordingly, a first time tl 48, a second time t2 50, a third time t3 52, a fourth time t4 54 and a fifth time t5 56 are marked with respect to the time axis 38.

The lambda 32.2 to be checked belongs to a pair of values 13 to be checked, shown in FIG. 2, on the reference voltage lambda characteristic curve 20 of the two-point lambda probe. In the embodiment, this has to

lambda 32.2 checking a value of 0.95.

The two-point lambda probe is part of a controlled system for adjusting an air / fuel mixture supplied to the internal combustion engine. In a first method step for determining a delay time of the controlled system, the air / fuel mixture supplied to the internal combustion engine is changed at the first time t.sub.18 such that the lambda 32.2 to be checked is present corresponding to the reference voltage / lambda characteristic curve 20. After a predetermined stabilization time for the probe voltage takes place at the second time t2 50 a jump-shaped lambda change over lambda = 1 addition to a lean lambda 44, for example, 1.05.

The jump-shaped lambda change from a rich to the lean lambda 44 causes a jump of the probe voltage at lambda = 1. This jump in the probe voltage is delayed due to dynamic effects. The delay time between the imprinting of the jump-shaped

Lambda change and the jump of the probe voltage at lambda = 1 is measured.

Once the delay time of the controlled system has been determined, the lambda 32.2 to be checked is set again in a second method step at the third time t3 52 and kept constant for a stabilization time. At the fourth time t4 54, the output voltage U (t4) of the two-point lambda probe is measured. Starting from the lambda 32.2 to be checked, a ramp-shaped starting from the fourth time t4 54 takes place Lambda change in the direction of lean lambda values. The slope of the ramp-shaped lambda change is preferably constant and adapted to the operating point of the internal combustion engine. Also, the ramp-shaped lambda change from a rich to a lean one

Lambda causes a jump of the probe voltage at lambda = 1. This jump is also delayed at the fifth time t5 56th Die

Delay time corresponds to the measured in the first process step delay time.

Immediately after the jump of the probe voltage at lambda = 1, the ramp-shaped lambda change can be aborted and a desired desired lambda can be set. The actual value of lambda 34 at the fourth time t4 is immediately closed

The beginning of the ramp-shaped lambda change corresponds to the lambda change which was necessary until the probe voltage jumped at lambda = 1 at the fifth time t5, minus the lambda change which took place during the delay time measured in the first method step.

The deviation between the actual value of lambda 34 determined at the fourth time t4 54 and the lambda 32.2 expected and to be checked in the output voltage U (t4) according to the reference voltage lambda characteristic 20 corresponds to the characteristic curve offset at this point of the voltage lambda Characteristic 18.

By determining the influence of dynamic effects immediately before measuring the actual value of lambda 34, the

Lambda measurement compared to previous methods much more accurate. The determined characteristic curve offset can subsequently be used for an adaptation of the

Sensor characteristic or for a compensation of causes that led to the offset used.

The jump-shaped or ramp-shaped described in the first method step and the second method step

Lambda changes are particularly beneficial for fast and accurate Recognition of a characteristic offset. In principle, however, other types of lambda changes are conceivable, which allow the determination of the influence of dynamic effects and the determination of the actual lambda at a certain probe voltage.

The stabilization times and the ramp gradient can be adapted to the respective operating point of the internal combustion engine to the

To increase recognition accuracy.

Is a characteristic offset, as shown in the embodiment in Fig. 2, in different areas of the voltage-lambda characteristic 18th

If different, the method can be used for a number of value pairs to be checked and the voltage offset can be determined in sections.

The determined voltage offset can be made plausible by repeating the measurement at the same point or at other points in the voltage-lambda curve 18. By averaging or filtering the measurement result, the recognition can be improved.

Following a measurement in the rich lambda region 28 of the voltage-lambda characteristic curve 18, a corresponding measurement can take place in the lean lambda region 30 and vice versa. As a result, the desired lambda is maintained in the time average and the method can be carried out with no emissions.

So that the change of the air / fuel mixture is not unsuccessful, it is proposed according to the invention that information about current operating conditions of the internal combustion engine 10 and information about operating conditions to be expected with a predetermined probability be obtained. The expected operating conditions are obtained for a period corresponding to at least one duration of the detection, wherein the change in the composition of the internal combustion engine 10th

supplied air / fuel mixture takes place only if the information on current operating conditions correspond to a desired value and the

Information about the expected operating conditions with a predetermined threshold of the probability corresponding to the desired value, as will be described in more detail below.

Outside the internal combustion engine 10 and also outside the exhaust duct 14 at least one sensor 58 is arranged. The sensor 58 may be a GPS sensor, a distance radar or a camera. It is understood that in the

Internal combustion engine and / or the inlet channel 12 and / or the exhaust duct 14 further sensors may be present, for detecting

Operating conditions of the internal combustion engine 10 are suitable. The

Operating conditions are selected based on at least one size of the

Group consisting for example of: operating point of the internal combustion engine, exhaust gas mass flow, temperature in the exhaust duct, injection time, pressure in an intake port of the internal combustion engine, operating mode of the internal combustion engine.

By means of these sensors and the sensor 58, information about current operating conditions is acquired, as well as information about future expected operating conditions. The future operating conditions are based on the information provided by the sensors with a

Valued probability of their occurrence. The setpoint value is set, for example, as constant operating conditions or a predetermined or permissible deviation from constant operating conditions. Now the

Probability of occurrence of certain operating conditions compared to a threshold of probability. In other words, it checks if the probable occurrence of certain

Operating conditions exceeds a threshold or not. If the threshold is exceeded, this indicates that the predetermined

Operating conditions seem to perform a detection of the voltage offset and the change of the air-fuel mixture. Give

For example, the data from the sensors that with a probability of 95% in the next 5 s is a constant speed drive, the internal combustion engine 10 is currently also moving at a constant speed and a threshold for the change of the air-fuel mixture at a constant Speed as operating condition is 80%, so the change of the air-fuel mixture for the detection can be performed. However, based on the data, if the probability is only 75% or the threshold is 98%, the change in

Fuel mixture for detection not performed. The threshold itself in turn, depends on the operating conditions required for detection, and thus may vary. For example, the threshold for a downhill run is 98% for the next 4 seconds.

For example, a GPS sensor is usually installed in a navigation device. Using navigation data, the most probable route can be determined, even if route guidance is not active. From this, in turn, predictions can be made about the quantities exemplified above, e.g. how much they are likely to change in the next few seconds, or whether the engine operating mode is likely to change in the next few seconds. With additional sensor data, the environment of the vehicle can be taken into account and thus the prediction accuracy can be further increased. For example, based on the data of the

Distance radar or cameras the probability of one

Derive forthcoming braking or acceleration process, which would directly affect the above sizes.

As described, it is intended to respond to the information on expected operating conditions in the form that a change of the air / fuel mixture is activated only if the probability that the quantities exemplified above in at least the period that the Detecting the voltage offset would last, remain stable, and / or that the engine operating mode does not change, a certain threshold

exceeds. Unsuccessful changes of the air / fuel mixture without

Measurement result can be avoided.

In addition, information about a time course of

Operating conditions for the threshold. An assessment of the stability is possible by comparing several successive values. The threshold may take into account a predetermined value for a change over time in the operating conditions. The predetermined value can be 0 and thus constant in time. Accordingly, the threshold is based on constant operating conditions.

The threshold can be variable. Thus, the threshold value as a function of a time interval to an immediately preceding recognition be varied. For example, the threshold for the probability from which the change of the air / fuel mixture is activated may make the urgency of detection of characteristic shifts. If, for example, a detection has already been carried out shortly before, the threshold value can be set high because of a

Characteristic shift usually changed only slowly. If the last successful recognition is a long time ago or has not yet been successfully detected ("Uradaption"), the threshold value is usefully lowered, because the threshold value has not been compensated

Characteristic curve more permanently than the emissions generated by the detection.

In addition to the information on expected operating conditions, these dependent variables can be taken into account. So can not only from the information about expected operating conditions

Predictions on the above-mentioned directly relevant influencing variables are derived, but also on these sizes and their development dependent variables, such as the

Sensor element temperature. For example, it may be the case that the directly relevant inputs themselves would allow successful detection but are so dynamic that it is expected that the heater control will not be able to maintain the sensor element temperature within the relatively narrow temperature band suitable for detection. In this case too, an unsuccessful activation of the change of the air / fuel mixture can be made with the help of the information on the expected

Avoid operating conditions.

Claims

Claims 1. Method for detecting a voltage offset, at least in one

Range of a voltage lambda characteristic curve (18) of a arranged in an exhaust passage of an internal combustion engine two-point lambda probe relative to a reference voltage lambda characteristic (12) of the two-point lambda probe, wherein information about current operating conditions of the internal combustion engine and information about with a predetermined

Probability expected operating conditions are obtained, the expected operating conditions are obtained for a period corresponding to at least one duration of the detection, wherein a change in the composition of the internal combustion engine supplied air / fuel mixture for detection takes place only if the

Information about current operating conditions a setpoint

correspond and the information about the expected

Operating conditions with a predetermined threshold of

Probability equal to the setpoint.

2. The method of claim 1, wherein the two-point lambda probe is part of a controlled system for adjusting an internal combustion engine supplied air / fuel mixture, wherein a characteristic deviation of the voltage lambda characteristic (18) to the reference voltage lambda characteristic (18 ) is corrected at lambda = 1, wherein, starting from a to be checked

Value pair (13) on the reference voltage lambda characteristic (18) with a lambda to be checked (32.2) and one to be checked

Voltage (32.1), a change in the composition of the

Internal combustion engine supplied air / fuel mixture to lambda = 1 and where from the change in the composition of the air

/ Fuel mixture is closed until Lambda = 1 on the actual value of lambda (34), wherein information about current operating conditions of the internal combustion engine and information about expected to be expected with a predetermined probability operating conditions, the expected operating conditions for a

Period of at least one duration of detection corresponds to the change in the composition of the

Internal combustion engine supplied air / fuel mixture takes place only if the information about current operating conditions correspond to a desired value and the information about the expected

Operating conditions with a predetermined threshold of

Probability equal to the setpoint.

The method of claim 1 or 2, wherein the setpoint constant

Operating conditions or a predetermined deviation from constant operating conditions.

Method according to one of claims 1 to 3, wherein the information about at least for the duration of the detection of future operating conditions of at least one sensor are obtained, which are arranged outside the internal combustion engine and the exhaust duct.

The method of claim 4, wherein the sensor is a GPS sensor

Distance radar or a camera is.

Method according to one of claims 1 to 5, wherein the operating conditions are determined based on at least one size selected from the group consisting of: operating point of the internal combustion engine,

Exhaust gas mass flow, temperature in the exhaust duct, injection time, pressure in an intake passage of the internal combustion engine, operating mode of

Internal combustion engine.

Method according to one of claims 1 to 6, wherein in addition information about a temporal course of operating conditions for the threshold value are taken into account.

Method according to one of claims 1 to 7, wherein the threshold takes into account a predetermined value for a temporal change of the operating conditions.

The method of claim 8, wherein the predetermined value is 0.

10. The method according to any one of claims 1 to 9, wherein the threshold value is variable.

11. The method of claim 10, wherein the threshold is varied in dependence on a time interval to an immediately preceding detection.

12. The method according to any one of claims 1 to 11, wherein in addition to the expected operating conditions of these dependent sizes

be taken into account.

13. The method according to any one of claims 1 to 12, wherein in a first

Process step, a delay time of the controlled system is determined, wherein in a second process step, starting from the zu

verifying value pair (32), the change in the composition of the air / fuel mixture to lambda = l is carried out, wherein the change of the composition with the delay time of the controlled system is corrected, wherein the actual value of lambda (34) in the pair of values from the corrected Changing the composition of the air / fuel mixture is determined and wherein from a deviation of the actual value of lambda (34) from the value to be checked by lambda (32.2) a voltage offset of the voltage lambda characteristic (18) is detected.

14. Computer program which is set up to perform each step of the method according to one of claims 1 to 13.

15. An electronic storage medium on which a computer program according to claim 14 is stored.

16. An electronic control unit comprising an electronic storage medium according to claim 15.