DE102014211069A1 - Method for evaluating the deviation of a characteristic - Google Patents

Abstract

The invention relates to a method and a device for evaluating the deviation (18) of at least one region of a characteristic curve of an exhaust gas sensor arranged in an exhaust passage of an internal combustion engine of at least one reference value. A robust method for characteristic curve correction for reliable pollutant optimization is obtained in that for assessing the deviation (18) at least one threshold is specified, which forms a criterion for the distinction between a tolerable and an intolerable correction requirement.

Description

State of the art

The invention relates to a method for evaluating the deviation of at least one region of a characteristic curve of an exhaust gas sensor arranged in an exhaust passage of an internal combustion engine from at least one reference value.

Furthermore, the invention relates to a device for evaluating the deviation of at least one region of a characteristic of an exhaust gas duct of an internal combustion engine disposed exhaust gas sensor of reference values, wherein a control device is provided, and wherein in the control device, a program sequence or a circuit is provided.

To optimize pollutant emissions in today's internal combustion engines, exhaust gas sensors are used to control the combustion process and the exhaust aftertreatment, such as two-point and / or broadband lambda probes and / or NO _x sensors. Optimization requires that the measured quantities are determined reliably and accurately via the sensors. A decisive factor here is the unambiguous relationship between a physically measured variable and the measured variable to be determined, which as a rule is present over a characteristic curve. A shift in the characteristic curve with respect to a reference characteristic, for example due to aging, can lead to a much higher emission of pollutants.

This applies in particular to a two-point lambda probe, also called a jump or Nernst probe, if this is to be used for continuous lambda control. Their voltage lambda characteristic curve, hereinafter referred to as the lambda characteristic, has a jump in the transition between the rich and the lean region (λ = 1) and otherwise runs relatively flat. Therefore, the two-point lambda probe generally differs substantially between rich exhaust gas (λ <1) when operating the internal combustion engine with excess fuel and lean exhaust gas (λ> 1) when operating with excess air. By linearizing the lambda characteristic, however, even with a two-point lambda probe, which is more cost-effective than a broadband lambda probe, a continuous lambda control in front of the catalytic converter is possible, at least in a limited lambda range. Due to the rather flat characteristic curve, this requires good agreement with a reference lambda characteristic over the entire service life of the probe. Otherwise, the accuracy of the control is insufficient and unacceptably high emissions may occur.

This condition is usually not met. Instead, the actual lambda characteristic can be shifted by several superimposed effects compared to the reference lambda characteristic. Therefore, two-point lambda probes upstream of the catalytic converter are usually used with a two-point control with regulation to lambda = 1. However, this has the disadvantage that in operating modes for which a lean or rich air-fuel mixture is necessary (for example catalyst diagnosis or component protection), the target lambda can only be adjusted in a precontrolled manner, but can not be regulated.

From the DE 10 2010 211 687 A1 is a method for detecting a deviation and from the DE 10 2012 211 683 A1 a method for correcting a lambda characteristic of a arranged in an exhaust passage of an internal combustion engine two-point lambda probe relative to a corresponding reference lambda characteristic known. In particular, it describes how a constant characteristic curve offset or a temperature-dependent deviation of the actual lambda characteristic curve of a two-point probe upstream of the catalytic converter from the reference lambda characteristic curve can be detected and compensated. Thus, a continuous lambda control with a two-point lambda probe is possible.

However, it may happen that an implausibly high correction requirement is determined, which indicates, for example, a defective probe or another malfunction. If a correction were carried out in this case, this could possibly lead to a failure of the desired safe regulation for optimized pollutant emissions.

The invention is therefore based on the object to provide a robust method for characteristic correction to ensure reliable pollutant optimization, and an apparatus for performing such a method.

Disclosure of the invention

The object of the invention relating to the method is achieved by specifying at least one threshold for the assessment of the deviation, which forms a criterion for the distinction between a tolerable and a non-tolerable correction requirement. The application of the criterion allows a differentiated reaction by different measures. In this case, the at least one threshold may be located above and / or below the at least one reference value. Also, it can be absolute or relative.

Particularly advantageous is when the exhaust gas sensor is a lambda probe, in particular a two-point lambda probe, when the Characteristic is a lambda characteristic and if the reference values of a reference lambda characteristic are taken. The application of the method according to the invention with respect to a lambda, in particular a two-point lambda probe, allows the more reliable use of such a probe for emission-optimized control of the engine combustion process.

When applying the method according to the invention with a two-point lambda probe, it is expedient if a change in the composition of the air / fuel mixture supplied to the internal combustion engine takes place to Lambda = 1 for determining the deviation, starting from a pair of values on the reference lambda characteristic if it is concluded from the change in the composition of the air / fuel mixture to the actual value of lambda. In this case, for example, tolerance, temperature and age-related deviations or a deviation can be detected quickly and accurately by superimposing at least two such effects. At the same time, dynamic effects which would distort the recognition can be compensated. In addition, other methods come into question, which are used to determine the actual value of lambda and thus can close to the deviation between the actual value and a reference value, for example, a method involving the heating power and / or another, in particular a resistance temperature Characteristic curve of the lambda probe. Such methods may have other advantages, e.g. that they can be carried out in part independently of the lambda characteristic (which here denotes the voltage lambda characteristic curve). The chosen method or a combination of several methods can be applied multiple times, and the deviation can be determined in each case and / or determined from one or more average values. In this way the results can be made plausible.

It is likewise advantageous if the deviation from at least one reference value of a reference lambda characteristic curve is determined after a characteristic deviation to the reference lambda characteristic curve is corrected at lambda = 1. Thus, errors in the determination of the deviation due to an effect causing an additional displacement in the abscissa can be eliminated, making the evaluation of the deviation more reliable.

In a simplified way, a deviation can be evaluated if the at least one threshold delimits a plausibility range from an area outside the plausibility range.

Likewise, for a simplified evaluation of the deviation, it is advantageous if the at least one threshold and thus the plausibility range are set flexibly. It makes sense, for example, a definition according to the tolerances of a faultless exhaust gas sensor.

The goal is that the deviation is compared with the threshold, wherein the deviation within the plausibility range is assessed as a tolerable correction requirement and the deviation outside the plausibility range as a non-tolerable correction requirement. This evaluation can be used as part of a decision procedure with regard to the selection of which of the differentiated reactions is to be used advantageously in the present case. In the case of a deviation outside the plausibility range, a malfunction of, in particular, the exhaust gas sensor, its electrical wiring in an associated control unit or the control unit software for operating the exhaust gas sensor is assumed, so that a reaction other than a complete correction of the deviation is likely to make sense.

A response adapted to the case of need can be achieved by correcting the deviation in the event of a tolerable correction requirement and by triggering a different reaction when a non-tolerable correction requirement is detected. By correcting the deviation with a tolerable correction requirement, the required accuracy of an exhaust gas sensor can be ensured. It is advantageous if this correction is made by remedying the cause of a deviation, as in the aforementioned DE 10 2012 211 683 A1 described. Another reaction in case of an intolerable need for correction is to increase the robustness of the entire error detection and compensation process. This means that inappropriate corrective measures, which would have a negative rather than a positive effect, can be intercepted and replaced by correspondingly more meaningful measures. Corrective action, which would not be feasible to the extent necessary, can be replaced by other reactions.

In a preferred variant of the method, it is provided that the other reaction is triggered depending on the diagnosed cause. In particular, it is triggered when a temperature offset detection points to a significantly too cold temperature of the two-point lambda probe or the temperature offset detection indicates a significantly high temperature of the two-point lambda probe or an implausible high positive voltage offset is detected or an implausibly high negative voltage offset is detected , In such cases, a different reaction is particularly useful because the necessary corrections may not be feasible, or there is a high probability of another known, but not immediately correctable cause of the deviation. If the probe temperature is significantly too low or too high, for example, the probe element temperature would have to be increased implausibly as a corrective measure, for which the heating power may not be available, or it would have to be lowered, which may not be possible. A non-tolerable correction requirement arises, for example, if the temperature would have to be changed by more than -50 K to +0 K with respect to the nominal temperature of the probe, which may be 730 ° C., for example, in order to correct the determined deviation. With respect to the voltage offset, there is a non-tolerable correction requirement, for example if this is more than ± 15 mV. An implausibly high positive voltage offset may indicate, for example, a shunt between the probe signal line and the battery voltage, an implausibly negative voltage offset, for example, to a poisoning of the oxygen reference of the probe.

• – Begrenzung der Korrektur der Abweichung auf den Schwellwert,
• – Begrenzung der Korrektur auf einen Ersatzwert,
• – Setzen einer Statusinformation zur Kenntlichmachung der Abweichung außerhalb des Plausibilitätsbereiches
• – Eintrag in einen Fehlerspeicher einer Steuereinrichtung umfasst.

It is advantageous if the other reaction is at least one of the measures

• Limiting the correction of the deviation to the threshold value,
• - limitation of the correction to a substitute value,
• - Setting a status information to identify the deviation outside the plausibility range
• - Entry in a fault memory of a control device comprises.

By limiting the correction to a threshold, malfunctions should be avoided, e.g. Damage to the exhaust gas sensor due to overheating. The limitation of the correction to a substitute value is provided in particular for the case when a complete correction is not possible and a correction to the threshold value would obscure the deviation outside the plausibility range, in particular for other diagnosis units, so that the exhaust gas sensor e.g. would not be displayed as faulty, though it would be required. The replacement value can also mean that no correction is made. Instead of or in addition to a correction, it may be provided to set status information which indicates the limited function of the exhaust gas sensor. By an entry in a fault memory of a control unit, e.g. the lambda control is deactivated and switched to lambda pilot control, so that excessively high emissions or increased fuel consumption due to the intolerable deviation are avoided.

The method according to the invention can be used particularly purposefully if different other reactions are triggered, depending on how far the deviation lies outside the plausibility range and / or that different other reactions are triggered depending on the cause of the deviation from the plausibility range.

Preferred areas of application arise when using a two-point lambda probe, which is located in front of or behind a catalytic converter. Thus, the method according to the invention can be used flexibly for differently positioned two-point lambda probes and is not limited to a particular probe installation location.

The object of the invention relating to the device is achieved in that at least one reference value and one comparison step are predetermined in the program sequence or in the circuit, in which the determined deviation is compared with the at least one reference value and in that the control device is either one depending on the comparison result Correcting the deviation or triggering another reaction.

An expedient field of use of the device is when the exhaust gas sensor is a lambda probe, in particular a two-point lambda probe, that the characteristic is a lambda characteristic and that the reference values are formed by a stored reference lambda characteristic and that a characteristic deviation from the reference Lambda characteristic is already corrected at lambda = 1 before comparison with the reference values. This allows the more reliable use of a lambda, in particular a two-point lambda probe for emission-optimized control of the combustion process.

The invention will be explained in more detail with reference to an embodiment shown in the figure. It shows:

1 a voltage lambda diagram of a two-point lambda probe 1 shows a voltage lambda diagram 10 a two-point lambda probe, with a voltage axis 11 and a lambda axis 12 , For a brand new two-point lambda probe under standard conditions, ie without tolerances, is the relationship between a measured voltage 170 and the corresponding air ratio λ clearly over the reference lambda characteristic 15 established. The reference lambda characteristic 15 has a fat area 13 (λ <1) and a lean region 14 (λ> 1), where at λ = 1 there is a nearly sudden change in the course. At a measured voltage 170 is determined by the assumed reference lambda characteristic 15 to a reference lambda 171 closed.

In addition to the reference lambda characteristic 15 is in 1 a lambda characteristic 16 shown, compared to the reference lambda characteristic 15 in the fat area 13 moved upwards. Such a shift can result, for example, due to tolerances, aging or temperature effects, or by a superposition of several effects. If there is such a shift, which is not corrected, the voltage corresponds 170 real the actual lambda 172 instead of the reference lambda 171 , which is a deviation 18 different.

With the method according to the invention can be assessed by comparison with at least one threshold, whether the deviation 18 within a plausibility range. Then it makes sense to correct them preferably by remedying the cause. For example, while [fey2si1] tolerances of the electrical wiring of the probe to a constant offset with corresponding deviations in the rich and lean range ( 13 . 14 ), as a result of a faulty probe temperature, a different deviation in the rich and lean region ( 13 . 14 ). This is typically in the lean area 14 about 1/6 of the shift in the fat area 13 so that a mere offset shift would not allow complete correction.

In the case of a non-tolerable shift, outside the plausibility range, then other reactions, in particular those previously described as beneficial, are initiated, either individually or in a suitable combination. The detection of an exhaust probe error taking into account a non-tolerable high correction requirement makes it possible to detect corresponding errors faster and with improved selectivity. In this way, a robust method of characteristic correction can be provided, and an apparatus for carrying out the method to provide reliable pollutant optimization available.

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 102010211687 A1 [0006]
• DE 102012211683 A1 [0006, 0016]

Claims (14)

Method for evaluating a deviation ( 18 ) of at least one region of a characteristic curve of an exhaust-gas sensor arranged in an exhaust-gas channel of an internal combustion engine of at least one reference value, characterized in that in order to assess the deviation ( 18 ) is predetermined at least one threshold, which forms a criterion for the distinction between a tolerable and a non-tolerable correction need. A method according to claim 1, characterized in that the exhaust gas sensor is a lambda probe, in particular a two-point lambda probe, that the characteristic curve has a lambda characteristic ( 16 ) and that the at least one reference value of a reference lambda characteristic ( 15 ) is taken. A method according to claim 2, characterized in that for determining the deviation ( 18 ) is based on a pair of values on the reference lambda characteristic curve, a change in the composition of the internal combustion engine supplied air / fuel mixture towards lambda = 1 and that is concluded from the change in the composition of the air / fuel mixture to the actual value of lambda , Method according to claim 2 or 3, characterized in that the deviation ( 18 ) of at least one reference value of the reference lambda characteristic ( 15 ) is determined after a characteristic deviation from the reference lambda characteristic ( 15 ) is corrected at lambda = 1. Method according to one of the preceding claims, characterized in that the at least one threshold delimits a plausibility range against an area outside the plausibility range. Method according to one of the preceding claims, characterized in that the at least one threshold and thus the plausibility range is set flexibly. Method according to one of the preceding claims, characterized in that the deviation ( 18 ) is compared with the threshold, the deviation ( 18 ) within the plausibility range as a tolerable correction requirement and the deviation ( 18 ) is assessed outside the plausibility range as a non-tolerable correction requirement. Method according to one of the preceding claims, characterized in that at a tolerable correction requirement, a correction of the deviation ( 18 ) and that when a non-tolerable correction requirement is detected, a different response is triggered. Method according to claim 8, insofar as this is dependent on claims 2 to 7, characterized in that the other reaction is triggered, in particular, when - a temperature offset detection indicates a significantly too cold temperature of the two-point lambda probe or - the temperature offset detection on a clear indicates too high temperature of the two-point lambda probe or - an implausibly high positive voltage offset is detected or - an implausibly high negative voltage offset is detected. Method according to claim 8 or 9, characterized in that the other reaction comprises at least one of the measures - limiting the correction of the deviation ( 18 ) to the threshold value, - limitation of the correction to a substitute value, - setting of status information for indicating the deviation ( 18 ) outside the plausibility range - entry in a fault memory of a control device comprises. A method according to claim 10, characterized in that different other reactions are triggered, depending on how far the deviation ( 18 ) is outside the plausibility range and / or that depends on the cause of the deviation ( 18 ) different other reactions are triggered from the plausibility range. Method according to one of the preceding claims, characterized in that a two-point lambda probe is used, which is located in front of or behind a catalyst. Device for evaluating the deviation ( 18 ) of at least a portion of a characteristic curve of an exhaust gas passage of an internal combustion engine of at least one reference value, wherein a control device is provided and wherein in the control device a program sequence or a circuit is provided, characterized in that in the program sequence or in the circuit at least a reference value and a comparison level are specified, in which the determined deviation ( 18 ) is compared with the at least one reference value and that the control device depends on the Result of the comparison either a correction of the deviation ( 18 ) or trigger another reaction. Apparatus according to claim 13, characterized in that the exhaust gas sensor is a lambda probe, in particular a two-point lambda probe, that the characteristic curve has a lambda characteristic ( 16 ) and that the reference values are represented by a stored reference lambda characteristic ( 15 ) are formed and that a characteristic deviation with respect to the reference lambda characteristic ( 15 ) is already corrected at lambda = 1 before comparison with the reference values.

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