EP1180594A2 - Method for testing an exhaust gas recirculation system - Google Patents

Abstract

Process for monitoring an exhaust gas in a recirculating device of an I.C. engine comprises adjusting a determined change of the exhaust gas recirculating rate; measuring the NOx concentration in the exhaust gas; and establishing a defect in the recirculating device from the concentration difference depending on the change of the exhaust gas recirculating rate. Preferred Features: The concentration difference from the NOx concentration measured before and after the change of the exhaust gas recirculating rate. The NOx concentration is measured downstream of a NOx storage catalyst and the catalyst is saturated to its maximum storage capability before adjusting the determined change of the exhaust gas recirculating rate. Saturation is recognized downstream of the catalyst. Monitoring is only carried out when the operating parameters of the engine lie within a determined region and/or have limited dynamics.

Description

The invention relates to a method for checking a Exhaust gas recirculation system of an internal combustion engine.

To continue the fuel consumption of Otto internal combustion engines to reduce, come more and more internal combustion engines to be used with a stoichiometric mixture as well lean combustion can be operated. With Otto internal combustion engines with lean combustion the excess air becomes chosen as large as it is the load requirement on the Internal combustion engine allowed; with low load requirement In a stratified charge operation, the fuel / air mixture, with which the internal combustion engine is operated, lambda values of 3 and more.

To meet the required exhaust emission limit values are at such internal combustion engines require special measures, otherwise the emitted NOx masses would be too large. This also applies to diesel internal combustion engines. In addition to use of NOx storage catalysts due to their coatings are able to remove NOx compounds from the exhaust gas with lean combustion occur in a storage phase absorb and in a regeneration phase with the addition of a Convert reducing agent into harmless compounds, So-called exhaust gas recirculation systems are also known. In Such exhaust gas recirculation systems become part of the exhaust gas flow mixed with the fresh gas stream flowing into the cylinders. There Exhaust gas for combustion is an inert gas, the NOx raw emissions of the internal combustion engine. The regulation of recirculated exhaust gas flow, the so-called exhaust gas recirculation rate, usually takes place via a switch in the return line Exhaust gas recirculation valve.

Such an exhaust gas recirculation system is a emission-relevant component. Such components are due applicable or future regulations in the operation of a Internal combustion engine to undergo a review Failure or incorrect operation of the exhaust gas recirculation system the emission behavior of an internal combustion engine drastically deteriorate and exceed given Limit values could result.

One that is particularly threatened by the failure or particularly in the event of failure Component of an exhaust gas recirculation system leading to increased emissions is the exhaust gas recirculation valve, through which the exhaust gas recirculation rate is set. So far, one relies on diagnosis this exhaust gas recirculation valve arranged in the intake manifold Pressure sensor that detects the intake manifold pressure. at the same time the intake air mass is determined using an air mass meter. From the air mass sucked in, one can expected position of the exhaust gas recirculation valve Intake manifold pressure downstream of an internal combustion engine throttle valve to calculate. If there is a discrepancy between the measured and calculated intake manifold pressure, will be a faulty one Exhaust gas recirculation valve diagnosed. This principle is for example described in DE 44 06 281 A1.

From DE 42 16 044 A1 it is known the function of a Exhaust gas recirculation system based on the smooth running of the internal combustion engine recognizable because the frequencies of dropouts or the Uneven running of an internal combustion engine with the exhaust gas recirculation rate increases.

It is also known from DE 36 24 441 A1, at idle to change the exhaust gas recirculation rate of an internal combustion engine and monitor the speed fluctuation of the internal combustion engine. A similar process is also in EP 0 635 629 A1 disclosed.

The invention has for its object a method for Examination of an exhaust gas recirculation system to indicate which none Pressure measurement in the intake manifold is required.

This object is characterized by that in claim 1 Invention solved.

The invention uses the knowledge that changes in the exhaust gas recirculation rate the NOx emissions of an internal combustion engine can strongly influence. Now change the exhaust gas recirculation rate to a certain extent, can be due to a lack of expected change in the NOx emission of the Internal combustion engine detected a faulty exhaust gas recirculation system become. This concept is for everyone with exhaust gas recirculation systems equipped internal combustion engines.

This check is particularly easy to carry out if the NOx emission of the internal combustion engine is otherwise constant would be what especially in static operating conditions the internal combustion engine is the case, especially if so the temporal change in load and / or speed of the internal combustion engine remains below a certain, appropriate limit.

To prevent the expected NOx concentration in the Detecting exhaust gas from the internal combustion engine is different Approaches possible. First, you can see a concentration difference from the NOx concentration measured in the exhaust gas before and after changing the exhaust gas recirculation rate. This difference in concentration depends of course on the change made the exhaust gas recirculation rate. Remains despite the change Exhaust gas recirculation rate is an expected concentration difference off, the exhaust gas recirculation system is defective. The NOx concentration can be anywhere in the exhaust system be measured, especially upstream of a catalyst.

One of these can be used to determine the concentration difference NOx concentration measurements also through a model determination of raw NOx emissions, replacing known models can be used from the operating parameters of the Internal combustion engine emitted for this operating state Estimate NOx concentration. With such a model value for the NOx concentration can be the concentration difference along with measuring the NOx concentration after the change form and either the model value for the NOx concentration before changing the exhaust gas recirculation rate or the model value for the operating state after the change the exhaust gas recirculation rate. It is useful here however, that otherwise largely constant operating conditions of the internal combustion engine, since then the fault when determining the NOx concentration, if possible is low.

If the internal combustion engine has a NOx storage catalytic converter, you can also use a NOx concentration sensor for diagnosis use as usual to control a NOx storage catalyst of this catalyst is provided. The same applies to internal combustion engines with a 3-way catalytic converter in the exhaust system. A well-known arrangement is e.g. a sensor located downstream of the catalyst. Because such a NOx storage catalytic converter is in usually the NOx compounds absorbed in the exhaust gas must this arrangement for carrying out the check that this absorption does not take place temporarily. In a preferred development of the invention, this can be done can be achieved by having the catalyst before checking saturated to its maximum storage capacity becomes. One can reach the state of saturation with the downstream NOx concentration sensor capture, e.g. by comparing a modeled NOx concentration with a measured NOx concentration or by appropriate interpretation of the during a storage process resulting gradients of the NOx concentration downstream of the NOx storage catalytic converter.

If the NOx catalyst is saturated, changes in the NOx concentration upstream of the catalytic converter to the catalytic converter outlet through, so that a check is then possible.

Saturation can be reached particularly quickly if for high raw NOx emissions upstream of the NOx storage catalytic converter is taken care of, for example by the Exhaust gas recirculation rate below a certain threshold or particularly preferred is set near zero.

Basically you get a particularly good diagnosis if the exhaust gas recirculation rate from a maximum value to a minimum value is provided. To do this in the variant with the accelerated To achieve saturation of a NOx storage catalytic converter, must, if it is determined that the NOx storage catalyst is in saturation, the EGR rate first increased from the value below the minimum value so that they are then reduced again can to form the concentration difference.

Like the change in the exhaust gas recirculation rate set for checking is carried out in principle is irrelevant. If you make a ramp-like change in the exhaust gas recirculation rate the diagnosis runs with a particularly low level Effects on the operation of the internal combustion engine since the inevitably associated with the change in the exhaust gas recirculation rate Change in the smooth running of the internal combustion engine slowly runs. If you want to make the diagnosis as safe as possible, it offers itself, the exhaust gas recirculation rate suddenly to increase. This procedure has the further advantage that the Verification takes a very short amount of time therefore only a very slight increase in the emitted NOx mass due to the review.

Advantageous developments of the invention are the subject of subclaims.

Figur 1

eine schematische Darstellung einer Brennkraftmaschine mit einer Abgasrückführanlage,

Figur 2

ein Ablaufdiagramm eines Verfahrens zur Überprüfung einer Abgasrückführanlage und

Figur 3

ein weiteres Ablaufdiagramm für ein abgewandeltes Überprüfungsverfahren.

The invention is explained in more detail below with reference to the drawings in exemplary embodiments. The drawing shows:

Figure 1

1 shows a schematic illustration of an internal combustion engine with an exhaust gas recirculation system,

Figure 2

a flowchart of a method for checking an exhaust gas recirculation system and

Figure 3

another flow chart for a modified verification procedure.

In Figure 1 is an Otto engine in the form of a block diagram shown with direct injection, whereby only those components are shown that are for the Understanding of the invention are necessary; are in particular the fuel circuit and an exhaust gas aftertreatment system not shown.

The internal combustion engine of FIG. 1 has an intake tract 1 with an air collector 2 on a suction pipe 3 in one Cylinder 6 of the internal combustion engine opens. The better clarity only one cylinder 6 is shown for the sake of this; the number of cylinders is not important.

In the cylinder 6 is controlled by a control unit 10 Injector 20 fuel injected. in the Air collector 2, there is a throttle valve 5 by one Throttle valve actuator 12 is operated, which is also from Control unit 10 is controlled. Next is an air mass meter 4 provided upstream of the throttle valve 5 in the intake tract 1. Downstream of the throttle valve 5 opens into the intake tract 1 an exhaust gas recirculation line 8, which on the other hand to the exhaust tract 7 of the internal combustion engine is connected, in which the Combustion gases flow out of cylinder 6. In the exhaust gas recirculation line 8 there is an exhaust gas recirculation valve 9, which is actuated by an actuator 14 which is operated by the control unit 10 is controlled. There is a position feedback provided, via which the control unit 10 on the exhaust gas recirculation valve 9 detected degree of opening.

Furthermore, a crankshaft sensor 13 is provided, which Speed of the crankshaft 15 senses.

Finally, there is a NOx sensor in exhaust tract 7 16, which measures the NOx concentration in the exhaust gas by the Exhaust tract flows. Any catalysts provided in the exhaust tract, NOx storage or 3-way catalysts are the Not shown for the sake of clarity.

The control device 10 has a plurality of program modules 11, 17, 19 and 18, which will be discussed later.

To check the exhaust gas recirculation valve 9, the following is now process shown as a flow chart in Figure 2 carried out. The reference numerals designate the Letter "S" precedes steps of the procedure.

First, in a step S1, a first NOx concentration NOxl measured. This is done using the measuring module 11 of the Control unit 10, which reads out the NOx sensor 16. Subsequently becomes a in step S2 on the exhaust gas recirculation valve 9 preset change in the exhaust gas recirculation rate in the memory module 17 set; this is done by the EGR module 18 of the control unit 10 made. The change is chosen so that the exhaust gas recirculation rate has a predetermined jump of high Exhaust gas recirculation rate to low exhaust gas recirculation rate, for example from a high setpoint to 0%. After this change in the exhaust gas recirculation rate is again over the NOx sensor 16 the NOx concentration in the exhaust gas of the internal combustion engine measured and as the value NOx2 in the memory module 17 of the control unit 10 stored. This is also done again the measuring module 11 (step S3). Then it is checked in step S4 whether the difference between NOx1 and NOx2 is also one threshold value SW1 stored in the memory module 17 exceeds. If this is not the case (N branch), then in a step S5 an error of the exhaust gas recirculation system (in particular of the exhaust gas recirculation valve 9). Otherwise (J-branch) becomes a proper return system in step S6 diagnosed.

Instead of forming the difference between the measured NOx concentration in NOx1 and NOx2 in step S4 can be as a value NOx1 also a NOx concentration determined in a model be used. This model is determined in the NOx model module 19 of the control unit 10. The NOx model module 19 calculates the raw emission of NOx in the exhaust gas in a known manner the internal combustion engine. So that this model calculation is possible fails exactly, the review process will only performed when the crankshaft sensor 13 indicates that the Speed of the crankshaft 15 and the engine remains within a certain window, preferably constant is. The accuracy is further increased if at the same time the load, i.e. that indicated by the air mass meter 4, Air mass flowing into the internal combustion engine in certain Limits is constant.

The difference formation in step S4 then takes place between the modeled NOx concentration and the measured NOx concentration NOx2 after changing the exhaust gas recirculation rate in step S2. Step S1 can be omitted in this modification, since no longer the measured NOx concentration NOx1, but a modeled value is input in step S4.

Of course, the saved values (SW1, ...) can also depend on the operating parameters to get voted. The memory module 17 then contains suitable maps.

In an internal combustion engine with a NOx storage catalytic converter are upstream of the NOx sensor 16 before performing the method the steps shown in Figure 3 as a flow chart carried out. First, in a step S7, the exhaust gas recirculation rate to a level below a threshold Value, in this case set to zero. Then in step S8 the NOx concentration is measured by means of the NOx sensor 16 and stored as the value NOx3 in the memory module 17. In step S9 it is then checked whether the value NOx3 exceeds a threshold value.

If this is not the case (N branch), step S8 jumps back. Only when the query in step S9 to a leads to a positive result (J-branching) is the NOx storage catalytic converter in saturation and NOx levels supplied to it punch through to its exit. Then in step S10 the exhaust gas recirculation rate to a high value, for example 100% set and the process steps of the figure follow Second

Claims (9)

Method for checking an exhaust gas with an exhaust gas recirculation rate from the exhaust tract to the intake tract exhaust gas recirculation system an internal combustion engine in which a certain Change the exhaust gas recirculation rate set that NOx concentration measured in the exhaust gas and in the absence of one certain dependent on the change in the exhaust gas recirculation rate Concentration difference is a defect in the exhaust gas recirculation system is detected. A method according to claim 1, characterized in that the concentration difference is determined from the NOx concentration measured before and after the change in the exhaust gas recirculation rate in the exhaust gas. A method according to claim 1, characterized in that the concentration difference from the NOx concentration measured in the exhaust gas after the change in the exhaust gas recirculation rate and a NOx concentration obtained with a model of operating parameters of the internal combustion engine for the operating state of the internal combustion engine before or after the change in the exhaust gas recirculation rate is determined. Method according to one of the preceding claims, characterized in that the NOx concentration is measured downstream of a NOx storage catalytic converter and the NOx storage catalytic converter is saturated to its maximum storage capacity before the specific change in the exhaust gas recirculation rate is set. A method according to claim 4, characterized in that the saturation is detected at a predetermined NOx concentration downstream of the catalyst. Method according to Claim 4 or 5, characterized in that the exhaust gas recirculation rate is set below a certain minimum value, preferably close to zero, in order to achieve saturation quickly. Method according to one of the preceding claims, characterized in that the specific change in the exhaust gas recirculation rate is a ramp or step-shaped reduction. Method according to claims 6 and 7, characterized in that the exhaust gas recirculation rate for reaching the saturation quickly below a certain minimum value is increased again and then reduced in the specific change. Method according to one of the preceding claims, characterized in that the check is only carried out if the operating parameters of the internal combustion engine, in particular the load and / or speed, are within a certain range and / or have limited dynamics.

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