CN115199428A

CN115199428A - Diagnostic method for an intake section of an internal combustion engine, diagnostic circuit, and motor vehicle

Info

Publication number: CN115199428A
Application number: CN202210362247.2A
Authority: CN
Inventors: M.豪普特沃格尔; W.拉赫曼; T.宾德; M.巴克霍尔兹
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 2021-04-07
Filing date: 2022-04-07
Publication date: 2022-10-18
Also published as: DE102021203432A1

Abstract

The present invention generally relates to a diagnostic method for an intake section of an internal combustion engine, which includes: -carrying out (41; detecting (42, 52) whether a regulating command is present on the basis of a lambda regulating deviation, wherein the lambda regulating deviation is determined on the basis of a measurement of a lambda sensor (10; and determining (43, 53) a deviation of the actual gas mixture from the nominal gas mixture in the intake section (3, 12) of the internal combustion engine (7) on the basis of the regulating command. The invention also relates to a diagnostic circuit and a motor vehicle.

Description

Diagnostic method for an intake section of an internal combustion engine, diagnostic circuit, and motor vehicle

Technical Field

The invention relates to a diagnostic method for an intake section of an internal combustion engine, a diagnostic circuit and a motor vehicle.

Background

It is known to determine the gas mixture by means of a lambda sensor. For example, a lambda value indicative of a ratio of fuel and air may be determined. Generally, the lambda value is used to determine the efficiency with which combustion occurs. If the lambda value is too low, this may indicate too little fuel or too much air is involved in combustion. If the lambda value is too high, this may indicate that too much fuel or too little air is involved in combustion.

If such a lambda offset is determined, the lambda adjustment may adjust that the mixture should be "enriched" or "leaned", i.e., more or less fuel or air is added.

Disclosure of Invention

The object of the present invention is to provide a diagnostic method, a diagnostic circuit and a motor vehicle for an intake section of an internal combustion engine, which overcome at least partially the above-mentioned disadvantages.

This object is achieved by a diagnostic method according to the invention as claimed in claim 1, a diagnostic circuit according to the invention as claimed in claim 14 and a motor vehicle as claimed in claim 15.

Further advantageous embodiments of the invention result from the dependent claims and the following description of preferred embodiments of the invention.

Drawings

Embodiments of the invention are described herein by way of example and with reference to the accompanying drawings, in which:

fig. 1 schematically shows a circuit diagram of an embodiment of an internal combustion engine according to the invention;

fig. 2 shows a diagram symbolically representing the AGR ratio in the case of active knock detection and jerk detection;

FIG. 3 shows a graph of relative fuel mass versus relative air charge;

FIG. 4 shows a block diagram of a diagnostic method according to the invention;

FIG. 5 shows a block diagram of another embodiment of a diagnostic method according to the invention; and

fig. 6 shows a motor vehicle with a diagnostic circuit according to the invention.

As mentioned at the outset, it is known to determine a lambda regulation deviation.

It is recognized, however, that these lambda regulation deviations can be used outside their usual applications for diagnosing defects or errors in the intake section.

Accordingly, some embodiments relate to a diagnostic method for an intake section of an internal combustion engine, which includes: implementing exhaust gas recirculation; detecting whether a regulating command is present on the basis of a lambda regulating deviation, wherein the lambda regulating deviation is determined on the basis of a measurement of a lambda sensor, which is arranged in an exhaust gas line of the internal combustion engine; and a deviation of the actual gas mixture from the nominal gas mixture in the intake section of the internal combustion engine is determined on the basis of the control command of the lambda sensor.

According to the invention, the diagnostic method can be carried out during the occurrence of exhaust gas recirculation.

As is generally known, exhaust gas recirculation may include recirculating gases (exhaust gases) produced during combustion into the intake section. The intake section here comprises a fresh air supply system and a low-pressure exhaust gas recirculation system, i.e. the intake section is defined by all branches that supply gas (fresh air-inert gas mixture) for the combustion process.

Further, in some embodiments it is determined whether an adjustment command is present. The lambda sensor is arranged in the exhaust gas line, wherein the invention is not restricted to a defined position of the lambda sensor. The exhaust gas line may furthermore comprise a plurality of lambda sensors which can generate the regulating command according to the invention. For example, a first lambda sensor may be arranged before the exhaust gas recirculation system, and a second lambda sensor (and a third lambda sensor etc.) may be arranged in the exhaust gas line parallel to the exhaust gas recirculation system and/or in the exhaust gas recirculation system.

As is well known, the lambda value produced by the lambda sensor is, for example, indicative of the mass ratio of air to fuel (e.g., 14kg of air to 1kg of fuel may correspond to a standard value).

Based on the deviation of the actual mass ratio in the exhaust line (actual mass ratio) from the nominal mass ratio in the exhaust line (e.g. the above-mentioned standard value), an adjustment command may be generated based on the measurement of the lambda sensor(s) arranged in the exhaust line, which adjustment command may cause the mass ratio to be changed.

The adjustment command (or the adjustment) may include, for example, "dilute" or "enrich". In this case, dilution means that the mass ratio is shifted in favor of the air fraction, whereas enrichment means that the mass ratio is shifted in favor of the fuel fraction.

As mentioned, in some embodiments, the lambda value is determined for the exhaust line. It is recognized that the lambda value may indicate a deviation of the actual gas mixture in the inlet section from the nominal gas mixture.

For example, if it is determined that the lambda value is too low and the lambda sensor therefore generates an "enrichment" control command, this may for example indicate an error in the fresh air supply system, which leads to too much fresh air being drawn in. The errors may include pump errors, sensor errors, leaks, etc., wherein the type of deviation of the actual gas mixture from the nominal gas mixture is explained in more detail below.

For the sake of explanation, the following table is first inserted, which lists some possible errors (sources) by way of example, but not exclusively, and which may be related to the structure of the internal combustion engine:

first the rows in the table above relating to the adjustment commands of the lambda sensor are discussed.

If the adjustment command is "enrichment" and/or if too low a mass flow is detected in the exhaust line (e.g., a low flow error), the deviation may include:

i) Excess fresh air in the intake section; or

ii) too little residual gas from the off-gas recirculation section.

For example, too much fresh air in the intake section may be generated, for example, as a result of incorrect sensor values of an air mass meter, for example an HFM (hot film air mass meter). An erroneous sensor value may indicate that too little fresh air is being inhaled. However, if the inspiratory volume is actually approximately equal to the preset value, this may result in too much air being inhaled based on the wrong sensor value, so that the gas mixture is too lean and should be enriched. This difference can be identified by lambda tuning offset, as described herein.

Too little residual gas from the exhaust gas recirculation section may be generated, for example, due to: AGR rate calculation errors (described in detail below), line narrowing in the exhaust gas recirculation system, and/or erroneous AGR valve positions.

Furthermore, too little residual gas from the AGR section may be generated by too much fresh air being drawn in due to leakage between the AGR valve and the extraction of the exhaust line.

When the adjustment command is "dilute," the deviation may include at least one of:

i) Excess residual gas from the off-gas recirculation section;

ii) excess residual gas in the gas inlet section; and

iii) Too little fresh air is present in the intake section.

Excessive residual gas from the AGR (i.e., exhaust gas recirculation, acronym: EGR) may be generated, for example, due to leaks in the AGR valve (e.g., when the AGR valve is not sealed) and/or due to a negative offset of the differential pressure sensor and/or an incorrect AGR valve position.

Furthermore, excess residual gas in the intake section may result from a false simulation of the AGR rate, for example due to a line leak to (or to) the differential pressure sensor after the AGR valve or a line drop to the differential pressure sensor before the AGR valve.

The lack of fresh air in the intake section can be caused, for example, by incorrect fresh air mass meter sensor values (e.g., HFM sensors).

However, despite errors, it is possible to determine that no deviation of the gas mixture is present. As shown in the above table, for example, although the lambda sensor determines no deviation, there may be excessive fresh air in the intake section (e.g., due to leakage in the air section after the AGR valve).

Thus, to more accurately characterize errors and/or to be able to detect other errors, in some embodiments the diagnostic method further comprises: a comparison of the mass flow of the exhaust gas recirculation section and the fresh air section is carried out.

The corresponding mass flow does not have to be precisely quantified here. In some embodiments, it may be sufficient that the mass flow is outside of the standard (i.e., too high or too low, for example).

For example, the mass flow comparison may be based on further diagnostic methods suitable for evaluating mass flow in a (low pressure) AGR, such as:

a diagnostic method of low pressure exhaust gas recirculation of an internal combustion engine, comprising: implementing exhaust gas recirculation; detecting a current diagnostic sensor value of the low-pressure exhaust gas recirculation system by means of a diagnostic sensor, wherein the diagnostic sensor value indicates a deviation of an actual exhaust gas flow of the low-pressure exhaust gas recirculation system from a setpoint exhaust gas flow; and is

Whether a deviation exists is derived based on the diagnostic sensor value.

The diagnostic sensor may include a plurality of (different or identical) sensors that may be directly or indirectly indicative of various parameters of the exhaust gas. For example, an exhaust gas mass flow sensor, a temperature sensor, a pressure sensor and/or a lambda sensor (or probe) or the like may be provided.

Thus, the diagnostic sensor value may include one or more values.

In some embodiments, the diagnostic sensor value indicates a deviation of the actual exhaust flow of the low pressure AGR from the nominal exhaust flow. The nominal exhaust gas flow comprises the exhaust gas mass flow which is to be complied with on the basis of various preset values, for example legal provisions, plant provisions, efficiency considerations, etc.

The deviation can be inferred directly or indirectly based on the diagnostic sensor value. For example, the diagnostic sensor values may directly include mass flow, such that deviations above or below a predetermined threshold correspond to deviations of the actual exhaust flow from the nominal exhaust flow.

In some embodiments, when implementing an AGR, the error identification process may be implemented based on diagnostic sensors that can infer that there is an error in the AGR. For example, knock identification may be implemented, which does not identify any errors during the absence of implementing AGR. However, if an error is identified when the AGR is activated, it can be concluded that there is an error in the AGR (e.g., a low flow error, i.e., too little exhaust gas being recirculated).

In such an embodiment, it is not necessary to explicitly determine the deviation, as it is sufficient to identify the presence of the deviation.

Internal combustion engines may be designed in various types, for example based on gasoline engines or diesel engines, etc.

Detailed Description

Fig. 1 shows a circuit diagram of an internal combustion engine 1 according to the invention, with various optional branches (dashed lines) and components of the circuit diagram also being shown. Alternative branches and elements may be used for implementing various embodiments of the diagnostic method according to the invention.

The non-optional components and branches of the engine 1 will therefore be described first.

The internal combustion engine 1 has an air filter 2, after which a fresh air section 3 is arranged. Fresh air can thereby be supplied to the compressor 4 and the charge air cooler 5. Behind the charge air cooler 5 a throttle valve 6 is arranged behind which a combustion engine 7 is situated.

Downstream of the combustion engine 7, a turbine 8 is arranged, which is coupled to the compressor 4 via a shaft 9 and thus drives the compressor. Therefore, the exhaust gas turbocharger is used in the internal combustion engine 1, but the present invention is not limited thereto. For example, the turbine may also be electrically driven, as is well known.

Furthermore, the internal combustion engine 1 has a lambda sensor 10, which is arranged downstream of the turbine 8, and a branching point 11 is located downstream of the lambda sensor, as a result of which the exhaust gas section is branched off. A portion of the exhaust gases produced is fed back to the air section via an exhaust gas recirculation branch 12 (AGR branch). Another portion of the exhaust gas is discharged.

The AGR branch 12 has an AGR valve 13.

Catalytic converters 14 and/or 15 and further lambda sensors 16 and/or 17 and exhaust flaps 18 can optionally be provided for discharging exhaust gases. The lambda sensors 10, 16 and 17 are suitable for determining the deviation of the gas mixture, as described herein. It is generally sufficient to provide a lambda sensor 10, which is realized, for example, as a broadband sensor. In this case, the sensors 16 and 17 can be arranged in a further control loop and have a higher sensitivity than the sensor 10, in order to be able to determine the deviation more accurately, but this is not always necessary.

Thus, in some embodiments, an exhaust gas recirculation rate may be determined.

Accordingly, in some embodiments, the diagnostic method further comprises: and obtaining the exhaust gas recirculation rate.

By deriving the exhaust gas recirculation rate, the actual exhaust gas flow through the AGR relative to the total exhaust gas flow can be determined.

In some embodiments, the diagnostic method further comprises: the jerk is identified based on the current diagnostic sensor values.

If during activation of the AGR, the identification of a misfire (or combustion misfire identification) identifies a misfire (or one or more combustion misfires), it may be inferred that there is a high AGR flow error, i.e., excessive exhaust gas is being recirculated.

Thus, in some embodiments, the deviation indicates a high exhaust gas recirculation flow error.

If the AGR rate is additionally determined as described above (i.e. when additional lambda sensors 16 and 17 are provided), it can also be determined how much exhaust gas is recirculated so that the AGR rate can be adjusted accordingly.

In some embodiments, the diagnostic method further comprises: as described above, knock is identified based on the current diagnostic sensor values.

In this case, the deviation indicates an AGR low flow error, as described above.

In addition, the AGR ratio can also be determined here (if additional lambda sensors 16 and 17 are provided), so that the exhaust gas quantity can be adjusted accordingly.

Fig. 2 shows a diagram 30 symbolically representing the AGR ratio in the case of active knock detection and jerk detection. When the unstable operation is recognized, the AGR rate rapidly increases. But there are high traffic errors. When knocking is recognized, the AGR rate rapidly decreases, so that there is a low flow error.

Alternatively or additionally, the combustion engine 1 may have a differential pressure sensor 19 around the AGR valve 13 or separate pressure sensors before and after the AGR valve. From this, the pressure or pressure difference before and after the AGR valve can be determined. Furthermore, a temperature sensor 20 can be arranged upstream of the AGR valve 13, which temperature sensor is provided for determining the temperature of the recirculated exhaust gas.

Furthermore, an AGR filter 21 and an AGR cooler 22 can be provided in order to filter the recirculated exhaust gas and cool it before it is recirculated into the fresh air branch 3. These two elements are not absolutely necessary, but can contribute to a more accurate determination of the mass flow model of the recirculated exhaust gas.

As mentioned before, the air intake section according to the invention comprises an AGR branch 12 (or AGR section) and a fresh air section 3.

That is, according to the present invention, it is not mandatory to measure the mass flow rate or the AGR rate directly (as described above), since it can also be simulated based on the pressure difference and the temperature.

In such embodiments, the diagnostic method further comprises: a mass flow comparison is performed based on the current diagnostic sensor value.

The corresponding diagnostic sensors are here pressure and temperature sensors (or differential pressure and temperature sensors).

The mass flow comparison may be based on a model of the air charge around throttle 6. For example, the mass flow comparison may be initially based on the AGR rate, which may be mathematically expressed as follows:

the AGR ratio is described herein based on the recirculated exhaust gas mass flow relative to the total mass flow. Mass flow mf of fresh air _Luft May be determined by an air mass meter (HFM) 22.

Further, the model of the air charge around the throttle valve is based on a function f that is related to parameters such as engine speed, intake pipe pressure, exhaust pressure, ambient pressure, camshaft position, intake air temperature, and the like.

mf _AGR Can be expressed mathematically as follows:

here, A is _eff Is the position feedback of the AGR valve, p _vor Is the pressure before the AGR valve, p _nach Is the pressure after the AGR valve (alternatively, the quotient can also be measured directly as a differential pressure), T _vor Is the temperature before the AGR valve, ψ is the flow function, and κ is the isentropic index.

Correspondingly mf can also be determined _Luft . For this purpose, corresponding pressure and temperature sensors can be installed around the throttle flap.

Accordingly, in some embodiments, the mass flow comparison is based on a throttle model.

In some embodiments, the mass flow comparison is further based on a fresh air mass flow value, as described herein.

The comparison of mass flow rates with each other can be used to assess high/low flow errors. In some embodiments, the comparison of mass flow may be expressed as the difference between the simulated throttle mass flow and the mass flow of the air mass meter 22 and the simulated AGR mass flow, mathematically expressed as: j is a function of _D -(j _F +j _AGR ). Here, j represents the mass flow, D represents the throttle, and F represents the fresh air.

If the result of this comparison is above a predetermined threshold, then there is a high flow error. If the result is below a predetermined (other) threshold, then there is a low flow error.

In order to increase the sensitivity of the measured or model value, a comparison of the mass flow values by the throttle valve and by the measured HFM value can be carried out.

The comparison of the mass flow (HFM and throttle) can be made, for example, in a defined speed/load range of the engine with no AGR or with a known (or plausible) (external) AGR value.

If there is a deviation, the value of the air mass meter 22 can be matched to the value of the simulated throttle mass flow (and vice versa). The match may be provided with an error threshold. If the error threshold is exceeded, an error (e.g., a slope error) of the air mass meter 22 may be inferred.

When AGR is inactive, the HFM match may be exemplarily expressed as follows:

j _D ＝k _HFM *j _F 。

wherein k is _HFM Is the matching coefficient for the mass flow of the air mass flow meter.

When an external AGR is active, the HFM match can be exemplarily expressed as follows:

Δj _AGR ＝j _D -((k _HFM *j _HFM )+j _AGR )，

wherein, Δ j _AGR Indicating the deviation of the mass flow comparison from the external AGR.

Here, the deviation of the mass flow comparison from the external AGR is compared to a range of values (related to engine speed/load). If the deviation is outside the value range (within a defined debounce time (endprelzeit)), this can be stored as an error in an error memory.

If a mass flow comparison is implemented, which is above a predetermined threshold and the lambda sensor regulation command is "enrichment", this may indicate an excess of fresh air in the intake section (as shown in the above table).

If the mass flow is below a predetermined threshold and the adjustment command is "enrichment," this may indicate that there is too little residual gas from the AGR section due to a miscalculation of the AGR rate. In such embodiments, the erroneous calculation may be based on, for example, a positive offset of a differential pressure sensor in the AGR segment, and/or a line narrowing in the AGR segment, and/or an erroneous AGR valve position.

In some embodiments, the mass flow comparison indicates a mass flow within a predetermined range (which is indicated in the table by "within range"). This may also indicate that there is too little residual gas from the AGR section due to erroneous calculation of the AGR rate when the adjustment command is still "enrichment".

In such a case, the miscalculation may be based on a line blockage leading to the differential pressure sensor before (or upstream of) the AGR valve.

However, too little residual gas in the case of a "in range" mass flow ratio and in the case of "enrichment" of the lambda sensor can also be caused by fresh air intake in the case of a leak between the AGR valve and the extraction point of the exhaust gas line.

If the adjustment command is "dilute", but the mass flow comparison yields a mass flow above a predetermined threshold, this may indicate that the residual gas from the AGR section is excessive.

This may be caused, for example, by a leak in the AGR valve and/or by a negative offset of the differential pressure sensor and/or an incorrect AGR valve position.

In the case of "dilution", too much mass flow may also indicate too much residual gas in the intake section.

This may be based, for example, on a false simulation of the AGR rate, which may be caused, for example, by a leak in the line leading to the differential pressure sensor after the AGR valve. Furthermore, this may also be caused by a drop in the line leading to the differential pressure sensor before the AGR valve.

In some embodiments, the mass flow is below a predetermined threshold and the adjustment command is "dilute". This may indicate that the fresh air in the intake section is too low, which may be caused, for example, by an incorrect HFM sensor value in some embodiments.

As mentioned above, despite errors, the control command of the lambda sensor may not be present. However, if the mass flow comparison still determines that the mass flow is excessive, this may correspond to an excessive amount of fresh air in the intake section. This may be caused, for example, by a leak in the air section after the AGR valve.

However, this may also correspond to a sensitivity of the lambda sensor being too low.

Some embodiments relate to a diagnostic circuit arranged to implement a diagnostic method according to the invention.

The diagnostic circuit may be any circuit that can be provided in or connected to the motor vehicle, such as a controller, a central on-board computer, a CPU (central processing unit), a GPU (graphics processing unit), an FPGA (field programmable gate array), etc.

If the circuit is external to the motor vehicle, it can be provided, for example, for a test stand. The method according to the invention can be carried out during operation of the vehicle when the circuit is located in a motor vehicle.

Accordingly, some example embodiments relate to a motor vehicle having a diagnostic circuit according to the present invention.

The motor vehicle may be any type of vehicle having an internal combustion engine (e.g., a gasoline engine, a diesel engine, or an internal combustion engine as discussed below in fig. 1). In this respect, the method according to the invention may be implemented in a hybrid vehicle, if an AGR is present.

In some embodiments, the lambda value may also be used to identify errors in mass flow. In such an embodiment, a lambda adjustment offset is determined.

In some embodiments, the lambda adjustment bias is determined based on a least squares method between the air amount and the fuel amount, as described herein.

The determination of the lambda control deviation is described in more detail below, wherein these explanations also apply to the above-described case (lambda control deviation in the case of knock/jerk detection).

The charge detection described here and the thus determined mass flow difference or mass flow can only determine the mass flow and compare them with one another, i.e. the residual gas fraction and the fresh air fraction cannot be measured but can only be simulated.

The proportion of residual gas which is located in the air section 3 and is supplied to the combustion can be determined by determining the recirculated AGR mass flow and can be included in the preliminary control of the lambda regulation.

But these mass flows may still be erroneous (e.g. due to leaks, blockages in the air path/AGR path) and the model may deviate significantly from reality.

Thus, to verify (or refute) the prediction of mass flow, one of the sensors 10, 16 and/or 18 (or all of the sensors) has been designated for determining the lambda regulation deviation. In other words, the measured lambda value is compared with the predicted lambda value. If the comparison yields a deviation above a predetermined threshold, it can be concluded that there is an error in the mass flow model.

In other words, the trend or the measure of the recirculated residual gas can be determined by the lambda control deviation (for example even in the case of activation of the AGR), since the residual gas (inert gas) no longer participates in the combustion and the residual gas fraction is taken into account in the preliminary control.

For example, if there is an undesired increase in recirculated residual gas at this time, less fresh air mass supplied during combustion is provided by the pre-control. If there is an error in the AGR, the lambda value (at the same operating point and compared to the error-free AGR) indicates a rich mixture, so the lambda regulator can indicate dilution of the mixture. But this may have an effect on engine power or engine torque.

On the other hand, if the recirculated residual gas is undesirably reduced in the faulty AGR, a lean mixture occurs by providing more fresh air mass for combustion by the pre-control, and the lambda regulator attempts to compensate for this by enrichment. However, this may also have an effect on the engine power or the engine torque.

As previously mentioned, the lambda adjustment deviation can be estimated based on a least squares method.

Thus, offset errors and slope errors can be distinguished, so that error symptoms can be distinguished.

As mentioned above, load point movement may be triggered due to engine power or engine torque effects that may result from an undesirably high or low flow error.

The least squares method makes it possible to evaluate errors with the load point remaining unchanged, since slope errors and offset errors can be differentiated at the measurement points, for example, by matching the value profiles.

FIG. 3 shows a graph 35 of relative fuel mass versus relative air charge. In the diagram 35, the measurement points 36 and the simulation curve 37 for the relative fuel mass are shown. The deviation of each measurement point 36 from the simulated curve 37 can be attributed to an offset error or a slope error by means of the least squares method.

Embodiments of the invention are now described, by way of example and with the aid of the accompanying drawings. In the drawings:

fig. 4 shows a diagnostic method 40 according to the invention.

At 41, exhaust gas recirculation is implemented as described herein.

At 42, the presence of an adjustment command is detected as described herein.

At 43, a deviation of the actual gas mixture from the nominal gas mixture in the intake section is determined based on the adjustment command as described herein.

Fig. 5 shows a diagnostic method 50 according to the invention.

At 51, exhaust gas recirculation is implemented as described herein.

At 52, the presence of an adjustment command is detected as described herein.

At 53, a deviation of the actual gas mixture from the nominal gas mixture in the intake section is determined based on the adjustment command as described herein.

At 54, a mass flow comparison of the exhaust gas recirculation section and the fresh air section is performed as described herein.

Fig. 6 shows a motor vehicle 60 according to the invention.

The motor vehicle 60 comprises the internal combustion engine 7 as described with reference to fig. 1 and a diagnostic circuit 61 which is designed as a controller and is provided for acquiring the respective values of the sensors and probes as described herein.

List of reference numerals

1. Internal combustion engine

2. Air filter

3. Fresh air section

4. Compressor with a compressor housing having a discharge port

5. Charge air cooler

6. Air throttle

7. Combustion engine

8. Turbine engine

9. Shaft

10. Lambda sensor

11. Branch point

12 AGR branch

13 AGR valve

14. 15 catalytic converter

16. 17 lambda sensor

18. Exhaust valve

19. Differential pressure sensor

20. Temperature sensor

21 AGR filter

22 AGR cooler

23. Throttle valve

30. Diagram for detecting knocking or uneven running

35. Least squares method chart

36. Measuring point

37. Simulation curve

40; 50. diagnostic method

41; 51. implementing exhaust gas recirculation

42; 52. detecting the presence of an adjustment command

43; 53. determining the deviation of the actual gas mixture from the target gas mixture

54. Implementing a mass flow comparison

60. Motor vehicle

61. Diagnostic circuit/controller

Claims

1. A diagnostic method for an intake section of an internal combustion engine, comprising:

-carrying out (41;

detecting (42, 52) whether a regulating command is present on the basis of a lambda regulating deviation, wherein the lambda regulating deviation is determined on the basis of a measurement of a lambda sensor (10; and is

Determining (43, 53) a deviation of the actual gas mixture from the nominal gas mixture in an intake section (3, 12) of the internal combustion engine (7) on the basis of the regulating command.

2. The diagnostic method of claim 1, wherein the adjustment commands include "enrichment" and "dilution".

3. The diagnostic method of any one of the preceding claims, wherein, when the adjustment command is "enrichment", the deviation comprises:

i) Excess fresh air in the intake section (3, 12); or

ii) too little residual gas from the exhaust gas recirculation section (12).

4. A diagnostic method of a second possibility according to claim 3, wherein the residual gas from the exhaust gas recirculation section (12) is too low based on a false determination of the exhaust gas recirculation rate and/or a leak (13) of the exhaust gas recirculation valve.

5. The diagnostic method of claim 1 or 2, wherein, when the adjustment command is "dilute", the deviation comprises one of:

i) Excess residual gas from the exhaust gas recirculation section (12);

ii) excess residual gas in the gas inlet section (3, 12); and

iii) The fresh air in the intake section (3, 12) is too low.

6. The diagnostic method of any one of the preceding claims, further comprising: a comparison of the mass flows of the exhaust gas recirculation section (12) and the fresh air section (3) is carried out.

7. The diagnostic method of claim 6 as far as the first possibility cited in claim 3 is concerned, wherein the mass flow comparison indicates a mass flow above a predetermined threshold.

8. The diagnostic method of claim 6 when dependent on claim 4, wherein if the mass flow comparison indicates a mass flow below a predetermined threshold, the miscalculation is based on at least one of: a positive offset of a differential pressure sensor (19) in the exhaust gas recirculation section (12); the line in the exhaust gas recirculation section (12) is narrowed; and an erroneous AGR valve position (13).

9. The diagnostic method of claim 6 when dependent on claim 4, wherein if the mass flow comparison indicates a mass flow within a predetermined range, the error calculation is based on: a line leading to the differential pressure sensor is blocked before the exhaust gas recirculation valve in the exhaust gas recirculation section (12).

10. The diagnostic method of claim 6 when dependent on claim 5, when the deviation is "excessive residual gas from the exhaust gas recirculation section (12)" wherein the mass flow ratio is higher than a predetermined threshold value.

11. The diagnostic method according to claim 6 as dependent on claim 5, when the deviation is "excessive residual gas in the intake section (3, 12"), wherein the mass flow ratio is higher than a predetermined threshold value.

12. The diagnostic method of claim 6 when dependent on claim 5, when the deviation is "fresh air in the intake section (3, 12) is too little", wherein the mass flow comparison is below a predetermined threshold.

13. The diagnostic method of claim 6 when dependent on claim 1, wherein if no adjustment command is present and the mass flow comparison indicates that the mass flow is above a predetermined threshold, the deviation comprises: the fresh air in the intake section (3, 12) is excessive.

14. A diagnostic circuit arranged to implement a diagnostic method (40.

15. A motor vehicle having a diagnostic circuit (61) according to claim 14.