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

Abstract

The present invention generally relates to a diagnostic method for an intake section of an internal combustion engine, comprising: implementing (41; 51) exhaust gas recirculation; detecting (42; 52) whether a regulation command exists based on a lambda regulation deviation, wherein said The lambda regulation deviation is determined based on the measurement of a lambda sensor (10; 16; 17), which is arranged in the exhaust gas line (12) of the internal combustion engine (7); 7) The deviation of the actual gas mixture from the rated gas mixture in the intake section (3, 12). The invention also relates to a diagnostic circuit and a motor vehicle.

Description

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

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 technique

It is known that gas mixtures are determined by means of lambda sensors. For example, a lambda value indicative of the ratio of fuel to air may be determined. Typically, the lambda value is used to determine how efficiently combustion occurs. If the lambda value is too low, this may indicate that too little fuel or too much air is participating in the combustion. If the lambda value is too high, this may indicate that too much fuel or too little air is participating in the combustion.

If such a lambda deviation is determined, the lambda adjustment may adjust whether the mixture should be "rich" or "lean," ie, more or less fuel or air is added.

SUMMARY OF THE INVENTION

The technical problem to be solved by 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 that at least partially overcome the above disadvantages.

This technical problem is solved by the diagnostic method according to the invention according to claim 1 , the diagnostic circuit according to the invention according to claim 14 and the motor vehicle according to claim 15 .

Further advantageous embodiments of the invention emerge from the subclaims and the following description of preferred embodiments of the invention.

Description of 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 graph symbolically representing the AGR rate with activated knock recognition and jerky recognition;

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

Figure 4 shows a block diagram of a diagnostic method according to the present invention;

Figure 5 shows a block diagram of another embodiment of the diagnostic method according to the present 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 the lambda regulation deviation.

It is recognized, however, that these lambda adjustment deviations may be used to diagnose defects or errors in the intake section outside of their usual application.

Accordingly, some embodiments relate to a diagnostic method for an intake section of an internal combustion engine, comprising: implementing exhaust gas recirculation; detecting the presence of an adjustment command based on a lambda adjustment deviation, wherein the lambda adjustment deviation is determined based on measurements of a lambda sensor, The lambda sensor is arranged in the exhaust gas line of the internal combustion engine; and the deviation of the actual gas mixture from the target gas mixture in the intake section of the internal combustion engine is determined based on the regulation 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 recirculation of gases (exhaust gas) produced during the combustion process into the intake section. Here, the intake section includes the fresh air supply system and the low-pressure exhaust gas recirculation system, ie the intake section is defined by all branches supplying the combustion process with gas (fresh air-inert gas mixture).

Additionally, in some embodiments it is determined whether an adjustment command exists. The lambda sensor is arranged in the exhaust gas line, wherein the invention is not limited to the specific position of the lambda sensor. Furthermore, the exhaust gas line can also comprise a plurality of lambda sensors capable of generating regulation commands according to the invention. For example, the first lambda sensor can be arranged before the exhaust gas recirculation system and the second lambda sensor (and the third lambda sensor etc.) can be arranged in the exhaust gas line parallel to the exhaust gas recirculation system and/or in the exhaust gas recirculation system middle.

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

Based on the deviation of the actual mass ratio (actual mass ratio) in the exhaust gas line from the nominal mass ratio in the exhaust gas line (eg the above-mentioned standard value), a regulation can be generated based on the measurement of one (or more) lambda sensors arranged in the exhaust gas line command, the adjustment command can cause the mass ratio to be changed.

The adjustment command (or the adjustment) may include, for example, "dilute" or "enrich". Here, dilution refers to a shift of the mass ratio in favor of the air fraction, while enrichment refers to a shift of the mass ratio in favor of the fuel fraction.

As mentioned, in some embodiments, the lambda value is determined for the exhaust line. It is recognized, however, that the lambda value may indicate a deviation of the actual gas mixture in the intake 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 a "rich" adjustment command, this may for example indicate an error in the fresh air supply system which results in too much fresh air being drawn in. The errors may include pump errors, sensor errors, leaks, etc., wherein the types of deviations of the actual gas mixture from the nominal gas mixture are explained in more detail below.

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

The row in the table above that refers to the adjustment commands for the lambda sensor is discussed first.

If the regulation command is "enrich" and/or if too low mass flow is detected in the exhaust line (eg a low flow error), the deviation can include:

i) Excessive fresh air in the intake section; or

ii) Too little residual gas from the exhaust gas recirculation section.

For example, excess fresh air in the intake section may result, for example, due to erroneous sensor values of an air mass meter (eg HFM (Hot Film Air Mass Meter)). Incorrect sensor values can indicate that too little fresh air is being drawn in. However, if the intake volume is actually approximately equal to the preset value, this may result in the intake of too much air based on erroneous sensor values, so that the gas mixture is too lean and should be enriched. As described herein, this difference can be identified by the lambda adjustment bias.

Too little residual gas from the EGR section may result, for example, from miscalculation of the AGR rate (described in detail later), narrowing of lines in the EGR system and/or incorrect AGR valve position.

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

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

i) Excessive residual gas from the exhaust gas recirculation section;

ii) Excessive residual gas in the intake section; and

iii) Too little fresh air in the intake section.

Excessive residual gas from AGR (ie Exhaust Gas Recirculation, English abbreviation: EGR) may for example be due to leaks in the AGR valve (eg when the AGR valve is not sealing) and/or due to a negative offset of the differential pressure sensor and/or Incorrect AGR valve position generated.

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

Too little fresh air in the intake section can be caused, for example, by erroneous fresh air mass meter sensor values (eg HFM sensors).

However, despite the error, it is possible to determine that there is no bias in the gas mixture. As shown in the table above, there may be too much fresh air in the intake section (eg due to leaks in the air section after the AGR valve), for example although the lambda sensor determines no bias.

Therefore, in order to more accurately characterize the error and/or to be able to detect other errors, the diagnostic method in some embodiments further includes performing a mass flow comparison of the exhaust gas recirculation section and the fresh air section.

The corresponding mass flow does not have to be quantified precisely here. In some embodiments, it may be sufficient that the mass flow is outside the norm (ie, eg, too high or too low).

For example, mass flow comparisons can be based on additional diagnostic methods suitable for evaluating mass flow in (low pressure) AGRs, such as:

A method for diagnosing low pressure exhaust gas recirculation of an internal combustion engine, comprising: implementing exhaust gas recirculation; detecting a current diagnostic sensor value of a low pressure exhaust gas recirculation system by a diagnostic sensor, wherein the diagnostic sensor value indicates an actual exhaust gas flow of the low pressure exhaust gas recirculation Deviation from rated exhaust gas flow; and

Based on the diagnostic sensor value it is determined whether there is a deviation.

Diagnostic sensors may include multiple (different or identical) sensors that may directly or indirectly indicate various parameters of the exhaust gas. For example, exhaust gas mass flow sensors, temperature sensors, pressure sensors and/or lambda sensors (or probes) etc. 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 gas flow of the low pressure AGR from the nominal exhaust gas flow. The nominal exhaust gas flow includes the exhaust gas mass flow which should be observed based on various preset values, eg legal regulations, factory regulations, efficiency considerations, and the like.

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

In some embodiments, when implementing AGR, the error identification process may be implemented based on diagnostic sensors that may infer that there is an error in the AGR. For example, a knock detection can be carried out which does not detect any errors during the period when AGR is not carried out. However, if an error is detected when the AGR is activated, it can be concluded that there is an error in the AGR (eg a low flow error, ie too little recirculated exhaust gas).

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

Internal combustion engines can be designed in various types, eg based on gasoline or diesel engines, among others.

Detailed ways

Figure 1 shows a circuit diagram of an internal combustion engine 1 according to the invention, wherein various optional branches (dashed lines) and elements of the circuit diagram are also shown. Optional branches and elements may be used to implement various embodiments of the diagnostic method according to the present invention.

The non-optional elements and branches of the internal combustion engine 1 are therefore first described.

The internal combustion engine 1 has an air filter 2 behind which a fresh air section 3 is arranged. As a result, fresh air can be supplied to the compressor 4 and the charge air cooler 5 . A throttle valve 6 is arranged downstream of the charge air cooler 5, behind which the combustion engine 7 is located.

A turbine 8 is arranged downstream of the combustion engine 7 , which is coupled to the compressor 4 via a shaft 9 and thus drives the compressor. Therefore, an exhaust gas turbocharger is used in this internal combustion engine 1, but the present invention is not limited to this. For example, the turbine can also be driven electrically, 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 branch point 11 is located downstream of the lambda sensor, whereby the exhaust gas section is branched. A portion of the generated exhaust gas is fed back to the air section via the exhaust gas recirculation branch 12 (AGR branch). Another part of the exhaust gas is discharged.

The AGR branch 12 has an AGR valve 13 .

Catalytic converters 14 and/or 15 as well as further lambda sensors 16 and/or 17 and exhaust valves 18 may optionally be provided for discharging exhaust gases. Lambda sensors 10, 16 and 17 are suitable for use in determining deviations of gas mixtures, as described herein. It is usually sufficient to provide a lambda sensor 10 , which is implemented, 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.

Accordingly, in some embodiments, the exhaust gas recirculation rate may be determined.

Accordingly, in some embodiments, the diagnostic method further includes deriving the exhaust gas recirculation rate.

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

In some embodiments, the method of diagnosing further comprises: identifying rough running based on current diagnostic sensor values.

If the rough running identification (or combustion misfire identification) during AGR activation identifies rough running (or one or more combustion misfires), then it can be inferred that there is an AGR high flow error, i.e. too much exhaust gas is being recirculated cycle.

Thus, in some embodiments, the deviation is indicative of an EGR high flow error.

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

In some embodiments, the diagnostic method further includes identifying knock based on current diagnostic sensor values, as described above.

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

Furthermore, the AGR rate 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 graph 30 which symbolically represents the AGR rate with activated knock detection and jerky detection. The AGR rate increases rapidly when unsteady operation is recognized. But there is a high traffic error here. When knocking is recognized, the AGR rate drops rapidly, resulting in a low flow error.

Alternatively or additionally, the internal combustion engine 1 can have a differential pressure sensor 19 surrounding the AGR valve 13 or have separate pressure sensors before and after the AGR valve. From this, the pressure or differential pressure 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 mandatory, but may contribute to a more accurate determination of the mass flow model of the recirculated exhaust gas.

As previously mentioned, the intake section according to the present invention includes the AGR branch 12 (or AGR section) and the fresh air section 3 .

That is, according to the present invention, (as described above) a direct measurement of mass flow or AGR rate is not mandatory, as it can also be modeled based on differential pressure and temperature.

In such embodiments, the diagnostic method further includes performing a mass flow comparison based on current diagnostic sensor values.

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

The mass flow comparison may be based on an air charge model around throttle 6 . For example, mass flow comparisons can initially be based on AGR rates, which can be expressed mathematically as follows:

The AGR rate is described here based on the recirculated exhaust gas mass flow relative to the total mass flow. The mass flow of fresh air, mf _Luft , can be determined by means of an air mass meter (HFM) 22 .

In addition, the charging model around the throttle is based on the function f, which is related to parameters such as engine speed, intake manifold pressure, exhaust gas pressure, ambient pressure, camshaft position, intake air temperature, etc.

mf _AGR can be expressed mathematically as follows:

Here, A _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 directly measured as a differential pressure), and T _vor is the AGR temperature before the valve, ψ is the flow function, and κ is the isentropic exponent.

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

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

In some embodiments, the mass flow comparison is also based on fresh air mass flow values, as described herein.

Comparison of mass flows with each other can be used to evaluate 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, expressed mathematically as: j _D -(j _F +j _AGR ). Here, j represents mass flow, D represents throttle, and F represents fresh air.

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

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

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

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

When AGR is not activated, HFM matching can be exemplarily expressed as follows:

j _D =k _HFM *j _F .

where k _HFM is the matching factor of the mass flow of the air mass flowmeter.

When the external AGR is activated, HFM matching can be exemplarily expressed as:

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

where Δj _AGR represents the deviation of the mass flow comparison from the external AGR.

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

If a mass flow comparison is performed that is above a predetermined threshold and the lambda sensor adjustment command is "enrich", this may indicate too much fresh air in the intake section (as shown in the table above).

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

In some embodiments, the mass flow comparison indicates mass flow within a predetermined range (this is represented in the table by "within range"). This can also indicate that there is too little residual gas from the AGR section due to a miscalculation of the AGR rate when the regulation command is still "rich".

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

However, too little residual gas in the case of a mass flow comparison "in range" and in the case of "enrichment" of the lambda sensor may also be due to a leak between the AGR valve and the extraction of the exhaust gas line caused by inhalation of fresh air.

If the adjustment command is "dilute", but the mass flow comparison results in a mass flow above a predetermined threshold, this may indicate too much residual gas from the AGR section.

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

Excessive mass flow may also indicate excess residual gas in the intake section in the case of "dilution".

This may eg be based on a false simulation of the AGR rate, which may eg be caused by a leak in the line to the differential pressure sensor after the AGR valve. Also, this could 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 there is too little fresh air in the intake section, which in some embodiments may be caused, for example, by erroneous HFM sensor values.

As previously mentioned, there may be no adjustment commands for the lambda sensor despite the error. However, if the mass flow comparison still determines that there is too much mass flow, this may correspond to too much fresh air in the intake section. For example, this could be caused by a leak in the air section after the AGR valve.

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

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

The diagnostic circuit can be any circuit that can be provided in the motor vehicle or can be connected to the motor vehicle, such as a controller, a central on-board computer, CPU (Central Processing Unit), GPU (Graphics Processing Unit), FPGA (Field Programmable Gate Array) Wait.

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

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

A motor vehicle may be any type of vehicle having an internal combustion engine, such as a gasoline engine, a diesel engine, or an internal combustion engine as discussed under FIG. 1 . In this respect, the method according to the invention can be implemented in a hybrid vehicle if AGR is present.

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

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

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

By means of the charge detection described here and the mass flow difference or mass flow determined therefrom, only the mass flow can be determined and compared with one another, ie, the residual gas fraction and the fresh air fraction cannot be measured but only simulated.

For example, the fraction of the residual gas located in the air section 3 and supplied to the combustion can be determined by determining the recirculated AGR mass flow and can be included in the pilot control of the lambda regulation.

But these mass flow rates can still be wrong (eg due to leaks, blockages in the air path/AGR path), so the model can deviate significantly from reality.

Therefore, in order to validate (or refute) predictions of mass flow, one (or all of) sensors 10, 16 and/or 18 have been designated for use in determining the lambda regulation bias. In other words, the measured lambda value is compared with the predicted lambda value. If the comparison yields a deviation above a predetermined threshold, an error in the mass flow model can be inferred.

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

For example, if there is an undesired increase in the recirculated residual gas at this time, then a smaller supply of fresh air mass is provided during combustion by means of the pre-control. If there is an error in the AGR, the lambda value (at the same operating point and compared to AGR without error) 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 residual gas recirculated in a faulty AGR is undesirably reduced, the pre-control provides more fresh air mass for combustion, resulting in a lean mixture, which the lambda regulator attempts to compensate by enriching This situation. However, this may also have an effect on engine power or engine torque.

As previously mentioned, the lambda modulation bias can be evaluated based on the least squares method.

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

As discussed above, a load point shift may be triggered due to an undesired high flow or low flow error that may have engine power or engine torque effects.

Errors can be evaluated by the least squares method with the load point remaining constant, since slope errors and offset errors can be distinguished at the measurement points, eg by matching value formation.

FIG. 3 shows a graph 35 of relative fuel mass versus relative air charge. Measurement points 36 and a simulated curve 37 for the relative fuel mass are shown in diagram 35 . Deviations of each measurement point 36 from the simulated curve 37 can be attributed to offset errors or slope errors by means of the least squares method.

Embodiments of the invention will now be described by way of example and with the aid of the drawings. In the attached image:

Figure 4 shows a diagnostic method 40 according to the present invention.

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

At 42, the presence or absence 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.

Figure 5 shows a diagnostic method 50 according to the present invention.

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

At 52, the presence or absence 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 , the 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 an 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 corresponding values of the sensors and probes as described herein.

List of reference signs

1 Internal combustion engine

2 air filter

3 Fresh Air Section

4 compressor

5 Charge air cooler

6 Throttle

7 Combustion engine

8 Turbines

9 axes

10 lambda sensor

11 branch points

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 Graphs to identify knocking or rough running

35 Least Squares Chart

36 measuring points

37 Simulation curve

40;50 Diagnostic Methods

41;51 Implement exhaust gas recirculation

42;52 Detect if there is an adjustment command

43;53 Determining deviation of actual gas mixture from nominal gas mixture

54 Implementing mass flow comparisons

60 Motor vehicles

61 Diagnostic circuit/controller

Claims (15)

1. A diagnostic method for an intake section of an internal combustion engine, comprising: implementing (41; 51) exhaust gas recirculation; The presence of an adjustment command is detected ( 42 ; 52 ) based on the lambda adjustment deviation, which is determined on the basis of the measurement of a lambda sensor ( 10 ; 16 ; 17 ), which is arranged in the exhaust gas line ( ) of the internal combustion engine ( 7 ). 12); and The deviation of the actual gas mixture from the target gas mixture in the intake section ( 3 , 12 ) of the internal combustion engine ( 7 ) is determined ( 43 ; 53 ) on the basis of the control command. 2. The diagnostic method of claim 1, wherein the adjustment command includes "enrichment" and "dilution". 3. A diagnostic method according to any preceding claim, wherein, when the adjustment command is "enriched", the deviation comprises: i) Excessive fresh air in the intake section (3, 12); or ii) Too little residual gas from the exhaust gas recirculation section (12). 4. Diagnostic method according to the second possibility of claim 3, wherein the residual gas from the EGR section (12) is too low on the basis of an incorrect determination of the EGR rate and/or leakage of the EGR valve (13). ). 5. The diagnostic method according to claim 1 or 2, wherein, when the adjustment command is "dilution", the deviation comprises one of the following: i) excess residual gas from the exhaust gas recirculation section (12); ii) Excessive residual gas in the intake section (3, 12); and iii) Too little fresh air in the intake section (3, 12). 6. The diagnostic method according to any one of the preceding claims, further comprising performing a mass flow comparison of the exhaust gas recirculation section (12) and the fresh air section (3). 7. The diagnostic method of claim 6 when dependent on the first possibility of claim 3, 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 the following: Positive offset of differential pressure sensor (19); narrowing of lines in exhaust gas recirculation section (12); and incorrect 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 erroneous calculation is based on: in the exhaust gas recirculation section (12) The line to the differential pressure sensor before the exhaust gas recirculation valve is blocked. 10. The diagnostic method according to claim 6 when dependent on claim 5, when the deviation is "too much residual gas from the exhaust gas recirculation section (12)", wherein the mass flow ratio is above a predetermined threshold. 11. The diagnostic method according to claim 6 when dependent on claim 5, when the deviation is "too much residual gas in the intake section (3, 12)", wherein the mass flow ratio is above a predetermined threshold. 12. The diagnostic method according to claim 6 when dependent on claim 5, when the deviation is "too little fresh air in the intake section (3, 12)", wherein the mass flow is comparatively below a predetermined threshold. 13. The method of diagnosis according to claim 6 when dependent on claim 1, wherein if there is no regulation command and the mass flow comparison indicates that the mass flow is above a predetermined threshold, the deviation comprises: Too much fresh air. 14. A diagnostic circuit arranged to implement the diagnostic method (40; 50) according to any one of the preceding claims. 15. A motor vehicle having a diagnostic circuit (61) according to claim 14.

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