DE102005006362A1 - Method for functional diagnosis of two functional components of exhaust gas recirculation system involves establishing of deviation in set value-/actual value of operating parameters of exhaust gas recirculation system - Google Patents

Abstract

The method involves establishing the deviation in set value-/actual value of the operating parameters of the exhaust gas recirculation system. In case the established deviation of the set value of the operating parameter is changed, the resulting change establishes at least one operating variable of at least two functional components. The established change, in at least one operating parameter of at least two functional components, closes the malfunction which may possibly exist in at least one of the two functional component of the exhaust gas recirculation system. An independent claim is also included for the device for functional diagnosis of two functional components of an exhaust gas recirculation system of exhaust gas recirculation internal combustion engine.

Description

The The invention relates to a method and a device for functional diagnosis an exhaust gas recirculation system an exhaust gas recirculating Internal combustion engine, in particular of a motor vehicle according to the preambles the respective independent claims.

A here exhaust gas recirculation system of an internal combustion engine of a motor vehicle is, for example, from the DE 42 07 541 A1 out. The device described therein can be used in all types of internal combustion engines, ie both in self-igniting (diesel) engines and in spark-ignited (petrol) engines.

by virtue of existing "OBD" rules all components directly or indirectly involved in combustion an exhaust gas recirculation, whose Failure can lead to a noticeable deterioration of the exhaust emission, from a controller the internal combustion engine is constantly monitored to become. The abbreviation "OBD" or better "EOBD" stands as an abbreviation for "European On-Board Diagnostics ", which requires self-diagnosis in motor vehicles, i. the provision one in the control unit the internal combustion engine integrated diagnostic system, which is constantly exhaust gas relevant (Control) systems and components of a control system of the internal combustion engine monitors. The EOBD is part of the Euronorm Level 3, which officially took place on 01.01.2001 came into force for vehicle registration. Such Diagnostic system includes an exhaust gas warning lamp, which in the case of an emissions-related Malfunction of one of the mentioned parts lights up.

The called diagnostic system monitors it For example, the fuel system and the aforementioned exhaust gas recirculation. Not permanently monitored components and systems are checked only when driving through a driving cycle, which in particular a cold start idling phase and a constant travel in at least two speed ranges includes. A malfunction of the exhaust gas recirculation will then assumed when specified diagnostic thresholds or limits exceeded become.

in the Upcoming certifications for the EOBD have been in existing Control programs (applications) of the aforementioned control units a so-called "flow check Test "introduced by means of whose effectiveness of exhaust gas recirculation is checked. This test runs independently of the so-called "HFM plausibility check", in which the Measured data of a arranged in the (fresh air) intake tract of the internal combustion engine Air flow meter (HFM) in a conventional manner already one functional test be subjected.

At the Flow check test can now be the case that a jamming or blocking Exhaust gas recirculation valve falsely a plausibility error caused by the HFM. Conversely, an HFM, which is not plausible Returns values, causing a flow check error. In both mentioned make it is impossible, to reliably diagnose a defective component in question. Thereby There is a need for the exchange of all possible Components of exhaust gas recirculation and thus an excessive cost burden for all Involved.

Of the Invention is therefore based on the object, an aforementioned Method and an apparatus to improve in that the above-described Ambiguity avoided in a functional diagnosis affected here and in particular a secure and reliable location of a defective component the exhaust gas recirculation system is possible.

Advantages of invention

The Invention proposes before, in a method involved here for functional diagnosis at least two functional components of an exhaust gas recirculation system an exhaust gas recirculating Internal combustion engine, in particular a motor vehicle in the frame an additional test provide that a setpoint / actual value control deviation at least one operating characteristic of the exhaust gas recirculation system, preferably the amount of air, it is found that in case of a detected Control deviation of the setpoint of the operating characteristic is changed, that one about resulting change at least one operating size of the at least two functional components, preferably the duty cycle one exhaust gas recirculation actuator, is determined and that out the change detected the at least one operating size of the at least two functional components on the possible existence of a malfunction at least one of the at least two functional components of the exhaust gas recirculation system is closed.

The additional test proposed according to the invention considerably improves the quality of the functional diagnosis of an exhaust gas recirculation system affected here, since it enables a reliable and reliable locating of a defective component or another fault cause for the defect and thus a subsequent targeted repair. In particular, the invention enables a reliable distinction of an exhaust gas recirculation or HFM plausibility error in an internal combustion engine affected here.

Especially thanks to the additional test is a reading of a arranged approximately in a control unit Fault memory required only if the two mentioned Errors / defects occur simultaneously, i. that a pinching or blocking Exhaust gas recirculation valve falsely a plausibility error of the HFM and an HFM that does not provide plausible values, in turn causes a flow check error.

Of the inventive additional test can be performed directly on a motor vehicle and avoids it a complex investigation of the exhaust gas recirculation system in a workshop. Of the Additional test thus means a significant potential savings as well as the vehicle manufacturer as well as the supplier (s) and the end customer (s), because then only one actually defective component must be replaced.

Of the Additional test fulfilled all EOBD regulations, as it is continuous and freely programmable (applicable) can be applied, if necessary, even during a prescribed European Driving cycle. Does not function by means of the additional test diagnosed, diagnostic results obtained by other means not affected by this.

Of the Additional test can be beneficial in easier and cheaper Way in an existing control unit of an exhaust gas recirculation Internal combustion engine, preferably in the form of a corresponding control program, be implemented.

The according to the invention also proposed device for functional diagnosis of an exhaust gas recirculation system an internal combustion engine affected here comprises at least one logic circuit, by means of which the additional test according to the invention is realized.

drawing

The The invention will be described below with reference to the attached drawing. based on embodiments described in more detail, from which further features and benefits of the invention.

In show the drawing in detail

1 a schematic representation of an apparatus for controlling a supercharged internal combustion engine with exhaust gas recirculation according to the prior art;

2 an embodiment of a logic circuit for determining a "critical" duty cycle of the exhaust gas recirculation (ARF) of an internal combustion engine affected here;

3 an embodiment of a logic circuit for testing minimum requirements for the feasibility of the additional test according to the invention;

4 an embodiment of a logic circuit for the offset of an air mass setpoint in an exhaust gas recirculation system affected here;

5 a flowchart illustrating the flow of the additional test according to the invention according to a preferred embodiment; and

6 an embodiment of a logic circuit for evaluating the test result of the additional test according to the invention.

Description of exemplary embodiments

The 1 shows schematically an apparatus for controlling the exhaust gas recirculation rate in a diesel internal combustion engine of a motor vehicle according to the prior art. It should be noted, however, that the present invention grds. can also be used in all other equipped with an exhaust gas recirculation engine types.

The in the 1 only schematically indicated diesel engine 100 receives via a fresh air supply line 105 Fresh air supplied. The exhaust gas flow is via an exhaust pipe 110 derived. The exhaust gas passes through a turbine 115 in an exhaust pipe 120 , The turbine 115 drives a loader 130 which, in turn, passes through a suction line 135 flowing fresh air ("intake air") of the fresh air supply line 105 supplies. The amount of incoming fresh air is measured via an air flow meter (not shown). Via an exhaust gas recirculation valve 138 stand the exhaust pipe 110 and the fresh air supply 105 in pressure-conductive connection.

The diesel engine 100 further comprises an electronic control unit 140 which is a quantity control 142 and an exhaust gas recirculation control 144 having. The quantity control 142 acts on an injection pump 145 with signals, where the quantity control 142 Depending on these signals, a defined amount of fuel of the internal combustion engine attaches. The exhaust gas recirculation control 144 stands with an electropneumatic converter 150 in combination, which is said Exhaust gas recirculation valve 138 actuated. About the exhaust gas recirculation valve 138 the composition of the air supplied to the internal combustion engine can be influenced. The exhaust gas recirculation control 144 this is a signal with a corresponding duty cycle to the electropneumatic converter 150 out. At a high duty cycle opens the exhaust gas recirculation valve 138 and there is a large exhaust gas recirculation rate. Accordingly, a small exhaust gas recirculation rate results with a small duty cycle.

A device described above is essentially from the above-mentioned document DE 42 07 541 A1 previously known. From the cited document, in particular the local 2 , A preferred method of operation of this device is also already known, in which in a nominal characteristic map - depending on the rotational speed of the internal combustion engine and the fuel quantity to be injected - a desired value, for example. Is stored for the amount of air. The quantity of fuel to be injected is predetermined by a quantity specification depending on, for example, the accelerator pedal position delivered by a pedal value transmitter (PWG). The desired value of the intake air quantity is compared with a corresponding actual value and, depending on the result of this comparison, a control value is output by a controller to an associated controlled system. This controlled system preferably comprises the internal combustion engine, a fuel pump, which determines the output of the internal combustion engine, and said device for returning exhaust gas into the intake air.

The proposed and subsequently with reference to the 2 to 5 The additional test described in more detail is essentially based on the air mass difference between a nominal value specification and an actual value detected by means of said air flow meter (HFM) and the duty cycle (TV) of an exhaust gas recirculation controller (ARF) during idling speed in the operating state of the internal combustion engine. If the HFM is implausible or if the ARF valve has a defect, ie the ARF valve is stuck, for example, a control deviation (ie air mass difference) between the setpoint specification and the actual value can be determined during idling. In addition, the duty cycle TV of the ARF controller will assume the maximum or minimum possible value. This value is therefore either 0% or 100%, but no value in between. Furthermore, this duty cycle TV ARF is referred to as "critical duty cycle".

in the Following are the procedure and interpretation of the result the proposed additional test using preferred embodiments described.

In the present 2 First, an embodiment of a logic circuit is shown, by means of which a present duty cycle, TV 'of an exhaust gas recirculation (ARF) can be assessed as "critical." The circuit shown there is composed of two circuit parts, wherein one of the outputs of the circuit part shown above right as Input of the circuit part shown below left is used.

The input is the circuit via the line 200 the respective current value of the duty cycle TV ARF supplied. Via a branch line 215 this value is simultaneously at a first comparator (comparison operator) 205 and on a second comparator 220 at. It is only then a signal (logical, 1 ') at the output of a comparator 205 . 220 if the two input signals are the same. The second entrance of the upper comparator 205 corresponds to a presettable (calibratable) maximum value of TV ARF and the second input of the lower comparator 220 a likewise calibratable minimum value of the TV ARF.

Located at the exit 230 of the comparator 205 a signal, then this corresponds to the input 200 adjacent TV ARF a value TV ARF Max. Conversely, a value TV ARF Min is present when at the output 255 of the comparator 220 a signal is present. The two outputs of the comparator 205 and 220 serve as inputs to a logical OR gate 240 , at the exit 250 only a signal (logical, 1 ') is present when the input signal 235 or the input signal 245 is greater than zero. A logical output signal, 1 'on the line 250 of the logical OR gate 240 means that at the entrance 200 adjacent duty ratio TV ARF is in the stop.

That at the exit 250 The signal applied to the upper circuit part now serves as one of the input signals of the lower circuit part and there becomes a logical AND gate 297 fed. As further input variables of the AND gate serve the air mass setpoint 260 , the air mass actual value 265 and a predeterminable (calibratable) minimum deviation of the air mass 285 , The air mass setpoint 260 and the air mass actual value 265 become at a difference-forming node 270 added up, the air mass setpoint 260 a positive and air mass actual value 265 receives a negative sign. Since the difference 'air mass setpoint - air mass actual value' thus formed may also assume negative values, this difference value will subsequently be determined by means of an absolute value forming element 275 as a positive difference 280 output. This difference serves as an input, a 'of a subsequent comparator 290 , which implements the logic operation a> b by means of a second input, b '. The second input, b 'is doing on the line 285 the mentioned minimum deviation of the air mass.

At the output of the logical AND gate 297 is therefore only a signal (logical, 1 ') on, ie there is a "critical" duty cycle, if that at the input 200 applied duty ratio is both in the attack and the difference, a 'is greater than the predetermined minimum deviation. Is the TV ARF either out of control or is the air mass set point? 260 smaller the air mass actual value, therefore no "critical" TV is accepted.

If one establishes the preconditions described above and for reasons of the most reliable diagnosis also those in the 3 fulfilled further minimum conditions, now the idle speed of the internal combustion engine, the air quantity setpoint default is offset with a calibratable value. The in the 3 shown minimum conditions are the air temperature 340 , the speed 350 , the water temperature 370 , the position of a provided for operating the internal combustion engine Pedalwertgebers and the air pressure. These sizes are made by comparators 305 . 310 . 315 . 320 . 325 and 330 Logically preprocessed and finally a logical AND gate 300 fed to the output 397 only a signal (logical, 1 ') is present when all of the signals in the aforementioned preprocessing correspond to a logical, 1', ie the conditions mentioned there are fulfilled.

So is the air temperature by means of the comparator 305 compared with a predetermined (calibratable) minimum temperature and it is at the output of the comparator 305 only a signal (logical, 1 '), if the measured air temperature is higher than the predetermined minimum temperature. Similarly, at the speed 350 checked whether this is both smaller than a predefinable maximum value 355 and at the same time via the parallel line 360 whether the speed 350 also larger than a predefinable minimum value 365 is. The result is thus by means of the comparative links 310 and 315 determines whether the speed value applied to the circuit is within a predefinable speed range.

In addition, by means of the comparator 320 checked if the present water temperature 370 the internal combustion engine higher than a predetermined minimum temperature 375 is. By means of the comparator 325 it is further checked whether the current position of the pedal encoder (PWG) of the motor vehicle is smaller than a predefinable PWG threshold. Finally, by means of the comparator 330 checked whether the detected and provided by a conventional pressure gauge outside air pressure 390 greater than a predefinable minimum air pressure 395 is.

Additionally goes at the AND gate 300 as a condition 335 that exhaust gas recirculation (ARF) is actually active.

It should be noted that the above-described comparison values 345 . 355 . 365 . 375 . 385 and 395 be determined empirically, for example, in advance at a test facility for the internal combustion engine or the entire motor vehicle.

The mentioned offset of the air mass setpoint will now be referred to in the 4 shown preferred embodiment of a corresponding logic circuit described in more detail.

At the entrance of the in the 4 shown circuit are initially a predeterminable (calibratable) air mass offset value 410 and an air mass set point 415 at. At a connection point 425 is from the over lines 420 and 435 supplied values 410 . 415 the difference (air mass setpoint - Luftmassenoffsetwert) formed and a first input of a first switch 405 fed. The over a line 440 "Looped through" air mass offset value 410 is at a second node 445 added to the also looped air mass setpoint. This added value now represents the input value of the second input of the switch 405 dar. The switch 405 is now triggered by the in the 2 At the output of the local circuit present minimum value of the duty cycle TV ARF Min 255 , When the duty cycle is at the minimum stop, the switch gives 405 the second entrance on; otherwise the first entrance 430 ,

The output of the first switch 405 serves as the first input of a second switch 400 , whose second input from the air mass setpoint 415 is fed. The trigger signal of the second switch is a so-called "measurement channel test state", which in the present exemplary embodiment assumes either the value "4" or "16." At the output of the second switch 400 then lies the offset air mass setpoint 460 in front. The air mass setpoint 460 is thus deliberately increased (at minimum stop) or lowered (at maximum stop) by this arrangement. This ensures that the control deviation is reduced or disappears. When the control deviation disappears, the duty cycle TV of the exhaust gas recirculation controller ARF no longer assumes extreme values.

The offset air mass target value is thus calculated in the present embodiment using the following equation: Offset air mass setpoint = air mass setpoint +/- offset (equation 1)

• a) liegt eine Abweichung oder eine Fehlfunktion des im Ansaugtrakt der Brennkraftmaschine angeordneten Luftmengenmessers (HFM) vor, so wird sich das Tastverhältnis gegenüber dem nicht offsetierten Luftmengensollwert ändern und keine extremen Tastverhältnisse mehr annehmen. Auch die Regelabweichung wird dann ebenfalls geringer werden. Im Ergebnis kann hierdurch auf einen defekten HFM geschlossen werden;
• b) klemmt der ARF-Steller oder ist die Unterdruckversorgung des Stellers abgefallen oder undicht, so bleibt das Tastverhältnis TV des ARF-Stellers maximal oder minimal und die Regelabweichung wird geringer, bleibt aber dennoch bestehen. Im Ergebnis kommt dabei heraus, daß der ARF-Steller klemmt.

The following two case constellations are distinguished:

• a) If there is a deviation or a malfunction of the air flow meter (HFM) arranged in the intake tract of the internal combustion engine, then the duty cycle will change with respect to the non-offset air quantity setpoint and no longer assume extreme duty cycles. The control deviation will then also be lower. As a result, it can be concluded that a defective HFM;
• b) If the ARF controller is stuck or if the negative pressure supply of the actuator is dropped or leaking, the duty cycle TV of the ARF controller remains maximum or minimum and the control deviation becomes smaller, but it still remains. As a result, it turns out that the ARF controller is stuck.

It It should be noted that the Duty cycle of ARF-Steller's for the named assignment authoritative Size represents.

In the 5 it is shown in which order the proposed additional test preferably proceeds and which experiences of two measuring channels that describe the state of the test, uses this. The respective state of the measuring channel is shown in the left-hand column, a brief description of the respective test state in the middle column and the test result of the respective measuring channel to be expected in each test step in the right-hand column.

At the When the routine starts, the test result is first initialized with the value '0'. In cases in which the additional test is interrupted or terminated, the Test state again set to the value '0'.

The first test state with the value '0' represents a waiting loop in which the fulfillment of the in 3 The minimum conditions for the additional test are awaited. The test state shown with the value '1' is present if the minimum conditions are met. In this case, the timer T1 described above is started and waited until the timer T1 is finished again. The test state with the value '2' is present when the timer 'T1' has expired, the mentioned minimum conditions are still fulfilled and the condition 'TV ARF not critical' is present. 2 'off.

The test state with the value '4' is present when the timer 'T1' has expired, the minimum conditions are still fulfilled and the test result 'TV-ARF critical' is present Additionally, the additional test results in an offset 1 for the air mass setpoint In this test state, only the said timer 'T2' is started and waited until it has expired, a test result is not output in this case, the test condition with the value '8' is present when the minimum conditions are still met and the test condition In this case, a test result '1' is output, after which the duty cycles are classified as "TV ARF critical" and the test is considered completed and completed. The duty cycle is then classified as "critical" when the in the 2 shown criteria are met.

Of the Test state with the value '16' before, when the timer, T2 'expired is, the minimum conditions are still met and the test result is "TV-ARF not critical ". additionally ergbit the test that at the air mass setpoint is an offset 2. In this test condition the said timer, T3 'is started and wait until it has expired. In this test condition no test result is output.

It It should be noted that in Test condition, 16 'the duty cycle Although not considered critical in itself, but the additional test can not be finished here yet. It will be in this state, however a second offset added to the air mass setpoint and the Timer, T3 'started, while whose expiration of said minimum conditions also be met have to. With this second offset is at a blocking ARF valve avoided the situation that the The setpoint applied to the first offset in the blocked offset Position of the ARF controller is achieved, so that coincidentally, the new setpoint and the actual value match. Thereby would the Condition of a non-clamping valve simulated. At a different offset value ( "Offset 2 ") can this Do not repeat special case.

Of the penultimate test state with the value, 32 'is present when the timer, T3' has expired and the minimum conditions still met are. The additional test gives the already mentioned test result in this test condition , 1 ', after which the duty cycles as "TV ARF classified critically and the additional test is terminated.

Of the last test state with the value, 64 'is present when the timer, T3' has expired and the minimum conditions still met are. However, the supplemental test in this test condition yields that already called test result, 2 ', after which the duty cycles as "TV ARF not critical " and the additional test is terminated.

It is finally to mention, that by means of Timer T1 - T3 it is ensured that the Supplementary test is carried out in each case in a stable state.

The 6 shows a preferred embodiment of a logic circuit for evaluating the test result obtained by means of the additional test according to the invention. At a first comparator 515 , which supplies an output signal (logical '1') only if the sinewave present at the input is equal, lies both the numerical value '1' 530 a first possible test result of the measuring channel ( 5 ) as well as the test result of the measuring channel itself 525 at. If the test result is '1', then it is at the output of the comparator 515 a logical '1', otherwise a logical '0'. A corresponding second comparator 520 with inputs 535 and 540 only supplies a logical, 1 'at its output if the test result of the measuring channel is'2'.

Further input variables for the present circuit are the already mentioned HFM plausibility errors 545 and the already mentioned Flow Check error 550 which is connected to an AND gate 50 issue. That is, only in case that both mentioned errors 545 . 550 occur, is located at the exit 555 of the AND gate 505 a logical, 1 '; otherwise a logical '0'.

The outputs of the two comparators 515 and 520 as well as the output 555 of the AND gate 505 be in the in the 6 shown way via lines 560 . 565 two other AND gates 500 and 510 fed. The first of these two AND members 500 only supplies a logical '1' to its output 570 if it is to be assumed or is concluded that the ARF-actuator blocked or jammed or any pressure lines are leaking. In case of a logical, 1 'at the output 575 the second of these two AND gates 510 it is concluded that there is an HFM error. While the error messages "HFM plausibility error" 545 and "Flow Check Error" 550 Both can be caused by HFM or ARF errors, so are ambiguous, provide the signals 570 and 575 clear information about the respective cause of the error.

From the 6 It can also be seen how the supplemental test is typically completed. If the additional test was carried out and concluded with a duty cycle TV ARF = "critical", ie in the present exemplary embodiment the value "1" for the test result and the values "8" or "32" for the test state are present, and additional errors occur in the case of the two variables "HFM plausibility" and "Flow check", the ARF actuator is assumed to be (finally) defective and the cause of the two errors mentioned. In this case, therefore, the HFM need not be replaced.

Becomes the additional test, however, with the result that the duty cycle TV-ARF "not critical "is, completed, i.e. in the present embodiment then results in a value "2" for the test result and a value of "2" or "64" for the test condition, and are additional Mistake regarding the "HFM Plausibility" and the "Flow Check" occurred, so is the HFM considered (finally) defective and accepted as the cause of the two mentioned errors. In this case, therefore, the ARF actuator and the pneumatic guide together with of the electropneumatic valve can not be replaced.

It should also be noted that instead of the "Flow Check" error, the results of other monitoring functions can be used as well, such monitoring functions are generally applicable, which generally report faults in the air system or EGR system of the internal combustion engine, such as detection a permanent control deviation of an air mass regulator or an exhaust gas recirculation rate regulator 6 In this case, the parameter "Flow Check Error" must be replaced by the corresponding error message of this monitoring function.

Alternatively, said offset of the air mass setpoint may alternatively be relative to the mass air flow actual value, rather than relative to the air mass setpoint. In this exemplary embodiment, the calculation of the aforementioned offset value takes place, in comparison with equation Eq. 1, using the following equation: Offset air mass setpoint = air mass actual value +/- offset (equation 2)

These Approach has opposite that according to Eq. 1 the further advantage that the Offset value can not be chosen very large must, so that offset air mass setpoint in any case, i. depending on the positive or negative control deviation, either below or above the current actual value. Instead, with the procedure according to the present embodiment checked, whether it is possible to adjust an air mass that is slightly different from the current one Actual value is different. The evaluation in terms of the said "critical Duty cycle "is correct in this Case however with the above procedure.

It should be noted that in the latter embodiment in the 4 the signal "air mass nominal value" 415 is to be replaced by the parameter "air mass actual value".

Claims (11)

Method for functional diagnosis of at least two functional components of an exhaust gas recirculation system of an exhaust gas recirculating internal combustion engine, in particular of a motor vehicle, characterized in that a setpoint / actual value deviation of at least one operating characteristic of the exhaust gas recirculation system is determined that in the case of a detected deviation of the setpoint of the operating characteristic is changed, that thereby approximately resulting change of at least one operating variable the at least two functional components are detected and that from the determined change of the at least one operating variable of the at least two functional components to the possible existence of a malfunction of at least one of the at least two functional components of the exhaust gas recirculation system is closed. Method according to claim 1, characterized in that that one by means of an air flow meter detected air mass difference between an airflow setpoint and an air quantity actual value in the operating state of the internal combustion engine checked under idle speed becomes and from the grasped Air mass difference to the presence of a malfunction at least a component of the exhaust gas recirculation system is closed. Method according to claim 1 or 2, characterized that in addition the Duty cycle of a Exhaust gas recirculation plate detected becomes. Method according to claim 3, characterized that is being tested whether the value of the detected duty cycle a maximum or minimum possible Takes value. Method according to one of the preceding claims, characterized characterized in that mentioned test steps only then done when at least one operating condition of the internal combustion engine Fulfills is, namely preferably the air temperature and / or the speed and / or the Water temperature and / or the position of a pedal encoder and / or the external air pressure. Method according to one of claims 2 to 5, characterized that the Air quantity setpoint is offset with a predetermined value. Method according to Claim 6, characterized that the Offset using the equation "Offset air mass setpoint = Air mass setpoint +/- offset "or using the equation "Offset Air mass setpoint = air mass actual value +/- offset "is carried out. Method according to one of claims 3 to 7, characterized that on a critical or non-critical duty cycle of the exhaust gas recirculation actuator is closed. Device for functional diagnosis of at least two Function components of an exhaust gas recirculation system of an exhaust gas recirculating Internal combustion engine, in particular a motor vehicle, characterized by at least one logic circuit, which means for detection a setpoint / actual value control deviation at least one operating characteristic of the exhaust gas recirculation system, Means of change the setpoint of the operating characteristic in the case of a detected Deviation, means for determining a change resulting thereby at least one operating size of the at least two functional components and means for assessing the change detected the at least one operating size of the at least two functional components with regard to the possible existence of a malfunction at least one of the at least two functional components of the exhaust gas recirculation system having. Apparatus according to claim 9, characterized by Means for detecting and evaluating the duty cycle of an exhaust gas recirculation controller the internal combustion engine, in particular with regard to a maximum and minimal possible Value of the duty cycle. Apparatus according to claim 9 or 10, characterized by means for offsetting an air quantity setpoint with a predefinable value.