Abstract:
The invention relates to a waste gas probe which is disposed in an internal combustion engine, comprising a plurality of cylinders and injection valves associated with the cylinders, in order to measure fuel. The waste gas probe is arranged in a waste gas tract and the measuring signal thereof is characteristic for the air/fuel ratio in the respective cylinder. The measuring signal is detected in relation to a reference position of the piston of the respective cylinder at a predefined crankshaft angle and associated with a respective cylinder. A manipulated variable which is used to influence the air/fuel ration in the respective cylinder according to the measuring signal detected for the respective cylinder is produced by means of a controller. The predefined crankshaft angle is adapted according to an instability criterion of the controller.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is the U.S. National Stage of International Application No. PCT/EP2004/053065, filed Nov. 23, 2004 and claims the benefit thereof. The International Application claims the benefits of German Patent application No. 10 2004 004 291.8 filed Jan. 28, 2004. All of the applications are incorporated by reference herein in their entirety.  
       FIELD OF THE INVENTION  
       [0002]     The invention relates to a method for adapting the detection of a measuring signal of a waste gas probe which is disposed in an internal combustion engine comprising a plurality of cylinders and injection valves associated with the cylinders which supply measured amounts of fuel. The waste gas probe is arranged in a waste gas tract and the measuring signal thereof is characteristic for the air/fuel ratio in the respective cylinder.  
       BACKGROUND OF THE INVENTION  
       [0003]     Ever more stringent regulations regarding permissible pollutant emissions by motor vehicles fitted with internal combustion engines make it necessary to keep the pollutant emissions as low as possible during operation of the internal combustion engine. One of the ways in which this can be done is by reducing the emissions which occur during the combustion of the air/fuel mixture in the relevant cylinder of the internal combustion engine. Another is to use waste gas handling systems in internal combustion engines which convert the emissions which are generated during the combustion process of the air/fuel mixture in the relevant cylinder into harmless substances. Catalyzers are used for this purpose, which convert carbon monoxide, hydrocarbons and nitrous oxide into harmless substances. Both the explicit influencing of the generation of the pollutant emissions during the combustion and also the conversion of the pollutant components with a high level of efficiency by an exhaust gas catalyzer require a very precisely set air/fuel ratio in the respective cylinder.  
         [0004]     The later published patent application DE 103 04 245 B3 discloses a method for adapting signal sampling of Lambda probe signal values for use in a cylinder-selective Lambda control for a multi-cylinder internal combustion engine. A Lambda probe records the oxygen values in the waste gas for individual cylinders in the waste gas tract at predefined points in time. From the Lambda values measured in this way for individual cylinders control deviations for the cylinders are reconstructed from which a characteristic value is computed. The times for measuring the Lambda values of the individual cylinders are related to the crankshaft angle such that the characteristic value assumes an extreme value.  
         [0005]     A method for cleansing waste gas is known from US 2003/0014967 A1 in conjunction with a waste gas system. A gas sensor is arranged so that it is subjected to a passing stream of waste gas and this occurs in chronological sequence from the respective cylinders. A time characteristic of the sensor signal includes information about the air/fuel ratio of the individual cylinders (see paragraph 0012). A control device can also comprise a cylinder-selective injection system with which the air/fuel ratio can be individually adapted to the individual cylinders. To this end the injection time is influenced in a cylinder-selective manner. From US 2002/0139354 A1 (D2) controlling a simultaneous injection of fuel into all cylinders after the start of the internal combustion engine is known. A cylinder identification means is provided to identify the individual cylinders based on the crankshaft angle and in this case to generate a cylinder identification signal. A fuel dispensing control means to control the fuel injection valves of the individual cylinders is provided, based on the crankshaft angle signal. A fuel injection volume correction means is provided for correcting the activation periods of the injection valves.  
         [0006]     From the Patent Abstracts of Japan for JP 57 140 529 A method for deactivation of cylinders in an internal combustion engine with a plurality of cylinders is known in which for a down shift of a gear a check is made as to whether fuel supply is to be suppressed to all cylinders or merely to one cylinder group.  
         [0007]     U.S. Pat. No. 4,495,924 discloses a fuel injection control system with means for computing an injection start in relation to a crankshaft angle and for computing the duration of the fuel-injection. An injection signal means is provided for each cylinder to generate an injection signal which increases at the point of the computed start time of the injection and which has a duration which corresponds to the computed duration of the fuel injection.  
         [0008]     A method is known from US 2003/0110845 A1 for detecting misfires, and this is done for each cylinder. For a cylinder with misfires the fuel delivery is suppressed. An error in the mechanism is determined if a parameter based on the oxygen concentration indicates a richer value of the current air/fuel mixture of the waste gas than a predefined reference value makes this.  
         [0009]     A method is known from US 2002/0088446 in which an air/fuel ratio detection period is predefined in relation to an air/fuel ratio sensor which includes waste gas packets of all cylinders. Depending on a peak value phase, which is maximized on a rich or a lean side, induced by variations of the air/fuel ratio, a cylinder is determined, in which the air/fuel ratio is to be corrected and the fuel delivery is adapted accordingly.  
         [0010]     A method is know from DE 102 06 402 C1, in which for a global Lambda setpoint, which is provided for all cylinders, the excitation amplitude is added to one of the cylinders. A first injection correction for the cylinder is computed from the excitation time. The added Lambda value is delayed and/or filtered and subtracted as Lambda setpoint value for the cylinder from the actual Lambda value for the cylinder. The difference is applied as control deviation to a Lambda controller which determines a second injection correction for the cylinder.  
         [0011]     WO 90/02874 discloses a method for detecting misfires of an internal combustion engine with a plurality of cylinders, in which the output voltage of a Lambda sensor is monitored in the exhaust system and compared with a reference voltage. A deviation of the difference between the sensor and the reference voltage from an expected value is signaled as a misfire in at least one of the cylinders. An expected gas delay time is determined as a function of an empirically determined engine map which is stored on a computer.  
         [0012]     A method for a multi-cylinder internal combustion engine for cylinder-selective controlling of an air/fuel mixture to be burnt is known from DE 199 03 721 C1, in which the Lambda values for different cylinders or cylinder groups are sensed and controlled separately. To this end a probe evaluation unit is provided, in which a time-triggered evaluation of the waste gas probe signal is undertaken and thus a cylinder-selective Lambda value for each cylinder of the internal combustion engine determined. Each cylinder is assigned an individual controller which is embodied as a PI or PID controller and for which the control variable is a cylinder-individual Lambda value and of which the guide variable is a cylinder-individual setpoint value of the Lambda. The manipulated variable of the relevant controller then influences the injection of the fuel into the relevant assigned cylinder.  
         [0013]     The quality of the cylinder-individual Lambda regulation is decisively dependent on how precisely the measuring signal of the waste gas probe is assigned to the waste gas of the relevant cylinder. During the operation of the waste gas probe its response behavior can change and thus also the degree of precision of the assignment of the measuring signal of the waste gas probe to the waste gases of the respective cylinder.  
       SUMMARY OF THE INVENTION  
       [0014]     The object of the invention is to create a method for adapting detection of a measuring signal of a waste gas probe which, over a long operating life, allows simple and precise control of an internal combustion engine in which the waste gas probe can be disposed.  
         [0015]     The object is achieved by the features of the independent claims. Advantageous embodiments of the invention are identified in the subclaims.  
         [0016]     The outstanding feature of the invention is a method and a corresponding device for adapting the detection of a measuring signal of a waste gas probe. The waste gas probe is disposed in an internal combustion engine comprising a plurality of cylinders and with injection valves assigned to the cylinders which deliver fuel. The waste gas probe is arranged in a waste gas tract of the internal combustion engine and the measuring signal thereof is characteristic for the air/fuel ratio in the respective cylinder.  
         [0017]     The measuring signal is detected and assigned to the respective cylinder for a predefined crankshaft angle, in relation to a reference position of the piston in the respective cylinder. A manipulated variable for influencing the air/fuel ratio in the respective cylinder is generated by means of a controller in each case depending on the measuring signal detected for the respective cylinder. The predefined crankshaft angle is adapted as a function of an instability criterion of the controller.  
         [0018]     The invention is based on the surprising knowledge that the control quality of the controller is only influenced decisively by the crankshaft angle at which the measuring signal is detected if an instability criterion is fulfilled, that is if the controller is operating unstably. The invention makes use of the knowledge by adapting the predefined crankshaft angle as a function of the instability criterion of the controller. The adaptation can be very simple and at the same time can be undertaken very rapidly and thus guarantees a high a control quality of the controller in a simple manner.  
         [0019]     In an advantageous embodiment of the invention the instability criterion depends on the manipulated variable or variables of the controller assigned to the respective cylinder and/or further controllers which are assigned to other cylinders. Thus the measuring signal can be adapted especially simply and quickly.  
         [0020]     In a further advantageous embodiment of the invention the instability criterion is fulfilled if the manipulated variable or the manipulated variables respectively is or are the same for a predefined period as their maximum limit value to which they are limited by the controller or the controllers respectively, or is or are the same as their minimum limit value to which they are limited by the controller or controllers respectively. This makes it possible to detect in a simple manner whether the control is unstable and then make a corresponding adjustment to the predefined crankshaft angle.  
         [0021]     In a further advantageous embodiment of the invention it is necessary to fulfill the instability criterion, for all manipulated variables to be the same for the predefined period as their maximum fine to which they are limited by the controller or to be the same as their minimum value to which they are limited by the controller, and for this to apply to the manipulated variables of all cylinders. This enables the instability of the controller to be detected in an especially reliable manner, and in particular prevents a component error, for example that of the injection valve, being incorrectly detected as an instability of the controller.  
         [0022]     In a further advantageous embodiment of the invention it is necessary to fulfill the instability criterion, that with an even number of cylinders the one half of the manipulated variables is equal to the maximum value and the other half is equal to the minimum value, and with an odd number of cylinders a first number of manipulated values is equal to the maximum value and a second number of manipulated values is equal to the minimum value, in which case the first number differs from the second by one and the sum of the first and second numbers is equal to the odd number of cylinders. This is based on the knowledge that this is characteristic of an unstable controller with an even number of cylinders and accordingly with an odd number of cylinders.  
         [0023]     In a further advantageous embodiment of the invention an error of the injection valve or of an actuating element is detected which exclusively influences the air feed to the respective cylinder if the manipulated variable of the respective cylinder is equal for a predefined period to its maximum value to which it is limited by the controller or is equal to its minimum value to which it is limited by the controller, and at least one manipulated variable which is assigned to another cylinder is not equal to the maximum value or the minimum value. This additionally allows an error of an injection valve to be detected and the crankshaft angle of the detection of the measuring signal to not be changed incorrectly.  
         [0024]     In a further advantageous embodiment of the invention the instability criterion is fulfilled if at least the manipulated variable assigned to a cylinder oscillates at an amplitude which is greater than a predefined amplitude threshold. Thus the instability of the controller can be securely detected, especially for an odd number of cylinders.  
         [0025]     In a further advantageous embodiment of the invention the controllers each feature a monitor which determines a status variable depending on the measuring signal of the waste gas probe detected, in which case a variable characterizing the status variable of the monitor is fed back and for which the instability criterion depends on one or more of the status variables. This enables the instability criterion to be particularly simple.  
         [0026]     Further advantageous embodiments of the invention in respect of the status variable or the status variables correspond to those in relation to the manipulated variable or the manipulated variables and have the same advantages.  
         [0027]     It is further advantageous for the adaptation of the predefined crankshaft angle to be undertaken using a step which corresponds to a predefined fraction of the expected stability range of the controller. The fraction is preferably selected as about ⅕ of the expected stability range of the controller. This enables the predefined crankshaft angle to be adapted very quickly and this can be done in accordance with the selected increment, and at the same time a lower computing overhead is necessary since it is only important that the stability range be achieved.  
         [0028]     If the measuring signal of the waste gas probe is characteristic for the air/fuel ratio in the respective cylinder of a first part of all cylinders and a further waste gas probe is provided for which the measuring signal is characteristic for the air/fuel ratio in the respective cylinder of a second part of all cylinders, the adaptation of the detection of the measuring signal and of the further waste gas probe are advantageously undertaken separately and related in each case to the first part or the second part of all cylinders respectively. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]     Exemplary embodiments of the invention are explained below with reference to schematic diagrams. The figures show:  
         [0030]      FIG. 1 a  internal combustion engine with a control device,  
         [0031]      FIG. 2 a  block diagram of the control device,  
         [0032]      FIG. 3 a  first flowchart of a program for adapting at the detection of a measuring cylinder of a waste gas probe,  
         [0033]      FIG. 4 a  further program for adapting the detection of the measuring signal of the waste gas probe and  
         [0034]      FIG. 5 a  further flowchart of a program for adapting the detection of the measuring signal of the waste gas probe. 
     
    
       [0035]     Elements for which the construction and function are the same are labeled by the same reference symbols in all figures.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0036]     An internal combustion engine ( FIG. 1 ) comprises an induction tract  1 , an engine block  2 , a cylinder head  3  and a waste gas tract  4 . The induction tract  1  preferably comprises a throttle valve  11 , also a collector  12  and an induction pipe  13 , which is routed through to the cylinder Z 1  via an inlet channel in the engine block  2 . The engine block  2  further comprises a crankshaft  21 , which is coupled via a connecting rod  25  to the piston  24  of the cylinder Z 1 .  
         [0037]     The cylinder head  3  comprises a valve drive with a gas inlet valve  30 , a gas outlet valve  31  and valve drives  32 ,  33 . The cylinder head  3  further comprises an injection valve  34  and a spark plug  35 . Alternatively the injection valve can also be arranged in the induction channel.  
         [0038]     The waste gas tract  4  comprises a catalyzer  40 , which is preferably embodied as a three-way catalyzer. A waste gas return line can be routed back to the induction tract  1  from the waste gas tract  4 , especially back to the collector  12 .  
         [0039]     In addition a control device  6  is provided to which sensors are assigned which detect different measuring variables and determine the measured value of the measuring variable in each case. Depending on at least one of the measuring variables, the control device  6  controls the actuation elements by means of corresponding actuation drives.  
         [0040]     The sensors are a pedal positions sensor  71 , which detects the position of the gas pedal  7 , an air mass measurer  14 , which detects an air mass stream upstream from the throttle valve  11 , a temperature sensor  15 . which detects the induction air temperature, a pressure sensor  16 , which detects the induction pipe pressure, a crankshaft angle sensor  22 , which detects a crankshaft angle to which a speed N is then assigned, a further temperature sensor  23 , which detects a coolant temperature, a camshaft angle sensor  36   a , which detects the camshaft angle and a waste gas probe  41 , which detects a residual oxygen content of the waste gas and of which the measuring signal is characteristic for the air/fuel ratio in the cylinder Z 1 . The waste gas probe  41  is a preferably embodied as a linear Lambda probe and thus generates over a wide range of the air/fuel ratio, in measuring signal proportional to this.  
         [0041]     Depending on the form of embodiment of the invention any given subset of the said sensors or also additional sensors can be present.  
         [0042]     The actuating elements are for example the throttle valve  11 , the gas inlet and gas outlet valves  30 ,  31 , the injection valve  34  and the spark plug  35 .  
         [0043]     As well as the cylinder Z 1  further cylinders Z 2 -Z 4  are also provided to which corresponding actuation elements are also assigned. Preferably a waste gas probe is assigned to each waste gas bank of cylinders. Thus the internal combustion engine can comprise six cylinders for example with three cylinders being assigned to one waste gas bank and correspondingly to one waste gas probe  41  in each case.  
         [0044]     A block diagram of parts of the control device  6  which can be referred to as a unit for controlling the internal combustion engine is shown with reference to  FIG. 2 .  
         [0045]     A block B 1  corresponds to the internal combustion engine. An air/fuel ratio LAM_RAW detected by the waste gas probe  41  is fed to a block B 2 . At predefined crank-shaft angles CRK_SAMP respectively, in relation to a reference position of the respective piston of the respective cylinder Z 1  to Z 4 , an assignment is then undertaken in the block B 2  of the air/fuel ratio currently detected at this point in time which is derived from the measuring signal of the waste gas probe  41 , to the relevant air/fuel ratio of the respective cylinder Z 1  to Z 4  and thus the cylinder-individually detected air/fuel ratio LAM_I [Z 1 -Z 4 ] I assigned.  
         [0046]     The reference position of the relevant piston  24  is preferably its top dead center. The predefined crankshaft angle CRK_SAMP is for example applied as a fixed value the first time that the internal combustion engine is put into service and is subsequently adapted where necessary on the basis of the programs described below.  
         [0047]     In a block B 2   a an average air/fuel ratio LAM_MW is determined by averaging the air/fuel ratios LAM_I [Z 1 -Z 4 ] detected for the individual cylinders. Furthermore in the block B 2   a an actual value D_LAM_I [Z 1 ] of a deviation of an individual cylinder air/fuel ratio is determined from the difference between the average air/fuel ratio LAM_MW and the air/fuel ratio detected for the individual cylinder LAM_I [Z 1 ]. This is then fed to a controller which is formed by block B 3   a.    
         [0048]     In a summation unit S 1  for the difference between the indicated value D_LAM_I [Z 1 ] and an estimated value D_LAM_I_EST [Z 1 ] of the cylinder-individual air/fuel ratio the deviation is determined and then assigned to a block B 3  which is part of the monitor and comprises an integration element which integrates the variables present at its input. The I-element of the block B 3  then makes a first estimated value EST 1  [Z 1 ] available at its output. The first estimated value EST 1  [Z 1 ] is limited in the integration element of block B 3  to a minimum value MINV 1  and a maximum value MAXV 1  which are preferably fixed.  
         [0049]     The first estimated value EST 1 [Z 1 ] is then fed to a delay element which is also a component of the monitor which is embodied in the block B 4 . The delay element is preferably embodied as a PT1 element. Where necessary the first estimated values EST 1 [Z 2 -Z 4 ], in relation to the further cylinders [Z 2 -Z 4 ] in each case are also fed to the delay element.  
         [0050]     The first estimated value EST 1 [Z 1 ] forms a status variable ofthe monitor.  
         [0051]     The first estimated value EST 1 [Z 1 ] is also fed to a block B 5  in which a further integrator element is embodied, which integrates the first estimated value EST 1 [Z 1 ] and then creates at its output a cylinder-individual Lambda control factor LAM_FAC_I [Z 1 ] as manipulated variable of the controller. In the I element of the block B 5  the cylinder-individual Lambda control factor LAM_FAC_I [Z 1 ] is limited to a maximum value MAXV 2  and a minimum value MINV 2 .  
         [0052]     The second estimated value EST 2  [Z 1 ] depending on the cylinder-individual Lambda control factor LAM_FAC_I [Z 1 ] is determined in a block B 6 . This is done especially simply by setting the second estimated value EST 2  [Z 1 ] equal to the cylinder-individual Lambda control factor LAM_FAC_I [Z 1 ]. In the summation unit S 2  the difference between the first estimated value EST 1  [Z 1  ]filtered via the delay element of the block B 4  and the second estimated value EST 2  [Z 1 ] is formed and fed back as estimated value D_LAM_I_EST [Z 1 ] of the cylinder-individual air/fuel ratio deviation to the summation unit S 1  and subtracted here from the current value D_LAM_I [Z 1 ] of the respective air/fuel ratio deviation and coupled back and then injected again into the block B 3 .  
         [0053]     A Lambda controller in provided in block B 8 , for which the guide value is an air/fuel ratio predefined for all cylinders of the internal combustion engine and for which the control variable is the average air/fuel ratio LAM_MW The manipulated variable of the Lambda controller is a Lambda control factor LAM_FAC_ALL. The Lambda controller thus has the task of setting the predefined air/fuel ratio viewed over all cylinders Z 1  to Z 4  of the internal combustion engine.  
         [0054]     Alternatively this can also be achieved by determining from block B 2  the current value D_LAM_I of the cylinder-individual air/fuel ratio deviation from the difference of the air/fuel ratio predefined for all cylinders Z 1  to Z 4  of the internal combustion engine and the cylinder-individual air/fuel ratio LAM_I[Z 1 -Z 4 ]. In this case the third controller of block B 8  can then be omitted.  
         [0055]     In a block B 9  a measured fuel flow MFF depending on a mass air flow MAF in the relevant cylinder Z 1  to Z 4  and where necessary the speed N and a setpoint value LAM_SP of the air/fuel ratio for all cylinders Z 1 -Z 4  can be determined.  
         [0056]     In the multiplier unit M 1  a corrected mass fuel flow MFF_COR is determined by multiplying the mass fuel flow MFF, the Lambda control factor LAM_FAC_ALL and the cylinder-individual Lambda control factor LAM_FAC_I[Z 1 ]. Depending on the corrected measured fuel flow MFF_COR, a control signal is then generated which controls the respective injection valve  34 .  
         [0057]     As well as the controller structure shown in the block diagram of  FIG. 2 , the corresponding controller structures B_Z 2  to B_Z 4  are provided in each case for the respective further cylinders Z 2  to Z 4  for each further cylinder Z 1  to Z 4 .  
         [0058]     Alternatively a proportional element can also be embodied in block B 5 .  
         [0059]     A program for adapting the detection of the measurement signal of the waste gas probe  41  is started in a step S 1 , preferably close to the time at which internal combustion engine is started. In step S 1  variables are initialized if necessary ( FIG. 3 ).  
         [0060]     In a step S 2  a check is performed as to whether the cylinder-individual Lambda control factor LAM_FAC_I [Z 1 ], which is assigned to the cylinder Z 1  is the same as the maximum value MAXV 2  or a minimum value MINV 2  and if it is in this state for a predefined period lasting for example between five and ten seconds, or whether the amplitude AMP of the cylinder-individual Lambda control factor LAM_FAC_I [Z 1 ], which is assigned to the cylinder Z 1  exceeds a predefined amplitude threshold AMP_THR. If this is not the case an instability criterion is deemed not to be fulfilled and the processing is continued in a step S 4  in which the program is interrupted for a predefined waiting time T_W before the step S 2  condition is tested again.  
         [0061]     If on the other hand the step S 2  condition is fulfilled, the instability criterion is deemed to be fulfilled and the predefined crankshaft angle CRK_SAMP in relation to the reference position of the piston  24  of the respective cylinder Z 1  to Z 4 , in which the measuring signal of the waste gas probe  41  was detected is assigned to the relevant cylinder, is adapted in the step S 6 , preferably by the predefined crankshaft angle CRK_SAMP being either decreased or increased by a predefined angle of change D. The angle of change D is preferably a predefined fraction of the expected range of crankshaft angles within which the control is stable This expected range of crankshaft angles is preferably determined empirically and this is done when the internal combustion engine is new. For a 4-cylinder internal combustion engine the crankshaft angle can be 180° for example. The angle of change D is preferably a large angle in relation to the crankshaft angle range and amounts for example to 20% of the crankshaft angle range, that is to a crankshaft angle of around 40°. The direction of adaptation of the predefined crankshaft angle CRK_SAMP is preferably determined by two or more consecutive executions of the steps S 2  and S 6 , taking into account the starting state, that is the instability criterion with different leading signs of the angle of change D.  
         [0062]     The preferably large increment of the adaptation of the predefined crankshaft angle CRK_SAMP as a result of the large angle of change D enables the stable range of control to be found within very few executions of the steps S 2  and S 6 , a range which is characterized by the fact that the instability criterion of step S 2  is not fulfilled.  
         [0063]     As a result of the knowledge that the quality of the control is approximately the same within the stability range, a search for an optimum quality of control which is expensive in terms of computing and time can be dispensed with and thereby a very high-quality control set within a very short time.  
         [0064]     A second embodiment of a program for adapting the detection of the measuring signal of the waste gas probe  41  is shown with reference to  FIG. 4 . The program is started in a step S 10  in which variables are initialized where necessary. It is typically described for an internal combustion engine in which three cylinders Z 1 -Z 3  are assigned a waste gas probe  41 . This can for example be the case for an internal combustion engine with three cylinders Z 1 -Z 3  or also for an internal combustion engine with six cylinders in which the waste channels of three cylinders Z 1 -Z 3  are routed to a waste gas probe  41  in each case. With this type of internal combustion engine with six cylinders the program is then executed for each three cylinders once in parallel, in accordance with the following steps. The program is however also suitable for execution if the relevant waste gas probe  41  is assigned to a different number of cylinders, in which case the conditions are then adapted according to this number.  
         [0065]     In the step S 12  the cylinder-individual Lambda control factors LAM_FAC_I [Z 1 ], LAM_FAC_I [Z 2 ], LAM_FAC_ 1  [Z 3 ], which are assigned to the cylinders Z 1  to Z 3 , are checked as to whether they assume the maximum value MAXV 2  or the minimum value MINV 2  for the predefined period, or whether their timing oscillates with amplitude AMP which is greater than the predefined amplitude threshold AMP_THR.  
         [0066]     In a simple embodiment of step S 12  the amplitude AMP can also be determined in each case by detecting the maximum and minimum values of the timing sequence of the cylinder-individual Lambda control factor LAM_FAC_I [Z 1  to Z 3 ] occurring during the predefined period and equating their difference with the amplitude AMP.  
         [0067]     in a step S 14  a check is subsequently undertaken as to whether the number of cylinder-individual Lambda control factors LAM_FAC_I [Z 1  to Z 3 ], which were detected in step S 12  were equal for the predefined period, that the maximum value MAXV 2  or minimum value MINV 2  is greater than zero and simultaneously the number is less than three.  
         [0068]     If this is the case, an error of a component is detected in a step S 16 . This component can be the respective injection valve  34  of the cylinder or cylinders Z 1 -Z 3  for which the cylinder-individual Lambda control factor LAM_FAC_I [Z 1  to Z 3 ] has assumed the maximum value MAXV 2  or the minimum value MINV 2  for the predefined period. This is based on the knowledge that, if not all cylinder-individual Lambda control factors LAM_FAC_I [Z 1  to Z 3 ] which are each assigned a waste gas probe  41 , but only some of them assume the maximum value MAXV 2  or the minimum value MINV 2 , this is not to be attributed to an instability of controller but to an error in a component. The component can be the respective injection valve or also an actuating element which exclusively influences the air fed to the respective cylinder Z 1 -Z 3 . This type of actuating element can for example be the inlet valve  30  or also what is known and a pulse charge valve.  
         [0069]     In the step S 16  for example an emergency mode of the internal combustion engine can then be activated or if necessary measures can also be taken to rectify the error of the component. After step S 16  processing is continued in step S 18  in which the program is interrupted for the predefined waiting time T_W before the processing is continued again in step S 12 .  
         [0070]     If on the other hand the condition of step S 14  is not fulfilled, an instability criterion is checked in a step S 20 . A check is undertaken in step S 20  as to whether the number ANZ of the cylinder-individual Lambda control factors LAM_FAC_I [Z 1  to Z 3 ], which for the predefined period in the step S 12  have assumed the maximum value MAXV 2 , is equal to two and the corresponding number of those which have assumed the minimum value MINV 2  is equal to one or the number ANZ of those which have assumed the maximum value MAXV 2  is equal to one or the number of those which have assumed the minimum value MINV 2  is equal to two, or the number of those cylinder-individual Lambda control factors LAM_FAC_I [Z 1  to Z 3 ], of which the amplitude AMP is greater than the amplitude threshold AMP_THR, is greater than zero.  
         [0071]     If the condition of step S 20  and thereby of the instability criterion is not fulfilled, processing is continued at step S 18 .  
         [0072]     The condition of step S 20  is based on the knowledge that, in the case of an instability of control for an odd number of cylinders, all cylinder-individual Lambda control factors LAM_FAC_I [Z 1  to Z 3 ] assume either a maximum value MAXV 2  or the minimum value M 1 NV 2  and in addition one part assumes the minimum value M 1 NV 2  and the other part assumes the maximum value MAXV 2 , with the number of those which assume the maximum value MAXV 2  only differing by one from the number which assume the minimum value MINV 2 . For an even number of cylinders in this case precisely one half of the cylinder individual Lambda control factors LAM_FAC_I [Z 1  to Z 3 ] are equal to the maximum value MAXV 2  and the other half are equal to the minimum value MINV 2 . Investigations have shown that especially with an add number of cylinders there is an instability of the control even if the amplitude AMP of the oscillation of the sequence of the respective cylinder-individual Lambda control factors LAM_FAC_I [Z 1  to Z 3 ] is greater than the predefined amplitude threshold AMP_THR, which preferably corresponds to around two thirds of the difference between the maximum value MAXV 2  and of the minimum value MINV 2 .  
         [0073]     If the condition of step S 20  is fulfilled, the predefined crankshaft angle CRK_SAMP is adapted in a step S 22  in accordance with step S 6 . After step S 22  the processing of the program is continued at step S 18 .  
         [0074]     A further embodiment of the program for adapting the detection of the measuring signal of the waste gas probe  41  is described below with reference to  FIG. 5 , with only the differences from the embodiment in accordance with  FIG. 4  being explained. The program is started in a step S 30 . Subsequently a step S 32  is processed, which is like step S 12 . By contrast with step S 12 , the time sequences of the first estimated value EST 1  [Z 1  to Z 3 ] in each case of the controller assigned to the relevant cylinder Z 1  to Z 4  are investigated as to whether, for the predefined period, they assume the maximum value MAXV 1  or minimum value MINV 1  or whether their timing oscillates with an amplitude AMP which is greater than the amplitude threshold AMP_THR.  
         [0075]     Alternatively in step S 32 , instead of the respective first estimated value EST 1 , the first estimated value EST 1  filtered by means of the block B 4  can be investigated.  
         [0076]     The steps S 34  and S 40  correspond to the steps S 14  or S 20  respectively with the proviso that here the conditions, instead of being in relation to the cylinder-individual Lambda control factors LAM_FAC_I [Z 1  to Z 3 ], are in relation to the respective first estimated values EST 1  [Z 1  to Z 3 ]. Steps S 36 , S 38  and S 42  correspond to steps S 16 , S 18  and S 22 .