EP1336728B1 - Method and device for regulating the air/fuel ratio of an internal combustion engine - Google Patents

Description

State of the art

The invention relates to a method for controlling the fuel / air ratio of a combustion process, which is operated alternately with excess air and lack of air, with at least one catalyst volume in the exhaust gas of the combustion process, which stores oxygen at excess oxygen in the exhaust gas and releases it in an oxygen deficiency, in which method determining the oxygen inputs into the catalyst volume and the oxygen discharges resulting from air deficiency from the catalyst volume and controlling the fuel / air ratio such that the sum of the oxygen inputs and oxygen discharges determined in a predetermined interval assumes a predetermined value. The invention further relates to an electronic control device for carrying out the method. Such a method and such a device are known from DE 40 01 616 C2 and the WO 01/61165 A1 known.

In general, the invention relates to the regulation of the fuel / air ratio or the air ratio lambda of a combustion process. Lambda is known to be the ratio of the actual combustion process amount of air to the amount of air required for a stoichiometric combustion of a certain amount of fuel. Combustion process exhaust gases are often passed through a catalyst to convert exhaust gas constituents such as nitrogen oxides (NOx), unburned hydrocarbons (HC) and carbon monoxide (CO) into nitrogen, water and carbon dioxide. For example, three-way catalysts are used for exhaust gas purification in automobiles.

Optimum conversion efficiency, which is characterized by a minimum of NOx, HC and CO downstream of the catalyst at defined inputs of NOx, HC and CO into the catalyst, requires the most accurate adjustment of a desired air / fuel ratio for the combustion process. This can also include the most precise possible setting of a desired temporal behavior, for example a periodic fluctuation of lambda about a mean desired value.

With regard to the optimized conversion of catalytic converter systems in motor vehicles, various approaches are known which ensure the optimal pollutant operation with an exhaust gas probe behind a catalytic converter. Nernst probes are used in the first place. A Nernst probe is understood to be the known oxygen-sensitive exhaust gas sensor whose characteristic curve above the mixture composition in the thermodynamic equilibrium in the region of the stoichiometric mixture composition has a steep transition between a low (about 100 mV) and a high (about 900 mV) signal level.

Here, methods are known, which can be summarized under the generic term two-step control. In this case, the term of the two-step control comprises a control in which an actual value of the probe signal, which corresponds to an actual oxygen concentration in the exhaust gas and thus a specific lambda actual value, is compared with a desired value and depending on the sign of the deviation enrichment or emaciation of the fuel / air ratio is generated. This regulation is characterized by the fact that, so to speak, only the sign, but not the amount of deviation is processed by a control algorithm.

Conceptually, two-point controls are applied both to two-point probes in front of a catalyst and behind a catalyst. These methods have in common that they respond to the said steep transition of the probe signal with a sudden change in the manipulated variable, for example, an injection pulse width. The sudden adjustment is followed by an approximately continuous change of the manipulated variable whose time course corresponds to a ramp (linear). The lambda value of the optimal pollutant conversion in the catalytic converter does not exactly correspond to the lambda value of the steep change in the Nernst probe signal. Nevertheless, in order to be able to set the optimal lambda value for the catalyst with the Nernst probe, a different and thus asymmetrical jump height, a jump following a jump and an asymmetrical ramp with respect to the jump direction or a predetermined delay time between a probe signal change and a manipulated variable change can be used become. As a result, the mean value of the time profile of the manipulated variable is shifted so that the catalyst in its optimal Operating point is operated. This is usually easy on the fat side, since in particular a safety margin is avoided with respect to the lean side critical with regard to undesired NOx emissions. This type of two-step control is often based on the signal of an exhaust gas sensor located in front of the catalytic converter. The oscillation in the oxygen content of the exhaust gas, which occurs during a jump-ramp control, is averaged out by the catalyst, provided that it is functional. This averaging results from the fact that the catalyst stores the oxygen excess from the exhaust gas during the half wave of oscillation with oxygen excess and emits the stored oxygen back to the exhaust gas in the half-wave of the oscillation with lack of oxygen. In this case, an exhaust gas probe arranged behind the (sufficiently large) catalytic converter registers the mean value of the oscillation. Since the upstream catalyst protects the rear probe from excessive temperature fluctuations and also promotes the adjustment of the thermodynamic equilibrium of the exhaust components, the signal of the rear probe is less affected by temperature influences and cross sensitivity of the exhaust probe. Cross-sensitivity is understood as meaning an undesired shift of the probe characteristic above the oxygen content of the exhaust gas in the presence of other exhaust gas constituents. The rear probe therefore measures more accurately and can be effectively used to guide the front probe. For example, if the front probe is adjusting to an incorrect setpoint due to a characteristic shift, it will be detected by the rear exhaust probe signal and the front probe loop reference will be corrected accordingly.

Furthermore, so-called continuous methods are known. These do not use the steep change of the Nernstsondensignals, but, for example, the relatively linear course of the pump current above the lambda value in a broadband probe. These methods not only use the sign, but also the amount of deviation of an actual value from a setpoint. Again, make sure that the catalyst is operated with a slightly rich mixture. Since smaller probe signal changes are utilized in these methods, cross sensitivities, temperature sensitivities and aging-specific shifts of pollutant dependencies have a comparatively strong effect.

Another group of processes is based on an optimized catalyst filling strategy. The methods of this group balance the registered components and try to compensate for a false balance before it is measured on the arranged behind a certain catalyst volume probe. The Nernst probe is also operated here in your fat branch and compensates only for a false balance zero. The above DE 40 01 616 A1 shows such a method for controlling the air-fuel ratio of a combustion process, which is operated alternately with excess air and lack of air. A catalyst volume in the exhaust gas of the combustion process stores oxygen in excess of oxygen in the exhaust gas and releases it again in the event of a lack of oxygen. In this known method, the oxygen excesses taking place in the excess of air into the catalyst volume and the oxygen discharges resulting from lack of air from the catalyst volume are determined with the aid of a Nernst probe arranged upstream of the catalytic converter and the fuel / air ratio is controlled so that the sum the determined in a predetermined interval oxygen inputs and Sauerstoffausträge assumes a predetermined value.

It has been found that the future legislative requirements, for example the SULEV claims (S uper U ltra L ow E mission V ehicle) from the United States further improvements in the known control strategies with a view to an optimized catalyst operating in conjunction with a further increase in robustness and Require control speed.

This requirement is based on the from the DE 40 01 616 known method characterized in that the combustion process is operated in each case at least as long as oxygen excess or lack of oxygen until it occurs at an oxygen-sensitive Nernst probe behind the catalyst volume. In a modification of the known method, no exhaust gas probe in front of the catalyst is required in one embodiment of the invention. In another embodiment, a broadband probe is used in front of the catalyst instead of the prior art Nernst probe.

The inventive method allows the required optimized catalyst operation and thereby improves the above-mentioned methods in terms of robustness and control speed decisively in operating points in which the above methods do not have sufficient robustness or in which these methods are affected by cross-sensitivities. This improvement results from the fact that the invention contains sub-aspects of the methods described above, and these are supplemented by shares, which cause a substantial increase in robustness.

The method of the invention utilizes the two-point characteristic of a Nernst probe downstream of the catalyst in conjunction with balancing, i. consideration of oxygen input and oxygen emissions related to the catalyst.

Due to the conservation of mass, these entries and discharges must be the same in the mixture control according to the invention. If this method were used in its simplest form and neglected nonlinearities, then a jump probe voltage of 450 mV would be set behind a the jump probe subsequent catalyst volume (due to asymmetries may here also set a deviating from 450mV voltage). However, this generally does not correspond to optimized catalyst operation.

To ensure the optimized operation, a controlling part is connected to the regulating part. This part is based on a balance sheet optimum for the catalyst operation. Due to the necessary balance sheet optimization of the regulatory phase, an additional amount required with regard to the balance sheet zero point is determined. Based on the zero point of the balance, a controlled proportion of fat or lean is attached to the flanks fat-lean or lean-fat of the jumping probe. This proportion should be calculated in such a way that a maximum pollutant level is established behind an overall catalytic system.

A development of the invention therefore provides that the change between oxygen excess and lack of oxygen is controlled in the operation of the internal combustion engine so that the difference between the oxygen excesses occurring in excess of air in the catalyst volume and the taking place in the absence of air oxygen discharges from the catalyst volume assumes a predetermined value.

A further embodiment provides that a quantity is used to determine the taking place at excess oxygen in the catalyst volume and the taking place in lack of air oxygen discharges from the catalyst volume, which at least co-determines the fuel flow to the engine.

According to another embodiment, said quantity is formed on the basis of an intake air amount calculated from measured quantities and on the basis of an amount of fuel added to this amount of intake air.

According to an alternative preferred embodiment, said size is formed as a function of the signal of an exhaust gas probe arranged in front of the catalyst volume.

A further embodiment provides that the said variable is an input variable for a second control loop in which the air-fuel ratio is regulated with a smaller time constant compared to the first control loop.

Another embodiment is characterized in that the formation of said size is changed when the oxygen inputs and Sauerstoffausträge differ from each other.

According to a development of this embodiment, the change takes place so that said deviation becomes smaller.

According to a preferred embodiment of this development, the change is formed as a function of the integral of said deviation.

According to a further embodiment, the fuel / air ratio is predetermined by a superimposed control loop.

A further embodiment provides that the values of the specific oxygen inputs and oxygen emissions are used to determine a real zero value between oxygen excess and oxygen deficiency.

In a further embodiment, the invention can also be understood as a method for controlling the fuel / air ratio of a combustion process with a lambda probe behind a partial catalyst volume, wherein the lambda probe indicates when the degree of filling of the partial catalyst volume with oxygen exceeds a first predetermined value, or falls below a second predetermined value. If the value falls below the second predetermined value, the fuel / air ratio is defined on average defined leaner (fuel-poor). If the second predetermined value is exceeded as a result, the amount is enriched accordingly on average. This results in a characteristic for the operating point of the combustion process and the catalyst frequency of the emaciation and Anfettungen. In an internal combustion engine, an operating point is defined, for example, by a specific value of the combustion chamber charge at a certain speed. In addition, the oxygen input and the oxygen discharge is accounted for. The fuel metering in such a way that the balance of the oxygen inputs and the oxygen discharges averages over a period (an oxygen contribution and an oxygen discharge) to a predetermined value, preferably the value zero, which corresponds to a defined average lambda value. By a defined delay of the change between medium fat and lean fuel / air mixture, any average lambda value can be set because each delay to some extent an additional entry of oxygen (in delayed change to rich mixture) or discharge of oxygen (with a delayed change to lean mixture) causes. The defined delay is preferably such that the resulting additional entry or additional discharge with respect to a period corresponds to a predetermined value. The invention also relates to a control device, preferably an electronic control device for carrying out at least one of the above-mentioned methods, developments and embodiments.

In the following, embodiments of the invention will be explained with reference to the figures.

Fig. 1 shows the structure of a first technical environment in which the invention has its effect.

Fig. 2 discloses an embodiment of the invention related to this structure in the form of a functional block diagram.

The 3 and 4 show waveforms to illustrate the effect of said embodiment.

Fig. 5 shows the structure of a second technical environment for the application of the invention.

Fig. 6 discloses a related embodiment of the invention in functional block representation.

Fig. 7 discloses the structure of a preferred technical environment of the invention for meeting the above SULEV requirements.

Fig. 8 shows a corresponding embodiment of the invention in functional block diagram.

The FIGS. 9 to 13 represent time courses of signals to illustrate the effect of the invention in the context of the preferred technical environment.

description

The numeral 10 in the FIG. 1 denotes an internal combustion engine that burns a mixture of fuel and air in a combustion process. The amount or mass of the air flowing to the combustion process is detected by an air flow meter 14. The signal of the air flow meter 14 is supplied to an electronic control device 18. The electronic control unit 18 calculates therefrom and optionally from further operating parameters of the combustion process a fuel metering signal with which a fuel metering means 16 is actuated. In the presentation of the FIG. 1 For example, the fuel metering means 16, for example an injection valve or an arrangement of injection valves, is arranged in a suction pipe 12 of the internal combustion engine. In this case, the mixture formation, that is the Mixing of sucked air and metered fuel in the intake manifold instead. Alternatively, however, the mixture formation can also take place directly in the combustion chambers of the internal combustion engine, as is known from the diesel engine and the petrol engine with gasoline direct injection. The exhaust gases of the combustion process in the internal combustion engine are passed through an exhaust pipe 20 to a catalyst volume 22. An exhaust gas probe 24 arranged upstream of the catalyst volume 22 preferably detects the oxygen concentration in the exhaust gas between the combustion process and the catalyst volume 22. In addition, the exhaust gas probe 24 is also referred to as a pre-sample probe 24. Another exhaust gas probe is arranged behind the catalyst volume 22. This exhaust gas probe is preferably a so-called Nernst probe 26, while the Vorkatsonde 24 is preferably realized as a broadband probe. An embodiment of a Nernst probe 26 is the Automotive Handbook, 22nd edition, VDI-Verlag Dusseldorf, ISBN 3-18-419122-2 (Automotive Handbook 4 ^th Edition, SAE Society of Automotive Engineers, USA, ISBN 1-56091-918-3 , page 491 (491), on page 492 (492) of the same book also discloses a broadband probe as an embodiment of precursor probe 24. Broadband probe 24 has a metering gap connected to the exhaust via a gas inlet port. The measuring gap is further provided with an electrochemical pumping cell, with which oxygen can be pumped out of the measuring gap or into the measuring gap An electronic circuit regulates the voltage applied to the pumping cell such that the composition of the gas in the measuring gap remains constant at lambda = 1 The pumping current Isvk required for this purpose provides a measure of the oxygen content of the exhaust gas, in other words, the broadband probe supplies a current si gnal I S V onde- or- K at. In contrast, the Nernst 26 provides a voltage signal U S onde- H inter- K at. The signals of the two exhaust gas probes 24 and 26 are also supplied to the electronic control device 18 and additionally influence the fuel metering. The internal combustion engine 10 effectively represents a controlled system as part of a first control circuit of internal combustion engine 10, exhaust gas probe 24, electronic control device 18 and fuel metering device 16. An oxygen deficiency in the exhaust gas is registered by the exhaust gas probe 24 and leads through a corresponding processing by a control algorithm in the electronic control device 18 to increase the injection pulse width, with which the fuel metering means 16 is driven. This control loop is superimposed on a further control loop, which is based on the signal of the Nernst probe 26. The interaction of the two control circuits according to the invention is described below with a view to the structure of FIG. 2 explained. The dashed line 27 in the FIG. 2 separates the functional structure designated by the numeral 18 of the electronic control device according to the invention of the other components of the structure of FIG. 1 , in particular of the internal combustion engine 10, the Vorkatsonde 24, the catalyst volume 22 and the Nernstsonde 26. The numeral 28 denotes a map, which is addressed for example by input variables such as the measured air quantity and the engine speed and the base pulse width t_Basis as the output value for the Fuel metering supplies. This output value is linked in the rule link 30 with a control factor fr from a first controller 34. The result of this combination determines, as the injection pulse width ti, the amount of fuel that is supplied to the combustion process in the internal combustion engine 10. From the combustion process results in a certain concentration of oxygen in the exhaust gas, which in Signal Ushk of the Nernst probe 26 images. This signal Ushk of the Nernst probe 26 is fed to a two-point controller 36. This two-point controller 36 represents a true two-point controller in the classical sense, in which the manipulated variable can only correspond to one of two values. In the case of the controller 36, the signal Ushk of the exhaust gas probe 26 is compared with a threshold of, for example, 450 millivolts. If there is an excess of oxygen behind the catalyst 22, the signal Ushk has an order of magnitude of approximately 100 millivolts. In this case, the two-position controller 36 enriches, for example by outputting a factor of 1.02, with which the manipulated variable formed in the first controller is multiplied, which ultimately leads to an increase in the injection pulse width and thus to an enrichment of the mixture. If, on the other hand, there is a lack of oxygen behind the catalyst volume 22, the signal Ushk has an order of magnitude of approximately 900 millivolts, and the two-position regulator 36 accordingly empties, for example by outputting a factor of 0.98. This factor 0.98 reduces in the first controller 34, the manipulated variable fr, which ultimately leads to a shortening of the injection pulse widths ti and thus to an emaciation. The Nernst probe 26 thus forms in conjunction with the two-point controller 36 and the other controlled system (34, 30, 10, 24, 22) a second control loop. This second control circuit ensures that the catalyst volume 22 is filled with an average-lean mixture when the probe indicates oxygen deficiency behind the catalyst volume 22. This lean mixture ensures that the Nernst probe 26 eventually displays oxygen excess behind the catalyst volume 22. If this happens, the catalyst volume 22 is then filled with an average-rich mixture (oxygen deficiency = reducing agent entry) and the signal of Nernst probe 26 eventually jumps back to 900 millivolts.

Thus, the two-point control algorithm fills and deflates the catalyst volume 22 again and again. Since the oxygen storage can only deliver the amount of oxygen that it has previously stored, the real oxygen excess and oxygen deficiency levels must be equal. In other words, the oxygen introduced into the catalyst volume 22 in oxygen excess phases corresponds in its quantity to the oxygen discharged from the catalyst volume 22 in the absence of oxygen. According to the invention, these two quantities are detected by measurement using equal amounts and used to correct the first control loop. For this purpose, the FIG. 2 the structure 38, 40, 42, 44, 46 and 32 on. In this case, the numeral 38 denotes a trigger signal path with which a signal integrator 40 is set to zero and triggered. The signal integrator 40 is supplied in parallel to the trigger signal 38, the signal Isvk the Vorkatsonde 24, and a corrected signal Isvk_korr the Vorkatsonde 24. This signal integrator is wired and designed to integrate only the excess oxygen part of the Isvk signal. The integration is triggered when the two-position controller 36 outputs a leaning signal and it is stopped when the two-position controller 36 switches to enriching mixture. The final value of the oxygen storage integrator 40 thus provides a measure of the oxygen storage capacity (OSC). Analogously, in oxygen deficiency phases, integrator 42 calculates a negative oxygen deficiency an oxygen output -OSC.

In the difference link 44, the output signals of the integrators 40 and 42 are subtracted from each other. Since they must be physically the same by definition, a nonzero result of the difference linkage 44 in a sense a calculation error. In the context of this invention, it is assumed that such a calculation error is based on a characteristic shift of the signal Isvk of the precursor probe 24. A characteristic shift has the consequence, for example, already fat mixture signaled, although still present in real lean mixture. As a result, the value of the MINUS_OSC integrator 42 will be greater than the value of the OSC integrator 40. The difference in both values is applied to an integrator 46 whose output signal corrects the signal Isvk of the pre-sample probe 24 via an offset correction link 32. As a result, the shifted characteristic is effectively compensated so that the values of the OSC integrator 40 and of the MINUS_OSC integrator 42 are equal again after the correction has settled. These connections are made by the FIG. 3 in conjunction with the FIG. 4 further clarified. The number 52 in the FIG. 3 denotes a first time range in which the offset correction has not yet settled. By contrast, the numeral 54 in the FIG. 3 a second time range in which the offset correction has settled. Overall, the shows FIG. 3 the time course of the signal Isvk over time t. The dashed line 48 marks the (false) zero measurement value of the pre-sample probe 24. The zero value, that is, the value that separates oxygen excess from the oxygen deficiency, is of fundamental importance for the formation of said OSC and MINUS_OSC amounts. This "zero value" between oxygen excess and oxygen deficiency is provided by a probe in front of the catalyst or a stored value is used, for example an injection time assuming a stoichiometric mixture composition. This zero value can be incorrect. According to the invention, the excess oxygen or oxygen deficiency quantities based on this - possibly faulty zero value. The relative deviation from the assumed zero value is known. With the measured amount of air can be determined from the absolute value for the oxygen input or oxygen discharge. Since the oxygen storage can only deliver the amount of oxygen that it has previously stored, the real oxygen excess and oxygen deficiency levels must be equal. If the calculated quantities are not equal, this can only be because the assumed zero value does not correspond to the real zero value, so that, for example, in the calculation a real entry was evaluated as a discharge. Subsequently, the assumed zero value is changed in the direction of the larger amount. That is, if in the previous calculation, the oxygen excess amount was larger than the oxygen deficiency amount, the zero value is shifted toward oxygen excess. Starting from this new zero value, the same amounts are enriched and emaciated again. This procedure is repeated until the said calculated quantities are the same. The associated zero value corresponds to the real zero value. In other words, the values of the specific oxygen inputs and oxygen emissions are used to determine a real zero value between oxygen excess and oxygen deficiency.
This can be used to correct either a front probe or a pilot zero value. This procedure is described with continuing reference to Fig. 3 further explained. The dashed line 50 indicates the real zero value. In the broadband probe, the low signal level corresponds to a rich mixture, ie an oxygen deficiency, and the high signal level corresponds to a lean mixture, ie oxygen excess. The hatched area 64 represents the integral of an oxygen excess period over the real one The hatched area 66 correspondingly represents the integral of an oxygen deficiency period above the real zero value 50. Both areas are equal because the switching between rich and lean mixture is performed by the accurately measuring Nernst probe 26 behind the catalyst volume 22. The hatched area 68 corresponds to the integral over the (false) zero value of the exhaust gas probe 24 during an oxygen excess period, and the area 70 corresponds to the integral of an oxygen deficiency above the false zero during an oxygen deficiency period. The surfaces 68 and 70 are metrologically detected by the integrators 40 and 42, respectively. It can be clearly seen that in the non-steady state, the OSC value (68) deviates greatly from the MINUS_OSC value (70). The second time range (54), however, shows the steady state. As a result of the integration in block 46 and the engagement in the offset correction link 32, the signal Isvk is shifted down so that the zero measurement line 48 coincides with the real zero line 50. The signal in the second time range 54 thus reflects the course of the corrected signal Isvk_korr again. As can be seen from the drawing, in this case the OSC quantities (72) and MINUS_OSC quantities (74) are the same. In the FIG. 4 is that to the waveform of the FIG. 3 corresponding signal Ushk the Nernst probe 26 shown. The signal Isvk effectively indicates the oxygen concentration in front of the catalyst and the signal Ushk effectively indicates the oxygen concentration behind the catalyst. From the comparison of FIG. 3 and FIG. 4 It can be seen that as long as the oxygen excess (lean mixture) is generated before the catalyst as the rear exhaust gas probe 26 detects oxygen deficiency. Conversely, oxygen deficiency (rich mixture) is produced in front of the catalyst as long as that behind the catalyst arranged exhaust gas probe 26 indicates lean mixture. The rear exhaust gas probe measures the principle of the transition from rich to lean mixture and vice versa very precisely, since it has there the steep signal level change between 900 and 100 millivolts. It also measures very precisely because the upstream catalyst 22 protects the exhaust gas probe 26 from major temperature fluctuations and also brings the exhaust gas components into thermodynamic equilibrium.

In other words, it is a total system that accounts for the balance, which is based on the leap of the lambda probe behind a partial catalyst volume. With regard to the two-step control is evaluated on the basis of symmetry thoughts as well as robustness aspects after a period (possible even after half-period) which 02 amount in the catalyst and was discharged. Due to the balance, these areas must be the same. If an imbalance results, the offset (the probe characteristic) before the catalyst is adjusted so that the balance is met again. If, due to gas runtimes, there is a delayed system reaction due to the jump of the probe, this proportion can also be taken into account in the balancing. If, in this method, an abrupt error occurs which is greater than the amplitude fluctuation of the oxygen concentration, the control will no longer be able to work. Therefore, it is decided according to a maximum criterion that a critical time is exceeded and then the offset is adjusted until it comes back to a probe jump.

The FIG. 5 shows a modification of the structure of FIG. 1 , In contrast to FIG. 1 is in the structure of FIG. 5 no Vorkatsonde 24 provided. The structure of FIG. 6 discloses an embodiment of the invention without Vorkatsonde 24. Again, the injection pulse widths ti determine the amount of fuel that is attributed to the internal combustion engine 10 to match the measured amount of air. The Nernst probe 26 arranged behind the catalyst volume 22 again supplies the voltage signal Ushk to the two-position controller 36. The two-position controller 36 modulates basic pulse widths t_basis supplied by a multiplicative link 30 from a pilot control map 28. It extends these basic pulse widths by, for example, outputting an enriching factor of 1.02 in the case of a lean mixture behind the catalyst volume 22. Likewise, in the absence of oxygen, it leaches behind the catalyst volume 22 by emitting a factor of 0.98. The injection pulse widths ti are also supplied to a differential link 58, which are additionally supplied to comparison pulse widths ti_L1. The ti_L1 values represent to some extent assumed zero values in the sense that ti> ti_L1 assumes a rich mixture and ti_L1> ti a lean mixture. Analogous to the explanation of FIG. 2 Here, too, the integrator 40 provides a measure of the oxygen storage capacity of the catalyst volume and the integrator 42 provides a measure of the reducing agent storage capacity of the catalyst. Again, the difference of both values in the difference link 44 is formed and integrated in the integrator 46. The integrator output acts on the injection times via the offset correction link 32. The mode of action of the structure after the FIGS. 5 and 6 This corresponds largely to the effect of the structures after the Figures 1 and 2 , The FIG. 3 can also be seen on the structure of FIG. 5 and FIG. 6 read. This is in the FIG. 3 only to replace the value Isvk by the injection time ti. The zero line 48 corresponds in the case of FIG. 6 then a value ti_L1. If this value ti_L1 does not deliver the true Lambdal value, the results in the first Time range 52 of the FIG. 3 represented conditions. The settling of the correction then results in the ratios shown in the second time range 54. In other words: by the offset correction, the injection times ti are evenly shortened to the extent that the desired symmetrical oscillation results around the real lambda = 1 value. The structure of FIGS. 5 and 6 owns over the structure of the FIG. 1 and FIG. 2 the big advantage that a Vorkatsonde 24 can be saved.

The structure of FIGS. 7 and 8 represents a presently preferred embodiment. This embodiment differs from the subject of Figures 1 and 2 by a main catalyst volume 60 behind the Nernst probe 26 and by another Nernst probe 62 behind the main catalyst volume 60. Basically, the main catalyst volume 60 has the function of compensating for the oscillation in the oxygen content of the exhaust gas behind the partial catalyst volume 22 that inevitably occurs in this control concept. Since optimum medium-duty operation is desired for optimum catalyst operation, the structure described hitherto must be extended by a component which provides this desired fat shift or, in other cases, optionally a desired lean shift. This is done in the context of this preferred embodiment further Nernst 62. Their signal UsnHK (U - s onde n ACh H aupt- K at) acts on a delay timer 63, the signal transitions in the output of the two-point controller 36 is delayed to the first controller 34 passes , This results in the FIGS. 9 to 13 displayed desired signal behavior. The FIGS. 9 and 10 show the previously explained signals Ushk and Isvk in the steady state. The FIG. 11 shows the course of the signal Ushk in the context of this embodiment. From the FIG. 12 is It can be seen that a change from lean to rich in the signal Ushk is only delayed by a delay period tv to the controller 34, which is shown in the time course of the Isvk signal. The hatched areas 76 thus represent a desired additional MINUS_OSCE entry into the catalyst volumes, which ultimately results in the FIG. 13 shown, relatively even in the rich area above 450 millivolts extending signal of the other Nernst probe 62 shows.

Claims (13)

1. Method for regulating the fuel/air ratio of a combustion process which is operated alternately with an excess of air and a deficiency of air, and having at least one catalytic converter volume in the exhaust gas of the combustion process, which catalytic converter stores oxygen when there is an excess of oxygen in the exhaust gas and releases oxygen when there is a deficiency of oxygen, in which method the oxygen admissions into the catalytic converter volume occurring when there is an excess of air and the oxygen discharges from the catalytic converter volume occurring when there is a deficiency of air are determined, and in which method the fuel/air ratio is adjusted in a first regulating loop such that the sum of the oxygen admissions and oxygen discharges determined in a predetermined interval assumes a predetermined value,
   characterized in that the combustion process is operated in each case on average with an excess of oxygen or a deficiency of oxygen at least until said excess of oxygen or deficiency of oxygen arises at an oxygen-sensitive Nernst cell downstream of the catalytic converter volume, wherein the Nernst cell forms a second regulating circuit in conjunction with a two-position regulator and the rest of the regulating path.
2. Method according to Claim 1, characterized in that the predetermined interval extends over a period in which the combustion process is operated once on average with an excess of oxygen and once on average with a deficiency of oxygen.
3. Method according to Claim 1, characterized in that the change between an excess of oxygen and a deficiency of oxygen during the operation of the internal combustion engine is controlled such that the difference between the oxygen admissions into the catalytic converter volume occurring when there is an excess of air and the oxygen discharges from the catalytic converter volume occurring when there is a deficiency of air assumes a predetermined value.
4. Method according to Claim 1, 2 or 3, characterized in that, to determine the oxygen admissions into the catalytic converter volume occurring when there is an excess of air and the oxygen discharges from the catalytic converter volume occurring when there is a deficiency of air, a parameter is used which at least co-determines the inflow of fuel to the internal combustion engine.
5. Method according to Claim 4, characterized in that the stated parameter is formed on the basis of an intake air quantity calculated from measurement values, and on the basis of a fuel quantity metered to said intake air quantity.
6. Method according to Claim 4, characterized in that the stated parameter is formed as a function of the signal of an exhaust-gas probe arranged upstream of the catalytic converter, which will be referred to hereinafter as pre-cat probe.
7. Method according to Claim 6, characterized in that the stated parameter is an input parameter for a second regulating loop in which the fuel/air ratio is regulated with a smaller time constant than the first regulating circuit.
8. Method according to one of Claims 5 to 7, characterized in that the formation of the stated parameter is varied if the oxygen admissions and oxygen discharges deviate from one another.
9. Method according to Claim 8, characterized in that the variation takes place such that the stated deviation becomes smaller.
10. Method according to Claim 9, characterized in that the variation is formed as a function of the integral of the stated deviation.
11. Method according to Claim 1, characterized in that the fuel/air ratio is predefined by a superposed regulating circuit (24, 18, 16, 10).
12. Method according to Claim 3 or 4, characterized in that the values of the determined oxygen admissions and oxygen discharges are utilized to determine a real zero value between an excess of oxygen and a deficiency of oxygen.
13. Control device having means for carrying out at least one of the methods according to Claims 1 to 10.

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