EP1336728A2 - Method and device for regulating the air/fuel ratio of an internal combustion engine - Google Patents

Abstract

In an internal combustion engine (ICE) (10), an airflow sensor (14) signals to an electronic controller (18) to calculate a fuel proportion signal and trigger a fuel apportioning device (16) in an ICE intake pipe (12). Oxygen introduced/emitted in a preset time assumes a preset value so that combustion operates with rich/lean oxygen mixtures until an oxygen-sensitive Nernst sensor is triggered. An Independent claim is also included for a control device for carrying out the method of the present invention.

Description

State of the art

The invention relates to a method for controlling the Fuel / air ratio of a combustion process, which operated alternately with excess air and lack of air is, with at least one catalyst volume in the exhaust gas of the Combustion process that occurs when there is an excess of oxygen in the exhaust gas Stores oxygen and releases it when there is a lack of oxygen, in which procedure the ones that take place with excess air Oxygen inputs into the catalyst volume and at A lack of air discharges oxygen from the Catalyst volume can be determined and at which the Air / fuel ratio is controlled so that the sum that determined at a predetermined interval Oxygen inputs and oxygen discharges assumes a predetermined value. The invention further relates an electronic control device for performing the Process. Such a procedure and one Devices are known from DE 40 01 616 C2.

In general, the invention relates to the regulation of Air / fuel ratio or air ratio Lambda of a combustion process. Lambda is known to exist the ratio of actually in the combustion process air volume involved to the air volume that for a stoichiometric combustion of a particular one Amount of fuel is required. Exhaust gases from Combustion processes are often catalyzed led to exhaust gas components such as nitrogen oxides (NOx), unburned hydrocarbons (HC) and carbon monoxide (CO) convert to nitrogen, water and carbon dioxide. To the Examples are three-way catalysts for exhaust gas purification Motor vehicles used.

An optimal conversion efficiency, which at defined entries of NOx, HC and CO in the catalyst by a minimum of NOx, HC and CO behind the catalytic converter is characterized as precise as possible Setting a desired fuel / air ratio for the combustion process. This can also be the most possible precise setting of a desired temporal behavior include, for example, a periodic variation in Lambda around an average setpoint.

Regarding the optimized conversion of Catalytic converter systems in motor vehicles are different Approaches known with an exhaust gas probe behind a Catalyst whose pollution-free operation guarantee. In the first place, Nernst probes are used used. The well-known is here under a Nernst probe understood oxygen-sensitive exhaust gas sensor, its Characteristic curve of the mixture composition in the thermodynamic equilibrium in the area of stoichiometric mixture composition a steep Transition between a low (approx. 100 mV) and a high (approx. 900 mV) signal level.

Here, methods are known which are under the generic term Two-point control can be summarized. there the concept of two-point control includes a regulation at which is an actual value of the probe signal, that of an actual oxygen concentration in the exhaust gas and thus a certain one Corresponds to the actual lambda value, compared with a setpoint and in which, depending on the sign of the deviation, a An increase in fat or an emaciation of the Air / fuel ratio is generated. This regulation is characterized by the fact that only that Sign, but not the amount of deviation by one Control algorithm is processed.

Conceptually, two-point regulations are used both with regard to Two-point probes in front of a catalytic converter and behind one Catalyst applied. These procedures have in common that with the steep transition of the probe signal a sudden change in the manipulated variable, for example respond to an injection pulse width. The leaping Adjustment follows an approximately constant change the manipulated variable, the time course of a ramp (linear) corresponds. The lambda value of the optimal Pollutant conversion in the catalytic converter does not correspond exactly the lambda value of the steep change in Nernstsondensignals. To nevertheless with the Nernst probe set the optimal lambda value for the catalytic converter can, depending on the direction of the sign change different and thus asymmetrical jump height, one following a jump and regarding the jump direction unbalanced ramp or a predetermined delay time between a probe signal change and one Manipulated variable change can be used. This will make the Average value of the manipulated variable over time shifted that the catalyst in its optimal Operating point is operated. This is usually easy the fat side, since this is especially a Safety distance from that with regard to unwanted NOx emissions more critical lean side is avoided. This The type of two-point control is often based on the Signals from an exhaust gas probe arranged in front of the catalytic converter. The vibration that occurs with a jump ramp control in the oxygen content of the exhaust gas is due to the catalyst, if this is functional, averaged. This Averaging results from the fact that the catalyst during the half-wave of vibration with an excess of oxygen Excess oxygen from the exhaust gas stores and the stored oxygen in the half wave of the vibration with Lack of oxygen returns to the exhaust gas. One behind the (Sufficiently large) catalytic converter arranged exhaust gas probe in this case registers the mean value of the vibration. There the upstream catalyst precedes the rear probe protects excessive temperature fluctuations and also the Setting the thermodynamic equilibrium Conveying exhaust gas components is the signal from the rear probe less due to temperature influences and cross-sensitivities affects the exhaust gas probe. One understands one Cross sensitivity an undesirable shift in the Probe characteristic curve over the oxygen content of the exhaust gas in Presence of other exhaust gas components. The rear one The probe therefore measures more precisely and can be used as a guide the front probe. If, for example the front probe due to a shift in the characteristic regulates an incorrect setpoint, this is done via the Rear exhaust probe signal detected and setpoint for the control loop of the front probe is made accordingly corrected.

So-called continuous processes are also known. This don't take advantage of the steep change in the Nernst probe signal, but for example the comparatively linear course of the pump current over the lambda value for a broadband probe. These methods not only use the sign, but also also the amount of the deviation of an actual value from one Setpoint. It is also important to ensure that the Catalyst is operated with a slightly rich mixture. There with this method utilizes small changes in the probe signal cross-sensitivities, Temperature sensitivity and age-specific Comparative shifts in pollutant dependencies strong.

Another group of processes is based on an optimized one Filling strategy of the catalyst. The procedures of this group balance the entered components and try one Compensate for the imbalance before moving on to the one behind to measure certain catalyst volume arranged probe is. The Nernst probe is also in your fat branch here operated and is just like a wrong one Balance zero point. The above-mentioned DE 40 01 616 A1 shows such a method of regulating the fuel / air ratio of a combustion process that takes turns is operated with excess air and lack of air. On Catalyst volume in the exhaust gas of the combustion process stores oxygen in the exhaust gas if there is an excess of oxygen and releases it when there is a lack of oxygen. With this known methods are those that take place with excess air Oxygen inputs into the catalyst volume and at A lack of air discharges oxygen from the Catalyst volume using a pre-catalyst arranged Nernst probe determined and that The air / fuel ratio is controlled so that the sum that determined at a predetermined interval Oxygen inputs and oxygen discharges 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 DE 40 01 616 known method in that the Combustion process with at least as long Excess oxygen or lack of oxygen is operated, until it is connected to an oxygen sensitive Nernst probe occurs behind the catalyst volume. As a variation of the known method is in one embodiment Invention no exhaust probe upstream of the catalyst required. Another example is before Catalyst instead of the Nernst probe according to the prior art Technique uses a broadband probe.

The method according to the invention enables the required optimized catalyst operation while improving the above procedures mentioned regarding robustness and Control speed crucial in working points, in which the above methods do not have sufficient robustness have or in which these procedures by Cross-sensitivity can be impaired. This improvement results from the fact that the invention Contains partial aspects of the methods described above and this supplemented by shares, which is a significant increase of robustness.

The inventive method uses the Two-point characteristic of a Nernst probe behind the Catalyst in connection with a balancing, i.e. one Taking into account related to the catalyst Oxygen inputs and oxygen discharges.

Due to mass conservation, these entries and Discharge in the mixture control according to the invention the same his. Would this procedure in its simplest form applied and neglected nonlinearities, so would behind one of the jump probes Catalyst volume a step condensate voltage of 450mV adjust (due to asymmetries may also occur here set a voltage other than 450mV). This but does not correspond to one in the common opinion optimized catalyst operation.

In order to ensure optimized operation, the regulating part connected to a regulating part. This Part is based on a balance sheet optimum for the Catalyst operation. Because of the necessary Balance sheet optimization of the regulating phase becomes one regarding Balance zero point necessary additional quantity determined. Based at the zero point of the balance, fat-lean or Lean fat of the jump probe a controlled proportion of fat or Lean attached. This proportion is to be measured in such a way that behind an overall catalyst system, a pollutant optimum established.

A development of the invention therefore provides that the Alternation between excess oxygen and lack of oxygen is controlled during operation of the internal combustion engine so that the difference between the excess air Oxygen inputs into the catalyst volume and at A lack of air discharges oxygen from the Catalyst volume assumes a predetermined value.

Another embodiment provides that for determination the oxygen inputs into the air in excess Catalyst volume and that in the absence of air Oxygen discharges from the catalyst volume one size is used, the fuel flow to the internal combustion engine at least co-determined.

According to a further embodiment, the size mentioned on the basis of one calculated from measured variables Intake air quantity and based on one to this Intake air quantity formed fuel quantity.

According to an alternative preferred embodiment, the mentioned size depending on the signal one before Exhaust gas probe arranged catalyst volume formed.

Another embodiment provides that the aforementioned Size is an input value for a second control loop, in which the air / fuel ratio is compared with one smaller time constant is regulated for the first control loop.

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

According to a development of this embodiment, the Change so that the mentioned deviation becomes smaller.

According to a preferred embodiment of this training the change becomes a function of the integral of the mentioned deviation formed.

According to a further embodiment, the Air / fuel ratio through a superimposed Control loop specified.

Another embodiment provides that the values of the certain oxygen inputs and oxygen outputs used be between a real zero value Determine excess oxygen and lack of oxygen.

In a further embodiment, the invention can also as a method of controlling the air-fuel ratio a combustion process with a lambda sensor behind a partial catalyst volume can be understood, in which the Lambda sensor indicates when the degree of filling of the Partial catalyst volume with oxygen a first exceeds a predetermined value or a second falls below a predetermined value. When falling below the The second predetermined value is the air / fuel ratio defined leaner on average (less fuel) set. If the resulting excess is exceeded second predetermined value is correspondingly averaged defined greased. This results in one for the Operating point of the combustion process and the catalyst characteristic frequency of emaciation and enrichment. An internal combustion engine becomes an operating point for example by a certain value of Defined combustion chamber filling at a certain speed. in the further the oxygen entry and the Balance of oxygen discharge. The fuel metering takes place in such a way that the balance of the oxygen inputs and of oxygen discharges on average over a period (a Oxygen contribution and an oxygen discharge) predetermined value, preferably the value zero gives what corresponds to a defined mean lambda value. By a defined delay in switching between on average rich and lean fuel / air mixture can be Set any average lambda value since each Sort of delay an additional entry of Oxygen (if there is a delay in switching to a rich mixture) or Discharge of oxygen (with a delayed change to lean Mixture). The defined delay takes place preferably so that the resulting additional entry or Additional discharge based on a period a predetermined Value corresponds. The invention also relates to a Control device, preferably an electronic one Control device for carrying out at least one of the above specified procedures, further training and Embodiments.

The following are exemplary embodiments of the invention Explained with reference to the figures.

1 shows the structure of a first technical environment, in which the invention takes effect.

Fig. 2 discloses one related to this structure Embodiment of the invention in the form of a Function block diagram.

3 and 4 show waveforms for illustration the effect of the above embodiment.

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

Fig. 6 discloses an embodiment related thereto the invention in functional block diagram.

Fig. 7 discloses the structure of one for fulfilling the above. SULEV demands preferred technical environment of the Invention.

Fig. 8 shows a corresponding embodiment of the Invention in functional block representation.

Figures 9 to 13 represent temporal courses of signals to illustrate the effect of the invention in the context of preferred technical environment.

description

Numeral 10 in 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 recorded by an air flow meter 14. The signal from the air flow meter 14 is fed to an electronic control device 18. The electronic control device 18 calculates a fuel metering signal from this and, if appropriate, from further operating parameters of the combustion process, with which a fuel metering means 16 is activated. In the illustration in FIG. 1, the fuel metering means 16, for example an injection valve or an arrangement of injection valves, is arranged in an intake manifold 12 of the internal combustion engine. In this case, the mixture formation, that is, the mixing of the intake air and the metered fuel takes place in the intake manifold. Alternatively, 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 from the gasoline engine with direct petrol injection. The exhaust gases from 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 in front of the catalyst volume 22 preferably detects the oxygen concentration in the exhaust gas between the combustion process and the catalyst volume 22. In the further text, the exhaust gas probe 24 is also referred to as a pre-catalyst 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 pre-cat probe 24 is preferably implemented 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 , on page 491 (491) On the following page 492 (492) of the same book, a broadband probe is also disclosed as an exemplary embodiment of the pre-cat probe 24. The broadband probe 24 has a measuring gap which is connected to the exhaust gas via a gas inlet opening. The measuring gap is further equipped with an electrochemical pump 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 pump cell so that the composition of the gas in the measuring gap is constant at Lambda = 1 The pump current Isvk required for this 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 sensors 24 and 26 of the electronic control means 18 are also supplied to and influence the additional fuel metering. The internal combustion engine 10 effectively represents a controlled system as a component of a first control circuit comprising the internal combustion engine 10, the exhaust gas probe 24, the electronic control device 18 and the fuel metering device 16. A lack of oxygen in the exhaust gas is registered by the exhaust gas probe 24 and leads through appropriate processing by a control algorithm in the electronic control device 18 to an increase in the injection pulse width with which the fuel metering means 16 is controlled. A further control loop, which is based on the signal of the Nernst probe 26, is superimposed on this control loop. The interaction of the two control loops according to the invention is explained below with reference to the structure of FIG. 2. The dashed line 27 in FIG. 2 separates the functional structure of the electronic control device according to the invention designated by the number 18 from the other components of the structure of FIG. 1, in particular from the internal combustion engine 10, the pre-cat probe 24, the catalyst volume 22 and the Nernst probe 26. The number 28 designates a characteristic diagram which is addressed, for example, by input variables such as the measured air quantity and the speed of the internal combustion engine and which supplies a base pulse width t_base as an output value for the fuel metering. This output value is linked in the control link 30 to 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. The combustion process results in a certain oxygen concentration in the exhaust gas, which is reflected in the signal Ushk of the Nernst probe 26. This signal Ushk of the Nernst probe 26 is fed to a two-point controller 36. This two-point controller 36 represents a real two-point controller in the classic 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 value of 450 millivolts, for example. If there is an excess of oxygen behind the catalytic converter 22, the signal Ushk has an order of magnitude of approximately 100 millivolts. In this case, the two-point controller 36 is enriched by, for example, outputting a factor of 1.02 by 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-point controller 36 lean accordingly, for example by outputting a factor of 0.98. This factor 0.98 reduces the manipulated variable fr in the first controller 34, which ultimately leads to a shortening of the injection pulse widths ti and thus to a thinning. The Nernst probe 26 thus forms a second control loop in connection with the two-point controller 36 and the remaining control system (34, 30, 10, 24, 22). This second control circuit ensures that the catalyst volume 22 is filled with an average lean mixture when the probe behind the catalyst volume 22 indicates a lack of oxygen. This lean mixture ensures that the Nernst probe 26 at some point indicates excess oxygen behind the catalyst volume 22. When this happens, the catalyst volume 22 is then filled with an average rich mixture (lack of oxygen = reducing agent input) and the signal from the Nernst probe 26 jumps again after 900 millivolts.

The two-point control algorithm thus fills and empties this Catalyst volume 22 again and again. Since the Oxygen storage can only release the amount of oxygen that he previously saved must be real Excess oxygen and oxygen deficiency amounts the same his. In other words, the one in excess oxygen phases oxygen introduced into the catalyst volume 22 corresponds in quantity to that in the lack of oxygen from the Catalyst volume 22 discharged oxygen. According to the invention, these two will be the same by definition Quantities measured and corrected for the first Control loop used. For this purpose, FIG. 2 shows structure 38, 40, 42, 44, 46 and 32. Inscribed the number 38 a trigger signal path with which a Signal integrator 40 is set to zero and triggered. the Signal integrator 40 becomes parallel to trigger signal 38 the signal Isvk of the pre-cat probe 24, or a corrected signal Isvk_korr the pre-cat probe 24 is supplied. This signal integrator is wired and designed that it is only the excess oxygen part of the Isvk signal integrated. The integration is triggered when the Two-point controller 36 outputs a lean signal and it is stopped when the two-point controller 36 is at the greasing Mixture switches. The final value of the Oxygen storage integrators 40 thus provide a measure of the oxygen storage capacity of the catalyst (Oxygen Storage Capacity OSC). The integrator 42 in calculates analogously Oxygen deficiency phases a negative oxygen deficiency one Oxygen discharge -OSC.

The output signals of the integrators 40 and 42 are subtracted from one another in the differential link 44. Since they must be physically the same by definition, a non-zero result of the difference link 44 indicates a calculation error to a certain extent. In the context of this invention, it is assumed that such a calculation error is based on a characteristic curve shift of the signal Isvk of the pre-cat probe 24. A shift in the characteristic curve results, for example, in a signal that the mixture is already rich, even though the mixture is actually still lean. As a result, the value of the MINUS_OSC integrator 42 will be greater than the value of the OSC integrator 40. The difference between the two values is fed to an integrator 46, whose output signal corrects the signal Isvk of the pre-cat probe 24 via an offset correction link 32. As a result, the shifted characteristic curve is compensated so that the values of the OSC integrator 40 and the MINUS_OSC integrator 42 are the same again after a steady correction. These relationships are further illustrated by FIG. 3 in conjunction with FIG. 4. Numeral 52 in FIG. 3 denotes a first time range in which the offset correction has not yet settled. In contrast, the number 54 in FIG. 3 denotes a second time range in which the offset correction has settled. Overall, FIG. 3 shows the time profile of the signal Isvk over time t. The dashed line 48 marks the (wrong) measurement zero value of the pre-cat probe 24. The zero value, that is to say the value which separates the excess of oxygen from the lack of oxygen, is of fundamental importance for the formation of the stated OSC and MINUS_OSC quantities. This "zero value" between the excess of oxygen and the lack of oxygen is supplied by a probe in front of the catalytic converter or a stored value is used, for example an injection time, in which a stoichiometric mixture composition is assumed. However, this zero value can be incorrect. According to the invention, the excess oxygen or oxygen deficiency amounts are determined based on this - possibly faulty zero value. The relative deviation from the assumed zero value is known. From the measured air volume, the absolute value for the oxygen input or output can be determined. Since the oxygen store can only deliver the amount of oxygen that it has previously stored, the real amounts of excess oxygen and oxygen deficiency must be the same. If the calculated quantities are not the same, this can only be because the assumed zero value does not correspond to the real zero value, so that, for example, a real entry was evaluated as a discharge during the calculation. Then the assumed zero value is changed in the direction of the larger quantity. That is, if, in the previous calculation, the excess oxygen quantity was greater than the insufficient oxygen quantity, the zero value is shifted in the direction of the excess oxygen. Starting from this new zero value, the same amounts are greased and emaciated again. This procedure is repeated until the calculated quantities mentioned are the same. The associated zero value corresponds to the real zero value. In other words, the values of the determined oxygen inputs and oxygen outputs are used to determine a real zero value between excess oxygen and lack of oxygen.
This can be used to correct either a front probe or a pre-controlled zero value. This procedure is explained further with continuous reference to FIG. 3. The dashed line 50 denotes the real zero value. With the broadband probe, the low signal level corresponds to a rich mixture, i.e. lack of oxygen, and the high signal level corresponds to a lean mixture, i.e. an excess of oxygen. The hatched area 64 represents the integral of an oxygen excess period above the real zero value 50. The hatched area 66 accordingly represents the integral of an oxygen deficiency period above the real zero value 50. Both areas are the same because the switch between rich and lean mixture by the precisely measuring Nernst probe 26 is made behind the catalyst volume 22. The hatched area 68 corresponds to the integral over the (incorrect) measurement 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 over the incorrect measurement zero value during an oxygen deficiency period. Areas 68 and 70 are measured by integrators 40 and 42, respectively. It is clearly evident that the OSC value (68) deviates greatly from the MINUS_OSC value (70) in the non-steady state. The second time period (54) shows the steady state. As a result of the integration in block 46 and the intervention in the offset correction link 32, the signal Isvk is shifted downwards such that the measurement zero 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. As can be seen from the drawing, the OSC quantities (72) and MINUS_OSC quantities (74) are the same in this case. FIG. 4 shows the signal Ushk of the Nernst probe 26 corresponding to the signal curve in FIG. 3. The signal Isvk indicates the oxygen concentration upstream of the catalytic converter and the signal Ushk indicates the oxygen concentration downstream of the catalytic converter. It can be seen from the comparison of FIGS. 3 and 4 that an excess of oxygen (lean mixture) is generated in front of the catalytic converter as long as the rear exhaust gas probe 26 registers a lack of oxygen. Conversely, oxygen deficiency (rich mixture) is generated in front of the catalytic converter as long as the exhaust gas probe 26 arranged behind the catalytic converter signals a lean mixture. In principle, the rear exhaust gas probe measures the transition from a rich to a lean mixture and vice versa very precisely, since it shows the steep signal level change between 900 and 100 millivolts. It also measures very precisely because the upstream catalytic converter 22 protects the exhaust gas probe 26 against major temperature fluctuations and also brings the exhaust gas components into thermodynamic equilibrium.

In other words: it is an accounting Overall system, which is based on the jump of the lambda probe supports or calibrates behind a partial catalyst volume. Regarding the two-point control, due to Thoughts of symmetry as well as robustness aspects after expiry a period (also possible after a half-period) what amount of 02 entered and discharged into the catalyst has been. Due to the balance, these areas must be the same. If there is an imbalance, the offset (the Probe curve) in front of the catalytic converter so that the Balance is fulfilled again. If it is due to Gas runtimes due to a delayed system reaction when the probe jumps, this portion can also be in accounting are taken into account. Results in this method a sudden error that greater than the amplitude fluctuation of the Is oxygen concentration, the regulation is no longer can work. Therefore, according to a maximum criterion decided that a critical time has passed and then the offset is adjusted until it becomes one again Probe jump is coming.

FIG. 5 shows a modification of the structure of FIG. 1. In contrast to FIG. 1, the structure of FIG. 5 is no pre-cat probe 24 is provided. The structure of Figure 6 discloses an embodiment of the invention without Precat probe 24. Again determine the injection pulse widths ti the amount of fuel that fits the engine 10 to the measured air volume. The behind the Catalyst volume 22 arranged Nernst probe 26 delivers again the voltage signal Ushk to the two-point controller 36. The two-point controller 36 modulates by a multiplicative Link 30 supplied by a pilot control map 28 Base pulse widths t_basis. He extends it Base pulse widths, for example, by at lean mixture behind the catalyst volume 22 a outputs an enriching factor of 1.02. Similarly, he laments Lack of oxygen behind the catalyst volume 22 Output a factor of 0.98. The injection pulse widths ti are also fed to a difference link 58 which in addition, comparison pulse widths ti_L1 are supplied. The ti_L1 values represent assumed zero values in the sense that at ti> ti_L1 rich mixture and at ti_L1> ti lean mixture is assumed. Analogous to The integrator 40 also provides an explanation of FIG. 2 a measure of the oxygen storage capacity of the Catalyst volume and integrator 42 provides a measure for the reducing agent storage capacity of the catalyst. Again, the difference between the two values in the Difference link 44 formed and in integrator 46 integrated. The integrator output works via the Offset correction link 32 on the injection times. The mode of operation of the structure according to FIGS. 5 and 6 largely corresponds to the way the structures work according to Figures 1 and 2. Figure 3 can also be read the structure of Figure 5 and Figure 6. This is in the Figure 3 only the value Isvk by the injection time ti to replace. In the case of FIG. 6, the zero line 48 corresponds to then a value ti_L1. If this value ti_L1 is not the provides the actual Lambdal value, the result is the first Time range 52 of Figure 3 relationships. By the settling of the correction then results in the conditions shown in the second time range 54. With in other words: the offset correction will Injection times ti shortened evenly so that the desired symmetrical oscillation around the real lambda = 1 value results. The structure of Figures 5 and 6 has compared to the structure of Figure 1 and Figure 2 the large Advantage that a pre-cat probe 24 can be saved.

The structure of FIGS. 7 and 8 represents a currently preferred exemplary embodiment. This exemplary embodiment differs from the subject matter of FIGS. 1 and 2 by a main catalyst volume 60 behind the Nernst probe 26 and by a further Nernst probe 62 behind the main catalyst volume 60. The main catalyst volume 60 basically has that Function to compensate for the oscillation inevitably occurring in this control concept in the oxygen content of the exhaust gas behind the partial catalyst volume 22. Since, on average, a slightly rich operation is desired for optimal catalytic converter operation, the structure described so far has to be expanded by a component which provides this desired fat shift or, in other cases, possibly a desired lean shift. For this purpose, the further Nernst probe 62 is used in the context of this preferred exemplary embodiment. Its signal UsnHK ( U - s onde n nach- H aupt- K at) acts on a delay timer 63, which transmits signal transitions in the output of the two-point controller 36 to the first controller 34 with a delay , This results in the desired signal behavior shown in FIGS. 9 to 13. FIGS. 9 and 10 show the signals Ushk and Isvk previously explained in the steady state. FIG. 11 shows the course of the signal Ushk in the context of this exemplary embodiment. It can be seen from FIG. 12 that a change from lean to rich in the signal Ushk is only forwarded to the controller 34 with a time delay tv by a delay period tv, which is shown in the time profile of the Isvk signal. The shaded areas 76 thus represent a desired additional MINUS_OSC entry into the catalyst volumes, which ultimately results in the signal of the further Nernst probe 62 shown in FIG. 13, which runs relatively evenly in the fat region above 450 millivolts.

Claims (13)

Method for regulating the fuel / air ratio of a combustion process, which is operated alternately with excess air and lack of air, and with at least one catalyst volume in the exhaust gas of the combustion process, which stores oxygen in the exhaust gas when there is an excess of oxygen and releases it in the event of a lack of oxygen, in which method the excess air takes place Oxygen inputs into the catalyst volume and the oxygen outputs occurring in the event of lack of air are determined from the catalyst volume and in which the fuel / air ratio is set in a first control loop so that the sum of the oxygen inputs and oxygen outputs determined in a predetermined interval takes on a predetermined value,
characterized in that the combustion process is operated at least on average with an excess of oxygen or a lack of oxygen until this occurs on an oxygen-sensitive Nernst probe behind the catalyst volume. Method according to Claim 1, characterized in that the predetermined interval extends over a period in which the combustion process is operated on average with an excess of oxygen and once on average with a lack of oxygen. A method according to claim 1, characterized in that the change between excess oxygen and lack of oxygen during operation of the internal combustion engine is controlled so that the difference between the excess oxygen in the catalyst volume and the lack of air from the catalyst volume assumes a predetermined value. A method according to claim 1, 2 or 3, characterized in that a size is used to determine the oxygen inputs into the catalyst volume when there is excess air and the oxygen volume from the catalyst volume when there is a lack of air, a quantity which at least also determines the fuel flow to the internal combustion engine. A method according to claim 4, characterized in that said variable is formed on the basis of a quantity of intake air calculated from measured quantities and on the basis of a quantity of fuel added to this quantity of intake air. A method according to claim 4, characterized in that said variable is formed as a function of the signal of an exhaust gas probe arranged in front of the catalytic converter, which is hereinafter referred to as pre-cat probe. A method according to claim 6, characterized in that said variable is an input variable for a second control loop in which the air / fuel ratio is controlled with a smaller time constant compared to the first control loop. Method according to one of claims 5 to 7, characterized in that the formation of said size is changed when the oxygen inputs and oxygen outputs differ from one another. A method according to claim 8, characterized in that the change takes place so that the said deviation becomes smaller. A method according to claim 9, characterized in that the change is formed as a function of the integral of said deviation. Method according to claim 1, characterized in that the fuel / air ratio is predetermined by a superimposed control circuit (24, 18, 16, 10). Method according to Claim 3 or 4, characterized in that the values of the determined oxygen inputs and oxygen outputs are used to determine a real zero value between excess oxygen and lack of oxygen. Control device for carrying out at least one of the Process according to claims 1 to 10.

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