EP0140083B1 - Control method for the a/f ratio of an internal-combustion engine - Google Patents

Description

State of the art

The invention is based on a method for air-fuel mixture formation for an internal combustion engine with an oxygen probe exposed to the exhaust gas and sensitive to the oxygen content of the exhaust gas, according to the preamble of the main claim.

In principle, a large number of methods and devices for mixture formation have become known which use an oxygen probe. Oxygen probes are often used, which suddenly change their output size in the case of a 1 = 1 mixture. In a closed control loop, the oxygen probe normally switches back and forth between the two output variables "high" and "low".

The output signal of the oxygen probe is usually used to correct the values applied in a permanently preprogrammed map, for example determining the injection time. Based on the signal of the lambda probe, which is approximately to be regarded as binary, the map correction factor is continuously corrected by, for example, a PI controller. Since the transport time of the air through the internal combustion engine and the reaction time of the probe are not taken into account, there is a limit cycle for the correction factor of the lambda controller and, of course, also for the torque of the internal combustion engine. This torque limit cycle can be felt by the driver of the vehicle equipped with the internal combustion engine, in particular at low engine speeds and a sufficiently large load, and appears uncomfortably as so-called uneven running. In addition, the exhaust gas emission increases with falling frequency.

• - den Kennfeldwerten zeitlich veränderliche Störungen verlagert werden,
• - die Ausgangssignale der Sauerstoffsonde auf ihre Änderung hinsichtlich der Steuergröße ausgewertet werden, und
• - die Kennfeldwerte auf ein Luft-Kraftstoff-Verhältnis in der Umgebung λ= korrigiert werden.

US Pat. No. 4,200,064 describes a device for metering an air-fuel mixture into an internal combustion engine, in which a computer selects injection times as a function of, for example, a map with injection times. B. engine speed and pressure in the intake duct. Furthermore, from this US-PS-'064 a calibration is disclosed in which

• - the characteristic values are shifted over time,
• - The output signals of the oxygen probe are evaluated for their change with respect to the control variable, and
• - The map values are corrected to an air-fuel ratio in the environment λ =.

It has now been shown that the known device cannot work fully satisfactorily because the time delay between the corresponding metering disturbance and the signal response is largely ignored.

The method according to the invention with the features of the main claim is based on the object of improving known lambda control methods in such a way that, during all operating conditions of the internal combustion engine that occur in practice, the internal combustion engine runs smoothly in conjunction with an optimally composed exhaust gas emission with regard to the pollutant components. Above all, it is about achieving the greatest possible smoothness at low machine speeds with a very precise R = 1 control.

drawing

Embodiments of the invention are shown in the drawing and are described in more detail below. To explain the basic problem, FIG. 1 shows characteristic output signals of the lambda probe in relation to the lambda value of the air-fuel mixture in known control methods, FIG. 2 shows a diagram for explaining the method according to the invention and FIG. 3 shows a possible device for carrying out the inventive method.

Description of the embodiment

Although the following exemplary embodiment is described in connection with an intermittently operated fuel injection system (sequential or parallel injection), the lambda control itself is independent of the type of mixture formation, so that the invention can also be used, for example, in conjunction with carburetor systems or continuous injection.

The diagrams in FIG. 1 serve to explain the problems encountered with the lambda control. In FIG. 1a, the lambda value of the air / fuel mixture supplied to the internal combustion engine and the output signal of an oxygen probe are plotted as a function of the time t, the lambda Control includes an I controller in a known manner. The lambda value of the air-fuel mixture fluctuates periodically with an amplitude dependent on the integration time constant of the I controller and the delay time by the value lambda == 1. Would the oxygen probe work without delay and if the mixture reached the probe infinitely quickly, its output signal UA would have to change abruptly at times t ₁ and t ₂ , at which the air-fuel mixture passes the value λ = 1. In fact, the jump only occurs with a certain delay time T + τ, which is composed of the transport time T of the air components through the internal combustion engine and the response time _{T of} the oxygen probe. In the present example, the (λ = 1) passage is only recognized at times when the mixture has already been heavily enriched again. Due to this delayed switching behavior of the oxygen probe, a limit cycle is set which has a period P-4 (T + τ). Since the transport time T, which has a strong speed dependency, can take values up to T-1 second (the response time _{T of} the oxygen probe, however, can be neglected at low speeds), this limit cycle takes on frequency values that are perceived by the driver of the internal combustion engine can.

The signal sequence shown in FIG. 1b differs from that in FIG. 1a in that a PI controller is used in the lambda control loop. In this case, when a switching operation of the oxygen probe occurs, an abrupt change in the lambda value is triggered in addition to the reintegration in the direction of λ = 1 in order to accelerate the (λ = 1) passage. The compromise is made here that the switching period of the oxygen probe takes on smaller values, but the lambda variation increases by the value λ = 1 depending on the steepness of the ramp. With a clever choice of the P component, the period can be reduced to the minimum value P = 2 (T + τ).

Since this delay time is also not taken into account in a PI control, a limit cycle, albeit a smaller one than in the example in FIG. 1a, is established when determining the amount of fuel to be injected. The consequences of this limit cycle are noticeably noticeable to the driver in the form of fluctuations in smooth running, especially at low engine speeds and high loads.

The previous consideration referred to constant or only slowly changing operating conditions of the internal combustion engine.

In the event of sudden changes in load, these control systems usually have "exhaust peaks". Because of the above-mentioned transport time T and the response time _T, a certain period of time passes until the control loop responds to the new settings, so that during the period there is a sharp increase in pollutants that cannot be broken down by the catalytic converter installed in the exhaust pipe, for example.

One tries to get this problem under control by storing the values for the fuel metering in a map as a function of operating parameters of the internal combustion engine, for example as a function of the amount of air drawn in and the rotational speed, and to retrieve them as required. This is a controlled fuel metering in which the relevant values are available very quickly. However, there is a difficulty that slow changes such as. B. temperature fluctuations, pressure fluctuations or wear-related changes to the internal combustion engine that affect the air-fuel ratio are not taken into account.

This difficulty can be overcome by replacing the permanently preprogrammed map with a similar one, which, however, can be adapted to the changed parameters in each support point via a lambda control. After moving to a new support point due to changed operating parameters, the old, optimal value is stored at the corresponding point. With such a known measure, it can be achieved that errors in the fuel metering do not occur during rapid load changes, that is to say during the transient operation of the internal combustion engine. The behavior of the internal combustion engine under constant or very slowly changing operating conditions is, however, still determined by the limit cycle of the lambda control loop.

The main idea of the present invention is based on the fact that the output signal U _{λ of} the oxygen probe has a quasi binary character (λ <1 → U _λ = H, λ> 1 → U _λ = L, with H = "high" and L = "low") and thus no statement about the exact lambda value is allowed, but only allows the determination "λ S 1". In fact, with its switching behavior at λ = 1, the oxygen probe responds to very small λ strokes.

In order to increase the switching frequency of the oxygen probe, provision is therefore made to superimpose a high frequency and small amplitude disturbance on the values read from the adaptive map, which are responsible for the fuel quantity, that is to say to modulate these map values. The amplitude of the disturbance should be as small as possible, but nevertheless assume such values that a switching operation of the λ probe normally occurs. The following requirements must be placed on the frequency of the modulation, which of course can lead to various individual determinations from internal combustion engine to internal combustion engine. The modulation frequency should assume the highest possible values so that the torque fluctuations that may occur in the internal combustion engine are no longer perceived. The upper limit is given either by the response time of the oxygen probe, which in particular varies very greatly with the temperature of the oxygen probe, or by the speed of the internal combustion engine. The dependency on the rotational speed is based on the fact that repeated modulation of the amount of fuel to be metered into a cylinder compensates one another and thus has no advantages. Thus, in the case of sequential injection, a malfunction per fuel metering represents the maximum modulation frequency for each individual cylinder. It should be emphasized once again that this information serves as a rough guideline for determining the modulation stroke and the modulation frequency and is left to the expert in the respective application, to define the most favorable values.

The reaction of the oxygen probe to this high-frequency interference with a small amplitude becomes measured and evaluated according to the sign of the fault in such a way that the currently approached support point of the map is changed such that the air-fuel mixture approaches the lambda value λ = 1 and thus assumes the optimum value.

• Wurde eine günstige Frequenz und Amplitude (in Figur 2a ±ε) für die den Kennfeldwerten F, zu überlagernden Störung ΔF_± ausgewählt, so könnte sich eine Modulation des Luft-Kraftstoff-Gemisches um den Wert λ=1 beispielsweise wie in Figur 2a darstellen. Unter Vernachlässigung der Ansprechzeit _T der Sauerstoffsonde würde eine Einstellung der maximal noch sinnvoll auszunutzenden Modulationsfrequenz - in Figur 2a beispielsweise für eine 4-Zylinderbrennkraftmaschine mit Einzeleinspritzung dargestellt - bedeuten, daß in der Phase eins Zylinder 1 angereichert, in der Phase zwei Zylinder 2 abgemagert, in der Phase drei Zylinder 3 angereichert usw. wurde (hierbei entspricht die Numerierung der Zylinder der Zündfolge). Wie weiter unten noch näher dargestellt wird, sind natürlich auch andere Modulationsschemata denkbar.

The method according to the invention is to be explained in more detail with reference to FIG. 2:

• If a favorable frequency and amplitude (in FIG. 2a ± ε) were selected for the disturbance ΔF _± to be superimposed on the characteristic map values F, a modulation of the air-fuel mixture by the value λ = 1 could be shown, for example, as in FIG. 2a. Neglecting the response time _{T of} the oxygen probe, a setting of the maximum modulation frequency that can still be used sensibly - shown in FIG phase three cylinder 3 was enriched etc. (the numbering of the cylinders corresponds to the firing order). As will be explained in more detail below, other modulation schemes are of course also conceivable.

The reaction of the probe to such a modulation of the amount of fuel to be metered to the individual cylinders of an internal combustion engine can be described by a case distinction in three cases. All other output signals correspond to a mixed form of these three possibilities shown in Figure 2b, c, d.

In the case of FIG. 2b, the output signal of the oxygen probe follows the variation of the lambda value according to FIG. 2a with the delay typical of the air components by the transport time T and the response time _{T of} the probe. From this it follows that the average lambda value λ is correct with λ = 1.

For the situation in FIG. 2c, the oxygen probe shows a constantly lean mixture, regardless of the interference AF ₊ superimposed on the interpolation point value F _λ . From this it can be concluded that F corresponds to an insufficient amount of fuel. The same applies to FIG. 2d, in which the oxygen probe constantly indicates a rich mixture, that the default setting of F _A corresponds to an excessive amount of fuel. A mixed form of the output signal of the oxygen probe could, for example, consist in the fact that individual switching processes would fail in the diagram in FIG. 2b. This would mean that the mean lambda value λ, after temporarily staying at a low (lean mixture) or high (rich mixture) output voltage, would tend to λ = 1 + ε or λ = 1-ε.

If one considers this interference ΔF _± superimposed on the FA map values as a kind of test series for querying the current lambda value, the output signal of the oxygen probe represents the test result. Because of the binary character of the output signal of the oxygen probe, only a statement is possible as to whether the test result is in accordance with the sign of the fault ΔF _± or not.

If, for example, the engine AF fault AF ₊ offers a rich air-fuel mixture, the oxygen probe can react to this either with a high or a low output level. A high level (indicating a rich mixture) would normally be expected and the test result would be described as "normal". There was no reason to make a change to the factor Fλ or to adapt it. If the probe had a low (indicating lean mixture) output level in the case of the AF ₊ fault, this test result would be described as "catastrophic". Then there would be a need to change the factor F _A in the direction of higher injection quantities by a value labeled + Δ ₂ . The same applies to the other possible cases, so that the adjustment scheme for the factors F _{λ is} as follows:

According to this, each individual fault ΔF _{± represents} a test, the test result (namely the value H / L of the oxygen probe output voltage) being used to determine the relevant map value F _A , which currently determines the fuel metering as a function of at least one operating parameter of the internal combustion engine, adapt to the value λ = 1.

It should be emphasized here that the scope for choosing the values ΔF _± and Δ _{1/2 is} very large. For example, AF _{+ can be} not equal to ΔF_ and Δ _1/2 can be varied depending on the sign of the disturbance ΔF _± . Furthermore, it may be useful to change the amplitude (s) of the disturbance variable ΔF _± as "normal" or "catastrophic" depending on the measurement result. If very few "catastrophic" results occur (this is a sign that λ is very precisely at λ = 1), the amplitude of the disturbance variable (the modulation stroke) can be reduced to a lower limit, for example, which is fixed from the outside. The same applies to the opposite case.

The modulation scheme described in FIG. 2a was given only by way of example, and there are no limits to the possibility of variation in the modulation sequence. It may prove advantageous, for example, for engines with an even number of cylinders, to reverse the chronological sequence of the interference signal sequence after a selectable period of time, for example depending on the operating parameters, so that the same cylinder is not always enriched or emaciated by the interference.

In the case of sequential injection, cylinder-specific adaptation of the fuel metering is also possible. For this purpose, depending on the frequency of the measurement result "catastrophic", or at defined time intervals, or only in customer service intervals, a checking algorithm is switched on. This check algorithm can be used to determine whether individual cylinders differ significantly from the average behavior of the others. In the case of larger deviations, this information can also be used for engine diagnosis purposes. The most extensive embodiment would consist in the use of cylinder-specifically corrected maps. In the practical exemplary embodiment, however, a cylinder-specific multiplicative or additive valve correction factor for the injection quantity, which corrects the injection quantity of the specific valve in a positive or negative direction, would also suffice under normal conditions. In the practical implementation, the storage space requirement for the situation of the single cylinder adaptation would increase by a maximum of the factor n, which is given by the number of cylinders.

Especially in the case of higher speed or longer interference signal sequences (see below), a cylinder-specific correction adjustment would also be conceivable in such a way that during the test cycle it is ensured that the fuel mixture of (n-1) cylinders of the n-cylinder internal combustion engine is preferably preferred is on the rich (or lean) side and only the nth cylinder is modulated. Due to the tilting of the lambda signal of this single cylinder, this cylinder is individually calibrated according to the general specification already given and the associated map value of the injection quantity is compared with the individually determined mean value of the other cylinders. In this way, any outliers that may occur can be suppressed in an advantageous manner. If necessary, a corresponding valve correction value is then stored for this cylinder.

So far, it was assumed that each injection valve is controlled separately for internal combustion engines with injection. Then there is a maximum frequency f _{max of} the torque fluctuations or the switching sequence of the oxygen probe for a 4 (6) -cylinder internal combustion engine at f _max = n (3 / 2n). Such a modulation method can of course also be used for parallel, jointly controlled injection valves. Since one injection is made once per crankshaft revolution, the disturbance ΔF _± in the sequence AF ₊ , ΔF _- , ΔF +, (with | ΔF ₊ | = | ΔF _- |) produces no fluctuation in the air-fuel mixture at all, since each cylinder has a rich one and receives a lean injection per combustion process. Here it is favorable to use, for example, the sequence AF ₊ , ΔF ₊ , ΔF _- , ΔF _- , ..., but then the switching frequency of the oxygen probe is reduced to the value f _{max /} 2. Such an interference sequence would cause a lambda modulation Δλ = + ε, 0, -ε, 0, + ε, ... In this case, the modulation Δλ = 0, which would result in a random signal from the binary oxygen probe, would have to be suppressed accordingly when adapting the map values F _x .

The Δ _1/2 corrections to the map values F _A are in turn responsible for a cut-off frequency, which, however, assumes very low-frequency values, since only slow drift phenomena, such as air pressure, height above sea level, fuel temperature or signs of aging, need to be compensated.

After this presentation of the general idea of the invention, a possible implementation will be explained below. In practice, the problem essentially arises of correlating the sign (possibly also the amplitude) of the disturbance ΔF _± with the associated reaction of the oxygen probe to the respective disturbance, since the oxygen probe output signal only shows T after the transport mentioned above and response time τ is available after attaching the fault. The transport time T is very much dependent in particular on the speed and also on the intake pressure or air mass flow rate of the internal combustion engine. As already mentioned, the response time τ of the oxygen probe depends on the temperature of the probe or on the internal resistance of the probe, which is a clear function of the temperature. The following options are available for determining the total time T + T: The transport time can be determined from the speed n and, if appropriate, from the intake pressure p or the intake air mass Q _L. A load measurement is recommended for τ since the exhaust gas temperature and thus also the oxygen probe temperature and the internal resistance are essentially dependent on the load. By heating the probe for temperature control, on the other hand, it would also be possible to keep the response time τ at a value that is almost independent of the operating parameters of the internal combustion engine, ie almost constant. A direct measurement of the internal resistance of the probe would also be possible, as is carried out in arrangements known per se for detecting the operational readiness of the oxygen probe.

A preferred embodiment for the experimental detection of the time period T + _T consists in the possibility of determining T + T directly during the operation of the internal combustion engine. Instead of the regular interference sequence AF ₊ , AF_, AF ₊ , ... a coded interference sequence is used and the unknown time period T + _T via a cross-correlation analysis of the signals ΔF _± (t) and the fluctuation ΔU _λ (t) of the oxygen probe output voltage around their Average determined. The cross correlation function R (t ') = E {ΔF _± (t) · AU _λ (t + t')} with E for expected value takes a maximum for t '= T + _T , so that with a correlator known per se (see RC Dixon, "Spread Spectrum Systems", Chapter 3, Wiley-Intersciene, New York, 1976) the time period T + τ can be determined experimentally.

• Ein mit der Nummer 10 bezeichneter Kennfeldspeicher dient zur Speicherung des Kennfeldes F_A (n, Q_L) und ist über einen Datenßus 11 mit einer ALU 12 (arithmetische logische Einheit (unit)), einem Modulator 13 und

einer Kontrolleinheit 14 verbunden, wobei die Kontrolleinheit 14 von verschiedenen, durch Pfeile angedeuteten Parametern eine Brennkraftmaschine 19, wie z. B. der Drehzahl n und der angesaugten Luftmasse Q_L angesteuert wird. Der Kennfeldspeicher 10 steht weiterhin über einen Adressen-Bus 15 mit der Kontrolleinheit 14, der ALU 12 und einem Zwischenspeicher 16 in Verbindung. Der Modulator 13 erhält Taktsignale von einem Taktgenerator 17, wobei die Taktfrequenz in Abhängigkeit von beispielsweise der Temperatur T, einer in einem Abgasrohr 18 der Brennkraftmaschine 19 angebrachten Sauerstoffsonde 20, von der Drehzahl n der Brennkraftmaschine, der angesaugten Luftmasse GL oder aber auch der Last geändert werden kann. Ebenso ist es aber auch möglich, die Taktfrequenz z. B. über einen Quarzoszillator 21 drehzahlunabhängig zu gestalten Mittels eines weiteren, gestrichelt eingezeichneten Einganges 22 ist auch eine Kodierung der Störsequenz zur experimentiellen Bestimmung der Verzögerungszeit T+τ (wie schon weiter oben dargestellt) möglich. Die digitalen Ausgangssignale des Modulators 13 werden von einem D/A-Wandler 23 in analoge Signale gewandelt und zur Ansteuerung von Einspritzendstufen 24 verwendet, die die nicht dargestellten Einspritzventile der Brennkraftmaschine 19 für die Kraftstoffzumessung betätigen.An embodiment of the method according to the invention is to be explained in more detail with reference to the block diagram shown in FIG. 3:

• A map memory designated by number 10 is used to store the map F _A (n, Q _L ) and is connected via a data base 11 to an ALU 12 (arithmetic logic unit), a modulator 13 and

a control unit 14 connected, the control unit 14 of various parameters indicated by arrows an internal combustion engine 19, such as. B. the speed n and the intake air mass Q _{L is} controlled. The map memory 10 is also connected via an address bus 15 to the control unit 14, the ALU 12 and an intermediate memory 16. The modulator 13 receives clock signals from a clock generator 17, the clock frequency changing as a function of, for example, the temperature T, an oxygen probe 20 fitted in an exhaust pipe 18 of the internal combustion engine 19, the speed n of the internal combustion engine, the air mass GL being sucked in or else the load can be. But it is also possible to change the clock frequency z. B. using a quartz oscillator 21 to make it independent of the speed. By means of a further input 22 shown in broken lines, it is also possible to code the interference sequence for experimentally determining the delay time T + τ (as already shown above). The digital output signals of the modulator 13 are converted into analog signals by a D / A converter 23 and used to control injection output stages 24 which actuate the injection valves (not shown) of the internal combustion engine 19 for metering fuel.

The output signal of the oxygen probe 20, which is dependent on the oxygen content of the exhaust gases of the internal combustion engine 19, is fed to an A / D converter 25, which, due to the quasi-binary probe signal, is preferably a 1-bit converter (a 2-bit converter is necessary for ternary evaluation of the probe signal). is trained. The temperature of the oxygen probe 20 is either output by a temperature sensor with the output line 26 or, for example by means of a temperature monitoring unit 27 known per se, actively regulated to a constant temperature by means of a heater 28. A catalytic converter 34 is also provided in the exhaust gas duct 18 of the internal combustion engine 19 for exhaust gas purification.

The output of the A / D converter 25 is connected to a logic unit 29 which receives further input signals from the buffer memory 16 via a line 30. On the output side, the logic unit 29 supplies one- or multi-valued bit information which is fed to the ALU 12.

In addition to the input variables F, (n, Q _L ), the intermediate memory 16, which can be designed, for example, as a shift register, receives a modulation bit as further input information, which indicates whether the mixture has been enriched or emaciated by the modulator 13. The storage time of the buffer can be influenced by a clock unit 31 as a function of various operating parameters of the internal combustion engine 19, indicated by arrows, such as. B. the temperature of the oxygen probe T, the speed n, the intake air mass Q _L or other quantities.

Finally, a correlator 32 is also provided which receives its input signals from the A / D converter 25 and from the modulator 13 and influences the clock unit 31 by means of its output variable. In addition, a line 33 leads from the logic unit 29 to the modulator 13.

• Ausgehend von einem bestimmten Betriebszustand der Brennkraftmaschine wird ein entsprechender Wert im Kennfeldspeicher 10 angewählt, vom Modulator 13 in Abhängigkeit von der Taktfrequenz des Taktgenerators 17 mit einer positiven bzw. negativen Störung überlagert, im D/A-Wandler analogisiert und der jeweiligen Einspritzstufe 24 zugeführt um das Einspritzventil für eine entsprechende Zeitdauer zu öffnen. Gleichzeitig wird im Zwischenspeicher 16 die Adresse des angewählten Kennfeldwertes und das Vorzeichen der im Modulator 13 erzeugten Störung abgespeichert. Die Speicherzeit dieser beiden Informationen im Zwischenspeicher wird durch die Clock-Einheit 31 in Abhängigkeit von Betriebsparametern der Brennkraftmaschine bestimmt. Ebensogut ist es möglich, die Clock-Einheit mit dem Ausgang des Korrelators 32 anzusteuern, mit dem die notwendige Speicherzeit experimentiell bestimmt wird. Auf jedem Fall ist dafür zu sorgen, daß die Speicherzeit der Informationen im Zwischenspeicher genau der Verzögerungszeit (T+_τ) im Ansprechverhalten der Sauerstoffsonde 20 entspricht. Ist dies der Fall, so lassen sich in der Logik-Einheit 29 die entsprechenden Versuche (Vorzeichen der Störung) mit den zugehörigen Versuchsergebnissen (Ausgangssignal der Sauerstoffsonde) korrelieren. In der ALU 12 wird der betreffende Kennfeldwert, dessen Adressen ebenfalls über die Verzögerungszeit im Zwischenspeicher gespeichert war, entsprechend dem Versuchsergebnis "normal" oder "katastrophal" (siehe Tabelle oben) den neuen Bedingungen angepaßt.

The arrangement works as follows:

• Starting from a specific operating state of the internal combustion engine, a corresponding value is selected in the map memory 10, superimposed by the modulator 13 with a positive or negative disturbance depending on the clock frequency of the clock generator 17, analogized in the D / A converter and supplied to the respective injection stage 24 open the injection valve for a corresponding period of time. At the same time, the address of the selected map value and the sign of the disturbance generated in the modulator 13 are stored in the buffer memory 16. The storage time of these two pieces of information in the intermediate store is determined by the clock unit 31 as a function of operating parameters of the internal combustion engine. It is equally possible to control the clock unit with the output of the correlator 32, with which the necessary storage time is determined experimentally. In any case, it must be ensured that the storage time of the information in the buffer memory corresponds exactly to the delay time (T + _τ ) in the response behavior of the oxygen probe 20. If this is the case, the corresponding tests (sign of the fault) can be correlated in the logic unit 29 with the associated test results (output signal of the oxygen probe). In the ALU 12, the relevant map value, whose addresses were also stored in the buffer over the delay time, is adapted to the new conditions according to the test result "normal" or "catastrophic" (see table above).

The control unit 14 is responsible for a correct timing. If, for example, the map value was changed by the ALU, the logic must be shut down during the delay time T + τ so that the effect of the latest change is recognized by the oxygen probe. That is, in the stationary case, the map value can be changed at most in time units T + τ.

A simplified embodiment of the arrangement consists in dispensing with a very precise knowledge of the delay time T + τ and in evaluating longer interference signal sequences instead of individual positive or negative interference signals. Then it would only have to be examined whether no new map value was approached during the course of this interference signal sequence. If this is the case, the simplified view assumes that this map value cannot be of great importance for the driving behavior of the internal combustion engine, since it was only started for a very short time. However, if the map value remains unchanged during the course of the entire sequence, the procedure is again based, as before, on the waveform of the oxygen probe output signal (see FIG. 2). In addition to the measures specified in the table for changing the map value, the length of the fault sequence could also be shortened in this simplified procedure in order to be able to carry out a faster corrective action again.

If you want to reduce the computational effort even further, it may be useful to dispense with an adjustment of each individual map value F, and a single correction factor or several Correction factors, e.g. B. are responsible for different zones in the map area, adaptive tracking. The high modulation frequency would also be retained in this simplified embodiment.

The exemplary embodiment was explained using a block diagram with various individual components. However, it goes without saying that it is no problem for the person skilled in the art to carry out the method according to the invention with the aid of a suitably programmed microcomputer.

Claims (16)

1. Method for forming the air/fuel mixture for an internal combustion engine, having an oxygen probe which is exposed to the exhaust gas and is sensitive to the oxygen content of the exhaust gas, a signal processing device which processes the output signals of the oxygen probe and a memory for storing an engine map, which is dependent on at least one operating parameter of the internal combustion engine, including engine map values (F_λ) which determine the fuel quantity to be metered, time-variable disturbances (AF₊, ΔF_-) being superimposed on the engine map values (F,) and the out-put signals (Ux) of the oxygen probe being evaluated for their change with respect to the disturbance variable (AF₊, ΔF_-), and the engine map values being corrected for an air/fuel ratio in the vicinity of λ=1, characterized in that an oxygen probe is used which has a quasi-binary output signal when the air/fuel ratio exceeds or drops below λ=1, and that the output signals (U_k) of the oxygen probe are evaluated taking into consideration the time delay (T+τ) of the corresponding metering disturbance and of the signal response of the oxygen probe, in such a manner that the output signal (U_x) is compared with an output signal to be expected in accordance with the corresponding disturbance (AF₊, ΔF_-), and a respective predetermined correction (±Δ₁, ±A₂) is made in the engine map values in dependence on the comparison value.

2. Method according to Claim 1, characterized in that the time-variable disturbance of the engine map values (Fx) is implemented by adding or subtracting a disturbance variable (ΔF_±) to or from the engine map values.

3. Method according to at least one of the preceding claims, characterized in that the time-variable disturbance variable (ΔF_±) is superimposed especially on the engine map value (F_x) read out in dependence on at least one operating parameter of the internal combustion engine.

4. Method according to at least one of the preceding Claims, characterized in that the disturbance variable (ΔF_±) is varied in time in dependence on at least one operating parameter of the internal combustion engine.

5. Method according to at least one of Claims 1 to 3, characterized in that the disturbance variable (ΔF_±) is varied in time with a constant frequency.

6. Method according to at least one of the preceding Claims, characterized in that the time delay (T+τ) between the output signals (U_x) of the oxygen probe and the disturbance is compensated by storing the disturbance variable (ΔF_±) in a temporary memory.

7. Method according to Claim 6, characterized in that the storage time of the intermediate memory can be adjusted in dependence on operating parameters of the internal combustion engine.

8. Method according to Claim 6, characterized in that the storage time of the temporary memory is carried out in dependence on the result of a cross-correlation analysis of the disturbance variable (ΔF_±) and the oxygen probe output signal (U_A).

9. Method according to at least one of Claims 1 to 8, characterized in that the amplitude of the disturbance variable (ΔF_±) is changed in dependence on the result of the comparison of the disturbance variable with the output signal of the oxygen probe output variable (U_λ).

10. Method according to one of the preceding Claims, characterized in that the engine map values are corrected to a value of the air/fuel ratio at which the pollutants contained in the exhaust gas are reduced to minimum values, for example, by catalytic post treatment.

11. Method according to one of the preceding Claims, characterized in that the engine map values are stored in the engine map memory in dependence on the speed (n) and on intake air quantity (Q_L) or the intake pipe pressure (p_L) of the internal combustion engine.

12. Method according to one of the preceding Claims, characterized in that for the case of each individual injection valve being separately driven, a disturbance (ΔF_±) is superimposed on the relevant engine map value (F_x), which determines the fuel quantity, once per fuel metering for each individual cylinder at a maximum.

13. Method according to one of Claims 1 to 11, characterized in that the modulation frequency of the engine map values (F_λ), which determine the fuel metering, is reduced for the case where several injection valves are jointly driven, compared with the case of the injection valves separately driven.

14. Method according to one of Claims 1 to 12, characterized in that the engine map values (F_λ) are cylinder- specifically corrected and stored.

15. Method according to one of Claims 1 to 12, characterized in that cylinder-specific engine map values are determined for one cylinder, are compared with the mean value from the cylinder-specific engine map values of the other cylinders and, if necessary, cylinder-specific correction values for this cylinder are stored.

16. Method according to one of Claims 14, 15, characterized in that the single-cylinder adaptation of the engine map values (F_x) is performed at defined time intervals.

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