DE102008005093B3 - Air/fuel ration determining method for e.g. petrol engine, involves determining hydrocarbon concentration of unburnt hydrocarbon downstream of sensor, and determining non-oxidized fuel-mass flow by downstream hydrocarbon concentration - Google Patents

Abstract

The method involves determining hydrocarbon concentration of unburnt hydrocarbon upstream of a lambda sensor. Air-mass flow delivered to an internal combustion engine e.g. petrol engine, is determined, and an air/fuel ratio upstream to the sensor is determined. The hydrocarbon concentration of unburnt hydrocarbon downstream of the sensor is determined by the upstream unburnt hydrocarbon and hydrocarbon concentration. The fuel-mass flow non-oxidized at the sensor is determined by the downstream hydrocarbon concentration.

Description

The The invention relates to a method for determining the air ratio λ by means of a arranged in the exhaust system of an internal combustion engine lambda probe.

The Knowledge of the air ratio λ is in the frame the operation or the control of an internal combustion engine of particular Importance.

So is the air ratio λ to determine the amount of fuel to be injected, the injection timing and / or needed to control an exhaust gas recirculation, but also for monitoring and to operate the different exhaust aftertreatment systems, which are used according to the prior art for the reduction of pollutants and will be discussed below by way of example. In this Context, it will become clear that the air ratio λ is an essential Operating parameters of the internal combustion engine, in particular with regard to on the exhaust aftertreatment, is.

To The prior art are internal combustion engines for reduction Pollutant emissions with various exhaust aftertreatment systems fitted. Although it takes place at a sufficiently high temperature level and the presence enough greater Oxygen levels an oxidation of the unburned hydrocarbons (HC) and carbon monoxide (CO) instead. However, usually special Reactors and / or filters are provided in the exhaust tract to pollutant emissions under all Operating conditions noticeable to reduce. In the context of the present invention, the carbon monoxide (CO) and the unburned hydrocarbons (HC) under the term the "reducing Exhaust gas constituents "or" oxidizing exhaust gas constituents "summarized.

In gasoline engines, catalytic reactors are used which, using catalytic materials which increase the speed of certain reactions, ensure oxidation of HC and CO even at low temperatures. If, in addition, nitrogen oxides are to be reduced, this can be achieved by using a three-way catalytic converter which, however, requires a narrow-flow stoichiometric operation (λ≈1) of the gasoline engine. The nitrogen oxides NO _{x are} reduced by means of the existing unoxidized exhaust gas components, namely the carbon monoxides and the unburned hydrocarbons, wherein at the same time these exhaust gas components are oxidized.

at Bremkraftmaschinen that are operated with an excess of air, for example in lean-burn gasoline engines, but also direct injection Diesel engines and direct injection gasoline engines, the In principle, due to the inherent nitrogen oxides in the exhaust gas d. H. due to the missing reducing agent can not be reduced.

to Oxidation of unburned hydrocarbons (HC) and carbon monoxide (CO) Therefore, an oxidation catalyst is provided in the exhaust system. Both of these for Direct injection internal combustion engines used oxidation catalysts as well as the conventional ones Petrol engines used three-way catalysts require one certain operating temperature to keep the pollutants in sufficient Dimensions too convert and reduce the pollutant emissions noticeably. The three-way catalysts are intended in the context of the present invention to the oxidation catalysts counted become.

Should only the usual In the exhaust gas contained unburned hydrocarbons or the present Carbon monoxide can be oxidized, a minimum operating temperature of 150 ° C up to 250 ° C be considered sufficient. Especially because of the high HC emissions during the cold start phase, the oxidation catalyst is usually the Exhaust after-treatment system, which is located closest to the outlet of the internal combustion engine is and first of the hot ones Exhaust gases flowed through becomes.

to Oxidation of the exhaust components to be reduced by means of oxidation catalyst oxygen is required, which may be present in the exhaust gas itself and / or the predominantly during of the superstoichiometric Operating (λ> 1) of the internal combustion engine in the surface coating of the oxidation catalyst is stored and during the superstoichiometric Operation (λ <1) of the internal combustion engine released and used for oxidation.

to Determination of stored and released oxygen quantities using computational models, upstream and downstream of the Oxidation catalyst, a lambda probe can be provided. to Determining the oxygen content of the exhaust gas can be a lambda probe upstream of the Serve oxidation catalyst.

Selective catalysts, so-called SCR catalysts, are used to reduce the nitrogen oxides, in which reducing agent is introduced into the exhaust gas in a targeted manner in order to selectively reduce the nitrogen oxides. As a reducing agent, not only ammonia and urea but also unburned hydrocarbons are used. The latter is also referred to as HC enrichment, the un burned hydrocarbons are introduced directly into the exhaust system or else by internal engine measures, for example by a post-injection of additional fuel into the combustion chamber after the actual combustion, are supplied. In this case, the nacheingespritzte fuel is not ignited in the combustion chamber by the still running main combustion or by - even after completion of the main combustion - high combustion gas temperatures, but are introduced during the charge exchange in the exhaust system.

In principle, the nitrogen oxide emissions can also be reduced with a so-called nitric oxide storage catalyst (LNT - Lean NO _x trap).

there The nitrogen oxides are first - during a lean operation of the internal combustion engine - absorbed in the catalyst d. H. collected and then stored during a regeneration phase for example, by means of a substoichiometric operation (for example, λ <0.95) of the internal combustion engine be reduced when lack of oxygen, with the exhaust gas located unburned hydrocarbons serve as a reducing agent. Further inner engine possibilities for enriching the exhaust gas with reducing agent, in particular with unburned hydrocarbons, provides the exhaust gas recirculation (EGR) and - at Diesel engines - the Throttling in the intake tract. As already for the SCR catalysts on stated above can enrich the exhaust gas with unburned hydrocarbons be realized by means of Nacheinspritzung of fuel or the reducing agent is introduced directly into the exhaust tract, for example, by injecting additional fuel upstream of the LNT.

During the regeneration phase, the nitrogen oxides are released and converted essentially into nitrogen dioxide (N ₂ ), carbon dioxide (CO ₂ ) and water (H ₂ O). For initiating and controlling the regeneration phase, a lambda probe arranged upstream of the LNT can be used with which the instantaneous air ratio λ present in the exhaust gas flow is determined.

Of the Sulfur contained in the exhaust gas is also absorbed in the LNT and must be in As part of a so-called desulfurization regularly removed. For this, the LNT to high temperatures, usually between 600 ° C and 700 ° C, heated and - as for regeneration previously described - with be supplied to a reducing agent.

to Minimizing the emission of soot particles According to the prior art so-called regenerative particle filters used the soot particles Filter out and store the exhaust, these soot particles burned intermittently during the regeneration of the filter become. For this purpose, oxygen or an excess of air in the exhaust gas is required to the soot in the Oxidize filter, for example, by a stoichiometric operation (λ> 1) of the internal combustion engine can be achieved. In general, for the regeneration of the filter an oxygen concentration of at least 3 to 5% is required.

In principle, the functionality of an oxidation catalytic converter and / or an LNT can also be monitored by means of lambda probes, as described in US Pat EP 1 936 140 A1 is described.

In the metrological determination of the air ratio λ by means of lambda probe is a metrological failure of the lambda probe to observe. When a certain HC concentration HC _threshold in the exhaust gas is exceeded, the lambda sensor delivers a value λ _meas for the air ratio deviating from the actual air ratio λ _tat .

In this case, the probe outputs a measured variable λ _mess that is above the actual air ratio λ _tat , ie the lambda probe determined air ratio λ _mess is greater than the actual air ratio λ _tat .

The deviation of the measured air ratio λ _mess of actually present air ratio λ _tat is dependent on the HC concentration upstream of the probe and the space velocity of the exhaust gas or the residence time of the probe passing the exhaust gases at the probe, the measurement error with increasing HC concentration increases, as in 1 shown.

1 shows in a diagram the measurement error in [%] ie (λ _tat - λ _mess ) / λ _mess in [%] over the HC concentration [ppm] in the exhaust gas at a given space velocity. Shown are a variety of value pairs and the associated regression line.

The technical relationships which lead to the faulty behavior of the probe or to the measurement error described above in the determination of the air ratio λ, will be briefly described below with reference to 2 explained.

According to 2 the exhaust gas passes the arranged in the exhaust system or the exhaust pipe probe 1 (indicated by arrows). Upstream of the probe 1 the exhaust gas has an O ₂ concentration O _{2, up} . Furthermore, the exhaust gas contains, inter alia, carbon dioxide (CO ₂ ), carbon monoxide (CO) and unburned hydrocarbons (HC) in the Kon CO _{2, up} , CO _up and HC _up .

At least a part of the reducing exhaust gas constituents d. H. the one to be oxidized Exhaust components d. H. carbon monoxide (CO) and unburned Hydrocarbons (HC) are emitted when the probe passes the probe oxidized. These oxidation processes are similar to those occurring in an oxidation catalyst reactions; also because the probe at least partially with similar or identical materials coated is like an oxidation catalyst.

As a result of the oxidation processes, the concentrations of particulate matter involved decrease so that the concentration of carbon monoxide (CO), unburned hydrocarbons (HC) and oxygen downstream of the probe - CO _down , HC _down and O _{2, down} - is below the CO _up , HC _up , O _{2, up} upstream of the probe.

The decrease in the oxygen concentration from O _{2, up} to O _{2, down} results from the oxygen consumption in the context of the oxidation processes taking place at the probe. The value λ _measured by the probe outputs as measured variable, based on the oxygen concentration downstream of the probe (O _{2, down),} so that λ _{be measured} can be referred to as λ _down. The following applies: λ down = λ mess

However, the oxidation processes taking place at the probe can not assume an arbitrarily large extent. If the HC concentration upstream of the probe exceeds a certain threshold with HC _up > HC _threshold , the probe is no longer able to oxidize further HC.

3a shows this functional relationship, where the HC concentration upstream of the probe (HC _up ) is plotted on the abscissa and the HC concentration (ΔHC _probe ) degraded on the probe is plotted on the ordinate; each in ppm.

For example, if the exhaust gas has an HC concentration of HC _up = 20,000 ppm, and the probe has a maximum oxidation capacity, ie threshold threshold of HC _threshold = 8,000 ppm, unburned hydrocarbons in the exhaust downstream of the probe are HC _down = 12,000 ppm in front.

3b Figure 11 shows the functional relationship between the HC concentration upstream of the probe (HC _up ) plotted again on the abscissa and the concentration downstream of the probe (HC _down ) plotted on the ordinate. The 3a and 3b correspond with each other.

Referring to the aforementioned example thus corresponds to the measured value determined by the sands λ _measuring the actual air ratio λ _{was doing} as long as the following applies: HC _up <HC _threshold.

If, however, HC _up > HC _threshold , the above-mentioned actual air ratio λ _{tat represents} only a theoretical value in which it is assumed that the reducing exhaust gas constituents are actually completely oxidized at the probe, so that the HC concentration downstream of the probe is zero would. This theoretical air ratio λ _tat is useful for a variety of applications. The algorithms stored in the engine control for the operation of the internal combustion engine are based in part on this - in some cases only theoretical - air ratio λ _tat .

With the actual air ratio λ _tat , it is also possible to determine or calculate an actual oxygen concentration downstream of the probe (O _{2, down, tat} ), again assuming complete oxidation of the reducing exhaust gas constituents on the probe. The concentration O _{2, down, tat} thus indicates the oxygen concentration downstream of the probe for the - occasionally theoretical - case that for the HC concentration downstream of the probe: HC _down = 0.

Frequently, however, it is also helpful to know the air ratio λ _up upstream of the probe, this air ratio being based on the concentrations of exhaust components present upstream of the probe.

Thus, according to the DE 697 19 460 T2 an oxygen sensor is used to determine the oxygen concentration in the exhaust gas upstream of the sensor. This O ₂ concentration is needed to control the EGR rate of exhaust gas recirculation (EGR) and an exhaust aftertreatment system to reduce nitrogen oxides, particularly the amount of fuel (HC) supplied thereto by post injection.

Known is that the oxidation processes at the oxygen sensor to do so to lead, that the oxygen concentration emitted by the sensor is lower is as the actual upstream the concentration present in the sensor. To this measurement error To correct, the HC concentration is near the sensor estimated, calculates the oxygen concentration that is necessary to these hydrocarbons to oxidize and the determined in this way oxygen concentration or amount of oxygen used to correct the sensor signal.

The fact that the oxidation processes taking place at the sensor are limited, as stated above, and that the oxidation at the sensor comes to a halt when a certain HC concentration HC _{threshold is} exceeded, is not recognized as a source of error and is therefore not taken into account.

Against this background, it is the object of the present invention to provide a method for determining the air ratio λ _tat or λ _up in the exhaust system of an internal combustion engine downstream or upstream of a arranged in the exhaust system lambda probe.

• • die HC-Konzentration der unverbrannten Kohlenwasserstoffe HC_up stromaufwärts der Lambda-Sonde ermittelt wird,
• • die an der Sonde oxidierte HC-Konzentration ΔHC_Sonde in Abhängigkeit von HC_up bestimmt wird,
• • der der Brennkraftmaschine zugeführte Luftmassenstrom m_air bestimmt wird,
• • das Luftverhältnis λ_mess mittels Lambda-Sonde meßtechnisch bestimmt wird,
• • der bis stromabwärts der Sonde effektiv oxidierte Kraftstoffmassenstrom m_fuel,eff bestimmt wird mit m_fuel,eff = (m_air/λ_mess)/L_st,
• • das Luftverhältnis λ_up stromaufwärts der Sonde bestimmt wird mit λ_up = (m_air/m_fuel,up)/L_st, wobei
• – der an der Sonde oxidierte Kraftstoffmassenstrom Δm_fuel,Sonde unter Verwendung der HC-Konzentration ΔHC_Sonde bestimmt wird, und
• – der bis stromaufwärts der Sonde oxidierte Kraftstoffmassenstrom m_fuel,up mit m_fuel,up = m_fuel,eff – Δm_fuel,Sonde bestimmt wird, und/oder das Luftverhältnis λ_tat bestimmt wird mit λ_tat = [m_air/(m_fuel,eff + Δm_{fuel unburnt,Sonde})]/ L_st, wobei
• – die HC-Konzentration der unverbrannten Kohlenwasserstoffe HC_down stromabwärts der Lambda-Sonde unter Verwendung von HC_up und ΔHC_Sonde bestimmt wird, und
• – der an der Sonde nicht oxidierte Kraftstoffmassenstrom Δm_{fuel unburnt,Sonde} unter Verwendung der HC-Konzentration HC_down bestimmt wird.

This object is achieved by a method for determining the air ratio λ in the exhaust system of an internal combustion engine by means of a lambda probe arranged in the exhaust system, in which

• The HC concentration of the unburned hydrocarbons HC _up upstream of the lambda probe is determined,
• • which is determined on the probe oxidized HC concentration ΔHC _probe as a function of HC _up,
• The mass air flow m _air supplied to the internal combustion engine is determined,
• The air ratio λ _{mess is determined} by means of lambda probe by measurement,
• The _{fuel mass flow} m _{fuel, eff} , effectively oxidized downstream of the probe is determined with m _{fuel, eff} = (m _air / λ _mess ) / L _st ,
• The air ratio λ _up upstream of the probe is determined with λ _up = (m _air / m _{fuel, up} ) / L _st , where
• The fuel mass flow Δm _fuel oxidized at the probe is determined using the HC concentration ΔHC _probe , and
• - the up upstream of the probe oxidized fuel mass flow m _{fuel, up} to m _{fuel, up} = m _{fuel, eff} - Dm _{fuel, the probe} is determined, and / or the air ratio _did λ is determined by λ _tat = [m _air / (m _{fuel , eff} + Δm _{fuel unburnt, probe} )] / L _st , where
• The HC concentration of the unburned hydrocarbons HC _down downstream of the lambda probe is determined using HC _up and ΔHC _probe , and
• - The unoxidized fuel mass flow Δm _{fuel unburnt} at the probe _{, probe} is determined using the HC concentration HC _down .

With the method according to the invention, the air ratio λ _up upstream of the lambda probe and / or the actual air ratio λ _{tat is} determined with knowledge of the metrological faulty behavior of the lambda probe.

In a first method step, the concentration of unburned hydrocarbons HC _up upstream of the lambda probe is determined. For this purpose, the HG concentration can either be detected by measurement with a sensor or else the unburned fuel component contained in the exhaust gas is determined and converted into an HC concentration.

The latter requires the determination of the fuel fraction, although the cylinders fed to the combustion but the cylinders are unburned as part of the charge cycle or incomplete burned leaves. Possibly is a fuel share to consider, the downstream of the exhaust gas the cylinder and upstream the probe, for example in the context of an enrichment with reducing agent by injection, fed has been.

The HG concentration HC _up determined in this way is used in a second method step to determine the HC concentration ΔHC _probe oxidized at the probe. The functional relationship between HC _up and ΔHC _probe was previously discussed above 3a discussed and is characteristic of each probe.

In addition, the internal combustion engine supplied air mass flow m _{air is} determined, which can be done for example by means of a arranged in the intake tract of the engine heating wire, and the air ratio λ _mess detected by means of arranged in the exhaust system lambda probe by measurement.

The air mass flow m _air supplied to the internal combustion engine can alternatively also be calculated or estimated using the rotational speed, the number of cylinders, the cylinder volume and the cylinder pressure.

The air mass flow m _air determined in the third method step and the air ratio λ _{mess detected} in the fourth method step are used in a fifth method step to determine the _fuel mass flow m _{fuel, eff} effectively oxidized downstream of the probe, where: m fuel, eff = m air / λ mess ) / L st

The fuel mass flow m _{fuel, eff} corresponds to the detected by means of lambda probe air ratio λ _mess , since both parameters take into account both the upstream of the probe burned fuel component m _{fuel, up} and oxidized at the probe fuel mass flow Δm _{fuel, probe} . The constant L _st stands for the stoichiometric air requirement.

In a sixth method step, the air ratio λ _up upstream of the probe is determined by: λ up = (m air / m fuel, up ) / L st

For the fuel _{mass flow} m _{fuel, up} oxidized upstream of the probe: m fuel, up = m fuel, eff - Δm fuel, probe

In this case, the oxidized fuel mass flow at the _{probe is} determined using the HC concentration ΔHC _probe , which takes place by converting the concentration of unburned hydrocarbons in a fuel mass flow.

In the sixth method step, alternatively or additionally, the actual air ratio λ _{tat is} determined with: λ did = [m air / (M fuel, eff + Δm fuel unburnt, probe )] / L st

For this purpose, the HC concentration downstream of the probe HC _{down is} determined with the previously determined HC concentrations HC _up and ΔHC _probe , where the following applies: HC down = HC up - ΔHC probe

The functional relationship between HC _down and HC _up has already been discussed above 3b discussed and is characteristic of each probe.

Subsequently, the fuel mass flow .DELTA.m.sub.fuel not oxidized on the probe is _{determined, and the probe} is determined using _{thisconcentration} HC _down .

The method according to the invention thus achieves the object on which the invention is based, namely a method for determining the air ratio λ _tat or λ _up in the exhaust system of an internal combustion engine downstream or upstream of a lambda probe arranged in the exhaust system.

Further advantageous method variants according to the subclaims explained below.

Advantageous embodiments of the method are those in which the air ratio λ _up is used to determine the oxygen concentration O _{2, up} upstream of the probe.

Further advantageous are embodiments of the method in which the air ratio λ _tat was used to determine the oxygen concentration O _{2, down, tat} .

As already explained at the beginning was, can by means of two lambda probes the functionality an oxidation catalyst and / or a LNT be monitored.

The supervision can also according to the invention the determination of oxygen concentrations and their comparison which should be considered functional, if sufficient Oxygen is consumed d. H. the oxygen concentration decreases.

there are the oxygen concentrations downstream and upstream of the respective exhaust aftertreatment system of interest. At the downstream arranged Probe is thus the oxygen concentration upstream of the Probe decisive, while at the upstream arranged probe the oxygen concentration downstream of the Probe is important.

With regard to the last-mentioned probe, the air ratio λ _mess recorded by means of a probe could in principle also be used to determine the oxygen concentration O _{2, down} downstream of the probe.

However, if it is to be determined by means of calculation models how much oxygen is stored or released in the exhaust aftertreatment system, the determination of the oxygen concentration O _{2, down, tat} using the air ratio λ _{tat is} to be preferred.

Regarding the regeneration of a particulate filter, a lambda probe may be used upstream of the filter to control regeneration. Oxygen is required to oxidize the soot particles collected in the filter, ie an air ratio λ> 1. The oxygen concentration upstream of the filter should be at least 3 to 5%. A monitoring of the required minimum oxygen concentration can thus be carried out with the method according to the invention, wherein as a control variable, for example, the oxygen concentration O _{2, down, tat is} used.

Advantageous are embodiments of the method taking into account the space velocity becomes.

As already stated above, the metrological error of the lambda probe also depends on the space velocity of the exhaust gas or on the residence time of the exhaust gases passing through the probe at the probe (see also FIG 1 ).

The functional relationship between the HC concentration upstream of the probe HC _up and the HC concentration ΔHC _probe degraded at the probe is also influenced by the space velocity. So the more so at the probe unburned hydrocarbons oxidize the lower the space velocity, ie the greater the residence time at the probe (see also FIG 3a ).

Due to the principle depends on in 3b represented functional relationship between the HC concentration upstream of the probe HC _up and the concentration downstream of the probe HC _down also from the space velocity.

A consideration the space velocity in the context of the method according to the invention thus leads to a higher one Accuracy in the determined air conditions or oxygen concentrations.

Advantageous are embodiments the method in which the carbon monoxide contained in the exhaust gas considered in such a way that the carbon monoxide concentrations in an adequate one HC concentration converts and the carbon monoxide in the further how unburned hydrocarbons are treated.

As already executed was formed, the carbon monoxide contained in the exhaust gas (CO) together with the unburned hydrocarbons (HC) the "reducing exhaust components" or "exhaust components to be oxidized". Not just the unburned Hydrocarbons (HC), but also the carbon monoxide (CO) is oxidized when passing the probe to the probe at least partially. Ie. Part of the oxygen contained in the exhaust gas becomes oxidation of carbon monoxide used.

In the calculation of the actual air ratio λ _tat , a complete oxidation of the reducing exhaust gas constituents on the probe is assumed according to the process variant in question. The concentration O _{2, down, tat} indicates the oxygen concentration downstream of the probe for the - occasionally theoretical - case that for the HC concentration downstream of the probe HC _down = 0 and for the CO concentration downstream of the probe also CO _down = 0 applies.

insofar forms the present embodiment of the proceedings - due the consideration of the Carbon monoxide - the indeed processes taking place at the probe or reactions even more realistically, so that the determined air conditions or oxygen concentrations have a higher accuracy.

In the method variant in question, the HC concentrations used, ie HC _down , HC _up , ΔHC _probe and HC _threshold thus also include the CO concentrations CO _down , CO _up and ΔCO _probe .

In the following the invention according to the 1 to 4 described in more detail. Hereby shows:

1 schematically in a diagram the measurement error of a arranged in the exhaust system of an internal combustion engine lambda probe (λ _tat - λ _mess ) / λ _mess [%] on the HC concentration [ppm] at a given space velocity,

2 schematically a lambda probe arranged in the exhaust gas flow, together with the exhaust gas components and the concentrations downstream and upstream of the probe,

3a in a diagram, the functional relationship between the HC concentration upstream of the probe HC _up and the HC concentration at the probe degraded ΔHC _probe ,

3b in a diagram, the functional relationship between the HC concentration upstream of the probe HC _up and the HC concentration downstream of the probe HC _down , and

4 an embodiment of the method in the form of a flow chart.

The 1 to 3b have already been described above in connection with the measurement behavior of a lambda probe.

4 shows an embodiment of the method in the form of a flow chart.

In a first method step, the concentration of unburned hydrocarbons HC _up upstream of the lambda probe is determined (S1).

The HC concentration HC _up determined in this way is used in a second method step to determine the HC concentration ΔHC _probe oxidized at the probe (S2). The functional relationship between HC _up and ΔHC _probe is used, possibly considering the space velocity.

Subsequently, in a third method step, the air mass flow m _air supplied to the internal combustion engine is determined (S3) and in a fourth method step the air ratio λ _{mess is detected} by means of the lambda probe arranged in the exhaust gas system (S4).

In the subsequent fifth method step, the air mass flow m _air (S3) and the air ratio λ _mess (S4) are used to determine the _fuel mass flow m _{fuel, eff} effectively oxidized downstream of the probe (S5). m fuel, eff = (m air / λ mess ) / L st

The constant _Lst denotes the stoichiometric air requirement.

In the further procedure, the air ratio λ _up upstream of the lambda probe and / or the actual air ratio λ _{tat is} determined.

If the air ratio λ _up upstream of the probe is to be determined, the fuel mass flow Δm _fuel, probe oxidized at the probe is first determined in a sixth method step using the HC concentration ΔHC _probe , which takes place by converting the concentration of unburned hydrocarbons into a fuel mass flow (S6).

Subsequently, in a seventh process step (S7), the fuel _{mass flow} m _{fuel, up} oxidized upstream of the probe is determined with: m fuel, up = m fuel, eff - Δm fuel, probe

In an eighth method step, the determined air mass flow m _air (S3) and the fuel mass flow m _{fuel, up} (S7) are then used to determine the air ratio λ _up upstream of the probe (S8). The following applies: λ up = (m air / m fuel, up ) / L st

If additionally or alternatively the actual air ratio λ _{tat is to be} determined, the HC concentration downstream of the probe HC _down is first determined in a ninth method step (S9) with the previously determined HC concentrations HC _up (S1) and ΔHC _probe (S2) where: HC down = HC up - ΔHC probe

Subsequently, in a tenth method step (S10), the fuel mass flow Δm _fuel , which is not oxidized at the probe, is _unburnt , and the probe is determined using this concentration HC _down .

In the eleventh method step (S11), the actual air ratio λ _tat is then determined with: λ did = [m air / (M fuel, eff + Δm fuel unburnt, probe )] / L st

1

Lambda probe

CO ₂

carbon dioxide

CO _{2, down}

CO ₂ concentration downstream of the probe

CO _{2, up}

CO ₂ concentration upstream of the probe

CO

Carbon monoxide

CO _down

CO concentration downstream of the probe

CO _up

CO concentration upstream the probe

ΔCO _probe

at the probe oxidized CO concentration

HC

unburned hydrocarbons

HC _down

HC concentration downstream the probe

HC _threshold

at the probe maximum oxidizable HC concentration

HC _up

HC concentration upstream the probe

ΔHC _probe

at the probe oxidized HC concentration

m _air

of the the internal combustion engine supplied Air mass flow

m _{fuel, eff}

to downstream the probe effectively oxidized fuel mass flow

m _{fuel, up}

to upstream the probe oxidized fuel mass flow

Δm _{fuel, probe}

at the probe oxidized fuel mass flow

Δm _{fuel unburnt, probe}

at the probe does not oxidise fuel mass flow

L _st

stoichiometric air requirements

O ₂

oxygen

O _{2, down}

O ₂ concentration downstream of the probe

O _{2, down, did}

actual O ₂ concentration downstream of the probe

O _{2, up}

O ₂ concentration upstream of the probe

ppm

Parts per million air ratio

λ

air ratio

λ _down

Air ratio downstream of the probe

λ _eff

effective air ratio

λ _mess

by means of Lambda probe measuring technology determined air ratio

λ _did

actual air ratio

λ _up

Air ratio upstream of the probe

Claims (5)

Method for determining the air ratio λ in the exhaust system of an internal combustion engine with means of a lambda probe arranged in the exhaust system ( 1 ), in which • the HC concentration of the unburned hydrocarbons HC _up upstream of the lambda probe ( 1 ) at the probe (s) 1 ) the oxidized HC concentration ΔHC _{probe is determined} as a function of HC _up , • the air mass flow m _air supplied to the internal combustion engine is determined, • the air ratio λ _meas by means of lambda probe ( 1 ) is determined by measuring technique, • the downstream of the probe ( 1 ) effectively oxidized fuel _{mass flow} m _{fuel, eff is} determined with m _{fuel, eff} = (m _air / λ _mess ) / L _st , and • the air ratio λ _up upstream of the probe ( 1 ) is determined with λ _up = (m _air / m _{fuel, up} ) / L _st , where - at the probe ( 1 ) oxidized fuel mass flow Δm _{fuel, probe} is determined using the HC concentration ΔHC _probe , and - the upstream of the probe ( 1 ) oxidized fuel mass flow m _{fuel, up} with m _{fuel, up} = m _{fuel, eff} - Δm _{fuel, probe is} determined, and / or the air ratio λ _{tat is} determined with λ _tat = [m _air / (m _{fuel, eff} + Δm _{fuel unburnt, probe} )] / L _st , where - the HC concentration of the unburned hydrocarbons HC _down downstream of the lambda probe ( 1 ) is determined using HC _up and ΔHC _probe , and - at the probe ( 1 ) unoxidized fuel mass flow Δm _{fuel unburnt, probe} is determined using the HC concentration HC _down . Method according to Claim 1, characterized in that the air ratio λ _up is used to determine the oxygen concentration O _2, upstream of the probe ( 1 ) to investigate. A method according to claim 1 or 2, characterized in that the air ratio λ _tat is used to determine the oxygen concentration O _{2, down, tat} . Method according to one of the preceding claims, characterized characterized in that the space velocity is taken into account. Method according to one of the preceding claims, characterized characterized in that the carbon monoxide contained in the exhaust gas takes into account in the way that the carbon monoxide concentrations in an adequate Converted HC concentration and further as unburned hydrocarbons be treated.