EP2080886B1 - Method for determining the air ratio - Google Patents

Description

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 context of the operation or the control of an internal combustion engine of particular importance.

Thus, the air ratio λ for determining the amount of fuel to be injected, the injection timing and / or control of exhaust gas recirculation is required, but also for monitoring and operating the different exhaust aftertreatment systems that are used in the prior art to reduce the pollutants and on the following is taken as an example. In this context, it will become clear that the air ratio λ is an essential operating parameter of the internal combustion engine, in particular with regard to the exhaust gas aftertreatment.

In the prior art, internal combustion engines are equipped with various exhaust aftertreatment systems to reduce pollutant emissions. Although at a sufficiently high temperature level and the presence of sufficiently large amounts of oxygen, an oxidation of the unburned hydrocarbons (HC) and carbon monoxide (CO) takes place. However, special reactors and / or filters usually have to be provided in the exhaust tract in order to noticeably reduce pollutant emissions under all operating conditions. In the context of the present invention, the carbon monoxide (CO) and the unburned hydrocarbons (HC) are combined under the concept of "reducing exhaust gas constituents" or "exhaust gas constituents to be oxidized".

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 by means of existing unoxidized exhaust gas components, namely the carbon monoxides and the unburned hydrocarbons, while simultaneously oxidizing these exhaust gas components.

In internal combustion engines, which are operated with an excess of air, for example, working in lean-burn gasoline engines, but also direct injection diesel engines and direct injection gasoline engines, the nitrogen oxides located in the exhaust gas principle d. H. due to the lack of reducing agents can not be reduced.

For the oxidation of the unburned hydrocarbons (HC) and of carbon monoxide (CO), an oxidation catalyst is therefore provided in the exhaust system. Both these used for direct injection internal combustion engines oxidation catalysts and the three-way catalysts used in conventional gasoline engines require a certain operating temperature in order to convert the pollutants sufficiently and to reduce the pollutant emissions noticeably. The three-way catalysts are to be counted in the context of the present invention to the oxidation catalysts.

If only the normally contained in the exhaust gas unburned hydrocarbons or the present carbon monoxide are oxidized, a minimum operating temperature of 150 ° C to 250 ° C can be considered sufficient. In particular, due to the high HC emissions during the cold start phase of the oxidation catalyst is usually the exhaust aftertreatment system, which is located closest to the outlet of the internal combustion engine and is first flowed through by the hot exhaust gases.

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

To determine the stored and released amounts of oxygen by means of computational models upstream and downstream of the oxidation catalyst, a Lambda probe can be provided. To determine the oxygen content of the exhaust gas, a lambda probe can serve upstream of the oxidation catalyst.

To reduce the nitrogen oxides u. a. Selective catalysts, so-called SCR catalysts, used in which targeted reducing agent is introduced into the exhaust gas 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, wherein the unburned hydrocarbons are introduced directly into the exhaust tract or else by internal engine measures, for example by a post-injection of additional fuel into the combustion chamber after the actual combustion 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 nitrogen oxide storage catalyst (LNT lean NO _x trap).

The nitrogen oxides are first - during a lean operation of the internal combustion engine - absorbed in the catalyst and collected and then reduced during a regeneration phase, for example by means of a substoichiometric operation (for example, λ <0.95) of the engine in oxygen deficiency, the in Exhausted unburned hydrocarbons serve as a reducing agent. Further internal engine options for enriching the exhaust gas with reducing agent, in particular with unburned hydrocarbons, provides the exhaust gas recirculation (EGR) and - in diesel engines - the throttling in the intake system. As already stated above for the SCR catalysts, an enrichment of the exhaust gas with unburned hydrocarbons can also be realized by post-injection of fuel or else 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.

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

To minimize the emission of soot particles so-called regenerative particulate filters are used in the prior art, which filter out and store the soot particles from the exhaust gas, these soot particles are intermittently burned in the regeneration of the filter. For this purpose, oxygen or an excess of air in the exhaust gas is required to oxidize the soot in the filter, which can be achieved for example by a superstoichiometric operation (λ> 1) of the internal combustion engine. As a rule, an oxygen concentration of at least 3 to 5% is required for the regeneration of the filter.

Basically, the functionality of an oxidation catalyst and / or an LNT can be monitored by means of lambda probes, as in the application EP 06126595.5 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 _mass , which lies above the actual air ratio λ _tat , ie the lambda probe determined air ratio A _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 FIG. 1 shown.

FIG. 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 FIG. 2 explained.

According to FIG. 2 the exhaust gas passes the probe 1 arranged in the exhaust system or the exhaust gas line (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 concentrations CO _{2, up} , CO _up and HC _up .

At least part of the reducing exhaust components d. H. the exhaust components to be oxidized d. H. of carbon monoxide (CO) and unburned hydrocarbons (HC) are oxidized as the probe passes the probe. These oxidation processes are similar to those occurring in an oxidation catalyst reactions; also because the probe is at least partially coated with similar or identical materials as 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 _brown. The following applies: $${\lambda }_{\mathrm{down}}={\lambda }_{\mathrm{mess}}$$

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.

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

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

FIG. 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 FIGS. 3a and 3b correspond with each other.

With reference to the aforementioned example, the measured value λ _mess determined by the probe thus corresponds to the actual air ratio λ _tat as long as: 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 _did 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.

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 unbumt,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,
• Is determined ■ the oxidized at the probe concentration of HC ΔHC _probe as a function of HC _up,
• ■ the air mass 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 _fuel mass flow m _fuel oxidized to the upstream of the probe _{, up} with m _{fuel, up} = m _{fuel, eff} - Δm _{fuel, 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 is determined using HC _up and ΔHC _probe , and
  • the fuel mass flow Δm _{fuel unbumed} at the probe is determined _{unbound, probe} 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 HC concentration can either be detected by measurement with a sensor or it is determined the unburned fuel contained in the exhaust gas and converted into an HC concentration.

The latter requires the determination of the proportion of fuel which, although admitted to the cylinders for combustion, leaves the cylinders unburned or incompletely burned as part of the change of charge. Optionally, account must be taken of a proportion of fuel which has been supplied to the exhaust gas downstream of the cylinder and upstream of the probe, for example as part of an enrichment with reducing agent by means of injection.

The HC concentration HC _up determined in this way is used in a second method step to add the HC concentration ΔHC _probe oxidized at the probe determine. The functional relationship between HC _up and ΔHC _probe was previously discussed above FIG. 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: $${\mathrm{m}}_{\mathrm{fuel}.\mathrm{eff}}\mathrm{=}\left({\mathrm{m}}_{\mathrm{air}}\mathrm{/}{\mathrm{\lambda }}_{\mathrm{mess}}\right)\mathrm{/}{\mathrm{L}}_{\mathrm{st}}$$

The fuel mass flow m _fuel.eff corresponding to the detected by the lambda probe air ratio λ _measured since both parameters take into account both the upstream burned fuel portion of the probe m _fuel.up and oxidized at the probe Kraftstoffinassenstrom Dm _fuel.Sonde. 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: $${\mathrm{\lambda }}_{\mathrm{up}}\mathrm{=}\left({\mathrm{m}}_{\mathrm{air}}\mathrm{/}{\mathrm{m}}_{\mathrm{fuel}\mathrm{.}\mathrm{up}}\right)\mathrm{/}{\mathrm{L}}_{\mathrm{st}}$$

For the fuel _{mass flow} m _{fuel, up} oxidized upstream of the probe: $${\mathrm{m}}_{\mathrm{fuel}\mathrm{.}\mathrm{up}}\mathrm{=}{\mathrm{m}}_{\mathrm{fuel}\mathrm{.}\mathrm{eff}}\mathrm{-}\mathrm{\Delta }{\mathrm{m}}_{\mathrm{fuel}\mathrm{.}\mathrm{probe}}$$

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

In the sixth method step, alternatively or additionally, the actual air ratio λ _{tat is} determined with: $${\mathrm{\lambda }}_{\mathrm{did}}\mathrm{=}\left[{\mathrm{m}}_{\mathrm{air}}\mathrm{/}\left({\mathrm{m}}_{\mathrm{fuel}\mathrm{.}\mathrm{eff}}\mathrm{+}\mathrm{\Delta }{\mathrm{m}}_{\mathrm{fuel\; unburnt}\mathrm{.}\mathrm{probe}}\right)\right]\mathrm{/}{\mathrm{L}}_{\mathrm{st}}$$

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: $${\mathrm{HC}}_{\mathrm{down}}={\mathrm{HC}}_{\mathrm{up}}-{\mathrm{\Delta HC}}_{\mathrm{probe}}$$

The functional relationship between HC _down and HC _up has already been discussed above FIG. 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 process variants according to the subclaims are 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, the functionality of an oxidation catalytic converter and / or an LNT can be monitored by means of two lambda probes.

According to the invention, the monitoring can also be directed to the determination of the oxygen concentrations and their comparison, it being considered to be functional if sufficient oxygen is consumed, ie. the oxygen concentration decreases.

The oxygen concentrations downstream or upstream of the respective exhaust aftertreatment system are of interest. Thus, in the downstream probe, the oxygen concentration upstream of the probe is critical, while in the upstream 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.

If, however, 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.

Embodiments of the method in which the space velocity is taken into account are advantageous.

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 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. Thus, the lower the space velocity, ie, the greater the residence time at the probe, the more unburned hydrocarbons are oxidized at the probe (see also FIG FIG. 3a ).

Due to the principle depends on in FIG. 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.

Taking into account the space velocity in the context of the method according to the invention thus leads to a higher accuracy in the determined air ratios or oxygen concentrations.

Advantageous embodiments of the method in which the carbon monoxide contained in the exhaust gas is taken into account in such a way that the carbon monoxide concentrations are converted to an adequate HC concentration and the carbon monoxide are further treated as unburned hydrocarbons.

As already stated, the carbon monoxide (CO) present in the exhaust gas together with the unburned hydrocarbons (HC) forms the "reducing exhaust components" or "exhaust components to be oxidized". Not only the unburned hydrocarbons (HC) but also the carbon monoxide (CO) is at least partially oxidized as the probe passes the probe. Ie. Part of the oxygen contained in the exhaust gas is used to oxidize the carbon monoxide.

When calculating the actual air ratio λ _tat according to the process variant in question of a complete oxidation of the reducing exhaust gas components the probe went out. 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 applies and for the CO concentration downstream of the probe also CO _down = 0 applies.

In this respect, the present embodiment of the method - due to the consideration of the carbon monoxide - even more realistically from the processes or reactions actually occurring at the probe, 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 .

Fig. 1

schematisch in einem Diagramm den Meßfehler einer im Abgassystem einer Brennkraftmaschine angeordneten Lambda-Sonde (λ_tat - λ_mess)/ λ_mess [%] über der HC-Konzentration [ppm] bei einer vorgegebenen Raumgeschwindigkeit,

Fig. 2

schematisch eine im Abgasstrom angeordnete Lambda-Sonde mitsamt den Abgasbestandteilen und den Konzentrationen stromabwärts und stromaufwärts der Sonde,

Fig. 3a

in einem Diagramm den funktionalen Zusammenhang zwischen der HC- Konzentration stromaufwärts der Sonde HC_up und der an der Sonde abgebauten HC-Konzentration ΔHC_Sonde,

Fig. 3b

in einem Diagramm den funktionalen Zusammenhang zwischen der HC- Konzentration stromaufwärts der Sonde HC_up und der HC-Konzentration stromabwärts der Sonde HC_down, und

Fig. 4

eine Ausführungsform des Verfahrens in Gestalt eines Flußdiagramms.

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

Fig. 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,

Fig. 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,

Fig. 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 ,

Fig. 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

Fig. 4

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

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

FIG. 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 thus determined concentration of HC HC is used _up in a second process step to determine the oxidized at the probe concentration of HC ΔHC _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). $${\mathrm{m}}_{\mathrm{fuel}.\mathrm{eff}}\mathrm{=}\left({\mathrm{m}}_{\mathrm{air}}\mathrm{/}{\mathrm{\lambda }}_{\mathrm{mess}}\right)\mathrm{/}{\mathrm{L}}_{\mathrm{st}}$$

The constant _Lst denotes the stoichiometric air requirement.

In the further process, 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 is achieved by the conversion of the Concentration of unburned hydrocarbons in a fuel mass flow takes place (S6).

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

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: $${\mathrm{\lambda }}_{\mathrm{up}}\mathrm{=}\left({\mathrm{m}}_{\mathrm{air}}\mathrm{/}{\mathrm{m}}_{\mathrm{fuel}\mathrm{.}\mathrm{up}}\right)\mathrm{/}{\mathrm{L}}_{\mathrm{st}}$$

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: $${\mathrm{HC}}_{\mathrm{down}}={\mathrm{HC}}_{\mathrm{up}}-{\mathrm{\Delta HC}}_{\mathrm{probe}}$$

Subsequently, in a tenth method step (S 10), 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: $${\mathrm{\lambda }}_{\mathrm{did}}\mathrm{=}\left[{\mathrm{m}}_{\mathrm{air}}\mathrm{/}\left({\mathrm{m}}_{\mathrm{fuel}\mathrm{.}\mathrm{eff}}\mathrm{+}\mathrm{\Delta }{\mathrm{m}}_{\mathrm{fuel\; unburnt}\mathrm{.}\mathrm{probe}}\right)\right]\mathrm{/}{\mathrm{L}}_{\mathrm{st}}$$

reference numeral

1

Lambda probe

CO ₂

carbon dioxide

Co _{2nd 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 of the probe

ΔCO _probe

oxidized CO concentration at the probe

HC

unburned hydrocarbons

HC _down

HC concentration downstream of the probe

HC _threshold

maximum oxidizable HC concentration at the probe

HC _up

HC concentration upstream of the probe

ΔHC _probe

oxidized HC concentration at the probe

m _air

the internal combustion engine supplied air mass flow

m _fuel.eff

effectively oxidized fuel mass flow down to the downstream of the probe

m _fuel.eff

oxidized fuel mass flow to upstream of the probe

Δm _{fuel probe}

oxidized fuel mass flow at the probe

Δm _{fuel unhurnt.Sonde}

Unoxidized fuel mass flow at the probe

L _st

stoichiometric air requirement

O ₂

oxygen

O _{2nd down}

O ₂ concentration downstream of the probe

O _{2nd down}

actual O ₂ concentration downstream of the probe

O _2.up

O ₂ concentration upstream of the probe

ppm

parts per million

λ

air ratio

λ _down

Air ratio downstream of the probe

λ _off

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)

1. Method for determining the air ratio λ in the exhaust system of an internal combustion engine by means of a lambda probe (1) arranged in the exhaust system, in which method

   ■ the HC concentration of the unburned hydrocarbons HC_up upstream of the lambda probe (1) is determined,

   ■ the HC concentration ΔHC_probe oxidized at the probe (1) 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 is determined by measurement by means of the lambda probe (1),

   ■ the effective fuel mass flow m_fuel,_eff oxidized up to downstream of the probe (1) is determined using m_fuel,eff (m_air / λ_meas) / L_st, with the constant L_st indicating the stoichiometric air demand, and

   ■ the air ratio λ_up upstream of the probe (1) is determined using λ_up = (m_air / m_fuel,up) / L_st, with

   - the fuel mass flow Δm_fuel,probe oxidized at the probe (1) being determined using the HC concentration ΔHC_probe, and

   - the fuel mass flow m_fuel,up oxidized up to upstream of the probe (1) being determined using m_fuel,up = m_fuel,eff - Δm_fuel,probe,

   and/or
   the air ratio λ_act is determined using λ_act = [m_air / (m_fuel,eff + Δm_{fuel unbumt,probe})]/ L_st, with

   - the HC concentration of the unburned hydrocarbons HC_down downstream of the lambda probe (1) being determined using HC_up ΔHC_probe, and

   - the fuel mass flow Δm_fuel unbumt,probe not oxidized at the probe (1) being determined using the HC concentration HC_down.
2. Method according to Claim 1, characterized in that the air ratio λ_up is used to determine the oxygen concentration O₂,_up upstream of the probe (1).
3. Method according to Claim 1 or 2, characterized in that the air ratio λ_act is used to determine the oxygen concentration O₂,_down,_act.
4. Method according to one of the preceding claims, characterized in that the spatial velocity is taken into consideration.
5. Method according to one of the preceding claims, characterized in that the carbon monoxide contained in the exhaust gas is taken into consideration, specifically in such a way that the carbon monoxide concentrations are converted into an adequate HC concentration and are thereafter treated as unburned hydrocarbons.

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