DE102019106228A1 - Method and device for operating an internal combustion engine with a low-pressure exhaust gas recirculation system - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine (2) with a low-pressure exhaust gas recirculation (8) based on a corrected mass flow specification (mf) of a mass flow in the area of the low-pressure exhaust gas recirculation (8), with the following steps: Determining (S1) a first estimated mass flow specification ( mf) according to a first physical model based on several input variables subject to tolerances; - determining (S2) a tolerance of the first estimated mass flow specification (mf) according to the first physical model based on the tolerances of the several input variables subject to tolerances; - determining (S3) a second estimated mass flow specification ( mf) according to a second physical model based on several input variables subject to tolerances, at least one of which is identical to the input variables subject to tolerances of the first physical model; - determining (S4) a tolerance (σ) of the second estimated mass flow rate (mf) according to the Wide physical model based on the tolerances of the several input variables subject to tolerances; - Determination (S5) of the corrected mass flow specification (mf) depending on the first and second estimated mass flow specification (mf: mf) and the tolerances (σ) of the first and second estimated mass flow specifications (mf , mf).

Description

Technical area

The invention relates to internal combustion engines, in particular internal combustion engines with low-pressure exhaust gas recirculation. The invention also relates to a method for determining mass flows in the internal combustion engine.

Technical background

Supercharged internal combustion engines have high pressure exhaust gas recirculation (HP exhaust gas recirculation) to optimize pollutant emissions and / or fuel consumption, through which the intake air can be provided with inert gases. To further optimize pollutant emissions and fuel consumption, low-pressure exhaust gas recirculation (LP exhaust gas recirculation) can also be provided, through which combustion exhaust gas is added to the fresh air before it is sucked in by the compressor of the charging device.

The operation of the internal combustion engine is based on a precise setting of the ratio between fresh air and recirculated combustion exhaust gas. For this purpose, the mass flows are either measured or modeled from other measured state variables. A conventional procedure for determining a mass flow through the LP exhaust gas recirculation uses the so-called throttle equation. However, as a rule, the measured mass flows and also the other input variables are subject to tolerances, so that the modeled variables used for controlling the internal combustion engine, such as the exhaust gas recirculation rate (EGR rate) or the like, are also subject to tolerances.

From the pamphlet DE 10 2011 017 779 A1 a method for determining a low pressure exhaust gas recirculation mass flow in an air system of an internal combustion engine with low pressure exhaust gas recirculation is known. The low-pressure exhaust gas recirculation mass flow is determined on the basis of a preliminary low-pressure exhaust gas recirculation mass flow, which takes into account the pressure upstream and the pressure downstream of a low-pressure exhaust gas recirculation valve, the temperature upstream of the low-pressure exhaust gas recirculation valve and the geometry of the low-pressure exhaust gas recirculation valve. At least one mass balance-based variable is also taken into account in the determination of the low-pressure exhaust gas recirculation mass flow.

It is known to determine an optimal exhaust gas recirculation mass flow (EGR mass flow), which is calculated based on a measured concentration after the EGR mixing point, the concentrations of the inflowing mass flows, the second inflowing mass flow and the input variables of a throttle equation to determine the EGR mass flow. Depending on the operating point, the partially redundant information is evaluated in order to obtain an optimal EGR mass flow.

Disclosure of the invention

According to the invention, a method for operating an engine system based on a mass flow specification of a low pressure exhaust gas recirculation LP exhaust gas recirculation according to claim 1 and a device and an engine system according to the independent claims are provided.

Further refinements are given in the dependent claims.

• - Ermitteln einer ersten geschätzten Massenstromangabe gemäß einem ersten physikalischen Modell basierend auf mehreren toleranzbehafteten Eingangsgrößen;
• - Bestimmen einer Toleranz der ersten geschätzten Massenstromangabe gemäß des ersten physikalischen Modells basierend auf den Toleranzen der mehreren toleranzbehafteten Eingangsgrößen;
• - Ermitteln einer zweiten geschätzten Massenstromangabe gemäß eines zweiten physikalischen Modells basierend auf mehreren toleranzbehafteten Eingangsgrößen, von denen mindestens eine zu den toleranzbehafteten Eingangsgrößen des ersten physikalischen Modells identisch ist;
• - Bestimmen einer Toleranz der zweiten geschätzten Massenstromangabe gemäß dem zweiten physikalischen Modell basierend auf der Toleranzen der mehreren toleranzbehafteten Eingangsgröße;
• - Bestimmen der korrigierten Massenstromangabe abhängig von der ersten und zweiten geschätzten Massenstromangabe und den Toleranzen der ersten und zweiten geschätzten Massenstromangaben.

According to a first aspect, a method for operating an internal combustion engine with a low-pressure exhaust gas recirculation based on a corrected mass flow specification of a mass flow in the area of the low-pressure exhaust gas recirculation is provided, with the following steps:

• - Determination of a first estimated mass flow rate according to a first physical model based on a plurality of tolerance-affected input variables;
• - Determination of a tolerance of the first estimated mass flow specification according to the first physical model based on the tolerances of the plurality of input variables subject to tolerances;
• - Determination of a second estimated mass flow rate according to a second physical model based on a plurality of input variables with tolerances, of which at least one is identical to the input variables with tolerances of the first physical model;
• - Determining a tolerance of the second estimated mass flow rate according to the second physical model based on the tolerances of the plurality of input variable with tolerances;
• - Determination of the corrected mass flow information as a function of the first and second estimated mass flow information and the tolerances of the first and second estimated mass flow information.

The aim of the above method is to first determine a corrected mass flow information in the area of LP exhaust gas recirculation of an internal combustion engine. This mass flow specification can specify a fresh air mass flow, an LP EGR mass flow and / or an exhaust gas mass flow downstream of the LP exhaust gas recirculation. The corrected mass flow information is determined from estimated mass flow information on the basis of redundant variables of the gas routing system. The tolerances of the input variables are defined so that the tolerances of the estimated mass flow data determined using two independent methods can be determined in accordance with the associated tolerances. Depending on the tolerances determined in this regard, the corrected mass flow data can be determined from the two mass flow data determined independently of one another.

The physical and therefore more precise modeling of the corrected mass flow information based on input variables subject to tolerances results in lower pollutant emissions and lower fuel consumption of the engine system.

Furthermore, the first physical model can correspond to a throttle model and / or the second physical model can correspond to a mass flow balance.

Provision can be made for the tolerances of the first and / or second estimated mass flow information to be determined as a function of a linearization of the first or second physical model with respect to each of the corresponding input variables with tolerances.

Furthermore, the corrected mass flow specification can correspond to a low-pressure EGR mass flow.

• - Messen eines weiteren Massenstroms, um eine weitere Massenstromangabe zu erhalten,
• - Ermitteln eines ersten geschätzten Massenstromverhältnisses basierend auf der ersten geschätzten Massenstromangabe und der weiteren Massenstromangabe;
• - Bestimmen einer Toleranz des ersten geschätzten Massenstromverhältnisses abhängig von der Toleranz der ersten geschätzten Massenstromangabe und der Toleranz der gemessenen weiteren Massenstromangabe;
• - Ermitteln eines zweiten geschätzten Massenstromverhältnisses basierend auf der zweiten geschätzten Massenstromangabe und der weiteren Massenstromangabe;
• - Bestimmen einer Toleranz des zweiten geschätzten Massenstromverhältnisses abhängig von der Toleranz der zweiten geschätzten Massenstromangabe und der Toleranz der gemessenen weiteren Massenstromangabe;
• - Bestimmen der weiteren korrigierten Massenstromangabe abhängig von den ersten und zweiten geschätzten Massenstromverhältnissen, der korrigierten Massenstromangabe und den Toleranzen des ersten und des zweiten geschätzten Massenstromverhältnisses.

In particular, a further corrected mass flow specification for a further mass flow, in particular a corrected fresh air mass flow, can be determined by the following steps:

• - Measuring a further mass flow in order to obtain a further mass flow information,
• - Determining a first estimated mass flow ratio based on the first estimated mass flow specification and the further mass flow specification;
• - Determining a tolerance of the first estimated mass flow ratio as a function of the tolerance of the first estimated mass flow indication and the tolerance of the measured further mass flow indication;
• Determining a second estimated mass flow ratio based on the second estimated mass flow specification and the further mass flow specification;
• - Determining a tolerance of the second estimated mass flow ratio as a function of the tolerance of the second estimated mass flow indication and the tolerance of the measured further mass flow indication;
• - Determination of the further corrected mass flow rate as a function of the first and second estimated mass flow ratios, the corrected mass flow rate and the tolerances of the first and the second estimated mass flow ratio.

Furthermore, depending on the corrected mass flow information and / or the further corrected mass flow information, the corrected values of the input variables subject to tolerance can be calculated back so that the corrected values of the input variables subject to tolerances as well as the corrected mass flow information and / or the further corrected mass flow information satisfy the first or second physical model . Thus, in a further step, the corrected mass flow information can be calculated back into concrete values of the input variables based on the underlying functional dependencies in order to continue to ensure the validity of the calculation function for the corrected mass flow information.

In particular, the adapted values of the input variables can be determined according to the difference in their tolerances from one another and their sensitivities with regard to the mass flow specification or the further mass flow specification.

Furthermore, the adapted values of the input variables can be adapted successively in such a way that a mass flow specification determined according to the first and / or second physical model approaches the corrected mass flow specification.

Provision can be made for a base point to be determined for each of the input variables subject to tolerances, to which the relevant input variable must be corrected while the other input variables subject to tolerances are kept constant in order to assign the corrected mass flow information or the further corrected mass flow information according to the first or second physical model The interpolation points determined in this way define a hyperplane, with an auxiliary point on this hyperplane being determined as a function of the interpolation points and the tolerances assigned to them, depending on the tolerances of the input variables subject to tolerances, the adjusted input variables being defined by the intersection of a straight line through one through the original Values of the tolerance-afflicted input variables defined point and the auxiliary point with a manifold determined by the model equation and the corrected mass flow information.

Figure list

• 1 eine schematische Darstellung eines Motorsystems mit einem Verbrennungsmotor mit einer ND-Abgasrückführung;
• 2 eine schematische Darstellung zur Veranschaulichung der Beziehung der einzelnen Zustandsgrößen der ND-Abgasrückführung;
• 3 ein Flussdiagramm zur Veranschaulichung eines Verfahrens zum Betreiben des Motorsystems der 1; und
• 4 ein Verfahren zur Ermittlung von angepassten Eingangsgrößen basierend auf der korrigierten Massenstromangabe.

Embodiments are explained in more detail below with reference to the accompanying drawings. Show it:

• 1 a schematic representation of an engine system with an internal combustion engine with LP exhaust gas recirculation;
• 2 a schematic representation to illustrate the relationship of the individual state variables of the LP exhaust gas recirculation;
• 3 a flow chart illustrating a method for operating the engine system of FIG 1 ; and
• 4th a method for determining adapted input variables based on the corrected mass flow rate.

Description of embodiments

1 shows a schematic representation of an engine system 1 with an internal combustion engine 2 , of a number (in the given embodiment four) of cylinders 3 having. The internal combustion engine 2 corresponds for example to a reciprocating piston engine, in particular an Otto engine or a diesel engine, and is controlled by the controlled supply of air and fuel into the cylinders 3 operated.

The supply of fresh air into the cylinders 3 of the internal combustion engine 2 takes place via an air supply system 4th . Combustion exhaust gases are via an exhaust system 5 from the internal combustion engine 2 discharged.

It is an exhaust-gas powered charger 6th provided that an exhaust turbine 61 has through which the combustion exhaust gas is passed. The exhaust turbine 61 is mechanical in particular via a shaft 63 with a compressor 62 coupled so that in the exhaust turbine 61 Exhaust gas enthalpy converted into rotational kinetic energy to drive the compressor 62 is used to have an inlet side of the compressor 62 Suck in gas mixture. The ambient air is compressed and under an increased boost pressure in a boost pressure section 43 of the air supply system 4th provided. The proportion of the exhaust gas enthalpy converted into mechanical energy can be determined by an on the exhaust gas turbine 61 arranged loader 64 (e.g. VTG actuator (VTG: variable turbine geometry), wastegate valve or the like) are controlled.

In the air supply system 4th can be a throttle 41 be arranged having a downstream suction pipe section 47 from the upstream boost section 43 separates. Upstream of the throttle 41 can an intercooler 42 be arranged to cool the charge air.

The engine system 1 can also be a high pressure exhaust gas recirculation line in a manner known per se 7th with a HP (high pressure) exhaust gas recirculation cooler 71 and a high pressure exhaust gas recirculation valve 72 have to take part of the combustion exhaust gas from the exhaust system 5 in the Air supply system 4th , especially in the suction pipe section 47 respectively. This enables the amount of fresh air for a combustion process in the cylinders by supplying inert combustion exhaust gas 3 to reduce the formation of nitrogen oxides.

In the air supply system 4th can still be on the inlet side of the compressor 62 an air mass sensor 44 be provided.

Furthermore, a boost pressure sensor 45 be provided on the output side of the compressor 62 is arranged to be in a boost pressure section of the air supply system 4th a boost pressure (compressor outlet pressure), ie a pressure which is in the boost pressure section 43 to determine the gas present. Alternatively, it can be used in conjunction with a model of a pressure drop across an intercooler 42 that is downstream to the compressor 62 connects, and possibly with a model of a throttle valve 41 also based on one using an intake manifold pressure sensor 50 showing a gas pressure in a suction pipe section 47 of the air supply system measures, a boost pressure can be modeled.

Furthermore, the engine system 1 in a manner known per se, an LP exhaust gas recirculation with a LP exhaust gas recirculation line 8th , with an LP (low pressure) exhaust gas recirculation cooler 81 and with an LP (low pressure) exhaust gas recirculation valve 82 comprise to a portion of the combustion exhaust gas from a downstream of the exhaust gas turbine 61 arranged part of the exhaust system 5 in one upstream of the compressor 62 arranged part of the air supply system 4th respectively. This enables the amount of fresh air for a combustion process in the cylinders by supplying inert combustion exhaust gas 3 to reduce the formation of nitrogen oxides.

In addition, a speed sensor 65 be provided in order to detect a supercharger speed. The speed sensor 65 can on the shaft 63 , on the turbine 61 or on the compressor 62 be arranged and determines a speed of the compressor based on known detection methods 62 .

Furthermore, a pressure sensor can be provided which measures an input-side pressure on the compressor 62 (Compressor inlet pressure p ₁₁ ) measures. Alternatively, an ambient pressure sensor 48 be provided in order to measure an ambient pressure. With the provision of an air filter 9 can using the ambient pressure sensor 48 and a model of the pressure drop across the air filter 9 the pressure directly on the inlet side of the compressor 62 than the compressor inlet pressure p ₁₁ to be determined.

Furthermore, an intake temperature sensor 49 be provided to measure an ambient temperature, so that a compressor inlet temperature T _Air is known. When using LP exhaust gas recirculation 8th can be the compressor inlet temperature T _Air on the inlet side of the compressor 62 using a model depending on a measured or modeled temperature on the outlet side of the LP exhaust gas recirculation cooler 81 can be determined in connection with an LP exhaust gas recirculation rate.

The engine system 1 is made using an engine control unit 10 operated by controlling various actuators, such as the charge generator 64 , the throttle valve 41 , the EGR valves 72 and 82 , and the injection valves for specifying a fuel injection quantity the operation of the internal combustion engine 2 certainly. The actuators can be controlled based on a setpoint load specification, which can be derived, for example, from a torque desired by the driver or a position of an accelerator pedal, and based on one or more sensor variables, which are for example provided by the boost pressure sensor 45 measured boost pressure, one by the charge air temperature sensor 46 measured charge air temperature, one by an exhaust gas temperature sensor 51 measured exhaust gas temperature, a fresh air mass flow (e.g. measured by a mass flow sensor 44 (HFM sensor)), one by a speed sensor 22nd measured engine speed and the like.

The engine control unit 10 takes over the direct control of the combustion engine 2 also the setting of a boost pressure to a target boost pressure with the help of a boost pressure control. The charge pressure regulation controls the setting of the charge generator as a function of the exhaust gas enthalpies provided and the desired, predetermined target charge pressure 64 so that an actual boost pressure in a boost pressure section 43 in front of the throttle 41 follows the specified target boost pressure as closely as possible.

Downstream of the exhaust turbine 61 the charger 6th the combustion exhaust gas passes through an exhaust gas aftertreatment device 9 , which can include, for example, an oxidation catalytic converter, a NOx storage catalytic converter and / or a diesel particle filter. Downstream of this is an LP Exhaust gas recirculation branch point 83 for LP exhaust gas recirculation. Downstream of the LP exhaust gas recirculation junction 83 can be an exhaust flap 52 and a muffler 53 be arranged.

To operate the engine system 1 by the engine control unit 10 Mass flow information must be determined for mass flows in the area of the LP exhaust gas recirculation, such as the LP EGR mass flow. This can be done in the engine control unit 10 can be used, for example, for a model-based concentration control. Since both the input variables that are used for the model-based determination of the mass flow data and the mass flow sensors, such as the HFM air mass meter, are subject to tolerances, when using the LP EGR mass flow data, i.e. the mass flows in the area of the LP exhaust gas recirculation , come to a deviation from the real value, so that the functions of the engine control unit based on it 10 can only be executed with errors.

It is therefore desirable to provide a corrected mass flow information for a mass flow in the area of the LP exhaust gas recirculation.

In the following, a determination of a mass flow specification that corresponds to a corrected LP-EGR mass flow (LP-EGR mass flow) is described as an application of the following method.

To illustrate the relationship between the individual state variables, in 2 the relationship of the air system variables of the LP exhaust gas recirculation is shown schematically. Oxygen concentrations of the gases carried are used as the concentration variable r _O2 . One or more functions f, which describe the relationship between the mass flow data mf, the pressures p, the cross-sectional areas area of throttles or valves and a temperature T as input or output variables, are used for the individual gas ducts. For this purpose, the route of the LP exhaust gas recirculation (through the LP EGR line 8th by the function f ₁ , the distance of the fresh air from the environment to the mixing point 84 with the LP exhaust gas recirculation as f ₁₁ and the route from the LP exhaust gas recirculation junction 83 the exhaust system 5 referred to as f ₅₀ until behind the silencer.

The functions f ₁ , f ₁₁ and f ₅₀ each take the form of a throttle equation that is assumed to be trustworthy herein. Only the input and output variables of these functions f ₁ , f ₁₁ and f ₅₀ can be subject to tolerances.

In 3 a method for determining a corrected mass flow specification for the LP exhaust gas recirculation is described using a flow chart.

wobei die Eingangsgrößen mf_Afs dem Massenstrom durch die Frischluftstrecke, p₀ dem Umgebungsdruck, T_Air der Umgebungslufttemperatur, area_FrshAir einem Öffnungsquerschnitt, der die Drosselwirkung auf den durch den Luftfilter 9 gedrosselten Frischluftmassenstrom angibt, mf_Sil einem Abgasmassenstrom über dem Schalldämpfer 53, T_Exh einer Abgastemperatur, area_Exh einem Öffnungsquerschnitt, der die Drosselwirkung auf den durch den Schalldämpfer 53 und die Abgasklappe 52 gedrosselten Abgasmassenstrom angibt, und area_EgrLoP einem Öffnungsquerschnitt, der die Drosselwirkung auf den durch den ND-AGR-Kühler 81 und den ND-AGR-Ventil 82 gedrosselten ND-AGR-Massenstrom angibt, entsprechen. Die zu berechnende Größe entspricht hier mf_{EgrLoP Thr} aber kann auch eine andere der in obiger Formel verwendeten Größen nach entsprechender Umformung als zu berechnende Größe angenommen werden, wobei die übrigen Größen die Eingangsgrößen darstellen.In step S1 With the above functions f ₁ , f ₁₁ and f _50, a first mass flow _{specification} mf _{EgrLoP Thr} (first LP EGR mass flow) is determined as follows: $$\text{m}{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}=f_1\left(\begin{array}{c}{f}_{11}\left(m{f}_{\mathrm{A.}fs},p_0,T_{\mathrm{A.}ir},are{a}_{\mathrm{F.}rsH\mathrm{A.}ir}\right),\\ f_{50}\left(m{f}_{sil},p\mathrm{0,}{T}_{\mathrm{E.}xH},are{a}_{\mathrm{E.}xH}\right),\\ T_{\mathrm{E.}xH},are{a}_{\mathrm{E.}Gr\mathrm{L.}OP}\end{array}\right)$$

where the input quantities mf _Afs the mass flow through the fresh air section, p ₀ the ambient pressure, T _Air the ambient _air temperature, area _FrshAir an opening cross-section, which the _{throttling effect} on the through the air filter 9 throttled fresh air mass flow, mf _Sil an exhaust gas mass flow above the silencer 53 , T _Exh an exhaust gas temperature, area _Exh an opening cross-section, which is the _{throttling effect} on the through the silencer 53 and the exhaust flap 52 indicates the throttled exhaust gas mass flow, and area _EgrLoP an opening cross-section, which the _{throttling effect} on the through the LP-EGR cooler 81 and the LP EGR valve 82 indicating throttled LP-EGR mass flow. The size to be calculated here corresponds to mf _{EgrLoP Thr} however, another of the quantities used in the above formula can also be assumed as the quantity to be calculated after corresponding transformation, with the remaining quantities representing the input quantities.

der resultierenden ersten Massenstromangabe mf_{EgrLoP Thr} bestimmt werden. Die Toleranz wird hierin als Standardabweichung σ angegeben. Dafür werden die entsprechenden Gleichungen linearisiert und die einzelnen Terme quadratisch addiert und mit der entsprechenden Standardabweichung multipliziert. Aus der Summe wird die Wurzel gezogen: $${\sigma }_{\text{m}{f}_{EgrLo{P}_{Thr}}}=\sqrt{{\left(\frac{df}{d{x}_1}\right)}^2\ast {\sigma }_{x1}^2+\cdots +{\left(\frac{df}{d{x}_n}\right)}^2\ast {\sigma }_{xn}^2}$$

wobei x₁...x_n den obigen toleranzbehafteten Eingangsgrößen entspricht.Based on the specified tolerances of the above input variables, step S2 correspondingly a resulting tolerance ${\sigma }_{\text{m}{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}}$

the resulting first mass flow rate mf _{EgrLoP Thr} to be determined. The tolerance is given herein as the standard deviation σ. To do this, the corresponding equations are linearized and the individual terms are added squarely and multiplied by the corresponding standard deviation. The root is taken from the sum: $${\sigma }_{\text{m}{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}}=\sqrt{{\left(\frac{df}{d{x}_1}\right)}^2\ast {\sigma }_{x1}^2+\cdots +{\left(\frac{df}{d{x}_n}\right)}^2\ast {\sigma }_{xn}^2}$$

where x ₁ ... x _n corresponds to the above tolerance-affected input variables.

wobei σ_index der Toleranz der mit index angegebenen Eingangsgröße entspricht.In general: $${\sigma }_{mf\mathrm{E.}Gr\mathrm{L.}OPTHr}={\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="DE102019106228A1\_0034.png"\; state="\{\{state\}\}">f</figure-callout>}}_{1\sigma }=\left(\begin{array}{c}{f}_{11\sigma }\left({\sigma }_{m{f}_{\mathrm{A.}fs}},{\sigma }_{P_0},{\sigma }_{T_{air}},{\sigma }_{are{a}_{\mathrm{F.}rsH\mathrm{A.}ir}}\right),\\ {\mathrm{<figure-callout\; id="50"\; label="f"\; filenames="DE102019106228A1\_0032.png"\; state="\{\{state\}\}">f</figure-callout>}}_{50\sigma }\left({\sigma }_{m{f}_{sil}},{\sigma }_{P_0},{\sigma }_{T_{\mathrm{E.}xH}},{\sigma }_{are{a}_{\mathrm{E.}xH}}\right),\\ {\sigma }_{T_{\mathrm{E.}xH}},{\sigma }_{are{a}_{\mathrm{E.}Gr\mathrm{L.}OP}}\end{array}\right)$$

where σ _index corresponds to the tolerance of the input variable specified with index.

wobei mf_Afs dem Frischluftmassenstrom, r_O2,Env , der Sauerstoffkonzentration in der Frischluft, r_O2,Mix der Sauerstoffkonzentration nach der ND-AGR-Mischstelle 84, r_O2,Exh der Sauerstoffkonzentration im Verbrennungsabgas entsprechen. Die zu berechnende Größe entspricht hier mf_{EgrLoP MBal} aber kann auch eine andere der in obiger Formel verwendeten Größen nach entsprechender Umformung als zu berechnende Größe angenommen werden, wobei die übrigen Größen die Eingangsgrößen darstellen.According to one step S3 a second mass flow _{specification} mf _{EgrLoP MBal} determine with the function g: $$m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{\mathrm{M.}\mathrm{B.}al}}=m{f}_{\mathrm{A.}fs}\ast \frac{r_{O\mathrm{2,}\mathrm{E.}nv}-r_{O\mathrm{2,}\mathrm{M.}ix}}{r_{O\mathrm{2,}\mathrm{M.}ix}-r_{O\mathrm{2,}\mathrm{E.}xH}}=G\left(m{f}_{\mathrm{A.}fs},r_{O\mathrm{2,}\mathrm{E.}nv},r_{O\mathrm{2,}\mathrm{M.}ix},r_{O\mathrm{2,}\mathrm{E.}xH}\right)$$

in which mf _Afs the fresh air mass flow, r _{O2, env} , the oxygen concentration in the fresh air, r _{O2, mix} the oxygen concentration after the LP-EGR mixing point 84 , r _{O2, Exh} correspond to the oxygen concentration in the combustion exhaust gas. The size to be calculated here corresponds to mf _{EgrLoP MBal} however, another of the quantities used in the above formula can also be assumed as the quantity to be calculated after corresponding transformation, with the remaining quantities representing the input quantities.

Correspondingly, in step S4 As above, a tolerance can be determined based on the tolerances of the input variables: $${\sigma }_{mf\mathrm{E.}Gr\mathrm{L.}O{P}_{\mathrm{M.}\mathrm{B.}al}}=G_{\sigma }\left({\sigma }_{m{f}_{\mathrm{A.}fs}},{\sigma }_{r_{O\mathrm{2,}\mathrm{E.}nv}},{\sigma }_{r_{O\mathrm{2,}\mathrm{M.}ix}}\right)$$

angenommen werden. Die Konstante c₁ ermittelt sich dabei als Funktion aus den Toleranzen σ_mfEgrLoPThr, σ_{mfEgrLoP MBal} der ersten und zweiten Massenstromangabe, wobei die Konstante c₁ einen Wert zwischen 0 und 1 annehmen kann. Beispielsweise kann c1 wie folgt aus den Toleranzen, die als Standardabweichungen angegeben sind, ermittelt werden: $$c1=\frac{{\sigma }_{mfEgrThr}^2}{{\sigma }_{mfEgrThr}^2+{\sigma }_{mfEgrBal}^2}$$

From the two estimated mass flow data, in step S5 determine a corrected mass flow rate as a function of the particular tolerances of the mass flow information. As a model for this, for example $$m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{\mathrm{E.}st}}=m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}+{\mathrm{<figure-callout\; id="1"\; label="c"\; filenames="DE102019106228A1\_0034.png"\; state="\{\{state\}\}">c</figure-callout>}}_1\ast \left(m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{\mathrm{M.}\mathrm{B.}al}}-m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}\right)$$

be accepted. The constant c _{1 is} determined as a function from the tolerances σ _mfEgrLoPThr , σ _{mfEgrLoP MBal} the first and second mass flow rate, where the constant c ₁ can assume a value between 0 and 1. For example, c1 can be determined from the tolerances, which are specified as standard deviations, as follows: $$c1=\frac{{\sigma }_{mf\mathrm{E.}GrTHr}^2}{{\sigma }_{mf\mathrm{E.}GrTHr}^2+{\sigma }_{mf\mathrm{E.}Gr\mathrm{B.}al}^2}$$

benötigt. Dafür werden mit den in Formel 1 und Formel 2 angegebenen Massenstromangaben zwei Massenstromverhältnisse bestimmt und entsprechende Toleranzen berechnet. Durch eine Gewichtung der beiden Verhältnisse abhängig von den Toleranzen lässt sich das korrigierte Massenstromverhältnis bestimmen: $$\frac{m{f}_{EgrLo{P}_{Est}}}{m{f}_{Af{s}_{Est}}}=\frac{m{f}_{EgrLo{P}_{Thr}}}{m{f}_{Afs}}+c_2\ast \left(\frac{m{f}_{EgrLo{P}_{MBal}}}{m{f}_{Afs}}-\frac{m{f}_{EgrLo{P}_{Thr}}}{m{f}_{Afs}}\right)$$

mit $$c_2=f_{RatioMFlow}{\left({\sigma }_{\frac{mfEgrLo{P}_{Thr}}{m{f}_{Afs}}},{\sigma }_{\frac{mfEgrLo{P}_{MBal}}{m{f}_{Afs}}}\right)|}_{c_2=0\dots 1}$$

Next, a corrected fresh air mass flow can be determined. For this purpose, the corrected ratio of the EGR mass flow and the fresh air mass flow is first used $\frac{m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{\mathrm{E.}st}}}{m{f}_{\mathrm{A.}f{s}_{\mathrm{E.}st}}}$

needed. For this purpose, two mass flow ratios are determined with the mass flow data given in formula 1 and formula 2 and corresponding tolerances are calculated. The corrected mass flow ratio can be determined by weighting the two ratios depending on the tolerances: $$\frac{m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{\mathrm{E.}st}}}{m{f}_{\mathrm{A.}f{s}_{\mathrm{E.}st}}}=\frac{m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}}{m{f}_{\mathrm{A.}fs}}+c_2\ast \left(\frac{m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{\mathrm{M.}\mathrm{B.}al}}}{m{f}_{\mathrm{A.}fs}}-\frac{m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}}{m{f}_{\mathrm{A.}fs}}\right)$$

With $$c_2=f_{\mathrm{R.}atiO\mathrm{M.}\mathrm{F.}lOw}{\left({\sigma }_{\frac{mf\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}{m{f}_{\mathrm{A.}fs}}},{\sigma }_{\frac{mf\mathrm{E.}Gr\mathrm{L.}O{P}_{\mathrm{M.}\mathrm{B.}al}}{m{f}_{\mathrm{A.}fs}}}\right)|}_{c_2=0...1}$$

Thus, the corrected fresh air mass flow results from formulas 3 and 4 as: $$m{f}_{\mathrm{A.}f{s}_{\mathrm{E.}st}}=m{f}_{\mathrm{A.}fs}\frac{m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}+{\mathrm{<figure-callout\; id="1"\; label="c"\; filenames="DE102019106228A1\_0034.png"\; state="\{\{state\}\}">c</figure-callout>}}_1\ast \left(m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{\mathrm{M.}\mathrm{B.}al}}-m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}\right)}{m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}+c_2\ast \left(m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{\mathrm{M.}\mathrm{B.}al}}-m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}\right)}$$

However, the correction of the mass flow information means that the assumed values of the input variables and the corresponding corrected mass flow information no longer satisfy the underlying functional equation, both based on the throttle equations and based on the mass flow balance. Hence, in step S6 the input _variables are adapted or corrected according to their tolerances specified by σ _x1 ... σ _xn . The correction is made using one of the model equations (formula 1 or 2) based on the respective estimated value of the relevant input variable.

Furthermore, the degree of correction of each of the input variables takes place as a function of the ratio of the input variable tolerances of the respective input variables to one another and as a function of the ratio of the sensitivities of the input variables with regard to the mass flow information to be calculated. In this way, the ratio of the products of the sensitivities of the input variables considered and their respective tolerances, the degree of correction of the relevant estimated input variable is determined.

Since the model equations of formulas 1 and 2 should still be fulfilled, depending on the tolerances of the input variables and the sensitivities assigned to the input variable, each of these input variables can be adapted or corrected in such a way that the corrected mass flow information (the corrected fresh air mass flow) is obtained according to the model equations. or the corrected further mass flow specification (the corrected EGR mass flow) results from the adjusted input variables. This can be done in that, in an adaptation process, each of the input variables with tolerances is successively based on their tolerances and sensitivity / gradient with regard to the variable to be calculated, i.e. of the corrected mass flow specification, is adjusted in a direction by which the resulting mass flow specification to be calculated is changed according to the selected model equation in the direction of the corrected mass flow specification. The adjustment procedure provides for every input variable Xtol still subject to tolerances to be adjusted as follows:

des Zwischenwerts Xzwisch der betreffenden Eingangsgröße wird ein Faktor c3 berechnet $$c3=\frac{{\sigma }_{Xtol}^2}{{\sigma }_{Xzwisch}^2+{\sigma }_{Xtol}^2}$$

wobei die angepasste Eingangsgröße Xadapt sich wie folgt ergibt: $$Xadapt=Xtol+c_3\ast \left(Xzwisch-Xtol\right)$$

One of the input variables subject to tolerance is selected and an intermediate value Xbetween the relevant input variable based on one of the model equations (formula 1 or 2), the corrected mass flow rate and while retaining the measured values of the input variables still subject to tolerances and the actual values of the input variables that are not (no longer) subject to tolerance calculated. Likewise, for the intermediate value Xbetween the relevant input variable, as described above, a tolerance is determined from the tolerances of the tolerance-affected input variables. From the tolerance σ _Xtol specified by the standard _{deviation of} the measured value of the relevant input variable and the tolerance specified by the standard deviation ${\sigma }_{XzwiscH}^2$

A factor c3 is calculated for the intermediate value Xbetween the relevant input variable $$c3=\frac{{\sigma }_{XtOl}^2}{{\sigma }_{XzwiscH}^2+{\sigma }_{XtOl}^2}$$

where the adjusted input variable Xadapt results as follows: $$Xadapt=XtOl+c_3\ast \left(XzwiscH-XtOl\right)$$

This method is carried out for each of the input variables subject to tolerances, with the last remaining input variable subject to tolerances being able to be determined by inserting the adjusted input variables, the corrected mass flow information, into the relevant model equation.

Alternatively, depending on the corrected mass flow information, an N-dimensional manifold M can be formed with the aid of one of the model equations under consideration (formula 1-2 or a corresponding transformation). This is the two-dimensional example of 4th with the exemplary input variables x1, x2. The input variables provided are specified as an input variable vector. Subsequently, for each of the tolerance-affected input variables x1, x2 ... support points y1, y2, ... are determined, which result from the respective non-observance of the value of the relevant input variable as the intersection with the manifold M. The support points form a hyperplane H in N-dimensional space. Depending on the tolerances (standard deviations) of the tolerance-affected input variables (illustrated here by the ellipse with the ellipse radii depending on the tolerances), an auxiliary point PH is determined on this hyperplane H based on the support points y1, y2, ... $$c\mathrm{4th}=\frac{{\sigma }_{x1}^2}{{\sigma }_{x1}^2+{\sigma }_{x2}^2}$$

The sensitivity is taken into account by the slope resulting from the support points x1, y2 and x2, y1. The distances between the auxiliary point PH and the support points y1, y2 are determined linearly according to the weighting given by c4, in particular the auxiliary point PH has a distance from point y2 which corresponds to the product of the factor c4 with the distance between the support points.

In other words, with N input variables subject to tolerances for the N support points, an n-dimensional ellipsoid is formed around the point of the input variable. The ellipsoid is spanned over the variances of the input variables. A scaling factor is now determined in order to obtain the auxiliary point PH as an intersection with the hyperplane H determined by the above method.

Since this auxiliary point PH does not yet fulfill the underlying model equation because of the non-linearity, an intersection of a straight line G through the point of the original input variable vector x1, x2, ... and through the auxiliary point PH on the hyperplane H with the manifold M is determined. The intersection of this straight line G with the manifold M of the model equation results in the adapted input variable vector x1 ', x2'.

QUOTES INCLUDED IN THE DESCRIPTION

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Patent literature cited

• DE 102011017779 A1 [0004]

Claims (12)

Method for operating an internal combustion engine (2) with a low-pressure _{exhaust gas recirculation} system (8) based on a corrected mass flow _{specification} (mf _{EgrLoP Est} ) a mass flow in the area of the low-pressure _{exhaust gas recirculation} (8), with the following steps: - Determination (S1) of a first estimated mass flow _{specification} (mf _{EgrLoP Thr} ) according to a first physical model based on a plurality of input variables subject to tolerances; - Determining (S2) a tolerance $\left({\sigma }_{\text{m}{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}}\right)$

the first estimated mass flow rate (mf _{EgrLoP Thr} ) according to the first physical model based on the tolerances of the plurality of input variables subject to tolerances; - Determination (S3) of a second estimated mass flow _{specification} (mf _{EgrLoP MBal} ) according to a second physical model based on a plurality of input variables subject to tolerances, at least one of which is identical to the input variables subject to tolerances of the first physical model; - Determination (S4) of a tolerance (σ _{mfEgrLoP MBal} ) of the second estimated mass flow rate (mf _{EgrLoP MBal} ) according to the second physical model based on the tolerances of the plurality of input variables with tolerances; - Determination (S5) of the corrected mass flow _{specification} (mf _{EgrLoP Est} ) depending on the first and second estimated mass flow _data (mf _{EgrLoP Thr} , mf _{EgrLoP MBal} ) and the tolerances ( ${\sigma }_{\text{m}{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}},$

σ _{mfEgrLoP MBal} ) of the first and second estimated mass flow _data (mf _{EgrLoP Thr} , mf _{EgrLoP MBal} ). Procedure according to Claim 1 , wherein the first physical model corresponds to a throttle model and / or the second physical model corresponds to a mass flow balance. Procedure according to Claim 1 or 2 , where the tolerances ( ${\sigma }_{\text{m}{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}},$

σ _{mfEgrLoP MBal} ) the first and / or second estimated mass flow rate (mf _{EgrLoP Thr} , mf _{EgrLoP MBal} ) is determined depending on a linearization of the first or the second physical model with respect to each of the corresponding tolerance-affected input variables. Method according to one of the Claims 1 to 3 , where the corrected mass flow specification corresponds to a low pressure EGR mass flow. Procedure according to Claim 4 , a further corrected mass flow specification for a further mass flow, in particular a corrected fresh air mass flow, is determined by the following steps: measuring a further mass flow in order to obtain a further mass flow _{specification} (mf _Afs ), determining a first estimated mass flow _ratio based on the first estimated one Mass flow rate (mf _{EgrLoP Thr} ). and the further mass flow _{specification} (mf _Afs ); - Determining a tolerance $\left(\frac{{\sigma }_{\text{m}{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}}}{m{f}_{\mathrm{A.}fs}}\right)$

the first estimated mass flow ratio $\left(\frac{m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}}{m{f}_{\mathrm{A.}fs}}\right)$

depending on the tolerance of the first estimated mass flow rate (mf _{EgrLoP Thr} ). and the tolerance of the further measured mass flow rate; - Determining a second estimated mass flow ratio $\left(\frac{m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{\mathrm{M.}\mathrm{B.}al}}}{m{f}_{\mathrm{A.}fs}}\right)$

based on the second estimated mass flow rate (mf _{EgrLoP MBal} ) and the further mass flow rate (mf _Afs ); - Determining a tolerance $\left(\frac{{\sigma }_{mf\mathrm{E.}Gr\mathrm{L.}OP}}{m{f}_{\mathrm{A.}fs}}\right)$

the second estimated mass flow ratio $\left(\frac{m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{\mathrm{M.}\mathrm{B.}al}}}{m{f}_{\mathrm{A.}fs}}\right)$

depending on the tolerance of the second estimated mass flow rate (mf _{EgrLoP MBal} ) and the tolerance of the further measured mass flow rate (mf _Afs ); and - Determination of the further corrected mass flow _{specification} (mf _{Afs Est} ) depending on the first and second estimated mass flow ratios $\left(\frac{m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}}{m{f}_{\mathrm{A.}fs}},\frac{m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{\mathrm{M.}\mathrm{B.}al}}}{m{f}_{\mathrm{A.}fs}}\right),$

the corrected mass flow rate (mf _{EgrLoP Est} ) and the tolerances $\left({\sigma }_{\frac{{}_{mf\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}}{m{f}_{\mathrm{A.}fs}}},{\sigma }_{\frac{mf\mathrm{E.}Gr\mathrm{L.}O{P}_{\mathrm{M.}\mathrm{B.}al}}{m{f}_{\mathrm{A.}fs}}}\right)$

the first and second estimated mass flow ratios $\left(\frac{m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}}{m{f}_{\mathrm{A.}fs}},\frac{m{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{\mathrm{M.}\mathrm{B.}al}}}{m{f}_{\mathrm{A.}fs}}\right).$

Procedure according to Claim 5 , whereby depending on the corrected mass flow rate (mf _{EgrLoP Est} ) and / or the further corrected mass flow _information (mf _Afs ) is _calculated back to adjusted values of the input variables subject to tolerances, so that the adjusted input variables and the corrected mass flow _information (mf _{EgrLoP Est} ) or the further corrected mass flow _data (mf _Afs ) satisfy the first or second physical model. Procedure according to Claim 6 , whereby the adjusted values of the input variables correspond to the difference between their tolerances and their sensitivities with regard to the corrected mass flow rate (mf _{EgrLoP Est} ) or the further corrected mass flow _information (mf _Afs ). Procedure according to Claim 7 , the adapted values of the input variables successively by approximating a mass flow specification determined according to the first and / or second physical model to the corrected mass flow specification (mf _{EgrLoP Est} ) or the further corrected mass flow _information (mf _Afs ) can be adapted. Procedure according to Claim 7 , whereby a base point is determined for each of the tolerance-affected input variables, to which the relevant input variable must be corrected _{while keeping} the other tolerance-affected input variables constant in order to obtain the corrected mass flow rate (mf _{EgrLoP Est} ) or the further corrected mass flow _information (mf _Afs ) according to the first or second physical model, the _{interpolation points} thus determined defining a hyperplane (H), with an auxiliary point (PH) on this hyperplane depending on the tolerances of the input variables subject to tolerances (H) is determined as a function of the interpolation points and the tolerances assigned to them, with the adapted input variables being the intersection of a straight line through a point defined by the original values of the input variables subject to tolerances and the auxiliary point with a given by the model equation and the corrected mass flow rate (mf _{EgrLoP Est} ) or the further corrected mass flow _information (mf _Afs ) certain manifold can be determined. Device for operating an internal combustion engine (2) with a low-pressure _{exhaust gas recirculation} (8) based on a corrected mass flow rate (mf _{EgrLoP Est} ) a mass flow in the area of the low-pressure _{exhaust gas recirculation} (8), the device being designed to: - Determine a first estimated mass flow _indication (mf _{EgrLoP Thr} ) according to a first physical model based on a plurality of input variables subject to tolerances; - Determining a tolerance ${\sigma }_{\text{m}{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}}$

the first estimated mass flow rate (mf _{EgrLoP Thr} ) according to the first physical model based on the tolerances of the plurality of input variables subject to tolerances; - Determination of a second estimated mass flow rate (mf _{EgrLoP MBal} ) according to a second physical model based on a plurality of input variables subject to tolerances, at least one of which is identical to the input variables subject to tolerances of the first physical model; - Determining a tolerance (σ _{mfEgrLop MBal} ) of the second estimated mass flow rate (mf _{EgrLoP MBal} ) according to the second physical model based on the tolerances of the plurality of input variables with tolerances; - Determination of the corrected mass flow _{specification} (mf _{EgrLoP Est} ) depending on the first and second estimated mass flow _data (mf _{EgrLoP Thr} , mf _{EgrLoP MBal} ) and the tolerances ( ${\sigma }_{\text{m}{f}_{\mathrm{E.}Gr\mathrm{L.}O{P}_{THr}}},$

σ _{mfEgrLoP MBal} ) of the first and second estimated mass flow _data (mf _{EgrLoP Thr} , m _{fEgrLoP MBal} ). Computer program which is set up to carry out all steps of a method according to one of the Claims 1 to 9 execute. Machine-readable storage medium on which a computer program is based Claim 11 is stored.

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