DE102018219486A1 - Method for monitoring an air mass flow of an internal combustion engine with exhaust gas recirculation - Google Patents

Abstract

Method for monitoring an air mass flow (ṁ) of an internal combustion engine (2) with an exhaust gas recirculation, a first air mass flow (ṁ) being determined using a throttle equation, a second air mass flow (ṁ) being determined as a function of an exhaust gas recirculation rate, a comparison value for a deviation is formed between the first and the second air mass flow and, depending on the deviation, an error reaction of the internal combustion engine (2) is carried out.

Description

State of the art

The state of the art is that in the case of supercharged internal combustion engines with natural gas and high-pressure exhaust gas recirculation, the air mass flow is calculated using the throttle valve model. This is determined using the sizes of the opening cross-section of the throttle valve, the pressure in the flow direction before the throttle valve (boost pressure) and the pressure in the flow direction after the throttle valve (intake manifold pressure), the density of the air and the flow function of the throttle valve.

• - Plausibilisierung des Zulaufdrucks zur Drosselklappe (Ladedruck) in definierten Betriebspunkten
• - Plausibilisierung des Öffnungswinkels der Drosselklappe mit Hilfe von 2 redundanten Potentiometern
• - Plausibilisierung des Drucks in Strömungsrichtung nach der Drosselklappe (Saugrohrdrucksensor) mit Hilfe des Ladedrucksensors (Druck in Strömungsrichtung vor der Drosselklappe).

A diagnosis of this calculated air mass flow is carried out by diagnosing individual signals - from which the air mass flow is calculated - as follows:

• - Plausibility check of the inlet pressure to the throttle valve (boost pressure) at defined operating points
• - Plausibility check of the opening angle of the throttle valve using 2 redundant potentiometers
• - Plausibility check of the pressure in the flow direction after the throttle valve (intake manifold pressure sensor) with the help of the boost pressure sensor (pressure in the flow direction before the throttle valve).

In its entirety, the air mass flow calculated with the help of the throttle valve model can be diagnosed at defined operating points (by plausibility checking of individual signals) - a continuous diagnosis of the calculated air mass flow is not possible.

Disclosure of the invention

In a first aspect, a method for monitoring an air mass flow of an internal combustion engine with an exhaust gas recirculation is determined, wherein a first air mass flow is determined by means of a throttle equation, a second air mass flow being determined as a function of an exhaust gas recirculation rate, a comparison value for a deviation between the first and the second Air mass flow is formed and an error reaction of the internal combustion engine is carried out depending on the deviation.

The method has the particular advantage that the monitoring of the air mass flow can be carried out continuously. Additional sensors for determining the air mass flow can thus be dispensed with. The throttle valve model can thus take over the function of a main filling sensor, since the continuous monitoring of the air mass flow ensures reliable torque monitoring. The method enables reliable diagnosis of the air mass flow of the internal combustion engine. The method is still suitable for vehicles with natural gas drive.

It is also advantageous if an exhaust gas recirculation valve is opened to recirculate exhaust gas. This ensures continuous and safe monitoring of the air mass flow.
It is advantageous if the exhaust gas recirculation valve is a high-pressure exhaust gas recirculation valve.

Furthermore, it can be provided that if the comparison value of the deviation exceeds a predefinable threshold value, the air mass flow is diagnosed as faulty and an error reaction is carried out.
A particularly simple, continuous and reliable monitoring of the air mass flow can thus be carried out.

It is advantageous if an emergency operation for the internal combustion engine is activated as a fault reaction. Damage or faulty activation of the internal combustion engine can thus be prevented in the event of a fault.

It is a further advantage if the first air mass flow is at least dependent on a cross-sectional area of a throttle valve and / or a pressure in the flow direction in front of the throttle valve and / or a temperature in the flow direction in front of the throttle valve and / or a pressure at the location of the intake valves and / or Temperature at the location of the intake valves and / or an engine speed of the internal combustion engine and / or a coolant temperature of the internal combustion engine is determined. The first air mass flow can thus be determined particularly simply, continuously and precisely by the control device.

Method according to one of the preceding claims, characterized in that the second modeled mass flow at least depending on a cross-sectional area of a high pressure Exhaust gas recirculation valve and / or a temperature upstream of the high pressure exhaust gas recirculation valve and / or a pressure upstream of the high pressure exhaust gas recirculation valve and / or a pressure at the location of the intake valves and / or a temperature at the location of the intake valves and / or an engine speed the internal combustion engine and / or a coolant temperature of the internal combustion engine is determined.
The second air mass flow can thus be determined particularly simply, continuously and precisely by the control device.

In further aspects, the invention relates to a device, in particular a control device and a computer program, which are set up, in particular programmed, for executing one of the methods. In a still further aspect, the invention relates to a machine-readable storage medium on which the computer program is stored.

Figure list

• 1 eine schematische Darstellung einer Brennkraftmaschine mit Hochdruck-Abgasrückführung,
• 2 einen beispielhaften Ablauf des Verfahrens zur Überwachung eines Luftmassenstroms einer Brennkraftmaschine mit einer Hochdruck-Abgasrückführung.

The invention is described in more detail below with reference to the accompanying drawings and using exemplary embodiments. Show

• 1 1 shows a schematic illustration of an internal combustion engine with high-pressure exhaust gas recirculation,
• 2nd an exemplary sequence of the method for monitoring an air mass flow of an internal combustion engine with a high-pressure exhaust gas recirculation.

The 1 shows a schematic representation of the engine system 1 with an internal combustion engine 2nd , the air through an air duct system 61 is supplied and exhaust gas via an exhaust gas discharge 71 can be traced back.

In the air supply system 61 is in the direction of air flow 51 seen arranged the following: a compressor 30th of an exhaust gas turbocharger 6 , an intercooler 40 , an air mass sensor 50 , especially a Pressure Based Air Flow Meter 50 , a throttle valve 60 , a pressure and temperature sensor 65 and an internal combustion engine 2nd . The air mass sensor 50 is included as a Pressure Based Air Flow Meter Sensor 50 formed, which can determine a pressure p ₁₂ and a temperature T ₁₂ at the location of the sensor in the intake manifold. The pressure and temperature sensor 65 determines a pressure p ₂₂ and a temperature T ₂₂ at the location of the intake valves of the internal combustion engine 2nd . Furthermore, a cross-sectional area ar _{THRVIv of} the throttle valve 60 detected by a sensor system and sent to the control unit 100 transferred and saved.

In the exhaust system 71 is based on the internal combustion engine 2nd in the flow direction of the exhaust gas 52 Arranged the following: an exhaust gas turbine 70 , an exhaust after-treatment system 80 . The exhaust aftertreatment system 80 can z. B. include various exhaust gas purification systems, such as. B. a three-way catalyst, a particle filter and a nitrogen oxide catalyst.

Upstream of the exhaust gas turbine 70 , ie on a high pressure side of the exhaust system 71 , branches from the exhaust system 71 a high pressure exhaust gas recirculation line 47 (HD EGR line) from upstream of the internal combustion engine 2nd and the downstream of the throttle valve 60 into the fresh air system 61 flows. Downstream of the internal combustion engine 2nd are located along the HD EGR line 47 an HD EGR cooler 43 , a temperature sensor 44 , a pressure sensor 45 and an HD EGR valve 46 . By means of e.g. B. the temperature sensor 44 can be a temperature T _EGR between the HD EGR cooler 43 and the HD EGR valve 46 be determined. Furthermore, by means of the pressure sensor 45 a pressure p _EGR between the HD EGR valve 46 and the HD EGR cooler 43 be determined. The sizes described can e.g. B. present as sensor values or as model values. The recirculation of exhaust gas serves to reduce the peak temperatures in the combustion chamber of the internal combustion engine 2nd .
Furthermore, a cross-sectional area ar _{EGRVIv of} the HD EGR valve 46 detected by a sensor system and sent to the control unit 100 transferred and saved. The pressure and temperature values are sent from the sensors to a control unit 100 transferred and saved there. Alternatively or additionally, the sizes can also be corresponding models using the control unit 100 be determined.

mit $$\psi =\sqrt{\frac{\chi }{\chi -1}\times \left[{\left(\frac{p_{22}}{p_{12}}\right)}^{\frac{2}{\chi }}-{\left(\frac{p_{22}}{p_{12}}\right)}^{\frac{\chi +1}{\chi }}\right]}$$

The air mass flow ṁ _air can be calculated as follows using the known throttle equation: $${\dot{m}}_{\text{air}}={\dot{m}}_{\text{THRVIv}}=\sqrt{\mathrm{2nd}\times p_{12}\times {\rho }_{12}}\times {\text{ar}}_{THRVlv}\times \mathrm{\mu }\text{x}\psi \left(\frac{p_{22}}{p_{12}},\chi \right)$$

With $$\psi =\sqrt{\frac{\chi }{\chi -1}\times \left[{\left(\frac{p_{22}}{p_{12}}\right)}^{\frac{\mathrm{2nd}}{\chi }}-{\left(\frac{p_{22}}{p_{12}}\right)}^{\frac{\chi +1}{\chi }}\right]}$$

With ar _THRVIv the opening cross-section of the throttle valve, µ the discharge coefficient, p ₁₂ the pressure in the flow direction in front of the throttle valve, ρ ₁₂ the density of the air in the flow direction in front of the throttle valve, p ₂₂ the pressure 60 in the direction of flow after the throttle valve 60 and χ the isentropic exponent of the air at the throttle valve 60 .

The density ρ _{12 of} the air in the flow direction in front of the throttle valve 60 can be calculated using the gas equation: $$\begin{array}{l}{p}_{12}\times v_{12}=R_s\times T_b\hfill \\ \text{With}{v}_b=\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{${\rho }_{12}$}\right.\hfill \\ \to {\rho }_{12}=\frac{p_{12}}{R_s\times T_b}\hfill \end{array}$$

With v ₁₂ the specific volume of air, the absolute temperature T ₁₂ in the flow direction in front of the throttle valve 60 and R _s the specific gas constant for air.

mit ṁ₂₂ dem Luftmassenstrom am Ort der Einlassventile der Brennkraftmaschine 2. Dieser kann wie folgt aus der Luftmasse im Brennraum und einem von der Motordrehzahl der Brennkraftmaschine 2 abhängigen Faktor berechnet werden. $${\dot{m}}_{22}=\left(p_c\times V_c\right)/\left(R_c\times T_c\right)\times n\times Factor$$

Alternatively, the air mass flow can also be calculated depending on the _recirculated exhaust gas mass flow ṁ _EGR : $${\dot{m}}_{air}={\dot{m}}_{22}-{\dot{m}}_{EGR}$$

with ṁ ₂₂ the air mass flow at the location of the intake valves of the internal combustion engine 2nd . This can be as follows from the air mass in the combustion chamber and one of the engine speed of the internal combustion engine 2nd dependent factor can be calculated. $${\dot{m}}_{22}=\left(p_c\times V_c\right)/\left(R_c\times T_c\right)\times n\times FactOr$$

With p _c the pressure in the combustion chamber, V _c the effective stroke volume of the internal combustion engine 2nd , T _c the absolute temperature in the combustion chamber before the intake valves are closed, n the engine speed, factor a multiplication factor and the specific gas constant R _c .
Before closing the internal combustion engine intake valves 2nd can be approximately assumed that the pressure p _c in the combustion chamber corresponds to the pressure p ₂₂ in the intake manifold. Furthermore, it is assumed that the temperature T _c is calculated from the temperature T ₂₂ and other variables such as the cooling water temperature T _{coolant of} the internal combustion engine.

mit $$\Psi =\sqrt{\frac{{\chi }_{EGR}}{{\chi }_{EGR}{}^{-1}}\times \left[{\left(\frac{p_m}{p_{EGR}}\right)}^{\frac{2}{{\chi }_{EGR}}}-{\left(\frac{p_m}{p_{EGR}}\right)}^{\frac{{\chi }_{EGR}+1}{{\chi }_{EGR}}}\right]}$$

Applying the well-known throttle equation to the high pressure exhaust gas recirculation valve 46 then the mass flow is obtained via the high pressure exhaust gas recirculation valve 46 to: $${\dot{m}}_{EGR}=a{r}_{EGRVlv}\times {\mathrm{\mu }}_{EGR}\times \Psi \left(\frac{p_m}{p_{EGR}},{\chi }_{EGR}\right)\times \sqrt{\mathrm{2nd}\times p_{EGR}\times {\rho }_{EGR}}$$

With $$\Psi =\sqrt{\frac{{\chi }_{EGR}}{{\chi }_{EGR}{}^{-1}}\times \left[{\left(\frac{p_m}{p_{EGR}}\right)}^{\frac{\mathrm{2nd}}{{\chi }_{EGR}}}-{\left(\frac{p_m}{p_{EGR}}\right)}^{\frac{{\chi }_{EGR}+1}{{\chi }_{EGR}}}\right]}$$

Here, αr _{EGR is} the opening cross-section of the high-pressure exhaust gas recirculation valve 46 , µ _{EGR is} the discharge number of the high pressure exhaust gas recirculation valve 46 , p _{EGR is} the pressure of the exhaust gas in the flow direction _upstream of the high-pressure exhaust gas recirculation valve 46 , ρ _EGR the density of the exhaust gas in the flow direction _upstream of the high-pressure exhaust gas recirculation valve 46 , p ₂₂ the pressure of the mixture of air and EGR in the flow direction after the throttle valve 40 , χ _{EGR is} the isentropic exponent of the recirculated exhaust gas.

The density ρ _{EGR of} the exhaust gas in the flow direction _upstream of the high-pressure exhaust gas recirculation valve 46 can be calculated from the gas equation using the pressure p _EGR and the temperature T _EGR : $$\begin{array}{l}{p}_{EGR}\times v_{EGR}=R_{EGR}\times T_{EGR}\hfill \\ \text{With}{v}_{EGR}=\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{${\rho }_{EGR}$}\right.\text{surrendered}\hfill \\ \to {\rho }_{EGR}=\frac{p_{EGR}}{R_{EGR}\times T_{EGR}}\hfill \end{array}$$

With v _EGR the specific volume of the recirculated exhaust gas, T _EGR the absolute temperature of the exhaust gas in the flow direction upstream of the high-pressure exhaust gas recirculation valve 46 , R _{EGR of} the specific gas constant of the recirculated exhaust gas.

The pressure p _EGR and the temperature T _{EGR of} the exhaust gas in the flow direction _upstream of the high-pressure exhaust gas recirculation valve 46 are available either as measurement signals from sensors or as signals calculated using computing models. Alternatively, the pressure p _EGR and the temperature T _{EGR can} also be present via signals obtained from series of measurements on the engine test bench.

The _air mass flow ṁ _{αir_diag} calculated for the diagnosis of the air mass flow ṁ _air results from the difference of the air mass flow ṁ ₂₂ through the intake manifold, which is the sum of the air mass drawn in and that through the HD EGR line 47 recycled exhaust gas mass minus the exhaust gas mass flow ṁ _EGR .

The mass flow through the intake manifold with active exhaust gas recirculation - when modifying equation (3) results in: $${\dot{m}}_{mEGR}=\left(p_{22}\times V_c\right)/\left(R_{mEGR}\times T_c\right)\times n\times FactOr$$

With p ₂₂ the pressure in the intake manifold in front of the intake valves of the internal combustion engine 2nd , V _c the effective stroke volume of the internal combustion engine 2nd , T _c the absolute temperature in the combustion chamber before the intake valves close, calculated from the intake manifold temperature T ₂₂ and / or from other variables such as engine water _temperature , R _mEGR the specific gas constant of the mixture of air and exhaust gas in the combustion chamber, n the engine speed and factor a multiplication factor.

For the diagnosis of the air mass flow ṁ _air, the calculated air mass flow ṁ _{air_diag results} as: $${\dot{m}}_{air\_diaG}={\dot{m}}_{mEGR}-{\dot{m}}_{EGR}$$

Überschreitet die Abweichung den vorgebbaren Grenzwert, kann auf ein fehlerhaftes Signal für den Luftmassenstrom geschlossen werden. D.h. mindestens eines der Eingangssignale Ladedruck, Temperatur vor Drosselklappe, Öffnungsquerschnitt der Drosselklappe, Saugrohrdruck, Temperatur T_EGR vor dem Hochdruck-Abgasrückführ-Ventil 46, Druck p_EGR vor dem Hochdruck-Abgasrückführ-Ventil 46 ist fehlerhaft.Advantageously, a difference between the air mass flows ṁ _air and ṁ _{air_diag is formed} from equations (7) and (8) and checked against a predefinable limit value. $$\left|{\dot{m}}_{air}-{\dot{m}}_{air\_diaG}\right|\le Gren\mathrm{e.g.}wert$$

If the deviation exceeds the predefinable limit value, a faulty signal for the air mass flow can be concluded. Ie at least one of the input signals boost pressure, temperature upstream of the throttle valve, opening cross section of the throttle valve, intake manifold pressure, temperature T _{EGR upstream} of the high-pressure exhaust gas recirculation valve 46 , Pressure p _{EGR in} front of the high pressure exhaust gas recirculation valve 46 is faulty.

2nd the exemplary sequence of a method for monitoring an air mass flow of an internal combustion engine with high-pressure exhaust gas recirculation.

In a first step 500 the input signals for calculating the air mass flows ṁ _air and ṁ _{air_diag are} determined. For the air mass flow ṁ _air , this is done by the control unit 100 the signals of the opening cross-section ar _{THRVIv of} the throttle valve 60 , the pressure p ₁₂ and the temperature T _{12 in} front of the throttle valve 60 , the pressure p ₂₂ at the location of the intake valves and the engine speed n. The control unit 100 receives these quantities from sensors and / or calculates them from models.
The air mass flow ṁ _air can thus be determined using the throttle equation from equation (1).
At the same time as the calculation of the air mass flow ṁ _air , the input signals for the calculation of the air mass flow ṁ _{air_diag are given} by the control unit via equation (6) 100 received and saved. For the air mass flow ṁ _{air_diag} , this is _done by the control unit 100 the signals of the opening cross-section ar _{EGRVIv of} the high-pressure exhaust gas recirculation valve 46 , the pressure p ₂₂ at the location of the intake valves, the engine speed n, the temperature T ₂₂ at the location of the intake valves, the cooling water temperature T _coolant , the temperature T _{EGR upstream} of the high-pressure exhaust gas recirculation valve 46 and the pressure P _{EGR upstream} of the high pressure exhaust gas recirculation valve 46 determined. The control unit 100 receives these quantities from sensors and / or calculates them from models.

In one step 510 A deviation is formed for the two determined air mass flows ṁ _air and ṁ _{air_diag} , for example as a difference in amount and in the control unit 100 saved: $$\left|{\dot{m}}_{air}-{\dot{m}}_{air\_diaG}\right|\le ScHwellenwert.$$

The limit value can be a predetermined threshold value, which is in the control unit 100 is saved.

If the deviation exceeds the specified threshold value, then in one step 520 an error by the control unit 100 recognized and it can be assumed that at least one of the input signals is faulty. Alternatively, a debouncing time can be specified for how long an error must exist before an error from the control unit 100 is recognized and saved.
In the event of a fault, a known emergency run for the internal combustion engine can be carried out as a substitute reaction. Preferably, the throttle valve 60 are transferred to their emergency running position and / or an engine control lamp in the dashboard is switched on.
If the deviation falls below the limit value, the procedure in step 500 started over.

Claims (10)

Method for monitoring an air mass flow (ṁ _air ) of an internal combustion engine (2) with an exhaust gas recirculation, a first air mass flow (ṁ _air ) being determined by means of a throttle _equation , a second air mass flow (m _{air_diag} ) being determined as a function of an exhaust gas recirculation rate, a comparison value is formed for a deviation between the first and the second air mass flow and, depending on the deviation, an error reaction of the internal combustion engine (2) is carried out. Procedure according to Claim 1 , characterized in that an exhaust gas recirculation valve for recycling exhaust gas is open. Procedure according to Claim 1 , characterized in that the exhaust gas recirculation valve is a high-pressure exhaust gas recirculation valve (46). Method according to one of the preceding claims, characterized in that if the comparison value of the deviation exceeds a predeterminable threshold value, the air mass flow (ṁ _air ) is diagnosed as faulty and an error reaction is carried out. Method according to one of the preceding claims, characterized in that an emergency operation for the internal combustion engine (2) is activated as a fault reaction. Method according to one of the preceding claims, characterized in that the first air mass flow (ṁ _air ) at least as a function of a cross-sectional area (ar _THRVIv ) of a throttle valve (60) and / or a pressure (p ₁₂ ) in the flow direction in front of the throttle valve (60) and / or a temperature (T ₁₂ ) in the flow direction upstream of the throttle valve (60) and / or a pressure (p ₂₂ ) at the location of the inlet valves of the internal combustion engine (2). Method according to one of the preceding claims, characterized in that the second modeled mass flow at least as a function of a cross-sectional area (ar _EGRVIv ) of a high-pressure exhaust gas recirculation valve (46) and / or a temperature (T _EGR ) _upstream of the high-pressure exhaust gas recirculation valve ( 46) and / or a pressure (P _EGR ) _upstream of the high-pressure exhaust gas recirculation valve (46) and / or a pressure (p ₂₂ ) at the location of the intake valves of the internal combustion engine (2) and / or a temperature (T ₂₂ ) at the location the intake valves of the internal combustion engine (2) and / or an engine speed (n) of the internal combustion engine (2) and / or a coolant temperature (T _coolant ) of the internal combustion engine (2) is determined. Computer program which is set up to carry out a method according to one of the Claims 1 to 7 perform. Electronic storage medium with a computer program Claim 8 . Device, in particular control device (100), which is set up to implement a method according to one of the Claims 1 to 7 to execute.

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