DE102009037272A1 - Method for operating an internal combustion engine - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine, in which a thermodynamic cyclic process is performed cyclically in at least one working cylinder of the internal combustion engine. The following steps are performed:
(a) controlling an indicated mean pressure in working cylinders of the internal combustion engine as a function of a cylinder pressure as an actual value, so that a desired torque output by the internal combustion engine results;
(b) determining an injection quantity for fuel per cycle and per cylinder from the output torque by means of values for injection quantities of fuel which are predetermined as a function of the torque;
(C) determining a fresh air mass per cycle and per cylinder from the injection quantity for fuel and a signal of a arranged in the exhaust tract of the internal combustion engine lambda probe.

Description

The The invention relates to a method for operating an internal combustion engine, in which in at least one working cylinder of the internal combustion engine thermodynamic cycle is carried out cyclically, according to the preamble of claim 1.

From the DE 601 16 531 T2 For example, there is known a method of controlling the temperature of an air mass in an internal combustion engine, wherein the pressure of the gaseous mass trapped in a cylinder is measured. Furthermore, the change in pressure during the compression phase is analyzed and from this a calculation of the mass of the trapped charge and the mean temperature of this mass at the time of closing the inlet is derived.

Previous Motoransteuerungsverfahren, especially in the passenger car diesel engine, use an air mass measurement, for example by means of a Heißfileinuftmassenmessers (HFM) at the entrance of the air exhaust system as a central input for metering exhaust gas recirculation and for monitoring the soot limit. The component is steady over the years optimized and improved. Experience shows that this Sensor has the following critical points. Pulsations, for example by AGR, distort the signal (pulsation sensitivity). The measuring accuracy is extremely dependent on the air flow in front of and behind the installation site. It results in a pressure loss through an installation of the HFM after an air filter. Based on the current sensor configuration (HFM with various pressure / temperature sensors in the air / exhaust system of the Motors) become physical models (throttles, gas tanks) calculates the at all essential places of the air / exhaust system the current state (pressure, temperature, mass and concentrations) to know. For example, thereby the mass flow through EGR valve calculated. The HFM signal becomes the total charge mass modeled.

There are numerous methods for determining the aspirated gas mass m _Z in the combustion chamber of an internal combustion engine. Most approaches consider the internal combustion engine as a pump, which draws a volume flow from an exhaust-fresh air mixture before the intake valves. The density of this gas mixture before the inlet valves is calculated from the pressure and the temperature of the gas. This density is determined by models for pressure and temperature and / or via direct measurement by sensors. Subsequently, with the help of the so-called delivery rate, which is mainly dependent on the speed, the sucked gas mass in the cylinder is modeled. This method of modeling the intake gas mass can also be called a conventional forward path.

The Accurate determination of the aspirated gas mass will be for future Combustion engine concepts with variable valve trains or additional actuators in the intake and exhaust tract of internal combustion engines are increasingly difficult, because the pressure is in the Usually in front of the throttle points (throttle, swirl flap, VVT, ...) measured so that the pressure is just above the inlet valves above Models must be determined. There is also an additional one Errors due to the modeling of the throttle points and the temperature to the inlet valves. This becomes the destination of the announced Cylinder gas mass over this approach increasingly unreliable.

Of the Invention is based on the object, a method of the above Art to improve that state variables for the metering of an EGR rate and for monitoring a soot boundary without the modeling errors of the conventional one Forward path.

These The object is achieved by a method of the abovementioned type with the method steps characterized in claim 1 solved. Advantageous embodiments of the invention are in the further claims.

• (a) Regeln eines indizierten Mitteldruckes in Arbeitszylindern der Brennkraftmaschine in Abhängigkeit von einem Zylinderdruck als Istwert, so dass sich ein gewünschtes, von der Brennkraftmaschine abgegebenes Moment ergibt;
• (b) Bestimmen einer Einspritzmenge für Kraftstoff pro Zyklus und pro Arbeitszylinder aus dem abgegebenen Moment mittels in Abhängigkeit von dem Moment vorbestimmten Werten für Einspritzmengen von Kraftstoff;
• (c) Bestimmen einer Frischluftmasse pro Zyklus und pro Arbeitszylinder aus der Einspritzmenge für Kraftstoff und einem Signal einer im Abgastrakt der Brennkraftmaschine angeordneten Lambdasonde.

For this purpose, it is provided according to the invention in a method of the above-mentioned type that the following steps are carried out

• (a) controlling an indicated mean pressure in working cylinders of the internal combustion engine as a function of a cylinder pressure as an actual value, so that a desired torque output by the internal combustion engine results;
• (b) determining an injection quantity for fuel per cycle and per cylinder from the output torque by means of values for injection quantities of fuel which are predetermined as a function of the torque;
• (C) determining a fresh air mass per cycle and per cylinder from the injection quantity for fuel and a signal of a arranged in the exhaust tract of the internal combustion engine lambda probe.

This has the advantage of being a surveillance size for a metering of an exhaust gas recirculation and for monitoring a soot boundary, a fresh air mass is available, which without the need of a Hot-film air flow meter (HFM) is determined.

A consideration of transit times of the gases in the system is achieved in that in step (c) a signal of the lambda probe at a time t ₁ an injection quantity to a previous Time t ₀ = t ₁ - .DELTA.t is assigned, wherein .DELTA.t corresponds to a time interval which elapses from the time of determination of the injection quantity to the arrival of exhaust gas from combustion with this specific injection quantity at the lambda probe.

In In a preferred embodiment, in step (a) the Cylinder pressure by means of a cylinder pressure sensor or by means of a Pressure sensor in an intake manifold of the internal combustion engine certainly.

• (d) Bestimmen einer gesamten Gasmasse in einem Arbeitszylinder pro Zyklus aus einem Zylinderdruckverlauf oder einem Saugrohrdruck in Verbindung mit einer Temperatur im Arbeitszylinder vor Kompressionsbeginn. Hierbei wird die Temperatur im Arbeitszylinder vor Kompressionsbeginn beispielsweise gemessen oder modelliert.

For further determination of state variables, the following further step is carried out,

• (D) determining a total gas mass in a working cylinder per cycle from a cylinder pressure curve or an intake manifold pressure in conjunction with a temperature in the working cylinder before the start of compression. In this case, the temperature in the working cylinder is measured or modeled, for example, before the start of compression.

• (e) Bestimmen der Massenströme durch wenigstens ein AGR-Ventil mittels Drosselgleichungen aus Druck- und Temperaturmodellen in Abhängigkeit von einer Öffnung des wenigstens einen Ventils.

For further determination of state variables, the following further step is carried out,

• (E) determining the mass flows through at least one EGR valve by means of throttle equations of pressure and temperature models as a function of an opening of the at least one valve.

• (f) Bestimmen der AGR-Rate aus einem Verhältnis der AGR-Massenströme zur gesamten Gasmasse.

To determine a controlled variable for a NO _x reduction, the following further step is carried out,

• (f) determining the EGR rate from a ratio of EGR mass flows to total gas mass.

The The invention will be explained in more detail below with reference to the drawing explained. This shows in

1 a graphical representation of a cylinder pressure pz as a function of a crank angle φ and

2 a schematic flow diagram of a calculation of a gas mass in a combustion chamber.

at the inventive method is used instead air mass measurement a cylinder pressure sensor (one sensor per engine or per cylinder bank or per cylinder) is used as a central element and for monitoring and plausibility of a lambda probe and resorted to a boost pressure sensor.

The Cylinder pressure signal is used to control the indicated mean pressure or moment used. This will be the desired moment adjusted. An injection quantity stored in a control unit (efficiency model) corresponds by regulating the measured injection quantity with high accuracy even in dynamic transitions and different injection curves.

at now known injection quantity with high accuracy is by means of the lambda probe on the fresh air mass, so the air mass, the the HFM would measure, closed. Here are the terms the signals involved. This only applies to limited HC emissions, as the lambda probe is cross-sensitive to HC.

Of the so well-known proportion of fresh air is to avoid soot formation favorable observation size.

The total gas mass in the cylinder is determined by evaluation of the cylinder pressure curve or intake manifold pressure and by modeling and / or measuring the Temperature detected before start of compression in the cylinder.

The Mass flows through one or more EGR valves are over Throttle equations depend on the pressure and temperature models modeled from the opening of the valves.

The ratio of the EGR mass flows to the total gas mass is the EGR rate, the actually desired control variable for the NO _x reduction.

alternative for the use of cylinder pressure sensor (s) is a concept with a pressure sensor in the intake manifold in addition used for or as a replacement of the boost pressure sensor, depending on it then the gas mass in the engine combustion chamber and turn it over Models calculate the fresh air mass flow or the fresh air mass in the combustion chamber becomes. As the use of the lambda probe for fresh air mass determination or correction / adaptation functions for air mass determination requires a good knowledge of the injected fuel mass, is the injection quantity via alternative approaches, for example, from the speed signal determined. Alternatively it is the injection system designed such that the specifications of the injection masses be followed very closely.

The computation step sequence and the combination of these submodels is to be adapted such that instead of the input signal HFM, ie calculation in the flow direction of the engine, the model for the total charge mass, advantageously based on the cylinder pressure signal, alternatively based on a pressure sensor in the intake manifold, used as close to the engine inlet valves becomes. This means that the calculation sequence for the intake range of the Air / exhaust system is calculated substantially against the flow direction. In this way, from the model of the total charge mass, the intake fresh air mass flow at the inlet of the air / exhaust system can be modeled. In known systems, the calculation is exactly the opposite, from the HFM signal ultimately the total charge mass is modeled.

The Control concept for the air / exhaust system is such adapted to a measured fresh air mass signal, such as HFM, is waived. The control concept works for the setting of the defined target values the modeled state variables of the above Models and / or the existing measured variables of the rest Sensors back.

This results in many advantages. The "raw" sensor information is local to the control technically better place. The state in the inlet defines the emissions, because at this point the fuel is supplied. The total charge amount is an important quantity for modeling the EGR rate. It is determined in the method according to the invention without the modeling errors of the conventional forward path. The cylinder pressure (for the concept with cylinder pressure sensor) enables precise information about the fuel mass through the torque control so that a plausibility check with the lambda probe (dynamically corrected) is possible. When the throttle valve is in front of the intake manifold, a 3-fold plausibility check of the intake manifold pressure is possible: p _suction via duosensor + throttle = p _suction from cylinder pressure + duct model = p _suction from tank model intake manifold. The inherent measurement inaccuracies of the HFM, such as the pulsation dependence, are not included in the monitoring! Thus, a separation between errors in the air mass and errors in the injection is better assigned. The costs for the component of the HFM and the constructive / functional integration into the air / exhaust system are eliminated (high constructive effort for long calming distances). In addition, the pressure loss due to the inlet and outlet sections and the actual air mass sensor is eliminated.

at the method according to the invention becomes a determination allows the gas mass in the combustion chamber, in which the pressure measurement on a cylinder pressure sensor at the point of interest in the combustion chamber he follows. There are two different methods, the gas mass in the Determine combustion chamber via the cylinder pressure measurement.

die Zylindermasse im Brennraum, d. h. die gesamte Gasmasse inklusive Restgasmasse und nicht nur die von außen angesaugte Gasmasse, nach dem Schließen der Einlassventile (ES) bestimmt. Dann ist der Zylinder ein abgeschlossener Behälter, in dem die Gasmasse im Zylinder über die oben genannte ideale Gasgleichung berechnet wird. Der Druck p(φ) am Kurbelwinkel φ wird gemessen, das Volumen des Brennraums zum Kurbelwinkel φ ist bekannt und wird beispielsweise in einer Tabelle abgelegt und ausgelesen. Die Gaskonstante R wird als konstant angesehen oder als Funktion der Temperatur abgelegt und die Temperatur T(φ) wird aus der Ansaugtemperatur vor den Einlassventilen modelliert. Damit sind alle Größen auf der rechten Seite der oben genannten idealen Gasgleichung bekannt und die Gasmasse m_Z im Zylinder lässt sich berechnen. Dabei wird der Druck p(φ) direkt in der Nähe des unteren Totpunktes (UT) gemessen, wo kleine Absolutdruckwerte herrschen, oder über die Polytropengleichung aus Druckwerten p₃₄₀ nahe dem oberen Totpunkt (OT), wo große Druckwerte herrschen, aber noch in der Kompressionsphase vor der Kraftstoffeinspritzung berechnet, gemäß der Formel

In a first method is about the equation

the cylinder mass in the combustion chamber, ie the total gas mass including residual gas mass and not just the gas mass sucked from the outside, determined after closing the inlet valves (ES). Then, the cylinder is a sealed container in which the gas mass in the cylinder is calculated via the above-mentioned ideal gas equation. The pressure p (φ) at the crank angle φ is measured, the volume of the combustion chamber to the crank angle φ is known and is stored and read in a table, for example. The gas constant R is considered constant or stored as a function of temperature and the temperature T (φ) is modeled from the intake temperature upstream of the intake valves. Thus, all variables on the right side of the above-mentioned ideal gas equation are known and the gas mass m _Z in the cylinder can be calculated. In this case, the pressure p (φ) is measured directly in the vicinity of the bottom dead center (UT), where small absolute pressure values prevail, or via the polytropic equation from pressure values p ₃₄₀ near top dead center (TDC), where high pressure values prevail, but still in the Compression phase calculated before the fuel injection, according to the formula

In a second method, the pressure in the cylinder at UT (bottom dead center) is calculated from a pressure value near TDC in the compression phase (for example 20 ° before TDC - p ₃₄₀ ) according to the formula

This is in 1 illustrated. This is on a horizontal line 10 a crank angle φ and on a vertical line 12 a cylinder pressure p _Z plotted. With 14 is a bottom dead center UT, with 16 is an inlet that includes ES, with 18 is an upper dead center OT, with 20 is a cylinder pressure p ₃₄₀ , with 22 is a cylinder pressure p ₁₈₀ and with 24 is a cylinder pressure p _{UT (340)} .

Based on this pressure value, a gas mass in the combustion chamber is then calculated, taking into account the modeled temperature of the intake gas upstream of the intake valves and a total charge level, and, in addition, an aspirated gas mass flow from the gas mixture upstream of the intake valves is determined. This is in 2 illustrated. In 2 designated 26 "Pressure at UT from cylinder pressure", 28 "Temperature intake manifold", 30 "Correction pressure measurement", 32 "Temperature Model ES", 34 "Total charging efficiency" 36 "Residual gas model" 38 "Density", 40 "Theo. Flow " 42 "Engine mass flow m _Z " and 44 "Sucked mass flow m _F ".

LIST OF REFERENCE NUMBERS

10

horizontal Straight line: crank angle φ

12

vertical Straight line: cylinder pressure pZ

14

lower Dead center UT

16

inlet closes ES

18

upper Dead center OT

20

cylinder pressure p340

22

cylinder pressure p180

24

cylinder pressure pUT (340)

26

print at UT from cylinder pressure

28

temperature suction tube

30

correction pressure measurement

32

Temperature model IT

34

Total charge level

36

Residual gas model

38

density

40

Theo. flow

42

Motor mass flow mZ

44

aspirated Mass flow mF

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 60116531 T2 [0002]

Claims (7)

Method for operating an internal combustion engine, in which in at least one working cylinder of the internal combustion engine, a thermodynamic cycle is performed cyclically, characterized in that the following steps are performed, (a) controlling an indicated mean pressure in working cylinders of the internal combustion engine as a function of a cylinder pressure as the actual value, so that results in a desired output from the internal combustion engine torque; (b) determining an injection quantity for fuel per cycle and per cylinder from the output torque by means of values for injection quantities of fuel which are predetermined as a function of the torque; (C) determining a fresh air mass per cycle and per cylinder from the injection quantity for fuel and a signal of a arranged in the exhaust tract of the internal combustion engine lambda probe. A method according to claim 1, characterized in that in step (c) a signal of the lambda probe at a time t _1, an injection quantity is assigned to a previous time t ₀ = t ₁ - .DELTA.t, where .DELTA.t corresponds to a time interval from the time of Determining the injection quantity until the arrival of exhaust gas from a combustion with this specific injection quantity at the lambda probe passes. Method according to at least one of the preceding Claims, characterized in that in step (a) the cylinder pressure by means of a cylinder pressure sensor or by means of a pressure sensor in an intake manifold of the internal combustion engine determined becomes. Method according to at least one of the preceding Claims, characterized in that the following further Step is executed (d) determining an entire Gas mass in a cylinder per cycle from a cylinder pressure curve or an intake manifold pressure in conjunction with a temperature in the working cylinder before the start of compression. Method according to claim 4, characterized in that in step (d), the temperature in the working cylinder before the start of compression measured or modeled. Method according to at least one of the preceding Claims, characterized in that the following further Step is executed (e) determining the mass flows by at least one EGR valve by means of throttle equations of pressure and temperature models as a function of an opening the at least one valve. Method according to at least one of the preceding Claims, characterized in that the following further Step is executed (f) determining the EGR rate from a ratio of EGR mass flows determined in step (e) to in step (d) determined total gas mass.

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