DE102017129391A1 - Method for determining a particle mass flow of an internal combustion engine - Google Patents

Abstract

The invention relates to a method for determining a particle mass flow of an internal combustion engine. According to the invention, the dependence of the particle mass flow on a lambda value λ of the internal combustion engine is modeled by means of an exponential function at at least one selected operating point of the internal combustion engine, the exponential function in the exponent comprising the product of the lambda value λ and an exponential coefficient E.

Description

The invention relates to a method for determining a particle mass flow of an internal combustion engine.

It is known to use filters in vehicles with diesel internal combustion engines, which filter harmful particles from the exhaust gas of the internal combustion engine. If the maximum load condition of such a diesel particulate filter ("DPF") is reached, the DPF must be regenerated. In order to determine whether a regeneration of the DPF is necessary, it is known to deposit in a control unit of the vehicle an existing model of maps usually with the basis of the vehicle state, a particle emission and thus the current load state of the DPF can be determined.

The inventive method for determining a particle mass flow of an internal combustion engine of a vehicle provides that at least one selected operating point of the internal combustion engine, the dependence of the particle mass flow of a lambda λ of the engine is modeled by means of an exponential function, wherein the exponential function in the exponent the product of the lambda value λ and an exponential coefficient E.

The operating point of the internal combustion engine is determined by the speed and the torque of the internal combustion engine. The lambda value reflects the relationship between air and fuel compared to a combustion stoichiometric mixture. The particle mass flow is the mass flow of the particles in the exhaust gas of the internal combustion engine, which arise during combustion.

The invention makes it possible to replace measurements of the particle mass flow at least partially by considerably less complicated calculations. This makes it possible, in particular, to reduce the number of measurements on the real vehicle for the determination of a characteristic map for a particle mass flow model. The modeling according to the invention has proven to be a good approximation of the actual conditions. The modeling of the particle mass flow can be used, for example, to determine a loading state of a diesel particulate filter.

verwendet, wobei

der Partikelmassenstrom ist,

einen Abgasmassenfluss des Verbrennungsmotors beschreibt und K eine Konstante ist. Der Exponentialkoeffizient E_i wird vorzugsweise über Messungen am Verbrennungsmotor an einem Motorenprüfstand TB („test bench”) bei unterschiedlichen Betriebspunkten i bestimmt. Messungen an einem Motorenprüfstand haben gegenüber Messungen auf der Straße den Vorteil, dass diese erheblich effizienter durchgeführt werden können. Messungen an einer Mehrzahl von unterschiedlichen Betriebspunkten haben den Vorteil, dass die Modellierung für unterschiedliche Fahrzustände gültig ist. Dabei ist es möglich, durch eine geeignete Wahl der Betriebspunkte einen Teil der Messungen durch Interpolation zu ersetzen.Preferably, the exponential function is the function

used, where

the particle mass flow is,

describes an exhaust gas mass flow of the internal combustion engine and K is a constant. The exponential coefficient E _i is preferably determined via measurements on the internal combustion engine on an engine test bench TB ("test bench") at different operating points i. Measurements on an engine test bench have the advantage over measurements on the road that they can be carried out considerably more efficiently. Measurements at a plurality of different operating points have the advantage that the modeling is valid for different driving conditions. It is possible to replace a part of the measurements by interpolation by a suitable choice of the operating points.

bestimmt. Dabei kennzeichnet i einen Betriebspunkt,

ist, an einem Betriebspunkt i, der am Prüfstand ermittelte Partikelmassenstrom,

der am Prüfstand ermittelte Abgasmassenfluss,

der Lambdawert der Prüfstandmessung, m ._i(t) der zu einem Zeitpunkt t während des Fahrzyklus vorliegende Abgasmassenfluss, λ_i(t) der zu einem Zeitpunkt t während des Fahrzyklus vorliegende Lambdawert, und E_i der Exponentialkoeffizienten. Die Summe läuft vorzugsweise über die Gesamtheit n der Betriebspunkte. Die auf diese Weise bestimmbare Partikelemission ermöglicht es, für verschiedene Fahrzyklen, wie „Stadt”, „Überland” oder „Autobahn”, entsprechende Partikelemissionen zu ermitteln. Diese können dann, beispielsweise hinterlegt in einem Steuergerät des Fahrzeuges, dazu verwendet werden, um den Beladungszustand eines DPFs zu bestimmen.According to a preferred embodiment, the particulate emission over a time T for a driving cycle of the vehicle on the road by means of the formula

certainly. I denotes an operating point,

is, at an operating point i, the particle mass flow determined at the test stand,

the exhaust gas mass flow determined on the test bench,

the lambda value of the test bench measurement, m. _i (t) the exhaust gas mass flow present at a time t during the drive cycle, λ _i (t) of the lambda value present at a time t during the drive cycle, and E _{i of} the exponential coefficients. The sum preferably runs over the entirety of the operating points. The way this way Determinable particulate emissions make it possible to determine corresponding particle emissions for different driving cycles, such as "city", "overland" or "motorway". These can then be used, for example, deposited in a control unit of the vehicle, to determine the loading state of a DPF.

umfasst, wobei ρ die Dichte der umgebenden Luft und ρ_SL eine Referenzdichte ist.A further method for determining a particle mass flow of an internal combustion engine of a vehicle provides that a dependency of the particle mass flow on an ambient condition is modeled by means of an exponential function, the exponential function in the exponent being the term

where ρ is the density of the surrounding air and ρ _{SL is} a reference density.

An ambient condition is the air temperature, the air pressure and / or the air density of the environment. Temperature, pressure and density are linked by a physical equation.

By means of the modeling it is possible to calculate from a particle mass flow or ratio determined under reference conditions or from a particle emission a particle mass flow, a particle mass flow ratio or a particle mass flow for an ambient condition other than the reference condition. Real measurements of the above values under different environmental conditions can thus be reduced and replaced by calculations. The values calculated in this way can be used, for example, to determine the loading state of a particle filter in an environment-dependent manner.

gilt.By means of the modeling, it is possible in particular also to describe internal combustion engines which have a turbocharger. This is especially true on the assumption that the change in a turbocharger speed and a pressure ratio of the turbocharger inlet and outlet is independent of the change in the altitude at which the engine is located, and thus

applies.

It is particularly advantageous to supplement the method described here for determining the particle emission, which does not take into account the ambient conditions, in order to supplement the second method in order to take account of the ambient conditions.

The methods are preferably used to create a model with which the loading state of a diesel particulate filter can be determined. The model can in particular be map-based.

An exemplary embodiment of a method according to the invention is described below.

verwendet, wobei

der Partikelmassenstrom ist,

einen Abgasmassenfluss des Verbrennungsmotors beschreibt und K eine Konstante ist. Der Exponentialkoeffizient E_i wird über Messungen am Verbrennungsmotor an einem Motorenprüfstand TB an unterschiedlichen Betriebspunkten i bestimmt.In accordance with the method for determining a particle mass flow of an internal combustion engine of a vehicle, the dependence of the particle mass flow on a lambda value λ of the internal combustion engine is modeled at least at one selected operating point of the internal combustion engine by means of an exponential function, the exponential function in the exponent comprising the product of the lambda value λ and an exponential coefficient E. , As an exponential function becomes the function

used, where

the particle mass flow is,

describes an exhaust gas mass flow of the internal combustion engine and K is a constant. The exponential coefficient E _i is determined via measurements on the internal combustion engine on an engine test bench TB at different operating points i.

Since it is too expensive to perform measurements at all operating points, it is advantageous to make a selection of operating points, and to determine values at further operating points via an interpolation. In order to make such a selection, in this embodiment, for a selected Driving cycle, here for the cycle "city", created a table that represents a frequency distribution of the operating points, see Table 1.

Tabelle 1

Table 1

Tabelle 2 Using black smoke measurements at individual operating points, it is possible to determine the operating-point-dependent percentage distribution of soot emissions specific to the cycle. Black smoke measurements were chosen because they can be performed with little effort compared to particle emission measurements and there is a sufficient correlation between black smoke and particle emission. The result is shown in Table 2:

Table 2

It can be seen that only a subset of the operating points for the particulate emissions is relevant for the cycle "city". Within this subarea, several, here 15, operating points were selected (marked in red) at which the particle emission is to be determined by means of measurements. The selection of the operating points is made under the condition that they are as representative as possible for the subarea. For this purpose, for example, a cubic-body-centered approach can be taken. Values at other operating points can be determined in a subsequent step, for example by means of interpolation.

an den ausgewählten Betriebspunkten i erfolgt in einem stationären Zustand. Stationär heißt, dass die Motorbedingungen (und somit auch der Lambdawert

und die Umgebungsbedingungen über den Zeitraum, in dem die Messung erfolgt, konstant sind. Mittels Interpolation, hier mit Spline-Kurven, wurden die Werte des Partikelmassenstroms

für den gesamten Bereich der Betriebspunkte ermittelt. Die Interpolation führt zudem zu einer Glättung eines solchen Kennfeldes. Tabelle 3 zeigt das Kennfeld für den Partikelmassenstrom, Tabelle 4 das Kennfeld für den Lambdawert.

Tabelle 3

Tabelle 4 The measurements of the particle mass flow at the selected operating points are made on the test bench. The particulate mass flow at the selected operating points is determined by weighing a particulate filter disposed in an exhaust system of the internal combustion engine. The measurement of the particle mass flow

at the selected operating points i takes place in a stationary state. Stationary means that the engine conditions (and therefore also the lambda value

and the ambient conditions are constant over the period of time in which the measurement is taken. By means of interpolation, here with spline curves, the values of the particle mass flow became

determined for the entire range of operating points. The interpolation also leads to a smoothing of such a map. Table 3 shows the map for the particle mass flow, Table 4, the map for the lambda value.

Table 3

Table 4

In the following step, the exponential coefficient E _{i is} determined. For this purpose, for an operating point, in this case for the above selection of 15 operating points, the lambda value is set in a non-stationary state and the particle mass flow is determined at this lambda value.

interpoliert. Für E_i ergibt sich für diesen Betriebspunkt ein Wert von –6.51. Da die Abhängigkeit des Partikelmassenstroms von Lambda näherungsweise der der Rußemissionen entspricht, entspricht in guter Näherung der über die Schwarzrauchmessung ermittelte Exponentialkoeffizient E_i dem des Partikelmassenstroms.In this exemplary embodiment, the particulate mass flow itself is not measured, but the soot emissions at different lambda values are measured by means of a black smoke measurement. The figure shows such a measurement by way of example for a selected operating point at which the soot emission was measured for nine different lambda values by means of black smoke measurements. The curve resulting from the measurements was given the function

interpolated. For E _i , a value of -6.51 results for this operating point. Since the dependence of the particle mass flow of lambda approximately corresponds to the soot emissions, corresponds to a good approximation of the determined via the black smoke measurement exponential E _i that of the particle mass flow.

After the exponential coefficient E _{i has been} determined for the selection of the operating points, values for the entire characteristic field are determined by means of interpolation. The result is shown in Table 5.

Tabelle 5

Table 5

The map advantageously be used to control particulate emissions PM a vehicle with the internal combustion engine for a drive cycle or for several driving cycles to determine.

Die Werte für

und E_i werden den obigen Kennfeldern entnommen. Für den Abgasmassenstrom

wird über Messungen am Prüfstand ein entsprechendes Kennfeld erzeugt. Methoden zur Bestimmung des Abgasmassenstroms sind dem Fachmann hinlänglich bekannt. Der Wert T entspricht der Gesamtdauer oder eines Zeitabschnitts des Fahrzyklus. Der Abgasmassenstrom m ._i(t) wird gemäß Fahrzyklus durch eine Fahrt auf der Straße ermittelt. Die Formel ergibt sich aus dem Ansatz, dass die Beziehung PM ._i = m ._i·K·exp(–E_i·λ_i) sowohl unter Prüfstandbedingungen als auch „auf der Straße” gültig ist, und die Konstanten K und E für beide Fälle identisch sind.The determination of the particle emission is carried out according to the invention via formula

The values for

and E _i are taken from the above maps. For the exhaust gas mass flow

a corresponding characteristic field is generated via measurements on the test bench. Methods for determining the exhaust gas mass flow are well known to those skilled in the art. The value T corresponds to the total duration or a period of the drive cycle. The exhaust gas mass flow m. _i (t) is determined according to the driving cycle by driving on the road. The formula results from the approach that the relationship PM. _i = m. _i · K · exp (-E _i · λ _i ) is valid under both test stand conditions and on the road, and the constants K and E are identical for both cases.

The result can be used, for example in the form of a table, for a model for determining a loading state of a DPF of the vehicle. According to the driving cycle "city", particle emissions for further driving cycles, for example for cycles "highway driving" or "overland travel", can advantageously be determined by the above method. The model is preferably set up on a control unit of the vehicle.

The method can be used to determine particulate loading in the diesel particulate filter for each driving profile (eg, city, overland, highway). This approach reduces the number of real particle weighings. The combination of stationary examinations on the engine test bench and measurements on the road can reduce the time-consuming and costly measurement effort on the road. The methodology is transferable to various ECU software.

und

einen Einfluss haben, möglichst den Bedingungen entsprechen, unter denen die Werte E_i, λ_i und m ._i(t) bestimmt werden. Dies betrifft die Temperatur eines Gases in einem Ansaugtrakt des Verbrennungsmotors, hier der für die Verbrennung angesaugten Luft und gegebenenfalls des über eine Abgasrückführung zurückgeführten Abgases, der Wassertemperatur eines Kühlsystems des Verbrennungsmotors und/oder der Temperatur des verwendeten Kraftstoffes. Damit wird gewährleistet, dass die berechnete durchschnittliche Partikelemission möglichst genau dem tatsächlichen Wert entspricht.Furthermore, it is advantageous that the conditions under which the test bench measurements are carried out and those on the parameters

and

have an influence, as far as possible correspond to the conditions under which the values E _i , λ _i and m. _i (t) can be determined. This relates to the temperature of a gas in an intake tract of the internal combustion engine, here the air sucked in for combustion and optionally the exhaust gas recirculated via an exhaust gas recirculation, the water temperature of a cooling system of the internal combustion engine and / or the temperature of the fuel used. This ensures that the calculated average particle emission is as close as possible to the actual value.

According to the invention, only one trip on the road would be necessary to determine the particulate emission for one cycle. A trip for the determination of the measuring points at which the particle mass flow is to be measured at the test stand is advantageous in order to optimize the number of measurements, but not absolutely necessary.

umfasst, wobei ρ die Dichte der umgebenden Luft und ρ_SL eine Referenzdichte ist.In order to take into account the dependence of the particle emission or the particle mass flow of the internal combustion engine on the ambient conditions air density, air temperature and air pressure, a dependence of the particle mass flow of an environmental condition is modeled by means of an exponential function, wherein the exponential function in the exponent the term

where ρ is the density of the surrounding air and ρ _{SL is} a reference density.

bestimmt. Anschließend wird mit der Gleichung

für weitere Luftdichten der Partikelmassenstrom oder ein Partikelmassenstromverhältnis berechnet.In this exemplary embodiment, a first measurement of a particle mass flow PM. _SL at a reference density ρ _SL and a second measurement of a particle mass flow PM. performed at a density ρ. The measured values become the constant a of the equation

certainly. Subsequently, with the equation

for further air densities the particle mass flow or a particle mass flow ratio is calculated.

The method can be used to take into account the dependence of the particulate emission on the ambient conditions for a driving cycle, for example the above driving cycle "city".

For example, in two measurements under different environmental conditions, the values of ambient temperature, ambient pressure, air density, average speed, soot emission per unit distance and soot emission per time shown in Table 6 were measured. The first measurement "Rüsselsheim" is the reference measurement SL. environmental conditions Temperature ° C Air pressure mbar Air tight kg / m3 Average speed Km / h Soot emission mg / km Soot emission g / h 80 m asl 7.09 1000 1,247 25 51.77 1,315 Granada 800 m asl 27.7 940 1087 20 70.09 1,527 Table 6

der Wert 1,16. Für die Konstante a ergibt sich der Wert 2,258.Assuming that the ratio of the measured soot emission corresponds to the ratio of the particulate emission, the ratio results

the value 1.16. For the constant a, the value is 2.258.

wird über den Zusammenhang p = ρ·R·T, wobei R die spezifische Gaskonstante für Luft ist, für weitere Temperaturen und Drücke das jeweilige Verhältnis berechnet. Das Ergebnis ist in Tabelle 7 dargestellt.About the equation

is calculated via the relationship p = ρ · R · T, where R is the specific gas constant for air, for further temperatures and pressures the respective ratio. The result is shown in Table 7.

Tabelle 7

Table 7

Table 7 is a characteristic diagram whose entries represent environmental conditions dependent correction factors for a particle mass flow / particle emission determined under reference conditions (here at p = 100 kPa and T = 7.09 ° C.). With the correction factors can be a particle emission PM . here the particle emission PM for the driving cycle city, assuming that it was measured under the same reference conditions (here at p = 100 kPa and T = 7 ° C), adapt to different environmental conditions.

Such a map, together with the particulate emissions determined for one or different driving cycles, is preferably stored in a control device of the vehicle. This makes it possible to determine a load condition of a particulate filter with sufficient accuracy under various environmental conditions.

In this embodiment, the internal combustion engine is a diesel engine with an exhaust gas recirculation and a turbocharger. In addition, the invention can be applied to all internal combustion engines for which a particle mass flow or a particle emission is to be determined.

Claims (14)

Method for determining a particle mass flow of an internal combustion engine of a vehicle, wherein at least one selected operating point of the internal combustion engine, the dependence of the particle mass flow of a lambda value λ of the internal combustion engine is modeled by means of an exponential function, wherein the exponential function in the exponent comprises the product of the lambda value λ and an exponential coefficient E. , The method of claim 1, wherein as an exponential function

is used, where

describes an exhaust gas mass flow of the internal combustion engine and K and E are constants. Method according to one of the preceding claims, wherein the exponential coefficient E is determined via measurements on the internal combustion engine on an engine test bench. A method according to claim 3, wherein temperature of a gas in an intake tract of the internal combustion engine, water temperature of a cooling system of the internal combustion engine and / or fuel temperature on the test stand are adjusted so that they correspond to the corresponding values of the internal combustion engine used in the vehicle. Method according to one of the preceding claims, wherein for a plurality of operating points, the particulate mass flow for stationary case at a constant lambda value by means of measurements of the particulate mass flow at a subset of operating points and interpolation is determined, and the value of the particulate mass flow at the lambda value is used at an operating point to determine the exponential coefficient E for this operating point. Method according to one of the preceding claims, wherein for the at least one operating point of the lambda value is set so that a non-stationary state is present, the particle mass flow is determined at this lambda value, and the value of the particulate mass flow is used for this lambda value, for this operating point to determine the exponential coefficient E. Method according to one of the preceding claims, wherein the particle mass flow is determined at an operating point by means of weighing a arranged in an exhaust system of the internal combustion engine particulate filter. Method according to one of the preceding claims, wherein the particle emission for a driving cycle of the vehicle on the road by means of the formula

where i denotes an operating point determined by load and speed,

the particle mass flow determined at the test bench,

the exhaust gas mass flow determined on the test bench,

the lambda value of the test bench measurement, m. _i (t) is the exhaust gas mass flow present at a time t during the drive cycle, λ _i (t) is the lambda value present at a time t during the drive cycle, and E _{i is} the exponential coefficient, in each case at the operating point i. A method for determining a particle mass flow of an internal combustion engine of a vehicle, wherein a dependence of the particle mass flow of an environmental condition by means of an exponential function is modeled, wherein the exponential function in the exponent the term

where ρ is the density of the surrounding air and ρ _{SL is} a reference density. The method of claim 9, wherein by means of the model dependent on the environmental condition correction factor for a determined under reference conditions particulate mass flow is determined. Method according to claim 9 or 10, wherein at least one first measurement of a particle mass flow PM. _SL at a reference density ρ _SL and a second measurement of a particle mass flow PM. is performed at a density ρ, with the measured values the constant a of the equation

is determined and with the equation

for further air densities the particle mass flow or a particle mass flow ratio is calculated. Method according to one of claims 9 to 11 in conjunction with one of claims 1 to 8. Use of a method according to one of the preceding claims for the creation of a model for determining the loading of a particulate filter. Application of a method according to one of the preceding claims, wherein a loading state of a particle filter is determined by means of the modeled particle mass flow or the specific particle emission.

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