DE10252732A1 - Method and device for operating an exhaust gas aftertreatment device of an internal combustion engine - Google Patents

Abstract

In a method and a device for operating an exhaust gas aftertreatment device of an internal combustion engine, in particular of a motor vehicle, having a particle filter, wherein at least one variable that is characteristic of the loading condition of the particle filter is determined from operating parameters of the particle filter, it is provided to achieve increased accuracy in determining the loading of the particle filter the spatial distribution of exhaust gas particles is modeled essentially in the longitudinal direction of the particle filter and the characteristic size is corrected by means of the modeled spatial distribution of the exhaust gas particles.

Description

The invention relates to a method and a device for operating an exhaust gas aftertreatment device an internal combustion engine according to the preambles the respective independent Expectations.

Motor vehicles powered by diesel engines have in many countries To have facilities for exhaust gas aftertreatment. Because of the soot formation particulate filters are used to reduce emissions of soot particles in the To minimize exhaust emissions from these engines by filtering them out. To this Particle filters will become even stricter due to future emission limit values increased Requirements placed on the efficiency of exhaust gas aftertreatment. About that In addition, such particle filters are also noticed in gasoline engines Direct injection is becoming increasingly important, particularly in the so-called "shift operation" of these engines soot formation occurs in the exhaust gas.

From the DE 100 14 224 A1 and the DE 101 00 418 A1 is a method for controlling an internal combustion engine with such an exhaust gas aftertreatment device. The state of the exhaust gas aftertreatment device must be known for precise control of the internal combustion engine. In particular, the loading condition of the particle filter, ie the current amount of soot particles filtered out, must be known as precisely as possible.

Checking the filter load and regeneration monitoring the particle filter is known to be made by means of pressure sensors, because the pressure drop across the Filter conclusions on the mass of soot collected in the filter allows. The pressure signal supplied by the pressure sensors becomes dependent evaluated from the current operating point of the internal combustion engine and considering by the pressure drop, the flow conditions, the temperature, the exhaust gas volume flow etc. the flow resistance in the filter of the filter, which in turn is representative of the soot load. Here will Simplifyingly assumed that the soot mass is spatially evenly distributed in the filter is. For determining soot mass is calculated from the exhaust gas volume flow V and the differential pressure p_Diff along the Particle filter a flow resistance R_Gleich calculated according to the relationship R_Gleich = p_Diff / V.

The present invention lies the task of a method and an apparatus of the beginning mentioned type to improve that increased accuracy is enabled when determining the loading of the particle filter.

This task is solved by the characteristics of the independent Expectations. Advantageous refinements are the subject of the respective subclaims.

The invention is based on the idea that spatial Distribution of exhaust gas particles essentially in the longitudinal direction to model the particle filter. From the spatial distribution of the particle mass / volume then becomes a correction factor for at least one from operating parameters of Internal combustion engine and / or the exhaust gas aftertreatment device calculated characteristic size of the particle filter determined. The characteristic variable is, for example, that in the filter accumulated particle mass / volume or the flow resistance of the particle filter into consideration. The characteristic size is therefore characteristic for the Loading status of the filter. That the correction factor is preferred used one according to the state the technology calculates the aforementioned characteristic size of the particle filter correct, in the end the accuracy for the determination to increase the load of the filter.

A correction of the mentioned flow resistance due to the uneven distribution of the particles in the longitudinal direction of the particle filter R_Unleich preferably takes place in a linear approximation according to the relationship R_Ungleich - R_Gleich · (1 + Kappa), where Kappa is a dimensionless correction quantity.

According to a preferred embodiment of the inventive method becomes the modeling of the particle filter in the longitudinal direction divided into segments of preferably the same length. The inflowing particle mass or volume flow is distributed to the individual segments using a distribution function distributed and at a given time in each segment inflowing particle mass or volume added up to the distribution of the particle mass or of the volume in the direction of flow to determine the particle flow.

According to an advantageous further development from the for each segment determined particle flow by means of one for the respective Particle filter material characteristic curve of flow resistance of a single segment of the particle filter.

According to a further embodiment becomes from the distribution resulting from the individual segments the flow resistance over the particle filter length by means of a weighting function over the segments one over the total length the resulting total flow resistance of the particle filter is calculated.

By using the method according to the invention in an exhaust gas aftertreatment device affected here increases the accuracy of the determination of the particle mass accumulated in the particle filter.

The invention will be described below with reference to the accompanying drawings preferred embodiments explained in more detail, from which further features and advantages of the invention emerge.

Show in detail

1 a block diagram of a device for operating an exhaust gas aftertreatment device of an internal combustion engine according to the prior art;

2 a detailed representation of a method for determining the load in a particle filter according to the prior art;

3 a schematically illustrated particle filter for further illustration of the method according to the invention, in particular the modeling of the spatial distribution of exhaust gas particles in a particle filter; and

4a . b Diagrams to illustrate a particle distribution function according to the method according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to the 1 A device for operating an exhaust gas aftertreatment device of an internal combustion engine according to the prior art, in which the method according to the invention can be implemented, is described. In the present example, the device is arranged in a self-igniting internal combustion engine, for example a diesel engine. In this internal combustion engine, the fuel metering is controlled by means of a so-called common rail system. However, the procedure according to the invention is not limited to these systems and can generally. can also be used in other internal combustion engines.

With 100 the internal combustion engine is called, which has an intake line 102 Fresh air is supplied and via an exhaust pipe 104 Exhaust fumes. In the exhaust pipe 104 is an exhaust gas aftertreatment agent 110 arranged, from which the cleaned exhaust gases via the line 106 get into the environment. The exhaust aftertreatment agent 110 essentially comprises a pre-catalyst 112 and a particle filter downstream 114 , Preferably between the pre-catalyst 112 and the filter 114 is a temperature sensor 124 arranged, which provides a temperature signal, T '. Before the pre-catalyst 112 and behind the particle filter 114 are sensors 120a and 120b intended. Overall, these sensors act as a differential pressure sensor 120 and provide a differential pressure signal, DP ', which characterizes the differential pressure between the inlet and outlet of the exhaust gas aftertreatment agent.

In a particularly advantageous embodiment, there is a sensor 125 provided that provides a signal that characterizes the oxygen concentration in the exhaust gas. As an alternative or in addition, it can be provided that this variable is calculated on the basis of other measured values or is determined by means of a simulation. The internal combustion engine 100 is via a fuel metering unit 140 Fuel metered. This measures via injectors 141 . 142 . 143 and 144 the individual cylinders of the internal combustion engine 100 Fuel too. The fuel metering unit is preferably a so-called common rail system. A high pressure pump delivers fuel to an accumulator. The fuel reaches the internal combustion engine via the injectors.

At the fuel metering unit 140 are different sensors 151 arranged, which provide signals that characterize the state of the fuel metering unit. In the case of a common rail system, this is, for example, the pressure "P" in the pressure accumulator. On the internal combustion engine 100 are also sensors 152 arranged, which characterize the state of the internal combustion engine. This is preferably a speed sensor that provides a speed signal, N 'and other sensors that are not shown here.

The output signals from these sensors go to a controller 130 that from a first partial control 132 and a second partial control 134 is composed. Before preferably the two sub-controls form a structural unit. The first partial control 132 preferably controls the fuel metering unit 140 with control signals, AD ', which influence the fuel metering. For this purpose, the first partial control includes 132 a fuel quantity control 136 , This supplies a signal 'NW', which characterizes the quantity to be injected, to the second partial control 134 ,

The second partial control 134 preferably controls the exhaust gas aftertreatment system and for this purpose detects the corresponding sensor signals. Furthermore, the second partial control swaps 134 Signals, in particular the injected fuel quantity, ME ', with the first partial control 132 out. Preferably, the two partial controls mutually use the sensor signals and the internal signals.

The first partial control, which is also called an engine control 132 a control signal, AD 'for controlling the fuel metering unit 140 ready, depending on various signals that indicate the operating state of the internal combustion engine 100 , the state of the fuel metering unit 140 and characterize the environmental condition. Here, a signal can also be taken into account, which characterizes the power and / or torque desired by the internal combustion engine. Such devices are known and used in a variety of ways.

Particle emissions can occur in the exhaust gas, especially in diesel engines. For this purpose, it is provided that the exhaust gas aftertreatment agent 110 filter them out of the exhaust gas. This filtering process collects in the particle filter 114 Exhaust gas particles. These particles are then burned in certain operating states and / or after certain times have elapsed in order to clean the particle filter. For this purpose, it is usually provided that the filter is regenerated 114 the temperature in the exhaust gas treatment agent 110 is increased so far that the particles burn.

The pre-catalyst is used to increase the temperature 112 intended. The temperature is increased, for example, by increasing the proportion of unburned hydrocarbons in the exhaust gas. These unburned hydrocarbons then react in the pre-catalyst 112 and thereby increase its temperature and thus the temperature of the exhaust gas that enters the filter 114 arrives. This temperature increase of the pre-catalytic converter and the exhaust gas temperature requires an increased fuel consumption and should therefore only be carried out when this is necessary, ie the filter 114 is loaded with a certain proportion of particles.

One way of recognizing the loading condition of the particle filter is to record the differential pressure 'DP' between the inlet and outlet of the exhaust gas aftertreatment agent and to determine the loading condition on the basis thereof. This requires a differential pressure sensor 120 , The expected particle emission is determined on the basis of various variables, in particular the speed, N 'and the injected fuel quantity, NM', thereby simulating the loading condition. If a corresponding loading condition is reached, the fuel metering unit is activated 140 the regeneration of the filter 114 carried out.

Instead of the speed, N 'and the injected Fuel quantity, ME 'can also other signals that characterize this quantity be used. For example, the control signal, in particular the Control duration for the injectors and / or a torque variable are used as fuel quantity, ME '.

In addition to the amount of fuel injected, NM 'and the speed, N', the temperature, T 'in the exhaust gas aftertreatment system is also used to calculate the loading condition. For this purpose, the sensor is preferably used 124 used. The quantity for the load state calculated in this way is then used to control the exhaust gas aftertreatment system, ie, depending on the load state, the regeneration is then initiated via the temperature increase.

A method known in the prior art for determining the loading state of a particle filter is shown in US Pat 2 shown as a block diagram. The state of loading ultimately characterizes the state of the exhaust gas aftertreatment system. Already in the 1 elements described are referenced with corresponding reference numerals.

A basic map 200 become the output signals N of a speed sensor 152 , a quantity, NM` of the fuel metering control 136 , which characterizes the amount of fuel injected, and / or a quantity which characterizes the oxygen concentration. The variable which characterizes the oxygen concentration is preferably determined by means of a sensor or a calculation 125 specified.

The basic map 200 applies a first connection point 205 with a size, GR ', which characterizes the basic value of the particle emission. The first link point 205 applies a second connection point 210 with a signal that in turn is an integrator 220 with a size, KR ', which indicates the particle increase in the filter 114 characterize, acted upon. The integrator 220 delivers a quantity, B ', which characterizes the state of the exhaust gas aftertreatment system. This size, B 'corresponds to the loading condition of the filter 114 and becomes the controller 130 made available.

At the second input of the connection point 205 is the output signal of a first correction 230 which is the output signal of various sensors 235 is forwarded. The sensors 235 provide signals that characterize the environmental conditions in particular. These are, for example, the cooling water temperature 'TW', the air temperature and the air pressure, PL '. The second input of the connection point 210 is via a switching means 245 the output signal of a second correction 240 fed. The second correction 240 becomes the output signal, T 'of the sensor 124 fed.

In the basic map 200 are, depending on the operating state of the internal combustion engine, in particular characterized by the rotational speed, N ', the amount of fuel injected, NM' and / or a quantity which characterizes the oxygen concentration, the basic value, GR 'of the particle emission. In addition to these sizes, other sizes can also be taken into account. Instead of the quantity 'NM', a quantity can also be used which characterizes the quantity of fuel injected.

In the first link point 205 this value is corrected depending on the temperature of the cooling water and the ambient air as well as the atmospheric pressure. This correction takes into account their influence on the particle emission of the internal combustion engine 100 , In the second tie point 210 the influence of the temperature of the catalyst is taken into account. The correction takes into account that from a certain temperature, T1 ', the particles are not deposited in the filter, but are immediately converted into harmless components. No conversion takes place below this temperature, T1 'and the particles are all deposited in the filter. The second correction 240 there, depending on the temperature, T 'of the exhaust gas aftertreatment agent 110 , a factor 'F' by which the base emission, GR 'is preferably multiplied.

The Indian 3 schematically represented particle filter is in the modeling according to the invention in a preferred embodiment in Longitudinal direction in 1 + 1 preferably divided segments of equal length. These segments are first individually modeled or simulated with respect to the particle filtering of preferably soot particles. A size required for this modeling (simulation) is the total particle mass flow dm / dt flowing into the particle filter (corresponds to the aforementioned size, KR '), where m is the particle mass. This particle mass flow is largely determined by the course of the combustion, in the present case in the diesel engine, and can be determined in a manner known per se from a particle filter simulation. Assuming the assumption that the incoming particle mass flow is 100% filtered out by the particle filter, ie no more particles are flowing out at the outlet of the particle filter, the incoming particle mass flow is distributed to the individual segments of the particle filter. This distribution results in a particle distribution along the segments, such as in the 4a and 4b shown.

The particle distribution is in the frame the modeling by a linear, in the sum of all segments distribution function V (k) normalized to 1, where k is a segment index that runs from 0 to 11. The particle mass flow is calculated using the distribution function V (k) dm / dt of a single segment k according to dm / dt (k) = V (k) · dm / dt.

In one considered time step the particle mass dm / dt (k) flowing into each segment k summed up. This results in the overall distribution of the particle mass in the direction of flow m (k). For each segment is made from it a characteristic curve precalculated in a manner known per se is a value for the flow resistance R (k) derived. From the flow resistances R (k) of the individual segments is calculated using a weighting function w (k) according to the following Formula a resulting total flow resistance R is calculated.

Kappa = Σ [w (k) / R (k)] (1), the sum running over all segments k = 0 to 1. The weighting function w (k) has the unit mbar / (m ^ 3 / h).

It should be noted that by appropriate choice the weighting function w (k) with positive and negative values can be achieved that Kappa takes positive or negative values.

In the exemplary embodiment according to the equation, the correction variable Kappa determined by the above-described modeling, ie determined from the spatial distribution of the particle mass in the longitudinal direction of the particle filter, becomes R_Unqual = R_Equal · (1 + Kappa) (2) the corrected flow resistance R_nleich is calculated on the basis of the uneven distribution of the particles in the longitudinal direction of the particle filter.

Alternatively or in addition to flow resistance can also the particle mass accumulated in the particle filter with high precision be determined. The load state that can be determined more precisely by means of the above-mentioned variables the particle filter can be improved in a manner known per se Control of the diesel engine can be used.

Based on 4a and 4b the calculation of the aforementioned particle distribution function V (k) will be described in greater detail. In the present example, the particle filter is divided into eight segments. The modeling is based on four time steps. As from the 4a can be seen, in each of these time steps a certain particle mass represented by vertical bars enters the particle filter. It is assumed here that the height of the inflowing particle mass at the different times is different according to the different bar sizes. Due to the distribution function V (k) recalculated in each time step, after the four time steps have elapsed, the result in the 4b Particle distribution shown m (0) to m (7) over the individual segments. The particle proportions from the individual inflowing particle masses represented by the bars are from the distribution diagram in FIG 4a removable.

The device described above as well the method is preferably used as a control program in an engine control unit Motor vehicle implemented. In addition to the diesel engine described above however, the invention also in petrol engines, in particular those with a direct petrol injection, with the advantages mentioned be used. It is understood that the principles of the invention also outside automotive engineering in other areas where particle filters the An described at the beginning are used, such as Water or aircraft or even non-vehicles such as For example, incinerators can be used advantageously.

Claims (8)

Method for operating an exhaust gas aftertreatment device of an internal combustion engine, in particular of a motor vehicle, having a particle filter, wherein at least one parameter characteristic of the loading condition of the particle filter is determined from operating parameters of the particle filter, characterized in that the spatial distribution of exhaust gas particles is modeled essentially in the longitudinal direction of the particle filter and by means of the modeled spatial distribution of the exhaust gas particles a correction of the characteristic size is carried out. A method according to claim 1, characterized in that the for the loading state of the Particle filter characteristic size is formed by the particle mass aggregated in the particle filter or by the aggregated particle volume or by the flow resistance of the particle filter. A method according to claim 1 or 2, characterized in that that the correction of the characteristic quantity is linear according to the relationship R_Unqual = R_equal · (1 + Kappa), where R_Gleich is the characteristic size when assumed Uniform distribution of particles in the particle filter, R_Unqual the characteristic size with assumed Unequal distribution of particles and kappa represent a correction factor. Method according to one of the preceding claims, characterized characterized that when modeling the particle filter in longitudinal direction is divided into segments, the mass flow of particles flowing onto the individual segments or particle volume flow distributed by means of a distribution function and that at a given point in time in each segment incoming Particle mass or particle volume is added up to the distribution the particle mass or the particle volume in the particle filter the direction of flow to determine the particle flow. A method according to claim 4, characterized in that out of for particle volume flow or particle mass flow determined by means of one for the characteristic curve of the respective particle filter material the flow resistance of a single segment of the particle filter is calculated. A method according to claim 5, characterized in that from the distribution resulting from the individual segments the flow resistance longitudinal of the particle filter by means of a weighting function over the Segments one over the overall length of the particle filter resulting total flow resistance is calculated. Device for operating a particle filter having exhaust gas aftertreatment device of an internal combustion engine in particular a motor vehicle, with means for calculation at least one for the loading condition of the particle filter characteristic size from operating parameters of the Particle filter, characterized by computing means for modeling the spatial Distribution of exhaust gas particles essentially in the longitudinal direction of the particle filter and to carry out a correction of the characteristic Size by means of modeled spatial Distribution of the exhaust gas particles. Apparatus according to claim 7, characterized in that the computing means for modeling the spatial distribution of exhaust gas particles longitudinal of the particle filter by the method according to any one of claims 1 to 6 are formed.