DE10252732B4 - Method and device for operating an exhaust aftertreatment device of an internal combustion engine - Google Patents

Abstract

A method for operating an exhaust aftertreatment device of an internal combustion engine, in particular of a motor vehicle, having at least one characteristic for the load state of the particulate filter, characterized in that the spatial distribution of exhaust particles is modeled substantially in the longitudinal direction of the particulate filter and by means of modeled spatial distribution of the exhaust particles a correction of the characteristic size is performed.

Description

The The invention relates to a method and an apparatus for operation an exhaust aftertreatment device of an internal combustion engine according to the preambles the respective independent Claims.

With Diesel engine driven vehicles have facilities in many countries to have the exhaust aftertreatment. Due to the soot formation particulate filters are used in particular to control the emission of soot particles in the To minimize exhaust of these engines by filtering out. To this Particulate filters will become even more stringent emission limits in the future increased Requirements placed on the efficiency of the exhaust aftertreatment. About that In addition, such particulate filter also get along in gasoline engines Direct injection is becoming more and more important, especially in so-called "shift operation" Engines increase soot formation occurs in the exhaust gas.

From the DE 100 14 224 A1 and the DE 101 00 418 A1 shows a method for controlling an internal combustion engine with such an exhaust gas aftertreatment device. For precise control of the internal combustion engine, the state of the exhaust aftertreatment device must be known. In particular, the loading state of the particulate filter, ie the instantaneous amount of filtered-out soot particles, must be known as accurately as possible.

The Control of filter loading and regeneration monitoring the particulate filter is known to be done by means of pressure sensors, because the pressure gradient over the Filter conclusions on the soot mass accumulated in the filter allows. The pressure signal supplied by the pressure sensors is dependent evaluated from the current operating point of the internal combustion engine and considering the by the pressure gradient, the temperature, the exhaust gas volume flow etc. conditioned flow conditions in the filter the flow resistance of the filter, which in turn is representative of the soot loading. This is simplifying assumed that the soot mass in the filter spatially distributed equally is. For soot mass determination is from the exhaust gas flow V and the differential pressure p_Diff along the Particulate filter a flow resistance R_Calculated according to the relationship R_Gleich = p_Diff / V.

In the FR 2 778 118 A1 For example, a method and apparatus for locally regenerating a particulate filter are described. In this case, the local loading of the particulate filter should first be determined on the basis of the flow resistance. For this purpose, the Pratikelfilter is divided into several zones viewed in the longitudinal direction. The temperature is measured in the individual zones. Based on the measured temperatures, the loading and the flow resistance of each individual zone are concluded.

Of the The present invention is based on the object, a method and to improve a device of the type mentioned in that an increased Accuracy in the determination of the loading of the particulate filter is made possible.

These Task is solved by the characteristics of the independent Claims. Advantageous embodiments are the subject of the respective subclaims.

Of the The invention is based on the idea of the spatial distribution of exhaust particles essentially in the longitudinal direction of the particulate filter. From the spatial distribution of the particle mass / volume will then be a correction factor for at least one from operating characteristics of the Internal combustion engine and / or the exhaust gas aftertreatment device calculated characteristic size of the particulate filter determined. The characteristic variable comes, for example, in the filter accumulated particle mass / volume or the flow resistance of the particulate filter into consideration. The characteristic size is therefore characteristic for the Loading condition of the filter. Ie. the correction factor is preferred used to one according to the state The technique calculated pre-called characteristic size of the particulate filter to ultimately correct the accuracy for the determination increase the loading condition of the filter.

A correction of said flow resistance due to the unequal distribution of the particles in the longitudinal direction of the particle filter R_Ungleich preferably takes place in a linear approximation according to the relationship R _- unequal = R_simultaneous (1 + kappa), where kappa represents a dimensionless correction variable.

According to one preferred embodiment of the method according to the invention is mentioned Modeling the particle filter in the longitudinal direction in preferably the same divided into long segments. The incoming particle mass or Volume flow is applied to the individual segments by means of a distribution function distributed and at a given time in each segment incoming particle mass or volume added to the distribution of the particle mass or the volume in the flow direction to determine the particle flow.

According to an advantageous development of the determined for each segment particle flow by means of a characteristic of the respective particle filter material characteristic of the flow resistance of a single segment of the Partikelfil calculated.

According to one Another embodiment is made of the individual segments resulting distribution of the flow resistance over the particle filter length means a weighting function over the segments over the total length of the particulate filter resulting total flow resistance is calculated.

By the application of the method according to the invention increases in an exhaust aftertreatment device affected here the accuracy of determining the particulate matter accumulated in the particulate filter.

The The invention will be described below with reference to the attached drawing. using preferred embodiments explained in more detail.

in the Show individual

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

2 a detailed illustration of a method for determining the loading in a particulate filter according to the prior art;

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

4a , b are diagrams for illustrating a particle distribution function according to the method of the invention.

With reference to the 1 An apparatus for operating an exhaust aftertreatment device of an internal combustion engine according to the prior art, in which the inventive method is implemented, will be 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 of the invention is not limited to these systems and can grds. can also be used in other internal combustion engines.

With 100 is the internal combustion engine referred to, which has a suction line 102 Fresh air is supplied and the via an exhaust pipe 104 Gives off exhaust gases. In the exhaust pipe 104 is an exhaust aftertreatment agent 110 arranged, from which the cleaned exhaust gases over the line 106 get into the environment. The exhaust aftertreatment agent 110 essentially comprises a precatalyst 112 and downstream of a particulate filter 114 , Preferably between the precatalyst 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 each sensors 120a and 120b intended. Altogether, these sensors act as differential pressure sensors 120 and provide a differential pressure signal, DP ', which characterizes the differential pressure between the inlet and outlet of the exhaust aftertreatment agent.

In a particularly advantageous embodiment, a sensor 125 provided, which provides a signal that characterizes the oxygen concentration in the exhaust gas. Alternatively or additionally, it may be provided that this variable is calculated on the basis of other measured values or determined by means of a simulation. The internal combustion engine 100 is via a fuel metering unit 140 Metered in fuel. This measures via injectors 141 . 142 . 143 and 144 the individual cylinders of the internal combustion engine 100 Fuel too. Preferably, the fuel metering unit is a so-called common rail system. A high-pressure pump delivers fuel into a pressure accumulator. From the memory of the fuel passes through the injectors in the internal combustion engine.

At the fuel metering unit 140 are different sensors 151 arranged to provide signals characterizing the state of the fuel metering unit. In this case, a common rail system is, for example, the pressure P 'in the pressure accumulator. At 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, which provides a speed signal, N 'and to other sensors, which are not shown here.

The output signals of these sensors reach a controller 130 , which consists of a first partial control 132 and a second part control 134 is composed. Before preferably form the two sub-controls a structural unit. The first part control 132 preferably controls the fuel metering unit 140 with control signals, AD ', which influence the fuel metering. This includes the first part control 132 a fuel quantity control 136 , This supplies a signal, NW ', which characterizes the amount to be injected, to the second sub-controller 134 , The second part control 134 preferably controls the exhaust aftertreatment system and detects for this purpose the corresponding sensor signals. Furthermore, the exchange second part control 134 Signals, in particular the injected fuel quantity, ME ', with the first part control 132 out. Preferably, the two sub-controllers mutually use the sensor signals and the internal signals.

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

Especially in diesel engines particulate emissions can occur in the exhaust gas. For this purpose, it is provided that the exhaust aftertreatment agent 110 filter them out of the exhaust gas. Through this filtering process accumulate in the particulate filter 114 Exhaust particles on. These particles are then burned in certain operating conditions and / or after expiry of certain times to clean the particulate filter. For this purpose, it is usually provided that for the regeneration of the filter 114 the temperature in the exhaust aftertreatment agent 110 so far increased that the particles burn.

To increase the temperature is the precatalyst 112 intended. The temperature increase takes place, for example, in that the proportion of unburned hydrocarbons in the exhaust gas is increased. These unburned hydrocarbons then react in the precatalyst 112 and thereby increase its temperature and thus also the temperature of the exhaust gas entering the filter 114 arrives. This temperature increase of the precatalyst and the exhaust gas temperature requires increased fuel consumption and should therefore only be carried out if this is necessary, ie the filter 114 loaded with a certain proportion of particles.

One way to detect the load condition of the particulate filter is to detect the differential pressure 'DP' between the input and output of the exhaust aftertreatment agent and to determine from this the load state. This requires a differential pressure sensor 120 , Based on various variables, in particular the rotational speed, N 'and the injected fuel quantity, NM', the expected particle emission is determined, thereby simulating the loading state. If a corresponding loading state is achieved, by driving the fuel metering unit 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 size can be used. Thus, for example, the drive signal, esp. The drive time for the injectors and / or a moment size, as Fuel quantity, ME 'used become.

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

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

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

The basic map 200 acts on a first point of connection 205 with a size, GR ', which characterizes the basic value of the particle output. The first node 205 acts on a second node 210 with a signal, which in turn is an integrator 220 with a size, KR ', which increases the particle in the filter 114 characterize, charged. The integrator 220 provides a quantity, B ', which characterizes the condition of the exhaust aftertreatment system. This quantity, 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 of a first correction 230 , which is the output of various sensors 235 is forwarded. The sensors 235 provide signals that particularly characterize the environmental condition. These are z. As the cooling water temperature 'TW', the air temperature and the air pressure, PL '. The second input of the node 210 is via a switching means 245 the exit signal 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 condition of the internal combustion engine, in particular characterized by the rotational speed, N ', the injected fuel quantity, NM' and / or a variable which characterizes the oxygen concentration, the base value, GR 'of the particle emission stored. In addition to these sizes, other sizes can be considered. Instead of the amount 'NM', a size may also be used which characterizes the amount of injected fuel.

In the first node 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 node 210 the influence of the temperature of the catalyst is considered. The correction takes into account that, as of a certain temperature, T1 ', the particles are not deposited in the filter, but are directly converted into harmless constituents. Below this temperature, T1 ', no reaction takes place and the particles are all deposited in the filter. The second correction 240 depending on the temperature, T 'of the exhaust aftertreatment agent 110 , a factor, F ', with which the basic emission, GR' is preferably multiplied.

The Indian 3 In the modeling according to the invention, in a preferred exemplary embodiment, schematically illustrated particle filters are divided into / + 1 preferably longitudinal segments in the longitudinal direction. These segments are first modeled or simulated individually with respect to the particulate filtering of preferably soot particles. A variable required for this modeling (simulation) is the total particulate mass flow dm / dt (corresponding to the aforementioned size, KR ') that flows into the particulate filter, where m is the particulate mass. This particle mass flow is largely determined by the course of combustion, in this case in the diesel engine, and can be determined in a conventional manner from a particle filter simulation. Under the first approximation certainly satisfied assumption that the inflowing particle mass flow is filtered out by the particulate filter to 100%, ie at the output of the particulate filter no more particles flow, the einömende particle mass flow is distributed to the individual segments of the particulate filter. Due to this distribution results along the segments a particle distribution such as in the 4a and 4b shown.

The Particle distribution is modeled by a linear, in the sum of all segments to 1 normalized distribution function Considers V (k), where k is a segment index running from 0 to /. By means of the distribution function V (k) is the particle mass flow dm / dt of a single calculated Segment k according to dm / dt (k) = V (k) · dm / dt.

In a considered time step, the particle mass dm / dt (k) flowing into each segment k is added up. This results in a total distribution of the particle mass in the flow direction m (k). For each segment, a value for the flow resistance R (k) is derived therefrom by way of a characteristic which is precalculated in a manner known per se. From the flow resistances R (k) of the individual segments, a correction quantity χ is calculated by means of a weighting function w (k) according to the following formula. 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 It should be noted that by suitable choice of the weighting function w (k) with positive and negative values can be achieved that Kappa takes positive or negative values.

From the determined by the above modeling, ie determined from the spatial distribution of the particle mass in the longitudinal direction of the particulate filter correction value kappa, is in the embodiment according to the equation R_Ungleich = R_Same (1 + Kappa) (2) the corrected flow resistance R_Ungleich calculated due to the unequal distribution of the particles in the longitudinal direction of the particulate filter.

alternative or additionally to the flow resistance can also be accumulated in the particulate filter particle mass with high precision be determined. The more precisely determinable by means of the sizes mentioned load condition of the particulate filter can be improved in a conventional manner Control of the diesel engine can be used.

Based on 4a and 4b the calculation of said particle distribution function V (k) shall be described in greater detail. In the present example, the particulate filter is divided into eight segments. The modeling is based on four time steps. Like from the 4a In each of these time steps, a specific mass of particles represented by vertical bars enters the particle filter. It is assumed that the height of the incoming particle mass to is different at different times according to different bar sizes. Due to the distribution function V (k), which is recalculated in each time step, the results in the 4b shown particle distribution m (0) to m (7) over the individual segments. The particle fractions from the individual inflowing particle masses represented by the bars are from the distribution diagram in FIG 4a removable.

The The device described above and the method are preferred implemented as a control program in an engine control unit of a motor vehicle. In addition to the above-described diesel engine, the invention can thereby but also in gasoline engines, especially those with a Gasoline direct injection, used with the advantages mentioned become. It is understood that the principles of the invention also outside automotive engineering in other fields where particulate filters the type described above are used, such as, for example Water or air vehicles or even non-vehicles like For example, incinerators, are advantageously used.

Claims (8)

Method for operating a particulate filter having exhaust aftertreatment system of an internal combustion engine, particularly a motor vehicle, wherein at least one characteristic of the loading state of the particle filter size of operating parameters of the particle filter is determined, characterized in that the spatial distribution of exhaust particulates substantially modeled in the longitudinal direction of the particulate filter and by means of modeled spatial distribution of the exhaust particles a correction of the characteristic size is performed. Method according to claim 1, characterized in that that for the load condition of the particulate filter characteristic size the particle mass aggregated in the particulate filter or by the aggregated one Particle volume or by the flow resistance of the particulate filter is formed. Method according to claim 1 or 2, characterized that the correction of the characteristic quantity is linear according to the relation R_Ungleich = R_same (1 + Kappa), where R_ is the same size as assumed Equal distribution of particles in the particle filter, R_Ungleich the characteristic size at assumed Unequal distribution of particles and kappa represent a correction factor. Method according to one of the preceding claims, characterized characterized in that when modeling the particulate filter in longitudinal direction is divided into segments, the particle mass flow flowing to the individual segments or particle volume flow distributed by means of a distribution function and that at a given time in each segment incoming Particle mass or particle volume is added up to the distribution the particulate mass or the particle volume in the particulate filter in the flow direction to determine the particle flow. Method according to claim 4, characterized in that that from the for each segment determined particle volume flow or particle mass flow means one for the particular particle filter material characteristic curve the flow resistance of a single segment of the particulate filter. Method according to claim 5, characterized in that that from the distribution resulting from the individual segments of flow resistance longitudinal of the particulate filter by means of a weighting function over the Segments on the overall length of the particulate filter resulting total flow resistance is calculated. Apparatus for operating a particulate filter having exhaust aftertreatment device of an internal combustion engine in particular of a motor vehicle, with means for calculating at least one for the load condition of the particulate filter characteristic size from operating characteristics of Particulate filter, characterized by computing means for modeling the spatial Distribution of exhaust particles substantially in the longitudinal direction of the particulate filter and to perform a correction of the characteristic Size by means of modeled spatial Distribution of exhaust particles. Device according to claim 7, characterized in that that the computing means for modeling the spatial distribution of exhaust particles longitudinal of the particulate filter according to the method of any one of claims 1 to 6 are formed.