DE102008014509A1 - Method for determining mass of soot arranged in particle filter in exhaust gas system of internal combustion engine, involves determining parameter of particulate filter laden with soot using particulate specific input size - Google Patents

Abstract

The method involves determining parameter of particulate filter laden with soot, using a particulate specific input size. Exhaust gas of an internal combustion engine flows through an exhaust gas system. Physical characteristic of the soot is used as a function of an input variable, and this functional relationship is used for determining the parameter of the particulate filter. A calculated concentration of nitric oxide is detected in exhaust gas system as a particulate specific input. An independent claim is included for a device for determining mass of soot arranged in particle filter in exhaust gas system of internal combustion engine.

Description

The The invention relates to a method for determining a mass of carbon black arranged in an exhaust line of an internal combustion engine and exhaust gas of the internal combustion engine perfused particulate filter, in which at least one particle filter-specific input variable which is used to determine a characteristic the optionally loaded with soot particulate filter used is, and in which this characteristic with the Mass of the soot loading of the particulate filter is correlated. Furthermore, the invention relates to a device for determining a mass of soot one in an exhaust line of an internal combustion engine arranged particulate filter.

The DE 60 2004 001 913 T2 describes a method for determining a mass of soot in a particulate filter. In this case, values of a pressure at an input and at an output of the particle filter, a mass flow of an exhaust gas flowing through the particle filter and a temperature of the particle filter are detected at particle filter-specific input variables.

These particle filter-specific input variables for determining a permeability as a characteristic used of the particulate filter. The permeability of the Particulate filter becomes with the mass of soot in the particulate filter correlates, with a linear relationship between the permeability of the Particulate filter and the mass of soot in the particulate filter is taken as a basis.

When disadvantageous in the described method for determining the mass of soot in the particulate filter, the circumstance is to be considered, that the real in the particulate filter mass of soot from deviate from the mass of soot determined by the linear relationship can.

task The present invention is therefore a method or a To provide device of the type mentioned, by means of which or by means of which a particularly accurate determination of the mass Soot is allowed in the particulate filter.

These The object is achieved by a method with the features of claim 1 and by a device solved with the features of claim 9. advantageous Embodiments with expedient developments The invention are defined in the dependent claims specified.

at the method according to the invention for determining a mass of soot one in an exhaust line of an internal combustion engine arranged and traversed by exhaust gas of the internal combustion engine Particulate filter becomes at least one particulate filter specific input detected. The input is used to determine a characteristic of the optionally loaded with soot Used particle filter. This characteristic with the mass of the soot loading of the particulate filter correlated. Here, at least one physical property of the soot as a function of the at least one input variable and this functional context for determining the characteristic of the particulate filter used.

Of the Invention is based on the finding that a given mass soot in the particulate filter different physical Properties may have. One or more of these properties typically affect the characteristic of the Particulate filter, such as a permeability of the optionally loaded with soot particulate filter or an over the total particulate filter effective total pressure drop, by the Exhaust gas flow is caused by the particulate filter. Especially is typically only by the soot loading itself caused fraction of the total pressure loss over the particulate filter from the physical properties of the soot in the particulate filter affected.

One Consider the physical properties of the carbon black as a function of about a temperature of the exhaust gas allows thus a particularly accurate determination of the mass of soot in the particulate filter, in particular for different operating conditions the internal combustion engine or for different driving cycles a motor vehicle driven by the internal combustion engine. It is advantageous in the characterization of the physical Property (s) of soot a time course at least a particle filter specific input such as the temperature as a relevant factor to take into account. This can be a history of factors be considered, which is significant for the physical properties of the carbon black, especially for its permeability can be.

Due to the particularly accurate determination of the mass of soot in the particulate filter, a time for thermal regeneration can be set particularly precisely. During thermal regeneration of the particle filters is at least partially oxidized by means of fuel post-injection elevated temperature of the exhaust gas, the mass of the deposited in the particulate filter carbon black with oxygen and reduced by discharging oxidation products.

By the exact setting of the time for thermal regeneration can avoid too frequent regeneration and consequently Fuel can be saved. Likewise, an accelerated aging a catalytic coating of the particulate filter due to short regeneration intervals avoided.

Of Further, by determining a particularly favorable Regeneration time can be avoided, that regenerating of the particulate filter in the presence of a particularly large Mass of soot in the particulate filter to a thermal Damaging the particulate filter as a result of an uncontrolled Burning the soot leads. A number of that Motor vehicle zurückergbarer kilometer to the thermal Regenerating can be so comparatively high, because of accurately determining the mass of soot in the particle filter an unnoticed accumulation of questionable high Masses of soot in the particulate filter not to be feared is.

The in connection with the method according to the invention described advantages and preferred embodiments also apply to the invention Device for determining the mass of soot in the particulate filter.

Further Advantages, features and details of the invention will become apparent the following description of a preferred embodiment and with reference to the drawings in which the same or the same function Elements are provided with identical reference numerals. Showing:

1 a schematic flow diagram of a method for determining a mass of soot disposed in an exhaust line of an internal combustion engine particulate filter; and

2 a schematic flow diagram of a method for detecting physical properties of the soot.

According to 1 for detecting a mass m _soot on soot of a arranged in an exhaust line of an internal combustion engine of a motor vehicle particulate filter detection 10 of particle filter-specific input variables.

The particulate filter-specific input variables here comprise an exhaust gas mass flow dm _Abg , an exhaust gas volume flow dVol, a surface temperature of the particulate filter T _DPF , an ambient pressure p _Atm , a concentration of nitrogen oxides cNOx and a differential pressure Δp _DPF between an input and an output of the particulate filter. It is also possible to take into account less than the stated input variables or additional input variables.

To describe a physical property of the carbon black, the physical property is used as a function of at least one of the input quantities. For example, a permeability k _{soot of} the soot changes due to an increase in temperature in the particulate filter. Typically, soot permeability increases by exposure to elevated temperature. An increased concentration of NO ₂ can additionally increase this effect. Similarly, a density of the soot ρ _{soot is} dependent on the temperature in the particulate filter. Due to this functional relationship between the particulate filter specific input variables and the physical properties of the soot, a function of the input variables takes place according to 1 a description 12 of physical properties of the carbon black or of the carbon black layer, such as its height h _{carbon black} , its density ρ _{carbon black} and / or its permeability k _{carbon black} .

The particulate filter-specific input variables and the physical properties h _soot , ρ _soot , k _{soot of} the soot become a calculation 14 a partial pressure drop Ap _{carbon black} used as a parameter over a deposited in the particle filter layer of carbon black. The partial pressure drop Δp _soot caused only by the soot itself decisively influences the total pressure drop Δp _{DPF which} can be detected directly via the entire particle filter component, for example by means of pressure sensors. The partial pressure drop Δp _soot preferably results from the formula: Ap soot = Δp DPF - Δp Empty - Δp EK - Δp FH where Δp _{Leer describes} a pressure drop of the empty, unloaded particulate filter, Δp _EK indicates a pressure drop a narrowed inlet and / or outlet region of the particulate filter component (inlet or outlet funnel), and Δp _FH a volume flow-dependent, for example, resulting from turbulence portion of the pressure drop. Here, the index FH stands for "Forchheimer" and the term Δp _FH typically describes the corresponding Forchheimer term of the equation. If appropriate, the latter term may also be omitted or neglected. The quantities Δp _empty , Δp _EK can be determined empirically and kept available in a data store retrievable.

wobei A_DPF eine Oberfläche des Partikelfilters, V_Abgas einen Volumenstrom des Abgases und eine dynamische Viskosität des Abgases beschreiben.The particulate filter-specific input variables, the physical properties of the soot and the pressure drop Δp _soot are used to determine 16 the mass m _{soot of} the soot used in the particulate filter. This is preferably a law of Darcy in the form:

where A _{DPF describe} a surface of the particulate filter, V _exhaust a volumetric flow of the exhaust gas and a dynamic viscosity of the exhaust gas.

Describing 12 The physical properties of the carbon black due to the functional relationship of the physical properties of the carbon black and the input variables enables a particularly accurate, realistic determination of the mass m _soot of soot in the particulate filter.

As mentioned, the physical properties of the carbon black depend on the temperature of the exhaust gas and the NO ₂ concentration in the exhaust gas. For example, provide a relatively high temperature and a relatively high concentration of NO ₂ for an increase in the permeability of the soot, so does the permeability of the carbon black again when the temperature and / or the NO ₂ concentration decrease again, while at the same time of additional carbon black into the particulate filter is stored.

Thus, as a functional relationship between the permeability of the soot and, for example, the temperature of the exhaust gas is based on a progressively increasing proportionality. Likewise, the NO ₂ concentration has an influence on the permeability k _{soot of} the soot and on the density ρ _{soot of} the soot.

Therefore, in the present case, the detection takes place 10 the particulate filter-specific input variables, a detection of the concentration of nitrogen oxides NO ₂ by means of a calculation 18 which are shown in the flowchart in FIG 2 is shown. The calculation 18 in this case preferably uses a model according to which concentrations of NO ₂ generated by means of an oxidation catalyst are calculated as a function of operating parameters of the oxidation catalytic converter and / or of the internal combustion engine. The oxidation catalyst is present upstream of the particulate filter in the exhaust line.

Thus, NO ₂ formed in the oxidation catalyst by oxidation of NO contained in the exhaust gas is supplied to the particulate filter. This NO ₂ is capable of oxidizing present in the particulate filter soot. This effect is used in a regeneration process known as CRT (Continuous Regeneration Trap) to regenerate diesel particulate filters, in which continuous regeneration of the particulate filter is desired.

Based on the calculated concentration of NO ₂ is carried out according to 2 in one to the calculation 18 subsequent step estimating 20 a reaction rate of oxidizing soot for an uncoated particulate filter. Since the particle filter in the present case has a coating which also contributes to the formation of NO ₂ , takes place according to 2 an inclusion 22 an influence of the coating in determining 24 a reaction rate of the soot oxidation.

The determining 24 Thus, calculating a total reaction rate which is the estimating 20 the reaction rate for the uncoated particulate filter and incorporation 22 the coating influence resulting reaction rates integrated.

With the help of the total reaction rate is done according to 2 a description 26 an oxidation state of the soot in the particulate filter. The oxidation state describes how much the soot is oxidized. The oxidation state is a result of past reaction rates for oxidizing the carbon black. For example, very high reaction rates acting over a short time have a comparable influence as compared to comparatively low reaction rates acting over a long time. On the basis of the oxidation state of the soot in the particulate filter can according to 2 Changes in physical property th h _{of carbon black, carbon black} k, ρ _{carbon black} of the carbon black will be described. In an analogous manner, an amount-weighted duration of action of further input variables is preferably used in the determination of the physical soot properties and for determining a parameter of the particle filter.

The presently described method for determining the mass m _soot of soot in the particulate filter is consistent with physical approaches of literature and can be easily integrated into a differential pressure-based charging model of the particulate filter because of its simplicity.

Thus, the particulate filter used herein to reduce soot emissions from the motor vehicle can be thermally regenerated in a particularly fuel-efficient manner and at a greatly reduced risk of thermal damage to the particulate filter. The thermal regeneration is initiated in this case if the particularly accurately determined mass m _soot reaches a predetermined value in soot retained in the particle filter.

• • Einlaufeffekt eines neuen und/oder frisch regenerierten Partikelfilters auf der Basis von Laufzeit und/oder Kraftstoffverbrauch
• • Einfluss abgelagerter Asche auf Gegendruck und filterwirksamer Filterfläche
• • Einfluss von Alterungseffekten insbesondere im Oxidationskatalysator und/oder im Partikelfilter auf die NO₂-Bildung
• • Einfluss der Rußeigenschaften während der thermischen Regeneration des Partikelfilters aufgrund:
• – eines Sauerstoffgehalts im Abgas,
• – eines Abgasmassenstrom
• – einer Abgas- und/oder einer Partikelfiltertemperatur
• – der aktuellen Rußmasse.

The method for detecting a mass of the soot charge in a particulate filter can be further improved by considering the following influences.

• • Infeed effect of a new and / or freshly regenerated particulate filter on the basis of running time and / or fuel consumption
• • Influence of deposited ash on back pressure and filter effective filter surface
• • Influence of aging effects, especially in the oxidation catalyst and / or in the particle filter on the NO ₂ formation
• • Influence of the soot properties during the thermal regeneration of the particulate filter due to:
• - an oxygen content in the exhaust gas,
• - An exhaust gas mass flow
• An exhaust gas and / or a particulate filter temperature
• - the current soot mass.

following is on the other, preferably also considered Influences entered into.

to Consideration of an enema effect for a new and / or freshly regenerated particulate filter is preferably a temporal change of soot deposition properties considered. Soot deposition is typical depending on the mileage of the particulate filter and correlated For example, with the amount of fuel consumed, the operating period, mileage or similar since installation of an unused or new particle filter or since the last thermal particle filter regeneration by Rußabbrand. This can be done for example by a with one or more of the latter sizes linked, temporally increasing or decreasing factor become.

While the operation of the particulate filter become combustible substances (Soot) and on the other non-combustible substances (ash) deposited. While a soot loading at a thermal Regeneration by conversion to a gaseous reaction product can be removed from the particulate filter, remain non-combustible Substances as ash in the particle filter. This increases and decreases after the back pressure of the soot-empty particulate filter at. Without consideration of this temporally increasing ash load consequently, the soot mass would become increasingly defective be calculated. Therefore, it is preferred in the calculation of the soot mass in the particle filter, the pressure loss due to ash loading is considered. Preferably, on the one hand, the reduction of soot filtering available filter surface and the other Pressure loss due to ashing of the filter is taken into account by a characteristic map.

The catalytic properties of the coating of an oxidation catalyst upstream of the particulate filter and of the particulate filter influence the oxidation of nitrogen monoxide (NO) to nitrogen dioxide (NO ₂ ). In the soot loading model explained above, the NO ₂ concentration in the exhaust gas before the particulate filter is calculated, for example, taking account of exhaust gas temperature after oxidation catalyst, NOx concentration in the exhaust gas and exhaust gas mass flow. The soot oxidation rate is determined from the NO ₂ concentration and the previously detected soot mass in the particulate filter. This describes the Rußabbrand by the CRT effect and thus significantly the change in the physical properties of the soot. Due to high thermal loads of the oxidation catalyst and the particulate filter, in particular during regeneration ages the coating of the oxidation catalyst and the particulate filter. Thus, over the life of the turnover of NO to NO ₂ decreases. Preferably, therefore, in a model aging of the coating of oxidation catalyst and the particulate filter and their influence on the NO ₂ concentration in the exhaust gas, for example, depending on the exhaust gas temperature and the soot mass at the beginning of a regeneration determined.

at the thermal particle filter regeneration at a comparatively high Exhaust temperatures of more than 550 ° C takes place oxidation of soot with oxygen. In some driving conditions, z. B. full load, such thermal regenerations occur without further Additional measures inevitably. The burning off soot from the diesel particulate filter typically changes the permeability of the carbon black. In the present Soot loading model is therefore preferred for the thermal regeneration determines a soot reaction rate in Dependence on exhaust gas temperature, degree of oxidation of the soot, Oxygen content in the exhaust gas, exhaust gas mass flow and / or soot mass in the particle filter. With this carbon black reaction rate will both the Rußabbrand in Partikelfiter as well as the change determined or calculated by carbon black properties.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• - DE 602004001913 T2 [0002]

Claims (9)

Method for determining a mass (m _soot ) of soot of a arranged in an exhaust line of an internal combustion engine and exhaust gas of the internal combustion engine particulate filter, wherein at least one particulate filter specific input variable is detected, which is used to determine a characteristic of the optionally loaded with soot particulate filter, and in which this parameter is correlated with the mass (m _soot ) of the soot loading of the particulate filter, characterized in that at least one physical property (h _soot , k _soot , h _soot ) of the soot is used as a function of at least one input quantity, and this functional relationship is used to determine the characteristic of the particulate filter. Method according to claim 1, characterized in that the at least one physical property (h _soot , k _soot , ρ _soot ) of the soot has a height (h _soot ) and / or a density (ρ _soot ) and / or a permeability (k _soot ) of the carbon black. A method according to claim 1 or 2, characterized in that the characteristic of the particulate filter is represented by a value for a partial pressure drop (Δp _soot ) caused by the exhaust gas flow to the soot load of the particulate filter portion of an effective over the entire particulate filter total pressure drop. Method according to one of claims 1 to 3, characterized in that as at least one particulate filter specific Input variable one, in particular calculated, concentration is detected in nitrogen oxides in the exhaust system. Method according to one of claims 1 to 4, characterized in that as a functional relationship between the at least one physical property (h _soot , k _soot , ρ _soot ) of the soot and the at least one input variable is based on a progressively increasing proportionality. Method according to one of claims 1 to 5, characterized in that in determining the at least one physical property (h _soot , k _soot , ρ _soot ) of the soot, an oxidation state of the soot is taken into account. Method according to Claim 6, characterized for determining the oxidation state, a reaction rate of Soot oxidation is taken into account. Method according to claim 7, characterized in that that the reaction rate depends on one, in particular calculated, concentration of nitrogen oxides in the exhaust gas strand and / or is determined by a coating of the particulate filter. Apparatus for determining a mass (m _soot ) of soot of a particulate filter disposed in an exhaust line of an internal combustion engine, comprising: means for detecting at least one particulate filter specific input; means for determining a characteristic of the particulate filter as a function of the at least one input variable means for correlating the particulate filter Characteristic of the particulate filter with the mass (m _soot ) of soot in the particulate filter, characterized in that in the means for determining the characteristic of the particulate filter, a functional relationship between at least one physical property (h _soot , k _soot , ρ _soot ) of the soot and the at least one input variable is used, wherein the means for determining the characteristic are adapted to the at least one physical property (h _soot , k _soot , ρ _soot ) of the soot as a function of at least one input variable in determining the characteristic of the particle elfilters.