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EP2652280A2 - Method for operating a soot sensor - Google Patents

Method for operating a soot sensor

Info

Publication number
EP2652280A2
EP2652280A2 EP11815758.5A EP11815758A EP2652280A2 EP 2652280 A2 EP2652280 A2 EP 2652280A2 EP 11815758 A EP11815758 A EP 11815758A EP 2652280 A2 EP2652280 A2 EP 2652280A2
Authority
EP
European Patent Office
Prior art keywords
soot
soot sensor
sensor
internal combustion
electrode structure
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP11815758.5A
Other languages
German (de)
French (fr)
Inventor
Johannes Ante
Markus Herrmann
Andreas Ott
Willibald Reitmeier
Denny SCHÄDLICH
Manfred Weigl
Andreas Wildgen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Continental Automotive GmbH
Original Assignee
Continental Automotive GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Continental Automotive GmbH filed Critical Continental Automotive GmbH
Publication of EP2652280A2 publication Critical patent/EP2652280A2/en
Ceased legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/06—Investigating concentration of particle suspensions
    • G01N15/0656—Investigating concentration of particle suspensions using electric, e.g. electrostatic methods or magnetic methods
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N9/00—Electrical control of exhaust gas treating apparatus
    • F01N9/002—Electrical control of exhaust gas treating apparatus of filter regeneration, e.g. detection of clogging
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
    • F01N2560/05—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being a particulate sensor
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

Definitions

  • the invention relates to a method for operating a soot sensor, in the exhaust system of an internal combustion engine, the soot sensor has an interdigitated electrode structure, to which a measuring voltage is applied, wherein depositing on the interdi ⁇ gitalen electrode structure soot particles from an exhaust stream and the on the soot particles and interdigital electrode structure flowing measuring current is evaluated as a measure of the soot loading of the soot sensor and wherein the soot sensor comprises a heating element for burning the interdigital electrode structure.
  • soot sensors are used to measure the currently emitted with the exhaust stream soot, so that the engine management in an automobile in a current driving situation information to come to reduce with regulatory adjustments the emission levels.
  • active exhaust gas purification can be initiated by exhaust soot filters or exhaust gas recirculation to the internal combustion engine can take place.
  • Rußfilterung be
  • regenerable filters are used, which filter out a significant part of the carbon black content from the exhaust gas.
  • Soot sensors are required for the detection of soot in order to monitor the function of the soot filters or to control their regeneration cycles.
  • the soot filter which is also referred to as a diesel particulate filter, may be preceded by a soot sensor and / or a soot sensor connected downstream.
  • the upstream of the diesel particulate filter sensor serves to increase the system safety and to ensure an operation of the diesel particulate filter under optimum Bedingun ⁇ . Accordingly, as these depend greatly on the embedded in the diesel particulate filter soot, is an accurate measurement of the particle concentration before the diesel particulate filter system, in particular the determination of a high particle concentration before the diesel particulate filter, of great importance.
  • a diesel particulate filter downstream sensor provides the ability to perform on-board diagnostics and also helps ensure proper operation of the exhaust after-treatment system.
  • German laid-open specification DE 199 59 871 A1 discloses a sensor and an operating method for the sensor, both based on thermal considerations.
  • the sensor consists of an open-porous shaped body such as a honeycomb ceramic, a heating element and a temperature sensor. If the sensor is associated with a sample gas volume, soot deposits on it. For measurement, the soot deposited in a period of time is ignited by means of the heating element and burnt. The temperature increase resulting from the combustion is measured.
  • particle sensors for conductive particles are known, in which two or more metallic electrodes are provided, which have comb-like interdigitated electrodes. These comb-like structures are also called interdigital structures. Soot particles that are deposited on these Sen ⁇ sor Jardin, connect the electrodes short and therefore change the impedance of the electrode structure. With increasing particle concentration on the sensor surface in this way, a decreasing resistance or an increasing current at constant applied voltage between the electrodes can be measured. Such a soot sensor is disclosed, for example, in DE 10 2004 028 997 A1. In order to measure a current between the electrodes, however, a certain amount of soot particles must be present between the electrodes.
  • the soot sensor is virtually blind to the soot concentration in the exhaust stream.
  • the soot sensor must be cleaned at regular intervals.
  • the regeneration of the sensor is done by burning off the accumulated soot. This process is also referred to as burnout of the interdigital electrode structure.
  • the sensor element after the soot accumulation is usually free ⁇ burned with the help of an integrated heating element.
  • the time required for regenerative burnout of the sensor structure is also referred to as the dead time of the sensor. It is therefore important to make the burn-off phase and the subsequent reconditioning phase of the soot sensor as short as possible in order to be able to reuse the soot sensor as soon as possible for soot measurement.
  • the object of the invention is therefore to provide a method of operating a soot sensor, which provides good measurement resulting ⁇ nit, wherein the soot sensor should have the least possible dead times.
  • An operating state of the internal combustion engine after which a time for burning out the soot sensor is determined, may be, for example, the crank shaft speed of the internal combustion engine and / or the temperature of the internal combustion engine, in particular its coolant temperature.
  • a development of the invention is characterized in that the time for burning the soot sensor is a restart of the internal combustion engine.
  • a restart of the internal combustion engine can be detected, for example, by monitoring the crankshaft speed.
  • the burn-out of the interdigital electrode structure is started by heating the soot sensor with the heating element.
  • a soot measurement is in any case not meaningful, so that the burning of the interdigi ⁇ tal electrode structure costs no measurement time.
  • the time to burn off the soot sensor is the restart of the fully bring ⁇ cooled internal combustion engine.
  • a fully cooled internal combustion engine there are conditions in the exhaust system that make soot measurement virtually impossible. Only after setting a thermal equilibrium between the hot exhaust gas and the soot sensor, the measurement of soot loading of the exhaust stream is useful. The time until the setting of this thermal equilibrium between the hot exhaust gas and the soot sensor can be usefully used for cleaning, so the burn-out, the interdigital electrode structure of the soot sensor. However, care should be taken to the dew point of the soot ⁇ sensor.
  • the achievement of the dew point of the soot sensor is well suited as a time to start the process of burning the soot sensor.
  • Up to a certain temperature in the exhaust gas system are small drops of water in the exhaust, which can condense on a cold soot sensor. If the soot sensor is heated under these circumstances, the condensed water can lead to the destruction of the interdigital electrode structure.
  • Even the parking of the internal combustion engine is a good time to forward the process of burn the soot sensor a ⁇ .
  • ⁇ ren with start / stop automatic standstill of the engine can be very well used during vehicle stop, for example at a red light, to regenerate the soot sensor through a free burning.
  • the operating condition of stationary combustion ⁇ motors can be easily detected, for example, using a sensor that monitors the speed of the crankshaft.
  • the time for burnout of the soot sensor is within the time of regeneration of the diesel particulate filter.
  • Exhaust gas is already very hot during regeneration of the diesel particulate filter. Therefore, only a small amount of electrical energy is required for self-heating of the soot sensor.
  • the time to burn out the soot sensor is achieved in a full load operation of the Ver ⁇ internal combustion engine. In this operating state, the exhaust gas is already very hot and therefore only low electrical energy for self-heating of the soot sensor is required.
  • soot ⁇ slip is low at a possibly damaged diesel particulate filter.
  • FIG. 1 shows a soot sensor
  • FIG. 2 shows the mode of operation of the soot sensor
  • Figure 3 is a permanently installed in a motor vehicle ⁇ profiled control unit for operation of the carbon black ⁇ sensors
  • Figure 5 shows the inventive method in one
  • FIG. 1 shows a soot sensor 10, which is constructed from a shaped body 1, a heating element, not shown here, and a structure of interdigitated measuring electrodes 3.
  • the molded body 1 may be made of a ceramic material, or consist of another material which has electrically insulating properties and easily withstands the Abbrandt- temperature of carbon black.
  • the soot sensor 10 is typically heated to temperatures between 500 and 800 ° C by means of electrical resistance heating. These temperatures must tolerate the electrically insulating molded body 1 without damage.
  • the structure of the measuring electrodes 3 is here exemplified as a comb-like structure, which is also referred to as interdigitated electrode structure, wherein between two measuring ⁇ electrodes 3 is always an electrically insulating region of the molded body 1 can be seen.
  • the measuring electrodes 3 and the spaces between the measuring electrodes 3 form the interdigital electrode structure.
  • the interdigital electrode structure 3 is constructed, for example, of annular measuring electrodes 3, which are arranged concentrically.
  • the width of a measuring electrode 3 may be, for example, between 50 and 100 ⁇ and the distance between the individual measuring electrodes 3 may also be 50 and 100 ⁇ .
  • An interdigital electrode structure 3 having such dimensions can be easily fabricated in thick film technology. In Dick ⁇ Layer technology produced interdigital electrode ⁇ structures 3 are robust, durable and cost-effective.
  • the measuring current I M between the measuring electrodes 3 is measured by means of a current measuring element 7. As long as the soot sensor 10 is completely free of soot particles 4, no measuring current I M will be measurable with the current measuring element 7, since there is always a region of the shaped body 1 between the measuring electrodes 3 which has an electrically insulating effect and which is also not bridged by soot particles 4 ,
  • FIG. 1 shows a temperature sensor 11 as a component of the soot sensor 10 with a temperature evaluation electronics 12 which serves to monitor the temperature prevailing in the soot sensor 10, above all during combustion of the soot load from the interdigital electrode structure 3 of the soot sensor 10.
  • FIG. 1 shows a voltage source 15 which determines the voltage applied to the measuring electrodes 3. Measuring voltage can be applied to the measuring electrodes 3 with the voltage source 15.
  • FIG. 2 shows the mode of operation of the soot sensor 10.
  • the soot sensor 10 is arranged in an exhaust pipe 5 of a motor vehicle, through which an exhaust gas flow laden with soot particles 4 is conducted.
  • the flow direction of the exhaust gas stream 6 is indicated by the arrow.
  • the task of the soot sensor 10 is now to measure the concentration of the soot particles 4 in the exhaust gas stream 6.
  • the soot sensor 10 is arranged in the exhaust pipe 5, that the structure of interdigitated measuring electrodes 3, the exhaust gas stream 6 and thus the soot particles 4 faces. From the exhaust gas flow 6, soot particles 4 settle both on the measuring electrodes 3 and in the spaces between the measuring electrodes 3, that is, on the insulating regions of the shaped body 1.
  • soot particles 4 If enough soot particles 4 have deposited on the insulating regions between the measuring electrodes 3, due to the voltage applied to the measuring electrodes 3 Measuring voltage and the conductivity of the soot particles 4 flow a measuring current I M between the measuring electrodes 3, which can be detected by the current measuring element 7. The soot particles 4 thus bridge the electrically insulating gaps between the measuring electrodes 3. In this way, the loading of the exhaust gas flow 6 with soot particles 4 can be measured with the soot sensor 10 shown here.
  • the soot sensor 10 in Figure 2 shows the heating element 2, which can be supplied with the heating circuit 13 from the heating power supply 8 with electrical heating current I H.
  • the heating current switch 9 is closed, whereby the heating current I H heats the heating element 2 and thus the entire soot sensor 10 is heated.
  • a temperature sensor 11 is integrated in the soot sensor 10, the process of heating the soot sensor 10 and thus the burning process of the soot particles 4, which is also referred to as burnout of the soot sensor 10, monitored and monitored by means of Temperaturausnceelektronik 12.
  • the current measuring element 7, the temperature evaluation electronics 12, the controllable voltage source 15, the temperature sensor 11 and the heating current switch 9 are shown here as examples as discrete components.
  • these components can be realized as Be ⁇ constituent parts of a micromechanical system together with the interdigital electrode structure 3 on a chip or components of a microelectronic circuit, which is integrated, for example, in a control unit 14 for the soot ⁇ sensor 10.
  • Figure 3 shows a in a motor vehicle 16 are fixedly installed control unit 14 to the functional diagnosis, operation and for the regeneration of the soot sensor 10.
  • the soot sensor 10 has a finger interdigitated (interdigital) measuring electric ⁇ den réelle 3, which comprises of an intact soot sensor 10 no metallic shorts , On and between the measuring electrodes 3 ⁇ set in the measuring operation of the sensor soot particles 4, which lead to a current flow between the measuring electrodes 3, which serves as a measure of the soot load of the exhaust gas stream. From a certain amount of deposited soot particles 4 on the measuring electrodes 3, however, a maximum conductivity is achieved via the soot layer, which can not be further increased even with a further soot deposition.
  • the soot sensor 10 becomes "blind” from a certain amount of deposited soot particles for further measurement of soot concentration in the exhaust gas. It is now necessary to regenerate the soot sensor 10 by burning off the soot layer on the interdigital measuring electrodes 3. For this purpose, a heating current is passed through the switching of the heating current switch 9 from the heating power supply 8 to the heating element 2. The soot sensor 10 is heated in a controlled manner. The control of the heating of the soot sensor 10 is performed with the off formed on or in the soot sensor 10 temperature sensor 11. This burning off of the soot sensor 10 is a function of the operating state of the United ⁇ brennungsmotors 17.
  • the free burning process is started at a time ⁇ point where the operating state of the combustion ⁇ motor 17 does not allow meaningful soot measurement.
  • the interdigital electrode structure 3 of the soot sensor 10 is cleaned exactly when no soot measurement would be possible or useful anyway.
  • the soot sensor 10 is also ready for operation, which permits continuous monitoring of soot loading of the exhaust gas flow 6.
  • the operating state of the engine 17 may, for example, with an engine temperature sensor 18 that detects the temperature of the cooling liquid of the combustion ⁇ motor 17 or the oil temperature and / or monitored with a crankshaft rotational speed sensor 19 which detects the rotational speed of the crankshaft.
  • a motor vehicle 16 with an internal combustion engine 17 is shown in FIG.
  • the internal combustion engine 17 discharges the exhaust gas stream 6 generated by it via an exhaust pipe 5.
  • a diesel particulate filter 20 can be seen in the exhaust pipe 5.
  • a soot sensor 10 is arranged in the exhaust pipe 5, the is connected to a controller 14, which may also include the current measuring element 7.
  • the crankshaft speed sensor 19 and the engine temperature sensor 18 provide the control unit 14 with information about the operating state of the Ver ⁇ combustion engine 17. With this information, a time is selected, to which the burning of the interdigital electrode structure 3 of the soot sensor 10 is initiated.
  • This time can be, for example, a restart of the internal combustion engine 17, which is detected by the control unit 14 with the aid of the crankshaft speed sensor 19.
  • the restart of the fully from ⁇ cooled internal combustion engine 17 is detected by the control unit 14 by means of the crankshaft ⁇ speed sensor 19 and the engine temperature sensor 18.
  • the time of the dew point release of the soot sensor should be awaited.
  • the time of stopping the internal combustion engine 17 is in turn he ⁇ known with the help of the crankshaft speed sensor 19.
  • sensors that determine combustion and / or emission-related parameters. These are, for example, temperature sensors, oxygen sensors, sensors for determining the fuel-air ratio lambda and nitrogen oxide sensors.
  • temperature sensors for example, temperature sensors, oxygen sensors, sensors for determining the fuel-air ratio lambda and nitrogen oxide sensors.
  • sensors for determining the fuel-air ratio lambda and nitrogen oxide sensors In the exhaust gas of an internal combustion engine 17 is water vapor. The water vapor condenses in the cold exhaust system and can form drops of liquid water there. Since liquid water can destroy hot sensors, the sensors do not heat after the engine cold start or very little and wait for the water freedom of the exhaust gas. The sensors do not send any data to the engine management system or merely the information "Sensor present, wait for approval".
  • the engine control of the internal combustion engine 17 calculates from the engine operating data and the measured temperatures, the time from which at the sensor position, for example after the catalyst or the diesel particulate filter 20, no more liquid water is expected. Is this time reached, the motor control sends a signal to the sensor "no more water, permission granted". The sensor detects this signal and begins its heating process.
  • the information of the engine control to the sensor "no more liquid water at the point A" is usually called dew point A release. If heated and measured beforehand, the sensor could be destroyed by the drops of water. For the soot sensor 10, the dew point release at its position is the earliest possible time after the engine start, from which it is free to burn .
  • the dew point is released after a cold engine start after a few minutes.
  • 5 shows the method according to the invention for operating a soot sensor 10 in a flowchart.
  • the monitoring of the operating state of the internal combustion engine 17 takes place.
  • the monitoring of the Kurbelwel ⁇ lennaviere occurs in step 22
  • the monitoring of the temperature of the engine 17 and in step 23 is carried out takes place over ⁇ monitoring the dew point of release of the soot sensor.
  • burnout of the interdigital electrode structure 3 of the soot sensor is initiated.
  • the quantities measured in steps 21, 22 and 23 can contribute to the decision individually or in combination with one another.
  • step 21 it is conceivable that the monitoring of Kurbelwel ⁇ lennaviere in step 21 to result that is detected by the control unit 14 that a restart of the internal combustion engine has taken place 17 and due to the carried out in step 22, operation of the monitoring of the temperature of the combustion Motos 17 is detected in that this restart of the internal combustion engine 17 was a cold start, ie a restart of the completely cooled internal combustion engine 17.
  • step 24 the position 26 is jumped when the dew point release 23 takes place, wherein the burn-out of the interdigital electrode structure 3 is recognized as meaningful, whereupon in step 27, the burning of the interdigital Electrode structure 3 of the soot sensor 10 is started. After the burning of the interdigital electrode structure 3, the sequence returns to step 20, that is to say the monitoring of the operating state of the internal combustion engine 17.
  • step 24 it is decided in step 24 that due to a restart of the internal combustion engine 17, which was detected by monitoring the crankshaft speed in step 21, in combination with a detected in step 22 high temperature of the internal combustion engine 17 is not initiated burnout should.
  • This decision for Tinkebumble the interdigital electrode structure is carried out in point 25, whereupon the process is continued again with the monitoring of the operating ⁇ state of the engine 17 at point 20.

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  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
  • Processes For Solid Components From Exhaust (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)

Abstract

The invention relates to a method for operating a soot sensor in the exhaust gas tract of an internal combustion engine. Said soot sensor comprises an inter-digital electrode structure to which a measurement voltage is applied. Soot particles from the exhaust gas flow deposit themselves on the inter-digital electrode structure and the measuring current flowing over the soot particles and the inter-digital electrode structure is evaluated as a measurement for the soot concentration of the soot sensor. Said soot sensor comprises a heating element for burning clean the inter-digital electrode structure. The aim of the invention is to provide a method for operating a soot sensor which has good measurement results, said soot sensor should have the shortest possible idle time. To this end, a point in time for burning clean the soot sensor is determined in accordance with the operational state of the internal combustion engine and then, the burning clean of the inter-digital electrode structure starts by heating the soot sensor by means of the heating element.

Description

Beschreibung description
Verfahren zum Betreiben eines Rußsensors Method for operating a soot sensor
Die Erfindung betrifft ein Verfahren zum Betreiben eines Rußsensors, im Abgasstrang eines Verbrennungsmotors, wobei der Rußsensor eine interdigitale Elektrodenstruktur aufweist, an die eine Messspannung angelegt wird, wobei sich auf der interdi¬ gitalen Elektrodenstruktur Rußpartikel aus einem Abgasstrom ablagern und der über die Rußpartikel und die interdigitale Elektrodenstruktur fließende Messstrom als Maß für die Rußbeladung des Rußsensors ausgewertet wird und wobei der Rußsensor ein Heizelement zum Freibrennen der interdigitalen Elektrodenstruktur aufweist. The invention relates to a method for operating a soot sensor, in the exhaust system of an internal combustion engine, the soot sensor has an interdigitated electrode structure, to which a measuring voltage is applied, wherein depositing on the interdi ¬ gitalen electrode structure soot particles from an exhaust stream and the on the soot particles and interdigital electrode structure flowing measuring current is evaluated as a measure of the soot loading of the soot sensor and wherein the soot sensor comprises a heating element for burning the interdigital electrode structure.
Verbrennungsmotoren im Sinne dieser Patentanmeldung sind alle Motoren, bei denen ein Treibstoff-Sauerstoffgemisch verbrannt wird, wobei mechanische Energie freigesetzt wird. Diese Patent¬ anmeldung bezieht sich vor allem auf Dieselmotoren, da diese besonders zur Entwicklung von Rußemissionen neigen, aber auch auf benzin- oder gasbetriebene Verbrennungsmotoren. Internal combustion engines in the context of this patent application are all engines in which a fuel-oxygen mixture is burned, whereby mechanical energy is released. This patent application relates ¬ mainly on diesel engines, as they are particularly prone to the development of soot emissions, but also on gasoline or gas-powered internal combustion engines.
Die Anreicherung der Atmosphäre mit Schadstoffen aus Abgasen wird derzeit viel diskutiert. Damit verbunden ist die Tatsache, dass die Verfügbarkeit fossiler Energieträger begrenzt ist. Als Reaktion darauf werden beispielsweise Verbrennungsprozesse in Brennkraftmaschinen thermodynamisch optimiert, so dass deren Wirkungsgrad verbessert wird. Im Kraftfahrzeugbereich schlägt sich dies in der zunehmenden Verwendung von Dieselmotoren nieder . Der Nachteil dieser Verbrennungstechnik gegenüber optimierten Otto-Motoren ist jedoch ein deutlich erhöhter Ausstoß von Ruß. Der Ruß ist besonders durch die Anlagerung polyzyklischer Aromate stark krebserregend, worauf in verschiedenen Vorschriften bereits reagiert wurde. So wurden beispielsweise Abgas- Emissionsnormen mit Höchstgrenzen für die Rußemission erlassen. Daher besteht die Notwendigkeit, preisgünstige Sensoren an- zugeben, die den Rußgehalt im Abgasstrom von Kraftfahrzeugen zuverlässig messen. The enrichment of the atmosphere with pollutants from exhaust gases is currently much discussed. Linked to this is the fact that the availability of fossil fuels is limited. In response, for example, combustion processes in internal combustion engines are thermodynamically optimized, so that their efficiency is improved. In the automotive sector this is reflected in the increasing use of diesel engines. The disadvantage of this combustion technique compared to optimized Otto engines, however, is a significantly increased emissions of soot. The soot is particularly carcinogenic due to the addition of polycyclic aromatics, which has already been reacted in various regulations. For example, exhaust emission standards with maximum limits for soot emissions were issued. Therefore, there is a need to provide low-cost sensors to which reliably measure the soot content in the exhaust stream of motor vehicles.
Der Einsatz derartiger Rußsensoren dient der Messung des aktuell mit dem Abgasstrom ausgestoßenen Rußes, damit dem Motormanagement in einem Automobil in einer aktuellen Fahrsituation Informationen zukommen, um mit regelungstechnischen Anpassungen die Emissionswerte zu reduzieren. Darüber hinaus kann mit Hilfe der Rußsensoren eine aktive Abgasreinigung durch Abgas-Rußfilter eingeleitet werden oder eine Abgasrückführung zur Brennkraft- tmaschine erfolgen. Im Falle der Rußfilterung werden The use of such soot sensors is used to measure the currently emitted with the exhaust stream soot, so that the engine management in an automobile in a current driving situation information to come to reduce with regulatory adjustments the emission levels. In addition, with the aid of the soot sensors active exhaust gas purification can be initiated by exhaust soot filters or exhaust gas recirculation to the internal combustion engine can take place. In the case of Rußfilterung be
regenerierbare Filter verwendet, die einen wesentlichen Teil des Ruß- gehaltes aus dem Abgas herausfiltern. Benötigt werden Rußsensoren für die Detektion von Ruß, um die Funktion der Rußfilter zu überwachen bzw. um deren Regenerationszyklen zu steuern . regenerable filters are used, which filter out a significant part of the carbon black content from the exhaust gas. Soot sensors are required for the detection of soot in order to monitor the function of the soot filters or to control their regeneration cycles.
Dazu kann dem Rußfilter, der auch als Dieselpartikelfilter bezeichnet wird, ein Rußsensor vorgeschaltet sein und/oder ein Rußsensor nachgeschaltet sein. For this purpose, the soot filter, which is also referred to as a diesel particulate filter, may be preceded by a soot sensor and / or a soot sensor connected downstream.
Der dem Dieselpartikelfilter vorgeschaltete Sensor dient zur Erhöhung der Systemsicherheit und zur Sicherstellung eines Betriebes des Diesel-Partikel-Filters unter optimalen Bedingun¬ gen. Da diese in hohem Maße von der im Diesel-Partikel-Filter eingelagerten Rußmenge abhängen, ist eine genaue Messung der Partikelkonzentration vor dem Diesel-Partikel-Filtersystem, ins- besondere die Ermittlung einer hohen Partikelkonzentration vor dem Diesel-Partikel-Filter, von hoher Bedeutung. The upstream of the diesel particulate filter sensor serves to increase the system safety and to ensure an operation of the diesel particulate filter under optimum Bedingun ¬. Accordingly, as these depend greatly on the embedded in the diesel particulate filter soot, is an accurate measurement of the particle concentration before the diesel particulate filter system, in particular the determination of a high particle concentration before the diesel particulate filter, of great importance.
Ein dem Diesel-Partikel-Filter nachgeschalteter Sensor bietet die Möglichkeit, eine On-Board-Diagnose vorzunehmen und dient ferner der Sicherstellung des korrekten Betriebes der Abgasnachbehandlungsanlage . A diesel particulate filter downstream sensor provides the ability to perform on-board diagnostics and also helps ensure proper operation of the exhaust after-treatment system.
Im Stand der Technik hat es verschiedene Ansätze zur Detektion von Ruß gegeben. Ein in Laboratorien weithin verfolgter Ansatz besteht in der Verwendung der Lichtstreuung durch die Rußpartikel. Diese Vorgehensweise eignet sich für aufwändige Messgeräte. Wenn versucht wird, dies auch als mobiles Sen¬ sorsystem im Abgasstrang einzusetzen, muss festgestellt werden, dass derartige Ansätze zur Realisierung eines Sensors in einem Kraftfahrzeug durch den aufwändigen optischen Aufbau mit hohen Kosten verbunden sind. Weiterhin bestehen ungelöste Probleme bezüglich der Verschmutzung der benötigten optischen Fenster durch Verbrennungsabgase. There have been various approaches to detecting soot in the prior art. A widely used approach in laboratories consists in the use of light scattering by the soot particles. This procedure is suitable for complex measuring instruments. When trying to use it as a mobile Sen ¬ sorsystem in the exhaust system, it must be noted that such approaches to the realization of a sensor in a motor vehicle by the complex optical structure are associated with high costs. Furthermore, there are unresolved problems regarding the pollution of the required optical windows by combustion exhaust gases.
Die deutschen Offenlegungsschrift DE 199 59 871 AI offenbart einen Sensor und ein Betriebsverfahren für den Sensor, wobei beide auf thermischen Betrachtungen basieren. Der Sensor besteht aus einem offen porösen Formkörper wie beispielsweise einer waben- förmigen Keramik, einem Heizelement und einem Temperaturfühler. Wird der Sensor mit einem Messgasvolumen in Verbindung gebracht, so lagert sich Ruß darauf ab. Zur Messung wird der in einem Zeitraum abgelagerte Ruß mit Hilfe des Heizelementes zum Zünden gebracht und verbrannt. Die bei der Verbrennung entstehende Temperaturerhöhung wird gemessen. German laid-open specification DE 199 59 871 A1 discloses a sensor and an operating method for the sensor, both based on thermal considerations. The sensor consists of an open-porous shaped body such as a honeycomb ceramic, a heating element and a temperature sensor. If the sensor is associated with a sample gas volume, soot deposits on it. For measurement, the soot deposited in a period of time is ignited by means of the heating element and burnt. The temperature increase resulting from the combustion is measured.
Derzeit sind Partikelsensoren für leitfähige Partikel bekannt, bei denen zwei oder mehrere metallische Elektroden vorgesehen sind, die kammartig ineinandergreifende Elektroden aufweisen. Diese kammartigen Strukturen werden auch als Interdigital- strukturen bezeichnet. Rußpartikel, die sich auf diesen Sen¬ sorstrukturen ablagern, schließen die Elektroden kurz und verändern damit die Impedanz der Elektrodenstruktur. Mit steigender Partikelkonzentration auf der Sensorfläche wird auf diese Weise ein abnehmender Widerstand bzw. ein zunehmender Strom bei konstanter angelegter Spannung zwischen den Elektroden messbar. Ein derartiger Rußsensor wird zum Beispiel in der DE 10 2004 028 997 AI offenbart. Um überhaupt einen Strom zwischen den Elektroden messen zu können, muss jedoch eine gewisse Menge von Ruß-Partikeln zwischen den Elektroden vorhanden sein. Bis zum Erreichen dieser minimalen Partikelbeladung ist der Rußsensor gewissermaßen blind für die Rußkonzentration im Abgasstrom. Darüber hinaus muss der Rußsensor in regelmäßigen Abständen gereinigt werden. Die Regeneration des Sensors erfolgt durch das Abbrennen des angelagerten Rußes. Dieser Vorgang wird auch als Freibrennen der interdigitalen Elektrodenstruktur bezeichnet. Zur Regeneration wird das Sensorelement nach der Rußanlagerung in der Regel mit Hilfe eines integrierten Heizelementes frei¬ gebrannt. Während der Freibrennphase kann der Sensor die Ru߬ beladung des Abgasstroms nicht erfassen. Die Zeit die zum regenerativen Freibrennen der Sensorstruktur benötigt wird, wird auch als Totzeit des Sensors bezeichnet. Es ist also wichtig, die Freibrennphase und die sich daran anschließende Neukonditio- nierungsphase des Rußsensors so kurz wie möglich zu gestalten, um den Rußsensor so schnell wie möglich wieder zur Rußmessung einsetzen zu können. At present, particle sensors for conductive particles are known, in which two or more metallic electrodes are provided, which have comb-like interdigitated electrodes. These comb-like structures are also called interdigital structures. Soot particles that are deposited on these Sen ¬ sorstrukturen, connect the electrodes short and therefore change the impedance of the electrode structure. With increasing particle concentration on the sensor surface in this way, a decreasing resistance or an increasing current at constant applied voltage between the electrodes can be measured. Such a soot sensor is disclosed, for example, in DE 10 2004 028 997 A1. In order to measure a current between the electrodes, however, a certain amount of soot particles must be present between the electrodes. Until this minimum particle load is reached, the soot sensor is virtually blind to the soot concentration in the exhaust stream. In addition, the soot sensor must be cleaned at regular intervals. The regeneration of the sensor is done by burning off the accumulated soot. This process is also referred to as burnout of the interdigital electrode structure. For regeneration, the sensor element after the soot accumulation is usually free ¬ burned with the help of an integrated heating element. During the free burning phase of the sensor can not detect the soot load-¬ of the exhaust stream. The time required for regenerative burnout of the sensor structure is also referred to as the dead time of the sensor. It is therefore important to make the burn-off phase and the subsequent reconditioning phase of the soot sensor as short as possible in order to be able to reuse the soot sensor as soon as possible for soot measurement.
Die Aufgabe der Erfindung ist es daher, ein Verfahren zum Betreiben eines Rußsensors anzugeben, welches gute Messergeb¬ nisse liefert, wobei der Rußsensor möglichst geringe Totzeiten aufweisen soll. The object of the invention is therefore to provide a method of operating a soot sensor, which provides good measurement resulting ¬ nit, wherein the soot sensor should have the least possible dead times.
Die Aufgabe wird durch die Merkmale der unabhängigen Ansprüche gelöst . The object is solved by the features of the independent claims.
Dadurch, dass in Abhängigkeit vom Betriebszustand des Ver¬ brennungsmotors ein Zeitpunkt zum Freibrennen des Rußsensors bestimmt wird und dann das Freibrennen der interdigitalen Elektrodenstruktur durch ein Aufheizen des Rußsensors mit dem Heizelement beginnt, können gezielt solche Zeiten für den Frei- brennprozess gewählt und genutzt werden, in denen eine Rußmessung ohnehin nicht sinnvoll oder möglich ist. Mit dem erfindungs¬ gemäßen Verfahren kann die Rußbeladung des Abgasstroms eines Kraftfahrzeuges genau dann effektiv gemessen werden, wenn diese Messung aufgrund des Betriebszustandes des Verbrennungsmotors sinnvolle Ergebnisse liefert, wodurch es möglich wird die Emis¬ sion von Schadstoffen erheblich reduzieren. Ein Betriebszustand des Verbrennungsmotors nach denen ein Zeitpunkt zum Freibrennen des Rußsensors bestimmt wird, kann zum Beispiel die Kurbel- wellendrehzahl des Verbrennungsmotors und/oder die Temperatur des Verbrennungsmotors, insbesondere seine Kühlmitteltemperatur sein . Eine Weiterbildung der Erfindung ist dadurch gekennzeichnet, dass der Zeitpunkt zum Freibrennen des Rußsensors ein Neustart des Verbrennungsmotors ist. Ein Neustart des Verbrennungsmotors kann zum Beispiel durch die Beobachtung der Kurbelwellendrehzahl erkannt werden. Wenn der Verbrennungsmotor neu gestartet wird, wird zusätzlich das Freibrennen der interdigitalen Elektrodenstruktur durch ein Aufheizen des Rußsensors mit dem Heizelement begonnen. In diesem Betriebszustand ist eine Rußmesssung ohnehin nicht sinnvoll, so dass das Freibrennen der interdigi¬ talen Elektrodenstruktur keine Messzeit kostet. Characterized in that depending on the operating state of the Ver ¬ internal combustion engine, a time is determined for burning the soot sensor and then the burning of the interdigital electrode structure by heating the soot sensor starts with the heating element, such times can be selected and used for the free-burning process specifically in which a soot measurement anyway not useful or possible. With the process according to Inventive ¬ soot loading of the exhaust stream of a motor vehicle can be accurately measured then effective when this measurement provides meaningful results due to the operating condition of the engine, thereby making it possible to greatly reduce the emis sion of harmful substances ¬. An operating state of the internal combustion engine, after which a time for burning out the soot sensor is determined, may be, for example, the crank shaft speed of the internal combustion engine and / or the temperature of the internal combustion engine, in particular its coolant temperature. A development of the invention is characterized in that the time for burning the soot sensor is a restart of the internal combustion engine. A restart of the internal combustion engine can be detected, for example, by monitoring the crankshaft speed. In addition, when the internal combustion engine is restarted, the burn-out of the interdigital electrode structure is started by heating the soot sensor with the heating element. In this operating state, a soot measurement is in any case not meaningful, so that the burning of the interdigi ¬ tal electrode structure costs no measurement time.
Bei einer Ausgestaltung der Erfindung ist der Zeitpunkt zum Freibrennen des Rußsensors der Neustart des vollständig abge¬ kühlten Verbrennungsmotors. Bei einem vollständig abgekühlten Verbrennungsmotor liegen im Abgasstrang Bedingungen vor, die eine Rußmessung nahezu unmöglich machen. Erst nach der Einstellung eines thermischen Gleichgewichtes zwischen dem heißen Abgas und dem Rußsensor, ist die Messung der Rußbeladung des Abgasstromes sinnvoll. Die Zeit bis zur Einstellung dieses thermischen Gleichgewichtes zwischen dem heißen Abgas und dem Rußsensor kann sinnvoll für die Reinigung, also das Freibrennen, der interdigitalen Elektrodenstruktur des Rußsensors genutzt werden. Dabei sollte jedoch auf die Taupunktfreigäbe vom Ru߬ sensor geachtet werden. Auch das Erreichen der Taupunktfreigäbe des Rußsensors eignet sich gut als Zeitpunkt, um den Vorgang des Freibrennens des Rußsensors zu starten. Bis zu einer bestimmten Temperatur im Abgasstrang befinden sich kleine Wassertropfen im Abgas, die auf einem kalten Rußsensor kondensieren können. Wird der Rußsensor unter diesen Umständen erhitzt, so kann das kondensierte Wasser zur Zerstörung der interdigitalen Elektrodenstruktur führen. Auch das Abstellen des Verbrennungsmotors eignet sich gut als Zeitpunkt, um den Vorgang des Freibrennens des Rußsensors ein¬ zuleiten. Gerade bei modernen Fahrzeugen mit Verbrennungsmoto¬ ren mit Start/Stoppautomatik kann der Stillstand des Verbrennungsmotors beim Fahrzeugstopp zum Beispiel an einer roten Ampel sehr gut genutzt werden, um den Rußsensor durch ein Freibrennen zu regenerieren. Der Betriebszustand des stehenden Verbrennungs¬ motors kann zum Beispiel sehr leicht mit Hilfe eines Sensors erfasst werden, der die Drehzahl der Kurbelwelle überwacht. In one embodiment of the invention, the time to burn off the soot sensor is the restart of the fully abge ¬ cooled internal combustion engine. In a fully cooled internal combustion engine, there are conditions in the exhaust system that make soot measurement virtually impossible. Only after setting a thermal equilibrium between the hot exhaust gas and the soot sensor, the measurement of soot loading of the exhaust stream is useful. The time until the setting of this thermal equilibrium between the hot exhaust gas and the soot sensor can be usefully used for cleaning, so the burn-out, the interdigital electrode structure of the soot sensor. However, care should be taken to the dew point of the soot ¬ sensor. Also, the achievement of the dew point of the soot sensor is well suited as a time to start the process of burning the soot sensor. Up to a certain temperature in the exhaust gas system are small drops of water in the exhaust, which can condense on a cold soot sensor. If the soot sensor is heated under these circumstances, the condensed water can lead to the destruction of the interdigital electrode structure. Even the parking of the internal combustion engine is a good time to forward the process of burn the soot sensor a ¬. Especially in modern vehicles with internal combustion engines ¬ ren with start / stop automatic standstill of the engine can be very well used during vehicle stop, for example at a red light, to regenerate the soot sensor through a free burning. The operating condition of stationary combustion ¬ motors can be easily detected, for example, using a sensor that monitors the speed of the crankshaft.
Bei einer Ausgestaltung der Erfindung liegt der Zeitpunkt zum Freibrennen des Rußsensors innerhalb der Zeit der Regeneration des Diesel-Partikel-Filters. Während der Regeneration des Diesel-Partikel-Filters ist Abgas bereits sehr heiß. Deshalb ist zur Eigenheizung des Rußsensors nur eine geringe elektrische Energie erforderlich. In one embodiment of the invention, the time for burnout of the soot sensor is within the time of regeneration of the diesel particulate filter. Exhaust gas is already very hot during regeneration of the diesel particulate filter. Therefore, only a small amount of electrical energy is required for self-heating of the soot sensor.
Bei einer nächsten Ausgestaltung ist der Zeitpunkt zum Freibrennen des Rußsensors bei einem Volllastbetrieb des Ver¬ brennungsmotors erreicht. In diesem Betriebszustand ist das Abgas bereits sehr heiß und deshalb ist nur geringe elektrische Energie zur Eigenheizung des Rußsensors erforderlich. In a next embodiment, the time to burn out the soot sensor is achieved in a full load operation of the Ver ¬ internal combustion engine. In this operating state, the exhaust gas is already very hot and therefore only low electrical energy for self-heating of the soot sensor is required.
Es kann aber auch vorteilhaft sein, wenn der Zeitpunkt zum Freibrennen des Rußsensors bei niedrigen Lastpunkten des Verbrennungsmotors erreicht ist. Bei niedriger Last ist der Ru߬ schlupf an einem eventuell geschädigten Diesel-Partikel-Filter gering. Am Sensor ergibt sich kaum ein Signalzuwachs und man verliert keine Daten durch ein Freibrennen des Rußsensors. But it may also be advantageous if the time is reached for burning the soot sensor at low load points of the internal combustion engine. At low load, the soot ¬ slip is low at a possibly damaged diesel particulate filter. At the sensor, there is hardly any signal increase and you lose no data by burning the soot sensor.
Die Erfindung wird nachfolgend anhand der Figuren erläutert. Die nachfolgenden Darstellungen zeigen in: The invention will be explained below with reference to the figures. The following illustrations show in:
Figur 1 einen Rußsensor, FIG. 1 shows a soot sensor,
Figur 2 die Wirkungsweise des Rußsensors, Figur 3 ein in einem Kraftfahrzeug fest instal¬ liertes Steuergerät zum Betrieb des Ru߬ sensors, FIG. 2 shows the mode of operation of the soot sensor, Figure 3 is a permanently installed in a motor vehicle ¬ profiled control unit for operation of the carbon black ¬ sensors,
Figur 4 ein Kraftfahrzeug mit einem Verbrennungs¬ motor, 4 shows a motor vehicle with a combustion motor ¬,
Figur 5 das erfindungsgemäße Verfahren in einem Figure 5 shows the inventive method in one
Ablaufdiagramm.  Flowchart.
Figur 1 zeigt einen Rußsensor 10, der aus einem Formkörper 1, einem hier nicht dargestellten Heizelement sowie einer Struktur aus interdigital ineinander greifenden Messelektroden 3 aufgebaut ist. Der Formkörper 1 kann aus einem Keramikmaterial hergestellt sein, oder aus einem anderen Material bestehen, das elektrisch isolierende Eigenschaften aufweist und der Abbrandt- temperatur von Ruß problemlos standhält. Um den Rußsensor 10 von Ruß freizubrennen, wird der Rußsensor 10 typischer Weise mit Hilfe einer elektrischen Widerstandsheizung auf Temperaturen zwischen 500 und 800 °C erhitzt. Diese Temperaturen muss der elektrisch isolierende Formkörper 1 ohne Beschädigungen vertragen. Die Struktur der Messelektroden 3 ist hier beispielhaft als kammartige Struktur ausgebildet, die auch als interdigitale Elektrodenstruktur bezeichnet wird, wobei zwischen zwei Mess¬ elektroden 3 immer ein elektrisch isolierender Bereich des Formkörpers 1 zu erkennen ist. Die Messelektroden 3 und die Zwischenräume zwischen den Messelektroden 3 bilden die interdigitale Elektrodenstruktur. Es ist aber auch denkbar, dass die interdigitale Elektrodenstruktur 3 zum Beispiel aus ringförmigen Messelektroden 3 aufgebaut ist, die konzentrisch angeordnet sind . FIG. 1 shows a soot sensor 10, which is constructed from a shaped body 1, a heating element, not shown here, and a structure of interdigitated measuring electrodes 3. The molded body 1 may be made of a ceramic material, or consist of another material which has electrically insulating properties and easily withstands the Abbrandt- temperature of carbon black. In order to free the soot sensor 10 of soot, the soot sensor 10 is typically heated to temperatures between 500 and 800 ° C by means of electrical resistance heating. These temperatures must tolerate the electrically insulating molded body 1 without damage. The structure of the measuring electrodes 3 is here exemplified as a comb-like structure, which is also referred to as interdigitated electrode structure, wherein between two measuring ¬ electrodes 3 is always an electrically insulating region of the molded body 1 can be seen. The measuring electrodes 3 and the spaces between the measuring electrodes 3 form the interdigital electrode structure. However, it is also conceivable that the interdigital electrode structure 3 is constructed, for example, of annular measuring electrodes 3, which are arranged concentrically.
Die Breite einer Messelektrode 3 kann zum Beispiel zwischen 50 und 100 μπι liegen und der Abstand zwischen den einzelnen Messelektroden 3 kann ebenfalls 50 und 100 μπι betragen. Eine interdigitale Elektrodenstruktur 3 mit derartigen Abmessungen kann leicht in Dickschichttechnologie hergestellt werden. In Dick¬ Schichttechnologie hergestellte interdigitale Elektroden¬ strukturen 3 sind robust, langlebig und kostengünstig. The width of a measuring electrode 3 may be, for example, between 50 and 100 μπι and the distance between the individual measuring electrodes 3 may also be 50 and 100 μπι. An interdigital electrode structure 3 having such dimensions can be easily fabricated in thick film technology. In Dick ¬ Layer technology produced interdigital electrode ¬ structures 3 are robust, durable and cost-effective.
Der Messstrom IM zwischen den Messelektroden 3 wird mit Hilfe eines Strommesselementes 7 gemessen. Solange der Rußsensor 10 völlig frei von Rußpartikeln 4 ist, wird mit dem Strommesselement 7 kein Messstrom IM messbar sein, da zwischen den Messelektroden 3 immer ein Bereich des Formkörpers 1 vorhanden ist, der elektrisch isolierend wirkt und der auch nicht von Rußpartikeln 4 überbrückt wird. The measuring current I M between the measuring electrodes 3 is measured by means of a current measuring element 7. As long as the soot sensor 10 is completely free of soot particles 4, no measuring current I M will be measurable with the current measuring element 7, since there is always a region of the shaped body 1 between the measuring electrodes 3 which has an electrically insulating effect and which is also not bridged by soot particles 4 ,
Weiterhin zeigt Figur 1 einen Temperatursensor 11 als Bestandteil des Rußsensors 10 mit einer Temperaturauswerteelektronik 12, die zur Überwachung der im Rußsensor 10 herrschenden Temperatur vor allem beim Abbrand der Rußbeladung von der interdigitalen Elektrodenstruktur 3 des Rußsensors 10 dient. Furthermore, FIG. 1 shows a temperature sensor 11 as a component of the soot sensor 10 with a temperature evaluation electronics 12 which serves to monitor the temperature prevailing in the soot sensor 10, above all during combustion of the soot load from the interdigital electrode structure 3 of the soot sensor 10.
Zudem ist in Figur 1 eine Spannungsquelle 15 zu erkennen, die die an den Messelektroden 3 anliegende Spannung bestimmt. Mit der Spannungsquelle 15 kann Messspannung an die Messelektroden 3 angelegt werden. In addition, FIG. 1 shows a voltage source 15 which determines the voltage applied to the measuring electrodes 3. Measuring voltage can be applied to the measuring electrodes 3 with the voltage source 15.
Figur 2 zeigt die Wirkungsweise des Rußsensors 10. Hier ist der Rußsensor 10 in einem Abgasrohr 5 eines Kraftfahrzeuges an- geordnet, durch das ein mit Rußpartikeln 4 beladener Abgasstrom geleitet wird. Die Strömungsrichtung des Abgasstromes 6 wird durch den Pfeil angedeutet. Die Aufgabe des Rußsensors 10 ist es nun, die Konzentration der Rußpartikel 4 im Abgasstrom 6 zu messen. Dazu ist der Rußsensor 10 so im Abgasrohr 5 angeordnet, dass die Struktur aus interdigital angeordneten Messelektroden 3, dem Abgasstrom 6 und somit den Rußpartikeln 4 zugewandt ist. Aus dem Abgasstrom 6 setzen sich Rußpartikel 4 sowohl auf den Messelektroden 3 als auch in den Zwischenräumen zwischen den Messelektroden 3, also auf den isolierenden Bereichen des Formkörpers 1 ab. Wenn sich genügend Rußpartikel 4 auf den isolierenden Bereichen zwischen die Messelektroden 3 abgesetzt haben, wird aufgrund der an den Messelektroden 3 angelegten Messspannung und der Leitfähigkeit der Rußpartikel 4 ein Messstrom IM zwischen den Messelektroden 3 fließen, der vom Strommesselement 7 erfassbar ist. Die Rußpartikel 4 überbrücken somit die elektrisch isolierenden Zwischenräume zwischen den Messelektroden 3. Auf diese Art und Weise kann mit dem hier abgebildeten Rußsensor 10 die Beladung des Abgasstromes 6 mit Rußpartikeln 4 gemessen werden. FIG. 2 shows the mode of operation of the soot sensor 10. Here, the soot sensor 10 is arranged in an exhaust pipe 5 of a motor vehicle, through which an exhaust gas flow laden with soot particles 4 is conducted. The flow direction of the exhaust gas stream 6 is indicated by the arrow. The task of the soot sensor 10 is now to measure the concentration of the soot particles 4 in the exhaust gas stream 6. For this purpose, the soot sensor 10 is arranged in the exhaust pipe 5, that the structure of interdigitated measuring electrodes 3, the exhaust gas stream 6 and thus the soot particles 4 faces. From the exhaust gas flow 6, soot particles 4 settle both on the measuring electrodes 3 and in the spaces between the measuring electrodes 3, that is, on the insulating regions of the shaped body 1. If enough soot particles 4 have deposited on the insulating regions between the measuring electrodes 3, due to the voltage applied to the measuring electrodes 3 Measuring voltage and the conductivity of the soot particles 4 flow a measuring current I M between the measuring electrodes 3, which can be detected by the current measuring element 7. The soot particles 4 thus bridge the electrically insulating gaps between the measuring electrodes 3. In this way, the loading of the exhaust gas flow 6 with soot particles 4 can be measured with the soot sensor 10 shown here.
Zudem zeigt der Rußsensor 10 in Figur 2 das Heizelement 2, das mit dem Heizstromkreis 13 aus der Heizstromversorgung 8 mit elektrischem Heizstrom IH versorgt werden kann. Um den Rußsensor 10 auf die Abbrandtemperatur der Rußpartikel 4 zu erhitzen, wird der Heizstromschalter 9 geschlossen, womit der Heizstrom IH das Heizelement 2 erwärmt und somit der gesamte Rußsensor 10 erhitzt wird. Darüber hinaus ist ein Temperatursensor 11 im Rußsensor 10 integriert, der mit Hilfe der Temperaturauswerteelektronik 12 den Vorgang des Aufheizens des Rußsensors 10 und damit den Abbrandvorgang der Rußpartikel 4, der auch als Freibrennen des Rußsensors 10 bezeichnet wird, kontrolliert und überwacht. In addition, the soot sensor 10 in Figure 2 shows the heating element 2, which can be supplied with the heating circuit 13 from the heating power supply 8 with electrical heating current I H. In order to heat the soot sensor 10 to the burnup temperature of the soot particles 4, the heating current switch 9 is closed, whereby the heating current I H heats the heating element 2 and thus the entire soot sensor 10 is heated. In addition, a temperature sensor 11 is integrated in the soot sensor 10, the process of heating the soot sensor 10 and thus the burning process of the soot particles 4, which is also referred to as burnout of the soot sensor 10, monitored and monitored by means of Temperaturauswerteelektronik 12.
Das Strommesselement 7, die Temperaturauswerteelektronik 12, die regelbare Spannungsquelle 15, der Temperatursensor 11 sowie der Heizstromschalter 9 sind hier exemplarisch als diskrete Bauteile dargestellt. Selbstverständlich können diese Bauteile als Be¬ standteile eines mikromechanischen Systems zusammen mit der interdigitalen Elektrodenstruktur 3 auf einem Chip realisiert werden oder Bestandteile einer mikroelektronischen Schaltung sein, die beispielsweise in einem Steuergerät 14 für den Ru߬ sensor 10 integriert ist. The current measuring element 7, the temperature evaluation electronics 12, the controllable voltage source 15, the temperature sensor 11 and the heating current switch 9 are shown here as examples as discrete components. Of course, these components can be realized as Be ¬ constituent parts of a micromechanical system together with the interdigital electrode structure 3 on a chip or components of a microelectronic circuit, which is integrated, for example, in a control unit 14 for the soot ¬ sensor 10.
Figur 3 zeigt ein in einem Kraftfahrzeug 16 fest installiertes Steuergerät 14 zur Funktionsdiagnose, zum Betrieb und zur Regeneration des Rußsensors 10. Der Rußsensor 10 weist eine fingerartig ineinandergreifende (interdigitale) Messelektro¬ denstruktur 3 auf, die bei einem intakten Rußsensor 10 keinerlei metallische Kurzschlüsse aufweist. Auf und zwischen die Mess¬ elektroden 3 setzen sich im Messbetrieb des Sensors Rußpartikel 4 ab, die zu einem Stromfluss zwischen den Messelektroden 3 führen, der als Maß für die Rußbeladung des Abgasstroms dient. Ab einer bestimmten Menge abgelagerter Rußpartikel 4 auf den Messelektroden 3 wird jedoch eine maximale Leitfähigkeit über die Rußschicht erreicht, die auch bei einer weiteren Rußablagerung nicht weiter vergrößert werden kann. Daher wird der Rußsensor 10 ab einer bestimmen Menge abgelagerter Rußpartikel "blind" für eine weitere Messung der Rußkonzentration im Abgas. Es ist nun notwendig den Rußsensor 10 durch das Abbrennen der Rußschicht auf den interdigitalen Messelektroden 3 zu regenerieren. Dazu wird ein Heizstrom durch das Einschalten des Heizstromschalters 9 von der Heizstromversorgung 8 zum Heizelement 2 geleitet. Der Ruß sensor 10 wird kontrolliert erwärmt. Die Kontrolle der Erwärmung des Rußsensors 10 erfolgt mit dem am oder im Rußsensor 10 aus- gebildeten Temperatursensor 11. Dieses Freibrennen des Rußsensors 10 erfolgt in Abhängigkeit vom Betriebszustand des Ver¬ brennungsmotors 17. Der Freibrennprozess wird zu einem Zeit¬ punkt gestartet, in dem der Betriebszustand des Verbrennungs¬ motors 17 keine sinnvolle Rußmessung zulässt. Damit wird die interdigitale Elektrodenstruktur 3 des Rußsensors 10 genau dann gereinigt, wenn ohnehin keine Rußmessung möglich oder sinnvoll wäre. Zu Zeitpunkten, in denen dann die Rußmessung in Abgasstrom durchführbar ist, ist auch der Rußsensor 10 betriebsbereit, was eine kontinuierliche Überwachung der Rußbeladung des Abgas- Stromes 6 ermöglicht. Der Betriebszustand des Verbrennungsmotors 17 kann zum Beispiel mit einem Verbrennungsmotortemperatursensor 18, der die Temperatur der Kühlflüssigkeit des Verbrennungs¬ motors 17 oder die Öltemperatur erfasst und/oder mit einem Kurbelwellendrehzahlsensor 19, der die Drehzahl der Kurbelwelle erfasst, überwacht werden. Figure 3 shows a in a motor vehicle 16 are fixedly installed control unit 14 to the functional diagnosis, operation and for the regeneration of the soot sensor 10. The soot sensor 10 has a finger interdigitated (interdigital) measuring electric ¬ denstruktur 3, which comprises of an intact soot sensor 10 no metallic shorts , On and between the measuring electrodes 3 ¬ set in the measuring operation of the sensor soot particles 4, which lead to a current flow between the measuring electrodes 3, which serves as a measure of the soot load of the exhaust gas stream. From a certain amount of deposited soot particles 4 on the measuring electrodes 3, however, a maximum conductivity is achieved via the soot layer, which can not be further increased even with a further soot deposition. Therefore, the soot sensor 10 becomes "blind" from a certain amount of deposited soot particles for further measurement of soot concentration in the exhaust gas. It is now necessary to regenerate the soot sensor 10 by burning off the soot layer on the interdigital measuring electrodes 3. For this purpose, a heating current is passed through the switching of the heating current switch 9 from the heating power supply 8 to the heating element 2. The soot sensor 10 is heated in a controlled manner. The control of the heating of the soot sensor 10 is performed with the off formed on or in the soot sensor 10 temperature sensor 11. This burning off of the soot sensor 10 is a function of the operating state of the United ¬ brennungsmotors 17. The free burning process is started at a time ¬ point where the operating state of the combustion ¬ motor 17 does not allow meaningful soot measurement. Thus, the interdigital electrode structure 3 of the soot sensor 10 is cleaned exactly when no soot measurement would be possible or useful anyway. At times when the soot measurement in the exhaust gas flow can then be carried out, the soot sensor 10 is also ready for operation, which permits continuous monitoring of soot loading of the exhaust gas flow 6. The operating state of the engine 17 may, for example, with an engine temperature sensor 18 that detects the temperature of the cooling liquid of the combustion ¬ motor 17 or the oil temperature and / or monitored with a crankshaft rotational speed sensor 19 which detects the rotational speed of the crankshaft.
Zur Veranschaulichung des Gesamtsystems ist in Figur 4 ein Kraftfahrzeug 16 mit einem Verbrennungsmotor 17 dargestellt. Der Verbrennungsmotor 17 führt den von ihm erzeugten Abgasstrom 6 über ein Abgasrohr 5 ab. Im Abgasrohr 5 ist ein Diesel-Partikel- Filter 20 zu erkennen. Vor und/oder nach dem Diesel-Partikel- Filter 20 ist ein Rußsensor 10 im Abgasrohr 5 angeordnet, der mit einem Steuergerät 14 verbunden ist, das auch das Strommesselement 7 enthalten kann. Der Kurbelwellendrehzahlsensor 19 und der Verbrennungsmotortemperatursensor 18 liefern dem Steuergerät 14 Informationen über den Betriebszustand des Ver¬ brennungsmotors 17. Mit diesen Informationen wird ein Zeitpunkt ausgewählt, zu dem das Freibrennen der interdigitalen Elektrodenstruktur 3 des Rußsensors 10 eingeleitet wird. Dieser Zeitpunkt kann zum Beispiel ein Neustart des Verbrennungsmotors 17 sein, der mit Hilfe des Kurbelwellendrehzahlsensors 19 vom Steuergerät 14 erkannt wird. Der Neustart des vollständig ab¬ gekühlten Verbrennungsmotors 17 wird mit Hilfe des Kurbel¬ wellendrehzahlsensors 19 und des Verbrennungsmotortemperatursensors 18 vom Steuergerät 14 erkannt. Dabei sollte allerdings der Zeitpunkt der Taupunktfreigäbe des Rußsensors abgewartet werden. Der Zeitpunkt des Abstellens des Verbrennungsmotors 17 wird wiederum mit Hilfe des Kurbelwellendrehzahlsensors 19 er¬ kannt . To illustrate the overall system, a motor vehicle 16 with an internal combustion engine 17 is shown in FIG. The internal combustion engine 17 discharges the exhaust gas stream 6 generated by it via an exhaust pipe 5. In the exhaust pipe 5, a diesel particulate filter 20 can be seen. Before and / or after the diesel particulate filter 20, a soot sensor 10 is arranged in the exhaust pipe 5, the is connected to a controller 14, which may also include the current measuring element 7. The crankshaft speed sensor 19 and the engine temperature sensor 18 provide the control unit 14 with information about the operating state of the Ver ¬ combustion engine 17. With this information, a time is selected, to which the burning of the interdigital electrode structure 3 of the soot sensor 10 is initiated. This time can be, for example, a restart of the internal combustion engine 17, which is detected by the control unit 14 with the aid of the crankshaft speed sensor 19. The restart of the fully from ¬ cooled internal combustion engine 17 is detected by the control unit 14 by means of the crankshaft ¬ speed sensor 19 and the engine temperature sensor 18. However, the time of the dew point release of the soot sensor should be awaited. The time of stopping the internal combustion engine 17 is in turn he ¬ known with the help of the crankshaft speed sensor 19.
Im Abgassystem moderner Verbrennungsmotoren 17 befinden sich zahlreiche Sensoren, die verbrennungs- und/oder abgasrelevante Parameter bestimmen. Dies sind zum Beispiel Temperatursensoren, SauerstoffSensoren, Sensoren zur Bestimmung des Brennstoff- Luft-Verhältnisses Lambda und Stickoxidsensoren. Im Abgas eines Verbrennungsmotors 17 befindet sich Wasserdampf. Der Wasserdampf kondensiert im kalten Abgassystem und kann dort Tropfen von flüssigem Wasser bilden. Da flüssiges Wasser heiße Sensoren zerstören kann, heizen die Sensoren nach dem Motorkaltstart nicht oder sehr wenig und warten die Wasserfreiheit des Abgases ab. Die Sensoren senden der Motorsteuerung keine Daten oder lediglich die Information "Sensor vorhanden, warte auf Messerlaubnis" . In the exhaust system of modern internal combustion engines 17 are numerous sensors that determine combustion and / or emission-related parameters. These are, for example, temperature sensors, oxygen sensors, sensors for determining the fuel-air ratio lambda and nitrogen oxide sensors. In the exhaust gas of an internal combustion engine 17 is water vapor. The water vapor condenses in the cold exhaust system and can form drops of liquid water there. Since liquid water can destroy hot sensors, the sensors do not heat after the engine cold start or very little and wait for the water freedom of the exhaust gas. The sensors do not send any data to the engine management system or merely the information "Sensor present, wait for approval".
Die Motorsteuerung des Verbrennungsmotors 17 berechnet aus den Motorbetriebsdaten und den gemessenen Temperaturen den Zeitpunkt, ab dem an der Sensorposition, zum Beispiel nach dem Katalysator oder dem Diesel-Partikel-Filter 20, kein flüssiges Wasser mehr zu erwarten ist. Ist dieser Zeitpunkt erreicht, sendet die Motorsteuerung dem Sensor ein Signal "kein Wasser mehr, Messerlaubnis erteilt". Der Sensor erkennt dieses Signal und beginnt seinen Aufheizvorgang. Die Information der Motorsteuerung an den Sensor "kein flüssiges Wasser mehr an der Stelle A" wird üblicherweise Taupunktfreigäbe A genannt. Würde vorher aufgeheizt und gemessen werde, könnte der Sensor von den Wassertropfen zerstört werden. Für den Rußsensor 10 ist die Taupunktfreigäbe an seiner Position der frühestmögliche Zeitpunkt nach dem Motorstart, ab dem frei¬ gebrannt werden darf. Bei einem typischen Fahrzeug aktueller Bauart erfolgt die Taupunktfreigäbe nach einem Motorkaltstart nach einigen Minuten. Fig. 5 zeigt das erfindungsgemäße Verfahren zum Betreiben eines Rußsensors 10 in einem Ablaufdiagramm. Bei Punkt 20 findet die Überwachung des Betriebszustandes des Verbrennungsmotors 17 statt. In Schritt 21 erfolgt die Überwachung der Kurbelwel¬ lendrehzahl, in Schritt 22 erfolgt die Überwachung der Temperatur des Verbrennungsmotors 17 und im Schritt 23 erfolgt die Über¬ wachung der Taupunkt-Freigabe des Rußsensors. Anhand dieser Schritte wird entschieden, ob ein Freibrennen der interdigitalen Elektrodenstruktur 3 des Rußsensors eingeleitet wird. Dabei können die in Schritt 21, 22 und 23 gemessenen Größen einzeln oder in Kombination miteinander zur Entscheidung beitragen. ZumThe engine control of the internal combustion engine 17 calculates from the engine operating data and the measured temperatures, the time from which at the sensor position, for example after the catalyst or the diesel particulate filter 20, no more liquid water is expected. Is this time reached, the motor control sends a signal to the sensor "no more water, permission granted". The sensor detects this signal and begins its heating process. The information of the engine control to the sensor "no more liquid water at the point A" is usually called dew point A release. If heated and measured beforehand, the sensor could be destroyed by the drops of water. For the soot sensor 10, the dew point release at its position is the earliest possible time after the engine start, from which it is free to burn . In a typical vehicle of current design, the dew point is released after a cold engine start after a few minutes. 5 shows the method according to the invention for operating a soot sensor 10 in a flowchart. At point 20, the monitoring of the operating state of the internal combustion engine 17 takes place. In step 21, the monitoring of the Kurbelwel ¬ lendrehzahl occurs in step 22 the monitoring of the temperature of the engine 17 and in step 23 is carried out takes place over ¬ monitoring the dew point of release of the soot sensor. On the basis of these steps, it is decided whether burnout of the interdigital electrode structure 3 of the soot sensor is initiated. The quantities measured in steps 21, 22 and 23 can contribute to the decision individually or in combination with one another. To the
Beispiel ist es denkbar, dass die Überwachung der Kurbelwel¬ lendrehzahl im Schritt 21 dazu führt, dass vom Steuergerät 14 erkannt wird, dass ein Neustart des Verbrennungsmotors 17 stattgefunden hat und aufgrund der in Schritt 22 durchgeführten Operation der Überwachung der Temperatur des Verbrennungsmotos 17 wird erkannt, dass dieser Neustart des Verbrennungsmotors 17 ein Kaltstart, also ein Neustart des vollständig abgekühlten Verbrennungsmotors 17, war. Diese beiden Kriterien werden im Schritt 24 dazu führen, dass die Position 26 angesprungen wird, wenn die Taupunktfreigäbe 23 erfolgt, wobei das Freibrennen der interdigitalen Elektrodenstruktur 3 als sinnvoll erkannt wird, woraufhin in Schritt 27 das Freibrennen der interdigitalen Elektrodenstruktur 3 des Rußsensors 10 gestartet wird. Nach dem Freibrennen der interdigitalen Elektrodenstruktur 3 kehrt der Ablauf zum Schritt 20, also der Überwachung des Betriebszustandes des Verbrennungsmotors 17 zurück. For example, it is conceivable that the monitoring of Kurbelwel ¬ lendrehzahl in step 21 to result that is detected by the control unit 14 that a restart of the internal combustion engine has taken place 17 and due to the carried out in step 22, operation of the monitoring of the temperature of the combustion Motos 17 is detected in that this restart of the internal combustion engine 17 was a cold start, ie a restart of the completely cooled internal combustion engine 17. These two criteria will result in step 24 that the position 26 is jumped when the dew point release 23 takes place, wherein the burn-out of the interdigital electrode structure 3 is recognized as meaningful, whereupon in step 27, the burning of the interdigital Electrode structure 3 of the soot sensor 10 is started. After the burning of the interdigital electrode structure 3, the sequence returns to step 20, that is to say the monitoring of the operating state of the internal combustion engine 17.
Es ist aber auch denkbar, dass in Schritt 24 entschieden wird, dass aufgrund eines Neustartes des Verbrennungsmotors 17, der durch die Überwachung der Kurbelwellendrehzahl in Schritt 21 erkannt wurde, in Kombination mit einer in Schritt 22 erkannten hohen Temperatur des Verbrennungsmotors 17 kein Freibrennen eingeleitet werden soll. Diese Entscheidung zum Nichtfreibrennen der interdigitalen Elektrodenstruktur erfolgt in Punkt 25, woraufhin der Ablauf erneut mit der Überwachung des Betriebs¬ zustandes des Verbrennungsmotors 17 in Punkt 20 fortgesetzt wird. However, it is also conceivable that it is decided in step 24 that due to a restart of the internal combustion engine 17, which was detected by monitoring the crankshaft speed in step 21, in combination with a detected in step 22 high temperature of the internal combustion engine 17 is not initiated burnout should. This decision for Nichtfreibrennen the interdigital electrode structure is carried out in point 25, whereupon the process is continued again with the monitoring of the operating ¬ state of the engine 17 at point 20.

Claims

Patentansprüche claims
Verfahren zum Betreiben eines Rußsensors (10) im Abgas¬ strang eines Verbrennungsmotors, wobei der Rußsensor (10) eine interdigitale Elektrodenstruktur (3) aufweist, an die eine Messspannung angelegt wird, wobei sich auf der in¬ terdigitalen Elektrodenstruktur (3) Rußpartikel (4) aus einem Abgasstrom (6) ablagern und der über die RußpartikelA method of operating a soot sensor (10) in the exhaust gas ¬ strand of an internal combustion engine, the soot sensor (10) having an interdigital electrode structure (3) to which a measuring voltage is applied, wherein on the in ¬ terdigitalen electrode structure (3) particulate matter (4 ) from an exhaust stream (6) and the deposit on the soot particles
(4) und die interdigitale Elektrodenstruktur (3) fließende Messstrom (IM) als Maß für die Rußbeladung des Rußsensors(4) and the interdigital electrode structure (3) flowing measuring current (I M ) as a measure of the soot load of the soot sensor
(10) ausgewertet wird und wobei der Rußsensor (10) ein Heizelement (2) zum Freibrennen der interdigitalen Elektrodenstruktur (3) aufweist, d a d u r c h g e k e n n z e i c h n e t , dass in Abhängigkeit vom Betriebszustand des Verbrennungsmotors (17) ein Zeitpunkt zum Freibrennen des Rußsensors (10) bestimmt wird und dann das Freibrennen der interdigitalen Elektrodenstruktur (3) durch ein Aufheizen des Rußsensors (10) mit dem Heizelement (2) beginnt. 2. Verfahren zum Betreiben eines Rußsensors (10) nach Anspruch(10) is evaluated and wherein the soot sensor (10) has a heating element (2) for burning the interdigital electrode structure (3), characterized in that depending on the operating condition of the internal combustion engine (17) a time for burning the soot sensor (10) is determined and then burning the interdigital electrode structure (3) begins by heating the soot sensor (10) with the heating element (2). 2. A method for operating a soot sensor (10) according to claim
1, d a d u r c h g e k e n n z e i c h n e t , dass der Zeitpunkt zum Freibrennen des Rußsensors (10) ein Neustart des Verbrennungsmotors ist. 3 . Verfahren zum Betreiben eines Rußsensors (10) nach Anspruch1, that is, that the time to burn out the soot sensor (10) is a restart of the internal combustion engine. 3. A method of operating a soot sensor (10) according to claim
2, d a d u r c h g e k e n n z e i c h n e t , dass der Zeitpunkt zum Freibrennen des Rußsensors (10) der Neustart des vollständig abgekühlten Verbrennungsmotors ist. 4 . Verfahren zum Betreiben eines Rußsensors (10) nach Anspruch 1, 2 oder 3, d a d u r c h g e k e n n z e i c h n e t , dass der Zeitpunkt zum Freibrennen des Rußsensors (10) das Erreichen der Taupunktfreigäbe des Rußsensors (10) ist. 5 . Verfahren zum Betreiben eines Rußsensors (10) nach Anspruch 1, 2, 3 oder 4, d a d u r c h g e k e n n z e i c h n e t , dass der Zeitpunkt zum Freibrennen des Rußsensors (10) da Abstellen des Verbrennungsmotors ist. 2, characterized in that the time to burn off the soot sensor (10) is the restart of the fully cooled internal combustion engine. 4. A method of operating a soot sensor (10) according to claim 1, 2 or 3, characterized in that the time to burn off the soot sensor (10) is to reach the dew point enable of the soot sensor (10). 5. Method for operating a soot sensor (10) according to claim 1, 2, 3 or 4, characterized in that the time for burnout of the soot sensor (10) is because the internal combustion engine is switched off.
Verfahren zum Betreiben eines Rußsensors (10) nach mindestens einem der vorgenannten Ansprüche, d a d u r c h g e k e n n z e i c h n e t , dass der Zeitpunkt zum Frei brennen des Rußsensors (10) innerhalb der Zeit der Regene ration des Diesel-Partikel-Filters (20) liegt. A method for operating a soot sensor (10) according to at least one of the preceding claims, characterized in that the time for free burning of the soot sensor (10) within the time of Regene ration of the diesel particulate filter (20).
Verfahren zum Betreiben eines Rußsensors (10) nach mindestens einem der vorgenannten Ansprüche, d a d u r c h g e k e n n z e i c h n e t , dass der Zeitpunkt zum Frei brennen des Rußsensors (10) bei einem Volllastbetrieb de Verbrennungsmotors (17) erreicht ist. Method for operating a soot sensor (10) according to at least one of the preceding claims, characterized in that the time for free burning of the soot sensor (10) in a full load operation of the internal combustion engine (17) is reached.
Verfahren zum Betreiben eines Rußsensors (10) nach mindestens einem der vorgenannten Ansprüche, d a d u r c h g e k e n n z e i c h n e t , dass der Zeitpunkt zum Frei brennen des Rußsensors (10) bei niedrigen Lastpunkten de Verbrennungsmotors (17) erreicht ist. A method for operating a soot sensor (10) according to at least one of the preceding claims, characterized in that the time for free burning of the soot sensor (10) at low load points de internal combustion engine (17) is reached.
EP11815758.5A 2010-12-15 2011-12-14 Method for operating a soot sensor Ceased EP2652280A2 (en)

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