EP1825247A1 - Resistive particle sensors with measuring electrodes - Google Patents

Resistive particle sensors with measuring electrodes

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Publication number
EP1825247A1
EP1825247A1 EP05796929A EP05796929A EP1825247A1 EP 1825247 A1 EP1825247 A1 EP 1825247A1 EP 05796929 A EP05796929 A EP 05796929A EP 05796929 A EP05796929 A EP 05796929A EP 1825247 A1 EP1825247 A1 EP 1825247A1
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EP
European Patent Office
Prior art keywords
measuring
sensor
electrodes
electrode
measuring electrode
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.)
Withdrawn
Application number
EP05796929A
Other languages
German (de)
French (fr)
Inventor
Lutz DORFMÜLLER
Ralf Schmidt
Markus Siebert
Sabine Rösch
Helmut Marx
Henrik Schittenhelm
Gerd Teike
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.)
Robert Bosch GmbH
Original Assignee
Robert Bosch 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 Robert Bosch GmbH filed Critical Robert Bosch GmbH
Publication of EP1825247A1 publication Critical patent/EP1825247A1/en
Withdrawn legal-status Critical Current

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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

Definitions

  • the invention relates to a sensor for determining the concentration of particles in gases, in particular soot particles, according to the preamble of claim 1.
  • a sensor with a device for detecting soot particles in the exhaust pipe can be mounted.
  • a resistive particle sensor which has at least one non-conductive carrier element, measuring electrodes being arranged on a carrier element.
  • the measuring electrodes are usually designed in an interdigital comb structure.
  • each measuring electrode is formed of a series of so-called individual finger electrodes, which are electrically connected to each other.
  • the finger electrodes of both measuring electrodes intermesh alternately like a comb, hence the term "interdigital
  • an increasing current can be measured at a constant applied voltage between the measuring electrodes, and the change in the respective measured variable - the sensor signal - can be used to derive the deposition or rate of deposition of the particles.
  • This measuring method corresponds to a collecting measuring principle and the sooted sensor surface therefore has to increase from time to time
  • an integrated heater may heat the sooty sensor so that the accumulated soot is completely burned off.
  • the sensor is then returned to its original state after the soot particles are burned, and a new measurement cycle with re-deposition and measurement of particles is thereby made possible.
  • Measuring and regeneration phases thus always alternate in time.
  • a disadvantage of this procedure results from the fact that no new attachment of the particles is possible during combustion.
  • the sensor according to the invention for determining the concentration of particles in gases, in particular soot particles has the advantage that the sensitivity of the measurement is improved.
  • the rate of deposition of particles can be increased at the same particle concentration and thus the measured values can be increased.
  • the measuring phase is increased compared to the regeneration phase.
  • the sensor can be kept longer in the measurement phase before the sensor signal shows saturation phenomena.
  • Figures Ia and Ib each an embodiment of a particle sensor with arranged on a support member measuring electrodes in plan view, and
  • Figures 2a, 2b and 2c each show a further embodiment of a particle sensor with arranged on a support element measuring electrodes in plan view.
  • the senor 1 has a determination of the concentration of particles in FIG. 1 a.
  • the space between the measuring electrodes 10, 15 serves as a measuring area 12, on which the particles to be detected are deposited.
  • the two measuring electrodes 10, 15 are connected via contacts 20, 25 with a measuring and control unit, not shown in the figures and can be acted upon with a voltage.
  • the measured value changes.
  • the measured value is the resistance
  • the two measuring electrodes 10, 15 are according to the invention so designed that upon application of a voltage between the measuring electrodes 10, 15, an asymmetrical electric field is formed on the measuring area 12.
  • a symmetrical electric field is characterized in that the field has a constant direction and strength throughout the field.
  • Such a field is formed, for example, by interdigital comb electrodes known in the art.
  • the individual finger electrodes are typically realized by unstructured, linear conductor tracks, which are all arranged parallel to one another. This results in a constant electric field between the finger electrodes.
  • the mutually facing sides 30, 35 of the first 10 and the second measuring electrode 15 are not arranged parallel to one another in the case of the sensor 1. Rather, the distance between the first 10 and the second measuring electrode 15 increases or decreases continuously along the course of the electrode. This results in a region with closely spaced sides 30, 35 of the measuring electrodes 10, 15, and a region with widely spaced sides 30, 35 of the measuring electrodes 10, 15. The transition from one region to the other is continuously flowing. When a voltage is applied, a non-constant field is created. Particles which precipitate on the measuring region 12 of the sensor 1 cause, via the formation of conductive paths, a reduction in resistance between the measuring electrodes 10, 15 and thereby lead to a sensor current. First, a conductive path is created in the region of the closely adjacent sides 30, 35. Because the distance between the measuring electrodes 10, 15 is very narrow at this point, a comparatively small range is sufficient
  • the measuring electrodes 10, 15 Since, due to the special design and arrangement of the measuring electrodes 10, 15, a larger measuring area 12 can be formed for the attachment of the particles, higher currents can also be achieved until they reach the saturation range compared to previously known interdigital measuring electrodes. The sensor signal is thus amplified.
  • At least one measuring electrode 10, 15 may have finger electrodes 40 of varying width. While in FIG. 1a the first and the second measuring electrodes 10, 15 have the shape of a triangle, in FIG. 2b the individual finger electrodes 40 of a measuring electrode 10, 15 have the shape of a triangle. As a result, the distance between two adjacent finger electrodes 40 continuously changes along the length of the finger electrodes 40. This results in the same advantageous effects as described in the first embodiment. Also, areas are generated by the tip-shaped design with a targeted preferential growth direction of the deposited soot particles.
  • FIG. 2 a or in addition (FIGS. 2 b, 2 c), ie combined with one another for the varying spacing of the measuring electrodes 10, 15 or finger electrodes 40, it is proposed that at least one measuring electrode 10, 15 pass along the other measuring electrode 15, 10 facing side 30, 35 or along the finger electrodes 40 has a structure 45.
  • Structure 45 is formed by regularly arranged peaks, squares, dots or other geometric shapes. Such structures 45 on the electrode sides lead to an increased field at an applied voltage.
  • the structured finger electrodes 40 as in FIG. 2 a, lead to a non-constant electric field on the measuring region 12.
  • the polarisable or already charged particles are preferentially deposited in comparison with electrodes without structured sides with uniformly applied voltage. Due to the increased field gradients, this increases the particle accumulation rate. Consequently, higher sensor currents are achieved at a given particle concentration. This can then allow the use of simplified measuring electronics in the control unit for signal evaluation, since leakage currents or the EMC currents (electromagnetic compatibility) exert only small disturbances.
  • the measuring electrodes 10, 15 are designed so that upon application of a voltage between the measuring electrodes 10, 15, an asymmetric electric field is formed on the measuring area 12.
  • the asymmetric electric field is a spatially inhomogeneous electrical Field.
  • the special design of the field distribution enables targeted spatial control of particle accumulation. In particular, the formation of conductive paths in preferred areas can be controlled. The temporal path growth can therefore be directed in a desired direction.
  • more than two measuring electrodes 10, 15 can be provided for this, z.
  • at least one center electrode can be arranged between the first and the second measuring electrodes 10, 15. The geometric shape and the applied potential at all electrodes must be adapted to the desired field distribution.

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  • Chemical & Material Sciences (AREA)
  • Dispersion Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

Abstract

The invention relates to a sensor (1), for determination of the concentration of particles in gases, in particular, of soot particles, comprising at least one support element (5) and a measuring region (12) between at least one first (10) and one second measuring electrode (15). Both measuring electrodes (10, 15) are embodied such that, on application of a voltage between the measuring electrodes (10, 15), an asymmetric electrical field is generated in the measuring region (12), for example, the facing sides (30, 35) of the first (10) and the second measuring electrode (15) may not be arranged parallel to each other. It is also possible that at least one measuring electrode (10, 15) comprises a structure (45) along the side (30, 35) thereof facing the other measuring electrode (15, 10) or along the finger electrodes (40).

Description

Resistive Partikelsensoren mit MesselektrodenResistive particle sensors with measuring electrodes
Stand der TechnikState of the art
Die Erfindung betrifft einen Sensor zur Bestimmung der Konzentration von Partikeln in Gasen, insbesondere von Rußpartikeln, nach dem Oberbegriff des Anspruchs 1.The invention relates to a sensor for determining the concentration of particles in gases, in particular soot particles, according to the preamble of claim 1.
Im Zuge der umweltfreundlichen Bemühungen, den Rußausstoß von Dieselmotoren zu reduzieren, entsteht die Notwendigkeit, die Konzentration der Rußpartikeln im Abgas einfach bestimmen zu können. Insbesondere ist eine Überwachung des Rußgehalts nach einem Dieselpartikelfilter (DPF) während des Fahrbetriebes sinnvoll. Darüber hinaus ist eine Beladungsprognose eines Dieselpartikelfilters zur Regenerationskontrolle notwendig, um eine hohe Systemsicherheit zu erreichen.In the course of the environmentally friendly efforts to reduce the soot emissions of diesel engines, the need arises to be able to easily determine the concentration of soot particles in the exhaust gas. In particular, it makes sense to monitor the soot content after a diesel particle filter (DPF) during driving. In addition, a load forecast of a diesel particulate filter for regeneration control is necessary in order to achieve high system safety.
Zur Bestimmung der Rußkonzentration im Abgas vonTo determine the soot concentration in the exhaust gas of
Brennkraftmaschinen kann ein Sensor mit einer Vorrichtung zur Detektion von Rußpartikeln im Abgasrohr montiert werden.Internal combustion engines, a sensor with a device for detecting soot particles in the exhaust pipe can be mounted.
Aus DE 101 33 384 Al oder auch aus DE 33 04 548 Al ist jeweils ein resistiver Partikelsensor bekannt, der mindestens ein nichtleitendes Trägerelement aufweist, wobei auf einem Trägerelement Messelektroden angeordnet sind. Die Messelektroden sind üblicherweise in einer interdigitalen Kammstruktur ausgeführt. In einer interdigitalen Kammstruktur wird jede Messelektrode aus einer Reihe von sogenannten einzelnen Fingerelektroden gebildet, die elektrisch miteinander verbunden sind. Die Fingerelektroden beider Messelektroden greifen kammartig abwechselnd ineinander, daher die Bezeichnung „interdigitaleFrom DE 101 33 384 A1 or also from DE 33 04 548 A1, a resistive particle sensor is known, which has at least one non-conductive carrier element, measuring electrodes being arranged on a carrier element. The measuring electrodes are usually designed in an interdigital comb structure. In an interdigital Comb structure, each measuring electrode is formed of a series of so-called individual finger electrodes, which are electrically connected to each other. The finger electrodes of both measuring electrodes intermesh alternately like a comb, hence the term "interdigital
Kammstruktur". Eine Anlagerung von Partikeln auf der zwischen den Elektroden aufgespannten Messfläche, der sogenannten Kriechstromfläche, führt zu einer Leitfähigkeits- oder Impedanzänderung der Messfläche zwischen den Fingern der Elektroden. Mit steigender Partikelkonzentration auf der Messfläche nimmt beispielsweise der Widerstand, der Realteil der Impedanz, ab. Alternativ kann ein zunehmender Strom bei konstanter angelegter Spannung zwischen den Messelektroden gemessen werden. Aus der Änderung der jeweiligen Messgröße - dem Sensorsignal - lässt sich die Anlagerung bzw. die Anlagerungsrate der Partikeln ableiten.An accumulation of particles on the measuring surface spanned between the electrodes, the so-called leakage current surface, leads to a change in the conductivity or impedance of the measuring surface between the fingers of the electrodes With increasing particle concentration on the measuring surface, for example, the resistance, the real part of the impedance, increases. Alternatively, an increasing current can be measured at a constant applied voltage between the measuring electrodes, and the change in the respective measured variable - the sensor signal - can be used to derive the deposition or rate of deposition of the particles.
Dieses Messverfahren entspricht einem sammelnden Messprinzip und die verrußte Sensoroberfläche muss daher von Zeit zuThis measuring method corresponds to a collecting measuring principle and the sooted sensor surface therefore has to increase from time to time
Zeit - immer wenn ein definierter Sättigungsstrom oder ein anderer Schwellwert erreicht ist - von den leitfähigen Rußpartikeln befreit werden. Für eine Regeneration der verrußten Oberfläche kann eine Hochspannung zwischen den Elektroden angelegt werden, um über den Stromfluss dieTime - always when a defined saturation current or another threshold is reached - are freed from the conductive soot particles. For regeneration of the sooted surface, a high voltage may be applied between the electrodes to conduct the current flow
Rußpartikeln zu verbrennen. Alternativ kann ein integrierter Heizer den mit Ruß behafteten Sensor heizen, so dass der angesammelte Ruß vollständig abgebrannt wird. Der Sensor befindet sich dann nach der Verbrennung der Rußpartikeln wieder im ursprünglichen Zustand, und ein neuer Messzyklus mit erneuter Anlagerung und Messung von Partikeln wird dadurch ermöglicht. Mess- und Regenerationsphasen wechseln sich also zeitlich immer ab. Ein Nachteil dieser Vorgehensweise ergibt sich dadurch, dass während der Verbrennung keine neue Anlagerung der Partikeln möglich ist. Auch nach der Regeneration kann nicht sofort Ruß wieder angesammelt werden, der Sensor benötigt aufgrund seiner thermischen Trägheit für die Thermalisierung des Sensorelementes mit dem Abgas eine bestimmte Zeit. Da während der Regenerations- und der darauffolgenden Abkühlphase des Sensors kein Ruß angesammelt werden kann, ist der Sensor während dieser Phasen unempfindlich gegenüber einer möglicherweise vorhandenen Rußkonzentration. Eine möglichst lange Messphase ist daher anzustreben. Gleichzeitig muss der Messwert so groß sein, dass eine frühe und deutliche Aussage zu der Partikelkonzentration ermöglicht wird.To burn soot particles. Alternatively, an integrated heater may heat the sooty sensor so that the accumulated soot is completely burned off. The sensor is then returned to its original state after the soot particles are burned, and a new measurement cycle with re-deposition and measurement of particles is thereby made possible. Measuring and regeneration phases thus always alternate in time. A disadvantage of this procedure results from the fact that no new attachment of the particles is possible during combustion. Even after the regeneration can not be immediately accumulated soot, the sensor requires due to its thermal inertia for the thermalization of the sensor element with the exhaust gas for a certain time. Since no soot can accumulate during the regeneration and the subsequent cooling phase of the sensor, the sensor is insensitive to any soot concentration during these phases. A long measurement phase is therefore desirable. At the same time, the measured value must be large enough to provide an early and clear indication of the particle concentration.
Vorteile der ErfindungAdvantages of the invention
Der erfindungsgemäße Sensor zur Bestimmung der Konzentration von Partikeln in Gasen, insbesondere von Rußpartikeln, hat den Vorteil, dass die Empfindlichkeit der Messung verbessert wird. Insbesondere kann auch die Anlagerungsrate von Partikeln bei gleicher Partikelkonzentration verstärkt und damit die Messwerte erhöht werden.The sensor according to the invention for determining the concentration of particles in gases, in particular soot particles, has the advantage that the sensitivity of the measurement is improved. In particular, the rate of deposition of particles can be increased at the same particle concentration and thus the measured values can be increased.
Gleichzeitig wird die Messphase gegenüber der Regenerationsphase erhöht. Auf eine einfache Weise wird erreicht, dass der Sensor länger in der Messphase gehalten werden kann, bevor das Sensorsignal Sättigungserscheinungen zeigt.At the same time, the measuring phase is increased compared to the regeneration phase. In a simple way it is achieved that the sensor can be kept longer in the measurement phase before the sensor signal shows saturation phenomena.
Vorteilhafte Weiterbildungen des Sensors sind in den Unteransprüchen angegeben und in der Beschreibung beschrieben. ZeichnungAdvantageous developments of the sensor are specified in the subclaims and described in the description. drawing
Ausführungsbeispiele der Erfindung werden anhand der Zeich- nung und der nachfolgenden Beschreibung näher erläutert. Es zeigen:Embodiments of the invention will be explained in more detail with reference to the drawing and the following description. Show it:
Figuren Ia und Ib jeweils ein Ausführungsbeispiel eines Partikelsensors mit auf einem Trägerelement angeordneten Messelektroden in Draufsicht, undFigures Ia and Ib each an embodiment of a particle sensor with arranged on a support member measuring electrodes in plan view, and
Figuren 2a, 2b und 2c jeweils ein weiteres Ausführungsbeispiel eines Partikelsensors mit auf einem Trägerelement angeordneten Messelektroden in Draufsicht.Figures 2a, 2b and 2c each show a further embodiment of a particle sensor with arranged on a support element measuring electrodes in plan view.
Beschreibung der AusführungsbeispieleDescription of the embodiments
In einem ersten Ausführungsbeispiel nach Figur Ia weist der Sensor 1 zur Bestimmung der Konzentration von Partikeln inIn a first exemplary embodiment according to FIG. 1 a, the sensor 1 has a determination of the concentration of particles in FIG
Gasen, insbesondere von Rußpartikeln, ein Trägerelement 5 auf, auf welchem als Messvorrichtung eine erste 10 und eine zweite Messelektrode 15 angeordnet sind. Der Raum zwischen den Messelektroden 10, 15 dient als Messbereich 12, auf dem sich die zu detektierenden Partikeln anlagern. Die beiden Messelektroden 10, 15 sind über Kontaktierungen 20, 25 mit einer in den Figuren nicht dargestellten Mess- und Steuereinheit verbindbar und mit einer Spannung beaufschlagbar. Je nach Anlagerungszustand der Partikeln auf dem Messbereich 20 ändert sich der Messwert. Abhängig vom Messmodus ist der Messwert der WiderstandGases, in particular of soot particles, a carrier element 5, on which a first measuring device 10 and a second measuring electrode 15 are arranged. The space between the measuring electrodes 10, 15 serves as a measuring area 12, on which the particles to be detected are deposited. The two measuring electrodes 10, 15 are connected via contacts 20, 25 with a measuring and control unit, not shown in the figures and can be acted upon with a voltage. Depending on the accumulation state of the particles on the measuring range 20, the measured value changes. Depending on the measuring mode, the measured value is the resistance
(Impedanz) oder die Stromstärke, die über die Messelektroden 10, 15 gemessen werden. Wie zuvor erläutert, kann aus den Messwerten schließlich die Rußkonzentration in einem Gas bestimmt werden. Die beiden Messelektroden 10, 15 sind dabei erfindungsgemäß so gestaltet, dass unter Beaufschlagung einer Spannung zwischen den Messelektroden 10, 15 ein asymmetrisches elektrisches Feld auf dem Messbereich 12 gebildet wird. Ein symmetrisches elektrisches Feld ist dadurch gekennzeichnet, dass das Feld überall im Feld eine konstante Richtung und Stärke aufweist. Solch ein Feld wird beispielsweise von aus dem Stand der Technik bekannten interdigitalen Kammelektroden gebildet. Die einzelnen Fingerelektroden werden typischerweise durch unstrukturierte, lineare Leiterbahnen realisiert, die alle zueinander parallel angeordnet sind. Daraus resultiert ein konstantes elektrisches Feld zwischen den Fingerelektroden.(Impedance) or the current, which are measured via the measuring electrodes 10, 15. As explained above, finally, the soot concentration in a gas can be determined from the measured values. The two measuring electrodes 10, 15 are according to the invention so designed that upon application of a voltage between the measuring electrodes 10, 15, an asymmetrical electric field is formed on the measuring area 12. A symmetrical electric field is characterized in that the field has a constant direction and strength throughout the field. Such a field is formed, for example, by interdigital comb electrodes known in the art. The individual finger electrodes are typically realized by unstructured, linear conductor tracks, which are all arranged parallel to one another. This results in a constant electric field between the finger electrodes.
Wie aber aus Figur 1 erkennbar, sind beim Sensor 1 die zueinander zugewandten Seiten 30, 35 der ersten 10 und der zweiten Messelektrode 15 nicht parallel zueinander angeordnet. Vielmehr nimmt der Abstand zwischen der ersten 10 und der zweiten Messelektrode 15 entlang des Elektrodenverlaufs kontinuierlich zu bzw. ab. Dadurch entsteht ein Bereich mit eng beieinander liegenden Seiten 30, 35 der Messelektroden 10, 15, und ein Bereich mit weit voneinander liegenden Seiten 30, 35 der Messelektroden 10, 15. Der Übergang von einem zum anderen Bereich ist dabei kontinuierlich fließend. Bei Anlegen einer Spannung entsteht ein nicht konstantes Feld. Partikel, die sich auf dem Messbereich 12 des Sensors 1 niederschlagen, verursachen über die Bildung leitfähiger Pfade eine Widerstandsreduktion zwischen den Messelektroden 10, 15 und führen dadurch zu einem Sensorstrom. Zunächst wird im Bereich der eng aneinanderliegenden Seiten 30, 35 ein leitfähiger Pfad erzeugt. Weil der Abstand zwischen den Messelektroden 10, 15 an dieser Stelle sehr eng ist, reicht eine vergleichsweise geringeHowever, as can be seen from FIG. 1, the mutually facing sides 30, 35 of the first 10 and the second measuring electrode 15 are not arranged parallel to one another in the case of the sensor 1. Rather, the distance between the first 10 and the second measuring electrode 15 increases or decreases continuously along the course of the electrode. This results in a region with closely spaced sides 30, 35 of the measuring electrodes 10, 15, and a region with widely spaced sides 30, 35 of the measuring electrodes 10, 15. The transition from one region to the other is continuously flowing. When a voltage is applied, a non-constant field is created. Particles which precipitate on the measuring region 12 of the sensor 1 cause, via the formation of conductive paths, a reduction in resistance between the measuring electrodes 10, 15 and thereby lead to a sensor current. First, a conductive path is created in the region of the closely adjacent sides 30, 35. Because the distance between the measuring electrodes 10, 15 is very narrow at this point, a comparatively small range is sufficient
Anlagerung der Partikel aus, um schnell einen leitfähigen Pfad auszubilden und ein Messsignal auszulösen. Damit steigt die Empfindlichkeit des Sensors 1. Im Verlauf der sukzessiven Anlagerung weiterer Partikel werden auch leitfähige Pfade zwischen Seiten 30, 35 der Messelektroden 10, 15 gebildet, die weiter voneinander entfernt liegen. Aufgrund der Perkolationseigenschaften des angelagerten Rußes wird bei jeder Vollendung eines zusätzlichen leitfähigen Pfades ein starker Anstieg der Leitfähigkeit des gesamten Messbereichs 12 stattfinden, der über die Messelektroden 10, 15 bestimmt werden kann. Dadurch wird eine stärkere Signalerhöhung über einen längeren Zeitraum erreicht, als dies bei parallel zueinander angeordneten Messelektroden möglich wäre. Nach dem Kurzschließen der Messelektroden 10, 15 entlang der gesamten Seiten 30, 35 erhöhen weitere Anlagerungen die Leitfähigkeit zusätzlich kontinuierlich weiter, d. h. eine Messung ist auch während dieser Phase möglich. Da durch die besondere Gestaltung und Anordnung der Messelektroden 10, 15 ein größerer Messbereich 12 zur Anlagerung der Partikel gebildet werden kann, können zudem höhere Ströme erreicht werden bis sie in den Sättigungsbereich gelangen als im Vergleich zu bisher bekannten interdigitalen Messelektroden. Das Sensorsignal wird also verstärkt.Accumulation of the particles to quickly form a conductive path and trigger a measurement signal. Thus, the sensitivity of the sensor 1 increases. In the course of the successive addition of additional particles also become conductive paths formed between sides 30, 35 of the measuring electrodes 10, 15, which are farther apart. Due to the percolation properties of the deposited soot, a large increase in the conductivity of the entire measuring region 12 will occur with each completion of an additional conductive path, which can be determined via the measuring electrodes 10, 15. As a result, a stronger signal increase over a longer period of time is achieved than would be possible with measuring electrodes arranged parallel to one another. After short-circuiting the measuring electrodes 10, 15 along the entire sides 30, 35 further additions further increase the conductivity continuously, ie a measurement is also possible during this phase. Since, due to the special design and arrangement of the measuring electrodes 10, 15, a larger measuring area 12 can be formed for the attachment of the particles, higher currents can also be achieved until they reach the saturation range compared to previously known interdigital measuring electrodes. The sensor signal is thus amplified.
Auch bei herkömmlicher interdigitaler Kammstruktur kann ein variierender Abstand zwischen den Fingerelektroden durch eine Modifizierung der Form erzielt werden. Wie in Figur Ib dargestellt, kann mindestens eine Messelektrode 10, 15 Fingerelektroden 40 mit variierender Breite aufweisen. Während in Figur Ia die erste und die zweite Messelektrode 10, 15 die Form eines Dreiecks aufweist, haben in Figur 2b die einzelnen Fingerelektroden 40 einer Messelektrode 10, 15 die Form eines Dreiecks. Dadurch ändern sich der Abstand zwischen zwei benachbarten Fingerelektroden 40 entlang der Länge der Fingerelektroden 40 kontinuierlich. Daraus resultieren die gleichen vorteilhaften Effekte wie bei der ersten Ausführungsform beschrieben. Auch werden durch die spitzenförmige Ausführung Bereiche mit einer gezielten Vorzugswachstumsrichtung der angelagerten Rußpartikel erzeugt. Bisher beschriebene Ausführungsbeispiele weisen stets glatte, unstrukturierte Seiten der Messelektroden 10, 15 oder der einzelnen Fingerelektroden 40 auf. Alternativ (Fig. 2a) oder zusätzlich (Fig. 2b, 2c), d. h. miteinander kombiniert zum variierenden Abstand der Messelektroden 10, 15 bzw. Fingerelektroden 40 wird vorgeschlagen, dass mindestens eine Messelektrode 10, 15 entlang an der der anderen Messelektrode 15, 10 zugewandten Seite 30, 35 oder entlang an den Fingerelektroden 40 eine Struktur 45 aufweist. DieEven with conventional interdigital comb structure, a varying distance between the finger electrodes can be achieved by modifying the shape. As shown in FIG. 1b, at least one measuring electrode 10, 15 may have finger electrodes 40 of varying width. While in FIG. 1a the first and the second measuring electrodes 10, 15 have the shape of a triangle, in FIG. 2b the individual finger electrodes 40 of a measuring electrode 10, 15 have the shape of a triangle. As a result, the distance between two adjacent finger electrodes 40 continuously changes along the length of the finger electrodes 40. This results in the same advantageous effects as described in the first embodiment. Also, areas are generated by the tip-shaped design with a targeted preferential growth direction of the deposited soot particles. Embodiments described so far always have smooth, unstructured sides of the measuring electrodes 10, 15 or of the individual finger electrodes 40. Alternatively (FIG. 2 a) or in addition (FIGS. 2 b, 2 c), ie combined with one another for the varying spacing of the measuring electrodes 10, 15 or finger electrodes 40, it is proposed that at least one measuring electrode 10, 15 pass along the other measuring electrode 15, 10 facing side 30, 35 or along the finger electrodes 40 has a structure 45. The
Struktur 45 wird dabei durch regelmäßig angeordnete Spitzen, Quadrate, Punkte oder andere geometrische Formen gebildet. Solche Strukturen 45 an den Elektrodenseiten führen bei einer angelegten Spannung zu einer Feldüberhöhung. Schon allein die strukturierten Fingerelektroden 40 wie in Figur 2a führen zu einem nicht konstanten elektrischen Feld auf dem Messbereich 12. Durch diese Feldüberhöhung werden die polarisierbaren oder bereits geladenen Partikel im Vergleich zu Elektroden ohne strukturierte Seiten bei gleich stark angelegter Spannung bevorzugt angelagert. Aufgrund der verstärkten Feldgradienten erhöht sich damit die Partikelanlagerungsrate. Folglich werden höhere Sensorströme bei gegebener Partikelkonzentration erzielt. Dies kann dann die Verwendung vereinfachter Messelektronik im Steuergerät zur Signalauswertung ermöglichen, da Leckströme bzw. die EMV-Ströme (elektromagnetische Verträglichkeit) nur noch kleine Störeinflüsse ausüben.Structure 45 is formed by regularly arranged peaks, squares, dots or other geometric shapes. Such structures 45 on the electrode sides lead to an increased field at an applied voltage. The structured finger electrodes 40, as in FIG. 2 a, lead to a non-constant electric field on the measuring region 12. By means of this field enhancement, the polarisable or already charged particles are preferentially deposited in comparison with electrodes without structured sides with uniformly applied voltage. Due to the increased field gradients, this increases the particle accumulation rate. Consequently, higher sensor currents are achieved at a given particle concentration. This can then allow the use of simplified measuring electronics in the control unit for signal evaluation, since leakage currents or the EMC currents (electromagnetic compatibility) exert only small disturbances.
Zusammenfassend wird festgestellt, dass bei allen Ausführungsbeispielen die Messelektroden 10, 15 so gestaltet sind, dass unter Beaufschlagung einer Spannung zwischen den Messelektroden 10, 15 ein asymmetrisches elektrisches Feld auf dem Messbereich 12 gebildet wird. Das asymmetrische elektrische Feld ist ein räumlich inhomogenes elektrisches Feld. Durch die spezielle Ausbildung der Feldverteilung wird eine gezielte räumliche Steuerung der Partikelanlagerung ermöglicht. Insbesondere kann die Ausbildung leitfähiger Pfade in bevorzugten Bereichen gesteuert werden. Das zeitliche Pfadwachstum kann also in eine gewünschte Richtung gelenkt werden. Falls notwendig, können hierfür mehr als zwei Messelektroden 10, 15 vorgesehen werden, z. B. kann zusätzlich mindestens eine in den Figuren nicht dargestellte Mittelelektrode zwischen der ersten und der zweiten Messelektrode 10, 15 angeordnet werden. Dabei ist die geometrische Form und das angelegte Potential an allen Elektroden der gewünschten Feldverteilung anzupassen. In summary, it is found that in all embodiments, the measuring electrodes 10, 15 are designed so that upon application of a voltage between the measuring electrodes 10, 15, an asymmetric electric field is formed on the measuring area 12. The asymmetric electric field is a spatially inhomogeneous electrical Field. The special design of the field distribution enables targeted spatial control of particle accumulation. In particular, the formation of conductive paths in preferred areas can be controlled. The temporal path growth can therefore be directed in a desired direction. If necessary, more than two measuring electrodes 10, 15 can be provided for this, z. For example, in addition at least one center electrode, not shown in the figures, can be arranged between the first and the second measuring electrodes 10, 15. The geometric shape and the applied potential at all electrodes must be adapted to the desired field distribution.

Claims

Ansprüche claims
1. Sensor (1) zur Bestimmung der Konzentration von Partikeln in Gasen, insbesondere von Rußpartikeln, mit mindestens einem Trägerelement (5) und einem Messbereich (12) zwischen mindestens einer ersten (10) und einer zweiten Messelektrode (15) , d a d u r c h g e k e n n z e i c h n e t, dass die beiden Messelektroden (10, 15) so gestaltet sind, dass unter Beaufschlagung einer Spannung zwischen den Messelektroden (10, 15) ein asymmetrisches elektrisches Feld auf dem Messbereich (12) gebildet wird.1. Sensor (1) for determining the concentration of particles in gases, in particular soot particles, with at least one carrier element (5) and a measuring region (12) between at least a first (10) and a second measuring electrode (15), characterized in that the two measuring electrodes (10, 15) are designed so that an asymmetrical electric field is formed on the measuring area (12) when a voltage is applied between the measuring electrodes (10, 15).
2. Sensor (1) nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t, dass die zueinander zugewandten Seiten (30, 35) der ersten (10) und der zweiten Elektrode (15) nicht parallel zueinander angeordnet sind.2. Sensor (1) according to claim 1, characterized in that the mutually facing sides (30, 35) of the first (10) and the second electrode (15) are not arranged parallel to each other.
3. Sensor (1) nach Anspruch 1 oder 2, d a d u r c h g e k e n n z e i c h n e t, dass der Abstand zwischen der ersten (10) und der zweiten Messelektrode (15) entlang des Elektrodenverlaufs kontinuierlich zu- oder abnimmt.3. Sensor (1) according to claim 1 or 2, characterized in that the distance between the first (10) and the second measuring electrode (15) along the course of the electrode continuously increases or decreases.
4. Sensor (1) nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t, dass die erste (10) und zweite Messelektrode (15) zusammen eine interdigitale Kammstruktur bilden, wobei mindestens eine Messelektrode (10, 15) Fingerelektroden (40) mit variierender Breite aufweist. 4. Sensor (1) according to claim 1, characterized in that the first (10) and second measuring electrode (15) together form an interdigitated comb structure, wherein at least one measuring electrode (10, 15) finger electrodes (40) having varying width.
5. Sensor (1) nach einem der Ansprüche 1 bis 4, d a d u r c h g e k e n n z e i c h n e t, dass mindestes eine Messelektrode (10, 15) oder die Fingerelektroden (40) mindestens einer Messelektrode (10, 15) die Form eines Dreiecks aufweist.5. Sensor (1) according to one of claims 1 to 4, in that a minimum of one measuring electrode (10, 15) or the finger electrodes (40) of at least one measuring electrode (10, 15) has the shape of a triangle.
6. Sensor (1) nach einem der Ansprüche 1 bis 5, d a d u r c h g e k e n n z e i c h n e t, dass mindestens eine Messelektrode (10, 15) entlang an der der anderen Messelektrode (15, 10) zugewandten Seite (30, 35) oder entlang an den Fingerelektroden (40) eine Struktur (45) aufweist.6. Sensor (1) according to one of claims 1 to 5, characterized in that at least one measuring electrode (10, 15) along on the other measuring electrode (15, 10) facing side (30, 35) or along the finger electrodes (40 ) has a structure (45).
7. Sensor (1) nach Anspruch 6, d a d u r c h g e k e n n z e i c h n e t, dass die Struktur (45) durch regelmäßig angeordnete Spitzen, Quadrate, Punkte oder andere geometrische Formen gebildet wird.7. Sensor (1) according to claim 6, characterized in that the structure (45) is formed by regularly arranged peaks, squares, points or other geometric shapes.
8. Sensor (1) nach einem der Ansprüche 1 bis 7, d a d u r c h g e k e n n z e i c h n e t, dass mindestens eine Mittelelektrode zwischen der ersten (10) und der zweiten Messelektrode (15) angeordnet ist. 8. Sensor (1) according to claim 1, wherein at least one center electrode is arranged between the first (10) and the second measuring electrode (15).
EP05796929A 2004-12-10 2005-10-17 Resistive particle sensors with measuring electrodes Withdrawn EP1825247A1 (en)

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