DE10322427A1 - Soot or particle detector for a gas flow, especially an exhaust gas flow, comprises a solid state electrolyte with at least two oxygen pump cells each assigned to at least an electrode pair - Google Patents

Abstract

Sensor for detecting particles in a gas flow, especially soot particles in an exhaust gas flow, has measurement electrodes (9A, 9B, 10A, 10B) that are arranged on a substrate (8) of insulating material that incorporates a solid state electrolyte in which there are at least two oxygen pump cells, each assigned to at least one electrode pair. At least one of the oxygen pump cells has a diffusion barrier (19, 20) pre-connected to it with two further electrodes allocated to it for application of a high voltage.

Description

State of technology

The Invention is based on a sensor for the detection of particles in one Gas flow, especially soot particles in an exhaust gas flow, according to the in Preamble of claim 1 further defined kind.

The Detection of particles in a gas stream is based on practice made different ways. There is a possibility of detection in the measurement of charges by a measuring electrode system passing electrically charged particles can be influenced. Moreover is the determination of particles in a gas stream using optical Methods such as B. known from a light barrier or turbidity.

Of another is the detection of particles in a gas stream with a known sensor of the type mentioned in the introduction, which in particular in a motor vehicle with a diesel internal combustion engine to check the functionality a soot filter arranged in an exhaust line is used.

For example is a known sensor of the type mentioned in the introduction Exposed substrate to an exhaust gas, so that possibly in the Particles containing exhaust gas, such as soot particles, on the substrate can deposit. By the deposition of the soot particles the electrical resistance on the substrate decreases. Two electrodes are used to measure the electrical resistance, which are arranged on the substrate.

Advantages of invention

The Sensor for the detection of particles in a gas stream, in particular of soot particles in an exhaust gas flow, with the features according to the preamble of Claim 1, wherein the substrate is a solid electrolyte comprises, in which at least two oxygen pump cells are formed which are each assigned a pair of electrodes has the The advantage of using this sensor is a semi-continuous, high-temperature-resistant measuring method carried out can be long-term stable with little effort can be used.

The Sensor according to the invention can for example be arranged in a Exhaust system of a motor vehicle with a diesel engine or for use in the field of house technology for oil heating be designed, being a simple and inexpensive review of the operability of filters. Depending on the area of application, the sensor can be designed accordingly casing be arranged.

The Solid electrolyte the sensor according to the invention is, for example, a ceramic, which is conductive for oxygen from a temperature of approximately 400 ° C.

The Oxygen pumping cells formed in the solid electrolyte have interfaces on, which are each formed by an electrode and on both sides of the solid electrolyte are arranged. If the oxygen content of the respective two interfaces differs present medium, so occurs between the two interfaces a voltage gradient on which as a measure of yourself differing oxygen content can be used. insofar this mode of operation of the oxygen pump cells corresponds to the mode of operation one with λ probes trained oxygen pump cell.

The Sensor according to the invention can be designed so that one of the Oxygen pumping cells through particles contained in an exhaust gas like this impaired is that their oxygen pumping power is stronger than that of the others Oxygen pump cell wears off. From this leaves deduce a particle concentration in the exhaust gas.

The two electrode pairs can be in a special embodiment a common electrode can be assigned. In this case includes the sensor has three electrodes that connect the two oxygen pump cells assigned.

The Electrodes of the sensor according to the invention can be made of platinum, for example exist and according to a thick film technology process the substrate must be printed.

The Sensor can be formed from several planar layers, wherein the solid electrolyte forms one of these planar layers. Then the electrode pairs of the oxygen pump cells on both sides of this planar layer arranged. The electrodes arranged on one side of this layer are each exposed to a reference, such as the environment.

In an advantageous embodiment of the sensor according to the invention, at least one of the oxygen pump cells is preceded by a diffusion barrier, so that when the sensor is in potentiometric operation, a temporal measurement signal difference between the two pump cells or, in the case of amperometric operation of the sensor, a current density that differs between the two pump cells is established. With a particle-free exhaust gas, there is a constant, small time difference of the measurement signals or a constant differing current density. Because one of the oxygen pump cells is exposed to a more strongly decreasing oxygen flow in the case of particles contained in an exhaust gas stream, the signal difference between the two pump cells changes significantly. The rate of change and the magnitude of the signal differences can be used as a measure of the concentration of particles in the exhaust gas in question.

Preferably is a diffusion barrier for both oxygen pump cells upstream, the diffusion coefficients of the two Diffusion barriers can then differentiate.

The Diffusion barriers can consist of structures of different porosity. It is also conceivable that the at least one diffusion barrier is formed in this way is that it consists of a chamber with a small diffusion hole or a diffusion gap.

The Diffusion barrier can act as at least one protective layer for an electrode be trained. It then preferably provides a highly porous layer which is permeable to oxygen in a clean or unloaded state and serves as protection against abrasive exhaust gas components. At in one This protective layer is clogged by exhaust gas particles.

at a special embodiment the sensor is one electrode of the two pairs of electrodes arranged on the exhaust gas-facing top of the sensor, wherein provide these two electrodes with a common highly porous protective layer are both protecting the electrodes against abrasive exhaust gas components guaranteed as well as a diffusion barrier with the amperometric functioning of the sensor for the each formed as a pump cell electrochemical cells. Advantageously, one of the electrodes on the top is also included covered with a layer of lower porosity.

Are located particles to be detected in the exhaust gas are stored particularly effective at the covering structure of lower porosity, so that this is preferably blocked. This changes with potentiometric Operating mode, the time difference between the two measurement signals and the difference in signal amplitudes in amperometric mode of the two pumping cells clearly. The speed of this change and the amount of Signal differences can be used as a measure of concentration of particles in the exhaust gas in question.

Corresponding can the mouths of the diffusion channels each be covered with a protective layer.

To an advantageous embodiment of the Sensors according to the invention are the diffusion barriers and the Pump cells thermally separated. This separation enables operate the pump cells at a temperature level of 800 ° C, for example, so that a limit current operation with high pump current density is possible. Can at the same time the diffusion barriers operated at temperatures of about 300 ° C. so that there are soot particles can invest without being decomposed.

The Sensor according to the invention can work with a pumped reference and / or have at least one channel. Taking a pumped reference is understood a reference electrode that is in contact with a closed inner gas space of the sensor or its surface with a porous Solid electrolyte layer is covered.

is If a channel is provided, it is preferably in a separate one Layer formed and either connected to the environment for reference or exposed to the exhaust gas in which the sensor is arranged. In the former In this case, the channel is designed as a reference channel. In the latter case the channel is designed as a so-called reference diffusion channel.

To a preferred embodiment the sensor has two reference diffusion channels, each with a diffusion barrier are trained. The diffusion barriers each have a different one Porosity so that the one with the lower porosity when particles appear in clogged the exhaust gas to be measured faster and thereby the amount of Oxygen, each located on one side of the substrate Electrode arrives, is different in size or becomes clogged with particles changed to different degrees.

The diffusion channels are, for example, with the medium to be measured, i.e. H. the Exhaust gas connected that they are each assigned a hole that is formed in the preferably layer-like substrate. The two holes can be covered with layers of different porosity have different diffusion coefficients.

The holes in the substrate and the diffusion channels formed in a second layer can either be formed as cavities which are produced by means of a free-burning material, such as, for example, glassy carbon, or else filled in the case of production using a screen printing method. In the latter case, they are made with a porous material, such as porous zirconium dioxide, to which glass carbon or aluminum oxide is added. The formation of the diffusion channels and the holes as pressure layers favors the strength of the diffusion barriers, particularly when they are formed as porous layers.

It is possible, too, the holes to be filled with diffusion barriers, which also take on the function of protective layers and are different porous Material. Then can the protective layers, which are arranged above the holes, are eliminated.

Around clean the sensor according to the invention of deposited particles to be able it preferably has at least one heating element. For cleaning the diffusion barriers it is advantageous if a heating element is arranged in the region of the diffusion barriers.

Around one if possible great Measurement signal, i.e. preferably size pump currents in the oxygen pumping cells, it is advantageous to obtain the two diffusion barriers, each an oxygen pump cell are assigned to form thermally separated from each other.

Advantageous is one of the diffusion barriers near the oxygen pump cell arranged so that this diffusion barrier during the operation of the sensor is permanently heated and therefore oxidizable particles do not accumulate can or burn quickly. At the second diffusion barrier, the the sensor is operating at a lower temperature level is, however, an accumulation of particles is possible, so that if there are particles in the gas stream in question are a high oxygen permeability difference between the clogged, unheated and the non-clogged, permanently heated diffusion barrier.

Of can further if a heating element in the area of the diffusion barriers is arranged, with such a thermal separation of the diffusion barrier this heating element on the area of that diffusion barrier limited clogged when particles are present in the gas stream. This means that only a comparatively small geometric surface has to be used of the heating element are heated so that the heating element is small and can be designed to save energy.

at a preferred embodiment According to the invention, the sensor has a capture structure for in the gas flow located particles on, so that the attachment of particles to supports the diffusion barriers becomes. The catch structure can for example be a catch sleeve or as a relief-like surface be trained.

The Solid electrolyte can, for example, from a material such as yttrium-stabilized Zirconium dioxide exist.

The The sensor can also have a carrier layer have which, for example, also made of yttrium-stabilized Zirconium dioxide exists and which are provided with an aluminum oxide insulation layer is.

To In an embodiment that is advantageous in terms of production technology, the sensor can According to the invention at least partially manufactured in screen printing technology his.

Further Advantages and advantageous developments of the subject the invention will become apparent from the description, the drawing and the Claims.

drawing

Five working examples of the sensor according to the invention are schematic in the drawing are shown in simplified form and are described in the following description explained in more detail. It demonstrate

1 an exploded view of a soot sensor;

2 an alternative embodiment of a soot sensor;

3 a third embodiment

4 a fourth embodiment and

5 a section of the in 4 shown soot sensor according to a fifth embodiment.

description of the embodiments

In 1 is a sensor 1 for the detection of soot particles in an exhaust gas of a motor vehicle. The sensor 1 is designed for installation in an exhaust line and for this purpose is arranged in a housing, not shown here.

The sensor 1 is manufactured in a so-called thick-film technology according to a screen printing process and includes a carrier layer 2 , which consists of yttrium-stabilized zirconium dioxide and is coated with an insulating layer of aluminum oxide, not shown. In the carrier layer 2 is an electric heating element 3 integrated that via contacts 4 and 5 can be connected to a voltage source. The heating element 3 is used to clean the sensor 1 of soot particles possibly accumulating on the sensor.

On the backing 2 is a second layer 6 arranged in which a so-called reference channel 7 is formed, which extends in the longitudinal direction of the second layer 6 extends and which is connected to the environment, ie is filled with air. The second layer 6 is from a third layer 8th covered, which represents a solid electrolyte made of yttrium-stabilized zirconium dioxide and in which two oxygen pump cells, ie two electrochemical cells, are formed. The two oxygen pump cells are by means of two pairs of electrodes 9A . 9B and 10A . 10B formed, each with an electrode 9B respectively. 10B on the second layer 6 facing side of the solid electrolyte 8th is arranged so that it is the reference channel 7 limited, and the other electrode 9A respectively. 10A on the second layer 6 opposite side of the solid electrolyte 8th is arranged. This side of the solid electrolyte 8th is exposed to the exhaust gas flowing in the exhaust system during operation.

The side of the solid electrolyte exposed to the exhaust gas 8th arranged electrodes 9A and 10A are over lines 11 and 12 with contacts 13 and 14 connected. The the reference channel 7 limiting electrodes 9B and 10B are over lines 15 and 16 with so-called vias 17 respectively. 18 connected. The contacts 13 and 14 as well as the vias 18 and 17 that the solid electrolyte 8th reach through, can be connected to a measuring and control unit.

The electrodes 9A and 10A are for protection against abrasive exhaust gas components with a highly porous protective layer 19 provided when operating by means of the electrode pairs 9A . 9B and 10A . 10B as well as the solid electrolyte 8th formed electrochemical cells represents a diffusion limitation or barrier.

Above the electrode 10A is an additional layer 20 on the protective layer 19 appropriate. The layer 20 has a defined structure with low porosity and forms a further diffusion barrier for oxygen. The layer 20 If particles such as soot particles appear in the exhaust gas, this builds up preferentially, so that the permeability to oxygen decreases.

In 2 is an alternative embodiment of a soot sensor 30 shown, which can be used for installation in an exhaust system of a motor vehicle. According to the sensor

1 is the soot sensor 30 arranged in a housing, not shown.

The sensor 30 comprises a carrier layer 2 whose structure follows that of the carrier layer of the sensor 1 equivalent.

On the backing 2 is a second layer 31 arranged, in which two on the of the carrier layer 2 So-called diffusion channels arranged on the opposite side 32 and 33 are trained.

On the second layer 31 is again a third layer 34 arranged, which consists of yttrium-stabilized zirconium dioxide and on the second layer 31 facing side two electrodes 35 and 36 are arranged in an end region of the diffusion channels 32 and 33 and the second layer 31 facing away from a third electrode 37 is arranged. The electrodes 35 and 36 each form with the third electrode 37 a so-called oxygen pump cell, ie an electrochemical cell.

On the electrodes 35 and 36 opposite ends of the diffusion channels 32 and 33 are in the solid electrolyte 34 two holes 38 and 39 trained in the diffusion channels 32 and 33 open and for example by means of porous protective layers 40 respectively. 41 are covered. The protective layers 40 and 41 have different porosities, each form a diffusion barrier and ensure protection of the electrodes 35 and 36 against abrasive exhaust gas components.

The diffusion barriers 40 and 41 whose diffusion coefficients differ are due to the distance to the electrodes 35 . 36 and 37 thermally separated from the electrochemical cells formed by these electrodes.

On the solid electrolyte 34 is a heating element 42 trained to burn the protective layers 40 and 41 of soot particles.

In 3 is a third embodiment of a soot sensor 50 shown, which is also arranged in a housing, not shown, adapted to the respective application.

The structure of the sensor 50 corresponds essentially to that of the sensor 2 , However, the sensor is 50 designed so that the diffusion barriers 40 and 41 are thermally separated. This is ensured by the diffusion barrier 40 preferably in the vicinity of the pump electrodes assigned to the oxygen pump cells 35 . 36 and 37 is arranged. The area of the pump electrodes 35 . 36 . 37 puts in the operating state of the sensor 50 is a permanently heated zone. The hole is accordingly 38 , which the diffusion barrier 40 is assigned, near the permanently heated zone with the two from the electrodes 35 and 37 respectively. 36 and 37 and the substrate 34 shape th oxygen pumping cells in the substrate 34 educated.

The hole 38 leads to one in the second layer in this embodiment 31 trained diffusion channel 32 that of the electrodes 35 and 37 Associated formed oxygen pump cell and a smaller longitudinal extent than the second diffusion channel 32 has the one from the electrodes 36 and 37 formed oxygen pump cell is assigned and the diffusion barrier 41 assigned. The porosity of the diffusion barriers 40 and 41 are different.

Furthermore, is on the solid electrolyte 34 a heating element 42 formed that the diffusion barrier or protective layer 41 is assigned and by means of which a free burning of the same is possible.

The distances between the two diffusion barriers preferably correspond 40 and 41 and the respective electrodes 35 respectively. 36 essentially. This is achieved, for example, by a U-shaped structure (not shown) of the shorter diffusion channel 32 reached.

In operation of the sensor 50 the temperature difference between the two diffusion barriers 40 respectively. 41 set to a constant value. The resulting different temperatures in the two diffusion channels 32 and 33 cause different diffusion constants and thus a time offset between the two by means of the electrodes 35 and 37 respectively. 36 and 37 measured signal currents. However, the time offset is constant and can be done electronically or by appropriate formation of the diffusion channels 32 and 33 be compensated.

With the amperometric mode of operation of the electrode pairs 35 and 37 respectively. 36 and 37 results from pumping oxygen from the diffusion channels 32 . 33 towards the electrode 37 with a particle-free exhaust gas flow, a constant difference between the so-called pump current densities. This difference is due to the different diffusion constants of the two diffusion barriers 40 and 41 ,

If particles are present in the exhaust gas stream, they preferentially accumulate on the sensor during operation 50 non-heated diffusion barrier 41 which has a lower porosity than the diffusion barrier 40 having. The diffusion barrier 41 is therefore preferably blocked, which leads to a change in the difference between the pump current densities and thus the measured signal amplitudes of the two electrode systems 35 . 37 respectively. 36 . 37 leads. The speed of this change and the magnitude of the signal amplitude differences serve as a measure of the concentration of particles in the relevant exhaust gas flow.

In the designs described above, the two heating elements 3 and 42 in addition to its cleaning function, also for measuring the temperature at the diffusion barriers 40 . 41 and the oxygen pump cells 35 . 37 respectively. 36 . 37 serve.

A fourth embodiment of a soot sensor 70 is in 4 shown, which is also arranged in a housing, not shown, adapted to the respective application.

The structure of the sensor 70 corresponds essentially to that of the sensor 3 , However, there is at least one diffusion barrier in the area 40 . 41 two more electrodes each 51a . 5lb respectively. 52a . 52b provided, to which a corresponding high voltage can be applied if necessary, so that there is a dielectric barrier discharge. The resulting excited species or the ozone formed thereby supports the removal of the diffusion barriers 40 . 41 deposited particles. In particular, the diffusion barriers can be cleaned 40 . 41 Discharge compared to purely thermal cleaning also the removal of oil or additive pockets. Around the electrodes 51a . 5lb respectively. 52a . 52b One of the other electrodes can protect against aggressive exhaust gas components 51a . 51b respectively. 52a . 52b or both electrodes are each provided with a corrosion-resistant protective layer, not shown.

In a further embodiment of the present sensor is in the vicinity of the diffusion barrier 41 a further heating device, not shown, is provided, so that, if necessary, both diffusion barriers 40 . 41 accumulated particles can be freed both thermally and via a discharge. In order to obtain the largest possible effective discharge area, the areas of the further electrodes can be 51a . 51b respectively. 52a . 52b different sizes.

Furthermore, between the other electrodes 51a . 51b respectively. 52a . 52b two dielectrics with different dielectric constants can be provided. Such an embodiment is excerpted in 5 shown. Between the other electrodes 51a . 51b is a first dielectric 61 preferably in duplicate, for example in each case adjacent to the corresponding further electrode 51a . 5lb provided as well as a second electric, preferably in the form of the diffusion barrier 41 ,

Claims (12)

Sensor for the detection of particles in a gas stream, in particular soot particles in an exhaust gas stream, with measuring electrodes ( 9A . 9B . 10A . 10B ; 35 . 36 . 37 ) on a substrate ( 8th ; 34 ) are made of an insulating material, the substrate being a solid electrolyte ( 8th ; 34 ), in which at least two oxygen pump cells are formed, each of which is associated with a pair of electrodes. characterized in that at least one of the oxygen pumping cells has a diffusion barrier ( 19 . 20 . 40 . 41 ) is connected upstream, the two further electrodes ( 51a . 51b . 52a . 52b ) are assigned to which a high voltage can be applied. Sensor according to claim 1, characterized in that the high voltage is selected so that it on the other electrodes ( 51a . 51b . 52a . 52b ) there is a dielectric discharge. Sensor according to claim 1 or 2, characterized in that the surface of one of the further electrodes ( 51a . 51b . 52a . 52b ) is smaller than the area of the other further electrode. Sensor according to one of claims 1 to 3, characterized in that the two oxygen pump cells have a diffusion barrier ( 19 . 20 . 38 . 39 ) is connected upstream and the diffusion barriers ( 19 . 20 . 38 . 39 ) consist of structures of different porosity. Sensor according to one of claims 2 to 4, characterized in that the diffusion barrier ( 40 . 41 ) and the oxygen pump cells are thermally separated. Sensor according to one of claims 1 to 5, characterized in that a diffusion channel ( 32 ; 33 ) is provided. Sensor according to claim 6, characterized by two diffusion channels ( 32 ; 33 ), each with a diffusion barrier ( 40 ; 41 ) are trained. Sensor according to claim 7, characterized in that the diffusion channels ( 32 . 33 ) one hole each ( 38 . 39 ) assigned in the substrate ( 34 ) is trained. Sensor according to one of claims 1 to 10, characterized by at least one heating element ( 3 ; 42 ) in the area of diffusion barriers ( 40 . 41 ). Sensor according to one of the preceding claims, characterized in that the diffusion barrier ( 40 ), which is upstream of one of the two oxygen pumping cells, from the diffusion barrier ( 41 ), which is upstream of the other of the two oxygen pumping cells, is thermally separated. Sensor according to one of the preceding claims, characterized through a catch structure for Particles in the gas stream. Sensor according to one of the preceding claims, characterized by a carrier layer ( 2 ), which preferably consists of yttrium-stabilized zirconium dioxide and is provided with an aluminum oxide insulation layer.