DE102010038613A1 - Method for regenerating sensor utilized for detecting particles in exhaust line of e.g. diesel engine, of motor car, involves heating electrodes during time period to temperature, and maintaining temperature for another time period - Google Patents

Abstract

The method involves creating or maintaining an electric field between two electrodes (12, 14) of a sensor (10) that is utilized for resistive detecting of particles. The electrodes are heated during a first time period to temperature, which corresponds to oxidization temperature of a soot particle (18). The temperature is maintained for a second time period. The electrodes are heated during a third time period to another temperature, where the latter temperature is greater than the former temperature. The latter temperature is maintained for a fourth time period. A time period ranging from 5s to 20 s is selected as the first time period. A time period ranging from 0s to 10s is selected as the second time period. A time period ranging from 1s to 15s is selected as the third time period. A time period ranging from 5s to 30s is selected as the fourth time period. Temperature ranging from 450 degree Celsius to 650 degree Celsius is utilized as the first temperature. Temperature above 650 degree Celsius is utilized as the second temperature.

Description

The present invention relates to a method for regenerating a sensor, in particular a sensor for detecting particles in the exhaust system of a vehicle.

State of the art

It is known from practice to measure by means of two electrodes a concentration of particles or solid particles, such as soot, ash or dust particles, in an exhaust gas. This is particularly important in the exhaust gas system of a vehicle since it monitors the emission of soot by the engine or after a diesel particulate filter during driving and the functionality of this monitoring must be ensured, for example by an on-board diagnosis (OBD). In addition, a diesel particulate filter loading prediction is needed to achieve high system safety with few efficient, fuel-efficient regeneration cycles and to use more cost-effective filter materials, such as cordierite. One possibility for this is provided by a resistive soot sensor, which uses the change in resistance of an electrode structure due to soot accumulation to detect the soot.

Such soot sensors are for example off DE 101 49 333 A1 and WO 03/006976 A2 known. These are resistive particle sensors for conductive particles, in which two or more metallic electrodes are provided. Under the effect of an electrical measuring voltage, particles or particles, such as soot particles, are deposited on the electrodes or on the sensor. These deposited particles short the electrodes, resulting in a decreasing resistance or an impedance change between the electrodes. This resistance change can be determined with a constantly applied measuring voltage. To regenerate the sensor after Rußanlagerung the sensor is heated by means of a heating element and burned free.

Disclosure of the invention

• – Anlegen oder Beibehalten eines elektrischen Felds zwischen den Elektroden;
• – Erhitzen der Elektroden während eines Zeitraums t₁ auf eine Temperatur T₁, die im Wesentlichen der Oxidationstemperatur von Ruß entspricht;
• – Beibehalten der Temperatur T₁ für einen Zeitraum t₂;
• – Erhitzen der Elektroden während eines Zeitraums t₃ auf eine Temperatur T₂, wobei T₂ > T₁;
• – Beibehalten der Temperatur T₂ für einen Zeitraum t₄.

The subject matter of the present invention is a method for regenerating a sensor, wherein the sensor has at least two electrodes, in particular for the resistive detection of particles, comprising the steps

• - applying or maintaining an electric field between the electrodes;
• - Heating the electrodes during a period t ₁ to a temperature T ₁ , which corresponds substantially to the oxidation temperature of carbon black;
• Maintaining the temperature T ₁ for a period t ₂ ;
• - Heating the electrodes during a period t ₃ to a temperature T ₂ , wherein T ₂ > T ₁ ;
• Maintaining the temperature T ₂ for a period t ₄ .

The method according to the invention provides a regeneration method with which the ashing of the particle sensor is minimized and a regeneration process is optimized.

Incineration can occur in such sensors by an accumulation of soot and ash particles forming during combustion. Over time, these particles worsen the measurement result or make the sensor useless by forming an insulating layer, in particular on the electrodes, thereby passivating the sensor. It is therefore necessary a regeneration process to rid the sensor and in particular the electrodes of the particles. The regeneration of a sensor is therefore according to the invention a detachment of deposited particles, in particular of soot and ash particles, from the sensor, in particular from the electrodes of the sensor.

In the method according to the invention, use is made of the fact that the soot particles and ash particles formed during a combustion process are not separate or pure, but rather that a complex mixture of soot particles and ash particles is produced due to coagulation processes of the primary particles formed after the combustion. Therefore, during a so-called collection phase of soot measurement, a mixture of carbon and ash primary particles deposits on the sensors. The amount of primary carbon particles outweighs that of the ash particles significantly.

In the context of the invention, carbon black or soot particles are understood as meaning particles which to a large extent, in particular from 80 to 99.5%, consist of carbon. Ash particles in the invention are particles such as oil-ash or Si-additives as non-carbon constituents of the fuel or the exhaust gas, which the sensor is also exposed to over its lifetime and the same as soot to a signal change of the sensor and pollution to lead.

The deposition of the particles takes place during the measurement phase or collection phase, essentially along the electric field lines, which are generated by the measurement current or the measurement voltage. As a result, the accumulated particles form particle chains that are not close to the Sensor abut, but protrude into the space above the electrodes.

In order to regenerate the sensors, ie to free them from the deposited particles, an electric field is applied between at least two electrodes or the electric field formed during the measurement is maintained. As a result, the particles are also aligned during the regeneration in the form of a particle chain along the electric field and protrude into the space above the electrodes. In addition, the electrodes are heated during a period t ₁ to a temperature T ₁ which substantially corresponds to the oxidation temperature of carbon black. This ensures that the soot particles located on the sensor are oxidized and thus significantly reduces the adhesion of the particle chain or particle bridge to the electrodes. A large part of the particles, or particle bridges, can thus detach themselves from the sensor. In this case, the gas flow flowing along the electrodes can remove the detached particles by hydrodynamic forces from the electrodes and discharge them from the system.

In essence, the oxidation temperature of carbon black here means a temperature T ₁ at which soot is burned or oxidized. In detail, substantially the oxidation temperature of carbon black means a temperature T ₁ in a range of 450 ° C-650 ° C.

In this case, the period of time t _{1 can} in particular last quite a long time, ie the temperature can be slowly approached to the temperature T ₁ . In this way it can be ensured that initially only the soot particles are oxidized, which adhere to the sensor and fasten the particle chains.

In order to oxidize these soot particles as completely as possible, the temperature T ₁ should be maintained for a certain period t ₂ , or kept constant.

Subsequent to the time period t ₂ , the electrodes are heated to a temperature T ₂ during a period t ₃ , where T ₂ > T ₁ . As a result, in particular a temperature T ₂ can be set, which is significantly higher than the temperature T ₁ . In this way, the regeneration process can be continued during a period of time t ₄ as part of a full regeneration. Thus, it is possible to remove all particles from the electrodes or from the sensor which still adhere after the regeneration period t ₂ . These are in particular ash particles, which were not part of the detached particle chain, but adhere directly to the electrodes or the substrate or carbon compounds, which oxidize completely only at higher temperatures. But also possibly during the period t ₂ not dissolved soot particles can be removed in this step. This can ensure that the electrodes, or the sensor, after a regeneration cycle completely free of soot and also freed from other particles.

Further, the effect of keeping the particle chains aligned by the maintained voltage along the field lines does not cause them to collapse as in the prior art, for example, during the heating process, and to directly contact the surface of the electrodes. As a result, in the prior art, in the case of sudden heating, glasses have formed on the electrodes which have passivated the electrodes. According to the invention, therefore, a passivation of the electrodes is avoided on the one hand by the maintenance of the voltage. Moreover, glass formation almost does not take place at temperatures substantially equal to the oxidation temperature of carbon black. As a result, many particles are in aligned form above the electrodes and thus do not pollute them, so that the ashing behavior is also improved.

Within the scope of an advantageous embodiment of the present invention, a period in a range from ≥ 5 s to ≦ 20 s is selected as the time period t ₁ . By such a selected period can be ensured that the temperature is slowly approached to the oxidation temperature of soot, so that in particular the soot particles are removed, which connects the particle bridge directly to the electrodes. As a result, even a particularly large proportion of the adhering particles can be removed, whereby an advantageously subsequent full regeneration can be limited in time.

Within the scope of a further advantageous embodiment of the method according to the invention, the temperature T _{1 used is} a temperature in a range of 450 ° C. to ≦ 650 ° C., in particular of 550 ° C. This temperature is sufficient to oxidize the carbon black holding the particle bridges and thus to remove the adhering particles. However, the temperature is still low enough to reduce energy costs and to keep the thermal load of the sensor low.

Within the scope of a further advantageous embodiment of the present invention, a period in a range from ≥ 0 s to ≦ 10 s is selected as the time period t ₂ . By choosing such a period, it can be ensured that all particle bridges have detached without requiring a disproportionately long period of time. The duration of the regeneration as well as the energy consumption and the thermal load of the Sensors can be kept so low. A period of 0 s means a continuous heating of the sensor or of the electrodes. This may already be sufficient if all particle bridges have already been released by slowly heating to a temperature T ₁ .

In the context of a further advantageous embodiment of the present invention, the resistance between the electrodes is measured during the period t ₂ and at constant resistance, the electrodes are heated to a temperature T ₂ . In this way conclusions are possible as to whether there are any particle bridges between the electrodes or whether the first step of the regeneration has been completed. The regeneration method according to the invention can thus be adapted to the processes actually taking place at the electrodes, as a result of which the regeneration method can be carried out in a particularly timely manner and thus energy-saving and cost-effectively.

It is also advantageous that a time period in a range from ≥ 1 s to ≦ 15 s is selected as the time period t ₃ . As a result, the temperature T ₂ can be reached very quickly, which shortens the regeneration cycle and thus reduces costs. A slow start of the temperature T ₂ is not necessary here.

In the context of a further advantageous embodiment of the present invention, a temperature of ≥ 650 ° C is selected as the temperature T ₂ . This will ensure that any particles that still adhere to the electrodes are safely removed.

Within the scope of a further advantageous embodiment of the present invention, the period of time t ₄ chosen is a period in a range of ≥ 5 s to ≦ 30 s. By choosing such a period, it can be ensured that all the particles are detached. In this way, the regeneration is certainly completely stopped.

In the context of a further advantageous embodiment of the present invention, the resistance between the electrodes is measured during a period t ₄ and the regeneration is terminated at a constant resistance. In this way, conclusions are possible as to whether particles are still present on the sensor, or whether the second step of the regeneration is completed. The regeneration method according to the invention can thus be adapted to the actual processes taking place at the sensor, as a result of which the regeneration method can be carried out in a particularly timely manner and thus in an energy-saving and cost-effective manner.

In the context of a further advantageous embodiment of the present invention, comb electrodes are used as the at least two electrodes. Comb electrodes offer a favorable measurement behavior and can be easily printed on a plate-shaped substrate, for example. Comb electrodes are also referred to as interdigital electrodes and each have a structure of a plurality of parallel electrode fingers, which engage in parallel.

Further advantages and advantageous embodiments of the subject invention are illustrated by the drawings and explained in the following description. It should be noted that the drawings have only descriptive character and are not intended to limit the invention in any way. Show it

1 a schematic side view of a sensor with attached particles;

2 a schematic side view of a sensor with alternatively deposited particles;

3 a process scheme of the method according to the invention;

4 a schematic side view of a sensor with partially detached particles;

5 a schematic side view of a sensor with alternatively partially detached particles.

In 1 is a sensor 10 for the detection of particles in a gas stream. The sensor 10 is used in particular for installation in an exhaust system of a motor vehicle with an internal combustion engine, such as a diesel engine, and is here preferably arranged downstream of a soot filter. The sensor 10 However, it can be used equally in the field of building services, such as oil heating. However, in the following, non-limiting reference will be made to an insert in the exhaust system of a vehicle.

The sensor 10 serves to detect particles, such as soot or ash particles, which are located in the exhaust gas of an internal combustion engine, so as to allow, for example, conclusions about the soot emissions. This is indicated by the sensor 10 at least two electrodes 12 and 14 on that on a substrate 16 are arranged, and are conveniently connected to a measuring and control unit. The electrodes 12 . 14 may be two individual electrodes, which are arranged at a certain distance from each other. Preferably, the electrodes are 12 . 14 however, comb electrodes, or interdigital electrodes. In this case, the electrodes 12 . 14 designed comb-like interlocking. Comb electrodes have the advantage that they form a favorable and well-defined measurement behavior and easily on the substrate 16 can be arranged, for example by imprinting. The electrodes 12 . 14 form a resistance measuring structure on the substrate.

The substrate 16 may be configured plate-shaped and is expediently highly insulating, so that here no electrical connection between the electrodes 12 . 14 is possible, which adversely affects the measurement behavior. In addition, the substrate 16 preferably temperature resistant, so that the substrate 16 can not be decomposed or otherwise damaged or destroyed by the high temperatures prevailing, in particular, in the exhaust gas system of a vehicle. A suitable material from which the substrate 16 is formed, for example, a ceramic material such as alumina.

During the measuring process, ie when the internal combustion engine is in operation and burns fuel, such as diesel fuel, the sensor is deposited 10 or at the electrodes 12 . 14 Solid particles on. These solid particles are in particular soot particles 18 and ash particles 20 and usually electrically conductive. Thus, when such particles settle, they provide an electrical connection between the electrodes 12 . 14 and thus reduce the electrical resistance, or change the impedance between the electrodes 12 . 14 and increase the flow of electricity. This change can be detected by a suitable resistance measurement, whereby conclusions about the particles contained in the exhaust gas are possible. In detail, the soot or particle concentration in the exhaust gas in question can be determined on the basis of the time change of the resistance. The sensor 10 is therefore also called a resistive exhaust gas sensor.

The deposition of the particles takes place as a mixture of all particles contained in the exhaust gas. In particular, these are to a large extent soot particles 18 , but also other ash particles 20 such as oil-ash or Si-additives as non-carbon constituents of the fuel. As for a determination of the particle concentration, as described above, between the electrodes 12 . 14 A voltage is applied and as a current flows, forms between the electrodes 12 . 14 an electric field. The particles then align according to the orientation of this electric field, so that they are in the space above the sensor 10 or above the electrodes 12 . 14 protrude. In particular, the accumulated particles form 18 . 20 while particle bridges 22 that the electrodes 12 . 14 connect with each other. The particle bridges 22 adhere by only a few particles on the electrodes 12 . 14 and are located with a large part above the electrodes 12 . 14 , and thus in the area of the exhaust gas flow.

In addition to an attachment of the particle bridges 22 due to few end particles only at the electrodes 12 . 14 like this in 1 is shown, is a further attachment of the particle bridges 22 in 2 shown. So can the particle bridges 22 For example, both at its end to the electrodes 12 . 14 , as well as in a central region on the surface of the substrate 16 be liable. In addition, a particle bridge can also be from an electrode 12 or 14 only to the surface of the substrate 16 be educated.

Because the mass of adhering particles 18 . 20 successively increases, the measurement behavior of the sensor 10 over time by the adhering particles 18 . 20 negatively affected, until a certain point in time, reliable measurements are no longer possible. Then it is necessary to use the sensor 10 or the electrodes 12 . 14 to regenerate, so of the adhering particles 18 . 20 to free. This is particularly useful by heating the sensor possible.

Therefore, to perform regeneration, it is preferable in the substrate 16 arranged a heating element which is connected via contacts with a suitable voltage source. The heating element serves to the electrodes 12 . 14 and the substrate 16 to heat to the electrodes 12 . 14 or the sensor 10 to regenerate.

The regeneration process according to the invention is as a process scheme in 3 shown. In detail is in 3 the electrode temperature (T) along time (t).

During the measuring process flows through the electrodes 12 . 14 an electric current. This creates an electric field that determines the orientation of the deposited particles 18 . 20 affected. According to the invention, the electric field is maintained during the regeneration, when a regeneration cycle, for example, directly adjoins a measurement phase. In the event that a regeneration is performed independently of a measurement phase, the electric field should be built up so that particle bridges 22 form, at least partially rich in the gas stream. The electric field can have a field strength in a range of ≥ 50 kv / m to ≦ 5 MV / m.

During a measurement, the sensor will point 10 and in particular the electrodes 12 . 14 a measurement temperature T _m on. To start the regeneration process at the initial time t _a , the temperature of the electrodes becomes 12 . 14 on a Temperature T ₁ increased. The heating takes a predetermined period of time t ₁ until the electrodes 12 . 14 have reached the temperature T ₁ . The temperature T ₁ corresponds essentially to the oxidation temperature of carbon black. Suitable temperatures to which the electrodes 12 . 14 are in the range of ≥ 450 ° C to ≤ 650 ° C. Particularly advantageous as a temperature T _1, a temperature of 550 ° C is selected. Such a temperature is already sufficient, since at this time only the soot particles 18 to be oxidized, which are the particle bridges 22 directly with the sensor 10 connect. A locally expanding heat is therefore not necessary. It is advantageous if the temperature is raised slowly. In this way it can additionally be ensured that in particular only the soot particles 18 oxidizes the soot particles bridges 22 directly with the sensor 10 connect. Therefore, as a time period t ₁ , which determines the first heating operation, preferably a period in a range of ≥ 5 s to ≤ 20 s is selected.

If the electrodes have a temperature of T ₁ , this temperature is kept substantially constant for a period t ₂ in order to completely detach the particle bridges 22 to ensure. In this case, a period in a range from ≥ 0 s to ≦ 10 s is preferably selected as a suitable period t ₂ .

The detachment of the particle bridges 22 depending on their attachment or their position is in the 4 and 5 shown. It can be seen that even the oxidation of fewer particles can be sufficient to complete the particle bridge 22 from the sensor 10 to be removed and removed by the gas flow and removed from the system ( 4 ). However, it is possible that even more particles on the substrate surface or on the electrodes ( 12 . 14 ) which have not been replaced during the period t ₂ ( 5 ).

After the period t ₂ , the electrodes become 12 . 14 during a period t ₃ , which is preferably in a range of ≥ 1 s to ≤ 15 s, heated and adjusted to a temperature T ₂ . The temperature T ₂ is greater than the temperature T ₁ . The temperature T ₂ is also large enough to also the remaining soot 18 and ash particles 20 from the sensor 10 to remove. Preferably, a temperature of ≥ 650 ° C, in particular ≥ 750 ° C is selected as the temperature T ₂ . In this case, the temperature T _{2 is} kept substantially constant for a time t ₄ , so that it is ensured that the adhered particles 18 . 20 at least for the most part, preferably completely, of the sensor 10 are removed. In this case, a period in a range from ≥ 5 s to ≦ 30 s can be selected as the time period t ₄ . After this period, the regeneration process according to the invention can be terminated.

It is advantageous if, during the period t ₂ and / or during the period t _4, the resistance between the electrodes 12 . 14 is measured. In this way, the inventive method with respect to the actual pollution, or on the really existing mass of deposited particles 18 . 20 , respond. With constant resistance in the period t ₂ , the electrodes can be heated to a temperature T ₂ , whereas with constant resistance in the period t _4, the regeneration process can be terminated.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10149333 A1 [0003]
• WO 03/006976 A2 [0003]

Claims (10)

Method for regenerating a sensor ( 10 ), whereby the sensor ( 10 ) at least two electrodes ( 12 . 14 ), in particular for the resistive detection of particles, comprising the steps of: - applying or maintaining an electric field between the electrodes ( 12 . 14 ); - heating the electrodes ( 12 . 14 ) during a period t ₁ to a temperature T ₁ which substantially corresponds to the oxidation temperature of carbon black; Maintaining the temperature T ₁ for a period t ₂ ; - Heating the electrodes during a period t ₃ to a temperature T ₂ , wherein T ₂ > T ₁ ; Maintaining the temperature T ₂ for a period t ₄ . A method according to claim 1, characterized in that as a time period t ₁ a period in a range of ≥ 5 s to ≤ 20 s is selected. A method according to claim 1 or 2, characterized in that a temperature in a range of ≥ 450 ° C to ≤ 650 ° C is used as the temperature T ₁ . Method according to one of claims 1 to 3, characterized in that as a time period t _2, a period in a range of ≥ 0 s to ≤ 10 s is selected. Method according to one of claims 1 to 3, characterized in that during the period t _2, the resistance between the electrodes ( 12 . 14 ) and with constant resistance the electrodes ( 12 . 14 ) are heated to a temperature T ₂ . Method according to one of claims 1 to 5, characterized in that is selected as the time period t _3, a period in a range of ≥ 1 s to ≤ 15 s. Method according to one of claims 1 to 6, characterized in that a temperature of ≥ 650 ° C is selected as the temperature T ₂ . Method according to one of claims 1 to 7, characterized in that as a time period t _4, a period in a range of ≥ 5 s to ≤ 30 s is selected. Method according to one of claims 1 to 7, characterized in that during the period t _4, the resistance between the electrodes ( 12 . 14 ) is measured and with constant resistance, the regeneration is terminated. Method according to one of claims 1 to 9, characterized in that are used as the at least two electrodes comb electrodes.

Images