Method and device for operating a particle sensor

Abstract

The invention relates to a method and to a device, in particular a control and evaluating unit, for operating a particle sensor (20) for determining a particle content in a gas flow, wherein the particle sensor (20) has, on the surface of the particle sensor, a sensor structure for determining a soot load and at least one heating element (26) separated from the sensor structure by an insulating layer, by means of which at least one heating element the particle sensor (20) can be heated up in a regeneration phase and in the process a soot load on the particle sensor (20) can be removed, and by means of the heating element (26) a heating phase can be performed at least at times before the regeneration phase, wherein in said heating phase a temperature that is significantly lower than the regeneration temperature is set, wherein short-term temperature drops as a result of wetting with water can be detected by means of a temperature sensor (27) integrated in the particle sensor (20). According to the invention, during the heating phase before the regeneration phase, the duration of the heating phase is extended if a temperature deviation from a certain temperature bandwidth around a temperature target value is detected for a certain time. Thus, it can be achieved that the sensor element is always completely dried throughout the sensor element, such that regeneration can be performed at high temperatures without damage as a result of thermal shock to the sensor element.

Claims

1. A method for operating a particle sensor (20) for determining a particle content in a gas flow, wherein the particle sensor (20) comprises on a surface thereof a sensor structure for determining a soot load and at least one heating element (26) that is separated by an insulating layer from the sensor structure, the heating element being configured to heat up the particle sensor (20) in a regeneration phase to remove a soot load on the particle sensor (20), and the heating element being configured to carry out a heating phase at least at times before the regeneration phase, wherein a significantly lower temperature is controlled in said heating phase compared to a temperature of the regeneration phase, wherein a temperature sensor (27) is configured to detect brief drops in temperature as a result of wetting by water, the temperature sensor (27) being integrated within the particle sensor (20), the method comprising, during said heating phase before the regeneration phase, extending the duration of said heating phase whenever a temperature deviation from a defined temperature bandwidth about a target temperature value is detected for a certain time, wherein a timer is provided for control of the duration of the heating phase before the regeneration phase, wherein the timer is reset and/or restarted whenever a temperature deviation from the defined temperature bandwidth about the target temperature value is detected.

2. The method as claimed in claim 1, characterized in that the temperature bandwidth about the target temperature value is predefined.

3. The method as claimed in claim 1, characterized in that during each resetting and/or restarting of the timer, a counter is incremented and the count is analyzed to enable the regeneration phase.

4. The method as claimed in claim 3, characterized in that, on reaching an applicable number of reset and/or restart processes, the regeneration phase is blocked for a defined driving cycle.

5. The method as claimed in claim 3, characterized in that using a frequency of the reset and/or restart processes of the timer, heavy wetting by water of an exhaust system (17) of an internal combustion engine (10) is detected.

6. The method as claimed in claim 1, wherein the particle sensor (20) is disposed in an exhaust system (17) of an internal combustion engine (1), further comprising performing an on-board diagnosis of a particle filter.

7. The method as claimed in claim 6, wherein the internal combustion engine is a diesel engine.

8. The method as claimed in claim 6, wherein the internal combustion engine is a gasoline engine.

9. A method for operating a particle sensor (20) for determining a particle content in a gas flow, wherein the particle sensor (20) comprises on a surface thereof a sensor structure for determining a soot load and at least one heating element (26) that is separated by an insulating layer from the sensor structure, the heating element being configured to heat up the particle sensor (20) in a regeneration phase to remove a soot load on the particle sensor (20), and the heating element being configured to carry out a heating phase at least at times before the regeneration phase, wherein a significantly lower temperature is controlled in said heating phase compared to a temperature of the regeneration phase, wherein a temperature sensor (27) is configured to detect brief drops in temperature as a result of wetting by water, the temperature sensor (27) being integrated within the particle sensor (20), the method comprising, during said heating phase before the regeneration phase, extending the duration of said heating phase when a temperature deviation from a defined temperature bandwidth about a target temperature value is detected for a certain time, characterized in that using a frequency of reset and/or restart processes of a timer, heavy wetting by water of an exhaust system (17) of the particle sensor installed in an internal combustion engine (10) is detected.

10. A method for operating a particle sensor (20) for determining a particle content in a gas flow, wherein the particle sensor (20) comprises on a surface thereof a sensor structure for determining a soot load and at least one heating element (26) that is separated by an insulating layer from the sensor structure, the heating element being configured to heat up the particle sensor (20) in a regeneration phase to remove a soot load on the particle sensor (20), and the heating element being configured to carry out a heating phase at least at times before the regeneration phase, wherein a significantly lower temperature is controlled in said heating phase compared to a temperature of the regeneration phase, wherein a temperature sensor (27) is configured to detect brief drops in temperature as a result of wetting by water, the temperature sensor (27) being integrated within the particle sensor (20), the method comprising, during said heating phase before the regeneration phase, extending the duration of said heating phase if a temperature deviation from a defined temperature bandwidth about a target temperature value is detected for a certain time, characterized in that a timer for control of the duration of the heating phase before the regeneration phase is reset and/or restarted whenever a temperature deviation from the defined temperature bandwidth about the target temperature value is detected.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described in detail below using an exemplary embodiment that is illustrated in the figures. In the figures:

(2) FIG. 1 shows in a schematic representation the technical environment in which the method can be used and

(3) FIG. 2 shows schematically a particle sensor in an exploded representation.

DETAILED DESCRIPTION

(4) FIG. 1 shows schematically the technical environment in which the method according to the invention can be used. An internal combustion engine 10, which can be implemented as a diesel engine, receives combustion air that is delivered by means of an air feed 11. During this the amount of the combustion air can be determined by means of an air mass flowmeter 12 in the air feed 11. The amount of air can be used during the correction of a probability of deposition of particles present in the exhaust gas of the internal combustion engine 10. The exhaust gas of the internal combustion engine 10 is discharged by means of an exhaust system 17 in which an emission control system 16 is disposed. Said emission control system 16 can be implemented as a diesel particle filter. Furthermore, an exhaust gas probe that is implemented as a lambda probe 15 and a particle sensor 20 are disposed in the exhaust system 17, the signals of which are fed to an engine controller 14 or a special control and analysis unit 30 (Sensor Control Unit SCU), which can be implemented as a component of the engine controller 14 or as an independent unit, for example close to the particle sensor 20. The engine controller 14 is also connected to the air mass flowmeter 12 and determines, based on the data delivered to it, an amount of fuel that can be fed to the internal combustion engine 10 by means of a fuel metering means 13.

(5) In this case the particle sensor 20 can also be disposed after the emission control system 16 in the direction of flow of the exhaust gas, which brings with it advantages in respect of the homogenization of the flow of exhaust gas at this point and in particular when used during the on-board diagnosis. With the devices shown, observation of the particle emissions of the internal combustion engine 10 and a prognosis of the load on the emission control system 16 in the form of a diesel particle filter (DPF) are possible.

(6) FIG. 2 shows in a schematic representation a particle sensor 20 corresponding to the prior art in an exploded representation.

(7) An IDE measurement structure 22 in the form of a first electrode and a second electrode is mounted on insulating support layers 21 of ceramic, for example of aluminum oxide. The electrodes are implemented in the form of two interdigital, intermeshed comb electrodes and are referred to as IDE electrodes 23 and constitute the actual sensor element. The IDE connections 24 (IDE+ and IDE), by means of which the IDE electrodes 23 are connected to the control and analysis unit 30 (not shown in FIG. 2) for supplying voltage and for performing the measurement, are provided on the end faces of the IDE electrodes 23. In addition, in the example shown a heating element 26, which is connected to the control and analysis unit 30 by means of additional heating element connections 25 (H+, OV), is integrated between the insulating support layers 21.

(8) In addition, a temperature sensor 27 can be provided in the layer structure of the particle sensor 20 for measuring the temperature, wherein a temperature sensor connection 28 (TM) is also led out of the particle sensor 20. For example, resistance structures of platinum can be used as a temperature sensor 27. Alternatively, at least a part of the structure of the heating element 26 can also be used as a temperature sensor 27.

(9) If such a particle sensor 20 is operated in a gas flow carrying soot particles 29, for example in an exhaust duct of a diesel engine or a furnace, then soot particles 29 from the gas flow are deposited on the particle sensor 20. Said particles have a certain electrical conductivity. During this the rate of deposition of the soot particles 29 on the particle sensor 20 depends, besides on the particle concentration in the exhaust gas, among other things also on the voltage that is applied to the IDE electrodes 23. An electrical field is produced by the applied voltage and exerts a corresponding attraction on electrically charged soot particles 29. Therefore, the rate of deposition of the soot particles 29 can be influenced by the suitable selection of the voltage applied to the IDE electrodes 23.

(10) In the exemplary embodiment, the IDE electrodes 23 and the top insulating support layer 21, on which the IDE electrodes 23 are disposed, are covered by means of a protective layer (shown in dashed form). Said optional protective layer protects the IDE electrodes 23 against corrosion at the generally prevailing high operating temperatures of the particle sensor 20. In the present exemplary embodiment, it is made of a material with a low conductivity, but can also be made of an insulator.

(11) Soot particles 29 from the gas flow have been deposited in the form of a layer on the protective layer. Owing to the low conductivity protective layer, the soot particles 29 form a conductive path between the IDE electrodes 23, so that, depending on the amount of deposited soot particles 29, a change of resistance between the IDE electrodes 23 results. This can for example be measured by applying a constant voltage to the IDE connections 24 of the IDE electrodes 23 and determining the change of the current that is due to the collected soot particles 29. If the protective layer is made insulating, the deposited soot particles 29 result in a change of the impedance of the particle sensor 20, which can be analyzed by means of a suitable measurement, preferably with an alternating voltage.

(12) If the particle sensor 20 is loaded so much with a layer of soot particles 29 that additional deposited soot particles 29 do not result in an additional change of the resistance or the impedance of the particle sensor 20, then the particle sensor 20 is regenerated within a regeneration phase. At the same time the particle sensor 20 is heated up using the heating element 26 to the extent that the deposited soot particles 29 are combusted. This usually happens at temperatures >600 C.

(13) Before regeneration of the particle sensor 20, protective heating is carried out for a certain time before the dew point end (DPE), as initially described. According to the invention, it is provided in this case that a timer for the time in the protective heating before the dew point end phase is reset if the sensor temperature leaves a predefinable temperature window for an applicable time during the protective heating.

(14) Typically, the predefinable temperature window is 200 C.15 K. A time duration for the protective heating before the dew point end phase can typically be 80 s for this, with which the timer is initialized at the start of said phase. Wetting the sensor element with water in the protective heating before the dew point end phase results in a larger temperature deviation, because the heating regulator for the heating element 26 is only operated with an applicable maximum heating power and thus cannot evaporate the water fast enough.

(15) As long as the sensor element is in the temperature range of for example 200 C.T K, the timer is decremented every second until the protective heating before the dew point end phase is ended, and then the sensor regeneration phase can be started. The parameter T can be predefined for this. It is assumed that no heavy wetting and cooling connected therewith have taken place and the particle sensor 20 can be safely regenerated at suitable high temperatures following said protective heating.

(16) Once the sensor element leaves the predefinable temperature window for an applicable time duration as a result of strong cooling, the timer is reset again and re-initialized with the predefinable time duration for the protective heating before the dew point end phase, in this case for example 80 s, wherein each re-initialization of the timer results in an incrementation of a re-initialization of protective heating timer counter. On reaching a likewise applicable number of re-initializations of the counter, a sensor regeneration in this driving cycle is blocked because it is assumed therefrom that the sensor is not yet sufficiently dried out as a result of frequent and/or heavy water contact during said phase.

(17) The functionality described above is preferably implemented as a software module in a local controller of the particle sensor 20, i.e. in a control and analysis unit 30 of the particle sensor 20. However, this can also be an integral component of the overarching engine controller 14 (cf. FIG. 1).

(18) Thus it can be achieved that the sensor element is always fully dried out, so that a regeneration can be carried out at high temperatures without damage as a result of a thermal shock to the sensor element.