METHOD FOR OPERATING A SENSOR FOR DETECTING PARTICLES IN A MEASURING GAS

Description

State of the art

[0001] Numerous methods and devices for detecting particles, such as soot or dust particles, are known from the prior art.

[0002] The invention is described below, without limitation to further embodiments and applications, in particular with reference to sensors for the detection of particles, especially soot particles, in an exhaust gas stream of an internal combustion engine.

[0003] It is a known practice to measure the concentration of particles, such as soot or dust particles, in exhaust gas using two electrodes mounted on a ceramic surface. This can be done, for example, by measuring the electrical resistance of the ceramic material separating the two electrodes. More precisely, the electric current flowing between the electrodes when an electrical voltage is applied is measured. Due to electrostatic forces, the soot particles are deposited between the electrodes and, over time, form electrically conductive bridges. The more bridges are present, the higher the measured current. This creates an increasing short circuit between the electrodes. The sensor element is periodically regenerated by heating it to at least 700°C using an integrated heating element, which burns off the soot deposits.

[0004] Such sensors are used, for example, in the exhaust system of an internal combustion engine, such as a diesel engine. These sensors are typically located downstream of the exhaust valve or the diesel particulate filter.

[0005] Despite the numerous advantages of existing particle detection devices, there is still room for improvement. The ceramic sensor element is sensitive to incoming moisture and susceptible to hydrothermal aging. Various damage mechanisms to the sensor element caused by water or condensate are known, and reliable detection of electrode drying is not yet possible.

[0006] Such sensors and associated operating procedures are known, for example, from DE 10 2011 086 148 A1, EP 1 898 205 A2, US 2018 / 313 739 A1, US 2011 / 107 815 A1, US 2012 / 031 168 A1 and DE 10 2015 215 848 A1. Disclosure of the invention

[0007] Therefore, according to claim 1, a method for operating a sensor for detecting particles, in particular soot particles, is proposed which at least largely avoids the disadvantages of known operating methods and in particular allows the detection of moisture in the electrode area and is not solely dependent on dew point data to infer moisture in the sensor element.

[0008] In a method according to the invention for operating a sensor for detecting particles, in particular soot particles, in a measuring gas, especially in the exhaust gas of an internal combustion engine, wherein the sensor comprises a sensor element, the sensor element comprising at least one electrically insulating substrate, a first electrode, and a second electrode, wherein the first electrode and the second electrode are arranged on the electrically insulating element, the first electrode and the second electrode perform a current and / or voltage measurement. The sensor is operated in at least one measurement phase. During the measurement phase, a first electrical voltage is applied to the first electrode and the second electrode. During a predetermined period outside the measurement phase, a second electrical voltage is applied to the first electrode and the second electrode.The second electrical voltage is lower than the decomposition voltage for water (1.23 V). The presence of water on the sensor element is inferred if the current and / or voltage measurement, when the second electrical voltage is applied, yields a value that exceeds a threshold for an electric current.

[0009] The operating strategy proposed here makes it possible to detect moisture that short-circuits the electrodes, thus preventing regeneration or the application of the measuring voltage. Both moisture during regeneration and applying the measuring voltage to a moist sensor element would damage the sensor element, resulting in chipping and platinum embrittlement. In particular, this method allows moisture to be determined whenever the sensor is not being used for particle measurement. The method is therefore used, among other things, for the active determination of moisture on a sensor used for particle measurement.

[0010] During further processing, sensor regeneration or a switch to the measurement phase is prevented if the current and / or voltage measurement, when a second electrical voltage is applied, yields a value that exceeds a first threshold for an electric current. If an electric current is measured by the comparatively low second electrical voltage, it is clear that the sensor is wetted by moisture, and to protect the sensor element, regeneration or a measurement phase is prevented or blocked.

[0011] During further training, sensor regeneration or a switch to the measurement phase is enabled if the current and / or voltage measurement falls below a second threshold for an electric current after exceeding the first threshold. The first and second thresholds can be different or identical. If an electric current is measured due to the comparatively low second voltage, it is clear that the sensor is wetted by moisture, and to protect the sensor element, regeneration or a measurement phase is only initiated after a decrease in the current at the electrodes. This provides additional protection for the electrodes. Applying this very low voltage to the electrodes prevents damage from electrolysis, thus actively protecting them.

[0012] During further training, sensor regeneration or a switch to the measurement phase is enabled after a predetermined time following a drop below the second threshold. A modification of the procedure involves waiting a certain amount of time after the current at the electrodes has decayed due to moisture, in order to ensure that moisture has been completely removed from the deeper ceramic layers of the sensor element before the sensor element is regenerated or connected to a measuring voltage.

[0013] During further training, sensor regeneration or a switch to the measurement phase is enabled if the sensor receives a dew point release signal from an external source, preferably a control unit. Therefore, the sensor regeneration or switch to the measurement phase is only enabled if no moisture is (or is no longer) detected on the sensor element and a dew point release signal is also present.

[0014] During further training, the sensor is heated for a predetermined period outside of the measurement phase. This heating is also known as protective heating. Thus, to protect the ceramic sensor element, the sensor is operated with a protective heating strategy to prevent further moisture accumulation and to dry the sensor element.

[0015] During further training, the sensor is heated to a temperature whose level depends on the current and / or voltage measurement when a second electrical voltage is applied. Thus, the current level during the application of the second electrical voltage and during the protective heating process is evaluated, and the protective heating temperature is adjusted to either accelerate or gently dry the sensor element.

[0016] In a further training, the sensor is arranged in an exhaust tract of an internal combustion engine, whereby the predetermined period outside the measurement phase is after a cold start of the internal combustion engine, in the absence of dew point release by an engine control unit of the internal combustion engine and / or when a predetermined temperature in the exhaust tract is undershot.

[0017] Another variation of the method involves significantly reducing the protective heating temperature to the point of being unheated and using the sensor's inactive periods to connect the electrodes with 1V and determine the moisture content in the exhaust tract based on the resulting current, and providing this additional information to the engine control unit, or determining the dew point end by measurement and not relying on models.

[0018] In further training, the second electrical voltage has a value in the range of 0.005 V to 1.2 V and preferably 0.05 V to 1.0 V.

[0019] Furthermore, according to claim 10, a computer program comprising commands is proposed which cause an electronic control unit connected to a sensor for detecting particles to carry out each step of the method according to the invention.

[0020] Furthermore, according to claim 11, an electronic storage medium is proposed on which such a computer program is stored.

[0021] Furthermore, according to claim 12, an electronic control unit is proposed which includes such an electronic storage medium.

[0022] A particle within the meaning of the present invention is understood to be a particle, in particular an electrically conductive particle, such as soot or dust particles.

[0023] Within the scope of the present invention, an electrode is understood to be a component suitable for measuring current and / or voltage. The terms "first electrode" and "second electrode" are used within the scope of the present invention solely to distinguish the electrodes conceptually and do not imply any specific order or weighting of these components.

[0024] Within the scope of the present invention, the electrodes can be configured as interdigital electrodes. Interdigital electrodes, as used in the present invention, are understood to be electrodes arranged in such a way that they interlock, in particular in a comb-like manner.

[0025] Within the scope of the present invention, a current and / or voltage measurement is understood to mean the measurement of an electric current and / or an electric voltage. The measurement is performed between two electrodes or between an electrode and a reference potential. A specific electric voltage can be applied to the electrodes and a current flow between the electrodes measured, or an electric current can be applied to the electrodes and a voltage between the electrodes measured. A current and / or voltage measurement can, in particular, be a resistance measurement, whereby the resistance of the structure formed by the electrodes and the substrate can be measured. For example, a voltage-controlled or voltage-regulated measurement and / or a current-controlled and / or current-regulated measurement can be performed.The application of current and / or voltage can be continuous or pulsed. For example, a DC voltage and / or current can be applied, and a current or voltage response can be recorded. Alternatively, a pulsed voltage and / or current can be applied, and a current or voltage response can be recorded. Instead of the instantaneous current flow through the electrodes, the resistance of the electrodes or its reciprocal (conductance) can be used as the measured quantity. It can also be useful to integrate a charge quantity from an instantaneous current flow. Furthermore, it is possible to apply a high voltage to an electrode and measure an electric current, such as a discharge current, at a counter electrode or an electrical ground.

[0026] In the context of the present invention, a measurement phase is understood to be a period during which a voltage or voltage waveform applied to the electrodes is selected such that it enables the most accurate possible determination of the resistance or impedance, and thus the particle loading, of the sensor. The voltage during the measurement phase does not need to be suitable or optimized for collecting particles from the sample gas.

[0027] In the context of the present invention, a substrate is understood to be an object having a plate-shaped, cube-shaped, cuboid-shaped or any other geometric form, which has at least one flat surface and is made of a ceramic material, metallic material, semiconductor material or combinations thereof.

[0028] In the context of the present invention, the decomposition voltage for water is understood to be the minimum difference in electrode potentials between the anode and cathode required to carry out the electrolysis of water. At this voltage, the decomposition of the electrolyte begins due to electrical attraction forces acting between the electrodes on the one hand and the oppositely charged anions and cations on the other. Electrolysis is a process in which an electric current forces a redox reaction. Electrolysis requires a direct current voltage source, which supplies the electrical energy and drives the chemical reactions. A portion of the electrical energy is converted into chemical energy. For water, the decomposition voltage in the context of the present invention is 1.23 V.

[0029] A fundamental concept of the present invention is to apply a voltage below the decomposition voltage of water to the electrodes during protective heating, in order to detect moisture by means of a short circuit caused by water on the electrodes. If an electric current is measured by this low voltage, it is clear that the sensor is wetted by moisture, and to protect the sensor element, a regeneration or measurement phase is only enabled after the dew point has been cleared and the current at the electrodes has decreased. This provides additional protection for the electrodes. Applying this very low voltage to the electrodes prevents damage from electrolysis, thus actively protecting them. Brief description of the drawings

[0030] Further optional details and features of the invention will become apparent from the following description of preferred embodiments, which are shown schematically in the figures.

[0031] They show: Figure 1 a top view of a sensor for detecting particles according to an embodiment of the present invention and Figure 2 a flowchart of a method for operating a sensor for detecting particles according to an embodiment of the present invention. Embodiments of the invention

[0032] Figure 1Figure 1 shows a top view of a sensor 10 for detecting particles in a measuring gas according to an embodiment of the present invention. The sensor 10 is designed, in particular, for detecting soot particles in a gas stream, such as an exhaust stream from an internal combustion engine, and for installation in the exhaust system of a motor vehicle. For example, the sensor 10 is configured as a soot sensor and can be arranged downstream or upstream of a diesel particulate filter in a motor vehicle with a diesel combustion engine. In the example shown, the measuring gas is exhaust gas from an internal combustion engine. In the illustrated embodiment, the sensor 10 is configured as a resistive particle sensor.

[0033] The sensor 10 comprises a sensor element 12. The sensor element 12 comprises an electrically insulating element 14. The electrically insulating element 14 is a substrate. The substrate is, for example, a silicon wafer. Alternatively, the substrate is made of a ceramic material. The electrically insulating element 14 is essentially cuboidal. The sensor element 10 further comprises a first electrode 16, a second electrode 18, a first lead 20, and a second lead 22. The first electrode 16, the second electrode 18, the first lead 20, and the second lead 22 are arranged on a top surface 24 of the substrate 14. The first electrode 16 and the second electrode 18 are configured as interdigital electrodes. The first electrode 16 is connected to the first lead 20. The second electrode 18 is connected to the second lead 22.The first supply line 20 and the second supply line 22 are connection contacts designed for electrically contacting the first electrode 16 and the second electrode 18. The first electrode 16 and the second electrode 18 are designed for performing current and / or voltage measurements. The sensor 10 may optionally include additional components, such as a protective tube and / or a heating element, which are not shown in detail. The sensor operates in at least one measurement phase. During the measurement phase, an initial electrical voltage of, for example, 45 V is applied to the first electrode 16 and the second electrode 18.

[0034] Sensor 10 is connected to an electronic control unit 26. The electronic control unit 26 is, for example, an engine control unit of the internal combustion engine. The electronic control unit has an electronic storage medium 28, such as a chip, on which a computer program is stored. The computer program contains instructions for carrying out a procedure for operating sensor 10. Such a procedure is described in more detail below.

[0035] Figure 2 Figure 1 shows a flowchart of a method for operating a sensor 10 for detecting particles according to an embodiment of the present invention, such as the one described in Figure 1. Figure 1The sensor 10 shown is used in step S10. In step S12, the internal combustion engine is started. In step S12, it is checked whether sensor 10 is outside the measurement phase. This period outside the measurement phase occurs, for example, during a cold start of the internal combustion engine, when the engine control unit has not released the dew point, and / or when the exhaust gas temperature falls below a predetermined level. If the check in step S12 shows that it is not a cold start, when the dew point has been released, and / or when the exhaust gas temperature has been exceeded, the presence of moisture on sensor element 12 can be ruled out. In this case, the procedure proceeds to step S14, where the measurement phase begins.

[0036] If the test in step S12 reveals that a cold start is occurring, a dew point release is not present, and / or the predetermined temperature in the exhaust tract has been undershot, a predetermined period outside the measurement phase is determined, and the procedure proceeds to step S16. In step S16, during the predetermined period outside the measurement phase, a second electrical voltage is applied to the first electrode 16 and the second electrode 18, wherein the second electrical voltage is lower than a decomposition voltage for water. The second electrical voltage is a value in the range of 0.005 V to 1.2 V, and preferably 0.05 V to 1.0 V, for example, 0.8 V or 1.0 V. In addition to potential releases from outside the sensor 10, the sensor 10 itself is checked for the possible presence of water on the sensor element 12. The sensor 10 is heated during the predetermined period outside the measurement phase.If the current and / or voltage measurement with a second electrical voltage applied yields a value exceeding a threshold for an electric current, the presence of water on the sensor element 12 is inferred. The first threshold is, for example, 0 A. If the current and / or voltage measurement with a second electrical voltage applied in step S16 yields a value exceeding a first threshold for an electric current, the procedure proceeds to step S18, and regeneration of the sensor 10 or a switch to the measurement phase is prevented. If the first threshold is not exceeded, water or moisture can be ruled out, and the procedure proceeds to step S14, switching to the measurement phase.Following step S18, step S20 occurs, in which sensor regeneration or a switch to the measurement phase is enabled if the current and / or voltage measurement value falls below a second threshold for an electric current after exceeding the first threshold. The second threshold can be identical to the first threshold or different from it. Thus, the regeneration is only enabled after the current at electrodes 16 and 18 has decreased. The process then proceeds to step S14 and switches to the measurement phase.

[0037] The procedure can be modified as follows. Sensor 10 regenerates or switches to the measurement phase after a predetermined time following a fall below the second threshold. In other words, after the current at the electrodes has decayed due to moisture, a certain period of time is allowed to ensure that moisture has been completely removed from the deeper ceramic layers of the sensor element 12 before the sensor element 12 is regenerated or connected to a measuring voltage. Sensor 10 regenerates or switches to the measurement phase if, in addition to the current decreasing at electrodes 16 and 18, the sensor 10 receives a dew point release signal from an external source, such as the control unit 26. The sensor is heated to a temperature whose value depends on the current and / or voltage measurement when the second electrical voltage is applied.In other words, the current level is evaluated during the protective heating phase by applying a second electrical voltage. This allows the protective heating temperature to be adjusted for faster or gentler drying of the sensor element. Another variation of the method involves significantly reducing the protective heating temperature, even to the point of being unheated, and utilizing the sensor's inactive periods to apply a 1V voltage to electrodes 16 and 18. The resulting current is then used to determine the humidity in the exhaust system and provide this additional information to the engine control unit. Alternatively, the dew point can be determined by measurement, eliminating the need for models.

Claims

1. Method for operating a sensor (10) for detecting particles, in particular soot particles, in a measurement gas, in particular in the exhaust gas of an internal combustion engine, wherein the sensor (10) comprises a sensor element (12), wherein the sensor element (12) has at least one electrically insulating element (14), a first electrode (16) and a second electrode (18), wherein the first electrode (16) and the second electrode (18) are arranged on the electrically insulating element (14), wherein the first electrode (16) and the second electrode (18) carry out a current and / or voltage measurement, wherein the sensor (10) is operated in at least one measurement phase, wherein a first electrical voltage is applied to the first electrode (16) and the second electrode (18) during the measurement phase, wherein a second electrical voltage is applied to the first electrode (16) and the second electrode (18) during a predetermined period outside the measurement phase, wherein the presence of water on the sensor element (12) is inferred if the current and / or voltage measurement, when the second electrical voltage is applied, produces a value that exceeds a threshold value for an electrical current, characterized in that the second electrical voltage is less than a decomposition voltage for water, which is 1.23 V.

2. Method according to Claim 1, wherein a regeneration of the sensor (10) or a change into the measurement phase is prevented if the current and / or voltage measurement, when the second electrical voltage is applied, produces a value that exceeds a first threshold value for an electrical current.

3. Method according to Claim 2, wherein a regeneration of the sensor (10) or a change into the measurement phase is enabled if the value of the current and / or voltage measurement, after exceeding the first threshold value, undershoots a second threshold value for an electrical current.

4. Method according to Claim 3, wherein a regeneration of the sensor (10) or a change into the measurement phase is enabled after a predetermined time after the second threshold value has been undershot.

5. Method according to one of Claims 2 to 4, wherein a regeneration of the sensor (10) or a change into the measurement phase is enabled if the sensor (10) receives a dew point end release from the outside, preferably a control unit (26).

6. Method according to one of Claims 1 to 5, wherein the sensor (10) is heated during the predetermined period outside the measurement phase.

7. Method according to Claim 6, wherein the sensor (10) is heated to a temperature, the level of which depends on the value of the current and / or voltage measurement when the second electrical voltage is applied.

8. Method according to one of Claims 1 to 7, wherein the sensor (10) is arranged in an exhaust gas tract of an internal combustion engine, wherein the predetermined period outside the measurement phase is after a cold start of the internal combustion engine, in the absence of a dew point end release, by an engine control unit of the internal combustion engine and / or when a predetermined temperature in the exhaust gas tract is undershot.

9. Method according to one of Claims 1 to 8, wherein the second electrical voltage is a value in a range of 0.005 V to 1.2 V and preferably 0.05 V to 1.0 V.

10. Computer program comprising instructions which cause an electronic control unit connected to a sensor for detecting particles to carry out each step of the method according to one of Claims 1 to 9.

11. Electronic storage medium (28) on which a computer program according to Claim 10 is stored.

12. Electronic control unit (26) which comprises an electronic storage medium (28) according to Claim 11.