METHOD FOR CONTROLLING THE FUNCTION OF A SENSOR FOR DETECTING PARTICLES

Abstract

A method is provided for controlling the function of a sensor for detecting particles, in particular soot particles, the sensor including at least two measuring electrodes and a substrate on which the measuring electrodes are situated. The method includes the following: carrying out a first current-voltage measurement for ascertaining a first measured variable; carrying out a second current-voltage measurement for ascertaining a second measured variable, one measuring electrode of the measuring electrodes being applied to another electrical potential; carrying out a third current-voltage measurement for ascertaining a third measured variable; an configured forming a correction value for correcting the second measured variable with the aid of the first measured variable and the third measured variable.

Claims

1-12. (canceled)

13. A method for controlling a function of a sensor for detecting particles, the sensor including at least two measuring electrodes and a substrate on which the measuring electrodes are situated, the method comprising: carrying out a first current-voltage measurement for ascertaining a first measured variable; carrying out a second current-voltage measurement for ascertaining a second measured variable, one measuring electrode of the measuring electrodes being applied to another electrical potential; carrying out a third current-voltage measurement for ascertaining a third measured variable; and forming a correction value for correcting the second measured variable with the aid of the first measured variable and the third measured variable.

14. The method of claim 13, wherein the first current-voltage measurement is carried out prior to the second current-voltage measurement and the third current-voltage measurement is carried out following the second current-voltage measurement.

15. The method of claim 13, wherein the first current-voltage measurement and the third current-voltage measurement are carried out, without a measuring electrode of the measuring electrodes being applied to an electrical potential.

16. The method of claim 13, wherein the correction value is ascertained based on a decay behavior of the first measured variable and the third measured variable.

17. The method of claim 13, wherein the correction value for correcting is subtracted from the second measured variable.

18. The method of claim 13, wherein the first measured variable, the second measured variable and/or the third measured variable is/are an electric current.

19. The method of claim 13, wherein the method is carried out when a heating element is operated.

20. The method of claim 9, wherein the heating element is operated by applying a voltage.

21. The method of claim 19, wherein the voltage applied to the heating element is about 12 V, the electrical potential applied to the one measuring electrode while carrying out the second current-voltage measurement, being about 8.4 V.

22. A computer readable medium having a computer program, which is executable by a processor, comprising: a program code arrangement having program code for controlling a function of a sensor for detecting particles, in particular soot particles, the sensor including at least two measuring electrodes and a substrate on which the measuring electrodes are situated, by performing the following: carrying out a first current-voltage measurement for ascertaining a first measured variable; carrying out a second current-voltage measurement for ascertaining a second measured variable, one measuring electrode of the measuring electrodes being applied to another electrical potential; carrying out a third current-voltage measurement for ascertaining a third measured variable; and forming a correction value for correcting the second measured variable with the aid of the first measured variable and the third measured variable.

23. The computer readable medium of claim 22, wherein the first current-voltage measurement is carried out prior to the second current-voltage measurement and the third current-voltage measurement is carried out following the second current-voltage measurement.

24. An electronic control unit, comprising: a computer readable medium having a computer program, which is executable by a processor, including: a program code arrangement having program code for controlling a function of a sensor for detecting particles, in particular soot particles, the sensor including at least two measuring electrodes and a substrate on which the measuring electrodes are situated, by performing the following: carrying out a first current-voltage measurement for ascertaining a first measured variable; carrying out a second current-voltage measurement for ascertaining a second measured variable, one measuring electrode of the measuring electrodes being applied to another electrical potential; carrying out a third current-voltage measurement for ascertaining a third measured variable; and forming a correction value for correcting the second measured variable with the aid of the first measured variable and the third measured variable.

25. The method of claim 13, wherein the particles include soot particles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 shows an exploded view of a sensor for detecting particles.

[0033] FIG. 2 shows a block diagram of the sensor including the associated control unit including possible measuring electrodes, and heating element potentials during the regeneration.

[0034] FIG. 3 shows an exemplary chronological characteristic of the electrodes and heating potentials during the regeneration phase and up to the beginning of the measuring phase.

DETAILED DESCRIPTION

[0035] FIG. 1 shows a sensor 10 for detecting particles, in particular soot particles, in a gas flow, such as in an exhaust gas flow of an internal combustion engine which is used for installation into an exhaust tract of a motor vehicle. Sensor 10 is configured as a soot sensor, for example, and may be situated downstream from a soot filter of a motor vehicle having a diesel combustion engine.

[0036] Sensor 10 includes a carrier layer 12 which may be manufactured at least partially from an electrically insulating material, e.g., a ceramic, such as aluminum oxide. Into carrier layer 12, a heating element 14 is integrated which is connectable to a suitable voltage source (not shown in greater detail) via contacts 16 and which is used to burn potentially deposited particles, such as soot particles, off sensor 10.

[0037] On carrier layer 12, a plate-shaped substrate 18 is situated which may be manufactured at least partially from an electrically insulating material, e.g., a ceramic, such as aluminum oxide. A structure formed by two measuring electrodes 20, 22 is situated on substrate 18. Measuring electrodes 20, 22 are designed, for example, as interdigital electrodes so that they mesh in a comb-like manner, as shown. Measuring electrodes 20, 22 are connectable to an electronic control unit 26 via contacts 24.

[0038] In the area in which measuring electrodes 20, 22 mesh in a comb-like manner, measuring electrodes 20, 22 may be covered at least partially by a dielectric 28, so that measuring electrodes 20, 22 may be used as electrodes of a capacitor having a measurable capacitance. Dielectric 28 may, in turn, be provided with a protective layer 30 so that it is separated from the surrounding medium whereby a degeneration of dielectric 28 is excluded.

[0039] Sensor 10 may further include a housing which surrounds the structure illustrated in FIG. 1 and is not shown in FIG. 1 for the sake of simplicity of the explanation of the structure of sensor 10. For example, the housing may be configured as a catch sleeve which is provided with an opening in an area lying above measuring electrodes 20, 22 and which is used to settle a gas flow flowing in the exhaust tract so that soot particles or other particles present in the gas flow may accumulate in the area of measuring electrodes 20, 22.

[0040] Sensor 10 according to FIG. 1 may work as follows. If soot or other electrically conductive particles accumulate on substrate 18, an electrical resistance between the two measuring electrodes 20, 22 is reduced. Measuring the impedance between the two measuring electrodes 20, 22 results in a behavior which is typical for a so-called RC member. This means that the soot or particle concentration in the particular exhaust gas may be determined based on the change over time of the resistance portion of the RC member.

[0041] In order to regenerate sensor 10 the deposited particles are burned off with the aid of heating element 14, which is integrated into carrier layer 12, after a certain period of time. If sensor 10 works properly, the resistance between measuring electrodes 20, 22 should considerably increase after this so-called bake-out and may rise toward infinity. Since the mode of operation of sensor 10 for detecting the particle concentration is known per se, e.g., from the related art of WO 2003/006976 A2 named above, the typical mode of operation of sensor 10 will not be discussed here in greater detail and the content of the related art named above which relates to the description of the functionality of sensor 10 is completely included herein by this reference. Instead, the method according to the present invention for controlling the function of sensor 10 is described in the following. The method may, for example, be carried out by control unit 26 named above. In particular, the method is described based on FIGS. 2 and 3.

[0042] FIG. 2 shows a block diagram of sensor 10 and the activation through control unit 26 with the aid of possible electrode and heating element potentials during the regeneration. Here, control unit 26 is illustrated on the left including a circuit 32 of a voltage source and an evaluation unit 34. Furthermore, control unit 26 includes a circuit 36 for heating element 14 and an evaluation unit 38 for a temperature sensor 40 of sensor 10. Temperature sensor 40 may in this case be a part of heating element 14 so that evaluation unit 38 may determine the temperature based on a change in the electrical resistance of heating element 14. It is apparent from the illustration in FIG. 2 that heating element 14 is operated during regeneration in that a voltage of 12 V, for example, is applied to heating element 14. It is furthermore apparent from FIG. 2 that negative measuring electrode 20 is connected to ground and that. an electrical potential of 8.4 V, for example, is applied to positive measuring electrode 22 during regeneration.

[0043] FIG. 3 shows an exemplary chronological characteristic of electrodes and heating element potentials during the regeneration phase and up to the beginning of a measuring phase as described below in greater detail. The time is plotted on x axis 42 and the temperature is plotted on y axis 44. Located in the lines from top to bottom above x axis 42, are a voltage 46 of heating element 14 and a voltage 48 of measuring electrodes 20, 22, an electrical potential 50 of positive measuring electrode 22, and an electrical potential 52 of negative measuring electrode 20. Heating element 14 is operated at a point in time 54. Heating element 14 is operated by applying a voltage of 12 V, for example, to heating element 14. As a result, heating element 14 heats up sensor 10.

[0044] Starting from a point in time 56 particles accumulated on sensor 10, such as soot, are burned off. The burning off takes place for a time period of more than 30 seconds, for example. Toward the end of the burning off of soot, heating element 14 is temporarily not operated from a point in time 58 to a point in time 60, in that no voltage is applied to it for the purpose of reaching a defined temperature. Starting from point in time 60 heating element 14 is operated again, in that a voltage of 12 V, for example, is applied to it. No voltage is applied to measuring electrodes 20, 22 up to a point in time 62. At point in time 62, an electrical potential of 8.4 V is applied to positive measuring electrode 22. This is the actual measuring phase up to a point in time 64 as described in the following in greater detail. At point in time 64, electrical potential is no longer applied to measuring electrode 22, however heating element 14 continues to be operated up to a point in time 66. The method according to the present invention is now described in great detail in the following.

[0045] Shortly before point in time 62, a first current-voltage measurement is carried out for ascertaining a first measured variable. As illustrated in FIG. 3, for example, an electric current is measured between measuring electrodes 20, 22 shortly before point in time 62, i.e., at point in time 68, without a voltage being applied to measuring electrodes 20, 22. At a point in time 70 between points in time 62 and 64, for example shortly before point in time 64, a second current-voltage measurement is carried out for ascertaining a second measured variable. In the time period between points in time 62 and 64 and thus also at point in time 70, the electrical potential of 8.4 V is applied to positive measuring electrode 22 and the electric current between measuring electrodes 20, 22 is detected. Following point in time 64, e.g., at point in time 72, a third current-voltage measurement is carried out for ascertaining a third measured variable. At this point in time, an electrical potential is not applied to positive measuring electrode 22.

[0046] A correction value for correcting the second measured variable is formed with the aid of the first and the third measured variables. In particular, the correction value is ascertained based on a decay behavior of the first measured variable and the third measured variable. The electric current measured between measuring electrodes 20, 22 fluctuates, for example, up to point in time 68 based on the heated-up sensor element and the heater input described above.

[0047] At point in time 68, however, the first measured variable has stabilized and thus decayed to a certain value. The decay behavior of the third measured variable is ascertained analogously. Consequently, even if electrical potential is no longer applied to measuring electrode 22, a polarization takes place and thus a fluctuation of the electric current. However, the latter decays after a certain period of time so that the third measured variable may be ascertained at point in time 70. The correction value for correcting thus ascertained may then be subtracted from the second measured variable.

[0048] In other words, the operation of sensor 10 is controlled by control unit 26. In the case of an application in a motor vehicle, such as a passenger car, the electrical potentials at measuring electrodes 20, 22 and heating element 14 occur during the regeneration and up to the beginning of the actual soot collection phase, as illustrated in FIG. 2. It becomes apparent that the positive potential of heating element 14 is always, except for very short phases, higher than the two potentials of measuring electrodes 20, 22. The potential ratios during the regeneration as well as the positions of the three measuring points in time for compensating the heating input are illustrated in detail in FIG. 3. According to the method described above cations, such as sodium ions, which are by design driven from the depth of sensor 10 toward negative measuring electrode 20 during the self-diagnosis no longer falsify the result of the self-diagnosis. Only that electric current is diagnosed which is generated through the measuring pulse. Changing the heater input over the service life of the sensor no longer has an effect on the diagnosis result either.