METHOD FOR MONITORING A SENSOR ARRANGED IN AN EXHAUST GAS REGION OF AN INTERNAL COMBUSTION ENGINE

Abstract

A method for monitoring a sensor arranged in the exhaust gas region of an internal combustion engine. The method includes determining a sensor temperature using the sensor, determining a model temperature of the sensor, integrating changes in the sensor temperature and integrating changes in the model temperature if the changes in the sensor temperature exceed a predetermined first threshold value and the changes in the model temperature exceed a predetermined second threshold value, and comparing the integral of the changes in the sensor temperature with a predetermined fourth threshold value.

Claims

1-12. (canceled)

13. A method for monitoring a sensor arranged in the exhaust gas region of an internal combustion engine, comprising the following steps: determining a sensor temperature using the sensor; determining a model temperature of the sensor; integrating changes in the sensor temperature and integrating changes in the model temperature when the changes in the sensor temperature exceed a predetermined first threshold value and changes in the model temperature exceed a predetermined second threshold value; and comparing the integral of the changes in the sensor temperature with a predetermined fourth threshold value.

14. The method according to claim 13, further comprising: comparing the integral of the changes in the sensor temperature with the predetermined fourth threshold value when the integral of the changes in the model temperature exceeds a predetermined third threshold value.

15. The method according to claim 13, wherein the determination of the model temperature is based at least on an exhaust gas temperature and/or a wall temperature of the exhaust gas region at an installation location of the sensor.

16. The method according to claim 13, further comprising low-pass filtering the sensor temperature and/or the model temperature.

17. The method according to claim 13, further comprising: forming a sensor temperature quotient and/or a model temperature quotient with a predetermined time step.

18. The method according to claim 13, further comprising: identifying a removal and/or functionally improper installation of the sensor when the integral of the changes in the sensor temperature falls below the predetermined fourth threshold value, and identifying an installation and/or functionally proper installation of the sensor when the integral of the changes in the sensor temperature reaches or exceeds the predetermined fourth threshold value.

19. The method according to claim 13, wherein the sensor is a particle sensor.

20. The method according to claim 13, wherein the internal combustion engine is a diesel engine, wherein the method is carried out in the context of on-board diagnostics of the diesel engine.

21. An apparatus configured to monitor a sensor arranged in an exhaust gas region of an internal combustion engine, wherein the apparatus comprises: a control configured to: determine a sensor temperature using the sensor; determine a model temperature of the sensor; integrate changes in the sensor temperature and integrate changes in the model temperature when the changes in the sensor temperature exceed a predetermined first threshold value and changes in the model temperature exceed a predetermined second threshold value; and compare the integral of the changes in the sensor temperature with a predetermined fourth threshold value.

22. A non-transitory computer-readable medium on which is stored a computer program for monitoring a sensor arranged in the exhaust gas region of an internal combustion engine, the computer program, when executed by a processor, causing the processor to perform the following steps: determining a sensor temperature using the sensor; determining a model temperature of the sensor; integrating changes in the sensor temperature and integrating changes in the model temperature when the changes in the sensor temperature exceed a predetermined first threshold value and changes in the model temperature exceed a predetermined second threshold value; and comparing the integral of the changes in the sensor temperature with a predetermined fourth threshold value.

23. An electronic control device for monitoring a sensor arranged in the exhaust gas region of an internal combustion engine, the electronic control device configured to: determine a sensor temperature using the sensor; determine a model temperature of the sensor; integrate changes in the sensor temperature and integrate changes in the model temperature when the changes in the sensor temperature exceed a predetermined first threshold value and changes in the model temperature exceed a predetermined second threshold value; and compare the integral of the changes in the sensor temperature with a predetermined fourth threshold value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Other optional details and features of the present invention will emerge from the following description of preferred embodiment examples which are shown schematically in the figures.

[0028] FIG. 1 shows the technical environment in which the method according to the present invention can be used.

[0029] FIG. 2 shows schematically, the sensor element of a sensor embodied as a particle sensor in plan view.

[0030] FIG. 3 shows a flowchart of the method according to an example embodiment of the present invention.

[0031] FIG. 4 shows example progressions of the temperatures and integrals of the positive temperature changes in the intact case.

[0032] FIG. 5 shows example progressions of the temperatures and integrals of the positive temperature changes in the defect case.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0033] FIG. 1 shows the technical environment in which the method according to the present invention can be used. The technical environment can also comprise exhaust gas aftertreatment devices which include measures to mitigate at least one other statutorily limited component, e.g., NOx mitigation measures.

[0034] An internal combustion engine 10, which can be embodied as a diesel engine, is supplied with combustion air via an air feed inlet 12. The quantity of combustion air can be determined by means of an air mass flow meter 14 in the air feed inlet 12. The quantity of air can be used in a correction of an accumulation probability of particles present in the exhaust gas from the internal combustion engine 10. The exhaust gas from the internal combustion engine 10 is discharged via an exhaust gas line 16 in which an exhaust emission control system 18 is disposed. This exhaust emission control system 18 can be embodied as a diesel particle filter. Also disposed in the exhaust gas line 16 in the shown example are an exhaust gas probe 20 embodied as a lambda probe and a sensor 22 embodied as a particle sensor, the signals of which are fed to an engine control 24. Viewed in the direction of flow of the exhaust gas, the sensor 22 is disposed downstream of the exhaust emission control system 18. The engine control 24 is also connected to the air mass flow meter 14 and, based on the data provided to it, determines a fuel quantity that can be delivered to the internal combustion engine 10 via a fuel metering unit 26. The sensor 22 or an additional sensor 22 can also be disposed upstream of the exhaust emission control system 18 in the direction of flow of the exhaust gas. The shown apparatuses make it possible to observe the particle emissions of the internal combustion engine 10 (on-board diagnostics) and to predict the load on and/or identify a defect of the exhaust emission control system 18 configured as a diesel particle filter (DPF).

[0035] FIG. 2 shows a schematic illustration of a sensor element of a sensor 22 embodied as a particle sensor in plan view. A first electrode 30 and a second electrode 32 are applied to an insulating carrier 28, for example made of aluminum oxide. The electrodes 30, 32 are embodied as two interdigital, intermeshing comb electrodes. A first connector 34 and a second connector 36, via which the electrodes 30, 32 can be connected to a not-depicted control unit for voltage supply and for carrying out the measurement, are provided on the end faces of the electrodes 30, 32. The sensor 20 further comprises a temperature sensor 38 that can be used to directly determine a sensor temperature. The temperature sensor 38 can be embodied as a platinum meander, wherein additional electrodes determine a temperature-dependent resistance, which can be evaluated in the engine control 24.

[0036] The sensor 22 further comprises a heating element 40, which is integrated in the carrier 28, and an optional protective layer 42. It can be provided that the heating element 40 is simultaneously embodied as a temperature sensor 38, or that the heating element 40 and the temperature sensor 38 are embodied as separate electrical conductors with separate electrodes.

[0037] The mode of operation of such particle sensors has already been adequately described in the literature and will therefore be described only briefly in the following.

[0038] If such a sensor 22 is operated in a gas flow carrying particles, for example in an exhaust duct of a diesel engine, particles from the gas flow will settle on the sensor 22. In the case of the diesel engine, the particles are in particular soot particles with a corresponding electrical conductivity. The rate at which the particles settle on the sensor 22 depends not only on the particle concentration in the exhaust gas but, among other things, also on the voltage applied to the electrodes 30, 32. The applied voltage generates an electrical field which exerts a corresponding attraction on electrically charged particles and particles having a dipole charge. The rate at which the particles settle can therefore be influenced by a suitable selection of the voltage applied to the electrodes 30, 32.

[0039] In the embodiment example, at least the lead portions of the electrodes 30, 32 and the carrier 28 are coated on the electrode side with the optional protective layer 42. The optional protective layer 42 protects the electrodes 30, 32 from corrosion at the high operating temperatures of the sensor 22 that usually prevail. In the present embodiment example, it is made of a material having a low conductivity, but it can also be made of an insulator.

[0040] After a certain amount of time, particles from the gas flow have settled on the protective layer 42 in the form of a layer. Due to the low conductivity of the protective layer 42, the particles form a conductive path between the electrodes 30, 32, so that, depending on the quantity of deposited particles, there is a change in resistance between the electrodes 30, 32. This can be measured, for example, by applying a constant voltage to the connectors 34, 36 of the electrodes 30, 32 and determining the change in the current due to the accumulated particles.

[0041] If the protective layer 42 has an insulating structure, the deposited particles lead to a change in the ohmic resistance of the sensor 22, which can be evaluated by means of a corresponding measurement, preferably with a DC voltage.

[0042] The diagnostic method according to the present invention is described in more detail in the following. The functionality of the method according to the present invention with the variants described above or in the following can be implemented particularly advantageously as software in the engine control 24 of the internal combustion engine 10, in diesel internal combustion engines in the electronic diesel control (EDC) system. The engine control 24 can therefore be used by its control as an apparatus or control device to carry out the method. The method is carried out in the context of on-board diagnostics of the diesel engine, for example.

[0043] FIG. 3 shows a flowchart of the method according to the present invention. In step S10, the method according to the present invention provides that a sensor temperature is determined by means of the sensor 22. The sensor temperature can be determined directly or indirectly. In a subsequent step S12, the sensor temperature is low-pass filtered. Changes in temperature and in particular increases in the temperature of the sensor temperature are recorded as well. In order to be able to observe temperature changes, a difference quotient of the sensor temperature is formed with a predetermined time step dt in a subsequent step S14. If the changes in the sensor temperature exceed a predetermined first threshold value, the changes in the sensor temperature are integrated in step S16. The first threshold value is selected such that changes due to signal noise are hidden. Small changes for which no corresponding counterpart can be found in the changes in a model temperature of the sensor 22 are not taken into account. The focus here is not on a comparison of temperature changes within a single time step, but within a longer period of time, for example of several seconds.

[0044] In parallel to steps S10 to S16, the method provides in step S18 that the model temperature of the sensor 22 is determined. The model temperature can be determined by means of another sensor, for example. The model temperature is based at least on an exhaust gas temperature and/or a wall temperature of the exhaust gas region at an installation location of the sensor. In a subsequent step S20, the model temperature is low-pass filtered. Changes in temperature and in particular increases in the temperature of the model temperature are recorded as well. In order to be able to observe temperature changes, a difference quotient of the model temperature is formed with a predetermined time step dt in a subsequent step S22. If the changes in the model temperature exceed a predetermined second threshold value, the changes in the model temperature are integrated in step S24. The second threshold value is selected such that changes due to signal noise are hidden. The only model temperature increases that are taken into account are those for which a corresponding reaction of the sensor temperature can be observed as well. The focus here is not on a comparison of temperature changes within a single time step, but within a longer period of time, for example of several seconds.

[0045] If the integral of the changes in the model temperature exceeds a predetermined third threshold value in a subsequent step S26, the integral of the changes in the sensor temperature is compared with a predetermined fourth threshold value in a step S28. Otherwise, the method ends after step S26. If the integral of the changes in the sensor temperature falls below the predetermined fourth threshold value in step S28, a removal and/or functionally improper installation of the sensor 22 is identified in step S30. If the integral of the changes in the sensor temperature reaches or exceeds the predetermined fourth threshold value in step S28, an installation and/or functionally proper installation of the sensor 22 is identified in step S32.

[0046] FIG. 4 shows example progressions of the temperatures and integrals of the positive temperature changes in the intact case. The time is plotted on the x-axis 44. The y-axis 46 shows the sensor temperature, the model temperature, the integral of the positive sensor temperature changes and the integral of the positive model temperature changes. The curve 48 represents the progression of the sensor temperature. The curve 50 represents the progression of the model temperature for the sensor. The curve 52 represents the progression of the integral of the positive sensor temperature changes. The curve 54 represents the progression of the integral of the positive model temperature changes. As can be seen from FIG. 4, when the sensor 22 is intact, the sensor temperature follows the model temperature, so that the curves 52 and 54 have a similar progression of the respective integrals.

[0047] FIG. 5 shows example progressions of the temperatures and integrals of the positive temperature changes in the defect case. Only the differences to FIG. 4 are discussed in the following and the same or comparable features are provided with the same reference signs. As can be seen from FIG. 5, when the sensor 22 is defective, the sensor temperature does not follow the model temperature. The sensor temperature thus remains constant as the model temperature increases, as can be seen from curves 48 and 50. The curve 54 therefore increases, but not the curve 52.

[0048] Another advantage of this evaluation method lies in the expectation of a high selectivity, because the integral of the sensor temperature changes will increase not at all or only slightly in the defect case. The defect threshold can thus be set very low, which also enables an evaluation after comparatively few model temperature increases. In exceptional cases, a sensor temperature increase in the defect case can be caused by the influence of trapped heat, for example if the vehicle is parked in the garage immediately after a trip with high engine load. The temperature increase in such a scenario will firstly be low and secondly comparatively slow, however, so that integration of such increases can be prevented by a suitable selection of the integration threshold.

[0049] The evaluation method implemented in this invention utilizes temperature changes, which means that it requires a comparatively dynamic driving style. The currently used methods tend to assume static conditions with little changes in the model temperature. The evaluation methods thus cover complementary travel conditions, which is why they can advantageously both be used at the same time to identify a removed sensor. In this case, the method that arrives at a diagnostic result first can trigger the setting of the error. The exclusive use of the described new evaluation method is possible too.

[0050] The use of the present invention can be demonstrated by an analysis of the relevant software. The present invention could also be demonstrated in the manner in which a corresponding diagnosis is to be applied to sensor removal. A demonstration would moreover be possible if a sensor is operated with a control device according to the present invention and relevant software.