DE102018217201A1 - Method and device for evaluating a sensor signal of a soot sensor - Google Patents

Abstract

The invention relates to a method and a device for evaluating a sensor signal from a soot sensor (1), the soot sensor (1) being arranged in an exhaust gas stream of an internal combustion engine (3). Means (6) are provided for measuring an amount of soot deposited on the soot sensor by measuring the conductivity between electrodes of the soot sensor (1). The means (6) determine a soot amount of the exhaust gas by means of a model and the measurement of the conductivity is assessed as plausible or not plausible by evaluating the soot amount of the exhaust gas predicted by the model.

Description

The invention is based on a method and a device according to the type of the independent claims. From the DE 10 2005 040 790 A1 a method and a device for evaluating a sensor signal of a soot sensor is already known, the soot sensor being arranged in an exhaust gas stream of an internal combustion engine. By measuring the conductivity between electrodes of the soot sensor, an amount of soot deposited on the soot sensor is detected, whereby the particles contained in the exhaust gas are measured. For this purpose, a change in the conductivity is set in relation to a measurement time.

Advantages of the invention

The method according to the invention and the device according to the invention have the advantage over the prior art that the measurement of the conductivity of the soot sensor is made plausible by comparison with a model of the amount of soot in the exhaust gas. The quality of the measured sensor signal can thus be improved with regard to its meaningfulness. In particular, such a plausibility check makes it possible to identify a possible failure of a particle filter particularly quickly, as a result of which an overall improved diagnosis of the internal combustion engine, the exhaust gas flow of which is to be cleaned by the particle filter, can be achieved.

Further advantages and improvements result from the features of the dependent claims. In order to ensure stable measurement operation of the measurement, an evaluation of the sensor signal and a plausibility check should only take place if the measured conductivity exceeds a threshold value. A resistance between the electrodes or a current flow between the electrodes can be evaluated to measure the conductivity. An examination of the gradient of the conductivity is particularly meaningful, particularly since a problematic measurement signal can be recognized particularly quickly in this way. In order to check the plausibility of the measurement signal, particularly meaningful time phases can be evaluated. Such particularly meaningful phases are phases of a high soot concentration and / or a high soot concentration gradient, which are predicted by the model. The soot concentration or the soot concentration gradient is modeled in particular by modeling the formation of soot particles in the internal combustion engine by means of operating parameters of the internal combustion engine. Furthermore, a runtime of the soot particles from the internal combustion engine to the soot sensor should also be taken into account. Both measures can achieve a high quality of the plausibility check of the measured conductivity signal relative to the predicted amount of soot. Due to the plausibility checks of the soot sensor, a particularly quick detection of defective particle filters can take place. If the measurement cannot be determined as correct on the basis of the plausibility check, the sensor signal must be evaluated over a longer period of time in order to detect a possible malfunction of the particle filter.

Figure list

• 1 eine Brennkraftmaschine mit einem Partikelfilter und einem Rußsensor,
• 2 ein Messsignal des Rußsensors und eine Rußmenge im zeitlichen Verlauf,
• 3 ein Messsignal eines Rußsensors und eine Rußmenge im zeitlichen Verlauf und
• 4 einzelne Schritte des erfindungsgemäßen Verfahrens.

Embodiments of the invention are shown in the drawings and explained in more detail in the following description. Show it:

• 1 an internal combustion engine with a particle filter and a soot sensor,
• 2nd a measurement signal from the soot sensor and an amount of soot over time,
• 3rd a measurement signal from a soot sensor and an amount of soot over time and
• 4th individual steps of the method according to the invention.

Description of the invention

In the 1 is an internal combustion engine schematically 3rd shown whose combustion gases through an exhaust pipe 4th through a particle filter 2nd to an exhaust pipe 5 is directed. The exhaust gases are through the exhaust pipe 5 released to the environment. At the internal combustion engine 3rd it is a common gasoline or diesel engine, in which a fuel is introduced together with air and burned. The exhaust gases from the internal combustion engine 3rd are cleaned by catalysts, for example in the exhaust pipe 4th are arranged. Details of these catalysts are for simplification reasons 1 not shown. Furthermore, the exhaust gases are through the particle filter 2nd headed. The particle filter 2nd consists of a porous material through which the exhaust gas flows. Possibly in the exhaust gas of the internal combustion engine 3rd Particles contained, such as soot particles, are removed from the particle filter 2nd from the exhaust gas flow of the internal combustion engine 3rd filtered out.

To monitor the function of the particle filter 2nd is in the exhaust pipe 5 a soot sensor 1 arranged. The soot sensor 1 protrudes into the exhaust gas flow and soot particles still present in the exhaust gas are deposited on the surface of the soot sensor 1 on. The surface of the soot sensor 1 is provided with electrodes between which a measuring voltage is applied. If soot particles get into sufficient amount on the surface of the soot sensor 1 deposit, so conductive connections between the electrodes can form, so that there is a current flow due to the applied measuring voltage. With increasing amount of soot particles on the surface of the soot sensor 1 have accumulated, the conductivity changes or correspondingly the resistance or the current flow between the electrodes. With an increasing amount of soot particles, the resistance or the conductivity or the current flow between the electrodes of the soot sensor decrease 1 . If there is a large number of soot particles on the soot sensor 1 have deposited and the conductivity between the electrodes is very high, so the soot sensor 1 a further accumulation of soot particles no longer recognize that the conductivity no longer increases above a certain threshold. For this purpose, a free-burning process takes place from time to time, in which the soot sensor 1 is so strongly heated that the soot particles that are on the surface of the soot sensor 1 have accumulated, burn, that means to be converted back into a gaseous state. After such a free burning process, the soot sensor is 1 again in an initial state in which the resistance between the electrodes is very high or the conductivity between the electrodes is very low.

Furthermore, in the 1 another control unit 6 shown which one over a line 7 the signals from the soot sensor are fed. The control unit can also 6 also by applying appropriate signals to the lines 7 a free burning of the soot sensor 1 trigger. Furthermore, the control unit 6 still over lines 8th with the internal combustion engine 3rd connected. Over these lines 8th can the control unit 6 corresponding sensor signals from sensors of the internal combustion engine 3rd read or also actuators of the internal combustion engine 3rd influence / control.

Through the soot sensor 1 can thus monitor the correct function of the particle filter 2nd respectively. This is done each time the engine is started 3rd first waited for a certain heating of the exhaust system and in particular water, which is also on the soot sensor during a standstill 1 has deposited, is removed from the exhaust system. The soot sensor is then heated 1 through the control unit, leaving soot residues from previous combustion cycles on the soot sensor 1 are deposited by the soot sensor 1 be removed. After this free burning the normal measuring operation then takes place, that is to the electrodes of the soot sensor 1 a measuring voltage is applied and it is awaited whether there is a current flow between the electrodes and thus an indication of an increase in the conductivity between the electrodes due to deposited soot on the soot sensor 1 can be demonstrated. A meaningful evaluation of the signal of the soot sensor takes place only when a certain conductivity, ie a certain current flow between the electrodes of the soot sensor 1 is detectable.

If it is then determined that the conductivity between the electrodes of the soot sensor 1 is too high too quickly, ie after too short a current flows between the electrodes due to the applied measuring voltage, this can be an indication of a defective particle filter 2nd be seen. The particle filter 2nd can be damaged by mechanical damage or by local overheating, so that of the exhaust pipe 4th exhaust gas flow no longer completely through a porous material of the particle filter 2nd flows through, but at one or more points of the particle filter 2nd a direct connection between the exhaust pipe 4th and the exhaust pipe 5 is available. In such a case, particles can be filtered through the particle filter 2nd directly from the exhaust pipe 4th into the exhaust pipe tail pipe 5 arrive, so that the filter effect of the particle filter 2nd is no longer given. Such a defective particle filter 2nd leads to an increased occurrence of soot particles in the exhaust pipe 5 and thus also to an increased deposition of soot particles on the particle filter 1 . Such damage to the particle filter must be reliably recognized.

Even with a working particle filter 2nd However, it can occasionally lead to the formation of larger soot particles in the exhaust pipe 5 come, for example, because of one in front of the soot sensor 1 located point of the exhaust pipe 5 soot particles have accumulated and then a larger soot particle, which is also referred to as soot flake, from the wall of the exhaust pipe 5 loosens and briefly on the soot sensor 1 comes to rest. Such a larger soot particle or soot flake would thus reduce the conductivity between the electrodes of the soot sensor 1 greatly increased, although no general defect in the particle filter 2nd is present, but only a larger soot particle happens to be on the soot sensor 1 has struck down. However, such soot flakes have the property that they are only temporarily on the soot sensor due to their sizes 1 adhere so that the originally very high increase in conductivity is only of a temporary nature. It is therefore common for the soot sensor to have a rapidly increased conductivity 1 to be evaluated only if this effect occurs for a certain time, for example more than 60 seconds. This means that if the particle filter is suddenly damaged 2nd a corresponding defect in the particle filter 2nd can only be recognized after a certain delay time. According to the invention, a plausibility check is now proposed with which the Time from which a defect in the particle filter 2nd is reliably recognized, is shortened.

In the 2nd and the 3rd are therefore each a modeled soot concentration CR and a current flow I. of the soot sensor 1 shown. The soot concentration CR is calculated using a model from the operating parameters of the internal combustion engine. For this purpose, in the control units 6 the operating data of the internal combustion engine 3rd processed and based on a model of soot formation in the internal combustion engine 3rd , which models the soot particles generated during combustion. Furthermore, the flow rate of air through the internal combustion engine must also be used in this model formation 3rd are taken into account and the duration that the exhaust gases from the internal combustion engine 3rd through the exhaust system to the soot sensor 1 need. The in the 2nd and 3rd shown soot concentration CR thus represented the soot concentration determined from a model at the location of the soot sensor 1 Furthermore, the 2nd and 3rd one current flow each I. which is proportional to the conductivity between the electrodes of the soot sensor 1 is. By measuring the current flow between the electrodes of the soot sensor, the soot on the soot sensor 1 amount of soot deposited can be determined. According to the invention, it is now provided that the measured values for the conductivity are checked for plausibility with the model values for the soot concentration. A defect in the particle filter can be caused by a corresponding plausibility check of the measured values 2nd can be recognized much faster than without such a plausibility check.

In the 2nd a time course is shown in which, due to the plausibility check of the measured conductivity signal, a significantly faster detection of a defective particle filter 2nd took place than at the 3rd .

In the 2nd the soot concentration is shown in the upper area of the diagram CR versus time t shown. At the bottom of the diagram the 2nd becomes the measured current I. between the electrodes of the soot sensor 1 versus time t shown. As can be seen from the course of time, no current is initially measured. Then the current increases I. , this increase is not continuous, especially there are phases of a stronger and phases with little or almost no increase. At a time T1 becomes an initial value I0 reached for the current. From this threshold I0 there is a suspicion that the particulate filter 2nd is damaged. Alternatively, however, this threshold can be exceeded I0 be triggered by a larger soot particle or soot flake. Because such soot flakes are also coming from the soot sensor 1 can solve is to exceed the threshold I0 not a sufficient criterion for a defect in the particle filter 2nd ascertain. It will therefore be at the time T1 a period started up to the point in time T4 lasts. It continues at the time T1 a plausibility check of the measured current signal is started at which the measured current I. by means of the concentration of soot particles CR is checked for plausibility. This will be done at the time T2 a sharp increase in the soot concentration CR detected. This sharp increase continues until now T3 on. This means that at the time window T2-T3 a significantly increased amount of soot particles was contained in the exhaust gas and also between the time T2 and T3 a significant increase in the soot concentration was predicted by the model. The current signal is now correspondingly in this time window T2-T3 examined. In this time interval T2 - T3 there is a clear increase in the measured current, which is plausible, in addition to the increase in the soot concentration in the exhaust gas calculated by the model CR . At the time T3 it is thus determined that in the time interval T2-T3 the increase in current flow is plausible in relation to the calculated gradient of the soot concentration. At the time T3 the measured current signal is thus plausibly recognized in relation to the calculated soot signal and can therefore already at the time T3 a defect in the particle filter 2nd can be reliably determined.

In the 3rd becomes the same course of the soot concentration and an implausible course of the current signal I. shown. The course up to the point in time T2 corresponds to the course as it was for 2nd has been described. At the time T3 it is then also determined that the predicted time window T2-T3 a characteristic increase, ie a high gradient of the soot concentration CR exhibited. The measured current signal I. in the time interval T2-T3 but was not plausible for this gradient of the soot concentration CR , since the increase in conductivity or the current flow is not proportional to the soot concentration. It can thus with the measured course of the 3rd at the time T3 it cannot be determined with certainty whether the particle sensor is defective or not. Likewise, at the time T5 found that before the date T5 there was a high gradient of the soot concentration. But this gradient does not lead to a plausible rise in the current signal either I. led, since the gradient of the current is not plausible for the gradient of the soot concentration CR is. Even at the time T5 Therefore, it cannot be safely concluded that the particle sensor 2nd is broken. Only at the time T4 ie after an appropriate waiting time of, for example, 60 seconds after the time T1 is used for safety reasons on a defective particle filter 2nd closed because the current signals I. for a long period, namely the period from T1-T4 was above the threshold value of I0. Point of time T4 but is significantly later than the time T3 of the 1 , so that when the measured current signal is checked for plausibility by the Soot concentration in the exhaust gas is a defect in the particle filter much faster 2nd can be recognized.

Individual steps in the process are described in the 4th another schematically represented. In step 41 the soot sensor is ready to measure 1 detected. This is after starting the internal combustion engine 3rd wait for an adequate warm-up time of the exhaust system to ensure that no condensed water is left on the soot sensor 1 or anywhere else in the exhaust system. The soot sensor is also burned free 1 and thus a removal of all already on the soot sensor 1 collected soot particles from the previous measurement phase of the soot sensor. If in step 41 then the operational readiness of the soot sensor 1 the method according to the invention begins in step 42 . In step 42 the measurement signals of the soot sensor are continuously 1 examined with regard to the conductivity or the current flowing between the electrodes. As long as the current flow is lower than the threshold value, the method according to the invention is not started, ie on the step 42 the step follows again 41 . If in step 42 it is determined that the current flow is greater than the threshold value I0 alternatively the steps will follow 43 and 44 . In step 43 is examined whether a plausibility of the current signal relative to the soot concentration CR or the gradient of the soot concentration CR is available. If this is the case, follow the step 43 the step 45 which determines that the particulate filter 2nd is broken. In parallel is the step 44 examines whether the measured current is still above the threshold 10th lies and whether the time T4 is reached. If the time T4 is reached and the current is still above the threshold 10th lies on the step 44 the step 45 in which a defect in the particle filter is found. For both steps 43 and 44 applies that if after the time T1 the measured current again below the threshold 10th falls, the process is ended or back to step 41 jumps. In this case, the threshold was exceeded 10th only the result of a single isolated soot flake.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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.

Patent literature cited

• DE 102005040790 A1 [0001]

Claims (9)

Method for evaluating a sensor signal of a soot sensor (1), the soot sensor (1) being arranged in an exhaust gas stream of an internal combustion engine (3) and by measuring the conductivity between electrodes of the soot sensor (1) an amount deposited on the soot sensor (1) Detects soot, characterized in that a soot amount of the exhaust gas is determined by a model and the measurement of the conductivity is assessed as plausible or not plausible by evaluating the soot amount of the exhaust gas predicted by the model. Procedure according to Claim 1 , characterized in that the plausibility check is only activated when the measured conductivity exceeds a threshold value (10). Method according to one of the preceding claims, characterized in that the gradient of the conductivity is evaluated. Procedure according to Claim 3 , characterized in that the sensor signal is considered plausible if temporal phases of a high soot concentration and / or a high soot concentration gradient coincide with a high conductivity gradient. Method according to one of the preceding claims, characterized in that the model models the formation of soot particles in the internal combustion engine (3) on the basis of operating parameters of the internal combustion engine (3). Method according to one of the preceding claims, characterized in that the model takes into account a running time of the soot from the internal combustion engine (3) to the soot sensor (1). Method according to one of the preceding claims, characterized in that a particle filter (2) arranged in front of the soot sensor (1) is regarded as defective in a measurement which is judged to be plausible. Method according to one of the preceding claims, characterized in that a particle filter (2) arranged in front of the soot sensor (1) is considered defective in a measurement which is judged to be not plausible if the conductivity exceeds a threshold value for a predetermined period of time. Device for evaluating a sensor signal of a soot sensor (1), the soot sensor (1) being arranged in an exhaust gas stream of an internal combustion engine (3), with means (6) by measuring the conductivity between electrodes of the soot sensor (1) one deposited on the soot sensor To detect the amount of soot, characterized in that the means (6) determine a soot amount of the exhaust gas by means of a model and assess the measurement of the conductivity as plausible or not plausible by evaluating the soot amount of the exhaust gas predicted by the model.

Images