DE102016216432A1 - Method for determining the measuring readiness of a particle filter of an internal combustion engine - Google Patents

Abstract

The invention relates to a method for determining the measuring readiness of a particle sensor of an internal combustion engine during a particle filter diagnosis. The method includes determining a theoretical particulate mass concentration value in the exhaust downstream of a particulate filter based at least in part on operating parameters of the internal combustion engine and a predetermined particulate filter efficiency. The method further includes temporally integrating the theoretical particulate mass concentration value to determine a theoretical particulate mass total flowed downstream of the particulate filter in the exhaust gas, and determining that the particulate sensor is ready for measurement when the particulate mass total exceeds a predetermined particulate mass threshold.

Description

The present invention relates to a method for determining the measuring readiness of a particle filter of an internal combustion engine, in particular a method for determining the measuring readiness of a particle sensor arranged in an exhaust gas line downstream of a particle filter during a particle filter diagnosis.

The reduction of exhaust emissions in motor vehicles is an important goal in the development of new motor vehicles. Therefore, combustion processes in internal combustion engines are thermodynamically optimized, so that the efficiency of the internal combustion engine is significantly improved. In the automotive sector diesel engines are increasingly used, which, with modern design, have a very high efficiency. The disadvantage of this combustion technique over optimized Otto engines, however, is the emission of soot or particles. The soot or the particles are particularly carcinogenic because of the polycyclic aromatics, which has already been reacted in various regulations. For example, exhaust emission standards with maximum limits for soot emissions were issued. In order to meet the exhaust emission standards nationwide for motor vehicles with diesel engines, there is a need to produce low-cost sensors that reliably measure the soot content in the exhaust stream of the motor vehicle.

In the case of soot filtering, regenerable filters, such as particulate filters, are used which filter and trap a substantial portion of the soot content from the exhaust. Soot sensors are required for the detection of soot in order to monitor the function of the soot filters or to control their regeneration cycles. For this purpose, the soot filter, which is also referred to as a diesel particulate filter, a soot sensor before and / or be downstream.

The soot or particle sensor upstream of the particulate filter serves to increase system safety and to ensure operation of the particulate filter under optimum conditions. Since this depends to a great extent on the amount of particulates stored in the particulate filter, accurate measurement of the particulate concentration upstream of the particulate filter system, in particular the determination of a high particulate concentration upstream of the particulate filter, is of great importance.

A soot or particle sensor arranged downstream of the particle filter offers the possibility of making an on-board diagnosis and also serves to ensure the correct operation of the exhaust gas aftertreatment system.

If a downstream particle sensor indicates a signal that exceeds a particulate mass concentration in the exhaust gas downstream of a particulate filter a predetermined threshold, this may indicate, for example, a defect of the particulate filter. However, a particle sensor such. As an electrostatic particle sensor, only then provide further processable signals and is accordingly ready to measure, if this has a predetermined particle pre-loading.

At present, the measuring readiness of a particle sensor can not be determined satisfactorily in real measuring operation, so that a plausibility check of the signal of the particle filter can not be carried out. For example, there are attempts to determine the particle pre-loading of particle sensors and thus also the readiness for measurement of the particle sensor on the basis of the measured current. The disadvantage here, however, is that with an intact particulate filter, the necessary particle pre-loading of the particle sensor is not achieved and consequently no particle filter diagnosis can be performed.

It is therefore an object of the present invention to provide a method with which the readiness for measurement of a particle sensor during a particle filter diagnosis can be reliably determined.

This object is achieved by a method according to independent claim 1, a computer program according to claim 8, a computer program product according to claim 9 and a measurement readiness determination system according to claim 10. Preferred embodiments are specified in the subclaims.

The invention is based essentially on the idea during operation of the internal combustion engine, in particular during a particle filter diagnosis, to determine a theoretical particulate mass concentration value present downstream of a particulate filter based at least in part on operating parameters of the internal combustion engine and assuming a predetermined particulate filter efficiency and this theoretical value determined continuously Particle mass concentration values for determining a temporally integrated theoretical mass particle mass flow downstream in the exhaust gas downstream of the particulate filter. If the determined total theoretical particle mass exceeds a predetermined total particulate mass threshold, it can be assumed that the particulate sensor has reached its necessary particle preload so that the signals provided by the particulate sensor can be identified as valid and used for further processing for particulate filter diagnostics.

Thus, by means of a model, the particle mass concentrations are estimated or determined using the operating parameters of the internal combustion engine and integrated over time to determine the theoretical particle mass total value. Thus, the theoretical time can be estimated or determined, at which the particle sensor has the necessary pre-charge. In particular, for this purpose, a particle filter arranged upstream of the particle sensor is used, which has a predetermined efficiency.

In the temporal integration, in addition to the theoretical particle mass concentration value, the chronologically constant geometry of the exhaust pipe at the position of the particle sensor is taken into account. In particular, the particle mass concentration is converted by means of the geometry of the exhaust pipe and then integrated in time.

The inventive method is preferably carried out at each cold start of the internal combustion engine. A cold start of the internal combustion engine can be determined, for example, by the fact that the cooling water and / or exhaust gas flow temperature of the internal combustion engine is below a respective threshold value. In particular, the method according to the invention is carried out at the beginning of a particle filter diagnosis in order to check the validity of the particle filter signals for the particle filter diagnosis. In a particle filter diagnosis is to determine whether the particulate filter is still working properly, d. H. whether the particulate filter efficiency is within a desired range and the particulate filter still captures enough particulate matter from the exhaust gas.

Accordingly, a method for determining the readiness for measurement of a particle sensor of an internal combustion engine is disclosed, which is a particulate filter, which is adapted to be arranged in an exhaust line of the internal combustion engine and at least partially capture the particles located in the exhaust gas, and the particle sensor, which in the exhaust line disposed downstream of the particulate filter and configured to generate a signal indicative of an actual particulate mass concentration located downstream of the particulate filter in the exhaust gas. The method according to the invention has a determination of a theoretical particle mass concentration value in the exhaust gas downstream of the particulate filter based at least in part on operating parameters of the internal combustion engine and a predetermined particulate filter efficiency. The theoretical particulate mass concentration value indicates a theoretical particulate mass concentration as downstream of the particulate filter in the exhaust gas, assuming the predetermined particulate filter efficiency. The inventive method further comprises time-integrating the theoretical particulate mass concentration value to determine a total theoretical particulate mass flowed downstream of the particulate filter in the exhaust gas, and determining that the particulate sensor is ready to measure when the particulate mass total exceeds a predetermined particulate mass threshold.

With the determination of the theoretical particle mass total value on the assumption of the predetermined particle filter efficiency, the theoretical particle mass flowed downstream of the particle filter can be estimated or determined and consequently make possible a statement about the theoretical particle pre-loading of the particle sensor. In this case, the predetermined particle mass threshold value has a value at which the particle sensor has theoretically reached its particle precharge.

In particular, the method according to the invention finds a specific application during a particle filter diagnosis, since the particle filter diagnosis can be carried out using the particle sensor signals. For this purpose, the validity of the particle sensor signals for the particle filter diagnosis is checked by means of the method according to the invention.

According to a preferred embodiment of the method according to the invention, the predetermined particulate filter efficiency corresponds to a value at which the particulate filter just enough particles from the exhaust gas traps and thus the actual particulate matter concentration downstream of the particulate filter is below a legal threshold. In an alternative embodiment, the predetermined particulate filter efficiency may correspond to a value at which the particulate filter no longer captures sufficient particulate matter from the exhaust gas and hence the actual particulate matter concentration downstream of the particulate filter is above the legal threshold.

A particulate filter having the predetermined particulate filter efficiency may also be referred to as a particulate matter filter because particulate filters having an efficiency greater than or equal to the predetermined particulate filter efficiency may be determined to be functional and particulate filters having an efficiency less than the predetermined particulate filter efficiency may be diagnosed as non-functional.

According to a further advantageous embodiment of the method according to the invention, the predetermined particle mass threshold value is dynamically adjusted as a function of the operating state of the internal combustion engine. This means that when determining a predetermined operating state of the internal combustion engine during the temporal integration of the theoretical particle mass concentration values of the predetermined particle mass threshold value can be adjusted. For example, with a speed increase of the internal combustion engine over a predetermined speed threshold value, the predetermined particle mass threshold value can be increased, whereas with a fuel cut-off phase the predetermined particle mass threshold value can be reduced.

The dynamic decrementing of the predetermined particle mass threshold value therefore takes place, for example, in the case of a speed increase of the internal combustion engine to a rotational speed greater than the rotational speed threshold, it can be assumed that the particle pre-charge already accumulated in the particle sensor is at least partially removed again by the resulting higher flow velocity of the exhaust gas in the exhaust gas line or blown out and thus a higher theoretical particle mass in the exhaust gas is necessary until the required particle pre-loading is reached again.

According to a further advantageous embodiment of the method according to the invention, the total theoretical particle mass value determined by means of temporal integration of the theoretical particle mass concentration value is set to zero when the internal combustion engine is restarted. This happens because, after switching off the internal combustion engine, the particle pre-charge still present in the particle sensor is blown out when the internal combustion engine is switched on again.

The theoretical particle mass concentration values determined continuously over time are calculated or determined based at least in part on operating parameters of the internal combustion engine and a predetermined particle filter loading value. For example, to determine a theoretical particle mass concentration value, the amount of fuel injected for combustion, the amount of fresh air supplied for combustion, the combustion temperature, the opening duration of the exhaust valve and / or the ignition time are used as operating parameters of the internal combustion engine.

According to a further aspect of the present invention, a computer program for determining the measuring readiness of a particulate filter arranged in an exhaust tract of an internal combustion engine is disclosed. The computer program is designed to carry out a method according to the invention when executed on a data processing device.

According to another aspect of the present invention, there is disclosed a computer program product comprising a computer readable medium and program code stored on the computer readable medium which, when executed on a computing unit, directs the computing unit to perform a method of the invention.

According to a further aspect of the present invention, a measurement readiness determination system for determining the readiness for measurement of a particle filter arranged in an exhaust line of an internal combustion engine is disclosed. The measurement standby detection system includes a particle sensor configured to be located in the exhaust line of the internal combustion engine downstream of the particulate filter, and a control device connected to the particulate sensor and configured to perform a method according to the invention.

Further features and objects of the invention will become apparent to those skilled in the art from practicing the present teachings as well as consideration of the accompanying drawings, in which:

1 is a flowchart of a method according to the invention, and

2 a schematic diagram of different cases of the method according to the invention.

In the following, a method according to the invention for determining the measuring readiness of a particle sensor during a particle filter diagnosis is shown by way of example. The internal combustion engine has a particle filter arranged in the exhaust gas line and a particle sensor arranged in the exhaust gas line downstream of the particle filter. The particulate filter is designed to at least partially trap the particles in the exhaust gas, so that they are not released into the environment. The particle sensor is designed to deliver a signal which indicates the particulate mass concentration present in the exhaust gas line at the measuring point.

The procedure of 1 starts at the crotch 100 and then comes to the step 110 in which it is queried whether the internal combustion engine is started cold. In this case, for example, it can be queried whether an ignition of the internal combustion engine has been actuated and / or the cooling water and / or exhaust gas station temperature is below a respective predetermined threshold value.

When in step 110 is determined that the internal combustion engine has been cold or started at all, the process goes to the step 120 , However, in step 110 determines that the internal combustion engine has not been cold-started, the process goes directly to the step 130 ,

In step 120 determines whether a particulate filter diagnosis of the particulate filter is necessary. The particle filter diagnosis is necessary at any time according to OBD regulations, for example, and is also carried out continuously accordingly. In particular, the particulate filter diagnosis is performed after each cold start of the internal combustion engine.

When in step 120 if it is determined that no particulate filter diagnosis is necessary, the process goes to the step 180 and will be finished. However, if in step 120 is determined that a particulate filter diagnosis is to be performed, the process comes to the step 130 ,

In step 130 is determined based at least partially on the operating parameters of the internal combustion engine and assuming a predetermined Partikelfilterbeladungswert a theoretical particle mass concentration value. The theoretical particulate mass concentration value indicates the particulate mass concentration theoretically present downstream of the particulate filter assuming the predetermined particulate filter efficiency. The theoretical particle mass concentration value is preferably given in units of milligrams per cubic meter [mg / m ³ ]. Alternatively, the theoretical particle mass concentration value can be given in units of [mg / m ³ s].

The predetermined particulate filter efficiency corresponds to a value at which the particulate filter can be diagnosed as being just sufficiently functional. This means that the particle filter still captures enough particles to comply with legal regulations. For example, the predetermined particulate filter efficiency is in a range between about 70% and about 90%, preferably between about 75% and about 85%, and more preferably about 80%.

In the following step 140 will be the one in the step 130 determined theoretical particle mass concentration value for determining a theoretical particle mass total value integrated in time. The theoretical particle mass total value indicates the particle mass past the particle sensor over time, for example in the unit milligram [mg].

In step 150 will be the one in the step 140 determined theoretical particle mass total value compared with a particle mass threshold. Will in step 150 determines that the determined total mass of particulate matter is smaller than the particle mass threshold, the method moves to the step 160 in which the particle sensor is defined as not ready to measure, and then back to the steps again 120 and 130 in which the temporal integration is continued. In step 160 Thus, it can be determined that the particle sensor has theoretically not reached its required particle pre-charge assuming the predetermined particle filter efficiency.

Will in step 150 determines that the determined total mass of particulate matter is greater than the particle mass threshold, the method goes to the step 170 , in which the particle sensor is now defined as ready to measure. In step 170 it can be assumed that the particle sensor now has the required particle pre-charge since at least the predetermined particle mass threshold value has passed by particles at the particle sensor and has partly flowed into the particle sensor.

One in the step 170 certain particulate sensor ready for measurement can then be used for particulate filter diagnosis (see following description with reference to the 2 ).

With reference to the 2 a total of four different cases or scenarios are shown, in which each of the bars 10 indicates the actual particle preload of the particulate sensor versus time and the bar 20 the evaluation of the particulate filter diagnostic function indicates, in particular whether the particulate filter is working properly or not.

In the 2 Time t0 indicates the system start time at which, for example, the engine is cold-started. The time t1 indicates the time at which the particle sensor is theoretically determined to be ready for measurement. That is, the theoretical total particulate mass value determined on the assumption of the predetermined particulate filter efficiency has exceeded the predetermined particulate mass threshold value at time t1, and thus at time t1, it can be assumed that the particulate sensor has reached its necessary particulate pre-charge.

From the time t1, the actual particle mass concentration in the exhaust gas is thus determined by means of the particle sensor and compared with the theoretical particle mass concentration at the time t1. If the actual particulate mass concentration value is less than or equal to the theoretical particulate mass concentration value, the particulate filter may be diagnosed as functional. But if the actual particle mass concentration value is greater than the theoretical particle mass concentration value, the particle filter can be diagnosed as not functioning.

In the case 1 It is assumed that there is a particulate filter operating at an actual efficiency of 100%. As a result, the particle sensor reaches in this case 1 in fact never the necessary particle pre-charge, as it can be assumed that the particulate filter has already captured all the soot particles.

At time t1, however, assuming the predetermined particle filter efficiency, the sensor is determined to be theoretically ready for measurement, ie, the particle sensor would have achieved the necessary particle pre-charge due to the theoretical calculation. At this time, a signal is detected by means of the particulate sensor that, because of the particulate filter efficiency of 100% in this case, one is a very small signal. More specifically, at this time t1, it can be said that the particulate sensor is less than the particulate filter efficiency of the case assuming the cutoff filter efficiency 1 Although, theoretically, the required particle pre-loading has been achieved, but in fact has not been achieved.

Consequently, it can be concluded that the particle mass concentration actually present downstream of the particulate filter is smaller than the theoretical particulate mass concentration. This means that the particulate filter actually works better than theoretically assumed, so that the particulate filter can be diagnosed as functional.

In the case 2 It is assumed that a particle filter with an efficiency of approximately 90% is present. At the beam 10 of the case 2 It can be seen that the particle sensor actually reaches its pre-charge required for proper measurement at a time t2. However, since the time t2 is later than the time t1, the particulate filter can be diagnosed as being correct even at the time t1.

The case 3 represents a borderline case in which the particulate filter can just be diagnosed as working properly. In particular, in the case 3 of the 2 by the bar 10 can be seen that just at the time t1, the particle sensor actually reaches its required particle pre-charge. Thus, at time t1, the particulate filter can barely be diagnosed as operating properly, for example at an efficiency of about 80%.

The case 4 represents a case in which the particulate filter works with an efficiency of, for example, only 70%. In this case 4 The particle sensor reaches its particle sensor charge state already at a time t3, which is temporally before the time t1. This means that there are actually more particles in the exhaust gas line than the theoretical total mass of particles determined by means of temporal integration of the particle mass concentration values. As a result, the particle sensor actually reaches its necessary particle pre-charge before time t1. Thus, at time t1, the particulate filter can be diagnosed as non-functional.

Claims (10)

A method for determining the measuring readiness of a particle sensor of an internal combustion engine during a particle filter diagnosis, wherein the internal combustion engine has a particle filter, which is designed to be arranged in an exhaust line of the internal combustion engine and at least partially capture the particles located in the exhaust gas, and the particle sensor which in Exhaust line disposed downstream of the particulate filter and configured to generate a signal indicative of an actual particulate mass concentration located downstream of the particulate filter in the exhaust gas, the method comprising the steps of: Determining a theoretical particulate mass concentration value in the exhaust gas downstream of the particulate filter based at least in part on operating parameters of the internal combustion engine and a predetermined particulate filter efficiency, the theoretical particulate mass concentration value indicating a theoretical particulate mass concentration downstream of the particulate filter in the exhaust gas assuming the predetermined particulate filter efficiency; Temporally integrating the theoretical particle mass concentration value to determine a total theoretical particle mass flow that has flowed downstream of the particulate filter in the exhaust gas, and - determining that the particulate matter filter particulate sensor is ready for measurement when the particulate mass total exceeds a predetermined particulate mass threshold. The method of claim 1, wherein the predetermined particulate filter efficiency corresponds to a value at which the particulate filter still traps a sufficient number of particulates from the exhaust gas and the actual particulate matter concentration downstream of the particulate filter is below a legal threshold. The method of claim 1, wherein the predetermined particulate mass threshold corresponds to a value at which it can be assumed that the particulate sensor assumes the predetermined particulate filter efficiency after flowing past the same Particle mass has reached its predetermined particle pre-loading. Method according to one of the preceding claims, wherein the predetermined particle mass threshold value is dynamically adjusted as a function of the operating state of the internal combustion engine. The method of claim 4, wherein at a speed increase of the internal combustion engine, the predetermined particle mass threshold is increased dynamically. Method according to one of the preceding claims, wherein the theoretical particle mass total value determined by means of temporal integration of the theoretical particle mass concentration value is set to zero when the internal combustion engine is restarted. Method according to one of the preceding claims, wherein the operating parameters used for determining a theoretical particle mass concentration value of the internal combustion engine, the amount of fuel injected for combustion, the amount of fresh air supplied for combustion, the combustion temperature, the opening duration of the exhaust valve and / or the ignition timing. Computer program for determining the measuring readiness of a particulate filter arranged in an exhaust line of an internal combustion engine, wherein the computer program is designed to carry out a method according to one of the preceding claims when executed on a data processing device. A computer program product comprising a computer readable medium and program code stored on the computer readable medium which, when executed on a computing unit, directs the computing unit to perform a method according to any one of claims 1 to 7. Measuring readiness determination system for determining the measuring readiness of a particle filter arranged in an exhaust line of an internal combustion engine, comprising: A particle sensor adapted to be arranged in the exhaust line of the internal combustion engine downstream of the particle filter, and - A control device which is connected to the particle sensor and adapted to carry out a method according to any one of claims 1 to 7.

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