DE102017223162B4 - Method and device for diagnosing a particulate filter arranged in the exhaust tract of a gasoline engine operated with direct fuel injection - Google Patents

Abstract

Method for diagnosing a particle filter (2) arranged in the exhaust tract (1) of a gasoline engine operated with direct fuel injection, comprising the following steps: - measuring the pressure by means of a first pressure sensor (3) arranged upstream of the particle filter, - measuring the pressure by means of a downstream of the particle filter arranged second pressure sensor (4), - Determination of the loading state of the particle filter (2) and / or the presence of the particle filter (2) by evaluating the pressure signals measured by the two pressure sensors (3, 4), whereby the signal curves of the pressure signals measured by the two pressure sensors (3, 4) are taken into account during a crankshaft segment and in which the area between the pressure signals of the pressure signals measured by the two pressure sensors (3, 4) is determined when evaluating the signal curves.

Description

The invention relates to a method and a device for diagnosing a particle filter arranged in the exhaust tract of a gasoline engine operated with direct fuel injection.

It is already known to equip gasoline engines operated with direct fuel injection with a particle filter in order to be able to comply with predetermined particle emission limit values. These particle filters filter most of the particles produced during combustion, in particular soot particles, out of the exhaust gas. The separated particles remain in the particle filter, provided that the conditions present in the particle filter, for example increased temperature, oxygen in the exhaust gas, do not lead to regeneration of the particle filter.

If the driving conditions are unfavorable, especially in the case of many cold starts and short journeys, the soot loading of the particulate filter can reach a critical value at which the particulate filter can be damaged during a subsequent soot conversion (regeneration). The high soot load can lead to high temperatures and high temperature gradients in the particle filter. These can melt the filter material or lead to high mechanical stresses in the filter material. Both of the aforementioned mechanisms can irreversibly damage the particle filter.

In order to avoid such irreversible damage, an active regeneration of the particle filter is initiated as soon as a critical soot load is exceeded. This regeneration of the particle filter can be carried out in various ways. For example, the temperature of the exhaust gas can be increased for regeneration of a particle filter. Furthermore, the proportion of oxygen in the exhaust gas can also be increased to regenerate the particle filter.

As described above, the active regeneration of the particulate filter is triggered in response to an increased soot load in the particulate filter. As a result, the soot load in the particulate filter is a variable that must be determined by the engine control unit. In this context, it is known to model the soot loading of a particle filter using its influencing variables. These aforementioned influencing variables include, in particular, the engine speed and the engine load.

Considered over the service life of a particulate filter or due to a fault, however, the soot emissions of an engine change in practice. As a result, the modeled soot load of the particulate filter exhibits greater deviations from the real load. This can lead to the damage mentioned above occurring.

To avoid this, the load would not only have to be modeled, but measured.

One possibility for this, known from the field of particle filters for diesel vehicles, would be to describe the loading of the particle filter using the differential pressure. When designing particle filters for gasoline engines operated with direct fuel injection, however, the differential pressures that occur are significantly lower than in the diesel sector. As a result, no differential pressure sensor was installed in gasoline engines operated with direct fuel injection and therefore no evaluation of the differential pressure could be carried out.

In the DE 10 2014 215 659 A1 describes a method for monitoring the condition of a particle filter arranged in an exhaust gas duct by means of a measuring device arranged downstream of the particle filter. The measuring device has a sensor and a particle-absorbing material, which at least partially separates the sensor from an exhaust gas stream flowing through the particle filter, the method comprising the following steps: exposure of the measuring device with exhaust gas over a loading interval; - Detecting a pulsation of a signal from the sensor or a variable derived from the signal; - comparing the pulsation with a reference pulsation; - Assessment of the state of the particle filter as a function of the comparison and the loading interval.

The DE 10 2016 218 687 A1 shows a method for detecting a degree of loading of a particle filter arranged in an exhaust system of an internal combustion engine, the absolute exhaust gas pressure in the exhaust system of the internal combustion engine being determined downstream of an exhaust valve and the degree of loading of the particle filter being determined as a function of the determined absolute exhaust gas pressure, the absolute exhaust gas pressure in the exhaust system immediately ahead an opening of the exhaust valve is determined.

In order to identify the failure of a particle filter precisely and at an early stage after an error has occurred, the JP 2004-308 454 A proposed to detect the extent of a discontinuous change in the exhaust gas state amount on the downstream side of the particulate filter in order to detect failure of the particulate filter by comparing with a predetermined value. In one embodiment, the exhaust gas pressure on the downstream side of the particulate filter is detected as an exhaust gas state quantity in order to calculate its pulsation amplitude. It will determined that an error occurs when the pulsation amplitude exceeds a predetermined value.

In the DE 10 2013 226 565 A1 a method for monitoring a component arranged in an exhaust duct of an internal combustion engine is described, which is characterized in that, when the exhaust gas pressure changes, the time delay between the exhaust gas pressure upstream in front of the component and the exhaust gas pressure downstream after the component is detected and that when the exhaust gas pressure changes, Time delay an error signal is provided.

The DE 10 2015 119 416 A1 describes a method and system for diagnosing a particulate filter disposed in an exhaust passage of an engine cylinder. In one example, a method may include directing exhaust gas from a first cylinder through a first particulate filter in a first passage and directing exhaust gas from a second cylinder through a second particulate filter in a second passage. The method may further include adjusting engine operation in response to particulate filter degradation, the particulate filter degradation distinguishing between first and second particulate filter degradation based on exhaust pressure pulsation timing relative to combustion events.

The object of the invention is to develop a method and a device such that a correct diagnosis of a particle filter arranged in the exhaust tract of a gasoline engine operated with direct fuel injection can be carried out.

This object is achieved by a method with the features specified in claim 1. Advantageous refinements and developments of the invention are given in the dependent claims. Claim 8 relates to a device for diagnosing a particle filter arranged in the exhaust tract of a gasoline engine operated with direct fuel injection.

• - Messung des Drucks mittels eines vor dem Partikelfilter angeordneten ersten Drucksensors,
• - Messung des Drucks mittels eines hinter dem Partikelfilter angeordneten zweiten Drucksensors,
• - Ermittlung des Beladungszustands des Partikelfilters und/oder des Vorhandenseins des Partikelfilters durch eine Auswertung der von den beiden Drucksensoren gemessenen Drucksignale, wobei
• - bei dieser Auswertung die Signalverläufe der von den beiden Drucksensoren gemessenen Drucksignale während eines Kurbelwellensegments berücksichtigt werden und bei welchem bei der Auswertung der Signalverläufe die Fläche zwischen den Drucksignalen der von den beiden Drucksensoren gemessenen Drucksignale ermittelt wird.

According to the present invention, the following steps are carried out in a method for diagnosing a particle filter arranged in the exhaust tract of a gasoline engine operated with direct fuel injection:

• - Measurement of the pressure by means of a first pressure sensor arranged in front of the particle filter,
• - Measurement of the pressure by means of a second pressure sensor arranged behind the particle filter,
• - Determination of the loading state of the particle filter and / or the presence of the particle filter by evaluating the pressure signals measured by the two pressure sensors, wherein
• - In this evaluation, the signal curves of the pressure signals measured by the two pressure sensors are taken into account during a crankshaft segment and in which the area between the pressure signals of the pressure signals measured by the two pressure sensors is determined during the evaluation of the signal curves.

The advantages of the invention are, in particular, that it creates the possibility that an accurate diagnosis of the particle filter can also be carried out in gasoline engines operated with direct fuel injection, whereby individual circumstances of the individual system present are also taken into account.

In particular, the invention provides the possibility of obtaining precise information about the soot load in the particle filter. The invention also provides the possibility of obtaining precise information as to whether or not a particle filter is installed in the vehicle in question.

The information received can be shown on a display to the driver of the respective vehicle and the workshop personnel.

The pressure is advantageously measured at high resolution by means of the two pressure sensors.

A high-resolution measurement is understood to mean that the respective measurement of the pressure by means of the two pressure sensors takes place at a sampling rate that is less than or equal to 1 ms.

According to a preferred embodiment, the area between the pressure signals of the pressure signals measured by the two pressure sensors is determined when the signal curves are evaluated.

The area determined is preferably compared with a stored expected value.

This expected value is advantageously taken from a stored characteristic diagram in which a large number of different expected values are stored, each expected value being assigned a combination of a value describing the soot load of the particle filter with a value describing the exhaust gas volume flow.

Values describing the exhaust gas volume flow are in particular the measured exhaust gas volume flow, the exhaust gas mass flow, the engine speed, the engine torque or a combination of one or more of these parameters.

The expected value can advantageously be an expected value assigned to a missing particle filter.

An advantageous embodiment of the invention consists in providing a device for diagnosing a particle filter arranged in the exhaust tract of a gasoline engine operated with direct fuel injection, which has a control unit designed to control a method according to one of the preceding claims.

• 1 eine Blockdarstellung, in welcher die zum Verständnis der Erfindung wesentlichen Bauteile einer Vorrichtung zur Diagnose eines im Abgastrakt eines mit Kraftstoff-Direkteinspritzung betriebenen Benzinmotors angeordneten Partikelfilters gezeigt sind, und
• 2 Diagramme zur Erläuterung der Erfindung.

Further advantageous properties of the invention emerge from the following exemplary explanation based on the figures. It shows

• 1 a block diagram in which the components of a device for diagnosing a particulate filter arranged in the exhaust tract of a gasoline engine operated with direct fuel injection are shown which are essential for understanding the invention, and
• 2 Diagrams to explain the invention.

The 1 shows a block diagram in which the essential components for understanding the invention of a device for diagnosing a particulate filter arranged in the exhaust tract of a gasoline engine operated with direct fuel injection are shown. This includes the exhaust tract 1 a gasoline engine operated with direct fuel injection, one in this exhaust tract 1 arranged particle filter 2 , a first pressure sensor arranged in front of the particle filter 3 , one behind the particle filter 2 arranged second pressure sensor 4th , a control unit 5 and a display 6th . On the display 6th can be under control of the control unit 5 the results of the diagnostic results obtained in the method according to the invention are displayed.

The first pressure sensor 3 is for measuring the before the particle filter 2 prevailing pressure provided. The output of this first pressure sensor is sent to the control unit 5 fed.

The second pressure sensor 4th is for measuring the downstream of the particle filter 2 prevailing pressure provided. The output signal of this second pressure sensor is also sent to the control unit 5 fed.

The control unit 5 , which also includes a computing unit, is designed to receive the pressure sensor signals provided by the pressure sensors and to evaluate them in order to determine the loading status of the particle filter and / or the presence of the particle filter. In this evaluation, it takes into account the signal curves of the pressure signals measured by the two pressure sensors during a crankshaft segment.

The mentioned measurement of the pressure by means of the two pressure sensors 3 and 4th is done in high resolution. High resolution is understood to mean that the pressure is measured by means of the two pressure sensors at a sampling rate that is less than or equal to 1 ms.

For this purpose, when evaluating the signal curves, the area between the pressure signals of the pressure signals measured by the two pressure sensors is determined.

The area determined is compared with a stored expected value.

This expected value is taken from a stored characteristic map in which a large number of different expected values are stored, each expected value being assigned a combination of a value describing the soot load of the particle filter with a value describing the exhaust gas volume flow. A value describing the exhaust gas volume flow is, for example, the measured exhaust gas volume flow itself, the exhaust gas mass flow, the engine speed, the engine torque or a combination of one or more of these parameters.

Furthermore, the expected value can also be an expected value assigned to a missing particle filter. In this case, it is possible the presence or absence of a particulate filter in the exhaust tract 1 to detect.

In the method described above, the amplitudes of two pressure signals are evaluated, one of which is provided by a pressure sensor arranged in front of the particle filter and the other of which is provided by a pressure sensor arranged behind the particle filter, in order to determine the loading state of the particle filter. Furthermore, the method described can be used to carry out an installation test in which it is recognized whether or not there is a particle filter in the exhaust tract.

Previously known methods for estimating the soot loading of a particulate filter are based on an open-loop model. However, such a model cannot take into account individual changes in the individual system under consideration. For example, if there is a known method increased soot entry into the particle filter due to a defective injector, the model mentioned cannot take this into account. If there is a particle filter in the exhaust system of a diesel engine, the loading of the particle filter is determined using a differential pressure sensor. In gasoline engines operated with direct fuel injection, such a differential pressure measurement does not lead to success, since there is only a very small pressure drop across the particle filter.

In contrast to the aforementioned known methods, a method with the features specified in claim 1 enables an exact diagnosis of the particulate filter arranged in the exhaust tract, ie an exact determination of the loading state of the particulate filter and also enables a reliable installation test, even when gasoline engines are operated with direct fuel injection, which recognizes whether or not there is a particle filter in the exhaust tract.

For an installation test it was previously known to use a temperature sensor arranged in front of the particle filter and a further temperature sensor arranged behind the particle filter. Since the particle filter has a thermal mass, the presence or absence of the particle filter can be deduced from the difference in temperature in front of and behind the particle filter. However, this procedure has the disadvantage that an additional temperature sensor is required behind the particle filter. This disadvantage is avoided by a method according to the invention.

The method according to the invention takes into account that the pressure signal upstream and downstream of the particle filter has a high level of noise. Therefore, in known methods, the signals were filtered and mean values of the signals were used to determine the load and for the installation test.

In the method according to the invention, in contrast to this, the signal profile of the pressure signals, which are preferably measured in high resolution, is evaluated during a crankshaft segment (720 ° crank angle / number of cylinders). The inventors have recognized that this signal curve changes significantly more markedly during a crankshaft segment than the signal mean values when the particle filter is removed or its soot load is increased. In particular, the difference between the maximum values of the pressure signals derived from the two pressure sensors during a crankshaft segment changes significantly more strongly than the difference between the mean values when the load increases and when the particle filter is removed. Therefore, the area between the pressure signals in front of and behind the particle filter is evaluated. This also changes more than the mean values of the pressure signals. The parameter derived from the high-resolution pressure signal is then compared with an expected value stored in the engine control. As already stated above, this expected value is a function of the exhaust gas volume flow itself or of derived values such as exhaust gas mass flow, engine speed, engine torque or a combination of two or more of these parameters and the soot load of the particle filter. Furthermore, the expected value - as has also already been explained above - can also be assigned to a particle filter that is not installed.

The advantages of the invention will be explained again below with reference to the 2 illustrated diagrams.

In the in the 2 The diagrams shown show the pressure difference dp in hPa upwards and the time in s to the right.

The exemplary signal curves shown in the diagrams were determined at a speed n of 2500 revolutions per minute and a fresh air mass flow maf of 165 kg / h.

The curve K1 (dp.up.mes) describes the measured differential pressure between the exhaust gas in front of the particle filter and the environment. The curve K2 (dp.up.mes.fil) describes the low-pass filtered value of this differential pressure.

The curve K3 (dp.dw.mes) describes the measured differential pressure between the exhaust gas after the particle filter and the environment. The curve K4 (dp.dw.mes.fil) describes the low-pass filtered value of this differential pressure.

The signal curves shown in the diagram above were determined when a particle filter was not installed.

The signal curves shown in the middle diagram were determined for a new particle filter with a soot load of 0 g / l (completely regenerated).

The signal curves shown in the diagram below were determined for a new particle filter with a soot load of 4 g / l (highly loaded).

It can be seen that the differences between the determined maxima of the pressure amplitudes are significantly greater than the averaged pressure differences between the different particle filter states.

Consequently, the described method according to the invention is better suited to detecting the different particle filter states (not installed, completely regenerated, highly charged) than known methods in which low-pass filtering or averaging is carried out.

Claims (8)

Method for diagnosing a particle filter (2) arranged in the exhaust tract (1) of a gasoline engine operated with direct fuel injection, comprising the following steps: - Measurement of the pressure by means of a first pressure sensor (3) arranged in front of the particle filter, - Measurement of the pressure by means of a second pressure sensor (4) arranged behind the particle filter, - Determination of the loading state of the particle filter (2) and / or the presence of the particle filter (2) by evaluating the pressure signals measured by the two pressure sensors (3, 4), wherein - In this evaluation, the signal curves of the pressure signals measured by the two pressure sensors (3, 4) are taken into account during a crankshaft segment and in which the area between the pressure signals of the pressure signals measured by the two pressure sensors (3, 4) is determined during the evaluation of the signal curves . Procedure according to Claim 1 , in which the pressure is measured with the two pressure sensors (3, 4) in high resolution. Procedure according to Claim 2 , in which the pressure is measured by means of the two pressure sensors (3, 4) with a sampling rate that is less than or equal to 1 ms. Method according to one of the preceding claims, in which the area determined is compared with a stored expected value. Procedure according to Claim 4 , in which the expected value is taken from a stored characteristic map in which a large number of different expected values is stored, each expected value being assigned a combination of a value describing the soot load of the particle filter (2) with a value describing the exhaust gas volume flow. Procedure according to Claim 5 , for which a value describing the exhaust gas volume flow is the measured exhaust gas volume flow, the exhaust gas mass flow, the engine speed, the engine torque or a combination of one or more of these parameters. Procedure according to Claim 4 , at which the expected value is an expected value assigned to a missing particle filter (2). Device for diagnosing a particle filter (2) which is arranged in the exhaust tract of a direct injection gasoline engine and which has a control unit (5) which is designed to control a method according to one of the preceding claims.

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