DE102014211902B4 - Method for monitoring the condition of a particle filter, exhaust system and measuring device - Google Patents

Abstract

Method (200) for monitoring the condition of a particle filter (12) arranged in an exhaust duct (11) by means of a measuring device (14) arranged downstream of the particle filter (12), wherein the measuring device (14) has a first temperature sensor (16) encased in a particle-absorbing material (18), wherein the particle-absorbing material (18) at least partially separates the first temperature sensor (16) from an exhaust gas flow (20) flowing through the particle filter (12), wherein the method comprises the following steps:
- subjecting the measuring device (14) to exhaust gas over a loading interval (I _B );
- detecting a dynamic (D _M ) of a signal of the first temperature sensor (16) encased in the particle-absorbing material (18) or of a variable (T _M ) derived from the signal;
- determining a reference temperature by means of a second temperature sensor (32) which is free of particle-absorbing material;
- comparing the dynamics (D _M ) of the first temperature sensor (16) encased in the particle-absorbing material (18) with a reference dynamics (D _R ) of the second temperature sensor (32);
- Evaluating the condition of the particulate filter (12) depending on the comparison and the loading interval (I _B ).

Description

The invention relates to a method for monitoring the condition of a particle filter arranged in an exhaust duct by means of a measuring device arranged downstream of the particle filter, wherein the measuring device has a sensor and a particle-absorbing material which at least partially separates the sensor from an exhaust gas flow flowing through the particle filter. The invention further relates to an exhaust system which is designed to carry out the method, and to a measuring device for carrying out the method and/or for the exhaust system.

Exhaust systems with several exhaust aftertreatment components are used to reduce emissions from internal combustion engines and to comply with current exhaust gas legislation. For example, an exhaust system for reducing emissions from an internal combustion engine running on diesel fuel can include an oxidation catalyst, an SCR catalyst (selective catalytic reduction) and a particle filter (diesel particulate filter, or DPF for short).

The use of particle filters in motor vehicles requires functional and efficiency monitoring of the component in accordance with the guidelines of emissions legislation. Up to now, sufficient monitoring has been ensured by evaluating a differential pressure across the particle filter. The functional status of the particle filter is determined based on the measured pressure drop. The particle mass is not recorded directly.

The monitoring of the significantly reduced threshold values of currently applicable or next stages of emissions legislation in Europe and the USA is probably no longer possible with the previous method due to the insufficient sensitivity and accuracy of the available pressure sensors.

Currently existing particle sensors only measure the proportion of elemental carbon in the particle mass due to their principle. They require complex signal evaluation in the form of an independent control unit. This complex structure increases the probability of failure, application effort and costs. They have not been tested much to date. In particular, there is a lack of long-term experience.

The DE 10 2006 010 497 B4 describes an exhaust gas purification device which comprises a DPF unit (diesel particulate filter unit) with a main DPF and a secondary DPF. The two DPFs are each provided with a temperature sensor. The secondary DPF is provided to detect a fault in the main DPF. Before the main DPF captures soot up to the upper limit of a (maximum) soot absorption capacity, a regeneration process must be carried out using a post-injection control. In addition, the secondary DPF temperature is measured and the amount of particles captured in the secondary DPF (secondary DPF accumulation amount) is calculated on this basis. For this purpose, the temperature of hot exhaust gases that are fed to the DPF unit when the DPF regeneration control is carried out is determined from a map using auxiliary engine parameters (for example the engine speed and the engine load). This results in a reference exhaust gas temperature. A temperature rise amount is calculated from a difference between a maximum value of a measured sub-DPF temperature during execution of the regeneration control and the reference exhaust gas temperature. Further, a table is retrieved according to the temperature rise amount to calculate the sub-DPF accumulation amount. A main-DPF accumulation amount is determined similarly. In addition, a ratio of the main-DPF accumulation amount to a total accumulation amount is calculated and checked to see if it is less than or equal to a determination threshold (for example, 0.8). If it is, it is determined that the main-DPF is defective. Through the above steps, it can be determined whether there is a crack or hole in the main-DPF because in such a case, particulates pass through the main-DPF and are trapped by the sub-DPF.

The US 2013 / 0 047 841 A1 discloses an exhaust system with a particle filter which is arranged in a main exhaust path. A detection filter with similar filtering properties to the particle filter is arranged in a secondary path connected parallel to the main exhaust path downstream of the particle filter. If the particle filter is defective, the detection filter filters particles passed through by the particle filter from the exhaust gas flow flowing through the secondary path. As a result, the detection filter gradually becomes clogged and the gas flow through the secondary path is reduced. The amount of soot that is passed through the particle filter can be determined by measuring a temperature gradient of the gas flowing in and out through the detection filter. If the flow of gases directed through the detection filter is reduced due to a clogged detection filter, a temperature loss through the detection filter and thus the temperature gradient increases. If no soot escapes from the particle filter, the temperature gradient of the gas flowing in and out remains constant.

From the DE 102 18 218 A1 A device and method for detecting a malfunction of a particle filter are known. The device comprises a chamber which can be introduced into the gas stream to be cleaned in addition to the filter, which is at least partially closed with a filter body and has at least one opening through which gas entering the chamber through the filter body can exit again. At least one gas sensor is arranged in the chamber for detecting the concentration of at least one component of the gas to be cleaned, and at least one second gas sensor is arranged outside the chamber for detecting the concentration of the at least one component of the gas to be cleaned.

The DE 199 59 870 A1 describes a measuring arrangement and a method for monitoring the functionality of a soot particle filter. A partial flow of an exhaust gas flow flows through at least one molded body that is open and porous at least in the direction of flow. Furthermore, the temperature of the molded body is measured with at least one temperature sensor. The problem arises of creating a measuring arrangement and a method with which the functionality of a soot particle filter can be monitored in a reliable and direct manner. The problem is solved for the measuring arrangement in that at least one soot sensor, which has at least one molded body that is open and porous at least in the direction of flow, at least one electrical heating element and at least one temperature sensor, is assigned to the soot particle filter.

Furthermore, the DE 10 2007 002 205 A1 a device for detecting particles in a gas flow with a particle sensor is known. The particle sensor comprises a housing with a flow divider to provide a first flow path and a second flow path. A heating device is arranged and designed to provide uniform heating of the two flow paths. A first temperature sensor is arranged downstream of the heating device in the first flow path. A second temperature sensor is arranged downstream of the heating device in the second flow path. A fine filter is arranged in the second flow path and designed to capture carbon-containing particles.

Requirements for diagnosing particle filters, as required by the EU6 or LEV2 emissions standards, can be met with current methods, but only with increased design effort (for example, measuring the pressure difference across an exhaust gas recirculation filter) and/or using complex sensors (particle sensor). Overall, this is associated with high costs and the accuracy needs to be improved.

The invention is based on the object of providing a method and means for improved and more cost-effective condition monitoring of a particle filter.

• - Beaufschlagen der Messvorrichtung mit Abgas über ein Beladungs-Intervall;
• - Erfassen einer Dynamik eines Signals des von dem partikelaufnehmenden Material ummantelten ersten Temperatursensors oder einer aus dem Signal abgeleiteten Größe;
• - Ermitteln einer Referenztemperatur durch einen frei von partikelaufnehmendem Material ausgeführten zweiten Temperatursensor;
• - Vergleichen der Dynamik des von dem partikelaufnehmenden Material ummantelten ersten Temperatursensors mit einer Referenzdynamik des zweiten Temperatursensors;
• - Bewerten des Zustands des Partikelfilters in Abhängigkeit des Vergleichs und des Beladungs-Intervalls.

According to the invention, a method for monitoring the condition of a particle filter arranged in an exhaust duct is provided. The method is carried out by means of a measuring device arranged downstream of the particle filter, wherein the measuring device has a first temperature sensor encased in a particle-absorbing material, wherein the particle-absorbing material at least partially separates the first temperature sensor from an exhaust gas flow flowing through the particle filter, wherein the method comprises the following steps:

• - Exposing the measuring device to exhaust gas over a loading interval;
• - detecting a dynamic of a signal of the first temperature sensor encased in the particle-absorbing material or of a quantity derived from the signal;
• - Determining a reference temperature by means of a second temperature sensor which is free of particle-absorbing material;
• - comparing the dynamics of the first temperature sensor encased in the particle-absorbing material with a reference dynamics of the second temperature sensor;
• - Evaluating the condition of the particulate filter depending on the comparison and the loading interval.

Preferably, the exhaust duct is an exhaust duct of an internal combustion engine of a motor vehicle.

The method according to the invention ensures a robust efficiency diagnosis of the particulate filter for low emission limits.

The particle-absorbing material can, in particular, absorb or attach particles reversibly. This means that it can be loaded and unloaded with particles.

By means of the particle-absorbing material, the sensor is at least partially separated from the exhaust gas flow, i.e. separated from the exhaust gas flow in such a way that at most a part of the exhaust gas flow penetrates into the measuring device. The particle-absorbing material is arranged between the sensor sensor and the exhaust gas flow in such a way that with increasing loading of the particle-absorbing material, the dynamics of the sensor signal and thus also the dynamics of the variable derived from the signal (i.e. determined) are reduced, i.e. the inertia of the sensor signal and thus also of the variable derived from it is increased. The dynamics therefore refers to the dynamics of the signal recorded by measurement or the variable derived from it and not to the dynamics of an actual physical variable to be measured. The dynamics can therefore also be viewed as the speed or rate of change of the recorded signal or the variable derived from it. Due to the reduced dynamics, a course of the sensor signal (e.g. a voltage signal) or the variable derived from the signal (e.g. a determined temperature) only follows the actual course of a variable to be measured (e.g. a temperature) with an increased time delay. In order to facilitate particle absorption by the material and thus a change in the dynamics, the particle-absorbing material is arranged in particular upstream of the sensor.

In the event of a defect in the particulate filter, the particle-absorbing material is loaded with particles from the exhaust gas stream more quickly than before the defect. As the material is loaded, the dynamics of the signal or the quantity derived from it decreases, which is determined by comparing this dynamics with the reference dynamics.

The assessment of the condition of the particle filter is carried out depending on this comparison and the loading interval. The loading interval can extend to any chosen or predetermined point in the past. It can therefore extend between this point in the past and the point at which a current signal, which forms the basis for assessing the condition, is output by the sensor.

Preferably, the loading interval includes or is a loading time interval, a loading distance interval and/or a loading mass interval. While a relatively small decrease in the dynamics of the signal or the quantity derived from it within a relatively long loading time interval may be permissible due to the particle filter not being 100% effective, a relatively large decrease in the measurement dynamics within a relatively short loading time interval may indicate a defective particle filter. The loading distance interval can also be used to carry out an assessment based on the distance traveled. By using the loading mass interval, an assessment of the state underlying a particle mass can also be carried out. The particle mass can be a particle mass expected at the outlet of the particle filter when the particle filter is functioning correctly. This can be determined, for example, using a calculation model. A combination of the intervals mentioned can also be advantageous, since it can be important, for example, which particle mass was emitted at what time.

The loading interval is preferably an interval since the last regeneration of the particle-absorbing material. When the particle-absorbing material is regenerated, which can preferably take place during regeneration of the particle filter, the particle-absorbing material is cleaned of particles that have accumulated or been deposited. The loading interval therefore represents a maximum possible interval, which reduces distortions when assessing the condition of the particle filter due to temporary, unrecorded events.

Preferably, it is provided that the exhaust gas flow is emitted by an internal combustion engine and the assessment of the state of the particle filter takes place depending on operating points of the internal combustion engine and/or depending on a driving profile of a motor vehicle comprising the internal combustion engine. The operating points and the driving profile provide additional information for a more precise assessment of the state of the particle filter. For example, a raw particle emission of an internal combustion engine (i.e. a particle emission at an outlet of the internal combustion engine) depends on the operating points at which the internal combustion engine is operated. Furthermore, the raw particle emission depends on a driving profile if the internal combustion engine is used to drive a motor vehicle.

According to the invention, the reference dynamics are determined using a reference sensor. Thus, parallel to the measurement using the sensor, which provides the dynamics of the sensor signal or the variable derived therefrom, a further measurement is carried out using a reference sensor in order to determine the reference dynamics. Furthermore, the reference dynamics can be determined using characteristic curves and/or a calculation model. In addition, a combination of the above-mentioned possibilities can also be used. The reference sensor can also be arranged downstream of the particle filter in the same exhaust duct as the sensor.

Preferably, it is provided that in the case of an unloaded, particle-absorbing material the reference dynamics correspond to the dynamics of the sensor signal or the dynamics of the quantity derived from the signal. Even in the case of an unloaded particle-absorbing material, the dynamics of the signal or the quantity derived from it can have a lower dynamic than the reference dynamics output by the reference sensor due to the presence of the particle-absorbing material. To take this into account, the reference dynamics are preferably determined by first determining a dynamics of a signal or a quantity derived from it of the reference sensor. This dynamics is then adjusted (i.e. artificially reduced) by means of a calculation model and/or characteristic curves to the dynamics of the signal output by the sensor or the quantity derived from it in the case of an unloaded, particle-absorbing material. This simplifies a subsequent comparison of the dynamics of the sensor signal or the quantity derived from it with the reference dynamics.

Instead of the loading interval being an interval since the last regeneration of the particle-absorbing material, and the reference dynamics corresponding to a dynamic of the signal emitted by the sensor or the value derived from it for an unloaded, particle-absorbing material, alternatives are also conceivable. The loading interval can also be any length of past interval. The reference dynamics can be a dynamic that corresponds to the dynamic of the signal emitted by the sensor or the value derived from it at the beginning of the previous interval. This means that an increase in particle leakage from the particle filter can also be determined between two regenerations. This can be used, for example, to determine whether the particle filter needs regeneration.

According to the invention, the sensor is a temperature sensor. The value derived from the signal thus corresponds to a temperature. Exhaust gas temperatures can be measured particularly easily and inexpensively.

Furthermore, an exhaust system is provided with a particle filter arranged in an exhaust duct of the exhaust system and a measuring device arranged downstream of the particle filter, wherein the measuring device has a first temperature sensor encased in a particle-absorbing material, wherein the particle-absorbing material at least partially separates the first temperature sensor from an exhaust gas flow flowing through the particle filter. The exhaust system is set up to carry out the method according to the invention. For this purpose, the exhaust system can comprise a control unit (in particular an engine control unit which is set up to control operating parameters of the internal combustion engine) on which a computer model set up to carry out the method is stored. An exhaust system is thus provided which is characterized by particularly low costs with sufficiently precise condition monitoring of the particle filter.

Preferably, the measuring device is arranged in a main exhaust path of the exhaust system and extends only partially into a flow-through cross section of the main exhaust path. Preferably, a proportion of a cross section of the part of the measuring device that protrudes into the exhaust duct is less than 20%, in particular less than 10%, of a free cross section of the exhaust duct. Thus, a flow resistance is only insignificantly increased when the particle-absorbing material is loaded.

In addition, a measuring device is provided for carrying out the method according to the invention and/or for an exhaust system according to the invention. The measuring device comprises a first temperature sensor encased in a particle-absorbing material, wherein it is characteristically provided that the measuring device comprises a casing of the sensor (i.e. a measurement-sensitive part of the measuring device) which has or consists of the particle-absorbing material. Using the measuring device according to the invention, the method can be carried out with particularly low flow loss and low flow loss change within the exhaust duct. The measuring device therefore has a particularly low impact on the exhaust gas flow.

Preferably, the particle-absorbing material has openings formed through the casing, or the particle-absorbing material has openings formed through the casing, which can be closed by loading the particle-absorbing material with particles from the exhaust gas flow. The particle-absorbing material can be sieve-like, grid-like or net-like. Thus, open openings into and out of the interior of the measuring device are increasingly reduced when the material is loaded with particles, thereby reducing the exposure of the sensor to exhaust gas from the exhaust gas flow. This results in an intentional deterioration of the dynamics of the signal or the size of the sensor derived from it.

Preferably, the particle-absorbing material can also be a layer arranged on the sensor, wherein the sensor is a temperature sensor sensor. By loading the material, the thermal conductivity of the layer decreases and thus the heat conduction from the exhaust gas flow to the sensor.

Further preferred embodiments of the invention result from the remaining features mentioned in the subclaims.

The various features and/or embodiments of the invention mentioned in this application can be advantageously combined with one another, unless stated otherwise in individual cases.

• 1 eine Abgasanlage in einer schematischen Ansicht,
• 2 eine Messvorrichtung in einer schematischen Ansicht,
• 3 einen schematischen Verfahrensablauf zur Zustandsüberwachung eines Partikelfilters, und
• 4 tatsächliche und gemessene Temperaturverläufe.

The invention is explained below in exemplary embodiments with reference to the accompanying drawings. They show:

• 1 an exhaust system in a schematic view,
• 2 a measuring device in a schematic view,
• 3 a schematic process flow for monitoring the condition of a particle filter, and
• 4 actual and measured temperature curves.

1 shows a schematic view of an exhaust system 10 according to the invention in accordance with a preferred embodiment of the invention. The exhaust system 10 comprises a particle filter 12 (for example a diesel particle filter) and a measuring device 14 arranged downstream of the particle filter 12 in a main exhaust path 13. The measuring device 14 has a sensor 16, which is a temperature sensor 16, and a particle-absorbing material 18 (for example a filter fabric). The particle-absorbing material 18 at least partially separates the sensor 16 from an exhaust gas flow 20 flowing through the particle filter 12.

The sensor 16 is in 2 shown enlarged. Accordingly, a sensor 16 is encased in the particle-absorbing material 18. The sensor 16 further comprises a housing 22, which can be screwed into an exhaust duct 11 of the exhaust system 10. In addition, the sensor 16 comprises a measuring line 26, with which a signal from the sensor 16 can be output. The particle-absorbing material 18 can be attached to a perforated protective tube 26 of the measuring device 14, which also encloses the sensor 14. The particle-absorbing material 18 has openings (not visible) through the casing 19, which can be closed by loading the particle-absorbing material 18 with particles (soot particles) from the exhaust gas flow 20. Alternatively, the particle-absorbing material 18 can also be realized by means of a protective tube 26 with a sufficiently small perforation so that the particles attach themselves directly to the perforation of the protective tube 26 and close it.

The exhaust system 10 according to 1 comprises a control unit 28, which is connected to the sensor 16 via the measuring line 26. In addition, the control unit 28 is connected to an internal combustion engine 30, for example preferably of a motor vehicle 100. The control unit 28 determines, for example, depending on a specification from a driver of the motor vehicle 100, an operating point of the internal combustion engine 30, i.e. a load and a speed of the internal combustion engine 30, whereby a raw particle emission of the internal combustion engine 30 is influenced. The internal combustion engine 30 can be a diesel engine, for example.

Furthermore, the exhaust system 10 can comprise a reference sensor 32, which is also a temperature sensor 16 and is connected to the control unit 28.

3 shows a schematic process flow for monitoring the condition of a particle filter 12 according to a preferred embodiment of the invention.

First, the internal combustion engine 30 is put into operation, which emits the exhaust gas stream 20 with particles (in particular soot particles) contained therein depending on the operating points BP reached or depending on a driving profile of the vehicle 100.

A large proportion of the particles are filtered out of the exhaust gas flow 20 by the particle filter 12. However, even with a correctly functioning particle filter 12, a small proportion of particles typically reach parts of the exhaust system 10 downstream of the particle filter 12. This is generally referred to as particle slip. Some of the particles emerging from the particle filter 12 are absorbed by the particle-absorbing material 18 of the measuring device 14.

In 4 Simplified temperature curves are plotted over time t. For a simplified representation of the basic behavior of the sensor 16 and the reference sensor 32 (both sensors 16 and 32 are exhaust gas temperature sensors), an actual exhaust gas temperature T _AG is shown as a sudden curve. This increases approximately without time delay by a temperature difference ΔT, and then falls back to the original value after a phase of constant exhaust gas temperature T _AG . In addition, in 4 a temperature T _M is shown, which is a value derived from a signal of the sensor 16, i.e. a numerical value with a unit of temperature. Furthermore, a temperature T _R is shown, which is a quantity derived from a signal of the reference sensor 32, i.e. a numerical value with a unit of temperature.

At a time t = 0, the particulate filter 12 was regenerated and, in the course of this, the particle-absorbing material of the measuring device 14 was also regenerated. As a result, in the time range A, the curve of the temperature T _M largely corresponds to the curve of the temperature T _R . The temperature curves therefore reach their maximum at approximately the same time, and therefore also the maximum of the exhaust gas temperature T _AG , so that a delay t _M of the temperature T _M and a delay t _R of the temperature T _R are the same, starting from the start of the rise of the temperatures T _M and T _R until they reach their maxima. A deviation of the temperatures T _AG , T _M , and T _R before and after their rise is neglected below, so that the temperature differences between the temperatures T _M and T _R are equal to the temperature difference ΔT of the actual exhaust gas temperature T _AG .

When using the same sensor model for the sensor 16 and the reference sensor 32, the delay t _R could be somewhat shorter than the delay t _M even with an unloaded particle-absorbing material 18. The delay t _M would then be defined as a time period from the rise in temperature T _M to the temperature T _R being reached. Such a deviation of the delays t _R and t _M could occur because the reference sensor 32 is not surrounded by a particle-absorbing material. These influences can be corrected using a calculation model and/or using characteristic curves. By correcting the courses of the temperatures T _M and T _R, they are essentially identical in area A.

Alternatively, the temperature T _R can also be determined without using a reference sensor 32 solely by means of a calculation model and/or characteristic curves.

In a time range B, the course of the temperature T _M shows a different behavior to that in range A. The sensor 16 only detects the same temperature difference ΔT after a much longer delay t _M . The delay t _M extends from the start of the rise in the temperature T _M until the temperature T _R output by the reference sensor 32 is reached. This is due to an interim loading of the particle-absorbing material 18, which reduces a heat flow from the exhaust gas flow to the sensor 16. A reproducible proportion of the particle mass of the exhaust gas flow 20 is deposited by the particle-absorbing material 18. The resulting reduction in an effective passage area of the casing 19 reduces a partial flow of the exhaust gas flow 20 through the measuring device 14 depending on the degree of loading of the material 18. This results in a lower dynamic D _M of the temperature T _M delivered by the sensor 16 for each operating point compared to the unloaded state. However, the delay t _R of the temperature T _R output by the reference sensor 32 remains the same as in region A, since the reference sensor 32 does not have any particle-absorbing material.

Thus, a reference dynamics D _R of the temperature T _R in region B is the same as in region A, while a dynamics D _M of the temperature T _M in region B is smaller than in region A.

In the time range C, after a further relevant loading of the measuring device 14 with particles, a further deterioration of the dynamics D _M can be seen while the reference dynamics D _R remains the same.

The dynamics D _M of the temperature T _M output by the sensor 16 can be recorded, for example, as the ratio of the measured temperature difference ΔT to the delay t _M , while the reference dynamics D _R can be recorded as the ratio of the temperature difference ΔT to the delay t _R . The two dynamics D _M and D _R at the time of the process execution t _V form input variables 201 for the process sequence according to 3 . The time at which the process is carried out t _V can correspond to a time at which the delay ends t _M, i.e. the time at which the temperature T _M reaches the temperature T _R.

Alternatively, the dynamics D _M and D _R can also be determined at any time, i.e. not only after the temperature T _M has reached the temperature T _R. For this purpose, the dynamics D _M can be determined as a ratio of a current temperature difference of the temperature T _M to a time elapsed since the temperature T _M rose. The reference dynamics D _R can be determined as a ratio of a current temperature difference of the temperature T _R to the time elapsed since the temperature T _R rose. The dynamics D _M in areas B and C is therefore smaller than the reference dynamics D _R for the same underlying elapsed time since the temperatures T _M and T _R rose, because the currently output temperature T _M is lower than the current temperature T _R.

A comparison of the dynamics D _M with the reference dynamics D _R can be made, for example, by forming a ratio 202 of the dynamics D _M and D _R and a subsequent decision 204. First, the dynamics D _M are related to the reference dynamics D _R according to the ratio formation 202. This gives a ratio V _D which provides information about the relative size of the dynamics D _M and D _R to one another.

Subsequently, according to a decision 204, it can be checked whether the ratio V _D is smaller than a ratio limit value V _G. If this is not the case, the dynamics D _M have not changed relevantly compared to the reference dynamics D _R and the method confirms according to 206 that the particle filter 12 is functioning properly.

However, if the decision 204 shows that the ratio V _D is smaller than the ratio limit value V _G , a subsequent decision 208 can check whether a loading time interval t _B is smaller than a loading time interval limit value t _G . To this end, it was first determined in a step 207 that a loading interval I _B is realized using the loading time interval t _B . The loading time interval t _B can be the time interval between the (thermal) regeneration at time t = 0 and the time of the process execution t _V , i.e. a time when the ratio falls below the limit value V _G .

Because the loading interval I _B is realized by means of the loading time interval t _B , a temporal criterion is included in the evaluation of the state of the particle filter 12. Alternatively or additionally, a loading mass interval could also be included in the evaluation, for example.

The loading time interval limit value t _G can be determined in a step 205, for example by means of a calculation model and/or characteristic curves as a function f(BP) of operating points BP approached during the loading time interval t _B. This is useful because a raw particle emission of the internal combustion engine 30 changes depending on the selected operating points.

If the loading time interval t _B is not less than the loading time interval limit value t _G , the dynamics D _M have changed significantly compared to the reference dynamics D _R , but this change occurred too slowly to indicate a problem with the particle filter 12. Such a slow change can occur, for example, due to a normal and permissible particle slip of the particle filter 12. The method can thus confirm, according to a function confirmation step 206, that the particle filter 12 is functioning properly.

However, if it turns out in decision 208 that the loading time interval limit value t _G has been undershot, the dynamic change in the dynamics D _M relative to the reference dynamics D _R has taken place so quickly that it can be concluded that the particle slip is impermissibly high, which is output in an error output step 210. Accordingly, the control unit 28 can report a defect in the particle filter 12.

Alternatively, the loading time interval t _B can also be a past time interval of any length. The reference dynamics T _R can be a dynamic that corresponds to the dynamics of the temperature T _M at the beginning of the past time interval. For example, the loading time interval t _B can start at the beginning of the time range B and end at the beginning of the measurement in range C (where the dynamics D _M flowing into the method 200 was determined). The dynamics D _M of the sensor at the beginning of the alternatively selected loading time interval t _B can be defined as the reference dynamics R _D. This can be done by appropriately correcting the dynamics of the reference sensor 32. This can be used to determine, for example, a need for regeneration of the particle filter. If no correction is made, this can be taken into account via the comparison limit value V _G.

The above method 200 ensures a robust efficiency diagnosis of the particle filter 12 for low emission limits, the basis of which is a temperature measurement in the exhaust gas flow 20 after the particle filter 12. Due to the accumulation of the particles on the material 18, i.e. the direct detection of solid components (particle mass) in the exhaust gas, the method 200 takes on the character of an integral measurement.

In summary, it can be stated that by a suitable evaluation of the change in the dynamics D _M of the signal or the variable derived therefrom (temperature T _M ) of the sensor 16 in comparison to a reference dynamics D _R of a value modelled in a calculation model or a second, unmodified, soot-insensitive temperature sensor (reference sensor 32), conclusions can be drawn about the efficiency of the particle filter 12 and/or an emitted particle mass in the exhaust gas. This can be done taking into account the operating points BP of the internal combustion engine 30 and/or the driving profile of the motor vehicle 100.

The signal detection of the sensor 16 and the reference sensor 32 corresponds to a standard signal detection of exhaust gas temperature sensors. The sensor 16 can be installed directly in the main exhaust gas flow be arranged, a bypass, i.e. a branch of a

partial exhaust gas flow is not necessary. This reduces the complexity of the exhaust system 10 and also ensures a more representative soot load.

Sooting of the measuring device 14 has essentially no effect on the exhaust gas flow 20, since the part of the measuring device 14 that protrudes into the exhaust duct 11 is relatively small in relation to a free cross-section of the exhaust duct 11. Thus, regardless of the amount of soot or the efficiency of the particle filter 12 to be diagnosed, the loading of the material 18 does not result in any (relevant) change or increase in the flow resistance of the exhaust system 10.

Another particularly advantageous feature is that the method can be applied to any course of the exhaust gas temperature T _AG , regardless of whether it is heating or cooling, and not to predictable courses (such as those according to 4 ) is limited.

This is possible because a change in the inertia of the measuring device 14 is considered, which depends on the degree of sooting of the measuring device 14, and the method is therefore not based on considering the dynamics of an actually existing exhaust gas temperature T _AG . One and the same change in an exhaust gas temperature T _AG (the temperature difference ΔT) is measured more quickly at an earlier point in time and more slowly at a later point in time (after exposure to soot). A dynamic change in a signal emitted by the sensor 16 or a variable derived therefrom (temperature T _M ) is thus evaluated, and not, as is known from the prior art, a dynamic of a cause (exhaust gas temperature T _AG ).

According to the method, as described, the change in the actual measurement detection is evaluated by comparing the increasingly sooted measuring device 14 with a non-soot-covered reference sensor 32 or a temperature calculated by a model, thus keeping the cause constant.

List of reference symbols

10

Exhaust system

11

exhaust duct

12

Particle filter

13

main exhaust path

14

measuring device

16

sensor

18

particle-absorbing material

19

sheathing

20

exhaust gas mass flow

22

Housing

25

measuring line

26

protective tube

28

Control unit

30

internal combustion engine

32

reference sensor

100

motor vehicle

200

Proceedings

201

input variable

202

relationship formation dynamics

204

decision regarding dynamics

205

Step for determining the loading time interval limit t _G

206

function confirmation step

207

step of determining the loading interval

208

decision regarding loading time interval

210

error output step

T

temperature

DAY

exhaust gas temperature curve

TM

temperature from sensor

TR

temperature from reference sensor

ΔT

temperature difference

tM

sensor delay

tR

delay of the reference sensor

TV

time of the procedure

IB

loading interval

tB

loading time interval

tG

loading time interval limit

A, B, C

time period

DM

Dynamics of a sensor signal or a value derived from it

DR

reference dynamics

VD

relationship of dynamics

VG

ratio limit

BP

operating point

F(BP)

function of operating points

j

Yes

n

no

Claims (7)

Method (200) for monitoring the condition of a particle filter (12) arranged in an exhaust duct (11) by means of a measuring device (14) arranged downstream of the particle filter (12), wherein the measuring device (14) has a first temperature sensor (16) encased in a particle-absorbing material (18), wherein the particle-absorbing material (18) at least partially separates the first temperature sensor (16) from an exhaust gas stream (20) flowing through the particle filter (12), wherein the method comprises the following steps: - supplying the measuring device (14) with exhaust gas over a loading interval (I _B ); - detecting a dynamic (D _M ) of a signal of the first temperature sensor (16) encased in the particle-absorbing material (18) or of a variable derived from the signal (T _M ); - determining a reference temperature by means of a second temperature sensor (32) designed free of particle-absorbing material; - comparing the dynamics (D _M ) of the first temperature sensor (16) encased in the particle-absorbing material (18) with a reference dynamics (D _R ) of the second temperature sensor (32); - evaluating the state of the particle filter (12) as a function of the comparison and the loading interval (I _B ). Procedure (200) according to Claim 1 , characterized in that the loading interval (I _B ) comprises or is a loading time interval (t _B ), a loading path interval and/or a loading mass interval. Method (200) according to one of the preceding claims, characterized in that the exhaust gas flow (20) is emitted by an internal combustion engine (30) and the evaluation of the state of the particle filter (12) takes place as a function of operating points (BP) of the internal combustion engine (30) and/or as a function of a driving profile of a motor vehicle (100) comprising the internal combustion engine (30). Exhaust system (10) comprising a particle filter (12) arranged in an exhaust duct (11) of the exhaust system (10) and a measuring device (14) arranged downstream of the particle filter (12), wherein the measuring device (14) has a first temperature sensor (16) encased in a particle-absorbing material (18), wherein the particle-absorbing material (18) at least partially separates the temperature sensor (16) from an exhaust gas flow (20) flowing through the particle filter (12), wherein the exhaust system (10) is designed to carry out the method (200) according to one of the Claims 1 until 3 is set up. Exhaust system (10) after claim 4 , characterized in that the measuring device (14) is arranged in a main exhaust path (13) of the exhaust system (10) and extends only partially into a flow-through cross-section of the main exhaust path (13). Measuring device (14) for carrying out the method (20) according to one of the Claims 1 until 3 and/or for an exhaust system according to claim 4 or 5 , wherein the measuring device (14) has a first temperature sensor (16) encased in a particle-absorbing material (18), characterized in that the measuring device (14) comprises a casing (19) of the sensor (16), which has or consists of the particle-absorbing material (18). measuring device according to claim 6 , characterized in that the particle-absorbing material (18) forms openings through the casing (19), which can be closed by loading the particle-absorbing material (18) with particles from the exhaust gas stream (20).

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