DE102021202020A1 - Method and computing unit for monitoring a particle filter - Google Patents

Abstract

The invention relates to a method (200) for operating a particle filter (130) downstream of an internal combustion engine (110), comprising determining (220) an expected particle number concentration downstream of the particle filter (130), determining (210) an actual particle number concentration downstream of the particle filter ( 130), comparing (230) the actual and expected particle number concentrations, and carrying out a measure (240) depending on the result of the comparison. A computing unit (140) and a computer program product for carrying out such a method (200) are also proposed .

Description

The present invention relates to a method for monitoring a particle filter downstream of an internal combustion engine, as well as a computing unit and a computer program for carrying it out.

Background of the Invention

Limit values for particle emissions from vehicles with petrol and diesel engines have already been enacted in many regions around the world. The underlying operating conditions were successively expanded from narrowly defined conditions on the test bench to far more comprehensive tests on the road (Real Driving Emissions RDE). In particular, these also include cold starts and dynamic states with high loads.

The primary task of the particle filter is to remove solid particles from the exhaust gases as completely as possible. This function is described with the filter efficiency η, which is particularly dependent on the particle size and the loading condition of the filter. The filter efficiency is usually the higher, the more load there is in the filter, because the exhaust gas has to flow through the already existing filter cake in the filter. The filter cake itself acts as a filter for the exhaust gas and significantly increases the effectiveness of the filter.

In many cases, a functional defect in the particle filter cannot be detected or only detected relatively late, for example during regular external checks, but not during a normal operating phase.

Disclosure of Invention

According to the invention, a method for monitoring a particle filter downstream of an internal combustion engine as well as a computing unit and a computer program for its implementation with the features of the independent patent claims are proposed. Advantageous configurations are the subject of the dependent claims and the following description.

The invention uses a comparison between an expected, in particular modeled, particle number concentration (PN) and an actual particle number concentration downstream of the particle filter to diagnose the functionality of the particle filter as part of an on-board diagnosis. This can ensure that malfunctions are detected early and particle emissions are effectively minimized.

With conventional sensors that can detect a particle mass concentration (PM), such a monitoring with regard to the particle number concentration is not possible.

In detail, a method according to the invention for operating a particle filter downstream of an internal combustion engine includes determining an expected particle number concentration downstream of the particle filter, determining an actual particle number concentration downstream of the particle filter, comparing the actual and the expected particle number concentrations, and carrying out a measure depending on the result of comparison. In this way it can be determined whether the particle filter is working according to specification.

Determining the expected particle number concentration advantageously includes modeling based on input variables, including one or more from the group consisting of an operating parameter of the internal combustion engine, a parameter of the internal combustion engine, a parameter of the particle filter and an environmental parameter. As a result, these particularly relevant influencing variables can be taken into account when assessing the functionality of the particle filter. Such modeling takes into account in particular the influence of the engine load, the speed, the number of injections and other injection parameters on the particle formation in the combustion chamber. It is possible to use these variables to model a particle number concentration downstream of the filter or to use an additional model function for the particle filter. Such a model can be derived at least empirically, for example on a test stand.

In a preferred embodiment, the determination of the expected particle number concentration is based on a filtration performance that is just no longer acceptable (best performing unacceptable, BPU) and the measure is then carried out in such configurations when the actual particle number concentration reaches or exceeds the expected particle number concentration, i.e. the filter has at most one straight has unacceptable (BPU) filtration performance.

The actual particle number concentration is preferably determined on the basis of a sensor signal from a sensor downstream of the particle filter. This represents a particularly reliable basis for assessing the filtration efficiency. In principle, all known devices for detecting particles in a fluid flow can be considered for this purpose. For example, such particle sensors can work on the basis of scattered light, light extinction or laser diffraction. Also sensors that are on Laser- or light-induced incandescence (Light Induced Incandescence; LII), condensation particle counting (Engl. Condensation Particle Counter; CPC) or high-voltage methods (escaping current, electrostatic method) can be used for this purpose

Several physical mechanisms are relevant to the filtration effect, such as sedimentation. The effectiveness of these mechanisms, in turn, depends on the particle size. Overall, the filter efficiency is therefore strongly dependent on the particle size and thus overall on the particle size distribution. As a rule, very small particles are separated well in the filter due to their high mobility. The same applies to comparatively large particles, which are also separated well locally in the filter due to their inertia when the direction of flow changes. On the other hand, the filtration efficiency is worse in the middle size range, because both mechanisms mentioned are less effective for separating the particles in this size range. Determining the expected and actual particle number concentrations therefore advantageously includes determining the particle number concentration within at least one predetermined particle size range, the at least one particle size range for the expected and actual particle number concentrations being identical in each case. In the particle size range from 10 nm to 70 nm, a significant change in the number of particles is to be expected if the filter is damaged. In particle size ranges above 150 nm, it is expected that slight damage to the filter will no longer be robustly distinguishable from a fault-free filter. It is therefore advantageous if the particle number value recorded by the sensor can also detect particles that are as small as possible, in particular with a particle size of less than 70, 60, 50, 40, 30 or 20 nm, in order to increase the robustness of the diagnosis.

The comparison is advantageously carried out over a predefinable comparison period in order to compensate for short-term signal fluctuations and to avoid incorrect diagnosis results. In particular, actual particle number concentrations, which were determined, for example, from measurements carried out directly one after the other, can be calculated to form a mean value (sliding mean value and/or low-pass filtering) before the comparison with the expected particle number concentration takes place. Carrying out the measure only after several corresponding comparison results within the comparison period is also conceivable and may be advantageous.

In particular, the measure includes one or more from the group of outputting a signal (e.g. so-called OBD error), saving an error entry and replacing the particle filter. As a result, a permanent increased emission of excessively high particle concentrations can be avoided and the particle filter can be restored to a desired state.

A computing unit according to the invention, e.g. a control unit of a motor vehicle, is set up, in particular in terms of programming, to carry out a method according to the invention.

The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is advantageous because this causes particularly low costs, especially if an executing control unit is also used for other tasks and is therefore available anyway. Suitable data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard drives, flash memories, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and refinements of the invention result from the description and the attached drawing.

The invention is shown schematically in the drawing using an exemplary embodiment and is described below with reference to the drawing.

character list

• 1 shows an arrangement with internal combustion engine and particle filter, as can be used within the scope of the invention.
• 2 shows an embodiment of a method according to the invention in the form of a greatly simplified flowchart.

embodiment(s) of the invention

In 1 1 is an arrangement with an internal combustion engine and particle filter, as can be used within the scope of the invention, shown schematically and denoted overall by 100 .

The arrangement 100, which can in particular be part of a motor vehicle, comprises at least one internal combustion engine 110 and a particle filter 130, which is arranged downstream of the internal combustion engine 110. The internal combustion engine can be designed as an Otto engine, a diesel engine, a rotary engine or as a lean-burn engine with spark ignition. Also internal combustion engines for operation with regene Alternative and/or fossil gaseous and/or liquid fuels may be used as the internal combustion engine 110 .

In the embodiment of the arrangement 100 shown, an exhaust gas catalytic converter 120, for example a three-way catalytic converter, is provided between the internal combustion engine 110 and the particle filter 130. In alternative configurations, the catalytic converter 120 can also be arranged elsewhere downstream of the internal combustion engine 110, for example downstream of the particle filter 130. An integrated design of the particle filter 130 and catalytic converter 120, for example in the form of a so-called four-way catalytic converter, can also be used within the scope of the present invention.

A particle number sensor 145 is provided downstream of particle filter 130, which during operation detects a particle number concentration actually emitted downstream of particle filter 130 and sends a corresponding signal to a computing unit 140, for example a control unit of the internal combustion engine.

The particle filter 130 is set up to at least partially retain particulate components of the exhaust gas, so that the exhaust gas leaving the particle filter 130 is depleted of the particulate components in comparison to the exhaust gas entering the particle filter 130 . For this purpose, the particle filter 130 comprises, for example, a suitable filter material, for example a porous material of a ceramic or metallic type. Such filter materials retain the particulate components of the exhaust gas in that the particles interact mechanically with the filter material, in particular by colliding. Following such a mechanical interaction and/or alternatively thereto, adhesive forces can occur (e.g. electrostatic or chemical bonds, in particular van der Waals forces), which prevent particles once deposited in the filter from being transported further through the filter material.

In some configurations of the particle filter 130, electrodes for retaining the particulate exhaust gas components can also be provided. In such filter systems, particles present in the exhaust gas are pushed in the direction of the electrodes by electrostatic and/or electrodynamic interactions and are separated there. In such electric filters, the particle size distribution of the separated particles can be influenced by changing the potential applied to the electrodes.

In principle, all known devices for detecting particles in a fluid flow can be considered as the particle sensor 145 . For example, such particle sensors work on the basis of scattered light, light extinction or laser diffraction. Sensors based on laser or light-induced incandescence (LII), condensation particle counting (CPC) or high-voltage methods (escaping current, electrostatic method) can also be used for this purpose. However, high-voltage methods cannot measure PN directly. In such cases, the measurement signal can be converted into the particle number PN using a raw emission model.

Control unit 140 can also be connected to internal combustion engine 110 and/or particulate filter 130 and/or catalytic converter 120 in a data-conducting manner and can receive signals from the respective components that contain information about the operating state or parameters, characteristics and/or sensor readings, etc. of the respective component included.

In 2 An advantageous embodiment of a method according to the invention is shown schematically in the form of a greatly simplified flow chart and is denoted overall by 200 . The method 200 can in particular essentially by a control unit 140, as in connection with 1 already mentioned, can be carried out.

If reference is made below to method steps, these relate in particular to 2 , while references to device components in particular related to 1 are to be understood.

In a first step 210 of the method 200, an expected particle number concentration PN is determined. For this purpose, on the basis of operating parameters of internal combustion engine 110, for example speed, load, temperature, air-fuel ratio, etc., raw emissions from the internal combustion engine can be calculated using a raw emissions model and, using characteristics of particulate filter 130, a filtration efficiency and thus an expected remaining particle number concentration downstream of the particle filter can be modelled. Other influencing variables can also be included in this modelling. Particularly relevant parameters here are all system and operating parameters that influence the output variables, such as exhaust gas mass flow, exhaust gas temperature, fuel (quality), environment (e.g. pressure, temperature, composition of the atmosphere), driver behavior, driving profile, system properties including variance of the individual vehicle, aging and defects.

In a second step 220, an actual particle number concentration PN downstream of the particle filter 130 is determined. In particular, a sensor 145 provided for this purpose can be used for this purpose, the signal of which is evaluated accordingly. The measurement preferably takes place in accordance with the valid PMP standards (Particle Measurement Program) of the UN/ECE or in accordance with comparable standards or based on them. If necessary, these can be adapted for a measurement in the vehicle's exhaust system.

Emission limit values usually relate to the distance driven, which results in the dimension of an inverse length or a unit of 1/km in the case of a limit value for the particle number concentration. Such concentrations related to the distance traveled represent an average of the current emissions in a driving cycle.

Within any given driving cycle, the instantaneous emission values scatter between “infinity” (vehicle stationary) and “0” (vehicle rolling with engine stopped). Even if only the engine emissions (e.g. in relation to the exhaust gas volume) are considered without taking into account the fluctuating driving speed, there is a very large scattering of the particle emissions over several orders of magnitude.

It is therefore sensible and advantageous to suitably filter or smooth the current particle emission in order to be able to determine a statement for a driving cycle. Legal requirements are preferably used for this purpose, which are necessary for the expected introduction of OBM. Minimum requirements for a driving cycle could, for example, define a minimum driving distance of a few km, which represents a sensible reference value for determining total emissions.

In some configurations of the method 200, provision can also be made for the expected and/or actual particle number concentration to be determined only in certain operating states of the internal combustion engine in which a high level of validity with regard to the functionality of the particle filter 130 is to be expected in order to increase the reliability of the method 200 to increase overall. Quasi-stationary driving conditions with low load changes or certain transient events can be suitable for this if the particle number emissions can be easily predicted and measured in these areas. These determinations can also be limited to one or more particularly relevant particle size ranges, for example to a size range that is particularly susceptible to malfunctions or defects in particle filter 130 .

For the determination of the expected particle number concentration in step 210, a so-called best-performing unacceptable (BPU) particle filter can advantageously be assumed in order to arrive at a relevant statement regarding a filter performance that is just no longer acceptable. Such a procedure also has the advantage that the method 200 can also be subsequently adapted to limit values that are becoming stricter by updating the corresponding modeling basis.

In a comparison step 230, the expected value is compared with the actually determined value for the particle number concentration downstream of the particle filter 130. As mentioned, suitable averaged or filtered signals of the expected and/or actual particle number concentration can be used for this purpose. For example, both values can be integrated over a predeterminable period of time and the integrated values can be compared with one another in order to achieve sufficiently reliable statistics.

Depending on the result of the comparison, method 200 can either return to step 210, in particular if the actual value corresponds to the expected value or the actual particle concentration downstream of the particle filter is below a maximum concentration expected according to the modeling from step 210. If, on the other hand, an actual particle number concentration is determined that is higher than the expected one, this is an indication of a defect in the particle filter, so that the method continues with step 240, in which a measure is carried out or initiated. For example, a signal can be output to activate a warning light that draws attention to the defect. A corresponding entry in a fault memory or the replacement of the particle filter 130 can also be carried out as the measure. An automatic appointment request from a stored service partner can also be advantageous, in particular if the method is used in (partially) autonomous vehicles.

It goes without saying that certain steps can be interchanged with one another or combined into a common step without changing the general functioning of the method 200 . It should also be emphasized here that a step-by-step implementation of the method 200 is not absolutely necessary, and continuous monitoring can therefore also be achieved without the step-by-step procedure described. This was only chosen for explanation purposes to make it easier to understand the individual partial aspects of the method 200 .

Claims (11)

A method (200) for monitoring a particulate filter (130) downstream of an internal combustion engine (110), comprising: determining (220) an expected particle number concentration downstream of the particle filter (130), determining (210) an actual particle number concentration downstream of the particle filter (130), comparing (230) actual and expected particle number concentrations, and taking an action (240) depending on the result of the comparison. Method (200) according to claim 1 , wherein the determination (220) of the expected particle number concentration is modeling based on input variables, comprising one or more from the group consisting of an operating parameter of the internal combustion engine (110), a parameter of the internal combustion engine (110), a parameter of the particle filter (130) and an environmental parameter. Method (200) according to claim 1 or 2 , wherein the determination (210) of the actual particle number concentration is based on a sensor signal from a sensor (145) downstream of the particle filter (130). Method (200) according to one of the preceding claims, wherein the comparison (230) is carried out over a predeterminable comparison period and the measure is only carried out if the comparison result fails several times during the comparison period and/or using an average value over the comparison period. Method (200) according to one of the preceding claims, wherein the measure (240) comprises one or more from the group of outputting a signal, storing an error entry and replacing the particle filter (130). Method (200) according to any one of the preceding claims, wherein determining the expected (220) and actual (210) particle number concentrations includes determining the particle number concentration within at least one predetermined particle size range, the at least one particle size range for the expected and actual particle number concentrations being identical in each case. Method (200) according to one of the preceding claims, wherein the determination (220) of the expected particle number concentration is based on a filtration performance which is just no longer acceptable and the measure (240) is carried out when the actual particle number concentration reaches or exceeds the expected particle number concentration. Method (200) according to one of the preceding claims, wherein the determination (210) of the actual particle number concentration is only carried out during periods in which quasi-stationary operating states of the internal combustion engine (110) with small load changes or certain transient events are present. Arithmetic unit (140) which is set up to carry out all method steps of a method (200) according to one of the preceding claims. Computer program that causes a computing unit (140) to perform all method steps of a method (200) according to one of Claims 1 until 8th to be performed when it is executed on the computing unit (140). Machine-readable storage medium with a computer program stored on it claim 10 .

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