DE102010039020A1 - Method and apparatus for regeneration of a particulate filter - Google Patents

Abstract

The invention relates to a method for the targeted initiation of a regeneration of a particle filter in an exhaust duct of an internal combustion engine, which has a catalyst downstream of the particle filter in the flow direction of the exhaust gas, the regeneration of the particle filter taking place by oxidative burning of the particles during the regeneration phase. According to the invention it is provided that when the internal combustion engine is warm, but when the temperature is still insufficient for a regeneration of the particle filter, measures are taken to increase the exhaust gas temperature before or in the particle filter. The invention also relates to a corresponding device with a control unit in which, by means of a program routine implemented in this, time-limited measures can be carried out for the targeted increase of the temperature in front of or in the particle filter. It is advantageous here that the regeneration of the particle filter can be initiated in a targeted manner in operating states that do not yet allow regeneration to take place independently, if regeneration is necessary. At the same time, sufficient conversion can be ensured for all other harmful exhaust gas components during regeneration. The sensors of the lambda probes around the particle filter can be used for this. A preferred use of the method provides for use in Otto engines.

Description

The invention relates to a method for the targeted initiation of a regeneration of a particulate filter in an exhaust passage of an internal combustion engine having a catalyst downstream of the particulate filter in the flow direction of the exhaust gas, the regeneration of the particulate filter being effected by an oxidative combustion of the particles during the regeneration phase.

The invention further relates to a device for carrying out the method according to the invention.

State of the art

Particle filters are used in the exhaust duct of the internal combustion engines to reduce particulate emissions from diesel engines and, increasingly, in the future also from gasoline engines (limit values to EU6 from 2014). The exhaust gas is passed through the particulate filter, which deposits the particulate matter contained in the exhaust gas and retains it in a filter substrate. As a result of the soot masses stored in the filter substrate, the particle filter increases over time, which is manifested by an increase in the exhaust gas counterpressure with a negative effect on engine performance and fuel consumption. For this reason, the stored soot mass must be discharged from time to time. This filter regeneration takes place during separate regeneration phases via an oxidative burnup of the particles, which takes place automatically as an exothermic reaction, provided that an exhaust gas temperature of at least 580 ° C. and a sufficiently high oxygen concentration are present in the exhaust gas. About the composition of the exhaust gas and the exhaust gas temperature, the course of the regeneration can be controlled.

In addition to the particulate filter, the exhaust aftertreatment of internal combustion engines requires additional components. Thus, in gasoline engines, which are operated according to a homogeneous concept, the pollutants hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ) are converted via a three-way catalyst. For lean concepts, a storage catalytic converter for nitrogen oxides is usually connected downstream. A lowest possible emission of pollutants is achieved by a lambda control, wherein the internal combustion engine supplied fuel-air mixture is controlled on the basis of the present in the exhaust gas oxygen concentration. The oxygen content present in the exhaust gas is described by a lambda value which is 1 for stoichiometric combustion,> 1 for oxygen excess and <1 for oxygen deficiency. The lambda value is measured by corresponding lambda probes arranged in the exhaust gas duct.

The regeneration of the particulate filter usually takes place when, as already mentioned above, a limit value for an exhaust counterpressure is exceeded. This can be detected by a suitable model and compared via a differential pressure measurement. The soot oxidation and thus the regeneration of the filter is significantly influenced by the exhaust gas temperature and the residual oxygen content. Since the combustion of the particles requires an excess of oxygen in the exhaust gas, in this phase the mixture composition of the internal combustion engine can not be freely selected according to the requirements of the driving operation. It is therefore desirable to be able to determine an end of the regeneration in order to be able to switch to normal driving operation.

From a not yet published patent application of the applicant with the official application number DE 10 2009 028237.8 a method for monitoring and controlling the regeneration of a particulate filter in an exhaust passage of an internal combustion engine is known, wherein the regeneration of the particulate filter is carried out by an oxidative combustion of the particles during a regeneration phase. It is provided that during the regeneration phase of the particulate filter, the internal combustion engine is operated at least temporarily during lean operating phases or during a Gemischoszillation in a lean operating point and that over the time course of a second signal disposed in the exhaust direction after the particulate filter second lambda probe or a second characteristic derived therefrom compared to the time course of a first signal of a first lambda probe disposed in front of the particulate filter in the exhaust gas direction or a first characteristic derived therefrom during the lean operating phases or during the Gemischoszillation the regeneration of the particulate filter is monitored. The disadvantage here is that the regeneration takes place within a lean phase in which other harmful exhaust gas components can not be optimally removed.

In addition, since it can not be ensured that the engine is regularly in an operating state in which the regeneration of the particulate filter can proceed on its own, there must also be possibilities for forced initiation of the regeneration.

It is therefore an object of the invention to provide a method for forced initiation of regeneration, which allows reliable control and monitoring of the regeneration of the particulate filter.

It is a further object of the invention to provide a device suitable for carrying out the method.

Disclosure of the invention

The object of the invention relating to the method is achieved by temporarily taking measures to increase the exhaust gas temperature before or in the particle filter in the warm operating state of the internal combustion engine, but at a temperature which is still insufficient for regeneration of the particulate filter.

The object concerning the device is achieved in that the device has a control unit with which the initiation, control and monitoring of the regeneration of the particulate filter takes place and with the signals of a first lambda probe arranged upstream of the particulate filter in the exhaust gas direction, signals downstream of the particulate filter in the exhaust gas direction or arranged behind the catalyst second lambda probe and / or signals from at least one temperature sensor can be evaluated, with a program routine implemented in the control unit time-limited measures for the targeted increase in temperature before or in the particulate filter are feasible.

In the regeneration of a particulate filter makes use of the fact that, if the exhaust gas temperature is in a range which allows regeneration, the regeneration automatically proceeds in compliance with the conversion for the other pollutant components, as in the raw exhaust still has a certain residual oxygen content (0.5 to 0.7%). In addition, under appropriate conditions can also be effected via a regeneration of the so-called heterogeneous water-gas equilibrium reaction (C + H ₂ O ← → CO + H _2). One makes use of the fact that changes in the lack of oxygen, the reaction kinetics for the regeneration of the particulate filter. In this case, no additional oxygen in the exhaust gas is required. The water is always present in the exhaust gas from the combustion. However, this reaction only occurs at higher temperatures, ie> 800 ° C. The requirement for regeneration of the particulate filter can be from a suitable model or by means of a corresponding sensor, for. B. differential pressure measurement, are detected, with the introduction of the regeneration first the other environmental conditions, such as the exhaust gas temperature and the current mode are checked.

With the method and the device, a regeneration of the particulate filter can also be initiated within operating states of the internal combustion engine, in which the environmental conditions for the regeneration are not optimal. This is the case, for example, if the internal combustion engine is operated for a very long time in part-load operation or at low loads, as is often the case, for example, in city traffic. In addition, sufficient conversion must be ensured during this phase for all harmful exhaust gas components, which can also be achieved with the process.

One possibility for this is targeted efficiency degradation with the aim of increasing the exhaust gas temperature. For this purpose, strategies can be used, which are usually used to heat a catalyst with still cold engine. A preferred variant of the method therefore provides that the ignition angle is shifted in the direction of a late ignition point for targeted initiation of the regeneration of the particulate filter and thus increasingly shift the exothermic reaction into the exhaust stroke, which leads to an increase in the exhaust gas temperature, whereby the regeneration of the particulate filter, as described above, can proceed by itself.

To compensate for the deterioration in efficiency and the associated loss of torque, it can be provided that a throttling of the internal combustion engine is withdrawn during the displacement of the ignition angle. Since it is still regulated to a stoichiometric air ratio, this strategy is exhaust-neutral, d. H. It can ensure a sufficient conversion of all harmful exhaust gas components. Due to the deterioration in efficiency, however, a certain increase in consumption must be accepted in this regeneration phase.

In addition to the retardation, in another variant of the method, in addition to the retardation of the ignition angle, the so-called homogeneous-split (HSP) operating mode can be used. This mode of operation is used, for example, to remove the catalyst after the startup phase, i. H. when the engine is still cold, to bring it up to operating temperature as quickly as possible. In this case, a stabilizing second injection in the compression stroke is used to delay the ignition extremely, so that a large proportion of the combustion energy can be used to increase the exhaust gas enthalpy, which in the inventive application of the method, the particulate filter in a very short time (within a few seconds ) is heated to the operating temperature necessary for the regeneration. By this second or possibly by further injection high ignition safety can be achieved. In addition, an increased burn-through stability can be achieved by placing the rich mixture close to the spark plug.

Another way to actively initiate regeneration is to increase the exothermic reaction in a three-way catalyst. there is provided that controlled by a Lambdaegelbetrieb by a lambda value of 1 temporally limited to a lambda value of> 1 (lean operation) and thus an oxygen storage of the catalyst is filled and then, after the filling of the oxygen storage, a lambda value of <1 is precontrolled the oxygen storage is emptied in the catalyst. This process, which is highly exothermic in total, leads to the heating of the exhaust system and is approximately neutral with respect to the conventional exhaust gas components due to the sum lambda of 1.

This change of the Lambdaregelbetriebs, which is hitherto known for heating the catalyst or for desulfurization of a NO _x storage catalytic converter, can be used particularly effectively if the particle filter is designed as a combined particle filter / catalyst and has a catalytic coating. In this case, a particularly effective heating of the particulate filter can be achieved by this measure.

For all active measures, the regeneration must be monitored. Therefore, it is provided that the temperature in the particulate filter is used as the control variable for the initiation of regeneration and for monitoring the regeneration, which is determined directly by means of at least one temperature sensor, which is arranged in or on the particulate filter or signals from lambda probes, which in Exhaust duct are arranged in front of and behind the particulate filter and the catalyst and are used for lambda control, derived or modeled from an exhaust gas temperature model is determined. Thus, the intensity and the duration of the heating process can be specifically influenced.

A device variant therefore provides that an exhaust-gas temperature model is implemented within the control unit and the controlled variable for the regeneration of the particulate filter is a modeled temperature of the particulate filter derived therefrom. This ensures continuous monitoring.

A preferred use of the method, as described above in its variants, envisages the use for the regeneration of a particle filter close to the engine in the exhaust gas duct of an internal combustion engine designed as a gasoline engine with intake manifold or direct injection. The advantage here is that it can be used on existing lambda probes or on existing sensor concepts, since lambda probes are already provided for the lambda control in the exhaust duct of gasoline engines, so that their signals for the initiation, control and regulation of the regeneration of the particulate filter can be used with, whereby the process can be implemented particularly cost-effective in future gasoline engines with particulate filter.

Brief description of the drawings

The invention will be explained in more detail below with reference to an embodiment shown in FIGS. It shows:

1 an internal combustion engine having disposed in the exhaust passage particulate filter and a downstream pre-catalyst and a main catalyst or an LNT / SCR catalyst and

2 the internal combustion engine with a combined particulate filter / catalyst and a downstream main catalyst or an LNT / SCR catalyst.

1 shows an internal combustion engine 10 with an air supply 11 and one in an exhaust duct 12 arranged particle filter 15 and a downstream pre-catalyst 17 and a main catalyst 18 , which may be formed as a three-way catalyst. That in the particle filter 15 and the catalysts 17 . 18 cleaned exhaust gas of the internal combustion engine 10 is via an exhaust outlet 20 dissipated. The lambda value of the exhaust gas in the exhaust passage 12 directly after the internal combustion engine 10 is by means of a first lambda probe 13 certainly. In this area, in addition, the temperature of the exhaust gas by means of a temperature sensor 14 certainly. In operation of the internal combustion engine 10 become particles in the particle filter 15 deposited. This increases the exhaust back pressure. Therefore, the particulate filter needs 15 If necessary, burned free and so regenerated. Regeneration can only take place if the exhaust gas temperature is above about 580 ° C; this is with the temperature sensor 14 ascertainable. Furthermore, sufficient oxygen must be available for combustion. This is with the first lambda probe 13 ascertainable. In the exhaust duct 12 after the particle filter 15 and the downstream pre-catalyst 17 is a second lambda probe 16 arranged. For a Hinterkat lambda control this can also be behind the main catalyst 18 be arranged.

From the difference of the output signals of the first lambda probe 13 and the second lambda probe 16 it can be determined to what extent the burnup of particles in the particulate filter 15 Oxygen consumed. If no difference between the signals can be detected, burnup is complete. The signals of the first lambda probe 13 and the second lambda probe 16 as well as the output signal of the temperature sensor 14 are a control unit 21 fed.

In the control unit 21 a program sequence for comparing the signals and for initiating, controlling and monitoring the regeneration is implemented. It is provided that the signals of the first lambda probe 13 , the signals of the second lambda probe 16 and / or signals of the temperature sensor 14 can be evaluated as a significant control variable, with the in the control unit 21 Implemented program routine time-limited measures for targeted increase in temperature before or in the particulate filter 15 are feasible. In a further embodiment is within the control unit 21 implemented an exhaust gas temperature model. As a controlled variable for the regeneration of the particulate filter 15 is a derived modeled temperature of the particulate filter 15 intended. The control unit 21 can in the engine control of internal combustion engines 10 , in which the lambda control is usually implemented, be integrated.

This basic structure is shown for an operating variant in which a lambda value of 1 is regulated. For a lean mode with a lambda value λ> 1, alternatively, instead of the main catalyst 18 an LNT / SCR catalyst 19 be provided. LNT stands for "lean NO _x trap" or "lean NO _x traps" and refers to a catalyst whose surface is impregnated with barium salts and platinum or other precious metals, and thus nitrogen oxides can be adsorbed from the engine exhaust. SCR stands for "selective catalytic reduction" and refers to a selective catalytic reduction of nitrogen oxides in exhaust gases. The chemical reaction on the SCR catalyst is selective, that is, it is preferably the nitrogen oxides reduced, while undesirable side reactions (such as the oxidation of sulfur dioxide to sulfur trioxide) are largely suppressed. These nitrogen oxides, typically NO and NO _2, can be stored on the catalyst surface. If such a catalyst periodically exposed to a rich fuel-air mixture, these nitrogen oxides can be converted into nitrogen, carbon dioxide and water.

2 shows the schematic arrangement 1 in a modified arrangement. In contrast to 1 here is the particle filter 15 and the pre-catalyst 17 combined into a combined particulate filter / catalyst, wherein the particulate filter has a catalytic coating. Here, too, is a main catalyst for an operating variant in which is controlled to a lambda value of 1, a main catalyst 18 intended. For a lean mode with a lambda value λ> 1, as in 1 shown, alternatively, instead of the main catalyst 18 an LNT / SCR catalyst 19 be provided.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009028237 [0006]

Claims (10)

Method for the targeted initiation of a regeneration of a particulate filter ( 15 ) in an exhaust duct ( 12 ) an internal combustion engine ( 10 ), which in the flow direction of the exhaust gas behind the particulate filter ( 15 ) a catalyst ( 17 . 18 ), wherein the regeneration of the particulate filter ( 15 ) by an oxidative combustion of the particles during the regeneration phase, characterized in that in the warm operating state of the internal combustion engine ( 10 ), but at still insufficient temperature for a regeneration of the particulate filter ( 15 ) temporary measures to increase the exhaust gas temperature before or by particulate filter ( 15 ). A method according to claim 1, characterized in that for the targeted initiation of the regeneration of the particulate filter ( 15 ) the firing angle is shifted in the direction of a late ignition timing. Method according to one of claims 1 or 2, that during the displacement of the ignition angle, a throttling of the internal combustion engine is withdrawn. Method according to one of claims 1 to 3, characterized in that in addition to the retardation of the ignition angle, the operating mode homogeneous split is used. Method according to one of claims 1 to 4, characterized in that controlled by a Lambdaegelbetrieb by a lambda value of 1 temporally limited to a lambda value of> 1 and thus an oxygen storage of the catalyst ( 17 . 18 ) is filled and then, after the filling of the oxygen storage, a lambda value of <1 is precontrolled. A method according to claim 5, characterized in that the change of Lambdaregelbetriebs in a particulate filter ( 15 ) performed as a combined particulate filter / catalyst and having a catalytic coating is performed. Method according to one of claims 1 to 6, characterized in that as a controlled variable for the initiation of regeneration and for monitoring the regeneration, the temperature in the particulate filter ( 15 ) is used, whereby these by means of at least one temperature sensor ( 14 ) in or on the particulate filter ( 15 ), determined directly or from signals from lambda probes ( 13 . 16 ), which in the exhaust duct ( 12 ) in front of or behind the particulate filter ( 15 ) and the catalyst ( 17 . 18 ) are arranged and used for lambda control, derived or modeled from an exhaust gas temperature model is determined. Use of the method according to one of claims 1 to 7 for the regeneration of a particulate filter ( 15 ) in the exhaust duct ( 12 ) of an engine designed as a gasoline engine ( 10 ). Device for the targeted initiation and monitoring and regulation of the regeneration of a particulate filter ( 15 ) in an exhaust duct ( 12 ) an internal combustion engine ( 10 ), which in the flow direction of the exhaust gas behind the particulate filter ( 15 ) a catalyst ( 17 . 18 ), wherein the regeneration of the particulate filter ( 15 ) is carried out by an oxidative combustion of the particles during a regeneration phase and wherein the initiation, control and monitoring of the regeneration of the particulate filter ( 15 ) via a control unit ( 21 ) and signals one in the exhaust gas direction in front of the particle filter ( 15 ) arranged first lambda probe ( 13 ), Signals one in the exhaust direction behind the particulate filter ( 15 ) or behind the catalyst ( 17 . 18 ) arranged second lambda probe ( 16 ) and / or signals from at least one temperature sensor ( 14 ) are evaluable, characterized in that with a in the control unit ( 21 ) implemented program routine time-limited measures for the targeted increase in temperature before or in the particulate filter ( 15 ) are feasible. Device according to claim 9, characterized in that within the control unit ( 21 ) implemented an exhaust gas temperature model and the controlled variable for the regeneration of the particulate filter ( 15 ) derived therefrom modeled temperature of the particulate filter ( 15 ).

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