DE10148128A1 - Method and device for reducing pollutant emissions from an internal combustion engine - Google Patents

Abstract

The invention relates to a method for reducing pollutant emissions from a spark - ignited internal combustion engine (12), with at least one catalyst (18, 28, 30) connected downstream of the internal combustion engine (12) for converting and / or storing at least one exhaust gas component of an exhaust gas of the internal combustion engine (12) and a device for performing the method according to the invention. DOLLAR A It is provided that, depending on a conversion and / or storage activity of the at least one catalytic converter (18, 28, 30), an ignition angle (ZW) of at least one cylinder (14) of the internal combustion engine (12) with respect to a basic ignition angle (ZW¶0 ¶) is adjusted.

Description

The invention relates to a method and a device for reducing a Pollutant emission from a spark-ignition internal combustion engine with the Features of the preambles of claim 1 and 15 respectively.

In order to achieve a reduction in environmentally harmful exhaust gas components in exhaust gases from internal combustion engines, it is known to arrange catalyst systems with at least one catalyst in an exhaust gas duct of the internal combustion engine. Depending on the type of catalyst, the catalyst converts one or more exhaust gas components, such as unburned hydrocarbons HC, carbon monoxide CO and nitrogen oxides NO _x , into less environmentally relevant products. In addition, catalysts are known which have storage components which are able to absorb certain pollutants. Thus, especially in lean-burn internal combustion engines, NO _x storage catalysts are used which absorb NO _x in lean operating phases with λ> 1 and reduce the stored NO _x with λ <1 in intermediate rich regeneration phases.

In practically all catalyst systems, there is a greater or lesser drop in conversion and / or storage activity compared to the original activity of the catalyst during operation. The activities related to the conversion or storage of different pollutants can decrease to different degrees. In particular in the case of NO _x storage catalysts, various damage patterns are known which, for example, lead to a significant deactivation of the NO _x conversion with a good HC conversion. Exactly opposite damage behavior is also known.

In order to counteract increased pollutant emissions due to damage to the catalyst system, a raw pollutant emission generated by the internal combustion engine can be reduced by specifically influencing the internal combustion engine. In direct injection gasoline engines, for example, it is known to restrict lean stratified operation in favor of homogeneous stoichiometric operation in the event of catalyst damage, in order to take advantage of the higher NO _x conversion rate in stoichiometric exhaust gas compared to a low NO _x conversion rate in lean exhaust gas. The disadvantage here is a higher fuel consumption in homogeneous stoichiometric operation compared to the shift mode which is more economical in terms of consumption.

The object of the present invention is a method for reducing a Provide pollutant emissions of an internal combustion engine with which one Largely counteracted increase in final emissions with damaged catalyst system can be. In particular, the process is intended to be an increased Avoid fuel consumption. A device is also intended to be made available with which the method can be carried out.

This object is achieved by a method with the features of claim 1. By doing depending on a conversion and / or storage activity at least one of the Internal combustion engine downstream catalyst has an ignition angle at least of a cylinder of the internal combustion engine is adjusted relative to a basic ignition angle is, a pollutant raw emission of the Internal combustion engine and thus the pollutant emissions with decreasing Reduce catalyst activity. With appropriate determination of intensity and Direction of the ignition angle adjustment compared to the preferably efficiency-optimized one Basic ignition angle no significantly increased fuel consumption observed.

The ignition angle is preferably adjusted as a function of damage, that is to say a drop in activity of the at least one catalyst, the damage being determined by comparing a conversion activity and / or storage activity that is currently present with a conversion activity and / or storage activity that is present when the catalyst is fresh. It is particularly advantageously provided that the ignition angle is adjusted as a function of the type of damage with regard to the exhaust gas component concerned and / or as a function of the intensity of the damage. For example, if an HC deactivation of the catalytic converter, that is to say a drop in its current HC conversion and / or HC storage activity, is determined, the ignition angle can be adjusted in relation to the basic ignition angle in the direction of an earlier ignition point. In this way, a reduction in the raw HC emission of the internal combustion engine and thus the final HC emission is brought about. On the other hand, a retardation of the ignition angle is advantageously provided if a corresponding deactivation of the at least one catalyst is observed with regard to its current conversion and / or storage activity of nitrogen oxides NO _x and / or carbon monoxide CO.

To constant, even with the slightest drop in the conversion and / or Memory activity required control intervention with regard to the ignition angle To prevent, it is intended to limit the current conversion and / or To specify storage activity or for the catalyst damage or exceeding the intervention in the ignition angle according to the invention is made.

In the event of the occurrence of a single damage affecting only one exhaust gas component, for example HC deactivation, while the NO _x activity is still sufficiently high, the strength and direction of the ignition angle adjustment can be easily determined in the manner described above. However, mixed damage patterns often occur, in which a simultaneous deactivation of the catalyst with regard to its conversion and / or storage activity of different exhaust gas components, for example HC and NO _x , is observed. In this case, provision is advantageously made to calculate the new ignition angle as a function of the level of the individual deviations from the various limit values, preferably taking into account the legal emission limit values of the various exhaust gas components.

The present object is further achieved by a device according to claim 15, which is characterized by means with which, depending on a conversion and / or Storage activity of the at least one catalyst, the ignition angle of the at least one Cylinder of the internal combustion engine is adjustable relative to the basic ignition angle. These means preferably comprise a control unit in which a procedure for Implementation of the ignition angle adjustment according to the invention is stored in digital form. The control unit can particularly advantageously be integrated into an existing engine control unit his.

According to a further, particularly advantageous embodiment of the device, the means further comprise a measuring device downstream of the at least one catalytic converter, with which a content of at least one exhaust gas component in the exhaust gas can be measured. This measuring device can in particular be an oxygen-sensitive lambda probe, in particular a step response lambda probe, or a NO _x sensor. Since such gas sensors are often already provided for monitoring the exhaust system, the method according to the invention can be carried out with a minimum of additional design effort.

Other advantageous embodiments of the invention are the subject of the rest Dependent claims.

The invention is described below in exemplary embodiments on the basis of the associated Drawings explained in more detail. Show it:

Figure 1 shows a first embodiment of the device according to the invention with a single catalyst.

Fig. 2 shows a second advantageous embodiment of the device according to the invention with two catalysts and

Fig. 3 curves of emission and fuel consumption changes in an internal combustion engine in response to an adjustment of an ignition angle with respect to a basic ignition angle efficiency-optimized.

Referring to FIG. 1, the generally designated 10 device on an internal combustion engine 12 includes four cylinders 14 in accordance with the example shown. The internal combustion engine 12 is particularly advantageously a gasoline engine which has a direct fuel injection system and which can be stratified in low and part-load operation. In stratified charge operation, an ignitable fuel cloud is generated only in the area of a spark plug of the cylinder 14 , while practically pure air is present in the rest of the combustion chamber. Particularly lean air-fuel mixtures can be achieved in stratified charge mode. Compared to homogeneous operation set at the same operating point, shift operation is characterized by particularly low fuel consumption.

An exhaust gas leaving the internal combustion engine 12 is passed through an exhaust gas duct 16 , where at least one exhaust gas component of the exhaust gas is converted and / or stored on a catalytic converter 18 arranged therein. The catalytic converter 18 can be a 3-way catalytic converter, for example, which catalyzes both the oxidation of unburned hydrocarbons HC and carbon monoxide CO and the reduction of nitrogen oxides NO _x . The catalyst 18 may further include a memory component, in particular an NO _x storage have, which incorporates in the lean operating phases of the internal combustion engine 12 NO _x and releases in rich or stoichiometric operating phases again and converted.

Arranged downstream of the catalytic converter 18 is an oxygen-sensitive measuring device 20 , which is usually a lambda probe, preferably a step response lambda probe. According to the example, a further oxygen-sensitive measuring device 22 is arranged upstream of the catalytic converter 18 , usually a lambda probe, preferably a broadband lambda probe. Alternatively, the lambda signal corresponding to the oxygen content upstream of the catalytic converter 18 can also be modeled by arithmetic, known methods depending on suitable operating parameters (engine load, speed, etc.). The device 10 can furthermore have a temperature sensor 24 arranged in the exhaust gas duct 16 upstream or downstream of the catalytic converter 18 for detecting the exhaust gas temperature. The temperature of the catalytic converter 18 can be determined in a known manner from the exhaust gas temperature. Here, too, it is alternatively possible to model the exhaust gas or catalyst temperature using known methods.

The signals provided by sensors 20 , 22 , 24 find their way into a control unit 26 , which determines the activity of the catalytic converter with regard to the conversion and / or storage of the various exhaust gas components in a manner yet to be explained and as a function of the various activities or a determined damage to the Catalyst 18 determines the ignition angle of the cylinder 14 of the engine 12 and controls. A cylinder-selective ignition angle control is also conceivable.

A further construction of an exhaust gas cleaning system according to the invention, designated overall by 10 ', is shown in FIG. 2, the same reference numerals as in FIG. 1 being used for the same components. In contrast to the structure shown in FIG. 1, the catalyst system according to FIG. 2 comprises two catalysts. A small-volume pre-catalytic converter 28 arranged close to the engine is preferably a 3-way catalytic converter. This is followed by a main catalytic converter 30 , preferably an NO _x storage catalytic converter.

Downstream of the main catalytic converter 30 , an oxygen-sensitive gas probe 20 , preferably a step response lambda probe, is arranged in the exhaust gas duct 16 . If the main catalytic converter 30 is a NO _x storage catalytic converter, the lambda probe 20 can also be replaced or supplemented by a NO _x sensor 32 , also shown. NO _x sensors are used to control the NO _x regeneration intervals of NO _x storage catalytic converters and usually also have a lambda signal in addition to the NO _x signal. Shown further includes a broadband lambda probe configured preferably as gas probe 22, which is connected upstream of the primary catalytic converter 28, and a the catalysts 28 and 30 connected between temperature sensor 24th As explained above, both sensor signals can alternatively also be computationally modeled using suitable models as a function of operating parameters of the internal combustion engine 12 . If separate monitoring of both catalysts 28 and 30 is desired, a further oxygen-sensitive gas probe 20 can be connected downstream of the pre-catalyst 28 , as shown. This in turn is usually a lambda sensor, preferably a step response lambda sensor, but can also be a NO _x sensor in NO _x storage catalytic converter systems.

The process sequence according to the invention for reducing the pollutant emissions of the internal combustion engine 12 according to the structure shown in FIGS. 1 and 2 is to be explained below:
First of all, damage to the catalytic converter or catalytic converters 28 and 30 is detected via the sensor system shown, in particular via the step response lambda probes 20 or NO _x sensors 32 connected downstream of the catalysts 18 , 28 , 30 . Different methods are currently available for this.

According to a first approach, the oxygen sensors 20 are used to determine the oxygen storage capacity of the catalytic converter 18 , 28 , 30 in a manner known per se in a so-called OSC test (for oxygen storage capacity). The catalyst system is alternately supplied with lean (λ> 1) and rich (λ <1) exhaust gas. At the same time, the step response lambda probes 20 measure the oxygen content of the exhaust gas downstream of the catalytic converter 18 , 28 , 30 . This oxygen content is compared with the oxygen content present upstream of the catalytic converter 18 , 28 , 30 , which in turn is measured or modeled with the broadband lambda probe 22 . The oxygen storage capacity and from this a current catalyst activity, in particular the HC conversion activity, can be derived from the difference between the lambda profiles upstream and downstream of the catalyst 18 , 28 , 30 . Alternatively, or in addition thereto may further with the aid of the _NOx sensor 32 of the NO _x content in lean exhaust gas are captured downstream of the NO _x storage catalyst as the main catalyst configured 30th The current NO _x storage and conversion activity during lean operation of the internal combustion engine 12 can be determined by comparison with the NO _x content determined upstream of the NO _x storage catalytic converter 30 by measurement or modeling.

Damage to the catalyst 18 , 28 , 30 is determined by comparing the exhaust gas component-specific catalyst activities determined in this way with the corresponding activities of a catalyst in the fresh state. These fresh activities are preferably determined from characteristic maps stored in the control unit 26 as a function of current operating parameters of the internal combustion engine 12 , for example speed, vehicle speed or engine load. If a measured current catalyst activity of an exhaust gas component deviates from the corresponding fresh activity by a measure that exceeds a predeterminable limit value, damage to the catalyst 18 , 28 , 30 with regard to the conversion and / or storage of this exhaust gas component is determined.

To avoid significant, random influences in the catalyst activity determination suppress, the activities or damage determined are advantageously heavily filtered. For this, at least three, in particular at least ten, preferably at least twenty activity or damage values that are in each other following monitoring intervals are determined, averaged. You can also optionally a weighting of the values of individual intervals can be provided.

The ignition angle of at least one cylinder 14 is then adjusted in relation to a basic ignition angle depending on the type of exhaust gas component and the intensity of the damage. The effect of an ignition angle adjustment on the raw emissions of various pollutant components and on the specific fuel consumption is shown in FIG. 3. The percentage changes in emissions and consumption as a function of the ignition angle adjustment ΔZW are plotted relative to a basic ignition angle ZW ₀ . The basic ignition angle ZW ₀ is designed for the highest possible efficiency and is adjusted from this optimum according to the state of the art only in dependence on other requirements, such as knock protection or smooth running or for catalyst heating (spark ignition). All data refer to an operating point, at a speed of 2000 rpm and an effective medium pressure of 2 bar in a 1.6 liter 4-cylinder gasoline engine with direct injection. At this operating point, the ignition angle can be shifted in a range of approximately ± 5 ° without misfiring being observed. In the case of other engines or operating points, ignition angle adjustments of up to ± 10 ° are possible without misfires.

In the range of ΔZW = ± 5 ° shown, the raw HC emission changes overall by about 80%. In particular, the raw HC emission increases by 51% when the ignition angle is retarded by + 5 ° compared to the basic ignition angle and decreases by 30% when the ignition angle is shifted by -5 °. On the other hand, the raw emissions of NO _x and CO change in opposite directions to the raw HC emissions depending on the ignition angle adjustment.

The graph also shows that the specific fuel consumption (solid Line) in the area shown only slightly less than 1% compared to efficiency-optimized basic ignition angle changed. In this respect, with appropriate Catalyst damage significant reductions in individual raw emissions with only a small More consumption can be achieved.

In the case of a single damage to a catalytic converter 18 , 28 , 30 that only affects one exhaust gas component, the ignition angle shift ΔZW can easily be determined. If, for example, HC deactivation is determined while NO _x activity is still sufficient, the raw HC emission is reduced by shifting the ignition angle in the "early" direction while accepting an increased NO _x emission. If, on the other hand, a drop in the NO _x conversion and / or NO _x storage activity is detected with sufficient HC activity, the ignition angle is shifted in the "late" direction.

However, mixed damage patterns, typically with a deactivation with regard to both critical exhaust gas components HC and NO _x , are observed more frequently. The intensities of both activation dips must be taken into account here, preferably using statutory emission limit values. This means that, for example, a higher HC raw emission can be tolerated in a low-emission, but NO _x -critical vehicle, while a slight ignition _x intervention in the "late" direction to reduce the raw NO _x emission is already possible with a slight NO _x deactivation must be done. The same applies to the reverse case.

It also makes sense to carry out the ignition angle adjustment ΔZW as a function of the operating point, that is to say as a function of the current operating parameters of the internal combustion engine 12 and of the temperatures determined in the catalysts ( 18 , 28 , 30 ) by measurement or modeling. If the catalytic converters ( 18 , 28 , 30 ) are thermally deactivated, the HC conversion can be expected to improve both in homogeneous stoichiometric operation and in lean operation when the catalyst temperature rises at the same engine operating point, while the NO _x storage capacity in lean operation is not equally improved.

However, the ignition angle adjustment, which is dependent on a large number of parameters, is associated with a higher computational effort than a general ignition angle adjustment. The determination of the ignition angle adjustment is carried out particularly advantageously using a method of the so-called fuzzy logic technology. With this simple calculation method, the desired data can be quickly determined with a particularly low computing capacity. REFERENCE SIGN LIST 10 , 10 'device
12 internal combustion engine
14 cylinders
16 exhaust duct
18 catalyst
20 Lambda probe / step response lambda probe
22 Lambda probe / broadband lambda probe
24 temperature sensor
26 control unit
28 pre-catalytic converter
30 main catalyst
32 NO _x sensor
ZW ignition angle
ZW ₀ basic ignition angle
ΔZW ignition angle adjustment (= ZW ₀ - ZW)

Claims (19)

1. A method for reducing pollutant emissions from a spark-ignition internal combustion engine ( 12 ) with at least one catalyst ( 18 , 28 , 30 ) connected downstream of the internal combustion engine ( 12 ) for converting and / or storing at least one exhaust gas component of an exhaust gas of the internal combustion engine ( 12 ), characterized in that that an ignition angle (ZW) of at least one cylinder ( 14 ) of the internal combustion engine ( 12 ) is adjusted relative to a basic ignition angle (ZW ₀ ) as a function of a conversion and / or storage activity of the at least one catalyst ( 18 , 28 , 30 ). 2. The method according to claim 1, characterized in that the basic ignition angle (ZW ₀ ) is optimized essentially with regard to an efficiency of the internal combustion engine ( 12 ). 3. The method according to claim 1 or 2, characterized in that the ignition angle (ZW) is adjusted depending on damage to the at least one catalyst ( 18 , 28 , 30 ), the damage by comparing a current conversion and / or storage activity with a conversion and / or storage activity in a fresh state of the at least one catalyst ( 18 , 28 , 30 ) is determined. 4. The method according to claim 3, characterized in that the ignition angle (ZW) is adjusted depending on the type and / or intensity of damage to the at least one catalyst ( 18 , 28 , 30 ). 5. The method according to any one of the preceding claims, characterized in that the ignition angle (ZW) is adjusted in a range of ± 10 ° KW, in particular by ± 5 ° KW, compared to the basic ignition angle (ZW ₀ ). 6. The method according to any one of the preceding claims, characterized in that the ignition angle (ZW) is adjusted in the "early" direction when the current conversion and / or storage activity for hydrocarbons (HC) of the at least one catalyst ( 18 , 28 , 30 ) falls below a limit. 7. The method according to any one of the preceding claims, characterized in that the ignition angle (ZW) is adjusted in the "late" direction when the current conversion and / or storage activity for nitrogen oxides (NO _x ) and / or for carbon monoxide (CO) of the at least one catalyst ( 18 , 28 , 30 ) falls below a limit value. 8. The method according to any one of the preceding claims, characterized in that when the limit values for the conversion and / or storage activity of different exhaust gas components, in particular for CO and NO _x , are undershot, the strength and direction of the ignition angle adjustment as a function of the deviations from the limit values and / or depending on the emission limit values of the various exhaust gas components. 9. The method according to any one of the preceding claims, characterized in that the strength and / or direction of the ignition angle adjustment as a function of current operating parameters of the internal combustion engine ( 12 ), an exhaust gas temperature at at least one point in the exhaust system and / or a temperature of the at least one catalyst ( 18 , 28 , 30 ). 10. The method according to any one of the preceding claims, characterized in that Strength and / or direction of the ignition angle adjustment using a fuzzy Logic method can be determined. 11. The method according to any one of the preceding claims, characterized in that the conversion and / or storage activity of the at least one catalyst ( 18 , 28 , 30 ) by means of a measuring device ( 20 , 32 ) arranged downstream of the catalyst ( 18 , 28 , 30 ) that is sensitive to at least one exhaust gas component is determined. 12. The method according to claim 11, characterized in that the measuring device ( 20 , 24 ) is an oxygen-sensitive lambda probe, in particular a step response lambda probe ( 20 ), with the aid of which an oxygen storage capacity of the at least one catalyst ( 18 , 28 , 30 ) is determined and the damage to the catalyst ( 18 , 28 , 30 ), in particular with regard to the HC conversion and / or HC storage capacity, is determined as a function of the oxygen storage capacity. 13. The method according to claim 11, characterized in that the measuring device ( 20 , 32 ) is a NO _x- sensitive measuring device, in particular a NO _x sensor ( 32 ), and the NO _x conversion and / or NO _x storage activity the at least one catalyst ( 18 , 28 , 30 ) is determined as a function of the NO _x concentration downstream of the catalyst ( 18 , 28 , 30 ). 14. The method according to any one of the preceding claims, characterized in that the determined conversion and / or storage activities (Akt) by averaging several values measured in succession can be filtered. 15. Device ( 10 , 10 ') for reducing pollutant emissions of a spark-ignition internal combustion engine ( 12 ) with at least one catalyst ( 18 , 28 , 30 ) connected downstream of the internal combustion engine ( 12 ) for converting and / or storing at least one exhaust gas component of an exhaust gas of the internal combustion engine ( 12 ), characterized by means with which, depending on a conversion and / or storage activity (Akt) of the at least one catalytic converter ( 18 , 28 , 30 ), an ignition angle (ZW) of at least one cylinder ( 14 ) of the internal combustion engine ( 12 ) relative to one Basic ignition angle (ZW ₀ ) of the internal combustion engine ( 12 ) is adjustable. 16. The device ( 10 , 10 ') according to claim 15, characterized in that the means comprise a control unit ( 26 ) in which a procedure for adjusting the ignition angle as a function of the conversion and / or storage activity (act) is stored in digital form. 17. The device ( 10 , 10 ') according to claim 16, characterized in that the control unit ( 26 ) is integrated in an engine control unit. 18. Device ( 10 , 10 ') according to one of claims 15 to 17, characterized in that the means comprise a measuring device ( 20 , 32 ) connected downstream of the at least one catalytic converter ( 18 , 28 , 30 ), which is sensitive to at least one exhaust gas component is. 19. The device ( 10 , 10 ') according to one of claims 15 to 18, characterized in that the measuring device ( 20 , 32 ) is a lambda probe, in particular a step response lambda probe ( 20 ), or a NO _x sensor ( 32 ) ,