DE102021209420A1 - Method for operating an internal combustion engine with at least one catalytic converter - Google Patents

Abstract

The invention relates to a method (100) for operating an internal combustion engine with at least one catalytic converter which is arranged downstream of the internal combustion engine, comprising, in a heating-up period, introducing fuel into a combustion chamber of the internal combustion engine (210), setting an early ignition angle (α2 ) in a combustion chamber heating mode (H2) and adjusting a retarded ignition angle (α1) in a catalyst heating mode (H1), and igniting the fuel in the combustion chamber at the adjusted ignition angle (α1, α2). A computing unit and a computer program for carrying out such a method (100) are also proposed.

Description

The present invention relates to a method for operating an internal combustion engine with at least one catalytic converter, as well as a computing unit and a computer program for carrying it out.

Background of the Invention

To achieve legally prescribed emission limit values, three-way catalysts (TWC) can be used, which enable the relevant gaseous pollutants NO _x , HC and CO to be converted into harmless products such as N ₂ , H ₂ O and CO ₂ become. In order for these catalytic reactions to take place as intended, the temperatures in the catalyst must generally exceed the so-called light-off temperature of typically 300-400°C. As soon as this is reached or exceeded, the catalytic converter converts the relevant pollutants almost completely (so-called catalytic converter window).

In order to reach this state as quickly as possible, so-called in-engine catalytic converter heating can be used. The efficiency of the gasoline engine is reduced by retarded ignition angles, which increases the exhaust gas temperature and the enthalpy input into the catalytic converter. At the same time, combustion stability can be ensured by means of adapted injection strategies (e.g. multiple injections).

In addition to these internal engine catalytic converter heating measures, external catalytic converter heating measures can also be used, for example by means of electrically heatable catalytic converters or exhaust gas burners. Such external heating measures are, for example, in the DE 41 32 814 A1 and the DE 195 04 208 A1 described.

Disclosure of Invention

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

A method according to the invention for operating an internal combustion engine with at least one catalytic converter, which is arranged downstream of the internal combustion engine, comprises, in a heating-up period, introducing fuel into a combustion chamber of the internal combustion engine, setting an early ignition angle in a combustion chamber heating mode and setting a late ignition angle in a catalyst heating mode and igniting the fuel in the combustion chamber according to the adjusted ignition angle.

In the context of the invention, an “advanced” ignition angle is understood to be an ignition angle that is earlier than an ignition angle for optimum efficiency or maximum torque of the internal combustion engine. Analogous to this, a "retard" ignition angle is later within the respective stroke of the working cycle of the internal combustion engine in comparison to that for the optimum efficiency or the maximum torque.

Both of these spark advances reduce engine efficiency to provide a higher exhaust gas temperature, where the exhaust gas can be used to heat the combustion chamber (firing early) or the catalyst (firing retarded). In this way, it is possible to specifically select which component is to be heated. As a result, the catalytic converter can be quickly brought to its operating temperature (so-called light-off) and the combustion chamber to a temperature at which no condensation of fuel on the wall of the combustion chamber with the associated negative effects is to be expected. Faster heating of the combustion chamber means less additional fuel needs to be injected to compensate for the fuel removed from combustion by condensation. This brings a consumption advantage and reduces oil dilution. A hot combustion chamber also has a positive effect on the first run (first acceleration from idle) with regard to particle emissions, since there are significantly fewer unburned hydrocarbons and therefore fewer particles are generated.

In order to achieve rapid heating, it is expedient if the combustion chamber heating mode and the catalyst heating mode together account for at least half of the ignitions during the heating period, preferably more - up to 100%. A start and/or end of the heating-up period can be determined in particular as a function of a temperature, in particular of the combustion chamber and/or of the catalytic converter to be heated. A transition from heating operation to normal operation (or back) can be achieved in the sense of smooth running, in particular by gradually changing the ignition angle, i.e. the adjustments become smaller and smaller until the optimum ignition angle is finally reached (and vice versa).

The combustion chamber heating mode and the catalyst heating mode can be carried out in the heating-up period for each combustion chamber of the internal combustion engine. So each combustion chamber can be heated in the manner described and at the same time tig the catalyst can be heated via the light-off. Preferably, the share of the individual heating modes in the total number of ignitions for the individual combustion chambers is the same in order to bring about heating that is as uniform as possible while running quietly at the same time.

In particular, the combustion chamber heating mode is carried out continuously for a first number of ignitions and the catalyst heating mode is carried out continuously for a second number of ignitions. As a result, one of the two heating modes can be carried out preferentially at certain times in order to at least temporarily reinforce the respective effect. The first number of ignitions and the second number of ignitions preferably take place directly one after the other in order to avoid torque fluctuations or to keep them low.

The method advantageously includes determining the first number and the second number as a function of at least one operating parameter of the internal combustion engine and/or the catalytic converter, with the at least one operating parameter in particular including at least one temperature. The method can thus be carried out in such a way that the operating parameters are adequately taken into account. For example, a respective heating requirement can be determined based on a catalytic converter temperature and a temperature of the internal combustion engine, and the two heating modes can be implemented according to the heating requirements.

The first number and/or the second number are preferably chosen from the natural numbers. In this way, the proportion of the respective ignitions in the total number, their relationship to one another and also the duration of a continuous combustion chamber and exhaust gas heating process can be set in a targeted manner.

The first and second numbers can be different or the same. In particular, it makes sense to choose them equally if the collective heating requirement of all combustion chambers essentially coincides with the heating requirement of the catalytic converter. In some configurations, the heating of the combustion chambers can also be preferred first, for example in order to minimize particle emissions, before the heating of the catalytic converter is started to produce the conversion capability.

The combustion chamber heating mode and the catalytic converter heating mode are preferably carried out several times in succession in alternation in order to achieve a sufficient heating effect on the one hand and a homogeneous heat distribution on the other.

In particular, the advanced ignition angle and the retarded ignition angle can be selected in such a way that the torque provided is the same in each case. This improves the smooth running of the internal combustion engine, since there are no torque jumps as a result of successive ignitions in different heating modes.

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. Finally, a machine-readable storage medium is provided with a computer program stored thereon as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical and electrical storage devices such as hard drives, flash memories, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.). Such a download can be wired or wired or wireless (e.g. via a WLAN network, a 3G, 4G, 5G or 6G connection, 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 exemplary embodiments and is described below with reference to the drawing.

character list

• 1 shows an advantageous embodiment of a method according to the invention in a schematic representation in the form of a block diagram.
• 2 shows a relationship between the ignition angle and the torque output, on the basis of which the method according to the invention can be carried out.
• 3 , 4 and 5 Fig. 12 schematically show various exemplary ignition sequences as can be used within the scope of the invention.
• 6 Figure 12 shows an example of a motor vehicle that can be used within the scope of the invention, in a schematic representation.

embodiment(s) of the invention

In 6 1 is an example of a motor vehicle as can be used within the scope of the invention, shown schematically and denoted overall by 200. FIG. Vehicle 200 includes an internal combustion engine 210, here for example with four indicated cylinders, an exhaust system 220, which has a plurality of cleaning components 222, 224, e.g. catalytic converters and/or particle filters, and a computing unit 230, which is set up to control internal combustion engine 210 and exhaust system 220 and is connected to it in a data-conducting manner. Furthermore, the computing unit 230 in the example shown is connected in a data-conducting manner to sensors 212, 227, which detect the operating parameters of the internal combustion engine 210 and/or the exhaust gas system 220, in particular a temperature of the catalytic converter 222. It goes without saying that further sensors, which are not shown, can be present. In addition, relevant variables can also be calculated using appropriate models, for example using known catalytic converter models.

In 1 an advantageous embodiment of a method according to the invention is shown in a schematic representation in the form of a block diagram and denoted overall by 100 . In the following, the method 100 is also described with reference to with regard to FIG 6 described vehicle 200 explained.

In method 100, a prioritization weighting 110 is carried out based on at least one operating parameter B1, in particular one or more temperatures (e.g. of a catalytic converter 222 and/or an internal combustion engine 210), within the framework of which a ratio between a heating requirement of catalytic converter 222 and a heating requirement of the internal combustion engine 210 is fixed.

Based on this ratio, an ignition order is determined in an ignition order determination 112 according to which the internal combustion engine 210 is to be operated in order to quickly heat both the catalytic converter 222 and the internal combustion engine 210 to their respective operating temperatures.

A combustion chamber heating mode controller 122 and a catalytic converter heating mode controller 121 use operating parameters B2, B3 (essentially speed and load) to determine an ignition angle that is optimal for carrying out the respective heating mode and, if necessary, other control variables (e.g. throttle valve position, fuel mass flow, injection time, ...) . The optimum ignition point for the respective heating mode H1, H2 is earlier (H2) or later (H1) than an “optimal” ignition angle for maximum efficiency or for maximum torque. In particular, the ignition angle can be selected so that a required torque is provided exactly, while excess power from internal combustion engine 210 is given off as completely as possible as waste heat to the component to be heated (internal combustion engine 210 or catalytic converter 222, 224). It goes without saying that the efficiency-optimized ignition angle is also dependent on operating parameters of the internal combustion engine. In particular, speed (the higher, the sooner) and load should be mentioned here, with the load in turn determining the quantity of mixture to be introduced into the combustion chamber. These two operating parameters are also referred to in combination as the operating point of the internal combustion engine and are taken into account when determining the ignition angle adjustment.

An ignition controller 130 selects one of the two heating modes individually for each combustion chamber on the basis of the ignition sequence determination 112 and transmits one or more corresponding control parameters S1, in particular the ignition angle to be used, from the combustion chamber heating mode controller 122 or the catalytic converter heating mode controller 121 to the internal combustion engine 210 or .to their components (e.g. an ignition system and/or an injection system). Internal combustion engine 210 can thus be operated in the combustion chamber heating mode and/or in the catalytic converter heating mode in a combustion-chamber-specific manner.

Alternatively or additionally, the ignition angle can also be selected via a torque model implemented in engine control unit 230 . An efficiency characteristic curve can be stored in this, which contains the instantaneously optimal ignition point α0 and covers the late side H1. The corresponding ignition point α1 can thus be calculated based on the desired torque M1. A conventional torque model, which only covers late ignition angles (H1), can be expanded to include the early side H2 for method 100, so that ignition point α2 can also be calculated accordingly for torque M1 as an alternative.

In 2 is a relationship between the ignition angle and the torque output, on the basis of which a preferred method, for example that relating to 1 illustrated method 100, can be performed, shown in the form of an efficiency diagram. A torque M that is provided is plotted against a set ignition angle α. A with respect to the efficiency of the internal combustion engine 210 optimal Ignition angle is denoted by α0. A maximum possible torque M0 is generated at this operating point. It should be noted here that the diagram in 2 This is a schematic representation and the torque curve in real systems can vary significantly. In principle, however, it is correct that the respectively provided torque decreases as the time distance between the actual ignition time angle and the optimum ignition time angle α0 increases. If, on the other hand, a later ignition angle α1 is selected in comparison to the optimum ignition angle α0, a lower torque M1 results, with energy from the combustion not used to generate the torque M1 being released as heat. Since the combustion takes place later in comparison to an operating mode for generating the maximum torque M0, a large part of this heat is discharged into the exhaust system 220 of the internal combustion engine 210 so that it is available for heating the catalytic converter 222. Depending on the extent of the ignition angle adjustment, more or less heat can be provided for this catalyst heating mode H1.

Analogously to this, the torque also falls when an early ignition angle α2 is selected, at which the air-fuel mixture introduced into internal combustion engine 210 is ignited earlier in comparison to the optimal ignition angle α0. In this case, too, more energy is released as heat. In such a case, however, the hot exhaust gases remain longer in the respective combustion chamber, so that more heat is given off to the combustion chamber in order to implement an H2 combustion chamber heating mode. The heat transferred in each case in the combustion chamber is consequently no longer available for heating the catalytic converter 222 . Again, the extent of the torque reduction can be influenced by the extent of the ignition angle shift away from the efficiency-optimal ignition angle α0.

Since the two heating operating modes H1, H2 are preferably carried out alternately and at the same time in different combustion chambers, it is advantageous to select the early α2 and late α2 ignition angle in such a way that the same torque M1 results in each case in order to ensure that internal combustion engine 210 runs as smoothly as possible to achieve.

In order nevertheless to enable individual control of the amounts of heat introduced into combustion chambers and catalytic converter 222, combustion chamber heating mode H2 and catalytic converter heating mode H1 can be carried out with different frequency. This is in the 3 , 4 and 5 illustrated by way of example, each showing schematically different ignition sequences as can be used within the scope of the invention. In each case, a combustion chamber number Z is plotted against time t. The heating mode H1, H2 carried out in the respective combustion chamber is marked by the shading of the area under the graph. In the examples presented here, an internal combustion engine 210 with four combustion chambers is assumed. However, the invention can be implemented with any internal combustion engine 210 . Both the type of internal combustion engine 210 (e.g. reciprocating piston, rotary piston, 2-stroke, 4-stroke internal combustion engine) and the number of combustion chambers (e.g. 1, 2, 3, 4, 6, 8, 12, . ..) irrelevant.

In 3 an ignition sequence is shown in which one combustion chamber is operated in combustion chamber heating mode H2 and three combustion chambers in catalyst heating mode H1 in each working cycle. In this case, the combustion chamber heating mode H2 is cyclically swapped over the four combustion chambers in order to achieve the most uniform possible development of heat both in the combustion chambers and in the catalytic converter 222 downstream of the internal combustion engine 210 . In the ignition sequence shown here, the combustion chamber heating mode H2 accounts for 25% of the ignitions.

In comparison, in 4 a firing order with a proportion of the combustion chamber heating mode H2 of 50% is shown. One combustion chamber is alternately ignited in combustion chamber heating mode H2 and one in catalyst heating mode H1, with the combustion chambers being operated alternately in one working cycle in combustion chamber heating mode H2 and one working cycle in catalyst heating mode H1.

In 5 is an essentially reverse firing order as in 3 shown, with a proportion of the combustion chamber heating mode of 75% resulting from one combustion chamber being operated in the catalyst heating mode H1 and three combustion chambers being operated in the combustion chamber heating mode H2 in each working cycle.

As already mentioned several times, these examples are only for illustration purposes, so that significantly different ignition sequences can also be implemented within the scope of the invention. For example, it may also be advantageous to heat certain combustion chambers less than other combustion chambers (e.g. in an in-line engine, the outer combustion chambers can have a higher heating requirement than inner combustion chambers, since they only have one neighboring combustion chamber), or several working cycles exclusively for one of the to carry out heating operating modes H1 or H2.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was 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.

Patent Literature Cited

• DE 4132814 A1 [0004]
• DE 19504208 A1 [0004]

Claims (10)

Method (100) for operating an internal combustion engine (210) with at least one catalytic converter (222, 224) which is arranged downstream of the internal combustion engine (210), comprising, in a heating-up period: introducing fuel into a combustion chamber of the internal combustion engine (210), setting an early ignition angle (α2) in a combustion chamber heating mode (H2) and setting a retarded ignition angle (α1) in a catalyst heating mode (H1), Ignition of the fuel in the combustion chamber at the set ignition angle (α1, α2). Method (100) according to claim 1 , wherein the combustion chamber heating mode (H2) and the catalyst heating mode (H1) are performed for each combustion chamber of the internal combustion engine (210). Method (100) according to claim 1 or 2 wherein the combustion chamber heating mode (H2) is continuously performed for a first number of ignitions and the catalyst heating mode (H1) is continuously performed for a second number of ignitions. Method (100) according to claim 3 , comprising determining (110, 130) the first number and the second number as a function of at least one operating parameter (B1) of the internal combustion engine (210) and/or the catalytic converter (222, 224), in particular the at least one operating parameter including at least one temperature includes. Method (100) according to claim 3 or 4 , the first and second numbers being different or the same. Method according to one of the preceding claims, wherein the combustion chamber heating mode and the catalytic converter heating mode are carried out several times in succession in alternation. Method (100) according to one of the preceding claims, wherein the advanced ignition angle (α2) and the retarded ignition angle (α1) are selected such that the same torque (M1) provided results in each case. Arithmetic unit (230) which is set up to carry out all method steps of a method (100) according to one of the preceding claims. Computer program that causes a computing unit (230) to carry out all method steps of a method (100) according to one of Claims 1 until 7 to be performed when it is executed on the computing unit (230). Machine-readable storage medium with a computer program stored on it claim 9 .

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