DE102019113730A1 - Internal combustion engine with variable exhaust valve actuation and with at least two SCR catalytic converters - Google Patents

Abstract

An internal combustion engine is provided with a four-stroke internal combustion engine 1, which forms a combustion chamber 4, and with an exhaust gas line that integrates an exhaust gas aftertreatment device, with exhaust gas being discharged from the combustion chamber 4 and into the exhaust gas line 7 by means of an outlet valve 9 assigned to the combustion chamber 4 , wherein the outlet valve 9 can be actuated by means of a valve actuation device 10 which is designed such that the valve opening of the outlet valve 9 can be changed during the exhaust stroke when the internal combustion engine 1 is in operation. The exhaust gas aftertreatment device comprises a first SCR catalytic converter 12 and a second SCR catalytic converter 15; 16, wherein the first SCR catalytic converter 12 upstream of the second SCR catalytic converter 15; 16 is arranged. During a heating operation of the internal combustion engine, in order to achieve a relatively high temperature of the exhaust gas, the valve opening of the exhaust valve 9 which occurs during an exhaust stroke of the internal combustion engine 1 is set smaller in comparison to normal operation. This relatively hot exhaust gas is used to the first SCR catalyst 12, which as a result of the combination with the second SCR catalyst 15; 16 can have only a relatively small volume and thus only a relatively small thermal mass, in order to make at least this first SCR catalytic converter 12 effective as quickly as possible after a cold start of the internal combustion engine.

Description

The invention relates to an internal combustion engine with a four-stroke internal combustion engine, which forms at least one combustion chamber, and with an exhaust gas line that integrates an exhaust gas aftertreatment device for discharging exhaust gas from the internal combustion engine, exhaust gas being discharged from the combustion chamber and into the exhaust gas line by means of at least one exhaust valve of the combustion chamber is controllable, wherein the exhaust valve can be actuated by means of a valve actuation device which is designed such that the valve opening of the exhaust valve can be changed during an exhaust stroke of the internal combustion engine by means of this.

Such an internal combustion engine is from DE 10 2004 016 386 B4 known. There a method for operating such an internal combustion engine is disclosed in which, after a cold start of the internal combustion engine, an exhaust valve assigned to a combustion chamber of a four-stroke internal combustion engine is actuated with a valve opening that is relatively small compared to normal operation. As a result, the gas exchange work is increased and exhaust gas is thus discharged into an exhaust line at a relatively high temperature via the correspondingly opened exhaust valve, which is intended to cause an exhaust gas aftertreatment device integrated in the exhaust line to heat up as quickly as possible.

The invention was based on the object of specifying an internal combustion engine which is characterized by the lowest possible pollutant emissions, in particular after a cold start of the internal combustion engine.

This object is achieved by means of an internal combustion engine according to patent claim 1. A method for operating such an internal combustion engine is the subject matter of patent claim 10. Advantageous embodiments of the internal combustion engine according to the invention and preferred embodiments of the method according to the invention are the subject matter of the further patent claims and / or result from the following description of the invention.

According to the invention, an internal combustion engine, in particular for a motor vehicle, is provided with a four-stroke internal combustion engine that forms at least one combustion chamber, and with an exhaust gas line that integrates an exhaust gas aftertreatment device for discharging exhaust gas from the internal combustion engine, with exhaust gas being discharged from the combustion chamber and into the exhaust gas line is controllable by means of at least one exhaust valve assigned to the combustion chamber, the exhaust valve being operable by means of a valve actuating device which is designed such that the valve opening of the exhaust valve can be changed during the exhaust stroke when the internal combustion engine is operating. In particular, the valve opening of the outlet valve can be changed in such a way that at least one relatively large valve opening and one relatively small valve opening (which is greater than zero) can be set. According to the invention, the exhaust gas aftertreatment device comprises a first SCR catalytic converter and a second SCR catalytic converter, the first SCR catalytic converter being arranged upstream of the second SCR catalytic converter.

A method according to the invention for operating such an internal combustion engine provides that temporarily during a heating operation of the internal combustion engine to achieve a relatively high temperature of the exhaust gas discharged from the combustion chamber, the valve opening of the exhaust valve that occurs during an exhaust stroke of the internal combustion engine is set smaller in comparison to normal operation of the internal combustion engine .

The invention aims to basically result from the DE 10 2004 016 386 B4 known measure for the temporary generation of a relatively hot exhaust gas to use the first SCR catalytic converter, which is arranged relatively close to the internal combustion engine and which, as a result of the combination with the second SCR catalytic converter, has only a relatively small volume and therefore only a relatively small thermal mass in comparison to the SCR catalytic converters usually used in comparable internal combustion engines for motor vehicles) to warm up, in particular to make at least this first SCR catalytic converter effective as quickly as possible after a cold start of the internal combustion engine. Since an internal combustion engine of a motor vehicle is usually only operated at relatively low speeds and loads immediately after a cold start, the exhaust gas mass flow to be discharged from the internal combustion engine via the exhaust system is then also relatively low. The relatively small volume of the first SCR catalytic converter is then sufficient to achieve a catalytically effective reduction of the pollutants contained in the exhaust gas train mass flow and to be reduced by means of the first (and also the second) SCR catalytic converter to a sufficient extent and in particular as completely as possible, in particular nitrogen oxides to realize. If the internal combustion engine is then operated at relatively high speeds and / or loads, as a result of which it generates a correspondingly large exhaust gas mass flow, a catalytically effective reduction of the pollutant or pollutants to be reduced by the first SCR catalytic converter and then already due to the ongoing operation of the Internal combustion engine also warmed up second SCR catalytic converter can be realized. Ask for it the at least two SCR catalysts in combination provide a sufficient volume.

The first SCR catalyst preferably has a smaller volume compared to the second SCR catalyst. The volume of the first SCR catalytic converter can be in particular between 10% and 35% and preferably approx. 15% (i.e. 15 ± 2%) of the volume of the second SCR catalytic converter. Starting from a total volume of the SCR catalytic converters of the internal combustion engine, which is designed for a sufficient reduction of the pollutant (s) to be reduced in the maximum exhaust gas mass flow generated by the internal combustion engine during operation, such a configuration of the first SCR catalytic converter which is different in terms of volume can be used and the second SCR catalytic converter can be made possible in an advantageous manner to dimension the first SCR catalytic converter particularly small, whereby its effectiveness can be achieved particularly quickly, especially after a cold start of the internal combustion engine.

According to the invention, a “cold start” of the internal combustion engine is understood to mean a start-up of the internal combustion engine at which the exhaust gas aftertreatment device has a temperature that is below a limit temperature of 120 ° C. and which can in particular essentially (ie ± 5 ° C.) correspond to the ambient temperature . In this case, the temperature of the SCR catalytic converters is also well below their respective light-off or light-off temperature, from which a sufficiently high effectiveness with reduction rates of, for example, at least 90% can be assumed.

The "volume" of an SCR catalytic converter is the overall space size of the component comprising the catalytically active material, around and / or through which the exhaust gas flows for the selective catalytic reduction of pollutants, in particular nitrogen oxides (NO _X ), Understood.

The internal combustion engine of an internal combustion engine according to the invention can in particular be a (self-igniting and quality-controlled) diesel engine. However, there is also the possibility that the internal combustion engine is a (spark-ignition and quantity-controlled) Otto engine or a combination thereof, e.g. an internal combustion engine with homogeneous compression ignition. The internal combustion engine can be operated or be operable both with liquid fuel (i.e. diesel fuel or gasoline) and with a gaseous fuel (in particular natural gas, LNG or LPG).

The internal combustion engine of an internal combustion engine according to the invention can preferably form a plurality of combustion chambers. Likewise, it can preferably be provided that a plurality of exhaust valves are assigned to each of these combustion chambers. It can be provided that the valve opening can be changed during the exhaust stroke for all or only individual ones, in particular also for only a single one of the exhaust valves assigned to each combustion chamber.

A change in the valve opening of the exhaust valve in an internal combustion engine according to the invention can preferably be done by shifting the start of opening during the exhaust stroke (preferably in combination with a change in the duration of the opening, ie the end of opening is not shifted or is shifted to a different extent than the start of opening) and / or Variation of the opening stroke (ie the maximum opening travel of the exhaust valve) can be realized.

A switching device can advantageously be used to vary the valve opening of the outlet valve, which accordingly has at least two and preferably exactly two discrete switching positions that differ with regard to the valve opening of the outlet valve caused by the switching device. Such a switching device can be distinguished by a relatively simple structural design, in particular in comparison to an adjusting device that can also be used, by means of which the valve opening of the outlet valve can be continuously adjusted. Such a switching device can particularly preferably be based on the use of different cams of a camshaft of the valve actuating device provided for actuating the exhaust valve, the cams alternatively being able to be brought into operative connection with the exhaust valve by means of an actuator of the switching device.

To vary the valve opening of the outlet valve, however, an adjusting device can also be used in an advantageous manner, by means of which the valve opening of the outlet valve can be continuously adjusted.

When carrying out a method according to the invention, it can preferably be provided that, during the heating operation of the internal combustion engine, the exhaust valve is opened between 70 ° CA before LW-OT (° CA: crankshaft angle) and 50 ° CA before LW-OT and, furthermore preferably between 20 ° CA. before LW-OT and 0 ° CA before LT-OT, especially at 10 ° CA before LT-OT. Likewise, it can preferably be provided that the opening stroke is between 1 mm and 2 mm. The valve actuation device of an internal combustion engine according to the invention can be brought into a corresponding actuation position for this purpose.

In addition, it can preferably be provided when carrying out a method according to the invention that during normal operation of the internal combustion engine the exhaust valve is opened between 210 ° CA before LW-OT and 190 ° CA before LW-OT, in particular at 200 ° CA before LW-OT, and, furthermore preferred, between 20 ° CA before LW-OT and 0 ° CA before LW-OT, in particular at 10 ° CA before LW-OT, is closed. For normal operation, it can furthermore preferably be provided that the opening stroke is between 8 mm and 10 mm, in particular 9 mm.

The details of the control times can refer to a stroke threshold of 1 mm or 0.5 mm, from which it can be assumed that the exhaust valves will open effectively. In particular, a stroke threshold of 1 mm for an opening stroke of at least 2 mm and a stroke threshold of 0.5 mm for an opening stroke of less than 2 mm can be applied.

According to a preferred embodiment of an internal combustion engine according to the invention, it can be provided that the second SCR catalytic converter is designed as a catalytically coated particle filter. As a result, an advantageous dual functionality can be implemented for this component of the exhaust gas aftertreatment device.

Furthermore, it can preferably be provided that the exhaust gas aftertreatment device of an internal combustion engine according to the invention comprises a third SCR catalytic converter and possibly also further SCR catalytic converters, which is / are arranged downstream of the second SCR catalytic converter. As a result, the individual SCR catalytic converters can be made particularly small, and in combination with a time-graded heating of the SCR catalytic converters, the SCR catalytic converters can take effect as quickly as possible and also ensure that the SCR catalytic converters are sufficiently effective in all operating states of the internal combustion engine.

An internal combustion engine according to the invention enables at least two of the SCR catalytic converters to be configured differently with regard to the catalytically active materials, as a result of which, overall, a particularly advantageous effectiveness of the exhaust gas aftertreatment device can be achieved.

Furthermore, it can preferably be provided that the first SCR catalytic converter has an effective temperature range which is lower than the effective temperature range of the second SCR catalytic converter and / or the third SCR catalytic converter. This can be achieved in particular through an appropriate selection of the catalytically active materials of these SCR catalysts. Such a configuration of an internal combustion engine according to the invention supports the first SCR catalyst to take effect as quickly as possible, in particular after a cold start of the internal combustion engine, whereas the second and / or the third SCR catalyst is as effective as possible at relatively high temperatures, which usually only occur at operation of the internal combustion engine at operating temperature can be optimized.

According to a preferred embodiment of an internal combustion engine according to the invention, the exhaust gas aftertreatment device can furthermore comprise an NO _x storage catalytic converter and / or an oxidation catalytic converter which is / are arranged upstream of the first SCR catalytic converter. As a result, the pollutant emission behavior of the internal combustion engine, in particular immediately after a cold start, can be further improved.

The invention also relates to a motor vehicle, in particular a wheel-based and not rail-bound motor vehicle (preferably a car or a truck), with an internal combustion engine according to the invention. The internal combustion engine or the internal combustion engine thereof can in particular be provided for (direct or indirect) provision of the drive power for the motor vehicle.

The indefinite articles (“a”, “an”, “an” and “an”), in particular in the claims and in the description that generally explains the claims, are to be understood as such and not as numerals. Components specified in this way are therefore to be understood in such a way that they are present at least once and can be present several times.

• 1: eine erfindungsgemäße Brennkraftmaschine in vereinfachter Darstellung;
• 2: die Ventilerhebungskurven für die Einlass- und Auslassventile während eines Heizbetriebs der Brennkraftmaschine; und
• 3: die Ventilerhebungskurven für die Einlass- und Auslassventile während eines Normalbetriebs der Brennkraftmaschine.

The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawings. In the drawings shows:

• 1 : an internal combustion engine according to the invention in a simplified representation;
• 2 : the valve lift curves for the intake and exhaust valves during a heating operation of the internal combustion engine; and
• 3 : the valve lift curves for the intake and exhaust valves during normal operation of the internal combustion engine.

The 1 shows a schematic representation of an internal combustion engine according to the invention. This includes a four-stroke internal combustion engine 1 , the example in the form of a reciprocating engine with four cylinders arranged in series 2 is trained. The cylinders 2 limit with reciprocating pistons guided therein 3 and a cylinder head each have a combustion chamber 4th . These combustion chambers 4th is used in the operation of the Internal combustion engine 1 and thus fresh gas to the internal combustion engine via a fresh gas line 5 fed. This fresh gas is primarily air which is sucked in from the environment and which is then passed through a compressor (not shown). This compressor is part of an exhaust gas turbocharger, which continues to be an exhaust gas turbine 6th includes, which is in an exhaust line 7th the internal combustion engine is integrated. Exhaust gas that is produced during the combustion of mixture quantities that are obtained from the fresh gas and, for example, directly via fuel injectors (not shown) into the combustion chambers 4th injected fuel is created via the exhaust system 7th discharged and flows through the exhaust gas turbine 6th and then an exhaust gas aftertreatment device of the internal combustion engine.

Each combustion chamber is in accordance with the 1 illustrated embodiment example two inlet valves 8th and two exhaust valves 9 assigned, via a valve operating device 10 which, for example, each have a camshaft for the inlet valves on the one hand 8th and on the other hand the exhaust valves 9 can include, operated. In operation of the internal combustion engine 1 are the reciprocating pistons 3 due to the combustion processes in the combustion chambers 4th moves in an oscillating manner between a top dead center (TDC) and a bottom dead center (BDC), with the reciprocating piston 3 alternately perform a gas exchange stroke, which includes an exhaust stroke and an intake stroke, and a power stroke, which includes a compression stroke and an expansion stroke. The reciprocating piston 3 are connected to a crankshaft (not shown) via connecting rods (not shown), with the oscillating movements of the reciprocating pistons 3 cause the crankshaft to rotate. Depending on a crankshaft angle in the gas exchange stroke of the individual reciprocating pistons 3 become the inlet valves 8th and the exhaust valves 9 by means of the valve operating device 10 open and closed at precisely defined valve opening times, as shown in the 2 and 3 is shown. With LW-OT the top dead center of the individual reciprocating pistons is 3 marked during the respective gas exchange stroke.

The exhaust gas aftertreatment device comprises a first exhaust gas aftertreatment device viewed in the flow direction of the exhaust gas 11 , which can be an oxidation catalyst or an NO _X storage catalyst or a combination of such an oxidation catalyst and such a NO _X storage catalyst.

This first exhaust aftertreatment device 11 a second exhaust gas aftertreatment device closes 12 in the form of a first SCR catalytic converter. A (first) metering device is arranged in front of this 13 for a reducing agent, which can in particular be ammonia or an ammonia-containing solution, assigned. Between the (first) dosing device 13 and the first SCR catalyst 12 is a (first) mixing device 14th arranged, which can be designed for example in the form of flow guide elements that cause turbulence in the flow of the exhaust gas already mixed with the reducing agent.

The first SCR catalytic converter 12 a third exhaust gas aftertreatment device closes 15th in the form of a particle filter. It can optionally be provided that this particle filter 15th or the filter body forming this has a catalytically active coating, whereby the particle filter 15th then at the same time represents a second SCR catalytic converter of the exhaust gas aftertreatment device. The presence of reducing agent in the second SCR catalytic converter required for the catalytic reduction of pollutants contained in the exhaust gas, in particular nitrogen oxides 15th Exhaust gas flowing through is controlled by a correspondingly strong metering of the reducing agent by means of the (first) metering device 13 realized. If using the second SCR catalytic converter 15th a reduction of pollutants contained in the exhaust gas is provided, can with this (first) metering device 13 more reducing agent can be introduced into the exhaust gas than in the first SCR catalytic converter 12 can be implemented. That in the first SCR catalytic converter 12 unconverted reducing agents (so-called reducing agent slip) can then be used for the catalytic reduction of the pollutants in the second SCR catalytic converter 15th be used.

The first SCR catalytic converter 12 and the particle filter, which may also act as a (second) SCR catalyst 15th are according to the 1 Integrated into the same housing of the exhaust system to enable the exhaust system to be as compact as possible.

The exhaust gas aftertreatment device can, in an arrangement downstream of the particulate filter 15th , a further SCR catalytic converter as a fourth exhaust gas aftertreatment device 16 include, which consequently has a third SCR catalyst 16 the exhaust aftertreatment device represents when the particulate filter 15th is also effective as a (second) SCR catalyst. Otherwise, this is another SCR catalytic converter 16 a second SCR catalytic converter of the exhaust gas aftertreatment device. The particulate filter works 15th also at the same time as the second SCR catalytic converter of the exhaust gas aftertreatment device, this additional SCR catalytic converter 16 be waived.

The other SCR catalytic converter 16 is a second in an arrangement upstream thereof Dosing device 17th for a reducing agent and, in an arrangement between this second metering device 17th and the further SCR catalytic converter 16 , a mixing device 18th assigned. This second metering device 17th can be particularly useful or necessary when, as described in the 1 is shown between the particulate filter 15th and this second metering device 17th an exhaust gas recirculation line 19th from the exhaust system 7th goes off, via which, if necessary, part of the exhaust gas in the fresh gas line 5 can be traced back. If such an exhaust gas recirculation is carried out, it should be avoided that the exhaust gas recirculated in the process does not contain reducing agent which has not yet been converted. Dosing by means of the first dosing device 13 should therefore take place at least when exhaust gas recirculation is carried out in such a way that downstream of the particle filter 15th If possible, no more reducing agent is contained in the exhaust gas. This consequently requires an additional introduction of reducing agent into the exhaust gas upstream of the further SCR catalytic converter 16 in order to be able to achieve a reduction in pollutants through this.

The last component in the flow direction or the fifth exhaust gas aftertreatment device of the exhaust gas aftertreatment device is a blocking catalyst 20th intended. This is an oxidation catalytic converter in the additional SCR catalytic converter 16 converts unreacted reducing agent (in particular ammonia to form N ₂ and H ₂ O) in order to avoid releasing this reducing agent into the environment.

The volume of the first SCR catalyst 12 is in comparison to the particle filter, which may act as an SCR catalytic converter 15th as well as in comparison to the other SCR catalytic converter 16 significantly smaller. As a result, after a cold start of the internal combustion engine, the light-off temperature of this first SCR catalytic converter should be reached as quickly as possible 12 and thus the fastest possible reduction in the pollutants contained in the exhaust gas to be reduced can be achieved.

For warming up the first SCR catalytic converter as quickly as possible 12 it is additionally provided to operate the internal combustion engine in a heating mode after a cold start by, according to the 2 at least one, preferably both, of each of the combustion chambers 4th associated exhaust valves 9 can be operated with a significantly smaller valve opening than is provided for in normal operation (cf. 3 ). Will only one of the exhaust valves during heating operation 9 per combustion chamber 4th actuated with a relatively small valve opening, it can preferably be provided that the associated second outlet valve 9 is kept completely closed.

The relatively small valve opening of the exhaust valve or valves 9 the combustion chambers 4th is realized according to the embodiment in that on the one hand the opening start is shifted late or closer in the direction of LW-OT compared to normal operation and on the other hand the opening stroke is reduced, whereas the opening end is the same compared to normal operation. The reduced opening stroke can also be a consequence of the reduced opening duration achieved, since an opening stroke that remains the same with a reduced opening duration leads to impermissibly high accelerations of the exhaust valves 9 could lead. As a result of the relatively late start of the opening movement of the exhaust valves 9 takes place in the exhaust stroke initially (with the exhaust valves closed 9 ) a relatively strong compression of the exhaust gases contained in the combustion chambers, which is already associated with a heating of these exhaust gases. Will the exhaust valves 9 then opened, this relatively strongly compressed exhaust gas flows through the exhaust valves, which are only opened with a relatively small opening stroke 9 This results in high flow velocities that contribute to further heating of the exhaust gas. Through the opening of the exhaust valves 9 consequently, with a relatively small valve opening, relatively hot exhaust gas is discharged into the exhaust system and thus the fastest possible heating, particularly of the first exhaust gas aftertreatment device 11 and the first SCR catalyst 12 realized.

As soon as sufficient heating of the first SCR catalytic converter 12 has been reached, can be switched from the heating mode to the normal mode of the internal combustion engine, in which according to the 3 the opening time for the exhaust valves 9 Extends over the entire exhaust stroke and also the opening stroke of the exhaust valves 9 is significantly larger than in the heating mode of the internal combustion engine. This serves to reduce the gas exchange work during normal operation of the internal combustion engine 1 To minimize as much as possible, which is beneficial to the efficiency and thus the fuel consumption of the internal combustion engine 1 affects.

Switching between heating operation and normal operation of the internal combustion engine can preferably take place by means of a switchable camshaft, which is used for each of the exhaust valves 9 provides two different cams, one of these cams alternately with the respective exhaust valve by means of a switching device 9 can be brought into operative connection.

List of reference symbols

1

(Four-stroke) combustion engine

2

cylinder

3

Reciprocating piston

4th

Combustion chamber

5

Fresh gas line

6

Exhaust gas turbine

7th

Exhaust system

8th

Inlet valve

9

outlet valve

10

Valve actuation device

11

first exhaust gas aftertreatment device / oxidation catalytic converter / NO _X storage catalytic converter

12

second exhaust aftertreatment device / first SCR catalytic converter

13

first dosing device

14th

first mixing device

15th

third exhaust aftertreatment device / particulate filter / second SCR catalytic converter

16

fourth exhaust gas aftertreatment device / further SCR catalytic converter / third SCR catalytic converter

17th

second dosing device

18th

Mixing device

19th

Exhaust gas recirculation line

20th

fifth exhaust aftertreatment device / slip catalyst

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed 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 102004016386 B4 [0002, 0007]

Claims (12)

Internal combustion engine with a four-stroke internal combustion engine (1) which forms at least one combustion chamber (4) and with an exhaust gas line (7) that integrates an exhaust gas aftertreatment device for discharging exhaust gas from the internal combustion engine (1), with exhaust gas being discharged from the combustion chamber (4 ) and can be controlled in the exhaust gas line (7) by means of at least one exhaust valve (9) assigned to the combustion chamber (4), wherein the exhaust valve (9) can be actuated by means of a valve actuation device (10) which is designed in such a way that it can be used to operate the Internal combustion engine (1) the valve opening of the exhaust valve (9) can be changed during the exhaust stroke, characterized in that the exhaust gas aftertreatment device comprises a first SCR catalyst (12) and a second SCR catalyst (15; 16), the first SCR catalyst (12) is arranged upstream of the second SCR catalytic converter (15; 16). Internal combustion engine according to Claim 1 , characterized in that the first SCR catalytic converter (12) has a smaller volume compared to the second SCR catalytic converter (15; 16). Internal combustion engine according to Claim 1 or 2 , characterized in that the volume of the first SCR catalytic converter (12) is between 10% and 35%, preferably approx. 15%, of the volume of the second SCR catalytic converter (15; 16). Internal combustion engine according to one of the preceding claims, characterized in that the second SCR catalytic converter (15) is designed as a catalytically coated particle filter (15). Internal combustion engine according to one of the preceding claims, characterized in that the exhaust gas aftertreatment device comprises a third SCR catalytic converter (16) which is arranged downstream of the second SCR catalytic converter (15). Internal combustion engine according to one of the preceding claims, characterized in that at least two of the SCR catalytic converters (12, 15, 16) differ with regard to the catalytically active materials. Internal combustion engine according to one of the preceding claims, characterized in that the first SCR catalytic converter (12) has an effective temperature range which is lower than the effective temperature range of the second SCR catalytic converter (15; 16) and / or the third SCR catalytic converter (16) . Internal combustion engine according to one of the preceding claims, characterized by a controllable bypass to the first SCR catalytic converter (12). Internal combustion engine according to one of the preceding claims, characterized in that the exhaust gas aftertreatment device comprises an NO _X storage catalytic converter (11) and / or an oxidation catalytic converter (11) which is / are arranged upstream of the first SCR catalytic converter (12). Method for operating an internal combustion engine according to one of the preceding claims, characterized in that temporarily during a heating operation of the internal combustion engine to achieve a relatively high temperature of the exhaust gas discharged from the combustion chamber (4) the valve opening of the exhaust valve (1) occurring during an exhaust cycle of the internal combustion engine (1) 9) is set smaller in comparison to normal operation of the internal combustion engine. Procedure according to Claim 10 , characterized in that the exhaust valve is opened between 70 ° KW before LW-OT and 50 ° KW before LW-OT and is closed between 20 ° KW and 0 ° KW before LW-OT during the heating operation of the internal combustion engine. Procedure according to Claim 10 or 11 , characterized in that the opening stroke of the exhaust valve is between 1 mm and 2 mm during the heating operation of the internal combustion engine.

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