EP2657487A1 - Self-ignited combustion engine with partial shut-down and method for operating such a combustion engine with optimised emissions - Google Patents

Abstract

The engine (10) has two groups in which each group is provided with two cylinders (30). One cylinder of first group is formed as the cylinder that can be switched in a load-dependent manner. The two groups are characterized by different compression ratios. The cylinder of a first group is provided with a lower compression ratio and the cylinder of a second group is provided with a higher compression ratio. The cylinder of the first group is in operation during the event of a partial deactivation in the lower portion-load range. An independent claim is included for a method for operation of an internal combustion engine.

Description

The invention relates to a self-igniting internal combustion engine having at least two cylinders, in which at least two cylinders are configured in such a way that they form at least two groups each having at least one cylinder, wherein the at least one cylinder of at least one group is designed as a load-dependent switchable cylinder.

Furthermore, the invention relates to a method for emission-optimized operation of such an internal combustion engine.

In the development of internal combustion engines, in addition to the reduction of fuel consumption, a fundamental goal is to reduce pollutant emissions.

In the reduction of pollutant emissions, two fundamentally different approaches can be distinguished. On the one hand, the raw emissions of the internal combustion engine can be reduced by internal engine measures, so that the exhaust gas discharged from the cylinders from home, d. H. original, contains less pollutants. On the other hand, the combustion gases discharged from the cylinders into the exhaust gas removal system can be aftertreated, so that the exhaust gas released into the environment has lower pollutant concentrations.

The internal engine measures include, for example, the recirculation of exhaust gases by means of external and / or internal exhaust gas recirculation. Since the formation of nitrogen oxides requires not only an excess of air but also high temperatures, a concept for reducing nitrogen oxide emissions is to develop combustion processes with lower combustion temperatures. Here, the exhaust gas recirculation is targeted, in which the nitrogen oxide emissions can be significantly reduced with increasing exhaust gas recirculation rate. Exhaust gas recirculation is also suitable for reducing emissions of unburned hydrocarbons in the partial load range.

By a suitable choice of the operating parameters of the internal combustion engine, for example the timing, the start of injection, the duration of injection, the ignition timing, the fuel quantity or the air ratio λ and by advantageous structural design of the cooling, the combustion chamber and / or the intake ports, the raw emissions of the internal combustion engine can also reduce.

Since internal engine measures are not sufficient to lower the pollutant concentrations to the limits set by law, state-of-the-art engines for reducing pollutant emissions are equipped with various exhaust aftertreatment systems.

For the oxidation of the unburned hydrocarbons (HC) and carbon monoxide (CO) oxidation catalysts are used. In order to realize a sufficient conversion, a minimum temperature is required.

In internal combustion engines, which are operated with an excess of air, such as self-igniting internal combustion engines, the nitrogen oxides contained in the exhaust gas, in principle, d. H. due to the lack of reducing agents can not be reduced.

As a result, exhaust aftertreatment systems must be provided to reduce nitrogen oxides, for example, storage catalysts in which the nitrogen oxides are first absorbed in the catalyst, d. H. collected and stored, and then reduced during a regeneration phase. As the reducing agent, fuel, d. H. unburned hydrocarbons, or urea can be used. The temperature of the storage catalyst during the regeneration phase should preferably be in a temperature window between 200 ° C and 450 ° C. Due to the sulfur contained in the exhaust gas, the storage catalyst for desulfurization must be heated regularly to high temperatures, usually between 600 ° C and 700 ° C, and supplied with a reducing agent. Such high temperatures can damage the storage catalyst and contribute to the thermal aging of the catalyst.

To minimize the emission of soot particles so-called regenerative particulate filters are used in the prior art, the soot particles from the exhaust filter out and store, with these soot particles are intermittently burned as part of the regeneration of the filter. The high temperatures for the regeneration of the particulate filter - about 550 ° C in the absence of catalytic support - are achieved in operation only at high loads and high speeds. Therefore, additional measures must be used to ensure regeneration of the filter under all operating conditions.

In contrast to the internal engine measures to reduce pollutant emissions, the exhaust aftertreatment is associated with high costs for the different exhaust aftertreatment systems. In particular, legislated NOx emission limits may require on-board diagnostics (OBD) to monitor conversion. More complex, more efficient and therefore more expensive exhaust aftertreatment systems are required in order to comply with the limits set by law.

In addition, the various exhaust aftertreatment systems adversely affect the operation of the internal combustion engine when, for example, for the regeneration of a particulate filter or for regeneration or desulfurization of a storage catalyst high temperatures must be generated or an oxidation catalyst should be heated to operating temperature as quickly as possible after a cold start.

Against the background of the above, it is an object of the present invention to provide a self-igniting internal combustion engine according to the preamble of claim 1, which is optimized in terms of their raw emissions, in particular of nitrogen oxides.

Another object of the present invention is to provide a method for emission-optimized operation of such an internal combustion engine.

• sich die mindestens zwei Gruppen durch unterschiedliche Verdichtungsverhältnisse ε_i auszeichnen, wobei
• der mindestens eine Zylinder einer ersten Gruppe ein Verdichtungsverhältnis ε₁ aufweist und der mindestens eine Zylinder einer zweiten Gruppe ein Verdichtungsverhältnis ε₂ aufweist mit ε₂ > ε₁ , und
• bei Teilabschaltung im unteren Teillastbereich der mindestens eine Zylinder der ersten Gruppe der mindestens eine in Betrieb befindliche Zylinder ist.

The first sub-task is solved by a self-igniting internal combustion engine having at least two cylinders, in which at least two cylinders are configured in such a way that they form at least two groups each having at least one cylinder, the at least one cylinder of at least one group formed as a load-dependent switchable cylinder is, and which is characterized in that

• the at least two groups are characterized by different compression ratios ε _i , where
• the at least one cylinder of a first group has a compression ratio ε ₁ and the at least one cylinder of a second group has a compression ratio ε ₂ with ε ₂ > ε ₁ , and
• when partial shutdown in the lower part load range, the at least one cylinder of the first group is the at least one in-service cylinder.

To reduce the raw emissions is carried out according to the invention a cylinder shutdown, d. H. a shutdown of individual cylinders in certain load ranges.

The so-called partial shutdown is a known from the prior art concept for reducing fuel consumption. The efficiency of a diesel engine, d. H. a self-igniting internal combustion engine, can be improved in part-load operation by a partial shutdown, d. H. be increased, because the shutdown of at least one cylinder of a multi-cylinder internal combustion engine increases the load of the remaining still operating cylinders at constant engine power, so that these cylinders operate in areas of higher loads, in which the specific fuel consumption is lower. The load collective in partial load operation of the diesel engine is thereby shifted to higher loads. Further efficiency advantages result from the fact that a deactivated cylinder as a result of the lack of combustion no wall heat losses generated as a result of heat transfer from the combustion gases to the combustion chamber walls.

In the internal combustion engine according to the invention, the at least one cylinder of the first group at partial shutdown in the lower part load range of at least one in-service cylinder, a low load T _low , ie a load in the lower part load range, a load is less than 50%, preferably is less than 30% of the maximum load T _{max, n} at the instantaneous speed n. In order to optimize the partial shutdown with regard to the raw emissions, the at least one cylinder of the first group in operation during partial shutdown is provided with a smaller compression ratio ε ₁ , ie with a compression ratio ε ₁ which is smaller than the compression ratio ε ₂ of at least a cylinder of the second group. The following applies: ε ₁ < ε ₂ .

Although the efficiency η of the first cylinder group decreases with the smaller compression ratio, since the efficiency η correlates more or less with the compression ratio ε _i . However, it should be considered that the low compression ratio ε ₁ leads to a lower temperature and pressure level, so that the formation of nitrogen oxides is counteracted.

While with regard to the reduction of fuel consumption, ie in terms of efficiency, usually a higher compression ratio ε _{1 would be} expedient and to choose, according to the invention and unusually the at least one cylinder of the first group, ie the at least one during operation of the partial shutdown in cylinder, equipped with a lower compression ratio ε ₁ . In this respect, an additional fuel consumption may have to be accepted in order to reduce the raw emissions.

The at least one cylinder of the second group is equipped with a higher compression ratio ε ₂ and can be designed for higher loads or higher efficiency. At least the cylinders of the second cylinder group are switchable, so that these cylinders can be switched to higher loads or - if the cylinders of the first group are also formed switchable - can be switched to the cylinder of the second group.

The internal combustion engine can be safely started with the at least one cylinder of the second group, if the low compression ratio ε _{1 of} the first group is not sufficiently high. It should be considered that a self-igniting internal combustion engine to initiate auto-ignition a certain compression ratio, ie, a minimum compression ratio required, especially at start, ie the first time initiation of combustion at optionally still cold internal combustion engine. For example, compression ratios ε _i ≈ 18 may be required to ensure safe autoignition during a cold start unless other measures are taken that make a lower compression ratio tolerable. Under purely thermodynamic aspects, a compression ratio ε _i ≈ 16 is to be preferred in order to optimize the efficiency of the internal combustion engine.

From the above it follows that also process variants are possible in which the internal combustion engine is started with the second cylinder group, immediately after the Start is switched to the first cylinder group to reduce the raw emissions of nitrogen oxides in the lower part load range, and when a predetermined load T _up of at least one cylinder of the second group is switched on or is switched to this cylinder. The various process variants result from the different embodiments of the internal combustion engine, the essential difference being whether only one of the at least two cylinder groups or more than one cylinder group is shiftable. The latter not only allows a connection, but rather a switching, ie a change between the cylinder groups.

The at least two cylinder groups may also differ from each other in other operating parameters or design features, for example, the cooling, the combustion process, the air ratio λ , the intake ports, the exhaust ports and / or the injectors.

With the internal combustion engine according to the invention a self-igniting internal combustion engine is provided according to the preamble of claim 1, which is optimized in terms of their raw emissions. Thus, the first object of the invention is solved.

The internal combustion engine according to the invention has at least two cylinders or at least two groups each having at least one cylinder. As such, three-cylinder engines configured in three groups of one cylinder each, or six-cylinder engines configured in three groups of two cylinders, are also internal combustion engines of the present invention. The three cylinder groups can have different compression ratios ε _i and can be switched on successively as part of a partial shutdown or switched off individually and independently of each other, whereby a two-way switching can be realized. The partial shutdown is thereby further optimized. The cylinder groups may also comprise a different number of cylinders.

Further advantageous embodiments of the self-igniting internal combustion engine are discussed in connection with the subclaims.

Advantageous embodiments of the self-igniting internal combustion engine, in which the at least one cylinder of the second group is designed as a switchable cylinder, which is switched off when falling below a predetermined load T _down and is switched on when a predetermined load T _up is exceeded.

The at least one cylinder of the first group is in the present case a cylinder in constant operation. Optionally, the internal combustion engine is started with the at least one cylinder of the second group, which then shuts off at low loads and reactivates to higher loads, d. H. is switched on.

In part-load operation, the at least one cylinder of the second group is switched off when falling below a predefinable load, whereby the at least one remaining cylinder of the first group with its lower compression ratio ε ₁ ensures or enables emission-optimized operation of the internal combustion engine. The advantages are those already mentioned above.

Embodiments of the self-igniting internal combustion engine in which both the at least one cylinder of the first group and the at least one cylinder of the second group is designed as a switchable cylinder are also advantageous.

In contrast to the embodiment described above, in the present case both cylinder groups are designed as switchable groups. This not only allows switching but also switching between the at least two cylinder groups and also a combination of switching and connecting. In connection with the description of the method according to the invention or the method variants, the different approaches are discussed.

Embodiments of the self-igniting internal combustion engine in which the at least two cylinders form two groups each having at least one cylinder are advantageous.

Two cylinder groups have the advantage over multi-cylinder group embodiments that the partial shutdown control is less complex. In addition, it should be noted that the realization of a mass and moment compensation, which is preferably also switchable in parts, due to the different Compression ratios ε _{i is} difficult and the cost increases significantly with the increase in the number of cylinder groups.

Embodiments of the self-igniting internal combustion engine in which the at least one cylinder of the first group has a compression ratio ε ₁ and the at least one cylinder of the second group has a compression ratio ε ₂ with ε ₂ > ε ₁ + 1 are advantageous.

Also advantageous are embodiments of the self-igniting internal combustion engine in which the at least one cylinder of the first group has a compression ratio ε ₁ and the at least one cylinder of the second group has a compression ratio ε ₂ with ε ₂ > ε ₁ + 2 .

Also advantageous are embodiments of the self-igniting internal combustion engine in which the at least one cylinder of the first group has a compression ratio ε ₁ and the at least one cylinder of the second group has a compression ratio ε ₂ with ε ₂ > ε ₁ + 3 .

While the three above embodiments are based on the relative difference of the two cylinder groups in the compression ratio ε _i , the following embodiments relate to the absolute compression ratio of the two groups.

Embodiments of the self-igniting internal combustion engine in which the at least one cylinder of the second group has a compression ratio ε ₂ with 15 < ε ₂ < 20 , preferably with 16 < ε ₂ < 19, are advantageous.

The at least one cylinder of the second group has a high compression ratio ε ₂ , which offers advantages in terms of the efficiency η of the internal combustion engine, can satisfy a high load requirement and ensures safe auto-ignition even with a cold start.

Embodiments of the self-igniting internal combustion engine in which the at least one cylinder of the first group has a compression ratio ε ₁ with 12 < ε ₁ <16, preferably with 13 < ε ₁ < 16 or with 13 < ε ₁ < 15, are also advantageous.

The at least one cylinder of the first group has a lower compression ratio ε ₁ , in order to optimize the internal combustion engine in the lower part load range with respect to the raw nitrogen oxide emissions.

• sich die mindestens zwei Gruppen durch unterschiedliche Zylindervolumen V_i auszeichnen, wobei
• der mindestens eine Zylinder der ersten Gruppe ein Zylindervolumen V₁ aufweist und der mindestens eine Zylinder der zweiten Gruppe ein Zylindervolumen V₂ aufweist mit V₂ > V₁ .

Embodiments of the self-igniting internal combustion engine are advantageous in which

• the at least two groups are characterized by different cylinder volumes V _i , wherein
• the at least one cylinder of the first group having a cylinder volume V ₁ and the at least one cylinder of the second group a cylinder volume V ₂ having V _{2> V1.}

The equipment of the two cylinder groups with different cylinder volumes V _i again serves to optimize the partial shutdown. For this purpose, again a constructive feature of the internal combustion engine or the cylinder, namely the cylinder volume V _{i is} used and in addition to the compulsory different compression ratios ε _i .

The cylinders of the first group have a smaller, preferably a significantly smaller, cylinder volume V ₁ , so that - assuming equal number of cylinders per group - the majority of the total volume of the internal combustion engine is provided by cylinders of the second group.

Embodiments of the self-igniting internal combustion engine are advantageous in which the at least one cylinder of the first group has a cylinder volume V ₁ and the at least one cylinder of the second group has a cylinder volume V ₂ with 1 • V ₁ < V ₂ < 2 • V ₁ .

Embodiments of the self-igniting internal combustion engine in which the at least one cylinder of the first group has a cylinder volume V ₁ and which are advantageous are embodiments at least one cylinder of the second group has a cylinder volume V ₂ with 1.3 • V ₁ < V ₂ < 2 • V ₁ .

Embodiments of the self-igniting internal combustion engine are advantageous in which the at least one cylinder of the first group has a cylinder volume V ₁ and the at least one cylinder of the second group has a cylinder volume V ₂ with 1.3 • V ₁ < V ₂ < 1.75 • V ₁ .

Embodiments of the self-igniting internal combustion engine in which each cylinder is equipped with direct injection for introducing fuel are advantageous.

Embodiments in which each cylinder is equipped with an injection nozzle for the purpose of direct injection are advantageous.

Nonetheless, embodiments of the auto-ignition internal combustion engine may be advantageous in which a port injection is provided for the purpose of fuel supply.

The second sub-task on which the invention is based, namely a method for emission-optimized operation of a self-igniting internal combustion engine of a type described above, is achieved by a method which is characterized in that the at least one switchable cylinder of the at least one group is dependent on the load T. the internal combustion engine is switched.

What has already been said for the internal combustion engine according to the invention also applies to the method according to the invention, which is why reference is generally made at this point to the statements made above with regard to the internal combustion engine. The various internal combustion engines sometimes require different process variants.

• bei Unterschreiten einer vorgebbaren Last T_down abgeschaltet wird, und
• bei Überschreiten einer vorgebbaren Last T_up zugeschaltet wird.

For operating an internal combustion engine in which the at least one cylinder of the second group is designed as a switchable cylinder, variants of the method are advantageous in which the at least one cylinder of the second group

• is switched off below a predetermined load T _down , and
• is switched on when a predetermined load T _up is exceeded.

The prescribed for falling below or exceeding limit loads T _down and T _up can be the same size, but also different sizes. When the internal combustion engine is in operation, the cylinders of the first cylinder group in the present case are permanently in operation. There is only a switching of the second cylinder group, ie a connection or disconnection of this second group.

Advantageous are process variants in which the at least one cylinder of the second group is switched off as soon as the predetermined load T _{down is} undershot and the instantaneous load for a predefinable time interval Δt _{1 is} lower than this predetermined load T _down .

The introduction of an additional condition for the shutdown of the cylinders of the second group, ie the partial shutdown is to prevent too frequent switching on and off, in particular a partial shutdown when the load only temporarily _falls below the predetermined load T _down and then increases or again the predetermined value for the load T _down fluctuates, without the falling below would justify or require a partial shutdown.

For these reasons, method variants are also advantageous in which the at least one cylinder of the second group is switched on as soon as the predetermined load T _{up is} exceeded and the instantaneous load is higher for a predefinable time interval Δt ₂ than this predetermined load T _up .

• auf den mindestens einen Zylinder der zweiten Gruppe bei Überschreiten einer ersten vorgebbaren Last T_up,1 umgeschaltet wird.

For operating an internal combustion engine in which both the at least one cylinder of the first group and the at least one cylinder of the second group is designed as a switchable cylinder, variants of the method are advantageous in which starting from an operation of the at least one cylinder of the first group at low loads

• is switched to the at least one cylinder of the second group when a first predetermined load T _{up, 1} is exceeded.

According to the above embodiment of the method according to the invention, starting from low loads, first of all the at least one cylinder of the first group is fired, ie operated in order to provide the requested power, while the at least one cylinder of the second group is switched off. With increasing load then switching between the at least two cylinder groups, wherein the at least one cylinder of the first group is switched off and the at least one cylinder of the second group is switched on as soon as a load T _{up, 1 is} exceeded.

In this connection, embodiments of the method can be advantageous in which, starting from an operation of the at least one cylinder of the second group with further increasing load, the at least one cylinder of the first group is switched on again when a second predefinable load T _{up, 2 is} exceeded. As a result, the power output of the internal combustion engine can be further increased.

Embodiments of the method in which the predefinable load T _down , T _up , T _{up, 1} and / or T _{up, 2} is dependent on the rotational speed n of the internal combustion engine are advantageous. Then there is not just a concrete load whose falling below or exceeding is switched independent of the speed n. Rather, speed-dependent procedure and an area defined in the map, is switched off in the part.

In principle, further operating parameters of the internal combustion engine can be used as a criterion for a partial shutdown, for example the engine temperature or the coolant temperature after a cold start of the internal combustion engine.

Advantageous embodiments of the method in which the at least one cylinder of the second group is switched on when starting the internal combustion engine. Reference is made to the statements already made in this connection.

Embodiments of the method in which the fuel supply of a deactivated cylinder is deactivated are advantageous. There are advantages in terms of fuel consumption and pollutant emissions, which supports the goal of the partial shutdown, namely to reduce nitrogen oxide emissions.

Fig. 1

schematisch die Zylinder einer ersten Ausführungsform der selbstzündenden Brennkraftmaschine.

In the following, the invention is based on an embodiment of the self-igniting internal combustion engine according to the FIG. 1 explained in more detail. Hereby shows:

Fig. 1

schematically the cylinder of a first embodiment of the self-igniting internal combustion engine.

FIG. 1 schematically shows the four cylinders 1, 2, 3, 4 of a self-igniting four-cylinder in-line engine.

The four cylinders 1, 2, 3, 4 arranged in series form two groups of cylinders each having two cylinders 1, 2, 3, 4, the first group comprising the inner cylinders 2, 3 and the second group comprising the outer cylinders 1, 4. In the snapshot shown, the pistons 1a, 2a of the first and second cylinders 1, 2 are at bottom dead center and the pistons 3a, 4a of the third and fourth cylinders 3, 4 are at top dead center.

The two cylinder groups are distinguished by different compression ratios, wherein the cylinders 2, 3 of the first group have a compression ratio ε ₁ and the cylinders 1, 4 of the second group have a compression ratio ε ₂ with ε ₂ > ε ₁ .

The cylinders 1, 4 of the second group are designed as switchable cylinders 1, 4, which are switched off in partial load operation falls below a predetermined load. As a result, the load requirement increases to the further operating cylinders 2, 3 of the first group. In addition, this reduces the raw emissions of nitrogen oxides as a result of the smaller compression ratio ε _{1 of} the first group in the partial load operation of the internal combustion engine.

reference numeral

1

first cylinder

1a

Piston of the first cylinder

2

second cylinder

2a

Piston of the second cylinder

3

third cylinder

3a

Piston of the third cylinder

4

fourth cylinder

4a

Piston of the fourth cylinder

_i

Compression ratio of a cylinder or a group of cylinders

ε ₁

Compression ratio of a first group of cylinders

ε ₂

Compression ratio of a second group of cylinders

λ

air ratio

η

efficiency

n

Speed of the internal combustion engine

T

load

T _down

predefinable load for falling below a load

T _low

Load in the lower part load range

T _{max, n}

maximum load at a given speed n

T _up

predefinable load for exceeding a load

T _{up, 1}

first definable load for exceeding a load

T _{up, 2}

second predefinable load for exceeding a load

V _i

cylinder volume

V ₁

Cylinder volume of a first group of cylinders

V ₂

Cylinder volume of a second group of cylinders

Claims (16)

A self-igniting internal combustion engine having at least two cylinders (1, 2, 3, 4) in which at least two cylinders (1, 2, 3, 4) are configured such that they have at least two groups each having at least one cylinder (1, 2 , 3, 4), wherein the at least one cylinder (2, 3) of at least one group is designed as a load-dependent switchable cylinder (2, 3), characterized in that - The at least two groups are characterized by different compression ratios ε _i , wherein - The at least one cylinder (1, 4) of a first group has a compression ratio ε ₁ and the at least one cylinder (2, 3) of a second group has a compression ratio ε ₂ with ε ₂ > ε ₁ , and - When partial shutdown in the lower part load range, the at least one cylinder (1, 4) of the first group is the at least one in-service cylinder. A compression-ignition internal combustion engine according to claim 1, characterized in that the at least one cylinder (2, 3) of the second group is designed as a switchable cylinder, which is switched off when falling below a predefinable load T _down and is switched on when a predetermined load T _up is exceeded. An autoignition internal combustion engine according to claim 1, characterized in that both the at least one cylinder (1, 4) of the first group and the at least one cylinder (2, 3) of the second group is designed as a switchable cylinder. A compression-ignition internal combustion engine according to one of the preceding claims, characterized in that the at least two cylinders (1, 2, 3, 4) form two groups each having at least one cylinder (1, 2, 3, 4). A compression-ignition internal combustion engine according to one of the preceding claims, characterized in that the at least one cylinder (1, 4) of the first group has a compression ratio ε ₁ and the at least one cylinder (2, 3) of the second group has a compression ratio ε ₂ with ε ₂ > ε ₁ + 1 . A compression-ignition internal combustion engine according to one of the preceding claims, characterized in that the at least one cylinder (1, 4) of the first group has a compression ratio ε ₁ and the at least one cylinder (2, 3) of the second group has a compression ratio ε ₂ with ε ₂ > ε ₁ + 2 . A self-igniting internal combustion engine according to one of the preceding claims, characterized in that the at least one cylinder (2, 3) of the second group has a compression ratio ε ₂ with 15 < ε ₂ < 20. A compression-ignition internal combustion engine according to one of the preceding claims, characterized in that the at least one cylinder (1, 4) of the first group has a compression ratio ε ₁ with 12 < ε ₁ < 16. A compression-ignition internal combustion engine according to one of the preceding claims, characterized in that - The at least two groups are characterized by different cylinder volumes V _i , wherein - the at least one cylinder (1, 4) of the first group having a cylinder volume V ₁ and the at least one cylinder (2, 3) of the second group a cylinder volume V ₂ having V _{2> V1.} A compression-ignition internal combustion engine according to one of the preceding claims, characterized in that each cylinder (1, 2, 3, 4) is equipped to introduce fuel with a direct injection. Method for operating a spark-ignition internal combustion engine according to one of the preceding claims, characterized in that the at least one switchable cylinder (2, 3) of the at least one group is switched in dependence on the load T of the internal combustion engine. The method of claim 11 for operating an internal combustion engine, wherein the at least one cylinder (2, 3) of the second group is formed as a switchable cylinder, characterized in that - Is switched off when falling below a predetermined load T _down , and - Is switched on when a predetermined load T _up is exceeded. A method according to claim 11 for operating an internal combustion engine, in which both the at least one cylinder (1, 4) of the first group and the at least one cylinder (2, 3) of the second group is designed as a switchable cylinder, characterized in that starting from an operation of the at least one cylinder (1, 4) of the first group at low loads - Is switched to the at least one cylinder (2, 3) of the second group when a first predetermined load T _{up, 1} is exceeded. A method according to claim 13, characterized in that starting from an operation of the at least one cylinder (2, 3) of the second group with further increasing load, the at least one cylinder (1, 4) of the first group when a second predetermined load T _{up is} exceeded _{, 2 is} switched on. Method according to one of claims 11 to 14, characterized in that the predefinable load T _down , T _up , T _{up, 1} and / or T _{up, 2} is dependent on the rotational speed n of the internal combustion engine. Method according to one of claims 11 to 15, characterized in that the at least one cylinder (2, 3) of the second group is switched on when starting the internal combustion engine.

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