DE102017212065B4 - Supercharged internal combustion engine with turbines arranged in parallel and a method for operating such an internal combustion engine - Google Patents

Abstract

Supercharged internal combustion engine (1) with at least two cylinders (2), an intake system (11) for supplying charge air and an exhaust gas removal system (5) for removing exhaust gas, in which each cylinder (2) has at least two outlet openings (4, 4a, 4b ) for discharging the exhaust gases, of which at least one is designed as a switchable outlet opening (4a), each outlet opening (4, 4a, 4b) being connected to an exhaust line (5a, 5b) for discharging the exhaust gases via an exhaust gas discharge system (5), - At least two exhaust gas turbochargers (8, 9) are provided, each of which comprises a compressor (8b, 9b) arranged in the intake system (11) and a turbine (8a, 9a) arranged in the exhaust gas discharge system (5), the turbines (8a, 9a) are arranged in parallel in the exhaust gas discharge system (5), - the exhaust lines (5a) of the connectable outlet openings (4a) of the at least two cylinders (2) to form a first exhaust manifold (6a) merge to form a first overall exhaust line (7a), which with theTurbine (8a) of the first exhaust gas turbocharger (8) is connected, - the exhaust lines (5b) of the other outlet openings (4b) of the at least two cylinders (2) to form a second exhaust manifold (6b) merge to form a second overall exhaust line (7b), which is connected to the turbine (9a) of the second exhaust gas turbocharger (9), and a first exhaust gas recirculation (3) is provided, comprising a first recirculation line (3a), the upstream of the turbine (9a) of the second exhaust gas turbocharger (9) from the exhaust gas discharge system (5) branches off and downstream the compressor (8b, 9b) opens into the intake system (11) forming a first junction (3d), the first return line (3a) with a first EGR valve (3b) for adjusting the amount of recirculated exhaust gas is equipped, characterized in that a second exhaust gas recirculation (15) is provided, comprising a second recirculation line (15a), which from the turbine (8a) of the first exhaust gas turbocharger (8) associated exhaust gas exhaust ührsystem (5) branches off, wherein the second return line (15a) is equipped with a second EGR valve (15b).

Description

• - jeder Zylinder mindestens zwei Auslassöffnungen zum Abführen der Abgase aufweist, von denen mindestens eine als zuschaltbare Auslassöffnung ausgebildet ist, wobei sich an jede Auslassöffnung eine Abgasleitung zum Abführen der Abgase via Abgasabführsystem anschließt,
• - mindestens zwei Abgasturbolader vorgesehen sind, von denen jeder einen im Ansaugsystem angeordneten Verdichter und eine im Abgasabführsystem angeordnete Turbine umfasst, wobei die Turbinen parallel im Abgasabführsystem angeordnet sind,
• - die Abgasleitungen der zuschaltbaren Auslassöffnungen der mindestens zwei Zylinder unter Ausbildung eines ersten Abgaskrümmers zu einer ersten Gesamtabgasleitung zusammenführen, welche mit der Turbine des ersten Abgasturboladers verbunden ist,
• - die Abgasleitungen der anderen Auslassöffnungen der mindestens zwei Zylinder unter Ausbildung eines zweiten Abgaskrümmers zu einer zweiten Gesamtabgasleitung zusammenführen, welche mit der Turbine des zweiten Abgasturboladers verbunden ist, und
• - eine erste Abgasrückführung vorgesehen ist, umfassend eine erste Rückführleitung, die stromaufwärts der Turbine des zweiten Abgasturboladers aus dem Abgasabführsystem abzweigt und stromabwärts der Verdichter unter Ausbildung eines ersten Knotenpunktes in das Ansaugsystem mündet, wobei die erste Rückführleitung mit einem ersten AGR-Ventil zur Einstellung der rückgeführten Abgasmenge ausgestattet ist.

The invention relates to a supercharged internal combustion engine with at least two cylinders, an intake system for supplying charge air and an exhaust gas discharge system for discharging exhaust gas, in which

• - Each cylinder has at least two outlet openings for discharging the exhaust gases, of which at least one is designed as an outlet opening that can be switched on, each outlet opening being followed by an exhaust line for discharging the exhaust gases via an exhaust gas discharge system,
• - At least two exhaust gas turbochargers are provided, each of which comprises a compressor arranged in the intake system and a turbine arranged in the exhaust gas discharge system, the turbines being arranged in parallel in the exhaust gas discharge system,
• - The exhaust lines of the connectable outlet openings of the at least two cylinders combine to form a first exhaust manifold to form a first overall exhaust line, which is connected to the turbine of the first exhaust gas turbocharger,
• - the exhaust lines of the other outlet openings of the at least two cylinders combine to form a second exhaust manifold to form a second overall exhaust line which is connected to the turbine of the second exhaust gas turbocharger, and
• - A first exhaust gas recirculation is provided, comprising a first recirculation line, which branches off from the exhaust gas discharge system upstream of the turbine of the second exhaust gas turbocharger and downstream of the compressor opens into the intake system with the formation of a first node, the first return line having a first EGR valve for setting the recirculated exhaust gas is equipped.

The invention also relates to a supercharged internal combustion engine for carrying out such a method.

An internal combustion engine of the type mentioned is used, for example, as a motor vehicle drive. In the context of the present invention, the term internal combustion engine includes, in particular, gasoline engines, but also diesel engines and hybrid internal combustion engines that use a hybrid internal combustion process, as well as hybrid drives that, in addition to the internal combustion engine, include an electric machine that can be driven with the internal combustion engine and that provides power from the internal combustion engine absorbs or delivers additional power as a switchable auxiliary drive.

The US 2012/0 279215 A1 discloses a supercharged internal combustion engine with four cylinders, an intake system for supplying charge air and an exhaust gas removal system for removing exhaust gas, in which each cylinder has two outlet openings for removing the exhaust gases, each outlet opening being followed by an exhaust line for removing the exhaust gases via an exhaust gas removal system. Two exhaust gas turbochargers are provided, each of which comprises a compressor arranged in the intake system and a turbine arranged in the exhaust gas discharge system, the turbines being arranged in parallel in the exhaust gas discharge system.

The exhaust lines of one outlet opening of the four cylinders each merge with the formation of a first exhaust manifold to form a first overall exhaust line which is connected to an exhaust gas aftertreatment system.

The exhaust lines of the other outlet openings of the four cylinders merge with the formation of two separate exhaust manifolds to form two total exhaust lines, each of the two total exhaust lines being connected to the turbine of an exhaust gas turbocharger.

Independent valve actuation devices can be used for the two groups of outlet openings, i.e. the associated valves can be actuated independently of one another.

The DE 10 2015 211 437 A1 and the DE 10 2010 010 480 A1 also have a supercharged internal combustion engine with two exhaust gas turbochargers as their subject. The prior art also includes JP 2005-54 771 A .

In recent years, there has been a development towards supercharged engines, with the economic importance of these engines for the automotive industry increasing steadily.

Supercharging is primarily a process for increasing performance, in which the air required for the engine combustion process is compressed, so that a larger air mass can be supplied to each cylinder per work cycle. This allows the fuel mass introduced and thus the mean pressure to be increased.

Supercharging is a suitable means of increasing the output of an internal combustion engine with unchanged cubic capacity or reducing the cubic capacity with the same output. In any case, the charging leads to an increase in the installation space performance and a more favorable power mass. If the cubic capacity is reduced, the collective load becomes possible Shift towards higher loads at which the specific fuel consumption is lower.

The supercharging consequently supports the constant effort in the development of internal combustion engines to minimize fuel consumption, i. H. to improve the efficiency of the internal combustion engine.

With a suitable transmission design, so-called downspeeding can also be implemented, which also results in a lower specific fuel consumption. Downspeeding takes advantage of the fact that the specific fuel consumption is regularly lower at low engine speeds, especially at higher loads.

Often an exhaust gas turbocharger is used for charging, in which a compressor and a turbine are arranged on the same shaft. The hot exhaust gas flow is fed to the turbine and relaxes with the release of energy in the turbine, causing the shaft to rotate. The energy released by the exhaust gas flow to the turbine and finally to the shaft is used to drive the compressor, which is also located on the shaft. The compressor conveys and compresses the charge air supplied to it, as a result of which the cylinders are charged. A charge air cooler is advantageously provided downstream of the compressor in the intake system, with which the compressed charge air is cooled before it enters the at least one cylinder. The cooler lowers the temperature and thus increases the density of the charge air, so that the cooler also provides better filling of the cylinders, i.e. H. contributes to a larger air mass.

The advantage of an exhaust gas turbocharger compared to a supercharger that can be driven by an auxiliary drive is that an exhaust gas turbocharger uses the exhaust gas energy of the hot exhaust gases, while a charger draws the energy required for its drive directly or indirectly from the internal combustion engine and thus, at least as long as the drive energy does not originate from energy recovery, adversely affects the efficiency, d. H. diminishes.

If it is not an electric machine, i. H. Electrically drivable charger is a mechanical or kinematic connection for power transmission between the charger and the internal combustion engine, which also influences the packaging in the engine compartment.

The advantage of a supercharger over an exhaust gas turbocharger is that the supercharger can always generate and provide the requested boost pressure, often independently of the operating state of the internal combustion engine. This applies in particular to a charger that can be driven electrically by means of an electric machine and is therefore independent of the speed of the crankshaft.

According to the prior art, it is difficult to increase the performance by means of exhaust gas turbocharging in all speed ranges. A greater drop in torque is observed when the speed falls below a certain level. This torque drop becomes understandable if it is taken into account that the boost pressure ratio depends on the turbine pressure ratio or the turbine power. If the engine speed is reduced, this leads to a smaller exhaust gas mass flow and thus to a smaller turbine pressure ratio or a smaller turbine output. Consequently, the boost pressure ratio also decreases towards lower engine speeds. This is equivalent to a torque drop.

According to the prior art, attempts are made to improve the torque characteristics of a supercharged internal combustion engine by means of various measures.

For example, through a small design of the turbine cross-section and simultaneous exhaust gas blow-off. Such a turbine is also referred to as a waste gate turbine. If the amount of exhaust gas exceeds a critical value, part of the exhaust gas flow is guided past the turbine by means of a bypass line as part of the so-called exhaust gas blow-off. This procedure has the disadvantage that the charging behavior is inadequate at higher speeds or larger amounts of exhaust gas.

The torque characteristic can also be advantageously influenced by means of several exhaust gas turbochargers connected in series. By connecting two exhaust gas turbochargers in series, of which one exhaust gas turbocharger serves as the high pressure stage and one exhaust gas turbocharger serves as the low pressure stage, the compressor map can be expanded in an advantageous manner, both towards smaller compressor flows and towards larger compressor flows.

In particular, in the case of the exhaust gas turbocharger serving as a high-pressure stage, it is possible to shift the surge limit to smaller compressor flows, which means that high boost pressure ratios can be achieved even with small compressor flows, which significantly improves the torque characteristics in the lower speed range. This is achieved by designing the high-pressure turbine for small exhaust gas mass flows and providing a bypass line with which exhaust gas is increasingly led past the high-pressure turbine as the exhaust gas mass flow increases.

The torque characteristics of a supercharged internal combustion engine can furthermore be improved by a plurality of turbochargers arranged in parallel, ie by a plurality of turbines arranged in parallel with a smaller turbine cross-section, with the turbines being switched on successively as the amount of exhaust gas increases.

The internal combustion engine, which is the subject of the present invention, has at least two exhaust gas turbochargers for the purpose of charging, the turbines of which are arranged in parallel in the exhaust gas discharge system. At least one turbine is designed as a switchable turbine, which is only acted upon with exhaust gas in the case of larger amounts of exhaust gas, i. H. is activated.

Each cylinder of the internal combustion engine according to the invention is equipped with at least two outlet openings, of which at least one is designed as a switchable outlet opening. The exhaust lines of the at least two cylinders are then brought together in groups in such a way that the exhaust lines of the connectable outlet openings and the exhaust lines of the other outlet openings are each combined to form an overall exhaust line with the formation of an exhaust manifold.

The exhaust lines of the connectable outlet openings lead to the turbine of the first exhaust gas turbocharger and the exhaust lines of the other outlet openings lead to the turbine of the second exhaust gas turbocharger. The first turbine assigned to the connectable outlet openings is thus designed as a connectable turbine. Only in the case of larger amounts of exhaust gas are the switchable outlet openings opened as usual during the gas exchange, thereby activating the switchable turbine, i.e. H. charged with exhaust gas.

Compared to concepts in which a single coherent exhaust pipe system is provided upstream of the two turbines, the above-described grouping improves, i. H. the use of two separate exhaust systems, the operating behavior of the internal combustion engine noticeable, especially with small amounts of exhaust gas; also because the line volume upstream of the second turbine, through which exhaust gas flows continuously, is reduced by this measure, which at low loads or speeds, ie. H. low amounts of exhaust gas, is advantageous and in particular improves the response. The thermal inertia of the exhaust gas discharge system of the second turbine through which exhaust gas flows continuously is also reduced, which results in advantages in exhaust gas aftertreatment, in particular with regard to the light-off time after a cold start.

But there are also disadvantages. The speed of the switchable turbine drops sharply when it is deactivated, so that when it is switched on again, the rotating parts of this turbine must first be accelerated in order to be able to generate and provide the desired boost pressure on the compressor side. The responsiveness thus deteriorates.

A fundamental disadvantage when using an exhaust gas turbocharger is the exhaust gas aftertreatment by means of exhaust gas aftertreatment systems arranged in the exhaust gas discharge system. In the present case, downstream of the outlet openings, the exhaust gases are first fed to the turbines of at least two exhaust gas turbochargers and only then, if appropriate, to one or more systems for exhaust gas aftertreatment.

The background to this arrangement is that efforts are generally made to arrange the turbine of an exhaust gas turbocharger as close as possible to the cylinder outlet openings in order to make optimal use of the exhaust gas enthalpy of the hot exhaust gases, which is largely determined by the exhaust gas pressure and temperature and, on the other hand, to ensure fast response of the turbine and thus of the turbocharger. In this context, the aim is to minimize the thermal inertia and the volume of the line system between the outlet openings of the cylinder and the turbine, which can be achieved by reducing the mass and length of the exhaust lines.

As a result, arranging an exhaust gas aftertreatment system close to the engine in exhaust gas turbocharged internal combustion engines proves difficult in practice, especially in concepts in which several turbines are to be arranged in parallel in the exhaust gas discharge system.

Further or additional measures are therefore required in order to be able to comply with future limit values for pollutant emissions. The focus of the development work is on reducing nitrogen oxide emissions, which are particularly relevant for diesel engines. Since the formation of nitrogen oxides not only requires excess air but also high temperatures, one concept for reducing nitrogen oxide emissions is to develop combustion processes with low combustion temperatures.

Exhaust gas recirculation (EGR), ie the recirculation of combustion gases from the outlet side to the inlet side, is expedient, in which the nitrogen oxide emissions can be significantly reduced as the exhaust gas recirculation rate increases. The exhaust gas recirculation rate x _{EGR is} determined as x _EGR = m _EGR / (m _EGR + m _air ), where m _EGR denotes the mass of recirculated exhaust gas and m air denotes the _air supplied. The oxygen provided via exhaust gas recirculation may have to be taken into account.

In order to achieve a significant reduction in nitrogen oxide emissions, high exhaust gas recirculation rates are required, which can be in the order of magnitude of x _EGR ≈ 60% to 70% and more. Such high recirculation rates regularly require cooling of the exhaust gas to be recirculated.

The internal combustion engine according to the invention is also equipped with exhaust gas recirculation. The recirculation line of this exhaust gas recirculation branches off from the exhaust gas discharge system upstream of the turbine of the second exhaust gas turbocharger and opens into the intake system downstream of the compressor, forming a first junction. This routing ensures that exhaust gas can also be recirculated when the turbine of the first exhaust gas turbocharger, i.e. H. the first turbine, shut down, d. H. is deactivated.

In the present case, it is a high-pressure EGR in which exhaust gas is returned to the inlet side, which is taken from the exhaust gas discharge system upstream of a turbine and is therefore no longer available to drive the turbine. A cooler and an EGR valve for adjusting the amount of recirculated exhaust gas are regularly provided in the return line.

The advantage of high-pressure EGR compared to low-pressure EGR, in which exhaust gas is recirculated, which has already flowed through the turbine in the exhaust gas removal system, is that the driving pressure gradient between the exhaust gas removal system and the intake system, which is absolutely necessary for the recirculation of the exhaust gas , can be implemented in a simple manner or is readily available. This essentially results from the fact that the exhaust gas pressure upstream of the turbine is significantly higher than downstream of the turbine.

In addition, the exhaust gas returned to the inlet side by means of low-pressure EGR, which is to be passed through at least one compressor, has to be regularly subjected to exhaust gas aftertreatment downstream of the turbine, in particular in a particle filter, since deposits in the compressor change the geometry of the compressor, in particular the flow cross-sections and in this way would degrade the efficiency of the compressor.

The exhaust gas recirculation described above proves to be problematic if the first turbine is switched on and the exhaust gas coming from the cylinders is distributed to both turbines. Half of the exhaust gas is then led past the second continuously operated turbine and is no longer available a priori for exhaust gas recirculation.

It is therefore not always possible to achieve high return rates, which are necessary for a significant reduction in nitrogen oxide emissions. However, it must be taken into account that concepts are required with which high feedback rates can be implemented in all map points, in particular also at high loads and / or high speeds, in order to be able to comply with future limit values for pollutant emissions.

Consequently, measures are required with which high feedback rates can be achieved in all map points.

Against the background of what has been said, it is an object of the present invention to provide a supercharged internal combustion engine according to the preamble of claim 1, with which high return rates can be achieved in all map points, in particular also at high loads and / or high speeds.

Another sub-object of the present invention is to provide a method for operating such an internal combustion engine.

• - jeder Zylinder mindestens zwei Auslassöffnungen zum Abführen der Abgase aufweist, von denen mindestens eine als zuschaltbare Auslassöffnung ausgebildet ist, wobei sich an jede Auslassöffnung eine Abgasleitung zum Abführen der Abgase via Abgasabführsystem anschließt,
• - mindestens zwei Abgasturbolader vorgesehen sind, von denen jeder einen im Ansaugsystem angeordneten Verdichter und eine im Abgasabführsystem angeordnete Turbine umfasst, wobei die Turbinen parallel im Abgasabführsystem angeordnet sind,
• - die Abgasleitungen der zuschaltbaren Auslassöffnungen der mindestens zwei Zylinder unter Ausbildung eines ersten Abgaskrümmers zu einer ersten Gesamtabgasleitung zusammenführen, welche mit der Turbine des ersten Abgasturboladers verbunden ist,
• - die Abgasleitungen der anderen Auslassöffnungen der mindestens zwei Zylinder unter Ausbildung eines zweiten Abgaskrümmers zu einer zweiten Gesamtabgasleitung zusammenführen, welche mit der Turbine des zweiten Abgasturboladers verbunden ist, und
• - eine erste Abgasrückführung vorgesehen ist, umfassend eine erste Rückführleitung, die stromaufwärts der Turbine des zweiten Abgasturboladers aus dem Abgasabführsystem abzweigt und stromabwärts der Verdichter unter Ausbildung eines ersten Knotenpunktes in das Ansaugsystem mündet, wobei die erste Rückführleitung mit einem ersten AGR-Ventil zur Einstellung der rückgeführten Abgasmenge ausgestattet ist,

und die dadurch gekennzeichnet ist, dass

• - eine zweite Abgasrückführung vorgesehen ist, umfassend eine zweite Rückführleitung, die aus dem der Turbine des ersten Abgasturboladers zugehörigen Abgasabführsystem abzweigt, wobei die zweite Rückführleitung mit einem zweiten AGR-Ventil ausgestattet ist.

The first sub-task is achieved by a supercharged internal combustion engine with at least two cylinders, an intake system for supplying charge air and an exhaust gas discharge system for discharging exhaust gas

• - Each cylinder has at least two outlet openings for discharging the exhaust gases, of which at least one is designed as an outlet opening that can be switched on, each outlet opening being followed by an exhaust line for discharging the exhaust gases via an exhaust gas discharge system,
• - At least two exhaust gas turbochargers are provided, each of which comprises a compressor arranged in the intake system and a turbine arranged in the exhaust gas discharge system, the turbines being arranged in parallel in the exhaust gas discharge system,
• - The exhaust lines of the connectable outlet openings of the at least two cylinders combine to form a first exhaust manifold to form a first overall exhaust line, which is connected to the turbine of the first exhaust gas turbocharger,
• - The exhaust lines of the other outlet openings of the at least two cylinders with the formation of a second exhaust manifold to one merge the second overall exhaust gas line which is connected to the turbine of the second exhaust gas turbocharger, and
• - A first exhaust gas recirculation is provided, comprising a first recirculation line, which branches off from the exhaust gas discharge system upstream of the turbine of the second exhaust gas turbocharger and downstream of the compressor opens into the intake system with the formation of a first node, the first return line having a first EGR valve for setting the recirculated exhaust gas is equipped,

and which is characterized in that

• - A second exhaust gas recirculation is provided, comprising a second recirculation line which branches off from the exhaust gas removal system belonging to the turbine of the first exhaust gas turbocharger, the second recirculation line being equipped with a second EGR valve.

The internal combustion engine according to the invention is equipped with a further, namely a second exhaust gas recirculation system. The return line of this exhaust gas recirculation branches off from the exhaust gas removal system upstream or downstream of the turbine of the first exhaust gas turbocharger, i.e. H. from the exhaust gas removal system, which is assigned to the first switchable turbine.

Using this second exhaust gas recirculation, exhaust gas originating from the cylinders, which is discharged into the exhaust gas removal system via the connectable outlet openings when the first turbine is connected, can be recirculated. In this respect, according to the invention, the entire exhaust gas of the internal combustion engine is available for exhaust gas recirculation if, in addition to the second continuously operated turbine, the first turbine is also operated; H. is switched on.

The high return rates required for a significant reduction in nitrogen oxide emissions can thus be achieved according to the invention at any time, i. H. in all map points of the internal combustion engine under all operating conditions. In particular, the inventive concept ensures that even at high loads and / or high speeds, when the first turbine is operated in addition to the second continuously operated turbine and the exhaust gas is distributed to the turbines arranged in parallel, high recirculation rates can be achieved, so that future limit values for pollutant emissions can also be met.

To activate the first turbine, the switchable outlet openings, i.e. H. the switchable lift valves belonging to the switchable outlet openings are switched on; all at the same time or successively little by little, in one step or in a multi-stage stroke. I.e. not all switchable lift valves have to be fully switched on and operated at the same time. The connection can take place very differently, i. H. have very different characteristics.

The recirculation line of the second exhaust gas recirculation can basically open downstream of the compressor into the intake system, but also upstream of the compressor of the first exhaust gas turbocharger or into the recirculation line of the first exhaust gas recirculation, as explained in connection with the preferred embodiments.

In this respect, the second exhaust gas recirculation can be both a high pressure EGR and a low pressure EGR.

With the internal combustion engine according to the invention, the first sub-task on which the invention is based is achieved, namely an internal combustion engine according to the preamble of claim 1 with which high feedback rates can be achieved in all map points, especially at high loads and / or high speeds.

An internal combustion engine according to the invention can also have three or more exhaust gas turbochargers. The concept according to the invention can be applied without problems to three-cylinder in-line engines.

Embodiments are therefore also advantageous in which the supercharged internal combustion engine has three cylinders or a cylinder head with three cylinders.

Further advantageous embodiments of the internal combustion engine according to the invention are discussed in connection with the subclaims.

Embodiments of the supercharged internal combustion engine are advantageous in which the second return line branches off from the associated exhaust gas discharge system upstream of the turbine of the first exhaust gas turbocharger.

According to this embodiment, the second exhaust gas recirculation is designed or executed as a high-pressure EGR, in which exhaust gas is returned to the inlet side, which is taken from the exhaust gas removal system upstream of the first connected turbine and thus no longer flows through the first turbine. The advantage of a high pressure EGR compared to a low pressure EGR is that the driving pressure gradient between the Exhaust gas discharge system and the intake system is present a priori.

Embodiments of the supercharged internal combustion engine are advantageous in which the second return line branches off from the first overall exhaust line upstream of the turbine of the first exhaust gas turbocharger. A branch from the first overall exhaust line has the advantage over a branch from the exhaust manifold or an individual exhaust line of a cylinder that all of the exhaust gas discharged into the exhaust gas discharge system via the connected outlet openings can be returned to the inlet side via the second return line without a return flow of exhaust gas in the exhaust gas removal system would be required.

In this context, embodiments of the supercharged internal combustion engine in which the second return line opens into the first return line are advantageous. This embodiment has several advantages and can serve as a basis or starting point for additional advantageous developments.

On the one hand, an additional cooler in the second return line can be dispensed with if a cooler is provided in the first return line and the second return line opens into the first return line upstream of this cooler. This leads to cost savings and weight reduction. The space requirement of the drive unit in the engine compartment is reduced and tight packaging is supported. On the other hand, the second EGR valve can be designed to be switchable in two stages if the second return line opens into the first return line upstream of the first EGR valve. Then only the first EGR valve is used to adjust the amount of recirculated exhaust gas. This also leads to cost savings and weight reduction. In addition, the control of the exhaust gas recirculation is simplified. The overall length of the return lines is reduced.

For the reasons mentioned above, embodiments of the supercharged internal combustion engine are advantageous in which the second return line opens into the first return line upstream of the first EGR valve.

For the above reasons, embodiments in which the second EGR valve can be switched in two stages are also advantageous in this context.

Embodiments of the supercharged internal combustion engine are advantageous in which the first return line is equipped with a first cooler. The cooler lowers the temperature of the exhaust gas to be recirculated and thus increases the density. There is a compression by cooling, whereby high or very high return rates can be achieved.

Embodiments of the supercharged internal combustion engine are advantageous in which the first cooler is arranged downstream of the first EGR valve. However, embodiments in which the first cooler is arranged upstream of the first EGR valve can also be advantageous.

Embodiments of the supercharged internal combustion engine can also be advantageous in which the second return line branches off from the first overall exhaust line downstream of the turbine of the first exhaust gas turbocharger and opens into the intake system upstream of the compressor of the first exhaust gas turbocharger, forming a second junction.

According to this embodiment, the second exhaust gas recirculation is designed or implemented as a low-pressure EGR, in which exhaust gas is returned to the inlet side, which is already flowing through the first connected turbine. The second return line opens into the intake system upstream of the compressor of the first exhaust gas turbocharger.

The advantage of low-pressure EGR over high-pressure EGR is that all of the exhaust gas discharged into the exhaust gas discharge system via the connected outlet openings is available at the first turbine in order to drive the associated first compressor and to be able to generate a requested boost pressure.

If the second exhaust gas recirculation is designed as a low-pressure EGR, embodiments of the supercharged internal combustion engine in which the second recirculation line is equipped with a second cooler are advantageous.

Since the cooler of the first exhaust gas recirculation cannot be used if the second exhaust gas recirculation is designed as a low-pressure EGR, the provision of an additional second cooler is advantageous in order to lower the temperature of the exhaust gas recirculated by means of the second exhaust gas recirculation and to be able to achieve high recirculation rates.

In this context, embodiments of the supercharged internal combustion engine are advantageous in which the second cooler is arranged upstream of the second EGR valve.

Then, when the second exhaust gas recirculation is deactivated, no fresh air from the intake system can get into the second cooler, which is present - with the first turbine switched on - is permanently exposed to hot exhaust gas. The closed second EGR valve serves as a barrier against the ingress of fresh air, the second cooler being permanently connected to the exhaust gas removal system of the first turbine by arranging the second EGR valve downstream of the second cooler. Permanent exposure of the second cooler and the second recirculation line upstream of the second EGR valve with hot exhaust gas heats this part of the second exhaust gas recirculation, which counteracts the formation of condensate through wall contact. The evaporation of previously formed condensate is even promoted.

For this reason, embodiments are also particularly advantageous in the present context in which the second EGR valve is arranged at the second node. The entire second return line can then be blocked up to the intake system or protected against the ingress of cool fresh air.

If the second exhaust gas recirculation is designed as a low-pressure EGR, embodiments of the supercharged internal combustion engine are advantageous in which the second EGR valve is continuously adjustable for setting the recirculated exhaust gas quantity.

• - jeder Verdichter in einer separaten Ansaugleitung des Ansaugsystems angeordnet ist, und
• - die separaten Ansaugleitungen stromabwärts der Verdichter zu einer Gesamtansaugleitung zusammenführen, wobei stromabwärts des Verdichters des ersten Abgasturboladers ein erstes Absperrelement in der zugehörigen Ansaugleitung angeordnet ist.

Embodiments of the supercharged internal combustion engine are advantageous in which the compressors of the at least two exhaust gas turbochargers are arranged in parallel in the intake system, with

• - Each compressor is arranged in a separate suction line of the suction system, and
• - Merge the separate intake lines downstream of the compressors to form a total intake line, with a first shut-off element being arranged in the associated intake line downstream of the compressor of the first exhaust gas turbocharger.

In the present case, the compressors are arranged in parallel and the first compressor can be separated from the rest of the intake system when the first turbine is switched off, so that the second compressor does not feed into the first compressor. For this purpose, a first shut-off element, which is used to deactivate this compressor, is arranged in the associated suction line downstream of the first compressor.

The first compressor is not driven when the first turbine is switched off. So that the first compressor does not deliver against the resistance of the closed first shut-off element, a blow-off line is advantageous, via which the charge air can escape or be discharged.

In this context, embodiments of the supercharged internal combustion engine are also advantageous in which a blow-off line is provided, which branches off from the associated suction line between the first compressor and the first shut-off element and opens into the other suction line upstream of the second compressor, with a further suction line in the blow-off line Shut-off element is arranged.

The fact that the blow-off line opens into the intake system upstream of the second compressor has advantages, since there is usually negative pressure upstream of the second compressor, which creates a pressure gradient that supports the delivery of the charge air compressed by the first compressor.

Embodiments of the supercharged internal combustion engine can also be advantageous in which the compressors of the at least two exhaust gas turbochargers are arranged in series in an overall intake line of the intake system, the compressor of the second exhaust gas turbocharger being arranged downstream of the compressor of the first exhaust gas turbocharger in the overall intake line.

In this context, embodiments of the supercharged internal combustion engine are advantageous in which the compressor of the first exhaust gas turbocharger is equipped with a bypass line that branches off from the overall intake line upstream of the compressor of the first exhaust gas turbocharger and into the overall intake line between the compressor of the second exhaust gas turbocharger and the compressor of the first exhaust gas turbocharger opens, a shut-off element being arranged in the bypass line.

The bypass line is used to bypass the first compressor when the first turbine is switched off and the first compressor is not driven and only represents a flow resistance for the sucked in air. In principle, however, the bypass line can also be used as a blow-off line.

Embodiments of the supercharged internal combustion engine are advantageous in which a charge air cooler is arranged in the intake system downstream of the compressor of the at least two exhaust gas turbochargers.

Embodiments of the supercharged internal combustion engine are advantageous in which a throttle element is arranged in the intake system between the compressor of the second exhaust gas turbocharger and the first node. The throttle element can serve as a throttle valve for load control, but also to generate a driving pressure gradient across the first return line.

Embodiments of the supercharged internal combustion engine are advantageous in which the turbine of at least one exhaust gas turbocharger has a variable turbine geometry that allows extensive adaptation to the respective operating point by adjusting the turbine geometry or the effective turbine cross-section. In this case, guide vanes are arranged upstream of the impeller of the turbine to influence the direction of flow. In contrast to the rotating blades of the rotating impeller, the guide blades do not rotate with the shaft of the turbine, i. H. the impeller. The guide vanes are arranged in a stationary manner, but not completely immobile, but rotatable about their axis, so that the flow to the rotor blades can be influenced. If, on the other hand, a turbine has a fixed, unchangeable geometry, the guide vanes are not only stationary, but also completely immobile, i.e. H. rigidly fixed, if a guide device is provided at all.

Embodiments of the supercharged internal combustion engine in which the turbine of at least one exhaust gas turbocharger is designed as a waste gate turbine can be advantageous.

Embodiments of the supercharged internal combustion engine are advantageous in which each switchable outlet opening is equipped with a switchable lift valve, with a deactivated lift valve switching off the associated outlet opening and keeping it closed and an activated lifting valve moving between an open position and a closed position with the formation of a valve lift Δh _max and thereby releases the associated outlet opening during an opening period Δt _max .

When activating the first turbine, the number of connected outlet openings can be increased successively. In this way, the amount of exhaust gas discharged from the cylinders via the connected outlet openings, i. H. the exhaust gas volume flow, likewise successively when the first turbine is switched on, d. H. gradually, increased and not suddenly in full. As a result, the exhaust gas flow passed through the second turbine does not decrease abruptly when the first turbine is switched on, and a torque drop due to a loss of boost pressure is reduced or avoided.

The switchable outlet openings can also be equipped with lift valves that are not only switchable, i. H. can not only be switched on and off, but are adjustable in such a way that a stepless or multi-stage adjustment is possible with regard to the valve lift Δh and / or the opening duration Δt.

A lift valve that can be adjusted in valve lift Δh, for example, enables at least one additional activated operating mode with reduced stroke or several additional activated operating modes with different strokes in addition to the switched-off state without a lift and the activated mode with normal lift Δh _max . The maximum lift of the valve when running through the valve lift curve of the respective mode is regarded and referred to as the lift.

Embodiments of the supercharged internal combustion engine can also be advantageous in which each switchable outlet opening is equipped with a switchable lift valve, with a disconnected lift valve not completely deactivating and not completely closing the associated outlet opening, so that the first turbine that is switched off is always subjected to a small amount of exhaust gas.

Embodiments of the supercharged internal combustion engine are advantageous in which the exhaust lines of the at least two cylinders merge within the at least one cylinder head to form the overall exhaust lines.

The integration of the exhaust manifold into the cylinder head reduces the mass and length of the exhaust gas removal systems from the exhaust ports to the turbines. This allows the exhaust gas enthalpy of the hot exhaust gases to be optimally used and ensures that the turbochargers respond quickly. In addition, exhaust gas aftertreatment systems arranged near the outlet reach their operating temperature or light-off temperature more quickly, in particular after a cold start of the internal combustion engine. The integration of the exhaust manifold in the cylinder head also allows the drive unit to be packaged as tightly as possible and also has the advantage that it is possible to participate in any liquid cooling provided in the cylinder head in such a way that the manifolds are not made of thermally highly stressable and therefore cost-intensive materials must be manufactured.

The integration of the exhaust manifold into the cylinder head also leads to a lower number of components and consequently to a reduction in costs, in particular the assembly and preparation costs.

Embodiments of the supercharged internal combustion engine are advantageous in which the overall exhaust gas lines merge into a common exhaust gas line downstream of the turbines. Exhaust gas aftertreatment of the entire exhaust gas of the at least two cylinders can then take place, namely with one arranged in the common exhaust line Exhaust aftertreatment system. This can be, for example, a particle filter, an oxidation catalytic converter and / or an exhaust gas aftertreatment system for reducing nitrogen oxides.

The second sub-task on which the invention is based, namely to show a method for operating a supercharged internal combustion engine of the type described above, is achieved by a method in which the switchable outlet openings are switched on if a predefinable load M. and / or a predefinable speed n _{mot of} the internal combustion engine is exceeded.

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 supercharged internal combustion engines sometimes require different process variants.

Embodiments of the method are advantageous in which the second exhaust gas recirculation is activated when the connectable outlet openings are switched on in order to return a requested amount of exhaust gas, for which purpose the second EGR valve is opened.

• 1a schematisch eine erste Ausführungsform der aufgeladenen Brennkraftmaschine,
• 1b schematisch eine zweite Ausführungsform der aufgeladenen Brennkraftmaschine,
• 2a schematisch eine dritte Ausführungsform der aufgeladenen Brennkraftmaschine,
• 2b schematisch eine vierte Ausführungsform der aufgeladenen Brennkraftmaschine, und
• 3 das Motorenkennfeld einer aufgeladenen Brennkraftmaschine.

In the following, the invention is based on four exemplary embodiments and according to FIGS 1a , 1b , 2a , 2 B and 3 described in more detail. Here shows:

• 1a schematically a first embodiment of the supercharged internal combustion engine,
• 1b schematically a second embodiment of the supercharged internal combustion engine,
• 2a schematically a third embodiment of the supercharged internal combustion engine,
• 2 B schematically a fourth embodiment of the supercharged internal combustion engine, and
• 3 the engine map of a supercharged internal combustion engine.

1a shows schematically a first embodiment of the supercharged internal combustion engine 1 that have two exhaust gas turbochargers 8th , 9 Is provided. Every exhaust gas turbocharger 8th , 9 includes a turbine 8a , 9a and a compressor 8b , 9b . The hot exhaust gas relaxes in the turbines 8a , 9a taking energy out, causing the compressor 8b , 9b are driven. The compressors 8b , 9b compress the charge air via the intake system 11 , Intercooler 10 and plenary 12a the cylinders 2 is supplied, whereby a supercharging of the internal combustion engine 1 is realized. Both turbines 8a , 9a are equipped with a variable turbine geometry; each indicated by an arrow.

It is a four-cylinder in-line engine 1 in which the four cylinders 2 along the longitudinal axis of the cylinder head, ie arranged in series. Every cylinder 2 has two outlet openings 4th , 4a , 4b , to which exhaust pipes 5a , 5b to discharge the exhaust gases via the exhaust gas removal system 5 connect. One outlet each 4th , 4a each cylinder 2 is as a switchable outlet opening 4a formed, which is only opened as part of the gas exchange when the amount of exhaust gas exceeds a predetermined amount of exhaust gas and the downstream first turbine 8a activated, that is to be charged with exhaust gas.

Every switchable outlet opening 4a is equipped with a switchable lift valve for this purpose, with a disconnected lift valve opening the associated outlet 4a switched off and locked. A connected lift valve moves between an open position and a closed position with the formation of a valve lift Δh _max and thereby gives the associated outlet opening 4a free during an opening period Δt _max . Based on switched off outlet openings 4a becomes the first turbine 8a when a predeterminable amount of exhaust gas is exceeded, activated by switching to the switchable outlet openings 4a belonging switchable lift valves are switched on.

The exhaust pipes 5a the switchable outlet openings 4a all cylinders 2 lead with the formation of a first exhaust manifold 6a to a first overall exhaust line 7a together which one with the turbine 8a of the first exhaust gas turbocharger 8th connected to it as a switchable turbine 8a is executed and functions. The exhaust pipes 5b the other outlet openings 4b all cylinders 2 lead with the formation of a second exhaust manifold 6b to a second overall exhaust line 7b together which one with the turbine 9a of the second exhaust gas turbocharger 9 connected is. As a result, the two turbines are 8a , 9a present in parallel in the exhaust gas discharge system 5 arranged.

The internal combustion engine 1 has a suction system 11 for supplying charge air to the cylinders 2 , the compressor 8b , 9b the turbocharger 8th , 9 in the intake system 11 are arranged; also in parallel. The first compressor 8b is in a first suction line 11a arranged and the second compressor 9b in a second suction line 11b . The suction lines 11a , 11b lead downstream of the compressor 8b , 9b to a total suction line 12 together.

Downstream of the first compressor 8b is a first shut-off element 13a in the associated suction line 11a arranged so that the first compressor 8b with the first turbine switched off 8a from the rest of the intake system 11 can be disconnected, ie deactivated, and the second compressor 9b not in the first compressor 8b promotes into it.

The first compressor 8b becomes when the first turbine is switched off 8a not powered. So the first compressor 8b Under no circumstances against the resistance of the closed first shut-off element 13a must convey is a blow-off line 14th provided through which the charge air into the second intake line 11b upstream of the second compressor 9b can be promoted. In the blow-off line 14th is another shut-off element 14a arranged.

In the 1a internal combustion engine shown 1 is with an exhaust gas recirculation 3 , 15th equipped with which exhaust gas can be returned from the outlet side to the inlet side.

A first exhaust gas recirculation 3 includes a first return line 3a upstream of the turbine 9a of the second exhaust gas turbocharger 9 from the exhaust system 5 branches off and downstream the compressor 8b , 9b with the formation of a first node 3d into the intake system 11 flows out. This first return line 3a is with a first EGR valve 3b equipped to adjust the amount of recirculated exhaust gas and a first cooler 3c , the downstream of the first EGR valve 3b is arranged.

A second exhaust gas recirculation 15th includes a second return line 15a upstream of the turbine 8a of the first exhaust gas turbocharger 8th from the first overall exhaust line 7a branches off and into the first return line 3a flows out. The second return line opens 15a upstream of the first EGR valve 3b into the first return line 3a so that the second EGR valve 15b can be switched in two stages.

Upstream of the first junction 3d is a throttle element 17th in the intake system 11 provided with which the driving pressure drop of the exhaust gas recirculation 3 , 15th between the exhaust system 5 and the intake system 11 set, in particular can be enlarged.

1b shows schematically a second embodiment of the supercharged internal combustion engine 1 . Only the differences to the one in 1a illustrated embodiment are discussed, which is why reference is otherwise made to 1a . The same reference numerals have been used for the same components.

The two turbines are also here 8a , 9a in parallel in the exhaust gas removal system 5 arranged. The two compressors are, however 8b , 9b arranged in series in a total suction line 12 of the intake system 11 . The compressor 9b of the second exhaust gas turbocharger 9 is downstream of the compressor 8b of the first exhaust gas turbocharger 8th arranged, the compressor 8b of the first exhaust gas turbocharger 8th with a bypass line 16 upstream of this first compressor 8b from the entire intake line 12 branches off and between the second compressor 9b and the compressor 8b into the overall suction line 12 flows out. In the bypass line 16 is a shut-off element 16a arranged. The bypass line 16 serves to bypass the first compressor 8b if the first turbine 9b is switched off and does not drive the first compressor.

2a shows schematically a third embodiment of the supercharged internal combustion engine 1 . Only the differences to the one in 1a illustrated embodiment are discussed, which is why reference is otherwise made to 1a . The same reference numerals have been used for the same components.

In contrast to the first embodiment according to FIG 1a branches off the second return line 15a downstream of the turbine 8a of the first exhaust gas turbocharger 8th from the first overall exhaust line 7a from. This second return line 15a opens upstream of the compressor 8b of the first exhaust gas turbocharger 8th with the formation of a second node 15d into the intake system 11 . The second EGR valve 15b is steplessly adjustable to adjust the amount of recirculated exhaust gas and at the second junction 15d arranged, with a second cooler 15c upstream of the second EGR valve 15b in the second return line 15a is arranged. The present is the second exhaust gas recirculation 15th a low pressure EGR 15th and no high pressure EGR.

2 B shows schematically a fourth embodiment of the supercharged internal combustion engine 1 . Only the differences to the one in 1b illustrated embodiment are discussed, which is why reference is otherwise made to 1b . The same reference numerals have been used for the same components.

In contrast to the second embodiment according to 1b branches off the second return line 15a downstream of the turbine 8a of the first exhaust gas turbocharger 8th from the first overall exhaust line 7a from. This second return line 15a opens upstream of the compressor 8b of the first exhaust gas turbocharger 8th with the formation of a second node 15d into the intake system 11 . The second EGR valve 15b is steplessly adjustable to adjust the amount of recirculated exhaust gas and at the second junction 15d arranged, with a second cooler 15c upstream of the second EGR valve 15b in the second return line 15a is arranged. The present is the second exhaust gas recirculation 15th a low pressure EGR 15th and no high pressure EGR.

3 shows the engine map of a supercharged internal combustion engine. The load is shown M. over the speed n _{mot of} the internal combustion engine.

The map area in which only the second exhaust gas turbocharger is operated or only the second turbine is acted upon with exhaust gas is identified by A. The first switchable turbine is deactivated and is only activated if the amount of exhaust gas exceeds a predetermined amount of exhaust gas or a predetermined load M. and / or a predefinable speed nmot the internal combustion engine is exceeded.

In order to activate the first turbine, the switchable outlet openings are switched on. The map area in which both exhaust gas turbochargers are operated or both turbines are subjected to exhaust gas is marked with B. In map area B, the second exhaust gas recirculation can then also be used to recirculate a requested amount of exhaust gas, for which purpose the second EGR valve of this exhaust gas recirculation must be opened.

List of reference symbols

1

supercharged internal combustion engine, four-cylinder in-line engine

2

cylinder

3

first exhaust gas recirculation, high pressure EGR

3a

first return line

3b

first EGR valve

3c

first cooler

3d

first junction

4th

Outlet opening

4a

switchable outlet opening

4b

other outlet opening

5

Exhaust gas removal system

5a

Exhaust pipe of a switchable outlet opening

5b

Exhaust pipe

6a

first exhaust manifold

6b

second exhaust manifold

7a

first overall exhaust line

7b

second overall exhaust line

8th

first exhaust gas turbocharger

8a

first turbine, switchable turbine

8b

first compressor

9

second exhaust gas turbocharger

9a

second turbine

9b

second compressor

10

Intercooler

11

Suction system

11a

first separate suction line

11b

second separate suction line

12

Total suction line

12a

plenum

13a

first shut-off element

14th

Blow-off line

14a

another shut-off element

15th

second exhaust gas recirculation

15a

second return line

15b

second EGR valve

15c

second cooler

15d

second junction

16

Bypass line

16a

Shut-off element

17th

Throttle element

M.

Internal combustion engine load

nmot

Speed of the internal combustion engine

Claims (23)

Supercharged internal combustion engine (1) with at least two cylinders (2), an intake system (11) for supplying charge air and an exhaust gas discharge system (5) for discharging exhaust gas, in which - each cylinder (2) has at least two outlet openings (4, 4a, 4b ) for discharging the exhaust gases, of which at least one is designed as a switchable outlet opening (4a), each outlet opening (4, 4a, 4b) being connected to an exhaust pipe (5a, 5b) for discharging the exhaust gases via an exhaust gas discharge system (5), - At least two exhaust gas turbochargers (8, 9) are provided, each of which comprises a compressor (8b, 9b) arranged in the intake system (11) and a turbine (8a, 9a) arranged in the exhaust gas discharge system (5), the turbines (8a, 9a) are arranged in parallel in the exhaust gas discharge system (5), - the exhaust lines (5a) of the connectable outlet openings (4a) of the at least two cylinders (2) forming a first exhaust manifold (6a) a first overall exhaust line (7a) which is connected to the turbine (8a) of the first exhaust gas turbocharger (8), - the exhaust lines (5b) of the other outlet openings (4b) of the at least two cylinders (2) forming a second exhaust manifold (6b) ) merge into a second overall exhaust gas line (7b) which is connected to the turbine (9a) of the second exhaust gas turbocharger (9), and - a first exhaust gas recirculation (3) is provided, comprising a first recirculation line (3a), which is upstream of the turbine ( 9a) of the second exhaust gas turbocharger (9) branches off from the exhaust gas discharge system (5) and downstream the compressor (8b, 9b) opens into the intake system (11) forming a first junction (3d), the first return line (3a) having a first EGR valve (3b) is equipped for adjusting the amount of recirculated exhaust gas, characterized in that - a second exhaust gas recirculation (15) is provided, comprising a second recirculation line (15a), which consists of d The exhaust gas discharge system (5) belonging to the turbine (8a) of the first exhaust gas turbocharger (8) branches off, the second return line (15a) being equipped with a second EGR valve (15b). Supercharged internal combustion engine (1) after Claim 1 , characterized in that the second return line (15a) branches off from the associated exhaust gas discharge system (5) upstream of the turbine (8a) of the first exhaust gas turbocharger (8). Supercharged internal combustion engine (1) after Claim 1 or 2 , characterized in that the second return line (15a) branches off from the first total exhaust line (7a) upstream of the turbine (8a) of the first exhaust gas turbocharger (8). Supercharged internal combustion engine (1) according to one of the Claims 1 to 3 , characterized in that the second return line (15a) opens into the first return line (3a). Supercharged internal combustion engine (1) after Claim 4 , characterized in that the second return line (15a) opens into the first return line (3a) upstream of the first EGR valve (3b). Supercharged internal combustion engine (1) after Claim 5 , characterized in that the second EGR valve (15b) can be switched in two stages. Supercharged internal combustion engine (1) according to one of the preceding claims, characterized in that the first return line (3a) is equipped with a first cooler (3c). Supercharged internal combustion engine (1) after Claim 7 , characterized in that the first cooler (3c) is arranged downstream of the first EGR valve (3b). Supercharged internal combustion engine (1) after Claim 1 , characterized in that the second return line (15a) branches off downstream of the turbine (8a) of the first exhaust gas turbocharger (8) from the first overall exhaust gas line (7a) and upstream of the compressor (8b) of the first exhaust gas turbocharger (8) forming a second junction ( 15d) opens into the suction system (11). Supercharged internal combustion engine (1) after Claim 9 , characterized in that the second return line (15a) is equipped with a second cooler (15c). Supercharged internal combustion engine (1) after Claim 10 , characterized in that the second cooler (15c) is arranged upstream of the second EGR valve (15b). Supercharged internal combustion engine (1) according to one of the Claims 9 to 11 , characterized in that the second EGR valve (15b) is steplessly adjustable for setting the amount of recirculated exhaust gas. Supercharged internal combustion engine (1) according to one of the preceding claims, characterized in that the compressors (8b, 9b) of the at least two exhaust gas turbochargers (8, 9) are arranged in parallel in the intake system (11), wherein - each compressor (8b, 9b) in a separate suction line (11a, 11b) of the suction system (11) is arranged, and - the separate suction lines (11a, 11b) merge downstream of the compressors (8b, 9b) to form a total suction line (12), with downstream of the compressor (8b) des First exhaust gas turbocharger (8), a first shut-off element (13a) is arranged in the associated intake line (11a). Supercharged internal combustion engine (1) after Claim 13 , characterized in that a blow-off line (14) is provided, which branches off between the compressor (8b) of the first exhaust gas turbocharger (8) and the first shut-off element (13a) from the associated suction line (11a) and upstream of the compressor (9b) of the second Exhaust gas turbocharger (9) opens into the other intake line (11b), a further shut-off element (14a) being arranged in the blow-off line (14). Supercharged internal combustion engine (1) according to one of the previous ones Claims 1 to 12 , characterized in that the compressors (8b, 9b) of the at least two exhaust gas turbochargers (8, 9) are arranged in series in a total intake line (12a) of the intake system (11), the compressor (9b) of the second exhaust gas turbocharger (9) is arranged downstream of the compressor (8b) of the first exhaust gas turbocharger (8) in the overall intake line (12). Supercharged internal combustion engine (1) after Claim 15 , characterized in that the compressor (8b) of the first exhaust gas turbocharger (8) is equipped with a bypass line (16), which branches off from the overall intake line (12) upstream of the compressor (8b) of the first exhaust gas turbocharger (8) and between the compressor ( 9b) of the second exhaust gas turbocharger (9) and the compressor (8b) of the first exhaust gas turbocharger (8) opens into the overall intake line (12), a shut-off element (16a) being arranged in the bypass line (16). Supercharged internal combustion engine (1) according to one of the preceding claims, characterized in that a charge air cooler (10) is arranged in the intake system (11) downstream of the compressors (8b, 9b) of the at least two exhaust gas turbochargers (8, 9). Supercharged internal combustion engine (1) according to one of the preceding claims, characterized in that a throttle element (17) is arranged in the intake system (11) between the compressor (9b) of the second exhaust gas turbocharger (9) and the first node (3d). Supercharged internal combustion engine (1) according to one of the preceding claims, characterized in that the turbine (8a, 9a) of at least one exhaust gas turbocharger (8, 9) is equipped with a variable turbine geometry. Supercharged internal combustion engine (1) according to one of the preceding claims, characterized in that the turbine (8a, 9a) of at least one exhaust gas turbocharger (8, 9) is designed as a waste gate turbine. Supercharged internal combustion engine (1) according to one of the preceding claims, characterized in that each switchable outlet opening (4a) is equipped with a switchable lift valve, a disconnected lift valve switching off the associated outlet opening (4a) and keeping it closed, and a connected lift valve between an open position and moves to a closed position with the formation of a valve lift Δh _max and thereby releases the associated outlet opening (4a) during an opening period Δt _max . Method for operating a charged internal combustion engine (1) according to one of the preceding claims, characterized in that the switchable outlet openings (4a) are switched on if a predeterminable load M and / or a predeterminable speed n _{mot of} the internal combustion engine (1) is exceeded. Procedure according to Claim 22 , characterized in that the second exhaust gas recirculation (15) is activated when the switchable outlet openings (4a) are switched on, in order to return a requested amount of exhaust gas, for which purpose the second EGR valve (15b) is opened.

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