DE102019212774A1 - Two-stage chargeable internal combustion engine with exhaust gas aftertreatment and method for operating such an internal combustion engine - Google Patents

Abstract

The invention relates to a supercharged internal combustion engine (1) with an intake system (2) and an exhaust gas discharge system (4) and with at least two exhaust gas turbochargers (6, 7) connected in series, each of which has a turbine (6a, 7a) arranged in the exhaust gas discharge system (4). and a compressor (6b, 7b) arranged in the intake system (2) and of which a first exhaust gas turbocharger (6) serves as a low-pressure stage (6) and a second exhaust gas turbocharger (7) serves as a high-pressure stage (7), a first bypass line (12 ) is provided, which branches off from the exhaust gas removal system (4) upstream of the second turbine (7a) and which opens again into the exhaust gas removal system (4) between the first turbine (6a) and the second turbine (7a) forming a first node (8a) and in which a shut-off element (13) is arranged, and at least one selective catalytic converter (15, 16) for reducing nitrogen oxides is arranged in the exhaust gas discharge system (4). A first selective catalytic converter (16) for reducing g of nitrogen oxides is arranged between the second turbine (7a) and the first node (8a) in the exhaust gas removal system (4), and a device (17) for introducing a reducing agent into the exhaust gas removal system (4) is provided upstream of the second turbine (7a) This means that after a cold start, high boost pressure and rapid heating of the exhaust gas aftertreatment systems can be achieved at the same time.

Description

• - die zweite Turbine des zweiten Abgasturboladers stromaufwärts der ersten Turbine des ersten Abgasturboladers angeordnet ist und der zweite Verdichter des zweiten Abgasturboladers stromabwärts des ersten Verdichters des ersten Abgasturboladers angeordnet ist,
• - eine erste Bypassleitung vorgesehen ist, die stromaufwärts der zweiten Turbine vom Abgasabführsystem abzweigt und die zwischen der ersten Turbine und der zweiten Turbine unter Ausbildung eines ersten Knotenpunktes wieder in das Abgasabführsystem einmündet und in der ein Absperrelement angeordnet ist, und
• - im Abgasabführsystem mindestens ein selektiver Katalysator zur Reduzierung von Stickoxiden angeordnet ist.

The invention relates to a supercharged internal combustion engine with an intake system for supplying charge air and an exhaust gas discharge system for discharging exhaust gas and with at least two exhaust gas turbochargers connected in series, each comprising a turbine arranged in the exhaust gas discharge system and a compressor arranged in the intake system and of which a first exhaust gas turbocharger is used The low-pressure stage is used and a second exhaust gas turbocharger is used as the high-pressure stage, with

• - The second turbine of the second exhaust gas turbocharger is arranged upstream of the first turbine of the first exhaust gas turbocharger and the second compressor of the second exhaust gas turbocharger is arranged downstream of the first compressor of the first exhaust gas turbocharger,
• - A first bypass line is provided which branches off from the exhaust gas removal system upstream of the second turbine and which opens into the exhaust gas removal system again between the first turbine and the second turbine forming a first junction and in which a shut-off element is arranged, and
• - At least one selective catalyst for reducing nitrogen oxides is arranged in the exhaust gas discharge system.

The invention also relates to a method for operating a supercharged internal combustion engine of the type mentioned above.

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 compression ignition diesel engines, but also hybrid combustion engines that use a hybrid combustion process with compression ignition, as well as hybrid drives that, in addition to a compression ignition diesel engine, include an electric machine that can be driven with the diesel engine and that provides power from the Diesel engine takes up or delivers additional power as a switchable auxiliary drive.

The charging of an internal combustion engine is primarily used to increase performance. The air required for the combustion process is compressed, which means that a larger air mass can be supplied to each cylinder per work cycle. This allows the fuel mass 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 displacement is reduced, the load spectrum can be shifted towards higher loads, at which the specific fuel consumption is lower. By means of supercharging in combination with a suitable gear design, so-called downspeeding can also be achieved, in which a lower specific fuel consumption can also be achieved.

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

As a rule, an exhaust gas turbocharger is used for supercharging, 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 while releasing energy in this 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. If necessary, charge air cooling is also provided with which the compressed charge air is cooled before it enters the cylinder.

The advantage of an exhaust gas turbocharger, for example compared to a mechanical charger, is that there is or is no mechanical connection for power transmission between the charger and the internal combustion engine, which additionally takes up space in the engine compartment and influences the arrangement of the units in a not inconsiderable way. While a mechanical charger draws the energy required for its drive entirely from the internal combustion engine and thus reduces the power provided and thus adversely affects the efficiency, the exhaust gas turbocharger uses the exhaust gas energy of the hot exhaust gases.

The design of the exhaust gas turbocharger causes difficulties, with a noticeable increase in performance in all speed ranges being aimed for. In the case of internal combustion engines charged with an exhaust gas turbocharger, a noticeable drop in torque is observed when the speed falls below a certain level. This effect is undesirable and is one of the most serious disadvantages of exhaust gas turbocharging.

This torque drop becomes understandable if it is taken into account that the boost pressure ratio depends on the turbine pressure ratio. Becomes For example, if the engine speed is reduced, this leads to a smaller exhaust gas flow and thus to a smaller turbine pressure ratio. As a result, the boost pressure ratio also decreases towards lower engine speeds, which is equivalent to a drop in torque.

According to the prior art, attempts are made to improve the torque characteristics of an internal combustion engine charged by means of exhaust gas turbocharging 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 exhaust gas mass flow exceeds a critical value, part of the exhaust gas flow is guided past the turbine by means of a bypass line as part of a so-called exhaust gas blow-off. However, this approach has the disadvantage that the charging behavior is inadequate at higher speeds.

The torque characteristics of a supercharged internal combustion engine can furthermore be improved by several turbochargers arranged in parallel, i.e. by several turbines with a smaller turbine cross-section arranged in parallel, with the turbines being switched on successively as the amount of exhaust gas increases; similar to register charging.

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 towards smaller compressor flows, which means that high boost pressure ratios can be achieved even with small compressor flows and the torque characteristics in the lower speed range are significantly improved. This is achieved by designing the high-pressure turbine for small exhaust gas flows and providing a bypass line with which exhaust gas is increasingly led past the high-pressure turbine as the exhaust gas flow increases. For this purpose, the bypass line branches off from the exhaust gas discharge system upstream of the high-pressure turbine and flows back into the exhaust gas discharge system upstream of the low-pressure turbine. A shut-off element is arranged in the bypass line in order to control the exhaust gas flow that is guided past the high-pressure turbine. A two-stage chargeable internal combustion engine of the above type is described, for example, in the European patent application EP 1 640 596 A1 described. The German Offenlegungsschrift DE 10 2013 215 574 A1 also has such an internal combustion engine as its subject.

The internal combustion engine of the present invention also has at least two turbochargers arranged in series.

Two exhaust gas turbochargers connected in series offer other advantages beyond what has already been said. The performance of the internal combustion engine can be increased even further by two-stage charging. Furthermore, the response behavior of an internal combustion engine charged in this way, in particular in the partial load range, is significantly improved compared to a comparable internal combustion engine with single-stage charging. The reason for this is to be found in the fact that the smaller high-pressure stage is less sluggish than a larger exhaust-gas turbocharger used in the context of single-stage charging. The running gear or impeller of a smaller exhaust gas turbocharger can be accelerated and decelerated more quickly.

This also has advantages with regard to particle emissions. When the internal combustion engine accelerates, the air mass to be supplied to the cylinders basically only follows the increased fuel quantity with a delay due to the inertia of the running wheels. In the case of a smaller high-pressure turbocharger, on the other hand, the charge air supplied to the engine is adjusted almost without delay, which is why operating states with increased particle emissions are avoided.

When designing the exhaust gas turbocharger, efforts are made to arrange the turbine or turbines as close as possible to the exhaust of the internal combustion engine, i.e. close to the cylinder outlet openings, in order to determine the exhaust gas enthalpy of the hot exhaust gases, which is largely determined by the exhaust gas pressure and the exhaust gas temperature to be able to use it optimally and to ensure a quick response of the turbocharger. Not only is the path of the hot exhaust gases to the turbine shortened by an arrangement close to the engine, the volume of the exhaust gas removal system upstream of the turbine also decreases. The thermal inertia of the exhaust gas removal system also decreases, namely by reducing the mass and length of the section of the exhaust gas removal system up to the turbine. For the reasons mentioned above, the turbines are usually arranged on the cylinder head on the outlet side. For the same reasons, the prior art exhaust manifold is often integrated in the cylinder head. The integration of the exhaust manifold also allows a tight packaging of the drive unit. In addition, a liquid cooling that may be provided in the cylinder head can be used, so that the manifold does not must be made of thermally highly resilient materials that are cost-intensive. In the case of two-stage turbocharging, however, the arrangement of the turbine close to the engine of the low-pressure stage causes problems.

Exhaust gas turbocharging in combination with exhaust gas aftertreatment has proven to be problematic.

In internal combustion engines that are operated with an excess of air, for example direct-injection diesel engines, the nitrogen oxides NO _x in the exhaust gas cannot be reduced due to the principle, ie due to the lack of reducing agents.

As a result, an exhaust gas aftertreatment system must be provided to reduce the nitrogen oxides, for example a selective catalytic converter, which is also referred to as an SCR catalytic converter and in which reducing agent is specifically introduced into the exhaust gas in order to selectively reduce the nitrogen oxides. In addition to ammonia NH ₃ and urea, unburned hydrocarbons are also used as reducing agents. The latter is also referred to as HC enrichment, with the unburned hydrocarbons being introduced directly into the exhaust gas discharge system or by means of measures within the engine, for example by post-injection of additional fuel into the combustion chamber. The post-injected fuel should not be ignited in the combustion chamber by the main combustion still taking place or by the high combustion gas temperatures - even after the main combustion has ended - but instead should be introduced into the exhaust gas discharge system upstream of the selective catalytic converter during the gas exchange.

Internal combustion engines that make use of post injection are inherently susceptible to dilution or contamination of the oil by unburned hydrocarbons. Depending on the quantity of post-injected fuel and the time of injection, a more or less large proportion of the post-injected fuel reaches the inner wall of the cylinder, mixes there with the adhering oil film and thus contributes to the dilution of the oil. In addition, the use of additional fuel as a reducing agent increases the overall fuel consumption of the internal combustion engine due to the principle involved.

Therefore, more and more selective catalysts are used to reduce nitrogen oxides, in which ammonia or urea is provided as a reducing agent.

Due to the toxicity of ammonia NH ₃ , ammonia is generally not stored in its pure form in motor vehicles and made available as a reducing agent. Rather, urea is often used as the starting product for the production of ammonia, because urea can be split into ammonia and isocyanic acid with the input of energy as part of a thermolytic reaction, ammonia NH ₃ can be recovered from the isocyanic acid in the presence of water.

When providing the urea for the production of ammonia, a distinction can be made between two fundamentally different concepts. On the one hand, the urea can be stored and made available in liquid form, i.e. as an aqueous solution, the urea being introduced as an aqueous solution into the exhaust gas upstream of the selective catalyst. On the other hand, there is the possibility of making the urea available in solid form. Urea in solid form is less voluminous and is characterized by a higher ammonia content than an aqueous solution. The storage tank can therefore be designed with a smaller storage volume, which is a significant advantage, in particular with regard to use in motor vehicles, in which packaging that is as dense and effective as possible is sought.

Both concepts require the introduction of heat into the urea in order to produce ammonia. This can cause problems in certain operating modes. If, for example, an aqueous urea solution is introduced into the exhaust gas upstream of a selective catalyst, exhaust gas temperatures of around 150 ° C to 170 ° C are required in order to evaporate the urea solution _{, generate ammonia NH 3} and this ammonia, which serves as a reducing agent, suffice with the exhaust gas to mix, so that the exhaust gas ammonia mixture is as homogeneous as possible and flows through the catalytic converter.

In the case of diesel engines, it can be difficult to generate or achieve exhaust gas temperatures in the required, above-mentioned level in inner-city traffic. It must be taken into account that exhaust gas temperatures of only 100 ° C are usually reached when idling and internal combustion engines require a certain warm-up phase after a cold start so that the individual exhaust gas aftertreatment systems reach their operating temperature and convert pollutants.

Selective catalysts can not only reduce nitrogen oxides in the presence of a reducing agent, for example ammonia, but also store, store and, if required, ammonia when suitable temperatures are present Release reduction of nitrogen oxides again. In order to be able to store ammonia, certain minimum temperatures of the catalyst are required. As a rule, catalytic converter temperatures between 180 ° C and 300 ° C are aimed for in order to ensure satisfactory exhaust gas aftertreatment using an SCR catalytic converter. Temperatures that are too high or too high a heat input can damage the catalytic converter, contribute to thermal aging of the catalytic converter and adversely affect the desired conversion of the nitrogen oxides.

It should also be taken into account that a selective catalytic converter releases stored ammonia at very high catalytic converter temperatures above approx. 400 ° C without reducing nitrogen oxides. Both the released ammonia and the untreated nitrogen oxide-containing exhaust gas are then discharged into the environment via an exhaust gas discharge system.

Although the current regulations do not necessarily require on-board diagnostics (OBD), future limit values for nitrogen oxide emissions stipulated by law could make this necessary. The EURO VI regulation prescribes the monitoring of raw nitrogen oxide emissions. In particular, the safe avoidance of the introduction of ammonia into the environment could make on-board diagnosis (OBD), namely the monitoring of the ammonia concentration in the aftertreated exhaust gas, indispensable.

The statements made above make it clear that it is advantageous to place selective catalytic converters as close as possible to the exhaust of the internal combustion engine, ie close to the engine, in order to give the exhaust gases little time and opportunity to cool down and to ensure that the catalytic converter reaches its operating temperature as quickly as possible, in particular after a cold start of the internal combustion engine. However, overheating of the catalytic converter, especially at high loads and high speeds, should also be avoided.

In addition, selective catalysts require a certain amount of space. On the one hand for storing and introducing the reducing agent into the exhaust gas and mixing the reducing agent with the exhaust gas to generate a homogeneous mixture. On the other hand, the catalytic converter as such requires a certain amount of installation space, which can be smaller or larger depending on the volume of the catalytic converter. The volume of the catalytic converter is determined by the mass of exhaust gas to be post-treated, with the exhaust gas taking up a certain amount of time in the catalytic converter as part of exhaust gas post-treatment.

Arranging the exhaust gas turbocharger close to the engine on the one hand and the exhaust gas aftertreatment systems on the other hand leads to a conflict in the design of the exhaust gas removal system with the various units. It should also be taken into account that an internal combustion engine generally has a large number of exhaust gas aftertreatment systems.

The technical relationships described above make it clear that concepts are required with which selective catalytic converters can be optimally operated in a multi-stage charged internal combustion engine. Such concepts should, in particular, take into account that different exhaust gas temperatures and different exhaust gas quantities place different demands on the selective catalytic converter, so that these demands can vary greatly during operation of an internal combustion engine.

A two-stage chargeable internal combustion engine with exhaust gas aftertreatment is for example in the European patent application EP 1 396 619 A1 described. The EP 1 396 619 A1 deals with the simultaneous use of exhaust gas turbocharging and exhaust gas aftertreatment, the aim being to arrange the exhaust gas aftertreatment system as close as possible to the exhaust of the internal combustion engine. Several concepts are shown.

In an embodiment according to EP 1 396 619 A1 the exhaust gas flow is directed by means of suitable switching devices and bypass lines in such a way that it is guided past both turbines. This offers advantages with regard to a catalytic converter arranged in the exhaust gas discharge system downstream of the turbines, especially after a cold start or in the warm-up phase of the internal combustion engine, since the hot exhaust gas is fed directly to the catalytic converter and is not first passed through the turbines, which are regarded as a temperature sink, with heat being given off. In this way, the catalytic converter reaches its light-off temperature more quickly after a cold start or in the warm-up phase. Another embodiment provides for the arrangement of a second catalytic converter in the bypass line bypassing the two turbines.

The disadvantage of that in the EP 1 396 619 A1 The concept described is that in the warm-up phase of the internal combustion engine, all of the exhaust gas is fed to the catalytic converters for the purpose of heating and no exhaust gas is passed through the turbines. During the warm-up phase, therefore, no charging of the internal combustion engine can take place or be carried out, since no boost pressure can be generated using the exhaust gas energy. The conflict between exhaust gas turbocharging and exhaust gas aftertreatment is resolved in favor of exhaust gas aftertreatment.

The DE 10 2013 215 574 A1 describes a concept in which the low-pressure turbine is equipped with a bypass line. After a cold start or in the warm-up phase of the internal combustion engine, the hot exhaust gas is fed via the bypass line past the low-pressure turbine and directly to an exhaust gas aftertreatment system provided downstream in the exhaust gas discharge system. This eliminates the low-pressure turbine, which can be seen as a temperature sink. In this way, the exhaust gas aftertreatment system reaches the required temperature more quickly after a cold start or in the warm-up phase. In the meantime, the high-pressure turbine ensures that the required boost pressure is provided.

Further measures are required in order to comply with future limit values for pollutant emissions. In addition to unburned hydrocarbons, nitrogen oxide emissions are of particular relevance.

Against this background, it is an object of the present invention to provide a supercharged internal combustion engine according to the preamble of claim 1 with which the disadvantages known from the prior art are eliminated and with which the exhaust gas aftertreatment by means of a selective catalytic converter is effective and optimized under all operating conditions of the internal combustion engine can be carried out.

Another sub-object of the present invention is to provide a method for operating a supercharged internal combustion engine of the type mentioned above.

• - die zweite Turbine des zweiten Abgasturboladers stromaufwärts der ersten Turbine des ersten Abgasturboladers angeordnet ist und der zweite Verdichter des zweiten Abgasturboladers stromabwärts des ersten Verdichters des ersten Abgasturboladers angeordnet ist,
• - eine erste Bypassleitung vorgesehen ist, die stromaufwärts der zweiten Turbine vom Abgasabführsystem abzweigt und die zwischen der ersten Turbine und der zweiten Turbine unter Ausbildung eines ersten Knotenpunktes wieder in das Abgasabführsystem einmündet und in der ein Absperrelement angeordnet ist, und
• - im Abgasabführsystem mindestens ein selektiver Katalysator zur Reduzierung von Stickoxiden angeordnet ist, und die dadurch gekennzeichnet ist, dass
• - ein erster selektiver Katalysator zur Reduzierung von Stickoxiden zwischen der zweiten Turbine und dem ersten Knotenpunkt im Abgasabführsystem angeordnet ist, und
• - eine Vorrichtung zum Einbringen eines Reduktionsmittels in das Abgasabführsystem stromaufwärts der zweiten Turbine vorgesehen ist.

The first sub-task is achieved by a supercharged internal combustion engine with an intake system for supplying charge air and an exhaust gas discharge system for discharging exhaust gas and with at least two exhaust gas turbochargers connected in series, each comprising a turbine arranged in the exhaust gas discharge system and a compressor arranged in the intake system, one of which first exhaust gas turbocharger is used as a low pressure stage and a second exhaust gas turbocharger is used as a high pressure stage, with

• - The second turbine of the second exhaust gas turbocharger is arranged upstream of the first turbine of the first exhaust gas turbocharger and the second compressor of the second exhaust gas turbocharger is arranged downstream of the first compressor of the first exhaust gas turbocharger,
• - A first bypass line is provided which branches off from the exhaust gas removal system upstream of the second turbine and which opens into the exhaust gas removal system again between the first turbine and the second turbine forming a first junction and in which a shut-off element is arranged, and
• - At least one selective catalyst for reducing nitrogen oxides is arranged in the exhaust gas discharge system, and which is characterized in that
• - A first selective catalyst for reducing nitrogen oxides is arranged between the second turbine and the first node in the exhaust gas discharge system, and
• - A device for introducing a reducing agent into the exhaust gas discharge system is provided upstream of the second turbine.

The internal combustion engine according to the invention is equipped with two series-connectable turbines arranged in series in the exhaust gas discharge system and two compressors arranged in series in the intake system.

Embodiments are advantageous in which the first compressor is designed larger than the second compressor because the first compressor forms the low-pressure stage as part of a two-stage compression, whereas the second compressor compresses the already pre-compressed air and thus represents the high-pressure stage.

For the same reason, embodiments are advantageous in which the first turbine is designed to be larger than the second turbine. This is because the second turbine serves as a high-pressure turbine as part of a two-stage supercharging process, while an exhaust gas flow expands in the first turbine, which already has a lower pressure and a lower density as a result of passing through the high-pressure stage.

According to the invention, the turbine of the high pressure stage has a bypass line via which exhaust gas can be passed past the high pressure turbine. The turbine of the low pressure stage can also be equipped with a bypass line.

A first selective catalytic converter for reducing the nitrogen oxides is arranged downstream of the second turbine, i.e. the high-pressure turbine. A device is provided upstream of the second turbine in order to introduce a reducing agent into the exhaust gas. The first selective catalytic converter is designed for exhaust gas aftertreatment of the small amounts of exhaust gas that pass through the high-pressure turbine.

Despite the use of a selective catalytic converter, the space requirement for the exhaust gas aftertreatment is comparatively small, since, according to the invention, the high-pressure turbine functions as a mixing device in which the reducing agent introduced upstream of the high-pressure turbine is efficient and in is mixed sufficiently with the exhaust gas. This results in a satisfactory homogenization of the mixture and a final processing of the reducing agent, the high exhaust gas temperatures upstream of the high-pressure turbine advantageously supporting the processing of the reducing agent introduced. The exhaust gas aftertreatment mixing section is significantly shorter than in the prior art. The catalytic converter as such only takes up a small amount of space, since only a small volume of the catalytic converter is required due to the design for small amounts of exhaust gas.

The first bypass line opens downstream of the first selective catalytic converter with the formation of the first junction in the exhaust gas discharge system, so that the high-pressure turbine and the exhaust gas aftertreatment can be bypassed by means of the SCR catalytic converter via the first bypass line. This procedure is recommended to protect the first selective catalytic converter from overheating or thermal overload. As soon as the exhaust gas mass flow exceeds a predetermined limit value, it may be necessary or useful to transfer the internal combustion engine from a first operating mode, in which the internal combustion engine is charged using the first and second exhaust gas turbocharger, to a second operating mode, in which the internal combustion engine is only under Using the first exhaust gas turbocharger is charged in order to protect the first selective catalytic converter from overheating or thermal overload in this way.

With the internal combustion engine according to the invention, the first object on which the invention is based is achieved, namely a supercharged internal combustion engine according to the preamble of claim 1, with which the disadvantages known from the prior art are eliminated and with which the exhaust gas aftertreatment by means of a selective catalytic converter under all operating conditions of the Internal combustion engine can be carried out effectively and optimized.

The arrangement of the first SCR catalytic converter close to the engine immediately downstream of the high-pressure turbine enables the SCR catalytic converter to be heated up quickly without the use of additional measures.

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 a second bypass line is provided which branches off between the first selective catalytic converter and the first node, forming a third node from the exhaust gas discharge system.

Bypassing the low-pressure turbine via a bypass line is advisable if the low-pressure compressor is not used to charge or generate the boost pressure.

During the warm-up phase, the exhaust gas flow, preferably the entire exhaust gas flow, is passed through the second turbine, i.e. through the turbine of the high pressure stage. It can be advantageous or sensible to bypass the large first turbine via a second bypass line, for example in order to apply hot exhaust gas to a further exhaust gas aftertreatment system arranged downstream of the turbines and to heat it up or to keep it at temperature. By bypassing the first turbine, the larger first turbine is eliminated as a temperature sink.

If the exhaust gas flow is passed through the smaller, second turbine during the warm-up phase, a sufficiently high boost pressure can be generated and, at the same time, an effective exhaust gas aftertreatment can take place using the first SCR catalytic converter.

Embodiments of the supercharged internal combustion engine are advantageous in which the second bypass line opens back into the exhaust gas discharge system downstream of the first turbine with the formation of a fourth junction.

Embodiments of the supercharged internal combustion engine are advantageous in which a further shut-off element is arranged in the exhaust gas discharge system at the third junction.

The further shut-off element can in the warm-up phase according to a first In the working position, block the exhaust gas discharge system to the first turbine and open the second bypass line, so that the exhaust gas flow is bypassed the larger first turbine. This is an advantage compared to embodiments in which the valve is arranged in the bypass line itself and, when the shut-off element is open, exhaust gas can continue to flow into the turbine of the low-pressure stage. It is true that the turbine of the low-pressure stage then also forms a certain flow resistance. Nonetheless, some of the exhaust gas flows through the larger first turbine. In the operating modes considered here, however, this partial flow is a not inconsiderable percentage of the total exhaust gas flow, which is then not directly available to the at least one exhaust gas aftertreatment system downstream of the turbines - for example for heating.

The shut-off element arranged at the third node can, according to a second working position, release the exhaust gas discharge system to the first turbine and block the second bypass line.

The internal combustion engine is preferably charged either in two stages according to a first operating mode using the first exhaust gas turbocharger and the second exhaust gas turbocharger or in one stage according to a third operating mode using the second exhaust gas turbocharger.

In the first operating mode, the shut-off element arranged at the first node is then in the second working position, whereas in the third operating mode the shut-off element is in the first working position.

Embodiments of the supercharged internal combustion engine are advantageous in which the shut-off element at the first node is a 3-2-way valve, i.e. a valve with three connections and two switching positions.

Embodiments of the supercharged internal combustion engine are advantageous in which at least one further exhaust gas aftertreatment system is provided in the exhaust gas removal system downstream of the fourth node.

The at least one further exhaust gas aftertreatment system downstream of the turbines can be an oxidation catalytic converter, a three-way catalytic converter, a storage catalytic converter, a selective catalytic converter and / or a particle filter. A combination of two or more of the abovementioned exhaust gas aftertreatment systems can also be used.

Embodiments of the supercharged internal combustion engine in which at least one exhaust gas aftertreatment system can be electrically heated are advantageous.

Embodiments of the supercharged internal combustion engine are advantageous in which the at least one further exhaust gas aftertreatment system is a second selective catalyst for reducing nitrogen oxides.

If the internal combustion engine is charged in a single stage according to a second operating mode using only the first exhaust gas turbocharger, the high-pressure turbine and the first SCR catalytic converter are bypassed via the first bypass line. The first SCR catalytic converter then does not impair the exhaust gas flow, as a result of which the charging is improved.

In this context, embodiments of the supercharged internal combustion engine are advantageous in which the second selective catalytic converter is designed for exhaust gas aftertreatment of larger amounts of exhaust gas, since in particular the second operating mode is usually characterized by high loads and / or high speeds, i.e. by large amounts of exhaust gas.

As already discussed, embodiments of the supercharged internal combustion engine in which the first selective catalytic converter is designed for the exhaust gas aftertreatment of smaller amounts of exhaust gas are advantageous.

Embodiments of the supercharged internal combustion engine are advantageous in which a third bypass line is provided which opens into the intake system between the first compressor and the second compressor forming a second junction and in which an additional shut-off element is arranged.

The third bypass line can be used to blow off charge air compressed in the first compressor. In particular, however, the third bypass line can be used to suck in charge air, specifically by bypassing the first compressor, which in the case of single-stage charging by means of a high-pressure stage according to the third operating mode only represents a flow resistance.

Embodiments of the supercharged internal combustion engine are advantageous in which a charge air cooler is arranged in the intake system between the first compressor and the second compressor.

In the present case, a charge air cooler is arranged in the intake system between the compressors. As part of a two-stage compression, the charge air cooler lowers the temperature of the charge air compressed in the low-pressure stage and thus increases the density of the charge air, whereby the compression in the high-pressure stage is improved and the outlet temperature of the high-pressure stage can be lowered with the same overall pressure ratio of the supercharging group. This also offers protection against thermal overload. The charge air cooler can also be used to increase the overall pressure ratio of the compressor group and thus further increase the output, i.e. further drive the increase in output.

Embodiments of the supercharged internal combustion engine in which the high-pressure compressor is equipped with a bypass line are advantageous. This makes it possible in principle to bypass the second compressor in the context of a single-stage compression using a low-pressure stage.

Embodiments of the charged ones are advantageous in the above context Internal combustion engine in which the third bypass line opens into the intake system between the charge air cooler and the second compressor, forming the second junction.

Then the charge air is not cooled as part of the single-stage compression in the high-pressure stage before entering the high-pressure compressor, but only as part of the two-stage compression. It should also be taken into account that such a single-stage compression is implemented during the warm-up phase, in particular with an internal combustion engine that is not yet at operating temperature, in which it is particularly useful to supply the charge air to the high-pressure compressor in an uncooled manner in order not to unnecessarily delay the internal combustion engine's heating process.

Embodiments of the supercharged internal combustion engine are advantageous in which the third bypass line branches off from the intake system upstream of the first compressor.

Embodiments of the supercharged internal combustion engine in which the first compressor is designed to be larger than the second compressor are advantageous.

Embodiments of the supercharged internal combustion engine in which the first turbine is designed to be larger than the second turbine are advantageous.

Embodiments of the supercharged internal combustion engine are advantageous in which the second turbine of the second exhaust gas turbocharger has a variable turbine geometry.

A variable turbine geometry increases the flexibility of the supercharging. It allows a stepless adaptation of the turbine geometry to the respective operating point of the internal combustion engine or to the current exhaust gas mass flow. In contrast to a turbine with a fixed geometry, a more or less satisfactory charging can be realized in a wide speed or load range.

In particular, the combination of a turbine with variable turbine geometry and a bypass line bypassing this turbine allows the high-pressure turbine to be designed for very small exhaust gas flows and thus for the lower partial load range. As a result, high turbine pressure ratios can be achieved even at low speeds or even with very small amounts of exhaust gas.

The second sub-task on which the invention is based is achieved by a method which is characterized in that the internal combustion engine is either charged in two stages according to a first operating mode using the first exhaust gas turbocharger and the second exhaust gas turbocharger or is charged in one stage according to a second operating mode using the first exhaust gas turbocharger becomes.

While the internal combustion engine is in the second operating mode and is charged in a single stage using the low-pressure compressor, the upstream first SCR catalytic converter is bypassed via a bypass line so that it does not hinder the charging process or disrupt the flow resistance, which improves the torque characteristic. A second SCR catalytic converter arranged downstream of the low-pressure compressor is only finally flowed through.

What has been said in connection with the internal combustion engine according to the invention also applies to the method according to the invention.

Method variants are advantageous in which the internal combustion engine is transferred from the first operating mode to the second operating mode as soon as the exhaust gas mass flow exceeds a predeterminable limit value.

Method variants in which the internal combustion engine is operated in the warm-up phase according to the first operating mode are advantageous.

To operate a supercharged internal combustion engine, in which a second bypass line is provided, which branches off between the first selective catalytic converter and the first junction with the formation of a third junction from the exhaust gas discharge system and opens back into the exhaust gas discharge system downstream of the first turbine, with a further shut-off element at the third junction is arranged, method variants are advantageous, which are characterized in that the internal combustion engine is transferred from the first operating mode by actuating the shut-off element and releasing the second bypass line in a third operating mode, according to which the exhaust gas after-treated in the first selective catalytic converter is guided past the first turbine becomes.

• 1 schematisch eine erste Ausführungsform der aufgeladenen Brennkraftmaschine.

In the following the invention is based on an exemplary embodiment according to 1 described in more detail. Here shows:

• 1 schematically a first embodiment of the supercharged internal combustion engine.

1 shows a first embodiment of the supercharged internal combustion engine 1 using the example of a four-cylinder in-line engine. The four cylinders 3rd the internal combustion engine 1 are arranged in series along the longitudinal axis of the cylinder head. The exhaust pipes of the cylinders 3rd lead to one common exhaust gas removal system 4th together, as a result of which all exhaust pipes are connected to one another and the same exhaust gas pressure prevails in all exhaust pipes. The internal combustion engine also has 1 via a suction system 2 to supply the cylinders 3rd with charge air.

The internal combustion engine 1 is with two in series switchable, in the exhaust gas removal system 4th arranged turbines 6a , 7a and two in series switchable in the intake system 2 arranged compressors 6b , 7b equipped, each with a turbine 6a , 7a and a compressor 6b , 7b to an exhaust gas turbocharger 6th , 7th are summarized. Thus, that of the internal combustion engine 1 supplied charge air are compressed in two stages, with a first exhaust gas turbocharger 6th as a low pressure stage 6th serves and a second exhaust gas turbocharger 7th as a high pressure stage 7th . The second turbine 7a of the second exhaust gas turbocharger 7th is upstream of the first turbine 6a of the first exhaust gas turbocharger 6th arranged and the second compressor 7b of the second exhaust gas turbocharger 7th downstream of the first compressor 6b of the first exhaust gas turbocharger 6th .

The first compressor 6b is designed larger than the second compressor 7b as the first compressor 6b as part of a two-stage compression, the low-pressure stage 6th forms, whereas the second compressor 7b the already pre-compressed air is compressed and thus the high pressure stage 7th represents.

For the same reason is the first turbine 6a is designed larger than the second turbine 7a . Because the second turbine 7a serves as a high pressure turbine 7a while in the first turbine 6a In the course of a two-stage charge, an exhaust gas flow is relaxed, which already as a result of passing through the high-pressure stage 7th has a lower pressure and a lower density. In the second operating mode, the internal combustion engine is charged in one stage using the low-pressure compressor, and large and large amounts of exhaust gas have to be dealt with. The latter also requires a larger turbine.

In the intake system 2 between the first compressor 6b and the second compressor 7b is an intercooler 5a arranged. Downstream the compressor 6b , 7b is another intercooler 5b intended. The air temperature is lowered and thus the density of the charge air is increased, resulting in better filling of the cylinders 3rd is achieved with air.

The first compressor 6b is with a third bypass line 10 equipped upstream of the first compressor 6b from the intake system 2 branches off and between the first compressor 6b and the second compressor 7b with the formation of a second node 8b into the intake system 2 joins. The third bypass line 10 has another shut-off element 11 and opens downstream of the intercooler 5a into the intake system 2 . The second compressor 7b is also equipped with a bypass line (not shown).

The high pressure turbine 7a has a variable turbine geometry and a first bypass line 12th upstream of the high pressure turbine 7a from the exhaust system 4th branches off and the one between the low pressure turbine 6a and the high pressure turbine 7a with the formation of a first node 8a back into the exhaust system 4th joins. In this bypass line 12th is a shut-off element 13th arranged to the bypass line 12th to release or to block.

In the exhaust gas removal system 4th are two selective catalysts 15th , 16 arranged to reduce nitrogen oxides. A first selective catalyst 16 is downstream of the high pressure turbine 7a placed between the high pressure turbine 7a and the first node 8a . Upstream of the high pressure turbine 7a is there is a device 17th for introducing a reducing agent into the exhaust gas, with urea or ammonia preferably being introduced. Before the reducing agent enters the SCR catalytic converter 16 this is achieved by means of the high temperatures upstream of the high-pressure turbine 7a processed, for example evaporated, to then flow through the high-pressure turbine 7a to be effectively mixed with the exhaust gas. In this way, a sufficiently homogenized mixture of exhaust gas and reducing agent is created at the inlet of the SCR catalytic converter 16 provided.

A second bypass line 14th branches between the first selective catalyst 16 and the first node 8a with the formation of a third node from the exhaust gas removal system 4th from. There is another shut-off element at the third junction 9 arranged, which either the exhaust path to the low-pressure turbine 6a or the second bypass line 14th releases. The second bypass line 14th can also be used to bypass the low pressure turbine 6a can be used. Downstream of the low pressure turbine 6a the second bypass line opens 14th back into the exhaust gas removal system with the formation of a fourth junction 4th .

Downstream of the turbines 6a , 7a is in the overall exhaust line 4th another exhaust aftertreatment system 15th arranged; a second selective catalyst 15th , which is designed for larger amounts of exhaust gas.

List of reference symbols

1

supercharged internal combustion engine

2

Suction system

3

cylinder

4th

Exhaust gas removal system, overall exhaust line

5a

Intercooler

5b

further intercooler

6th

first exhaust gas turbocharger, low pressure stage

6a

first turbine

6b

first compressor

7th

second exhaust gas turbocharger, high pressure stage

7a

second turbine

7b

second compressor

8a

first junction

8b

second junction

9

another shut-off element

10

third bypass line

11

additional shut-off element

12th

first bypass line

13th

Shut-off element

14th

second bypass line

15th

Exhaust aftertreatment system, second selective catalytic converter, second SCR catalytic converter

16

first selective catalytic converter, first SCR catalytic converter

17th

Device for introducing a reducing agent

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 1640596 A1 [0015]
• DE 102013215574 A1 [0015, 0039]
• EP 1396619 A1 [0036, 0037, 0038]

Claims (16)

Supercharged internal combustion engine (1) with an intake system (2) for supplying charge air and an exhaust gas removal system (4) for removing exhaust gas and with at least two exhaust gas turbochargers (6, 7) connected in series, each of which has a turbine (4) arranged in the exhaust gas removal system (4). 6a, 7a) and a compressor (6b, 7b) arranged in the intake system (2) and of which a first exhaust gas turbocharger (6) serves as a low pressure stage (6) and a second exhaust gas turbocharger (7) serves as a high pressure stage (7), wherein - the second turbine (7a) of the second exhaust gas turbocharger (7) is arranged upstream of the first turbine (6a) of the first exhaust gas turbocharger (6) and the second compressor (7b) of the second exhaust gas turbocharger (7) is arranged downstream of the first compressor (6b) of the first exhaust gas turbocharger (6) is arranged, - a first bypass line (12) is provided, which branches off upstream of the second turbine (7a) from the exhaust gas discharge system (4) and which between the first turbine (6a) and the second turbine (7a) un ter formation of a first node (8a) opens again into the exhaust gas discharge system (4) and in which a shut-off element (13) is arranged, and - in the exhaust gas discharge system (4) at least one selective catalytic converter (15, 16) for reducing nitrogen oxides is arranged, characterized in that - a first selective catalyst (16) for reducing nitrogen oxides is arranged between the second turbine (7a) and the first node (8a) in the exhaust gas discharge system (4), and - a device (17) for introducing a reducing agent into the exhaust gas discharge system (4) is provided upstream of the second turbine (7a). Supercharged internal combustion engine (1) after Claim 1 , characterized in that a second bypass line (14) is provided which branches off between the first selective catalytic converter (16) and the first node (8a) to form a third node from the exhaust gas discharge system (4). Supercharged internal combustion engine (1) after Claim 2 , characterized in that the second bypass line (14) opens downstream of the first turbine (6a) with the formation of a fourth junction again into the exhaust gas discharge system (4). Supercharged internal combustion engine (1) after Claim 2 or 3rd , characterized in that a further shut-off element (9) is arranged in the exhaust gas discharge system (4) at the third junction. Supercharged internal combustion engine (1) after Claim 3 or 4th , characterized in that at least one further exhaust gas aftertreatment system (15) is provided in the exhaust gas discharge system (4) downstream of the fourth node. Supercharged internal combustion engine (1) after Claim 5 , characterized in that the at least one further exhaust gas aftertreatment system (15) is a second selective catalyst (15) for reducing nitrogen oxides. Supercharged internal combustion engine (1) after Claim 6 , characterized in that the second selective catalytic converter (15) is designed for exhaust gas aftertreatment of larger amounts of exhaust gas. Supercharged internal combustion engine (1) according to one of the preceding claims, characterized in that the first selective catalytic converter (16) is designed for the exhaust gas aftertreatment of smaller amounts of exhaust gas. Supercharged internal combustion engine (1) according to one of the preceding claims, characterized in that a third bypass line (10) is provided which between the first compressor (6b) and the second compressor (7b) with the formation of a second node (8b) in the intake system (2) opens and in which an additional shut-off element (11) is arranged. Supercharged internal combustion engine (1) according to one of the preceding claims, characterized in that a charge air cooler (5a) is arranged in the intake system (2) between the first compressor (6b) and the second compressor (7b). Supercharged internal combustion engine (1) after Claim 10 with a third bypass line (10), characterized in that the third bypass line (10) opens into the intake system (2) between the charge air cooler (5a) and the second compressor (7b) forming the second node (8b). Supercharged internal combustion engine (1) according to one of the preceding claims, characterized in that a further charge air cooler (5b) is arranged in the intake system (2) downstream of the compressors (6b, 7b). Method for operating a supercharged internal combustion engine (1) according to one of the preceding claims, characterized in that the internal combustion engine (1) is charged in two stages either according to a first operating mode using the first exhaust gas turbocharger (6) and the second exhaust gas turbocharger (7) or according to a second operating mode using the first exhaust gas turbocharger (7) is charged in one stage. Procedure according to Claim 13 , characterized in that, starting from the first operating mode, the internal combustion engine is transferred to the second operating mode as soon as the exhaust gas mass flow exceeds a predeterminable limit value. Procedure according to Claim 13 or 14th , characterized in that the internal combustion engine (1) is operated in the warm-up phase according to the first operating mode. Method according to one of the Claims 13 to 15th for operating a supercharged internal combustion engine (1), in which a second bypass line (14) is provided, which branches off between the first selective catalytic converter (16) and the first node (8a) to form a third node from the exhaust gas discharge system (4) and downstream of the first turbine (6a) opens again into the exhaust gas discharge system (4), a further shut-off element (9) being arranged at the third junction, characterized in that the internal combustion engine (1) starting from the first operating mode by actuating the shut-off element (9) and releasing the second bypass line (14) is transferred to a third operating mode, according to which the exhaust gas after-treated in the first selective catalytic converter (16) is guided past the first turbine (6a).

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