DE102015207545A1 - Two-stage rechargeable internal combustion engine with exhaust aftertreatment and method for operating such an internal combustion engine - Google Patents

Abstract

Internal combustion engine (1) with min. two exhaust gas turbochargers (6, 7) connected in series, of which a first exhaust gas turbocharger (6) serves as a low pressure stage (6) and a second exhaust gas turbocharger (7) as a high pressure stage (7), wherein - the second turbine (7a) upstream of the first turbine (6a) is arranged and the second compressor (7b) downstream of the first compressor (6b) is arranged, - a first bypass line (14) is provided between the first turbine (6a) and the second turbine (7a) to form a a second bypass line (12) is provided which branches off from the exhaust gas removal system (4) upstream of the second turbine (7a) and which connects between the first turbine (6a) and the second turbine (8a). 7a) again into the Abgasabführsystem (4) opens and in which a shut-off element (13) is arranged, - a third bypass line (10) is provided between the first compressor (6b) and the second compressor (7b) under Ausbildu ng a second node (8b) opens into the intake system (2) and in which a further shut-off element (11) is arranged, - downstream of the turbines (6a, 7a) at least one exhaust aftertreatment system (15) in Abgasabführsystem (4) is provided, and - An exhaust gas recirculation is provided, - at the first node (8a) a valve (9) is arranged, and - between the first compressor (6b) and the second compressor (7b) a charge air cooler (5a) is arranged.

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 zwischen der ersten Turbine und der zweiten Turbine unter Ausbildung eines ersten Knotenpunktes vom Abgasabführsystem abzweigt,
• – eine zweite Bypassleitung vorgesehen ist, die stromaufwärts der zweiten Turbine vom Abgasabführsystem abzweigt und die zwischen der ersten Turbine und der zweiten Turbine wieder in das Abgasabführsystem einmündet und in der ein Absperrelement angeordnet ist,
• – eine dritte Bypassleitung vorgesehen ist, die zwischen dem ersten Verdichter und dem zweiten Verdichter unter Ausbildung eines zweiten Knotenpunktes in das Ansaugsystem einmündet und in der ein weiteres Absperrelement angeordnet ist,
• – stromabwärts der Turbinen mindestens ein Abgasnachbehandlungssystem im Abgasabführsystem vorgesehen ist, und
• – eine Abgasrückführung vorgesehen ist.

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

• 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 between the first turbine and the second turbine to form a first node from the exhaust gas removal system,
• A second bypass line is provided, which branches off from the exhaust gas removal system upstream of the second turbine and which opens again into the exhaust gas discharge system between the first turbine and the second turbine and in which a shut-off element is arranged,
• A third bypass line is provided which opens into the intake system between the first compressor and the second compressor to form a second node and in which a further shut-off element is arranged,
• - At least one exhaust aftertreatment system is provided in the Abgasabführsystem downstream of the turbines, and
• - An exhaust gas recirculation is provided.

Furthermore, the invention 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 as a motor vehicle drive. In the context of the present invention, the term internal combustion engine includes gasoline engines, diesel engines, but also hybrid internal combustion engines that use a hybrid combustion process, as well as hybrid drives, which in addition to the internal combustion engine comprise an electric motor which can be connected to the internal combustion engine, which receives power from the internal combustion engine or as switchable auxiliary drive additionally delivers power.

The charging of the internal combustion engine serves primarily to increase performance. The air required for the combustion process is compressed, which allows each cylinder per working cycle, a larger air mass can be supplied. As a result, the fuel mass and thus the medium pressure can be increased.

The charge is a suitable means to increase the capacity of an internal combustion engine with unchanged displacement, or to reduce the displacement at the same power. In any case, the charging leads to an increase in space performance and a lower power mass. If the displacement is reduced, the load spectrum can be shifted to higher loads, where the specific fuel consumption is lower. By charging in combination with a suitable transmission design and a so-called downspeeding can be realized, in which also a lower specific fuel consumption can be achieved.

Charging thus supports the constant effort in the development of internal combustion engines to minimize fuel consumption, d. H. to improve the efficiency of the internal combustion engine.

As a rule, an exhaust gas turbocharger is used for the supercharging, in which a compressor and a turbine are arranged on the same shaft. The hot exhaust stream is supplied to the turbine and relaxes with energy release in this turbine, causing the shaft to rotate. The energy emitted by the exhaust gas flow to the turbine and finally to the shaft is used to drive the compressor, which is also arranged on the shaft. The compressor conveys and compresses the charge air supplied to it, whereby a charging of the cylinder is achieved. Optionally, a charge air cooling is additionally provided, with which the compressed charge air is cooled before entering the cylinder.

The advantage of an exhaust gas turbocharger, for example compared to a mechanical supercharger, is that there is no mechanical connection to the power transmission between the supercharger and the internal combustion engine. While a mechanical supercharger obtains the energy required for its drive completely 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 interpretation of the turbocharger turbocharger is difficult, with basically a noticeable increase in performance in all speed ranges is sought. When charged with an exhaust gas turbocharger internal combustion engines, a noticeable torque drop is observed when falling below a certain speed. This effect is undesirable and one of the disadvantages of turbocharging.

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

The torque characteristic of a charged by turbocharging internal combustion engine is trying to improve the prior art by various measures.

For example, by a small design of the turbine cross-section and simultaneous Abgasabblasung. 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 by means of a bypass line. However, this approach has the disadvantage that the charging behavior at high speeds is insufficient.

The torque characteristic of a supercharged internal combustion engine may be further characterized by a plurality of turbochargers arranged in parallel, i. H. be improved by a plurality of parallel turbines of smaller turbine cross-section, with successively switched turbines with increasing exhaust gas quantity; similar to a register charge.

The torque characteristic can also be advantageously influenced by means of a plurality of exhaust-gas turbochargers connected in series. By switching in series of two exhaust gas turbochargers, one of which is an exhaust gas turbocharger as a high pressure stage and an exhaust gas turbocharger as a low pressure stage, the compressor map can be widened in an advantageous manner, both towards smaller compressor streams as well as towards larger compressor streams.

In particular, in the case of the exhaust gas turbocharger serving as a high-pressure stage, the pumping limit can be shifted toward smaller compressor flows, whereby high boost pressure ratios can be achieved even with small compressor flows, which significantly improves the torque characteristic in the lower rpm range. This is achieved by designing the high-pressure turbine for small exhaust gas mass flows and providing a bypass line, with which increasing exhaust gas mass flow increasingly exhaust gas is passed to the high-pressure turbine. For this purpose, the bypass line branches off the exhaust-gas removal system upstream of the high-pressure turbine and returns to the exhaust-gas removal system upstream of the low-pressure turbine. In the bypass line, a shut-off element is arranged to control the exhaust gas flow passed past the high-pressure turbine. A two-stage rechargeable internal combustion engine of the above type is, for example, in the European patent application EP 1 640 596 A1 described.

The internal combustion engine, which is the subject of the present invention, has at least two turbochargers arranged in series.

Two turbochargers connected in series offer even more advantages beyond those already mentioned. The increase in performance through charging can be further increased. Furthermore, the response of such a supercharged internal combustion engine, especially in the partial load range, significantly improved over a comparable internal combustion engine with single-stage supercharging. The reason for this is that the smaller high-pressure stage is less sluggish than a larger exhaust-gas turbocharger used in the context of a single-stage supercharger because the rotor or impeller of a smaller exhaust-gas turbocharger accelerates and decelerates faster.

This also has advantages in terms of particle emissions. When accelerating, the air mass of the increased fuel quantity to be supplied to the cylinders basically only delays due to the inertia of the wheels. In contrast, with a smaller high-pressure turbocharger, the charge air is supplied to the engine almost instantaneously, which is why operating states with increased particle emission are virtually avoided.

However, the use of multiple turbochargers also has disadvantages. When designing the exhaust turbocharger, efforts are made to arrange the turbine or turbines as close as possible to the outlet of the internal combustion engine, ie near the outlet openings of the cylinders, 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 optimally and to ensure a fast response of the turbocharger. Not only the way of the hot exhaust gases to the turbine is shortened by a close-coupled arrangement, also the volume of Abgasabführsystems upstream of the turbine decreases. The thermal inertia of the Abgasabführsystems also decreases by reducing the mass and the length of the portion of Abgasabführsystems to the turbine. For the reasons mentioned above, the turbines are usually arranged on the exhaust side of the cylinder head. The exhaust manifold is commonly used in the prior art Integrated cylinder head. The integration of the exhaust manifold also allows a dense packaging of the drive unit. In addition, it is possible to participate in a liquid cooling system, which may be provided in the cylinder head, so that the manifold does not have to be manufactured from materials capable of bearing high thermal loads, which are cost-intensive. In a two-stage supercharging prepares the close-coupled arrangement of the turbine of the low pressure stage problems.

Turbocharging also proves to be problematic in combination with exhaust aftertreatment. A two-stage rechargeable internal combustion engine with exhaust aftertreatment is described for example in the European patent application EP 1 396 619 A1 described. The EP 1 396 619 A1 has the simultaneous use of an exhaust turbocharging and exhaust aftertreatment to the object, with the closest possible arrangement of the exhaust aftertreatment system is sought at the outlet of the internal combustion engine. Several concepts are shown.

In an embodiment according to the EP 1 396 619 A1 the exhaust gas flow is controlled 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 downstream of the turbines in the exhaust-gas removal system, in particular 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 passed through the turbines to be regarded as a temperature sink. In this way, the catalyst reaches its light-off temperature faster 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.

A disadvantage of the in the EP 1 396 619 A1 The concept described is that in the warm-up phase of the internal combustion engine, the entire exhaust gas for the purpose of heating the catalysts supplied 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 charge pressure can be generated by utilizing the exhaust gas energy.

The indicated conflict between exhaust turbocharging and exhaust aftertreatment can not be resolved according to the prior art.

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 overcome and with the high load pressures can be generated simultaneously after a cold start and a fast Heating the exhaust aftertreatment systems can be realized.

Another object of the present invention is to provide a method of 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 zwischen der ersten Turbine und der zweiten Turbine unter Ausbildung eines ersten Knotenpunktes vom Abgasabführsystem abzweigt,
• – eine zweite Bypassleitung vorgesehen ist, die stromaufwärts der zweiten Turbine vom Abgasabführsystem abzweigt und die zwischen der ersten Turbine und der zweiten Turbine wieder in das Abgasabführsystem einmündet und in der ein Absperrelement angeordnet ist,
• – eine dritte Bypassleitung vorgesehen ist, die zwischen dem ersten Verdichter und dem zweiten Verdichter unter Ausbildung eines zweiten Knotenpunktes in das Ansaugsystem einmündet und in der ein weiteres Absperrelement angeordnet ist,
• – stromabwärts der Turbinen mindestens ein Abgasnachbehandlungssystem im Abgasabführsystem vorgesehen ist, und
• – eine Abgasrückführung vorgesehen ist, und die dadurch gekennzeichnet ist, dass
• – am ersten Knotenpunkt ein Ventil im Abgasabführsystem angeordnet ist, und
• – im Ansaugsystem zwischen dem ersten Verdichter und dem zweiten Verdichter ein Ladeluftkühler angeordnet ist.

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

• 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 between the first turbine and the second turbine to form a first node from the exhaust gas removal system,
• A second bypass line is provided, which branches off from the exhaust gas removal system upstream of the second turbine and which opens again into the exhaust gas discharge system between the first turbine and the second turbine and in which a shut-off element is arranged,
• A third bypass line is provided which opens into the intake system between the first compressor and the second compressor to form a second node and in which a further shut-off element is arranged,
• - At least one exhaust aftertreatment system is provided in the Abgasabführsystem downstream of the turbines, and
• - An exhaust gas recirculation is provided, and which is characterized in that
• - At the first node, a valve in the Abgasabführsystem is arranged, and
• - In the intake between the first compressor and the second compressor, a charge air cooler is arranged.

The internal combustion engine according to the invention is equipped with two series-connected turbines arranged in series in the exhaust-gas removal system and two compressors which can be switched in series and are arranged in series in the intake system.

Advantageously, therefore, embodiments in which the first compressor is designed to be larger than the second compressor, because in this embodiment of the internal combustion engine or charging the first compressor as part of a two-stage compression forms the low-pressure stage, 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. Because the second turbine is used as a high-pressure turbine in the context of a two-stage charge, while in the first turbine relaxes an exhaust gas flow, which already has a lower pressure and a lower density as a result of passing through the high-pressure stage.

According to the invention, both the turbine of the high-pressure stage and the turbine of the low-pressure stage have a bypass line via which exhaust gas can be conducted past the respective turbine.

During the warm-up phase, the exhaust gas flow, preferably the entire exhaust gas flow, through the second turbine, i. H. passed through the turbine of the high-pressure stage, and downstream of the second turbine via the first bypass line, which branches off from the Abgasabführsystem upstream of the first turbine to form a first node, passed the first turbine and preferably returned to the Abgasabführsystem.

If the exhaust gas flow in the warm-up phase through the smaller second turbine, a sufficiently high boost pressure can be generated. At the same time, by bypassing the first turbine, the larger turbine to be regarded as a temperature sink is eliminated and the hot exhaust gas is fed to the at least one exhaust aftertreatment system, which is why this system reaches its light-off temperature faster after a cold start or in the warm-up phase.

At the first node, at which the first bypass line branches off from the exhaust gas removal system, a valve is arranged, which blocks the Abgasabführsystem to the first turbine and releases the first bypass line in the warm-up phase according to a first operating position, so that the exhaust gas flow past the larger first turbine to be led. This is a significant advantage compared to conventional embodiments in which the valve is arranged in the bypass line itself and, with the valve open, further exhaust gas can flow into the turbine of the low-pressure stage. Although the turbine of the low-pressure stage forms a certain flow resistance even then.

Nonetheless, part of the exhaust flow passes through the larger first turbine. However, this partial flow is a not inconsiderable percentage of the total exhaust gas flow in the operating modes considered here, which is then not directly available to the exhaust aftertreatment system after a cold start for heating.

With the internal combustion engine according to the invention, the first object underlying the invention is achieved, namely provided a supercharged internal combustion engine according to the preamble of claim 1, with the high charge pressures can be generated after a cold start and at the same time a rapid heating of the exhaust aftertreatment systems can be realized.

The internal combustion engine according to the invention is equipped with an exhaust gas recirculation, which comprises a line which branches off from the exhaust gas discharge system and opens into the intake system to recirculate exhaust gas.

To meet future limits for nitrogen oxide emissions, an exhaust gas recirculation is increasingly used, ie the return of exhaust gases from the Abgasabführsystem in the intake system, in which the nitrogen oxide emissions can be significantly reduced with increasing exhaust gas recirculation rate. In this case, the exhaust gas recirculation rate x _{AGR is} determined as x _AGR = m _AGR / (m _AGR + m _{fresh air} ), where m _{AGR denotes} the mass of recirculated exhaust gas and m _{fresh air} the supplied fresh air or combustion air, possibly guided and compressed by a compressor. Exhaust gas recirculation is also suitable for reducing emissions of unburned hydrocarbons in the partial load range.

The at least one exhaust aftertreatment system may be an oxidation catalyst, a three-way catalyst, a storage catalyst, a selective catalyst, and / or a particulate filter.

Embodiments in which the valve arranged at the first node is advantageous according to a second operating position releases the exhaust-gas removal system to the first turbine and obstructs the first bypass line.

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

In the first mode of operation, the valve located at the first node is then in the first working position, whereas the valve is in the second operating position in the second operating mode.

According to the invention, a charge air cooler is arranged in the intake system between the compressors. The intercooler lowers the temperature of the charge air compressed in the low-pressure stage as part of a two-stage compression 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 at the same total pressure ratio of the Aufladegruppe. This also provides protection against thermal overload. By means of intercooler but can also increase the total pressure ratio of the compressor group and thus further increase the performance, d. H. to further boost performance.

The intercooler according to the invention arranged between the compressors also opens up the possibility of omitting a bypass line, which according to the prior art is mandatory to be provided on the high-pressure compressor, d. H. to eliminate. Such a bypass line is not required according to the invention. Either the high-pressure compressor compresses smaller amounts of charge air in the context of a single-stage compression or larger charge air quantities in the context of a two-stage compression, with larger charge air quantities are precompressed in the low-pressure stage and intercooled in the intercooler before the pre-treated charge air in the second compressor stage, d. H. the second compressor enters. Bypassing the second compressor is not required in any of these two modes of operation. A dense packaging of the charge or the entire drive unit is possible.

An operating mode in which charge air is compressed in the low-pressure stage as part of a single-stage compression and then bypassed via the bypass line at the high-pressure compressor is not necessary and preferably also not provided according to the invention. In this respect also eliminates a transfer of the internal combustion engine or the charge in this mode of operation. An unwanted torque drop, which would normally occur in such a transfer, is eliminated with the transfer operation.

In this respect, the internal combustion engine according to the invention also has an improved torque characteristic and a fundamentally improved operating behavior. In individual cases, the internal combustion engine can be charged and operated in two stages at higher loads over the entire speed range according to the second operating mode.

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

Advantageous embodiments of the supercharged internal combustion engine, in which the valve at the first node is a 3-2-way valve, d. H. a valve with three connections and two switching positions.

Advantageous embodiments of the supercharged internal combustion engine, in which the valve at the first node is a pivotable flap.

In this connection, embodiments of the supercharged internal combustion engine in which the flap is pivotable against the exhaust gas flow starting from an obstructed first bypass line when the first bypass line is released are advantageous. Then, the flap, if it is defective, pivoted from the exhaust gas flow into the position in which the first bypass line is blocked, and both turbines are flowed through by the exhaust gas.

Advantageous embodiments of the supercharged internal combustion engine, in which the valve is electrically, hydraulically, pneumatically, mechanically or magnetically controlled, preferably by means of motor control.

Embodiments of the supercharged internal combustion engine in which the first bypass line downstream of the first turbine again opens into the exhaust gas removal system are advantageous.

The fact that the first bypass line opens again into the exhaust-gas removal system has the advantage that the entire exhaust gas can then be supplied to the at least one exhaust-gas aftertreatment system provided in the exhaust-gas removal system.

Therefore, embodiments of the supercharged internal combustion engine in which the first bypass line upstream of the at least one exhaust aftertreatment system provided in the exhaust-gas removal system again opens into the exhaust-gas removal system are also advantageous.

Embodiments of the supercharged internal combustion engine in which at least one further exhaust aftertreatment system is provided in the first bypass line are advantageous. This further exhaust gas aftertreatment system is generally placed closer to the outlet of the internal combustion engine than the at least one exhaust aftertreatment system provided in the exhaust gas removal system. Therefore, this further exhaust aftertreatment system achieves the required light-off temperature faster after a cold start.

Advantageous embodiments of the supercharged internal combustion engine, in which the second bypass line upstream of the first node again opens into the Abgasabführsystem.

If the valve arranged at the first node is then in its first operating position in which the first bypass line is released and the exhaust-gas removal system is blocked to the first turbine, the internal combustion engine is charged in one stage using the second exhaust-gas turbocharger according to a first operating mode, the entire exhaust gas being the first bypass line happens and no exhaust gas is routed to the first turbine.

But can also be advantageous embodiments of the supercharged internal combustion engine, in which the second bypass line downstream of the first node opens again into the Abgasabführsystem.

In contrast to the previous embodiment, the exhaust gas can also be supplied to the first turbine when the valve arranged at the first node blocks the exhaust gas removal system to the first turbine according to its first operating position, namely by the second bypass line being released by opening the shut-off element. In this way, the first turbine can be maintained at a predetermined minimum speed, whereby the response of the charge is improved.

Advantageous embodiments of the supercharged internal combustion engine, in which the third bypass line branches off upstream of the first compressor from the intake system.

Although this bypass line can basically also serve the charge air blow, whereby the charge air compressed in the first compressor is returned. To control the blown or recycled charge air, a further shut-off element is provided in the third bypass line.

However, the third bypass line can also serve for the intake of fresh air and indeed in those cases where hardly or no exhaust gas flows through the first large turbine and therefore makes the second, smaller turbine the compressor work. Then, the first compressor is only a flow resistance for the fresh air sucked in by the second compressor. A bypass line then allows the bypassing of the first compressor and thus a dethrottling of the intake system.

Advantageous embodiments of the supercharged internal combustion engine, in which the third bypass line between the intercooler and the second compressor opens to form the second node in the intake system.

Then, the charge air is not cooled in the context of single-stage compression before entering the high-pressure compressor, but only in the context of two-stage compression between the compressors.

Advantageous embodiments of the supercharged internal combustion engine, in which the first compressor is designed to be larger than the second compressor.

Advantageous embodiments of the supercharged internal combustion engine, in which the first turbine is designed to be larger than the second turbine.

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

A variable turbine geometry increases the flexibility of charging. It allows a stepless adjustment 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 charge can be realized in a wide speed or load range.

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

Embodiments of the supercharged internal combustion engine in which a further intercooler in the intake system is arranged downstream of the compressor are advantageous. The further intercooler lowers the air temperature and thus increases the density of the finally compressed air, whereby the further radiator to a better filling of the combustion chamber with air, d. H. contributes to a larger air mass.

Advantageous embodiments of the supercharged internal combustion engine, in which no bypass line is provided, which bypasses the second compressor.

Embodiments of the supercharged internal combustion engine in which the first turbine has a fixed, unchangeable, are advantageous Turbine geometry has. This embodiment has particular cost advantages. On the one hand eliminates the complex and costly adjustment mechanism in this turbine design. On the other hand, in principle no control of the turbine is necessary.

Embodiments of the supercharged internal combustion engine in which the first compressor has a fixed, unchangeable compressor geometry are advantageous. Solid geometry compressors have cost advantages for the same reasons as fixed geometry turbines, due to their simpler construction.

Advantageous embodiments of the supercharged internal combustion engine, in which the line for exhaust gas recirculation opens downstream of a charge air cooler in the intake system. In this way, the exhaust gas flow is not passed through the intercooler and consequently can not pollute this radiator by deposits of pollutants contained in the exhaust stream, in particular soot particles and oil.

Embodiments of the supercharged internal combustion engine in which an additional cooler is provided in the line for exhaust gas recirculation are advantageous. This additional cooler lowers the temperature in the hot exhaust gas flow and thus increases the density of the exhaust gases. The temperature of the cylinder fresh charge, which occurs during the mixing of the charge air with the recirculated exhaust gases, is consequently further reduced, whereby the additional radiator contributes to a better filling of the combustion chamber with fresh mixture.

Embodiments of the supercharged internal combustion engine in which a shut-off element is provided in the line for exhaust gas recirculation are advantageous. This shut-off element is used to control the exhaust gas recirculation rate.

In order to achieve a significant reduction in nitrogen oxide emissions, high exhaust gas recirculation rates are required, which can be on the order of x _EGR ≈ 60% to 70%.

However, this results in a conflict in the operation of an internal combustion engine with exhaust gas turbocharging and simultaneous use of exhaust gas recirculation, when the recirculated exhaust gas is removed according to a high-pressure EGR upstream of the turbine from the Abgasabführsystem and is no longer available for driving the turbine. Based on a single-stage supercharged internal combustion engine with an exhaust gas turbocharger, this conflict can be easily clarified.

With an increase in the exhaust gas recirculation rate, the remaining exhaust gas flow supplied to the turbine simultaneously decreases. The smaller exhaust gas mass flow through the turbine leads to a smaller turbine pressure ratio. With decreasing turbine pressure ratio, the boost pressure ratio also decreases, which is synonymous with a smaller compressor mass flow. In addition to decreasing boost pressure, additional compressor operation problems may arise with regard to the surge limit of the compressor.

For this reason, it may be advantageous to provide a low pressure EGR, optionally in addition to a high pressure EGR.

Nevertheless, embodiments of the supercharged internal combustion engine can be advantageous, in which a high-pressure EGR is provided.

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

The comments made in connection with the internal combustion engine according to the invention also apply to the inventive method.

Advantageous are process variants in which in the warm-up phase, the first bypass line is released and an exhaust gas flow to the first turbine via the second turbine is inhibited, wherein the internal combustion engine is charged in one stage according to the first operating mode using the second exhaust gas turbocharger.

In the following the invention is based on an embodiment according to the 1 and 2 described in more detail. Hereby shows:

1 schematically a first embodiment of the supercharged internal combustion engine, and

2 schematically the engine map of the first embodiment.

1 shows a first embodiment of the supercharged internal combustion engine 1 the example of a four-cylinder in-line engine. The four cylinders 3 the internal combustion engine 1 are arranged in series along the longitudinal axis of the cylinder head. The exhaust pipes of the cylinders 3 lead to a common Abgasabführsystem 4 together, whereby all the exhaust pipes communicate with each other and in all the exhaust pipes the same exhaust pressure prevails. Furthermore it has the internal combustion engine 1 via an intake system 2 to supply the cylinders 3 with charge air.

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

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

For the same reason, 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 an exhaust stream, which already as a result of passing through the high-pressure stage 7 has a lower pressure and a lower density.

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

Downstream of the turbines 6a . 7a is in the total exhaust gas line 4 an exhaust aftertreatment system 15 intended.

At the in 1 illustrated embodiment, the first turbine 6a via a fixed, unchangeable turbine geometry and a first bypass line 14 that between the first turbine 6a and the second turbine 7a forming a first node 8a from the exhaust system 4 branches. The first bypass line 14 joins downstream of the first turbine 6a and upstream of the exhaust system 4 provided exhaust aftertreatment system 15 back into the exhaust system 4 , At the first junction 8a is a valve 9 , in this case a 3-2-way valve 9 arranged.

The second turbine 7a the second exhaust gas turbocharger 7 has a variable turbine geometry and a second bypass line 12 that is upstream of the second turbine 7a from the exhaust system 4 branches off and between the first turbine 6a and the second turbine 7a downstream of the first node 8a back into the exhaust system 4 opens. In the second bypass line 12 is a shut-off element 13 arranged.

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 forming a second node 8b into the intake system 2 opens. The third bypass line 10 has another shut-off element 11 and flows between the intercooler 5a and the second compressor 7b into the intake system 2 one.

The internal combustion engine 1 is equipped with exhaust gas recirculation (not shown).

2 schematically shows the engine map of the first embodiment according to 1 , The internal combustion engine 1 is either according to a first operating mode A using the second exhaust gas turbocharger 7 single-stage charged or according to a second operating mode B using the first and the second exhaust gas turbocharger 6 . 7 charged in two stages.

LIST OF REFERENCE NUMBERS

1

 charged internal combustion engine

2

 intake system

3

 cylinder

4

 Exhaust system, total exhaust gas line

5a

 Intercooler

5b

 further intercooler

6

 first exhaust gas turbocharger, low-pressure stage

6a

 first turbine

6b

 first compressor

7

 second turbocharger, high-pressure stage

7a

 second turbine

7b

 second compressor

8a

 first node

8b

 second node

9

 Valve, 2-3 way valve

10

 third bypass line

11

 further shut-off element

12

 second bypass line

13

 shut-off

14

 first bypass line

15

 aftertreatment system

A

 first operating mode, single-stage charging

B

 second operating mode, two-stage charging

n _mot

 Engine speed

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• EP 1640596 A1 [0015]
• EP 1396619 A1 [0020, 0020, 0021, 0022]

Claims (17)

Charged internal combustion engine ( 1 ) with an intake system ( 2 ) for supplying charge air and an exhaust gas discharge system ( 4 ) for discharging exhaust gas and with at least two exhaust gas turbochargers connected in series ( 6 . 7 ), each one in Abgasabführsystem ( 4 ) arranged turbine ( 6a . 7a ) and one in the intake system ( 2 ) arranged compressors ( 6b . 7b ) and of which a first exhaust gas turbocharger ( 6 ) as a low-pressure stage ( 6 ) and a second exhaust gas turbocharger ( 7 ) as a high-pressure stage ( 7 ), wherein - the second turbine ( 7a ) of the second exhaust gas turbocharger ( 7 ) 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 ) downstream of the first compressor ( 6b ) of the first exhaust gas turbocharger ( 6 ), - a first bypass line ( 14 ) provided between the first turbine ( 6a ) and the second turbine ( 7a ) forming a first node ( 8a ) from the exhaust gas removal system ( 4 ) branches off, - a second bypass line ( 12 ), which upstream of the second turbine ( 7a ) from the exhaust gas removal system ( 4 ) and between the first turbine ( 6a ) and the second turbine ( 7a ) back into the exhaust gas removal system ( 4 ) and in which a shut-off element ( 13 ), - a third bypass line ( 10 ) provided between the first compressor ( 6b ) and the second compressor ( 7b ) forming a second node ( 8b ) into the intake system ( 2 ) and in which a further shut-off element ( 11 ), - downstream of the turbines ( 6a . 7a ) at least one exhaust aftertreatment system ( 15 ) in the exhaust gas removal system ( 4 ) is provided, and - an exhaust gas recirculation is provided, characterized in that - at the first node ( 8a ) a valve ( 9 ) in the exhaust gas removal system ( 4 ), and - in the intake system ( 2 ) between the first compressor ( 6b ) and the second compressor ( 7b ) a charge air cooler ( 5a ) is arranged. Charged internal combustion engine ( 1 ) according to claim 1, characterized in that the valve ( 9 ) at the first node ( 8a ) a 3-way valve ( 9 ). Charged internal combustion engine ( 1 ) according to claim 1, characterized in that the valve ( 9 ) at the first node ( 8a ) is a pivotable flap. Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that the first bypass line ( 14 ) downstream of the first turbine ( 6a ) back into the exhaust gas removal system ( 4 ) opens. Charged internal combustion engine ( 1 ) according to claim 4, characterized in that the first bypass line ( 14 ) upstream of the at least one exhaust gas removal system ( 4 ) exhaust gas aftertreatment system ( 15 ) back into the exhaust gas removal system ( 4 ) opens. Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that in the first bypass line ( 14 ) at least one further exhaust aftertreatment system is provided. Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that the second bypass line ( 12 ) upstream of the first node ( 8a ) back into the exhaust gas removal system ( 4 ). Charged internal combustion engine ( 1 ) according to one of claims 1 to 6, characterized in that the second bypass line ( 12 ) downstream of the first node ( 8a ) back into the exhaust gas removal system ( 4 ). Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that the third bypass line ( 10 ) upstream of the first compressor ( 6b ) from the intake system ( 2 ) branches off. Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that the third bypass line ( 10 ) between the intercooler ( 5a ) and the second compressor ( 7b ) forming the second node ( 8b ) into the intake system ( 2 ). Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that the first compressor ( 6b ) is designed to be larger than the second compressor ( 7b ). Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that the first turbine ( 6a ) is designed to be larger than the second turbine ( 7a ). Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that the second turbine ( 7a ) of the second exhaust gas turbocharger ( 7 ) has a variable turbine geometry. Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that downstream of the compressor ( 6b . 7b ) another intercooler ( 5b ) in the intake system ( 2 ) is arranged. Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that no bypass line is provided, which the second compressor ( 7b ) bypasses. Method for operating a supercharged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that the internal combustion engine ( 1 ) either according to a first operating mode using the second exhaust gas turbocharger ( 7 ) is charged in one stage or according to a second mode of operation using the first exhaust gas turbocharger ( 6 ) and the second exhaust gas turbocharger ( 7 ) is charged in two stages. A method according to claim 16, characterized in that in the warm-up phase, the first bypass line ( 14 ) and an exhaust gas flow to the first turbine ( 6a ) via the second turbine ( 7a ) is prevented, wherein the internal combustion engine ( 1 ) according to the first operating mode using the second exhaust gas turbocharger ( 7 ) is charged in one stage.

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