DE202014102710U1 - Charged internal combustion engine with exhaust gas turbochargers arranged in series - Google Patents

Abstract

Supercharged internal combustion engine (1) with - an intake system (2) for supplying charge air, - an exhaust gas discharge system (4) for discharging the exhaust gas, and - at least two exhaust gas turbochargers (6, 7) connected in series, each in the exhaust gas discharge system (4) arranged turbine (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) 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) , in which - an auxiliary drive (8) is provided to support an exhaust gas turbocharger (6, 7), characterized in that - the auxiliary drive (8) with the first compressor (6b) of the first exhaust gas turbola serving as a low pressure stage (6) whose (6) is at least drive-connectable.

Description

• – einem Ansaugsystem zum Zuführen von Ladeluft,
• – einem Abgasabführsystem zum Abführen des Abgases, und
• – mindestens zwei in Reihe geschalteten Abgasturboladern, die jeweils eine im Abgasabführsystem angeordnete Turbine und einen im Ansaugsystem angeordneten Verdichter umfassen und von denen ein erster Abgasturbolader als Niederdruckstufe und ein zweiter Abgasturbolader als Hochdruckstufe dient, wobei 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 angeordnet ist, bei der
• – ein Hilfsantrieb zur Unterstützung eines Abgasturboladers vorgesehen ist.

The invention relates to a supercharged internal combustion engine with

• An intake system for supplying charge air,
• An exhaust gas discharge system for discharging the exhaust gas, and
• At least two exhaust gas turbochargers connected in series, each comprising a turbine arranged in the exhaust gas removal system and a compressor arranged in the intake system, of which a first exhaust gas turbocharger serves as a low pressure stage and a second exhaust gas turbocharger as a high pressure stage, the second turbine of the second exhaust gas turbocharger upstream of the first turbine of the first exhaust gas turbocharger the first exhaust gas turbocharger is arranged and the second compressor of the second exhaust gas turbocharger is arranged downstream of the first compressor, in which
• - An auxiliary drive to support an exhaust gas turbocharger is provided.

Such an internal combustion engine describes the US 2013/0209291 A1 , wherein the electric auxiliary drive supports the compressor of the second exhaust gas turbocharger serving as a high-pressure stage, ie can drive.

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 diesel engines and gasoline engines, but also hybrid internal combustion engines, which use a hybrid combustion process, and hybrid drives, which in addition to the internal combustion engine comprise an electric motor which can be electrically connected to the internal combustion engine, which receives power from the internal combustion engine or as switchable auxiliary drive additionally delivers power.

In recent years, there has been a trend toward small, supercharged engines, with supercharging primarily a method of increasing performance by compressing the air needed for the engine combustion process. The economic importance of these engines for the automotive industry continues to increase.

Frequently, an exhaust gas turbocharger is used for charging, 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 the 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. Advantageously, a charge air cooler is provided downstream of the compressor in the intake system, with which the compressed charge air is cooled before entering the at least one cylinder. The radiator lowers the temperature and thus increases the density of the charge air, so that the cooler to a better filling of the cylinder, d. H. contributes to a larger air mass. There is a compaction by cooling.

The advantage of an exhaust gas turbocharger compared to a mechanical supercharger is that there is no mechanical connection to the power transmission between the supercharger and the internal combustion engine or is required. 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 charge is - as already mentioned - the increase in 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, then the load spectrum can be shifted to higher loads, where the specific fuel consumption is lower. By charging in combination with suitable transmission designs and a so-called downspeeding can be realized, in which also a lower specific fuel consumption can be achieved. Charging therefore 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.

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.

Another fundamental goal is to reduce pollutant emissions. In the solution of this task, the charging can also be effective. With targeted design of the charge Namely advantages in efficiency and exhaust emissions can be achieved.

The interpretation of the turbocharger turbocharger is difficult, with basically a noticeable increase in performance in all speed ranges is sought. In the prior art, however, a strong torque drop is observed when falling below a certain speed. This effect is undesirable because the driver expects a correspondingly large torque in the lower speed range in comparison with a non-supercharged engine of the same maximum power, and is one of the most serious 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. If the engine speed is reduced, this leads to a smaller exhaust gas mass flow and thus to a smaller turbine pressure ratio. Consequently, the boost pressure ratio also decreases toward lower speeds. This is synonymous with a torque drop.

In practice, the relationships described above often result in a small exhaust gas turbocharger, i. H. an exhaust gas turbocharger with a small turbine cross section is used, whereby the turbine pressure ratio can be increased. However, this degrades the charge at high speeds and shifts the torque drop only towards low speeds. In addition, this approach, d. H. the reduction of the turbine cross-section limits, since the desired charging and performance increase should be possible without restriction and to the desired extent, even at high speeds.

The torque characteristic of a supercharged internal combustion engine is tried to improve in the prior art by various measures.

For example, by a small design of the turbine cross-section and simultaneous Abgasabblasung, the Abgasabblasung can be controlled by means of boost pressure or by means of exhaust pressure. Such a turbine is also referred to as a waste gate turbine. If the exhaust gas mass flow exceeds a critical size, part of the exhaust gas flow is conducted past the turbine by means of a bypass line as part of the so-called exhaust gas blow-off. However, this approach has - as already mentioned above - the disadvantage that the charging behavior at higher speeds is insufficient.

The torque characteristic of a supercharged internal combustion engine may be increased by a plurality of turbochargers arranged in parallel, i. H. be improved by a plurality of parallel turbines of smaller turbine cross-section, with turbines are switched successively with increasing exhaust gas quantity.

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 engine map can be widened in an advantageous manner, both towards smaller compressor streams and towards larger compressor streams. The internal combustion engine, which is the subject of the present invention, has at least two in series, d. H. exhaust turbocharger connected in series.

In particular, in the case of the exhaust gas turbocharger serving as a high-pressure stage, the pumping limit can be shifted towards smaller compressor flows, which means that 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.

The downsizing is continued by a multi-stage turbocharger charge. Furthermore, the response of such a supercharged internal combustion engine is significantly improved over a comparable internal combustion engine with single-stage supercharging. The smaller high-pressure stage is less sluggish, because the running gear of a smaller exhaust gas turbocharger accelerates faster. The smaller and lighter rotor of a smaller sized exhaust gas turbocharger has but in the context of multi-stage or two-stage charging also adverse effects.

Because the low-pressure compressor is designed to be larger than the downstream high-pressure compressor and thus the low-pressure compressor has the larger and heavier rotor than the high-pressure compressor, the Low-pressure compressor follow the high-pressure compressor in a load change, ie at an increased power requirement on the part of the driver, not delay. In this case, the delayed response of the low-pressure compressor leads to a decrease in pressure, ie to an unwanted pressure drop between the low-pressure compressor and the downstream high-pressure compressor.

Due to the low pressure between the compressors, oil is sucked from the loader shaft bearings into the intake system which, together with the charge air, enters the cylinders, participates in combustion and results in unfavorable increases in pollutant emissions, particularly unburned hydrocarbons and the particle.

Based on an unchanged boost pressure ratio at the high pressure compressor results from the pressure reduction between the compressors, through which the input pressure is lowered at the high pressure compressor, also a lower pressure at the outlet of the high pressure compressor, which simultaneously represents the boost pressure at the inlet into the cylinders of the internal combustion engine. The cylinders are therefore supplied with less charge air than requested and required to meet the power requirement at an increased power demand.

Against this background, it is the 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 their charging behavior is noticeably improved, especially under transient operating conditions.

• – einem Ansaugsystem zum Zuführen von Ladeluft,
• – einem Abgasabführsystem zum Abführen des Abgases, und
• – mindestens zwei in Reihe geschalteten Abgasturboladern, die jeweils eine im Abgasabführsystem angeordnete Turbine und einen im Ansaugsystem angeordneten Verdichter umfassen und von denen ein erster Abgasturbolader als Niederdruckstufe und ein zweiter Abgasturbolader als Hochdruckstufe dient, wobei 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 angeordnet ist, bei der
• – ein Hilfsantrieb zur Unterstützung eines Abgasturboladers vorgesehen ist,

und die dadurch gekennzeichnet ist, dass

• – der Hilfsantrieb mit dem ersten Verdichter des ersten als Niederdruckstufe dienenden Abgasturboladers zumindest antriebsverbindbar ist.

This problem is solved by a supercharged internal combustion engine

• An intake system for supplying charge air,
• An exhaust gas discharge system for discharging the exhaust gas, and
• At least two exhaust gas turbochargers connected in series, each comprising a turbine arranged in the exhaust gas removal system and a compressor arranged in the intake system, of which a first exhaust gas turbocharger serves as a low pressure stage and a second exhaust gas turbocharger as a high pressure stage, the second turbine of the second exhaust gas turbocharger upstream of the first turbine of the first exhaust gas turbocharger the first exhaust gas turbocharger is arranged and the second compressor of the second exhaust gas turbocharger is arranged downstream of the first compressor, in which
• An auxiliary drive is provided to support an exhaust gas turbocharger,

and which is characterized in that

• - The auxiliary drive with the first compressor of the first low-pressure stage exhaust gas turbocharger is at least drive-connected.

If the pressure between the compressors decreases unfavorably because, for example, the inertial low-pressure compressor can not follow the smaller-sized high-pressure compressor quickly enough with an increased load requirement, the internal combustion engine can be equipped with the first compressor, d. H. accelerate the running gear of this first compressor, using an auxiliary drive and thereby increase the pressure between the compressors and to counteract a further pressure drop between the compressors.

An unfavorable decrease of the boost pressure at the inlet of the cylinder can be avoided. The cylinders are supplied with the amount of charge air required to meet the power requirement even with an increased power demand.

The risk that due to the low pressure or negative pressure between the compressors oil is fed into the charge air or promoted and participates in the combustion, can be eliminated.

As a result, the object underlying the invention is achieved, namely provided a supercharged internal combustion engine, with which the disadvantages known from the prior art are overcome and their charging behavior is noticeably improved, especially under transient operating conditions.

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

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

The internal combustion engine according to the invention is equipped with two turbines arranged in series, arranged in the exhaust-gas removal system, and two compressors arranged in series and arranged in the intake system. It is therefore advantageous to make the first compressor larger than the second compressor, since in this arrangement, the second compressor compresses the already pre-compressed in the low-pressure stage air, d. H. forms 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 serves as a high-pressure turbine while itself relaxed in the first turbine, an exhaust stream, which already as a result of passing through the high-pressure stage has a lower pressure and a lower density.

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

Also advantageous are embodiments of the internal combustion engine in which a first bypass line is provided, in which a shut-off element is arranged and branches off upstream of the second turbine from Abgasabführsystem and opens downstream of this second turbine back into the Abgasabführsystem.

In the present case, the turbine of the high-pressure stage has a variable turbine geometry and / or a bypass line, by means of which, when the turbine bypasses, exhaust gas can be conducted past the high-pressure turbine.

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, in particular to the current exhaust gas mass flow. Unlike a fixed-geometry turbine, the turbine does not have to be designed for specific amounts of exhaust gas, which is why the turbine provides a satisfactory boost in a wide range of speeds and loads, namely the desired charge pressure on the intake side.

In particular, the combination of turbine with variable turbine geometry and a bypass line bridging this turbine allows the design of the high-pressure turbine to very 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.

With an appropriate design of the high-pressure compressor, the surge limit is shifted towards smaller compressor flows, which high charge pressure ratios can be achieved even with small exhaust gas streams or compressor streams, whereby the charge is optimized in the lower part load range. In this load range, the majority of the exhaust gas flow is passed through the second turbine. However, it is also possible for the entire exhaust gas flow to be conducted completely through the second turbine of the second exhaust gas turbocharger. To generate high boost pressures in the lower and middle part load range of the exhaust gas flow is essentially passed through the small turbine of the high-pressure stage.

With increasing load or increasing amount of exhaust gas, an increasing proportion of the exhaust gas flow is conducted past the high-pressure turbine via the first bypass line. Downstream of the high-pressure turbine, the exhaust gas then flows through the first turbine, d. H. the turbine of the low pressure stage. This first turbine can be designed for large exhaust gas mass flows, so that the first exhaust gas turbocharger with large exhaust gas mass flows, as they occur at high loads, especially at full load, ensures a sufficiently high boost pressure.

Consequently, a high boost pressure can be realized in all operating points of the internal combustion engine. In contrast to conventional supercharging concepts, no compromise has to be made in the design of the exhaust gas turbocharger in order to realize more or less satisfactory charging in all engine speed ranges.

Embodiments of the internal combustion engine are advantageous in which, for the purpose of Abgasabblasung a second bypass line is provided, which branches off upstream of the first turbine from Abgasabführsystem and preferably downstream of this first turbine back into the Abgasabführsystem, advantageously for controlling the Abgasabblasung a shut-off in the second bypass line is provided.

In particular, when the low-pressure turbine has a fixed, unchangeable geometry, with increasing exhaust gas flow, a larger proportion of the exhaust gas can be guided past the turbine via the second bypass line. To control the Abgasabblasung a shut-off is provided in the bypass line. Such a wastegate turbine is less expensive than a variable geometry turbine. In addition, the control is simpler and therefore also cheaper than a variable turbine geometry.

According to the embodiment in question, the turbine of the low pressure stage is not designed for the maximum amount of exhaust gas incurred, so that in these amounts of exhaust gas even with the larger-sized low-pressure turbine has a Abgasabblasung to make.

Nevertheless, embodiments of the internal combustion engine can be advantageous in which the first turbine has a variable turbine geometry. The statements made above for the high-pressure turbine have analogous validity for the low-pressure turbine, which is why reference is made to these statements.

Embodiments of the internal combustion engine in which the first compressor is equipped with a third bypass line are advantageous branches off from the intake system downstream of the first compressor.

The third bypass line can serve the charge air blower and can flow back into the intake system upstream of the first compressor, whereby the charge air compressed in the first compressor is not blown off, but only returned. To control the blown or recycled charge air, a shut-off element is provided in the bypass line.

The third bypass line can also serve for the intake of charge air and that in cases where hardly any exhaust gas flows through the first large turbine, but the second smaller turbine and therefore the second smaller compressor performs at least the vast compressor work. Then the first compressor is only a flow resistance for the charge air sucked in by the second compressor. The third bypass line allows the bypassing of the first compressor and thus a de-throttling.

Advantageous embodiments of the internal combustion engine, in which the first compressor has a fixed, unchangeable compressor geometry.

But can also be advantageous embodiments of the internal combustion engine, in which the first compressor has a variable compressor geometry. Advantages of the variable compressor geometry of the first compressor, especially in the operating conditions in which hardly any exhaust gas flows through the first, larger turbine and therefore little power is provided by the first turbine to compress the charge air. In these cases, the first compressor only represents a flow resistance for the fresh air sucked in by the second compressor. A variable compressor geometry then allows the intake line to be de-throttled by increasing the flow cross-section of the first compressor.

Embodiments of the internal combustion engine in which a fourth bypass line is provided, which branches off from the intake system upstream of the second compressor and opens into the intake system again downstream of this second compressor, wherein a shut-off element is arranged in this fourth bypass line.

The fourth bypass line allows the bypass of the high pressure compressor. This allows the tuning of the charge air mass flow guided by the high-pressure compressor to the exhaust gas mass flow guided through the high-pressure turbine and thus to the available turbine power.

In the cases in which the exhaust gas predominantly or completely flows through the first large turbine and therefore the second, smaller turbine delivers almost no or no power and the first, large compressor almost alone or completely generates the necessary boost pressure, the second Compressor only a flow resistance for the compressor sucked by the first and compressed charge air on the way to the cylinders. A fourth bypass line then allows the bypass of the second compressor.

The shut-off allows the division of the charge air flow into partial streams, namely in a partial flow, which is passed through the fourth bypass line, and a partial flow, which is passed through the high-pressure compressor.

Embodiments of the internal combustion engine in which the second compressor has a variable compressor geometry (VVG) can also be advantageous. This embodiment is particularly advantageous when the turbine of the second exhaust gas turbocharger has a variable turbine geometry, since the compressor geometry can be continuously adapted to the turbine geometry.

In particular, if only a small exhaust gas mass flow is passed through the second turbine, a variable compressor geometry proves to be advantageous, since by adjusting the blades, the surge limit of the compressor in the compressor map to small compressor flows can be moved, thus avoiding working of the compressor beyond the surge line becomes.

Advantages of the variable compressor geometry of the second compressor but especially in the operating conditions in which the exhaust predominantly or completely flows through the first large turbine and the second, smaller turbine gives almost no or no power and the first, large compressor almost alone or completely generates the necessary boost pressure. In these cases, the second compressor merely provides a flow resistance for the fresh air drawn in and compressed by the first compressor on the way to the cylinders. A variable compressor geometry then allows the intake line to be throttled by increasing the flow cross-section of the second compressor. A variable compressor geometry can make the fourth bypass line superfluous in individual cases, since the compressor can be adapted to the charge air flow. For this purpose, the geometry of the compressor or the flow cross-section of the compressor must be adjustable over a wide range, so that the compressor can be adapted to both very small and very large charge air flows.

But can also be advantageous embodiments of the internal combustion engine, in which the second compressor has a fixed, unchangeable compressor geometry. In contrast to the previously described variable geometry compressor, control is eliminated. There are cost advantages.

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

Embodiments of the supercharged internal combustion engine in which exhaust gas recirculation is provided are advantageous.

Advantageous in this connection are embodiments of the supercharged internal combustion engine in which an exhaust gas recirculation is provided which comprises a line which branches off from the exhaust gas removal system upstream of the two turbines and opens into the intake system, preferably downstream of the compressor.

To comply with future limits for nitrogen oxide emissions, an exhaust gas recirculation is increasingly used, ie the return of exhaust gases from the exhaust side to the inlet side, 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 by x _AGR = m _AGR / (m _AGR + m _{fresh air} ), where m _{AGR is} the mass of recirculated exhaust gas and m _{fresh air is} 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.

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%.

Embodiments in which the line for exhaust gas recirculation leads downstream of a charge air cooler into the intake system are advantageous. 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 in which an additional cooler is provided in the exhaust gas recirculation line 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 in the mixture of fresh air with the recirculated exhaust gases, is consequently further reduced, whereby the additional radiator contributes to a better filling of the combustion chamber with charge air.

Embodiments 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 or the mass fraction of combustion products.

Also advantageous are embodiments of the supercharged internal combustion engine in which an exhaust gas recirculation is provided, which comprises a line which branches off from the Abgasabführsystem downstream of the two turbines and opens into the intake system, preferably upstream of the compressor.

In contrast to the high-pressure EGR already mentioned, which removes exhaust gas from the exhaust-gas removal system upstream of the turbines and introduces into the intake system downstream of the compressor, in a low-pressure EGR, exhaust gas is returned to the inlet side, which has already passed through the turbines. For this purpose, the low-pressure EGR comprises a return line, which branches off downstream of the turbines from the Abgasabführsystem and opens upstream of the compressor in the intake system.

The exhaust gas, which is returned to the inlet side by means of low-pressure EGR and is preferably cooled, is mixed with fresh air upstream of the compressor. The mixture of fresh air and recirculated exhaust gas produced in this way forms the charge air, which is supplied to the compressors and compressed.

It is harmless that, as part of the low-pressure EGR exhaust gas is passed through the compressor, since usually exhaust gas is used, which downstream of the turbines of an exhaust aftertreatment, in particular in the particulate filter was subjected. Deposits in the compressor, which change the geometry of the compressor, in particular the flow cross-sections, and thus worsen the efficiency of the compressor, are therefore not to be feared.

Embodiments of the internal combustion engine in which the auxiliary drive is a mechanically driven auxiliary drive are advantageous.

Embodiments of the internal combustion engine in which the auxiliary drive is an electrically driven auxiliary drive are advantageous. In contrast to a mechanically driven auxiliary drive no mechanical connection to the internal combustion engine is required.

Embodiments of the internal combustion engine in which the auxiliary drive is at least drive-connectable to the shaft of the first exhaust-gas turbocharger serving as a low-pressure stage are advantageous.

Embodiments of the internal combustion engine in which the shut-off element in the first, second, third and / or fourth bypass line is a valve or a throttle flap are advantageous.

In this case, embodiments in which the shut-off element is electrically, hydraulically, pneumatically, mechanically or magnetically controllable, preferably by means of motor control, are advantageous.

Embodiments in which the second exhaust gas turbocharger serves as an auxiliary drive are advantageous. Thus, the two shafts of the exhaust gas turbocharger can be drivingly connected to each other, optionally with the interposition of a transmission.

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

1 schematically a first embodiment of the internal combustion engine.

1 shows a first embodiment of the supercharged internal combustion engine 1 the example of a three-cylinder in-line engine.

For removing the hot exhaust gases via Abgasabführsystem 4 have the three cylinders arranged in series 3 each via an exhaust pipe, which to a common exhaust pipe 4a to merge. Furthermore, the cylinders have 3 each via a suction line for supplying charge air via intake system 2 ,

The internal combustion engine 1 is with two turbochargers connected in series 6 . 7 equipped, each one in the exhaust system 4 arranged turbine 6a . 7a and one in the intake system 2 arranged compressor 6b . 7b comprising, wherein 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 serves. The second turbine 7a the second exhaust gas turbocharger 7 is upstream of the first turbine 6a of the first exhaust gas turbocharger 6 in the common exhaust pipe 4a arranged and the second compressor 7b the second exhaust gas turbocharger 7 downstream of the first compressor 6b in the common intake pipe 2a ,

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

Downstream of the compressors 6b . 7b is a charge air cooler 5 in the common intake pipe 2a arranged. The intercooler 5 lowers the charge air temperature and thus increases the density of the air, which is why the radiator 5 to a better filling of the cylinder 3 contributes with charge air.

The internal combustion engine 1 may further be provided with an exhaust gas recirculation, which includes a conduit upstream and downstream of the two turbines 6a . 7a from the common exhaust pipe 4a branches off and downstream or upstream of the two compressors 6b . 7b in the intake pipe 2a flows (not shown).

The second turbine 7a the second exhaust gas turbocharger 7 has a variable turbine geometry (indicated by the arrow). In addition, a first bypass line 9 provided upstream of the second turbine 7a from the exhaust pipe 4a branches off and downstream of this second turbine 7a back into the exhaust pipe 4a opens, wherein in the bypass line 9 a shut-off element 10 is arranged.

The combination of variable turbine geometry and bypass line 9 allows the design of the high-pressure turbine 7a on the lower part load range or on very small exhaust gas mass flows, whereby the charge is improved in this load range. As a result, a high charge pressure is generated even at the lower part load range and at the same time a sufficiently high exhaust back pressure is provided, which is required or can be used for exhaust gas recirculation by means of high-pressure EGR.

When in the 1 illustrated embodiment, the first turbine 6a via a fixed, unchangeable turbine geometry. For the purpose of Abgasabblasung is a second bypass line 11 provided upstream of the first turbine 6a from the exhaust pipe 4a branches off and downstream of this first turbine 6a back into the exhaust pipe 4a opens, wherein for controlling the Abgasabblasung a shut-off 12 in the second bypass line 11 is provided. This is the turbine 6a the low pressure stage 6 designed as a so-called waste gate turbine.

The compressors 6b . 7b may have a fixed geometry or also be designed with a variable geometry. A variable geometry is advantageous if the associated turbine 6a . 7a has a variable turbine geometry and the compressor geometry is continuously tuned to the turbine geometry.

The first compressor 6b can with a third bypass line 13 equipped (indicated by dashed lines), the downstream of the first compressor 6b from the intake pipe 2a branches. This bypass line 13 Serves the charge air blower and can be upstream of the first compressor 6b back into the intake pipe 2a open, causing the first compressor 6b compressed charge air is not blown off, but only returned.

To control the blown or recycled fresh air quantity is a shut-off 14 in the third bypass line 13 intended. The third bypass line 13 can also bypass the first compressor 6b serve, via the high pressure compressor 7b Charge air sucks.

To support the first exhaust gas turbocharger 6 is an auxiliary drive 8th provided with the first compressor 6b the first as a low pressure stage 6 serving exhaust gas turbocharger 6 at least drive-connected.

The auxiliary drive 8th is used at an increased load request, ie activated to the pressure between the compressors 6b . 7b increase or counteract a boost pressure drop counter.

LIST OF REFERENCE NUMBERS

1

 charged internal combustion engine

2

 intake system

2a

 common intake pipe

3

 cylinder

4

 Abgasabführsystem

4a

 common exhaust pipe

5

 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

8th

 auxiliary drive

9

 first bypass line

10

 shut-off

11

 second bypass line

12

 shut-off

13

 third bypass line

14

 shut-off

AGR

 Exhaust gas recirculation

m _AGR

 Mass of recirculated exhaust gas

_{Fresh air}

 Mass of supplied fresh air or combustion air

x _AGR

 Exhaust gas recirculation rate

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

• US 2013/0209291 A1 [0002]

Claims (14)

Charged internal combustion engine ( 1 ) with an intake system ( 2 ) for supplying charge air, - an exhaust gas removal system ( 4 ) for discharging the exhaust gas, and - 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 ), 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 ) is arranged, in which - an auxiliary drive ( 8th ) to support an exhaust gas turbocharger ( 6 . 7 ), characterized in that - the auxiliary drive ( 8th ) with the first compressor ( 6b ) of the first as a low-pressure stage ( 6 ) exhaust gas turbocharger ( 6 ) is at least drive connectable. Charged internal combustion engine ( 1 ) according to claim 1, characterized in that the first compressor ( 6b ) is designed to be larger than the second compressor ( 7b ). Charged internal combustion engine ( 1 ) according to claim 1 or 2, 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 a first bypass line ( 9 ) is provided, in which a shut-off ( 10 ) and the upstream of the second turbine ( 7a ) from the exhaust gas removal system ( 4 ) branches off and downstream of this second turbine ( 7a ) back into the exhaust gas removal system ( 4 ) opens. Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that for the purpose of Abgasabblasung a second bypass line ( 11 ) provided upstream of the first turbine ( 6a ) from the exhaust gas removal system ( 4 ) branches off and downstream of this first turbine ( 6a ) back into the exhaust gas removal system ( 4 ), wherein for controlling the Abgasabblasung a shut-off ( 12 ) in the second bypass line ( 11 ) is provided. Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that the first compressor ( 6b ) with a third bypass line ( 13 ) downstream 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 first compressor ( 6b ) has a fixed, unchangeable compressor geometry. Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that a fourth bypass line is provided upstream of the second compressor ( 7b ) from the intake system ( 2 ) branches off and downstream of this second compressor ( 7b ) back into the intake system ( 2 ), wherein in this fourth bypass line a shut-off element is arranged. Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that downstream of the compressor ( 6b . 7b ) a charge air cooler ( 5 ) in the intake system ( 2 ) is arranged. Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that the auxiliary drive ( 8th ) a mechanically driven auxiliary drive ( 8th ). Charged internal combustion engine ( 1 ) according to one of claims 1 to 10, characterized in that the auxiliary drive ( 8th ) an electrically driven auxiliary drive ( 8th ). Charged internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that the auxiliary drive ( 8th ) with the shaft of the first as a low-pressure stage ( 6 ) exhaust gas turbocharger ( 6 ) is at least drive connectable. Charged internal combustion engine ( 1 ) according to one of claims 1 to 11 or claim 13, characterized in that as an auxiliary drive ( 8th ) the second exhaust gas turbocharger ( 7 ) serves.

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