DE102014220655A1 - A spark-ignition internal combustion engine with two exhaust gas turbochargers and method for operating such an internal combustion engine - Google Patents

Abstract

The invention relates to a spark ignition internal combustion engine (1) having - at least one cylinder head, - an intake system (7) for supplying charge air, - an exhaust system (3) for discharging the exhaust gases, - at least one cylinder (2), each cylinder (2 ) has at least one outlet opening and at each outlet opening an exhaust pipe (3a) for discharging the exhaust gases via Abgasabführsystem (3) connects, and - two exhaust gas turbochargers (5, 6), each of which in the intake system (7) arranged compressor (5b, 6b) and in the Abgasabführsystem (3) arranged turbine (5a, 6a). It is an internal combustion engine (1) are provided, the exhaust gas turbocharging is further improved. This object is achieved by an internal combustion engine (1) of the type mentioned, which is characterized in that - the turbine (5a) of a first exhaust gas turbocharger (5) has a variable turbine geometry, - the turbine (6a) of a second exhaust gas turbocharger (6) has a fixed invariable geometry, and - a switching device (11) is provided, either the turbine (5a) of the first exhaust gas turbocharger (5) or the turbine (6a) of the second exhaust gas turbocharger (6) via Abgasabführsystem (3) with at least one Cylinder (2) connects.

Description

• – mindestens einem Zylinderkopf,
• – einem Ansaugsystem zum Zuführen von Ladeluft,
• – einem Abgasabführsystem zum Abführen der Abgase,
• – mindestens einem Zylinder, wobei jeder Zylinder mindestens eine Auslassöffnung aufweist und sich an jede Auslassöffnung eine Abgasleitung zum Abführen der Abgase via Abgasabführsystem anschließt, und
• – zwei Abgasturboladern, von denen jeder einen im Ansaugsystem angeordneten Verdichter und eine im Abgasabführsystem angeordnete Turbine aufweist.

The invention relates to a spark-ignition internal combustion engine with

• At least one cylinder head,
• An intake system for supplying charge air,
• An exhaust gas removal system for discharging the exhaust gases,
• - At least one cylinder, each cylinder having at least one outlet opening and is connected to each outlet opening an exhaust pipe for discharging the exhaust gases via Abgasabführsystem, and
• - Two exhaust gas turbochargers, each of which has a compressor disposed in the intake and a turbine disposed in the Abgasabführsystem turbine.

Furthermore, the invention relates to a method for operating such an internal combustion engine.

In the context of the present invention, the term internal combustion engine or spark-ignited internal combustion engine includes in particular spark ignited gasoline engines, but also hybrid internal combustion engines, which use a hybrid combustion process with spark ignition, and hybrid propulsion systems, which in addition to the spark-ignited internal combustion engine comprise an electric machine which can be drive-connected to the internal combustion engine, which power from the internal combustion engine absorbs or gives additional power as a switchable auxiliary drive.

Internal combustion engines have a cylinder block and at least one cylinder head, which are connected together to form the cylinder. In order to control the charge cycle, an internal combustion engine requires control devices - usually in the form of globe valves - and actuators to operate these controls. The required for the movement of the valves valve actuating mechanism including the valves themselves is referred to as a valve train. Often, the cylinder head serves to accommodate the valve train.

As part of the change of charge, the exhaust gases are exhausted via the outlet openings of the cylinders and the cylinders are filled with charge air via the inlet openings. It is the task of the valve drive to release the intake and exhaust ports in time or to close, with a quick release of the largest possible flow cross sections is sought to keep the throttle losses in the incoming and outflowing gas flows low and the best possible filling or an effective, d. H. To ensure complete removal of the exhaust gases. In the prior art, therefore, each cylinder is also often equipped with two or more inlet and outlet ports.

The inlet ducts leading to the inlet openings and the exhaust ducts adjoining the outlet openings are at least partially integrated in the cylinder head according to the prior art. The exhaust pipes of the cylinders are usually combined to form a common total exhaust gas line or in groups to two or more total exhaust gas lines. The combination of exhaust pipes to an overall exhaust line is generally and in the context of the present invention referred to as exhaust manifold. The Abgasabführsystem the internal combustion engine according to the invention is a coherent Abgasabführsystem, in which the exhaust pipes of all cylinders of a cylinder head are in communication with each other.

Downstream of the outlet openings, the exhaust gases in the present case are supplied to the turbocharger of an exhaust gas turbocharger for charging the internal combustion engine and, if appropriate, one or more systems for exhaust gas aftertreatment.

The advantages of an exhaust gas turbocharger, for example compared to a mechanical supercharger, are 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.

An exhaust gas turbocharger includes a compressor and a turbine disposed 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, as a result of which charging of the at least one cylinder is achieved. Optionally, a charge air cooling is provided, with which the compressed charge air is cooled before entering the at least one cylinder.

The charge is used primarily to increase the performance of the internal combustion engine. The air required for the combustion process is compressed, which allows each cylinder per working cycle, a larger air mass can be supplied. This allows the fuel mass and thus the medium pressure 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 charge leads to an increase in engine capacity and a lower power mass. At the same vehicle boundary conditions, the load collective can thus be shifted to higher loads in which the specific fuel consumption is lower.

The design of the exhaust turbocharger often causes difficulties, in principle, a noticeable increase in performance in all speed ranges is sought. In the prior art, however, a torque drop is observed when falling below a certain speed. 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, the boost pressure ratio and the charge pressure also decrease at lower speeds, which is equivalent to a torque drop.

In principle, the drop in charge pressure can be counteracted by reducing the size of the turbine cross-section and the associated increase in the turbine pressure ratio. Thus, the torque drop is only shifted to lower speeds. In addition, this approach, d. H. the reduction of the turbine cross-section limits, as the exhaust back pressure upstream of the turbine increases towards larger amounts of exhaust gas, whereby the charge cycle is adversely affected and fuel consumption is increased.

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. 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. This approach has the disadvantage that the charging behavior at higher speeds or larger amounts of exhaust gas is insufficient.

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 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 from the exhaust-gas removal system upstream of the high-pressure turbine and flows back into the exhaust-gas removal system upstream of the low-pressure turbine, wherein a shut-off element is arranged in the bypass line in order to control the exhaust gas flow conducted past the high-pressure turbine.

The response of such a supercharged internal combustion engine is significantly improved over a comparable internal combustion engine with single-stage charging, since the smaller high-pressure stage is less sluggish and can accelerate the running gear of a smaller sized exhaust gas turbocharger faster.

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 with a smaller turbine cross-section, with increasing exhaust gas quantity - similar to a register charging - turbines are switched successively.

The turbocharger can also be used at high speeds, d. H. large volumes of exhaust gas to be designed with a large turbine cross section. In this case, the suction system is preferably designed in such a way that a dynamic charging takes place by wave processes at low speeds. Disadvantages are the high construction costs and the sluggish behavior with changes in speed.

A turbine with variable turbine geometry allows an adjustment of the turbine geometry or the effective turbine cross section at the respective operating point of the internal combustion engine, so that a control of the turbine geometry both in terms of lower and higher speeds as well as in terms of lower and higher Loads can be made. In this case, adjustable guide vanes for influencing the flow direction are arranged in the inlet region of the turbine. Unlike the vanes of the rotating impeller, the vanes do not rotate with the shaft of the turbine. If the turbine has a fixed invariable geometry, the vanes are not only stationary, but also completely immovable arranged in the inlet region, ie rigidly fixed. With a variable geometry, however, the vanes are indeed arranged stationary, but not completely immobile, but rotatable about its axis, so that the flow of the blades can be influenced.

Turbines with variable turbine geometry are used in the prior art almost without exception in diesel engines. Due to the high or higher exhaust gas temperatures, such turbines are of minor importance in spark-ignited internal combustion engines. The production costs for the thermally highly stressed turbine and the adjustable, also thermally highly loaded guide are very high, especially compared to the cost of a waste gate turbine commonly used. Not only the material costs per se are comparatively high, but also the costs for the processing of these materials.

From the above, it follows that in spark-ignited internal combustion engines to form a one-stage charging usually waste-gate turbines are used, namely at the expense of the associated and already mentioned disadvantages.

In view of the foregoing, it is an object of the present invention to provide a spark-ignition internal combustion engine according to the preamble of claim 1, whose exhaust gas turbocharging is further improved.

A further sub-task of the present invention is to show a method for operating such an internal combustion engine.

• – mindestens einem Zylinderkopf,
• – einem Ansaugsystem zum Zuführen von Ladeluft,
• – einem Abgasabführsystem zum Abführen der Abgase,
• – mindestens einem Zylinder, wobei jeder Zylinder mindestens eine Auslassöffnung aufweist und sich an jede Auslassöffnung eine Abgasleitung zum Abführen der Abgase via Abgasabführsystem anschließt, und
• – zwei Abgasturboladern, von denen jeder einen im Ansaugsystem angeordneten Verdichter und eine im Abgasabführsystem angeordnete Turbine aufweist,

und die dadurch gekennzeichnet ist, dass

• – die Turbine eines ersten Abgasturboladers über eine variable Turbinengeometrie verfügt,
• – die Turbine eines zweiten Abgasturboladers über eine feste unveränderliche Geometrie verfügt, und
• – eine Umschaltvorrichtung vorgesehen ist, die entweder die Turbine des ersten Abgasturboladers oder die Turbine des zweiten Abgasturboladers via Abgasabführsystem mit mindestens einem Zylinder verbindet.

The first partial task is solved by a spark-ignited internal combustion engine

• At least one cylinder head,
• An intake system for supplying charge air,
• An exhaust gas removal system for discharging the exhaust gases,
• - At least one cylinder, each cylinder having at least one outlet opening and is connected to each outlet opening an exhaust pipe for discharging the exhaust gases via Abgasabführsystem, and
• Two exhaust gas turbochargers, each of which has a compressor arranged in the intake system and a turbine arranged in the exhaust gas discharge system,

and which is characterized in that

• The turbine of a first exhaust gas turbocharger has a variable turbine geometry,
• - The turbine of a second exhaust gas turbocharger has a fixed fixed geometry, and
• - A switching device is provided which connects either the turbine of the first exhaust gas turbocharger or the turbine of the second exhaust gas turbocharger via Abgasabführsystem with at least one cylinder.

According to the invention, the two turbines of the two turbochargers in any operating condition of the internal combustion engine, d. H. in no map point of the internal combustion engine, at the same time flows through exhaust gas, which is why always only one turbine or an exhaust gas turbocharger is operated. The turbines used have a different design, which can noticeably improve the charging behavior of the internal combustion engine compared to the prior art. Depending on the current map point, either a turbine with variable turbine geometry or a turbine with fixed fixed geometry is used. This has advantages over the use of a single exhaust gas turbocharger according to the prior art.

Contrary to the usual procedure, according to the invention, a turbine with variable turbine geometry is used in a spark-ignited internal combustion engine, wherein it is possible to dispense with materials which are particularly resistant to high temperatures. This is made possible by the fact that this turbine of the first exhaust gas turbocharger, which is also referred to below as the first turbine, is operated only up to a predetermined thermal load or exhaust gas temperature and at higher thermal load or higher exhaust gas temperatures, the other second turbine of a second exhaust gas turbocharger is used for charging. In this way, the advantages of the variable turbine geometry can be used without incurring high production costs for this turbine. In particular, a variable turbine geometry allows improved charging behavior with small amounts of exhaust gas and thus improved torque characteristics at low speeds.

Basically, the thermal load of the turbine increases with the speed and the load of the internal combustion engine, which usually increases the exhaust gas temperature with the load and the amount of exhaust gas increases primarily with the speed.

In a non-supercharged gasoline engine with quantity control, the amount of exhaust gas increases even with constant speed with increasing load, because with load change and constant speed, the mixture amount varies. At constant speed, the amount of exhaust gas correlates with the load, with the amount of exhaust gas increasing with increasing load and decreasing with decreasing load. The internal combustion engine according to the invention is a supercharged internal combustion engine, so that in addition the charge pressure on the intake side is to be considered, which can change with the load and / or the speed and has an influence on the exhaust gas quantity.

In addition to the exhaust gas temperature, the amount of exhaust gas for the thermal load of the turbine is important because with the amount of exhaust gas regularly increases the flow velocity and thus the heat input due to convection.

In this respect, the first turbine with variable turbine geometry is used at lower loads or speeds, whereas at higher loads or speeds the other second turbine with fixed geometry is used or preferred.

The second turbine can thus be designed advantageously for large amounts of exhaust gas, which can improve the charging behavior at higher speeds or higher loads.

Thus, the first object of the invention is solved, namely provided a spark-ignition internal combustion engine according to the preamble of claim 1, the exhaust gas turbocharging is further improved.

An internal combustion engine according to the invention may also have two cylinder heads, wherein the exhaust pipes of the cylinder of each cylinder head can be connected in each case via switching device with the turbine of a first exhaust gas turbocharger or with the turbine of a second exhaust gas turbocharger.

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

Embodiments of the spark-ignited internal combustion engine in which the charge is a single-stage charge are advantageous. This embodiment determines that no further loaders are provided, i. H. neither a mechanical supercharger nor another exhaust gas turbocharger are used. The charge is thus a single-stage charge at each operating point of the internal combustion engine.

The elimination of another loader brings cost advantages. In addition, the space requirement of the charge is reduced, whereby a compact design of the internal combustion engine and a dense packaging of the entire drive unit in the engine compartment are made possible and not only as a result of the omission of another loader. It also eliminates additional cables.

Embodiments of the spark-ignited internal combustion engine in which the turbine of the second exhaust-gas turbocharger is designed as a waste-gate turbine are advantageous, wherein a bypass line branches off from the exhaust-gas removal system upstream of the turbine and a shut-off element is provided in the bypass line.

The wastegate design is particularly suitable for the second turbine when the map area in which the turbine is used is comparatively large, ie. H. covers a wide speed range or load range, and thus more varying amounts of exhaust gas are to be handled. If the exhaust gas flow exceeds a critical size, part of the exhaust gas flow is conducted past the second turbine as part of the so-called exhaust gas blowdown via the bypass line.

In this context, embodiments of the spark-ignition internal combustion engine in which the bypass line opens downstream of the second turbine into the exhaust-gas removal system are advantageous. This offers advantages in particular with regard to exhaust aftertreatment, since the exhaust gas guided through the turbine and the exhaust gas guided past the turbine can be subjected to a common aftertreatment.

Embodiments of the spark-ignited 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 charge air, whereby the radiator to a better filling of the cylinder with charge air, d. H. contributes to a larger air mass. It is advantageous to provide the intercooler with a bypass line, which allows bypassing the radiator, especially in the warm-up phase.

Embodiments of the spark-ignited internal combustion engine in which at least two cylinders are provided are advantageous.

Embodiments of the spark-ignited internal combustion engine in which three cylinders arranged in series along the longitudinal axis of the at least one cylinder head are advantageous.

Also advantageous are embodiments of the spark-ignition internal combustion engine, in which four cylinders arranged in series along the longitudinal axis of the at least one cylinder head are provided.

Embodiments of the spark-ignited internal combustion engine in which each cylinder has at least two outlet openings are advantageous. As already mentioned, it is a primary goal during the expelling of the exhaust gases in the context of the charge exchange to release the largest possible flow cross sections as quickly as possible to ensure an effective discharge of the exhaust gases, which is why the provision of more than one outlet opening is advantageous.

Embodiments of the spark-ignition internal combustion engine in which the exhaust pipes merge upstream of the turbines to form an overall exhaust gas line are advantageous. The total length of all exhaust pipes is reduced by such merging. In addition, the provision of the switching device is simplified.

Embodiments of the spark-ignition internal combustion engine in which the exhaust pipes of the at least one cylinder merge within the at least one cylinder head to form an overall exhaust gas line are advantageous.

It is basically endeavored to arrange the turbine of an exhaust gas turbocharger as close as possible to the outlet openings of the cylinders in order to make the path of the hot exhaust gases to the turbine runner as short as possible and the line volume upstream of the turbine runner small. The most extensive integration of the exhaust pipes or the exhaust manifold in the cylinder head is purposeful.

The length of the exhaust pipes is reduced. On the one hand thereby the line volume, d. H. reduces the exhaust gas volume of the exhaust pipes upstream of a turbine, so that the response of this turbine is improved. On the other hand, the shortened exhaust pipes also lead to a lower thermal inertia of the exhaust system upstream of the turbine, so that the temperature of the exhaust gases is increased at the turbine inlet, which is why the enthalpy of the exhaust gases at the inlet of the turbine is higher. Optionally provided exhaust aftertreatment systems achieve a required minimum operating temperature faster.

The integration of the exhaust manifold in the cylinder head allows dense packaging of the drive unit and also has the advantage that can be participated in an optionally provided in the cylinder head liquid cooling in such a way that the manifold does not have to be made of thermally highly resilient and therefore costly materials ,

The integration of the exhaust manifold in the cylinder head also leads to a smaller number of components and thus to a reduction in costs, in particular the installation and deployment costs.

The cylinder head of an internal combustion engine is basically a thermally and mechanically highly loaded component. The requirements for the at least one cylinder head according to the invention are particularly high. It should be noted in this context that supercharged internal combustion engines are subject to particularly high thermal loads. With an integration of the exhaust manifold, the thermal load of the internal combustion engine or the cylinder head increases again, so that increased cooling requirements are to be set.

Advantageously, therefore, embodiments in which a liquid cooling is provided. In this context, embodiments of the internal combustion engine in which the at least one cylinder head is equipped with at least one integrated coolant jacket are advantageous. The cylinder block which can be connected to the at least one cylinder head can likewise be equipped with at least one integrated coolant jacket.

Embodiments of the spark-ignited internal combustion engine in which the compressors of the two exhaust-gas turbochargers are arranged in parallel in intake passages of the intake system are advantageous. The parallel arrangement of the compressors ensures that the compressors do not interfere with each other and accounts for the fact that only one compressor is ever compressing charge air while the other compressor is resting, d. H. not operated.

Embodiments of the spark-ignited internal combustion engine in which the intake lines merge downstream of the compressors are advantageous. This shortens the total length of the suction lines of the intake system.

In this context, embodiments of the spark-ignition internal combustion engine in which at least one shut-off element is arranged downstream of the compressor are advantageous, with which either the compressor of the first exhaust gas turbocharger or the compressor of the second exhaust gas turbocharger can be separated from the intake system.

In each operating condition of the internal combustion engine, only one compressor is operated, each of the other compressor is silent and therefore from remaining intake system can be separated. The separation prevents the active compressor from feeding into the other closed compressor. The shutdown compressor is no longer driven by the associated turbine. In order for a decommissioned compressor does not have to promote against the resistance of the closed shut-off, each compressor is preferably equipped with a bypass line, in which also a shut-off is to be arranged.

Embodiments of the spark-ignition internal combustion engine in which the turbine of the first exhaust-gas turbocharger is designed as a waste-gate turbine are advantageous, wherein a bypass line branches off from the exhaust-gas removal system upstream of the turbine and a shut-off element is provided in the bypass line. What has been said for the second turbine with regard to the wastegate construction applies in the present case to the first turbine in an analogous manner. If a bypass line is provided in addition to the variable geometry, this further increases the flexibility of charging.

In this connection, embodiments of the spark-ignition internal combustion engine in which the bypass line opens downstream of the turbine into the exhaust-gas removal system are advantageous.

The second of the invention underlying subtask, namely to identify a method for operating an internal combustion engine of the type described above, is achieved by a method in which, starting from an exhaust gas flowed turbine of the first exhaust gas turbocharger, the switching device is actuated as soon as the thermal load of the turbine predeterminable thermal load exceeds, so that the turbine of the second exhaust gas turbocharger via Abgasabführsystem is connected to the at least one cylinder. At the same time, the first turbine is separated from the at least one cylinder and consequently not further charged with hot exhaust gas. In this way, a thermal overload of the first turbine is prevented.

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, starting from a turbine exhaust gas flowed through the first exhaust gas turbocharger, the switching device is actuated as soon as an exhaust gas temperature T _{exhaust of} the internal combustion engine exceeds a predetermined exhaust gas temperature T _{exhaust, max} , so that the turbine of the second exhaust gas turbocharger via Abgasabführsystem with the at least one cylinder is connected.

Although not only the exhaust gas temperature is important for the thermal load of the turbine, but also the amount of exhaust gas. The exhaust gas temperature can be determined without further ado and considered and used as a meaningful indication of the thermal load of the turbine.

Advantageous embodiments of the method in which the exhaust gas temperature T _exhaust is determined by calculation. The mathematical determination of the temperature takes place by means of simulation, in which models known from the prior art, for example dynamic heat models and kinetic models, are used to determine the heat of reaction generated during the combustion. As input signals for the simulation operating parameters of the internal combustion engine are preferably used, which are already present, that are determined in another context.

The simulation calculation is characterized in that no further components, in particular no sensors, have to be provided in order to determine the temperature, which is favorable in terms of cost. The disadvantage, on the other hand, is that the exhaust gas temperature determined in this way is merely an estimated value.

For estimating the exhaust gas temperature T _exhaust, it is also possible to use a component temperature, for example, the cylinder head, the turbine or the exhaust gas removal system, which is detected, for example, by measurement by means of a sensor. According to this variant, the exhaust gas temperature is determined indirectly - using a different temperature.

Also advantageous are embodiments of the method in which the exhaust gas temperature T _{exhaust is} detected by measurement directly by means of a sensor. However, the metrological detection of the temperature can be difficult because of the extremely high temperatures. The arrangement of a temperature sensor in the turbine housing can cause problems.

If the temperature is detected by means of a sensor, embodiments of the method are advantageous in which the sensor is arranged to detect the temperature in the inlet region of the turbine.

In principle, the component temperature of the turbine itself can also be used as an indication of the thermal loading of the turbine, which in turn is determined by calculation or measured by means of a sensor.

Advantageous embodiments of the method, in which the switching device only then is actuated when the thermal load of the turbine exceeds a predetermined thermal load and for a predetermined period of time is greater than this predetermined thermal load.

The introduction of an additional condition for the actuation of the switching device is to prevent a too frequent or hasty change of the turbine, especially if the thermal load of the turbine only briefly exceed a predetermined thermal load and then decreases again, without exceeding would justify a switch.

Advantageous in this context are process variants in which the switching device is only actuated when the exhaust gas temperature T _{exhaust of} the internal combustion engine exceeds a predefinable exhaust gas temperature T _{exhaust, max} and is greater than this predetermined exhaust gas temperature T _{exhaust, max} for a predefinable time period.

Embodiments of the method in which the changeover device is actuated as a function of the rotational speed n _mot and / or of the load T of the internal combustion engine are advantageous. The speed n _mot and the load T are operating parameters of the internal combustion engine, which are regularly determined as part of the engine control and thus already exist. In addition, a map point in the engine map can be clearly addressed by means of speed and load. If the thermal load on the turbine or the exhaust gas temperature in a map point is known, the information or instruction can be stored specifically for the map point, as to whether the switching device is to be actuated or not.

Embodiments of the method in which the predefinable exhaust gas temperature T _{exhaust, max} is valid are: 750 ° _{C.≤T exhaust, max≤880} ° C.

Embodiments of the method in which the exhaust gas temperature T _{exhaust, max can be given} are: 780 ° C. ≦ T _{exhaust, max} ≦ 850 ° C.

Embodiments of the method in which the predefinable exhaust gas temperature T _{exhaust, max} are: 800 ° _{C.≤T exhaust,} max≤ 850 ° C. are advantageous.

Embodiments of the method in which the predefinable exhaust gas temperature T _{exhaust, max} is valid are: 780 ° C. ≦ T _{exhaust, max} ≦ 880 ° C.

Embodiments of the method in which the predefinable exhaust gas temperature T _{exhaust, max} are: 800 ° _{C.≤T exhaust, max≤880} ° C. are advantageous.

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 internal combustion engine, and

2 the map of in 1 shown first embodiment of the internal combustion engine.

1 schematically shows a first embodiment of the spark-ignition internal combustion engine 1 that with two exhaust gas turbochargers 5 . 6 Is provided. Every turbocharger 5 . 6 includes one in the exhaust system 3 arranged turbine 5a . 6a and one in the intake system 7 arranged compressor 5b . 6b , The hot exhaust gas relaxes in the turbines 5a . 6a under energy release. The compressors 5b . 6b compress the charge air via the intake system 7 , Intercooler 9 and plenum 8th the cylinders 2 is supplied, whereby a charge of the internal combustion engine 1 is reached. Between the intercooler 9 and the plenum 8th is for the purpose of load control of the spark-ignited internal combustion engine 1 a throttle element 10 arranged.

It is a four-cylinder in-line engine 1a in which the four cylinders 2 along the longitudinal axis of the cylinder head, that are arranged in series. Every cylinder 2 has an outlet opening, connected to an exhaust pipe 3a for discharging the exhaust gas via Abgasabführsystem 3 connects, with all the exhaust pipes 3a merge and indeed to a first and second total exhaust line 4a . 4b , In the sense of the invention is an overall exhaust gas line 4a . 4b a conduit which at least temporarily the entire exhaust gas of the cylinder 2 the cylinder head leads or can lead.

The exhaust pipes 3a the cylinder 2 open into a switching device 11 which are the four cylinders 2 via exhaust gas removal system 3 and total exhaust gas line 4a . 4b either with the turbine 5a of the first exhaust gas turbocharger 5 or with the turbine 6a the second exhaust gas turbocharger 6 combines.

The first turbine 5a of the first exhaust gas turbocharger 5 has a variable turbine geometry and is in a first overall exhaust line 4a arranged, which of the switching device 11 emanates. The second turbine 6a the second exhaust gas turbocharger 6 has a fixed fixed geometry and is in a second overall exhaust line 4b , which also from the switching device 11 goes out, arranged. The total exhaust pipes 4a . 4b lead downstream of the turbines 5a . 6a to a common exhaust pipe together, whereby the exhaust aftertreatment is simplified.

The second turbine 6a is designed as a waste-gate turbine whose bypass line 6c upstream of the turbine 6a from the second total exhaust line 4b branches off and downstream of the turbine 6a back into the second total exhaust line 4b empties. To control the Abgasabblasung is a shut-off 6d in the bypass line 6c intended.

Every compressor 5b . 6b is in a suction line 7a of the intake system 7 arranged, with the two parallel intake pipes 7a downstream of the compressor 5b . 6b merge to form a node. At the junction is a 3-2 way valve 12 arranged, which as a shut-off element 12 serves and with either the compressor 5b of the first exhaust gas turbocharger 5 or the compressor 6b the second exhaust gas turbocharger 6 from the remaining intake system 7 can be separated. As always only one compressor 5b . 6b is operated, the separation prevents that the active compressor 5b . 6b in the other shutdown compressors 5b . 6b into it. The supply of the cylinders 2 with charge air is retained.

In the illustrated internal combustion engine 1 Different single-stage charging concepts can be realized. Depending on the current map point either the first turbine 5a with its variable geometry or the waste gate turbine 6a used with solid invariable geometry.

The first turbine 5a is only operated up to a predefinable maximum permissible exhaust gas temperature. At higher exhaust gas temperatures then comes the second turbine 6a for use. In this way, a thermal overload of the variable turbine geometry is prevented.

As a result, the first turbine comes 5a with variable turbine geometry at lower loads and speeds T n _mot used (map range A), while the second turbine 6a with fixed geometry at higher loads T or speeds is used (map area B). 2 schematically shows the map of the internal combustion engine, wherein the abscissa, the speed n _mot and the ordinate, the load T is plotted.

The variable turbine geometry of the first turbine 5a allows a satisfactory charging behavior with small amounts of exhaust gas and thus in particular an improved torque characteristic at low speeds. The second turbine 6a Can be designed for large volumes of exhaust gas, which can improve the charging behavior at higher speeds or higher loads.

LIST OF REFERENCE NUMBERS

1

 spark ignition internal combustion engine

1a

 Four-cylinder in-line engine

2

 cylinder

3

 Abgasabführsystem

3a

 exhaust pipe

4a

 first total exhaust gas line

4b

 second total exhaust line

5

 first exhaust gas turbocharger

5a

 Turbine of the first exhaust gas turbocharger

5b

 Compressor of the first exhaust gas turbocharger

6

 second exhaust gas turbocharger

6a

 Turbine of the second exhaust gas turbocharger

6b

 Compressor of the second exhaust gas turbocharger

6c

 Bypass line, blow-off line

6d

 shut-off

7

 intake system

7a

 suction

8th

 plenum

9

 Intercooler

10

 Shut-off element, throttle element

11

 switching

12

 Shut-off element, 3-way valve

n _mot

 Speed of the internal combustion engine

T

 Load of the internal combustion engine

T _exhaust

 Exhaust gas temperature of the internal combustion engine

T _{exhaust, max}

 predefinable maximum permissible exhaust gas temperature

Claims (19)

Third-ignition internal combustion engine ( 1 ) with - at least one cylinder head, - an intake system ( 7 ) for supplying charge air, - an exhaust gas removal system ( 3 ) for discharging the exhaust gases, - at least one cylinder ( 2 ), each cylinder ( 2 ) has at least one outlet opening and at each outlet opening an exhaust pipe ( 3a ) for discharging the exhaust gases via Abgasabführsystem ( 3 ), and - two exhaust gas turbochargers ( 5 . 6 ), each one in the intake system ( 7 ) arranged compressors ( 5b . 6b ) and one in the exhaust system ( 3 ) arranged turbine ( 5a . 6a ), characterized in that - the turbine ( 5a ) of a first exhaust gas turbocharger ( 5 ) has a variable turbine geometry, - the turbine ( 6a ) of a second exhaust gas turbocharger ( 6 ) has a fixed invariable geometry, and - a switching device ( 11 ) which is either the turbine ( 5a ) of the first exhaust gas turbocharger ( 5 ) or the turbine ( 6a ) of the second Exhaust gas turbocharger ( 6 ) via exhaust gas removal system ( 3 ) with at least one cylinder ( 2 ) connects. Third-ignition internal combustion engine ( 1 ) according to claim 1, characterized in that the charge is a single-stage charge. Third-ignition internal combustion engine ( 1 ) according to claim 1 or 2, characterized in that the turbine ( 6a ) of the second exhaust gas turbocharger ( 6 ) is designed as a waste-gate turbine, wherein upstream of the turbine ( 6a ) a bypass line ( 6c ) from the exhaust gas removal system ( 3 ) branches off and a shut-off element ( 6d ) in the bypass line ( 6c ) is provided. Third-ignition internal combustion engine ( 1 ) according to claim 3, characterized in that the bypass line ( 6c ) downstream of the turbine ( 6a ) into the exhaust gas removal system ( 3 ) opens. Third-ignition internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that downstream of the compressor ( 5b . 6b ) a charge air cooler ( 9 ) in the intake system ( 7 ) is arranged. Third-ignition internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that at least two cylinders ( 2 ) are provided. Third-ignition internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that each cylinder ( 2 ) has at least two outlet openings. Third-ignition internal combustion engine ( 1 ) according to claim 6 or 7, characterized in that the exhaust pipes ( 3a ) upstream of the turbines ( 5a . 6a ) to an overall exhaust gas line ( 4a . 4b ) merge. Third-ignition internal combustion engine ( 1 ) according to one of claims 6 to 8, characterized in that the exhaust pipes ( 3a ) of the at least one cylinder ( 2 ) within the cylinder head to an overall exhaust gas line ( 4a . 4b ) merge. Third-ignition internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that the compressors ( 5b . 6b ) of the two exhaust gas turbochargers ( 5 . 6 ) parallel in suction lines ( 7a ) of the intake system ( 7 ) are arranged. Third-ignition internal combustion engine ( 1 ) according to claim 10, characterized in that the suction lines ( 7a ) downstream of the compressors ( 5b . 6b ) merge. Third-ignition internal combustion engine ( 1 ) according to claim 11, characterized in that downstream of the compressor ( 5b . 6b ) at least one shut-off element ( 12 ) with which either the compressor ( 5b ) of the first exhaust gas turbocharger ( 5 ) or the compressor ( 6b ) of the second exhaust gas turbocharger ( 6 ) from the intake system ( 7 ) is separable. Third-ignition internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that the turbine ( 5a ) of the first exhaust gas turbocharger ( 5 ) is designed as a waste-gate turbine, wherein upstream of the turbine ( 5a ) a bypass line from the exhaust system ( 3 ) branches off and a shut-off element is provided in the bypass line. Third-ignition internal combustion engine ( 1 ) according to claim 13, characterized in that the bypass line downstream of the turbine ( 5a ) into the exhaust gas removal system ( 3 ) opens. Method for operating a spark-ignited internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that, starting from a turbine through which exhaust gas flows ( 5a ) of the first exhaust gas turbocharger ( 5 ) the switching device ( 11 ) is actuated as soon as the thermal load of the turbine ( 5a ) exceeds a predetermined thermal load, so that the turbine ( 6a ) of the second exhaust gas turbocharger ( 6 ) via exhaust gas removal system ( 3 ) with the at least one cylinder ( 2 ) is connected. A method according to claim 15, characterized in that starting from a turbine through which exhaust gas flows ( 5a ) of the first exhaust gas turbocharger ( 5 ) the switching device ( 11 ) is actuated as soon as an exhaust gas temperature T _{exhaust of} the internal combustion engine ( 1 ) exceeds a predefinable exhaust gas temperature T _{exhaust, max} , so that the turbine ( 6a ) of the second exhaust gas turbocharger ( 6 ) via exhaust gas removal system ( 3 ) with the at least one cylinder ( 2 ) is connected. Method according to claim 15 or 16, characterized in that the switching device ( 11 ) as a function of the rotational speed n _mot and / or of the load T of the internal combustion engine ( 1 ) is pressed. A method according to claim 16 or 17, characterized in that for the predefinable exhaust gas temperature T _{exhaust, max} : 750 ° C ≤ T _{exhaust, max} ≤ 880 ° C. Method according to one of claims 16 to 18, characterized in that for the predefinable exhaust gas temperature T _{exhaust, max} applies: 780 ° C ≤ T _{exhaust, max} ≤ 850 ° C.

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