Method for operating a parallel-charged internal combustion engine with switchable turbine and internal combustion engine for carrying out such a process

Abstract

Method for operating a turbocharged internal combustion engine (1) with at least one cylinder head (2), at least two cylinders (3) and an intake system (11) for supplying charge air to the at least two cylinders (3), in which - each cylinder (3) has at least two exhaust ports (4, 4a, 4b) for discharging the exhaust gases, at least one of which is designed as a switchable exhaust port (4a), wherein an exhaust line (5a, 5b) for discharging the exhaust gases via exhaust system (5) is connected to each exhaust port (4, 4a, 4b), - at least two exhaust gas turbochargers (8, 9) are provided, each exhaust gas turbocharger (8, 9) comprising a turbine (8a, 9a) and a compressor (8b, 9b) arranged on the same shaft (8d) rotatably mounted in an oil-lubricated bearing, - the compressors (8b, 9b) of the at least two exhaust gas turbochargers (8, 9) are arranged in parallel in the intake system (11), each compressor (8b, 9b) being arranged in a separate intake line (11a, 11b) of the intake system (11) and the separate intake lines (11a, 11b) being joined downstream of the compressors (8b, 9b) to form a total intake line, - downstream of the first compressor (8b) a first shut-off element (13a) is arranged in the associated suction line (11a), - combine the exhaust pipes (5a) of the switchable exhaust ports (4a) of the at least two cylinders (3) to form a first exhaust manifold (6a) to form a first total exhaust pipe (7a), which is connected to the turbine (8a) of the first exhaust turbocharger (8), and - combine the exhaust pipes (5b) of the other outlet openings (4b) of the at least two cylinders (3) to form a second exhaust manifold (6b) to form a second total exhaust pipe (7b), which is connected to the turbine (9a) of the second exhaust turbocharger (9), characterized in that - starting from a first turbine (8a) deactivated with the exhaust ports (4a) closed, the pressure at the compressor-side end of the bearing of the shaft (8d) of the first exhaust gas turbocharger (8) is increased using a second supply line (16b) that branches off downstream of the second compressor (9b) from the intake system (11) and provides charge air serving as compressed air, wherein the pressure at the compressor-side end of the bearing of the shaft (8d) of the first exhaust gas turbocharger (8) is increased using the second supply line (16b) if a charge pressure p is present downstream of the second compressor (9b) in the intake system (11). chargeis greater than a predefinable minimum boost pressure p charge,min with p charge ≥ p charge,min , characterized in that the compressed air is used to drive the first compressor (8b) and to set the shaft (8d) in rotation.

Description

[0001] The invention relates to a method for operating a parallel-charged internal combustion engine with a switchable turbine and an internal combustion engine for carrying out said method.

[0002] In the publication DE 10 2007 046 655 A1, a method for operating a turbocharged internal combustion engine is described in which two turbochargers are arranged in parallel in the exhaust tract, wherein the second can be switched on by opening a second exhaust port of the cylinders as required, through which exhaust gas is directed to the second turbocharger.

[0003] Publication US 2012 / 0 328 418 A1 describes an arrangement of an internal combustion engine with a turbocharger, in particular disclosing oil-lubricated bearings for the turbocharger shafts.

[0004] Another description of an arrangement with two turbochargers can be found, for example, in publication DE 10 2007 043 585 A1. Publication EP 2 589 770 A1 describes an arrangement of a turbocharger of a gas turbine with an additional compressor for generating compressed air.

[0005] The invention relates to a method for operating a turbocharged internal combustion engine with at least one cylinder head, at least two cylinders and an intake system for supplying charge air to the at least two cylinders, wherein - each cylinder has at least two exhaust ports for discharging the exhaust gases, at least one of which is designed as a switchable exhaust port, with an exhaust pipe for discharging the exhaust gases via an exhaust system connected to each exhaust port, - at least two exhaust gas turbochargers are provided, each comprising a turbine and a compressor arranged on the same shaft rotatably mounted in an oil-lubricated bearing, - the compressors of the at least two exhaust gas turbochargers are arranged in parallel in the intake system, with each compressor in a separate intake line of the - intake system is arranged and the separate intake lines downstream of the compressors merge into a single intake line, - a first shut-off element is arranged downstream of the first compressor in the associated intake line, - combine the exhaust pipes of the switchable exhaust ports of the at least two cylinders to form a first exhaust manifold, creating a first overall exhaust pipe which is connected to the turbine of the first exhaust turbocharger, and - combine the exhaust pipes of the other outlet openings of at least two cylinders to form a second exhaust manifold, which is connected to the turbine of the second exhaust turbocharger.

[0006] Furthermore, the invention relates to a turbocharged internal combustion engine for carrying out such a method.

[0007] Within the scope of the present invention, the term internal combustion engine includes in particular gasoline engines, but also diesel engines and hybrid internal combustion engines that utilize a hybrid combustion process, as well as hybrid drives that, in addition to the internal combustion engine, include an electric machine that can be connected to the internal combustion engine for drive purposes and which receives power from the internal combustion engine or provides additional power as a switchable auxiliary drive.

[0008] Internal combustion engines consist of a cylinder block and at least one cylinder head, which are joined at a mounting face to form the cylinders. To control the gas exchange, an internal combustion engine requires control devices—usually in the form of poppet valves—and actuating mechanisms to actuate these control devices. Each poppet valve moves, during a stroke, between an open and a closed position, releasing the corresponding valve opening for a specified duration. The valve actuation mechanism required for the valve's movement, including the valve itself, is called the valve train. The cylinder head often serves as the mounting point for the valve train.

[0009] During the charge exchange process, the combustion gases are expelled through the exhaust ports of the cylinders, and charge air is drawn in through the intake ports. The task of the valve train is to open and close the intake and exhaust ports in a timely manner. Generally, the aim is to open the largeest possible flow cross-sections as quickly as possible to minimize throttling losses in the incoming and outgoing gas flows and to ensure optimal cylinder filling and effective exhaust gas removal. According to the prior art, cylinders are therefore often equipped with two or more intake and / or exhaust ports. The at least two cylinders of the internal combustion engine that is the subject of the present invention are also equipped with at least two exhaust ports.

[0010] According to the prior art, the intake manifolds leading to the intake ports and the exhaust manifolds connecting to the exhaust ports are at least partially integrated into the cylinder head. The exhaust manifolds of the cylinders are generally combined into a common exhaust manifold or – as in the internal combustion engine according to the invention – grouped together to form two or more exhaust manifolds. The merging of exhaust manifolds into a single exhaust manifold is generally, and within the scope of the present invention, referred to as an exhaust manifold, wherein the section of the exhaust manifold located upstream of a turbine arranged in the exhaust manifold is considered, according to the invention, to belong to the exhaust manifold.

[0011] Downstream of the manifold, the exhaust gases are fed to the turbines of at least two exhaust gas turbochargers for the purpose of charging the internal combustion engine and, if necessary, to one or more exhaust gas aftertreatment systems.

[0012] The advantages of an exhaust gas turbocharger, for example, compared to a mechanical supercharger, lie in the fact that no mechanical connection exists or is required for power transmission between the turbocharger and the internal combustion engine. While a mechanical supercharger draws all the energy required for its operation from the internal combustion engine, thus reducing the available power and negatively impacting efficiency, the exhaust gas turbocharger utilizes the energy of the hot exhaust gases.

[0013] An exhaust gas turbocharger comprises a compressor and a turbine mounted on the same shaft. The hot exhaust gas stream is fed to the turbine and expands within it, releasing energy and causing the shaft to rotate. The energy transferred from the exhaust gas stream to the turbine and ultimately to the shaft is used to drive the compressor, which is also mounted on the shaft. The compressor forces and compresses the intake air, thereby supercharging at least two cylinders. Optionally, charge air cooling is provided to cool the compressed intake air before it enters the cylinders.

[0014] Turbocharging primarily serves to increase the power output of the internal combustion engine. The air required for combustion is compressed, allowing a larger mass of air to be supplied to each cylinder per combustion cycle. This increases the fuel mass and thus the mean effective pressure. Turbocharging is a suitable method for increasing the power output of an internal combustion engine with the same displacement, or for reducing the displacement while maintaining the same power output. In either case, turbocharging leads to increased power output in a given volume and a more favorable power-to-weight ratio. Reducing the displacement allows the load spectrum to be shifted towards higher loads, resulting in lower specific fuel consumption. Turbocharging, in combination with suitable transmission designs, can also achieve a so-called downspeeding, which likewise results in lower specific fuel consumption.Turbocharging therefore supports the ongoing effort in the development of internal combustion engines to minimize fuel consumption, i.e., to improve the efficiency of the internal combustion engine.

[0015] The general aim is to position the turbine of an exhaust gas turbocharger as close as possible to the cylinder exhaust ports. This allows for optimal utilization of the exhaust gas enthalpy of the hot exhaust gases, which is primarily determined by exhaust pressure and temperature, and ensures a rapid response from the turbine and thus the turbocharger. Therefore, minimizing the thermal inertia and volume of the piping system between the cylinder exhaust ports and the turbine is also a primary objective. This can be achieved by reducing the mass and length of the exhaust pipes.

[0016] Designing exhaust gas turbocharging systems often presents challenges, as the goal is generally to achieve a noticeable increase in power across the entire engine speed range. However, current technology reveals a significant drop in torque when the engine speed falls below a certain threshold. This torque drop becomes understandable when considering that the boost pressure ratio depends on the turbine pressure ratio. For example, reducing the engine speed results in a lower exhaust gas mass flow and consequently a lower turbine pressure ratio. This leads to a decrease in both the boost pressure ratio and boost pressure at lower engine speeds, resulting in a drop in torque.

[0017] According to the current state of the art, various measures are being taken to improve the torque characteristics of a turbocharged internal combustion engine.

[0018] For example, this can be achieved by using a small turbine cross-section and simultaneously venting the exhaust gas. Such a turbine is also known as a wastegate turbine. If the exhaust gas volume exceeds a critical level, a portion of the exhaust flow is diverted around the turbine via a bypass line as part of the so-called exhaust gas venting process. This approach has the disadvantage that the boost pressure is insufficient at higher engine speeds or with larger exhaust gas volumes.

[0019] The torque characteristics can also be advantageously influenced by several exhaust gas turbochargers connected in series. By connecting two exhaust gas turbochargers in series, one serving as the high-pressure stage and the other as the low-pressure stage, the compressor map can be advantageously broadened, both towards lower and higher compressor flow rates.

[0020] In particular, the high-pressure stage of the exhaust gas turbocharger allows for a shift of the surge line towards lower compressor flows, enabling high boost pressure ratios even at low compressor flows. This significantly improves the torque characteristics in the lower engine speed range. This is achieved by designing the high-pressure turbine for low exhaust gas mass flows and incorporating a bypass line. As the exhaust gas mass flow increases, this bypass line diverts more exhaust gas around the high-pressure turbine. The bypass line branches off from the exhaust system upstream of the high-pressure turbine and rejoins the exhaust system upstream of the low-pressure turbine. A shut-off element is integrated into the bypass line to control the exhaust gas flow bypassing the high-pressure turbine.The responsiveness of such a turbocharged internal combustion engine is significantly improved compared to a similar internal combustion engine with single-stage turbocharging, since the smaller high-pressure stage is less sluggish, i.e., the rotating assembly of a smaller exhaust gas turbocharger can accelerate faster.

[0021] The torque characteristics of a turbocharged internal combustion engine can be further improved by several parallel turbochargers, i.e., by several parallel turbines with smaller turbine cross-sections, whereby turbines are successively switched on as the exhaust gas volume increases.

[0022] A turbocharged internal combustion engine with at least two turbines arranged in parallel is also part of the present invention. At least one turbine is designed as a switchable turbine, which is only supplied with exhaust gas, i.e., activated, when larger quantities of exhaust gas are present.

[0023] To further improve the torque characteristics, each cylinder of the internal combustion engine according to the invention is equipped with at least one switchable exhaust port. The exhaust pipes of at least two cylinders are then grouped together in such a way that the exhaust pipes of the switchable exhaust ports and the exhaust pipes of the other exhaust ports are each combined to form a single exhaust manifold.

[0024] The exhaust pipes from the switchable outlets lead to the turbine of the first exhaust gas turbocharger, and the exhaust pipes from the other outlets lead to the turbine of the second exhaust gas turbocharger. The first turbine, associated with the switchable outlets, is thus designed as a switchable turbine. Only with larger volumes of exhaust gas are the switchable outlets actuated during the charge exchange, thereby activating the switchable turbine, i.e., subjecting it to exhaust gas.

[0025] In comparison to concepts where a single, continuous exhaust system is provided upstream of the two turbines, the grouping described above, i.e., the use of two separate exhaust systems, noticeably improves the operating behavior of the internal combustion engine, especially at small exhaust gas volumes; also because the duct volume upstream of the second turbine, through which exhaust gas flows continuously, is reduced by this measure, which is advantageous at low loads or speeds, i.e., low exhaust gas volumes, and particularly improves the responsiveness.

[0026] However, there are also disadvantages. The rotational speed of the switchable turbine drops sharply when deactivated, so that when it is switched back on, the turbine's rotor must first be accelerated to generate and provide the desired boost pressure on the compressor side. This impairs the throttle response.

[0027] To ensure a minimum rotational speed of the switchable turbine, it could be supplied with a small exhaust gas flow even when the exhaust ports are closed. This would require a corresponding line connecting the second exhaust manifold to the first turbine, possibly using at least one additional shut-off valve. However, this would disadvantageously increase the complexity and space requirements of the exhaust system upstream of the turbines. Furthermore, the line would create a connection between the two exhaust manifolds, eliminating the grouping described above. The effects achieved by using two separate exhaust manifolds would therefore be at least diminished.

[0028] The deactivated first turbine could also be supplied with a small exhaust gas flow by continuing to operate the lift valve of at least one deactivated outlet port with a reduced stroke and / or a shortened opening duration, thus ensuring that the deactivated first turbine continues to receive exhaust gas. The valve of at least one switchable outlet port would not actually be deactivated in the true sense when the first turbine is shut down, but would continue to be operated and actuated with a reduced stroke or a shortened opening duration. The deactivated first turbine would then receive a reduced or small amount of exhaust gas. However, this requires that the lift valves belonging to the switchable outlet ports are not merely switchable, i.e., not simply able to be switched on or off, but rather adjustable to a greater extent, at least in multiple stages.

[0029] If the deactivated first turbine is supplied with a small amount of exhaust gas, its rotational speed drops less sharply, and a minimum speed of the turbocharger shaft can be ensured or maintained. The latter has another significant advantage. If the turbocharger shaft speed falls below a minimum or even comes to a standstill, the seal of the oil-lubricated turbocharger shaft bearing can leak on the compressor side. Intake-side oil leakage has serious disadvantages. If oil enters the intake system via the associated first compressor, the oil-contaminated fresh charge supplied to the cylinders adversely affects the combustion process, which can significantly increase raw particulate emissions. The oil can also accumulate on the inner walls of the intake system and impair the flow conditions within the intake system.deteriorate the compressor and contaminate a downstream charge air cooler.

[0030] The reasons for the oil leakage are manifold. Firstly, the labyrinth seal regularly used in turbocharger shafts appears to seal satisfactorily only when the shaft is rotating at a certain minimum speed. Secondly, when the first turbine is switched off or the first compressor is not driven, a vacuum regularly exists at the compressor-side end of the bearing. This vacuum draws the oil out of the bearing and into the intake system downstream of the undriven first compressor. In this context, it should be noted that when the first turbine is switched off, the undriven first compressor is regularly isolated from the common intake system. Preferably, a blow-off line is provided, acting as a bypass line, which branches off from the intake system downstream of the first compressor and rejoins the intake system upstream of the second, operating compressor.Such an intake system facilitates the formation of a vacuum at the compressor-side end of the bearing when the first turbine is switched off or the first compressor is not driven. Fabric bushings or rings are frequently provided in the labyrinth seal, i.e., arranged in it, preferably rings with an open joint.

[0031] In light of the above, it is an object of the present invention to disclose a method according to the preamble of claim 1 by which a compressor-side oil leakage can be counteracted when the first turbine is switched off.

[0032] Another sub-objective of the present invention is to provide a turbocharged internal combustion engine for carrying out such a method.

[0033] The first sub-problem according to claim 1 is solved by a method for operating a turbocharged internal combustion engine with at least one cylinder head, at least two cylinders and an intake system for supplying charge air to the at least two cylinders, wherein - each cylinder has at least two exhaust ports for discharging the exhaust gases, at least one of which is designed as a switchable exhaust port, with an exhaust pipe for discharging the exhaust gases via an exhaust system connected to each exhaust port, - at least two exhaust gas turbochargers are provided, each comprising a turbine and a compressor arranged on the same shaft rotatably mounted in an oil-lubricated bearing, - the compressors of the at least two exhaust gas turbochargers are arranged in parallel in the intake system, with each compressor being arranged in a separate intake line of the intake system and the separate intake lines merging downstream of the compressors into a total intake line, - a first shut-off element is arranged downstream of the first compressor in the associated intake line, - combine the exhaust pipes of the switchable exhaust ports of the at least two cylinders to form a first exhaust manifold, creating a first overall exhaust pipe which is connected to the turbine of the first exhaust turbocharger, and - combine the exhaust pipes of the other outlet openings of the at least two cylinders to form a second exhaust manifold, which is connected to the turbine of the second exhaust turbocharger, and is characterized in that - Starting from a first turbine deactivated with the exhaust ports closed, the pressure at the compressor-side end of the bearing of the shaft of the first exhaust gas turbocharger is increased using a second supply line that branches off from the intake system downstream of the second compressor and provides charge air serving as compressed air, wherein the pressure at the compressor-side end of the bearing of the shaft of the first exhaust gas turbocharger is increased using the second supply line if a charge pressure p is present downstream of the second compressor in the intake system charge is greater than a predefinable minimum boost pressure p charge,min with p charge ≥ p charge,min .

[0034] According to the inventive method, the formation of a negative pressure at the compressor-side end of the bearing when the first turbine is switched off or the first compressor is not driven is counteracted, or the pressure present at the compressor-side end of the bearing is increased. For this purpose, a supply line, which is hereinafter referred to as the second supply line, is used, which branches off from the intake system downstream of the second compressor and provides charge air serving as compressed air in order to increase the relevant pressure.

[0035] The oil-lubricated bearing of a turbocharger shaft is typically connected to the crankcase of the internal combustion engine via a return line, where ambient pressure or overpressure prevails. In conjunction with the negative pressure regularly present at the compressor-side end of the bearing when the first turbine is switched off or the first compressor is not driven, this creates a pressure differential across the bearing seal. This pressure differential causes oil leakage, forcing oil from the bearing into the intake system.

[0036] According to the invention, the second supply line branches off from the intake system downstream of the second compressor and provides charge air serving as compressed air, whereby the pressure at the compressor-side end of the bearing of the shaft of the first exhaust gas turbocharger is increased using the second supply line if a charge pressure p is present downstream of the second compressor in the intake system.charge is greater than a predefinable minimum boost pressure p charge,min with p charge ≥p charge,min .

[0037] The pressure at the compressor-side end of the shaft bearing is thus increased using the boost pressure that is present and tapped off downstream of the second operating compressor in the intake system.

[0038] Extracting charge air downstream of the second compressor results in a reduction of the supplied boost pressure. Since a sufficiently high boost pressure must be provided to meet a required torque or power demand, operating conditions of the internal combustion engine may exist that prohibit and even prevent the extraction of charge air from the intake system to supply compressed air.

[0039] A reduction in the supplied boost pressure as a result of charge air extraction is not possible under all operating conditions of the internal combustion engine.

[0040] Additional aids can be used to increase the pressure; these can be of very different types, and several aids can be provided that are used together, i.e. simultaneously, or alternatively, i.e. alternately and complementing each other.

[0041] The method according to the invention solves the first problem underlying the invention, namely to demonstrate a method according to the preamble of claim 1 with which a compressor-side oil leakage can be counteracted when the first turbine is switched off.

[0042] An internal combustion engine according to the invention can also have two cylinder heads. It can also be equipped with three exhaust gas turbochargers.

[0043] According to the prior art, three-cylinder in-line engines are rarely equipped with two turbines arranged in parallel. However, the merging of the exhaust lines according to the invention makes this possible without difficulty, even though three-cylinder in-line engines are usually difficult to access for grouping, in particular, a cylinder grouping.

[0044] Therefore, embodiments in which the internal combustion engine has a cylinder head with three cylinders are also advantageous.

[0045] Further advantageous embodiments of the method according to the invention are discussed in connection with the dependent claims.

[0046] In this process, compressed air is used to drive the first compressor and set the shaft in rotation.

[0047] With the first turbine switched off, a small amount of air is supplied to the first compressor, causing the compressor impeller (or impeller) mounted on the shaft, and thus the shaft itself, to rotate. This reduces the drop in shaft speed and ensures a minimum rotational speed of the supercharger shaft. The rotating impeller of the first compressor also increases the pressure downstream in the intake system. This counteracts oil leakage from the compressor side in two ways: firstly, by rotating the shaft, and secondly, by increasing the compressor-side pressure. The latter reduces the driving pressure differential across the compressor-side seal of the oil-lubricated supercharger shaft bearing, which would otherwise cause oil leakage and force oil into the intake system.

[0048] In principle, oil from the storage can also enter the exhaust system on the turbine side via the deactivated first turbine, which would contaminate downstream exhaust aftertreatment systems, i.e. catalysts and particulate filters, with oil and significantly worsen the conversion rates of these exhaust aftertreatment systems.

[0049] In some cases, the lifespan of the exhaust aftertreatment systems may even be shortened, and their functionality may also be fundamentally compromised.

[0050] Advantageous embodiments of the method may be those in which compressed air is used to directly increase the pressure at the compressor-side end of the bearing of the shaft of the first exhaust gas turbocharger.

[0051] According to the aforementioned method variant, the pressure at the compressor-side end of the bearing of the shaft of the first exhaust gas turbocharger is increased directly by pressurizing the bearing or bearing seal on the compressor side with compressed air via a second supply line, thus increasing the pressure present there. The driving pressure differential, which forces oil into the intake system via the compressor-side seal, is thereby reduced.

[0052] Advantageous embodiments of the method may be those in which the compressed air is used to increase the pressure in the separate intake line of the first compressor.

[0053] According to the aforementioned method variant, the pressure at the compressor-side end of the bearing for the shaft of the first exhaust gas turbocharger is not increased directly, but rather indirectly. For this purpose, the pressure in the intake system is increased using compressed air, which inevitably also increases the pressure at the compressor-side end of the shaft bearing, thus reducing the pressure differential responsible for the oil leakage, which forces oil past the compressor-side seal into the intake system.

[0054] In principle, embodiments of the method can be advantageous in which the pressure at the compressor-side end of the bearing of the shaft of the first exhaust gas turbocharger is increased using an electric auxiliary drive which is at least drive-connectable to the shaft of the first exhaust gas turbocharger, wherein an activated electric auxiliary drive sets the shaft and at least one compressor impeller mounted on the shaft into rotation.

[0055] The electric auxiliary drive is used to power the first compressor and rotate the shaft. This prevents the shaft from stalling, ensuring or maintaining a minimum rotational speed of the compressor shaft. The rotating impeller of the first compressor also reduces the negative pressure present downstream in the intake system. This counteracts oil leakage on the compressor side, both by rotating the shaft and by reducing the negative pressure. The latter reduces the pressure differential across the bearing seal on the compressor side, which causes oil leakage.

[0056] In this case, the first compressor does not generate boost pressure. The first compressor essentially runs idle and not under load like the second compressor, which is operational and provides the required boost pressure.

[0057] In embodiments where, in addition to a second supply line, an electric auxiliary drive of the type described above is available or used to increase the pressure, method variants are advantageous in which the pressure at the compressor-side end of the bearing of the shaft of the first exhaust gas turbocharger is increased using the electric auxiliary drive if a boost pressure p is present downstream of the second compressor in the intake system. charge is smaller than a predetermined minimum boost pressure p charge,min with p charge < p charge,min .

[0058] The second sub-problem underlying the invention, namely to provide a turbocharged internal combustion engine for carrying out a method of the type described above, is solved according to claim 6 by a turbocharged internal combustion engine with at least one cylinder head, at least two cylinders and an intake system for supplying charge air to the at least two cylinders, in which - each cylinder has at least two exhaust ports for discharging the exhaust gases, at least one of which is designed as a switchable exhaust port, with an exhaust pipe for discharging the exhaust gases via an exhaust system connected to each exhaust port, - at least two exhaust gas turbochargers are provided, each comprising a turbine and a compressor arranged on the same shaft rotatably mounted in an oil-lubricated bearing, - the compressors of the at least two exhaust gas turbochargers are arranged in parallel in the intake system, with each compressor in a separate intake line of the - intake system is arranged and the separate intake lines downstream of the compressors merge into a single intake line, - a first shut-off element is arranged downstream of the first compressor in the associated intake line, - combine the exhaust pipes of the switchable exhaust ports of the at least two cylinders to form a first exhaust manifold, creating a first overall exhaust pipe which is connected to the turbine of the first exhaust turbocharger, and - combine the exhaust pipes of the other outlet openings of the at least two cylinders to form a second exhaust manifold, which is connected to the turbine of the second exhaust turbocharger, and which is characterized in that - starting from a first turbine deactivated with the exhaust ports closed, a second supply line is provided to increase the pressure at the compressor-side end of the bearing of the shaft of the first exhaust gas turbocharger, wherein this second supply line branches off downstream of the second compressor from the intake system and provides charge air serving as compressed air.

[0059] What has been said in connection with the method according to the invention also applies to the internal combustion engine according to the invention.

[0060] Advantageous embodiments of the turbocharged internal combustion engine may include a second supply line leading into a first supply line, in which, for example, an electrically driven pump may be arranged to provide compressed air.

[0061] In this context, advantageous are embodiments of the turbocharged internal combustion engine in which the second supply line merges into the first supply line at a junction point, with a shut-off element being arranged at the junction point.

[0062] For the reasons mentioned above, embodiments of the internal combustion engine are advantageous in which a pump is provided as an auxiliary device, wherein a pump in operation provides compressed air by means of a first supply line.

[0063] According to the invention, the first compressor can be isolated from the rest of the intake system when the first turbine is switched off, so that the second compressor does not pump air into the first compressor. For this purpose, a first shut-off element is arranged downstream of the first compressor in the associated intake line, which serves to deactivate this compressor.

[0064] When the turbine is switched off, the first compressor is not actively driven, meaning it is not typically driven with the intention of generating boost pressure. To prevent the first compressor from potentially working against the resistance of the closed first shut-off valve, a blow-off line is advantageous, allowing the charge air to escape or be discharged.

[0065] In the turbocharged internal combustion engine, a blow-off line is provided which branches off from the associated intake line between the first compressor and the first shut-off element and opens into the other intake line upstream of the second compressor, with a second shut-off element arranged in the blow-off line.

[0066] Since there is usually a negative pressure upstream of the second compressor, an open discharge line has the effect that there is also a negative pressure in the intake system downstream of the deactivated first compressor, thus creating a pressure gradient across the bearing seal.

[0067] Advantageous are embodiments of the internal combustion engine in which the exhaust pipes of the at least two cylinders merge within the at least one cylinder head to form the total exhaust pipes.

[0068] Integrating the exhaust manifolds into the cylinder head reduces the mass and length of the exhaust system from the exhaust ports to the turbines. This allows for optimal utilization of the exhaust gas enthalpy from the hot exhaust gases and ensures a rapid response from the turbochargers. Furthermore, exhaust aftertreatment systems located close to the exhaust outlet reach their operating or activation temperature quickly, especially after a cold start of the internal combustion engine. Integrating the exhaust manifolds into the cylinder head also allows for the most compact possible packaging of the powertrain and has the added advantage of utilizing any liquid cooling system integrated into the cylinder head, thus eliminating the need to manufacture the manifolds from thermally stressed and therefore expensive materials.

[0069] The integration of the exhaust manifolds into the cylinder head also leads to a smaller number of components and consequently to a reduction in costs, especially assembly and supply costs.

[0070] Advantageous embodiments of the internal combustion engine are those in which each switchable exhaust port is equipped with a switchable lift valve, wherein a deactivated lift valve shuts off the associated exhaust port and an activated lift valve moves between an open position and a closed position, forming a valve stroke Δh mar moved and thereby the associated outlet opening remains open for an opening duration Δt max releases.

[0071] Advantageous embodiments of the internal combustion engine are those in which each switchable exhaust port is equipped with an adjustable lift valve, wherein an adjustable lift valve is a lift valve adjustable with respect to the valve stroke Δh and / or the opening duration Δt. The adjustable lift valve can be a staged adjustable lift valve, in particular a three-stage adjustable lift valve, or a continuously adjustable lift valve.

[0072] Advantageous are embodiments of the internal combustion engine in which the exhaust gas lines merge into a common exhaust gas line downstream of the turbines. This allows for exhaust aftertreatment of the entire exhaust gas from at least two cylinders using an aftertreatment system located within the common exhaust gas line. This system could include, for example, a particulate filter, an oxidation catalyst, and / or an exhaust aftertreatment system for reducing nitrogen oxides.

[0073] Advantageous embodiments of the internal combustion engine are those in which at least one turbine has a variable turbine geometry, allowing for extensive adaptation to the respective operating point by adjusting the turbine geometry or the effective turbine cross-section. Guide vanes are arranged upstream of the turbine runner to influence the flow direction. Unlike the rotor blades of the rotating runner, the guide vanes do not rotate with the turbine shaft, i.e., the runner. The guide vanes are stationary but not completely immobile; they are rotatable about their axis, allowing the flow towards the rotor blades to be influenced. In contrast, if a turbine has a fixed, unchanging geometry, the guide vanes are not only stationary but also completely immobile, i.e., rigidly fixed.

[0074] Advantageous are embodiments of the internal combustion engine in which at least one turbine is designed as a wastegate turbine.

[0075] In this context, advantageous embodiments of the internal combustion engine are those in which the turbine of the first exhaust gas turbocharger is designed as a wastegate turbine, wherein upstream of this first turbine a first bypass line branches off from the exhaust gas discharge system forming a first node and a shut-off element is provided in the first bypass line.

[0076] In this context, advantageous embodiments of the internal combustion engine are those in which the turbine of the second exhaust gas turbocharger is designed as a wastegate turbine, wherein upstream of this second turbine a second bypass line branches off from the exhaust gas discharge system forming a second node and a shut-off element is provided in the second bypass line.

[0077] The cylinder head of a turbocharged internal combustion engine is inherently a component subjected to high thermal and mechanical stress. The thermal load on the engine and cylinder head increases further, particularly when the exhaust manifold is integrated, thus placing higher demands on the cooling system. Therefore, turbocharged internal combustion engine designs that incorporate liquid cooling are advantageous.

[0078] The invention is described below using an exemplary embodiment and in accordance with Fig. 1 described in more detail. This shows: Fig. 1 schematically an embodiment of the internal combustion engine.

[0079] Fig. Figure 1 schematically shows a first embodiment of the turbocharged internal combustion engine 1, which is equipped with two exhaust gas turbochargers 8, 9. Each exhaust gas turbocharger 8, 9 comprises a turbine 8a, 9a and a compressor 8b, 9b, which are arranged on the same shaft 8d, rotatably mounted in an oil-lubricated bearing. The hot exhaust gas expands in the turbines 8a, 9a, releasing energy. The compressors 8b, 9b compress the charge air, which is supplied to the cylinders 3 via the intake system 11, charge air cooler 10, and plenum 12, thereby turbocharging the internal combustion engine 1.

[0080] This is a four-cylinder in-line engine 1, in which the four cylinders 3 are arranged in a line along the longitudinal axis of the cylinder head 2. Each cylinder 3 has two exhaust ports 4, 4a, 4b, to which exhaust lines 5a, 5b are connected for the discharge of exhaust gases via the exhaust system 5. One exhaust port 4, 4a of each cylinder 3 is designed as a switchable exhaust port 4a, which is opened during the charge exchange only when the exhaust gas volume exceeds a predetermined volume and the downstream first turbine 8a is to be activated, i.e., supplied with exhaust gas.

[0081] The exhaust pipes 5a of the switchable exhaust ports 4a of all cylinders 3 lead together to form a first exhaust manifold 6a to a first total exhaust pipe 7a, which is connected to the turbine 8a of the first exhaust turbocharger 8, which thereby functions as a switchable turbine 8a.

[0082] The exhaust pipes 5b of the other outlet openings 4b of all cylinders 3 lead together to form a second exhaust manifold 6b, which is connected to the turbine 9a of the second exhaust turbocharger 9.

[0083] Both turbines 8a, 9a are of wastegate design, with a bypass line 8c, 9c branching off upstream of each turbine 8a, 9a from the associated main exhaust line 7a, 7b and rejoining the main exhaust line 7a, 7b downstream of this turbine 8a, 9a. The bypass lines 8c, 9c are equipped with shut-off elements.

[0084] The internal combustion engine 1 has an intake system 11 for supplying charge air to the cylinders 3, wherein the compressors 8b, 9b of the turbochargers 8, 9 are arranged in parallel within the intake system 11. The first compressor 8b is located in a first intake line 11a and the second compressor 9b in a second intake line 11b. The intake lines 11a, 11b converge downstream of the compressors 8b, 9b to form a single intake line.

[0085] Downstream of the first compressor 8b, a first shut-off element 13a is arranged in the associated intake line 11a, so that the first compressor 8b can be isolated from the rest of the intake system 11 when the first turbine 8a is switched off, i.e. deactivated, and the second compressor 9b does not pump into the first compressor 8b.

[0086] The first compressor 8b is not actually driven when the turbine 8a is switched off. However, to prevent the first compressor 8b from pumping against the resistance of the closed first shut-off element 13a, a blow-off line 14 is provided, through which the charge air can be conveyed into the second intake line 11b upstream of the second compressor 9b. A second shut-off element 13b is arranged in the blow-off line 14.

[0087] With the outlet openings 4a closed, the first turbine 8a is deactivated, and therefore the first compressor 8b is not driven. A vacuum then regularly exists at the compressor-side end of the shaft bearing, which draws the oil from the bearing into the intake system 11. To prevent oil leakage, the pressure at the compressor-side end of the bearing of the shaft 8d of the first exhaust gas turbocharger 8 is increased using auxiliary devices 17.

[0088] According to Fig.1 A second supply line 16b is provided, which branches off downstream of the second compressor 9b from the intake system 11 and provides charge air serving as compressed air.

[0089] The second supply line 16b merges into a first supply line 16a by forming a junction 18, with a shut-off element 18a being arranged at the junction 18.

[0090] The pressure at the compressor-side end of the bearing of the shaft 8d of the deactivated first exhaust gas turbocharger 8 is increased using the second supply line 16b if a boost pressure p is present downstream of the second compressor 9b in the intake system 11 charge is greater than a predefinable minimum boost pressure p charge,min . The pressure differential which forces oil into the intake system 11 via the compressor-side seal of the bearing is reduced in this way.

[0091] If the boost pressure p present downstream of the second compressor 9b in the intake system 11 charge is smaller than a predetermined minimum boost pressure p charge,min No charge air suitable for use as compressed air can be provided via the second supply line 16b.

[0092] If necessary, other aids 17 may be provided to increase the pressure at the compressor-side end of the bearing, for example a pump that supplies compressed air to the bearing seal on the compressor side via the first supply line 16a. Reference sign 1 turbocharged internal combustion engine, four-cylinder in-line engine 2 cylinder heads 3 cylinders 4 Outlet opening 4a switchable outlet opening 4b other outlet opening 5 Exhaust system 5a Exhaust pipe of a switchable outlet opening 5b Exhaust pipe 6a first exhaust manifold 6b second exhaust manifold 7a first total exhaust pipe 7b second total exhaust pipe 8 first exhaust gas turbocharger 8a first turbine, switchable turbine, wastegate turbine 8b first compressor 8c first bypass line 8d Charging shaft of the first exhaust gas turbocharger 9 second exhaust gas turbocharger 9a second turbine, wastegate turbine 9b second compressor 9c second bypass line 10 intercoolers 11 Intake system 11a first separate intake pipe 11b second separate intake pipe 12th Plenary 13a first shut-off element 13b second shut-off element 14 Blow-off line 16a first supply line 16b second supply line 17 Aids for increasing the pressure at the compressor-side end of the bearing of the shaft of the first exhaust gas turbocharger 18 junctions 18a Shut-off element

Claims

[1] Method for operating a turbocharged internal combustion engine (1) with at least one cylinder head (2), at least two cylinders (3) and an intake system (11) for supplying charge air to the at least two cylinders (3), wherein - each cylinder (3) has at least two exhaust ports (4, 4a, 4b) for discharging the exhaust gases, at least one of which is designed as a switchable exhaust port (4a), wherein an exhaust line (5a, 5b) for discharging the exhaust gases via exhaust system (5) is connected to each exhaust port (4, 4a, 4b), - at least two exhaust gas turbochargers (8, 9) are provided, each exhaust gas turbocharger (8, 9) comprising a turbine (8a, 9a) and a compressor (8b, 9b) arranged on the same shaft (8d) rotatably mounted in an oil-lubricated bearing, - the compressors (8b, 9b) of the at least two exhaust gas turbochargers (8, 9) are arranged in parallel in the intake system (11), each compressor (8b, 9b) being arranged in a separate intake line (11a, 11b) of the intake system (11) and the separate intake lines (11a, 11b) being joined downstream of the compressors (8b, 9b) to form a total intake line, - downstream of the first compressor (8b) a first shut-off element (13a) is arranged in the associated suction line (11a), - combine the exhaust pipes (5a) of the switchable exhaust ports (4a) of the at least two cylinders (3) to form a first exhaust manifold (6a) to form a first total exhaust pipe (7a), which is connected to the turbine (8a) of the first exhaust turbocharger (8), and - combine the exhaust pipes (5b) of the other exhaust ports (4b) of the at least two cylinders (3) to form a second exhaust manifold (6b) to form a second total exhaust pipe (7b), which is connected to the turbine (9a) of the second exhaust turbocharger (9), characterized by , that - starting from a first turbine (8a) deactivated with the exhaust ports (4a) closed, the pressure at the compressor-side end of the bearing of the shaft (8d) of the first exhaust gas turbocharger (8) is increased using a second supply line (16b) that branches off downstream of the second compressor (9b) from the intake system (11) and provides charge air serving as compressed air, wherein the pressure at the compressor-side end of the bearing of the shaft (8d) of the first exhaust gas turbocharger (8) is increased using the second supply line (16b) if a charge pressure p is present downstream of the second compressor (9b) in the intake system (11). chargeis greater than a predefinable minimum boost pressure p charge,min with p charge ≥ p charge,min , characterized by , that the compressed air is used to drive the first compressor (8b) and to set the shaft (8d) in rotation. [2] Method according to claim 1, characterized by , that the compressed air is used to directly increase the pressure at the compressor-side end of the bearing of the shaft (8d) of the first exhaust gas turbocharger (8). [3] Method according to claim 1, characterized by , that the compressed air is used to increase the pressure in the separate intake line (11a) of the first compressor (8b). [4] Method according to claim 1, characterized by, that the pressure at the compressor-side end of the bearing of the shaft (8d) of the first exhaust gas turbocharger (8) is increased using an electric auxiliary drive which is at least drive-connectable to the shaft (8d) of the first exhaust gas turbocharger (8), wherein an activated electric auxiliary drive sets the shaft (8d) and at least one compressor impeller mounted on the shaft (8d) into rotation. [5] Method according to claim 4, characterized by , that the pressure at the compressor-side end of the bearing of the shaft (8d) of the first exhaust gas turbocharger (8) is increased using the electric auxiliary drive if a boost pressure p is present downstream of the second compressor (9b) in the intake system (11). charge is smaller than a predetermined minimum boost pressure p charge,min with p charge < p charge,min . [6] Supercharged internal combustion engine (1) for carrying out a method according to one of the preceding claims, comprising at least one cylinder head (2), at least two cylinders (3) and an intake system (11) for supplying charge air to the at least two cylinders (3), wherein - each cylinder (3) has at least two exhaust ports (4, 4a, 4b) for discharging the exhaust gases, at least one of which is designed as a switchable exhaust port (4a), wherein an exhaust line (5a, 5b) for discharging the exhaust gases via exhaust system (5) is connected to each exhaust port (4, 4a, 4b), - at least two exhaust gas turbochargers (8, 9) are provided, each exhaust gas turbocharger (8, 9) comprising a turbine (8a, 9a) and a compressor (8b, 9b) arranged on the same shaft (8d) rotatably mounted in an oil-lubricated bearing, - the compressors (8b, 9b) of the at least two exhaust gas turbochargers (8, 9) are arranged in parallel in the intake system (11), each compressor (8b, 9b) being arranged in a separate intake line (11a, 11b) of the intake system (11) and the separate intake lines (11a, 11b) being joined downstream of the compressors (8b, 9b) to form a total intake line, - downstream of the first compressor (8b) a first shut-off element (13a) is arranged in the associated suction line (11a), - combine the exhaust pipes (5a) of the switchable exhaust ports (4a) of the at least two cylinders (3) to form a first exhaust manifold (6a) to form a first total exhaust pipe (7a), which is connected to the turbine (8a) of the first exhaust turbocharger (8), and - combine the exhaust pipes (5b) of the other exhaust ports (4b) of the at least two cylinders (3) to form a second exhaust manifold (6b) to form a second total exhaust pipe (7b), which is connected to the turbine (9a) of the second exhaust turbocharger (9), - a second supply line (16b) is provided to increase the pressure at the compressor-side end of the bearing of the shaft (8d) of the first exhaust gas turbocharger (8), wherein this second supply line (16b) branches off downstream of the second compressor (9b) from the intake system (11) and provides charge air serving as compressed air, characterized by , that a blow-off line (14) is provided which branches off from the associated suction line (11a) between the first compressor (8b) and the first shut-off element (13a) and opens upstream of the second compressor (9b) into the other suction line (11b), wherein a second shut-off element (13b) is arranged in the blow-off line (14). [7] Supercharged internal combustion engine (1) according to claim 6, characterized by , that the second supply line (16b) leads into a first supply line (16a). [8] Supercharged internal combustion engine (1) according to claim 7, characterized by , that the second supply line (16b) merges into the first supply line (16a) by forming a node (18), with a shut-off element (18a) being arranged at the node (18).

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