Internal combustion engine with cooled modular exhaust gas recirculation

Abstract

Internal combustion engine (1) with - at least one cylinder, - an intake system (3) for supplying air to at least one cylinder, - an exhaust gas discharge system (2) for the discharge of exhaust gases, - an exhaust gas recirculation system (4) comprising at least two recirculation lines (4a, 4b), wherein each recirculation line (4a, 4b) is provided with a cooler (5a, 5b) and the coolers (5a, 5b) are arranged in parallel and can be used independently of each other for cooling exhaust gas, and - at least three actuators (2b, 7, 8) for setting a predefinable amount of recirculated exhaust gas, at which - each cooler (5a, 5b) can be used for cooling exhaust gas for the purpose of energy recovery, - a first return line (4a) is provided, which branches off from the exhaust system (2) by forming a first node (2a) and opens into the intake system (3) by forming a second node (3a), in which a first cooler (5a) is arranged and which can be connected to the exhaust system (2) upstream of the first cooler (5a) and to the intake system (3) downstream of the first cooler (5a) using at least one actuating element (7), - a second return line (4b) is provided, which branches off from the exhaust system (2) forming a third node (2c) and opens into the first return line (4a) downstream of the first cooler (5a) forming a fourth node (10), in which a second cooler (5b) is arranged and which can be connected upstream of the second cooler (5b) to the exhaust system (2) and downstream of the second cooler (5b) optionally to the intake system (3) or the exhaust system (2) using at least one actuating element (7, 8), and - a second actuating element (8) is provided in the second return line (4b) downstream of the second cooler (5b), characterized by the fact that - an exhaust gas line (11) is provided which branches off from the second return line (4b) by forming a fifth node (12) between the second cooler (5b) and the second actuator (8) and leads into the exhaust gas discharge system (2) by forming a sixth node (2d), wherein - in the first return line (4a) at the second node (3a) a first actuating element (7) is provided, - the sixth node (2d) is located downstream of the first and third nodes (2a, 2c) in the exhaust system (2) and - a third actuating element (2b) is arranged at the sixth node (2d) and wherein - the second actuating element (8) is a two-stage switchable actuating element for connecting or disconnecting the second cooler (5b) with or from the first return line (4a) and - the third actuating element (2b) is a continuously adjustable throttle element for adjusting an operating state between blocking or releasing the exhaust gas line (11) and blocking or releasing the exhaust gas system (2) upstream of the sixth node (2d).

Description

[0001] The invention relates to an internal combustion engine with - at least one cylinder, - an intake system to supply at least one cylinder with air, - an exhaust gas removal system for removing exhaust gases, - an exhaust gas recirculation system comprising at least two recirculation lines, each recirculation line having a cooler, the coolers being arranged in parallel and being independently usable for cooling exhaust gas, and - at least three actuators for setting a predefinable amount of exhaust gas to be recirculated.

[0002] An internal combustion engine of the type mentioned is used as a motor vehicle drive. Within the scope of the present invention, the term internal combustion engine relates to diesel engines and gasoline engines, but also to hybrid internal combustion engines, i.e., internal combustion engines that are operated with a hybrid combustion process, as well as hybrid drives that, in addition to the internal combustion engine, comprise at least one further torque source for driving a motor vehicle, for example, an electric machine that can be connected to or is connected to the drive of the internal combustion engine and which delivers power instead of or in addition to the internal combustion engine.

[0003] In the development of internal combustion engines, constant efforts are made to minimize fuel consumption. Furthermore, a reduction in pollutant emissions is pursued in order to comply with future emission limits.

[0004] Internal combustion engines are therefore increasingly being equipped with turbocharging, which is primarily a method for increasing performance by compressing the intake air required for the combustion process, thus supplying a larger mass of intake air to each cylinder per combustion cycle. This allows the fuel mass and therefore the mean effective pressure to be increased.

[0005] Supercharging is a suitable means of increasing the power output of an internal combustion engine without changing its displacement, or of reducing the displacement while maintaining the same power output. In either case, supercharging leads to increased power output per unit volume and a more favorable power-to-weight ratio. If the displacement is reduced, the load spectrum can be shifted towards higher loads, resulting in lower specific fuel consumption, under the same vehicle operating conditions. Supercharging an internal combustion engine therefore supports efforts to minimize fuel consumption, i.e., to improve the engine's efficiency.

[0006] A suitable transmission design can also enable downspeeding, which further reduces specific fuel consumption. Downspeeding takes advantage of the fact that specific fuel consumption is generally lower at low engine speeds, especially under higher loads.

[0007] With targeted turbocharging design, advantages can also be achieved in terms of exhaust emissions. For example, with suitable turbocharging, nitrogen oxide emissions from diesel engines can be reduced without compromising efficiency. At the same time, hydrocarbon emissions can be favorably influenced. Carbon dioxide emissions, which correlate directly with fuel consumption, also decrease with lower fuel consumption.

[0008] To comply with future emission limits, further measures are necessary. A key focus of development work is the reduction of nitrogen oxide emissions, which are particularly relevant for diesel engines. Since the formation of nitrogen oxides requires not only excess air but also high temperatures, one approach to reducing nitrogen oxide emissions involves using combustion processes with lower combustion temperatures.

[0009] Exhaust gas recirculation (EGR), i.e., the recirculation of combustion gases from the exhaust side to the intake side, is a promising approach, as nitrogen oxide emissions can be significantly reduced with an increasing exhaust gas recirculation rate. The exhaust gas recirculation rate x AGR is determined to x AGR = m AGR / (m AGR + mFrischluft ), where m AGR the mass of recirculated exhaust gas and m FrischluftThis refers to the supplied fresh air. The oxygen provided via exhaust gas recirculation must be taken into account, if applicable.

[0010] To achieve a significant reduction in nitrogen oxide emissions, high exhaust gas recirculation rates may be required, on the order of x AGR The recirculation rate can be approximately 60% to 70% or more. Such high recirculation rates require cooling of the recirculated exhaust gas, which lowers the exhaust gas temperature and increases its density, allowing a larger mass of exhaust gas to be recirculated. Consequently, exhaust gas recirculation systems are regularly equipped with a cooler. The exhaust gas recirculation system of the internal combustion engine, which is the subject of the present invention, also features cooling, namely at least two EGR coolers, each with a coolant jacket that facilitates heat transfer between the exhaust gas and the coolant.

[0011] Problems can arise when introducing the recirculated exhaust gas into the intake system if the temperature of the recirculated hot exhaust gas decreases and condensation forms.

[0012] Firstly, condensation can form when the recirculated hot exhaust gas in the intake system comes into contact with and mixes with cooler fresh air. The exhaust gas cools down, while the temperature of the fresh air rises. The temperature of the mixture of fresh air and recirculated exhaust gas, i.e., the temperature of the combustion air, is lower than the exhaust gas temperature of the recirculated exhaust gas. As the exhaust gas cools, liquids previously present in gaseous form in the exhaust gas or combustion air, especially water, can condense if the dew point of a component of the gaseous combustion air stream is reached. This leads to condensation in the free combustion air stream, with impurities in the combustion air often serving as the starting point for the formation of condensate droplets.

[0013] Secondly, condensation can form when the recirculated hot exhaust gas or combustion air hits the inner wall of the intake system, since the wall temperature is usually below the dew point of the relevant gaseous components.

[0014] Condensate and condensate droplets are undesirable and lead to increased noise emissions in the intake system, potentially damaging the impeller blades of a compressor wheel in a turbocharger or exhaust gas turbocharger located in the intake system. The latter is associated with a reduction in the compressor's efficiency.

[0015] Regarding the problem of condensation described above, an EGR cooler can also be effective and helpful. Cooling the recirculated exhaust gas has the advantageous effect that the condensate forms not in the intake system, but already during recirculation, and can be separated during this process.

[0016] German patent application DE 10 2009 015 656 A1 describes an internal combustion engine of the type mentioned above with several recirculation lines, each containing a cooler. The recirculation lines and coolers are arranged in parallel and can be successively switched on or off according to the current demand. The exhaust gas recirculation and the cooling of the recirculated exhaust gas by means of EGR coolers are controlled by actuators in such a way as to reduce or prevent deposits in the EGR coolers.

[0017] A disadvantage of current EGR coolers is that the usable exhaust gas energy, i.e., the heat that can be extracted from the exhaust gas in the cooler using coolant, is only available and usable if exhaust gas is recirculated. If exhaust gas recirculation is deactivated, so that no exhaust gas is recirculated, the energy of the hot exhaust gas remains unused according to current technology. If this exhaust gas energy could be utilized, i.e., recovered through energy recovery, further efficiency improvements could be achieved in the internal combustion engine.

[0018] The energy from the hot exhaust gas could, for example, be used to reduce friction and thus the fuel consumption of the internal combustion engine. Rapidly warming the engine oil using exhaust heat, especially after a cold start, could be beneficial in this regard. Rapid heating of the engine oil during the warm-up phase of the internal combustion engine leads to a correspondingly rapid decrease in the oil's viscosity and thus to a reduction in friction and frictional power, particularly in the oil-lubricated bearings, such as the crankshaft bearings.

[0019] The oil could, for example, be actively heated using a heating device. A coolant-operated oil cooler can be repurposed during the warm-up phase and used to heat the oil.

[0020] In principle, rapid heating of the engine oil to reduce friction can also be promoted by rapid heating of the internal combustion engine itself, which in turn is supported, i.e. forced, by ensuring that as little heat as possible is extracted from the internal combustion engine during the warm-up phase.

[0021] Therefore, in a liquid-cooled internal combustion engine, it can also be beneficial to supply heat to the engine cooling coolant, especially during the warm-up phase or after a cold start. Exhaust gas energy could be used to heat the engine cooling coolant.

[0022] A disadvantage of current EGR coolers is that they are not designed for effective energy recovery, but rather primarily for cooling the exhaust gas – i.e., the cooling effect alone. The cooler must be able to handle all exhaust gas volumes recirculated during the operation of the internal combustion engine. Particular attention must be paid to the maximum amount of exhaust gas to be recirculated and cooled. The wide range of exhaust gas volume recirculated results in highly variable pressure conditions across the cooler. The pressure differential across the cooler changes noticeably depending on the amount of exhaust gas recirculated, to such a significant degree that it must be considered when controlling or adjusting the recirculation rate. This interaction leads to a certain degree of dynamics and necessitates a correspondingly complex and sophisticated control system for the exhaust gas recirculation.

[0023] German patent DE 20 2016 105 742 U1 describes an internal combustion engine with an intake system and an exhaust system, wherein a first return line with a first cooler and a parallel second return line with a second cooler are connected to the exhaust system and can be connected to the intake system via a combination valve. A 3-4-way valve is also provided, which allows the cooled exhaust gas from the second cooler to be routed either together with the cooled exhaust gas from the first cooler into the intake system or back into the exhaust system via an exhaust pipe. Furthermore, with the return line closed, the cooled exhaust gas from both coolers can be discharged via the exhaust pipe, and a throttling element can be used to increase the exhaust pressure upstream in the exhaust system.

[0024] JP 2013-245 563 A describes an exhaust gas recirculation system for an internal combustion engine in which several coolers are arranged in parallel to each other in order to increase the overall capacity of the cooling device and to reduce an increase in the flow resistance.

[0025] German patent DE 10 2016 214 008 A1 describes an internal combustion engine comprising an air intake, an exhaust gas path, a turbocharger, and an exhaust gas recirculation line connecting the exhaust gas path to the air intake. The system provides for cooling the exhaust gas with a cooler and directing it either into the air intake or, via the exhaust gas recirculation line, into the exhaust gas path.

[0026] In light of the above, the object of the present invention is to provide an internal combustion engine according to the preamble of claim 1 in which the exhaust gas energy can be used more effectively than according to the prior art and which is further improved with regard to exhaust gas recirculation.

[0027] This problem is solved by an internal combustion engine according to claim 1.

[0028] The internal combustion engine according to the invention is provided with several coolers for cooling recirculated exhaust gas. These coolers can be successively activated and used to cool the recirculated exhaust gas. In this way, the cooling capacity of the EGR cooling system, or the number of EGR coolers, can be adapted to the volume of exhaust gas to be cooled. This has several advantageous effects.

[0029] The pressure gradient across a single cooler changes less during operation than in the prior art, because the exhaust gas quantities to be cooled or handled by this cooler vary less.

[0030] At lower recirculation rates, a cooler can be used to cool the recirculated exhaust gas according to the invention. If the amount of recirculated and cooled exhaust gas then increases, another cooler can be activated – for example, when a predefined amount of exhaust gas is exceeded – to cool the exhaust gas and contribute to cooling the recirculated exhaust gas. Depending on the number of EGR coolers provided, for example, if three, four, or more coolers are provided, activation can occur multiple times or successively. The control or adjustment of the recirculation rate reacts less dynamically.

[0031] Furthermore, the exhaust gas piping system can be designed or switched in such a way that a cooler is used to cool exhaust gas even when exhaust gas recirculation is deactivated and no exhaust gas is recirculated, so that, in contrast to the state of the art, the energy inherent in the exhaust gas can be used or made usable within the framework of energy recovery even when exhaust gas recirculation is deactivated.

[0032] Exhaust gas energy can be used, for example, during the warm-up phase or after a cold start to heat the engine oil of the internal combustion engine, thereby reducing friction. In a liquid-cooled internal combustion engine, exhaust gas energy can be used to heat the engine cooling coolant, thus accelerating the engine's warm-up process. Both measures improve or increase the efficiency of the internal combustion engine.

[0033] The EGR coolers of the internal combustion engine according to the invention are designed both for effective cooling and for energy recovery, i.e., the utilization of the exhaust gas energy. Both aspects are taken into account according to the invention.

[0034] The internal combustion engine according to the invention thus solves the problem underlying the invention, namely to provide an internal combustion engine according to the preamble of claim 1 in which the exhaust gas energy can be used more effectively than according to the prior art and which is further improved with regard to exhaust gas recirculation.

[0035] According to the invention, the at least two return lines belong to an exhaust gas recirculation system, i.e., to a single or the same exhaust gas recirculation system. An internal combustion engine equipped with a low-pressure EGR comprising one return line and with a high-pressure EGR comprising one return line has two return lines, but not an exhaust gas recirculation system according to the invention.

[0036] Advantageous are internal combustion engine designs in which the radiators form an integral structural unit. A pre-assembled module that includes the radiators and constitutes the entire cooling unit simplifies the assembly of the exhaust gas recirculation system and the internal combustion engine as a whole, thereby also reducing costs.

[0037] Engine designs in which the coolers are separate, individual units can also be advantageous. Following a modular principle, different exhaust gas recirculation systems or different internal combustion engines can then be implemented using individual coolers.

[0038] Advantageous are embodiments of the internal combustion engine in which the coolers have a bypass line or each cooler has a bypass line.

[0039] Advantageous are embodiments of the internal combustion engine in which the coolers have a condensate separation device or each cooler has a condensate separation device.

[0040] Advantageous are embodiments of the internal combustion engine in which turbocharging is provided. Reference is made to the advantages and explanations already mentioned in connection with turbocharging.

[0041] Further advantageous embodiments of the internal combustion engine are discussed in connection with the dependent claims.

[0042] Advantageous are embodiments of the internal combustion engine in which each cooler has at least one coolant-carrying coolant jacket for energy recovery, which serves for heat transfer between the exhaust gas and the coolant.

[0043] Advantageous are embodiments of the internal combustion engine in which - a first return line is provided in which a first cooler is arranged and which can be connected to the exhaust gas discharge system upstream of the first cooler and to the intake system downstream of the first cooler using at least one actuating element, and - a second return line is provided in which a second cooler is arranged and which, using at least one actuating element, can be connected upstream of the second cooler to the exhaust gas discharge system and downstream of the second cooler optionally to the intake system or the exhaust gas discharge system.

[0044] After a cold start of the internal combustion engine, exhaust gas is preferably not recirculated, as introducing the recirculated exhaust gas into the still-cold intake system would inevitably lead to the formation of a particularly large amount of condensate. With exhaust gas recirculation deactivated, the energy of the hot exhaust gas cannot be utilized according to current technology, even though there is a specific need to heat the engine oil and / or the engine itself, especially after a cold start.

[0045] In contrast, according to the preceding embodiment, the exhaust energy of the hot exhaust gas can also be utilized even with exhaust gas recirculation deactivated, at least by means of the second cooler, which can be selectively connected downstream to either the intake system or the exhaust system. At least one actuator serves this purpose, allowing the exhaust gas lines to be switched accordingly, namely to the exhaust system. Thus, even with exhaust gas recirculation deactivated, heat can be transferred from the exhaust gas to the coolant of the second cooler. The coolant flowing or circulating through the second cooler removes the heat from its interior and makes it available for a predetermined use, thereby increasing the efficiency of the internal combustion engine. In this respect, the exhaust energy inherent in the exhaust gas of the exhaust system cannot be utilized according to the prior art, but can be according to the invention.

[0046] Advantageous are embodiments of the internal combustion engine in which the first return line downstream of the first cooler can be selectively connected to either the intake system or the exhaust system using at least one actuating element.

[0047] According to the above embodiment, the exhaust energy of the hot exhaust gas can also be used by means of the first cooler when exhaust gas recirculation is deactivated, which in this case can also be optionally connected downstream to the intake system or the exhaust gas discharge system, for which purpose at least one actuating element serves, with which the exhaust gas lines can be switched accordingly, namely connected to the exhaust gas discharge system.

[0048] With exhaust gas recirculation deactivated, both exhaust gas recirculation coolers can be used for energy recovery and to improve the efficiency of the internal combustion engine.

[0049] The first or second cooler can also be permanently connected upstream to the exhaust system, whereby at least one actuating element provided downstream of the cooler is adjusted or switched in such a way that the cooler is connected downstream to the intake system or the exhaust system.

[0050] Advantageous are embodiments of the internal combustion engine in which the first return line branches off from the exhaust gas removal system by forming a first node and leads into the intake system by forming a second node.

[0051] In this context, embodiments of the internal combustion engine are advantageous in which a first actuating element is provided in the first return line at the second node.

[0052] The first actuator acts as an EGR valve and, when exhaust gas recirculation is activated, serves to adjust the recirculation rate, or at least the amount of exhaust gas recirculated via the first recirculation line. The use of a combination valve located at the second junction allows for the measurement of the recirculated exhaust gas volume and, simultaneously, the throttling of the intake air volume.

[0053] Such a combination valve could, for example, be a flap that can be pivoted around an axis running perpendicular to the fresh air flow in such a way that, in a first end position, the front of the flap blocks the intake system and simultaneously opens the return line, and in a second end position, the back of the flap covers the return line and simultaneously opens the intake system. An additional valve body, connected to the flap and thus mechanically coupled, either opens or closes the return line. While the flap serves to adjust the amount of air supplied via the intake system, the valve body regulates the amount of exhaust gas recirculated.

[0054] Advantageous embodiments of the internal combustion engine can be those in which the second return line branches off from the exhaust gas removal system by forming a third node and leads into the intake system by forming a fourth node.

[0055] However, in the context described above, embodiments of the internal combustion engine are particularly advantageous in which the second return line branches off from the exhaust gas removal system by forming a third node and flows into the first return line downstream of the first cooler by forming a fourth node.

[0056] Then, an actuator provided at the second node can be used to adjust the total recirculation rate when exhaust gas recirculation is activated, specifically both the amount of exhaust gas recirculated via the first recirculation line and the amount of exhaust gas recirculated via the second recirculation line.

[0057] Advantageous are embodiments of the internal combustion engine in which a second actuating element is provided in the second return line downstream of the second cooler.

[0058] This second actuator can be a two-stage switchable actuator and can be used to connect or disconnect the second cooler from or from the first return line.

[0059] The second actuator can therefore also be used to connect the second cooler downstream to the exhaust system and to introduce the exhaust gas passed through the second cooler into the exhaust system, for which additional exhaust gas lines may be required. In this case, the second cooler does not cool recirculated exhaust gas. Rather, the second cooler cools exhaust gas that has been extracted from the exhaust system and is being reintroduced into it. Thus, in this case, the second cooler serves only for energy recovery, i.e., for utilizing the energy inherent in the exhaust gas.

[0060] For the reasons mentioned above, embodiments of the internal combustion engine are also advantageous in which a further exhaust gas-carrying line is provided, which branches off from the second return line by forming a fifth node between the second cooler and the second actuating element and leads into the exhaust gas discharge system by forming a sixth node.

[0061] In embodiments where the second return line connects to the first return line downstream of the first cooler, forming a fourth junction, the first cooler can also be connected downstream to the exhaust system via the further exhaust gas-carrying line. In this case, the first cooler does not cool recirculated exhaust gas, but rather exhaust gas that is reintroduced into the exhaust system. With exhaust gas recirculation deactivated, both coolers then serve for energy recovery.

[0062] In embodiments where an exhaust gas line branches off from the second return line downstream of the second cooler and enters the exhaust gas discharge system by forming a sixth node, it is advantageous to arrange the sixth node downstream of the first and third nodes in the exhaust gas discharge system.

[0063] In this context, embodiments of the internal combustion engine are advantageous in which a third actuating element is arranged at the sixth node. This third actuating element can preferably be used to block or release the further exhaust gas line or to block or release the exhaust system upstream of the sixth node. Using the third actuating element, the further exhaust gas line can be connected to the exhaust system both downstream and upstream of the radiators. The amount of exhaust gas introduced into the exhaust system via the further exhaust gas line can be controlled using the third actuating element.

[0064] The third actuating element can also serve as a continuously adjustable throttle element to increase the exhaust pressure upstream in the exhaust system, thereby also increasing the driving pressure differentials across the coolers and preventing the exhaust gas from escaping around the coolers or making it more difficult to bypass them.

[0065] To generate the required pressure differential, an additional shut-off element can be provided upstream of the exhaust gas recirculation inlet in the intake system in order to reduce the pressure downstream of the shut-off element on the inlet side.

[0066] Advantageous are embodiments of the internal combustion engine in which at least one compressor, which can be driven by means of an auxiliary drive, is arranged in the intake system.

[0067] The advantage of a compressor driven by an auxiliary drive, i.e., a supercharger, compared to an exhaust gas turbocharger, is that the supercharger can always generate and provide the required boost pressure, regardless of the operating condition of the internal combustion engine. This is particularly true for a supercharger that is electrically driven by an electric motor and therefore independent of the crankshaft speed.

[0068] According to current technology, increasing power output using exhaust gas turbocharging across all engine speed ranges is difficult. A significant drop in torque is observed below a certain engine speed. This torque drop becomes understandable when considering that the boost pressure ratio depends on the turbine pressure ratio and / or turbine power. Reducing the engine speed results in a lower exhaust gas mass flow and thus a lower turbine pressure ratio and / or turbine power. Consequently, the boost pressure ratio also decreases at lower engine speeds. This is equivalent to a drop in torque.

[0069] However, embodiments of the internal combustion engine can be advantageous in which at least one exhaust gas turbocharger is provided, comprising a turbine arranged in the exhaust system and a compressor arranged in the intake system. In an exhaust gas turbocharger, a compressor and a turbine are arranged 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 shaft is used to drive the compressor, which is also arranged on the shaft. The compressor forces and compresses the intake air, thereby supercharging the cylinders. Advantageously, an intercooler is provided downstream of the compressor in the intake system, which cools the compressed intake air before it enters the at least one cylinder.The cooler lowers the temperature and thus increases the density of the intake air, so the cooler also contributes to better cylinder filling, i.e., a greater air mass. In a sense, compression occurs through cooling.

[0070] The advantage of an exhaust gas turbocharger compared to a turbocharger driven by an auxiliary drive is that an exhaust gas turbocharger utilizes the exhaust energy of the hot exhaust gases, while a turbocharger obtains the energy required for its drive directly or indirectly from the internal combustion engine and thus, at least as long as the drive energy does not come from energy recovery, adversely affects, i.e. reduces, the efficiency.

[0071] If it is not a turbocharger driven by an electric machine, i.e., electrically driven, a mechanical or kinematic connection for power transmission between the turbocharger and the internal combustion engine is regularly required, which also adversely affects or determines the packaging in the engine compartment.

[0072] To counteract a drop in torque at low engine speeds, internal combustion engine designs with at least two exhaust gas turbochargers are particularly advantageous. Reducing the engine speed results in a smaller exhaust gas mass flow and thus a lower boost pressure ratio.

[0073] By using multiple exhaust gas turbochargers, for example several exhaust gas turbochargers connected in series or parallel, the torque characteristics of a turbocharged internal combustion engine can be noticeably improved.

[0074] To improve the torque characteristics, in addition to at least one exhaust gas turbocharger, another compressor can also be provided, namely either a turbocharger driven by an auxiliary drive or a compressor of another exhaust gas turbocharger.

[0075] In this context, embodiments of the turbocharged internal combustion engine in which the return lines lead downstream of the compressor into the intake system may be advantageous.

[0076] In a so-called high-pressure EGR system, the exhaust gas is introduced into the intake system downstream of the compressor. To provide or ensure the necessary pressure differential between the exhaust gas discharge system and the intake system for recirculation, the exhaust gas is preferably and regularly extracted from the exhaust gas discharge system upstream of the turbine in the case of an exhaust gas turbocharger. High-pressure EGR has the advantage that the exhaust gas does not pass through the compressor and therefore does not require any exhaust aftertreatment, such as in a particulate filter, before recirculation. Deposits in the compressor, which could alter the compressor's geometry, particularly the flow cross-sections, and thus reduce its efficiency, are not a concern.Condensation, if it occurs at all, takes place downstream of the compressor, which also heats the supplied charge air during compression and thus prevents or counteracts condensation.

[0077] However, designs of the turbocharged internal combustion engine in which the return lines lead upstream of the compressor into the intake system can also be advantageous.

[0078] When operating an internal combustion engine with exhaust gas turbocharging and simultaneously using high-pressure EGR, a conflict can arise if the recirculated exhaust gas is taken from the exhaust gas discharge system upstream of the turbine and is no longer available to drive the turbine.

[0079] When the exhaust gas recirculation rate increases, the exhaust gas flow introduced into the turbine decreases simultaneously. The reduced exhaust gas mass flow through the turbine results in a lower turbine pressure ratio, which in turn reduces the boost pressure ratio, equating to a lower compressor mass flow. In addition to the decreasing boost pressure, problems can arise during compressor operation, particularly regarding the surge line. Further disadvantages can result in increased pollutant emissions, such as soot formation in diesel engines during acceleration.

[0080] For this reason, concepts are needed that ensure sufficiently high boost pressures while simultaneously maintaining high exhaust gas recirculation rates. One solution is the so-called low-pressure EGR, which recirculates exhaust gas into the intake system that has already passed through the turbine. To achieve this, the low-pressure EGR system extracts exhaust gas from the exhaust system downstream of the turbine and preferably directs it upstream of the compressor into the intake system to create the pressure differential between the exhaust system and the intake system required for recirculation.

[0081] The exhaust gas recirculated via low-pressure EGR is mixed with fresh air upstream of the compressor. The resulting mixture of fresh air and recirculated exhaust gas forms the charge air, which is fed to the compressor and compressed. The compressed charge air is preferably cooled in a charge air cooler downstream of the compressor.

[0082] Since exhaust gas passes through the compressor, it is preferably subjected to exhaust gas aftertreatment downstream of the turbine. Low-pressure EGR can also be combined with high-pressure EGR.

[0083] For the reasons already mentioned, it can therefore be advantageous to design the turbocharged internal combustion engine in which the return lines branch off from the exhaust gas discharge system upstream of the turbine.

[0084] Advantageous are embodiments of the turbocharged internal combustion engine in which the turbine of a planned exhaust gas turbocharger has a variable turbine geometry, allowing for further adaptation to the operation of the internal combustion engine by adjusting the turbine geometry or the effective turbine cross-section. Adjustable guide vanes are arranged in the turbine inlet area to influence the flow direction. Unlike the rotor blades of the rotating impeller, the guide vanes do not rotate with the turbine shaft.

[0085] If the turbine has a fixed, unchanging geometry, the guide vanes are not only stationary but also completely immobile in the inlet area, i.e., rigidly fixed, if a guide vane system is even provided. With a variable geometry, however, the guide vanes are indeed stationary but not completely immobile; they can rotate around their axis, allowing the flow towards the rotor blades to be influenced.

[0086] By adjusting the turbine geometry, it is possible to influence the exhaust gas pressure upstream of the turbine, thus influencing the pressure differential between the exhaust gas removal system and the intake system, and therefore the recirculation rate of the high-pressure EGR.

[0087] For the reasons already mentioned, it can also be advantageous to design the turbocharged internal combustion engine in which the return lines branch off from the exhaust gas removal system downstream of the turbine.

[0088] In this context, advantageous embodiments of the turbocharged internal combustion engine are those in which at least one exhaust aftertreatment system is provided in the exhaust system between the turbine and the branching return lines. Since exhaust gas passes through the compressor, it is preferably subjected to exhaust aftertreatment downstream of the turbine.

[0089] Advantageous are embodiments of the turbocharged internal combustion engine in which a particulate filter is provided as an exhaust aftertreatment system for the aftertreatment of the exhaust gas.

[0090] To minimize soot emissions, a regenerative particulate filter is used, which filters and stores the soot particles from the exhaust gas. These soot particles are then intermittently burned off during the filter's regeneration process. Without catalytic assistance, the temperatures required for regenerating the particulate filter are approximately 550°C. Therefore, additional measures are regularly employed to ensure filter regeneration under all operating conditions.

[0091] The filter regeneration process introduces heat into the exhaust gas, increasing the exhaust gas temperature and thus the exhaust gas enthalpy. At the filter outlet, an energy-rich exhaust gas is therefore available, which can be used in the manner according to the invention.

[0092] It can also be advantageous to use a turbocharged internal combustion engine in which an oxidation catalyst is provided as an exhaust aftertreatment system for the aftertreatment of the exhaust gas.

[0093] Although oxidation of unburned hydrocarbons and carbon monoxide in the exhaust system occurs even without additional measures at sufficiently high temperatures and with adequate oxygen levels, these reactions quickly cease due to the rapidly decreasing exhaust gas temperature downstream and the consequent rapid reduction in reaction rate. Therefore, catalytic reactors are used, which, through the use of catalytic materials, ensure oxidation even at low temperatures. If nitrogen oxides also need to be reduced, this can be achieved in a gasoline engine by using a three-way catalytic converter.

[0094] Oxidation is an exothermic reaction, whereby the released heat increases the temperature and thus the enthalpy of the exhaust gas. A more energy-rich exhaust gas is therefore available at the outlet of the oxidation catalyst. In this respect, the provision of an oxidation catalyst is particularly useful and advantageous with regard to the utilization of exhaust gas energy according to the invention.

[0095] Advantageous are embodiments of the internal combustion engine in which a bypass line is provided to circumvent the coolers, which bridges the EGR coolers and with which the exhaust gas recirculated via exhaust gas recirculation can be introduced into the intake system bypassing the coolers.

[0096] It can be advantageous to bypass the EGR cooling system, for example, to prevent additional heat from being introduced into the engine's liquid cooling system. This approach is particularly useful if the engine's liquid cooling system is already under heavy load, such as at full throttle. If exhaust gas recirculation is used for engine braking, it is also beneficial to return the hot exhaust gas uncooled.

[0097] Advantageous are embodiments of the internal combustion engine in which liquid cooling is provided to form engine cooling.

[0098] Advantageous are embodiments of the internal combustion engine in which the at least one cylinder head of the internal combustion engine is equipped with at least one coolant jacket integrated in the cylinder head to form liquid cooling.

[0099] Liquid cooling proves particularly advantageous in turbocharged engines, as the thermal load on turbocharged engines is significantly higher compared to conventional internal combustion engines. If the cylinder head has an integrated exhaust manifold, it is subject to a higher thermal load than a conventional cylinder head equipped with an external manifold. This places increased demands on the cooling system.

[0100] In this context, advantageous are embodiments of the internal combustion engine in which the liquid cooling has a cooling circuit that includes the coolers of the exhaust gas recirculation.

[0101] If the EGR coolers are integrated into the engine cooling circuit, many components and assemblies required to form a circuit only need to be provided in a single version, since they can be used for both the EGR cooler cooling circuit and the engine cooling circuit, which leads to synergies and cost savings, but also to weight savings.

[0102] Preferably, only one pump for circulating the coolant and one container for storing the coolant are provided. The heat transferred to the coolant by the internal combustion engine and the EGR cooling system can be extracted from the coolant in a common heat exchanger.

[0103] The exhaust gas energy or heat absorbed by the coolant in the EGR cooling system can also be used more easily in this way, for example to heat the internal combustion engine or the engine oil.

[0104] The invention is described below using an exemplary embodiment and in accordance with the Fig. 1, Fig. 2, Fig. 3, Fig. 4 and Fig. 5 described in more detail. This shows: Fig. 1 schematically a first embodiment of the internal combustion engine including exhaust gas recirculation in a first operating mode, Fig. 2 schematically the first embodiment of the internal combustion engine including exhaust gas recirculation in a second operating mode, Fig. 3 schematically the first embodiment of the internal combustion engine including exhaust gas recirculation in a third operating mode, Fig. 4 schematically the first embodiment of the internal combustion engine including exhaust gas recirculation in a fourth operating mode, and Fig. 5 schematically the first embodiment of the internal combustion engine including exhaust gas recirculation in a fifth operating mode.

[0105] Fig. Figure 1 schematically shows a first embodiment of the internal combustion engine 1 including exhaust gas recirculation 4 in a first operating mode.

[0106] The internal combustion engine 1 has an intake system 3 to supply the cylinders with charge air and an exhaust system 2 to remove the exhaust gases from the cylinders.

[0107] The internal combustion engine 1 is equipped with an exhaust gas turbocharger 6 for the purpose of turbocharging, which comprises a turbine 6b arranged in the exhaust gas discharge system 2 and a compressor 6a arranged in the intake system 3.

[0108] Furthermore, an exhaust gas recirculation system 4 is provided with two recirculation lines 4a, 4b, each containing a cooler 5a, 5b. The coolers 5a, 5b each have a coolant-carrying jacket, which serves for heat transfer between the exhaust gas and the coolant. The coolers 5a, 5b are arranged in parallel, can be used independently of each other for cooling the exhaust gas or for energy recovery, and are fluidically connected or connectable to the engine cooling system.

[0109] The first recirculation line 4a branches off from the exhaust gas discharge system 2 downstream of the turbine 6b, forming a first junction 2a, and enters the intake system 3 upstream of the compressor 6a, forming a second junction 3a. A first actuator 7 is provided at the second junction 3a. A combination valve 7a is used as the first actuator 7, which serves to adjust the recirculated exhaust gas quantity, i.e., the recirculation rate, and thus also to deactivate the exhaust gas recirculation 4.

[0110] The second return line 4b also branches off downstream of the turbine 6b and downstream of the first node 2a, forming a third node 2c from the exhaust gas discharge system 2 and flows into the first return line 4a downstream of the first cooler 5a, forming a fourth node 10.

[0111] A further exhaust gas line 11 is provided, which branches off from the second return line 4b by forming a fifth node 12 downstream of the second cooler 5b and flows into the exhaust gas discharge system 2 by forming a sixth node 2d.

[0112] The sixth node 2d is located downstream of the first and third nodes 2a, 2c in the exhaust system 2. A third actuator 2b is located at the sixth node 2d. The third actuator 2b is a continuously adjustable flap 2b' and, in the first operating mode, serves to block the further exhaust gas-carrying line 11.

[0113] In the second return line 4b, a second actuator 8 is provided downstream of the second cooler 5b and downstream of the fifth junction 12. The second actuator 8 is a two-stage switchable 2-2-way valve 8a, which has two line connections and two switching positions and connects both coolers 5a, 5b to the intake system 3 via the second junction 3a or to the exhaust system 2 via the sixth junction 2d, or alternatively deactivates the second cooler 5b or disconnects it from the first return line 4a and connects it to the exhaust system 2 via the sixth junction 2d.

[0114] Both coolers 5a and 5b can therefore be used to cool recirculated exhaust gas, but also for energy recovery when exhaust gas recirculation is deactivated. This will be explained below using the following examples: Fig. 2 to 5 explained in more detail.

[0115] In the first operating mode of the Fig. 1 is the second actuator 8 in the open position, and the first actuator 7 disconnects the first return line 4a from the intake system 3. This deactivates the exhaust gas recirculation 4. Due to the blocked exhaust gas line 11, no energy recovery occurs using the EGR coolers 5a and 5b.

[0116] Fig. Figure 2 schematically shows the first embodiment of the internal combustion engine 1 including exhaust gas recirculation 4 in a second operating mode. It is intended only as a supplement to Fig. 1 will be carried out, which is why reference is made to it. Fig. 1. The same reference symbols were used for the same parts or components.

[0117] In the second operating mode, both coolers 5a and 5b cool the recirculated exhaust gas. The second recirculation line 4b is connected to the first recirculation line 4a, and the first recirculation line 4a is connected to the intake system 3. The first actuator 7 is switched or set accordingly. The second actuator 8 remains in the open position, and the exhaust gas line 11 remains closed.

[0118] Especially when the internal combustion engine has been or is being operated under higher loads and the coolant or coolers 5a, 5b are heated up, it can be advantageous to recirculate exhaust gas through both coolers 5a, 5b. In this case, the heated coolers 5a, 5b and the hot coolant cool the exhaust gas less effectively. In some cases, the heated coolers 5a, 5b and the hot coolant may even transfer heat into the exhaust gas. The high-temperature exhaust gas is recirculated into the cylinders, thereby increasing the cylinder temperature and reducing friction.

[0119] Fig. Figure 3 schematically shows the first embodiment of the internal combustion engine 1 including exhaust gas recirculation 4 in a third operating mode. It is intended only as a supplement to Fig. 1 or 2 are to be carried out, which is why reference is made to Fig. 1 or 2. The same reference symbols were used for the same parts or components.

[0120] In the third operating mode, only the first cooler 5a cools the recirculated exhaust gas. For this purpose, the first recirculation line 4a is connected to the intake system 3 via the second junction 3a. The second recirculation line 4b, along with the second cooler 5b, is disconnected from the first recirculation line 4a and connected to the exhaust system 2 via the exhaust gas line 11 and the sixth junction 2d. The second cooler 5b thus serves for energy recovery. The first actuator 7 connects the first recirculation line 4a to the intake system 3, and the second actuator 8 is in the closed position, disconnecting the second recirculation line 4b from the first recirculation line 4a. In the third operating mode, the third actuator 2b opens the additional exhaust gas line 11.

[0121] Fig. Figure 4 schematically shows the first embodiment of the internal combustion engine 1 including exhaust gas recirculation 4 in a fourth operating mode. It is intended only as a supplement to the previous ones. Fig. 1, Fig. 2 and Fig. 3 will be carried out, which is why reference is made to the Fig. 1, Fig. 2 and Fig. 3. The same reference symbols were used for the same parts or components.

[0122] In the fourth operating mode, exhaust gas recirculation 4 is deactivated, and both coolers 5a and 5b are used for energy recovery when exhaust gas recirculation 4 is deactivated. The first and second actuators 7 and 8 are switched or set accordingly. Both coolers 5a and 5b are connected to the exhaust gas discharge system 2 via the sixth node 2d and are separated from the intake system 3.

[0123] The first actuator 7 disconnects the first return line 4a from the intake system 3, and the second actuator 8 is in the open position and connects the two return lines 4a and 4b. In the fourth operating mode, the third actuator 2b releases the further exhaust gas line 11.

[0124] Fig. Figure 5 schematically shows the first embodiment of the internal combustion engine 1 including exhaust gas recirculation 4 in a fifth operating mode. It is intended only as a supplement to Fig. 3 will be carried out, which is why reference is made to it. Fig. 3. The same reference symbols were used for the same parts or components.

[0125] In the fifth operating mode, the first cooler 5a cools the recirculated exhaust gas. For this purpose, the first actuator 7 connects the first recirculation line 4a to the intake system 3.

[0126] The second return line 4b, together with the second cooler 5b, is separate from the first return line 4a and connected to the exhaust system 2 via the exhaust gas line 11 and the sixth junction 2d. The second cooler 5b thus serves for energy recovery. The second actuator 8 is in the closed position and separates the second return line 4b from the first return line 4a.

[0127] In the fifth operating mode, the third actuator 2b releases both the further exhaust gas line 11 and the exhaust gas discharge system 2 upstream of the sixth node 2d. The latter accommodates large volumes of exhaust gas that can occur at high loads or high speeds, where, to prevent excessive exhaust back pressure, the pivotable flap 2b' acts as a pressure relief valve and releases the exhaust gas discharge system 2. This pressure relief function can also be triggered in other operating modes and, in the first embodiment shown in the figures, is implemented passively and self-regulatingly by means of a spring. Reference sign 1 internal combustion engine 2 Exhaust gas discharge system 2a first junction 2b third actuator 2b' continuously adjustable flap 2c third node 2d sixth node 3 Intake system 3a second junction 4 Exhaust gas recirculation 4a first return line 4b second return line 5a first cooler 5b second cooler 6 exhaust gas turbochargers 6a Compressor of the exhaust gas turbocharger 6b Turbine of the exhaust gas turbocharger 7 first actuating element 7a Combination valve 8 second actuator 8a 2-way valve 9 Exhaust aftertreatment system 10 fourth junction 11 exhaust pipe 12 fifth junction EGR Exhaust Gas Recirculation m MAGR Mass of recirculated exhaust gas m Frischluft Mass of supplied fresh air or combustion air n mot Engine speed x AGR Exhaust gas recirculation rate

Claims

[1] Internal combustion engine (1) with - at least one cylinder, - an intake system (3) for supplying air to at least one cylinder, - an exhaust gas discharge system (2) for the discharge of exhaust gases, - an exhaust gas recirculation system (4) comprising at least two recirculation lines (4a, 4b), wherein each recirculation line (4a, 4b) is provided with a cooler (5a, 5b) and the coolers (5a, 5b) are arranged in parallel and can be used independently of each other for cooling exhaust gas, and - at least three actuators (2b, 7, 8) for setting a predefinable amount of recirculated exhaust gas, at which - each cooler (5a, 5b) can be used for cooling exhaust gas for the purpose of energy recovery, - a first return line (4a) is provided, which branches off from the exhaust system (2) by forming a first node (2a) and opens into the intake system (3) by forming a second node (3a), in which a first cooler (5a) is arranged and which can be connected to the exhaust system (2) upstream of the first cooler (5a) and to the intake system (3) downstream of the first cooler (5a) using at least one actuating element (7), - a second return line (4b) is provided, which branches off from the exhaust system (2) forming a third node (2c) and opens into the first return line (4a) downstream of the first cooler (5a) forming a fourth node (10), in which a second cooler (5b) is arranged and which can be connected upstream of the second cooler (5b) to the exhaust system (2) and downstream of the second cooler (5b) optionally to the intake system (3) or the exhaust system (2) using at least one actuating element (7, 8), and - a second actuating element (8) is provided in the second return line (4b) downstream of the second cooler (5b), characterized by , that - an exhaust gas line (11) is provided which branches off from the second return line (4b) by forming a fifth node (12) between the second cooler (5b) and the second actuator (8) and leads into the exhaust gas discharge system (2) by forming a sixth node (2d), wherein - in the first return line (4a) at the second node (3a) a first actuating element (7) is provided, - the sixth node (2d) is located downstream of the first and third nodes (2a, 2c) in the exhaust system (2) and - a third actuating element (2b) is arranged at the sixth node (2d) and wherein - the second actuating element (8) is a two-stage switchable actuating element for connecting or disconnecting the second cooler (5b) with or from the first return line (4a) and - the third actuating element (2b) is a continuously adjustable throttle element for adjusting an operating state between blocking or releasing the exhaust gas line (11) and blocking or releasing the exhaust gas system (2) upstream of the sixth node (2d). [2] Internal combustion engine (1) according to claim 1, characterized by , that each cooler (5a, 5b) has at least one coolant jacket carrying a coolant for energy recovery, which serves to transfer heat between the exhaust gas and the coolant. [3] Internal combustion engine (1) according to claim 1 or 2, characterized by , that the first return line (4a) downstream of the first cooler (5a) can be optionally connected to either the intake system (3) or the exhaust system (2) using at least one actuator (7, 8). [4] Internal combustion engine (1) according to any one of the preceding claims, characterized by, that at least one compressor which can be driven by means of an auxiliary drive is arranged in the intake system (3). [5] Internal combustion engine (1) according to any one of the preceding claims, characterized by , that at least one exhaust gas turbocharger (6) is provided, comprising a turbine (6b) arranged in the exhaust gas discharge system (2) and a compressor (6a) arranged in the intake system (3). [6] Internal combustion engine (1) according to claim 4 or 5, characterized by , that the return lines (4a, 4b) flow into the intake system (3) downstream of the compressor (6a). [7] Internal combustion engine (1) according to claim 4 or 5, characterized by , that the return lines (4a, 4b) flow into the intake system (3) upstream of the compressor (6a). [8] Internal combustion engine (1) according to any one of claims 5 to 7, characterized by , that the return lines (4a, 4b) branch off from the exhaust gas discharge system (2) upstream of the turbine (6b). [9] Internal combustion engine (1) according to claim 7, characterized by, that the return lines (4a, 4b) branch off from the exhaust gas discharge system (2) downstream of the turbine (6b). [10] Internal combustion engine (1) according to claim 9, characterized by , that at least one exhaust aftertreatment system (9) is provided in the exhaust system (2) between the turbine (6b) and the branching return lines (4a, 4b). [11] Internal combustion engine (1) according to claim 10, characterized by , that a particulate filter is provided as an exhaust aftertreatment system (9) for the aftertreatment of the exhaust gas. [12] Internal combustion engine (1) according to any one of the preceding claims, characterized by , that liquid cooling is provided for the formation of engine cooling. [13] Internal combustion engine (1) according to claim 12, characterized by , that the liquid cooling system has a cooling circuit which includes the coolers (5a, 5b) of the exhaust gas recirculation (4).

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