Supercharged internal combustion engine with cooled exhaust gas recirculation

Abstract

Supercharged internal combustion engine (1) with - at least one cylinder, - an intake system (3) for supplying the at least one cylinder with air, - an exhaust gas removal system (2) for removing the exhaust gases, and - an exhaust gas recirculation system (4) comprising at least two recirculation lines (4a, 4b), in each of which a cooler (5a, 5b) is arranged, wherein the coolers (5a, 5b) are arranged in parallel and at least one adjusting element (7, 8) is provided for setting a predeterminable amount of exhaust gas to be recirculated, characterized in that - the coolers (5a, 5b) can be used independently of one another to cool exhaust gas for the purpose of energy recovery, for which purpose the exhaust gas discharge system (2) is designed and switchable in such a way that a cooler (5a, 5b) can be used to cool exhaust gas even when the exhaust gas recirculation (4) is deactivated.

Description

[0001] The invention relates to a supercharged internal combustion engine with at least one cylinder, an intake system for supplying at least one cylinder with air, an exhaust gas removal system for removing the exhaust gases, and an exhaust gas recirculation system comprising at least two recirculation lines (4a, 4b), in each of which a cooler (5a, 5b) is arranged, wherein the coolers (5a, 5b) are arranged in parallel and at least one adjusting element (7, 8) is provided for setting a predeterminable amount of exhaust gas to be recirculated.

[0002] Such an internal combustion engine is known from JP 2013- 245 563 A. However, the two coolers cannot be used independently of each other to cool exhaust gas when exhaust gas recirculation is deactivated for the purpose of energy recovery.

[0003] Another internal combustion engine with exhaust gas recirculation and multiple exhaust gas recirculation cooler modules is known from DE 10 2009 015 656 A1. Although the cooler modules each have bypass sections for the respective cooler sections, they are arranged one behind the other and therefore cannot be flowed through separately.

[0004] DE 10 2008 020 408 A1 discloses an internal combustion engine with exhaust gas recirculation and energy recovery from a cooler.

[0005] From EP 2 025 912 A1 an internal combustion engine is known with a high-pressure circuit and a low-pressure circuit for exhaust gas recirculation, wherein the low-pressure circuit has an exhaust gas cooler.

[0006] The internal combustion engine described in FR 2 930 280 A1 has two exhaust gas coolers arranged one behind the other, with a branch line with a valve located between the first and second coolers for exhaust gas recirculation into the intake line. After the second cooler, the exhaust gas is recirculated into the exhaust system.

[0007] 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" encompasses diesel engines and gasoline engines, but also hybrid internal combustion engines that utilize a hybrid combustion process, as well as hybrid drives that, in addition to the internal combustion engine, comprise an electric motor that can be connected to the internal combustion engine for driving purposes, which absorbs power from the internal combustion engine or delivers additional power as a switchable auxiliary drive.

[0008] In the development of internal combustion engines, constant efforts are made to minimize fuel consumption. Furthermore, the goal is to reduce pollutant emissions in order to comply with future emissions limits.

[0009] Internal combustion engines are increasingly being equipped with turbocharging. Turbocharging is primarily a method for increasing performance by compressing the charge air required for the engine's combustion process, allowing a larger mass of charge air to be supplied to each cylinder per combustion cycle. This allows the fuel mass and thus the mean effective pressure to be increased.

[0010] Turbocharging is a suitable means of increasing the power of an internal combustion engine without changing the displacement, or of reducing the displacement while maintaining the same power. In either case, turbocharging increases the package power and improves power-to-weight ratio. If the displacement is reduced, the load spectrum can be shifted toward higher loads, where specific fuel consumption is lower, under the same vehicle conditions. Turbocharging an internal combustion engine therefore supports efforts to minimize fuel consumption, i.e., improve the efficiency of the internal combustion engine.

[0011] With a suitable transmission design, so-called downspeeding can also be achieved, which also results in lower specific fuel consumption. Downspeeding takes advantage of the fact that specific fuel consumption is generally lower at low engine speeds, especially at higher loads.

[0012] With a targeted turbocharging design, benefits can also be achieved in terms of exhaust emissions. For example, with suitable turbocharging in diesel engines, nitrogen oxide emissions can be reduced without compromising efficiency. At the same time, hydrocarbon emissions can be positively influenced. Carbon dioxide emissions, which are directly correlated with fuel consumption, also decrease with lower fuel consumption.

[0013] However, further measures are necessary to comply with future limits for pollutant emissions. The focus of development work is, among other things, on reducing 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 concept for reducing nitrogen oxide emissions is to use combustion processes with lower combustion temperatures.

[0014] Exhaust gas recirculation (EGR), i.e. the recirculation of combustion gases from the exhaust side to the intake side, is effective in this case, as increasing the exhaust gas recirculation rate can significantly reduce nitrogen oxide emissions. The exhaust gas recirculation rate x AGR is determined to be x AGR = m AGR / (m AGR + m Frischluft ), where m AGR the mass of recirculated exhaust gas and m Frischluftrefers to the supplied fresh air. The oxygen provided via exhaust gas recirculation must be taken into account if necessary.

[0015] To achieve a significant reduction in nitrogen oxide emissions, high exhaust gas recirculation rates may be required, which can be in the order of x AGR ≈ 60% to 70% and more. Such high recirculation rates require cooling of the recirculated exhaust gas, which lowers the temperature of the exhaust gas and increases its density, allowing a larger exhaust gas mass to be recirculated. Consequently, exhaust gas recirculation is regularly equipped with a cooler. The exhaust gas recirculation of the internal combustion engine, which is the subject of the present invention, also has a cooling system, i.e., at least one EGR cooler having a coolant jacket carrying coolant, which serves to transfer heat between the exhaust gas and the coolant.

[0016] Problems can arise when introducing the recirculated exhaust gas into the intake system if the temperature of the recirculated hot exhaust gas decreases and condensate forms.

[0017] Firstly, condensate can form when the recirculated hot exhaust gas meets and mixes with cool fresh air in the intake system. The exhaust gas cools down, whereas 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 below the exhaust gas temperature of the recirculated exhaust gas. As the exhaust gas cools down, liquids, in particular water, previously contained in gaseous form in the exhaust gas or combustion air can condense if the dew point of a component of the gaseous combustion air flow is undershot. This leads to condensate formation in the free combustion air flow, with impurities in the combustion air often forming the starting point for the formation of condensate droplets.

[0018] On the other hand, condensate 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.

[0019] Condensate and condensate droplets are undesirable and lead to increased noise emissions in the intake system, potentially damaging the impeller blades of a compressor impeller located in the intake system, such as a supercharger or exhaust gas turbocharger. The latter is associated with a reduction in compressor efficiency.

[0020] An EGR cooler can also be effective and helpful with regard to the problem of condensate formation described above. Cooling the recirculated exhaust gas during the recirculation process has the advantageous effect that the condensate does not form in the intake system, but rather during the recirculation process, and can be separated during the recirculation process.

[0021] A disadvantage of state-of-the-art EGR coolers is that, by design, the usable exhaust energy—that is, the heat extracted from the exhaust gas in the cooler using coolant—is only generated and usable when exhaust gas is recirculated. If exhaust gas recirculation is deactivated, meaning no exhaust gas is recirculated, the exhaust energy of the hot exhaust gas remains unused according to the state-of-the-art technology. If this exhaust energy could be utilized—that is, recovered through energy recovery—further efficiency improvements could be achieved in the internal combustion engine.

[0022] 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. Rapid heating of the engine oil using exhaust heat could be effective in this regard, particularly after a cold start. Rapid heating of the engine oil during the warm-up phase of the internal combustion engine ensures a correspondingly rapid decrease in oil viscosity and thus a reduction in friction and friction, particularly in oil-supplied bearings, such as the crankshaft bearings.

[0023] The oil could be actively heated using a heater, for example. A coolant-driven oil cooler can be used for this purpose during the warm-up phase and to heat the oil.

[0024] 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 removing as little heat as possible from the internal combustion engine during the warm-up phase.

[0025] In this respect, it may also be beneficial to add heat to the engine cooling system in a liquid-cooled internal combustion engine, especially during the warm-up phase or after a cold start. Exhaust gas energy could be used to heat the engine cooling system.

[0026] Another disadvantage of state-of-the-art EGR coolers is that they are not designed for effective energy recovery, but rather for exhaust gas cooling, i.e. the pure cooling effect is the main focus. The cooler must be able to handle all of the exhaust gas volumes that are recirculated via exhaust gas recirculation during operation of the internal combustion engine. In particular, the maximum amount of exhaust gas that can be recirculated and cooled must be taken into account. The range of variation in the amount of exhaust gas that is recirculated via exhaust gas recirculation leads to very different pressure conditions at the cooler. The pressure gradient across the cooler changes noticeably depending on the amount of exhaust gas that is being recirculated, i.e. in such a significant way that this must be taken into account when controlling or setting the recirculation rate. The resulting interaction leads to a certain dynamic and requires a correspondingly complex orcomplex control of exhaust gas recirculation.

[0027] Against the background of the above, it is the object of the present invention to provide a supercharged internal combustion engine according to the preamble of claim 1, in which the exhaust gas energy can be used more effectively than in the prior art and which is further improved with regard to exhaust gas recirculation.

[0028] This task is solved by the coolers being able to be used independently of one another to cool exhaust gas for the purpose of energy recovery, for which purpose the exhaust gas removal system is designed and switchable in such a way that a cooler can be used to cool exhaust gas even when exhaust gas recirculation is deactivated.

[0029] The internal combustion engine according to the invention provides several coolers with which recirculated exhaust gas can be cooled. The coolers can be switched on successively in individual cases and used to cool the recirculated exhaust gas. In this respect, the cooling capacity of the EGR cooling system or the number of EGR coolers can be adapted to the amount of exhaust gas to be cooled. This has several advantageous effects.

[0030] The pressure gradient across a single cooler changes less during cooler operation than in the prior art, since the exhaust gas quantities to be cooled or handled by this cooler vary less.

[0031] At lower recirculation rates, a cooler can be used according to the invention to cool the recirculated exhaust gas. If the amount of exhaust gas to be recirculated and cooled increases, for example, if a predefined exhaust gas amount is exceeded, another cooler can be switched on, i.e. activated, 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, it can be switched on multiple times or successively. The control or adjustment of the recirculation rate reacts less dynamically.

[0032] In addition, the piping system of the exhaust gas lines can be designed or switchable in such a way that a cooler is used and utilized to cool exhaust gas even when exhaust gas recirculation is deactivated and no exhaust gas is recirculated, so that, in contrast to the prior art, the energy inherent in the exhaust gas can be used or utilized within the framework of energy recovery even when exhaust gas recirculation is deactivated.

[0033] For example, exhaust gas energy can be used during the warm-up phase or after a cold start to heat the engine's engine oil and thus reduce the engine's friction. In a liquid-cooled engine, exhaust gas energy can be used to heat the engine's cooling system and thus accelerate the engine's warm-up. Both measures improve or increase the engine's efficiency.

[0034] 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 exhaust gas energy. Both aspects are taken into account by the invention.

[0035] The internal combustion engine that is the subject of the present invention is a turbocharged internal combustion engine. Reference is made to the advantages and statements already mentioned in connection with turbocharging.

[0036] The internal combustion engine according to the invention thus achieves the object underlying the invention, namely to provide a supercharged internal combustion engine according to the preamble of claim 1, in which the exhaust gas energy can be used more effectively than in the prior art and which is further improved with regard to exhaust gas recirculation.

[0037] 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 system comprising a return line and with a high-pressure EGR system comprising a return line has two return lines, but not an exhaust gas recirculation system according to the invention.

[0038] Embodiments of the internal combustion engine in which the coolers form an integral structural unit are advantageous. A pre-assembled assembly that includes the coolers and constitutes the entire cooling unit simplifies the assembly of the exhaust gas recirculation system and the internal combustion engine as a whole, thus reducing costs.

[0039] Embodiments of the internal combustion engine in which the coolers are designed as individual, separate coolers can also be advantageous. According to the modular principle, different exhaust gas recirculation systems can then be formed with individual coolers or equipped with different internal combustion engines.

[0040] Further advantageous embodiments of the internal combustion engine according to the invention are discussed in connection with the subclaims.

[0041] Embodiments of the supercharged internal combustion engine are advantageous in which - a first return line is provided, in which a first cooler is arranged and which, using at least one adjusting element, can be connected upstream of the first cooler to the exhaust gas discharge system and downstream of the first cooler to the intake system, - a second return line is provided, in which a second cooler is arranged and which, using at least one adjusting 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, and - each cooler has at least one coolant jacket carrying coolant for the purpose of energy recovery, which serves to transfer heat between the exhaust gas and the coolant.

[0042] 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 result in the formation of particularly large amounts of condensate. With exhaust gas recirculation deactivated, the state of the art does not allow the exhaust gas energy of the hot exhaust gas to be utilized, even though there is a need to specifically heat the engine oil or the internal combustion engine, especially after a cold start of the internal combustion engine.

[0043] In contrast, according to the above embodiment, the exhaust gas energy of the hot exhaust gas can be utilized even when exhaust gas recirculation is deactivated; at least by means of the second cooler, which can be connected downstream selectively to the intake system or the exhaust gas removal system, for which purpose at least one actuating element is used to switch the exhaust gas lines accordingly, namely to the exhaust gas removal system. Even when exhaust gas recirculation is deactivated, heat can thus be transferred from the exhaust gas to the coolant of the second cooler, with the coolant flowing or circulating through the second cooler removing the heat from the interior of the second cooler and supplying it to a predeterminable use, thereby increasing the efficiency of the internal combustion engine. In this respect, the exhaust gas energy inherent in the exhaust gas of the exhaust gas removal system cannot be utilized according to the prior art, but can be utilized according to the invention.

[0044] Embodiments of the supercharged internal combustion engine are advantageous in which the first return line downstream of the first cooler can be selectively connected to the intake system or the exhaust gas discharge system using at least one actuating element.

[0045] According to the above embodiment, the exhaust gas energy of the hot exhaust gas can also be used when exhaust gas recirculation is deactivated by means of the first cooler, which in this case can also be connected downstream optionally to the intake system or the exhaust gas discharge system, for which purpose at least one actuating element is used with which the exhaust gas-carrying lines can be switched accordingly, namely connected to the exhaust gas discharge system.

[0046] When exhaust gas recirculation is deactivated, both exhaust gas recirculation coolers can be used to recover energy and improve the efficiency of the internal combustion engine.

[0047] The first or second cooler can also be permanently connected upstream to the exhaust gas discharge system, wherein 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 gas discharge system.

[0048] Embodiments of the supercharged internal combustion engine are advantageous in which the first return line branches off from the exhaust gas discharge system to form a first node and opens into the intake system to form a second node.

[0049] In this context, embodiments of the supercharged internal combustion engine are advantageous in which a first actuating element is provided in the first return line at the second node.

[0050] The first control element acts as an EGR valve and, when exhaust gas recirculation is activated, adjusts 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 the amount of recirculated exhaust gas to be measured and the intake of fresh air to be throttled at the same time.

[0051] Such a combination valve can, for example, be a flap that can be pivoted about 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. In a second end position, the rear of the flap covers the return line and simultaneously opens the intake system. An additional valve body, which is connected to the flap and thus mechanically coupled, either opens or blocks the return line. While the flap serves to adjust the amount of air supplied via the intake system, the valve body controls the amount of recirculated exhaust gas.

[0052] Embodiments of the supercharged internal combustion engine in which the second return line branches off from the exhaust gas discharge system to form a third node and opens into the intake system to form a fourth node can be advantageous.

[0053] However, in the context described above, embodiments of the supercharged internal combustion engine are particularly advantageous in which the second return line branches off from the exhaust gas discharge system to form a third node and opens into the first return line to form a fourth node downstream of the first cooler.

[0054] Then, when exhaust gas recirculation is activated, an adjusting element provided at the second junction point can be used to adjust the total recirculation rate, namely both the exhaust gas quantity recirculated via the first recirculation line and the exhaust gas quantity recirculated via the second recirculation line.

[0055] Embodiments of the supercharged internal combustion engine are advantageous in which a second control element is provided in the second return line downstream of the second cooler. This second control element can be used to activate or deactivate the second cooler.

[0056] In individual cases, however, the second actuator can also be used to connect the second cooler downstream to the exhaust gas removal system, for which additional exhaust gas lines may be provided. In this case, the second cooler does not cool recirculated exhaust gas. Rather, the second cooler cools exhaust gas that has been removed from the exhaust gas removal system and is fed back into the exhaust gas removal system. This means that the second cooler serves only for energy recovery, i.e., for harnessing the energy inherent in the exhaust gas.

[0057] For the reasons stated above, embodiments of the supercharged internal combustion engine are also advantageous in which an exhaust gas-carrying line is provided which branches off from the second return line downstream of the second cooler, forming a fifth node, and opens into the exhaust gas discharge system, forming a sixth node.

[0058] Embodiments of the supercharged internal combustion engine in which the second actuating element is arranged at the fifth node are advantageous.

[0059] In embodiments in which the second recirculation line flows into the first recirculation line, forming a fourth junction point downstream of the first cooler, the first cooler can also be connected downstream to the exhaust gas removal system via the additional exhaust gas-carrying line. In this case, the first cooler does not cool the exhaust gas to be recirculated, but rather the exhaust gas that is fed back into the exhaust gas removal system. Both coolers then serve to recover energy when exhaust gas recirculation is deactivated.

[0060] In embodiments in which an exhaust gas-carrying line branches off from the second return line downstream of the second cooler and opens into the exhaust gas discharge system to form a sixth node, it is advantageous to arrange the sixth node downstream of the first and third nodes in the exhaust gas discharge system.

[0061] In this context, embodiments of the supercharged internal combustion engine are advantageous in which a throttle element is arranged in the exhaust gas discharge system upstream of the sixth node and downstream of the first and third nodes. The throttle element serves to increase the exhaust gas pressure upstream in the exhaust gas discharge system, which also increases the driving pressure gradients across the coolers and prevents the exhaust gas from escaping the coolers or makes it more difficult to bypass the coolers.

[0062] To generate the required pressure drop, a shut-off element can also be provided upstream of the exhaust gas recirculation inlet in the intake system in order to reduce the pressure upstream of the compressor on the inlet side.

[0063] Embodiments of the supercharged internal combustion engine are advantageous in which at least one compressor drivable by means of an auxiliary drive is arranged in the intake system.

[0064] The advantage of a compressor driven by an auxiliary drive, i.e., a supercharger, over an exhaust gas turbocharger is that the charger can always generate and deliver the required boost pressure, regardless of the operating state of the internal combustion engine. This is especially true for a charger that is electrically driven by an electric motor and is therefore independent of the crankshaft speed.

[0065] The current state of the art makes it difficult to increase power across all engine speed ranges using exhaust gas turbocharging. A more pronounced drop in torque is observed below a certain engine speed. This torque drop becomes understandable when one considers that the boost pressure ratio depends on the turbine pressure ratio or turbine power. Reducing the engine speed leads to a lower exhaust gas mass flow and thus to a lower turbine pressure ratio or turbine power. Consequently, the boost pressure ratio also decreases at lower engine speeds. This is synonymous with a drop in torque.

[0066] Nevertheless, embodiments of the supercharged internal combustion engine can be advantageous in which at least one exhaust gas turbocharger is provided, which comprises a turbine arranged in the exhaust gas discharge 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 flow is fed to the turbine and expands, releasing energy in the turbine, which causes the shaft to rotate. The energy released by the exhaust gas flow to the shaft is used to drive the compressor, which is also arranged on the shaft. The compressor conveys and compresses the charge air supplied to it, thereby achieving supercharging of the cylinders. Advantageously, an intercooler is provided downstream of the compressor in the intake system, with which the compressed charge air is cooled before it enters the at least one cylinder.The cooler lowers the temperature and thus increases the density of the charge air, so the cooler also contributes to better filling of the cylinders, i.e., a larger air mass. In a sense, compression occurs through cooling.

[0067] The advantage of an exhaust gas turbocharger compared to a charger driven by an auxiliary drive is that an exhaust gas turbocharger uses the exhaust energy of the hot exhaust gases, whereas a charger draws 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 the efficiency, i.e. reduces it.

[0068] If the charger is not driven by an electric motor, i.e. electrically, a mechanical or kinematic connection is usually required to transmit power between the charger and the internal combustion engine, which also adversely affects or determines the packaging in the engine compartment.

[0069] To counteract a torque drop at low engine speeds, engine designs that incorporate at least two exhaust gas turbochargers are particularly advantageous. Reducing the engine speed results in a lower exhaust gas mass flow and thus a lower boost pressure ratio.

[0070] By using several exhaust gas turbochargers, for example several exhaust gas turbochargers connected in series or in parallel, the torque characteristics of a turbocharged internal combustion engine can be noticeably improved.

[0071] To improve the torque characteristics, in addition to the at least one exhaust gas turbocharger, a further compressor can be provided, namely both a charger driven by an auxiliary drive and a compressor of a further exhaust gas turbocharger.

[0072] In this context, embodiments of the supercharged internal combustion engine in which the return lines open into the intake system downstream of the compressor can be advantageous.

[0073] In a so-called high-pressure EGR, the exhaust gas is introduced into the intake system downstream of the compressor. In order to provide or ensure the pressure gradient required for recirculation between the exhaust gas removal system and the intake system, the exhaust gas is preferably and regularly taken from the exhaust gas removal system upstream of the associated turbine in the case of exhaust gas turbocharging. High-pressure EGR has the advantage that the exhaust gas does not pass through the compressor and therefore does not require exhaust gas aftertreatment, for example, in a particulate filter, before recirculation. There is no risk of deposits in the compressor, which could change the geometry of the compressor, particularly the flow cross-sections, and thus impair the compressor's efficiency.Condensation occurs - if at all - downstream of the compressor, which also heats the charge air supplied to it during compression and thus prevents or counteracts condensation formation.

[0074] However, embodiments of the supercharged internal combustion engine in which the return lines open into the intake system upstream of the compressor can also be advantageous.

[0075] When operating an internal combustion engine with exhaust gas turbocharging and simultaneous use of high-pressure EGR, a conflict can arise if the recirculated exhaust gas is taken from the exhaust gas removal system upstream of the turbine and is no longer available to drive the turbine.

[0076] As the exhaust gas recirculation rate increases, the exhaust gas flow fed into the turbine decreases simultaneously. The reduced exhaust gas mass flow through the turbine results in a lower turbine pressure ratio, which also reduces the boost pressure ratio, which in turn reduces the compressor mass flow. In addition to the decreasing boost pressure, problems can also arise during compressor operation regarding the surge limit. Disadvantages can also arise in pollutant emissions, for example, with regard to soot formation in diesel engines during acceleration.

[0077] For this reason, concepts are required that ensure sufficiently high boost pressures combined with high exhaust gas recirculation rates. One solution is the so-called low-pressure EGR, which recirculates exhaust gas back into the intake system, which has already flowed through the turbine. To achieve this, the low-pressure EGR takes exhaust gas from the exhaust gas removal system downstream of the turbine and directs it into the intake system, preferably upstream of the compressor, in order to achieve the pressure gradient required for recirculation between the exhaust gas removal system and the intake system.

[0078] 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 downstream of the compressor in an intercooler.

[0079] Since exhaust gas passes through the compressor, the exhaust gas downstream of the turbine is preferably subjected to exhaust aftertreatment. Low-pressure EGR can also be combined with high-pressure EGR.

[0080] For the reasons already mentioned, embodiments of the supercharged internal combustion engine in which the return lines branch off from the exhaust gas removal system upstream of the turbine can be advantageous.

[0081] Advantageous embodiments of the supercharged internal combustion engine are those in which the turbine of a provided exhaust gas turbocharger has a variable turbine geometry, which allows 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 inlet area of ​​the turbine to influence the flow direction. Unlike the rotor blades of the rotating impeller, the guide vanes do not rotate with the turbine shaft.

[0082] 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 device is provided at all. With a variable geometry, however, the guide vanes are stationary but not completely immobile. Instead, they can rotate around their axes, allowing the flow to the rotor blades to be influenced.

[0083] By adjusting the turbine geometry, the exhaust gas pressure upstream of the turbine can be influenced, thus the pressure gradient between the exhaust gas discharge system and the intake system and thus the recirculation rate of the high-pressure EGR.

[0084] For the reasons already mentioned, embodiments of the supercharged internal combustion engine in which the return lines branch off from the exhaust gas removal system downstream of the turbine can also be advantageous.

[0085] In this context, embodiments of the supercharged internal combustion engine are advantageous in which at least one exhaust gas aftertreatment system is provided in the exhaust gas removal system between the turbine and the branching recirculation lines. Since exhaust gas is passed through the compressor, the exhaust gas is preferably subjected to exhaust gas aftertreatment downstream of the turbine.

[0086] Embodiments of the supercharged internal combustion engine in which a particulate filter is provided as an exhaust gas aftertreatment system for the aftertreatment of the exhaust gas are advantageous.

[0087] To minimize soot emissions, a regenerative particulate filter is used in this engine. It filters and stores the soot particles from the exhaust gas. These soot particles are intermittently combusted during filter regeneration. The temperatures required to regenerate the particulate filter are approximately 550°C without catalytic support. Therefore, additional measures are regularly used to ensure filter regeneration under all operating conditions.

[0088] Regeneration of the filter introduces heat into the exhaust gas, increasing the exhaust gas temperature and thus the exhaust gas enthalpy. Thus, an energy-rich exhaust gas is available at the filter outlet, which can be utilized in the manner according to the invention.

[0089] Embodiments of the supercharged internal combustion engine in which an oxidation catalyst is provided as an exhaust gas aftertreatment system for aftertreating the exhaust gas can also be advantageous.

[0090] Oxidation of unburned hydrocarbons and carbon monoxide in the exhaust gas removal system occurs even without additional measures at sufficiently high temperatures and in the presence of sufficient oxygen. However, these reactions quickly cease due to the rapidly decreasing exhaust gas temperature downstream and the resulting rapid reduction in reaction rate. Therefore, catalytic reactors are used, which use catalytic materials to ensure oxidation even at low temperatures. If nitrogen oxides are also to be reduced, this can be achieved in gasoline engines by using a three-way catalyst.

[0091] Oxidation is an exothermic reaction, with the released heat increasing the temperature and thus the enthalpy of the exhaust gas. A more energy-rich exhaust gas is thus available at the outlet of the oxidation catalyst. In this respect, the provision of an oxidation catalyst is sensible and advantageous, particularly with regard to the inventive utilization of exhaust energy.

[0092] Embodiments of the supercharged internal combustion engine are advantageous in which a bypass line is provided to bypass the coolers, which bypasses the EGR coolers and with which the exhaust gas recirculated via exhaust gas recirculation can be introduced into the intake system while bypassing the coolers.

[0093] It may be advisable to bypass the EGR cooling, for example, to prevent additional heat from being introduced into the engine's liquid cooling system. This approach is recommended if the engine's liquid cooling system is already under heavy strain, for example, at full load. If exhaust gas recirculation is used for engine braking, it is also advisable to recirculate the hot exhaust gas without cooling.

[0094] Embodiments of the supercharged internal combustion engine in which liquid cooling is provided to form an engine cooling system are advantageous.

[0095] Embodiments of the supercharged internal combustion engine are advantageous 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 a liquid cooling system.

[0096] Liquid cooling is particularly advantageous for turbocharged engines, as the thermal load on turbocharged engines is significantly higher than on conventional internal combustion engines. If the cylinder head has an integrated exhaust manifold, it is subject to higher thermal loads than a conventional cylinder head equipped with an external manifold. This places increased demands on the cooling system.

[0097] In this context, embodiments of the supercharged internal combustion engine are advantageous in which the liquid cooling has a cooling circuit that includes the exhaust gas recirculation coolers.

[0098] If the EGR coolers are integrated into the engine cooling circuit, many of the components and assemblies required to create a circuit generally only need to be provided in a single version, as these can be used for both the EGR cooler cooling circuit and the engine cooling circuit, which leads to synergies and cost savings, but also brings with it weight savings.

[0099] For example, only one pump for pumping the coolant and one container for storing the coolant are preferably 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.

[0100] The exhaust energy or exhaust 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.

[0101] In the following, the invention is explained using an embodiment and according to the Fig. 1, Fig. 2, Fig. 3, Fig. 4 and Fig. 5 is described in more detail. Here: Fig. 1 schematically shows a first embodiment of the supercharged internal combustion engine including exhaust gas recirculation, Fig. 2 schematically shows the first embodiment of the supercharged internal combustion engine including exhaust gas recirculation in a first operating mode, Fig. 3 schematically shows the first embodiment of the supercharged internal combustion engine including exhaust gas recirculation in a second operating mode, Fig. 4 schematically shows the first embodiment of the supercharged internal combustion engine including exhaust gas recirculation in a third operating mode, and Fig. 5 schematically shows the first embodiment of the supercharged internal combustion engine including exhaust gas recirculation in a fourth operating mode.

[0102] Fig. 1 schematically shows a first embodiment of the supercharged internal combustion engine 1 including exhaust gas recirculation 4.

[0103] The internal combustion engine 1 has an intake system 3 for supplying the cylinders with charge air and an exhaust gas removal system 2 for removing the exhaust gases from the cylinders.

[0104] The internal combustion engine 1 is equipped with an exhaust gas turbocharger 6 for charging purposes, which comprises a turbine 6b arranged in the exhaust gas discharge system 2 and a compressor 6a arranged in the intake system 3.

[0105] Furthermore, an exhaust gas recirculation system 4 is provided with two return lines 4a, 4b, with a cooler 5a, 5b arranged in each return line 4a, 4b. The coolers 5a, 5b each have a coolant jacket carrying coolant, which serves to transfer heat between the exhaust gas and the coolant. The coolers 5a, 5b are arranged in parallel, can be used independently of one another for cooling exhaust gas or for energy recovery, and are or can be connected fluidically to the engine cooling system.

[0106] The first recirculation line 4a branches off from the exhaust gas discharge system 2, forming a first junction 2a downstream of the turbine 6b, and flows into the intake system 3 upstream of the compressor 6a, forming a second junction 3a. A first control element 7 is provided at the second junction 3a. A combination valve 7a is used as the first control element 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.

[0107] The second return line 4b also branches off from the exhaust gas discharge system 2 downstream of the turbine 6b and downstream of the first node 2a, forming a third node 2c, and flows into the first return line 4a, forming a fourth node 10 downstream of the first cooler 5a.

[0108] A further exhaust gas line 11 is provided, which branches off from the second return line 4b downstream of the second cooler 5b, forming a fifth node 12, and opens into the exhaust gas discharge system 2, forming a sixth node 2d.

[0109] The sixth node 2d is presently arranged downstream of the first and third nodes 2a, 2c in the exhaust gas discharge system 2. Upstream of the sixth node 2d and downstream of the first and third nodes 2a, 2c, a throttle element 2b is arranged in the exhaust gas discharge system 2. The throttle element 2b serves to increase the exhaust gas pressure upstream in the exhaust gas discharge system 2, which also increases the driving pressure gradients across the coolers 5a, 5b.

[0110] In the second return line 4b, downstream of the second cooler 5b, a second actuating element 8 is provided, which is arranged at the fifth node 12. The second actuating element 8 is a 3-4-way valve 8a, which has three line connections and four switching positions and connects both coolers 5a, 5b to the intake system 3 via the second node 3a or to the exhaust gas removal system 2 via the sixth node 2d, or deactivates the second cooler 5b or separates it from the first return line 4a and connects it to the exhaust gas removal system 2 via the sixth node 2d.

[0111] Both coolers 5a, 5b can therefore be used to cool recirculated exhaust gas, but also for energy recovery when exhaust gas recirculation is deactivated. This is explained below using the Fig. 2 to 5 are explained in more detail.

[0112] Fig. Figure 2 schematically shows the first embodiment of the supercharged internal combustion engine 1 including exhaust gas recirculation 4 in a first operating mode. It is intended only as a supplement to Fig. 1, which is why reference is made to Fig. 1. The same reference symbols were used for the same parts or components.

[0113] In the first operating mode, both coolers 5a, 5b cool recirculating 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 and second actuators 7, 8 are switched or adjusted accordingly.

[0114] Fig. Figure 3 shows schematically the first embodiment of the supercharged internal combustion engine 1 including exhaust gas recirculation 4 in a second operating mode. It is intended only as a supplement to Fig. 1, which is why reference is made to Fig. 1. The same reference symbols were used for the same parts or components.

[0115] In the second operating mode, only the first cooler 5a cools recirculating exhaust gas, for which purpose the first return line 4a is connected to the intake system 3 via the second node 3a. The second return line 4b, including the second cooler 5b, is separated from the first return line 4a and connected to the exhaust gas removal system 2 via the sixth node 2d. The second cooler 5b thus serves for energy recovery. The first and second actuators 7, 8 are switched or adjusted accordingly.

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

[0117] In the third operating mode, exhaust gas recirculation 4 is deactivated, and both coolers 5a, 5b are used for energy recovery when exhaust gas recirculation 4 is deactivated. The first and second actuators 7, 8 are switched or adjusted accordingly. Both coolers 5a, 5b are connected to the exhaust gas removal system 2 via the sixth node 2d and are separated from the intake system 3.

[0118] Fig. Figure 5 schematically shows the first embodiment of the supercharged internal combustion engine 1 including exhaust gas recirculation 4 in a fourth operating mode. It is intended only as a supplement to Fig. 1, which is why reference is made to Fig. 1. The same reference symbols were used for the same parts or components.

[0119] Both coolers 5a, 5b are deactivated or unusable, both with regard to cooling the recirculated exhaust gas and with regard to energy recovery. Exhaust gas recirculation 4 and energy recovery are deactivated. The first and second actuators 7, 8 are switched or adjusted accordingly. Reference symbol 1 supercharged internal combustion engine 2 Exhaust gas removal system 2a first junction 2b Throttle element 2c third junction 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 control element 7a Combi valve 8 second control element 8a 3-4-way valve 9 Exhaust aftertreatment system 10 fourth junction 11 exhaust pipe 12 fifth junction EGR exhaust gas recirculation m AGR Mass of recirculated exhaust gas m Frischluft Mass of supplied fresh air or combustion air n mot Speed ​​of the internal combustion engine x AGR Exhaust gas recirculation rate

Claims

[1] Supercharged internal combustion engine (1) with - at least one cylinder, - an intake system (3) for supplying the at least one cylinder with air, - an exhaust gas removal system (2) for removing the exhaust gases, and - an exhaust gas recirculation system (4) comprising at least two recirculation lines (4a, 4b), in each of which a cooler (5a, 5b) is arranged, wherein the coolers (5a, 5b) are arranged in parallel and at least one adjusting element (7, 8) is provided for setting a predeterminable amount of exhaust gas to be recirculated, characterized by , that - the coolers (5a, 5b) can be used independently of one another to cool exhaust gas for the purpose of energy recovery, for which purpose the exhaust gas removal system (2) is designed and switchable in such a way that a cooler (5a, 5b) can be used to cool exhaust gas even when the exhaust gas recirculation (4) is deactivated. [2] Supercharged internal combustion engine (1) according to claim 1, characterized by , that - a first return line (4a) is provided, in which a first cooler (5a) is arranged and which can be connected upstream of the first cooler (5a) to the exhaust gas discharge system (2) and downstream of the first cooler (5a) to the intake system (3) using at least one adjusting element (7), - a second return line (4b) is provided, in which a second cooler (5b) is arranged and which, using at least one adjusting element (7, 8), can be connected upstream of the second cooler (5b) to the exhaust gas removal system (2) and downstream of the second cooler (5b) selectively to the intake system (3) or the exhaust gas removal system (2), and - each cooler (5a, 5b) has at least one coolant jacket carrying coolant for the purpose of energy recovery, which serves to transfer heat between the exhaust gas and the coolant. [3] Supercharged internal combustion engine (1) according to claim 2, characterized bythat the first return line (4a) downstream of the first cooler (5a) can be selectively connected to the intake system (3) or the exhaust gas discharge system (2) using at least one adjusting element (7, 8). [4] Supercharged internal combustion engine (1) according to claim 2 or 3, characterized by that the first return line (4a) branches off from the exhaust gas discharge system (2) to form a first node (2a) and opens into the intake system (3) to form a second node (3a). [5] Supercharged internal combustion engine (1) according to claim 4, characterized by that a first control element (7) is provided in the first return line (4a) at the second node (3a). [6] Supercharged internal combustion engine (1) according to claim 4 or 5, characterized bythat the second return line (4b) branches off from the exhaust gas discharge system (2) to form a third node (2c) and opens into the first return line (4a) downstream of the first cooler (5a) to form a fourth node (10). [7] Supercharged internal combustion engine (1) according to claim 6, characterized by that a second adjusting element (8) is provided in the second return line (4b) downstream of the second cooler (5b). [8] Supercharged internal combustion engine (1) according to claim 6 or 7, characterized by that an exhaust gas-carrying line (11) is provided which branches off from the second return line (4b) downstream of the second cooler (5b) to form a fifth node (12) and opens into the exhaust gas discharge system (2) to form a sixth node (2d). [9] Supercharged internal combustion engine (1) according to claim 8, characterized by that the second adjusting element (8) is arranged at the fifth node point (12). [10] Supercharged internal combustion engine (1) according to claim 8 or 9, characterized by that the sixth node (2d) is arranged downstream of the first and third nodes (2a, 2c) in the exhaust gas discharge system (2). [11] Supercharged internal combustion engine (1) according to claim 10, characterized by that a throttle element (2b) is arranged in the exhaust gas discharge system (2) upstream of the sixth node (2d) and downstream of the first and third nodes (2a, 2c). [12] Supercharged internal combustion engine (1) according to one of the preceding claims, characterized by that at least one compressor drivable by means of an auxiliary drive is arranged in the intake system (3). [13] Supercharged internal combustion engine (1) according to one of the preceding claims, characterized by that at least one exhaust gas turbocharger (6) is provided, which comprises a turbine (6b) arranged in the exhaust gas discharge system (2) and a compressor (6a) arranged in the intake system (3). [14] Supercharged internal combustion engine (1) according to claim 12 or 13, characterized by that the return lines (4a, 4b) open into the intake system (3) downstream of the compressor (6a). [15] Supercharged internal combustion engine (1) according to claim 12 or 13, characterized by that the return lines (4a, 4b) open into the intake system (3) upstream of the compressor (6a). [16] Supercharged internal combustion engine (1) according to one of claims 13 to 15, characterized by that the return lines (4a, 4b) branch off from the exhaust gas discharge system (2) upstream of the turbine (6b). [17] Supercharged internal combustion engine (1) according to claim 15, characterized by that the return lines (4a, 4b) branch off from the exhaust gas removal system (2) downstream of the turbine (6b). [18] Supercharged internal combustion engine (1) according to claim 17, characterized bythat at least one exhaust gas aftertreatment system (9) is provided in the exhaust gas discharge system (2) between the turbine (6b) and the branching return lines (4a, 4b). [19] Supercharged internal combustion engine (1) according to claim 18, characterized by that a particle filter is provided as an exhaust gas aftertreatment system (9) for the aftertreatment of the exhaust gas. [20] Supercharged internal combustion engine (1) according to one of the preceding claims, characterized by that liquid cooling is provided to create engine cooling. [21] Supercharged internal combustion engine (1) according to claim 20, characterized by that the liquid cooling has a cooling circuit which comprises the coolers (5a, 5b) of the exhaust gas recirculation (4).

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