DE102016218995A1 - Internal combustion engine with cooled exhaust gas recirculation - Google Patents

Abstract

The invention relates to an internal combustion engine (1) having - at least one cylinder, - an intake system (3) for supplying the at least one cylinder with air, - a Abgasabführsystem (2) for discharging the exhaust gases, and - an exhaust gas recirculation (4), the at least a return line (4a, 4b), wherein in the at least one return line (4a, 4b) at least one cooler (5a, 5b) and at least one adjusting element (7, 8) are provided for setting a predetermined recirculating exhaust gas amount. An internal combustion engine (1) of the above type is to be provided in which the exhaust gas energy can be used more effectively than in the prior art and which is further improved in terms of exhaust gas recirculation. This is achieved by an internal combustion engine (1) of the type mentioned, which is characterized in that at least two return lines (4a, 4b) are provided, in each of which a radiator (5a, 5b) is arranged, wherein the radiator (5a, 5b ) are arranged in parallel and are used independently for the cooling of exhaust gas for the purpose of energy recovery.

Description

• – mindestens einem Zylinder,
• – einem Ansaugsystem zur Versorgung des mindestens einen Zylinders mit Luft,
• – einem Abgasabführsystem zur Abführung der Abgase, und
• – einer Abgasrückführung, die mindestens eine Rückführleitung umfasst, wobei in der mindestens einen Rückführleitung mindestens ein Kühler und mindestens ein Stellelement zur Einstellung einer vorgebbaren rückzuführenden Abgasmenge vorgesehen sind.

The invention relates to an internal combustion engine with

• At least one cylinder,
• An intake system for supplying the at least one cylinder with air,
• An exhaust gas removal system for exhausting the exhaust gases, and
• - An exhaust gas recirculation, comprising at least one return line, wherein in the at least one return line, at least one cooler and at least one adjusting element are provided for setting a predetermined recirculating exhaust gas amount.

An internal combustion engine of the type mentioned is used as a motor vehicle drive. In the context of the present invention, the term internal combustion engine includes diesel engines and gasoline engines, but also hybrid internal combustion engines that use a hybrid combustion process, as well as hybrid drives, which in addition to the internal combustion engine include an electric motor that can be connected to the engine, which receives power from the internal combustion engine or as switchable auxiliary drive additionally delivers power.

In the development of internal combustion engines, efforts are constantly being made to minimize fuel consumption. In addition, the aim is to reduce pollutant emissions in order to be able to comply with future limit values for pollutant emissions.

Internal combustion engines are increasingly equipped with a charge, the charge is primarily a method of increasing performance, in which the charge air required for the engine combustion process is compressed, whereby each cylinder per cycle a larger charge air mass can be supplied. As a result, the fuel mass and thus the medium pressure can be increased.

The charge is a suitable means to increase the capacity of an internal combustion engine with unchanged displacement or to reduce the displacement at the same power. In any case, the charging leads to an increase in space performance and a lower power mass. If the cubic capacity is reduced, the load spectrum can be shifted to higher loads at the same vehicle boundary conditions, where the specific fuel consumption is lower. The charging of an internal combustion engine thus supports the efforts to minimize fuel consumption, d. H. to improve the efficiency of the internal combustion engine.

By means of a suitable transmission design, a so-called downspeeding can additionally be realized, as a result of which a lower specific fuel consumption is likewise achieved. Downspeeding exploits the fact that the specific fuel consumption at low speeds is regularly lower, especially at higher loads.

With targeted design of the charge also benefits in the exhaust emissions can be achieved. Thus, by means of suitable charging, for example in the diesel engine, the nitrogen oxide emissions can be reduced without sacrificing efficiency. At the same time, the hydrocarbon emissions can be favorably influenced. The emissions of carbon dioxide, which correlate directly with fuel consumption, also decrease with decreasing fuel consumption.

However, further measures are needed to meet future emission limits. Among other things, the development work focuses on reducing nitrogen oxide emissions, which are of particular relevance to diesel engines. Since the formation of nitrogen oxides requires not only an excess of air but also high temperatures, one concept for reducing nitrogen oxide emissions is to use combustion processes with lower combustion temperatures.

Here, the exhaust gas recirculation (EGR), ie the return of combustion gases from the exhaust side to the inlet side, expedient in which with increasing exhaust gas recirculation rate, the nitrogen oxide emissions can be significantly reduced. In this case, the exhaust gas recirculation rate x _{AGR is} determined as x _AGR = m _AGR / (m _AGR + m _{fresh air} ), where m _{AGR designates} the mass of recirculated exhaust gas and m _{fresh air} the fresh air supplied. The oxygen provided via exhaust gas recirculation may need to be considered.

In order to achieve a significant reduction in nitrogen oxide emissions, high exhaust gas recirculation rates may be required, which may be on the order of x _AGR ≈ 60% to 70% and more. Such high recirculation rates require cooling of the recirculated exhaust gas, with which the temperature of the exhaust gas is lowered and the density of the exhaust gas is increased, so that a larger exhaust mass can be returned. Consequently, exhaust gas recirculation is regularly equipped with a radiator. Also, the exhaust gas recirculation of the internal combustion engine, which is the subject of the present invention, has a cooling, ie via at least one EGR cooler, which has a coolant jacket leading coolant, which serves the heat transfer between the exhaust gas and coolant.

Problems may arise in introducing the recirculated exhaust gas into the intake system as the temperature of the recirculated hot exhaust gas decreases and condensate forms.

On the one hand, condensate can form when the recirculated hot exhaust gas in the intake system coincides with cool fresh air and is mixed. The exhaust gas cools, whereas the temperature of the fresh air is raised. The temperature of the mixture of fresh air and recirculated exhaust gas, d. H. the temperature of the combustion air is below the exhaust gas temperature of the recirculated exhaust gas. As part of the cooling of the exhaust gas previously contained gaseous in the exhaust gas or in the combustion air, especially water, condense out when the taut temperature of a component of the gaseous combustion air flow is exceeded. It comes to a condensation in the free combustion air flow, often impurities in the combustion air form the starting point for the formation of condensate droplets.

On the other hand, condensate can form when the recirculated hot exhaust gas or the combustion air strikes the inner wall of the intake system, since the wall temperature is generally below the taut temperature of the relevant gaseous components.

Condensate and condensate droplets are undesirable and lead to increased noise emission in the intake system, possibly damaging the blades of a compressor arranged in the intake compressor of a supercharger or an exhaust gas turbocharger. The latter is associated with a reduction in the efficiency of the compressor.

Also with regard to the problem of the condensate formation described above, an EGR cooler can be effective or helpful. The cooling of the recirculated exhaust gas in the context of the return has the advantageous effect that the condensate forms not only in the intake system, but already during recycling and can be deposited in the context of recycling.

A disadvantage of the EGR coolers according to the prior art is that the usable exhaust gas energy, d. H. the heat which can be withdrawn from the exhaust gas in the cooler by means of coolant, inherently only arises and can be used when exhaust gas is recirculated. If the exhaust gas recirculation is deactivated so that no exhaust gas is recirculated, the exhaust gas energy of the hot exhaust gas according to the prior art remains unused. Could this exhaust energy be used, d. H. be recovered in the context of energy recovery, further efficiency advantages could be achieved in the internal combustion engine.

The energy of the hot exhaust gas could be used, for example, to reduce the friction and thus the fuel consumption of the internal combustion engine. In this case, rapid heating of the engine oil by means of exhaust heat, in particular after a cold start, could be expedient. Rapid heating of the engine oil during the warm-up phase of the engine provides for a correspondingly rapid decrease in the viscosity of the oil and thus for a reduction of friction or friction, especially in the oil-bearing, for example, the bearings of the crankshaft.

The oil could be actively heated, for example by means of a heater. A coolant-operated oil cooler can be used for this purpose in the warm-up phase and used to heat the oil.

In principle, rapid heating of the engine oil to reduce friction losses can also be achieved by rapid heating of the internal combustion engine itself, which in turn is assisted by d. H. forced, is that the internal combustion engine during the warm-up phase as little heat is removed.

In this respect, it may also be expedient in a liquid-cooled internal combustion engine to supply heat to the coolant of the engine cooling, in particular in the warm-up phase or after a cold start. For heating the coolant of the engine cooling, the exhaust gas energy could be used.

A disadvantage of the EGR coolers of the prior art is also that the coolers are not designed with a view to effective energy recovery, but rather the cooling of the exhaust gas, d. H. the pure cooling effect is in the foreground. In this case, the radiator must be able to cope with all the amounts of exhaust gas to be recirculated via exhaust gas recirculation during operation of the internal combustion engine. In particular, the maximum amount of exhaust gas to be recirculated and cooled must be taken into account. The range of variation of the amount of exhaust gas to be recirculated via exhaust gas recirculation leads to very different pressure conditions at the radiator. The pressure gradient across the radiator changes appreciably depending on the amount of exhaust gas to be recirculated, ie. H. in such a relevant way that this must be taken into account in the control or adjustment of the return rate. The resulting interaction leads to a certain dynamics and requires a correspondingly complex or complex control of exhaust gas recirculation.

In view of the foregoing, it is the object of the present invention 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 in the prior art and which is further improved in terms of exhaust gas recirculation.

• – mindestens einem Zylinder,
• – einem Ansaugsystem zur Versorgung des mindestens einen Zylinders mit Luft,
• – einem Abgasabführsystem zur Abführung der Abgase, und
• – einer Abgasrückführung, die mindestens eine Rückführleitung umfasst, wobei in der mindestens einen Rückführleitung mindestens ein Kühler und mindestens ein Stellelement zur Einstellung einer vorgebbaren rückzuführenden Abgasmenge vorgesehen sind,

die dadurch gekennzeichnet ist, dass

• – mindestens zwei Rückführleitungen vorgesehen sind, in denen jeweils ein Kühler angeordnet ist, wobei die Kühler parallel angeordnet sind und unabhängig voneinander zur Kühlung von Abgas zwecks Energierückgewinnung verwendbar sind.

This problem is solved by an internal combustion engine

• At least one cylinder,
• An intake system for supplying the at least one cylinder with air,
• An exhaust gas removal system for exhausting the exhaust gases, and
• An exhaust gas recirculation, which comprises at least one return line, wherein at least one cooler and at least one adjusting element are provided in the at least one return line for setting a predefinable recirculating exhaust gas quantity,

which is characterized in that

• - At least two return lines are provided, in each of which a radiator is arranged, wherein the radiator are arranged in parallel and are independently usable for cooling exhaust gas for the purpose of energy recovery.

In the internal combustion engine according to the invention a plurality of coolers are provided with which recirculating exhaust gas can be cooled. The coolers can be switched on successively in individual cases and used for the exhaust gas to be recirculated. In this respect, the cooling capacity of the EGR cooling or the number of EGR coolers of the amount of exhaust gas to be cooled can be adjusted. This has several beneficial effects.

The pressure gradient across a single radiator changes less during operation of the radiator than in the prior art, since the exhaust gas quantities to be cooled or managed by this radiator vary less strongly.

For smaller recirculation rates, according to the invention, a cooler can be used for cooling the recirculating exhaust gas. If the amount of exhaust gas to be recirculated and to be cooled then increases, another cooler can be switched on, for example if a predefinable amount of exhaust gas is exceeded. H. be activated to cool exhaust gas and contribute to the cooling of the recirculating exhaust gas. Depending on the number of provided EGR cooler, if, for example, three, four or more radiators are provided, can be switched on several times or successively. The control or adjustment of the return rate is less dynamic.

In addition, the line system of the exhaust-carrying lines can be designed or switchable in such a way that a cooler is used and used for cooling exhaust gas even when the exhaust gas recirculation is deactivated, if no exhaust gas is recirculated, so that in contrast to the prior art also When the exhaust gas recirculation is deactivated, the energy inherent in the exhaust gas can be utilized or utilized in the context of energy recovery.

The exhaust energy can be used for example in the warm-up phase or after a cold start to heat the engine oil of the engine and thus reduce the friction of the engine. In a liquid-cooled internal combustion engine, the exhaust gas energy can be used to heat the coolant of the engine cooling and thus to accelerate the heating of the internal combustion engine. Both measures improve or increase the efficiency of the internal combustion engine.

The EGR coolers of the internal combustion engine according to the invention are both in terms of effective cooling and in terms of energy recovery, d. H. the use of exhaust energy, designed. Both aspects are taken into account according to the invention.

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 energy can be used more effectively than in the prior art and further improved in terms of exhaust gas recirculation.

The at least two return lines according to the invention belong to an exhaust gas recirculation, d. H. to a single or the same exhaust gas recirculation. An internal combustion engine, which is equipped with a low-pressure EGR comprising a return line and with a high-pressure EGR comprising a return line, has two return lines, but not an exhaust gas recirculation according to the invention.

Embodiments of the internal combustion engine in which the radiators form an integral structural unit are advantageous. A preassembled module, which comprises the radiator and represents the entire cooling unit, simplifies the assembly of the exhaust gas recirculation or of the internal combustion engine as a whole and thus also reduces the costs.

Embodiments of the internal combustion engine may also be advantageous, in which the radiators are designed as isolated, separate coolers. According to the modular principle can then with individual coolers different exhaust gas recirculations are formed or different internal combustion engines are equipped.

Advantageous embodiments of the internal combustion engine, in which a charge is provided. Reference is made to the already mentioned in connection with the charging advantages and statements made.

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

• – eine erste Rückführleitung vorgesehen ist, in der ein erster Kühler angeordnet ist und die unter Verwendung mindestens eines Stellelementes stromaufwärts des ersten Kühlers mit dem Abgasabführsystem und stromabwärts des ersten Kühlers mit dem Ansaugsystem zumindest verbindbar ist,
• – eine zweite Rückführleitung vorgesehen ist, in der ein zweiter Kühler angeordnet ist und die unter Verwendung mindestens eines Stellelementes stromaufwärts des zweiten Kühlers mit dem Abgasabführsystem und stromabwärts des zweiten Kühlers wahlweise mit dem Ansaugsystem oder dem Abgasabführsystem zumindest verbindbar ist, und
• – jeder Kühler zwecks Energierückgewinnung mindestens einen Kühlmittel führenden Kühlmittelmantel aufweist, welcher der Wärmeübertragung zwischen dem Abgas und dem Kühlmittel dient.

Embodiments of the internal combustion engine are advantageous in which

• A first return line is provided in which a first radiator is arranged and which is at least connectable to the intake system using at least one actuating element upstream of the first radiator with the exhaust-gas removal system and downstream of the first radiator,
• A second return line is provided in which a second radiator is arranged and which is at least connectable to the intake system or the Abgasabführsystem using at least one actuating element upstream of the second radiator with the Abgasabführsystem and downstream of the second radiator, and
• - Each cooler for the purpose of energy recovery has at least one coolant-carrying coolant jacket, which serves the heat transfer between the exhaust gas and the coolant.

After a cold start of the internal combustion engine, preferably no exhaust gas is recirculated, since unavoidable and particularly large amounts of condensate would form when the recirculated exhaust gas is introduced into the still cold intake system. When then deactivated exhaust gas recirculation, the exhaust gas energy of the hot exhaust gas can not be used in the prior art, although just after a cold start of the internal combustion engine there is a need to specifically heat the engine oil or the internal combustion engine.

In contrast, the exhaust gas energy of the hot exhaust gas according to the above embodiment can be used even when the exhaust gas recirculation is deactivated; at least by means of the second radiator, which is optionally connectable downstream with either the intake system or the Abgasabführsystem, including at least one actuator serves with which the exhaust-gas lines switch accordingly, namely connect to the Abgasabführsystem. Thus, even with deactivated exhaust gas recirculation heat can thus be transferred from the exhaust gas to the coolant of the second radiator, wherein the coolant flowing through the second radiator or coolant dissipates the heat from the interior of the second radiator and supplies a predetermined use, whereby the efficiency of the internal combustion engine increases becomes. In that regard, the exhaust gas energy, which is inherent in the exhaust gas of Abgasabführsystems not according to the prior art, but according to the invention already use.

Embodiments of the internal combustion engine in which the first return line downstream of the first radiator is at least connectable to the intake system or the exhaust gas removal system by using at least one actuating element are advantageous.

According to the above embodiment, the exhaust gas energy of the hot exhaust gas can also be used with the exhaust gas recirculation deactivated by means of the first radiator, which in the present case can also optionally be connected downstream to the intake system or the exhaust-gas removal system, for which purpose at least one actuating element is used, with which the exhaust-gas-conveying lines switch accordingly, namely connect to the Abgasabführsystem.

When deactivated exhaust gas recirculation can thus use both cooler exhaust gas recirculation for energy recovery and improve the efficiency of the internal combustion engine.

The first and second radiators may also be permanently connected upstream to the exhaust gas removal system, wherein at least one actuator provided downstream of the radiator is adjusted such that the radiator is connected downstream to the intake system or the exhaust system.

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

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

The first control element acts as an EGR valve and, when the exhaust gas recirculation is activated, serves to set the return rate, or at least the amount of exhaust gas recirculated via the first return line. The use of a composite valve arranged at the second node allows the design of the recirculated exhaust gas quantity and at the same time the throttling of the intake fresh air quantity.

Such a combination valve may for example be a flap which is pivotable about an axis extending transversely to the fresh air flow in such a way that in a first end position the front of the flap obstructs the intake system and at the same time the return line is released and in a second end position the rear of the flap conceals the return line and at the same time the intake system is released. An additional valve body, which is connected to the flap and in this way mechanically coupled, either releases or blocks the return line. While the flap is used to adjust the amount of air supplied via the intake system, the valve body accomplishes the metering of the amount of recirculated exhaust gas.

Advantageously, embodiments of the internal combustion engine in which the second return line branches off from the Abgasabführsystem to form a third node and opens to form a fourth node in the intake system.

However, embodiments of the internal combustion engine in which the second return line branches off from the exhaust gas removal system to form a third node point and opens into the first return line downstream of the first radiator, forming a third node, are advantageous in the context described above.

Then provided at the second node actuator can be used with activated exhaust gas recirculation of the setting of the total return rate, both the via the first return line and the recirculated via the second return line exhaust gas.

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

The second control element can also be used in individual cases to connect the second radiator downstream with the Abgasabführsystem, including optionally further exhaust-gas lines are provided. Then, the second radiator does not cool recirculated exhaust gas. Rather, the second radiator cools exhaust gas that has been removed from the exhaust system and is reintroduced into the exhaust system. Ie. the second cooler is used here only for energy recovery, d. H. the utilization of the immanent the exhaust gas energy.

Therefore, embodiments of the internal combustion engine in which an exhaust-gas-conducting line is provided which branches off from the second return line to form a fifth node downstream of the second cooler and opens into the exhaust-gas removal system to form a sixth node are advantageous.

Embodiments of the internal combustion engine in which the second actuating element is arranged at the fifth node point are advantageous.

In embodiments in which the second return line opens into the first return line downstream of the first cooler forming a fourth node, the first cooler downstream of the further exhaust-carrying line can then also be connected to the exhaust gas removal system. Then, the first radiator does not cool exhaust gas to be recirculated, but exhaust gas that is returned to the exhaust exhaust system. Both coolers are then used with deactivated exhaust gas recirculation of energy recovery.

In embodiments in which an exhaust-carrying conduit branches off from the second return conduit downstream of the second cooler and opens into the exhaust-gas removal 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 removal system.

In this connection, embodiments of the internal combustion engine in which upstream of the sixth node and downstream of the first and third nodes a throttle element is arranged in the exhaust-gas removal system are advantageous. The throttle element serves to increase the exhaust pressure upstream in the Abgasabführsystem, thereby increasing the driving pressure gradient across the radiator also and the exhaust gas is taken around the radiator Ausweichmöglichkeit around or bypassing the radiator is made difficult.

To generate the required pressure gradient, a shut-off element can additionally be provided upstream of the inlet of the exhaust gas recirculation in the intake system in order to lower the pressure upstream of the compressor on the intake side.

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

The advantage of a drivable by auxiliary drive compressor, ie supercharger, compared to a Exhaust gas turbocharger is that the loader can always generate and provide the requested boost pressure, regardless of the operating condition of the internal combustion engine. This is especially true for a loader that is electrically driven by electric motor and therefore independent of the speed of the crankshaft.

In fact, according to the state of the art, it is difficult to increase the power by means of turbocharging in all engine speed ranges. It is observed a greater torque drop when falling below a certain speed. This torque drop becomes understandable if it is taken into account that the boost pressure ratio depends on the turbine pressure ratio or the turbine output. If the engine speed is reduced, this leads to a smaller exhaust gas mass flow and thus to a smaller turbine pressure ratio or a smaller turbine power. Consequently, the boost pressure ratio also decreases toward lower speeds. This is synonymous with a torque drop.

However, embodiments of the internal combustion engine may still be advantageous in which at least one exhaust-gas turbocharger is provided which comprises a turbine arranged in the exhaust-gas removal 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 supplied to the turbine and relaxes with release of energy in the turbine, causing the shaft to rotate. The output from the exhaust stream to the shaft energy is used to drive the also arranged on the shaft compressor. The compressor conveys and compresses the charge air supplied to it, whereby a charging of the cylinder is achieved. Advantageously, a charge air cooler is provided downstream of the compressor in the intake system, with which the compressed charge air is cooled before entering the at least one cylinder. The radiator lowers the temperature and thus increases the density of the charge air, so that the cooler to a better filling of the cylinder, d. H. contributes to a larger air mass. There is a certain amount of compression by cooling.

The advantage of an exhaust gas turbocharger in comparison to a - drivable by auxiliary drive - loader is that an exhaust gas turbocharger uses the exhaust gas energy of the hot exhaust gases, while a loader requires the energy required for its drive directly or indirectly from the internal combustion engine and thus, at least as long as the drive power does not come from an energy recovery, adversely affects the efficiency, d. H. decreases.

If it is not an electric machine, d. H. is electrically driven supercharger is regularly a mechanical or kinematic connection for power transmission between the charger and the internal combustion engine is required, which also adversely affects or determines the packaging in the engine compartment.

In order to counteract a torque drop at low speeds, particularly embodiments of the internal combustion engine are advantageous in which at least two exhaust gas turbochargers are provided. If the engine speed is reduced, this leads to a smaller exhaust gas mass flow and thus to a lower boost pressure ratio.

By using a plurality of exhaust gas turbochargers, for example a plurality of exhaust gas turbochargers connected in series or in parallel, the torque characteristic of a supercharged internal combustion engine can be appreciably improved.

To improve the torque characteristic, in addition to the at least one exhaust gas turbocharger, a further compressor may be provided, namely both a supercharger drivable by means of an auxiliary drive and a compressor of a further exhaust gas turbocharger.

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

In a so-called high pressure EGR, the exhaust gas is introduced downstream of the compressor into the intake system. In order to provide or to ensure the pressure gradient between the exhaust gas removal system and the intake system required for a return, the exhaust gas is preferably taken from the exhaust gas removal system at an exhaust gas turbocharging and regularly upstream of the associated turbine. The high-pressure EGR has the advantage that the exhaust gas does not pass through the compressor and therefore no exhaust aftertreatment, for example in a particle filter, has to be subjected before the recirculation. Deposits in the compressor, which change the geometry of the compressor, in particular the flow cross-sections, and thus worsen the efficiency of the compressor, are not to be feared. Condensation takes place - if at all - downstream of the compressor, which also heats the charge air supplied to it as part of the compression and prevents or counteracts condensation in this way.

But can also be advantageous embodiments of the supercharged internal combustion engine, in which the return lines open upstream of the compressor in the intake system.

When operating an internal combustion engine with turbocharging and simultaneous use of a high-pressure EGR, a conflict may arise when the recirculated exhaust gas is taken from the Abgasabführsystem upstream of the turbine and is no longer available for driving the turbine.

With an increase in the exhaust gas recirculation rate, the exhaust gas flow introduced into the turbine simultaneously decreases. The reduced exhaust gas mass flow through the turbine causes a smaller turbine pressure ratio, whereby the charge pressure ratio also decreases, which is equivalent to a smaller compressor mass flow. In addition to the decreasing boost pressure, additional problems with the operation of the compressor with regard to the surge limit can occur. Disadvantages can also arise in the pollutant emissions, for example, with regard to the formation of soot in diesel engines during acceleration.

For this reason, concepts are required which ensure sufficiently high boost pressures with simultaneously high exhaust gas recirculation rates. One solution is the so-called low-pressure EGR, with which exhaust gas is fed back into the intake system, which has already flowed through the turbine. For this purpose, the low-pressure EGR takes exhaust gas from the Abgasabführsystem downstream of the turbine and passes this preferably upstream of the compressor in the intake system in order to realize the required for a return pressure drop between the Abgasabführsystem and the intake system can.

The exhaust gas recirculated by means of low-pressure EGR is mixed with fresh air upstream of the compressor. The mixture of fresh air and recirculated exhaust gas thus produced forms the charge air which is supplied to the compressor and compressed, the compressed charge air preferably being cooled downstream of the compressor in an intercooler.

As exhaust gas is passed through the compressor, the exhaust gas downstream of the turbine is preferably subjected to exhaust aftertreatment. The low pressure EGR can also be combined with a high pressure EGR.

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

Embodiments of the supercharged internal combustion engine in which the turbine of a proposed exhaust-gas turbocharger has a variable turbine geometry which permits further adaptation to the operation of the internal combustion engine by adjusting the turbine geometry or the effective turbine cross-section are advantageous. In this case, adjustable guide vanes for influencing the flow direction are arranged in the inlet region of the turbine. Unlike the vanes of the rotating impeller, the vanes do not rotate with the shaft of the turbine.

If the turbine has a fixed invariable geometry, the vanes are not only stationary, but also completely immovable in the entry area, i. H. fixed rigidly, if any guide is provided. With a variable geometry, however, the vanes are indeed arranged stationary, but not completely immobile, but rotatable about its axis, so that the flow of the blades can be influenced.

By adjusting the turbine geometry, it is possible to influence the exhaust gas pressure upstream of the turbine, thereby influencing the pressure gradient between the exhaust gas removal system and the intake system and thus the high-pressure EGR return rate.

For 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 may also be advantageous.

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

Embodiments of the supercharged internal combustion engine in which a particle filter is provided as an exhaust aftertreatment system for the after-treatment of the exhaust gas are advantageous.

To minimize the emission of soot, a regenerative particle filter is used in the present case, which filters out and stores the soot particles from the exhaust gas, wherein these soot particles intermittently burned as part of the regeneration of the filter become. The temperatures required for the regeneration of the particulate filter are at about 550 ° C with no catalytic support. Therefore, additional measures are regularly used to ensure regeneration of the filter under all operating conditions.

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

Embodiments of the supercharged internal combustion engine may also be advantageous in which an oxidation catalytic converter is provided as exhaust gas aftertreatment system for the after-treatment of the exhaust gas.

Although it takes place without additional measures at a sufficiently high temperature level and the presence of sufficiently large amounts of oxygen oxidation of the unburned hydrocarbons and carbon monoxide in Abgasabführsystem instead. However, these reactions come to a halt quickly due to the rapidly decreasing exhaust gas temperature downstream and consequently rapidly decreasing reaction rate. Therefore, catalytic reactors are used which ensure oxidation even at low temperatures using catalytic materials. If additional nitrogen oxides are to be reduced, this can be achieved in the gasoline engine by using a three-way catalyst.

The oxidation is an exothermic reaction, the heat released increases the temperature and thus the enthalpy of the exhaust gas. At the outlet of the oxidation catalyst is thus a higher-energy exhaust gas available. In this respect, the provision of an oxidation catalyst is meaningful and advantageous in particular also with regard to the use of the exhaust gas energy according to the invention.

Embodiments of the internal combustion engine in which a bypass line for bypassing the radiator is provided which bridges the EGR cooler and with which the exhaust gas recirculated via exhaust gas recirculation can be introduced into the intake system when the radiator bypasses are advantageous.

It may be useful to bridge the EGR cooling, for example, to avoid that additional heat is added to the liquid cooling of the internal combustion engine. Such a procedure lends itself to, if the liquid cooling of the internal combustion engine is already heavily stressed, for example, at full load. If the exhaust gas recirculation is used in the context of an engine brake, it is also useful to recirculate the hot exhaust without cooling.

Embodiments of the internal combustion engine in which liquid cooling is provided to form an engine cooling are advantageous.

Embodiments of the internal combustion engine in which the at least one cylinder head of the internal combustion engine is equipped to form a liquid cooling system with at least one coolant jacket integrated in the cylinder head are advantageous.

A liquid cooling proves to be particularly advantageous in turbocharged engines, since the thermal load of turbocharged engines compared to conventional internal combustion engines is significantly higher. The cylinder head has an integrated exhaust manifold, this is thermally higher load than a conventional cylinder head, which is equipped with an external manifold. There are increased demands on the cooling.

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

If the EGR coolers are integrated into the cooling circuit of the engine cooling system, many components and units required for forming a circuit generally only have to be provided in a single copy since these can be used both for the cooling circuit of the EGR coolers and for the engine cooling, which leads to synergies and cost savings, but also brings a weight savings.

Thus, preferably only one pump for conveying the coolant and a container for storing the coolant are provided. The heat emitted by the internal combustion engine and the EGR cooling to the coolant heat can be removed from the coolant in a common heat exchanger.

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

In the following, the invention will be described with reference to an embodiment and according to the 1 . 2 . 3 . 4 and 5 described in more detail. Hereby shows:

1 schematically a first embodiment of the internal combustion engine together with exhaust gas recirculation,

2 schematically the first embodiment of the internal combustion engine together with exhaust gas recirculation in a first operating mode,

3 schematically the first embodiment of the internal combustion engine together with exhaust gas recirculation in a second operating mode,

4 schematically the first embodiment of the internal combustion engine together with exhaust gas recirculation in a third mode of operation, and

5 schematically the first embodiment of the internal combustion engine together with exhaust gas recirculation in a fourth mode of operation.

1 schematically shows a first embodiment of the internal combustion engine 1 together with exhaust gas recirculation 4 ,

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

The internal combustion engine 1 is for charging with an exhaust gas turbocharger 6 equipped, the one in the exhaust system 2 arranged turbine 6b and one in the intake system 3 arranged compressor 6a includes.

Furthermore, an exhaust gas recirculation 4 provided with two return lines 4a . 4b , wherein in each return line 4a . 4b a cooler 5a . 5b is arranged. The coolers 5a . 5b each have a coolant-carrying coolant jacket, which serves to transfer heat between the exhaust gas and the coolant. The coolers 5a . 5b are arranged in parallel, independently usable for cooling exhaust gas or for energy recovery and fluidly connected to the engine cooling or connectable.

The first return line 4a branches to form a first node 2a downstream of the turbine 6b from the exhaust system 2 and ends upstream of the compressor 6a forming a second node 3a into the intake system 3 , At the second junction 3a is a first control element 7 intended. A combination valve 7a is used as the first control element 7 used, the setting of the recirculated exhaust gas quantity, ie the return rate, and thus also the deactivation of the exhaust gas recirculation 4 serves.

The second return line 4b also branches downstream of the turbine 6b and downstream of the first node 2a forming a third node 2c from the exhaust system 2 and ends with the formation of a fourth node 10 downstream of the first radiator 5a in the first return line 4a ,

Another exhaust-carrying line 11 is provided, forming a fifth node 12 downstream of the second radiator 5b from the second return line 4b branches off and forming a sixth node 2d into the exhaust system 2 empties.

The sixth node 2d is present downstream of the first and third nodes 2a . 2c in the exhaust system 2 arranged. Upstream of the sixth node 2d and downstream of the first and third nodes 2a . 2c is a throttle element 2 B in the exhaust system 2 arranged. The throttle element 2 B This serves to increase the exhaust pressure upstream in the exhaust system 2 increase, thereby increasing the driving pressure gradient across the radiator 5a . 5b also increase.

In the second return line 4b is downstream of the second radiator 5b a second actuator 8th provided, which at the fifth node 12 is arranged. The second control element 8th is a 3-4 way valve 8a which has three line connections and four switch positions and both coolers 5a . 5b via second node 3a with the intake system 3 or via the sixth node 2d with the exhaust gas removal system 2 connects or the second cooler 5b deactivated or from the first return line 4a separates and via sixth node 2d with the exhaust gas removal system 2 combines.

Both coolers 5a . 5b can therefore be used for cooling recirculated exhaust gas, but also with deactivated exhaust gas recirculation for energy recovery. In the following, this is based on the 2 to 5 explained in more detail.

2 schematically shows the first embodiment of the internal combustion engine 1 together with exhaust gas recirculation 4 in a first mode of operation. It should only be supplementary to 1 For that reason, reference is made to FIG 1 , The same reference numerals have been used for the same components.

In the first operating mode both cool coolers 5a . 5b recirculated exhaust gas. The second return line 4b is with the first return line 4a connected and the first return line 4a is with the intake system 3 connected. The first and second actuator 7 . 8th are switched or set accordingly.

3 schematically shows the first embodiment of the internal combustion engine 1 together with exhaust gas recirculation 4 in a second mode of operation. It should only be supplementary to 1 For that reason, reference is made to FIG 1 , The same reference numerals have been used for the same components.

In the second operating mode, only the first cooler cools 5a recirculated exhaust gas, including the first return line 4a via second node 3a with the intake system 3 connected is. The second return line 4b together with the second cooler 5b is from the first return line 4a separated and via the sixth node 2d with the exhaust gas removal system 2 connected. The second cooler 5b thus serves the energy recovery. The first and second actuator 7 . 8th are switched or set accordingly.

4 schematically shows the first embodiment of the internal combustion engine 1 together with exhaust gas recirculation 4 in a third mode of operation. It should only be supplementary to 1 For that reason, reference is made to FIG 1 , The same reference numerals have been used for the same components.

In the third operating mode is the exhaust gas recirculation 4 disabled and both coolers 5a . 5b be with deactivated exhaust gas recirculation 4 used for energy recovery. The first and second actuator 7 . 8th are switched or set accordingly. Both coolers 5a . 5b are via sixth node 2d with the exhaust gas removal system 2 connected and from the intake system 3 separated.

5 schematically shows the first embodiment of the internal combustion engine 1 together with exhaust gas recirculation 4 in a fourth mode of operation. It should only be supplementary to 1 For that reason, reference is made to FIG 1 , The same reference numerals have been used for the same components.

Both coolers 5a . 5b Both are switched off in terms of cooling recirculating exhaust gas as well as in terms of energy recovery or not used. The exhaust gas recirculation 4 and energy recovery are disabled. The first and second actuator 7 . 8th are switched or set accordingly.

LIST OF REFERENCE NUMBERS

1

 Internal combustion engine

2

 Abgasabführsystem

2a

 first node

2 B

 throttle element

2c

 third node

2d

 sixth node

3

 intake system

3a

 second node

4

 Exhaust gas recirculation

4a

 first return line

4b

 second return line

5a

 first cooler

5b

 second cooler

6

 turbocharger

6a

 Compressor of the exhaust gas turbocharger

6b

 Turbine of the exhaust gas turbocharger

7

 first actuator

7a

 Combination valve

8th

 second actuator

8a

 3-4-way valve

9

 aftertreatment system

10

 fourth node

11

 exhaust gas line

12

 fifth node

AGR

 Exhaust gas recirculation

m _AGR

 Mass of recirculated exhaust gas

_{Fresh air}

 Mass of supplied fresh air or combustion air

n _mot

 Speed of the internal combustion engine

x _AGR

 Exhaust gas recirculation rate

Claims (21)

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 the removal of the exhaust gases, and - an exhaust gas recirculation ( 4 ), the at least one return line ( 4a . 4b ), wherein in the at least one return line ( 4a . 4b ) at least one cooler ( 5a . 5b ) and at least one actuator ( 7 . 8th ) are provided for setting a predefinable recirculating exhaust gas amount, characterized in that - at least two return lines ( 4a . 4b ) are provided, in each of which a cooler ( 5a . 5b ), the radiators ( 5a . 5b ) are arranged in parallel and are used independently for the cooling of exhaust gas for the purpose of energy recovery. Internal combustion engine ( 1 ) according to claim 1, characterized in that - a first return line ( 4a ) is provided, in which a first cooler ( 5a ) is arranged and by using at least one actuating element ( 7 ) upstream of the first radiator ( 5a ) with the exhaust gas removal system ( 2 ) and downstream of the first radiator ( 5a ) with the intake system ( 3 ) is at least connectable, A second return line ( 4b ) is provided, in which a second cooler ( 5b ) is arranged and by using at least one actuating element ( 7 . 8th ) upstream of the second radiator ( 5b ) with the exhaust gas removal system ( 2 ) and downstream of the second radiator ( 5b ) optionally with the intake system ( 3 ) or the exhaust gas removal system ( 2 ) is at least connectable, and - each cooler ( 5a . 5b ) For the purpose of energy recovery at least one coolant-carrying coolant jacket has, which serves the heat transfer between the exhaust gas and the coolant. Internal combustion engine ( 1 ) According to claim 2, characterized in that the first return line ( 4a ) downstream of the first radiator ( 5a ) using at least one actuating element ( 7 . 8th ) optionally with the intake system ( 3 ) or the exhaust gas removal system ( 2 ) is at least connectable. Internal combustion engine ( 1 ) according to claim 2 or 3, characterized in that the first return line ( 4a ) forming a first node ( 2a ) of the exhaust gas removal system ( 2 ) branches off and forming a second node ( 3a ) into the intake system ( 3 ) opens. Internal combustion engine ( 1 ) according to claim 4, characterized in that in the first return line ( 4a ) at the second node ( 3a ) a first actuator ( 7 ) is provided. Internal combustion engine ( 1 ) according to claim 4 or 5, characterized in that the second return line ( 4b ) forming a third node ( 2c ) of the exhaust gas removal system ( 2 ) branches off and forming a fourth node ( 10 ) downstream of the first radiator ( 5a ) in the first return line ( 4a ) opens. Internal combustion engine ( 1 ) according to claim 6, characterized in that in the second return line ( 4b ) downstream of the second radiator ( 5b ) a second actuator ( 8th ) is provided. Internal combustion engine ( 1 ) according to claim 6 or 7, characterized in that an exhaust gas-carrying line ( 11 ), which, with the formation of a fifth node ( 12 ) downstream of the second radiator ( 5b ) from the second return line ( 4b ) branches off and forming a sixth node ( 2d ) into the exhaust gas removal system ( 2 ) opens. Internal combustion engine ( 1 ) according to claim 8, characterized in that the second actuating element ( 8th ) at the fifth node ( 12 ) is arranged. Internal combustion engine ( 1 ) according to claim 8 or 9, characterized in that the sixth node ( 2d ) downstream of the first and third nodes ( 2a . 2c ) in the exhaust gas removal system ( 2 ) is arranged. Internal combustion engine ( 1 ) according to claim 10, characterized in that upstream of the sixth node ( 2d ) and downstream of the first and third nodes ( 2a . 2c ) a throttle element ( 2 B ) in the exhaust gas removal system ( 2 ) is arranged. Internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that at least one drivable by means of auxiliary drive compressor in the intake system ( 3 ) is arranged. Internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that at least one exhaust gas turbocharger ( 6 ) is provided, the one in Abgasabführsystem ( 2 ) arranged turbine ( 6b ) and one in the intake system ( 3 ) arranged compressors ( 6a ). Internal combustion engine ( 1 ) according to claim 12 or 13, characterized in that the return lines ( 4a . 4b ) downstream of the compressor ( 6a ) into the intake system ( 3 ). Internal combustion engine ( 1 ) according to claim 12 or 13, characterized in that the return lines ( 4a . 4b ) upstream of the compressor ( 6a ) into the intake system ( 3 ). Internal combustion engine ( 1 ) according to one of claims 13 to 15, characterized in that the return lines ( 4a . 4b ) upstream of the turbine ( 6b ) from the exhaust gas removal system ( 2 ) branch off. Internal combustion engine ( 1 ) according to claim 15, characterized in that the return lines ( 4a . 4b ) downstream of the turbine ( 6b ) from the exhaust gas removal system ( 2 ) branch off. Internal combustion engine ( 1 ) according to claim 17, characterized in that between the turbine ( 6b ) and the branching return lines ( 4a . 4b ) at least one exhaust aftertreatment system ( 9 ) in the exhaust gas removal system ( 2 ) is provided. Internal combustion engine ( 1 ) according to claim 18, characterized in that for the aftertreatment of the exhaust gas, a particulate filter as an exhaust aftertreatment system ( 9 ) is provided. Internal combustion engine ( 1 ) according to one of the preceding claims, characterized in that for the formation of a motor cooling liquid cooling is provided. Internal combustion engine ( 1 ) according to claim 20, characterized in that the liquid cooling has a cooling circuit, the cooler ( 5a . 5b ) of exhaust gas recirculation ( 4 ).

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