DE102015219628A1 - Supercharged internal combustion engine with low-pressure exhaust gas recirculation and method for operating such an internal combustion engine - Google Patents

Abstract

The invention relates to a supercharged internal combustion engine having - an intake system (1) for supplying charge air, - a Abgasabführsystem (2) for discharging exhaust gas, - at least one exhaust gas turbocharger (3) arranged in the Abgasabführsystem (2) turbine (3b) and a compressor (3a) arranged in the intake system (1), and - a low-pressure exhaust gas recirculation (4) comprising a return line (4a) which branches off from the exhaust gas removal system (2) downstream of the turbine (3b) of the at least one exhaust gas turbocharger (3) upstream of the compressor (3a) of the at least one exhaust gas turbocharger (3) opens into the intake system (1). It is an internal combustion engine of the type mentioned are provided, which is improved in terms of condensate formation in the low-pressure EGR (4). This is achieved by an internal combustion engine of the type mentioned, in which the low-pressure exhaust gas recirculation (4) with at least one exhaust-side shut-off (4d, 5c) is provided, which downstream of the first node (5a) and upstream of the second node (5b) is arranged ,

Description

• – einem Ansaugsystem zum Zuführen von Ladeluft,
• – einem Abgasabführsystem zum Abführen von Abgas,
• – mindestens einem Abgasturbolader, der eine im Abgasabführsystem angeordnete Turbine und einen im Ansaugsystem angeordneten Verdichter umfasst, und
• – einer Niederdruck-Abgasrückführung umfassend eine Rückführleitung, die stromabwärts der Turbine des mindestens einen Abgasturboladers vom Abgasabführsystem abzweigt und stromaufwärts des Verdichters des mindestens einen Abgasturboladers in das Ansaugsystem mündet, wobei in der Rückführleitung ein Kühler und stromabwärts des Kühlers ein Steuerelement angeordnet sind, und eine Bypassleitung zur Umgehung des Kühlers, die unter Ausbildung eines ersten Knotenpunktes stromaufwärts des Kühlers von der Rückführleitung abzweigt und unter Ausbildung eines zweiten Knotenpunktes zwischen dem Kühler und dem Steuerelement in die Rückführleitung mündet, wobei am zweiten Knotenpunkt eine ansaugseitige Umschaltvorrichtung angeordnet ist, die in einer ersten Schaltposition die Rückführleitung freigibt und die Bypassleitung versperrt und in einer zweiten Schaltposition die Bypassleitung freigibt und die Rückführleitung versperrt.

The invention relates to a supercharged internal combustion engine with

• An intake system for supplying charge air,
• An exhaust gas removal system for removing exhaust gas,
• At least one exhaust-gas turbocharger comprising a turbine arranged in the exhaust-gas removal system and a compressor arranged in the intake system, and
• A low-pressure exhaust gas recirculation system comprising a return line which branches off from the exhaust gas removal system downstream of the turbine of the at least one exhaust gas turbocharger and opens into the intake system upstream of the compressor of the at least one exhaust gas turbocharger, a control element being arranged in the return line and a control element downstream of the cooler; Bypass line for bypassing the radiator, which branches off to form a first node upstream of the radiator from the return line and opens to form a second node between the radiator and the control in the return line, wherein at the second node a suction-side switching device is arranged in a first Switching position releases the return line and blocks the bypass line and in a second switching position releases the bypass line and the return line obstructed.

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

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 which can be connected to the engine, which receives power from the internal combustion engine or as switchable auxiliary drive additionally delivers power.

In recent years, there has been a trend toward small, supercharged engines, with supercharging primarily a method of increasing performance by compressing the air needed for the engine combustion process. The economic importance of these engines for the automotive industry continues to increase.

Frequently, an exhaust gas turbocharger is used for charging, in which a compressor and a turbine are arranged on the same shaft. The hot exhaust stream is supplied to the turbine and relaxes with energy release in the turbine, causing the shaft to rotate. The energy emitted by the exhaust gas flow to the turbine and finally to the shaft is used to drive the compressor, which is also arranged on the shaft. The compressor conveys and compresses the charge air supplied to it, whereby a charging of the cylinder is achieved. Regularly, 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 intercooler lowers the temperature and thus increases the density of the charge air, so that the intercooler for a better filling of the cylinder, d. H. contributes to a larger air mass. There is a compaction by cooling.

The advantage of an exhaust gas turbocharger compared to a mechanical supercharger is that there is no mechanical connection to the power transmission between the supercharger and the internal combustion engine or is required. While a mechanical supercharger obtains the energy required for its drive completely from the internal combustion engine and thus reduces the power provided and thus adversely affects the efficiency, the exhaust gas turbocharger uses the exhaust gas energy of the hot exhaust gases.

The charge is - as already mentioned - the increase in performance. The air required for the combustion process is compressed, which allows each cylinder per working cycle, a larger 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 displacement is reduced, the load spectrum can be shifted to higher loads, where the specific fuel consumption is lower.

Charging thus supports the constant effort in the development of internal combustion engines to minimize fuel consumption, d. H. to improve the efficiency of the internal combustion engine.

Another fundamental goal is to reduce pollutant emissions. In solving this problem, charging can also be helpful. In a targeted interpretation of the charge can namely advantages in efficiency and in the Exhaust emissions are achieved. In order to comply with future limits for pollutant emissions but in addition to the charging further internal engine measures are required.

Exhaust gas recirculation, for example, reduces nitrogen oxide emissions. The recirculation rate x _{AGR is} determined to be 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. If necessary, oxygen returned via the return line must also be taken into account, ie the unburned portion of the fresh charge previously supplied to the cylinder.

The inventive supercharged by exhaust gas turbocharger internal combustion engine is equipped with an exhaust gas recirculation (EGR) and that with a low-pressure EGR. In contrast to a high pressure EGR, which introduces exhaust gas taken from the exhaust gas removal system upstream of the turbine into the intake system downstream of the compressor, at a low pressure EGR, exhaust gas is returned to the inlet side which has already passed through the turbine. For this purpose, the low-pressure EGR comprises a return line, which branches off downstream of the turbine from the Abgasabführsystem and opens upstream of the compressor in the intake system. According to the invention, a cooler is provided in the return line to cool the hot exhaust gas as part of the recirculation, wherein downstream of the cooler, d. H. suction side, a control for adjusting the return rate is arranged. A bypass line serves to bypass the radiator, for example after a cold start.

The main advantage of the low-pressure EGR compared with the high-pressure EGR is that the exhaust gas flow introduced into the turbine is not reduced by the amount of recirculated exhaust gas in the case of exhaust gas recirculation. It is always the entire exhaust gas flow to the turbine to generate a sufficiently high boost pressure available.

The exhaust gas, which is returned to the inlet side by means of low-pressure EGR and is preferably cooled, is mixed with fresh air upstream of the compressor. The mixture of fresh air and recirculated exhaust gas produced in this way forms the charge air, which is supplied to the compressor and compressed.

It is harmless that exhaust gas is passed through the compressor in the context of the low-pressure EGR, since exhaust gas is recirculated, which downstream of the turbine of an exhaust aftertreatment, in particular in a particulate filter was subjected. 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 therefore not to be feared.

However, problems may arise upstream of the compressor as the temperature of the recirculated hot exhaust gas decreases and condensate forms. There are two scenarios to distinguish.

On the one hand, condensate can form when the returned hot exhaust gas 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 charge air temperature is below the exhaust gas temperature of the recirculated exhaust gas. As part of the cooling of the exhaust gas previously liquids in gaseous form in the exhaust gas or in the charge air, in particular water, condense out when the taut temperature of a component of the gaseous charge air flow is exceeded.

It comes to a condensation in the free charge air flow, often impurities in the charge air form the starting point for the formation of condensate droplets.

On the other hand, condensate can form if the recycled hot exhaust gas or the charge air strikes the inner wall of the intake system or on the inner wall of the compressor housing, since the wall temperature is usually below the taut temperature of the relevant gaseous components.

Condensate and condensate droplets are undesirable and lead to increased noise in the intake system, possibly damaging the blades of the at least one compressor impeller. The latter is associated with a reduction in the efficiency of the compressor.

The problem described above is exacerbated with increasing recirculation rate, since with the increase in the amount of recirculated exhaust gas, the proportions of the individual exhaust gas components in the charge air inevitably increase, in particular the proportion of water contained in the exhaust gas. According to the prior art, therefore, the amount of exhaust gas recirculated by means of low-pressure EGR is often limited in order to prevent or reduce the condensation out. The necessary limitation of the low-pressure EGR on the one hand and the high exhaust gas recirculation rates required for a significant reduction in nitrogen oxide emissions on the other hand lead to different objectives in the dimensioning of the recirculated exhaust gas quantity. According to the state of Technology is therefore used in addition to the low-pressure EGR regularly a high-pressure EGR.

The problem of condensate formation does not only affect the intake system. Also, the low-pressure EGR as such, d. H. the return line, the radiator and the bypass line are vulnerable and suitable for the formation of condensate and this - in contrast to the intake system - not only during exhaust gas recirculation, but also when no exhaust gas is returned, d. H. the intake-side EGR valve is closed. Namely, according to the prior art, both the return line and the bypass line are on the hot side of the low pressure EGR, that is, the low pressure EGR. H. Exhaust side, permanently open to the exhaust system.

On the cold side of the low-pressure EGR, d. H. suction side, in addition to the EGR valve, which is closed to deactivate the exhaust gas recirculation, also a switching device is provided which releases the return line in a first switching position and blocks the bypass line and in a second switching position releases the bypass line and blocks the return line.

If the exhaust gas recirculation is deactivated, as a result, condensate can form and collect in the cooler and in the return line and the bypass line at least as far as the switching device. If the exhaust gas recirculation is then activated by opening the EGR valve, the condensate formed in the low-pressure EGR can be released suddenly and in larger quantities and introduced into the intake system. The latter can not only lead to a serious failure of the operation of the internal combustion engine, but also to irreversible damage to the compressor.

Against this background, it is an object of the present invention to provide a supercharged internal combustion engine according to the preamble of claim 1 which is improved in condensate formation in the low-pressure EGR.

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

• – einem Ansaugsystem zum Zuführen von Ladeluft,
• – einem Abgasabführsystem zum Abführen von Abgas,
• – mindestens einem Abgasturbolader, der eine im Abgasabführsystem angeordnete Turbine und einen im Ansaugsystem angeordneten Verdichter umfasst, und
• – einer Niederdruck-Abgasrückführung umfassend eine Rückführleitung, die stromabwärts der Turbine des mindestens einen Abgasturboladers vom Abgasabführsystem abzweigt und stromaufwärts des Verdichters des mindestens einen Abgasturboladers in das Ansaugsystem mündet, wobei in der Rückführleitung ein Kühler und stromabwärts des Kühlers ein Steuerelement angeordnet sind, und eine Bypassleitung zur Umgehung des Kühlers, die unter Ausbildung eines ersten Knotenpunktes stromaufwärts des Kühlers von der Rückführleitung abzweigt und unter Ausbildung eines zweiten Knotenpunktes zwischen dem Kühler und dem Steuerelement in die Rückführleitung mündet, wobei am zweiten Knotenpunkt eine ansaugseitige Umschaltvorrichtung angeordnet ist, die in einer ersten Schaltposition die Rückführleitung freigibt und die Bypassleitung versperrt und in einer zweiten Schaltposition die Bypassleitung freigibt und die Rückführleitung versperrt, die dadurch gekennzeichnet ist, dass
• – die Niederdruck-Abgasrückführung mit mindestens einem abgasseitigen Absperrelement ausgestattet ist, das stromabwärts des ersten Knotenpunktes und stromaufwärts des zweiten Knotenpunktes angeordnet ist.

The first subtask is solved by a supercharged internal combustion engine

• An intake system for supplying charge air,
• An exhaust gas removal system for removing exhaust gas,
• At least one exhaust-gas turbocharger comprising a turbine arranged in the exhaust-gas removal system and a compressor arranged in the intake system, and
• A low-pressure exhaust gas recirculation system comprising a return line which branches off from the exhaust gas removal system downstream of the turbine of the at least one exhaust gas turbocharger and opens into the intake system upstream of the compressor of the at least one exhaust gas turbocharger, a control element being arranged in the return line and a control element downstream of the cooler; Bypass line for bypassing the radiator, which branches off to form a first node upstream of the radiator from the return line and opens to form a second node between the radiator and the control in the return line, wherein at the second node a suction-side switching device is arranged in a first Switching position releases the return line and blocks the bypass line and in a second switching position releases the bypass line and the return line is blocked, which is characterized in that
• - The low-pressure exhaust gas recirculation is equipped with at least one exhaust-side shut-off, which is arranged downstream of the first node and upstream of the second node.

The low-pressure exhaust gas recirculation of the internal combustion engine according to the invention is exhaust-side, d. H. on the hot side, equipped with at least one shut-off element which separates the return line, the radiator and / or the bypass line from the exhaust system in the closed position. Condensation in the return line, the radiator and / or the bypass line can be prevented or reduced in this way.

When exhaust gas recirculation is activated by opening the EGR valve, no large amounts of condensate are released or introduced into the intake system. A serious failure of the operation of the internal combustion engine and irreversible damage to the compressor are not to be feared. The efficiency of the compressor thus remains unaffected by the exhaust gas recirculation by means of low-pressure EGR. The condensate also eliminates the increased noise emission due to the condensate.

Thereby, the first object of the invention is achieved, namely provided a supercharged internal combustion engine, which is improved in terms of condensate formation in the low-pressure EGR.

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

Embodiments of the internal combustion engine in which an exhaust gas-side shut-off element is arranged in the bypass line are advantageous.

In the present case, the low-pressure exhaust gas recirculation on the hot side is equipped with an exhaust-side shut-off element which in the closed position separates the bypass line from the exhaust-gas removal system, whereas the return line and the radiator remain open on the exhaust side. Condensation in the return line or the radiator is not prevented in this way.

In this connection, embodiments of the internal combustion engine in which the exhaust-gas-side shut-off element is arranged close to the first node point are advantageous. The closest possible arrangement of the shut-off element at the junction ensures that the bypass line is prevented from condensate formation as far as possible by separating the longest possible section of the bypass line from the rest of the exhaust-gas removal system.

Also advantageous are embodiments of the internal combustion engine, in which an exhaust-gas-tight shut-off element is arranged in the return line downstream of the first node and upstream of the radiator.

In the present case, the low-pressure exhaust gas recirculation on the hot side is equipped with an exhaust-side shut-off element which in the closed position separates the return line and the radiator from the exhaust-gas removal system, whereas the bypass line remains open on the exhaust side. Condensation in the bypass line is not prevented in this way.

Embodiments of the internal combustion engine in which the exhaust-gas-side shut-off element is arranged close to the first node point are advantageous in this connection. By the closest possible arrangement of the shut-off element at the junction, the return line and the radiator should be protected as far as possible against condensation.

Embodiments of the internal combustion engine may also be advantageous in which a first exhaust-gas-side shut-off element is arranged in the bypass line and a second exhaust-side shut-off element is arranged in the return line downstream of the first node and upstream of the radiator. According to this embodiment, both the bypass line and the return line together with the radiator are largely protected from condensate formation by the closest possible arrangement of the shut-off elements at the junction.

Also advantageous in this context are embodiments of the internal combustion engine in which the exhaust-gas-side shut-off elements are arranged close to the first node.

Embodiments of the internal combustion engine in which a shut-off element in the exhaust-gas removal system is arranged downstream of the turbine of the at least one exhaust-gas turbocharger are advantageous, wherein the return line between the turbine and the shut-off element branches off from the exhaust-gas removal system. The shut-off element may be used to increase the exhaust pressure upstream in the exhaust system and thus contribute to an increase in the pressure differential between the exhaust system and the intake system. This offers particular advantages at high recirculation rates, which require a larger pressure gradient.

Embodiments of the internal combustion engine in which upstream of the compressor of the at least one exhaust-gas turbocharger a shut-off element is arranged in the intake system are advantageous, with the return line opening into the intake system between the compressor and the shut-off element. The shut-off element is used on the inlet side to reduce the pressure in the intake system and can thus - as the previously treated shut-off - contribute to an increase in the pressure gradient between the Abgasabführsystem and the intake system. Both shut-off elements can be designed as pivotable flaps or be, as for example, the switching device.

Namely advantageous embodiments of the internal combustion engine, in which the switching device is a pivotable flap.

Embodiments of the internal combustion engine in which at least one exhaust aftertreatment system is arranged in the exhaust system downstream of the turbine of the at least one exhaust gas turbocharger are advantageous, wherein the return line between the turbine and the at least one exhaust aftertreatment system branches off from the exhaust system.

In this context, embodiments of the internal combustion engine in which the at least one exhaust aftertreatment system comprises a particle filter are advantageous.

Embodiments of the internal combustion engine in which the intake system is equipped with a heating device are advantageous. By means of heating means, the temperature of the inner wall of the intake system can be increased, wherein the wall temperature on the taut temperature of the gaseous components of the exhaust gas or the charge air can be lifted out. Condensation on the inner wall of the intake system or on the inner wall of the compressor housing can be avoided or reduced in this way.

In principle, embodiments in which the heating device is arranged on the outside of the intake system are advantageous, so that there is no influence on the charge air flow in the intake system. It is advantageous in this context to integrate the heater in a wall of the intake system.

Embodiments in which the heating device is an electrical heating device are advantageous. An electric heater can be used at any time in case of need and be activated independently of the operating condition of the internal combustion engine for heating the inner wall of the intake system. A supply of energy to the electric heater can be done for example by means of the on-board battery of a vehicle.

Also advantageous are embodiments of the internal combustion engine, in which the return line is equipped with a heating device, wherein the heating device is arranged downstream of the control element.

Embodiments of the internal combustion engine in which the compressor of the at least one exhaust-gas turbocharger is a radial compressor are advantageous. This embodiment allows a tight packaging of the exhaust gas turbocharger and thus the overall charge. The compressor housing can be designed as a spiral or worm housing, wherein the deflection of the charge air flow in the compressor of the exhaust gas turbocharger can be used advantageously to the compressed charge air on the shortest route from the outlet side, on which the turbine of the exhaust gas turbocharger is regularly arranged on the Lead inlet side.

In this context, embodiments of the internal combustion engine in which the turbine of the at least one exhaust-gas turbocharger is a radial turbine are advantageous. This embodiment also allows a tight packaging of the exhaust gas turbocharger and thus the overall charge.

Unlike the turbines, compressors are defined by their outflow. A radial compressor is thus a compressor whose outflow from the blades takes place substantially radially. In the context of the present invention, essentially radial means that the velocity component in the radial direction is greater than the axial velocity component.

Embodiments of the internal combustion engine in which the compressor of the at least one exhaust gas turbocharger is an axial compressor can also be advantageous. The outflow from the impeller blades of an axial compressor takes place substantially axially.

Embodiments of the internal combustion engine in which the compressor of the at least one exhaust-gas turbocharger has an inlet region which runs coaxially to the shaft of the compressor and is designed so that the flow of the charge air to the compressor takes place essentially axially are advantageous.

In an axial flow of the compressor often eliminates a deflection or change in direction of the charge air flow in the intake upstream of the at least one compressor impeller, whereby unnecessary pressure losses in the charge air flow due to flow deflection can be avoided and the pressure of the charge air is increased at the inlet to the compressor of the exhaust gas turbocharger. The lack of change in direction also reduces the contact of the exhaust gas or the charge air with the inner wall of the intake system or with the inner wall of the compressor housing and thus reduces the heat transfer and condensation.

Embodiments of the internal combustion engine may be advantageous in which the control element which serves to adjust the recirculated exhaust gas quantity is arranged at the point at which the return line opens into the intake system. Then, the control can also be designed as a combined valve with which both the amount of recirculated exhaust gas and the amount of fresh air can be adjusted.

Embodiments of the internal combustion engine in which at least two exhaust-gas turbochargers are provided are advantageous.

Often, the design of the turbocharger turbocharger is difficult, with basically a noticeable increase in performance in all speed ranges is sought. But it is often observed a strong 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. If the engine speed is reduced, this leads to a lower exhaust gas flow and thus to a smaller turbine pressure ratio. Consequently, the boost pressure ratio also decreases toward lower speeds. This is equivalent to a boost pressure drop or torque drop.

If a smaller exhaust gas turbocharger, ie an exhaust gas turbocharger with a smaller turbine cross section, used, thereby the turbine pressure ratio can be increased. If the exhaust gas flow exceeds a critical size, part of the exhaust gas flow is guided past the turbine by means of a bypass line as part of the so-called exhaust gas blow-off. Such a turbine is also referred to as a waste gate turbine. However, this variant has the disadvantage that the charging behavior at high speeds is insufficient and the torque drop is only shifted to low speeds. In addition, this approach, ie the reduction of the turbine cross section, limits, since the desired charging and performance increase should be possible without restriction and to the desired extent, even at high speeds.

The torque characteristic of a supercharged internal combustion engine may be further characterized by a plurality of turbochargers arranged in parallel, i. H. be improved by a plurality of parallel turbines of smaller turbine cross-section, with successive turbines are switched on with increasing exhaust gas.

The torque characteristic can also be advantageously influenced by means of a plurality of exhaust-gas turbochargers connected in series. By switching in series of two exhaust gas turbochargers, one of which is an exhaust gas turbocharger as a high pressure stage and an exhaust gas turbocharger as a low pressure stage, the compressor map can be widened in an advantageous manner, both towards smaller compressor streams as well as towards larger compressor streams.

In particular, in the case of the exhaust gas turbocharger serving as a high-pressure stage, the pumping limit can be shifted towards smaller compressor flows, which means that high boost pressure ratios can be achieved even with small compressor flows, which significantly improves the torque characteristic in the lower rpm range. This is achieved by designing the high-pressure turbine for small exhaust gas mass flows and providing a bypass line, with which increasing exhaust gas mass flow increasingly exhaust gas is passed to the high-pressure turbine. For this purpose, the bypass line branches off the exhaust-gas removal system upstream of the high-pressure turbine and returns to the exhaust-gas removal system upstream of the low-pressure turbine. In the bypass line, a shut-off element is arranged to control the exhaust gas flow passed past the high-pressure turbine.

In order to achieve a significant reduction in nitrogen oxide emissions, high exhaust gas recirculation rates are required. Advantageous may therefore be embodiments in which an additional exhaust gas recirculation is provided, which comprises a line which branches off upstream of the turbine of the at least one exhaust gas turbocharger from the Abgasabführsystem and opens downstream of the compressor of the at least one exhaust gas turbocharger back into the intake system.

In contrast to the low-pressure EGR already mentioned, exhaust gas is taken from the exhaust system at a high-pressure EGR upstream of the turbine and introduced into the intake system downstream of the compressor, i. H. Exhaust gas recirculated, which has not yet passed through the turbine. One advantage of the high-pressure EGR is that there is a sufficiently high pressure gradient for conveying the exhaust gas and the exhaust gas does not have to undergo any exhaust gas aftertreatment.

The second sub-task on which the invention is based, namely to disclose a method for operating an internal combustion engine of the type described above, is achieved by a method for operating an internal combustion engine with an exhaust-gas-side shut-off element arranged in the bypass line, in which this shut-off element is opened during a warm-up phase of the internal combustion engine is to release the bypass line.

What has already been said for the internal combustion engine according to the invention also applies to the method according to the invention, which is why at this point in general reference is made to the statements made above with regard to the supercharged internal combustion engine. The various internal combustion engines sometimes require different process variants.

In the following the invention is based on two embodiments according to the 1 and 2 described in more detail. Hereby shows:

1 schematically the arranged in the intake compressor and arranged in Abgasabführsystem turbine of a first embodiment of the internal combustion engine including low-pressure exhaust gas recirculation, and

2 schematically the arranged in the intake compressor and arranged in the Abgasabführsystem turbine of a second embodiment of the internal combustion engine together with low-pressure exhaust gas recirculation.

1 schematically shows the intake system 1 on the suction side 1 arranged compressor 3a and those in the exhaust system 2 on the exhaust side 2 arranged turbine 3b a first embodiment of the internal combustion engine together with low-pressure exhaust gas recirculation 4 ,

For supplying the charge air to the cylinders, the internal combustion engine has an intake system 1 and for exhausting the exhaust gases from the cylinders is an exhaust discharge system 2 intended.

For the purpose of charging the cylinder, the internal combustion engine with an exhaust gas turbocharger 3 equipped, the one in the exhaust system 2 arranged turbine 3b and one in the intake system 1 arranged compressor 3a includes.

The internal combustion engine is further equipped with a low-pressure exhaust gas recirculation 4 equipped, which is a return line 4a includes, the downstream of the turbine 3b from the exhaust system 2 branches off and upstream of the compressor 3a into the intake system 1 empties. In the return line 4a are a cooler 4c and downstream of the radiator 4c a control 4b arranged to adjust the amount of recirculated exhaust gas.

A bypass line 5 that under formation of a first node 5a upstream of the radiator 4c from the return line 4a branches off and forming a second node 5b between the radiator 4c and the control 4b back into the return line 4a opens, serves the bypass of the radiator 4c , At the second junction 5b is a hinged flap 6a arranged as the suction-side switching device 6 serves, which in a first switching position, the return line 4a releases and the bypass line 5 locked and in a second switching position, the bypass line 5 releases and the return line 4a blocked.

In the present case, the low-pressure exhaust gas recirculation 4 on the hot side with an exhaust-side shut-off element 4d equipped in the closed position, the return line 4a and the radiator 4c from the exhaust system 2 separates, whereas the bypass line 5 exhaust side remains open or executed. In this way, a condensate formation in the return line 4a and the radiator 4c especially with deactivated exhaust gas recirculation 4 prevented. The exhaust-side shut-off element 4d is near the first node 5a arranged, whereby the return line 4a as well as the radiator 4c be protected circumferentially from condensation.

2 schematically shows the intake system 1 on the suction side 1 arranged compressor 3a and those in the exhaust system 2 on the exhaust side 2 arranged turbine 3b A second embodiment of the internal combustion engine together with low-pressure exhaust gas recirculation 4 , It should only the differences to the in 1 Otherwise, reference will be made to FIG 1 , The same reference numerals have been used for the same components.

Unlike the in 1 embodiment shown is in the in 2 illustrated internal combustion engine 1 an exhaust-side shut-off element 5c in the bypass line 5 arranged.

This on the hot side of the AGR 4 provided exhaust-side shut-off 5c separates in the closed position, the bypass line 5 from the exhaust system 2 whereas the return line 4a and the radiator 4c on the exhaust side remain open or executed. Condensation in the bypass line 5 in this way, especially with deactivated exhaust gas recirculation 4 prevented. The exhaust-side shut-off element 5c is near the first node 5a arranged to the bypass line 5 circumferentially to protect against condensation.

LIST OF REFERENCE NUMBERS

1

 Intake system, intake side

2

 Exhaust system, exhaust side

3

 turbocharger

3a

 Compressor of the exhaust gas turbocharger

3b

 Turbine of the exhaust gas turbocharger

4

 Low-pressure exhaust gas recirculation

4a

 Return line

4b

 Exhaust gas recirculation control, EGR valve

4c

 Radiator, EGR cooler

4d

 Exhaust gas shut-off element, radiator-related shut-off element

5

 bypass line

5a

 first node

5b

 second node

5c

 Exhaust gas shut-off element, the bypass line associated shut-off element

6

 suction-side switching device

6a

 swiveling flap

7

 aftertreatment system

7a

 particulate Filter

AGR

 Exhaust gas recirculation

m _AGR

 Mass of recirculated exhaust gas

_{Fresh air}

 Mass of supplied fresh air or charge air

x _AGR

 Exhaust gas recirculation rate

Claims (15)

Charged internal combustion engine with - an intake system ( 1 ) for supplying charge air, - an exhaust gas removal system ( 2 ) for the removal of exhaust gas, - at least one exhaust gas turbocharger ( 3 ), one in the exhaust system ( 2 ) arranged turbine ( 3b ) and one in the intake system ( 1 ) arranged compressors ( 3a ), and - a low pressure exhaust gas recirculation ( 4 ) comprising a return line ( 4a ) downstream of the turbine ( 3b ) of the at least one exhaust gas turbocharger ( 3 ) from the exhaust gas removal system ( 2 ) branches off and upstream of the compressor ( 3a ) of the at least one exhaust gas turbocharger ( 3 ) into the intake system ( 1 ), wherein in the return line ( 4a ) a cooler ( 4c ) and downstream of the radiator ( 4c ) a control ( 4b ) are arranged, and a bypass line ( 5 ) to bypass the radiator ( 4c ) forming a first node ( 5a ) upstream of the radiator ( 4c ) from the return line ( 4a ) branches off and forming a second node ( 5b ) between the radiator ( 4c ) and the control ( 4b ) in the return line ( 4a ), wherein at the second node ( 5b ) a suction-side switching device ( 6 ) is arranged, which in a first switching position, the return line ( 4a ) and the bypass line ( 5 ) and in a second switching position, the bypass line ( 5 ) and the return line ( 4a ), characterized in that - the low pressure exhaust gas recirculation ( 4 ) with at least one exhaust-side shut-off element ( 4d . 5c ) located downstream of the first node ( 5a ) and upstream of the second node ( 5b ) is arranged. Supercharged internal combustion engine according to claim 1, characterized in that in the bypass line ( 5 ) an exhaust-side shut-off element ( 5c ) is arranged. Supercharged internal combustion engine according to claim 2, characterized in that the exhaust-side shut-off element ( 5c ) near the first node ( 5a ) is arranged. Supercharged internal combustion engine according to claim 1, characterized in that in the return line ( 4a ) downstream of the first node ( 5a ) and upstream of the radiator ( 4c ) an exhaust-side shut-off element ( 4d ) is arranged. Supercharged internal combustion engine according to claim 4, characterized in that the exhaust-side shut-off element ( 4d ) near the first node ( 5a ) is arranged. Supercharged internal combustion engine according to one of the preceding claims, characterized in that in the bypass line ( 5 ) a first exhaust-side shut-off element ( 5c ) and in the return line ( 4a ) downstream of the first node ( 5a ) and upstream of the radiator ( 4c ) a second exhaust-gas shut-off element ( 4d ) is arranged. Supercharged internal combustion engine according to claim 6, characterized in that the exhaust-side shut-off elements ( 4d . 5c ) near the first node ( 5a ) are arranged. Supercharged internal combustion engine according to one of the preceding claims, characterized in that downstream of the turbine ( 3b ) of the at least one exhaust gas turbocharger ( 3 ) a shut-off element in the exhaust gas removal system ( 2 ), wherein the return line ( 4a ) between the turbine ( 3b ) and the shut-off element of the exhaust gas removal system ( 2 ) branches off. Supercharged internal combustion engine according to one of the preceding claims, characterized in that upstream of the compressor ( 3a ) of the at least one exhaust gas turbocharger ( 3 ) a shut-off element in the intake system ( 1 ), wherein the return line ( 4a ) between the compressor ( 3a ) and the shut-off element in the intake system ( 1 ) opens. Supercharged internal combustion engine according to one of the preceding claims, characterized in that the switching device ( 6 ) a pivotable flap ( 6a ). Supercharged internal combustion engine according to one of the preceding claims, characterized in that downstream of the turbine ( 3b ) of the at least one exhaust gas turbocharger ( 3 ) at least one exhaust aftertreatment system ( 7 ) in the exhaust gas removal system ( 2 ), wherein the return line ( 4a ) between the turbine ( 3b ) and the at least one exhaust aftertreatment system ( 7 ) of the exhaust gas removal system ( 2 ) branches off. Supercharged internal combustion engine according to claim 11, characterized in that the at least one exhaust aftertreatment system ( 7 ) a particle filter ( 7a ). Supercharged internal combustion engine according to one of the preceding claims, characterized in that the intake system ( 1 ) is equipped with a heater. Supercharged internal combustion engine according to one of the preceding claims, characterized in that the return line ( 4a ) is provided with a heating device, wherein the heating device downstream of the control ( 4b ) is arranged. Method for operating a supercharged internal combustion engine according to one of the preceding claims, in which in the bypass line ( 5 ) an exhaust-side shut-off element ( 5c ), characterized in that the exhaust side Shut-off element ( 5c ) is opened during a warm-up phase of the internal combustion engine to the bypass line ( 5 ).

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