WO2018114027A1

WO2018114027A1 - Internal combustion engine having exhaust gas recirculation

Info

Publication number: WO2018114027A1
Application number: PCT/EP2017/001343
Authority: WO
Inventors: Rolf Pfeifer; Günther Schmidt; Ralf Speetzen
Original assignee: Mtu Friedrichshafen Gmbh
Priority date: 2016-12-21
Filing date: 2017-11-16
Publication date: 2018-06-28
Also published as: DE102016125285A1

Abstract

The invention relates to an exhaust gas routing system for an internal combustion engine having exhaust gas recirculation, wherein the internal combustion engine has at least one second cylinder group having at least one cylinder, which is connected on the exhaust side to an exhaust gas recirculation device via a collection line, wherein the exhaust gas recirculation device has an exhaust cooler, characterized in that a first exhaust flap for controlling the exhaust gas recirculation rate is arranged downstream of the exhaust gas cooler in the exhaust gas recirculation device and a first exhaust line for non-recirculated exhaust is arranged having a second exhaust flap downstream of the exhaust cooler between the exhaust cooler and a turbine.

Description

DESCRIPTION OF THE INVENTION Internal combustion engine with exhaust gas recirculation

The invention relates to an exhaust system for an internal combustion engine with an exhaust gas recirculation and a control unit and an internal combustion engine. Such internal combustion engines and exhaust gas stirring systems are known from the prior art such as DE 10 2004 015 108 AI or DE 10 2007 01 1 680 AI.

In the concepts known from the prior art, the exhaust gas cooler is exposed to changes in the operating state, in particular between operating points with and without exhaust gas recirculation, thermal load changes, which leads to shortening the service life of the exhaust gas cooler. Desirable is therefore an extension of the life.

This is where the invention begins, the object of which is to improve the service life of exhaust gas coolers, in particular in internal combustion engines with exhaust gas recirculation.

This object is achieved by an exhaust system according to claim 1. This is in particular an exhaust system for an internal combustion engine with an exhaust gas recirculation, wherein the internal combustion engine having a first cylinder group having at least one cylinder and a second cylinder group having at least one cylinder and at least the second cylinder group on the exhaust side via a Manifold is connected to an exhaust gas recirculation device, wherein the exhaust gas recirculation device comprises an exhaust gas cooler, characterized in that in the exhaust gas recirculation means a first exhaust valve for controlling the exhaust gas recirculation rate downstream of the exhaust gas cooler is arranged and that a first exhaust pipe for non-recirculated exhaust gas with a second exhaust valve downstream of the exhaust gas cooler is arranged.

The first and second exhaust valves are used to set a desired EGR rate for the respective operating state. The desired EGR rate is determined by the setting set of advantageously matched opening states of the first and second exhaust valve. The opening states may include full-opening states or partial opening states of the first and / or second exhaust gas flap, which are advantageously matched to one another. In particular, the required back pressure for the pressure gradient between an exhaust gas side and a charge air side of the internal combustion engine is set via the first and second exhaust gas flaps. Furthermore, the amount of cooled exhaust gases can be adjusted via the exhaust flaps. The exhaust flaps can be designed for example as valves or fixed blinds. The invention is based on the consideration that the life of the exhaust gas cooler is largely determined by the number of thermal load changes. Any change in the exhaust gas temperature and / or the exhaust gas mass flow leads to internal stresses of the exhaust gas cooler and thus to a lifetime consumption. In particular, in the prior art dispenser cylinder concept, as shown in FIG. 1, but also at high pressure exhaust gas recirculation and to a lesser extent at low pressure exhaust gas recirculation, the control of the exhaust valves causes additional thermal load alternation as the engine operating condition approaches, for example, a map point without exhaust gas recirculation a map point with exhaust gas recirculation changes. At the operating point without exhaust gas recirculation, the exhaust gas cooler is cooled almost to coolant temperature (80 ° C to 95 ° C), at other map points, the inlet temperature of the exhaust gas depending on the concept rise to 700 ° C. For this reason, even small changes in the operating point in the map can cause a high thermal (and mechanical) alternating load is caused in the exhaust gas cooler, resulting in an increased service life consumption. To solve the problem, the invention is based on the recognition that a low thermal load can be achieved by thermal load changes in the exhaust gas cooler when the amount of exhaust gas that is passed through the exhaust gas cooler can be adjusted independently of the EGR rate. This is realized via the arrangement of the first exhaust pipe downstream of the exhaust gas cooler.

It is thus achieved that at least a portion of the non-recirculated exhaust gas is passed over the exhaust gas cooler. As a result, even at low EGR rates or when the exhaust gas recirculation is switched off, a certain amount of exhaust gas is conducted via the exhaust gas cooler. Since now always, even with switched off exhaust gas recirculation, exhaust gas on the Is passed exhaust gas cooler, it is avoided that the temperature of the exhaust gas cooler is lowered to the coolant temperature. The lowest temperature in the exhaust gas cooler thus corresponds to the minimum exhaust gas temperature in the map of the respective internal combustion engine. For example, it can be achieved that the minimum temperature in the exhaust gas cooler of about 85-90 ° C is increased to 200 ° C, which reduces the maximum temperature difference between two operating points of the internal combustion engine in the exhaust gas cooler from 620 K to about 500 K. Due to the low thermal load change as an extension of the life of the exhaust gas cooler is achieved.

Exhaust gas recirculation may be a low pressure exhaust gas recirculation, a high pressure exhaust gas recirculation or an exhaust gas recirculation according to the donor cylinder concept.

In an advantageous development of the exhaust gas cooler is integrated with a bypass in an exhaust stream or an exhaust pipe of the internal combustion engine and the first and second exhaust valve downstream of the exhaust gas cooler, the EGR rate and the pressure gradient is controlled or regulated.

Advantageously, the first exhaust pipe (211) for non-recirculated exhaust gas is arranged with the second exhaust valve downstream of the exhaust gas cooler between the exhaust gas cooler (EGR-WT) and a turbine. In this embodiment, the amount of cooled exhaust gas supplied to a turbine can be adjusted via the first and second exhaust valves.

This is particularly advantageous in internal combustion engines with high-pressure exhaust gas recirculation or exhaust gas recirculation according to the dispenser cylinder concept. In particular, an exhaust gas recirculation in the form of a donor cylinder exhaust gas recirculation is advantageous, with only the second cylinder group is connected on the exhaust side via a manifold with a Abgasräckführungseinrichtung.

A prior art dispenser cylinder system is shown in FIG. The system only takes part of the cylinders of the engine as exhaust gas recirculation dispensers. An exhaust flap (dispenser cylinder flap) accumulates the exhaust gas flow to the donor cylinders and thus ensures the necessary pressure gradient between the exhaust and charge air side. As a result, the charge can be optimized to very good efficiencies, of the charge cycle losses are affected only the donor cylinder. Compared to a conventional high-pressure exhaust gas recirculation, the known donor cylinder concept ensures less consumption, because it reduces the motor charge cycle losses and allows higher turbocharger efficiencies. This requires an additional dispenser cylinder exhaust damper compared to high pressure exhaust gas recirculation. Depending on the operating state of the internal combustion engine, different exhaust gas recirculation rates (EGR rates) are set or exhaust gas recirculation is also completely switched off.

In the case of high-pressure exhaust gas recirculation or exhaust gas recirculation according to the dispenser cylinder concept, according to an embodiment of the invention, the first exhaust gas flap from the region of the uncooled exhaust gas with temperatures of up to 700 ° C. (as known in the prior art) is laid according to the invention in the region of the cooled exhaust gas, where the maximum exhaust gas temperature is only 140 ° C. The thermal requirements for the first exhaust flap are thus significantly reduced. This contributes to a longer life of the first exhaust flap and thus lower costs. By adding the cooled exhaust gas of the donor cylinder donor cylinder concept to the exhaust gas of the remaining cylinders, the exhaust gas temperature is reduced. Due to the reduced exhaust gas temperature, the turbine of the exhaust gas turbocharger is thermally less stressed overall. This also results in a longer service life of the turbine. In particular, it is advantageous if only the first exhaust gas line is available for discharging the exhaust gas of the second cylinder group to the turbine. With this development it is ensured that in each case the complete amount of exhaust gas is passed through the exhaust gas cooler and so the temperature fluctuations in the exhaust gas cooler are minimized. In this development, with the second exhaust flap in the first exhaust pipe only one exhaust flap for the non-recirculated exhaust gas and that in the range of cooled exhaust gas is present, so that the donor cylinder concept also this is significantly less thermally loaded, as the usual donor cylinder exhaust flap in Area of hot exhaust gas.

In a further development of the exhaust gas guidance system, a second exhaust gas line with a third exhaust gas valve is arranged in addition to the first exhaust gas line, which is connected via the manifold to the second cylinder group and connects them directly to the turbine. In this development, the third exhaust flap for adjusting the required back pressure for the pressure gradient between the exhaust gas side and the charge air side of the internal combustion engine can be used in addition. In addition, about the second and the third Exhaust damper sets the amount of non-recirculated exhaust gas to be cooled, which is passed over the exhaust gas cooler. This amount of exhaust gas is correspondingly not conducted via the second exhaust pipe to the turbine, but via the first exhaust pipe. In this development, when exhaust gas recirculation is deactivated, only as much exhaust gas is passed through the exhaust gas cooler as is necessary in order to keep the exhaust gas cooler at a specific exhaust gas temperature. The enthalpy for driving the turbine is thus larger and the amount of heat to be dissipated is lower.

Advantageously, the exhaust gas cooler has a coolant circuit with a bypass around the exhaust gas cooler, in which a bypass flap is arranged. About this bypass and a corresponding opening of the bypass valve, the amount of coolant in the exhaust gas cooler can be regulated so that in the event that less or colder exhaust gas is passed in the current operating state via the exhaust gas cooler. The cooling can be reduced and the temperature of the exhaust gas cooler is subject to reduced fluctuations despite reduced exhaust gas quantity or temperature in certain operating states.

According to a second aspect, the invention relates to a control unit for an internal combustion engine with an exhaust gas routing system as described above, wherein the control unit is designed, to a detected current operating state out, a required exhaust gas recirculation rate and a quantity of cooling gas needed to maintain a predetermined temperature range in the exhaust gas cooler not to determine recirculated exhaust gas and to cause one of the required Abgasrückfuhrungsrate and the required amount corresponding matched opening of the first exhaust valve and the second and / or the third exhaust valve. This is advantageously achieved that regardless of the exhaust gas recirculation rate always a predetermined amount of non-recirculated exhaust gas is passed through the exhaust gas cooler via the appropriate setting of the second and / or existing third exhaust valve and a desired temperature range is maintained in the exhaust gas cooler.

Preferably, the control unit is additionally designed to initiate the setting of a predetermined coolant rate in the exhaust gas cooler via a corresponding opening of the bypass valve according to the required exhaust gas recirculation rate and the required amount of non-recirculated exhaust gas to be cooled. In this development, the temperature of the exhaust gas cooler is influenced both by the amount of exhaust gas and by the amount of coolant. Thus, a regulation of the exhaust gas cooler temperature is possible that at lower Exhaust gas amounts or low exhaust gas temperature less coolant is used to cool the exhaust gas and so the temperature of the exhaust gas cooler can be maintained at a higher level than in conventional exhaust system and thus the life of the exhaust gas cooler can be further extended.

According to a third aspect, the invention relates to an internal combustion engine with a previously described exhaust system according to the first aspect. The internal combustion engine shares the advantages of the exhaust system according to the first aspect. In particular, an internal combustion engine is advantageous, which additionally has a control device according to the second aspect of the invention.

Embodiments of the invention will now be described below with reference to the drawing. This is not necessarily to scale the embodiments, but the drawing, where appropriate for explanation, executed in a schematized and / or slightly distorted form. With regard to additions to the teachings directly recognizable from the drawing reference is made to the relevant prior art. It should be noted that various modifications and changes may be made in the form and detail of an embodiment without departing from the general idea of the invention. The disclosed in the description, in the drawing and in the claims features of the invention may be essential both individually and in any combination for the development of the invention. In addition, all combinations of at least two of the features disclosed in the description, the drawings and / or the claims fall within the scope of the invention. The general idea of the invention is not limited to the exact form or detail of the preferred embodiments shown and described below or limited to an article that would be limited in comparison with the subject matter claimed in the claims. For the given design ranges, values within the stated limits should also be disclosed as limit values and be arbitrarily usable and claimable. For simplicity, the same reference numerals are used below for identical or similar parts or parts with identical or similar function.

Further advantages, features and details of the invention will become apparent from the following description of the preferred embodiments and from the drawing; this shows in: Fig. 1 is a schematic representation of an internal combustion engine with exhaust gas recirculation according to the donor cylinder concept according to the prior art;

2 shows a schematic representation of an embodiment of an internal combustion engine with an exhaust system according to the invention;

3 shows a schematic illustration of an alternative embodiment of an internal combustion engine with an exhaust gas duct according to the invention; In Fig.l an internal combustion engine 100 with exhaust gas recirculation according to the dispenser cylinder concept according to the prior art is shown. The internal combustion engine 100 includes an engine 101 with two cylinder groups 120, 130 and a control unit ECU - shown here only symbolically. The internal combustion engine 100 further comprises a high-pressure turbocharger 121 with a turbine and a compressor and two low-pressure turbochargers 122, 123, wherein a respective air filter LF upstream and downstream of the compressor of the low-pressure turbocharger each intercooler ZwK is arranged upstream of the compressor air side. The charge air is then passed through a high-pressure turbocharger 121 and fed to a throttle valve 4 a charge air cooler 140 and then the cylinders Al -A6, Bl - B6 of the two cylinder groups 120, 130. On the exhaust side, the exhaust gases of the cylinders of the respective cylinder group 120, 130 are collected. The exhaust gases of the first cylinder group 130 are then supplied to the turbine of the high-pressure turbocharger 121. A portion of the exhaust gases of the first cylinder group 130 is thereby passed via a bypass of the high-pressure turbocharger HD stage of the first cylinder group 130 directly to the turbines of the low-pressure turbocharger LP stage. In the bypass, an exhaust bypass door 3 is arranged.

The cylinders A1-A6 serve as donor cylinders. Their exhaust gas is partly via an exhaust gas recirculation device, in which an exhaust gas cooler AGR-WT is arranged, which is designed here as a heat exchanger, mixed with charge air from the intercooler and the charge air side the cylinders of the first and second cylinder group fed again. The exhaust gas recirculation rate is set via the exhaust flaps 1 and 2. The exhaust valves 1 and 2 also serve the backflow of the exhaust gas to produce a necessary for the functioning of the system back pressure for the required pressure difference between the charge air and exhaust side. The amount of exhaust gas required to comply with the emissions becomes set in the system shown here with donor cylinder exhaust gas recirculation through the exhaust valves 1 and 2 and only this amount of exhaust gas is passed through the exhaust gas cooler, the rest of the exhaust gas from the donor cylinder flows through the exhaust valve 1 on the exhaust gas cooler over to the turbine. As already described with regard to the internal combustion engine according to FIG. 1, the internal combustion engine shown in FIG. 2 is also constructed according to the dispenser cylinder concept for exhaust gas recirculation. Therefore, the differences between the internal combustion engine with exhaust gas routing system according to the prior art of FIG. 1 and that with exhaust gas routing system according to FIG. 2 will be described below, wherein like reference numerals generally designate like components and configurations.

The internal combustion engine 200, like the internal combustion engine 100, has an engine 101 with two cylinder banks 120, 130 as well as a control unit ECU. The internal combustion engine 200 further comprises a high-pressure turbocharger 121 with a turbine and a compressor and two low-pressure turbochargers 122, 123, wherein an air filter LF upstream of the compressor of the low-pressure turbocharger and an intercooler ZwK downstream is arranged upstream of the compressor of the low-pressure turbocharger. Here, too, the charge air is subsequently conducted via a high-pressure turbocharger 121 and a throttle valve 4 is supplied to a charge air cooler 140 and then to the cylinders AI-A6, B-B6 of the two cylinder groups 120, 130. On the exhaust side, the exhaust gases of the cylinders of the respective cylinder group 120, 130 are collected. The exhaust gases of the first cylinder group 130 are then supplied to the turbine of the high-pressure turbocharger 121. A portion of the exhaust gases of the first cylinder group 130 is thereby passed via a bypass of the high-pressure turbocharger HD stage of the first cylinder group 130 directly to the turbines of the low-pressure turbocharger LP stage. In the bypass, an exhaust bypass door 3 is arranged.

The cylinders A1-A6 serve as donor cylinders. Some of their exhaust gas is mixed with charge air from the intercooler 140 via an exhaust gas routing system 210, in which an exhaust gas cooler AGR-WT is arranged here as a heat exchanger, and returned to the cylinders of the first and second cylinder groups on the charge air side. The exhaust gas recirculation rate is set via a first exhaust gas flap 2 'and a second exhaust gas flap. In contrast to the exhaust system 1 10 of FIG. 1, the first exhaust flap 2 'downstream of the exhaust gas cooler EGR-WT arranged in the exhaust system 210 and a first exhaust pipe 21 1 for non-recirculated exhaust gas with the second Exhaust flap 1 'is disposed downstream of the exhaust gas cooler between the exhaust gas cooler EGR-WT and the turbine of the high-pressure turbocharger 121. Thus, in the illustrated embodiment, all of the exhaust gas from the donor cylinders of the second cylinder group 120 is directed via the exhaust gas cooler EGR-WT, thus increasing the minimum temperature in the exhaust gas cooler compared to the system of FIG. The second exhaust flap also serves the backflow of the exhaust gas to generate a necessary for the functioning of the system dynamic pressure for the required pressure gradient between the charge air and exhaust side. The flaps are controlled so that only a subset of the cooled exhaust gas is mixed via the first exhaust flap 2 'of the fresh air, the remaining cooled exhaust gas is mixed via the second exhaust valve the uncooled exhaust gas of the other cylinder of the first cylinder group 130 and the turbine of the high-pressure turbocharger 121st directed.

FIG. 3 shows a further embodiment of an internal combustion engine 300 with a donor cylinder exhaust gas recirculation. The exhaust gas routing system 310 here, like that in FIG. 2, has a first exhaust gas line 31 1 with a second exhaust gas valve, which connects the latter with the turbine downstream of the exhaust gas cooler AGR-WT. In addition, the exhaust gas routing system 310 has a second exhaust pipe 312, which is connected via a manifold 313 on the exhaust side with the second cylinder group 120. In the second exhaust pipe 312, a third exhaust valve 5 is arranged. The amount of exhaust gas needed to maintain the emissions is set to an operating condition of the internal combustion engine via the first and third exhaust gas flaps 2 ', 5. The second exhaust valve may be closed in this operating state. The amount of exhaust gas not required for the return then flows via the third exhaust flap 5 to the turbine. If no exhaust gas or only a small amount of exhaust gas is to be recirculated, the first exhaust gas flap 2 'is completely or partially closed and the exhaust gas flows via the exhaust gas flaps 5 and 1' to the turbine. The second exhaust valve 1 'is adjusted so that further at least a small amount of exhaust gas flows through the exhaust gas cooler. In this embodiment, the exhaust gas cooler AGR-WT has a coolant circuit 320 with a bypass 321 around the exhaust gas cooler EGR-WT. In the bypass 321, a bypass flap 6 is arranged. By way of the bypass 321 and the bypass flap 6, the coolant quantity in the exhaust gas cooler AGR-WT can be regulated in this embodiment. If, in an operating state, little exhaust gas or exhaust gas flows with a relatively cold inlet temperature into the exhaust gas cooler, the bypass flap 6, here designed as a bypass valve, opens so far that the coolant quantity through the exhaust gas cooler is reduced. By suitable control of the second exhaust flap and the bypass flap 6 by the control unit ECU, the exhaust gas cooler can thus Exhaust gas temperature are maintained, a cooling to coolant temperature is thus avoided.

LIST OF REFERENCE NUMBERS

1,1 'first exhaust flap

2, 2 'second exhaust flap

3 exhaust bypass flap

4 throttle

5 third exhaust flap

6 Bypass flap

100, 200, 300 internal combustion engine 101 engine

1 10, 210, 310 exhaust system

120 first cylinder group

130 second cylinder group

140 intercooler

121 high-pressure turbo vein

122, 123 low-pressure turbocharger

211, 311 first exhaust pipe

312 second exhaust pipe

313 Manifold

320 coolant circuit

321 bypass

A1-A6 cylinder

EGR-WT exhaust gas cooler

B1-B6 cylinder

ECU control unit

LF air filter

ZwK intercooler

Claims

An exhaust system (210) for an internal combustion engine (200) with an exhaust gas recirculation, the internal combustion engine (200) having a first cylinder group (120) comprising at least one cylinder (A1-A6) and a second cylinder group (130) comprising at least one cylinder (B1 -B6) and at least the second cylinder group (130) on the exhaust side via a manifold (313) is connected to an exhaust gas recirculation device, wherein the exhaust gas recirculation device comprises an exhaust gas cooler (AGR-WT), characterized in that

in the exhaust gas recirculation device, a first exhaust gas valve (16) for controlling the exhaust gas recirculation rate downstream of the exhaust gas cooler (EGR-WT) is arranged and that a first exhaust pipe (211) for non-recirculated exhaust gas with a second exhaust flap (2 ') downstream of the exhaust gas cooler (EGR-WT ) is arranged.

An exhaust gas routing system (210) for an internal combustion engine (200) according to claim 1, wherein the first exhaust gas non-return exhaust passage (21 1) communicates with the second exhaust gas passage (2 ') downstream of the exhaust gas cooler (EGR-WT) between the exhaust gas cooler (EGR -WT) and a turbine is arranged.

The exhaust gas routing system (210) for an internal combustion engine (200) according to claim 1, wherein the exhaust gas recirculation is a donor cylinder exhaust gas recirculation and only the second cylinder group (130) is connected to the exhaust gas recirculation means via the manifold (313).

4. exhaust system (210) according to claim 2 or 3, wherein in addition to the first exhaust pipe (211) a second exhaust pipe (312) with a third exhaust valve (5) is arranged, which via the manifold (313) with the second cylinder group (130 ) and connects them directly to the turbine.

5. exhaust system (210) according to one of the preceding claims, wherein the exhaust gas cooler (EGR-WT) has a coolant circuit (320) with a bypass (321) to the exhaust gas cooler (EGR-WT), in which a bypass flap (6) is arranged ,

6. An ECU for an internal combustion engine having an exhaust gas routing system according to claim 1, which is designed to be responsive to a detected current operating state, a required exhaust gas recirculation rate and an amount to maintain a predetermined temperature range in the exhaust gas cooler. EGR-WT) required to be cooled to determine non-recirculated exhaust gas, and one of the required exhaust gas recirculation rate and the required amount appropriate coordinated opening of the first exhaust flap () and the second (2 ') and / or the third exhaust flap (5) to cause.

7. Control unit (ECU) according to claim 6, which is additionally designed to cause the setting of a predetermined coolant rate in the exhaust gas cooler (AGR -WT) via a corresponding opening of the bypass valve according to the required exhaust gas recirculation rate and the required amount of non-recirculated exhaust gas to be cooled ,

8. Internal combustion engine (200) with an exhaust gas routing system (210) according to one of claims 1 to 5.

9. Internal combustion engine (200) according to claim 8 additionally comprising a control unit (ECU) according to one of claims 6 or 7.