Title:
Internal Combustion Engine Featuring Exhaust Gas Aftertreatment and Method For the Operation Thereof
Kind Code:
A1


Abstract:
An internal combustion engine with exhaust gas aftertreatment and method for the operation thereof are provided. The internal combustion engine includes at least one first and one second group of one or more combustion chambers, in which the one or more combustion chambers of the first group may be supplied with fuel independently of the one or more combustion chambers of the second group, an exhaust system having a first exhaust branch line which leads away from the first combustion chamber group, and a second exhaust branch line which leads away from the second combustion chamber group, and at least one exhaust gas aftertreatment unit which, at the inlet side, is connected to the first and second exhaust branch lines. Also, a bypass line, which leads away from the second exhaust branch line, for bypassing the exhaust gas aftertreatment unit is provided.



Inventors:
Scheinert, Helmut (Ebersbach, DE)
Application Number:
11/631643
Publication Date:
09/04/2008
Filing Date:
07/01/2005
Assignee:
Daimlerchrysler AG (Stugart, DE)
Primary Class:
Other Classes:
60/303, 60/288
International Classes:
F01N3/00; F01N13/08
View Patent Images:
Related US Applications:



Primary Examiner:
DENION, THOMAS E
Attorney, Agent or Firm:
CROWELL & MORING LLP (WASHINGTON, DC, US)
Claims:
1. 1-11. (canceled)

12. An internal combustion engine comprising: at least one first and one second group of one or more combustion chambers, the one or more combustion chambers of the first group being supplied with fuel independently of the one or more combustion chambers of the second group; an exhaust system including a first exhaust branch line which leads away from the first combustion chamber group, a second exhaust branch line which leads away from the second combustion chamber group, at least one exhaust gas aftertreatment unit which, at the inlet side, is connected to the first and second exhaust branch lines, and a bypass line, which leads away from the second exhaust branch line, for bypassing the exhaust gas aftertreatment unit; and a control unit configured to carry out ignition in the second combustion chamber group with a reduced fuel quantity in comparison with the first combustion chamber group in a reduced-power operating mode of the internal combustion engine.

13. The internal combustion engine as claimed in claim 12, further comprising: an exhaust gas recirculation line including a controllable valve, which exhaust gas recirculation line leads away from the second exhaust branch line or from the bypass line which leads away from the second exhaust branch line to bypass the exhaust gas aftertreatment unit.

14. The internal combustion engine as claimed in claim 12, further comprising: a controllable valve disposed in the bypass line.

15. An internal combustion engine, as claimed in claim 12, further comprising: an exhaust gas recirculation line including a controllable valve, which exhaust gas recirculation line leads away from the second exhaust branch line or from a bypass line which leads away from the second exhaust branch line to bypass the exhaust gas.

16. The internal combustion engine as claimed in claim 12, further comprising: at least one exhaust gas turbocharger, an exhaust gas turbine of which is connected at the inlet side to the first and second exhaust branch lines.

17. The internal combustion engine as claimed in claim 16, further comprising: a controllable valve disposed in the second exhaust branch line upstream of the exhaust gas turbine and downstream of a point at which the bypass line opens out.

18. The internal combustion engine as claimed in claim 16, further comprising: a controllable switching flap, from which the bypass line leads away, disposed in the second exhaust branch line upstream of the exhaust gas turbine.

19. The internal combustion engine as claimed in claim 16, further comprising: a wastegate line, which leads away upstream of the first exhaust branch line and bypasses the exhaust gas turbine, including an actuable wastegate valve.

20. The internal combustion engine as claimed in claim 13, further comprising: at least one exhaust gas turbocharger, an exhaust gas turbine of which is connected at the inlet side to the first and second exhaust branch lines.

21. The internal combustion engine as claimed in claim 14, further comprising: at least one exhaust gas turbocharger, an exhaust gas turbine of which is connected at the inlet side to the first and second exhaust branch lines.

22. The internal combustion engine as claimed in claim 15, further comprising: at least one exhaust gas turbocharger, an exhaust gas turbine of which is connected at the inlet side to the first and second exhaust branch lines.

23. The internal combustion engine as claimed in claim 20, further comprising: a controllable valve disposed in the second exhaust branch line upstream of the exhaust gas turbine and downstream of a point at which the bypass line opens out.

24. The internal combustion engine as claimed in claim 21, further comprising: a controllable valve disposed in the second exhaust branch line upstream of the exhaust gas turbine and downstream of a point at which the bypass line opens out.

25. The internal combustion engine as claimed in claim 22, further comprising: a controllable valve disposed in the second exhaust branch line upstream of the exhaust gas turbine and downstream of a point at which the bypass line opens out.

26. The internal combustion engine as claimed in claim 20, further comprising: a controllable switching flap, from which the bypass line leads away, disposed in the second exhaust branch line upstream of the exhaust gas turbine.

27. The internal combustion engine as claimed in claim 21, further comprising: a controllable switching flap, from which the bypass line leads away, disposed in the second exhaust branch line upstream of the exhaust gas turbine.

28. The internal combustion engine as claimed in claim 22, further comprising: a controllable switching flap, from which the bypass line leads away, disposed in the second exhaust branch line upstream of the exhaust gas turbine.

29. The internal combustion engine as claimed in claim 17, further comprising: a wastegate line, which leads away upstream of the first exhaust branch line and bypasses the exhaust gas turbine, including an actuable wastegate valve.

30. A method for operating an internal combustion engine including at least one first and one second group of one or more combustion chambers, the one or more combustion chambers of the first group being supplied with fuel independently of the one or more combustion chambers of the second group; an exhaust system including a first exhaust branch line which leads away from the first combustion chamber group, a second exhaust branch line which leads away from the second combustion chamber group, at least one exhaust gas aftertreatment unit which, at the inlet side, is connected to the first and second exhaust branch lines, and a bypass line, which leads away from the second exhaust branch line, for bypassing the exhaust gas aftertreatment unit; and a control unit configured to carry out ignition in the second combustion chamber group with a reduced fuel quantity in comparison with the first combustion chamber group in a reduced-power operating mode of the internal combustion engine, the method comprising: in a partial ignition operating mode, reducing the fuel quantity supplied to the second combustion chamber group in comparison with the first combustion chamber group; and in operating modes in which the fuel quantity supplied to the second combustion chamber group is reduced to a value greater than zero, guiding the exhaust gas passing out of the second combustion chamber group entirely via the exhaust gas recirculation line.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of PCT International Application No. PCT/EP2005/007109, filed Jul. 1, 2005, which claims priority under 35 U.S.C. ยง119 to German Patent Application No. 10 2004 032 589.8, filed Jul. 6, 2004, the entire disclosures of which are herein expressly incorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to an internal combustion engine including at least first and second groups of one or more combustion chambers, in which the one or more combustion chambers of the first group may be supplied with fuel independently of the one or more combustion chambers of the second group. An exhaust system of the internal combustion engine includes a first exhaust branch line which leads away from the first combustion chamber group, and a second exhaust branch line which leads away from the second combustion chamber group, and at least one exhaust gas aftertreatment unit which, at the inlet side, is connected to the first and second exhaust branch lines. The present invention also relates to a method for operating an internal combustion engine as described above.

A variety of internal combustion engines and operating methods are known from the prior art. For example, German patent document DE 30 07 370 C2 describes an internal combustion engine having two cylinder groups which are connected to one intake line. A throttle valve is provided in the intake line, and downstream of the throttle valve, the intake line is divided into two intake branch lines, each of which is connected to one of the two cylinder groups. At low loads of the internal combustion engine, a fuel supply to the second cylinder group is interrupted, and the exhaust gas from the cylinder group is recirculated into the intake branch line of the second cylinder group by an exhaust gas recirculation line. This is intended to avoid a reduction in the exhaust gas temperature, which would lead to a deterioration in the exhaust gas purification performance of an exhaust gas aftertreatment unit.

German patent document DE 30 17 468 C2 describes an internal combustion engine having cylinder shut-off, including first and second cylinder groups and an intake system with two intake chambers, each of which is connected to one of the two cylinder groups. A blockable connection is provided between the intake chambers. An exhaust system has two exhaust gas chambers, each of which is connected to one of the cylinder groups and joins together at a point downstream of cylinder outlets. In a state of high load, both cylinder groups are kept in operation, but in a state of low load, only the first cylinder group is kept in operation. The intake chambers are connected by one exhaust gas recirculation line to one of the exhaust gas chambers. The exhaust gas recirculation lines are connected to one another by a branch line having a switching valve. In a state of high load, the switching valve closes off the branch line and, in a state of low load, closes off that part of the first exhaust gas recirculation line which is situated upstream of the point at which the branch line opens out. Thus, the internal combustion engine may be operated in such a way that, at a state of low load, the first cylinder group, which is then the only one in operation, is supplied only with low-temperature exhaust gas in order to keep the formation of nitrogen oxides as low as possible in the operating state.

German patent document DE 30 36 508 A1 describes a multi-cylinder piston internal combustion engine which has an intake pipe which is connected to the cylinders, a first exhaust gas collecting line which is connected to a first cylinder group and a second exhaust gas collecting line which is connected to a second cylinder group. An exhaust gas aftertreatment unit is located downstream of a joining point of the two exhaust gas collecting lines. A first fuel supply device is provided for feeding the first cylinder group with a fuel quantity corresponding to the power output. A second fuel supply device is provided for feeding the second cylinder group with a fuel quantity corresponding to the power output and has a blocking device for blocking the second fuel supply device. A deflecting device provided in the second exhaust gas collecting line is designed to selectively recirculate exhaust gas from the second cylinder group into the intake pipe when the second fuel supply device is blocked.

German patent document DE 195 00 761 C2 describes a multi-cylinder piston internal combustion engine having at least two cylinder groups, each of which includes one inlet duct for supplying combustion air and one exhaust system with a catalytic converter, in which one cylinder group may be shut off in part-load operation of the internal combustion engine. At least some of the exhaust gas of the firing cylinder group may be supplied to the inlet duct of the shut-off cylinder group via a recirculation line, which branches off upstream or downstream of the associated catalytic converter. The cylinder groups can be shut off alternately, and the exhaust systems of one or more firing cylinder groups are connected by one recirculation line to the inlet ducts of one or more shut-off cylinder groups. Thus, uniform heating, or maintenance of the operating temperature, may be provided in each catalytic converter.

German patent document DE 195 29 835 A1 describes an exhaust system of a gasoline engine including an exhaust gas pipe line, having a three-way oxidation catalytic converter regulated by a lambda probe, and having an SCR catalytic converter. The SCR catalytic converter is arranged in a bypass pipe running parallel to the exhaust gas pipe line between the lambda probe and the oxidation catalytic converter. The bypass pipe and/or the exhaust gas pipe line are provided with an exhaust flap which is controlled as a function of the temperatures of the SCR catalytic converter and the oxidation catalytic converter and of the oxygen proportion of the exhaust gas at the lambda probe. Thus, the gasoline engine may be operated in a fuel-saving lean mode. The increased exhaust gas temperature occurring here is advantageous for the fast response of an optional start-up catalytic converter in the exhaust gas pipe line and of the oxidation catalytic converter.

German patent document DE 44 12 742 A1 describes a device for controlling catalytic converter temperatures in an exhaust system of an internal combustion engine. The exhaust system includes a relatively small precatalytic converter relatively close to the engine and a catalytic main or supported catalytic converter. The precatalytic converter is located in an exhaust line branch which the exhaust gas can bypass via a bypass line which joins the exhaust line branch again upstream of the main catalytic converter.

U.S. Pat. No. 4,287,716 A1 describes an exhaust gas system of a V-engine having two cylinder banks with a regulable bypass line for bypassing an exhaust gas aftertreatment unit.

An internal combustion engine in which the two groups of cylinders have separate exhaust branch lines from one another is known from U.S. Pat. No. 4,107,921 A1. An exhaust gas aftertreatment unit is arranged in the exhaust system. Exhaust gas from both exhaust branch lines can be branched into a bypass line in order to bypass the exhaust gas aftertreatment unit.

Japanese patent document JP 59-007747-A describes an internal combustion engine including at least first and second groups of one or more combustion chambers, wherein the combustion chamber(s) of the first group can be supplied with fuel independently of the combustion chamber(s) of the second group, and having an exhaust system with a first exhaust branch line which leads off from the first combustion chamber group and having a second exhaust branch line which leads away from the second combustion chamber group, and at least one exhaust gas aftertreatment unit which is connected at the inlet side to the first and second exhaust branch lines. A bypass line which leads from the second exhaust branch line is provided for bypassing the exhaust gas aftertreatment unit.

An object of the present invention is to provide an internal combustion engine and an associated operating method of the type which, in a relatively simple manner, permit operation of the internal combustion engine and of the exhaust gas aftertreatment unit with a high degree of efficiency.

This and other objects and advantages are achieved by an internal combustion engine and an operating method according to the present invention, which allows the exhaust gas flows of the first and second combustion chamber groups to be guided as a function of the operating mode of the internal combustion engine. Depending on the situation, the exhaust gas can be conducted past the exhaust gas aftertreatment unit via the bypass line. For example, in a combustion chamber shut-off operating mode of the internal combustion engine, which is favorable in terms of efficiency, the pollutant-containing exhaust gas generated by the first group of combustion chambers can be conducted through the exhaust gas aftertreatment unit, while the exhaust gas generated by the second group of combustion chambers when the fuel supply to the combustion chambers is completely shut off can be guided past the exhaust gas aftertreatment unit.

In an operating state as described above, the exhaust gas of the second combustion chamber group is substantially free of pollutants and is at a relatively low temperature. It is therefore possible to avoid undesirable cooling of the exhaust gas aftertreatment unit, and to prevent the latter from being unnecessarily subjected to pollutant-free exhaust gas, by guiding the exhaust gas via the bypass line past the exhaust gas aftertreatment unit. It is possible in this way to obtain a more stable high efficiency of the exhaust gas aftertreatment unit.

Here, a control unit is provided which is set up to supply the second combustion chamber group with a reduced fuel quantity in comparison with the first combustion chamber group in a reduced-power operating mode of the internal combustion engine. In this operating mode, the power to be output by the internal combustion engine is provided substantially by the first group of combustion chambers, with the contribution of the second combustion chamber group being relatively low in comparison.

As a result of the increased load on the first combustion chamber group, these combustion chambers can operate in a particularly advantageous efficiency range, because, for example, less throttling losses occur in an intake device provided for the combustion chambers. Ignition can be carried out in the second combustion chamber group with a reduced fuel quantity as a function of the load to be provided. This makes it possible to reduce undesirable vibrations of the internal combustion engine in such load states in comparison with a complete fuel shut-off, and to prevent undesired cooling of the second combustion chamber group. As a result, a desired load level for the first combustion chamber group is also ensured.

In an exemplary embodiment of the invention, a controllable valve is provided in the bypass line. The valve may be used to generate a dynamic pressure in the bypass line, which dynamic pressure may lead, in particular in the fuel-reduced or fuel shut-off operating mode of the second combustion chamber group, to a partial or complete discharge of the exhaust gas generated by the second combustion chamber group into the exhaust gas aftertreatment unit.

In another exemplary embodiment of the internal combustion engine, a recirculation line which leads away from the second exhaust branch line or from the bypass line is provided with a controllable valve. Thus, the exhaust gas generated by the second combustion chamber group to be selectively guided in a controllable fashion into the bypass line or at least partially recirculated into an intake device and therefore into the combustion chambers of the first and/or second combustion chamber groups. This is of interest, in particular, if a fuel-reduced mode is provided for the second combustion chamber group, in which mode the exhaust gas cannot be discharged via the bypass line downstream of the exhaust gas aftertreatment unit in order to adhere to pollutant limit values.

In a further embodiment of the invention, a wastegate line which leads away upstream of the first exhaust branch line and bypasses the exhaust gas turbine is provided with an actuable wastegate valve. Thus, the exhaust gas flow generated by the first combustion chamber group to be at least partially deflected past the exhaust gas turbine, so that overloading of the exhaust gas turbine at excessively high flow speeds, exhaust gas pressures and/or exhaust gas temperatures can be prevented.

The method according to the invention utilizes the fact that, in the event of a reduction of the fuel quantity supplied to the second combustion chamber group to zero, the exhaust gas generated by the second combustion chamber group is substantially free from pollutants. The exhaust gas can therefore be completely or partially discharged via the bypass line so as to bypass the exhaust gas aftertreatment unit. This prevents mostly relatively cool exhaust gas from flowing into the exhaust gas aftertreatment unit, and consequently prevents undesirable cooling and an associated reduction in efficiency thereof.

In operating phases in which the fuel quantity supplied to the second combustion chamber group is reduced to a value greater than zero, according to the invention, the exhaust gas passing out of the second combustion chamber group can be guided entirely via the exhaust gas recirculation line. The exhaust gases generated in the second combustion chamber group can therefore be re-burned and, while maintaining the operating temperature necessary for a high degree of efficiency of the exhaust gas aftertreatment unit, can be conducted into the exhaust gas aftertreatment unit and purified there.

In one embodiment of the method, the controllable valve in the bypass line is adjusted into an open position in the partial ignition operating mode, and is adjusted into a closed position in a full ignition operating mode of the internal combustion engine. Thus, it is possible during a partial ignition mode of the second combustion chamber group for the exhaust gas generated by said second combustion chamber group to be re-burned in the first and/or second combustion chamber group via the exhaust gas recirculation line, while in the full ignition operating mode, the exhaust gas can be entirely discharged directly via the exhaust gas aftertreatment unit.

In a further embodiment of the method, the switching flap is adjusted into a position which is open to the bypass line or to the exhaust gas recirculation line in the partial ignition operating mode, and is adjusted into a position which closes off the bypass line in a full ignition operating mode of the internal combustion engine. This ensures that the exhaust gas generated by the second combustion chamber group is conducted to the exhaust gas aftertreatment unit in the full ignition operating mode, while in the partial ignition operating mode, recirculation takes place to supply the first and/or second combustion chamber group, and/or a discharge takes place via the bypass line such that the exhaust gas aftertreatment unit is bypassed.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a schematic illustration of an internal combustion engine having an exhaust gas turbocharger, an exhaust gas aftertreatment unit and a bypass line with a throttle valve,

FIG. 2 is a schematic illustration of an internal combustion engine having an exhaust gas turbocharger, an exhaust gas aftertreatment unit, a bypass line and adjusting valves,

FIG. 3 is a schematic illustration of an internal combustion engine having an exhaust gas turbocharger, an exhaust gas aftertreatment unit and a bypass line with a switching flap, and

FIG. 4 is a schematic illustration of an internal combustion engine having an exhaust gas turbocharger, an exhaust gas aftertreatment unit and switchable exhaust gas recirculation.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an internal combustion engine 1 embodied in particular as a direct-injection diesel engine which has six combustion chambers which are divided into two combustion chamber groups 2, 3. The combustion chambers of the first combustion chamber group 2 are denoted by the reference symbols A1 to A3, and the combustion chambers of the second combustion chamber group 3 are denoted by the reference symbols B1 to B3. Both combustion chamber groups 2 and 3 are provided with fuel injectors (not illustrated in any more detail) which are in each case assigned to the individual combustion chambers and are themselves combined to form injector groups 4 and 5 corresponding to the combustion chamber groups 2 and 3. Both injector groups 4 and 5 can be actuated by an engine control unit 11 via control lines 14a, 14b. The control lines 14a, 14b can be embodied as a bus system making it possible for each fuel injector of the injector groups 4 and 5 to be addressed separately via the common control lines 14a, 14b.

Fresh gas, supplied via an intake line 17, with fuel, which is introduced via the fuel injectors, is compressed and ignited in the combustion chambers A1 to B3 of the internal combustion engine 1. The exhaust gas generated in the combustion chambers A1 to B3 is led away via a first exhaust collecting pipe 6 which is assigned to the first combustion chamber group 2 and via a second exhaust collecting pipe 7 which is assigned to the second combustion chamber group 3. The exhaust collecting pipes are embodied as exhaust branch lines. Both the first exhaust collecting pipe 6 and the second exhaust collecting pipe 7 open out into an exhaust gas turbine 8 of an exhaust gas turbocharger which is coupled by a driveshaft 21 to a compressor 15 of the turbocharger. The compressor 15 sucks fresh air from the environment of the internal combustion engine 1 and compresses it. After passing through a charge air cooler 13 provided in the intake line 17, the pre-compressed fresh air is provided to the combustion chambers A1 to B3.

A wastegate line, which is denoted as an overpressure pipe 22, is attached to the first exhaust collecting pipe 6 upstream of the inlet into the exhaust gas turbine 8, it being possible for the overpressure pipe 22 to be closed off by an overpressure valve 9, also denoted as a wastegate valve. The overpressure valve 9 is actuated by the engine control unit 11 by a control line 14c and, for example, an electromechanical adjusting device 16c, and allows a partial exhaust gas flow which is guided into the exhaust collecting pipe 6 to be discharged past the exhaust gas turbine 8. The overpressure pipe 22 is joined to a lead-off pipe 23, which leads off from the exhaust gas turbine 8, upstream of an exhaust gas aftertreatment unit embodied as an exhaust gas converter 10. The exhaust gas converter 10 is designed for selective catalytic reduction according to the SCR method, and has an efficiency which is dependent inter alia on the exhaust gas temperature and the exhaust gas volume flow rate. In an embodiment of the invention which is not illustrated, the exhaust gas converter can be embodied as a soot filter.

A bypass line, denoted as an exhaust pipe 18, branches off from the exhaust collecting pipe 7 of the second combustion chamber group 3 upstream of the exhaust gas turbine 8, which exhaust pipe 18 can be closed off by a throttle valve 12. The throttle valve 12 is actuated by the engine control unit 11 via a control line 14d and, for example, an electromechanical adjusting device 16d, and serves to influence the exhaust gas volume flow rate through the exhaust pipe 18 which opens out downstream of the exhaust gas converter 10 into an exhaust tailpipe 24 which leads away from the exhaust gas converter 10. The throttle valve 12 can be embodied, for example, as an annular slide valve as is known from exhaust gas turbochargers and turbobrakes.

The efficiency of the exhaust gas converter 10 and therefore the quality of the exhaust gas being treated, in terms of a residual pollutant content and soot content, is determined substantially by the temperature prevailing in the exhaust gas converter 10. The temperature is itself determined substantially by the temperature, the pressure and the volume flow rate of the exhaust gas which is flowing into the exhaust gas converter 10 and by the flow resistance of the exhaust gas converter 10. An advantageous operating state of the exhaust gas converter 10 is obtained if exhaust gases flow into the exhaust gas converter 10 at a high temperature and low volume flow rate. The exhaust gas temperature, the exhaust gas pressure and the exhaust gas volume flow rate are dependent on the load state of the internal combustion engine 1.

In order to provide advantageous exhaust gas aftertreatment in the exhaust gas converter 10 in such operating states, the fuel supply to the second combustion chamber group 3 is reduced, if appropriate to zero, so that in the latter case, the entire load is to be provided by the first combustion chamber group 2. Since this reduces the throttling losses which occur in the intake line 17 and are determined by a throttle flap (not illustrated), the internal combustion engine can be operated with a high degree of efficiency with regard to the utilization of the available fuel. In addition, the exhaust gas generated by the first combustion chamber group 2 has a high exhaust gas temperature. As a result, the exhaust gas introduced into the exhaust gas converter 10 from the first combustion chamber group 2 via the first exhaust collecting pipe 6 and the exhaust gas turbine 8 is advantageously suitable for exhaust gas aftertreatment despite the low load state of the internal combustion engine 1.

The exhaust gas generated by the second combustion chamber group 3 with reduced fuel or with the fuel shut off can, depending on demand, be selectively guided via the exhaust gas collecting pipe 7 of the exhaust gas turbine 8 and therefore subsequently to the exhaust gas converter 10. Alternatively, the exhaust gas can be at least partially discharged past the exhaust gas converter 10 via the exhaust pipe 18 and into the exhaust tailpipe 24, by virtue of the throttle valve 12 being correspondingly actuated by the engine control unit 11. The supply of the exhaust gas of the second combustion chamber group 3 to the exhaust gas converter 10 can be controlled as a function of the pressure and temperature conditions in the exhaust gas converter 10 and of the respective operating state of the internal combustion engine 1. Here, the throttle valve 12 can be set in particular in such a way that a pressure level is generated in the second exhaust collecting pipe 7 which is substantially identical to the pressure level in the first exhaust collecting pipe 6. This makes it possible for a predominant part of the exhaust gas flow from the second combustion chamber group 3 to be conducted into the exhaust gas turbine 8 and from there into the exhaust gas converter 10.

An adjustment of the throttle valve 12 can be carried out on the basis of exhaust gas pressure sensors (not illustrated), which are attached in the first and second exhaust collecting pipes 6 and 7 and output corresponding sensor signals to the engine control unit 11. The maximum throughput cross section of the throttle valve 12 can be dimensioned to be smaller than an outlet cross section of the exhaust collecting pipes 6 and 7, so that it is possible to substantially avoid exhaust gas flowing over from the first combustion chamber group 2 into the exhaust pipe 18 even when the throttle valve is completely open. A minimum solution is to provide a valve cross section which can be connected and disconnected and is connected only at idle. In the closed state, the throttle valve 12 separates the exhaust pipe 18 from the exhaust collecting pipe 7 in a gas-tight fashion. In the partially shut-off operating state of the engine 1, the throttle valve 12 can be opened in such a way that a dynamic pressure remains in the exhaust pipe 18, which dynamic pressure is at least slightly higher than the exhaust gas pressure of the first combustion chamber group 2. The exhaust gas temperature in the exhaust gas converter 10 can, if required, be increased by a more intense pressure build-up.

The throttle valve 12 is actuated independently of the overpressure valve 9 if the latter is embodied as a conventional, charge-pressure-controlled valve. If the overpressure valve 9 is also open in the lower load range, the throttle valve 12 and the overpressure valve 9 are advantageously actuated in a coordinated fashion by the engine control unit 11.

In an embodiment of the invention which is not illustrated but is similar to the embodiment of FIG. 1, the position of the throttle valve 12 is regulated on the basis of the parameters including intake pipe pressure, engine speed and load state of the internal combustion engine 1, which are also measured for other engine control purposes. For this purpose, a corresponding characteristic diagram is stored in the engine control unit 11. If the internal combustion engine 1 experiences a significant increase in load, the throttle valve 12 is closed and all the combustion chambers A1 to B3 are supplied equally with fuel.

The embodiment of the invention shown in FIG. 2 is a variant of the example from FIG. 1, in which the throttle valve 12 is replaced by a first adjusting valve 19 and a second adjusting valve 20, which valves are both provided in the second exhaust collecting pipe 7. Otherwise, for the sake of clarity, the same reference symbols are used here and in the further variants of FIGS. 3 and 4 for identical or in any case functionally equivalent elements, and reference can in this respect be made to the above statements regarding FIG. 1.

The two adjusting valves 19, 20 allow a controlled or regulated discharge of the exhaust gas passing from the second combustion chamber group 3 in the direction of the exhaust gas turbine 8 and/or in the direction of the exhaust pipe 18. For this purpose, the two adjusting valves 19, 20 are connected by control lines 14e, 14f to the engine control unit 11 and can be correspondingly actuated by electromechanical adjusting devices 16e, 16f as a function of the operating state of the internal combustion engine 1. In the event of the second combustion chamber group 3 being supplied with fuel, the exhaust gas flow is discharged via the exhaust gas turbine 8 and the exhaust gas converter 10 which is connected downstream.

In the event of the fuel supply to the second combustion chamber group 3 being partially or completely shut off, the exhaust gas flow from the second combustion chamber group 3 is conducted via the second exhaust collecting pipe 7 and the open second adjusting valve 20 into the exhaust pipe 18, and therefore into the exhaust tailpipe 24, downstream of the exhaust gas converter 10. For this purpose, at the same time as the shut-off or reduction of the fuel supply to the second injector group 5 by the engine control unit 11, the adjusting valves 19 and 20 are actuated such that the exhaust gas from the second combustion chamber group 3 can be conducted into the exhaust pipe 18. In an embodiment which is not illustrated, the adjusting valves 19, 20 can also be embodied as separate flap valves or slide valves.

In the embodiment of the invention illustrated in FIG. 3, a switching flap 25 replaces the throttle valve 12 of FIG. 1 and allows the exhaust gas flow from the second combustion chamber group 3 to be switched in a particularly simple fashion between a supply to the exhaust gas turbine 8 or a discharge through the exhaust pipe 18. The switching flap 25 is actuated by the engine control unit 11 via a control line 14g.

In the embodiment of the invention shown in FIG. 4, an exhaust gas recirculation line 26 leads from the second exhaust collecting pipe 7 instead of the bypass line 18, which bypasses the exhaust gas converter, of FIGS. 1 to 3, in which exhaust gas recirculation line 26 is provided an adjusting valve 20a. The recirculation line 26 opens out into an intake line section 28b which is assigned to the second combustion chamber group 3.

As in the example of FIG. 2, the adjusting valve 19 is situated in the second exhaust collecting pipe 7 which leads to the exhaust gas turbine 8. An adjusting valve 27 is provided between an intake line section 28a which is assigned to the first combustion chamber group 2 and the intake line section 28b, which actuating valve 27 can open or close a connection between the intake line sections 28a, 28b depending on the operating state of the internal combustion engine 1. Thus, an exhaust gas flow from the second combustion chamber group 3 may be recirculated into the second combustion chamber group 3 and optionally also into the first combustion chamber group 2 during an operating state in which the fuel supply is shut off or reduced in comparison with the first combustion chamber group 2. The exhaust gas flow from the second combustion chamber group 3 can also, as desired, circulate at least at times in a closed circuit including the second combustion chamber group 3, the exhaust gas collecting pipe 7, the recirculation line 26 and the intake line section 28b. This reduces charge exchange losses, since the exhaust gas flow from the second combustion chamber group 3 is merely pumped around the circuit.

When the connection between the two intake line sections 28a, 28b is open, it is possible for the exhaust gas flow generated by the second combustion chamber group 3 and recirculated to be mixed together with the fresh air flow provided by the fresh air turbine 15. This ensures that the exhaust gas generated by the second combustion chamber group 3, in the event of an increase in load of the internal combustion engine 1, is supplied to a proper combustion process and is correspondingly aftertreated by the exhaust gas converter 10.

A pressure cell 29 is provided in the intake line section 28a, by means of which pressure cell 29 the adjusting device 16 actuates the overpressure valve 9 as a function also of the feed pressure of the fresh air turbine 15. This can prevent an excessively high feed pressure of the fresh air turbine.

In an embodiment of the invention which is not illustrated, there is a permanent connection between the recirculation line 26 and the intake line section 28b by virtue of the adjusting valve 20 being dispensed with. This makes it possible in particular to easily provide fuel-reduced operation of the second combustion chamber group 3. The exhaust gas flow generated here is recirculated into the intake line sections 28a, 28b via the recirculation line 26, and is available to the first and second combustion chamber groups 2, 3 for renewed combustion.

In a further, simplified embodiment which is not illustrated, all the previously described embodiments can also be designed without the overpressure valve 9 and without the overpressure pipe 22 which is actuated by the overpressure valve 9.

In a further embodiment of the invention which is not illustrated, a plurality of exhaust gas turbochargers are provided, with each of the exhaust collecting pipes of the different combustion chamber groups being provided with a separate exhaust gas turbine.

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.