Patent Application
20070107430
The invention relates to an internal combustion engine having two exhaust gas turbochargers, each including a turbine and a compressor, disposed in series circuits and an exhaust gas recirculation line including a non-return valve connected to an exhaust duct upstream of an exhaust gas turbine for returning exhaust gas to a compressor air intake duct.
DE 101 44 663 A1 discloses an internal combustion engine having two exhaust gas turbochargers, a first turbocharger forming a high pressure stage, and the second turbocharger forming a low pressure stage. The high pressure stage is arranged near to the engine, and the low pressure stage is in contrast located at a relatively large distance from the internal combustion engine. The compressors of the two exhaust gas turbochargers are connected in series in the intake section, and the exhaust gas turbines of the two turbochargers are likewise arranged one behind the other in the exhaust gas section. Both the compressor and the turbine of the high pressure stage are each bypassed by a bypass which can be shut off, each bypass being able to be opened or closed as a function of engine state variables and engine operating variables. When the loads and engine speeds are low, the bypass around the compressor or the exhaust gas turbine of the high pressure stage is closed and the high pressure stage is activated. As the load and the engine speed increase, the bypass around the compressor or the turbine of the high pressure stage can be opened, as a result of which the high pressure stage is deactivated and the compressor work is to be carried out solely by the low pressure stage.
Such internal combustion engines with two-stage supercharging have a transient behavior which is improved compared to single stage supercharging. However, two stage supercharging does not have any direct influence on the exhaust gas behavior of the internal combustion engine.
In order to improve the exhaust gas behavior, in particular in order to reduce the NOx emissions it is basically known to re-circulate exhaust gas from the exhaust gas section into the intake section. Such recirculation of exhaust gas is carried out in particular in the partial load operating mode of the internal combustion engine and is described, for example, in document DE 101 52 804 A1. The internal combustion engine is equipped with an exhaust gas turbocharger whose exhaust gas turbine has two different exhaust gas flows of different sizes via which exhaust gas can be fed to the turbine wheel. Each cylinder bank of the internal combustion engine is in communication with one exhaust line. A recirculation line of the exhaust gas recirculation device branches off the smaller exhaust line which has a higher exhaust gas back pressure. The recirculation line extends to an intake duct section downstream of the compressor for returning the recirculation exhaust gas to the engine. The higher exhaust gas back pressure supports the recirculation of exhaust gases into the intake section and permits exhaust gas to be re-circulated over a wide operating range of the engine.
U.S. Pat. No. 6,397,598 B1 discloses an internal combustion engine with two exhaust gas turbochargers connected in series. The internal combustion engine has two cylinder banks with three cylinders each, the exhaust gas of each cylinder bank being fed into a separate exhaust line. The first exhaust line leads into the exhaust gas turbine which is near to the engine and which has a flow connection via a further line section to the second exhaust gas turbine which is remote from the engine. The second exhaust line leads directly into the second exhaust gas turbine which is remote from the engine.
Furthermore, in U.S. Pat. No. 6,397,598 B1 an exhaust gas recirculation device is provided which branches off from the first exhaust line which is connected to the exhaust gas turbine which is near the engine. An adjustable nonreturn valve is arranged in the recirculation line of the exhaust gas recirculation device.
With this configuration it is possible to bring about different exhaust gas backpressures in the two exhaust lines, which can be utilized for improved exhaust gas recirculation. However, the adjustment possibilities are restricted to regulating the nonreturn valve in the exhaust gas recirculation line. The level of the exhaust gas back pressure, in particular in the exhaust line which is coupled to the recirculation line, cannot be influenced—with the exception of regulating the nonreturn valve in the recirculation line.
Document U.S. Pat. No. 6,378,308 B1 discloses an internal combustion engine with two cylinder banks whose exhaust gas is fed in each case into one exhaust line, each exhaust line leading into an exhaust gas flow of a turbine which is near the engine. A further exhaust gas turbine which is remote from the engine is connected downstream of the two-flow exhaust gas turbine which is near the engine. A recirculation line which leads into the intake section downstream of the compressor and which is assigned to the exhaust gas turbine which is near the engine branches off from the exhaust gas collector of one of the two cylinder banks.
Furthermore, U.S. Pat. No. 6,378,308 B1 discloses a bypass in each exhaust line for optionally bypassing the exhaust gas turbine which is near the engine. Each bypass branches off upstream of the exhaust gas turbine which is near the engine and leads again into the exhaust line downstream of this exhaust gas turbine. The bypass mass flow rate can in each case be regulated via one intermediate nonreturn valve in each bypass.
It is the object of the present invention to improve the exhaust behavior of an internal combustion engine with two-stage supercharging by simple means.
In an internal combustion engine provided with two exhaust gas turbochargers which each comprise a turbine in an exhaust line and one compressor in an intake section of the engine, two exhaust lines are provided which are each assigned to at least one of the exhaust gas turbines, an exhaust gas recirculation device being arranged between an exhaust line upstream of an exhaust gas turbine and the intake section downstream of a compressor and the two exhaust lines including bypass lines with a control valve for selectively permitting the exhaust gas to bypass the turbine closer to the engine.
This arrangement requires only simple means for adjusting asymmetrical exhaust gas back pressures in the two exhaust lines in the section between the outlet of the cylinders of the internal combustion engine and the exhaust gas turbines. The asymmetry in the exhaust gas back pressures can be utilized for improved exhaust gas recirculation since that exhaust line participates in the recirculation of exhaust gas in which the exhaust gas back pressure exceeds the charge pressure in the intake section in certain operating states while, with the same operating conditions, a pressure which is below the charge pressure can be maintained in the second exhaust line.
The asymmetry can be achieved with structurally simple means. According to one advantageous embodiment, one of the two exhaust gas turbines is equipped with two separate exhaust gas inlet flows passages via which the exhaust gas is to be fed to the turbine wheel of the respective exhaust gas turbine. The two exhaust gas flows passages are each connected to one of the two separate exhaust lines. Using a different cross-sectional geometry and/or a different size of the two exhaust flow passages it is possible to generate different exhaust gas back pressures in the respective line sections between the internal combustion engine and the inlet to each exhaust gas flow passage.
Each of the two exhaust lines is expediently connected to some of the cylinders of the internal combustion engine so that likewise only the exhaust gases of the respective cylinders can be discharged via the exhaust line assigned to them. Usually the internal combustion engine has two cylinder banks with the same number of cylinders, the exhaust gases of each cylinder bank being discharged via one exhaust line in each case. However, it is also possible to have an asymmetrical distribution of the cylinders, and, with such an asymmetrical distribution, the particular exhaust line to which the exhaust gases of the larger number of cylinders are fed, also expediently participates in the recirculation of exhaust gas.
The two-flow gas turbine can be arranged either near to the engine or remote from the engine in the exhaust gas section. The exhaust gas recirculation line advantageously branches off upstream of the first of the two exhaust gas turbines connected in series, which is near the engine.
If the exhaust gas turbine which is near the engine includes two exhaust gas inlet flow passages, each of the two exhaust lines extending to one exhaust gas flow passages of the first exhaust gas turbine which is near the engine. The two exhaust lines are thus connected to the exhaust gas turbine which is near the engine. The exhaust gas recirculation line branches off from the exhaust line which carries the smaller of the two exhaust gas flows. The second exhaust gas turbine which is remote from the engine is connected via an exhaust line section in series with the first exhaust gas turbine which is near the engine.
In an alternative embodiment, wherein the second exhaust gas turbine which is remote from the engine includes two flow passages, one of the two exhaust gas flow passages is supplied with exhaust gases directly by the cylinders of the internal combustion engine via one of the exhaust lines while the second exhaust gas flow passage is connected in series with the first exhaust gas turbine which is near the engine, via the other exhaust line; in this embodiment the two exhaust lines are assigned to different exhaust gas turbines.
The two exhaust gas lines are advantageously in communication with one another via a bypass line with a nonreturn valve arranged therein. The bypass line permits exhaust gas to be transferred from the exhaust gas line with relatively high exhaust gas pressure to the exhaust gas line with relatively low exhaust gas back pressure in certain operating states of the internal combustion engine. This transfer process constitutes an additional possible way of intervening in order to influence the operating mode of the internal combustion engine.
The invention will become more readily apparent from the following description of an embodiment of the invention with reference to the accompanying drawings:
The internal combustion engines illustrated in
The internal combustion engine 1 illustrated in
Each cylinder bank 1a, 1b of the internal combustion engine 1 is assigned one exhaust line 10 and respectively, 11, the two exhaust lines 10 and 11 being part of the exhaust gas section of the internal combustion engine. The first exhaust line 10 extends from the first cylinder bank 1a to the exhaust gas turbine 4 which is near the engine. The turbine outlet of the turbine 4 is connected via a further line section of the first exhaust line 10 to the exhaust gas turbine 7 which is remote from the engine. The second exhaust line 11 collects the exhaust gases of the second cylinder bank 1b and feeds them directly to the exhaust gas turbine 7 which is remote from the engine.
The exhaust gas turbine 7 which is remote from the engine is a two-flow turbine and has two exhaust gas inlet flow passages 7a and 7b. The first exhaust gas flow passage 7a of the exhaust gas turbine 7 which is remote from the engine is connected via the line section 10 to the outlet of the exhaust gas turbine 4 which is near the engine. The second exhaust gas flow passage 7b is supplied with the exhaust gases from the cylinder bank 1b via the second exhaust line 11. The exhaust gas flow passage 7a and 7b are expediently made separate so that a direct exchange of gas between the exhaust gas flows is prevented. The exhaust gases in the exhaust gas flow passages 7a and 7b are fed to the turbine wheel of the exhaust turbine 7.
The exhaust gas turbine 7 which is remote from the engine can also be provided with a variable turbine geometry 22 which permits the turbine inlet cross-section to be adjusted in a variable fashion between a minimum backpressure cross-section and a maximum opening cross-section. The variable turbine geometry 22 permits, inter alia, the implementation of a turbo-braking function.
Furthermore, the internal combustion engine 1 is equipped with an exhaust gas recirculation device 15 which comprises an exhaust gas recirculation line 16, an exhaust gas cooler 17 arranged therein and an adjustable nonreturn valve 18. The exhaust gas recirculation line 16 branches off from the first exhaust line 10 upstream of the first exhaust gas turbine 4 which is near the engine, and leads into the intake duct 12 downstream of the second charge air cooler 14 which is assigned to the compressor 5 which is near the engine. The non-return valve 18 of the exhaust gas recirculation device 15 can be opened in order to transfer exhaust gas into the intake duct 12 in operating states in which the exhaust gas back pressure in the exhaust line 10 exceeds the charge pressure in the intake section 12.
The two exhaust lines 10 and 11 are in communication with one another via a bypass line 21 which branches off from the exhaust line 11 upstream of the exhaust gas turbine 7 which is remote from the engine, and leads into the exhaust line 10 downstream of the exhaust gas turbine 4 which is near the engine. An adjustable nonreturn valve 20 is arranged in the bypass line 21. Exhaust gas can be transferred between the exhaust lines using the bypass line 21.
Furthermore, the first exhaust line 10 is connected via a line section 19 to the bypass line 21, upstream of the exhaust gas turbine 4 which is near the engine, via the nonreturn valve 20. The non-return valve 20 can assume various positions. In a first position of the non-return valve 20, only the line section 19 is opened and the upper section of the bypass line 21 which branches off from the exhaust line 11 is shut off, as a result of which a bypass bypassing the exhaust gas turbine 4 which is near the engine is established. In a second position of the non-return valve, the line section 19 is shut off and the upper section of the bypass line 21 which branches off from the exhaust line 11 is opened so that an exchange of gas can be brought about between the second exhaust line 11 upstream of the second exhaust gas turbine 7 which is remote from the engine and the first exhaust line 10 downstream of the exhaust gas turbine 4 which is near the engine. In a third position, both the line section 19 and the upper section of the bypass line 21 can be opened. In a fourth position, both lines or line sections are shut off.
In the exemplary embodiment according to
The line section 19 branches off from the first outlet line 10 upstream of the exhaust gas turbine 4 which is near the engine and leads via the nonreturn valve 20 into the bypass line 21 which branches off from the second exhaust line 11 upstream of the exhaust gas turbine 4 which is near the engine, and leads again into the exhaust line section bypassing the exhaust gas turbine 4. As described in the preceding exemplary embodiment, the nonreturn valve 20 can assume various positions in which the bypass line 21 and/or the line section 19 are optionally shut off or opened.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 009 794.1 | Feb 2004 | DE | national |
This is a Continuation-In-Part Application of International Application PCT/EP2005/001908 filed Feb. 04, 2005 and claiming the priority of German Application 102004009794.1 filed Feb. 02, 2004.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP05/01908 | Feb 2005 | US |
| Child | 11508738 | Aug 2006 | US |
