Supercharging system for two-stage supercharging of V-type internal combustion engines

A supercharging system, in particular an at least two-stage supercharging system, including a first stage and a second stage for an internal combustion engine having two cylinder banks. The at least two-stage supercharging system includes at least two charge air coolers. An exhaust gas turbocharger representing the first stage and an exhaust gas turbocharger representing the second stage are each situated next to one of the cylinder banks of the internal combustion engine.

BACKGROUND INFORMATION

The power limits of a supercharging system such as an exhaust gas turbocharger are increased, for example by regulated two-stage supercharging, as is known from Bosch, Kraftfahrtechnisches Taschenbuch [Automotive Handbook], 23rdEdition, Vieweg, 1999, pages 445 through 446. In regulated two-stage supercharging, two exhaust gas turbochargers of different sizes are connected in series. The exhaust gas mass flow first flows into an exhaust gas manifold. From there, the exhaust gas mass flow is expanded via a high pressure turbine. In the case of large exhaust gas volumes, which can occur at high speeds, a portion of the exhaust gas mass flow may be redirected around the high pressure turbine via a bypass. The entire exhaust gas mass flow is subsequently used by a low pressure turbine connected downstream from the high pressure turbine. The incoming fresh air mass flow is first precompressed by a low pressure stage and then further compressed in the high pressure stage. Ideally, the fresh air mass flow undergoes intermediate cooling between the low pressure stage and the high pressure stage.

At approximately 50% to 60% of the nominal speed, the exhaust gas is completely redirected around the high pressure turbine via a bypass. As a result, the high pressure compressor, which is driven by the high pressure turbine and is connected in series to a low pressure compressor driven by the low pressure turbine, is simultaneously taken out of operation. In this case, the high pressure compressor is bypassed via a charge air line in which a nonreturn valve is provided to prevent charge air from flowing back via the charge air line during operation of the high pressure compressor.

Two-stage supercharging in a supercharging system is generally carried out by two series-connected exhaust gas turbochargers. This achieves a two-stage expansion via the two turbine parts of the two exhaust gas turbochargers as well as a two-stage compression on the compressor side of the two series-connected exhaust gas turbochargers. The disadvantages of unregulated two-stage supercharging are avoided by regulating devices for bypassing the high pressure turbine and high pressure compressor.

Cutting off the exhaust gas mass flow upstream from the high pressure turbine regulates the power of the high pressure turbine. The exhaust gas mass flow leaving the high pressure turbine mixes with a portion of the exhaust gas mass flow flowing through the bypass valve and is subsequently expanded in the low pressure turbine. A disadvantage of this procedure is the fact that the difference in pressure present between the outlet side of the internal combustion engine and the output of the high pressure turbine is expanded by a bypass valve without reducing work. In the case of unregulated two-stage supercharging, the fact that the entire exhaust gas mass flow is expanded in an unregulated manner in the high pressure and low pressure turbines is disadvantageous. This means that the power of the two-stage supercharging system rises in an unregulatable manner between a specific load point and the maximum load point, which is unsuitable for use in an internal combustion engine of a passenger car. Due to the design of the high pressure and low pressure turbines in the case of unregulated two-stage supercharging, an unsatisfactory response characteristic exists in the operating range up to and above the design point.

European Patent Application No. EP 0 718 481 relates to an exhaust gas recirculation system for a supercharged internal combustion engine. To lower exhaust emissions, in particular to substantially reduce NOxlevels in the partial load range of the internal combustion engine, a method is known for recirculating a portion of the exhaust gas to suppress NOxformation by reducing the oxygen content. In supercharged engines, recirculating the exhaust gas directly results in a noticeable decrease in the power of the exhaust gas turbine. This decrease is even more pronounced in a two-stage supercharging system. To avoid power decreases of this type, which usually go hand-in-hand with increased fuel consumption, a method is described in which the exhaust gas to be recirculated is removed from between the high pressure turbine part and the low pressure turbine part and supplied to the inlet of the low pressure compressor which is higher in relation to the low pressure turbine. This ensures an exhaust gas recirculation method which minimizes increased fuel consumption.

The design of a two-stage supercharging system poses a particular difficulty in internal combustion engines having a V-shaped cylinder layout, because the two cylinder banks must be uniformly impinged upon by the turbochargers. If only one turbocharger is used as the high pressure stage and one turbocharger as the low pressure stage, the supercharging system may be positioned in front of or behind the internal combustion engine without taking up a lot of space. Although this provides a number of advantages, it nevertheless has the disadvantage that there is not always enough room in the engine compartment.

SUMMARY OF THE INVENTION

According to the present invention, the two stages of a two-stage supercharging system should each be accommodated on the side of an internal combustion engine, or a flat engine, having a V-shaped cylinder bank layout mounted in the longitudinal direction in relation to the vehicle. In the design according to the present invention, two embodiment variants are provided below, one embodiment variant representing a supercharging system having intermediate cooling and the other embodiment variant representing a supercharging system having no intermediate cooling.

In the two-stage supercharging system having intermediate cooling according to the present invention, the air compressed by the low pressure compressor of the two-stage supercharging system is precooled in a heat exchanger on the fresh air side. The heat exchanger may be conveniently accommodated in an advantageous manner in the wheel box located on the same side of the vehicle. Downstream from this intercooler, the intermediately cooled, precompressed fresh air may be supplied to a charge air cooler via both the high pressure compressor and a bypass line. The bypass line is advantageously released by an automatic compressor bypass.

The charge air cooler may be accommodated in a particularly advantageous manner in the area of a wheel box in the engine compartment. In the case of a two-stage supercharging system having no intermediate cooling, two charge air coolers are employed which are used for final cooling of the fresh air precompressed in the low pressure compressor and in the high pressure compressor before entering the combustion chambers of the internal combustion engine. In this embodiment variant, both charge air coolers may be parallel-connected in a particularly advantageous manner, which enables the pressure loss to be minimized on the fresh air side. Bypass valves may be used to cut off the flow through the two charge air coolers when, for example, the high pressure compressor is in use, and the pressure may be built up faster thereby due to smaller container volumes. According to the embodiment variant of the two-stage supercharging system having no intermediate cooling, the two exhaust gas turbochargers may also be positioned to the left and right of the internal combustion engine. The exhaust gas manifolds of the internal combustion engine are connectable to each other via a common exhaust gas line.

According to a preferred embodiment of the above-outlined embodiment variant of the supercharging system according to the present invention for internal combustion engines having V-shaped cylinder bank layouts or designed as flat engines, the supercharging systems are connected to the relevant cylinder bank as far to the front or rear as possible, i.e., viewed in relation to the direction of vehicle travel, on an end face of the engine (in front) or a back end of the engine (in the rear). This results in short exhaust gas pipes leading to the cylinder banks, and minimal flow losses as a consequence thereof, as well as an end-face surface that dissipates little heat. In a preferred embodiment with regard to the efficiency of the overall system, a thermally insulated design of the exhaust gas system, in particular of connecting lines, is provided, using air gap insulated pipes between the supercharging systems and the cylinder banks. The design according to the present invention supports the shortest possible connecting pipes so that the flow losses may be kept within narrow limits.

DETAILED DESCRIPTION

The illustration according toFIG. 1shows a schematic flow chart of a regulated two-stage supercharging system.

According to the illustration inFIG. 1, a two-stage supercharging system12has a first exhaust gas turbocharger14and a second exhaust gas turbocharger24. Fresh air10, which has a state (1), is compressed via a low pressure compressor part16of first exhaust gas turbocharger14. The precompressed fresh air is cooled in a first charge air cooler22connected downstream from low pressure compressor part16of first exhaust gas turbocharger14. In addition to low pressure compressor part16, first exhaust gas turbocharger14also includes a low pressure turbine part20which is coupled with low pressure compressor part16via a shaft. After passing through first charge air cooler22, the precompressed fresh air flows to a high pressure compressor part26of a second exhaust gas turbocharger24. High pressure compressor part26of second exhaust gas turbocharger24may also be bypassed via a first bypass32, so that the precompressed fresh air flows directly to a second charge air cooler34in which the precompressed fresh air is recooled.

If the precompressed fresh air cooled in first charge air cooler22is supplied to high pressure compressor part26of second exhaust gas turbocharger24, the precompressed fresh air which was cooled in first charge air cooler22may be compressed again. In addition to high pressure compressor part26, second exhaust gas turbocharger24also includes a high pressure turbine part28. High pressure compressor part26and high pressure turbine part28of second exhaust gas turbocharger24are coupled with each other via a shaft30.

A second charge air cooler34is connected downstream from first bypass32and high pressure compressor part26, respectively. Either the fresh air which was recompressed in high pressure compressor part26of second exhaust gas turbocharger24or the precompressed fresh air passing through first bypass32is recooled in this second charge air cooler. On the inlet side of an internal combustion engine36, the fresh air leaving second charge air cooler34assumes state (2). Exhaust gas leaves internal combustion engine36on the outlet side and assumes a state (3), the exhaust gas being supplied to the exhaust gas tract of internal combustion engine36via an exhaust line38. The exhaust gas may be routed via either a second bypass40or high pressure turbine part28of second exhaust gas turbocharger24. At the output of high pressure turbine part28, the exhaust gas assumes state (3′) before flowing to either low pressure turbine part20or a third bypass44via a supply line42. After passing through low pressure turbine part20, the exhaust gas assumes state (4), the pressure in state (4) being essentially equal to the ambient pressure.

The illustration according toFIG. 2shows a two-stage supercharging system for an internal combustion engine having at least two cylinder banks and including series-connected charge air coolers having intermediate cooling.

According toFIG. 2, fresh air10flows to an air filter50, downstream from which a mass air flow meter52is connected. Fresh air10is precompressed in low pressure compressor part16of first exhaust gas turbocharger14, low pressure compressor part16of first exhaust gas turbocharger14being coupled with low pressure turbine part20via shaft18. The precompressed fresh air is cooled in first charge air cooler22. The precompressed, cooled fresh air subsequently flows to high pressure compressor part26of second exhaust gas turbocharger24via a branch54. High pressure compressor part26of second exhaust gas turbocharger24is connected to high pressure turbine part28via shaft30and driven via high pressure turbine part28of second exhaust gas turbocharger24. The fresh air which was recompressed in high pressure compressor part26of second exhaust gas turbocharger24flows to second charge air cooler34, in which the recompressed fresh air is cooled again. A valve56, which is designed, for example, as a nonreturn valve, is provided between first charge air cooler22and second charge air cooler34, which are situated in a series circuit74, to prevent the fresh air which was recompressed in high pressure turbine part26of second exhaust turbocharger24from flowing back in the direction of first charge air cooler22before passing through second charge air cooler34, so that pressure losses are avoided. The highly compressed fresh air which was recooled in second charge air cooler34flows to internal combustion engine36via a throttle device58. Internal combustion engine36according to the illustration inFIG. 2includes a first cylinder bank60and a second cylinder bank62according to the design principle of V-type engines. These are generally internal combustion engines36having 6, 8, 10, 12 or more cylinders which are used in high-performance passenger cars or commercial vehicles, including spark-ignition and auto-ignition internal combustion engines36. The individual cylinders accommodated in cylinder banks60and62, respectively, are identified by reference numeral64. An inlet side on which the highly compressed and cooled fresh air enters the combustion chambers of cylinders64downstream from throttle device58is indicated by reference numeral66in the illustration according toFIG. 2, while reference numeral68identifies the outlet side where the exhaust gas leaves the combustion chambers of internal combustion engine36. On the outlet side, internal combustion engine36having two cylinder banks60,62includes exhaust gas manifolds which empty into a common exhaust gas line38. Common exhaust gas line38, which runs in the exhaust gas tract of the internal combustion engine, accommodates an exhaust gas regulating device70, and a supply line which is connected downstream from high pressure turbine part28of second exhaust gas turbocharger24empties downstream from this exhaust gas regulating device. Low pressure turbine part20of first exhaust gas turbocharger14, in which the exhaust gas is fully expanded and leaves the exhaust gas tract of the internal combustion engine in a cleaned and expanded state in the form of exhaust gas72, which essentially has the ambient pressure level, is accommodated downstream from the point at which the supply line from high pressure turbine part28empties into exhaust gas line38. The supply line from high pressure turbine part28of second exhaust gas turbocharger24to exhaust gas line38is identified by reference numeral76in the illustration according toFIG. 2.

In the two-stage supercharging system illustrated inFIG. 2, fresh air10flowing through low pressure compressor part16is precooled by first charge air cooler22. This first charge air cooler may be conveniently accommodated in a particularly advantageous manner in front of or behind one of the wheel boxes in the area of the engine compartment located, for example, next to first cylinder bank60. After leaving first charge air cooler22, the precompressed fresh air may flow through both high pressure compressor part26of second exhaust gas turbocharger24and a bypass line, which is assigned to high pressure compressor part26and accommodates nonreturn valve56. The bypass line accommodating nonreturn valve56, which runs parallel to high pressure compressor part26of second exhaust gas turbocharger24, may also be provided with an automatic compressor bypass. Second charge air cooler34may be advantageously accommodated in the area of the vehicle engine compartment facing second cylinder bank62of internal combustion engine36. The two-stage supercharging system provided according to the present invention, including series-connected charge air coolers22,34having intermediate cooling, may be advantageously accommodated in the vehicle so that first charge air cooler22and first exhaust gas turbocharger14are located adjacent to first cylinder bank60of internal combustion engine36, while second exhaust gas turbocharger24and second charge air cooler34are situated on the side facing second cylinder bank62of internal combustion engine36. Since the vehicle wheel boxes are connectable to the surroundings, accommodating series-connected first and second charge air coolers22,34in the area of the wheel boxes for the front wheels in the engine compartment makes it possible to particularly effectively cool either fresh air10which was precompressed in low pressure compressor part16or the recompressed fresh air entering second charge air cooler34. If exhaust gas regulating valve70is closed, the entire exhaust gas mass flow may be first supplied to high pressure turbine part28of second exhaust gas turbocharger24.

A further connecting line76is routed around internal combustion engine36having two cylinder banks60,62to supply the exhaust gas leaving high pressure turbine part28to low pressure turbine part20of first exhaust gas turbocharger14. Low pressure turbine part20is situated on the side of internal combustion engine36where the latter's first cylinder bank60is located. An attempt should be made to keep the pipes, i.e., connecting line76from high pressure turbine part28to exhaust gas line38as well as the section of exhaust gas line38from outlet side68of internal combustion engine36to low pressure turbine part20, as short as possible to keep flow losses to a minimum, in particular, to minimize the heat-dissipating surface of exhaust gas line38and connecting line76, respectively. The thermally insulated design of the exhaust gas system, in particular of the connecting lines between the supercharging systems and the cylinder banks using air gap insulated pipes, is particularly advantageous for the embodiment variant of the two-stage supercharging system illustrated inFIG. 2. In the design according to the present invention, the connecting lines may be kept very short.

The illustration according toFIG. 3shows an embodiment variant of the two-stage supercharging system for internal combustion engines having two cylinder banks, in which the charge air coolers are parallel-connected and there is no intermediate cooling of the fresh air.

According to the embodiment variant illustrated inFIG. 3, fresh air10flows via air filter50and mass air flow meter52to low pressure turbine part16of first exhaust gas turbocharger14. As illustrated in connection withFIG. 2, low pressure compressor part16of first exhaust gas turbocharger14is connected to low pressure turbine part20of first exhaust gas turbocharger14via shaft18. On the one hand, precompressed fresh air10flows to high pressure compressor part26of second exhaust gas turbocharger24via a bypass line82and on the other hand passes, in part, through a branch80, which runs to first charge air cooler22. A first nonreturn valve84is connected downstream from first charge air cooler22for cooling precompressed fresh air10. First nonreturn valve84performs a sequence valve function when the pressure loss in charge air cooler34increases. Fresh air10which was precompressed in low pressure compressor part16flows to a junction88. The flow of precompressed fresh air passing through bypass line82flows to high pressure compressor part26of second exhaust gas turbocharger24. A further, second nonreturn valve86is parallel-connected thereto. Second nonreturn valve86acts as a compressor bypass when low pressure compressor part16supplies an excessive air volume and high pressure compressor part26switches to “blocked mode.”

Fresh air10which was recompressed in high pressure compressor part26is cooled in charge air cooler34connected downstream from high pressure compressor part26and supplied to junction88, which is located upstream from throttle device58. The highly compressed fresh air flow leaving second charge air cooler34and the portion of the fresh air flow which was cooled in first charge air cooler22via branch80mix in junction88and flow via first nonreturn valve84of junction88. The illustration according toFIG. 3shows that first charge air cooler22and second charge air cooler34are situated in a parallel circuit90. Throttle device58, via which the precompressed fresh air flows on inlet side66to cylinders64of first cylinder bank60and second cylinder bank62of internal combustion engine36, is located downstream from junction88and upstream from internal combustion engine36. When exhaust gas regulating valve70is closed, exhaust gas flows from outlet side68to high pressure turbine part28of second exhaust gas turbocharger24and is resupplied, via connecting line76, to exhaust gas line38downstream from exhaust gas regulating valve70and upstream from low pressure turbine part20of first exhaust gas turbocharger14. After the exhaust gas has been fully expanded in low pressure turbine part20, exhaust gas72leaves the exhaust gas tract of the internal combustion engine at the ambient pressure level.

In the embodiment variant of the two-stage supercharging system according to the illustration inFIG. 3, first exhaust gas turbocharger14may be situated on the side of internal combustion engine36where first cylinder bank60is located. Likewise, second exhaust gas turbocharger24may be situated diametrically opposed to second cylinder bank62of internal combustion engine36. An attempt should be made to keep both connecting line76to high pressure turbine part28of second exhaust gas turbocharger24to exhaust gas line38as well as exhaust gas line38to low pressure turbine part20as short as possible to minimize flow losses on the one hand and, to minimize the heat-dissipating surfaces of these pipes, i.e., exhaust gas line38and connecting line76on the other hand.

In the two-stage supercharging systems illustrated inFIGS. 2 and 3, providing the exhaust gas lines, i.e., pipes76and38, with a thermally insulated design and using air gap insulated pipes have an advantageous effect on the efficiency of the overall system.

In the two embodiment variants according toFIGS. 2 and 3, exhaust gas turbochargers14and24, respectively, should be situated as far as possible to the front or rear of cylinder banks60,62of internal combustion engine36having a V-shaped cylinder layout. If both exhaust gas turbochargers14and24are located as close as possible to cylinder banks60and62, respectively, their distance from one another is minimized and pipes76and38may be kept as short as possible. To utilize the compact mounting space in the engine compartment of a motor vehicle which includes an internal combustion engine36having a V-shaped cylinder layout, connecting line76, which connects high pressure turbine part28of second exhaust gas turbocharger24to exhaust gas line38leading to low pressure turbine part20of first exhaust gas turbocharger14, is routed in the engine compartment in such a way that pipes do not have to be routed beneath the oil pan of internal combustion engine36.