FR2904365A1 - Internal combustion engine for motor vehicle, has air supercharging device with low pressure turbo compressor that is mounted in series with high pressure turbo compressors, where low pressure turbo compressor feeds air to turbo compressors - Google Patents

Abstract

The engine (1) has an air supercharging device (2) with two high pressure turbo compressors (3, 4) that are mounted in parallel and supply air to cylinder assemblies (16, 17) of the engine. The air supercharging device has a low pressure turbo compressor mounted in series with the high pressure turbo compressors, where the low pressure turbo compressor feeds air to the turbocompressors (3, 4). The device has an intake derivation circuit (18) provided with a control valve (35) for by-passing an intake compressor (5) of the turbo compressors (3, 4) along an operating point of the engine. An independent claim is also included for a method for supercharging an internal combustion engine for motor vehicle.

Description

1 Internal combustion engine comprising a supercharging device

  The present invention relates to an internal combustion engine comprising a device for supercharging air, in particular for a motor vehicle. The invention more particularly relates to an internal combustion engine comprising an air supercharging device provided with a first and a second high pressure turbocharger connected in parallel and supplying air to a first and a second set of cylinders of the engine. No. 4,709,552 discloses an internal combustion engine comprising an air supercharging device provided with first and second high pressure turbochargers connected in parallel and supplying the cylinders of the engine. Thus, even at low rotational speeds of the engine, the turbine of the first turbocharger can deliver a significant power to the associated compressor, and thus allow the engine to provide a substantial load. Such an assembly does not make it possible to adapt finely to variations in the speed of rotation of the motor. In addition, such an assembly does not effectively manage the operation of the engine under transient conditions, that is to say between two relatively stable operating states of the motor, respectively included in a range of engine rotational speed values. .

  An object of the invention is to overcome these disadvantages, at reduced cost. Another object of the invention is to improve the nervousness of the motor at low rotational speed of the engine.

Also, according to one aspect of the invention, there is provided an internal combustion engine, especially for a motor vehicle, comprising an air supercharging device. The air supercharger is provided with a first high pressure turbocharger and a second high pressure turbocharger connected in parallel and supplying air to a first set of cylinders and a second set of engine cylinders. The supercharger further includes a third low pressure turbocharger serially connected to said first and second high pressure turbochargers and capable of supplying air to said first and second turbochargers. Such a supercharging device makes it possible to better manage the operation of the engine under transient conditions, and to limit the pressure upstream of the exhaust turbines, which makes it possible to reduce the consumption of the engine at a high rotational speed. According to one embodiment, the supercharging device further comprises an intake bypass circuit equipped with a controlled valve for bypassing at least one compressor of said high pressure turbochargers, according to the operating point of the engine. . The intake bypass circuit bypass or bypass bypassing the first and second compressors, so that they do not compress the air admitted into the engine. According to one embodiment, at least one of the compressors 25 of said high pressure turbochargers is equipped with a controlled flow control valve for isolating said compressor.

2904365 Thus, it is possible to manage the flows of fresh air supply gases from the engine in the compressors of high-pressure turbochargers. According to one embodiment, the supercharging device 5 further comprises an exhaust gas bypass circuit of the engine for bypassing at least one turbine of said high pressure turbochargers according to the operating point of the engine . The exhaust bypass circuit bypasses or bypasses the first and second turbines, so as not to supply energy to the compressors of the high-pressure turbochargers that do not compress. The admitted air can, in this case be compressed by the compressor of the third turbocharger at low pressure.

According to one embodiment, at least one of said turbines of said high pressure turbochargers is equipped with a controlled flow control valve for isolating said turbine. Thus, it is possible to manage engine exhaust flows in turbines of high pressure turbochargers. In one embodiment, the size of the first and second high pressure turbochargers is small relative to the size of the third low pressure turbocharger. According to one embodiment, the supercharging device 25 further comprises means for controlling said controlled valves according to operating parameters of the engine, which can, for example, include the speed of rotation of the motor and / or the load of the motor.

In one embodiment, the cylinders of the motor are aligned or arranged in V. According to another aspect of the invention, a method of supercharging an internal combustion engine is also proposed, in particular for a motor vehicle. in which two separate sets of engine cylinders are supplied with compressed air, differently depending on the rotational speed of the engine, using different combinations of intake air circulation and engine exhaust. in two high pressure turbochargers and a low pressure turbocharger. According to one embodiment, when the engine operates at high rotational speed, the two sets of cylinders are supplied with compressed air only by the low pressure compressor.

Other objects, features and advantages of the invention will appear on reading the following description of some non-limitative examples and with reference to the appended drawings, in which: FIG. 1 represents an internal combustion engine provided with An air boosting device according to one aspect of the invention; FIG. 2 illustrates a first mode of operation of the motor of FIG. 1 in a first range of rotational speeds of the motor; FIG. 3 illustrates a second mode of operation of an engine according to FIG. 1 in a second range of rotational speeds of the engine; FIG. 4 illustrates a third mode of operation of an engine according to FIG. 1 in a second range of rotational speeds of the engine; and FIG. 5 illustrates a fourth mode of operation of an engine according to FIG. 1 in a third range of rotational speeds of the engine. As illustrated in FIG. 1, a motor 1 is provided with an air supercharging device designated by the general reference numeral 2.

A first high pressure turbocharger 3 is connected in parallel with a second high pressure turbocharger 4. The first high pressure turbocharger 3 comprises a first intake compressor 5 and a first exhaust turbine 6, and the second turbocharger 4 comprises a second intake compressor 7 and a second exhaust turbine 8. The two turbochargers 3 and 4 may be identical or of different size in order to better adapt them to the operation of the engine at full load or at partial load. . A third low pressure turbocharger 9, comprising a third intake compressor 10 and a third exhaust turbine 11, is connected in series with all of the two high pressure turbochargers 3 and 4 connected in parallel. Turbochargers 3, 4 and 9 can be of fixed geometry or variable geometry depending on the applications. The turbines of the fixed geometry turbochargers may be provided with an internal bypass circuit with a discharge valve. Preferably, the high pressure turbochargers 3 and 4 are relatively small in size compared to the low pressure turbocharger 9.

The compressor 10 delivers at its outlet compressed air whose pressure can be further increased by the two compressors 5 and 7 at high pressure. In the present description, the turbocharger will be described as "low pressure". The turbine 11 is of high permeability compared to the permeability of the two turbines 6 and 8. The permeability represents the ability to be traversed by a fluid. The intake and exhaust manifolds of the engine 1 are respectively referenced 12 and 13.

In the example illustrated, the engine 1 also comprises a partial exhaust gas recirculation (EGR) circuit equipped with a controlled recirculation valve 15 making it possible to manage the rate of recirculation of the exhaust gases in the engine 1 In the illustrated example, the engine 1 comprises a first set of four cylinders 16 and a second set of four cylinders 17 arranged in V. Alternatively, these two sets of cylinders can be aligned or arranged in another way. The invention can also be applied to engines comprising two sets of three cylinders.

An intake bypass circuit 18 connects the output of the third compressor 10 to the outputs of the first and second compressors 5 and 7, and makes it possible to avoid or bypass the first compressor 5 and / or the second compressor 7. A circuit exhaust branch 19 connects the exhaust manifolds 13 of the first and second sets of cylinders 16 and 17 of the engine 1 to the inlet of the third turbine 11. The exhaust bypass circuit 19 makes it possible to avoid or bypass the first turbine 6 and / or the second turbine 8.

The air enters via a conduit 20 conveying the intake air to an air filter 21 connected to the inlet of the third low pressure compressor 10 via a conduit 22. A conduit 23 connects the outlet of the third compressor to low pressure 10 at the inlet of the first 5 high pressure compressor 5 with the interposition of an optional charge air cooler 25, for cooling the compressed air by the third compressor 10. A first controlled valve 24 of flow control gas is arranged on the pipe 23, upstream of the first high-pressure compressor 5.

The output of the first high pressure compressor 5 is connected to the inlet of the first set of cylinders 16 via a duct 26 equipped with a charge air cooler 27 intended to cool the compressed air coming from the first compressor 5. On the conduit 23, upstream of the controlled valve 24, a conduit 28 connecting the duct 23 to the inlet of the second high-pressure compressor 7 is ducted. The duct 28 is provided with a controlled flow control valve 29. . The output of the second compressor 7 is connected to the inlet of the second set of cylinders 17 of the engine 1 by a conduit 30 provided with a charge air cooler 31 intended to cool the compressed air coming from the second compressor 7. The supply circuit further comprises a conduit 33 establishing a communication between the duct 26 and the duct 30. The intake bypass circuit 18 comprises a conduit 25 stitched on the duct 23 upstream of the controlled valve 24, and on the conduit 26, between the outlet of the first compressor 5 and the inlet of the charge air cooler 27. The intake bypass circuit 18 is provided with a controlled flow control valve 35, mounted on the duct 34.

2904365 The exhaust manifold 13 of the cylinders 16 is connected by a conduit 36 to the inlet of the first exhaust turbine 6. The duct 36 is provided with a controlled valve 37 of flow control. The outlet of the first turbine 6 is connected to the inlet of the third turbine 11 via a duct 38, and the outlet of the third turbine 11 is connected to a duct 39 for discharging the combustion gases from the engine 1 The exhaust circuit 13 of the cylinders 17 is connected by a duct 40 to the inlet of the second exhaust turbine 8. The duct 40 is equipped with a controlled flow control valve 41 arranged upstream of the turbine 8. The output of the turbine 8 is connected to the duct 38 by a duct 42. In addition, the exhaust bypass circuit 19 comprises a duct 43 stitched on the duct 40 upstream of the controlled valve 15 and on the duct 36 upstream of the controlled valve 37. The exhaust bypass circuit 19 also comprises a duct 44 stitched on the duct 36 upstream of the controlled valve 37 and on the duct 38. The duct 44 is equipped with a valve controlled 45 flow control.

The EGR exhaust gas recirculation is carried out by a duct 46 connecting the duct 26 to the duct 30, and a duct 47, connecting the duct 43 and the duct 46, and provided with the controlled recirculation valve 15 or EGR valve. An electronic control unit UCE 50 allows the flow control valves 35, 45, 29, 24, 41, 37 and 15 to be controlled by connections 51, 52, 53, 54, 55, 56 and 57, respectively. The electronic control unit 50 receives engine operating parameter values provided by sensors or estimators, not shown in the figure, and capable in particular of determining the rotational speed and the load of the engine 1. In FIGS. The following are illustrated various operating modes of the system shown in FIG. 1, in which the ducts shown in thick or bold lines correspond to the ducts in which the gases actually circulate, as a function of the closures and openings of the various controlled valves. FIG. 2 illustrates a mode of operation of the system represented in FIG. 1 for a rotational speed of the motor 10 included in a first range of values corresponding to an operation of the engine with a low rotational speed, for example at a rotational speed between 800 rpm and 2000 rpm. In this mode of operation, it is sought to promote the torque and the brio at very low rotational speed of the engine. For this purpose, the controlled valves 29, 35, 45 and 41 are closed. Also, the engine exhaust gases first pass through the first small turbine 6, which makes it possible to recover a maximum of energy in order to drive the first high-pressure compressor 5. The exhaust gases pass through then the third turbine 11, which is controlled so as to have a high permeability by opening the discharge valve if it is provided, or by acting on the variable geometry of the turbine. In this case, there is almost no relaxation in this turbine and it is virtually inactive.

The fresh air first passes through the third low-pressure compressor 10, which hardly compresses the gas because, as explained above, the third turbine 11 is virtually inactive, and thus provides virtually no energy to the third. Low pressure compressor 10. The third low pressure compressor 10 is thus transparent or inactive for the flow of the supply air to the engine 1. The air is compressed only by the first high pressure compressor 5 and then passes through the two charge air coolers 27 and 31, before feeding the cylinders 16 and 17 of the engine 1. Also, given the relatively small size of the compressor 5 even for low airflows power supply, it is possible to obtain relatively high compression ratios even for low air flows without being limited by the pumping phenomena of the compressor 5.

Since the first turbocharger 3 is small, the inertia of the compressor and turbine wheels is relatively small. This configuration makes it possible to minimize the transient operating response time and thus to improve the motor's nervousness in the first range of values, or, in other words, at low motor rotation speed. The EGR recirculation circuit allows recirculation of the engine exhaust gas for such rotational speeds of the engine 1, the latter not operating at full load. In this configuration, only the two high-pressure turbochargers 3 and 4 are active, which makes it possible to obtain high torque and brilliance at low and medium rotational speeds of the engine, while maintaining a high recycling rate for the engine gases. EGR exhaust to limit pollution. FIG. 3 illustrates a first mode of operation of the system of FIG. 1 for a rotational speed of the motor included in a second range of values corresponding to an operation of the engine with a medium rotation speed, for example at a rotational speed engine speed between 1500 rpm and 2750 rpm.

Since the controlled valves 35 and 45 are closed, there is therefore no gas circulation in the intake and exhaust bypass circuits 18 and 19. The exhaust gases pass through the first and second turbines 6 and 8 exhaust, then the third exhaust turbine 11. When the flow of the exhaust gas of the engine 1 is relatively small for the size of the third turbine 11, the low pressure compressor 10 hardly compresses the However, depending on the setting of the third turbine 11, i.e. depending on the opening of the discharge valve for a fixed geometry turbine, or the adjustment rack for a variable geometry turbine, the low pressure turbocharger 10 can participate in the supercharging of the engine 1 when it is desired to have a higher compression ratio. Often this is a relatively moderate compression in the third low pressure compressor 10, which does not necessarily imply the presence of the optional charge air cooler. Indeed, the charge air cooler 25 can be suppressed when the compression ratio of the turbocharger 9 is not high. When it is not necessary to use the low pressure turbocharger 9, this configuration allows a good transient response, because the first and second turbocharger high pressure 3 and 4 have low inertia given their relatively small size. The EGR recirculation circuit permits recirculation of the engine exhaust gas for such rotational speeds of the engine 1, which does not operate at full load. FIG. 4 illustrates another operating mode of the system of FIG. 1, as a variant of the operating mode of FIG. 3, for engine rotation speeds included in the second range of values corresponding to average rotation speeds. the engine, in particular to maximize the compression ratio, for example in the vicinity of the maximum torque of the engine. The controlled valves 45, 35, 29, 41 and 37 are closed. In contrast, the third turbine 11 is regulated by closing the discharge valve for a fixed geometry turbine, or acting on the adjusting rack for a variable geometry turbine, to relax the exhaust gases in the turbine. and thereby recovering energy to drive the third low pressure compressor 10 which compresses the intake air. The EGR recirculation circuit allows recirculation of the engine exhaust gas for such rotational speeds of the engine 1, the latter not operating at full load. The presence of the charge air cooler 25, 15 optional, allows to cool the intake air before it reaches the first and second high-pressure compressors 5 and 7, and thus increase the air filling of the engine 1. The FIG. 5 illustrates a mode of operation of the system of FIG. 1 for engine rotational speeds in a third range of values, corresponding to high engine rotational speeds, for example, at higher engine rotational speeds. at 2750 rpm, for example in the vicinity of the maximum power. The ranges of engine speeds indicated are not limiting since they may be different depending on the engine performance objectives. The controlled valves 37, 24, 29 and 41 are closed, and thus the intake air is only compressed by the third low-pressure compressor 10, and the exhaust gases pass through only the third turbine 11. The intake air of the engine 1 passes only through the intake bypass circuit 18, and the exhaust gas from the engine 1 only through the exhaust bypass circuit 19. The EGR recirculation circuit is closed, by means of the recirculation valve 15, for such rotational speeds of the engine 1, the latter operating at full load. The charge air coolers 27 and 31, and the optional charge air cooler 25 allow the air to be cooled before it enters the cylinders 16 and 17 of the engine 1. Thus, when the engine 1 is operating at high speed As a result of the rotation, the large intake air flow rate does not pass through the high-pressure turbochargers 3 and 4, thus avoiding the risk of this turbocharger overspeeding. In this configuration, only the low-pressure turbocharger 9 is used for the high-speed engine rotation power, which makes it possible to limit the pressure upstream of the exhaust turbine 11, and thus to limit the engine consumption. for such high rotational speeds, and improve engine efficiency.

Claims (11)

  1. Internal combustion engine (1), especially for a motor vehicle, comprising an air supercharging device (2) provided with a first high pressure turbocharger (3) and a second high pressure turbocharger (4) mounted in parallel and supplying air a first set of cylinders (16) and a second set of cylinders (17) of said engine, characterized in that the supercharging device (2) further comprises a third turbocharger at low pressure (9). ) connected in series with said first and second high-pressure turbochargers (3, 4) and capable of supplying air to said first and second turbochargers (3, 4).   The engine according to claim 1, wherein the supercharging device (2) further comprises an intake bypass circuit (18) provided with a controlled valve (35) for bypassing at least one compressor ( 5, 7) of said high-pressure turbochargers (3, 4), depending on the operating point of the engine (1).   3. Motor according to claim 1 or 2, wherein at least one of said compressors (5, 7) of said high-pressure turbochargers (3,   4) is equipped with a controlled flow control valve (24, 29) for isolating said compressor. 4. Motor according to one of claims 1 to 3, wherein the supercharging device (2) further comprises an exhaust bypass circuit (19) of the exhaust gas engine (1) for by- passing at least one turbine (6, 8) of said high-pressure turbochargers (3, 4) according to the operating point of the engine (1).   5. Motor according to one of claims 1 to 4, wherein at least one of said turbines (6, 8) of said high-pressure turbochargers (3, 4) is equipped with a controlled valve (37, 41). flow control for isolating said turbine.   6. Engine according to one of claims 1 to 5, wherein the size of the first and second high-pressure turbochargers (3, 4) is small compared to the size of the third low-pressure turbocharger (9).   7. Motor according to one of claims 1 to 6, wherein the supercharging device (2) further comprises control means (50) of said valves controlled according to 10 operating parameters of the engine (1).   An engine according to claim 7, wherein said operating parameters of the engine (1) comprise the rotational speed of the engine (1) and / or the engine load.   9. Motor according to one of claims 1 to 8, wherein the cylinders of the motor are aligned or arranged in V.   10. Supercharging process of an internal combustion engine (1), in particular for a motor vehicle, in which two separate sets of cylinders of the engine are supplied with compressed air, differently depending on the rotational speed of the engine and / or 20 the engine load, using different combinations of intake air circulation and engine exhaust in two high pressure turbochargers (3, 4) and a low pressure turbocharger (9).   The method of claim 10 wherein, when the engine (1) is operating at high rotational speed, the two sets of cylinders (16, 17) are supplied with compressed air only by the low pressure compressor (9). .30