JP2010151101A - Internal combustion engine with supercharger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent oil leak from a turbine side of a second turbocharger during a single mode in an internal combustion engine with superchargers including two supercharges. <P>SOLUTION: The internal combustion engine with the superchargers includes first and second turbochargers, a catalyst disposed in an exhaust gas passage at a downstream of the first turbocharger, an exhaust gas passage between a turbine of the first turbocharger and the catalyst, an exhaust gas bypass passage communicating to the exhaust gas passage at an upstream of the turbine of the second turbocharger, and an exhaust gas bypass valve disposed in the exhaust gas bypass passage. The exhaust gas bypass valve opens when a difference of exhaust gas pressures of an outlet of the turbine of the first turbocharger and an inlet of the turbine of the second turbocharger is not less than a predetermined value during the single turbo mode. Consequently, part of exhaust gas of a high exhaust gas pressure at the downstream of the turbine of the first turbocharger is introduced to the turbine of the second turbocharger through the exhaust gas bypass passage. As the result, rotation of the second turbocharger is accelerated during the single turbo mode and oil leak from the turbine side of the second turbocharger is prevented. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a supercharged internal combustion engine.

  2. Description of the Related Art Conventionally, an engine with a supercharger configured by arranging two turbochargers having different supercharging capacities in parallel with an intake system and an exhaust system of an engine is known (see, for example, Patent Document 1). .

  In such an engine with a supercharger, when the engine operating region is a low speed region or the like, supercharging is performed by operating only the primary turbocharger (hereinafter also referred to as “single turbo mode”), and the engine operating region is a high speed region. In such a case, supercharging is performed by operating both the primary turbocharger and the secondary turbocharger (hereinafter also referred to as “twin turbo mode”). Thereby, the output performance of the engine can be improved from the low speed range to the high speed range.

  By the way, in such a turbocharged engine, oil for performing lubrication and cooling is supplied to the bearing portion of each turbocharger through the oil passage during the operation. The oil sealability at the bearing is ensured by the rotation of the turbocharger. However, in the single turbo mode, the rotation of the secondary turbocharger stops, so that the oil sealability at the bearing portion of the secondary turbocharger deteriorates and oil leaks from the turbine side of the secondary turbocharger. It becomes easy.

  In addition, in such an engine with a supercharger, the rotation of the secondary turbocharger is stopped in the operation region where the internal pressure of the crankcase is low near the idle speed, so that the oil is discharged from the compressor side to the intake passage side by the intake negative pressure. Will be sucked out.

  In relation to the above point, for example, Patent Document 2 describes an engine with a supercharger that can prevent oil leakage from the turbine side of a secondary turbocharger.

  This turbocharged engine is provided with a leak hole in the exhaust shut-off valve for shutting off the exhaust to the secondary turbocharger. When the operating area is in single mode, the exhaust through the leak hole Rotate the secondary turbocharger at a slow speed. Thereby, it is supposed that the oil leakage from the turbine side of the secondary turbocharger can be prevented.

  In the engine with a supercharger described in Patent Document 1, in order to improve the effect of exhaust gas purification, a precatalyst as a catalyst device is disposed in an exhaust passage portion downstream of the turbine of the primary turbocharger. Yes.

Japanese Patent Laid-Open No. 4-12132 Japanese Utility Model Publication No. 7-25241

  In the engine with a supercharger described in Patent Document 2 described above, the exhaust gas upstream of the turbine of the primary turbocharger is introduced into the turbine of the secondary turbocharger. There exists a subject that the exhaust energy for operating a turbocharger will fall.

  The present invention has been made in order to solve the above-described problems, and the oil leakage from the turbine side of the primary turbocharger is achieved without reducing the exhaust energy for operating the primary turbocharger. An object of the present invention is to provide a supercharger-equipped internal combustion engine capable of preventing the engine.

  In one aspect of the present invention, a supercharged internal combustion engine includes a first turbocharger, a second turbocharger, a catalyst disposed downstream of the first turbocharger, and the first turbocharger and the catalyst. And a communication passage communicating with the upstream side of the second turbo, and the communication passage is provided with an on-off valve that opens at a pressure higher than a predetermined pressure.

  According to the above-described supercharger-equipped internal combustion engine, the exhaust pressure (exhaust pressure) is increased by the catalyst provided downstream of the first turbo in the operation region using only the first turbo. And when the exhaust pressure of a communicating path becomes more than predetermined pressure, the on-off valve provided in the communicating path will open. Thereby, a part of the exhaust gas downstream of the first turbo flows into the upstream of the second turbo. Thereby, rotation of the 2nd turbo is promoted and the oil sealing performance of the bearing part is improved. As a result, it is possible to prevent oil leakage from the bearing portion on the second turbo side.

  In one aspect of the above-described supercharger-equipped internal combustion engine, a mechanically driven on-off valve that opens when the communication passage is at a pressure higher than the predetermined pressure can be used.

  In another aspect of the internal combustion engine with a supercharger, the control device further includes control means for controlling opening and closing of the on-off valve, and the control means is configured to open and close the open / close valve when the communication passage is at a pressure higher than the predetermined pressure. It is desirable to open the valve.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

[Configuration of internal combustion engine with supercharger]
FIG. 1 is a schematic diagram showing a configuration of a supercharged internal combustion engine 100 according to an embodiment of the present invention. In FIG. 1, solid arrows indicate gas flow, and broken arrows indicate signal input / output. FIG. 1 shows the gas flow when the supercharging mode is set to the single turbo mode.

  The supercharger-equipped internal combustion engine 100 mainly includes an air cleaner 2, an intake passage 3, an intake bypass passage 31, an intake bypass valve 32, turbochargers 4 and 5, an intake switching valve 6, and a reed valve. 7, an internal combustion engine 8, a supercharging pressure sensor 9, an exhaust passage 10, an EGR passage 11, an EGR valve 14, an exhaust switching valve 15, an exhaust bypass passage 16, an exhaust bypass valve 17, and a catalyst 18. , 19 and an ECU (Engine Control Unit) 50.

  The air cleaner 2 purifies air (intake air) acquired from the outside and supplies it to the intake passage 3. The intake passage 3 is branched into intake passages 3a and 3b on the way. A compressor 4a of the turbocharger 4 is disposed in the intake passage 3a, and a compressor 5a of the turbocharger 5 is disposed in the intake passage 3b. The compressors 4a and 5a compress the intake air that passes through the intake passages 3a and 3b, respectively.

  An intake switching valve 6 and a reed valve 7 are provided in the intake passage 3b. The intake switching valve 6 is configured to be opened and closed by a control signal S6 supplied from the ECU 50 so that the flow rate of intake air passing through the intake passage 3b can be adjusted. For example, by opening and closing the intake air switching valve 6, it is possible to switch the intake air flow / blockage in the intake passage 3b. The reed valve 7 is configured to open when the pressure in the passage exceeds a predetermined value. Further, a boost pressure sensor 9 is provided in the intake passage 3 on the downstream side of the compressors 4a and 5a. The supercharging pressure sensor 9 detects the pressure of supercharged intake air (hereinafter also referred to as “actual supercharging pressure”) and supplies a detection signal S9 corresponding to the actual supercharging pressure to the ECU 50.

  One end of the intake bypass passage 31 is connected to the intake passage 3 between the air cleaner 2 and the compressor 4 a, and the other end is connected to the intake passage 3 between the compressor 5 a and the intake air switching valve 6. The intake bypass passage 31 guides intake air introduced from the air cleaner 2 side to the downstream side of the compressor 5a, bypassing the compressors 4a and 5a. An intake bypass valve 32 is provided in the intake bypass passage 31. The intake bypass valve 32 is configured to open when the pressure in the passage exceeds a predetermined value.

  The internal combustion engine 8 is configured as a V-type 8-cylinder engine in which four cylinders (cylinders) 8La and 8Ra are provided in each of the left and right banks (cylinder groups) 8L and 8R. The internal combustion engine 8 is a device that generates power by burning an air-fuel mixture of intake air and fuel supplied from the intake passage 3. The internal combustion engine 8 is constituted by, for example, a gasoline engine or a diesel engine. Exhaust gas generated by combustion in the internal combustion engine 8 is discharged to the exhaust passage 10. The internal combustion engine 8 is not limited to being configured with 8 cylinders.

  An EGR passage 11 is connected to the exhaust passage 10. The EGR passage 11 has one end connected to the exhaust passage 10 and the other end connected to the intake passage 3. The EGR passage 11 is a passage for returning exhaust gas (EGR gas) to the intake system. Specifically, the EGR passage 11 is provided with an EGR cooler 12, an EGR valve 14, a bypass passage 11a, and a bypass valve 13. The EGR cooler 12 is a device that cools the EGR gas, and the EGR valve 14 is a valve that adjusts the flow rate of the EGR gas that passes through the EGR passage 11, in other words, the amount of EGR gas that is recirculated to the intake system (that is, the EGR rate). Is the valve. In this case, the opening degree of the EGR valve 14 is controlled by a control signal S14 supplied from the ECU 50. The bypass passage 11a is a passage that bypasses the EGR cooler 12, and a bypass valve 13 is provided on the passage. The bypass valve 13 adjusts the flow rate of EGR gas passing through the bypass passage 11a. In this case, the opening degree of the bypass valve 13 is controlled by a control signal S13 supplied from the ECU 50. In FIG. 1, since the EGR valve 14 is set to be closed, the EGR gas is not recirculated.

  The exhaust passage 10 branches into the exhaust passages 10a and 10b on the way. A turbine 4b of the turbocharger 4 is disposed in the exhaust passage 10a, and a turbine 5b of the turbocharger 5 is disposed in the exhaust passage 10b. The turbines 4b and 5b are rotated by exhaust gas passing through the exhaust passages 10a and 10b, respectively. The rotational torque of the turbines 4b and 5b is transmitted to the compressor 4a in the turbocharger 4 and the compressor 5a in the turbocharger 5 to rotate, whereby the intake air is compressed (that is, supercharged). The Rukoto. The turbocharger 4 corresponds to the first turbocharger of the present invention, and is configured as a low-capacity low-speed supercharger with a large supercharging capability in a low and medium speed range. On the other hand, the turbocharger 5 corresponds to the second turbocharger of the present invention, and is configured as a large-capacity high-speed supercharger having a large supercharging capability in a medium to high speed range.

  Further, the exhaust passage 10b is provided with an exhaust switching valve 15 and catalysts 18 and 19, respectively.

  The exhaust gas switching valve 15 is controlled to be opened and closed by a control signal S15 supplied from the ECU 50, and is configured to be able to adjust the flow rate of the exhaust gas passing through the exhaust passage 10b. For example, by opening and closing the exhaust gas switching valve 15, it is possible to switch the flow / blocking of the exhaust gas in the exhaust passage 10b. The catalyst 18 is connected to the exhaust passage 10 downstream of the turbine 4b. The catalyst 18 mainly has the role of purifying atmospheric pollutants contained in the exhaust gas discharged from the turbine 4b side to reduce emissions and the role of increasing the temperature of the exhaust gas. The catalyst 19 is connected to the exhaust passage 10 downstream of the catalyst 18 and the turbine 5b. The catalyst 19 mainly has a role of reducing emissions by purifying air pollutants contained in the exhaust gas discharged from the catalyst 18 and the turbine 5b side.

  The exhaust bypass passage 16 corresponds to a communication passage of the present invention, and one end is connected to the exhaust passage 10 between the turbine 4b and the catalyst 18, and the other end is upstream of the inlet of the turbine 5b and the exhaust gas switching valve 15. Are connected to the exhaust passage 10. The exhaust bypass passage 16 guides the exhaust gas discharged from the turbine 4b side to the exhaust passage 10 upstream of the inlet of the turbine 5b, bypassing the catalyst 18. An exhaust bypass valve 17 is provided in the exhaust bypass passage 16. The exhaust bypass valve 17 is configured to open when the pressure in the passage exceeds a predetermined value.

  The ECU 50 includes a CPU, a ROM, a RAM, an A / D converter, and the like (not shown). The ECU 50 performs various controls on the internal combustion engine 8 and the like based on outputs supplied from various sensors in the vehicle.

(Supercharge mode switching control)
Next, a supercharging mode switching control method will be described with reference to FIG.

  FIG. 2 (a) schematically shows an example of an operation region map relating to three supercharging modes defined based on the engine speed Ne and the engine torque. In FIG. 2A, the horizontal axis indicates the engine speed Ne, and the vertical axis indicates the engine torque.

  The ECU 50 performs opening / closing control on the intake switching valve 6, the intake bypass valve 32, the EGR valve 14, the exhaust switching valve 15, the exhaust bypass valve 17, and the like based on the engine speed Ne, the engine torque, and the like. Switch to one of the supercharging modes. Here, the three supercharging modes include a single turbo mode (without running), a single turbo mode (with running), and a twin turbo mode.

  The “single turbo mode (without running)” is a low / medium speed region operation mode and corresponds to the region A1 in FIG. In this operation mode, the ECU 50 performs control to close all of the intake switching valve 6, the exhaust switching valve 15, the exhaust bypass valve 17, and the like. As a result, the intake and exhaust gases are supplied only to the turbocharger 4 out of the turbochargers 4 and 5, and only the turbocharger 4 operates.

  The “single turbo mode (with running)” is an operation mode in the middle speed range, and corresponds to the region A2 in FIG. Here, the running is an operating state in which the turbocharger 5 is rotated in advance in order to eliminate the step of the actual supercharging pressure that occurs when switching from the single turbo mode to the twin turbo mode. In this operation mode, the ECU 50 performs control to slightly open the exhaust gas switching valve 15 when switching from the single turbo mode to the twin turbo mode. As a result, a relatively small flow rate of exhaust gas is supplied to the turbocharger 5, and the turbocharger 5 can be gradually operated (ie, run up). In FIG. 2A, “graph g1” indicates a switching line between a single turbo mode region (without running) and a single turbo mode region (with running).

  The “twin turbo mode” is an operation mode in the medium to high speed range, and corresponds to the region A3 in FIG. In this operation mode, the ECU 50 performs control to open the intake switching valve 6, the exhaust switching valve 15, and the like. Thereby, intake and exhaust gas are supplied to both turbochargers 4 and 5, and both turbochargers 4 and 5 operate. In FIG. 2A, “graph g2” indicates a switching line between the single turbo mode region (with running) and the twin turbo mode region.

(Turbocharger oil leak prevention control)
In an internal combustion engine with a supercharger, oil for lubrication / cooling is supplied to the bearing portion of the turbocharger through an oil passage during its operation. The oil sealability at the bearing is ensured by the rotation of the turbocharger. However, in the single turbo mode, since the turbocharger 5 does not rotate, the oil sealability in the bearing portion of the turbocharger 5 is deteriorated, and oil leakage from the turbine 5b side of the turbocharger 5 occurs. There is a concern that this will occur.

  In order to prevent the occurrence of such a problem, it is effective to perform control that promotes the rotation of the turbocharger 5 in the single turbo mode. Therefore, in the present embodiment, the catalyst 18 is provided downstream of the turbine 4b of the turbocharger 4 to increase the exhaust pressure (hereinafter also referred to as “exhaust pressure”) at the outlet of the turbine 4b. A part of the exhaust gas having a high exhaust pressure downstream of 4b is introduced into the turbine 5b of the turbocharger 5. Thereby, the rotation of the turbocharger 5 is promoted in the single turbo mode, the oil sealability at the bearing portion of the turbocharger 5 is improved, and the oil leakage from the turbine 5b side of the turbocharger 5 is prevented. .

  The specific control method will be described below with reference to FIG.

  FIG. 2 (b) shows the turbine 4b of the turbochargers 4 and 5 in the single turbo mode, with and without the catalyst 18 provided downstream of the turbine 4b of the turbocharger 4. It is a graph which illustrates about how the exhaust pressure of the exit of 5b changes. In FIG. 2B, the horizontal axis indicates the fuel injection amount, and the vertical axis indicates the exhaust pressure at the turbine outlet of the turbocharger. In FIG. 2B, both the exhaust switching valve 15 and the exhaust bypass valve 17 are closed.

  In FIG. 2B, “graph g11” is a graph showing the relationship between the fuel injection amount and the exhaust pressure at the outlet of the turbine 4b of the turbocharger 4 according to the present embodiment. “Graph g12” is a graph showing the relationship between the fuel injection amount and the exhaust pressure at the outlet of the turbine 5b of the turbocharger 5 according to the present embodiment. “Graph g13” is a graph showing the relationship between the fuel injection amount and the exhaust pressure at each outlet of the turbines 4b and 5b of the turbochargers 4 and 5 according to the comparative example. Here, the comparative example is different from the present embodiment only in that the catalyst 18 is not provided downstream of the turbine 4b of the turbocharger 4, and the rest is the same.

  In the present embodiment, as shown in graphs g11 and g12 of FIG. 2B, the exhaust pressure at the outlet of the turbine 4b of the turbocharger 4 is the outlet of the turbine 5b of the turbocharger 5 in the single turbo mode. The exhaust pressure is higher than (= inlet) exhaust pressure, and there is a difference in exhaust pressure between the outlet of the turbine 4 b of the turbocharger 4 and the outlet of the turbine 5 b of the turbocharger 5. This is because the catalyst 18 is provided only downstream of the turbine 4 b of the turbocharger 4. On the other hand, in the comparative example, since the catalyst 18 is not provided downstream of the turbine 4b of the turbocharger 4, the outlet of the turbine 4b of the turbocharger 4 and the turbine of the turbocharger 5 are in the single turbo mode. There is no difference in the exhaust pressure between the outlet of 5b.

  Thus, in the present embodiment, in the single turbo mode, there is a difference in exhaust pressure between the outlet of the turbine 4b of the turbocharger 4 and the inlet of the turbine 5b of the turbocharger 5. For this reason, if a communication passage communicating from the outlet of the turbine 4b of the turbocharger 4 to the inlet of the turbine 5b of the turbocharger 5 is provided, a part of the exhaust gas having a high exhaust pressure downstream of the turbine 4b is removed. Then, it can be introduced into the turbine 5b of the turbocharger 5 through the communication path, and thereby the rotation of the turbine 5b of the turbocharger 5 can be promoted.

  Therefore, in the present embodiment, the exhaust passage 10 between the turbine 4b of the turbocharger 4 and the catalyst 18, and the exhaust passage between the upstream of the inlet of the turbine 5b of the turbocharger 5 and the exhaust switching valve 15 is provided. 10 is provided in the exhaust bypass passage 16, and the difference in exhaust pressure between the outlet of the turbine 4b of the turbocharger 4 and the inlet of the turbine 5b of the turbocharger 5 is greater than a predetermined value. Then, an exhaust bypass valve 17 of a mechanical drive system that opens at that time is provided.

  According to this, in the single turbo mode, when the exhaust pressure is increased by the catalyst 18 provided downstream of the turbine 4b of the turbocharger 4 and the exhaust pressure of the exhaust bypass passage 16 becomes a predetermined pressure or higher, the exhaust bypass valve 17 Opens. As a result, a part of the exhaust gas downstream of the turbine 4 b flows upstream of the inlet of the turbine 5 b of the turbocharger 5 through the exhaust bypass passage 16. Thereby, rotation of the turbine 5b of the turbocharger 5 is promoted, and the oil sealability of the bearing portion can be enhanced. As a result, it is possible to prevent oil leakage from the bearing portion of the turbocharger 5 on the turbine 5b side.

  Further, according to this configuration, the rotation of the turbocharger 5 is promoted in the single turbo mode, so that the oil is sucked from the compressor 5a side of the turbocharger 5 to the intake passage 3 side by the intake negative pressure. It can also be prevented.

  Furthermore, according to this configuration, a part of the exhaust gas upstream of the turbine 4 b of the turbocharger 4 is not introduced into the turbine 5 b of the turbocharger 5. It is also possible to prevent the exhaust energy for operating 5b from being lowered.

[Modification]
In the above-described embodiment, the exhaust bypass valve 17 is a pressure in which the difference in exhaust pressure between the outlet of the turbine 4b of the turbocharger 4 and the inlet of the turbine 5b of the turbocharger 5 is greater than or equal to a predetermined value in the single turbo mode. It was a mechanically driven on-off valve that opens when In the present invention, the opening and closing of the exhaust bypass valve 17 may be controlled by a control signal supplied from the ECU 50. In this case, the exhaust bypass valve 17 is controlled to be opened by the ECU 50 when the exhaust pressure of the exhaust bypass passage 16 becomes a predetermined pressure or more in the single turbo mode.

  In the present invention, the ECU 50 may control the exhaust bypass valve 17 to be opened when the operating region of the internal combustion engine 8 is at least one of the following operating regions. Here, as the operation region where the exhaust bypass valve 17 is opened, the operation region other than the time when the catalyst 18 and / or the catalyst 19 is cold (first mode), the entire region of the single turbo mode (see FIG. 2A). A region A1, a second mode), and a low rotation and low load region that does not enter the surge of the turbocharger 5 (the hatched region A4 in FIG. 2A, the third mode).

  Here, in the case of the first aspect, the reason why the exhaust bypass valve 17 is opened is that the catalyst 18 and / or the catalyst is prevented rather than preventing oil leakage from the bearing portion of the turbocharger 5 on the turbine 5b side. This is because priority is given to the prevention of exhaust gas containing toxic substances into the atmosphere by heating 19 quickly. Further, in the case of the second mode, the reason why the exhaust bypass valve 17 is opened is that the turbine 5b of the turbocharger 5 is not rotating, so that oil leakage from the bearing portion is completely prevented. is there. Further, in the case of the third mode, the reason for opening the exhaust bypass valve 17 is that if the turbocharger 5 is rotated too much in the state of each on-off valve in the single mode, a surge is caused. This is because there is a fear. The surge generally refers to a phenomenon in which the operation becomes unstable due to periodic fluctuations in the pressure and flow rate of the intake air when the internal combustion engine 8 rotates at a low speed.

The block diagram of the internal combustion engine with a supercharger which concerns on embodiment of this invention is shown. The operation map of an exhaust gas bypass valve, and the graph which shows the exhaust pressure change of the exit of the turbine of a turbocharger are shown.

Explanation of symbols

4 First turbo 5 Second turbo 4b, 5b Turbine 8 Internal combustion engine 10 Exhaust passage 16 Exhaust bypass passage (communication passage)
17 Exhaust bypass valve (open / close valve)
18 catalyst 50 ECU (control means)
100 Internal combustion engine with a supercharger

Claims (3)

First and second turbo,
A catalyst disposed downstream of the first turbo,
A communication path communicating between the first turbo and the catalyst and the upstream side of the second turbo,
An internal combustion engine with a supercharger, wherein the communication passage is provided with an on-off valve that opens at a pressure higher than a predetermined pressure.   2. The internal combustion engine with a supercharger according to claim 1, wherein the on-off valve is a mechanically-driven on-off valve that opens when the communication passage is at a pressure higher than the predetermined pressure. Further comprising control means for controlling opening and closing of the on-off valve;
2. The internal combustion engine with a supercharger according to claim 1, wherein the control means opens the on-off valve when the communication passage reaches a pressure higher than the predetermined pressure.

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