JP2009264335A - Multistage supercharging system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for raising the intake temperature in cold starting of an internal combustion engine, in a multistage supercharging system for the internal combustion engine. <P>SOLUTION: This multistage supercharging system has a high pressure turbocharger 4 having a high pressure turbine 4b and a high pressure compressor 4a, a low pressure turbocharger 5 having a low pressure turbine 5b arranged in an exhaust passage 3 downstream of the high pressure turbine 4b and a low pressure compressor 5a arranged in an intake passage 2 upstream of the high pressure compressor 4a, an intake side bypass passage 6 for bypassing the high pressure compressor 4a, and an intake side bypass valve 7 arranged in the intake side bypass passage 6 and controlling an intake quantity flowing in the intake side bypass passage 6. In the cold starting of the internal combustion engine 1, the intake side bypass valve 7 is opened, and intake air is passed to the downstream side from the upstream side of the high pressure compressor 4a, and the intake air is passed to the upstream side from the downstream side of the intake side bypass passage 6, and an intake recirculating flow is formed for circulating the intake air. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a multistage supercharging system for an internal combustion engine.

In a multistage supercharging system for an internal combustion engine, a technique for increasing the pressure of the intake passage so that the intake air temperature increases during deceleration is disclosed (for example, see Patent Document 1). In this patent document 1, variable nozzle mechanism control of a high-pressure turbocharger, variable nozzle mechanism control of a low-pressure turbocharger, exhaust-side bypass passage opening / closing control, throttle opening control, and EGR valve opening / closing control are combined. On the other hand, in a multistage supercharging system for an internal combustion engine, a technique for forming an intake air recirculation is disclosed (for example, see Patent Document 2).
JP 2006-183605 A JP 11-315725 A

  By the way, when the internal combustion engine is cold-started, it has been desired to increase the intake air temperature in order to improve the ignitability.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique for increasing the intake air temperature when the internal combustion engine is cold-started in a multistage supercharging system for an internal combustion engine.

In the present invention, the following configuration is adopted. That is, the present invention
A high pressure turbocharger having a high pressure turbine disposed in the exhaust passage of the internal combustion engine and a high pressure compressor disposed in the intake passage of the internal combustion engine;
A low pressure turbocharger having a low pressure turbine disposed in the exhaust passage downstream of the high pressure turbine and a low pressure compressor disposed in the intake passage upstream of the high pressure compressor;
An intake-side bypass passage that bypasses the high-pressure compressor;
An intake side bypass valve that is disposed in the intake side bypass passage and controls the amount of intake air flowing through the intake side bypass passage;
With
When the internal combustion engine is cold started, the intake-side bypass valve is opened to allow intake air to pass from upstream to downstream of the high-pressure compressor and to pass intake air from downstream to upstream of the intake-side bypass passage. The multistage supercharging system for an internal combustion engine is characterized by forming an intake air recirculation.

According to the present invention, the intake side bypass valve is opened when the internal combustion engine is cold-started. At this time, the high-pressure compressor is driven. Then, the intake pressure in the intake side bypass passage becomes higher than the intake pressure in the intake passage between the low pressure compressor and the high pressure compressor. With such a pressure relationship, the intake air flows through the intake side bypass passage from the downstream side to the upstream side in the intake flow direction. Accordingly, an intake air circulation is formed in which the intake air is passed from the upstream side to the downstream side of the high-pressure compressor and the intake air is passed from the downstream side to the upstream side of the intake side bypass passage to circulate the intake air. Since the intake air in the intake air circulation is repeatedly compressed by the high-pressure compressor, the heat of compression is stored and the temperature is raised. Then, the intake air with the raised intake air flow is supplied to the internal combustion engine. Therefore, the intake air temperature can be raised at the time of cold start of the internal combustion engine, and the ignitability at the time of cold start of the internal combustion engine can be improved.

  A high-pressure variable nozzle mechanism that is provided in the high-pressure turbocharger and adjusts the amount of exhaust to the high-pressure turbine, and the high-pressure variable valve is opened when the intake-side bypass valve is opened during a cold start of the internal combustion engine. The nozzle passage sectional area of the nozzle mechanism may be reduced.

  Since the high pressure compressor repeatedly compresses the intake air in the intake air flow, the work of the high pressure compressor increases and the supercharging pressure of the high pressure turbocharger decreases. And when the supercharging pressure of the high-pressure turbocharger decreases, it becomes difficult to form the intake air circulation. According to the present invention, when the intake side bypass valve is opened during cold start of the internal combustion engine, the nozzle passage cross-sectional area of the high-pressure variable nozzle mechanism is reduced. Then, the supercharging pressure of the high-pressure turbocharger can be increased and the intake air circulation can be maintained. Further, the exhaust pressure in the exhaust passage upstream of the high-pressure turbine becomes high, and the internal EGR gas amount of the internal combustion engine can be increased. Since the internal EGR gas is burnt gas, it has a high temperature. Since a large amount of this high-temperature internal EGR gas is supplied to the internal combustion engine, it is also possible to improve the ignitability at the cold start of the internal combustion engine.

  The low-pressure turbocharger is provided with a low-pressure variable nozzle mechanism that adjusts an exhaust amount to the low-pressure turbine, and the low-pressure variable valve is opened when the intake-side bypass valve is opened during cold start of the internal combustion engine. The nozzle passage sectional area of the nozzle mechanism may be reduced.

  If the intake air recirculation is formed, the amount of intake air sent to the internal combustion engine decreases, and the internal combustion engine may misfire. According to the present invention, when the intake side bypass valve is opened during cold start of the internal combustion engine, the nozzle passage cross-sectional area of the low-pressure variable nozzle mechanism is reduced. Then, the supercharging pressure of the low pressure turbocharger can be increased, and the intake air amount taken in by the low pressure compressor can be increased. As a result, the amount of intake air supplied to the intake recirculation increases, so that the amount of intake air fed into the internal combustion engine can be increased while maintaining the recirculation flow rate of the intake recirculation, and misfire of the internal combustion engine can be prevented. Further, even when new low-temperature intake air taken in by the low-pressure compressor enters the intake air circulation, the high-temperature intake air circulation flow rate is maintained, so that a decrease in temperature of the intake air circulation can be suppressed. In addition, since the temperature of the intake air taken in by the low-pressure compressor rises due to supercharging of the low-pressure turbocharger, this can also suppress the temperature drop of the intake air circulation.

  An intake air amount detecting means for detecting an intake air amount in the intake passage upstream of the low pressure compressor, and when the intake air amount detected by the intake air amount detecting means is less than a predetermined amount, the nozzle passage of the low pressure variable nozzle mechanism is disconnected. It is better to reduce the area.

  Here, the predetermined amount is an amount that becomes a threshold value that may cause the internal combustion engine to misfire if the intake air amount is less than that and the intake air amount fed to the internal combustion engine decreases.

  According to the present invention, when the intake air amount detected by the intake air amount detecting means is less than a predetermined amount, the nozzle passage cross-sectional area of the low pressure variable nozzle mechanism is reduced. Then, the supercharging pressure of the low pressure turbocharger can be increased, and the intake air amount taken in by the low pressure compressor can be increased. As a result, the amount of intake air supplied to the intake recirculation increases, so that the amount of intake air fed into the internal combustion engine can be increased while maintaining the recirculation flow rate of the intake recirculation, and misfire of the internal combustion engine can be prevented.

  According to the present invention, in the multistage supercharging system for an internal combustion engine, the intake air temperature can be raised when the internal combustion engine is cold-started.

  Specific examples of the present invention will be described below.

<Example 1>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the multistage turbocharging system for an internal combustion engine according to the present embodiment is applied and its intake system and exhaust system. An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-stroke cycle diesel engine having multiple cylinders. The internal combustion engine 1 is mounted on a vehicle. An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1.

  In the middle of the intake passage 2 connected to the internal combustion engine 1, a high-pressure compressor 4a of a high-pressure turbocharger 4 that operates using exhaust energy as a drive source is arranged. In the intake passage 2 upstream of the high-pressure compressor 4a, a low-pressure compressor 5a of a low-pressure turbocharger 5 that operates using the energy of the exhaust as a drive source, as with the high-pressure turbocharger 4, is disposed.

  An intake side bypass passage 6 is provided between the intake passage 2 upstream of the high pressure compressor 4a and downstream of the low pressure compressor 5a and the intake passage 2 downstream of the high pressure compressor 4a. In other words, the intake side bypass passage 6 bypasses the high-pressure compressor 4a. An intake side bypass valve 7 that controls the amount of intake air flowing through the intake side bypass passage 6 by adjusting the cross-sectional area of the intake side bypass passage 6 is disposed in the intake side bypass passage 6. The intake side bypass valve 7 is opened and closed by an electric actuator.

  An air flow meter 8 that detects an intake air amount (fresh air amount) taken into the intake passage 2 upstream of the low-pressure compressor 5a is disposed in the intake passage 2 upstream of the low-pressure compressor 5a. The air flow meter 8 in this embodiment corresponds to the intake air amount detection means of the present invention.

  In the intake passage 2 downstream of the connection portion with the intake-side bypass passage 6 downstream of the high-pressure compressor 4a, the amount of intake air flowing through the intake passage 2 is controlled by adjusting the passage cross-sectional area of the intake passage 2. A throttle valve 9 is arranged. The throttle valve 9 is opened and closed by an electric actuator. The intake passage 2 and the devices arranged in the intake passage 2 constitute an intake system for taking intake air into the internal combustion engine 1.

  On the other hand, a high-pressure turbine 4 b of a high-pressure turbocharger 4 is disposed in the middle of the exhaust passage 3 connected to the internal combustion engine 1. The high-pressure turbine 4b is driven by the exhaust gas flowing through the exhaust passage 3, and the high-pressure compressor 4a rotates together with the driven high-pressure turbine 4b to supercharge the intake air flowing through the intake passage 2. A plurality of high-pressure variable nozzles 4c are provided in a turbine chamber that accommodates the high-pressure turbine 4b so as to surround the entire circumference of the high-pressure turbine 4b. By rotating each of the high-pressure variable nozzles 4c, a space between the high-pressure variable nozzles 4c is obtained. The formed nozzle passage cross-sectional area is changed. When the nozzle passage cross-sectional area is reduced by rotating the high-pressure variable nozzle 4c, the supercharging of the internal combustion engine 1 can be increased. Thus, the high-pressure variable nozzle 4c that changes the nozzle passage cross-sectional area and the electric actuator that drives the high-pressure variable nozzle 4c constitute a high-pressure variable nozzle mechanism.

A low pressure turbine 5b of a low pressure turbocharger 5 is disposed in the exhaust passage 3 downstream of the high pressure turbine 4b. The low-pressure turbine 5b is driven by exhaust gas flowing through the exhaust passage 3, and the low-pressure compressor 5a rotates together with the driven low-pressure turbine 5b to supercharge intake air flowing through the intake passage 2. A plurality of low-pressure variable nozzles 5c are provided in a turbine chamber that accommodates the low-pressure turbine 5b so as to surround the entire circumference of the low-pressure turbine 5b. The formed nozzle passage cross-sectional area is changed. By reducing the nozzle passage cross-sectional area by rotating the low-pressure variable nozzle 5c, the supercharging of the internal combustion engine 1 can be increased. The low-pressure variable nozzle 5c that changes the nozzle passage sectional area and the electric actuator that drives the low-pressure variable nozzle mechanism constitute a low-pressure variable nozzle mechanism.

  A first exhaust-side bypass passage 10 is provided between the exhaust passage 3 upstream of the high-pressure turbine 4b and the exhaust passage 3 downstream of the high-pressure turbine 4b and upstream of the low-pressure turbine 5b. In other words, the first exhaust-side bypass passage 10 bypasses the high-pressure turbine 4b. The first exhaust-side bypass passage 10 includes a first exhaust-side bypass valve 11 that controls the amount of intake air flowing through the first exhaust-side bypass passage 10 by adjusting the passage cross-sectional area of the first exhaust-side bypass passage 10. Has been placed. The first exhaust side bypass valve 11 is opened and closed by an electric actuator.

  A second exhaust side bypass passage 12 is provided between the exhaust passage 3 downstream of the high pressure turbine 4b and upstream of the low pressure turbine 5b and the exhaust passage 3 downstream of the low pressure turbine 5b. In other words, the second exhaust-side bypass passage 12 bypasses the low-pressure turbine 5b. The second exhaust-side bypass passage 12 includes a second exhaust-side bypass valve 13 that controls the amount of intake air flowing through the second exhaust-side bypass passage 12 by adjusting the cross-sectional area of the second exhaust-side bypass passage 12. Has been placed. The second exhaust side bypass valve 13 is opened and closed by an electric actuator. The exhaust passage 3 and the devices arranged in the exhaust passage 3 constitute an exhaust system for exhausting exhaust gas from the internal combustion engine 1.

The internal combustion engine 1 is provided with an EGR (Exhaust Gas Recirculation) passage 14 that recirculates (recirculates) part of the exhaust gas flowing through the exhaust passage 3 to the intake passage 2. In the present embodiment, the exhaust gas recirculated by the EGR passage 14 is referred to as EGR gas. The EGR passage 14 connects the exhaust passage 3 upstream of the high-pressure turbine 4 b and the intake passage 2 downstream of the throttle valve 9. Through this EGR passage 14, a part of the exhaust is sent to the internal combustion engine 1 as EGR gas at a high pressure. An EGR valve 15 that controls the amount of EGR gas flowing through the EGR passage 14 by adjusting the passage sectional area of the EGR passage 14 is disposed in the EGR passage 14. The EGR valve 15 is opened and closed by an electric actuator.

  The internal combustion engine 1 configured as described above is provided with an ECU 16 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 16 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  Various sensors such as an air flow meter 8, a crank position sensor 17, and an accelerator position sensor 18 are connected to the ECU 16 through electrical wiring, and output signals from these various sensors are input to the ECU 16. On the other hand, the ECU 16 includes electric actuators for the high pressure variable nozzle 4c, the low pressure variable nozzle 5c, the intake side bypass valve 7, the throttle valve 9, the first exhaust side bypass valve 11, the second exhaust side bypass valve 13, and the EGR valve 15. They are connected via electric wiring, and the ECU 16 controls these devices.

  The ECU 16 receives the output signals from the air flow meter 8, the crank position sensor 17, the accelerator position sensor 18, and the like to determine the operating state of the internal combustion engine 1, and determines the internal combustion engine 1 and the above devices based on the determined engine operating state. Control electrically.

  By the way, when the internal combustion engine 1 is cold-started, the ignitability is deteriorated. For this reason, when the internal combustion engine 1 is cold started, it is desired to raise the intake air temperature in order to improve the ignitability.

Therefore, in this embodiment, when the internal combustion engine is cold-started, the intake side bypass valve 7 is opened to allow intake air to pass from the upstream to the downstream in the intake flow direction with respect to the high-pressure compressor 4a and to intake air by the intake side bypass passage 6 In contrast, an intake air circulation is formed in which the intake air is circulated by passing it from downstream to upstream in the intake flow direction.

  Specifically, in this embodiment, the intake side bypass valve 7 is opened when the internal combustion engine is cold-started. At this time, the high-pressure compressor 4a is driven. Then, the intake pressure P1 in the intake side bypass passage 6 shown in FIG. 2 becomes higher than the intake pressure P2 in the intake passage 2 between the low pressure compressor 5a and the high pressure compressor 4a (P1> P2). Due to the pressure relationship of P1> P2, the intake air flows through the intake side bypass passage 6 from the downstream side to the upstream side in the intake flow direction. Accordingly, the intake air is allowed to pass from the upstream to the downstream in the intake flow direction of the high-pressure compressor 4a and the intake air is passed from the downstream to the upstream in the intake flow direction of the intake side bypass passage 6 to circulate the intake air as shown by the arrows in FIG. A reflux is formed. The intake recirculation continues to circulate as shown by the arrows shown in FIG. 2, and the intake air in the intake recirculation is repeatedly compressed by the high-pressure compressor 4a. Then, the intake air with the increased intake air flow is supplied to the internal combustion engine 1. Therefore, the intake air temperature can be raised when the internal combustion engine 1 is cold started, and the ignitability when the internal combustion engine 1 is cold started can be improved.

  By the way, since the high pressure compressor 4a repeatedly compresses the intake air in the intake air circulation, the work amount of the high pressure compressor 4a increases and the supercharging pressure of the high pressure turbocharger 4 decreases. And when the supercharging pressure of the high-pressure turbocharger 4 decreases, it becomes difficult to form the intake air circulation.

  Therefore, in this embodiment, when the intake side bypass valve 7 is opened during the cold start of the internal combustion engine 1, the high-pressure variable nozzle 4c is rotated to reduce the nozzle passage cross-sectional area.

  According to this embodiment, the supercharging pressure of the high-pressure turbocharger 4 can be increased, and the intake air circulation can be maintained. Further, the exhaust pressure in the exhaust passage 3 upstream from the high-pressure turbine 4b becomes high, and the internal EGR gas amount of the internal combustion engine 1 can be increased. Since the internal EGR gas is burnt gas, it has a high temperature. Since a large amount of this high-temperature internal EGR gas is supplied to the internal combustion engine 1, it is possible to improve the ignitability when the internal combustion engine 1 is cold started.

  By the way, if the intake air recirculation is formed, the intake air flowing into the internal combustion engine 1 does not flow downstream from the internal combustion engine 1 and the amount of intake air sent to the internal combustion engine 1 is reduced, and the internal combustion engine 1 may be misfired.

  Therefore, in the present embodiment, when the intake side bypass valve 7 is opened during the cold start of the internal combustion engine 1 and the intake air amount detected by the air flow meter 8 is less than a predetermined amount, the nozzle passage of the low pressure variable nozzle 5c. The cross-sectional area was made small.

  Here, the predetermined amount is an amount that is a threshold value that, when the intake amount is less than that, the amount of intake air that is sent to the internal combustion engine 1 decreases and the internal combustion engine 1 may misfire.

  According to the present embodiment, the supercharging pressure of the low-pressure turbocharger 5 can be increased, and the intake air amount taken in by the low-pressure compressor 5a can be increased. As a result, the amount of intake air supplied to the intake recirculation increases, so that the amount of intake air fed into the internal combustion engine 1 can be increased while maintaining the recirculation flow rate of the intake recirculation, and misfire of the internal combustion engine 1 can be prevented. . Further, even if new low-temperature intake air taken in by the low-pressure compressor 5a enters the intake air circulation, the high-temperature intake air circulation flow rate is maintained, so that a decrease in temperature of the intake air circulation can be suppressed. In addition, since the temperature of the intake air taken in by the low-pressure compressor 5a increases due to the supercharging of the low-pressure turbocharger 5, it is also possible to suppress the temperature reduction of the intake air circulation.

Next, an intake air circulation formation control routine at the time of cold start according to the present embodiment will be described. FIG. 3 is a flowchart showing an intake air circulation formation control routine at the time of cold start according to the present embodiment. This routine is repeatedly executed every predetermined time.

  In step S101, the ECU 16 determines whether or not the internal combustion engine 1 has been cold started. Whether or not the internal combustion engine 1 has been cold-started is determined from the output values of various sensors. If it is determined in step S101 that the internal combustion engine 1 has not been cold started, this routine is temporarily terminated. If it is determined in step S101 that the internal combustion engine 1 has been cold started, the process proceeds to step S102.

  In step S102, the ECU 16 forms an intake air recirculation. Specifically, the intake side bypass valve 7 is opened, the high pressure compressor 4a is driven, and the intake air is allowed to pass from the upstream to the downstream in the intake flow direction of the high pressure compressor 4a as indicated by the arrows in FIG. An intake air recirculation that circulates the intake air by passing the intake side bypass passage 6 from the downstream to the upstream in the intake flow direction is formed.

  In step S102, the ECU 16 turns the high-pressure variable nozzle 4c to reduce the nozzle passage cross-sectional area. At the same time, the opening of the throttle valve 9 is adjusted. As a result, the intake air recirculation during the cold start of the internal combustion engine 1 can be maintained. Further, by rotating the high-pressure variable nozzle 4c to reduce the nozzle passage cross-sectional area, the exhaust pressure in the exhaust passage 3 upstream from the high-pressure turbine 4b becomes high, and the amount of internal EGR gas in the internal combustion engine 1 is increased. You can also. At this time, the first exhaust-side bypass valve 11 is closed as shown in FIG. 2 so that the high-pressure turbine 4b flows through the exhaust.

  In step S103, the ECU 16 determines whether or not the intake air amount detected by the air flow meter 8 is less than a predetermined amount. If it is determined in step S103 that the intake air amount detected by the air flow meter 8 is greater than or equal to the predetermined amount, the process proceeds to step S105. If it is determined in step S103 that the intake air amount detected by the air flow meter 8 is less than the predetermined amount, the process proceeds to step S104.

  In step S104, the ECU 16 rotates the low-pressure variable nozzle 5c to reduce the nozzle passage cross-sectional area. Thereby, the supercharging pressure of the low-pressure turbocharger 5 is increased, and the intake air amount taken in by the low-pressure compressor 5a is increased. Accordingly, the amount of intake air supplied to the intake air circulation increases, so that the amount of intake air fed into the internal combustion engine 1 can be increased while maintaining the circulation flow rate of the intake air circulation. At this time, the second exhaust-side bypass valve 13 is closed as shown in FIG. 2 so that the low-pressure turbine 5b is allowed to flow through the exhaust.

  In step S105, the ECU 16 determines whether or not the warm-up at the cold start of the internal combustion engine 1 is completed. Whether or not the warm-up at the cold start of the internal combustion engine 1 has been completed may be determined from the output values of various sensors, or may be determined from the passage of a fixed time since the cold start. If it is determined in step S105 that the warm-up of the internal combustion engine 1 has not been completed, the process proceeds to step S102. If it is determined in step S105 that the warm-up of the internal combustion engine 1 has been completed, the process proceeds to step S106.

  In step S106, the ECU 16 stops forming the intake air circulation and returns to normal. Specifically, the intake side bypass valve 7 is closed to prevent the intake side bypass passage 6 from flowing through the intake air. Alternatively, the high-pressure variable nozzle 4c, the intake-side bypass valve 7 and the throttle valve 9 are controlled so that the intake air passes through the intake-side bypass passage 6 from upstream to downstream in the intake flow direction so as to bypass the high-pressure compressor 4a. . After the processing of this step, this routine is once ended.

According to this routine described above, the intake air recirculation can be formed when the internal combustion engine 1 is cold started.
And while the intake air in the intake air circulation circulates, it accumulates compression heat and is heated. Since the intake air with the raised intake air flow can be sent to the internal combustion engine 1, the intake air temperature can be raised when the internal combustion engine 1 is cold-started, and the ignitability can be improved.

  The multistage supercharging system for an internal combustion engine according to the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the gist of the present invention.

1 is a diagram showing a schematic configuration of an internal combustion engine and an intake system / exhaust system thereof according to Embodiment 1. FIG. The figure which shows a mode that the intake air circulation which concerns on Example 1 was formed. 3 is a flowchart showing an intake air circulation formation control routine at the time of cold start according to the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Intake passage 3 Exhaust passage 4 High pressure turbocharger 4a High pressure compressor 4b High pressure turbine 4c High pressure variable nozzle 5 Low pressure turbocharger 5a Low pressure compressor 5b Low pressure turbine 5c Low pressure variable nozzle 6 Intake side bypass passage 7 Intake side bypass valve 8 Air flow meter 9 Throttle valve 10 First exhaust side bypass passage 11 First exhaust side bypass valve 12 Second exhaust side bypass passage 13 Second exhaust side bypass valve 14 EGR passage 15 EGR valve 16 ECU
17 Crank position sensor 18 Accelerator position sensor

Claims (4)

A high pressure turbocharger having a high pressure turbine disposed in the exhaust passage of the internal combustion engine and a high pressure compressor disposed in the intake passage of the internal combustion engine;
A low pressure turbocharger having a low pressure turbine disposed in the exhaust passage downstream of the high pressure turbine and a low pressure compressor disposed in the intake passage upstream of the high pressure compressor;
An intake-side bypass passage that bypasses the high-pressure compressor;
An intake side bypass valve that is disposed in the intake side bypass passage and controls the amount of intake air flowing through the intake side bypass passage;
With
When the internal combustion engine is cold started, the intake-side bypass valve is opened to allow intake air to pass from upstream to downstream of the high-pressure compressor and to pass intake air from downstream to upstream of the intake-side bypass passage. A multistage supercharging system for an internal combustion engine, characterized in that an intake air recirculation is formed. A high-pressure variable nozzle mechanism that is provided in the high-pressure turbocharger and adjusts an exhaust amount to the high-pressure turbine;
2. The multistage engine for an internal combustion engine according to claim 1, wherein when the intake side bypass valve is opened during a cold start of the internal combustion engine, a nozzle passage sectional area of the high-pressure variable nozzle mechanism is reduced. Supply system. A low-pressure variable nozzle mechanism that is provided in the low-pressure turbocharger and adjusts an exhaust amount to the low-pressure turbine;
3. The internal combustion engine according to claim 1, wherein when the intake side bypass valve is opened during a cold start of the internal combustion engine, a nozzle passage sectional area of the low pressure variable nozzle mechanism is reduced. Multistage supercharging system. An intake air amount detecting means for detecting an intake air amount in the intake passage upstream of the low pressure compressor;
The multistage supercharging system for an internal combustion engine according to claim 3, wherein when the intake air amount detected by the intake air amount detecting means is less than a predetermined amount, the nozzle passage cross-sectional area of the low pressure variable nozzle mechanism is reduced.

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