JP2010013963A - Multi-stage supercharging system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for avoiding a bad effect in the case of opening a low-pressure exhaust side bypass valve in a multi-stage supercharging system for internal combustion engine. <P>SOLUTION: This multi-stage supercharging system for internal combustion engine includes: a high-pressure turbocharger; a low-pressure turbocharger; a low-pressure exhaust side bypass passage bypassing a low-pressure turbine; and a low-pressure exhaust side bypass valve for controlling the exhaust quantity flowing in the low-pressure side bypass passage. In the case of requiring catalyst warm-up (S101-YES) and opening the low-pressure exhaust side bypass valve, when a predetermined condition relative to reduction of the number of revolution of a low-pressure compressor is satisfied (S102-NO), the low-pressure exhaust side bypass valve is closed (S104). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

In a multi-stage turbocharging system for an internal combustion engine, a high pressure exhaust side bypass passage that bypasses the high pressure turbine of the high pressure turbocharger, a high pressure exhaust side bypass valve provided in the high pressure exhaust side bypass passage, and a low pressure that bypasses the low pressure turbine of the low pressure turbocharger A technique including an exhaust-side bypass passage and a low-pressure exhaust-side bypass valve provided in the low-pressure exhaust-side bypass passage is disclosed (see, for example, Patent Document 1). In a parallel supercharging system for an internal combustion engine, lubricating oil is supplied to the bearing portion when the secondary turbocharger is operating, and the lubricating oil supply to the bearing portion is shut off or throttled when the secondary turbocharger is not operating. Thus, a technique for controlling an electromagnetic switching valve is disclosed (for example, see Patent Document 2). A multi-stage turbocharging system for an internal combustion engine, comprising: a high-pressure exhaust side bypass passage introduced into a low-pressure turbine of a low-pressure turbocharger; and a high-pressure exhaust side bypass valve provided in the middle of the high-pressure exhaust side bypass passage. In the region where the engine speed exceeds the first predetermined speed, the closed state of the high pressure exhaust side bypass valve is released, and the exhaust energy supplied to the high pressure turbine of the high pressure turbocharger is supercharged by controlling the opening of the variable nozzle. A technique for controlling the pressure is disclosed (for example, see Patent Document 3). In a multi-stage supercharging system for an internal combustion engine, a technique for forming a low-pressure exhaust-side bypass passage that bypasses a low-pressure turbine of a low-pressure turbocharger in exhaust during catalyst warm-up is disclosed (for example, see Patent Document 4).
JP 2005-98250 A JP-A-6-10688 JP-A-2005-146906 Japanese Utility Model Publication No. 2-94332

  By the way, in the multistage supercharging system for an internal combustion engine, the low pressure exhaust side bypass passage for bypassing the low pressure turbine of the low pressure turbocharger, and the low pressure exhaust side for controlling the exhaust amount arranged in the low pressure exhaust side bypass passage and flowing through the low pressure exhaust side bypass passage And a bypass valve. In order to warm up the catalyst, the low-pressure exhaust side bypass valve is opened, and the exhaust gas is supplied to the catalyst through the low-pressure exhaust side bypass passage.

  If the low-pressure exhaust side bypass valve is opened at light load, the rotation speed of the low-pressure turbocharger is low because the low-pressure turbocharger is lubricated with lubricating oil or from the region where supercharging is performed only with the high-pressure turbocharger. There are cases where the rotational speed is below the minimum required rotational speed for shifting to a region where supercharging is performed in both the turbocharger and the high-pressure turbocharger. If the low-pressure exhaust side bypass valve is open, depending on the operating condition of the high-pressure turbocharger, the pressure in the intake passage between the low-pressure compressor and the high-pressure compressor will drop and become excessively negative. Compressor lubricating oil may be sucked out. As described above, when the low pressure exhaust side bypass valve is opened, the above-described adverse effects occur.

  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 avoiding adverse effects when the low-pressure exhaust-side bypass valve is opened in a multistage supercharging system for an internal combustion engine. There is to do.

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;
A low pressure exhaust side bypass passage for bypassing the low pressure turbine;
A low-pressure exhaust-side bypass valve that is disposed in the low-pressure exhaust-side bypass passage and controls an amount of exhaust flowing through the low-pressure exhaust-side bypass passage;
With
When the low-pressure exhaust-side bypass valve is open, the low-pressure exhaust-side bypass valve is closed when a predetermined condition relating to a decrease in the rotational speed of the low-pressure compressor is satisfied. It is a multistage supercharging system.

  Here, the predetermined condition is satisfied when the pressure in the intake passage between the low-pressure compressor and the high-pressure compressor is lower than a predetermined pressure.

  The predetermined pressure is the higher pressure of the pressure derived from the necessary minimum rotational speed line on the low pressure compressor map or the pressure at which the lubricating oil of the low pressure compressor or the high pressure compressor is sucked out.

  The other predetermined conditions are satisfied when the rotation speed of the low-pressure turbocharger is such that the low-pressure turbocharger is lubricated with lubricating oil or is supercharged only in the high-pressure turbocharger. It may be the time when the number of revolutions is less than the minimum required for shifting to the supercharging region in both chargers. The other predetermined condition is satisfied when, for example, the rotational speed of the high-pressure compressor is increased despite the decrease in the rotational speed of the low-pressure compressor, and the pressure in the intake passage between the low-pressure compressor and the high-pressure compressor is increased. It may be when the pressure decreases and becomes excessively negative, and the lubricating oil of the low-pressure compressor or the high-pressure compressor is sucked out.

  According to the present invention, when the low pressure exhaust side bypass valve is opened and the predetermined condition as described above is satisfied, the low pressure exhaust side bypass valve is closed, so the low pressure exhaust side bypass valve is opened. The adverse effects of being in can be avoided. Specifically, when the low-pressure exhaust-side bypass valve is open at light load, the rotation speed of the low-pressure turbocharger is excessive only for lubricating the low-pressure turbocharger with lubricating oil or only with the high-pressure turbocharger. It can be avoided that the rotational speed is less than the minimum required rotational speed for shifting from the region where charging is performed to the region where supercharging is performed by both the low pressure turbocharger and the high pressure turbocharger. In addition, when the low-pressure exhaust side bypass valve is opened, for example, the rotational speed of the high-pressure compressor increases even though the rotational speed of the low-pressure compressor decreases, and the intake air between the low-pressure compressor and the high-pressure compressor is increased. It can be avoided that the pressure in the passage is reduced to an excessively negative pressure and the lubricating oil of the low-pressure compressor or the high-pressure compressor is sucked out.

  The case where the low pressure exhaust side bypass passage is provided in the exhaust passage downstream of the low pressure turbine downstream side connecting portion, the catalyst for purifying exhaust gas is provided, and the low pressure exhaust side bypass valve is opened. In order to warm up the engine, the low pressure exhaust side bypass valve is opened, and the exhaust gas is supplied to the catalyst through the low pressure exhaust side bypass passage.

  According to the present invention, it is possible to avoid the adverse effects of opening the low pressure exhaust side bypass valve when warming up the catalyst.

  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 controls the opening and closing of the low-pressure exhaust side bypass valve, and at the same time, the nozzle passage cross-sectional area of the high-pressure variable nozzle mechanism It is preferable to control the pressure of the intake air sent to the internal combustion engine by changing

  According to the present invention, when the pressure of the intake air sent to the internal combustion engine is likely to fluctuate due to the opening / closing control of the low pressure exhaust side bypass valve, the intake passage sent to the internal combustion engine is changed by changing the nozzle passage cross-sectional area of the high pressure variable nozzle mechanism. The pressure can be controlled to a desired pressure. Thereby, even if the low pressure exhaust side bypass valve is controlled to open and close, the pressure of the intake air sent to the internal combustion engine is maintained at a desired pressure, and the internal combustion engine can continue to maintain a good combustion state.

  According to the present invention, in the multistage supercharging system for an internal combustion engine, it is possible to avoid the adverse effects when the low pressure exhaust side bypass valve is opened.

  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 multi-stage turbocharging system for an internal combustion engine according to this 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 for detecting an intake air amount (fresh air amount) Ga 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. An intake air temperature sensor 9 that detects the temperature T1 of the intake air taken into the intake air passage 2 upstream of the low-pressure compressor 5a is disposed in the intake air passage 2 upstream of the low-pressure compressor 5a. A first intake pressure sensor 10 that detects the pressure P1 of the intake air 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.

  In the intake passage 2 upstream of the high-pressure compressor 4a and downstream of the low-pressure compressor 5a, the pressure of the intake air (hereinafter referred to as inter-compressor pressure) P2 flowing through the intake passage 2 between the high-pressure compressor 4a and the low-pressure compressor 5a. A second intake pressure sensor 11 to be detected is arranged.

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 12 is arranged. The throttle valve 12 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 pressure of the high-pressure turbocharger 4 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 high-pressure exhaust-side bypass passage 13 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 high pressure exhaust side bypass passage 13 bypasses the high pressure turbine 4b. The high-pressure exhaust-side bypass passage 13 is provided with a high-pressure exhaust-side bypass valve 14 that controls the amount of intake air flowing through the high-pressure exhaust-side bypass passage 13 by adjusting the cross-sectional area of the high-pressure exhaust-side bypass passage 13. . The high pressure exhaust side bypass valve 14 is opened and closed by an electric actuator.

  A low-pressure exhaust-side bypass passage 15 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 low pressure exhaust side bypass passage 15 bypasses the low pressure turbine 5b. The low pressure exhaust side bypass passage 15 is provided with a low pressure exhaust side bypass valve 16 that controls the amount of intake air flowing through the low pressure exhaust side bypass passage 15 by adjusting the cross-sectional area of the low pressure exhaust side bypass passage 15. . The low pressure exhaust side bypass valve 16 is opened and closed by an electric actuator.

  An exhaust purification device 17 for purifying exhaust gas is disposed in the exhaust passage 3 downstream of the low pressure turbine downstream side connection portion downstream of the low pressure turbine 5b of the low pressure exhaust side bypass passage 15. The exhaust purification device 17 is configured to include an oxidation catalyst and a diesel particulate filter (hereinafter simply referred to as a filter) disposed at the subsequent stage of the oxidation catalyst. The filter carries a NOx storage reduction catalyst (hereinafter simply referred to as NOx catalyst). The filter has a characteristic of collecting particulate matter (Particulate Matter: hereinafter referred to as PM) such as soot (SOOT) and SOF in the exhaust flowing through the exhaust passage 3. The NOx catalyst has a characteristic of storing NOx and SOx in the exhaust gas flowing through the exhaust passage 3 when the exhaust air-fuel ratio is lean. The oxidation catalyst and NOx catalyst (hereinafter simply referred to as catalyst) of the exhaust purification device 17 correspond to the catalyst of the present invention. 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 18 that recirculates (recirculates) part of the exhaust gas flowing through the exhaust passage 3 to the intake passage 2. In this embodiment, the exhaust gas recirculated by the EGR passage 18 is referred to as EGR gas. The EGR passage 18 connects the exhaust passage 3 upstream of the high-pressure turbine 4 b and the intake passage 2 downstream of the throttle valve 12. Through this EGR passage 18, a part of the exhaust is sent to the internal combustion engine 1 as EGR gas at a high pressure. An EGR valve 19 that controls the amount of EGR gas flowing through the EGR passage 18 by adjusting the passage sectional area of the EGR passage 18 is disposed in the EGR passage 18. The EGR valve 19 is opened and closed by an electric actuator.

  The internal combustion engine 1 configured as described above is provided with an ECU 20 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 20 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, an intake air temperature sensor 9, a first intake air pressure sensor 10, a second intake air pressure sensor 11, a crank position sensor 21, and an accelerator position sensor 22 are connected to the ECU 20 through electric wiring. Output signals of these various sensors are input to the ECU 20. On the other hand, the high-pressure variable nozzle 4c, the intake-side bypass valve 7, the throttle valve 12, the high-pressure exhaust-side bypass valve 14, the low-pressure exhaust-side bypass valve 16, and the EGR valve 19 are electrically connected to the ECU 20 through electric wiring. The ECU 20 controls these devices.

  The ECU 20 receives the output signals from the various sensors and the like, determines the operating state of the internal combustion engine 1, and electrically controls the internal combustion engine 1 and the devices based on the determined engine operating state.

  By the way, when the internal combustion engine 1 is started, the catalyst of the exhaust gas purification device 17 is in an inactive state in which it cannot exhibit its function of purifying exhaust gas because of its low temperature. For this reason, when the internal combustion engine 1 is started, the temperature of the catalyst of the exhaust gas purification device 17 is raised to quickly shift to an active state where the exhaust gas can be purified. Raising the temperature of the catalyst in this way is called catalyst warm-up. In this embodiment, the catalyst warm-up is performed by opening the low pressure exhaust side bypass valve 16. When the low-pressure exhaust-side bypass valve 16 is opened, the low-pressure exhaust-side bypass passage 15 is circulated through the exhaust to avoid a reduction in exhaust energy in the low-pressure turbine 5b. The catalyst can be supplied.

  However, when the low pressure exhaust side bypass valve 16 is opened, there are the following problems. First, if the low-pressure exhaust side bypass valve 16 is opened at a light load, the rotation speed of the low-pressure turbocharger 5 is set so that the low-pressure turbocharger 5 is lubricated with lubricating oil, or the high-pressure turbocharger 4 There is a case where the rotational speed is lower than the minimum required rotational speed for shifting from a region where only supercharging is performed to a region where supercharging is performed by both the high pressure turbocharger 4 and the low pressure turbocharger 5. When the rotational speed of the low-pressure turbocharger 5 becomes less than the necessary minimum rotational speed, the low-pressure turbocharger 5 cannot be lubricated with lubricating oil, or the high-pressure turbocharger 4 starts from a region where only the high-pressure turbocharger 4 is supercharged. Therefore, it is not possible to smoothly shift to a region where supercharging is performed in both the 4 and the low-pressure turbocharger 5. Second, when the low pressure exhaust side bypass valve 16 is opened, for example, when the rotational speed of the high pressure compressor 4a is increased despite the decrease in the rotational speed of the low pressure compressor 5a, the pressure between the compressors is increased. In some cases, P2 is lowered to an excessively negative pressure, and the lubricating oil of the high-pressure compressor 4a or the low-pressure compressor 5a is sucked out to the intake passage 2 side. When the lubricating oil from the high-pressure compressor 4a or the low-pressure compressor 5a is sucked out to the intake passage 2 side in this way, the high-pressure compressor 4a or the low-pressure compressor 5a is insufficiently lubricated.

Therefore, in this embodiment, when the low pressure exhaust side bypass valve 16 is opened for warming up the catalyst, when the compressor pressure P2 detected by the second intake pressure sensor 11 becomes lower than a predetermined pressure, The low-pressure exhaust side bypass valve 16 is closed.

  Here, the predetermined pressure will be described. The predetermined pressure is either the pressure α derived from the necessary minimum rotational speed line on the low pressure compressor map shown in FIG. 2 or the pressure β at which the lubricating oil of the high pressure compressor 4a or the low pressure compressor 5a shown in FIG. Or higher pressure.

  FIG. 2 is a low-pressure compressor map. In the low-pressure compressor map shown in FIG. 2, the horizontal axis represents the low-pressure compressor corrected flow rate, and the vertical axis represents the low-pressure compressor pressure ratio. The low-pressure compressor correction flow rate is obtained by Ga√ (Tref / T1). Here, Ga is an intake air amount detected by the air flow meter 8, Tref is a low-pressure compressor temperature derived from a previously determined low-pressure turbocharger performance map, and T1 is an intake air temperature detected by the intake air temperature sensor 9. . The low pressure compressor pressure ratio is determined by P2 / P1. P1 is the pressure of the intake air detected by the first intake pressure sensor 10, and P2 is the pressure of the intake air detected by the second intake pressure sensor 11.

  In such a low-pressure compressor map shown in FIG. 2, a necessary minimum rotational speed line exists in the lower left part. The necessary minimum rotational speed line is obtained in advance by experiments, verifications, etc. The rotational speed of the low-pressure turbocharger 5 is set so that the low-pressure turbocharger 5 is lubricated with lubricating oil or only in the high-pressure turbocharger 4. This is a line for maintaining the minimum number of revolutions required for shifting from the supercharging region to the supercharging region in both the high pressure turbocharger 4 and the low pressure turbocharger 5.

  And in order to maintain the rotation speed of the low-pressure turbocharger 5 at the required minimum rotation speed, the intercompressor pressure P2 needs to be equal to or higher than the pressure α derived from the required minimum rotation speed line, based on FIG. That is, it is necessary to satisfy the relationship of α / P1 = f (Ga√ (Tref / T1)) by polynomial approximation. When this pressure α is obtained, α = f (Ga√ (Tref / T1)) × P1.

  On the other hand, FIG. 3 is a diagram showing a pressure change in the intake passage 2. In FIG. 3, the horizontal axis represents the position in the intake flow direction, and the arrangement position X1 of the first intake pressure sensor 10, the arrangement position X2 of the second intake pressure sensor 11, and the downstream position X3 of the high-pressure compressor 4a are shown. Is the intake pressure.

  Then, at the arrangement position X2 of the second intake pressure sensor 11 shown in FIG. 3, the inter-compressor pressure P2 detected by the second intake pressure sensor 11 is excessively negative. The lubricating oil of the high pressure compressor 4a or the low pressure compressor 5a is taken into the intake passage. It is necessary to be equal to or higher than the pressure β sucked out to the second side. This pressure β is obtained in advance by experiment, verification, or the like. However, when the low pressure exhaust side bypass valve is opened, the compressor pressure P2 decreases as shown by the arrow in FIG.

  As described above, if the intercompressor pressure P2 falls below either the pressure α or the pressure β when the low pressure exhaust side bypass valve is opened, the above-described various problems occur.

  Therefore, in this embodiment, the predetermined pressure = MAX (α, β) shown by the solid line in FIG. 4 is determined so that the pressure P2 between the compressors is equal to or higher than the higher one of the pressure α and the pressure β. FIG. 4 is a diagram showing a change in the predetermined pressure in accordance with a change in the conditions of the internal combustion engine 1. In FIG. 4, the horizontal axis represents a change in the condition of the internal combustion engine 1, and the vertical axis represents the pressure. As described above, the predetermined pressure indicated by the solid line is the higher pressure of the pressure α which is a dashed curve or the pressure β which is a dashed line.

  According to this embodiment, when the low pressure exhaust side bypass valve 16 is opened, the low pressure exhaust side bypass valve 16 is closed when the intercompressor pressure P2 becomes lower than a predetermined pressure. The adverse effects when the bypass valve 16 is opened can be avoided. Specifically, as shown in FIG. 2, the low pressure exhaust side bypass valve 16 is closed when it falls below the required rotational speed line, so when the low pressure exhaust side bypass valve 16 is opened at light load, The rotation speed of the low-pressure turbocharger 5 is supercharged by both the high-pressure turbocharger 4 and the low-pressure turbocharger 5 in order to lubricate the low-pressure turbocharger 5 with lubricating oil or from a region where supercharging is performed only by the high-pressure turbocharger 4. It can be avoided that the rotational speed is less than the minimum required rotational speed for shifting to the region where the operation is performed. Also, as shown in FIG. 3, when the pressure is lower than β, the low pressure exhaust side bypass valve 16 is closed, so that, for example, when the low pressure exhaust side bypass valve 16 is opened, the rotational speed of the low pressure compressor 5a decreases. In spite of this, the rotation speed of the high-pressure compressor 4a increases, the inter-compressor pressure P2 decreases and the negative pressure is excessively avoided, and the lubricating oil from the high-pressure compressor 4a or the low-pressure compressor 5a is prevented from being sucked out. it can.

  Incidentally, when the low pressure exhaust side bypass valve 16 is controlled to open and close, the pressure of the intake air fed into the internal combustion engine 1 fluctuates.

  FIG. 5 is a view showing a pressure change in the intake passage 2. In FIG. 5, the horizontal axis represents the intake flow direction position, and the arrangement position X1 of the first intake pressure sensor 10, the arrangement position X2 of the second intake pressure sensor 11, and the downstream position X3 of the high-pressure compressor 4a are shown. Is the intake pressure. When the low pressure exhaust side bypass valve 16 is controlled to open and close, the compressor pressure P2 detected by the second intake pressure sensor 11 varies at the position X2 of the second intake pressure sensor 11 shown in FIG. Here, since the supercharging pressure of the high-pressure turbocharger 4 at the position of the high-pressure compressor 4a downstream from the arrangement position X2 of the second intake pressure sensor 11 is constant, the high-pressure compressor 4a downstream position X3 as shown by the broken line in FIG. The pressure P3 of the intake air at fluctuates as indicated by a dotted circle. As a result, the pressure of the intake air fed into the internal combustion engine 1 fluctuates, and the combustion state of the internal combustion engine may deteriorate.

  In this embodiment, therefore, the low pressure exhaust side bypass valve 16 is controlled to open and close, and at the same time, the high pressure variable nozzle 4c is rotated to change the nozzle passage cross-sectional area to control the pressure of the intake air sent to the internal combustion engine to a desired pressure. I tried to do it.

  Specifically, when the low-pressure exhaust side bypass valve 16 is opened, the high-pressure variable nozzle 4c is rotated to close the nozzle passage cross-sectional area, and the pressure P3 is increased as shown by the upward arrow shown in FIG. On the other hand, when the low pressure exhaust side bypass valve 16 is closed, the high pressure variable nozzle 4c is rotated to open the nozzle passage cross-sectional area, and the pressure P3 is lowered as shown by the downward arrow shown in FIG.

  According to this embodiment, when the pressure of the intake air sent to the internal combustion engine 1 is likely to fluctuate due to the opening / closing control of the low pressure exhaust side bypass valve 16, the high pressure variable nozzle 4c is rotated to change the nozzle passage sectional area. Thus, the pressure of the intake air fed into the internal combustion engine 1 can be controlled to a desired pressure. Thereby, even if the low pressure exhaust side bypass valve 16 is controlled to open and close, the pressure of the intake air sent to the internal combustion engine 1 is maintained at a desired pressure, and the internal combustion engine 1 can continue to maintain a good combustion state.

  Next, the catalyst warm-up control routine according to this embodiment will be described. FIG. 6 is a flowchart showing a catalyst warm-up control routine according to this embodiment. This routine is repeatedly executed every predetermined time.

In step S101, the ECU 20 determines whether or not catalyst warm-up is necessary. It is determined that the catalyst warm-up is necessary when the internal combustion engine 1 is cold started. If it is determined in step S101 that catalyst warm-up is not necessary, this routine is temporarily terminated. If it is determined in step S101 that catalyst warm-up is necessary, the process proceeds to step S102.

  In step S102, the ECU 20 determines whether or not the compressor pressure P2 is equal to or higher than a predetermined pressure. The intercompressor pressure P2 can be acquired from the output value detected by the second intake pressure sensor 11. As described above, the predetermined pressure is the predetermined pressure in FIG. 4 = MAX (α, β), which is the higher pressure of the pressure α and the pressure β. The pressure α is obtained by substituting output values detected by various sensors into the equation α = f (Ga√ (Tref / T1). The pressure β is obtained in advance by experiment, verification, etc., and step S102. If it is determined affirmative that the intercompressor pressure P2 is equal to or higher than the predetermined pressure in step S103, the process proceeds to step S103, and if it is determined in step S102 that the intercompressor pressure P2 is lower than the predetermined pressure, step S104 is performed. Here, since the intercompressor pressure P2 is equal to or higher than a predetermined pressure at the start of catalyst warm-up, the process basically proceeds from step S102 to step S103.

  In step S103, the ECU 20 opens the low pressure exhaust side bypass valve 16. As a result, the exhaust gas is allowed to flow through the low-pressure exhaust-side bypass passage 15 to avoid a decrease in the energy of the exhaust gas in the low-pressure turbine 5 b, and high-temperature exhaust gas is supplied to the catalyst of the exhaust gas purification device 17. Here, when the low pressure exhaust side bypass valve 16 is opened, if the pressure P3 is likely to decrease with respect to a desired pressure, the high pressure variable nozzle 4c is rotated to close the nozzle passage cross-sectional area. The pressure P3 is increased as indicated by an upward arrow indicated by 5.

  In step S104, the ECU 20 closes the low pressure exhaust side bypass valve 16. This avoids adverse effects when the low pressure exhaust side bypass valve 16 is opened. If the pressure P3 is likely to increase with respect to a desired pressure when the low pressure exhaust side bypass valve 16 is closed, the high pressure variable nozzle 4c is rotated to open the nozzle passage sectional area. The pressure P3 is reduced as indicated by the downward arrow shown in FIG.

  In step S105, the ECU 20 determines whether the catalyst warm-up has been completed. Whether or not catalyst warm-up has been completed may be determined from the output values of various sensors, or may be determined from the passage of a fixed time from the start of catalyst warm-up. If it is determined in step S105 that the catalyst warm-up has not been completed, the process proceeds to step S102. If it is determined in step S105 that the catalyst warm-up has been completed, the process proceeds to step S106.

  In step S106, the ECU 20 closes the low pressure exhaust side bypass valve 16. Then, after the processing of this step, this routine is once ended.

  According to this routine described above, the low-pressure exhaust side bypass valve 16 can be controlled to open and close to warm up the catalyst, and the adverse effects of opening the low-pressure exhaust side bypass valve 16 can be avoided.

  In the above embodiment, the catalyst warm-up is given as an example of opening the low-pressure exhaust side bypass valve 16, but the present invention is not limited to this, and the other low-pressure exhaust side bypass valve 16 is opened. The present invention can also be applied.

  In the above embodiment, the pressure P1 is detected by the first intake pressure sensor 10 and the pressure P2 is detected by the second intake pressure sensor 11. However, the present invention is not limited to this. It may be estimated from the operating state of the engine 1.

Further, in the above embodiment, when the low pressure exhaust side bypass valve 16 is opened, the low pressure exhaust side bypass valve 16 is closed when the pressure P2 between the compressors becomes lower than a predetermined pressure. However, the present invention is not limited to this, and when the low pressure exhaust side bypass valve 16 is opened, the low pressure exhaust side bypass valve 16 may be closed when a predetermined condition is satisfied. The predetermined condition here is satisfied when, for example, the rotation speed of the low-pressure turbocharger 5 is such that the low-pressure turbocharger 5 is lubricated with lubricating oil, or from a region where only the high-pressure turbocharger 4 is supercharged. For example, there are times when the rotational speed is below the minimum required rotational speed for shifting to a region where supercharging is performed in both the 4 and the low-pressure turbocharger 5. In addition, when the predetermined condition is satisfied, for example, the rotational speed of the high-pressure compressor 4a increases even though the rotational speed of the low-pressure compressor 5a decreases, and the intercompressor pressure P2 decreases, resulting in excessive negative pressure. An example is when the lubricating oil of the high-pressure compressor 4a or the low-pressure compressor 5a is sucked out.

  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 the low voltage | pressure compressor map which concerns on Example 1. FIG. The figure which shows the pressure change of the intake passage which concerns on Example 1. FIG. The figure which shows the change of the predetermined pressure according to the condition change of the internal combustion engine which concerns on Example 1. FIG. The figure which shows the pressure change of the intake passage which concerns on Example 1. FIG. 3 is a flowchart showing a catalyst warm-up control routine 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 6 Intake side bypass passage 7 Intake side bypass valve 8 Air flow meter 9 Intake temperature sensor 10 first intake pressure sensor 11 brother 2 intake pressure sensor 12 throttle valve 13 high pressure exhaust side bypass passage 14 high pressure exhaust side bypass valve 15 low pressure exhaust side bypass passage 16 low pressure exhaust side bypass valve 17 exhaust purification device 18 EGR passage 19 EGR valve 20 ECU
21 Crank position sensor 22 Accelerator position sensor

Claims (5)

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;
A low pressure exhaust side bypass passage for bypassing the low pressure turbine;
A low-pressure exhaust-side bypass valve that is disposed in the low-pressure exhaust-side bypass passage and controls an amount of exhaust flowing through the low-pressure exhaust-side bypass passage;
With
When the low-pressure exhaust-side bypass valve is open, the low-pressure exhaust-side bypass valve is closed when a predetermined condition relating to a decrease in the rotational speed of the low-pressure compressor is satisfied. Multistage supercharging system.   The multistage engine for an internal combustion engine according to claim 1, wherein the predetermined condition is satisfied when the pressure in the intake passage between the low pressure compressor and the high pressure compressor is lower than a predetermined pressure. Supply system.   The predetermined pressure is a pressure that is derived from the minimum required rotational speed line on the low-pressure compressor map or a pressure at which the lubricating oil of the low-pressure compressor or the high-pressure compressor is sucked out, whichever is higher. The multistage supercharging system for an internal combustion engine according to claim 2, wherein the multistage supercharging system is used. A catalyst for purifying exhaust gas, disposed in the exhaust passage downstream of the low pressure turbine downstream side connection portion of the low pressure exhaust side bypass passage;
When the low-pressure exhaust side bypass valve is opened, in order to warm up the catalyst, the low-pressure exhaust side bypass valve is opened, and the exhaust gas is exhausted through the low-pressure exhaust side bypass passage. The multistage supercharging system for an internal combustion engine according to any one of claims 1 to 3, wherein the catalyst is supplied to the catalyst. A high-pressure variable nozzle mechanism that is provided in the high-pressure turbocharger and adjusts an exhaust amount to the high-pressure turbine;
5. The pressure of intake air fed to the internal combustion engine is controlled by changing the nozzle passage cross-sectional area of the high pressure variable nozzle mechanism simultaneously with opening / closing control of the low pressure exhaust side bypass valve. The multistage turbocharging system for an internal combustion engine according to any one of the above.

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