JP2008175114A - Supercharger control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To smoothly move from one-turbo mode to two-turbo mode by utilizing an EGR gas. <P>SOLUTION: Two superchargers are installed in a suction passage and an exhaust passage of an internal combustion engine parallel to each other. Two superchargers include a first supercharger with a small capacity and a second supercharger with a capacity larger than that of the first supercharger. Also, the internal combustion engine has an EGR passage for circulating the exhaust gas to the suction side. In the normal control, only the first supercharger with a small capacity is operated in the low speed range (one-turbo mode), and both the first and second superchargers are operated in the high speed range (two-turbo mode). While the mode is in transit from one-turbo mode to two-turbo mode, a control means reduces the amount of the EGR gas. The exhaust gas which has been utilized for EGR is thereby supplied to the superchargers, particularly the second supercharger to be newly operated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus for controlling an exhaust flow rate for two superchargers arranged in parallel in an intake passage and an exhaust passage.

  Conventionally, a technique has been proposed in which two superchargers are arranged in parallel in an intake system and an exhaust system, and the number of operating these superchargers is appropriately switched. For example, Patent Document 1 describes an example of an internal combustion engine in which a primary turbocharger and a secondary turbocharger are arranged in parallel. In the internal combustion engine, the secondary turbocharger is configured to have a larger capacity than the primary turbocharger. When the engine operating region is in the low speed region, only the primary turbocharger is operated (single turbo mode), and when the engine operating region is in the high speed region, the two superchargers are operated simultaneously (twin turbo mode). Thereby, the output performance is improved from the low speed range to the high speed range. Patent Document 1 describes a method of pre-rotating the secondary turbocharger when shifting from the single turbo mode to the twin turbo mode.

Japanese Patent Laid-Open No. 5-288069

  In the supercharging system as described above, when the preliminary rotation of the secondary turbocharger is insufficient at the time of transition from the single turbo mode to the twin turbo mode, a large torque step occurs and the driver may feel uncomfortable. is there.

  The present invention has been made to solve the above-described problems, and an object thereof is to smoothly shift from a single turbo mode to a twin turbo mode using EGR gas.

  In one aspect of the present invention, a supercharger control device for an internal combustion engine includes a first supercharger and a second supercapacitor that are arranged in parallel with an intake passage and an exhaust passage and have a capacity larger than that of the first supercharger. From the turbocharger, the EGR passage connected to the intake passage and the exhaust passage and circulating the exhaust to the intake side, and the single turbo mode for operating only the first supercharger. Control means for reducing the amount of EGR gas passing through the EGR passage at the time of mode transition to the two turbo mode for operating the two turbochargers.

  In the above supercharger control apparatus, the internal combustion engine is provided with two superchargers in parallel with the intake passage and the exhaust passage. The two superchargers include a first supercharger having a small capacity and a second supercharger having a larger capacity than the first supercharger. In addition, an EGR passage that circulates exhaust gas to the intake side is provided. In normal control, only the first supercharger having a small capacity is operated in the low speed range (single turbo mode), and both the first and second superchargers are operated in the high speed range (two turbo mode). ).

  Here, the control means reduces the EGR gas amount at the time of mode transition from the single turbo mode to the dual turbo mode. As a result, the exhaust gas previously used for EGR can be supplied to the supercharger, in particular, the second supercharger to be newly operated, and the preliminary rotation of the second supercharger is sufficiently increased by that amount. Can be done. Therefore, it is possible to prevent the occurrence of a torque step or the like when shifting to the two turbo mode thereafter.

  In one aspect of the above supercharger control device, the control means shuts off the supply of exhaust gas to the second supercharger in the single turbo mode, and the second supercharger during the mode transition The exhaust can be supplied to Thereby, the exhaust gas used for EGR can be used for the preliminary rotation of the second supercharger.

  In another aspect of the supercharger control device, the exhaust passage includes a first exhaust passage to the first supercharger, and a second exhaust passage to the second supercharger. An exhaust switching valve provided in the second exhaust passage, a bypass passage that bypasses the second exhaust passage narrower than the second exhaust passage, and an exhaust bypass valve provided in the bypass passage. And the control means closes the exhaust gas switching valve and the exhaust bypass valve in the single turbo mode, closes the exhaust gas switching valve and opens the exhaust bypass valve at the time of transition to the mode, In the two turbo mode, the exhaust switching valve is opened.

  In this aspect, the EGR amount is first reduced at the time of mode transition, and the exhaust gas is supplied to the second supercharger using only the exhaust bypass valve. Since the exhaust bypass valve is thinner than the exhaust gas switching valve, the pressure before the turbine of the second supercharger can be increased more effectively and the preliminary rotation can be sufficiently performed.

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

[overall structure]
First, the overall configuration of a system to which the supercharger control device for an internal combustion engine according to the present embodiment is applied will be described.

  FIG. 1 is a schematic diagram illustrating a configuration of a vehicle to which a supercharger control device for an internal combustion engine according to the present embodiment is applied. In FIG. 1, solid arrows indicate gas flow, and broken arrows indicate signal input / output. FIG. 1 shows the gas flow when the single turbo mode is set.

  The vehicle mainly includes an air cleaner 2, an intake passage 3, turbochargers 4 and 5, an intake switching valve 6, a reed valve 7, an internal combustion engine 8, a supercharging pressure sensor 9, and an exhaust passage 10. And an EGR passage 11, an EGR valve 14, an exhaust gas switching valve 15, an exhaust gas bypass valve 16, 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 provided in the intake passage 3b. Is arranged. 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 supercharging pressure sensor 9 is provided in the intake passage 3 on the downstream side of the compressors 4a and 4b. 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.

  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 the left and right banks (cylinder groups) 8L and 8R, respectively. 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. The exhaust gas generated by the 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 in 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 FIG. 1, since the EGR valve 14 is set to be closed, the EGR gas is not recirculated.

  The exhaust passage 10 is branched into exhaust passages 10a and 10b, and the turbine 4b of the turbocharger 4 is disposed in the exhaust passage 10a. The turbine 5b of the turbocharger 5 is disposed in the exhaust passage 10b. Is arranged. 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 is configured as a low-capacity low-speed supercharger having a large supercharging capability in the low / medium speed range, and the turbocharger 5 is a large capacity having a large supercharging capability in the medium / high speed range. It is configured as a high-speed supercharger.

  The turbocharger 4 is provided with a rotation speed sensor 4c that detects the turbo rotation speed, that is, the rotation speed of the turbine 4b. Similarly, the turbocharger 5 is provided with a rotation speed sensor 5c that detects the turbo rotation speed, that is, the rotation speed of the turbine 5b. The rotation speed detection signals S18 and S19 output from the rotation speed sensors 4c and 5c, respectively, are supplied to the ECU 50.

  Further, an exhaust switching valve 15 is provided in the exhaust passage 10b, and an exhaust bypass passage 10ba is connected to the exhaust passage 10b. 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 exhaust bypass passage 10ba is configured as a passage that bypasses the exhaust passage 10b in which the exhaust switching valve 15 is provided. Specifically, the exhaust bypass passage 10ba is configured to have a smaller passage diameter than the exhaust passage 10b in which the exhaust switching valve 15 is provided. An exhaust bypass valve 16 is provided in the exhaust bypass passage 10ba. The exhaust bypass valve 16 adjusts the flow rate of the exhaust gas passing through the exhaust bypass passage 10ba.

  When the intake switching valve 6, the exhaust switching valve 15, and the exhaust bypass valve 16 are all closed, intake and exhaust gas are supplied only to the turbocharger 4, and the turbocharger 5 is supplied to the turbocharger 5. Intake and exhaust gas are not supplied. Therefore, only the turbocharger 4 operates, and the turbocharger 5 does not operate. On the other hand, when the intake switching valve 6 is open and either the exhaust switching valve 15 or the exhaust bypass valve 16 is open, intake and exhaust gas are supplied to both the turbochargers 4 and 5. Therefore, both turbochargers 4 and 5 operate.

  The ECU 50 includes a CPU, a ROM, a RAM, an A / D converter, and the like (not shown). The ECU 50 performs in-vehicle control based on outputs supplied from various sensors in the vehicle. Specifically, the ECU 50 acquires the actual boost pressure from the boost pressure sensor 9, and based on the actual boost pressure and the like, the intake air switching valve 6, the EGR valve 14, the exhaust gas switching valve 15, and the exhaust gas bypass. Control the valve 16 and the like.

  In the present embodiment, the ECU 50 mainly controls the intake air switching valve 6, the exhaust gas switching valve 15, and the exhaust gas bypass valve 16 to operate only the turbocharger 4 (“one turbo mode”). And a mode for operating both turbochargers 4 and 5 (referred to as “two turbo mode”). Specifically, the ECU 50 executes switching from the single turbo mode to the double turbo mode and switching from the double turbo mode to the single turbo mode based on, for example, the engine speed and the required torque. .

  Here, basic control executed when switching between the single turbo mode and the dual turbo mode will be briefly described. As described above, the mode is switched by the ECU 50 controlling the intake switching valve 6, the exhaust switching valve 15, and the exhaust bypass valve 16. Specifically, when switching from the single turbo mode to the dual turbo mode, the ECU 50 controls the intake switching valve 6, the exhaust switching valve 15, and the exhaust bypass valve 16 from closed to open. In this case, the ECU 50 basically performs switching by opening the exhaust bypass valve 16, the exhaust switching valve 15, and the intake switching valve 6 in this order. More specifically, the exhaust bypass valve 16 is first opened little by little, the exhaust switching valve 15 is opened when a predetermined condition is satisfied in this state, and then the intake switching valve 6 is opened. In this case, the exhaust bypass valve 16 is first opened a little by supplying the turbocharger 5 with a relatively small flow rate of exhaust gas (because the diameter of the exhaust bypass passage 10ba is small). Is to gradually operate (ie, run up). In other words, by opening the exhaust gas switching valve 15 first, it is possible to prevent a relatively large flow rate of exhaust gas from flowing into the turbocharger 5 at a stretch and causing a torque shock or the like. On the other hand, when switching from the single turbo mode to the dual turbo mode, the ECU 50 controls the intake switching valve 6, the exhaust switching valve 15, and the exhaust bypass valve 16 from open to closed in the same manner as described above.

  FIG. 2 schematically shows an operation region map of the single turbo mode and the double turbo mode. In the graph of FIG. 2, the horizontal axis indicates the engine speed, and the vertical axis indicates the required torque (fuel injection amount). In FIG. 2, a thin solid line 61 and a thick solid line 63 indicate operating characteristics of the turbocharger 4 having a small capacity, and a broken line 62 and a thick solid line 64 indicate operating characteristics of the turbocharger 5 having a large capacity. When the operating point determined by the engine speed and the required torque (fuel injection amount) is below the solid line 61, the internal combustion engine operates in the single turbo mode. When the engine speed and torque increase and the operating point enters the hatched area above the solid line 61, the internal combustion engine operates in the two-turbo mode.

[Exhaust flow control]
Next, exhaust flow control according to the present invention will be described. As described above, at the time of mode transition from the single turbo mode to the double turbo mode, a large torque step is generated if the rotational speed of the turbocharger 5 is not sufficiently increased. Therefore, in the present invention, at the time of the mode transition, the EGR amount is decreased and the exhaust gas corresponding thereto is used for the preliminary rotation (running) of the turbocharger 5 to sufficiently increase the rotation speed of the turbocharger 5. This prevents the occurrence of a torque step during mode transition.

  FIG. 3 shows a timing chart of the exhaust flow control according to the present invention. FIG. 3 shows temporal changes in the open / closed state of the EGR valve 14, the exhaust bypass valve 16 and the exhaust switching valve 15. Now, it is assumed that the internal combustion engine is operating in the single turbo mode until time t1, and that the condition for switching to the dual turbo mode is satisfied at time t1. At time t1, the ECU 50 closes the EGR valve 14 to decrease the EGR amount and opens the exhaust bypass valve 16. Thus, the exhaust gas that has been used for EGR until then flows into the exhaust passage 10. The exhaust gas basically tries to flow into the exhaust passages 10a and 10b, but the exhaust switching valve 15 remains closed, and as a result, flows into the exhaust passage 10a and the exhaust bypass passage 10ba. As a result, the exhaust gas can flow through the exhaust passage 10a and the exhaust bypass passage 10ba by an amount corresponding to the exhaust gas that has been used for EGR until then, and the turbine 5b of the turbocharger 5 is sufficiently preliminarily rotated. Can do.

  The ECU 50 opens the EGR valve 14, closes the exhaust bypass valve 16, and opens the exhaust gas switching valve 15 at time t <b> 2 when the predetermined time tc has elapsed. Thereby, EGR is restarted. Further, the exhaust gas flows into the exhaust passages 10a and 10b, and the internal combustion engine operates in the two-turbo mode using the turbochargers 4 and 5. The predetermined time tc is set to a time during which the turbocharger 5 can be sufficiently preliminarily rotated by using the EGR gas, so that a torque step is not generated when the two turbo mode is shifted to time t2. Therefore, a smooth mode transition is possible. In order to stop EGR, it is desirable that the predetermined time tc is as short as possible.

  In the above example, the EGR valve 14 is closed and the EGR amount is zero for a predetermined time tc from time t1, but the application of the present invention is not limited to this. Even if the EGR amount is not set to zero, the exhaust gas can be used for the preliminary rotation of the turbocharger 5 by reducing it to some extent, and the effect of the present invention can be obtained. The amount of EGR to be decreased can be determined using a map or the like with the engine speed and the fuel injection amount as inputs.

  In this embodiment, when the condition for switching to the two-turbo mode is satisfied, the EGR amount is decreased, only the exhaust bypass valve 16 is opened, and the increased exhaust gas is caused to flow to the exhaust bypass valve 16. Yes. Since the exhaust bypass passage 10ba is narrower than the exhaust passage 10b, even if the same amount of exhaust gas flows, it is more likely that the exhaust bypass passage 10ba is sent to the exhaust bypass passage 10ba than the exhaust passage 10b on the input side of the turbine 5b of the turbocharger 5. The back pressure can be increased more effectively, and the turbocharger 5 can be pre-rotated more effectively.

  FIG. 4 shows an example of a flowchart of exhaust flow control according to the present invention. This control is realized by the ECU 50 executing a program prepared in advance.

  First, the ECU 50 determines whether or not the operating state of the internal combustion engine is in the single turbo operation region based on, for example, the engine speed and the required torque (step S101). Specifically, this determination is executed by referring to the motion region map shown in FIG. When the operating state is in the single turbo operating range, the ECU 50 operates the small-capacity turbocharger 4 to operate the internal combustion engine in the single turbo mode (step S102). At this time, as described above, the intake switching valve 7, the exhaust switching valve 15, and the exhaust bypass valve 16 are all closed.

  Next, the ECU 50 determines whether or not the operating state of the internal combustion engine is in the turbo operating range (step S103). This determination is also executed by referring to the operation area map shown in FIG. When the operating state is in the two-turbo operation range, that is, when the condition for switching to the two-turbo mode is satisfied, the ECU 50 closes the EGR valve 14 to reduce the EGR gas amount and opens the exhaust bypass valve 16 ( Step S104). Note that the exhaust gas switching valve 15 remains closed. As a result, the exhaust gas previously used for EGR can be caused to flow through the exhaust passage 10a and the exhaust bypass passage 10ba, so that the turbocharger 5 can be preliminarily rotated.

  Next, the ECU 50 determines whether or not the predetermined time tc has elapsed (step S105), and when it has elapsed, the ECU 50 shifts to the two-turbo mode (step S106). Specifically, the ECU 50 opens the EGR valve 14, closes the exhaust bypass valve 16, and opens the exhaust gas switching valve 15. Thereafter, the internal combustion engine operates in the two-turbo mode while executing EGR.

  As described above, in the present invention, the EGR amount is reduced at the time of the mode shift from the single turbo mode to the double turbo mode, and the exhaust gas corresponding to that amount is used for the preliminary rotation of the turbocharger 5. It is possible to prevent a torque step from occurring.

[Modification]
In the above example, the exhaust bypass valve 16 is closed after shifting to the two-turbo mode, but it may be left open.

  In the above example, in the exhaust gas flow control shown in FIGS. 3 and 4, the ECU 50 shifts to the two-turbo mode after a predetermined time tc has elapsed since the EGR amount was decreased. Instead, for example, the rotational speed of the turbine 5b of the turbocharger 5 may be detected by a rotational speed sensor or the like, and the two-turbo mode may be shifted to a sufficient rotational speed. Further, the pressure at the outlet of the compressor 5a of the turbocharger 5 is detected, and when this pressure exceeds a predetermined pressure value, it is assumed that sufficient preliminary rotation has been obtained and the mode is shifted to the two-turbo mode. Also good.

1 is a diagram illustrating a schematic configuration of a vehicle to which a supercharger control device for an internal combustion engine according to an embodiment is applied. The operation area | region map of 1 turbo mode and 2 turbo mode is shown roughly. 3 shows a timing chart of exhaust flow control according to the present invention. It is a flowchart of the exhaust flow control by this invention.

Explanation of symbols

2 Air cleaner 3 Intake passage 4, 5 Turbocharger 4 a, 5 a Compressor 4 b, 5 b Turbine 6 Intake switching valve 8 Internal combustion engine 8 a Cylinder 9 Supercharging pressure sensor 10 Exhaust passage 11 EGR passage 14 EGR valve 15 Exhaust switching valve 16 Exhaust bypass Valve 50 ECU

Claims (3)

A first supercharger and a second supercharger having a larger capacity than the first supercharger, arranged in parallel with the intake passage and the exhaust passage;
An EGR passage connected to the intake passage and the exhaust passage and circulating the exhaust to the intake side;
The amount of EGR gas passing through the EGR passage at the time of mode transition from the single turbo mode that operates only the first supercharger to the dual turbo mode that operates the first and second superchargers A supercharger control device for an internal combustion engine, comprising:   The control means cuts off the supply of exhaust gas to the second supercharger in the single turbo mode, and supplies exhaust gas to the second supercharger during the mode transition. The supercharger control device for an internal combustion engine according to claim 1. The exhaust passage includes a first exhaust passage to the first supercharger, a second exhaust passage to the second supercharger, and an exhaust switching valve provided in the second exhaust passage. And a bypass passage that bypasses the second exhaust passage narrower than the second exhaust passage, and an exhaust bypass valve provided in the bypass passage,
The control means closes the exhaust switching valve and the exhaust bypass valve in the single turbo mode, closes the exhaust switching valve and opens the exhaust bypass valve at the time of transition to the mode, and The supercharger control device for an internal combustion engine according to claim 1, wherein the exhaust gas switching valve is opened in the individual turbo mode.

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