JP2010190054A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine capable of balancing suppression of increase of NOx and suppression of torque level difference. <P>SOLUTION: The control device of the internal combustion engine includes first and second superchargers arranged in an intake air passage and an exhaust gas passage, an intake air switch valve and an exhaust gas switch valve for regulating the quantities of intake air and exhaust gas supplied to the second supercharger, an EGR passage for circulating EGR gas from the exhaust gas passage to the intake air passage and an EGR valve arranged in the EGR passage. The control device of the internal combustion engine includes an EGR control means for calculating a feedback quantity based on deviation of an actual air quantity and a target air quantity and setting a value calculated by correcting a basic opening by using the feedback quantity as an opening of the EGR valve. In this case, the EGR control means changes the feedback quantity on switching a turbo mode between the feedback quantity when using the single turbo mode and the feedback quantity when using the twin turbo mode. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine of a twin turbo system.

  Conventionally, a twin turbo system 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 discloses an EGR (Exhaust Gas Recirculation) amount when switching from a single turbo mode in which only a primary turbocharger is operated to a twin turbo mode in which two turbochargers are operated in a twin turbo system. There is described a technique for reducing the torque step generated at the time of switching by reducing the amount and pre-rotating the secondary turbo. Patent Document 2 describes a technique for setting the opening degree of an EGR valve in accordance with each exhaust pressure in a first stage turbocharging and a second stage turbocharging in an in-line turbo system. Patent Document 3 also describes a technique related to the present invention.

JP 2008-175114 A Japanese Patent Laid-Open No. 4-17765 JP 2004-156458 A

  By the way, in the technique described in Patent Document 1, the EGR amount is reduced only for the purpose of reducing the torque step at the time of switching. However, in the technique described in Patent Document 1, since there is no clear correlation between the occurrence of the torque step and the amount of decrease in the EGR amount, there is a possibility that NOx may increase significantly by reducing the amount of EGR too much. .

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide a control device for an internal combustion engine capable of achieving both suppression of NOx increase and torque step suppression. To do.

  In one aspect of the present invention, first and second superchargers disposed in an intake passage and an exhaust passage, and intake air for adjusting the amount of intake air and exhaust gas supplied to the second supercharger. An internal combustion engine control device comprising: a switching valve and an exhaust switching valve; an EGR passage that recirculates EGR gas from the exhaust passage to the intake passage; and an EGR valve provided in the EGR passage. And a turbo mode between a single turbo mode for operating only the first supercharger and a twin turbo mode for operating both the first and second superchargers by controlling the exhaust gas switching valve. Switching control means for switching between, a target air amount setting means for setting a minimum air amount necessary for burning the fuel supply amount supplied to the internal combustion engine as a target air amount, and an actual flow flowing into the intake passage air The actual air amount detection means for detecting the feedback amount, the feedback amount is calculated based on the deviation between the actual air amount and the target air amount, and the value obtained by correcting the basic opening degree by the feedback amount is used as the opening degree of the EGR valve. EGR control means for setting, wherein the EGR control means sets the feedback amount when the turbo mode is switched to the feedback amount when the single turbo mode is set and the feedback when the twin turbo mode is set. Vary between quantity.

  The control device for an internal combustion engine includes a first and a second supercharger disposed in the intake passage and the exhaust passage, and an intake air for adjusting the amount of intake air and exhaust gas supplied to the second supercharger. A switching valve and an exhaust switching valve; an EGR passage that recirculates EGR gas from the exhaust passage to the intake passage; and an EGR valve provided in the EGR passage. The control device for an internal combustion engine includes switching control means for switching the turbo mode, target air amount setting means, EGR control means, and actual air amount detection means for detecting the actual air amount. These switching control means, target air amount setting means, and EGR control means are realized by an ECU (Engine Control Unit), for example. The actual air amount detection means is, for example, an air flow meter. The switching control means controls the intake switching valve and the exhaust switching valve to operate only the first turbocharger and the twin turbo mode that operates both the first and second turbochargers. Switch between turbo modes. The target air amount setting means sets the minimum air amount necessary for burning the fuel supply amount supplied to the internal combustion engine as the target air amount. The EGR control means calculates a feedback amount based on the deviation between the actual air amount and the target air amount, and sets a value obtained by correcting the basic opening by the feedback amount as the opening of the EGR valve. Here, the EGR control means changes the feedback amount when the turbo mode is switched between the feedback amount when the single turbo mode is set and the feedback amount when the twin turbo mode is set. In this way, the actual air amount can easily follow the target air amount, hunting can be prevented, and the actual air amount can be held near the target air amount. Thereby, during the switching of the turbo mode, it is possible to suppress a torque step and to suppress an increase in NOx and a sudden change in noise.

  Another aspect of the control device for the internal combustion engine includes an exhaust gas switching valve opening degree detecting unit that detects an opening degree of the exhaust gas switching valve, and the EGR control unit is configured to detect the exhaust gas when the turbo mode is switched. The feedback amount is changed according to the opening of the switching valve. The exhaust gas switching valve opening degree detecting means is, for example, an opening degree sensor. Thereby, the feedback amount in the turbo mode switching period can be accurately obtained.

  In another aspect of the control device for an internal combustion engine, the EGR control means sets an upper and lower limit width of the feedback amount. As a result, even when an obviously inappropriate feedback amount is calculated, it is possible to prevent the opening degree of the EGR valve from being controlled accordingly.

  According to another aspect of the control device for an internal combustion engine, an actual EGR rate calculation means for calculating an actual EGR rate when the EGR gas is recirculated from the exhaust passage to the intake passage, and a target value of the EGR rate is set as a target. Target EGR rate setting means for setting as an EGR rate, and the EGR control means is configured to change the target EGR when the actual air amount is equal to or greater than the target air amount when the turbo mode is switched. The opening degree of the EGR valve is set according to a deviation between the actual EGR rate and the actual EGR rate, and when the actual air amount is smaller than the target air amount, the EGR valve is controlled to be closed. . The actual EGR rate calculating means and the target EGR rate setting means are realized by an ECU, for example. As a result, it is possible to prevent the actual EGR rate from deviating greatly from the target EGR rate, and to prevent occurrence of a torque step.

  In another aspect of the control device for an internal combustion engine, the actual EGR rate calculation means calculates the actual EGR rate according to the opening of the exhaust gas switching valve. As a result, the exhaust pressure can be calculated with high accuracy, and the actual EGR rate can be calculated with high accuracy.

  In another aspect of the control device for an internal combustion engine, the actual EGR rate calculation means calculates the actual EGR rate according to the opening of the intake air switching valve. As a result, the actual EGR rate can be calculated with higher accuracy.

1 is a schematic diagram showing a configuration of a vehicle to which a control device for an internal combustion engine according to an embodiment is applied. Only the components near the turbochargers 4 and 5 are shown. It is a graph which shows the change with respect to time about the opening degree of an exhaust gas switching valve, the opening degree of an intake air switching valve, air quantity, the opening degree of an EGR valve, fuel supply amount, and torque. It is a flowchart which shows the control processing of the internal combustion engine which concerns on 1st Embodiment. It is a graph which shows the change of the air quantity (or EGR rate) with respect to an EGR valve opening degree. It is a graph which shows the change with respect to the time about the opening degree of an exhaust gas switching valve, the opening degree of an intake air switching valve, the air quantity, and the opening degree of an EGR valve. It is a graph which shows the change with respect to the time about the opening degree of an exhaust gas switching valve, the opening degree of an intake air switching valve, an EGR rate, an air quantity, and an EGR valve. It is a flowchart which shows the control processing of the internal combustion engine which concerns on 3rd Embodiment. It is a graph which shows the change with respect to the time of the opening degree of an exhaust gas switching valve, and exhaust pressure. It is a flowchart which shows the calculation method which calculates a real EGR rate.

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

[Device configuration]
First, the overall configuration of a system to which the 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 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. In addition, in FIG. 1, the gas flow at the time of setting to single turbo mode is shown.

  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 (engine) 8, a supercharging pressure sensor 9, An exhaust passage 10, an EGR passage 11, an EGR valve 14, an exhaust gas switching valve 15, an exhaust bypass valve 16, and an ECU (Engine Control Unit) 50 are provided. That is, the vehicle has a so-called twin turbo system.

  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. An air flow meter 21 is provided in the intake passage 3. The air flow meter 21 detects the amount of intake air (actual air amount) and supplies a detection signal S21 corresponding to the actual air amount to the ECU 50. 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 the supercharged intake air (supercharging pressure), and supplies a detection signal S9 corresponding to this 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 each of the left and right banks (cylinder groups) 8L and 8R. The internal combustion engine 8 is a device that generates power by burning an air-fuel mixture of intake air and fuel supplied from the intake passage 3. The internal combustion engine 8 is configured by, for example, a diesel engine. The cylinder 8La is supplied with fuel from the fuel injection valve 22a, and the cylinder 8Ra is supplied with fuel from the fuel injection valve 22b. The fuel injection valves 22a and 22b are controlled by control signals S22a and 22b from the ECU 50. Exhaust gas generated by combustion in the internal combustion engine 8 is discharged to the exhaust passage 10. The internal combustion engine 8 is not limited to being configured with eight 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 that passes 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. That is, the turbocharger 4 corresponds to a so-called primary turbocharger, and the turbocharger 5 corresponds to a so-called secondary turbocharger. The turbocharger 4 corresponds to the first supercharger in the present invention, and the turbocharger 5 corresponds to the second supercharger in the present invention.

  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 exhaust gas flow / shutoff in the exhaust passage 10b. Here, the exhaust gas switching valve 15 is provided with an opening degree sensor 15a. The opening sensor 15a detects the opening of the exhaust gas switching valve 15, and supplies a detection signal S15a corresponding to the detected opening to the ECU 50. 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, and 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 are supplied only to the turbocharger 4, and the turbocharger 5 is And exhaust is 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 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 obtains the actual air amount from the air flow meter 21, obtains the supercharging pressure from the supercharging pressure sensor 9, and based on the actual air amount and the supercharging pressure, the intake air switching valve 6, EGR Control is performed on the valve 14, the exhaust gas switching valve 15, the exhaust bypass valve 16, and the like. In each embodiment, the ECU 50 mainly controls the intake switching valve 6, the exhaust switching valve 15, and the exhaust bypass valve 16 to operate only the turbocharger 4 (single turbo mode), turbo, Control which switches turbo mode between the modes (twin turbo mode) which operate both the superchargers 4 and 5 is performed.

  Here, the basic control executed when switching between the single turbo mode and the twin 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 twin 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 a relatively small flow amount of exhaust (because the diameter of the exhaust bypass passage 10ba is small) to the turbocharger 5. This is for gradually operating (ie, running). In other words, by opening the exhaust gas switching valve 15 first, it is possible to prevent a relatively large flow amount 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 twin 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.

  Next, gas flows in the single turbo mode and the twin turbo mode will be described with reference to FIG. FIG. 2 shows only components near the turbochargers 4 and 5 in FIG. FIG. 2 (a) shows a diagram when the single turbo mode is set, and FIG. 2 (b) shows a diagram when the twin turbo mode is set. As shown in FIG. 2 (a), in the single turbo mode, the intake switching valve 6, the exhaust switching valve 15, and the exhaust bypass valve 16 are all closed, so that intake and exhaust are supplied only to the turbocharger 4. Thus, intake and exhaust are not supplied to the turbocharger 5. Therefore, only the turbocharger 4 operates, and the turbocharger 5 does not operate. On the other hand, as shown in FIG. 2B, in the twin turbo mode, the intake air switching valve 6 is open and the exhaust gas switching valve 15 and the exhaust bypass valve 16 are open. Intake and exhaust are supplied to both. Therefore, both turbochargers 4 and 5 operate.

[First Embodiment]
A control method for the internal combustion engine according to the first embodiment will be described.

  In the twin turbo system, when switching between the single turbo mode and the twin turbo mode, a step may be generated in the output torque of the internal combustion engine. Therefore, in the control of a general twin turbo system, in order to prevent a step in the output torque, the amount of EGR gas recirculated to the intake system (EGR amount) is decreased and the actual air amount flowing into the internal combustion engine is increased. I am letting. However, in this case, if the EGR amount is decreased too much, the NOx emission amount may increase.

  Here, when the internal combustion engine is a diesel engine, the output torque of the internal combustion engine may not be reduced as long as the minimum amount of air that can completely burn the fuel supplied to the internal combustion engine is supplied. Are known. Therefore, in the control method for the internal combustion engine according to the first embodiment, the ECU 50 determines the minimum air amount necessary for burning the fuel supply amount when switching between the single turbo mode and the twin turbo mode. The target air amount is set, and the EGR valve 14 is controlled based on the magnitude relationship between the actual air amount and the target air amount. This will be specifically described below.

  FIG. 3 shows the opening degree of the exhaust gas switching valve 15 (exhaust gas switching valve opening degree), the opening degree of the intake air switching valve 6 (intake air switching valve opening degree), the air amount, the opening degree of the EGR valve 14 (EGR valve opening degree), The change with respect to time about the fuel supply amount and the torque output from the internal combustion engine 8 is shown. In FIG. 3, “single period” indicates a period in which the turbo mode is set in the single turbo mode, and “twin period” indicates a period in which the turbo mode is set in the twin turbo mode. Further, the “switching period” indicates a period during which the turbo mode is switched.

  The ECU 10 obtains in advance a minimum target air amount necessary for burning the fuel supply amount as an appropriate value, and holds it in a memory or the like as the target air amount Gntrg. Since the target air amount Gntrg indicates the minimum air amount necessary for burning the fuel supply amount, the target air amount Gntrg also increases as the fuel supply amount increases as shown in FIG. .

  The ECU 50 performs control so that the actual air amount Gn follows the target air amount Gntrg during the switching period. Specifically, when the actual air amount Gn is equal to or greater than the target air amount Gntrg, the ECU 50 controls the opening degree of the EGR valve 14 to open to increase the EGR amount, thereby increasing the actual air amount Gn. Decrease. On the other hand, when the actual air amount Gn is smaller than the target air amount Gntrg, the ECU 50 increases the actual air amount Gn by controlling the opening of the EGR valve 14 to the closed side and decreasing the EGR amount. Let

  For example, since the actual air amount Gn is smaller than the target air amount Gntrg at the time Ta1 during the switching period, the ECU 50 controls the opening degree of the EGR valve 14 to the closed side to decrease the EGR amount. The actual air amount Gn is increased. At the time Ta2, the actual air amount Gn is equal to or greater than the target air amount Gntrg. Therefore, the ECU 50 controls the opening degree of the EGR valve 14 to open to increase the EGR amount, thereby reducing the actual air amount Gn. .

  By doing in this way, as shown by the surrounding broken line A1, the actual air amount Gn is held in the vicinity of the target air amount Gntrg during the switching period. Therefore, according to the above-described control method, the minimum air amount necessary for burning the fuel supply amount is supplied to the internal combustion engine 8, so that a decrease in torque during the switching period is suppressed and occurrence of a torque step is suppressed. can do. In addition, by doing so, the EGR amount is not excessively reduced, so that an increase in NOx emission and noise can be suppressed.

  Next, the control process of the internal combustion engine according to the first embodiment will be described with reference to FIG. FIG. 4 is a flowchart showing a control process of the internal combustion engine according to the first embodiment.

  In step S101, the ECU 50 determines whether or not the turbo mode is being switched. For example, the ECU 50 can determine whether or not the turbo mode is being switched by determining whether or not the control signal S15 for controlling the exhaust gas switching valve 15 to open is supplied. When the ECU 50 determines that the turbo mode is not being switched (step S101: No), that is, when it is determined that the single turbo mode or the twin turbo mode is set, the ECU 50 proceeds to the process of step S105 and performs normal control. I do. As normal control, the ECU 50 performs control for causing the EGR rate (actual EGR rate) when the EGR gas is recirculated from the exhaust passage 10 to the intake passage 3 to follow the target EGR rate. Here, the actual EGR rate is a value calculated based on the supercharging pressure, the exhaust pressure, or the like, and the target EGR rate is a value calculated in advance as an appropriate value by experiment or the like. In step S105, the ECU 50 performs the normal control, and then returns this control process. On the other hand, if the ECU 50 determines in step S101 that the turbo mode is being switched (step S101: Yes), the process proceeds to step S102.

  In step S102, the ECU 50 calculates a target air amount Gntrg based on the fuel supply amount Qfin. The target air amount Gntrg is obtained using, for example, a function funcA of the fuel supply amount Qfin. This function funcA is a function obtained in advance by experiments or the like.

  In step S103, the ECU 50 obtains the actual air amount Gn based on the detection signal S21 from the air flow meter 21. Needless to say, the process of step S102 and the process of step S103 may be performed in reverse order or simultaneously.

  In step S104, the ECU 50 determines whether or not the actual air amount Gn is smaller than the target air amount Gntrg. When the ECU 50 determines that the actual air amount Gn is smaller than the target air amount Gntrg (step S104: Yes), the ECU 50 performs control to close the EGR valve 14 by a predetermined amount (step S105), and then returns to this control process. To do. On the other hand, if the ECU 50 determines that the actual air amount Gn is equal to or greater than the target air amount Gntrg (step S104: No), the ECU 50 performs control to open the EGR valve 14 by a predetermined amount (step S106), and then Return control processing. Here, the predetermined amount is calculated as a function of a deviation between the actual air amount Gn and the target air amount Gntrg.

  As described above, in the control method of the internal combustion engine according to the first embodiment, the ECU 50 sets the minimum air amount necessary for burning the fuel supply amount as the target air amount during the switching period, When it is determined that the actual air amount is smaller than the target air amount, the EGR valve 14 is controlled to be closed, and when it is determined that the actual air amount is equal to or greater than the target air amount, the EGR valve 14 is Control to open side. By doing so, it is possible to suppress the occurrence of a torque step during the switching of the turbo mode, and to suppress an increase in NOx and a sudden change in noise.

[Second Embodiment]
Next, a control method for the internal combustion engine according to the second embodiment will be described.

  In the twin turbo system, for example, when the turbo mode is switched from the single turbo mode to the twin turbo mode, the intake switching valve 6 and the exhaust switching valve 15 are opened, so that the paths of the intake passage 3 and the exhaust passage 10 are expanded. The supercharging pressure and the exhaust pressure are reduced. Therefore, when the turbo mode is switched from the single turbo mode to the twin turbo mode, the change sensitivity of the air amount with respect to the change in the opening degree of the EGR valve 14 (EGR valve opening degree) is lowered.

  FIG. 5 is a graph showing changes in the air amount (or EGR rate) with respect to the EGR valve opening. As shown in FIG. 5, when the EGR valve opening changes by the change amount Wn, the change amount of the air amount (or EGR rate) in the single turbo mode becomes Vs, and the air amount in the twin turbo mode (or The amount of change in the EGR rate is Vt. Here, the change amount Vt is smaller than the change amount Vs. That is, when the turbo mode is switched from the single turbo mode to the twin turbo mode, the supercharging pressure and the exhaust pressure are reduced, so that the change sensitivity of the air amount with respect to the change in the EGR valve opening degree is lowered. On the contrary, when the turbo mode is switched from the twin turbo mode to the single turbo mode, the supercharging pressure and the exhaust pressure increase, so that the change sensitivity of the air amount with respect to the change of the EGR valve opening increases.

  Even during the switching of the turbo mode, the opening degree of the exhaust gas switching valve 15 gradually changes, so that the change sensitivity of the air amount gradually changes with respect to the change in the EGR valve opening degree. Therefore, in the processing of steps S105 and S106 in the flowchart of FIG. 4 described above, the EGR valve 14 is controlled based only on the deviation between the target air amount and the actual air amount without considering the opening degree of the exhaust gas switching valve 15. When the predetermined amount of opening is determined, there is a possibility that followability is deteriorated and hunting is caused.

  Therefore, in the control method for the internal combustion engine according to the second embodiment, the ECU 50 sets the value obtained by correcting the basic opening degree by the feedback amount as the opening degree of the EGR valve 14, and at the time of switching to the turbo mode, the exhaust switching valve 15 is set. The feedback amount is changed according to the opening degree. Here, the basic opening is a value obtained in advance as an appropriate value, and is set to be on the open side in the twin turbo mode than in the single turbo mode.

  FIG. 6 shows the opening degree of the exhaust gas switching valve 15 (exhaust gas switching valve opening degree), the opening degree of the intake air switching valve 6 (intake air switching valve opening degree), the air amount, and the opening degree of the EGR valve 14 (EGR valve opening degree). The change with respect to time is shown.

  In the graph showing the change in the opening degree of the EGR valve 14 in FIG. 6, the basic opening degree is indicated by a broken line, the feedback amount with respect to the basic opening degree is indicated by a solid line, and the feedback control width which is the upper and lower limit width of the feedback amount Is shown.

  As can be seen from this graph, the basic opening of the EGR valve 14 is set so that the opening in the twin period is more open than the opening in the single period. The basic opening in the switching period is set to a value between the basic opening in the twin period and the basic opening in the single period.

  The feedback amount is set so that the feedback amount in the twin period is larger than the feedback amount in the single period. Here, the feedback amount is calculated based on the deviation between the actual EGR rate and the target EGR rate in the single period and the twin period, and in the switching period, the deviation between the actual air amount Gn and the target air amount Gntrg and the exhaust gas switching. Calculated based on the opening of the valve.

  The feedback control width is obtained by experiments or the like as a conforming value based on the basic opening. Here, the feedback control width in the twin period is set to be larger than the feedback control width in the single period. The feedback width in the switching period is set to be a value between the feedback control width in the twin period and the feedback width in the single period. By providing the feedback control range, it is possible to prevent the opening degree of the EGR valve from being controlled in accordance with a case where a clearly inappropriate feedback amount is calculated due to a sensor failure or the like.

  Next, a method for calculating the feedback amount during the turbo mode switching period will be specifically described. The ECU 50 calculates the feedback amount based on the deviation between the actual air amount Gn and the target air amount Gntrg for each of the turbo mode being the single turbo mode and the twin turbo mode, and the exhaust gas switching valve between these feedback amounts. A value changed according to the opening degree of 15 is calculated as a feedback amount in the switching period.

  The feedback amount eegrfbs in the single turbo mode is obtained by the following equation (1).

eegrfbs = funcB (Grtrg−Gn) (1)
Here, funcB is a function obtained by experiments or the like. The feedback amount eegrfbs is a feedback amount for causing the actual air amount Gn to follow the target air amount Gntrg when the turbo mode is the single turbo mode.

  The feedback amount eegrfbs in the twin turbo mode is obtained by the following equation (2) obtained by multiplying the above equation (1) by the coefficient K.

eegrfbt = K × funcB (Grtrg−Gn) (2)
The feedback amount eegrfbt is a feedback amount for causing the actual air amount Gn to follow the target air amount Gntrg when the turbo mode is set to the twin turbo mode. Here, the coefficient K in Equation (2) is a value larger than 1, and the feedback amount eegrfbt in the twin turbo mode is set to a value larger than the feedback amount eegrfbs in the single turbo mode. Specifically, the coefficient K is set based on the graph shown in FIG. 5 so that the change sensitivity of the air amount with respect to the change in the opening degree of the EGR valve 14 is the same in the single turbo mode and the twin turbo mode. The

  The feedback amount eegrfbch in the turbo mode switching period is expressed by the following equation (3) based on the feedback amounts eegrfbt and eegrfbs calculated from the above equations (1) and (2) and the opening of the exhaust gas switching valve 15. Is calculated using In the following equation (3), a value changed according to the opening degree ecvact of the exhaust gas switching valve 15 between the feedback amounts eegrfbt and eegrfbs is calculated as the feedback amount eegrfbch in the switching period. Note that the opening degree ecvacact of the exhaust gas switching valve 15 is obtained based on a detection signal from an opening degree sensor 15 a that detects the opening degree of the exhaust gas switching valve 15.

eegrfbch = eegrfbs × (ecvacact / 100)
+ Eegrfbt × ((100−ecvact) / 100)
... (3)
The ECU 50 sets a value obtained by correcting the basic opening with the feedback amount eggrfbch as the EGR valve opening when the turbo mode is switched. According to this method, since the opening degree of the exhaust gas switching valve 15 detected by the opening degree sensor 15a is used, the feedback amount in the switching period can be accurately obtained as a value corresponding to the opening degree of the exhaust gas switching valve 15. As a result, the actual air amount can easily follow the target air amount, hunting can be prevented, and the actual air amount can be held near the target air amount.

  Note that the feedback amount eggrfbch in the switching period is not necessarily obtained by detecting the opening degree ecvact of the exhaust gas switching valve 15 as shown in Expression (3). As shown in FIG. 6, during the switching period, the opening degree of the exhaust gas switching valve 15 changes at a constant rate with respect to time. Therefore, the following formula (4) may be used instead of using the above formula (3). In the following equation (4), the opening degree ecvcat of the exhaust gas switching valve 15 is obtained in advance as a function U (t) of time t. For example, in the example shown in FIG. 6, U (t) is a linear function with respect to time t.

eegrfbch = eegrfbs × (U (t) / 100)
+ Eegrfbt × ((100−U (t)) / 100)
... (4)
According to the method using Expression (4), the feedback amount in the switching period can be calculated according to the time without detecting the opening degree of the exhaust gas switching valve 15 by the opening degree sensor 15a.

  As described above, in the control method for the internal combustion engine according to the second embodiment, the ECU 50 determines the feedback amount in the single turbo mode and the feedback amount in the twin turbo mode as the feedback amount in the switching period. Will be changed between. In this way, the actual air amount can easily follow the target air amount, hunting can be prevented, and the actual air amount can be held near the target air amount.

[Third Embodiment]
Next, a control method for the internal combustion engine according to the third embodiment will be described.

  In the control method for the internal combustion engine according to the first and second embodiments, the ECU 50 controls the EGR valve 14 so that the actual EGR rate follows the target EGR rate except during the switching period. The EGR valve 14 is controlled so that the amount follows the target air amount.

  However, if the EGR valve 14 is controlled so that the actual air amount always follows the target air amount during the switching period, the actual EGR rate may deviate significantly from the target EGR rate. On the other hand, when the EGR valve 14 is controlled so that the actual EGR rate always follows the target EGR rate during the switching period, as described in the first embodiment, the actual air amount is excessively decreased, resulting in a torque step. May occur.

  Therefore, in the control method for the internal combustion engine according to the third embodiment, the ECU 50 determines whether or not the actual air amount is smaller than the target air amount during the switching period, and the actual air amount is smaller than the target air amount. When it is determined that the actual air amount is not equal to or smaller than the target air amount, control for causing the actual EGR rate to follow the target EGR rate is performed. On the other hand, if the ECU 50 determines that the actual air amount is smaller than the target air amount, the ECU 50 follows the target air amount without performing control for causing the actual EGR rate to follow the target EGR rate. Therefore, the EGR valve 14 is controlled to be closed.

  7 shows the opening degree of the exhaust gas switching valve 15 (exhaust gas switching valve opening degree), the opening degree of the intake air switching valve 6 (intake air switching valve opening degree), the EGR rate, the air amount, the opening degree of the EGR valve 14 (EGR valve opening degree). It is a graph which shows the change with respect to time about degree. In the graph showing the EGR rate in FIG. 7, the solid line is a graph showing the change of the actual EGR rate egr with respect to time, and the broken line is a graph showing the change of the target EGR rate egtrtrg with respect to time.

  As shown in FIG. 7, in the period Tn in the switching period, the actual EGR rate egr is larger than the target EGR rate egtrtrg. At this time, the ECU 50 controls the EGR valve 14 to the closed side in order to cause the actual EGR rate to follow the target EGR rate. On the other hand, in the period Tm in the switching period, the actual EGR rate egr is smaller than the target EGR rate egtrtrg. Accordingly, when the actual EGR rate is made to follow the target EGR rate, the EGR valve 14 should be controlled to the open side. However, since the actual air amount Gn is smaller than the target air amount Gntrg during the period Tm, if the EGR valve 14 is controlled to open, the actual air amount may decrease and a torque step may occur. There is. Therefore, at this time, the ECU 50 controls the EGR valve 14 to the closed side in order to prevent the occurrence of a torque step.

  That is, in the control method for the internal combustion engine according to the third embodiment, the ECU 50 performs control for causing the actual EGR rate to follow the target EGR rate only when the actual air amount is equal to or greater than the target air amount during the switching period. If the actual air amount is smaller than the target air amount, the EGR valve is controlled to be closed so that the actual air amount follows the target air amount. By doing so, it is possible to prevent the actual EGR rate from deviating significantly from the target EGR rate during the switching period, and to prevent occurrence of a torque step.

  Next, a control process for the internal combustion engine according to the third embodiment will be described with reference to FIG. FIG. 8 is a flowchart showing a control process of the internal combustion engine according to the third embodiment.

  In step S301, the ECU 50 determines whether or not the turbo mode is being switched. For example, the ECU 50 can determine whether or not the turbo mode is being switched by determining whether or not the control signal S15 for controlling the exhaust gas switching valve 15 to open is supplied. When it is determined that the turbo mode is not being switched (step S301: No), that is, when it is determined that the single turbo mode or the twin turbo mode is set, the ECU 50 proceeds to the process of step S310 and performs normal control. That is, control is performed so that the actual EGR rate follows the target EGR rate. In step S310, the ECU 50 returns to the control process after performing the normal control. On the other hand, if the ECU 50 determines in step S301 that the turbo mode is being switched (step S301: Yes), the process proceeds to step S302.

  In step S302, the ECU 50 calculates a target air amount Gntrg based on the fuel supply amount Qfin. The target air amount Gntrg is obtained by using a function funcA of the fuel supply amount Qfin obtained in advance by experiments or the like, for example. Thereafter, the ECU 50 proceeds to the process of step S103.

  In step S303, the ECU 50 determines the actual air amount Gn based on the detection signal from the air flow meter 21. Needless to say, the processing in step S302 and the processing in step S303 may be performed in reverse order or simultaneously. Thereafter, the ECU 50 proceeds to the process of step S304.

  In step S304, the ECU 50 determines whether or not the actual air amount Gn is smaller than the target air amount Gntrg. If the ECU 50 determines that the actual air amount Gn is smaller than the target air amount Gntrg (step S304: Yes), the ECU 50 performs control to close the EGR valve 14 by a predetermined amount (step S309), and then returns to this control process. To do. On the other hand, when the ECU 50 determines that the actual air amount Gn is equal to or greater than the target air amount Gntrg (step S304: No), the ECU 50 proceeds to the process of step S305.

  In step S305, the ECU 50 calculates a target EGR rate egrtrg. The target EGR rate egtrtrg is obtained as an appropriate value. In step S306, the ECU 50 calculates the actual EGR rate egr based on the supercharging pressure or the exhaust pressure. Needless to say, the process of step S305 and the process of step S306 may be performed in reverse order or simultaneously.

  In step S307, the ECU 50 determines whether or not the actual EGR rate egr is smaller than the target EGR rate egtrtrg. If the ECU 50 determines that the actual EGR rate egr is smaller than the target EGR rate egtrtrg (step S307: Yes), the ECU 50 performs control to open the EGR valve 14 by a predetermined amount (step S308), and then returns to this control process. To do. On the other hand, when the ECU 50 determines that the actual EGR rate egr is equal to or higher than the target EGR rate egtrtrg (step S307: No), the ECU 50 performs control to close the EGR valve 14 by a predetermined amount (step S309), and then Return control processing.

  As can be seen from the above description, in the control method for the internal combustion engine according to the third embodiment, the ECU 50 determines the actual EGR rate only when the actual air amount is equal to or greater than the target air amount during the switching period. Control to match the target EGR rate is performed. On the other hand, when the actual air amount is smaller than the target air amount during the switching period, the ECU 50 controls the EGR valve to the closed side so that the actual air amount follows the target air amount. By doing so, it is possible to prevent the actual EGR rate from deviating greatly from the target EGR rate and to prevent occurrence of a torque step.

[Fourth Embodiment]
Next, a control method for an internal combustion engine according to the fourth embodiment will be described.

  In the turbo mode switching period and before and after it, the supercharging pressure and the exhaust pressure change greatly according to the changes in the opening degree of the intake switching valve 6 and the exhaust switching valve 15, and accordingly, based on the supercharging pressure and the exhaust pressure. The calculated actual EGR rate also changes greatly. Therefore, it is difficult for the ECU 50 to accurately calculate the actual EGR rate before and after the switching period. FIG. 9 is a graph showing changes in the opening degree of the exhaust gas switching valve 15 and the exhaust pressure with respect to time. As shown in FIG. 9, the exhaust pressure decreases as the opening of the exhaust gas switching valve 15 increases.

  Therefore, in the control method for the internal combustion engine according to the fourth embodiment, the ECU 50 calculates the actual EGR rate according to the opening degrees of the intake switching valve 6 and the exhaust switching valve 15. Hereinafter, a calculation method for calculating the actual EGR rate will be described using the flowchart shown in FIG.

  First, in step S401, the ECU 50 calculates the exhaust pressure p4 based on the opening degree vnfin of the exhaust gas switching valve 15. Specifically, the exhaust pressure p4 is calculated using a function funcD1 of the opening degree vnfin of the exhaust gas switching valve 15. This function funcD1 is obtained based on the relationship between the opening degree of the exhaust gas switching valve 15 and the exhaust pressure shown in FIG. Instead of doing this, the exhaust pressure p4 may be calculated using a map obtained by interpolating the exhaust pressure values when the exhaust switching valve 15 is fully closed and fully opened at two points.

  In step S402, the ECU 50 calculates the exhaust temperature t4 based on the exhaust pressure p4. Specifically, the exhaust temperature t4 is calculated using the function funcD2 of the exhaust pressure p4 derived by using the Boyle Charles' law.

  In step S403, the ECU 50 calculates the EGR amount gegr based on the exhaust pressure p4 and the opening degree pegfin of the EGR valve 14. The EGR amount gegr is calculated by substituting the exhaust pressure p4 and the opening degree pegfin of the EGR valve 14 into a function funcD3 obtained through experiments or the like. Needless to say, the process of step S402 and the process of step S403 may be performed in reverse order or simultaneously.

  In step S404, the ECU 50 calculates the EGR gas cooling efficiency itaegr based on the exhaust gas temperature t4, the EGR amount gegr, and the temperature thw of the cooling water flowing in the EGR cooler 12. Specifically, the EGR gas cooling efficiency itaegr is calculated by substituting the exhaust temperature t4, the EGR amount gegr, and the cooling water temperature thw into a function funcD4 obtained through experiments or the like.

  In step S405, the ECU 50 calculates the EGR gas temperature tegr based on the exhaust gas temperature t4, the EGR gas cooling efficiency itaegr, and the cooling water temperature thw. Specifically, the EGR gas temperature tegr is calculated by substituting the exhaust gas temperature t4, the EGR gas cooling efficiency itaegr, and the cooling water temperature thw into a function funcD5 obtained through experiments or the like.

  In step S406, the ECU 50 calculates the intake air temperature tb based on the EGR amount gegr, the EGR gas temperature tegr, and the actual air amount Gn. Specifically, the intake air temperature tb is calculated by substituting the EGR amount gegr, the EGR gas temperature tegr, and the actual air amount Gn into a function funcD6 obtained through experiments or the like.

  In step S407, the ECU 50 calculates the cylinder inflow gas amount gcyl flowing into each of the cylinders 8Ra and 8La based on the intake air temperature tb and the supercharging pressure pb. Specifically, the cylinder inflow gas amount gcyl is calculated by substituting the intake air temperature tb and the supercharging pressure pb into the function funcD7 obtained through experiments or the like. The supercharging pressure pb is obtained by substituting the value of the supercharging pressure when the intake switching valve 6 is fully closed and fully opened by substituting the opening degree of the intake switching valve 6 into a function obtained through experiments or the like. It is calculated by using the map. In the twin turbo system, the pressure loss of the intake system and the gas charging efficiency to the cylinder greatly change due to the opening degree change of the intake switching valve 6. Therefore, by doing so, the cylinder inflow gas amount gcyl can be accurately calculated. Here, as the supercharging pressure pb, the supercharging pressure detected by the supercharging pressure sensor 9 may be used without calculating the opening degree of the intake air switching valve 6. However, when the position of the supercharging pressure sensor 9 is away from the internal combustion engine 8, the value of the supercharging pressure detected by the supercharging pressure sensor 9 actually flows into the cylinders 8La and 8Lb. It may be different from the supercharging pressure pb. Therefore, it is preferable to calculate the boost pressure pb according to the opening degree of the intake switching valve 6 because the cylinder inflow gas amount gcyl can be calculated with higher accuracy.

  In step S408, the ECU 50 calculates an actual EGR rate egr based on the cylinder inflow gas amount gcyl and the actual air amount Gn. Specifically, the actual EGR rate egr is calculated by substituting the cylinder inflow gas amount gcyl and the actual air amount Gn into a function funcD8 obtained through experiments or the like.

  As described above, in the control method for the internal combustion engine according to the fourth embodiment, the ECU 50 calculates the actual EGR rate egr based on the opening degrees of the intake switching valve 6 and the exhaust switching valve 15. By doing in this way, the cylinder inflow gas amount gcyl and the exhaust pressure can be accurately calculated throughout the single period, the switching period, and the twin period, and the actual EGR rate can be accurately calculated.

[Modification]
In the above-described embodiment, the engine system in which two superchargers are arranged in parallel has been described as an example. However, an example to which the present invention can be applied is not limited thereto, and two superchargers are provided. The present invention can also be applied to an engine system that is arranged in series and can be switched between an operation mode that operates with one supercharger and an operation mode that operates with two superchargers.

6 Intake switching valve 8 Internal combustion engine
10 Intake passage 11 Exhaust passage 15 Exhaust gas switching valve 14 EGR valve 50 ECU

Claims (6)

First and second superchargers disposed in the intake passage and the exhaust passage, and an intake switching valve and an exhaust switching valve for adjusting the amount of intake air and exhaust gas supplied to the second supercharger, A control device for an internal combustion engine, comprising: an EGR passage for recirculating EGR gas from the exhaust passage to the intake passage; and an EGR valve provided in the EGR passage,
By controlling the intake switching valve and the exhaust switching valve, a single turbo mode for operating only the first supercharger and a twin turbo mode for operating both the first and second superchargers Switching control means for switching the turbo mode between,
Target air amount setting means for setting, as a target air amount, a minimum air amount necessary to burn the fuel supply amount supplied to the internal combustion engine;
An actual air amount detecting means for detecting an actual air amount flowing into the intake passage;
EGR control means for calculating a feedback amount based on a deviation between the actual air amount and the target air amount, and setting a value obtained by correcting the basic opening by the feedback amount as the opening of the EGR valve,
The EGR control means is configured to change the feedback amount at the time of switching between the turbo modes between the feedback amount when the single turbo mode is set and the feedback amount when the twin turbo mode is set. Control device. An exhaust gas switching valve opening degree detecting means for detecting the opening degree of the exhaust gas switching valve;
2. The control device for an internal combustion engine according to claim 1, wherein the EGR control unit changes the feedback amount according to an opening degree of the exhaust gas switching valve when the turbo mode is switched.   The control apparatus for an internal combustion engine according to claim 1 or 2, wherein the EGR control means sets an upper and lower limit width of the feedback amount. An actual EGR rate calculating means for calculating an actual EGR rate when the EGR gas is recirculated from the exhaust passage to the intake passage;
A target EGR rate setting means for setting the target value of the EGR rate as the target EGR rate,
When the actual air amount is equal to or greater than the target air amount when the turbo mode is switched, the EGR control means determines the EGR valve according to a deviation between the target EGR rate and the actual EGR rate. The internal combustion engine control according to any one of claims 1 to 3, wherein when the actual air amount is smaller than the target air amount, the EGR valve is controlled to be closed. apparatus.   The control device for an internal combustion engine according to claim 4, wherein the actual EGR rate calculation means calculates the actual EGR rate according to an opening degree of the exhaust gas switching valve.   6. The control device for an internal combustion engine according to claim 5, wherein the actual EGR rate calculation means calculates the actual EGR rate according to an opening of the intake air switching valve.

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