JP2018184901A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a backflow of an EGR gas while suppressing the deviation of boost pressure from a target value.SOLUTION: A control device of an internal combustion engine comprises: an exhaust supercharger 5 having a compressor 5c and a turbine 5t having a variable nozzle 5n; an exhaust control pipe 25; an exhaust control valve 26; an EGR pipe 30, an EGR control valve 31; and an electronic control unit 50. The electronic control unit controls an opening of the variable nozzle while maintaining an opening of the exhaust control valve at full-closing so that boost pressure reaches a target value, or controls the opening of the exhaust control valve while maintaining the opening of the variable nozzle at full-opening so that the boost pressure reaches the target value, determines whether or not the EGR pipe is in a backflow state, and when it is determined that the EGR pipe is in the backflow state, controls the opening of the variable nozzle and the opening of the exhaust control valve so that the boost pressure reaches the target value, and the EGR pipe is brought into a forward flow state at middle openings, respectively.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device for an internal combustion engine.

  An exhaust supercharger having a compressor disposed in the engine intake passage, a turbine with a variable nozzle disposed in the engine exhaust passage, and an engine intake passage downstream of the compressor and an engine exhaust passage upstream of the turbine are connected to each other. And an EGR control valve disposed in the EGR, and the EGR gas reduces the opening of the variable nozzle when the EGR gas flows backward in the EGR passage from the engine intake passage toward the engine exhaust passage. An engine control device is known (see, for example, Patent Document 1). When the opening of the variable nozzle is reduced, the pressure in the engine exhaust passage upstream of the turbine, that is, the engine back pressure is increased, and thus the EGR gas is returned to the forward flow. In Patent Document 1, the opening of the variable nozzle is further reduced until the EGR gas becomes a forward flow.

JP, 2006-003614, A

  However, if the opening degree of the variable nozzle is changed, the flow rate of the exhaust gas that drives the turbine is changed, which may change the pressure in the engine intake passage downstream of the compressor, that is, the supercharging pressure. For this reason, there exists a possibility that a supercharging pressure may deviate from a target value.

  According to the present invention, an exhaust turbocharger including a compressor disposed in an engine intake passage, a turbine with a variable nozzle disposed in an engine exhaust passage, and an engine upstream of the turbine bypassing the turbine An exhaust control passage connecting the exhaust passage and the engine exhaust passage downstream of the turbine; an exhaust control valve disposed in the exhaust control passage; an engine intake passage downstream of the compressor; and an engine exhaust passage upstream of the turbine Are connected to each other, an EGR control valve disposed in the EGR passage, and the opening of the variable nozzle is opened while maintaining the opening of the exhaust control valve so that the supercharging pressure becomes a target value. An electronic device configured to control the degree of opening or the degree of opening of the exhaust control valve while maintaining the degree of opening of the variable nozzle fully open so that the supercharging pressure becomes the target value. The electronic control unit further determines whether or not the EGR passage is in a backflow state, and determines that the EGR passage is in a backflow state. The opening of the variable nozzle and the opening of the exhaust control valve are controlled at intermediate openings so that the supercharging pressure becomes the target value and the EGR passage is in a forward flow state. A control device for an internal combustion engine configured as described above is provided.

  The backflow of EGR gas can be suppressed while suppressing the supercharging pressure from deviating from the target value.

1 is an overall view of an internal combustion engine. It is a fragmentary sectional view of the 1st turbine. It is a flowchart which shows the EGR control routine of the Example by this invention. It is a figure which shows the control structure of the supercharging control of the Example by this invention. (A) It is a diagram which shows an example of the feedforward term of the opening degree of a variable nozzle, and (B) an example of the feedforward term of the opening degree of an exhaust control valve. It is a flowchart which shows the supercharging mode determination routine of the Example by this invention. It is a flowchart which shows the supercharging mode determination routine of the Example by this invention. It is a flowchart which shows the supercharging mode determination routine of the Example by this invention. It is a flowchart which shows the supercharging mode determination routine of the Example by this invention. (A) An example of the feedforward term of the opening of the variable nozzle, (B) An example of the feedforward term of the opening of the exhaust control valve, and (C) An example of the feedforward term of the opening of the exhaust bypass valve. FIG.

  Referring to FIG. 1, the internal combustion engine 1 includes an engine body 2, and the engine body 2 includes a plurality of, for example, four cylinders 3. Each cylinder 3 is provided with an electronically controlled fuel injection valve 4. In the example shown in FIG. 1, the internal combustion engine 1 is composed of a compression ignition internal combustion engine. In this case, for example, light oil is injected from the fuel injection valve 4 as fuel. In another embodiment (not shown), the internal combustion engine 1 comprises a spark ignition internal combustion engine. In this case, for example, gasoline is used as the fuel. In the embodiment according to the present invention, the internal combustion engine 1 includes two exhaust-drive superchargers 5 and 6. The first supercharger 5 includes a first compressor 5c and a first turbine 5t. The second supercharger 6 includes a second compressor 6c and a second turbine 6t.

  The cylinder 3 is connected to the outlet of the first compressor 5 c via the intake manifold 10 and the first intake pipe 11. The inlet of the first compressor 5c is connected to the outlet of the second compressor 6c through the second intake pipe 12. The inlet of the second compressor 6 c is connected to the air cleaner 14 via the third intake pipe 13. An electronically controlled throttle valve 15 and an intercooler 16 are disposed in the first intake pipe 11. The throttle valve 15 is configured to control the amount of intake gas flowing through the first intake pipe 11. The intercooler 16 is configured to cool the intake gas flowing in the first intake pipe 11. The first intake pipe 11 and the second intake pipe 12 upstream of the throttle valve 15 are connected to each other by an intake control pipe 17 that bypasses the first compressor 5c. An electronically controlled intake control valve 18 is disposed in the intake control pipe 17. The intake control valve 18 is configured to control the amount of intake gas flowing through the intake control pipe 17. In the embodiment according to the present invention, the intake control valve 18 is normally fully closed.

  The cylinder 3 is connected to the inlet of the first turbine 5t through the exhaust manifold 20 and the first exhaust pipe 21. The outlet of the first turbine 5t is connected to the inlet of the second turbine 6t via the second exhaust pipe 22. The outlet of the second turbine 6t is connected to the catalyst 24 via the third exhaust pipe 23. The first exhaust pipe 21 and the second exhaust pipe 22 are connected to each other by an exhaust control pipe 25 that bypasses the first turbine 5t. An electronically controlled exhaust control valve (ECV) 26 is disposed in the exhaust control pipe 25. The exhaust control valve 26 is configured to control the amount of exhaust gas flowing through the exhaust control pipe 25. In the embodiment according to the present invention, the second exhaust pipe 22 and the third exhaust pipe 23 are connected to each other by an exhaust bypass pipe 27 that bypasses the second turbine 6t. An electronically controlled exhaust bypass valve (EBV) 28 is disposed in the exhaust bypass pipe 27. The exhaust bypass valve 28 is configured to control the amount of exhaust gas flowing through the exhaust bypass pipe 27. In an embodiment according to the present invention, the exhaust bypass valve 28 is normally fully closed.

  In another embodiment (not shown), the second supercharger 6 is omitted. In this example, the exhaust bypass pipe 27 and the exhaust bypass valve 28 are also omitted.

  The first intake pipe downstream of the throttle valve 15 and the first exhaust pipe 21 upstream of the first turbine 5t are connected to each other by an EGR (exhaust gas recirculation) pipe 30. An electronically controlled EGR control valve 31 and an EGR cooler 32 are disposed in the EGR pipe 30. The EGR control valve 31 is configured to control the amount of EGR gas flowing through the EGR pipe 30. The EGR cooler 32 is configured to cool the EGR gas flowing in the EGR pipe 30.

  As shown in FIG. 1, in the embodiment according to the present invention, an air flow meter 40 is incorporated in the air cleaner 14. The air flow meter 40 is configured to detect the amount of fresh air. A pressure sensor 41 is attached to the first intake pipe 11 upstream of the throttle valve 15. The pressure sensor 41 is configured to detect the pressure between the throttle valve 15 and the first compressor 5c. A pressure sensor 42 is attached to the intake manifold 10. The pressure sensor 42 is configured to detect the pressure in the intake manifold 10. A pressure sensor 43 is attached to the exhaust manifold 20. The pressure sensor 43 is configured to detect the pressure in the exhaust manifold 20. A pressure sensor 44 is attached to the first exhaust pipe 21. The pressure sensor 44 is configured to detect the pressure in the first exhaust pipe 21.

  Further, an air-fuel ratio sensor 45 is attached to the third exhaust pipe 23. The air-fuel ratio sensor 45 is configured to detect the air-fuel ratio. Further, a temperature sensor 46 is attached to the EGR pipe 30 between the first intake pipe 11 and the EGR cooler 32. The temperature sensor 46 is configured to detect the temperature of the EGR gas in the EGR pipe 30 between the first intake pipe 11 and the EGR cooler 32. A temperature sensor 47 is attached to the EGR pipe 30 between the first exhaust pipe 21 and the EGR cooler 32. The temperature sensor 47 is configured to detect the temperature of the EGR gas in the EGR pipe 30 between the first exhaust pipe 21 and the EGR cooler 32.

  The first turbine 5t is composed of a turbine provided with a variable nozzle (VN) 5n. As shown in FIG. 2, the variable nozzle 5 n includes a plurality of vanes 72 disposed in an exhaust gas passage 71 that faces the turbine impeller 70 of the first turbine 5 t. Each of the vanes 72 can be rotated around a corresponding rotation shaft 73 and controlled to the same angular position by a common actuator 74. When the angular position of the vane 72 is changed, the flow passage area of the nozzle 75 formed between the adjacent vanes 72 is changed, thereby changing the supercharging pressure. For example, when the vane 72 is rotated from the position indicated by the solid line in FIG. 2 to the position indicated by the broken line, the flow path area of the nozzle 75 is reduced. As a result, the flow rate of the exhaust gas flowing through the nozzle 75 is increased, and therefore the supercharging pressure is increased.

  The electronic control unit 50 is composed of a digital computer, and is connected to each other by a bidirectional bus 51. A ROM (read only memory) 52, a RAM (random access memory) 53, a CPU (microprocessor) 54, an input port 55, and an output port 56. It comprises. The output voltages of the air flow meter 40, the pressure sensors 41, 42, 43, 44, the air-fuel ratio sensor 45, and the temperature sensors 46, 47 are input to the input port 55 via the corresponding A / D converters 57, respectively. Further, a load sensor 60 that generates an output voltage proportional to the amount of depression of the accelerator pedal 59 is connected to the accelerator pedal 59, and the output voltage of the load sensor 60 is input to the input port 55 via the corresponding AD converter 57. The Further, a crank angle sensor 61 for detecting the crank angle CA is connected to the input port 55. The CPU 54 calculates the engine speed based on the output pulse from the crank angle sensor 61. On the other hand, the output ports 56 are respectively connected to the fuel injection valve 4, the throttle valve 15, the intake control valve 18, the exhaust control valve 26, the exhaust bypass valve 28, the EGR control valve 31, and the variable nozzle 5n through corresponding drive circuits 58. Each is connected to an actuator 74 (FIG. 2).

  Next, the EGR control of the embodiment according to the present invention will be described. FIG. 3 shows a routine for executing the EGR control of the embodiment according to the present invention. The routine shown in FIG. 3 is executed by interruption every predetermined time. Referring to FIG. 3, in step 100, it is determined whether or not the EGR control valve 31 is open. When the EGR control valve 31 is open, the routine proceeds to step 101, where it is judged if the EGR gas amount QEGR flowing through the EGR pipe 30 is greater than zero. In the embodiment according to the present invention, it is determined that QEGR> 0 when the temperature of the EGR gas detected by the temperature sensor 46 is lower than the temperature of the exhaust gas detected by the temperature sensor 47, otherwise QEGR ≦ It is determined that it is zero. In another embodiment (not shown), the EGR gas amount QEGR is estimated using a calculation model. In one example, the EGR gas amount QEGR is calculated by subtracting the fresh air amount detected by the air flow meter 40 from the in-cylinder gas amount calculated based on the pressure and temperature of the intake pipe downstream of the throttle valve 15. . When it is determined that QEGR> 0, the routine proceeds to step 102 where it is determined that the EGR pipe 30 is in a forward flow state. In the subsequent step 103, normal control of the EGR control valve 31 is performed. That is, for example, the opening degree of the EGR control valve 31 is controlled so that the amount of EGR gas supplied to the engine becomes a target amount determined according to the engine operating state (for example, engine load and engine speed).

  On the other hand, when QEGR ≦ 0 at step 101, the routine proceeds to step 104 where it is determined that the EGR pipe 30 is in the backflow state. In the subsequent step 105, the EGR control valve 31 is fully closed.

  On the other hand, when the EGR control valve 31 is fully closed in step 100, the routine proceeds to step 106, where it is determined whether or not the differential pressure dP before and after the EGR control valve 31 is larger than a predetermined adaptation value dPX. This differential pressure dP is, for example, of the pressure in the exhaust manifold 20, the pressure in the first exhaust pipe 21, and the pressure in the EGR pipe 30 on the first exhaust pipe 21 side of the EGR control valve 31. From one of the pressure in the intake manifold 10, the pressure in the first intake pipe 11 downstream of the throttle valve 15, and the pressure in the EGR pipe 30 on the first intake pipe 11 side from the EGR control valve 31. Is calculated by subtracting one of The conforming value dPX is a differential pressure necessary for the EGR gas to flow well from the first exhaust pipe 21 toward the first intake pipe 11, and is 2 kPa in one example. Another example is 5 kPa. When it is determined that dP> dPX, the routine proceeds to step 104 where it is determined that the EGR pipe 30 is in the backflow state, and at the subsequent step 105, the EGR control valve 31 is fully closed. On the other hand, when it is determined that dP ≦ dPX, the routine proceeds to step 102 where it is determined that the EGR pipe 30 is in the forward flow state, and the normal control of the EGR control valve 31 is performed at the subsequent step 103.

  As a result, when it is determined that the EGR pipe 30 is in the forward flow state, a good EGR gas supply operation is ensured, and when it is determined that the EGR pipe 30 is in the reverse flow state, the EGR gas passes through the EGR pipe 30. The flow from the first intake pipe 11 toward the first exhaust pipe 21, that is, the backflow of EGR gas is prevented. In another embodiment (not shown), whether the EGR pipe 30 is in a forward flow state according to the differential pressure dP before and after the EGR control valve 31 regardless of whether the EGR control valve 31 is open or not. It is determined whether or not a reverse flow state exists.

  Next, the supercharging control of the embodiment according to the present invention will be described. FIG. 4 shows a control structure of supercharging control according to the embodiment of the present invention. Referring to FIG. 4, the supercharging mode is determined as indicated by block B1. The supercharging mode will be described later. Next, a feed forward (F / F) term of the opening degree of the variable nozzle (VN) 5n and a feed forward (F / F) term of the opening degree of the exhaust control valve (ECV) 26 are respectively calculated.

  FIG. 5A shows an example of the feedforward term of the opening of the variable nozzle 5n (VN), and FIG. 5B shows an example of the feedforward term of the opening of the exhaust control valve (ECV) 26. Indicated. In the example shown in FIGS. 5 (A) and 5 (B), the engine operating state region determined by the fuel injection amount Q and the engine speed Ne representing the engine load is set to the first region by a predetermined division line L1. It is partitioned into R1 and second region R2. The first region R1 is located on the low load / low rotation side. The second region R2 is located on the high load / high rotation side.

  As shown in FIG. 5 (A), the feed forward term of the opening degree of the variable nozzle (VN) 5n is high load / high from the low load / low rotation side when the engine operating state belongs to the first region R1. It becomes larger toward the rotation side, and is fully opened when the engine operation state belongs to the second region R2. On the other hand, as shown in FIG. 5B, the feedforward term of the opening degree of the exhaust control valve (ECV) 26 is fully closed when the engine operating state belongs to the first region R1, and the engine operating state is When belonging to the second region R2, it becomes larger from the low load / low rotation side toward the high load / high rotation side. In the embodiment according to the present invention, the feedforward term of the opening of the variable nozzle 5n (VN) and the feedforward term of the opening of the exhaust control valve (ECV) 26 are such that the amount of NOx discharged from the engine body 2 is the target NOx. And the amount of NOx per unit output torque (kg / kwh) is the minimum opening, as a function of the engine operating state, in the form of maps shown in FIGS. 5 (A) and 5 (B). It is stored in the ROM 52 in advance. In another embodiment (not shown), the feed forward term of the opening of the variable nozzle 5n (VN) and the feed forward term of the opening of the exhaust control valve (ECV) 26 are calculated using a calculation model.

  Referring to FIG. 4 again, when the supercharging pressure feedback control by the variable nozzle (VN) 5n is performed in the determined supercharging mode, the feedback (F / B) term of the opening degree of the variable nozzle (VN) 5n. Is calculated. Alternatively, when the supercharging pressure feedback control by the exhaust control valve (ECV) 26 is performed in the determined supercharging mode, the feedback (F / B) term of the opening degree of the exhaust control valve (ECV) 26 is calculated. The In the embodiment according to the present invention, the supercharging pressure is represented by the pressure between the throttle valve 15 and the first compressor 5 c detected by the pressure sensor 41. The feedback (F / B) term of the opening degree of the variable nozzle (VN) 5n and the feedback (F / B) term of the opening degree of the exhaust control valve (ECV) 26 are respectively used for setting the supercharging pressure to a target value. In the embodiment according to the present invention, it is calculated based on the pressure detected by the pressure sensor 41. In another embodiment (not shown), the boost pressure is represented by the pressure in the intake manifold 10 detected by the pressure sensor 42. In yet another embodiment (not shown), the supercharging pressure is represented by the pressure in the first exhaust 21 detected by the pressure sensor 44. Note that the target value of the supercharging pressure is stored in advance in the ROM 52 as a function of the engine operating state, for example.

  On the other hand, the restriction compensation opening degree of the variable nozzle (VN) 5n and the restriction compensation opening degree of the exhaust control valve (ECV) 26, which are determined from restrictions on the back pressure, the expansion ratio, the supercharger rotation speed, and the like, are calculated. Next, the feed forward (F / F) term of the opening degree of the variable nozzle (VN) 5n, or the feed forward (F / F) term of the opening degree of the variable nozzle (VN) 5n and the opening of the variable nozzle (VN) 5n. The smaller one of the total feedback (F / B) term and the restriction compensation opening of the variable nozzle (VN) 5n is output as a command value for the opening of the variable nozzle (VN) 5n, and the exhaust control is performed. The feed forward (F / F) term of the opening degree of the valve (ECV) 26 or the feed forward (F / F) term of the opening degree of the exhaust control valve (ECV) 26 and the opening degree of the exhaust control valve (ECV) 26 The smaller of the feedback (F / B) terms and the restriction compensation opening of the exhaust control valve (ECV) 26 is output as a command value for the opening of the exhaust control valve (ECV) 26.

  Next, the operation for determining the supercharging mode of the embodiment according to the present invention will be described. FIGS. 6 to 9 show a routine for executing the supercharging mode determining operation of the embodiment according to the present invention. The routines shown in FIGS. 6 to 9 are executed by interruption every predetermined set time. Referring to FIGS. 6 to 9, in step 200, it is determined whether or not feedback control (F / B) of the supercharging pressure is permitted. In the embodiment according to the present invention, it is determined that the supercharging pressure feedback control is permitted when the following two conditions are satisfied, and otherwise, it is determined that the supercharging pressure feedback control is not permitted. Is done. That is, the first condition is that the pressure between the throttle valve 15 and the first compressor 5c detected by the pressure sensor 41, that is, the supercharging pressure is equal to or higher than a predetermined set value. This is because in order to accurately perform the feedback control, it is necessary that a significant change appears in the supercharging pressure when the opening of the variable nozzle 5n, the exhaust control valve 26, or the like is changed. In another embodiment (not shown), the first condition is that the fuel injection amount Q is equal to or greater than a predetermined set amount and the engine speed Ne is equal to or greater than a predetermined set value. On the other hand, the second condition is that elements necessary for feedback control such as the variable nozzle 5n, the exhaust control valve 26, and the pressure sensor 41 are functioning normally.

  When it is determined at step 200 that feedback control of the supercharging pressure is permitted, the routine proceeds to step 201 where it is determined whether or not the EGR pipe 30 is in a forward flow state. In the embodiment according to the present invention, whether or not the EGR pipe 30 is in the forward flow state is determined in the routine shown in FIG. When it is determined that the EGR pipe 30 is in the forward flow state, the routine proceeds to step 202, where feedback control (F / B) or feedforward control (F / F) by the variable nozzle (VN) 5n was performed in the previous routine. It is determined whether or not. If it is determined in the previous routine that the feedback control or feedforward control by the variable nozzle 5n has been performed, then the routine proceeds to step 203, where whether or not the command value of the variable nozzle (VN) 5n in the previous routine is fully open. Determined. When it is determined that the command value of the variable nozzle 5n in the previous routine is fully open, the routine then proceeds to step 204 where the supercharging mode is shifted to the feedback control (F / B) mode by the exhaust control valve (ECV) 26. . On the other hand, when it is determined that the command value of the variable nozzle 5n in the previous routine is not fully open, the routine proceeds to step 205 where the supercharging mode is maintained in the feedback control (F / B) mode with the variable nozzle (VN) 5n. Is done.

  On the other hand, when it is determined in step 202 that the feedback control (F / B) and the feedforward control (F / F) by the variable nozzle (VN) 5n are not performed in the previous routine, the process then proceeds to step 206. Then, it is determined whether or not the command value of the exhaust control valve (ECV) 26 in the previous routine is fully closed. If it is determined that the command value of the exhaust control valve 26 in the previous routine is fully closed, then the routine proceeds to step 207, where the supercharging mode is shifted to the feedback control (F / B) mode with the variable nozzle (VN) 5n. The On the other hand, when it is determined that the command value of the exhaust control valve 26 in the previous routine is not fully closed, the routine proceeds to step 208 where the supercharging mode is feedback control (F / B) by the exhaust control valve (ECV) 26. Maintained in mode.

  That is, when it is determined that the feedback control of the supercharging pressure is permitted, it is determined that the EGR pipe 30 is in the forward flow state, and the engine operating state belongs to the first region R1 (FIG. 5), The supercharging mode is determined as the feedback control (F / B) mode using the variable nozzle (VN) 5n. In the feedback control (F / B) mode using the variable nozzle (VN) 5n, the opening degree of the variable nozzle 5n is feedback controlled while the exhaust control valve 26 is kept fully closed so that the supercharging pressure becomes the target value. The In this case, the command value for the opening of the variable nozzle 5n is calculated using the feedforward term and the feedback term, and the command value for the opening of the exhaust control valve 26 is calculated using the feedforward term without using the feedback term. The

  Further, when it is determined that the feedback control of the supercharging pressure is permitted, it is determined that the EGR pipe 30 is in the forward flow state, and the engine operation state belongs to the second region R2 (FIG. 5), The supercharging mode is determined as the feedback control (F / B) mode by the exhaust control valve (ECV) 26. In the feedback control (F / B) mode by the exhaust control valve (ECV) 26, the opening degree of the exhaust control valve 26 is feedback controlled while the variable nozzle 5n is kept fully open so that the supercharging pressure becomes a target value. The In this case, the command value for the opening of the exhaust control valve 26 is calculated using the feedforward term and the feedback term, and the command value for the opening of the variable nozzle 5n is calculated using the feedforward term without using the feedback term. The

  On the other hand, when it is determined in step 201 that the EGR pipe 30 is not in the forward flow state, the process proceeds to step 209, where the supercharging mode is determined as the first backflow avoidance mode. That is, when it is determined that the feedback control of the supercharging pressure is permitted and it is determined that the EGR pipe 30 is in the backflow state, the supercharging mode is determined to be the first backflow avoidance mode. In the first backflow avoidance mode, the opening degree of the variable nozzle 5n and the opening degree of the exhaust control valve 26 are respectively opened so that the supercharging pressure becomes the target value and the EGR pipe 30 is in the forward flow state. Degree (opening larger than fully closed and smaller than fully opened). In the embodiment according to the present invention, the opening degree of the variable nozzle 5n is set to a predetermined intermediate opening degree, and the opening degree of the exhaust control valve 26 is feedback-controlled at the intermediate opening degree. In this case, the command value for the opening of the variable nozzle 5n is calculated using a feedforward term different from that shown in FIG. 5A without using a feedback term. On the other hand, the command value for the opening degree of the exhaust control valve 26 is calculated using a feedforward term and a feedback term different from those shown in FIG. In this case, the feedforward term of the opening of the variable nozzle 5n and the feedforward term of the opening of the exhaust control valve 26 are set so that the supercharging pressure becomes a target value and the EGR pipe 30 flows forward during steady operation. It is for making it in a state, and is stored in the ROM 52 in advance as a function of the engine operating state.

  In another embodiment (not shown) according to the present invention, in the first backflow avoidance mode, the opening degree of the variable nozzle 5n is feedback controlled at the intermediate opening degree while the opening degree of the exhaust control valve 26 is set to the intermediate opening degree. . However, if it does in this way, there exists a possibility that supercharging control may diverge. That is, when the opening degree of the variable nozzle 5n is reduced, for example, the new nozzle is less likely to pass through the variable nozzle 5n, and the supercharging pressure may decrease. This phenomenon is different from the normal relationship between the variable nozzle 5n and the supercharging pressure, and as a result, the feedback control may diverge. In the embodiment according to the present invention, the opening degree of the exhaust control valve 26 is feedback-controlled while the opening degree of the variable nozzle 5n is fixed, so that stable supercharging control can be obtained.

  In the first backflow avoidance mode, for example, the opening degree of the variable nozzle 5n is reduced, thereby increasing the engine back pressure or the pressure in the first exhaust pipe 21. As a result, the EGR pipe 30 is prevented from being in a reverse flow state. However, when the opening degree of the variable nozzle 5n is reduced, the flow rate of the exhaust gas flowing into the first turbine 5t is increased, and the supercharging pressure may be higher than the target value. Therefore, the opening degree of the exhaust control valve 26 is increased so that the supercharging pressure becomes the target value. Alternatively, for example, the opening degree of the exhaust control valve 26 is reduced, thereby increasing the pressure in the first exhaust pipe 21 and preventing the EGR pipe 30 from being in a reverse flow state. In this case, since the amount of exhaust gas flowing into the first turbine 5t increases, the supercharging pressure may be higher than the target value. Therefore, the opening of the variable nozzle 5n is increased so that the supercharging pressure becomes the target value. Therefore, the first backflow avoidance mode can suppress the backflow of EGR gas while suppressing the supercharging pressure from deviating from the target value. As a result, good drivability can be ensured.

  On the other hand, when it is determined at step 200 that the feedback control (F / B) of the supercharging pressure is not permitted, the routine proceeds to step 210 where it is determined whether or not the EGR pipe 30 is in a forward flow state. When it is determined that the EGR pipe 30 is in the forward flow state, the routine proceeds to step 211 where the supercharging mode is determined as the feed forward control (F / F) mode. In the feedforward control (F / F) mode, the command value for the opening of the variable nozzle 5n is calculated using the feedforward term without using the feedback term, and the command value for the opening of the exhaust control valve 26 is fed back. It is calculated using the feedforward term without using the term.

  On the other hand, when it is determined in step 210 that the EGR pipe 30 is not in the forward flow state, the process proceeds to step 212 and the supercharging mode is determined as the second backflow avoidance mode. That is, when it is determined that the feedback control of the supercharging pressure is not permitted and it is determined that the EGR pipe 30 is in the backflow state, the supercharging mode is determined to be the second backflow avoidance mode. In the second backflow avoidance mode, the command value for the opening of the variable nozzle 5n is calculated using the same feedforward term as in the first backflow avoidance mode without using the feedback term. On the other hand, the command value for the opening degree of the exhaust control valve 26 is calculated using the same feedforward term as in the first backflow avoidance mode without using the feedback term.

  Therefore, conceptually expressed, the electronic control unit 50 controls the opening degree of the variable nozzle 5n while keeping the opening degree of the exhaust control valve 26 fully closed so that the supercharging pressure becomes a target value, or The opening degree of the exhaust control valve 26 is controlled while the opening degree of the variable nozzle 5n is kept fully open so that the supercharging pressure becomes a target value, and the EGR passage is in a backflow state. And when it is determined that the EGR passage is in the reverse flow state, the opening degree of the variable nozzle 5n and the EGR passage so that the supercharging pressure becomes the target value and the EGR passage is in the forward flow state. The exhaust control valve 26 is configured to control the opening degree of each at an intermediate opening degree.

  In the embodiments described so far, the supercharging pressure is controlled by the variable nozzle 5 n and the exhaust control valve 26. In another embodiment according to the present invention, the supercharging pressure is controlled by the variable nozzle 5n, the exhaust control valve 26, and the exhaust bypass valve 28.

  FIG. 10A shows an example of the feed forward term of the opening of the variable nozzle 5n (VN), and FIG. 10B shows an example of the feed forward term of the opening of the exhaust control valve (ECV) 26. 10 (C) shows an example of a feedforward term of the opening degree of the exhaust bypass valve (EBV) 28, respectively. In the example shown in FIGS. 10 (A), 10 (B), and 10 (C), an engine operating state region determined by the fuel injection amount Q representing the engine load and the engine speed Ne is determined in advance. L1 and L2 define the first region R1, the second region R2, and the third region R3. The first dividing line L1 is located on the low load / low rotation side, and the second dividing line L2 is located on the high load / high rotation side. The first region R1 is demarcated by the first demarcation line L1, and is located on the low load / low rotation side. The third region R3 is partitioned by the second partition line L2, and is located on the high load / high rotation side. The second region R2 is partitioned by the first partition line L1 and the second partition line L2, and is located between the first region R1 and the third region R3.

  As shown in FIG. 10 (A), the feed forward term of the opening of the variable nozzle (VN) 5n is high load / high from the low load / low rotation side when the engine operating state belongs to the first region R1. When the engine operating state belongs to the second region R2 and the third region R3, the engine is fully opened. On the other hand, as shown in FIG. 10B, the feedforward term of the opening degree of the exhaust control valve (ECV) 26 is fully closed when the engine operating state belongs to the first region R1, and the engine operating state is When it belongs to the second region R2, it increases from the low load / low rotation side to the high load / high rotation side, and when the engine operating state belongs to the third region R3, it is fully opened. As shown in FIG. 10C, the feedforward term of the opening degree of the exhaust bypass valve (EBV) 28 is fully closed when the engine operating state belongs to the first region R1 and the second region R2. When the engine operating state belongs to the third region R3, the engine operating state increases from the low load / low rotation side toward the high load / high rotation side. In this way, the supercharging pressure can be accurately controlled over a wider engine operating state region. Other configurations and operations of another embodiment according to the present invention are the same as those of the above-described embodiment according to the present invention, and thus description thereof is omitted.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Engine main body 5 1st supercharger 5c 1st compressor 5n Variable nozzle 5t 1st turbine 10 Intake manifold 11, 12, 13 Intake pipe 20 Exhaust manifold 21, 22, 23 Exhaust pipe 25 Exhaust control pipe 26 Exhaust control valve 44 Pressure sensor 30 EGR pipe 31 EGR control valve

Claims (1)

An exhaust supercharger comprising a compressor disposed in the engine intake passage and a turbine with a variable nozzle disposed in the engine exhaust passage;
An exhaust control passage that bypasses the turbine and connects the engine exhaust passage upstream of the turbine and the engine exhaust passage downstream of the turbine;
An exhaust control valve disposed in the exhaust control passage;
An EGR passage connecting the engine intake passage downstream of the compressor and the engine exhaust passage upstream of the turbine;
An EGR control valve disposed in the EGR passage;
The opening of the exhaust control valve is controlled to be fully closed so that the supercharging pressure becomes a target value, or the opening of the variable nozzle is controlled, or the supercharging pressure is set to the target value. An electronic control unit configured to control the opening of the exhaust control valve while maintaining the opening of the variable nozzle fully open;
A control device for an internal combustion engine comprising:
The electronic control unit further includes
Determining whether the EGR passage is in a reverse flow state;
When it is determined that the EGR passage is in the reverse flow state, the opening of the variable nozzle and the exhaust control valve are set so that the supercharging pressure becomes the target value and the EGR passage is in the forward flow state. Control the opening of each at an intermediate opening,
An internal combustion engine control apparatus configured as described above.

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