JP2013060914A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine including a variable nozzle turbocharger, in which the generation of a turbocharger overspeed and a turbocharger surge is inhibited even when a driving environment is changed.SOLUTION: The device includes: a controller 501 for calculating an opening command value of a variable nozzle so that a plurality of intake system quantity of state (boost pressure and EGR rate) of the internal combustion engine become respective target value; a restriction model 502 for outputting at least any of predicted values of a turbine speed and a pressure ratio P3/P1, with an opening detection value of the variable nozzle, an air volume detection value and an atmospheric pressure detection value as an input parameter; a determination part 503 for determining that the predicted value output from the restriction model 502 has exceeded a predetermined threshold; and a guard part 504 for providing a closed guard value to the opening command value of the variable nozzle calculated by the controller 501, when the condition is determined to be met in the determination part 503.

Description

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

  Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-256724, in a control device for an exhaust drive supercharger capable of variably controlling supercharging efficiency, a turbo in which intake air in an intake passage flows backward to the supercharger side A technique for suppressing the occurrence of a surge is known. In this apparatus, when the engine speed of the internal combustion engine decreases, the supercharging efficiency of the exhaust drive supercharger is limited to the low efficiency side. As a result, an increase in the pressure difference can be suppressed when the engine rotational speed is reduced when the pressure difference between the intake air suction side and the discharge side of the turbocharger increases, thereby suppressing the occurrence of turbo surge due to the pressure difference. Is done.

JP 2005-256724 A

  Although the conventional technology described above suppresses turbo surge that occurs when the engine speed decreases, there are other situations where the risk of occurrence of surge increases. Specifically, when operating in a highland that is in a low-pressure environment, the turbo rotational speed for obtaining an equal supercharging pressure increases as compared with the normal atmospheric pressure due to the low air density. For this reason, for example, in model-based control that calculates a variable nozzle opening, an EGR valve opening, a throttle opening, etc. as an operation amount of an actuator for realizing a target supercharging pressure, a target EGR rate, etc. The variable nozzle opening at that time is operated in the closing direction more than the normal atmospheric pressure, and there is a concern that the turbine rotational speed will be over-rotated or that turbo surge will occur. In this regard, in the above-described conventional technology, no consideration has been given to the risk of occurrence of turbo overspeed or turbo surge accompanying such environmental changes, and there is still room for improvement.

  The present invention has been made to solve the above-described problems. In an internal combustion engine having a variable nozzle turbocharger, even if the operating environment changes, the turbo overspeed and the turbo surge can be prevented. It is an object of the present invention to provide a control device for an internal combustion engine that can suppress generation.

In order to achieve the above object, a first invention is a control device for an internal combustion engine that operates a plurality of actuators including a turbocharger including a variable nozzle to operate an internal combustion engine.
A controller for calculating an operation amount of the actuator including an opening command value of the variable nozzle so that a plurality of intake system state quantities of the internal combustion engine become respective target values;
Using the variable nozzle opening detection value, the air amount detection value taken into the internal combustion engine, and the atmospheric pressure detection value as input parameters, the turbine rotation speed of the turbocharger and the compressor downstream of the turbocharger A model that outputs a predicted value of at least one of the pressure ratios to the upstream;
A determination unit that determines that a predicted value output from the model exceeds a predetermined threshold;
A guard unit that provides a closing guard value for the opening command value of the variable nozzle calculated by the controller when the determination unit determines that the condition is satisfied;
It is characterized by having.

According to a second invention, in the first invention,
The guard unit is characterized in that the previous opening command value of the variable nozzle is set as the guard value for the closing limit.

According to a third invention, in the first invention,
The guard unit is characterized in that the opening command value of the variable nozzle opening when the predicted value reaches a predetermined threshold is set as the guard value for the closing limit.

  According to the first invention, the model uses at least one of the turbine rotation speed and the pressure ratio to the upstream downstream of the compressor using the variable nozzle opening detection value, the air amount detection value, and the atmospheric pressure detection value as input parameters. Output the predicted value. When the predicted value exceeds a predetermined threshold value, a closing limit guard value is provided for the opening command value of the variable nozzle calculated by the controller. For this reason, according to the present invention, it is possible to effectively suppress the occurrence of turbo overspeed and turbo surge even in a low pressure environment such as highland.

  According to the second invention, the previous value of the opening command value of the variable nozzle is set as the closed guard value in a period in which the predicted value calculated by the model exceeds a predetermined threshold. According to the present invention, since the variable nozzle opening is not operated in the closing direction during the period when the predicted value exceeds the predetermined threshold, the occurrence of turbine overspeed and intake backflow (turbo surge) to the compressor is prevented. It can be effectively suppressed.

  According to the second invention, in the period when the predicted value calculated by the model exceeds the predetermined threshold, the opening command value of the variable nozzle at the time when the predicted value becomes the predetermined threshold is a guard for closing. Set as a value. Therefore, according to the present invention, since the variable nozzle opening is not operated in the closing direction during the period when the predicted value exceeds the predetermined threshold, the occurrence of turbo overspeed and turbo surge is effectively suppressed. can do.

It is a figure for demonstrating schematic structure of the internal combustion engine system as Embodiment 1 of this invention. It is a figure which shows the outline | summary of a general model base control system. 4 is a timing chart showing vehicle speed, target supercharging pressure, variable nozzle opening, and turbo rotation speed when an acceleration request is issued to a vehicle equipped with a general model-based control system. It is a figure for demonstrating the generation | occurrence | production principle of a turbo surge. It is a figure which shows the outline | summary of the model base control system of Embodiment 1 of this invention. 4 is a timing chart showing vehicle speed, target supercharging pressure, variable nozzle opening, and turbo rotation speed when an acceleration request is issued to a vehicle equipped with the model-based control system of Embodiment 1 of the present invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining a schematic configuration of an internal combustion engine system as an embodiment of the present invention. As shown in FIG. 1, the system of the present embodiment includes a four-cycle diesel engine 10 having a plurality of cylinders (four cylinders in FIG. 1). It is assumed that the diesel engine 10 is mounted on a vehicle and used as a power source.

  Hereinafter, although this embodiment demonstrates the case where this invention is applied to control of a diesel engine (compression ignition internal combustion engine), this invention is not limited to a diesel engine, A gasoline engine (spark ignition internal combustion engine) It can be applied to control of various other internal combustion engines.

  Each cylinder of the diesel engine 10 is provided with an injector 12 for directly injecting fuel into the cylinder. The injectors 12 of each cylinder are connected to a common common rail 14. Fuel in a fuel tank (not shown) is pressurized to a predetermined fuel pressure by a supply pump 16, stored in the common rail 14, and supplied from the common rail 14 to each injector 12. Further, the exhaust passage 18 of the diesel engine 10 is branched by an exhaust manifold 20 and connected to an exhaust port (not shown) of each cylinder.

  The diesel engine 10 includes a variable nozzle type turbocharger 24. The turbocharger 24 includes a turbine 24a that is operated by the exhaust energy of the exhaust gas, and a compressor 24b that is integrally connected to the turbine 24a and is rotationally driven by the exhaust energy of the exhaust gas that is input to the turbine 24a. ing. Further, the turbocharger 24 has a variable nozzle 24c for adjusting the flow rate of the exhaust gas supplied to the turbine 24a.

  The variable nozzle 24c can be opened and closed by an actuator (for example, an electric motor) not shown. When the opening of the variable nozzle 24c is reduced, the inlet area of the turbine 24a is reduced, and the flow rate of the exhaust gas blown to the turbine 24a can be increased. As a result, the rotational speeds of the compressor 24b and the turbine 24a (hereinafter referred to as “turbo rotational speed”) are increased, so that the supercharging pressure can be increased. Conversely, when the VN opening is increased, the inlet area of the turbine 24a is increased, and the flow rate of the exhaust gas blown to the turbine 24a is decreased. As a result, the turbo rotation speed decreases, so that the supercharging pressure can be reduced.

  The turbine 24 a of the turbocharger 24 is disposed in the middle of the exhaust passage 18. A post-treatment device 26 for purifying exhaust gas is provided in the exhaust passage 18 on the downstream side of the turbine 24a. As the post-processing device 26, for example, an oxidation catalyst, a NOx catalyst, a DPF (Diesel Particulate Filter), a DPNR (Diesel Particulate-NOx-Reduction system), or the like can be used.

  An air cleaner 30 is provided near the inlet of the intake passage 28 of the diesel engine 10. The air sucked through the air cleaner 30 is compressed by the compressor 24 b of the turbocharger 24 and then cooled by the intercooler 32. The intake air that has passed through the intercooler 32 is distributed by an intake manifold 34 to intake ports (not shown) of each cylinder.

  An intake throttle valve (diesel throttle) 36 is installed between the intercooler 32 and the intake manifold 34 in the intake passage 28. The intake throttle valve 36 is configured to be electrically opened and closed by an actuator (not shown). An air flow meter 52 for detecting the amount of intake air is installed in the intake passage 28 near the downstream of the air cleaner 30.

  One end of an EGR (Exhaust Gas Recirculation) passage 40 is connected to the vicinity of the intake manifold 34 in the intake passage 28. The other end of the EGR passage 40 is connected to the vicinity of the exhaust manifold 20 in the exhaust passage 18. In the present system, a part of the exhaust gas (burned gas) can be recirculated to the intake passage 28 through the EGR passage 40, that is, external EGR can be performed.

  An EGR cooler 42 for cooling the EGR gas is provided in the middle of the EGR passage 40. An EGR valve 44 is provided downstream of the EGR cooler 42 in the EGR passage 40. By changing the opening degree of the EGR valve 44, the amount of exhaust gas passing through the EGR passage 40, that is, the EGR amount can be adjusted.

  The system according to the present embodiment includes an ECU (Electronic Control Unit) 50 as shown in FIG. In addition to the air flow meter 52 described above, an atmospheric pressure sensor 54 for detecting atmospheric pressure, and an accelerator position sensor (not shown) for detecting the amount of depression of the accelerator pedal (accelerator opening) are provided at the input portion of the ECU 50. Various sensors for controlling the diesel engine 10 such as a crank angle sensor (not shown) for detecting the crank angle of the diesel engine 10 are connected. In addition to the injector 12, the intake throttle valve 36, the EGR valve 44, and the turbocharger 24, various actuators for controlling the diesel engine 10 are connected to the output unit of the ECU 50. The ECU 50 drives each device in accordance with a predetermined program based on various types of input information.

[One Operation of Embodiment]
Next, the operation of the first embodiment will be described. As described above, the internal combustion engine 10 according to the present embodiment controls the internal combustion engine 10 in addition to the injector 12, the intake throttle valve 36, the EGR valve 44, and the variable nozzle 24c as actuators for controlling the operation thereof. Various actuators are provided. The control device according to the present embodiment controls the internal combustion engine by so-called model-based control. The control state is estimated using a lot of predictions by a plant model, and the operation amounts of the various actuators described above are determined.

  FIG. 2 is a diagram showing an outline of a general model-based control system. The model base control system shown in FIG. 2 is realized as part of the function of the ECU 50 shown in FIG. The model-based control system includes a controller 501 that calculates operation amounts of a plurality of actuators such as the EGR valve 44, the intake throttle valve 36, and the variable nozzle 24c included in the internal combustion engine 10. The controller 501 takes in target value information of various state quantities including the target boost pressure and the target EGR rate. Based on the acquired information, the controller 501 uses the EGR valve opening, which is the operation amount of the EGR valve 44, and the throttle opening, which is the operation amount of the intake throttle valve 36, as the optimum actuator operation amount for realizing the target value. And the variable nozzle opening, which is the operation amount of the variable nozzle 24c, is calculated and output to the internal combustion engine 10.

  When such a controller 501 is used, the internal combustion engine 10 is operated as shown in FIG. 3, for example. FIG. 3 shows (a) vehicle speed, (b) target boost pressure, (c) variable nozzle opening, and (d) when an acceleration request is issued to a vehicle equipped with a general model-based control system. It is a timing chart which shows turbo rotation speed, respectively. In this figure, a solid line indicates a timing chart in a normal environment (lowland), and a broken line indicates a timing chart in a low-pressure environment (highland).

  As shown in (a) and (b) of this figure, when the vehicle accelerates and the vehicle speed increases, the target supercharging pressure increases accordingly. As described above, the controller 501 calculates the variable nozzle opening for realizing the target supercharging pressure. For this reason, in the examples shown in (c) and (d) in the figure, as the target supercharging pressure increases, the opening of the variable nozzle is operated to the closing limit (closing limit), thereby increasing the turbo rotation speed. doing.

  Here, in a low pressure environment such as a highland, the air density is relatively low as compared to a normal environment such as a lowland. For this reason, as shown in (c) in the figure, the variable nozzle opening in the low pressure environment (highland) is operated to the opening on the closing side than in the normal environment (lowland). It will be higher than normal. Therefore, in such a low-pressure environment (high altitude), as shown in (d) in the figure, there is a risk of so-called turbo overspeed in which the turbo speed exceeds the system limit.

  The same can be said for the occurrence of turbosurge. FIG. 4 is a diagram for explaining the principle of occurrence of turbo surge. As shown in this figure, when the pressure on the intake upstream side (intake suction side) of the compressor 24b (≈atmospheric pressure) is P1, and the pressure on the intake downstream side (intake discharge side) of the compressor 24b is P3, the pressure P1 is low. Decreases as the environment (highlands) is reached. For this reason, if the turbo rotation speed increases and the pressure ratio (P3 / P1) of the pressure P3 to the pressure P1 becomes too large, the so-called turbo surge that causes the compressor 24b to idle may occur due to the reverse flow of the intake air. There is.

  Therefore, in the system of the present embodiment, the model-based control system shown in FIG. 5 is used to predict the occurrence of turbo overspeed or turbo surge, and the variable nozzle calculated by the controller 501 prior to this is predicted. A predetermined limit is provided for the opening command value. FIG. 5 is a diagram showing an overview of the model-based control system according to the first embodiment of the present invention. In the system shown in FIG. 5, elements common to the system shown in FIG. 2 described above are denoted by the same reference numerals, and detailed description thereof is omitted or simplified.

  The model base control system shown in FIG. 5 is realized as a part of the function of the ECU 50 shown in FIG. 1. Specifically, the controller 501, the constraint model 502, the determination unit 503, and the guard unit 504 are implemented. And. The controller 501 uses the target boost pressure and target EGR rate, which are target values of the state quantity of the internal combustion engine 10, as input parameters, and calculates the operation amount of each actuator for realizing these target values. The constraint model 502 calculates a predicted value of the current turbo speed and pressure ratio P3 / P1 using the variable nozzle opening detection value, the air amount detection value taken into the internal combustion engine 10 and the atmospheric pressure detection value as input parameters. To do. These input parameters are, for example, from the operation amount of the actuator that operates the variable nozzle 24c if the opening detection value of the variable nozzle is detected, from the detection value of the air flow meter 52 if it is the air amount detection value, or from the atmospheric pressure. If it is a detection value, it can each be calculated from the detection value of the atmospheric pressure sensor 54.

  Here, turbo overspeed and turbo surge are likely to occur during transient operation such as acceleration. For this reason, the calculation using the constraint model 502 needs to consider a transient change. Specifically, among the input parameters to the constraint model 502, the atmospheric pressure detection value does not change transiently, but the opening detection value and the air amount detection value of the variable nozzle change transiently. For this reason, the pressure ratio P3 / P1 and the turbo rotation speed, which are model outputs, are items that change transiently. Therefore, in the constraint model 502 of the present embodiment, as shown in the following formula (1), the pressure ratio P3 / P1, the turbo rotation speed, the variable nozzle opening, and the delay in the transient of the air amount are considered, The model configuration is such that the current pressure ratio P3 / P1 and turbo rotational speed can be calculated using these past histories.

In the above equation (1), “u ₁ ” is a variable nozzle opening detection value, “u ₂ ” is an air amount detection value, “u ₃ ” is an atmospheric pressure detection value, and “θ “ _1-8 ” is a model coefficient, and “y” is a pressure ratio P3 / P1 or turbo rotation speed as a model output. As described above, in the above equation (1), the past history is used for the variable nozzle opening detection value “u ₁ ”, the air amount detection value “u ₂ ”, and the model output “y”. The above equation (1) is an example of the model configuration of the constraint model 502. Depending on the model accuracy and the identification man-hour, the model configuration may be further traced back to the past history.

  The determination unit 503 compares the turbo rotation speed or the pressure ratio P3 / P1 output from the constraint model 502 described above with a predetermined threshold value, and turns on the guard flag when these model output values exceed the predetermined threshold value. And As the threshold value, a preset value is used as the turbo rotation speed or pressure ratio P3 / P1 at which turbo overspeed or turbo surge occurs in the internal combustion engine 10.

  The guard unit 504 determines whether or not the opening command value of the variable nozzle has shifted in the closing direction from the previous opening command value, and whether or not the guard flag is ON in the determination unit 503. When the opening command value of the variable nozzle changes in the closing direction from the previous opening command value and the guard flag is ON, the previous opening command value is used as the closing guard value. The opening operation in the closing direction of the variable nozzle 24c is limited.

  FIG. 6 shows (a) vehicle speed, (b) target supercharging pressure, and (c) variable nozzle opening when an acceleration request is issued to a vehicle equipped with such a model-based control system according to an embodiment of the present invention. It is a timing chart which shows a degree and (d) turbo rotation speed, respectively. In FIG. 6, a solid line indicates a timing chart in a normal environment (lowland), and a broken line indicates a timing chart in a low-pressure environment (highland).

  As shown in this figure, when the vehicle is accelerated and the target supercharging pressure is increased, the variable nozzle opening is operated in the closing direction, thereby increasing the turbo rotation speed. Then, as shown in (d) in the figure, when the turbo rotation speed or the pressure ratio P3 / P1 reaches a predetermined threshold value in a low pressure environment, the operation in the closing direction of the supercharging nozzle opening is restricted. For this reason, even in a low-pressure environment such as a high altitude, it is possible to suppress a situation in which the turbine speed or the pressure ratio P3 / P1 rises exceeding a threshold value, so that it is possible to effectively generate turbo overspeed or turbo surge. It becomes possible to deter.

[One Specific Process of Embodiment]
Next, specific processing of the first embodiment will be described with reference to FIG. FIG. 7 is a flowchart of a routine executed in the first embodiment of the present invention. In the routine shown in FIG. 7, first, it is determined whether or not the ignition switch (IG) of the internal combustion engine 10 is turned on (step 100). As a result, when IG is not turned ON, the process returns to the beginning of this routine, and the process of step 100 is executed again. On the other hand, if it is determined in this step 100 that the IG is ON, the process proceeds to the next step, and it is determined whether or not the model base control can be executed (step 102). As a result, if it is determined that the model-based control is not in an executable state, the process returns to step 100.

  On the other hand, if it is determined in step 102 that the model base control is in an executable state, the model base control is immediately started. Specifically, first, in the constraint model 502, the pressure ratio P3 / P1 and the turbo rotation speed are calculated (step 200). Next, the determination unit 503 receives the pressure ratio P3 / P1 calculated in step 200 and the turbo rotation number, and determines whether or not these model output values exceed a predetermined threshold (step 202). . As a result, if the model output value of the constraint model 502 does not exceed the predetermined threshold value, it is determined that there is no possibility of turbo overspeed or turbo surge, and the process returns to step 200 described above. The model output value calculation is performed again.

  On the other hand, if the model output value of the constraint model 502 exceeds a predetermined threshold value in step 202, it is determined that turbo overspeed or turbo surge may occur, the process proceeds to the next step, and the guard The flag is turned on (step 204).

  In parallel with the processing in steps 200 to 204, the controller 501 calculates a variable nozzle opening command value for achieving the target boost pressure (step 104). Next, the opening command value of the variable nozzle calculated by the controller 501 is sent to the guard unit 504 (step 106). Next, the guard unit 504 determines whether or not the current opening command value of the variable nozzle is closer to the closing direction than the previous opening command value (step 108). As a result, when it is determined that the current variable nozzle opening command value is the opening in the closing direction with respect to the previous command value, the process proceeds to the next step, and it is determined whether or not the guard flag is ON. (Step 110). As a result, when it is determined that the guard flag is ON, the process proceeds to the next step, and the operation in the closing direction of the variable nozzle opening is restricted (step 112). Specifically, in the guard unit 504, the previous opening command value is set as the closed guard value. As a result, the variable nozzle opening calculated by the controller 501 is output as a final opening command value after the guard of the closing limit is applied in the guard unit 504. After the process of step 112, the processes after step 104 are repeatedly executed.

  On the other hand, when it is determined in step 108 that the calculated opening command value of the current variable nozzle is not the opening in the closing direction with respect to the previous opening command value, or in step 110, the guard flag Is determined not to be ON, it is determined that there is no risk of turbo overspeed or turbo surge, and the variable nozzle opening calculated by the controller 501 is used as it is as the opening command value. 24c is operated. Next, it is determined whether or not the boost pressure of the internal combustion engine 10 has reached the target boost pressure (step 114). As a result, if the supercharging pressure has not yet reached the target supercharging pressure, the processing from step 104 onward is executed again, and if the supercharging pressure has reached the target supercharging pressure, this routine Ends promptly.

  As described above, according to the system of the first embodiment, occurrence of turbo overspeed or turbo surge is predicted based on the pressure ratio P3 / P1 calculated by the constraint model 502 or the turbo speed. When these occurrences are predicted, a closed limit guard is provided for the variable nozzle opening. As a result, an increase in the turbo rotational speed can be suppressed, so that the occurrence of turbo overspeed or turbo surge can be effectively suppressed.

  By the way, in the system of the first embodiment described above, in determining whether or not to provide a closed limit guard value, both the turbo rotational speed and the compression ratio P3 / P1 calculated in the constraint model 502 are used. The determination may be made using only one of the model output values.

  In the system of the first embodiment described above, the model configuration shown in the above equation (1) is adopted in the controller 501, but the model configuration that can be adopted in the controller 501 is not limited to this. That is, as the optimum actuator operation amount for realizing the target value of the state quantity of the internal combustion engine 10, as long as the model configuration calculates at least the opening of the variable nozzle, another known model configuration is used. Also good.

  In the system of the first embodiment described above, the previous opening command value of the variable nozzle is set as the guard value. However, the guard value to be set is not limited to this, and when the guard flag is turned ON. The opening command value of the variable nozzle may be set as the guard value, or the opening on the open side may be set as the guard value in anticipation of safety.

  In the first embodiment described above, the controller 501 is the “controller” in the first invention, the constraint model 502 is the “model” in the first invention, and the determination unit 503 is the first invention. The guard unit 504 corresponds to the “determination unit” and corresponds to the “guard unit” in the first aspect of the present invention. Further, when the ECU 50 executes the process of step 200, the calculation performed by the “controller” in the first invention executes the process of step 102, thereby the “model” in the first invention. When the determination performed by the “determination unit” in the first aspect of the invention performs the process of step 112, the calculation performed by step S202 executes the process of step 112. The calculations performed by the “part” are realized.

10 Diesel engine (engine)
18 Exhaust passage 24 Variable nozzle type turbocharger 24a Turbine 24b Compressor 24c Variable nozzle 28 Intake passage 36 Intake throttle valve 40 EGR passage 44 EGR valve 50 ECU (Electronic Control Unit)
54 Atmospheric pressure sensor 501 Controller 502 Restriction model 503 Determination unit 504 Guard unit

Claims (3)

A control device for an internal combustion engine that operates a plurality of actuators including a turbocharger including a variable nozzle to operate an internal combustion engine,
A controller for calculating an operation amount of the actuator including an opening command value of the variable nozzle so that a plurality of intake system state quantities of the internal combustion engine become respective target values;
Using the variable nozzle opening detection value, the air amount detection value taken into the internal combustion engine, and the atmospheric pressure detection value as input parameters, the turbine rotation speed of the turbocharger and the compressor downstream of the turbocharger A model that outputs a predicted value of at least one of the pressure ratios to the upstream;
A determination unit that determines that a predicted value output from the model exceeds a predetermined threshold;
A guard unit that provides a closing guard value for the opening command value of the variable nozzle calculated by the controller when the determination unit determines that the condition is satisfied;
A control device for an internal combustion engine, comprising:   2. The control device for an internal combustion engine according to claim 1, wherein the guard unit sets a previous opening command value of the variable nozzle as the guard value for the closing limit.   2. The internal combustion engine according to claim 1, wherein the guard unit sets the opening command value of the variable nozzle opening when the predicted value reaches a predetermined threshold as the guard value for the closing limit. Control device.

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