JP2020076391A - Control device of engine, control method of engine, and engine - Google Patents

Abstract

To further prevent generation of surge sound.SOLUTION: An engine includes a turbocharger including a turbine disposed in an exhaust passage and rotated by flow of an exhaust gas, and a compressor disposed on an intake passage for supercharging intake air by torque of the turbine, an EGR device including an EGR passage connecting the exhaust passage at a downstream side with respect to the turbine and the intake passage at an upstream side with respect to the compressor, and an EGR valve disposed on the EGR passage for opening and closing the EGR passage, and recycling a part of the exhaust gas in the exhaust passage to the intake passage, a throttle valve disposed in the intake passage at a downstream side with respect to the compressor, and opening and closing the intake passage, and a special valve disposed at an upstream side with respect to a connection portion of the EGR passage and the intake passage for opening and closing the intake passage. A control device controls the special valve to a closed state for a prescribed time in a prescribed state before a state of generating surge sound from an intake port, and controls the EGR valve to an opened state, when the EGR valve is in a closed state (S101-S107).SELECTED DRAWING: Figure 4

Description

  The present disclosure relates to an engine control device, an engine control method, and an engine, and particularly to an engine control device including an EGR device, an engine control method, and an engine.

  Conventionally, in a turbocharged engine, when the throttle valve is suddenly closed, the intake pressure of the intake air of the compressor of the turbocharger or the rotational inertia of the compressor wheel causes a temporary increase in the intake pressure of the intake air. As a result, the compressed intake air flows back into the turbocharger, and a surge noise is generated.

  As a measure against this surge noise, there is a technique disclosed in Patent Document 1. The technique of Patent Document 1 determines the deceleration of a vehicle in a turbocharged engine equipped with an EGR device having an EGR passage communicating between an intake passage and an exhaust passage, and an EGR valve provided in the EGR passage. And a deceleration determining means that opens the EGR valve to flow a part of the intake air in the intake passage to the exhaust passage through the EGR passage when the deceleration determining means determines that the vehicle is decelerating. It is equipped with and. This prevents the occurrence of surging that causes surge noise.

JP, 2004-360525, A

  However, in the case of the technique of Patent Document 1, the connection between the EGR passage and the exhaust passage is between the outlet of the combustion chamber of the engine and the turbine of the turbocharger. For this reason, since the pressure of the exhaust gas at the connection portion is high, it is difficult for the pressure of the intake air that has temporarily increased rapidly to escape to the exhaust passage via the EGR passage. As a result, it is difficult to suppress the generation of surge noise.

  The present disclosure has been made to solve the above problems, and an object thereof is to provide an engine control device, an engine control method, and an engine capable of better preventing generation of surge noise. It is to be.

  The engine in the engine control device according to this disclosure is provided in an exhaust passage through which exhaust gas from the combustion chamber flows, and is provided in a turbine that rotates by the flow of the exhaust gas and an intake passage that supplies intake air to the combustion chamber. A turbocharger including a compressor for supercharging intake air, an EGR passage connecting an exhaust passage downstream of the turbine and an intake passage upstream of the compressor, and an EGR valve provided in the EGR passage for opening and closing the EGR passage An EGR device for recirculating a part of the exhaust gas in the exhaust passage to the intake passage, a throttle valve provided in the intake passage downstream of the compressor for opening and closing the intake passage, and an EGR passage and the intake passage. A special valve that is provided upstream of the connection portion and that opens and closes the intake passage is provided. The control device controls the special valve to be in the closed state for a predetermined period of time when the predetermined state before the state in which the surge noise is generated from the intake port which is the inlet of the intake passage is brought into the predetermined state. If the EGR valve is closed, the EGR valve is controlled to open.

  Preferably, the predetermined state is a state before the pressure in the intake passage upstream of the compressor rises to a pressure at which surge noise is generated.

  More preferably, the control device sets a combination of the first condition that the throttle valve is controlled to be in the closed state, the pressure ratio of the pressure at the outlet of the compressor to the atmospheric pressure, and the flow rate of the intake air in the intake passage upstream of the compressor. When the second condition that the surge noise is easily generated is satisfied, the predetermined state is determined.

  More preferably, the control device determines that the first condition is satisfied when the operation amount of the accelerator pedal becomes zero.

Preferably, the predetermined period is a predetermined constant period.
An engine in an engine control method according to another aspect of the present disclosure is provided in an exhaust passage through which exhaust gas from a combustion chamber flows, and is provided in a turbine that rotates by the flow of exhaust gas and an intake passage that supplies intake air to the combustion chamber. A turbocharger including a compressor that supercharges intake air by the rotational force of the turbine, an EGR passage that connects an exhaust passage downstream of the turbine and an intake passage upstream of the compressor, and an EGR passage are provided in the EGR passage. An EGR device that includes an EGR valve that opens and closes and recirculates a part of the exhaust gas in the exhaust passage to the intake passage, a throttle valve that is provided in the intake passage downstream of the compressor and that opens and closes the intake passage, and an EGR passage. A special valve that is provided upstream of the connection with the intake passage and opens and closes the intake passage is provided. The control method includes a step of controlling the special valve to be in a closed state for a predetermined period when the engine control device is in a predetermined state before the surge sound is generated from the intake port which is the inlet of the intake passage. And, when the EGR valve is in the closed state when the predetermined state is reached, the step of controlling the EGR valve to be in the open state is included.

  An engine according to still another aspect of the present disclosure is provided in an exhaust passage through which exhaust gas from a combustion chamber flows, and is provided in a turbine that rotates by the flow of the exhaust gas and an intake passage that supplies intake air to the combustion chamber. A turbocharger including a compressor for supercharging intake air, an EGR passage connecting an exhaust passage downstream of the turbine and an intake passage upstream of the compressor, and an EGR valve provided in the EGR passage for opening and closing the EGR passage An EGR device for recirculating a part of the exhaust gas in the exhaust passage to the intake passage, a throttle valve provided in the intake passage downstream of the compressor for opening and closing the intake passage, and an EGR passage and the intake passage. A special valve that is provided upstream of the connection portion and that opens and closes the intake passage is provided. The special valve is closed for a predetermined period when it is in a predetermined state before the surge noise is generated from the intake port which is the inlet of the intake passage. The EGR valve is opened when it is in the closed state when the predetermined state is reached.

  According to this disclosure, the pressure of the intake air in the intake passage can be released to the exhaust passage via the EGR passage, so that the pressure in the intake passage can be prevented from rapidly increasing. As a result, it is possible to provide an engine control device, an engine control method, and an engine capable of better preventing generation of surge noise.

It is a figure showing an outline of an example of composition of a diesel engine according to an embodiment of this indication. It is a figure for explaining generation of a surge sound. It is a figure which shows the relationship between the pressure ratio of supercharging pressure with respect to atmospheric pressure at the time of generating a surge sound, and the amount of intake air. It is a flow chart which shows a flow of surge noise prevention processing in this embodiment. It is a 1st figure for demonstrating the effect in this Embodiment. It is a 2nd figure for demonstrating the effect in this Embodiment.

  Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts will be denoted by the same reference characters and description thereof will not be repeated.

[Overall engine configuration]
FIG. 1 is a schematic configuration diagram of a diesel engine 1 shown as an example of the engine according to the embodiment of the present disclosure. Referring to FIG. 1, diesel engine 1 is mounted on a vehicle. The diesel engine 1 has a plurality of cylinders 28. Although the number of the cylinders 28 is not shown in the diesel engine 1 in FIG. 1, the number of the cylinders 28 may be four or other numbers.

  The diesel engine 1 includes an air cleaner 12, a turbocharger 14, an intercooler 20, a throttle valve 24, an intake valve 29, an exhaust valve 30, a piston 32, an injector 31, an exhaust filter 34, and an EGR device 44. An air flow meter 25, a pressure sensor 26, an atmospheric pressure sensor 27, and an accelerator opening sensor 59.

  The air flow meter 25 is provided on the outlet side of the air cleaner of the intake passage 13 and detects the flow rate (intake air amount) Qin of the intake air (air sucked from the outside, fresh air) flowing in the intake passage 13. The air flow meter 25 transmits a signal indicating the detected intake air amount Qin to the ECU 60.

  The air cleaner 12 is provided in the intake passage 13 and cleans the intake air by adsorbing impurities contained in the air sucked from the intake port 10.

  The turbocharger 14 includes a compressor 16 and a turbine 18. The compressor 16 is provided in the intake passage 13. The turbine 18 is provided in the exhaust passage 36. The compressor 16 and the turbine 18 are mechanically connected to each other and rotate integrally. The turbine 18 is rotated by receiving the exhaust gas, and the intake air is pressurized by the compressor 16 which is rotated in conjunction with the turbine 18.

  The pressure sensor 26 is provided on the outlet side of the compressor 16 and detects the pressure on the outlet side of the compressor 16 (hereinafter also referred to as “supercharging pressure”). The pressure sensor 26 transmits a signal indicating the detected pressure on the outlet side of the compressor 16 to the ECU 60.

  The atmospheric pressure sensor 27 is provided at a location where the atmospheric pressure of the vehicle can be measured, and detects the atmospheric pressure. The atmospheric pressure sensor 27 transmits a signal indicating the detected atmospheric pressure to the ECU 60.

  The intercooler 20 is provided between the turbocharger 14 (compressor 16) and the cylinder 28. The intercooler 20 cools the intake air pressurized by the compressor 16. The intercooler 20 may be air-cooled or water-cooled.

  The throttle valve 24 is provided upstream of the cylinder 28 and adjusts the intake air amount. The opening of the throttle valve 24 is adjusted by the ECU 60.

  Each cylinder 28 has one or more intake ports. The intake valve 29 is provided in the intake port and opens and closes the intake port according to the stroke of the operation cycle of the diesel engine 1. Each cylinder 28 has one or more exhaust ports. The exhaust valve 30 is provided in the exhaust port and opens and closes the exhaust port according to the stroke of the operation cycle of the diesel engine 1. The piston 32 constitutes a combustion chamber 33 together with the cylinder 28, the intake valve 29 and the exhaust valve 30.

  The piston 32 sucks intake air from the intake port by being pushed down by the operation of a crank (not shown). The piston 32 is pushed up by the operation of the crank to compress the inhaled air. The injector 31 is controlled by the ECU 60 to inject fuel into the intake air of the compressed combustion chamber 33. The piston 32 is pushed down by the expansion force generated by the combustion of the injected fuel, and transmits power to the crank. The piston 32 is pushed up by the operation of the crank, so that the exhaust gas after combustion in the combustion chamber 33 is pushed out of the combustion chamber 33 from the exhaust port.

  The turbine 18 of the turbocharger 14 is provided downstream of the exhaust port, and receives exhaust gas whose flow velocity has increased due to the reduced cross-sectional area of the exhaust passage 36, and rotates.

  The exhaust filter 34 is provided downstream of the turbocharger 14 (turbine 18) and traps particulate matter in the exhaust gas. A catalyst device that purifies the exhaust gas using a catalyst may be combined with the exhaust filter 34.

  The EGR device 44 includes an EGR passage 46, an EGR cooler 48, and an EGR valve 50. The EGR passage 46 connects the exhaust passage 36 downstream of the exhaust filter 34 (that is, downstream of the turbine 18 of the turbocharger 14) to the intake passage 13 upstream of the compressor 16 of the turbocharger 14, and connects the exhaust filter 34. A part of the exhaust gas is recirculated from the downstream side of the exhaust gas to the upstream side of the compressor 16. The EGR cooler 48 is provided in the EGR passage 46 and cools the exhaust gas recirculated to the intake passage 13 through the EGR passage 46. The EGR valve 50 is provided in the EGR passage 46, and the opening degree of the EGR valve 50 is adjusted by the ECU 60. By using the EGR device 44, effective NOx reduction can be realized.

  The accelerator opening sensor 59 detects the amount of depression of the accelerator pedal as the accelerator opening. The accelerator opening sensor 59 transmits a signal indicating the detected accelerator opening to the ECU 60.

  The diesel engine 1 further includes an ECU (Electronic Control Unit) 60. The ECU 60 includes a CPU (Central Processing Unit), a storage device, an input / output buffer, etc. (none of which are shown). The ECU 60 detects the intake air amount detected by the air flow meter 25, the pressure at the outlet of the compressor 16 detected by the pressure sensor 26, the atmospheric pressure detected by the atmospheric pressure sensor 27, and the accelerator opening sensor 59. Each signal indicating the accelerator opening etc. is input. Then, the ECU 60 controls each device of the diesel engine 1 based on each of these signals. As an example, the ECU 60 controls the opening degree of various valves, the fuel injection timing, the fuel injection amount, and the like so that the diesel engine 1 is operated at a desired operating point according to the traveling state of the vehicle. Further, the ECU 60 executes the control described later for preventing a surge sound generated when the throttle valve 24 is suddenly closed. The various controls (processes) executed by the ECU 60 are not limited to the processes by software, and may be processed by dedicated hardware (electronic circuit).

[Control to prevent surge noise]
FIG. 2 is a diagram for explaining generation of a surge sound. Referring to FIG. 2, in the diesel engine 1 shown in FIG. 1, as shown in the second graph, the throttle valve 24 is suddenly opened at time t1 because the accelerator opening suddenly becomes 0. When closed, the intake pressure of the intake air of the compressor 16 of the turbocharger 14 or the rotational inertia of the compressor wheel causes a temporary increase in the intake pressure of the intake air. Therefore, as shown in the third graph, the pressure ratio of the supercharging pressure to the atmospheric pressure increases. As a result, the compressed intake air flows back to the turbocharger 14, and a surge noise is generated during the period in which the intake air amount is hunting in the fourth graph.

  FIG. 3 is a diagram showing the relationship between the pressure ratio of the supercharging pressure to the atmospheric pressure and the amount of intake air when a surge sound is generated. Referring to FIG. 3, the operating point is a point specified by the pressure ratio and the intake air amount on the graph shown in FIG. At point P (corresponding to time t1 in FIG. 2), when the accelerator pedal is turned off, the intake air amount decreases and the operating point moves to the left on the solid line W.

  The surge line L is a boundary line in which the air compressed by the compressor 16 of the turbocharger 14 flows backward and passes through the compressor 16 in response to the closing of the throttle valve 24 to generate a surge sound. .. When the operating point reaches the surge region on the left side of the surge line L, a surge noise is generated as indicated by the solid line W hunting.

  Therefore, in this embodiment, the special valve 55 that opens and closes the intake passage 13 is provided upstream of the connecting portion between the EGR passage 46 and the intake passage 13. Then, the ECU 60 controls the special valve 55 to be in the closed state for a predetermined period when the predetermined state before the state in which the surge sound is generated from the intake port 10 which is the inlet of the intake passage 13 is brought into the predetermined state. If the EGR valve 50 is closed at this time, the EGR valve 50 is controlled to be open.

  As a result, the pressure of the intake air in the intake passage 13 that has rapidly risen can be released to the exhaust passage 36 via the EGR passage 46, so that the pressure in the intake passage 13 can be prevented from rapidly increasing. As a result, it is possible to better prevent the generation of surge noise.

  FIG. 4 is a flow chart showing the flow of surge noise prevention processing in this embodiment. This surge noise prevention processing is called from the main processing and is executed by the CPU of the ECU 60. Referring to FIG. 4, ECU 60 determines whether throttle valve 24 is controlled to be closed by setting the accelerator opening to 0 or the like (step (hereinafter referred to as “S”) 101. ).

  When it is determined that the throttle valve 24 is controlled to be closed (YES in S101), the ECU 60 identifies the atmospheric pressure based on the signal from the atmospheric pressure sensor 27, and the supercharging pressure based on the signal from the pressure sensor 26. Is specified, the intake air amount is specified based on the signal from the air flow meter 25, the pressure ratio of the supercharging pressure to the atmospheric pressure is calculated, and the graph of the pressure ratio and the intake air amount as shown in FIG. The operating point is specified, and it is determined whether the operating point has entered the surge region (S102).

  When it is determined that the operating point has entered the surge region (YES in S102), the ECU 60 controls the special valve 55 to be in the closed state (S103). The EGR valve 50 is controlled so as to adjust the flow rate of the exhaust gas flowing from the exhaust passage 36 to the intake passage 13 in accordance with the operating conditions and running conditions of the diesel engine 1, but the ECU 60 closes the EGR valve 50. If it is in the open state, the open state is controlled (S104). As a result, the pressure in the intake passage 13 that has suddenly increased can be released to the EGR passage 46 and the exhaust passage 36. As a result, generation of surge noise can be prevented.

  It should be noted that since the exhaust gas is normally flowed to the EGR cooler 48, the EGR passage 46, and the EGR valve 50, particulate matter such as soot adheres to the EGR cooler 48, the EGR valve 50, and the EGR valve 50. The particulate matter is cleaned by being blown off to the exhaust passage 36 side. Further, since the intake air passes through the EGR device 44 (particularly, the EGR cooler 48), a silencing effect can be expected, which can contribute to the reduction of surge noise.

  After S104, when it is determined that the throttle valve 24 is not controlled to be closed (NO in S101), and that the operating point between the pressure ratio and the intake air amount is not within the surge region (NO in S102). When the determination is made, the ECU 60 determines whether or not a predetermined second has passed since the special valve 55 was closed (S105).

  When it is determined that a predetermined number of seconds have passed since the special valve 55 was closed (YES in S105), the ECU 60 controls the special valve 55 to be in the open state (S106) and returns to the condition before the EGR valve 50 is closed. (That is, a state in which the EGR valve 50 is controlled so as to adjust the flow rate of the exhaust gas flowing from the exhaust passage 36 to the intake passage 13 in accordance with the operating conditions and running conditions of the diesel engine 1) (S107). When it is determined that the predetermined time has not elapsed (NO in S105), and after S107, the ECU 60 returns the process to be executed to the calling process of this process.

  5 and 6 are first and second diagrams, respectively, for explaining the effect of this embodiment. By executing the control for preventing the surge sound shown in FIG. 4 with reference to FIGS. 5 and 6, the intake air is compared with the case of FIG. 2 and FIG. 3 in which this control is not executed. The amount of hunting has stopped. This prevents the generation of surge noise.

[Modification]
(1) The above-described embodiment can be regarded as a disclosure of a control device for an engine (for example, the diesel engine 1) such as the ECU 60. Further, it can be regarded as disclosure of an engine control method and disclosure of the engine itself.

  (2) In the above-described embodiment, the engine is the diesel engine 1. However, the engine is not limited to this, and the engine may be another engine such as a gasoline engine as long as the engine includes a turbocharger and an EGR device.

  (3) The surge line L in the above-described embodiment may be located on the right side of that shown in FIG. Thereby, the surge noise can be prevented more reliably. Further, the surge line L may be located on the left side of that shown in FIG. As a result, the frequency of control for preventing the generation of the surge noise can be reduced when the generation of the surge noise can be permitted to some extent.

  (4) In the above-described embodiment, as shown in S104 of FIG. 4, the EGR valve 50 is fully opened in the control for preventing the generation of surge noise. However, the present invention is not limited to this, and if the EGR valve 50 is opened, for example, it may be opened at a predetermined rate (for example, 80%).

  (5) In the above-described embodiment, as shown in S105 and S106 of FIG. 4, after the special valve 55 is closed, the special valve 55 is opened after a lapse of a predetermined time. .. However, the present invention is not limited to this, and the period in which the special valve 55 is opened may be any appropriate period, for example, operating conditions and running conditions of the diesel engine 1 (for example, atmospheric pressure, supercharging pressure with respect to atmospheric pressure). Pressure ratio, intake air amount), and may be set such that the larger the intake air amount is, the longer the period is, or the larger the pressure ratio is, the longer the period is. May be set.

  (6) In the above-described embodiment, as shown in S101 to S107 of FIG. 4, the EGR valve 50 is controlled at the same timing as the special valve 55. However, the timing for controlling the EGR valve 50 is not limited to this, and may be different from the timing for controlling the special valve 55. For example, the special valve 55 may be closed after a predetermined time from when the EGR valve 50 is opened. In this case, it is preferable to open the EGR valve 50 a predetermined number of seconds before the condition of S102 is expected to hold. Further, the EGR valve 50 may be returned to the original state after a predetermined period in which the special valve 55 is opened, or the EGR valve 50 is returned to the original state before the predetermined period in which the special valve 55 is closed. You may do it.

[effect]
(1) The diesel engine 1 is provided in the exhaust passage 36 through which exhaust gas from the combustion chamber 33 flows, and is provided in the turbine 18 that rotates by the flow of exhaust gas and the intake passage 13 that supplies intake air to the combustion chamber 33. Of the turbocharger 14 that includes a compressor 16 that supercharges intake air by the rotational force of the EGR passage 46, an EGR passage 46 that connects the exhaust passage 36 downstream of the turbine 18 and the intake passage 13 upstream of the compressor 16, and an EGR passage 46. And an EGR valve 50 that opens and closes the EGR passage 46 and is provided in the intake passage 13 downstream of the compressor 16 and an EGR device 44 that recirculates a part of the exhaust gas in the exhaust passage 36 to the intake passage 13. A throttle valve 24 that opens and closes the intake passage 13 and a special valve 55 that is provided upstream of the connection between the EGR passage 46 and the intake passage 13 and that opens and closes the intake passage 13 are provided. The ECU 60 sets a predetermined state before the surge noise is generated from the intake port 10 which is the inlet of the intake passage 13 (for example, the operating point between the pressure ratio of the supercharging pressure to the atmospheric pressure and the intake air amount is in the surge region). When the EGR valve 50 is closed, the special valve 55 is controlled to be closed for a predetermined period. If the EGR valve 50 is closed, the EGR valve 50 is controlled to be open.

  As a result, the pressure of the intake air in the intake passage 13 can be released to the exhaust passage 36 via the EGR passage 46, so that the pressure in the intake passage 13 can be prevented from rapidly increasing. As a result, it is possible to better prevent the generation of surge noise.

  (2) The above-mentioned predetermined state is a state before the pressure in the intake passage 13 upstream of the compressor 16 rises to a pressure at which surge noise is generated. Accordingly, it is possible to prevent the surge sound from being generated before the surge sound is generated.

  (3) The ECU 60 determines that the combination of the first condition that the throttle valve 24 is controlled to be in the closed state and the pressure ratio of the supercharging pressure to the atmospheric pressure and the intake air amount falls within a surge region where a surge noise is likely to occur. If the above second condition is satisfied, it is determined that the above-mentioned predetermined state has been achieved. As a result, the control for preventing the generation of the surge sound can be accurately executed.

  (4) The ECU 60 determines that the above-mentioned first condition is satisfied when the accelerator opening, which is the operation amount of the accelerator pedal, becomes zero. As a result, it is possible to accurately execute the control for preventing the generation of the surge sound.

  (5) The above-mentioned predetermined period is a predetermined fixed period. This can simplify the control for preventing the generation of surge noise.

  The embodiments disclosed this time are also planned to be implemented in appropriate combination. The embodiments disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the present disclosure is shown not by the above description of the embodiments but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

  1 diesel engine, 10 intake port, 12 air cleaner, 13 intake passage, 14 turbocharger, 16 compressor, 18 turbine, 20 intercooler, 24 throttle valve, 25 air flow meter, 26 pressure sensor, 27 atmospheric pressure sensor, 28 cylinder, 29 Intake valve, 30 exhaust valve, 31 injector, 32 piston, 33 combustion chamber, 34 exhaust filter, 36 exhaust passage, 44 EGR device, 46 EGR passage, 48 EGR cooler, 50 EGR valve, 55 special valve, 59 accelerator opening sensor , 60 ECU.

Claims (7)

An engine controller,
The engine is
A turbine that is provided in an exhaust passage through which exhaust gas from the combustion chamber flows, rotates by the flow of the exhaust gas, and a compressor that is provided in an intake passage that supplies intake air to the combustion chamber and that supercharges intake air by the rotational force of the turbine are provided. Including a turbocharger,
An EGR passage that connects an exhaust passage downstream of the turbine and an intake passage upstream of the compressor, and an EGR valve that is provided in the EGR passage and opens and closes the EGR passage are included. An EGR device for returning to the intake passage,
A throttle valve provided in the intake passage downstream of the compressor, for opening and closing the intake passage;
A special valve that is provided upstream of the connection between the EGR passage and the intake passage and opens and closes the intake passage,
The control device is
When a predetermined state before a state in which a surge noise is generated from the intake port that is the inlet of the intake passage is reached, the special valve is controlled to be in the closed state for a predetermined period,
An engine control device that controls the EGR valve to open when the EGR valve is closed when the predetermined state is reached.   The engine control device according to claim 1, wherein the predetermined state is a state before the pressure in the intake passage upstream of the compressor rises to a pressure at which a surge noise is generated.   The control device sets a combination of a first condition that the throttle valve is controlled to be in a closed state, a pressure ratio of pressure at the outlet of the compressor to atmospheric pressure, and a flow rate of intake air in an intake passage upstream of the compressor. The engine control device according to claim 2, wherein the predetermined state is determined when a second condition that a surge sound easily enters a range is satisfied.   The engine control device according to claim 3, wherein the control device determines that the first condition is satisfied when the accelerator pedal operation amount becomes zero.   The engine control device according to claim 1, wherein the predetermined period is a predetermined constant period. A method of controlling the engine,
The engine is
A turbine that is provided in an exhaust passage through which exhaust gas from the combustion chamber flows, rotates by the flow of the exhaust gas, and a compressor that is provided in an intake passage that supplies intake air to the combustion chamber and that supercharges intake air by the rotational force of the turbine are provided. Including a turbocharger,
An EGR passage that connects an exhaust passage downstream of the turbine and an intake passage upstream of the compressor, and an EGR valve that is provided in the EGR passage and opens and closes the EGR passage are included. An EGR device for returning to the intake passage,
A throttle valve provided in the intake passage downstream of the compressor, for opening and closing the intake passage;
A special valve that is provided upstream of the connection between the EGR passage and the intake passage and opens and closes the intake passage,
The engine control device is
A step of controlling the special valve to be in a closed state for a predetermined period of time when a predetermined state before a state in which a surge sound is generated from the intake port which is the inlet of the intake passage is achieved;
When the EGR valve is in the closed state when the predetermined state is reached, the EGR valve is controlled to be in the open state. A turbine that is provided in an exhaust passage through which exhaust gas from the combustion chamber flows, rotates by the flow of the exhaust gas, and a compressor that is provided in an intake passage that supplies intake air to the combustion chamber and that supercharges intake air by the rotational force of the turbine are provided. Including a turbocharger,
An EGR passage that connects an exhaust passage downstream of the turbine and an intake passage upstream of the compressor, and an EGR valve that is provided in the EGR passage and opens and closes the EGR passage are included. An EGR device for returning to the intake passage,
A throttle valve provided in the intake passage downstream of the compressor, for opening and closing the intake passage;
A special valve that is provided upstream of the connection between the EGR passage and the intake passage and opens and closes the intake passage,
The special valve is closed for a predetermined period when it is in a predetermined state before a state in which a surge noise is generated from an intake port which is an inlet of an intake passage,
The engine in which the EGR valve is opened when it is in the closed state when it is in the predetermined state.

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