JPH074319A - Egr device of diesel engine - Google Patents

Abstract

PURPOSE:To provide an EGR device of a diesel engine which maintains appropriate the EGR rate according to variation of intake air charging efficiency or variation of operation characteristic of an intake throttle valve. CONSTITUTION:In the EGR device of a dicsel engine provided with a means 21 by which the opening of an EGR valve 4 and an intake throttle valve 9 are controlled so as to obtain the target intake air quantity Qt in response to the operating condition of an engine based on a detected intake air quantity Qa, it is provided with a means 23 detecting variation of the intake air charging charging efficiency based on the intake air quantity Qa detected at cutting EGR, and a means 22 correcting the target value Qt of an intake air quantity according to variation of the detected intake air charging efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved EGR device for diesel engines.

[0002]

2. Description of the Related Art In automobile engines and the like, in order to suppress the generation of NOx which is a harmful component in exhaust gas,
Recirculating inert exhaust gas to the intake pipe, so-called E
A GR device is provided.

An example of this EGR device is shown in FIG. 11 (reference material: "Mercedes-B").
enz Passenger Cars with D
iesel engine "Mercedes-Ben
z company issued).

In the figure, 30 is a diesel engine,
31 is an intake passage, 32 is an exhaust passage, 33 is an intake passage 31
An intake throttle valve 34 is provided in the exhaust gas recirculation passage 34, which returns a part of the exhaust gas (EGR gas) introduced from the exhaust passage 32 to the intake passage 31 on the downstream side of the intake throttle valve 33 (hereinafter referred to as an EGR passage). ) And 35 are EGR valves (control valves) for controlling the EGR amount (exhaust gas recirculation amount).

The intake throttle valve 33 and the EGR valve 35 are interlocked with a diaphragm actuator, and operate according to the negative pressure supplied from the vacuum pump 42 through the vacuum modulators 36 and 37, and the vacuum modulators 36 and 37. The control negative pressure is adjusted based on the signal from the control unit 38. In accordance with a command from the control unit 38, the intake throttle valve 33 and E
By controlling the opening of the GR valve 35 and returning a predetermined amount of EGR gas to the intake passage 31, the maximum temperature during combustion is lowered and the amount of NOx in the exhaust gas is reduced.

An air flow meter 40 for measuring the intake air amount (fresh air amount) upstream of the intake throttle valve 33 in the intake passage 31.
Is provided. The control unit 38 uses the intake air amount signal from the air flow meter 40 and signals representing the engine operating state, such as engine speed, accelerator pedal opening (control sleeve of the fuel injection pump 43 or control rack position), engine cooling. A signal representing a water temperature or the like is input, a preset control target value of the intake air amount corresponding to these engine operating states is selected by table lookup, and this is used as a command value for the EGR valve 35 and the intake throttle valve 33. It is designed to control the opening.

This control is based on the assumption that the total intake air amount (intake air amount + EGR amount) taken into the engine, that is, the intake charging efficiency of the engine is constant under operating conditions basically determined according to the engine speed. Assuming that the target intake air amount set in advance is maintained, the EGR
The rate (= EGR amount / intake air amount × 100%) is managed.

[0008]

However, in such a conventional EGR device, the total intake air amount taken into the engine is changed due to the high altitude running of the vehicle, the clogging of the air cleaner, and the like. Can be considered. By performing control to keep the intake air amount constant without responding to this decrease in intake charge efficiency (mass of air sucked into the cylinder / cylinder volume), the actual EGR rate falls below the target value and the NOx emission amount is reduced. There is a problem that is increased.

In addition, when there is a setting error in the operating characteristics of a diaphragm actuator or the like for driving the intake throttle valve 33, or when the operating characteristics change due to deterioration over time, etc., the operating characteristics of the intake throttle valve 33. Can change. By performing control to keep the intake air amount constant without responding to the change in the operation characteristic of the intake throttle valve 33, the actual EGR rate becomes higher than the target value, which causes an increase in exhaust particulates and deterioration of drivability. However, there is a problem that the actual EGR rate becomes low and the NOx emission amount increases.

The present invention focuses on the above problems and responds to changes in the intake charging efficiency and changes in the operating characteristics of the intake throttle valve.
An object of the present invention is to provide an EGR device for a diesel engine that maintains a proper GR rate.

[0011]

The invention according to claim 1 is
As shown in FIG. 1, an EGR passage 3 connecting an exhaust passage 2 and an intake passage 1 of a diesel engine, an EGR valve 4 provided in the middle of the EGR passage 3, and an EGR passage 3 in the intake passage 1.
Intake air throttle valve 9 provided upstream of the confluence portion with the air flow meter 10 for detecting the intake air amount Qa taken in through the intake throttle valve 9, and the detected intake air amount Qa
In the EGR device of the diesel engine, which includes means 21 for controlling the opening degree of the EGR valve 4 and the intake throttle valve 9 so as to obtain the target intake air amount Qt according to the engine operating state based on Means 23 for detecting a change in intake air charging efficiency of the engine on the basis of the intake air amount Qa detected during the closing EGR cut, and correcting the target value Qt of the intake air amount according to the detected change in intake air charging efficiency. Means 22 are provided.

According to the second aspect of the present invention, as shown in FIG. 2, the EGR valve 4 and the EGR valve 4 are provided so that the target intake air amount Qt corresponding to the engine operating state can be obtained based on the similarly detected intake air amount Qa. In an EGR device for a diesel engine equipped with a means 21 for controlling the opening degree of the intake throttle valve 9, an inspection means 25 for narrowing the opening degree of the intake throttle valve 9 at the time of EGR cut for fully closing the EGR valve 4 and an intake throttle for the EGR cut time. A means 24 for detecting a change in the operating characteristic of the intake throttle valve 9 based on the intake air amount Qa detected in the operating state in which the opening of the valve 9 is throttled, and a detected change in the operating characteristic of the intake throttle valve 9. And a means 22 for correcting the target value Qt of the intake air amount according to the above.

[0013]

In the invention according to claim 1, the control target value Qt of the intake air amount preset according to the engine operating state is set.
Is selected by table lookup, and the opening of the EGR valve 4 and the intake throttle valve 9 is controlled using this as a command value.

In this EGR control, it is assumed that the total intake air amount (intake air amount + EGR amount) sucked into the engine, that is, the intake charging efficiency is constant under the operating condition determined depending on the engine speed. , EGR rate (= EGR rate by maintaining a preset target intake air amount
(Amount / intake air amount × 100%). E
At the time of EGR cut when the GR valve 4 is fully closed, the intake air amount Qa detected by the air flow meter 10 and the target value Qt of the intake air amount sucked into the engine are essentially the same, so they are read at the time of EGR cut. Based on the detected value Qa of the intake air amount, it is possible to detect that the intake charging efficiency (mass of air taken into the cylinder / cylinder volume) decreases.

In this way, the engine operating condition is reduced by correcting the target value Qt of the intake air amount in response to a decrease in the intake charging efficiency due to, for example, high altitude running of the vehicle or clogging of the air cleaner. Target EG according to the state
An R rate is obtained, and increasing NOx emissions is avoided.

In the invention according to claim 2, the EGR valve 4
Even when the intake throttle valve 9 is in an operating state in which the opening degree of the intake throttle valve 9 is narrowed when the EGR is fully closed, the intake air amount Qa detected by the air flow meter 10 and the target value Qt of the intake air amount taken into the engine are originally Since they match, EG
Based on the detected value Qa of the intake air amount read during the R cut, the target value Qt of the intake air amount can be corrected corresponding to the change in the operating characteristic of the intake throttle valve 9.

[0017]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 3 shows an outline of the EGR device. EG connecting the exhaust passage 2 and the intake passage 1 of the diesel engine
An R passage 3 is provided, and a diaphragm type EGR valve 4 is provided in the middle of the EGR passage 3. A signal negative pressure passage 5 is connected to the diaphragm chamber 13 of the EGR valve 4. The signal negative pressure passage 5 communicates with the vacuum pump 7, and a negative pressure control valve 8 is provided in the middle thereof. The negative pressure control valve 8 appropriately dilutes the negative pressure introduced into the diaphragm chamber 13 of the EGR valve 4 to control the opening degree of the EGR valve 4.

As the opening degree of the EGR valve 4 increases, the EG
The EGR amount recirculated to the intake passage 1 via the R passage 3 increases.

A butterfly type intake throttle valve 9 is provided in the intake passage 1 upstream of the confluence of the EGR passage 3. The intake throttle valve 9 is opened and closed via the actuator 6.
In the intake passage 1 on the downstream side of the intake throttle valve 9, intake negative pressure is generated as the opening degree of the intake throttle valve 9 decreases, and E
The amount of EGR recirculated to the intake passage 1 via the GR passage 3 increases.

An air flow meter 10 for detecting the intake air amount (fresh air amount) Qa upstream of the intake throttle valve 9 in the intake passage 1.
Is provided and the intake air amount signal Qa detected by the air flow meter 10 is sent to the control unit 11.

The control unit 11 uses the intake air amount signal Qa of the air flow meter 10 and signals representing the engine operating state, for example, the engine speed, the control lever opening (accelerator pedal opening) of the fuel injection pump, and the fuel injection. A signal representing the time, engine cooling water temperature, engine oil temperature, etc. is input, a predetermined EGR region is determined based on these signals, and a control target of the intake air amount preset in accordance with the engine operating state in this EGR region is determined. The value Qt is selected by table lookup, and the opening of the EGR valve 4 and the intake throttle valve 9 is controlled by using this as a command value, and exhaust gas recirculation is performed.

In this exhaust gas recirculation control, it is assumed that the total intake air amount (intake air amount + EGR amount) taken into the engine, that is, the intake charging efficiency is constant under the operating condition determined depending on the engine speed. Therefore, the EGR rate (= EG
R amount / intake air amount × 100%) is managed.

FIG. 4 shows data of the target value Qth of the total intake air amount with respect to the engine speed. Under normal operating conditions, as shown by the solid line, the target value of the total intake air amount increases as the engine speed increases. Qth increases.

On the other hand, in the EGR cut region, EGR
The valve 4 is held in the fully closed position and the exhaust gas recirculation is stopped.

By the way, under the operating conditions in which the intake charge efficiency of the engine is lowered due to running of the vehicle at high altitude or clogging of the air cleaner, the actual total intake air amount is at a predetermined ratio as shown by the broken line in FIG. Decrease.

To deal with this, the control unit 11 detects a change in intake air charging efficiency of the engine based on the intake air amount Qa detected by the air flow meter 10 at the time of EGR cut, and the detected change in intake air charging efficiency. The control for correcting the target value Qt of the intake air amount is performed in accordance with the above.

Since the flow of the EGR gas flowing into the intake passage 1 via the EGR passage 3 is stopped when the EGR valve 4 is fully closed and the EGR is cut off, the intake air amount Qa detected by the air flow meter 10 becomes equal to that of the engine. Total intake air amount Q
Although it is essentially equal to the target value of th, if the intake air charging efficiency of the engine decreases due to traveling at high altitude, clogging of the air cleaner, etc., the intake air amount Qa detected by the air flow meter 10 at the time of EGR cutoff becomes the total intake air of the engine. The target value of the air amount Qth is different.

The flow chart of FIG. 5 shows a program executed by the control unit 11 for detecting a change in the intake charging efficiency, which is executed at regular intervals during operation of the engine.

First, the detection signals of the engine cooling water temperature, the control lever opening of the fuel injection pump, and the engine speed are read, and it is determined whether or not it is in the EGR region (steps 1 and 2).

In the case of the EGR cut region, the intake air amount Qa detected by the air flow meter 10 and the detected value of the engine speed are read, respectively, and the engine speed is calculated based on the map data shown in FIG. The total intake air amount Qth is read (steps 3 and 4).

Subsequently, an operating condition is judged in which the detected intake air amount Qa is larger than the read value of the total intake air amount Qth, which is the allowable value dQ of the flow rate variation error, and the engine speed and this EGR are stored in the learning map table. The detected value Qth 'of the total intake air amount at the time of cutting is written, and the atmospheric pressure flag 1 indicating that the intake charging efficiency is decreasing is set (steps 5, 6, 7).

On the other hand, when it is determined that the detected intake air amount Qa is an operating condition that is equal to or less than the allowable value dQ of the flow rate variation error with respect to the read total intake air amount Qth, it means that the intake charging efficiency is normal. The atmospheric pressure flag 0 is set (steps 5 and 8).

The flowchart of FIG. 6 shows a control program executed by the control unit 11 for correcting the deviation of the EGR rate due to the change of the intake charging efficiency, which is executed at regular time intervals during the operation of the engine. It

First, each detection signal of the engine cooling water temperature, the control lever opening of the fuel injection pump, and the engine speed is read to determine whether it is in the EGR region (steps 9 and 10).

In the EGR cut region in which the atmospheric pressure flag 1 that indicates that the intake charging efficiency is changed is set, the intake air amount Qa and the engine speed detected by the air flow meter 10 are read, and the engine speed is read. To read the total intake air amount Qth based on the map data shown in FIG. 4 and read the total intake air amount Qth ′ based on the learning map data (steps 11, 12, 13,
14).

Based on the read Qth and Qth 'and the target intake air amount Qt in the map data, the target intake air amount Qt' when the intake charging efficiency decreases is calculated by the following equation.

Qt ′ = Qt × Qth ′ / Qth (1) When the calculated Qt ′ and the detected intake air amount Qa are different, the duty ratio of the negative pressure control valve 8 is changed to EGR. By appropriately diluting the negative pressure introduced into the diaphragm chamber 13 of the valve 4, the opening degree of the EGR valve 4 is corrected (steps 15, 16, 17).

With the above construction, the target value Qt of the intake air amount is reduced and corrected in response to a decrease in intake charging efficiency due to high altitude running of the vehicle or clogging of the air cleaner. Proper EGR rate is maintained and NOx
Increased emissions can be avoided.

Next, another embodiment shown in FIG. 7 will be described. The parts corresponding to those in FIG. 3 are designated by the same reference numerals.

A butterfly type intake throttle valve 9 is provided in the intake passage 1 upstream of the confluence portion of the EGR passage 3, and the intake throttle valve 9 is interlocked with a diaphragm actuator 15. Diaphragm actuator 15 of intake throttle valve 9
A signal negative pressure passage 16 is connected to. The signal negative pressure passage 16 communicates with the vacuum pump 7, and an electromagnetic opening / closing type negative pressure control valve 18 and an atmospheric valve 17 are provided in the middle of the signal negative pressure passage 16.

The negative pressure control valve 18 opens in the energized state to guide the negative pressure from the vacuum pump 7 to the diaphragm actuator 15, and closes in the non-energized state to shut off this negative pressure.

The atmosphere valve 17 is opened in the energized state to dilute the negative pressure introduced to the diaphragm actuator 15, and is closed in the de-energized state.

When both the negative pressure control valve 18 and the atmosphere valve 17 are in the non-energized state, the negative pressure is cut off by being guided to the diaphragm actuator 15, the intake throttle valve 9 is held in the fully open position, and the intake air flow is reduced. I can't squeeze.

When the negative pressure control valve 18 is energized while the atmospheric valve 17 is de-energized, a small negative pressure is introduced to the diaphragm actuator 15 and the intake throttle valve 9 is held in the half-open position, so that the intake valve is closed. The airflow is slightly throttled.

When both the negative pressure control valve 18 and the atmosphere valve 17 are energized, a strong negative pressure is introduced to the diaphragm actuator 15, the intake throttle valve 9 is maintained at a minute opening, and the intake air flow is large. Squeezed.

The control unit 11 uses the intake air amount signal Qa of the air flow meter 10 and signals representing the engine operating state, for example, the engine speed, the control lever opening (accelerator pedal opening) of the fuel injection pump, and the fuel injection. A signal representing the timing, engine cooling water temperature, engine oil temperature, or the like is input, and based on these, a control target value Qt of the intake air amount that is preset according to the engine operating state is selected by table lookup, and this is commanded. The opening of the EGR valve 4 and the intake throttle valve 9 is controlled as a value.

By the way, it is conceivable that there is a setting error in the operating characteristics of the diaphragm actuator 15 for driving the intake throttle valve 9 or the like, or the operating characteristics change due to deterioration with time or the like. This intake throttle valve 9
By performing control to keep the intake air amount constant without responding to changes in the operating characteristics of, the actual EGR rate becomes higher than the target value, leading to an increase in exhaust particulates and deterioration of drivability,
Alternatively, the actual EGR rate becomes low and the NOx emission amount increases.

In order to deal with this, the control unit 11 throttles the opening of the intake throttle valve 9 at the time of EGR cut to fully close the EGR valve 4, and makes the intake throttle valve 9 at the time of EGR cut.
Intake air amount Qa detected in the operating state in which the opening of the
A change in the operating characteristic of the intake throttle valve 9 is detected based on the above, and the target value Qt of the intake air amount is corrected according to the detected change in the operating characteristic of the intake throttle valve 9.

The flowchart of FIG. 9 shows a control program executed by the control unit 11 for detecting changes in the operating characteristics of the intake throttle valve, which is executed at regular time intervals during engine operation.

First, the detection signals of the engine cooling water temperature, the control lever opening of the fuel injection pump, and the engine speed are read, and it is determined whether or not it is in the EGR region (steps 21 and 22).

In the EGR cut region, after holding the intake throttle valve 9 in the half-open position, the intake air amount Qa detected by the air flow meter 10 and the detected value of the engine speed are read and stored in advance from the detected engine speed. Based on the map data shown in FIG. 8, the total intake air amount Qth
Is read (steps 23, 24, 25).

Subsequently, it is judged whether or not the detected intake air amount Qa is larger than the permissible value dQ of the flow rate variation error with respect to the read total intake air amount Qth, and the learning map is used under the operating condition larger than the permissible value dQ. The engine speed and the detected value Qth 'of the total intake air amount at the time of EGR cut are written in the table, and the valve change flag 1 is set to indicate that the operating condition of the intake throttle valve 9 is too small (step 26). , 27, 28).

On the other hand, when it is determined that the detected intake air amount Qa is an operating condition that is equal to or less than the allowable value dQ with respect to the read total intake air amount Qth, the operating characteristics of the intake throttle valve 9 are normal. The valve change flag 0 indicating is set (steps 26 and 35).

Subsequently, after holding the intake throttle valve 9 at the minute opening position, the intake air amount Qa detected by the air flow meter 10 and the detected value of the engine speed are read and stored in advance from the detected engine speed. The total intake air amount Qth is read based on the map data shown in FIG. 8 (steps 29, 30, 31).

Subsequently, it is judged whether or not the detected intake air amount Qa is larger than the permissible value dQ of the flow rate variation error with respect to the read total intake air amount Qth, and the learning map is used under the operating condition larger than the permissible value dQ. The engine speed and the detected value Qth 'of the total intake air amount at the time of EGR cut are written in the table, and a valve change flag +1 indicating that the operating condition is an opening of the intake throttle valve 9 is too small is set (step 32). 33, 34).

On the other hand, if it is determined that the detected intake air amount Qa is an operating condition that is equal to or less than the allowable value dQ with respect to the read total intake air amount Qth, then the operating characteristics of the intake throttle valve 9 are normal. Is set (steps 32 and 36).

The flow chart of FIG. 10 shows a control program executed by the control unit 11 for correcting the deviation of the EGR rate due to the change of the operating characteristic of the intake throttle valve 9, which is carried out for a predetermined time during the operation of the engine. It is executed every time.

First, the detection signals of the engine cooling water temperature, the control lever opening of the fuel injection pump, and the engine speed are read, and it is determined whether or not it is in the EGR region (steps 41 and 42).

In the EGR cut region in which the valve change flag is set to notify that the operating characteristic of the intake throttle valve 9 is changed, the intake air amount Qa detected by the air flow meter 10 and the engine speed are read, From the engine speed, the total intake air amount Qth is read based on the map data shown in FIG. 8, and the total intake air amount Qth ′ is read based on the learning map data (steps 43 and 4).
4, 45, 46).

Based on the read Qth and Qth 'and the target intake air amount Qt in the map data, the target intake air amount Qt' when the operating characteristic of the intake throttle valve 9 changes is calculated by the following equation.

Qt ′ = Qt × Qth ′ / Qth (1) When the calculated Qt ′ and the detected intake air amount Qa are different, the duty ratio of the negative pressure control valve 8 is changed to EGR. The opening degree of the EGR valve 4 is corrected by appropriately diluting the negative pressure introduced into the diaphragm chamber 13 of the valve 4 (steps 47, 48, 49).

With the above configuration, the opening characteristic of the intake throttle valve 9 is different from the set value due to a setting error in the operating characteristics of the diaphragm actuator 15 or due to deterioration over time. By correcting the target value Qt of the intake air amount, an appropriate EGR rate is maintained, and the actual EGR rate becomes higher than the target value, causing an increase in exhaust particulates and deterioration of drivability, or the actual EGR rate. It is possible to prevent the NOx from increasing and the NOx emission amount to increase.

[0064]

As described above, according to the first aspect of the invention, the target intake air amount Qt corresponding to the engine operating state is obtained based on the detected intake air amount Qa.
In an EGR device for a diesel engine equipped with means for controlling the opening of a GR valve and an intake throttle valve, a change in intake charge efficiency of the engine is detected based on an intake air amount Qa detected at the time of EGR cut to fully close the EGR valve. And a means for correcting the target value Qt of the intake air amount in accordance with the detected change in the intake charging efficiency, the intake charging efficiency changes due to the vehicle traveling at high altitude or the air cleaner clogging. The EGR control can be accurately performed without being affected by, and an increase in the NOx emission amount can be avoided.

According to the second aspect of the present invention, the opening degrees of the EGR valve and the intake throttle valve are controlled so that the target intake air amount Qt corresponding to the engine operating state is obtained based on the detected intake air amount Qa. In an EGR device for a diesel engine equipped with a means, an inspection means for narrowing the opening of the intake throttle valve at the time of EGR cut to fully close the EGR valve, and an operating state in which the opening of the intake throttle valve at the time of EGR cut is narrowed are detected. Since a means for detecting a change in the operating characteristic of the intake throttle valve based on the intake air amount Qa and a means for correcting the target value Qt of the intake air amount according to the detected change in the operating characteristic of the intake throttle valve are provided. The EGR control can be performed accurately without being affected by the deviation of the opening of the intake throttle valve, which leads to an increase in exhaust particulates, deterioration of drivability, or an increase in NOx emission amount. It is avoided.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to claims of the invention according to claim 1.

FIG. 2 is a diagram corresponding to claims of the invention according to claim 2;

FIG. 3 is a schematic configuration diagram of an EGR device showing an embodiment of the present invention.

FIG. 4 is a graph showing characteristics of engine speed and total intake air amount.

FIG. 5 is a flowchart showing a control content for detecting a change in intake charging efficiency.

FIG. 6 is a flowchart showing a control content for similarly correcting the opening degree of the EGR valve according to a change in intake charge efficiency.

FIG. 7 is a schematic configuration diagram of an EGR device showing an embodiment of the present invention.

FIG. 8 is a graph showing characteristics of engine speed and total intake air amount.

FIG. 9 is a flowchart showing a control content for detecting a change in operating characteristic of the intake throttle valve.

FIG. 10 is a flowchart showing a control content for similarly correcting the opening degree of the EGR valve according to the change in the operating characteristic of the intake throttle valve.

FIG. 11 is a schematic configuration diagram of an EGR device similarly showing a conventional example.

[Explanation of symbols]

 1 intake passage 2 exhaust passage 3 EGR passage 4 EGR valve 9 intake throttle valve 10 air flow meter 21 EGR control means 22 correction means for intake air amount target value Qt 23 change means for intake charging efficiency 24 change in operating characteristics of intake throttle valve Detecting means 25 Intake throttle valve opening inspection means

Claims (2)

[Claims] 1. An EGR passage connecting an exhaust passage and an intake passage of a diesel engine, an EGR valve provided in the middle of the EGR passage, and an intake passage. Based on the detected intake air amount Qa, an intake throttle valve provided upstream of the confluence portion with the EGR passage of the passage, an air flow meter for detecting the intake air amount Qa taken in through the intake throttle valve, and the detected intake air amount Qa. To obtain the target intake air amount Qt according to the engine operating condition, E
In an EGR device for a diesel engine equipped with means for controlling the opening of a GR valve and an intake throttle valve, a change in intake charge efficiency of the engine is detected based on an intake air amount Qa detected at the time of EGR cut to fully close the EGR valve. An EGR device for a diesel engine, characterized by comprising: a means for performing the above, and a means for correcting the target value Qt of the intake air amount according to the detected change in the intake charging efficiency. 2. An EGR passage that connects an exhaust passage and an intake passage of a diesel engine, an EGR valve that is provided in the middle of the EGR passage, and an intake passage that is provided upstream of a confluence portion of the EGR passage of the intake passage. A throttle valve and an air flow meter for detecting an intake air amount Qa taken in through the intake throttle valve,
Based on the detected intake air amount Qa, EGR is performed so as to obtain a target intake air amount Qt according to the engine operating state.
In an EGR device for a diesel engine equipped with a valve and a means for controlling the opening of an intake throttle valve, an inspection means for restricting the opening of the intake throttle valve at the time of EGR cut to fully close the EGR valve, and an opening of the intake throttle valve at the time of EGR cut A means for detecting a change in the operating characteristic of the intake throttle valve based on the intake air amount Qa detected in a reduced operating state, and an intake air amount corresponding to the detected change in the operating characteristic of the intake throttle valve. Target value Qt
An EGR device for a diesel engine, which is provided with a means for correcting