JPH07166971A - Exhaust-recycling control device for diesel engine - Google Patents

Abstract

PURPOSE:To provide an exhaust-recycling control device for a diesel engine which can perform diagnosis as to whether or not the operation of an intake throttle valve is abnormal. CONSTITUTION:An exhaust-recycling control device for a diesel engine includes a diagnostic region detection means 107 for detecting whether a condition for diagnosing the abnormality of an intake throttle means 105 is met; an intake air quantity detection means 108 for detecting the actual quantity GA of intake air taken in via the intake throttle means 105 ; a target value storage means 109 for storing a target quantity GaN of intake air; and a comparison means 110 for calculating the difference DELTAGa=GaN-Ga between the actual quantity Ga of intake air by which the diagnostic region is recognized and the target quantity GaN of intake air. The control unit also includes a n abnormality recognition means 11 which, when the difference DELTAGa calculated is greater than a reference value DELTAGamax, determines that the intake throttle means 105 is abnormal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an exhaust gas recirculation control device for a diesel engine.

[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,
A so-called exhaust gas recirculation control device for recirculating an inert exhaust gas is provided in the intake pipe.

An example of this exhaust gas recirculation control device is shown in FIG.
There is something like the one shown in (Reference material: “Mercede
s-Benz Passenger Cars wit
hDiesel Engine "Mercedes-
Published by Benz).

In the figure, 30 is a diesel engine,
31 is an intake passage, 32 is an exhaust passage, 33 is an intake passage 31
Is an EGR passage for returning a part of the exhaust gas introduced from the exhaust passage 32 to the intake passage 31 on the downstream side of the intake throttle valve 33, and 35 is an EGR valve for controlling the exhaust gas recirculation amount. Is shown.

The intake throttle valve 33 and the EGR valve 35 are interlocked with a diaphragm actuator, and operate in accordance with the negative pressure supplied from the vacuum pump 42 via the vacuum modulators 36 and 37, and the vacuum modulators 36 and 37. Adjusts the control negative pressure based on the signal from the control unit 38.

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 opening (control sleeve of the fuel injection pump 43 or control rack position), A signal indicating the engine cooling water temperature or the like is input, and the opening degrees of the intake throttle valve 33 and the EGR valve 35 are controlled according to these engine operating states.

By the way, in such an exhaust gas recirculation control device, various malfunctions may occur due to the influence of carbon contained in the exhaust gas. It is desirable to diagnose.

For example, the one disclosed in Japanese Patent Application Laid-Open No. 57-44760 has a structure in which carbon or the like is deposited in the EGR passage and
When the GR passage is clogged, it is determined that the EGR passage is clogged when the actual intake air amount detected by the air flow meter is larger than a preset target intake air amount, and the EGR valve is blocked. The opening is largely corrected.

[0009]

However, in such a conventional exhaust gas recirculation control device, it is possible to cause so-called valve sticking, in which the intake throttle valve 33 is stuck due to carbon contained in the exhaust gas. There is a nature. Due to this valve sticking, for example, in an operating state in which the intake throttle valve 33 is stuck at the minimum opening position, the intake air amount becomes insufficient, and problems such as an increase in the amount of particulates discharged in the medium and high load regions occur.

In view of the above problems, it is an object of the present invention to provide an exhaust gas recirculation control device for a diesel engine which can diagnose that the operation of the intake throttle valve is abnormal.

[0011]

The invention according to claim 1 is
As shown in FIG. 1, the exhaust passage 10 of the diesel engine
2 and the EGR passage 103 connecting the intake passage 101, and the EGR
An EGR valve 104 provided in the middle of the passage 103, an intake throttle means 105 provided upstream of a confluence portion of the EGR passage 103 of the intake passage 101, the EGR valve 104 and the intake air depending on the engine operating state. In an exhaust gas recirculation control device for a diesel engine, which comprises a means 106 for controlling the opening degree of the throttle means 105, a diagnostic region determination means 107 for determining whether or not a condition for diagnosing an abnormality of the intake throttle means 105, and an intake throttle means. Intake air amount detecting means 10 for detecting the actual intake air amount Ga taken in via 105
8, a target value storage means 109 that stores a target intake air amount GaN, and an actual intake air amount G that is detected when the diagnosis area is reached.
Difference between a and target intake air amount GaN ΔGa = GaN-Ga
Comparing means 110 for calculating the above, and abnormality determining means 111 for determining that the intake throttle means is abnormal when the calculated difference ΔGa is larger than the reference value ΔGamax.

According to a second aspect of the present invention, in the first aspect of the present invention, the diagnosis region is set at the time of fuel injection cut when the control for reducing the opening degree of the fuel intake throttle means is performed.

According to a third aspect of the present invention, in the first aspect of the present invention, the diagnosis region is set at a full load when control is performed to maximize the opening of the intake throttle means.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, EG is determined when an abnormality is determined.
A control means for fully closing the R valve and reducing the maximum fuel injection amount is provided.

[0015]

In the invention according to claim 1, the intake throttle means 1
In the diagnostic region where the intake throttle means 105 is controlled to the half-open position or the full-open position when 05 is stuck to the minimum opening degree due to, for example, carbon contained in the exhaust gas, the actual intake air amount Ga is the target. Since it is smaller than the intake air amount GaN, the actual intake air amount Ga and the target intake air amount GaN
When the difference ΔGa is larger than the reference value ΔGamax, it can be determined that an abnormality has occurred in the operation of the intake throttle means 105.

According to a second aspect of the invention, the intake throttle means 10 is provided.
When 5 is fixed to the fully open position by carbon or the like, the actual intake air amount Ga is equal to the target intake air amount G at the time of fuel injection cut when control for reducing the opening degree of the intake throttle means is performed.
Since it is larger than aN, it can be determined that an abnormality has occurred in the operation of the intake throttle means 105 when the difference ΔGa between the actual intake air amount Ga and the target intake air amount GaN is larger than the reference value ΔGamax.

According to a third aspect of the invention, the intake throttle means 10 is provided.
Since the actual intake air amount Ga becomes smaller than the target intake air amount GaN at full load when the control for maximizing the opening amount of the intake throttle means is performed when 5 is fixed to the minimum opening amount by carbon or the like. When the difference ΔGa between the actual intake air amount Ga and the target intake air amount GaN is larger than the reference value ΔGamax, it can be determined that the operation of the intake throttle means 105 is abnormal.

According to a fourth aspect of the present invention, the EG
By fully closing the R valve and performing control to reduce the maximum fuel injection amount, a large amount of exhaust gas is recirculated to deteriorate drivability, and the fuel injection amount becomes excessive in the high load range to cause particulate matter. It is possible to prevent the amount of emissions of water from significantly deteriorating.

[0019]

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

FIG. 2 schematically shows the exhaust gas recirculation control device. An EGR passage 23 that connects the exhaust passage 22 and the intake passage 21 of the diesel engine 20 is provided.
A diaphragm type EGR valve 4 is interposed in the middle of the process.
As the opening degree of the EGR valve 4 increases, the amount of EGR recirculated to the intake passage 21 via the EGR passage 23 increases.

A signal negative pressure passage 5 is connected to the diaphragm chamber 13 of the EGR valve 4. The signal negative pressure passage 5 is opened to the atmosphere through the orifice 8 and communicates with the vacuum pump through the duty control valve 7 and the orifice 18. The duty control valve 7 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 an intake throttle means, E is provided in the intake passage 21.
A butterfly-type intake throttle valve 9 is provided on the upstream side of the confluence portion of the GR passage 23. A signal negative pressure passage 16 is connected to the diaphragm chamber 15 of the diaphragm actuator 6 with which the intake throttle valve 9 is interlocked. This signal negative pressure passage 16 is O
It communicates with the vacuum pump via the N / OFF type solenoid valve 1 and is open to the atmosphere via the ON / OFF type solenoid valve 2.

When the solenoid valves 1 and 2 are both in the non-energized state, the atmospheric pressure is introduced into the diaphragm chamber 15 and the intake throttle valve 9 is held in the fully open position.

When the solenoid valve 1 is in the energized state and the solenoid valve 2 is in the de-energized state, a weak negative pressure diluted with the atmospheric pressure is introduced into the diaphragm chamber 15, and the intake throttle valve 9 is held at a predetermined half open position. To be done.

When the solenoid valves 1 and 2 are both energized, a strong negative pressure from the vacuum pump is introduced into the diaphragm chamber 15, and the intake throttle valve 9 is held at the minimum opening position.

In the intake passage 21 on the downstream side of the intake throttle valve 9, an intake negative pressure is generated as the opening degree of the intake throttle valve 9 becomes smaller, and is returned to the intake passage 21 via the EGR passage 23. EGR amount increases.

An air flow meter 10 for detecting the actual intake air amount (fresh air amount) Ga is provided upstream of the intake throttle valve 9 in the intake passage 21, and an output Va from the air flow meter 10 is sent to the control unit 11.

The control unit 11 includes a CPU (central processing unit) 2 as shown in the block diagram of FIG.
6, ROM (read-on memory) 24, RAM (random access memory) 25, I / O (interface)
It is composed of a microcomputer of 23. I /
Signals from the engine speed sensor 51, the accelerator opening sensor 52, the air flow meter 10, the lift sensor 3 of the EGR valve 4, the brake switch 53, the water temperature sensor 54, and the fuel temperature sensor 55 serve as operating condition detecting means in O23. Each is entered.

The CPU 26 fetches the information from the I / O 23 according to the program stored in the ROM 24,
A fuel injection pump 12 that performs arithmetic processing and adjusts the fuel injection timing and injection amount, each solenoid valve that adjusts the exhaust gas recirculation amount 1,
2. The data which is the control amount for controlling the duty control valve 7 for adjusting the intake air amount is set in the I / O 23. The RAM 26 is used to temporarily save the data related to the arithmetic processing of the CPU 26. The I / O 23 controls the fuel injection pump 12, the solenoid valves 1 and 2, and the duty control valve 7 based on the data output from the CPU 26.

By the way, the carbon stick contained in the exhaust gas causes a valve stick to which the intake throttle valve 9 is fixed,
There is a possibility of causing a malfunction that the predetermined opening cannot be obtained.

In response to this, the CPU 26 sets the intake throttle valve 9 to a predetermined opening in the operating state in which the fuel cut is performed in accordance with the operation of the engine brake, while the actual intake air detected by the air flow meter 10 is set. The difference ΔGa between the amount Ga and the target intake air amount GaN is calculated, and when the calculated difference ΔGa is larger than the reference value ΔGamax, it is determined that the operation of the intake throttle valve 9 is abnormal, and when the abnormality is determined, E
The GR valve 4 is fully closed, and the maximum value of the fuel injection amount is corrected to be small.

Next, the control operation executed by the CPU 26 will be described with reference to the flowchart of FIG. This is executed at regular intervals while the engine is operating.

First, at step 310, the engine speed N
e, accelerator opening Acc, output V of the air flow meter 10
Various data of operating conditions such as a, EGR valve lift Le, cooling water temperature Tw, and fuel temperature Tf are read.

Next, in step 320, the basic fuel injection amount QN, the basic fuel injection timing ITN, the basic intake air amount GaN, and the basic EGR valve lift are based on the maps shown in FIGS. Amount LeN, basic duty ratio DpN of duty control valve 7, solenoid valves 1 and 2
Control signals Vs1 and Vs2 are calculated.

Next, at step 330, step 310.
Engine speed Ne and accelerator opening Ac read in
Based on the value of c, it is determined whether or not the operating state is such that fuel cut is performed in accordance with the operation of the engine brake or the like. If not in the fuel cut state, this routine ends.

If it is judged at step 330 that the fuel is in the fuel cut state, the routine proceeds to step 340, where, for example, the opening of the intake throttle valve 9 is set according to the engine speed Ne at the accelerator opening Acc = 15%. So that each solenoid valve 1, 2
Control signals Vs1 and Vs2 are output to set the intake throttle valve 9 to a predetermined opening.

Next, at step 350, the output Va of the air flow meter 10 is read again.

Next, in step 360, the difference Δ between the target value GaN of the intake air amount previously stored in the ROM 24 and the actual intake air amount Ga detected by the air flow meter 10 is obtained.
Ga (= GaN-Ga) is calculated.

Next, the difference Δ calculated in step 370.
It is determined whether Ga is larger than the reference value ΔGamax. If it is determined that the disparity ΔGa is less than or equal to the reference value ΔGamax, this routine ends.

If it is determined in step 370 that the difference ΔGa is larger than the reference value ΔGamax, it is determined that the operation of the intake throttle valve 9 is abnormal, and the process proceeds to step 380 to stop the exhaust gas recirculation. In addition, in order to correct the maximum value of the fuel injection amount to a small value, the correction amount ΔQ of the fuel injection amount is calculated according to the disparity ΔGa and the accelerator opening degree Acc based on the map shown in FIG. .

Next, the routine proceeds to step 390, where the correction amount ΔQ of the fuel injection amount and the outputs Vs1 = 0, Vs2 = 0 and the EGR valve 4 for fully opening the intake throttle valve 9 via the respective solenoid valves 1, 2 are fully opened. The output Dp = 0 to be closed is stored in a predetermined address, and this routine ends.

When the intake throttle valve 9 is constructed as described above and is fixed at the fully open position by, for example, carbon contained in the exhaust gas, the difference ΔGa in the intake air amount is the reference in the operating state where the fuel cut is performed. Since it becomes larger than the value ΔGamax, it can be determined that an abnormality has occurred in the operation of the intake throttle valve 9.

Further, in the case where the intake throttle valve 9 is stuck at the minimum opening position due to, for example, carbon contained in the exhaust gas, the difference ΔGa in the intake air amount is greater than the reference value ΔGamax even in the operating state where the fuel cut is performed. If it becomes larger, it can be determined that an abnormality has occurred in the operation of the intake throttle valve 9.

At the time of this abnormality determination, the EGR valve 4 is fully closed and control is performed to correct the maximum value of the fuel injection amount to a small value, so that a large amount of exhaust gas is recirculated and the drivability deteriorates, and the high load is increased. It is possible to prevent the amount of fuel injection in the region from becoming excessively large and the amount of particulate matter discharged from significantly deteriorating.

Next, another embodiment will be described. It should be noted that the same parts as those in FIGS.

In response to the malfunction of the intake throttle valve 9, CP
U26 is the intake throttle valve 9 at full load when the accelerator is fully opened.
Is set to the fully open position, while the actual intake air amount Ga and the target intake air amount Ga detected by the air flow meter 10 are set.
The difference ΔGa of N is calculated, and when the calculated difference ΔGa is larger than the reference value ΔGamax, it is determined that an abnormality has occurred in the operation of the intake throttle valve 9, and at the time of the abnormality determination, the EGR valve 4 is fully closed and the combustion charge is increased. Control is performed to correct the maximum injection amount to a small value.

The control operation executed by the CPU 26 will be described with reference to the flowchart of FIG. This is executed at regular intervals while the engine is operating.

First, at step 410, the engine speed N
e, accelerator opening Acc, output V of the air flow meter 10
Various data of operating conditions such as a, EGR valve lift Le, cooling water temperature Tw, and fuel temperature Tf are read.

Next, in step 420, the basic fuel injection amount QN, the basic fuel injection timing ITN, the basic intake air amount GaN, and the basic EGR valve lift are based on the maps shown in FIGS. Amount LeN, basic duty ratio DpN of duty control valve 7, solenoid valves 1 and 2
Control signals Vs1 and Vs2 are calculated.

Next, in step 430, step 410
It is determined whether or not the accelerator opening Acc read in step 3 is a full load state equal to or larger than a predetermined value, that is, the accelerator is fully open. If the accelerator is not fully opened, this routine ends.

When the accelerator is fully opened, the intake throttle valve 9 is set to the fully open position.

If it is determined in step 430 that the accelerator is fully open, the process proceeds to step 440 and the ROM
The target value GaN of the intake air amount stored in advance in 24 and the actual intake air amount G detected by the air flow meter 10
The difference ΔGa of a is calculated.

Next, the disparity Δ calculated in step 450
It is determined whether Ga is larger than the reference value ΔGamax. If it is determined that the disparity ΔGa is less than or equal to the reference value ΔGamax, this routine ends.

If it is determined in step 450 that the difference ΔGa is larger than the reference value ΔGamax, it is determined that the operation of the intake throttle valve 9 is abnormal, and the process proceeds to step 460 to stop the exhaust gas recirculation. In addition, in order to correct the maximum value of the fuel injection amount to a small value, the correction amount ΔQ of the fuel injection amount is based on each map shown in FIG.
Calculate according to.

Next, the routine proceeds to step 470, where the correction amount ΔQ of the fuel injection amount and the outputs Vs1 = 0, Vs2 = 0 for fully opening the intake throttle valve 9 through the respective electromagnetic valves 1, 2 and the EGR valve 4 are fully opened. The output Dp = 0 to be closed is stored in a predetermined address, and this routine ends.

With the above construction, when the intake throttle valve 9 is stuck to a small opening due to, for example, carbon contained in the exhaust gas, the difference ΔGa in the intake air amount at full load is larger than the reference value ΔGamax. Therefore, it can be determined that an abnormality has occurred in the operation of the intake throttle valve 9.

At the time of abnormality determination, the EGR valve 4 is fully closed and the maximum value of the fuel injection amount is corrected to a small value, so that a large amount of EGR gas is recirculated to deteriorate the drivability or the high load range. It is possible to prevent the intake air amount from being narrowed down and the discharge amount of particulates from being significantly deteriorated.

Next, another embodiment will be described. It should be noted that the same parts as those in FIGS.

In response to the malfunction of the intake throttle valve 9, CP
U26 The intake throttle valve 9 is set to a predetermined opening when exhaust gas recirculates, while the difference ΔGa between the actual intake air amount Ga detected by the air flow meter 10 and the target intake air amount GaN is calculated, and the calculated difference ΔGa is the reference value. When it is larger than ΔGamax, it is determined that an abnormality has occurred in the operation of the intake throttle valve 9, and when the abnormality is determined, the EGR valve 4 is fully closed and the maximum value of the fuel injection amount is corrected to be small.

The control operation executed by the CPU 26 will be described with reference to the flowchart of FIG. This is executed at regular intervals while the engine is operating.

First, at step 510, the engine speed N
e, accelerator opening Acc, output V of the air flow meter 10
Various data of operating conditions such as a, EGR valve lift Le, cooling water temperature Tw, and fuel temperature Tf are read.

Next, in step 520, the basic fuel injection amount QN, the basic fuel injection timing ITN, the basic intake air amount GaN, and the basic EGR valve lift are based on the maps shown in FIGS. Amount LeN, basic duty ratio DpN of duty control valve 7, solenoid valves 1 and 2
Control signals Vs1 and Vs2 are calculated.

Next, in step 530, the difference Δ between the target value GaN of the intake air amount previously stored in the ROM 24 and the actual intake air amount Ga detected by the air flow meter 10 is set.
Calculate Ga.

Next, the disparity Δ calculated in step 540
It is determined whether Ga is larger than the reference value ΔGamax. If it is determined that the disparity ΔGa is less than or equal to the reference value ΔGamax, this routine ends.

If it is determined in step 540 that the difference ΔGa is larger than the reference value ΔGamax, it is determined that the operation of the intake throttle valve 9 is abnormal, and the process proceeds to step 550 to stop the exhaust gas recirculation. In addition, in order to correct the maximum value of the fuel injection amount to a small value, the correction amount ΔQ of the fuel injection amount is based on each map shown in FIG.
Calculate according to.

Next, the routine proceeds to step 560, where the correction amount ΔQ of the fuel injection amount and the outputs Vs1 = 0, Vs2 = 0 and the EGR valve 4 for fully opening the intake throttle valve 9 via the respective electromagnetic valves 1, 2 are fully opened. The output Dp = 0 to be closed is stored in a predetermined address, and this routine ends.

When the intake throttle valve 9 is constructed as described above and is fixed at a small opening position by, for example, carbon contained in the exhaust gas, the difference Δ in intake air amount during exhaust gas recirculation.
When Ga is larger than the reference value ΔGamax, it can be determined that the operation of the intake throttle valve 9 is abnormal.

At the time of abnormality determination, the EGR valve 4 is fully closed, and control is performed to correct the maximum value of the fuel injection amount to a small value, so that a large amount of EGR gas is recirculated and the drivability deteriorates, and the high load range is increased. It is possible to prevent the intake air amount from being narrowed down and the discharge amount of particulates from being significantly deteriorated.

[0069]

As described above, the invention according to claim 1 is an exhaust gas recirculation control device for a diesel engine,
Diagnostic region determining means for determining whether or not the condition for diagnosing abnormality of the intake throttle means, intake air amount detecting means for detecting the actual intake air amount Ga taken in through the intake throttle means, and target intake air amount GaN , A comparison means for calculating a difference ΔGa = GaN-Ga between the actual intake air amount Ga detected in the diagnosis region and the target intake air amount GaN, and the calculated difference ΔGa is the reference value ΔGa.
Since the abnormality determining means for determining that there is an abnormality in the intake throttle means when it is larger than max is provided, it can be determined that the intake throttle means is stuck at the minimum opening degree due to, for example, carbon contained in the exhaust gas. The determination result can be reflected in the control of the exhaust gas recirculation amount and the fuel injection amount to improve the exhaust performance and the operation performance.

According to a second aspect of the present invention, in the first aspect of the present invention, the diagnosis region is set at the time of fuel injection cut when control is performed to reduce the opening of the intake throttle means of the fuel. When the fuel injection is cut when the control for reducing the opening degree of the intake throttle means is performed when the valve is stuck in the fully open position due to the above reasons, the actual intake air amount Ga becomes larger than the target intake air amount GaN, so that the actual intake air amount is increased. When the difference ΔGa between the air amount Ga and the target intake air amount GaN is larger than the reference value ΔGamax, it can be determined that an abnormality has occurred in the operation of the intake throttle means.

According to a third aspect of the present invention, in the first aspect of the present invention, the diagnosis region is set at a full load when the control for maximizing the opening degree of the intake throttle means is performed. Therefore, the intake throttle means is made of carbon or the like. When stuck at the minimum opening,
At the time of full load when the control for maximizing the opening degree of the intake throttle means is performed, the actual intake air amount Ga is equal to the target intake air amount Ga.
When the difference ΔGa between the actual intake air amount Ga and the target intake air amount GaN is larger than the reference value ΔGamax, it can be determined that the operation of the intake throttle means is abnormal by making the value smaller than N.

The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein EG
Since the R valve is fully closed and the control means for reducing the maximum fuel injection amount is provided, a large amount of exhaust gas is recirculated to deteriorate the drivability, and the fuel injection amount becomes excessive in the high load range, and the particulates are generated. It is possible to prevent the amount of emissions of water from significantly deteriorating.

[Brief description of drawings]

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

FIG. 2 is a system diagram of an exhaust gas recirculation control device showing an embodiment of the present invention.

FIG. 3 is a block diagram of a control unit of the same.

FIG. 4 is a flowchart showing the same control contents.

FIG. 5 is a characteristic diagram of an example of control data.

FIG. 6 is a characteristic diagram of an example of control data.

FIG. 7 is a characteristic diagram of an example of control data.

FIG. 8 is a characteristic diagram of an example of control data.

FIG. 9 is a characteristic diagram of an example of control data.

FIG. 10 is a characteristic diagram of an example of control data.

FIG. 11 is a characteristic diagram of an example of control data.

FIG. 12 is a flowchart showing control contents in another embodiment.

FIG. 13 is a flowchart showing control contents in still another embodiment.

FIG. 14 is a system diagram of an exhaust gas recirculation control device showing a conventional example.

[Explanation of symbols]

 101 intake passage 102 exhaust passage 103 EGR passage 104 EGR valve 105 intake throttle means 106 control means 107 diagnostic area determination means 108 intake air amount detection means 109 target value storage means 110 comparison means 111 abnormality determination means

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location F02D 43/00 301 N K

Claims (4)

[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 air provided upstream of a confluence portion of the EGR passage of the intake passage. In an exhaust gas recirculation control device for a diesel engine including throttle means and means for controlling the opening of the EGR valve and the intake throttle means according to the engine operating state, it is judged whether or not there is a condition for diagnosing an abnormality of the intake throttle means. Diagnostic area determining means, intake air amount detecting means for detecting the actual intake air amount Ga taken in through the intake throttle means, target value storing means for storing the target intake air amount GaN, and the detection area detection means The comparing means for calculating the difference ΔGa = GaN-Ga between the actual intake air amount Ga and the target intake air amount GaN, and the calculated difference ΔGa is the reference value ΔGamax. Exhaust gas recirculation control device for a diesel engine characterized by comprising an abnormality judging means for judging that there is an abnormality of the intake throttle means when larger. 2. An exhaust gas recirculation control device for a diesel engine in which control is performed to reduce the opening of an intake throttle means at the time of fuel injection cut when fuel supply is stopped, wherein the diagnosis region is set at the time of fuel injection cut. The exhaust gas recirculation control device for a diesel engine according to claim 1, 3. The exhaust gas recirculation control device for a diesel engine in which control is performed to maximize the opening degree of the intake throttle means at full load, wherein the diagnosis region is set at full load. Exhaust gas recirculation control device for diesel engine. 4. The exhaust gas of a diesel engine according to claim 1, further comprising control means for fully closing the EGR valve at the time of abnormality determination and reducing the maximum fuel injection amount. Reflux control device.