JP3189001B2 - Diagnosis device for exhaust gas recirculation system of internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation system for an internal combustion engine, and more particularly to a technique for diagnosing a failure of the system.

[0002]

2. Description of the Related Art Conventionally, in an internal combustion engine, as a device for reducing NOx in engine exhaust, a part of the engine exhaust is returned to an intake manifold by returning a part of the engine exhaust to an intake manifold. An exhaust gas recirculation (hereinafter, EGR) device that lowers the maximum combustion temperature to reduce the generation of NOx is known.

If the intended EGR cannot be performed due to such a failure of the EGR device, the amount of NOx emission increases, and a device for diagnosing the failure of the EGR device is required. Therefore, the present applicant has focused on a characteristic in which the output torque of the engine changes depending on the presence or absence of EGR, and has a diagnostic device that performs diagnosis based on a change in combustion pressure when EGR is forcibly turned ON / OFF. It has been previously proposed (see Japanese Patent Application No. 5-78177).

As a diagnostic technique based on such a change in combustion pressure, EGR is performed based on a deviation of a parameter change amount such as a crank angle at which a heat release rate calculated from a cylinder pressure becomes a predetermined value, an indicated average effective pressure, a compression pressure, and the like. There is known an apparatus that estimates an amount, compares the estimated EGR amount with a specified value, diagnoses whether the EGR amount is appropriate, and diagnoses a failure of the EGR device.

[0005]

However, the above-mentioned conventional EGR diagnosis technology has a configuration in which the diagnosis is performed by performing ON / OFF control of the EGR which causes a change in the output of the engine. If the EGR amount changes normally, an output change actually occurs, and adverse effects such as deterioration of drivability and an increase in the amount of generated NOx occur with the diagnosis control.

FIG. 9 shows the relationship among the EGR control valve (EGR / V) opening, the ignition timing ADV, the output torque, and the NOx emission amount in the conventional diagnostic control. A change in the / V opening indicates that the ignition timing ADV changes, the output torque fluctuates, and that NOx is excessively discharged as indicated by the grid lines in the figure.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional circumstances, an object of the present invention is to prevent adverse effects such as deterioration in drivability and an increase in the amount of NOx generated due to the diagnostic control of an exhaust gas recirculation system. I do.

[0008]

Therefore, according to the present invention, as shown in FIG. 1, a part of the engine exhaust gas flows through an exhaust gas recirculation passage provided with an exhaust gas recirculation control valve. A diagnostic device for an exhaust gas recirculation device for an internal combustion engine that recirculates air to an intake system, comprising: an idle operating state determining unit configured to determine an idle operating state of the engine; and an idle operating state determined by the idle operating state determining unit. Exhaust gas recirculation control valve opening control means for forcibly opening the exhaust gas recirculation control valve, and compression pressure detection for detecting the compression pressure of the engine before and after opening control of the exhaust gas recirculation control valve when an idle operation state is detected, respectively. Means for calculating a change in the compression pressure of the engine before and after the opening control of the exhaust gas recirculation control valve, a change in the compression pressure of the engine, and a change in the calculated compression pressure and a target change in the compression pressure. And base There the exhaust gas recirculation amount change rate calculating means for calculating an exhaust gas recirculation amount change rate and a failure diagnosis means for diagnosing a failure of the exhaust gas recirculation device based on the exhaust gas recirculation amount change rate which is the arithmetic, the diagnosis frequency of the failure measurement Measuring hand
Exhaust that opens forcibly according to the step and the number of times the diagnosis has been taken
Exhaust gas recirculation control valve opening degree changing means for changing the degree of recirculation control valve opening
And a step .

In this configuration, diagnostic control is performed by opening and closing the exhaust gas recirculation control valve during idle operation. Therefore,
If the output of the engine does not change, no adverse effects such as an increase in the amount of generated NOx will occur, and if the operating speed of the exhaust gas recirculation control valve is reduced, there is no danger that the idle stability will be degraded with the diagnosis control. The invention according to claim 2 is shown in FIG.
As described above, part of the engine exhaust is exhausted with an exhaust recirculation control valve
Internal combustion engine that recirculates to the intake system of the engine via an air recirculation passage
Diagnostic device for the exhaust gas recirculation system,
An idling operation state determining means for determining a running state;
Idle operating state is determined by idle operating state determining means
The exhaust gas recirculation control valve is forcibly opened when
Flow control valve opening control means and idle operation state detected
Of engine before and after opening control of exhaust gas recirculation control valve
Compression pressure detection means for detecting pressures respectively, and the exhaust gas recirculation
The change in the compression pressure of the engine before and after the control valve
Calculating means for calculating a compression pressure change, and calculating the calculated pressure.
Based on compression pressure change allowance and target compression pressure change allowance
Exhaust gas recirculation amount change ratio calculation to calculate exhaust gas recirculation amount change ratio
Means, first comparing means for comparing the calculated change rate of exhaust gas recirculation amount with the abnormality determination value, and second comparing means for comparing the calculated change rate of exhaust gas recirculation amount and the normal determination value. When the calculated exhaust gas recirculation amount change ratio is equal to or less than the abnormality determination value based on the comparison result by the comparing means, it is determined that the exhaust gas recirculation device is abnormal, and the calculated exhaust gas recirculation amount change ratio is abnormal. Determining means for determining that the exhaust gas recirculation device is normal when the value exceeds the determination value and is equal to or greater than the normal value, and performing diagnosis when the calculated change rate of the exhaust gas recirculation amount exceeds the abnormality value and is less than the normal value And holding means for holding.

In this configuration, it is easily determined whether the exhaust gas recirculation device is normal or abnormal, whether it is not possible to determine whether the exhaust gas recirculation device is normal or abnormal, and whether the diagnosis is suspended, based on the exhaust gas recirculation amount change rate. The invention according to claim 3 is the invention according to claim 2.
In the invention, there is provided a measuring means for measuring the number of times of diagnosis of the failure, and an exhaust gas recirculation control valve opening changing means for changing the opening of the exhaust gas recirculation control valve which is forcibly opened according to the measured number of times of diagnosis. It consisted of.

According to a fourth aspect of the present invention, there is provided a measuring means for measuring the number of times the diagnosis is suspended, and an exhaust gas recirculation control for changing the opening of an exhaust gas recirculation control valve which is forcibly opened according to the measured number of times the diagnosis is suspended. And a valve opening changing means.

[0012] In the configuration according to the third and fourth aspects of the present invention, the influence on drivability is prevented as much as possible, and the accuracy of failure detection is improved as the diagnosis proceeds. Claim 5
The invention according to the present invention includes a measuring means for measuring the number of times of diagnosis or suspension of the failure, and a judgment value changing means for changing a normal judgment value and an abnormality judgment value according to the measured number of times of diagnosis or suspension. It consisted of.

[0013] In this configuration, the diagnostic result is reliably obtained while the diagnostic accuracy is enhanced and erroneous diagnosis is prevented. The invention according to claim 6 is a measurement means for measuring the number of times of diagnosis or suspension of the failure, and an exhaust gas for changing the opening of the exhaust gas recirculation control valve that is forcibly opened according to the number of times of diagnosis or suspension of measurement. A recirculation control valve opening degree changing means and a judgment value changing means for changing a normal judgment value and an abnormality judgment value in accordance with the measured number of times of diagnosis or the number of holdings are included.

In such a configuration, the influence on drivability is prevented as much as possible, and the accuracy of failure detection is improved as the diagnosis proceeds, and the accuracy of diagnosis is increased to prevent erroneous diagnosis. Is surely obtained.

[0015]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In FIG. 2 showing a system according to a common embodiment of the inventions according to claims 1 to 6, air is sucked into an internal combustion engine 1 of a vehicle via an air cleaner 2, an intake duct 3, and an intake manifold 4.

The intake duct 3 is provided with a butterfly type throttle valve 5 interlocked with an accelerator pedal (not shown), and the throttle valve 5 regulates the intake air amount of the engine. Each branch of the intake manifold 4 is provided with an electromagnetic fuel injection valve 6 for each cylinder. The electronic control of the amount of fuel injected and supplied from the fuel injection valve 6 enables the mixing of a predetermined air-fuel ratio. Qi is formed. The air-fuel mixture sucked into the cylinder via the intake valve 7 is ignited and burned by spark ignition by the ignition plug 8, and the combustion exhaust gas is discharged via the exhaust valve 9 and guided to a catalyst and a muffler (not shown) by the exhaust manifold 10. I will

An EGR passage 11 is provided for communicating the exhaust manifold 10 with the intake manifold 4, and an EGR control valve 12 is provided in the EGR passage 11. When the EGR control valve 12 is opened, a part of the exhaust gas is recirculated to the engine intake system due to the pressure difference between the exhaust system and the intake system, and the EGR lowers the combustion temperature.
x emission is reduced.

The EGR control valve for controlling the effective opening area of the EGR passage 11 is, for example, a combination of a diaphragm valve and a solenoid valve for controlling the supply of operating pressure (engine negative pressure) to the valve. May be.
A control unit 13 for controlling the fuel injection valve 6 and the EGR control valve 12 includes a microcomputer. The control unit 13 includes an intake air amount signal Q from a hot wire air flow meter 14 and a throttle valve opening signal TVO from a throttle sensor 15. , A crank angle signal (engine rotation signal) from the crank angle sensor 16, an in-cylinder pressure signal from the in-cylinder pressure sensor 17, and the like.

The air flow meter 14 detects the amount of intake air of the engine 1 as a mass flow rate based on, for example, a change in resistance of the temperature-sensitive resistance due to the amount of intake air. The crank angle sensor 16 includes, for example, an electromagnetic pickup that detects a ring gear of a flywheel, and outputs a detection pulse for each unit angle. The engine speed Ne can be calculated based on the detection signal from the crank angle sensor 16.

The in-cylinder pressure sensor 17 is provided by
As disclosed in Japanese Patent Publication No. 7432, this is a ring-shaped sensor including a piezoelectric element, and the ignition plug 8 is lifted by receiving the combustion pressure to change its set load. It outputs the corresponding signal. The in-cylinder pressure sensor 17 is provided in a specific cylinder of the engine 1.

The control unit 13 determines the required EGR rate based on the engine operating conditions.
The opening of the EGR control valve 12 is controlled based on the R ratio, and the amount of fuel injected by the fuel injection valve 6 is controlled. The control of the injection amount of the fuel injection valve 6 is performed as follows. That is,
Based on the intake air amount Q detected by the air flow meter 14 and the engine speed Ne calculated from the detection signal from the crank angle sensor 16, the basic fuel injection amount Tp (= K × Q
/ Ne: K is a constant), and the basic fuel injection amount Tp is corrected according to the operating conditions such as the cooling water temperature to obtain the final fuel injection amount Ti.

Then, a drive pulse signal having a pulse width corresponding to the fuel injection amount Ti is output to the fuel injection valve 6 at a predetermined timing. Fuel adjusted to a predetermined pressure by a pressure regulator (not shown) is supplied to the fuel injection valve 6, and an amount of fuel proportional to the pulse width of the drive pulse signal is injected and supplied. On the other hand, the control of the EGR control valve 12 by the control unit 13 (EGR control) basically determines a required EGR rate in accordance with the engine load and the engine rotation speed Ne.
The conversion is performed into a control signal to the control valve 12.

The control unit 13 is provided with an EGR
It has a function of performing a failure diagnosis of the EGR device including the passage 11 and the EGR control valve 12. Details of the failure diagnosis of the EGR device will be described with reference to the flowcharts of FIGS. Note that, in the present embodiment, the idling operation state determining means, the EGR control valve opening control means, the compression pressure change calculating means, the failure diagnosing means, the first comparing means, the second comparing means, the determining means, the holding of the present invention The functions of the means, the measuring means, the exhaust gas recirculation control valve opening changing means, and the judgment value changing means are provided by software in the control unit 13 as shown in the flowcharts of FIGS.

In the flowchart of FIG. 3, in step 1 (hereinafter abbreviated as S1; the same applies hereinafter), the engine is in idling operation, that is, the idle switch is turned on.
It is determined whether the feedback control of the idle speed control ISC is being performed (CLOSEG control is being performed) and the load of various auxiliary devices such as an air conditioner is constant (the various auxiliary devices are fixed to ON or OFF). .

When the condition of step 1 is satisfied, the exhaust gas recirculation is not performed by the normal control, but before the start of EGR. When the condition of step 1 is satisfied, step 2
Proceed to. In step 2, the compression pressure before the start of EGR (at the time of EGR control valve closing control) is detected.

This compression pressure can be detected by the following calculation or measurement. That is, based on the signal from the in-cylinder pressure sensor 17, the in-cylinder pressure integrated value during the predetermined crank angle is calculated or the in-cylinder pressure value at the predetermined crank angle is measured by the in-cylinder pressure sensor 17. The predetermined crank angle is before TDC.

In step 3, the EGR control valve (EGR /
V) 12 is forcibly opened by a predetermined opening.
The compression pressure after opening the GR control valve 12 by a predetermined opening is measured. Note that the opening of the EGR control valve 12 that is forcibly opened in step 3 is changed according to the number of diagnoses or the number of suspensions described later. In step 5, since EGR was forcibly performed in step 3, EGR was performed in order to cut EGR.
The R control valve 12 is fully closed.

In the next step 6, diagnosis is executed. Here, in the present invention, a change in the compression pressure of the engine before and after the opening control of the EGR control valve 12 is calculated,
An exhaust gas recirculation amount change ratio is calculated based on the calculated compression pressure change amount and a target compression pressure change amount, and a failure of the exhaust gas recirculation device is diagnosed based on the calculated exhaust gas recirculation amount change ratio.

Such a diagnosis is determined as shown in the flowchart of FIG. In this flowchart, in step 21, a change in the compression pressure of the engine before and after the opening control of the EGR control valve 12 is calculated. That is, FIG.
The relationship between the EGR control valve opening and the compression pressure is shown. To detect the compression pressure before the start of EGR. In E
1. Detecting the compression pressure when GR is opened; And the compression pressure value at 1. Is calculated from the compression pressure value in (compression compression change amount = compression pressure value in 2.−).
1. Compression pressure value).

In step 22, a target compression pressure change is determined from the opening of the EGR control valve 12.
In this case, as shown in FIG. 6, a target compression pressure change amount with respect to the EGR control valve opening degree is set in advance by a map,
The target compression pressure change amount with respect to the EGR control valve opening at that time may be read with reference to a map.

In step 23, the EGR amount change rate is calculated based on the calculated compression pressure change allowance and target compression pressure change allowance (EGR amount change rate = calculated compression pressure change allowance / target compression pressure change allowance). . In step 24, the EGR amount change ratio calculated in step 23 and NG
Compare with the judgment value.

If it is determined that the EGR amount change ratio ≦ NG determination value, it is determined in step 25 that the EGR device is NG, and the diagnosis is terminated. On the other hand, the EGR amount change ratio>
If it is determined that the value is NG, the process proceeds to step S26. In step 26, the EGR amount change ratio calculated in step 23 is compared with the OK determination value.

If it is determined that the EGR amount change ratio ≧ OK determination value, it is determined in step 27 that the determination is OK, and the diagnosis is terminated. That is, if the EGR device is normal, the EGR amount change rate should be large. Therefore, the operating state of the EGR device can be determined by looking at the EGR amount change ratio.

On the other hand, if it is determined in step 26 that the EGR amount change ratio <OK determination value, the process proceeds to step 28 and determines that the diagnosis is suspended. Step 25, Step 2
7. In step 29 after step 28, the number of diagnoses is counted and the routine returns. Step 24
The NG determination value and the OK determination value used for the diagnosis in step 26 are changed according to the number of times of diagnosis or the number of times of suspension, which will be described later.

Here, in the flowchart of FIG.
In step 3, the opening of the EGR control valve 12, which is forcibly opened, is changed according to the number of diagnoses. As shown in FIG. 7, the opening of the EGR control valve 12 is changed so as to gradually increase as the number of diagnoses increases. . Also, N used for diagnosis in steps 24 and 26 of the flowchart of FIG.
The G determination value and the OK determination value are changed according to the number of diagnoses. For example, the NG determination value is gradually changed as the number of diagnosis increases as shown in FIG.
As shown in the figure, the K determination value gradually decreases as the number of diagnoses increases.

Instead of the number of diagnoses, the number of suspensions may be measured, and the opening of the EGR control valve 12 and the NG determination value and the OK determination value that are forcibly opened may be changed according to the number of suspensions. Next, in the flowchart of FIG. 3, the process proceeds to step 7 to determine whether the diagnosis determination result is NG. If the result is NG, the process proceeds to step 8 and the EGR device malfunctions (clogging of the EGR system, EGR If the diagnosis determination result is not NG, the process proceeds to step 9 and determines whether or not the diagnosis determination result is OK. If the diagnosis determination result is OK, the process proceeds to step 10 and the EGR is performed. When it is determined that the apparatus is normal and the diagnosis determination result is not OK (determined as suspension), the process returns to step 1.

In this diagnostic control, the EGR amount change ratio may be calculated for each diagnosis, an average value of the calculated EGR amount change ratios may be calculated, and this may be used as a determination parameter. As described above, EG during idling operation
The amount of change in the compression pressure of the engine when the R control valve 12 is closed and thereafter when the R control valve 12 is forcibly opened is calculated, and the EGR amount change ratio is calculated based on the amount of change in the compression pressure and the amount of change in the target compression pressure. Is compared with the determination value to diagnose the failure of the EGR device. Therefore, the opening and closing of the EGR control valve 12 during the idling operation does not cause a change in engine output, and NOx
There is no adverse effect such as an increase in generation amount.

Further, if the operating speed of the EGR control valve 12 is reduced, there is no possibility that the idling stability is deteriorated with the diagnosis control. In particular, in the above-described diagnosis determination, the opening of the EGR control valve 12 that is forcibly opened is changed in accordance with the number of diagnoses. By keeping the degree small,
If the determination is OK in the early stage of the diagnosis, the influence on the drivability can be almost eliminated, and the opening of the EGR control valve 12 which is forcibly opened is greatly changed as the number of diagnoses increases. By doing so, the accuracy of failure detection can be improved as the diagnosis progresses.

Further, an abnormal judgment value and a normal judgment value are set,
When the calculated exhaust gas recirculation amount change ratio exceeds the abnormality determination value and is less than the normal determination value, the diagnosis is suspended, so that the diagnosis can be performed more accurately.
Since the NG determination value is changed to a large value and the OK determination value is changed to a small value, the diagnosis ranges of OK and NG are narrowed at the beginning of the diagnosis, and the O / D is increased as the number of diagnoses is increased due to the suspended state.
The diagnostic range of each of K and NG can be expanded, and a diagnostic result can be reliably obtained while improving diagnostic accuracy and preventing erroneous diagnosis.

[0040]

As described above, according to the first aspect of the present invention, since the diagnostic control is performed by opening and closing the exhaust gas recirculation control valve during idling operation, the output of the engine does not change and the NOx generation amount does not increase. No adverse effects such as increase
If the operating speed of the exhaust gas recirculation control valve is reduced, there is no possibility that the idle stability is deteriorated with the diagnosis control , and the diagnosis is not performed.
As the process proceeds, the accuracy of failure detection can be improved.

According to the invention of claim 2, according to claim 1,
Similarly, diagnosis by opening and closing the exhaust gas recirculation control valve during idle operation
Because of the disconnection control, there is no change in engine output,
No adverse effects such as an increase in the amount of generated NOx
If the operating speed of the recirculation control valve is reduced,
There is no risk of deteriorating the idle stability, and it is easy to determine whether the exhaust gas recirculation device is normal or abnormal, whether it is normal or abnormal, and whether to suspend diagnosis based on the exhaust gas recirculation amount change rate. it can. According to the third and fourth aspects of the present invention, it is possible to minimize the influence on drivability, and to improve the accuracy of failure detection as the diagnosis progresses.

According to the fifth aspect of the present invention, it is possible to reliably obtain a diagnosis result while improving diagnosis accuracy and preventing erroneous diagnosis. According to the invention according to claim 6, the influence on the drivability can be prevented as much as possible, and as the diagnosis progresses, the accuracy of detecting a failure can be improved, and the accuracy of diagnosis can be increased to prevent erroneous diagnosis. Thus, a diagnosis result can be reliably obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of the invention according to claims 1 and 2 ;

FIG. 2 is a system diagram common to the embodiments of the invention according to claims 1 to 6;

FIG. 3 EGR diagnosis flow

FIG. 4 is a flow chart of a diagnosis judgment

FIG. 5 is a diagram showing the relationship between the EGR control valve opening and the compression pressure.

FIG. 6 is a characteristic diagram for explaining setting of a target compression pressure according to an EGR control valve opening degree;

FIG. 7 is a characteristic diagram illustrating the setting of the EGR control valve opening according to the number of diagnoses.

FIG. 8 is a characteristic diagram illustrating setting of an OK determination value and an NG determination value according to the number of times of diagnosis.

FIG. 9 is a time chart for explaining a conventional problem.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 4 Intake manifold 10 Exhaust manifold 11 EGR passage 12 EGR control valve 13 Control unit 17 In-cylinder pressure sensor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-288303 (JP, A) JP-A-2-130252 (JP, A) JP-A-4-81557 (JP, A) 1254 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) F02M 25/07 550 F02M 25/07 570

Claims (6)

(57) [Claims] 1. A diagnostic device for an exhaust gas recirculation system for an internal combustion engine for recirculating a part of engine exhaust to an intake system of the engine through an exhaust gas recirculation passage provided with an exhaust gas recirculation control valve. An idling operation state judging means for judging a state; an exhaust gas recirculation control valve opening control means for forcibly opening the exhaust gas recirculation control valve when the idling operation state is judged by the idling operation state judging means; Compression pressure detecting means for detecting the compression pressure of the engine before and after the opening control of the exhaust gas recirculation control valve when detected, and a change in the compression pressure of the engine before and after the opening control of the exhaust gas recirculation control valve. Compression pressure change amount calculating means for calculating a change amount, and an exhaust gas recirculation amount change ratio calculating means for calculating an exhaust gas recirculation amount change ratio based on the calculated compression pressure change amount and a target compression pressure change amount. A failure diagnosis means for diagnosing a failure of the exhaust gas recirculation device based on the exhaust gas recirculation amount change ratio that is the calculation, a measurement means for measuring the number of diagnoses of the fault, depending on the measured number of diagnoses, opened forcibly Exhaust recirculation system
A diagnostic device for an exhaust gas recirculation device for an internal combustion engine, comprising: an exhaust gas recirculation control valve opening changing means for changing an opening of a control valve . 2. An exhaust gas recirculation control valve intervenes a part of the engine exhaust gas.
Recirculated to the intake system of the engine through the exhaust gas recirculation passage
A diagnostic device for an exhaust gas recirculation device of a fuel engine, comprising: an idle operating state determination device for determining an idle operating state of the engine.
Setting means and the idling operation state determining means
The exhaust gas recirculation control valve is forcibly opened when it is determined that
Exhaust gas recirculation control valve opening control means, and opening of the exhaust gas recirculation control valve when an idle operation state is detected
Compression that detects the compression pressure of the engine before control and after the open control, respectively.
A pressure detecting means, and a compression pressure of the engine before and after the exhaust gas recirculation control valve is opened.
Means for calculating a change in the force of the compression pressure, a means for calculating the change in the compression pressure,
Exhaust gas return that calculates the rate of change in exhaust gas recirculation based on chemical allowance
Flow rate change rate calculating means, first comparing means for comparing the calculated exhaust gas recirculation amount change rate with the abnormality determination value, and second comparing means for comparing the calculated exhaust gas recirculation amount change rate with the normal determination value and comparison means, based on the comparison result by the comparison means, the computed exhaust gas recirculation amount change ratio exhaust gas recirculation system when: the abnormality determination value is determined to be abnormal, the computed discharge Kikae Determining means for determining that the exhaust gas recirculation device is normal when the flow rate change rate exceeds the abnormality determination value and is equal to or greater than the normal determination value; and the calculated exhaust gas recirculation amount change rate exceeds the abnormality determination value and determines the normality. diagnostic device for an exhaust gas recirculation apparatus for an internal combustion engine you characterized in that the holding means for the diagnosis pending, and configured to include at below. 3. An exhaust gas recirculation control valve opening degree changing means for changing an opening degree of an exhaust gas recirculation control valve which is forcibly opened according to the measured number of times of diagnosis. 3. The diagnostic device for an exhaust gas recirculation device for an internal combustion engine according to claim 2 , wherein the diagnostic device comprises: 4. An exhaust gas recirculation control valve opening change means for changing an opening of an exhaust gas recirculation control valve which is forcibly opened according to the measured number of times of diagnosis suspension. The diagnostic device for an exhaust gas recirculation device for an internal combustion engine according to claim 2, wherein the diagnostic device comprises: 5. A measuring means for measuring the number of times of diagnosis or suspension of the failure, and a judgment value changing means for changing a normal judgment value and an abnormality judgment value according to the measured number of times of diagnosis or suspension. 3. The diagnostic device for an exhaust gas recirculation system for an internal combustion engine according to claim 2, wherein: 6. A measurement means for measuring the number of times of diagnosis or suspension of the failure, and an exhaust gas recirculation control valve for changing an opening of an exhaust gas recirculation control valve which is forcibly opened according to the measured number of times of diagnosis or suspension. The internal combustion engine according to claim 2, comprising: an opening degree changing means; and a judgment value changing means for changing a normal judgment value and an abnormality judgment value according to the measured number of diagnoses or the number of holdings. Diagnosis device for engine exhaust gas recirculation system.