JPH09158787A - Diagnostic device for exhaust gas recirculation device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent operability from being worsened in association with the diagnostic control of an exhaust gas recirculation device by forcibly opening an exhaust gas recirculation control valve at the time of an idle operating state being judged, detecting the compression pressure of an engine respectively before and after valve opening control to compute a change margin, and diagnosing the failure of the exhaust gas recirculation device on the basis of a change rate. SOLUTION: During the operation of an engine, a control unit 13 judges whether an idle switch is on, idling engine speed is under feedback control and the load of various auxiliary machines is constant. At the time of judging affirmative, the cylinder internal pressure integrated value between specified crank angles is obtained on the basis of a signal from a cylinder internal pressure sensor 17. An EGR control valve 12 is then opened forcibly to specified opening, and compression pressure at this time is measured. The change margin of compression pressure before and after the opening control of the EGR control valve 12 is computed, and on the basis of this change margin and a target compression pressure change margin, an exhaust gas recirculation quantity change rate is computed. On the basis of this computed exhaust gas recirculation quantity change rate, the failure of an exhaust gas recirculation device is diagnosed.

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 its failure.

[0002]

2. Description of the Related Art Conventionally, in an internal combustion engine, as a device for reducing NOx in the engine exhaust, a part of the engine exhaust is recirculated to an intake manifold to recirculate a part of the engine exhaust to the intake manifold. Accordingly, an exhaust gas recirculation (hereinafter referred to as EGR) device that lowers the maximum combustion temperature to reduce the production of NOx is known.

By the way, if the desired EGR cannot be performed due to such a failure of the EGR device, the amount of NOx emission will be increased, so that a device for diagnosing the failure of the EGR device is required. Therefore, the applicant of the present invention has focused on the characteristic that the output torque of the engine changes depending on the presence or absence of EGR, and provides a diagnostic device that performs diagnosis based on the change in combustion pressure when the EGR is forcibly turned on and off. It has been previously proposed (see Japanese Patent Application No. 5-78177).

A diagnostic technique based on such a change in combustion pressure is EGR based on a deviation of a parameter change amount such as a crank angle at which a heat release rate calculated from an in-cylinder pressure has a predetermined value, an indicated mean effective pressure, a compression pressure and the like. It is known that the amount is estimated, the estimated EGR amount is compared with a prescribed value, and whether the EGR amount is proper is diagnosed to diagnose a failure of the EGR device.

[0005]

However, in the above-mentioned conventional EGR diagnosis technique, the EGR ON / OFF control that causes a change in the output of the engine is performed to perform the diagnosis. If the EGR amount normally changes, an output change actually occurs, and adverse effects such as deterioration of drivability and an increase in the amount of NOx generation occur due to the diagnostic 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 above conventional diagnostic control. This indicates that the / V opening changes, the ignition timing ADV changes, the output torque fluctuates, and NOx is excessively discharged by the amount shown by the grid line in the figure.

In view of the above conventional circumstances, it is an object of the present invention to prevent adverse effects such as deterioration of drivability and increase of NOx generation amount due to diagnostic control of the exhaust gas recirculation system. To do.

[0008]

Therefore, in the invention according to claim 1, as shown in FIG. 1, part of the engine exhaust gas is passed through the exhaust gas recirculation passage in which the exhaust gas recirculation control valve is interposed. A diagnostic device for an exhaust gas recirculation system for an internal combustion engine, which recirculates to an intake system, comprising: an idle operating state determining means for determining an idle operating state of the engine; and an idle operating state determining means for determining an idle operating state when the idle operating state is determined. Exhaust gas recirculation control valve opening control means forcibly opening the exhaust gas recirculation control valve, and compression pressure detection for detecting the compression pressure of the engine before and after the exhaust gas recirculation control valve opening control when an idle operation state is detected Means, a compression pressure change margin calculation means for calculating a variation margin of the compression pressure of the engine before and after the exhaust recirculation control valve opening control, and the calculated compression pressure variation margin and a target compression pressure variation margin. Based on And exhaust gas recirculation amount change rate calculating means for calculating an exhaust gas recirculation amount change rate you are, and configured to include a fault 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.

In such a configuration, diagnostic control is performed by opening / closing the exhaust gas recirculation control valve during idle operation. Therefore,
The output of the engine is not changed, adverse effects such as an increase in the amount of NOx produced do not occur, and if the operating speed of the exhaust gas recirculation control valve is slowed, there is no risk of deterioration of idle stability accompanying diagnostic control. According to a second aspect of the present invention, the failure diagnosing means includes first comparing means for comparing the calculated exhaust gas recirculation amount change rate with an abnormality determination value, and the calculated exhaust gas recirculation amount change rate and normality determination. A second comparing means for comparing the value with a value, and based on the comparison result by the comparing means, it is determined that the exhaust gas recirculation device is abnormal when the calculated change rate of the exhaust gas recirculation amount is equal to or less than the abnormality determination value, A determination unit that determines that the exhaust gas recirculation device is normal when the calculated change rate of the exhaust gas recirculation amount of the entire cylinder exceeds the abnormality determination value and is equal to or higher than the normal determination value; and the calculated change rate of the exhaust gas recirculation amount is abnormal. And a holding means that puts the diagnosis on hold when the judgment value is exceeded and the judgment value is less than the normal value.

In such a configuration, it is easy to determine whether the exhaust gas recirculation device is normal or abnormal, whether the normal or abnormal cannot be judged, and the diagnosis is suspended based on the exhaust gas recirculation amount change ratio. According to a third aspect of the present invention, a measuring means for measuring the number of times of diagnosis of the failure, and an exhaust gas recirculation control valve opening degree change for changing the opening degree of the exhaust gas recirculation control valve forcibly opened according to the measured number of times of diagnosis. And means.

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

In the structures of the inventions according to claims 3 and 4, the influence on the drivability is prevented as much as possible, and the accuracy of failure detection is improved as the diagnosis progresses. Claim 5
The invention according to, includes a measuring means for measuring the number of times of diagnosis of the failure or the number of holding times, and a judgment value changing means for changing the normal judgment value and the abnormality judgment value according to the measured number of diagnoses or the number of holding times. Composed of.

In such a structure, the diagnostic accuracy can be improved and erroneous diagnosis can be prevented, and the diagnostic result can be obtained reliably. According to a sixth aspect of the present invention, a measuring unit that measures the number of times of diagnosis or the number of times of failure of the failure, and exhaust that changes the opening degree of the exhaust gas recirculation control valve that is forcibly opened according to the measured number of times of diagnosis or the number of times of holding are measured The recirculation control valve opening changing means and the judgment value changing means for changing the normal judgment value and the abnormal judgment value according to the measured number of times of diagnosis or the number of times of holding are included.

In such a structure, the influence on the drivability is prevented as much as possible, the accuracy of detecting a failure is improved as the diagnosis progresses, and the accuracy of the diagnosis is increased to prevent erroneous diagnosis, and the diagnosis result is improved. Is definitely 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 of a common embodiment of the invention according to claims 1 to 6, air is sucked into an internal combustion engine 1 of a vehicle through 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 interlocking with an accelerator pedal (not shown), and the throttle valve 5 adjusts the intake air amount of the engine. An electromagnetic fuel injection valve 6 is provided for each cylinder in each branch portion of the intake manifold 4, and a predetermined air-fuel ratio is mixed by electronically controlling the amount of fuel injected and supplied from the fuel injection valve 6. Qi is formed. The air-fuel mixture sucked into the cylinder through the intake valve 7 is ignited and burned by the spark ignition by the spark plug 8, and the combustion exhaust gas is discharged through the exhaust valve 9 and guided to a catalyst and a muffler (not shown) by the exhaust manifold 10. Get burned.

An EGR passage 11 that connects the exhaust manifold 10 and the intake manifold 4 is provided, and an EGR control valve 12 is interposed 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 combustion temperature is lowered by the EGR, so that NO
x emission amount can be 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.
The control unit 13 for controlling the fuel injection valve 6 and the EGR control valve 12 is configured by including a microcomputer, and the intake air amount signal Q from the hot wire air flow meter 14 and the throttle valve opening signal TVO from the throttle sensor 15. The crank angle signal (engine rotation signal) from the crank angle sensor 16 and the in-cylinder pressure signal from the in-cylinder pressure sensor 17 are input.

The air flow meter 14 detects the intake air amount of the engine 1 as a mass flow rate, for example, based on the resistance change of the temperature-sensitive resistance due to the intake air amount. 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 rotation speed Ne can be calculated based on the detection signal from the crank angle sensor 16.

The in-cylinder pressure sensor 17 is a practically open type 63-1.
As disclosed in Japanese Patent No. 7432, a ring-shaped sensor including a piezoelectric element, in which the ignition plug 8 receives combustion pressure and lifts to change its set load, the combustion pressure changes to It outputs a 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, and the required EGR rate is determined.
The opening degree of the EGR control valve 12 is controlled based on the R ratio, and the fuel injection amount of 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,
The basic fuel injection amount Tp (= K × Q) based on the intake air amount Q detected by the air flow meter 14 and the engine rotation speed Ne calculated from the detection signal from the crank angle sensor 16.
/ 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. The fuel, which is adjusted to a predetermined pressure by a pressure regulator (not shown), is supplied to the fuel injection valve 6, and the fuel is injected and supplied in an amount proportional to the pulse width of the drive pulse signal. On the other hand, the control (EGR control) of the EGR control valve 12 by the control unit 13 basically determines the required EGR rate according to the engine load and the engine rotation speed Ne, and the required EGR rate is determined by the EGR rate.
It is performed by converting the control signal to the control valve 12.

Further, the control unit 13 has an EGR
It has a function of diagnosing a failure 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. 3 and 4. In the present embodiment, the idle operation state determination means, the EGR valve opening control means, the compression pressure change amount calculation means, the failure diagnosis means, the first comparison means, the second comparison means, the determination means, and the hold of the present invention are provided. As shown in the flowcharts of FIGS. 3 and 4, the control unit 13 is provided with software for each function of the means, the measuring means, the exhaust gas recirculation control valve opening degree changing means, and the determination value changing means.

In the flowchart of FIG. 3, in step 1 (hereinafter abbreviated as S1. The same applies hereinafter), the engine is in idle operation, that is, the idle switch is ON.
In addition, it is determined whether or not the feedback control of the idle speed control ISC is being performed (CLOSEG control is being performed) and the loads of various auxiliary devices such as an air conditioner are constant (the various auxiliary devices are fixed to ON or OFF). .

When the condition of step 1 is satisfied, it is a region where exhaust gas recirculation is not performed by the normal control and before the EGR is started. When the condition of step 1 is satisfied, step 2
Proceed to. In step 2, the compression pressure before starting EGR (during 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 between the predetermined crank angles 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 degree, and in step 4, E
The compression pressure after opening the GR control valve 12 by a predetermined opening is measured. The opening degree of the EGR control valve 12 that is forcibly opened in step 3 is changed depending on the number of times of diagnosis or the number of times of holding described later. In step 5, since EGR was forcibly performed in step 3, EG is cut in order to cut EGR.
The R control valve 12 is fully closed.

Next, in step 6, a diagnostic judgment is executed. Here, in the present invention, the change margin of 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 malfunction of the exhaust gas recirculation device is diagnosed based on the calculated exhaust gas recirculation amount change ratio.

The diagnosis determination is executed as shown in the flowchart of FIG. In this flowchart, in step 21, the change margin of 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 in FIG. The compression pressure before the start of EGR is detected at step 2. At E
1. The compression pressure when the GR is opened is detected. Compression pressure value and 1. The change margin of compression compression is calculated from the compression pressure value at (compression change amount = compression pressure value at 2.
1. Compression pressure value).

In step 22, the target compression pressure change margin is obtained from the opening degree of the EGR control valve 12.
In this case, as shown in FIG. 6, the target compression pressure change margin with respect to the EGR control valve opening 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 the map.

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

When it is determined that the EGR amount change rate ≦ NG determination value, it is determined in step 25 that the EGR device is NG, and the diagnosis is ended. On the other hand, EGR amount change rate>
If it is determined to be the NG determination value, the process proceeds to step 26. In this step 26, the EGR amount change rate 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 it is OK, and the diagnosis is ended. 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 rate.

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

Here, in the flowchart of FIG.
The opening degree of the EGR control valve 12 which is forcibly opened in step 3 is changed according to the number of times of diagnosis, but as shown in FIG. 7, this is changed so that the EGR control opening degree is gradually increased as the number of times of diagnosis increases. . Also, N used for diagnosis in steps 24 and 26 of the flowchart of FIG.
The G judgment value and the OK judgment value are changed depending on the number of diagnoses. For example, as shown in FIG. 8, the NG judgment value is gradually changed as the number of diagnoses increases.
The K determination value is gradually decreased as the number of diagnoses increases, as shown in FIG.

Instead of the number of times of diagnosis, the number of times of holding may be measured and the opening degree of the EGR control valve 12 forcibly opened and the NG judgment value and the OK judgment value may be changed depending on the number of times of holding. Next, in the flowchart of FIG. 3, the routine proceeds to step 7, where it is determined whether or not the diagnosis determination result is NG. If the result is NG, the routine proceeds to step 8 where a failure of the EGR device (clogging of EGR system, EGR system, If the diagnosis judgment result is not NG, the process proceeds to step 9, and it is judged whether the diagnosis judgment result is OK. If it is OK, the process proceeds to step 10 and EGR is performed. When it is determined that the device is normal and the diagnosis determination result is not OK (held), the process returns to step 1.

In this diagnostic control, the EGR amount change rate may be calculated for each diagnosis, and the average value of the calculated EGR amount change rates may be calculated and used as a determination parameter. As described above, the EG during idle operation
The change margin of the compression pressure of the engine when the R control valve 12 is closed and the forced opening thereafter is calculated, and the EGR amount change ratio is calculated based on the compression pressure change margin and the target compression pressure change margin. Is configured to diagnose a failure of the EGR device by comparing with the determination value, and thus opening and closing of the EGR control valve 12 during idle operation does not cause a change in the output of the engine, and NOx
There will be no adverse effects such as increased generation.

Further, if the operating speed of the EGR control valve 12 is slowed, there is no fear that the idle stability will deteriorate due to the diagnostic control. In particular, in the above-described diagnosis determination, the opening degree of the EGR control valve 12 that is forcibly opened is changed according to the number of diagnoses. Therefore, when the number of diagnoses is small, the EGR control valve 12 that is forcibly opened is opened. By keeping the degree small,
When the OK determination is made in the early stage of the diagnosis, the influence on the drivability can be almost eliminated, and the opening degree of the EGR control valve 12 that is forcibly opened is largely changed as the number of times of diagnosis increases. By doing so, the failure detection accuracy can be improved as the diagnosis progresses.

Further, by setting an abnormal judgment value and a normal judgment value,
Since the diagnosis is suspended when the calculated exhaust gas recirculation amount change ratio exceeds the abnormality determination value and is less than the normal determination value, the diagnosis can be performed more accurately, and in particular, depending on the number of times of diagnosis,
Since the NG judgment value is changed to a large value and the OK judgment value is changed to a small value, the diagnosis range of each of OK and NG is narrowed at the beginning of the diagnosis, and as the number of diagnoses increases as the number of diagnoses increases due to the suspended state.
The diagnostic range of each of K and NG can be expanded, the diagnostic accuracy can be improved, and erroneous diagnosis can be prevented, and the diagnostic result can be reliably obtained.

[0040]

As described above, according to the first aspect of the invention, since the diagnostic control is performed by opening and closing the exhaust gas recirculation control valve during idle operation, the output of the engine is not changed and the NOx generation amount is not increased. There is no adverse effect such as increase,
If the operating speed of the exhaust gas recirculation control valve is slowed, there is no fear that the idle stability will deteriorate due to the diagnostic control.

According to the second aspect of the present invention, it is easy to determine whether the exhaust gas recirculation device is normal or abnormal based on the exhaust gas recirculation amount change rate, and whether the diagnosis can be suspended because normality or abnormality cannot be determined. Can be determined. According to the inventions according to claims 3 and 4, the influence on the drivability can be prevented as much as possible, and the accuracy of the failure detection can be improved as the diagnosis progresses.

According to the fifth aspect of the present invention, the diagnostic result can be surely obtained while enhancing the diagnostic accuracy and preventing the erroneous diagnosis. According to the invention of claim 6, the influence on the drivability can be prevented as much as possible, the accuracy of detecting a failure can be improved as the diagnosis progresses, and the accuracy of the diagnosis can be increased to prevent erroneous diagnosis. Therefore, the diagnosis result can be surely obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an invention according to claim 1.

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] Diagnostic judgment flow

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

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

FIG. 7 is a characteristic diagram illustrating setting of an EGR control valve opening degree 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 diagnoses.

FIG. 9 is a time chart explaining conventional problems.

[Explanation of symbols]

 1 Internal Combustion Engine 4 Intake Manifold 10 Exhaust Manifold 11 EGR Passage 12 EGR Control Valve 13 Control Unit 17 Cylinder Pressure Sensor

Claims (6)

[Claims] 1. A diagnostic device for an exhaust gas recirculation system for an internal combustion engine, which recirculates a part of engine exhaust gas to an intake system of the engine through an exhaust gas recirculation passage having an exhaust gas recirculation control valve, and an engine idle operation. An idle operation state determination means for determining a state; an exhaust gas recirculation control valve opening control means for forcibly opening the exhaust gas recirculation control valve when the idle operation state determination means determines the idle operation state; and an idle operation state A compression pressure detecting means for detecting the compression pressure of the engine before and after the exhaust recirculation control valve opening control when detected, respectively, and a change in the compression pressure of the engine before and after the exhaust recirculation control valve opening control And an exhaust gas recirculation amount change ratio calculating unit for calculating an exhaust gas recirculation amount change ratio based on the calculated compression pressure change amount and the target compression pressure change amount. Diagnostic device for an exhaust gas recirculation system for an internal combustion engine, characterized in that configured to include a a fault 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. 2. The failure diagnosing means compares the calculated exhaust gas recirculation amount change rate with an abnormality judgment value, and the calculated exhaust gas recirculation quantity change rate and a normal judgment value. Based on the comparison result by the second comparing means for comparing and the comparing means, it is determined that the exhaust gas recirculation device is abnormal when the calculated change rate of the exhaust gas recirculation amount is equal to or less than the abnormality determination value, and the calculation is performed. Determining means for determining that the exhaust gas recirculation device is normal when the change rate of the exhaust gas recirculation amount in the entire cylinder exceeds the abnormality determination value and is equal to or higher than the normal determination value; 2. The diagnostic device for an exhaust gas recirculation system for an internal combustion engine according to claim 1, further comprising: a holding means that holds the diagnosis when the value is over and less than the normal determination value. 3. A measuring means for measuring the number of times of diagnosis of the failure, and an exhaust gas recirculation control valve opening degree changing means for changing the opening degree of the exhaust gas recirculation control valve which is forcibly opened according to the measured number of times of diagnosis. The diagnostic device for an exhaust gas recirculation device for an internal combustion engine according to claim 1 or 2, wherein 4. A measuring means for measuring the number of times of holding the diagnosis, and an exhaust gas recirculation control valve opening degree changing means for changing the opening degree of the exhaust gas recirculation control valve which is forcibly opened according to the measured number of times of holding the diagnosis. 3. A diagnostic device for an exhaust gas recirculation system for an internal combustion engine according to claim 2, wherein 5. A measuring means for measuring the number of times of diagnosis of the failure or the number of times of holding, and a judgment value changing means for changing a normal judgment value and an abnormal judgment value according to the measured number of times of diagnosis or holding. The diagnostic device for an exhaust gas recirculation device for an internal combustion engine according to claim 2, wherein 6. A measuring means for measuring the number of times of diagnosis of the failure or the number of times of holding, and an exhaust gas recirculation control valve for changing the opening of the exhaust gas recirculation control valve which is forcibly opened according to the measured number of times of diagnosis or the number of times of holding. The internal combustion engine according to claim 2, further comprising: an opening degree changing means; and a judgment value changing means for changing the normal judgment value and the abnormal judgment value according to the measured number of diagnoses or the number of times of holding. Diagnostic device for engine exhaust gas recirculation system.