JP3089390B2 - Diagnostic 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 a diagnostic device for an exhaust gas recirculation device of an internal combustion engine, and more particularly to a device for making a diagnosis based on a change in combustion pressure when an exhaust gas recirculation amount is changed.

[0002]

2. Description of the Related Art Conventionally, in automobile internal combustion engines,
BACKGROUND ART As a device for reducing NOx in engine exhaust, an exhaust gas recirculation device (EGR) that lowers the maximum combustion temperature and reduces NOx generation by recirculating a part of the engine exhaust to an intake manifold is known. I have.

[0003] Here, if the intended exhaust gas recirculation cannot be performed due to the failure of the exhaust gas recirculation device, the amount of NOx emission will increase. Therefore, a device capable of diagnosing the failure of the exhaust gas recirculation device is required. . Therefore, the present applicant pays attention to the characteristic that the output torque of the engine changes according to ON / OFF of the exhaust gas recirculation, and makes a diagnosis based on the change in the combustion pressure when the exhaust gas recirculation is forcibly turned ON / OFF. A diagnostic device has been previously proposed (see Japanese Patent Application No. 5-78177).

[0004]

However, the conventional diagnostic apparatus is configured to perform the diagnosis by performing the ON / OFF control of the exhaust gas recirculation, which causes a change in the output of the engine. If it changes, there is a problem that an output change actually occurs, and the drivability deteriorates with the diagnosis control.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a diagnostic apparatus for an exhaust gas recirculation apparatus capable of performing a diagnosis based on a change in a combustion pressure generated by controlling an exhaust gas recirculation amount and avoiding the occurrence of output fluctuation. The purpose is to provide.

[0006]

According to the present invention, there is provided a diagnostic apparatus for recirculating a part of engine exhaust to an intake system of an engine through an exhaust recirculation passage provided with an exhaust recirculation control valve. This is a diagnostic device in the exhaust gas recirculation device of the engine, and is configured as shown in FIG. In FIG. 1, an in-cylinder pressure detecting means detects an in-cylinder pressure of a specific cylinder of the engine.

The forced opening / closing means forcibly controls the opening / closing of the exhaust gas recirculation control valve when a predetermined diagnostic condition is satisfied. The diagnosis means determines whether there is an abnormality in the exhaust gas recirculation device based on a change in the in-cylinder pressure in the specific cylinder detected by the in-cylinder pressure detection means in accordance with the opening / closing control of the exhaust gas recirculation control valve by the forced opening / closing means. Determine.

[0008] Here, the ignition timing correction means, when the opening / closing control of the exhaust gas recirculation control valve is performed by the forcible opening / closing means, suppresses a change in engine output torque due to a change in the amount of exhaust gas recirculation in a direction other than the specific cylinder. Correct the ignition timing. In the diagnostic device for an exhaust gas recirculation device for an internal combustion engine according to the invention of claim 2, the forcible opening / closing means is configured to gradually change the opening of the exhaust gas recirculation control valve in a stepwise manner.

According to a third aspect of the present invention, in the diagnostic apparatus for the exhaust gas recirculation system for an internal combustion engine, the diagnostic means integrates the in-cylinder pressure detected by the in-cylinder pressure detecting means in a predetermined integration section,
The variation in the in-cylinder pressure integrated value caused by the opening / closing control of the exhaust gas recirculation control valve is compared with a predicted value of the variation based on operating conditions to determine whether there is an abnormality.

[0010]

According to the diagnostic apparatus for the exhaust gas recirculation system for an internal combustion engine according to the first aspect of the present invention, the exhaust gas recirculation amount is changed by forcibly controlling the opening and closing of the exhaust gas recirculation control valve. The determination is made based on the in-cylinder pressure (combustion pressure) change in the specific cylinder.

On the other hand, even in a cylinder other than the specific cylinder in which the in-cylinder pressure is detected for the diagnosis, a change in the combustion pressure occurs with a change in the exhaust gas recirculation amount. The change occurs in the same manner, resulting in a large output fluctuation. Here, it is not necessary to cause a change in the combustion pressure corresponding to the change in the exhaust gas recirculation amount except for the specific cylinder irrelevant to the diagnosis. ,
In the engine as a whole, output fluctuations due to changes in the amount of exhaust gas recirculation are sufficiently suppressed.

According to the diagnostic apparatus for an exhaust gas recirculation system for an internal combustion engine according to the second aspect of the present invention, the opening degree of the exhaust gas recirculation control valve is gradually changed in a stepwise manner to suppress a large sudden change in the exhaust gas recirculation amount. Thus, the effect of suppressing the torque fluctuation by correcting the ignition timing can be stably obtained. It is difficult to completely eliminate fluctuations in output torque due to changes in the amount of exhaust gas recirculation by correcting the ignition timing, causing relatively large torque fluctuations that cannot be corrected as much as the amount of exhaust gas recirculation changes suddenly. Therefore, the change in the exhaust gas recirculation amount is made small to minimize the torque fluctuation that occurs without being corrected.

According to the diagnostic apparatus for an exhaust gas recirculation system for an internal combustion engine according to the third aspect of the present invention, in the diagnosis using the in-cylinder pressure detected in a specific cylinder, a predetermined integral value is used instead of using the instantaneous value of the in-cylinder pressure. By using the integral value in the section, it is possible to avoid the occurrence of erroneous diagnosis due to the influence of noise or the like, while the change in the in-cylinder pressure (combustion pressure) due to the change in the exhaust gas recirculation amount varies depending on the operating condition. By comparing the predicted change width with the actually detected change width, highly accurate diagnosis can be performed for each operating condition.

[0014]

Embodiments of the present invention will be described below. In FIG. 2 showing a system configuration of an embodiment, an internal combustion engine 1 includes:
Air is sucked in through the air cleaner 2, the intake duct 3, and the 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 adjusts 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. A predetermined amount of fuel is injected by electronic control of the amount of fuel injected and supplied from the fuel injection valve 6. A fuel-fuel mixture is formed. The air-fuel mixture sucked into the cylinder via the intake valve 7 is ignited and burned by spark ignition by the spark plug 8, and the combustion exhaust is discharged through the exhaust valve 9 and is guided to a catalyst and a muffler (not shown) by the exhaust manifold 10. I will

An exhaust gas recirculation passage 11 is provided for communicating the exhaust manifold 10 with the intake manifold 4.
An EGR control valve 12 (exhaust gas recirculation control valve) is interposed in the exhaust gas recirculation 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 exhaust gas recirculates, thereby lowering the combustion temperature, thereby reducing the NOx emission. Is achieved.

The exhaust gas recirculation control valve for controlling the effective opening area of the exhaust gas recirculation 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. It may be. A control unit 13 for controlling the fuel injection valve 6 and the EGR control valve 12 includes a microcomputer, and includes an intake air amount signal Q from an air flow meter 14 and a throttle valve opening signal T from a throttle sensor 15.
VO, a crank angle signal (engine rotation signal) from the crank angle sensor 16, an in-cylinder pressure signal from an in-cylinder pressure sensor 17 (in-cylinder pressure detecting means) and the like are input.

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 resistance change of the temperature-sensitive resistance due to the amount of intake air. The throttle sensor 15 detects the opening TVO of the throttle valve 5 with a potentiometer. 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. Here, the crank angle sensor
The engine rotation speed Ne can be calculated based on the detection signal from the engine 16.

The in-cylinder pressure sensor 17 is provided by
As disclosed in Japanese Patent Publication No. 432, a ring-shaped sensor including a piezoelectric element is mounted as a washer for the spark plug 8, and the spark plug 8 is lifted by receiving the combustion pressure. When the set load changes, a signal corresponding to the combustion pressure is output. In this embodiment, 4
In the cylinder engine 1, the in-cylinder pressure sensor 17 is provided only in the # 1 cylinder as a specific cylinder. It should be noted that the in-cylinder pressure sensor 17 may be provided for all cylinders. However, at least in the diagnosis of the exhaust gas recirculation device described later, only the in-cylinder pressure of some cylinders is used. The configuration including the sensor 17 is necessary and sufficient.

The control unit 13 determines the required exhaust gas recirculation rate based on the engine operating conditions, controls the opening of the EGR control valve 12 based on the required exhaust gas recirculation rate, and controls the fuel injection valve 6. Control the fuel injection amount.
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 / Ne: based on the intake air amount Q detected by the hot wire type air flow meter 14 and the engine speed Ne calculated from the detection signal from the crank angle sensor 16). K is a constant)
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 the fuel is injected and supplied in an amount proportional to the pulse width of the drive pulse signal.

On the other hand, the EG by the control unit 13
The control of the R control valve 12 (exhaust gas recirculation control) basically obtains a required exhaust gas recirculation rate according to the engine load and the engine rotation speed Ne, and outputs the required exhaust gas recirculation rate to a control signal to the EGR control valve 12. The conversion is performed. Also, the control unit
Reference numeral 13 has a function of performing an abnormality diagnosis of the exhaust gas recirculation device including the exhaust gas recirculation passage 11 and the EGR control valve 12. The details of the abnormality diagnosis will be described with reference to the flowchart of FIG.

In this embodiment, the functions of the forced opening / closing means, the diagnosis means, and the ignition timing correction means are performed by the control unit 13 as shown in the flowchart of FIG.
Is provided as software. In the flowchart of FIG. 3, in step 1 (S1 in the figure, the same applies hereinafter), it is determined whether or not a diagnosis prohibition condition is satisfied.

Here, when the cooling water temperature at the time of starting is lower than a predetermined temperature, or when the cooling
It is preferable that the period from when the determination of G is made to when the key switch is turned off be the prohibition condition. If the prohibition condition has not been satisfied, the routine proceeds to step 2, where it is determined whether or not the predetermined diagnosis area is satisfied.

In the diagnostic region, the engine speed, the engine load, and the coolant temperature are specified in advance as operating conditions within predetermined ranges, respectively. The diagnostic region is a region where exhaust gas recirculation is performed by normal control. If the engine is in the diagnostic region, it is determined in step 3 whether the engine is in a steady operation state. The steady state determination is performed based on whether or not the time rate of change of the engine speed, the engine load, and the throttle valve opening is within a predetermined range.

If a steady determination is made, the process proceeds to step 4, where E
The GR control valve 12 is forcibly closed until it is fully closed to stop exhaust gas recirculation. In the diagnosis of this embodiment, when the exhaust gas recirculation amount is changed, a change in the exhaust gas recirculation amount corresponding to the control actually occurs based on whether or not an in-cylinder pressure (combustion pressure) change corresponding to the change has occurred. The EGR control valve
If the exhaust gas recirculation amount is largely changed by fully closing 12, the engine output torque will be suddenly changed.

For this reason, in this embodiment, the change in the engine output torque due to the change in the exhaust gas recirculation amount is canceled by the correction of the ignition timing to suppress the fluctuation in the engine output torque. Since the diagnosis of the exhaust gas recirculation device is performed based on whether only the combustion pressure change has occurred, even if the ignition timing is corrected even in the # 1 cylinder in which the in-cylinder pressure is detected for diagnosis, the diagnosis cannot be substantially performed. It will be.

Therefore, in the next step 5, in the # 2 to # 4 cylinders except for the # 1 cylinder for detecting the in-cylinder pressure for diagnosis, the ignition timing is set to cancel the increase in the output torque due to the stop of the exhaust gas recirculation. The retard is corrected by a predetermined angle (see FIG. 4). As a result, even if the exhaust gas recirculation is stopped for diagnosis, a large change in the output torque is suppressed, and deterioration in drivability is avoided.

It is not necessary to correct the ignition timing for all cylinders except for the # 1 cylinder for detecting in-cylinder pressure for diagnosis.
For example, a configuration may be employed in which only two of the # 2 to # 4 cylinders are used. Further, the cylinder for detecting the in-cylinder pressure for diagnosis may be, for example, two cylinders, and the ignition timing may be corrected by the other two cylinders. In step 6, while the exhaust gas recirculation is stopped by the processing in step 4, the in-cylinder pressure sensor 11 detects # 1.
The in-cylinder pressure of the cylinder is set to a predetermined integration interval (for example, TDC to AT
(DC 100 °) to obtain an in-cylinder pressure integrated value IMEP. As described above, the diagnosis is performed by integrating the in-cylinder pressure in a predetermined integration section instead of the instantaneous value of the in-cylinder pressure for diagnosis.
A change in combustion pressure due to the influence of exhaust gas recirculation can be accurately detected without being affected by noise or the like.

It is preferable that the integral value IMEP is calculated after a predetermined time has passed since the EGR control valve 12 was fully closed and the engine was stabilized in a state where the exhaust gas recirculation was stopped. When the exhaust gas recirculation is stopped, the in-cylinder pressure integrated value IM
When the EP is obtained, the process proceeds to step 7 where the EGR control valve
12 is forcibly opened to a predetermined opening (full opening or predetermined intermediate opening) to restart exhaust gas recirculation.

Since restarting the exhaust gas recirculation decreases the engine output torque, in the next step 8, the retard correction amount given to the cylinders # 2 to # 4 in step 5 is returned to zero. When the exhaust gas recirculation is stopped, the ignition timing is advanced and the output is suppressed from decreasing due to the resumption of the exhaust gas recirculation, thereby suppressing the output torque from fluctuating.

In step 9, the in-cylinder pressure integrated value IMEP in the # 1 cylinder after the exhaust gas recirculation is restarted is determined in the same manner as in step 6. In step 10, the deviation (change width) ΔIMEP between the in-cylinder pressure integrated value obtained when the exhaust gas recirculation is stopped and the in-cylinder pressure integrated value obtained during the exhaust gas recirculation is calculated for the # 1 cylinder in which the ignition timing correction has not been performed. That is, since the combustion pressure tends to decrease when the exhaust gas recirculation is performed, a deviation commensurate with the presence or absence of the exhaust gas recirculation should occur in the in-cylinder pressure integrated value IMEP of the # 1 cylinder due to the forcible ON / OFF control of the exhaust gas recirculation. This is obtained in step 10.

On the other hand, in step 11, the deviation ΔIME
The predicted value of P is determined based on the in-cylinder pressure integrated value IMEP and the exhaust gas recirculation rate obtained for the # 1 cylinder when the exhaust gas recirculation is stopped. This is because, as the exhaust gas recirculation rate increases, the change in the in-cylinder pressure integrated value IMEP caused by forcibly opening and closing the EGR control valve 5 increases. If the value IMEP (cylinder intake air amount) is large, the combustion pressure changes due to the presence or absence of exhaust gas recirculation, in other words, the deviation ΔIMEP becomes small. Therefore, the deviation ΔIMEP is predicted in accordance with such characteristics.

At step 12, a value ΔNRZ is obtained by dividing the actually generated deviation ΔIMEP obtained at step 8 by the predicted value obtained at step 9. Then, in step 13, the ΔNRZ is compared with a predetermined value (fixed value) set in advance. Here, the ΔNRZ is set to a smaller value as the change in the combustion pressure due to the forced ON / OFF of the exhaust gas recirculation is smaller than the predicted value, and the fact that the change in the combustion pressure is smaller than the predicted value means that the exhaust gas recirculation is smaller. This indicates indirectly that the change in the exhaust gas recirculation amount corresponding to the forcible ON / OFF control has not actually occurred.

Therefore, when it is determined in step 13 that the ΔNRZ is smaller than a predetermined value,
Since some trouble (clogging of the exhaust gas recirculation passage 4, sticking of the EGR control valve 12, etc.) has occurred in the exhaust gas recirculation device, a change in the amount of exhaust gas recirculation corresponding to forcible ON / OFF control of exhaust gas recirculation actually occurs. It is determined that the exhaust gas recirculation device has not failed, and the routine proceeds to step 14, where it is determined whether a failure (NG) has occurred in the exhaust gas recirculation device.

On the other hand, when it is determined in step 13 that the AVΔNRZ is equal to or larger than a predetermined value,
Since it is estimated that a change in the exhaust gas recirculation amount corresponding to the forcible ON / OFF control of the exhaust gas recirculation actually occurred, the process proceeds to step 15, and the normality (OK) of the exhaust gas recirculation device is determined. The diagnosis result may be notified to the driver by a display device provided in the driver's seat of the vehicle, for example.

As described above, in this embodiment, the diagnosis of the exhaust gas recirculation system is performed based on the in-cylinder pressure change when the exhaust gas recirculation amount is forcibly changed, but the exhaust gas recirculation amount is forcibly changed. As a result, the engine output torque can be prevented from greatly fluctuating, and diagnosis can be performed without deteriorating drivability. By the way, in the above embodiment, when the exhaust gas recirculation is stopped for diagnosis, a step change is performed at one time until the exhaust gas recirculation is completely closed. In the opening / closing control of the diagnostic EGR control valve 12, as shown in FIG. 5, the opening degree of the EGR control valve 12 is gradually changed in a stepwise manner. It is also possible to adopt a configuration in which the retard correction amount of the ignition timing is gradually changed in accordance with the stepwise change in the opening degree.

With this configuration, the change in the amount of exhaust gas recirculation is performed in a plurality of times, and the change in the amount of exhaust gas recirculation in each stage becomes small. Torque fluctuations can be minimized.

[0038]

As described above, according to the diagnostic apparatus for the exhaust gas recirculation system of the internal combustion engine according to the first aspect of the present invention, the diagnosis of the exhaust gas recirculation device is performed based on the in-cylinder pressure change when the exhaust gas recirculation amount is changed. While performing, there is an effect that generation of output fluctuation due to a change in the exhaust gas recirculation amount can be sufficiently suppressed to prevent deterioration in drivability.

According to the diagnostic apparatus for an exhaust gas recirculation system for an internal combustion engine according to the second aspect of the present invention, the degree of opening of the exhaust gas recirculation control valve is gradually changed stepwise in the diagnosis, thereby suppressing a large sudden change in the exhaust gas recirculation amount. Therefore, the effect of suppressing the torque fluctuation by correcting the ignition timing can be obtained stably. According to the diagnostic apparatus for an exhaust gas recirculation system for an internal combustion engine according to the third aspect of the present invention, in the diagnosis using the in-cylinder pressure detected in the specific cylinder, the instantaneous value of the in-cylinder pressure is used instead of the integration in a predetermined integration section. By using the value, it is possible to avoid the occurrence of erroneous diagnosis due to the influence of noise or the like, while the change of the in-cylinder pressure (combustion pressure) due to the change of the exhaust gas recirculation amount changes depending on the operating condition, and is therefore predicted from the operating condition. By comparing the change width with the actually detected change width, there is an effect that highly accurate diagnosis can be performed for each operation condition.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of the invention of claim 1;

FIG. 2 is a system schematic diagram showing one embodiment of the present invention.

FIG. 3 is a flowchart illustrating diagnostic control in the embodiment.

FIG. 4 is a time chart showing how ignition timing is corrected in the embodiment.

FIG. 5 is a time chart showing how the opening degree of the EGR control valve changes and how the ignition timing is corrected in another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 4 Intake manifold 5 Throttle valve 6 Fuel injection valve 10 Exhaust manifold 11 Exhaust recirculation passage 12 EGR control valve (Exhaust recirculation control valve) 13 Control unit 14 Hot-wire air flow meter 15 Throttle sensor 16 Crank angle sensor 17 In-cylinder pressure sensor

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-288303 (JP, A) JP-A-5-263718 (JP, A) JP-A-6-159152 (JP, A) JP-A-4- 81557 (JP, A) JP-A-4-347355 (JP, A) JP-A-3-1254 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02M 25/07 550 F02D 45/00

Claims (3)

(57) [Claims] 1. A diagnostic device for an exhaust gas recirculation system of an internal combustion engine for recirculating a part of the engine exhaust gas to an intake system of the engine through an exhaust gas recirculation passage provided with an exhaust gas recirculation control valve, wherein a specific cylinder of the engine is provided. An in-cylinder pressure detecting means for detecting the in-cylinder pressure, a forcible opening / closing means for forcibly opening and closing the exhaust gas recirculation control valve when a predetermined diagnostic condition is satisfied, and an opening / closing control of the exhaust gas recirculation control valve by the forcible opening / closing means. Diagnostic means for determining the presence or absence of an abnormality in the exhaust gas recirculation device based on a change in the in-cylinder pressure in the specific cylinder detected by the in-cylinder pressure detecting means. And ignition timing correction means for correcting the ignition timing of a cylinder other than the specific cylinder in a direction to suppress a change in engine output torque due to a change in the exhaust gas recirculation amount. Diagnostic device in an exhaust gas recirculation system for an internal combustion engine to be. 2. The diagnostic device for an exhaust gas recirculation system for an internal combustion engine according to claim 1, wherein said forcible opening / closing means gradually changes an opening degree of said exhaust gas recirculation control valve in a stepwise manner. 3. The in-cylinder pressure detected by the in-cylinder pressure detecting means is integrated in a predetermined integration interval, and the diagnostic means integrates the in-cylinder pressure integrated value generated by opening and closing control of the exhaust gas recirculation control valve. The presence or absence of an abnormality is determined by comparing the predicted value of the change width based on the operating condition with the predicted value.
A diagnostic device for an exhaust gas recirculation device for an internal combustion engine according to Claim 1.