JPH08312467A - Diagnoses device in exhaust gas circulating device for internal combustion engine - Google Patents

Abstract

PURPOSE: To prevent operability from being degraded owning to a diagnostic control by correcting ignition timing for cylinders having nothing to do with diagnoses in such a way that fluctuation in output for the aforesaid cylinders is restrained, while changing an exhaust gas circulating flow rate with an exhaust gas circulating control valve forcibly controlled for opening/closing, thereby judging whether or not an exhaust gas circulating flow rate is actually changed for diagonoses. CONSTITUTION: When the specified diagnostic areas of an internal combustion engine, that is, when engine revolutions, engine loading and cooling water temperature fall in the specified ranges of operating conditions, it is judged whether or not the engine is in a normal operating condition at a control unit 13, if it is judged YES, exhaust gas circulating flow is suspended with an EGR control valve 12 forcibly entirely opened. And at this time, change in pressure in the cylinder (combustion pressure) is detected by a cylinder inner pressure sensor 17, and the device is thereby diagnosed by judging whether or not change in an exhaust gas circulating flow rate matching to the aforesaid control is actually caused. At this time, #2 through #4 cylinders excluding #1 cylinder concerned with diagnosis are delayed in angle for correction by a specified angle for ignition timing in order to cancel an increase in output torque caused by the suspension of exhaust gas circulating flow.

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 system for an internal combustion engine, and more particularly to a device for diagnosing the exhaust gas recirculation system based on a change in combustion pressure when the exhaust gas recirculation amount is changed.

[0002]

2. Description of the Related Art Conventionally, in an internal combustion engine for automobiles,
As a device for reducing NOx in engine exhaust, an exhaust gas recirculation device (EGR) is known that lowers the maximum combustion temperature by recirculating a part of engine exhaust to an intake manifold to reduce NOx production. There is.

Here, if the desired exhaust gas recirculation cannot be performed due to the malfunction of the exhaust gas recirculation device, the NOx emission amount will be increased, so a device capable of diagnosing the malfunction 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 depending on the ON / OFF of the exhaust gas recirculation, and makes a diagnosis based on the change of the combustion pressure when the exhaust gas recirculation is forcibly turned ON / OFF. A diagnostic device was previously proposed (see Japanese Patent Application No. 5-78177).

[0004]

However, since the conventional diagnosis device is configured to perform the diagnosis by performing the ON / OFF control of the exhaust gas recirculation, which causes the output change of the engine, the exhaust gas recirculation amount is normally determined. If there is a change, there is a problem in that the output actually changes, which deteriorates the drivability due to the diagnostic control.

The present invention has been made in view of the above problems, and a diagnostic device for an exhaust gas recirculation device that can avoid the occurrence of output fluctuation while performing a diagnosis based on a combustion pressure change that occurs with exhaust gas recirculation amount control. The purpose is to provide.

[0006]

Therefore, in the diagnostic device according to the invention of claim 1, the internal combustion engine recirculates a part of the engine exhaust gas to the intake system of the engine 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 of an engine, which is configured as shown in FIG. In FIG. 1, the in-cylinder pressure detecting means detects the 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. Then, the diagnosis means determines whether or not there is an abnormality in the exhaust gas recirculation device based on the change in the cylinder pressure in the specific cylinder detected by the 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 controls the change of the engine output torque due to the change of the exhaust gas recirculation amount in the cylinders other than the specific cylinder during the opening / closing control of the exhaust gas recirculation control valve by the forced opening / closing means. Correct the ignition timing. In the diagnostic device for an exhaust gas recirculation system for an internal combustion engine according to a second aspect of the invention, the forced opening / closing means is configured to gradually change the opening degree of the exhaust gas recirculation control valve stepwise.

In the exhaust gas recirculation system for an internal combustion engine according to the third aspect of the present invention, the diagnostic means integrates the in-cylinder pressure detected by the in-cylinder pressure detecting means in a predetermined integration section,
The presence or absence of abnormality is determined by comparing the variation width of the in-cylinder pressure integrated value generated with the opening / closing control of the exhaust gas recirculation control valve with the predicted value of the variation width based on the operating conditions.

[0010]

According to the diagnostic device for the exhaust gas recirculation system for an internal combustion engine according to the first aspect of the invention, the exhaust gas recirculation amount is actually changed by forcibly controlling the opening / closing of the exhaust gas recirculation control valve to change the exhaust gas recirculation amount. Whether or not it is determined based on the change in cylinder pressure (combustion pressure) 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 above-mentioned diagnosis, the combustion pressure changes with the change of the exhaust gas recirculation amount as it is. Changes occur in the same way, which causes large output fluctuations. Here, since it is not necessary to cause the combustion pressure change corresponding to the change of the exhaust gas recirculation amount in the cylinders other than the specific cylinder which is irrelevant to the diagnosis, the ignition timing is corrected in the direction of suppressing the output fluctuation in the cylinders other than the specific cylinder. ,
The engine as a whole is designed so that output fluctuations due to changes in the exhaust gas recirculation amount are sufficiently suppressed.

According to the diagnosing device for the 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 stepwise to prevent a large sudden change in the exhaust gas recirculation amount. Therefore, the effect of suppressing the torque fluctuation by correcting the ignition timing is stably obtained. It is difficult to completely eliminate the fluctuation of the output torque due to the change of the exhaust gas recirculation amount by the correction of the ignition timing, and a relatively large torque fluctuation that cannot be corrected as much as when the exhaust gas recirculation amount changes suddenly is generated. Therefore, the change in the exhaust gas recirculation amount is reduced to minimize the torque fluctuation that occurs without being corrected.

According to the diagnostic device for the exhaust gas recirculation system for an internal combustion engine according to the third aspect of the invention, in the diagnosis using the in-cylinder pressure detected in a specific cylinder, a predetermined integral is used instead of using the instantaneous value of the in-cylinder pressure. By using the integrated value in the section, while avoiding erroneous diagnosis due to the influence of noise, etc., the change in the in-cylinder pressure (combustion pressure) due to the change in the exhaust gas recirculation amount changes depending on the operating conditions. 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 the system configuration of one embodiment, the internal combustion engine 1 is
Air is taken 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.

An electromagnetic fuel injection valve 6 is provided for each cylinder at each branch portion of the intake manifold 4, and a predetermined amount is controlled by electronic control of the amount of fuel injected and supplied from the fuel injection valve 6. A fuel-air mixture 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 exhaust gas recirculation passage 11 is provided for connecting the exhaust manifold 10 and the intake manifold 4 to each other,
An EGR control valve 12 (exhaust gas recirculation control valve) is provided in the exhaust gas recirculation passage 11. When the EGR control valve 12 is opened, 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 recirculation lowers the combustion temperature, thereby reducing the NOx emission amount. Is planned.

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 an electromagnetic 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 is configured to include a microcomputer, and has 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 detection means), etc. 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 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 16.

The in-cylinder pressure sensor 17 is a practically open type 63-17.
As disclosed in Japanese Patent No. 432,432, a ring-shaped sensor including a piezoelectric element is mounted as a washer of the spark plug 8, and the spark plug 8 is lifted by receiving combustion pressure. The set load changes, and 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. The cylinder pressure sensor 17 may be provided in all the cylinders, but at least the cylinder pressures of some of the cylinders are used in the diagnosis of the exhaust gas recirculation system, which will be described later. The configuration including the sensor 17 is necessary and sufficient.

The control unit 13 determines the required exhaust gas recirculation rate based on engine operating conditions, controls the opening degree of the EGR control valve 12 based on the required exhaust gas recirculation rate, and controls the fuel injection valve 6 to operate. Control the fuel injection amount.
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 hot wire air flow meter 14 and the engine rotation 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)
The final fuel injection amount Ti is obtained by correcting the basic fuel injection amount Tp according to the operating conditions such as the cooling water temperature. 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 EG by the control unit 13
The control of the R control valve 12 (exhaust gas recirculation control) basically determines the required exhaust gas recirculation ratio according to the engine load and the engine speed Ne, and outputs the required exhaust gas recirculation ratio to the EGR control valve 12 as a control signal. Will be converted to. Also the control unit
Reference numeral 13 has a function of diagnosing an abnormality in 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 the present embodiment, the functions of the forcible opening / closing means, the diagnosing means, and the ignition timing correcting means are controlled by the control unit 13 as shown in the flow chart of FIG.
Is equipped with software. In the flowchart of FIG. 3, in step 1 (denoted as S1 in the figure. The same applies hereinafter), it is determined whether or not a diagnosis prohibition condition is satisfied.

Here, when the temperature of the cooling water at the time of starting is lower than a predetermined temperature, or by the following diagnosis, OK or N
The prohibition condition is preferably set between the time when the determination of G is made and the time when the key switch is turned off. If the prohibition condition is not satisfied, the process proceeds to step 2 and it is determined whether or not the condition falls within a predetermined diagnostic region.

In the diagnosis area, the engine speed, engine load, and cooling water temperature are specified in advance as operating conditions within predetermined ranges. The diagnosis area is an area where exhaust gas recirculation is performed by normal control. If it falls within the above-mentioned diagnosis range, it is then determined in step 3 whether or not the engine is in a steady operation state. The steady determination is performed based on whether or not the time rate of change of engine speed, engine load, and throttle valve opening is within a predetermined range.

When the steady state is determined, the process proceeds to step 4 and E
The GR control valve 12 is compulsorily closed to completely close the exhaust gas recirculation. In the diagnosis of the present 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 a change in the cylinder pressure (combustion pressure) corresponding to the change occurs. It is determined whether or not the EGR control valve
If 12 is fully closed and the exhaust gas recirculation amount is greatly changed, the engine output torque will suddenly change.

Therefore, in the present 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 change in the engine output torque, but it is commensurate with the change in the exhaust gas recirculation amount. Since the exhaust gas recirculation device is diagnosed based on whether or not only the combustion pressure change has occurred, 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. I will end up.

Therefore, in the next step 5, in the cylinders # 2 to # 4 except for the cylinder # 1 which detects the 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 output torque is suppressed, and deterioration of drivability is avoided.

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

It is preferable that the integrated value IMEP is calculated after a predetermined time has passed after the EGR control valve 12 was fully closed and the engine was stabilized in a state where exhaust gas recirculation was stopped. In-cylinder pressure integrated value IM for cylinder # 1 when exhaust gas recirculation is stopped
Once the EP is determined, the process proceeds to step 7 and the EGR control valve
12 is forcibly opened to a predetermined opening (fully opened or a predetermined intermediate opening) to restart exhaust gas recirculation.

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

Then, in step 9, the in-cylinder pressure integrated value IMEP in the # 1 cylinder after the exhaust gas recirculation is restarted is obtained in the same manner as in step 6. In step 10, a 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 when the exhaust gas recirculation is stopped is calculated in the # 1 cylinder in which the ignition timing correction is not performed. That is, since the combustion pressure tends to decrease due to the execution of exhaust gas recirculation, the compulsory ON / OFF control of exhaust gas recirculation should cause a deviation in the in-cylinder pressure integrated value IMEP in the # 1 cylinder that corresponds to the presence or absence of exhaust gas recirculation. This is what is obtained in step 10.

On the other hand, in step 11, the deviation ΔIME
The predicted value of P is calculated based on the in-cylinder pressure integrated value IMEP and the exhaust gas recirculation rate which are calculated for the # 1 cylinder when the exhaust gas recirculation is stopped. This is because the greater the exhaust gas recirculation rate, the greater the change in the in-cylinder pressure integrated value IMEP due to the forced opening and closing of the EGR control valve 5, and the same in-cylinder pressure integration at that time even at the same exhaust gas recirculation rate. If the value IMEP (cylinder intake air amount) is large, the combustion pressure change due to the presence or absence of exhaust gas recirculation, in other words, the deviation ΔIMEP becomes small, so the deviation ΔIMEP is predicted in accordance with such characteristics.

In step 12, the deviation ΔIMEP actually generated in step 8 is divided by the predicted value calculated in step 9 to obtain a value ΔNRZ. Then, in step 13, the ΔNRZ is compared with a preset predetermined value (fixed value). Here, the ΔNRZ is set as a smaller value when the combustion pressure change due to forced ON / OFF of the exhaust gas recirculation is smaller than the predicted value, and the fact that the combustion pressure change is smaller than the predicted value means that the exhaust gas recirculation is smaller than the predicted value. It indirectly indicates that the change in the exhaust gas recirculation amount commensurate with the forced ON / OFF control is not actually occurring.

Therefore, when it is determined in step 13 that the ΔNRZ is less than the preset predetermined value,
Some kind of failure (clogging of the exhaust gas recirculation passage 4, sticking of the EGR control valve 12, etc.) has occurred in the exhaust gas recirculation device, so that a change in the exhaust gas recirculation amount commensurate with the compulsory ON / OFF control of the exhaust gas recirculation actually occurs. Considering that the exhaust gas recirculation device has not been operated, the process proceeds to step 14 and it is determined whether the exhaust gas recirculation device has failed (NG).

On the other hand, when it is determined in step 13 that the AVΔNRZ is equal to or more than the preset predetermined value,
Since it is estimated that the change in the exhaust gas recirculation amount commensurate with the compulsory ON / OFF control of the exhaust gas recirculation has actually occurred, the routine proceeds to step 15, where the exhaust gas recirculation device is judged to be normal (OK). 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 exhaust gas recirculation device is diagnosed based on the change in the cylinder pressure when the exhaust gas recirculation amount is forcibly changed, but the exhaust gas recirculation amount is forcibly changed. This makes it possible to prevent the engine output torque from fluctuating greatly and to make a diagnosis without deteriorating the drivability. By the way, in the above-mentioned embodiment, when the exhaust gas recirculation is stopped for diagnosis, it is configured to change the step at once until it is fully closed. In the opening / closing control of the diagnostic EGR control valve 12, the opening degree of the EGR control valve 12 is gradually changed stepwise as shown in FIG. The retardation correction amount of the ignition timing may be gradually changed in accordance with the gradual change of the opening degree.

With this structure, the change in the exhaust gas recirculation amount is divided into a plurality of times, and the change in the exhaust gas recirculation amount at each stage becomes small. Therefore, the exhaust gas recirculation amount cannot be corrected by the ignition timing correction. The torque fluctuation that occurs can be minimized.

[0038]

As described above, according to the diagnosis device for the exhaust gas recirculation system for an internal combustion engine according to the invention of claim 1, the diagnosis of the exhaust gas recirculation system is performed based on the change in the cylinder pressure when the exhaust gas recirculation amount is changed. While performing, it is possible to sufficiently suppress the occurrence of output fluctuation due to the change of the exhaust gas recirculation amount and prevent the deterioration of drivability.

According to the second aspect of the present invention, there is provided a diagnostic device for an exhaust gas recirculation system for an internal combustion engine, in which the degree of opening of the exhaust gas recirculation control valve is gradually changed during the diagnosis to prevent a large sudden change in the exhaust gas recirculation amount. Therefore, there is an effect that the effect of suppressing the torque fluctuation by the correction of the ignition timing can be stably obtained. According to the diagnostic device for the exhaust gas recirculation system for an internal combustion engine according to the invention of claim 3, in the diagnosis using the in-cylinder pressure detected in the specific cylinder, the instantaneous value of the in-cylinder pressure is not used, but the integration in a predetermined integration interval is performed. By using the value, it is possible to avoid the occurrence of erroneous diagnosis due to the influence of noise, etc., while the change in the in-cylinder pressure (combustion pressure) due to the change in the exhaust gas recirculation amount changes depending on the operating condition, so it is predicted from the operating condition By comparing the change width with the actually detected change width, it is possible to perform highly accurate diagnosis for each operating condition.

[Brief description of 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 showing diagnostic control in the embodiment.

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

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

[Explanation of symbols]

 1 Internal Combustion Engine 4 Intake Manifold 5 Throttle Valve 6 Fuel Injection Valve 10 Exhaust Manifold 11 Exhaust Gas Recirculation Passage 12 EGR Control Valve (Exhaust Gas Recirculation Control Valve) 13 Control Unit 14 Heat Wire Air Flow Meter 15 Throttle Sensor 16 Crank Angle Sensor 17 Cylinder Pressure Sensor

Claims (3)

[Claims] 1. A diagnostic device in 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, the cylinder being a specific cylinder of the engine. In-cylinder pressure detection means for detecting the in-cylinder pressure, forced opening / closing means for forcibly opening / closing the exhaust gas recirculation control valve when a predetermined diagnostic condition is satisfied, and opening / closing control of the exhaust gas recirculation control valve by the forced opening / closing means. Based on a change in the in-cylinder pressure in the specific cylinder detected by the in-cylinder pressure detecting means, a diagnostic means for determining whether or not there is an abnormality in the exhaust gas recirculation device, and the opening / closing control of the exhaust gas recirculation control valve by the forced opening / closing means. An ignition timing correction means for correcting the ignition timing of a cylinder other than the specific cylinder in a direction of suppressing a change in the 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 the forced opening / closing means gradually changes the opening degree of the exhaust gas recirculation control valve in a stepwise manner. 3. A change range of the integrated value of the in-cylinder pressure generated by the opening / closing control of the exhaust gas recirculation control valve, wherein the diagnosing means integrates the in-cylinder pressure detected by the in-cylinder pressure detecting means in a predetermined integration section. The presence or absence of abnormality is determined by comparing with a predicted value of the change width based on operating conditions.
A diagnostic device for an exhaust gas recirculation device for an internal combustion engine according to claim 1.