JPH09137753A - Failure diagnostic device for exhaust circulation device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve precision of failure diagnosis of an exhaust circulation device in simple, constitution. SOLUTION: A heat generation rate and a combustion period NETAD1 are found in accordance with a cylinder inside pressure signal from a cylinder inside pressure sensor 11 at the time when an EGR is on (S5). Thereafter, the EGR is forcibly put off (S6), and a heat generation rate at the time and a combustion period NETAD2 are found (S9). Thereafter, existence of failure of the EGR device is diagnosed (S12) in accordance with difference of NETAD (NETAD1-NETAD2). Consequently, even if ignition timing is changed to maintain torque variation at a specified value, it is possible to highly precisely and easily detect a difference of a combustion process by ON.OFF of the EGR device, and accordingly, it is possible to highly precisely and easily diagnose existence of failure of the EGR device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved technique of a failure diagnosis device for diagnosing whether or not there is a failure in an exhaust gas recirculation system of an internal combustion engine which recirculates a part of engine exhaust gas to an intake system.

[0002]

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

If the desired exhaust gas recirculation amount cannot be obtained due to the malfunction of the exhaust gas recirculation device, the NOx emission amount may be increased. On the other hand, if it exceeds the desired exhaust gas recirculation amount, combustion deteriorates. Since there is a fear that the drivability deteriorates and the emission amount of HC, CO, black smoke, etc. increases too much, it is desired to provide a device capable of diagnosing whether the desired exhaust gas recirculation is being performed. .

[0004] Therefore, the Applicant has proposed that exhaust gas recirculation (EGR)
Paying attention to the characteristic that the combustion state changes depending on ON / OFF, the combustion pressure when the exhaust gas recirculation is forcibly turned ON / OFF (for example, it is converted to the indicated mean effective pressure in order to improve the diagnostic accuracy). ) Was previously proposed (Japanese Patent Application No. 7-3
No. 0857).

[0005]

By the way, as shown in FIG. 9, for example, the diagnostic device is based on a cylinder pressure (combustion pressure) or the like which changes when the exhaust gas recirculation is forcibly switched on and off. Calculated mean indicated effective pressure change (Δ
IMEP) and a predetermined value are compared to diagnose whether or not there is an abnormality (for example, if ΔIMEP ≧ predetermined value is normal, and ΔIMEP <abnormal if it is a predetermined value), the diagnostic apparatus is provided and Engine drivability (engine torque fluctuation, etc.)
There is an engine provided with an ignition timing control device for retarding or advancing the ignition timing so as to maintain the desired value.

When the diagnostic device and the ignition timing control device are provided at the same time as described above, the following problems may occur. That is, for example, as shown in FIG. 10, when the exhaust gas recirculation device is normal, E
Even if the combustion state changes and the indicated mean effective pressure changes to a predetermined value or more by switching GR on and off, operability is prioritized and ignition timing control is performed, that is, combustion with respect to the crank angle. By controlling the timing of, the timing at which the combustion pressure is effectively applied to the piston is controlled, and as a result, the change in the indicated mean effective pressure (ΔIMEP) becomes a value smaller than the predetermined value, and Therefore, the exhaust gas recirculation device may be erroneously diagnosed as abnormal.

The cause of such erroneous diagnosis is that the indicated mean effective pressure, which is conventionally used for failure diagnosis, is a parameter for grasping an average combustion state in a predetermined combustion period, that is, it acts on the piston. It represents the average value of combustion pressure. For example, EGR is ON.
Even if there is a difference in the combustion process with respect to the crank angle by switching OFF, if the average value of the combustion pressure acting on the piston does not differ (regardless of the difference in the process), the EGR is turned on during normal operation. There is a case where the change amount of the indicated mean effective pressure when turned off and the change amount of the indicated mean effective pressure recovered by the ignition timing control are substantially equal to each other even if the exhaust gas recirculation device is out of order. It is due to it.

It should be noted that it is possible to accurately detect and detect a combustion state that changes when the EGR is turned from ON to OFF during normal operation and a combustion state that changes due to ignition timing control even if the exhaust gas recirculation device has a failure. If possible, it is possible to solve the above problem, but since the indicated mean effective pressure and the cylinder internal pressure waveform include the volume change of the combustion chamber that changes from moment to moment, the indicated mean effective pressure and the cylinder If the internal pressure waveform is used as it is, it is not possible to extract only the difference in the pure combustion process with a simple configuration and with high accuracy, and thus the difference in the combustion state described above is accurately detected and detected. There is also the problem that it is difficult to do.

The present invention has been made in view of such a conventional situation, and in the case of performing the failure diagnosis by switching the EGR ON / OFF, the ignition timing control or the like for making the drivability desired is performed. Even so, it is an object of the present invention to provide a failure diagnosis device for an exhaust gas recirculation device for an internal combustion engine, which is capable of performing a failure diagnosis for the exhaust gas recirculation device with high accuracy.

[0010]

Therefore, as shown in FIG. 1, a failure diagnosis device for an exhaust gas recirculation system for an internal combustion engine according to the invention described in claim 1 has a part of engine exhaust gas with an exhaust gas recirculation control valve. A failure diagnosis device for an exhaust gas recirculation device of an internal combustion engine, which recirculates to an intake system of an engine through an interposed exhaust gas recirculation passage, comprising: an in-cylinder pressure detecting means for detecting an in-cylinder pressure of the engine; and the in-cylinder pressure detecting means. A heat release rate detecting means for detecting a heat release rate based on the detected in-cylinder pressure, a forcible opening / closing means for forcibly opening / closing the exhaust gas recirculation control valve, and a forcible opening / closing means for opening the exhaust gas recirculation control valve. The combustion process difference detecting means for detecting a difference in the combustion process based on the heat release rate detected by the heat release rate detecting means and the combustion process difference detecting means for the control and the closed control respectively. Based on the difference in combustion process And so configured to include a diagnostic means for diagnosing the presence or absence of abnormality of the exhaust gas recirculation system, the by have.

As described above, the in-cylinder pressure (combustion pressure) signals from the in-cylinder pressure detecting means are detected before and after the exhaust gas recirculation (EGR) is forcibly executed (ON) and stopped (OFF) for failure diagnosis. ON / OFF of EGR by determining the heat generation rate that can grasp the pure combustion state (combustion process) by eliminating the influence of the combustion chamber volume change based on
Change in heat release rate before and after switching (that is, difference in combustion process)
Since the failure diagnosis of the EGR device is performed based on the above, even if the ignition timing and the like are controlled so as to suppress the engine torque fluctuation, the change in the combustion state (combustion process) due to ON / OFF of the EGR is performed. Can be detected with high accuracy with a simple configuration (see FIG. 8), and thus the accuracy of EGR failure diagnosis can be significantly improved. In the invention according to claim 2, the combustion process difference detection means detects a predetermined combustion period based on the heat generation rate detected by the heat generation rate detection means, and based on the detected predetermined combustion period. It was configured to detect differences in combustion processes.

That is, even if the ignition timing is changed by the ignition timing control and the relative position of the heat release rate curve to the crank angle (time) changes, the length of the combustion period that can be easily detected from the heat release rate is Since it does not affect much, EGR is turned on.
The change in combustion state (difference in combustion process) due to OFF can be detected with high accuracy and easily, and thus the accuracy of EGR failure diagnosis can be significantly improved. In the invention according to claim 3, the combustion process difference detection means detects the combustion ratio based on the heat generation rate detected by the heat generation rate detection means, and the combustion process difference based on the detected combustion ratio. Is configured to detect.

That is, even if the ignition timing is changed by the ignition timing control and the relative position of the heat release rate with respect to the crank angle (time) changes, the combustion rate that can be easily detected from the heat release rate is not significantly affected. , The change in the combustion state (difference in the combustion process) due to ON / OFF of the EGR can be detected with high accuracy and easily, and thus the accuracy of EGR failure diagnosis can be significantly improved. Claim 4
In the invention described in (1), the combustion process difference detection means is configured to detect the difference in the combustion process based on the detected degree of change in the combustion ratio.

That is, even if the ignition timing is changed by the ignition timing control and the relative position of the heat release rate with respect to the crank angle (time) changes, the degree of change in the combustion rate that can be easily detected from the combustion rate is greatly affected. I ’m not doing so
The change in the combustion state (difference in the combustion process) due to N / OFF can be detected with high accuracy and easily, and thus the accuracy of EGR failure diagnosis can be greatly improved. According to a fifth aspect of the present invention, a predictive value setting means for setting a predictive value of the difference in the combustion process according to operating conditions is provided, and the diagnosis means is provided for the combustion process detected by the combustion process difference detecting means. The difference is compared with the predicted value set by the predicted value setting means to diagnose whether or not there is an abnormality in the exhaust gas recirculation device.

That is, since the difference in the combustion process caused by the ON / OFF of the EGR differs depending on the operating condition at that time, the difference in the combustion process that would occur during normal operation is predicted based on the operating condition, If the difference in the actually obtained combustion process is compared with this prediction result to diagnose whether or not the difference in the actually obtained combustion process is normal, the diagnostic accuracy will be further improved. It can be improved. According to a sixth aspect of the present invention, the predicted value setting means sets the predicted value based on the engine speed, the engine load, and the target exhaust gas recirculation rate, or the engine speed, the indicated mean effective pressure, and the target exhaust gas recirculation rate. Configured to set.

That is, as the exhaust gas recirculation rate increases, the EG
The combustion process (combustion period, combustion ratio, etc.) changes greatly when R is turned ON / OFF, and even at the same exhaust gas recirculation rate, the operating state at that time (engine speed, engine load, indicated average effective) Since the combustion process changes according to the pressure, etc., if the predicted value can be set in accordance with such characteristics, the diagnostic accuracy can be further improved.
In the invention according to claim 7, the diagnosis means compares a value obtained by dividing the difference in the combustion process detected by the combustion process difference detection means by the predicted value set by the predicted value setting means with a predetermined value. Then, the presence or absence of abnormality of the exhaust gas recirculation device is diagnosed.

According to this structure, the difference between the actually obtained combustion processes is divided by the predicted value set by the predicted value setting means, and the predetermined value is compared with the predetermined value. Differences in process can be standardized, and operating conditions (engine speed, engine load, indicated mean effective pressure, etc.)
Regardless of the above, the failure diagnosis can be easily performed by making a comparison with a predetermined value. In the invention according to claim 8, when the diagnosis means diagnoses the presence or absence of abnormality of the exhaust gas recirculation device based on the average value of the difference in the combustion process, the difference in the combustion process when the average value is calculated. The dead zone of the diagnosis is changed according to the number of data of.

According to this structure, the reliability of the average value increases as the number of data of the difference in the combustion process when obtaining the average value of the difference in the combustion process increases. Therefore, the dead zone of the diagnosis is set according to the number of the data. It is possible to perform highly accurate diagnosis when the number of data is increased and the reliability is increased while avoiding erroneous diagnosis when the reliability is changed.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. In FIG. 2 showing the system configuration according to the first embodiment of the present invention, an exhaust gas recirculation passage 4 that connects the exhaust manifold 2 and the intake manifold 3 of the engine 1 is provided. The EGR control valve 5 (exhaust gas recirculation control valve) is opened and closed.

The EGR control valve 5 is a diaphragm type valve which is opened by applying a suction negative pressure of the engine against the urging force of the coil spring in the valve closing direction. 6 is provided with a negative pressure introducing passage 7 that communicates with the intake manifold 3 on the downstream side, and the valve is opened by introducing the negative suction pressure of the engine 1 into the pressure chamber through the negative pressure introducing passage 7.

An EGR control solenoid 9 which is on / off controlled by a control unit 8 is interposed in the negative pressure introducing passage 7, and the EGR control valve 5 is controlled by opening / closing the EGR control solenoid 9. Opening / closing, that is, on / off of exhaust gas recirculation can be controlled. In the case of 10, the diaphragm operates due to the exhaust pressure and the manifold negative pressure, and
It is a diaphragm type BPT valve that determines the negative pressure for controlling the R control valve 5.

The control unit 8 receives detection signals such as cooling water temperature, engine speed, intake air amount, etc. from each sensor, and also inputs / outputs an ignition switch on / off signal for determination. The EGR control solenoid 9 based on the engine operating conditions
On / off control. In addition, an in-cylinder pressure detection signal is input to the control unit 8 from an in-cylinder pressure sensor (in-cylinder pressure / S) 11 as in-cylinder pressure detecting means. The cylinder pressure sensor 11 is a 63-17
This is an in-cylinder pressure sensor of the type mounted as a washer of the spark plug 12 as disclosed in Japanese Patent No. 432. However, in addition to the type in which the spark plug 12 is mounted as a washer as described above, a type in which the sensor portion is directly exposed to the combustion chamber and the in-cylinder pressure is detected as an absolute pressure may be used.

As in the conventional case, the crank angle sensor (C
A / S) 13 is provided, and the crank angle (CA or θ) signal from the crank angle sensor (CA / S) 13 is also input to the control unit 8. By the way, as shown in the flow chart of FIG. 3 below, the control unit 8 has software functions of the heat release rate detecting means, the forced opening / closing means, the combustion process difference detecting means, and the diagnosing means according to the present invention. . The control unit 8 has an ignition timing control function for advancing or retarding the ignition timing so that the engine torque variation (indicated average pressure variation) is desired. Needless to say, the failure diagnosis control in this embodiment described below is useful even if it is not provided.

Here, the failure diagnosis control of the exhaust gas recirculation device performed by the control unit 8 will be described. As will be described later, the EGR failure diagnosis according to the present embodiment is performed so that the heat release rate and thus the combustion period are obtained, and these are compared before and after the EGR is turned ON / OFF to perform the failure diagnosis. There is. This is EGR
Even if ignition timing control is controlled with emphasis on engine operability when the engine is switched on and off, EGR is turned on during normal operation.
Compared to the magnitude of the change in the combustion process (that is, the heat generation rate and thus the combustion period, etc.) that appears due to N / OFF,
The magnitude of the change in the combustion process caused by the ignition timing control or the like is sufficiently small (see FIG. 8). Therefore, if the magnitude of the change in the combustion process (heat generation rate and thus combustion period, etc.) is grasped, This is because even if the ignition timing control is performed at the same time, the EGR failure can be detected with high accuracy with a simple configuration.

The failure diagnosis control of the exhaust gas recirculation device performed by the control unit 8 will be described in detail below with reference to the flowchart of FIG. That is, in step 1 (indicated as S1 in the figure. The same applies hereinafter), various data (engine speed Ne, engine load Tp, cooling water temperature TWN, throttle valve opening TVO, vehicle speed VSP, etc.) are read.

At step 2, it is judged whether or not the diagnosis permission condition is satisfied. The determination can be made, for example, based on whether or not the engine speed, engine load, cooling water temperature, throttle valve opening, vehicle speed, etc. are each within a predetermined range during EGR control. If yes, then continue with step 3; if no, then return.

In step 3, it is determined whether or not the steady-state determination condition is satisfied, that is, whether or not the engine is in the steady-state operation state. The conditions for establishing the steady state determination are engine speed, engine load,
This is performed based on whether the time rate of change of the throttle valve opening is within a predetermined range. In the case of YES (when the steady state is determined), the process proceeds to step 4. If NO, the process returns.

In step 4, the subroutine A shown in FIG. 4 is executed to sample the data. Here, the subroutine A shown in FIG. 4 for performing data sampling will be described. In step 21, the crank angle signal from the crank angle sensor (CA / S) 13 and the in-cylinder pressure signal from the in-cylinder pressure sensor (in-cylinder pressure / S) 11 are read.

[0029] In step 22, based on the various signals read in step 21, it calculates the heat generation rate q _j at the crank angle theta _j. The calculation can be performed according to the following formula, for example. q _j = A / (κ−1) × [V _j × dP / dθ + κ × P _j
XdV / dθ] q _j ; heat generation rate (kcal / deg) A; work equivalent of heat [= 4.2 (J)] κ; specific heat ratio [= 1.4] P _j ; cylinder pressure V _j ; Cylinder (combustion chamber) volume In step 23, it is determined whether or not the heat generation rate q _j has dropped to a predetermined value (for example, a value at which it can be determined that the combustion has almost ended). If YES, proceed to step 24, N
If it is O, the process returns to step 22.

In step 24, the crank angle θ _j when the heat generation rate q _j becomes the predetermined value after it has decreased (for example, approximately at the end of combustion) is stored as NETAD ₀ . In step 25, ignition start timing (ADV)
From the time when the heat generation rate q _j decreases to the predetermined value (for example, the period from the start of combustion to the almost end) NE
TAD is calculated according to the following equation.

NETAD = ADV + NETAD _{0 It} should be noted that the ignition start timing (ADV) is calculated from the heat generation rate, that is, the combustion start timing, that is, the heat generation rate q _j starts to rise (or reaches a predetermined value after the rise starts). Of course, it is good. In this way, the subroutine A is completed, and then the process proceeds to step 5 in the flowchart of FIG.

Here, the description returns to the flowchart of FIG. In step 5, the NE obtained in step 4
Store TAD as NETAD ₁ . In step 6, the EGR control valve 5 is forcibly closed to stop the exhaust gas recirculation (EGR / OFF).
The control solenoid 9 is controlled.

In step 7, it is determined whether or not a predetermined time has elapsed since the processing in step 6 was performed. That is, it is determined whether or not the combustion state after turning off EGR is stable. If YES, the process proceeds to step 8, and if NO, the process waits until a predetermined time elapses. In step 8, E
Data sampling is performed in the GR / OFF state. The data sample is performed by executing the subroutine A described in the flowchart of FIG. 4 described above.

In step 9, the NETAD obtained in step 8 is stored as NETAD ₂ . In step 10, the EGR control solenoid 9 is controlled to forcibly open the EGR control valve 5 and restore the exhaust gas recirculation. In step 11, the subroutine B shown in FIG. 5 is executed to perform the failure diagnosis.

Here, FIG. 5 for performing a failure diagnosis is shown.
Subroutine B will be described. In step 31
Is the combustion period NE at the time of EGR / ON obtained in step 4.
TAD ₁And the fuel at EGR / OFF obtained in step 8
Baking period NETAD_TwoAnd the deviation ΔNETAD (= NET
AD₁-NETAD_Two).

In step 32, the deviation ΔNETAD
The predicted target value of the operating condition (engine speed, engine load,
Calculated based on the indicated average effective pressure, etc.) and the target exhaust gas recirculation rate. This is because as the exhaust gas recirculation rate increases, the degree of deterioration of combustion increases and the combustion period deviation ΔNETAD due to the forced opening and closing of the EGR control valve 5 increases. Since the combustion period deviation ΔNETAD changes depending on the state (engine speed, engine load, indicated mean effective pressure, etc.), it is preferable to set the predicted target value of the deviation ΔNETAD in accordance with such characteristics. is there. In addition,
Since it also changes somewhat depending on the advance width or retard width of the ignition timing, these may be included in the predicted target value.

The target exhaust gas recirculation rate can be obtained from the target EGR flow rate (EGRQ) and the intake air flow rate (Q). That is, the target EGR rate = EGRQ / (EGRQ + Q) In step 33, the average value of the values obtained by dividing the deviation ΔNETAD by the predicted target value is calculated as the EGR flow rate decrease ratio DLTP.
N is calculated according to the following formula.

DLTPN = 1 / n × Σ (ΔNETAD / prediction target value) That is, every time the deviation ΔNETAD is obtained, the deviation ΔNETAD is divided by the prediction target value at that time for standardization.
It is possible to eliminate the influence of the difference in the engine load, the exhaust gas recirculation rate, and the like when AD is calculated, and to accurately detect the change in the combustion period due to the ON / OFF switching of EGR, that is, the change in the EGR flow rate.

In step 34, the determination value (NG determination value and OK determination value) of the EGR flow rate decrease rate DLTPN is set according to the sample number n of the deviation ΔNETAD when the EGR flow rate change rate DLTPN is obtained. The characteristics of the determination value setting will be described later. Step 35
Then, it is determined whether or not the EGR flow rate decrease ratio DLTPN is less than or equal to the NG determination value. When DLTPN is less than or equal to the NG determination value, the process proceeds to step 36, and it is determined that an abnormality has occurred in the exhaust gas recirculation control device. , NG judgment.

That is, when the change in the combustion period due to ON / OFF of EGR is smaller than that in the normal state, it is determined that the exhaust gas recirculation amount has not changed in response to the control, and the occurrence of abnormality is determined. To do. When it is determined that an abnormality has occurred, the determination result may be warned by a lamp display or the like, and the exhaust gas recirculation control thereafter may be stopped.

On the other hand, when it is determined in step 35 that DLTPN exceeds the NG determination value, step 37
Then, the process proceeds to and it is determined whether or not the DLTPN is equal to or more than the OK determination value. Here, if the DLPTN is equal to or greater than the OK determination value, the process proceeds to step 38, where it is determined that the exhaust gas recirculation control device is normal, and the OK determination is performed.

When the DLTPN is less than the OK judgment value, that is, the DLTPN is recognized as abnormal,
Is not small, but is not large enough to be recognized as normal, the process proceeds to step 39 and the diagnosis is suspended. Therefore, the range that exceeds the NG determination value and is less than the OK determination value is a dead zone for diagnosis, and in step 34,
When the number of samples n of the deviation ΔNEATD when obtaining the DLTPN is smaller, the dead zone is expanded.
The OK determination value is made larger and the NG determination value is made smaller.

This is the sample number n of the deviation ΔNETAD.
When the number is small, the reliability of the DLTPN is low, and it is not possible to make a final decision at an early stage. Therefore, the diagnosis is suspended and the sample number n becomes large except when it is clearly recognized as abnormal or normal. When the reliability of DLTPN becomes high, the dead zone sandwiched between the OK determination value and NG is narrowed so that either determination result is given.

After the subroutine B is executed, the process returns to step 12 in the flowchart of FIG. In step 12, the failure judgment result is NG judgment or O.
It is determined whether the K determination is made, and this flow is repeated until either determination is made. As described above, according to the present embodiment, the in-cylinder pressure (combustion pressure) from the in-cylinder pressure sensor 11 before and after the EGR ON / OFF switching is performed.
Based on the signal, the influence of the change in the volume of the combustion chamber is eliminated, and the heat generation rate that can grasp the pure combustion state (combustion process) is obtained. Then, the combustion period is changed)
Since the failure diagnosis of the EGR device is performed based on the above, even if the ignition timing and the like are controlled so as to suppress the engine torque fluctuation, the change in the combustion state (combustion process) due to ON / OFF of the EGR is performed. Since only this can be detected with high accuracy with a simple configuration (see FIG. 8), the accuracy of EGR failure diagnosis can be greatly improved.

In this embodiment, the diaphragm type EGR control valve 5 provided in the exhaust gas recirculation passage 4 is provided.
And an EGR control solenoid 9 for controlling the introduction of the engine suction negative pressure to the valve 5, the exhaust gas recirculation device having a structure in which a solenoid valve is directly interposed in the exhaust gas recirculation passage 4. Of course, it is okay.

Further, the exhaust gas recirculation is forced to O for the purpose of diagnosis.
Exhaust gas recirculation ON / OFF when turning N / OFF
It is also possible to gradually change the exhaust gas recirculation amount in order to avoid the occurrence of a sudden change in torque due to. In the present embodiment, the EGR control is forcibly performed (EGR / ON state) to forcibly perform EGR / OFF to perform the failure diagnosis. However, the EGR is switched from OFF to ON.
It is also possible to adopt a configuration in which the failure diagnosis is performed. However,
Needless to say, the present embodiment is more advantageous in terms of exhaust performance, drivability, and the like. Next, the second embodiment of the present invention
An embodiment will be described.

The second embodiment has the same system configuration as that of the first embodiment, and only the failure diagnosis control routine shown in FIGS. 6 and 7 is different. Will be explained only. The first
The steps common to those in the flowcharts of FIGS. 3 and 4 already described in the above embodiment are indicated by the same steps, and the detailed description thereof will be omitted. Steps different from those in the flowcharts of FIGS. It will be described in detail.

That is, step 1 of the flowchart of FIG.
~ Step 3 is performed in the same manner as in the first embodiment. In step 4A, the subroutine A'shown in FIG. 7 is executed to sample the data.

Here, the subroutine A'shown in FIG. 7 for performing data sampling in the second embodiment will be described. In step 21 and step 22, FIG.
The same processing as that of the subroutine A is performed. In the following step 22A, the combustion (heat generation) ratio (%) with respect to the crank angle as shown in FIG. 8C is obtained. That is, the value (total area) obtained by time-integrating the heat release rate curve shown in FIG. 8B obtained in step 22 is set to, for example, 100%, and the integrated value of the combustion rate up to a predetermined crank angle in the next combustion cycle is calculated. , What percentage, in other words, the degree of progress of combustion with respect to the crank angle is obtained.

In step 23A, it is determined whether or not the predetermined section calculation has been completed. If YES, step 24A
If NO, the process waits until the predetermined section calculation is completed. In step 24A, the combustion ratio (heat generation ratio) is
The crank angle when the point a (predetermined value) in FIG. 8C is reached is determined and stored as NETADA.

Since this process is a process for detecting the approximate start time of combustion, it is also possible to detect the time when the combustion ratio is 0%, that is, the rising time of the heat release rate. In this case, since the degree of change in the heat release rate is small (because the degree of increase in the heat release rate curve is moderate), the detection error is slightly large, but as described above, after a certain degree of combustion progresses, Slice level (a
If the intersection point with (point) is obtained, there is an advantage that the detection error can be reduced.

In step 24B, the crank angle when the combustion ratio (heat generation ratio) reaches point b (predetermined value) in FIG. 8B is determined and stored as NETADB. It should be noted that this process is a process for detecting the approximate end time of combustion, so it may be possible to detect when the combustion ratio is 100%. In this case, however, the combustion is approaching the end time and heat is generated. Since the degree of change in the generation rate is small (because the curvature of the heat generation rate curve is gentle), the detection error is slightly large, but as described above, the predetermined slice level (point b) before the combustion is completed. If the intersection point with is obtained, there is an advantage that the detection error can be reduced.

In step 25A, a predetermined period NETAD from the point a to the point b (for example, the period from the start of combustion to the end thereof) is calculated according to the following equation. NETAD = NETADB-NETADA In this way, the subroutine A'is completed, and then the process proceeds to step 5A in the flowchart of FIG.

Here, the description returns to the flowchart of FIG. 6 again. In step 5A, the NETAD obtained in step 4A is stored as NETAD ₁ . Steps 6 and 7 perform the same processing as in the first embodiment. In step 8A, data sampling is performed in the EGR / OFF state. The data sample is shown in FIG.
This is performed by executing the subroutine A ′ described in the flowchart of FIG.

At step 9A, the NETAD obtained at step 8A is stored as NETAD ₂ . In step 10, as in the first embodiment, the EGR control solenoid 9 is controlled to forcibly open the EGR control valve 5 and restore the exhaust gas recirculation.

In step 11, as in the first embodiment, the subroutine B shown in FIG. 5 is executed to make a failure diagnosis. In step 12, as in the first embodiment,
As the failure determination result, it is determined whether the NG determination or the OK determination is made, and the above flow is repeated until either determination is made.

Thus, according to the second embodiment, E
Before and after the GR is switched ON / OFF, heat that can grasp the pure combustion state (combustion process) by eliminating the influence of the combustion chamber volume change based on the cylinder pressure (combustion pressure) signal from the cylinder pressure sensor 11 respectively. Change of combustion ratio before and after EGR ON / OFF switching (specifically, combustion period change) by calculating combustion ratio from occurrence rate
Since the failure diagnosis of the EGR device is performed based on the above, even if the ignition timing and the like are controlled so as to suppress the engine torque fluctuation, the change in the combustion state (combustion process) due to ON / OFF of the EGR is performed. Since only this can be detected with high accuracy with a simple configuration (see FIG. 8), the accuracy of EGR failure diagnosis can be greatly improved.

In the present embodiment, the change in the combustion period before and after the switching of the EGR ON / OFF is substantially detected based on the combustion ratio, but the EGR ON is described.
・ EGR ON / O is detected even if the change in the inclination of the combustion ratio curve before and after the OFF switching is detected (the degree of change in the combustion ratio).
A change in the combustion state (process) due to FF switching and a change in the combustion state (process) due to ignition timing control can be distinguished with high accuracy, so the slope of the combustion ratio curve before and after EGR ON / OFF switching May be detected (the degree of change in the combustion ratio) to perform the EGR failure diagnosis.

[0059]

As described above, according to the failure diagnosis device for the exhaust gas recirculation system for an internal combustion engine according to the invention of claim 1, the heat release rate change before and after the EGR is turned ON / OFF is changed for failure diagnosis. Since the failure diagnosis of the EGR device is performed based on (that is, the difference in the combustion process), even if the ignition timing and the like are controlled so as to suppress the engine torque fluctuation, it is caused by the ON / OFF of the EGR. Since the change in the combustion state (combustion process) can be detected with high accuracy and with a simple structure, the accuracy of EGR failure diagnosis can be greatly improved.

According to the inventions of claims 2 to 4, even if the ignition timing is changed by the ignition timing control and the relative position of the heat release rate curve to the crank angle (time) is changed, it is too much affected. In addition, the change of the combustion state (difference in the combustion process) due to ON / OFF of the EGR can be performed with high accuracy and easily based on the combustion period, the combustion ratio, and the degree of change of the combustion ratio that can be easily detected from the heat release rate. Since it can be detected, the EGR failure diagnosis accuracy can be improved with high accuracy and easily.

According to the invention described in claim 5, even if the difference in the combustion process caused by ON / OFF of the EGR is different depending on the operating condition at that time, it can be absorbed, so that The diagnostic accuracy can be further improved. According to the sixth aspect of the invention, as the exhaust gas recirculation rate increases, the change in the combustion process (combustion period, combustion ratio, etc.) due to turning the EGR on and off increases, and the exhaust gas recirculation rate remains the same. However, the operating state at that time (engine speed, engine load, indicated mean effective pressure, etc.)
Even if the combustion process changes in accordance with the above, since the predicted value can be set in accordance with such characteristics, the diagnostic accuracy can be further improved.

According to the invention described in claim 7, the difference between the actually obtained combustion processes is divided by the predicted value set by the predicted value setting means, and the predetermined value is compared. By doing so, since the difference in the combustion process can be standardized, it can be compared with a certain predetermined value regardless of the operating conditions (engine speed, engine load, indicated mean effective pressure, etc.). Therefore, failure diagnosis can be easily performed.

According to the invention described in claim 8, the reliability of the average value increases as the number of data of the difference of the combustion process when obtaining the average value of the difference of the combustion process increases.
The dead zone of the diagnosis is changed in accordance with the number of data to avoid erroneous diagnosis when the reliability is low, and the highly accurate diagnosis can be performed when the number of data increases and the reliability increases.

[Brief description of the drawings]

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

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

FIG. 3 is a flowchart showing a failure diagnosis control in the above embodiment.

FIG. 4 is a flowchart illustrating a data sample (subroutine A) in the above embodiment.

FIG. 5 is a flowchart illustrating a failure diagnosis (subroutine B).

FIG. 6 is a flowchart illustrating failure diagnosis control according to the second embodiment.

FIG. 7 is a flowchart illustrating a data sample (subroutine A ′) in the above embodiment.

FIG. 8A is a time chart showing changes in in-cylinder pressure. (B) is a time chart showing changes in heat generation rate.
(C) is a time chart showing changes in the combustion ratio (heat generation ratio).

FIG. 9 is an EG when the conventional ignition timing control is not performed.
The time chart which shows the engine torque fluctuation accompanying R ON / OFF, the indicated effective average pressure change, etc. (example at normal time).

FIG. 10 is an EG when conventional ignition timing control is performed.
The time chart which shows the engine torque fluctuation accompanying R ON / OFF, the indicated effective average pressure change, etc. (example at normal time).

[Explanation of symbols]

 1 internal combustion engine 2 exhaust manifold 3 intake manifold 4 exhaust gas recirculation passage 5 EGR control valve 6 throttle valve 7 negative pressure introducing passage 8 control unit 9 EGR control solenoid 10 BPT valve 11 cylinder pressure sensor 12 spark plug 13 crank angle sensor

Claims (8)

[Claims] 1. A failure 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, the cylinder of the engine. In-cylinder pressure detecting means for detecting the internal pressure, heat release rate detecting means for detecting the heat release rate based on the in-cylinder pressure detected by the in-cylinder pressure detecting means, and forced opening / closing control of the exhaust gas recirculation control valve Combustion for detecting a difference in combustion process based on the heat release rate detected by the heat release rate detection means when the exhaust gas recirculation control valve is opened and closed by the open / close means and the forced open / close means, respectively. An internal combustion engine comprising: a process difference detection means; and a diagnosis means for diagnosing whether or not there is an abnormality in the exhaust gas recirculation device based on the difference in the combustion processes detected by the combustion process difference detection means. Exhaust recirculation system Failure diagnosis system. 2. The combustion process difference detection means detects a predetermined combustion period based on the heat generation rate detected by the heat generation rate detection means, and the combustion process difference based on the detected predetermined combustion period. The failure diagnosis device for an exhaust gas recirculation device for an internal combustion engine according to claim 1, wherein 3. The combustion process difference detection means detects a combustion ratio based on the heat generation rate detected by the heat generation rate detection means, and detects a difference in combustion processes based on the detected combustion ratio. The failure diagnosis device for an exhaust gas recirculation device for an internal combustion engine according to claim 1. 4. The malfunction of the exhaust gas recirculation system for an internal combustion engine according to claim 3, wherein the combustion process difference detection means detects a difference in the combustion process based on the degree of change in the detected combustion ratio. Diagnostic device. 5. Prediction value setting means for setting a prediction value for the difference in the combustion process according to operating conditions, wherein the diagnosis means and the difference in the combustion process detected by the combustion process difference detection means and the prediction. The exhaust gas of the internal combustion engine according to any one of claims 1 to 4, wherein the presence or absence of abnormality of the exhaust gas recirculation device is diagnosed by comparing with a predicted value set by a value setting means. Failure diagnosis device for reflux device. 6. The predicted value setting means sets the predicted value based on the engine speed, the engine load, and the target exhaust gas recirculation rate, or the engine speed, the indicated mean effective pressure, and the target exhaust gas recirculation rate. The failure diagnosis device for an exhaust gas recirculation device for an internal combustion engine according to claim 5. 7. The diagnosing means compares a difference between combustion processes detected by the combustion process difference detecting means with a predicted value set by the predicted value setting means and compares the value with a predetermined value. The failure diagnosis device for an exhaust gas recirculation device for an internal combustion engine according to claim 5 or 6, wherein the presence or absence of abnormality of the exhaust gas recirculation device is diagnosed. 8. When the diagnosing means diagnoses the presence or absence of an abnormality in the exhaust gas recirculation device based on the average value of the difference in the combustion process, the number of data of the difference in the combustion process is calculated when calculating the average value. The failure diagnosis device for an exhaust gas recirculation device for an internal combustion engine according to any one of claims 1 to 7, wherein the dead zone for diagnosis is changed in accordance with the above.