JPH07293351A - Failure diagnosis method for exhaust gas recirculation system of internal combustion engine - Google Patents

Abstract

PURPOSE:To enable failure detection without suspending recirculation of exhaust gas by comparing characteristics of detected ion current to those of the ion current according to an operation condition for detecting failure of an exhaust gas recirculation system. CONSTITUTION:A biasing power source 24 is connected to an ignition plug 18 through a high pressure diode 23. Ion current is detected by means of an ion current measuring circuit 25. Normally, when bias current is applied to a spark plug 18 immediately after starting electric discharge, the ion current is applied to a combustion chamber 10 according to a combustion condition after electric discharge. In a normal combustion, the ion current is abruptly applied immediately after ignition, and decreased before the top dead center. Afterward, it is increased again, and shows a peak value in the vicinity of a crank angle where a combustion pressure is maximum value. When the peak value of the ion current exceeds a failure judgment level, and the integration value exceeds a specified value, for instance four, at any of cylinders, failure of an exhaust gas recirculation system is judged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for diagnosing a failure in an exhaust gas recirculation system of an internal combustion engine, which mainly reduces harmful components in the exhaust gas of the internal combustion engine for automobiles.

[0002]

2. Description of the Related Art A part of exhaust gas is taken out from an exhaust system,
2. Description of the Related Art An exhaust gas recirculation device (EGR) that recirculates to an intake system by controlling appropriate temperature, timing, flow rate, etc. is known.
This is due to the heat capacity of the inert gas in the exhaust gas,
The maximum combustion temperature is lowered to reduce NOx. In such an exhaust gas recirculation device, output reduction,
Since there are disadvantages such as deterioration of drivability due to unstable combustion,
It is essential to control the recirculation amount and timing according to the operating conditions. For this reason, a failure of the device deteriorates drivability and deteriorates HC emission. Therefore, the negative pressure applied to the EGR valve is forcibly changed to intermittently recirculate the exhaust gas (EGR gas). Failure diagnosis is performed by the change of intake pipe pressure.

[0003]

However, when the EGR gas is interrupted for failure diagnosis during traveling as described above, the drivability may be deteriorated because the combustion state changes each time. Further, if a failure occurs and is left as it is, exhaust gas does not circulate in the intake system, so that the NOx emission amount increases. On the other hand, failure diagnosis cannot be performed at any time during operation.If the exhaust gas recirculation device is accelerated during failure diagnosis operation, failure detection conditions will change and detection will not be possible. However, when a failure occurs, the response is delayed, making it difficult to find the cause of the deterioration of drivability.

An object of the present invention is to eliminate such a problem.

[0005]

The present invention takes the following means in order to achieve such an object. That is, the failure diagnosis method for an exhaust gas recirculation system of an internal combustion engine according to the present invention is an ion generated in a combustion chamber in an internal combustion engine including an exhaust gas recirculation system for recirculating a part of exhaust gas to an intake system. The characteristics of the current are detected, and it is determined that the characteristics of the detected ion current exceed the characteristics of the ion current that is the reference in the operating state corresponding to the operating state at the time of detection, and the exhaust gas circulation is based on the result of the determination. It is characterized by judging the abnormality of the system.

The characteristics of the ion current in the present invention refer to the maximum value, the integrated value within a predetermined time, the position where the maximum value appears (converted to crank angle), the duration, and the like. These may use the values as they are when they are detected, or may be those that have undergone arithmetic processing such as averaging and smoothing.

[0007]

With such a structure, the characteristic of the ion current that changes according to the actual combustion state is detected, and the characteristic exceeds the characteristic of the reference ion current in the corresponding operating state. In this case, it is not necessary to intermittently circulate the exhaust gas because the abnormality of the exhaust gas circulation system is determined. That is, if the exhaust gas does not circulate, combustion improves, so if the characteristics of the ion current generated at each combustion are detected and the combustion state is judged from the characteristics, whether the exhaust gas circulates or circulates Can be determined if the is stopped. In this case, the control of the exhaust gas circulation system remains in the normal operating state, in other words, the normal operating state without changing the operating state of the exhaust gas circulation system to the state for diagnosing the failure of the exhaust gas circulation system. It makes it possible to detect failures. Therefore, it is possible to prevent a problem in which the supply state changes due to the exhaust gas circulation stoppage and the like, which deteriorates the operating state.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

An engine 100 schematically shown in FIG. 1 is a four-cylinder engine for an automobile, and its intake system 1 has a throttle valve 2 which opens and closes in response to an accelerator pedal (not shown).
Is provided, and the surge tank 3 is provided on the downstream side thereof. A fuel injection valve 5 is further provided near one end communicating with the surge tank 3, and the opening of the fuel injection valve 5 is controlled by the electronic control unit 6 based on a basic injection amount TP described later. ing. Also the exhaust system 20
An O ₂ sensor 21 for measuring the oxygen concentration in the exhaust gas is attached to a position upstream of the three-way catalyst 22 arranged in a pipe line leading to a muffler (not shown).
Further, a pipe 41 communicating with the vicinity where the O ₂ sensor is attached is connected to an exhaust gas recirculation device (hereinafter referred to as an EGR device) 40. The EGR device 40 is connected to a pipe 42 that leads the exhaust gas from the pipe 41 to the intake system 1, and a pipe 43 that introduces the intake pipe pressure upstream of the throttle valve 2. This EGR device 40 and the respective pipes 41, 4
An exhaust gas recirculation system EGS is constituted by the two and 43. The exhaust gas recirculation system EGS itself may have a configuration similar to that well known in the art.

A spark plug 18 is attached at a position corresponding to the ceiling of the combustion chamber 10. An igniter 32 and an ignition coil 33 are electrically connected to the spark plug 18 via a diode 31. The spark plug 18, the igniter 32, and the ignition coil 33 are typically an ignition system IGS, and may include diodes 23 and 33 that prevent current from flowing around. Although only one system is shown in FIG. 1 for this ignition system IGS excluding the igniter 32, one system is connected to each cylinder. It should be noted that the engine 100 is not limited to having four cylinders, and may have three cylinders, 12 cylinders, or the like.

The electronic control unit 6 includes a central processing unit 7
And a memory device 8, an input interface 9, and an output interface 11 are mainly configured, and the input interface 9 is for detecting the pressure in the surge tank 3. Intake pressure signal a output from the intake pressure sensor 13,
A cylinder determination signal G1, a crank angle reference position signal G2, an engine speed signal b output from a cam position sensor 14 for detecting the rotational state of the engine 100, and a vehicle speed output from a vehicle speed sensor 15 for detecting a vehicle speed. Signal c, LL signal d from the idle switch 16 for detecting the opening / closing state of the throttle valve 2, water temperature signal e from the water temperature sensor 17 for detecting the cooling water temperature of the engine, current from the air-fuel ratio sensor 21 described above. The signal h or the like is input. On the other hand, the output interface 11 outputs the fuel injection signal f to the fuel injection valve 5 and a plurality of signals including the ignition signal IGt to the igniter 32. Although not shown, the electronic control unit 6 has a built-in A / D converter that converts an analog signal into a digital signal.

A bias power supply 24 for measuring an ion current and an ion current measuring circuit 25 are connected to the spark plug 18 via a high voltage diode 23 to form an ion current detecting system IDL. As the ion current measuring circuit 25 itself including the bias power source 24, various circuits known in the art can be used,
In order to detect the ion current for each cylinder, the same number as the number of cylinders, that is, one ion current detection system IDL is provided for one cylinder.

The electronic control unit 6 includes an intake pressure signal a output from the intake pressure sensor 13 and a cam position sensor 14.
The rotational speed signal b output from the engine is used as main information, and the basic injection time TP is corrected by various correction coefficients determined according to the operating state of the engine to determine the fuel injection valve opening time, that is, the injector final energization time T. Then, a program for controlling the fuel injection valve 5 according to the determined energization time and injecting fuel according to the engine load from the fuel injection valve 5 into the intake system 1 is incorporated. Further, the storage device 8 detects the characteristic of the ion current generated in the combustion chamber 10 and determines that the characteristic of the detected ion current exceeds the characteristic of the ion current corresponding to a predetermined combustion state, A program for retarding the ignition timing based on the determination result is stored.

The outline of this ignition timing control program is shown in FIG.
.About.3.

First, step S1a (step S1b,
Step S1c) is a step of determining a cylinder by the cylinder number NTCRANK. Cylinder number NTCRANK
0 is set to 1 cylinder, 3 is set to 2 cylinders, and 1 is set to 3 cylinders. Step S2a (Step S2b, Step S2
c, step S2d) compares the maximum value IMAX of the peak value IONP of the ion current stored at that time with the peak value IONP of the ion current during the current combustion stroke, and determines the maximum value at that time. Then, the maximum value IMAX is determined. Step S3a (Step S3b, Step S3
c, step S3d), the peak value IONP is set to the maximum value I
This is a step of updating the data as MAX. The steps up to this point are executed for each cylinder. Step S1a, Step S2a and Step S3a are 1
Step for cylinder, similarly step S1b
~ S3b has 2 cylinders, steps S1c to S3c have 3 cylinders,
Steps S4b and S4c are steps for four cylinders.

Next, in step S4, the cycle counter NTCYC is incremented to count that the maximum value IMAX has been judged / updated once. Step S5
Is a step of determining whether or not the specified number of times has been reached. In the case of this embodiment, the prescribed number of times is 8 cycles for one cylinder. A step S6 decides whether or not the maximum value IMAX of the ion current exceeds a reference value, and it is determined that one of the cylinders is in a combustion state that is not suppressed by the exhaust gas, that is, the EGR device 40 fails. In the determination subroutine, if any of the cylinders is determined to be out of order, the diagnosis required flag is set. A step S7 resets the cycle counter NTCYC. Step S8 is the maximum value IMAX of each cylinder.
Is set to an initial value, that is, 0.

The details of the failure diagnosis subroutine are shown in FIG.
Shown in. First, step S11a (step S11b,
In step S11c), step S1a (step S1c
1b, step S1c), the cylinder is determined. That is, in step S11a, one cylinder is determined, if it is not one cylinder, two cylinders are determined in step S11b, if it is not two cylinders, three cylinders are determined in step S11c, and if it is determined that it is not three cylinders in step S11c. The remaining four cylinders will be determined. Step S12a (step S12b, step S12c, step S12d)
Then, the maximum value IMAX of each cylinder is the abnormality determination level LVI.
It is determined whether or not it exceeds ON. Abnormality judgment level L
VION is set by the engine speed and the intake pressure as parameters indicating the operating state of the engine, and is stored in the storage device 8 as a two-dimensional map. Then, in detail, interpolation calculation is performed to determine the abnormality determination level LVION corresponding to the operating state at that time.

In step S13a (step S13b, step S13c, step S13d), the abnormality determination counter is incremented. Step S14a (step S14b, step S14c, step S14d)
Then, it is determined whether or not the content of the abnormality determination counter exceeds 4. In step S15a (step S15b, step S15c, step S15d), the content of the abnormality determination counter is set to 4. Step S16a (Step S16b, Step S16c, Step S16
In d), the abnormality determination counter is decremented. Step S17a (Step S17b, Step S17c,
In step S17d), it is determined whether the content of the abnormality determination counter is not negative. In step S18a (step S18b, step S18c, step S18d), the content of the abnormality determination counter is set to 0. In step S19, it is determined whether the content of the abnormality determination counter is 4. In step S20, the EGR diagnostic flag is set (= 1). In step S21, EGR
The diagnosis flag is reset (= 0).

In such a structure, when the measurement of the ion current is completed eight times in each cylinder, one failure diagnosis of the EGR device 40 is completed. In the following, the progress of the control for one cylinder will be described, and only the different parts will be described for the remaining cylinders.

The ion current is measured for each cylinder for each ignition, and the peak value IONP is determined by, for example, the method described below. Normally, when a bias voltage is applied to the spark plug 18 from the bias power source 24 immediately after the start of discharge, the ionic current flows into the combustion chamber 10 according to the degree of combustion at the time of combustion after discharge. In the case of normal combustion, the ion current rapidly flows immediately after ignition, and then the top dead center TD.
A peak value I at which the value of the ion current becomes maximum near the crank angle at which the combustion pressure becomes maximum after decreasing at C and then increasing again
It becomes ONP (shown in FIG. 4). Therefore, the ion current is measured by A / A set according to the engine speed NE.
Top dead center TDC in D conversion cycle (unit based on crank angle)
The A / D conversion is started from, the analog current value is converted to a converted value which is digital data, and the obtained converted value is assigned a data number DTn in ascending order from the top dead center TDC to the RAM of the storage device 8. It is done by storing in. The stored conversion value is compared with the maximum value at that time in each measurement once, and the maximum conversion value is stored with the maximum value flag. A / D conversion is at TDC
Converted from DC to a predetermined time, for example, crank angle, 30
Do only CA. In this way, by adding the data number DTn to the converted value, it is possible to easily specify the maximum value position (based on the crank angle conversion).

After the ion current of one cylinder is detected, the peak value IONP of the ion current is stored in the maximum value I.
If it is larger than MAX, the control is step S1a → S.
2a → S3a → S4 → S5, and cycle counter N
Steps S1a → S2a until TCYC counts 32
→ S3a → S4 → S5 are repeatedly executed. When the cycle counter NTCYC counts 32, that is, when the maximum value IMAX and the peak value IONP are compared and updated eight times for one cylinder, step S6 is executed.

In the case where the exhaust gas recirculation system EGS is out of order, when the exhaust gas is not supplied to the intake system 1 through the EGR device 40, as compared with the case where the combustion introduces the exhaust gas. Therefore, the detected maximum value IMAX1 becomes high. This state is 4 for 1 cylinder
When it occurs more than once, the control in the failure diagnosis subroutine is performed in steps S11a → S12a → S13a →
The process proceeds from S14a → S15a → S19 → S20 to set the EGR diagnostic flag XEGRER. On the other hand, once the maximum value IMAX increases, the EGR abnormality determination level LV increases.
When the abnormality determination counter EDIG1 does not reach 4 after exceeding the ION but thereafter, the control proceeds to steps S11a → S12a → S13a → S16a → depending on the value of the abnormality determination counter EDIG1 at that time. Steps S16a → S17a → S18 → S19 → S2
1 or → Step S16a → S19 → S21, and E
The GR diagnosis flag XEGRER is reset.

In this subroutine, when the content of the abnormality determination counter EDIGn exceeds 4 in any one of the cylinders, the content of the abnormality determination counter EDIGn is set to 4 in steps S15a, 15b, 15c and 15d, and the EGR diagnosis flag is set. Set XEGRR. That is, if at least one cylinder is abnormal, EG
The R diagnosis flag XEGRER is set, and it is diagnosed that the exhaust gas recirculation system EGS has failed.

Thus, the maximum value I of the peak value IONP is
If MAX exceeds the abnormality determination level LVION and even one cylinder whose integrated value exceeds a predetermined value of 4 occurs,
By setting the EGR diagnosis flag XEGRER as an abnormality of the exhaust gas recirculation system EGS, it becomes possible to promptly respond to a failure diagnosis. Further, the EGR device 40 does not particularly change its operation for failure diagnosis during normal operation, and can detect failure even when the throttle valve 2 is opened. Good combustion can be achieved for cylinders that have been burned normally.

The present invention is not limited to the embodiment described above. For example, although the ignition system IGS using the igniter 32 has been described in the above embodiment, a distributor may be used. Further, in the above-described embodiment, the setting is made such that 8 cycles are spent to determine the peak value IMAX, but it may be set to 10 cycles, for example, and a value capable of promptly detecting a change in combustion may be used.

Further, in the above embodiment, the peak value of the ionic current is detected in order to determine the degree of combustion, but the degree of combustion is determined using the integrated value of the ionic current, in other words, the area of the ionic current waveform. It may be one. further,
In one cylinder, when the abnormality determination counter EDIGn exceeds the set value and becomes abnormal, the cylinder is discriminated from the abnormality determination counter EDIGn to determine in which cylinder the abnormality has occurred. Good. In other words, by not determining whether an abnormality has occurred in any cylinder, but by determining up to the cylinder in which the abnormality has occurred, an abnormality in which the opening portion of the intake manifold of the intake system 1 is clogged is found. It will be easier.

Besides, the configuration of each part is not limited to the illustrated example, and various modifications can be made without departing from the spirit of the present invention.

[0028]

As described above in detail, the present invention detects the characteristics of the ion current, and compares the characteristics with the characteristics of the ion current according to the operating state at that time, and based on the result, the exhaust gas. Since the abnormality of the recirculation system is detected, it is not necessary to temporarily stop the exhaust gas recirculation, and therefore the combustion state does not change due to the fluctuation of the exhaust gas, and the exhaust gas recirculation system failure diagnosis is performed. It is possible to secure and maintain stable drivability even while performing.

[Brief description of drawings]

FIG. 1 is a schematic configuration explanatory view showing an embodiment of the present invention.

FIG. 2 is a flowchart showing a control procedure of the embodiment.

FIG. 3 is a flowchart showing a control procedure of the embodiment.

FIG. 4 is a waveform diagram showing a typical ion current waveform in the example.

[Explanation of symbols]

 5 ... Fuel injection valve 6 ... Electronic control device 7 ... Central processing unit 8 ... Storage device 9 ... Input interface 10 ... Combustion chamber 11 ... Output interface 24 ... Bias power supply 25 ... Ion current measurement circuit

Front Page Continuation (72) Inventor Takahiro Iida 2-1-1 Taoyuan, Ikeda City, Osaka Daihatsu Industry Co., Ltd.

Claims (1)

[Claims] 1. A characteristic of an ion current generated in a combustion chamber in an internal combustion engine having an exhaust gas recirculation system for recirculating a part of exhaust gas to an intake system is detected, and a characteristic of the detected ion current is detected. Exhaust gas from an internal combustion engine characterized by determining that the characteristics of the ion current, which is the reference in the operating state corresponding to the current operating state, are exceeded, and the abnormality of the exhaust gas circulation system is determined based on the determination result. Failure diagnosis method for gas recirculation system.