JPS63261134A - Fault detecting method for exhaust reflux device - Google Patents

Abstract

PURPOSE:To accurately ad securely detect whether or not a device is abnormal by inhibiting a fault from being decided until a specific time passes after the start of an engine. CONSTITUTION:An electronic control unit (ECU) 20 compares exhaust reflux gas temperature TG detected by a temperature sensor 22 with preset fault decision temperature TGX to decide whether or not the exhaust reflux gas temperature TG is higher than the decision temperature TGX. Then when a valve 16 is opened and exhaust reflux gas flows normally through an exhaust reflux path 15, the exhaust reflux gas temperature TG detected by the temperature sensor 22 is much higher than the decision temperature TGX and the decision result is affirmative. When the exhaust reflux temperature TG is lower than the decision temperature TGX, on the other hand, the ECU 20 decides whether or not the specific time tG is elapsed after the point of the in affirmative decision making. When not, it is not decided immediately that the device is fault even if the exhaust reflux gas temperature TG is lower than the decision temperature TGX. Consequently, misdecision due to a noise, etc., can be evaded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a failure detection method for an exhaust gas recirculation device that recirculates part of the exhaust gas of an internal combustion engine to an intake passage.

(Prior Art and Problems Thereof) Conventionally, an exhaust gas recirculation device that recirculates a portion of the exhaust gas of an internal combustion engine to an intake passage to reduce the amount of harmful gas components such as NOx in the exhaust gas is well known. This exhaust recirculation device is
An exhaust gas recirculation passage that communicates the exhaust passage and the intake passage, an exhaust gas recirculation valve (hereinafter referred to as "EGR valve") that is disposed in the middle of the exhaust gas recirculation passage and opens and closes the exhaust gas recirculation passage, and operation control of the EGR valve. The EGR valve is configured to control the opening and closing of the EGR valve according to the engine operating state, so that an appropriate amount of exhaust gas is returned to the intake passage.

However, there is a problem in that if carbon, etc. in the exhaust gas accumulates on the EGR valve of the exhaust gas recirculation device and blocks the passage, and the required amount of exhaust gas cannot be returned to the intake passage, the exhaust gas characteristics deteriorate. . Normally, it is difficult for a driver or the like to detect an abnormality or failure in the exhaust gas recirculation system unless some kind of failure detection means is provided to detect the abnormality or failure.

Therefore, when the exhaust gas recirculation device is in the state where it should be operating, a temperature sensor (hereinafter referred to as "EGR temperature sensor") is installed exposed in the exhaust recirculation passage near the EGR valve or across a wall, and the exhaust gas recirculation A method of detecting a failure of an exhaust gas recirculation device by detecting gas temperature is known. This method is used when the EGR valve etc. is operating normally and the required amount of exhaust recirculation gas is flowing, and when the EGR valve etc. is abnormal and the exhaust recirculation gas does not flow at all or even if it is flowing, the amount of gas is extremely low. There is a large difference in the temperature detected by the above-mentioned EGR'IjL temperature sensor between when the temperature is low and when the EGR
If the exhaust gas recirculation gas temperature detected by the R temperature sensor is below a predetermined failure determination temperature, it is determined that the exhaust gas recirculation device is malfunctioning.

However, in the above-described failure detection method for the exhaust gas recirculation system, when the engine has not yet been warmed up immediately after starting, the operating state of the engine is not stable, and therefore the temperature of the exhaust gas recirculation is also unstable. in a state. If the failure of the exhaust gas recirculation device is determined when the engine is in such a state, the failure cannot be determined accurately and there is a risk of misdiagnosis.

The present invention has been made to solve such problems, and it is an object of the present invention to provide a failure detection method for an exhaust gas recirculation system that can accurately and reliably detect abnormalities or failures in the exhaust gas recirculation system.

(Means for Solving the Problems) According to the present invention, in order to achieve the above-mentioned object, an exhaust gas recirculation device that recirculates a part of exhaust gas of an internal combustion engine to an intake passage is in a state where it should be operating. At some point, in a failure detection method that detects a temperature related to the temperature of gas recirculating through the exhaust gas recirculation device, and determines that the exhaust gas recirculation device is malfunctioning when the detected temperature is lower than a failure determination value, There is provided a failure detection method for an exhaust gas recirculation device, characterized in that the failure determination is prohibited until a predetermined period of time has elapsed.

(Function) After a predetermined period of time has elapsed after the engine has been started, engine warm-up is completed, and once engine warm-up is completed, the engine operates stably and the temperature of the exhaust gas recirculation is also stabilized. If the failure of the exhaust gas recirculation device is determined in such a state, the failure can be determined more accurately and reliably. Therefore, if failure determination is prohibited until a predetermined time has elapsed after the engine is started, misdiagnosis of failure determination can be avoided.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings. □ First, the overall configuration of the exhaust gas recirculation system for carrying out the method of the present invention will be explained with reference to FIG. Connected = A throttle valve 14 is disposed in the middle of the intake pipe 12, and the intake pipe 12 downstream of the valve 14
One end of the exhaust recirculation path 15 is connected to the other end of the exhaust recirculation path 1.
The other end of 5 is connected to the exhaust pipe 13. .

The exhaust gas recirculation path 15 is the exhaust gas recirculation valve (EGR'' valve).
1i is installed. This F, G R valve 16 consists of a valve body 16a that opens and closes the exhaust gas recirculation path 15, and an actuator 16b that drives the valve body 16a to open and close.
C, which is divided into a negative pressure chamber 16f and an atmospheric pressure chamber 16g.
and a diaphragm 16 connected to the valve body 16a.
(I) and a spring 16e that is housed in the negative pressure chamber 16f and presses the diaphragm 16d in the direction of valve body 16.1.

One end of a negative pressure path 17 is connected to the negative pressure chamber 16f of the actuator 16b, and the other end of the negative pressure path 17 is connected to the throttle valve 14.
It is connected to the downstream intake pipe 12, and the negative pressure chamber 1'6'f
The negative pressure generated in the intake pipe 12 downstream of the throttle valve 14 is introduced to the intake pipe 12 through a negative pressure path 17. A normally closed solenoid valve 18 is disposed in the negative pressure path 17, and the solenoid valve 18 is electrically connected to an electronic control unit (ECU) 20, which will be described later. The valve is opened by the supplied valve opening drive signal, and the negative pressure is transferred to the negative pressure chamber 1 of the actuator 16b.
Supply to 6f.

An EGR temperature change sensor 22 is installed on the side wall 16h of the EGR valve 16.
is attached, and its tip temperature sensor part 222
is a valve body], which is exposed facing into the exhaust gas recirculation path 15 of the T: flow from 6f, and this EGR & degree sensor 22 detects the exhaust gas recirculation gas temperature and sends a detection signal to the electronic controller I.
- Supplied to the roll unit 20.

On the input side of the electronic control unit t.20, there are various sensors that detect the operating state of the engine 10, such as an intake air temperature sensor 24 that is attached near the air-opening end of the intake pipe 12 and that detects the intake air temperature, and an engine temperature A water temperature sensor 25 that detects the cooling water temperature of the engine 10, an atmospheric pressure sensor 26 that detects atmospheric pressure, an engine rotation speed sensor (not shown), an intake air amount sensor, etc. are connected, and detection signals from these various sensors are electronically transmitted. It is supplied to the control unit 20. An alarm lamp 28 is connected to the output side of the electronic control unit 20 to warn of a failure when a failure of the exhaust gas recirculation system is detected. It is being

Next, the operation of the exhaust gas recirculation device configured as described above will be explained.

The valve body 16a of the EGR valve 16 is normally pressed in the valve closing direction by the spring 16e, and the EGR valve 16 is closed. Then, when the engine 10 is in a predetermined operating state based on detection signals from the various sensors described above, the electronic control unit outputs a valve opening drive signal to the electromagnetic valve 18 to open the valve.

When the solenoid valve 18 opens, the negative pressure generated in the intake pipe 12 downstream of the throttle valve 14 is supplied to the negative pressure chamber 16f of the actuator 16b via the negative pressure path 17. Negative pressure chamber 1
When negative pressure is supplied to 6f, the atmospheric pressure acting on the atmospheric pressure chamber 16g side of the diaphragm 16d becomes the negative pressure chamber]. The EGR valve 16 is opened by overcoming the negative pressure acting on the f side and moving the diaphragm 16d, and therefore the valve body 16a, in one direction (as shown in the figure) against the spring force of the spring 16e. When the EGR valve 16 opens, a portion of the exhaust gas in the exhaust pipe 13 will flow back to the intake pipe 12 via the exhaust gas recirculation path 5.

Next, a procedure for detecting a failure in the exhaust gas recirculation system using the electronic control unit 20 will be explained with reference to FIGS. 2 to 5.

FIG. 2 shows a state in which the exhaust gas recirculation device should be operating, that is, a state in which the EGR valve 16 should be open and exhaust gas should be flowing back to the intake pipe 12 via the exhaust gas recirculation path 5. This program routine is used to determine whether or not the exhaust gas recirculation system is in a state where it is possible to perform failure determination.

ELECTRONIC CONTROL UNISO I-20 C. In step 30, it is determined whether or not the engine 10 starting time 11tS (, # position) has elapsed. Immediately after the engine 10 is started, it has not been warmed up yet, and during this time the temperature of the exhaust gas recirculated via the exhaust gas recirculation path 15 is not stable. There is a risk of misjudgment.

Therefore, if the determination result in step 30 is negative (NO), that is, if the engine 10 has not been warmed up yet, the program routine is ended without executing the failure determination described later.

The time required to complete warm-up after starting the engine 10 is influenced by the cooling water temperature state at the time of starting the engine 10. It is desirable to set it according to the engine water temperature detected by. FIG. 3 is a graph showing the relationship between the judgment prohibition time t5 and the water temperature Tw at the time of starting,
The determination prohibition time ts is set to a shorter time as the water temperature TW is higher, depending on the water temperature Tw detected immediately after the engine 10 is started. Further, even if the water temperature Tw at the time of starting the engine 10 is equal to or higher than the temperature Two at which it can be considered that the engine 10 is in a warm-up state, the determination prohibition time t is set to the minimum time t. (for example, 2 minutes) and wait until the engine 10 is completely stabilized before making a failure determination as described below.

If the determination result in step 30 is affirmative (Yes), the engine water'/L T W is set at a predetermined value Twx (for example, 80
℃) or more is determined (step 32). Together with the determination in step 30 described above, it is determined whether the engine 10 has been sufficiently warmed up, and if the determination result is negative, the program routine is executed without executing the failure determination described later. end.

If the determination result in step 32 is affirmative, the electronic control unit 20 determines whether the intake air temperature Ta detected by the intake air temperature sensor 24 is lower than a predetermined determination value Tax (for example, 60° C.) (step 34).

If the intake air temperature Ta is high (if the determination in step 34 is negative), the EGR valve 16 and the EC'R temperature sensor 22 themselves become high temperature even if the exhaust gas is not recirculated through the exhaust gas recirculation path 15. In such a case, the exhaust gas recirculation gas temperature cannot be accurately measured, so the program routine is ended without executing the failure determination described later.

Next, if the determination result in step 34 is affirmative, the process proceeds to step 36, where it is determined whether the atmospheric pressure Pa detected by the atmospheric pressure sensor 26 is equal to or higher than a predetermined determination value Fax (for example, 700 mmHg). When the engine 10 is operated under atmospheric conditions with low atmospheric pressure, such as at high altitudes, the exhaust gas temperature decreases, and the exhaust gas recirculation gas temperature also decreases.

Therefore, if the atmospheric pressure pa is lower than the predetermined determination value Pax and the decrease in exhaust gas recirculation gas temperature cannot be ignored (if the determination result in step 36 is negative), the program routine is executed without executing the failure determination described later. finish.

If the determination results in each of the above steps are positive, it means that there is no problem in determining the failure of the exhaust gas recirculation system, and in such a case, the electronic control unit 20 proceeds to step 40 and A failure determination routine for the exhaust gas recirculation system (EGR system) shown in the figure is executed.

First, in step 41 of the failure determination routine, the electronic control unit 20 sets failure determination temperatures T and X based on the exhaust gas recirculation gas temperature. This determination temperature TGX is read out from a table stored in a storage device (not shown) of the electronic control unit 20 in accordance with the intake air temperature Ta detected by the intake air temperature sensor 24. FIG. 5 shows a discrimination temperature TGX table stored in the storage device, and the discrimination temperature TGX is set to a higher temperature 1 value as the intake air temperature Ta increases. This discrimination temperature TGX is given as a function of the intake air temperature Ta, but the shape of the EGR valve 16, the size of the exhaust gas recirculation path 15, the amount of recirculation of exhaust gas recirculation, and the mounting position of the EGR temperature sensor 22 depend on various factors such as the position of the EGR temperature sensor 22. It is preferable that the determination temperature TGX table shown in FIG. 5 is experimentally set for each engine.

Next, the 74 child control unit 20 compares the exhaust recirculation gas temperature T detected by the EGR temperature sensor 22 with the determination temperature TGX set in step 41, and determines whether the exhaust recirculation gas temperature T0 is higher than the determination temperature TGX. (Step 42). When the EGR valve 16 is opened and the exhaust recirculation gas is normally recirculating through the exhaust gas recirculation path 15, that is, when the exhaust gas recirculation device is operating normally, the exhaust gas detected by the EGR temperature sensor 22 The reflux gas temperature T is sufficiently higher than the discrimination temperature T6X, and in such a case,
The determination result in step 42 is affirmative, and the electronic control unit 20 resets a timer, which will be described later (step 44), and ends the failure determination routine.

When the exhaust gas recirculation temperature T is lower than the determination temperature TGX,
That is, when the determination result in step 42 is negative, the electronic control unit 20 waits for a predetermined time tc (for example, 30
In other words, it is determined whether the timer reset in step 44 during the normal operation of the exhaust gas recirculation system has counted for a predetermined time t6. This counter may be a hard timer built into the electronic control unit 20, or may be a so-called soft timer that measures the passage of time by executing a program. If the predetermined time t6 has not elapsed, the failure determination routine is ended without immediately determining that the exhaust gas recirculation device is malfunctioning even if the exhaust gas recirculation gas temperature T6 is lower than the determination temperature TGX. This makes it possible to avoid erroneous determinations caused by noise or the like.

Only when the exhaust recirculation gas temperature TG continues to be lower than the determination temperature TGX, step 46 is repeatedly executed, and the predetermined time 1G has elapsed, the electronic control unit 2
0, it is determined that the exhaust gas recirculation device is malfunctioning, and step 4 is performed.
8, the alarm lamp 28 is turned on to warn the driver etc. of the failure of the exhaust gas recirculation system. In this way, the driver can recognize the failure of the exhaust gas recirculation system, and the driver who recognizes the failure can immediately take appropriate measures.

In the above embodiment, the engine cooling water temperature was used as an example of the engine temperature, but the present invention is not limited to this.
Engine oil temperature or the like may be used as the engine temperature.

(Effects of the Invention) As described in detail below, according to the method for detecting failure of an exhaust gas recirculation device of the present invention, the exhaust gas is not allowed to flow until a set time elapses after the engine is started, that is, until the warm-up of the engine is completed. Since failure determination of the recirculation device is prohibited, failure determination of the exhaust gas recirculation device can be accurately and reliably performed without misdiagnosis.

[Brief explanation of drawings]

The drawings show an embodiment of a failure detection method for an exhaust gas recirculation device according to the present invention, FIG. 1 is a block diagram showing a schematic configuration of an exhaust gas recirculation device that implements the method of the present invention, and FIG. A third program flowchart showing a procedure executed by the electronic control unit (ECU) 20 shown in FIG.
The figure is a graph showing the relationship between the failure determination prohibition time tS and the cooling water temperature Tw immediately after engine startup, Figure 4 is a flowchart of the EGR failure determination routine not shown in step 40 of Figure 2, and Figure 5 is the failure determination temperature. It is a graph showing the relationship between T6X and intake air temperature Ta. DESCRIPTION OF SYMBOLS 10... Internal combustion engine, 12... Intake pipe (intake passage), 13... Exhaust pipe, 15... Exhaust recirculation path, 16...
・・Exhaust return tJffy valve (EGR valve), 20・・
・Electronic control unit (ECU), 24...
Intake temperature sensor, 25...engine coolant temperature sensor,
28...Alarm lamp. Applicant Mitsubishi Motors Corporation Agent Patent Attorney Kan Nagato 2□10゛Figure 3 ts (min) Figure 5 Intake air temperature ('C) Figure 4

Claims (2)

[Claims] (1) When the exhaust gas recirculation device that recirculates part of the exhaust gas of the internal combustion engine to the intake passage is in a state where it should be operating, detect a temperature related to the temperature of the gas recirculating the exhaust gas recirculation device; A failure detection method for determining that the exhaust gas recirculation device is malfunctioning when the temperature is lower than a failure determination value, characterized in that the failure determination is prohibited until a predetermined time has elapsed after engine startup. Detection method. (2) The method for detecting a failure in an exhaust gas recirculation system according to claim 1, wherein the predetermined period of time is set in accordance with an engine temperature detected immediately after starting the internal combustion engine.