JP2658314B2 - Exhaust gas recirculation device failure diagnosis device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to exhaust gas recirculation (hereinafter abbreviated as EGR) of an internal combustion engine.
The present invention relates to a device, and particularly to a device for diagnosing a failure of an EGR device.

<Prior Art> In an internal combustion engine for a vehicle, various measures have been taken to improve the exhaust properties from the viewpoint of preventing air pollution, and one of them is an EGR device.

That, EGR device, by the recirculating part of the exhaust gas to the intake system, but is intended to reduce the emissions of the NO _x by reducing the maximum combustion temperature of the engine, combustion of when the heavily reflux exhaust engine The characteristics become unstable and the engine output decreases. Therefore, it is necessary to control the EGR amount, the air-fuel ratio, or the ignition timing according to the engine operating state, and a control device for controlling the EGR device, the air-fuel ratio, or the ignition timing is provided.

In such EGR control, it is important to accurately know the operation state of the EGR device in order to improve control accuracy or to perform failure diagnosis.

Therefore, conventionally, as a failure diagnosis device for an EGR device, for example, a device disclosed in Japanese Patent Application Laid-Open No. 51-94025 has been proposed.

This device is equipped with a temperature sensor such as a thermistor in the EGR passage equipped with an EGR valve.
Diagnose failure of EGR equipment. Specifically, in the operating region where the recirculation of the exhaust gas should be originally performed, it is diagnosed based on the temperature whether or not the exhaust gas is actually recirculated,
When exhaust gas recirculation is not detected, a failure of the EGR device is diagnosed and a warning is issued to the driver. The region where the diagnosis is performed is determined using, for example, the engine load (a basic injection amount obtained from the intake air flow rate and the engine speed in the case where the fuel injection control device is provided) and the engine speed,
It is set to almost overlap with the EGR work area.

Further, in the apparatus disclosed in Japanese Patent Application Laid-Open No. Sho 60-21374, a temperature sensor is provided in the EGR passage, and when the detected temperature is equal to or lower than a predetermined value, a failure of the EGR device is diagnosed.

<Problem to be Solved by the Invention> However, in such a conventional EGR device failure diagnosis device, in the former case, the EG is determined from the presence or absence of a temperature rise.
The R device is diagnosed for failure, and in the latter case, a failure is diagnosed when the detected temperature is below a predetermined position. However, there are the following disadvantages.

That is, the former case will be described with reference to FIG. 5. In FIG. 5, a region surrounded by a dashed line indicates an operation region in which EGR control is actually performed, and an operation region of a hatched portion is a basic injection amount T _p ( 2 shows a diagnosis area determined by the engine load) and the engine speed. In the figure, when the operating state of the engine shifts from the low speed / low load area (A in FIG. 5) to the diagnosis area (B in FIG. 5), a sufficient temperature change is obtained, while the EGR control area Since the EGR control is performed when shifting from (C in FIG. 5) to the diagnostic region (A in FIG. 5), the temperature change is small. For this reason, it is necessary to set a predetermined temperature change used for diagnosis to a small value, so that it is necessary to make the detection device highly accurate, which leads to an increase in cost. In other words, it is difficult to perform highly accurate diagnosis unless the detection device has high accuracy.

In the latter case, the detected exhaust gas temperature in the BGR passage is compared with a predetermined judgment level to diagnose the presence or absence of a failure. Therefore, when the outside air temperature is low as shown by the broken line in FIG. Response is degraded. For this reason, since the temperature rise to the temperature of the determination level is delayed, it is necessary to lengthen the diagnosis waiting time until the determination is performed. That is, in order to increase the chances of diagnosis, it is desirable that the diagnosis waiting time be short.

The present invention has been made in view of such a situation, and an EGR device capable of performing a failure determination with high accuracy without incurring an increase in cost and increasing a chance of failure diagnosis by setting an appropriate diagnosis waiting time. An object of the present invention is to provide a failure diagnosis device.

<Means for Solving the Problems> Therefore, as shown in FIG. 1, in the present invention, a part of the exhaust gas of the engine A is recirculated to the intake system through the exhaust recirculation passage B. Operating state detecting means C for detecting the operating state of the engine, temperature signal detecting means D for detecting the exhaust gas temperature of the exhaust gas recirculation passage B, and being in a predetermined diagnostic operating area based on the detected engine operating state And an operating range determining means E for determining the target exhaust gas temperature so as to become smaller as the actual exhaust gas temperature detected immediately after entering the diagnostic operating region becomes higher when it is determined to be in the predetermined diagnostic operating region. A target increasing rate changing means F for setting the increasing rate by changing the increasing rate; and, during the predetermined diagnostic operation area determination, the detected actual exhaust temperature is equal to or less than a set value and the detected increasing rate of the exhaust temperature is reduced. Above the set target rate of increase Failure determination means G that determines that the exhaust gas recirculation device has failed when
Was prepared.

<Operation> In this way, after the target increase rate is set to a smaller value as the exhaust gas temperature immediately after entering the diagnostic operation region becomes higher, the detected exhaust gas temperature is equal to or less than the set value and is detected. When the rate of increase of the exhaust gas temperature is equal to or lower than the target rate of increase, it is determined that the EGR device has failed.

Embodiment An embodiment of the present invention will be described below with reference to FIGS.

In FIG. 2, intake air is supplied to each cylinder of the engine 1 via an intake pipe 2 and an intake manifold 3. The intake pipe 2 is provided with a throttle valve 4, and the intake pipe 2 upstream of the throttle valve 4 is provided with a fuel injection valve 5. A catalytic converter (not shown) is provided downstream of the exhaust pipe 6 of the engine 1. One end of an EGR passage 6 is attached to the exhaust pipe 6 upstream of the catalytic converter.
The other end of the GR passage 7 is attached to the intake manifold 3 via an EGR control valve 8, and a part of the exhaust gas is recirculated to the intake manifold 3.

The intake pipe 2 is provided with an air flow meter 9 for detecting an intake air flow rate and a throttle opening sensor 10 for detecting an opening of the throttle valve 4.

Further, a crank angle sensor 11 for detecting a crank angle of the engine 1 is provided, and an engine rotation speed can be detected by the pulse signal. Further, the EGR passage 7 is provided with a temperature sensor 12 as temperature detecting means for detecting the exhaust gas temperature in the EGR passage 7. Further, the air flow meter 9 and the crank angle sensor 10 constitute an engine operating state detecting means.

The detection signals of the air flow meter 9, the throttle opening sensor 10, the crank angle sensor 11, and the temperature sensor 12 are input to a control device 13 including a microcomputer or the like. The control device 13 operates in accordance with the flowchart of FIG. 3 to diagnose the presence or absence of a failure in the EGR, and in the event of a failure, turns on an alarm lamp 14 to notify the driver of the abnormality of the EGR device. The EGR control valve 8 is the fifth
The valve is driven to open in an operation region surrounded by a dashed line in the figure to control the EGR amount.

Here, the control device 13 constitutes a target increase rate changing means, an operation area determining means, and a failure determining means.

Next, the operation will be described with reference to the flowchart of FIG. The routine shown in the flowchart of FIG. 3 is executed for each predetermined engine.

In step (hereinafter, abbreviated as S in the drawings) 1, it is determined whether or not the current engine operation state is in the diagnostic operation range. Determination of the diagnostic operating range, for example, by whether the engine the engine operating state by the basic injection quantity T _P and the engine operating speed that indicates the load on the diagnostics operating region as shown in FIG. 5 in the hatched portion,
Do.

In S2, it is determined whether or not the diagnostic area flag FEGRJA is 1; if YES, the process proceeds to S3; if NO, the process proceeds to S13.
FEGRJA = 1 indicates that the engine operation state is already in the diagnostic operation area.

In S3, the diagnostic area timer TMEGRJ is incremented (TM
EGRJ ← TMEGRJ + 1), measure the stay time in the diagnostic operation area, and proceed to S4.

In S4, it is determined whether or not the tire TMEGRJ is equal to or longer than the waiting time EGRJD.If YES, it is determined that the waiting time EGRJD has elapsed from the point of entering the diagnostic operation region, and the process proceeds to S5, and if NO, the routine is ended. Let it.

In S5, the exhaust temperature TEGR2 of the EGR passage 7 is measured based on the output from the temperature sensor 12.

In S6, it is determined whether or not the timer TMEGRJ is equal to the waiting time EGRJD. If YES, the process proceeds to S7, and if NO, the process proceeds to S8 without passing through S7.

In S7, the exhaust gas temperature TEGR2 at the time of TMEGRJ = EGRJD
Then, the temperature rise rate DTEGR during the waiting time EGRJD is calculated by the following equation based on the exhaust gas temperature TEGR1 measured in S14 described later.

DTEGR = TEGR2-TEGR1 In S8, it is determined whether or not the exhaust gas temperature TEGR2 is equal to or higher than a set temperature TEGROK, and if YES, the EGR device is determined to be normal and S1
Proceed to 2 and if NO, proceed to S9.

In S9, a target increase rate DEGROK is searched from the map based on the exhaust gas temperature TEGR1 measured in S14. As shown in FIG. 4, the target increase rate DEGROK is determined by the exhaust gas temperature TEGR1.
Is set to a large value and a constant value in a low temperature region below a predetermined temperature, and in a region exceeding the predetermined temperature, the exhaust gas temperature TE
It is set so that it gradually decreases as GR1 increases.

In S10, it is determined whether or not the temperature rise rate DEGR calculated in S7 is equal to or higher than the target rise rate DEGROK.
If it is determined that the GR device is normal and the process proceeds to S12, if NO, the EGR device is determined to be faulty and the process proceeds to S11.

In S11, a failure flag indicates that the EGR device has failed.
FEGRNG = 1 is stored in the RAM. On the other hand, in S12, EGR
The fault flag FEGRNG = that the device is operating normally
0 is stored in the RAM.

When the diagnostic region flag FEGRJA ≠ 1 in S2, it is determined that the vehicle has entered the diagnostic operation region for the first time, the diagnostic region flag FEGRJA is set to 1 in S13, and the routine proceeds to S14.

In S14, after measuring the exhaust gas temperature TEGR1 at the time of entering the diagnostic operation region from the output of the temperature sensor 12, the routine ends.

If it is determined in S1 that the vehicle is not in the diagnostic operation region, the routine is terminated after clearing the diagnostic region flag FEGRJA and the timer TEMGRJ in S15.

As described above, the actual temperature increase rate DEGR of the exhaust temperature TEGR1 and the exhaust temperature TEGR2 after the elapse of the predetermined waiting time is less than the target increase rate DEGROK, and the exhaust temperature TEGR2 is equal to the set temperature TEG.
When it is less than ROK, it is determined that the EGR device is out of order, so that the following effects are obtained.

That is, the failure of the EGR device is determined by comparing the rate of increase of the exhaust gas temperature and the comparison of the exhaust gas temperature.
The failure determination can be performed with high accuracy without increasing the detection accuracy of the device, the cost of the apparatus can be suppressed, and the waiting time can be set to an appropriate length, so that the opportunity for diagnosis can be increased.

Further, since the target increase rate DEGROK is changed and set based on the exhaust gas temperature TEGR1 immediately after entering the diagnostic operation region, the following effects are obtained. That is, the rate of increase of the exhaust gas temperature changes according to the exhaust gas temperature immediately after entering the diagnostic operation range (the lower the exhaust gas temperature, the higher the rate of increase). Therefore, the target increase rate DEGROK based on the exhaust gas temperature TEGR1.
Is set, the failure of the EGR device can be determined with high accuracy. It is also conceivable to set the target increase rate DEGROK to a small constant value from the beginning regardless of the exhaust gas temperature TEGR1, but in this case, the exhaust gas temperature may rise slowly due to clogging of the EGR passage 7 or the like. While this time is erroneously determined to be a failure of the EGR device, a device that changes the target increase rate DEGROK can accurately determine the failure.

When the exhaust gas temperature TEGR1 is low, the target increase rate DEGROK is set to a substantially constant value as shown in FIG. 4. However, in a low exhaust gas temperature range, the exhaust gas temperature is cooled by outside air heat. Target increase rate from the viewpoint of preventing erroneous judgment
DEGROK is set to a substantially constant value.

<Effects of the Invention> As described above, the present invention sets the target increase rate by changing the target increase rate so that it becomes smaller as the exhaust gas temperature immediately after entering the diagnostic operation region becomes higher, Since it is determined that the EGR device has failed when the rate of increase is equal to or less than the target rate of increase and the exhaust gas temperature is equal to or less than the set temperature, failure determination can be performed with high accuracy while suppressing an increase in cost of the apparatus. The waiting time can be set to an appropriate length.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims of the present invention, FIG. 2 is a block diagram showing one embodiment of the present invention, FIG.
FIG. 4 is a characteristic diagram of the above, and FIGS. 5 and 6 are diagrams for explaining the conventional disadvantages and the operation of the above. DESCRIPTION OF SYMBOLS 1 ... Engine, 7 ... EGR passage, 8 ... EGR device, 9 ... Air flow meter, 11 ... Crank angle sensor, 12 ... Temperature sensor, 13 ... Control device

Claims (1)

(57) [Claims] 1. An exhaust gas recirculation system for an internal combustion engine wherein a part of the exhaust gas of the engine is recirculated to an intake system via an exhaust gas recirculation device. Temperature detecting means for detecting the exhaust gas temperature in the recirculation passage; operating area determining means for determining that the engine is in a predetermined diagnostic operating area based on the detected engine operating state; and when the predetermined diagnostic operating area is determined. A target increase rate changing means for changing and setting a target increase rate such that the actual exhaust gas temperature detected immediately after entering the diagnostic operation region becomes smaller as the actual exhaust gas temperature increases, and the predetermined diagnostic operation Failure determination for determining that the exhaust gas recirculation device has failed when the detected actual exhaust gas temperature is equal to or less than a predetermined value and the detected exhaust gas temperature increase rate is equal to or less than the set target increase rate during the area determination. Means Trouble diagnosis device for an exhaust gas recirculation device characterized by comprising a.