JP3497247B2 - Abnormality diagnosis device for exhaust gas recirculation device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation device abnormality diagnosing device for determining whether or not there is an abnormality in an exhaust gas recirculation device for recirculating a part of exhaust gas to an intake pipe of an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, an exhaust gas recirculation device (E) which recirculates a part of exhaust gas of an internal combustion engine into an intake passage and sucks it into the engine.
GR device) is known. The EGR device is used to reduce the NO _x (nitrogen oxide) generated by combustion by lowering the engine combustion temperature by supplying exhaust gas to the engine combustion chamber.

When an abnormality occurs in the EGR device as described above, the exhaust property deteriorates due to an increase in the NO _x component. Therefore, the presence or absence of an abnormality in the EGR device is diagnosed and the driver is informed when the abnormality occurs. Various devices have been devised.
An example of this type of abnormality diagnosis device is, for example, Japanese Patent Laid-Open No.
There is one described in Japanese Patent No. 416553. The device of the publication is related to a mechanical EGR device in which an exhaust gas recirculation control valve (EGR valve) driven by negative pressure in an intake pipe is provided in an EGR passage connecting an intake pipe and an exhaust pipe of an internal combustion engine for a vehicle. Yes, by arranging a temperature sensor in the EGR passage,
The abnormality of the EGR device is diagnosed by detecting the presence or absence of high-temperature exhaust gas (EGR gas) that recirculates through the passage. That is, in the device of the same publication, if the temperature increase is not detected by the temperature sensor even though the EGR valve is opened, it is determined that the exhaust gas is not flowing through the EGR passage. It is determined that an abnormality has occurred in any part of the EGR device such as the control device or the control device.

Further, in the device disclosed in the above publication, the intake pipe negative pressure E
Since the GR valve is driven, the negative pressure of the intake pipe (the differential pressure between the atmospheric pressure and the absolute pressure in the intake pipe) decreases when the atmospheric pressure decreases, for example, during high-altitude driving, especially during high load operation. The driving force of the EGR valve becomes insufficient, and the EGR valve may not open even if the intake pipe negative pressure is supplied to the EGR valve. If the above abnormality diagnosis is executed in this state, exhaust gas recirculation does not occur even though the EGR valve is being opened, so it is erroneously determined that an abnormality has occurred even though there is no abnormality in the EGR device. There is a risk.

Therefore, in the device of the above-mentioned publication, in order to prevent this erroneous determination, the abnormality diagnosis on the high load operation side of the engine is carried out by setting the throttle valve opening to a certain value or less (or the intake pipe negative pressure). Is above a certain value). Accordingly, the abnormality diagnosis is executed only when the intake pipe negative pressure sufficient to open the EGR valve is obtained, and erroneous determination is prevented.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the device of Japanese Patent No. 653, a temperature sensor is arranged in the EGR passage to detect the presence or absence of an EGR gas flow passing through the EGR passage to determine whether or not an abnormality has occurred in the EGR device. The presence or absence of can also be detected by monitoring the intake pipe pressure. For example, when EGR gas is supplied to the intake pipe in the same operating state, the intake pipe pressure rises (the intake pipe negative pressure decreases) as compared with the case where the EGR gas is not supplied, according to the supplied EGR gas amount. Therefore, by forcibly opening and closing the EGR valve during engine operation and measuring the change in intake pipe pressure during opening and closing of the EGR valve, if the amount of change is small, the EGR valve is opened. Since the EGR gas is not being supplied when the valve is opened, it can be determined that an abnormality has occurred in the EGR device.

In the device disclosed in Japanese Patent Laid-Open No. 63-41653, it is necessary to dispose a dedicated temperature sensor in the EGR passage for diagnosing the abnormality of the EGR device. However, the intake pipe is originally provided for other control. In an engine that requires a pressure sensor (for example, an engine that performs fuel injection control based on the intake pipe pressure), this intake pipe pressure sensor can also be used for abnormality diagnosis of the EGR device, and is exclusively used for abnormality diagnosis. Since it is not necessary to provide a sensor, it is particularly advantageous to perform abnormality diagnosis of the EGR device based on the intake pipe pressure.

However, in the case of diagnosing the abnormality of the EGR device based on the intake pipe pressure, the above-mentioned JP-A-63-416 is used.
A problem may occur if the operating region in which abnormality diagnosis is performed is uniformly defined by the values (upper limit value or lower limit value) of operating state parameters such as the throttle valve opening, as in the device disclosed in Japanese Patent No. 53. That is, the amount of EGR gas supplied to the intake passage when the EGR valve is opened changes intricately depending on the EGR valve opening, the intake pipe negative pressure, the exhaust gas pressure, and the like. For this reason,
If the operating region in which the abnormality diagnosis is performed is uniformly defined by the values of operating state parameters such as the throttle valve opening as in the above publication, there will be a portion with a large EGR amount and a portion with a small EGR amount in the region for performing the abnormality diagnosis. Become.

When the EGR gas flow is detected using the temperature sensor as in the device of the above publication, the EGR gas flow is detected even when the EGR gas amount is relatively small because the EGR gas temperature is high. You can However, when detecting the EGR gas flow based on the change in the intake pipe pressure, if the EGR gas amount is small, the change in the intake pipe pressure when the EGR valve is opened and closed becomes small, and the EGR device actually operates normally. However, there is a case where it is erroneously determined that an abnormality has occurred.

This problem will be described below with reference to FIG. In the following description, for simplification of description, a case where the operating region in which the abnormality diagnosis is performed is defined by using two operating state parameters, that is, the throttle valve opening TA and the engine speed NE, is shown. The same problem occurs when the operating state parameter of No. 3 is used, or when three or more operating state parameters are used.

In FIG. 14, the operating range in which abnormality diagnosis is carried out (the range enclosed by the solid line A in the figure) is the lower limit TA ₁ and the upper limit TA ₂ (TA ₁ ≤TA) of the throttle opening TA.
≦ TA ₂ ) and _two lower limit values NE ₁ and upper limit value NE ₂ (NE ₁ ≦ NE ≦ NE ₂ ) of the engine speed NE are defined. This region corresponds to the region where the intake pipe negative pressure is obtained in which the EGR valve can be opened.
Therefore, the EGR valve is always open within the range of the area A. However, the same EGR gas amount is not always obtained in the region A even when the EGR valve is open, and the EGR amount changes in the region A as shown in FIG. The amount of EGR gas is large in the vicinity of the central portion, and the amount of EGR gas decreases toward the peripheral portion.

Therefore, if the abnormality is uniformly diagnosed when the operating condition parameter is within the region A, the EGR valve is operating normally near the corners of the region indicated by C ₁ to C ₄ in the figure, for example. Nevertheless, the amount of EGR gas decreases, and when performing abnormality diagnosis based on the intake pipe pressure, a problem arises in which a normal EGR device is abnormally diagnosed. In order to prevent this, the abnormality diagnosis area may be set narrow so that the abnormality diagnosis area does not include a portion having a small amount of EGR gas as shown by the dotted line A ′ in the figure. If the operating range to be performed is narrowed, the frequency of the abnormality diagnosis is reduced accordingly, and there is a problem that the abnormality of the EGR device cannot be detected early.

The above description has been made with reference to the two operating state parameters of the throttle valve opening degree and the engine speed, but other operating state parameters (for example, the intake pipe negative pressure and the pulse width of the fuel injection signal) are used. In this case, if the abnormality diagnosis execution area is uniformly defined by the operating state parameter values (upper limit value and lower limit value), the EGR gas amount will always be large or small within the area, resulting in erroneous diagnosis or abnormality diagnosis execution frequency. Therefore, problems such as decrease in

In view of the above problems, the present invention provides an abnormality diagnosis device for an EGR device, which does not cause erroneous diagnosis or a decrease in the frequency of abnormality diagnosis when diagnosing an abnormality in the EGR device based on the intake pipe pressure. Is intended.

[0015]

According to a first aspect of the present invention, there is provided an abnormality diagnosis device for diagnosing whether or not there is an abnormality in an exhaust gas recirculation device that recirculates a part of exhaust gas into an intake passage of an internal combustion engine. An intake pressure detecting means for detecting the pressure in the intake passage, and the intake gas pressure in the exhaust gas recirculation device based on the pressure in the intake passage when the exhaust gas recirculation device is operating and the pressure in the intake passage when the exhaust gas recirculation device is not operating. An abnormality determining means for determining the presence or absence of abnormality, a parameter detecting means for detecting an operating condition parameter related to the engine load condition, and an exhaust gas recirculation device in a normal condition by using the detected operating condition parameter, the engine When operating with the detected operating condition parameter, the standard pressure for calculating the difference in the intake passage pressure between when the exhaust gas recirculation device is operating and when it is not operating, based on a predetermined relationship. An abnormality including a difference calculating means and a prohibiting means for prohibiting the abnormality determining means from determining the presence / absence of the abnormality when the intake passage pressure difference calculated by the standard pressure difference calculating means is smaller than a predetermined determination value. A diagnostic device is provided.

According to a second aspect of the present invention, in the first aspect of the invention, the standard pressure difference calculating means uses the detected operating condition parameter so that the engine operates under a standard atmospheric pressure condition. Of the intake passage pressure between when the exhaust gas recirculation device is operating and when the exhaust gas recirculation device is operating when the engine is operating at the detected operating condition parameter. The difference is calculated based on a predetermined relationship, and the prohibition means further includes atmospheric pressure detection means for detecting atmospheric pressure, and the standard pressure difference calculation means based on the detected atmospheric pressure and standard atmospheric pressure. And a correction means for correcting the intake passage pressure difference calculated by the above, and when the corrected intake passage pressure difference is smaller than a predetermined determination value, the abnormality determination means prohibits the abnormality determination by the abnormality determination means. Apparatus is provided.

[0017]

According to the first aspect of the invention, the standard pressure difference computing means uses the detected operating condition parameters such as the throttle valve opening and the engine speed to operate the engine with this operating condition parameter. When the exhaust gas recirculation device is operating normally and when the exhaust gas recirculation device is not operating, the intake passageway pressure difference is calculated. If the calculated pressure difference is less than the predetermined judgment value, the intake passage pressure between when the system is operating and when it is not operating will be small in the current operating state regardless of whether there is an abnormality in the exhaust gas recirculation system, resulting in a false determination. Is likely to occur. When the calculated pressure difference is smaller than a predetermined judgment value, the prohibiting means prohibits the abnormality diagnosis of the exhaust gas recirculation device, thereby prohibiting the abnormality diagnosis in an operating state where an erroneous determination is likely to occur.

According to the second aspect of the present invention, the standard pressure difference calculating means calculates the intake passage pressure difference when the engine is operating under the standard atmospheric pressure condition, and the prohibiting means detects the current atmospheric pressure. At the same time, the calculated intake passage pressure difference is corrected based on the detected atmospheric pressure and the standard atmospheric pressure, and whether the abnormality diagnosis can be performed or not is determined using the corrected intake passage pressure difference. When the atmospheric pressure changes, the exhaust gas recirculation amount changes according to the atmospheric pressure even if the engine operating state parameters have the same value, so the operating range in which abnormality diagnosis can be performed also changes, but the prohibition means is the current one. The intake passage pressure difference under the standard atmospheric pressure condition is corrected based on the atmospheric pressure and the standard atmospheric pressure, and whether or not abnormality diagnosis can be performed is determined based on the corrected intake passage pressure difference. Therefore, it is prohibited to perform abnormality diagnosis in an operating state where erroneous determination is likely to occur.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of an embodiment when the abnormality diagnosis device of the present invention is applied to a vehicle internal combustion engine. In FIG. 1, 1 is an internal combustion engine body, 3 is an intake passage, and 5 is an exhaust passage.

In the intake passage 3, a throttle valve 7 which restricts the intake passage 3 in response to a driver's operation of an accelerator pedal (not shown) is provided downstream of the air cleaner 6, and intake air is provided downstream of the throttle valve 7. A surge tank 9 for damping pulsation is arranged. Further, reference numeral 11 in FIG. 1 denotes a fuel injection valve for injecting fuel into each cylinder intake port of the engine 1.

The exhaust passage 5 is opened to the atmosphere through a catalytic converter, a muffler, etc. not shown. 2 in FIG.
Reference numeral 0 denotes an EGR device that recirculates a part of the exhaust gas flowing through the exhaust passage 5 into the surge tank 9 of the intake passage 3. In this embodiment, the EGR device 20 includes an EGR valve 21, an EGR modulator 23, an EGR control valve 27, and the intake passage 3
A so-called mechanical EGR device is used that performs exhaust gas recirculation according to the negative pressure inside.

The EGR valve 21 includes an exhaust passage 5 and an intake passage 3
Is provided in the EGR passage 22 that communicates with the surge tank 9 of FIG. Further, the EGR valve 21 includes two pressure chambers 21c and 21d formed on both sides of the diaphragm 21b. The valve body 21a is connected to the diaphragm 21b, and moves by an amount according to the deformation amount of the diaphragm 21b. The pressure chamber 21c is connected to the EGR modulator 23 via the EGR control valve 27, and the pressure chamber 21c
d is open to the atmosphere. Reference numeral 21e in the drawing denotes a spring that presses and urges the diaphragm 21b in the direction in which the valve body 21a closes the EGR passage 22. As will be described later, the EG from the surge tank 9 via the EGR control valve 27.
The negative pressure regulated by the R modulator 23 is the pressure chamber 21.
When it is supplied to c, the diaphragm 21b moves to the spring 2
It deforms against the biasing force of 1e and moves the valve body 21a in the valve opening direction. Therefore, the EGR valve 21 has an opening degree according to the magnitude of the negative pressure supplied via the EGR control valve 27.

The EGR control valve 27 is a solenoid type three-way switching valve arranged on a negative pressure passage 28 connecting the pressure chamber 21c of the EGR valve 21 and the surge tank 9, and is a pressure chamber of the EGR valve 21 when the solenoid is energized. 21c communicates with the atmosphere, and when the solenoid is neutralized, the pressure chamber 21c and the negative pressure passage 28
Communicate with. The energization of the solenoid of the EGR control valve 27 is controlled by the control circuit 50 described later.

The EGR modulator 23 includes pressure chambers 23b and 23c formed on both sides of the diaphragm 23a. The EGR valve 2 is connected to the pressure chamber 23b via a pressure guiding pipe 26.
Exhaust pressure in the EGR passage 22 on the upstream side is supplied. The pressure chamber 23c communicates with the atmosphere through a port (23f) through a throttle (not shown). Furthermore, the pressure chamber 2
3c communicates with a throttle port 25 arranged in the throttle valve 7 portion of the intake passage 3 via a pressure guiding pipe 24. In addition, the pressure chamber 23c is provided with a port 23e communicating with the negative pressure passage 28 described above. Diaphragm 2
When 3a is deformed upward in the figure, the port 23e is provided with a diaphragm according to the amount of deformation of the diaphragm 23a. Reference numeral 23g in the drawing denotes a spring for pressing and urging the diaphragm 23a in the direction in which the port 23e is opened.

When the negative pressure supplied to the pressure chamber 23c through the pressure guiding pipe 24 is small, the pressure in the pressure chamber 23c becomes a value close to the atmospheric pressure due to the atmosphere flowing in from the port 23f, and the diaphragm 23a becomes The port 23e is opened by being pressed by the spring 23g. As a result, the negative pressure passage 2
Atmosphere flows into port 8 from port 23e, and the negative pressure in negative pressure passage 28 becomes a small value. Therefore, the EGR control valve 27
Thus, even when the negative pressure passage 28 and the pressure chamber 21c of the EGR valve 21 communicate with each other, the EGR valve 21 does not open. On the other hand, when the negative pressure supplied through the pressure guiding tube 24 increases, the pressure inside the pressure chamber 23c decreases, the diaphragm 23a deforms against the spring 23g toward the pressure chamber 23c, and the port 23e gradually narrows. To be Therefore, the negative pressure in the negative pressure passage 28 increases, and when the EGR control valve 27 connects the negative pressure passage 28 and the pressure chamber 21c of the EGR valve 21, the EGR valve 21 opens.

The throttle port 25 to which the pressure guiding pipe 24 is connected is provided with a throttle port 7 when the throttle valve 7 is fully closed.
The valve is opened at a position slightly upstream of the valve body.
Therefore, the throttle port 25 (that is, the pressure guiding tube 2
The pressure in the intake passage upstream of the throttle valve 7 (approximately atmospheric pressure) acts on 4) until the throttle valve 7 is opened from a fully closed state to a certain opening degree (for example, about 8 °). Further, when the throttle valve 7 is further opened and exceeds the above-mentioned certain opening degree, a negative pressure in the intake passage on the downstream side of the throttle valve 7 acts on the throttle port 25. Therefore, the pressure in the pressure guiding pipe 24 becomes a negative pressure according to the opening degree of the throttle valve. on the other hand,
When the throttle valve 7 is further opened, the pressure in the intake passage on the downstream side of the throttle valve 7 increases, so that the negative pressure in the pressure guiding pipe 24 decreases. Therefore, the EGR modulator 23 and the EG
The negative pressure in the negative pressure passage 28 between the R control valve 27 and the exhaust gas recirculation amount (EGR amount) changes as follows according to the throttle valve opening.

First, from the time when the throttle valve 7 is fully closed until the above-mentioned constant opening is reached, the pressure in the pressure guiding pipe 24 becomes substantially atmospheric pressure, and the negative pressure is not supplied to the pressure chamber 23c of the EGR modulator 23. , The port 23e is opened, and the negative pressure in the negative pressure passage 28 decreases (absolute pressure increases). Therefore, during engine idle and low load operation, the EGR valve 21 does not open even if the EGR control valve 27 opens, and exhaust gas recirculation (EGR) does not occur.

Next, when the opening of the throttle valve 7 exceeds the above-mentioned constant opening, a negative pressure is generated in the pressure guiding pipe 24. Further, this negative pressure changes according to the throttle valve opening and the engine speed. Therefore, the port 23 of the EGR modulator 23
The opening degree of e also changes according to this negative pressure, and the negative pressure generated in the negative pressure passage 28 also changes according to the throttle valve opening degree and the engine speed. When the EGR control valve 27 is opened, the EG
Since the opening degree of the R valve 21 changes according to the negative pressure in the negative pressure passage 28, the EGR amount in the opening degree region of the throttle valve 7 (corresponding to the medium load operation region) is the throttle valve opening amount and the engine speed. Will change accordingly.

On the other hand, when the throttle valve 7 is further opened and is almost fully opened, the negative pressure itself on the downstream side of the throttle valve 7 decreases. Therefore, in the high load operation region, the EGR valve 21
Does not open and exhaust gas recirculation does not occur. Next, in FIG.
The control circuit indicated by 0 will be described. Control circuit 50
Is, for example, a RAM (random access memory) 51,
ROM (read only memory) 52, CPU (microprocessor) 53, input port 55, output port 56
Are connected by a bidirectional bus 57 to constitute a known digital computer. Further, reference numeral 54 in the drawing denotes a control circuit 50 for outputting a clock signal to the CPU 53.
It is a clock signal generation circuit of.

The control circuit 50 executes basic control such as fuel injection amount control and ignition timing control of the engine 1 and, in the present embodiment, switches the EGR control valve 27 when a predetermined EGR execution condition is satisfied. By allowing the negative pressure passage 28 to communicate with the pressure chamber 21c of the EGR valve 21, execution of EGR is permitted. EGR execution permission conditions include, for example, that the engine cooling water temperature is equal to or higher than a predetermined value (that is, engine warm-up has ended), and intake passage negative pressure (atmospheric pressure and absolute pressure in intake passage). Difference) is equal to or greater than a predetermined value (a sufficient intake passage negative pressure is generated to open the EGR valve 21), etc., and EGR is executed only when these conditions are satisfied at the same time. Allow

For the above control, the output port 56 of the control circuit 50 is connected to the fuel injection valve 11 and the spark plug 12 of the engine through a drive circuit or an ignition circuit not shown, and a drive circuit not shown. It is connected to the EGR control valve 27 via the and controls the energization of the solenoid of the EGR control valve 27. In addition, the input port 5 of the control circuit 50
In FIG. 5, a voltage signal corresponding to the intake passage internal pressure (absolute pressure) in the surge tank and the intake temperature from the intake pressure sensor 42 and the intake air temperature sensor 43 provided in the surge tank 9 of the intake passage 3 and not shown AD In addition to being input via the converter, a voltage signal corresponding to the throttle valve opening from the throttle position sensor 41 provided near the throttle valve 7 and a cooling water temperature sensor 45 provided in the cooling water passage of the engine 1 A voltage signal corresponding to the cooling water temperature is input through an AD converter (not shown).

Reference numeral 44 in the drawing is a rotation speed sensor provided in the ignition distributor of the engine 1 for generating pulse signals at intervals corresponding to the engine rotation speed, and 46 is a rotation speed sensor.
It is a vehicle speed sensor that is provided on an output shaft of an engine transmission and that generates pulse signals at intervals according to the vehicle speed. These outputs are also supplied to the input port 55 of the control circuit 50. In addition, 4
Denoted at 7 is an atmospheric pressure sensor that generates a voltage signal according to the atmospheric pressure (absolute pressure). The output of the atmospheric pressure sensor 47 is also supplied to the input port 55 of the control circuit 50 via an AD converter (not shown).

The output of the atmospheric pressure sensor 47 is the control circuit 50.
Is used for correcting the atmospheric pressure in the fuel injection control of the above, and for calculating the intake pipe negative pressure together with the output of the intake pressure sensor 42, and as will be described later, the intake passage pressure at the time of determining the abnormality diagnosis execution region of the EGR device. It is used to correct the difference at atmospheric pressure. In this embodiment, an independent sensor 47 is provided for measuring the atmospheric pressure. However, for example, it is detected by the intake pressure sensor 42 immediately before the engine is started (that is, when the flow of intake air does not occur in the intake passage 3). The atmospheric pressure may be obtained without providing the atmospheric pressure sensor 47 by using the above-mentioned pressure as an approximate value of the atmospheric pressure or by calculating the atmospheric pressure using an operating state parameter during engine operation.

Next, a method of diagnosing an abnormality in the EGR device of this embodiment will be described. In the present embodiment, during EGR execution (the EGR control valve 27 is switched to a position where the negative pressure passage 28 communicates with the pressure chamber 21c of the EGR valve 21) and when EGR is stopped (the EGR control valve 27 is the pressure chamber). 21c
Whether or not there is an abnormality in the EGR device is diagnosed based on the change in the intake passage pressure (the output of the intake pressure sensor 42) in the state in which is switched to the position where it communicates with the atmosphere).

During engine operation, when EGR is stopped, the intake passage pressure is uniquely determined by the throttle valve opening 7 TA and engine speed NE in that operating state. Also, EG
When R is performed, when the EGR device is operating normally, the EGR gas is recirculated to the surge tank 9, so that the intake passage pressure rises as compared with when the EGR is stopped. Increases as the amount of EGR gas supplied increases. Therefore, when the EGR device has an abnormality and the EGR gas amount decreases from the normal state, the intake passage pressure decreases as compared with the case where the EGR is normally performed. Therefore, if the intake passage pressure (judgment value) corresponding to the allowable lower limit value of the EGR gas amount is previously obtained under the conditions of each throttle valve opening and the number of revolutions, the actual intake passage pressure during the execution of EGR is If it becomes lower than the determination value, it should be possible to determine that an abnormality has occurred in the EGR device.

However, in practice, when the intake passage pressure (judgment value) corresponding to the EGR gas amount allowable lower limit value fluctuates due to variations among engines, changes over time, fluctuations in the environment (for example, atmospheric pressure), and the like. Therefore, if an abnormality of the EGR device is determined based only on the determination value, an erroneous determination occurs.
Therefore, in the present embodiment, the intake passage pressure (PM _OFFCAL ) when EGR is stopped in a standard state (for example, when the engine is operated in a new state under standard atmospheric pressure) and the intake air amount corresponding to the EGR gas amount allowable lower limit value. The passage pressure (PM _ABCAL ) is obtained in advance by experiments for the values of each throttle valve opening TA and the engine speed NE, and is stored in the ROM 52 of the control circuit 50 in the form of a map using TA and NE. .
Then, the intake passage pressure (PM _ON ) measured during the execution of EGR during actual operation and the intake passage pressure (PM _E ) that is measured by forcibly closing the EGR valve 21 (stopping EGR) during the execution of EGR ( PM _OFF ) and PM at the same throttle valve opening and rotation speed as when measuring PM _ON and PM _OFF
OFFCAL and PM _ABCAL are obtained from the above map, and the presence or absence of EGR device abnormality is determined based on these values.

FIG. 2 is a diagram for explaining the above determination principle. In FIG. 2, it is _assumed that the values of PM _ON and PM _OFF and the values of PM _OFFCAL and PM _ABCAL for the same TA and NE have the illustrated relationship. In Fig. 2, the engine is operating outside of the standard conditions, so PM _OFF and PM
_Does not match _OFFCAL . Therefore, it is expected that the intake passage pressure (judgment value) corresponding to the allowable lower limit value of the EGR gas amount in the current operating state will also differ from the judgment value PM _{ABCAL in the} standard state, and PM _ON and PM _ABCAL will be Whether or not there is an abnormality in the EGR device cannot be accurately determined only by comparison. However, as shown in the figure, if the measured value PM _OFF of the intake passage pressure when EGR is stopped changes from the value PM _OFFCAL in the standard state by D, the actual judgment value in the current operating state is also PM _ABCAL. It is considered that only D has changed.

Therefore, in this embodiment, a value obtained by adding the above D to the judgment value PM _ABCAL in the standard state is used as the judgment value (PM _TH ) in the present operating state, and PM _TH and E
EG by comparing the measured value PM _ON during GR
The presence or absence of abnormality in the R device is determined. That is, PM _ON is P
When M _TH + β or more (PM _{ON ≥PM ABCAL} + D + β), the EGR device is normal, and when PM _TH + α or less (PM _ON ≤
PM _ABCAL + D + α) determines that the EGR device is abnormal. If PM _TH + α <PM _ON <PM _TH + β, it is judged neither normal nor abnormal, and the judgment is performed again.
Note that α and β are constant values, and in this embodiment, for example, α
= 10 mmHg and β = 15 mmHg.

Here, a constant value α with respect to the judgment value PM _TH ,
The reason why the presence / absence of abnormality is determined by the intake passage pressure higher by β is to eliminate the possibility that the abnormality is overlooked and a normal determination is made, and to make a determination safety. Also, PM _TH + α <
When PM _ON <PM _TH + β, normality / abnormality is not determined because there is a possibility of being erroneously determined to be abnormal in this region even though the EGR device is normal. In addition,
The determination value PM _ABCAL in the standard state may be the same value as the value in a state where no EGR gas flows, that is, the same value as PM _OFFCAL .

3 and 4 show the above-mentioned abnormality diagnosis routine executed by the control circuit 50. This routine is executed at regular time intervals (for example, every 65 ms). When the routine starts in FIG. 3, in step 301, the throttle valve opening TA, the rotational speed NE, and the intake passage pressure PM are read from the corresponding sensors 41, 44, 42, respectively.

Next, at step 303, it is judged if the value of the diagnosis area flag F1 indicating whether the current operating state is the area where the abnormality diagnosis can be performed is set to 1 or not. The value of the flag F1 is set by a separately executed routine, and F1 = 1 indicates that the current operating state is in the abnormality diagnosis feasible region. The determination of the diagnosis execution area will be described in detail later.

In step 305, a flag F indicating whether or not a precondition for carrying out the abnormality diagnosis is satisfied.
It is determined whether the value of 2 is set to 1. F
2 = 1 indicates that the precondition is satisfied. This precondition will also be described in detail later, but the fact that the EGR is currently being performed is also one of the preconditions. Step 3
If a negative determination is made in either 03 or 305, the routine proceeds to step 304, resets the condition satisfaction counter T to zero, stores the current throttle valve opening TA as a variable TAMS in step 306, In step 347 of FIG. 4, the routine is finished as it is. As a result, the value of the variable TAMS represents the throttle valve opening immediately before the precondition is satisfied (that is, when the abnormality diagnosis is started). The value of the variable TAMS is used to determine whether the precondition (step 305) for carrying out the abnormality diagnosis is satisfied, as described later.

If a positive determination is made in both steps 303 and 305, the value of the condition satisfaction counter T is incremented by a predetermined value ΔT in step 305. Here, ΔT is set to a value corresponding to the execution interval of the routines of FIGS. 3 and 4 (ΔT = 65 in this embodiment). Therefore, the value of the counter T represents the elapsed time (ms) after the conditions of both steps 303 and 305 are satisfied.

In this routine, the value of the counter T is
When the specified value (specified elapsed time) below is reached, the next operation will be performed.
Done. T = T₁Then, the current intake passage pressure PM is EGR
Inside intake passage pressure PM _ONStored in RAM 51 as
(Step 311) together with the judgment value P in the standard state
M_ABCALUses the throttle valve opening TA and the rotational speed NE.
Read from the map stored in ROM 52, RAM
It is stored in 51 (step 313).

Next, from the current throttle valve opening TA and the rotational speed NE, the intake passage pressure PM _ONCAL during EGR operation in the standard state is similarly read from the map and stored in the RAM as P ₁ (step 315). This P ₁
The value of is used to determine whether the operating conditions have changed during abnormality diagnosis. Also, for the same purpose, the current PM,
The value of NE is stored in the RAM51 as the PM _1, NE ₁ respectively (step 317).

The above operation is performed when the value of the counter T reaches T ₁ in consideration of the case where the EGR is executed immediately before the conditions of steps 303 and 305 are satisfied, and the value of PM is stabilized. This is because the parameter is read after waiting for. Here, T ₁ is set to, for example, T ₁ = 520 (corresponding to the passage of about 0.5 seconds after the conditions of steps 303 and 305 are satisfied).

After the above operation is completed, the EGR control valve 27
Is switched to forcibly close the EGR valve 21 for abnormality diagnosis (step 318) to stop the EGR. The steps 311 to 318 are operations that are executed only once when the value of the counter T reaches T ₁ . At T = T ₂ (step 319), the current PM is PM
It is stored in the RAM as _OFF (step 321). It should be noted that the reason for waiting for reading of PM _OFF until T = T ₂ after EGR stop in step 318 is to wait for the fluctuation of the intake passage pressure accompanying EGR stop to converge and for the PM value to stabilize. In this embodiment, for example, T ₂ = 1040 (that is, about 0.5 second has elapsed after EGR was stopped).

After reading PM _OFF , step 32
In 3, PM _OFFCAL is calculated using the current TA and NE, and then in step 325 in FIG. 4, the correction amount D (see FIG. 2) is calculated using these values as D = PM _OFF −PM _OFFCAL , It is stored in the RAM 51. After the above operation is completed, in step 327, the EGR control valve 27 is switched again to open the EGR valve 21, and the execution of EGR is restarted.

T = T₃(Step 329)
In step 331, the current TA and NE are used again to perform P
M_ONCALIs calculated and P₂Stored in RAM 51 as
It Similarly, in step 332, the current PM and NE
Value of PM₂, NE ₂Stored in RAM51 as
To be done. These values are stored in steps 315 and 317.
Whether the operating conditions fluctuated during abnormality diagnosis with
Is used to determine In addition, the counter T
Value T₃In this embodiment, for example, 1950 (after restarting EGR
PM is stable after restarting EGR, which is equivalent to the passage of about 1 second)
It is set to a value sufficient to

After the above operation is completed, in steps 333 and 335, it is judged whether or not a condition for executing the judgment of abnormality diagnosis, which will be described later, is satisfied, and if either of the steps 333 and 335 is negatively judged, it is judged. Is step 337
To 343 without executing the abnormality diagnosis, the process proceeds to step 345, the counter T is cleared, and the routine ends. That is, the data read so far is not used for abnormality diagnosis. The determination execution conditions of steps 333 and 335 will be described later. If the determination execution conditions are satisfied in both steps 333 and 335, it is determined in steps 337 to 343 whether the EGR device is abnormal. That is, PM _ON stored in the above operation (step 3
11), PM _ABCAL (step 313) and D (step 325) are in the relationship of PM _ON ≤ PM _ABCAL + D + α, the EGR device is determined to be abnormal (step 337,
339), if the relationship of PM _ON ≧ PM _{ABCA L} + D + β is satisfied, the EGR device is determined to be normal.

If PM _TH + α <PM _ON <PM _TH + β, the abnormality diagnosis based on the data read this time is not performed. After the steps 337 to 343 are completed, the value of the counter T is cleared in step 345,
This routine ends. In a routine (not shown) that is separately executed, the abnormality determination (step 33
When 9) is performed, an alarm is activated to notify the driver of the occurrence of abnormality.

As described above, in the present embodiment, the abnormality of the EGR device is not determined simply by using the difference between the intake passage pressures when the EGR is performed and when the EGR is stopped, but the intake passage pressure PM _OFF when the EGR is stopped and the standard Based on the difference between the intake passage pressure PM _OFFCAL when the EGR is stopped in the state, the deviation amount D of the intake passage pressure in the actual operating state from the intake passage pressure in the standard state is calculated, and this deviation amount D is used. Judgment value P
Although M _ABCAL is corrected, this deviation amount D hardly changes in the range where the throttle valve opening TA and the rotation speed NE are relatively close. Therefore, according to the present embodiment, EG
Accurate abnormality diagnosis can be performed even when the throttle valve opening degree and the rotational speed slightly change between the measurement of the intake passage pressure PM _ON during R execution and the measurement of the intake passage pressure PM _OFF during EGR stop.

Next, the determination execution conditions for the abnormality diagnosis in steps 333 and 335 will be described. As mentioned above,
In the present embodiment, the accuracy of abnormality diagnosis is not greatly affected even when the operating states such as the throttle valve opening degree and the rotational speed change slightly during PM _ON measurement and PM _OFF measurement. However, when the change in the operating state is too large, the change in the deviation amount D becomes large,
The accuracy of abnormality diagnosis may be affected. Therefore, in steps 333 and 335 described above, it is determined whether or not the change in the operating state during the abnormality diagnosis is within the allowable range. I have to.

FIG. 5 is a flow chart showing details of the judgment execution condition of step 333 of FIG. In step 333, the rotational speed NE ₁ , the intake passage pressure PM ₁ (step 317 in FIG. 3) stored during PM _ON measurement, and E after PM _OFF measurement are recorded.
The rotational speed NE ₂ measured after restarting GR and the intake passage pressure PM ₂ (step 332 in FIG. 4) are compared, and it is determined that the determination execution condition is satisfied only when the difference between them is within a predetermined value. Note that, as will be described later, the change in the throttle valve opening is constantly monitored as a prerequisite for abnormality diagnosis (step 305 in FIG. 4), and therefore is not determined here.

That is, in step 333-1 in FIG. 5, the difference (absolute value) between the rotational speeds NE ₂ and NE ₁ is the predetermined value ΔNE _0.
(100 rpm in this embodiment) or less, step 3
In 33-2, the difference (absolute value) between the intake passage pressures PM ₂ and PM ₁ is a predetermined value ΔDP ₀ (30 mmHg in this embodiment).
It is respectively determined whether or not If both of the above conditions are satisfied at the same time, it is considered that the operating state has not changed significantly, so the process proceeds to step 335 in FIG. 4 and it is determined whether another determination execution condition is satisfied. If any of the above conditions is not satisfied, the execution of the determination as to whether there is an abnormality is stopped and the process proceeds to step 345 in FIG. As a result, the presence / absence of abnormality is determined only when the change in the operating state during abnormality diagnosis is small, and erroneous determination is prevented.

Next, the judgment execution condition of step 335 in FIG. 4 will be described. In step 333, when the change in the intake passage pressure during the abnormality diagnosis is equal to or more than the predetermined value, the determination of the presence or absence of the abnormality is stopped. However, even if the intake passage pressure change is within the predetermined value range, if the intake air amount of the engine actually changes, the EGR amount also changes, and accurate abnormality diagnosis may not be possible. For example, it is assumed that the intake passage pressure decreases during the execution of the EGR diagnosis, and a change occurs that exceeds the predetermined value in step 333-2. Normally, this change is detected by the determination in step 333-2, but if a situation occurs in which the engine intake air amount increases at the same time due to another factor, the decrease in the intake passage pressure due to the change in the operating state will occur. This is offset by an increase in the intake air amount, and the intake passage pressure may not drop significantly even though the operating state is changing. However, in this case as well, the EGR gas amount changes due to an increase in the intake air amount, so if the presence / absence of an abnormality is determined in this state, accurate abnormality diagnosis may not be possible.

In such a case, for example, when the opening of the ISC valve (idle speed control valve) is increased by the operation of the air conditioner and the intake air amount is increased, the control circuit 50 makes an abnormality diagnosis based on the air conditioner operation signal. If it is stopped, erroneous judgment can be prevented. However, for example, when air is introduced into the intake passage from an air valve that is mechanically operated by operating the power steering hydraulic pump, or when air is introduced into the intake passage by operating a negative pressure booster of the brake booster, or When the flow rate of the crankcase ventilation gas increases, a signal is not input to the control circuit 50, and the abnormality diagnosis may be performed.

Therefore, in this embodiment, the above step 333 is performed.
In addition, intake passage pressure PM measured at the start of abnormality diagnosis
(PM in step 317₁) And at that time
A target calculated from the throttle valve opening TA and the rotational speed NE.
Intake passage pressure PM in quasi state_{ONCA L}(In step 315
K P₁) And ΔP₁And P just before the judgment execution condition is judged
M (PM in step 332₂) And PM_ONCAL(Su
P in step 331 ₂) And ΔP₂Compare with
, | ΔP₂-ΔP₁If | is greater than or equal to the predetermined value DP,
It is judged that the intake air amount is changing due to the above causes
I am trying to stop the regular diagnosis.

FIG. 6 is a diagram for explaining the above determination. In FIG. 6, it is assumed that the intake passage pressure, which was PM ₁ at the start of EGR diagnosis, changed to PM ₂ immediately before the execution of the abnormality determination. In this case, the difference between PM ₁ and PM ₂ is within the predetermined value in step 333-2 described above. However, in reality, P
If the intake air that does not pass through the throttle valve in the intake passage is increased during the measurement of M ₁ and PM _{2 due} to, for example, the operation of the power steering pump, PM ₂ rises above the original value due to the increase in the intake air amount. Therefore, assuming that the intake air amount has not increased, the intake passage pressure should have originally decreased to PM ₂ ′ in FIG. 6 immediately before the execution of the abnormality determination. Therefore, an increase in the intake air amount cannot be detected by simply comparing PM ₁ and PM ₂ .

However, even in such a case, the intake passage pressure PM _ONCAL in the standard state, which is calculated from the throttle valve opening and the rotational speed, becomes the original PM ₂ ′ regardless of the increase in the intake air amount. It will be the corresponding value. Therefore, in such a case, as shown in FIG. 6, the deviations of PM ₁ and PM ₂ from PM _ONCAL at the respective _times greatly change.

Therefore, in step 335, PM ₁ , P
M ₂ and PM _ONCAL calculated at each measurement point
And the difference ΔP ₁ and ΔP ₂ (see FIG. 6) are calculated. If the difference is equal to or greater than a predetermined value DP (eg, 17 mmHg or more), it is determined that the intake air amount is increased due to the above cause. The abnormal diagnosis is stopped. Next, determination of the abnormality diagnosis execution area of this embodiment (step 303 in FIG. 3)
Will be described.

The abnormality diagnosis after step 307 in FIG.
It is necessary to perform the operation in a state where there is a sufficient difference in the intake passage pressure between when the GR is performed and when the GR is stopped. If this pressure difference is small,
Since the values of PM _OFF and PM _{ON in} FIG. 2 are close to each other,
This is because it is not possible to accurately diagnose whether or not the EGR device is abnormal. On the other hand, if the operating range in which abnormality diagnosis is uniformly performed by the upper limit value and the lower limit value of the operating condition parameters such as the throttle valve opening degree and the rotational speed is defined as in the conventional case, the above-mentioned operation is performed within the diagnostic range as described in FIG. There is a problem that there is a portion where the pressure difference is small, and in order to prevent this, it is necessary to set the diagnostic region narrow.

Therefore, in the present invention, when the abnormal diagnosis operating region is defined by using the value of the operating condition parameter, the operating condition parameter value is not defined by the upper limit value or the lower limit value of the operating condition parameter itself. The diagnostic region is defined by the difference ΔPM between the intake passage pressures when the EGR is performed and when the EGR is stopped in the standard state calculated from the values. Hereinafter, an example in which the throttle valve opening TA and the engine speed NE are used as the operating state parameters will be described. However, combinations of other parameters (for example, the intake air amount Q / rotation of the engine Q /
The same result can be obtained by a combination of NE and engine speed NE).

FIG. 7 shows a map for determining an abnormality diagnosis area in this embodiment. In the present embodiment, an actual engine is used in a new state under standard atmospheric pressure (for example, 1 atmospheric pressure) to change the throttle valve opening TA and the rotational speed NE, and the operation is performed in each operating state. The intake passage pressure PM _ON when the EGR is performed and the intake passage pressure PM _OFF when the EGR is stopped are measured, and the value of the difference ΔPM (= PM _ON −PM _OFF ) is
It is stored in the ROM 52 of the control circuit 50 in the form of a map using TA and NE as shown in FIG.

The control circuit 50 calculates the intake passage pressure difference ΔPM in the standard state from the throttle valve opening TA and the rotational speed NE during engine operation using the map of FIG. 7, and this ΔPM
If the value obtained by adding the atmospheric pressure correction, which will be described later, is equal to or greater than a predetermined value, it is determined that the engine is operating in the abnormality diagnosis region.
The solid line in FIG. 7 is a line showing the EGR gas amount at the time of performing EGR in the standard state, which coincides with the equal EGR gas amount line in FIG. 14. In this case, the abnormality diagnosis area is shown in FIG.
The area indicated by diagonal lines in FIG. 14 does not include a portion in which the EGR gas amount is small and an erroneous determination is likely to occur, and the diagnosis area can be widened as shown in FIG.

By the way, the EGR gas amount is affected by the atmospheric pressure in addition to TA and NE. That is, when the atmospheric pressure falls below the standard state, the intake negative pressure (difference between the atmospheric pressure and the intake passage pressure) is maintained even if the throttle valve opening and the rotational speed are the same.
1 becomes smaller, the driving force of the EGR valve 21 in FIG.
The opening degree of 1 decreases. Therefore, when the atmospheric pressure decreases, E
The amount of GR gas tends to decrease. Further, the EGR gas amount decreases as the exhaust pressure decreases, but when the atmospheric pressure decreases, the back pressure of the exhaust system decreases and the exhaust pressure decreases, so the EGR gas amount further decreases. Therefore, when the atmospheric pressure has changed, if the abnormality diagnosis region is judged with the value of ΔPM as it is, the difference in intake passage pressure between when EGR is performed and when it is stopped is actually small. Abnormality diagnosis may be performed, resulting in erroneous determination. Therefore, in this embodiment, when the control circuit 50 determines whether or not ΔPM is equal to or greater than a predetermined value, ΔP calculated from FIG. 7 is multiplied by a correction coefficient KP based on the current atmospheric pressure, KP × ΔPM. Using,
When this value is a predetermined value or more (for example, 25 mmHg or more), it is determined that the engine is operating in the abnormality diagnosis region.

FIG. 8 is a diagram showing changes in the correction coefficient KP with respect to atmospheric pressure. As shown in FIG. 8, KP is set to 1.0 when the atmospheric pressure is standard atmospheric pressure (for example, 1 atmospheric pressure),
Below the standard atmospheric pressure, it is set smaller as the atmospheric pressure decreases. FIG. 9 shows the above abnormality diagnosis area determination routine executed by the control circuit 50. This routine is shown in FIGS.
3 is executed at the same time interval (for example, 65 ms) as the routine of FIG.
The value of the diagnosis area F1 of 03 is set.

When the routine starts in FIG. 9,
In step 901, the current throttle valve opening TA and the rotational speed NE are read from the sensors 41 and 44, and the current atmospheric pressure PA is read from the atmospheric pressure sensor 47, respectively. Next, in Step 903, the above-mentioned TA and NE are used as shown in FIG.
Is used to calculate the value of ΔPM, and in step 905, the atmospheric pressure correction coefficient KP is calculated from the atmospheric pressure PA using FIG. In step 907, ΔPM calculated as described above
And KP, KP x ΔPM is a predetermined value (25 m
Hg) or more is determined, and if it is a predetermined value or more,
It is determined that the engine is currently operating in the abnormality diagnosis area, and the value of the diagnosis area flag F1 is set to 1 in step 909. When KP × ΔPM is smaller than the predetermined value,
Judging that the engine is currently operating outside the abnormality diagnosis area,
In step 911, the value of the diagnostic area flag F1 is reset to zero and the routine ends.

As described above, by executing this routine,
The abnormality diagnosis is executed only in a region where the difference between the intake passage pressures when the EGR is performed and when the EGR is stopped is irrelevant regardless of the change in the atmospheric pressure, so that the erroneous determination is prevented. Next, the determination of the precondition (step 305 in FIG. 3) for executing the abnormality diagnosis of this embodiment will be described. In the present embodiment, a situation in which an erroneous determination occurs outside the abnormality diagnosis area of FIG. 9 is determined, and the execution of the abnormality diagnosis is permitted only when all the prerequisites for executing the abnormality diagnosis described below are satisfied. The accuracy of abnormality diagnosis is improved.

FIG. 10 shows a precondition judging routine executed by the control circuit 50. This routine is shown in FIGS.
The routine is executed at the same time interval (65 ms) as the routine. In FIG. 10, when any one of the conditions of steps 1001 to 1019 is not satisfied, the value of the precondition flag F2 is reset to zero in step 1023, the execution of the abnormality diagnosis is prohibited, and the abnormality diagnosis is performed. If it has already started, it is canceled (step 30 in FIG. 3).
5). If all the conditions in steps 1001 to 1019 are satisfied, the flag F2 is set in step 1021.
Is set to 1, and the abnormality diagnosis is permitted to be performed.

Each of the conditions will be described below. In step 1001, it is determined from the drive signal of the EGR control valve 27 whether or not the EGR is being performed.
Abnormality diagnosis is allowed only when EGR is performed. In step 1003, the intake passage negative pressure PM _V is calculated from the current intake passage pressure PM and the atmospheric pressure PA as PM _V = PA−.
It is calculated as PM, and the abnormality diagnosis is permitted only when PM _V is a predetermined value or more (200 mmHg or more in this embodiment). When the negative pressure in the intake passage is low, the EGR valve 21 does not have a problem because the driving force of the EGR valve 21 is insufficient.
May not open. Therefore, the abnormality diagnosis is EG
This is because it is necessary to perform the operation in a state in which a negative pressure sufficient to open the R valve 21 is generated.

In step 1005, it is judged whether or not the feedback control of the engine air-fuel ratio (for example, the feedback control of the air-fuel ratio based on the output of the air-fuel ratio sensor arranged in the exhaust passage) is being executed, and only during the feedback control is being executed. Abnormality diagnosis is permitted. EGR during EGR diagnosis
Therefore, the abnormality diagnosis is performed only during the feedback control in order to prevent the air-fuel ratio from fluctuating due to these operations such as stop and restart.

In step 1007, it is determined whether or not a predetermined time (160 seconds in this embodiment) has elapsed since the engine was started, and the abnormality diagnosis is permitted only when the predetermined time has elapsed. This is because it is necessary to execute the abnormality diagnosis in a stable operating state. Step 100
Reference numeral 9 indicates a determination as to whether or not the current throttle valve opening TA is equal to or larger than a predetermined value. The flag FTA is a flag that is set to 1 when the current throttle valve opening is greater than or equal to a predetermined value, and abnormality diagnosis is permitted only when the flag FTA is 1, that is, when the throttle valve opening is greater than or equal to the predetermined value. To be done. The determination of the throttle valve opening will be described below.

As described with reference to FIG. 1, the mechanical EGR device is used in this embodiment, and the EGR valve 21 is driven by the negative pressure in the intake passage. The negative pressure is controlled by the throttle negative pressure acting on the EGR modulator 23 from the throttle port 25 via the pressure guiding pipe 24.
Therefore, in order for the EGR valve 21 to open, the throttle port must be located downstream of the valve body of the throttle valve, and the throttle port must be in a state in which a negative pressure downstream of the throttle valve acts. Therefore, it is necessary to carry out the abnormality diagnosis at an opening of the throttle valve which exceeds the throttle port position or more. Therefore, in this embodiment, execution of the abnormality diagnosis is permitted only when the throttle valve opening is equal to or larger than a predetermined value.

However, in actual operation, there is a problem that the throttle valve opening at which the EGR valve 21 operates changes depending on the operating condition. For example, since the intake negative pressure on the downstream side of the throttle valve is large when the rotational speed is high, a large negative pressure acts on the EGR valve 21 immediately after the throttle valve opening reaches the throttle port position. On the other hand, if the rotation speed is low, the intake negative pressure will also be small, so the throttle valve opening will sufficiently exceed the throttle port position and the throttle port will not be in the state fully open downstream of the throttle valve. Negative pressure required to open the valve does not work.

Further, the opening degree of the throttle valve at which the EGR valve operates also changes depending on the intake air temperature. As mentioned above, EGR
The magnitude of the negative pressure acting on the valve 21 depends on the EGR modulator 2
3 of the pressure chamber 23c (see FIG. 1). However, since the resin used for sealing each part of the pressure chamber 23c is hardened when the intake air temperature is low, the airtightness of the pressure chamber 23c is lowered, and a problem arises that air enters the pressure chamber 23c (negative pressure leaks). . For this reason,
When the intake air temperature is low, the EGR valve 21 does not open unless a large negative pressure is supplied from the pressure guiding pipe 24 as compared with the case where the temperature is high. That is, when the intake air temperature is low, the EGR valve 2
The throttle valve opening required for opening No. 1 increases.

Further, another problem is that the throttle valve opening required for the EGR valve 21 to open from the closed state and the throttle valve opening when the EGR valve 21 is changed from the open state to the closed state. Is different. That is, in order to open the EGR valve in the closed state, a large negative pressure is required to overcome the frictional resistance of each part of the EGR valve, but once the EGR valve opens, a negative pressure is reduced to some extent. Even if the pressure drops, the EGR valve is kept open. That is, in order to determine whether or not the EGR valve is open based on the throttle valve opening, a hysteresis is provided in the determination value (throttle valve opening) when the EGR valve is opened and closed. The need arises.

In the present embodiment, in consideration of the above, the judgment value of the throttle valve opening for judging whether or not the abnormality diagnosis can be executed is shown in FIG.
As shown in 1, engine speed, intake air temperature, EGR
The valve is changed according to the three conditions of whether the valve is open or not. In FIG. 11, solid lines A and B are E
The throttle valve opening required to open the GR valve from the closed state, the broken lines A'and B'indicate the throttle valve opening to close the EGR valve from the opened state. . A and A'indicate the case where the intake air temperature is high, and B and B'indicate the case where the intake air temperature is low. As shown in FIG. 11, A,
In each of A ′, B, and B ′, the higher the rotational speed, the smaller the throttle valve opening, and the higher the intake temperature, the smaller the throttle valve opening.

In this embodiment, when the EGR valve 21 is closed, the throttle valve opening is A or B in FIG.
EG when larger than (selected according to intake air temperature)
The R valve is judged to have opened and the abnormality diagnosis is permitted. On the other hand, when the EGR valve 21 is open (when the throttle valve opening once exceeds A or B in FIG. 11), the throttle valve opening is lowered to A ′ or B ′ in FIG. Occasionally, the EGR valve 21 is closed and the abnormality diagnosis is prohibited.

FIG. 12 shows the above-mentioned throttle valve opening degree determination routine which is executed by the control circuit 50 at regular time intervals (for example, every 65 ms). In this routine, the value of the flag FTA in step 1009 of FIG. 10 is set. When the routine starts in FIG. 12, in step 1201, the intake air temperature H _A is detected by the intake air temperature sensor 43, the rotational speed NE and the throttle valve opening TA are detected by the sensors 44, 4 respectively.
Read from 1. Then, in step 1203,
11, the rotational speed NE and the intake air temperature H _A are used to determine the throttle valve opening TA ₀ when the EGR valve is opened (curves A and B in FIG. 11) and the throttle valve opening TA ₀ ′ when the valve is closed.
(FIG. 11 curves A ′ and B ′) are calculated.

Next, at step 1205, the current EG
Whether or not the R valve is open is determined from the value of the flag FTA. If the valve is not open (FTA ≠ 1), the current throttle valve opening TA is EGR at step 1207.
It is determined whether or not the throttle valve opening TA ₀ at the time of valve opening operation is equal to or larger than TA ₀ . If TA ≧ TA ₀ in step 1207, it is considered that the EGR valve has been opened this time.
In step 1209, the value of the flag FTA is set to 1 to permit abnormality diagnosis. When TA <TA ₀ , the value of the flag FTA is not changed and the routine is ended as it is.

On the other hand, when FTA = 1 at step 1205, the routine proceeds to step 1211, where it is judged if the EGR valve has been closed this time. That is, it is determined whether the current throttle valve opening TA is smaller than the throttle valve opening TA ₀ ′ when the EGR valve is closed, and TA <T
In the case of A ₀ ′, it is determined that the EGR valve has closed, and the process proceeds to step 1213 to set the value of the flag FTA to zero and prohibit the abnormality diagnosis. If TA ≧ TA ₀ ′, the routine is finished as it is.

By executing the above routine, the throttle valve opening degree is determined in consideration of the rotational speed, the temperature, and the hysteresis of the determination value itself with respect to the determination value of the throttle valve opening. To be judged. Next, returning to FIG. 10, step 1011 will be described. In step 1011, it is determined whether or not the current vehicle speed is stable, and execution of the abnormality diagnosis is permitted only when the vehicle speed is stable.

For example, when the vehicle is accelerating, a gear shift is performed, and in a vehicle with a manual transmission, the throttle valve opening greatly changes at each shift. The diagnosis will be discontinued. When the abnormality is diagnosed, the EGR is stopped and restarted, so if the diagnosis is stopped at each shift, the EG
Since the number of R stop and restart operations increases, problems such as deterioration of exhaust properties occur. Therefore, in the present embodiment, the abnormality diagnosis is permitted only when the vehicle speed is stable for a predetermined period to prevent the above problem.

In this embodiment, the vehicle traveling speed detected by the vehicle speed sensor 46 is monitored by a routine (not shown) executed by the control circuit 50 separately, and the vehicle speed at the time of executing the previous routine and the time of executing the current routine is monitored. When the difference is equal to or less than a predetermined value (for example, a value of about 3 km / h or less when the vehicle speed monitoring routine is executed every 65 ms), the value of the vehicle speed stability counter is increased by a constant value, and the difference in vehicle speed is the predetermined value In the above cases, the value of the vehicle speed stability counter is cleared. Figure 1
In step 011 of 0, execution of abnormality diagnosis is permitted when the value of the vehicle speed stability counter exceeds the determination value determined by the current transmission shift position.

For example, in the case of a vehicle with an automatic transmission, the above judgment value is a value corresponding to 2 seconds when the drive range has a shift position. That is, when the vehicle speed stable state continues for 2 seconds, execution of the abnormality diagnosis is permitted. Further, at shift positions other than the drive range, the determination value is a value corresponding to 5 seconds. Further, in the case of a vehicle with a manual transmission, the above-mentioned determination value is a value corresponding to 2 seconds when the shift position is on the higher gear side of the fourth speed or higher, and 5 seconds in other cases.

The reason why the judgment value of the vehicle speed stability counter is made small when the shift position is on the high gear side is that the shift position on the high gear side allows the vehicle to continue to run at this shift position without further upshifting. This is because the probability increases. In step 1013 of FIG.
It is determined whether or not the warm-up of the GR valve 21 is completed, and E
Execution of the abnormality diagnosis is permitted only when the warm-up of the GR valve 21 is completed.

Since exhaust gas containing water vapor flows through the EGR valve, the EGR valve may malfunction due to freezing of water in the EGR valve during a stop after traveling at a low temperature. Therefore, it is necessary to perform the abnormality diagnosis in a state where the temperature of the EGR valve is sufficiently increased and the malfunction due to freezing does not occur. In the present embodiment, a routine executed by the control circuit 50 separately is used to determine the CEG value of the warm-up counter, which is incremented at regular intervals by an amount determined according to the intake air temperature (air temperature) and the engine cooling water temperature. It is determined whether the EGR valve may freeze.

FIG. 13 is a flowchart showing a count-up operation routine of the warm-up counter. This routine is executed by the control circuit 50 at regular intervals (1 in this embodiment).
It is executed every 0 seconds. When the routine starts in FIG. 13, it is determined in step 1301 whether or not the engine has been started for a predetermined time or longer (for example, 30 seconds or longer). If the engine has been started for a predetermined time or longer, step 1301 Proceed to 1311. That is, step 1 in FIG.
Steps 303 to 1309 are executed only for a predetermined time after the engine is started. If the predetermined time has not elapsed since the engine was started, the current intake air temperature is read from the intake air temperature sensor 43 in step 1303, and the intake air temperature H _A is set to the predetermined value H _A.
It is determined whether _A0 or more. H _A0 is the intake air temperature at which it can be determined that the EGR valve is not frozen, for example, 1
It is set to about 5 ° C. If the current intake air temperature H _A is equal to or higher than the predetermined value H _A0 at step 1303, it is determined that the EGR valve is not frozen, and the routine proceeds to step 1305, where the value of the warm-up counter CEG is set to the upper limit value CEG _MAX (CEG _MAX
≧ 200) and the routine proceeds to step 1311. When the current intake air temperature H _A is lower than the predetermined value H _A0 , the routine proceeds to step 1307.

In step 1307, the current cooling water temperature THW is read from the cooling water temperature sensor 45 and it is determined whether or not this cooling water temperature THW is equal to or higher than a predetermined value THW ₀ .
Here, THW ₀ is a cooling water temperature at which it can be determined that the EGR valve is not frozen, and is set to, for example, about 10 ° C. If THW <THW ₀ in step 1307, there is a possibility that icing is currently occurring, so in step 1309 the value of the warm-up counter CEG is set to zero.
BR> Rear and go to step 1311. Also, THW ≧
In the case of THW ₀ , the warm-up counter value is not operated and the process proceeds directly to step 1311.

In step 1311, the cooling water temperature is the reference.
Temperature THW₁(In this embodiment, THW ₁＝ 10 ℃) or more
It is judged whether or not it is lower than the above reference temperature.
The process proceeds to step 1313. In addition, the cooling water temperature THW is
Reference temperature THW₁If so, proceed to step 1315
The warm-up counter CEG value (THW-THW₁) /
Increase by K. K is a constant, and in this embodiment, for example,
For example, K = 30 is set.

That is, at step 1313, the warm-up counter CEG is incremented by an amount according to the current cooling water temperature. Next, at steps 1315 and 1317, the value of the warm-up counter CEG is limited by the upper limit value CEG _MAX , and this routine is ended. When the temperature and the cooling water temperature are within the range where the EGR valve may freeze due to the execution of the routine of FIG. 13, the warm-up counter is set to zero (step 1309), and from this state, the cooling water temperature is set. Rises, the warm-up counter is incremented at a rate according to the rate of rise of the cooling water temperature (step 1313). Therefore, when the warm-up counter exceeds a certain value, it can be determined that the EGR valve is not frozen.

In step 1013 of FIG. 10, EGR is performed when the value of the warm-up counter CEG is, for example, 200 or more.
It is judged that the valve is not frozen, and the abnormality diagnosis is permitted. This prevents erroneous determinations due to freezing of the EGR valve at low temperatures. In step 1015 of FIG. 10, it is determined whether the throttle valve opening has changed by a predetermined value or more since the start of the abnormality diagnosis, and the abnormality diagnosis is permitted only when the change is within the predetermined value. Here, TAM of step 1015
S is the throttle valve opening read in step 306 in FIG. 3 and is a value (value at the start of abnormality diagnosis) immediately before the precondition (step 305 in FIG. 3) is satisfied. When the current throttle valve opening TA changes from the throttle valve opening TAMS at the start of diagnosis by a predetermined value (for example, 2 degrees) or more, the precondition is not satisfied because the engine operating state changes largely. As a result, the abnormality diagnosis is stopped.

In step 1017 of FIG. 10, the current throttle valve opening TA and the throttle valve opening T 500 ms before are set.
A _i-1 is compared, and the difference between them is determined by a predetermined value (for example, 0.
(9 degrees) Permit the execution of abnormality diagnosis only in the following cases. This is because when the rate of change of the throttle valve opening is large, acceleration, deceleration, etc. are being performed and the change of the operating state is large.

Next, at step 1019 in FIG. 10, the ISC valve (idle speed control valve) opening VI ₀ at the start of the abnormality diagnosis is compared with the current ISC valve opening VI, and the difference between them is set to a predetermined value (for example, full opening). Only when the value is less than or equal to 3% of the time), the abnormality diagnosis is allowed to be continued (continued). Since the ISC valve supplies intake air to the intake passage without passing through the throttle valve, ISC is not available during abnormality diagnosis.
When the valve opening changes, the intake air amount changes, and the abnormality diagnosis cannot be performed accurately. Therefore, it is preferable to fix the ISC valve opening during the abnormality diagnosis.
Since the valve has the function of adjusting the intake air amount according to load fluctuations such as operation and stop of the air conditioner, if the ISC valve opening is fixed, fluctuations in the engine speed will occur when the air conditioner is operating. However, there is a problem that the riding comfort of the vehicle deteriorates. Therefore, in the present embodiment, instead of fixing the ISC valve opening, the IS is activated by stopping or operating the air conditioner during abnormality diagnosis.
The abnormality diagnosis is stopped when the C valve opening changes by a predetermined value or more. In addition, I at the start of abnormality diagnosis
The SC valve opening degree VI ₀ is read at the same timing as TAMS in step 306 and stored in the RAM 51.

As described above, according to this embodiment, E
The operating range in which the abnormality diagnosis of the GR device can be performed and the preconditions are accurately determined, and the accuracy of the abnormality diagnosis is improved. In the above embodiment, the abnormality diagnosis and the determination of the diagnosis area are performed based on the engine speed and the intake passage pressure, but other operating state parameters related to the intake passage pressure are replaced with the intake passage pressure. Even if it is used, the determination can be performed in the same manner.
For example, the engine intake air amount exactly corresponds to the intake passage pressure, and the engine intake air amount decreases according to the EGR gas amount during the EGR. Therefore, in an engine provided with an air flow meter for detecting the amount of engine intake air at the inlet of the engine intake passage,
By measuring the engine intake air amount instead of the intake passage pressure in the above embodiment, it is possible to perform the abnormality diagnosis of the EGR device and the determination of the abnormality diagnosis region. In this case, if the engine intake air amount when the EGR is performed and when the engine is stopped in the standard state is measured in advance and stored in the control circuit as a map using the throttle valve opening and the engine speed, the same as in the above embodiment. The abnormality diagnosis and the diagnosis area determination can be performed by various methods.

[0097]

According to the present invention described in each claim, EG
Since it is possible to accurately determine the area in which the abnormality diagnosis can be performed without narrowing the area in which the abnormality diagnosis of the R device is performed, it is possible to improve the diagnostic accuracy while maintaining a high frequency of the abnormality diagnosis. Produce an effect.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram illustrating an embodiment of an internal combustion engine to which the present invention is applied.

FIG. 2 is a diagram illustrating a method of diagnosing an abnormality in an EGR device.

FIG. 3 is a part of a flowchart showing an abnormality diagnosis operation of the EGR device.

FIG. 4 is a part of a flowchart showing an abnormality diagnosis operation of the EGR device.

FIG. 5 is a part of a flowchart showing an abnormality diagnosis operation of the EGR device.

FIG. 6 is a diagram illustrating determination execution conditions at the time of abnormality diagnosis.

FIG. 7 is a diagram illustrating an example of a map used for determining an abnormality diagnosis implementation area.

FIG. 8 is a diagram showing a value of an atmospheric pressure correction coefficient used for determining an abnormality diagnosis execution region.

FIG. 9 is a flowchart showing details of determination of an abnormality diagnosis area.

FIG. 10 is a flowchart showing details of abnormality diagnosis prerequisites.

FIG. 11 is a diagram illustrating details of abnormality diagnosis preconditions.

FIG. 12 is a flowchart showing details of a prerequisite condition for carrying out abnormality diagnosis.

FIG. 13 is a flowchart showing details of abnormality diagnosis prerequisites.

FIG. 14 is a diagram illustrating an example of setting a conventional abnormality diagnosis execution area.

[Explanation of symbols]

1. Main body of internal combustion engine 3 ... Intake passage 5 ... Exhaust passage 7 ... Throttle valve, 20 ... EGR return device 21 ... EGR valve 23 ... EGR modulator 27 ... EGR control valve 42 ... Intake pressure sensor 50 ... Control circuit

   ─────────────────────────────────────────────────── ─── Continued front page       (56) References JP-A-64-3257 (JP, A)                 JP-A-4-362260 (JP, A)                 JP-A-63-215863 (JP, A)                 JP-A-63-192944 (JP, A)                 Actual Kaihei 1-166752 (JP, U)

Claims (2)

(57) [Claims] 1. An abnormality diagnosis device for diagnosing an abnormality of an exhaust gas recirculation device for recirculating a part of exhaust gas to an intake passage of an internal combustion engine, comprising: intake pressure detection means for detecting pressure in an intake passage; An abnormality determining means for determining whether or not there is an abnormality in the exhaust gas recirculation device based on the pressure in the intake passage when the exhaust gas recirculation device is operating and the pressure in the intake passage when the exhaust gas recirculation device is not operating; When the engine is operated at the detected operating condition parameter while the exhaust gas recirculation device is in a normal state using the parameter detecting means for detecting the operating condition parameter related to the state and the detected operating condition parameter. And a standard pressure difference calculation means for calculating a difference in intake passage pressure between when the exhaust gas recirculation device is operating and when the exhaust gas recirculation device is not operating, and the standard pressure difference calculation If the intake passage pressure difference calculated by the step is smaller than a predetermined determination value, the abnormality diagnosis apparatus and an inhibiting means for inhibiting the determination of the abnormality presence or absence by said abnormality judgment means. 2. The standard pressure difference calculation means uses the detected operating condition parameter to operate the engine under standard atmospheric pressure conditions, the exhaust gas recirculation device is normal, and the engine detects the detected value. When operating with the specified operating state parameter, the difference between the intake passage pressure when the exhaust gas recirculation device is operating and when the exhaust gas recirculation device is not operating is calculated on the basis of a predetermined relationship. Based on the detected atmospheric pressure and the standard atmospheric pressure,
A correction unit that corrects the intake passage pressure difference calculated by the standard pressure difference calculation unit, and if the corrected intake passage pressure difference is smaller than a predetermined determination value, the abnormality determination unit determines whether there is an abnormality. The abnormality diagnosis device according to claim 1, wherein the abnormality is prohibited.