JPH0478831B2 - - Google Patents

Abstract

PURPOSE:To easily discover any failure in an exhaust gas recirculation system by temporarily changing over a negative pressure switching valve, detecting whether or not variation in intake pressures before and after the changeover is within a specified range, and judging whether or not the exhaust gas recirculation system is in failure on the basis of the detected result. CONSTITUTION:When a throttle opening is free from large variation and an engine load is in a stable state, the start or stop of EGR (exhaust gas recirculation control) varies an intake pressure on condition that an EGR valve 9 is in a normal operation state. In order to control the operation of the EGR valve 9, a negative pressure switching valve 13 interposed in a negative pressure passage 12 is temporarily changed over during the execution of the EGR so as to stop the EGR only for a fixed period, and as well, it is detected whether or not the intake pressure before and after the changeover are within a specified range. Therefore, whether or not an EGR system normally operates can be judged on the basis of the varying value of the intake pressure. That is, when the varying value of the intake pressure is small enough to be within the specified range, some failure in the EGR system is judged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a failure diagnosis method for an exhaust gas recirculation control device mainly applied to an automobile engine.

[Prior Art] Generally, in an automobile engine, the intake system and the exhaust system are connected to an exhaust gas recirculation passage (hereinafter referred to as an EGR passage).
At the same time, a part of the exhaust gas is returned to the intake system through this EGR passage, thereby suppressing the maximum combustion temperature of the fuel and reducing the generation of NO _x contained in the exhaust gas. So-called
EGR control is performed. In this case, the operation of the exhaust gas recirculation control valve (hereinafter referred to as the EGR valve) installed in the EGR passage is controlled according to the engine operating conditions, rather than constantly recirculating exhaust gas to the intake system while the engine is operating. By doing so, the timing of EGR execution and the amount of EGR are controlled. For example, in low engine load ranges where fuel combustion is not good and NO _x is produced relatively little, exhaust gas recirculation (hereinafter referred to as EGR) is stopped;
When applying this, the amount of EGR is usually limited so that the exhaust gas contained in the intake air remains at a substantially constant ratio.

However, initial EGR control may not be performed due to an operational error or malfunction of the EGR valve or a modulator that controls the operation of the valve. As a specific prior art for dealing with such problems, for example, as shown in Japanese Patent Application Laid-Open No. 57-212358, there is a method for diagnosing EGR valve failure by directly detecting the operating position of the EGR valve. There are examples of this.

However, in the above-mentioned prior art, not only is it necessary to provide a special detection device to detect the operating position of the EGR valve, but the system structure including a control circuit that processes information sent from this detection device is complicated. Therefore, it cannot be said to be preferable.

As a prior art for dealing with such problems, as described in Japanese Patent Application Laid-Open No. 62-51746, the above-mentioned method is installed in the negative pressure passage that leads the intake pressure to the EGR valve.
A negative pressure switching valve is installed to control the operation of the EGR valve, and this negative pressure switching valve is temporarily switched while EGR is being executed and the engine load is stable. There is a system that detects whether the fluctuation is within a certain range and determines whether the EGR system is malfunctioning based on the detection result. In other words, this diagnostic method indicates that if the EGR valve actually operates,
It was developed focusing on the fact that fluctuations occur in the intake pressure.By switching the supply state of the negative pressure that controls the operation of the EGR valve and examining the fluctuations in the intake pressure before and after the switching, the EGR valve and The purpose is to discover failures in peripheral equipment.

By the way, this thing works at fixed time intervals (e.g.
12ms) to determine whether the amount of change in throttle opening is within the set range.
One condition is that the amount of change in throttle opening is within a set range, and it is determined that the engine load is stable. Then, it is determined that the engine load is stable every 12 ms, and if this occurs multiple times in a row, the negative pressure switching valve is temporarily switched.

[Problems to be Solved by the Invention] However, the amount of change in the throttle opening is calculated by subtracting the throttle opening detection value at the time of determination and the throttle opening detection value detected 12 ms before. Therefore, if the throttle opening is changing slowly, there is a risk of erroneous diagnosis. In other words, as shown in Fig. 4, when the throttle opening detection value TA is changing slowly and continuously, in each judgment every 12ms,
It is determined that the rate of change of the detected throttle opening value TA is within the set range, and that the engine load is in a stable state. When this determination is repeated multiple times, the negative pressure switching valve is temporarily switched, and the intake pressures PM and PM2 before and after the switching are compared. In that case, if the throttle opening gradually changes, even though the EGR valve is operating normally due to the switching, the apparent intake pressure PM1 before the switching and the switching control Intake pressure PM2
It may happen that there is no difference between In that case, it is mistakenly diagnosed that the exhaust gas recirculation system is out of order, and a display to that effect is displayed. Note that in FIG. 4, a indicates the state of change of the throttle opening detection value TA. Further, b shows the change in the intake pressure PM in the EGR execution state, and c shows the change in the intake pressure PM in the EGR stopped state.

The present invention not only makes it possible to easily detect a malfunction in the exhaust recirculation system without attaching a special detection device to the EGR valve, etc., but also enables the detection of faults in the exhaust recirculation system even when the throttle opening is changing slowly. It is an object of the present invention to provide a fault diagnosis method for an exhaust gas recirculation control device that does not cause erroneous diagnosis.

[Means for solving the problems] In order to achieve such objects, the present invention has the following features:
The following measures were adopted.

That is, in the fault diagnosis method for an exhaust recirculation control device according to the present invention, a load switching valve that controls the operation of the exhaust recirculation control valve is interposed in a negative pressure passage that leads intake pressure to the exhaust recirculation control valve. During execution, it is repeatedly determined at regular time intervals whether the difference between the detected throttle opening value and the learned throttle opening value is within the set range, and it is determined that the difference is not within the set range. In this case, the throttle opening learning value is changed to the same value as the throttle opening detection value at the time of the determination, and it is determined that the difference is always within the set range at each determination time. In this case, the negative pressure switching valve is temporarily switched, and it is detected whether the fluctuation in intake pressure before and after switching is within a certain range, and based on the detection result, it is determined whether the exhaust recirculation system is malfunctioning. The feature is that it is determined whether or not there is a person.

[Effect] If EGR is started or stopped when the engine load is stable and there is no major change in the throttle opening, the intake pressure will fluctuate if the EGR valve is in normal operating condition. Therefore, in order to control the operation of the EGR valve, the negative pressure switching valve installed in the negative pressure passage is temporarily switched during EGR execution to stop EGR for a certain period of time, and the intake pressure remains constant before and after switching. If it is detected whether or not it is within the range, the exhaust recirculation system (hereinafter referred to as
It is possible to determine whether or not the EGR system (referred to as the EGR system) is operating normally. That is, if the amount of change in intake pressure is small and within a certain range, it is determined that the EGR system is faulty, and if the amount of change in intake pressure is outside the certain range, it is determined that the EGR system is normal.

The above diagnosis is performed on the condition that it is repeatedly and continuously determined that the difference between the detected throttle opening value and the learned throttle opening value is within the set range. The throttle opening learning value is updated only when the difference deviates from a set range. Therefore, if the difference continues to fall within the set range, the throttle opening learning value remains not updated. Therefore, if the throttle opening is changing slowly in the same direction, the difference between the detected throttle opening value and the learned throttle opening value will cumulatively increase as the number of judgments increases. Become. As a result, the difference deviates from the set range, and the above-mentioned requirements are no longer met.
Failure diagnosis is canceled midway through. Therefore, in such a case, it is possible to prevent the diagnosis from being mistakenly determined to be a failure, thereby improving the reliability of the failure diagnosis.

[Example] Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 schematically shows an automobile engine. In the drawing, 1 indicates the engine body;
Reference numeral 2 indicates an intake passage communicating with the combustion chamber 3 of the engine body 1, and reference numeral 4 indicates an exhaust passage. A surge tank 7 is provided between the throttle body 5 of the intake passage 2 and the intake pipe 6 to prevent intake pulsation. Then, the inside of this surge tank 7 and the inside of the exhaust passage 4 are
In addition to communicating through the EGR passage 8, this
An EGR valve 9 is provided in the EGR passage 8 and is operated by a pressure difference between atmospheric pressure and intake pressure PM. EGR
The valve 9 is for guiding a part of the exhaust gas in the exhaust passage 4 into the surge tank 7 interposed in the intake passage 2 by opening the valve according to the operating condition of the engine. I am doing it. The negative pressure chamber 9a of this EGR valve 9 and the EGR port 11 near the throttle valve 10 are communicated via a negative pressure passage 12, so that intake pressure PN is introduced into the negative pressure chamber 9a. When the pressure difference between the negative pressure chamber 9a and the constant pressure chamber 9b on the atmospheric side provided across the diaphragm exceeds the operating pressure of the EGR valve 9, the valve body 9c opens and exhaust gas in the exhaust passage 4 is released. The air is set to flow back into the surge tank 7 according to the amount of intake air.

On the other hand, the negative pressure passage 12 is provided with a negative pressure switching valve 13 for controlling the operation of the EGR valve 9 according to the engine load. Negative pressure switching valve 1
Reference numeral 3 denotes a vacuum switching type three-way valve configured to be able to selectively connect the outside air and the inside of the intake passage 2. Specifically, the first input port 13a is connected to the EGR port 11. connect to the side,
The second input port 13b is opened to the outside air through a filter, and the output port 13c is connected to the negative pressure chamber 9a side of the EGR valve 9. When the electrical input terminal is not energized, the first input port 13a on the intake pressure side and the output part 13c communicate with each other and are in the "open" state, and when the electrical input terminal is energized. At this time, the second input port 13b on the atmospheric pressure side and the output port 13c communicate with each other to be in a "closed" state.

Further, an EGR modulator 1 is provided in the negative pressure passage 12 between the negative pressure switching valve 13 and the EGR valve 9.
4 are installed. The EGR modulator 14 is
This is a normal system in which the exhaust pressure in the EGR passage 8 on the upstream side of the EGR valve 9 is used to adjust the negative pressure introduced into the negative pressure chamber 9a of the EGR valve 9.

On the other hand, on the surge tank 7 side, the intake pressure PM
An intake pressure sensor 15 is provided for detecting. The intake pressure sensor 15 can be selectively connected to the outside air and the inside of the surge tank 7 via a switching valve 16 that switches the pressure detection area. Specifically, the switching valve 16 is a vacuum switching type three-way switching valve that is substantially similar to the negative pressure switching valve 13, and communicates the first input port 16a with the inside of the surge tank 7, and connects the second input port 16a with the inside of the surge tank 7. The input port 16b of is opened to the outside air through a filter,
The output port 16c is connected to the intake pressure sensor 15. When the electric input terminal is not energized, the first input port 16a on the intake pressure side and the output port 16c communicate with each other, and when the electric input terminal is energized, the first input port 16a on the intake pressure side and the output port 16c are connected, and when the electric input terminal is energized, the first input port 16a on the intake pressure side and the output port 16c are connected. The second input port 16b and output port 16c are configured to communicate with each other. This switching valve 16
is normally held at a position where its first input port 16a and output port 16c communicate with each other.

The microcomputer system 17 uses signals from various sensors as input information to perform various controls including fuel injection amount control, and includes a central processing unit 18, a memory 19, and an input/output interface 20. , 21. The input interface 20 is provided with at least a signal a from a throttle sensor 22 that detects the opening degree of the throttle valve 10, a signal b from a water temperature sensor 23 that detects the engine cooling water temperature, and a distributor 24. A signal c from a rotation speed sensor (not shown) and a signal d from an intake pressure sensor 15 are respectively input, and output interfaces 21 output signals to a negative pressure switching valve 13 and a switching valve 1.
6, and signals e, f, and g are output to a diagram lamp 25 that displays the results of EGR system failure diagnosis, respectively.

And the above microcomputer system 1
7 has a built-in program as shown in FIG. 3 in order to carry out the fault diagnosis method according to the present invention. First, in step 50, the increment counter C is counted for a certain period of time, which is the measurement period, for example, 12 mmsec.
It is determined whether the count has counted up to 0. If the count has not counted up, the process proceeds to step 63, and if the count has elapsed, the process proceeds to step 51. In step 51, it is determined whether the engine cooling water temperature has reached 70°C based on the signal b from the water temperature sensor 23. If it has not reached 70°C, the process proceeds to step 62, and if it exceeds 70°C, the process proceeds to step 52. . In step 52, the engine speed is determined based on the signal c from the speed sensor.
Determine whether NE is within a certain range (3000 to 3200 rpm), and if it is not within a certain range, proceed to step 60.
If it is within a certain range, proceed to step 53. In step 53, it is determined whether the difference between the throttle opening detection value TA corresponding to the signal a from the throttle sensor 22 and the throttle opening learning value TAGKS, which will be described later, is within a set range. Specifically, the absolute value of the difference between the throttle opening detection value TA and the throttle opening learned value TAGKS is the set value.
Determine whether it is smaller than 0.49deg. and,
If it is determined that the difference is larger than the set value 0.49deg, that is, the throttle opening detection value
If it is determined that the difference between TA and the throttle opening learning value TAGKS is not within the set range, the process proceeds to step 54. In step 54, the throttle opening learning value TAGKS is updated to the same value as the final throttle opening detection value TA at the time of determination, and the process proceeds to step 60. On the other hand, if it is determined in step 53 that the difference is smaller than the set value 0.49 degrees, the process proceeds to step 55, where a value obtained by adding 1 to the counter CDIAG is set, and the process proceeds to step 56. In step 56, the counter
Whether the value of CDIAG has reached 20 or not, in other words, 240 mmsec (12 mmsec x 20) after the counter CDIAG is cleared and starts counting at step 55.
It is determined whether or not the time period has elapsed. If not, the process proceeds to step 58, and if it has elapsed, the process proceeds to step 57, where the negative pressure switching valve 13 is switched from "open" to "closed". In step 58, the intake pressure PM is within a certain range (300 to 350) based on the signal d from the intake pressure sensor 15.
mmHg) and if it is within the range,
Proceed to step 60, and if within a certain range, proceed to step 60.
Proceed to 59. In step 59, check the latest intake pressure PM.
Set to PM1 and proceed to step 62. step
At 60, clear counter CDIAG and step 61
Proceed to , switch the negative pressure switching valve 13 from "closed" to "open" and restart EGR. In step 62, increment counter C is cleared and step 63
Proceed to. In step 63, the value of counter CDIAG is
Whether it has reached 80 or not, in other words, the counter
Determine whether 980 mmsec has elapsed since the start of CDIAG measurement, and if not, proceed to step 50.
If the time has elapsed, proceed to step 64, where the negative pressure switching valve 13 is switched to "close".
It is determined whether the difference between the intake pressure PM1 immediately before stopping EGR and the latest intake pressure PM (indicated as PM2 in Figure 2) is less than a certain value (60 mmHg). As a result, if it is determined that the difference is less than a certain value, the process proceeds to step 65 and sets the diagnosis result indicating that the EGR system including the EGR valve 9 is malfunctioning in a predetermined memory location. Proceed to step 66. On the other hand, if it is determined that the difference exceeds a certain value, the process directly proceeds to step 66. In step 66,
By switching the negative pressure switching valve 13 from "closed" to "open", the EGR valve 9 is returned to a state in which negative pressure can be supplied, and the process proceeds to step 67. At step 67, the increment counter CDIAG is cleared and the process returns to step 50.

According to this configuration, when diagnosing a failure of the EGR system mainly consisting of the EGR valve 9 and the modulator 14, first the air pressure PM is applied to the EGR valve 9 via the negative pressure switching valve 13 based on information from the water temperature sensor 23, etc. It is determined whether or not the engine is in the EGR execution region where the EGR has been introduced (step 51). It is repeatedly determined every 12 mmsec whether the difference between the detected throttle opening value TA and the learned throttle opening value TAGKS is within the set range, and whether the intake pressure PM is within a certain range. (steps 50, 52, 53, 58). When it is determined that all of these conditions are satisfied 20 times in succession, a command signal e is issued from the microcomputer system 17 to the negative pressure switching valve 13 (step 57), and the The pressure switching valve 13 is switched to "closed". As a result, the second input port 13b and the output port 13 of the negative pressure switching valve 13
Since atmospheric pressure is introduced into the negative pressure passage 12 through communication with the negative pressure chamber 9a of the EGR valve 9, the intake pressure PM
The EGR valve 9 is closed.
That is, EGR is stopped. Note that during the period from the time when the engine load enters a stable state until approximately 240 mmsec has elapsed, that is, after the above conditions are met until the counter CDIAG reaches 20,
In step 59, the intake pressure PM1 is constantly updated to the same value as the latest detected value PM. and,
After the counter CDIAG counts up to 20 or more, its updating is stopped. Therefore, the negative pressure switching valve 13 is "closed" at that intake pressure PM1.
The intake pressure PM immediately before EGR is stopped will be captured and saved. Then, when approximately 960 mmsec has passed since the engine load entered a stable state, that is, when the counter CDIAG reaches 80 or more, the intake pressure immediately before EGR is started.
It is determined whether the difference between the latest intake pressure PM corresponding to PM2 and the intake pressure PM1 measured immediately before EGR is stopped is below a certain value (60 mmHg),
If it is determined that the EGR valve 9
A failure determination is made on the assumption that the components are not operating normally, and the failure determination results are displayed on the diagram lamp 25 (steps 64 and 65). Immediately thereafter, the negative pressure switching valve 13 is switched to the "open" state, and the normal operating state is restored.

As is clear from the above explanation, according to such a method, in the EGR execution region, the engine speed NE and intake pressure PM are within a certain range, and the throttle opening detection value TA and the throttle opening When the difference from the learned value TAGKS is within the set range, the negative pressure switching valve 13 is switched to temporarily stop EGR, and the intake pressure before and after switching is changed.
By simply comparing the amount of change in PM, it is possible to reliably determine the operating state of the EGR valve 9, etc., and diagnose its failure.

According to this embodiment, the water temperature sensor 23, pressure sensor 15, throttle sensor 22, negative pressure switching valve 13, etc. that are normally installed are used, and the microcomputer 17 is used to control the heating injection. Since failure diagnosis can be performed by utilizing the remaining power of the EGR valve 9, there is no need to provide a special detection device to directly detect the operating position of the valve body 9a of the EGR valve 9, which is convenient from a cost perspective. becomes.

Moreover, as mentioned above, the above diagnosis is based on the throttle opening detection value TA and the throttle opening learning value.
This is executed on the condition that the determination that the difference with TAGKS is within the set range is repeatedly and consecutively made. The throttle opening learning value TAGKS is updated only when the difference deviates from the set range. Therefore, if the difference continues to fall within the set range, the throttle opening learning value TAGKS remains not updated. Therefore, if the throttle opening is changing slowly in the same direction, the throttle opening detection value TA is
The difference between the throttle opening learned value TAGKS and the throttle opening learning value TAGKS increases cumulatively. As a result, the difference deviates from the set range, the above-mentioned requirements are no longer satisfied, and the fault diagnosis is stopped midway (steps 53, 54, 60, 61). Therefore, if there is a problem like the one explained based on Fig. 4, that is, when the throttle opening is gradually increasing,
It is possible to reliably eliminate the problem of causing an erroneous failure.

Although one embodiment has been described above, the present invention is not necessarily limited to the above embodiment, and for example, the numerical values in the illustrated example may be changed depending on the engine characteristics.

[Effects of the Invention] As described above, the present invention sets the difference between the detected value and the learned value of the throttle opening to the same setting range as the criterion for failure diagnosis and learning value update, and if it is within the setting range, the failure is detected. This is a diagnostic operation, and if it is outside the setting range, the throttle opening learning value is updated.
EGR system failures can be easily diagnosed by effectively utilizing normally installed equipment without the need to attach a special diagnostic detection device to the EGR valve, etc., and the throttle opening learning value can be updated. A method for diagnosing a fault in an exhaust recirculation control device that can improve the efficiency of fault diagnosis by stopping the fault diagnosis, thereby effectively preventing erroneous diagnosis and obtaining highly reliable diagnostic results. can be provided. Furthermore, in a microcomputer system with limited processing power for controlling an automobile engine, it is practical to share the setting range for two judgment operations because it can reduce the number of judgment steps. Very informative.

[Brief explanation of the drawing]

FIG. 1 is a system explanatory diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing control setting conditions of the same embodiment,
FIG. 3 is a flowchart showing the control procedure of the same embodiment. FIG. 4 is an explanatory diagram for explaining the conventional problems. 1...Engine body, 2...Intake passage, 4...
Exhaust passage, 7...Surge tank, 8...Exhaust recirculation passage (EGR passage), 9...Exhaust recirculation control valve (EGR valve), 12...Negative pressure passage, 13...Negative pressure switching valve, 14... EGR modulator, 15...
...Intake pressure sensor, 17...Microcomputer system, 22...Throttle sensor, 23...
Water temperature sensor, 25...Diagram lamp, TA...
Throttle opening detection value, TAGKS... Throttle opening learning value.

Claims (1)

[Claims] 1 A load switching valve that controls the operation of the exhaust recirculation control valve is installed in the negative pressure passage that leads intake pressure to the exhaust recirculation control valve, and when exhaust recirculation is executed, the throttle opening detection value and the throttle opening learning value are It is repeatedly determined at regular time intervals whether or not the difference is within the set range, and only when it is determined that the difference is not within the set range, the throttle opening learned value is The throttle opening detection value is changed to the same value as the throttle opening detection value, and if it is determined that the difference is always within the set range at each judgment point, the negative pressure switching valve is temporarily switched. , an exhaust system characterized in that it detects whether or not fluctuations in intake pressure before and after switching are within a certain range, and determines whether or not the exhaust gas recirculation system is malfunctioning based on the detection result. Fault diagnosis method for reflux control device.