JPH0733794B2 - Failure diagnosis device for air-fuel ratio control system - Google Patents

Description

The present invention relates to an air-fuel ratio control system failure diagnosis device.

[Conventional technology]

In Japanese Patent Laid-Open No. 59-91509, a diagnostic circuit is made independent by a signal system that can be diagnosed in an arbitrary operating state and a signal system that can be diagnosed only in a specific operating state to diagnose only in a specific operating state. A self-diagnosis device for an internal combustion engine control device is disclosed, in which a circuit for diagnosing a possible signal system is provided with switching means for switching its operation and non-operation.

Conventionally, in the failure diagnosis of a signal system that can be diagnosed only in the specific operating state described above, in order to prevent erroneous diagnosis, for example, when the engine speed, the intake pipe negative pressure, the water temperature, the vehicle speed, etc. are within a certain range. In other words, the failure diagnosis is made only when it is within the failure diagnosis area.

[Problems to be Solved by the Invention]

However, in this device, for example, if the intake pipe negative pressure fluctuates and goes out of the failure diagnosis area even for a short period of time, the failure diagnosis is interrupted even in the failure diagnosable state. There is a problem that the failure diagnosis area is narrowed. Further, for example, a pressure switch detects the intake pipe negative pressure, and in the case of generating an output signal of only ON-OFF, when the output signal is shared for detecting a failure diagnostic area of a plurality of diagnostic items, Has a problem that when the operating pressure of the pressure switch is set to an optimum value for a certain diagnostic item, the failure diagnostic area for other diagnostic items becomes narrow.

In view of the above problems, it is an object of the present invention to provide a failure diagnosis device for an air-fuel ratio control system that can expand the failure diagnosis area.

[Means for Solving the Problems]

According to the invention described in claim 1, as shown in the configuration diagram of the invention of FIG. 1A, the engine operating state detecting means 100 for detecting the engine operating state and the detection signal of the detecting means are in the failure diagnosis area. When the engine air-fuel ratio control system failure diagnosis means 102 and failure detection continuation means for continuing the failure diagnosis for a predetermined period from the time when the detection signal deviates from the failure diagnosis region There is provided an air-fuel ratio control system failure diagnosis device including:

According to the invention described in claim 2, as shown in the configuration diagram of the invention of FIG. 1B, the engine operating state detecting means 200 for detecting the engine operating state, and the detection signal of the detecting means are the air-fuel ratio feedback control. Air-fuel ratio feedback control means 201 for feedback-controlling the air-fuel ratio when in the region, and performing a failure diagnosis of the air-fuel ratio control system when the detection signal is in the failure diagnosis region included in the air-fuel ratio feedback control region. Failure diagnosis means 202, failure diagnosis continuation means 203 for continuing the failure diagnosis of the air-fuel ratio control system for a predetermined period from the time when the detection signal deviates from the failure diagnosis area, and the failure diagnosis continuation means When the detection signal deviates from the air-fuel ratio feedback control area even during the period when the failure diagnosis of the air-fuel ratio control system is continued by the air-fuel ratio control system Air-fuel ratio control system failure diagnosis apparatus having fault and interrupting fault diagnosis continued interrupting means 204 to continue diagnosis is provided.

[Work]

In the invention of claim 1, the failure diagnosis means 102 carries out a failure diagnosis of the engine air-fuel ratio control system when the detection signal of the engine operating state detection means 100 is within the failure diagnosis area. Further, the failure diagnosis continuing means 103, even if the detection signal of the engine operating state detection means 100 deviates from the failure diagnosis area during the failure diagnosis, performs the failure diagnosis by the failure diagnosis means 102 for a predetermined period from the deviation. To continue.

Further, in the invention of claim 2, as in the invention of claim 1, the failure diagnosing means 202 causes the failure of the engine air-fuel ratio control system when the detection signal to the engine operating state detecting means 200 is within the failure diagnosing area. Diagnosis is performed, and the failure diagnosis continuation means 203 is a failure diagnosis means 202 for a predetermined period from the time when the detection signal of the engine operating state detection means 200 deviates from the failure diagnosis area during the failure diagnosis. Continue fault diagnosis by. However, the failure diagnosis continuation interruption means 204, even during the failure diagnosis continuation period by the failure diagnosis continuation means 203, the detection signal of the engine operating state detection means 200 is from the air-fuel ratio feedback control area by the air-fuel ratio feedback control means 201. When it comes off, the continuation of the failure diagnosis by the failure diagnosis means 202 is interrupted.

〔Example〕

 The present invention will be described below with reference to illustrated embodiments.

In FIG. 2, 1 is the engine body, 2 is the intake manifold,
3 is a surge tank, 4 is a carburetor, 5 is an exhaust manifold,
6 is a distributor, 7 is a water temperature sensor that detects the engine cooling water temperature, 8 is an O ₂ sensor that is arranged in the exhaust passage in the exhaust manifold 5 and that detects the oxygen concentration in the exhaust gas, 9
Is a fuel tank, 10 is an evaporative fuel adsorption device including a charcoal canister, 21 is a vehicle speed sensor, 22 is a failure indicator light, and 30 is an electronic control unit. An air bleed pipe 12 opens in the main fuel passage 11 of the carburetor 4, and a linear solenoid valve 13 for controlling the air bleed amount is inserted in the air bleed pipe 12. Linear solenoid valve 13 is O ₂
Feedback control is performed based on the output signal of the sensor 8 so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. That is, in the linear solenoid valve 13, the electric current flowing through the solenoid is increased or decreased by the electronic control unit 30, so that the opening of the valve port of the linear solenoid valve 13 is increased or decreased. In this way, the amount of air supplied from the air bleed tube 12 is controlled, and the air-fuel ratio is controlled to be the stoichiometric air-fuel ratio.

In order to control the air-fuel ratio, auxiliary air may be supplied into the intake passage downstream of the carburetor throttle valve. In this case, the air supply passage is connected to the intake passage downstream of the carburetor throttle valve. .

On the other hand, the evaporated fuel adsorbing device 10 is connected to the fuel tank 9 via the evaporated fuel conduit 14 on the one hand, and the evaporated fuel conduit on the other hand.
It is connected to the surge tank 3 via 15. A solenoid valve 16 for purge control is inserted into the vaporized fuel conduit 15. The evaporative fuel adsorption device 10 has an activated carbon 17 incorporated therein, and the fuel vapor generated in the fuel tank 9 is activated by the activated carbon 17
Is adsorbed on. When the solenoid valve 16 is opened, the atmosphere is sent into the vaporized fuel conduit 15 through the activated carbon 17, at which time the activated carbon is activated.
The fuel vapor adsorbed by 17 is desorbed from the activated carbon 17 and sent into the vaporized fuel conduit 15 together with the atmosphere. The fuel vapor is then fed into the surge tank 3 and thus the vaporized fuel conduit 15
Form an evaporated fuel purge passage.

The distributor 6 has a built-in crank angle sensor 20 that outputs a crank angle signal according to the rotation of the distributor shaft. Reference numerals 23, 24 and 25 denote first, second and third negative pressure switches. Each negative pressure switch 23 to 25 is connected in the surge tank 3. The first negative pressure switch 23 is turned on at a negative pressure of 540 mmHg, for example. The second negative pressure switch 24 is, for example, 400 m
It turns on at a negative pressure of mHg. The third negative pressure switch 25
For example, it turns on at a negative pressure of 80 mmHg.

The electronic control unit 30 is composed of a digital computer, and has a ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, and an input port 35 which are mutually connected by a bidirectional bus 31.
And an output port 36. Input port 35 is A / D
The converter 37 and 38 are connected to the water temperature sensor 7 and the O ₂ sensor 8, respectively. The input port 35 includes a crank angle sensor 20, a vehicle speed sensor 21, a first to a third negative pressure switch 23.
Connected to ~ 25 respectively.

On the other hand, the output port 36 is connected to the failure indicator lamp 22, the purge control solenoid valve 16 and the linear solenoid valve 13 via drive circuits 39, 40 and 41, respectively.

Next, the failure diagnosis of the air-fuel ratio feedback system will be described with reference to FIG. When diagnosing this failure, it may be occurring because the vehicle is operating under the operating conditions that a certain phenomenon should originally occur, or it should be operated under the operating conditions that a certain phenomenon should not occur. However, it is difficult to judge whether a certain phenomenon occurs due to some abnormality. Therefore, the failure diagnosis is performed only in the latter case, and the failure diagnosis is performed only within a predetermined failure diagnosis area. That is, in the present embodiment, the detection value of the intake pipe negative pressure, for example, in order to prevent failure diagnosis during idling or during rapid acceleration, for example, a predetermined area included in the feedback control area as a failure diagnosis area, Failure diagnosis is performed within this area.

Figure 3 shows the linear solenoid valve 13 in the fault diagnosis area.
The control current I is shown. The control current I is changed by the detection signal from the O ₂ sensor 8, and the control current I increases as the air-fuel ratio becomes richer, which increases the valve port opening of the linear solenoid valve 13 to increase the air bleed amount. Be increased. On the contrary, as the air-fuel ratio becomes leaner, the control current I decreases, whereby the valve port opening of the linear solenoid valve 13 is decreased and the air bleed amount is decreased. Thus, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio.

In FIG. 3, when a predetermined current value, for example, 480 mA is exceeded at the time point a, and the state continues for 3 seconds, the control current I is forcibly skipped to 370 mA and the purge control solenoid valve 16 is set at the time point 3 seconds. Purge is interrupted by closing the valve. The reason why the purging is interrupted is that it is difficult to determine whether the control current I exceeds 480 mA due to the air-fuel ratio becoming rich due to the purging influence. This is because the fault diagnosis is performed except for. As shown by the solid line,
If the control current I is maintained at 480 mA or less from the time point b, the normal determination is made at the time point c when 30 seconds have elapsed.

On the other hand, as shown by the dotted line, when the current exceeds 480 mA again at the second point after the point b, and the state continues for 4 seconds, an abnormality determination is made at the point 4 seconds e and the failure indicator lamp 22 is turned on.
That is, in the failure diagnosis region, the engine operating condition, for example, the intake pipe negative pressure, is within a relatively stable predetermined value included in the feedback control region, and the control current I is usually 480 mA or less in this region. If 480 mA is continuously exceeded for a predetermined time, it is considered that some abnormality has occurred.

When the intake pipe negative pressure falls out of the failure diagnosis area and the failure diagnosis is interrupted during the determination of normality or abnormality, the failure determination is made after the control current I again exceeds 480 mA for 3 seconds, as at the time point a.

However, in this failure diagnosis, for example, before the normal determination is made after the passage of time point B or before the abnormality determination is made after the passage of time point 2, for example, the intake pipe negative pressure is reduced and the failure diagnosis area is detected even for a short time. If it comes off, the failure diagnosis is interrupted even if the failure diagnosis is possible. Therefore, there is a problem that the chance of failure diagnosis is reduced, and as a result, the failure diagnosis area is narrowed.

Next, the operation of this embodiment will be described with reference to FIG. It is assumed that the engine cooling water temperature, the engine speed and the vehicle speed detected by the water temperature sensor 7, the crank angle sensor 20 and the vehicle speed sensor 21 are within the failure diagnosis area. The failure diagnosis region of the intake pipe negative pressure is set to the region between 400 mmHg and 540 mmHg, and the feedback control region is set to the region between 80 mmHg and 540 mmHg. When the intake pipe negative pressure fluctuates as shown in the figure, conventionally, when the intake pipe negative pressure becomes lower than 400 mmHg, for example,
， The failure diagnosis was interrupted at that point. However, for example, as described above, at least 7 seconds are required for the abnormality determination in the failure diagnosis
It takes at least 33 seconds to judge normality
When all of t ₁ , t ₂ , t ₃ and t ₄ are 7 seconds or less, it cannot be judged as normal or abnormal.

In this example, even if it is lower than 400 mmHg at the time,
Time lower than mmHg, ie time between, eg 2
If it is within seconds, the diagnosis continues without interruption. Then, if it is lower than 400 mmHg at the time point and lower than 400 mmHg even after 2 seconds have passed, the diagnosis is interrupted for the first time. This substantially extends the diagnostic time. However, if the fault diagnosis is continuously executed for a predetermined time from the time when the fault is out of the diagnosis area, the following problems occur. I.e. 40 at the time
It becomes lower than 0mmHg, and the accelerator pedal is depressed at this time, and it becomes lower than 80mmHg at that point and is out of the feedback control range. On the other hand, it is assumed that the control current I exceeds 480 mA at the time point and the control current I is forcibly set to 370 mA and the evaporative purge is interrupted after the elapse of 3 seconds at the time point. At this point, the intake pipe negative pressure deviates from the feedback control region, so feedback control is prohibited and the control current I becomes zero. At this time, the open loop control is performed, and the fuel supply amount from the carburetor 4 is forcibly increased for the acceleration increase correction. This makes the air-fuel ratio rich. Next, when the intake pipe negative pressure becomes 80 mmHg or more and enters the feedback control region again, feedback control is started and the control current I skips to 300 mA. If the intake pipe negative pressure becomes 400 mmHg or more at the time and the interval is within 2 seconds, the failure diagnosis is continued even in the interval as described above. On the other hand, the air-fuel ratio becomes rich due to the above-described acceleration increase correction, and therefore the control current I increases, and when it exceeds 480 mA at the time point and 4 seconds elapse as shown by the dotted line, an abnormality determination is made at the time point. In this case, the reason why the control current I becomes 480 mA or more during the interval is not due to a failure but due to the fuel increase correction. The reason why such an erroneous diagnosis occurs is that the failure diagnosis is continued during the failure diagnosis continuation period even though the intake pipe negative pressure is out of the feedback control region.

For this reason, in the present embodiment, even if the interval is within the failure diagnosis continuation period, the failure diagnosis is interrupted at the time when it deviates from the feedback region at the time. Due to the interruption of the failure diagnosis, the evaporative purge is restarted.
At this point, when the fault diagnosis area is entered again, the fault diagnosis is restarted. When the control current I exceeds 480 mA at the time point, the control current I is forcibly set to 370 mA and the evaporative purge is interrupted at the time point 3 seconds after the time point, as shown by the solid line. Then, after the time point, normality or abnormality is determined. Therefore, there is no risk of erroneous diagnosis at the time. Further, the failure diagnosis time can be lengthened as compared with the conventional one like t ₅ , t ₆ , and t ₇ , and the failure diagnosis area can be substantially expanded.

As described above, in this embodiment, it is possible to increase the chances of failure determination by prolonging the diagnosis time without erroneous diagnosis, and it is possible to substantially expand the failure diagnosis area.

Further, for example, when the detection signal of the second negative pressure switch 24 is shared for detecting the diagnostic region of both the air-fuel ratio control and the EGR control, the optimum intake pipe negative pressure in each control is different. , For example, air-fuel ratio control is 300mmH
Assuming that the g and EGR control is optimal at 400 mmHg, the switching negative pressure of the second negative pressure switch 24 is set to 400 mmHg, and the failure diagnosis of the air-fuel ratio control is performed as in this embodiment, thereby switching the second negative pressure switch 24. This is similar to the case where the negative pressure is lower than 400 mmHg, and the failure diagnosis area for air-fuel ratio control is expanded, so that one negative pressure switch can be used under optimal conditions for both diagnoses.

Next, a routine for executing this embodiment will be described with reference to FIG. This routine is executed by interruption at regular time intervals. First, in step 50, the cooling water temperature TW,
It is determined whether the engine speed NE and the vehicle speed V are within the failure diagnosis range. If the determination is negative, the failure diagnosis is not executed. When a positive determination is made, the routine proceeds to step 51, where it is determined whether or not the intake pipe negative pressure VAC is lower than 540 mmHg. VAC is 540
If it is higher than mmHg, for example, 580 mmHg, it is in idle operation and feedback control is not performed, so failure diagnosis is not executed. VAC is lower than 540mmHg, for example
If it is 480 mmHg, the routine proceeds to step 52, where it is judged if VAC is higher than 400 mmHg. If the determination is affirmative, the fault diagnosis is executed in step 53 because it is within the fault diagnosis area.
If a negative determination is made in step 52, VAC is 400 in step 54.
It is determined whether or not 2 seconds have elapsed from when it became lower than mmHg. When 2 seconds have passed, the failure diagnosis is not executed. If 2 seconds have not passed, go to step 55.
It is determined whether VAC is higher than 80 mmHg. If the determination is negative, the failure diagnosis is not executed. That is, even within the failure diagnosis continuation period, the failure diagnosis is interrupted when the intake pipe negative pressure VAC becomes lower than 80 mmHg. If a positive determination is made in step 55, failure diagnosis is executed in step 53.

Although the air-fuel ratio control system of the carburetor has been described in this embodiment, the present invention can be applied to the air-fuel ratio feedback control system of the engine having the fuel injection valve.

〔The invention's effect〕

According to the first and second aspects of the present invention, the failure diagnosis of the air-fuel ratio control system is continued during a predetermined period even if the engine operating state deviates from the failure diagnosis area. The failure diagnosis area of the failure diagnosis device can be expanded, and even when the failure diagnosis area of a plurality of diagnosis items is detected using one engine operating state detection switch, the failure diagnosis area of each diagnosis item can be expanded. It has a common effect that it can be expanded and an optimum failure diagnosis area can be set for each diagnosis item.

According to the second aspect of the present invention, further, even during the failure diagnosis continuation period, if the engine operating state deviates from the air-fuel ratio feedback control region, the failure diagnosis of the air-fuel ratio control system is stopped. By doing so, in addition to the common effects described above, there is an effect that erroneous diagnosis can be further prevented and the accuracy of failure diagnosis can be improved.

[Brief description of drawings]

1A and 1B are configuration diagrams of the present invention, FIG. 2 is an overall configuration diagram showing an embodiment of the present invention, FIG. 3 is an explanatory diagram of failure diagnosis,
FIG. 4 is an operation explanatory diagram of the present embodiment, and FIG. 5 is a flow chart for executing the present embodiment. 12 …… Air bleed tube, 13 …… Linear solenoid valve, 23 …… First negative pressure switch, 24 …… Second negative pressure switch, 25 …… Third negative pressure switch, 30 …… Electronic control unit.

Claims (2)

[Claims] 1. An engine operating state detecting means for detecting an engine operating state, a failure diagnosing means for diagnosing a failure of an engine air-fuel ratio control system when a detection signal of the detecting means is within a failure diagnosing area, and the detection signal. A fault diagnostic device for an air-fuel ratio control system, comprising: fault diagnostic continuation means for continuing the fault diagnostic for a predetermined period from the time when the vehicle deviates from the fault diagnostic region. 2. An engine operating state detecting means for detecting an engine operating state, an air-fuel ratio feedback controlling means for feedback controlling an air-fuel ratio when a detection signal of the detecting means is in an air-fuel ratio feedback control region, and the detecting signal. Is in a failure diagnosis area included in the air-fuel ratio feedback control area, a failure diagnosis means for performing a failure diagnosis of the air-fuel ratio control system, and even if the detection signal deviates from the failure diagnosis area Failure detection continuation means for continuing the failure diagnosis of the air-fuel ratio control system for a predetermined period, and the detection signal is the above even during a period in which the failure diagnosis of the air-fuel ratio control system is continued by the failure diagnosis continuation means. An air-fuel ratio control including failure diagnosis continuation interruption means for interrupting continuation of the failure diagnosis of the air-fuel ratio control system when the air-fuel ratio feedback control is out of the range. System of fault diagnosis system.