JPS6385237A - Failure diagnosis method for air-fuel ratio control system - Google Patents

Abstract

PURPOSE:To make the failure diagnosis easy, by closing a purge control closing valve for a predetermined time when an air-fuel ratio feedback quantity reaches an upper limit and an engine is operated under low load, and determining that an air-fuel ratio control system has failed if the air-fuel ratio feedback quantity reaches the upper limit thereafter. CONSTITUTION:A vaporized fuel adsorbing device 22 is connected through a vaporized fuel pipe 26 to a fuel tank 21, and is also connected through a vaporized fuel pipe 27 to an intake manifold 12. A purge control solenoid valve 28 is provided in the vaporized fuel pipe 27. When it is determined that an engine operational condition satisfies conditions for carrying out failure diagnosis, and when an air-fuel ratio feedback quantity to be obtained according to an output from an exhaust gas sensor 18 reaches an upper limit and an engine load is small, the purge control closing valve is closed for a predetermined time. Under the condition, if the feedback quantity reaches the upper limit thereafter, it is determined that an air-fuel ratio control system has failed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fault diagnosis method for an air-fuel ratio control system for an internal combustion engine.

[Conventional technology]

A three-way catalyst that can simultaneously reduce harmful components HC, Co, and NOx in exhaust gas has the highest purification rate when the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder reaches the stoichiometric air-fuel ratio. Therefore, when using this three-way catalyst, it is necessary to make the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder coincide with the stoichiometric air-fuel ratio.

For this purpose, an auxiliary air supply control valve is provided to control the air-fuel ratio of the air-fuel mixture, and the auxiliary air supply control valve is feedback-controlled based on the output signal of an exhaust gas sensor installed in the exhaust passage. An air-fuel ratio control device is known that controls the air-fuel ratio of air-fuel mixture to match the stoichiometric air-fuel ratio.

On the other hand, mainly to prevent the evaporated fuel in the fuel tank from being released into the atmosphere, the evaporated fuel is first adsorbed in a thin fuel adsorption device, and then this evaporated fuel is transferred into the intake passage along with the atmosphere during engine operation. A vaporized fuel adsorption device that supplies vaporized fuel to fuel vapor is known.

Now, in an internal combustion engine that is equipped with an air-fuel ratio control device and an evaporative fuel adsorption device at the same time, even if the air-fuel ratio control system is normal, depending on the engine operating conditions, the evaporative fuel trapping device traps evaporative fuel into the intake passage. As a result, the air-fuel ratio becomes rich and the feedback amount in the air-fuel ratio control system continues to be at the upper limit value, making it impossible to control the air-fuel mixture to the stoichiometric air-fuel ratio. When a control system is diagnosed for failure, a misdiagnosis is made in order to maintain the feedback amount at the upper limit value.

As a method for diagnosing the failure of an air-fuel ratio control system without being affected by evaporated fuel, the applicant has proposed
In No. 144782, when the feedback amount of the air-fuel ratio substantially reaches the upper limit value, the purge control on-off valve of the evaporative fuel adsorption device is closed for a predetermined period of time, and then the feedback amount substantially reaches the upper limit value. We proposed a fault diagnosis method to determine that the air-fuel ratio control system is malfunctioning.

[Problem that the invention seeks to solve]

In this proposed method, when the purge control on-off valve is closed for fault diagnosis when the amount of fuel vapor evaporation is large, the air-fuel ratio becomes lean, so the feedback amount decreases, but the speed of this decrease is Since this is not so large, the air-fuel ratio temporarily becomes over-lean, which causes a problem in that the engine's drivability temporarily deteriorates.

Furthermore, if the purge control on-off valve is frequently closed, there is a problem in that there is a high possibility that fuel vapor will be released into the atmosphere from the evaporative fuel adsorption device, which may worsen evaporative emissions.

[Means for solving problems]

In order to solve the above problems, the fault diagnosis method according to the present invention closes the purge control on-off valve when the air-fuel ratio is in a lean state without affecting engine operability. The feature is that it performs failure diagnosis.

〔Example〕

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

In Fig. 2, 11 is the engine body, 12 is the intake manifold, 13 is the carburetor, 14 is the exhaust manifold, 15 is the distributor, 16 is the water temperature sensor that detects the engine cooling water temperature, and 17 is the negative pressure inside the intake manifold. 18 is an exhaust gas sensor consisting of an oxygen concentration detector installed in the exhaust passage in the exhaust manifold 14; 19 is a rotation speed sensor attached to the distributor 15;
21 is a fuel tank, 22 is an evaporated fuel adsorption device consisting of a charcoal canister, and 41 is an electronic control unit. An air bleed pipe 24 opens in the main fuel passage 23 of the carburetor 13, and an auxiliary air control J'll solenoid valve 25 is inserted into the air bleed pipe 24. Solenoid valve 25
When the valve opens, auxiliary air is supplied into the main fuel passage 23 through the air bleed pipe 24, thereby changing the amount of fuel supplied from the main fuel passage 23, thereby reducing the amount of air-fuel mixture supplied into the engine cylinder. Air/fuel ratio changes. Therefore, the air bleed pipe 24 forms a supply path for auxiliary air for air-fuel ratio control. In order to control the air-fuel ratio, auxiliary air may be supplied into the intake passage downstream of the carburetor throttle valve, in which case the supply passage is connected to the intake passage downstream of the carburetor throttle valve.

On the other hand, the evaporated fuel adsorption device 22 is connected to the evaporated fuel conduit 2 on the other hand.
6 to the fuel tank 21 and, on the other hand, to the intake manifold 12 via an evaporated fuel conduit 27 . A solenoid valve 28 for purge control is provided in this evaporated fuel conduit 27.
is inserted. The evaporated fuel adsorption device 22 has activated carbon 29 built therein, and the fuel vapor generated within the fuel tank 21 is adsorbed by the activated carbon 29. When the electromagnetic valve 28 opens, the atmosphere is sent into the evaporated fuel conduit 27 through the activated carbon 29, and at this time, the fuel vapor adsorbed by the activated carbon 29 is desorbed from the activated carbon 29 and flows into the evaporated fuel conduit 2 together with the atmosphere.
Sent into 7. Fuel vapor is then fed into the intake manifold 12, such that the evaporated fuel conduit 27 forms a evaporated fuel purge passage.

An electronic control unit (ECU) 41 includes a microprocessing unit 42, a memory 43, and an input board 4.
4 and an output port 45, which are interconnected by a bus 46. Water temperature sensor 16, negative pressure sensor 17
, the exhaust gas sensor 18, the rotation speed sensor 19, the throttle sensor 32 connected to the throttle valve 31, and the choke sensor 34 connected to the choke valve 33 are each connected to an input boat 44, and the output signals of these sensors are inputted. It is stored in the memory 43 via the port 44.

The solenoids of the electromagnetic valves 25, 28 are connected to the output port 45, and are deenergized based on a command signal output from the output port 45, thereby opening and closing the electromagnetic valves 25, 28.

The exhaust gas sensor 18 outputs a voltage signal as shown in FIG. 3 depending on the air-fuel ratio (A/F) of the exhaust gas.

That is, a high voltage signal (rich signal) is output when the air-fuel ratio is in a rich state, a low voltage signal (lean signal) is output when the air-fuel ratio is in a lean state, and a voltage signal of, for example, about 0.45 V is output when the air-fuel ratio is in a stoichiometric state. The ECU 41 controls an air-fuel ratio control system to adjust the operating state of the engine to bring the air-fuel mixture to the stoichiometric air-fuel ratio based on information such as water temperature, engine speed, negative pressure in the intake manifold 12, and opening degree of the throttle valve 31. Determine whether or not the system is in a state of feedback control. If the operating state is in a feedback control state, the fICO 41 calculates a correction value ■, according to the output signal of the exhaust gas sensor 18, so that the air-fuel mixture becomes the stoichiometric air-fuel ratio, as shown in FIG. . The correction value V becomes larger as the air-fuel ratio of the air-fuel mixture becomes richer, and takes an upper limit value 1tmax when the air-fuel ratio becomes richer than a predetermined value, and takes a lower limit value 1ain when the air-fuel ratio becomes leaner than a predetermined value. The ECU 41 then adjusts the opening degree of the solenoid valve 25 of the carburetor 13 based on this correction value vF, changes the amount of air bleed, and controls the amount of fuel supplied into the intake passage.

Furthermore, the ECU 41 performs failure diagnosis of the air-fuel ratio control system, as described below, based on the operating state of the engine and the magnitude of the correction value v2.

FIG. 1 shows a flowchart of a fault diagnosis routine. This routine is interrupted, for example, every 200 m5e.

In step 101, it is determined whether the operating state of the engine satisfies the conditions for fault diagnosis. That is, the opening degree of the choke valve 33 is greater than or equal to a predetermined value, and the engine speed is within a predetermined range (for example, 2000 to 4000).
rpm) and the intake negative pressure is within a predetermined range (for example -
350 to -150 sdg), it is determined that the diagnostic conditions are satisfied and the process proceeds to step 102. If it is determined that the diagnostic conditions are not satisfied, the process proceeds to step 113 and the solenoid valve 28 is opened. Issue the command and exit this routine. In steps 102 and 103, it is determined whether the feedback correction value (2), that is, the feedback 11, is within the normal range L to (2). This normal range II ~1. is the lower limit value login and the upper limit value Ima
x, that is, the lowest value 11 of the normal range is greater than the lower limit 1IIIin, and the highest value I2 of the normal range is smaller than the upper limit Imax. However, if the correction value VF is not within the normal range ■1 to ■2, the process proceeds to step 104 and subsequent steps for fault diagnosis, and the normal range 1
If the value is between + and ■2, there is no need to perform a failure diagnosis, so the process advances to step 113, where a command is issued to open the solenoid valve 28, and this routine is ended.

When diagnosing a failure, first, in step 102, it is determined whether there is a lean abnormality or not, that is, the correction value vF is the lowest value ■.

It is determined whether the correction value V is equal to or less than the minimum value I, and if the correction value V is equal to or less than the minimum value I, the process proceeds to step 105, and the correction value vF is equal to or less than the minimum value 1. If it is larger than , the process proceeds to step 103, where it is determined whether or not there is a rich abnormality (the correction value ■ is greater than or equal to the maximum value I2). If the correction value VF is greater than or equal to the maximum value 11, there is a possibility that a rich fault has occurred, and before diagnosing the rich fault, it is determined in step 104 whether or not the vehicle is currently decelerating.

For example, if the engine speed is higher than 200 rpm and the intake negative pressure is lower than 1300 mm), it is determined that the engine is decelerating. Even if the air-fuel ratio becomes lean during deceleration, engine drivability is hardly affected, so the next step is to diagnose the rich fault (proceed to step 106, close the purge control solenoid valve 28, and step 107).
In this step, the time t of the timer is cleared to 0. When the air-fuel ratio is not decelerating, the engine's drivability will deteriorate, so purge! The control solenoid valve 28 should not be closed, but a command to open the solenoid valve 28 is issued in step 113, and this routine ends.

In step 102, if the correction value (7) is not greater than the maximum value 12, the correction value (2) is less than or equal to the minimum value (2), so a diagnosis of a lean failure will be made next. In the case of diagnosing a lean failure, closing the solenoid valve 28 prevents the air-fuel ratio from shifting too much toward the lean side, so step 104 is performed.
There is no need to execute , and the process advances to step 105.

When diagnosing a failure, first, in step 106, the purge control solenoid valve 28 is closed, and in step 107, the time t of the timer is cleared to 0. In step 108, it is determined whether time t has exceeded a predetermined value. That is, if the predetermined diagnostic waiting time T has not elapsed since the solenoid valve 28 was closed, 1 is added to the time t in step 112 and this routine is ended, and conversely, the diagnostic waiting time T-t-elapsed If so, it is determined in step 109 whether or not the correction value V is normal, that is, the correction value ■ is within the normal range 1. -1
Judge whether it is between 2 or not. If the correction value vF is within the normal range, the purge control solenoid valve 28 is opened in step 113. If it is not within the normal range, the process proceeds to step 110, where it is determined whether the time t has passed the time required to determine an abnormality, that is, the diagnostic time T'. If the diagnosis time T' has not passed, step 11
2, 1 is added to time t, and this routine ends. Conversely, if the diagnostic time T' has passed, an abnormality flag is set in step 111, and then the solenoid valve 28 is opened in step 119, and this routine is ended. When the abnormality flag is set, a warning lamp (not shown) provided on the driver's seat lights up. This concludes this diagnostic routine.

Note that once this diagnostic routine has determined whether or not the air-fuel ratio control system is malfunctioning, it may not be determined again during that run. In other words, the fault diagnosis may be performed only - times while the vehicle is running.

FIG. 5 shows temporal changes in the correction value V and the air-fuel ratio A/F at the time of fault diagnosis using the fault diagnosis routine shown in FIG. 1, and this illustrated example is for a case where the air-fuel ratio control system is normal.

The correction value vF is set to the upper limit value 1o by closing the solenoid valve 28.
From +ax, it descends once at a slope of K11, and then rises (slope of K11).
t) and descending (inclination K11), it approaches the intermediate value between the upper and lower limit values Imax and lm1n. At this time, the air-fuel ratio temporarily changes from a rich state to a lean state (indicated by diagonal iH) by closing the electromagnetic valve 28, and then settles to the stoichiometric air-fuel ratio (λ=1) by feedback control. The reason why the solenoid valve 28 suddenly becomes lean when the solenoid valve 28 is closed is because the correction value V is slow to follow even when the solenoid valve 28 is closed, so the air-fuel ratio control system determines that the air-fuel ratio control system is still in a slightly rich state. This is because the solenoid valve 25 of the carburetor 13 is controlled so that the air-fuel ratio becomes lean. However, when the purge control solenoid valve 28 is closed, the air flow suddenly changes from a rich state to a lean state, but when performing a fault diagnosis because the correction value Vv has reached the upper limit In+ax, the engine decelerates. Even if the air-fuel ratio becomes lean, engine drivability will not be impaired.

In the explanation of the above embodiment, it was assumed that in step 105 of FIG. 1 it was determined whether the engine was decelerating or not, but it is also necessary to detect a state that does not affect drivability even if the air-fuel ratio becomes lean. Therefore, it may be determined whether the engine load is less than or equal to a predetermined value.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to perform a fault i diagnosis without deteriorating the engine drivability, and since the frequency of closing the purge control on-off valve is reduced, fuel is removed from the dim light fuel adsorption device. The amount of steam released into the atmosphere is reduced, and deterioration of evaporative emissions can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a flowchart of a fault diagnosis routine according to an embodiment of the present invention, Fig. 2 is a schematic diagram showing an internal combustion engine to which the present invention is applied, and Fig. 3 shows the relationship between the air-fuel ratio and the output signal of the exhaust gas sensor. FIG. 4 is a graph showing the relationship between the air-fuel ratio and the feedback correction value, and FIG. 5 is a graph showing the temporal change in the air-fuel ratio and the correction value in one embodiment. 14... Exhaust passage, 18... Exhaust gas sensor,
22... Fuel vapor adsorption device, 27... Fuel vapor purge passage, 28... Purge control on-off valve. Lean-A/F-Rich Figure 5

Claims (1)

[Claims] 1. A purge control on-off valve is provided in the evaporated fuel purge passage that connects the evaporated fuel adsorption device and the intake passage, and the air-fuel ratio of the air-fuel mixture is controlled based on the output signal of the exhaust gas sensor installed in the exhaust passage. In an air-fuel ratio control system configured to feedback-control the air-fuel ratio, when the feedback amount of the air-fuel ratio substantially reaches the upper limit and the engine load is small, the purge control on-off valve is closed for a predetermined period of time, and then the feedback control is performed. 1. A failure diagnosis method for an air-fuel ratio control system, comprising determining that the air-fuel ratio control system is malfunctioning if the amount has substantially reached an upper limit value.