JPH05332207A - Air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To overcome the problem of air-fuel ratio enriched in an instant when a solenoid valve is opened by controllably increasing the fundamental inclination of feed-back control according to the opening-closing changing-over operation of the valve in trouble shooting the solenoid valve interposed in a vent path between a canister and intake path. CONSTITUTION:A first solenoid valve 18 is interposed on the way of a purge path 24 interconnecting a canister 16 for adsorbing evaporated fuel generated in a fuel tank 22 and an intake path 6. Also, a second solenoid valve 30 is interposed on the way of an atmospheric port 28 provided on the lower part of the canister 16. While the first solenoid valve 18 opens the second solenoid valve 30 in the trouble shooting by a controller section 32, the first solenoid valve 18 is closed to check whether or not pressure in the fuel tank 22 is then equal to the atmospheric pressure. After the checking, the inclination of feed- back integration constant is enlarged according to the opening of the first solenoid valve 18 as soon as the second solenoid valve 30 is closed, so that a feed-back correcting amount is abruptly reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an internal combustion engine, and more particularly to supplying evaporated fuel from a canister to the internal combustion engine and performing feedback control of the air-fuel ratio.
Moreover, the present invention relates to an air-fuel ratio control device for an internal combustion engine that performs a failure diagnosis of the first solenoid valve.

[0002]

2. Description of the Related Art In a vehicle, evaporated fuel leaking into the atmosphere from a fuel tank, a float chamber of a carburetor, etc. contains a large amount of hydrocarbons (HC) and is one of the causes of air pollution. At the same time, it leads to fuel loss,
Various techniques for preventing this are known.

Further, the air-fuel ratio of the internal combustion engine is feedback-controlled by the controller to bring the air-fuel ratio close to the stoichiometric air-fuel ratio,
There are those that purify exhaust gas.

Then, in the air-fuel ratio control device of the internal combustion engine, the evaporated fuel in the fuel tank is separated (purged) from the canister containing the adsorbent such as the above-mentioned activated carbon and supplied to the internal combustion engine during operation of the internal combustion engine. Some are equipped with control means.

As the air-fuel ratio control system for the internal combustion engine,
There is one disclosed in Japanese Patent Laid-Open No. 62-203039. The self-diagnosis device for an air-fuel ratio control system disclosed in this publication is provided with a pressure switch for detecting the pressure in the fuel tank, and when the pressure switch detects that the pressure in the fuel tank is a predetermined value or more. In addition, the operation of the abnormality determining means is configured to be stopped to avoid erroneous abnormality determination of the air-fuel ratio feedback control system caused by the introduction of the evaporation due to the pressure increase in the fuel tank.

Further, there is one disclosed in JP-A-1-151763. The air-fuel ratio feedback control method for an internal combustion engine disclosed in this publication stops the calculation of the average value of the coefficient that changes according to the output of the exhaust gas concentration detector when the pressure in the fuel tank is higher than a predetermined pressure. ,
The present invention prevents leaning of the supply air-fuel ratio and engine stall due to leaning when the internal combustion engine, to which vaporized fuel in the fuel tank is supplied, shifts to the feedback control operation region.

[0007]

In the conventional air-fuel ratio control system for an internal combustion engine, first of all, when diagnosing a failure of the first solenoid valve arranged in the air passage between the canister and the intake passage, , The second solenoid valve disposed in the middle of the atmospheric port of the canister is opened and the first solenoid valve is closed, and it is confirmed that the pressure in the fuel tank is equal to the atmospheric pressure (see part A in FIG. 4). ).

Next, the second solenoid valve is closed and at the same time the first solenoid valve is closed.
The solenoid valve is opened, and it is determined whether the pressure in the fuel tank drops. If the pressure in the fuel tank drops, it is determined that the first solenoid valve, that is, the purge system is normal. (See B and C in FIG. 4).

However, in the process of diagnosing the failure of the first solenoid valve, at the moment when the second solenoid valve is closed and at the same time the first solenoid valve is opened, a very rich evaporated fuel from the fuel tank is transferred to the first solenoid valve. And is supplied to the internal combustion engine.

As a result, the air-fuel ratio is instantly enriched despite the feedback control of the air-fuel ratio by the control unit, and the feedback control of the air-fuel ratio is too late in the portion B of FIG. 4, which is high. A large amount of carbon monoxide (CO) is emitted, the exhaust gas is not sufficiently cleaned, which is disadvantageous in practical use.

Further, in portions B and C of FIG. 4, the first solenoid valve is closed after the failure of the purge system is determined, so that the supply of rich evaporated fuel to the internal combustion engine is stopped, and the portion of FIG. In the portion D, the air-fuel ratio becomes lean, and there is a disadvantage that drivability deteriorates.

[0012]

Therefore, in order to eliminate the above-mentioned inconvenience, the present invention proposes an evaporation method that occurs in the fuel tank in the middle of a ventilation passage that connects the inside of the fuel tank with the intake passage of the intake system of the internal combustion engine. A canister is provided for adsorbing and holding the fuel and for releasing the evaporated fuel adsorbed and held by the introduction of fresh air to supply it to the intake passage, and a first solenoid valve is provided in the air passage between the canister and the intake passage.
Second in the middle of the atmospheric port that opens the canister to the atmosphere
In an air-fuel ratio control device for an internal combustion engine, which includes a solenoid valve, feedback-controls an air-fuel ratio, and has a control unit for diagnosing a failure of the first solenoid valve, a first section is provided when performing a failure diagnosis of the first solenoid valve. It is characterized in that a function for controlling the feedback control to increase the basic inclination according to the opening / closing switching operation of the solenoid valve is added to the control unit.

[0013]

According to the invention as described above, when diagnosing a failure of the first solenoid valve, the control unit controls the basic inclination of the feedback control to be large in accordance with the opening / closing switching operation of the first solenoid valve. The exhaust gas is sufficiently cleaned and the drivability is prevented from being deteriorated.

[0014]

Embodiments of the present invention will be described in detail below with reference to the drawings.

1 to 3 show an embodiment of the present invention. In FIG. 2, 2 is an internal combustion engine mounted on a vehicle (not shown), 4 is an intake manifold, 6 is an intake passage, and 8 is an intake passage.
Is a surge tank, 10 is a throttle valve, and 12 is evaporated fuel control means. The evaporated fuel control means 12 has a ventilation passage 14, a canister 16, and a first solenoid valve 18 which is a purge valve (VSV).

The evaporation passage 2 forming a part of the ventilation passage 14.
0 has one end communicating with the inside of the fuel tank 22 and the other end opening into the upper portion of the canister 16.

The purge passage 24, which constitutes a part of the ventilation passage 14, has one end opening parallel to the evaporation passage 20 in the upper portion of the canister 16 and the other end having a surge downstream of the throttle valve 10. It communicates with the purge port 26 of the tank 8.

The canister 16 accommodates an adsorbent such as activated carbon that adsorbs and holds the evaporated fuel from the fuel tank 22 side, and the lower atmospheric port 2 according to the operating state of the internal combustion engine 2.
By introducing fresh air from 8, the evaporated fuel adsorbed and held by the adsorbent is released (purged) and made to flow to the purge passage 20 side. In the middle of the atmosphere port 28,
The second solenoid valve 30 is provided.

The first solenoid valve 18 is provided in the middle of the purge passage 24. The first solenoid valve 18 allows the purge passage 24 to be divided into a first purge passage 24-1 and a second purge passage 24-. The first solenoid valve 18 connects and disconnects the first purge passage 24-1 and the second purge passage 24-2.

The first solenoid valve 18 is operated by a control unit 32 for inputting the operating state of the internal combustion engine 2, and the control unit 32 has an O ₂ sensor arranged in an exhaust passage 34 of the internal combustion engine 2. 36 and a tank internal pressure sensor 38 for detecting the pressure in the fuel tank 22 are connected to each other.

The control unit 32 controls the internal combustion engine 2
It has a function of performing feedback control so as to bring the air-fuel ratio of the above into close to the stoichiometric air-fuel ratio and performing a failure diagnosis of the first solenoid valve 18.

Further, the control section 32 includes the first solenoid valve 1
8 is added with a function of controlling the opening / closing switching operation of the first solenoid valve 18 when performing the failure diagnosis, that is, controlling the feedback control to increase the basic inclination of the feedback control.

More specifically, the control unit 32 controls the first solenoid valve 1
In the failure diagnosis of No. 8, first, the second solenoid valve 30 disposed in the middle of the atmospheric port 28 of the canister 16 is opened and the first solenoid valve 18 is closed so that the pressure in the fuel tank is equal to the atmospheric pressure. Make sure that. Then, after the confirmation, at the same time as the closing operation of the second solenoid valve 30, the inclination of the feedback integration constant, which is the basic inclination of the feedback control, is large according to the opening operation of the first solenoid valve 18, that is, as shown in FIG. The correction amount is controlled so as to be rapidly reduced.

Further, the control unit 32 closes the first electromagnetic valve 18 after determining the failure of the first electromagnetic valve 18, so that the slope of the feedback integration constant during the closing operation of the first electromagnetic valve 18. Is large, that is, as shown in FIG. 3, the feedback correction amount is controlled so as to be rapidly increased.

Reference numeral 40 is a check valve disposed in the middle of the evaporation passage 20 and allowing only the flow from the fuel tank 22 to the canister 16 side.

Next, the operation of this embodiment will be described with reference to the flow chart for failure diagnosis of the first solenoid valve 18 in FIG.

In the control unit 32, when the program starts (100), the first solenoid valve 30 disposed in the atmosphere port 28 of the canister 16 is closed when the first solenoid valve 30 is closed.
Judgment whether or not the solenoid valve 18 is in the opening or closing operation (1
02), and if this determination (102) is YES, the slope of the feedback (F / B) integration constant is set to be larger than the normal value (104), and the feedback correction amount is determined by the large slope of the feedback integration constant. Is rapidly changed, and if the determination (102) is NO, the process shifts to the return (110).

Further, after making the slope of the feedback integration constant larger than the normal value, it is judged whether a predetermined time Tsec has passed or whether the output of the O ₂ sensor 36 is inverted (106).

If the judgment (106) is NO, the process is repeated until the judgment (106) becomes YES, and if the judgment (106) is YES, the slope of the feedback integration constant is restored (108). , Return (110).

As a result, in the failure diagnosis of the first solenoid valve 18 in the LA4 mode, when the second solenoid valve 30 is closed,
When the first solenoid valve 18 is opened, the control unit 32 can perform control so as to sharply reduce the feedback correction amount according to the opening operation of the first solenoid valve 18, and when the first solenoid valve 18 is opened, the feedback correction amount can be reduced. Instantaneous enrichment of the fuel ratio can be avoided, the concentration and emission amount of carbon monoxide (CO) can be reduced, and exhaust gas can be sufficiently cleaned, which is practically advantageous.

When the first solenoid valve 18 is closed after the failure determination of the first solenoid valve 18, the supply of rich evaporated fuel to the internal combustion engine 2 is stopped. The control unit 32 can control the feedback correction amount to rapidly increase in accordance with the closing operation of the first solenoid valve 18, so that the air-fuel ratio becomes instantly lean when the first solenoid valve 18 is closed. It can be avoided as much as possible, the time during which drivability deteriorates can be reduced, and the usability can be improved.

Further, since it can be dealt with only by changing the program of the control unit 32, the structure does not become complicated, the manufacture is easy, the cost can be kept low, and the cost is economical. It is advantageous.

The present invention is not limited to the above-mentioned embodiment, but various application modifications are possible.

For example, in the embodiment of the present invention, the control by the control unit is started at the same time as the opening / closing switching timing of the first solenoid valve, but only for a predetermined time from the detection of the opening / closing switching timing of the first solenoid valve. It is also possible to delay and start the control by the control unit.

[0035]

As described in detail above, according to the present invention, the first solenoid valve is provided in the middle of the air passage between the canister and the intake passage, and the second solenoid valve is provided in the middle of the atmosphere port for opening the canister to the atmosphere. In an air-fuel ratio control device for an internal combustion engine, which has a control unit that performs feedback control of the air-fuel ratio and performs failure diagnosis of the first solenoid valve, according to the opening / closing switching operation of the first solenoid valve when performing failure diagnosis of the first solenoid valve. Since the control unit is provided with a function for controlling the feedback control to increase the basic inclination, the basic inclination of the feedback control according to the opening / closing switching operation of the first electromagnetic valve in the failure diagnosis of the first electromagnetic valve. Can be controlled to be large, it is possible to avoid instantaneous enrichment of the air-fuel ratio when the first solenoid valve is opened, and it is possible to reduce the concentration and emission amount of carbon monoxide (CO), Together to obtain sufficiently fulfill the cleaning of air gases, in which the air-fuel ratio at the time of closing of the first solenoid valve is able to avoid the lean instantaneously, can reduce the time to deterioration in drivability.

[Brief description of drawings]

FIG. 1 is a flow chart for failure diagnosis of an air-fuel ratio control system for an internal combustion engine showing an embodiment of the present invention.

FIG. 2 is a schematic diagram of an air-fuel ratio control device for an internal combustion engine.

FIG. 3 is a time chart at the time of failure diagnosis of the air-fuel ratio control device of the internal combustion engine.

FIG. 4 is a time chart at the time of failure diagnosis of the air-fuel ratio control device for the internal combustion engine showing the conventional technique of the present invention.

[Explanation of symbols]

2 Internal Combustion Engine 4 Intake Manifold 6 Intake Passage 8 Surge Tank 10 Throttle Valve 12 Evaporative Fuel Control Means 14 Ventilation Passage 16 Canister 18 First Solenoid Valve 20 Evaporation Passage 22 Fuel Tank 24 Purge Passage 28 Atmosphere Port 30 Second Solenoid Valve 32 Control Unit 34 Exhaust passage 36 O ₂ sensor 38 Tank internal pressure sensor 40 Check valve

Claims (1)

[Claims] 1. An evaporative fuel generated in the fuel tank is adsorbed and held in the middle of a ventilation passage that connects the inside of the fuel tank with an intake passage of an intake system of the internal combustion engine, and the adsorbed and retained evaporative fuel is separated by introducing fresh air. A canister for supplying the intake air to the intake passage, a first solenoid valve provided in the air passage between the canister and the intake passage, and a second solenoid valve provided in the air port for opening the canister to the atmosphere. Feedback control of the fuel ratio and the first
In an air-fuel ratio control device for an internal combustion engine having a control unit for diagnosing a failure of a solenoid valve, when performing a failure diagnosis of the first solenoid valve, a basic gradient of feedback control is set in accordance with an opening / closing switching operation of the first solenoid valve. An air-fuel ratio control device for an internal combustion engine, wherein the control section is provided with a function of controlling to be large.