JPH02248638A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To uniformize an air-fuel ratio by correcting the learning value of fuel vapor purging quantity at the time of idle purging on the basis of the output of an exhaust gas sensor, and setting the correction value of the learning control every cylinder at the time of idling up. CONSTITUTION:When an internal combustion engine (b) is in the idling operating state, and fuel vapor is purged in an intake passage, a fuel vapor purging quantity learning means (d) learns the purging quantity of fuel vapor on the basis of the output voltage of an exhaust gas sensor (c), and corrects the learning value. When an intake air is given through a bypass intake passage for idling up, a cylinder-based correction value setting means (f) sets correction values every cylinder according to the intra-cyclindrical distributing characteristic of the purged fuel vapor at that time. Based on the correction value determined according to the purging quantity of fuel vapor, a fuel injection quantity correcting means (e) corrects the fuel injection quantity by each fuel injector (a). Hence, the unevenness of air-fuel ratio in each cylinder can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an air-fuel ratio control device for an internal combustion engine, and particularly to an air-fuel ratio control device that controls an air-fuel ratio in connection with purging of fuel vapor.

[Prior art] Fuel vapor generated in a fuel tank or the like is guided to a fuel vapor adsorption device such as a charcoal canister, and the fuel vapor adsorbed in the fuel adsorption device is purged into the intake passage with negative pressure in the intake pipe, and the fuel vapor is released into the atmosphere. Prevention of release into the internal combustion engine of vehicles such as automobiles has conventionally been carried out. It has also been considered to purge fuel vapor into the intake passage even during idling operation by opening a solenoid valve provided in the middle of the fuel vapor purge passage at high temperatures when a large amount of fuel vapor is generated.

Purging of fuel vapor during idling operation is started or stopped by opening and closing a solenoid valve provided in the fuel vapor purge passage. Therefore, when the solenoid valve is opened or closed, the amount of fuel vapor purged to the intake passage is reduced. Change suddenly. For this reason, according to normal air-fuel ratio feedback control, considering the air-fuel ratio control speed specific to feedback control, when starting or stopping an idle barge where the amount of fuel vapor purge changes suddenly, the air-fuel ratio may not be properly adjusted at times. The value deviates greatly from the value, and a so-called overrich or overlean phenomenon occurs. To prevent this, the purge amount of fuel vapor to the intake passage is determined by learning control, and based on this, the fuel supply amount during idle purge is corrected to prevent overrich or overlean phenomena when starting or stopping idle purge. It has already been proposed to prevent this from occurring, as shown in, for example, Japanese Patent Publication No. 60-222534.

The learning control of the purge amount of fuel vapor is based on the average value of the skip-by-skip air-fuel ratio feedback control signal that is skipped every time the output voltage of an exhaust gas component sensor such as the 02 sensor changes across a predetermined reference voltage. This is done by correcting the learned value using a predetermined correction value for each skip that deviates from the control center value in the balanced state.

[Problems to be Solved by the Invention] The purge port for purging fuel vapor during idling operation is preferably located directly below the throttle valve in order to ensure good mixing of fuel vapor and intake air, considering the distribution of fuel vapor between cylinders. , For this reason, the idle purge port is provided directly below the throttle valve.

However, if the idle purge port is provided directly under the throttle valve, the supply port for the intake passage of the bypass intake passage used to increase the idle in air conditioners may not be provided directly below the throttle valve due to space constraints. For this reason, the supply port of the bypass intake passage may be unavoidably provided at a position where good distribution between cylinders cannot be achieved.

In such a case, good intake air distribution characteristics between the cylinders are maintained during non-idle-up mode when intake air is not supplied from the supply port of the bypass intake passage, but at idle-up mode when intake air is supplied from the supply port of the bypass intake passage. Sometimes, the distribution characteristics of intake air between cylinders deteriorate. Therefore, during idle up, the distribution characteristics between the cylinders of the fuel vapor purged into the intake passage at this time also deteriorate, and the disturbance in the air-fuel ratio between the cylinders increases. In this case, even if the air-fuel ratio of the engine as a whole reaches a predetermined air-fuel ratio such as the stoichiometric air-fuel ratio, the air-fuel ratio of the cylinders is over-rich, the air-fuel ratio of other cylinders is over-lean, and the output of each cylinder is Torque fluctuates and idle vibration increases.

In view of the above-mentioned problems, the present invention is designed to accurately correct the air-fuel ratio by learning control of the idle purge amount even when the intake air distribution characteristics between the cylinders deteriorates as the idle increases. It is an object of the present invention to provide an improved air-fuel ratio control device to compensate for fuel ratio variations.

[Means for Solving the Problem] According to the present invention, as shown in FIG. In an air-fuel ratio control device for an internal combustion engine using an independent injection method,
An exhaust gas component sensor C changes the output voltage according to the exhaust gas component, and the purge amount of fuel vapor is learned based on the output voltage of the exhaust gas component sensor when fuel vapor is purged into the intake passage during idling operation. a fuel vapor purge amount learning means d to correct the fuel injection amount by the fuel injector a with a correction value determined according to the fuel vapor purge amount learned by the fuel vapor purge amount learning means d; correction means e, and cylinder-specific correction value setting means r for setting the correction value for each cylinder according to the inter-cylinder distribution characteristics of purge fuel vapor at this time when intake air is provided from the bypass intake passage for idle up. This is achieved by an air-fuel ratio control device for an internal combustion engine characterized by having the following.

[Operations and Effects of the Invention] According to the above-described configuration, the learned value of the purge amount of fuel vapor during idle purge is corrected based on the output voltage of the exhaust gas component sensor, and the cylinder-specific correction value is corrected. Since the setting means is provided, a correction value for idle barge learning control is individually set for each cylinder during idle up, and the fuel injection amount for each cylinder is corrected based on this correction value. This prevents the air-fuel ratio in each cylinder from becoming non-uniform even if fuel vapor purge is performed in a state where the inter-cylinder distribution characteristic of intake air is deteriorated during idle up. As a result, even if fuel vapor is purged during idle up, the output torque does not vary from cylinder to cylinder, and highly stable idling performance can be achieved.

[Example] The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 2 shows one embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In the figure, 10 indicates an internal combustion engine, for example, a four-cylinder internal combustion engine, and a surge tank 12 and an exhaust manifold 14 are connected to the internal combustion engine 10, respectively.

The surge tank 12 has a surge tank section 16 and a branch pipe section 18 that distributes and supplies intake air from the surge tank 16 to each cylinder. A fuel injector 20 is attached to each of the branch pipe sections 18 for injecting fuel such as gasoline to each cylinder at individual predetermined times, for example, during the intake stroke.

A throttle body 22 is connected to the surge tank portion 12 of the surge tank 16. The throttle body 22 is provided with a throttle valve 24 that controls the flow rate of intake air to the surge tank 16 .

An idle purge boat 26 is provided directly below the throttle valve 24, that is, downstream of the throttle valve 24 in terms of intake flow, and a normal barge boat 28 is provided upstream of the throttle valve 24. There is.

A bypass intake passage 30 for idle up is provided between the throttle body 22 and the surge tank 12, bypassing the throttle valve 24. The supply boat 32 of the bypass intake passage 30 is provided in the surge tank section 16 of the surge tank 12. The position of this supply boat 32 is not a very good position from the viewpoint of distribution of intake air between cylinders.

An idle up control device 34 is provided in the middle of the bypass intake passage 30. Idle up control device 34
is adapted to control the intake air flow rate flowing through the bypass intake passage 30.

Idle purge boat 26 and conventional barge boat 28 are each connected to charcoal canister 40 by fuel vapor purge passages 36,38. The charcoal canister 40 is connected to the fuel tank 4 by a fuel vapor introduction pipe 42.
4, so that fuel vapor generated in the fuel tank 44 can be supplied.

Idle purge boat 2 from charcoal canister 40
A throttle element 46 for setting the amount of fuel vapor purge and a solenoid valve 48 for opening and closing the passage are provided in the middle of the fuel vapor purge passage 36 leading to the fuel vapor purge passage 36.

The fuel injection amount control by the fuel injector 20, the idle up control by the idle up control device 34, and the idle purge control by opening and closing the solenoid valve 48 are performed by an electronic control device 50 including a microcomputer with a general structure. .

The electronic control unit 50 receives information regarding the intake air amount from an intake air amount sensor 52 such as an air flow meter, information regarding the intake air temperature from an intake temperature sensor 54, and information regarding the intake air temperature from a water temperature sensor 5.
6, information regarding the cooling water temperature of the internal combustion engine 10, information regarding the output rotation speed of the internal combustion engine 10 from the rotation speed sensor 58, and information regarding whether or not the throttle valve 24 is at the idle opening position from the throttle switch 60. The 02 sensor 62 provides information on whether oxygen is present in the exhaust gas, and the air conditioner switch 64 provides information on whether the air conditioner is operating, and the fuel injector 20 injects fuel according to these information. An idle up control device determines the time, and when the air conditioner switch 64 is on, that is, when the air conditioner is operating, additional air is supplied from the supply boat 36 of the bypass intake passage 30 to perform idle up. 34, and the intake air temperature detected by the intake air temperature sensor 54 or the cooling water temperature detected by the water temperature sensor 56 is above a predetermined value, and the throttle valve 24 is at the idle opening position by the throttle switch 60. When this is found, that is, during high temperature idle, the solenoid valve 48 is controlled to open so that fuel vapor is purged from the idle purge boat 26.

Regarding the air-fuel ratio control by fuel injection control, the electronic control device 50 includes a basic injection time calculation means 70 that calculates the basic injection time from the intake air amount and the engine speed, and an 02 sensor 62.
a third step that compares the output voltage of the output voltage with a predetermined reference voltage and skips each time the output voltage changes across the reference voltage;
The air-fuel ratio feedback control signal generating means 72 generates an air-fuel ratio feedback control signal as shown in the figure, and when fuel vapor is purged into the intake passage during idling operation, that is, when the solenoid valve 48 is opened. a purge amount learning means 74 for learning the purge amount of fuel vapor using a predetermined correction value for each skip in which the average value of the air-fuel ratio feedback control signal for each skip deviates from the control center value in the feedback control equilibrium state when the air-fuel ratio feedback control signal is in the feedback control equilibrium state; , cylinder-specific correction value setting means 76 that sets a correction value for learning control by the purge amount learning means 74 for each cylinder when intake air is supplied from the bypass intake passage 30 for idle up, and learning by the purge amount learning means 74. The fuel injection time determining means 78 corrects the basic injection time according to the value and determines the final fuel injection time for each cylinder.

Next, the operation of the air-fuel ratio control device according to the present invention will be explained using FIGS. 4 and 5.

FIG. 4 shows a fuel injection time calculation routine that is executed as an interrupt routine at predetermined time intervals, and in this routine, the basic injection time TP is first calculated. Then, it is determined whether or not idle purge is in progress. When idle purge is not in progress, the basic injection time TP is directly used as fuel injection time TAU, whereas when idle purge is in progress, whether or not the air conditioner is on is determined.
That is, it is determined whether additional air is being supplied to the surge tank 12 from the supply port 32 through the bypass intake passage 30. When the air conditioner is not on, the cylinder distribution characteristics of intake air are good, and at this time, the purge amount learning value FPURG, which indicates the purge amount of fuel vapor, is subtracted from the basic injection time TP, and this is set as the fuel injection time TAU. things are done. In this case, the purge amount correction value for the fuel injection time is uniform for all cylinders.

On the other hand, when the air conditioner is on, it is possible to determine the number of the next fuel injection cylinder and select 2 m Ka + 4 for the cylinder-specific correction coefficient Kl according to this cylinder. be exposed. In addition, KI is a cylinder-specific correction coefficient for the first cylinder, K2 is a cylinder-specific correction coefficient for the second cylinder,
Ka is a cylinder-specific correction coefficient for the third cylinder, and K4 is a cylinder-specific correction coefficient for the fourth cylinder, and these are determined in the idle barge learning routine described later.

Next, the product FPURGψKn of the purge amount learning value FPURG and the cylinder-specific correction coefficient Kn (Kn is 2, 2, 3, or Ka) selected as described above is subtracted from the basic injection time TP, and this is calculated as follows. The fuel injection time of the fuel injection cylinder is set to TAU. In this case, the purge amount correction value for the fuel injection time differs for each cylinder according to the cylinder-specific correction coefficient Kn.

FIG. 5 shows an idle barge learning routine executed as a time interrupt routine. In this learning routine, first, it is determined whether or not idle purge is in progress. When the idle purge is in progress, it is then determined whether the air-fuel ratio feedback control signal as shown in FIG. 2 has been newly skipped. When a new skip occurs, the next step is to calculate the average value FAFAV of the air-fuel ratio feedback control signal for each skip. The calculation of this average value FAFAV may be an arithmetic average value of the maximum value a and the minimum value of the air-fuel ratio feedback control signal for each skip.

Once the average value FAFAV has been calculated, it is then determined whether this average value FAFAV is equal to the control center value 1.0 of the feedback control equilibrium state position. The feedback control balanced state corresponds to when the air-fuel ratio feedback correction value FAF by the air-fuel ratio feedback control signal becomes 1.0, and when it is FAFAV-1, 0, no new correction of the purge amount learning value FPURG is performed. If not, it is determined whether the average value FAFAV is smaller than the control center value 1.0. When FAFAV<1°0, it is assumed that the current purge amount learned value FPURG is smaller than the actual purge amount of fuel vapor, and the purge amount learned value FPURG is corrected to increase with a correction value α. On the other hand, when FAFAV<1.0, it is assumed that the current purge amount learned value FPURG is larger than the actual fuel vapor purge amount, and this purge amount learned value FPU
Decreasing correction of RG with a correction value α is performed.

Next, according to the purge amount learning value FPURG, the cylinder-specific correction coefficient KI of each cylinder is set to 2. Then, 31 K< is determined from a data map of characteristics as shown in FIG. Correction coefficient K for each cylinder.

K2, 3 * K4 is the surge tank 1 from the supply boat 32 of the bypass intake passage 30 for idle up.
2, it is determined according to the uneven distribution of intake air into the cylinders that occurs when additional air is supplied. Ru.

With the above configuration, when additional air is supplied to the surge tank 12 from the bypass intake passage 3° and the intake air distribution characteristics between cylinders deteriorates, - is added to the above-mentioned cylinder-specific correction coefficient.
At step 4, the fuel injection amount is corrected by idle purge individually for each cylinder, thereby preventing the air-fuel ratio from becoming uneven among the cylinders and making the air-fuel ratio in each cylinder uniform.

[Brief explanation of drawings]

FIG. 1 is a diagram corresponding to claims of an air-fuel ratio control device for an internal combustion engine according to the present invention, FIG. 2 is a schematic configuration diagram showing one embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention, and FIG. 3 is a diagram showing the air-fuel ratio control device for an internal combustion engine according to the present invention. FIG. 4 is a flowchart showing the fuel injection time calculation routine; FIG. 5 is the idle purge learning routine in the air-fuel ratio control device according to the present invention. The flowchart, FIG. 6, is a graph showing the correction coefficient characteristics for each cylinder. 10... Internal combustion engine, 12... Surge tank, 14.
...Exhaust manifold, 16...Surge tank part, 1
8... Branch pipe portion, 20... Fuel injector, 22...
...Throttle body, 24...Throttle valve, 26
...Idle purge boat, 28...Purge port, 30...Bypass intake passage, 34...Supply port, 36...Idle up control device, 36.38...
- Fuel vapor purge passage, 40... Charcoal canister, 42... Fuel vapor conduit, 44... Fuel tank,
46... Throttle element, 48... Solenoid valve, 50... Electronic control device, 52... Intake air amount sensor, 54...
Intake temperature sensor, 56... Water temperature sensor, 58... Rotation speed sensor, 60... Throttle switch, 62...
02 sensor, 64... air conditioner switch, 70...
Basic injection time calculation means, 72... Air-fuel ratio feedback control signal generation means, 74... Purge amount learning means, 7
6...Cylinder-specific correction value setting means, 78...Fuel injection time determining means Permission Application Attorney Person Toyota Motor Corporation

Claims (1)

[Claims] In an air-fuel ratio control device for an internal combustion engine with an independent injection system, the fuel injector installed in each cylinder injects fuel into each cylinder at a predetermined time, and changes the output voltage according to the exhaust gas components. a fuel vapor purge amount learning means for learning a purge amount of fuel vapor based on an output voltage of the exhaust gas component sensor when fuel vapor is purged into an intake passage during idling operation; a fuel injection amount correction means for correcting the fuel injection amount by the fuel injector with a correction value determined according to the purge amount of fuel vapor learned by the vapor purge amount learning means; and cylinder-specific correction value setting means for setting the correction value for each cylinder according to the inter-cylinder distribution characteristic of purge fuel vapor at this time when the air-fuel ratio of the internal combustion engine is given. Control device.