JPH08284710A - Engine air-fuel ratio controlling method - Google Patents

Abstract

PURPOSE: To prevent air-fuel ratio from becoming over-riched even immediately after starting an engine with a foot down on an accelerator pedal and releasing the accelerator pedal after the engine has started. CONSTITUTION: An idle switch is judged whether or not it is turned on at the time of starting an engine (S53) and if it is turned off (the throttle valve opened), an after-starting increasing factor KAS of a value higher as compared with that when the idle switch is turned on is set by making reference to a map based on a cooling water temperature Tw (S57), while an attenuation quantity KASS after starting the engine is also set to a value higher than as compared with that at the time of starting the engine with the idle switch turned on (S58). As a result, it becomes KAS=0 at an early stage enabling fuel increase correction to be suddenly reduced by the after-starting increasing factor corresponding to the change of suction air quantity and avoid over-riching of air-fuel ratio immediately after starting the engine even when the suction air quantity is suddenly throttled by starting the engine with the accelerator pedal footed down and released after the engine has started because the after-starting increasing correction factor KAS is attenuated by an attenuation quantity KASS of a high value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine air-fuel ratio control method for setting a post-starting increase coefficient, which is incorporated as a correction term for a basic fuel injection amount, to a different value depending on whether or not a throttle valve at start is fully closed. .

[0002]

2. Description of the Related Art Conventionally, the amount of fuel injected from an injector is corrected by various correction factors in order to set the air-fuel ratio according to all situations. The post-starting increase coefficient is a correction coefficient for stabilizing the engine speed immediately after the engine is started, and is gradually reduced to a value set immediately after the start and eventually becomes 0.

In an engine employing an injector, since the intake air amount at the time of starting is controlled by the opening of an ISC (idle speed control) valve, it is common to start the engine with the accelerator pedal unpressed. However, depending on the driver, it may be possible to start the engine with the accelerator pedal depressed. In such a case, a larger amount of intake air is supplied than in the case of a normal start without the accelerator pedal depressed, so it is necessary to increase the fuel injection amount and prevent the air-fuel ratio from becoming lean.

For example, Japanese Unexamined Patent Publication No. 61-34326 discloses a technique for preventing the air-fuel ratio from becoming lean at the time of starting by correcting the increase coefficient after starting according to the opening of the throttle valve. .

[0005]

By the way, even if the engine is started with the accelerator pedal depressed, it is common to release the accelerator pedal once to prevent the engine from blowing up after the complete explosion of the engine.

When the accelerator pedal that is depressed at the time of starting is released after starting, the intake air amount is sharply throttled. Therefore, if the above-mentioned increase coefficient after starting is reduced with the same amount of attenuation as when the accelerator pedal is not depressed, this amount of intake is absorbed. There is a problem in that the air-fuel ratio becomes overrich without catching up with the amount of decrease in air, and the idle speed becomes unstable.

The present invention has been made in view of the above circumstances. Even if the engine is started with the accelerator pedal depressed, and the accelerator pedal is released after the start, the air-fuel ratio does not become overrich, and good controllability is achieved. It is an object of the present invention to provide an air-fuel ratio control method for an engine that can obtain the above.

[0008]

In order to achieve the above object, an engine air-fuel ratio control method according to the present invention uses a post-starting increase coefficient for increasing and correcting a fuel injection amount immediately after starting based on an engine temperature at starting. In the air-fuel ratio control method of the engine that sets the value and gradually decreases with the set attenuation amount after starting, set the above initial value and the above attenuation amount to a larger value when the throttle valve at start is open than when it is fully closed. It is characterized by doing.

[0009]

[Operation] In the present invention, the throttle valve state is used to determine whether the accelerator pedal at the time of starting is in the unpressed state or in the depressed state, and when the throttle valve is open, a larger value is started than when it is fully closed. The post-increase coefficient is set based on the engine temperature, and immediately after the start, the post-start increase coefficient that has been set to the initial value is gradually decreased with a larger attenuation amount than when the throttle valve is fully closed. As a result, even if the engine is started with the accelerator pedal depressed, the accelerator pedal is released after the start, the throttle valve is fully closed, and the intake air amount is sharply reduced, the air-fuel ratio may become overrich. To be prevented.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 8 shows the overall configuration of the engine. Reference numeral 1 in FIG.
Is an engine, and in the present embodiment is a horizontally opposed engine with a supercharger, and an intake manifold 3 is communicated with the intake ports 2a of the cylinder heads 2 provided on both the left and right banks of the cylinder block 1a, and the intake manifold 3 is upstream of the intake manifold 3. A throttle valve passage 5 is connected to the side collecting portion via an air chamber 4. An air cleaner 7 is attached to the upstream side of the throttle valve passage 5 via an intake pipe 6, and the air cleaner 7 is in communication with an air intake chamber 8. Further, an exhaust pipe 10 is communicated with the exhaust port 2b through an exhaust manifold 9, and a catalytic converter 11 is provided in the exhaust pipe 10 to connect the muffler 1 to the exhaust port 2b.
It is connected to 2.

On the other hand, a throttle valve 5a interlocking with an accelerator pedal is provided in the throttle valve passage 5, an intercooler 13 is provided in the intake pipe 6 immediately upstream of the throttle valve passage 5, and the intake air A resonator chamber 14 is provided downstream of the air cleaner 7 in the pipe 6.

Further, a bypass passage 1 which connects the resonator chamber 14 and the intake manifold 3 and bypasses the upstream side and the downstream side of the throttle valve 5a.
5, an ISC (idle speed control) valve 16 for adjusting the amount of idle air is provided. Furthermore, the above ISC
A check valve 17 that opens when the intake pressure is a negative pressure and closes when the intake pressure is a negative pressure supercharged by a turbocharger 18 is provided immediately downstream of the valve 16.

The compressor of the turbocharger 18 is installed downstream of the resonator chamber 14 in the intake pipe 6, and the turbine is installed in the exhaust pipe 10. Further, a wastegate valve 19 is provided at the turbine housing inlet of the turbocharger 18 and is connected to a wastegate valve operating actuator 20.

The waste gate valve actuating actuator 20 is partitioned into two chambers by a diaphragm, one of which forms a pressure chamber communicating with the waste gate valve controlling duty solenoid valve 21, and the other of which closes the waste gate valve 19. It forms a spring chamber that houses a spring that biases in the direction.

The waste solenoid valve controlling duty solenoid valve 21 is provided in a passage that connects the resonator chamber 14 and the compressor downstream of the turbocharger 18 of the intake pipe 6, and is provided with a controller 50 which will be described later. (See FIG. 9) The pressure on the resonator chamber 14 side and the pressure on the compressor downstream side are adjusted according to the duty ratio of the control signal output to the pressure chamber of the waste gate valve operating actuator 20. Supply.

That is, the wastegate valve control duty solenoid valve 21 is controlled by the control device 50, and the wastegate valve actuating actuator 2 is operated.
By operating 0 to adjust the exhaust gas relief by the waste gate valve 19, the boost pressure by the turbocharger 18 is controlled.

An injector 25 faces the upstream side of each intake port 2a of each cylinder of the intake manifold 3. Further, for each cylinder of the cylinder head 2, a spark plug 26a exposing the tip thereof to the combustion chamber is provided.
Is attached, and an igniter 27 is connected to the ignition plug 26a via an ignition coil 26b arranged for each cylinder.

The injector 25 includes a fuel tank 2
Fuel is pressure-fed from an in-tank type fuel pump 29 provided inside 8 through a fuel filter 30, and a pressure regulator 31 regulates the fuel pressure to the injector 25.

Next, the arrangement of the sensors will be described.
Reference numeral 22 denotes an absolute pressure sensor, which selectively detects the intake pipe pressure (intake pressure in the intake manifold 3) and the atmospheric pressure by the intake pipe pressure / atmospheric pressure switching solenoid valve 23. Further, a thermal type intake air amount sensor 32 using a hot wire or a hot film is provided immediately downstream of the air cleaner 7 of the intake pipe 6, and the throttle valve 5a is provided with
A throttle sensor 33 having a built-in throttle opening sensor 33a and an idle switch 33b that is turned on when the throttle is fully closed is connected in series. Further, a knock sensor 34 is attached to the cylinder block 1a of the engine 1, and a water temperature sensor 36 is exposed to a cooling water passage 35 communicating between the left and right banks of the cylinder block 1a, so that the exhaust manifold 9 of the exhaust pipe 10 is exposed. The O2 sensor 37 is exposed to the collecting portion of the. Further, a crank angle sensor 39 is provided on the outer periphery of a crank rotor 38 pivotally attached to the crankshaft 1b, and further, a camshaft 1 is provided.
A cam angle sensor 41 for discriminating a cylinder is provided opposite to a cam rotor 40 that is continuously provided to c.

The crank rotor 38 has protrusions (or slits) formed on the outer periphery thereof at predetermined intervals. In the control device 50, the protrusion interval (or slit) detected by the crank angle sensor 39 is calculated from the input interval time. A cylinder for fuel injection and a cylinder for ignition are calculated from an interrupt signal when the engine speed NE is calculated and a projection (or slit) for cylinder discrimination formed on the outer circumference of the cam rotor 40 is detected by the cam angle sensor 41. Cylinder discrimination of a cylinder is performed.

The above fuel injection control, ignition timing control, idle speed control, etc. are executed by the control device 50 shown in FIG. The control device 50 includes a main computer 51 that performs fuel injection control, ignition timing control, idle speed control, and the like, and a sub computer 5 dedicated to knock detection processing.
2 and 2 and mainly includes a constant voltage circuit 53 for supplying a predetermined stabilizing power source and various peripheral circuits.

The constant voltage circuit 53 includes an ECU relay 54.
Is connected to the battery 55 via the relay contact of
A relay coil of the ECU relay 54 is connected to the battery 55 via an ignition switch 56,
When the ignition switch 56 is turned on, the EC
When the relay contact of the U relay 54 is closed, control power is supplied to the computers 51 and 52. The battery 55 is directly connected to the backup RAM 61 via the constant voltage circuit 53. The battery 55 includes a fuel pump relay 57.
The fuel pump 29 is connected via the relay contact of the.

The main computer 51 has a CPU 5
8, ROM59, RAM60, backup RAM6
1, a counter / timer group 62, a serial communication interface SCI 63, and an I / O interface 64 are microcomputers connected via a bus line 65, and the backup RAM 61 includes:
Regardless of whether the ignition switch 56 is ON or OFF, backup power is constantly supplied from the constant voltage circuit 53 directly connected to the battery 55 to retain data.

The counter / timer group 62 includes various counters such as a free-run counter, a counter for counting the input of the cam angle sensor signal, a fuel injection timer, an ignition timer,
For convenience, various timers such as a periodic interrupt timer for generating a periodic interrupt, a timer for measuring an input interval of a crank angle sensor signal, and a watchdog timer for monitoring a system abnormality are collectively referred to for convenience. In addition, various software counters and timers are used.

The sub-computer 52, like the main computer 51, has a CPU 71 and a ROM 7.
2, RAM 73, counter / timer group 74, SCI7
5 and the I / O interface 76 is the bus line 7
7, the main computer 51 and the sub computer 52 are connected to each other by a serial communication line via the SCIs 63 and 75.

At the input port of the I / O interface 64 of the main computer 51, an intake air amount sensor 32, a throttle opening sensor 33a, a water temperature sensor 36,
The O2 sensor 37 and the absolute pressure sensor 22 are connected via the A / D converter 66, and the idle switch 33
b, the vehicle speed sensor 42, the starter switch 43, the crank angle sensor 39, the cam angle sensor 41, the lead memory connector 71, and the battery 55 are connected to monitor the battery voltage. The read memory connector 71 is turned on at the time of inspection in a factory inspection line or dealer.
By (connecting), the control in the control device 50 is switched from the normal control mode to the special control mode for checking, and the fuel injection amount is set to a value reduced as compared with the normal control mode.

An igniter 27 is connected to the output port of the I / O interface 64, and
ISC valve 16, injector 25, fuel pump relay 5
7, a waste coil valve controlling duty solenoid valve 21, and an intake pipe pressure / atmospheric pressure switching solenoid valve 23 are connected via a drive circuit 67.

On the other hand, the I / O of the sub computer 52
In the interface 76, the crank angle sensor 39 and the cam angle sensor 41 are connected to the input port, and A
The knock sensor 34 is connected via the D / D converter 78, the frequency filter 79, and the amplifier 80. The knock detection signal from the knock sensor 34 is amplified to a predetermined level by the amplifier 80, and then the frequency filter 79. The necessary frequency components are extracted by the A / D converter 78.
Is converted into a digital signal and input.

The main computer 51 processes detection signals from the sensors and switches to perform fuel injection control, ignition timing control, idle speed control, etc., while the sub-computer 52 controls engine speed and A sample section of the signal from the knock sensor 34 is set based on the engine load, and the signal from the knock sensor 34 is A / D-converted at high speed in this sample section to faithfully convert the vibration waveform into digital data. The presence or absence of knock is determined based on the data.

The output port of the I / O interface 76 of the sub computer 52 is connected to the input port of the I / O interface 64 of the main computer 51, and the knock determination result of the sub computer 52 is I / O. It is output to the interface 76. Then, in the main computer 51, when the knocking occurrence determination result is output from the sub computer 52, knock data is read from the sub computer 52 from the serial communication line via the SCI 63, and immediately based on this knock data The ignition timing of the cylinder is delayed to avoid knock.

In such an engine control system, when the ignition switch 56 is turned on, the ECU relay is released.
54 is turned on, and in the main computer 51, a constant voltage is supplied to each unit via the constant voltage circuit 53 to execute various controls. That is, the main CPU 58 causes the ROM 5 to
Based on the program stored in the memory 9, the detection signals from the sensors and switches input via the I / O interface 64, the battery voltage, etc. are processed, and RA
Various control amounts are calculated based on various data stored in the M60 and the backup RAM 61, fixed data stored in the ROM 59, and the like. And the drive circuit 6
The fuel pump relay 57 is turned on by 7 and the fuel pump 2
9 is energized and driven, and the wastegate valve control duty solenoid valve 2 is driven via the drive circuit 67.
1 to output a duty signal to control supercharging pressure, and to turn on / off the intake pipe pressure / atmospheric pressure switching solenoid valve 23.
The F signal is output, the atmospheric pressure and the intake pipe pressure are alternately detected by the absolute pressure sensor 22, and a drive pulse signal corresponding to the calculated fuel injection pulse width is output to the injector 25 of the corresponding cylinder at a predetermined timing. To perform fuel injection control, output an ignition signal to the igniter 27 at a timing corresponding to the calculated ignition timing to execute ignition timing control, and further output a control signal to the ISC valve 16 to control the idle speed. And so on. Since the sub computer 52 is a computer dedicated to knock detection processing, its operation description is omitted.

The air-fuel ratio control (fuel injection control) executed by the main computer 51 will be described below with reference to the flow charts shown in FIGS. This air-fuel ratio control routine is executed every set time (for example, 10 msec) after turning on the ignition switch 56.

When the controller 50 is powered on by turning on the ignition switch 56, the system is initialized (clearing each flag and each variable value). When the fuel injection pulse width setting routine shown in FIGS. 2 to 4 is executed, first, in step S1, the basic fuel injection pulse width TP per simultaneous injection is calculated from the engine speed NE and the intake air amount Q. To calculate. TP ← K × Q / NE
K: Injector characteristic correction constant After that, in step S2, the operating state of the starter switch 43 is detected, and O
If it is N (starting), the process proceeds to step S3, the starting increase coefficient KST is set to the set value CKST (however, CKST> 1.0), and if OFF, the starting increase coefficient KST is set to 1.0 (start increasing). No correction) is set and the process proceeds to step S5. The above-mentioned start-up increasing coefficient KST is for increasing the fuel amount only at the time of starting during starter motor operation in order to improve engine startability.

In step S5, the mixture ratio allocation coefficient KMR is set based on the basic fuel injection pulse width TP and the engine speed NE. This mixing ratio allocation coefficient KMR is stored in ROM5
The table is set by referring to the table stored at a series of addresses 9 together with interpolation calculation. The table is specified by the basic fuel injection pulse width TP and the engine speed NE which represent the engine load. The optimum coefficient obtained in advance by experiments or the like is stored so that the proper air-fuel ratio can be obtained in each region of the engine operating state. With this mixing ratio allocation coefficient KMR, fine controllability can be obtained even when the injector 25 and the intake air amount sensor 32 are deviated from the uniqueness.

Next, at step S6, the throttle valve opening T detected by the throttle opening sensor 33a is detected.
A full increase coefficient KFULL is set based on h, the basic fuel injection pulse width TP, and the engine speed NE. This full increase coefficient KFULL is used when the throttle valve opening Th indicates that the throttle valve is fully opened or when the basic fuel injection pulse width T
When P indicates a high load state, a table set in advance based on the engine speed NE is referenced with interpolation calculation and set. As a result, when the throttle valve is fully opened, or when the engine is in an operating state in which output is required, such as during high load, fuel is increased and output performance is improved. When the throttle valve opening Th is other than full open and the engine load is other than high load,
KFULL ← 0 is set.

Next, in step S7, the connection state of the read memory connector 71 is detected, and when the special control mode of ON (connection) is selected, the process proceeds to step S8,
The line-off fuel coefficient KPKBA is set based on the cooling water temperature Tw by the water temperature sensor 36, and the process proceeds to step S10. The line-off fuel coefficient KPKBA is for preventing the air-fuel ratio from becoming excessively high when the engine is repeatedly restarted. For example, by turning on (connecting) the read memory connector 71 at the time of inspection at a line end in a factory, that is, an inspection line or a dealer, a special control for checking from a normal control mode is performed. Control mode,
The fuel injection amount is reduced and corrected by the line-off fuel coefficient KPKBA to prevent smoldering of the spark plug 26a due to residual fuel when the engine was stopped last time. Since the air-fuel ratio is controlled to be higher as the cooling water temperature Tw, that is, the lower the engine temperature, the line-off fuel coefficient KPKBA is set so that the decreasing rate increases as the cooling water temperature Tw decreases, as shown in the figure. ing.

Further, the read memory connector 71 is turned off.
When the (open) normal control mode is selected, the routine proceeds to step S9, where the line-off fuel coefficient KPKBA is set to 1.0.
(No correction) is set and the process proceeds to step S10.

In step S10, the water temperature increasing coefficient KTW is set based on the cooling water temperature Tw. This water temperature increase coefficient KTW
Is for increasing and correcting the fuel injection amount in order to ensure drivability when the engine is cold. As shown in the figure, the cooling water temperature T
w, that is, the lower the engine temperature, the higher the fuel increase rate.

Next, in step S11, the post-starting amount-increasing coefficient KAS is set based on the cooling water temperature Tw representing the engine temperature. The post-starting increase coefficient KAS is for ensuring the stability of the engine speed immediately after the engine is started, and is executed by the post-starting increase coefficient setting routine shown in FIG.

The post-starting amount increase coefficient setting routine will be described below. When this routine is executed, the operating state of the starter switch 43 is first determined in step S51,
In step S52, the engine speed NE is referred to. When the starter switch 43 is ON, or when the starter switch 43 is OFF, the engine speed N
When E is NE = 0, it is determined that the engine is starting or is preparing to start, and the process proceeds to step S53. Further, when the starter switch 43 is OFF and the engine speed NE is NE ≠ 0, after starting, And proceeds to step S54.

When it is judged in step S51 or S52 that the engine is being started or is preparing to start, and the process proceeds to step S53, the output of the idle switch 33b is referred to and the accelerator pedal is fully closed when the throttle valve with the idle switch ON is fully closed. It is determined whether the pedal is not stepped on or the throttle valve is open with the idle switch off and the accelerator pedal is stepped on. When it is determined that the idle switch 33b is ON, step S
55, the table MAP1 is referenced with interpolation calculation based on the cooling water temperature Tw to set the initial value KASINI when the throttle valve is fully closed and the accelerator pedal is not depressed. Then, in step S56, the attenuation amount KASS is calculated from the following equation based on the initial value KASINI. KASS ← KASINI / A This A is a fixed value and is a value until the increase coefficient KAS after starting is set to 0 after a lapse of a fixed time after starting, for example, A = 20.
0, that is, the attenuation rate is equivalent to 0.5%, and the calculation cycle is 10
If it is msec, KAS = 0 is set 2 seconds after the start.

Then, in step S59, the initial value KASIN set in step S55 when the accelerator pedal is not depressed
Set the increase coefficient KAS after starting with I and exit the routine.

If it is determined in step S53 that the idle switch 33b is OFF, step S5
7, the table MAP2 is referenced with interpolation calculation based on the cooling water temperature Tw to set the initial value KASINI when the accelerator pedal is opened to open the throttle valve. Then, in step S58, the attenuation amount KASS is calculated from the following equation based on the initial value KASINI. KASS ← KASINI / B This B is a fixed value smaller than the above A. For example, B
= 100, that is, the attenuation rate is equivalent to 1%, and the calculation cycle is
If it is 10 msec, KAS = 0 is set 1 second after starting.

Then, in step S59, the initial value KAS when the accelerator pedal is depressed which is set in step S57 is set.
The post-starting amount increase coefficient KAS is set in INI, the routine is exited, and the process returns to step S12 of the air-fuel ratio control routine.

FIG. 5 shows the above tables MAP1 and MAP2.
The characteristics of the initial value KASINI stored in are shown below. As shown in the figure, the initial value KASINI stored in the table MAP2 that is referred to when the accelerator pedal is depressed, that is, when the throttle valve is opened is the throttle valve fully closed when the accelerator pedal is not depressed. It is set to a value larger than the initial value KASINI stored in the table MAP1 which is referred to at the time of starting. As a result, when the engine is started with the accelerator pedal depressed (throttle valve is open), the fuel injection amount corresponding to the increase in the intake air amount can be obtained.
Lean air-fuel ratio is prevented. Further, in order to make the connection from the starting judgment to the control after starting smooth according to the cooling water temperature TW, both initial values KANSAI are set to a larger value as the cooling water temperature TW is lower.

When the post-starting amount increase coefficient setting routine is executed again after the engine is started, the starter switch 43 is turned off and the engine is rotated (NE ≠ 0), and the steps S51, S52, and then step S54 are performed.
Then, it is determined whether the increase coefficient KAS after starting is 0. Since the post-starting increase coefficient KAS immediately after the start is KAS = KASINI, KAS ≠ 0, and the process proceeds to step S60, where after the start-up increase coefficient KAS is set by a value obtained by subtracting the attenuation amount KASS,
Step S of the air-fuel ratio control routine exiting the routine
Return to 12. Thereafter, the post-starting increase coefficient KAS is gradually decreased in step S60 until the post-starting increase coefficient KAS becomes 0, and when the post-starting increase coefficient KAS becomes 0, the above-mentioned step S54 is performed. Then, the routine is exited as it is, and the process returns to step S12 of the air-fuel ratio control routine.

As a result, as shown by the solid line in step S11 of FIG. 2, in the start with the accelerator pedal depressed, compared to the accelerator pedal unpressed start shown with the broken line in FIG.
In a short time, the amount of increase after startup becomes 0, and the rich air-fuel ratio can be prevented. That is, generally, even when the engine is started with the accelerator pedal depressed, immediately after the start, the accelerator pedal is released to prevent the rotation speed from rising. As a result, immediately after the start, in order to prevent the air-fuel ratio from becoming lean, the post-start amount increase coefficient KAS is set to a large value, but the throttle valve is fully closed by the subsequent release of the accelerator pedal. Attenuation amount KASS and starting increase factor KA
If S is reduced, the time until it becomes 0 becomes long and the air-fuel ratio becomes rich. Therefore, when the throttle valve 5a with the idle switch OFF is opened and started with the accelerator pedal depressed, the attenuation amount KASS of the post-start increase coefficient KAS is greater than when the throttle valve with the idle switch ON is started. Is increased to end the fuel quantity increase correction by the post-start quantity increase coefficient KAS to prevent the air-fuel ratio from becoming rich.

When the routine returns from step S12 of the fuel injection pulse width setting routine shown in FIG. 3 to the post-idle increase coefficient KAI, the post-idle increase coefficient KAI is set. The post-idle amount increase coefficient KAI is for preventing a rattling at the time of releasing the idle, and is set to an initial value based on the cooling water temperature Tw when the vehicle speed is equal to or lower than the set vehicle speed and when the throttle valve is closed to open. After that, as shown, each time the routine is executed, the set value is decreased until it becomes zero.

Next, in step S13, various increase factors COEF are calculated from the following equations. COEF ← KST × (1 + KMR + KFULL + KPKBA × (KTW
Then, in step S14, the air-fuel ratio feedback correction coefficient α for making the air-fuel ratio close to the target air-fuel ratio is set based on the output voltage of the O2 sensor 37, and the correction correction amount for the basic fuel injection pulse width TP is set. The learning correction coefficient KBLRC is set.

Then, in step S15, the basic fuel injection pulse width TP is corrected by the various increase factors COEF, the air-fuel ratio feedback correction factor α, and the learning correction factor KBLRC, which is suitable for one-cylinder one-rotation once injection. The effective pulse width Te is calculated. Te ← TP × α × COEF × KBLRC After that, the routine proceeds to step S16, refers to the normal time control determination flag F1 (initial value is 0), and when F1 = 0 (previous start control), proceeds to step S17 and starts. The normal control discriminating rotation speed NST as a reference value for discriminating between the control and the normal control is updated with a preset setting value NST1 (for example, 500 rpm), and F1 = 1 (previous normal control). Sometimes, the process branches to step S18 to set the normal control determination rotation speed NST to the set value NST2 (where NST1> NST2,
For example, it is updated at 300 rpm) and the process proceeds to step S19.

The normal time control determination flag F1 is set in step S21, which will be described later, in the normal time control, and is cleared in step S35, which will be described later, in the start time control.
In this way, by providing the hysteresis in the normal control discrimination speed NST, as shown in FIG. 6, control hunting at the time of shifting from the starting fuel injection control to the normal fuel injection control is prevented.

In step S19, the engine speed NE
Is compared with the above-mentioned normal-time control determination rotation speed NST, and NE> NS
When T, the routine proceeds to step S20 to execute the normal-time fuel injection control, and when NE ≦ NST, step S20.
23 to execute the fuel injection control at startup.

In the following description, the fuel injection control routine at the start will be described first, and then the fuel injection control routine at the normal time will be described.

When the process branches from step S19 to step S23, the starting injection pulse width Ti0 is calculated by adding the effective pulse width Te to the voltage correction pulse width TS set based on the battery voltage for correcting the invalid time. To do. Ti0 ← Te + TS Then, in step S24, the read memory connector 71 is used.
Is detected, and if it is OFF, the process proceeds to step S25, where the first basic value table TB is determined based on the cooling water temperature Tw.
The basic value TCST is set by referring to LCST with interpolation calculation, and when ON, the process branches to step S26 and the second basic value table TBCSTK is referenced with interpolation calculation based on the cooling water temperature Tw. Set TCST, and proceed to step S27.

The basic value TCST is a base value for calculating the cold start pulse width TiST at the start,
As shown in FIG. 7, the lower the cooling water temperature Tw, the larger the value set. In addition, the second memory selected in the special control mode in which the read memory connector 71 shown by the broken line in the figure is ON.
The basic value TCST stored in the basic value table TBCSTK of the read memory connector 71 indicated by the solid line is OF.
The first basic value table selected in the normal control mode of F
It is set to a value smaller than the basic value TCST stored in Bull TBLCST. As described above, the read memory connector 71 is used for the inspection line of the factory or the die.
It is turned on (connected) when the engine is repeatedly restarted at the time of inspections such as LA, and normally it is turned off.
It is in the (open) state.

Therefore, the read memory connector 71 is turned on.
By doing so, a small basic value TCST based on the second basic value table TBCSTK is selected, and the corresponding basic value TCST is selected.
Similarly, the fuel amount is corrected when calculating the start pulse width TiST, and even when restarting is repeated, the spark plug 2
Smoldering of 6a is prevented.

In step S27, the rotation correction coefficient TCSN is set by referring to the table based on the engine speed,
In step S28, the time correction coefficient TKCS is set. As shown in the figure, the time correction coefficient TKCS is fixed at 1.0 for a predetermined time when the starter switch 43 is turned on, and then gradually decreases until it becomes zero. Therefore,
If the starting injection control is not completed within a predetermined time after the starter switch 43 is turned on, the cold start pulse width TiST set in step S31 described later is
It gradually decreases, and finally TiST = 0.

Next, at step S29, the voltage correction coefficient TCSL for compensating the dead time is set by referring to the table with interpolation calculation based on the battery voltage. The voltage correction coefficient TCSL is set to a large value because the ineffective time becomes longer as the battery voltage becomes lower.

Next, at step S30, the throttle opening correction coefficient TCSA is set by referring to the table based on the throttle valve opening Th. The throttle opening correction coefficient TCSA is set to a larger value for increasing correction as the throttle valve opening Th increases.

Then, in step S31, the basic value TCST
Is corrected by the above correction coefficients TCSN, TKCS, TCSL, TCSA to calculate the cold start pulse width TiST. TiST ← TCST × TCSN × TKCS × TCSL × TCSA Then, in step S32, the starting injection pulse width T
i0 is compared with the cold start pulse width TiST to obtain Ti0
When ≧ TiST, the routine proceeds to step S33, where the fuel injection pulse width Ti is set to the starting fuel injection pulse width Ti0, and T
When iO <TiST, the routine proceeds to step S34, where the fuel injection pulse width Ti is set by the cold start pulse width TiST, and then at step S35, the normal control discrimination flag F1 is cleared and the routine returns to step S22 to carry out the fuel injection. Set the pulse width Ti and exit the routine.

In the starting fuel injection control, the starting fuel injection pulse width Ti set in step S22 is set.
Is output as a drive pulse signal to the injectors 25 of all the cylinders at a predetermined timing every engine revolution, and the injectors 25 of all the cylinders simultaneously inject a predetermined amount of fuel.

Here, in the starting fuel injection control,
Starting injection pulse width TiO and cold start pulse width T
By comparing with iST and adopting the larger one as the fuel injection pulse width Ti, the cold start pulse width TiST
Therefore, the connection of the fuel injection amount by the starting injection pulse width TiO is smoothed to prevent the sudden change of the fuel injection amount, suppress the sudden change of the air-fuel ratio, and deteriorate the engine drivability accompanying the sudden change of the air-fuel ratio.
Prevent stalling.

Then, when the engine speed NE increases and eventually NE> NST, it is determined in step S19 that the engine is in a completely detonated state, and the routine proceeds to step S20, where normal-time fuel injection control is performed. In the normal-time fuel injection control, the fuel injection pulse width Ti is set by adding the voltage correction pulse width TS for compensating the invalid time to twice the effective injection pulse width Te. Ti ← 2 × Te + TS That is, in the normal-time fuel injection control, since sequential injection (injection for each cylinder once every two revolutions of the engine) is executed, simultaneous injection by the fuel injection control at startup (one per revolution of the engine is performed). A double fuel amount (2 × Te) is required for the simultaneous injection in all cylinders.

After that, the routine proceeds to step S21, where the normal control discrimination flag F1 is set, and at step S22, the fuel injection pulse width Ti calculated at step S20 is set to exit the routine. In the normal fuel injection control, the fuel injection pulse width Ti set in step S22 is output as a drive pulse signal to the injector 25 of the fuel injection target cylinder at a predetermined timing, and the injector 25 measures a predetermined amount of fuel. Is jetted.

As described above, in this embodiment, when the accelerator pedal is depressed to start the throttle valve in the open state,
By setting the initial value of the post-starting increase coefficient KAS to a larger value than when starting with the throttle valve fully closed when the accelerator pedal is not stepped on, the air-fuel ratio becomes lean as the fuel injection amount corresponding to the increase in the intake air amount. And further, by setting the attenuation amount KASS of the above-mentioned increase coefficient KAS after starting to be larger than the attenuation amount KASS when the accelerator pedal is not depressed,
Since KAS = 0 at an early stage after the start, overriching of the air-fuel ratio immediately after the start is avoided.

[0066]

As described above, according to the present invention,
When the throttle valve is opened at startup, the initial value of the after-start increase coefficient that corrects the amount of fuel injection immediately after startup is set to a larger value than when the throttle valve is fully closed. When the engine is started in the valve open state, a fuel amount increase corresponding to the increase of the intake air amount is obtained, and the lean air-fuel ratio can be prevented.

Further, since the damping amount for gradually decreasing the post-starting increase coefficient after the starting is set to a larger value when the throttle valve is opened than in the case where the throttle valve is fully closed, it is set. Even if the engine is started in the open state and the throttle valve is fully closed after the engine is started, the fuel increase correction by the above-mentioned start increase coefficient is rapidly reduced in response to the sudden narrowing of the intake air amount, and the air-fuel ratio is exceeded. It is possible to prevent rich and obtain good controllability.

[Brief description of drawings]

FIG. 1 is a flowchart showing a routine for setting an increase coefficient after starting.

FIG. 2 is a flowchart showing a fuel injection pulse width setting routine.

FIG. 3 is a flowchart showing a fuel injection pulse width setting routine (continued).

FIG. 4 is a flowchart showing a fuel injection pulse width setting routine (continued).

FIG. 5 is a characteristic diagram of an initial value of an increase coefficient after starting stored in a map.

FIG. 6 is an explanatory diagram showing a switching state between a fuel injection control at startup and a fuel injection control at normal time.

FIG. 7 is a characteristic diagram of a basic value when setting a cold start pulse width stored in a table.

FIG. 8 is an overall schematic diagram of an engine

FIG. 9 is a circuit configuration diagram of an electronic control system.

[Explanation of symbols]

 1 ... Engine 5a ... Throttle valve 25 ... Injector 50 ... Control device KAS ... Increase coefficient after start KASINI ... Initial value KASS ... Attenuation Ti ... Fuel injection amount Tw ... Engine temperature

Claims (1)

[Claims] 1. An air-fuel ratio control method for an engine, wherein an after-start increase coefficient for increasing and correcting a fuel injection amount immediately after a start is set to an initial value based on an engine temperature at a start, and gradually decreased by a set attenuation amount after the start. In the above method, the initial value and the attenuation amount are set to be larger when the throttle valve at the time of starting is opened than when it is fully closed.