JPH048841A - Air-fuel ratio controller for engine - Google Patents

Abstract

PURPOSE:To prevent variation of an air-fuel ratio and stabilize an engine speed by fixing an air-fuel ratio feedback compensation coefficient in a range of air-fuel ratio rich side compensation values from a control central value, when the air-fuel ratio is compensated to the rich side in response to increase in an engine load. CONSTITUTION:In an air-fuel ratio controller, an air-fuel ratio is feedback- controlled by an air-fuel ratio feedback compensation coefficient based on an output of an air-fuel ratio sensor. In this constitution, an air-fuel ratio enriching means M1 which is provided to compensate the air-fuel ratio to the rich side in response to increase in the engine load. When the air-fuel ratio is compensated to the rich side by the air-fuel ratio enriching means M1, an air-fuel ratio feedback compensation coefficient fixing means M2 is provided to fix an air-fuel ratio feedback compensation coefficient in the range of air-fuel ratio rich side compensation values from a control central value. At the time of enriching air-fuel ratio in response to increase in the engine load, compensation to the rich air-fuel ratio side by feedback control is stopped, and lean variation in accordance with control hunting of the air-fuel ratio is prevented so as to stabilize the engine speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio control device for an engine that enriches the air-fuel ratio in order to prevent a decrease in engine speed due to fluctuations immediately after an increase in load.

[Conventional technology 1] Conventionally, in an engine air-fuel ratio control system, when the engine load suddenly increases due to the operation of an air conditioner switch (air conditioner), etc., the air-fuel ratio is enriched to prevent the engine speed from decreasing. For example, Japanese Unexamined Patent Publication No. 60-69246 discloses a method for increasing the basic fuel injection time by a predetermined period of time in response to the operation of the air conditioner at least when the engine is idling. A technique has been disclosed for preventing lean fluctuations in the air-fuel ratio during idle up.

[Problems to be Solved by the Invention] However, in the conventional air-fuel ratio feedback control system, when the air-fuel ratio is enriched, an air-fuel ratio sensor such as the 02 sensor detects the added amount of the air-fuel ratio, and the air-fuel ratio is enriched. It is determined that this is the case, and feedback is provided to normalize the air-fuel ratio.

Therefore, the amount added toward the rich air-fuel ratio decreases,
The effect of enriching the air-fuel ratio to cope with an increase in engine load is reduced. In addition, the larger the air-fuel ratio addition, the greater the feedback that acts to bring the air-fuel ratio closer to stoichiometry, resulting in control hunting, resulting in lean fluctuations in the air-fuel ratio, resulting in unstable engine speed.

[Object of the Invention] The present invention has been made in view of the above circumstances, and aims to stabilize the engine speed by preventing fluctuations in the air-fuel ratio when enriching the air-fuel ratio to cope with an increase in engine load. The purpose of the present invention is to provide an air-fuel ratio control device for an engine that can control the air-fuel ratio of an engine.

[Means for Solving the Problems] In order to achieve the above object, an engine air-fuel ratio control device according to the present invention provides engine air-fuel ratio control that performs feedback control of the air-fuel ratio using an air-fuel ratio feedback correction coefficient based on the output of an air-fuel ratio sensor. In the device, as shown in FIG. 1, the air-fuel ratio enriching means M1 corrects the air-fuel ratio to the rich side in response to an increase in engine load, and the air-fuel ratio enriching means M1 corrects the air-fuel ratio to the rich side. In this case, the air-fuel ratio feedback correction coefficient fixing means M2 is provided for fixing the air-fuel ratio feedback correction coefficient in the range from the control center value to the air-fuel ratio rich side correction value.

[Function] In the engine air-fuel ratio control device having the above configuration, when the air-fuel ratio is corrected to the rich side by the air-fuel ratio enriching means M1 in response to an increase in engine load, the air-fuel ratio feedback correction coefficient fixing means M2 The air-fuel ratio feedback correction coefficient is fixed within the range from the control center value to the air-fuel ratio rich side correction value.

[Embodiments of the invention] Hereinafter, the present invention will be described in detail with reference to the drawings.

Figure 2 and subsequent figures show one embodiment of the present invention, Figure 2 is a schematic diagram of an engine control system, Figure 3 is a flowchart showing a fuel injection control procedure, and Figure 4 shows a procedure for setting an air-fuel ratio feedback correction coefficient. Flowchart, Fig. 5 is a flowchart showing the procedure for setting the air conditioner increase coefficient, and Fig. 6 is a time chart showing changes in the air conditioner increase coefficient, 02 sensor output voltage, air-fuel ratio feedback correction coefficient, and air-fuel ratio as the air conditioner switch is turned on and off. It is.

(Configuration of Engine Control System) Reference numeral 1 in the figure is an engine body, and the figure shows a horizontally opposed four-cylinder engine.The intake manifold 3 is connected to an intake boat 2a formed in the cylinder head 2 of this engine body l. A throttle champer is connected to the upstream side of the intake manifold 3 via an air chamber 4, and an air cleaner 7 is attached to the upstream side of the throttle champer via an intake pipe 6.

Further, an intake air amount sensor (in the figure, a hot wire air flow meter) 8 is interposed immediately downstream of the air cleaner 7 in the intake pipe 6, and a throttle valve 5a provided in the throttle champara is connected to a throttle valve 5a provided in the throttle chamber. A bypass passage 5b is provided with an opening sensor 9a and an idle switch 9b for detecting fully closed throttle valve, and communicates the upstream side and the downstream side of the throttle valve 5a.
Idle speed control valve (ISCV) 5
c is interposed.

Further, an injector 10 is disposed immediately upstream of each intake boat 2a of each cylinder of the intake manifold 3, and a spark plug 11 whose tip is exposed to the combustion chamber is provided for each cylinder of the cylinder head 2. installed.

The injector 10 is communicated with a fuel tank 13 via a fuel supply path 12, and a fuel pump 14 and a fuel filter 1 are connected to the fuel supply path 12 from the fuel tank 13 side.
5 is interposed.

Further, the injector 10 communicates with a pressure regulator 17 via a return passage 16, and the downstream side of the pressure regulator 17 is connected to the fuel tank 1.
It is connected to 3.

Further, a crank rotor 18 is pivotally attached to the crankshaft 1b of the engine main body 1, and this crank rotor 1
A crank angle sensor 19 consisting of an electromagnetic pickup or the like for detecting the crank angle is provided on the outer periphery of the crank angle 8 . Furthermore, 1/2 of the above rank shaft 1b
A cam rotor 20 is pivotally attached to the rotating camshaft 1c, and a cam angle sensor 21 for cylinder discrimination is provided opposite to the outer periphery of the cam rotor 20.

In addition, a cooling water temperature sensor 22 is installed in a cooling water passage 8 (not shown) forming a riser formed in the intake manifold 3.
An air-fuel ratio sensor such as an 02 sensor 24 is provided on the exhaust pipe 23 communicating with the exhaust boat 2b of the cylinder head 2. Note that the reference numeral 25 is a catalytic converter.

(Circuit configuration of control device) On the other hand, reference numeral 30 is a control device (ECU) consisting of a microcomputer, and the CPU 31 . R
OM32. RAM33, backup RAM34,
The I10 interfaces 35 are connected to each other via a pass line 36, and a predetermined stabilized voltage is supplied from a constant voltage circuit 37.

The ECU 3O realizes an air-fuel ratio control function that performs feedback control of the air-fuel ratio using an air-fuel ratio feedback correction coefficient based on the output of the air-fuel ratio sensor, and other functions such as ignition timing control.

The constant voltage circuit 37 is connected to a battery 39 via a control relay 38, and supplies control power to each part when the key switch 40 is turned on and the relay contact of the control relay 38 is closed. It is directly connected to the battery 39, and when the key switch 40 is turned off and the relay contact of the control relay 38 is opened, backup power is supplied to the backup RAM 34 to hold data.

The input port of the I10 interface 35 also includes the sensors 8, 9a, 19.21°22.24,
The idle switch 9b is connected, the positive terminal of the battery 39 is connected, and its terminal voltage VB is monitored, and the vehicle speed sensor 27 and air conditioner switch 28 are also connected.

On the other hand, the spark plug 11 is connected to the output port of the I10 interface 35 via an igniter 26, and the I5C is connected via a drive circuit 41.
V5c, injector 10, and fuel pump 14 are connected.

The ROM 32 stores a control program and fixed data for control, and the RAM 33 stores output values from each sensor after data processing and the CP
Data processed in U31 is stored. Also,
The backup RAM 34 stores learning value data and the like, and the stored data is retained even when the key switch 40 is OFF.

The CPU 31 calculates the intake air amount from the output signal of the intake air amount sensor 8 according to the control program stored in the ROM 32, and calculates the intake air amount based on various data stored in the RAM 33 and the backup RAM 34. In addition to calculating the fuel injection amount commensurate with the above, the ignition timing is calculated, and the duty ratio of the drive signal for l5CV5c is calculated.

Then, a drive pulse width signal corresponding to the fuel injection amount is outputted via the drive circuit 41 to the injector 10 of the corresponding cylinder at a predetermined timing to inject fuel, and via the igniter 26 at a predetermined timing. An ignition signal is output to the spark plug 11 of the cylinder. In addition, when the air conditioner switch 28 is turned on during idling, the above I
5CV5C is driven to control the amount of air in the bypass passage 5b and idle up.

(Operation) Next, the operation of the embodiment having the above configuration will be explained according to the flowcharts shown in FIG. 3 and subsequent figures.

(Fuel Injection Control Procedure) FIG. 3 is a flowchart showing the fuel injection control procedure, which is repeated at predetermined intervals synchronized with engine rotation.

First, in step 5101, 'crank angle sensor 19,
The output signal from the intake air amount sensor 8 is read, and the engine rotation speed N and intake air amount Q are calculated.

Next, the process proceeds to step 5102, and the step 510 described above is performed.
Calculate the basic fuel injection pulse width Tp from the engine speed N and intake air amount Q calculated in step 1. Tp −KXQ/N
:K=constant), the process advances to step 5103.

In step 5103, the coolant temperature Tw, throttle opening θ,
The idle switch output signal ID and the air conditioner switch signal AC are read, and the process proceeds to step 5104, where various coefficients such as the air conditioner volume increase coefficient KACON, the coolant temperature volume increase coefficient KTW, the post-idle volume increase coefficient KAI, the fuel cut coefficient KFC, etc. are set. Then, in step 5105, various increase correction coefficients C0EF are set from these coefficients (C0
EF 4-RFC (1+ K ACON+ KTI4+
KAl+...) Next, in step 3106, the air-fuel ratio feedback correction coefficient α is set based on the output signal of the 02 sensor 24, and in step 5107, the acceleration increase coefficient KACC1, the deceleration increase coefficient KDC1, and the terminal of the battery 39 are set. The voltage correction pulse width TS for interpolating the invalid injection time of the injector 10 is set based on the voltage VB, and the process proceeds to step 8108.

In step 8108, the basic fuel injection pulse width Tp calculated in step 5102 is converted to the basic fuel injection pulse width Tp calculated in step 8106'.
In addition to correcting the air-fuel ratio using the air-fuel ratio feedback correction coefficient α set in step 5105, correction is performed using the various increase correction coefficients C0FF set in step 5105, acceleration increase coefficient KACC1 deceleration increase coefficient KDC set in step 5107, and voltage correction pulse The final fuel injection pulse width Ti is set by adding the width Ts (Ti←'rpxαx
(COEF+KACC-KDC) 10TS).

Then, in step 5109, the drive signal having the fuel injection pulse width Ti set in step 8108 is output to the injector 10 of the corresponding cylinder at a predetermined timing to execute fuel injection, and the routine ends.

(Air-fuel ratio feedback correction coefficient setting procedure) Next, the setting procedure of the air-fuel ratio feedback correction coefficient α will be explained according to the flowchart of FIG.

The program for setting the air-fuel ratio feedback correction coefficient α is a program that is repeated at predetermined time or predetermined intervals. First, in step 5201, engine rotation speed N, basic fuel injection pulse width Tp, cooling water temperature T1,
Based on operating state parameters such as the output voltage VAF of the 1I and 02 sensors 24, it is determined whether air-fuel ratio feedback (F/B) control conditions are satisfied.

This air-fuel ratio feedback control condition is, for example, when the cooling water temperature Tw is below a predetermined value (for example, 50 degrees Celsius or below), and when the engine rotation speed N is above the set rotation speed NS (for example, 5200 r
ps+), when the basic fuel injection pulse width Tp is equal to or greater than the set value T18 (throttle approximately fully open region), and when a fuel cut is executed, it is determined that the condition is not satisfied; otherwise, and Only when the output voltage ■^F of the 02 sensor 24 is equal to or higher than the set value and is in the active state, it is determined that the condition is met.

Then, when the air-fuel ratio feedback control condition is not satisfied in step 5201, step 5201
Then, the process proceeds to step 5202, where the air-fuel ratio feedback correction coefficient α is fixed at “1.0” and α←l.

0), in step 5203, clear the oven loop control determination flag FLAG3 when the air conditioner is operating.
O) When the count value C of the counter CT is cleared in step 5222 and the routine is exited, and the air-fuel ratio feedback control condition is satisfied, the process proceeds from step 5201 to step 5204, where it is determined whether the air conditioner switch 28 is ON or not. .

The open-loop control discrimination flag F and G3 is used to control the air-conditioner switch O when the air-fuel ratio is enriched to prevent the engine speed N from decreasing due to air-conditioner operation, which will be described later.
This is a discrimination flag for switching to oven loop control at N time and for a predetermined period thereafter, and when the air conditioner switch 28 is ON and FLAG3=0, it indicates that the air conditioner switch 28 is turned ON for the first time.

Then, in step 5204 above, the air conditioner switch 28
is OFF, the process proceeds from step 5204 to step 5205 and the open loop control determination flag F is set.
Clear LAG3 FL^G3-0), Step 82
The process advances to 06 and the output voltage VAf of the 02 sensor 24 is read.

Next, in step 5207, the output voltage VAF of the 02 sensor 24 read in step 8206 is compared with a predetermined slice level VS to determine whether the air-fuel ratio A/F is currently on the rich side or lean side. Determine, VAF≧
■When S, that is, the air-fuel ratio A/F is determined to be rich, the process proceeds from step 5207 to step 5208,
Rich/lean switching discrimination flag FLAG1 is set (
FLAGI = 1).

The rich/lean switching discrimination flag FLAGI is determined by the reversal of the output voltage VAF of the 02 sensor 24 from the air-fuel ratio one side to the air-fuel ratio rich side, or from the air-fuel ratio rich side to the air-fuel ratio lean side. The value changes and changes from 1 to O when the air-fuel ratio is reversed from the lean side to the rich side.
With the reversal from the air-fuel ratio rich side to the air-fuel ratio lean side, O→1.

Therefore, in step 5208 above, FLAGl = 1
In the case of , the air-fuel ratio feedback correction coefficient α is skipped in the positive direction by the proportional constant P of the proportional-integral control and then corrected by the integral constant 1, and the air-fuel ratio A/F is in a rich state. Proceeding from step 8208 to step 5209, the air-fuel ratio feedback correction coefficient α is skipped in the negative direction by a proportionality constant P (α←α−P).In step 5211, the rich/lean switching discrimination flag F is set and AGl is cleared. Te(FLAG
1←0) Proceed to step 5222. Furthermore, if FLAGI = O in step 5208, that is, skipping in the negative direction using the proportionality constant P has already been performed on the air-fuel ratio feedback correction coefficient α,
The process proceeds to step 5210, where the air-fuel ratio feedback correction coefficient α is decreased by the integral constant I (α←α−■), and the process proceeds to step 5222 via the above-mentioned step 5211.

On the other hand, if it is determined in step 5201 that VAF<VS, that is, the air-fuel ratio A/F is lean, the process proceeds from step 5207 to step 5212, where the rich/lean switching determination flag FLAGI is similarly set. FLAGl = O, that is, the air-fuel ratio feedback correction coefficient α is skipped in the negative direction by the proportionality constant P, and then gradually reduced by the integral constant ■, so that the air-fuel ratio A/F becomes phosphorus. If this is the case, the process proceeds to step 5213, where the air-fuel ratio feedback correction coefficient α is skipped in the positive direction by the proportionality constant P (α←
α+P), and in step 5215, the rich/lean switching discrimination flag FLAGI is set (FLAG1
←1) Proceed to step 5222. Also, step 5 above
If FLAGl = 1 in step 212, that is, skipping in the positive direction using the proportionality constant P is performed for the air-fuel ratio feedback correction coefficient α, step 5
The process proceeds to step 214, where the air-fuel ratio feedback correction coefficient α is increased by the integral constant ■α←α+I), and similarly, step 52
15, the rich/lean switching discrimination flag FLAG?
is set and the process proceeds to step 5222 (F[AGl-1).

On the other hand, when the air conditioner switch 28 is ON in step 5204, steps 5204 to 8
Proceed to 216 and check the value of the oven loop control determination flag FLAG3 when the air conditioner is operating, and set FLAG3 = Ol.
That is, when the air conditioner switch 28 is turned on for the first time, the process advances to step 5217, and FLAG31,
That is, if the air conditioner switch 28 has already been turned on for a predetermined period of time or more, the process branches from step 8216 to step 5206 and subsequent steps described above.

In step 5217, the count value C of the counter CT that measures the elapsed time after the air conditioner switch 28 was turned on is counted up (C+-C+1), and step 8218
The count value C of the counter CT is set to the set value C3ET.
(For example, a value corresponding to I SeC) is determined.

When C≧CSET in the above step 5218, the oven loop control discrimination flag FLAG3 during air conditioner operation is set in step 5219 (FLAG3←1), and the process proceeds to step 5222 to clear the count value C of the counter CT (C10). Exit the routine, C< C
When SET, the process proceeds from step 8218 to step 5220, and the air-fuel ratio feedback correction coefficient α is set to α.
1. Determine whether or not O.

Then, in step 5220 above, α<1. When O, the air-fuel ratio feedback correction coefficient α is fixed at “1.0” in step 5221 (α←1,0), and α
When ≧1.0, the routine exits from step 5220, and the air-fuel ratio feedback correction coefficient α is fixed at the value at that time.

That is, when the air conditioner switch 28 is turned on, the fuel injection amount is increased by the air conditioner increase coefficient K ACON and the air fuel ratio A/F is enriched. As shown by the broken line, the air-fuel ratio ^/F suddenly decreases to a small value as the air-fuel ratio becomes leaner, and hunting occurs as the air-fuel ratio A/F tries to return to stoichiometry immediately by feedback in response to the air-fuel ratio becoming richer due to air conditioner operation. As a result, the air-fuel ratio ^/F fluctuates as shown by the broken line in FIG. 6, and the engine speed N becomes unstable.

On the other hand, in the present invention, the air conditioner switch 28 is turned OFF.
When the state changes from F to ON, the air-fuel ratio feedback correction coefficient α is maintained for a set time C3ET (for example, 1 sec).
When the value of α<1.0, it is fixed at α=1.0, and when α≧1.0, it is fixed at that value and the air-fuel ratio feedback control is stopped, and oven loop control is performed. The air-fuel ratio A/F is maintained in a rich state.

As a result, fluctuations in the air-fuel ratio A/F are prevented, and the engine speed N can be stabilized without decreasing due to load fluctuations associated with the operation of the air conditioner.

(Air conditioner increase coefficient setting procedure) On the other hand, the air conditioner increase coefficient K ACON in the above-mentioned fuel injection control procedure is set according to the flowchart shown in FIG. A/F is enriched.

Then, as time passes, the air conditioner increase coefficient K A
CON is reduced and returned to the base air-fuel ratio state.

Next, a program for setting the air conditioner increase coefficient will be explained. This program is an interrupt routine that is activated at predetermined intervals. First, in step 5301, it is determined whether or not the air conditioner switch 28 is ON. If the air conditioner switch 28 is OFF, step 5302 is executed.
Set the air conditioner increase coefficient K ACON to O'' with K A
CON←0), air conditioner switch 2 in step 5303
Clear the air conditioner switch switching determination flag F[^G2 (FLAG2←0) to determine whether the air conditioner switch has been switched (FLAG2←0) and exit the routine.

On the other hand, when the air conditioner switch 28 is ON in step 5301, the Stella 75
Proceed to 304 and check the air conditioner switch switching determination flag FL
From the value of AG2, the air conditioner switch 28 changes from OFF to O.
It is determined whether the air conditioner switch 28 has been switched to the N state or whether the air conditioner switch 28 is already in the ON state.

In step 5304, if FLAG2 = 1, that is, the air conditioner switch 28 is already in the ON state, steps 5304 to 5305 are executed.
Proceed to the air conditioner increase coefficient K set in the previous routine.
Subtract the set value K ACONSET from ACON to decrease the air conditioner increase coefficient K ACON (KACON ←
KACON-KACONSET'), step 83
Proceed to 06.

In this case, the set value K ACONSET is set to a relatively small value to avoid sudden fluctuations when returning from the rich air-fuel ratio A/r to the base air-fuel ratio, thereby reducing the slope of the air-fuel ratio A/F. 5 Then, when the process proceeds from step 5305 to step 8306, it is determined whether or not the air conditioner increase coefficient K ACON has reached "0", and if K ACON > O, the process jumps to step 5309. and set the air conditioner switch switching discrimination flag FLAG2 (FL^G2←
1) When the routine is exited and KAC ≦0, the process advances to step 5307 and the air conditioner increase coefficient KAC is
Clear ON (K ACOH-〇), and similarly, in step 5309, set the air conditioner switch switching determination flag FLA.
Set G2 (FL^G2←1) and exit the routine.

On the other hand, when FLAG2 = O in step 5304, that is, the air conditioner switch 28 is not switched from OFF to ON, the process proceeds from step 5304 to step 3308, where the air conditioner increase coefficient KACON
to the initial value K ACONINI (for example, KACON
INI=02) to initial set K ACO
N 4-K ACON (XI), as described above, the air conditioner switch switching determination flag FL is set in step 5309.
Set AG2 (FLAG2-1) and exit the routine.

[Effects of the Invention] As explained above, according to the present invention, when the air-fuel ratio is corrected to the rich side by the air-fuel ratio enriching means in response to an increase in engine load, the air-fuel ratio feedback correction coefficient fixing means Since the fuel ratio feedback correction coefficient is fixed in the range from the control center value to the air-fuel ratio rich side correction value, the air-fuel ratio correction to the lean side by feedback control is stopped when the air-fuel ratio is enriched in response to an increase in engine load. This provides excellent effects such as being able to prevent lean fluctuations due to air-fuel ratio control hunting and stabilizing the engine speed.

[Brief explanation of drawings]

Fig. 1 is a block diagram corresponding to claims showing the basic configuration of the present invention, Fig. 2 and the following show an embodiment of the present invention, Fig. 2 is a schematic diagram of the engine control system, and Fig. 3 is a fuel injection control procedure. FIG. 4 is a flowchart showing the air-fuel ratio feedback correction coefficient setting procedure, FIG. 5 is a flowchart showing the air-conditioner increase coefficient setting procedure, and FIG.
02 sensor output voltage, air-fuel ratio feedback correction coefficient,
5 is a time chart showing changes in air-fuel ratio. Ml...Air-fuel ratio enrichment means M2...Air-fuel ratio feedback correction coefficient fixing means third
figure

Claims (1)

[Scope of Claims] An air-fuel ratio control device for an engine that performs feedback control of an air-fuel ratio using an air-fuel ratio feedback correction coefficient based on the output of an air-fuel ratio sensor, wherein the air-fuel ratio is corrected to the rich side in response to an increase in engine load. a fuel ratio enriching means; and an air-fuel ratio feedback correction coefficient for fixing the air-fuel ratio feedback correction coefficient within a range from a control center value to an air-fuel ratio rich side correction value when the air-fuel ratio is corrected to the rich side by the air-fuel ratio enrichment means. An air-fuel ratio control device for an engine, comprising: a fixing means.