JPH048842A - Air-fuel ratio controller for engine - Google Patents

Abstract

PURPOSE:To prevent variation of an air-fuel ratio and stabilize an engine speed by setting a low limit limitter of an air-fuel ratio feedback compensation coefficient according to a temperature in an engine, 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 device, an air-fuel ratio enriching means M1 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 rich means M1, an air-fuel ratio feedback compensation coefficient low limitter set means M2 is provided to a low limit of the air fuel-ratio feedback compensation coefficient according to the temperature of an engine. A feedback compensation quantity by the feedback control is decreased so that lean variation of the air-fuel ratio is prevented, and stabilation of enriching of air-fuel ratio to cope with increase in an engine load is attained.

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.

[Prior Art] 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 for a predetermined period of time to prevent the engine speed from decreasing. For example, in Japanese Patent Application Laid-open No. 60-69246, the basic fuel injection time is increased by a predetermined time in response to the operation of the air conditioner at least during idling, so that the closing of the air conditioner switch during idling is corrected. A technique has been disclosed to prevent lean fluctuations in the air-fuel ratio during idle up due to engine speed.

[3ME 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 addition of the air-fuel ratio and determines that it is rich. , feedback correction is performed to increase the air-fuel ratio.

Therefore, the amount added toward the air-fuel ratio ridge is reduced,
The effect of enriching the air-fuel ratio to cope with an increase in engine load is reduced. Moreover, as the air-fuel ratio addition increases, the feedback correction amount increases in an attempt to bring the air-fuel ratio closer to stoichiometry, resulting in control hunting, resulting in lean fluctuations in the air-fuel ratio, and resulting in unstable engine speed.

[Purpose 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 lower limit setting means M2 is provided for setting the lower limit limiter of the air-fuel ratio feedback correction coefficient according to the engine temperature.

[Operation] In the engine air-fuel ratio control device having the above configuration, when the air-fuel ratio is corrected to the rich side in response to an increase in engine load by the air-fuel ratio enriching means M1, the air-fuel ratio feedback correction coefficient lower limit setting means M2 sets the lower limiter of the air-fuel ratio feedback correction coefficient according to the engine temperature.

Then, when the air-fuel ratio feedback correction coefficient becomes leaner due to the air-fuel ratio rich output from the air-fuel ratio sensor, and becomes smaller than the lower limiter, for example,
Clamped by the lower limiter above.

[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 an explanatory diagram of the air-fuel ratio feedback correction coefficient lower limit map, Fig. 6 is a flowchart showing the procedure for setting the air conditioner increase coefficient, Fig. 7 is the air conditioner increase coefficient as the air conditioner switch is turned on and off,
02 sensor output voltage, air-fuel ratio feedback correction coefficient,
The time chart is 1. There is no fluctuation in the air-fuel ratio.

(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 the engine body 1. A throttle chamber 5 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 chamber 5 via an intake pipe 6.

Further, an intake air amount sensor (a pot wire type air flow meter in the figure) 8 is interposed immediately downstream of the air cleaner 7 in the intake pipe 6, and a throttle valve 5a provided in the throttle chamber etc. 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 controller) Roll valve (ISCV)
5c is interposed.

Further, an injector 10 is disposed immediately upstream of each intake bow 1-2a of each cylinder of the intake manifold 3, and furthermore, an injector 10 is disposed immediately upstream of each intake bow 1-2a of each cylinder of the intake manifold 3, and furthermore, an injector 10 is disposed for each air CI of the cylinder head 2, and its tip is exposed to the combustion chamber. A spark plug 11 is attached.

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, for the above crank shirts l to lb, 1/
A cam rotor 20 is pivotally attached to a camshaft IC that rotates twice, and a cam angle sensor 21 for cylinder discrimination is provided on the outer periphery of the cam rotor 20.

In addition, a cooling water temperature sensor 22 is installed in a cooling water passage (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 an exhaust pipe 23 communicating with the exhaust bow 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 this ECU 3O has a CPU (central processing unit > 31. ROM 32° RAM 33, backup RAM 34, and I10 interface 35). They 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 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 three batteries, 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 buffer tube RAM 34 to hold data.

In addition, the input port of the I10 interface 35 includes the respective 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 fixed data such as a control program and an air-fuel ratio feedback correction coefficient lower limit map to be described later, and the RAM 33 stores output values from each sensor after data processing and the CPU 31
Contains data processed by . Further, the backup RAM 34 stores learning value data and the like, and the stored data is retained even when the key switch 40 is in the OFF state.

The CPU 31 calculates the intake air amount from the output signal of the intake air base 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 flAM 33 and the backup RAM 34. In addition to calculating the fuel v1 injection amount commensurate with the above, the ignition timing is calculated, and the duty ratio of the drive signal to l5CV5c is determined.

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 ignition plug 11 of the corresponding 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 5lot, the output signals from the crank angle sensor 19 and the intake air scene sensor 8 are read, and the engine rotation speed N and intake air iQ are calculated.

Next, the process proceeds to step 5102, and the step 510 described above is performed.
Calculate the basic fuel injection pulse width TI) from the engine speed N calculated in step 1 and the intake air ff1Q.
Q/N: K (constant), proceed to step 5103.

In step 5103, the coolant temperature Tw, throttle opening θ,
The idle switch output signal IO and the air conditioner switch signal AC are read, and the process proceeds to step 5104, where various coefficients such as the air conditioner increase coefficient KACON, the cooling water temperature increase coefficient KTJ, the post-idle increase coefficient KAI, the fuel cut coefficient KFC, etc. are set. Then, in step 5105, various increase correction coefficients C0FF are set from these coefficients (C0
EF 4-K FC (1+K ACON+KTW+K
AI+...).

Next, in step 8106, the air-fuel ratio feedback correction coefficient α is set, and in step 5107, the acceleration tvI
The voltage correction pulse width TSe for interpolating the ineffective injection time of the injector 10 is set based on the quantity coefficient KACC1, the deceleration and increase coefficient KDC1, and the terminal voltage VB of the battery 39, and the process proceeds to step 3108.

In step 6108, the basic fuel injection pulse width Tp calculated in step 5102 is corrected using the air-fuel ratio feedback correction coefficient α set in step 8106, and the various increase correction coefficients C0Er set in step 5105 and the The final fuel injection pulse width Ti is set by correcting the acceleration increase coefficient KACC1 and the deceleration increase coefficient KDC set in step 5107, and adding the voltage correction pulse width TS (Ti 4 - Tll Xα
X (COLr+KACC-KDC) +TS).

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 in FIG. 4).

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,
4.02 Based on the operating state parameters such as the output voltage VAF of the sensor 24, it is determined whether the 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
pm or more), when the basic fuel injection pulse width Tp is equal to or more than the set value TpS (substantially fully open throttle region), or when a fuel cut is executed, it is determined that the condition is not satisfied, and in any other case, and Only when the output voltage VAF 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, if the air-fuel ratio feedback control condition is not satisfied in step 5201, step 520
1, proceeds to step 5202, fixes the air-fuel ratio feedback correction coefficient α to '1.0'' (α←-1,0), exits the routine, and when the air-fuel ratio feedback control condition is satisfied, proceeds to step 5203. 02 sensor 24
Read the output voltage VAr of

Next, the process proceeds to step 5204, and the step 520 described above is performed.
Compare the output voltage ■^) of the 02 sensor 24 read in step 3 with the slice level ■S corresponding to the base air-fuel ratio,
It is determined whether the air-fuel ratio A/F is currently on the rich side or on the lean side.

In step 5204, if it is determined that F≧S, that is, the air-fuel ratio A/F is rich, step 52
Proceeding from step 04 to step 5205, the rich/lean switching determination flag [LAGl = cellar l-(FLAGl =
l) Determine whether or not it has been done.

The rich/lean switching discrimination flag F[^G1 is the reversal of the output voltage of the 02 sensor 24 from the air-fuel ratio one side to the air-fuel ratio rich side, or the air-fuel ratio lean from the air-fuel ratio rich side. When the air-fuel ratio is reversed from the lean side to the rich side, the value changes from 1 to 0.
With the reversal from the air-fuel ratio rich side to the air-fuel ratio lean side, O→1.

Therefore, in step 5205 above, FLAGI = 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 I, and the air-fuel ratio A/F becomes rich. The process proceeds from step 5205 to step 8206, in which the air-fuel ratio feedback correction coefficient α is skipped in the negative direction by the proportionality constant P (α←α−P), and in step 5208, the rich/lean switching discrimination flag [[AGI is cleared. Te(FLAG
I←0) Proceed to step 5213.

Further, in step 5205, if FLAG1=O1, 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, then steps 5205 to 52
The process proceeds to step 07, where the air-fuel ratio feedback correction coefficient α is decreased by the integral constant I (α←α−■), and the process proceeds to step 5213 via the above-mentioned step 8208.

On the other hand, if it is determined in step 5204 that VAF<VS, that is, the air-fuel ratio is on the lean side, step 5
Proceeding from step 204 to step 5209, similarly, rich/
It is determined whether the lean switching determination flag FLAGI is set.

In step 5209, FLAG1=O1, 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 1, so that the air-fuel ratio A/r becomes lean. In this case, the process proceeds to step 5210, where the air-fuel ratio feedback correction coefficient α is skipped in the positive direction by the proportionality constant F) (
α←α+P), and in step 5212 set the rich/lean switching discrimination flag [[AGl (FL
81←1) Proceed to step 5213.

Also, in step 5209 above, [LAGl = 1
In other words, when skipping in the positive direction using the proportionality constant P is performed for the air-fuel ratio feedback correction coefficient α, steps 5209 to 52 are executed.
11, the air-fuel ratio feedback correction coefficient α is increased by the integral constant ■α←α+■), and similarly, step 521
At step 2, the rich/lean switching discrimination flag FLAG1 is set (FLAG1←1) and the process proceeds to step 5213.

Then, step 8208 or step 521
2 to step 5213, it is determined whether the air-fuel ratio feedback correction coefficient α has reached the upper limit value α11, and if α≧α11, that is, step 82 described above is performed.
Air-fuel ratio feedback correction coefficient α after 09 to 5212
is increased and becomes equal to or higher than the upper limit value 08, the process proceeds from step 5213 to step 5214, where the air-fuel ratio correction coefficient α is fixed at the upper limit value α11 (α←α11) and the routine is exited. In step 5213 above,
The process advances to step 5215, where the coolant temperature TIE from the coolant temperature sensor 22 and the ON/OFF state of the air conditioner switch 28 are determined.
The lower limit value α[ of the air-fuel ratio feedback correction coefficient α is read from the air-fuel ratio feedback correction coefficient α lower limit map MPαL using the F state as a parameter, and this lower limit value α[ and the air-fuel ratio feedback correction coefficient α are compared in step 5216.

The above air-fuel ratio feedback correction coefficient lower limit map MPα [
is the lower limit value of the air-fuel ratio feedback correction coefficient α, that is, the lower limit α1. As shown in FIG.
When the air-fuel ratio is enriched by the air conditioner expansion coefficient K ACON, which will be described later, for example, before the engine warm-up is completed at TW<60°C and when TW≧60° This is to change the air-fuel ratio feedback control width after engine warm-up in step C is completed.

Then, when α>αL in step 8216 above,
Exit the routine as it is, and when α≦α[, that is,
If the air-fuel ratio feedback correction coefficient α is decreased through steps 8205 to 8208 described above and becomes equal to or less than the lower limit value αL, steps 8216 to 5217 are performed.
Proceed to and fix the air-fuel ratio correction coefficient α to the lower limit value αL (α
←αL) Exit the routine.

(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. The air-fuel ratio ^/' is enriched.Then, as time passes, the air conditioner increase coefficient K increases.
ACON is reduced and returned to the base air/fuel ratio condition.

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, the air conditioner increase coefficient K ACON is set in step 5302. 0″ K AC
ON←0), air conditioner switch 28 in step 5303
Clear the air conditioner switch switching determination flag F[^G2 (FLAG2←0) to exit the routine.

On the other hand, when the air conditioner switch 28 is ON in step 5301, steps 5301 to 5
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 rLAG2 = 1, that is, the air conditioner switch 28 is already in the ON state, steps 5304 to 5305 are performed.
Proceed to the air conditioner increase coefficient K set in the previous routine.
Subtract the setting value K ACONSET from ACON to reduce the air conditioner increase coefficient K ACON.
ON 4-K ACONKACONSET), proceed to step 8306.

The above set value K ACONSET is set to a relatively small value in order to avoid sudden fluctuations when returning from a rich air-fuel ratio A/F to the base air-fuel ratio.
I'm trying to make the slope smaller.

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 °O'', and if K ACON > O, step 5309 jumps and the air conditioner switch switching determination flag is set. [LAG2 is set to Sera l-([LAG2
←1) When exiting the routine and K ACON≦0,
Proceed to Step 5307 and enter the air conditioner increase coefficient K.
Clear ACON (K ACON←0), and similarly, in step 5309, set the air conditioner switch switching determination flag F.
Set LAG2 (Fl, 802←1) and exit the routine.

On the other hand, when FLAG2 = O in step 5304, that is, the air conditioner switch 28 is switched from OFF to ON, the process proceeds from step 5304 to step 8308, where the air conditioner increase coefficient KACON
to the initial value K ACONINI (for example, KACON
INI = 02) to initial cellar l-L (K AC
ON +-K ACONINI), as mentioned above,
In step 5309, the air conditioner switch switching determination flag FLAG2 is set (FLAG2←1) and the routine exits.

That is, conventionally, when the air conditioner switch 28 is turned on and the air-fuel ratio A/F is enriched, the air-fuel ratio formula /F is corrected to the lean side as shown by the broken line in FIG.
In order to make the output voltage V^F of 4 below the slice level ■S, the air-fuel ratio feedback correction coefficient α suddenly decreases, which not only causes hunting of the air-fuel ratio^/[, but also reduces the air-fuel ratio to cope with the increase in load. Enrichment of ^/[ is prevented, and the engine speed N decreases. Moreover, the lean fluctuation of the air-fuel ratio ^/' due to this hunting is significant in the engine low temperature range where the increase correction is large.

In contrast, in the present invention, the air-fuel ratio feedback correction coefficient α is regulated by the lower limiter α set according to the engine temperature, and as shown in FIG. During this period, the air-fuel ratio feedback correction coefficient α is fixed to the lower limiter αL and feedback is stopped, thereby preventing fluctuations in the air-fuel ratio equation /F and preventing a decrease in engine speed due to an increase in load.

[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 lower limit setting means Since the lower limiter of the air-fuel ratio feedback correction coefficient is set according to the engine temperature, the feedback correction amount by feedback control is reduced to prevent lean fluctuations in the air-fuel ratio and reduce the air-fuel ratio to cope with increases in engine load. A rich fuel ratio can be stably achieved. Therefore, excellent effects such as being able to stabilize the engine rotational speed against an increase in load can be achieved.

[Brief explanation of the drawing]

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 1 showing the air-fuel ratio feedback correction coefficient setting procedure, FIG. 5 is an explanatory diagram of the air-fuel ratio feedback correction coefficient lower limit map, and FIG. 6 is a flowchart showing the air-conditioner increase coefficient setting procedure. 1.,
FIG. 7 is a time chart showing the air conditioner increase coefficient, 02 sensor output voltage, air-fuel ratio feedback correction coefficient, and air-fuel ratio fluctuations as the air conditioner switch is turned on and off. Ml...Air-fuel ratio enrichment means M2...Air-fuel ratio feedback correction coefficient lower limiter setting means Fig. 1 Fig. 5 Fig. 3

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 lower limit setting means for setting a lower limit limiter of the air-fuel ratio feedback correction coefficient in accordance with engine temperature 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, characterized by comprising: