JPH06137242A - Air-fuel ratio control device of engine - Google Patents

Abstract

PURPOSE:To suppress the variation of engine rotating speed so as to reduce discomfortable vibration by making the ignition timing lag or advance corresponding to a dither correction amount when the dither is corrected to the rich side or the lean side. CONSTITUTION:When a key switch 17 is closed, a microcomputer 16 in ECU (control unit) 11 starts to operate and discriminates the operating condition of an engine according to the air intake quantity A detected by an air flow sensor 3, the output RL from an air-fuel ratio sensor 6 and a reference angle signal SG from a turning angle sensor 7. The microcomputer 16 generates an injection signal INJ and an ignition signal IGT according to the operating condition to conduct the fuel injection control and the ignition timing control. At this time, the air-fuel ratio feedback control is conducted by adding dither correction thereto and when the dither correction is the correction to the rich side, the ignition timing of an engine is made lag with an angle corresponding to the dither correction amount. On the other hand, when the dither correction is the correction to the lean side, the ignition timing is made advance with an angle corresponding to the dither correction amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an engine, which feedback-controls an air-fuel ratio detected from exhaust gas components to a target air-fuel ratio.

[0002]

2. Description of the Related Art Conventionally, as an air-fuel ratio control device for an engine of this type, there is one disclosed in, for example, Japanese Patent Publication No. 56-17533. The device disclosed in this publication adds a dither correction to a signal from an air-fuel ratio sensor provided in an exhaust system to obtain a target air-fuel ratio per unit time (for example, an exhaust gas component that maximizes conversion efficiency in a catalyst device is The structure was such that the frequency of crossing the center value of the air-fuel ratio) was increased. That is, the dispersion of the air-fuel ratio distribution is reduced, the conversion efficiency of the three-way catalyst is improved, and the exhaust purification performance is enhanced.

[0003]

However, when the air-fuel ratio feedback control is performed by adding the dither correction to the signal from the air-fuel ratio sensor in this way, the engine speed tends to fluctuate. Body vibrations could occur.

This is because when the air-fuel ratio should be controlled to the rich side, the dither correction becomes correction to the rich side (the air-fuel ratio becomes too rich), or lean (the air-fuel ratio becomes too thin). This is because the dither correction may be a correction to the lean side when it should be controlled to the side. That is,
The degree of becoming richer or leaner with respect to the target air-fuel ratio becomes higher, and the engine speed periodically increases or decreases. The engine speed increases when rich, and decreases when lean.

The present invention has been made in order to solve such problems, and suppresses fluctuations in the engine speed and reduces unpleasant vibration while performing feedback control of the air-fuel ratio with dither correction. It is an object of the present invention to obtain an air-fuel ratio control device for an engine that can perform.

[0006]

The engine air-fuel ratio control system according to the present invention retards the ignition timing in correspondence with the dither correction amount when the dither correction is correction to the rich side, and dither correction. Is a correction to the lean side, the ignition timing is advanced in accordance with the dither correction amount.

[0007]

When the ignition timing is retarded, the engine speed decreases, and when the ignition timing is advanced, the engine speed increases. Therefore, when the feedback control is performed by adding the dither correction, the increase / decrease in the engine speed depends on the ignition timing. It is offset by advancing and retarding.

[0008]

【Example】

Example. 1 Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. 1 is a schematic configuration diagram of an air-fuel ratio control device according to the present invention, FIG. 2 is a block diagram of a control unit, FIG. 3 is a flow chart for explaining the operation of the air-fuel ratio control device according to the present invention, and FIG. 4 is an ignition timing. 5 is a graph showing the advance / retard correction function of.

In these figures, 1 is an engine, an air flow sensor 3 for detecting an air intake amount A of the engine 1 is provided in an intake passage 2 of the engine 1, and an exhaust purification device 5 is provided in an exhaust pipe 4. And an air-fuel ratio sensor 6 is provided. The exhaust gas purification device 5 is a catalyst device, a reactor device, or the like. Further, the air-fuel ratio sensor 6 has a structure for outputting an RL signal to a control unit described later.

Reference numeral 7 denotes a rotation sensor for detecting the number of revolutions of the engine 1 and for generating a reference angle signal SG corresponding to the crank angle. Reference numeral 8 denotes an injector arranged in the intake passage 2 for supplying fuel. Is the injection signal IN
The structure is such that fuel is injected according to J. Reference numeral 9 is a spark plug, and 10 is an ignition device for energizing the spark plug 9. The ignition device 10 has a structure for controlling on / off of a primary current of an ignition coil (not shown) according to an applied ignition signal IGT, and includes an igniter, an ignition coil, a distributor, and the like.

Reference numeral 11 denotes a control unit (hereinafter, simply referred to as ECU) which calculates a fuel injection amount and an ignition timing according to an engine speed and an air intake amount, and injects an injection signal INJ and an ignition signal IGT with reference to a reference angle signal SG. Is output. Here, the configuration of the ECU 11 will be described in more detail with reference to FIG.

As shown in FIG. 2, the ECU 11 comprises input interfaces 12 and 13, a power supply circuit 14, an output interface 15, a microcomputer (microcomputer) 16 connected to these, and the like. The input interface 12 is for taking in the reference angle signal SG from the rotation sensor 7, and the input interface 13 is for taking in the air intake amount A from the air flow sensor 3 and the output RL from the air-fuel ratio sensor 6. is there.

The power supply circuit 14 has a structure in which power is supplied from the battery 18 when the key switch 17 is closed. Further, the output interface 15 outputs the injection signal INJ from the output terminal 19 to the injector 8 and outputs the ignition signal IG from the output terminal 20 to the ignition device 10.
It is for outputting T.

The microcomputer 16 constitutes a control means according to the present invention, and a CPU 21 for performing various calculations and determinations,
RAM 22 and ROM 23 belonging to this CPU 21
And a counter 24 for counting the number of generations of the reference angle signal SG and the like.
And a timer 25 for detecting the lapse of a predetermined time, and an AD for converting the output RL from the air-fuel ratio sensor 6 and the intake air amount A from the air flow sensor 3 input via the input interface 13 into a digital signal. Converter 2
6 and the injection signal IN via the output interface 15.
Output port 27 for outputting J and ignition IGT, etc.
And a bus 28 connecting the CPU 21 and the respective elements 22 to 27.

The CPU 21 performs air-fuel ratio feedback control with dither correction, and when the dither correction is correction to the rich side, retards the ignition timing of the engine 1 at an angle according to the dither correction amount, Moreover, when the dither correction is a lean correction, the ignition timing of the engine 1 is advanced at an angle corresponding to the dither correction amount.

Next, the operation of the air-fuel ratio control device according to the present invention constructed as described above will be described in detail with reference to FIG. The configuration of the ECU 11 will be described in more detail while explaining the operation.

When the key switch 17 is closed, the ECU
The microcomputer 16 in 11 starts to operate, and the engine 1 is operated based on the air intake amount A detected by the air flow sensor 3, the output RL from the air-fuel ratio sensor 6, and the reference angle signal SG from each rotation sensor 7. Determine the operating state of. The microcomputer 16 generates an injection signal ING and an ignition IGT according to the operating state, and performs combustion injection control and ignition timing control.

That is, the ECU 11 has a reference angle B of 75 °.
S at (crank angle position 75 ° before top dead center TDC)
In the G interrupt routine (FIG. 3), first, step S
_As shown in ₁ , the actual engine speed N _e is calculated according to the reference angle signal SG. Next, in step S ₂ , the charging efficiency E _C (E _C ∝A / N _e ) is calculated from the air intake amount A from the air flow sensor 3 and the previously calculated actual engine speed N _e . Then, in step S _{3, the} actual engine speed N
_{Based on e} and the charging efficiency E _C , a basic ignition timing θ _B is obtained by performing a two-dimensional map mapping or the like.

In step S ₄ , the output R of the air-fuel ratio sensor 6
The L signal is compared with a predetermined target value (in this embodiment, the exhaust purification device 5 is set to a value that maximizes the exhaust purification efficiency), and the basic F / B correction value CFBB is calculated.
As the basic F / B correction value CFBB, RL signal the fuel amount if the rich to the target value to the basic fuel injection amount Q _B calculated from the actual engine speed N _e and the charging efficiency E _C To the target value and R
If the L signal is lean, the fuel amount is increased. After the basic F / B correction value CFBB is calculated in this way, the process proceeds to step S ₅ .

In step S _5, the value of DIZZ stored in the RAM 22 as a memory is read. If the value of DIZZ is XDZL, the process proceeds to step S ₆ , if it is XDZR, the process proceeds to step S ₇ , and if 1 For example, it is a conditional branch that proceeds to step S ₈ . The value of DIZZ (XDZ
R, XDZL, 1) are stored in the ROM 23 in advance as data values. This value is, for example, XDZR = 1.1,
It is a fixed value such as XDZL = 0.9.

In step S ₆ , the basic F / B correction value CFBB obtained in step S ₄ is added to the DIZZ value (for example, 0.
9) is multiplied to obtain the target F / B correction value CFB (becomes lean). Along with this, the function value f ( _DIZZ ) by DIZZ as shown in FIG. 4 is added to the basic ignition timing θ _B obtained in the step S ₃ [at this time, if the value of DIZZ is 0.9, f ( _DIZZ ) is The target ignition timing θ _ADV . At this time, the target ignition timing θ _ADV has a value shifted to the advance side with respect to the basic ignition timing θ _B. Then, substitute XDZR for DIZZ and R
Stored in the AM22, the process proceeds to step S _9.

At step S ₇ , the target F / B correction value is multiplied by the basic F / B correction value CFBB by a value of DIZZ (for example 1.1) so that the air-fuel ratio becomes rich, as in step S _6. Calculate CFB. Also, the basic ignition timing θ _B
For example, the function value f is set so that the ignition timing is shifted to the retard side.
( _DIZZ ) [At this time, if the value of DIZZ is 1.1, f (
_DIZZ ) becomes the retard angle side below the horizontal axis] to obtain the target ignition timing θ _ADV . At this time, the target ignition timing θ
_ADV has a value shifted to the retard side with respect to the basic ignition timing θ _B. Then, 1 is assigned to DIZZ and stored in the RAM 22, and the process proceeds to step S ₉ .

The value of DIZZ similarly in principle F / B correction value CFBB and the step S ₆ even Step S ₈ (eg 1)
The target F / B correction value CFB is obtained by multiplying by, and the function value f ( _DIZZ ) [the function value f ( _DIZZ ) becomes 0 if the value of _DIZZ is 1] is added to the basic ignition timing θ _B. To obtain the target ignition timing θ _ADV . At this time, basic ignition timing θ _B = target ignition timing θ _ADV . Then, XDZL is substituted for DIZZ and stored in the RAM 22, and the process proceeds to step S ₉ .

The water temperature sensor by multiplying the target F / B correction value CFB obtained in the step S ₆ to S ₈ to step S ₉ in the basic fuel injection amount Q _B, for detecting the temperature of other various sensors (for example, engine coolant The fuel injection amount Q _INJ is calculated by adding the correction amount based on the output from (1). In step S ₁₀ ,
The fuel injection amount Q _INJ and the target ignition timing θ _ADV are converted into time units and stored in the timer 25. As a result, the microcomputer 16 operates the injector 8 and the spark plug 9 via the output port 27 and the output interface 15.

[0025] Then, after the fuel supply and the ignition is terminated in step S ₁₀ to repeat the above operation returns to step S _1. It should be noted that steps S _{6 to} S ₈ are sequentially switched to steps S ₆ → S ₇ → S _{8 for} each control cycle.

Therefore, when the dither correction is correction to the rich side, the target ignition timing θ _ADV is retarded with respect to the basic ignition timing θ _B by an angle according to the dither correction amount. When the dither correction is a lean correction, the target ignition timing θ _ADV is advanced with respect to the basic ignition timing θ _B at an angle according to the dither correction amount.
If you retard the ignition timing, the engine speed will decrease,
When advanced, the engine speed increases.

That is, if feedback control is performed by adding dither correction, the degree of becoming richer or leaner with respect to the target air-fuel ratio becomes higher, and the engine speed increases or decreases. Is
This is offset by advancing or retarding the ignition timing as described above.

[0028]

As described above, in the engine air-fuel ratio control apparatus according to the present invention, when the dither correction is correction to the rich side, the ignition timing is retarded in accordance with the dither correction amount, and the dither correction is performed. When the correction is to the lean side, the ignition timing is advanced in correspondence with the dither correction amount.
An increase / decrease in the engine speed when feedback control is performed by adding dither correction is offset by advancing / retarding the ignition timing.

Therefore, the air-fuel ratio feedback control can be performed by adding the dither correction to enhance the exhaust gas purification efficiency, and the fluctuation of the engine speed can be suppressed to prevent the unpleasant vibration from occurring.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an air-fuel ratio control device according to the present invention.

FIG. 2 is a block diagram of a control unit.

FIG. 3 is a flowchart for explaining the operation of the air-fuel ratio control device according to the present invention.

FIG. 4 is a graph showing an ignition timing advance / retard correction function f ( _DIZZ ).

[Explanation of symbols]

 1 Engine 3 Air Flow Sensor 5 Exhaust Purification Device 6 Air-Fuel Ratio Sensor 8 Injector 9 Spark Plug 11 Control Unit

Claims (1)

[Claims] 1. An air-fuel ratio control device for an engine, wherein a dither correction is applied to a control signal when performing feedback control so that an air-fuel ratio detected from an exhaust gas component becomes a target air-fuel ratio. A control means for retarding the ignition timing at an angle according to the dither correction amount during correction and advancing the ignition timing at an angle according to the dither correction amount during dither correction to the lean side. An air-fuel ratio control device for an engine, which is provided.