JP2958595B2 - Air-fuel ratio feedback control device for internal combustion engine - Google Patents

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 feedback control device for an internal combustion engine, and more particularly to a technique for improving the convergence of the air-fuel ratio feedback control.

[0002]

2. Description of the Related Art As an air-fuel ratio feedback control device for an internal combustion engine, a rich / lean determination of an actual air-fuel ratio with respect to a target air-fuel ratio (the stoichiometric air-fuel ratio) is determined based on the oxygen concentration in exhaust gas detected by an oxygen sensor. Japanese Patent Application Laid-Open No. 60-240840 discloses a method of performing feedback control of a fuel supply amount to an engine based on a result of the determination so that an actual air-fuel ratio approaches a stoichiometric air-fuel ratio (a target air-fuel ratio). reference).

More specifically, as shown in FIG. 6, when the air-fuel ratio is inverted from rich to lean (lean to rich), the air-fuel ratio feedback correction coefficient α is increased (decreased) by a predetermined proportion in a direction to approach the target air-fuel ratio. After that, the air-fuel ratio feedback correction coefficient α is gradually increased (decreased) by a predetermined integral until the air-fuel ratio is inverted to rich (lean), and the basic fuel injection amount is corrected with the air-fuel ratio feedback correction coefficient α. I am trying to do it.

[0004]

According to the above-described conventional air-fuel ratio feedback control, when the air-fuel ratio is inverted to, for example, lean, the air-fuel ratio detected by the oxygen sensor is reduced to eliminate the lean state. Since the air-fuel ratio feedback correction coefficient α is gradually increased and corrected by the integral control until the air-fuel ratio is richly inverted, it takes time for the air-fuel ratio of the air-fuel mixture actually sucked into the cylinder to be richly inverted. Also, since the air-fuel ratio in the cylinder is already richly inverted, the injection amount is further increased and corrected, so that high convergence is maintained while avoiding control overshoot. There was a problem that was difficult.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a feedback control of an air-fuel ratio of an engine intake air-fuel mixture to a target air-fuel ratio based on a result of a rich / lean determination of an actual air-fuel ratio with respect to a target air-fuel ratio. It is an object of the present invention to obtain high convergence while avoiding occurrence of overshoot.

[0006]

Accordingly, an air-fuel ratio feedback control device for an internal combustion engine according to the present invention is configured as shown in FIG. In FIG. 1, the air-fuel ratio detecting means detects the air-fuel ratio of the engine intake air-fuel mixture, and the reversal determining means compares the air-fuel ratio detected by the air-fuel ratio detecting means with the target air-fuel ratio to obtain a rich air-fuel ratio with respect to the target air-fuel ratio.・ Lean reversal is determined.

The inversion cycle measuring means includes an inversion determination means.
Measures and controls the period of rich / lean reversal determined by
The period setting means is configured to control the inversion cycle measured by the inversion cycle measurement means.
The first control period is set based on the period . On the other hand, the correction amount
Setting means for controlling the first control based on an operating condition of the engine;
A first correction amount used in the control period, and the first control period
The correction amount used in the control period that follows,
A second correction amount smaller than the positive amount is set. And
The feedback correction value setting means is an air-fuel ratio detecting means.
The air-fuel ratio is set so that the detected air-fuel ratio approaches the target air-fuel ratio.
Means for correcting the feedback correction value, wherein
When rich / lean reversal is determined by the reverse determination means
The air-fuel ratio feedback correction value of
Until the first control period elapses after the lean reverse.
During the period, the reference value was corrected by the first correction amount.
Value after the first control period has elapsed.
Holding the reference value at a value corrected by the second correction amount.
You.

Here, air-fuel ratio feedback correction means
Controls the correction of the fuel supply amount to the engine based on the air-fuel ratio feedback correction value set by the feedback correction value setting means .

[0009]

According to this configuration, rich / lean reversal of the actual air-fuel ratio with respect to the target air-fuel ratio is determined, and the air-fuel ratio feedback correction value at the time of the reversal determination is set as a reference value. Then, the reference value is corrected so that the actual air-fuel ratio approaches the target air-fuel ratio.
The first correction is made in the first control period immediately after the air-fuel ratio inversion.
A control period following this first control period,
In the second correction amount smaller than the first correction amount.
It is done.

That is, when the air-fuel ratio reverses to rich or lean, a relatively large correction necessary and sufficient to cancel the rich or lean state and reverse the air-fuel ratio is made in the first step .
By adding during the first control period, the rich / lean state of the air-fuel ratio is eliminated at an early stage .
In the control period after the control period has elapsed, smaller corrections
Overshoot occurs by modifying the amount
Work around.

[0011]

Embodiments of the present invention will be described below. In FIG. 2 showing one embodiment, air is sucked into an internal combustion engine 1 from an air cleaner 2 through an intake duct 3, a throttle valve 4 and an intake manifold 5. The intake manifold 5
In each of the branch portions, a fuel injection valve 6 is provided for each cylinder.

The fuel injection valve 6 is an electromagnetic fuel injection valve which is energized by a solenoid to open, and is deenergized and closed by being energized by an injection pulse signal from a control unit 12 which will be described later. Then, the fuel which is pressure-fed from a fuel pump (not shown) and adjusted to a predetermined pressure by the pressure regulator is injected and supplied to the engine 1. Institution 1
Each of the combustion chambers is provided with an ignition plug 7 for igniting and sparking the mixture by spark ignition. And institution 1
From the exhaust manifold 8, exhaust duct 9, three-way catalyst
Exhaust gas is exhausted through 10 and muffler 11.

The control unit 12 includes a CPU, an RO,
A microcomputer including an M, a RAM, an A / D converter, an input / output interface, and the like is provided. The microcomputer receives input signals from various sensors, performs arithmetic processing as described later, and operates the fuel injection valve 6. Control. As the various sensors, an air flow meter 13 is provided in the intake duct 3, and outputs a signal corresponding to the intake air flow rate Q of the engine 1.

A crank angle sensor 14 is provided to output a reference angle signal REF for each reference piston position and a unit angle signal POS for each crank angle of 1 ° or 2 °. Here, the engine rotation speed Ne can be calculated by measuring the cycle of the reference angle signal REF or the number of occurrences of the unit angle signal POS within a predetermined time. Further, a water temperature sensor 15 for detecting a cooling water temperature Tw of the water jacket of the engine 1 is provided.

An oxygen sensor 16 as an air-fuel ratio detecting means is provided at a collecting portion of the exhaust manifold 8. The oxygen sensor 16 detects the oxygen concentration in the atmosphere (reference oxygen concentration).
An oxygen concentration cell that generates an electromotive force in accordance with the ratio of the oxygen concentration in the exhaust to the exhaust gas, utilizing the sudden change in the oxygen concentration in the exhaust at the stoichiometric air-fuel ratio (the target air-fuel ratio in this embodiment), Only the stoichiometric air-fuel ratio due to a sudden change in output near the stoichiometric air-fuel ratio (rich / lean relative to the stoichiometric air-fuel ratio)
Is a known sensor that can detect the

Here, the CPU of the microcomputer built in the control unit 12 determines the basic fuel injection amount corresponding to the target air-fuel ratio (the stoichiometric air-fuel ratio in this embodiment) based on the intake air flow rate Q and the engine speed Ne. While calculating Tp (basic injection pulse width), the cooling water temperature Tw is calculated.
Various correction coefficients COEF including a basic correction coefficient and an acceleration / deceleration correction coefficient are set based on the above, and further, the actual air-fuel ratio is feedback-controlled to the target air-fuel ratio (the stoichiometric air-fuel ratio) based on the detection result by the oxygen sensor 16. -Fuel ratio feedback correction coefficient (air-fuel ratio feedback correction value) α
Is calculated. Then, the basic fuel injection amount Tp is multiplied by the various correction coefficients COEF and the air-fuel ratio feedback correction coefficient α to obtain an effective injection amount Te (← Tp × COEF × α).
Is calculated, and a correction amount Ts for correcting a change in the effective valve opening time of the fuel injection valve 6 due to a change in the battery voltage is added to the effective injection amount Te. The quantity (injection pulse width) is set as Ti (← Te + Ts).

Further, the control unit 12 outputs an injection pulse signal having a pulse width corresponding to the calculated fuel injection amount Ti to the fuel injection valve 6 at a predetermined timing, so that the fuel supply amount to the engine is electronically controlled. Control. here,
The manner in which the control unit 12 calculates the air-fuel ratio feedback correction coefficient α will be described in detail with reference to the flowchart of FIG.

In this embodiment, inversion means, feedback correction value setting means, air-fuel ratio feedback correction means, inversion cycle measuring means, control period setting means , correction amount
The function as the setting means is provided by the control unit 12 as software. In the flowchart of FIG. 3, first, in step 1 (referred to as S1 in the figure, the same applies hereinafter), the output voltage Vs of the oxygen sensor 16 is read.

In the next step 2, the output voltage Vs read in the step 1 is compared with a threshold value SL corresponding to a target air-fuel ratio (stoichiometric air-fuel ratio) of the output voltage Vs. Here, when it is determined that the output voltage Vs is higher than the threshold value SL and the exhaust air-fuel ratio detected by the oxygen sensor 16 is richer than the target air-fuel ratio (the stoichiometric air-fuel ratio),
Proceeding to step 3, the period T of the rich determination state is measured.

In the next step 4, the control period tφ (first control period) at the time of the current rich determination is based on the cycle T measured at the time of the previous rich determination.
The control period t1 is set. The control periods tφ and t1 are:
When tφ> t1 and the period T becomes longer, the control periods tφ and t1 are both made longer.
On the other hand, in step 5, the air-fuel ratio feedback correction coefficient α at the first time of the reversal determination (at the time of lean → rich reversal) is read, and is read as the reference value α in the current rich determination state.
Set to _B.

In step 6, it is determined whether or not the period is from the lean to rich inversion of the air-fuel ratio until the control period tφ set in step 4 elapses. proceeds to step 7, the subtracted value to said reference value alpha predetermined correction value from the _{B αφ} (first correction amount) is set as the air-fuel ratio feedback correction coefficient alpha (see FIG. 5). Note that the decrease correction of the air-fuel ratio feedback correction coefficient α is performed by setting the fuel injection amount Ti to be smaller.
This is a correction in a direction in which the state richer than the target air-fuel ratio approaches the target air-fuel ratio.

The control period t from the inversion of the air-fuel ratio
When φ elapses, it is determined in step 8 whether or not the period from when the control period tφ elapses to when the control period t1 set together with tφ in step 4 further elapses. In step 8 , during the control period tφ (first control period)
If it is followed by the control period t1 is determined, the process proceeds to step 9, from the reference value alpha _B predetermined correction value [alpha] 1 (second
A value obtained by subtracting the correction amount: α1 <αφ) is set as the air-fuel ratio feedback correction coefficient α (see FIG. 5).

If it is determined in step 8 that the control period is not within the control period t1, that is, if a time equal to or longer than tφ + t1 has elapsed after the air-fuel ratio has been richly inverted, the routine proceeds to step 10, and setting the value alpha _B as the air-fuel ratio feedback correction coefficient alpha. That is, when the air-fuel ratio is reversed from lean to rich, the air-fuel ratio feedback correction coefficient α
Is the reference value α _B with the correction coefficient α at the time of inversion, the reference value α _B −αφ in the first period tφ, and the period t
During the period 1, when the period of the reference value α _B −α1 and tφ + t1 elapses, the control value gradually changes to α _B every control period tφ and t1 (see FIG. 5).

Here, the reference value α _B given immediately after the inversion
Since -αφ is the largest, the injection amount is corrected to be reduced, and when the injection is reversed from lean to rich, the fuel injection amount is greatly reduced within a predetermined period tφ immediately after that, and the rich state is eliminated early. Then, actually be inverted to the lean air-fuel ratio in the cylinder, taking into account the time lag until the lean inversion according by the oxygen sensor 16 is detected, the predetermined period tφ after is relatively reference value alpha _B By making the transition at a close value, the occurrence of control overshoot is avoided.

On the other hand, in step 2, it is determined that the output voltage Vs of the oxygen sensor 16 is smaller than the threshold value SL and the exhaust air-fuel ratio detected by the oxygen sensor 16 is leaner than the target air-fuel ratio (the stoichiometric air-fuel ratio). When, the process proceeds to step 11 and subsequent, similarly to the time of the rich determination, the alpha air-fuel ratio feedback correction coefficient in the rich → lean inversion as a reference value alpha _B (step
13), the reference value α _B is set in the control periods tφ and t1 (step 1).
The air-fuel ratio feedback correction coefficient α is set by correcting the correction amounts αφ and α1 according to (1, 12) (steps 14 to 18). However, during the lean inversion, in order to correct the fuel injection quantity Ti to the rich direction, the correction amount Arufafai, [alpha] 1 is added to the reference value alpha _B.

As shown in the flow chart of FIG. 4, the correction amounts αφ and α1 are determined in advance for each of the operating regions which are divided into a plurality of parameters using the basic fuel injection amount Tp representing the engine load and the engine speed Ne as parameters. And is set for each operation area with reference to the map. Note that the routine shown in the flowchart of FIG. 4 is processed as a background job (BGJ).

According to the above embodiment, during the predetermined period tφ immediately after the air-fuel ratio inversion, the air-fuel ratio feedback correction coefficient α (reference value α _B ) at the time of the inversion by the large correction amount αφ.
Maintained at a value that fixes, to perform sufficient correction can eliminate the rich or lean state of the air-fuel ratio correction in such control period tφ in, then, allowed to remain at a level close by the reference value alpha _B, The process waits until the air-fuel ratio inversion is actually detected by the oxygen sensor 16. If the air-fuel ratio inversion cycle becomes longer, the control periods tφ and t1 are made longer to cope with an increase in the correction request level. It has become.

If the air-fuel ratio feedback correction coefficient α is set as described above, the correction coefficient α is largely corrected in the direction of the target air-fuel ratio immediately after the air-fuel ratio inversion, and the correction value is set based on the cycle T. Since the control period tφ is maintained, the convergence to the target air-fuel ratio is ensured, and after a predetermined period tφ elapses, the transition is made at a relatively small correction level, so that control overshoot can be avoided.

In the above embodiment, the air-fuel ratio at the time of air-fuel ratio inversion is
The ratio feedback correction coefficient α is set to the reference value α._BAnd the control period
The reference value α based on the time tφ, t1_BFixed in two stages
However, the combination of the control period tφ and the correction amount αφ
The reference value α _BOnly during the control period tφ
Alternatively, the configuration may be modified.

[0030]

As described above, according to the present invention, the convergence is improved in the air-fuel ratio feedback control for feedback-correcting the air-fuel ratio of the engine intake air-fuel mixture to the target air-fuel ratio based on the rich / lean determination with respect to the target air-fuel ratio. It is possible to suppress the occurrence of control overshoot while improving the air-fuel ratio, thereby improving the air-fuel ratio controllability.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is a system schematic diagram showing one embodiment of the present invention.

FIG. 3 is a flowchart illustrating setting of a feedback correction value.

FIG. 4 is a flowchart showing a correction amount setting of a feedback correction value.

FIG. 5 is a time chart showing a change in a feedback correction value according to the embodiment.

FIG. 6 is a time chart showing a state of conventional feedback correction.

[Explanation of symbols]

 1 engine 6 fuel injection valve 12 control unit 13 air flow meter 14 crank angle sensor 15 water temperature sensor 16 oxygen sensor

Claims (1)

(57) [Claims] An air-fuel ratio detecting means for detecting an air-fuel ratio of an engine intake air-fuel mixture; Reversal determining means for determining the period, and the rich / lean reversal cycle determined by the reversal determining means
Inversion cycle measuring means for measuring the inversion cycle measured by the inversion cycle measurement means .
Control period setting means for setting a first control period; and a control period setting means for setting the first control period based on operating conditions of the engine.
A first correction amount, and control following the first control period.
The correction amount used in the period, which is smaller than the first correction amount
Correction amount setting means for setting a second correction amount; and setting the air-fuel ratio detected by the air-fuel ratio detection means to a target air-fuel ratio.
Correct the air-fuel ratio feedback correction value in the direction to get closer
Means, wherein rich / lean is determined by the inversion determination means.
The air-fuel ratio feedback correction value when reversal is determined
The first control is performed based on the rich / lean inversion as a reference value.
Until the control period elapses, the reference value is changed to the first repair value.
The first control period is maintained at a value corrected by a positive amount.
After elapse, the reference value is calculated by the second correction amount.
Feedback correction value setting means for holding the corrected value
And an air-fuel ratio feedback correction unit that corrects and controls the amount of fuel supplied to the engine based on the air-fuel ratio feedback correction value set by the feedback correction value setting unit. Engine air-fuel ratio feedback control device.