JP2579565B2 - Air-fuel ratio 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 control device for an internal combustion engine.

[0002]

2. Description of the Related Art A conventional air-fuel ratio control device for an internal combustion engine measures intake air flow using various intake air flow detecting means as shown in FIGS. 6A to 6C. Generally, the air supply ratio is controlled by determining the fuel supply amount based on the fuel supply amount. FIG. 6A shows a vane type in which the amount of rotation of the vane which rotates in response to the intake pressure is detected by a potentiometer to detect the intake air flow rate.
FIG. 2B is a hot wire type in which the current to the bridge circuit is controlled based on a change in the resistance value of the hot wire resistance according to the intake flow rate, and the control current value is detected as the intake air flow rate;
FIG. 5C shows a Karman vortex type in which the amount of vortex downstream of the probe is measured to detect the intake air flow rate (published by Sankaido Co., Ltd. on October 15, 1980, “Automotive Engineering Encyclopedia”. 10-volume electrical equipment, vehicle body equipment, engine parts ”second
See page 63).

[0003]

However, in such an air-fuel ratio control system which detects the intake air flow rate, the above-mentioned intake air flow rate detecting means is not affected by the atmospheric pressure, humidity and temperature. As a result, it is conceivable that the detection accuracy decreases, a response delay occurs in a transient state, or a failure occurs due to some influence. In such a case, the engine cannot execute accurate air-fuel ratio control,
In the worst case, the operation may be stopped.

The present invention has been made in view of such a conventional problem, and controls the fuel supply amount in accordance with the estimated air-fuel ratio state by detecting the in-cylinder pressure, and based on the control result. Accordingly, it is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine in which the estimation of the air-fuel ratio state is made reliable and the correction control is performed so that the air-fuel ratio approaches a target value.

[0005]

Therefore, an air-fuel ratio control apparatus for an internal combustion engine according to the present invention, as shown in FIG. 1, comprises an in-cylinder pressure detecting means for detecting an in-cylinder pressure of the engine, cylinder pressure peak value crank angle detecting means for detecting a crank angle providing the peak value and the peak value for each combustion stroke, and the fuel supply quantity setting means for setting a fuel supply amount, setting
Based on the combustion under the specified fuel supply,
Air-fuel ratio deviation estimating means for estimating a deviation amount of a current air-fuel ratio from a target air-fuel ratio based on the in-cylinder pressure peak value detected by the pressure peak value / crank angle detecting means and the crank angle; Rich / lean assumption means for assuming whether the deviation amount of the air-fuel ratio is on the rich side or lean side with respect to the target air-fuel ratio, and the estimated deviation amount of the air-fuel ratio and its assumption on the rich side or lean side. the fuel supply quantity correcting means for setting and correcting the fuel supply quantity to approximate the air-fuel ratio to the target air-fuel ratio, under the corrected fuel supply amount
For combustion, the cylinder pressure peak value / crank angle detection
Cylinder pressure peak value and crank angle detected by
The deviation of the current air-fuel ratio from the target air-fuel ratio based on the
The corrected air-fuel ratio deviation estimating means and the fuel supply amount correction
By comparing the previous air-fuel ratio deviation amount with the corrected air-fuel ratio deviation amount,
An assumption that determines whether the rich / lean assumption is correct based on whether or not the amount of deviation is increased, and an assumption that corrects the assumption by the rich / lean assumption means in accordance with the determination result by the determination means. And a correcting means.

[0006]

The peak value of the in-cylinder pressure detected by the in-cylinder pressure detecting means for each combustion stroke and the crank angle giving the peak value are detected by the in-cylinder pressure peak value / crank angle detecting means. The air-fuel ratio deviation estimating means is provided by the fuel supply amount setting means.
Under the set fuel supply amount, the in-cylinder pressure peak value
Based on the peak value of the in-cylinder pressure detected by the rank angle detecting means and the crank angle, the deviation amount of the current air-fuel ratio from the target air-fuel ratio is estimated, and the rich / lean assuming means estimates the deviation amount as the target air-fuel ratio. On the other hand, it is assumed that it is shifted to the rich side or to the lean side.

The fuel supply amount correcting means estimates the air-fuel ratio deviation amount.
The fuel supply amount is corrected and set so that the air-fuel ratio approaches the target air-fuel ratio based on the amount of deviation of the current air-fuel ratio from the target air-fuel ratio estimated by the determining means and the rich-lean assumption by the rich-lean assumption means. I do. Air-fuel ratio deviation after correction
The estimating means performs combustion under the corrected fuel supply amount.
About the in-cylinder pressure peak value / crank angle detecting means.
Based on the detected in-cylinder pressure peak value and crank angle
To estimate the deviation of the current air-fuel ratio from the target air-fuel ratio.
You. The assumption correct / wrong determining means compares the air-fuel ratio deviation amount before the fuel supply amount correction and the corrected air-fuel ratio deviation amount, and determines whether the rich / lean assumption is correct based on whether the deviation amount is enlarged. Is determined, and the assumption correcting means corrects the rich / lean assumption based on the determination result.

[0008] Based on the above premise, the microcomputer
The air-fuel ratio control performed by the computer 6 is shown in FIGS.
The description will be given according to the flow chart shown. Steps (in the diagram
Is denoted as S. In the following, the intake air flow rate and air-fuel ratio
Fuel injection amount determined based on the preset initial value of
A fuel amount corresponding to the initial value T ₀ is injected from the fuel injection valve 9.
Is done. Here, the initial value T ₀ of the fuel injection amount is determined.
The function corresponds to a fuel supply amount setting unit. By correcting the rich / lean assumption in the correct direction in this manner, it is possible to control the air-fuel ratio to approach the target air-fuel ratio correctly.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2 showing the configuration of one embodiment, an in-cylinder pressure sensor (in-cylinder pressure detecting means) 2 for detecting an in-cylinder pressure is attached to a portion where an ignition plug 1 is seated on a cylinder head.
Cylinder pressure signal from the input to the P _max · θ _Pmax detecting circuit 4 through an amplifier 3. Crank angle signal P _max · theta _Pmax detection circuit 4 from other crank angle sensor 5 of the in-cylinder pressure signal is also inputted, for each combustion stroke of the cylinder where the cylinder pressure sensor 2 is attached, the peak value P _max of the in-cylinder pressure Is detected. That is,
P _max · theta _Pmax detecting circuit 4 and the crank angle sensor 5 and in-cylinder pressure peak crank angle detection means is constituted.

The in-cylinder pressure peak value _Pmax and the crank angle _θPmax for each combustion stroke detected in this way are input to the microcomputer 6. Microcomputer 6
Controls the air-fuel ratio by estimating the amount of deviation of the current air-fuel ratio from the target air-fuel ratio based on each of the detected values and setting the fuel supply amount assuming that the air-fuel ratio is rich or lean. On the other hand, the deviation amount of the air-fuel ratio for each operating condition such as constant speed, acceleration, and start detected by the state of the throttle valve opening α detected by the throttle sensor 7 and the cooling water temperature T _W detected by the water temperature sensor 8. Judge whether the rich / lean assumption is right or wrong according to the change state of
If not, correct the assumptions.

The fuel injection valve 9 is for injecting and supplying a set amount of fuel to the engine, thereby controlling the air-fuel ratio. Next, the operation will be described. First, consider the case where the stoichiometric air-fuel ratio is set as the target air-fuel ratio. FIG. 3 shows an in-cylinder pressure waveform with respect to the air-fuel ratio. In other words, the in-cylinder pressure changes substantially in the same manner regardless of whether the target air-fuel ratio is shifted to the rich side or the lean side. Therefore, if it is known whether the air-fuel ratio is shifted to the rich side or the lean side,
The predicted value of the air-fuel ratio is determined by the pattern of the in-cylinder pressure change.

The air-fuel ratio control performed by the microcomputer 6 based on the above premise will be described with reference to the flowcharts shown in FIGS. In step (denoted as S in the figure; the same applies hereinafter), in step 1, the fuel amount corresponding to the initial value T ₀ of the fuel injection amount determined based on the preset initial value of the intake air flow rate and the air-fuel ratio is determined. Injected from.

In step 2, it is determined whether or not the combustion stroke of the cylinder (hereinafter referred to as a specific cylinder) to which the in-cylinder pressure sensor 2 is mounted has been completed, based on a cylinder discrimination signal from the crank angle sensor 5, and the end of the combustion stroke is determined. Then, proceed to step 3.
In step 3, the peak value P _max of the in-cylinder pressure for each combustion stroke detected by the P _max · θ _Pmax detection circuit 4 and the crank angle θ _Pmax at the time when the P _max occurs are input.

The program then proceeds to step 4, to estimate the amount of deviation from the target air-fuel ratio on the basis of the P _max and theta _Pmax input in step 3. More specifically, this is set by searching a three-dimensional map stored in the ROM of the microcomputer 6, for example, from the relationship between the in-cylinder pressure and the air-fuel ratio shown in FIG. In step 5, step when the change amount [Delta] [alpha] per unit time Δt on the basis of the valve opening degree α signals from the throttle sensor 7 determines whether acceleration or not exceeding a predetermined positive value [Delta] [alpha] _0, it is determined accelerated It is assumed that the process proceeds to step 6 and proceeds to step 6 in order to increase the fuel injection amount of the next time (after Δt seconds) with respect to the increase in the intake air flow rate, and the air-fuel ratio is shifted to the lean side.

On the other hand, if the determination in step 5 is NO, the process proceeds to step 7 where the amount of change .DELTA..alpha.
It is determined whether or not the vehicle is decelerating below Δα _0, and if it is determined that the vehicle is decelerating, the process proceeds to step 8 and the air-fuel ratio shifts to the rich side in order to correct the next fuel injection amount to reduce the intake air flow rate. Assume that The determination in step 7 is NO
(−Δα ₀ ≦ α ≦ Δα ₀ ) In the steady state, the process proceeds to step 9 and the cooling water temperature T _W detected by the water temperature sensor 8.
It is determined whether the engine is started and warmed up at a set value T _W0 (for example, 60 ° C.) or less. If YES, a step is taken to increase the combustion temperature by increasing the combustion temperature by leaning the air-fuel ratio. 8 and assuming that the current air-fuel ratio is shifted to the rich side,
When the warm-up is substantially completed (NO), the process proceeds to step 10 and the same assumption as the previous (Δt seconds ago) is maintained. still,
At the first time after the start of control, the initial assumption (rich or lean) is set.

In step 11, based on the deviation of the air-fuel ratio estimated in step 4 and the assumption of the deviation direction in steps 6, 8, and 10, the fuel injection amount is set to an initial value so as to approach the target air-fuel ratio. It is set by performing increase / decrease correction.
Next, in step 12, it is determined whether or not the fuel of the set fuel injection amount has been supplied to the specific cylinder and combustion has been terminated, based on the cylinder discrimination signal. After the completion of the combustion stroke, _Pmax newly detected in step 13 is determined. , Θ _Pmax .

[0017] At step 14, the P _max, sets the shift amount from an air-fuel ratio based on the theta _Pmax. In step 15, the deviation amount of the air-fuel ratio estimated in step 14 this time is compared with the deviation amount estimated in the previous time, and whether the previous rich / lean assumption was correct is determined based on whether the deviation amount is expanded. I do.

That is, if the rich / lean assumption is correct, the correction of the increase / decrease of the fuel injection amount performed in the correct direction is performed in the correct direction, so that the in-cylinder pressure increases and the deviation amount of the air-fuel ratio decreases. Therefore, it is determined in step 15 that the assumption is correct. In this case, after resetting the erroneous determination repetition counter to 0 in step 16, the process returns to step 5 again based on the rich / lean assumption according to the operating conditions and the friction amount of the air-fuel ratio estimated in step 14.
In step 11, the fuel injection amount is corrected and set, and the air-fuel ratio control is performed.

On the other hand, if it is determined in step 15 that the air-fuel ratio deviation has increased and the assumption is incorrect, the process proceeds to step 17, and the present assumption is reversed to the previous assumption (if rich, Lean, rich if lean). Then after counting up the counter C repeatedly indetermination in step 18, the count value C of the counter proceeds to step 19 to determine whether a predetermined value C ₀ or more to Step 5 and when less than the predetermined value C ₀ The process returns to step 20 if the value is equal to or greater than the predetermined value C ₀ .

That is, in a relatively stable state in which the air-fuel ratio does not repeat rich / lean many times, the air-fuel ratio converges to the target air-fuel ratio by correcting the deviation of the air-fuel ratio and the assumption of the rich / lean. Can be done. On the other hand, the air-fuel ratio sometimes repeats rich / lean during sudden acceleration / deceleration with the throttle valve opening changed abruptly. Therefore, even if the air-fuel ratio control is performed, the reliability is poor, so that the fluctuation of the air-fuel ratio may be rather increased.

For this reason, if it is determined in step 19 that the correction of the rich / lean assumption has been continuously performed a predetermined number of times C ₀ , it is determined that the above-mentioned rapid increase / decrease operation has been performed and step 20 is performed. Then, the fuel injection amount is set in accordance with a predetermined constant reference air-fuel ratio. Then, after it is determined in step 21 that the combustion has been completed for the set fuel injection amount, the process proceeds to step 22, where the change amount | Δα | of the throttle valve opening is equal to or more than a predetermined value Δα ₁ (> Δα ₀ ). Is determined.

[0022] When the amount of change is still large movement of the throttle valve by a predetermined amount [Delta] [alpha] ₁ or more, but continues the same air-fuel ratio control returns to step 20 again stable becomes [Delta] [alpha] is less than the predetermined value [Delta] [alpha] ₁ Thereafter, the flow returns to step 13 to restart the above-described air-fuel ratio control. Thus, the air-fuel ratio state is predicted,
In addition, by correcting the predicted value, the operation of the engine can be continued even when the intake air flow rate detecting means breaks down. In addition, the present invention is applied to an air-fuel ratio control device using an intake air flow rate detecting means, and the detection accuracy of the intake air flow rate detecting means is reduced, and response delay in a transient state is corrected to improve control performance. Reliability can be improved and accuracy can be compensated.

[0023] Incidentally, in FIG. 4 and FIG. 5, <br/> part of Step 4 corresponds to the air-fuel ratio shift amount estimating means, part of step 11
The minute corresponds to the fuel supply amount correction means, and the portion of step 14 is
The corrected air-fuel ratio deviation amount estimating means corresponds to step S15, and the step S15 corresponds to assumed correctness determining means. The step S17 corresponds to assumed correction means. Further, in the present embodiment, the case where the stoichiometric air-fuel ratio is set as the target air-fuel ratio has been described.
Of course, it can be applied to any other target air-fuel ratio.

[0024]

As described above, according to the present invention, the operation of the engine can be continued even if the intake air flow detecting means fails, and the present invention is applied to an air-fuel ratio control device using the intake air flow detecting means. Thus, the reliability of the intake air flow detecting means can be enhanced or the accuracy can be compensated, for example, by correcting the detection accuracy of the intake air flow detecting means or the response delay in a transient state to improve the control performance.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 3 is a diagram showing a change in in-cylinder pressure characteristics with respect to a shift of an air-fuel ratio toward a rich side and a change in a cylinder pressure characteristic with respect to a shift toward a lean side;

FIG. 4 is a flowchart showing a control routine of the embodiment.

FIG. 5 is a flowchart showing a control routine of the embodiment.

FIG. 6 is a diagram showing an outline of various detection means for detecting an intake air flow rate.

[Explanation of symbols]

2-cylinder pressure sensor 4 P _max · θ _Pmax detecting circuit 5 crank angle sensor 6 microcomputer

Claims (1)

(57) [Claims] 1. An in-cylinder pressure detecting means for detecting an in-cylinder pressure of an engine, and an in-cylinder pressure peak value / crank angle detection for detecting a peak value of the detected in-cylinder pressure for each combustion stroke and a crank angle giving the peak value. Means, a fuel supply amount setting means for setting a fuel supply amount, and the cylinder based on combustion under the set fuel supply amount.
Air-fuel ratio deviation estimating means for estimating a deviation amount of a current air-fuel ratio from a target air-fuel ratio based on an in-cylinder pressure peak value and a crank angle detected by an internal pressure peak value / crank angle detecting means; Rich / lean assumption means for assuming whether the deviation amount of the air-fuel ratio is on the rich side or the lean side with respect to the target air-fuel ratio, and the estimated deviation amount of the air-fuel ratio and the assumption on the rich side or the lean side. A fuel supply amount correcting means for correcting and setting the fuel supply amount so as to bring the air-fuel ratio closer to the target air-fuel ratio, and performing combustion in the cylinder under the corrected fuel supply amount.
Cylinder detected by pressure peak value / crank angle detection means
The current air-fuel ratio based on the internal pressure peak value and the crank angle
Air-fuel ratio deviation to estimate deviation from target air-fuel ratio
Amount estimating means, air-fuel ratio deviation before and after correction of fuel supply amount
And an assumption correct / incorrect determining means for determining whether the rich / lean assumption is correct based on whether or not the amount of deviation is increased; and a rich / lean assuming means in accordance with the determination result by the determining means. An air-fuel ratio control device for an internal combustion engine, comprising: an assumption correcting means for correcting an assumption based on the above.