JPH0625555B2 - Air-fuel ratio controller for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio control device for an internal combustion engine, which detects a parameter correlated with output torque and corrects the air-fuel ratio.

(Prior Art) In general, the amount of fuel required by an engine under a certain operating condition has an intake air amount of the engine at that time as one important parameter.

The following three methods are known as methods for determining such an intake air amount. That is, there are a method of directly detecting the air amount, a method of detecting the pressure in the intake pipe, and a method of detecting the throttle valve opening.

A conventional technique for determining the amount of fuel required by the engine from this type of intake air amount is described in, for example, "New Edition of Automotive Engineering Handbook, 4th Edition" (published by the Society of Automotive Engineers, September 30, 1983). There is something.

In this technique, the air flow rate is extracted from the rotational displacement of the measuring plate of the air flow meter provided in the intake pipe, and converted into an electric signal by the potentiometer. This electric signal is input to the control unit and divided by a predetermined trigger corresponding to the engine speed. The divided electric signal corresponds to the intake air amount for each cylinder, and the fuel supply amount is determined based on the intake air amount so that the target air-fuel ratio is achieved based on the steady state condition.

(Problems to be Solved by the Invention) However, in such a conventional technique, since the fuel supply amount corresponding to the target air-fuel ratio is determined from the intake air amount in the steady state, When the throttle valve is opened abruptly during rapid acceleration or the like (hereinafter referred to as transient operation), the inflow air also increases rapidly, and the fuel supply amount is determined based on the air flow rate and is supplied into the air supply pipe.

However, the internal pressure of the air supply pipe is increased by the above-mentioned rapid increase in the air flow rate, and the supplied fuel is condensed into liquid fuel. The generation of the liquid fuel produces partially ineffective fuel that adheres to and stays on the pipe wall, and makes the air-fuel mixture flowing into the combustion chamber lean. Therefore, since an appropriate air-fuel ratio required for transient operation cannot be obtained (that is, deviates from the target air-fuel ratio), the engine output torque does not follow the throttle opening, and the drivability including acceleration performance deteriorates. There was a problem.

(Object of the Invention) Therefore, in addition to the conventional method (which obtains the fuel supply amount from the intake air amount), the present invention further detects a parameter correlated with the output torque, estimates the air-fuel ratio by the parameter, and mixes. By correcting the ratio, it is intended to eliminate drastic fluctuations in the air-fuel ratio due to the adherence of fuel to the wall surface during transient operation, and to improve drivability.

(Means for Solving the Problems) In order to achieve the above object, the air-fuel ratio control apparatus for an internal combustion engine according to the present invention has a basic conceptual diagram shown in FIG. Means a, operating state detecting means b for detecting the operating state of the engine using load and rotation speed as parameters, and basic supply amount calculating means c for calculating the basic supply amount of fuel based on the value detected by the operating state detecting means b. A parameter calculation means d for calculating a parameter correlated with the output torque of the engine as a parameter detection value based on the output of the pressure detection means a; and a correlation with the output torque of the engine based on the detection value by the operating state detection means b. The target value setting means e for setting the target value of the parameter, and the excess / deficiency of the fuel supply amount are obtained from the difference between the parameter detection value and the target value. Correction amount calculation means f for calculating a correction amount for the next fuel supply amount based on the amount, and supply amount calculation means g for correcting the basic supply amount with the correction amount to calculate the fuel supply amount to the engine. Fuel supply means h for supplying fuel to the engine based on the output of the supply amount calculation means g.

(Operation) In the present invention, the parameter correlated with the output torque is detected, the air-fuel ratio is estimated by this parameter, and the fuel supply amount is corrected. Therefore, large fluctuations in the mixing ratio during transient operation are suppressed, and drivability is improved.

(Example) Hereinafter, the present invention will be described with reference to the drawings.

2 to 7 are views showing a first embodiment of the present invention.

First, the configuration will be described. In FIG. 2, reference numeral 1 denotes an engine, intake air is supplied to each cylinder from an air cleaner (not shown) through an intake pipe 2, and fuel is injected by an injector (fuel supply means) 3 based on an injection signal Si. Then, the air-fuel mixture in the cylinder is ignited and explodes by the discharge action of the spark plug 4, becomes exhaust gas, and is introduced into a catalytic converter (not shown) through the exhaust pipe 5, and harmful components (CO, HC, NOx) is cleaned by a three-way catalyst and discharged.

The flow rate of the intake air is detected by the air flow meter 6,
The electric signal Q having an analog value is output to the A / D converter 7. The A / D converter 7 converts this electric signal Q into a digital signal Qa and outputs it to the microcomputer 8.

On the other hand, 9 is an in-cylinder pressure sensor (pressure detecting means), and the in-cylinder pressure sensor 9 changes the combustion pressure in the cylinder into an electric charge by a piezoelectric element and outputs an electric charge signal S ₁ . As shown in detail in FIGS. 3A and 3B, the in-cylinder pressure sensor 9 is screwed to the cylinder head 10 and is formed as a washer of the ignition plug 4, and is formed on the outer recess of the cylinder head 10. The spark plug 4 is pressed and fixed by the tightening portion 4a of the spark plug 4.

The sensor output S ₁ is input to the charger amplifier 11,
The charger amplifier 11 is an operational amplifier OP, an input resistor R1,
Feedback resistor R2 and the so-called charge consisting integrating capacitor C - form a voltage conversion amplifier, and outputs to the A / D converter 12 converts the sensor output S ₁ into a voltage signal S _2. A / D
The converter 12 converts the voltage signal S ₂ into a digital signal S ₃ and outputs it to the microcomputer 8.

Further, the crank angle of the engine is detected by the crank angle sensor 13, and the crank angle sensor 13 outputs a unit signal S ₄ corresponding to 2 ° of the crank angle and a discrimination signal S ₅ for cylinder discrimination to the microcomputer 8.

The air flow meter 6 and the crank angle sensor 13 are
The operating state detecting means 14 is configured.

The microcomputer 8 has functions as a basic supply amount calculation means, a parameter calculation means, a target value setting means, a correction amount calculation means, and a supply amount calculation means, and is a CPU 21 and a ROM.
22, RAM 23 and I / O port 24. C
The PU21 fetches external data required from the I / O port 24 according to the program written in the ROM22, and also exchanges data with the RAM23 to perform arithmetic processing and process it as necessary. Data I
Output to / O port 24. The I / O port 24 receives signals from the A / D converters 7 and 12 and the operating state detecting means 14, and the I / O port 24 outputs an injection signal (injector drive pulse) Si. ROM22 is C
RAM that stores the calculation program for PU21
Reference numeral 23 is a so-called working memory for temporarily storing data used for calculation and calculation results.

Next, the operation will be described.

In general, the amount of fuel supplied to the engine during a transient operation such as acceleration has a relationship substantially proportional to the intake air amount. The sudden increase in the intake air amount due to acceleration or the like increases the internal pressure of the intake pipe and promotes the condensation action of the fuel to generate liquid fuel. A part of the liquid fuel adheres and accumulates on the pipe wall, and the fuel involved in combustion is greatly reduced. Taking the case of acceleration as an example of the state during such transient operation, the air-fuel ratio becomes significantly lean immediately after acceleration as shown in FIG. 8 (A), and gradually approaches the target thereafter. Looking at the change in the detected cylinder pressure at this time, as shown by the solid line in FIG. 7B, it drops sharply immediately after acceleration and gradually increases as the air-fuel ratio approaches the target value, and stabilizes at a constant value. . Here, the target in-cylinder pressure required for acceleration (substantially equal to the intake air amount) is indicated by a broken line.

Therefore, in the present embodiment, attention is focused on the causal relationship that the difference between the detected in-cylinder pressure and the target in-cylinder pressure (that is, the difference in output torque) corresponds to the amount of ineffective fuel adhering to and accumulated on the wall surface, and the correlation with the output torque during transient operation A large variation in the air-fuel ratio is suppressed by calculating the parameter for calculating the ineffective fuel amount, estimating the air-fuel ratio from this, and correcting the fuel supply amount.

4 to 6 are flowcharts showing a program for fuel supply control based on the above-mentioned basic principle.

FIG. 4 is a flowchart showing an interrupt subroutine (IRQ1) for determining the fuel injection amount, and this interrupt subroutine (IRQ1) is executed once every time the cylinder discrimination signal S ₅ is input.

First, the engine speed N is calculated from the input interval of the cylinder discrimination signal S ₅ at P ₁ , and the intake air amount Qa is read at P ₂ . Then, N, Qa calculation ...... However the basic fuel injection pulse width Tp as a function of at P _3, C _pw ':. Previous value, "one of the computing a" basic supply quantity Tp example, (However, K: constant) Tp is calculated by an arithmetic expression. P ₄
Then, the background job program (BG
J) is used to calculate the transient correction coefficient C _pw for _obtaining the fuel supply amount Ti by correcting the basic supply amount Tp using the basic transient correction coefficient C _pwo .

C _pw = C _pw ′ −A + C _pwo, where C _pw ′ is the previous transient correction coefficient, A is a constant, and in the formula, the constant A is a constant accumulation of unburned fuel due to wall adhesion and then flows into the cylinder. , Is a correction term for preventing the air-fuel ratio from swinging to the rich side, whereby the correction function is performed within the swing range indicated by the amount in FIG. 7. P ₅
Then, the basic supply amount Tp is corrected with the current transient correction coefficient C _pw to calculate the fuel supply amount Ti (Ti = Tp × C _pw ), and P ₆
At the designated injection timing, the injector drive signal (injection signal) Si having the injection pulse width corresponding to this Ti is output, and the interrupt subroutine (IRQ1) ends.

FIG. 5 is a flowchart showing an interrupt subroutine (IRQ2) for obtaining a parameter correlated with the output torque. This interrupt subroutine (IRQ2) is executed once every time the crank angle unit signal S ₄ is input. .

First, at P ₁₁ , the current crank angle (crank angle at the interrupt timing) θ is calculated based on the unit signal S ₄ , and P ₁₂
The combustion pressure signal S ₃ is read in and the combustion pressure signal S ₃ is replaced with the current cylinder pressure P. Next, at P ₁₃ , the cylinder internal volume V corresponding to the crank angle θ at the interrupt timing is obtained, and the cylinder internal volume difference ΔV between this V and the previous cylinder internal volume V ′ (ΔV = V′−V) is calculated. To do.

At P ₁₄ , the cylinder pressure P is multiplied by the cylinder volume difference ΔV to obtain P
Calculate ΔV. PΔV is an area per predetermined crank angle (for example, 2 °) in a so-called P-V diagram, and is a unit area for obtaining a detected indicated effective pressure Pi described later.

Next, at P ₁₅ , the cumulative value SU of PΔV obtained corresponding to the current interrupt timing crank angle θ and PΔV up to the previous time is calculated.
M is added and the process proceeds to the crank angle 0 ° determination step P ₁₆ . At P ₁₆ , when the crank angle is 0 °, the routine proceeds to P ₁₇ and the accumulated value SUM is replaced as the detected indicated effective pressure Pi.
Further, the cumulative value SUM is cleared at P ₁₈ , and the interrupt subroutine (IRQ2) is ended.

On the other hand, when θ ≠ 0 ° at P ₁₆ , it is determined that the value of the cumulative value SUM has not yet reached the area of the closed curved surface in the so-called PV diagram, and the value of SUM up to the present is retained. The interrupt subroutine (IRQ2) is completed.

In this way, the parameter correlated with the output torque is obtained, but the point is that the method is not limited to this method as long as it is based on the piecewise quadrature method, and may be obtained by another method.

FIG. 6 is a flow chart showing the background job program (BGJ) for obtaining the basic transient correction coefficient, and the interrupt subroutines (IRQ1), (IR
This is a program that is always executed while Q2) is not executed.

First, P ₂₁ is a step of calculating the target indicated effective pressure Pi ', which is determined as a function of engine speed N and the basic supply quantity Tp. Next, P ₂₂ is the basic transient correction coefficient Cpw
This is a step for obtaining o, which is obtained from the target indicated effective pressure Pi ′ and the detected indicated effective pressure Pi. To explain this, the fuel supplied from the injector is divided into a combusted component and an uncombusted component due to adhesion of wall surfaces and the like in a transient operation such as acceleration.

The concept of correction is shown in FIG. That is, in the figure, if the difference between the target indicated effective pressure Pi 'and the detected indicated effective pressure Pi is a difference value, the basic transient correction coefficient Cpwo is determined so that the air-fuel ratio becomes rich by the amount. It Specifically, the relationship between the fuel supply amount and the indicated effective pressure is expressed by the following equation.

Fuel supply amount: unburned amount = Pi ′: Pi′−Pi, where Pi ′: target indicated effective pressure, Pi: detected indicated effective pressure.

Expanding the above equation into the equation for obtaining the unburned component, the following equation is obtained.

The unburned component thus obtained is determined as the basic transient correction coefficient Cpwo. As a result, the fuel supply amount Ti becomes Cpwo as shown in FIG. 8 (C).
Thus, the amount is appropriately increased and corrected to follow a lean change in the air-fuel ratio during acceleration. Therefore, the change in the in-cylinder pressure after the correction has a characteristic substantially in accordance with the target in-cylinder pressure, and the transient operation performance during acceleration is improved.

Therefore, the effect of this embodiment is remarkable as shown in the experimental results shown in FIGS. Specifications 1 to 3 shown by three types of bar graphs in FIG. 9 are as shown in the following table.

As shown in FIG. 10, the experimental method was performed by measuring the time from when the throttle switch was turned on to when the detected cylinder pressure Pi reached the target cylinder pressure Pi 'shown in FIG. . As is apparent from FIG. 9, according to this embodiment, the time required to reach the target cylinder pressure Pi ′ is 1
It is shortened to about / 3 and the acceleration performance is greatly improved.

FIG. 11 is a diagram showing a second embodiment of the present invention. In the interrupt subroutine (IRQ1) for determining the fuel injection amount, the transient correction coefficient Cpw is calculated according to the following equation, and the coefficient K of the equation is calculated. It is different from the first embodiment in that it is set to 1 or less (see FIG. reference).

Cpw = (Cpw ′ + Cpwo) × K .. Comparing this with the correction term −A of the first embodiment,
The value of −A is set by A = f _UNC (N). Here, N is the engine speed, that is, its set value changes depending on the acceleration condition.

Correspondingly, K has a constant value that does not depend on the acceleration condition, and therefore has the advantages that the program is simplified and the processing speed is improved.

Therefore, also in this embodiment, the same effect as that of the first embodiment can be obtained.

FIG. 12 is a diagram showing a third embodiment of the present invention. In the interrupt subroutine (IRQ1) for determining the fuel injection amount, the fuel supply amount Ti is set to the basic transient correction amount Cpw for this time only.
It is obtained from o (Fig. reference). That is, according to the current transient correction amount Cpwo,
The next detected in-cylinder pressure Pi becomes substantially equal to the target in-cylinder pressure Pi '. Therefore, the next basic transient correction amount Cpwo based on that becomes naturally small, and a deviation occurs between the next detected in-cylinder pressure Pi and the target in-cylinder pressure Pi '.

To make this easier to understand, the flow is as follows: C
Ti corrected by pwo → “Pi≈Pi ′” → Pi
From Cpwo → Ti corrected by Cpwo →
“Pi ≠ Pi ′” → Cpwo is calculated from Pi → Ti corrected by Cpwo → “Pi≈Pi ′” ...
“Pi≈Pi ′” and “Pi ≠ Pi ′” are sequentially repeated. Therefore, as understood from the fact that every other "Pi≈Pi '" occurs, in the present embodiment, the program processing speed is increased (real time) by keeping the correction accuracy practically sufficient. Therefore, also in this embodiment, the same effect as that of the first embodiment can be obtained.

FIG. 13 is a diagram showing a fourth embodiment of the present invention. In the interrupt subroutine (IRQ1) for determining the fuel injection amount, the fuel supply amount Ti is obtained from the transient correction amount Cpwo only this time, and the coefficient K is set to 1 or less (the same figure) reference).

According to this embodiment, practically sufficient correction accuracy can be obtained, and the program processing can be further speeded up (real time).

(Effect of the Invention) According to the present invention, the parameter that correlates with the output torque is detected, and the air-fuel ratio is estimated based on the parameter to correct the mixture ratio. It can be suppressed and the drivability can be improved.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram of the present invention, FIGS. 2 to 7 are diagrams showing a first embodiment of the present invention, FIG. 2 is its schematic configuration diagram, and FIG. 3 (A) is its cylinder pressure sensor. 3B is a plan view showing only the in-cylinder pressure sensor, FIG. 4 is a flow chart showing an interrupt subroutine (IRQ1) for determining the fuel injection amount, and FIG. Is a flowchart showing an interrupt subroutine (IRQ2) for obtaining a parameter correlated with the output torque, FIG. 6 is a flowchart showing the background job program (BGJ), and FIG. 7 is a characteristic diagram showing the concept of the correction. 8 (A) to 8 (D) are views for explaining the action, FIG. 9 is a graph for explaining the effect, FIG. 10 is a timing chart showing the method of the experiment, FIG. Shows a second embodiment of the present invention. FIG. 12 is a flow chart showing an interruption subroutine for determining the fuel injection amount, FIG. 12 is a flow chart showing an interruption subroutine for determining the fuel injection amount showing the third embodiment of the present invention, and FIG. It is a flowchart which shows the interruption subroutine for determining the fuel injection quantity which shows the 4th Example of this invention. 3 ... Injector (fuel supply means), 8 ... Microcomputer (basic supply amount calculation means, parameter calculation means, target value setting means, correction amount calculation means,
Supply amount calculation means), 9 ... In-cylinder pressure sensor (pressure detection means), 17 ... Operating state detection means.

Claims (1)

[Claims] 1. A) pressure detecting means for detecting engine combustion pressure; b) operating state detecting means for detecting engine operating state using load and rotational speed as parameters; and c) detected value by operating state detecting means. A basic supply amount calculating means for calculating a basic supply amount of fuel based on d), d) a parameter calculating means for calculating a parameter correlated with the output torque of the engine as a parameter detection value based on the output of the pressure detecting means, and e) Target value setting means for setting a target value of a parameter correlated with the output torque of the engine based on the value detected by the operating state detecting means, and f) excess or deficiency of the fuel supply amount from the difference between the parameter detected value and the target value. Correction amount calculating means for calculating the amount and calculating the correction amount for the next fuel supply amount based on this excess / deficiency amount; and g) the basic supply amount by the correction amount. An internal combustion engine comprising: a supply amount calculation means for calculating the amount of fuel supplied to the engine; and h) a fuel supply means for supplying fuel to the engine based on the output of the supply amount calculation means. Air-fuel ratio controller.