JPH0625557B2 - Fuel supply control device for internal combustion engine - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel supply control device for an internal combustion engine that corrects an air-fuel ratio by detecting a parameter correlated with output torque.

(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.

As a conventional fuel supply control device for an internal combustion engine that determines the amount of fuel required by the engine from this type of intake air amount,
For example, "New Edition of Automotive Engineering Handbook, 4th Edition" (September 30, 1983)
Published by Japan Automotive Engineering Society).

In this device, 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, such a conventional fuel supply control device is configured to determine the fuel supply amount corresponding to the target air-fuel ratio from the intake air amount in the steady state. Therefore, when suddenly accelerating the vehicle (hereinafter referred to as transient operation), if the throttle valve is opened suddenly, the inflow air will also increase rapidly, and the fuel supply amount will be determined based on the air flow rate and supplied to the air supply pipe. To be done.

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 output torque of the engine does not follow the throttle opening, and the drivability including acceleration performance deteriorates. There was a problem.

On the other hand, the method of fuel supply in a multi-cylinder engine is performed, for example, for each group, and the amount of ineffective fuel that causes deterioration of drivability at this time is the same as the total amount of fuel adhering to each pipe wall in the group. Become.

(Object of the Invention) Therefore, the present invention detects a parameter that correlates with the output torque, estimates the air-fuel ratio for each cylinder group having the same fuel supply timing based on the detected information, and corrects the mixture ratio. The purpose of the present invention is to improve the drivability by eliminating the large fluctuation of the air-fuel ratio due to the adhesion of the fuel to the pipe wall during the transient operation.

(Means for Solving Problems) In order to achieve the above object, a combustion supply control apparatus for an internal combustion engine according to the present invention has a basic conceptual diagram thereof as shown in FIG. An operating state detecting means a for detecting the operating state, a pressure detecting means b for detecting the combustion pressure of the engine from a plurality of cylinders, and a basic supply amount calculating means for calculating the basic supply amount of fuel based on the engine load and the rotational speed. c, 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 b, and a correlation with the output torque of the engine based on the detection value by the operating state detection means a. Target value setting means e for setting the target value of the parameter to be set, and the excess or deficiency of the fuel supply amount based on the difference between the parameter detection value and the target value. The correction amount calculation means f for calculating the amount and calculating the correction amount for the next fuel supply amount based on this excess / deficiency amount, and the basic injection amount for each of a plurality of cylinder groups to which fuel is supplied at the same timing. A supply amount calculation means g for calculating the fuel supply amount to the engine after being corrected by the correction amount, and a fuel supply means h for supplying fuel to the engine based on the output of the supply amount calculation means g are provided.

(Operation) In the present invention, the parameter that correlates with the output torque is detected, the air-fuel ratio for each cylinder group having the same fuel supply timing is estimated based on the detected information, and the mixture ratio is corrected. Therefore, a drastic fluctuation of the air-fuel ratio due to the adhesion of the fuel to the pipe wall in the transient operation is suppressed, and the drivability is improved.

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

2 to 7 are diagrams showing a first embodiment of the present invention, which is an example in which the present invention is applied to a group injection type 6-cylinder engine.

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 (fuel supply means) 3 for each cylinder based on an injection signal Si. Is injected by. Then, the air-fuel mixture in the cylinder is ignited and exploded by the discharge action of the spark plug 4, becomes exhaust gas, is introduced into a catalytic converter (not shown) through the exhaust pipe 5, and harmful components (CO, H) in the exhaust gas are exhausted in the catalytic converter.
C, NOx) are 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 detection 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 charge amplifier 11,
The charge amplifier 11 constitutes a so-called charge-voltage conversion amplifier including an operational amplifier OP, an input resistor R1, a feedback resistor R2 and an integrating capacitor C, and converts the sensor output S ₁ into a voltage signal S ₂ to be an A / D converter 12. Output. The A / D converter 12 converts the voltage signal S ₂ into a digital signal S ₃ and outputs it to the microcomputer 8.

The in-cylinder pressure sensor 9, charge amplifier 11 and A / D
Although only one converter 12 is shown in the present embodiment, this is for the purpose of avoiding duplication of description, and the converters 12 are actually provided in the number corresponding to the number of cylinders.

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 a function as a basic supply amount calculation means, a parameter calculation means, a target value setting means, a correction amount calculation means, a supply amount calculation means, and a CPU 21, ROM 22,
It comprises a RAM 23 and an I / O port 24. CPU
21 is I according to the program written in ROM 22
I / O port 24 takes in the required data from each unit and exchanges data with the RAM 23 to perform arithmetic processing, and I / O the processed data as necessary.
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 CP
Stores the calculation program in U21, RAM23
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, at P ₁ , the engine speed N is calculated from the input interval of the cylinder discrimination signal S ₅ , and at P ₂ , the intake air amount Qa is read. Next, at P ₃ , the basic fuel supply amount Tp is calculated, for example, by the following equation.

However, in F: constant P ₄ , a background job program (B
GJ) is used to calculate the transient correction amount C _pw for correcting the basic supply amount Tp to obtain the fuel supply amount Ti using the basic transient correction coefficient C _pwo .

C _pw = C _pw ′ −CONST + C _pwo …… where C _pw ′: previous transient correction coefficient CONST: constant In P ₅ , the basic supply amount T using the current transient correction coefficient C _pw
By correcting p, the fuel supply amount Ti (Ti = Tp × C _pw ) is calculated, and at the injection timing designated by P ₆ , an injector drive signal (injection signal) Si having an injection pulse width corresponding to this Ti is calculated. Outputs and ends the interrupt subroutine (IRQ1).

FIG. 5 is a flowchart showing an interrupt subroutine (IRQ2) for obtaining a parameter correlated with the output torque, and 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 θ _N for each cylinder is calculated based on the unit signal S ₄ and stored in a predetermined address of the RAM 23. It should be noted that the predetermined addresses are prepared for the number of cylinders, and in the present embodiment, since there are 6 cylinders, N = 6, that is, θ ₁ to
Up to θ ₆ . Below, N at each step
Similarly, ₁ to ₆ are also included.

Next, at P ₁₂ , the combustion pressure signal S ₃ of each cylinder is read, and this combustion pressure signal S ₃ is replaced with the current cylinder internal pressure P _N. Next, the cylinder internal volume V _N corresponding to the crank angle θ _N is calculated at P ₁₃ , and the cylinder internal volume difference ΔV _N between this V _N and the previous cylinder internal volume V _N ′ (for example, for the # 1 cylinder, , ΔV ₁ = V ₁ ′ −V ₁ ) is calculated.

Multiplying the in P ₁₄ cylinder internal pressure _{P N} and cylinder volume difference [Delta] V _N seek PderutaV _N and. This PΔV _N is an area per predetermined crank angle (for example, 2 °) in a so-called P-V diagram, and each unit area for obtaining a detected indicated effective pressure Pi _N for each cylinder described later.

Next, at P ₁₅ , the PΔV _N obtained corresponding to the current crank angle θ _N and the cumulative value SUM _N of PΔV _N up to the previous time are added, and the process proceeds to the crank angle 0 ° determination step P ₁₆ . P ₁₆
Then, when the crank angle is 0 °, the process proceeds to P ₁₇ and the accumulated value SU
Replace M _N with the detected indicated effective pressure Pi _N of the cylinder. Further, at P ₁₈ , the cumulative value SUM _N is cleared, and the interrupt subroutine (IRQ2) is completed.

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

In this way, the parameters (Pi _N → Pi ₁ , Pi ₂ ... Pi ₆ ) that correlate with the output torque of each cylinder can be obtained, but the point is that this is not limited to this method as long as it is based on the piecewise quadrature method, and other You may obtain by the method of.

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 the step of determining the cylinder group to which the fuel supply at the same timing is performed, for example, when cylinder group is a group of the group and ♯4~♯6 cylinders of ♯1~♯3 cylinder, former ♯3 The cylinder is determined after the top dead center, and the latter is determined after the # 6 cylinder after the top dead center.

That is, when it is determined that after top dead center of ♯3 cylinder in the flowchart adds detection shown effective pressure of ♯1~♯3 cylinders proceeds to P ₂₂ to _{(Pi 1, Pi 2, Pi} 3) respectively, the group detection illustrated The effective pressure Pi is calculated.

P ₂₃ is a step for calculating the target indicated effective pressure Pi ′, which is the engine speed N and the basic fuel supply amount Tp.
As a function of.

Next, P ₂₄ is a step for _{obtaining the} basic transient correction coefficient C _pwo , which is obtained from the target _indicated effective pressure Pi ′ and the group 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 group detected indicated effective pressure Pi is the difference value a, the basic transient correction coefficient C _pwo is determined so that the air-fuel ratio becomes rich by the amount of b. 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 ': a, where Pi': target indicated effective pressure Pi: group detected indicated effective pressure a = Pi'-Pi When expanded, it becomes as follows.

The unburned component / fuel supply amount _{thus obtained} is determined as the basic transient correction coefficient C _pwo . As a result, as shown in FIG. 8 (C), the fuel supply amount Ti is appropriately increased and corrected by this C _pwo, and follows the lean change of the air-fuel ratio during acceleration. For this reason,
As shown in FIG. 4D, the change in the corrected in-cylinder pressure has characteristics that are substantially in line 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. The contents of specifications ~ shown in Figure 9 as three types of line graphs are:
It is as shown in the following table.

As shown in FIG. 10, the experimental method is performed by measuring the time from when the throttle switch is turned on to when the detected cylinder pressure Pi reaches the target cylinder pressure Pi 'at the position indicated by T in the figure. It was As is clear from FIG.
According to this embodiment, the time required to reach the target cylinder pressure Pi 'is shortened to about 1/3, and the acceleration performance is greatly improved.

Furthermore, since the sum of the detected cylinder internal pressures is obtained for each cylinder group that supplies fuel at the same timing, and the same effect as averaging is obtained, the fuel correction amount is also an amount that is averaged correspondingly. Therefore, the detection error (so-called variation) of the individual detected cylinder internal pressure is alleviated, and the stable fuel correction amount can be controlled, whereby the combustion can be stabilized.

FIG. 11 is a diagram showing a second embodiment of the present invention, in which the processing procedure of the background job program (BGJ) for obtaining the basic transient correction coefficient is modified.

First, the basic supply quantity Tp of the engine speed N and fuel P ₃₁
'Seek, target indicated effective pressure Pi in P _32' target indicated effective pressure Pi from computing the respective cylinder fuel correction coefficient C _N from the detection shown effective pressure Pi _N. Then the first at P ₃₃
Determine the cylinder group in the same manner as in Example, if tentatively after top dead center of ♯3 cylinder, proceeds to P _34. Here, # 1 to # 3
The average value Av of the cylinder fuel correction coefficients (C _{1 to} C ₃ ) of each cylinder is calculated by the following equation.

However, C ₁ : Cylinder fuel correction coefficient for # 1 cylinder C ₂ : Cylinder fuel correction coefficient for # 2 cylinder C ₃ : Cylinder fuel correction coefficient for # 3 cylinder This average value Av is P ₃₅ and _{becomes the} basic transient correction coefficient C _pwo It is replaced.

Meanwhile, when determining that after top dead center of ♯6 cylinder at P ₃₃ is, P
Proceeding to ₃₆ , the average value Av of the cylinder fuel correction coefficients (C _{4 to} C ₆ ) of the # 4 to # 6 cylinders is calculated, and similarly, the basic transient correction coefficient C _pwo is replaced at P ₃₅ .

As described above, in this embodiment, the fuel correction coefficient for each cylinder is obtained, and the value obtained by averaging the fuel correction coefficient for each group is used as the basic transient correction coefficient C _pwo , so that it is stable as in the first embodiment. The fuel correction amount can be controlled, and the combustion can be stabilized.

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 transient correction coefficient C _pw is calculated according to the following equation, and the coefficient B of the equation is calculated. Is different from the first embodiment in that the value is 1 or less (see [P ₄₁ ] in the same figure), and similar effects can be obtained in this embodiment.

C _pw = C _pw ′ + C _pwo ) × B ... 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 the basic transient correction coefficient C only for this time
_{This is obtained} from _pwo (see (P ₅₁ ) in the figure), that is, the next detected in-cylinder pressure Pi becomes substantially equal to the target in-cylinder pressure Pi 'by the basic transient correction coefficient C _{pwo at} this time. The next basic transient correction coefficient C _{pwo on} the basis of which becomes naturally small, and the next detected cylinder pressure Pi
Between the target cylinder pressure Pi 'and the target cylinder pressure Pi', and this is repeated every other interval. As understood from this, in the present embodiment, the program processing speed is increased (real time) by keeping the correction accuracy practically sufficient. The same effect as the example can be obtained.

FIG. 14 is a diagram showing a fifth 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 coefficient C only for this time.
_{It is obtained} from _pwo and the coefficient B is set to 1 or less (see [P ₆₁ ] in the same figure).

According to this embodiment, practically sufficient correction accuracy can be obtained, and the speed of program processing (real time) can be increased.

It should be noted that the above-described embodiments have been described by taking the two-group injection system for a six-cylinder engine as an example, but it goes without saying that the present invention can be applied to other multi-cylinder engines and other group injection systems.

(Effect) According to the present invention, the parameter that correlates with the output torque is detected, and the air-fuel ratio is estimated for each cylinder group having the same fuel supply timing based on the detected information to correct the mixture ratio. The large fluctuation of the mixing ratio during the transient operation can be eliminated, 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 of the background job program, FIG. 12 is a flow chart of an interrupt subroutine for determining the fuel injection amount of the third embodiment of the present invention, and FIG. 13 is the fourth embodiment of the present invention. FIG. 14 is a flowchart of the interrupt subroutine for determining the fuel injection amount, and FIG. 14 is a flowchart of the interrupt subroutine for determining the fuel injection amount showing the fifth embodiment of the present 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), 14 ... Operating state detection means.

Claims (1)

[Claims] 1. A) operating state detecting means for detecting an operating state of the engine using engine load and engine speed as parameters; b) pressure detecting means for detecting combustion pressure of the engine from a plurality of cylinders; and c) engine load. And a basic supply amount calculation means for calculating a basic supply amount of fuel based on the number of revolutions, and d) a parameter calculation 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 detection means. A) target value setting means for setting a target value of a parameter correlated with the output torque of the engine based on a value detected by the operating state detecting means, and f) a fuel supply amount based on a difference between the parameter detected value and the target value. Correction amount calculation means for calculating the correction amount for the next fuel supply amount based on the excess / deficiency amount, and g) the base A supply amount calculating means for calculating the fuel supply amount to the engine by correcting the injection amount for each of a plurality of cylinder groups to which fuel is supplied at the same timing, and h) based on the output of the supply amount calculating means. And a fuel supply means for supplying fuel to the engine.