JPH0625556B2 - 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 intake pipe is increased by the rapid increase in the air flow rate described above, and the supplied fuel is condensed into liquid fuel. The generation of liquid fuel produces partially ineffective fuel that adheres to and stays on the pipe wall, and temporarily dilutes the air-fuel mixture flowing into the combustion chamber.

Further, the amount of the accumulated and accumulated fuel increases with the passage of time, and a part of the accumulated fuel flows into the combustion chamber to make the mixture rich.

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.

(Object of the invention) Therefore, the present invention detects a parameter that correlates with the output torque of the engine, corrects the fuel supply amount based on the parameter, and reduces the predetermined amount so as to suppress overrich with respect to the fuel supply amount. The purpose of this correction is to improve the drivability by eliminating a large change in the air-fuel ratio (particularly, overrich) due to the adherence of fuel to the wall surface in the transient operation.

(Means for Solving Problems) In order to achieve the above object, a fuel supply control device for an internal combustion engine according to the present invention has a basic conceptual diagram shown in FIG. The operating state detecting means a for detecting the operating state, the pressure detecting means b for detecting the combustion pressure of the engine, the basic fuel supply amount calculating means c based on the engine load and the number of revolutions, and the output of the pressure detecting means b. Parameter calculating means d for calculating a parameter correlated with the output torque of the engine as a parameter detection value based on the above, and a target value for setting a target value of the parameter correlated with the output torque of the engine based on the detection value by the operating state detection means a. The setting means e and an excess / deficiency of the fuel supply amount are obtained from the difference between the parameter detection value and the target value, and the next or next amount is calculated based on this excess / deficiency A correction amount calculating means f for calculating the fuel supply amount for one time, and an overrich preventing means g for preventing the overrich by correcting the fuel supply amount calculated by the correction amount calculating means f by further decreasing by a predetermined amount.
And a fuel supply means h for supplying the engine with the final supply amount of fuel determined by the overrich prevention means g.

(Operation) In the present invention, the fuel supply amount is corrected by the parameter that correlates with the output torque of the engine, and further, a predetermined amount of decrease correction is performed so as to prevent overrich against this fuel supply amount. 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, and the charger amplifier 11 has an operational amplifier OP and an input resistance R.
1, the so-called charge consisting feedback resistor R2 and the 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
The / D 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 an overrich prevention means, and the CPU 21, R
It is composed of an OM22, a RAM23 and an I / O port 24. The CPU 21 fetches external data required from the I / O port 24 in accordance with the program written in the ROM 22, and exchanges data with the RAM 23 to perform arithmetic processing and process it as necessary. Outputs data to I / O port 24. A for I / O port 24
The signals from the / D converters 7 and 12 and the operating state detecting means 14 are input, and the injection signal (injector drive pulse) Si is output from the I / O port 24. ROM
22 stores the calculation program in the CPU 21,
The RAM 23 is a so-called working memory that temporarily stores 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 then gradually approaches the target. 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.

By the way, the accumulated amount of the fuel adhering to and accumulated on the pipe wall increases with the passage of time, and a part thereof flows into the combustion chamber to bring the air-fuel ratio into an overrich state.

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 retained on the wall surface, and the correlation with the output torque during transient operation Calculate the above-mentioned ineffective fuel amount by calculating the parameter to estimate the air-fuel ratio from this and correct the fuel supply amount, and further perform a decrease correction of the fuel supply amount by a predetermined amount, thereby changing the air-fuel ratio during transient operation. It suppresses a large lean state and the subsequent rich state.

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 . Next, at P ₃ , the basic fuel supply amount Tp as a function of N and Qa
Is calculated according to the following equation.

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

Cpw = Cpw ′ + Cpwo−A, where Cpw ′: previous transient correction coefficient, A: overrich correction coefficient, where coefficient A in the formula flows into the cylinder after a certain amount of unburned fuel due to wall adhesion is accumulated. Then, it is a correction term for preventing the air-fuel ratio from swinging to the rich side, and the reduction correction of a predetermined amount, which is the point of the present invention, is performed by this.
To explain this, when the fuel supply amount Ti is controlled only by the basic transient correction coefficient Cpwo, the inflow of unburned fuel into the fuel chamber is not included as a control operator, so the air-fuel ratio becomes overrich rich ( There is a risk of becoming a region on the right side of the point C in FIG. 7). If overrich occurs, the detected value of the parameter that correlates to the output torque decreases, which increases the fuel supply amount Ti. As a result, the overrich is further promoted to fall into an uncontrollable state. Therefore, by performing the reduction correction by a predetermined amount, the correction function is performed within the swing range indicated by the amount b in FIG. In this embodiment, this correction term is calculated by the following equation.

A = func (N) ...... However, in N: rotation speed P ₅ , using the transient correction coefficient Cpw this time, the basic supply amount T
p is corrected, and the fuel supply amount Ti is calculated by the following equation.

Ti = Tp × Cpw ...... Then, when the injection timing designated by P ₆ comes, an injector drive signal (injection signal) Si having an injection pulse width corresponding to this Ti is output, and an interrupt subroutine (IRQ1)
To finish.

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

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. Then, the cylinder internal volume V corresponding to the crank angle θ at the interrupt timing is obtained at P ₁₃ , and the cylinder internal volume difference ΔV between this V and the previous cylinder internal volume V ′ is calculated by the following equation.

ΔV = V′−V ... At P ₁₄ , the cylinder internal pressure P is multiplied by the cylinder internal volume difference ΔV to obtain P
ΔV is obtained, and this PΔV is the area per predetermined crank angle (for example, 2 °) in the so-called PV diagram,
It becomes 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 (detected indicated effective pressure Pi) correlated with the output torque is obtained, but the point is that it is not limited to this method as long as it is based on the piecewise quadrature method, and may be obtained by other methods.

FIG. 6 is a flowchart showing a background job program (BGJ) for obtaining the basic transient correction coefficient Cpwo, which is the interrupt subroutine (IRQ1) described above.
This program is always executed while (IRQ2) is not executed.

First, a calculation coefficient K in P _21, obtained by the following equation.

However, K ′: the previous value, and then the target indicated effective pressure P which becomes a predetermined target value at P ₂₂
i'is calculated by the following equation.

Pi ′ = Tp × K ... Further, at P ₂₃ , a difference ΔPi between the detected indicated effective pressure Pi and the target indicated effective pressure Pi ′ is obtained. As will be described later in detail, this difference ΔPi has a value corresponding to the unburned portion of the fuel which is divided into the burned portion and the unburned portion due to the adhesion of the wall surface during the transient operation. Further, at P ₂₄ , the basic transient correction coefficient Cpwo is obtained using the above-mentioned difference ΔPi, and the concept is shown in FIG. 7. That is, in the figure, the difference ΔPi between the target indicated effective pressure Pi ′ and the detected indicated effective pressure Pi is ΔPi.
Is a difference value a, the basic transient correction coefficient Cpwo is determined so that the air-fuel ratio becomes rich by an amount of b. 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 ′: ΔPi ′, where Pi ′: target indicated effective pressure, Pi: detected indicated effective pressure ΔPi = Pi′−Pi Formula for obtaining unburned amount / fuel supply amount from the above formula When expanded to, the following formula is obtained.

The unburned component / fuel supply amount thus obtained is determined as the basic transient correction coefficient Cpwo. As a result, as shown in FIG. 8 (C), the fuel supply amount Ti
Is appropriately corrected by this Cpwo to follow the lean change of the air-fuel ratio during acceleration. Further, the final injection pulse width Ti is corrected to be reduced by the correction term -A, so that the air-fuel ratio is prevented from swinging to the overrich side. 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. 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.

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 B of the equation is calculated. The difference from the first embodiment is that it is set to 1 or less (see FIG. ₁₃ [P ₃₁ ]).

Cpw = (Cpw '+ Cpwo) * B ........ Comparing this with the correction term -A of the first embodiment,
The value of −A is set by A = func (N). Where N
Is the engine speed, that is, its set value changes depending on the acceleration condition.

On the other hand, B is a constant value that does not depend on the acceleration condition,
Therefore, there are 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 coefficient C only for this time.
It is obtained from pwo (see [P ₄₁ ] in the same figure). That is, the detected next in-cylinder pressure Pi becomes substantially equal to the target in-cylinder pressure Pi 'by the basic transient correction coefficient Cpwo of this time. Therefore, the next basic transient correction coefficient Cpwo based on it naturally becomes small, and the next detected cylinder pressure P
There is a deviation between i 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
Cpwo is calculated from → 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 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 ₅₁ ] in the same figure).

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

FIG. 14 is a diagram showing a fifth embodiment of the present invention, which is an example in which the target indicated effective pressure Pi ′ is reduced and corrected in the background job program (BGJ) for obtaining the basic transient correction coefficient (FIG. 14). [Refer to P ₆₁ ]. That is, the target indicated effective pressure Pi 'is reduced and corrected by the coefficient A set according to the acceleration condition, whereby the same effect as that of the first embodiment can be obtained. The same effect can be obtained by multiplying the constant B instead of the coefficient A.

Further, as another embodiment, it is obvious that the same effect as the reduction correction of the present invention can be obtained by increasing the value of the detected detection effective pressure Pi.

(Effect) According to the present invention, a parameter that correlates with the output torque of the engine is detected, the fuel supply amount is corrected by the parameter, and a predetermined amount of decrease correction is performed so as to suppress overrich with respect to the fuel supply amount. Therefore, a large change (especially, overrich) in the mixing ratio during transient operation can be eliminated, and 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. FIG. 14 is a flow chart showing an interrupt subroutine for determining the fuel injection amount according to the fourth embodiment of the present invention, and FIG. 14 is a flow chart showing the background job program 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, 9 ... In-cylinder pressure sensor (pressure detection means), 14 ... ... Operating state detecting means.

Claims (1)

[Claims] 1. An a) operating condition detecting means for detecting an operating condition of the engine using the engine load and a rotational speed as parameters; b) a pressure detecting means for detecting a combustion pressure of the engine; and c) an engine load and a rotational speed. A basic supply amount calculation means for calculating a basic supply amount of fuel based on the following: 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; 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 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. And the fuel calculated by the correction amount calculation means, which calculates the next fuel supply amount based on this excess / deficiency amount, and g) The fuel supply system further includes an overrich prevention unit that corrects the supply amount by a predetermined amount to prevent overrich, and h) a fuel supply unit that supplies the engine with a final supply amount of fuel determined by the overrich prevention unit. A fuel supply control device for an internal combustion engine, comprising: