JPH0413543B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to a fuel control device for an internal combustion engine, and in particular to correcting an imbalance between the amount of intake air and the amount of fuel supplied due to the dynamic characteristics of the air system and fuel system. Regarding technology.

(Prior art) As a conventional fuel control device, there is, for example, the one shown in FIG.
-35165, 55-134718, etc.)

In FIG. 1, 1 is an air cleaner, 2 is an intake pipe, 3 is a throttle valve, 4 is an air flow meter that outputs an air amount signal S1 corresponding to the amount of air passing through the intake pipe 2, and 5 is a fuel injection amount, which will be described later. a fuel injection valve that injects an amount of fuel according to the signal S3; 6 is a cylinder;
7 is a rotation sensor that outputs a rotation signal S2 synchronized with the rotation of the crankshaft, and 8 is mainly an air amount signal S.
1 and rotation signal S2, and outputs a fuel injection amount signal S3 according to the result, such as a CPU, RAM, ROM, I/O, etc. It consists of a microcomputer consisting of.

The calculation of the fuel injection amount in the above device is performed as follows.

That is, the intake air amount obtained from the air amount signal S1 measured by the air flow meter 4 is Q, the rotation speed of the internal combustion engine obtained from the rotation signal S2 is N,
When the coefficient is K, the fuel injection amount (fuel injection pulse width) Tp is calculated by the following equation (1).

Tp=KQ/N (1) The above coefficient K is a coefficient for adding correction according to the temperature of the internal combustion engine, etc.

As shown in equation (1) above, the fuel injection amount is set mainly depending on the intake air amount and rotation speed,
The actual fuel injection amount is obtained by adding corrections based on temperature, exhaust gas component concentration, etc.

However, in the conventional device, the air amount signal S1 of the air flow meter is used as it is as a signal indicating the intake air amount, and control is performed so that all the injected fuel is taken into the cylinder without any time delay.

In other words, in conventional devices, the air amount is the measured value of the air flow meter itself, and the fuel amount is the fuel injected into the intake pipe, and does not control the amount of air or fuel actually taken into the cylinder. Nakatsuta.

Therefore, accurate control is possible in a steady state, but in a transient state, errors occur due to the dynamic characteristics of the air system and fuel system, which causes the air-fuel ratio to deviate from the target value, resulting in poor fuel efficiency, exhaust purification performance, and operational performance. There was a problem that it had a negative effect on performance, etc.

(Objective of the Invention) The present invention was made to solve the above problem, and is an accurate method that corresponds well to the actual amount of intake air in the cylinder (hereinafter simply referred to as the amount of intake air) and the amount of fuel supplied. An object of the present invention is to provide a fuel control device that can perform control.

(Summary of the invention) In order to achieve the above object, the present invention includes:
Dynamic characteristics Ga of the air system measured and memorized in advance
The actual intake air amount is calculated from the air amount signal detected by the sensor, and the next intake air amount is predicted from the past and current intake air amounts, and the current and next required fuel is calculated from these intake air amounts. Calculate the amount,
Furthermore, the fuel system is configured to calculate the amount of fuel Ff(n) to actually be supplied from the dynamic characteristic Gf of the fuel system and the above-mentioned required fuel amount.

(Examples of the Invention) The present invention will be described in detail below based on Examples.

First, the dynamic characteristics of the air system and fuel system will be explained in detail based on FIG.

For example, when a throttle valve is opened and closed as shown in A in FIG. 2, a flap-type air flow meter (such as an air flow meter) outputs a signal as shown in B.

At this time, the intake air amount changes as shown by the broken line C1 of C.

On the other hand, fuel is injected with a substantially negligible delay time in response to signal B from the air flow meter. However, since the injected fuel has dynamic characteristics different from those of air, the amount of fuel actually drawn into the cylinder is as shown by the solid line C2, which does not match the change in the amount of intake air.

Therefore, the air-fuel ratio becomes as shown in D and deviates from the target value (for example, the stoichiometric air-fuel ratio).

FIG. 3 is a system diagram showing the above dynamic characteristics. In Figure 3, air flow meter output Aa(n)
In contrast, the intake air amount Ac(n) can be expressed as Ac(z)=Ga(z)Aa(z)...(2) using the transfer function Ga(z) that describes the dynamic characteristics of the air system. I can do it. However, in equation (2), (n) indicates the control period, and n is this time, n-1
indicates the previous control cycle, and n+1 indicates the next control cycle. Also
Ac(z) and Aa(z) are Ac(n) and Aa(n) respectively
is the z-transform of

Also, the actual intake fuel amount of the cylinder relative to the fuel amount Ff(n) injected by the injection pulse width Tp calculated by the fixed algorithm Tp = KAa/N
Fc(n) is a transfer function that describes the dynamic characteristics of the fuel system
Using Gf(z), it can be expressed as Fc(z)=Gf(z)Ff(z)...(3). However, Fc(z), Ff(z)
are the z-transforms of Fc(n) and Ff(n), respectively.

In the above equations (2) and (3), Ga(z) and Gf
If (z) are not the same, the ratio between the amount of intake air and the amount of fuel in the cylinder changes in a transient state, and the air-fuel ratio deviates from the target value.

The present invention solves the above problems and will be described in detail below.

FIG. 4 is a diagram showing an embodiment of the present invention, and the same reference numerals as in FIG. 1 indicate the same parts.

In FIG. 4, numeral 9 denotes a calculation device, including an intake air amount calculation section 10, a fuel calculation section 11, a storage section 12,
It consists of 13. Note that this configuration shows the contents of the arithmetic unit 9 by function, and in reality, it is configured by, for example, a microcomputer.

The intake air amount calculation unit 10 includes an air flow meter 4
The actual intake air amount is calculated from the air amount signal S1 given from the air amount signal S1 and the dynamic characteristics of the air system that have been determined in advance through experiments and stored in the storage unit 12, and an intake air amount signal S4 corresponding to the calculated value is output. .

The fuel calculation unit 11 receives the above-mentioned intake air amount signal S4.
The required fuel amount at that time is calculated from the above, and the actual amount of fuel to be injected is calculated from the required fuel amount and the dynamic characteristics of the fuel system that have been determined in advance through experiments and stored in the storage unit 13. Corresponding fuel supply amount signal S
Outputs 5.

The fuel injection valve 5 is controlled by this fuel supply amount signal S5.
By controlling this, it is possible to perform control corresponding to the actual intake air amount and fuel amount of the cylinder even during transient conditions, so the balance between the air amount and fuel amount is always maintained and the air-fuel ratio is kept at the target value. can be maintained.

Next, the calculations of the calculation device 9 will be explained in detail based on the flowchart of FIG.

In FIG. 5, first at P1, the air amount signal S1 of the air flow meter 4 is read and its value is set as Aa(n-1). Note that n-1 indicates a value in the previous control cycle.

Next, in P2, the intake air amount value Ac(n) in the current control cycle is calculated. This calculation is performed as follows.

The dynamic characteristics of the air system in the intake system of an internal combustion engine (air flow meter, intake pipe, etc.) are expressed, for example, by the second-order pulse transfer function Ga(z)=d ₁ z ^-1 +e ₁ z ^-2 /1+b ₁ z ^-1 +c ₁ z ^-2 …(4) can be well described.

Then, the above Aa (n-1), the value Aa (n
-2), the value Ac of the intake air amount before the first and second time
(n-1), Ac(n-2), and the above equation (4), the current intake air amount value Ac(n) is determined by the following equation (5).

Ac(n)=d ₁ Aa(n-1)+e ₁ Aa(n-2) -b ₁ Ac(n-1)+c ₁ Ac(n-2)...(5) Therefore, the above coefficient b ₁ , c ₁ , d ₁ , and e ₁ are determined in advance through experiments, Ac(n) can be determined by calculation.

Next, in P3, the value of the next intake air amount
Predictively calculate Ac(n+1).

This value can be determined as Ac(n+1)=2Ac(n)-Ac(n-1) from the current and previous intake air amounts using an extrapolation formula, for example. Note that the reason why the predictive calculation of Ac(n+1) is necessary will be described later.

Next, in P4, the intake air amount obtained in P2
Using Ac(n), the current required fuel amount Fc(n) is calculated from equation (6) below.

Fc(n)=KAc(n)/N (6) The above required fuel amount Fc(n) is the amount of fuel actually required within the cylinder corresponding to the actual intake air amount.

Next, in P5, using Ac (n+1) obtained in P3, calculate the next required fuel amount Fc (n+1) as shown below (7).
Calculate from the formula.

Fc(n+1)=KAc(n+1)/N...(7) Next, in P6, the amount of fuel Ff(n) that should actually be injected in order to supply the above required fuel amount to the cylinder.
Calculate.

For example, the dynamic characteristic Gf(z) of the fuel system is as follows (8)
It is shown by the formula.

Gf(z)=d ₂ z ^-1 +e ₂ z ^-2 /1+b ₂ z ^-1 +c ₂ z ^-2 = (d ₂ +e ₂ z ^-1 /1+b ₂ z ^-1 +c ₂ z ^-2 )Z ^-1 ...(8) In the above equation (8), the fractional part enclosed in brackets corresponds to the curve part of the dynamic characteristics, and the part z ^-1 outside the brackets corresponds to one sample delay time.
Note that the one-sample delay time is a predetermined delay time until the value of the above equation (8) starts to rise for the first time. In the dynamic characteristics of an actual fuel system, from the time when the injector drive signal rises until the time when the amount of fuel in the cylinder starts to increase, the activation delay time of the fuel injector and the amount of injected fuel in the cylinder are determined. Since there is a delay time that is the sum of the delay time until reaching the point, the actual dynamic characteristics can be well approximated by using an approximation equation that first has a delay time, such as the above equation (8). Note that the above equation (8) shows the equation of a second-order lag system, but the dynamic characteristics can be well approximated if the system is a second-order or higher order system.

If the dynamic characteristic Gf of the fuel system is given by the above equation (8), then
The amount of fuel Ff(n) to be injected this time is expressed by the following equation (9).

Ff(n)=1/d ₂ [Fc(n+1)+b ₂ Fc(n) +c ₂ Fc(n-1)−e ₂ Ff(n-1)] …(9) Therefore, the above coefficient b ₂ , c ₂ , d ₂ , and e ₂ are determined in advance through experiments, Ff(n) can be determined by calculation.

Next, in P7, fuel injection is performed by driving the fuel injection valve 5 according to the amount of fuel Ff(n) to actually be injected, which has been determined as described above.

By controlling as described above, it is possible to always maintain a balance between the amount of intake air and the amount of fuel in the cylinder, so that the air-fuel ratio can always be maintained at the target value even in a transient state.

Note that the reason why Ac(n+1) was predictively calculated in P3 was to calculate Fc(n+1) in P5, and Fc(n+1) was needed to calculate Ff(n) in P6. be.

It goes without saying that prediction calculations further ahead are also possible if necessary.

Further, in the above embodiment, an air flow meter is used as a sensor for measuring the amount of intake air, but a variable vane type, hot wire type, Karman vortex type, or other type of air flow meter may be used.

Furthermore, the present invention can be applied in the same manner as described above even in the case of a method in which the intake air amount is estimated from the intake negative pressure, the throttle valve opening, etc. without immediately measuring the intake air amount.

In addition, the dynamic characteristics Ga(z) and Gf of the air system and fuel system
It is more practical to describe (z) in synchronization with the rotation of the internal combustion engine, and therefore it is preferable to perform the calculation in FIG. 5 in rotation synchronization.

Furthermore, since the above-mentioned dynamic characteristics vary depending on the type of internal combustion engine and fuel supply system, and may also vary depending on the operating range of the internal combustion engine, it is preferable to have a plurality of them as necessary.

(Effects of the Invention) As explained above, according to the present invention, the amount of intake air and the amount of fuel actually taken into the cylinder are determined by taking into account the dynamic characteristics of the air system and fuel system that have been measured and stored in advance. Since it is configured to control the air-fuel ratio, it is possible to reduce the deviation from the target value of the air-fuel ratio even during transient conditions such as during acceleration and deceleration, thereby improving exhaust purification performance, fuel efficiency, driving performance, etc. can be improved. In particular, the dynamic characteristics of the fuel system
By using Gf and a means of predicting and calculating the next intake air amount required for that purpose, it is possible to put into practical use a control device that can perform control that is well adapted to the actual operation of the internal combustion engine. This effect can be obtained.

[Brief explanation of drawings]

Fig. 1 is an example diagram of a conventional device, Fig. 2 is an example characteristic diagram of the device shown in Fig. 1, and Fig. 3 is a system diagram showing dynamic characteristics.
FIG. 4 is a diagram showing an embodiment of the present invention, and FIG. 5 is a flowchart diagram showing an embodiment of the calculation of the present invention. Explanation of symbols, 1... Air cleaner, 2... Intake pipe, 3... Throttle valve, 4... Air flow meter, 5
. . . Fuel injection valve, 6 .

Claims (1)

[Scope of Claims] 1. A sensor that outputs an air amount signal related to the intake air amount of an internal combustion engine, and a sensor that calculates a required fuel amount of the internal combustion engine from the air amount signal and other engine operating variables, and provides fuel corresponding to the amount of fuel required for the internal combustion engine. In a fuel control device for an internal combustion engine, comprising a calculation means for outputting a signal and a fuel supply means for supplying an amount of fuel to the internal combustion engine according to the above fuel signal, Memorize the dynamic characteristic Ga between the amount of intake air and
a calculation means for calculating the current intake air amount from the air amount signal and the dynamic characteristic Ga of the air system, and further predicting the next intake air amount from the past intake air amount and the current intake air amount; The dynamic characteristics Gf of a predetermined order lag system (the predetermined order is 2 or more) with a one sample delay between and the amount of fuel actually taken into the cylinder are memorized, and the current and next intake air amounts mentioned above are calculated. The current required fuel amount Fc(n) and the next required fuel amount Fc(n+1) of the internal combustion engine are calculated using the above-described method, and the fuel amount to be supplied this time Ff( n) and a calculation means for outputting a fuel supply amount signal corresponding to the value, and the internal combustion engine is configured to control the fuel supply means based on the fuel supply amount signal. Engine fuel control system.