JPH06280651A - Method of controlling fuel injection of engine and device therefor - Google Patents

Abstract

PURPOSE:To determine a fuel injection volume with which the air-fuel ratio can be set to a stoichiometric air-fuel ratio by controlling the fuel injection volume in accordance with a fuel volume in an engine intake-air pipe which is estimated with the use of a specific fuel system model. CONSTITUTION:In a control mechanism incorporating an engine process 1 and fuel injection control in a computer, a liquid film model coefficient forming part 3 calculates a wall surface sticking rate and a liquid film evaporating time-constant, and an intake-air pipe air-mass calculating part 4 calculates an air-mass in an intake-air pipe from an intake-air pipe pressure. Further, an intake-air pipe condition estimating part 2 estimates a fuel volume in the engine intake-air pipe with the use of a fuel system model incorporating a time K-d at which the fuel injection volume is controlled, and a dead-time (d) corresponding to a difference from a time K at which a controlled result is observed. A fuel injection volume calculating part 5 delivers an estimated evaporated fuel value in accordance with thus estimated fuel volume. Thereby it is possible to precisely control the air-fuel ratio which is based upon an actual condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control for an engine, and more particularly to a fuel injection control method and apparatus for an engine suitable for a fuel injection type engine in which air and fuel are sent to a cylinder through an intake pipe.

[0002]

2. Description of the Related Art In conventional fuel injection control, the fuel injection amount is corrected by various methods so that a three-way catalyst for cleaning exhaust gas has a stoichiometric air-fuel ratio that works most effectively.

[0003]

There is a problem that the air-fuel ratio cannot be kept at the stoichiometric air-fuel ratio, especially during acceleration / deceleration. The cause of this is that the state of the fuel in the intake pipe is not taken into consideration despite various corrections being made.

An object of the present invention is to estimate and predict state quantities such as a liquid film and vapor fuel in the intake pipe from a dynamic characteristic model of the fuel system, and based on that, the fuel injection quantity so that the air-fuel ratio becomes the theoretical air-fuel ratio. A fuel injection control method and apparatus for determining

[0005]

[Means for Solving the Problems] The dynamic characteristic of the fuel system is that a part of the fuel injected into the intake pipe adheres to the wall surface of the intake pipe to form a liquid film, and the liquid film evaporates with a certain time constant and the injected fuel is injected. It is inhaled with the cylinder. However, here, not all the evaporated fuel is sucked into the cylinder, but a part of the fuel remains as vapor in the intake pipe (hereinafter, this is referred to as vapor fuel). In the present invention, by taking this phenomenon, the injection amount is controlled so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. In other words, the amount of liquid film and vapor fuel, which are important for knowing the fuel dynamics, are defined by the air mass Mat (k) flowing through the throttle, the throttle opening, the intake pipe pressure P (k), the water temperature, the engine speed, and the air-fuel ratio. It is estimated and predicted from the data, and based on this, the injection amount is controlled so that the stoichiometric air-fuel ratio is achieved.

[0006]

Since the dead time between the control time point and the observation time point is taken into consideration, highly accurate air-fuel ratio control according to the actual state becomes possible.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a control configuration of fuel injection control in an engine process 1 and a computer. The liquid film model coefficient creating unit 3 calculates the wall surface attachment rate X and the liquid film evaporation time constant τ as follows.

[0008]

[Equation 1]

[0009]

[Equation 2]

Here, k represents k time.

The intake pipe air mass calculation unit 4 calculates the intake pipe air mass M from the intake pipe pressure P (k) as follows.

[0012]

[Equation 3]

Here, a ₁ is a constant determined by the intake pipe internal volume and the intake pipe temperature.

Further, in the fuel injection amount calculation section 5, the X
(K), M (k), the mass of air flowing through the throttle obtained from the engine process, M _at (k), and the predicted value of the steam fuel M _v (k + 1) described later are added to the upper part of M. The fuel injection amount G _f is calculated as follows. In addition,
・ M is considered to be the same as the one that is attached to the upper part of M in the formula 4 and below.

[0015]

[Equation 4]

Here, (A / F) is the theoretical air-fuel ratio.

In the intake pipe internal state estimation unit 2, the liquid film deposition rate X, the evaporation time constant τ, the intake pipe air mass M, the air mass flowing through the throttle / M _at (k), and the engine rotation obtained from the engine process. From the number N, the intake pipe pressure P, and the air-fuel ratio A / F, the liquid film amount and the vapor fuel are estimated and predicted as the state inside the intake pipe, and in the embodiment, the vapor fuel predicted value is output to the fuel injection amount calculation unit 5. .

The structure and operation of the intake pipe internal state estimating unit 2 will be described with reference to FIG. The estimated value of the mass of air drawn into the cylinder, M _ap (^ attached to the upper part of M) is calculated by the calculation circuit 28 as follows.

[0019]

[Equation 5]

Here, a ₂ is a constant determined by the engine displacement and the gas constant.

The obtained estimated value of M _ap (k) is input to the shift register 29, shifted to the right, and then accumulated at the end. The coefficient creating circuit 21 is a part that creates the coefficients of the model for estimating and predicting the state in the intake pipe, and the above-mentioned X (k), τ (k), M (k), · M _at (k)
More as follows.

[0022]

[Equation 6]

[0023]

[Equation 7]

[0024]

[Equation 8]

[0025]

[Equation 9]

[0026]

[Equation 10]

[0027]

[Equation 11]

Here, ΔT is a sampling period.

The coefficients obtained by the coefficient creating circuit 21 are accumulated in the memory table 22, and the data previously accumulated is accordingly shifted to the right.

On the other hand, in the memory table 24, the fuel injection amount G _f (k + 1) obtained from the calculation unit 5 in FIG. 1 is added to the end while shifting to the right as in the memory table 22.

Air-fuel ratio data A / F obtained from O ₂ sensor
(K-d) has an exhaust gas flow delay in the exhaust pipe, and this delay also changes depending on the engine speed N (k). The calculation circuit 27 of FIG. 2 calculates the observation delay time (hereinafter referred to as dead time) d of the air-fuel ratio data as follows.

[0032]

[Equation 12]

Here, d is an integer multiple of the sampling period, and [] in the twelfth expression is an integer symbol.

Since the dead time d is obtained, the air-fuel ratio data obtained at the time k is the air-fuel ratio before the time d and can be written as A / F (k-d). From the A / F (k−d) and · M _ap (k−d) in the memory table 29, the calculation circuit 30 obtains the estimated value of the fuel sucked into the cylinder before d time as follows. .

[0035]

[Equation 13]

Next, knowing the dead time d, the G _fe
(K−d) and A obtained from the memory table 22.
₁ (k) to A ₁ (k-d), A ₂ (k) to A ₂ (k-
d), A ₃ (k) to A ₃ (k−d), B ₁ (k) to B ₁
(K−d), C ₁ (k) to C ₁ (k−d), D ₁ (k)
To D ₁ (k-d) information and G _f (k) to G _f (k-d) information obtained from the memory table 24 and M _fi1m (k) obtained from memory tables 25 and 26 described later.
From the predicted value of −d) and the information of M _v (k−d), the calculation circuit 23 of FIG. 2 estimates and predicts the liquid film and the vapor fuel as shown below. For simplicity, put the following.

[0037]

[Equation 14]

[0038]

[Equation 15]

[0039]

[Equation 16]

[0040]

[Equation 17]

Here, for example, (•) represents time.

[0042]

[Equation 18]

[0043]

[Formula 19]

[0044]

[Equation 20]

From the above equations, the predicted values of the liquid film in the intake pipe and the (k + 1) time of the vapor fuel were calculated.

The predicted vapor fuel value obtained by the equation (20) is output to FIG. In addition, M _fi1m (k−d +
1) to M _fi1m (k) and M _v (k−d + 1) to M
_{Store v} (k) in memory tables 25 and 26.

According to the embodiment of the present invention, taking into consideration the time change of the O ₂ sensor which changes depending on the engine speed,
The air-fuel ratio can be maintained near the stoichiometric air-fuel ratio by estimating and predicting the liquid film amount and steam fuel, and controlling the fuel injection amount based on the predicted steam fuel. This makes it possible to reduce harmful exhaust gas.

[0048]

According to the present invention, the air-fuel ratio can be maintained in the vicinity of the stoichiometric air-fuel ratio with high accuracy, and therefore, the harmful gas can be reduced. Hereinafter, the control effect of the present invention will be described with reference to FIGS. 3 and 4. FIG. 3 shows a conventional example.
During acceleration such that the throttle is opened from 10 ° to 20 °, the air-fuel ratio entering the cylinder becomes thin, and the air-fuel ratio shows a value higher than the theoretical air-fuel ratio. This causes a lot of harmful nitrogen oxides to be emitted. On the other hand, FIG. 4 shows an example of control performance according to the present invention. The air-fuel ratio and the fuel injection amount when controlled under the same conditions as those shown in FIG. 3 are shown. Compared with the conventional method, the air-fuel ratio can be maintained near the stoichiometric air-fuel ratio. This shows that harmful exhaust gas can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of an example of a control device for fuel injection control according to the present invention.

FIG. 2 is a configuration diagram of an intake pipe internal state estimation unit.

FIG. 3 is a diagram showing a conventional example of an air-fuel ratio and a fuel injection amount with respect to a change in throttle opening.

FIG. 4 is a diagram showing an air-fuel ratio and a fuel injection amount with respect to a change in throttle opening according to the present invention.

[Explanation of symbols]

1 ... Engine process, 2 ... Intake pipe state estimation unit, 3 ...
Liquid film model coefficient creation unit, 4 ... Intake pipe air mass calculation unit,
5 ... Fuel injection amount calculation unit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mikihiko Taisei 1099, Ozenji, Aso-ku, Kawasaki, Kanagawa, Ltd. System Development Laboratory, Hitachi, Ltd. Hitachi Sawa Factory

Claims (2)

[Claims] 1. A fuel quantity in an intake pipe of an engine is predicted and predicted based on a fuel system model incorporating a dead time corresponding to the difference between the time of controlling the fuel injection quantity of the engine and the time of observing the control result. Fuel injection control method for an engine, which controls the fuel injection amount based on the determined fuel amount. 2. A dead time corresponding to the difference between the means for observing the state quantity of the engine to be controlled, the means for controlling the fuel injection quantity of the engine, and the time for controlling and observing the state quantity as a result of the control. A fuel injection control device for an engine, comprising: a fuel system model incorporating time; and means for applying an observation result of the state quantity to the fuel system model to predict a fuel amount in an intake pipe of the engine.