JPH0742893B2 - Fuel system air amount estimation control method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to fuel injection control of an engine, and particularly to a fuel system suitable for fuel injection control without using an air amount sensor and an intake pipe negative pressure sensor. The present invention relates to an air amount estimation control method.

[Background of the Invention]

In the conventional fuel injection control, when the sensor for measuring the air amount does not operate normally, the basic fuel injection pulse of the fuel from the two-dimensional map centering on the throttle angle θ _th and the engine speed N as shown in FIG. Searching for width T _p .
However, since T _p obtained in this way is the basic injection amount during steady operation, even if closed loop control is performed based on the exhaust gas sensor, during transient operation, the injection amount commensurate with the intake air amount is calculated. Can not. Specifically, as shown in FIG. 2, for example, when the throttle angle is opened and the vehicle is accelerated as shown in FIG. 2A, the intake air amount Q _a is as shown in FIG. However, if the conventional method is used, the basic injection amount is retrieved from the map of FIG. 1, so that the basic fuel injection is almost the same as the change in the slot angle in (a) with respect to the transient fuel demand amount. Since the amount T _p is obtained ((c) in the figure), fuel shortage occurs. This causes a lean spike of the air-fuel ratio, which causes a breathing phenomenon and a surging phenomenon during acceleration, and also causes an increase in exhaust gas NO _X.

[Object of the Invention]

An object of the present invention is to perform a fuel injection that can calculate a fuel injection amount so as to obtain a target air-fuel ratio even during a transient operation without using an air amount sensor flowing into an intake air pipe and using an intake pipe negative pressure sensor. Providing a control method, or
Even in a fuel injection control system using an air amount sensor, it is an object of the present invention to provide a fuel injection control method for calculating the fuel injection amount so that the target air-fuel ratio is achieved when the air amount sensor becomes unusable.

[Outline of Invention]

In the D-jet method using a negative pressure sensor in the intake pipe, the intake air amount is obtained from the slot angle and the measured pressure.
On the other hand, a differential equation for the pressure change in the intake pipe is known. In this differential equation, the pressure change in the intake pipe is obtained by the air pressure amount flowing into the cylinder and the air density entering the intake pipe from the throttle portion, and can be calculated mainly from the intake air amount and the engine speed. In this way, by combining the mechanism that determines the intake air amount from the throttle angle and pressure and the mechanism that determines the intake pipe internal pressure from the intake air amount and the engine speed, transient changes occur even during transient operation when the throttle angle changes. Calculate the amount of air to
The engine speed is calculated from the obtained air amount to calculate the basic fuel injection amount T _p .

Example of Invention

An embodiment of the present invention will be described below with reference to the drawings. Third
The figure shows a flow chart for calculating the injection pulse width T _i . T _i is obtained by the following equation.

T _i = T _p (k) · COEF · α + T _B (1) where T _p is the basic injection pulse width, COEF is the sum of various correction factors, α is the feedback back gain, and T _{B is the} battery correction width. ,
k indicates the time.

This is a system for determining the fuel injection amount without using the air amount sensor or the intake pipe negative pressure sensor in the embodiment. As shown in FIG. 3, the basic fuel injection amount T _p (k) is the estimated air amount.
_{It is obtained from a} (k) and the engine speed N (k) as follows. In 4 of FIG. 3, the following equation is executed.

Here, k is a coefficient determined by the characteristics of the injector.

The part that calculates the estimated air amount, which is a feature of the present invention, will be described. As indicated by 3 in FIG. 3, the slot angle θ _th
The estimated air amount is obtained from (k) and the engine speed N (k). Measured slot angle θ at time k
_The estimated air amount is obtained from _th (k) and the intake pipe internal pressure p (k-1) (described later) obtained at 32 in FIG. 3 one hour before as follows.

A = a + b (1-cos (θ _th (k))) (3) where C is the inflow coefficient, Pa is the atmospheric pressure (1 atm in this embodiment), and Ta is the air temperature (in this embodiment). Room temperature), k: specific heat coefficient, g is gravitational acceleration, and R is gas constant. The equations (2) and (3) are executed at 31 in FIG.

From the obtained estimated air amount _a (k), the intake pipe internal pressure _p (k-1) calculated one time before, and the engine speed,
At 32, the intake pipe internal pressure at the current time is calculated as follows.

_{P (k) = E 1 (} k) P (k-1) + E 2 (k) Qa (k) ...
(6) where D is the total displacement of the engine cylinder, ηvol is the volumetric efficiency, V is the intake pipe internal volume, N (k) is the engine speed (R _p M), T _m is the water temperature, and τ is the calculation cycle. . In the present embodiment, considering that the change in the water temperature does not change suddenly, the water temperature T _{m in the} equation (5) is considered.
The equation (5) is calculated with a constant value, but the water temperature T _m in the equation (5) may be data measured by a water temperature sensor. That is, it is easy to change so that the data from the water temperature sensor can be input as the input to 32 in FIG.

Reference numeral 33 in FIG. 3 is a memory that holds the pressure in the intake pipe for one calculation cycle (that is, one time).

According to this embodiment, in (32) of FIG.
The pressure in the intake pipe at the time of opening / closing the slot angle is dynamically calculated by the calculation of the equations (5) and (6), and this is reflected in the estimated air amount, as shown in the example shown in FIG. , When the throttle is opened, the transient movement of the air amount is accurately estimated. As a result, the basic fuel injection amount that substantially matches the required fuel amount for achieving the target air-fuel ratio is calculated, so that the lean spike of the air-fuel ratio does not occur. Therefore, there is an effect that the surging and the breathing phenomenon caused by the lean spike can be avoided.

〔The invention's effect〕

According to the present invention, the intake air amount sensor and the negative pressure sensor in the intake pipe can be used for operation, and the intake air can be calculated by considering the pressure dynamic characteristic in the intake pipe even during the transient operation. Since the amount can be accurately estimated, the target air-fuel ratio can always be achieved. As a result, avoiding bad riding comfort due to the occurrence of lean spikes, and conversely, avoiding the harmful effects of increasing exhaust gas by setting the injection amount to a darker level in order to suppress the occurrence of lean spikes, which was conventionally done it can. Further, according to the present invention, since the air amount sensor or the intake pipe pressure sensor is unnecessary, the cost of the fuel injection control system can be reduced.

[Brief description of drawings]

FIG. 1 is a two-dimensional map that calculates the basic fuel from the throttle angle and the engine speed, FIG. 2 is the movement of the intake air amount during acceleration, and a control example by the conventional method, and FIG.
FIG. 4 is a configuration diagram of control showing an embodiment of the present invention, and FIG. 4 is a diagram showing movement of the estimated air amount and movement of the basic fuel injection amount according to the embodiment. 31 ... Air amount estimation unit, 32 ... Intake pipe pressure estimation unit, 33 ...
... Memory, 4 ... Basic injection amount calculation unit.

Claims (1)

[Claims] 1. An air amount estimating unit for estimating an intake air amount at a current time from a throttle angle measured at the current time and an intake pipe internal pressure estimated at a time before the current time, and an air amount measuring unit measured at the current time. An intake pipe internal pressure estimation unit for estimating the intake pipe internal pressure at the current time from the engine speed, the intake air amount estimated at the current time, and the intake pipe internal pressure estimated at the time before the current time is provided. A method for estimating and controlling the air amount in the fuel system.