JPH07139395A - Fuel injection control method - Google Patents

Abstract

PURPOSE:To prevent rapid lowering of engine rotation by a method wherein the initial value of a correction factor during return of fuel cut is decided according to a lowering speed detected when fuel injection is restarted and thereafter correction factor during return of fuel cut is gradually increased from an initial value. CONSTITUTION:Usually, fuel is injected in a fuel injection amount determined according to an engine running state. When at least a throttle valve is in a full closed state and the number NE of revolutions of an engine exceeds the set number Necut of revolutions, fuel cut is executed. When it is below the number of revolutions lower than the set number Necut of evolutions by a given value at S2, fuel injection is restarted. The lowering speed of the number NE of revolutions of an engine during a time in which fuel cut is executed is detected at S3. When fuel injection is restarted, the initial value KFFCI of a fuel cut return correction factor FFC is decided according to a detecting lowering speed at S4. Thereafter, since a correction factor FFC during return of fuel cut is gradually increased from the initial value KFFCI, a shock during return of fuel cut is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a fuel injection control method for an internal combustion engine for an automobile when a fuel cut is restored.

[0002]

2. Description of the Related Art Conventionally, as a fuel injection control method of this kind, as in the electronically controlled fuel injection method for an internal combustion engine disclosed in Japanese Patent Laid-Open No. 59-28029, for example, the throttle valve is fully closed and the engine speed. Ne is the set speed Necu
When it is determined that the deceleration does not require the supply of fuel when t or more, the fuel injection is stopped (fuel cut), and then the engine speed Ne becomes a value lower than the set speed by a certain speed Nehys, or It is known that the fuel cut is stopped (return to fuel cut) when the throttle valve is opened. In such a fuel injection control method, as a countermeasure against a shock after returning from the fuel cut, there is a set value KDN having a deviation DNEIG of the engine speed Ne.
When the value is smaller than EFFC, the correction coefficient FFC at the time of fuel cut is temporarily set smaller than the value at the time of fuel cut by the initial value KFFCI, and thereafter, the correction value KFFCDMP is set to the correction coefficient FFC _n-1 at the time of the previous fuel cut every unit time. The correction coefficient FFC at the time of fuel cut recovery is calculated by adding
_The fuel injection control is performed as _n (the operation is shown in FIG. 5).

[0003]

By the way, in the case of performing the fuel injection control as described above, the value of the initial value KFFCI is the engine speed Ne during fuel cut.
Is constant regardless of the change state of. That is, as shown in FIG. 6, regardless of whether the deviation DNEIG of the engine speed Ne during fuel cut is large or small, the correction coefficient FFC at the time of fuel cut is reduced by the set initial value KFFCI. And fuel injection is performed.

However, when the engine speed Ne rapidly decreases after the start of fuel cut, that is, the deviation DNEI.
When G is large (shown by the solid line in FIG. 6), if the fuel cut recovery correction coefficient FFC is uniformly reduced by the initial value KFFCI, the fuel injection amount becomes insufficient, and the engine speed Ne rapidly decreases and the operating state Changes suddenly, and if worse, the engine may stall, and in some cases the shock at the time of fuel cut recovery cannot be improved.

An object of the present invention is to eliminate such a problem.

[0006]

The present invention takes the following means in order to achieve such an object. That is, the fuel injection control method according to the present invention always performs fuel injection with a fuel injection amount required according to the engine operating state, at least the throttle valve is fully closed, and the engine speed is equal to or higher than the set speed. In this case, a fuel cut is performed, and in the fuel injection control method in which fuel injection is restarted when the number of revolutions is lower than the set number of revolutions by a predetermined value, the engine revolution number during the fuel cut is changed. When detecting the descent rate and restarting fuel injection, determine the initial value of the fuel cut return correction coefficient according to the detected descent rate, and then gradually increase the fuel cut return correction coefficient from the initial value. Is characterized by.

[0007]

With this structure, the initial value of the correction coefficient at the time of fuel cut recovery differs between when the engine speed drops sharply during fuel cut and when it falls gently, and Fuel injection after returning from the fuel cut is performed according to the engine operating state. In other words, for fuel injection after fuel cut recovery, the initial value of the fuel cut recovery correction coefficient is determined according to the engine speed descent rate during fuel cut, so the fuel cut recovery correction coefficient may become too small. There is no. Therefore, it is possible to prevent the engine from stalling, and it is possible to properly reduce the shock when returning from the fuel cut.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

The engine schematically shown in FIG. 1 is for an automobile, and its intake system 1 is provided with a throttle valve 2 which opens and closes in response to an accelerator pedal (not shown), and a surge tank is provided downstream thereof. 3 is provided. In the vicinity of the cylinder head 30 side end of the intake manifold 4 of the intake system 1 communicating with the surge tank 3, a fuel injection valve 5 is further provided.
An intake valve 31 is provided in the cylinder head 30 in front of the fuel injection valve 5. Further, an O ₂ sensor 21 for measuring the oxygen concentration in the exhaust gas is attached to the exhaust system 20 at a position upstream of a three-way catalyst 22 arranged in a pipe line up to a muffler (not shown).
The O ₂ sensor 21 outputs a voltage signal h corresponding to the oxygen concentration.

The electronic control unit 6 includes a central processing unit 7
An A / D converter (not shown) mainly composed of a microcomputer system including a memory device 8, an input interface 9, and an output interface 11 for converting an input analog signal into a digital signal. Is built in. The pressure in the surge tank 3, that is, the intake pressure (hereinafter,
Intake pressure signal a output from the intake pressure sensor 13 for detecting the intake pressure), a rotation speed signal b output from the rotation speed sensor 14 to detect the engine speed Ne, and a vehicle speed detection. The throttle sensor 16 for detecting the open / closed state of the throttle valve 2 has an idle switch 16a for outputting the vehicle speed signal c output from the vehicle speed sensor 15 and the idle signal i when the throttle valve 2 is fully closed. The throttle opening signal d and the idle signal i output from the engine, the water temperature signal e output from the water temperature sensor 17 for detecting the cooling water temperature of the engine, the voltage signal h output from the O ₂ sensor 21 are input. To be done. On the other hand, the output interface 11 outputs a fuel injection signal f corresponding to an effective injection time TAU described later to the fuel injection valve 5 and an ignition pulse g to the spark plug 18.

The electronic control unit 6 has an intake pressure signal a output from the intake pressure sensor 14 and a rotation speed signal b output from the rotation speed sensor 15 as main information, and is determined according to the rotation state of the engine. Basic injection time TP with various correction factors
To correct the fuel injection valve opening time, that is, the effective injection time T
AU is set, and the fuel injection valve 5 is set according to the set time.
The fuel injection valve 5 to control the fuel according to the engine load.
A program for injecting air into the intake system 1 near the cylinder head 30 is built in. Furthermore, in this program, basically, fuel injection is always performed with the fuel injection amount required according to the engine operating state, and at least when the throttle valve is fully closed and the engine speed is equal to or higher than the set speed. Is configured to execute fuel cut, and to restart fuel injection when the number of revolutions is lower than the set number of revolutions by a predetermined value. Particularly, when the fuel cut is restored, the fuel cut is performed. When the fuel injection is restarted, the initial value of the fuel cut return correction coefficient is determined according to the detected lower speed, and then the fuel cut return correction is performed from the initial value. It is programmed to gradually increase the coefficient.

The outline of this fuel injection control program is as shown in FIG. However, as the program itself for calculating the effective injection time TAU in consideration of various correction factors during steady operation, a conventionally known program can be used, and therefore illustration and description thereof will be omitted. This program
It has an initial value map that defines an initial value KFFCI of the fuel cut return correction coefficient FFC with respect to the deviation DNEIG which is the descent speed of the engine speed Ne while the fuel cut is being executed. The initial value KFFCI is, as shown in FIG. 3, directly proportional to the deviation DNEIG.

First, in step S1, it is determined whether or not the fuel is being cut. If the fuel is being cut, the process proceeds to step S2. If not, the process proceeds to step S5. The fuel cut is determined at least when the throttle valve 2 is fully closed and the engine speed Ne is the set speed Ne.
It is performed depending on whether or not the fact that it is cut or more is satisfied at the same time. Note that the fuel cut may be determined by adding the engine coolant temperature to the condition. In step S2, it is determined whether or not the engine speed Ne is lower than the set speed Necut by a constant speed Nehys.
If it is below the range, the process proceeds to step S3. If not, the process returns to another routine. In step S3, the falling speed of the engine speed Ne during the fuel cut, that is, the deviation DN
It is determined whether the EIG is below the deviation reference value KDNEFFL. If it is below the deviation reference value KDNEFFL, the process proceeds to step S4. If not, the process returns to another routine. This deviation DNE
IG is calculated by the change in the engine speed Ne per unit time. In step S4, the correction coefficient FFC at the time of fuel cut recovery is determined according to the detected deviation DNEIG.
The initial value KFFCI of is read from the initial value map. If there is no target deviation DNEIG in the initial value map, the initial value KFFCI is calculated by interpolation calculation. After this, the effective injection time TAU is calculated with the initial value KFFCI as the fuel cut return correction coefficient FFC.

In step S5, it is determined whether or not the correction coefficient FFC after the fuel cut is less than 1, and if it is less than 1, the process proceeds to step S6, and if not, the process proceeds to another routine. In step S6, the correction value KFFCDMP is added to the fuel cut return correction coefficient FFC at that time to calculate a new fuel cut return correction coefficient FFC.
The value of the correction value KFFCDMP is set to be constant regardless of the magnitude of the deviation DNEIG, in other words, regardless of the rate of decrease of the engine speed Ne.

According to this structure, the set rotational speed Ne is set.
When the engine is running above cut and the throttle valve 2 is fully closed, fuel cut is started,
When the engine speed Ne becomes smaller than the value obtained by subtracting the constant speed Nehys from the set speed Necut, the fuel cut is restored. In this case, the control proceeds from step S1 to S2, and when the deviation DNEIG of the engine speed Ne falls below the deviation reference value KDNEFFL, the control proceeds to step S3 →
In S4, the initial value KFFCI of the fuel cut return correction coefficient FFC corresponding to the descending speed of the engine speed Ne during fuel cut is set. The initial value KFFCI varies depending on the magnitude of the deviation DNEIG during the fuel cut, and is a value of the fuel cut return correction coefficient FFC suitable for the engine rotation speed decrease speed at the time of the fuel cut return. Therefore, the fuel injection amount at the time of returning to the fuel cut does not become excessive or insufficient with respect to the engine speed Ne at that time, and a shock is not felt in the operating state of the engine after returning to the fuel cut.

In this way, when returning from the fuel cut, the control proceeds from step S1 to S5, and the control proceeds to step S1 until the fuel cut return correction coefficient FFC becomes 1.
Repeat 1 → S5 → S6. By repeating step S6, the correction coefficient F at the time of fuel cut recovery
FC is the initial value KF set at the same time as the fuel cut return
Correction value KFFC every time step S6 is executed from FCI
It increases by DMP, and finally becomes 1 as shown in FIG. Correction factor FF after returning from fuel cut
The time until C becomes 1 is not constant and becomes longer as the deviation DNEIG of the engine speed Ne during fuel cut increases. Therefore, the shock after returning from the fuel cut can be improved, the engine can be prevented from stalling, and thereafter, the engine speed Ne can be converged to the idle speed according to the falling speed of the engine speed Ne during the fuel cut.

The present invention is not limited to the embodiment described above.

In addition, the configuration of each part is not limited to the illustrated example, and various modifications can be made without departing from the spirit of the present invention.

[0019]

As described in detail above, according to the present invention, the initial value of the correction coefficient at the time of fuel cut recovery after the fuel cut recovery is
Since the speed is set according to the engine speed drop rate during fuel cut, it is possible to prevent the engine speed from dropping sharply at the same time as the fuel cut returns when the engine drop rate is large, and to suppress the occurrence of engine stall. At the same time, it is possible to almost eliminate the shock when returning from the fuel cut.

[Brief description of drawings]

FIG. 1 is a schematic configuration explanatory view showing an embodiment of the present invention.

FIG. 2 is a flowchart showing a control procedure of the embodiment.

FIG. 3 is a graph showing the contents of an initial value map of the same embodiment.

FIG. 4 is an operation explanatory view of the same embodiment.

FIG. 5 is an operation explanatory view of a conventional example.

FIG. 6 is an explanatory view of the operation of the conventional example.

[Explanation of symbols]

 1 ... Intake system 2 ... Throttle valve 5 ... Fuel injection valve 6 ... Electronic control unit 7 ... Central processing unit 8 ... Storage device 9 ... Input interface 11 ... Output interface

Claims (1)

[Claims] 1. A fuel injection is always performed according to a fuel injection amount required according to an engine operating condition, and a fuel cut is executed at least when a throttle valve is fully closed and an engine speed is equal to or higher than a set speed. However, in the fuel injection control method in which fuel injection is restarted when the number of revolutions is lower than the set number of revolutions by a predetermined value, the decrease rate of the engine revolution number during the fuel cut is detected, Fuel injection control characterized in that, when the injection is restarted, an initial value of the fuel cut return correction coefficient is determined according to the detected descent speed, and thereafter the fuel cut return correction coefficient is gradually increased from the initial value. Method.