JPS61116038A - Fuel injection control method for internal-combustion engine - Google Patents

Abstract

PURPOSE:To reduce production of NOx, by a method wherein, in a device which fuel, providing a lean air-fuel ratio, in injected through a part of injection valves, the fuel is injected through said injection valve between the second stage of an exhaust stroke and a suction stroke, and the fuel is injected through other injection valve between a compression stroke and the first stage of the exhaust stroke. CONSTITUTION:In a drive in which a fuel injection valve 12 is installed in an intake air branch 11 communicated with an intake air port 5 of each cylinder for 4-cylinder engine, ignition is set in the order of #1, #3, #4, and #2, the #1 and #4 cylinders are set as a lean cylinder which provides a lean air-fuel ratio, and the #3 and #2 cylinders as a stoiki cylinder which provides a value near to a theorectical air-fuel ratio. In this internal-combustion engine, control is effected such that fuel is injected through a fuel injection valve 12 on the lean cylinder side between the second stage of an exhaust stroke and a suction stroke, and the fuel is injected through the fuel injection valve 12 on the stoiki cylinder side during a compression stork and the first stage of the exhaust stroke. This increases a learn combustion limit, and decrease production of NOx.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention has fuel injection valves corresponding to the number of cylinders, and some of the fuel injection valves inject fuel giving a relatively lean air-fuel ratio, and the remaining fuel injection valves inject fuel that provides a relatively lean air-fuel ratio. The present invention relates to a fuel injection control method for an internal combustion engine in which a fuel injection valve provides an air-fuel ratio close to the stoichiometric air-fuel ratio.

Conventional technology In the light and medium load range of engines, it is advantageous in terms of fuel consumption and exhaust purification to perform combustion at the leanest possible air-fuel ratio, and lean burn has recently been promoted.

In heavy vehicle weight classes, operating on all cylinders only at a lean air-fuel ratio where catalyst purification of NOx cannot be relied upon may not be sufficient in terms of exhaust purification. Therefore, N
In order to operate some cylinders at a stoichiometric air-fuel ratio that allows oxygen to be purified by the catalyst, fuel that provides a relatively lean air-fuel ratio is injected from some fuel injection valves, and the stoichiometric air-fuel ratio is injected from the remaining fuel injection valves. A fuel injection control method for an internal combustion engine is known in which fuel that provides an air-fuel ratio close to the fuel ratio (14,5) is injected. Further, fuel injection methods include simultaneous injection in all cylinders, injection by group, and independent injection in which each cylinder is injected during its intake stroke.

Problems to be Solved by the Invention When combustion is caused at a lean air-fuel ratio, there is a limit to the leanness in order to ignite the fuel and achieve good combustion, and this limit changes depending on when the fuel is injected. . When fuel is injected during the intake stroke, there is a problem in that the concentration of nitrogen oxides NOx increases in the exhaust gas from the cylinder set to the stoichiometric air-fuel ratio. The present invention provides an internal combustion engine in which fuel giving a relatively lean air-fuel ratio is injected from some fuel injection valves, and fuel giving an air-fuel ratio close to the stoichiometric air-fuel ratio is injected from the remaining fuel injection valves. An object of the present invention is to expand the lean burn limit and reduce NOx by appropriately setting fuel injection timing in a fuel injection control device.

Means for Solving the Problems The present invention provides a fuel injection control device as described above, in which fuel is injected from the exhaust gas ff1lL'4 gear from the fuel injection valve of the lean cylinder during the intake stroke, and the air-fuel ratio is close to the stoichiometric air-fuel ratio. It is characterized in that fuel is injected from the cylinder between the compression stroke and the first half of the exhaust stroke.

Embodiment In FIG. 1, a piston 2 is inserted into a cylinder block 1, and a combustion chamber 4 is formed between the top of the piston 2 and the inner surface of a cylinder head 3.

An intake port 5 and an exhaust port 6 communicate with the combustion chamber 4, and an intake valve 7 and an exhaust valve 8 are arranged respectively. The intake port 5 is connected to an intake pipe 9 leading to an air cleaner and an intake branch pipe 11 connected from a surge tank 10 .

A fuel injection valve 12 is arranged in the intake branch pipe 11 . The fuel injection valve can also be arranged directly in the intake port. In the present invention, a fuel injection valve 12 is provided for each cylinder.

13 is a spark plug, 14 is an air flow meter, and 15 is a throttle valve. The fuel injection valve 12 is constituted by a solenoid valve, and its opening timing and opening time are controlled by a control device 16. The control device 16 includes a central processing unit (CPU) 17,
It is composed of a read-only memory (ROM) 18, a random access memory (RAM) 19, and a clock (CL) 20, which are interconnected by a bus 21. The control device 16 receives a signal a from the air flow meter 14, a crank angle signal 6 using the rotor of the distributor,
Cooling water temperature signal C and other detector signals are input through the input/output port 22, and these detector signals and ROM
A control signal is output to the fuel injection valve 22 according to a program built in the fuel injection valve 18.

In the internal combustion engine configured as described above, some cylinders (5th and 6th
For the NOI and NO4 cylinders in the figure), the fuel injection amount is set to give a lean air-fuel ratio of approximately 20 to 25 as shown in Figure 4 (hereinafter referred to as lean cylinders), and for the remaining cylinders (the 5th
, NO3 and NO2 cylinders in Figure 6) are at the stoichiometric air-fuel ratio (14,
5) The fuel injection amount is set to give the air-fuel ratio (
(hereinafter referred to as stoichiometric cylinder). Such air fuel consumption can be given by the injection time determined by multiplying the basic injection time determined according to the intake air amount and intake pipe negative pressure by a coefficient set for each cylinder, and further, It can be corrected according to specific engine conditions by correction factors such as temperature and acceleration.

The fuel injection timing of the internal combustion engine having the lean cylinder and stoichiometric cylinder described above is set as follows. Second
3 and 3 respectively show the lean limit air-fuel ratio (A/F) and the NOx generation amount, which are the focus of the present invention, and these graphs are obtained through experiments. From Figure 2, the fuel injection start timing is several tens of degrees before the end of the exhaust stroke (approximately 4 degrees in Figure 2).
It was found that the lean limit is expanded to the lean side when it is set between 0 degrees) and the suction stroke. Also, from Figure 3, when fuel is injected from the exhaust during the intake stroke, N
It was found that the generation of Ox increased. Therefore, in a lean cylinder, by injecting between the exhaust stroke and the intake stroke, the air-fuel ratio can be further leanened to achieve good combustion, thereby reducing overall fuel consumption.

Further, in a stoichiometric cylinder, NOx can be reduced by performing injection between the compression stroke and the expansion stroke.

FIG. 5 shows an embodiment in which the present invention is applied to a group injection system. Cylinder discrimination is performed using a sensor (G720) that generates a pulse every 720 degrees of the crank angle and a sensor (G180) that generates a pulse every 180 degrees.
This can be done by counting up a counter (CYSL) every time a 0 pulse occurs, and discharging the value by 0 with a G720 pulse. Therefore, in the case of Figure 5, No.
The intake stroke of the cylinder is shown. In addition, in FIGS. 5 and 6, the cylinders are arranged according to the firing order. In the group injection shown in Fig. 5, when NO1 cylinder (lean) is in the intake stroke and NO4 cylinder (stoichiometric) is in the compression stroke, G18
Injection occurs simultaneously in both cylinders at a predetermined crank angle (or time) after the 0 pulse occurs, and then 3
At a time delayed by 60 degrees, when the NO4 cylinder (lean) is in the intake stroke and the NO3 cylinder (stoichiometric) is in the compression stroke, injection is performed in both cylinders simultaneously.

In the independent injection shown in Fig. 6, during the intake stroke of the No. 1 cylinder (lean), the No. 2 cylinder (lean) is delayed by 180 degrees.
Injection is performed during the expansion stroke of the NO4 cylinder (lean), during the expansion stroke of the NO3 cylinder (stoichiometric), and during the expansion stroke of the NO3 cylinder (stoichiometric).

As described in detail, according to the present invention, fuel efficiency and exhaust purification performance can be improved.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a fuel injection internal combustion engine, Figure 2 is a graph showing the lean limit, Figure 3 is a graph showing the amount of NOx generated, Figure 4 is a diagram for explaining lean and stoichiometric cylinders, and Figure 4 is a graph showing the lean limit. FIG. 5 is a timing chart showing an embodiment of group injection, and FIG. 6 is a timing chart showing an embodiment of independent injection. 12...Fuel injection valve, 16...Control device. . Figure 2 Injection start crank angle Injection start crank angle Figure 4 - Engine load Figure 5 Group injection Exhaust Suction pressure Expansion Exhaust Suction pressure Expansion #1 Stroke Figure 6 ゛ Yoyu'jjyo #2

Claims (1)

[Claims] It has fuel injection valves corresponding to the number of cylinders, some of the fuel injection valves inject fuel that provides a relatively lean air-fuel ratio, and the remaining fuel injection valves inject fuel that provides an air-fuel ratio close to the stoichiometric air-fuel ratio. In the fuel injection control method for an internal combustion engine, some of the fuel injection valves inject fuel from the latter half of the exhaust stroke to the intake stroke, and the remaining fuel injection valves inject fuel from the compression stroke to the exhaust stroke. A fuel injection control method for an internal combustion engine, characterized in that fuel is injected during the first half of the stroke.