JPH0240859B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel injection control method suitable for small cylinder engines.

Generally speaking, fuel injection devices that inject fuel into the intake pipe use a method that simplifies the control system for the amount of fuel injected at the same time every revolution. For example, in a six-cylinder engine, one revolution of the engine injects half of the amount required for combustion in all cylinders. is injected, and the remaining half is injected in the next revolution, and the injection timing is synchronized with the frequency division of the ignition signal. As shown in Figure 2, a method is often adopted in which the frequency of the ignition signal, which has three pulses per engine revolution, is divided by 1/3 and used as the injection timing signal. In the case of a four-cylinder engine, the injection timing signal is similarly obtained by dividing the frequency of the ignition signal, which has two pulses per engine revolution, by 1/2, so that simultaneous injection can be easily performed at every revolution.

However, in the case of a three-cylinder engine, as shown in Figure 1B, the ignition signal changes twice every revolution of the engine.
Since pulses and 1 pulse are repeated alternately,
Unlike 6-cylinder engines and 4-cylinder engines, the injection timing signal is synchronized with the divided wave of the ignition signal, and it is not possible to inject fuel once per revolution, so the ignition signal has 3 pulses per 2 revolutions. The frequency is divided into 3 and fuel injection is performed once every 2 revolutions. In other words, in a three-cylinder engine, the entire amount of fuel for three cylinders is injected once every two rotations of the engine.

For this reason, in a three-cylinder engine, the amount of injection per injection is large, and each cylinder has suction, compression, and
Intake conditions varied greatly depending on whether the engine was in the explosion or exhaust stroke, especially whether the intake valve was open or not, and fuel distribution among the three cylinders was unstable. Therefore, the air-fuel ratio increased due to overabsorption, mimicking an increase in unburned hydrocarbons (HC).

An object of the present invention is to provide a fuel injection control method that can stabilize fuel distribution among three cylinders and improve combustion balance, thereby achieving smooth engine rotation and improving exhaust gas (HC) characteristics. There is a particular thing.

In order to achieve the above object, a first fuel injection control method according to the present invention provides an engine that has a point type ignition device and generates an ignition signal three times in two rotations in synchronization with the rotation of the engine to ignite the engine. In the fuel injection control method, the ignition timing of the first cylinder is delayed by a predetermined period of time, and the crank angle of the third cylinder, which is in the intake stroke, is changed from 40 degrees before bottom dead center to 60 degrees after bottom dead center. It is configured to simultaneously inject fuel into each cylinder within a range.

A second fuel injection method according to the present invention is a fuel injection control method for an engine that has a point-type ignition device and generates an ignition signal three times in two rotations in synchronization with the rotation of the engine to perform ignition. It detects that the engine is idling or decelerating, and delays the ignition timing of the first cylinder by a predetermined period of time so that the ignition timing of the third cylinder, which is in the intake stroke, is delayed by a predetermined period of time from the ignition timing of the first cylinder.
Cylinder crank angle changes from 40 degrees before bottom dead center to after bottom dead center
Fuel is injected simultaneously into each cylinder within a range of 60 degrees, and in other conditions, fuel is injected simultaneously into each cylinder in synchronization with the ignition timing of the first cylinder.

According to the above structure, the object of the present invention can be completely achieved.

The present invention will be described in more detail below with reference to the drawings and in comparison with conventional examples.

FIG. 2 is a diagram showing the injection timing and the intake valve opening timing of each cylinder. In Fig. 2, 1, 3, and 2 on the vertical axis are the first cylinder, third cylinder, and second cylinder, respectively, and indicate the ignition order, the horizontal axis indicates the crank angle, T is the top dead center, and B is the top dead center. It is bottom dead center. Ignition timing S
is 10 degrees before the top dead center of each cylinder, and the conventional fuel injection timing was to divide the ignition signal by 1/3 and inject in synchronization with the ignition of the first cylinder. When the injection is synchronized with the ignition of the first cylinder (at the point I in Fig. 2), the intake valves of each cylinder are closed during the combustion stroke for the first cylinder, open during the intake stroke for the third cylinder, and open for the second cylinder during the intake stroke. It is in a closed state during the exhaust stroke, and it can be seen that there is a large difference in the intake conditions among the three cylinders. Of these, the intake valve of the 3rd cylinder is open at the time of fuel injection, so if fuel is injected when the piston of the 3rd cylinder descends to near the bottom dead center, there will be no suction action even if the intake valve is open. It can be seen that the suction conditions have weakened, approaching the intake conditions of the other two cylinders (at the time of J in FIG. 2).

In addition, the inventors of the present invention are concerned with delaying injection timing and evacuation.
The relationship with HC concentration was determined through experiments, and the results shown in Figure 3 were obtained. In FIG. 3, the horizontal axis shows the crank angle, and the vertical axis shows the discharged HC concentration. Here, we will focus on the exhaust HC in the third cylinder, which is the most problematic.
Although the concentration is shown, it is before bottom dead center from ignition synchronized injection.
It can be seen that up to about 40 degrees, the HC concentration is high and the combustion state is unstable, and after that, combustion is stable until about 60 degrees after bottom dead center. In other words, in the case of a 3-cylinder engine, if the crank angle of the cylinder on the intake stroke, here the 3rd cylinder, is in the range of 40 degrees before bottom dead center to 60 degrees after bottom dead center, the intake distribution for each cylinder can be adjusted. It was found that the fuel consumption was stabilized, the combustion balance was improved, and the exhaust gas characteristics were improved accordingly.

Next, the configuration of the present invention will be explained with reference to FIG. FIG. 4 is a block diagram showing an embodiment of a fuel injection control device implementing the first method according to the present invention. The frequency of the ignition signal 2 of the ignition device 1, which generates an ignition signal three times every two revolutions of the engine, is divided by 1/3 by the frequency dividing circuit 3. 3 cylinder crank angle 40 before bottom dead center
The fuel is injected from the injector 7 in response to an injection timing generation signal 6 obtained via a delay circuit 5 which delays the injection timing within a range of 60 degrees after the bottom dead center. Here, the delay circuit 5 is inserted after the frequency divider circuit 3, but it can also be provided before the frequency divider circuit 3.

FIG. 5 is a block diagram showing an embodiment of a fuel injection control device implementing the second method according to the present invention. Focusing on the fact that the above-mentioned error in the mixture distribution between the three cylinders is most apparent in light cylinder conditions such as when idling or decelerating, we developed an opening sensor installed on the accelerator pedal or throttle shaft. Based on the signal from 8, the circuit 9 determines whether or not it is in a light load state.
When the load is light, the injection timing signal 6 passed through the delay circuit 5 is used to inject fuel from the injector 7, and when the load is not light, the divided signal 4 is used as the injection timing signal without passing through the delay circuit 5. The structure is such that fuel is injected from 7. Further, the light load state can also be determined based on a signal from a negative pressure sensor provided in the suction pipe.

As explained in detail above, according to the present invention,
Since the fuel injection timing is set within the range of the third cylinder's crank angle from 40 degrees before bottom dead center to 60 degrees after bottom dead center, the intake action is weak even when the third cylinder's intake valve is open. The intake conditions are close to those of the other two cylinders, the intake distribution in each cylinder is stabilized, the combustion balance is good, and the exhaust gas characteristics are also improved accordingly.

[Brief explanation of drawings]

Figure 1 shows the ignition signal and fuel injection timing. Figure A shows the case of a 6-cylinder engine, Figure B shows the case of a 3-cylinder engine, and Figure 2 shows the case of a 3-cylinder engine.
A diagram showing each cylinder engine stroke and injection timing, FIG. 3 is a graph showing the relationship between injection timing and exhaust HC concentration, and FIG. 4 is an embodiment of a fuel injection control device implementing the first method according to the present invention. A block diagram showing
FIG. 5 is a block diagram showing an embodiment of a fuel injection control device implementing the second method. DESCRIPTION OF SYMBOLS 1... Ignition device, 2... Ignition signal, 3... Frequency division circuit, 4... Frequency division signal, 5... Delay circuit, 6...
Injection timing generation signal, 7... Injector, 8...
Opening sensor, 9...Discrimination circuit, T...Top dead center, B
...Bottom dead center.

Claims (1)

[Claims] In a fuel injection control method for an engine having a one-point ignition device and generating ignition signals three times in two rotations of the engine in synchronization with the rotation of the engine, The fuel is injected into each cylinder simultaneously when the crank angle of the third cylinder, which is on the intake stroke, is within the range of 40 degrees before bottom dead center to 60 degrees after bottom dead center when the ignition timing of the first cylinder is delayed by a predetermined period of time. A fuel injection control method characterized by comprising: 2. In a fuel injection control method for an engine that has a point-type ignition device and generates an ignition signal three times in two rotations of the engine in synchronization with the rotation of the engine to ignite, the engine is in an idling or decelerating state. is detected and delayed by a predetermined period of time from the ignition timing of the first cylinder so that the crank angle of the third cylinder in the intake stroke is within the range of 40 degrees before bottom dead center to 60 degrees after bottom dead center. 1. A fuel injection control method characterized in that fuel is simultaneously injected into each cylinder in other conditions, and fuel is simultaneously injected into each cylinder in synchronization with the ignition timing of the first cylinder in other conditions.