JPH07119507A - Inter-cylinder injection type spark ignition engine - Google Patents

Abstract

PURPOSE:To atomize and disperse injection fuel so as to prevent generation of smoke at the time of uniform combustion by dividing and injecting a fuel injection amount necessary at the time of low rotation by plural times, when fuel injection is started during intake stroke in an engine operating condition in which the uniform combustion is carried out. CONSTITUTION:A intake passage 1 is communicated with a base cylinder inside through an intake valve 2, and also an exhaust passage 3 is communicated therewith through an exhaust valve 4. An ignition plug 5 is arranged on the center of a cylinder upper part. A fuel injection valve 6 for injecting fuel into a cylinder is arranged between a plurality of intake valves 2. On the other hand, a recessed combustion chamber 7a is formed on the top surface of a piston 7. The fuel injection valve 6, starts fuel injection operation during intake stroke in such an engine operating condition that uniform combustion is carried out. In this case, necessary fuel injection amount is divided and injected by plural times, at least in engine operating condition of low rotation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-cylinder injection spark ignition engine in which a required amount of fuel is directly injected into a cylinder and an air-fuel mixture formed thereby is ignited and burned by an ignition plug.

[0002]

2. Description of the Related Art A cylinder injection type spark ignition engine as described above is used to form an air-fuel mixture having a good ignitability near the spark plug and a lean air-fuel mixture is formed around the air-fuel mixture. As a result, stratified charge combustion is known, which enables combustion with low fuel consumption while maintaining reliable ignitability. However, it has been found that uniform combustion is advantageous for obtaining high output, and JP-A-60-30420 discloses that fuel injection is started from the latter half of the compression stroke in order to realize stratified combustion at low engine load. However, there is described a cylinder injection type spark ignition engine in which fuel injection is started from the first half of the intake stroke in order to realize uniform combustion at high engine load.

This in-cylinder injection spark ignition engine starts fuel injection from the first half of the intake stroke when the engine is under high load where high output is required, so that the injected fuel is good in a relatively long time until ignition. It is intended to form a uniform air-fuel mixture in the combustion chamber by evaporating into air and mixing with intake air sufficiently.

[0004]

Generally, the fuel injection amount control is performed by changing the valve opening time of the injection valve according to the engine load while the injection pressure is constant. In the above-mentioned prior art, in the formation of a uniform air-fuel mixture at high engine load, if the engine speed is high, the piston descending amount per unit time is large, and the intake air flow velocity is very fast accordingly, and the piston descends continuously. At the end of injection, the fuel injected into was sufficiently atomized and diffused by the intake air that was supplied to the cylinder in a large amount, evaporated during the subsequent compression stroke, and was well homogenized by ignition. A mixture can be formed in the combustion chamber. On the other hand, when the engine speed is low, the amount of piston lowering per unit time is small, and the fuel injected at substantially the same amount from the same injection timing is at a certain level due to the intake air that is supplied in a small amount at the end of injection. Atomized. In the subsequent intake stroke, this mass of atomized fuel gradually diffuses into the internal space of the cylinder where it descends with the piston and is gradually increased in volume by the intake air supplied. By the time, all cannot be diffused into the entire space in the cylinder, and what remains in the vicinity of the top surface of the piston forms a rich air-fuel mixture there during the compression stroke and produces smoke.

Accordingly, an object of the present invention is to provide a cylinder injection type spark ignition engine capable of preventing the generation of smoke during uniform combustion.

[0006]

A cylinder injection type spark ignition engine according to the present invention has a fuel injection valve that starts fuel injection during an intake stroke in an engine operating state in which uniform combustion is performed, and at least the engine operating state. It is characterized in that the required fuel injection amount is divided into a plurality of injections at the time of low rotation in the state.

[0007]

In the cylinder injection type spark ignition engine described above, fuel injection is started during the intake stroke in the engine operating state in which uniform combustion is executed, and the required fuel injection amount is plural times at least during low engine speed in the engine operating state. It is divided and injected.

[0008]

1 and 2 are sectional views of a cylinder injection type spark ignition engine according to the present invention. In these drawings, 1 is an intake passage communicating with the inside of the cylinder via an intake valve 2, and 3 is an exhaust passage communicating with the inside of the cylinder via an exhaust valve 4. The intake passage 1 is a helical port that generates swirl in the cylinder, and although not shown, the front side of the drawing is a straight port that is another intake passage through another intake valve and another exhaust valve. Another exhaust passage communicates with the inside of each cylinder via the.

A spark plug 5 is provided at a substantially central position above the cylinder.
Is provided, and a fuel injection valve 6 that injects fuel into the cylinder from between the two intake valves is provided. This fuel injection valve 6
Is a swirl valve that injects fuel at a constant pressure, and the fuel injection amount control is performed by changing the valve opening time. Reference numeral 7 denotes a piston, which has a concave combustion chamber 7 on its top surface.
a is formed. The swirl valve 6 injects fuel in a conical shape in an atomized state.

FIG. 3 is a diagram showing a fuel injection period with respect to a load at a specific engine speed in a high engine speed region. As shown in the figure, when the engine load is low, the fuel injection valve is opened from the latter half of the compression stroke, and is closed when the valve opening time for injecting the required fuel amount according to the load has elapsed. Therefore, all of the injected fuel is supplied to the combustion chamber 7a on the top surface of the piston 7, and a mixture having a concentration with good ignitability is formed in the vicinity of the spark plug 5 to realize stratified combustion with good fuel economy. .

When the engine is under medium load, the fuel injection valve is opened from the first half of the intake stroke, and when the valve opening time for injecting the required fuel amount corresponding to the load excluding a fixed amount necessary for ignition elapses. The valve is closed and the fuel injection valve is opened again from the same timing as when the engine load is low in the latter half of the compression stroke, and it is closed when the valve opening time for injecting the aforementioned fixed amount has elapsed regardless of the load at this time. . In the fuel injection in the intake stroke, because of the high speed rotation range, the descending amount of the piston 7 per unit time is large, the accompanying intake air amount per unit time is large, and the intake air flow velocity is very fast. The fuel that is continuously injected in the atomized state as it descends is diffused by the intake air that is supplied in a relatively large amount in the cylinder at the end of injection, and this diffusion state is further supplied in the subsequent intake stroke. It becomes even better by the high-speed intake that is performed, and by the time the fuel injection in the compression stroke is started, it vaporizes sufficiently in the entire cylinder to form a good homogeneous mixture in the combustion chamber and The injected fuel forms an air-fuel mixture with a good ignitability near the spark plug as in the above, and this air-fuel mixture is surely ignited, and this flame is uniform as described above. To ensure that propagate in Aiki, good stratified combustion for at in engine load is achieved.

When the engine is under high load, the fuel injection valve is opened from the same timing as when the engine is under medium load in the first half of the intake stroke, and is closed when the valve open time for injecting the required amount of fuel according to the load has elapsed. . The fuel injected in this way has an increased injection amount (valve opening time of the fuel injection valve) as compared with the intake stroke injection at the time of the engine medium load described above, but at the injection end time, a large amount of fuel is injected by that amount. Since the intake air is supplied to the cylinder, it is likewise diffused throughout the cylinder, and during the subsequent compression stroke it is sufficiently evaporated to form a good homogeneous mixture in the combustion chamber to obtain high output. In addition, it is possible to realize uniform combustion which is more advantageous than the stratified combustion that is performed at low and medium loads.

FIG. 4 is a diagram showing a fuel injection period with respect to a load at a specific engine speed in the low engine speed region. Since the engine speed is in the low speed range, the crank angle range in which approximately the same amount of fuel is injected is narrower than in the high speed range shown in FIG. Therefore, in the intake stroke injection, the amount of lowering of the piston 7 per unit time becomes small, so that the amount of intake air per unit time accompanying it becomes small and the intake air flow velocity becomes slow.

When the engine is under a medium load, the fuel injected in the atomized state is diffused by the intake air that is supplied in a small amount into the cylinder at the end of injection. The space in the cylinder formed by is small. A mass of atomized fuel that spreads in this space descends together with the piston 7 in the subsequent intake stroke, and gradually diffuses into the in-cylinder space whose volume is gradually increased by the intake air supplied. This diffusion is not good because the intake air velocity at this time is slow, but the amount of fuel injected in the intake stroke at the time of engine medium load is still relatively small, so it is relatively good at the end of the intake stroke in the cylinder. Atomized fuel can be diffused throughout, and good stratified combustion can be realized as in the case of high engine load. However, at the time of high engine load, not only the required fuel amount increases, but also because of uniform combustion, all must be injected in the intake stroke, and as indicated by the chain line, the intake When continuously injecting from the first half of the stroke, especially in the vicinity of full load, the space volume in the cylinder at the end of injection is slightly increased compared to when the engine is under medium load, but a large amount of fuel is present in this space. As a result, the lump of atomized fuel formed here becomes very rich, and in the low-speed intake that is supplied in the subsequent intake stroke, the entire atomized fuel is completely dispersed in the cylinder by the end of the intake stroke. It cannot be diffused, and at the time of ignition, a very rich air-fuel mixture is formed near the top surface of the piston, causing smoke.

In the present embodiment, as shown in FIG. 4, in the vicinity of the full load at the time of high engine load, half the required fuel amount is injected from the first half of the intake stroke as shown in FIG. 1, and the remaining half is as shown in FIG. It is designed to inject fuel at the end of the intake stroke. The amount of fuel injected from the first half of the intake stroke is half the amount, so the fuel injection is the same as when the engine is under medium load, and as described above, the fuel is diffused throughout the cylinder by the end of the intake stroke, and the latter half of the intake stroke. As shown in FIG. 2, the fuel injected into the cylinder is large in the internal space of the cylinder formed by the piston 7 at this time, and the amount of the fuel is the remaining half. With the atomized fuel diffused in the entire cylinder space and injected and diffused in the first half of the intake stroke, it is possible to evaporate during the compression stroke and form a good homogeneous mixture in the combustion chamber before ignition. Can be prevented.

Further, in this embodiment, as shown in FIGS. 1 and 2, since the fuel injection valve 6 injects fuel obliquely to the piston 7, the atomization injected in the first half of the intake stroke. The position near the top surface of the piston 7 where the fuel in the state is concentrated is different from the position near the top surface of the piston 7 where the fuel injected in the latter half of the intake stroke is likely to be concentrated. Further improve the diffusivity of.

FIG. 5 is a map for determining the fuel injection start timing in the entire operation range, and as described above,
In the low load area I, it is set in the latter half of the compression stroke and
In II, it is set in the first half of the intake stroke and in the second half of the compression stroke, and in high load area III except in the low-speed near full-load area IV, it is set in the first half of the intake stroke. In the low-speed near full-load region IV, the intake stroke is in the first half and the intake stroke is in the second half. From the fuel injection start timing determined in this way, the required fuel amount corresponding to the load is injected continuously or in two steps as described above.

In the present embodiment, in order to surely form the uniform air-fuel mixture in the region near the low-speed full-load, as described above, the required fuel amount is divided into two injections and injected during the intake stroke. By reducing the amount of fuel injected at one time and making the injection interval time from the completion of the first fuel injection to the start of the second fuel injection relatively long, the fuel injected at the first injection is It is intended to spread almost completely over the time interval.

Therefore, even if the injection is performed three times or more during the intake stroke, the injection interval time is shorter than that of the second injection, but the amount of fuel injected at one time is further reduced, and similarly, the fuel is injected uniformly. It is possible to form a mixture. Also in this case, when the final fuel injection is completed, it is preferable to set the compression stroke to the initial stage at the latest in order to sufficiently evaporate the fuel injected at that moment before ignition.

The fuel injection valve 6 of the present embodiment injects fuel in an atomized state, but this does not limit the present invention. For example, the fuel is injected in a columnar shape such as a hole nozzle to form a piston. It is understood that it is advantageous to form a uniform air-fuel mixture by reducing the amount of fuel injected at one time and providing an injection interval time even when the fuel is atomized by colliding with the like.

[0021]

As described above, according to the in-cylinder injection spark ignition engine of the present invention, fuel injection is started during the intake stroke in the engine operating state where uniform combustion is performed, and at least in this engine operating state. Since the required fuel injection amount is divided into multiple injections at the time of rotation, the amount of fuel injected at one time becomes small, and the injected fuel is supplied at the injection interval time until the next fuel injection. Is sufficiently atomized and diffused, and is similarly atomized and diffused in the fuel injection from the next time onward, and all are vaporized in the entire cylinder before ignition to form a good homogeneous mixture in the combustion chamber.

[Brief description of drawings]

FIG. 1 is a sectional view of a cylinder injection type spark ignition engine according to the present invention, showing a state in a first half of an intake stroke.

FIG. 2 is a sectional view of a cylinder injection type spark ignition engine according to the present invention, showing a state in the latter half of the intake stroke.

FIG. 3 is a diagram showing a fuel injection period with respect to a load at a specific engine speed in a high engine speed region.

FIG. 4 is a diagram showing a fuel injection period with respect to a load at a specific engine speed in a low engine speed region.

FIG. 5 is a map for determining a fuel injection start timing in all operating regions.

[Explanation of symbols]

 1 ... Intake passage 2 ... Intake valve 3 ... Exhaust passage 4 ... Exhaust valve 5 ... Spark plug 6 ... Fuel injection valve 7 ... Piston

Claims (1)

[Claims] 1. A fuel injection valve that starts fuel injection during an intake stroke in an engine operating state in which uniform combustion is executed,
An in-cylinder injection spark ignition engine, characterized in that a required fuel injection amount is divided into a plurality of injections at least when the engine is operating at a low speed.