JP2000320336A - Two-cycle direct injection engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce generation of an unburned gas and soot at a low-rotation low-load operation time by installing an injector for injecting fuel toward around the center on the piston top part surface in a high temperature condition and installing an ignition plug closer to an exhaust port beyond the injector. SOLUTION: In the top of a cylinder head 2 of a 5-port scavenge 2-cycle direct injection engine, an injector mounting hole 2c is formed while sharing the central axis line with a cylinder 1, and an injector 6 is installed in the injection mounting hole 2c. In a position closer to an exhaust port 1b side beyond the injector mounting hole 2c in the cylinder head 2, an ignition plug mounting hole 2d extending slantedly to the central axis line of the cylinder 1 is formed, and an ignition plug 7 is installed in the ignition plug mounting hole 2d. In this way, a high temperature part of the piston 3 is expedited to be cooled down, while the temperature distribution in a combustion chamber is unified, and a mean effective pressure inside the combustion chamber in a normal operation time can be increased, so that the output of the engine is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark ignition type two-cycle direct injection engine.

[0002]

2. Description of the Related Art A two-cycle direct injection engine includes a cylinder having a scavenging port and an exhaust port, a cylinder head for closing an opening of the cylinder, a piston fitted to the cylinder, and an internal part provided at a lower portion of the cylinder. A crankcase having a space connected to the scavenging port, an injector mounted to inject fuel directly into the combustion chamber formed inside the cylinder and the cylinder head, and a spark plug that ignites a mixture in the combustion chamber. An intake pipe for introducing fresh air is connected to the crankcase, and an exhaust pipe is connected to the exhaust port.

On the inner surface of the cylinder head facing the combustion chamber, there is provided a dome-shaped recess constituting the combustion chamber when the piston is at the top dead center, and a tapered squish area is formed around the recess. ing. The recess inside the cylinder head is usually formed to have a spherical shape, and when the piston is at the top dead center, the combustion chamber is substantially defined by the recess inside the cylinder head.

In a two-cycle direct injection engine, fresh air that has passed through an intake pipe is primarily compressed in a crankcase as the piston descends, and the primary compressed fresh air is caused to flow into a combustion chamber through a scavenging port. Scavenge the room. Next, fuel is injected from the injector into the combustion chamber to generate a mixture of fuel and fresh air, and the mixture is ignited at a predetermined ignition timing to cause combustion. The combustion gas is exhausted through an exhaust port provided in the cylinder.

In this type of engine, when scavenging is performed,
Since fresh air having a low temperature flows from the crankcase into the cylinder through the scavenging port, the inflow path of the fresh air, that is, the scavenging passage, is cooled by the fresh air.

On the other hand, the high temperature burned gas in the cylinder is discharged from the exhaust port, so that the vicinity of the exhaust port is maintained at a high temperature by the burned gas.

The top of the piston is cooled from the periphery in contact with the scavenging port, while the center of the top and the periphery in contact with the exhaust port are kept at a high temperature.

[0008] Of the cylinders, cylinder heads and pistons constituting the combustion chamber, the cylinder head is easy to cool, but the piston is difficult to cool. Therefore, the top of the piston is the hottest part.

Since the normal combustion of fuel is completed by the propagation of the flame created by the spark plug, the shorter the time from ignition to completion of combustion, the higher the average effective pressure in the combustion chamber and the higher the engine effective pressure. The output increases. Therefore, the output can be improved by shortening the flame propagation distance.

From the above facts, in designing the combustion chamber of a two-stroke engine, the surface of the top of the piston, which is difficult to cool, is made flat to reduce its surface area.
The recess inside the cylinder head constituting the combustion chamber at the time of ignition has a hemispherical shape with the shortest flame propagation distance, and an ignition plug is arranged at the top of the cylinder head. The injector is often mounted on a cylinder.

However, the temperature distribution in the combustion chamber is higher on the exhaust port side than the center of the piston.
Increasing the calorific value in the combustion chamber without knocking causes a problem in that the area from the center of the top of the piston to the exhaust port side melts, which is a problem in improving engine output. Had been an obstacle.

Further, as described below, in a two-cycle engine, a misfire occurs at a low rotation speed and a low load, a half-burn phenomenon in which flame propagation is interrupted during combustion, and soot is generated in exhaust gas. There was a problem.

That is, a two-cycle engine having no valve mechanism has a smaller mechanical loss at low rotation than a four-cycle engine. Therefore, at low rotation and low load such as idling, combustion is reduced by reducing the amount of intake air. Although it is possible to lower the average effective pressure in the room, if the amount of intake air is reduced in order to lower the average effective pressure, the scavenging amount will decrease and scavenging will not be performed sufficiently. Therefore, the fresh air is diluted by the residual burned gas in the cylinder, and the air-fuel ratio of the air-fuel mixture is out of the ignitable range (the air-fuel mixture becomes lean), causing the engine to misfire or the flame to propagate. However, a semi-burning phenomenon in which the gas is interrupted during the combustion may occur. When a misfire or a half-burn phenomenon occurs, unburned gas is discharged, so that there is a problem that hydrocarbons (HC) in the exhaust gas increase.

The amount of scavenging is increased by increasing the throttle valve opening during idling or by forming a passage that bypasses the throttle valve.
When the concentration of fresh air in the combustion chamber is increased and the fuel injection timing is appropriately adjusted so as to keep the average effective pressure in the combustion chamber low, and the combustion chamber is in a stratified supply state, the air-fuel ratio of the air-fuel mixture (A / F ) Can be maintained in an ignitable range to prevent a misfire or a half-burn phenomenon.

However, when the engine speed is low and the load is low, the amount of heat generated per explosion is small, and the explosion interval is long. If the temperature is increased, the temperature in the cylinder decreases, causing problems such as a decrease in thermal efficiency and a failure in vaporization of the injected fuel to discharge soot.

[0016]

As described above, in the conventional two-cycle direct injection engine, when the combustion chamber is designed to shorten the flame propagation distance and the engine output is improved, Has a limit in improving the engine output because the top of the steel melts.

In a conventional two-cycle direct injection engine,
Misfire may occur at low rotation and low load, or a half-burn phenomenon may occur in which flame propagation is interrupted during combustion.
There has been a problem that soot is discharged when trying to prevent the occurrence of a misfire or a half-burn phenomenon.

An object of the present invention is to provide a two-cycle direct injection engine capable of obtaining a higher output than before even if the structure of the cooling system is the same as that of the prior art.

Another object of the present invention is to generate a misfire state or a semi-burn state at low rotation and low load to discharge unburned gas,
An object of the present invention is to provide a two-cycle direct injection engine that can prevent soot from being discharged.

[0020]

According to the present invention, there is provided a cylinder having a scavenging port and an exhaust port, a cylinder head for closing an opening of the cylinder, a piston fitted to the cylinder, and a cylinder inside the cylinder and the cylinder head. The present invention is directed to a spark-ignition two-cycle direct injection engine including an injector mounted to inject fuel directly into a formed combustion chamber and a spark plug for igniting an air-fuel mixture in the combustion chamber.

In the present invention, the injector is mounted so as to inject fuel near the center of the top surface of the piston in a high temperature state. The spark plug is attached at a position closer to the exhaust port than the injector.

Preferably, the injector is mounted on the cylinder head with the center axis of the fuel injection port aligned with the center axis of the piston.

It is preferable that the ignition plug is attached to the cylinder head in a state where the ignition plug is located closer to the exhaust port than the injector.

The piston is preferably formed (flat) so as to minimize the area of the top surface in contact with the combustion chamber.

As described above, when the fuel is injected from the injector toward the vicinity of the center of the piston, the high temperature portion of the piston is cooled by the latent heat of vaporization of the fuel, so that the temperature distribution in the combustion chamber is averaged.

When the spark plug is mounted at a position closer to the exhaust port than the injector as described above, the position of the spark plug is shifted from the center of the combustion chamber and the flame propagation distance becomes longer in some parts. Since it is arranged near the high temperature part of the combustion chamber, the averaging of the temperature distribution in the combustion chamber can be promoted.

The reason why it is easy to average the temperature distribution in the combustion chamber when the ignition plug is arranged in the high temperature portion is as follows.

That is, when the ignition plug is arranged in the high temperature part,
In the process of flame propagation, the previously burned fuel increases the pressure in the space where unburned fuel exists due to adiabatic expansion, so the flame propagation speed increases, and the amount of heat generated per unit time increases in the later stage of combustion . As a result, the calorific value at a low temperature location in the combustion chamber increases, and the temperature distribution in the combustion chamber is averaged.

With the configuration of the present invention, as described above, the cooling of the high temperature portion of the piston is promoted and the temperature distribution in the combustion chamber is averaged, so that the configuration of the cooling system is different from that of the conventional cooling system. Even if they are the same, it is possible to increase the calorific value in the combustion chamber, and increase the average effective pressure in the combustion chamber during steady operation to improve the output.

In the present invention, attention is paid to the point where the temperature is reduced due to the increase in the scavenging amount, in the vicinity of the scavenging passage, and by devising the mounting position of the injector, it occurs at low rotation and low load. Solved the problem.

As described above, the center of the top of the piston is a place where it is difficult to effectively perform cooling by the cooling system of the engine, and a place where it is hard to be exposed to the scavenging flow. Therefore,
The portion near the center of the top of the piston is kept at a relatively high temperature even at low rotation and low load. Therefore, when fuel is injected toward the top of the piston as in the present invention, the fuel vaporization time can be shortened. Since the swirling flow at the time of scavenging remains in the cylinder, the fuel vaporized on the top surface of the piston is carried to the exhaust port side on the swirling flow. When the fuel vaporized on the top surface of the piston is carried to the exhaust port side by a swirling flow, the vaporized fuel is kept warm by the temperature on the exhaust port side, which is not significantly affected by the temperature drop due to the scavenging flow, so that the air-fuel mixture Keeps it easy to ignite. When the piston rises to near the top dead center, the air-fuel mixture sandwiched between the piston and the squish area provided around the dome-shaped recess inside the cylinder head is pushed out to the spark plug side, and the spark generated by the spark plug Ignite by.

As described above, according to the present invention, it is possible to prevent a misfire state, a semi-burn state, and a discharge of soot at a low rotation speed and a low load.

In the present invention, it is preferable that the center axis of the fuel injection port of the injector is aligned with the center axis of the cylinder to inject the fuel toward the center of the piston. The fuel injection port of the injector may be directed to a position slightly deviated from the center of the cylinder, since it is not necessary to inject the fuel toward the portion, and the fuel may be injected toward the center of the top of the piston. For example, the fuel may be injected toward a position slightly closer to the exhaust port side than the center of the piston.

The fuel used in the engine of the present invention may be gasoline or alcohol fuel.

[0035]

1 and 2 show a configuration example of a two-cycle direct injection engine according to the present invention. It shows an example to which the invention is applied. FIG.
2 is a longitudinal sectional view of a main part, and FIG. 2 is a sectional view taken along line AA of FIG.

1 and 2, 1 is a cylinder, 2
Is a cylinder head for closing the opening of the cylinder 1, and a piston 3 is fitted in the cylinder 1. Cylinder 1
Are formed with five scavenging ports 1a and one exhaust port 1b. A crankcase (not shown) is provided below the cylinder 1, and a space in the crankcase is connected to the scavenging port 1a. Cylinder head 2
A spherical dome-shaped concave portion 2a which forms a part of the combustion chamber is formed on the inner surface of the inner surface of the inner surface of the inner surface of the dome, and a squeezer area 2b having a tapered surface shape is formed around the concave portion 2a. When the piston is at the top dead center, a combustion chamber is substantially formed by the recess 2a, the squish area 2b, and the piston. A cooling water passage 4 is formed in the cylinder 1 and the cylinder head 2, and a connector 5 for connecting a pipe for connecting the cooling water passage 4 to a radiator is attached to the cylinder head 2.

At the top of the cylinder head 2, a cylinder 1
Mounting hole 2c while sharing the central axis with the
The injector 6 is mounted in the mounting hole 2c with the center axis of the fuel injection port 6a aligned with the center axis of the cylinder 1 (same as the center axis of the piston).

The injector 6 is of a widely used top feed type, and has an injector body 6c having a fuel injection port 6a at a front end and a fuel connector 6b at a rear end, and a fuel injector disposed in the injector body. A valve 6d for opening and closing the injection port 6a and a solenoid 6e for driving the valve 6d are provided. A pipe from a fuel pump (not shown) is connected to the fuel connector 6b.

When a predetermined drive current is applied to the solenoid 6e, the injector 6 opens the valve 6d and injects fuel from the fuel injection port 6a.

At a position closer to the exhaust port 1b than the injector mounting hole 2c of the cylinder head 2, an ignition plug mounting hole 2d extending in a direction inclined with respect to the center axis of the cylinder 1 is formed. The spark plug mounting hole 2d is provided so as to be directed toward the center of the cylinder, and the spark plug 7 is mounted in the mounting hole 2d with its discharge gap g positioned in the combustion chamber.

In a conventional two-cycle direct injection engine, FIG.
Although the ignition plug is attached to the portion where the injector mounting hole 2c is provided, in the embodiment of the present invention shown in FIG. 1, the injector is attached to the portion where the conventional ignition plug is attached.

The temperature distribution on the top surface of the piston 3 in the two-cycle engine is, for example, as shown in FIG. FIG. 3B is a cross-sectional view taken along the line CC of FIG. 3A, omitting details and hatching. The maximum temperature at the top of the piston of a two-stroke engine is about 350 ° C. This is because the melting point of aluminum alloy for engines is about 400
° C. In the case of a water-cooled engine, the temperature of the inner wall of the cylinder is about 150 ° C., and the surface temperature of the dome-shaped concave portion forming the combustion chamber inside the cylinder head 2 is about 200 ° C.

The mixture state of the air-fuel mixture in the combustion chamber of the two-cycle direct injection engine is either a stratified charge state or a homogeneously mixed state (non-stratified charge state) depending on the operation state of the engine. The stratified supply state is a state at the time of low rotation and low load, and the homogeneous mixing state is a state at the time of steady operation other than low rotation and low load.

FIGS. 4A and 4B schematically show the inside of the cylinder in a homogeneously mixed state. As shown in FIG. 4A, the scavenging flow G flows from the scavenging port 1a. The air flows into the cylinder and turns to head toward the exhaust port 1b.

In FIG. 4B, Fo indicated by a broken line
Shows the outline of the fuel flow when the flow of the fuel injected from the injector is not affected by the scavenging flow, and when the injected fuel is not affected by the scavenging flow, the outline of the flow is almost It has a conical shape.

On the other hand, when the flow velocity of the scavenging flow is high to some extent and the flow of the injected fuel is affected by the scavenging flow, the injected fuel is injected as indicated by F1 shown by the solid line in FIG. 4B. The flow of the fuel is bent toward the exhaust port.

When the mixture in the combustion chamber is in a homogeneous mixture state, the throttle valve is opened to a certain degree or more and a large amount of fresh air flows into the crankcase.
The speed of the scavenging flow is high, and the scavenging flow is generally 4
It turns at a flow velocity of about 0 m / sec. On the other hand, since the initial velocity of the fuel injected from the injector is about 40 m / sec, the injected fuel is swept toward the exhaust port under the influence of the scavenging flow, as shown by the solid line F1 in FIG. Is bent toward the exhaust port 1b. Therefore, the injected fuel impinges on a region Af that is more deviated toward the exhaust port than the center of the top surface 3a of the piston 3, as shown in FIG. 4B.

As is clear from the temperature distribution shown in FIG. 3A, the high temperature portion on the top surface of the piston is located at a position deviated toward the exhaust port 1b. When configured as in the present invention,
Since a large amount of fuel is injected into the high temperature portion of the piston, latent heat of vaporization of the fuel effectively acts to lower the temperature of the high temperature portion of the piston. Since the fuel vaporized by the piston is present in molecular units, it is distributed uniformly in the cylinder along the swirling flow of the scavenging air, and the air-fuel mixture in the combustion chamber is in a homogeneously mixed state.

Thus, according to the present invention, the piston 3
By promoting the cooling of the high temperature part and averaging the temperature distribution in the combustion chamber, it is possible to increase the calorific value in the combustion chamber even if the configuration of the cooling system is the same as the conventional one. Therefore, the output can be improved by increasing the average effective pressure in the combustion chamber during steady operation.

According to the present invention, as shown below,
It is possible to prevent the air-fuel mixture from becoming too thin at low rotation speeds and low speeds, and from preventing the flame from being interrupted and causing a misfire state or a semi-burn state. According to the present invention also
Since it is not necessary to increase the scavenging amount in order to prevent a misfire or a semi-burn state, soot can be prevented from being generated due to a decrease in the temperature in the cylinder.

FIGS. 5A to 5E show the inside of the cylinder at low rotation and low load. In these figures, TDC means top dead center, and BTDC means top dead center. It means there is. 5 (A), (B), (C) and (D) show the states when the rotational angle position of the crankshaft is 20 °, 10 °, 7 ° and 2 ° before the top dead center, respectively.
(E) shows the state at the time of ignition which occurs almost simultaneously with (D).

In the example shown in FIG. 5, the rotation speed of the engine is set to 700 rpm, and 500 rpm from the position 10 ° before the top dead center.
Fuel is injected for μsec (approximately 3 °), and ignition is performed at a position 2 ° before top dead center.

At a position 20 ° before the top dead center, a scavenging flow G is generated in the combustion chamber as shown in FIG. 5 (A). Is limited, the scavenging flow is weak. The scavenging flow at this time is a weak swirling flow with a flow velocity of about 3 m / sec.

At a position 10 ° before the top dead center, fuel F is injected from the injector 6 as shown in FIG. Although the amount of fresh air is limited, it is sufficient for the amount of supplied fuel, and the average air-fuel ratio (A / F) in the cylinder
Is about 40-60. The injected fuel has an initial speed of about 4
At 0 m / sec, the flow speed is sufficiently higher than the flow velocity of the swirling flow of the scavenging gas, and therefore reaches the piston 3 with almost no influence of the scavenging flow.

As shown in FIG. 5C, the gasoline particles that have hit the piston 3 vaporize by obtaining heat of vaporization from the top surface of the piston 3. The vaporized gasoline molecules ride on the weak swirling flow G and move to the exhaust port side, where they are gathered in the illustrated portion a.

After the fuel injection is completed, it takes 1.2 msec.
As shown in (D), the crankshaft reaches a position 2 ° before the top dead center. At this time, most of the fuel has been vaporized,
Since the swirling flow is weak, the vaporized fuel is mainly distributed to the exhaust port side without diffusing to the entire combustion chamber. When the piston approaches the squish area 2b provided around the combustion chamber, gas at the outer periphery of the piston top surface is collected at the center, but fuel is supplied to the ignition plug 7 existing between the injector 6 and the exhaust port. It is mainly distributed nearby. The next instantaneous ignition occurs. When the ignition is performed, FIG.
As shown in (1), a cloud of vaporized fuel collected near the ignition plug 7 is ignited. The vaporized fuel ignited in the vicinity of the spark plug burns quickly without reducing its air-fuel ratio (A / F), and the flame propagates throughout the combustion chamber without interruption.

[0057]

As described above, according to the present invention, the injector is mounted so as to inject fuel toward the top surface of the piston, and the spark plug is arranged between the injector and the exhaust port. The following effects can be obtained.

(1) By accelerating the cooling of the high temperature part of the piston and averaging the temperature distribution in the combustion chamber, the amount of heat generated in the combustion chamber even if the structure of the cooling system is the same as the conventional one. Therefore, the output can be improved by increasing the average effective pressure in the combustion chamber during steady operation.

(2) It is possible to promote the vaporization of fuel when the combustion chamber is in a stratified intake state, such as during low rotation and low load, so that the generation of soot can be prevented.

(3) When the combustion chamber is in the stratified intake state, the air-fuel mixture can be retained near the exhaust port having a high temperature to maintain the temperature of the air-fuel mixture. The occurrence of a semi-burn state can be prevented.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a main part of a configuration example of a two-cycle direct injection engine according to the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

3A is a cross-sectional view showing a temperature distribution at the top of a piston of a two-stroke engine, and FIG. 3B is a cross-sectional view taken along line CC of FIG.

FIGS. 4A and 4B are explanatory diagrams showing a state of a scavenging flow and a state of a fuel flow when a mixture in a combustion chamber of a two-cycle engine is in a homogeneously mixed state.

FIGS. 5A to 5E are operation explanatory diagrams for sequentially explaining the operation of the two-cycle direct injection engine according to the present invention from a state immediately before fuel injection to a state immediately after ignition.

[Explanation of symbols]

1 ... cylinder, 1a ... scavenging port, 1b ... exhaust port,
Reference numeral 2 denotes a cylinder head, 2a denotes a dome-shaped recess inside the cylinder head constituting a combustion chamber, 2b denotes a squish area, 3 denotes a piston, 6 denotes an injector, and 7 denotes a spark plug.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02P 13/00 301 F02P 13/00 301A 302 302A

Claims (4)

[Claims] 1. A cylinder having a scavenging port and an exhaust port, a cylinder head closing an opening of the cylinder, a piston fitted to the cylinder, and a combustion chamber formed inside the cylinder and cylinder head. In a spark-ignition two-cycle direct injection engine including an injector mounted to inject fuel directly and a spark plug igniting an air-fuel mixture in the combustion chamber, the injector is located near a center of a top surface of the piston. And wherein the spark plug is mounted at a position closer to the exhaust port than the injector.
Cycle direct injection engine. 2. The two-stroke direct injection engine according to claim 1, wherein the injector is attached to the cylinder head with a center axis of a fuel injection port coinciding with a center axis of the cylinder. 3. The two-stroke direct injection engine according to claim 2, wherein the spark plug is arranged at a position closer to the exhaust port than the injector and attached to the cylinder head. 4. The piston according to claim 1, wherein said piston is formed so as to minimize an area of a top surface in contact with a combustion chamber.
Or a two-stroke direct injection engine according to 3.