JP3128030B2 - Fuel injection two-stroke engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection type two-stroke engine in which fuel is directly injected into a combustion chamber and ignited by a spark plug.

[0002]

2. Description of the Related Art In a spark-ignition type two-cycle engine in which fuel is directly injected into a combustion chamber and ignited by an ignition plug, it is necessary to promote vaporization and atomization of the fuel and to guide an ignitable air-fuel mixture to the ignition plug. It is.

Conventionally, a combustion chamber of a hemispherical type or a bathtub type is known, in which an ignition plug is arranged on one side of the combustion chamber and a fuel injection valve is arranged on the other side with respect to a cylinder center axis. In this case, the fuel is injected from the fuel injection valve across the combustion chamber toward the spark plug. There is also a piston in which a hemispherical concave portion is formed on the top surface of the piston, and an ignition plug and a fuel injection valve face the concave portion. In this case, the fuel injected into the concave portion is heated on the surface of the concave portion by the heat of the piston itself, and vaporization is promoted.

[0004]

2. Description of the Related Art In the former method, in which fuel is injected toward a spark plug across a hemispherical or bathtub-type combustion chamber, fine particles of fuel directly adhere to the ignition portion of the spark plug. For this reason, there is a problem that carbon easily accumulates on the ignition plug and misfires easily depending on the operation state.

[0005] In the case of the latter, in which fuel is injected into a concave portion formed on the top surface of the piston, low-load operation in which the piston temperature is low, or low-load high-speed operation in which the heating time of the fuel by the surface of the concave portion is significantly reduced. Sometimes fuel heating is insufficient. For this reason, there has been a problem that fuel vaporization becomes insufficient, ignitability deteriorates, and operation becomes unstable.
This problem is particularly important when using a lean mixture.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and even if the operating condition changes, the atomization and vaporization of fuel are not deteriorated, and the ignitability by the spark plug is improved over a wide operating range. It is an object of the present invention to provide a fuel injection type two-cycle engine capable of stabilizing the fuel injection.

[0007]

According to the present invention, a first object is to provide fuel pick-up.
In a port scavenging type fuel injection type two-stroke engine in which fuel is injected directly into a combustion chamber in a ston compression stroke and ignited by a spark plug, the spark plug is connected to an exhaust port with respect to a cylinder center axis.
The fuel injection valve is located on the front side while
The piston top surface on the exhaust port side is directed obliquely from the cylinder center axis side , and at low speed, the piston
The piston closes the exhaust port at high speed after closing
From before, the fuel injection type 2-cycle engine, characterized in that to start the injection of fuel is accomplished by.

[0008]

FIG. 1 is a conceptual view including an engine section according to an embodiment of the present invention, FIG. 2 is a plan view showing a piston top surface, and FIG.
FIG. 4 is a diagram showing the valve opening timing of the fuel injection valve, FIG. 4 is a diagram showing the flow of the fuel injection flow, and FIG. 5 is a diagram showing measured data of the spray state at 1500 rpm.

The fuel injection valve of this embodiment mixes high-pressure air and fuel (gasoline) at a fixed ratio and injects them into a combustion chamber, which is a so-called air-fuel injection system. FIG. 5 shows a case where a sensor having a photocoupler is mounted in place of the ignition plug, and the output level L of the photocoupler is indicated by voltage. That is, the photocoupler includes a light-emitting element and a light-receiving element that face each other with a certain gap therebetween, and the amount of light received by the light-receiving element changes according to the concentration of the fuel spray entering the gap between them, so that the output level L changes.
It detects the concentration of the spray.

In FIG. 1, reference numeral 10 denotes a crankcase preload type two-stroke engine, in which a cylinder 12, a piston 1
4, a cylinder head 16, a connecting rod 18, a crankshaft 20, and the like. An intake passage (not shown) provided with a reed valve is connected to a crank chamber that accommodates the crankshaft 20, and intake air is sucked into the crank chamber via the reed valve during a rising stroke (compression stroke) of the piston 14. .

The cylinder 12 has a plurality of scavenging ports 22.
(Only one is shown in FIG. 1) and an exhaust port 24 are formed. That is, this engine 10 is a port scavenging method
It is an expression. The top surface of the piston 14 is substantially flat, and is located on one side of the cylinder center axis A, that is, the exhaust port 24.
A concave portion 26 is formed on the side (FIGS. 1 and 2) . As shown in FIG. 2, the concave portion 26 has a substantially trapezoidal shape in which the cylinder center axis A side is wide and gradually narrows in the outer diameter direction (the exhaust port 24 side ), and the bottom surface thereof is as shown in FIG. It gradually becomes deeper in the outer diameter direction.

A substantially hemispherical combustion chamber 28 is formed on the cylinder head 16 side. The ignition portion of the ignition plug 30 faces the combustion chamber 28 so as to be deviated from the cylinder center axis A toward the exhaust port 24. Here, the ignition portion of the ignition plug 30 is the piston 1
4 is located above the edge of the recess 26 near the exhaust port 24.

Reference numeral 32 denotes an electromagnetic fuel injection valve,
The top surface of the piston 14 on the same side as 0 (exhaust port 24 side) is obliquely directed from the cylinder center axis A side. That is, the fuel injection valve 32 faces the concave portion 26 on the top surface of the piston 14.

The fuel injection valve 32 is connected to compressed air sent from an electric air pump 34 and to the electric fuel pump 3.
The fuel (gasoline) sent from 6 is mixed at a fixed ratio and injected. The mixed jet flow composed of air and fuel collides with the top surface of the piston 14 and is reflected and flows toward the spark plug 30 as shown in FIG.

In FIG. 4, B represents the injection center line of the fuel injection valve 32, and C conceptually shows the expansion of the injection range of the mixed injection flow. In practice, of course, the mixed flow also extends outside the injection range C. Further, the fuel injection valve 32 is not limited to a single-hole type having one injection hole, and may be a multi-hole type having a large number of injection holes.

In the engine 10 shown in FIGS. 1 and 2, as shown in FIG. 3, the scavenging port 22 is closed at about 100 ° before and after the top dead center (TDC), and is opened at other times. Further, the exhaust port 24 closes at 95 ° before and after the top dead center (TDC), and opens at other positions.

The rotation angle θ of the crankshaft 20 is detected by an angle sensor 38 and input to the CPU 40. CPU40
Further, data such as the opening a of a throttle valve (not shown), the intake air flow rate b, the intake air temperature c, and the like are input to the. CPU40
Is based on these data θ, a, b, c, etc.
Ignition timing 0 calculates the valve opening period T _j of I _g and the fuel injection valve 32. Signal i indicating the ignition timing I _g, the ignition circuit (C
DI) 42 to ignite the spark plug 30 at a predetermined timing. A signal for driving the fuel injection valve 32 during the valve opening period _Tj , that is, a drive pulse j is supplied to the fuel injection valve 32
_Is turned on / off slightly earlier than the valve-opening period Tj in consideration of the operation delay.

[0018] For example, when the crank shaft 20 is rotated at 1500rpm, since fuel injection valve 32 is opened and closed about 10 ° delayed crank angle θ to the drive pulse j, about the opening term T _j calculated in operation 10 As described earlier, the CPU 40 outputs a drive pulse j that is turned on between 72 ° (= t ₁ ) and 27 ° (= t ₂ ) before the top dead center (TDC).
The valve opening period T _j at this time is in the closed period of the exhaust port 24
It is in. At this time, the hydrant 30 is placed 3 in front of the top dead center (TDC).
It is ignited by an ignition signal i output at 6 °. In FIG. 3, j 'indicates the ON period of the drive pulse when the crankshaft 20 rotates at 5000 rpm. Valve opening at this time
Part of the period T _j ′ overlaps with the opening period of the exhaust port 24.
But the piston speed is sufficient for the fuel injection flow velocity
Since it is large, fuel blow-through hardly occurs.

FIG. 4 shows a state in which the piston 14 is in the position before the top dead center (BTD).
C) shows a state located at 72 °. Therefore, as apparent from FIG. 3, the fuel injection valve 32 continues to be opened in a stroke rising from the position of the piston 14. In other words, the mixed flow of air and fuel continues to be injected on the top surface of the piston 14 while the piston 14 is rising from the position shown in FIG.

The mixed flow injected from the fuel injection valve 32 violently collides with the top surface of the rising piston 14 and is reflected while being miniaturized. As shown in FIG. 4, the direction of injection of the mixed flow is from the center axis A of the cylinder to the top surface of the piston on the spark plug 30 side. It is led to the spark plug 30 by being guided by the inner wall of the cylinder 12 and the inner wall of the combustion chamber 28. FIG.
Since the mixed flow continues to be injected while the piston 14 rises above the position of the piston 14 shown in FIG. Therefore, the ignitability of the ignition plug 30 is improved.

The mixed flow collides with the top surface of the piston 14 and is heated by the heat of the piston 14 itself. Therefore, atomization of the fuel is promoted. At low load, especially at low load and high speed, the temperature of the piston 14 also decreases, and the effect of heating the fuel by the heat of the piston 14 weakens. However, also at this time, reflection of the top surface of the piston 14 promotes the miniaturization of the fuel and at the same time, the mixed flow is favorably collected in the spark plug 30, so that the ignitability is not reduced and the operation is stable.

According to the measured data of FIG. 5, the driving pulse j
When the fuel injection valve 32 starts to open at a timing t ₃ which is about 10 ° later, a part of the mixed flow is diffused and
Reach the ignition point. The first peak p ₁ of the output level L in FIG. 5 indicates an increase in concentration due to the mixed flow reaching the direct spark plug. The output level L again rises late for the peak p _1. This increase in the second peak p ₂ after the output level L indicates the concentration increased by mixing flow guided to the spark plug 30 is reflected by the piston 14.

In this embodiment, a concave portion 26 is formed on the top surface of the piston 14, and the injected mixed flow is
Of the spark plug 30 is smoothly guided by the slanted bottom surface.
For this reason, a thick mixed flow can be further concentrated near the ignition plug 30, and the effect of the present invention becomes more remarkable.

In the above embodiment, the fuel injection valve 32 of the present invention is mounted near the cylinder center axis A as shown in FIGS. 1 and 2, and its injection direction is directed obliquely to the concave portion 26 on the cylinder top surface. I have. However, the mounting position of the fuel injection valve is not limited to this. For example, it may be deviated to the ignition plug 30 side or the opposite side with respect to the cylinder center axis A.

In this embodiment, as is clear from FIGS. 1 and 2, the scavenging air obliquely flows into the combustion chamber 28 from the opposite side of the exhaust port 24 and reverses near the top of the combustion chamber (reversal scavenging, looping). Scavenging). Therefore, the fuel injected from the fuel injection valve 32 is smoothly carried to the scavenging flow, and the effect of the present invention is further enhanced.

FIG. 6 shows other various embodiments in which the shape of the combustion chamber and the arrangement of the fuel injection valve and the ignition plug are different. In these figures, 12 denotes a cylinder, 14 denotes a piston, 16 denotes a cylinder head, 28 denotes a combustion chamber, INJ denotes an injection center line of a fuel injection valve, and IG denotes a mounting position and a mounting direction of a spark plug.

In the embodiment shown in FIG. 2A, the cylinder 1 on the ignition plug side is used.
4, a recess 26 </ b> A opened to the inner surface was formed in the piston 14. In the embodiment of (B), a curved surface R is formed in a portion continuous from the periphery of the combustion chamber 28 on the spark plug side to the squish area, so that the reflected mixed flow on the piston top surface is easily guided to the spark plug.

In the embodiment (C), a recess 26C larger than that shown in FIGS.
In the embodiment of (D), the squish area on the ignition plug side was eliminated, and a curved surface R smoothly continuous with the inner surface of the cylinder 12 was formed on the cylinder head 16 side. . Example of (E) is a curved surface R ₁ of the bottom surface of the concave portion 26E of the piston 14 side and smoothly made continuous to the curved surface R ₂ of the combustion chamber surface of the cylinder head 16 side. In the embodiment (F), the combustion chamber 28 and the fuel injection valve are deviated toward the ignition plug.

In each of the above embodiments, the fuel injection valve 32 injects a mixed flow of air and fuel, but the present invention may inject only fuel.

[0030]

As described above, according to the first aspect of the present invention, the spark plug is deflected toward the exhaust port with respect to the cylinder center axis.
Since the fuel injection valve injects the fuel with the piston top surface on the same side as the spark plug, that is, on the exhaust port side , obliquely directed from the cylinder center axis side, the fuel is heated on the piston top surface. The mixed flow is reflected on the top surface of the piston, and is guided to the ignition plug from the corner on the ignition plug side in the combustion chamber surrounded by the piston top surface, the cylinder, and the cylinder head. For this reason, even when the piston temperature is low and the load is low, a thick mixed flow is always guided to the spark plug, the ignitability of the spark plug is improved, and the operation of the engine is stabilized. As a result, it is possible to further reduce the concentration of the air-fuel mixture to improve fuel economy.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram including an engine section according to an embodiment of the present invention.

FIG. 2 is a plan view showing a top surface of a piston.

FIG. 3 is a diagram showing opening / closing timing of a fuel injection valve;

FIG. 4 is a diagram showing a state of a flow of an injection flow.

FIG. 5 is a diagram showing actual measurement data of a spray state.

FIG. 6 is a diagram showing another embodiment.

[Explanation of symbols]

 Reference Signs List 10 2 cycle engine 12 cylinder 14 piston 16 cylinder head 30 spark plug 32 fuel injection valve

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-273872 (JP, A) JP-A-2-3022 (JP, U) JP-A-1-124041 (JP, U) 28841 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02M 39/00-71/04 F02B 1/00-23/10

Claims (1)

(57) [Claims] 1. A port scavenging fuel injection type two-cycle engine in which fuel is directly injected into a combustion chamber in a piston compression stroke and ignited by an ignition plug, wherein the ignition plug is displaced toward an exhaust port with respect to a cylinder center axis. while disposed by the fuel injection valve is directed obliquely piston top surface of the exhaust port side from the cylinder center axis side, the low speed
After the piston closes the exhaust port,
Before the tons closes the exhaust port, fuel injected 2-cycle engines, wherein <br/> Rukoto to initiate an injection of fuel.