JPS6048609B2 - 2 cycle engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-stroke engine in which the shape of the scavenging passage has been improved.

Conventionally, in two-stroke engines, in order to prevent so-called blow-by, where the scavenging air flow passes through the exhaust boat,
In order to properly guide the scavenging air flow into the cylinder, various improvements have been made to the shapes of the scavenging ports and the scavenging passages, but the above-mentioned guiding effect is not sufficient with the conventional shapes alone. However, the problem was that scavenging air (fresh air) flowed through to the exhaust port, resulting in insufficient scavenging action and resulting in poor fuel consumption.

This invention was made in order to eliminate the above-mentioned conventional drawbacks, and by narrowing a pair of scavenging passages provided on both sides of the piston toward the scavenging port side, scavenging air flows from the scavenging port into the cylinder. The main purpose is to increase the flow velocity of the airflow, increase the above-mentioned guiding effect, and improve the fuel consumption rate.

Embodiments of the present invention will be described below with reference to the drawings.

1 to 3 show the basic configuration of the present invention. In FIG. 1, a cylinder 12 is connected to the upper part of a crank case 11, and the inside of the crank case 11 and the inside of the cylinder 12 are communicated with each other. A pair of scavenging passages 13, 13 are provided facing each other on both sides of the piston 14.
The scavenging passage 13 opens into the cylinder 12 at a scavenging port 15 and opens into the crankcase 11 at a scavenging intake port 16 to send scavenging air A from inside the crankcase 11 into the cylinder 12. There is. Further, an exhaust boat 17 is provided in the cylinder 12 and located between the pair of scavenging ports 15, 15. 19 is a partition provided between the inside of the cylinder 12 and the scavenging passage 13, and 20 is a crankshaft.

Among the peripheral walls 22 forming the scavenging passage 13, the peripheral wall 22a on the exhaust boat 17 side shown in FIG. As a result, the scavenging passage 13 is narrowed toward the scavenging boat 15 side, and when the piston 14 is at the bottom dead center position shown in FIG.
Horizontal cross-sectional area S of the scavenging passage 13 facing the lower end 15a of
, is the horizontal cross-sectional area S of the scavenging passage 13 facing the upper end 16a of the scavenging air intake boat 16.

It is set to be 50% of The sizes of S, , S2 mentioned above are shown in FIG. In addition, in the figure, the scavenging passage 13 near the scavenging boat 15 is set in a direction eccentric to the cylinder center line 24, so that the scavenging air A
This has a guiding effect in that it flows along the cylinder inner surface 12a facing the exhaust boat 17, but this point is similar to the conventional one. In the above configuration, the scavenging passage 13 in FIG.
is narrowed upward and its horizontal cross-sectional area decreases from S2 to S, so the scavenging air A flows from the scavenging boat 15 into the cylinder 12 as shown in FIG. At this time, the inflow speed increases, and as a result, the inflowing scavenging air A is smoothly guided and flows along the cylinder inner surface 12a facing the exhaust boat 17.

Therefore, scavenging air flows to exhaust boat 1 as shown by arrow B?
This effectively prevents the scavenging air from blowing into the muffler, improving the fuel consumption rate, and also prevents the scavenging air from reaching the muffler (shown in the figure) through the exhaust boat 17, depositing carbon inside the muffler and impairing the function of the muffler. This solves the problem of the gas leaking or being discharged to the outside from the exhaust port as unburned gas, which becomes the third cause of pollution. The change in the fuel consumption rate (SFC) is expressed as the throttling rate S, /S of the scavenging passage 13.

Figure 4 shows the results of actual measurements on changes in . Conventional 2
S at a throttling rate of about 4.90%, which is the same as a cycle engine.
FC is about 430gIps-Hr, and the aperture rate is 40~
SFC is best at 50%, its value is about 330gIps
-Hr has been significantly improved.

If the aperture ratio is 60% or less, it can be said that the SFC has been sufficiently improved. FIG. 5 shows an embodiment of the present invention having the above-mentioned basic configuration. Here, a projecting wall 25 along the inner circumferential surface of the cylinder 2 is provided on the inner circumferential edge of the scavenging boat 15 on the exhaust boat 17 side. The protruding end surface 25a of the protruding wall 25 extends toward the exhaust boat 1 as it approaches the center line 24 of the cylinder 12, as shown by the virtual extension surface r-r.
It extends in the direction approaching 7. This arrangement not only provides the same effect as the embodiment shown in FIG. 3, but is also advantageous when die-casting the sill 12. That is,
When die-casting the cylinder 12 shown in FIG.
As shown in the figure, since the pair of molds 27 forming the periphery of the scavenging boat 15 must be pulled out in the direction of the arrow 28, the inner mold 29 forming the inner peripheral surface of the cylinder 12 is removed.
A portion 29a located on the opposite side of the exhaust boat 17 in
Cylinder 1 in Figure 5 has a very thin wall and may not be able to maintain the strength necessary for casting.
2, since the protruding end surface 25a of the protruding wall 25 of the scavenging boat 15 extends along the imaginary extension plane r-r, as shown in FIG. arrow 3
Since the core 29 can be pulled out in the 0 direction, the above-mentioned portion 29a of the core 29 has a sufficiently thick wall, and there is no problem with Guikasu casting.

As explained above, according to the present invention, scavenging air is effectively prevented from blowing into the exhaust boat, resulting in an improved fuel consumption rate, as well as a reduction in muffler function and the occurrence of pollution. Furthermore, there is an effect that manufacturing is facilitated.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing the basic configuration of a two-stroke engine according to the present invention, FIG. 2 is a sectional view taken along line 2-2 in FIG. 1, and FIG. 3 is a sectional view taken along line 3-3 in FIG. 1. Sectional view along 4th
The figure is a characteristic diagram showing the effect of improving the fuel consumption rate by the basic structure of the present invention, FIG. 7 is a sectional view showing a method for casting the cylinder; FIG. 7 is a sectional view showing a method for casting the cylinder of FIG. 5; 11... Crank case, 12... Cylinder, 13
...Scavenging passage, 14...Piston, 15...Scavenging boat, 15a...Lower end, 16...Scavenging air intake boat, 16a...Upper end, 17...Exhaust boat, 22,2
2a... Circumference 23... Direction of separation, 24... Center line, 25... Protrusion 25a... Projecting end surface, r... Virtual extension surface, S,,S.

Claims (1)

[Claims] 1 A pair of scavenging passages communicating between the inside of the cylinder and the inside of the crankcase are provided facing each other on both sides of the piston, and an exhaust port is opened between the scavenging ports in these scavenging passages that open into the cylinder, In a two-stroke engine, the scavenging port opens in a direction eccentric to the opposite side of the exhaust port from the center line of the cylinder, the peripheral wall on the exhaust port side of the peripheral wall forming the scavenging passage is
When the piston is at the dead center, the horizontal cross-sectional area of the scavenging passage facing the lower end of the scavenging port is such that the scavenging air in the scavenging passage opens into the crankcase. Set to be 60% or less of the horizontal cross-sectional area of the exhaust passage facing the upper end of the intake port, and further provided with a projecting wall along the circumferential direction of the cylinder on the inner peripheral edge of the scavenging port on the exhaust port side, A two-stroke engine characterized in that the projecting end surface of the projecting wall is set on a virtual extension surface that extends in a direction approaching the exhaust port as it approaches the center line of the cylinder.