JPS5842578Y2 - Air supply system for two-stroke internal combustion engine - Google Patents

Description

[Detailed description of the invention] This invention relates to an air supply system for a two-stroke internally twisted engine with a preloaded crank chamber, and improves scavenging by utilizing the pressure increase that occurs in the intake passage when the piston valve and rotary valve are closed. It is intended to.

Conventionally, various auxiliary scavenging ports have been employed to improve scavenging.

For example, the auxiliary scavenging port 1 shown in FIG. 1 communicates with an intake passage 3 via a bypass 2, and when the intake passage 3 is opened by a piston 4, it communicates with a precompression chamber 5 (crank chamber).

6 is an intake port, 7 is a check valve, 8 is a carburetor, 9 is an air cleaner, 10 is a port provided on the side wall of the piston 4, 11
is the piston pin, 12 is the connecting rod, 13 is the crank pin,
14 is a crankshaft, 15 is a cylinder, 16 is a combustion chamber, 1
7 is a scavenging port, 18 is an exhaust port, and 19 is a spark plug.

According to the structure shown in FIG. 1, since the check valve 7 is provided, the intake passage resistance increases, the preload chamber capacity also increases, and the preload ratio decreases.

Not only is it difficult to obtain high-speed output, but the cost of the check valve becomes high, and the low cost characteristic of the two-stroke engine is not utilized.

In FIG. 2 showing another conventional example, 21 is a booster port for auxiliary scavenging, and 22 is a port provided on the side wall of the piston 4.

In this case, since the piston valve type in which the intake port 6 is opened and closed by the piston 4 is adopted, when the intake passage 3 is closed, the water hammer effect caused by the intake air flow that had been flowing toward the intake port 6 and the crankshaft is caused. The pressure inside the intake passage 3 increases due to the blowback from the chamber 5.

This increases pressure fluctuations within the intake passage 3, making the air-fuel ratio unstable when passing through the carburetor.

Generally, just before the piston valve or rotary valve (reversible flow control means) stops the flow of fresh air into the precompression chamber, a positive pressure of about 0.2 kg/crA is generated in the intake passage, which causes the Air column vibrations occur within the passage.

This invention uses the above pressure (positive pressure) to move the mixed gas (fresh air) in the intake passage after the valve is closed through an auxiliary scavenging port installed at a position where the pressure is lower than that in the intake passage during the scavenging stroke. It is characterized by being introduced into the combustion chamber.

On the other hand, by adjusting the length of the bypass passage that serves as the auxiliary scavenging passage, the opening timing of the auxiliary scavenging port relative to the combustion chamber, the opening position to the intake passage, the length of the passage, etc., it is possible to improve the output particularly in the desired rotation speed range. It is also possible to aim for

FIG. 3 shows an embodiment of the present invention.

In FIG. 3, the same reference numerals as those in FIG. 1 indicate corresponding parts.

In FIG. 3, 25 is a piston, and its side wall and the intake passage 3 form a piston valve.

Reference numeral 26 denotes a bypass passage according to the present invention, one end of which opens into the passage 3 close to the intake port 6, and the other end of which is located within the inner surface of the cylinder on the opposite side from the exhaust port 18, a distance l from the upper edge of the scavenging port 17. It communicates with the auxiliary scavenging port 27 located at a lower position.

The fresh air sucked into the prepressure chamber 5 when the piston 25 ascends is then precompressed within the prepressure chamber 5 after the piston 25 closes the intake port 6 during the downward stroke of the piston 25. The scavenging air is supplied into the combustion chamber 16 from the open scavenging port 17.

On the other hand, when the intake port 6 is closed by the piston 25, a water hammer effect due to the intake flow occurs in the intake passage 3 due to the inertia of the fresh air that had been flowing inside the intake passage 3 toward the preload chamber 5. A positive pressure of about 0.2 kg/i is generated.

Furthermore, as the pressure within the preload chamber 5 increases, leakage occurs into the passage 3 from the gap between the piston 25 and the cylinder, which promotes the increase in pressure within the passage 3.

The auxiliary scavenging port 27 is positioned so that it is opened by the piston 25 when the opening on the passage 3 side of the bypass passage 26 becomes positive pressure, so that the pressurized mixed gas in the intake passage 3 after the piston valve is closed is can be introduced into the combustion chamber 16.

It is effective to locate the auxiliary scavenging port 27 on the exhaust port 18 and the inner surface of the cylinder on the opposite side in order to promote the scavenging action, and its height is such that during the scavenging stroke, the piston valve prevents the inflow into the prepressure chamber 5. As long as the pressure is lower than the pressure in the intake passage 3 immediately before or after the pressure is removed, there is no need to set the pressure lower than the scavenging port 17 as shown in FIG.

Further, in the present invention, a resonance box 28 is added in the middle of the bypass passage 26 in order to adjust pressure fluctuations in the bypass passage 26 and the intake passage 3.

According to this, it is possible to change the state of pressure fluctuation in the air passage 3, and it is possible to improve the output in a desired rotation speed range.

A side branch may be provided instead of the resonance box 28.

According to the structure of the present invention explained above, extra fresh air is supplied to the combustion chamber in addition to the fresh air that has entered the precompression chamber 5 by utilizing the water hammer effect caused by the intake air flow and the pressure increase caused by leakage from the crank chamber. Scavenging air is improved and a high-output engine can be obtained.

Moreover, since the intake passage 3 is not provided with a check valve, the intake passage resistance can be reduced and the inertia of fresh air within the intake passage 3 can be sufficiently increased, resulting in the effect of increasing pressure due to the water hammer effect. It is possible to increase the amount of fresh air supplied to the combustion chamber.

Since the intake passage 3 is not provided with a check valve, it is possible to promote the intake of fresh air into the precompression chamber 5 and improve the output, and it is also possible to simplify the structure and reduce costs.

Even if blowback occurs due to the water hammer effect caused by the intake air flow, pressure fluctuations caused by this will be absorbed by the bypass passage 26.
It is absorbed by.

Therefore, pressure fluctuations within the intake passage 3 are reduced, the air-fuel ratio is stabilized when passing through the carburetor, and engine performance is stably improved.

Furthermore, since a pressure fluctuation adjustment chamber consisting of a resonance box 28 or a side branch is provided in the middle of the bypass passage 26, the state of pressure fluctuation in the intake passage 3 and the bypass passage 26 can be adjusted.
It is possible to improve the output in the desired rotation speed range.

[Brief explanation of drawings]

1 and 2 are vertical sectional views showing a conventional structure, and FIG. 3 is a vertical sectional view of an embodiment according to the present invention. 3...Intake passage, 5...Precompression chamber, 8...
... Carburetor, 25 ... Piston 26.
... Bypass passage, 27 ... Auxiliary scavenging port, 28 ... Resonance box (pressure fluctuation control chamber).

Claims (1)

[Scope of utility model registration request] In a two-stroke internal combustion engine, the inflow of fresh air from the carburetor to the precompression chamber via the intake passage is controlled by a reversible flow control means such as a rotary valve on the piston side wall. The carburetor and the control means are connected, one end of the bypass passage is opened in the middle of the intake passage, the other end of the bypass passage is communicated with an auxiliary scavenging port at a position where the pressure is lower than that in the intake passage during the scavenging stroke, and the bypass passage is connected to the carburetor. 2 characterized in that a pressure fluctuation control chamber is provided in the middle of the passage.
Air supply system for cycle internal combustion engines.