JPH0245614A - Crank chamber preliminarily pressurized type two cycle engine - Google Patents

Abstract

PURPOSE:To reduce irregular combustion by arranging an auxiliary scavenging port toward a combustion recessed part provided on a cylinder head. CONSTITUTION:A main scavenging passage 12 and an auxiliary scavenging port 21 are opened on both sides of an exhaust port 13 in a cylinder inner wall. A carburetor 24 is provided in an auxiliary scavenging passage 22 communicated to the auxiliary scavenging port 21, while the auxiliary scavenging port 21 is arranged toward the combustion recessed part 3a of a cylinder head 5. Air-fuel mixture is injected at a high speed toward the combustion recessed part 3a so as to reach a sparking plug 7 at a time. Since flame is thus generated in new air with the arc of the sparking plug 7 not checked by burned out gas, irregular combustion can be reduced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a system for preventing irregular combustion during low-load operation in a crank chamber precompression type two-stroke engine/engine, and in particular relates to a ignition system for preventing irregular combustion during low-load operation. In the combustion chamber, atmospheric air is sucked into the crank chamber and fuel is supplied from an auxiliary scavenging port provided opposite to the exhaust port.

[Conventional technology]

Conventionally, in order to prevent burnt gas from accumulating on the inner wall portion of the cylinder facing the exhaust port, an auxiliary scavenging port was provided facing the exhaust port (for example,
In order to prevent this phenomenon, fuel is added to the auxiliary scavenging air flow to create scavenging air with two types of rich and light air-fuel ratios, and a part of the scavenging air is directly discharged from the exhaust port. A so-called stratified air supply system in which two types of mixture layers are formed is known (for example, Utility Model Application No. 52-170
Publication No. 913).

[Problem to be solved by the invention]

However, during low-load operation, the flow rate of scavenging air flowing into the combustion chamber is small, so scavenging air tends to be insufficient, and scavenging air near the ignition plug becomes insufficient, causing irregular combustion.
There were problems such as fresh air staying near the top of the piston and being discharged from the exhaust port during the piston's upward stroke, resulting in a large amount of fuel components that did not contribute to combustion, reducing fuel economy.

[Means to solve the problem]

The purpose of this invention is to eliminate the above-mentioned problems, provide a two-stroke engine with excellent fuel economy, and without irregular combustion during low-speed operation. The exhaust port is opened to the atmosphere on the inner wall of the cylinder, and an auxiliary scavenging port with a relatively small area is provided on the main scavenging passage adjacent to both sides of the exhaust port and on the wall facing the exhaust port. The auxiliary scavenging road connected to the auxiliary scavenging port is equipped with an auxiliary throttle valve and a fuel supply device,
The auxiliary scavenging port is directed to a combustion recess provided in a concave surface forming a combustion chamber of the cylinder head, and a storage means is provided for temporarily storing auxiliary scavenging air in the auxiliary scavenging passage.

[Operation] Atmospheric air sucked into the crank chamber during the upward stroke of the piston is forced into the combustion chamber through the main scavenging air port during the downward stroke. On the other hand, the pressure drop in the chamber caused by the rise of the piston spreads to the expansion chamber, which is a storage means, and the air-fuel mixture flows through the carburetor and is stored.

When the piston descends, the pressure in the crank chamber increases, which spreads to the expansion chamber and blows out the air-fuel mixture stored there from the auxiliary scavenging port into the combustion chamber near the spark plug as a thin, high-speed air stream, which accelerates the compression stroke. At the end of the process, a mixture layer is formed near the ignition plug.

〔Example〕

The present invention will be explained below with reference to the illustrated embodiments. In the figure, 1 indicates a two-stroke engine with precompression in the crank chamber;
is its crank chamber. 3 is a combustion chamber; combustion chamber 3
is formed by a cylinder 4, a cylinder head 5 and a piston 6.

The concave surface of the cylinder head 5 forming the combustion chamber 3 has a shallow hemispherical shape as a whole, and a slightly deeper hemispherical combustion recess 3a is formed in a part thereof toward the exhaust port 13 side, which will be described later, and the ignition plug is located in the center of the concave surface. 7 electrodes are facing.

Reference numeral 8 denotes an intake passage, which is provided with a check valve 9, which is an inflow valve that only allows airflow into the crank chamber, and a manual main throttle valve 10, which adjusts the intake flow rate.

In this embodiment, a carburetor or other fuel supply device is not provided in the intake passage 8, but a fuel supply device that generates a lean air-fuel mixture may also be provided for auxiliary scavenging, which will be described later.

Furthermore, the inflow valve is not limited to the check valve 9, and may of course be a so-called piston valve that is opened and closed by the skirt portion of the piston 6. 11 is crank chamber 2
This is a main scavenging passage that connects the inside of the cylinder 4 with the inside of the cylinder 4, and communicates with the main scavenging air port 12.12. Reference numeral 13 denotes an exhaust port connected to the exhaust passage 14, and main scavenging air ports 12 are provided symmetrically.
It will be opened between 0 and 0. The above configuration is essentially the same as a conventionally known configuration.

In this invention, an auxiliary scavenging port 21 with a relatively small area is provided on the inner wall of the cylinder 4 facing the exhaust port 13, and an auxiliary scavenging passage 22 connected to this port is partially enlarged. An expansion chamber 23 serving as a storage means is formed,
A carburetor 24 serving as a fuel supply device is provided upstream thereof.

24m is an auxiliary throttle valve attached to the carburetor. In addition,
It is of course possible to use an electronic fuel injection device instead of the carburetor as the fuel supply device;
4& is required to control the flow rate ratio of main scavenging air and auxiliary scavenging air. That is, the throttle valve 241 operates in conjunction with the main throttle valve 10, and, as shown in FIG. 3, is configured to increase the proportion of the auxiliary scavenging air flow in low engine load regions and decrease it in high engine load regions. .

In this embodiment, the expansion chamber 23 temporarily stores auxiliary scavenging air, and is formed into a vertically elongated cylindrical shape.A carburetor 24 is connected to the lower part of the expansion chamber 23, and the crank chamber 2 is connected to the upper part through a working passage 25. K is set so that the pressure inside the crank chamber 2 spreads.

In this example, the working passage 25 is connected tangentially to the upper part of the expansion chamber 23 so as not to mix with the auxiliary scavenging air flow introduced through the carburetor 24. If it is partitioned by a diaphragm 26, it will be even more reliable.

The auxiliary scavenging air port 21 is opened generally facing the spark plug 7, and is supplied as a relatively high-speed thin air stream toward the combustion recess 3a. As shown in this embodiment, the combustion recess 3a is located at the center of the cylinder 4 hole and at the exhaust port 13.
It is provided offset to the side, and its diameter in plan view is set to approximately half the cylinder diameter.

Next, the operation of this engine will be explained. When the engine is operated in a low load range, that is, when the opening degree of the main throttle valve 10 is low, a small amount of fresh air is sucked into the crank chamber 2 during the upward stroke of the piston 6.

On the other hand, the auxiliary throttle valve 24m provided in the auxiliary scavenging passage 22 is kept at a relatively large opening, and a relatively large amount of fresh air is introduced into the auxiliary scavenging passage 22.

When the piston 6 descends and the main scavenging port 12.12 opens, fresh air in the crank chamber flows into the combustion chamber and burnt gas is transferred to the exhaust port 1.
However, since the flow rate is small, the main scavenging airflow is generally weak, and most of it remains near the surface of the piston 60 and is not sufficient to scavenge the burned gas that remains in the upper part of the combustion chamber.

On the other hand, the auxiliary scavenging air flow has a larger flow rate than the main scavenging air and breaks through the main scavenging air and the layer of burnt gas to reach the combustion recess 3a near the spark plug 7.
At the end of the subsequent compression stroke, a mixture layer is formed near the spark plug. Therefore, when ignition is performed by the spark plug 7, good combustion is obtained at the beginning of combustion, so that combustion is stabilized as a whole and irregular combustion can be prevented.

〔Effect of the invention〕

As described above, the present invention jets the air-fuel mixture generated by the fuel supply device 24 from the auxiliary scavenging port 21 at high speed toward the combustion recess 31 formed in the cylinder head 5,
Since the main scavenging air breaks through the air layer formed by the main scavenging air and the remaining burnt gas layer and reaches the ignition plug 7, a combustible mixture layer is formed in the combustion recess 3a without being diffused at the top of the combustion chamber.

Therefore, in the subsequent ignition stroke, the arc generated in the ignition plug 7 is not inhibited by burnt gas and generates a flame in fresh air, which reduces irregular combustion, smoothes engine operation, and prevents fuel from blowing out. This has the effect of preventing this and increasing engine efficiency.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a cross-sectional view of the engine, FIG. 2 is a cross-sectional view taken along line 1--2, and FIG. 3 is a diagram showing opening characteristics of a throttle valve. 3 &... Combustion recess, 21... Auxiliary scavenging port, 23... War/expansion chamber. Figure 1 Special fraud applicant Yamaha Motor Co., Ltd.

Claims (1)

[Claims] The inside of the crank chamber is opened to the atmosphere through an inflow valve and a throttle valve, and an exhaust port is provided on the inner wall of the cylinder, and a relatively small area is provided on the main scavenging passage adjacent to both sides of the exhaust port and on the wall facing the exhaust port. In the case where an auxiliary scavenging air port is opened, an auxiliary scavenging air passage connected to the auxiliary scavenging air port is equipped with an auxiliary throttle valve and a fuel supply device, and the auxiliary scavenging air port is directed to a combustion recess provided in a concave surface forming a combustion chamber of the cylinder head. A two-stroke engine with a crank chamber precompression type, further comprising a storage means for temporarily storing auxiliary scavenging air in the auxiliary scavenging passage.