JPH0544490Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an exhaust system for a two-stroke gasoline engine.

[Conventional technology]

FIG. 2 shows an example of a conventional exhaust system for a two-stroke engine disclosed in Japanese Utility Model Application No. 62-121437. In FIG. 2, 1 is a crankcase, 2 is a cylinder, 3 is a cylinder head, 4 is a crankshaft, and 5 is a connecting rod. Combustion chamber 8
are cylinder 2, cylinder head 3 and piston 6
formed by The piston 6 makes a reciprocating motion by sliding along the cylinder 2 due to the rotation of the crankshaft 4, and an intake hole 21 and an exhaust hole 23 are formed around the cylinder 2, which are opened and closed by the outer circumference of the piston 6. . The exhaust hole 23 is connected to the exhaust hole partition 2
Similarly, the exhaust muffler 12 is divided by a muffler partition 27 into an upper muffler chamber 12a and a lower muffler chamber 12b. Muffler partition 2
A throttle 28 is installed in a part of the muffler 7 to communicate the upper chamber 12a and the lower chamber 12b, and the exhaust gas immediately after opening the exhaust hole enters the muffler upper chamber 12a from the upper exhaust hole 23a and expands. 28, enters the muffler lower chamber 12b, and is discharged to the atmosphere from the muffler outlet 25. Due to the effect of the throttle 28, the amount of exhaust gas passing through this part is suppressed, and the combustion gas in the cylinder is mainly transferred to the muffler lower chamber 12 from the lower exhaust hole 23b that opens following the upper exhaust hole 23a.
It is released into the atmosphere through b. That is, the outflow pattern of the combustion gas is leveled, and the high sound pressure immediately after the opening of the exhaust hole is attenuated by the throttle 28 and the muffler upper chamber 12a, thereby reducing noise.

[The problem that the idea aims to solve]

The partition 26 that divides the exhaust hole into upper and lower parts can be formed integrally with the muffler partition 27 and inserted into the exhaust port from the muffler side, but in this case, the tip should not come into contact with the piston, and the inner surface of the cylinder Since it is necessary to install it as concentrically as possible, high manufacturing precision is required. However, mufflers generally have a pressed and welded sheet metal structure, so it is difficult to process them with high precision.

Therefore, this partition 2 is usually used when forming the cylinder.
6 is formed integrally with the cylinder 2, but since the cylinder material is usually an aluminum alloy and the partition 26 is a thin plate and is exposed to high temperatures, a problem arises in terms of heat resistance. As a countermeasure to this problem, increasing the wall thickness of the partition 26 is not desirable because it inevitably causes the exhaust to open prematurely, which has an adverse effect on performance.

[Means to solve the problem]

Multiple exhaust holes with different opening timings are formed side by side on the cylinder wall, each exhaust passage is led independently to the muffler, and high-pressure exhaust from the exhaust hole that opens first in the muffler is passed through a silencing element ( For example, after passing through the aperture and cavity), it is discharged into the atmosphere,
Or lead it to an exhaust gas passage from an exhaust port that opens later.

[Effect]

The high-pressure exhaust gas in the exhaust chamber that opens first is subjected to a throttling action and flows to the exhaust chamber that opens next, resulting in a smooth flow within the muffler. The wall thickness of the partition between the horizontally arranged exhaust holes can be set to an appropriate thickness regardless of the opening timing, and heat resistance is improved.

〔Example〕

FIG. 1 shows an example of an exhaust system for a two-stroke engine according to the present invention. FIG. 1 is a plan view taken in section at an exhaust passage section. It is the same as Fig. 2 except for the exhaust hole and muffler. Exhaust holes 33 and 34 are formed side by side in the cylinder 2, separated by a partition 35, and the exhaust hole 34 opens later than the exhaust hole 33. 12 is a muffler, which is installed so as to communicate with the exhaust holes 33 and 34;
A partition 27 on the muffler side is installed continuously from 5, and the muffler volume part 12a on the exhaust hole 33 side and the muffler volume part 12b on the exhaust hole 34 side are partitioned off. A throttle 28 is formed in the muffler partition 27 to communicate the muffler volumes 12a and 12b, and the tail pipe 25 is installed in the muffler volume 12b.

When the piston descends after combustion and the exhaust hole 33 opens, the high pressure gas in the combustion chamber flows into the muffler volume 12a.
It expands inward, and a part of it expands into the throttle 28 and the muffler volume 12.
b. It is discharged into the atmosphere through the tail pipe 25, but its flow rate is suppressed by the effect of the throttle 28.

When the piston further descends and the exhaust hole 34 opens, the combustion gas, which has been considerably expanded and decompressed due to the opening of the exhaust hole 33, flows from the exhaust hole 34 to the muffler volume 1.
2b, and is discharged to the atmosphere through the tail pipe 25. In other words, the same effect as the conventional device shown in FIG. 2 can be obtained,
The flow of exhaust gas is leveled and high-pressure exhaust noise is suppressed, thereby achieving a reduction in exhaust noise. On the other hand, the partition wall 35 provided at the exhaust hole is relatively short (vertical length) and can be made thick.
Thermal problems can be avoided. In other words, if the exhaust hole is formed wide in the circumferential direction of the cylinder, a sufficient area can be secured for the exhaust to pass through, and since this partition 35 is also a part of the cylinder wall, the piston ring protrudes from the ring. There will be no chance of it breaking.

[Effect of idea]

In a two-stroke engine that opens and closes the exhaust hole provided on the side of the cylinder according to the stroke of the piston, a plurality of exhaust holes with different opening timings are arranged in the circumferential direction of the cylinder, and each exhaust hole is connected to the inside of the muffler. The muffler communicates with each muffler element and communicates each muffler element through a throttle, so that the engine exhaust flowing through each exhaust hole in the muffler passes through each muffler element and is discharged independently or jointly. By configuring this, the following effects are produced.

(1) The exhaust noise of a two-stroke engine can be suppressed by a simple exhaust system structure.

(2) Since the flow of the exhaust gas can be ensured as a whole, it is advantageous in terms of performance compared to a complicated exhaust system or an exhaust system with a small throttle.

(3) By oriented the port partition vertically, it is possible to solve the thermal problem of the partition.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the exhaust system for a two-stroke engine according to the present invention, in which a is a horizontal sectional view at the exhaust hole position, and b is a view from A in FIG. a, showing the arrangement of the exhaust holes. FIG. 2 is an overall vertical sectional view of the conventional device. 2... Cylinder, 8... Combustion chamber, 12... Muffler, 12a, 12b... Muffler volume part, 25...
Tail pipe, 27...Muffler partition wall, 28...
...Aperture, 33, 34...Exhaust hole, 35...Exhaust hole partition.

Claims (1)

[Scope of utility model registration request] In a two-stroke engine that opens and closes the exhaust hole provided on the side of the cylinder according to the stroke of the piston, a plurality of exhaust holes with different opening timings are arranged in the circumferential direction of the cylinder, and each exhaust hole is connected to the inside of the muffler. The exhaust hole is configured to communicate with each of the silencing elements and communicate with each of the silencing elements via a throttle, so that engine exhaust gas flowing through each exhaust hole passes through each of the silencing elements and is discharged independently or in combination. An exhaust system for a two-stroke engine featuring: