JPH0625532B2 - Two-cycle engine silencing method and equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for silencing a two-cycle engine and a device therefor, and more specifically to a two-cycle engine capable of effectively reducing exhaust noise in the entire frequency range. The present invention relates to a silencing method and its device.

[Conventional technology]

A conventional silencing method and device for a two-cycle engine will be described with reference to FIGS. 7 to 9.

FIG. 7 is a schematic vertical sectional view of the entire two-cycle engine. In this figure, a cylinder 10 has a combustion chamber 12 inside, and a spark plug 13 is mounted on the top of the cylinder 10 to expose the discharge gap in the combustion chamber 12. Piston 14
Divides the lower part of the combustion chamber 12 and slides in the cylinder 10. The crankcase 16 is joined to the lower end of the cylinder 10, the crankshaft 18 is disposed in the crankcase 16 at the center in the axial direction, and both ends of the crankcase 18 are rotatable via ball bearings 20a and 20b. It is pivotally supported by 16. The connecting rod 22 is rotatably connected to the piston 14 and the crankshaft 18 via pins at the upper and lower ends, and the seals 24a and 24b are fitted on the outer sides of the ball bearings 20a and 20b in the axial direction of the crankshaft 18, respectively. The crankcase 16 is kept airtight. An exhaust port 26 and a pair of scavenging ports 28, 28 below the exhaust port 26 are formed on the side wall of the cylinder 10 that divides the combustion chamber 12 in the radial direction. Scavenging passage 30,
30 is formed in the cylinder 10 and the crankcase 16 and communicates with the scavenging port 28 at the end on the downstream side, and mixes the mixed gas with the combustion chamber.
Lead to 12.

FIG. 8 is a block diagram of a conventional silencer, in which the muffler 32 is
Expansion chamber 34 having an expanded inner diameter and exhaust inlets provided at both ends of the expansion chamber 34 and communicating with the expansion chamber 34
36 and an exhaust outlet 38, which are joined to the exhaust port 26 at the exhaust inlet 36 with a packing 40 interposed therebetween.

The combustion gas generated by the combustion of the air-fuel mixture in the combustion chamber 12 is introduced into the expansion chamber 34 of the muffler 32 from the exhaust port 26 opening to the combustion chamber 12 as the piston 14 descends, and expanded there, and the exhaust outlet 38 Released into the atmosphere. In this way, the exhaust gas does not expand at once in the atmospheric space, but expands appropriately in the expansion chamber 34 of the muffler 32 and then expands in the atmospheric space, so that the exhaust sound is attenuated.

FIG. 9 shows a frequency spectrum of the exhaust gas attenuation amount by the muffler 32. The exhaust gas attenuation amount AT is expressed by the following equation.

In the equation (1), m: D ² / d ² (D and d are inner diameters of the expansion chamber 34 and the exhaust inlet 36 of FIG. 8) c: sound velocity of combustion gas f: frequency of exhaust sound l: first Length of Expansion Chamber 34 in FIG. 8 FIG. 9 is a graph of the equation (1), where f1,
f2, f3, ... Resonance frequencies, g1, g2, g3.
..The anti-resonance frequency is set.

[Problems to be solved by the invention]

In a conventional silencer, there is a frequency at which the exhaust sound attenuation amount becomes zero, such as g1, g2, g3, etc., and if the normal speed range of the two-cycle engine is within a specific limited range. The frequency range of exhaust noise is also limited, and the size of each part of the muffler can be determined accordingly to effectively attenuate the exhaust noise.However, when the normal rotation speed range of the two-cycle engine is wide, the frequency of the exhaust noise is There is also a problem that the range becomes wider and the anti-resonance frequency of the silencer is included, and exhaust noise cannot be sufficiently reduced.

An object of the present invention is to prevent the appearance of a frequency at which the exhaust noise is attenuated to zero and effectively attenuate the exhaust noise even when the normal rotation speed range of the two-cycle engine is wide. An object is to provide a method of silencing an engine and a device therefor.

[Means for solving problems]

According to the method for silencing the two-cycle engine of the present invention, the expansion type muffler is connected to each of the upper and lower exhaust port portions in the combustion chamber of the two-cycle engine, and the sound velocity difference of the exhaust gas passing through the upper and lower exhaust port portions is changed. The anti-resonance frequency is removed by causing a phase difference in the sound attenuation spectrum and combining them.

A muffler for a two-cycle engine according to the present invention includes an exhaust port formed on a wall surface of a combustion chamber of a two-cycle engine and separated into an upper exhaust port portion and a lower exhaust port portion, and upper and lower exhaust port portions, respectively. A first and a second muffler portion in communication with.

[Action]

The air-fuel mixture is ignited in the combustion chamber and the piston descends. The exhaust port on the side surface of the combustion chamber opens to the combustion chamber in the order of the upper exhaust port portion and then the lower exhaust port portion as the piston descends.

During a period in which only the upper exhaust port portion is open to the combustion chamber and the lower exhaust port portion is not yet open to the combustion chamber, the temperature of the combustion gas in the combustion chamber is high. Therefore, the hot combustion gas is introduced into the first muffler portion via the upper exhaust port portion of the exhaust port, and the exhaust noise is attenuated by the first muffler portion.

During the period when the lower exhaust port is also open to the combustion chamber,
The temperature of the combustion gas in the combustion chamber drops. Therefore, the low-temperature combustion gas is introduced into the second muffler portion via the lower exhaust port portion, and the exhaust noise is attenuated by the second muffler portion.

As the temperature of the combustion gas decreases, the sound velocity of the combustion gas also changes, so the anti-resonance frequency in each muffler part is different, and there is a phase difference in the frequency spectrum of the attenuation amount of the exhaust sound attenuated in each muffler part. Occurs. Therefore, in the frequency spectrum of the attenuation amount of the exhaust sound that attenuates in the entire expansion muffler, that is, in the combined frequency spectrum of the attenuation amount of the exhaust sound related to each muffler part, the frequency at which the attenuation amount becomes zero is removed. It

〔Example〕

 Hereinafter, the present invention will be described with reference to the embodiments of the drawings.

FIG. 1 is a configuration diagram of a silencer according to an embodiment. Muffler
42 is joined to the outer end portion of the exhaust port 26 at the inlet side portion 44, and the packing 46 is interposed at the joint portion between the inlet side portion 44 and the exhaust port 26 to maintain airtightness at the joint portion. The partition walls 48, 49 are provided in the exhaust port 26 and the muffler 42,
It is arranged at an intermediate position between them in the vertical direction, and partitions them vertically. As a result of partitioning by the partition wall 49 in the vertical direction, the inside of the muffler 42 is separated into a first expansion chamber 50 and a second expansion chamber 52 that are not in communication with each other, and the first expansion chamber 50
The second expansion chamber 52 and the second expansion chamber 52 function as independent first and second muffler portions, and have exhaust outlets 58 and 60 on the side opposite to the inlet side portion 44, respectively. Further, as shown in FIG. 2 when the exhaust port 26 of FIG. 1 is viewed from the combustion chamber 12 side, the exhaust port 26 is separated by the partition wall 48 so that the upper exhaust port portion 54 and the lower exhaust port 54 are not in communication with each other. Port part
It is separated into 56.

FIGS. 3 (a) and 3 (b) show the state when the upper exhaust port portion 54 and the lower exhaust port portion 56 are opened into the combustion chamber 12 in the embodiment of FIG. 1, respectively. Combustion chamber 12
The air-fuel mixture introduced therein is ignited by the spark discharge of the spark plug 13 and expanded, and the piston 14 descends. piston
As the valve 14 descends, the upper exhaust port portion 54 first opens and then the lower exhaust port portion 56 opens. Further, the temperature of the combustion gas in the combustion chamber 12 decreases as time passes, that is, as the piston 14 descends.

During a period in which only the upper exhaust port portion 54 is open to the combustion chamber 12 and the lower exhaust port portion 56 is not yet open to the combustion chamber 12 (Fig. 3 (a)), the temperature of the combustion gas in the combustion chamber 12 is increased. Is high. Therefore, the hot combustion gas passes through the upper exhaust port portion 54 to the first expansion chamber as the first muffler portion.
It is introduced into the first expansion chamber 50, expanded in the first expansion chamber 50, and discharged from the exhaust outlet 58 into the atmospheric space.

During a period in which the piston 14 is sufficiently lowered and both the upper exhaust port portion 54 and the lower exhaust port portion 56 are open to the combustion chamber 12 (FIG. 3 (b)), the combustion gas in the combustion chamber 12 The temperature has dropped. Therefore, the low-temperature combustion gas is introduced into the second expansion chamber 52 as the second muffler portion via the lower exhaust port portion 56, expands in the second expansion chamber 52, and enters the atmosphere space from the exhaust outlet 60. Is released.

FIG. 4 shows the exhaust sound attenuation amounts AT1, A by the first expansion chamber 50 and the second expansion chamber 52 as the first and second muffler parts.
The frequency spectrum of T2 and the frequency spectrum of the entire muffler 42 that combines the frequency spectra (attenuation AT
(corresponding to t). The sound velocity also changes as the temperature of the combustion gas changes, and the sound velocity of the high temperature combustion gas is higher than that of the low temperature combustion gas. Therefore, as understood from the above formula (1), the first expansion chamber 50 and the second expansion chamber 50
The anti-resonance frequencies at 52 are shifted from each other, and the frequency at which the attenuation amount is zero is removed from the frequency spectrum of the entire muffler 42.

The following formula is obtained by substituting a specific numerical value into the above formula (1).
The exhaust sound attenuation amount ATp due to the muffler 32 in the figure and the exhaust sound attenuation amounts AT1 and AT2 due to the muffler 42 in FIG. 1 are shown for comparison. In addition, in FIG. 8, d = 2 cm, D = 1
0 cm, l = 50 cm, combustion gas temperature = 500 ° C (sonic velocity 57
1 m / s), and in FIG. 1, d1 = d2, D1
= D2, d1 = 1 cm, D1 = 5 cm, l = 50 cm, temperature of combustion gas introduced into the first expansion chamber 50 = 600 ° C. (sonic velocity 631 m / s), introduced into the second expansion chamber 52 The temperature of the combustion gas was set to 400 ° C (sonic velocity of 511 m / s).

In the conventional muffler 32 of FIG. 8, In the muffler 42 according to the present invention in FIG. 1, FIGS. 5A and 5B show modifications of the muffler 42, respectively. In the muffler 42 of FIG. 5 (a), the exhaust outlet 58
Is connected to the middle of the exhaust outlet 60, and the exhaust gas of the first expansion chamber 50 and the second expansion chamber 52 is discharged from the common combined exhaust outlet 62 to the atmospheric space. In the muffler 42 of FIG. 5 (b), the exhaust outlet 58 is provided in the partition wall 49 to make the first expansion chamber 50 and the second expansion chamber 52 communicate with each other, and The exhaust gas passes through the second expansion chamber 52 and is discharged from the exhaust outlet 60 into the atmospheric space. In the type in which the exhaust gas in the first expansion chamber 50 and the second expansion chamber 52 merges like the muffler 42 in FIG. 5, the combined effect of damping the exhaust sound by each muffler portion increases.

FIG. 6 shows a modification of the partition wall 48 of FIG. 1 as viewed from the combustion chamber 12 side. The partition wall 48b is bent at its central portion so as to project downward. By changing the amount of protrusion, the temperature of the combustion gas introduced into the first expansion chamber 50 can be changed, and the piston ring mounted on the circumferential surface of the piston 14 has the exhaust port 26 at the exhaust port 26.
Since it moves while contacting not only the peripheral edge of the partition wall 48b but also the end edge of the partition wall 48b, it is possible to effectively prevent the piston ring from protruding into the exhaust port 26 and being damaged.

〔The invention's effect〕

As described above, according to the present invention, by separating the upper and lower exhaust ports opening on the side surface of the combustion chamber into the upper exhaust port portion and the lower exhaust port portion, respectively, the combustion gas in the combustion chamber can be heated to different temperatures. , I.e. at different sound speeds, are introduced into the first and second muffler parts via the upper and lower exhaust port parts. Therefore,
Since there is a phase difference in the frequency spectrum of the amount of exhaust sound attenuated in each muffler part, and the anti-resonance frequencies in each muffler part are displaced from each other, the frequency spectrum of the amount of exhaust sound attenuation in the entire expansion type muffler, that is, In the combination of the frequency spectra of the attenuation amounts of the muffler parts, the appearance of the frequency at which the attenuation amount becomes zero is prevented. As a result, exhaust noise can be attenuated in the entire frequency range, and exhaust noise can be effectively attenuated even in a two-cycle engine having a wide range of normal engine speed.

Furthermore, as a result of the exhaust port being separated into the upper exhaust port portion and the lower exhaust port portion, the cross-sectional area at each exhaust port portion is reduced, which increases the flow velocity of exhaust gas at that exhaust port portion. It is possible to suppress the deposition of carbon and the like on the exhaust port.

Further, when the exhaust port is separated by a partition wall or the like, the side edge of the partition wall on the combustion chamber side is brought into contact with the piston ring fitted to the peripheral surface of the piston so that the piston ring does not protrude to the exhaust port side. In addition, the piston ring is
Not only the peripheral edge of the exhaust port but also the side edge of the partition wall on the combustion chamber side at the same time, it is possible to contribute to prevention of breakage of the piston ring and reduction of hammering noise.

[Brief description of drawings]

FIGS. 1 to 7 relate to an embodiment of the present invention. FIG. 1 is an overall configuration diagram of a silencer, FIG. 2 is a view of an exhaust port of FIG. 1 seen from a combustion chamber side, and FIG. FIGS. 4A and 4B are views showing a state when the upper exhaust port portion and the lower exhaust port portion are opened into the combustion chamber in the embodiment of FIG. 1, and FIG. 4 is the first and second muffler portions. FIG. 5 is a diagram showing a frequency spectrum of the exhaust sound attenuation amount according to FIG. 5 and a frequency spectrum of the entire muffler in which the respective frequency spectra are combined, FIGS. FIG. 1 is a view showing a modification of the partition wall of FIG. 1 as seen from the combustion chamber side, FIG. 7 is a schematic vertical cross-sectional view of the entire two-cycle engine, and FIGS. 8 and 9 are related to a conventional silencer.
FIG. 9 is a configuration diagram of the silencer, and FIG. 9 is a diagram showing a frequency spectrum of the exhaust gas attenuation amount by the silencer of FIG. 12 ... Combustion chamber, 26 ... Exhaust port, 42 ... Muffler, 48, 48b, 49 ... Partition wall, 50 ... First expansion chamber (first muffler portion), 52 ... Second expansion chamber (Second muffler part), 54 ... Upper exhaust port part, 56 ...
... Lower exhaust port part.

Claims (7)

[Claims] 1. An expansion-type muffler is connected to each of the upper and lower exhaust port portions of a combustion chamber of a two-cycle engine, and is placed in a sound attenuation spectrum due to a difference in sound velocity between exhaust gases passing through the upper and lower exhaust port portions. A two-cycle engine silencing method that removes the anti-resonance frequency by creating a phase difference and combining them. 2. An exhaust port formed on a wall surface of a combustion chamber of a two-cycle engine and separated into an upper exhaust port portion and a lower exhaust port portion, and communicates with the upper and lower exhaust port portions, respectively. A silencer for a two-cycle engine, comprising a first muffler part and a second muffler part. 3. The silencer for a two-cycle engine according to claim 2, wherein the first and second muffler portions are arranged in a common inflatable muffler and are separated from each other by a partition wall. 4. The silencer for a two-cycle engine according to claim 3, wherein the exhaust outlets of the first and second muffler portions are separately communicated with the atmospheric space. 5. The muffler for a two-cycle engine according to claim 3, wherein the exhaust outlets of the first and second muffler portions are joined and then communicated with the atmospheric space. 6. The silencer for a two-cycle engine according to claim 3, wherein the first muffler portion communicates with the second muffler portion through an exhaust outlet thereof. 7. A separating member for separating the exhaust port into the upper exhaust port portion and the lower exhaust port portion is bent so as to project to one of the upper and lower exhaust port portions. A silencer for a two-cycle engine according to any one of claims 2 to 6.