JPH0411436B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an exhaust system for an outboard motor.

[Conventional technology]

The applicant has filed Japanese Patent Application No. 56-25282 (Japanese Unexamined Patent Publication No. 57-2528)
140293), it is stated that ``an expansion chamber that communicates with the outside through a main exhaust port is formed in the casing, an exhaust pipe that communicates with the exhaust passage of the engine is opened in the expansion chamber, and the exhaust pipe A pressure relief hole opening into the expansion chamber is provided in the intermediate side wall on the engine side, and a sub-discharge port is opened at a level above the main discharge port, and the expansion chamber and the sub-discharge port are communicated through an underwater chamber. We have already proposed a new outboard motor exhaust system.

According to the exhaust system already proposed above, in the low-speed, low-load operating range of the engine where the exhaust pipe opening is submerged in water, the engine exhaust gas is discharged from the sub-exhaust port through the pressure relief hole, the expansion chamber, and the submerged chamber. , prevents an increase in exhaust pressure in the engine exhaust passage,
It becomes possible to prevent the irregular combustion. In addition, the exhaust gas from the engine passes through the expansion chamber and the underwater chamber, thereby being muted in a wide frequency range.

[Problem to be solved by the invention]

However, with the exhaust system already proposed above, it is not possible to obtain a silencing effect in a predetermined frequency range that is unique to the low-speed, low-load operation range of the engine.

The present invention prevents improper combustion due to an increase in engine exhaust pressure in the low-speed, low-load operating range of the engine where the opening of the main exhaust pipe is submerged in water, and also aims to muffle noise in a wide frequency range. The purpose is to reduce noise.

[Means to solve the problem]

The present invention includes: an expansion chamber formed within a casing and communicating with the outside through a main discharge port; and a sub-discharge port that opens to the outside at a level above the main discharge port;
In an exhaust system for an outboard motor, the exhaust system for an outboard motor includes an underwater chamber that communicates the expansion chamber and the sub-exhaust port via water, and a main exhaust pipe that communicates with an exhaust passage of the engine and opens into the expansion chamber. A sub-exhaust pipe is provided that branches from the exhaust pipe, opens into the expansion chamber at a level above the opening position of the main exhaust pipe, and communicates the main exhaust pipe with the expansion chamber, and the sub-exhaust pipe performs a resonance-type noise muffling function. The length and cross-sectional shape are determined.

[Effect]

According to the present invention, there are the following effects.

In the engine's low-speed, low-load operating range where the opening of the main exhaust pipe is submerged in water, the engine exhaust gas passes through the sub-exhaust pipe, the expansion chamber, the underwater chamber, and is discharged from the sub-exhaust port, causing an increase in exhaust pressure in the engine exhaust passage. can be prevented and its unauthorized combustion can be prevented.

The exhaust gas from the engine passes through the expansion chamber and the underwater chamber, where it is muted in a wide range of frequencies.

When the engine exhaust passes through the sub-exhaust pipe, it obtains a resonance-type silencing effect and is also subjected to silencing in a specific frequency range.

FIG. 1 is a side view, cut away, of essential parts of an outboard motor 10 to which an embodiment of the present invention is applied. The outboard motor 10 has an engine 12 mounted on top of a propulsion unit 11. The output of the engine 12 is transmitted to the propeller shaft 14 via the drive shaft 13, and the propeller 15 is directly connected to the propeller shaft 14.
can be driven. The engine 12 is a water-cooled engine, and a water pump 16 driven by a drive shaft 13 pumps outside water taken in from an outside water intake port 17 to the engine 12. In addition, engine 1
The cooling water after cooling the propulsion unit 11 can be discharged into the casing 18 of the propulsion unit 11.

The casing 18 has a generally cylindrical inner wall 18B spaced apart from the outer wall 18A.
A cylindrical body 19 with wide openings at both ends is held inside B. The cylinder 19 defines an expansion chamber 20 therein. The expansion chamber 20 communicates with the outside water via a main discharge port 21 formed in the boss portion 15A of the propeller 15.

A main exhaust pipe 23 that communicates with an exhaust passage 22 of the engine 12 opens into the expansion chamber 20 . The main exhaust pipe 23 is designed to improve the air supply ratio and air supply efficiency of the engine 12 by utilizing pressure waves generated within the exhaust pipe in the high speed and high load range of the engine 12, thereby making it possible to improve the output of the engine 12. It is given a suitable length and cross-sectional shape. Note that the main exhaust pipe 23 is
In the low-speed, low-load operating range of the engine 12, as shown in FIG.
submerged in water entering the interior.

The cylinder 19 also defines an underwater chamber 24 adjacent to the expansion chamber 20. The underwater chamber 24 communicates with the expansion chamber 20 at its upper portion, and via a communication port 25 provided at its bottom side.
It communicates with an underwater chamber 26 defined between the inner wall 18B of the casing 18 and the cylindrical body 19. Underwater chamber 2
6 is an outer chamber 28 defined through an opening 27 between the outer wall 18A and the inner wall 18B of the casing 18.
is communicated with. The outer chamber 28 communicates with the outside space via a sub-exhaust port 29 that opens at the upper part of the outer wall 18A, thus at a level above the main exhaust port 21, and a drainage port that opens at the lower part of the outer wall 18A. It communicates with the outside water via 30.
Therefore, the expansion chamber 20 and the sub-discharge port 29 communicate with each other via the underwater chambers 24 and 26 and the outer chamber 28.

Note that the engine 1 is installed in the underwater chambers 24 and 26.
The cooling water after cooling the submersible chambers 24 and 26 falls and stagnates, and the water in the submersible chambers 24 and 26 overflows from the opening 27 of the submersible chamber 26 to the outer chamber 28 side, and can then be discharged to the outside from the drain port 30. ing. Therefore, a certain amount of water always remains in the underwater chambers 24, 26, which is set by the high level of the opening 27.

Furthermore, a sub-exhaust pipe 31 is provided which branches from the middle part of the main exhaust pipe 23 on the engine 12 side, and communicates the inside of the main exhaust pipe 23 with the expansion chamber 20 through a communication hole 32 . The expansion chamber side opening 33 of the auxiliary exhaust pipe is located above the lower opening of the main exhaust pipe 23.

The auxiliary exhaust pipe 31 is connected to the engine 12 when the opening of the main exhaust pipe 23 is submerged below the water surface level LL in the low-speed, low-load operating range of the engine 12.
The exhaust gas is discharged into the expansion chamber 20, thereby preventing an increase in exhaust pressure in the exhaust passage 22 of the engine 12, thereby making it possible to prevent improper combustion.

In addition, by selecting its length and cross-sectional shape, the sub-exhaust pipe 31 can perform a resonance-type muffling function, and can perform muffling in a specific frequency range.
By utilizing the pressure waves generated in the sub-exhaust pipe 31, it is possible to improve the air supply ratio and air supply efficiency in a specific speed range of the engine 12.

Note that the exhaust gas discharged from the exhaust pipe 31 to the expansion chamber 20 can be discharged to the outside from the sub-exhaust port 29 via the underwater chambers 24 and 26 and the outer chamber 28.

Next, the operation of the above embodiment will be explained.

In the low-speed, low-load operation range of the engine 12 where the opening of the main exhaust pipe 23 is submerged in water, the exhaust gas of the engine 12 flows from the sub-exhaust pipe 31 to the expansion chamber 20, the underwater chamber 24,
26 and is discharged from the sub-exhaust port 29, thereby preventing an increase in exhaust pressure in the exhaust passage 22 of the engine 12 and preventing irregular combustion. Also, engine 1
The exhaust gas of No. 2 passes through the expansion chamber 20 and also passes through the underwater chambers 24 and 26, thereby being subjected to noise reduction in a wide frequency range. Furthermore, by passing through the sub-exhaust pipe 31, the exhaust gas from the engine 12 obtains a resonance-type silencing effect, and is subjected to silencing in a specific frequency range. Further, at this time, the engine 12 is able to improve the air intake ratio and air intake efficiency in a specific speed range of the engine 12 by utilizing the pressure waves generated within the auxiliary exhaust pipe 31.

In addition, in the high-speed, high-load operation range of the engine 12, the exhaust gas from the engine 12 is discharged from the main exhaust port 21 via the expansion chamber 20, and by passing through the expansion chamber 20, noise is muted in a wide frequency range. be done. Also, at this time, the engine 12 is connected to the main exhaust pipe 2.
By utilizing the pressure waves generated within the engine 12
This will improve the air supply ratio and air supply efficiency.

FIG. 2 is a diagram showing the silencing effect of the structure of the present invention together with that of a comparative structure. The comparative structure is based on the above-mentioned patent application filed in 1983 in the conventional technology.
It is described in No. 25282 (Japanese Unexamined Patent Publication No. 140293/1983). The structure of the present invention, which includes a resonant sub-exhaust pipe, can obtain a greater noise reduction effect in a specific frequency range than a comparative structure that includes a simple pressure relief hole. The hatched area in the figure is the difference in the amount of damping between the two structures.

Here, the sub-exhaust pipe 31 is located above the level of water that enters the expansion chamber 20 during low-speed, low-load operation of the engine 12 in order to smoothly discharge exhaust gas in the low-speed, low-load operation range of the engine 12. It is preferable. However, the sub exhaust pipe 31
Even if the opening 33 of the sub-exhaust pipe 31 is submerged in water, since the opening 33 of the sub-exhaust pipe 31 is located above the opening of the main exhaust pipe 23, the exhaust air flows through the sub-exhaust pipe 31, which has a smaller water head. It is possible to obtain the above-mentioned effects by flowing the exhaust gas into the expansion chamber 20 through the opening 33 and exhausting it through the sub-exhaust pipe 31.

Although the above embodiment describes the case where a single sub-exhaust pipe 31 is used, in the present invention, if a plurality of sub-exhaust pipes with different lengths, cross-sectional shapes, etc. are arranged in the main exhaust pipe 23. Since each sub-exhaust pipe functions independently, it is possible to obtain a silencing effect in a plurality of different specific frequency ranges, and to improve the air intake ratio and air intake efficiency over a wide speed range of the engine 12. .

Further, in the above embodiment, the underwater chambers 24, 2
Cooling water after engine cooling is used as the water that stays in the submersible chambers 24 and 26, and a certain amount of water defined by the openings 27 can always stay in the submersible chambers 24 and 26, so that it flows out from the sub-exhaust pipe 31 to the expansion chamber 20. The exhausted exhaust gas always passes through the water in the underwater chambers 24 and 26, thereby making it possible to obtain a silencing effect. However, in the present invention, the water passing through the lower part of the underwater chambers 24, 26 and the expansion chamber 20 and flowing into the expansion chamber 20 may be supplied to the underwater chambers 24, 26.

Further, in the above embodiment, a case has been described in which the expansion chamber 20 is formed inside the casing 18 by using the cylindrical body 19 that is separate from the outer wall 18A and inner wall 18B of the casing 18. However, in the present invention, an expansion chamber may be formed inside the casing 18 by the wall of the casing 18 itself.

〔Effect of the invention〕

As described above, according to the present invention, in the low-speed, low-load operating range of the engine where the opening of the main exhaust pipe is submerged in water, irregular combustion due to an increase in engine exhaust pressure is prevented, and noise is muffled in a wide frequency range. At the same time, it is possible to muffle sound in a specific frequency range.

[Brief explanation of drawings]

Fig. 1 is a cutaway side view of essential parts of an outboard motor to which an embodiment of the present invention is applied, and Fig. 2 is a diagram showing the noise reduction effect of the structure of the present invention together with that of a comparative structure. It is. DESCRIPTION OF SYMBOLS 10... Outboard motor, 12... Engine, 18... Casing, 20... Expansion chamber, 21... Main exhaust port, 22... Exhaust passage, 23... Main exhaust pipe, 24, 26... Submersible chamber,
29... Sub-exhaust port, 31... Sub-exhaust pipe.

Claims (1)

[Claims] 1. An expansion chamber formed in a casing and communicating with the outside via a main discharge port, a sub-discharge port that opens to the outside at a level above the main discharge port, and an expansion chamber that is connected to the sub-discharge port by water. In an exhaust system for an outboard motor, the exhaust system includes a submersible chamber that communicates with the expansion chamber through a submersible chamber, and a main exhaust pipe that communicates with an exhaust passage of the engine and opens into the expansion chamber. A sub-exhaust pipe is provided that opens into the expansion chamber at a level above the main exhaust pipe and communicates the main exhaust pipe with the expansion chamber, and the sub-exhaust pipe has a length and a cross-sectional shape that performs a resonant noise reduction function. An outboard motor exhaust system featuring: