JPS6160250B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an engine exhaust system for a small boat.

Conventionally, in small ships, when exhaust engine exhaust is discharged from the stern, air exhaust is generally adopted because it is necessary to avoid air bubbles from getting into the propeller when going astern. The exhaust port for air exhaust was located in a position where it was exposed to the air even when the ship was in a submerged state, such as when the ship was at rest.

Since such an exhaust port is responsible for discharging exhaust gas in the entire range from the fully closed throttle to the fully open throttle, it is necessary to have a large opening area. Therefore, even during idling when a large exhaust port is not required, exhaust gas is exhausted through the large exhaust port.
There was a problem with the exhaust noise being loud and unpleasant.

The purpose of the present invention is to solve these problems.In small vessels, when stopping, moving forward at low speed, and moving backward, the hull sinks to a relatively deep position under the water surface, but when moving forward at high speed, it rises close to the water surface. The purpose of the present invention is to provide an engine exhaust system that solves the above-mentioned problems by utilizing the characteristic that

Furthermore, the present invention provides an engine exhaust system for a small boat that can muffle exhaust noise during idling, reduce exhaust resistance during high-speed forward movement, and prevent air bubbles from entering the propeller during reverse movement. It is.

That is, the engine exhaust system for a small boat according to the present invention has a main exhaust port that opens rearward at the lower part of the stern of the boat, and a sub-exhaust port that is always open to the air above the main exhaust port. The main exhaust port is formed at a position where it is submerged in the water when the ship is stopped or moving backwards, but emerges above the water surface when the ship is moving forward at high speed. Another feature of the present invention is that a valve device is provided that opens when the vessel moves forward at high speed and closes when it moves backward.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the structure of the rear part of the hull of a small boat equipped with the engine exhaust system of the present invention, in which an exhaust expansion chamber 14 is provided in the lower part of the stern plate 12. As shown in FIG. Exhaust gas from an engine 16 installed inside the hull exits a muffler 18 and is mixed with engine cooling water while being guided to a silencing chamber 22 through an exhaust pipe 20. The silencing chamber is partitioned into two sections by a perforated partition plate 26 having a large number of holes diagonally arranged in the housing 24. Further, a communication pipe 28 connecting the two sections is provided approximately at the center of the partition plate 26. The exhaust gas and cooling water led to this silencing chamber are connected to the perforated partition plate 26.
The cooling water collides with the perforated partition plate 26 and flows downward. On the other hand, some of the exhaust air is connected to the perforated partition plate 26.
The other part flows through the communication pipe 28 to the other compartment, respectively, and is led into the exhaust gas expansion chamber 14 through the outlet pipe 30.

While passing through the muffling chamber 22, the exhaust gas is muffled by repeated expansion and compression due to rapid changes in the cross-sectional area of the flow path, and also by mutual interference via the perforated partition plate. Furthermore, since the perforated partition plate 26 is arranged diagonally, its surface area can be larger than that of a normal partition plate arranged vertically, and cross-sectional changes in opposite directions can be achieved in each section on the inlet side and the outlet side. Therefore, the silencing effect due to the interference of exhaust sound can be further improved. In addition, since the cooling water flows down the perforated partition plate 26 relatively gently in the form of a film, it flows into the other compartment through a large number of holes provided in the partition plate, so that the exhaust gas flows into the other compartment. The silencing effect can also be enhanced by mixing with this cooling water when passing through the hole partition plate. Note that the perforated partition plate 26
As shown in the figure, since the volume near the inlet of the inlet side compartment is inclined in the direction of increasing, there is no adverse effect on engine performance due to an increase in exhaust resistance.

The cooling water and exhaust gas that have passed through the silencing chamber 22 are led to the exhaust expansion chamber 14 and then discharged to the outside.

The exhaust expansion chamber 14 is constructed by fixing a housing 31 to the stern plate 12 with a fastener 32, and its front wall is formed using the stern plate. A main exhaust port 33 opening to the rear is provided in the lower part of the exhaust expansion chamber, and a sub-exhaust port 34 having a relatively small cross-sectional area is provided in the upper part. The main exhaust port 33 is covered by a cover 38 attached to the rear wall of the exhaust expansion chamber with a stopper 36.
The cover 38 is made of a sheet of rubber-like elastic material, and is displaced rearward as shown by the chain double-dashed line in FIG. 1 when the differential pressure between the internal pressure and the external pressure of the exhaust expansion chamber 14 reaches a predetermined value or more. The main exhaust port 33 is opened.

The main exhaust port 33 is submerged in water when the ship is at a relatively low position relative to the water surface, such as when the ship is stopped, moving astern, or moving forward at low speed, but when the ship is at a relatively high position when moving forward at high speed, the main exhaust port 33 is submerged in water. The part that will be exposed above the water surface will be selected when the position is reached. The sub-exhaust port 34 is provided at a position where it is always open to the air. The positional relationship between the main exhaust port 33 and the sub-exhaust port 34 and the water surface in each operating state of these ships is as follows.
It is illustrated in FIGS.

Figure 2 shows the case where the throttle is fully opened and the ship is moving forward at high speed, and the hull is floating and the main exhaust port 33
is above the water surface X. In this case, since the pressure of the exhaust gas is high, the cover 38 is displaced rearward to open the main exhaust port 33, and the exhaust gas is discharged into the air from both the main exhaust port and the sub-exhaust port.

FIG. 3 shows the idling state, where the hull is lowered relative to the water surface X and the main exhaust port 33 is submerged in the water. In this case, since the exhaust pressure is low, the cover 38 does not move rearward and the main exhaust port remains closed. Therefore, the exhaust gas is discharged into the air only through the sub-exhaust port 34. Since the flow rate of exhaust gas during idling is small, engine performance is not adversely affected even if the exhaust gas is discharged only from the sub-exhaust port, which has a relatively small cross-sectional area.

When idling, the throttle is opened in order to smooth out the engine and the engine is sped up intermittently, but it goes without saying that at this time the exhaust pressure increases and the cover may open. In this case, exhaust gas is discharged not only from the sub-exhaust port 34 but also from the main exhaust port 33, but since the main exhaust port is submerged in water, the exhaust noise is quiet.

Figure 4 shows the state when moving astern; in this case as well, the hull is at a low position relative to the water surface, so the main exhaust port 33
is submerged in water. When the vehicle is traveling backwards, the dynamic pressure of the water that accompanies the vehicle's travels acts from behind, so the cover 38 cannot be displaced rearward and the main exhaust port remains closed. Therefore, the exhaust is from the sub-exhaust port 34.
It is discharged into the air through the chisel.

Now, returning to FIG. 1, the outline of the ship's propulsion system will be explained. The illustrated ship is equipped with a waterjet type propulsion device, and an impeller duct 40 is formed at the rear lower part of the stern plate 12, and an impeller is disposed within the duct. The impeller is driven by a driving force transmitted from the engine 16 through a gear box 42, a universal joint 44, and a propeller shaft 46. By rotationally driving the impeller, water is sucked in from an intake duct 50 formed at the rear of the ship's bottom 48 in the direction of the dotted arrow in FIG. 1, and is ejected rearward through the impeller to propel the ship. A steering nozzle 52 and a forward/reverse switching bucket 54 are provided at the rear of the impeller duct 40. The steering nozzle 52 controls the traveling direction of the ship by adjusting the direction in which water is ejected. Bucket 54 for forward/backward switching
When it is shifted upward as shown in the figure, it moves forward without affecting the propulsive force, but when it is rotated downward, the water flow from the impeller duct collides with it, causing the propulsive force to act in the opposite direction, causing the ship to move forward. It operates to move backwards.

Since the engine exhaust system for a small boat according to the present invention has the configuration described above, the following effects can be obtained.

In the idling state, the main exhaust port 33 is submerged in water, and exhaust gas is discharged only from the sub-exhaust port 34, which has a small cross-sectional area, so that there is little leakage of exhaust noise from the exhaust expansion chamber 14. Therefore, the exhaust noise during idling can be made quieter, and the discomfort experienced by the driver etc. can be greatly reduced.

When moving forward at high speed, the main exhaust port 33 comes out above the water surface, allowing smooth discharge from both the main and auxiliary exhaust ports.

When moving backward, the main exhaust port 33 is submerged in water and remains closed due to the dynamic pressure of the water, so no air is discharged from the main exhaust port, thus preventing air bubbles from entering the propeller. be able to.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view showing the main parts of the engine exhaust system for a small boat according to the present invention, and FIGS. 2 to 4 are diagrams showing changes in the positional relationship between the main exhaust port and the water surface depending on the operating state of the small boat. FIG. 2 shows the state during high-speed forward movement, FIG. 3 shows the state during idling or low-speed operation, and FIG. 4 shows the state during reverse movement. In each figure, the same reference numbers indicate the same or equivalent parts, 12... Stern plate, 14... Exhaust expansion chamber, 16... Engine, 22... Silence chamber, 33... Main exhaust port, 34... Sub-exhaust port, 38 ...cover, 40... impeller duct, 50... intake duct, X... water surface, respectively.

Claims (1)

[Claims] 1. In an engine exhaust system for a small boat, which has a main exhaust port that opens rearward at the lower part of the stern of the boat, and a sub-exhaust port that is always open to the air above the main exhaust port, An exhaust port is formed at a position that is submerged in water when the ship is stopped or moving backward, but emerges above the water surface when moving forward at high speed, and the main exhaust port is provided with a valve device that opens when the ship moves forward at high speed and closes when the ship moves backward. An engine exhaust system for a small boat, characterized by: