JP2725289B2 - Outboard exhaust system - Google Patents

Description

The present invention relates to an exhaust system for an outboard motor, and more particularly to an exhaust system for an outboard motor having an improved exhaust passage.

(Prior Art) An outboard motor mounted on a hull and propelling the hull has an engine 2 mounted on an upper portion of a drive shaft housing 1 and covered with an engine cover 3 as shown in FIG. A gear case 4 is joined to the lower part, and a propeller shaft (not shown) is supported by the gear case 4. The rotation of the engine 2 is transmitted through the drive shaft housing 1 and a rotation transmission mechanism in the gear case 4. The power is transmitted to the propeller shaft, and the propeller 6 is driven to rotate. The outboard motor is mounted on a transom of the hull via a bracket to propel the hull.

On the other hand, the exhaust of the engine 2 passes through the exhaust tube 9 from the exhaust port 8 of the engine 2 to the exhaust tube housing.
The gas is discharged to the outside through the exhaust chamber 10 of the gear case 4.

Generally, in the exhaust passage of a two-cycle engine,
It is known that the combustion efficiency is improved by arranging an enlarged portion for improving the discharge efficiency and a throttle portion for preventing the unburned air-fuel mixture from blowing through at an appropriate distance from the exhaust port 8. Further, it is also known that the combustion efficiency becomes more effective as the enlarged portion and the throttle portion are closer to the exhaust port 8 in the high-speed rotation region and are farther from the exhaust port 8 in the low-speed rotation region.

In the case of an outboard motor, the enlarged portion is configured by gradually expanding a downstream portion of the exhaust tube 9. The throttle section is configured by providing a gear case throttle section 12 in the gear case 4.

(Problems to be Solved by the Invention) However, in the case of an outboard motor, since the position of the propeller shaft is designed in accordance with the transom of the hull, the gear case 4 is composed of the engine 2 and is disposed at a long distance. As a result, the distance between the gear case throttle portion 12 and the exhaust port 8 is too long in the high engine speed range, so that a large amount of unburned air-fuel mixture blows through in the high engine speed range, the fuel consumption rate decreases, and the engine consumption decreases. The output may also decrease.

Therefore, as shown in FIG. 4, it is conceivable to form the tube constricted portion 13 by making the downstream portion of the exhaust tube 9 small in diameter. However, in this case, the expansion volume of the exhaust tube 9 is insufficient, which causes a decrease in output. In particular, the back pressure in the low-speed rotation range increases, so that combustion becomes unstable, and the output in the low-speed rotation range decreases. There is also a risk of doing so.

The present invention has been made in view of the above facts, and improves combustion efficiency in a high-speed and low-speed rotation range,
An object of the present invention is to provide an exhaust device for an outboard motor capable of improving engine output in both rotation ranges.

[Configuration of the invention]

(Means for Solving the Problems) In order to solve the above problems, an exhaust device for an outboard motor according to the present invention has an engine above a drive shaft housing and a engine below the drive shaft housing. A gear case provided with a propeller shaft is disposed, and an exhaust tube is connected to an exhaust port of the engine. A downstream side of the exhaust tube is gradually expanded and formed by an exhaust tube housing inside the drive shaft housing. A second exhaust chamber is formed at the top of the gear case, and a gear case throttle is provided at the bottom of the second exhaust chamber. An exhaust passage is formed by the tube, the first and second exhaust chambers, and a lower end of the exhaust tube housing is connected to a downstream end of the exhaust tube. A main throttle portion extending to an intermediate position with the gear case throttle portion and having an opening area substantially equal to an opening area of the gear case throttle portion is formed at a lower end portion of the exhaust tube housing.

(Operation) According to the exhaust device for an outboard motor according to the present invention, exhaust from the engine reaches the exhaust tube from the exhaust port, expands, passes through the main throttle portion, and is exhausted to the outside through the exhaust chamber. Since the main throttle portion is located on the upstream side of the gear case throttle portion, the combustion efficiency in the high-speed rotation range is increased. Also, since the main throttle is not too close to the downstream end of the exhaust tube,
Combustion in the low-speed rotation range is stabilized, and combustion efficiency is increased. As a result, the engine output in the high speed and low speed rotation ranges can be improved.

Further, in the exhaust device for an outboard motor according to the present invention, the lower end of the exhaust tube housing is extended to an intermediate position between the downstream end of the exhaust tube and the gear case throttle portion, while the main throttle formed at the lower end portion of the exhaust tube housing is provided. Since the opening area of the section is substantially equal to the opening area of the gear case throttle section, it is possible to effectively prevent blow-through of the unburned air-fuel mixture in the high-speed rotation range and the low-speed rotation range, especially in the low-speed rotation range, while the lower end of the exhaust tube housing is formed. Since the extension portion is used as the main throttle portion, a simple structure can be achieved without increasing the number of parts.

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

FIG. 1 is an overall view of an outboard motor to which an embodiment of an outboard motor exhaust system according to the present invention is applied, in which a part of the outboard motor is cut away and a propeller shaft and the like are omitted.

The outboard motor 21 is mounted on a transom of the hull via a bracket 22. Outboard motor 21 has a drive shaft housing
An engine holder (not shown) is provided above the drive shaft housing 23, and an engine 24 is fixed to the engine holder. The engine 24 is covered by an engine cover 25.

On the other hand, a gear case 26 is joined to a lower portion of the drive shaft housing 23, and a propeller shaft (not shown) is rotatably supported by the gear case 26. The rotation of the engine 24 is transmitted to the propeller shaft by a power transmission mechanism (not shown) accommodated in the drive shaft housing 23 and the gear case 26, and rotates the propeller 27 supported at the rear end of the propeller shaft. Drive.

An exhaust tube 29 is indirectly connected to an exhaust port 28 of the engine 24 via an exhaust manifold (not shown) or the like. An exhaust tube housing 30 is attached to the exhaust manifold so as to surround the exhaust tube. The exhaust tube 29 and the exhaust tube housing 30 are disposed in the drive shaft housing 23 in a double pipe structure.

The downstream side of the exhaust tube 29 gradually expands and expands.
29A is formed, and a downstream end of the expansion portion 29A, that is, a downstream end 31 of the exhaust tube 29 is opened in the exhaust tube housing 30. As shown in FIG. 1, the exhaust tube housing 30 has a first exhaust chamber 40 formed therein, while the exhaust tube housing 30 extends downstream from the lower end 32 of the conventional shape. A throttle section 33 is formed.

The main throttle portion 33 is formed in a tapered shape toward the downstream side, and is formed integrally or integrally with the exhaust tube housing 30. The aperture opening end 34 of the main aperture 33 is set to be substantially the same as the opening area of a gear case aperture 36 described later.

The aperture opening end 34 of the main aperture 33 is opened into a second exhaust chamber 35 formed in the gear case 26. This exhaust chamber 35
A gear case restricting portion 36 is formed at the bottom of the propeller 27 and communicates with the inside of the propeller 27. The exhaust tube 29, the first exhaust chamber 40 in the exhaust tube housing 30, the main throttle section 33, the second exhaust chamber 35, the gear case throttle section 36, etc.
An exhaust passage from is formed.

That is, the exhaust gas from the engine 24 passes through the exhaust port 28, expands from the expansion portion 29A in the exhaust tube 29 to the first exhaust chamber 39 in the exhaust tube housing 30, and thereafter expands the throttle opening end 34 of the main throttle portion 33. Through the second exhaust chamber 35
And expands again, and is discharged into the water via the propeller 27. Exhaust gas flows from the expansion section 29A of the exhaust tube 29 and the first exhaust chamber 39 in the exhaust tube housing 30 to the main throttle section.
During the passage through 33, the unburned air-fuel mixture is returned into the cylinder of the engine 24 by the exhaust pressure pulsation, and the fuel consumption rate and the engine output are improved.

In this case, the throttle opening end 34 of the main throttle unit 33 is installed at a substantially intermediate position between the downstream end 31 of the exhaust tube 29 and the gear case throttle unit 36, and the opening areas of the two throttle units 33 and 36 are substantially equal. The main throttle section 33 prevents the unburned air-fuel mixture from blowing through in the high-speed rotation range, and improves the fuel consumption rate as shown by the solid line in FIG. As a result, the combustion efficiency in the high-speed rotation range is increased, and the engine output can be improved.

Also, the diaphragm opening end 34 of the main diaphragm section 33 is an exhaust tube.
Since it is installed without being too close to the downstream end 31 of 29, the expansion of the exhaust gas by the expansion section 29A and the first exhaust chamber in the exhaust tube housing 30 is appropriately performed.

Further, in this case, the combustion in the low rotation speed region is also stabilized and the combustion efficiency is improved, and the fuel consumption rate and the engine output are improved as shown by the solid line in FIG. Here, the broken line in FIG. 2 indicates the fuel consumption rate and the engine output in the prior art shown in FIG. 3 or FIG.

Further, the main throttle section 33 is provided in the exhaust tube housing 30.
Since it is provided integrally or integrally, the production is easy and the cost does not increase.

Reference numeral 37 in FIG. 1 denotes a seal rubber 37, and a water chamber 38 is formed between the drive shaft housing 23 and the exhaust tube housing 30 by the seal rubber 37. By filling the water chamber 38 with water, the exhaust tube valve 30 is suitably cooled.

〔The invention's effect〕

As described above, according to the exhaust device for an outboard motor according to the present invention, the main throttle portion is installed at a substantially intermediate position between the downstream end of the exhaust tube and the gear case throttle portion. , The combustion efficiency can be improved, and the engine output in both rotation ranges can be improved.

Further, according to the exhaust device for an outboard motor according to the present invention, the lower end of the exhaust tube housing is extended to the intermediate position between the downstream end of the exhaust tube and the gear case throttle portion, while being formed at the lower end of the exhaust tube housing. Since the opening area of the main throttle section is equal to the opening area of the gear case throttle section, it is possible to effectively prevent the unburned air-fuel mixture from blowing through in the high-speed rotation range and the low-speed rotation range, particularly in the low-speed rotation range, and to reduce the exhaust tube housing. Since the lower end uses the main as a throttle, a separate structure is not required, and the number of parts does not increase, so that a simple structure can be achieved.

[Brief description of the drawings]

FIG. 1 is an overall view of an outboard motor to which an embodiment of an exhaust device for an outboard motor according to the present invention is applied, in which a part of the outboard motor is cut away and a propeller shaft and the like are omitted, and FIG. FIG. 3 is a graph showing the relationship between the engine output and fuel consumption rate and the engine speed in the embodiment of the present invention. FIGS. 3 and 4 are diagrams showing a conventional exhaust device for an outboard motor. 21 ... outboard motor, 23 ... drive shaft housing, 24
…… Engine, 26 …… Gear case, 28 …… Exhaust port,
29 …… Exhaust tube, 29A …… Expansion part, 30 …… Exhaust tube housing, 31 …… Downstream end of exhaust tube, 33 ……
Main throttle section, 35 ... second exhaust chamber, 36 ... gear case throttle section, 39 ... first exhaust chamber.

Claims (1)

(57) [Claims] An engine is disposed above a drive shaft housing, and a gear case provided with a propeller shaft is disposed below the drive shaft housing. An exhaust tube is connected to an exhaust port of the engine. The drive shaft housing is expanded and provided in a first exhaust chamber formed by an exhaust tube housing inside the drive shaft housing. A second exhaust chamber is formed above the gear case, and a second exhaust chamber is formed at a bottom of the second exhaust chamber. An exhaust port is provided by the exhaust port, the exhaust tube, and the first and second exhaust chambers, and a lower end of the exhaust tube housing is connected to a downstream end of the exhaust tube and the gear case restrictor. With the gear case throttle section at the lower end of the exhaust tube housing. Exhaust system for an outboard motor, characterized in that the formation of the main throttle portion which is opened at almost the same area as the mouth area.