JPH09112346A - Vaporizer air vent device - Google Patents

Abstract

(57) An object of the present invention is to provide an air vent device for a carburetor having a simple structure which can favorably maintain engine startability, low speed traveling performance and combustion efficiency. An air vent device for a carburetor that introduces ram pressure due to traveling wind into a venturi of a carburetor through an intake passage and also into a float chamber of the carburetor through an air vent passage branched from the intake passage. In the above, the air vent passage has a height difference such that a part of the air vent passage is located below the connection port with the float chamber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air vent device for a carburetor, and more particularly to a device for preventing air-fuel mixture from flowing back through the air vent passage and being mixed into the intake passage when a two-wheeled vehicle is stopped and runs at low speed. .

[0002]

2. Description of the Related Art In a motorcycle, when the vehicle is traveling, the wind from the front is taken into the intake passage so that the passage pressure is higher than atmospheric pressure (this pressure is called ram pressure), and this ram pressure is used as a venturi for the carburetor. The air vent device for the vaporizer has been developed, which is introduced into the float chamber of the vaporizer through an air vent passage branched from the intake passage and applied to the venturi and the float chamber. By applying such a ram pressure, the high-density air-fuel mixture is supercharged, the air-fuel mixture filling rate of the engine is improved, and the output at the time of high speed traveling is improved.

However, in such a carburetor air vent device utilizing ram pressure, when the engine is stopped or at a low speed, the fuel vaporized from the carburetor in a high temperature state flows back into the intake passage through the air vent passage. mixing.
Therefore, when the engine is restarted and 20 to 30 km / H
In the following low speed running (low air amount range), the air-fuel mixture becomes overrich against the predetermined optimum air-fuel ratio, and the startability is reduced or engine stall or so-called boggling (the rotational speed does not increase even if the throttle opening is increased) And the combustion efficiency also deteriorates. Air vent structures for carburetors that address such problems are disclosed in Japanese Utility Model Laid-Open No. 2-126066 and Japanese Patent Laid-Open No. 6-185414.

In the known art described in the above Utility Model Publication, a valve for shutting off the passage when the engine is stopped is provided in the middle of the air vent passage to prevent the backflow of vaporized fuel from the float chamber of the carburetor to the intake passage side. Has been.

Further, in the known technique described in the above-mentioned patent publication, the atmosphere vent passage is branched from the air vent passage for introducing the ram pressure, and a switching means is provided in these passages so that the engine is stopped and 20 to 30 km / h. During the following low speed traveling, the backflow of vaporized fuel to the intake passage side is prevented by switching the float chamber of the carburetor to the atmosphere open side.

[0006]

However, in the air vent device of the carburetor as disclosed in the above-mentioned respective publications, a cutoff valve for switching, a branch passage to the atmosphere, switching means such as a solenoid valve and a controller are required. Not only does the number of parts increase and the layout and structure become complicated,
There were drawbacks such as high cost.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and it is simple to prevent the backflow of the evaporated fuel to the intake passage side at the time of starting the engine or running at a low speed to maintain good combustion efficiency. An object is to provide an air vent device for a vaporizer having a structure.

[0008]

In order to achieve the above object, an air vent device for a carburetor according to the present invention introduces a ram pressure by traveling wind into a venturi of the carburetor through an intake passage and from the intake passage. In an air vent device for a carburetor which is also introduced into the float chamber of the carburetor through a branched air vent passage, there is a height difference such that a part of the air vent passage is located below a connection port with the float chamber. There is provided an air vent device for a carburetor, which is characterized in that it has a certain structure.

In a preferred embodiment, the lowermost part of the air vent passage is located below the carburetor.

In a further preferred embodiment, the air vent passage is characterized in that the lowermost portion thereof is constituted by a cooling pipe.

[0011]

[Function] When the engine is stopped and the vehicle is running at low speed, the fuel evaporated from the carburetor is once lowered from the outlet of the carburetor (connection port between the air vent passage and the float chamber of the carburetor) when flowing backward through the air vent passage. Since the passage that passes through the portion and flows backward from there is directed upward, movement to the upstream side is blocked, and mixing into the intake passage is suppressed.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram showing the basic construction of an embodiment of the present invention. The downdraft type carburetor 2 that sends the air-fuel mixture to the engine 1 of the motorcycle has its venturi (not shown) communicated with the intake passage 5 via the air cleaner 3 and its float chamber 12 (see FIG. 3) that has an air vent. It communicates with the intake passage 5 through the passage 4. The intake passage forms a ram chamber whose open end is directed forward to take in traveling wind and create a ram pressure higher than atmospheric pressure. The air vent passage 4 is made of rubber or resin and has a height difference such that a part of the air vent passage 4 is located below the connection port 4a with the carburetor 2. According to the air vent device of the carburetor having such a configuration, when the motorcycle is traveling, the traveling wind from the front is introduced into the intake passage 5 and is sent to the venturi of the carburetor 2 through the air cleaner 3 as ram pressure. , Is sent to the float chamber 12 of the carburetor 2 through the air vent passage 4. As a result, the venturi of the vaporizer 2 and the float chamber 12 are
Becomes the ram pressure, the high-density air-fuel mixture is supercharged to the engine 1, and the output of the engine rises more than when the atmospheric pressure is equal to or lower than the ram pressure.

When the engine 1 is stopped and running at low speed,
The float chamber 12 of the carburetor 2 is heated by the hot air of the engine.
The fuel vaporized inside flows back through the air vent passage 4. At this time, however, the vaporized fuel exiting from the connection port 4a between the air vent passage 4 and the carburetor once falls to a lower portion and rises from there, so that the upstream side To the intake passage 5 and is prevented from entering the intake passage 5.

In this case, if the lowermost portion 4b of the air vent passage 4 is located below the lower end of the downdraft type carburetor 2 as shown in the figure, a sufficient height difference can be obtained and backflow can be prevented more reliably. be able to. Also, this bottom 4
b may be configured by a cooling pipe made of stainless steel or the like as described later. The front and rear portions of the lowermost portion 4b of the air vent passage 4 may be higher or lower than the connection port 4a for the carburetor 2. FIG. 2 is a plan view showing a more specific embodiment of the air vent device for a vaporizer according to the present invention, and FIG. 3 is a side view thereof. In this example, a running air inlet 8 is provided below the headlamp 7 provided on the front cover 6. The introduction port 8 branches into the intake passages 5 that form the left and right ram chambers, and penetrates the left and right main frames 9 of the vehicle body and communicates with the air cleaner 3. The fresh air that has passed through the air cleaner 3 is introduced into the venturi of the downdraft type carburetor 2, and the main jet 1 is caused by negative intake pressure depending on the opening degree of the throttle valve 10.
The fuel in the float chamber 12 is sucked from 1 to form the air-fuel mixture having a predetermined air-fuel ratio. This mixture is
It is supplied from the intake port 14 of the engine 1 through the intake pipe 13 into the combustion chamber, and after combustion, is discharged to the outside through the exhaust port 15 and the exhaust pipe 16.

The running wind taken in from the inlet 8 is introduced into the ram chamber (intake passage 5) from the inlets 8a on both the left and right sides. At this time, a constriction 60 is formed near the inlet 8a, so that the running wind Is deflected downward as indicated by arrow B. Therefore, the dynamic pressure due to the wind speed disappears behind the constriction 60 in the intake passage 5, and only the high static pressure (ram pressure) is maintained. Therefore, the connection port 4c of the air vent passage 4 is provided behind the constriction 60, and the ram pressure can be taken out with the air vent passage 4 directed obliquely forward. In this way, the air vent passages 4, which are taken out from the intake passages 5 on both the left and right sides in a slightly inclined manner, join together in front of the handle stem (head pipe) 17 in the central portion and bypass the same to bypass the carburetor 2. The float chamber in the carburetor 2 is inclined downwards rearward through the sideways, extends to the lowermost portion 4b below the carburetor 2 and is inclined forward and upwards from the carburetor 2, and through the connection port 4a at the tip thereof. Connect to 12.

The handle stem 17 is connected to the front wheel 18 via a front fork.

The lowermost portion 4b of the air vent passage 4 is composed of a cooling pipe 19 made of stainless steel, and a drain discharge port 19a is provided at the lower portion of one end thereof. The cooling pipe 19 cools and liquefies the fuel flowing back through the air vent passage 4 evaporated from the carburetor 2 when the engine is stopped and running at low speed, and the liquefied fuel is discharged to the outside from the drain discharge port 19a. Therefore, it is possible to reliably prevent the mixture from entering the intake passage side. A drain pipe may be attached to the drain discharge port 19a.

In addition, due to the cooling structure of the water-cooled two-wheeled vehicle, the cooling efficiency may be different on the left and right sides of the vehicle body. In this embodiment, hot air rises in the upper right part due to the entanglement with the rotating direction of the radiator fan 31 on the right side of the vehicle body. Therefore, when a cooling pipe is provided on the upstream side of the air vent passage 4,
It is considered that the hot air of the radiator fan 31 hits, and it is difficult to obtain the cooling effect by the cooling pipe. Therefore, the cooling pipe of the air vent passage 4 needs to avoid the hot air from the radiator 30, and the cooling pipe is preferably provided slightly to the left of the vehicle body.

Although the above embodiment is applied to a motorcycle, it can be applied to other vehicles.

[0020]

As described above, according to the present invention, when the engine is stopped, the air vent passage is configured to have a height difference such that a part of the air vent passage is located below the connection port with the float chamber. In addition, it is possible to prevent the backflow action of the fuel evaporated from the carburetor during low-speed traveling, and prevent the fuel from entering the intake passage. Therefore, as compared with the conventional structure that requires the switching valve or the shutoff valve and the components associated therewith, the combustion efficiency can be increased by using the device which is simple in structure and inexpensive. In this case, if the lowermost part of the air vent passage is located below the carburetor, a sufficient height difference can be obtained, and the backflow can be prevented more effectively. Further, if the lowermost part of the air vent passage is formed of a cooling pipe, it is possible to liquefy the backflowing fuel or suppress the rising action by cooling and reliably prevent the fuel from entering the intake passage.

More specifically, the downdraft type carburetor is disposed above the cylinder head of the engine mounted on the frame with the cylinder tilted forward.
It is mounted at a relatively high position in the vehicle structure. On the other hand, in order to make the air vent pipe less visible to the rider and not to appear in the appearance and to improve the appearance, the middle part of the air vent pipe cannot be unnecessarily placed at a high place. Therefore, it is generally not easy to provide a predetermined height difference in the passage of the air vent pipe. However, in the present invention, by arranging a part of the air vent pipe below, a predetermined height difference (see FIG. 3) can be secured.

Further, since the highest part of the air vent passage is located above the intake passage and is connected to the intake passage (ram pressure forming chamber portion) from above, the height difference can be reliably formed and the height difference can be ensured. Can be further increased.

Further, in the embodiment, the cooling pipe (19)
Is placed at the bottom of the air vent pipe, and behind the cylinder head and the top of the cylinder body (the part that forms the combustion chamber), which are relatively hot in the engine, behind them. Therefore, it is possible to avoid the hot air rising from these high temperature portions while the vehicle is stopped or running at a low speed, and it is possible to obtain a reliable cooling action.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the basic configuration of an embodiment of the present invention.

FIG. 2 is a plan view showing an example of an air vent device for a vaporizer according to the present invention.

3 is a side view of the air vent device of FIG. 2. FIG.

[Explanation of symbols]

1: Engine, 2: Vaporizer, 3: Air cleaner, 4: Air vent passage, 4a: Connection port, 4b: Bottom part, 5: Intake passage, 8: Inlet port, 12: Float chamber, 19: Cooling pipe.

Claims (3)

[Claims] 1. An air vent of a carburetor, wherein ram pressure due to traveling wind is introduced into a venturi of the carburetor through an intake passage and also into a float chamber of the carburetor through an air vent passage branched from the intake passage. An air vent device for a carburetor, characterized in that the air vent passage has a height difference such that a part of the air vent passage is located below a connection port with the float chamber. 2. The air vent device for a carburetor according to claim 1, wherein a lowermost part of the air vent passage is located below the carburetor. 3. The air vent device for a carburetor according to claim 1, wherein the air vent passage has a cooling pipe at a lowermost portion thereof.