JP2001159383A - Carburetor with air by-pass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve four problems in a conventional carburetor for a spark- ignition internal combustion engine: (1) bleed air lead-in instability, (2) clogging of dust in fuel, (3) the necessity of repeated work in an air-fuel ratio characteristic improvement method of a low speed system due to two-point air-fuel ratio adjustment, which are all related to a pilot screw, and (4) the aging effect of an air-fuel ratio characteristic caused by sludge sticking to an intake passage, which is related to the pilot screw or an air screw. SOLUTION: To solve the problems (1), (2), an air by-pass is provided for communicating the upper reaches and lower reaches of a throttle valve at least during idling, and a by-pass control throttle is provided for controlling the ventilation resistance of the air by-pass. To solve the problems (3), (4), the air by-pass is constituted not to communicate the upper reaches with lower reaches of the throttle valve at a certain fixed opening or more of the throttle valve.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for stably introducing bleed air even at a small fuel flow rate in a low-speed system of a carburetor for a spark ignition internal combustion engine, and a technique for reducing clogging of dust in fuel in a passage. In order to adjust the air-fuel ratio at each point at two different large and small throttle valve openings, it is possible to limit the influence range of the adjustment suitable for two different air-fuel ratio adjustment methods. The present invention relates to a technology and a technology for minimizing a change over time of air-fuel ratio characteristics in a use process due to sludge adhesion.

[0002]

2. Description of the Related Art Most carburetors for a spark ignition internal combustion engine open a throttle valve for controlling the amount of intake air and open a portion where a negative pressure generated near the end of the throttle valve can be used as fuel measurement information to supply fuel. It has a low-speed system port for discharging and a low-speed system for introducing bleed air. Many of these carburetors include a port that opens to a portion of the throttle valve located downstream of the intake air flow, a so-called pilot outlet, and the like, in order to reduce the variation in the air-fuel ratio when the internal combustion engine is idling. A variable fuel throttle that controls the fuel flow to the port, a so-called pilot screw, etc.
, Or a semi-fixed air screw or the like that regulates the amount of bleed air introduced into the low-speed system. These air-fuel ratio adjustment devices
In any case, if the air-fuel ratio is adjusted during idling, the effect has a characteristic that affects the area other than idling. In addition, two different air-fuel ratio correction devices, for example, a pilot screw and an air screw, at two different points, a small opening point near the throttle valve opening during idling and a larger throttle valve opening point, A method of sequentially adjusting the air-fuel ratio at each point by using the air-fuel ratio and bringing the air-fuel ratio characteristics of the low-speed system between the two points closer to desired characteristics has been widely used as a method for increasing the flow rate accuracy of the carburetor. .

[0003]

The conventional carburetor has the following four problems related to the method of adjusting the air-fuel ratio near the throttle valve opening during idling.

The conventional carburetor which adjusts the air-fuel ratio near the throttle valve opening during idling by a pilot outlet and a pilot screw has the following three problems. First, since the fuel flow shared by the pilot outlet is small, it is difficult to stably introduce bleed air into a passage that branches long from another port to the pilot outlet. There is a problem that the fuel ratio tends to be unstable. Second, there is a problem that the gap between the pilot outlet and the pilot screw is small, and dust in fuel is clogged in the narrow gap during use, and the air-fuel ratio is likely to change. Third, in adopting a method of improving the air-fuel ratio characteristics using two air-fuel ratio correction devices different at two different points of the throttle valve opening point, the effect of pilot screw adjustment is affected by the idle of the throttle valve. There is a problem that the adjustment of the large opening point and the small opening point interferes with each other and must be repeated a plurality of times until a desired characteristic is obtained.

Further, a conventional carburetor for adjusting the air-fuel ratio near the throttle valve opening during idling by a pilot outlet and a pilot screw, and a conventional vaporizer for adjusting the air-fuel ratio near the throttle valve opening during idling by an air screw. When the pilot screw or the air screw is adjusted when sludge adheres to the vicinity of the throttle valve, there is a fourth problem that the air-fuel ratio characteristic in the throttle valve opening range larger than at the time of idling changes.

The fourth problem relating to sludge adhesion will be described in detail. In all types of carburetors, during use, particulates in the air collide with the wall of the intake passage at a high speed at a position downstream of the throttle valve where the flow of intake air is the highest, and adhere to that part as so-called sludge. I do. This sludge adheres to the intake pipe at a high negative pressure due to the high intake pipe negative pressure, and is concentrated on the downstream side of the flow of the intake air from the throttle valve during idling, which frequently occurs. However, it is well known to those skilled in the art that adhering fuel is always present near the low-speed system ports for discharging fuel and on the wall surface of the intake passage immediately downstream of the ports, and sludge does not adhere. .

Regardless of the type of carburetor, the gap between the wall of the intake passage and the end of the throttle valve becomes narrow due to sludge adhesion, and the amount of intake air at the throttle valve opening decreases. However, since the relative positional relationship between the end of the throttle valve and the fuel discharge port remains unchanged, the absolute value of the negative pressure applied to the fuel discharge port does not decrease. Therefore, the flow rate of the fuel sucked and discharged does not decrease, and the air-fuel mixture is concentrated.
Furthermore, if the opening of the throttle valve is increased to compensate for the amount of intake air reduced by sludge adhesion and keep the idling rotation speed constant, the amount of intake air returns to almost the old, but the end of the throttle valve and the fuel discharge port Is changed so as to suck and discharge more fuel, and the air-fuel mixture is also concentrated. In this state, if the mechanism for correcting the air-fuel ratio of idling such as the pilot screw or air screw described above is adjusted in a direction to make the air-fuel mixture thin, the air-fuel ratio at idling can be restored. . However, the effect of this adjustment extends to a region other than the opening of the throttle valve during idling, and the air-fuel ratio characteristics in the throttle valve opening region where the effect of sludge deposition no longer affects also change in the lean direction. That is, in the conventional vaporizer,
The air-fuel ratio characteristic of the entire low-speed system changes with time due to the adjustment of the air-fuel ratio during idling after the sludge adheres in the use process.

FIG. 5 is a graph showing an example of air-fuel ratio characteristics of a conventional carburetor under a negative pressure of an equal intake pipe, with the opening of the throttle valve on the horizontal axis and the air-fuel ratio on the vertical axis. In this figure, the initial characteristics of the conventional vaporizer are indicated by a chain line D, the characteristics before the bypass control valve is adjusted when sludge is attached are indicated by a dashed line E, and the characteristics after the bypass control valve is adjusted are indicated by a solid line F. In the conventional carburetor, the air-fuel ratio in the throttle valve opening area affected by sludge adhesion is determined by adjusting the pilot screw or air screw, etc., at the idling opening returned before sludge adhesion, and after the sludge adhesion area. Characteristics that smoothly connect the air-fuel ratio characteristics thinned by the influence of the adjustment of the pilot screw or the air screw. FIG.
If D and F are compared, thinning after adjustment is observed in a region where the throttle valve opening is large where the effect of sludge can be ignored.

[0009]

SUMMARY OF THE INVENTION In the vaporizer according to the present invention, the first and second problems among the problems of the conventional vaporizer are described.
In order to solve the above problem, an air bypass which communicates the upstream and downstream sides of the flow of the intake air from the throttle valve and a bypass control throttle which sets the air flow resistance of the air bypass are provided as the low opening side air-fuel ratio adjusting means. Adopt means. Also,
In order to solve the third problem and the fourth problem relating to sludge adhesion, when the opening of the throttle valve is equal to or more than a certain value, the upstream side and the downstream side of the flow of the intake air of the throttle valve. Means that uses an air bypass configured so as not to communicate with the air.

The structure of the vaporizer according to the present invention will be described with reference to FIG. FIG. 1 is a side cross-sectional view for explaining the concept of the present invention as viewed from the side at a center line of the intake passage (3) of an example of a carburetor according to the present invention.

In FIG. 1, the left side is the side connected to the internal combustion engine, the intake air flows from the right side to the left side, and the throttle valve (4) is set to the opening when the internal combustion engine is idling. . In the present carburetor, the opening during idling is the minimum use opening.

In FIG. 1, an intake passage (3) having a circular cross section penetrates the mixing body (1). A throttle shaft receiving hole (67) penetrates perpendicularly to the center line of the intake passage (3), and a throttle shaft (68) is mounted so as to be freely rotated and displaced in the throttle shaft receiving hole (67). I have. A throttle valve (4), which is a butterfly valve, is fixed to the throttle shaft (68). An idle adjusting screw (37), which is a semi-fixed screw, is mounted on the boss portion of the mixing body (1) while compressing a fixing spring (38), and a throttle lever ( 39). In the carburetor, the idle adjusting screw (37) is a throttle valve opening adjusting device (40) for maintaining the throttle valve (4) at the minimum use opening. A throttle return spring (57) is stretched and mounted between the mixing body (1) and the throttle lever (39).

The mixing body (1) is equipped with a slow jet (6), which is a fuel metering throttle of a low-speed system, and its upper end is connected to a slow passage (59). The slow passage (59) is connected to the chamber (61). A chamber plug (65) is press-fitted in a lower portion of the chamber (61), and a narrow groove serving as a flow path of a mixture of fuel and bleed air is provided in a right side surface and an upper surface of the chamber plug (65). I have. A first port (62), a second port (63), and a second port (63) having a circular cross-sectional shape are provided between the chamber (61) and a portion of the intake passage (3) facing the lower end of the throttle valve (4). Three ports (64) are provided. These three ports are low-speed ports (5) of the carburetor. One end of a bleed air passage (7) is connected to the slow passage (59), and the other end of the bleed air passage (7) is connected to the slow air jet (3) press-fitted into the mixing body (1).
It is connected to the intake passage (3) on the upstream side of the flow of intake air from the throttle valve (4) via 4). In the assembling process, the installation site of the slow air jet (34) includes:
First, a reference size jet is temporarily mounted by shallow press-fitting. In this state, the magnitude of the negative pressure applied to the slow jet (6) is measured on a test device under certain conditions in which the opening of the throttle valve (4) is larger than the opening during idling. The difference between the read negative pressure value unique to each carburetor and the reference negative pressure value that gives a desired air-fuel ratio is calculated, and if the negative pressure value difference of the temporarily mounted air jet is within the acceptable range, it is directly pressed and fixed. You. If it is outside the acceptable range, it is removed for replacement, and an air jet having a size calculated from the difference between the read negative pressure value and the reference negative pressure value is newly selected as a slow air jet (34). Pressed in to the normal position and fixed. In the present vaporizer, the slow air jet (34) is a bleed air introduction amount regulating throttle (10).

The mixing body (1) is provided with an air bypass (81). An inlet portion (82) of the air bypass (81) is opened on the upstream side of the flow of intake air from the throttle valve (4) in the intake passage (3). In addition, the outlet portion (83) of the air bypass (81) is located on the downstream side thereof and under the operating condition of the internal combustion engine to be used, the thickness of the throttle valve (4) is two minutes smaller than the region where sludge mainly adheres. Is located at the downstream side by one. Between the inlet (82) and the outlet (83) of the air bypass (81), there is provided a bypass control valve (84) which is a semi-fixed needle valve for controlling the ventilation resistance of the air bypass (81). ing. After the setting of the air screw (21), the bypass control valve (84) and the idle adjusting screw (37) are combined and set so as to give a desired intake air amount and an air-fuel ratio at the time of idling. In the present carburetor example, a combination of the bypass control valve (84) and its seat portion constitutes a bypass control throttle (85).

A float (5) is provided inside the fuel reservoir (51).
A constant oil level (53) controlled to a constant height is formed by 2). The mixing body (1) includes a main nozzle (71) and a main jet (7
2) is attached.

Next, the operation and effect will be described. The fuel in the fuel reservoir (51) is measured by the slow jet (6), and is mixed with the bleed air flowing from the bleed air passage (7) in the slow passage (59) by being measured by the slow air jet (34). Then, it reaches the chamber (61), and is sucked and discharged from the first port (62) and the second port (63) to the intake passage (3). Third
The air in the intake passage (3) flows into the port (64) toward the chamber (61) and mixes with the fuel.

The air in the intake passage (3) flows from the inlet (82) of the air bypass (81) to the bypass control valve (84).
Flows through the throttle valve (4) toward the outlet (83). The total amount of intake air sucked into a certain internal combustion engine is the sum of the amount of intake air passing through the throttle valve (4) and the amount of intake air passing through the bypass control valve (84). Opening of the throttle valve (4) and a bypass control valve (8
There are a plurality of combinations of the opening degrees in 4). The mixture becomes thinner if the proportion of the intake air flowing through the air bypass (81) not involved in fuel suction increases, and if the proportion decreases, the mixture increases. Therefore, the opening of the throttle valve (4) and the bypass control valve (8
By appropriately selecting the combination of the opening degrees in 4), the air-fuel ratio of the air-fuel mixture can be arbitrarily selected within a range where the total intake air amount is kept constant. In the present carburetor example, to give a predetermined intake air amount and a predetermined air-fuel ratio during idling,
Bypass control valve (84) and idle adjusting screw (3)
In the state shown in the drawing, 90% of the total intake air amount passes through the gap between the throttle valve (4) and the intake passage (3), and the remaining 10% is the air bypass (81). Pass).

When the opening of the throttle valve (4) is above a certain value, the outlet (83) of the air bypass (81) is located upstream of the flow of intake air from the throttle valve (4). In this state, the intake air does not bypass the throttle valve (4) and flow through the air bypass (81). Therefore, the air-fuel ratio of the air-fuel mixture in this region is
The presence or absence of the air bypass (81) and the bypass control valve (8
It is not affected by the opening setting of 4).

When the carburetor of this embodiment is mounted on an internal combustion engine and used, sludge adheres to a portion indicated by S in FIG. 1 on the wall surface of the intake passage (3) during use. Due to the adhesion of the sludge, the effective opening of the throttle valve (4) is reduced, the intake air amount is reduced, the idling rotational speed is reduced, and at the same time, the mixture is concentrated. In the carburetor according to the present invention, the bypass control valve (84) is opened to correct the intake air amount so as to cancel the decrease in the idling rotational speed.
Since the opening of the throttle valve (4) is not changed, the relative positional relationship between the end and the first port (62), the second port (63) and the third port (64) is unchanged. The inventor has noted that sludge does not adhere to the vicinity of these ports, and if these passage resistances do not change due to blockage of the sludge, and if the intake pipe negative pressure is maintained constant. It was also found that the flow near these ports did not change practically depending on the presence or absence of sludge, and that the applied negative pressure and the like did not change. Therefore, the bypass control valve (8
After the adjustment of 4), not only is the total intake air amount maintained equal to before sludge deposition, but also the fuel flow rate sucked and discharged from the low-speed system is maintained equal. At this time, of course, the passage resistance of the low-speed system and the amount of bleed air introduced have not been changed at all since before the sludge adhesion state.

In the present example of the vaporizer, as described above, the outlet portion (83) of the air bypass (81) is disposed close to and downstream of the sludge attachment area indicated by S in FIG. When the opening of the throttle valve (4) is increased from the opening during idling, the outlet (83) exits upstream of the throttle valve (4) at an opening exceeding the sludge adhesion region.
In this state, there is no intake air flowing through the air bypass (81) and bypassing the throttle valve (4). As described above, even after the adjustment of the bypass control valve (84), since the passage resistance of the low-speed system and the amount of bleed air introduced have not been changed at all before the sludge adhesion state, the throttle valve (4) is opened. The air-fuel ratio characteristics of the low-speed system in the region above the degree are not changed at all before the sludge deposition.
In the conventional carburetor, in this region, as described above, the air-fuel ratio characteristic is changed to a thinned air-fuel ratio characteristic by the influence of the adjustment of the pilot screw or the air screw.

FIG. 2 is a diagram showing an example of the air-fuel ratio characteristics of the carburetor according to the present invention under the negative pressure of the intake pipe, with the opening of the throttle valve on the horizontal axis and the air-fuel ratio on the vertical axis. In the figure, the initial characteristics of the vaporizer according to the present invention are indicated by a chain line A, the characteristics before the bypass control valve is adjusted when sludge is attached are indicated by a dashed line B, and the characteristics after the bypass control valve is adjusted are indicated by a solid line C. In the carburetor according to the present invention, the air-fuel ratio in the region where the opening of the throttle valve (4) is affected by the sludge adhesion is determined by the bypass control valve (8).
4) is adjusted so that the air-fuel ratio at the opening of the throttle valve at the time of idling is returned to the value before sludge adhesion, and the air-fuel ratio characteristics after the sludge adhesion region, which is basically the same as before sludge adhesion, are smoothly connected. A and C in FIG.
It can be seen from the comparison that the characteristics are not substantially changed in the entire low-speed system. As described above, in the vaporizer according to the present invention, even after the sludge is deposited, the air-fuel ratio characteristics before the sludge deposition is substantially maintained in the entire low-speed system, and the effect of reducing the change with time can be obtained.

In the carburetor described above, the air bypass (81)
The inlet (82) and outlet (83) are provided above the throttle shaft (68) in FIG. 1, that is, on the side opposite to the low-speed port, but are provided below the throttle shaft (68). In this case, the same operation and effect can be obtained by selecting the position of the inlet portion (82).

In this example of the carburetor, an air-fuel ratio adjusting device using a combination of a pilot outlet and a pilot screw for controlling low-speed system fuel is not provided. This makes it possible to omit the long and low-speed branch passage from the chamber (61) to the pilot screw, which reduces the flow rate of the fuel and makes the mixing of the fuel and the bleed air unstable. There is no passage branch where air introduction becomes unstable, and the air-fuel ratio is stabilized. Further, since there is no needle valve, it is possible to avoid the risk that dust mixed in the fuel in the course of long-term use may be clogged in the slit.

When the opening of the throttle valve (4) is above a certain value, the outlet (83) of the air bypass (81).
Is located on the upstream side of the flow of the intake air from the throttle valve (4), the intake air bypasses the throttle valve (4) and bypasses the air bypass (8
There is virtually no flow through 1). Therefore, the air-fuel ratio in this region is not affected by the adjustment of the bypass control valve (84). Therefore, first, a slow air jet is selected in this region to obtain a desired air-fuel ratio, and then a desired air-fuel ratio can be obtained by adjusting the bypass control valve (84) based on the throttle valve opening during idling. In this case, it is not necessary to return to the high opening point again and adjust the air-fuel ratio. That is, an effect that the number of man-hours for repeated adjustment can be reduced as compared with the case where the conventional pilot screw is employed is obtained.

In this carburetor, a through hole is provided in a portion of the throttle valve (4) near the low-speed port to communicate the upstream side and the downstream side of the flow of the intake air to increase the amount of the intake air flowing near the port. It is also free to promote the movement of fuel downstream. The vaporizer according to the present invention may be a so-called constant-vacuum vaporizer having a negative-pressure operating piston. Further, an air bypass separate from the one according to the present invention for introducing air from a high pressure portion between a venturi portion formed at a lower portion of the negative pressure piston and a throttle valve, and adjusting, exchanging, and processing the resistance of the air bypass. May be a constant-vacuum carburetor provided with a bypass control restrictor that is variable to suppress variation in the Venturi negative pressure due to entry of intake air from a gap between the mixing body and the negative pressure piston.

In the present invention, it is needless to say that the atmosphere is included on the upstream side of the flow of the intake air from the throttle valve (4). When the inlet portion (82) of the air bypass (81) is set to the atmosphere, the influence of the adjustment of the bypass control valve (84) affects the entire region of the low-speed system. Action and effect are obtained. The bypass control throttle (85) is not necessarily limited to a semi-fixed adjustable needle valve device, and the same operation and effect can be obtained even with a device that is adjusted by selection, replacement, or additional processing. it is obvious.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a side cross-sectional view of a cross section taken along a center line of the intake passage (3) of the carburetor according to the embodiment of the present invention. FIG. 4 is an upper partial cross-sectional view of a cross section taken along line XX in FIG. 3 viewed from a direction V in FIG.

In FIG. 3, the left side is the side connected to the internal combustion engine, the intake air flows from the right side to the left side, and the throttle valve (4) is set to the opening degree in the idling state of the internal combustion engine. . In this example, the opening during idling is the minimum use opening.

In FIG. 3, a throttle valve (4) having a circular cross section is inserted into a throttle valve housing hole (2) provided in a mixing body (1) and moves into and out of an intake passage (3). It is housed to be.

A slow jet (6), which is a fuel metering throttle of a low speed system, is mounted on the mixing body (1), and the slow jet (6) is connected to one end of a slow passage (59). The other end of the slow passage (59) has a low-speed system port (opened at a position located upstream of the flow of intake air, opposite to the end of the throttle valve (4) on the wall surface of the intake passage (3). 5). The bleed air passage (7) is connected to the slow passage (59). The bleed air passage (7) is provided with an air screw (21) which is a semi-fixed needle valve and an air screw seat (2).
The throttle valve (4) is connected to the intake passage (3) on the upstream side of the flow of the intake air through the variable throttle (2). The air screw (21) is provided at a certain point at the opening point of the throttle valve (4) on which the low-speed system and the main system share about half of the total fuel flow rate on the carburetor test device using the fuel substitute liquid. Is adjusted and set so that the total flow rate of the low-speed system and the main system becomes a desired value under the intake air amount of, that is, a desired air-fuel ratio is given.

The throttle valve (4) is provided with a communication hole (11) for communicating the inside thereof with the intake passage (3) on the upstream side of the flow of intake air from the throttle valve (4). The throttle valve (4) is provided with a groove-shaped movable recess (12) whose cross-sectional shape is substantially a half-moon shape composed of an arc and a chord. The throttle valve (4)
A ventilation hole (36) is provided for communicating the inside thereof with the movable recess (12). An air bypass (81) is provided in the mixing body (1), and an inlet portion (82) of the air bypass (81) having a circular cross section is provided on a wall surface of the throttle valve housing hole (2). Have been. When the throttle valve (4) is at the idling opening, the inlet portion (82) of the air bypass (81) is provided with the throttle valve through the movable recess (12), the inside of the throttle valve (4) and the communication hole (11). (4) It communicates with the intake passage (3) on the upstream side of the flow of the intake air. Between the inlet (82) and the outlet (83) of the air bypass (81), there is provided a bypass control valve (84) which is a semi-fixed needle valve for controlling the ventilation resistance of the air bypass (81). ing. In the vaporizer of this embodiment, a combination of the bypass control valve (84) and its seat portion constitutes a bypass control throttle (85).

The float (5) is provided inside the fuel reservoir (51).
A constant oil level (53) controlled to a constant height is formed by 2). A jet needle (54) constituting a main system is mounted on the throttle valve (4). The mixing body (1) is provided with a needle jet (55) constituting a variable fuel throttle of a main system together with a jet needle (54).

A throttle cable (56) for displacing the throttle valve (4) is connected to the throttle valve (4). An idle adjusting screw (37), which is a semi-fixed screw, is mounted on the mixing body (1) while compressing a fixing spring (38). The tip of the idle adjustment screw (37) is the throttle valve (4)
, Which is maintained at the opening during idling. In the carburetor of this embodiment, the idle adjusting screw (37) is a throttle valve opening adjusting device (40) for maintaining the throttle valve (4) at the minimum use opening.
A throttle return spring (57) for generating a force for closing the throttle valve (4) is housed in a compressed state inside the throttle valve (4). ) Is in contact while pressing.

In the carburetor according to the present embodiment, idle time during idling is selected by selecting a combination of the setting of the bypass control valve (84) and the opening of the throttle valve (4) determined by the setting of the idle adjustment screw (37). The fuel ratio and the amount of intake air can be set to desired values. Air bypass (8
The inlet (82) of (1) does not communicate with the movable recess (12) when the throttle valve (4) is above a certain value, and the air bypass (8) in the throttle valve opening region beyond that.
The effect of 1) on the air-fuel ratio is eliminated. Also in the present embodiment, the correction after sludge adhesion is performed only by the opening of the bypass control valve (84) and the opening of the throttle valve (4).
Obviously, the air-fuel ratio characteristics of the low-speed system do not change. It is also clear that the pilot screw is free from various problems.

In the present invention, of the four problems of the conventional carburetor described above, the third two-point air-fuel ratio adjustment requires repetitive work, and the fourth change with time of the air-fuel ratio characteristics due to sludge adhesion. If only the above problem is solved, it does not prevent the installation of the pilot screw. However, when a pilot screw is installed, the pilot screw is adjusted only for the purpose of correcting the individual difference of the carburetor between the individual carburetors near the throttle valve opening at the time of idling at the time of assembling the carburetor. No adjustments are made. The air-fuel ratio during idling during use is adjusted by a bypass control throttle (85) and a throttle valve opening adjustment device (4).
0) only. In this case, the combination of the pilot screw and the pilot outlet corresponds to a variable resistance of the first port (65) of the example of the carburetor shown in FIG. 1, and is used for the purpose of reducing the individual difference of the carburetor with higher accuracy. Useful.

[Brief description of the drawings]

FIG. 1 is a side sectional view taken along a center line of an intake passage of an example of a carburetor as an application example of the present invention.

FIG. 2 is a diagram showing an example of a throttle valve opening-air-fuel ratio characteristic of a carburetor according to the present invention.

FIG. 3 is a side sectional view taken along a center line of an intake passage of an example of a carburetor according to an embodiment of the present invention.

FIG. 4 is an upper partial cross-sectional view taken along line XX of the vaporizer of FIG. 3;

FIG. 5 is a view showing an example of a throttle valve opening-air-fuel ratio characteristic of a conventional carburetor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mixing body 3 Intake passage 4 Throttle valve 5 Low-speed system port 10 Bleed air introduction amount regulation restrictor 40 Throttle valve opening adjusting device 81 Air bypass 85 Bypass control restrictor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02M 9/06 F02D 33/00 318J

Claims (3)

[Claims] 1. A throttle valve (4) displaced to control an intake air amount in an intake passage (3) in a mixing body (1), and a semi-fixed throttle valve (4) being kept at a minimum use opening. A low-speed system port (5) for discharging fuel near the end of the throttle valve (4), and a bleed air introduction amount regulating throttle capable of changing the ventilation resistance, which is provided with a throttle valve opening adjusting device (40) of a type. (10) a carburetor for a spark ignition internal combustion engine provided with a low-speed system, comprising: a throttle valve (4) at least when the internal combustion engine is idling.
An air bypass (81) communicating between the upstream side and the downstream side of the flow of the intake air, and a bypass control throttle (85) placed in the path of the air bypass (81) and capable of changing the ventilation resistance
And a vaporizer. 2. The low-speed system does not have a variable fuel restrictor that changes only the resistance of a flow path leading to a fuel discharge port that is always open to a portion of the throttle valve (4) located downstream of the flow of intake air. The carburetor of claim 1, wherein the carburetor is a system. 3. The air bypass (81) prevents communication between the upstream side and the downstream side of the flow of intake air of the throttle valve (4) when the opening of the throttle valve (4) is equal to or greater than a predetermined value. 2. The carburetor of claim 1, wherein the carburetor is a configured air bypass (81).