JPH0444100B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable bench lily type carburetor equipped with an air-fuel ratio compensation mechanism.

Variable bench lily type carburetors are known that are equipped with a suction piston that responds to the amount of intake air. The bench lily area is changed by moving the suction piston forward and backward. Fuel is metered by an annular gap between a needle connected to the suction piston and a metering jet provided in an axially extending fuel passage of the needle, and is discharged into the bench lily. Air bleed may be applied to the metering jet section in order to promote fuel atomization and to control the air-fuel ratio. If the air bleed air inlet opens into the intake air upstream of the bench lily, the air bleed air pressure is affected by the current combustion intake air flow. When dynamic pressure is applied by the intake air flow, the air-fuel ratio tends to be lean in a high air amount region, and when static pressure is applied, the air-fuel ratio tends to be rich in a high air amount region. Depending on the mechanism that employs air bleed, it may be better to keep the air-fuel ratio fluctuation due to air bleed constant from a low air amount to a high air amount. For example, when controlling the air bleed amount and changing the air-fuel ratio when the engine is under high load and low load, if the engine is subjected to dynamic pressure or static pressure as described above, the The interval between the air-fuel ratio setting values becomes too wide or too narrow in high air flow areas, resulting in over-lean conditions in certain load areas, deteriorating drivability, and in certain load areas becoming rich, resulting in poor fuel efficiency. Getting worse. Therefore, in such a case, it is desirable that the air bleed amount be constant from a low air amount to a high air amount.

The present invention is a variable bench lily type carburetor that controls the air-fuel ratio by air bleed through a needle and a metering jet gap, and has a low air volume so as to be able to meet various air and fuel consumption requirements from low loads to high loads. It is an object of the present invention to provide a variable bench lily type carburetor that can maintain a constant air bleed amount from 1 to 2.

In order to achieve the above object, the variable bench lily type carburetor according to the present invention has an air inlet of the air bleed formed to receive a composite pressure of dynamic pressure and static pressure due to the intake air flow upstream of the bench lily part, and A sub air bleed passage having an outlet and an inlet is provided in the air bleed passage leading to the air inlet of the air bleed, and the sub air bleed passage is provided with a switching valve that opens at low load and closes at high load. This is a characteristic feature.

Hereinafter, the present invention will be described in detail with reference to examples.

FIG. 1 is a longitudinal cross-sectional view showing an embodiment of a variable bench lily type carburetor to which the present invention is applied, in which 1 is the carburetor body, 2 is a throttle valve, and 3 is a suction piston. flows down. A raised portion 4 provided on the carburetor body 1 and a suction piston 3
A bench lily portion 5 is formed with the tip of the tip. The suction piston 3 is housed in a casing 6, and a negative pressure chamber 7 is formed inside the casing 6 and inside the suction piston 3. Negative pressure chamber 7 communicates with bench lily portion 5 through suction hole 8 . Further, an atmospheric pressure chamber 9 is formed outside the suction piston 3, and the atmospheric pressure chamber 9 communicates with the atmosphere in the intake pipe through an air hole 10. The compression spring 11 urges the suction piston 3, and the suction piston 3 moves so that the differential pressure between the atmospheric pressure in the atmospheric pressure chamber 9 and the negative pressure in the negative pressure chamber 7 balances the spring force of the compression spring 11. do.

A needle 12 is connected to the suction piston 3 and enters a fuel passage 13 extending in the axial direction thereof. The fuel in the float chamber 14 reaches the fuel passage 13 through the fuel pipe 15, is metered by the annular gap between the outer diameter of the needle 12 and the metering jet 16 provided in the fuel passage 13, and is sucked into the bench lily part 5. and mixed with air.

An air bleed passage 17 opens in the metering jet section 16 at a position indicated by 18, and a small hole 19 also opens downstream of the opening 18. The air inlet 20 of the air bleed passage 17 opens to the intake air flow upstream of the bench lily portion 5. This air inlet 2
0 is a pipe protruding from the carburetor main body 1 into the intake pipe, and the open end 21 of the pipe 20 is opened parallel to the intake air flow shown by the arrow, and receives static pressure due to the intake air flow. A hole 22 is drilled near this open end 21 and opens at right angles toward the intake air flow. Therefore, air having a combined pressure of static pressure and dynamic pressure due to the intake air flow is introduced into the air bleed passage 17 from the pipe 20. FIG. 3 is an enlarged view of the vicinity of the air inlet.

In the embodiment shown in FIG. 1, air bleed allows the air-fuel ratio to be switched between high load and low load. Air bleed passage 17
An auxiliary air bleed passage 17a having an outlet passage 23 and an inlet passage 24 is branched from there. Exit passage 23
A first jet 25 is located between the inlet passage 24 and the inlet passage 24.
A second jet 26 is provided in each of the inlet passages 24. The outlet passage 23 is connected to a first port 28 of the negative pressure switching valve 27, and the inlet passage 24 is connected to a second port 29. The negative pressure switching valve 27 is 30 in the same figure.
Switching is activated by the negative pressure of the mixture at the position shown.

The operation of the variable bench lily type carburetor with the above configuration is as follows.

When the engine starts, the throttle valve 2 opens and negative pressure is generated in the bench lily portion 5. This negative pressure is introduced into the negative pressure chamber 7 through the suction hole 8,
Open the suction piston 3. When the suction piston 3 opens, air is sucked in as shown by the arrow in the figure and is throttled by the bench lily 5, increasing the negative pressure. The suction piston 3 moves to a position where the differential pressure between the suction piston 3 and the negative pressure balances the spring force of the compression spring 11.

Depending on the amount of opening of the suction piston 3, the needle 12 connected thereto moves forward and backward within the fuel passage 13. The shape of the needle 12 becomes thinner toward the tip so that the larger the amount of intake air is, that is, the more the suction piston 3 moves to the left in the figure, the larger the measured value of fuel becomes. Therefore, the suction piston 3 responds to the amount of intake air.
Depending on the extent to which the fuel is moved, the amount of fuel discharged also changes.

The negative pressure switching valve 27 allows the first port 28 and the second port 29 to communicate when the negative pressure downstream of the throttle valve 2 is at a value indicating a low load. Therefore, pipe 20
Air introduced from the outlet passage 23 enters the inlet passage 24 through the first port 28 and the second port 29, is metered by the second jet 26, and is discharged through the air bleed openings 18 and 19. . When the negative pressure downstream of the throttle valve 2 is at a value indicating a high load, the first port 28 and the second port 29 of the negative pressure switching valve 27 are shut off. At this time, only the air metered by the first jet 25 flows through the openings 18 and 1.
It is discharged from 9. Therefore, when the load is low, the amount of air bleed is large, and when the load is high, the amount of air bleed is small. However, the amount of air bleed is affected by the pressure of the air inlet 20.

Figure 2 is a characteristic diagram showing the air-fuel ratio with respect to the intake air amount, where A is the required characteristic at high load, B is the required characteristic at low load, C is when only static pressure is applied, and D is when only dynamic pressure is applied. Indicates the situation. If air is introduced under static pressure as shown in C, if it is adapted to a high air volume and a high load, when this is switched to a low load, the air will be introduced in a region with a small intake air volume as shown in C'. Become over lean. In addition, when dynamic pressure is received as indicated by D, if the dynamic pressure is adjusted to a high air quantity at a high load, if this is switched to a low load, over-richness occurs at a low air quantity as indicated by D'. Since the present invention is designed to receive pressure that is a combination of dynamic pressure and static pressure, as described above, C is shown in FIG.
Alternatively, the characteristic does not have a slope as shown by D, but has a substantially flat characteristic from the low air amount region to the high air amount region. Therefore, a characteristic similar to the air-fuel characteristic shown by A or B can be obtained depending on the high load or low load, and air-fuel ratio control suitable for the above-mentioned control target can be achieved.

As explained above, according to the present invention, it is possible to obtain an air-fuel ratio that meets the required characteristics at low load or high load in a region with a small amount of intake air to a region with a large amount of intake air, and other air-fuel ratios can be obtained. It becomes easier to apply the compensation mechanism, thereby having the effect of contributing to improving engine output and preventing troubles.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a variable bench lily type carburetor to which the present invention is applied, FIG. 2 is an air-fuel ratio characteristic diagram for intake air, and FIG. 3 is an enlarged view of the vicinity of the air inlet of FIG. 1. 1... Carburetor body, 3... Suction piston, 5... Bench lily part, 12... Needle, 1
3... Fuel passage, 16... Metering jet, 17...
...Air bleed passage, 18...Air bleed hole,
20... Air bleed introduction pipe, 21, 22...
...Air bleed introduction opening.

Claims (1)

[Claims] 1. A needle connected to a piston that changes the area of the bench lily in response to the amount of intake air, a metering jet section provided in a fuel passage extending in the axial direction of the needle, and a variable bench lily type that bleeds air to the metering jet section. In the carburetor, the air inlet of the air bleed is formed to receive a composite pressure of dynamic pressure and static pressure due to the intake air flow upstream of the bench lily, and an outlet is formed in the air bleed passage leading to the air inlet of the air bleed. 1. A variable bench lily type carburetor, characterized in that a sub-air bleed passage having an inlet and an inlet is provided, and the sub-air bleed passage is provided with a switching valve that opens at a low load and closes at a high load.