JPH04311659A - Fuel supply quantity control method and carburetor - Google Patents

Abstract

PURPOSE:To improve fuel consumption and reduce exhaust gas emission by reducing fuel supply quantity in a medium load region where fuel can be easily atomized in the warming-up state of an engine. CONSTITUTION:A float chamber 12 is provided with a float 13 for keeping the fuel oil level F1 constant. A main nozzle 20 is opened below the fuel oil level F1 in the float chamber 12. In the main nozzle 20, its upper end is opened to the venturi part 14 of an intake passage 10, and its side wall 24 is provided with plural bleed air holes 22. These bleed air holes 22 are communicated with the intake passage 10 through a bleed air chamber 23 provided at the outer periphery of the main nozzle 20, and a main air jet 25 so as to mix bleed air A1 into fuel F sucked out of the main nozzle 20 into the intake passage 10 to accelerate the atomization of fuel F. All the bleed air holes 22 are provided above the fuel oil level F1.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the amount of fuel supplied to an engine load and a carburetor used in this control method.

0002

[Prior Art] Generally, in a float type vaporizer,
Bleed air is mixed with fuel from the float chamber and supplied to the intake passage (for example, see Japanese Patent Laid-Open No. 51-57343). An example of this type of vaporizer is shown in FIG.

In FIG. 4, a float chamber 12 is provided below a carburetor body 11 forming an intake passage 10. As shown in FIG. The float chamber 12 is provided with a float 13 that controls the inflow of fuel F from a fuel tank (not shown) to keep the fuel oil level F1 constant. Float chamber 1
A main nozzle (fuel passage) 20 opens via a main jet 21 below the fuel oil level F1 at 2. The main nozzle 20 has an upper end connected to the intake passage 10.
It opens into the venturi portion 14, and has a plurality of bleed air holes 22A, 22B in its side wall 24. The bleed air holes 22A, 22B communicate with the upstream portion of the intake passage 10 via a bleed air chamber 23 and a main air jet 25 provided on the outer periphery of the main nozzle 20, and are connected to the intake passage 10 from the main nozzle 20. Bleed air A1 is mixed into the fuel F to be sucked out to promote atomization of the fuel F.

[0004] A choke valve 15 is provided at the upstream portion of the intake passage 10, and a slow air jet 30 shown by a broken line is opened. The slow air jet 30 supplies bleed air to a slow nozzle (not shown). The slow nozzle (not shown) has an opening 31 that opens into the intake passage 10 slightly downstream of the throttle valve 16 . Note that an air vent 17 is opened in the float chamber 12 .

Next, the operation of the above configuration will be briefly explained. When the load on the engine is small, for example, when the engine is idling, the intake passage 10 is throttled by the throttle valve 16. Therefore, the negative pressure generated in the intake passage downstream of the throttle valve 16 mainly affects the opening 31 of the slow nozzle.
From there, fuel F is sucked out into the intake passage 10. On the other hand, in the middle and high load range of the engine, the throttle opening is large, so fuel F is not supplied from the slow system and the main nozzle 2
Fuel F is sucked out from 0. These sucked-out fuels F are atomized in advance by being mixed with the bleed air A1, and are supplied together with the intake air A to a combustion chamber (not shown) as an air-fuel mixture M.

By the way, even in a low load range where the throttle valve 16 is opened slightly more than when idling, the air-fuel mixture M with a small air-fuel ratio is used to prevent misfire and improve rotational stability and acceleration. In other words, it is necessary to supply a rich mixture M to the combustion chamber (not shown). Therefore, in the above conventional technology, some of the bleed air holes 22A are provided at positions lower than the fuel oil level F1 to promote the mixing of bleed air A1 into the fuel F, and even during idling, the slow nozzle (Fig. Fuel F is supplied to the intake passage 10 not only from the main nozzle 20 (not shown) but also from the main nozzle 20. Also,
By setting the position of the other bleed air hole 22B at the same level as the fuel oil level F1, the fuel F and bleed air A are
By lengthening the passage for mixing 1 and 1, the bleed air A1 is sufficiently mixed into the fuel F,
Promotes atomization.

On the other hand, when the throttle valve 16 is fully opened at high speed and full load, the combustion chamber tends to become hot, so it is necessary to lower the temperature inside the combustion chamber. Therefore, even under full load, it is necessary to supply a rich mixture M to the combustion chamber. Therefore, as shown by the broken line in FIG. 2, conventional fuel supply characteristics are first determined by taking into consideration the idling, low load range, and high speed full load, and are varied linearly between them.

[0008]

However, for example, a general-purpose engine equipped with a governor is most often used at a constant rotation speed of 3,000 rpm or more, and in a medium load range. In such a state, since the engine is warmed up, the fuel F is likely to atomize, and therefore, with the fuel supply characteristics shown by the broken line above, the actual amount of fuel consumed increases, resulting in poor fuel efficiency. Moreover, emissions of HC, CO, etc. in the exhaust gas tend to increase. On the other hand, the temperature in the combustion chamber is not so high.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a method for controlling the amount of fuel supplied to an engine and a carburetor that can improve fuel efficiency and reduce exhaust gas emissions.

0010

[Means for Solving the Problems] In order to achieve the above object, the method of the present invention solves the problems in the engine in terms of the fuel supply amount characteristics with respect to the load, where the horizontal axis is the engine load and the vertical axis is the fuel supply amount. Control is performed so that the fuel supply curve becomes convex downward in the load range. On the other hand, in the engine carburetor of the present invention, all of the bleed air holes provided in the side wall of the fuel passage that opens into the venturi portion of the intake passage are located above the fuel oil level in the float chamber.

[0011]

According to the method of the present invention, the amount of fuel supplied is reduced in the medium load range where the engine is warmed up and fuel tends to atomize, resulting in a reduction in fuel consumption. On the other hand, according to the carburetor of the present invention, all of the bleed air holes are provided above the fuel oil level in the float chamber.
In a medium load range, even if the upper surface level of the fuel in the fuel passage rises due to the negative pressure in the venturi section, some or all of the bleed air holes are located above this upper surface level. Therefore, the amount of bleed air increases, the amount of fuel sucked into the intake passage decreases, and atomization is promoted.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a carburetor for a four-stroke general-purpose engine used in lawn mowers, small tractors, and the like. In FIG. 1, all of the plurality of bleed air holes 22 are provided at positions above the fuel oil level F1 of the float chamber 12. As shown in Fig. 2, the carburetor of this engine has a fuel supply amount characteristic with respect to load, where the horizontal axis is the engine load, or output, and the vertical axis is the fuel supply amount. The fuel supply amount curve L shown by the solid line is controlled so as to be convex downward. The rest of the configuration is the same as that of the conventional example shown in FIG. 4, and the same or corresponding parts are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

Next, a method of controlling the amount of fuel supplied by the carburetor will be explained. First, the medium load range will be explained. In the medium load range, as the negative pressure in the venturi section 14 shown in FIG. The amount increases.

Here, when the bleed air hole 22B is provided near the fuel oil level F1 as in the conventional example shown in FIG.
As the upper surface level of the fuel F in the main nozzle 20 rises above the bleed air hole 22B, pressure from the fuel F is applied to the bleed air hole 22B.
Bleed air A1 becomes difficult to enter the main nozzle 20. Therefore, the amount of bleed air A1 mixed into the fuel F does not increase much, and the fuel in the air-fuel mixture M becomes excessively rich. On the other hand, in the carburetor of the present invention, as shown in FIG. 1, all of the bleed air holes 22 are located above the fuel oil level F1, and are provided at a higher position than the conventional one. Even if the upper surface level of fuel F in the main nozzle 20 rises,
The pressure of the fuel F is not applied to the bleed air hole 22, or even if it is applied, the pressure is relatively small. Therefore, the bleed air A1 is transferred to the bleed air hole 22.
Since the amount of bleed air A1 is larger than that of the conventional method, the amount of the fuel F sucked out is correspondingly smaller than that of the conventional method. Moreover, since the bleed air A1 easily enters the main nozzle 20 in this way, the pressure within the main nozzle 20 does not drop unnecessarily. Therefore, the rise in the upper surface level of the fuel F in the main nozzle 20 is suppressed, and therefore the amount of fuel F sucked out is further reduced.

[0015] In this way, the amount of fuel F sucked out from the main nozzle 20 is reduced, so the amount of fuel supplied in the medium load range is smaller than in the conventional case, as shown by the solid line in FIG. 2, as shown by the broken line. . Therefore, in the medium load range where the engine is warmed up and fuel tends to atomize, the actual fuel consumption becomes appropriate, so as shown by the solid line in Figure 3, compared to the conventional case shown by the broken line, In addition to significantly improving fuel efficiency, it is possible to reduce exhaust gas emissions. here,
In the medium load range, the temperature of the combustion chamber is not so high, so the air-fuel ratio increases, resulting in a lean mixture M.
There is no problem even if the temperature of the combustion chamber increases.

Furthermore, since the bleed air hole 22 shown in FIG. 1 is provided above, the main nozzle 2
The upper surface level of the fuel F in 0 is near the bleed air hole 22. Therefore, since air bleed occurs near the upper surface level of this fuel F, the mixing effect of fuel F and bleed air A1 becomes greater.

On the other hand, in a low load range such as during idling, since the position of the bleed air hole 22 in FIG. 1 is above the fuel oil level F1, the fuel F does not sufficiently mix into the bleed air A1. However, in the low load range, the supply of fuel F from the slow system is dominant, so the fuel supply amount does not decrease much compared to the conventional system, and as shown by the two-dot chain line L1 in Fig. 2, it decreases slightly. There is a certain tendency to do so. Note that the amount of fuel supplied during idling can be made comparable to the conventional one, as shown by the solid line, by changing the settings of a slow system such as a slow nozzle (not shown).

Next, the full load range will be explained. In the full load range, the negative pressure in the venturi section 14 in FIG. Therefore, as in the case where the bleed air hole 22 is provided at a lower position, the amount of fuel F sucked out increases. Therefore, since the fuel F becomes excessively concentrated, there is no fear that the temperature of the combustion chamber becomes high.

By the way, in the fuel supply amount curve L in FIG. 2, with respect to the straight line connecting the idling state and the full load state,
The maximum value of the rate at which the fuel amount is reduced in the medium load range is:
That is, ΔF/F in FIG. 2 is set to about 10% to 30%. The reason is that if ΔF/F is set to less than 10%, almost no effect of reducing fuel consumption can be obtained;
This is because if the ratio is greater than 0%, the fuel becomes too thin and acceleration performance in the medium load range decreases.

In the method of the present invention, it is not necessary to use the carburetor shown in FIG. 1 as a method of reducing the amount of fuel supplied in the medium load range. For example, in an engine equipped with an electronic injection control device, the fuel passage may be throttled in a medium-high speed range (medium load range) to limit the amount of fuel supplied.

[0021]

[Effects of the Invention] As explained above, according to the method of the present invention, since the amount of fuel supplied is reduced in the medium load range where the engine is warmed up and fuel tends to atomize, fuel efficiency is improved and It is possible to reduce exhaust gas emissions. Furthermore, according to the carburetor of the present invention, all of the bleed air holes formed in the side wall of the fuel passage opening into the venturi part are located above the fuel oil level in the float chamber, so that even in the medium load range Even if the upper surface level of the fuel in the fuel passage rises, the amount of fuel supplied can be reduced because some or all of the bleed air holes are located above this upper surface level. Therefore, the method of the present invention can be realized with a vaporizer having a simple structure.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a carburetor of an engine showing one embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the fuel supply amount characteristics of the method of the present invention.

FIG. 3 is a characteristic diagram showing the relationship between output and fuel efficiency.

FIG. 4 is a longitudinal sectional view showing a conventional vaporizer.

[Explanation of symbols]

10...Intake passage, 12...Float chamber, 13...Float,
14...Venturi part, 20...Fuel passage (main nozzle), 22...Bleed air hole, 24...Side wall, A1...Bleed air, F...Fuel, F1...Fuel oil level, L...Fuel supply amount curve.

Claims (2)

[Claims] Claim 1: In fuel supply amount characteristics with respect to load, where the horizontal axis is the engine load and the vertical axis is the fuel supply amount,
A fuel supply amount control method that controls the fuel supply amount curve to be convex downward in the engine medium load range. 2. A float that maintains a constant fuel oil level in the float chamber, a fuel passage that supplies fuel from the float chamber to the venturi portion of the intake passage, and a fuel passage that is formed on a side wall of the fuel passage that supplies fuel from the float chamber. The engine carburetor is equipped with a plurality of bleed air holes for mixing bleed air into the engine carburetor, characterized in that all of the bleed air holes are provided above the fuel oil level in the float chamber. vaporizer.