JPH1122556A - Starting fuel feeding device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the fuel pressure regulating diaphragm of a constant fuel chamber from being applied with a high negative pressure and being unreasonably deformed to cause functional reduction and early deterioration when a starting pump is operated. SOLUTION: An air passage 36 sucking air into the starting pump chamber 35 of a manual starting pump 33 is branched from a fuel passage 15 to a constant fuel chamber 16 from a fuel pump 5, a fuel valve 22 is kept closed when the starting pump 33 is operated, and the starting fuel is retained in the fuel passage 15. The check valve 37 of the air passage 36 is fixed at the closed position by the engine intake negative pressure for a normal fuel feed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for supplying fuel for improving the startability of a general-purpose engine at a low temperature.

[0002]

2. Description of the Related Art Many of the general-purpose two-stroke engines that have long been used as driving sources for agricultural and forestry work machines, small vehicles, and the like, and general-purpose four-stroke engines that have recently attracted attention for exhaust control, Fuel is supplied by a membrane carburetor having a constant fuel chamber, which is separated from the atmosphere by a diaphragm and adjusts the fuel to a constant pressure.

The membrane carburetor has a diaphragm type fuel pump driven by a pulse pressure generated in an engine crankcase. Fuel from a fuel tank is introduced into a constant fuel chamber by the fuel pump. This structure sucks air into the intake passage and supplies it to the engine. In addition to this, means for introducing fuel into an empty constant fuel chamber prior to starting the engine, or for introducing extra fuel into the constant fuel chamber at a low temperature or sending it to the intake passage, generally, It is common to have a manual starting pump.

[0004] In the engine equipped with a starting pump, fuel flows in the order of fuel tank → fuel pump → constant fuel chamber (→ intake passage overflow) → starting pump (Japanese Patent Laid-Open No. 55-55980)
-69748) and the fuel is a fuel tank →
It can be broadly classified into those flowing in the order of starting pump → fuel pump → constant fuel chamber (→ external overflow) (see JP-A-47-38218). The former method of sucking and introducing can secure a sufficient amount of starting fuel at low temperatures compared to the latter method of pumping and introducing pressurized fuel into the fuel pump and the constant fuel chamber.Therefore, the former method is often used. ing.

FIG. 2 shows an example of a conventional film-type vaporizer adopting the former method. A dome-shaped pump member 53 of a starting pump 52 mounted on one side of a vaporizer main body 51 is shown.
By repeating the operation of pressing and releasing the finger with the fingertip, the reduction and expansion of the volume of the starting pump chamber 54 inside it are repeated, and the air in the constant fuel chamber 59 is released from the air passage 55, the check valve 56,
The fuel is discharged to the outside through the starting pump chamber 54, the check valve 57, and the discharge passage 58, whereby the constant fuel chamber 59 becomes a negative pressure and the fuel pressure regulating diaphragm is displaced toward the constant fuel chamber 59. 60 operates the fuel valve 61 to open the fuel passage 68.

As a result, the fuel in the fuel tank (not shown) is supplied from the fuel introduction pipe 62 to the suction passage 6 having the inlet check valve 64.
5, fuel pump chamber 66 of fuel pump 63, outlet check valve 6
The fuel is sucked and introduced into the constant fuel chamber 59 through the fuel passage 68 having the nozzle 7.

On the other hand, when the starting pump 52 is operated, the main nozzle 69, the idle port 70, and the slow port 71 prevent the air in the intake passage 72 from being sucked into the constant fuel chamber 59, which has become a negative pressure. Check valves 73 and 74 are provided in the fuel system and the low-speed fuel system, respectively.

[0008]

According to the above-mentioned membrane carburetor, a high negative pressure is generated in the constant fuel chamber 59 to suck and introduce the fuel in the fuel tank into the constant fuel chamber 59. For this reason, the diaphragm 60 is greatly displaced and is forcibly deformed, thereby causing a cause of impairment of a normal function and early deterioration. In order to generate a high negative pressure, it is necessary to make the constant fuel chamber 59 airtight. Therefore, the check valves 73 and 74 provided in the main fuel system and the low-speed fuel system must have a high-precision structure capable of completely sealing. Must be troublesome,
It can also increase production costs.

According to the present invention, a required amount of starting fuel can be ensured without generating a negative pressure in the constant fuel chamber in a system in which the starting pump is operated and the starting fuel is sucked by passing the fuel pump from the fuel tank. Therefore, the invention has been made with the object of providing a starting fuel supply device which does not have the above-mentioned problems such as forcibly deforming the diaphragm and requiring a high-precision check valve.

[0010]

That is, according to the present invention, an air passage for sucking air into a starting pump chamber of a starting pump is branched from a fuel passage from a fuel pump to a constant fuel chamber, and a check valve of the air passage is provided. The valve was fixed at the valve closing position by the engine suction negative pressure.

With this arrangement, when the starting pump is operated, the portion from the fuel tank to the fuel pump and the fuel passage become negative pressure, and the fuel valve at the inlet of the constant fuel chamber closes the fuel passage by this negative pressure. Works as a stop valve. For this reason, no negative pressure acts on the constant fuel chamber, so that the diaphragm is not forcedly deformed and the constant fuel chamber does not need to be highly airtight. Further, the fuel sucked from the fuel tank by the negative pressure fills the fuel passage and further enters the air passage.
When the suction negative pressure is generated by starting the engine, the check valve in the air passage is fixed at the valve closing position, and this negative pressure acts on the constant fuel chamber to open the fuel valve, and the fuel passage and the air passage are opened. Is stored in the constant fuel chamber and supplied to the engine as starting fuel.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an embodiment of the present invention will be described. A fuel pump 5 is fixed on the outer surface of a carburetor body 1 with an intake passage 4 having a venturi 2 and a throttle valve 3 interposed therebetween. A fuel chamber 16 is provided.

The fuel pump 5 has a pump diaphragm 6 and a flat inner cover 7 stacked on the side surface of the carburetor body 1 in order.
A well-known configuration is provided in which the carburetor body 1 and the inner cover body 7 are provided with depressions with the pump diaphragm 6 interposed therebetween, and these are used as a fuel pump chamber 8 and a pulse pressure chamber 9. The pulse pressure generated in the crankcase of the engine is supplied to the pulse pressure passage 9 in the pulse pressure chamber 9.
By operating the pump diaphragm 6 introduced through the fuel pump 0, the fuel in the fuel tank (not shown) is sucked into the fuel pump chamber 8 through the fuel introduction pipe 11 and the suction passage 13 having the inlet check valve 12, and then from there. The fuel is discharged to a constant fuel chamber 16 through a fuel passage 15 having an outlet check valve 14.

The constant fuel chamber 16 is formed by a recess provided on a side surface of the carburetor body 1 and is separated from an atmosphere chamber 19 formed on an inner surface of a diaphragm cover 18 by a diaphragm 17 overlapped on this side surface. Diaphragm 17
The base of a valve lever 20 is engaged with the center of the valve lever by the spring force of a spring 21. A fuel valve 22 engaged with the distal end of the valve lever 20 connects the outlet end of the fuel passage 15 to the constant fuel chamber 16 to the center. By opening and closing according to the displacement of the diaphragm 17,
The constant fuel chamber 16 is made to hold fuel specified at a constant pressure.
This configuration is the same as that conventionally known.

The fuel in the constant fuel chamber 16 passes through a main fuel passage 24 and a low-speed fuel passage 27 whose flow is regulated by fuel regulating valves 23 and 26 having a needle valve at the tip of a screw.
Are sucked into the intake passage 4 from the main nozzle 25 opened to the narrowest part of the throttle valve 3, the idle port 28 and the slow port 29 opened to the side of the throttle valve 3.

An auxiliary diaphragm 31 and an outer cover 32 are sequentially stacked on the side of the inner cover 7 opposite to the carburetor body 1, and a starting pump 33 is formed on the outer side of the outer cover 32. A dome-shaped pump member 34 made of an elastic material is attached. The space surrounded by the outer cover body 32 and the pump member 34 forms a starting pump chamber 35, which discharges air from the fuel tank to the fuel passage 15 and an air passage 36 for sucking fuel, and discharges air to the fuel tank. A discharge passage 38 is connected to the starting pump chamber 35.

The air passage 36 branches off from the surge chamber 15a for buffering the pulse pressure in which the outlet check valve 14 of the fuel passage 15 is installed, and reaches the starting pump chamber 35. On the other hand, the inner cover 7 and the outer cover 32 sandwich the auxiliary diaphragm 31.
A negative pressure chamber 40 and an air chamber 41 are formed by the recess provided in the air passage 36, and the air chamber 41 is provided in the middle of the air passage 36. The negative pressure chamber 40 is connected to the downstream side of the throttle valve 3 of the intake passage 4 or to the intake manifold by a negative pressure passage 43.

A check valve 37 for opening and closing the air passage 36 is connected to the auxiliary diaphragm 31 by a connecting rod 42, and the auxiliary diaphragm 31 is in the neutral position and the air chamber 41.
When the air passage 36 is displaced toward the negative pressure chamber 40, the air passage 36 is open.
The check valve 39 in the discharge passage 38 is a normal check valve that functions to discharge air from the starting pump chamber 35 but not to suck air.

If the operation of pressing and releasing the pump member 34 of the starting pump 33 with a fingertip before starting the engine is repeated, the starting pump chamber 35 and the air chamber 41 become positive pressure when pressed, so that the auxiliary diaphragm 31 becomes negative pressure. Displaced toward the chamber 40, the interlocking check valve 37 immediately closes the air passage 36, and the check valve 39 opens to discharge air to the fuel tank. At the time of release, the pump member 34 is restored and the starting pump chamber 35 becomes a negative pressure, the auxiliary diaphragm 31 and the check valve 37 are sucked, the air passage 36 is opened, and the check valve 39 closes the discharge passage 38, and the fuel tank is removed. The air is sucked up to the fuel introduction pipe 11, the suction passage 13, the fuel pump chamber 8, and the fuel passage 15, and the fuel is sucked into these.

On the other hand, the fuel valve 22 closes the fuel passage 15 because the fuel passage 15 is in a negative pressure state and the diaphragm 17 and the spring 21 apply a valve closing force. The fuel sucked by the above is not fed into the constant fuel chamber 16.

Therefore, when the starting pump 33 is operated several times, generally four or five times, the fuel is filled from the fuel tank to the fuel passage 15 and, depending on the number of operations, the fuel is filled into the air chamber 41 of the air passage 36. Will be filled up.

Next, when the engine is started to operate and a suction negative pressure due to cranking is generated in the intake passage 4 and the intake manifold, the suction negative pressure is introduced into the negative pressure chamber 40 through the negative pressure passage 43 and is supplied to the auxiliary diaphragm 31. Is displaced toward the negative pressure chamber 40 to fix the check valve 37 at the valve closing position. At the same time, the suction negative pressure mainly acts on the constant fuel chamber 16 through the idle port 28 to open the fuel valve 22, and the fuel passage 1
5 is introduced into the constant fuel chamber 16.

When the cranking is repeated about the same number of times as the conventional one, a sufficient amount of fuel flows into the constant fuel chamber 16 and is stored.
This is sucked into the intake passage 4 as starting fuel and supplied to the engine. After the complete explosion of the engine, the fuel pump 5 operates to send the fuel in the fuel tank to the constant fuel chamber 16 as in the conventional case.
1 is the average negative pressure of the pulsating suction air pressure, so that the check valve 37 is securely fixed to the closed position,
This eliminates the disadvantage that air is sucked into the fuel passage 15 and hinders normal fuel supply.

As described above, since the starting fuel is stored in the fuel passage 15 without generating a negative pressure in the constant fuel chamber 16 by operating the starting pump 33, the diaphragm 17 is largely displaced and forcibly deformed. And fuel valve 2
The problem of impairing normal functions such as changing the fuel pressure in the constant fuel chamber 16 or causing early deterioration by changing the opening and closing operation of the constant fuel chamber 16 is avoided. In addition, it is not necessary to make the constant fuel chamber 16 highly airtight. .

Further, since the high negative pressure generated by the starting pump 33 does not act on the constant fuel chamber 16, a check valve for preventing air from being sucked from the intake passage 4 becomes unnecessary. However, in order to prevent air from being temporarily sucked into the constant fuel chamber 16 from the intake passage 4 during rapid deceleration of the engine, in addition to the check valve 44 provided in the main nozzle 25, Nor does it hinder the installation of simple check valves.

Further, since the fuel can be stored in the air passage 36, a sufficient amount of starting fuel can be ensured by ensuring that the volume of the surge chamber 15a is large. It can be.

[0027]

As described above, according to the present invention, there is no need to worry about forcibly deforming the diaphragm for regulating the fuel pressure in the constant fuel chamber and to make the constant fuel chamber highly airtight and to operate the same starting pump as before. It is possible to secure a sufficient amount of starting fuel and start the engine satisfactorily.

[Brief description of the drawings]

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

FIG. 2 is a longitudinal sectional view showing a conventional example.

[Explanation of symbols]

1 carburetor body, 4 intake passage, 5 fuel pump, 8
Fuel pump chamber, 13 suction passage, 15 fuel passage, 16
Constant fuel chamber, 17 diaphragm, 22 fuel valve, 31
Auxiliary diaphragm, 33 starting pump, 35 starting pump chamber, 36 air passage, 37 check valve, 40 negative pressure chamber

Claims (1)

[Claims] 1. A constant fuel chamber for regulating the pressure of fuel sucked into an intake passage by a diaphragm, a fuel pump for feeding fuel from a fuel tank to the constant fuel chamber, and a fuel for the fuel tank being sucked through the fuel pump. A starter pump having a manual starter pump for supplying starting fuel to an intake system provided with a carburetor; and an air passage for sucking air into a starter pump chamber of the starter pump from the fuel pump to the constant fuel chamber. And a check valve in the air passage is fixed at a closed position by a negative engine suction pressure.