Internal-combustion engines – Two-cycle – Rear compression
Reexamination Certificate
2001-01-12
2002-04-23
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Two-cycle
Rear compression
C123S179110
Reexamination Certificate
active
06374782
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an air-fuel mixture generating device equipped with a diaphragm-type fuel pump, a fuel injection valve and a manual fuel pump, and in particular, to an air-fuel mixture generating device which is adapted to be employed, as an alternative to the conventional ordinary carburetor, for the intake system of an air-cooled two-stroke gasoline engine of the crankcase precompression type, which is particularly suitable for powering portable working machines and the like.
BACKGROUND OF THE INVENTION
For the intake system of a small air-cooled two-stroke gasoline engine of the crankcase precompression type (hereinafter referred to simply as an internal combustion engine), such as those used to power portable working machines such as chain saws or bush cutters, there is frequently employed, as an air-fuel mixture generating device, a floatless diaphragm-type carburetor equipped with a diaphragm-type fuel pump which is designed to induct fuel and to inject pressurized fuel in conformity with pressure changes (pulsating pressure) inside the crankcase of the internal combustion engine in order to ensure a stable supply of fuel to the engine irrespective of the posture of the engine.
However, it is difficult, with such a diaphragm-type carburetor, to precisely control the quantity of fuel in relation to the intake air (control of air/fuel ratio) and to achieve sufficient atomization of fuel and accurate response to the pulsating pressure, thereby making it difficult to effectively take measures for purifying the exhaust gas.
Under the circumstances, there has been recently proposed, as an alternative to the aforementioned carburetor, an air-fuel mixture generating device which is equipped with a fuel injection valve in addition to the aforementioned diaphragm-type fuel pump.
In an air-fuel mixture generating device of the aforementioned type, a diaphragm is disposed inside a main body that has a construction similar to that of a carburetor, a pulsating pressure chamber to which the pressure of the crankcase is transmitted is provided on one side of the diaphragm, and a pump chamber for inducting fuel and injecting it to a fuel passageway is provided on the other side of the diaphragm. The diaphragm is actuated (reciprocating movement) by taking advantage of the pressure changes (pulsating pressure) in the crankcase resulting from the movement of the piston of the internal combustion engine, i.e., the decrease in the pressure as the piston is moved upward and the increase in the pressure as the piston is moved downward, thereby enabling a pressurized fuel to be fed from the pump chamber to the fuel passageway and also enabling the fuel inside the fuel passageway to be pressurized. At the same time, the aforementioned fuel injection valve is allowed to open with a predetermined timing (for example, at the moment of the initiation of the suction stroke) for a predetermined period of time (for example, 1 to 3 milliseconds), depending on the operating condition of the internal combustion engine, to thereby enable the pressurized fuel in the fuel passageway to be injected into the intake system (for example, an intake passage portion located on the downstream side of the throttle valve) so as to be mixed into the inducted air, thereby producing an air-fuel mixture.
However, since the diaphragm-type fuel pump according to the aforementioned air-fuel mixture generating device is designed to be actuated by taking advantage of the pressure changes (pulsating pressure) inside the crankcase, the quantity of fuel to be injected by the diaphragm-type fuel pump is caused to greatly increase as the internal combustion engine is operated at a high speed (for example, 6000 rev/min or more), resulting in an excessive increase in pressure of the fuel disposed inside the fuel passageway (for example, the pressure will be increased up to nearly 0.1 MPa). As a result, the fuel is caused to be injected excessively from the fuel injection valve, thereby raising the problem that an excessively rich air-fuel mixture is fed to the combustion-actuating chamber of the internal combustion engine.
It may be considered, as one of the countermeasures for solving this problem, to incorporate a pressure-adjusting means such as a fuel pressure regulator, etc., into the pump chamber or the fuel passageway. However, the incorporation of the pressure-adjusting means such as the aforementioned regulator will make the resultant structure very complicated, thus increasing the manufacturing cost thereof.
SUMMARY OF THE INVENTION
The present invention has been made with a view to solving the aforementioned problems. It is, accordingly, an object of the present invention to provide an air-fuel mixture generating device which is equipped with a diaphragm-type fuel pump and a fuel injection valve, and is capable of preventing an excessive amount of fuel from being injected from the fuel injection valve, even if the internal combustion engine is operated at a high speed, without making the air-fuel mixture generating device complicated in construction and without greatly increasing the manufacturing cost thereof.
With a view to attaining the aforementioned objects, the present invention provides an air-fuel mixture generating device which essentially comprises:
a main body equipped with a diaphragm-type fuel pump which is designed to induct fuel and to inject the fuel into a fuel passageway in conformity with pressure changes inside the crankcase of the internal combustion engine;
a fuel injection valve attached to the main body for injecting the fuel of the fuel passageway into an intake system of the internal combustion engine with a predetermined timing;
a manual fuel pump attached to the main body for filling the fuel passageway with fuel on an occasion when the diaphragm-type fuel pump is not actuated, the manual fuel pump having an inlet port which is communicated with the fuel passageway; and
a pressure-adjusting valve disposed at the inlet port of the manual fuel pump, thereby enabling it to act not only as an intake valve on an occasion when the manual fuel pump is actuated but also as a relief valve for allowing the fuel inside the fuel passageway to escape into a manual pump chamber of the manual fuel pump on an occasion when the pressure of fuel inside the fuel passageway exceeds a predetermined pressure.
In a preferred embodiment of the air-fuel mixture generating device according to the present invention, the diaphragm-type fuel pump is constituted by a diaphragm disposed inside the main body, a pulsating pressure chamber formed on one side of the diaphragm for receiving a pulsating pressure of the crankcase, and a pulsating pressure pumping chamber formed on the other side of the diaphragm for inducting fuel and injecting the fuel to the fuel passageway.
In another preferred embodiment of the air-fuel mixture generating device, it further comprises an intake valve which is formed at a portion of the diaphragm located between the pulsating pressure pump chamber and a fuel intake passageway portion, and an injection valve which is formed at a portion of the diaphragm located between the pulsating pressure pump chamber and the fuel passageway.
In another preferred embodiment of the air-fuel mixture generating device, an escape valve is disposed at an escape port of the manual fuel pump, the escape valve being designed to be closed when the pressure inside the manual pump chamber is less than a predetermined pressure, and also designed to be opened when the pressure inside the manual pump chamber is increased higher than said predetermined pressure.
The internal combustion engine to which the air-fuel mixture generating device of the present invention can be preferably applied is an air-cooled two-stroke gasoline engine of crankcase precompression type, wherein the injection port of the fuel injection valve is disposed on the downstream side of the throttle valve of the intake passageway.
With an air-fuel mixture generating device of the present invention constructed as des
Enomoto Kiyoshige
Hironaka Yoshiaki
Ishikawa Takeshi
Sakaguchi Yukio
Baker & Botts L.L.P.
Kioritz & Corporation
McMahon Marguerite
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