Internal-combustion engines – Two-cycle – Rear compression
Reexamination Certificate
2001-08-13
2003-07-22
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Two-cycle
Rear compression
C123S0650WA
Reexamination Certificate
active
06595168
ABSTRACT:
CROSS REFERENCE AND CLAIM OF PRIORITY TO RELATED APPLICATIONS
This application claims priority to Japanese Patent Application No. 2000-245801, filed Aug. 14, 2000.
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates in general to a two-stroke internal combustion engine which is suited for use in a portable power working machine, and in particular to a two-stroke internal combustion engine which is designed to introduce air into a combustion actuating chamber prior to the introduction of the air-fuel mixture, thereby making it possible to minimize the quantity of so-called blow-by or the quantity of unburned air-fuel mixture discharged without being utilized for the combustion.
2. The Prior Art
An ordinary small air-cooled two-stroke internal combustion engine which is conventionally used in a portable power working machine, such as a chain saw and bush cutter, is constructed such that an ignition plug is disposed at the head portion of the cylinder and an intake port, a scavenging port and an exhaust port, which are to be opened and closed by a piston, are provided at the trunk portion of the cylinder. According to this two-stroke internal combustion engine, one cycle of the engine is accomplished by two strokes of the piston without undergoing a stroke which is exclusively assigned to the intake or exhaust.
More specifically, in the ascending stroke of the piston, an air-fuel mixture is introduced from the intake port into the crankcase disposed below the piston. During the subsequent descending stroke, the air-fuel mixture is pre-compressed producing a compressed gas mixture, which is then blown into a combustion actuating chamber which is disposed above the piston, thereby enabling waste combustion gas to be discharged through the exhaust port. In other words, since the scavenging of the waste combustion gas is effected by making use of the gas flow of the air-fuel mixture, the unburned air-fuel mixture is more likely to be mingled into the combustion gas (exhaust gas), thereby increasing the quantity of so-called blow-by or the quantity of air-fuel mixture that is discharged into atmosphere without being utilized for the combustion. Because of this, the two-stroke internal combustion engine is not only inferior in fuel consumption, but is also disadvantageous in that large amounts of poisonous components, such as HC (unburned components in fuel) and CO (incomplete combustion components in fuel), are included in the exhaust gas as compared with a four-stroke engine. Therefore, even if the two-stroke engine is small in capacity, the influence of these poisonous components on the environmental contamination should not be disregarded.
With a view to addressing these problems, there have proposed various kinds of so-called air-preintroduction type two-stroke internal combustion engines, in which an air inlet passageway for introducing external air is attached to a scavenging passageway so as to permit air to be introduced into the combustion actuating chamber in the descending stroke of the piston prior to the introduction of air-fuel mixture. The air thus pre-introduced functions to form an air layer between the waste combustion gas to be discharged and the unburned air-fuel mixture, thereby preventing the unburned air-fuel mixture from being mixed with the waste combustion gas and thus minimizing the quantity of blow-by of air-fuel mixture. See, for example, Japanese Patent Unexamined Publications H9-125966 and H5-33657, and Japanese Patent No. 3040758.
In such conventional air-preintroduction type two-stroke internal combustion engines, however, air inlet passageways (generally, since one or more pairs of right and left scavenging passageways are disposed, the air inlet passageway is bifurcated) are required to be separately installed outside the engine body (cylinder and crankcase) in order to introduce air into the scavenging passageway, etc. Also, a check valve, such as a reed valve, is required to be provided at a downstream end portion of each of air inlet passageways (at an upstream portion of each of one or more pairs of right and left scavenging passageways). Consequently, these conventional engines are accompanied by various problems, including an increased number of parts is required, the peripheral structure around the engine body, including the air-introducing passageways, is complicated, larger in size as a whole, and heavier in weight, the external appearance and assembling properties of the entire structure are poor, and a large space is required for the installation of the engine, which necessitates further improvements in order to mount the engine on a portable power working machine.
Additionally, since the crankcase is generally formed of a two-part structure (vertically split structure), it is troublesome both in working and assembly, and it is also difficult to reduce the weight and cost thereof.
The present invention overcomes the aforementioned problems associated with the conventional air-preintroduction type two-stroke internal combustion engine.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an air-preintroduction type two-stroke internal combustion engine which is capable of reasonably and compactly arranging the peripheral components of the internal combustion engine, thereby making it possible to reduce the number of parts, to lighten the weight thereof, to save the manufacturing cost thereof, and to simplify the working and assembling thereof.
The aforementioned and other objects of the invention are realized by the provision of a two-stroke internal combustion engine which, in accordance with the present invention, includes: a cylinder in which a piston is adapted to be fittingly inserted; a combustion actuating chamber disposed above the piston; a crankcase hermetically and contiguously disposed below the cylinder and defining a crank chamber; a means for forming an air-fuel mixture; one or more pairs of scavenging passageways, each allowing the combustion actuating chamber to be communicated with the crankcase, symmetrically provided on both sides of a longitudinal section which divides an exhaust port provided on the sidewall of the cylinder into two equal parts; the scavenging passageways allowing air to be introduced therein; the air-fuel mixture-forming means allowing the air-fuel mixture to be introduced therefrom into the crank chamber; in the descending stroke of the piston, the exhaust port is first opened before a scavenging port formed at a downstream end of each scavenging passageway is opened; air is introduced via the scavenging passageways into the combustion actuating chamber prior to the introduction of the air-fuel mixture; and an air inlet passageway for introducing air into the scavenging passageways is provided at the mating face between the cylinder and the crankcase.
In one embodiment, the crankcase is provided with an air inlet port for introducing air into the air inlet passageway, and the air inlet port is provided with a check valve. Preferably, the air inlet passageway is an annular passageway formed at and opening downwardly through the lower end portion of the cylinder, the underside of the annular passageway being closed by an upper wall of the crankcase. The crankcase is preferably provided with a communicating passageway which communicates the annular air inlet passageway with the crank chamber, and the air inlet passageway also functions as an upper (or upstream) portion of the scavenging passageway.
In another embodiment, the air inlet port is provided with a pair of inlet ports communicating with the air inlet passageway, and a single reed valve functioning as the check valve is provided for opening or closing the pair of inlet ports.
The crankcase is preferably formed of a horizontally split structure having an upper crankcase and a lower crankcase, wherein the crankcase is divided by a horizontal plane passing through the central axis of a crankshaft which is rotatably supported by the crankcase, thereby forming the upper crankcase and the low
Argenbright Tony M.
Baker & Botts LLP
Harris Katrina B.
Kioritz & Corporation
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