Internal-combustion engines – Two-cycle – Rear compression
Reexamination Certificate
2001-10-19
2003-12-16
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Two-cycle
Rear compression
C123S0650WA, C123S0730AE
Reexamination Certificate
active
06662766
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority of Japanese Patent Application No. 2000-318841, filed Oct. 19, 2000.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to two-stroke internal combustion engines which are suited for use in portable power working machines, and in particular to two-stroke internal combustion engines which are designed to introduce air into a combustion actuating chamber prior to the introduction of air-fuel mixture, thereby making it possible to minimize the quantity of air-fuel mixture discharged from the combustion actuating chamber without being utilized for the combustion.
2. Background of Related Art
An ordinary small air-cooled two-stroke internal combustion engine that is conventionally used in portable power machines, such as chain saws or bush cutters, is constructed such that an ignition plug is disposed at the head portion of the cylinder, and an intake port, scavenging ports and an exhaust port are provided at the trunk portion of the cylinder. The intake port, the scavenging ports, and the exhaust port are opened and closed by a piston. According to this type of 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 the exhaust.
More specifically, during 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 descending stroke of the piston, the air-fuel mixture is pre-compressed to produce a compressed gas mixture. This compressed gas mixture is then blown into a combustion actuating chamber disposed above the piston, thereby enabling waste combustion gas in the combustion actuating chamber to be discharged through the exhaust port. Since the scavenging of the waste combustion gas is effected by making use of the gas flow of the air-fuel mixture into the combustion actuating chamber, the unburnt air-fuel mixture is likely to be mingled with the waste combustion gas (i.e., exhaust gas), thereby increasing the quantity of air-fuel mixture to be discharged into the atmosphere without being utilized for combustion, this unburnt air-fuel mixture referred to herein as “blow-by.” Because of this aspect of combustion, the two-stroke internal combustion engine is not only inferior in fuel consumption as compared with a four-stroke internal combustion engine, but this engine is also disadvantageous in that a greater quantity of poisonous components such as HC (unburnt components in a fuel) and CO (incomplete combustion components in a fuel) may be included in the exhaust gas, as compared with the four-stroke engine. Therefore, even if the two-stroke engine is small in capacity, the effect of these poisonous components on environmental contamination may not be disregarded.
With a view to address these disadvantages of ordinary air-cooled two-stroke internal combustion engine, various kinds of “air-preintroduction” type two-stroke internal combustion engine have been proposed. Air-preintroduction type two-stroke internal combustion engines typically have an air inlet passageway for introducing external air attached to a scavenging passageway, thereby permitting air to be introduced into the combustion actuating chamber in the descending stroke of the piston, prior to the introduction of the air-fuel mixture. The air that is pre-introduced into the combustion actuation chamber forms a layer between the waste combustion gas to be discharged and the unburnt air-fuel mixture being introduced. This air layer is intended to prevent the unburnt air-fuel mixture from being mixed with the waste combustion gas, thus minimizing the quantity of blow-by. (For example, see Japanese Patent Unexamined Publications H9-125966 and H5-33657, and Japanese Patent No. 3040758).
However, these conventional air-preintroduction type two-stroke internal combustion engines include peripheral structure, such as air inlet passageways (e.g., one or more pairs of right and left scavenging passageways may be used, if the air inlet passageway is bifurcated), which are required to be separately installed outside the engine body (i.e., cylinder body and crankcase) in order introduce air into the scavenging passageway, etc. These conventional air-preintroduction type two-stroke engines have the disadvantage that this peripheral structure around the engine body, including the air-introducing passageways, becomes complicated, larger in size as a whole, and heavier in weight. In addition, the operation and assembly of this type of engine are rather troublesome, thus requiring further improvements to make it suitable for use in a portable power working machine.
Accordingly, there exists a need in the art for a two-stroke internal combustion engine which can overcome the aforementioned disadvantages associated with the conventional air-preintroduction type two-stroke internal combustion engine.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an air-preintroduction type two-stroke internal combustion engine which is capable of reasonably and compactly arranging the peripheral components of 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.
These and other objects of the invention, which will become apparent with reference to the disclosure herein, are accomplished by the two-stroke internal combustion engine according to the present invention, which comprises a cylinder body in which a piston is adapted to be fittingly inserted; a crankcase disposed below the cylinder body and defining a crank chamber; and means for forming an air-fuel mixture; and one or more pairs of Schnürle-type scavenging passages, each allowing the combustion actuating chamber disposed above the piston to be communicated with the crankcase. The scavenging passages may be symmetrically provided on both sides of the longitudinal section which divides an exhaust port provided on a sidewall of the cylinder into two equal parts, thereby allowing air to be introduced into the scavenging passages. The air-fuel mixture may be introduced into the combustion actuation chamber from the crank chamber. During a descending stroke of the piston, the exhaust port is first opened before a scavenging port formed at a downstream end of the scavenging passageway is opened, thereby enabling air to be introduced via the scavenging passageway into the combustion actuating chamber prior to the introduction of the air-fuel mixture.
This two-stroke internal combustion engine according to the present invention is also characterized in that an air inlet passageway for introducing air into the scavenging passageways is provided inside the wall portion of the cylinder.
In a preferred embodiment, the air inlet passageway is constituted by an air inlet port, a pair of right and left linear branch passageways communicated with the air inlet port, and a communicating passageway which permits the branch passageways to be communicated with the scavenging passageway.
This communicating passageway should preferably be formed with a cap member to be attached to the cylinder.
In a preferred embodiment, the air inlet passageway is provided with a check valve. Further, a check valve may be attached to the cap member or to the branch passageways.
In further preferred embodiment, the internal combustion engine is further provided with an air-feeding passageway for feeding external air to the air inlet passageway, and with an air-fuel mixture-feeding passageway for feeding, via an air-fuel mixture-inlet port, air-fuel mixture generated by the air-fuel mixture generating means to the crank chamber, the air-feeding passageway and the air-fuel mixture-feeding passageway being arranged side by side.
In further preferred embodiment, the air-fuel mixture-inlet port to be opened and closed is disposed below the air inlet port f
Araki Tsuneo
Liu Yumin
Baker & Botts L.L.P.
Kamen Noah P.
Kioritz & Corporation
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