Internal-combustion engines – Two-cycle – Rear compression
Reexamination Certificate
2002-03-18
2003-12-16
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Two-cycle
Rear compression
C123S0730AA
Reexamination Certificate
active
06662765
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates 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 capable of minimizing the quantity of so-called blow-by or the quantity of air-fuel mixture to be discharged without being utilized for the combustion.
2. Description of the Related 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 or brush 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 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 exclusively assigned to the intake or exhaust.
More specifically, in the ascending stroke of the piston, air-fuel mixture is introduced from the intake port into a crank chamber disposed below the piston. During the subsequent descending stroke, the air-fuel mixture is pre-compressed, and compressed gas mixture is then blown into a combustion actuating chamber (though it may be also called a combustion chamber, actuating chamber, cylinder chamber, etc., these chambers are generically referred to as combustion actuating chamber in the present specification) which is disposed above the piston, thereby enabling waste combustion gas to be discharged from 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 mixed into the combustion gas (exhaust gas), thereby increasing the quantity of so-called blow-by or the quantity of air-fuel mixture to be discharged into the atmospheric air without being utilized for the combustion. Because of this, two-stroke internal combustion engines are not only inferior in fuel consumption but also disadvantageous in that a large amount of poisonous components such as HC (unburned components in fuel) and CO (incomplete combustion components in fuel) are included in the exhaust gas when compared to four-stroke engines. 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, various proposals on the two-stroke internal combustion engine have been suggested. The proposals have included the introduction of air into the combustion actuating chamber prior to the introduction of air-fuel mixture so as to scavenge the combustion gas (for example, Japanese Patent Unexamined Publications H9-125966 and H5-33657).
In such conventional air-preintroduction type two-stroke internal combustion engines, however, air inlet passageways or check valves are required to be separately installed, so the resulting engine may be complicated in structure, and inevitably result in a sharp increase in manufacturing cost.
Additionally, since air is caused to be excessively introduced into the combustion actuating chamber, the combustion stability may easily deteriorate, thus creating problems, such as difficulties in the engine setting. Accordingly, there exists a need in the art for a two-stroke engine which can overcome the aforementioned disadvantages associated with the conventional two-stroke engines.
BRIEF 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 minimizing the quantity of so-called blow-by or the quantity of air-fuel mixture discharged without being utilized for combustion.
Another object of the present invention is to provide an air-preintroduction type two-stroke internal combustion engine with improved fuel consumption and engine power.
Yet another object of the present invention is to provide an air-preintroduction type two-stroke internal combustion engine capable of reducing the amount of poisonous components in the exhaust gas.
Still another object of the present invention is to reduce the manufacturing cost of an air-preintroduction type two-stroke internal combustion engine, without extensively altering its conventional structure.
These and other objects of the present 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 includes one or more pairs of Schnürle-type scavenging passageways, each allowing the combustion actuating chamber disposed above a piston to communicate with the crank chamber. The scavenging passageways are symmetrically provided on both sides of the longitudinal section that figuratively divides an exhaust port into two equal parts. A through-hole or a communication groove is provided at a skirt portion of the piston to thereby enable a scavenging inlet port provided at an upper end of the scavenging passageway to communicate with the crank chamber. In the descending stroke of the piston, combustion exhaust gas originating from the combustion actuating chamber is enabled to be introduced, via a scavenging outlet port provided at the downstream end of the scavenging passageway, into the scavenging passageway while closing the scavenging inlet port at the skirt portion of the piston. In synchronization with the descending stroke of the piston, the air-fuel mixture may be introduced from the crank chamber, via the through-hole or the communication groove, into the scavenging passageway. The combustion exhaust gas existing inside the scavenging passageway is designed to be introduced into the combustion actuating chamber prior to the introduction thereinto of the air-fuel mixture.
In a preferred embodiment, in the descending stroke of the piston, the scavenging outlet port is opened a moment after the exhaust port has been opened, which is followed by the opening of the scavenging inlet port through the through-hole or the communication groove.
Alternatively, the two-stroke internal combustion engine may include a pair of first Schnürle-type scavenging passageways located close to the exhaust port and a pair of second Schnürle-type scavenging passageways located away from the exhaust port, each passageway allowing the combustion actuating chamber, disposed above the piston, to communicate with the crank chamber. The scavenging passageways are symmetrically provided on both sides of the longitudinal section that figuratively divides the exhaust port into two equal parts. A through-hole or a communication groove is provided at a skirt portion of the piston to thereby enable a second scavenging inlet port, provided at an upper end of the second Schnürle-type scavenging passageway, to communicate with the crank chamber. The upper end of the first scavenging passageway communicates via a throttle passageway with the second scavenging passageway. In the descending stroke of the piston, combustion exhaust gas originating from the combustion actuating chamber is introduced, via the first scavenging outlet port provided at the downstream end of the first scavenging passageway, into the first scavenging passageway, while the second scavenging inlet port is closed at the skirt portion of the piston. In synchronization with the descending stroke of the piston, the air-fuel mixture fed from the crank chamber is subsequently introduced into the second scavenging passageway via the through-hole or the communication groove, as well as through the second scavenging inlet port, and also into the first scavenging passageway through the throttle passageway. The combustion exhaust gas existing inside the first scavenging passageway is designed to be introduced into the combustion actuating chamber prior to the introduction therei
Baker & Botts LLP
Benton Jason
Kioritz & Corporation
Yuen Henry C.
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