Internal-combustion engines – Two-cycle – Rear compression
Reexamination Certificate
2000-05-10
2002-04-09
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Two-cycle
Rear compression
C123S0650PD, C123S0730AE
Reexamination Certificate
active
06367432
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a two-stroke cycle internal combustion engine that is suited for use in a portable power working machine, for instance, and in particular to a two-stroke cycle internal combustion engine which is capable of minimizing the quantity of so-called blow-by, i.e., the quantity of unburned air-fuel mixture that is discharged from the engine with the exhaust gases.
An ordinary two-stroke cycle internal combustion engine which is conventionally used in a portable power working machine, such as a chain saw, 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, which are to be opened and closed by a piston, are provided at the trunk portion of the cylinder. In such a two-stroke cycle internal combustion engine, one cycle of the operation of the engine is accomplished by two strokes of the piston—the piston does not perform strokes which are exclusively assigned to the intake of an air-fuel mixture or the exhaust of combustion gases.
More specifically, during each ascending stroke of the piston, an air-fuel mixture is introduced from the intake port into the crank chamber disposed below the piston. When the piston descends, the air-fuel mixture in the crank chamber is pre-compressed, producing a compressed gas mixture, which is then utilized for exhausting the combustion gas from the exhaust port; i.e., the compressed gas mixture is blown into a combustion actuating chamber, which is disposed above the piston, so as to expel the combustion gas toward the exhaust port. (Although it might variously be called a combustion chamber, an actuating chamber, a cylinder chamber, etc., these chambers are generically referred to in the present specification as “the combustion actuating chamber.”) In other words, since the scavenging of the 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, i.e., the quantity of unburned air-fuel mixture that is discharged from the engine into the atmosphere with the exhaust gases. Because of this, the two-stroke cycle internal combustion engine is not only inferior in fuel efficiency but also disadvantageous in that a large amount of undesirable components, such as HC (unburned components in a fuel) and CO (incomplete combustion components in a fuel), are included in the exhaust gas as compared with a four-stroke cycle engine Therefore, even if the two-stroke cycle engine is small in capacity, the influence of these undesirable components on environmental contamination should not be disregarded.
With a view to solving these problems, various proposals have been made for two-stroke cycle internal combustion engines in which air is introduced into the combustion actuating chamber prior to the introduction of air-fuel mixture so as to scavenge the combustion gas (see, for example, Japanese Patent Unexamined Publications H9-125966 and H5-33657). However, even with these proposals, it is difficult to sufficiently reduce the quantity of blow-by. Additionally, the layout and structure of the parts of the engine, including the air-fuel mixture passageway and air passageway, are not sufficiently sophisticated, thus causing the engine to increase in overall size. Therefore, the two-stroke cycle internal combustion engines proposed in the aforementioned publications might be further improved for the purpose of mounting them on a portable power working machine.
A so-called binary scavenging system is now adopted in the conventional Schnürle-type scavenging two-stroke internal combustion engine, wherein a pair of scavenging ports are located symmetrically with respect to a longitudinal plane that bisects the exhaust port, and a portion of the scavenging flow of the air-fuel mixture that is blown out of the pair of scavenging ports impinges against a stationary inner wall of the cylinder (cylinder bore). A so-called quaternary scavenging system comprising two pairs of scavenging ports—i.e., an additional pair of scavenging ports is further added to the aforementioned binary scavenging system—is also known.
However, even in the two-stroke cycle internal combustion engine having a quaternary scavenging system, it is impossible to sufficiently minimize the quantity of so-called blow-by even if, according to the method conventionally proposed, the scavenging of combustion gas is performed by introducing air prior to the introduction of air-fuel mixture into the combustion actuating chamber as in the case of the two-stroke cycle internal combustion engine having a binary scavenging system. Furthermore, the layout and structure of the parts of the engine, including the air-fuel mixture passageway and air passageway, are not sufficiently sophisticated, thus causing the engine to increase in size. Therefore, there remains a need for the two-stroke cycle internal combustion engine having a quaternary scavenging system to be further improved for uses such as in portable power working machines
BRIEF SUMMARY OF THE INVENTION
The present invention has been made to solve the aforementioned problems. It is, accordingly, an object of the present invention to provide a two-stroke cycle internal combustion engine having a quaternary scavenging system, which is capable of minimizing the quantity of blow-by, capable of improving the fuel consumption and power of the engine, capable of reducing the content of undesirable components in the exhaust gas, and capable of rationally and compactly arranging the parts of the engine.
With a view to attaining the aforementioned objects, a two-stroke cycle internal combustion engine, which includes a cylinder and a piston defining a combustion actuating chamber and a crankcase below the piston and defining a crank chamber, has a quaternary Schnürle-type scavenging system that includes an exhaust port, a pair of first scavenging passageways communicating the combustion actuating chamber with the crank chamber and disposed closer to the exhaust port, and a pair of second scavenging passageways communicating the combustion actuating chamber with the crank chamber and disposed farther from the exhaust port. The first scavenging passageways are disposed symmetrically with respect to a longitudinal plane that bisects the exhaust port. Similarly, the second scavenging passageways are disposed symmetrically with respect to the longitudinal plane. An air passageway is arranged for introducing air into the first scavenging passageways, and an air-fuel mixture passageway is provided for introducing an air-fuel mixture from an air-fuel-generating device into the crank chamber. The scavenging system is configured such that during a descending stroke of the piston, the exhaust port opens first, a first scavenging port formed at a downstream end of each first scavenging passageway opens after the exhaust port opens, and a moment later, a second scavenging port disposed at a downstream end of each second scavenging passageway opens, whereby air is introduced into the combustion actuating chamber from each first scavenging port prior to the introduction of the air-fuel mixture into the combustion actuating chamber from each second scavenging port.
In an advantageous construction of the two-stroke cycle internal combustion engine according to the first embodiment, a communicating passageway communicating with the downstream end of the air-fuel mixture passageway communicates the crank chamber with the combustion actuating chamber via an air-fuel mixture-feeding port provided at the downstream end of the communicating passageway. The air-fuel mixture-feeding port is configured to open substantially simultaneously with the second scavenging ports.
In another preferred embodiment of the two-stroke cycle internal combustion engine according to the present invention, the air passageway and the air-fuel mixture passageway are provided respectively with
Baker & Botts L.L.P.
Benton Jason
Kioritz & Corporation
Wolfe Willis R.
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