Internal-combustion engines – Two-cycle – Rear compression
Reexamination Certificate
1999-04-12
2001-06-05
Kwon, John (Department: 3747)
Internal-combustion engines
Two-cycle
Rear compression
C123S0730SC
Reexamination Certificate
active
06240886
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a stratified scavenging two-cycle engine which takes in a fluid mixture and air separately.
BACKGROUND ART
Conventionally, as shown in FIG.
4
and
FIG. 5
, a stratified scavenging two-cycle engine, having a fluid mixture flow passage (not shown) for supplying a fluid mixture is connected to a crankcase
1
and an air flow passage
2
for supplying air is connected to a scavenging flow passage
3
, is known. A check-valve
20
is provided at the outlet port of the air flow passage
2
. The check-valve
20
is composed of a reed valve and is constructed to permit a flow from the air flow passage
2
to the scavenging flow passage
3
and prevent a flow from the scavenging flow passage
3
to the air flow passage
2
.
Meanwhile, the scavenging flow passage
3
extends between the crankcase
1
and a cylinder block
4
so as to allow communication between a crank chamber la and a cylinder chamber
4
a
. A scavenging port
3
a
leading to the scavenging flow passage
3
is opened to a cylinder inner surface
4
b
, and an exhaust port (not shown) is opened thereto for exhausting combustion gas.
Further, the crankcase
1
is provided with a crankshaft
5
, and a piston
7
is coupled to the crankshaft
5
with a connecting rod
6
between them. The piston
7
is fitted in the cylinder inner surface
4
b
and freely moves along an axial direction of the cylinder inner surface
4
b
. Further, the cylinder block
4
is provided with a cylinder head
8
, which is provided with an ignition plug
9
.
In the stratified scavenging two-cycle engine configured as above, as the piston
7
ascends, the pressure inside the crank chamber
1
a
starts to drop, and the scavenging port
3
a
and the exhaust port are sequentially closed. As a result, the fluid mixture in the cylinder chamber
4
a
is compressed, and the fluid mixture supplied from the fluid mixture flow passage is passed into the crank chamber
1
a
. In this situation, air also enters the crank chamber
1
a
through the scavenging flow passage
3
from the air flow passage
2
.
When the piston
7
reaches an area in the vicinity of an upper-most position, the fluid mixture in the cylinder chamber
4
a
is ignited by means of the ignition plug
9
, and thereby the pressure inside the cylinder chamber
4
a
rises and the piston
7
descends. When the piston
7
descends to a predetermined position, the exhaust port and the scavenging port
3
a
are sequentially opened. As a result of the exhaust port being opened, combustion gas is exhausted from the exhaust port, thereby the pressure inside the cylinder chamber
4
a
abruptly drops. As a result of the scavenging port
3
a
being opened, the air accumulated in the scavenging flow passage
3
spurts into the cylinder chamber
4
a
from the scavenging port
3
a
, and the combustion gas staying in the cylinder chamber
4
a
is compulsorily discharged from the exhaust port by the air. Thereafter, the fluid mixture in the crank chamber
1
a
enters the cylinder chamber
4
a
through the scavenging flow passage
3
from the scavenging port
3
a
. Thus the scavenging operation is completed.
Again the piston
7
ascends, and the aforesaid cycle is repeated once more.
According to the stratified scavenging two-cycle engine configured as above, the inside of the cylinder chamber
4
a
is scavenged first by air, and combustible gas is prevented from being discharged as a result of the fluid mixture blowing through, therefore obtaining a disadvantage that the exhaust gas is uncleaned.
In the aforesaid stratified scavenging two-cycle engine, a portion of the fluid mixture stays inside the scavenging flow passage
3
at a point in time when scavenging is completed, but most of the remaining fluid mixture is forced out toward the crank chamber
1
a
by the air supplied from the air flow passage
2
and is replaced by fresh air. The fluid mixture remaining at the exhaust port
3
a
of the scavenging flow passage
3
, however, cannot be forced out toward the crank chamber
1
a
and stays there as is. As a result, at the time of starting scavenging, fluid mixture remaining at the scavenging port
3
a
enters the cylinder chamber
4
a
, and the fluid mixture blows out of the exhaust port, thereby causing the disadvantage in the form of unclean exhaust gas.
SUMMARY OF THE INVENTION
The present invention is made to eliminate the aforesaid disadvantage, and its object is to provide a stratified scavenging two-cycle engine which can make exhaust gas cleaner.
In order to attain the aforesaid object, a stratified scavenging two-cycle engine according to the present invention is a stratified scavenging two-cycle engine, which includes a scavenging flow passage to connect a cylinder chamber and a crank chamber, and an air flow passage connected to the scavenging flow passage, and which is constructed so that pressure reduction in the crank chamber following an upward movement of a piston permits air to be drawn into the scavenging flow passage from the air flow passage, and is characterized in that a scavenging port, at which the scavenging flow passage is opened to a cylinder inner surface, is clear of a side wall of the piston and communicates with the crank chamber in a state when the piston is positioned at least at an upper-most position.
According to the above configuration, when the piston ascends, the pressure inside the crank chamber reduces, and for example, a fluid mixture flows into the crank chamber while air flows into the scavenging flow passage from the air flow passage. During a stroke in which air is taken in, the scavenging port, which is opened to the inner surface of the cylinder, communicates with the crank chamber in such a manner as to avoid being fully obstructed by the side wall of the piston. As a result, air taken into the scavenging flow passage flows into the crank chamber through the scavenging port. Accordingly, the scavenging flow passage is filled with air at least at the scavenging port side to remove a residual fluid mixture.
Next, when the piston descends as a result of the mixture being ignited, the scavenging port is closed and the pressure inside the crank chamber increases. When the piston descends by a predetermined amount, for example, the exhaust port opens, combustion gas then flows out of the exhaust port, the pressure in the cylinder chamber abruptly drops, and the scavenging port is opened. Air flows into the cylinder chamber from the scavenging port, and the fluid mixture inside the crank chamber then flows into the cylinder chamber from the scavenging port through the scavenging flow passage.
As described above, the scavenging flow passage is filled with air at least at the scavenging port side, therefore at a point in time at which scavenging is started, only air first flows into the cylinder chamber, and combustion gas is expelled from the exhaust port. Accordingly, a fluid mixture is prevented from blowing through, and exhaust gas can be made cleaner.
Next, the aforesaid scavenging port may be opened at a position lower than the bottom end of the piston when it is positioned at least at an upper-most position. According to the aforesaid configuration, in a process in which the piston reaches the upper-most position, the scavenging port opens, and air flows into the cylinder chamber from the scavenging port. The scavenging port may be formed so as to open only by a small amount from the bottom end of the piston, therefore providing an advantage of a simple structure.
Further, the aforesaid piston may be constructed to have a through-hole which is formed so as to allow communication between the scavenging port and the crank chamber in a state when the piston is positioned at least at an upper-most position. According to this configuration, in a process in which the piston reaches the upper-most position, the through-hole which is formed at the piston communicates with the scavenging port, and the scavenging port communicates with the crank chamber through the through-hole. As a result, even though the length of
Komatsu Zenoah & Co.
Kwon John
Sidley & Austin
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